As the race to create clean, renewable power heats up, the solar industry is focusing on a technology in hopes of producing utility-scale energy.
Concentrating photovoltaic (CPV) solar power -- which marries traditional solar photovoltaic technology to large-scale concentrated solar power plants -- could ramp up utility-scale solar production, advocates say, especially in niche markets. But as with all developing technologies, the effort faces significant hurdles.
CPV technology involves magnifying the sun's energy hundreds of times via lenses or mirrors and focusing it onto small, extremely efficient photovoltaic cells. By magnifying the solar energy, the technology can reduce the amount of semiconductor material needed for the photovoltaic cell.
"In a lot of ways, it's merging the advantages of photovoltaic technology with the efficiency and ability to capture more sunlight that you get with concentrated," said Nancy Hartsoch, vice president of marketing for SolFocus, a California company. "You're basically focusing 650 suns onto that cell, so you're able to use a very, very small amount of photovoltaic material to capture a tremendous amount of sunlight and then convert it at very high efficiency."
SolFocus is among a handful of companies working on CPV technology. Its model involves a two-mirrored system that directs sunlight down an optical rod onto a small (1 square centimeter) photovoltaic cell. Several mirrored units are placed together on a panel, which is mounted on a tracking apparatus to follow the sun throughout the day.
Other companies are trying the same concept, albeit with slightly different technology.
New Mexico-based Emcore Corp., for one, uses optical lenses to focus the energy of 500 suns onto a tiny, super-efficient photovoltaic cell. And other companies are using various incarnations of mirrors or lenses on pedestals, dishes, troughs or carousels to magnify solar energy on tiny, highly efficient photovoltaic cells.
A dozen or so startup companies are wading into the field, tweaking designs that they claim will give the best performance, cost the least and be the most reliable. Even established companies like Sharp Corp., which has been in the solar business for nearly 50 years, are entering the field.
"I think there's a huge space [for CPV technology]," said Brad Collins, director of the American Solar Energy Society. "Solar deployment on a utility scale will explode in the next five years."
CPV technology reduces the need for large amounts of photovoltaic material, which is often the most expensive part of a solar operation. But traditional photovoltaic companies installing panels on rooftops or in small arrays need not worry about the new kid in town. CPV is, by design, better suited for large utility-scale setups.
"It doesn't compete with traditional PV. The applications are different," Collins said. "One's going to be a power plant, and one is a distributed resource. It's not comparing apples to apples."
The technology, however, will compete with large concentrating solar power plants, Collins said.
Concentrating solar power, or solar thermal, involves using the sun's energy to create heat that can be turned into electricity.
Concentrating solar power and CPV are similar on many fronts. Both involve mirrors or lenses to magnify the sun's energy, both have the capability to produce utility-scale solar power, and both operate best in sunny areas like the southwestern United States.
The primary difference is the method used to convert the sun's energy into electricity.
"There are the big concentrating solar power plants -- the solar thermal stuff that's been around a long time -- and they use mirrors as we do in a different way," said Hartsoch, who is also director of the new trade group, CPV Consortium.
And as CPV requires less photovoltaic material than traditional photovoltaic technology, it likewise requires less water than concentrating solar power systems.
Hartsoch said SolFocus' design uses 4 gallons of water per megawatt-hour of electricity produced -- most of that to clean the panels -- compared with about 850 gallons per megawatt-hour at a solar thermal plant.
"I guess you could say it's a drop in the bucket," Hartsoch said.
The technology has some other perks, as well.
"When compared with solar thermal approaches, CPV provides a qualitatively different approach, typically with lower water usage, greater flexibility in size of installation and the ability to respond more quickly when the sun returns on a cloudy day," Sarah Kurtz, a CPV researcher at the Energy Department's National Renewable Energy Laboratory, wrote in a recent paper.
Hartsoch said SolFocus' design is particularly appealing because 97 percent of the materials that go into the arrays are recyclable. The vast majority of materials used to create the company's mirrored system are glass and aluminum, she said. And a cradle-to-cradle analysis of the company's design found an energy payback time of six months, she said. SolFocus' arrays can also be placed in irregular patterns to avoid sensitive areas or maximize land usage.
And because the systems track the sun's path throughout the day, "It's still possible to have crops grow under the arrays," she said. "It's possible to have grazing."
Needed: federal assistance
But it is cost that will likely determine whether CPV technology takes off.
Hartsoch said SolFocus' technology is currently more expensive than traditional photovoltaic or thin-film technologies, in terms of cost per kilowatt-hour, but it is on track to be on par by next year and cheaper by 2011.
A report published this spring by Spanish scientists estimates CPV technology will achieve grid parity between 2011 and 2015 as efficiency increases in cells and optics bring about significant cost reductions.
But the costs are not likely to drop without widespread deployment, and widespread deployment is not likely to occur without substantial investment in demonstration-scale projects.
Kurtz estimates that cumulative CPV investment currently stands at about $1 billion worldwide, but that investment represents a mere smattering of small-scale projects, mostly in Europe.
"The battle for a new technology like this, the challenge it faces, is the reason it's good," Hartsoch said. "What it brings is high efficiency, low carbon footprint, all those things. What comes with it is the risk of new technology."
Hartsoch said SolFocus and the CPV Consortium would like to see the federal government invest in the technology. It has already invested in research and development of CPV through its labs and grants to startup companies and academia. The next logical step, she said, is for the government to boost the scale-up process.
"You're now talking about small grants ... to develop new technologies and some showcasing, but if you want to take this big-scale, there's one more hurdle," Hartsoch said. "What can you do to help us assure that it's safe to deploy?"
She suggested federal loan guarantees or installation of CPV demonstration projects on federal properties.
While Hartsoch and her colleagues want to see CPV scaled up in the United States, they are concerned that won't happen without federal intervention. SolFocus has installed about half a megawatt of CPV in Spain and is currently installing a 10-megawatt project in Greece. But the company only has about 10 kilowatts of CPV technology installed in the United States.
"So many of these technologies have originated in the United States, but where they've really flourished and been taken to scale has been outside of the United States," said Anita Balachandra, senior vice president of Washington, D.C., consulting firm TechVision21. "They've drawn them, and long term, we lose competitive advantage."
SolFocus is not the only company having trouble entering the U.S. market.
Brian Gibson, director of business development for Emcore, said worldwide, his company has installed more than 1 megawatt of CPV capacity, but most of that is in Spain. Emcore currently is developing three pilot projects in the United States, but each will have a capacity of 100 kilowatts or less, he said.
"We are pursuing larger projects at this point in time, but as with any newer technology, there's going to be reluctance of the financial institution to take risk," Gibson said. "It's difficult to get anything sizable financed. We are looking at some 10- and 20-megawatt projects, but from a practical standpoint, you've got to do some 1- to 3-megawatt projects before anyone will finance you."
National Renewable Energy Laboratory's Kurtz remains optimistic, though. "In the last 10 years, the solar industry has mushroomed, and the CPV industry is now growing rapidly," she wrote. "With the overall PV market growing in the gigawatt range, CPV has an opportunity to enter the market with production of tens or hundreds of megawatts per year."
Kurtz added, "This is significant because CPV is unlikely to achieve low costs when manufacturing at less than tens of megawatts per year."
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