Solar and wind power are intermittent, and if enough of them are powering the grid, some kind of storage will be necessary. And storage means batteries, right?

Not necessarily. In Seabrook New Hampshire, a start-up is doing it with compressed air.

It’s pretty easy to see how energy stored as compressed air works: When you let go of a full balloon, it flies all around the room because of the energy stored inside. So if you use electricity to run an air compressor, you basically just need to find a way to run that compressor backwards to get electricity again.

There are places in the world that do this, one in Alabama and one in Germany, but just those two so far. That’s because they aren’t that efficient. Richard Brody is Vice President of the energy storage start-up SustainX. He says these facilities lose almost half of their energy as waste heat.

“So think of a bicycle pump, when you compress the air, it get’s warm, that’s waste heat,” Brody explains. SustainX is building a prototype of what’s basically a bicycle pump on steroids.

That means, a lot of heat. Brody says, “We’re talking about a potential change in temperature of a thousand degrees centigrade.” SustainX’s innovation is finding a way to put that waste heat to good use.

Tried and True

Standard compressed air storage just lets the waste heat, and the energy in it, vent into the atmosphere. Later, when they run the air back through to make electricity, there isn’t enough energy left in it to make a turbine spin. So they actually have to burn natural gas to warm it up enough generate electricity. That’s why they’re so inefficient.

But SustainX catches that heat in water. On the floor of the company’s workshop, Brody points out the prototype heat-transfer stand where that takes place. Later, when they need to make juice, the machine uses the hot water to warm up the air, instead of having to burn gas. While the size and speed of the

compressor determines how many homes a facility can power the amount of storage tanks attached to it determines how long it can keep that up for. This is the distinction between a megawatt and a megawatt hour.

Probably the biggest advantage this technology has going for it, is the technology behind it is tried and true. The air is stored in standard issue natural gas pipeline, and the engine that runs the compressor has a long track record.

“These type of engines, this family of engines powers 80 percent of the world’s marine fleets,” notes Brody, “so think about all the large ships on the sea – container, passenger – almost all of them are powered by these types of engines. Very dependable, very mature technology.”

That means it’s pretty cheap, and no hazardous chemicals to get rid of, which gives compressed air a leg-up over batteries.

"Battery, battery, battery, everywhere you go"

“That gets a lot of press. You hear battery, battery, battery everywhere you go,” says Dan Nocera, a chemist at MIT who studies storage technologies. “A lot of people might not realize that compressing air, that stores about as much energy as batteries. It’s kind of the under-represented kid on the block when it comes to energy storage technologies.”

He says it’s unlikely that any type of storage is going to become widespread anytime soon. Right now it’s cheap to get electricity from natural gas plants. And while the cost of wind and solar has come down a lot, if you have to add a storage facility to the bill, the investment won’t look so attractive.

But SustainX does see a niche for itself in the electricity market, and it’s not just in smoothing the irregular energy flow coming from renewables.

For example, maybe your community needs a little bit extra power in the heat of the day, but doesn’t want that unsightly new transmission line? Pop some storage in an industrial park, and save up the energy you need from your existing power plants during the night, when everyone is asleep.

Finding the Market for Storage.

And grid operators are imagining other ways to let storage facilities make money. Gordon Van Welie – the CEO of ISO New England, the not-for-profit that operates the region’s power grid – explains a concept called “negative pricing”.

“A nuclear power station is not built to be switched on and off every day, so it’s going to want to run and produce all the time,” he says. But when there’s too much power on the grid, those stations are told to shut down.

However, if they partner up with a storage facility, “you’ll end up with this curious situation where nuclear power stations will pay to run. It’s a great deal for storage operators, because at that point they’re being paid to store the energy.”

So, even though storage still faces serious market headwinds, there’s a good chance that companies like SustainX can actually make money.

One good indication of that is real live capitalists are taking them seriously. SustainX has signed up a CEO that took a solar panel manufacturer – GT Advanced Technologies – from scratch, up to a $500 million dollar initial stock offering.