Wind farm development and operation - A case study

APPLICATION NOTE
WIND FARM DEVELOPMENT AND OPERATION: A
CASE STUDY
Ton van der Wekken, KEMA Consulting
December 2016
ECI Publication No Cu0149
Available from www.leonardo-energy.org

Publication No Cu0149
Issue Date: December 2016
Page i
Document Issue Control Sheet
Document Title: Application Note – Wind Farm Development and Operation
Publication No: Cu0149
Issue: 01
Release: Public
Content provider(s) Ton van de Wekken (DNVGL (formerly KEMA Consulting)), Creara
Author(s): Ton van de Wekken (DNVGL (formerly KEMA Consulting))
Editorial and language review Bruno De Wachter (editorial), Noel Montrucchio (language)
Content review: Creara
Document History
Issue Date Purpose
1 January
2007
Initial publication
2 February
2012
Adaptation for adoption into the GPG
3 December
2016
Review by Creara
Disclaimer
While this publication has been prepared with care, European Copper Institute and other contributors provide
no warranty with regards to the content and shall not be liable for any direct, incidental or consequential
damages that may result from the use of the information or the data contained.
Copyright© European Copper Institute.
Reproduction is authorized providing the material is unabridged and the source is acknowledged.

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CONTENTS
Summary ........................................................................................................................................................ 1
Introduction.................................................................................................................................................... 2
Wind farm initiation and feasibility phase ...................................................................................................... 2
Site selection and wind assessment .......................................................................................................................2
Technical feasibility ................................................................................................................................................4
Main risk assessment..............................................................................................................................................4
Permitting requirements of local authorities .........................................................................................................5
Project financing.....................................................................................................................................................5
Pre-building phase.......................................................................................................................................... 7
Wind farm design including energy yield predictions ............................................................................................7
Wake losses..............................................................................................................................................7
Grid losses ................................................................................................................................................7
Availability................................................................................................................................................7
Permitting procedures............................................................................................................................................8
Environmental permit ..............................................................................................................................8
Noise.........................................................................................................................................................8
Safety........................................................................................................................................................8
Building permit.........................................................................................................................................8
Grid connection ......................................................................................................................................................8
Feed-in contract......................................................................................................................................................9
Selection of suppliers..............................................................................................................................................9
Project financing...................................................................................................................................................10
Building phase .............................................................................................................................................. 11
Overview of building process ...............................................................................................................................11
Quality control during production and construction............................................................................................11
Commissioning and take-over ..............................................................................................................................12
Operation and maintenance......................................................................................................................... 13
Daily operation .....................................................................................................................................................13
Warrantees and insurance ...................................................................................................................................13
Maintenance and repairs......................................................................................................................................13
Annex – Examples of two cash flow calculations for a 10 MW wind farm..................................................... 15

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Page 1
SUMMARY
This Application Note presents a case study for the development of a small wind farm. It discusses each of the
four phases of a wind project in detail.
The initiation and feasibility phase section includes site selection criteria and a discussion of the methodology
for the assessment of the likely energy yield – a critically important factor in the investment decision. Often,
several sites will need to be investigated before making a selection.
During the pre-building phase the necessary planning and building permissions must be obtained and a
connection contract negotiated with the local network operator. The feed-in tariff – the money received for
the energy produced – must also be negotiated. Decisions made during these early stages determine the
return on investment of the farm.
Building and Operation and Maintenance follow with details of the steps to be taken to ensure rapid
commissioning and reliable operation. The note concludes with a financial analysis highlighting the importance
of an accurate energy yield assessment and adequate feed-in tariff.

