Ohio City Puts Solar Panels on Its Drinking Water Reservoir, Projects $10 Million in Savings

Lima, Ohio, has finished building a 2-megawatt floating solar array on Twin Lakes Reservoir, the city’s primary source of drinking water, in a project officials say will save nearly $10 million in electricity costs over its lifetime.

The city celebrated completion of the Twin Lakes Floating Solar Project on Aug. 12. The finished array includes 3,120 panels covering about 3.6 acres of the reservoir, according to developer D3Energy. The reservoir serves roughly 35,000 residents.

The electricity feeds the nearby water treatment plant, which processes about 14 million gallons of water a day and consumes more power than any other city facility. City estimates put first-year savings at roughly $200,000, with lifetime savings projected near $10 million — though actual results will depend on future electricity prices and system performance.

The panels sit on floating platforms held in place by anchors and mooring lines rather than on ground-mounted racks. Lima used Ciel & Terre’s Hydrelio floating system, which is anchored to the banks and reservoir bottom and can rise or fall with water levels. The bifacial panels capture sunlight from both sides, and electricity runs from the array to eight onshore inverters before reaching the treatment plant.

Because the panels float on water the city already owns, the project avoids buying additional land. A ground-mounted system generating the same amount of power would reportedly need at least 10 acres, compared with the roughly four acres Lima’s floating array covers.

The system uses floats made from high-density polyethylene, which Ciel & Terre says complies with the BS 6920:2000 standard for materials in contact with water intended for human consumption. The National Renewable Energy Laboratory has studied environmental and regulatory questions around floating solar and notes that effects can vary depending on the specific water body.

The project cost about $5.3 million, roughly half of which was covered by federal support: a $2.4 million Department of Energy grant plus nearly $900,000 in federal direct-pay tax credits. Lima’s City Council approved the project in 2023, construction began in 2025, and the system came online this August.

Lima is not alone in Ohio. D3Energy and ARP Solar completed a 1.5-megawatt floating array for Del-Co Water in Delaware, Ohio, in 2024, and a 6-megawatt system in Monroeville is expected online before the end of 2026. Nationally, NREL researchers estimate federally owned or regulated reservoirs have technical potential for 861 to 1,042 gigawatts of floating solar capacity — a measure of theoretical potential, not a forecast that such projects will spread widely.

Where does the money go?

Lima’s projected savings won’t automatically translate into lower water bills. City officials could direct the savings toward other expenses, infrastructure upgrades, or offsetting future rate increases. Residents in towns considering similar projects may want to ask what happens to the savings, what the true construction and financing costs are, and what monitoring will be in place to protect drinking water supplies before local officials commit to a floating solar project.