Technologies for power generation in
rural contexts
Emanuela Colombo,
Rector’s Delegate to “Cooperation and Development” - Politecnico di Milano
UNESCO Chair in Energy for Sustainable Development
Department of Energy
Engineering Without Border
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Energy from SUN
Emanuela Colombo - POLIMI – UNESCO Chair
Electrification and Distributed Generation
Solar photovoltaic systems
Solar energy is the most abundant of REs resources.
Solar photovoltaic (SPV) generators
•
Semiconductor solar cells to convert solar radiation into electricity
ASSESSEMENT: Solar radiation is available at any location,
The value at the ground level varies due to geographic conditions
• higher values closer to the Equator,
SPV generation is also influenced by seasonal climatic variations
• Higher during warm than in cold months.
• Higher during the dry season then rainy season.
Databases are available to obtain an estimation of annual plant productivity
• Photovoltaic Geographical Information System (PVGIS)
• IRENA's Global Atlas
No Data
• Weather Modeling and Forecasting of PV Systems Operation (radiometers)
Emanuela Colombo - POLIMI – UNESCO Chair
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Electrification and Distributed Generation
Solar photovoltaic systems
TECHNOLOGY OVERVIEW
SPV generators convert energy from the sun with solar cells
•
Solar cells semiconductor materials: monocrystalline/polycrystalline silicon.
•
A number of solar cells are gathered together to form a solar panel.
• Typical power for each solar panel is 80-200W,
• The conversion efficiency of each panel is 15-18%.
•
More panels can be combined, high degree of modularity and scalability:
SPV systems consist of different components other then the cell
•
•
•
Batteries and Charge controller for energy storage;
Inverter
Wires/cables and other hardware for electric connections
The technology is suitable for different applications,
• from small lanterns up to mini-grid systems.
Emanuela Colombo - POLIMI – UNESCO Chair
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Electrification and Distributed Generation
Solar photovoltaic systems
TECHNOLOGY OVERVIEW
SPV systems are classified as follows:
1. SPV home-based systems
-
Pico SPV systems
Classical solar home systems
2. SPV community-based systems
3. Micro-grid SPV systems
SPV systems have higher performance in most developing countries
• Values of solar radiation :
•
1400 to 2300 kWh/m2 in Europe and US:
•
around of 2500 kWh/m2 in Tanzania , East Africa
• Advantages
•
High reliability, long lifetime, absence of moving parts, free fueled
Emanuela Colombo - POLIMI – UNESCO Chair
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Electrification and Distributed Generation
Solar photovoltaic systems
TECHNOLOGY OVERVIEW
1. SPV home-based Systems
• Solar home-based systems are stand-alone for specific end use
• Pico PVSs are small solar home systems
•
•
•
powered by a small solar panel coupled with a integrated battery
with a power output of 1 to 10 W,
used for lighting, to replace sources as kerosene lamps and candles
• Classical solar home systems
•
•
•
SPV module + charge regulator + battery + (optionally) an inverter
With a power output up to some hundred Watts
SPV generate DC power, so DC loads like energy saving lamps, radios and
special fridges make the inverter optional
• Without inverter, SPV systems are energy efficient (no losses)
• Charge controller controls the energy flow into/from the battery
bank, ensuring optimal charging and avoiding damages
Emanuela Colombo - POLIMI – UNESCO Chair
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Electrification and Distributed Generation
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Solar photovoltaic systems
TECHNOLOGY OVERVIEW
1. SPV home-based Systems
Pico SPV system.
Solar home system. Source
Emanuela Colombo - POLIMI – UNESCO Chair
Electrification and Distributed Generation
Solar photovoltaic systems
TECHNOLOGY OVERVIEW
2. SPV community-based systems
• Larger stand-alone PV systems
•
with a typical range from hundred to thousand Watts
• Main Components:
•
inverter is needed with embedded charge controller
•
12V or 24V batteries, bigger systems work with 48V
• Typical Applications to provide energy to community services
•
health centres, schools, factories…
•
Solar battery-charging stations
• the station is set up at a central place in a village,
• It has a battery bank charged by an array of SPV modules.