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INTRODUCTION
Nowadays most of the European countries are well acquainted with the phenomenon wind energy. In the
eighties and nineties of last century mainly in Denmark and Germany the knowledge on wind energy was
concentrated including the manufacturing and siting of a large number of wind turbines. The last decade
Germany is still at the top in yearly installed wind power, however, Spain is following at close distance. The last
5 to 10 years a large number of European governments developed policies on promoting renewable energy
sources including wind energy. Prominent examples are United Kingdom, France, Italy, the Netherlands and
Eastern European countries where wind energy is already present or incentives are defined to boost the
increase of renewables.
During the last 20 to 25 years the implementation of wind energy has changed dramatically. In the eighties and
early nineties of last century was stand-alone application of wind turbines with installed power between 100
and 500 kW quite common while the development of wind farms was rare. Due to several developments,
ranging from local policies to economic considerations, currently most initiatives concern wind farm
developments. The number of wind turbines in a wind farm varies from a few to more than 25.
The average installed power per wind turbine today (November 2016) is around 2.5 and 3 MW, with blades of
about 50 metres length. The largest wind turbine today is 8 MW, although 15 MW turbines are planned and 20
MW turbines are considered to be theoretically possible.
Besides the development of onshore wind farms a tendency is noticeable to offshore siting of wind farms.
Characteristic of offshore wind energy is the high installed power per wind turbine and initial investment costs
which are almost doubled with respect to onshore siting. The additional expenses are caused by the high costs
for offshore foundations, sea cable and special sea vessels for transport and erection of the wind turbines. Also
the operational costs are at least the double compared to onshore siting. A main advantage of offshore is the
low nuisance to the environment and the excellent wind resources leading to a high degree of utilisation.
The cost of onshore wind energy ranges from 52 to 110 EUR/MWh mainly depending on the wind resource.
For most locations wind energy is not cost effective and incentives are a prerequisite to make a wind farm
profitable.
Figure 1a – Overview European Wind Atlas (no
data of the Balkans and Eastern Europe available).
Figure 1b – Photograph 10 MW wind farm on flat
land near the Atlantic coastline.

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The European Wind Atlas demonstrates that Scandinavia, UK, Ireland and the Atlantic coastline of the
European continent have the best wind conditions for the developing of wind energy.
The time span from first initiative to final commissioning of a wind farm is subdivided into a development
period and a building period. The duration of the building period is well known, for a small to medium size
wind farm (< 15 MW) ¾ to 1 year and for a large wind farm 1 to 2 year. The technical life span of a wind
turbine is 20 years.
The duration of the development period is less predictable. Mainly the time required for an irrevocable
building permit is hard to predict. Depending on the mandatory procedure and the number and kind of
objections put forward by concerned parties the required time span may vary from approximately ½ year to
more than 5 years.
The financing of a wind farm is a matter of a special concern. In the past a stand-alone wind turbine was part
of the capital properties of a company. In such a case the wind turbine financing is comparable with the
finance of other capital expenses.
Nowadays, for most wind farms a separate legal entity is established with limited equity capital and for the
greater part founded on loans. It is clear that under such conditions the financer(s) will demand for extra
financial guarantees.
Generally the development and operation of a wind farm can be subdivided into the following four phases:
 Initiation and feasibility (concluded by go/no-go)
 Prebuilding (concluded by go/no-go)
 Building
 Operation and maintenance
The following case has been selected for this note:
 A small wind farm with 10 MW installed power
 Built up from five wind turbines of 2 MW
 Hub height 80 meter
 Rotor diameter 80 meter, 3 bladed rotor
 Octangular foundation, gross dimensions 18x18 meter
 Nacelle weight 100 ton, tower weight almost 200 ton
 Life span 20 years
The four phases of development will be discussed separately in the next paragraphs of this note.

