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Offshore Wind Energy Projects Feasibility Study Guidelines SEAWIND ALTENER PROJECT 4.1030/Z/01-103/2001 By Per Nielsen, EMD Ver. 3.0 June 2003

Cost (€/kW)

Offshore foundation cost 1.000 900 800 700 600 500 400 300 200 100 1 2 3

4

WTG s

- - 100 500 - 600

5

ize (

100 - 200 600 - 700

6

MW )

7

8

200 - 300 700 - 800

9

105

15

25

35

te Wa

45

) t (m p e rd

300 - 400 800 - 900

400 - 500 900 - 1.000

This document gives a number of guidelines for calculation of feasibility for offshore wind energy projects. The guidelines have to be seen as a help to get started identifying the more important factors going offshore with wind energy projects. The guidelines are mainly based on practical experience from the Danish offshore projects extrapolated based on simple assumptions, but also specific new developments in the WindPRO software tool (ver. 2.4) mainly for offshore purposes are introduced.

SEAWIND – Altener project – Feasibility Study Guidelines Energi- og Miljødata, Niels Jernesvej 10, DK-9220 Aalborg Ø, Tel: +45 9635 4444, Fax: +45 9635 4446, Email: [email protected], www.emd.dk

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SEAWIND – Altener project – Feasibility Study Guidelines Energi- og Miljødata, Niels Jernesvej 10, DK-9220 Aalborg Ø, Tel: +45 9635 4444, Fax: +45 9635 4446, Email: [email protected], www.emd.dk

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Content: MAIN DESIGN CRITERIA OVERVIEW...............................................................................5 POWER PURCHASE AGREEMENT (PPA)........................................................................7 WIND RESOURCE ASSESSMENT – MICRO LEVEL........................................................8 WATER DEPTH / FOUNDATION COSTS ..........................................................................9 GRID CONNECTION.........................................................................................................12 Internal cables between WTGs ......................................................................................................14 Transformer Station Off Shore ......................................................................................................14 Other Grid Connection Costs.........................................................................................................14 Grid Losses and Voltage Increase..................................................................................................14 EFFICIENCY VERSUS COST - WIND FARM LAYOUT – WTG PRICE AND MODIFICATIONS FOR OFFSHORE PURPOSE ..............................................................17 Wind farm layout ...........................................................................................................................18 Summing up on Feasibility Changes relative to on shore..............................................................19 VISUAL IMPACT/INTEGRATION .....................................................................................21 NOISE FROM OFF SHORE WIND FARMS ......................................................................22 PROTECTION INTERESTS ..............................................................................................23 SOFTWARE DEVELOPMENT FOR OFFSHORE OPTIMISATION ..................................24 More advanced park layout design (arc layout and parallel rows in radials)............................24 The Park Design Object .................................................................................................................24 The WTG Area Object ...................................................................................................................26 Optimisation of “regular pattern layouts” including water depth considerations ....................27 Output to spreadsheet for further optimisation............................................................................30 Example investigating best row and in row distance.....................................................................32

SEAWIND – Altener project – Feasibility Study Guidelines Energi- og Miljødata, Niels Jernesvej 10, DK-9220 Aalborg Ø, Tel: +45 9635 4444, Fax: +45 9635 4446, Email: [email protected], www.emd.dk

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SEAWIND – Altener project – Feasibility Study Guidelines Energi- og Miljødata, Niels Jernesvej 10, DK-9220 Aalborg Ø, Tel: +45 9635 4444, Fax: +45 9635 4446, Email: [email protected], www.emd.dk

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Main Design Criteria Overview Main design criteria's for offshore wind farm feasibility Offshore solutions will in generel beconsidered as "less feasible" than on shore. The higher energy production will normally not level out the higher costs. But due to the large development potential and environment issues offshore probably will expand fast in the future. Key figures: Energy production: DK-Off shore (Denmark) DK-inland Costs (Denmark)

DK-coast near

3500 MWh/MW 2200 MWh/MW 2800 MWh/MW

Offshore-extra: 159% 125%

Cost onshore Cost offshore

874 €/kW 1411 €/kW

Offshore-extra: 162%

Macro level: Regional wind climate - EU-Windatlas off shore. Power purchase agreements (PPA)

Micro level: Development Organisation

Wind resource assessment Water depth / foundation costs Grid connection Efficiency vs. cost - wind farm layout - WTG mod. Visual impact/integration (+Noise) Protection interests Birds/other environmental interests Fishing Military Flight routes Ship traffic/marks Tourism Local political involvement/approving Politicians (municipality/county) ---> Labour/industry ^ "Green people" movements ^ Local ownership ^ Investor / developer capability

The different main criteria to be considered are divided into two main groups Development and Organisation. This paper only deals with the Development criterias. (Technical aspects)

SEAWIND – Altener project – Feasibility Study Guidelines Energi- og Miljødata, Niels Jernesvej 10, DK-9220 Aalborg Ø, Tel: +45 9635 4444, Fax: +45 9635 4446, Email: [email protected], www.emd.dk

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Regional Wind Climate

WTG (MW)

1 1.3 1.7 2 3 4

From table above:

200

250

300

WTG Rotor diameter (m) M^2 50 1,963 60 2,827 70 3,848 80 5,027 90 6,362 100 7,854

0.4 1,376 1,981 2,697 3,523 4,458 5,504

0.4 1,720 2,477 3,371 4,403 5,573 6,880

0.4 2,064 2,972 4,045 5,284 6,687 8,256

350

400

450

500

550

600

650

700

750

800 W/m^2

WTG0.39 0.38 0.37 0.36 0.35 0.34 0.33 0.32 0.31 0.3 efficiency 2,348 2,614 2,864 3,096 3,311 3,509 3,689 3,853 3,999 4,128 MWh/year 3,381 3,765 4,124 4,458 4,768 5,053 5,313 5,548 5,759 5,944 MWh/year 4,602 5,124 5,613 6,068 6,490 6,877 7,231 7,552 7,838 8,091 MWh/year 6,010 6,693 7,331 7,926 8,476 8,983 9,445 9,863 10,238 10,568 MWh/year 7,607 8,471 9,279 10,031 10,728 11,369 11,954 12,483 12,957 13,375 MWh/year 9,391 10,458 11,455 12,384 13,244 14,035 14,758 15,411 15,996 16,512 MWh/year

50 m hub 100 m hub

Figure 1 The table at the bottom show how much a stand alone WTG in different sizes will produce at given colour code.

