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Summary:

Flow batteries are funky large batteries that use liquid tanks and pumps. There’s a new one being commercialized by a Silicon Valley startup.

Primus Power's flow battery

2014 seems poised to be the year that next-generation battery technologies become more widely available for the power grid. On Tuesday a five-year-old venture capital-backed startup called Primus Power announced that it’s raised another round of $20 million in funding, which it will use to get its battery technology to its first utility and power customers this year.

Primus Power makes “flow batteries,” which store energy like the batteries in your laptop do, but which have the electrolyte (the substance that acts as the medium for the charging and discharging) separated out of the battery cell in liquid-filled tanks. The systems use a pump to move the liquid electrolyte over the electrode, which in turn stores energy.

The Primus Power shipping container.

The Primus Power shipping container, filled with flow batteries.

The benefit of this design is that flow batteries can be cheaper, can be more easily refillable, and can provide prolonged amounts of energy storage compared to traditional enclosed batteries. Primus Power’s flow batteries are supposed to be able to provide energy storage for over a period of four or five hours, while a lithium ion battery can provide energy storage for about an hour, Primus Power’s CEO Tom Stepien told me in an interview a couple years ago.

Primus Power sells an “EnergyPod,” (see above) which is basically a shipping container that’s filled with around a dozen flow batteries stacked on top of each other. Each EnergyPod has capacity to store 250 kW of energy for a cost of $500 per kWh. For large installations a utility can install multiple shipping containers and manage them with the computing and software that Primus Power also provides.

The electrode sits at the top of the flow battery.

The electrode sits at the top of the flow battery.

Power companies are looking to add energy storage technologies like batteries and flow 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 over four or five hours as the wind dies down.

While flow batteries have been on the market for awhile, Primus Power’s flow battery is supposed to be more efficient because it uses one tank, one flow loop, one pump, and no separator (many current ones on the market use two tanks and a separator). Primus’ electrode is also made of metal, compared to the felt or plastic electrodes of some competitors (so higher conductivity) and the electrolyte itself — that flows through the system — is zinc-based.

An early version of Primus Power's electrode.

An early version of Primus Power’s electrode.

Other startups that are building the next-generation of low cost batteries for the power grid include Ambri, Eos Energy, Aquion Energy and others. Several of these companies are looking to commercialize their technology this year. And it’s not just batteries that are emerging for energy storage and the power grid — startups like LightSail Energy and SustainX are working on reinventing compressed air energy storage.

Primus Power has raised a total of $35 million from investors including Kleiner Perkins, Chrysalix, DBL Investors and I2BF Global Ventures. The new round was led by South Africa-based resource developer Anglo American Platinum Limited. Primus has also received $20 million worth of grants from U.S. government agencies, like the Department of Energy.

Primus Power is looking to use these latest funds to deliver their first EnergyPods to customers. Customers include a utility in Modesto, California, the Bonneville Power Administration in the Pacific Northwest, and a microgrid at the Marine Corps Air Station in Miramar, California. California could be home to many of these new power grid energy storage innovations, following the state’s decision to support a large amount of energy storage projects by 2020 in order to help the state meet its renewable energy mandate.

  1. Wow $500 per KWH. That’s a saving of minus 100% compared with current lithium ion. Exciting stuff.

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  2. @DangerousDave, it’s around the cost of lithium ion batteries now, and it’s in low volume first wave of production. The upside is in the longer capacity which can deliver different applications.

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  3. Just for clarification. Does “Each EnergyPod has capacity to store 250 kW” mean the EnergyPod is able to store 250 kWh of energy at a cost of 500$ per kWh ?
    Another important metric is the maximum power which can be delivered by the EnergyPod into the grid and at which rate the battery system can be charged (1C, 2C etc.) from the grid.

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  4. It might help to mention the business plan target cost for the EOS battery and its technology to help the reader see why that approach is indeed lower cost than the vague laundry list of startups.

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  5. Felix Hoenikker Wednesday, February 5, 2014

    longer capacity is just larger tanks, and they’re amp-in-out ratio is not great meaning ya its $500 but you can only cycle it so many times so your asset utilization is different, they also have significantly higher o&m costs. longer term operation hasn’t weighed in any companies favor yet often due to dendridic growths causing shorts. Basically if you don’t clean them real well all the time you get growths inside the cells that perforate the separator.

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  6. DrOmprakash G Kulkarni Saturday, February 8, 2014

    from above details it is not clear about this technology being Green Tech.
    It is also not clear that the initial cost + O&M cost i.e. CAPEX + OPEX for at least 10 years.
    What would be the life expectancy? % degradation per year ? and other technical details.
    If the pump has to operate the problems of pipeline, pump energy, maintenance cost etc. should be taken into consideration.

    Can any one through light on above factors ?

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  7. Firefly Energy is already at $250/ kwhr NOW, and can with modifications to the battery structure / manufacturing process hit $180/kwhr easily. WIth cycle lifetimes of >10 yrs maintenance free.

    A lot of the herculean efforts might be misplaced, technically

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