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WIND FARM INITIATION AND FEASIBILITY PHASE
Main subject during this phase is that one or more appropriate sites are selected for possible siting of a wind
farm. Main characteristics are investigated like number of turbines, installed power and hub height. The
feasibility study comprises an inventory and assessment of the main project risks like the presence of sufficient
wind resources, sufficient grid capacity and verification with the municipality zoning plan.
The phase is concluded with a go/no-go decision for the next process step.
SITE SELECTION AND WIND ASSESSMENT
In order to develop and construct an economical feasible wind farm an inevitable first step is to obtain one or
more appropriate areas of satisfactory dimensions. Already for a medium size wind farm, e.g. 5 wind turbines
of 2 MW, a substantial area is required. Depending on the rotor diameter the required mutual distance
between the wind turbines is 300 to 500 meter to limit losses. To limit losses, to limit nuisance and for safety
reasons, the distance to the nearest dwellings and company buildings is also at least 300 to 500 meter.
Next step, immediately following pre-selection of the area, is to assess the corresponding local long term wind
climate. Generally speaking, potential wind farm sites are preferably vacant areas at the flat land or on top of
hilly areas. In all cases the sites should be characterized with high and recurrent wind resources.
Purpose of the initial screening study is to identify and evaluate factors that may lead to a definitive cross out
of a pre-selected area.
In case the site screening does not identify any prohibitive limitations the feasibility study may proceed.
The financial feasibility is a prerequisite for the development of a wind energy project. The wind resource
assessment is of outstanding importance for the estimation of the yearly energy yield and determines for the
greater part the financial feasibility. The energy available in the wind is proportional with the wind speed to
the third power. Based on local wind speed data of meteo-stations can be determined a local wind atlas of the
planned wind farm. It is necessary to use minimal one year of wind data to avoid fluctuations in wind speed
during the seasons. The wind atlas is related to a roughness map of the area which is needed to determine the
wind speed at a specific site and height. The estimated wind distribution results in a yearly energy yield
representing the gross income of the wind farm.
The yearly energy yield is calculated by multiplying the wind turbine power curve with the wind distribution
function at site:
𝐸 𝑦𝑒𝑎𝑟𝑙𝑦 𝑦𝑖𝑒𝑙𝑑(𝑘𝑊ℎ) = 𝐸. 𝑓(𝑤𝑖). 𝑃(𝑤𝑖) 𝑤𝑖𝑡ℎ 𝑖 = 1, 𝑛
And with
f: wind distribution function (yearly hours per wind speed interval)
P: wind turbine power curve (power output as function of wind speed)
wi: wind speed at interval or “bin”i, common interval size is 0.5 to 1 m/s
i: number of wind intervals ”bins” between cut-in and cut-out wind speed; generally from 3 to
25 m/s
Figure 2a shows a power curve (PV) of a 2 MW wind turbine with optimal efficiency, i.e. without noise
reduction measures that usually lead to less energy generation. Figure 2b shows the most commonly used

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wind speed distribution based on the statistical Weibull function with shape factor 2 and average wind speed
of 7 m/s.
Based on the PV curve from figure 2a and Weibull wind speed distribution with shape factor 2.0 the gross
energy yield corresponding to 7 to 8.5 m/s is presented in table 1.
Figure 2a – Power curve of a 2 MW wind turbine (without noise reduction measures).
Figure 2b – Wind speed distribution, average wind speed 7.0 m/s and Weibull shape factor k= 2.0.

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Table 1 – Gross yearly energy yield of 10 MW wind farm as function of average wind speed.
Average wind speed 7.0 m/s 7.5 m/s 8.0 m/s 8.5 m/s
Weibull shape factor k=2
Wind Farm Power (MW) 10 10 10 10
Gross Annual Energy Yield (MWh) 27,000 31,000 34,000 37,000
Equivalent full load hours 2,700 3,100 3,400 3,700
Yearly gross energy yield of the 10 MW wind farm:
 7.0 m/s average wind speed at hub height
 Wind speed according Weibull distribution function, shape factor 2.0
 No noise reduction measures required
 Gross energy yield 27,000 MWh
 Equivalent with 2,700 full load hours (utilization 0.31)
TECHNICAL FEASIBILITY
Modern wind turbines are available in the power range from 0.75 to more than 3 MW having rotor diameters
varying from 55 to more than 100 meter. The vast majority of the turbines sold in the world market have three
blades, although two-bladed concepts also exist. Generally, the hub height varies from 0.9 to 1.25 times the
rotor diameter. Most manufacturers offer wind turbines with two or three different rotor diameters
corresponding to low (large rotor), medium (standard rotor) and high or offshore (small rotor) wind climate.
At a first screening the outer dimensions of the available terrain are of importance. Wind turbines require a
mutual spacing of at least four to five rotor diameters, corresponding with approximately 300 to 400 meter, as
already mentioned above. A flat and undisturbed area is to be preferred. Buildings, trees and other obstacles
lead to a lowering of the wind speed.
Next to the terrain orography it is well-advised to examine the local grid properties at an early phase. Main
question is the distance to the nearest medium or high voltage substation with sufficient feed in capacity. It is
advised to make already during the feasibility phase an appointment with the local grid operator to discuss
grid connection including corresponding cost and planning.
MAIN RISK ASSESSMENT
In most countries it is prohibited that wind turbine rotors rotate above roads, railway tracks and water ways. A
minimum distance has to be observed from wind turbines to public infrastructure. In northern countries and
countries with continental climate specific attention has to be paid to probable icing problems. Ice developed
on rotating rotor blades can be thrown far from the turbine and harm persons or result in material damage.

