A national laboratory of the U.S. Department of Energy

Office of Energy Efficiency & Renewable Energy

National Renewable Energy Laboratory 

Innovation for Our Energy Future 

Electrical Collection and 

Transmission Systems for 

Offshore Wind Power 

Preprint 

J. Green, A. Bowen, L.J. Fingersh, and Y. Wan 

National Renewable Energy Laboratory 

To be presented at the 2007 Offshore Technology Conference 

Houston, Texas 

April 30 – May 3, 2007 

Conference Paper 

NREL/CP-500-41135 

March 2007 

NREL is operated by Midwest Research Institute ● Battelle Contract No. DE-AC36-99-GO10337 
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Abstract 

The electrical systems needed for offshore wind farms to 

collect power from wind turbines—and transmit it to shore—

will be a significant cost element of these systems. This paper 

describes the development of a simplified model of the cost 

and performance of such systems. The performance prediction 

accounts for losses as a function of the power produced in the 

wind farm and the length and size of the cables. The cost 

prediction is flexibly formulated so wind farm configurations 

can be evaluated by parameters such as the number of wind 

turbines, wind turbine size, turbine array configuration and 

spacing, and distance from shore. The collection system—the 

medium-voltage electrical grid within the wind farm, and the 

transmission system—the high-voltage electrical connection to 

an on-shore transmission line—are treated independently in 

the model. Data sources for the model and limitations of the 

data are discussed, and comparison is made to costs reported 

by others. The choice of transmission system technology is 

also addressed. This electrical system model is intended for 

integration into a more comprehensive model of offshore wind 

farm design, cost, and performance that will be used for 

parametric studies and optimization of wind farm 

configurations. Because some concepts for future offshore 

wind installations in deep water use floating platforms, this 

paper briefly discusses the application of submarine cable 

technology to nonfixed termination points, a departure from 

current practice. 

Introduction 

The National Wind Technology Center (NWTC) of the 

National Renewable Energy Laboratory (NREL) in Golden, 

Colorado, has undertaken a series of concept studies to 

evaluate the cost and performance of offshore wind farms. The 

product of these studies will be a comprehensive model of 

offshore wind farm design, cost, and performance suitable for 

parametric studies and optimization of wind farm 

configurations. The overall goal of this effort is to help 

identify technology pathways for offshore wind energy 

development and deployment in the United States. Offshore 

wind farms present an attractive option because they allow for 

larger wind turbines that operate in higher wind resources than 

land-based [1,2]. Offshore installations are also more 

expensive, so an understanding of their performance, cost, and 

optimal configurations is needed. 

This paper is an overview of one of these concept studies. It 

focuses on the power losses in wind farm electrical power 

collection and transmission systems, as well as the costs of the 

system components and their installation. A hypothetical 

system was based loosely on the Horns Rev offshore wind 

farm in Denmark. Inquiries were made with manufacturers 

about electrical and cost data on the required components, 

which were then compiled in a spreadsheet model. The 

performance prediction accounts for losses as a function of 

power output of the wind farm and length and size of the 

cables. The cost prediction is flexibly formulated so wind farm 

configurations can be evaluated by parameters such as the 

number of wind turbines, wind turbine size, turbine array 

configuration and spacing, and distance from shore. 

Electrical Collection and Transmission Systems for Offshore Wind Power 

Jim Green, Amy Bowen, Lee Jay Fingersh, Yih-Huei Wan

National Renwable Energy Laboratory, Golden, Colorado

Electrical System Overview 

The electrical system for an offshore wind farm consists of a 

medium-voltage electrical collection grid within the wind farm 

and a high-voltage electrical transmission system to deliver 

the power to an onshore transmission line. 

Collection System 

The collection grid begins with transformers at each wind 

turbine, usually in the base of the tower, to step up from the 

generation voltage, typically 690 volts (V), to a medium 

voltage of typically 25–40 kilovolts (kV). This voltage range 

seems to be preferred because standardized equipment is 

available at competitive prices and because higher voltage 

transformers would be too big to fit readily into the tower 

cross sections. A grid of medium-voltage submarine cables, 

typically buried 1–2 meters (m) deep in the seabed, is used to 

connect the wind turbines to an offshore substation. 

