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Floating solar farms

Power plants on reservoirs and lakes offer a sustainable option for increasing electricity generation in the country

Photovoltaic panels on the largest floating solar park in Europe, operating in Piolenc, southern France, since 2019

Gerard Julien / AFP via Getty Images

Power generation by photovoltaic solar panels accounts for about 11% of the Brazilian electricity mix. This percentage could grow in the future as panels are increasingly installed on the roofs of houses and industrial buildings, in fields, and on floating platforms. A recent Brazilian study shows that installing floating solar farms on just 1% of dam reservoirs would allow the country to generate enough clean and renewable energy to supply 16% of the country’s electricity demand. That would be equivalent to the amount provided by the Itaipu hydroelectric plant, the second largest in the world.

Electricity generation is not the only benefit of floating photovoltaic (FPV) systems. They are also capable of reducing evaporation from reservoirs, improving retention in locations where water security is low, such as Brazil’s semiarid region.

The findings were made by the Energy Planning Program (PPE) team at the Alberto Luiz Coimbra Institute for Engineering Research and Graduate Studies of the Federal University of Rio de Janeiro (COPPE-UFRJ). Two articles describing the results were published in international scientific journals. The study on the technical potential of producing electricity using FPV systems was published in the January 2022 issue of Renewable Energy.

The second study, which focused on how FPV systems can prevent water evaporation at dams in semiarid areas, was initially defended as a doctoral thesis at the PPE by agricultural engineer Mariana Padilha Campos Lopes, supervised by Marcos Aurélio Vasconcelos Freitas and David Castelo Branco, both from COPPE. An article presenting the results of the thesis was later published in the Journal of Cleaner Production in November 2020.

“Any type of covering over the water affects the variables behind evaporation, such as direct solar radiation hitting the water’s surface, wind speed, and ambient temperature,” explains Lopes. “In addition to reducing evaporation, FPV systems generate energy that can be used to power water pumps and irrigation systems or even to supply electricity to the grid.”

The researcher based her work on the 618 dams in the Apodi-Mossoró basin, Rio Grande do Norte, where 45% of the water in the reservoirs evaporates every year, on average. This leads to dam reservoirs frequently reaching critically low levels, forcing public authorities to seek water from other locations to supply local residents using water trucks.

Alexandre Affonso / Revista Pesquisa FAPESP

Installing FPV panels over just dead volume areas at dams in the Apodi-Mossoró basin would generate enough electricity to supply 1.33 million homes, meaning it would easily supply the entire population of Rio Grande do Norte, where there are a total of 1.23 million homes. The dead volume refers to the deepest areas of a reservoir, where the water is below the catchment pipes. The study highlighted that 20.6 million cubic meters (m³) of water would be saved annually, around three times the entire volume of Rodrigo de Freitas Lagoon in Rio de Janeiro. If solar panels covered 50% of the total area of the reservoirs in the Apodi-Mossoró basin, enough energy would be generated to supply 5 million homes and the total volume of water preserved could fill Rodrigo de Freitas Lagoon 13 times.

The technology used in FPV systems is no different to that used in ground-based solar farms or panels installed on rooftops, which have become a common sight nationwide. The only difference is that the panels are mounted on a floating platform which is held in place by an anchoring system (see infographic below). The Brazilian Power Research Company (EPE), linked to the Ministry of Mines and Energy (MME), published a technical report in 2020 titled “Expansion of generation – floating photovoltaic solar” in which it calculated that floating platforms and anchors increase the cost of installing a solar farm by about 25% compared to ground-based systems. When all of the factors involved are taken into account—including the cost of purchasing and preparing land for installation of ground-based plants—the EPE estimated that floating systems are 18% more expensive, on average.

In the same report, the EPE noted that floating systems can generate energy more efficiently. The silicon cells in photovoltaic panels lose efficiency as temperatures increase. When they are installed on water, the operating temperature is between 5% and 20% lower than when placed on land, depending on the local climate. The extent of any efficiency gain, however, is disputed among international experts on the subject. Experimental studies show different results, ranging from no clear benefit to gains of more than 20%. The most common estimates are gains of between 9% and 15%.

Freitas from COPPE believes that the initial investment cost is hindering the advance of FPV systems in Brazil. “Floating solar farms have great potential, but they are not particularly attractive to investors,” he says. “Brazil has a lot of land available for ground-based photovoltaic plants, an approach that is well-known and tested.” Another obstacle is that there are still no studies in Brazil on the impact FPV systems have on the aquatic environment and no licensing or authorization procedures have been established by the National Water Agency (ANA) for the use of water bodies to generate energy.