SEAWIND – Altener project – Feasibility Study Guidelines Energi- og Miljødata, Niels Jernesvej 10, DK-9220 Aalborg Ø, Tel: +45 9635 4444, Fax: +45 9635 4446, Email: [email protected], www.emd.dk

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The wind resource is the basis for the off shore wind farm. Note that for off shore there are no hills or mountains to speed up the wind. On land, even the poor areas with green colours can give good wind sites due to high speed up when sited on a mountain ridge – this means e.g. that in Germany, where the southern part has “poor” colours (green), see below, there are wind turbines producing even more than the best in northern Germany with a much better regional wind climate (red colour) due to mountain speed up. In the table above, you can from the colour on the map go into the table below to get a rough impression on the possible energy production for an unobstructed off shore WTG at least 10 km from shore. Larger wind farms will typically have array losses of 5- 15%. Grid losses of approximately 5% must be subtracted additionally.

Figure 2 European Wind Atlas (Risø)

Power Purchase Agreement (PPA) Two things have to be fulfilled – there have be an agreement, that makes sure that it is possible to sell the electricity produced, and normally a reasonable knowledge about the price paid per kWh is needed at least 10 years ahead. It is the combination of the wind resource and the price paid per kWh that gives the most important input for the feasibility study. If there is no chance of paying back the investment within around 10 years (maximum 15 years), the project will normally not be regarded as feasible. In some countries, the PPA set up limits on the project size, normally measured in MW, in order to get a PPA.

SEAWIND – Altener project – Feasibility Study Guidelines Energi- og Miljødata, Niels Jernesvej 10, DK-9220 Aalborg Ø, Tel: +45 9635 4444, Fax: +45 9635 4446, Email: [email protected], www.emd.dk

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Wind Resource Assessment – micro level Based on the colour map the wind resource can only be estimated within an accuracy of around 40% - and if the wind farm is closer to land than 10 km, there can be large withdrawals to be added. For further info on expected energy yield, the possibilities are: 1. Calculation based on regional wind statistics based on terrain description and proposed wind farm layout. 2. Calculations based on other local measurements available off shore or near shore 3. Control/calibration of calculations with existing WTGs near (< 25 km) site. 4. Establishment of new measurement masts off shore Roughly, the uncertainty based on the 4 levels is: 1. 2. 3. 4.

25% 20% 15% 10%

For all levels the uncertainty depends much on how reliable the available data are and how well these are processed. Measure height, measure period and equipment quality are important parameters. To establish off shore measurements, minimum a 50 m high measure mast should be established which is rather costly. Rough price estimation for an on-shore mast with sensors and loggers is €10.000 - Off shore, the cost will probably be around €50.000 due to the off shore foundation and the extra installation costs. Besides the equipment comes the measurements (continuous data collection and validation) + final processing (long term correction). The cost can vary much – 30 – 50.000 € must be assumed. This means that a 1-year measuring campaign off shore will roughly cost 100.000 €. Examples of equipment and data can be seen at www.winddata.com, where some data are also available. Withdrawal due to the distance to the coastline can roughly be given by the graph below.

SEAWIND – Altener project – Feasibility Study Guidelines Energi- og Miljødata, Niels Jernesvej 10, DK-9220 Aalborg Ø, Tel: +45 9635 4444, Fax: +45 9635 4446, Email: [email protected], www.emd.dk

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3 MW - 80 m hub - on shore roughness class: 2

Improved energy yield

130% 120% 110%

Main wind direction:

100% 90%

From sea From land Along shore

80% 70%

-9000 -8000 -7000 -6000 -5000 -4000 -3000 -2000 -1000 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 11000 12000 13000 14000 15000 16000 17000 18000 19000 20000

60%

Distance from coastline (m) Figure 3 Change in energy production with distance from coastline

Based on a wind direction distribution, where around 60% of the energy production comes from the main wind direction (like in Denmark where 60% comes from west-southwest directions, the decrease typically will be 12%-28% at near-shore sites depending on the orientation of the coastline relative to main wind direction. At distances more than 5 km away there will be almost no reduction. If the wind direction is more uniform (e.g. at Creete, Greece, where almost 100% of the energy comes from north west), the sensitivity of the coastline orientation will be higher. Also if there are mountains or higher roughness of the land the decrease versus distance will change.

Water Depth / Foundation Costs So far, the water depths outside the range of 2m - 30m have not been considered relevant for off shore wind farms. Below 2 m there will be problems with accessibility by boat (but special designed vehicles might be an alternative for transportation of the equipment to site). More than 30 m has so far been considered too expensive – but there is not an exact upper limit. Even floating WTGs are considered for very large water depths. 3 types of foundations are normally considered as alternatives: Gravity (2- 20 m) Mono pillar (5 – 30 m) Jacket (15 – 30 m)

SEAWIND – Altener project – Feasibility Study Guidelines Energi- og Miljødata, Niels Jernesvej 10, DK-9220 Aalborg Ø, Tel: +45 9635 4444, Fax: +45 9635 4446, Email: [email protected], www.emd.dk

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Basis price for 8 m water depth based on experiences from Denmark so far: 250-300 €/kW complete with installation. Traditionally foundation cost on land are 40 – 50 €/kW, so the increase is around a factor 7.

