The World's Biggest Battery : Planet Money California has a ton of solar power. But as soon as night falls, it's gone. Today on the show: How to bottle the sun.
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The World's Biggest Battery

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The World's Biggest Battery

The World's Biggest Battery

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  • <iframe src="" width="100%" height="290" frameborder="0" scrolling="no" title="NPR embedded audio player">
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Hey, Scott. It's Dan Charles.


CHARLES: How are you?

FLAKE: I'm doing fine.

CHARLES: I'm in Washington, D.C. Scott Flake is in Sacramento, Calif.

What's the - what's it like out there in Sacramento today, just weather-wise?

FLAKE: A beautiful, sunny day, clear skies and warming up.


Scott's not in the forecasting business. He is in the energy business, so sunlight to him is money.

CHARLES: Take a look at this website, he says. Here's a chart showing where California's getting its electricity right at this moment. It shows nuclear plants, gas-burning plants, hydroelectric dams. And there's a chart with different colored lines showing renewable power. There's wind, geothermal. There's biomass.

SMITH: Most of these lines are pretty flat, except for one. Soaring above them all is a bright golden line.

CHARLES: That is solar power.

This is an incredible chart. This solar curve, it's just like...


CHARLES: It's like this mountain that suddenly appears in the middle of the day.

FLAKE: Starting about 6 o'clock this morning when the sun came up, it really started ramping up quickly.

CHARLES: It goes from zero to - like, where are we right now?

FLAKE: Just over 10,000 megawatts.

CHARLES: Which is almost half of all the electricity that California is using right now.

FLAKE: That's pretty incredible.

SMITH: And just as incredible - what that sunlight is doing to the price of electricity right now.

CHARLES: Here, I can see what utilities are paying for electricity, at dozens of different places across the state, minute by minute. Sometimes it's expensive, but there are times - especially on weekends when people are not using much electricity - this flood of solar energy does really weird things to those prices.

FLAKE: Oftentimes, you can have more supply of energy than demand. And so what happens is the - lot of those prices start to show up as negative numbers, so...

CHARLES: Negative prices?

FLAKE: Right, so...

CHARLES: How can there be negative prices? What does that mean?

FLAKE: Well, what it means is people don't need that much energy.

SMITH: And if electricity is worth less than nothing, the power company pays other people to use the power to take it off the grid.

CHARLES: Yeah, like that attic full of junk you'll pay somebody to get rid of. And there is even more solar power on the way. The law in California demands it. Companies are building vast solar arrays covering thousands of acres of California's desert.

SMITH: When you first came to us with this story, Dan, I thought this is really news to me, that within our lifetime, California will have the source of energy that is safe and renewable, that it can run everything in the state.

CHARLES: Until the sun goes down.

SMITH: Until the sun goes down. And this has always been the knock on solar energy - you build all the solar cells, you run all the transmission lines, and then the sun sets, as it does every day, and all of a sudden, you have to have gas-powered generators just to keep your lights on.

CHARLES: Which is why the biggest quest in energy right now is a way to store all that beautiful solar energy. Solve this problem, and you are well on your way to solving global warming.

SMITH: And all you need is a battery that can bottle the sun.


SMITH: Hello, welcome to PLANET MONEY. I'm Robert Smith.

CHARLES: And I'm Dan Charles. Today on the show, I visit the biggest battery in the world - a technology so old it's almost forgotten. It may save the planet.

SMITH: But it does involve moving mountains.


SMITH: We're going to begin with some high school physics. And like any good high school physics teachers, we've got props. We've got metaphors. And we're going to use them. Now, when the sun hits a solar cell, it starts electrons moving in a wire. The more light, the more electrons flow through that wire.

CHARLES: The wires come together. The flow of electricity becomes a mighty river.

SMITH: And it can power millions of smoothie blenders in Los Angeles.

CHARLES: Grow lights in Humboldt.

SMITH: The surveillance algorithms at Facebook in Silicon Valley - all of this power is a California treasure.

CHARLES: But the way the electrical grid works is you have to use the power as it's flowing. There are very few ways to store up electricity and use it later.

SMITH: So how do you capture it?

CHARLES: We called up one of the largest electricity companies in California, PG&E, Pacific Gas & Electric, arranged to talk with a senior vice president there, Fong Wan, and his PR guy, who accidentally got dropped off the conference call.

FONG WAN: I'm in trouble now. I'm not supposed to do these interviews without my communications department (laughter).

CHARLES: So there's an obvious place to store electricity - one we use every day.

