Gasch R., Twele J. (Eds.) Wind Power Plants: Fundamentals, Design, Construction and Operation

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492 15.1 Wind farm project planning

In the second half of the 1990s such a significant cost reduction was not achieved

any more despite the increasing annual installation of wind turbines.. This was

partly due to the strong market demand for larger wind turbines (cf. Fig. 1-1),

which could only be satisfied by time reduction of the entire design process mean-

ing less time for optimisation. Overall, the turbine costs fell by approx. 50% from

1990 to 2005.

Foundation

5.0%

Überagbesattion

4.1%

Grid connection (1,000 m)

4.1%

Access lane (400 m)

1.6%

Planning and

construction survey

2.1%

Administration /

legal and tax

advise

3.0%

Miscellaneous

3.0%

Wind turbine incl. transport

and erection

77.1%

Transformer substation

Foundation

5.0%

Überagbesattion

4.1%

Grid connection (1,000 m)

4.1%

Access lane (400 m)

1.6%

Planning and

construction survey

2.1%

Administration /

legal and tax

advise

3.0%

Miscellaneous

3.0%

Wind turbine incl. transport

and erection

77.1%

Transformer substation

Fig. 15-8 Typical investment cost structure for a project with a single wind turbine in Germany

(onshore)

200

400

600

800

1000

1200

1400

1600

0 250 500 750 1000 1250 150

Rated power in kW

Specific costs of wind turbine in

EUR/kW

1995

1997

2000

Potenziell (1995)

Potenziell (1997)

Potenziell (2000)

trend line

200

400

600

800

1000

1200

1400

1600

0 250 500 750 1000 1250 150

Rated power in kW

Specific costs of wind turbine in

EUR/kW

1995

1997

2000

Potenziell (1995)

Potenziell (1997)

Potenziell (2000)

trend line

Fig. 15-9 Specific investment costs (turbine, transport and erection, see Fig. 15-8) versus rated

power of wind turbines installed in Germany [3]

The cost structure of the production costs varies slightly depending on the wind

turbine concept (stall or pitch control) and the wind turbine size. Table 15.3 shows

the typical cost distribution. In general, the following tendencies can be stated:

- With growing wind turbine size the portion of the costs of the rotor

increases.

15 Planning, operation and economics of wind farm projects 493

- For variable-speed wind turbines with pitch control the portion of the

costs of generator and control increase.

In addition to the production costs, the total wind turbine investment costs include

share the design and development costs, the profit and further costs attributable to

warranty, transport and erection.

The other portions of the total investment costs mentioned in Fig. 15-8 are influ-

enced to a large extent by local site conditions such as the wind farm project size

(single wind turbine or wind farm), the type of soil and the distance to the grid-

connection point. Therefore, when comparing economically efficient wind farm

projects of the same size there will always a spreading of the actual project costs

be observed.

The grid connection costs are often the second-biggest investment cost factor,

Fig. 15-8. These vary strongly according to local conditions, i.e. the distance to the

next grid-connection point, and the requirements of the local grid operator as well.

The German Renewable Energy Sources Act (EEG) provides an unambiguous

definition as to whom the costs are to be allocated. Basically, the grid connection

costs are borne by the wind farm operator.

However, if the local grid is too weak for the planned wind farm capacity the

grid reinforcement costs have to be borne by the grid operator who is legally

obliged to permit wind power feeding. Therefore, the grid reinforcement costs do

not form part of the investment cost estimation.

Table 15.3 Cost structure of wind turbine components and assembly , typical values according

to [4, 5]

Rated power 600 kW 1,200 kW Typical span

Component € Share

in %

€ Share

in %

of cost share

in %

Gearbox and coupling 80,400 21.8 115,000 18.1 10 to 25

Rotor blades 63,800 17.3 150,000 23.6 15 to 25

Tower (incl. coating) 58,000 15.7 150,000 23.6 12 to 25

Generator and control 43,800 11.9 65,000 10.2 10 to 20

Nacelle frame and

yaw bearing

31,600 8.6 35,000 5.5 5 to 10

Hub and main shaft 29,000 7.9 40,000 6.3 5 to 10

Housing 16,600 4.5 18,000 2.8 2 to 5

Cables and sensors 13,400 3.6 18,000 2.8 2 to 5

Hydraulics 11,600 3.1 15,000 2.4 2 to 5

Yaw system 8,700 2.4 10,000 1.6 1 to 3

Assembly 11.600 3.1 20,000 3.2 2 to 5

Total 368,500 100.0 636,000 100.0

614 €/W 530 €/kW

Remark: The total wind turbine investment costs include additionally R&D

costs, risk, profit, warranty, transport and erection

494 15.1 Wind farm project planning

For the purpose of estimating the costs of the foundation, typical values for the

specific costs (per kW installed capacity) are available. For a flat foundation they

vary between approx. 70 and 100 €/kW depending on the hub height of the wind

turbine. If the geotechnical investigation report for the site reveals that the bearing

capacity of the ground is not strong enough, additional measures are required (e.g.

