EREC 2002
« ENERGIES RENOUVELABLES ET COGENERATION
POUR LE DEVELOPPEMENT DURABLE EN AFRIQUE »
SEMINAIRE ATELIER
SESSION HYDROELECTRICITE
Sous le haut patronage de :
• Ministère de l’Enseignement Supérieur du Cameroun
• Ministère des Mines, de l’Eau et de l’Energie, Cameroun
1.-
Faculty of Science Applied
FEASIBILITY STUDIES
Professor A. LEJEUNE
And
I. TOPLICEANU Assistant
December 2002
2.-
CHAPTER I
INTRODUCTION WATER POWER DEVELOPMENT
1.1.
Historical
The use of water power by crude devices dates back to ancient times.
The primitive wheels, actuated by river current, were used for raising water for
irrigation purposes, for mills in grinding corn, and in other simple applications. The
Chinese nora, or float wheel, built of bamboo, with woven paddles, is still in use, as
well as other forms of current wheel elsewhere (see figures 1.1 and 1.2). Such devices
have a very low efficiency and utilize but a small part of the power available in a
stream.
Figure 1.1 - Chinese bamboo water wheel
The undershot, breast, and overshot wheels were great advances in that water
was confined in a channel, brought to the wheel, and utilized under a head of fall.
These were, therefore, gravity wheels and gave efficiencies from perhaps 30 per cent for
the undershot wheel up to about 70 per cent for the breast, and 80 per cent or more for
overshot wheels. The last were extensively used up to about 1850 and have been
constructed and used to a limited extent since.
The development of the hydraulic turbine about the middle of the nineteenth
century, however, resulted in its completely superseding the overshot wheel, the latter,
while efficient, being of relatively large diameter and low speed and limited in head
usually to from about 3 to 15 meters, this limit being imposed by the size of the wheels
3.-
which could be constructed. The period between the middle and the end of the
nineteenth century saw the development of the American, or mixed or inward-flow
turbine in this country, the evolution from the Francis wheel of 1849, to gain greater
power and speed. The developments of these days were, however, limited to low heads,
usually 4 to 7 meters the use of a greater fall being made by canals in subdivisions, each
a unit of about 7 meters.
Figure 1.2 - Water wheel in use near Murcia, Spain.
1.2.
Development
Now, the present activity and interest displayed in water power development
are distributed all over the world and especially since the oil crisis.
In table 1.1, is given the percentage of water power in electric energy production in the
world.
Table 1.1 : Percentage of water power in electric energy production in the world
1925
1950
1963
1974
1985
2000
40%
36%
28%
23%
18.4
14%
4.-
Table 1.2. based upon estimate of O.C.D.E. experts, shows distribution of energy
resources up to 2020.
Table 1.2
RESOURCES
Coal
Petrol
Gaz
Nuclear resources
19 72
Total
20 00
20 20
EJ
%
EJ
%
EJ
%
EJ
%
66
115
46
2
24.5
45.7
17.1
0.7
115
216
77
23
23.6
44.26
15.77
4.7
170
195
143
88
24.6
28.3
20.7
12.7
259
106
12
314
16
10
12.5
31.4
85
Total of non renewable resources
Water power
Petrol and gaz (non conventionnal)
Renawable resources ( sun, wind, …
19 85
88
86
80
14
0
26
5
0
0.6
24
0
33
4.9
0
6.7
34
4
56
4.9
0.6
8.1
56
40
100
5.6
4
10
269
100
488
100
690
100
1000
100
(EJ = exajoule = 1018 joules)
The average increase in developed water power during the coming 40 years,
will be about 5 per cent yearly ; that means a capacity production multiplied by 3.
In table 1.3 is given the distribution of water power world potential.
5.-
Table 1.3
AREA
Asia
South America
Africa
North America
USSR
Europa
Oceania
World
Potential
Devel oped
MW
MW
%
610 000
431 900
358 300
356 400
250 000
163 000
45 000
53 079
34 049
17 184
128 872
30 250
96 007
6 795
9
8
5
36
12
59
15
2 200 000
Figure 1.3
366 236
16.6
6.-
CHAPTER II
GENERAL ARRANGEMENT OF WATER POWER DEVELOPMENTS
2.1.
Essential Features
A water development is essentially to utilize the available power in the fall of a
river, through a portion of its course, by means of hydraulic turbines, which, as
previously explained, are usually reaction wheels except for high heads, where impulse
wheels may be used. To utilize its power, water must be confined in channels or pipes
and brought to the wheels, so as to bring into action upon them substantially the full
pressure due to the head or fall utilized, except for such losses of head as are
unavoidable in bringing the water to the wheels.
The essential features of a water power development are therefore ( see figure
2.1):
1. The dam
The structure of masonry or materials built at a suitable location across the
river, both to create head and to provide a large area or pond of water from which draft
can readily be made. In many cases the power development is at or close the dam, and
the entire head utilized is that afforded at the dam itself, in which case the development
is one of concentrated fall.
2. The Waterway
More often the development must be by divided fall, utilizing in addition to the
head created by the dam an amount obtained by carrying the water in a waterway,
which may be a canal, penstock (or closed pipe), of a combination of these for some
distance downstream.
3. The powerhouse and equipment
Which include the hydraulic turbines and generators and their various
accessories and the building required for their protection and convenient operation.
Many existing water power developments also utilize the power from the wheels in
mechanical drive, i.e., operating machinery directly or by belting and gearing. The
tendency is, however, very markedly toward mill and factory electrification, so that
nearly all the never developments are hydroelectric.
4. The tailrace
Or waterway from the powerhouse back to the river. In many cases the
powerhouses located on the river bank so that no tailrace channel is required, but
occasionally, to develop additional fall ; a tailrace channel of some distance is used.
7.-
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
River
Dam with a spillway
Control gate
Water way
Intake structure
Trashrack
Overflow channel
Penstock
Valve
Turbine
Generator
Tailrace
Figure 2.1
2.2.
Gross and Net Head
The development losses, as they may be called, aside from losses at or in the
wheels, will vary in percentage amount depending upon the head and manner of
development but should not exceed perhaps 5 to 10 per cent at the most.
The gross head developed is the fall between pond level at the dam and river
level at junction with tailrace, or, in other words, the amount of fall of the river that is
developed. The net or effective head (see following chapter) is less than the gross head
by the losses sustained in bringing water to the wheels and, possibly, between tailrace
level and river below. As previously noted, wheel efficiencies from 85 to 90 per cent or
more are now obtained, so that a modern hydroelectric development should utilize in
power supplied to the generators at least 80 per cent of the gross head of the
development or not less than 75 per cent of the gross head at he switchboard.
8.-
2.3.
Essentials of General Plant Layout
The two basic principles to be kept in mind in planning a water power
development are economy and safety, or in other words a maximum of power output at
a minimum of cost, but at the same time a safe and proper construction than can meet
the exigencies of operation imposed by structures which control as far as may be, but of
necessity interfere somewhat with, natural forces, variable and often large in amount
and uncertain in regimen. The hazards due to floods, ice, etc... must be provided for not
only from the point of view of safety but also to minimize interruptions in plant
operation as far as practicable.
Owing to freedom from the uncertain and irregular natural forces to which a
water power development must of necessity be subjected, steam-electric plants were
formerly considered as more dependable prime movers, but the interruptions in service
at steam plants in the countries during the times of fuel shortage, when for times water
power alone was available for use, and later continued high fuel costs, have materially
changed our perspective in this respect. The trend of modern water power
developments toward simple and effective layout and also the greater use of stored
water have resulted in a better appreciation of the value and dependability of water
power, when properly utilized.
2.4.
Factors Affecting Economy of Plant
The factors or conditions affecting the relative economy of a water power
development may be divided into the characteristics of (1) site and (2) use and market.
1.- The site characteristics are those particularly affecting the construction and operating
cost of the plant and, therefore, the conditions which are most likely to decide first of all
whether a site is worthy of development and, if so, the best manner of making this
development.
These include geologic conditions as affecting available foundations for structures,
particularly the dam, whose type may be thus determined. The absence of suitable rock
foundations for the dam may even prevent the utilization of a power site.
Topographical conditions are also of great importance in determining the dimensions of
the dam and thus largely affecting its cost and the relative proportion of the fall or head
to be developed by the dam or by waterway, as well as the manner in which the
waterway may be constructed, whether canal or penstock or a combination of these.
The slope of the river is of importance, as affecting necessary length, cost of waterway,
and amount of poundage obtainable at the dam.
The relation of head to discharge also greatly affects the desirability of a power
development. For a given amount of available power the greater the head as compared
with the discharge, the less costly will be the development, owing to the greater
capacity required for all the features except the dam, as discharge increases. In general,
therefore, the higher head developments are always less expensive per horsepower of
capacity than those of lower head.
Storage possibilities at sites upstream are of especial importance, where storage cost is
reasonable, which will usually require the use of the stored water at several power
plants in order to lessen its cost a each plant, in increasing the dependability of the water
power development, and the proportion of its output which will be primary of
dependable power.
9.-
Operating costs may also be affected by especial condition which may prevail on a
given stream. Thus, a stream subject to frequent floods or high-water periods may have
the power at a given site frequently curtailed by backwater in the tailrace, and on such a
stream flashboards on the dam may require frequent renewal. The presence of ice,
particularly anchor or brazil ice, on streams having numerous falls or stretches of quick
water, also introduces troublesome problems of operation and often adds to its cost.
2. The characteristics of use and market include the conditions particularly affecting the
sale price and value of the developed power.
Thus proximity to market is a vital consideration. A water power site may be capable of
development at low cost, viz, with advantageous natural features, but situated so far
from any possible market as to be unworthy of consideration for development. In this
respect, the radius of possible transmission of power is constantly growing, and today
lines of 1000 are possible.
On the other hand, to transmit power such distances economically requires
relatively large blocks of power,and in any event the cost of transmission must be
included in power cost in competing with steam-electric plants at a distance. The
transmission of power across states lines is also in some cases hampered or prohibited
by state laws.
The cost of other at the available market is of importance as affecting the sale price of
water power. This order power is commonly steam-electric, whose cost is largely
affected by fuel cost. Hence, much variation in cost of power will be found in different
parts of the country, depending upon, the distance that coal (or oil fuel, in many cases)
must be transported, freight charges here constituting the important element.
Load factor as affecting the manner of use of power is of great importance, as certain
features of the water power development, particularly the powerhouse and equipment,
vary in cost nearly inversely as the load factor. It is of advantage, therefore, to keep the
load factor at a hydro-electric development as high as possible.
2.5.
Types of Water Power Developments
No two water power developments which are exactly alike will probably ever
be built, and every power site has its especial problems of design and construction
which must be met and solved. We may, however, distinguish certain general types of
plant layout consistent with the general site characteristics of importance-head,
available flow, topography of river and vicinity etc...all more or less interdependent,
which affect the manner of development as well as those characteristics of market and
type of load, etc... which affect the size of plant and number of its units.
Such a general classification of water developments is given in table 2.1, which
also shows to what extent head may and flow vary or affect the use of the different
types as given.
It must be kept in mind that the numerical limits given in table 2.1 are somewhat
variable and elastic for both head and flow. Thus, an open-flume installation may in
some cases be used for a head of more than 7 m and penstock developments are
sometimes made for capacities in excess of 15 m3/s. The figures given represent
ordinary of common usage.
In the case of a concentrated fall with steel flume, the ordinary upper limit of
head is placed at 150 m, although a dam of that height would seldom be economical for
power development unless it afforded at the same time substantial storage capacity.
10.-
Figure 2.2 :Three gorges Chine
11.-
Table 2.1 - Types of Water Power Developments
TYPE OF DEVELOPMENT
Range of Head
m
Flow
m3/s
A. Concentrated Fall
Open flume
Concrete scroll flume
Steel scroll flume
Up to 7
7 - 20
21 - 150
Not limited
Not limited
Not limited
Canal and open flume
Canal and concrete scroll flume
Canal and short penstock, steel scroll flume
Penstock, steel scroll flume
Up to 7
7 - 20
20 up
20 up
10 to 15
10 to 15
10 to 15
10 to 15
B. Divided Fall
Water power plants could be also divided in function of the head, in 3 ranges: low,
medium and hight head ( see figure 2.3)
Figure 2.3: Typical water power plants
2.6.
Typical of Arrangements of Water Power Plants
A. Concentrated Fall
The location of powerhouse with reference to dam will depend upon local
conditions. Often a low-cost development could be made by placing the power house in
the river at one end of the dam (figure 2.4.a).
12.-
(a)
(c)
Figure 2.4 - Arrangement of plants - concentrated and divided fall
This would generally result, however, in an undesirable limitation in length of spillway
and possible subjection of powerhouse to flood and ice hazards. To obtain necessary
spillway length, therefore, the powerhouse must often be located in some such manner
as shown in figure 2.4.b, c or d.
A few developments utilizing concentrated fall have been made using a hollow
concrete dam of the Ambursen type with powerhouse in the dam.
B. Divided Fall
Various typical plant arrangements with divided fall are shown in figure 2.4.e
and figure 2.4 f to k. Aside from capacity in second-feet to be handled, the dominating
feature is the topography of the region adjacent to the river. Thus, in figure 2.4.e, the
river bank remains high and affords room for a canal development, which with open
wheel pit could utilize a head of only about 7 m. but with concrete scroll flume settings
might make it possible to use a head of 20 m.
The arrangement in figure 2.5.f is typical of many developments where flow is
relatively large, where the river bank permits the use of a canal to a forebay near the
powerhouse, from whence individual penstock lines run to each wheel unit. The heat
utilized in such a development will nominally be more than about 20 m and is limited
above that amount only by the fall in the river between dam and tailrace level.
In figure 2.4 g the topography is such that a canal can be used for only a part of
the distance. If flow is large, it may be necessary here to use more than one penstock
line, although such a development would result in increased cost, as compared with
figure 2.5.f, for a given total length of waterway.
In figure 2.5.h the manner of development is similar to that of g, but advantage
is taken of a bend in the river to utilize a greater head for a given length of waterway.
13.-
In figure 2.5.k the flow is low enough to permit the use of a penstock
throughout, which is kept at relatively high level to save in cost, until pear the
powerhouse, where a quick descent is made, usually with individual penstocks to each
wheel unit. Here again a curve in the river is utilized to shorten the length of penstock.
Figure 2.5. - Arrangement of plants - divided fall
A modification of figure 2.5.k of service where the river bank between dam and
powerhouse site is very high, as with a hill, consists in constructing a tunnel penstock
with surge tank and individual penstock lines to each unit from the point on the hillside
where the tunnel emerges. The material most favoring tunnel construction is rock, and
usually the tunnel would be lined to increase its flow capacity. The tunnel grade would
be usually kept relatively flat, the sudden pitch being made with the penstock lines.
2.7.
Lowest Cost Power Developments
Keeping in mind variation in site, use, and market characteristics, it will be
seen that the lowest cost development, as well as of power produced will be secured
with the following conditions :
Conditions favoring low cost
1.
2.
3.
(A penstock development)
Relatively high head and small flow
Discharge assured by storage, the cost of which is carried by several plants
Favorable dam site
a. good foundations
b. Narrow valley and a minimum of material in dam
4. Good penstock location, fairly straight line with moderate grade for most of
distance,
and then quick drop to powerhouse site
5. A few large wheel units
6. Relatively short transmission to market
7. High load factor, often made possible where a plant is a unit of a large power
system.
14.-
2.8. Highest Cost Power Developments
Conversely, the highest cost development and of power produced will be for
the following conditions :
Conditions resulting in high cost
(A canal development)
1. Relatively low head and large flow
2. Variable flow with small minimum or primary power
3. Poor dam site
a. Poor foundations
b. Wide valley and relatively large material requirements
4. Poor canal location deep cut in hard material and circuitous route
5. A relatively large number of small-capacity wheel units
6. Long transmission to market
7. Low load factor, as with an isolated plant and poor load characteristics.
15.-
CHAPTER III
POWER FROM FLOWING WATER
We may change the form of energy, but we can neither create nor destroy it.
Water will work for us only to the extent that work has been performed on it. We
cannot realize all the potential inherent work of the water because there are inevitable
conversions of energy to unavailing forms that we style losses.
In the hydrologic cycle, water is evaporated from oceans and carried inland in the
form of vapor by air currents. Cooling by adiabatic expansion of these air currents
deflected upward by mountain ranges and by other means causes condensation of its
vapor and precipitation as rain, snow, dew, on the land from whence it flows back to the
ocean only to repeat the cycle. The work done on it by the energies of the sun, winds,
and cooling forces places it on the uplands where work may be extracted from it in its
descent to the oceans in direct correspondence to the work expended in putting it there.
3.1. Energy and Work
Energy is the capacity to perform work. It is expressed in terms of the product
of weight and length. The unit of energy is the product of a unit weight by a unit length,
i.e., the kilogram-meter, the foot-pound.
Work is utilized energy and is measured in the same units as energy. The
element of time is not involved.
Water in its descent to the oceans may be temporarily held in snow banks, glaciers,
lakes and reservoirs, and in underground storage. It may be moving in sluggish streams,
tumbling over falls, or flowing rapidly in rivers.
Some of it is lost by evaporation, deep percolation, and transpiration of plants. Only the
energy of water that is in motion can be utilized for work.
The energy of water exists in two forms (1) potential energy, that due to position or
elevation, and (2) kinetic energy, that due to its velocity of motion. These two forms
are theoretically convertible one to the other.
Energy may be measured with reference to any datum. The maximum potential energy
of a pound of water is measured by its distance above sea level.
The ocean has no potential energy because there is no lower level to which its water can
fall. The energy of ocean waves can of course be realized.
The potential energy of a given volume of stored water with reference to any
datum is the product of the weight of that volume and the distance of its center of
gravity above that datum.
Power is utilized energy per unit of unit of time, or the rate of performing work,
and is expressed in horsepower, or kilowatts.
The potential energy of a stream of water at any cross section must be
measured in terms of power, in which time is an indispensable element. It is the weight
of water passing per second X the elevation of its water surface (not center of gravity)
16.-
above the datum considered. The kinetic energy of a unit weight of the stream is
measured by its velocity. It must also be measured in terms of power since velocity
involves time. It is the weight per second times the velocity head, i.e., the height the
water would have to fall to produce that velocity.
The total energy of a stream is the sum of its potential and kinetic energies.
At the perfect turbine, all the potential energy has been converted to kinetic
energy.
Of course the perfect turbine does not exist. Some of the potential energy is
converted into heat by friction and turbulence so that the useful part is less than the
theoretical potential.
3.2. Energy Line
The energy head is a convenient measure of the total energy of a stream of
constant discharge at any particular section. It is the elevation of the water surface,
potential energy, plus the velocity head, kinetic energy, of a unit weight of the stream.
Although every unit of the stream has a different velocity, that usually considered is the
velocity head corresponding to the mean velocity of the stream. If the stream is flowing
in a pipe, the energy head is the elevation of the pressure line, or the height to which
water would stand in risers, plus the velocity head of the mean velocity in the pipe.
A line joining the energy heads at all points is the energy line.
The energy lines would be horizontal if the energy converted to heat were included.
Energy converted to heat however is considered lost ; hence the energy line always
slopes in the direction of low and its fall in any length represents losses by friction,
eddies, or impact in that length. Where sudden losses occur, the energy line drops more
rapidly. Where only channel friction in involved, the slope of the energy line is the
friction slope.