WAN: Are you familiar with the lithium ion batteries?

SMITH: Yes, batteries. You're probably using one in your phone right now. In fact, in California, you may have charged your phone with electricity from the sun and are now storing solar energy in your pocket.

CHARLES: Very good. PG&E is thinking of the same thing.

WAN: Right now, we are in the process of purchasing a lot of battery storage.

CHARLES: Big ones, though - the size of trailers lined up in a parking lot.

SMITH: Imagine a thousand Elon Musks, each with a thousand of the giant batteries that he's building out the desert.

CHARLES: This problem's too big, even for Elon Musk. PG&E is talking with him and five other battery makers.

SMITH: There is a slight problem here. If you remember at the beginning, we found out how much electricity the sun is producing right now in the middle of the day in California.

FLAKE: Just over 10,000 megawatts.

CHARLES: All those big batteries that PG&E is buying, when they are all built five years from now, they'll capture maybe 1 percent of the amount of electricity that California will need to store down the road. Fong Wan is looking for something bigger - better.

WAN: I think we need to go back to - be a little more daring, a little more risk taking.

SMITH: Says the man with no PR person around.

CHARLES: OK, so where can you find more battery power sitting around?

SMITH: Well, if you can't build that many big batteries, then maybe you could just find millions of small batteries. I mean, we mentioned the iPhone. Everyone has an iPhone with a little battery in it. A lot of people have electric cars.

CHARLES: PG&E is looking into this. The idea is if you could encourage people to charge up their electric cars when the sun's shining - when they're at work, maybe - then when they plug their cars in at home in the evening, PG&E could draw on that stored electricity - for a price, of course.

SMITH: Which is a pretty cool idea.

WAN: There's great potential, but - very challenging. We all - creatures of our own habits. At 7 p.m., I'm probably using the car.

SMITH: It's probably a bad idea to base your entire electrical grid on people getting home from work on time.

CHARLES: True, but we are not out of options. Energy is energy. You don't have to store it in the form of chemicals in a battery. You can convert electricity into something that's literally pent up physical energy.

SMITH: Like my teenagers right now in the last week of school.

CHARLES: (Laughter) Maybe that would work. But, no, imagine compressed air.

WAN: Compressed air storage is - it's very fascinating.

CHARLES: Basically, when the sun is shining, you use all that extra electricity to pump air into big underground caverns, like blowing up an incredibly strong and massive balloon.

SMITH: I've got one right here.


CHARLES: And then, at sunset, you open a valve, and all that super-compressed air comes blasting out.

SMITH: OK, I've been waiting for this.


CHARLES: It blows through a turbine, which spins and generates power.


SMITH: (Laughter) This is not going to work.

CHARLES: It can, apparently. PG&E actually tried this out. They got $50 million from the government to blow air into some old gas wells.

WAN: We were able to successfully drill into those wells, successively pump air at a very high pressure. And the air stayed pressurized underground. But we ran into a little bit of hiccup right now. That is it's not cheap.

SMITH: All right, compressed air - too expensive; batteries - too small. What else you got?

CHARLES: Here's another thing that stores energy - wheels.

SMITH: Wheels (laughter) - OK.

CHARLES: You know how when you pedal really fast on a bike, your momentum can carry you for blocks? You can do something similar with something called a flywheel, a giant wheel made out of really heavy stuff.

SMITH: Conservation of angular momentum, sure. You use the solar electricity to get this giant wheel spinning.

CHARLES: Think maybe a giant record player.

SMITH: Which radio studios - we happen to have one. If we get this thing moving with our finger...


BEATLES: (Singing) Here comes the sun. Here comes the sun.

CHARLES: Faster and faster and faster.

SMITH: Super fast.


BEATLES: (Singing) Little darling, it's been a long, cold, lonely...

SMITH: Then when the sun goes down, the record player's still spinning. It's still got momentum - slowing just a bit.


BEATLES: (Singing) Here comes the sun. Here comes the sun.

CHARLES: And then later in the evening when everybody turns on their TVs, that giant spinning wheel can drive a generator.


SMITH: It's going to be a very, very big wheel.

CHARLES: PG&E paid some people to build one.

WAN: But they were not able to deliver. They couldn't make it work.

CHARLES: OK, so flywheels don't work?

WAN: Well, economically. And technically...

CHARLES: (Laughter).

WAN: ...I think they actually do.

SMITH: I'm starting to see why, for the last hundred years, we have not made a ton of progress on storing massive amounts of power. You have all these good ideas in theory, but the scale is so incomprehensible. The record player is so large, how do you even get the money to test it out?

