“Lead-acid is even too expensive,” Miller says. “Aquion’s technology is getting to the range of pumped hydro in cost, which is two cents per kilowatt-hour [over the system’s lifetime]. They’re unique. I would say it’s very promising for grid storage.”
So far, no available technology meets all grid energy storage requirements, says Haresh Kamath, a program manager for energy storage at the Electric Power Research Institute. “Each technology has a different sweet spot” in terms of cost, safety, reliability, lifespan, and efficiency, he says.
Some power companies use lead-acid batteries and sodium-sulfur batteries for grid storage. Lead-acid batteries are cheap but only last for 500 to 1,000 cycles, while sodium-sulfur batteries are costly at $1,000 a kilowatt-hour. Other technologies on the horizon—lithium-ion, above ground compressed air storage, and flow batteries—remain expensive and unproven.
Grid-storage battery technology also “has to be plug-and-play, and not require extensive installation,” says Ali Nourai, an executive consultant at KEMA. Aquion’s batteries may have the disadvantage of being as large and heavy as lead-acid batteries, Nourai says, but their low cost and long cycle life make up for that. “The biggest barrier to grid storage is cost, and Aquion has an upper hand there,” he says. “People will tolerate low efficiency and high weight if the price is right.”
Kamath says that the sodium-ion battery is an interesting new technology, but grid-scale demonstrations will tell whether it has what utilities are looking for. “More than any other, this is a very early stage technology, and we don’t know what it’s capable of,” he says. “Based on principle, it looks very promising, and that’s why a lot of folks in this industry are excited about this. But it remains to be seen if the promises are actually played out.”
Whitacre has ambitious plans for Aquion, though. The company is making 35-watt-hour units that are modular and stackable at its research and development facility. Next year, the company wants to produce multiple megawatt-hours’ worth of batteries at this facility, launch its first commercial product, and break ground on a 500-megawatt-hour capacity factory.