• A DC-DC converter is used to charge batteries of single devices
Emanuela Colombo - POLIMI – UNESCO Chair
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Electrification and Distributed Generation
Solar photovoltaic systems
TECHNOLOGY OVERVIEW
2. SPV community-based systems
SPV community-based systems
Emanuela Colombo - POLIMI – UNESCO Chair
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Electrification and Distributed Generation
Solar photovoltaic systems
TECHNOLOGY OVERVIEW
3. Micro-grid SPV systems
• can provide electricity to many households and community services
• solar panels arrays are assembled in the range of hundreds of kWp
• a distribution network provides the electricity to the connected loads.
• The complexity of the system is higher, components are:
•
•
•
•
PV array(s)
Battery banks for electricity storage
Power conditioning unit (PCU) consisting of junction boxes, charge
controllers, inverters, distribution boards and necessary wiring/cabling
Power distribution network (PDN) consisting of poles, conductors,
insulators, wiring/cabling
Emanuela Colombo - POLIMI – UNESCO Chair
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Electrification and Distributed Generation
Solar photovoltaic systems
TECHNOLOGY OVERVIEW
4. Micro-grid SPV systems
Micro-grid SPV systems
Emanuela Colombo - POLIMI – UNESCO Chair
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Electrification and Distributed Generation
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Solar photovoltaic systems
TECHNOLOGY OVERVIEW
System
Production voltage Presence of inverter Loads
Home-based 12V DC
Pico SPV
No
Lamps, Radio, Mobile charger
Home-based 12-24V DC
Classical
Optional
Light, TV, Fridge, PC, Mobile
charger
Community- 12-24-48V DC
based SPV
Optional
pump,
Water
Cooler,
Light,
Hardware for artisanal work, ...
Yes
pump,
Water
Cooler,
Light,
Hardware for artisanal work, ...
SPV
grid
mini-24-48V DC
Comparison of different SPV systems
Emanuela Colombo - POLIMI – UNESCO Chair
Electrification and Distributed Generation
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Solar photovoltaic systems
ECONOMICS and ENVIRONMENTAL IMPACT in a glance
Prices of SPV generation are
•
in developed market around 2.5 $/Wp, in emerging markets below 1 $/Wp.
• For Micro-grid:
•
•
about 50-60% is due to the solar PV array,
About 10-15% to battery bank and 25-25% to power conditioning unit
The Levelized Cost of Energy (LCOE)
•
is in the range 0.26-0.75$/kWh. Average costs are
• for a 300W device 0.56$/kWh, for a 25kW plant 0.51$/kWh.
Life cycle energy required for silicon-based SPV is in 2699-5253 MJ/m2
Energy Pay-Back Time (EPBT) varies in the range 1.5-2.7 years.
Greenhouse gas (GHG) emissions range in 23-45 g CO2-eq./kWh,
•
•
an order of magnitude smaller than that of fossil-based electricity
emissions from a diesel generator are > than 700 g CO2-eq./kWh
Emanuela Colombo - POLIMI – UNESCO Chair
First level sizing
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Solar photovoltaic systems
1 Verify solar resource characteristics
Get the global horizontal solar daily irradiation for the selected site
Calculate daily average solar irradiation hours as the ratio between the solar daily irradiation and the maximum
irradiance on Earth surface (solar radiation energy flux (Rs = 1kW/m2)
2. Calculation of requested load to supply (daily average consumption L)
3. Estimating power output : The systems need to be designed considering the worst photovoltaic production and
the highest possible load. It is necessary to define the parameter  (performance ratio), that includes the location of
the modules and their status of maintenance: a value of 0,8 indicates good positioning and good maintenance
Calculation of power output P:
4. Selection of the modules and evaluation of the number of modules to be installed
5. Rough estimation for the accumulation system
Calculation of the energy to be stored
dd = number of days without solar radiation
= load-reload battery efficiency, 0,8
Batteries Capacity (@24 V):
6. Designing of the inverter on the power requested from user
7. Estimated Daily Energy Output
Emanuela Colombo - POLIMI – UNESCO Chair
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Energy from WIND
Emanuela Colombo - POLIMI – UNESCO Chair
Electrification and Distributed Generation
Wind Generators
Wind energy is site specific
A wind power generator (WPG) converts kinetic energy of wind into
electric power through rotor blades connected to a generator.
