Here Comes the Sun (Maybe)

Photovoltaics (PV) manufacturers see a growing market for their products, especially in areas offering installation incentives. At the same time, researchers are exploring new approaches—using nanotechnology and organic materials—for generating electricity from sunlight at greater efficiencies.

The Los Angeles Department of Water and Power (LADWP) is not only encouraging PV installation in its service area, but also in manufacturing through a $6 per watt rebate for residential and commercial customers who purchase systems manufactured in Los Angeles.

In response, Berkeley, Calif.-based PowerLight has signed an agreement with Siemens Solar Industries, L.P. PowerLight's PV roof tiles will be manufactured at Siemens' Chatsworth, Calif., plant, which can make up to 6 megawatts of solar roof tiles per year, and a potential expanded capacity ranging from 15 to 20 MW.

PowerLight has also expanded capacity at its own plant in Berkeley to create capacity to 20 MW per year—approximately 167,000 one-sq.-meter tiles.

One new possible approach to lowering the cost of solar-cell electricity—estimated by the U.S. Dept. of Energy to be 20 cents to 30 cents per kilowatt hour—is being studied at the DOE's Lawrence Berkeley National Laboratory and the University of California at Berkeley. Researchers there are combining nanotechnology with plastic electronics to create hybrid cells that could be less expensive to manufacture than traditional cells, and could be fabricated in an almost infinite variety of shapes.

The Berkeley Lab devices incorporate miniature cadmium selenide rods—measuring a mere 7 nanometers (one billionth of a meter) in diameter and 60 nanometers long—as semiconductors. Although power conversion rates have reached 6.9% in the lab, installations outside have only reached efficiency ratings of 1.7%. Researchers say they are confident that other semiconductor materials, such as cadmium telluride, would boost efficiency by increasing the spectrum of light the cells can absorb.

At the University of Arizona (UA), researchers are exploring the possibility that organic thin-film technology would offer the same flexibility as hybrid cells without needing the environmentally-costly heavy metals, such as the cadmium selenide and cadmium telluride that the Berkeley Lab investigators are using.

Organic-film approaches were first studied in the late 1970s, but their low efficiencies and potential instability discouraged development. Today, however, car-stereo and cell-phone displays successfully use the technology, and PV cells may be next. The concept has been proven by researchers at the University of Cambridge and the Max Planck Institute. The UA investigators are now hoping to identify the most effective organic materials for such thin-film assemblies.

From Pure Power, Summer 2002.