Renewable Energy 37 (2012) 37e44
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Renewable Energy
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Life cycle assessment of two different 2 MW class wind turbines
Begoña Guezuraga a, Rudolf Zauner a, *, Werner Pölz b
a
b
VERBUND Renewable Power GmbH, Schottengasse 4, A-1010 Vienna, Austria
Umweltbundesamt GmbH, Spittelauer Lände 5, A-1090 Vienna, Austria
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 22 October 2010
Accepted 10 May 2011
Available online 28 June 2011
Although wind technology produces no emissions during operation, there is an environmental impact
associated with the wind turbine during the entire life cycle of the plant, from production to dismantling. A
life cycle assessment is carried out to quantify the environmental impact of two existing wind turbines,
a 1.8 MW-gearless turbine and a 2.0 MW turbine with gearbox. Both technologies will be compared by means
of material usage, carbon dioxide emissions and energy payback time based on the cumulative energy
requirements for a 20 year life period. For a quantitative analysis of the material and energy balances over the
entire life cycle, the simulation software GEMISÒ (Global Emission Model of Integrated System) is used.
The results show, as expected, that the largest energy requirement contribution is derived mainly from
the manufacturing phase, representing 84.4% of the total life cycle, and particularly from the tower
construction which accounts for 55% of the total turbine production. The average energy payback time
for both turbines is found to be 7 months and the emissions 9 gCO2/kWh. Different scenarios regarding
operation performance, recycling of materials and different manufacturing countries such as Germany,
Denmark and China are analysed and the energy payback time and carbon dioxide values obtained.
Finally, the wind energy plant is compared with other renewable and non-renewable sources of energy
to conclude that wind energy is among the cleanest sources of energy available nowadays.
Ó 2011 Elsevier Ltd. All rights reserved.
Keywords:
Life cycle assessment
LCA
Wind turbine
Turbine materials
CO2
Energy payback time
1. Introduction
Wind energy technology has a significantly lower impact on the
environment than traditional fossil electricity generation technologies. However, although wind energy has no direct emissions during
operation it still has a negative impact on the environment during pre
and post operation phases. An impact assessment approach is
therefore important in order to identify the burdens associated with
the life cycle of a wind turbine, from extracting raw materials from
earth reservoirs to manufacturing the different parts of the turbine
until the plant is decommissioned. During the different stages,
greenhouse gas (GHG) emissions which are responsible for global
warming, especially CO2 emissions, are released into the environment. Identifying the main sources of CO2 emissions in the entire life
of the plants, could help to find ways to reduce them and make wind
power an even cleaner source of energy.
In order to assess the environmental impacts of the whole life
cycle of a wind turbine, a life cycle assessment (LCA) is carried out.
The objective of a LCA of a product or process is to capture a range of
environmental liabilities or impacts that accumulate over the entire
* Corresponding author. Tel.: þ43 50313 52464; fax: þ43 50313 152464.
E-mail address: [email protected] (R. Zauner).
0960-1481/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.renene.2011.05.008
life cycle, from cradle-to-grave period. There are different types of
impacts; the direct impacts are those that occur on the specific site
while the plant is producing energy. On the other hand, the indirect
impacts vary with structure and performance of background
industrial systems [1].
According to the ISO 14040 and 14044 standards, a LCA is
carried out in four stages:
1. Goal and scope definition.
2. Inventory analysis: collecting all inputs and outputs of the
system.
3. Impact assessment: evaluating the potential environmental
impacts associated with those inputs and outputs.
4. Interpretation: evaluating the significance of the potential
environmental impact of the system.
2. Goal and scope definition
The main objective of the study is to calculate a number of
relevant parameters related to the energy consumption, such as
CO2 emissions and energy payback time of two different wind
turbines located in two specific locations. These results are
compared with other sources of energy based on fossil fuels to
assess the potential of wind plants. The first turbine is a 2.0 MW
38
B. Guezuraga et al. / Renewable Energy 37 (2012) 37e44
turbine with gearbox (from now on referred to as turbine 2.0 MWgeared). The wind plant is currently in the commissioning stage.
However, accurate and reliable wind data is available from the
manufacturer and site measurements. Turbine 2.0 MW-geared is
a wind class IEC IIA turbine specially designed for the wind regimes
of continental Europe. The second turbine to be analysed is
a 1.8 MW turbine without gearbox (from now on referred to as
turbine 1.8 MW-gearless). This wind turbine is already in operation
and operating data is available.
2.1. Process flow chart
In this LCA, the entire life cycle of the wind turbine is considered,
from manufacture of the components until the turbine is decommissioned. Turbine transport to site and erection as well as operation
and decommissioning are included, since these phases are also part of
the lifetime of the wind turbine. The flow chart of the wind turbine
life cycle is represented in Fig. 1 where the red arrows symbolize the
emissions released and the blue arrows the electricity generated.