• Stand-alone applications, small wind (SW) turbines,
•
Are around 50-100 kW , with efficiency around 35%
• There is a variety of technologies for rural communities in DCs:
•
rely only on well proven and mature technologies
•
use artisanal turbines (lower costs and participative)
Emanuela Colombo - POLIMI – UNESCO Chair
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Electrification and Distributed Generation
Wind Generators
ASSESSEMENT: Wind power is site specific
Energy produced depends on wind speed at the site:
• Wind speed is highly influenced by topography and obstacles:
• Turbines >> along ridges/hilltops to minimize obstacle’s influence
Wind power changes during the day, and the seasons.
• Wind speeds of 4-5 m/s are required to achieve economic sustainability
Data all along the year are required.
• Direct measure can be taken with meteorological towers with
anemometers and wind vanes to have speed and directions
• Secondary data can be taken from other measuring meteorological or
airport installations, together with appropriate calculation models (model
selection is done according to available information and site characteristics)
Emanuela Colombo - POLIMI – UNESCO Chair
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Electrification and Distributed Generation
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Wind Generators
ASSESSEMENT: Wind power is site specific
No Data is available
• empirical method based on observation of trees are used (see fig.)
• online databases may be used, with care since
• wind speed depends on the side
• wind maps are measured at 50 m
• Ok, for traditional wind turbines
>= hundred of kW,
• KO for SW turbines need
< than 30 m.
Griggs-Putnam Index of Deformity.
Emanuela Colombo - POLIMI – UNESCO Chair
Electrification and Distributed Generation
Wind Generators
TECHNOLOGY OVERVIEW
SW systems are classified as follows
1. SW home-based systems
2. SW community-based systems
3. Micro-grid SW systems
Main General features are
•
•
•
The three-blades design is prevalent, it minimizes vibrations and noise
Have a direct drive, permanent magnet rotor generator
• simplest configuration, without gearbox: produces alternate current
Turbines are placed higher than 15 m on a pole out of ground turbulence
• Tilt-up poles/towers are ok up to some kW: easy to install/maintain
Emanuela Colombo - POLIMI – UNESCO Chair
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Electrification and Distributed Generation
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Wind Generators
TECHNOLOGY OVERVIEW
1. SW home-based systems
• pico-or micro-wind turbines up to about 1.5 kW
• The system requires some components
• the turbine mounted roof-top or on a pole.
• a bridge rectifier (an electronic device that converts alternate current in
direct current) OR
• a power conditioning unit (in order to deliver proper voltage and
frequency when AC loads are present)
• a charge regulator
• batteries for energy storage.
• Application: suitable for households (lighting, mobile charging, radio, TV, etc.)
Emanuela Colombo - POLIMI – UNESCO Chair
Electrification and Distributed Generation
Wind Generators
TECHNOLOGY OVERVIEW
2. SW community-based systems
• SW turbines in the range 1.5 - 15 kW.
• Application
• dwellings, schools, hospitals, telecom towers, water-pumps, etc., if
average wind speed is adequate.
• for battery charging, very similar to SPV battery-charging stations.
3. Micro-Grid SW systems
• Small and medium size turbines with a typical power range of 15-100 kW.
• The layout of the system is similar to SPV systems: few examples of minigrid systems supplied only by wind turbines.
• More frequently, micro-grid SW systems are hybrid systems coupled with a
diesel generator, a SPV system….
.
Emanuela Colombo - POLIMI – UNESCO Chair
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Electrification and Distributed Generation
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Wind Generators
ECONOMICS and ENVIRONMENTAL IMPACT in a glance
• The price depends on the size, material and construction process.
•
Costs of SW systems include
• turbine and components: tower or pale, battery storage, power
conditioning unit, wiring, and installation.
• overall costs are in the range 3000 - 6000 $/kW.