CHARLES: But here's the thing. Scott and Fong - both of them - they think there is a way to do this. When I got them talking about their dream way to store electricity, they started talking about a technology that's not some hot new invention. It's actually old. In fact, it's so old, some people write it off like a relic of an earlier age. But this is big. It is bold. It's hidden in the hills, Robert.

SMITH: And I'm sure you're going to tell us what it is...

CHARLES: Yes, Robert. After the break, I'm going to visit the biggest battery in the world, and it's made out of water.


CHARLES: The biggest battery in the world is a giant lake tucked away in the Appalachian Mountains on the border between Virginia and West Virginia.

It is just unbelievably beautiful driving into this place. We're driving down through this valley, a ridge of green on either side, blue sky above, grassy meadows with cows grazing on them. It is just idyllic here.

SMITH: You're listening to travels with Dan, the No. 2 insomnia podcast on iTunes.

CHARLES: It was kind of dreamy, until you get close. And, suddenly, I see these huge electrical transmission lines. And then, there's a sign - Dominion Energy - a gate, a guardhouse. It's empty. But there's a phone.

SMITH: Do not skimp on the sound effects here.


SMITH: I could picture it. Close the door. Did you just leave the door open?




BILL: Control room. Bill (ph).

CHARLES: Hi. My name's Dan Charles...

BILL: OK. So what we could do is I'll open the gate for you.


BILL: And you go up the hill, OK?

CHARLES: All right.

BILL: Then, when you go up the hill - you get to the top of the hill, you go one more mile, OK?

CHARLES: Got it.


CHARLES: Thank you so much.

BILL: Thank you.

CHARLES: All right. Bye.

I drive over the hill and realize it's actually a dam. And there is the lake. It fills this whole valley, 500 acres of blue water.

SMITH: And this is it?

CHARLES: Well, close. There is a windowless concrete building right on the shore of the lake. I go inside, meet Sean Fridley, the station director. We get in an elevator.


CHARLES: And we're going down into the ground, basically. Is that it?

SEAN FRIDLEY: Ground's on one side, and we've got the lower reservoir on our other side here, on the east side. So we will be well under water here.

CHARLES: We arrive at the beating heart of this monster - six motors the size of carousels lined up in a row in a cavernous hall. We're looking down on top of them.

SMITH: But those aren't the batteries.

CHARLES: These are pumps. They're pumping water from that lake I saw up through tunnels in the mountain - huge tunnels big enough to drive cars through - into a valley up above us where there's another dam. The water from this lower lake goes up, up, up and makes a new lake way up there.

And the water has to go up 1,200 feet?

FRIDLEY: Close to 1,200. That is correct.

CHARLES: So I was thinking last night, that's the height of the Empire State Building.

FRIDLEY: Is it? Yes.

CHARLES: You seem kind of nonchalant about it.

FRIDLEY: It's a massive project.

SMITH: So all that water stored high, high, high above the first lake, that is storing the energy?

CHARLES: That's right. We went up there. It's just sitting there ready for when people turn on their air conditioning and need more power. At that point, they'll open a valve. And millions of tons of water will rush back down through those tunnels in the mountain back down to those motors, which become generators instead of pumps. They spin the other way, generating electricity, sending power out to the country's electrical grid.

It seems awfully peaceful to have that much power tied up in this.

FRIDLEY: It's - the mountain of power and the quiet giant is some of the terminology we've used over the past...

CHARLES: That's real, isn't it? I mean...


CHARLES: You got cities' worth of power just waiting here.

FRIDLEY: That's correct.

CHARLES: An hour later and we're back at that concrete building, and a call comes in. The East Coast needs more electricity.

SMITH: All right. I made all those California jokes. We need East Coast uses of power. They need the electricity to overcool podcast startup offices...

CHARLES: Fire up the suntanning beds.

SMITH: High-frequency trading computers.

CHARLES: It's time to unleash the quiet giant.

SMITH: The mountain of power.


FRIDLEY: We'll watch things as they happen. And I'll try to talk loud and explain a little bit...

CHARLES: Below me, valves open. Water hits steel...

FRIDLEY: All right, so auxiliaries just came on.

CHARLES: You can't actually see the water, but you can hear it. You can actually feel it. The whole place is vibrating. It's an adrenaline rush being so close to so much raw force. It's scary, actually. The vertical shaft in front of me, 4 feet in diameter, starts to rotate slowly at first, then faster, faster.


