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The Chemistry Behind The Battery That Could Outperform Tesla's Powerwal

Posted by Owner   |   Filed under templates, internet

OK, so how does all this relate to lithium-ion batteries like the Tesla Powerwall? Recall that a flow battery is designed so that you can scale up the power (the hardware that converts chemical energy to electricity) and the energy storage (the tanks) independently. If you want your charge to last longer, and you have a flow battery, you build a bigger tank. That’s not the case for lithium batteries. “In order for a lithium battery to discharge over a long duration, many separate battery cells are required, rather than one larger battery,” Marshak says. He gave me a hypothetical example to further illustrate this concept:

Suppose for example, you want a battery to provide 2 kilowatts of power for 5 hours (10 kilowatt hours), like the Tesla Powerwall. This would require many smaller lithium battery cells, or one flow battery. If you then want to provide the same 2 kilowatts of power but for 10 hours (20 kilowatt hours), you would need 2x of your lithium battery cells (or two Powerwalls). For the flow battery, however, you just need larger plastic tanks filled with electrolyte. This example illustrates that as need increases for batteries with longer duration discharge, flow batteries can have a lower marginal cost of energy storage than lithium batteries. In our case the marginal cost would be the cost of larger storage tanks, water, alkali (potassium hydroxide), quinone, and ferrocyanide – all of which are inexpensive.

The flexibility with battery tank size also means you can design a flow battery that can last longer than a lithium battery would at peak power, Marshak says. Adds Aziz: “The value proposition of flow batteries is not new: the energy (measured in kilowatt hours) to power (measured in kilowatts) ratio is the number of hours you can discharge your battery before being drained. These two metrics (energy and power) come together in different ratios for different applications. If you want to store your rooftop solar energy so you can run your air conditioning when you get home from work, and run the rest of the electrical appliances in your home through the evening, you might want your battery to discharge over 4 to 16 hours before being drained.” Of course, this battery situation wouldn’t be ideal for powering a vehicle, because you could get heavy tanks pretty quickly. But for stationary storage, the design makes more sense.

Still to be determined is whether the technology will scale, and to what extent regulatory factors will influence the market for this kind of storage. The firm Green Energy Storage negotiated a license for Harvard’s 2014 technology (with bromine) for use in Europe, and is currently in discussions with the university for licensing the new technology. Harvard has not yet chosen a licensee for the U.S. or the rest of the world, Aziz says.

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Comments (3)   |   May 27, 2015   |   Edit