You wouldn't know it if you drove by. It's a collection of metal boxes the size of small shipping containers, sitting in what was formerly a truck storage yard in Santa Paula.
But it's a state-of-the-art energy storage facility that uses clean solar power to charge batteries, which then generate electricity when it’s needed most.
"It doesn't use water, it doesn't create emissions, and it's an efficient way for the state to meet peak resources that it needs," said Randolph Mann, CEO and founder of esVolta, a company that specializes in battery energy storage projects.
"We're buying energy during the middle of the day, when we've got plenty, and discharging it back into the grid in the evening, when we have more of a shortage," Mann explained. "It helps to offset the need for natural gas resources and other resources to provide power in the evening. We're essentially providing a peaking service, helping the grid meet those peak demand periods."
Es Volta has two facilities in Santa Paula. The company started work on the projects in 2019. In 2024, a 30-megawatt facility went online off 13th Street. Last year, a 15-megawatt facility on 12th Street, on an old truck parking lot, also went into service.
Company officials say together, the 45 megawatts of capacity can power around 45,000 homes for about four hours.
"There's not enough energy here to serve the demand at certain times. If you look at the California energy grid, you can see the map of prices. Prices indicate where there's a greater need for power," said Devin Hardman, esVolta's Senior Vice President of Commercial Operations. "It's telling you (during the day) we have more generation than we can consume. When solar turns off at night, typically in California, you have a lot of demand still that needs to be met."
The state’s power industry has changed. For decades, the main concern was that demand during hot summer days was overwhelming the power grid, leading to blackouts. The answer was building what are known as “peaker plants,” which are smaller, fossil fuel electrical generation facilities usually used during peak demand.
In 2018, Oxnard residents won a battle over efforts to build a new peaker plant in the city, with concerns over the pollution it would cause. Instead, a battery energy storage facility was built. It went online in 2021.
"Where they are especially useful is when the sun sets, and we're falling into what we call the net peak period," said Marci Palmstrom, esVolta’s Vice President of Asset Management.
At the new Black Walnut facility, there are 17 metal boxes, each about the size of a small shipping container. Each contains batteries and electronics, in effect creating a series of mini power-generating facilities.
"We're looking at the Black Walnut Battery Energy Storage facility. Each of these containers is 1.25 megawatts. Inside of each of those is DC batteries, AC inverters, to invert the DC to AC, through our transformers to our satellite substation, and then out to the Wakefield substation," said esVolta Operations Manager Warren Harrison III.
Harrison is a power industry veteran. But he started on the fossil fuel side, and then, a few years ago, decided he wanted to be a part of the growing green energy field.
"I saw that this would be the future, because I also wanted us to live in a place that would be more safe and livable for future generations," said Harrison.
One of the biggest concerns with the technology is safety. A fire at a five-year-old battery energy storage facility in northern California in 2025 raised a number of concerns, because fires involving lithium-ion batteries are more difficult to fight. Regulators, however, say the technology has evolved rapidly over the last few years, and the batteries are much safer.
"I think everyone across the storage industry is focused on being safe. When we design and build a facility, we're thinking about safety all the way through," said esVolta CEO and President Randolph Mann.
Company officials say they’re excited to have the second phase of their Santa Paula operation up and running, to serve an underserved part of Ventura County.
