Burton T. (et. al.) Wind energy Handbook
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In summary, it may be concluded that accurate analytical determination of the
way wind turbines may interfere with radio communication systems remains
difficult. In particular, techniques to determi ne the effects of irregular terrain and
the details of the blade shape and materials have yet to be developed and validated.
The approaches that rely on simplified assumptions to estimate the radar cross
section can only be considered approximate. However, they do provide a useful
qualitative understanding of the problem. In practice a dialogue with the local
telecommunications authorities is required in order to determine if a wind turbine
or wind farm development is likely to cause electromagnetic interference.
9.5 Ecological Assessment
Wind farms will often be constructed in areas of ecological importance and the
Environmental Statement will include a comprehensive assessment of the local
ecology, its conservation importance, the impact of the wind farm (during construc-
tion and operation) and mitigation measures. A study of the site hydrology is also
likely to be included because of its importance for the ecology. It is suggested by
English Nature (1994) that when considering the ecological impact of renewable
energy schemes the following categories of effects should be consi dered:
• immediate damage to wildlife habitats during construction,
• direct effects on individual species during operation,
• longer-term changes to wildlife habitats as a consequence of construction or
because of changed land use management practices.
Thus, the scope of the ecological assessment is likely to include:
• a full botanical survey including identification and mapping of plant species on
the site,
• a desk and field survey of existing bird and non-avian fauna,
• an assessment of how the site hydrological conditions relate to the ecology,
• evaluation of the conservation importance of the ecology of the site,
• assessment of the potential impa ct of the wind farm,
• proposed mitigation measu res, including which part(s) of the site should be
avoided.
Gipe (1995) suggests that the main impact on plants and wildlife (excluding
birds) is from road building and the disturbance of habitat. Direct loss of habitat
due to a wind-farm construction is small (approximately 3 percent) and this can be
reduced further by reinstating roads and construction areas once the wind farm is
built. However, during construction there is likely to be considerable disturbance
ECOLOGICAL ASSESSMENT 545
including frequent traffic of heavy vehicles and it may be necessary to timetable
major work to avoid sensitive periods (e.g. breeding seasons).
9.5.1 Impact on birds
The impact of wind energy devel opments on birds was particularly controversial in
the 1990s because of concern over raptors colliding with wind turbines in the USA
and in the south of Spain at Tarifa. Elsewhere in Europe the main concern was not
collisions of birds with turbines but issues associated with disturbance and habitat
loss (Colson, 1995, ETSU, 1996). Since then, there has been very considerable
research into the impact of wind farms on birds and it would appear that by careful
assessment and monitoring, before construction and during operation of the wind
farm, the environmental impact on birds may be managed effectively.
Lowther, in ETSU (1996), suggests that the presence of a wind farm may affect
bird life in one or more of the following ways:
• collision,
• disturbance,
• habitat loss.
However, Lloyd (ETSU, 1996) suggests that, because the removal of habitat is
comparatively small in a wind farm development, the main issues are the effect on
bird behaviour either from construction or operation and direct mortality from
birds colliding with wind turbines.
Gipe (1995) discusses US experience and provides Table 9.7 to give the estimated
number of birds killed in Northern California. Colson quotes an estimated range of
bird mortalities from wind-energy development in the USA prior to 1992 in the
range of 0–0.117 birds/turbine year.
Table 9.7 Estimated Number of Birds Killed by Wind Turbines in Northern California
(Gipe, 1995, Sources: for Altamont, Orloff and Flannery, California Energy Commission,
1992; for Solano, Howell and Noone, Solano County, 1992)
Solano
Altamont raptors All birds Raptors
Low High Low High Low High
Birds/year 164 403 17 44 11 2
Turbines 6800 6800 600 600 600 60
Birds/turbine year 0.024 0.059 0.029 0.074 0.018 0.04
MW 700 700 60 60 60 6
Birds/MW year 0.23 0.58 0.29 0.74 0.18 0.4
546
WIND TURBINE INSTALLATIONS AND WIND FARMS
The wind farms of the Altamont pass in the early 1990s are not typical of
European projects or even more recent developments in the USA. The turbines were
very numerous, some 7000 turbines in 200 km
2
, rather small in size (typically
100 kW), often on lattice steel towers and with close spacing along the rows facing
the prevailing winds. Lloyd (ETSU, 1996) suggests that a number of factors may
have led to the high collision rate among raptors. The Altamont turbines are often
located on low rises and ridges in the pass to exploit local acceleration of the wind
speed. A large number of the collisions appear to be at the end of the turbine rows
where the birds may be attempting to fly around the densely packed turbines . In
both Tarifa and Altamont there are few trees and it is suggested that some species
used the lattice steel towers as perches and even for nesting.