Increase per m additional water depth roughly: 2% The foundation costs represent 20-25% of the total project costs The foundation costs can vary very much with seabed conditions and weather conditions (high waves, tidal or icing)

In general the price does not vary much depending on type of foundation – it is more a question of finding the most suitable solution for the specific conditions. Note also that the foundation solution can affect the WTG price – in both directions. At Horns Rev, DK, a mono pillar foundation add 9 m height above sea level, which decreases the needs for tower height, but on the other hand the natural frequencies of the foundation demand that the tower construction have to be a 150 ton solution where the normal weight for this tower height is 110 t. The prices are of course very rough figures, but for a pre-feasibility study this should be good enough. Many factors influence the best choice of foundation type and the costs. For example the sea bottom conditions can change the costs radically. On bedrock seafloor cheaper solutions have been seen based on drilling holes in the rock for mono pillar implementation (Bockstigen, Gotland, Sweden). Below an example of the cost composition for a Gravity foundation on 8 m water is shown. (Samsø/ Niras).

SEAWIND – Altener project – Feasibility Study Guidelines Energi- og Miljødata, Niels Jernesvej 10, DK-9220 Aalborg Ø, Tel: +45 9635 4444, Fax: +45 9635 4446, Email: [email protected], www.emd.dk

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Gravity foundation cost (Niras)

Set-up of production facilities Foundation ex Cones Cones for ice break Installation Platform Weight fill Ground dig off/clapping Smoothing layer Erosion protection Cover for vessel Bollards, latter's etc Cable tubes Protection (corr/lightn) Unforeseen , 10% Design (consultant)

Figure 4 Gravity foundation cost breakdown

Note that cones for ice break are of course only a demand in northern regions – but not only the cone – also the all over dimension is affected if there is a risk of thick ice. Note also that weight fill is a quite large cost – but it is considered in the calculations, that using special heavy weight fill is cheaper than increasing the dimensions of the gravity foundation. A spreadsheet model developed for a rough calculation of foundation is shown below: Basis size: 2 MW

10 m dept

Basis cost 670 k€

335

€/kW

2% Percent change per m dept

80 Rotor 80% Percent change per load factor change Hub 70 height 112000 Load factor (hub x (RD/2)^2)

Based on those simple assumptions, the cost is calculated and shown in the below graph.

SEAWIND – Altener project – Feasibility Study Guidelines Energi- og Miljødata, Niels Jernesvej 10, DK-9220 Aalborg Ø, Tel: +45 9635 4444, Fax: +45 9635 4446, Email: [email protected], www.emd.dk

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1.000 900 800 700 600 500 400 300 200 100 1 2 3

4

WTG s

- - 100 500 - 600

5

ize (

100 - 200 600 - 700

6

MW )

7

8

200 - 300 700 - 800

9

5 15 25 35 45

Cost (€/kW)

Offshore foundation cost

10

te Wa

) t (m p e rd

300 - 400 800 - 900

400 - 500 900 - 1.000

Figure 5 The interesting fact is that there might be an upper limit in WTG size due to foundation costs, but new technical solutions might “break” the curve.

Grid Connection Grid connection costs can vary much. One of the main uncertainties is where the nearest connection point on land is which is “strong enough” to receive the power from the wind farm. Often it will be necessary to upgrade the grid on land and maybe install a new land based sub station. These cost we cannot give any guidelines for as it can be anything between zero and many millions of EURO. For the cable connection from the shore to the off shore wind farm, the following guidelines can be given.

SEAWIND – Altener project – Feasibility Study Guidelines Energi- og Miljødata, Niels Jernesvej 10, DK-9220 Aalborg Ø, Tel: +45 9635 4444, Fax: +45 9635 4446, Email: [email protected], www.emd.dk

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Cable cost (€/m)

Sea cable cost 500 450 400 350 300 250 200 150 100 50 -

Offshore trafo normally needed

120 30 0

25

150

60 50

75

100

125 150

500 450 400 350 y = 1,5x + 84,9 300 250 200 150 kV voltage 100 level 50 0 175 200 225 250

Wind farm size (MVA) Figure 6 Cost of different cable sizes - for each voltage group 300, 400, 500 mm^2 CU cables are shown - for 150 kV level also 630 mm^2 CU cables are shown as rightmost point.

The needed sea cable for connection between land and wind farm is mainly decided by the size of the Windfarm in MVA = MW/cosφ, where cosφ is around 0.85-0.95 dependent on the level of compensation for reactive power in the wind farm. Normally it is not allowed to perform a full compensation (cosφ=1) due to security reasons. As seen, the cable costs increases with the wind farm size due to cable size – the cables in the figure are 300, 400, 500 mm^2 CU and for 150 kV level also 630 mm^2 CU 3 phase sea cables. Prices of course also depend slightly on the length, as a larger deliverance will open the possibilities of getting a better price. Alternative to 3 phase cables 3 x 1 phase cables will allow higher MVA for same cable dimensions, but also higher prices. The above prices are only for the cable connecting the Windfarm to the shore. Other costs are: Grid connection: Off shore Sea cable, from wind farm to shore In row cables Rows to collect point cables Cable roll out/Wash down, variable Cable roll out/wash down, fixed cost Total number of WTG connectors Off shore HV station Connection (electrical work) Other fixed costs Other variable costs

Number or length (m) Voltage(kV) mm^2 35500 150 35850 30 3864 30 75214

Material 630 CU 300 CU 300 CU

Lines/cable Cable Cable Cable

80 1 150/30 kV

Prices k€ Per unit or For all per meter, € €/kW 17,750 500 3,585 100 386 100 3,761 50 500 500,000 2,000 25,000 15,000 15,000,000

74 15 2 16 2 8 63

2,000

2,000,000

8

34,320

34,320,000

143

On shore From shore to HV-grid HV station (if needed) Connection (electrical work) Compensation (reactive power) Other fixed costs Other variable costs Total

79,302

330

Figure 7 Example of estimated costs for a 240 MW Windfarm (80 x 3 MW) – the on shore costs are just roughly estimated and not divided into different parts as it will differ much from place to place.

