Photovoltaics Researchers Meet To Cast More Light on Solar Cells

Conference to address new cell materials, solar concentrators, space technologies, and more

6 April 2010

Energy from the sun is abundant and free. Electricity from solar energy, often less expensive than other alternative sources, isn’t abundant yet. But the physicists, engineers, and others attending the IEEE Photovoltaic Specialists Conference (PVSC) hope it will soon be.

The conference, sponsored by the IEEE Electron Devices and Photonics societies, is scheduled for 20 to 25 June in Honolulu. Hawaii’s abundant sunshine and expensive electricity make it one of the first places where photovoltaic (PV) power from semiconductor solar cells will soon reach parity with conventional energy costs, according to IEEE Member John Benner, who is the PV industry partnerships manager at the National Renewable Energy Laboratory, in Golden, Colo.

WORLDWIDE INCENTIVES
Nations around the world are supporting expanded use of solar cells through incentive programs designed to help build the industry, drive down costs, and prove reliability. But the electricity generated by the world’s solar installations is still a drop in the bucket, amounting to the energy produced by only five large coal-fired plants. The solar generators can be found on residential and commercial roofs, as well as in very-large-scale ground-mounted arrays, providing power close to the point of use.

“Many people in the industry have told me that in many places photovoltaics should be cost-competitive for general power production within five years without incentives,” says Benner, chair of one of the 10 subject “forums” in which the conference is divided

That was far from true when the conference began in 1961 and was held in a hotel basement. Then the cost of solar cells was so high that their only useful application was in space vehicles, where the power-to-weight ratio was more of a concern than cost. “When this conference first met,” says this year’s conference chair, Robert J. Walters, “we were creating photovoltaics to power space satellites. Now it’s becoming practical to bring it back to power Earth.”

This year the conference is expected to attract as many as 2000 people, more than half from outside the United States. About 900 papers and poster sessions will address new cell materials, solar concentrators, space technologies, characterization and measurement, terrestrial systems, and the accelerating progress in PV. Sustainability and environmental issues also will be discussed. Tutorials will be given on photovoltaic fundamentals, cell technologies and installation, reliability, measurement, and novel applications.

CLIMBING EFFICIENCY
Since the conference’s inception, says IEEE Member Walters, “solar-cell efficiency has risen from single digits to 42 percent, with 50 percent in sight. And dollars per watt are going down, thanks to larger cells that require fewer connections and to cheaper materials such as polysilicon instead of single-crystal silicon.”

But solar power is still expensive to install, Walters notes, in part because technical standards vary from state to state. “The next major breakthrough,” he says, “will be the unification of standards and codes to bring the system cost down.”

Another hurdle, he says, “is the evolution of our energy grid from the centralized power plant model to a smart, reliable, distributed-generation model.”

“We need to evolve our old and creaky grid to accept distributed power-production sites and generate the energy where it is needed,” he says.

He sees the need for what’s referred to as grid-rate parity, which would allow people with solar generation to sell their excess power to the transmission systems at the same rate they pay when buying power from the grid.

SMALLER FOOTPRINT
Integration with the grid will enable solar power at last to lessen many countries’ reliance on imported fossil fuels and minimize the carbon footprint of power systems, Walters says. “The photovoltaics community is very conscious of environmental issues, such as recycling PV materials,” he says. “The conference will include seminars on materials availability and on how the materials we need affect the sustainability and viability of solar manufacturing.”

Those materials are more varied than ever before. Silicon is still the main building block, but much research concentrates on new structures such as thin-film solar cells using other materials, multijunction cell materials, organic photovoltaics, amorphous materials, and nanotechnology.

“Lower-cost materials are just now reaching 19 percent efficiency, though,” Walters says. “For the best efficiencies you still want the best materials. That often leaves us competing with the semiconductor people for crystal silicon.”

STILL A SMALL PERCENTAGE
The photovoltaic field has grown about 35 percent annually in the past three years, according to Walters, who heads the solid-state devices branch of the U.S. Naval Research Laboratory in Washington, D.C. Companies that once produced a megawatt or two of solar cells each year are now making more than a gigawatt’s worth.

But the field is still small, Benner says. Although worldwide sales of photovoltaic equipment are more than US $20 billion annually, photovoltaics account for about 0.1 percent of the world’s generating capacity (but, since photovoltaics output varies with the weather and time of day, only about 0.02 percent of total generated power). Coal and gas deliver more kilowatt-hours per dollar than solar energy, but solar power keeps getting cheaper—and the cost of fossil fuel, once price fluctuations are averaged out, continues to go up.

“We’re at the threshold of being able to continue without government incentives,” Benner says.

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