In a typical supermarket, refrigerators and cold cases suck up about half of the energy used in the entire store—and they pull power from the grid around the clock.
A "refrigeration battery" is designed to help: Instead of storing electricity, it stores cooling. When the grid is overloaded—and electricity more expensive—during the day, grocery stores can turn to the batteries to keep food cool.
"During the nighttime when electricity is cheap, we store cooling by freezing tanks of saltwater," says Amrit Robbins, CEO of Axiom Exergy, the Bay Area-based startup making the new device. "Then we’re able to use those frozen tanks of saltwater to supply cooling services . . . during peak hours in the afternoon when electricity prices skyrocket."
For utility companies, the new system is a way to better manage increasingly unstable supply and demand. Wind and solar plants can’t supply steady power. At the same time, power use is also more unpredictable than it has been in the past, because of new technology such as electric cars, which are adding new surges to the grid as they charge overnight—usually a time when electricity demand is low. "The electricity grid is kind of stuck in the middle between all these highly destabilizing forces," she says.
With the new system, one big chunk of energy demand could be controlled and predictable. Central refrigeration accounts for around 15% of all electricity use in commercial buildings in the U.S. according to the latest numbers—or about 670 trillion BTUs.
"Any facility that has a large central refrigeration system, we enable them so rather than being a drag on the grid, they can be a flexible asset to the grid," he says. "They can respond to price signals, they can respond to direct commands from the utility—'turn on now, turn off now', in order to help stabilize the grid."
Most supermarkets are in areas with variable pricing, where electricity costs more during peak hours, so the new system can help cut power bills. Because grocery stores run on tiny margins—and electricity is a huge portion of operating costs—there's a big incentive for stores to adopt it.
The system plugs into the central refrigeration system hidden in a supermarket's back room, while another box is installed on a loading dock or in a parking lot. Unlike typical batteries, it doesn't have to be connected with the grid. It also works for long periods of time: Fridges can run for six hours on the batteries.
The startup announced $2.5 million in new funding today, including investment from Tesla cofounder and CTO JB Straubel (known for leading Tesla's own efforts in energy storage, from the PowerWall to the Gigafactory). Axiom plans to start shipping batteries to major supermarket chains this quarter.
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