Last week, a company called B2U Storage Solutions announced that it had started operations at a 25 Megawatt-hour battery facility in California. On its own, that isn't really news, as California is adding a lot of battery power. But in this case, the source of the batteries was unusual: Many of them had spent an earlier life powering electric vehicles.

The idea of repurposing electric vehicle batteries has been around for a while. To work in a car, the batteries need to be able to meet certain standards in terms of capacity and rate of discharge, but that performance declines with use. Even after a battery no longer meets the needs of a car, however, it can still store enough energy to be useful on the electric grid. So it was suggested that grid storage might be an intermediate destination between vehicles and recycling.

But there are some significant technical and economic challenges to implementing the idea. So we talked with B2U's CEO, Freeman Hall, to find out why the company decided it was the right time to put the concept into action.

Supply and demand

While the idea may go back a while, implementing it required two things: a steady supply of end-of-life car batteries and a regular excess of cheap power to charge the batteries with. Hall said his company started with solar project installs in California and began to see what's called the "duck curve," where solar generation starts to occur in excess in the mid-afternoon. The growth of electric vehicles had also started to ensure there was a steady supply of high-quality batteries to store the power in. "We're in the early days of the end-of-life EV batteries being available," Hall said. "But there has been a steady stream of those batteries becoming available."

Even after heavy usage in cars, the batteries can often hold a significant amount of charge. And, by working with battery OEMs, B2U is getting access to a number of batteries that never spent much time in cars. "They do have some powertrain warranty dynamics where they're replacing batteries that didn't meet certain promise specs, and there have been some pack replacement programs for some of the early vehicles like the Leaf," Hall said. "There are R&D batteries that are out there, they're going to use for R&D and then becoming available. There are other sort of industry growing pains where you get some batteries that are produced that don't quite meet specs for automotive use that can still be used for stationary storage."

The result is a growing collection of batteries that can still hold roughly 65-85 percent of their original capacity but can no longer provide the performance expected for automotive use. While the performance will continue to degrade over time, grid-level power storage doesn't require the rapid charge or discharge behavior that puts the most stress on the battery's capacity. So the company expects to get significant use from them before they're sent on for recycling. "These batteries work very well," Hall told Ars. "They're engineered for very demanding use cases, and the use case in stationary storage is far less demanding."