Distributed Energy Magazine

Floating Solar

Adding new value to wastewater treatment ponds

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Lake County Special District in Northern California faces the same problem that all water management districts face—rising energy costs. The biggest expense for any wastewater treatment plant is electricity, and energy providers continue to raise their rates at 3–5% per year, sometimes more. The only way to control rising energy costs is to find another source of electricity, which is why Lake County decided to install a solar power system for its Kelseyville County Waterworks Dist. #3 wastewater treatment plant. What they didn’t expect was to install an innovative floating solar system that would not only meet their energy needs, but would yield additional environmental benefits as well.

Installing solar panels to reduce reliance on the electric company is a logical move for any water treatment facility. To offset the rising costs of electricity from Pacific Gas & Electric (PG&E), Lake County would require a 252 kWp solar system. The objective was to generate enough electricity to run the water treatment plant during the day; at night, the plant would use PG&E electricity so the county’s utility bill is substantially reduced, but they still pay for some PG&E electricity charges. Annual electricity cost savings are projected to be approximately $90,000.

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The system was assembled on the banks of the wastewater treatment pond, floated,
and connected to the wastewater treatment plant’s electrical system.

It was clear to Lake County Special District management that installing solar would cut energy costs for their Kelseyville wastewater treatment facility, but they didn’t have a usable site or a suitable rooftop nearby. After issuing an RFP and reviewing the bids, it was clear that installing a floating solar system on the wastewater treatment pond was the best option. A floating solar power system promised to deliver sufficient electricity to run the pumps for the Kelseyville plant without the need for available land or a rooftop.

What made the floating solar bid even more attractive was that thanks to a municipal lease, the project would require no initial investment. And the green benefits were appealing. The floating solar system would reduce greenhouse gas emissions, saving 7,237 tons of carbon dioxide per year. It also would reduce water loss due to evaporation. And using the pond surface for a solar array would help control algae growth and minimize bank erosion since the system limits water movement.

By converting the unused pond surface into a productive area producing clean energy, the Lake County Special District installed the first public floating solar power system in California.

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The Hydrelio system is shipped as a series of interlocking pieces, like solar Legos

Why Floating Solar Makes Sense
North Coast Solar of Santa Rosa, which has been installing solar power systems since 1987, was the contractor that won the project with its proposal to install a solar array provided by Ciel & Terre, developers of the Hydrelio floating solar power system. Unlike conventional solar installations, Ciel & Terre’s floating solar system required no excavation or concrete footings. The system was assembled on the banks of the wastewater treatment pond, floated, and connected to the wastewater treatment plant’s electrical system.

According to Jan Coppinger, Special District Administrator for Lake County, there really were no other competitive bids that came close to meeting the District’s needs. “We chose floating solar because available land is limited,” says Coppinger. “We have other solar installations and know that they are more difficult to install, especially when you consider zoning and environmental regulations. This was a simple solution that makes good use of the treatment pond, and it helps reduce algae growth.”

Brian Hines, president of North Coast Solar, says the Ciel & Terre system took a five-man crew four weeks to assemble and install. The Hydrelio system is shipped as a series of interlocking pieces, like solar Legos. The primary floats are linked together to connect the solar panels into an array. Secondary maintenance floats are connected to the solar panels to provide a buoyant walkway for maintenance. The engineered floats are made of high-density polyethylene (HDPE), the same plastic approved for food packaging so it will not disintegrate or affect the water. The system resists UV and corrosion, is wind resistant, and, since it is installed in an enclosed pond, it is not subject to water movement.

According to Hines, the Kelseyville solar project required 720 solar panels and 360 Solar Edge solar power inverters, and it covers about half of the wastewater treatment pond.

Hines says the job would have been completed sooner except the crew had to be evacuated for a time because of the Mendocino Complex Fire, the largest wildfire in California history. Also, after the crew was allowed to enter the area after the evacuation, they worked in extreme heat and dense smoke for days afterward.

Hines is an advocate for using floating solar to power water treatment plants. In addition to reducing evaporation and algae growth, floating the panels on water means the solar system is cooler so it generates more power. Maintenance is easy as well. The solar panels are readily accessible using the floating walkways, and the water needed to clean the panels is right there below the array.

The system resists UV and corrosion and is wind-resistant.

Municipal Lease Delivers Immediate ROI
One of the real selling points for the North Coast Solar bid was the financing. By signing a municipal lease, Lake County has been able to generate positive cash flow starting in the first year, and no cash was required for installation. While the county is not eligible to take direct advantage of government solar rebate programs, the municipal lease-purchase agreement is tax exempt, and the return on investment is immediate. Coppinger reports that Lake County saves at least $1,000 per month in utility costs, and the savings will increase over time as PG&E rates increase while the monthly lease payments remain constant. Coppinger says the lease will be paid in 10 years, although the solar panels are warrantied for 25 years and the useful life of the solar system is expected to exceed 30 years.

“We are very pleased—in fact, this is the easiest project we ever implemented,” says Coppinger. “It’s a good deal for rate-payers and we expect better returns down the road. We will be considering more installations in Lake County, especially for sewer treatment facilities since there is no other use for their treatment ponds.”

Hines also sees a very bright future for floating solar use in water treatment ponds across Northern Califor­nia. “Municipal ponds are a great market for floating solar,” explains Hines. “The Kelseyville project is proof there is a reasonable payback. If municipalities decide to make carbon reduction a priority, a substantial percentage of the nation’s power could come from floating solar systems.” BE_bug_web

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