Southern California Utilities Go Solar California's renewable energy laws have pushed many utilities to sign contracts with solar startups like Stirling Energy Systems. Stirling CEO Steve Cowman and National Renewable Energy Laboratory solar engineer Mark Mehos discuss the future of large-scale solar plants.

Southern California Utilities Go Solar

Southern California Utilities Go Solar

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California's renewable energy laws have pushed many utilities to sign contracts with solar startups like Stirling Energy Systems. Stirling CEO Steve Cowman and National Renewable Energy Laboratory solar engineer Mark Mehos discuss the future of large-scale solar plants.


This is SCIENCE FRIDAY from NPR News. I'm Ira Flatow. You know, sometimes the old ways may be the best ways, and that may be true when it comes to solar energy. Solar engineers have announced that they have set a new record for energy production efficiency by taking two old concepts, the solar reflector and the Stirling engine, combining them together and creating a device that converts solar energy to electricity with an efficiency greater than 30 percent. And those Stirling engine solar dishes, thousands of them positioned out in the Mojave Desert, will soon become part of the renewable energy future of California, which is leading the way in converting to green renewable energy.

So how soon before we see those dishes tracking the sun, and what about those panels on your roof, those other kinds of solar generators? Why do we need installations out in the desert if there are so many open roofs? That's what we'll be talking about this hour. Our number, 1-800-989-8255, 1-800-989-TALK. You can also tweet us at our tweet location. That's @scifri, @-S-C-I-F-R-I.

Let me introduce my guests. Mark Mehos is a program manager for the Concentrating Solar Power Program at the Department of Energy's National Renewable Energy Lab in Golden, Colorado. Welcome back to SCI-FRI.

Mr. Mark Mehos (Program Manager, Concentrating Solar Power Program, National Renewable Energy Laboratory, Department of Energy): Happy to be here.

FLATOW: Thank you. Steve Cowman is CEO and board member for Stirling Energy Systems in Scottsdale, Arizona. Welcome to SCIENCE FRIDAY, Mr. Cowman.

Mr. STEVE COWMAN (Chief Executive Officer, Board Member, Stirling Energy Systems): Morning, Ira. How are you doing?

FLATOW: Mark, a lot of people probably think, you know, that solar panels are a lot of PV panels on rooftops. This solar concept is different, though, right?

Mr. MEHOS: Yes it is, Ira. This is what a good friend of mine and a colleague, Fred Morris(ph), likes to call the other white meat.

(Soundbite of laughter)

Mr. MEHOS: When people think of solar energy, often they think of what you are starting to see a lot of in the U.S. and around the world, these solar panels or photovoltaic systems, and this is not that. These are systems that use concentrating optics, typically mirrors as you described earlier, to generate very high temperatures that are used to heat a working fluid that drives some sort of a working turbine, or a Stirling engine in the case of the system we're talking about.

FLATOW: Tell us how you were able to break that record for efficiency.

Mr. MEHOS: Well, I think that's better for our other guest to discuss, although the national laboratories, both NREL and our sister laboratory, Sandia National Laboratory, have worked with Stirling Energy Systems on their particular technology, the Stirling engine, to help them break that record.

FLATOW: Well, Mark, let's talk about it. What did you do, and Steve, you have a very impressive picture of what looks to be like the old reflector with an engine sitting in the focal point.

Mr. COWMAN: That's right. I mean, you know, I see - I suppose, just as Mark said there, you know, PV has been around, photovoltaics have been around for probably 40 years. They're, you know, very reliable, obviously used quite widely.

You know, concentrating solar-thermal has been an emerging technology for a number of years, and there's a number of different technologies. The trough technology is pretty reasonably well-deployed, particularly the sags plants in California. And there are some new concentrating solar-thermal technologies, you know, for example the Tower technology and the Stirling engine. So there's a number of different concentrating solar-thermal. The technology we have is just one of a suite of different technologies that are out there. And there's an application-specific dimension to them. Some work well in certain applications. Some are best suited for other applications.

