New Technology Offers Ray of Hope for Affordable Solar Power
We have all heard stories about how solar energy will someday provide a cheap, inexhaustible supply of electricity that might free us from monthly utility bills while making the world a cleaner place to live.
We’ve been told how one day a collection of solar cells, perhaps designed to look like a tile roof, could supply enough juice to keep any homeowner happy.
So far that has remained largely just a dream, but scientists around the world are closing in on new technologies that could make it a reality in the next few years.
The high cost of solar cells has restricted their use to applications in which low maintenance and high reliability are essential, such as orbiting satellites. These cells directly convert sunlight into electricity, and photovoltaics has grown into a $1-billion-a-year industry.
But what about us common folk who would like to use solar cells but can’t afford them? Will our day ever come?
“It’s very clear to me that it’s going to happen,” said Ken Zweibel, who manages a 20-year-old partnership between researchers and industry for the Department of Energy’s National Renewable Energy Laboratory in Golden, Colo. He expects to see photovoltaics on a strong footing within five years and to emerge as a major player within a decade.
In time, he said, solar energy should supply 10% to 20% of electrical generation in developed countries, and more in underdeveloped areas where traditional power plants are limited or not available.
His optimism is based on a new generation of solar cells that are as different from the sophisticated devices used in space as a satellite is from a rooftop.
Most solar cells are made from very pure silicon wafers that work as semiconductors. Energy from sunlight frees up electrons in the wafer, causing a current to flow, thus producing electricity. Such solar cells, like those used in the space program, can convert more than 20% of the sunlight they receive into electricity.
But they are expensive, thus limiting their use.
The emphasis now is on refining thin-film solar cells, which have been around for years on such things as hand-held calculators. Instead of using wafers similar to those in the computer industry, thin-film cells use a very thin layer of semiconductor material deposited on a flexible surface made of stainless steel, glass, plastic or other material.
We’re talking really thin layers--much thinner than a human hair.
Unfortunately, the current generation of thin-film cells is good enough for calculators, but not much else. Zweibel said their efficiency usually ranges between 1% and 5%, meaning they convert less than 5% of the sunlight they receive into electricity.
To be viable for a broader market, thin-film cells must operate at 10% to 15% efficiency, according to industry sources.
And mass-producing such cells has proved to be a challenge, both technologically and economically.
More than a dozen universities, government laboratories and corporations are involved in the program Zweibel heads, including the University of Florida in Gainesville, which is exploring one of the most promising avenues. The university is making semiconductors out of a very inexpensive compound, copper indium diselenide.
“The material cost is minimal,” said Sheng Li, professor of electrical and computer engineering. The cell is 100 times thinner than current cells and has operated at efficiencies in the range of 8% to 10%.
But what works in the lab may not be easy to transfer to an industrial setting. The chemicals do not mix easily, and if the percentages are off by even 3 percentage points, the resulting semiconductor “may essentially be dead,” Zweibel said.
And they will have to be mass-produced to the tune of several square miles per year to be cost-effective. If the cost can be brought down to $50 a square meter, and the efficiency rate kept at about 10%, that boils down to 50 cents per watt, compared with $2 to $3 per watt for current solar cells, Zweibel said.
The process has now advanced to the refinement level, he added.
“We’re past the breakthrough stage,” Zweibel said. “I’m very confident it will happen.”
If they succeed, the applications are almost endless. Because thin-film cells can be deposited on a flexible surface, such as plastic, it’s possible to mold them into shapes that will fit on other devices, and they could be much lighter than conventional cells.
They could also be easier to disguise, so they wouldn’t have to look like those ugly hot-water heaters seen on some rooftops.
But the real payoff will come if they can be manufactured cheaply enough to cover substantial areas. Zweibel noted that only about 0.3% of the U.S. land area would be needed to supply the country’s electrical needs.
“That happens to be the same size as the bombing range used in Nevada for atomic testing,” he said.
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Lee Dye can be reached at leedye@ptialaska.net