Figure 3.1. illustrates the principles of the foregoing example. The potential
energy head of the tank full of water without inflow or outflow is that of the center of
gravity of the tank of water Z. With inflow and outflow equal, however, the potential
energy head is H. AS the water passes into the canal, a drop of the water surface equal
to the velocity head in the canal V12 /2g must occur. At the entrance to the pipe line, an
entrance loss h1 is encountered as well as an additional drop for the higher velocity in
the pipe. At any point line, the pressure head hp will be shown in a riser.
The energy head at any point is the pressure head plus the velocity head, and
the line joining the energy heads in the energy line. The energy lost (converted to heat)
is the sum of friction, entrance, bend, and other losses in all the conduits, including the
turbine and draft tube. The useful energy is that of the power developed by the turbine.
The sum of the useful energy and the lost energy must equal the original potential
energy.
17.-
Figure 3.1 - Energy relations in a typical hydroelectric plant.
3.3
The Bernoulli Theorem
The Bernoulli theorem expresses the law of flow in conduits. For a constant
discharge in a closed or open conduit, the theorem states that the energy head at any
cross section must equal that at any other downstream section plus the intervening
losses. Thus above any datum
V21
V22
Z1 + ------- = Z2 + ------ + hC
2g
2g
(1)
In figure 3.2. Z is the elevation of a free water surface above datum whether it be in a
piezometer tube or a quiescent or moving surface of a stream, V is the mean velocity, hc
the conduit losses between the two sections considered, and e the energy head above the
chosen datum.
Obviously Z may be made up of a number of elements such as elevation of stream bed
or pipe invert above datum k, pipe diameter D, depth in open channel y, or pressure
head above crown of pipe h. Frequently k and h are measured to the center line of the
pipe, but if the pipe is large a distinction is necessary.
Figure 3.2. - Energy relations in open and closed conduits.
3.4
Head
There are several heads involved in a hydroelectric plant which are defined as
follows.
18.-
Gross head, simultaneous difference in elevation of the stream surfaces between points
of diversion and return.
Operating head, simultaneous difference of elevations between the water surfaces of the
forebay and tailrace with allowances for velocity heads.
Neat or effective head, has different meaning for different types of development as
follows :
1. For an open-flume turbine, the difference in elevation between (1) headwater in
the flume at a section immediately in advance of the turbine plus velocity head,
and (2) the tail water velocity head.
2. For an encased turbine, the difference between (1) elevation corresponding to
the pressure head at entrance to the turbine casing plus velocity head in the
penstock at the point of measurement, and (2) the elevation of the tail water plus
velocity head at a section beyond the disturbances of exit from draft tube.
3. For an impulse wheel, including its setting, the difference between (1) elevation
corresponding to the pressure head at entrance to the nozzle plus velocity head at
that point, and (2) the elevation of the tail water as near the wheel as possible to
be free from local disturbances. When considered as a machine, the effective
head is measured from the lowest point of the pitch circle of the runner buckets
(to which the jet is tangent) to the water surface corresponding to the pressure
head at entrance to the nozzle plus velocity head.
Strictly speaking, the various heads above are the differences in energy heads.
For the gross head, the velocities in the stream are generally disregarded, as are the
velocity heads in the tailrace for the operating head. The net head, however, is
important in determining efficiency tests of a turbine in its setting ; hence is important
to use the difference in energy heads at entrance and exit of the setting.
The net head includes the losses in the casing, turbine, and draft tube, for they
are charged to the efficiency of the wheel.
Formulas for the net head of the three cases are as follows :
For one cased reaction wheel,
V21
V22
h = ( Z1 + ------ ) - ( Z2 + ------ ) = e1 - e2
2g
2g
where Z1 = elevation of pressure heat at entrance of turbine casing
V1 = mean velocity at entrance of turbine casing
Z2 = elevation of tail water at draft-tube exit
V2 = mean velocity in the draft tube at its exit
e1 and e2 = the respective energy heads.
For an open flume setting of a reaction wheel, the expression is the same as in
(2) but the quantities have slightly different meanings : z1 is the elevation of water
surface in the open flume just upstream of the turbine v1 the mean velocity in flume at
that section Z2 the elevation of water surface in tailrace at draft-tube exit, and V2 the
mean velocity in the draft tube at its exit.
For the impulse wheel,
(2)
V21
19.-
h = Z1 + ------ - Z2
2g
in which
(3)
Z1 = elevation of pressure head at entrance to nozzle casing
V1 = velocity at the same point
Z2 = elevation of tailrace near the wheel
The elevation of the nozzle above tailrace and the velocity head in the tailrace
are lost as there must be clearance above the tail water for the wheel to revolve.
Efficiencies of elements composing a hydroelectric system are all measured as the ratio
of energy output to impute or of useful to total energy.
No element is perfect, its functioning involves lost energy (conversion to heat). The
efficiency of a plant or system is the product of the efficiencies of its several elements,
thus
Es = EcEtEgEuElEd
(4)
where Es is the over-all system efficiency made up of the product of the several
efficiencies of the conduits,
Et turbines, including scroll case and draft tube,
Eg generators, including exciter
Eu step-up, transformers
E1 transmission lines
Ed step-down transformers
Ec canal, penstocks, tailrace
Formula (4) expresses the over-all efficiency from the river intake to the distribution
switches at the substation. To this could be added the efficiency of the distribution
system, even to the customer's meters, his lights, water heaters, ranges, motors, etc...
For a constant discharge the hydraulic efficiencies of the several elements can
be expressed in terms of elevations or head above a given datum, and since that datum
may be arbitrary such efficiencies will have different values depending upon the datum
of reference. If all such efficiencies were referred to sea level, plants at low levels
would have higher efficiencies that those at higher altitudes. Such a condition is, of
course, intolerable. In effect, the efficiency of an element is the ratio of (1) total energy
less losses to (2) total energy, but the datum of reference must be stated.
For purposes of illustration, the following analysis is presented.
For the head-works of a system, there is a loss through the control gates in passing from
stream to canal, and the efficiency becomes
2
V1
Z1 + ------ e
2g
1
------------------- = -----Z0
Z0
(5)
For the canal, the loss is mostly channel friction
2
Vf
20.-
Zf + ------ e
2g
f
------------------- = -----2
V1 e1
Z1 + -----2g
(6)
For the penstock, the loss is entrance and pipe friction
2
Vf
Zt + ------ e
2g
t
------------------ = -----2
Vf ef
Zf + -----2g
(7)
For the turbine, the loss is entrance, friction, impact and eddies in casing and draft tube
2
Vd
Zd + ------ e
2g
d
------------------ = -----2
et
Vt
Zt + -----2g
(8)
For the tailrace, the loss is eddying at draft-tube exists and channel friction
2
Vr
Zr + ------ e
2g
r
------------------ = -----2
Vd ed
Zd + -----2g
In the foregoing expressions, z represents elevation of water surface and e of
energy heads above datum, subscript 1 refers to the head of the canal below control
gates, f to forebay, t to the entrance of the turbine, d to the draft-tube exit, and r to the
river at its junction with the tailrace.
Zo is the elevation of the normal river surface at the intake before water enters the canal
(river velocities are neglected), and, as this may vary, the canal gates are manipulated to
hold a given elevation in the canal intake for a given discharge. The efficiency of the
headworks may therefore be variable even for a constant discharge. The elevation of
the water surface at the head of the tailrace (exit of draft tube) Zd may also be affected
by the river stage, and this is reflected in variation in the efficiency of the turbine. The
efficiencies of all the other elements will be sensibly constant for a constant discharge if
canal, racks, etc... are kept clean and in good order.
Turbine efficiencies are specified for certain flows under certain heads and
speeds and obviously must not vary arbitrarily with an arbitrary datum. The datum of
reference is therefore considered to be moved to the water surface just downstream of
the draft-tube exit where major turbulences have subsided.
The expression in Eq (8) therefore must be modified by introducing a power head that
represents the useful energy output of the wheel and is determined by tests ; thus
(9)
21.-
hp
hr
------------------------------------------------------- = ------------2
2
et - ed
Vt
Vd
( Zt + ------ ) - ( Zd + ------ )
2g
2g
(10)
becomes the correct expression for the efficiency of the turbine and setting under
constant discharge, the datum of reference being the water surface of the tailrace at exit
of the draft tubes.
With the preceding notation, the efficiency of the entire plant may be expressed
independent of an arbitrary datum ; thus
hp
---------------Z0 - Zr
(11)
velocity heads in the river at the headworks at its junction with the tail race being
neglected.
The term efficiency is not often used for plant elements other than the
generating equipment. It has been given herein merely to illustrate the relationship of
each element to the whole in this regard and to show the effect of the datum of reference
on indicated efficiencies. In practice, the lost head in each such elements is found and
deducted from the gross head to obtain the net power head.
The efficiency of a turbine depends upon the type, speed, head and load.
For moderate heads, the propeller type of turbine with adjustable blades has shown high
efficiencies over a wide range of load and head.
Most wheels show maximum efficiencies about 80 per cent gate opening.
The efficiency of generators are generally greater the larger the unit, but
they too depend upon the load carried. The efficiency of transformers increases rapidly
with capacity and load within certain limits, whereas that of transmission lines increase
with capacity but decrease with load.
The over-all efficiency of a plant is the product of the instantaneous
efficiencies of its several pieces of equipment referred to the gross head on the water
wheels. It obviously varies with capacity of units, head, load, and the number of units in
service. Plant efficiencies are not always observed and frequently involve many
complexities. In general, the plant efficiency is the ratio of the energy output of the
generator to the water energy corresponding to the gross head (difference of forebay and
tailrace levels) and that discharge and load for which the indicated efficiency of the
turbine is maximum. In any case, it should be clearly defined.
Power formulas
Theoretical power is 9,81 QH kW
If E is the efficiency of the plant, the power that can realised is given by
9,81 Q HE kW
22.-
In the expression, E is the plant efficiency and H is the head on the water wheel defined
by Esq (2), (3) or (4) as may be appropriate.
Useful energy is generally measured in terms of kilowatt hours. Where the
discharge and head are constant.
9,81 QH Et
were t is the time in hours for which the flow and head are constant or for which Q and
hare average values. When the flow and head vary materially, the period considered is
divided into smaller time intervals for which they are sensibly constant.
The kilowatt-year are terms sometimes used for power sales. On a 100 per
cent load factor the relationships are
0.746 kW-year = 6,540 kWhr
Power from any particular plant or system is limited by the capacity of the installed
equipment. It may be limited also by the available water supply, head characteristics, and
storage.
Firm power, or primary power, is that load, within the plant’s capacity and characteristics
that may be supplied virtually at all times. It is fixed by the minimum stream flow,
having due regard for the amount of regulating storage available and the load factor of
the market supplied.
Surplus power, or secondary power, is all available power in excess of the firm power. It
is limited by the generating capacity of the plant, by the head, and by the water available
in excess of the firm water. A certain amount of surplus power may very closely
approximate firm power in being available a large percentage of time, whereas other
amounts may be available for shorter periods.
Dump power is surplus power sold with no guarantee as the continuity of service i.e., it is
delivered when, as, and if available.
Secondary power of a power plant is not easily defined. Name-plate capacity or rated
capacity of a turbine is usually given in horsepower for a given head of these quantities
may vary within definite limits. The rated capacity of a.c. generators is usually stated in
terms of definite speed, power factor, and temperature rise and is usually given in
kilovolt-amperes. Each of these quantities may also may within definite limits.
The A.I.E.E. definition of generating station capacity is “the maximum net power output
that a generating station can produce without exceeding the operating limit of its
component parts”. The station or plant capacity can therefore be determinate for a given
station. It may be stated for a peak load over a given period as 15 minutes or 1 hour or
for a continuous service if storage regulation exists but is limited by the temperature rise
of generators. Until the station capacity has been fixed, the various factor having to do
with capacity cannot acquire definite meanings. Where the capacity of a plant has not
been fixed, it is customary to take name plate capacity of generators as the plant capacity,
which is often called installed capacity.
The average load of a plant or system during a given period of time is a hypothetical
constant load over the same period that would produce the same energy output as the
actual loading produced.
23.-
The peak load is a maximum load consumed or produced by a unit or a group of units in
a stated period of time. It may be maximum instantaneous load or a maximum average
load over a designated interval of time.
The maximum average load is generally used. In commercial transactions involving peak
load, it is taken as the average load during a time interval of specified duration occurring
within a given period of time, that time interval being selected during which the average
power is greatest.
The load factor is an index of the load characteristics. It is the ration of the
average load over a designated period to the peak load occurring in that period. It may
apply to a generating or a consuming station and is usually determined from recording
power meters. We may thus have a daily , weekly, monthly, or yearly load factor ; it may
apply to a single plant or to a system . Some plants of a system may be run continuously
at a high load factor, whereas variations in load are taken by others plants of the system ,
either hydro or steam. Hydro plants designed to take such variations must have sufficient
regulating storage to enable them to operate on a low factor. They are often called peakload plants. Operating on a 50 per cent load, there must be sufficient storage to enable
such a plant, in effect, to utilize twice the inflow for half the time: on a 25 per cent load
factor, the plant should be able to utilise four times the inflow for a quarter of the time,
etc… the lower the load factor, the greater the storage required.
As applied to the consumption of power , the load factor is the ration of
the average to maximum demand during any given period. If may apply to a single
motor, an industrial plant, a city, or a consuming system. The maximum demand may be
highest consumer load during a 5, 10 or 15 min interval, the average of the two highest 5
min intervals, or otherwise as fixed by the management or be regulatory bodies. It is
usually determined from a demand meter or taken from a graphic wattmeter. The period
usually considered is a month for purposes of billing, although the sale rates or power are
often based on the yearly load factor of the consumer.
The capacity factor is a measure of plant use. It is the ration of the average
load to the plant capacity. It may be computed for a day, month, year or any other period
of time. When the peak load just equals the plant capacity, the capacity factor and load
factor are obviously the same. If the maximum demand is les that the plant capacity, the
capacity factor may be either greater or less that the load factor, depending largely on the
load factor itself.
The utilisation factor is a measure of plant use as affected by water supply.
It is the ratio of energy output to available energy within the capacity and characteristics
of the plant. Where there is always sufficient water to run the plant capacity, the
utilisation factor is the same as the capacity factor. A shortage of water, however, will
curtail the output and may either decrease or increase the utilization factor according to
the plant load factor.
These several factors can be determined for any plant by analysing past
performance. They may also be forecast approximately by a complete analysis of stream
flow and plant characteristics.
24.-
CHAPTER IV
PLANNING AND BUILDING
4.1. Stage of planning
The stage of planning power stations may the grouped as follows :
1. Scientific and technical preparations: hydrographical, meteorological,
hydrogeological,
geological, soil-mechanical, etc... preliminary investigations and
studies ; geodetical surveys and comprehensive scale model tests (see Figure 4.1).
(The operations in hydrography, meteorology and hydrogeology may be summed up
in the comprehensive term of hydrology).
2. Power estimates. Power curves, investigation of load conditions. Plan of cooperation . Economic analysis.
3. Design of civil engineering works and hydraulic structures (including all hydraulic,
structural, soil-mechanical etc...investigations together with detailed scale model
analyses).
4. Design of mechanical and electrical equipment (including the necessary
computations, together with tests, hydraulic and other ).
5. The design of steel structures, closely related to that of civil engineering structures,
on the one hand, and with that of the mechanical equipment, on the other.
6. Architectural design.
7. Estimates of costs and economic considerations.
Figure 4.1: Nam Thun Laos Hydraulic Scale (Liège University laboratory)
25.-
Planning as such, especially that of hydraulic projects, is generally not feasible
in the final from in the above succession but, according to the requirements of each
stage of planning, studies including every detail are to be prepared with the required
degree of accuracy. Accordingly, various specialists should submit to the hydraulic
engineer as required by the progress of planning operations.
The right course of planning is gradual approximation. The following stages of
planning are usually distinguished :
1. Identification (a hydrological study in principle ; diagrammatic sketch with the
basic data; tentative power estimates ; estimates of investment costs). This
preliminary report is based on available data and maps, supplemented eventually
by experiences of site surveys.
2. Prefeasibility study (including informative power estimates and cost analysis). In
this stage informative explorations, surveys, borings, and/or geophysical
investigations, hydrographic surveys may become necessary.
3. Feasibility study (including detailed power estimates and detailed economic
analysis). At this stage of planning hydrological and geological research work,
topographical maps as well as petrographical and soil-mechanical examinations are
indispensable. For the preparation of the general plan, the results of hydrological
scale model tests shall be already available, and only those of smaller significance can
be postponed.
4. Detailed final plan (including all
estimates of investment costs).
the necessary computation and additional
Operations, plans and calculations listed under items 1-7 and falling within the
scope of different branches of technical sciences shall be brought into harmony in all
the phases of design.
The problem of scientific and technical preparation requires no special
explanation being similar to any other proceedings in hydraulic engineering as far as the
applied scientific principles and the customary practical methods are concerned. The
degree of accuracy in design work is always prescribed by the leading engineers taking
part in the planning of a power station.
Construction work and organization including production and installation of machinery,
may be divided as follows :
1. Construction schedule containing the accurate chronology of the following items :
simultaneous and subsequent operations, demand in materials, transport facilities,
manufacture and installation of machinery, financial time-table, required man power
and machine power. Virtually, this constitutes the technical and financial program of
executing the work.
2. A separate plan of execution shall be drafted for the technical realization for of
complicated civil and hydraulic engineering structures with special regard to the foundation
work provided by the design.
3. Layout of the construction site is generally closely related to item 2 and involves
the following : communication system in an outside the construction site, barracks for
26.-
housing and boarding the labour force, offices, transmission lines and substations, the
energy resources on the building site, water supply, depots, workshops, occasionally
works and plants (cement, concrete, etc...) building machines and their plan of
operation.
4. The manufacture of devices of mechanical, hydromechanical, electro-mechanic,
electric and other equipment and steel structures.
5.
The preparation of the plan site, i.e. the execution of work listed under item 3.
6.
The construction work and the installation of machines and other equipment.
7.
The performance test of machinery and other equipment prior to operation.
Finally, the fact, than in the course of planning the technical and economic
problems are inseparable, cannot be given sufficient emphasis. Within a generally wide
scope of technical possibilities the most favorable solution is determined ultimately by
economic considerations, consequently several alternatives should be taken into
account, at least at the stage of the preliminary design. The number of alternatives and
the degree of elaboration depend not only on site conditions but also on the magnitude
and significance of the project.
4.2. Potential water power
The first step towards developing the energy of a stream or river system is to
ascertain the physical power inherent in the relevant river section because, as we have
seen before, a certain portion of the work wasted to overcome resistance can be made
available for useful purposes.. Consequently, it is obvious that the upper theoretical
limit of development and physical power inherent in a river are identical terms. The
knowledge of this criterion is of primary importance for obtaining satisfactory
estimates as regards the quantity of water power available for useful purposes. Power
inherent in a river and wasted in overcoming resistance constitute the resources of water
power development.
