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The main project deliverable for the Mid-Atlantic Offshore Wind Integration & Transmission (MAOWIT) wind resource team during 2012 Quarter 4 was wind power forecasts for build blocks along the Atlantic Wind Connection (AWC). Blaise Sheridan, University of Delaware (UD) analyzed bathymetry and competing uses along the AWC and provided the wind forecasting team (Mike Dvorak, Sailor's Energy and Cristina Archer, UD) with geographic files of build-blocks for 5 different buildout scenarios of 8, 28, 40, 55, and 78 GW of installed offshore wind power capacity. For the PJM interconnection, these capacities correspond to 4, 12, 18, 24, and 34% penetration, respectively, based on 35% capacity factor assumption and the average 2010 PJM load of 79.6 GW.
Four buildout scenarios were defined over nine different blocks (1-9), located along the AWC. Nine different blocks were built out over four different build scenarios(1-4). Each sub-block is labeled as [block_ID].[build_order]. For example, sub-block 8.3 in Figure 1 would correspond to the third buildout of the eighth block. Nine build areas were identified by Sheridan, et al. (2012) based on bathymetric and use-conflict analysis.
Figure 1: Mean 90-m wind resource from 2006-2010 (Dvorak, et al., 2012), MAOWIT bulild blocks (Sheridan, et al., 2012), and NDBC observations used for "actuals" (buoy 44017 off Long Island, New York and 44020 in Nantucket Sound are not shown). Depth contours of 30, 50, and 200-m correspond to monopile, muti-leg, and floating-turbine foundations. Click on image for full-size map.
|Build order||Turbines (count)||Capacity (MW)||Cumulative capacity (MW)|
|Build order||Block ID||Turbines (count)||Capacity (MW)|
The power forecast is the average power output for the entire lease sub-block for that 10-minute period in MW. All of the WRF grid points covered by the sub-block are included in the average. The observed power is the nearest NDBC buoy or tower (i.e. the Chesapeake Lighthouse (CHLVW) at 43 m height) scaled up to 90-m using log-law with z0=2E-4 m, similar to Dvorak, et al. (2010). All nine NDBC buoys and towers used are shown in Figure 1.
The power is calculated for each sub-block with 10Dx10D spacing of a REpower 5M (D=126 m) as follows:
|Sub-block power [MW]||= blockAreaKm2/(10*126 m*10*126 m/1E6 m^2*km^2)/1000 kW/MW * forecastKw * arrayLossFactor|
|= blockAreaKm2 * 0.62988 MW/km^2 * forecastKw * arrayLossFactor|
where forecastKw is the average power output from the REpower 5M 5.0 MW turbine in kW (calculated with the average 90m wind speed for the entire sub-block) and the arrayLossFactor is set at 90%, similar to Dvorak, et al., 2012.
Power forecasts with 10-min time resolution were generated for each MAOWIT bulid-block every 24-hr using WRF-ARW on the UD Mills Cluster. WRF-ARW was initialized using the 12Z NAM forecast and started at 16Z during daylight saving time (DST) and 17Z for no DST. These times correspond to local noon (12:00 LST) for the US East Coast. Forecasts were started every 24-hr and run for 48-hr, creating power forecasts that overlapped by 24-hr. The NAM forecast was used to update the WRF-ARW boundary conditions every hour from 0-36 hr and every 3-hr after the 36-hr forecast.
Offshore meteorological observations are sparse and generally taken at the surface, making model validation at the turbine hub height of 90-m infeasible. A simplifying assumption was made to take the nearest offshore observation to the build block, scale that observation up to the turbine hub height using the log-law, and use this calculated wind speed to determine the "observed power" by running this wind speed through the REpower 5M power curve. Forecasting error is likely increased using this methodology due to the spatial offset of the forecast and in-situ observations. The validity of this assumption should be explored in future research.
The general algorithm to create the 10-min power forecast and "observed power" is as follows:
Sheridan, B., Baker, S. D., Pearre, N. S., Firestone, J., & Kempton, W. (2012). Calculating the offshore wind power resource: Robust assessment methods applied to the U.S. Atlantic coast. Renewable Energy, 43, 224-233. doi: 10.1016/j.renene.2011.11.029
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