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The idea of setting a solar panels out to float on top of reservoirs and other bodies of water seemed somewhat exotic and unnecessary just a few years ago, considering how many non-liquid surfaces are suitable for solar development. Nevertheless, in the right circumstances a floating solar array can fill in the gaps left by more conventional forms of renewable energy.

Floating Solar & Suitable Surfaces

When the topic turns to suitable surfaces for solar development, keep in mind that suitability does not necessarily mean availability. For example, back in 2020 the US Department of Defense was trying to figure out how to provide a source of resilient, on-site, clean electricity for one of its training grounds. They had plenty of land suitable for a ground-mounted solar array, but they needed that for training. Instead, they laid plans to install a 1.1-megawatt floating solar array on a lake within the property.

A 1.1-megawatt array is relatively small by today’s standards, but those numbers can add up. In 2018 the US Department of Energy released a survey indicating that solar panels on human-made reservoirs could account for about 10% of the electricity generating capacity in the US.

The figure of 10% is a conservative estimate, based on a set of 24,000 optimal reservoirs selected from a much larger pool of reservoirs in the US. In addition, the researchers envisioned that only a portion of each reservoir — about 27% — would need to be covered with solar panels in order to reach the 10% mark.

Utah Gets Its First Ever Floating Solar System …

The Energy Department study, produced by the National Renewable Energy Laboratory, also noted that a layer of solar panels can reduce evaporation and inhibit algae growth, two important considerations for water treatment systems.

Water treatment systems also require massive amounts of energy, so the potential for cutting utility costs is another significant attraction. In consideration of the piling-on of climate-fueled disasters, an on-site source of clean power adds security and resiliency to water treatment systems and other critical infrastructure.

That brings us to Utah, which is now the host of of its first-ever floating solar array. The new solar panels cover a portion of a retention pond at the Signal Hill water treatment plant, operated under the umbrella of the Mountain Regional Water Special Service District.

“Traditional ground or rooftop solar wasn’t an option for us at this facility,” notes Chris Braun, the water district’s Chief Technology Officer, “But this innovative floating solar installation makes use of an untapped resource.”

CleanTechnica first spotted the project back in 2023, when it was still on the drawing board. The array was funded with a grant of $400,000 from the utility Rocky Mountain Power. Rocky Mountain serves about 1.2 million ratepayers across Idaho, Utah, and Wyoming, raising the potential for the new array to serve as a model for replication in all three states.

That remains to be seen. For the here and now, the Signal Hill floating solar project practically jumped off the drawing boards and was finished ahead of schedule. On September 26 the facility held a ribbon-cutting ceremony to celebrate completion of the array, with a full operating permit to follow later this month.

Though the capacity of the array weighs in at just 587.5 kilowatts, Signal Hill anticipates that it will cut energy costs at the facility by 80%, by enabling the treatment plant to use electricity directly from the solar panels. The project is also expected to offset 92% of the plant’s consumption from the electricity grid.

… And Here Comes Ohio, Too

The floating solar movement has also come to Ohio for the first time, in another demonstration of the interplay between solar energy, land use, and water systems. The new project is located at the Olentangy treatment plant of the Ohio public water utility Del-Co Water.

“Floating solar enabled us to move forward with a substantial solar installation without encumbering any of our valuable ground which may be needed for future expansion,” noted Del-Co CEO Glenn Marzluf in a press statement last year, drawing attention to the land use issue. The array is part of a broader space-optimizing project within a major overhaul of the facility, that including solar panels on rooftops and carports.

All together, the solar projects are expected to offset almost half of the electricity consumption at the treatment plant, with a consequent reduction in energy costs. Marzluf also anticipates that shade from the floating solar panels will also help inhibit algae growth on the reservoir.

More Floating Solar For The USA

Ohio and Utah join a small but growing number of states to adopt floating solar projects. The movement seemed to get off the ground in 2008 when a California winery installed a floating solar array, but it didn’t begin to gather momentum until a water system in Sayreville, New Jersey adopted the technology in 2019. That was followed by plans for a reservoir in Short Hills, New Jersey.

The upstate New York city of Cohoes has also been planning for a floating array on its municipal reservoir since 2019, and all that hard work is beginning to pay off.

Last spring, public radio station WAMC reported the start of construction on the $8 million, 3.2-megawatt floating solar array. In a public statement, Cohoes Mayor Bill Keeler noted that the array will enable the city to cut $600,000 off its annual electricity bill without sacrificing its green spaces to build local ground-mounted solar projects.