San Diego Could Be First to Float Solar on Drinking Water

A south San Diego water district is thinking about powering itself with energy from the sun. 

Leaders at Sweetwater Authority, which serves National City, western Chula Vista and Bonita, hired a contractor to study how floating solar panels on its namesake reservoir could reduce its budget. If successful, Sweetwater could be the first drinking water reservoir in the United States to host renewable energy of this kind.  

Sweetwater’s board hired Noria Energy on June 28 to design a 3.75 megawatt solar array atop 10 acres of the reservoir. Noria has built floating solar arrays on top of a hydroelectric reservoir in Urra, Colombia and on wastewater treatment ponds in Healdsburg, California, both smaller than the solar panel array proposed at Sweetwater.  

Carlos Quintero, Sweetwater’s general manager, told Voice of San Diego he’d been thinking about floating solar since his previous job managing operations at the Santa Ana Watershed Project Authority in Riverside.  

“On my commute home every day I used to drive by Lake Matthews. Wouldn’t it be cool to have floating solar up there, was something I would think about,” Quintero said.  

Quintero said he learned about Noria Energy a year ago, started talking with the company and came up with an agreement to explore the idea.  

“Nowadays, you have to think about trying to maximize the assets that you have,” Quintero said.  

According to the terms of the contract, 3.75-megawatt array could save Sweetwater $500,000 in energy costs per year, money the agency could put toward lowering its expenses or water rates. Solar panels have other purported benefits, such as reducing evaporation and limiting algae growth which Quintero said has been a problem for that reservoir.  

Algae can overwhelm the reservoir so much that Sweetwater must buy and blend in expensive Colorado River water from the San Diego County Water Authority at a premium. The cost of water has skyrocketed in San Diego in recent years due to investments made by the Water Authority to secure water for the region. This year, the cost of water to the Water Authority’s 24 member agencies like Sweetwater rose 9.5 percent.  

The project was pitched as a sole-source contract, meaning the work is so unique only a single business could fulfill the requirements. But board member Steve Castaneda said he wouldn’t support building the actual project without a public competitive bid process. 

Quintero told the board in June it should move quickly to approve an agreement with Noria so the company could apply for competitive bill credits from San Diego Gas and Electric available to local governments or colleges that generate their own energy. If SDG&E OK’s the project for the credits, the board agreed that Sweetwater would negotiate whether to let Noria or another company build and own the array or Sweetwater could own and maintain it.  

But not everyone is stoked.  

Karen Henry, a Bonita resident and former water engineer, has been tracking the project since June when Sweetwater’s general manager brought an agreement with a floating solar company before the board for approval. She’s not against the concept but feels the Sweetwater Authority is rushing the project and hasn’t been transparent about its origins or plans to increase the size of the solar array. She’s filed public records requests and closely tracked meetings of the board.  

“It says in documents they’re looking at a future array, (larger) than the initial project but they’re not talking about it at all,” Henry said. “That’s when my jaw dropped. At least be honest with people.”  

Josie Calderon-Scott, a Sweetwater board member, questioned approving terms with Noria before getting more community input at the June board meeting.  

“(The reservoir) is a regional resource … there will be community opposition that could cause delay,” she said. “Generally for these kinds of projects you go in softly and work with the community to bring them on.”  

The board eventually approved the agreement with Noria in a 5 to 2 vote with National City Mayor Ron Morrison, a Sweetwater board director, and Calderon-Scott against it.  

Noria Energy’s director of business development, Jairo Criollo, told the board that the company hasn’t built solar on drinking water before. 

“We know there are specific requirements and the purpose of this term sheet is to find out what they’re going to be,” he said. 

This project is a kind of experiment as state regulators will likely be asking the same questions.   

“There’s nothing in the regulations that spell out specifically what the requirements are for this type of project,” said Sean Sterchi, San Diego’s district engineer with the State Water Resources Control Board’s department of drinking water. 

But anything built on or near a drinking water reservoir will have to pass the department’s scrutiny. Sterchi said the department’s priority is protecting public health. But a solar array is likely less complex in terms of permitting than, say, the horse trail built near the reservoir. 

Adding a concentrated activity like horse riding next to drinking water increases the risk of manure runoff carrying pathogens into the source, he said.  

Also, any structure that comes into contact with drinking water, like solar panels, has to use materials that are certified as safe by an independent and international public health standards organization called NSF.  

“We would want to see them develop a project such that there wasn’t any negative impact on water quality,” Sterchi said.