For any stretch of a watercourse, characterized by a difference in level of H
metres, conveying a discharge of Q m3/sec, the theoretical (potential) power expressed
in kilowatts is :
Np = 9.8 QH [kW]
If the rate of flow changes along a selected stretch (it normally increases
downstream, enhanced by the inflow of tributaries, and exceptionally diminishes by
losses or diversions), the mean value of the discharges pertaining to the two terminal
sections of the stretch is to be substituted into the formula :
Q = ( Q1 + Q2) / 2
The theoretical power resources of any river or river system are given by the
aggregate of the values computed for the individual stretches :
Np = 9.8 Σ QH [kW]
27.-
When determining the values of power resources the question arises as to what
values of H and Q should be used in the calculation. If we disregard very short river
stretches, the change of H with stage is negligible because the slope of water surfaces
pertaining to low, medium, or peak flow conditions can usually be regarded as constant.
On the other hand, the thorough examination of the different discharges is of great
importance.
Potential water power resources can be characterized by different values
according to the discharge taken as basis of computation. The conventional discharges
are ( see figure 4.1. )
1. Minimum potential power, or theoretical capacity of 100 per cent, is the term for
the value computed from the minimum flow observed. Denotation : NP100.
2. Small potential power. The theoretical capacity of 95 per cent can be derived from
the discharge of 95 per cent duration as indicated by the average flow duration curve.
(Power available for 8322 hours). Denotation : NP95.
3. Median or overage potential power. The theoretical capacity of 50 per cent can be
computed from the discharge of 50 per cent duration as represented by the average flow
duration curve. (Sometimes called "power available for 6 months or 4380 hours").
Denotation : NP50.
4. Mean potential power. The value of theoretical mean capacity can be ascertained
by taking into account the average of mean flow (system of area equalization). The
average of mean flow is understood as the arithmetic mean of annual mean discharges
for a period of 10 to 30 years. The annual mean discharge is the value that equalizes
the area of the annual-flow duration curve (Fig. ). The sum of the mean potential
powers for an entire stream is termed gross river power potential by the Economic
Commission for Europe (ECE), Committee on Electric Power. Denotation : Npm.
For the characterization of potential power resources, the joint tabulation of values
NP95, NP50 and NPm has recently been considered expedient. This view was adopted
by the World Power Conferences.
28.-
I must be remembered, however, that the values Np95 and Np50 are often
computed from the flow duration curve of a year considered as of "average flow type".
Considering that the flow duration curve for a chosen "average" year does not
necessarily represent the average flow duration curve for a longer period, but is likely to
differ considerably, moreover, that the choice of the year of "average flow" is a rather
intricate problem far from being unequivocal, it is obvious that correct data will be
obtained only if the average-flow duration curve for a longer period is developed.
4.2.1. Economic significance of potential power resources of a site is influenced by
a great number of factors other than hydraulic, such as geographical, geological and
topographical conditions, energy demand etc...Ignoring these and comparing relative
values of power potential as reflected by hydraulic conditions only, the following four
aspects are to be taken into consideration :
a) The absolute quantity of theoretical water power resources.
b) The relative share of discharge in the power. It is well known and can be readily
proved that, among the hydraulic possibilities representing equal magnitudes of power,
the more advantageous are those where the power in question originates from a smaller
flow and a higher head. This statement points out the advantage of highland
developments over power stations situated in hilly regions or lowland areas.
c) The relative annual fluctuation of available potential power. This can be
characterized by the ratio of the values Np50 to the values Np95 (or Np100). If the
hydraulic gradients in case of different medium and minor flows are approximately
equal, the ratio of powers can be substituted by that of the corresponding flows.
It is self-evident that a smaller quotient.
Νp50
α = ------------ or
Np95
Np50
α = -------------1
Np100
reflects a more favorable hydraulic possibility.
Moreover, in case of low-head developments the flood ratio is also a
considerable hydrological factor because it generally has an effect on the possible
duration of continuous energy production. With rivers of relatively minor flood waves,
damming as such can be maintained in many cases even during high-water periods (e.g.
power stations built on the Rhine, and some other low-head developments in
Switzerland); On the other hand, in rivers where relatively heavy floods occur, the
raising of the flood water level is not everywhere permissible. In order to ensure a free
runoff of freshets, in such cases damming during high-water periods is to be
discontinued. This, in turn, causes a more or less length break in energy production.
The relative degree of flood ratio can be characterized by the following factors :
Qmax
β = -----------Q50
or
Qmax
Qmax
β = ------------ = -----------1
Qmin
Q100
(It must not be overlooked that "flood" in itself is not an exact term. In
comparisons, the frequency or probability of flood discharges must also be taken into
account). However, it must be added that a complete hydrological picture cannot be
attained without plotting average stage and flow durations alike.
29.-
d) The over-year or multi-annual variation of potential power. This can be
characterized either by a simple diagram showing the annual potential power against
time, or by a summation curve of the annual values.
Power resource an be characterized even by annual values of potential energy in a river,
i.e. by the quantities of work :
E100, E95, E50 and Em
all expressed in the kilowatt-hours. These values can be computed as areas of the lower
parts of the potential-power - duration diagram, cut out at the corresponding power
ordinates. If the head is assumed to be a constant factor, independent of discharge, the
computation can be based on the discharge duration curve instead of the power diagram,
and so, according to Fig. 4.2.
Np = 9.8 HQt = a Qt (kW)
and
365
3645


E = 24 a Qt + 24 ∑ aQi = 24 a  Qt t + ∑ Qi  = 24 aF (kWh)


t
t
where t = the duration considered in days,
Qt = the selected discharge
Qi = the daily mean of actual discharge at any time.
It is evident that F is the area pertaining to Qt, cut out from the flow duration
diagram.
The upper limit of potential energy inherent in the river section is obtained in
this form
Emax = Nm 8760 [kWh]
where Nm is the annual mean power. The sum corresponding to the total flow of a
stream, i.e. the value of ΣEmax is termed gross river energy potential by ECE. It must
be noted that Emax as such has no special significance in practice.
30.-
If the technical, energy-economic and other local conditions of a country or
river basin are fundamentally known, the potential water power, as a physical upper
limit, permits some conclusions to be drawn as regards the magnitude of water power
capable of being developed technically and economically.
The value of water power capable of being developed technically is computed
from the potential water power by way of certain reductions. According to ECE, in
certain countries water power potential is expressed in net, rather than in gross, values
by using a coefficient allowing for inevitable losses in head, discharge and power. The
all-over coefficient for reducing the gross potential is estimated in general at about 0,75
or 0,80. Therefore, the formula and nomenclature recommended by ECE reads as
follows :
net river power potential
Nm net = (7.4 - 8.0) Σ QmH [kW]
where Qm = the arithmetic mean discharge, and
net river energy potential
Nm net = 8760 Σ Nm net [kW]
Then from the range of technically utilizable power the most favourable
possibilities can be selected and the process of development, including technical and
financial plans, determined on the basis of economic considerations.
It is evident from the above considerations that the first step towards the
systematic development of power, and especially water power, is to correctly determine
the potential resources.
Naturally, there are some river stretches which, for certain reasons, are entirely
incapable of being utilized. Such reasons occur usually in inhabited flat regions, where
the required damming of rivers cannot be permitted in the vicinity of existing
settlements or towns. Nor can the lower sections of major rivers, where the slope of bed
is extremely small, be taken into account, because the erection of hydraulic structures
on such sites would prove highly uneconomical. Therefore, according to the relevant
definition adopted by the World Power Conference, when determining potential water
power resources, the power of only such sections of stream shall be computed as are
supposed to be capable of being actually developed. Such sections are styled "power
sites". This distinction seems to be fundamentally logical, but is still remains
questionable what should be regarded, in a given case, as a power site "incapable of
being developed". At the present stage of technical development there is little chance to
call a problem of water development insoluble or to quality a river section "incapable
of being developed". The actual situation is that the application of the terms "capable"
largely depends on economic considerations. Therefore, great caution is necessary in
connection with the river stretches which are qualified incapable of being developed,
and thus excluded from the carefully compiled statistics of theoretical water power
resources on account of their being found uneconomical at the present time. Naturally,
the sections whose utilization does not appear to be economical at present, yet have
conditions differing but slightly from those generally required, may be included in the
statistics of water power. The omission of only such utilization possibilities is justified
as are completely unreasonable from the economical aspects. Considering the fact that
31.-
it is rather complicated to draw a definite limit, it seems to be expedient to determine
the amount of potential water power for the entire length of every watercourse as well.
32.-
4.3.
Energy output diagram
Final water power estimates should be prepared at a more advanced stage of
planning, careful consideration being given to the effect of all factors involved, such as
losses, possible changes in headwater level, and varying guaranteed efficiencies of
machinery to be installed. Rough as well as final water power estimates should
generally include the following details :
1. The average power curve constructed on the basis of the average duration (Mean
of 10 years at least).
2. The power curves for years of low, high and average river flow selected from a
period of considerable length.
3.
The graph power generation. This graph is readily constructed from any of the
power curves plotted for a given power plant by the aid of a rating curve or rating table
showing the power head relation, for essentially only the ordinates of the power curve
obtained on the basis of duration data are rearranged in actual order of occurrence.
Since the generated power is directly dependent upon the available head, the stage
record of the tailwater level can readily be transformed into the time order of power
generation. The graph thus obtained is also referred to as the energy output diagram.
4. Investigation of market conditions in order to determine the amount of
hydraulically available energy that can be delivered into the system. The possibilities
and conditions of co-operation with other power producers, with steam or hydroelectric
plants, or possibly with pumped storage plants, should be studied. All of the
hydraulically available energy should actually be utilized as far as possible.
5.
4.4
Calculations and graphs revealing the cost of hydroelectric power.
Evaluating the economic value of power stations
The viability of a hydro-hydraulic power station :
- increases with the rate of consumption of the power produced
- is a function of the skill with which it is operated and maintained.
However, it is also important to have regard to other criteria which go beyond the strict
bounds of the break-even calculation :
- the creation of productive activities of an industrial nature ;
- the development of communal services such as schools, dispensaries, water
pumping,
irrigation, and so on ;
- reduction in the cost of maintaining the headwaters.
In these circumstances the aim of this paragraph which follow is to establish basic
outlines and procedures which will help to provide a sound financial approach to a
project.
4.4.1 Cost estimates
The cost of a hydro-electric power station varies widely from one country to
another and depends on the site conditions and the expenditures on equipment and civil
engineering.
33.-
The range is from US$800 to US 3,300 per kW installed (Table 4.1). It must,
however, be viewed alongside other use for the water after it is extracted from the river,
such as irrigation, mains water, reduction in the upkeep costs associated with waterways
(e.g. banks and bridges) and so on.
Price
Place
Height
per installed
kW US $
% electromec.
% civil eng.
Power
Total
France
5m
20 kW
2 500 $
35/40%
60/65%
France/USA
10m
50 kW
1 900 $
20/40%
60/80%
France/USA
10m
200 kW
2 500 $
20/40%
60/80%
France
10m
500 kW
1 700 $
40%
60%
Pérou
50/ 60 m
20 kW
2 500 $
52%
48%
France
50/200 m
150/400 kW
1 100 $
50/60%
40/50%
France
50/200 m
200/1000 Kw
600 $
50/60%
40/50%
France
50/200 m
> 1000 kw
900 $
50/60%
40/50%
Table 4.1 - Examples of the division of investment in a number of installations
4.4.2.
Running costs
Bearing in mind that water power is free and naturally renewable, these costs
come down to the following elements :
- possible policing costs, upkeep of the buildings and installations;
- taxes ;
- insurance ;
- provision for repairs ;
- miscellaneous expenses (for example, way-leave charges for the canals or
penstock).
Under normal condition, those charge are 0,5% for civil engineering works, 1%
for electromechanical equipment, 2% for transmission lines. For the present time the
good range of the cost of the kWh is from 0,01 to 0,15 US$/kWh.
4.4.3 Elements to be considered in the economic calculation
Present-day techniques for analysing economic and financial feasibility are
based on analysing the following elements :
- the net present value ;
- the cost/benefits ;
- the economic life ;
34.-
- the rate of return ;
- the playback period.
The net present value of a project corresponds to the value of the net benefits
(i.e. the future benefits) less future costs. It therefore makes it possible to establish †Ìe
foreseeable profitability of a project in advance. This value will be compared to the
value of other projects with the same aim, so as to define priorities.
The cost/benefits. In order for a project to be viable, a cost/benefit analysis
must naturally conclude that the advantages outweigh the costs. However, definitions
are extremely flexible insofar as they take into account not only precise material data,
such as cost of equipment and labour, receipts from the sale of current, etc..., but also
intangible data such as social or health advantages, the impact on irrigation and mains
water supply, and so on.
Under normal conditions, the economic life is the following one :
- civil works
- electromechanical equipment
- transmission line
- oil/gas steam power plan
5 years,
25 years,
40 years,
25 years.
The rate of return is the relationship, expressed as a percentage, between the
annual income from the project (net benefits) and the investment costs.
The rate of return must be linked to the cost of borrowing, the risk in the
project, the method of financing, and the state of the economy, having regard to the
social impact of the project even though they may be difficult to give a value.
The playback period is a concept often used and expresses the relationship
between the total investment before tax and the annual income before tax.
Figures 4.3. to 4.5 show some concepts about the cost of an hydro - power plant.
35.-
Costs of a small hydropower plant and a low head large hydropower plant
Electrom. equ.
Studies
35%
Civil works
55%
10%
Small Power Plant - 1.5MW - Head 14 m
15%
Electrom. equ.
5%
Studies
Civil works
80%
Large power plant - 626 MW - Head 16 m
Figure 4.3.
36.-
TOTAL COST OF ONE HYDROPOWERPLANT
Item
Amount
Civil engineering works
Electromechanical equipment
A
B
Substation
=A+B
Contengencies
20% civil engineering works
10% electromechanical equipement
0.2 A
0.1 B
Subtotal
S = 1.2 A + 1.1 B
Survey, studies and administration
0.1 S
Total cost of the hydropower plant
T = 1.1 S
Figure 4.4.
Local currency
Foreign currency
Civil engineering works
70%
30%
Electromechanical equipement
10%
90%
Figure 4.5.
37.-
CHAPTER V
STUDY OF SMALL HYDROELECTRIC INSTALLATIONS
5.1
General arrangement of power developments basic principles
When deciding upon the location and general layout of a power plant, the following
main items should be carefully considered :
1. Potential power of the river or river section selected for utilization mentioned
previously. Watercourses are preferably classified according to the specific potential power
of the dimension kW/km. Any section for which this value is reasonably constant can be
characterized by the mean value pertaining to the stretch in question.
An illustrative notation may be adopted for mapping purposes, according to which the
specific potential power is represented by shaded areas of corresponding size or by lines of
corresponding number or thickness. The specific potential power of a watercourse
between major tributaries may also be represented by colored circles. Both methods are
illustrated in figure 5.1.
2. Geographic situation f existing and projected water and other power plants along with
the transmission network.
3. Location and nature (electrochemical or other industrial lighting, miscellaneous) as
well as predictable greatness of power demand.
4. Topographical conditions of the river valley and the stream bed play an important role
in deciding upon the types and location of the plant.
5. The general layout will be greatly influenced by the geology of the site.
6. Existing hydraulic developments and structures : power plants, weirs, flood protection
embankments, pumping stations, irrigation works, etc... cannot be neglected either.
7. Settlements and traffic conditions. Consideration should be given in addition to the
prevailing situation to future trends of development as well.
8. In designing low-head plants, existing and possible reservoir capacity should be
reckoned with, since operation of downstream plants benefits from the ensuing regulation.
9. Energy generation should be co-ordinated with order purposes. Structures appurtenant
to the power station should, therefore, be designed to serve wherever feasible, other
interests as well (irrigation, navigation, domestic and industrial water supply, etc...). A
significant reduction in the cost of hydro-electric power may result from a multipurpose
utilization of this kind.
10. Development plans for the entire river or preferably for the entire system, at least in the
preliminary stage, should be drafted before the location of individual plants is decided upon.
Great capacity storage reservoirs can usually be developed on steep upper sections
of the river valley and in valleys of tributaries. The water stored in these reservoirs of
relatively great capacity (seasonal, annual, over-year storage) not only aliment the high head
plant immediately supplied, but also a favorable effect on the flow in the whole downstream
section, as mentioned under point 8.
38.-
Figure 5.1 - Illustrative notation for specific potential power
Economics of downstream run-of-river plants may significantly be improved by artificially
increasing dry-water flow. Great-capacity storage reservoirs and only these, are capable at
the same time affording material flood control to sections downstream.
If the plant having sufficient storage, capacity operates in daily speak loads periods, i.e.
intermittently, a downstream regulating reservoir should be constructed, in order.
a. to protect the bed and banks of the river against detrimental effects of surge waves,
b. to protect navigation on the river downstream and
c. to ensure uniform water supply for the downstream plants.
It is sometimes desirable to operate several plants situated on middle or lower courses of a
canalized river as peak load plants to take care of daily or, in extreme cases, of weekly peak
load demands. The uppermost plant of the system should, in such cases, be provided with a
reservoir of great storage capacity to serve as the reservoir of the whole set.
A pond of similar storage capacity is required downstream below the last plant to serve as a
regulating basin for the whole system.
Naturally, it may become practicable to build a power plant at the dam of the regulating
basin too. This plant, however, cannot function as a peak load plant but only as one with
run-of river operation. All plants on a watercourse or within a river basin should co-operate
in a centralized system organized with due regard to all requirements of power generation
and multipurpose water utilization. Projecting will be most effective if regional plans are
drafted in accordance with, and on the basis of, a national power and hydraulic development
scheme.
In the more advanced stages of planning a number of additional factors affecting the
general layout should be taken into consideration ; these will be treated later, when
discussing individual structures.
The problem of choosing between the two main types of low-head developments
the run-of-river and the diversion canal type, will be mentioned last.
The head created by a diversion canal along a river having a float slope is obviously small,
unless there are loops of considerable length than can be shortcut. If at the same time the
discharge to be conveyed is significant, the relative costs of the canal will necessarily be
39.-
great. A fall of considerable height can be developed, on the other hand, by means of a
relatively economical diversion canal in the valley of a river with a steeper slope where the
discharge to be conveyed is generally smaller. Although no rule of general validity can be
established, certain basic conclusions can still be arrived at. The diversion canal type of
development is usually preferable on rivers with steeper slopes and as a rule with smaller
discharges, whereas the run-of-river type seems more advantageous on rivers having flat
slopes and ample runoff.
A diversion canal is preferable if it is possible to shootout a rocky stretch
interspersed with rapid or a shallow section, the regulation of which would be difficult. The
power canal would in such cases at the same time benefit navigation. This latter statement
relates obviously to middle and lower courses of major rivers only where the ensuring of
interrupted navigation possibilities is of primary importance. Owing to surrounding low
banks, inhabited and cultivated areas, a significant raising of the water surface is not always
feasible. On such reaches a number of low-head barrages would be required for
canalization. This solution however, would not be advantageous either for navigation or for
power generation. Therefore, wherever topographical and geological conditions are
favorable, the diversion canal type of development is used instead.
It would be difficult to establish general rules, whereby, economic limits of the two
alternatives could be determined. The decision is strongly influenced by conditions of
hydrology, topography and geology, in addition to those mentioned above. It may be
informative to mention that diversion canal types of development may prove economical
even in cases of slopes as flat as 20-30 cm/km. In rolling country, on the other hand, this
type is preferred if the slope of the river valley is 100-150 cm/km or even steeper. Under
intermediate slope conditions individual site features are decisive.