a piled foundation) which increase the costs significantly compared to those of a

standard flat foundation.

The costs incurred by the access lanes and roads again vary strongly depending

on the local site conditions and the optimum wind farm layout. The bearing capac-

ity of the access lanes, and therefore the specific costs in € per metre, are deter-

mined primarily by the transport weight of the cranes. They also depend on the

wind turbine size.

It must be differentiated between the access requirements which exist during

erection and those emerging from wind farm operation. Nevertheless, access for

cranes should be ensured in case larger repairs need to be carried out at a later

stage.

The costs for planning, permission and indemnification measures and so-called

„soft costs“ for the foundation and organisation of the operating company, as well

as the financing costs, are in the order of 3 and 6% of the total investment costs for

wind farm projects in Germany.

The first measure used to compare different wind farm projects is the power-

specific investment costs index

SIK

= Total investment costs / installed capacity in €/kW. (15.2)

However, this index does not provide any information on the yield potential of the

site, i.e. the annual energy yield or production. Therefore, the second measure

yield-specific investment costs index:

SIK

= Total investment costs / annual energy yield in €/kWh

(15.3)

In Germany, typical values of the power-specific investment costs index are

around SIK

= 1,100 €/kW, and for the yield-specific investment costs index in

the range of SIK

= 0,50...0,75 €/kWh

[6].

The type of financing plan is of particular importance when assessing the eco-

nomic efficiency of a wind farm project. A typical example of a financing plan for

a wind turbine with a rated power of 1.5 MW is given in table 15.4.

The required share of equity is set by the financing bank which also submits an

application to the KfW Bankengruppe (Kreditanstalt für Wiederaufbau) and

Deutsche Ausgleichsbank (DtA, merged with KfW in 2003) for the loan with re-

duced interest under the umbrella of its ERP environmental and energy efficiency

programme. The share of equity varies slightly depending on the site quality and

the financial standing of the investor. A higher share may be fixed if there is a

15 Planning, operation and economics of wind farm projects 495

higher financial risk due to a lower site quality or reduced financial standing of the

investor.

Table 15.4 Example of a financing plan for a wind farm project: wind turbine of 1.5MW rated

power, conditions in July 2000

Financing Condition Value Amount in

1000 €

Share in %

Equity 523 30

ERP loan by

KfW bank

Interest rate in %

Period in years

Cap in %

Years without re-

demption

5.25

872 50

Loan by

DtA bank

Interest rate in %

Period in years

Cap in %

Payout in %

Years without re-

demption

4.25

349 20

Total 1,744 100

In order to calculate the balance of annual proceeds and expenditures, the expected

proceeds from the electricity production are calculated using the predicted energy

yield and the feed-in tariff stated in the German Renewable Energy Sources Act

(German abbreviation: EEG). It is reasonable for safety reasons to assume a re-

duction in the expected proceeds by 10 to 15%. This should cover on one hand the

uncertainty of the the wind regime prognosis for the site and on the other hand the

statistical fluctuations of the annual wind regimes (cf. chapter 4, Fig. 4-17).

Apart from the return of capital on the basis of the financing conditions, the

annual operating costs must also be estimated. The typical cost structure is shown

in Fig. 15-10. In addition, some German Federal States require to include the ac-

crues for the decommission already in the application for building approval.

Careful attention should be paid to the portion of maintenance, repair and re-

placement costs. The annual costs, stated in empirical studies [2, 6], are in the

range of 2.5% of the wind turbine investment costs per year for the first decade of

wind turbine operation, and approx. 4.0% for the second decade of operation . The

higher costs in the second decade result from the replacement of worn compo-

nents, Fig. 15-11. An increasing number of wind turbine manufacturers are offer-

ing full-service contracts (including a guaranteed availability). These contracts in-

volve on the one hand increased running costs, on the other hand, they reduce the

exposure of the operator to technical risks. This is taken into account by some in-

surance companies through an reduced insurance contribution [3].