Transmission System 

The transmission system begins at the offshore substation, 

which steps up the voltage to a transmission voltage of 130–

150 kV, the highest voltages in use today for AC submarine 

cables. This higher voltage allows a much smaller diameter 

and lower cost submarine cables to be used for the long run to 

shore. Only three offshore wind farms in operation today have 

offshore substations. However, these stations are expected to 

be the least-cost option for wind farms that will be larger and 

further offshore than current practice. Such wind farms are the 

main target of this inquiry. 

1
From the offshore substation, a high-voltage submarine cable 

(which is also buried in the seabed for protection) carries the 

power to shore. Once it makes landfall, the run continues, 

either underground or overhead, to an onshore substation for 

connection to a transmission line. An additional transformer 

may be used in this substation to step up the voltage to a 

higher level to match the transmission grid. 

Two technology options are available for the transmission 

system: high-voltage AC (HVAC) and high-voltage DC 

(HVDC). The current consensus is that HVAC is the most 

economical option for distances shorter than 50 kilometers 

(km) [2,3,4]. This technology is assumed for our model. 

Between 50 and 80 km, HVAC and HVDC are expected to be 

similar in cost. Longer than 80 km, HVDC systems will likely 

be least cost, mainly because the capacity of a given HVAC 

cable drops off with distance due to the capacitive and 

inductive characteristics of the cable and their associated 

losses. DC transmission avoids these losses entirely, so it is 

the preferred technology for longer distances. 

Obtaining Cost and Performance Data 

Our study began by examining European offshore wind farms. 

One of the best documented is Horns Rev, a 160-megawatt 

(MW) farm that began operation off the coast of Denmark in 

2002 [5]. Horns Rev is also one of the two largest offshore 

wind farms in operation and was the first to use an offshore 

substation. The collection and transmission cables are rated at 

36 kV and 150 kV, respectively with XLPE (cross-linked 

polyethylene) insulation. We used these parameters to create a 

model of an example wind farm rated at 500 MW. Requests 

for high-voltage submarine power cable cost and performance 

were sent to five manufacturers. Three responded to our 

requests with preliminary engineering estimates. These 

estimates were converted to a value in U.S. $/m and loss, 

kilowatts (kW)/m, for application in our model. Similar 

methods were used to determine the shipping and installation 

costs for the cable. 

Submarine power cables are custom manufactured to meet the 

requirements of each unique project; as a result, extensive 

electrical and cost data on specific cable sizes and types are 

not readily available. We found that performance and cost data 

are highly variable between manufacturers. In fact, one 

manufacturer provided cable prices about twice as high as the 

other two. We have concluded those prices are not 

representative of the market and we are not reporting them 

here. During interviews with manufacturers, we determined 

that this variability could arise for numerous reasons: high 

demand for cable from a particular company, rapid inflation in 

commodity prices, company policy to bid conservatively 

(especially when little is known about the application), the 

customized nature of cable design, and setup and tooling costs 

that are unique to each design. 

Two manufacturers provided performance data for their 

cables. In addition to an inconsistency in these variables, we 

had too little information about the cables themselves to 

calculate losses from first principles. However, both data sets 

contained values for current rating or ampacity (amperes), 

Irated, and power losses (kW) at full capacity, Pc. We developed 

a method for calculating power losses that relies on Irated, Pc , 

and the resistance of the copper conductor, R (ohms). 

Although R was listed on only one data sheet, resistances are 

readily calculated for copper conductors of known size. The 

total losses were divided into two parts: losses (kW) that vary 

with current, which were modeled as a quadratic term, Pi; and 

a base loss (kW), Pb, that does not vary with current, modeled 

as a constant. Pi and Pb are calculated as follows: 

i rated ×= RIP 2

−= PPP icb 

A transformer manufacturer was contacted to request cost and 

performance data for three transformer applications. These 

transformers contain a special type of liquid coolant that is 

biodegradable, nontoxic, and suitable for offshore use [6]. 