• Maintenance: turbine requires cleaning and lubrication, while
batteries, guy wires, nuts and bolts, etc. require periodic inspection.
Costs depend on the cost of local spares and service.
• LCOE is in the range 0.15-0.40$/kWh depending on size
•
0.35$/kWh the cost for 300 W plant, 0.20$/kWh for a 100kW plant.
• Life Cycle Analysis (LCA) of wind systems state
•
SW turbines (1 kW) 3 times more energy/per power than large 1 MW
• GHG emissions values in the range 4.6-55.4 g CO2-eq./kWh.
Emanuela Colombo - POLIMI – UNESCO Chair
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Energy from WATER
Emanuela Colombo - POLIMI – UNESCO Chair
Electrification and Distributed Generation
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Small Hydropower Systems
SHP plants transform kinetic into mechanical energy with a hydraulic turbine
• Mechanic energy drives devices or is converted in EE via an electricity generator
• No unique definition of small hydropower (SHP), but it generally includes pico-,
micro- and mini-hydro, with generating capacities up to about 5 MW.
• Electricity production is continuous, as long as the water is flowing
ASSESSEMENT: Hydro resources are site specific
• the right combination of flow and fall is required to meet a load.
• A river flow can vary greatly during the seasons,
• a single measurement of instantaneous flow in a watercourse is of little use
• detailed information is required to estimate production potential
• also the evaluation of the best site is required.
Emanuela Colombo - POLIMI – UNESCO Chair
Electrification and Distributed Generation
Small Hydropower Systems
ASSESSEMENT: Hydro resources are site specific
• Data about water resources assessment can be obtained by databases
• Infohydro, a database provided by the World Meteorological Organisation
• FAO provides database of rainfall patterns to compute approx. hydrograph
• A direct evaluation may be required, several methods exist:
• Velocity-area method: this method is suitable for medium size rivers.
Evaluation is done by measuring cross sectional area and mean velocity.
• Weir method: in small rivers, a low obstacle in the stream to be gauged
with a “known” notch through which the water is channeled. The measure
evaluate the level difference between upstream water & bottom of notch
• Data can be organized in a Flow Duration Curve, a curve showing the proportion
of time during which the discharge equals/exceeds a value: to size the turbine
• Estimation of waterfall is required. Field measurements of gross head are usually
carried out using instruments such as theodolites, laser level or GPS.
Emanuela Colombo - POLIMI – UNESCO Chair
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Electrification and Distributed Generation
Small Hydropower Systems
ASSESSEMENT: Hydro resources are site specific
• SHP is the most mature REs technology and has conversion efficiency up to 90%
• Best geographical areas: presence of perennial rivers, hills or mountains.
• SHP generally require some infrastructures:
• a canalization system is necessary to send the flow to the turbine,
• the construction of a building to protect the generator
• SHP require low maintenance.
A typical SHP includes the following elements :
Weir, intake and channel
Forebay tank
Penstock
Turbine
Generator
Small hydro plant
scheme. Source
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Electrification and Distributed Generation
Small Hydropower Systems
ASSESSEMENT: Hydro resources are site specific
SHP can be classified as follows:
1. SHP home based systems
2. SHP community based systems
3. Micro-grid SHP systems
The turbine is the core element, type depending on the flow and head:
• High-head:
• Pelton, Turgo and Banki
• medium-head, and low-head:
• Kaplan or Francis,
• but also pumps as turbines: advantages - lower cost and a greater
availability of equipment – disadvantages lower conversion efficiency.
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Electrification and Distributed Generation
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Small Hydropower Systems
?
Emanuela Colombo - POLIMI – UNESCO Chair
Electrification and Distributed Generation
Small Hydropower Systems
ASSESSEMENT: Hydro resources are site specific
1. Home-based systems are pico-hydroelectric installations
•
electric power up to about 2-3 kW.
•
Electricity production is continuous and storage is optional.
•
A head of 5-6 meters can be sufficient for 1 kW output power.
