Evaporation reduction from floating photovoltaics: the hydropower-solar nexus

Floating photovoltaic (FPV) systems are becoming increasingly popular due to many advantages in comparison to conventional PV systems. Combining FPV systems with existing hydro power plants is relatively new, with few global sites, though many studies have explored it across different locations. However, a key unanswered question is how much water evaporation can be saved by adding FPV to a reservoir, and whether the saved volume is meaningful for water management. This paper addresses that gap by focusing on the hydro power plant in El Atazar in Spain and proposes the installation of a FPV covering 2.7% of the surface. The method uses a simplified version of Penman’s equation with local climate data from meteoblue to calculate the reduction in water evaporation caused by the shading effect of the FPV platform. The results show that the total water saved is calculated to be 61.73 m³/year, with a clear seasonal difference: approximately 2.14 m³/day saved in winter versus 8.85 m³/day in summer. To explore scalability, coverages of 15% and 50% are also analysed, yielding annual savings of 338 and 1127 m3, respectively. These transferable findings can be utilised by hydropower operators and water managers to estimate evaporation savings for different FPV coverages.