Sonoma County Is Building the Largest Floating Solar Project in the United States

Creativity is playing an increasingly important role in how we harvest energy from the sun. It’s not just a matter of choosing rooftops or ground-mount panels anymore. Check out the Dutch bike path called SolaRoad (, which acts like one large solar panel, or Bigbelly Solar Inc. of Newton, Mass. (, which sells solar trash and recycle compactors, which are powered by solar cells. Owners and energy users want solar technology, but they also want it affordably, efficiently and out of the way. That got the creative folks at the Sonoma County Water Agency thinking.

“We had been looking for ways to optimize the production of renewable energy at our various facilities,” explains Cordel Stillman, P.E. and deputy chief engineer at the Sonoma County Water Agency. “The difficulty of finding suitable ground-mounted solar locations prompted us to investigate the use of floating infrastructure. There had been several small-scale installations in our area that we used as examples, and we also found a few examples during an internet search. This gave us the confidence to issue a Request for Proposals [RFPs] on a larger scale system.”

Floating-solar-array-(Cut-1)The Sonoma County Water Agency identified the potential for floating solar panels on ponds that store fully treated wastewater. It was an ideal solution for the county that is very much known as the largest region in California’s wine country. The agency recognized the many benefits a floating solar system might provide, including minimizing aesthetic impact and preserving precious farm land.

The Sonoma County Water Agency brought the idea to Sonoma Clean Power — a locally controlled electricity provider in Sonoma County, which provides options of using environmentally-friendly power generated by renewable sources like solar, wind and geothermal (at competitive rates). Together, the two organizations decided this was an excellent method for building local renewable energy at a scale that kept costs competitive with fossil fuels. The agency then took steps to solicit developers and eventually leased the project sites to Pristine Sun, a solar developer based in San Francisco.

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“The challenge of building the largest floating solar project in the U.S. was really exciting to us, and we’re actively developing more of these projects throughout the country,” says Cary Hayes, vice president of sales at Pristine Sun. “Floatovoltaics are a new and exciting segment in the U.S. PV market, and we intend to be a leader in this space. We believe this project represents the largest floatovoltaic project in the U.S. market. We have commenced interconnection studies and plan on a summer 2016 build.”

The systems will be installed on six different storage ponds, two in northwest Santa Rosa and four in the Sonoma Valley. Development is expected to be completed by the end of 2016. In the end, the system is planned to supply enough power for 3,000 homes at completion. The Sonoma County Water Agency has identified additional potential sites for floating solar at local wineries and is planning to assist local vintners in developing smaller scale projects. Being located on irrigation water storage ponds, the project will protect Sonoma County farmland while reducing local dependence on fossil fuel.

“We issued a RFPs to place solar panels on seven recycled water ponds that we operate and maintain,” explains Stillman. “The RFP was issued generally, in that we did not target specific solar developers. We received four responses. Two developers were eliminated from consideration due to the high price of their proposal. The remaining two developers were interviewed by the Sonoma County Water Agency and Sonoma Clean Power. The interview was used to determine the level of experience and expertise each developer had in the California market — knowledge of interconnection procedures, financial stability, ability to perform, etc. Pristine was selected as the combination of their qualifications, and their price was better than the other developer.”

When finished, the array will produce 12.5 megawatts (MW) of new solar power in Sonoma County. It will also represent the largest floating solar project in the United States and the second largest in the world. Of course, because of the innovative location for the system, extra steps were taken to ensure that Sonoma Clean Power customers are protected against any risks. Agency CEO Geof Syphers worked with leading industry attorneys to make sure that the risks for non-performance lie with the developer and not with the agency’s customers.

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Pictured is a 1.6-MW DC solar project originated, developed, built, owned and operated by Pristine Sun. It’s located in the rolling hills of San Louis Obispo County on land that is not suitable for agriculture.

Pictured is a 1.6-MW DC solar project originated, developed, built, owned and operated by Pristine Sun. It’s located in the rolling hills of San Louis Obispo County on land that is not suitable for agriculture.

“The contract is a fairly standard Power Purchase Agreement,” says Stillman. “Using this contracting method insulates Sonoma Clean Power from the risk that may result from constructing a project of this type. The contract specifies that SCP will only be required to purchase the energy produced by the project, not own, operate and maintain it. This reduces, if not eliminates, any risk to SCP if the project does not perform as expected.”

Because of its uniqueness, the project will certainly have challenges. Anchoring the solar panels in a manner that holds them in place and allows access for maintenance will be a challenge. Maintenance of the panels is the responsibility of the developer throughout the life of the system, and the plan is for walkways for cleaning access to be provided. Right now, the project is one of a kind, but Pristine Sun seems prepared to overcome any hurdles.

“We understand this is an engineering challenge, but feel confident in our project solution,” Hayes said. “Electrical equipment, modules and wiring have to be water resistant and resilient. Additionally, fluctuations in the pond’s water levels must be taken into account when engineering the system. We’ll keep you guys updated.”

Why Water?

Five Good Reasons for a Floating Solar Project

1. Since the panels are floated on water that is generally below the sight line of the general public, there are no aesthetic issues.

2. Siting on ponds does not take prime agricultural land out of production.

3. Purchasing or leasing property for ground-mounted solar systems is very expensive. The cost of leasing space on a pre-existing pond is negligible.

4. Since the pond is a pre-existing structure, any environmental mitigations have already been dealt with, and there is minimal California Environmental Quality Act requirements.

5. Placing the panels next to water has a cooling effect that may increase production from the panels.

Keith Gribbins is associate publisher of Solar Builder.