SEAWIND – Altener project – Feasibility Study Guidelines Energi- og Miljødata, Niels Jernesvej 10, DK-9220 Aalborg Ø, Tel: +45 9635 4444, Fax: +45 9635 4446, Email: [email protected], www.emd.dk

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Cable roll out - wash down: from 15 – 70 €/m depending on the bottom conditions and the need of washing down the cable. On a rocky seabed, wash down is of course not possible, and other cover arrangements might be needed. But it might also not be needed if there is no sea traffic in the region.

Internal cables between WTGs In-between the WTGs normally 30 - 33 kV are used, as this is the typically transformer size in offshore WTGs (on land normally 10 – 20 kV are used). The reason for not using higher voltage in the WTGs is mainly that the space demand for higher voltage is much larger and the arrangement will not fit into the standard tower sizes. But the manufactures are working on solutions for this.

The cost of 150 mm2 CU interconnection cables is approximately 85 €/m. These are normally large enough for the internal connection (depending on the connection layout, larger cables might be used for a part of the connection) – also here cable wash down may be added.

Transformer Station Off Shore For larger wind farms, where more than 33 kV connection to land will be needed (larger than approx. 40 MW), an off shore transformer arrangement will be needed. The cost of this is quite high. For the Danish large off shore projects, 150/32 kV - 180 MW transformer are used with a cost of approximately € 8 million (60 mio. DKK) including foundation and installation.

Other Grid Connection Costs Cable roll out, connections in WTGs and the previously mentioned on shore costs are included in the table below as an example of the complete grid connection costs. Note that there is much to save at smaller projects (< 40 MW) where an offshore transformer station can be avoided.

Grid Losses and Voltage Increase Not only the costs are important, but also the losses and voltage increase can be deciding factors for choosing the right voltage level and cable dimensions.

SEAWIND – Altener project – Feasibility Study Guidelines Energi- og Miljødata, Niels Jernesvej 10, DK-9220 Aalborg Ø, Tel: +45 9635 4444, Fax: +45 9635 4446, Email: [email protected], www.emd.dk

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Loss and voltage at different loads, 5 km 30 kW - 30 kV - 3 x 300 mm^2 CU Cable 1.4% 1.2% 1.0% 0.8% 0.6% 0.4% 0.2% 0.0%

Full load loss (%)

y = 0.0004x + 3E-05

Volt increase (%)

0

5

10

15

20

25

30

35

Wind farm output ( MW) Figure 8 Loss and voltage increase versus load

The above figure shows a calculation example for a 30 kW Windfarm, which goes “to the limit” of the cable capacity. The losses (%) versus the wind farm output are calculated and it is seen to be a linear equation. This is used for calculating the real losses: Calculation of grid losses vs WTG output Loss percent of full load loss: 67% Weibull V mean: (m/s) 7.8 MWh/MW 3,003 Y-loss SUM loss - % 0.80% k 2 MW MWh/y 0.04% Sum loss (MWh) 71.93 A 8.77 3 9,008.4 Losses 5km 300 mm^2 CU-30kV line kWh/h MWh/y Wind speed freq hours Power Curv Prod. (MWh) % 3 6.9% 607.9 6 3.6 0.00 0.0001 0.00 4 8.4% 740.0 77 57.0 0.03 0.0237 0.02 5 9.4% 822.9 188 154.7 0.08 0.1414 0.12 6 9.8% 855.9 354 303.0 0.14 0.5013 0.43 7 9.6% 843.2 585 493.3 0.23 1.3689 1.15 8 9.1% 792.9 887 703.3 0.35 3.1471 2.50 9 8.2% 715.2 1255 897.5 0.50 6.3001 4.51 10 7.1% 620.7 1657 1,028.5 0.66 10.9826 6.82 11 5.9% 519.6 2056 1,068.4 0.82 16.9085 8.79 12 4.8% 420.3 2418 1,016.4 0.97 23.3869 9.83 13 3.8% 329.0 2695 886.7 1.08 29.0521 9.56 14 2.8% 249.4 2865 714.6 1.15 32.8329 8.19 15 2.1% 183.3 2948 540.3 1.18 34.7628 6.37 16 1.5% 130.7 2982 389.6 1.19 35.5693 4.65 17 1.0% 90.4 2994 270.6 1.20 35.8561 3.24 18 0.7% 60.7 2998 182.0 1.20 35.9520 2.18 19 0.5% 39.6 2999 118.8 1.20 35.9760 1.43 20 0.3% 25.1 3000 75.3 1.20 36.0000 0.90 21 0.2% 15.5 3000 46.4 1.20 36.0000 0.56 22 0.1% 9.3 3000 27.8 1.20 36.0000 0.33 23 0.1% 5.4 3000 16.2 1.20 36.0000 0.19 24 0.0% 3.1 3000 9.2 1.20 36.0000 0.11 25 0.0% 1.7 3000 5.1 1.20 36.0000 0.06

SEAWIND – Altener project – Feasibility Study Guidelines Energi- og Miljødata, Niels Jernesvej 10, DK-9220 Aalborg Ø, Tel: +45 9635 4444, Fax: +45 9635 4446, Email: [email protected], www.emd.dk

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The table shows how the information of a linear loss-% vs. WTG power output gives the loss vs. wind speed. With the given Weibull distribution, the total losses are calculated to 67% of the nominal output losses. This means that for evaluating the loss roughly, we only need to calculate the nominal power loss and withdraw 33%. So the loss versus cable length is given in next figure. Loss and voltage at full load, different cable lenghts, 30 kW - 30 kV - 3 x 300 mm^2 CU Cable 12.0%

Full load loss (%)

10.0%

Volt increase

8.0%

y = 0.0013x + 0.0021

Est. Real loss

6.0% 4.0% 2.0% 0.0% 0

10

20

30

40

50

60

Cable length to wind farm (km) Figure 9 Losses above around 2% will normally make it feasible to increase the voltage.

