Jul 042012

LightSail’s process recovers 70% of the energy it puts out

Danielle Fong might have dropped out of grade school, but that hasn’t stopped her and her company LightSail from finding a way to potentially drastically change how much power we can get from renewable energy.

It is not unreasonable to expect that the renewable energy collected by the world’s solar panels and wind farms is being stored somewhere, ready and waiting to power our microwaves and hairdryers at a moment’s notice. Bad news: mostly, it’s not. Sure, there are a few methods in practice–expensive batteries that degrade over time, a medieval-sounding technique that involves pumping water up and down a hill–but by and large, if there’s a lot of wind blowing but not enough lightbulbs to use it, that energy simply goes to waste.

Hopefully, that’s about to change. Danielle Fong is the chief scientist (and grade-school dropout) behind LightSail Energy, a Berkeley-based team that’s developing compressed-air technology to store the power we don’t use, and return it to the grid when needed. It’s a simple concept: Just use the electricity generated by your solar panel and/or windmill to power a compressor, pushing air into a tank. When you want your energy back, you release the air out of the tank, and use it to drive a generator, creating electricity. “That’s the basic idea,” says Fong. Sadly, there’s more bad news again.

Compressed-air technology has long struggled with efficiency–the heat energy generated via compression has always gone to waste–and that’s the almost part where LightSail’s greatest innovation swoops in. Fong was researching compressor-powered vehicles when she had her eureka moment: “It became clear that what you wanted to do for maximum efficiency was keep the temperature as close to constant as possible in compression and expansion,” she says. “It turned out nobody had figured out how to do that, and I read a Wikipedia article saying it was impossible to do it, and I said, ‘My god, that’s not true. You can just spray water in.’ And then I was like, ‘Wait. I could just spray water in.’ And thus the company and core idea was born.”

What does spraying water in do? Best to let the genius explain: “Instead of wasting the heat, we collect it by spraying water into the air during the compression process,” she says. “That keeps the temperature down, and it keeps the pressure down, so you have to put less energy in to compress the same amount of air. During expansion, spraying water sends heat back into the air, which keeps the pressure high, and increases the amount of energy you get back.” Science aside, the numbers don’t lie: LightSail’s process recovers 70% of the energy it puts out, pretty much doubling the efficiency of the standard compression method. “Eventually, we’re going to replace all of the energy requirements of the world,” says Fong. “Or so we plan. The world has a way of turning out with surprises.”

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