5.2 Definition of micro hydro-electricity
5.2.1 Context
One indicates under the hydroelectric term of micro hydro power plant (MHE), a
hydroelectric generating station of energy of low power. In fact it is allowed that the powers
of the MHE extend according to ranges going from 5 to 8 000 kW for falls from 1,5 to 300
meters height, for a flow of a few hundred liters to a few tens of meter-cubic a second.
It acts, in the majority of the cases, of run of the river power stations, with or without small
regulating tank (for example daily storage basin). It is often necessary to know well the
mode of the river (dry season, wet season) for the dimensioning of the turbines and the
control of the production. Work of civil engineering relating to the works of catch and
adduction is often completed at lower cost, with the average buildings.
5.2.2 Use of the MHE
The MHE can contribute to the food of a network inter-connected with other power stations,
but it much will be used in network isolated to provide electricity necessary to a village, a
40.-
small city, a complex medical, industrial or agricultural far away from the lines of
interconnections of the principal network.
As table 5.1 shows it, the powers and the daily consumptions for agro-industrial uses can
be covered by MHE.
Type of industry
Power of the power
Daily Consumption
station
Sawmill
30 - 60 kW
120 - 240 kWh
Carpentry
3 - 15 kW
15 - 75 kWh
Sugar plant
10 - 20 kW
50 - 100 kWh
Flour mill
3 - 20 kW
18 - 20 kWh
Spinning mill
2 - 6 kW
10 - 30 kWh
Treatment of coffee
5 - 30 kW
35 - 210 kWh
Quarry
6 - 30 kW
30 - 150 kWh
Ice plant
6 - 60 kW
48 - 480 kWh
Slaughterhouse
5 - 10 kW
25 - 50 kWh
Refrigerate rooms
6 - 60 kW
72 - 720 kWh
Tiles plant
2 - 12 kW
12 - 772 kWh
Pumps house
2 - 100 kW
8- 400 kWh
100 - 200 kW
500 - 1 000 kWh
Tea or cotton factory
A small station of much lower power (20 kW) is enough to ensure the electric production
necessary to the life of a village as shows it the example (table 5.2) of a calculation of
energy necessary for a village:
5.2.3 Characteristics
The MHE must be robust, simple and reliable. Moreover maintenance of the MHE must be
tiny room to its simpler expression and require only one simple manskill or not qualified
given that these power stations are often far away from the great centers. Finally the MHE
must be perfectly autonomous for their starting and their operation and thus in particular not
claim any fuel.
41.Need daily of a village
Energy necessary kWh
Pumping of 10 m3/jour of drinking water potable to a depth of 25 m
and storage in a tank raise, with 50% of output of pumping
1,65
Pumping of 6 m3/jour of water for the cattle (150 head) with a depth
of 25 m, with 50% of output of pumping
0,81
Pumping for the irrigation of 20 ha during all the year, at a rate of 50
m2 per hectare with a depth of 25 m with 50% of output of pumping
136,00
Lighting collective with 20 lamp fluorescent of 25 W during 10 hour
of night
(nigh) 5,00
Lighting of 100 dwelling have each one 3 lamp fluorescent
respectively functioning 5,3 and 2 hours the night
(night) 15,00
Village industry
90
Trade and administration
14
Total
262
Working installed capacity
20 kW
Tableau 5.2
5.2.4 Constraints
The constraints of the MHE are obviously identical to those of the hydroelectric power
stations of larger importance. Energy on the site concerned must be provided by a flow and
a fall.
However according to the localization and the production of electricity, it seems that one can
distinguish two cases.
In the industrialized countries, the constraints are rather of an economic nature by taking
account of the production and the economic parameters. Indeed according to the use of
electricity produced as subsistence farming, the resale, the exclusive resale with the network,
the various economic parameters such as up-dating rate, tariff, cost of kW installed, rate of
inflation, annual costs of maintenance will be considered various manners.
42.-
In the developing countries, the power stations must ensure a production of electricity with a
great maintainability, according to a simple technology. Within this framework it is
necessary to distinguish also two type of production:
A MHE in an isolated network, often managed by a community or private. It is
generally about a direct and sure answer, at a reasonable cost, with the energy needs
for a rural community. The production must be uninterrupted in order to meet mainly
social needs. It is obvious however that here also the economic parameters will have
to be also considered.
A MHE of years a interconnected network often exploited by a public utility. The
motivation of this service is also different. In this case, the cost of the MHE can be
amortized over all the duration of its exploitation, and thus to carry out a null profit, in
opposition to the private sector which tries to maximize the profit.
5.2.5 Environment
From the point of view of the environment, the MHE have only very seldom a negative
impact on the environment. Indeed because of their low importance and the use of natural
resources renewable, natural environment reception always very favorable this form of
production of electrical energy.
In certain exceptional cases indeed, the MHE can have on the natural environment
surrounding a qualitative impact. If it is true that one associates at the end microphone all
that is small, and thus small aggression or disorder, it should be recalled that the natural
environment is sometimes in an unstable balance and that a small disturbance can the create
a variation of balance.
The negative impacts on the environment often quoted can be as follows:
- unaesthetic aspect of the power station, the hydrant and control;
- noise of the turbines, the speed-increasing gear, the alternator, the transformer and the
water run-off.
- - the hydrant can be an obstacle for migrating fish;
- - the section ranging between the hydrant for the MHE and the restitution with the
river, must, for the maintenance of the watery life, to permanently receive a flow
corresponding at least to the medical flow;
- - in certain periods of the year, the tank upstream can suffer from eutrophization
accompanied by the biological effects which this phenomenon involves;
- - in the case of large tank, the natural transit of the sediments can be disturbed.
In all the cases, the evaluation of the harmful effects through the matrix of impact must be
accompanied by specific, technical and financial proposals, of measurements of mitigation
and repair, such as the installation of master keys with fish, the control of the reserved flow
and its chemical characteristics, the maintenance of the water level.
43.-
5.2.6 It is not hydro-electricity in model reduced
In conclusion of this first paragraph on the hydroelectric of micro power plant, it is
necessary to insist strongly on the fact that it micro hydro-electricity should not be regarded
as a small-scale model of the hydro-electricity of great and average importance.
The distribution of the costs of construction is very different from that met for the other
types of installations as figure 5.1 shows it hereafter. Moreover diagrams of design of the
works, as well of civil engineering as electromechanical different and will be adapted to the
special conditions of operation of the micro power plant. One will take in particular account
of the lack of logistical support and technique due to the distance and of the production in
isolated network.
5.3 Types of micro power plant
5.3.1 Works of civil engineering adapted to the micro power plant
Even in the case of the MHE, the geological nature of the grounds rivet also greatest
importance to determine the types of foundations and anchoring of the works of adduction
and hydrant, building sheltering the electromechanical equipment.
In the case of current works, one usually proceeds by simple recognitions like wells and
trenches, which can be carried out by local skill man and does not require specialized
equipment. The geological investigation will be however deepened by possible surveys
and special tests in the case of large-sized works to multiple goals: drinkable water
conveyance, irrigation, creation of water reserve.
The stability of the grounds will be examined on the unit of installation in order to avoid
any risk of dangerous movements.
The choice of the type of work of civil engineering will depend not only on the
topographic, geological and hydrological conditions, but also of the availabilities in skill
man and materials.
The share of the civil engineering reaches sometimes, as one showed, more than 50% of
the total cost of a MHE, and it is obvious that this station can be practically assured entirely
by local resources.
There is a very large variety of works of intake, since most rudimentary (submarines
intakes), until most elaborate technically (dams). The conditions of construction, and in
particular the sealing will be less severe, of course, for the run of the river works, that for
the dams with multiple purposes.
44.-
A dam submarine can be consisted a channel dug across the river.
A work in boards and riprap is a not very expensive construction which allows an easy
adjustment of the flow.
Works in gabions, made up of parallelepipeds of galvanized netting, filled with rollers, will
be clogged naturally by fine materials carted by the river or laid out on both sides of a clay
core.
The sheet piled walls usable in alluvial grounds, require the use of special machines. One
will use also the earth or rock fill dams. It will be noted that the spillways must be adapted
to each type of works, flexible or rigid
The departure of the adduction is equipped with grids intended to avoid the introduction of
floating bodies and solid materials. The installation of a valve will make it possible to
protect and insulate the channel.
The drain pipes, established by taking account of the stability of the grounds, will be with
free flow or flow in load.
The desilting basin, with system of purging, ensures the decantation of sands and the silts,
like their evacuation.
The room of setting does not charge, preceded by a valve of insulation, is the result of a
adduction with free flow, and the departure of the pressure pipe. The depth of this tank
must be sufficient to maintain the pipe pressure below the level of water, in order to avoid
the air intakes.
The chimney of balance is a tank arranged with the junction of a drain pipe and a pressure
pipe. It reduces the overpressures caused by the brutal closing of the tap of admission of
turbine (water hammer).
The pressure pipe directs water on the turbine while following preferably, the greatest slope
of the ground in order to reduce its length. It is out of steel or concrete (sometimes out of
cast iron or plastic in the case of the MHE) and must resist pressures which result the drop
height.
The buildings protect the equipment from production and the manual or automatic control
units, against the bad weather and the risings.
The tail water canal at the exit of the power station returns turbinate water in the bed of the
river. This channel, also called outlet channel, must be concreted in its higher part, to
avoid any risk of impoverishment of the soil and foundations.
5.3.2 Electro mechanics of the microcentrales
2.1. Turbines
One will not take again here the general description of the electromechanical part of the
hydroelectric power stations, but many considerations specific to the microcentrales.
45.-
Because of the low cost of traditional thermal energy and interest rate, the exploitation of
the hydroelectric sites of weak or average power was neglected in the last few years, those
were regarded as uneconomic.
Thus the equipment of sites of large, even of very great power, led the turbine manufacture
to develop a suitable technology. In addition, the cost of the studies for these great
installations, is such as it allows the dimensioning and the individual manufacture of each
machine to be conceived.
It is obvious that such a design is inapplicable with the cases of low powers where it is
necessary quite to the contrary to seek a capital cost and a minimum maintenance for one
duration as long as possible.
Thus, the various manufacturers of turbines managed from there to work out groups
standardized for the small hydroelectric units. This design is related to the following
principles:
1. Optimal use of the most modern knowledge acquired in the field of the turboshaft
engines.
2. Supply of the electromechanical whole in a compact form lends to the installation and
operation.
3. Hydraulic, simple, and robust design using standard elements (wheel, vacuum cleaner,
etc.) in order to lower the costs and the delivery periods. The output of the turbine is
not regarded any more as one of the essential elements intervening in the selection
criterion of the type of groups of production.
4. Renouncement of a technological sophistication useful, but fragile, asking a man skill
specialized for maintenance and repair.
This design of the development of micro the turbines aims at the powers between 100 and
2 000 kW. Below, solutions even newer and simpler were developed for these powers
considered to be wrongly until now economically uninteresting. It is true that in these
cases the social point of view must be also very largely considered. Certain light groups,
adaptable in particular to sites not having inter-connected networks, were developed to
make it possible to go down below 100 kW. Above 2 000 kW, one can return to the unit
design of the hydroelectric groups.
In the same way, the field of exploitable, according to this design, ranges between 1 and
300 m of fall (being able exceptionally to be wide up to 800 m in certain cases). In this
relatively wide field, the types of standardized turbines are, in accordance with the
preceding scale:
1. the turbines propellers (Kaplan) for the weak falls;
2. Francis for the falls average;
3. Pelton for the high falls;
4. Banki-Mitchell groups for a rather significant field of falls;
5. certain propellers groups and wheels of surface (see figures 2 and 3) for the very low
powers (≤ 100 kW),
46.-
It is mainly in the field of the weak falls that the large manufacturers made carry their efforts,
in order to develop the equipment for run of the river plant..
The solution which was most generally adopted is to develop propellers with adjustable
blades with the stop, by reason of mechanical and economic simplifications, in series in
standard diameters. Those are assembled on siphons groups so as to reduce the cost of the
civil engineering, or groups with traditional axial flow.
In the last few years of the turbine manufactures developed the manufacture of small bulbs
groups with bevel gearbox, on which an alternator was assembled whose axis of rotation was
perpendicular to that of the turbine. Others conceived a group bulb with bevel gearbox and
stationary feeder, equipped in a way interdependent of an alternator provided with its own
system with regulation and excitation. There is thus a compact and autonomous system,
assembled in factory. In the ranges of very low powers (of some kW to 100 kW),
manufacturers developed turbines propellers which one can place directly at the end of control
(figure n°2). They can be made up of a group bulb, completely careened, the careenage being
used as vacuum cleaner.
Other manufacturers also developed the principle of waterwheel floating at the surface of the
rivers (figure n°3). This system which does not require any civil engineering, is based on the
recuperation of the kinetic energy of the flow and is well adapted to the rivers with fast
current.
In coastal field and estuary, the mill of tide, in an improved form, can still appear interesting
for the supply of electricity in certain characteristic sites, making it possible to adapt the small
standardized equipment of production available in the trade.
One chooses the turbine according to the curve of the flows and head. The output of the
turbines according to the load varies considerably according to the type of turbine. The
turbines Banki and Pelton function up to 25% of their maximum flow while a turbine
propeller with stationary feeder hardly functions below 75% of the maximum capacity.
According to the minimum flow to harness, the guaranteed minimum capacity, the economic
optimum, one will consider the installation of one or more hydroelectric groups.
For the small powers, field of the MHE, the design of the standardized turbine are most
favorable.
2.2 Alternator
The regulation speed of the turbo alternators groups is identical to that under consideration
for the power stations of greater importance. One will point out some considerations more
specific to the MHE.
The generators of power must, in the ideal case, to satisfy the following conditions:
- the provided power must be constant in intensity and frequency, whatever the conditions
of load and the temporary variations that this one can undergo;
47.-
-
- the form of wave of the output tension must be, as far as possible, sinusoidal and
comprise only negligible harmonics. This mainly in the frequency band of radio
transmission.
In practice, one is however obliged, for economic reasons, to sometimes free some from
these too constraining criteria. Indeed, the types of load of an isolated network are
diversified generally enough and can comprise:
- systems of heating and lighting, affecting only the tension in amplitude;
- mechanical loads, assured generally by asynchronous motors affecting the tension in
amplitude and frequency, as well as the demand for reactive power;
- equipment of telecommunication (radio and television) which is very sensitive to the
variations of frequency and the disturbing emissions of the electric system.
In agreement with the preceding remarks, one was thus brought to define certain tolerances
on the characteristics of the provided electric power, which one will be able to retain this:
- the nominal voltage must vary in a beach of ± 5 % whatever the load;
- the reactivity power coefficient must remain equal to or higher than 0,8;
- the rated frequency must vary in a beach of ± 2 %;
- - the distortion of the harmonics and the interferences radio must remain as weak as
possible.
It is the whole of these constraints which result in equipping the groups with energy
production of systems of automatic regulation, reacting to the radial forces. The most
significant regulation and most delicate is that the speed which determines the frequency.
If the group feeds a small network, one is limited to the use of a synchronous generator. The
choice between the synchronous generator and the induction generator (more economic),
arises only for machines having to function on a significant network and which do not have
to take part in the adjustment of the tension.
The cost of the alternators is minimized when speed is high (750, 1.000 and 1.500 tr/min),
and particularly when they form part of a standardized series, in condition however which
they admit the values of the over speeds imposed by the turbine, which is not the case in
general.
If the dimensioning of the turbines leads to relatively low number of revolutions, one can be
brought to insert a speed-increasing gear between the turbine of the alternator provided that
the made economy overrides the cost of the multiplier, taking into account the brought up to
date value of the losses of energy.
The choice the speed of a turbine is influenced by the profile of the wheel and the beach
drop heights in which it has to function.
5.3.3
Distribution
The distribution of the electric power will be ensured by the air lines assembled in an
economic way on posts out of wooden. One will adapt the tension of these lines according
to the distance and the transported power. Here also the economy of the project will be
48.-
guided by the use of standardized parts. The cost of the distribution, including the
measurement and concerned with safety units (circuit breaker) (meter) is too often
forgotten in the calculation of a MHE.
5.4 Methodology for the realization of a site
4.1 Design
A micro power plant being a hydroelectric power station of low power, economic
considerations are at the base of the following characteristics:
a) it preferably functions run of the river plant with a small reserve of regulation day skill
man. Whenever the installation of a more significant reserve of storage is
particularly economic, the tank will be made up in particular for an irrigation, a agroagro-cattle reserve or a regulation of the flow downstream.
b) The equipment must above all be simple and robust in order to limit operating
expenses.
4.2 Methodology of the choice of the site
The criteria retained for the choice of the site are as follows:
a) Theoretical criterion: flow X drop height
This criterion is closely related to the hydrological mode. If it quasi totality of the flow
occurs during four months of the year, this type of mode requires the large ones and
expensive volumes of storing to regularize the flow, especially if one takes account of
the possible significant losses by evaporation.
One takes before a a whole option of high fall putting up with a proportionally reduced
flow. Moreover of the hydro-geological considerations will be taken into account to
select possible sites supplied with perennial tablecloths. However the equipment of low
fall, with agro-agro-pastoral tank must also be retained.
b) Criterion of proximity
The experiment makes it possible to say that the valid sites must be at a reasonable
distance from the centers of consumption in order to remain within the economic limits
imposed by the cost of the lines of transport.
c) Criterion of insulation
The selection must take into account either the centers isolated at cost price from diesel
production high, or of the agglomerations not yet served by the official public
distribution and deprived of reliable means of production, if not for a few hours of
lighting.
d) Criterion of the socio-economic effects induced
49.-
As far as possible, the study must evaluate the secondary macro-economic effects
induced by the control of the water created by installation: drinking water, agro-pastoral
water points and irrigation in particular.
4.3 Calendar of the realization the indicative course of the realization of a MHE is as
follows:
Phase 1: Diagnosis:
Data-gathering
Evaluation of the resources
Evaluation of the request
Approaches economic and financial
Diagnostic of abandonment or continuation of the project
Phase 2: Feasibility study:
Recognition of the ground
Hydrology, topography, geology
Installation of limnimetric scale
Preparatory project summary:
Outline, estimate, possible
Site surveys
Designs of the works and the electromechanical equipment economic
Economical and financial analysis
Plans of financing of administrative authorizations
Phase 3: Preparatory project detailed final
Drafting of the report and financial
Phase 4: Making of the contracts
Set up of the program
Launching of invitation to tender
Choice of companies and of the material
Phase 5: Completion of the work of assembly
Orders electromechanical equipment
Civil engineering works
Commissioning of the turbo alternator equipments and electric material
Transmissions lines construction
Phase 6: Starting test and introduction
Tests and acceptance of the power station
Staff training
Normal exploitation.
50.-
5.5
Studies
If the preceding enumeration takes again almost all the program of studies which one
carries out for significant hydroelectric installations, in the case of the MHE one will be
able rather often to decrease or concentrate this program.
Thus the feasibility study will be thorough directly until preparatory project detailed
what will make it possible to obtain surer prices of the standardized equipment.
It is necessary nevertheless to be attentive at the duration of the studies and their costs.
As well as the first graphs showed it, one can envisage approximately 15% of the total
cost of the investment, that is to say a fork from 150 to 450 $ US per kW installed. The
time between the startup of a project and the electric supply of power will be never short
and of the deadlines from 3 to 8 years are unfortunately normal.
