Wind Shadows Impact Planning of Large Offshore Wind Farms
The technical potential of offshore wind resources greatly exceeds current electricity use. However, areas suitable for bottom-mounted wind turbines close to large coastal demand centers are limited. Thus, an increasing number of offshore wind farms will operate in the wake (or wind shadow) of other wind farms. Maximizing system-wide electricity production and overall energy extraction from offshore wind, while being cognizant of other constraints, requires optimal siting of offshore wind energy lease areas to minimize ‘wind theft’ resulting from wakes generated by upstream wind turbine arrays. Uniquely detailed high-resolution WRF simulations are performed with two different wind farm wake parameterizations to quantify power generation and wake-induced power losses from all offshore wind energy lease areas along the U.S. East Coast.
The U.S. Department of Interior is committed to deploying 30 GW of offshore wind power by 2030. The wind power potential within areas auctioned by BOEM for offshore wind turbine deployments is constrained by available wind turbine technologies, electrical losses, and power losses due to wakes generated within the planned wind farm and wakes from remote (and independently owned and operated) wind farms. The optimal price for a given lease area is thus critically contingent on the estimated wake losses as is the optimal location of new lease areas for BOEM to auction. However, these wake losses are ill-defined due to the lack of quantitative and climatologically representative information regarding the extent and magnitude of wind shadows from other wind farms. Improved quantification of wind farm-wind farm interactions is a key goal of this research.
Based on numerical simulations, Annual Electricity Production (AEP) from areas that have been leased for offshore wind turbine deployments along the U.S. East Coast ranges from 139 to 173 TWh/yr (about 4-5% of current national electricity demand). However, wakes from both local and remote wind turbines are projected to reduce the AEP by 15 to 49 TWh/yr. The simulation output is used with new, robust, innovative tools to generate georeferenced data layers describing whole wind farm wakes (wind shadows) for use in planning and development. It is shown that wind shadows (wake reduction of wind speed) from the existing lease areas degrade the wind resource in up to 25% of the unleased area available after selecting areas with a good wind resource (mean wind speed > 8.2 ms-1) and applying restrictions for water depth, distance to shore and to avoid busy shipping lanes. These results demonstrate the value of efforts to reduce wake losses to maximize power production efficiency. They also emphasize the importance of considering wakes in multi-criteria analyses to identify new lease areas for auction and to determine the resulting purchase price.