Momentum transport in renewable energy systems: Wind farms and solar photovoltaic plants*

Renewable energy systems are an integral part of the critical need towards decreasing reliance on fossil fuels and having a direct positive impact on climate change. Both wind and solar energy are key technologies within the portfolio of renewable energy. Pertaining to fluid mechanics, wind and solar photovoltaic (PV) plants have a tight coupling with the atmospheric turbulent boundary layer and in the case of offshore wind plants there is also a dependence on the sea state. Given the complex interactions, there is a need for the understanding of the fluid flow physics of these systems with important benefits in power production, system reliability and improved models to name a few. Scaled experiments are performed and evaluated for these systems to explain the role of turbulence in the transport of momentum. Particle image velocimetry is used to obtain flow fields which ultimately lead to a momentum balance. Results demonstrate that the nonlinear dynamics of the flow capture fundamental aspects of the flow physics. In the case of offshore wind turbines, the wind-wave-wake coupling and flow structure are investigated and a dependence on the wave state is shown. In solar PV plants, strategies which decrease the operating temperature of the PV plant are examined playing a key role on power gains; here, the role of momentum transport is also elucidated. Findings are more broadly discussed in the context of their implementation and their impact on energy production.