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

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482 15.1 Wind farm project planning

turbines which then forms the basis for the initial prediction of the expected

energy yield.

In wind farm planning the yield is predicted for each wind direction sector

individually (cf. Fig. 4-22) using its individual wind frequency distribution func-

tion and the power curve of the chosen wind turbines. This is necessary in order to

find the optimum placing of the wind turbines in the mico-siting of the wind farm

which gives the maximum wind farm energy yield and also reduces the inevitable

interactions of the wind turbines. A resulting final wind farm layout is shown in

Fig. 15-2.

Road

Lane

Boundary of wind farm

Wind turbine (500 kW)

Industrial area

Living quarters

0 600m

Windfarm access lane

Windfarm internal cables

Transformer/ power switch

20 kV main transmission

Road

Lane

Boundary of wind farm

Wind turbine (500 kW)

Industrial area

Living quarters

0 600m

Windfarm access lane

Windfarm internal cables

Transformer/ power switch

20 kV main transmission

Fig. 15- 2 Wind farm layout and projected infrastructure

Wind farm micro-siting

The optimum arrangement of the wind turbines in the site area is obtained in the

course of the micro-siting. The main criterion is the maximisation of the overall

energy yield of the entire wind farm. However, the wind farm layout is as well in-

fluenced by the required infrastructure: the internal cabling from the wind turbines

to the transformer and substations and, in addition, the access lanes for transport,

erection, operation and maintenance costs (O&M) and service vehicles. Nowa-

days, established planning tools (e.g. WinPro, Windfarmer, a.s.o) exist, which

help to determine the optimum wind farm layout fast end efficiently.

There might be further restrictions influencing the siting, e.g. minimum dis-

tances to living quarters and working areas, environmental protection, a.s.o. Fur-

ther constraints, such as the allowed maximum total height, may be in place not

only due to technical issues but as well due to laws and regulations stipulated by

15 Planning, operation and economics of wind farm projects 483

public authorities. It would be advisable to gather information on these issues in

advance rather than having to change the planning later during the approval proc-

ess due to imposed restraints.

Local conditions

Ownership of the relevant field parts has to be clarified and land lease contracts

should be drawn up - or at least preliminary agreements.

Above all, investigation of the local conditions aims to ensure that the wind farm

project is realised in practical terms. It is clarified whether a stable erection of the

wind turbines is possible, the site can be accessed safely with all vehicles and ma-

chines required for transport, erection, service and O&M and whether for the grid

connection a power line extension is required. These issues are discussed here-

under:

- Foundation:

With regard to the wind turbine stability an individual geotechnical inves-

tigation report is required for each wind turbine to determine the load

bearing capacity of the soil below the foundation. The type and shape of

the foundation has to be chosen accordingly. Flat foundations are com-

mon, but if the soil is too soft, a pile foundation may be required.

- Accessibility and transportation to the site:

Access to the site and the options for transport and wind turbine erection

have to be checked and as well as the available suitable space for the

crane. The transport of huge components such as tower sections and rotor

blades to the building site may be limited by development, overhead

clearances under bridges, overhead power lines, traffic signs, railways,

antennas, waters, and many more.

- Investigation of the grid access:

The location and type (e.g. voltage level) of grid connection have to be

determined. The most simple case involves the connection of a short stub

from the wind farm to the feed-in point. If required, the power line has to

be extended directly to the next substation where either sufficient grid

capacity exists or a separate cell has to be added. Large wind farms often

have an individual substation which allows connection to a higher voltage

level.

- Grid connection:

The length and type of the cable route has to be checked having regard to

technical and economical aspects. If the cable route is very long quite

extensive planning with a separate environmental impact assessment is

required, see below.

484 15.1 Wind farm project planning

15.1.2 Legal aspects of the approval process

In Germany, the local community in whose area the site is located is responsible

for the approval of the wind farm or wind turbine. Uniform German federal laws

in conjunction with laws and regulations by individual federal states form the ba-

sis for the legal framework. An overview of the relevant federal laws and regula-

tions of the federal states is presented in Fig. 15-3.

