How thermally-induced secondary motions in offshore hybrid wind-solar farms improve wind-farm efficiency

TL;DR

This study uses large-eddy simulations to show that thermally-induced secondary motions in offshore hybrid wind-solar farms can significantly enhance wind farm efficiency by increasing wind speeds between solar arrays, leading to up to 30% power gains.

Contribution

First investigation of atmospheric boundary layer interactions with offshore hybrid wind-solar farms, revealing secondary flow effects that improve wind farm performance.

Findings

Secondary motions caused by temperature differences increase wind speeds.

Hybrid farms with aligned solar panels can boost power output by up to 30%.

The heterogeneity Richardson number $Ri_h$ influences secondary flow formation.

Abstract

Integrating floating photovoltaic (FPV) installations into offshore wind farms has been proposed as a major opportunity to scale up offshore renewable energy generation. The interaction between these hybrid wind-solar farms and the atmospheric boundary layer (ABL) is for the first time addressed in the present study. Idealized large-eddy simulations (LES) are used to investigate the flow through both isolated wind and solar farms, as well as combined wind-solar farms, in varying configurations and under different atmospheric conditions. When the FPV modules are arranged in long strips parallel to the flow direction, secondary motions arise due to the temperature difference between the warm FPV modules and colder sea surface, significantly affecting the horizontal distribution of mean wind speed in the ABL. Associated downdrafts between the strips increase entrainment of high-speed momentum from above, thereby increasing the wind speed at these locations. LES of hybrid wind-solar farms reveals that this is beneficial for wind turbines when they are located between the FPV arrays, leading, for the cases that we considered, to a farm-averaged power increase of up to 30% compared to an isolated wind farm. It is shown that the ratio between inertial and buoyancy forces, quantified by a heterogeneity Richardson number $Ri_h$, plays a crucial role in the formation of secondary flows and the resulting wind-farm power enhancement. We further show that no significant power gains, but also no losses emerge in situations when the solar panels are aligned perpendicular to the flow. Although the present results suggest a large potential for wind-solar hybridization, future research should focus on a wider range of scenarios, obtained from a realistic distribution of wind directions and speeds to quantify the potential beneficial impact on real annual power production.