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Flow Batteries: Coming to a wind farm near you?

A year ago while I was refreshing my knowledge of lithium-ion batteries, I started to hear chatter about other, newer types of batteries that were attracting attention and funding. One was a rather yoga-sounding technology: flow batteries.

I was reminded about flow batteries when I read that the last set of Recovery Act funding from DOE’s ARPA-E program would go to energy storage technologies. Three of the projects will be working on flow batteries, one of which will be led by Lawrence Berkeley National Laboratory.

But what is a flow battery? Basically, it’s a battery where the voltage differential is stored outside the cell in two separate tanks of electrolytes. Pumps circulate the two fluids into a cell chamber where they come together separated by a membrane that prevents them from mixing, but does allow select ions to pass through. Electrodes in the cell convert the chemical energy to electric current.

The benefits of flow batteries are that they are highly rechargeable – they can be recharged to 100% of capacity fairly quickly. They are “deep discharge” capable, which means you can deplete the battery charge completely without damaging it. These two characteristics allow you to use an external power source like a wind or solar farm to charge the batteries during the day and tap the batteries on a daily basis when those sources are off-line (i.e., at night).

The Berkeley Lab folks, led by researcher Venkat Srinivasan (who authors the This Week in Batteries Blog) will be working on a proof of concept flow battery using hydrogen-bromine chemistry. They have commercial partners on board as well, including DuPont, which will contribute membrane know-how, and the Bosch Group for catalysts.

There are a few technology firms already out there with flow battery technologies. They promote their products as useful for off the grid energy storage (for example to store energy from diesel generators) as well as for smoothing the supply of electricity derived from renewable sources like solar and wind. Deeya Energy is probably the most well-known; it uses an iron chromium chemistry to power its redox flow batteries. The company raised $30 million in its third round of venture financing in 2009 and has one battery product on the market, aimed at powering remote cell phone towers.

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