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Better Storage Options Sought as Wind, Sun Power Catch on

September 22, 2009 at 12:00 AM EDT
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Tom Bearden reports on new innovations that would allow for better storage of electricity generated by the wind and sun.

TOM BEARDEN, NewsHour correspondent: Solar panels like these may soon spread over 500,000 acres of California’s Mojave Desert and on public lands in many other states. Wind farms have already sprouted in 28 states, and more are on the way.

The Obama administration wants to spend $209 billion on renewable energy projects like these over the next 10 years, but there’s a huge obstacle to renewables taking a larger share of the nation’s utility burden: What happens when the sun isn’t shining and the wind isn’t blowing?

Two scientists at the Massachusetts Institute of Technology are experimenting with innovative approaches that might provide a way to store renewable energy.

DON SADOWAY, Massachusetts Institute of Technology: Just above us is the Radiation Laboratory where radar was first practiced.

TOM BEARDEN: Professor Donald Sadoway often jokes about the long, dark hallway that leads to his subterranean battery laboratory. He says the biosciences get better spaces because they’re currently considered sexier.

DON SADOWAY: It’s interesting how the upper electrode has more curvature to it.

TOM BEARDEN: But Sadoway and his group of graduate students think what they’re doing might turn out to be just as important.

DON SADOWAY: This is the key to enabling renewable energy. The big problems in photovoltaics, solar, and wind is storage. And you can’t just go to the auto store and buy a whole bunch of lead acid batteries and lie them down in a field. You’ve got to have high-density, high-powered energy storage capability, and so the battery is the key enabling technology.

TOM BEARDEN: Sadoway’s research is focused on what batteries are made of and how to scale them up to store large amounts of electricity. All batteries have an anode, where a current flows in, and a cathode, usually made of metal, where a current flows out. Both are immersed in a liquid electrolyte, something that conducts electricity.

Since Alessandro Volta invented the battery in 1800, scientists have been experimenting with various materials. Most of us have heard of some of these ingredients because today’s batteries are often described by what’s inside: lithium ion, nickel cadmium, lead acid.

But the Sadoway group is trying something completely different. They’re experimenting with batteries that contain liquid metals heated to high temperatures.

DON SADOWAY: So this is a battery that’s designed for large-scale energy storage. We’re talking here about in the extreme grid level storage, also important for things like renewables, solar and wind.

And it’s a very, very different design. It consists of three liquid layers, so we call it liquid battery. There’s no solid in here, except for, obviously, the case. But we have a liquid metal on top of a liquid salt on top of a liquid metal, and the two liquid metals are two different electrodes.

And they naturally — they separate, sort of like salad oil and vinegar, because when you’re storing the grid, you’ve got to be able to store not just a lot of energy, but take it down and give it back at very, very high current rates. So we need megawatt hour storage at megawatt power delivery rates.

TOM BEARDEN: This is just a small test device. Sadoway envisions liquid metal batteries the size of electrical substations routinely storing megawatts of power generated by solar collectors during the day or by wind farms. Sadoway is also working on much smaller batteries for more common applications, like this thin, flexible design that, unlike most, contains no liquid at all.

DON SADOWAY: You can imagine, in biomedical applications, this thing can’t leak if the case is punctured. You know, if you want to change the batteries in the watch, you change the band.

It opens up new design possibilities, impregnating fabrics, draperies with photo detectors, and then having a flexible battery so that the drapes actually harvest light and then give back electricity when it’s dark. And you can’t do that if you’ve got batteries that have the form factor of the regular right circular cylinder that will break your toe if you drop the thing.

The hydrogen economy

TOM BEARDEN: A short elevator ride up and a walk down the hall from Sadoway's lab, another MIT group is also experimenting with ways to make solar power more viable.

DANIEL NOCERA, Massachusetts Institute of Technology: Because then the voltage would shift, right?

TOM BEARDEN: Professor Daniel Nocera and his research assistants are taking a different approach. This small lab experiment is splitting water into its two component parts, hydrogen and oxygen. There's nothing new about that. It's call electrolysis, and most of us learned how to do it in high school chemistry class.

Just like a battery, electrolysis uses an anode and a cathode immersed in water. Feed in electricity and you generate hydrogen and oxygen gas, but it takes a lot of electricity to make that happen. Nocera has come up with a way to reduce the amount needed by using a catalyst in the water, cobalt phosphate. It reduces the energy requirement by nearly half.

DANIEL NOCERA: So you could have your photovoltaic, and then sunlight hits your photovoltaic and runs your house. If I take a little bit of that current from the photovoltaic and feed it to this catalyst, it will split water to oxygen and hydrogen. You could store that in some tanks, like a propane tank. And then at night, the sun goes down, but you have something extra on hand.

TOM BEARDEN: Nocera says the stored hydrogen could be burned in a fuel cell. A large fuel cell could power the house; a smaller one could be used to run a car. Proponents call the large-scale production and use of hydrogen as a fuel the hydrogen economy.

DANIEL NOCERA: I think this is a major step towards the hydrogen economy, this type of experiment. Now, why do I say that? Because what you're using as your source of hydrogen is water. And then, when you make the hydrogen and oxygen, it recombines, you get water back again, so it's a closed system.

TOM BEARDEN: It would also solve the main problem facing the hydrogen economy: storage and transportation.

DANIEL NOCERA: This type of experiment in advance takes that problem away, because the hydrogen is being made locally. You don't need to put it -- go to a gas station, a hydrogen gas station. You don't need a pipeline of hydrogen. You make it locally, fill your own car, take care of your own house. And so I think this type of experiment, this type of discovery, and this idea of this personalized energy really is the enabler for the hydrogen economy.

TOM BEARDEN: But both Sadoway and Nocera are quick to say that a lot more work remains to be done to verify whether any of these approaches are commercially viable.