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Local authorities and concerned parties may demand for an additional risk analyses in case in the vicinity of
the planned wind farm at least one of the following items count:
 Transport, storage or processing of hazardous goods
 Pipelines for transport of hazardous goods (also underground)
 Dwellings, company or public buildings
 Roads, railway tracks and water ways
 Medium and high voltage conductor
 Danger of icing
PERMITTING REQUIREMENTS OF LOCAL AUTHORITIES
The wind farm site has to meet national, regional and local requirements. In most countries special legislation
is formulated for the environmental planning and the building aspects.
During the wind farm planning phase it is necessary to meet special zoning plan requirements. For instance it
may be decided that a specific zoning plan prohibit wind turbines or have laid down maximum heights for
buildings. Under such conditions it has to be discussed with the local authorities what could be possible ways
and procedures to adopt the zoning plan to make the installation of a wind farm feasible.
In most European countries wind turbines have to be certified according to national or international safety
standards especially developed for wind turbines. Manufacturers have to demonstrate approved certification
by a valid “type-certificate”.
Planned area for the 10 MW wind farm:
 Check municipality zoning plan on competing activities and maximum building height;
 Mutual distance wind turbines 400 meter
 Wind turbines in line, required length 1.600 meter
 Preferable within 300 to 500 meter from the wind turbines no dwellings and other buildings and
further as less obstacles as possible
 Authorities or parties concerned may request a risk analyses if within 400 to 500 meter from the wind
turbines other activities take place
PROJECT FINANCING
In the following tables, the investment and operational cost of a wind farm of 10 MW is shown as an example.
Wind turbines investment and operational costs are fully proportional with the installed capacity. Investment
costs per MW installed are about 1.25 M€ and yearly operating cost somewhat more than 40 k€ per MW.
For a 10 MW wind farm, five wind turbines of 2 MW, the investment and refurbishment costs are estimated as
follows:

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Non-recurring investment costs
- price level 2006 -
Costs per wind turbine
[K€]
Wind farm costs
[K€]
Preparatory costs 100 500
5 wind turbines of 2 MW each 2.000 10.000
Wind farm civil and electrical
infrastructure
200 1.000
Grid connection 200 1.000
TOTAL INVESTMENT (year 1) 2.500 12.500
Refurbishment (at year 10)
250 1.250
TOTAL 2.750 13.750
Yearly recurring operating and maintenance costs:
Yearly recurring operating costs
Costs per wind turbine
[K€]
Wind farm costs
[K€]
Wind turbine service, maintenance and
insurance
50 250
Local taxes and contribution grid
connection
10 50
Land lease 15 75
Daily management 5 25
Own electrity consumption 5 25
TOTAL 85 425
Investment and operational costs 10 MW wind farm:
 Initial investment costs M€ 12.5 or 1.25 M€/MW
 Yearly operational costs M€ 0.425 or 42.5 k€/MW
 Estimated refurbishment costs halfway the life span M€ 1.25; i.e. 10% of the initial investment
In most cases the wind farm is financed by a mix of own capital (equity) and bank loan. The amount of equity is
mostly limited to 20 to 40% of total investment. It may be interesting for companies, investment groups and
private person to invest in wind energy for possible tax reduction benefits. A number of national governments
in Europe have incentives to promote electricity production by renewable sources. A well-known incentive is
tax reduction for investments in “green” energy sources.