Manufacturing phase includes the upstream processes such as
mining, refining, processing and construction of the main components of the wind turbine, which are:
Rotor: consists of hub, nose cone and 3 blades.
Nacelle: is normally made of the nacelle frame which covers
the generator, the gearbox, transformers and the electronics.
Tower
Foundation
Grid connection cables
Transport and on-site erection comprises the transport of the
turbine components to the wind farm and the erection of it.
Operation and maintenance includes routine actions to keep the
plant in order and fixing the devices that may become out of order.
The schedule maintenance covers oil change, lubricants and also
the transfer of workers during service operations. Some spare parts
replacement is required for the gearbox of the turbine.
Dismantling and recycling includes dismantling of turbines,
transportation by truck to the disposal site and in some cases
recycling of components.
2.2. Assumptions and limitations
The lifetime of the turbines is set to be 20 years. The wind
turbine itself defines the boundary limit of the system, whereas
transformers and substations are not included. Then, grid losses in
transformers and in the distribution grid are ignored. The paint
used in the rotor, nacelle and tower is also excluded from the scope
of this analysis as it was impossible to obtain data from the
manufacturers and it is of little relevance in the final result.
2.3. Software: GEMISÒ
To conduct the LCA, the simulation software GEMISÒ (Global
Emission Model of Integrated Systems) is used, which is widely
used for LCA in Europe. It enables a detailed description of all the
process steps of an energy system and the calculation of the
primary energy consumption involved in the process, the emissions
and the mass and energy flows.
The model can perform LCA for a variety of emissions and can
determine the resource use. Its database also provides information
on energy carriers (process chain and fuel data) as well as different
technologies for heat and electric power generation. In addition to
fossil energy carriers (hard coal, lignite, oil, natural gas), renewable
energies, household waste, uranium, biomass and hydrogen are
also covered in GEMISÒ.
The data required to be entered in the GEMISÒ software is:
materials and approximate masses
power and duty cycle
transport distances and modes
other energy requirements
The following can be obtained from the database:
Embodied energy of materials/kg
Energy for manufacture/kg
2.4. Impact assessment categories
2.4.1. Global warming potential
This indicator relates to the contribution of the process to
climate change, in other words, it is a measure of how much a given
mass of GHG gas is estimated to contribute to global warming. It is
a relative scale that compares the gas in question to that of the
same mass of carbon dioxide. The main GHG are carbon dioxide
(CO2), methane (CH4) and nitrous oxide (N2O). It is measured in
equivalents kgCO2/kWh. CO2 equivalents (CO2e) are the result of
the aggregation of GHG which takes into account their respective
global warming potential.
2.4.2. Cumulative energy requirements
This is the basic term for assessing the energy related part of
a life cycle analysis for energy systems. The total cumulative
energy requirement contains the energy requirements needed to
deliver a product or a service e valued as primary energy
measured in kWh.
2.4.3. Energy payback time
This is a term used to measure the net energy value of a wind
turbine, how long the plant has to operate to generate the amount
of energy that was required during its entire life. It is calculated as
the ratio of total primary energy requirements of the system
throughout its life cycle to annual electricity generated by a system,
so it is defined as the total cumulative energy requirements divided
by the total annual energy generated by the turbine, where the total
cumulative energy requirements comprises energy for production,
transport, maintenance and decommissioning.
2.5. Functional units and actual production
Manufacture of
components:
-Rotor
-Nacelle
-Tower
-Foundation
Transport and
on site
erection
Operation
&
Maintenance
Fig. 1. Life cycle flow chart.
Dismantling &
Recycling
For turbine 2.0 MW-geared no recorded data on operation is
available but the data provided by the manufacturer, typically
from a good wind site location, is used. It is assumed that the
turbine generates 5.98 GWh per year for 2990 operating hours. By
contrast, actual operating data is available for turbine 1.8 MWgearless, so 1822 annual operating hours are assumed on the basis
of the data obtained over 9 years with a total annual generation of
3.27 GWh.
B. Guezuraga et al. / Renewable Energy 37 (2012) 37e44
39
3. Life cycle inventory analysis
3.3. Transport and on-site assembly
The inventory analysis covers the resource inputs of metals,
sand, concrete, glass, and petrochemical products and energy
required for the manufacture of the different components of the
wind turbine.
Each turbine component is assumed to be transported from the
manufacture facility to the site by road truck. The distance covered
for turbine 2.0 MW-geared is estimated to be 2700 km, while the
distance cover for turbine 1.8 MW-gearless is 1100 km and the
transport typically consists of the following:
3.1. Turbines main characteristics
3.1.1. Turbine 2.0 MW-geared
Wind turbine 2.0 MW-geared is a three bladed upwind horizontal axis wind turbine. It is characterized by a large rotor (rotor
diameter is 90 m) with a large swept area and a hub height of
105 m. The average wind speed at hub height is 7.4 m/s.