Above an example showing the losses versus cable length. It is seen that the loss is 0.13% + 0.2% per km cable length for the connecting cable between land and off shore wind farm. So e.g. at 10 km connection it will be 1.3% + 0.2% = 1.5%. Additionally there will be losses in the internal cable connection in the wind farm. The voltage increase at 50 km cable length is below 6% so this should cause no problems.

SEAWIND – Altener project – Feasibility Study Guidelines Energi- og Miljødata, Niels Jernesvej 10, DK-9220 Aalborg Ø, Tel: +45 9635 4444, Fax: +45 9635 4446, Email: [email protected], www.emd.dk

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Efficiency versus cost - wind farm layout – WTG price and modifications for offshore purpose The price of the WTG is off shore as well as on shore the most important part of the project. What is important is the price increase of the offshore “versions”. From Vestas following add-ons for Horns Rev off shore project are identified: Extras at Vestas 2 MW off shore WTG Helio-platform (Helicopter landing) Stationary tool box in each WTG Improved tower surface Nacelle with heaters and temperature regulators Extra platforms in tower (for grid connection and handy room) Containers for garbage Survival kit for 3 days for service personnel 150 t tower where normal are 110 t to adapt to monopillar foundation 2 flight marking lamps on nacelle Red paint on blade tips The above mentioned increase price around 10% rel. to standard 2 MW

So a price increase of up to 10% can be expected, but not all off shore projects have all the mentioned extras. E.g. the Helicopter platform will normally not be required. This is mainly due to the rough wave climate in the North Sea that makes access for service sometimes very difficult by boat. Also the extra tower costs are special. On the other hand, off shore projects will often give a quantity discount due to the large size.

WTG price non offshore, per kW 1000

Land Offshore

Price (€/kW)

900 800 700 600 500 500

1000

1500

2000

2500

WTG size (kW) Figure 10 Examples on WTG prices mainly on shore from Danish WTG catalogue 2001 (EMD). The two very different offshore prices for 2 MW WTGs is Middelgrunden (Bonus) and Horns Rev (Vestas), where the Bonus turbines are with a smaller rotor diameter and a smaller hub height, but at the Horns rev solution there are also much extra equipment (e.g. Helicopter platform) that can explain the difference.

SEAWIND – Altener project – Feasibility Study Guidelines Energi- og Miljødata, Niels Jernesvej 10, DK-9220 Aalborg Ø, Tel: +45 9635 4444, Fax: +45 9635 4446, Email: [email protected], www.emd.dk

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WTG prices vary quite much. In the figure, the latest overview of Danish WTGs (WTGsurvey November 2001) and two offshore examples are shown. Note that the rotor diameter of course is important. The low WTG price offshore is from Middelgrunden, 2 MW Bonus with 76 m rotor, which can be considered as a DEMO project and thereby low price – the other offshore are Horns Rev, Vestas with 80 m rotor diameter (10% more swept area). This price must be considered realistic so far. So concluding a price level around 850 €/kW should be realistic for a feasibility study.

Wind farm layout Different analyses on layout have been made.

Park efficiency for different spacing. Square layout (9 x 9 WTGs) Park efficiency (%)

103 98 93 88

Note: The existing PARK model may calculate up to 20% to high energy yield at large wind farms.

8 diameter spacing in a larger array is probably close to the optimum, where cable costs and additionally losses are included.

83 78 0

5

10

15

20

25

30

Spacing (RD) Figure 11 See also the last parts of this report, where an example on economic optimisation of layout distances is performed

An important factor in a larger array is the spacing. The figure above illustrates a 9 x 9 matrix. One factor that can move the spacing decision is the offshore territory available and how much territory is within an appropriate water depth, relative to the desired project size. An important reason for not to be to exact on the “optimal” spacing is that the present array loss calculation model might not work correctly with large wind farms. There are some indications supporting this. (Steen Frandsen, RISØ). Steen Frandsen recommends increasing the roughness class within the wind farm area to class 2.4 (Z0 = 0.2m) in order to compensate for the model uncertainties. This gives for the Rødsand/Nysted project a decrease of 15% in calculated energy production. Rødsand has optimised layout and have North-South 5.8 RD spacing (9 WTGs per row) and East-West 10.5 RD spacing (8 row’s of WTGs). We have to await useable measurements from Horns Rev, and more research activity within this field.

SEAWIND – Altener project – Feasibility Study Guidelines Energi- og Miljødata, Niels Jernesvej 10, DK-9220 Aalborg Ø, Tel: +45 9635 4444, Fax: +45 9635 4446, Email: [email protected], www.emd.dk

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Park efficiency for different rotation angles of square layout (5 RD, 9 x 9 WTGs)

Park efficiency (%)

87 86.5

Best angle increase with 0.35 % relative to poorest

86 85.5 85 84.5 84 0

5

10

15

20

25

30

35

40

45

Base angle (deg) Figure 12 Rotation angle of a 9 x 9 matrix only change energy production very little.

Another investigation made is rotating the matrix. It is seen that it makes almost no difference, less than 0.35% (with the given wind climate, which is DK).

Summing up on Feasibility Changes relative to on shore Summing up all the findings considering energy production and prices, a final conclusion can be made based partly on site-specific conditions, where the Danish wind distribution has been used. Extra costs going offshore: WTG: up to 10% extra Foundation: A factor 7 more expensive – or 10 – 20% increase of total project price. Grid connection: Much dependent on land connection facilities (but this is also the case for land based wind farms) – the extra offshore part will typically increase the total project price 10% as a minimum Besides this add 0,25% per km. distance to shore can be considered. Additional losses, 0.13% per km + 0,2%. How the extra costs/losses compare with the extra energy production is then the very important question. This is solved for an example in the figure below. Here we add 30% total in the costs just for going off shore (this could be 5% for WTG, 15% for foundation and 10% for grid) + the variable costs and losses due to sea cable connection.

