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Many states want to increase the amount of electricity that comes from wind and solar energy. One challenge is that renewables are not reliable. The wind doesn't always blow, the sun doesn't always shine. So companies are now trying to develop better ways to store energy.
New Hampshire Public Radio's Sam Evans-Brown reports on a company that is working on a storage system that uses compressed air.
SAM EVANS-BROWN, BYLINE: 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 their energy as waste heat.
RICHARD BRODY: So think of a bicycle pump, when you compress the air, that it gets warm, that's waste heat.
EVANS-BROWN: So in Seabrook, New Hampshire, SustainX is building a prototype of what's basically a bicycle pump on steroids. And that means, a lot of heat.
BRODY: We're talking about a potential change in temperature of a thousand degrees centigrade.
EVANS-BROWN: But SustainX's innovation is finding a way to put that waste heat to good use.
BRODY: So we're on the floor of our engineering and development facility. Let's start over here.
EVANS-BROWN: Standard compressed air storage just let's that 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 the air up enough to generate electricity. That's why they're so inefficient. But SustainX catches the waste heat in water.
BRODY: And this is the heat transfer stand, that's actually the cylinder in which the heat transfer is taking place.
EVANS-BROWN: Later, when they need to make juice, it 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, say homes, a facility can power, the amount of storage tanks attached to it determines how long it can keep that up for.
Probably the biggest advantage that SustainX is 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.
BRODY: These types of engines, this family of engines, powers 80 percent of the world's marine fleets, 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.
EVANS-BROWN: That means it's pretty cheap with no hazardous chemicals to get rid of, which gives compressed air a leg-up over batteries.
DAN NOCERA: That gets a lot of press. You hear battery, battery, battery everywhere you go.
EVANS-BROWN: Dan Nocera is a chemist at MIT who studies storage technologies.
NOCERA: 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.
EVANS-BROWN: 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 solar and wind has come down a lot, if you have to add a storage facility to the bill, the investment won't look so attractive. But grid operators are imagining ways that storage facilities could make money.
Gordon Van Welie is the CEO of ISO New England, the not-for-profit that operates the region's power grid.
GORDON VAN WELIE: 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.
EVANS-BROWN: 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...
WELIE: And you'll end up with this curious situation where nuclear power stations will actually pay to run. It's a great deal for storage operators, because at that point they're being paid to store the energy.
BRODY: So, even though storage still faces serious market headwinds, there's a good chance that companies like SustainX can actually make money.
EVANS-BROWN: 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 from scratch, up to a $500 million initial stock offering.
For NPR News, I'm Sam Evans-Brown in Concord, New Hampshire. Transcript provided by NPR, Copyright NPR.
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