Making concentrated solar juice affordable.

Making concentrated solar juice affordable

Roughly 10 acres' worth of newly designed solar energy collectors could convert sunlight into electricity efficiently enough to keep lights burning and stereos blaring in a 300-home town with no change in utility bills, according to researches who designed the collector at Sandia National Laboratories in Albuquerque, N.M.

Though scientists differ in their prognoses for the Sandia device, known as a photovoltaic concentrator module, they agree the new collector marks an important step toward commercializing photovoltaic technology for applications such as generating electrical power.

"The fundamental problem in photovoltaic technology is that the cells cost too much," says Eldon C. Boes, supervisor of Sandia's Photovoltaic Technology Division. Sandia researchers now are adapting the molecule for large-scale production by solar energy companies, some of which already have expressed interest, Boes says.

To reduce the cost of solar-generated electricity, researchers strive both to make photovoltaic cells more efficient and to figure out how to make lots of less efficient cells cheaply. The experimental module, which Boes and his co-workers found converts 20.3 percent of high-noon, sunny-day sunlight into electricity, meets a goal set by the Department of energy in 1986 for concentrator efficiency. It's also a record for photovoltaic devices of this type.

The module consists of 12 high-efficiency photovoltaic cells, each cell a half-inch-square flake of crystalline silicon with an overlying grid of fine metal "fingers" that tap into the photovoltaic current. To maximize the power output of each cell and minimize the number of cells needed, a parquet of overlying lenses concentrates the sunlight 100-fold. A prismatic cover molded directly to the cells steers light away from the metal fingers, which otherwise would intercept the solar energy before it reached the underlying silicon. Secondary concentrators surrounding each cell compensate for misalignments that occur as a tracking device keeps the modules aimed at the continuously changing position of the sun and as the modules' components contract and expand during the season and climate changes.

"This module is important, but it isn't by itself enough," says Kenneth B. Zweibel, a research manager at the federally funded Solar Energy Research Institute in Golden, Colo. although the Sandia work probably boosts concentrators into the ballpark of other photovoltaic technologies, Zweibel places his long-term bet on thin films of photovoltaic materials whose low cost would outweigh their lesser efficiency. But he and Boes agree that interim, in-hand technologies such as the photovoltaic concentrator module could encourage utility companies and others to look sunward in the near term, priming them to choose improved photovoltaic technology as it becomes available.