Effect of surface waves on estimates of offshore wind energy and turbulence intensity

Abstract

Offshore wind resource assessment traditionally uses scaling formulas, such as power-law and logarithmic wind profiles with fixed surface roughness, to extrapolate near-surface wind measurements to turbine heights, overlooking the dynamic role of ocean waves. Here, the authors systematically examine how wave-informed scaling impacts offshore wind power and ambient turbulence estimates, considering a logarithmic wind profile with variable sea-surface roughness and a wave-spectrum-dependent drag coefficient formulation. Seasonal expected wind power density, turbulence energy density, and turbulence intensity are evaluated at a representative hub height of 110 m using high-resolution observations from a NOAA buoy in the Northwest Atlantic. The spectral-bandwidth-based formulation yields the highest estimates of power and turbulence across all seasons, outperforming the variable-roughness approach by approximately 20% in winter, 40% in summer, and up to 50% in transitional months, due to its sensitivity to mixed sea states. The power-law approach ranks second, yielding about 20% higher power than the constant-roughness method year-round. The wave-informed variable-roughness formulation offers intermediate estimates relative to the two wave-independent methods. Comparison with existing literature supports these results, showing that the spectral-bandwidth formulation exceeds the published annual mean power density by approximately 23%. Although these findings are not transferable to other oceanic regions and variations in air density and atmospheric stability have not been considered, this study clearly demonstrates the importance of incorporating wave characteristics into the analysis.