CHARLES: Five hundred megawatts of electricity from this one machine are flowing through wires up and down the East Coast.


SMITH: Don't mind me. I'm just plugging in my phone to get a little of the mountain power.

CHARLES: I've done the calculation. That lake can store enough electricity to keep your iPhone running for 8 million years.

SMITH: I can totally use that. I can do that.

CHARLES: When all six of these generators are operating, the Bath County Pumped Storage Station is one of the 10 biggest power plants in the country. And it's been doing this for 30 years - pumping water up the mountain, releasing the power.

SMITH: But I do know physics. I mean, you've got to lose some energy in this whole process of pumping it up and taking it down and pumping it up and taking it down.

CHARLES: You lose about 20 percent.

SMITH: That's not bad.

CHARLES: That's similar to what you lose in those big batteries we were talking about. Bath County is the biggest plant like this in the world, but there are lots of others, dozens of them. In the U.S., they were mainly built to store electricity from nuclear power plants. Those big nuclear plants, they run day and night. And people thought, we have all this electricity at night. Let's find a way to store it.

SMITH: So is this the solution? Is this the thing that we can build to store solar electricity?

CHARLES: Remember Scott Flake, the guy at the beginning of the show, was showing me the graph of solar energy? He first learned about these big water batteries 15 years ago when he worked for the Sacramento Municipal Utility District. And he was hooked.

FLAKE: What caught my imagination was this is a technology that could really move this idea of renewable energy forward.

CHARLES: Scott's now an independent consultant, and he is working on plans to build the first big new pumped storage plant in the United States in 30 years.

FLAKE: There are a couple of interesting projects. One is Southern California that uses an existing reservoir for water supply down by San Diego.

CHARLES: There's also a proposal to use an abandoned iron mine, also in Southern California. It has two huge open pits, one higher than the other. Another company wants to build one in Oregon.

SMITH: Which sounds promising. But I have to think that especially in California you can barely build a condo building without people objecting. And so this idea that you're going to be able to, you know, fill in some valley up in the gorgeous, beautiful Sierra Nevada Mountains and you're not going to get a thousand environmentalists chaining themselves to the gate to stop it from happening - it just doesn't feel like you can do this.

CHARLES: And that's all true. But a couple of things. First, there is a huge economic incentive to make this happen. Electricity prices in California already are three times higher in the evening as they are at noon. Think of all the money you could make if you could store that power, buy it at noon when it's cheap, sell it in the evening when it's expensive. And the second thing is, yes, there are environmental objections to these projects. But think of the environmental opportunity, too. Imagine if in 20 years California could exist just on solar power.

SMITH: On solar power alone. So shut down the fossil fuel plants.

CHARLES: To make that happen, you may have to do things that are this big and this ambitious.

SMITH: And, Dan, you told us that they're actually trying to build one of these in China right now.

CHARLES: Yeah, China's building one. It'll be the world's largest pumped storage plant - two dams up in the mountains just like Bath County. When it's done, that plant I visited will then be the second-largest pumped storage plant in the world.

SMITH: No shame in being the second-highest mountain of power.


SMITH: We're always looking for more stories about how the world works, especially you get to climb up to a dam somewhere. Let us know about them. Email us at We post every show on Facebook. And we're on Twitter and Instagram - @planetmoney.

CHARLES: Today's episode was produced by Nick Fountain. Our editor is Bryant Urstadt. Our supervising producer is Alex Goldmark. Special thanks to Mario Finnis (ph) and David Pliner (ph). I'm Dan Charles.

SMITH: And I'm Robert Smith.

CHARLES: Thanks for listening.


DAVID WALKER: (Singing) And all the people just clap your hands.

SMITH: Next time on travels with Dan...

CHARLES: You know, what's amazing to think about is we are in kind of an isolated valley on the far western edge of Virginia, right next to the West Virginia border. This is really back country here. And it's beautiful driving on this little country road overlooking Back Creek. And this - and Back Creek, you know, is the fuel. I mean, and Back Creek is leading us to an energy storage facility that they put here, you know, because of the creek and because of the valley.

And this electrical storage facility, it's supplying energy all the way to New York City, all the way down to North Carolina. And ultimately, you know, because all these electrical grids are interconnected, it's part of the national energy system. It's the - it's a big piece of a network that spans the country. There's a little dog, curious dog in the yard.

I mean, I start sounding really excited, but, you know, it feels like I should be cool. I should be calm. I should be, you know, journalistically jaded. But it's kind of an amazing thing.

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