3.1.2. Turbine 1.8 MW-gearless
Wind turbine 1.8 MW-gearless features a three blade, pitch
controlled rotor. The design includes a gearless direct drive
synchronous generator turbine. This turbine does not have
a gearbox and therefore has less rotating parts than turbine
2.0 MW-geared, which operates with a gearbox. The rotor is
directly connected to the generator by bearings in the generator
shaft. This wind turbine was designed to address component failure
concerns and therefore reduce maintenance cost and performance
reduction. This turbine features a 70 m rotor diameter and a hub
height of 65 m with an average wind speed of 6 m/s.
3.2. Wind turbine manufacture
3.2.1. Manufacturing of the rotor
3.2.1.1. Blade. The blades are made of a material consisting of
approximately 60% glass fibre and 40% epoxy. The material is delivered on rolls to the corresponding assembly facility where it is cut
into appropriate pieces to the spar and blade. Glue material is used to
assemble the blade shells and the spars.
3.2.1.2. Hub and nose cone. The hub and nose cone are generally
made of cast iron and fibre glass-reinforced polyester respectively [2].
3.2.2. Manufacturing of the nacelle
3.2.2.1. Nacelle cover. This is mainly made of fibreglass, plastic and
steel.
3.2.2.2. Generator. The generator is basically made of steel and
copper.
3.2.2.3. Gearbox. The gearbox is made of cast iron and stainless
steel [2].
The energy consumption in the manufacturing process of the
generator and gearbox has not been obtained directly from the
supplier, but data on material component weights is available.
3.2.3. Manufacturing of tower
The towers are made of steel, which is delivered to the turbine
manufacturer in steel plates so they do not need to cut up the plates
any further. Welding, sandblasting and surface treatment are performed at the manufacturing location [2].
3.2.4. Manufacturing of the foundation
The foundation is basically made of reinforced concrete and
reinforced steel. The foundation is generally concreted in situ and
after excavation, the hole is filled with concrete and reinforced
steel [2].
1 complete nacelle
3 extendible trailer for blade transport
4 trailers for towers
1 trailer loaded with cables and controllers
1 trailer with blade hub
1 trailer loaded with 40 ft container with tools and generation for erection.
It is measured in tkm (ton-kilometre(s)) freight transport
services. So if a truck transports 10 tonnes (t) over a distance of
2700 km this equals a transport service of 27,000 tkm.
3.4. Operation and maintenance
Energy input is required for the turbine operation, such as
starting the machine, break system operation, yaw and rotor pitch
control. Turbine operation consumption is normally estimated as
1% of the total electricity generated by the turbine [3]. For both
turbines service is assumed to be carried out three times a year in
the form of oil and lubricant. The distance covered is assumed to be
100 km per trip.
A conservative estimate of maintenance for the turbines is
assumed. It is expected that over a 20 years lifetime, turbine
2.0 MW-geared will require one gearbox replacement every 7
years. Turbine 1.8 MW-gearless requires less maintenance than
turbine 2.0 MW-geared mainly because of the smaller number of
rotating parts in the gearless turbines, only minor parts of the
generator may be replaced.
3.5. Dismantling and recycling
There is also an energy input requirement during the dismantling stage, which normally account of 2% of the total electricity
generated [3]. Table 1 shows the possible recycle scenarios for the
main materials involved in the turbine production.
3.6. Material requirements
Material requirements in tonnes and percentage for each wind
turbine are shown in Table 2, where it can be seen that turbine
2.0 MW-geared is 2.5 times heavier than turbine 1.8 MW-gearless.
Table 3 shows the material requirements per main turbine
component. Both turbines main component contribution comes
from the foundation, followed by the tower and nacelle.
Table 1
Possible recycle scenarios [4].
Stainless steel
Cast iron
Copper
Epoxy
Plastic
Fibreglass
Concrete
90% recycle, 10% landfill
90% recycle, 10% landfill
90% recycle, 10% landfill
100% incinerated
100% incinerated
100% incinerated
100% landfill
40
B. Guezuraga et al. / Renewable Energy 37 (2012) 37e44
Table 2
Material requirements.
Materials
Stainless steel
Cast iron
Copper
Epoxy
Plastic
Fibreglass
Reinforced Concrete
TOTAL
Table 4
Values for the entire cycle of both turbines.
