Energy store: A rendering shows what a grid storage plant based on zinc-air batteries might look like.
Oster says the company aims to sell megawatt-scale batteries with six hours of storage capacity at a capital cost of $160 per kilowatt-hour. By storing electricity when demand is low, he says, the batteries should be able to provide electricity at times of peak demand for 12 to 17 cents per kilowatt-hour, compared with 22 to 30 cents per kilowatt-hour for electricity produced by a natural-gas plant.
Jeff Dahn, a professor of physics and chemistry at Dalhousie University, says if the company has solved the electrolyte and membrane problems, it should be a significant step forward for zinc-air batteries. “But show us the data,” he says. “None of this has been shown.”
Dahn also says the maximum efficiency of a zinc-air battery—in terms of the amount of electricity that goes in versus the amount that comes out—is only 60 percent, compared with roughly 80 percent for lead-acid batteries and more than 95 percent for lithium-ion batteries. He says the low efficiency is the result of differences in voltage between charging and discharging and is inherent to the battery type.
Eos claims to have found ways to resolve the differences in voltage and increase efficiency, but Dahn is not convinced. “A lot of people have worked for a long time on rechargeable zinc-air and [the efficiency issue] hasn’t been cracked yet,” he says.