Petaluma plans floating solar array for its water treatment plant

The solar project would begin operation by the end of 2024, and is expected to save the Ellis Creek Water Recycling Facility $13.1 million in electricity bills over a 20-year span.|

In another step toward the city’s goal of achieving carbon neutrality by 2030, the Petaluma City Council has approved installation of a floating solar array at its Ellis Creek Water Recycling Facility.

The unanimous vote, made during a Dec. 19 public hearing, calls for the floating solar array atop a 17-acre pond at the water treatment center located at 3890 Cypress Drive across from Lakeville Highway. The array would cover about two-thirds of the pond’s surface.

“I’m really excited about this project,” said Patrick Carter, who is assistant to City Manager Peggy Flynn. “It’s a huge thing for the city to be undertaking, and I’m really grateful for our partners here to make this happen. It’s been a long time coming.”

Windsor and Healdsburg have recently installed similar arrays, according to city project manager Diane Ramirez, leading Petaluma city staff to discuss the “best way to identify a solar developer able to design, construct and operate a floating solar array” along the same lines. After receiving multiple proposals, staff decided on solar developer White Pine Renewables.

The solar project is expected to be up and running by the end of 2024.

Base electricity costs at the water recycling plant are usually near $2 million annually, but the solar project is expected to bring roughly $508,000 in savings in the first year alone, with $13.1 million estimated savings over White Pine’s 20-year contract term, according to city staff.

Electrical equipment associated with the floating solar array would be located adjacent to the northeastern corner of the pond on a structure elevated between two and three feet above grade and set about 820 feet away from the public frontage along Lakeville Highway, according to the project staff report.

One major concern that staff and White Pine are working to address was the possibility of an increasing mosquito population due to the installed solar array.

“The oxidation ponds historically have lower mosquito populations than the constructed wetlands” at Ellis Creek, the staff report said. “However, the floating solar project will change the pond environment and has the potential to exacerbate mosquito issues.”

To mitigate that problem, "White Pine is working with the float structure manufacturer to develop potential design modifications“ so that vector control specialists can reach places where mosquito larvae might hide.

The mitigation efforts prompted public commenter Susan Kirks to state that “even though mosquitoes are considered pests, mosquitoes are an incredible nutrition source and needed by many of our avian species who are in the Ellis Creek Ponds area.”

Amelia Parreira is a staff writer for the Argus-Courier. She can be reached at or 707-521-5208.

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