Turbine 2.0 MW-geared
Turbine 1.8 MW-gearless
Mass (t)
Wt.%
Mass (t)
Wt.%
296.4
39.35
2.40
10.00
2.40
24.30
1164
1538
19.3
2.6
0.2
0.6
0.2
1.6
75.6
100.0
178.4
44.10
9.90
4.80
1.85
10.20
360.0
609.2
29.9
5.9
1.6
1.8
0.3
2.6
57.9
100.0
1
2
3
4
5
Total CO2e
Total cumulative energy
requirements
Annual energy generated
Energy payback time (2)/(3)
CO2e
Rotor
Nacelle
Tower
Foundation
TOTAL
Turbine 1.8 MW-gearless
Mass (t)
Mass (t)
37.85
61.00
224.0
1216
1538
2.5
4.0
14.6
79.0
100.1
Turbine 1.8
MW-gearless
t
GWh
1164
3.91
578
2.11
GWh
yr
g/kWh
5.98
0.65
9.73
1.2%
Turbine 2.0 MW-geared
Wt.%
Turbine
2.0 MW-geared
4.3%
Wt.%
12.00
88.25
134.0
375.0
609.2
2.0
14.5
22.0
61.5
100.0
3.1%
7.0%
Manufacture
Transport
Maintenance
Operation
Dismantling
4. Life cycle implementation
4.1. Entire life cycle results
The total cumulative energy requirements for both turbines for
the entire life cycle is represented in Fig. 2.
From Fig. 2 it is clear that the total cumulative energy requirements for turbine 2.0 MW-geared are much larger than for turbine
1.8 MW-gearless. However, this result by itself is not a basis for
concluding that turbine 2.0 MW-geared has a higher negative
impact than turbine 1.8 MW-gearless. The energy generated by both
turbines must be taken into account to determine the final impact. It
is found that turbine 2.0 MW-geared produces more energy than
turbine 1.8 MW-gearless because it is located in a better location
with stronger and more constant winds, has a higher hub height,
and also has a more powerful engine. The results in Table 4 show the
energy payback time for both turbines: 7.8 and 7.7 months for
turbine 2.0 MW-geared and turbine 1.8 MW-gearless respectively.
Both turbines show very similar results, however turbine 1.8 MWgearless offers better results in terms of CO2e emissions.
The largest cumulative energy requirements contribution comes
from the manufacturing stage in both cases, reaching values of
79.2% and 89.5% of the total life cycle for turbine 2.0 MW-geared
and B respectively. The average share from each stage of the life
cycle for both turbines is shown in Fig. 3, where the manufacturing
stage dominates with 84.4% of the total share. The smallest
Entire life cycle cumulative energy requirements
Dismantling
GWh
4
Operation
Maintenance
3
Transport
Manufacture
2
1
0
2.0MW-geared
3.27
0.64
8.82
Total cumulative energy requirements share
Table 3
Turbine main components material requirements.
Main Components
Units
1.8MW-gearless
Fig. 2. Entire life cycle cumulative energy requirements.
84.4%
Fig. 3. Total life cycle cumulative energy requirements share.
contribution is derived from the operation phase, which accounts
for only 1.2% of the total energy requirements. A more detailed
analysis of the manufacture stage is performed in order to determine the sources of the largest burdens.
4.2. Manufacturing phase alone
Fig. 4 shows the relative cumulative energy requirements for the
manufacture of the different turbine components.
The most energy intensive component is the tower production,
while the second largest contribution for turbine 1.8 MW-gearless is
the nacelle construction. The nacelle construction energy requirements for turbine 1.8 MW-gearless (28%) are significantly larger
than those in turbine 2.0 MW-geared (12%) because of the heavy
direct drive gearless generator used in turbine 1.8 MW-gearless with
a larger volume. Nevertheless, the second largest contribution for
turbine 2.0 MW-geared is the foundation, which can be explained by
the need for larger support required from a more powerful engine
subjected to stronger loads. Taking into account the manufacturing
phase alone, the new calculated parameters are shown in Table 5.
In this case the better results are obtained for turbine 2.0 MWgeared, while emissions for turbine 1.8 MW-gearless are 3.8% larger and
the energy payback time is 10% larger than for turbine 2.0 MW-geared.
Turbine 2.0 MW-geared offers the best results because the service and
maintenance requirements are not taken into account and larger wind
turbines with gearbox normally require more maintenance.
The main contributor to the total cumulative energy requirements and CO2 for both turbines is the production of stainless steel,
followed by concrete and cast iron. On the other hand, plastic
production represents the most energy intensive process of all
B. Guezuraga et al. / Renewable Energy 37 (2012) 37e44
41
Table 6
Average annual production and new operation hours.
Component contribution to the total energy demand
60%
Turbine 2.0MW-geared
Turbine 1.8MW-gearless
Average annual production - Turbine 2.0 MW-geared
50%
Year
No degradation
2% degradation
Annual energy generated (MWh/a)
40%
30%
20%
10%
0%
Rotor
Nacelle
Tower
Fundation
Fig. 4. Component contribution to the total energy demand.