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PRE-BUILDING PHASE
During this phase all preparatory work is done needed to start the building phase. The wind farm developer
has to apply for all necessary permits. A concept for selling the wind energy that will be produced has to be
worked out, for instance through a power purchase agreement (PPA). The contractors for delivery of the wind
turbines and corresponding civil and electrical infrastructure have to be selected. And last but not least, the
project financing has to be arranged.
WIND FARM DESIGN INCLUDING ENERGY YIELD PREDICTIONS
Based on the wind resource assessment the most promising wind farm locations are studied in more detail.
The computer models WasP, Wind farmer and WindPRO are some of the most well-known models to calculate
the energy yield of planned wind farms.
Not only wind speed and wind direction distribution are taken into account but also the terrain orography; for
instance a steep slope in the terrain will cause higher winds at the hill top. Such details in the modeling make
that wind turbines are optimal sited by assuring optimal exposure to the wind. Generally the lay-out is
optimized for exposure from the prevailing wind direction.
The mutual distance between the wind turbines has to meet the requirements of the manufacturers. When
siting the wind turbines too close this may result in a lowering of the electricity production. Another, more
serious, consequence may be the damaging of primary structural parts caused by the wake of upwind sited
wind turbines. The minimum distance depends on the siting with regard to the prevailing wind direction.
When siting perpendicular to the prevailing wind direction the distance has to be at least four and otherwise
minimal five times the rotor diameter.
The gross energy yield of the wind farm is dominated by the local wind distribution and the siting of the wind
turbines. To calculate the net energy yield it is needed to determine the anticipated losses. The gross annual
energy yield has to be adjusted for:
 Wake losses
 Grid losses
 Availability
WAKE LOSSES
The wind speed downstream the rotor, the so-called wake, of the turbine is lower compared to the
undisturbed wind speed resulting in a somewhat reduced performance of downstream sited wind turbines.
The wake is characterized by extra turbulence which may lead to premature damage of main structural
components.
It is common practice to estimate the wind farm wake losses in the range of 3 to 4% of the gross energy yield.
GRID LOSSES
Grid losses are defined as the electrical losses between wind turbine switchgear and public grid connection, i.e.
the location of the accountable metering. Depending on the lay-out the electrical losses are in the range of 2
to 3% of the gross energy yield.
AVAILABILITY
The availability of a wind turbine is defined as the time the wind turbine is in operation or ready for operation
with external conditional, for instance too low wind or grid loss, preventing the system from energy
generation.

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The technical availability of the turbine is 97% or higher. This figure is based on data of modern operational
wind farms.
Yearly net energy yield of the 10 MW wind farm:
 Gross energy yield 27,000 MWh
 3% wake losses
 3% grid losses
 97% availability
 Nett energy yields 24,500 MWh
PERMITTING PROCEDURES
ENVIRONMENTAL PERMIT
The wind farm must comply with all regulations pertaining to environmental permitting. For the environmental
permit a site plan and various environmental studies, amongst others on plant and animal life, are necessary.
NOISE
The noise impact of the wind turbines on the environment is one of the major permitting issues. Wind
turbines produce noise, mostly caused by the rotor blades and drive train. The distance to nearby located
dwellings has to be sufficient to assure that the noise level at the house front is below the statutory norm.
Next to a noise assessment and visual impact study, most of the authorities demand safety and risk
assessment studies and shadow casting examinations. Shadow flickering is caused by sunlight reflecting on
non-rotating blades or tower. Shadow casting is due to periodically – about once per second – interrupting the
sunlight by the rotating blades. Both flickering and shadow casting on dwellings and offices can be very
annoying for people in there. Shadow casting is not regulated by law.
SAFETY
It is not allowed for wind turbines to rotate above roads or railway-tracks. In case icing on the rotor blades and
nacelle may cause danger for persons and material in the near environment, protective measures have to be
taken. A well-known measure is rotor standstill during icing up and release for starting up after visual
observation all ice has disappeared.
BUILDING PERMIT
Besides an environmental permit also a building permit is necessary for the wind farm. As part of the
application most authorities require information on the visual impact of the wind farm on the environment.
Visualizations of the planned wind farm in the existing environment serve as input for this assessment.
Another part of the application is a detailed description of the wind turbines including foundation, exact
locations of the wind turbines in the terrain, overview of the civil and electrical infrastructure and a copy of the
valid type-certificate.
GRID CONNECTION
Usually not each individual wind turbine is connected to the public grid separately.
For the wind farm an internal grid is designed and installed. The voltage of the internal grid is preferred at
medium voltage level, between 10 to 20 kV, in order to limit the losses. In most cases the wind turbines are