Transformer specifications were developed based on the 

system voltages and power levels throughout the collection 

and transmission systems. For installation in each wind turbine 

tower, we priced a 3.16-mega-volt-amperes (MVA) 

transformer to step up the voltage from an assumed 3-MW 

wind turbine’s 690-V generation voltage to the collection 

system’s 34 kV. The offshore substation contains three, 187-

MVA transformers that step up the voltage from 34 kV to the 

transmission system voltage of 138 kV. (We selected 

operating voltages that are slightly lower than the cable 

voltage ratings.) Lastly, a single 560-MVA transformer is 

located at an onshore substation to step up to an assumed 

onshore transmission system voltage of 345 kV. This voltage 

level is typical of a transmission system that can receive 500 

MW of generation. 

Results 

Unit Costs and Performance 

Table 1 is a cost summary (in $/m) for submarine cables from 

two companies. All cables are AC, contain a single layer of 

steel armor, and are XLPE insulated. Table 2 is a cost 

summary for the transformers for the tower base, the offshore 

substation, and the onshore substation. 

2
Table 1. Costs for cables with specific conductor sizes from 

two companies. Highlighted costs were 

extrapolated from known costs. 

Conductor Company A Company B 

Size mm2

Cost ($/m) Cost ($/m) 

Collection System 

95 152 455 

150 228 494 

400 381 609 

630 571 635 

800 600 731 

Transmission System 

630 755 860 

Table 2. Transformer unit costs. 

Location 

Voltage & 

Capacity Unit Cost 

Wind Turbine 

690/34 kV 

3.16 MVA $50,500 

Offshore 

Substation 

34/138 kV 

187 MVA $2,618,000

Onshore 

Substation 

138/345 kV 

560 MVA $5,600,000

Figures 1 and 2 show performance data for submarine cables 

from two companies. The power losses in Figures 1 and 2 are 

computed at steps that correspond to 3 MW of additional 

power in a 34-kV line. As the power level increases, the 

current on the line and thus the power loss increases. Electrical 

data were not available for the transmission system cables, so 

no power loss estimation for high voltage operation is 

provided here. The actual losses for an operating wind farm, 

which are a function of power level (and in turn a function of 

wind speed), will be applied in the final wind farm model. 

Company A Power Loss Summary 

for different conductor areas

0

20

40

60

80

100

120

140

0 200 400 600 800 1000

Current (Amps)

Power Loss (W/m)

95 mm2

150 mm2

400 mm2

630 mm2

800 mm2

Figure 1. Loss results for Company A cables at 

 various currents for several conductor sizes. 

Company B Power Loss Summary

for different conductor areas 

0

10

20

30

40

50

60

70

80

90

0 200 400 600 800 1000

Current (Amps)

Power Loss (W/m)

95 mm2

150 mm2

400 mm2

630 mm2

800 mm2

Figure 2. Loss results for Company B cables at 

various currents for several conductor sizes. 

We also contacted a domestic submarine cable installer who 

provided us with a preliminary engineering estimate for cable 

shipping and installation, which we then converted to a base 

value and a $/m value to allow for variability in cable length 

(see Table 3). Mobilization, demobilization, marine route 

survey, and route engineering costs are given as fixed costs; 

shipping and cable laying costs vary with cable length. 

Table 3. Installation cost breakdown. 

East Coast West Coast 

Marine Route Survey 

& Engineering $1,500 K $2,000 K 

Cable Transport 

Via Freighter from 

Europe ($/m) 

$58 $85 

Mobilization/ 

Demobilization $5,000 K $6,000 K 

Cable Laying 

Operations ($/m) $94 $103 

Cost for an offshore substation for a 240-MW farm was 

obtained from the SeaWind concept study [7]. We adjusted 

this number to account for the difference in size, foreign 

excahange rates, and inflation resulting in a value of $40.52 

million (2006 $) for a 500 MW offshore substation. 

500 MW Wind Farm 

After we compiled the unit cost data in the spreadsheet, we 

considered alternative layouts for an example 500 MW wind 

farm to assess impacts on wind farm power losses and costs. 

All collection grid layouts investigated were radial from the 

offshore substation. The numbers of rows and number of 

turbines per row were varied for different layouts; see Figure 3 

for a 21-row layout with eight turbines per row. 

3
Offshore 

Substation

Onshore

Substation

Figure 3. 500 MW wind farm layout with 3 MW qind turbines. 

Diagram not drawn to scale. 