Table 5
Turbine manufacturing phase results.
1
2
3
4
5
Total CO2e
Total cumulative energy
requirements
Annual energy generated
Energy payback time (2)/(3)
CO2e
Units
Turbine 2.0
MW-geared
Turbine 1.8
MW-gearless
t
GWh
907.4
3.10
517.6
1.89
5.98
0.52
7.59
3.27
0.58
7.89
GWh
yr
g/kWh
materials. However, it does not add a large contribution because
only small quantities of plastic and composite materials are found
in the rotor blades and in the nacelle transformers. After the plastic
production, the second process with the largest emissions is the
production of stainless steel.
Reinforced concrete is the main material used for turbine
2.0 MW-geared and turbine 1.8 MW-gearless, accounting for 75.6%
and 57.9% of the total turbine material, followed by stainless steel
with 19.3% and 29.9% for turbine 2.0 MW-geared and turbine 1.8
MW-gearless respectively. Unlike the concrete production, the
stainless steel plate production emits large quantities of GHG
during the manufacturing phase; this increases the environmental
impact of turbine 1.8 MW-gearless as it contains 10% more steel
than turbine 2.0 MW-geared and gain to turbine 2.0 MW-geared as
it has 17.7% more concrete material.
Year 1
Year 2
Year 3
Year 4
Year 5
Year 6
Year 7
Year 8
Year 9
Year 10
Year 11
Year 12
Year 13
Year 14
Year 15
Year 16
Year 17
Year 18
Year 19
Year 20
SUM
h/a average
5980
5980
5980
5980
5980
5980
5980
5980
5980
5980
5980
5980
5980
5980
5980
5980
5980
5980
5980
5980
119,600
2,990
5980
5860
5743
5628
5516
5405
5297
5191
5088
4986
4886
4788
4693
4599
4507
4417
4328
4242
4157
4074
99,385
2,485
1.8 MW-gearless is collected and recorded for 9 years for 5 identical
wind turbines. The average reduction in output is around 2% per
year. Now a similar degradation rate is taken into account for
turbine 2.0 MW-geared. To do so an average of the new output has
been calculated for a 20 year period and the new operation time is
calculated as the average production (kWh/a) divided by the power
(kW). In Table 6 this data is tabulated.
Secondly, grid curtailment is analysed. It occurs when a wind
turbine needs to reduce its generation output or even shut down
due to issues such lack of grid availability, planning conditions or
turbine overloading for instance. Normally the main reason for grid
curtailment is the congestion of the transmission grid and insufficient transmission capacity. Curtailment depends on a number of
factors and it represents a real problem in some countries where
the turbines cannot operate at full capacity. For this analysis 30%
grid curtailment is assumed as a worst case scenario. If the further
increase of installed capacity in a relatively small region would
continue, grid curtailment could become a major issue.
5.1. Operation scenarios
5.1.2. Assumptions
A 2% degradation reduction and 30% reduction due to grid
curtailment have been assumed. However, no additional maintenance or energy requirements have been considered due to regular
interruption of operation.
5.1.1. Introduction
In this section two different situations regarding the performance of the wind turbines are analysed, such as plant degradation
and grid curtailment. The generated output data for turbine
5.1.3. Results
New calculated energy payback time and CO2 emissions are
obtained for turbine 2.0 MW-geared, taking into account the new
full load hours calculated. When both situations are analysed
5. Possible scenarios and results
Table 7
Results for different operating scenarios.
1
2
3
4
5
Op. hours
Total cumulative energy
requirements
Annual energy generated
Energy payback time (2)/(3)
CO2e
Units
2%
Degradation
30% Grid
Curtailment
2% Degradation &
30% Grid Curtailment
hr
GWh
2485
3.91
2093
3.91
1738
3.91
GWh
yr
g/kWh
4.97
0.79
11.72
4.19
0.94
13.91
3.48
1.13
16.74
B. Guezuraga et al. / Renewable Energy 37 (2012) 37e44
5.2. Different recycling scenarios
5.2.1. Introduction
Nowadays 80% of a wind turbine system (including cables) can
be recycled, except for the blades which are made of composite
materials and the foundation which is made of concrete. There are
studies concerning a more environmentally friendly way of
disposing composite materials which state that 20% of composite
recycled materials can be used in future products [5], but at the
time of this assessment recycling of composite materials has not
been considered.
Two recycling scenarios are compared: the worst and the best
case recycling scenarios. The processes for secondary and primary
stainless steel, cast iron and copper production are described and the
results presented as they are the only materials that can be recycled.
5.2.2. Assumptions
The values obtained in section 4.1 have been calculated based on
the assumption that recycled materials have been used to produce the
different components until the maximum possible extent. However, it
must be noted that not all materials can be produced from recycled
materials and not all recycled materials are obtained 100% from scrap.
