Posters

Abstract

The impact of the planetary boundary layer height has recently become an area of focus following industry efforts to better understand the impact of blockage on operational offshore wind farms. It has been proposed that the impacts on wake losses and the distribution of energy production across turbines on offshore wind farms is dependent on the planetary boundary layer heights, as well as atmospheric stability. The effect of planetary boundary layer height has been explored on onshore sites in moderate to complex terrain through operational wind farm power curves as well as multi-point measurements on proposed sites. The approach on the operational sites considered how wind farm power curves vary by binning by stability metrics using day/night, Richardson Number, RMOL, meso-scale based turbulence and temperature gradient, as well as planetary boundary layer height. While the stability metrics impact the wind farm operational power curves to some degree, the largest variations were found when the data was binned for low values of boundary layer height (<500m), showing significant under performance against unbinned data. It is acknowledged that may factors can feed into performance deviations against expectations through the preconstruction modeling chain, so further assessments were carried out using preconstruction meteorological data from multi-point measurements comprising mast and remote sensing datasets, binned in a similar way. Previous assessments have shown variable wind speed ratios if binned using daytime/nighttime as rudimentary stability metric and given the strong coupling of boundary layer height with the day/night cycle a strong dependence on the site wind speed ratios as a function of boundary layer heights was found. Using a sample of multi-mast sites, the behavior was shown to exist across most sites where terrain showed moderate to complex topography, showing that a single wind resource grid blended for stability will not capture the monthly and diurnal cycles closely linked to the boundary layer height. An approach is proposed to capture this offering improvements to eliminate or reduce the risk of bias in preconstruction energy yield analyses on moderate to complex sites.