Wired Enterprise

Danielle Fong was 12 years old when her mother decided she should go to college. Danielle’s teachers didn’t agree. Though an aptitude test put her above 99 percent of students who had already graduated from high school, her teachers said the move to college would ruin her education. But her mother sent her anyway. “Why would I conceivably put my child through six more years of that bullshit?” remembers Danielle’s mother, Trudy Fong, who was 15 when she herself went to college. “I didn’t bring my kid into the world to have her tortured — and be treated like dirt for being brilliant.”

Little more than a decade later — after graduating from Canada’s Dalhousie University and then dropping out of the Ph.D. program at the Princeton plasma physics lab when she decided academic research was as broken as grade school — Danielle Fong is the chief scientist and co-founder of a company called LightSail Energy. Based in Berkeley, California, this tiny startup is built on an idea that’s as unorthodox as Fong’s education. LightSail aims to store the world’s excess energy in giant tanks of compressed air. The goal is to plug these tanks into wind and solar farms, so that they can squirrel away energy for times when it’s most needed, much like reservoirs store rain water. The wind and the sun are prime sources of renewable energy, but they generate power unpredictably. LightSail’s compressed air tanks, Fong and company say, will make the power grid that much more efficient — and ultimately make the world a greener place.

In 2010, Danielle Fong and LightSail took their compressed air storage idea to the U.S. Department of Energy’s Advanced Research Projects Agency, seeking a grant for their work. The agency turned them away, saying she and her team were unfit to manage a company, that the idea wouldn’t work anyway, and that her air compressor would likely explode. But like her mother, Danielle didn’t listen. Backed by $15 million in funding from green-minded venture capital outfit Khosla Partners and with a team of 32 employees, LightSail is pushing ahead with its plan to reinvent the power grid. Fong believes the potential market for compressed air tanks will exceed $1 trillion over the next 20 years. “People get skittish,” says Fong, who is now all of 24. “If you have your own resources and have a real effort, it doesn’t matter what the rest of the world thinks, in its knee-jerk, fight-or-flight response.”

“If you have your own resources and have a real effort, it doesn’t matter what the rest of the world thinks, in its knee-jerk, fight-or-flight response.”

— Danielle Fong

In a way, Fong is going back to the future. Compressed air tanks have been used to store energy as far back as the late 19th century. They were installed in cities across the globe, from Paris to Birmingham, England to Buenos Aires. Germany has been using the technology for the past 30 years, and a power company in Alabama opened a facility in 1991. The idea is a simple one: If you have a power source — whether it’s gas or coal or renewable sources such as wind — you can use the energy to cram air into a tank. When the air compresses, it heats up, as we all know from high school physics — or just from pumping up a bicycle tire. Then, when you need the energy at some point down the road, this stored heat can be turned back into power. It’s a bit like coiling and releasing a spring. The rub is that you lose power with each transfer, and you lose heat when the air is in storage. Because it’s less than efficient, compressed air storage never caught on in a big way. Current systems often lose more than 50 percent of the power originally put into them, since they use the released energy to run a generator — which only loses more power.

Since the 1700s, scientists have struggled to store energy in more efficient ways, working to refine everything from Galvanic fuel cells to modern-day batteries. The question is always the same: How do we build a system that lets us storage energy and then retrieve almost all of it? But Steve Crane — LightSail’s CEO and a geophysics Ph.D. — says Danielle Fong has cracked at least part of the code. “It’s a little arrogant to put it this way,” he says, “but I think that Danielle has succeeded where Edison and others have failed.” The trick? Fong added water. LightSail’s prototype sprays a dense mist into the compressed air tanks, and this absorbs the heat produced during compression. Water can store heat far more efficiently than air, and with this mist, Fong says, the prototype more easily stores and releases power. It heats up the tanks to temperatures that are only about 10 to 20 degrees warmer than the environment, as opposed to several thousand degrees. The tanks are still pressurized to about 3,000 pounds per square inch — and Fong hopes to increase that amount — but since the power is stored at lower-temperatures, it’s easier to insulate the tanks. Some compressed air storage systems sit deep underground, taking advantage of the earth’s natural insulation, but LightSail’s tanks sit above ground, which is less costly. When you want the heat back, you just reverse the process, spraying the warm water out of the compression tank as the air expands, and it drives a piston to reproduce the power. But in both storing the heat and spitting it out, you need just the right amount of water. LightSail has tested nearly 40 nozzle heads — not to mention various tank designs — in an effort to achieve just the right mix. According to Fong, her system doubles the efficiency of compressed air, from about 35 percent to roughly 70 percent.

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