5.2.3. Material recycling processes
5.2.3.1. Stainless steel production. For stainless steel production, it is
considered that the upstream materials are iron and steel scrap used
as a secondary resource for steel production. In electric steel plants,
electric arc furnaces of different types are used. Simple arc furnaces in
which steel scrap is melted by the use of electricity have been replaced
by electric furnaces in which oxygen and fuels are also added. Iron as
a basic metal and lime (CaO) as a material, are also included in the
process. Finally, the molten crude steel is poured into a continuous
strand casting machine. In a hot rolling mill, plates used to build the
tower are formed from the slab. Steel is also present in the foundation
and a number of components of the nacelle, such as gearbox, generator, nacelle cover, transformer and yaw system.
If recycling steel is not considered, exactly twice the amount of
primary energy is required for steel production (2.28 GWh vs.
4.59 GWh), taking into account the fact that steel represents 20% of
the total material component, the final results will be greatly
influenced by the material production process [6].
5.2.3.2. Cast iron production. Cast iron is considered to be produced
from iron and steel scrap melted in electric furnaces. For each tonne
of cast iron obtained, 1.57 tonnes of liquid iron are used. In addition,
methanol is required to obtain formaldehyde, ammonia to obtain
carbamide, minerals for clay and sand and water. When recycling is
not considered, the processes comprise the extraction of raw
materials from the earth until cast iron is produced and the amount
of primary energy required to obtain the necessary cast iron is five
times higher (0.16 GWh vs. 0.81 GWh) [6].
5.2.3.3. Copper production. Secondary copper is the pure metal
derived from secondary sources such as waste and scrap. The scrap
used for copper production can come from metallic scrap or from
copper containing waste as sludge. For copper production nonferrous copper scrap is used as a secondary resource and it is
assumed that secondary copper production is based on the pyrometallurgical process. In Germany 40% of total copper is produced
from secondary copper.
To obtain primary copper, the process starts with concentration of
the raw materials and finishes with pure metal after electrolysis. For
refining not only smelted material is used, but also copper scrap. As
co-products of this process unit, sulphuric acid, anode-dredges and
nickel sulphate are produced. When primary copper is used the
energy requirements are increased from 18.3 MWh to 47.3 MWh [6].
5.2.4. Results
Recycling of stainless steel, cast iron and copper is considered,
whereas epoxy, plastic, fibreglass and concrete production are
derived from crude oil or minerals. The results in Table 8 show the
worst case recycle scenario (WCRS) when turbine 2.0 MW-geared is
manufactured in Europe and no recycling of materials is considered, then the gCO2/kWh is raised from 9.78 to 17.35 and the energy
payback time from 0.65 to 1.15 compared to the best case recycle
scenario (BCRS). Now considering the WCRS and worst case operation scenario (WCOS) with 30% grid curtailment and a 2% degradation factor, the new energy payback time and gCO2/kWh are 1.99
and 29.48 respectively. Results are shown in Table 8 and Fig. 5.
Table 8
Results for different recycling and operating scenarios.
1
2
3
4
5
Total CO2e
Total cumulative energy
requirements
Annual energy generated
Energy payback time (2)/(3)
CO2e
Units
WCRS
WCRS and
WCOS
t
GWh
2074
6.91
2074
6.91
GWh
yr
g/kWh
5.98 (2990 h)
1.15
17.35
3.47 (1738 h)
1.99
29.48
Energy payback time and CO2e emissions
2.5
35
Energy payback time
2.0
30
CO2e emissions
25
1.5
20
1.0
15
g/kWh
together the payback period is raised to 1.13 years from 0.65 years.
New values are shown in Table 7.
years
42
10
0.5
5
0.0
0
BCRS
WCRS
WCRS + WCOS
Fig. 5. Cumulative energy requirements and CO2e for the different scenarios.
5.3. Turbine manufactured in different locations
5.3.1. Introduction
The manufacturing process of the wind turbine is analysed
assuming it takes place in three different countries: Germany,
Denmark and China with different mixes of energy. Germany and
Denmark have facilities to manufacture the different components
of both turbines. However, the production facilities are increasingly
being exported to Asian countries such as China where the labour
cost is significantly lower than in Europe. The end product is the
same whether produced in China or in Denmark, but the emissions
to produce the exact same product will vary depending on the mix
of energy used to produce electricity in each country. China’s main
source of energy is derived from coal fire power stations, whereas
in Denmark a larger share comes from wind power plants.
5.3.2. Assumptions
To compare the results from these three different countries, the
production process steps have been simplified to increase the
accuracy of the comparison with less room for errors. The processes
B. Guezuraga et al. / Renewable Energy 37 (2012) 37e44
comprise the extraction of raw materials from earth resources even
though in some cases they could be obtained from waste materials.