The bird strike rate for early UK wind farms is quoted by Lowther (ETSU, 1996)
and is shown in Table 9.8.
The three experimental turbines on Burgar Hill including a 3 MW 60 m diameter
prototype were adjacent to the habitats of a number of bird populations of national
significance, including 4 percent of the UK breeding population of the hen harrier.
Studies were undertaken over a 9 year period and during that time four mortalities
(three black-headed gulls and one peregrine) were noted as possibly being the
result of turbine strike.
The Blyth Harbour wind farm [Still et al., 1994] consists of nine 300 kW wind
turbines positioned along the breakwater of a harbour which has been designated a
Site of Special Scientific Interest. As it has the highest density of birds of any UK
wind-farm site (110 varieties identi fied with more than 1100 bird movements per
day) it was the subject of a monitoring programme. The main species that inhabit
the area are: cormorant, eider, purple sandpiper and three types of gull. There was
particular concern over the purple sa ndpiper, which winters in the harbour, and so
special measures were taken to improve its roosting habitat by providing additional
shelter. Over a 3 year period, 31 collision victims were identified. The mortality by
collision was mainly in eider and among the gulls. It was calculated not to have a
significant adverse impact on the local populations. In common with studies un der-
taken on Dutch and Danish coastal wind farms it appeared that most species had
adapted to the wind turbine structures. With respect to disturbance and habitat
loss, the study indicated that there was no significant long-term impact. The purple
sandpiper was not adversely affected by the wind farm and, although temporary
Table 9.8 Bird Strikes at Wind Farms in the UK (Lowther in
ETSU, 1996) (Reproduced by permission of ETSU on behalf of
DTI)
Wind farm Number of
turbines
Bird strikes/
turbine year
Burgar Hill, Orkney 3 0.15
Haverigg, Cumbria 5 0
Blyth Harbour, Northumberland 9 1.34
Bryn Titli, Powys 22 0
Cold Northcott, Cornwall 22 0
Mynydd y Cemmaes, Powys 24 0.04
ECOLOGICAL ASSESSMENT 547
displacement of cormorant occurred during construction, the population returned
to its precious haunts once construction was completed.
The Bryn Titli wind farm is adjacent to a Site of Special Scientific Interest, that
holds important, breeding communities of: buzzard, peregrine, red grouse, snipe,
curlew and raven. The wind farm was the subject of a bird impact study which
showed no statistically significant impact on breeding birds and a bird strike study
undertaken in 1994/95 indicated that it is unlikely that there were any collision
mortalities during that time.
Clausager (ETSU, 1996) has undertaken an extensive review of both the American
and European literature of the impact of wind turbines on birds. He concludes that,
of the mainly coastal locations studied, the risk of death by collision with wind
turbine rotors is minor and creates no immediate concern of an impact on the
population level of co mmon species. Drawing on 16 studies, and using a multiplier
of 2.2 for birds not found, he estimates the highest number of mortalities due to
collisions to be 6–7 birds/turbine year. With approximately 3500 wind turbines in
Denmark this leads to maximum number of birds dying from collision as 20 000–
25 000. This number is co mpared with at least one million birds being killed from
traffic in Denmark each year. He dismisses the direct loss of habitat as being small
and of minor importance but draws attention to the issues of changes in the area
due to the wind farm construction particularly draining of low-lying areas. He also
notes that some species of birds temporarily staying in an area may be adversely
effected and that an impact has been recorded within a zone of 250–800 m,
particularly for geese and waders. The need for further studies, particularly for
offshore wind farms and developments on uplands, where only a limited number
of investigations has been reported, is emphasized.
Both Lloyd and Col son propose mitigation measures that may be taken to protect
important bird species while allowing wind-energy development to continue. These
include the following.
• Baseline studies should be unde rtaken at every wind farm site to determine
which species are present and how the birds use the site. This should be a
mandatory part of the Environmental Statement for all wind turbines.