¾ Federal Building Code (Baugesetzbuch BauGB)

¾ Aviation Act (Luftverkehrsgesetz LuftVG)

¾ Road Traffic Regulation (Straßenrecht)

¾ Federal Nature Conservation Act (Bundesnaturschutzgesetz BNatSchG)

¾ Federal Act on Immission Protection (Bundesimmissionschutzgesetz BImSchG)

¾ Environmental Impact Assessment Act (Umweltverträglichkeits-Prüfungs-Gesetz UVPG)

Federal laws

Regulations by the federal states

¾ Federal Building Regulation (Landesbauordnung)

¾ Maximum height limitations and regulations on minimum distances

¾ Land use planning and regional development

Competence of the community

¾ Prescribed privileged areas

¾ Development of land use plans

¾ Verification of admissibility

¾ Issue of construction permit

¾ Federal Building Code (Baugesetzbuch BauGB)

¾ Aviation Act (Luftverkehrsgesetz LuftVG)

¾ Road Traffic Regulation (Straßenrecht)

¾ Federal Nature Conservation Act (Bundesnaturschutzgesetz BNatSchG)

¾ Federal Act on Immission Protection (Bundesimmissionschutzgesetz BImSchG)

¾ Environmental Impact Assessment Act (Umweltverträglichkeits-Prüfungs-Gesetz UVPG)

Federal laws

Regulations by the federal states

¾ Federal Building Regulation (Landesbauordnung)

¾ Maximum height limitations and regulations on minimum distances

¾ Land use planning and regional development

Competence of the community

¾ Prescribed privileged areas

¾ Development of land use plans

¾ Verification of admissibility

¾ Issue of construction permit

Fig. 15-3 Overview of the general legal regulations for the approval of wind turbine installation

in Germany

Since the amendment of the German Federal Building Code (BauGB) in 1998, the

erection of wind turbines in the outskirts is a privileged project. Since then, most

local communities designated suitable areas which were favourably examined for

approvability in cooperation with the public agencies and regional planning au-

thorities. If parcels are located in such a suitable area (or a privileged area for

wind energy projects) then nothing stands in the way of building approval with re-

spect to the building code. Approval is usually not granted to areas outside of

these designated suitable areas.

The German Aviation Act (LuftVG) may impose constraints on the project. The

approval of the aeronautical authority is a prerequisite for the permission to build

in the protected areas around airports and in any place if the wind turbine would

15 Planning, operation and economics of wind farm projects 485

exceed a certain total height (hub height plus rotor radius). In general, a wind tur-

bine with a total height of more than 100 m has to be equipped with obstacle

warning lights, and the rotor blades have to be marked by red-white-red colouring.

Red or white obstacle warning lights on the nacelle housing top are required dur-

ing night or daytime. The latter is only required in the vicinity of airports.

The Road Traffic Regulations determine the minimum distances to freeways,

highways, country roads. Wind turbine erection may be either restricted and need

the approval of the local road construction authority or may be completely prohib-

ited. However, in certain cases, the competent authority may make an exception.

The authorising agency decides on admissibility with regard to environmental

protection based on the Federal Nature Conservation Act (BNatG) for nature con-

servation and rural conservation. Since wind turbines are privileged projects

according to the Civil Building Code, contacting and informing the competent

authorities should be sufficient. This means that a statement from the responsible

nature conservation authority is requested in course of the approval process.

The erection of wind turbines constitutes interference with nature and land-

scape. This is considered to be permissible if it:

- Is in agreement with the aims of regional development and planning,

- Is inevitable in terms of significant and long term interference and

- Can be compensated by the adoption of appropriate measures.

According to the German Federal Nature Conservation Act, interference in nature

and landscape has to be compensated. A survey report which determines the na-

ture and extent of the compensation measures, called an accompanying landscape

conservation plan, is therefore required.

The approval process for wind farm is a procedure under the German Federal

Act on Immission Protection (German: Bundesimmissionsschutzgesetz,

BImSchG). The procedure depends on the number of wind turbines in the wind

farm, see Fig. 15-4.

