Untapped Wealth : Technical Methodology Oceana’s report, Untapped Wealth , provides an analysis of the technological feasibility and cost effectiveness of offshore wind power. It does not attempt to detail specific ecologically sound practices, methods, or specific areas for development of offshore wind farms. Nor does it represent the level of accuracy needed for establishing siting criteria for specific offshore wind farm projects. Untapped Wealth highlights the substantial offshore wind resources available considering current technology and economic limitations. As technology advances, the ability to harvest offshore wind energy is expected to become more efficient and the estimates in this analysis do not consider future learning curves, technology improvements or price reductions. The estimates herein represent near-term, achievable offshore wind resource potential. Overall, Untapped Wealth relies on multiple conservative assumptions in developing estimates for offshore wind power production. At the same time, it may overestimate potential for Atlantic offshore oil and gas production. Despite this attempt to understate the benefits of offshore wind power and overstate the benefits of oil and gas, the analysis shows that offshore wind power offers greater energy production potential than new offshore oil and gas development. This document explains in detail the methodology used to obtain the estimates in the report. For additional details please contact Oceana directly. Estimating Potential Capacity Analytical Constraints Untapped Wealth aims to evaluate the most economically attractive areas for offshore wind development, and therefore quantify the total area where offshore wind farms could reasonably be built in the near term given the physical and economic limitations. Not all offshore areas are technically or economically useful for offshore wind farm development, and development in some areas should be restricted due to competing uses or ecological concerns. Several limitations reduce the likelihood of offshore wind farm development in a given area. Important limiting variables include ocean depth, distance from shore, and wind speed. These parameters are rarely entirely dependant on technical capability, rather, they are more commonly dependent on economics. Table 1: Assumptions Used to Determine Area Available for Near-term Offshore Wind Potential Parameter Figure Used Potential Range Limitation basis Hub Height 50 meters 50 Meters NREL Map Availability Water Depth 0-30 meters 0-200 meters Economic Distance from Shore 3-24 nautical miles 0-200 nautical miles Aesthetic, Economic Wind Speed 15.7 MPH + 14.3 MPH - >19.7 MPH Economic (Class 4 +) (Class 3 – Class 7) Carrying Capacity 8 MW/km 2 6 MW/km 2 – 15 MW /km 2 Technological Exclusion Factor 67% 33% - 67% NREL Conservative Estimation 1/17 Hub Height For this analysis, we assume a hub height of 50 meters. This is a conservative assumption because all offshore wind turbines are expected to have hub heights greater than 50 meters. This figure was used, however, because it is the hub height for which wind resource data are provided by the National Renewable Laboratory (NREL). The NREL does not provide data for greater hub heights which would offer higher capacity factors and thus, more energy generation. As a result, the true amount of energy generated by higher hubs would be considerably greater in practice. Water Depth For this analysis, we limit the area available for offshore wind production to waters less than 30 meters deep. While it is likely that wind farms will be built in deeper waters in the coming decades, to date, all commercial offshore wind farms are in waters less than 30 meters deep. 1 The analysis is therefore limited to include only areas less than 30 meters deep, a conservative limitation. Bathymetry maps with a clear 30 meter delineation were generated in *.KMZ format and overlain in Google Earth using an application created by Columbia University (GeoMapApp) with a 100 meter resolution. 2 Distance from Shore The area between 3-24 nautical miles from shore was measured and considered to be the full extent of the area available for offshore wind farm development prior to the exclusion of some areas using the exclusion factor described below. Distance from shore is more of an aesthetic and economic constraint than a technological one. For this analysis, we assume there is no development within 3 nautical miles from shore, another conservative assumption to account for possible aesthetically driven limitations, as suggested by other, similar studies.3 As offshore wind farms move further offshore costs increase 4 making it less likely offshore wind farms will be built further than 24 nautical miles in the near-term so this analysis was limited to areas less than 24 nautical miles from shore. As technology advances, offshore wind farms very well may become economically competitive at greater distances making this assumption again, a conservative one. Wind Speed Only wind speeds of 15.7 mph or greater are included in the analysis. The Department of Energy (DOE) has estimated that a substantial amount of electricity can be generated with wind speeds of 15.7 miles per hour (mph) offshore (Class 4 winds) for close to 12 cents per kilowatt hour of electricity generated. 