5.3.3. Results
China has the largest impact, followed by Denmark and Germany.
The new energy payback time and CO2e emissions for turbine
2.0 MW-geared for the entire life cycle are shown in Table 9 and Fig. 6,
where an increase in transport requirements is considered for China
and raises the total emissions to 38.33 gCO2/kWh.
The cumulative energy requirements during the manufacturing
phase obtained from different processes retrieved from GEMISÒ are
given as the sum of non-renewable, renewable and other sources of
energy. Table 10 shows a breakdown of the energy balance, taking
into account their specific domestic mix of electricity generation,
oil products refinery model, heavy fuel oil boilers and gas boilers for
the processes carried out.
As observed in Table 10, the main source of energy used for the
manufacture process is derived from crude oil, with Denmark being
the country with the largest share. The second largest fuel used in
China is black coal, which represents 20% of the total fuel
requirements versus 7.5% in Denmark and 5.7% in Germany.
As the reader would expect that the energy requirements in
Denmark are smaller than in Germany, the results need to be
explained. The reason is because the resource use mix in Germany
is more assorted and therefore the black coal requirement is
smaller than in Denmark. Moreover, nuclear power contribution
represents 5.3% of the total share in Germany and only 0.1% in
Table 9
Results for different manufacturing locations.
Total CO2e
Total cumulative energy
requirements
Energy payback time
CO2e
1
2
3
4
Units
Germany
Denmark
China
t
GWh
2074
6.90
2782
8.06
4584
14.10
yr
g/kWh
1.15
17.35
1.35
23.26
2.36
38.33
43
Denmark. In addition, waste use in Denmark is 3% whereas there is
no use at all in China and only 1.2% use in Germany.
5.4. Comparison with other sources of energy
5.4.1. Introduction
An important part of the LCA is to make a comparison with other
sources of energy to assess the environmental impact caused by
wind power in relation to more traditional fossil fuel power plants
and also to other renewable sources such as:
Photovoltaic plants e amorphous, monocrystalline and polycrystalline silicon.
Hydropower plants
Nuclear power plants
Gas cogeneration power plants
Coal power plants
The three different photovoltaic technologies compared are
amorphous silicon, monocrystalline and polycrystalline silicon.
Amorphous silicone (a-Si) is the non-crystalline form of silicon
Monocrystaline silicon is a homogeneous single crystal silicon.
Polycrystalline silicon is composed of a number of smaller crystals
and it can reach a purity of 99.9999%. The mono and polycrystalline
silicon modules chosen for the analysis are assumed to use a sun
tracker for a better performance. The hydropower plant analysed is
a large hydro plant located in Austria.
The nuclear power plant applied in this comparison uses
a pressurized water reactor with some auxiliary electricity required
from a diesel system. Enriched uranium is used as a fuel input. For
the cogeneration plant a large scale gas fired combined cycle
cogeneration plant with low NOx burner fed with natural gas is
used. The credit allocated from cogeneration heat from combined
heat and power plants (CHP) replaces gas heating. The last power
plan compared is a big coal fired steam turbine power plant fuelled
with hard coal.
Cumulative energy requirements comparison
other
renewable
non renewable
16
GWh
12
8
4
0
DE
DK
CN
Fig. 6. Cumulative energy requirements for turbine 2.0 MW-geared in different
locations.
5.4.2. Assumptions
The results are measured as the environmental effects caused
for 1 kWh of electricity produced from the different sources of
energy.
5.4.3. Results
The results for the energy payback time and CO2e emissions for
the different sources of energy analysed are graphically represented in Figs. 7 and 8.
The nuclear power plant is the only fossil fuel source that emits
less CO2 than a renewable source of energy such as photovoltaic
energy, but hydro and wind power still offer the best results. The
reasons for the high values obtained for the solar systems are the
high energy intensive processes related to silicon extraction and
CO2e emissions
Table 10
Energy balance for turbine 2.0 MW-geared manufacture.
1200
type
Germany %
Denmark %
China %
Nuclear power
Brown coal
Natural gas
Crude oil
Black coal
Residual biomass
Hydropower
Wind power
Waste
NR
NR
NR
NR
NR
R
R
R
Others
5.3
4.9
7.2
74.9
5.7
0.2
0.3
0.1
1.2
0.1
0.1
8.1
80.2
7.5
0.0
0.0
0.8
3.1
0.1
0.0
2.0
75.0
20.4
0.0
2.4
0.0
0.0
1000
Amorphous Si PV
Monocrystaline Si PV
800
g /k W h
Sources of energy
Wind plant
600
Multycrystaline Si PV
Hydropower plant
400
Nuclear power plant
200
CHP
0
Coal power plant
Fig. 7. CO2 emissions for different energy sources.