5.6 Environmental impact
5.7 Realization
5.8 Legal aspects of production
The production of electricity is regulated in the case of a MHE feeding a wide-area
network of a national producer. The authorization of connection and the contracts
financial will be negotiated with the persons in charge, who often depend in the case of
public companies on energy production, for the Ministry for Energy. All these
legislative and lawful aspects are significant and can even be a barrier to the
development of the installation of private MHE, in the case of national producer thus
seeing escaping to him its monopoly production. The resale price of energy will be
maximized in order to increase the profit. This part will be thorough in the paragraph
devoted to the criteria of profitability.
In the case of a MHE functioning in isolated network, it will be necessary to set up an
administrative and technical structure able to ensure the production, the exploitation and
maintenance. The authorizations of production and construction, hydrant will be
negotiated with the administrative, political and usual authorities local. A tariff structure
will be put at its place. It will hold account at the same time financial requirements of
the exploitation (refunding the loan, cost of maintains and the replacement the small
equipment, damping of the equipment) and of the social role of the supply of the
electrical current. The tariff will take into account the standard of living of the future
users and the possibilities of economic development, their technical capabilities and
financial to use the electric power. Original solutions could be developed to avoid the
traditional but expensive structures in the case of MHE, individual meter. One should
not hide however which management can be particularly hazardous if it is not organized
by a respected official authority.
51.-
5.9 Economy of the project
The profitability of a MHE is
- increasing with the utilization ratio of produced energy
- a function of the nature of the request
- function of the quality of its exploitation and its maintenance.
However, it is necessary to take account of other criteria which overflow of the strict
calculation of profitability:
- creation of productive activities of the industrial type
- development of collective services, schools, dispensaries, pumping of water, irrigation
- improvement of the social life
- reduction of maintenance costs of the rivers upstream
Under these conditions, the object of the paragraph is to present basic indications and
methodologies suitable to facilitate a first financial approach of a project
5.1 Estimate of the costs
The cost of a MHE varies in great proportions according to the countries, the conditions of
the site and civil engineering and capital expenditures'.
The advanced figures go from 1000 to 38OO $$US kW installed. They will have however
to be balanced according to the other uses of water starting from the catch in river:
irrigation, adduction, reduction of the maintenance costs of the rivers and the works
(bridges, banks...). They will have to take account of the costs of the environmental
protection.
5.2 The running costs
Taking into account the exemption from payment of the hydraulic power, naturally
renewable, these loads are reduced to the following elements:
- possible guardings, maintenance of the buildings and the installations
- possible taxes
- insurances
- provision for repairs
- sundries (for example, right-of-way of the channels or the pressure pipe)
The whole of these annual loads accounts for approximately 3 to 5% of the investment. It is
however necessary to add to it the financial expenses of refunding of the interests and
refundings of the capital.
5.3 Economic calculation
The techniques of financial analysis of the MHE are comparable with those used for great
installations. Some particular points however here will be noted.
The following elements will be analyzed:
52.-
- brought up to date net amount
- the cost/benefits
- rates of profitability
- the time of return or the rate of profitability interns
The brought up to date net amount of a project corresponds to the value of the advantages
Nets (i.e. future advantages), less the future costs. It thus makes it possible to establish in
advance the foreseeable profitability of a project. This value will be compared with that of
other projects having similar objectives, so as to define priorities.
Cost/benefits Their analysis must of course lead, so that the project is valid, to a superiority
of the advantages on the costs. However their definition is extremely flexible insofar as it
takes into account, not only precise material data (cost of the equipment and skill man, sales
revenues of the current), but also of the immaterial data as the welfare benefits or medical,
the repercussions on the irrigation and the water conveyance, etc.
The rate of profitability is the relationship, expressed as a percentage, between the annual
incomes of the project (advantages Nets) and the investments (costs).
The rate of profitability must be connected to the borrowed interest rate, with the risks of the
project, the type of financing and the economic situation, by taking account of the social
repercussions of the project, even if they are difficult to evaluate; The concept of time of
return, often used, expresses the relationship between the total investment net of tax and the
annual receipt net of tax. This time of return usually varies between 5 and 6 years.
It should finally be specified that the design and the realization of a MHE imply a technical
analysis, economic and financial thorough, as well as a rigorous management and a
maintenance of quality.
The principal budget headings intervening in a MHE and their lifespan intervening in
calculations of depreciation are given to table 4.
Category
Engineering civil
Post office
- work of hydrant d' eau
Lifespan
30 with 50 year
- feeder canal d' amenée
- pass with fish
- spillways
- building of factory
Group hydroelectric
- turbine and its regulation
- alternator and its regulation
- multiplier
10 with 30 year
53.Component
electric
general
10 with 30 year
- transformer
- circuit
- breaker
- lighting
- line of transport
- transformer of line meter
General service
-drainage and draining
10 with 30 year
Material of stopping,
- valve and coffer dam of hydrant d' eau
10 with 30 year
of hydrant d' eau and
- valve of room of setting in load
of gallery of escape
- valve of crest gate of spillways
30 with 50 year
- control force
- shielding and accessory
Table 4
On profitability of a MHE will depend however much on the destination on produced
energy. If this one must be delivered to a network of great power, the objective will be to
sell a maximum of kWh, expensive possible, for the least investment. But if, as that
generally occurs, produced energy feeds an isolated network, the problem will be initially to
ensure a safety of supply for a satisfactory cost price, i.e. in relation to the social standing of
the future users and their capacity of payment.
In this case the cost-benefit analysis will hold account as socio-economic advantages as the
installation of a MHE would bring.
5.4 Financing
In all the countries, the local communities have more and more recourse to the credit to
answer their problems of equipment. Because of the international recession, it became more
difficult to find the appropriations necessary, than they are public or private.
It thus becomes essential to know well all the sources of financings available and to know to
present the dossiers of subsidy or loan application.
The technical-economic aspects, the priority character of the project and its social
repercussions will be taken into account, but it will have preferably to form part of an action
of overall development.
The funds of financing of the public sector come:
- international assistances: Agencies of the United Nations, the World Bank with the
International Agency of Development (AID), Banks international for the Rebuilding and
Development (BIRD), the International Finance Corporation (SFI), the European
Development Funds of the European Community (EDF). It is necessary to also note the
54.-
-
support of the Program of the Nations Linked for the development (UNDP) which
finance the feasibility studies and the formation of technician, and that of the Funds of
Equipment (FENU) for the purchase of equipment if the operation appears profitable.
The Organization for the Food and Agriculture (FAO) can also for certain projects of
more agricultural interest provide the budgets necessary for the studies and the
realization.
regional assistances, often ensured by banking organizations the such Bank Inter
American of development, the African Bank, on the basis of reasonable interest rate with
long times of refunding.
not-governmental gifts of organization (ONG), financed by religious associations or
humane, generally applied to isolated cases.
bilateral assistances brought by an industrialized country, in technical and financial
form, with a less advanced country.
55.-
CHAPTER VI
WATER TURBINES
In water turbines the kinetic energy of flowing water is converted into mechanical rotary
motion. As noted earlier, theoretical power is determined by head and mass flow rate. To
calculate available power, head losses due to friction of flow in conduits and the conversion
efficiency of machines employed must also be considered. The formula, thus, is the
following:
P(kW) = Hn.Q.g.ρ.Εtot = Hn.Q.Εtot.9.81
where:
p
Hn
Q
g
ρ
Εtot
=
=
=
=
=
=
Output power in kilo Watts (103W)
Net head = Gross head - losses (m)
Flow in m3/second
Specific gravity = 9.81 m/s2
Density (for water = 1000 kg/m3)
Overall efficiency = E1.E2 .En
For small outputs of interest here, and as a first approximation, the formula can be
simplified:
Hn (m) . Q (l/s)
P(kW) = ------------------------------------200
where Q is in liters par second and an overall efficiency of 51 % is implied. The "rule of
thumb" calculation is therefore on the conservative side.
The oldest form of "water turbine" is the water-wheel. The natural head - difference in water
level - of a stream is utilized to drive it. In its conventional form the water-wheel is made of
wood and is provided with buckets or vanes round the periphery. The water thrusts against
these, causing the wheel to rotate.
One water turbine is characterized by the following parameters:
N
Q
H
specific speed r/m
turbine discharge m3/s
design head m
The so called kinematic specific speed Ns, a dimensionless number is deduced from those
parameters:
56.-
Q1/2
Ns = N ---------H3/4
In practice, each type of turbine has Ns range for good operating, i.e.:
Pelton turbine
Ns = 3 to 14
Francis turbine
20 to 140
Kaplan turbine
140 to 300
Banki turbine
20 to 80
Figure 6.1 Stavelot turbine
6.1 Pelton Turbine
The principle of the old water-wheel is embodied in the modern wheel, which consists of a
wheel provided with spoon-shaped buckets round the periphery (fig. 6.1). A high velocity jet
of water emerging from a nozzle impinges on the buckets and sets the wheel in motion (fig.
6.2). The speed of rotation is determined by the flow rate and the velocity of the water; it is
controlled by means of a needle in the nozzle (the turbine operates most efficiently when the
wheel rotates at half the velocity of the jet). If the load on the wheel suddenly decreases, the
jet deflectors partially divert the jet issuing from the nozzle until the jet needle has
appropriately reduced the flow (fig. 6.3). This arrangement is necessary because if in the
event of sudden load decrease the jet needle were closed suddenly, the flow of water would
be reduced too abruptly, causing harmful "water hammer" phenomena in the water system.
In most cases the control of the deflector is linked to an electric generator. A Pelton wheel is
used in cases where large heads of water are available.
57.-
Figure 6.1. - Pelton Wheel
Figure 6.3. Operation of Jet Deflector and Needle
Pelton turbines belong to the group of the impulse (or free-jet) turbines, where the available
head is converted to kinetic energy at atmospheric pressure. Power is extracted from the
high velocity jet of water when it strikes the cups of the rotor. This turbine type is normally
applied in the high head range (>40 m). From the design point of view, adaptability exists
for different flow and head. Pelton turbines can be equipped with one, two, or more nozzles
for higher output (see fig. 6.4). In manufacture, casting is commonly used for the rotor,
materials being brass or steel. This necessitates an appropriate industrial infrastructure.
Figure 6.4. - Schematic of 2 Nozzle Pelton-Wheel
6.2. Francis And Kaplan Turbines
In the great majority of cases (large and small water flow rates and heads) the type of turbine
employed is the Francis or radialflow turbine. The significant difference in relation to the
Pelton wheel is that Francis (and Kaplan) turbines are of the reaction type, where the runner
58.-
is completely submerged in water, and both the pressure and the velocity of water decrease
from inlet to outlet. The water first enters the volute, which is an annular channel
surrounding the runner, and then flows between the fixed guide vanes, which give the water
the optimum direction of flow. It then enters the runner and flows radially through the latter,
i.e., towards the centre. The runner is provided with curved vanes upon which the water is
largely converted into rotary motion and is not consumed by eddies and another undesirable
flow phenomena causing energy losses. The guide vanes are usually adjustable so as to
provide a degree of adaptability to variations in the water flow rate in the load of the
turbine?
The guide vanes in the Francis turbine are the elements that direct the flow of the water, just
as the nozzle of the Pelton wheel does. The water is discharged through an outlet from the
centre of the turbine. A typical Francis runner is shown in fig. 6.5. The volute, guide vanes
and runner are shown schematically in fig. 6.6 and the diversion of the water at right-angles
to its direction of entry is clearly indicated in fig. 6.7, which is a cross-section through the
turbine.
In design and manufacture, Francis turbines are much more complex than Pelton turbines,
requiring a specific design fir each head/flow condition to obtain optimum efficiency.
Runner and housing are usually cast, on large units welded housings, or cast in concrete at
site, are common. With a big variety of designs, a large head range from about 30 m up to
700 m of head can be covered.
Figure 6.5. - Francis Runner
Turbine
Figure 6.6. - Schematic of Flow in Francis
59.-
Figure 6.7. - Cross Section through Francis Turbine
For very low heads and high flow-rates - e.g. at barrages in rivers - a different type of
turbine, the Kaplan or Propeller turbine is usually employed. In the Kaplan turbine the water
flows through the propeller and sets the latter in rotation. The water enters the turbine
laterally (fig. 6.8), is deflected by the guide vanes, and flows axially through the propeller.
For this reason, theses machines are referred to as axial-flow turbines. The flow rate of the
water through the turbine can be controlled by varying the distance between the guide vanes;
the pitch of the propeller blades must then also be appropriately adjusted (fig. 6.9). Each
setting of the guide vanes corresponds to one particular setting of the propeller blades in
order to obtain high efficiency.
Figure 6.8. - Kaplan Turbine Schematic
Figure 6.9. - Propeller of Kaplan Turbine
Specially in smaller units, either only vane adjustment or runner blade adjustment is
common to reduce sophistication but this affects part load efficiency. Kaplan and Propeller
turbines also come in a variety of designs. Their application is limited to heads from 1 m to
about 30 m. Under such conditions, a relatively larger flow as compared to high head
turbines is required for a given output. These turbines therefore are comparatively larger.
Manufacture of small Propeller turbines is possible in welded construction without the need
for casting facilities.
6.3 Cross-Flow (Banki) Turbine
The concept of the Cross-Flow turbine - although much less well-known than the three big
names Pelton, Francis and Kaplan - is not new. It was invented by an engineer named
Michell who obtained a patent for it in 1903. Quite independently, a Hungarian professor
with the name Donat Banki, re-invented the turbine again at the university of Budapest. By
1920 it was quite well known in Europe, through a series of publications. There is one single
company who produces this turbine since decades, the firm Ossberger in Bavaria, Germany.
More than 7,000 such turbines are installed worldwide, most of them made by Ossberger.
The main characteristic of the Cross-Flow turbine is the water jet of rectangular crosssection which passes twice through the rotor blades - arranged at the periphery of the
cylindrical rotor - perpendicular to the rotor shaft. The water flows through the blading first
60.-
from the periphery towards the centre (refer to fig. 6.10), and then, after crossing the open
space inside the runner, from the inside outwards. Energy conversion takes place twice; first
upon impingement of water on the blades upon entry, and then when water strikes the blades
upon exit from the runner. The use of two working stages provides no particular advantage
except that it is a very effective and simple means of discharging the water from the runner.
Figure 6.10. - Flow in Cross-Flow Model
The machine is normally classified as an impulse turbine. This is not strictly correct and is
probably based on the fact that the principal design was a true constant-pressure turbine. A
sufficiently large gap was left between the nozzle and the runner, so that the jet entered the
runner without any static pressure. Modern designs are usually built with a nozzle that
covers a bigger arc of the runner periphery. With this measure, unit flow is increased,
permitting to keep turbine size smaller. Theses designs work as impulse turbines only with
small gate opening, when the reduced flow does not completely fill the passages between
blades and the pressure inside the runner therefore is atmospheric. With increased flow
completely filling the passages between the blades, there is a slight positive pressure; the
turbine now works as a reaction machine.
Cross-Flow turbines may be applied over a head range from less than 2 m to more than 100
m (Ossberger has supplied turbines for heads up to 250 m). A large variety of flow rates may
be accommodated with a constant diameter runner, by varying the inlet and runner width (x
in fig. 6.10). This makes it possible to reduce the need for tooling, jigs and fixtures in
manufacture considerably. Ratios of rotor width/diameter, from 0.2 to 4.5 have been made.
For wide rotors, supporting discs welded to the shaft at equal intervals prevent the blades
from bending..
A valuable feature of the Cross-Flow turbine is its relatively flat efficiency curve, which
Ossberger are further improving by using a divided gate. This means that at reduced flow,
efficiency is still quite high, a consideration that may be more important than a higher
optimum-point efficiency of other turbines.
It is easy to understand why Cross-Flow turbines are much easier to make than other types,
by locking at fig. 6.11 et 6.12.
61.-
Figure 6.11. - Cross-Flow Runner
Figure 6.12. - Cross-Flow Schematic
6.4 Straflo Turbine
Low head hydro electricity from river flow covers the range of operating heads from the
smallest up to about 40 meters (130 feet).
At the lower end of the range economic considerations usually preclude developments
operating at heads of less than about 4 meters. It is feasible to utilize still lower heads, for
example where water is being controlled for other purposes than power generation the
installation of turbines may be economically justifiable. Such opportunities may occur in
connection with flood control works, compensation water channels and river regulation for
navigation, irrigation works.
The upper end of the low head range, about 40 meters, roughly coincides with the upper
economic limit for vertical-axis Kaplan and propeller turbines, above which Francis turbines
are more economical.
It is inherent in the exploitation of low head hydro-power resources that large volumes of
water must be used relative to the amount of power generated. Thus water passages and
turbine dimensions must be large. Conventional vertical-axis turbines for this duty are not
only correspondingly expensive in themselves, the changes in direction of water flow at inlet
and outlet imply large deep volumes of civil construction.
Arrangements with axial-flow machinery were devised to avoid theses disadvantages, but
are generally rather awkward and cumbersome because of the presence of the generator,
which must normally be on the turbine shaft but not exposed to the water.
Such horizontal (or near horizontal) turbines as the bulb and tubular types have hitherto
generally been used for operating heads of up to only about 20 metres.
The Polar wheel unit is a horizontal turbine able to operate through the whole low head
range as defined above for outputs from about 1 1/2 MW up to the largest.
In the polar unit, the generator is mounted at the periphery of the turbine runner, driven by it
but located externally to the water passage. The waterway could thus be straight, of
62.-
minimum possible length and unobstructed except for the small runner hub and any
necessary support ribs.
Figure 6.12. - Cross Section of a Power Station
Figure 6.12. – Cross Section of a Power Station
1. Turbine runner
2. Adjustable distributor
3. Generator motor
4. Generator stator
5. Access pit
6. Turbine governor
7. Transformer
8. Gantry crane
9. Control desk
10. Switchboard
11. Rack cleaning machine
12. Upstream stop logs
13. Intake screen
14 Operating gantry crane
15.Downstream stop logs
Advantages of the Polar wheel unit
Due to the purely axial flow, the efficiency of a Polar wheel turbine is higher than that of a
vertical Kaplan turbine. (This advantage increases with the head and is even more noticeable
when, instead of a semi-spiral, a full spiral casing is employed as is usual for heads above 30
m).
The rotating outer rim is, however, a source of losses because it rotates against the direction
of water flow.
This produces additional friction which makes the runner efficiency of a Polar wheel turbine
lower than that of a bulb unit with interior generator.
However, the water velocities at the intake of bulb units are about 20% higher than for Polar
<heel turbines with the same spacing. This leads to frictional losses in the intake of bulbs
units and secondary losses in the runner which can be considerably larger than the above
mentioned typical Polar wheel turbine losses.
63.-
Figure 6.13. - General arrangement of a polar wheel
1. Turbine runner
2. Runner crown
3. Generator rim
4. Generator stator
5. Upstream stay ring
6. Downstream stay ring
7. Shaft trunnions
8. Runner hub
9. Shaft cone webs
10. Prestressed bar
11. Distributor outer ring
12. Distributor inner ring
13. Guides vanes
14. Guide bearing
15. Guide bearing
16. Sealing boxes
17. Unit brakes
18 Excitation rings
19. Regulating ring
Main advantages of the Polar wheel unit over the bulb turbine (and even more over the
vertical propeller or Kaplan turbine) are:
1) Greater compactness.
2) Sufficient space around the runner periphery for generators of the largest capacities.
3) Simple and effective generator cooling.
4) Large natural inertia ensures stable operation and avoids power fluctuations.
