Behind the scenes of Primus Power’s battery lab

By the end of next year Primus Power, a startup in Hayward, Calif., could be installing the first commercial deployment of its grid-scale batteries, it calls EnergyPods, with a utility in Modesto, Calif., known as the Modesto Irrigation District. The $56 million deal is a major milestone for the three-year-old startup, and it also could be a significant breakthrough for the goal of adding more clean power to the grid.
Primus Power’s EnergyPods aren’t like the regular lithium ion batteries that fill your laptop or cell phone. The company makes flow batteries, which are large refrigerator-looking devices that pump liquid electrolyte over an electrode to store energy. Power companies are looking to add energy storage technologies like batteries to the grid as a way to store energy generated by clean power sources like solar and wind, which only provide energy when the sun shines and wind blows. The idea is that a flow battery could store energy from, say, a wind turbine, when the wind is blowing extra hard, and the battery can release the extra energy when the wind dies down.
While lithium ion batteries are also being connected to the power grid, they tend to offer a quick, fast burst of storage capacity for about an hour, explains Primus Power’s CEO Tom Stepien in an interview in the company’s labs in Hayward. Flow batteries, on the other hand, can provide prolonged storage for four or five hours, which makes it more ideal to match with clean power sources, he says. The Modesto utility will use the flow batteries to “firm up” wind power that is shipping from a wind farm in Oregon down to Modesto.
Primus’ EnergyPods are made up of 14 of these flow batteries that neatly fit in a shipping container and can provide 250 kW of storage. For utility deployments, the shipping containers are stacked together; connected with a computing and control container, they can provide 2 MW of storage, and more. The flow battery costs $500 per kWh — significantly less than many battery technologies — and can last for 20 years.
While flow batteries have been under development for years, Stepien says that some of Primus Power’s advantages are that its battery only has one tank, one flow loop, one pump, and no separator so the system is more efficient than current ones on the market that use two tanks and a seperator. The battery’s electrode is also made of metal, compared to the felt or plastic electrodes of competitors, which means it has higher conductivity. The electrolyte itself — that flows through the system — is zinc-based.
Stepien showed me around the company’s 16,000-square-foot lab in Hayward this week, and showed me an EnergyPod and its testing lab. We also chatted briefly with founder Rick Winter, who developed the original flow battery technology. Primus Power is backed by three rounds of venture capital funding — from Kleiner Perkins, Chrysalix, DBL Investors, and I2BF Global Ventures — and three grants from the Department of Energy, the ARPA-E program, and the California Energy Commission.