Startup Thinks It Can Make Flow Batteries Cheaper

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Power play: Primus Power provides this glimpse of part of its new flow battery cells. It’s keeping quiet about many of the details of the system as it develops its first full-scale battery.
Credit: Primus Power

ENERGY

Startup Thinks It Can Make Flow Batteries Cheaper

The key is a modular design, which could make the technology practical as a way to keep the grid stable and reduce electricity costs.

A startup called Primus Power has received $11 million in venture capital to help it build the first full-scale version of a new, low-cost flow battery. The company earlier received $18 million via multiple government grants. Its battery is designed to help stabilize the power grid, making electricity cheaper, and making it easier for utilities to integrate intermittent renewable power sources like wind and solar.

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.

The need for such batteries has been growing as utilities anticipate increases in demand that could overload the power grid. Also, many states, most notably California, require the use of large amounts of renewable energy, but because such forms of energy are intermittent, it's difficult for utilities to maintain the match between supply and demand needed to prevent blackouts.

Batteries could even out the spikes in supply and demand by rapidly charging or delivering power to the grid, preventing blackouts and reducing the need for new power lines. But they've been too expensive for widespread use. In almost all cases, it's cheaper to build new power lines or to use natural gas power plants to make up for changes in power output from solar and wind plants. While Primus Power's technology is still too expensive to solve all of the energy storage problems on the grid, it will have many uses.

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, says Haresh Kamath, a senior project manager for energy storage at the Electric Power Research Institute, a nonprofit research organization supported by the electricity industry. But so far, the high cost of initial demonstration projects has stifled investment. 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, says Primus CEO Tom Stepien.

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. These changes would allow for smaller, cheaper batteries that use less material, and that can be easily installed on existing utility property, such as at substations. The system, which is stored inside shipping containers, is portable. This can be a boon for utilities that need battery systems temporarily while waiting for new power lines to be installed. Some other companies are also working on modular systems, but these still use relatively large components capable of delivering one megawatt each or more. Primus Power is taking this approach further—its cells are smaller, delivering only 20 kilowatts each.

Primus 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.

Many other experimental storage technologies are being developed to reach these low costs. A "semi-solid" flow battery technology being developed by a startup called 24M uses much higher concentrations of energy storage materials in the electrolytes, which means they can stores 10 times as much energy as conventional flow batteries. A startup called Liquid Metal Battery is commercializing a battery that uses electrodes and electrolytes that are made of molten metals and salts.