Position of Offshore Wind Energy Resources
In response to a request from U.S. Department of Energy's Office of Energy Efficiency and Renewable Energy, NOAA's Office of Oceanic and Atmospheric Research (OAR) and the National Weather Service (NWS) have performed research to provide information about the type and spatial density of observations needed to characterize the wind resource in the offshore environment.
The goal is to lower risk to investors by reducing uncertainty in the offshore wind resource when sites are considered for development of offshore wind farms. The study focused on the Northeast Atlantic coastal region, and NOAA leveraged the 2004 New England Air Quality Study in the POWER project.
The POWER study included the following notable discoveries:
Composite maps of 80-m wind speed predictions from the High Resolution Rapid Refresh (HRRR) model, averaged over two years for the U.S. and coastal waters, revealed many interesting aspects of spatial variations in the offshore wind fields, such as the variability of the cross-shore gradient of wind speed.
The high-resolution Doppler lidar (HRDL) and Ron Brown Ship profiler measurements also illustrated significant spatial and temporal variability of the wind field aloft over the ocean.
The HRRR and its parent, the Rapid Refresh (RAP), generally showed model winds to be biased slowly by 0.5 to 2 m s-1, and model agreement with the measurements was within 2 m s-1 (root mean square error) above 100 m above sea level for the initial conditions.
Data denial experiments indicated that, in general, assimilating additional profiler data improved the model forecasts for several hours over the ocean at the Ron Brown Ship location by up to 0.2 m s-1 (8 percent).
The critical horizontal scales of wind variability offshore are unknown, so they must be determined by measurement, which then could be used to verify if the Numerical Weather Prediction (NWP) models are capable of reproducing the spatial flow variability observed. Long-term arrays of wind-profiling offshore buoys were recommended as an important component of a measurement strategy to understand offshore flow variability. A useful offshore wind-energy measurement network would consist of an appropriate mixture of cross-shore transects of buoy-mounted wind-profiling sensors and along-shore lines of these sensors (several options are presented, depending on the problem to be addressed). Mobile-sensing platforms, such as the Ron Brown Ship and/or aircraft, would be required, along with long-term arrays to characterize along-shore variability and discover recurrent areas of stronger and weaker flows. Intensive Observational Periods (IOPs) are recommended to focus resources and understand meteorological processes driving the flow variability in the along- and cross-shore directions.
An augmentation of boundary-layer profilers inland was recommended for better characterization of the regional meteorology and improved NWP assimilation results.