Table 4 summarizes the input parameters of this example wind 

farm. The 630 meter distance between rows and between 

turbines is 7 times the rotor diameter of 90 meters. A cable 

length between turbines of 830 meters allows ample room for 

installation and topographical differences in the ocean floor. 

The cables connecting the collection grid to the offshore 

substation vary in length based on their location but are each 

approximately 7 kilometers. The number of transformers and 

their costs for this 500 MW system are shown in Table 5. 

Table 4. 500 MW wind farm parameters 

Wind turbine rating 3 MW 

Number of wind turbines 167 

Rotor diameter 90 m 

Water depth 20 m 

Distance between turbines 630 m 

Distance between rows 630 m 

Cable length between turbines & 

between rows 

830 m 

Substation distance to shore 15 km 

Length of onshore transmission 15 km 

Table 5. Transformer cost summary for 

500 MW wind farm. 

Location Quantity Unit Cost Total Cost 

Wind Turbines 167 $50,500 $8,433,500

Offshore 

Substation 3 $2,618,000 $7,854,000

Onshore 

Substation 1 $5,600,000 $5,600,000

Table 6 is a summary of total wind farm costs and losses for 

Companies A and B. Cable cost, cable shipping and 

installation, tower transformers, offshore transformer 

substation, and onshore transmission and substation are 

included in these costs. Power losses are computed at the wind 

farm’s rated power and, thus, are not representative of actual 

operating losses. (Transmission losses are based on 

extrapolations of losses at medium voltage and should be 

considered rough estimates.) 

Table 6. Cost and performance summary for a 500 MW offshore 

wind farm. All costs are in millions $ and all power losses 

are in MW at rated power. 

Layout 1 Layout 2 Layout 3

Turbines per row 8 7 6 

# of Rows 20.9 23.9 27.9 

Turbine 

Transformer Cost $8.43 $8.43 $8.43 

Collection Cable 

Shipping & Install Cost $36.53 $38.36 $42.84 

Transmission Cable 

Shipping & Install Cost $6.83 $6.83 $6.83 

Offshore Substation 

w/Transformers $40.52 $40.52 $40.52 

Onshore Transmission 

& Substation $29.37 $29.37 $29.37 

Company A 

Collection 

Cable Cost $82.85 $86.64 $78.78 

Transmission 

Cable Cost $33.98 $33.98 $33.98 

Collection 

Losses (MW) 11.96 11.86 14.21 

Transmission 

Losses (MW) 2.88 2.88 2.88 

Total Cost and 

Unit Cost 

$238.57 

$477/kW 

$244.13

$488/kW

$240.75

$482/kW

Total Losses (MW) 14.84 14.74 17.09 

Company B 

Collection 

Cable Cost $123.15 $122.54 $136.88

Transmission 

Cable Cost $38.70 $38.70 $38.70 

Collection 

Losses (MW) 7.81 8.29 11.27 

Transmission 

Losses (MW) 2.88 2.88 2.88 

Total Cost and 

Unit Cost 

$283.53 

$567/kW 

$284.75

$570/kW

$303.57

$607/kW

Total Losses (MW) 10.69 11.17 14.15 

Cost Comparison to Other Sources 

The cost data used in this study were compared to the cost 

data reported by Neilson [7] and Gerdes et al. [8]. When a 

direct match could not be made between the cables used in 

these studies, the cable with the dimensions closest to those 

specified was used. The data was corrected for inflation and 

foreign exchange rates and are reported here as 2006 costs. 

For this comparison, we did not create wind farm array 

configurations. We simply calculated total cost by multiplying 

the length of the cable from the Seawind study [7] by the $/m 

data from both of the manufactures in our study. Table 7 

shows the individual cable costs and the total cost results for 

both Seawind and our study. 

4
Table 7. Comparison to Seawind cable costs. 

Length 

(m) 

 Voltage 

(kV) 

Area 

(mm2

) 

Cost 

$/m 

Total 

($M) 

Seawind 

35,500 150 630 641 22.76 

39,714 30 300 128 5.08 

27.84 

Company A 

35,500 170 630 755 26.80 

39,714 36 400 381 15.33 

42.13 

Company B 

35,500 150 630 860 30.53 

39,714 36 400 609 24.18 

54.71 

All our cable costs are higher than those in the Seawind report. 

