Save the Lake! Floating Solar Photovoltaic to Avoid Algae Blooms?

Floating solar photovoltaic modules (FPV) are an incipient technology in which the solar modules float on water bodies instead of being mounted on the ground. This provides an advantage especially for regions with limited space. FPV have other benefits when compared to conventional solar power plants, such as reducing the evaporation losses of the water body and operating at higher efficiency because water reduces the FPV temperature. So far, the literature has focused on the optimal design of FPV for energy production, evaporation reduction and cost analysis.

In this study, we extend the existing body of knowledge by numerically assessing the impact of FPV on the ecology of a hydropower reservoir (Rapel reservoir, central Chile) that suffers from algae blooms. For this purpose, we use a 3D-numerical-hydrodynamic water-quality model (ELCOM-CAEDYM). We compare the current case (no FPV) with scenarios in which FPVs cover the lake, thus reducing the incident short-wave solar radiation from 10% to 100%. We focus on key-indicators of water quality, such as dissolved oxygen, nutrients, and total chlorophyll A.

Furthermore, massively installing FPV on a reservoir may constrain the (minimum) water level to avoid the stranding of the structures. How this issue impacts the operational benefit of hydropower is a second phenomenon that we explore. For this, we use a tool for optimal operation scheduling considering different water and power price scenarios.

We found that installing FPV, such that the lake is shaded between 0 and 20%, has little or no effect on both ecology and hydropower. For FPV installations shading above 40%, the ecological condition improves significantly: algae blooms are avoided. Very high coverages of FPV (>60%) can harm the natural food web in the ecosystem. For coverages below 60%, the economic hydropower losses are small (<5%). Shading over 90% increases them dramatically.

Altogether, we identified that FPV should shade the lake between 40 and 60%, as a convenient trade-off between ecology and costs. However, the installation of FPV may affect the development of aquatic sports and other touristic activities in the reservoir, and these social impacts should also be quantified in the future. These findings are relevant for decision makers from the energy sector as well as from the field of ecohydrology.