5) Ability to compete with the vertical Kaplan turbine at heads up to 40 meters.
6.5 "Hydraulienne"...
The "Hydraulienne" provide electrical power using the velocity if the water way by
mean of a floating wheel. ( see figures 6.14. to 6.16 )
The depth of water must be at least 0.5 m and per each wheel the available power could be
up to 15 KW
64.-
Figure 6.14. - Example of "hydraulienne"
Figure 6.15. - Schematic view of an "hydraulienne"
(A gabion is a galvanised steel mesh basket, size 79x20x20 inches, filled with stones)
65.-
Figure 6.16. - Power chart of an "hydraulienne"
66.-
6.6 Comparison of Different Turbines
Figure 6.17. is a graphical presentation of a general turbine application range of
conventional designs. The usual range for commercially available Cross-Flow turbines is
shown in relation (dotted line). In the overall picture, it is clearly a small turbine.
Figure 6.18 - Turbine Application Range
Figure 6.18. shows efficiencies of some of the more important turbine types in relation to
gate opening, e.g. flow rate. Conventional and highly optimized turbines (including the
Pelton turbine which is not shown) achieve efficiencies of more than 90 % in large units.
67.-
Figure 6.19. Efficiency Curves of some Turbines Types
68.-
ANNEXE 1 : EXEMPLE OF TABLE OF CONTENT
1.
INTRODUCTION
2.
OBJECTIVE OF THE STUDY
3.
REVIEW OF PREVIOUS STUDIES
3.1. Financial and Economical Aspects
3.2. Hydrological Aspects
4.
ESTIMATION OF THE ELECTRICITY DEMAND IN THE
PEUSANGAN RIVER BASIN AREA
5.
SITE INVESTIGATIONS
6.
TOPOGRAPHY
6.1
Preliminary Comments
6.2. Changes from the original requirements
6.3
List of Topographic maps
6.4. Methodology
6.5
Data evaluation
6.6. Conclusion
7.
HYDROLOGY
7.1. Introduction
7.2. Data from previous studies
7.3. Site investigations
7.4. Comments on the data
7.5. Determination of the mean monthly discharges
7.6. Lake Tawar Compensation
7.7. Peak discharges
7.8. Peak discharges
7.9
Details of the hydrological analysis
8.
GEOLOGY
8.1. General geological setting
8.2. General seismicity
8.3. Regulating dam at Lake Tawar Outlet
8.4. Peusangan 1
8.5. Peusangan 2
8.6. Borrow materials
8.7. Conclusions
9.
GENERAL CONSTRUCTION SCHEME
9.1. General description
9.2. Regulating weir at Lake Tawar
9.3. Water intake for the Peusangan 1 Power Plant
9.4. Headrace tunnel and penstock
9.5. Peusangan 1 - Power House
9.6. Water intake for the Peusangan 2 Power plant
9.7. Head-race tunnel downstream of Peusangan 2 intake
9.8. Regulating poundage
9.9. Power tunnel and penstock for Peusangan 2
9.10. Peusangan 2 - Power house
9.11. Transmission line
10. ENGINEERING DESIGN
10.1. Regulating weir at the lake outlet
69.10.2.
10.3.
10.4.
10.5.
10.6.
10.7.
10.8.
Water intake and diversion weir for the Peusangan 1 - Power plant
Peusangan 1 - Headrace tunnel
Penstock Peusangan 1 - Penstock
Peusangan 2 - Water intake and diversion weir
Regulating Poundage dam
Power tunnel Peusangan 2 - tunnel
Peusangan 2 - Penstock
11.
AVAILABLE HYDROPOWER
12.
CHOICE OF OPTIMAL DISCHARGE
13.
THE MECHANICAL AND ELECTRICAL EQUIPMENT
13.1. Available discharges and electricity output
13.2. Choice of the generating units
13.3. Electricity output
13.4. Alternators
13.5. General electric schema
14.
ALTERNATIVE PROJECTS
14.1. Alternative 1
14.2. Alternative 2
14.3. Available power at Peusangan 2
15.
COST ESTIMATES AND SCHEDULE
15.1. Cost estimates
15.2. Implementation schedule
16.
ALTERNATIVE OPTIMISATION
16.1. Introduction
16.2. Cost stream
16.3. Benefit stream
16.4. Conclusions
17.
ECONOMIC ANALYSIS
17.1. Introduction
17.2. Criteria and assumptions
17.3. Costs
17.4. Benefits
17.5 Results and conclusions
18.
FINANCIAL ANALYSIS
18.1. Introduction
18.2. Investment profitability
18.3. Liquidity analysis
18.4. Summary and conclusions
19.
ENVIRONMENTAL PROBLEMS
20.
SUMMARY AND CONCLUSIONS
20.1. Summary
20.2. Conclusions
20.3. Works to be executed for the project design
70.-
ANNEXE 2 : EXAMPLE OF ECONOMIC AND FINANCIAL ANALYSIS
2.1. ECONOMIC ANALYSIS
2.1.1 INTRODUCTION
Shadow prices are considered in theory to reflect more appropriately the value of the resources in the context
of a national economy, as market prices are frequently distorted. This is especially the case for the prices of
electricity in the developing countries. But we join the opinion expressed in the UNIDO " Manual for
evaluation of industrial projects " (UN 1980) that the application of shadow prices to project evaluation in
developing countries is extremely difficult both on conceptual and practical grounds. Therefore we will
evaluate the project from the following point of view.
Benefits of the hydropower plants Peusangan 1 and 2 as a whole result from energy production and irrigation
of new areas; this latter one however will not be quantified in our economic analysis.
Power benefit of the optimal project is derived from the comparison with an alternate power plant providing
equivalent service with respect to the installed capacity and annual generated energy.
We found previously that the hydropower project providing 60 MW installed capacity and the plant factor of
59 % should be preferred and that this project could be compared with an oil or gas fired alternate power
plant with an installed capacity of 60 MW.
Peusangan 1 and 2 energy will be transported through the 80 km high voltage line to Bireuen where it will
link the coastal interconnecting line.
2.1..2. CRITERIA AND ASSUMPTIONS
2.1.2.1 The discounted cash flow method will be used to determine the economic internal rate of return
(EIRR), present value of cost, present value of benefit, benefit to cost ratio and present value of net benefit.
2.1..2.2 Economic life
civil works
electromechanical equipment
transmission line
oil/gas steam power plant
2.1..2.3 Alternate power plant
installed capacity
investment cost
fixed O & M costs
fuel and variable O & M
60
934
11.535
26.60
50 years
25 years
40 years
25 years
MW
$/kW
$/kW-year
$/MWh
2.1..2.4 Energy production
According to above considerations we will take into account the energy production figures of the gas steam
power plant forecasted by PLN.
This gives for both projects :
_____________________________________________________________
Year
Energy production (GWh)
_____________________________________________________________
6 (first year of HPP operation)
87.6
7
175.2
8
175.2
9
219.0
10
262.8
Year 11 and on
294.0
71._____________________________________________________________
2.1..2.5. Comparison is made on a constant price basis using price levels of 1987 and assuming 1 $ = 1650
Rp.
Cost and benefit are estimated at their economic value for the country. Interests during construction are not
considered for the calculation of the EIRR, as usually.
Import duties and taxes are internal transfers inside the country. Therefore they are not considered.
2.1..2.6 Sensitivity analysis has been prepared by increasing the investment cost of the HPP by 10 and 20
percent and corresponding to the cases with and without fuel escalation of 2 % per annum.
Above percentage could for instance allow for the necessity to considerate the extension of Peusangan Bireuen transmission line to Lhokseumawe i.e. from 80 to 120 km.
2.1..3. COSTS
Disbursements of the investment cost will be made in five years ; their schedule will include taxes and
duties.
The generation will start from the 6 th year and the O & M cost is estimated at 1 % per year of investment
cost.
Electromechanical equipment and transmission line are reinvested during the lifetime of the project (50 years)
according to their respective economic lifetime . Residual value is considered according to the same previous
explanations.
2.1..4. BENEFITS
The related investment cost for the alternate thermal power plant should be calculated from above
assumptions i.e. 934 $/kW. The disbursements during the construction time will be assumed to be 5, 20, 40,
30 and 5 % of the total investment cost.
The investment cost is reinvested during the lifetime of the project according to the economic lifetime of
thermal power plant. Residual value is considered according to the same previous explanations .
Fixed O & M costs, fuel and variable O & M costs are computed according to above mentioned assumptions
i.e. respectively 11.535 $/kW-year and 26.60 $/MWh .
2.1..5. RESULTS AND CONCLUSIONS
Six cases were envisaged for the HPP :
I.
II.
III.
IV.
V.
VI.
Investment and O & M costs of base case ;
Investment and O & M costs of base case ;
Investment and O & M costs increased by 10 % ;
Investment and O & M costs increased by 10 % ;
Investment and O & M costs increased by 20 % ;
Investment and O & M costs increased by 20 % ;
no fuel escalation.
fuel cost escalation by 2 % per annum.
no fuel cost escalation.
fuel cost escalation by 2 % per annum.
no fuel cost escalation.
fuel cost escalation by 2 % per annum.
The results of the economic analysis are given separately.
These Annexes show the cost stream, benefit stream and benefit balance ; they show also the present values
and benefit-cost ratio for several discount rates. Finally the economic rate of return is given.
72.Table here under summarises the sensitivity of the project. This sensitivity indicates that in all cases the
internal rate of return is greater than 10 % : even for the case with 20 % increase of investment and O & M
costs and no fuel escalation.
Therefore it can be concluded that the AC2 implementation of Peusangan 1 and 2 hydropower plants is
economically acceptable.
It will be remembered that this implies the bypass of Angkup I and 2 and a discharge of 18 m3/s.
____________________________________________________________________________________
Case
Investment and
Fuel
Net present
B/C
EIRR
O and M cost
escalation/Year
value
ratio
%
k$
%
____________________________________________________________________________________
I
Base case
0
5 440.14
1.064
11.52
II
Base case
2
16 431.56
1.194
13.75
III
Base case + 10 %
0
(2 853.14)
0.969
9.34
IV
Base case + 10 %
2
8 138.27
1.088
11.54
V
Base case + 20 %
0
(11.146.43)
0.890
7.76
VI
Base case + 20 %
2
(321.04)
0.997
9.95
____________________________________________________________________________________
Table- Summary of sensitivity analysis at 10 % discount rate
73.-
2.2. FINANCIAL ANALYSIS
2.2..1. INTRODUCTION
The purpose of the financial analysis of Peusangan 1 and 2 hydropower plant is to investigate the soundness
of the project from a financial point of view.
This will be evaluated by the financial internal rate of return (FIRR) and by investigating the cash flow
requirements to operate the project.
Various alternatives of sources of funds with respective interest charges will also be considered.
2.2..2. INVESTMENT PROFITABILITY
The investment profitability measures the profitability of the resources put into the project, no matter what the
sources of financing.
Appendix shows the cash outflow and inflow of the project.
The project life is assumed to be 50 years.
2.2..2.1 Cash outflows
The total project cost comprises direct investment costs, including taxes and duties, contingencies and
financial charges.
The investment cost will be disbursed over five years, according to the schedule shown .
Residual values and O & M cost follow the methods described previously .
Replacement of electromechanical equipment and transmission line are planned during the 29th and 30th and
44th and 45th year respectively according to the earlier described methods.
As the project is considered from the financial point of view, no consideration will be given to the economic
cost of bypassing Angkup I and II.
Only the cash generated by the project on itself will be studied.
2.2..2.2 Cash inflows
Revenues generated from the project will be those from selling electricity energy.
Let we call E the energy generated at the power plant (in GWh).
From PLN System Planning Division we learn that the average unit selling price to the consumer is 113.5
Rp/kWh/
This means an average unit selling price of 113.5/1.650 = 68.788 k$/GWh.
For purposes of this financial analysis, we will take prospective T and D losses at 20 % of the generated
energy.
Let we call R the corresponding sales revenue per year (k$/y)
R = E*(1-0.2)*68.788
Three cases are considered in this analysis : P1, P2 and P3 as explained in table here under:
Case
Average
Annual energy
Revenue
74.-
P1
P2
P3
unit sales price
to consumer
Generation
R//kWh
113.5
k$/GWh
68.7
E (GWh)
294
Sold
consumer
E (1 -O.2)
235.2
to
119.18
(P1 + 5%)
124.85
(P1 + 10%)
72.2
294
235.2
16,988
75.66
294
235.2
17,797
K$/y
16,179
2.2..2.3 Net cash flow
Annexes show the cash flows for P1, P2, P3
respectively.
2.2..2.4 FIRR
From Annexes the FIRR appears to be :
___________________________
P1
9.24 %
P2
9.71 %
P3
10.17 %
___________________________
Table : FIRR
2.2..3. LIQUIDITY ANALYSIS
Liquidity analysis aims at ensuring the flow of cash through the construction and operation of the project.
Therefore additional cash positions, concerned with financial transactions, must be taken into consideration in
the liquidity analysis, such as debt service charges, both principal and interest, etc. ...
On the basis of the resulting cash flow it is then possible to judge whether :
-
long term financing is adequate
cash deficits can be covered by recourse to short term bank credit, etc. ...
2.2..3.1 Cash outflows
2.2..3.1.1 Investment costs
Summary of the fund requirements (FR) for the construction period is presented below i
2.2..3.1.2 Interest during construction (IDC)
If the sources of above fund requirements are entirely financed by long term loans, then interests during
constructions (IDC) are shown thereunder, based on 1 % interest rate on the still unused funds.
2.2..3.1.3 Total fund requirements during the construction period
_______________________________________________________________
Year
FR
IDC
Total FR
_______________________________________________________________
1
3 575.58
1 156.11
4 731.69
2 2 383.72
1 132.27
3 515.99
75.3 8 343.03
4 63 168.63
5 41 175.14
1 048.84
417.15
0
--------------
9 391.86
63 585.78
41 715.14
------------
-------------
Total
119 186.10
3 754.37
122 940.47
(in k$)
_______________________________________________________________
3.1.4 Debt service
It is expected that PLN will commit the debt service to the lending agencies, from the sixth year after the
assumed grace period of 5 years.
The debt service is calculated considering :
-
equal yearly instalments of both principal and interest (a)
interest rate of r
loan period of n years
For 1 $ the formula is :
r
a = ------------------------------------n
1 -(1 + r)
For 20 years and an interest rate of 10 %,
a = 0.11746
If the source of funds required during the construction period has to be entirely financed by long term loans,
this debt service is then : = 0.11746 * 122 940.47
= 14 440.59 k$/year
2.2..3.2 Cash inflows
Apart from those considered we should also mention the loans as sources of funds.
2.2..3.3 Net cash flow
Appendix shows the cash outflows, cash inflows and net cash flows as discussed above.
2.2..3.4 Alternative cases - Partial financing
According to appendix it can be seen that the major part of the cost of the electromechanical equipment and
transmission line are to be paid with foreign currencies.
We could now suppose that only the foreign currency costs would be financed by long term loans.
Appendix assumes financing of 50 % of the total funds required during the construction period ; the loan has
a duration of 20 years and an interest rate of 10 %.
2.2..4 SUMMARY AND CONCLUSIONS
Table here under shows the summary of our financial investigations.
2.2..4.1 Investment profitability
76.From the results of the financial internal rate of return we conclude that the proposed hydropower project is
moderately attractive for the present selling prices of electricity.
Changes in oil or electricity price structure could favourably influence these results.
2.2..4.2 Liquidity analysis
In the project is 100 % financed, than the cumulative cash balance will be negative during 26 years owing to
the burdens of the debt service; thereafter it will remain positive.
The project requires a maximum of cash of 27 600 k$ in the 10th year.
The total project generates a net cash of 383 800 k$ in the 55th year.
If the project was 50 % financed with long term loans the project requires a maximum cash of 63 200 k$ in
the 6th year.
The project generates then a net cash of 468 619 k$ in the 55th year ; the cash balance become positive in the
17th year. This project is highly dependant on the loan conditions which we supposed to be at 10 % interest
rate.
2.2..4.3. Conclusions
a.
From the pure financial point of view we consider the project moderately attractive : indeed we
calculated a FIRR of about 9 % and this rate represents the return on capital invested called profitability.
This rate has to be related to a cut-off rate which is the lowest acceptable investment rate for the
invested capital.
As this FIRR was calculated on the average sales price to the consumer of electricity, we feel that this
approach is not sufficient to reflect the induced advantages of electrification of this part of Sumatra.
b.
As far as now, we have only made emphasis on finding the profits of the project in monetary terms and
not on its real contribution to the welfare of the society.
This is not a solid ground for investment decisions.
Investment decisions should take into account the national or regional profitability.
Identifying the indirect effects is not easy, measuring them is always difficult.
Factors which should be taken into account for the national profitability :
1.
Net foreign - exchange effect
on one side foreign (electromechanical) equipment should be imported
on the other side the quantities of gas or fuel oil burned in the thermal PP can no more
be exported in short or long term.
2.
Energy independence
Hydropower is a renewable energy, neither gas nor oil.
3.
Independence from energy price, on which the FIRR is very sensitive.
4.
Multiplicator effect on other sectors of the national economy
Power supply is an infrastructure facility and as such contributes to the economic
development of the country
5.
Also the social development of the country should be considered.
Concentration on HPP
77.Development of a technical know-how oriented to hydro-power generation in a country.
Simplification of finding manpower education and skills.
6.
Environmental implications
Hydropower versus thermal power can be considered as at the lowest level related to :
economical impact
climatic change
health risks for the workers and for the public health
injury to the workers.
Further, other factors should be considered as :
-
trend of the long term interest rate
-
evolution or non-evolution of the average sales price of electricity in the next years
-
actual cost price of the electricity generation in North-Sumatra versus the actual tariffs.
Calculation of the FIRR should always be done with the actual generation cost or domestic
market price, whichever is higher. In case the Public Authorities wish to maintain certain tariff levels, this
would imply (hidden) subsidies or social aspects which should be taken into consideration as stated above.
Due to energy efficiencies,
gas and oil should ideally be reserved for thermal energy, (industrial) steam generation, housecooking, while power energy should be reserved for lightening, air-conditioning, rotation power (in industrial
and household environment).
c,
In appreciating a power generation project one should not base the decision purely on the IRR :
if the project aims at electrification of a non-electrified country, one should appreciate the
economic internal rate of return taking above factors into consideration.
-
if the IRR is high, the project should be adopted
if the IRR is low, the project, appearing bad, could become interesting if tariffs were
updated in order to reflect the actual costs.
if the project aims at servicing an established market by increasing the installed power, the
project should be viewed in terms of :
-
satisfying the increase rate of the demand
-
improving the customer service.
In this case the IRR gives indications on forwarding or delaying the project.
d.
project attractiveness
What is PLN, what is Indonesia, prepared to pay for the benefits from the contribution of the
Peusangan 1 and 2 project to the country.
Can Indonesia afford to find the necessary funds for this development project and what will be
the conditions (loan with reduced interest rate, soft loan, ...) ?
Answering and quantifying those questions would give the true EIRR and FIRR respectively, which
could then appear very attractive.
78.But is should be remembered that only if the HPP is producing peak power and not base power that the
project can be considered as attractive.