If an environmental impact assessment (EIA) is not required, a simplified in

camera approval process, i.e. without participation of the public, is carried out. If

it is found that an EIA is required, a so-called formal approval process is carried

out meaning that after an announcement in the newspapers the application docu-

ments have to be publicly displayed. Objections may be lodged up to 14 days after

the end of public display. Thereafter, these objections are discussed in a meeting.

The approval authority prepares this meeting by making enquiries to the

concerned specialist authorities (e.g. nature conservation, waters or civil building

authority). If all requirements for admission are fulfilled, approval of immission

protection is granted which also includes the required building permission.

486 15.1 Wind farm project planning

Number of wind turbines Approval process

1 - 2

3 - 5

EIA obligation

- yes -

Simplified approval process

in camera

acc. to § 19 BImSchG

without EIA (Environmental

Impact Assessment)

Formal approval process

with public participation

acc. to § 10 BImSchG

with EIA

No EIA obligation

EIA obligatory

Screening procedure:

general preliminary

examination

6 - 19

EIA obligation

- no -

EIA obligation

- yes -

EIA obligation

- no -

Screening procedure:

Site related prelimi-

nary examination

t 20

Number of wind turbines Approval process

1 - 2

3 - 5

EIA obligation

- yes -

Simplified approval process

in camera

acc. to § 19 BImSchG

without EIA (Environmental

Impact Assessment)

Formal approval process

with public participation

acc. to § 10 BImSchG

with EIA

No EIA obligation

EIA obligatory

Screening procedure:

general preliminary

examination

6 - 19

EIA obligation

- no -

EIA obligation

- yes -

EIA obligation

- no -

Screening procedure:

Site related prelimi-

nary examination

t 20

Fig. 15-4 Approval process for wind turbines with a total height of more than 50 m according to

the German Federal Act on Immission Protection (Bundesimmissionsschutzgesetz, BImSchG)

Ecological effects of wind turbines

It is verified whether the disturbances caused by the erection and operation of

wind turbines is acceptable with respect to nature conservation. If necessary, the

protection of plants and animals is checked by additional expert reports. The gen-

eral focus is on the protection of nesting and resting places of birds.

In Germany, the environmental impact assessment is not mandatory for wind

farms of 3 to 19 wind turbines. On the contrary, the authority firstly assumes that

the legal criteria are all met and checks for this case if there would still be signifi-

cantly negative environmental effects. Only then, an EIA is requested. If there is

an obligation for an EIA, biotopes, plants and animal species have to be mapped,

e.g. bats, nesting, resting and migratory birds, and the landscape also has to be as-

sessed.

In Germany, the following supporting documents on the effects of wind tur-

bines on human and environment are integral parts of the admission documents:

- Mapping of the avifauna,

- Further aspects of animal and plant protection,

- Noise impact expertise,

- Shadow casting expertise and

- Aspects of protection of historical monuments.

15 Planning, operation and economics of wind farm projects 487

Noise impact

The noise impact of wind turbines is investigated for the site based on the acoustic

measurements results included in the wind turbine type approval. The acoustic

measurements are usually performed by accredited institutes according to the in-

ternational standard IEC 61400-11. They serve for the determination of the sound

power level of the wind turbine type and penalty supplements for tonality (e.g.

dominant single tones) and impulses (rhythmical pulses of low-frequency).

According to [1], the noise impact L

at a relevant point of immission at a distance

d from the noise source is estimated by

= L

- 10 log

(2 ·

S

· d

) -

· d + K (15.1)

where:

: Sound power level at the source (nacelle or hub of wind turbine)

in dB(A)

d: distance between source and (measuring) point of imission in m

 coefficient for absorption in dB(A)/m

K: penalty supplement for tonality and/or impulse in dB(A)

The sound power level L

is given on a logarithmic scale where an increase by

3.01 dB(A) is experienced as doubled volume. Depending on the soil properties

the coefficient for absorption is in the range

D

.

