Offshore wind profile extrapolation effects on energy production estimates in Southeast Brazil

This research examines how stable stratifications occur and influence energy production predictions along Brazil's Southeast offshore region. The investigation focuses on a notable stable condition on July 3, 2019, detailed in a spatiotemporal analysis using the reanalysis dataset and a numerical atmospheric model. Moreover, we analyze reanalysis data of the air temperature at 2 m and the sea surface temperature (SST) to investigate the influence of atmospheric stability in the surface layer. We also measured the wind up to a height of 150 m using a wind profiler at a floating production storage and offloading vessel located about 190 km off the coast in the pre-salt oil extraction region. Stable conditions arise when warm air in the vanguard of the cold front passes over a relatively colder sea surface. An important finding reveals that air and sea are locally decoupled, where the wind profile is modified before the air surface temperature surpasses the sea surface temperature at the vessel due to the stable upstream conditions associated with the upwelling of cold water near the coast. Finally, we assess the stable stratification effects on annual energy production using three methods to extrapolate wind speeds from reanalysis data at a reference altitude of 100 m to the hub height of 150 m for a reference 15 MW wind turbine. Our results indicate that extrapolation methods for stable conditions may lead to overprediction in annual energy production projections ranging from 1.2% to 9.7%.