According to an evaluation of the German scientific measuring and evaluation

programme WMEP [7], the power-specific value of the total annual operating

496 15.1 Wind farm project planning

costs amounts to approx. 35€/kW for wind turbines of a rated power below 500

kW, and to approx. 15€/kW for wind turbines of the MW class.

Miscellaneous

17%

Management

and taxes

21%

Lease of

land

18%

Maintenance & repair

26%

Electricity

consumption

Insurance

13%

Miscellaneous

17%

Management

and taxes

21%

Lease of

land

18%

Maintenance & repair

26%

Electricity

consumption

Insurance

13%

Fig. 15-10 Typical cost structure of the operating cost for a wind farm project in Germany; on-

shore and without capital service [2]

100

120

140

160

180

02468101214161820

Number of years between significant investments in maintenance or replacement

Maintenance and/or replacement costs in €/kW

Rotor blade

Gearbox

Generator

Shafts

Main bearing

Transformer

station

Tower

Foundation

Today’s period of experience

Critical components

Investments in replacement approx. 54%

of WEC investment costs (20 years period)

Uncritical components

Yawing system

Control and

electronics

Source: DEWI 2002

Pitch system

Brakes

Hydraulic system

100

120

140

160

180

02468101214161820

Number of years between significant investments in maintenance or replacement

Maintenance and/or replacement costs in €/kW

Rotor blade

Gearbox

Generator

Shafts

Main bearing

Transformer

station

Tower

Foundation

Today’s period of experience

Critical components Critical components

Investments in replacement approx. 54%

of WEC investment costs (20 years period)

Uncritical componentsUncritical components

Yawing system

Control and

electronics

Source: DEWI 2002

Pitch system

Brakes

Hydraulic system

Fig. 15-11 Estimated maintenance, repair and replacement costs according to [2]

Table 15.5 provides an example of a rough calculation of a wind farm project with

one 1.5 MW wind turbine erected in 2000 in the newly-formed Federal states at a

site with an average annual wind speed of 6.4 m/s at hub height,. The imputed an-

nual net income is given for capital costs calculated according to the annuity

method for the first decade of operation and without considering taxes.

Only if the estimated economic efficiency satisfies the investor, the planned

wind farm project will be continued and the next project phase, the implemen-

tation including erection and commissioning will be carried out.

15 Planning, operation and economics of wind farm projects 497

Table 15.5 Exemplary calculation of a wind farm project with one 1.5 MW wind turbine at a si-

te with an average annual wind speed of 6.4 m/s at hub height, erected in 2000 in the newly-

formed German Federal states

Investment costs Value Unit Share or comment

Wind turbine (incl. Crane and erection) 1,432,000 € 82.1%

Foundation 51,000 € 2.9%

Access lanes (400 m) 15,000 € 0.9%

Substation 77,000 € 4.4%

Grid connection (1000 m) 77,000 € 4.4%

Planning / Site supervision 31,000 €

1.8%

Site (land lease) 0 € 0.0%

Miscellaneous 31,000 € 1.8%

Business / tax and legal consultancy 31,000 € 1.8%

1,744,000 € 100.0%

Financing

(see table 15.4)

Annual proceeds

Wind speed at hub height 6.37 m / s

Calculated annual electricity production 3,074 MWh / a

Availability of wind turbine 98%

Effective annual electricity production 3,013 MWh / a

Reference yield (EEG-quality of site: 91.6% ) 3,288 MWh / a

Feed-in tariff (for 18 years until ’09 2018) 0.091 € / kWh

Feed-in tariff (for remaining 2 years 0.062 € / kWh

Feed-in tariff (average for 20 years) 0.088 € / kWh

Annual feeding-in proceeds (average) 265,400 € / a

Annual expenses

Capital costs (annuity) 158,000 € / a 63,8%

O&M costs 7,700 € / a 3,1%

Insurance (machine, 0.6% wind turbine cost) 9,200 € / a 3,7%

Insurance (BMU, 0.9% of annual yield) 2,600 € / a 1,0%

Power consumption / telecommunication 1,500 € / a 0,6%

Land lease 7,700 € / a 3,1%

Administration (1.0% of invest. costs) 17,400 € / a 7,0%

Reserve / repair (2.0% of invest. costs) 34,800 € / a 14,0%

Miscellaneous (0.5% of invest. costs) 8,700 € / a 3,5%

247,500 € / a 100,0%

Imputed annual net income

Annual feeding-in proceeds (average) 265,400 € / a

Annual expenses (calculatory) 247,500 € / a

Surplus 17,900 € / a

498 15.2 Erection and operation of wind turbines

15.2 Erection and operation of wind turbines

The flow chart of a wind farm project, cf. Fig. 15-1, illustrates that we are now in