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electrically connected in a loop to ensure redundancy. The wind turbine generators operate mostly below
1000 V and each wind turbine is equipped with a transformer to transform the power from low to medium
voltage level. The wind turbine transformer is located in the nacelle or tower base or in special housing next to
the tower.
It depends on the public grid voltage if a central wind farm transformer is required to transform the medium
voltage to grid voltage or only a switchgear installation including accountable metering provisions.
In some occasions no public grid to the wind farm is available or the existing grid has insufficient capacity. If
the grid has to be extended or reinforced for the wind farm only the costs have to be born fully by the wind
farm developer.
FEED-IN CONTRACT
In all cases a power purchase agreement (PPA) or feed in contract is necessary. The feed in tariff is composed
from a contribution for producing and delivery of electricity and in most cases increased with an extra
allowance for generating renewable energy or corresponding carbon credits. Depending at one hand on the
wind resources and on the other hand on the investment and operational cost a feed in tariff of at least 60
EUR/MWh is required and for an economical viable project a tariff of 80 to 90 EUR/MWh is needed.
SELECTION OF SUPPLIERS
Based on the scope of supply and own working procedures the wind farm developer has to decide for a public
tendering procedure or to decide to send only a pre-selected number of wind turbine suppliers a request for
tendering. All necessarily information for the tendering has to be included in the “tendering enquiry
documentation” also abbreviated to TED.
The TED has to include at least the following bid information:
 Sufficient information on the project including permitting status and project time planning
 Requested information from bidders, e.g. financial, technical and operational information
 Time schedule, a.o. tender closure date and assigned period for additional information, questions to
ask and site visit
 Contractual issues
 Scope of supply
 Technical specifications
 Maintenance and repair conditions
 Insurance and warrantee agreements
With regard to the scope of supply it may be decided that the contractor delivers a turnkey wind farm
including wind turbines, foundations, access roads, wind farm grid and connection to the public grid. Another
option is to subdivide the delivery in a number of sub-deliveries with different contractors, for instance to
separate wind turbine delivery and installation from the civil and electrical works. The latter may have cost
advantages, however the project developer shall act as main contractor and is responsible for the wind farm
entirely. Turnkey delivery by one main contractor is mostly the well-advised option.
It shall be noted that the offered wind turbine is certified by a recognized body and possesses a type-
certificate valid for the local wind climate and wind farm lay-out. In order to avoid any problems on
warrantees the contractor has to state formally that the delivered wind turbines are “fit for purpose” for the
site.

