Systems of solar cell panels installed on a structure that floats on a body of water
Floating photovoltaic on an irrigation pond
Floating solar or floating photovoltaics (FPV), sometimes called floatovoltaics, are solar panels mounted on a structure that floats. The structures that hold the solar panels usually consist of plastic buoys and cables. They are then placed on a body of water. Typically, these bodies of water are reservoirs, quarry lakes, irrigation canals or remediation and tailing ponds.[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 shortest 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 U.S. has more floating solar potential than any other country in the world.[12] Bodies of water suitable for floating solar are well-distributed throughout the U.S. The southeast and southern U.S. plains states generally have reservoirs with the largest capacities.[12]
The costs for a floating system are about 10-25% higher than for ground-mounted systems.[13][14][15] According to a researcher at the National Renewable Energy Laboratory (NREL), this increase is primarily due to the need for anchoring systems to secure the panels on water.[16]
Energy production from floating solar photovoltaic sources expanded dramatically in the last half of the 2010s, and is forecast to grow exponentially in the early 2020s.[17]
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.[18]
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][20] 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[21] using 50,000 solar panels.[22][23] 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.[24]
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]
Salt-water resistant floating farms are also being constructed for ocean use.[25] They have the potential to reduce spatial pressures on land or lakes.[26] Oceans of Energy (Netherlands) developed the world's first offshore solar system in the North Sea.[27] Floating solar can have positive and negative effects on the ocean environment: for instance, it can act as an artificial reef and protect small fish and other animals. On the other hand, the floating panels increase shading and their construction may disrupt seagrass and coral reef.[28]
The construction process for a floating solar project includes installing anchors and mooring lines that attach to the waterbed or shore, assembling floats and panels into rows and sections onshore, and then pulling the sections by boat to the mooring lines and secured into place.[15][29]
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.[30]
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.[31] 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.[32] This may be greater in Australia, and is a very useful feature if the basin is used for irrigation purposes.[33][34] Water conservation from FPV is substantial and can be used to protect disappearing terminal natural lakes[35] and other bodies of fresh water.[36] This positions FPV as a practical approach for renewable energy generation in regions facing water scarcity.[37] For example, a case study of Lake Nasser, which is in a region that suffers from water poverty, found that 50% coverage would result in 61.71% or 9.07 billion m3 annual water evaporation savings.[38]
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][39][40][41] 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).[42]
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%.[43]
Environment control:Algal blooms, a serious problem in industrialized countries, may be reduced when greater than 40% of the surface is covered.[44] Coverage of water basins reduces light just below the surface, reducing algal photosynthesis and growth. Active pollution control remains important for water management.[45]
Utilization of areas already exploited by human activity: Floating solar plants can be installed over water basins artificially created such as flooded mine pits[46] 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: A: Sun. B: Floating solar panels. C: Inverter. D: Electric connection cabinet. E: electricity grid. F: water intake. G: pumped water canal. H: pump/turbine body. I: discharge. Floating solar is often installed on existing hydropower.[47] This allows for additional benefits and cost reductions such as using the existing transmission lines and distribution infrastructure.[48] 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.[49] 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.[36] 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.[36]
Floating solar presents several challenges to designers:[50][51][52][53]
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. Severe storms have caused floating systems to fail and anchoring systems must be developed with these risks in mind.[54]
Societal use conflicts: Covering bodies of water with floating panels may interfere with societal uses. For example, covering reservoirs used for fisheries could undermine local populations reliant on those fisheries. The impact on scenery by floating panels may lower property prices causing opposition from nearby landowners.[55] One survey conducted with the local population of Oostvoornse lake, the Netherlands, demonstrated a 10% disapproval rate of short-term Floating PV projects in their community.[56] These concerns included obstruction of businesses and recreational activities in the lake area. Other surveyors showed concerns of floating solar technology ruining the lake's natural beauty, and disregarding the local people's personal attachments to Oostvoornse lake.[56]
Ecological challenges: The shading of bodies of water may inhibit harmful algal blooms, but the shade of floating PV panels may cause ecological damage via inhibiting photosynthesis and altering the behavior of light-responsive fish and zooplankton. Furthermore, the emission of polarized light by PV systems can effect animals sensitive to polarized light like many insects, birds, or amphibians.[57]
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