the phase of realisation. All steps in the planning procedure are accomplished; all

authorisations, at least preliminary ones, have been obtained. The erection starts

with the construction of access lanes and the laying of cables. The foundation is

then built. In accordance with the purchase contract, the wind turbine manufac-

turer will transport the wind turbine components to the construction site and erect

the wind turbine. The final completing works in and around the wind turbine are

followed by the commissioning procedure and testing phase. The wind turbine

will then commence its permanent operation. The first two years of operation are

usually the defect liability period in which the wind turbine is maintained and re-

paired by the manufacturer at his own expense.

It is only after this that the wind turbine is handed over to the operator who will

assume full responsibility for it.

At the end of the time of operation designated in the building approval, the wind

turbine has to be decommissioned, unless the operator applies on time for an ex-

tension of the building approval since he can give evidence of remaining useful

life due to weaker wind conditions on site than assumed in the course of the wind

turbine design. In 2009, GL Wind issued a guideline with general hints on how to

verify whether a used wind turbine has still some potential (remaining useful life)

for a continued operation beyond the 20 years of planned operating time [14].

An alternative, so-called “repowering”, is the anticipated replacement of the wind

turbine by a newer type of turbine with a higher rated power and correspondingly

increased yield.

The technical aspects of a wind farm project are closely interwoven with its

legal and economic aspects. Investors provided the equity, and the total funding

was negotiated with the bank. The invested capital and the monetary return flows

are organised in the operating company. Both, the energy production of the wind

farm and the preservation of the wind turbine’s value are important issues taken

into consideration by banks and insurances companies when carrying out a risk

assessment. Therefore, the main goal of wind farm operation is safe and reliable

operation producing maximised energy yield and minimised loss in value.

15.2.1 Technical aspects of erection and operation of wind

turbines

The type of wind turbines and their optimal arrangement in the wind farm (micro-

siting) were already determined in the planning phase (cf. Fig. 15-2). This also

provides requirements for the construction planning. The work of the technical

wind farm operator begins already in the course of the preparatory construction

15 Planning, operation and economics of wind farm projects 499

works on the site and the erection of the wind turbines. Later, he will be responsi-

ble for any technical issues of wind farm operation. The following four steps are

implemented during the phase of realisation and operation:

x Transport and erection,

x Commissioning and take-over

x Wind turbine operation

x Decommissioning or Repowering

Transport and erection of the wind turbine

In Germany, the typical duration of the wind farm erection phase is between three

and six months. All services stipulated in the course of construction planning are

now carried out.

Remote areas of the world pose far greater challenges for transport and erec-

tion. For these projects, e.g., the size of available cranes or the capacity or steep-

ness of the roads may be the limiting factor. Substantial consideration must be

given to this during already the technical and financial planning phase.

When the road and foundation works are finished and the areas for the cranes

have been well prepared, the wind turbine components may be delivered. A big

challenge for manufacturer and shipper is the timely delivery of the huge compo-

nents. Transportation is usually carried out on the road by long vehicles and heavy

trucks. Usually, tower sections, nacelle and rotor blades are delivered one after the

other because they often come from different factories and suppliers and because

for assembly they are needed in a certain order. More than ten flat-bed trailers,

classified as as heavy transport, may be required, not counting the ones for trans-

port of the crane. In Germany, they are only permitted to drive at night. When the

route is planned, all the radii of curves, the overhead heights below bridges and

other bottlenecks (e.g. inclinations) are checked to ensure the trailers can pass.

The designers try to reduce the weight of the tower segments, in particular for

the lowest tower segment. This has the biggest diameter and the largest wall thick-

ness. Moreover, the tower segment length should not exceed 22 m in order to al-

low the truck to be well manoeuvred and to avoid having to obtain special ship-

ping permits with further requirements for escort vehicles and closing off the

roads.