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PROJECT FINANCING
As said before, for most sites in Europe wind energy is not yet cost effective. To promote wind energy
incentives are essential, the most applied promotion measures are:
 Subsidies (governmental or local) on investments in renewable energy sources
 Tax benefits for investing in renewable energy sources
 Reduced interest tariffs on loans for renewables
 Subsidies on the production of renewable energy (increased feed in tariff)
In case the financing is based for the greater part on loans the financers may ask for additional securities to
guarantee that the loan can be repaid. The following securities can be asked for:
 Power purchase agreement with settled minimum feed in tariff for the loan period
 Guarantee that in years with moderate wind supply the income is sufficient for interest and re-
payment
 Warrantees on supplied components and wind farm performance (availability and power curve) for
the loan period
 Machine breakdown and business interrupt insurance.
 Service and maintenance contract
In annex A cash flow calculations with two different feed in tariffs are carried out for the 10 MW. In the
calculations the financing costs are not taken into account. All expenses and incomes are based on price level
2006 so the influence of inflation is implicitly included in case expenses and income increases yearly with equal
ratio.
Cash flow calculations for the 10 MW wind farm based on 20 year life span and price level 2006:
Feed in tariff 60 €/MWh 85 €/MWh
Gross income 1.47 M€/yr 2.08 M€/yr
Recovery period > 15 year > 9 year
Net present value over 20 year (NPV) 6.1 M€ 17.7 M€
Internal rate of return (IRR) 4% 11%
The calculations show that a feed in tariff of 60 €/MWh is needed to pay all costs without generating profit.
Presuming the project is fully financed by a bank loan the project generates just sufficient cash to pay yearly
interest (4%) and repay the loan and yearly operating costs. At a tariff of 85 €/MWh the project generates
value for the owner (7%) in case the yearly financing costs ask again 4%.

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BUILDING PHASE
The building phase includes all activities from commencement of the works up to take over of the operational
wind farm.
OVERVIEW OF BUILDING PROCESS
Following selection of the contractors and financial close of the project the manufacturing and building
process commences.
For the required exceptional transport the contractor has to verify the accessibility of supply routes towards
site. Also adjacent to each wind turbine location sufficient space has to available for storage of the main
components, assembly of the rotor and placing of the building crane. An area of approximately 50x80 square
meter suits most applications. A 2 MW wind turbine requires at least a 600 tons caterpillar crane for hoisting
of the tower parts, nacelle and rotor.
Manufacturing and assembly of the main components takes fully place in the factories of the wind turbine
supplier.
The following assembled main components are shipped to site:
 Foundation anchor or tube
 Three or four tubular tower parts
 Ground controller and switchgear
 Wind farm SCADA system
 Transformer (in case of ground based)
 Fully assembled nacelle (including gearbox, generator, yaw mechanism, mechanical break, converter
and if applicable the transformer))
 Hub and rotor blades
For a small and medium size wind farm the time between purchase order and transport ready is 6 to 9 months.
Meanwhile the wind farm civil, including access roads, wind turbine foundations and substation, and electrical
infrastructure is built. The time required for rotor assembly and constructing of the main structure takes two
to three working days per wind turbine. Subsequently it takes 7 to 10 working days to finish the installation
works and connecting to the grid.
From the time all material is at site, the building of a small or medium size wind farm takes only 2 to 3 months.
QUALITY CONTROL DURING PRODUCTION AND CONSTRUCTION
It is common use that the contractor assigns a number of so-called “hold and witness” points for the client.
These hold and witness moments are meant for the wind farm owner to audit the progress and quality of work
including the verification that the components are in conformity with the specifications. Hold and witness
moments are mostly planned immediately following a project milestone, for instance a main component ready
for transport to site. Mostly hold and witness moments are link with instalments.
The following hold and witness points are commonly used:
 Start of component production including audit of contractors quality system
 Factory acceptance test (FAT) of components ready for shipment
 Site acceptance test (SAT) of components delivered at site
 Several inspections during building at site, connected to milestones

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COMMISSIONING AND TAKE-OVER
Following completion of the building and installation period and before take-over of the wind farm an overall
inspection and commissioning of the works is carried out. Commissioning inspections are performed by
representatives of contractor and coming owner. The commissioning may comprehend an elaborate testing
and measuring plan but is mainly meant to verify proper installation and functioning of the installations. Also is
verified that the delivery is complete without the omission of more or less important details. Normally in
cooperation between the parties involved a check-list is formulated for the commissioning procedure.
It is quite common that the first commissioning inspection results in a “punch list” with residual items. It
depends on the gravity of the questions and further items on the “punch-list” if formal take-over may take
place immediately after the first commissioning inspection or has to be delayed to approve second
commissioning.
Approved commissioning and take-over is related to last project payments.