• Known bird migration corridors and areas of high bird concentrations should be
avoided unless site specific investigation indicates otherwise. Where there are
significant migration routes the turbines should be arranged to leave suitable
gaps, (e.g., by leaving large spaces between groups of wind turbines).
• Microhabitats, including nesting and roosting sites, of rare/sensitive species
should be avoided by turbines and auxiliary structures. (It may be noted that
meteorological masts as well as wind turbines can pose a hazard for birds).
• Particular care is necessary during construction and it is proposed that access for
contractors should be limited to avoid general disturbance over the entire site. If
possible, construction should take place outside the breeding season. If this is not
possible then construction should begin before the bre eding season to avoid
displacing nesting birds.
548 WIND TURBINE INSTALLATIONS AND WIND FARMS
• Tubular turbine towers are preferred to lattice structures. Consideration should
be given to using unguyed meteorological masts.
• Fewer large turbines are preferred to larger numbers of small turbines. Larger
turbines with lower rotationa l speeds are probably more readily visible to birds
then smaller machines.
• Within the wind farm the electrical power collection system should be under-
ground.
• Turbines should be laid out so that adequate space is available to allow the birds
to fly through them without encountering severe wake interaction. A minimu m
spacing of 120 m betwe en rotor tips is tentatively suggested as having led to
minimum collision mortalities on UK wind farms. Turbines should be set back
from ridges and avoid saddles and folds which are used by birds to traverse
uplands.
It is interesting to note that a 30 MW wind-farm development in Scotland was
only able to proceed after an extensive study of raptors and the conversion of
450 ha of coniferous forest to heather dominated moorland and the exclusion of
sheep from a further 230 ha (Madders and Walker, 1999). It is anticipated that this
extension of the moorland habitat will increase the amount of prey away from the
wind farm and so reduce the risk of collisions by golden eagles and other raptors.
9.6 Finance
9.6.1 Project appraisal
When evaluating power projects it has been conven tional for many years to use
techniques based on discounted cash flow (DCF) analysis (Khatib, 1997). This is
based on the recognition that most people and organizations have a time preference
for money and that they would rather receive money today not next year and would
rather pay out money next year rather than today. The use of DCF analysis, with a
high discount rate, tends to favour projects with short construction times, low
capital costs and high operating costs. Thus, it makes renewable energy schemes,
particularly offshore wind farms, rather difficult to justify, as a large initial capital
investment is required with an income stream stretching into the future.
The mechanics of DCF analysis are simple and the calculation may be implemen-
ted easily on a spreadsheet and the main functions are often included in commer-
cially available packages. Given a discount rate of r, the value of a sum in n years
time is given by:
V
n
¼ V
p
(1 þ r)
n
(9:31)
and so the present value of a sum received or paid in the future is given by:
FINANCE 549
V
p
¼
V
n
(1 þ r)
n
(9:32)
where V
n
is the value of a sum in year n, and V
p
is the present value of the sum.
Hence for a payment stream lasting m of years
V
p
¼
X
n¼m
n¼1
V
n
(1 þ r)
n
(9:33)
This is a geometric series which, for equal payments (A), sums to
V
p
¼
1 (1 þ r)
n
r
A (9:34)
This allows the calculation of the present value of any sum of money which is either
paid or received in the future. The net present value (NPV) is simply the summation
of all the present values of future income and expenditures. Using identical
discounting techniques, it is possi ble to calculate other financial indicators:
• the benefit/cost ratio is the present value of all benefits divided by the present
value of all costs,
• the internal rate of return (IRR) is the value of the discount rate that gives a net
present value of zero.
These should not be confused with indicators not based on discounted values such
as:
• payback period, expressed in years, which is the capital cost of the project
divided by the annual average return;
• return on investment, which is the average annual return divided by the capital
cost, expressed in percent.
For initial project appraisal some form of discounted cash flow is normally required
and the non-discounted indicators are not used. The discount rate chosen reflects
the value the lender places on the money and the risks that are anticipated in the
project. In economic terms, the discount rate is an indication of the opportunity cost
of capital to the organization. Opportunity cost is the return on the next best
investment and so is the rate below which it is not worthwhile to invest in the
project.
