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Sacramento utility rolls out its first long-duration grid batteries

The municipal utility is tapping flow batteries from ESS for on-demand clean power. The project, ESS’ biggest, will provide an early test of the tech’s potential.
By Julian Spector

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Two people in safety vests and hardhats inspect a large white rectangular metal unit with the letters EW displayed in blue
Sacramento's municipal utility takes delivery of multiple Energy Warehouse storage units made by ESS. (ESS)

Sacramento’s utility has installed its first batch of novel grid batteries to assist its quest for a carbon-free grid by 2030.

The Sacramento Municipal Utility District cut a deal one year ago with cleantech company ESS to deliver a total of 200 megawatts/​2 gigawatt-hours of long-duration energy storage, kicking off what would be the company’s largest installation by far.

Glossy announcements of novel energy storage technologies, like this one from SMUD and ESS, always deserve follow-up scrutiny; many times, the game-changing projects promised on paper never appear in the real world. But earlier this month, ESS delivered its first six iron flow batteries for Sacramento’s grid.

The installation could help SMUD solve a tricky decarbonization challenge: storing clean energy so it can be dispatched as needed when solar and wind aren’t available. It’s a problem that utilities face around the country and the world as renewables surge onto grids; increasingly popular battery storage technology has not reached the point of fully replacing on-demand coal or gas power plants.

The project will also serve as an early utility-scale test for flow batteries, which store energy by circulating liquid electrolytes and can cheaply scale up their tanks to add hours of extra storage capacity. Some flow batteries use nasty or expensive materials in their liquid electrolytes; ESS instead chose readily available iron to safely and economically store clean energy for longer periods of time than conventional lithium-ion batteries. It manufactures its iron flow batteries in Oregon.

Myriad other technologies could work for this cheap, long-term clean energy storage task: old-school pumped hydro storage, iron air batteries, domes of compressed carbon dioxide, air compressed into caverns, and many more.

Startups like ESS have been grinding away for years to find customers for their alternatives to the dominant lithium-ion batteries, but utilities tend to be skittish about adopting new technologies. Those that are less wary tend toward the overly studious, installing small pilot projects and observing them for years without a clear plan for large-scale deployment. ESS installed its first commercial product in 2015, but last year SMUD became the first utility willing to buy iron flow batteries in serious bulk.

SMUD’s incentive to move first is simple: It has one of the most aggressive grid-decarbonization goals of any utility in the country. While California is trudging toward a 2045 carbon-free grid target, the state capital has to achieve that in less than seven years. That’s just a blink of an eye in utility-planning terms, so SMUD has to move now to replace fossil fuels for on-demand power, especially in the post-sunset hours when solar production disappears. Other utilities can safely spend the 2020s buying lots of cheap wind and solar power and waiting for new technologies to solve their net-zero goals in the next decade or two; SMUD needs solutions now.

They’ve got a real business problem they’re solving — they’ve been very public about their goals,” said ESS CEO Eric Dresselhuys in an interview at the packed RE+ trade show in Las Vegas this week. It’s great to have everybody feeling the urgency to go get it done.”

Not that the utility is rushing the flow battery deployment — in fact, it’s taking a fairly measured pace. The company commissioned the first batch of batteries (each Energy Warehouse unit holds 75 kilowatts/​500 kilowatt-hours), but it is keeping them temporarily islanded from the grid to run tests and fine-tune the control systems, Dresselhuys said. The flow tech behaves differently than lithium batteries, and the utility wants to learn the ropes before throwing it into the broader grid mix.

It’s not terribly huge in terms of megawatts, but it kicks off the whole effort, and the SMUD team now has experience doing an installation along with us and getting everything plugged into their systems,” said Dresselhuys.

A substantially larger” installation will follow in 2024 as the second phase of the portfolio; batteries at the 100-megawatt level are slated to chase that round. As the scale ramps up, ESS and SMUD are planning workforce training programs with Sacramento State and local community colleges, so that they can hire locally to install the remainder of the 2-gigawatt-hour contract. That training could include an iron flow installation at the Sacramento State campus to give students hands-on experience with the mechanism.

That workforce doesn’t exist yet, because no utility has installed ESS batteries — or any flow battery, for that matter — at the scale that SMUD is working up to. Earlier this summer, ESS signed agreements to deliver similarly massive portfolios to a power company in Germany preparing for the loss of its coal generation.

Long-duration storage proponents still need to prove there’s a market for power plants that can store and discharge clean energy for eight, 10, 12 hours or more; utilities are still getting the hang of lithium-ion batteries that do that for four hours. But Sacramento offers a glimpse of the future: When full grid decarbonization moved from the abstraction of midcentury to an imminent deadline, the utility didn’t lose itself in theoretical debates. It bought something that could make solar power available all night long.

Julian Spector is a senior reporter at Canary Media. He reports on batteries, long-duration energy storage, low-carbon hydrogen and clean energy breakthroughs around the world.