The penalty supplements for tonality and impulses are given according to stan-

dards and are typically in the range K = 1…2 dB(A). The human ear is especially

sensitive to tonality or impulses. Mostly, they originate from the gearbox, the gen-

erator or the converter and are also determined by the standardised acoustic meas-

urements. The decay of the noise with increasing distance from the source can be

calculated with equation (15.1). Fig. 15-5 shows the example of a 1.5 MW wind

turbine with a typical total sound power level of 105 dB(A) at hub height (source

point) including the penalty supplements.

The noise emission of the wind turbine varies strongly depending on the current

wind speed and power production. A rough estimate is that for an increase of the

wind speed by 1 m/s the sound power level rises by 1 dB(A). The sound power

level relevant for the considerations on noise impact is given for a wind speed of

10 m/s, resp. at 95% of rated power. Furthermore, the noise emission varies with

the spatial direction, i.e. upwind, sideways or downwind the rotor of the wind tur-

bine. This must be taken into account in the acoustic measurements and also in the

course of the noise impact study using wind farm planning software.

The maximum value of the sound power level at an immission point must not

exceed the admissible limiting values provided in the legal regulations, table 15.1.

During wind farm planning the isophone lines, i.e. lines of constant sound power

level, are calculated and drawn on the site map. The superposition of the emis-

sions from the different wind turbines gives the total sound power level at the

488 15.1 Wind farm project planning

immission points shown exemplarily in Fig. 15-6. If other noise emission sources

already exist they also have to be considered when verifying the safety margin be-

tween noise impact and admissible values. In this way, critical areas are investi-

gated and turbine locations in the micro-siting may possibly be changed to reduce

the noise impact - or another more silent wind turbine type has to be chosen.

100

120

0 200 400 600 800 1000

Distance from wind turbine in m

105 dB (A) = L

WEC

+ K

Sound power level in dB (A)

100

120

0 200 400 600 800 1000

Distance from wind turbine in m

105 dB (A) = L

WEC

+ K

Sound power level in dB (A)

Fig. 15-5 Decay of the sound power level L

= L

WEC

+ K with the distance from the wind tur-

bine

Road

Lane

Boundary of wind farm

Isolines of the sound

power level (Isophone)

in dB (A)

Wind turbine (500 kW)

Industrial area

Living quarters

0 600m

Road

Lane

Boundary of wind farm

Isolines of the sound

power level (Isophone)

in dB (A)

Wind turbine (500 kW)

Industrial area

Living quarters

0 600m

Fig. 15-6 Wind farm site map with isophone lines from the noise impact study

15 Planning, operation and economics of wind farm projects 489

Table 15.1 Admissible sound power level according to the German Manual on Noise Impact

Regulations (TA Lärm)

3545Hospitals, health resorts

Exclusive living

4055Majority living

4560Mixed (living/ commerce)

5065Majority commerce

7070Industrial area

Night

dB(A)

Day

dB(A)

Area type

3545Hospitals, health resorts

Exclusive living

4055Majority living

4560Mixed (living/ commerce)

5065Majority commerce

7070Industrial area

Night

dB(A)

Day

dB(A)

Area type

If the actual sound power level of the operating wind turbines is questioned by

inhabitants at a later stage, on-site measurements by the trade supervision author-

ity are necessary. If for certain critical situations a problematic noise impact is

detected, e.g. at night for certain wind directions, the operator is forced to take

action. Variable-speed wind turbines with pitch control may then temporarily be

switched to a noise-reduced operation with a smaller rotational speed (i.e. less

circumferential speed). For stall-regulated wind turbines with a constant rotational

speed this measure cannot be applied due to technical reasons. In the worst case

there has to be a nightly shut-down which may cause significant yield loss. There-

fore, the noise impact investigation should be carried out carefully and with a rea-

sonable safety margin.