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3 MW - 80 m hub - on shore roughness class: 2 - main wind direction: along shore

Improved feasibility (Yield loss and cost increase)

130% 120% 110%

Yield increase

100%

Feasibility increase

90% 80% 70%

48000

45000

42000

39000

36000

33000

30000

27000

24000

21000

18000

15000

12000

9000

6000

3000

0

-3000

-6000

-9000

60%

Distance from coastline (m) Figure 13 Feasibility 6 km offshore is approximately the same as 6 km on shore - and the "ideal" distance off shore in this example.

Interesting in the example in the figure is that at the given assumptions, a site 6 km off shore are the most feasible – and at a distance of 6 km from shore on land (flat land), the feasibility is exactly the same (if the operational cost do not differ). Most feasible is a site directly on the coastline, but even better would be a mountain ridge or hill near the coast, see next example. Yield and feasibility change with distance to shore line (south) at "de Vandellos" Nuclear Power Plant, Catalunia, Spain 200% 180% 160%

Yiels increase Feasibility increase

140%

From here water dept is uncertain

120% 100% 80%

8,000

7,000

6,000

5,000

4,000

3,000

2,000

1,000

-

(1,000

(2,000

(3,000

(4,000

(5,000

60%

Distance offshore to shore line (m) Figure 14 Another example at the Ebro Delta south of Barcelona, Spain. Here the mountains on shore and the fact that the main wind direction is from shore makes things look much more complex.

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Visual impact/integration The visual impact is often considered as the most critical part for offshore installations. Here are two possibilities – to make a nice layout, that match the surroundings or to bring the wind farm so far away that it is almost invisible. A good example on a nice layout adapted to the surroundings is “Middelgrunden”. (See http://Middelgrunden.VentusVigor.com for many good photos etc. Visualisations are an efficient tool for demonstrating the visual influence. Here are 3 variants: Photomontage: Take photos from important locations and render WTGs on top of photo. 2D animation: Let the WTGs rotate – need a PC for presentation 3D animation: Build an artificial landscape of the surroundings and sail/fly around to see the wind farm from different angles. Need a PC for presentation. All 3 types can be performed with help from the WindPRO software tool.

Figure 15 An example of a photomontage from a water tower – normally locations on the coastline will be used for photomontages

To make the wind farm fully invisible from land, needs a large distance, see figure below.

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180 160 140 120 100 80 60 40 20 -

Eyeheight: 2 m

These values to the left of zero value show meter horison seen behind WTG

Eyeheight: 5 m Eyeheight: 10 m Eyeheight: 25 m

50000

45000

40000

35000

30000

25000

20000

15000

10000

Eyeheight: 50 m

5000

Meter, that "disapear"

Distance to make WTGs "invisible" due to earth curvature

Meter distance to "observer"

Eyeheight: 100 m Typically hub height, 3 MW (80m) Typically blade tip height, 3 MW (125m)

Figure 16 At a distance of 45 km and an eye height of 2 m, a 3 MW WTG with blade tip height of 125 m is just invisible. At larger eye heights, e.g. 25m, you need 50 km distance to hide 80 m behind the earth curvature.

Noise from off shore wind farms Noise is normally not considered a problem for off shore wind farms. But with the new Swedish calculation models, it might be become a problem in some areas. Below results of calculations with different models are shown. Minimum required distance regarding Noise for 9x9x3MW (108 dBA) square layout, 5RD (450 m) in row and row distance New Swedish off-shore

ISO-9613-2 (0 met) 40 dBA 45 dBA

DK-rules 0

500

1000

1500

2000

2500

3000

Figure 17 In order to stay below 40 dBA (this is the demand in Sweden and e.g. Poland – in Denmark and Germany 45 is the demand in “open land” – at villages it is also 40 dBA) 2.7 km distance is needed for a large wind farm with the new Swedish guidelines. Calculated with the international ISO regulations it is only 1.6 km.

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The map in next figure illustrates the noise emission.

Figure 18 Noise emissions from an offshore wind farm based on the new Swedish calculation model, which is integrated as an option in the WindPRO software tool.

Protection Interests These will often be mentioned as “killer assumptions”, as just one important protection interest can stop the project, no matter how good it is in all other senses. So it is important to start clearing if there are any and how important they seem to be. As an example the RAMSAR regions (EU-bird protection) can be mentioned as regions, where there are a VETO against wind farms. There should be a common EU databank on protection interests, but maybe it does not cover all offshore aspects – and one can never be sure it is complete. So a hearing round to all relevant partners will normally be needed – and based on the feedback, there might be a conclusion. Of course the individual countries standard procedures for getting permission has to be followed later on – in the feasibility phase pre-contacts will be a recommendable way to go.

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Software Development for Offshore Optimisation The WindPRO software tool is improved in several ways to better support offshore development. While WindPRO is a general tool for project development, it can already handle the most important issues for offshore development like park layout design, energy calculation, economy calculation and environmental documentation (noise, flicker, ZVI, photomontage and animation). But for offshore some needs for improvements has been identified, the most important of which are: 1. More advanced park layout design (arc layout and parallel rows in radials) 2. Optimisation of “regular pattern layouts” including water depth considerations These two developed features will here be introduced.

More advanced park layout design (arc layout and parallel rows in radials) The Park Design Object

The Park Design Object creates regular pattern layouts. Following regular patterns are available in latest version of WindPRO (2.4):

Below the four different regular patterns is illustrated:

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There are handles, which makes it possible with a mouse drag to change all figures defining the rotation, distances, position and specific angles/radius depending of type of pattern. The fixed WTG is marked with a circle around. This is the WTG in the pattern that always stay at the same position except if the middle point is moved, while this point can be used for a parallel move of the complete pattern. The fixed WTG can be changed to another WTG in the pattern simply by right clicking at a WTG symbol and choose “Mark as fixed WTG”.

Figure 19 Definition of base and side angles

. Figure 20 The only parameter that cannot be changed graphically is the row offset, see figure.

