Primus Power working on scaling up $500 per kilowatt hour flow batteries and has started a different $100 per kwh design

Primus Power has a low cost, versatile and power dense battery system that economically addresses a wide range of energy storage applications. They are working to commercialize, deploy and monitor a 25 MW • 75 MWh energy storage system for a California utility.

MIT Technology Review explains what Primus Power is doing to make flow batteries radically cheaper

Primus Power is trying to overcome one of the fundamental problems that have plagued flow batteries. The technology, in theory, at least, could be one of the cheapest forms of grid storage, since it requires inexpensive and abundant materials. But in practice, flow batteries have been very expensive, in part because they’re large and have to be custom-built on site. Primus is hoping get around this with a new design that can be mass-produced in factories


With flow batteries, a mixture of electrolyte and energy storage materials are stored in massive tanks—some as large as 10 meters high and 20 meters wide—and then pumped into a device where current is generated. Because flow batteries use cheap materials such as water-based electrolytes and energy storage materials made of abundant materials such as iron and zinc, the initial high costs could come down once enough of them are built.

Primus Power is replacing large storage tanks with cells the size of hot water tanks. This approach sacrifices some of the potential cost savings of large storage tanks, but it more than makes up for this with the savings possible from mass production in a factory.

The company is also using novel zinc-based energy storage materials and a better design to increase the power output of the battery by about four to five times.

rimus Power joins about 20 other companies that are attempting to make cheaper flow batteries. It’s aiming to reach costs near $500 per kilowatt hour of storage capacity. (It will be at least a year before the company can quote solid cost figures, Stepien says.) This would be much cheaper than ones that have been made so far, according to Kamath. Companies often don’t disclose their costs, but he estimates that many are upwards of $2,000 per kilowatt hour.

At $500 per kilowatt hour, the batteries would be cheap enough for widespread use on the grid for applications such as deferring power line construction, Kamath says. It would also be substantially cheaper than the technology’s key competitor now—lithium-ion batteries—which cost about $1,000 per kilowatt hour, he says. But it would still be too expensive to meet the U.S. Department of Energy’s goal of energy storage systems that cost less than $100 per kilowatt hour.

If flow batteries could supply power for as little as $100 per kilowatt hour, they’d be a cheaper option for utilities than the installation of a new fossil-fuel-based power plant to offset the daily variations in wind or solar power, Kamath says. Primus Power recently won a grant from the DOE’s Advanced Research Projects Agency for Energy to develop such a low-cost battery, but that will be a different design than the one it is currently scaling up, and the company isn’t saying much about it yet.

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