Shadow casting

Another aspect of the approval process involves investigation as to whether the

turning rotor casts a disturbing periodical shadow on any problematic spot in the

wind turbine’s surroundings. This can be simulated on the basis of the site-specific

sun’s orbit, the hub height and the rotor diameter for the “worst-case scenario”,

i.e. without considering atmospheric opacity or clouds. Fig. 15-7 shows for two of

the wind turbines of a wind farm the the isolines of annual shadow casting hours

as the result of such a prediction.. In Germany, the maximum admissible duration

is 30 hours per year in total and maximum 30 minutes per day for sensible inhab-

ited locations. If this limiting value is exceeded, the wind turbine should be

equipped with special sensors which shut it down automatically once the relevant

critical operating parameters are present: clear sky, relevant position of the sun,

relevant wind direction and a wind speed with the wind turbine in operation.

490 15.1 Wind farm project planning

Further constraints

Apart from the uniform Federal German approval process, additional regulations

and writs have also been prescribed by the individual Federal States. The regula-

tions of Schleswig-Holstein are mentioned by way of example in the following.

On November 25

, 2003 the Federal State Government of Schleswig-Holstein

amended the regulations on minimum distances for new wind turbines with a total

height h of more than 100 m ( h = hub height + rotor radius). The given values are

minimum values and should be respected by regional planning authorities when

allocating the privileged areas for wind turbines. Table 15.2 lists some examples

of the distance regulations.

Road

Lane

Boundary of wind farm

Wind turbine (500 kW)

Industrial area

Living quarters

0 600m

Annual shadow casting

in hours

Road

Lane

Boundary of wind farm

Wind turbine (500 kW)

Industrial area

Living quarters

0 600m

Annual shadow casting

in hours

Fig. 15-7 Wind farm site map with isolines of the annual shadow casting in hours for two wind

turbines

Land-use planning is an instrument of regional development used to regulate the

expansion of wind energy utilisation which may also include the allocation of

privileged areas and precautionary land. Privileged areas for wind energy utilisa-

tion exclude other regionally significant land use if it is incompatible with wind

energy utilisation.

At municipal level, a well organized land use plan offers the possibility of des-

ignating privileged areas for wind energy utilisation, thus keeping the remaining

planning area free of wind turbines as their erection at other sites would be

opposed in the interests of the general public.

15 Planning, operation and economics of wind farm projects 491

Table 15.2 Extract of the distance regulations for wind turbines of the German Federal State

Schleswig-Holstein

Type of land use

Minimum distance for

Wind turbines with a

total height of

h < 100 m

Minimum distance for

Wind turbines with a

total height of

h > 100 m

Single houses and scattered settlements 300 m 3.5 x h

Land settlements 500 m 5 x h

Urban settlements, areas with leisure

residences and camping sites

1000 m 10 x h

Federal freeways, highways and coun-

try roads and rail roads

In general 1 x h

National parks, nature reserves, etc. and

other woodland

min. 200 m,

up to 500 m

4 x h minus 200 m

Woodlands 200 m In general 200 m

Primary waters and waters with a pro-

tected regeneration strip

min. 50 m 1 x h minus 50 m

15.1.3 Estimation of economic efficiency

A first prediction of the economic efficiency of the wind farm project should be

performed already in the initial project phase (planning phase in Fig. 15-1). This is

done in order to assess whether the project will be an economic success. If this ini-

tial assessment is negative, planning should be halted in order to avoid incurring

any further costs. The expected investment costs and the wind regime are decisive

parameters when undertaking this assessment. Literature may provide the basis for

a rough estimation [2]. The composition of the investment costs varies slightly for

each project. Fig. 15-8 shows the typical distribution of the investment cost shares

according to a statistical evaluation of more than 500 onshore wind farm projects

[2].

The wind turbine itself has the biggest share of the investment costs. Mostly,

this share includes the costs for transport and on-site erection because these ser-

vices are often offered as a bundle by the wind turbine manufacturer. Fig. 15-9

shows that with growing rated power, the specific investment costs per kW

installed capacity decrease. The series effects and learning curves common in

mechanical engineering are also observed for commercial grid-connected wind

turbines. They lead to further cost reduction. The strongest reduction occurred in

the first half of the 1990s during the production of wind turbines of the 500 kW class.

(Decree of 4

July

1995)

(Decree of 25

November 2003)

Approx. 50 m to 100 m

for individual cases