Our system is a 25-kilowatt system, so it's a modular design. And as Mark said there, we, you know, developed jointly with the Sandia Labs, and we've done a lot of the testing there. And in fact, that's where we actually broke the world record, you know, for plus 30 percent, effectively, sun-to-grid-scale electricity production.

FLATOW: Why does the Stirling engine so well? Describe it for us a little bit.

Mr. COWMAN: Well, the Stirling engine - in fact, the Stirling engine was invented back in 1816, so…

FLATOW: Pretty old.

Mr. COWMAN: Yeah, it's been around a long time. So the engine itself has been around a long time. And I suppose really, you know, in terms of the technology we have here, the Stirling engine is a 25-kilowatt system. So for example, for the first project, which we will have in California, it'll be 12,000 of these deployed to generate 300 megawatts of power.

So what you have really is you've got an engine that generates 25 kilowatts of electrical power that sits in a dish reflector. You get a concentration of about 1,100 suns, and that concentrated heat actually drives the Stirling engine. The Stirling engine is an external combustion engine. So at a temperature of about 740 degrees C., the Stirling engine, actually which uses hydrogen as an internal fluid, actually uses that heat to drive the engine, to drive a generator to produce the power.

FLATOW: Mark, there seems to be, though, one shortcoming in Stirling engines, as they are used now, is that there is no way to store the electricity, or store the power, when the sun's not shining.

Mr. MEHOS: Yeah, and shortcoming I guess would be a strong word for it. But as described, there are different applications for different technologies. Some of the other technologies can make better use of thermal storage. And what we do with those technologies, and specifically that would be the parabolic-trough and the central receiver technology, is to take that working fluid, and you essentially bottle up some of that working fluid during the day, you drive your generator with that working fluid during the daytime, but then when a cloud comes over or at night or late in the evening, you take that leftover working fluid, and you can use that to continue to drive your generator, and typically in this case it would be a steam generator, not a Stirling engine.

FLATOW: Let's get a call in, 1-800-989-8255. Simon(ph) in Troy, Michigan. Hi, Simon.

SIMON (Caller): Yes, hi. How are you doing?

FLATOW: Hi there.

SIMON: Thanks for taking my call. I was wondering for solar panels, why don't we put them in the middle of the road because I understand that they cover up a lot of area, and then anything that's below probably has problem growing or anything. So you can't really put them in forests or anything else, but the middle, the median strip of the road isn't really being used for anything.

FLATOW: That's a great idea. Why don't we do that, Steve? Could you put those also in the middle? Could you make a smaller version of your Stirling system, maybe put it on a rooftop, also?

Mr. COWMAN: Well, you could do that. I suppose really, you know, I mean, when a lot of people think about PV, they think about it mainly for, you know, domestic-type applications. I mean, we're really focused on utility-grid scale. So typical projects would be, you know, 200, 300, all the way up to 750 megawatts, you know, providing enough heat, light and power for, you know, typically population centers of about half a million up to about two million people.

But you can certainly do that. I mean, you know, that's, I suppose, the beauty of PV is that you can actually deploy it, providing you have, you know, the right type of sunlight, provided you had the ability to connect it to a grid.

FLATOW: Mark, why not put all these photovoltaic systems on rooftops? There are a lot of rooftops around, and like I know California has the million-rooftop project, right?

Mr. MEHOS: That's right. A million isn't enough, though.

FLATOW: It's not enough?

Mr. MEHOS: It's a good question. There are a lot of people asking that question, and there's a couple points that come up. One is one can just look at the number of rooftops, both residential rooftops or commercial-industrial rooftops, and at NREL, we've done a lot of that analysis, and that analysis points to the fact that there just aren't enough rooftops. If you start looking at the orientation that you would need to best produce that electricity, and if you start looking at shading, then really what you're left with is somewhere around, let's say, 20 percent of the U.S. generation capacity could be served by those rooftop systems.

FLATOW: Steve, I know you said that you're building on the industrial scale, for industrial applications. Is it possible to build a home version, a smaller, working version that would work, you know, on a rooftop?

