A new design for solar thermal electric generators could bust the technology out of niche status and supply the country’s entire electric load, according to … people who make solar thermal electric generators.
… physicist David Mills, chief scientific officer and founder of Palo Alto, Calif.-based solar-thermal company Ausra, has bigger ideas: concentrating the sun’s power to provide all of the electricity needs of the U.S., including a switch to electric cars feeding off the grid. “Within 18 months, with storage, we will not only reduce [the] cost of [solar-thermal] electricity but also satisfy the requirements for a modern society,” Mills claims. “Supplying [electricity] 24 hours a day and effectively replacing the function of coal or gas.”
The company insists it can do this at a cost of just 10 cents per kilowatt-hour, analogous to the price of electricity from burning natural gas in California if a cost was imposed for the emission of carbon dioxide, the leading greenhouse gas (as the state’s Public Utilities Commission is considering).
The new design involves building lots of low-to-ground, resilient mirrors instead of one ginormous parabolic mirror:
Mills’s design — a compact linear Fresnel reflector — allows for greater ground coverage, lower weight and greater durability than precision-shaped parabolic mirrors. “You can drop stones on it and they bounce off,” Mills says. “We would be able to build these in Florida in the hurricane zone.”
This Fresnel solar thermal plant also eliminates oil, directly heating water to a lower temperature of roughly 535 degrees F (280 degrees C) at a higher pressure, about 50 bars, or 50 times atmospheric pressure. Then, it uses the resultant steam to turn the same low-temperature turbines as those employed in nuclear reactors.
The amount of electricity produced is simply a function of the sun’s bounty and the number of mirrors. “We’re moving from 80- to 100-megawatt designs to 700 megawatts and above,” says John O’Donnell, Ausra’s executive vice president.
Naturally, skeptics abound:
"The issue of the linear Fresnel concept is proof of performance of a large system, not just a prototype system in the field," says Mark Mehos, concentrating solar power program manager at the National Renewable Energy Laboratory (NREL) in Golden, Colo. Ausra and other companies that employ the same technology, such as New York City–based SkyFuel and Solar Power Group in Munich, Germany, "are making large claims," he says, "without testing in the field."
Of course, any renewable tech faces the same problem: they need a way of storing the electricity they make. Looks like Ausra’s got that handled too:
"The maximum you can get into the grid is about 25 percent from solar," including photovoltaics, Mills says. But "once you have storage, it changes from this niche thing to something that could be the big gorilla on the grid equivalent to coal."
Ausra claims to have solved the storage problem without using molten salts or other expensive means of conserving heat. In fact, the company estimates that the price of its electricity will drop to roughly 8¢ per kilowatt hour if it can store heat for 16 hours. "Thermal storage is generally considered to be quite a bit cheaper than electrical storage," says Nate Blair, a senior analyst at NREL. "There isn’t a lot of power generation combined with storage systems that can take advantage of that. [Concentrated solar power] has a leg up on storage in the grid or flow batteries or even ultracapacitors."
The system will employ pressure and a steam accumulator to accomplish the trick. "You allow some of the steam to recondense," O’Donnell explains. "It flashes back to steam when you reduce the pressure just by opening the valve to the turbine."
Of course that storage mechanism, coupled with baseload generation, is risky and unproven, but if it works out …
… such solar-thermal power plants could match the electricity needs of both California and Texas. And, by combining a system that would meet the needs of California and Texas, solar-thermal plants could supply 96 percent of the national electricity demand. "The entire energy use of 2006, the current technology including storage would use a patch of land 92 miles by 92 miles," O’Donnell says. "Ten percent of the [Bureau of Land Management] land in Nevada is enough."
Wouldn’t that be nice?