Global electricity production from FPV systems reached 2.6 gigawatt-peak (GWp) in 2020—a measurement that represents the maximum power generated at the production peak—according to the authors of the Renewable Energy article. The technology is most widely used in Japan and South Korea, due to the lack of land available for ground-based power plants, and in China, which primarily uses floating systems on mine pit lakes. In countries such as Australia, Spain, India, Iran, Jordan, Chile, and the USA, there is greater investment in the system in arid and semiarid regions, with the aim of reducing evaporation and increasing water security. Portugal is another country where the approach is already being used.

Brazil has great potential for FPV systems, says Lopes, due to the variety and number of water bodies in the country. There are around 241,000 water bodies cataloged by the ANA, including hydroelectric dam reservoirs, lakes, lagoons, rivers, and basins. The COPPE study encompassed 174,500 artificial water bodies, including reservoirs at hydroelectric dams and others used for irrigation and human consumption. Since they are manmade, rather than natural lakes, using them would have less of an environmental impact.

The study proposed that installing solar panels on 1% of the surface of these artificial water bodies, which would correspond to a total area of 45,500 square kilometers (km²), would generate 79,377 gigawatt hours (GWh) of electricity per year from nominal power of 43,276 megawatt-peak (MWp). That would represent about 12.5% of all electricity produced in Brazil, while Itaipu accounts for 12.7%. The energy generated by FPV systems would be enough to supply around 41 million homes.

Alexandre Affonso / Revista Pesquisa FAPESP

The most suitable sites for floating solar farms are the reservoirs of hydroelectric power plants. According to the study, they alone account for 73% of the country’s total potential. Freitas highlights that these dams offer an important competitive advantage for FPV projects based on potential synergies between hydroelectric and solar generation, such as joint use of the electricity grid.

Rodrigo Sauaia, executive president of the Brazilian Photovoltaic Solar Energy Association (ABSOLAR), says that there are many interesting characteristics of floating solar farms, especially their potential for use in flooded areas, reducing the demand for land, their higher efficiency, and the fact that they reduce evaporation in reservoirs. “This set of advantages is attracting the interest of investors. Several are currently seeking out more information,” he says.

According to Sauaia, adequate regulations for FPV systems had been lacking, but that changed when Law 14,300 came into effect in January 2022. The new legislation classified floating solar plants in the same category as micro- and mini-power generators (up to 5 MW) and granted them tax benefits designed to incentivize infrastructure development (the REIDI tax regime).

In November, Brazil’s solar energy generation capacity reached 22 gigawatts (GW) with large ground-based farms representing 7 GW and panels on roofs and small plots of land accounting for 15 GW. “Solar power is the fastest-growing energy source in the country and floating photovoltaic farms have great potential to further expand the generation of renewable energy,” says Sauaia.

The Brazilian experience
The country’s first commercial floating solar farm will be built in Fernando de Noronha

Brazil’s current floating photovoltaic plants are all experimental. Brazilian electric utilities company Eletrobras produces 5 megawatts (MW) at the Balbina hydroelectric plant in Amazonas and 1 MW on the reservoir of the Sobradinho hydroelectric plant in Bahia. The São Paulo Energy Company (CESP) produces 50 kilowatts (kW) at the Rosana plant in São Paulo.

Eletrobras-CHESFOne of Brazil’s experimental floating solar farms on a reservoir at the Sobradinho hydroelectric plant in BahiaEletrobras-CHESF

In October last year, the Neoenergia group and Pernambuco Sanitation Company (COMPESA) announced the construction of a floating photovoltaic plant on the reservoir of the Xaréu dam, a 4,900 m2 area on the Fernando de Noronha archipelago in Pernambuco. It is estimated that the system will be capable of generating 1,238 megawatt-hours (MWh) per year and will supply more than 40% of the island’s energy demand. Switching from thermal generation to solar will reduce the amount of carbon dioxide (CO2) emitted annually in Fernando de Noronha by 1,600 tons. Roughly R$10 million will be invested in the project.

According to Neoenergia’s head of energy efficiency Ana Christina Mascarenhas, building the new solar farm on the Xaréu dam reservoir, which accounts for about 25% of the water on the island, is important because there is limited space on land for photovoltaic plants in Fernando de Noronha. “The benefits of preventing evaporation and retaining water in the reservoir also influenced the decision, although it was not the main factor,” says Mascarenhas.

Scientific articles
LOPES, M. P. C. et al. Technical potential of floating photovoltaic systems on artificial water bodies in Brazil. Renewable Energy. jan. 18, 2022.
LOPES, M. P. C. et al. Water-energy nexus: Floating photovoltaic systems promoting water security and energy generation in the semiarid region of Brazil. Journal of Cleaner Production. nov. 10, 2020.