Covering 10% of the world's hydropower reservoirs with Floatovoltaics would provide the same amount of electrical capacity as is currently available for fossil-fuel power plants. However, the environmental and social consequences must be assessed.
|Reservoirs could be used instead of land to host solar panels. Credit: Valentyn Semenov/Alamy|
To decarbonize electricity, solar panels must be deployed over vast areas worldwide. The United States may require up to 61,000 square kilometers of solar panels by 2050, an area larger than the Netherlands1. Land-scarce countries like Japan and South Korea may have to dedicate 5% of their land to solar farms2.
The location of these panels is not a simple matter. The land is in high demand, as it is also required for food production and biodiversity conservation. Floating solar panels (' Floatovoltaics ') on reservoirs are one emerging solution.
The concept of Floatovoltaics holds great promise, and installation and investment have increased rapidly. However, many unknowns about the technology's environmental, social, technical, and economic implications.
These knowledge gaps must be filled as soon as possible to avoid overstating the benefits of this approach or having its implementation stymied by unexpected roadblocks.
Solar power requires at least 20 times the space of conventional fossil-fuel plants to produce one gigatonne (GW) of electricity3. Several environments have been proposed as potential locations for large-scale installations, each with advantages and disadvantages.
Deserts receive plenty of sunlight and have little competition for land use. However, there are trade-offs even here. For example, modeling suggests that the dark color of large swaths of solar panels in the Sahara would alter local temperatures and global airflow patterns, potentially causing droughts in the Amazon and sea-ice loss in the Arctic4.
Solar-energy developments in the Mojave Desert of the United States' southwest have reduced the cover of cacti that are culturally significant to local Native Americans. Furthermore, getting energy from remote desert regions to where it is needed can be difficult logistically.
Agricultural fields are another promising option, but researchers are only now beginning to understand how combining solar panels with crops in ' agrivoltaic ' systems affects food production6. Rooftops, parking lots, and highways are viable options, but their scale is limited.
Solar arrays on reservoirs could provide numerous benefits. The arrays are simply conventional solar panels mounted on floats and secured with mooring lines. Because of their proximity to water, floating panels are about 5% more efficient than land-based ones. Arrays protect the surface from the sun and may reduce evaporation, allowing water to be retained for hydropower, drinking, and irrigation.
Hydropower reservoirs already have grid infrastructure in place to transport electricity to consumers, lowering transmission costs. Combining solar and pumped-storage hydropower could address the dual challenges of providing energy when sunlight is scarce and storing it as potential energy in reservoirs when solar power production is abundant.
Floatovoltaics may also reduce the carbon intensity of some hydropower operations (emissions per unit of energy produced). Many hydropower plants emit the same amount of CO2 as other renewables. However, some projects emit so much methane — a potent greenhouse gas — from decaying submerged plant matter that they can emit the same amount of carbon per unit of energy as fossil-fuel power plants. For some of these sites, installing solar panels on just 2% of the reservoir's surface could double electricity production, halving carbon intensity — an important metric in climate policy.
For the time being, Floatovoltaics are a minor component of the electricity picture. The global installed capacity of floating solar panels was only 3 GW11 in 2020, compared to over 700 GW for land-based solar systems. However, given the vast number of reservoirs worldwide — with a total area roughly equivalent to that of France — the potential for expansion is significant. Covering 10% of the world's hydropower reservoirs with floating solar panels would result in nearly 4,000 GW of solar capacity — the equivalent of all fossil-fuel plants in operation worldwide.
Floatovoltaics are currently more expensive than land-based ones, but only marginally: despite the market's immaturity, the break-even cost of floating solar projects is only 4–8% higher than that of ground-mounted solar power. The market is rapidly expanding, with dozens of projects in the works. One project, scheduled to be completed by 2024 in Batam, Indonesia, aims to generate 2.2 GW by deploying solar panels across 16 km2 of water, nearly doubling global Floatovoltaics energy production.
The rapid adoption of any new energy technology can have unanticipated consequences. Wind turbines, for example, have been shown to harm birds and bats, and their installation offshore can cause noise pollution for marine life, disrupt whale migrations, and complicate commercial fisheries.
In both theory and practice, trade-offs between the expansion of Floatovoltaics and environmental, social, and economic goals remain largely unexplored. Reservoirs are man-made ecosystems that have been criticized for a variety of negative socio-environmental effects. However, in many places, they also serve as wildlife habitats and play an important role in fisheries and recreation. Reservoir management frequently serves multiple purposes in addition to water supply, such as flood control and hydropower. Climate change will put additional strain on reservoirs' multiple uses.
Neglecting these trade-offs may increase public opposition to Floatovoltaics, lengthen the environmental-impact approval process, and deter private investors, all of which could stymie the decarbonization transition.
Nature 606, 246-249 (2022) Doi: https://doi.org/10.1038/d41586-022-01525-1