The price of copper increased significantly between 2003 

(when the Seawind study was performed) and the summer of 

2006 (when our data were collected), at one time by more than 

300%. This increase may partially explain the differences 

between the costs in these two studies. A manufacturer 

reported that commodity prices are about one-third of the 

cable cost. Changing foreign exchange rates may also have 

been a factor 

In addition, the results from our loss calculation method were 

compared to the results obtained by the Seawind study. The 

Seawind study provided the losses at full load for different 

wind farm sizes with a 300 mm2

 conductor cable at 30 kV. 

Table 8 show these losses for Seawind and the full load losses 

based on our data for a 400 mm2

 conductor cable at 36 kVa. 

There is a reasonable match between these data sets, although 

lower losses might have been expected from our data given 

the larger cable size and higher assumed operating voltage. 

Table 8. Comparison to Seawind full load losses. 

Size 

(MW) 

Seawind 

(% lost) 

Company A 

(% lost) 

Company B 

(% lost) 

15 0.603 1.253 0.690 

30 1.203 1.234 0.950 

Table 9 shows a comparison of the actual transmission system 

costs for Horns Rev [8] and the predicted costs from our 

study. Note: the dimensions of the onshore cables differ 

between Horns Rev and our data. Our costs compare 

reasonably well with Horns Rev. 

Table 9. Comparison of transmission cable and 

substation costs to the actual cost for Horns Rev. 

Company 

Actual A B 

Onshore Cables 10.55 10.55 

Offshore Cables 15.86 18.06 

Offshore Substation 

w/Transformers 12.87 12.87 

Total ($M) 39.45 39.28 41.48 

Table 10 shows a similar comparison between the actual costs 

of the Nysted transmission system and our cost estimate. Note: 

the dimensions of the cables differ between Nysted and our 

study. Once again, the cost comparison is reasonably good. 

Table 10. Comparison of transmission cable and 

substation costs to the actual costs at Nysted. 

Company 

Actual A B 

Onshore Substation & 

Transformer 8.4 8.4 

Onshore Cables 5.59 5.59 

Offshore Cables 8.31 9.46 

Offshore Substation 

w/Transformers 13.32 13.32 

Total ($M) 37.80 35.62 36.77 

Reducing Cable Cost 

Several options for reducing electrical system cost emerged in 

the course of our study. These options may be technically 

feasible, but each comes with some added risk of reduced 

reliability. Because submarine cables require significant 

capital investments and are relatively inaccessible for 

maintenance, buyers are conservative with a strong preference 

for designs with proven records. 

1. Don’t bury the collection system cables in the seabed 

between wind turbines, since the risk of damage within 

the wind farm from boat anchors, commercial fishing, 

etc., is low compared to the more exposed transmission 

cable to shore. Laying cable on the seabed costs less than 

buried cable installation. 

2. For copper conductors, the lead sheath is not strictly 

necessary. A copper wire sheath can be used instead to 

provide an effective electrical shield. Lead sheathing is 

commonly specified as a conservative approach that 

provides one more seawater barrier for the conductors. 

Lead sheathing is more expensive because it uses a larger 

volume of material applied in an extrusion process. 

3. Alternatively, aluminum conductors can be used in place 

of copper can reduce both cost and weight. Conductor 

cost alone could be lower by about a factor of 6 (at 2006 

commodity prices), and cable costs might be reduced 

15%–20%. Seawater exposure of aluminum results in 

corrosion and off-gassing, so using a lead shield for 

maximum seawater isolation will be prudent. 

5
4. Power cables for wind farms should be designed with 

cable thermal mass in mind. One manufacturer noted that 

a buried cable/soil system has a thermal time constant of 

about one week. Typically, wind farms are not at peak 

power continuously. Intermittency of the wind resource 

may allow cable thermal design to be based on current 

level less than that at peak wind farm output. Temperature 

monitoring of cables is feasible with fiber optics, though 

the optical fibers are reported to be less robust than the 

cables. 

5. One cable manufacturer recommended that performancebased cable specifications be used instead of design-based 

specifications to give the manufacturers greater flexibility 

to use their knowledge and experience to explore costeffective designs. 

