Danielle Fong has a clever way to widen the use of renewable power: take the electricity produced by, say, a wind farm and use it to compress air in carbon-fiber tanks. When the wind quiets down, use the compressed air to drive an electric generator, eliminating the intermittency that consigns wind farms to a small role on the grid. The concept isn’t new, but it has been limited because air heats up as it is compressed, making it difficult to store. Fong figured out that spraying water into the compressor to cool the air makes it possible to store so much energy that it could be cheaper than using batteries. In 2009, she cofounded a company called LightSail Energy that has raised $70 million from the likes of Bill Gates and Peter Thiel, but it still is only on the verge of key demonstration projects. Fong, 28, spoke to MIT Technology Review’s executive editor, Brian Bergstein, about the challenges of commercializing energy technologies.

You’re planning to begin pilot tests in 2016. Why is it taking this long to scale up your technology from the lab?

We thought that we would be out in the market about twice as fast. We were going to cut some corners by converting an off-the-shelf natural-gas compressor. Ultimately, we decided that would be too much of a compromise. In early 2012 we decided to switch and just go directly to the product that we would ultimately want.

Part of it is there’s a lot more to do than we expected. Part of it is it’s difficult to find financing, although we have raised a decent amount.

Why hasn’t the money you’ve raised been enough?

It’s not actually a lot of money compared with how much it takes to develop an engine, for example, or a compressor. Say you’re a power plant company, and you’re trying to make a better gas turbine. Even when you hit volume, you’re going to be spending more than $100 million, maybe a couple hundred million dollars. Who writes those checks? There just aren’t that many. There used to be. Those times are over. Now what you need to do is figure out how to get to a commercial scale so that you can bring the unit cost down without spending that kind of money.

Our answer to that, by the way, is our tanks. We have the most advanced carbon-fiber tanks, we think, on the planet for bulk storage of gases. We’re manufacturing and selling the tanks, with a healthy profit, [to] the natural-gas industry.

And yet you still need to raise more money.

Our plan has us going profitable on less than $30 million [of] additional capital. Technically, we wouldn’t need to raise money after that, if all goes according to plan.

There were so many things when we started out that people said, “This is impossible. If you spray water into an air compressor, it’ll break. Will it transfer heat fast enough? Can you separate the water from the air? Can you compress and expand out of the same system? Can you build all of this stuff?” We’ve done the impossible on, I think, a reasonable budget.

Does it frustrate you that in other tech sectors, money is very easy to come by?

I will admit a fair amount of frustration. There are a dozen venture-funded apps to pick up your dry cleaning.

If we fail here, and it may well be the right solution, no one is ever going to get funded to do it again.

It must seem both promising and daunting that the opportunity is so huge.

We need energy storage in the terawatts. We’re talking about getting to half a megawatt [with each of LightSail’s storage machines]. That’s a factor of a million. That’s where my head is at.