•
Don’t need channels and penstock
•
easy to install, with electro-mechanical elements grouped in single device
•
The generator is permanent magnets type
•
Voltage/load regulation are suggested to avoid problems to electric loads:
simple regulators are mechanical (automatically driven valves which adjusts
the flow to meet variations in power demand) or electronic (excess
electrical power is switched in and out of a ballast load by a controller)
Emanuela Colombo - POLIMI – UNESCO Chair
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Electrification and Distributed Generation
Small Hydropower Systems
ASSESSEMENT: Hydro resources are site specific
2. Community-based systems
• micro-hydro plants with power from some kilowatt up to 20 kW.
• Most systems are run-of-river type, no water storage is needed.
• On the other hand, channels and penstock are in general used.
3. Micro-grid systems
• with electrical power from a few tens of kilowatt up to 5MW.
• Larger infrastructure works are required in this case
• could require a basin and/or a small dam
• the construction of an electricity distribution network is necessary.
• The generator is typically synchronous
• > 20 kW a proper Regulator is needed to guarantee optimal system functioning
Emanuela Colombo - POLIMI – UNESCO Chair
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Electrification and Distributed Generation
Small Hydropower Systems
ECONOMICS and ENVIRONMENTAL IMPACT in a glance
• SHP costs depend
•
•
•
•
•
on site characteristics, terrain and accessibility.
For micro-systems, the distance between the power house and the loads
can have a significant influence on overall capital costs
the use of local materials, local labor, and pumps as turbines reduces costs
In general, the investment range 500-5600 $/kW, being higher the costs of
small plants and lower those of larger size plants.
Operational costs are low due to high plant reliability , proven technology
• LCOE varies in the range 0.01-0.40$/kWh
•
for a 300W plant is 0.15$/kWh, for 100kW is 0.02$/kWh.
• GHG emissions vary greatly depending on the presence of a reservoir
•
•
run-of-river SHP emissions in the range 0.3-13 g CO2-eq./kWh,
For reservoir SHP range is 4.2-152 g CO2-eq./kWh
Emanuela Colombo - POLIMI – UNESCO Chair
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Energy from Biomass
Emanuela Colombo - POLIMI – UNESCO Chair
Technologies Overview
Biomass gasifier power station
Biomass indicates different sources
Refers to the biodegradable fraction of organic products and residuals:
•
•
agriculture, forestry, industrial activities dealing with organic matter.
organic fraction of urban waste
A number of thermo-chemical processes exist:
• Biomass gasification is suitable for low generation capacities
• Biogas reactors are mainly suitable for cooking purposes
ASSESSEMENT: Biomass assessment is not easy
Biomass resources assessment is very complex:
• a comprehensive analysis of the biomass production chain is always required
• biomass drivers and barriers need to include competition with other resources
• studies about biomass resources potentials refer to large areas
• very little or no information is available for specific sites in DCs
• GIS-based remote techniques can provide appropriate information
Emanuela Colombo - POLIMI – UNESCO Chair
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Technologies Overview
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Biomass gasifier power station
ASSESSEMENT: Biomass assessment is not easy
Forest residue
Agricultural residue Agro-processing residue
Forest pruning
Paddy straw
Rice husk
Wood from plantations
Wheat straw
Cashew nut shells
Wood from marginal lands Maize stalks
Oil seed shells
Grasses and bushes
Cotton stalks
Oil cakes
Wood pulp
Maize cobs
Coconut shells and fibre
Saw dust
Mustard stalks
Coffee and tea waste
Bamboo
Millet straw
Bagasse
Different types of biomass.
Emanuela Colombo - POLIMI – UNESCO Chair
Technologies Overview
Biomass gasifier power station
TECHNOLOGY OVERVIEW
The gasification process
- takes place in the gasification reactor, a closed vessel, normally cylindrical in shape
- biomass is subjected to partial combustion with limited supply of air
- the ultimate product is a combustible gas mixture known as producer gas: carbon
monoxide, hydrogen, nitrogen, carbon dioxide and methane
- thermal value depends on the type of biomass used: range 3800-6300kJ/Nm3
Gasification of biomass takes place in four distinct stages
- drying, pyrolysis, oxidation/combustion and reduction
- gasifiers are classified in 3 categories: fixed bed, fluidised bed, entrained flow
There are three types of fixed bed gasifiers:
- In downdraft gasifiers the gases and solids flows in a descending packed bed.