Cables for Floating Platforms 

Some concepts for future offshore wind installations in deep 

water use floating platforms [1], which will not provide static 

termination points for submarine power cables. These cables 

will be subjected to some finite motion: heave, sway, torsion, 

or some combination of the three. Clearly the medium- and 

high-voltage submarine cable designs in use today will not be 

adequate for this service, primarily because the lead sheathing 

around the electrical conductors has very poor fatigue 

properties. This issue has not been addressed by the oil and 

gas industry because the risers typically used for floating oil 

and gas platforms are communications cables and pipelines for 

oil and gas, not high-voltage power cables. These platforms 

typically operate with 13.8-V power, not the higher voltages 

needed for offshore wind. 

One option might be to switch from lead to copper sheathing 

around the electrical conductor. Removing the lead creates a 

much more fatigue-resistant cable. Of course, the fatigue 

properties of cables without lead sheathing will need to be 

determined and evaluated in light of the dynamic 

characteristics of particular floating platform designs. 

However, a copper sheath, typically a mesh of copper wires, 

which provides necessary electrical shielding, is not a 

seawater barrier as is a continuous lead sheath. Thus long-term 

resistance of the cable to seawater intrusion will be reduced. 

Other issues will include means to distribute cable bending, 

i.e. to limit bending radius; creating resistance to cable 

abrasion against the seabed; and finding suitable means to 

support cable weight if the cable must be used in a droop 

configuration. In contrast, experience with submarine cables is 

limited to stationary and fully supported installations, typically 

laid on or trenched into the seabed. Care is taken to protect 

cables from seabed scouring, in particular at the bottom of 

wind turbine towers, which could leave a length of cable 

suspended above the bottom and vulnerable to movement. 

Conclusion 

The NREL NWTC in Golden, Colorado, has undertaken a 

series of concept studies to evaluate the cost and performance 

of offshore wind farms. This paper reports on one of these 

concept studies that focused on the costs and losses in wind 

farm electrical power collection and transmission systems. 

We believe the cost and performance data reported here are 

well suited for parametric studies of wind farm size and 

configuration. However, we recommend some caution about 

the use of these data for estimating absolute costs. 

Uncertainties in absolute cost arise from factors such as 

changing commodity prices, changing foreign exchange rates, 

changing levels of demand for goods and service in this 

industry, and the impact of project-specific design parameters. 

Also, losses in submarine cables appear to depend on the 

specific cable design and, perhaps, the manufacturer. 

Submarine power cables are highly customized for each 

application, so generalizations about cost and performance are 

estimates at best. 

This study was limited to electrical system components—

submarine cables, the offshore substation, and transformers—

that contribute the most to system cost. Devices we have not 

addressed, including switches, circuit protection, and 

compensation devices, have much lower costs, but are 

nonetheless important to wind farm operation. Our cost model 

can be improved with further research of the cost and 

performance of these devices. Our model also needs data 

about losses in high-voltage transmission cables, which were 

not available from manufacturers during our study. 

Our studies illustrate how wind farm layout affects collection 

system cable losses and cost. Changes in cable size will move 

cable cost and performance in opposite directions. These 

tradeoffs between configuration, cost, and performance point 

to the importance of performing parametric studies of the 

entire system to seek optimum configurations. The 

comparisons we made of our transmission system cost data to 

published data for wind farms showed that our costs matched 

very well. 

One critical research need for offshore wind farm electrical 

systems is technology for nonstatic power cable terminations. 

Submarine power cable technology is vulnerable to fatigue 

failures. Fatigue-resistant cable technology must be developed 

if floating platforms are to be used for offshore wind farms in 

deep water. 

Acknowledgments 

This work was funded by the U.S. Department of Energy 

(DOE) Wind Technology Program. The DOE Office of 

Science funded the Student Undergraduate Laboratory Intern 

program that brought Ms. Bowen onto our team. The authors 

wish to acknowledge the support of our colleagues at the 

NWTC, Walt Musial, Maureen Hand, and Alan Laxson, for 

helping us to formulate and scope this study. Roger 

Rosenquvist, Ove Tollerz, and Bo Martinsson of ABB were 

particularly helpful in providing information as to the cost of 

and technologies used in submarine power cables. We are 

grateful to Neil Giles of Nexans and Safiq Virani of Fujikura 

for providing budgetary cost estimates for cables. Bill Wall of 

Caldwell Marine International was particularly helpful on the 

logistics of submarine cable installation. 