For the transport of the rotor blades of the MW class turbines, their length is a

critical issue. The passage of villages or curvy roads in the low mountain ranges of

Germany may pose a problem. Up to three rotor blades can be carried together on

specially designed long vehicles for blades of a length in the range between 35 and

40 m (wind turbines up to 2.5 MW). Longer rotor blades are carried individually

because their maximum chord length (blade depth) is the second limiting factor. If

it exceeds 3.5 m the passage below most bridges (overhead height 4.0 to 4.2 m) is

no longer possible with the blade in the vertical position. To solve this problem,

500 15.2 Erection and operation of wind turbines

special trucks are designed. E.g., the truck for the rotor blades of the ENERCON

E112 (4.5 MW rated power, max. chord length 5.8 m) has a blade pitching

mechanism which turns the blade into the horizontal position before passing be-

low bridges.

Weight is mostly the critical factor when it comes to the transportation of the

nacelle. Its dimensions depend strongly on the drive train concept, see section 3.2.

The 2 MW wind turbine Nordex N-80, e.g., has a nacelle with the dimensions

10 x 3 x 3 m (length, width, height); those for the 5 MW class turbines may reach

the dimensions of a single family house.

The entire process of wind turbine erection is strongly dependent on the

weather conditions on site. While the wind should blow strongly during wind farm

operation, low wind speeds are desired for the erection period in order to avoid the

collision of components (e.g. rotor and tower) upon hoisting and the toppling of

the crane.

Apart from the wind pressure on the components upon hoisting, there are fur-

ther dangerous fluid dynamic problems. For example, as long as the nacelle is not

mounted on the tower, periodic vortex shedding at the tower may occur, the so-

called “van Kármán vortex street”. Therefore, despite the requirement for accurate

positioning in the range of millimetres during the assembly, unfavourable mete-

orological conditions may impose an intense time pressure on certain assembly

steps. This is an even more critical issue for offshore wind turbine installation

where additional risks emerge from waves and currents, cf. chapter 16.

Fig. 15-12 Transport of a tower segment [8]

15 Planning, operation and economics of wind farm projects 501

The mobile crane hired to assemble the components and erect the wind turbine is

very expensive, time is again a big issue. In addition to the main crane most erec-

tion procedures require a much smaller auxiliary mobile crane, cf. Figs. 15-13 and

3-55. For common wind turbines of 2 MW class the crane has to be able to lift

approx. 70 tons to the hub height of 100 m, see Table 15.6. Due to the required

reach of the crane its nominal load will then be 500 tons.

Table 15.6 Characteristic data of wind turbines and correspondingly required mobile cranes

with guyed telescopic crane boom and jib [10]

Rated power of wind

turbine in kW

300 600 1.000 1.500 2.000

Nacelle weight in t

(without rotor)

15 20 40 50 70

Hub height in m 50 70 80 90 100

Maximum crane ca-

pacity load at reach

18 tons

/ 8 m

25 tons

/ 25 m

43 tons /

18 m

65 tons /

22 m

73 tons /

20 m

Maximum hook height

in m (with jib)

56 76 84 94 104

Self weight of crane

and ballast in t

60 50 72

87.5

100

165

160 )*

Number of wheel axes 5 6 7 8 8

)* Mobile crane cannot drive individually, accompanying trucks for telescopic jib

and ballast required.

The assembly and erection procedure, as described below, has its limitations. At

present (2007), for wind turbines between 3 MW and 5 MW rated power the ca-

pacities of the trucks for transport and of the mobile cranes reach their bearing

limits. The only solution will be a segmentation of the nacelle into components

which are hoisted separately and then assembled on the wind turbine tower.

First, the tower is erected. Procedure and duration vary depending on the tower

types. The erection of a conical steel tower with its 3 to 5 sections only takes up to

2 days. The assembly of a segmented concrete tower, with its approx. 100 pre-

manufactured concrete segments, takes several days. For an in-situ concrete tower

with jacking framework, the production even lasts several weeks, cf. Fig. 3-54.

The nacelle is then mounted on the tower. Depending on the manufacturer, ei-

ther the entire nacelle, comprising nacelle frame, drive train and nacelle housing,

is lifted or this is done component by component.

Finally, the complete rotor is lifted and fixed to the flange of the rotor shaft, on

the premise that the rotor blades and the hub have already been assembled on the

ground. Another way of final assembly is to fix the hub to the rotor shaft already

at the ground and hoist the hub together with the nacelle. The rotor blades are then

lifted one by one. Now the shell construction is finished and the wind turbine