- In updraft gasifiers, the gases and solids have counter-current flow.
- In crossdraft gasifier, solid fuel moves down and the airflow moves horizontally
Gas contains a high level of tar and organic condensable and requires cleaning
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Technologies Overview
Biomass gasifier power station
TECHNOLOGY OVERVIEW
Emanuela Colombo - POLIMI – UNESCO Chair
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Technologies Overview
37
Biomass gasifier power station
TECHNOLOGY OVERVIEW
A typical system includes the following components :
•
•
•
•
•
Reactor
Gas cooling system
Cleaning system: a cyclone and/or water scrubber or other systems (filters, ...)
Gas engine coupled with an alternator
Auxiliaries (blower, control system, ...)
Biomass gasification is not suitable for home-based applications:
- minimum size plant is around 7-8kW electric power
- with a power generation efficiency in the range 10-20% .
Energy for community services can be provided using gasifier power plants:
- The configuration can be both classical stand-alone (powering a specific load),
or mini-grid, the last case with an electric generation capacity up to some MW
Emanuela Colombo - POLIMI – UNESCO Chair
Technologies Overview
Biomass gasifier power station
Emanuela Colombo - POLIMI – UNESCO Chair
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Technologies Overview
Biomass gasifier power station
ECONOMICS and ENVIRONMENTAL IMPACT in a glance
Capital cost for gasifier varies
•
•
for small installation 10-35 kWe : 850-2200 $/kWe
for medium-large 50-2000kWe : 1200-7600$/kWe
The Levelized Cost of Energy (LCOE)
•
is 0.08-0.14$/kWh.
Greenhouse gas (GHG) emissions,
•
•
•
When the supply chain is managed in a proper way , CO2 emissions from
combustion are compensated by the growth of new biomass
other emissions: fuel supply, power station construction and maintenance
are considered.
This consideration leads to a range from 63-70 g CO2/kWh (only CO2 is
taken into consideration and non a CO2-equivalent emission)
Emanuela Colombo - POLIMI – UNESCO Chair
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40
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Comparisons
Emanuela Colombo - POLIMI – UNESCO Chair
Electrification and Distributed Generation
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Off- grid Systems: LCOE comparisons
The Levelised Cost of Energy is used: the ratio between the total cost of
supplying electricity plant and the plant lifetime taking in account the discount
rate. The included costs are:
- construction, operating and maintenance (with fuel)
- disassembling and decommissioning.
- external costs may be included
Emanuela Colombo - POLIMI – UNESCO Chair
Electrification and Distributed Generation
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Evaluating Levelised cost of energy produced
Levelized Cost of Energy (LCOE) is the constant unit cost (per kWh or MWh) of
a payment stream that has the same present value as the total cost of
building and operating a generating plant over its life (no ROI).
EEt
 LCOE   t 1
( 1  i )t
n
Pvalueof revenew
n
LCOE 

t 1
t
TCIt  O & Mt  FUELt
( 1  i )t
EEt
n
 t 1 ( 1  i )t
n
PvalueTotalAnnulCost   t
t 1
Euro/kWh
 TCI Z O&M  n FUELt
n  Z tot 

n  
t
(
1

i
)
t 1 ( 1  i )


LCOE 
EEt
n
 t 1 ( 1  i )t
Emanuela Colombo - POLIMI – UNESCO Chair
TCIt  O & Mt  FUELt
( 1  i )n
Technologies Overview
43
Technology comparisons
solar PV
wind
hydro
biomass
Efficiency
%
15-18
35
90
10-20
Min size
W
1-10
hundreds
thousands
7000-8000
Emanuela Colombo - POLIMI – UNESCO Chair
Costs
$/kWh
0.26-0.75
0.15-0.40
0.01-0.40
0.08-0.14
Emissions
gCo2 /kWh
23-45
4.6-55.4
0.3-13 /4.2-152
63-70 (C02)
Technologies Overview
44
Technology comparisons
Issue
Resource
Availability
Resource
assessment
Solar PV
Small-wind
Micro- hydro
Only during daylight and variableHigh short-term and seasonal variability Seasonal variability
according to the season.