In the UK at present, discount rates of 8–12 percent would not be uncommon for
commercial power projects reflecting the value placed on capital and the perceived
level of risks. Some years ago (when the electricity supply industry was state-
owned) the British Government discount rate requ ired for power projects was 5
percent which was then raised to 8 percent. A number of continental European
Governments still fund wind farm projects with rates of 4–5 percent.
550 WIND TURBINE INSTALLATIONS AND WIND FARMS
In simple DCF analysis, general inflation is usually ignored and the discount rate
is the so-called ‘real’ rate but it is possible to build in differential inflation if it is
thought that some costs or income will rise at different rates over the life of the
project. The financial model may be as sophisticated as required to reflect the
concerns of the lender. It may, for example, include: (1) variations in electricity
prices, (2) tax, (3) payments during construction, (4) residual value of the wind
farm, and (5) operation and maintenance costs that vary over the life of the project.
There are generally considerable uncertainties with any financial modelling and
it is often helpful to investigate the importance of the various assumptions and
estimates in the model using a spider diagram. This is constructed by varying each
of the important parameters one at a time from a base case. The slope of the
resulting curves then indicates the sensitivity of the outcome to that particular
parameter. The simple example of discounted cash flow analysis below is used to
illustrate the concepts.
Example 9.1
Consider a 10 MW wind-farm project.
Capital cost £6 000 000
Annual capacity factor 28 perce nt
Annual operation and maintenanc e cost (O&M) £100 000
Sale price of electricity 0.04 £/kWh
Discount rate 10 percent
Project lifetime 15 years
The annual capacity factor is defined as the energy generated during the year
(MWh) divided by wind farm rated power (MW) multiplied by the number of
hours in the year. The determination of the capacity factor will, of course, be based
on the best available information of wind speeds and turbine performance.
The annual energy yield is simply: 0:28 3 10 3 8760 ¼ 24 528 MWh
The gross annual income is: 24 528 3 10
3
3 0:04 ¼ £981 120
Table 9.9 shows the simple DCF analysis while Figure 9.16 is the spider diagram to
examine the sensitivity of the calculations.
The example serves to illustrat e a number of points.
1. The net present value (NPV) is positive and so the project is suitable for further
consideration.
2. With a 10 percent discount rate the discount factor in year 15 is 0.239. This
indicates that the present value of the income (and expenditure) stream in that
year is only 24 percent of its cash value.
3. The project is very sensitive to increase in capital costs or reductions in capacity
factor. Any reduction in capacity factor could be caused either by low availability
of the turbines or by low wind speed s. Steps need to be taken to control these
FINANCE 551
risks by obtaining a firm price for the wind farm, with guarantees on the
availability of the turbines, and by ensuring that the projections of the wind
speed at the site are based on the best data available.
4. The project is insensitive to operation and maintenance costs at the level
included in the model.
Table 9.9 Simple Discounted Cash Flow of a 10 MW Wind Farm
Year Expenditure Income Net cash
flow
Discount
factor
Discounted cash
flow
0 6 000 000 6 000 000 1.000 6 000 000
1 100 000 981 120 881 120 0.909 801 018
2 100 000 981 120 881 120 0.826 728 198
3 100 000 981 120 881 120 0.751 661 998
4 100 000 981 120 881 120 0.683 601 817
5 100 000 981 120 881 120 0.621 547 106
6 100 000 981 120 881 120 0.564 497 369
7 100 000 981 120 881 120 0.513 452 154
8 100 000 981 120 881 120 0.467 411 049
9 100 000 981 120 881 120 0.424 373 681
10 100 000 981 120 881 120 0.386 339 710
11 100 000 981 120 881 120 0.350 308 827
12 100 000 981 120 881 120 0.319 280 752
13 100 000 981 120 881 120 0.290 255 229
14 100 000 981 120 881 120 0.263 232 026
15 100 000 981 120 881 120 0.239 210 933
NPV 490 936
Sensitivity of NPV to parameter variations
-£1000000
-£500000
£0
£500 000
£1000000
£1500000
£2000000
80 90 100 110 120
Variation %
NPV
Capital cost
Capacity factor
O&M cost
Figure 9.16 Sensitivity of Financial Model to Variations in Parameters
552
WIND TURBINE INSTALLATIONS AND WIND FARMS
5. In this simple model the costs have been discounted to the commissioning date
(year zero). The complete payment for the wind farm is assumed to be made at
commissioning and the income and O&M flows are assumed to be at the end of
each years operation. If more precision is required then the financ ial model can
be constructed to consider each quarter and the timing of the flows adjusted
accordingly. Alternatively the annual income and expenditure may be taken to
be in the middle of each year.