44
B. Guezuraga et al. / Renewable Energy 37 (2012) 37e44
Energy payback time
Wind plant
3.5
Amorphous Si PV
3
Monocrystaline Si PV
years
2.5
Polycrystaline Si PV
2
Hydropower plant
1.5
Nuclear power plant
1
CHP
0.5
Coal power plant
0
Fig. 8. Energy payback time for different energy sources.
processing, the larger amounts of material requirements due to sun
trackers and the fact that the plant is assumed to be in Germany
where solar radiation is not optimal. Coal power plants and
combined heat and power plants represent the largest CO2 emission, although coal fire plants emissions are much higher
(228 gCO2/kWh vs. 1046 gCO2/kWh).
In terms of energy payback time, CHP becomes more attractive
and nuclear power becomes the least appealing source of all with
the largest energy payback time up to 3.16 years versus 1.12 years
for the CHP. In this case, CHP offers better results than the Photovoltaic plants with an energy payback time ranging between 1.31
and 1.57, but wind and hydropower plants are still the most
advantageous sources of energy in terms of energy payback time
and CO2 emissions.
6. Life cycle interpretation
This LCA shows the environmental impacts per kWh electricity
delivered from two wind turbines and the results turned out to be
very similar. This is due to the fact that although turbine 2.0 MWgeared has higher energy requirements, is sited at an extremely
optimal wind location and delivers more energy than turbine
1.8 MW-gearless which on the other hand, has less energy
requirements but also generates less electricity. For the base case
scenario, the energy payback time value of both turbines is 0.6 years,
which means that after 7.2 months of operation the amount of
energy needed for the turbine manufacture, operation and decommissioning will be returned. The CO2e emissions for the turbine with
the largest productivity are 9.73 g/kWh in comparison to 8.82 g/
kWh for turbine 1.8 MW-gearless, mainly because turbine 2.0 MWgeared requires more material and maintenance for operation.
One of the outcomes from this LCA analysis is, as expected, that
the main impacts originate from the production (84%) and transport (7%) of the turbine. The operating phase has an almost negligible environmental impact. Even the disposal scenario represents
only 3.1% of the total energy requirements; it is found that it is very
important for the environmental profile of the turbine to consider
recycling of materials because when no recycling of materials is
considered the energy requirements are increased by 43.4% and the
CO2e emissions by 43.9%. In contrast to the 0.6 years payback time
results when recycling is considered, the turbine would have to
operate for 1.1 years to pay for itself when no recycling of materials
is assumed and 2.3 years if the turbine is produced with China’s
electricity mix.
The tower, foundation and nacelle are found to add the largest
negative contribution to the final results. In the case of the tower, the
key element is the large amount of steel required for production.
However, its final impact is reduced because steel can be recycled.
The nacelle is also composed of high strength steel - adding a share
to the total stainless steel amount required - and also copper used in
various elements. Most ferrous alloy materials found in the nacelle
are recoverable, except for the glass fibre reinforced polymer.
Although the blades add a very small contribution to the total energy
requirement, some consideration should be taken into account
during waste treatment at the end of the life due to the fact that they
are made of epoxy and fibre glass. Improvements in composite
materials processing and reutilization are necessary to make wind
technology an even cleaner source of energy.
The material with the largest negative impact is stainless steel
and the smallest impact is derived from concrete production.
Nowadays, some turbine towers are made out of concrete instead of
steel to obtain better resistance to fatigue and loads. From an
environmental point of view, a shift towards turbines with a larger
share of concrete and smaller share of stainless steel is desired.
7. Conclusions
The most important parameters calculated in a LCA are the
CO2e emissions and the energy payback time. They vary
depending on the assumptions allocated. The most sensitive
scenario is the manufacturing phase, in particular the use of
recycled materials, and the electricity mix used for the production of the materials. The “greener” the energy used, the smaller
the environmental impact of the wind turbine. The analysis
shows that even most materials in the wind turbine can be
recycled, many fossil fuel based sources of energy are used to
produce these materials and the large amount of crude oil and
black coal used has a significant negative impact on the final
results. The energy payback time for a nuclear and a coal fire
power station are 3.16 and 2.72 times longer that those for wind
power. Hydropower has a slighter smaller environmental impact
than wind energy, and both sources of energy should undoubtedly be regarded as the energy of the future. Due to this fact and
the rapid growth in energy demand experienced in the recent
years, it is very important to invest in these technologies in
order to achieve a more sustainable development.
The results from this report should also be used as reliable data
to promote more sustainable policies to support wind energy
development. Visual and noise pollution are not considered in this
analysis, but they should be carefully considered as they represent
a barrier in the development process of this source of renewable
energy.
References
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in Taiwan, the 7th International Conference on EcoBalance, November 14e16
2006, Tsukuba, Japan, 2006.
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