_____________________________________________________________________________________
Case Average sales price
Financing
Net present value
B/C ratio FIRR
k$/GWh
k$
%
_____________________________________________________________________________________
P1
68.788
(6 851.90)
0.925
9.24
P2
72 227
(2 633.68)
0.971
9.71
P3
75 667
1 585.77
1.017
10.17
L1
68.788
100 %
(2 652.87)
0.984
9.12
L2
68.788
50 %
(4 752.39)
0.964
9.21
_____________________________________________________________________________________
The price of 68 788 k$/GWh corresponds to 113.50 Rp/kWh
Summary of financial analysis at 10 % discount rate
79.-
CONTENTS
Pages
CHAPTER I:
1.1
INTRODUCTION WATER POWER DEVELOPMENT
1
Historical
1
1.2 Development
3
CHAPTER II: GENERAL ARRANGEMENT OF WATER POWER DEVELOPMENTS 6
2.1 Essential Features
6
2.2
Gross and Net Head
7
2.3
Essentials of General Plant Layout
8
2.4
Factors Affecting Economy of Plant
8
2.5
Types of Water Power Developments
9
2.6
Typical of Arrangements of Water Plants
11
2.7
Lowest Cost Power Developments
13
2.8
Highest Cost Power Developments
14
15
CHAPTER III : POWER FROM FLOWING WATER:
3.1
Energy and Work
15
3.2
Energy Line
16
3.3
The Bernoulli Theorem
17
CHAPTER IV : PLANNING AND BUILDING
4.1
Stage of planning
24
4.2
Potential water power
26
4.3
Energy output diagram
32
4.4
Evaluating the economic value of power stations
32
4.4.1
Cost estimates
32
4.4.2
Running costs
33
4.4.3 Elements to be considered in the economic calculation
33
CHAPTER V : STUDY OF SMALL HYDROELECTRIC INSTALLATIONS
5.1.
5.2.
General arrangement of power developments basic principles
Definition of the hidro-microelectricity
2.1 Context
2.2 Use of the MHE
37
39
39
40
80.-
5.3.
2.3 Characteristics
2.4 Constraints
2.5 Environment
2.6 It is not hydroelectricity in model reduces
Types of micro power stations
40
41
42
42
43
3.1 Works of civil engineering adapted to the microphone-power stations
43
3.2 Electromechanics of the microphone-power stations
44
3.3 Distribution
47
5.4 Methodology for the realisation of a site
47
4.1 Design
47
4.2 Methodology of the choice of the site
48
4.3 Calendar of the realization
48
4.4 Studies
49
4.5 Environmental impact
50
4.6 Realization
50
4.7 Tally of production
50
5.5.Economie of the project
51
5.1 Estimate of the costs
51
5.2 The running costs
51
5.3 Economic calculation
51
5.4 Financing
53
CHAPTER VI WATER TURBINES
55
6.1 Pelton Turbie
56
6.2 Francis and Kaplan Turbines
57
6.3 Cross- flow Turbine
59
6.4 Straflo Turbine
61
6.5 Hydrauliennne
63
6.6 Comparaison of differents Turbines
66
Annexe 1 Exemple of table of contant
67
Annexe 2 Exemple of economic and financial analysis
69
1
INVENTAIRE DES SITES HYDROELECTRIQUES DU CAMEROUN.
Auteurs : J. KENFACK(1) ; A.G.H. LEJEUNE(2) ; T. TAMO TATIETSE(3),
J. NGUNDAM(4) ; M. FOGUE(5)
(1) Joseph KENFACK
Ecole Nationale Supérieure Polytechnique
B.P. 8390 Yaoundé Tél. 750 00 60 Fax +237 222 91 16
Email : [email protected], [email protected]
(2) A.G.H. LEJEUNE
Université de Liège
Ch. Des chevreuils, 1, B52 B – 4000 Liège
Tél. +32-4-366.95.60
Email : [email protected]
(3) Thomas TAMO TATSIETSE
Ecole Nationale Supérieure Polytechnique
B.P. 8390 Yaoundé Tél.+237 222-45-47 ; Fax +237 222-45-47
Email
[email protected]
(4) John NGUNDAM
Ecole Nationale Supérieure Polytechnique
B.P. 8390 Yaoundé Tél.+237 222-45-47 ; Fax +237 222-45-47
2
Email : [email protected]
(5) Médard FOGUE
Ecole Nationale Supérieure Polytechnique
B.P. 8390 Yaoundé Tél.+237 222-45-47 ; Fax +237 222-45-47
Email : [email protected]
3
INVENTAIRE DES SITES HYDROELECTRIQUES DU CAMEROUN.
Mots clés : électrification, hydroélectricité, potentiel, recensement, Cameroun, site
RESUME
Le Cameroun dispose du deuxième potentiel hydroélectrique en Afrique derrière
la République Démocratique du Congo. Malgré cela, seulement 722 MW est
installée contre 19,7 GW équipable avec un productible garanti annuel de 115
TWh. Le besoin en énergie électrique de la population notamment rurale nous a
inspiré à recenser le potentiel hydroélectrique du pays en y incluant les minis et
les microcentrales. Il ressort de ce travail effectué à l’aide de cartes et d’autres
travaux préliminaires un dispatching assez régulier des sites dans la partie centrale
et sud du pays, avec un réseau hydrographique assez dense. L’inventaire des sites
du potentiel hydroélectrique permet d’envisager l’électrification des sites isolés
avec plus de sérénité. La présentation du résultat à l’aide d’un système
d’information géographique permet de mieux apprécier l’opportunité des
solutions décentralisées pour l’électrification rurale.
ABSTRACT
Cameroon offers a wealth of hydro power opportunity. Cameroon owns the
second hydro potential in Africa behind Democratic Congo Although 722 MW of
this has already been utilized, about 19 more gigawatts of hydro power still
remain untapped with a hydro potential of 115 TWh. Electricity is not available
for the great majority of the Cameroonian, mainly in the rural areas. Assessing the
4
hydro power could help planning electrification projects. Based on maps and other
preliminary works, the work shows availability of the hydro power in the centre
and south part of the country. The results presented using a geographic
information system bring out the dispatching of the hydropower throughout the
country.
5
POTENTIEL HYDROELECTRIQUE DU CAMEROUN
INTRODUCTION
Le Cameroun est situé entre les // 2° et 12° Nord et entre les méridiens 8°
et 16° Est depuis l’océan Atlantique jusqu’au confins du lac Tchad.
L’écoulement des eaux s’effectuent vers l’atlantique, le Congo, la
Benoué ou le lac Tchad. Les altitudes vont de 0 à plus de 2000 mètres. Des
précipitations allant de 500 mm à plus de 10000 mm.
ECOULEMENT DES EAUX
LAC TCHAD
BENOUE PUIS
ATLANTIQUE
NIGERIA PUIS
ATLANTIQUE
OCEAN ATLANTIQUE
CONGO PUIS
ATLANTIQUE
6
Cette situation confère au Cameroun un important réseau hydrographique et donc
un potentiel important.
RESEAU HYDROGRAPHIQUE
7
POTENTIEL SAUVAGE
Le Cameroun possède un potentiel sauvage de 294 TWh dont 115 TWh
techniquement équipable. Il occupe de ce fait le 2ème rang dans la sous région
Afrique Centrale derrière le Congo Démocratique (1397 TWh).
Avec seulement 722 MW sur 19.7 GW du potentiel équipé, le secteur
hydroélectrique se trouve sous-exploité (sous équipé par rapport au besoin) au
point où l’énergie électrique arrive à manquer pendant les périodes d’étiage,
entraînant le délestage.
POTENTIEL EQUIPE
Quoique ayant aménagé en valeur relative plus que la moyenne africaine,
le Cameroun reste en recul par rapport à la moyenne mondiale
POURCENTAGE DU POTENTIEL MONDIAL ET CAMEROUNAIS DE
PRODUCTION HYDROELECTRIQUE ECONOMIQUEMENT
RENTABLE
EXPLOITE
EXPLOITABLE
100%
80%
60%
40%
20%
0%
AFRIQUE
AUSTRALIE
AMERIQUE
DU NORD
ET DU
CENTRE
CAMEROUN
8
POTENTIEL EQUIPABLE
Méthodologie d’identification des sites
L’approche est essentiellement documentaire. Les sources viennent de la Société
Nationale d’Electricité (SONEL), de l’Institut de Recherche pour le
Développement (IRD), de l’Institut de Recherche Géologique et Minière (IRGM),
du Ministère des Mines, de l’Eau et de l’Energie (MINMEE). Pour certains sites
de micro centrale, nous avons exploité uniquement des cartes.
CARACTERISATION D’UN SITE
Un site est caractérisé par la hauteur de chute et le débit. On calcule le potentiel
suivant la formule:
P = g.Q.H, P : potentiel puissance en (kW)
Q : débit turbiné en (m3/s)
H : chute en (m)
g : accélération due à la pesanteur
Les deux grandeurs Q et H (débit et hauteur de chute) sont capitales pour la
caractérisation du site et nécessitent des investigations sur site. On en déduit alors
le productible garanti.
9
RESULTATS
Micro
Centrales Total
centrales
Adamaoua
13
14
27
Centre
8
24
32
Est
6
6
12
Littoral
3
11
14
Nord
0
4
4
Nord-Ouest 8
8
16
Ouest
7
6
13
Sud
14
8
22
Sud-Ouest
15
8
23
10
REPARTITION DES SITES DE CENTRALES RECENSES PAR PROVINCE
Sud-Ouest
Adamaoua
Sud
Ouest
Centre
Nord-Ouest
Nord
Littoral
Est
11
REPARTITION DES SITES MICROCENTRALES RECENSES PAR PROVINCEs
Sud-Ouest
Adamaoua
Centre
Sud
Est
Littoral
Ouest
Nord
Nord-Ouest
SITES RECENSES PAR PROVINCE
Sud-Ouest
14%
Adamaoua
17%
Sud
13%
Centre
20%
Ouest
8%
Nord-Ouest
Nord
10%
2%
Est
Littoral 7%
9%
12
POTENTIEL HYDROELECTRIQUE
DU CAMEROUN (GWh)
Centrales.dbf
27 - 280
281 - 700
701 - 1660
N
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1661 - 3100
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3101 - 5080
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13
CONCLUSION
Ce travail est une étape du travail de recherche que nous menons sur les
énergies renouvelables au profit des zones rurales isolées, afin de contribuer à la
lutte contre la pauvreté qui y est plus répandue. Cet acquis constitue une base pour
la recherche en cours sur la valorisation des rivières et fleuves du Cameroun en
vue de l’électrification à moindre coût grâce à une technologie parfaitement
maîtrisée, qui demande qu’à être adaptée pour un développement durable. Il
ressort que l’essentiel du potentiel hydroélectrique du Cameroun est encore
inexploité.
République Centrafricaine
Unité – Dignité – Travail
Inventaire des sites hydroélectriques en République Centrafricaine
Facteurs de réussite et enseignements
Blaise – Léandre TONDO, ingénieur
Comité chargé de la mise en valeur des projets d’énergie électrique en RCA ( CMVPE )
Mars 2000. Chutes de La Mbi ( en amont de La Mbi – Colombe et de Boali )
« Dieu nous a dotés d’un important réseau hydrographique; à nous de l’assujettir … «
Situation géographique
La République Centrafricaine a une superficie d'environ 623000 km² avec une population
estimée à 3.4 million d'habitants. Elle est située en Afrique Centrale entre 2° 13' et 11° 01' de
latitude Nord et entre 14° 25' et 27° 27' de longitude Est.
Ses frontières sont bordées:
- au nord par le Tchad sur 1100 Km
184
- à l'Est par le Soudan sur 1000 Km
- au Sud par le Congo sur 400 Km, et le République démocratique de Congo ( RDC ) sur 1200
Km. Cette dernière frontière est matérialisée par le fleuve Oubangui.
- à l'Ouest par le Cameroun sur 700 Km .
La RCA, qui occupe une position extrêmement continentale, ne dispose que de deux
débouchés vers la mer. La voie terrestre, la "transcamerounaise", relie Bangui à Douala au
terme de 1500 km. L'autre voie, la "transéquatoriale" emprunte la voie fluviale jusqu'à
Brazzaville au Congo puis la voie ferrée pour atteindre le port de Pointe-Noire.
Cet enclavement occasionne les surcoûts de transport qui pèse sur la compétitivité des
produits centrafricains à l'exportation, renchérit le prix des produits importés et des biens
manufacturés.
Climatologie et hydrographie
Le climat Centrafricain est lié à l'influence alternée des centres de pression permanents des
hémisphères Nord et Sud. C'est un climat de transition entre le climat Sub-Sahélien et le
climat équatorial. On y trouve principalement deux types de saisons sur toute l'étendue du
pays. La saison sèche et la saison des pluies.
L'hydrographie de la République Centrafricaine est caractérisée par deux bassins importants:
le bassin sud du Tchad comprenant les affluents du Haut Chari et le bassin de l'Oubangui.
Dans le premier, le régime des eaux y est irrégulier, de type soudanien avec des sources qui se
tarissent en saison sèche: dans le second, le régime des eaux est plus régulier, les sources sont
permanentes, les débits ne sont pas considérablement réduits à l'étiage.
185
Potentialités hydro – énergétiques
Février 2000. Chutes de La Mbi ( La Colombe )
En général, les cours supérieurs des rivières sont rapides et encaissés avec des pentes
importantes, les cours moyens et inférieurs sont au contraire, lents et faiblement encaissés
mais sont parfois interrompus par des chutes ou des rapides au passage de seuils rocheux:
rapides de l'Oubangui, rapides de la Lobaye, chutes de la Kotto, chutes de la M'Bali, chutes de
la M'Becko , chutes de la Mbomou parmi les sites qui ont déjà fait l'objet d'un minimum
d'étude d'évaluation.
D'autres chutes et rapides sont connus: chutes de Gbassem à Boda, chutes de la Pama à
environ 100 km de Boali , chutes de la Mbi à 160 km de Bangui, chutes de la Chinko à 60
Km de Rafai, plusieurs chutes et rapides sur la Kotto, rapides de Yaméné sur la Kadei à 50
Km de Nola, chutes sur un affluent de la Mambéré près de Carnot, chutes de la Nana près de
Kaga-Bandoro, chutes de Matakil sur la Koumbala à 45 Km de Ndélé, chutes de Lancrenon à
la frontière RCA - Cameroun, etc.
186
La possibilité d'installer des
micro-centrales hydro-électriques dans des
centres jugés
prioritaires (Bocaranga, Paoua, Baboua, Bossangoa, Ndélé, Sibut, Bangassou, Bria, Kembe,
Bambari, Bouar , Carnot, Berbérati, Kaga-Bandoro,Mbaîki ), montre que dans le contexte
économique actuel, sur les centres envisagés, certains centres tels que: Bambari, Carnot,
Berberati, Mbaiki, Kaga-Bandoro, Bouar, Boda, peuvent être retenues dans l'immédiat.
Politique énergétique
La crise économique généralisée qui a affecté la plupart des pays du monde n'a pas épargné la
RCA. Le pays se trouve actuellement dans le processus de réforme du secteur de l’industrie
électrique.
Secteur électrique
Son organisation
L'alimentation en électricité de la République Centrafricaine est assurée par
l'entreprise publique ENERCA (Energie Centrafricaine), qui gère, d'une part, le réseau
interconnecté alimentant Bangui et, d'autre part, seize centres de provinces.
Les moyens de production et distribution
Un coup d'oeil sur les réalités montre que dans les Centres de Provinces, la génération
d'électricité s'effectue uniquement par des groupes diesels dont la puissance installée s'étend
de 40 kVA à 625 kVA. Ceux-ci ont été mis en place entre les années 1970 et 1999.
La puissance totale installée est d’environ 4675 kVA.
Les réseaux de distribution sont très peu étendus (en moyenne moins de 10 km par
centre), et alimentent un millier d'abonnés.
La qualité du service de l'électricité connaît des contraintes qui ne favorisent pas le
développement socio-économique de ces villes. En effet, l'alimentation est assurée 5
heures par jour en moyenne, et ne touche que 1,5 à 3% de la population. Les
principales causes en sont:
187
-un faible temps de production non adapté aux activités économiques et sociales,
-une faible étendue du réseau confiné au centre administratif,
-un coût de branchement et un niveau de tarif inadapté aux ressources de ces
populations.
Les tarifs
Les difficultés de gestion accentuent encore le déficit d'exploitation des centres isolés,
malgré un prix de vente de l'électricité très supérieur à celui consenti aux abonnés d'
ENERCA à Bangui ( 170 FCFA contre 66 FCFA par kWh ).
La place des producteurs indépendants ( autonomes )
La détérioration continue de la qualité de service conduit une fraction croissante de la
population à s'équiper individuellement de groupes à essence ou gas-oil; les puissances
unitaires vont de 2 KVA, et leur somme dans chaque centre est au moins du même
ordre de grandeur que la puissance installée par ENERCA.
Ces solutions coûteuses témoignent de l'existence d'une demande solvable, disposée à
payer le prix d'un service de qualité.
L'électrification rurale
Les problèmes et les solutions
Malgré le grand succès de la construction du barrage de la Mbali, l'énergie électrique
demeure encore pour la plupart de nos concitoyens un bien de luxe difficilement
accessible surtout à nos populations rurales;
Malgré les actions menées par l'ENERCA, pour la réduction de ses pertes techniques
et le retour à son équilibre financier, certains problèmes demeurent encore au niveau
du secteur électricité surtout en ce qui concerne la satisfaction en énergie électrique
des villes de l'intérieur et zones rurales.
188
C'est pourquoi l'Etat centrafricain, pour tenter de résoudre ces problèmes dans les
années à venir, oriente sa politique énergétique vers la valorisation de
l'hydroélectricité ; avec les objectifs suivants :
-satisfaction à moindre coût des besoins énergétiques;
-accès à l'électricité de toutes les couches sociales du pays;
En 2002, 16 villes de l'intérieur sont aujourd'hui électrifiées ; soit un taux de
pénétration pour l'ensemble du pays d'environ 3 ménages électrifiés pour mille
habitants.
Compte tenu du coût d'investissement, en regard de la rentabilité, les villes de
l'intérieur sont souvent électrifiées par raison sociale dans le but, essentiellement, de
dynamiser l'économie des villes de provinces afin de permettre leur développement,
évitant de ce fait l'exode rural.
La valorisation du potentiel hydroélectrique devra permettre à l'Etat d'intensifier et
d'améliorer la fourniture de l'énergie électrique dans les villes de provinces, ce qui
cadre avec l'un de ses objectifs principaux: favoriser l'accès à l'électricité de toutes les
couches sociales du pays.
Par manque de fourniture permanente d'électricité, la population des centres de provinces est
confrontée à de très graves problèmes sociaux ; par exemple:
- les Entreprises de production et de transformation ont d'énormes difficultés d'installation. Ce
qui entraîne un taux de chômage très élevé dans la population, un ralentissement des cultures
industrielles et des activités artisanales, le corollaire étant un exode rurale massif vers Bangui
la capitale.
L'organisation et le financement
Malgré des investissements importants réalisés dans le secteur de l'électricité depuis 1986 à
travers un ambitieux projet énergie 1 d'augmentation de la disponibilité de la production, de
renforcement et de réhabilitation des infrastructures de production, transport et distribution ;
189
la situation de l'Energie Centrafricaine (ENERCA) n'a cessé de se dégrader. Cette situation est
caractérisée, entre autre, par un faible taux de desserte (trois ménages électrifiés sur mille).