6
References 

[1] W. Musial et al. “Energy from Offshore Wind. 2006 

Offshore Technology Conference, Houston, Texas. May 

2006. NREL Report No. CP-500-39450. 

[2] T. Ackermann, “Transmission Systems for Offshore Wind 

Farms,” Wind Power in Power Systems, Ed. T. 

Ackermann, West Sussex, England: John Wiley & Sons, 

Ltd., 2005, pp. 479 - 503. 

[3] T. Ackermann, “Technical/Economic Feasibility Of 

Different Technologies for Transmission System Between 

Offshore Wind Farm and the Shore,” September, 2006. 

DOWNVInD Project, Deliverable no. 1-4. 

[4] S. D. Wright, A.L. Rogers, J. F. Manwell, and A. Ellis, 

“Transmission Options for Offshore Wind Farms in the 

United States,” in Proceedings of the AWEA Annual 

Conference, 2002, pp. 1 – 12. 

[5] Horns Rev Offshore Wind Farm Homepage, July 2006, 

http://www.hornsrev.dk/Engelsk/default_ie.htm 

[6] P. McShane, “Vegetable-Oil-Based Dielectric Coolants,” 

IEEE Industry Applications Magazine, vol. 8, no. 3, pp. 

34–41, May–June 2002. 

[7] P. Nielson, “Offshore Wind Energy Projects Feasibility 

Study Guidelines,” [Online document], 2003 June (Ver 

3.0), [cited 2006 Aug 07], http://www.emd.dk/Projects/ 

Projekter/Seawind/OTHER%20RELEVANT%20DOCOP

PERMENTS/Feasibility%20Study%20Guidelines.pdf 

[8] G. Gerdes, et al. Case Study: European Offshore Wind 

Farms – A Survey for the Analysis of the Experiences and 

Lessons Learnt by Developers of Offshore Wind Farms – 

Final Report. Published by the EU project “POWER – 

Pushing Offshore Windfarm Regions.” No date given. 

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PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ORGANIZATION.

1. REPORT DATE (DD-MM-YYYY)

March 2007 

2. REPORT TYPE

Conference paper 

3. DATES COVERED (From - To)

April 30 - May 3, 2007 

5a. CONTRACT NUMBER

DE-AC36-99-GO10337 

5b. GRANT NUMBER

4. TITLE AND SUBTITLE

Electrical Collection and Transmission Systems for Offshore Wind 

Power: Preprint 

5c. PROGRAM ELEMENT NUMBER

5d. PROJECT NUMBER

NREL/CP-500-41135 

5e. TASK NUMBER

WER7.6001 

6. AUTHOR(S)

J. Green, A. Bowen, L.J. Fingersh, and Y. Wan 

5f. WORK UNIT NUMBER

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

National Renewable Energy Laboratory 

1617 Cole Blvd. 

Golden, CO 80401-3393 

8. PERFORMING ORGANIZATION 

REPORT NUMBER

NREL/CP-500-41135 

10. SPONSOR/MONITOR'S ACRONYM(S)

NREL 

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

11. SPONSORING/MONITORING 

AGENCY REPORT NUMBER

12. DISTRIBUTION AVAILABILITY STATEMENT

National Technical Information Service 

U.S. Department of Commerce 

5285 Port Royal Road 

Springfield, VA 22161 

13. SUPPLEMENTARY NOTES

14. ABSTRACT (Maximum 200 Words)

The electrical systems needed for offshore wind farms to collect power from wind turbines—and transmit it to shore—

will be a significant cost element of these systems. This paper describes the development of a simplified model of the 

cost and performance of such systems. 

15. SUBJECT TERMS

wind energy; wind turbines; transmission systems; wind electrical systems; offshore wind development 

16. SECURITY CLASSIFICATION OF: 19a. NAME OF RESPONSIBLE PERSON 

a. REPORT 

Unclassified 

b. ABSTRACT 

Unclassified

c. THIS PAGE 

Unclassified

17. LIMITATION 

OF ABSTRACT

UL 

18. NUMBER 

OF PAGES 

19b. TELEPHONE NUMBER (Include area code)

Standard Form 298 (Rev. 8/98) 

Prescribed by ANSI Std. Z39.18