Mr. COWMAN: Well, it is, yeah. I mean, the 25-kilowatt system that we produce would be way too big for a domestic application, but there is smaller Stirling engine systems out there that run at typically one, two or three kilowatts. But again, I mean, our focus is mainly been on the, you know, large-scale utility-style projects, but you can certainly make a smaller Stirling engine.

I suppose one of the issues, actually, is the - you know, our strategy really is its high-volume manufacturing. And you know, the engine, for example, will be made using a lot of the capacity that's currently not being utilized up in, you know, Detroit in Michigan.

I mean, if you take, you know, the Detroit car market, they made 17 million cars in 2007. That dropped to less than 10 million cars last year. So there's a lot of available capacity. So we're looking to tap into that capacity for both the engine, for the dish, for the mirror and the facets.

So, you know, high-volume manufacturing allows you to drive down the cost, which allows you to be economical in terms of the end market, so it's - that's the segment that we have really focused on. But you could certainly do it for domestic applications, but it would require a much smaller engine.

FLATOW: You know, I hear more and more of this, Mark, that the demand is there, but you just can't build the parts fast enough, and I'm thinking about wind, also, you know? You can't build those turbines. Maybe you can't build the solar collectors fast enough.

Mr. MEHOS: Well, that can be correct I think one of the advantages of concentrating solar power technologies is they really don't rely on any special materials. They are more or less readily available. We're using steel and glass and mirrors and turbines, but we do need to build up that industry that can produce those materials. And so DOE has a large effort, a growing effort, in just trying to build up a U.S. industry rather than having that industry lie abroad.

CONAN: And it would certainly be good stimulus money well spent.

Mr. MEHOS: We hope so, and some money is going that direction.

Mr. COWMAN: (Unintelligible) are, as well. I mean, you know, I think there's two things here. I mean, you need the demand-side equation. I think the, you know, the recent RPS targets that have come out at both federal and state level is mandating a higher amount of electricity coming from renewables. And on top of that, you've got, you know, the innovative stimulus package that President Obama's administration is actually rolling out to help fund these projects.

So you know, although the credit markets are particularly tight, and funding for large-scale projects is difficult, you know, there is almost the perfect storm out there at the moment where you've got, you know, the utilities companies who are looking to bring on more renewables, and you've got the stimulus package that allows you to fund the projects, and you've got available capacity, you know, with a lot of the automakers in terms of spare capacity there. And I suppose, you know, so that's creating the context to actually really drive these large projects out there because what solar-thermal really needs is to gain momentum to drive volume to get the cost down because…

FLATOW: Well, can it be competitive with other forms - the kilowatt-hour?

Mr. COWMAN: Yeah, I mean, well, wind has been around for 10, 12 years. It's a really good technology, it's very reliable, and they've done a really good job of coming down the cost curve. So they're, you know, sort of 10 cents per kilowatt hour.

The problem with wind is that, you know, where it's a very good, renewable technology, it's intermittent. It's not - you know, it tends - the wind doesn't always blow when you need it. So you know, a good solar solution is a very nice compliment to wind, but obviously for that solar solution to work, you've got to have a product that's cost effective, and is reliable.

FLATOW: Mm-hmm.

Mr. COWMAN: So the answer to the question is yes, you can definitely get down the cost curve. You know, certainly from our point of view, we're competitive at the market reference point in California. And you know, I think once we drive volume through the supply chain that we have, and we work on the technology side - no reason why you can't get solar down close to where wind is.

FLATOW: All right, gentlemen, thank you very much for taking time to talk with us today.

Mr. MEHOS: Thank you.

Mr. COWMAN: You're welcome.

FLATOW: Steve Cowman is CEO and board member for Stirling Energy Systems. That's in Scottsdale Arizona. And Mark Mehos is program manager for the Concentrating Solar Power Program at the National Renewable Energy Lab in Golden, Colorado.

We're going to take a short break, switch gears, and come back and talk about space. Everybody likes to talk about space. What if we don't go to the moon or to Mars? Are there other places we might go to? Well, there's a new panel that's studying all of this. I have some recommendations. We'll be back to talk with you about it after this break. I'm Ira Flatow. This is SCIENCE FRIDAY from NPR News.

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