BIOLOGY
Mario Capecchi
Phyllis Coley
James Ehleringer
James Ehleringer
CHEMISTRY
Joel Miller
Thanh N. Truong
Peter J. Stang
MATHEMATICS
Graeme W. Milton
Jim Carlson
PHYSICS
Charles Jui
Charles Jui
Craig Taylor
Valy Vardeny
Valy Vardeny
By Lee Siegel
The Salt Lake Tribune
Utah researchers are trying to develop solar-power cells that are less expensive, longer-lived and more efficient at converting sunlight into electricty.
Photovoltaic cells will not become a major source of electricity in the foreseeable future. However, reducing their cost could make large arrays of solar panels a viable source of power during periods of peak demand -- times when utilities often crank up older, dirtier, less efficient coal- and oil-burning power plants.
 Craig Taylor of the University of Utah Department of Physics develops solar-power cells. Photo courtesy of Micahel J. Miller, The Salt Lake Tribune. |
"Solar power is unlikely to be a major component of the power used in big cities because it will remain too expensive, even with improvements in solar-cell efficiency," said University of Utah physicist Craig Taylor.
"But over the next 20 or 30 years, it is reasonable to expect solar power can provide a small percentage of electricity to major power grids. This is most likely in the southwestern United States where sunlight is more predictable. You might use power stations like these to supply electricity to cities like Los Angeles, Phoenix or maybe even Salt Lake at peak times in the middle of the day."
Taylor discussed prospects for solar-power cells during an interview and at Wednesday's Science at Breakfast lecture sponsored by the U's College of Science.
His lecture involved photovoltaic cells used in solar-power panels that convert sunlight to electricity. He did not discuss solar thermal systems in which sunlight is used to heat water, either to heat buildings directly or to drive electricity-producing turbines.
Small, inexpensive solar cells are used in devices such as calculators, wristwatches, toy cars and other products -- including "eternal flame" light bulbs on some graves in Italy, Taylors said.
Relatively small, commercial solar panels now are used to varying extents for microwave repeater stations and weather stations; for traffic lights and signals; to charge batteries on sailboats; for farmers' water pumps, lighting and electric fences; and in remote locations, such as oil-pumping stations.
Utah Power contributed assistance and $100,000 to a Department of Energy experiment in which solar arrays provide power for lighting, refrigerators, gas pumps and other uses at Dangling Rope Marina on Lake Powell in southern Utah, said company spokesman Dave Eskelson.
He estimated less than a tenth of a percent of U.S. electricity now comes from photovoltaic cells -- and his company has none in its grid. Utah Power and its parent, PacifiCorp, are involved in three small projects in which photovoltaic panels power a school in Wyoming, a museum in Bend, Ore., and Utah Power's service center in Moab.
Taylor said there are several solar-power-generating plants in California and elsewhere, but all are test facilities.
The cost of solar cells has dropped over the decade to about $4 per watt of electricity-producing capacity, but "in order to be commercially viable to provide a few percent of the power for a major city during peak times, the cost will have to be well below a dollar per watt," Taylor said. "Within the next 10 years, we should be close to that value."
In terms more relevant to consumers, Eskelsen said large arrays of solar panels produce electricity for about 20 cents per kilowatt hour -- three times the 6.7 cents per kWh Utah Power charges residential customers, Eskelsen said. A typical household uses 650 kWh each month.
Most solar panels are made of crystalline silicon. Taylor and his colleagues at the U. are trying to develop improved solar cells made from a thin film of amorphous silicon, which is much less expensive and can be made into larger panels than crystalline silicon.
A drawback is that only 8 percent to 10 percent of sunlight falling on amorphous silicon is converted to electricity, compared with up to 25 percent for crystalline silicon, said Taylor.
Another problem is that amorphous silicon is "metastable," which means that when sunlight hits it, some atoms move around in an undesirable manner. Taylor said that makes the material degrade over time, reducing the percentage of light that can be converted to electricity.
Engineers have been able to get around the problem to some extent by making amorphous silicon solar cells into a thin film, which reduces the degree to which degradation harms electric output.
Taylor and co-workers are trying to figure how to overcome the "metastabilities" in amorphous silicon. If they succeed, the material could be used for thicker solar cells, which would collect more sunlight and be more efficient at converting it to electricity.
So Taylor's team "dopes" amorphous silicon with sulfur. He said that causes a second metastability in the silicon, making hydrogen atoms move in such a manner that they cancel out the bad effects of the first metastability.
"It is like if you whirl a paddle in water and create some current motion, then a leaf in the water is going to move," he said. "But if I have another paddle that moves in the other direction, it will tend to keep the leaf stable between the two whirlpools." Unlike a leaf, the atoms could not move at all.
The technique reduced the degradation and increased the efficiency of a square-inch solar cell made at the university, showing the method works. But the improvement is not yet enough to make amorphous silicon solar cells economically attractive, Taylor said.
Also, sulfur contaminates solar-cell production equipment, so scientists need to find a better substance -- perhaps calcium or magnesium -- to use as a "dopant" in amorphous silicon.
"I am confident we will find something that works," Taylor said. "I am not confident we will find it in the next few years."
Eskelsen said huge areas of land would have to be covered with existing solar arrays to match the electricity output of a coal-fired plant. For photovoltaic arrays to be useful for peak power, they would need batteries and other means to ensure electricity could be produced within moments when needed, he added.
Originally published October 29, 1998, in The Salt Lake Tribune.