The city of Healdsburg, Calif.’s, new floating solar array didn’t start out to be a triple threat of environmental responsibility, but since its completion in January, it’s been generating quite a bit of buzz.

Not only does the 4.78-megawatt photovoltaic array produce 8% of the community’s annual electrical needs, but it also shades the ponds at the Healdsburg wastewater treatment facility, reducing algae build-up so the recycled water can be sold for agricultural purposes. As if that weren’t enough, it is the largest floating solar array in the U.S.

Made for shade

          According to Terry Crowley, P.E., utility director for the city of Healdsburg, having the largest floating array in the country was not the intent of the project, nor was producing nearly 5 megawatts of power for the city. The genesis of the project was the desire to mitigate algae growth within the city’s recycled water ponds.

          “The city explored various options to shade the ponds,” he said. “The two top tier options were shade balls (small balls that float on the water) or floating solar. In looking at the economics, float solar was found to be more economical due to the energy created.”

          Healdsburg’s wastewater treatment facility is a state-of-the-art tertiary treatment system, which processes raw sewage into clean and disinfected recycled water that can be used in orchards, vineyards and for other agricultural purposes. The water is stored in large thermoplastic-lined ponds and funneled through pipelines to those who need it, which reduces the demand for groundwater.

          The floating solar array is a concept that has been around for about 10 years, but the pricing was never within a range that was competitive with wholesale energy markets. After drafting the project with the support of the Northern California Power Agency and releasing a request for proposals, the contract was awarded to Dissingo as a power purchase agreement in June 2020. Construction began four months later and was completed in March.

          In addition to the novelty of being located on water and — at the present time — being the largest floating solar array in the nation, the floatation devices can be moved so city wastewater staff can inspect and repair the pond liners if necessary. Crowley said the project has a design life of 25 years but could operate a lot longer thanks to its ability to incorporate a future utility-scale battery storage system. The array is located on a 25 million-gallon tertiary pond and contains 11,600 panels.

          “Construction of the project went surprisingly smoothly, largely due to the efforts of White Pine Renewables and Collins Electrical,” Crowley said. “These two entities were able to bring real-world experience and knowledge to the project, completing it within an incredibly short period of time.”

A power play

In a PPA, the developer pays for the entire project and retains ownership of the array, while Healdsburg Electric pays a fair market price for the electricity that is delivered to its publicly owned utility. In addition to allowing the solar developer to apply for tax incentives that the governmental entities are not eligible for and cutting Healdsburg’s costs for energy, the new array helps Healdsburg meet the state of California’s environmental sustainability requirements and climate goals to add renewable and carbon-free energy.

“The city of Healdsburg owns and operates its own electric utility,” Crowley said. “This helps the city keep energy costs low, but also allows the city to commit to building new green energy sources for our customers. Not only will the floating solar project provide 8% of citywide annual energy needs, it fits within the city’s goal of providing 50% renewable energy by 2025 and 60% renewable energy by 2030.”

Crowley said community response to the project has been very supportive, and the knowledge of the project has helped raise awareness about how the city of Healdsburg meets the community’s energy needs. He suggests communities considering a similar project take the time to vet potential contractors regarding their experience in constructing large solar arrays and spend time developing a good power purchase agreement that contemplates future problems and end-of-life issues.

“It’s easy to get excited about these projects on the front end, but thought should be given to what might happen over the duration of the agreement,” he said.