Ocean waves could give offshore wind turbines a boost

Floating offshore wind turbines are a rising star among sustainable energy sources. They can be placed in areas too deep for fixed platforms, which gives them access to the strong winds of the open ocean.

But as they bob back and forth in the water, floating turbines experience surging motions that put uneven loads on the blades. While typically thought to be detrimental, some modeling has suggested that the surges of a rocking platform, if properly harnessed, could actually produce higher efficiencies.

Wei and Dabiri set out to test the effects of turbine surge motion on the turbine blade loads and if it could increase turbine efficiency. They first built a platform with rails for a small-scale model wind turbine and placed it inside a wind tunnel. To simulate surging motions, the turbine was then moved along the rails at different frequencies and amplitudes up to 23 percent of the wind speed.

Measuring the torque, rotation rate and turbine output power, the authors created an analytical model to describe the surge motions that depends only on measurements from land-based turbines. The authors also found time-averaged power enhancements up to 6 percent higher in a surging turbine relative to a stationary-turbine case.

“We believe that the model we derived will be of use for designers and operators of floating offshore wind farms, especially given the surge – pun intended – in offshore-wind development over the past few years,” said author Nathaniel Wei. “We hope that this study will inspire creative solutions for improving the efficiency of these wind farms while also increasing their lifespans even when subjected to extreme wind and wave conditions.”

Source: “Phase-averaged dynamics of a periodically surging wind turbine,” by Nathaniel J. Wei and John O. Dabiri, Journal of Renewable and Sustainable Energy, (2022). The article can be accessed at https://doi.org/10.1063/5.0076029 .