Floating photovoltaic plants: ecological impacts versus hydropower operation flexibility

Abstract

Floating photovoltaic power plants are a quickly growing technology in which the solar modules float on water bodies instead of being mounted on the ground. This provides an advantage, especially in regions with limited space. Floating modules have other benefits when compared to conventional solar power plants, such as reducing the evaporation losses of the water body and operating at a higher efficiency because the water reduces the temperature (of the modules). So far, the literature has focused on these aspects as well as the optimal design of such solar power plants. This study contributes to the body of knowledge by i) assessing the impact of floating solar photovoltaic modules on the water quality of a hydropower reservoir, more specifically on the development of algal blooms, and by ii) studying the impact that these modules have on the hydropower production. For the first part, a three-dimensional numerical-hydrodynamic water-quality model is used. The current case (without solar modules) is compared to scenarios in which the solar modules increasingly cover the lake, thus reducing the incident sunlight from 0% to finally 100%. The focus is on microalgal growth by monitoring total chlorophyll-a as a proxy for biomass. For the second part, as the massive installation of solar modules on a reservoir may constrain the minimum water level (to avoid the stranding of the structures), the impact on hydropower revenues is examined. Here, a tool for optimal hydropower scheduling is employed, considering both different water and power price scenarios. The Rapel reservoir in central Chile serves as a case study. The response of the system strongly depends on the percentage that the modules cover the lake: for fractions below 40%, the modules have little or no effect on both microalgal growth and hydropower revenue. For moderate covers (40-60%), algal blooms are avoided because of the reduction of light in the reservoir (which controls algal growth), without major economic hydropower losses. Finally, a large solar module cover can eradicate algal blooms entirely (which might have other impacts on the ecosystem health) and results in severe economic hydropower losses. Altogether, an optimum range of solar module covers is identified, presenting a convenient trade-off between ecology health and costs. However, a massive deployment of these floating modules may affect the development of touristic activities in the reservoir, which should be examined more closely. In general, the findings herein are relevant for decision-makers from both the energy sector and water management.