Floatovoltaics

It goes without saying that solar energy has its benefits, but one of the major complications to installation is figuring out where to put the panels.  Rooftops are a viable option, but a substantial amount of land is usually needed for larger projects.  In regions where unused land is scarce, how do you implement a utility-scale solar farm?  The answer may lie with floating panels, or “floatovoltaics.”

No, were not talking about destroying the natural beauty of our lakes, rivers, and ponds; there are other, less aesthetic bodies of water for solar panels.  In the United States alone, the surface area of wastewater ponds, reservoirs, and sewage treatment pools totals in the hundreds of thousands of acres.  These unused, open spaces are typically hidden from public view and provide an excellent opportunity for solar.

Photo Credit: The San Francisco Chronicle

Photo Credit: The San Francisco Chronicle

Since 2007, photovoltaic systems have been installed on a small number of water bodies in Japan, France, India, the U.K., and the United States.  The first of such systems was installed at a vineyard in Napa Valley, California.  In an effort to both conserve vine acreage and expand on their existing 1,300-panel system, Far Niente winery placed 1,000 solar panels over an irrigation pond on the property.  The panels were secured on 130 floating pontoons and connected to the land-based system to collectively generate 477 kW at peak output. Combined with the ground mounted system, the additional floating panels allow the facility to completely offset its electrical needs. By installing the panels over the pond, Far Niente was able to save more than ¾ of an acre of vines, equivalent to $150,000 worth of bottled wine annually.

Land conservation aside, floating panels offer benefits lacking in ground-mounted solar.  For one, the water underneath provides an effective, natural cooling system.  As solar panels continuously absorb sunlight throughout the day, they become very hot.  The efficiency of a typical silicon-based solar panel is reduced by about .5% for every °C increase over the module’s rated temperature (usually around 25°C).  Because of water’s cooler environment, floating panels do not experience a significant loss in power output when temperatures increase.  In fact, one study found that solar panels were 8-10% more efficient when paired with water.

Photo Credit: New Jersey American Water

Photo Credit: New Jersey American Water

Many water utilities are transitioning to renewable energy sources to combat the high costs of water treatment.  According to the Environmental Protection Agency (EPA), 3-4% of national electricity consumption is used for wastewater services and to provide drinking water. The addition of a floatovoltaic system to a treatment facility can offset some of these costs and also provide a valuable shading structure.  Reduced exposure to sunlight has the potential to decrease evaporation and algae growth in a water body.  Evaporation limits water conservation while algae buildup clogs piping and causes other issues, increasing maintenance costs for treatment facilities.

Floating solar has advantages over ground-mounted panels, but the absence of land is the main reason for installation.  The large percentage of underutilized municipal surface water in the United States presents a unique opportunity for renewable electricity generation.  Below are a few notable projects involving floatovoltaics:

  • New Jersey American Water installed 536 floating panels over a reservoir near their Canoe Brook treatment plant.  The system generates 135,000 kilowatt-hours per year with an estimated annual energy savings of $16,000.
  • Last year, Britain’s first floating solar array was installed over a reservoir on a soft fruit farm.  The 800-panel project has a 200 kW capacity and should generate a minimum profit of £620,000 over 20 years.
  • Two Japanese companies recently announced a joint venture to cover the country’s Yamakura Dam Reservoir with a 50,000-panel system.  The project would produce 15,635 megawatt-hours per year, enough to power 4,700 homes.  When completed, it will be the largest floatovoltaic system in the world.

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