UA engineering students hosted the American Society of Civil Engineers Pacific Southwest...
Concentrated Solar for the Nation
Roger Angel stood in a salvaged satellite dish behind Bear Down Gym inspecting his prototype for changing the nature of electric generation in America.
The center of the dish was carpeted with optical glass that focuses sunlight to such intensity that he's used it to burn a hole in a piece of steel in seconds. "Simply tells you this glass has a good shape," said Angel, the director of The University of Arizona's Steward Observatory Mirror Laboratory.
Angel approaches large-scale problems in a large-scale way. He's built one of the world's largest telescopes. He's proposed launching trillions of 2-foot-wide sunlight-deflecting disks to alleviate global warming. Now he's got an attention-getting proposal to replace coal and other fossil fuels as a source for utility-scale electric generation. His idea involves using optical mirrors – the centerpiece of his long and illustrious career – to concentrate sunlight on high-efficiency photovoltaic cells.
There were three pieces to the puzzle: converting sunlight to electricity cheaply, storing the power, and transmitting it across the country. He identified "pretty good technology and experience" for storing and transmitting power. Los Angeles gets a lot of its power via transmission lines from northern Oregon. A lot of electricity is held in pump-water storage to shift power from night to day, when demand peaks. "Now we need it shifted from day to night," he said. "There's reasonable technology in place to do that," Angel said.
The trick was in the first step – converting the sunlight into electricity. "You can either do that locally, or the alternative is to put your conversion in the Southwest desert, where's there's much more sun, and then transmit that energy to the East," he said. "And it seemed to me the economics of that look pretty good, so I think it's quite possible that we wind up with the Southwest desert basically being the electricity source for the nation."
The key, as with all renewables, is lowering the cost to the point where solar energy is competitive with fossil fuels. "I think there's an agreement that the breakpoint is $1 a watt," Angel said. "If you can install facilities that will make electricity out of solar for $1 a watt, then basically market forces will take over and renewable will replace fossil fuel – boom."
Photovoltaic panels are around $5 a watt but hold the potential of being half as expensive. Most concentrated systems now use cylindrically shaped mirrors to focus light on a pipe with oil in it that gets hot. "You pump the oil off and use that heat to make steam, and then you go through steam turbines," Angel said. "It's not very efficient and it's still pretty expensive."
He's been looking at a combination of the two. "You use the mirrors, but instead of focusing the light onto steam pipes, you focus it onto photovoltaic cells. The big advantage of that is if you focus it strongly, the area of photovoltaic cell needed to make a certain amount of energy can be reduced by a thousand times. So now you can afford to use very high quality photovoltaic cells, because you don't need much of them, which convert twice as much of the light to electricity as a normal photovoltaic cell, and the cost becomes very low."
"What's exciting to me is I've spent my life making telescopes and things to point them at the stars," Angel said. "At the University here, we have world-class, world-beating expertise in how to make optics-focusing systems and not just ivory tower PowerPoint stuff. We actually do it on campus."
He intends to leverage that expertise. "What's common when you're building the world's largest telescope, period, is you need the world's best engineers – otherwise you screw it up," he said. "And when you have very good engineers, and that's what we've built up here over the years, what we're good at is understanding the requirements of the problem and then designing a system – the whole integrated glass, steel, cells, optics – and teasing that system, always driving it. In the telescope, you're driving it toward the best possible images; on solar, you're driving it to the lowest possible price."
Other crucial parts of his plan are keeping steel – "the driving, controlling cost factor" – to a minimum, and creating the manufacturing process to produce 1 square meter of "sunlight reflecting, concentrating mirror" every second. "If you do all that and you get all that out in the desert and turn all that sunshine into electricity, then it takes you a year or two to make a power station with the same energy output as the Palo Verde station" near Phoenix.
The object of the focused light would be clusters of germanium cells designed to receive very bright light. "These things are new," he said. "They're not a simple cell; they're three stacked on top of each other and they go at the different wavelengths of light and basically suck all the energy out of the sunlight from all the different range of spectrum that you get from the sun. They were built for things like Space Station and Hubble Telescope because money is no object in space. There, they're not using focused light but they just make more energy from the regular sunlight. This is better than Tang; this is one of the things that's come out of the space program that's going to be extremely valuable."
Aside from being the kind of big challenge Angel has often confronted, renewable energy strikes a deeper chord.
"For anybody who has children or grandchildren or who loves nature or loves Arizona or whatever, nothing is certain," Angel said. "Every year things look more dire. It's an exercise that makes us who are in the business of science, makes me, completely terrified. Because you can't ignore what the projections are. It's not like you crank some enormous computer model and see what happens. You can see the effect of greenhouse warming."
As an astronomer, the physics involved "are daily bread and butter for how we've worked out how all the stars work and how the different planets in our solar system work," he said. "The odds are that we're headed to hell at an extremely fast rate. You would like our children and grandchildren to have a planet with some of the beauty that we've had."
After decades of exploring the universe as a famed astronomer, Angel has a new motivation – saving the world.
"When I get tired – and believe me I do, getting up after a few hours to keep working on a proposal – what moves me is thinking we have a planet to save, and maybe something that we know here is going to be helpful in doing that. I actually feel privileged that I can work on this problem. For most people, they say, ‘Well what can you do?'"