6. From trial and error calculations, the IRR is found to be 11.5 percent.
DCF modelling suffers from two major limitations. It does not reflect the external
costs of power production (e.g., gaseous emissions from thermal plants or loss of
visual amenity) and it does not represent cash flow. The lack of recognition of
external costs is of major importance when governments or international lending
agencies are considering alternative investments. Cash flow is a prime considera-
tion for private developers of wind farm projects.
9.6.2 Project finance
Large companies (e.g., power utilities or major energy companies) may choose to
develop small wind-farm projects using their own capital resources. The costs of
the project are met from the general equity raised by the company with the
liabilities of the project secured against the main corporate assets. The cost of
borrowing, which influences the required discount rate for the project, depends on
the financial strength of the company and it is possible to avoid the considerable
expense involved in raising external finance. Hence this approach may allow cash-
rich companies to develop pro jects at low cost.
Larger projects, and those developed by entrepreneurs, will tend to be based on
project financing with a loan obtained from a bank or other financial institution.
This has the advantage of reducing the requirement for capital from the developer
but the loan repayment will have the first call on the income of the project. Project
financing is also likely to offer tax advantages. If the loan is secured only on the
project cash flow itself, this is referred to as ‘limited recourse’ financing. Alterna-
tively, if the devel oper has a large parent company willing and able to pro vide
suitable guarantees then the loan may be secured against the assets of the parent
company which then appears as a liability on its balance sheet. Clearly the lenders
of the debt will prefer to guarantee thei r loan against the assets of a large stable
company rather than the project alone and this will be reflected in the repayment
terms that are available. The debt/equity ratio can be as high as 80 percent but all
risks must be identified and manageable if a suitable financial arrangement is to be
made. If a limited recourse loan is made bef ore a project is constructed then interest
rates of 10–20 percent would be typical while these would be significantly reduced
if the loan is re-financed after the project is commissioned and many of the
construction risks are no longer significant.
Figure 9.17 shows a typical commercial structure of a wind-farm project. This
is very similar to any other power project developed by independent power
FINANCE 553
producers (IPPs) where the Project Company is merely the vehicle by which a large
number of agreements are made. In order to limit risk, constr uction of the project
does not start until all the agreements are in place and so-called ‘financial close’ is
achieved.
The power purchase agreement is to sell the output electrical energy of the wind
farm. To reduce risk, this should be at a defined price for the duration of the project.
Under the UK Non Fossil Fuel Obligation or the German ‘Electricity Feed-in-Law’
this was reasonably easy to achieve but with the continuing liberalization of
markets for electrical energy throughout the world it will become increasingly
expensive to avoid exposure to varying energy prices.
The loan agreement is for the bank( s) to provide the debt finance for the project.
An accura te and verifiable assessment of the wind resource is an essential prerequi-
site for this agreement although there is also likely to be a ‘due diligence’ investiga-
tion of the whole project to ensure all major risks are addressed.
The construction agreement is to purchase the wind turbines and construct the
wind farm. To reduce risk this may be done on a ‘turn-key’ basis with the wind-
turbine manufacturer taking responsibility for the entire wind farm.
The O & M agree ment is to operate and maintain the wind farm for the life of the
project.
The site agreement is to define the relationship with the landowners and to ensure
access to the site and the wind resource for the duration of the project.
The connection agreement is to allow the wind farm to be connected to the electrical
power system and so export its output. In a deregulated power system this is
separate from the power purchase agreement.
The shareholder agreement is between the owners of the Project Company to define
their rights and obligations.
It may be seen that a large number of agreements are required and it will
typically take a year from project inception to financial close. During this time the
developer is operating at risk, expending considerable resources, and so full
development of this administrative/financial phase of the project is only com-
menced once feasi bility has been dem onstrated.
Shareholder
agreement
Insurance
Site agreement
Connection
agreement
Project
Company
Construction
agreement
Power purchase
agreement
Loan
agreement
O & M
agreement
Bank(s)
Wind-speed
assessment
Figure 9.17 Typical Commercial Structure of a Wind-Farm Project
554
WIND TURBINE INSTALLATIONS AND WIND FARMS