A start-up says it has a solution to an old problem: storing energy for public utility power grids.

It may not sound like a problem at first. But a big knock against using renewable energy such as wind and solar power is that the sun isn’t always shining and the wind always blowing. That makes the power source to unreliable for big power companies, who need to accommodate fluctuations in energy need.

Now, if somebody could find a way to store energy harvested from solar and wind power plants, that would great. Imagine a huge battery that soaks up the energy and just sits around until a power company needs to tap it. However, big batteries are expensive and have a limited number of recharge cycles.

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Eos Energy Storge, based in Easton, Penn., says it is developing a zinc-air battery that can be recharged thousands of times, enough to last 30 years. Zinc-air batteries aren't new; they're the button cells in small devices such as hearing aids and watches. They use oxygen that's abundant in the surround air to react with zinc to produce a charge.Zinc is cheap, and using atmospheric oxygen saves weight and obviates the need for a potentially toxic chemical to drive the reaction.


Ordinarily, though, it's difficult to build a rechargeable battery this way because a lot of energy is necessary to break down the zinc hydroxide that forms as a result of the reaction in the cell. Eos claims to have a rechargeable version that can go through thousands of cycles — 2,700 in their trials, though the goal is to hit 10,000.

The company says it uses novel chemistry in the electrolyte, avoiding the formation of dendrites (“whiskers”) when the zinc comes out of solution. Eos also says its electrolyte does better at maintaining the shape of the zinc anode.

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The total power in each battery will be up to a megawatt that would last six hours (6 MWh). A typical home in the United States uses about 958 kilowatt-hours in a month, so it’s enough to power a typical home for more than half a year. But the batteries are more likely to be used by industry, either by solar and wind power plants to store energy or as back-ups for businesses. (One of these batteries would fit in a 40-foot shipping container, so it’s a bit large for the backyard). Eos says the first ones should be produced in 2013.

The batteries will sell for about $1,000 per kilowatt, or about $160 per kWh. An SEC filing says Eos has received some $20 million in funding, so it’s a serious enough technology that some smart people are willing to part with their money to get it built.