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OPERATION AND MAINTENANCE
Starting from date of take-over the owner is responsible for daily operation of the wind farm. Also from that
date warrantee and maintenance contracts become valid. The technical and economic life span of a wind farm
is anticipated as 20 years.
DAILY OPERATION
Wind turbines are designed to operate unmanned. For normal operation no operator has to be available at
site. It is common practice that medium and large size wind farms are equipped with a wind farm control and
monitoring system (SCADA). By means of modem or internet remote access to the SCADA system is available.
The SCADA system provides reports on energy yield, availability and failure statistics. Main function of the
daily operator is to verify regularly that the wind farm is in optimal condition and performing according
expectation. Also the operator is responsible that maintenance and repairs are carried out accordance to
contract and within reasonable time.
WARRANTEES AND INSURANCE
The following warrantees are common for the first five years following take-over:
 On delivered goods, including repairs and modifications
 Availability of individual wind turbines and wind farm, values of 95% or higher are not uncommon
 Warrantee on performance, for the exact wind supply is not to be predicted for a given year the
warrantee is given on the power curve. Warrantees of 95% of the certified PV-curve of the wind
turbine are common.
In case the availability or performance is below the warranted value, the difference between the actual and
warrantee values has to be settled by the supplier. Some suppliers offer warrantees up to 8 to 12 years or at
least for a period comparable to the financing period.
Insurances are required for:
 Third party liability
 Machine breakdown (e.g. material flaws, lightning strokes, fire, vandalism, fault by maintenance
engineer and/or operator, etc.)
 Business interrupt (compensation for non-production days following a machine breakdown event)
MAINTENANCE AND REPAIRS
Modern wind turbines require twice a year a preventive maintenance service. For a wind turbine in the MW-
segment a planned preventive maintenance overhaul requires 2 to 3 working days for two engineers. The work
comprehends amongst others inspection and testing of the control and safety devices, repair of small defects,
replacement or filling up of consumables like bearing grease and gearbox lubrication. The gearbox is the most
vulnerable component and therefore subject of special interest during maintenance. At regular intervals oil
samples are taken and investigated on pollution, filters are replaced and gearings are inspected on damages.
The number of repairs differs largely between individual wind turbines and wind farms. The average yearly
number of corrective actions per wind turbine is 3 to 4. Only those corrective actions are counted that need a
visit on site of a service engineer. The mean down time per failure is 2 to 4 days. The cause of failure is equally
divided between mechanical and electrical problems.

Page 14
Although not formally admitted by the manufacturers it is common practice that after 10 to 12 years of
operation wind turbines need a major overhaul. The overhaul comprehends cleaning and repair work of the
rotor blades and refurbishment of the drive train, i.e. replacement of bearings and if necessary replacement of
gearbox parts.

Page 15
ANNEX – EXAMPLES OF TWO CASH FLOW CALCULATIONS FOR A 10 MW WIND
FARM
Summary of data scenario 1: wind farm of 10 MW
No financing costs included!
Price level 2006
Investment costs (year 1)
Refurbishment costs (year 10)
kWh feed in tariff
Yearly wind farm production in kWh
Gross income from energy production
Yearly recurring costs
Recovering period
Net Present Value (price level 2006, 20 year)
Internal Rate of Return
Low feed in tariff
€ 12.500.000
€ 1.250.000
€ 0,060
24.500.000
€ 1.470.000
€ 425.000
15 year
€ 6.100.000
4 %

Page 16
Summary of data scenario 1: wind farm of 10 MW
No financing costs included!
Price level 2006
Investment costs (year 1)
Refurbishment costs (year 10)
kWh feed in tariff
Yearly wind farm production in kWh
Gross income from energy production
Yearly recurring costs
Recovering period
Net Present Value (price level 2006, 20 jaar)
Internal Rate of Return
normal feed in tariff
€ 12.500.000
€ 1.250.000
€ 0,085
24.500.000
€ 2.082.500
€ 425.000
9 year
€ 17.750.000
11 %

Wind farm development and operation - A case study

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Wind farm development and operation - A case study