Ultraefficient Photovoltaics

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Sherif says that right now his company is focusing commercialization efforts on the older and better-known designs, which currently deliver 35 to 37 percent efficient modules and could improve to 40 percent efficiency within two to three years. But he says the metamorphic approach is more likely to achieve the 45 percent efficiency level the company hopes to hit within six to seven years. Sherif estimates that a 40 percent module would reduce overall cost by about 14 percent if Spectrolab holds at its current $10-per-square-centimeter module price, while a 45 percent cell would trim system costs by an additional 9 to 10 percent.

Boeing anticipates further cost reductions as other components improve or are mass-produced. Under a $29.8 million concentrated-photovoltaic development partnership with the Department of Energy announced this spring, Boeing promises to cut the delivered price of electricity via concentrated solar to 15 cents per kilowatt hour by 2010, from an estimated 32 cents per kilowatt hour today, and to cut that price in half again by 2015. That would make solar power less expensive than electricity from the grid in much of the United States, where the average price of electricity in recent months has been about 10 cents per kilowatt hour.

Spectrolab's competitors, meanwhile, see metamorphic materials as a way to reduce the use of relatively exotic and expensive semiconductor wafers on which they are now produced. NREL's design, for example, can be lifted off of the germanium wafers on which both NREL's and Spectrolab's cells are grown. The expensive wafers could then be reused. Metamorphic photovoltaic startup 4Power, of Windham, NH, proposes to employ metamorphic buffers to grow high-efficiency cells on the same wafers of silicon on which nearly all semiconductor chips are produced. Silicon wafers are cheaper to buy and process than germanium wafers. 4Power founder Eugene Fitzgerald, a materials engineering professor at MIT and a metamorphic-materials pioneer, claims that this would cut the cost of growing high-efficiency cells in half.

What remains to be demonstrated, notes NREL's Kurtz, who leads the lab's high-efficiency solar research, is whether solar concentrators--especially their sensitive optics--will prove reliable in the field.