Making Waves/The Wave of the Future: Floating Photovoltaic Arrays

By: Catherine Fink

Water and solar energy are the building blocks of life—especially in the arid West. An emerging technology takes advantage of both has the potential to provide 50% of the world’s ongoing energy needs through a clean, green new technology: Floating photovoltaics (FPVs). Alternatively known “aquavoltaics”1 (AVs), “floating solar arrays,” or “floatovoltaics,” FPVs can increase sustainable energy production while decreasing the costs and ecological concerns related to terrestrial solar arrays. FPVs are solar panels that float on the surface of a body of water while remaining anchored/moored and send an electric current through underwater cables to a transmission tower nearby. Florida House Bill 1411 further clarifies that, “FPVs can be placed on… wastewater treatment ponds, stormwater treatment ponds, reclaimed water ponds and other water storage reservoirs.” This diversity of host sites translates to great potential for U.S. cities interested in sustainable development. According to a study by the National Renewable Energy Lab (NREL) in 2018, FPVs installed on “‘suitable’ water reservoirs” could generate about 10% of the nation’s current annual electricity production. Currently, Portugal is building Europe’s largest FPV array, with 12,000 panels, which will allow it to generate 7.5 MW of energy, supplying 1,500 families with clean energy. And in China, the world’s largest array at 420 MW of energy provides energy for 100,000+ homes. This project also combines FPV tech with aquaculture, as people are practicing fish cultivation under the floating arrays. South Korea is currently building a 2.1 GW array, which will help it to achieve its goal of being carbon neutral by 2030.

Why are these projects so popular? FPVs have myriad benefits including increased energy production, reduced evaporation, algae reduction, reduced installation costs, and opportunities to repurpose existing resources. Research shows that FPVs not only produce 6-20% more energy than solar panels on land, but they also have the added benefit of decreasing the evaporation of the water on which they rest by 50-80%. They do so “by decreasing airflow and absorbing solar radiation that would ordinarily be absorbed by water.” Additionally, FPV arrays can slow or reduce algae growth in the water below by reducing the amount of sunlight that penetrates the water.

Traditionally, procuring new lands for solar arrays can be costly, contentious, and potentially environmentally detrimental. Land use concerns often stymie large solar projects as terrestrial solar requires on average 200 square feet per megawatt hour of capacity. FPVs, however, can sit on water surfaces already owned by a municipality, the federal government, conservation-based non-profits, or privately owned property such as wineries, irrigation co-ops, etc. This means those entities can repurpose an existing resource for added benefits. Additionally, it generally costs less to install FPVs since it requires less material per kilowatt of electricity produced, and there is no need to clear land or treat soil. Finally, FPVs can help to reach environmental justice goals by offering affordable power, as well as job-skills, to low-income residents when non-profits like GRID Alternatives bring residents into the FPV-building process.

However, there are some concerns with the technology, including potential wildlife impacts and lowered water temperatures, vulnerability of panels to extreme weather, a lack of U.S. installation guidelines, and zoning/permitting barriers. FPV racks may negatively impact ecosystems and animals in the water underneath by lowering the water temperature and slowing algae growth. The increase in frequency and intensity of storms could damage arrays, so scientists are working to better understand how to develop the most resilient FPV arrays. Additionally, the lack of U.S. design requirements and codes/installer certifications creates obstacles to FPV installation because it means each Authority Having Jurisdiction (AHJ) has to interpret existing codes, slowing the regulatory process. Finally, certain zoning rules prohibiting solar arrays and underinclusive solar classifications that limit definitions to terrestrial-only arrays can also inhibit development of innovative solar projects. Municipalities may need support working through these complexities.

Although the U.S. currently does not have any federal effort to develop FPVs, some representatives are taking action: “Representatives Paul D. Tonko (D-NY) and Jared Huffman (D-CA) today introduced the POWER our Reservoirs Act (Protect our Waters and Expand Renewables on our Reservoirs Act) to advance clean energy production and drought protection at our nation’s federal water reservoirs. This legislation will call on key federal agencies to study opportunities to deploy floating solar panels on their reservoirs and launch innovative pilot projects.” Arizona conducted a canal-top demonstration project as a case study to highlight the significant potential benefits of solar over water development, and California is also starting a canal-top solar panel demonstration project: “Project Nexus includes the installation of solar panel canopies over various sections of Turlock Irrigation District’s (TID) irrigation canals. Project Nexus will serve as a Proof of Concept to pilot and further study solar over canal design, deployment, and co-benefits on behalf of the State of California using TID infrastructure and electrical grid access.” Although neither the Arizona nor the California projects are specifically floating solar array projects, both aim to take advantage of the cooling effect of the canal water and to provide the dual benefits of increased power output and reduced evaporation that FPV arrays provide.

In Colorado, bipartisan bill SB23-092, sponsored by Sen. Hansen, Sen. Simpson, Rep. McCormick, and Rep. Soper, passed in the 2023 session directs Colorado agencies to conduct a feasibility report on “floatovoltaics.” Sen. Hansen’s Policy Director, Anna Evans, noted that, “Another bill in the future may also protect property tax benefits that agricultural land has. Land designated as agriculture gets special tax breaks, and adding energy generators can disqualify the landowners from those tax breaks. [Sen. Hansen would] make sure agri/aquavoltaic land also gets that special tax treatment.”

Nationwide, municipalities mostly face issues in three categories: code barriers, a lack of incentives, and regulatory gaps. In order to remove code barriers, municipalities can use standardized guidelines such as those offered by the World Bank ESMAP and Det Norske Veritas (DNV). They can also proactively change comprehensive plans, zoning codes, and solar definitions because certain statutes and ordinances prohibiting solar arrays and/or relying on underinclusive solar classifications that limit allowable array definitions to terrestrial-only systems can inhibit FPV development. With regard to creating incentives, municipalities can sell advertising space on arrays using the new “skin” technology featured on the Comcast array at Universal Orlando and, depending on the state regulations, pursue power-purchasing agreements (PPAs) with businesses to offset costs. They can also take advantage of Inflation Reduction Act changes that create 30% tax credits paid directly to municipalities that complete solar projects, look for NGO partnerships, and take advantage of changes to state laws where available, such as Florida’s HB 1411. Lastly, to fill regulatory gaps, municipalities should check with their State Engineer's office to better understand and/or to change water rights obligations due to any net water loss reductions because of reduced evaporation.

While still a nascent industry in the U.S., the success of international FPV arrays (see graph) and of the few American projects FPVs can deliver lower-cost, carbon-free energy to communities in need of affordable, sustainable power.