Possibility of extrapolation of
existing data concerning a
neighbouring area.
Possibility to install Yes, if roof or ground available
the system close to
the energy
utilization
Extrapolation of existing data requires
the use of dedicated software and a
thorough assessment of the site
configuration.
Biomass gasifier
Seasonal variability
Not always practical. In a few cases,
small wind turbines can be installed
directly on roofs. Consider also noise
problems.
In most cases, no existing data In most cases, no
available; on site measurement existing data
of flow and observation of
available; specific
seasonal variations required. study is often
required
Not always practical. The
Yes, but the
location is dependent on the discharge of
water resource.
combustion gases
should be considered
Space required
The ratio surface / power
installed is high for PV arrays
compared to other generators.
Space for setting up include the stays
installation and possibility to lay down
the turbine for maintenance.
The infrastructure is very
dependent on the
geomorphology of the site.
Installations are
compact and require
little space
Site restrictions
Shadowing
Roughness, obstacles, etc.
Accessibility to the water
resource.
-
Emanuela Colombo - POLIMI – UNESCO Chair
Technologies Overview
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Technology comparisons
Low to medium, depending on Medium to high depending on the
the configuration of the ground, configuration of the ground, the
the quality of the roofs, etc.
consistency of the soil or the quality of
the roof.
Low. High for maintenance and
Needed operation Low.
operation.
skills
Civil engineering
constraint level
Operation
constraints
Electrical
performance
Could be high depending on Low to medium,
the slope and width of the river strictly depending on
the size of the
installation
Low. High for maintenance
Medium. High for
and operation
maintenance and
operation
Batteries storage or hybridation Batteries storage or hybridation needed To adjust the settings of the
To adjust the settings
needed to adapt the production to adapt the production to the demand. turbine in relation to the
depending on
to the demand.
available flow and the
biomass type and
electricity demand
quality
Voltage regulation needed
Voltage and frequency regulation by an Voltage and frequency
Voltage and
(battery, hybridation).
external mean.
regulation by flow or demand frequency regulation
by demand
Storage to adapt production to Storage needed to adapt production to regulation.
regulation.
demand.
demand.
Energy conversion needed
Energy conversion needed if AC Energy conversion needed when using when using battery charging.
demand.
wind turbines for battery charging.
Safety issues
Electrical Mechanical
(wind effect on PV
array)
Electrical Moving parts
Electrical. Moving parts.
Mechanical (erection / laying down the Water pressure.
machine)
Environmental
impact
Visual. Ground occupation.
Battery recycling (if battery
storage)
Visual. Noise. Battery recycling (if
battery storage)
Emanuela Colombo - POLIMI – UNESCO Chair
Electrical. Moving
parts. Toxic gases.
High-temperature
heat sources.
Visual (especially due to the Possibility of impact
weir and the penstock, if any). on forests and of
Fauna and flora impact.
harmful emissions.
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Storage and the
Hybrid option
Emanuela Colombo - POLIMI – UNESCO Chair
Technologies Overview
Storage Systems
GENERAL CONSIDERATION
Storage is a key issue when renewable energy systems are used
- a number of technologies based on different principles are available but for small
scale systems up to some MW batteries are the most common device.
- battery storage is a mature technology, owing its success to the high energy
density and modularity (number of batteries can be connected together).
Most common type of batteries is lead- acid:
Lead Acid
- good energy density at reasonable price: deep-cycle - batteries must be used,
since storage must discharge large amounts of energy in a single cycle: the valveregulated lead–acid (VRLA) requires lower maintenance.
- Lifetime can be up to 10 years, but adverse environmental conditions (high
temperatures), intensive charge/discharge cycles, over-charging can shorten.
