Floating solar or floating photovoltaics (FPV), sometimes called floatovoltaics, are solar panels mounted on a structure that floats on a body of water, typically a reservoir or a lake such as drinking water reservoirs, quarry lakes, irrigation canals or remediation and tailing ponds. A growing number of such systems exist in China, France, Indonesia, India, Japan, South Korea, the United Kingdom, Singapore, and the United States.^{[1][2][3][4][5]}

The systems can have advantages over photovoltaics (PV) on land. Water surfaces may be less expensive than the cost of land, and there are fewer rules and regulations for structures built on bodies of water not used for recreation. Life cycle analysis indicates that foam-based FPV^[6] have some of the lowest energy payback times (1.3 years) and the lowest greenhouse gas emissions to energy ratio (11 kg CO₂ eq/MWh) in crystalline silicon solar photovoltaic technologies reported.^[7]

Floating arrays can achieve higher efficiencies than PV panels on land because water cools the panels. The panels can have a special coating to prevent rust or corrosion.^[8]

The market for this renewable energy technology has grown rapidly since 2016. The first 20 plants with capacities of a few dozen kWp were built between 2007 and 2013.^[9] Installed power grew from 3 GW in 2020, to 13 GW in 2022,^[10] surpassing a prediction of 10 GW by 2025.^[11] The World Bank estimated there are 6,600 large bodies of water suitable for floating solar, with a technical capacity of over 4,000 GW if 10% of their surfaces were covered with solar panels.^[10]

The costs for a floating system are about 10-20% higher than for ground-mounted systems.^[12][13]

History

American, Danish, French, Italian and Japanese nationals were the first to register patents for floating solar. In Italy the first registered patent regarding PV modules on water goes back to February 2008.^[15]

The first floating solar installation was in Aichi, Japan, in 2007, built by the National Institute of Advanced Industrial Science and Technology.^[9][16]

In May 2008, the Far Niente Winery in Oakville, California, installed 994 solar PV modules with a total capacity of 175 kW onto 130 pontoons and floating them on the winery's irrigation pond.^[9][17] Several small-scale floating PV farms were built over the next seven years. The first megawatt-scale plant was commissioned in July 2013 at Okegawa, Japan.

In 2016, Kyocera developed what was then the world's largest, a 13.4 MW farm on the reservoir above Yamakura Dam in Chiba Prefecture^[18] using 50,000 solar panels.^[19][20] The Huainan plant, inaugurated in May 2017 in China, occupies more than 800000 m² on a former quarry lake, capable of producing up to 40 MW.^[21]

Salt-water resistant floating farms are also being constructed for ocean use.^[22]

Floating solar panels are rising in popularity, in particular in countries where the land occupation and environmental impact legislations are hindering the rise of renewable power generation capabilities.

Global installed capacity passed 1 GW in 2018 and reached 13 GW in 2022, mostly in Asia.^[10] One project developer, Baywa r.e., reported another 28 GW of planned projects.^[10]

Advantages

There are several reasons for this development:

• No land occupancy: The main advantage of floating PV plants is that they do not take up any land, except the limited surfaces necessary for electric cabinet and grid connections. Their price is comparable with land based plants, but floatovoltaics provide a good way to avoid land consumption.^[23]
• Installation, decommissioning and maintenance: Floating PV plants are more compact than land-based plants, their management is simpler and their construction and decommissioning straightforward. The main point is that no fixed structures exist like the foundations used for a land-based plant so their installation can be totally reversible. Furthermore panels installed on water basins require less maintenance in particular when compared with installation on ground with dusty soil. As arrays are assembled at a single shore point before being moved into place, installations can be faster than ground-mounted arrays.^[10]
• Water conservation and water quality: Partial coverage of water basins can reduce water evaporation.^[24] This result depends on climate conditions and on the percentage of the covered surface. In arid climates such as parts of India this is an important advantage since about 30% of the evaporation of the covered surface is saved.^[25] This may be greater in Australia, and is a very useful feature if the basin is used for irrigation purposes.^[26][27] Water conservation from FPV is substantial and can be used to protect disappearing terminal natural lakes^[28] and other bodies of fresh water.^[29]
• Increased panel efficiency due to cooling: the cooling effect of the water close to the PV panels leads to an energy gain that ranges from 5% to 15%.^{[6][30][31][32]} Natural cooling can be increased by a water layer on the PV modules or by submerging them, the so-called SP2 (Submerged Photovoltaic Solar Panel).^[33]
• Tracking: Large floating platforms can easily be rotated horizontally and vertically to enable Sun-tracking (similar to sunflowers). Moving solar arrays uses little energy and doesn't need a complex mechanical apparatus like land-based PV plants. Equipping a floating PV plant with a tracking system costs little extra while the energy gain can range from 15% to 25%.^[34]
• Environment control: Algal blooms, a serious problem in industrialized countries, may be reduced when greater than 40% of the surface is covered.^[35] Coverage of water basins reduces light just below the surface, reducing algal photosynthesis and growth. Active pollution control remains important for water management.^[36]
• Utilization of areas already exploited by human activity: Floating solar plants can be installed over water basins artificially created such as flooded mine pits^[37] or hydroelectric power plants. In this way it is possible to exploit areas already influenced by the human activity to increase the impact and yield of a given area instead of using other land.
• Hybridization with hydroelectric power plants:

  

  Floating solar is often installed on existing hydropower.^[38] This allows for additional benefits and cost reductions such as using the existing transmission lines and distribution infrastructure.^[39] FPV provides a potentially profitable means of reducing water evaporation in the world's at-risk bodies of fresh water. Furthermore it is possible to install floating photovoltaic panels on the water basins of pumped-storage hydroelectric power plant. The hybridization of solar photovoltaic with pumped storage is beneficial in rising the capability of the two plant combined because the pumped hydroelectric plant can be used to store the high but unstable amount of electricity coming from the solar PV, making the water basin acting as a battery for the solar photovoltaic plant.^[40] For example, a case study of Lake Mead found that if 10% of the lake was covered with FPV, there would be enough water conserved and electricity generated to service Las Vegas and Reno combined.^[29] At 50% coverage, FPV would provide over 127 TWh of clean solar electricity and 633.22 million m³ of water savings, which would provide enough electricity to retire 11% of the polluting coal-fired plants in the U.S. and provide water for over five million Americans, annually.^[29]

Disadvantages

Floating solar presents several challenges to designers:^[41][42][43]

• Electrical safety and long-term reliability of system components: Operating on water over its entire service life, the system is required to have significantly increased corrosion resistance and long-term floatation capabilities (redundant, resilient, distributed floats), particularly when installed over salt water.
• Waves: The floating PV system (wires, physical connections, floats, panels) needs to be able to withstand relatively higher winds (than on land) and heavy waves, particularly in off-shore or near-shore installations.
• Maintenance complexity: Operation and maintenance activities are, as a general rule, more difficult to perform on water than on land.
• Floating technology complexity: Floating PV panels have to be installed over floating platforms such as pontoons or floating pears. This technology was not initially developed for accommodating solar modules thus needs to be designed specifically for that purpose.
• Anchoring technology complexity: Anchoring the floating panels is fundamental in order to avoid abrupt variation of panels position that would hinder the production. Anchoring technology is well known and established when applied to boats or other floating objects but it needs to be adapted to the usage with floating PV.

Largest floating solar facilities

Underwater solar

In addition to conventional FPV there are also a number of studies that have looked at underwater FPV systems called submerged PV.^[69] Due to losses from solar flux being absorbed by the water underwater photovoltaic systems tend to be encouraged for low power applications like sensing.^[70] The efficiency limits for conventional crystalline silicon solar cells indicate that higher bandgap PV materials would be more appropriate for submerged PV.^[71] Although the light intensity under water decreases with an increase in depths, the rate of decrease in power output for both dye sensitized solar cells (DSSCs) and amorphous silicon-based thin film solar cells both outperform conventional traditional monocrystalline and polycrystalline silicon PV by more than 20–25%.^[72] Applications includes:^[70]

• solar powered unmanned underwater vehicles (UUVs);
• solar pool heater;
• energy storage facility;
• offshore wind turbine foundation monitoring;
• bridges and underwater tunnel monitoring;
• algae farming;
• desalination and salt farming;
• marine life exploration.