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The row off set in the parallel row layout makes it possible to shift every second row from 0 to 1 in row distances. Here illustrated by the value 0.5.

Figure 21 Definition of layout in PARK design object.

It is possible to keep continuous control of number of WTGs or total installed capacity within the area specified by the WTG-area object (see next graphic) when the specific WTG area object is selected in the drop down menu in the bottom. The object can ensure that user defined minimum distances between WTGs and rows are met. Both meters and Rotor diameters (RD) can be used as measure unit. For support of the design, specific areas can be digitised and given properties helping with fulfilment of specific demands. The object used for this is the WTG area object.

The WTG Area Object

The WTG Area Object is used to define the areas to use for siting the WTGs. The limits of these areas are digitised directly using an on-screen map. You can also import coordinate files defining the limits - at present in the formats: .dxf (AutoCad/Autodesk) or .shp (Shape files from Arc View GIS files). For each partial area individual requirements can be set regarding: Number of WTGs (min and max)

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Total installed capacity (min and max) Minimum distance between two WTGs Putting the PARK design object on top of a WTG area object, gives the park designer the opportunity to design a Windfarm with regular pattern layout, where only the WTGs inside the WTG areas are included.

Figure 22 The green WTGs are inside the area, the purple outside. Right click at the park design object and choose “realize” and only the WTGs inside will appear as “real” WTGs, which then can be calculated by the respective modules.

Optimisation of “regular pattern layouts” including water depth considerations The module OPTIMIZE has been expanded to handle regular pattern optimisation. For regular pattern, the optimisation process differs from “random pattern” by keeping the relative positions of the WTGs within the specified layout. Starting the OPTIMIZE calculation module gives following options:

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Figure 23 First the wake decay constant should be set to 0.04 as this is the so far best experience for offshore wind farms.

Figure 24 At the Optimise tab sheet, the “regular pattern” method is chosen and the Park design object that is established will be chosen by default. If there are more Park design objects in the project, the one that shall be used must be selected here.

. The wind recourses can be taken from either a wind resource map file (.rsf) of from a meteo object, holding the wind distribution that is expected to cover the whole area of interest. This is common for offshore projects as the same wind distribution will be expected for the whole wind farm area. Onshore orography and roughness typically will result in varying wind distribution over the area.

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It can be chosen to ensure minimum park efficiency of, e.g. 95% (max. 5% array losses), which can be a design criterion in order to drop configurations that are estimated as nonrelevant from an economic point of view.

Figure 25 When the Optimise module is started, the layout and the optimise controller can be seen at one screen.

Now the task is to find the layout, which maximize the energy production, without going below specified (95%) park efficiency and, if this is chosen, is within the WTG area. The WTG in the lower left corner is fixed. Within the chosen pattern (here parallel rows) and the WTG type and hub height chosen at the park design object, following parameters can be varied: Change: • X and Y offset (can move the whole layout in steps in X or Y direction) • row count (number of rows) • WTGs per row • row distance • in row distance • base angle (see figure 19) • side angle (see figure 19) • row off set (see figure 20) The parameters to be tested are checked in the checkboxes and are set for each parameter:

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from, to, and step values

When the whole set up is created, the software performs a run with all combinations. So it can be a good idea not to test too many parameters in one optimisation, but maybe group the runs in order to limit the number of calculations – or to start running with a higher step value and then limit the from – to values based on the first run before fine optimisation with smaller step values. Results and layout specifications can be copied to clipboard for further processing in spreadsheet tools, e.g. MS Excel.

Figure 26 Figure above shows partly a calculation with the initial layout (previous figure) and a run where the highest production is found, here 10.4% higher production within same area are obtained, but based on 3 WTGs more, still within the selected area.

Output to spreadsheet for further optimisation A specific run can be dumped to clipboard, and then pasted into a spreadsheet, e.g. MS Excel.

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Name/ID:

xxxxxxx

Layout:

Parallel rows

WTG:

DUMMY;3000;XXXXXXxxxxxxx

WTG size:

3000 kW

Rotor diameter

90 m

Hub height (m)

80 m

Water dept (if not calculated) Coord system

20 m UTM WGS84_z33

WTGs 24 24 26 22 25 26 20

WTG Row In row Base Side offset angle angle (0-1 in dist dist Result x_Fixed_ y_Fixed_W Row per (deg) (deg) row (m) (m) (MWh/y) WTG TG count row 128.009 722.417 5.939.230 7 8 1500 900 90 55 0 128.064 722.417 5.939.230 7 8 1500 900 100 55 0 138.149 722.417 5.939.230 7 8 1500 900 110 55 0 117.730 722.417 5.939.230 7 8 1500 950 90 55 0 133.456 722.417 5.939.230 7 8 1500 950 100 55 0 138.413 722.417 5.939.230 7 8 1500 950 110 55 0 107.434 722.417 5.939.230 7 8 1500 1000 90 55 0

Figure 27 A part of the clipboard dump with the most important values. Besides these also the number of WTGs within specific water depths is included if this part of the calculation is activated.

With the clipboard dump to spreadsheet including all “runs” in the parameter variation, it is possible to perform an economic optimisation. A spreadsheet tool is prepared for this purpose, calculating cable lengths etc. There has been established a number of cost functions, in which a lookup function based on WTG size or installed MW find the relevant costs for each layout. Based on estimated costs and losses calculated in the spreadsheet and production calculated by WindPRO for each layout, the layout with highest production per investment can be found. This might not be the “best solution”, but it will be the layout with shortest payback time based on pure income vs. investment analyse. Budget for lowest cost/kWh:

Layout #:

Put your own data in the yellow cells

Number

100 Each

See also cell R5.. for foundation cost

Installed power

350 MW

And tab sheet Cost functions

Cost, 1000 € Cost €/kW Percent User input

WTG price; default WTG price, specific WTG price Dist to shore Area cost Cable losses, main cable Cable losses, internal cables

850 850 2.975.000 12000 2 0,15 0,1

k€/kW k€/kW k€/WTG m k€/ha %/km %/km

Clipboard layout: Paste in cell A14 ! Name/ID:

WTG cost

297.500

850

Foundation cost

125.821 53.430 10.080 8.100 46.000

359 153 29 23 131

540.931

1.546

Main grid connection cost Internal cable cost Area costs Other costs (planning, risk)

Total Production and cost/kWh/y

45

3,5 MW

927.961 MWh/y

Included losses

55,0% Array 23,3% 11,3% 9,9% Electric 1,9% 7,2% 1,5% 8,5% 100,0% 583 €/kWh/y

Guideline to offshore optimisation spreadsheet.