Emanuela Colombo - POLIMI – UNESCO Chair
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Technologies Overview
48
Storage Systems
GENERAL CONSIDERATION
lithium-ion (Li-Ion) batteries:
- Li-Ion batteries offer higher energy density and efficiency, and can handle deeper
discharges with less impact on lifetime.
- their lifetime is longer: on the other hand, Li-Ion batteries require more accurate
charge controllers and their cost is higher.
Deep-cycle lead-acid
Lithium-ion
Useful storage capacity
0.5-10kW per battery
0.5-10kW per battery
Lifetime
3-10 years
10-15 years
Roundtrip efficiency
70-90%
85-95%
Capital cost
150-500$/kWhcap
500-1500$/kWhcap
Emanuela Colombo - POLIMI – UNESCO Chair
Technologies Overview
49
Hybrid Systems
GENERAL CONSIDERATION
Hybrid systems can produce electricity even when one resources is off
A typical layout for rural areas includes the following components:
• One or more technology using unreliable renewable energy sources
• Secondary technology : typically a genset or a hydropower plant
• Storage system
• Inverter and charge controller
• Other electric material (cables, wires, etc.)
A hybrid system can be used
1. to provide electricity to single community services: health centers, schools,
water pumping systems,
2. to supply multiple loads in a micro-grid scheme, composed by 3 subsystems:
• Production subsystem, consisting of the above components
• Distribution subsystem, including all the distribution equipment
• Demand subsystem, including all the end-use equipment
Emanuela Colombo - POLIMI – UNESCO Chair
Technologies Overview
50
Hybrid Systems
GENERAL CONSIDERATION
Typical configuration
SPV/Diesel or Wind/Diesel
SPV or small wind coupled with a diesel genset is common and simple
- SPV or wind provides most of the electricity,
- the genset balances the production taking care of the long-term fluctuations.
- batteries meet short-term fluctuations,
SPV/Small hydro or Wind/Small hydro
- similar to the precedent
- small-size hydropower plant is used in place of the genset.
- Produced electricity is 100% from renewable sources (not frequently possible).
Emanuela Colombo - POLIMI – UNESCO Chair
Technologies Overview
51
Hybrid Systems
GENERAL CONSIDERATION
Typical configuration
PV/Wind (up to 50 kW)
The performance depends on local weather variations, and an accurate assessment
is mandatory. The system requires battery storage, inverter and charge regulator:
• if electricity demand < than wind turbine production,
=> the excess electricity form wind turbine and PV is stored
• if load demand is > than wind turbine production
=> the PV array cover the excess load
• if load demand is > additional energy is taken from the storage.
Other configurations
Other configurations are possible when more than two technologies are coupled
together in a complex hybrid system.
Emanuela Colombo - POLIMI – UNESCO Chair
Technologies Overview
Hybrid Systems
GENERAL CONSIDERATION
Connection scheme
Each power generation unit must be
connected to the electric grid:
• AC bus line: all generating units are
connected to an AC bus line for transmission.
PV arrays need a DC/AC converter, while
technologies generating alternate current
(hydro, wind, biomass gasifier, genset) are
allowed for direct coupling, even if a voltage
and/or frequency regulator may be
necessary, especially for wind. If the system
has a storage, a bidirectional master inverter
controls the energy supply for the AC loads
and the batteries.
Emanuela Colombo - POLIMI – UNESCO Chair
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Technologies Overview
Hybrid Systems
GENERAL CONSIDERATION
Connection scheme
Each power generation unit must be
connected to the electric grid:
• DC bus line: in this case all the
technologies generating alternate
current need AC/DC converter, while PV
is allowed for direct connection. DC
loads and batteries are directly coupled
to the DC bus line. Batteries are
controlled by a charge controller. AC
loads can be powered by an inverter.
Emanuela Colombo - POLIMI – UNESCO Chair
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Technologies Overview
Hybrid Systems
GENERAL CONSIDERATION
Connection scheme
Each power generation unit must be
connected to the electric grid:
• Mixed bus line: DC and AC generating
units are connected to the DC or AC
line. A master bi-directional inverter
controls the entire system
Emanuela Colombo - POLIMI – UNESCO Chair
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