Of course, the sun doesn't always shine and, at present, the eSolar design has limited capacity to store energy—either as heat or electricity—nor does it supplement production by burning natural gas as some other existing concentrating solar power plants do. "It's 100 percent solar," Tyner says, although he anticipates incorporating heat storage in molten salts or some other energy storage technology in the next generation design due in two years or so.
As it stands, eSolar expects to generate five megawatts of electricity with its refurbished 1940s-vintage General Electric steam turbines roughly 25 percent of the time, which coincides generally with peak demand for electricity, Tyner says. And the efficiency with which a field generates electricity can be improved in the future by moving to higher temperature operation, he adds; the current design employs steam at 440 degrees Celsius and 63 kilograms per square centimeter of pressure at peak capacity.
The company has paired with NRG Energy, Inc., to develop two full-scale power plants totalling 92 megawatts in New Mexico as well as 337 megawatts of further power towers in California. The company plans to begin construction of the New Mexico plant next spring and complete it by the summer of 2011. It has also partnered with the ACME Group in India to develop roughly one gigawatt of power tower capacity in that country. And eSolar is not alone. Rival developer BrightSource has contracted with Southern California Edison for 1,300 megawatts worth of similar power towers, among other projects gaining steam.
Whether this is truly the dawn of a new, cheap solar energy era will be proved at power towers like this one—as well as two operated by Abengoa in Spain. After all, "the one hurdle towers still face is demonstrated performance and reliability. This plant should help that," NREL's Mehos adds. "It's a big step forward for just demonstrating this technology. Every mirror counts."