Run the optimisation from WindPRO with "regular patterns", and dump each step to clipboard. Paste the clipboard content to this sheet where it is marked (put cursor in A14 before paste) WTG: DUMMY 3500 100.0 !O!Then copy the rows from AD 23 to AO 23 down to last calculation result row. Put your own data into the yellow cells both at this sheet and at the cost function sheet. WTG size: 3500 In column AM-AO you will find the cost figures for the individuel layouts, which helps you finding the Rotor diameter: 100 optimal layout. Hub height (m): 95 You might proceed finding the optimal WTG size by running more similar calculations based on other WTG types, sizes or hub heights. Water dept: (if not calculated) 20 Layout:

Parallel rows

Coord system:

UTM ED50 Zone: 30

WTGs

Result X Y 100 636143,96 722973 100 771595,463 722973

5934705,091 5934705,091

Row count WTGs per r Row distanIn row distaBase angleSide angle Row offset 10 10 500 100 11,94 98,01 0 10 10 500 200 11,94 98,01 0

Figure 28 The optimisation spreadsheet, where the clipboard dump simply is pasted, and the complete economic optimisation calculation is performed automatically.

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Total cost (€/kW) Cost (€/MWh/y) WTGs

Cost vs layout 2.000

35

1.800 1.400

25

1.200

20

1.000 800

15

600

10

400

Number of WTGs

30

1.600

5

200 154

145

136

127

118

109

100

91

82

73

64

55

46

37

28

19

10

0 1

-

Layout number Figure 29 A graphic presentation of a number of layouts auto generated from WindPRO.

With this tool, it is possible to run a number of systematic analyses calculating the layout with the best performance. Below an example on a simple run to illustrate the capability:

Example investigating best row and in row distance We assume here a fixed Wind farm size of 100 x 100 WTGs in a fixed layout shape, and that the water depth is equal for all WTGs.

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Figure 30 Layout left with same in row and row distance, right with the in row distance reduced, but same row distance. So in this example the rows are oriented from southeast to northwest.

With the optimise module in WindPRO, we perform a run where row distance is changed from 5 to 10 RD with 2.5 RD as step size (3 runs) The in row distance is varied from 1 RD to 20 RD in 20 step (20 run) – so in total 60 run is made which produce 60 result lines in the clipboard file.

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The 60 run is pasted into the spreadsheet, and the results (based on some cost functions, that might only mach a specific site) appear automatically.

Budget for lowest cost/kWh:

Layout #:

Number

100 Each

Installed power

350 MW

45

3,5 MW

Cost, 1000 € Cost €/kW Percent

Included losses

WTG cost

297.500

850

55,0% Array

Foundation cost

125.821

359

23,3%

53.430 10.080 8.100 46.000

153 29 23 131

540.931

1.546

Main grid connection cost Internal cable cost Area costs Other costs (planning, risk)

Total Production and cost/kWh/y

927.961 MWh/y

11,3%

9,9% Electric 1,9% 7,2% 1,5% 8,5% 100,0% 583 €/kWh/y

Figure 31 The spreadsheet tells immediately which run that has performed best with respect to lowest price per produced annual energy (after losses). Here run 45, which have 10 RD row distance and 5 RD in row distance.

10 x 10 WTG layout

Cost (€/MWh/y)

900 850 800 750 700 650 600 550

5 RD row spacing

7.5 RD row spacing

10 RD row spacing

1 3 5 7 9 11 13 15 17 19 1 3 5 7 9 11 13 15 17 19 1 3 5 7 9 11 13 15 17 19

500 450

In row distance (RD) Figure 32 There has been performed 30 runs varying the in row distance for tree different row distances. The 10 RD (Rotor Diameter) spacing performs best, –and has its optimum at 5 RD in row distance.

Below there will be given some details behind the calculations above.

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Array loss (%) Electric losses (%) Internal cable cost (k€) Area costs (k€) 50%

35000

45%

30000

40%

Loss

30%

20000

25% 15000

20% 15%

Cost (k€)

25000

35%

10000

10%

5000

5%

0

1 3 5 7 9 11 13 15 17 19 1 3 5 7 9 11 13 15 17 19 1 3 5 7 9 11 13 15 17 19

0%

In row distance (RD) Figure 33 The variables in this calculation: Array loss, electric loss, internal cable cost and area cost These in combination gives the differences in cost/production. But there might also be e.g. increased service costs by larger distances between the WTGs that should be taken into account. The spacing used are similar to figure 24

The variables in this test case are: 1.

Array loss

2.

Electric loss

3.

Internal cable cost

4.

Area cost

The area cost can be quite difficult, as often no “variable cost” will be paid reflecting the area used, but since a larger area is used, there will be poorer possibilities for future expansions, which have a price, that is very difficult to set. Here is just used a fixed price per ha used. Also the electric losses are difficult, as they depend on the chosen cable solution, which might vary with the size of the wind farm. Here is simply assumed a fixed loss in percent per km cable. For further information on the described optimisation features, which were not released in a final version when this report was written, please contact the WindPRO team at mail [email protected]

SEAWIND – Altener project – Feasibility Study Guidelines Energi- og Miljødata, Niels Jernesvej 10, DK-9220 Aalborg Ø, Tel: +45 9635 4444, Fax: +45 9635 4446, Email: [email protected], www.emd.dk

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