Concentrating on Solar

Continued from page 1

By Erik Sherman

May 30, 2003

This wasteful transformation of a thinly distributed source explains why solar power is so expensive. Converting a typical household to solar runs between $10,000 and $40,000, according to  BP Solar, a division of global petroleum company BP plc and a leading manufacturer of solar energy equipment. Large-scale solar electricity plants typically cost $3 million to $4 million per megawatt of capacity; by contrast, a plant fired with  fossil fuel, such as pulverized coal, runs between $1.5 million and $1.7 million per megawatt.

Solar cells built with existing technology "have reached a plateau," says Roland Winston, a University of Chicago physics professor who studies optics for concentrating sunlight. However, even if the efficiency of light-to-electricity conversion remains level, Gordon and his colleagues at Ben-Gurion University believe that they can raise the effectiveness of the system simply by funneling more solar energy from a wider area by combining a photovoltaic cell with their mirror concentrator. Increase the amount of power delivered onto even an inefficient cell, and electrical output will similarly increase.  Although the net generation of power with a concentrator might be the same as by placing solar cells over a bigger area, the overall cost would be less because fewer of the expensive photovoltaic devices are needed.

The Ben-Gurion scientists have been working with a team from Drexel University on a U.S. Department of Energy-sponsored project to marry the concentrator to a high-efficiency photovoltaic cell sitting at the other end of the fiber optic strand. Using this setup, the researchers have improved a typical cell's electrical output from 2 watts up to 3 watts-and they believe that they will be able to achieve 4 watts. The Drexel group is working to test a one-kilowatt mini-dish power plant with an expected conversion efficiency exceeding 20 percent. Others are also working on combining concentrators with solar cells. Spectrolab, a Boeing subsidiary and an industrial partner of the National Renewable Energy Lab, has driven a triple-junction solar cell, which uses a stack of three PV cells, to 34 percent efficiency under concentrated sunlight.

What makes the combination of photovoltaic cells and concentrators additionally interesting is that the resulting devices might lend themselves to mass production. "You stamp [the combined PV cell and concentrator] out," says Gordon. "Everyone is identical to the next."  The cells could then be connected, providing virtually any amount of power, at least in regions with plentiful sunshine. And if the wattage generated  per photovoltaic cell can indeed be doubled, then a solar power plant would need only half as many cells-bringing its costs much closer to those of conventional coal- or petroleum-stoked facility. Add a fuel supply that costs nothing, and a focus on the small might deliver big savings.