Propositions
Avec la mise en valeur des sites hydrauliques ; l'expérience des pays partenaires au
développement dans la francophonie peut nous amener a:
- rechercher et favoriser la création de ‘’comités villageois’’ qui prennent en charge eux
même, avec l'assistance technique de prestataire de services d'électricité, la production,
l'exploitation, et l'entretien de ces installations.
Ces’’ comités villageois’’ peuvent donc contribuer à l'amélioration de la situation c'est-à-dire:
- bonne gestion des installations et des stocks des pièces de rechanges
- diminution du prix de revient de kWh produit
Le choix de la formule ‘’comités villageois’’ permet l'implication directe des premiers
intéressés dans l'établissement des infrastructures de production et de distribution; cette
formule permettra de mieux relier la pénétration de l'électricité aux besoins des habitants des
zones rurales.
La RCA a besoin de micro-centrales hydroélectriques. Les conditions d'hydrologie ( hauteur
de chute favorable + débit régulier ) sont favorables sur l'ensemble du territoire.
Entre autres expérience, à travers le réseau d’Experts de francophonie, la RCA peut s'informer
du modèle sud-est asiatique où certaines micro-centrales sont réalisées, avec des moyens
locaux peu sophistiqués, par les habitants des zones rurales.
Méthodologie
Afin d'établir un classement de certaines localités à l'issue de l'analyse du potentiel
hydroélectrique existant à leur proximité (un rayon de 25 à 30 km), nous nous fixerons 5
critères de jugement concernant:
- le caractère prioritaire de l'aménagement hydroélectrique noté par deux critères: l'inscription
de la localité au programme prioritaire ( importance socio-économique ) défini par le
Politique et l'existence ou non d'un réseau de distribution d'électricité;
- le potentiel hydroélectrique noté par deux critères estimant le débit et la hauteur de chute de
l'aménagement prévu;
190
- la difficulté technique de réalisation des ouvrages évaluée par le contexte géologique du site
à équiper;
- l'accès au site;
- ligne de transport d'énergie.
Définition des critères de classement
a) Programme prioritaire: ce critère est évalué par une notation de 0 et 4 correspondant à:
0: localité non inscrite
4: localité inscrite
b) Réseau existant: deux valeurs évaluent ce critère:
1: réseau de distribution existant dans la localité et possédant une centrale
diesel
4: localité non alimentée en électricité
c) Potentiel hydroélectrique:
- apports: l'évaluation des apports et débits des cours d'eau concernés est noté de 1 à 4 suivant
l'estimation de leur débit moyen:
1: débit moyen inter annuel inférieure à 5 m3/s
2: débit moyen inter annuel compris entre 5 et 10 m3/s
3: débit moyen inter annuel compris entre 10 et 30 m3/s
4: débit moyen inter annuel supérieure à 30 m3/s
- dénivelée: l'évaluation des hauteurs de chute utilisable est notée de 1 à 4:
1: hauteur de chute estimée inférieure à 10 m
2: hauteur de chute estimée compris entre 10 et 20 m
3: hauteur de chute estimée compris entre 20 et 40 m
4: hauteur de chute estimée supérieure à 40 m
d) Géologie: l'estimation de la qualité du sol de fondation des ouvrages est notée de 1 à 4:
1: alluvions récentes peu ou pas consolidées
2: alluvions sablo - graveleux ou manque d'information,
4: rocher apparent reconnu ou supposé (chutes naturelles, rapides)
191
e) Accès au site: la longueur de la route d'accès aux ouvrages d'une route existante ou piste
existante est notée de 1 à 4 :
1: longueur supérieure à 10 km
2: longueur comprise entre 10 et 20 km
3: longueur comprise entre 5 et 10 km
4: longueur inférieure à 5 km
Conclusion
Avec la pré-identification de notre potentiel hydroélectrique; nous pensons que la promotion
des micro-centrales hydroélectriques aura des effets socio-économiques non négligeables tels
que:
- la fourniture permanente d'électricité,
- l'accélération du développement en milieu rural par l'amélioration des conditions de vie des
populations et l'opportunité accrue d'implantation d'activités artisanales ou semi-industrielles,
Certes, l'hydroélectricité est, à l'achat plus coûteuse que le thermique, mais sa durée de vie est
bien plus longue et son entretien est limité.
Le financement sur fonds propres est difficile à réaliser, l'hydroélectricité est donc
particulièrement adaptée pour la RCA, l'intervention des bailleurs de fonds couvrant, surtout
pour les BOOT, du même coup, l'essentiel des dépenses pour la quasi-totalité de la durée de
vie des équipements fournis.
La grande fiabilité, la durée de vie élevée des équipements, le coût nul de l'énergie utilisée, la
simplicité de fonctionnement sont autant d'éléments qui justifient le choix des micro-centrales
hydroélectriques face aux centrales diesel malgré l'investissement initial très élevé qu'elles
nécessitent.
L'électrification des zones rurales a pour objectif essentiel le développement économique du
pays en général et des zones rurales en particulier. Leur électrification constitue la seule
chance de promouvoir la décentralisation de l'activité économique, qui dans les pays du sudest asiatique s'est avérée une réussite.
Certains centres ruraux sont actuellement alimentés par des groupes diesel; mais, vu le prix
élevé du diesel et les problèmes posés par les pièces de rechange, leur production n'est
absolument pas fiable.
192
Les conditions hydrologiques et topographiques sont extrêmement favorables pour le
développement des ressources hydrauliques. De grandes parties du pays bénéficient de pluies
suffisantes et même de relativement petits cours d'eau sont pérennes. Des rivières au débit
satisfaisant se trouvent souvent à distance raisonnable des zones ruraux représentant une
demande potentielle.
Ces différents éléments indiquent que les coûts des ouvrages de génie civil et de transmission
seront peu élevés, ce qui est extrêmement important pour la rentabilité des projets de microcentrales.
Les micro-centrales hydroélectriques paraissent donc, en RCA, porteuses d'espoirs de
développement en procédant à une interconnexion progressive des aménagements à réaliser.
C’est pourquoi, il faut établir un inventaire complet des sites hydroélectriques pour mettre en
place la politique de mise en valeur de nos ressources naturelles .
193
MICRO-CENTRALES HYDROELECTRIQUES POUR UN
DEVELOPPEMENT DURABLE DU BURUNDI
Pr. Fidèle RURIHOSE ; Dr.Ir.
Université du Burundi
Energie et Développement
Il est établi et compréhensible qu’il y a une corrélation entre la
consommation de l’énergie et le développement.
Ainsi, en 1988, les habitants des Etats-Unis et du Canada consommaient en
moyenne plus de 40 barils équivalant pétrole par an et par habitant, soit à peu
près 64 000 KWh alors que l’habitant du Nigéria ne consommait en moyenne
que 2 barils soit à peu près 3 200 KWh et cela principalement sous forme de
combustibles traditionnels (1).
Si on s’intéresse uniquement à l’énergie commerciale, le même constat est
fait.
Ainsi en 1994, un burundais consommait en moyenne une énergie équivalente à
23 kg de pétrole par an, un rwandais 34 kg, un nigérian 162 kg, un sénégalais 97
kg alors qu’un français en consommait 4 042 kg, un japonais 3 856 kg, un
norvégien 5 318 kg et un américain 7 819 kg (2).
Cette disparité est par ailleurs amplifiée si l’on s’intéresse à la forme noble de
l’énergie, à savoir l’électricité, vu que dans les pays sous-développés, la forme
principale de l’énergie employée est le bois.
Ainsi en 1990, au Rwanda, l’électricité ne représentait que 0.4% de l’énergie
utilisée contre 96.6% pour le bois . Il est vrai aussi que 95.7% de l’énergie était
consommé dans le secteur domestique, contre 1.2% seulement pour le secteur
industriel.
1
2
« Pour la Science » n°157 , numéro Spécial Energie, Novembre 1990
. « Rapport 1997 sur le développement dans le monde », Banque Mondiale.
. La différence des consommations entre les pays développés est due au niveau du froid (chauffage en hiver)
et aux habitudes « énergivores » des américains.
1
Le Burundi connaissait pratiquement la même dépendance énergétique
par rapport au bois puisque ce dernier et le charbon(3) qu’on en tire représentait
95% du bilan énergétique global (4). Avec la guerre civile qui prévaut dans notre
pays, ce taux n’a malheureusement fait qu’augmenter. Ainsi il est passé à 95.3%
en 1993 et à 97.3% en 2000(5). Parallèlement, la part de l’électricité dans le
bilan énergétique n’a cessé de diminuer, passant de 0.6% en 1993 à 0.4% en
2000 et 0.3% en 2001 !
Aujourd’hui, l’énergie n’est souvent pas prise explicitement en compte
dans les projets de lutte contre la pauvreté dans nos pays en voie de
développement. Pourtant l’énergie n’est pas seulement indispensable à la
satisfaction des besoins quotidiens des populations ; elle constitue même une
composante essentielle de toute activité permettant d’assurer un minimum de
développement économique et social.
La satisfaction des besoins élémentaires de la population nécessite
l’utilisation de plusieurs formes de l’énergie.
Une des formes les plus en vue et les plus accessibles est la biomasse qui
sert essentiellement pour la cuisson et le chauffage et dans une moindre
mesure pour l’éclairage.
Cette forme de l’énergie comporte néanmoins quelques limites.
Il faut noter d’abord que son prélèvement de proximité, ou à distance pour
les habitants des villes, participe à la raréfaction des ressources et à la
dégradation de l’environnement, amplifiant ainsi à plus ou moins long terme
la pauvreté et la probabilité des catastrophes naturelles. Plus grave encore est
le fait que cette forme de l’énergie est employée dans des installations
d’efficacités énergétiques très réduites.
Ainsi la cuisson sur les 3 pierres traditionnelles a-t-elle un rendement
médiocre par rapport à celle faites sur un foyer métallique amélioré, lequel
foyer a lui aussi un rendement 5 à 8 fois inférieur à celui d’un fourneau à gaz.
3
Appellation commune inappropriée qu’il faudrait remplacer par « coke végétal ».
4
L’eau et l’Energie au service du développement socio-économique du Burundi, Journées Nationales de l’Eau
et de l’Energie, Bujumbura, 17-19 Mai 1990.
5
Bilan énergétique et statistiques de l’eau pour l’année 2000 et 2001 ; Ministère de l’Energie et des Mines,
République du Burundi
2
De même l’éclairage au bois a un rendement médiocre par rapport à
l’éclairage au kérosène, lequel a un rendement 30 à 40 fois plus petit que
l’éclairage au néon … (6).
La forme de l’énergie la plus propice à stimuler le développement est
celle pouvant substituer au travail humain celui de la machine, ou
pouvant faire des transformations que l’énergie humaine ne peut faire à
elle-seule.
Cela pourrait être un moteur thermique entraînant plusieurs équipements
comme les moulins, des décortiqueuses, des pompes, des machines de
menuiserie, des alternateurs qui à leur tour alimenteraient des postes de
soudure, des chargeurs de batterie et des moteurs électriques pour usages
divers…
Le moteur thermique susmentionné comporte néanmoins quelques
inconvénients vu qu’il doit employer un combustible totalement importé dans
le cas du Burundi(7) et que ce combustible n’est transformé en travail
mécanique qu’avec un rendement maximal de 35 à 40%, le solde de l’énergie
servant souvent à chauffer le milieu ambiant qui n’en a pas besoin(8)…
Il est donc clair que la forme d’énergie la plus utile au développement est
l’électricité et qu’aucune localité ne peut prétendre au développement si elle
n’est pas alimentée en électricité.
Si l’on regarde donc la disponibilité de l’électricité au Burundi, avec son
taux d’électrification (%
de ménages connectés) de 2.1% et une
consommation moyenne par habitant de 20 KWh/hab/an, on ne doit pas être
surpris que notre pays soit classé parmi les 3 derniers pays de la planète au
niveau du développement.
Le constat fait par plusieurs analystes de l’adéquation énergiedéveloppement est donc réel pour le Burundi, à savoir que « il existe une
frange très importante de populations rurales ou urbaines dont les capacités
de développement économique se heurtent à l’absence ou à la difficulté
d’accès à des quantités d’énergie suffisantes »( 9) et plus particulièrement de
l’électricité.
6
Benjamin Dessus, Energie et Développement durable : quatre enjeux pour la Francophonie ;
Liaison Energie-Francophonie n°55-56-57.
7
. Le Burundi a une centrale thermique (4 moteurs diesel ) de secours d’une puissance totale de 5.25 MW.
. L’usage du biogaz ou du gaz de gazogène pour alimenter les moteurs à combustion interne a été fait dans des
installations pilotes (en panne aujourd’hui) et n’a pas été vulgarisé.
8
D’où l’intérêt d’une cogénération quand c’est possible.
9
Benjamin Dessus ; op.cit.
3
De la voie des micro et pico-centrales hydroélectriques.
Le Burundi a un potentiel hydroélectrique de 1776 MW dont 300 MW(10)
sont économiquement exploitable. La puissance installée aujourd’hui, n’est
que de 32 MW ; soit un peu plus de 10% du potentiel facilement exploitable
C’est donc dire que le Burundi a de grands gisements d’ « or bleu » qui ne
sont pas mis à profit.
L’exploitation, ne fût-ce que d’une partie de ce potentiel non valorisé,
permettrait de rendre plus disponible l’énergie électrique nécessaire au
développement, le surplus pouvant alors être exporté vers les pays
limitrophes qui en ont besoin comme le Rwanda et la Tanzanie.
Bien évidemment, la construction des centrales hydroélectriques coûte
cher. Ainsi, la construction en 1989 par la Société Internationale d’Electricité
des pays(11) des Grands Lacs (SINELAC) de la centrale de RUZIZI II a coûté
95 millions de dollars, pour une puissance installée de 29.2 MW ; soit un
coût de plus de 3 millions de dollars par MW installé.
Les fonds nécessaires à la construction de cette centrale ont été
essentiellement des prêts (près de 90 %) négociés auprès de plusieurs
bailleurs de fonds comme l’Agence Internationale pour le Développement
(IDA), le Fond Européen de Développement (FED), la Banque Européenne
d’Investissement (BEI) et la Banque de Développement économique des
pays des Grands Lacs (BDEGL)…
Ces bailleurs ne vont sans doute pas continuer à accorder des crédits de ce
genre et si élevés, qui en plus seraient donnés à un seul pays qui de plus est,
n’a pas de solvabilité guarantie.
Une des solutions qu’il faudrait donc tenter est la construction de micro et
pico-centrales, ce qui est possible sur les nombreuses petites rivières qu’il y a
au Burundi.
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Soit beaucoup plus que le Rwanda qui n’a que 64 MW de potentiel sur les sites internes et 120 MW sur les
sites frontières…
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Ces pays, le Congo (RDC), le Rwanda et le Burundi forment la Communauté Economique des Pays des Grands
Lacs(CEPGL). Avec les turbulences de la sous-région, cette communauté est pratiquement en veilleuse
actuellement.
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Avantages des micro et pico-centrales hydroélectriques.
Les micro et pico-centrales hydroélectriques présentent plusieurs avantages
par rapport aux grandes centrales :
• Elles peuvent être construites avec des moyens à la portée de notre pays
ou des privés qui pourront alors injecter leur production sur le réseau
national pour l’exportation.
• Elles permettent une production locale et décentralisée de l’électricité
• Elle peuvent être intégrées dans une approche communautaire de
développement
• Elles nécessitent souvent des travaux de génie civil limités et perturbent
moins l’environnement ou l’alimentation en eau, ce qui peut être très
important par exemple pour le cas des micro-centrales qui seraient
installées sur des rivières alimentant le bassin du Nil(12), fleuve sur lequel
l’Egypte garde un œil vigilant ....
Considérations sur le choix des turbines à installer.
Il faut d’abord faire remarquer que si l’on opte pour les micro et picocentrales hydroélectriques, il est souhaitable qu’elles soient construites avec
la même technologie et si possible par le même fabricant.
Ce choix permet de négocier un prix de gros, d’avoir un stock de pièces
de rechange et éventuellement de négocier un transfert de technologie pour
une production locale de certains composants.
Ce choix doit aussi s’inscrire dans une vue à moyen et long terme, à
savoir la possibilité d’interconnexion avec le réseau national.
Une des turbines les plus appropriées aux micro-centrales de hauteurs de
chute et de débits variables est la turbine radiale, dite aussi à impulsion ou de
BANKI.
La version à 2 compartiments (1/3 + 2/3) de cette turbine garde un bon
rendement ( autour de 80 %) pour des débits variant entre 0.025et 13 m3/s et
pour des hauteurs de chute variant entre 1 m et 200m ; avec une puissance
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Le Burundi abrite la source la plus méridionale du Nil. Plus de la moitié des eaux de ruissellement du Burundi
sont drainées vers ce fleuve.
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variable entre 1 KW et 1.5 MW ; pour par exemple des débits de 0.1 m3/s
et 3.75 m3/s respectivement sous 1.50 m et 50m de hauteur de chute .
On pourrait aussi exploiter la voie des « turbines bulbes » dans certaines
conditions.
En guise de conclusion
L’énergie est une composante indispensable si pas la base du
développement. Viser le développement de nos pays passe donc par une
promotion de l’accès à l’énergie pour la population et plus particulièrement par
l’électrification du milieu rural. Cette voie ne sera néanmoins pas facilement
mise en œuvre car elle rencontre plusieurs contraintes multiformes. Contraintes
de moyens au niveau des Etats, contraintes de nature organisationnelle,
contraintes culturelles comme l’habitat dispersé dans le cas de certains pays de
l’Afrique Centrale dont le Burundi.
Ces contraintes ne doivent néanmoins pas laisser inactifs les décideurs
politiques et les scientifiques. Nous avons suggéré pour le cas du Burundi (et
sans doute pour d’autres pays) le recours aux micro et pico-centrales
hydroélectriques. Cette voie ne peut néanmoins être laissée à la seule initiative
des Etats dont beaucoup sont presque en banqueroute, sans parler de l’inertie
bureaucratique qui touche la plupart d’entre eux. C’est pourquoi nous avons
suggéré une approche communautaire de développement, approche articulée sur
une auto-prise en charge locale des communautés. Nous avons aussi suggéré
que la construction des micro et pico-centrales hydroélectriques ne soit plus un
monopôle des Etats mais plutôt libéralisée pour permettre aux privés d’y
investir.
Nous devons aussi faire remarquer que même si ces micro et picocentrales étaient construites en grand nombre, il subsistera toujours des zones
qu’on ne pourra pas alimenter facilement avec de l’hydroélectricité. Ces zones
pourront alors recourir aux autres énergies renouvelables. D’où la nécessité d’y
consacrer aussi un grand intérêt comme dans le cadre de ce séminaire.
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Annexe : Répartition de l’énergie consommée au Burundi en 2001
Répartition de l’énergie totale
• Bois, Charbon de bois et Déchets végétaux : 96.9%
(dont 88% pour les ménages ruraux, avec 2.93 kg /hab/jour)
• Produits Pétroliers : …………………………2.5%
• Electricité : …………………..………………0.3%
• Tourbe : ……………………………………...0.03%
• Energies Renouvelables (solaire et biogaz) : négligeables
Répartition de l’énergie commercialisée
•
•
•
•
Bois-énergie (principalement charbon de bois) : 76.9%
Produits Pétroliers : …………………………….19.2%
Electricité : ……………………………………….3.8%
Tourbe : ……………………………....…………..0.1%
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