5 As offshore wind turbines become technologically more efficient, lower wind speeds may prove more and more suitable for offshore wind development, which would increase the amount of wind energy that could be generated in the areas considered. However, this analysis excludes all offshore areas with wind speeds less than 15.7 mph (or less than Class 4 winds). Carrying Capacity Based on existing offshore wind farms and case studies, one square kilometer of sea area could support six to fifteen megawatts of offshore wind power capacity, using current technology (6 MW/km 2 - 15 MW/km 2). Untapped Wealth relies on a mid-range carrying capacity of 8 MW/ km 2, based on planned and operating offshore wind farms. The installed offshore wind farm most resembling this carrying capacity is Horns Rev, of Denmark; however, while other wind farms have higher values. Carrying capacity varies by turbine type, primary wind direction, wind velocity and turbulence. Actual projects would apply specialized studies to maximize output based on wind farm layout and would vary in carrying capacity – some farms would have lower carrying capacities and others would have higher capacities compared to the assumption used for this analysis. 2/17 Table 2: Planned and Operating Offshore Wind Farms Project Country Capacity Turbine size MW/km 2 ratio Gwynt y Môr 6 United Kingdom 750 MW 3 MW – 5 MW 6.1 MW/km 2 Maryland Case Study 7 United States - 5 MW 6.3 MW/km 2 Virginia Case Study 8 United States - 3 MW 6.4 MW/ km 2 Delaware Case Study 9 United States - 3.6 MW 6.7 MW/km 2 Cape Wind 10 United States 468 MW 3.6 MW 7.2 MW/km 2 Horns Rev 11 Denmark 160 MW 2 MW 8 MW/km 2 Barrow 12 United Kingdom 90 MW 3 MW 9 MW/km 2 Rhyl Flats 13 United Kingdom 90 MW 3.6 MW 9 MW/km 2 Kentish Flats 14 United Kingdom 90 MW 3 MW 9 MW/km 2 Clipper Wind United Kingdom - 10 MW 9.8 MW/km 2 MBE turbine 15 European Case Study 16 - 3 MW – 10 MW 10 MW – 15 MW/km 2 Alpha Ventus 17 Germany 60 MW 5 MW 15 MW/km 2 Italics indicate planned projects Bold indicates chosen carrying capacity Exclusion Factor Some areas that are technically available for wind power production might be off limits for a variety of reasons, including environmental concerns or national security. In order to account for such areas, an “exclusion factor” is often used to eliminate some otherwise available areas from estimations of available resource. To exclude such areas and determine the total available resource Untapped Wealth relies on an exclusion factor of 67 percent – thus excluding two thirds of the areas that would otherwise meet the criteria described above. This is at the conservative end of the range of exclusion factors generally used in this type of analysis.18 To be clear, for the technically and economically available resource, the analysis excludes 100 percent of areas between 0-3 nautical miles and beyond 24 nautical miles, and all areas greater than 30 meters deep. Then, it further excludes two thirds of the available area between 3 and 24 nautical miles and in waters less than 30 meters deep using the 67 percent exclusion factor This exclusion factor was chosen to prevent overstating the potential benefits of offshore wind development. Other analyses that attempt to map conflict zones have much lower exclusion factors – as low as 33 percent. 19 Capacity Factors The capacity factor takes into account the fact that the wind does not always blow. A project built in a Class 6 wind area would be expected to generate more electricity than if that exact same project were built in an area with Class 4 winds.20 To account for the benefits of higher wind class resources, capacity factors were based on DOE estimates which were developed by Black and Veach. 21 Table 3: Capacity Factors for Shallow Offshore Areas (<30m) at 50 Meter Altitude Power Class Capacity Factor Class 4 0.38 Class 5 0.42 Class 6 0.46 Class 7 0.50 Source: United States Department of Energy, Black & Veach 22 3/17 The capacity factors used in the analysis are also low-end estimates as several offshore wind farms already achieve greater than 45 percent capacity factors.23 Also, as turbines are installed further offshore in deeper areas and as they expand in height and size as expected, capacity factors would be expected to increase accordingly.24 See Capacity Factor Sensitivity Analysis below for a more detailed analysis of the capacity factors used in Untapped Wealth .