Solar energy experts anticipate that more efficient solar cell technology under development at the University of Minnesota will lure private investment to the state and help speed solar energy’s growth nationally.
Researchers will use a recent $695,000 university grant to demonstrate that their approach to improving solar cell efficiency works, said project leader Stephen Campbell, a professor of electrical and computer engineering at the U’s College of Science and Engineering in Minneapolis.
If they succeed, Campbell said, as many as six to 10 solar cell manufacturers likely would look to adopt the technology as it advances toward commercialization.
The U’s effort to develop more efficient and cheaper solar cells aligns closely with the goals of the SunShot Initiative — the U.S. Department of Energy’s (DOE) national push to achieve subsidy-free grid parity for solar energy. In other words: by decade’s end, the DOE wants to make solar energy technologies, without subsidies, cost-competitive with energy from conventional sources such as coal and nuclear power.
The DOE estimates that the cost of an installed solar system — which Campbell today puts at roughly $1.80 a watt — will need to fall to $1 a watt or less to reach cost parity with conventional energy rates.
The Energy Department expects grid parity will lead to rapid, large-scale adoption of solar electricity nationally at a time when the rate of megawatts of solar power sold already is growing at what Campbell termed an exponential rate of roughly 25 percent a year.
Early this year, the Maplewood-based 3M Co. received a $4.4 million SunShot Initiative grant from the DOE to accelerate further development and commercialization of its lightweight Ultra Barrier Solar Film, which replaces glass and protects solar cells from moisture. The grant, a 3M statement said, will be used for testing and development of a second-generation product with better performance and lower costs.
Campbell’s recent grant, from the Initiative for Renewable Energy and the Environment (IREE), a program of the U’s Institute on the Environment, could help leverage even larger federal grants. Campbell said he had discussed the U’s research with DOE officials, whom he described as “very complimentary and very encouraging.”
“The DOE is pushing very hard to get these costs down,” Campbell said. “There’s no really clear path forward. This is the most promising one I’ve seen.”
Rod Larkins, special projects director for IREE, said Campbell’s project emerged as officials last September began pulling together faculty members and solar energy stakeholders across the state to identify possible SunShot Initiative candidates.
“Dr. Campbell’s project was the only large solar program that we funded this year,” Larkins said of the latest rounds of IREE grants, announced last month. “We felt that it had real potential. It looks like it’s going to improve reliability and can have an impact on reducing costs and improving efficiency as well. It hits all the high points we consider essential.”
In all, IREE awarded $4.1 million in grants to 20 U of M research teams in July. The money comes from Xcel Energy’s Renewable Development Fund, which is financed by ratepayers, to help launch early-stage, high-potential renewable energy projects.
Campbell’s research is a positive development for the state’s solar energy industry, said Lynn Hinkle, policy director for the nonprofit Minnesota Solar Energy Industries Association, which promotes solar manufacturing in the state.
“It’s a good thing for the state of Minnesota to get on the map as one of the places that’s doing important solar research,” Hinkle said. “It’s great to have this kind of research going on because there’s always a chance with the right capital it could be commercialized in Minnesota.”
An early position in the market could prove a boon given solar energy’s projected explosive growth, Hinkle said.
“We’re on the threshold of being able to make a breakthrough,” Hinkle said. “We think the timing is perfect for developing a cluster for solar in Minnesota that involved R&D, strong installation and manufacturing.”
The intent of Campbell’s research is to reduce one of the largest contributors to the cost of a solar installation: the solar cell itself.
“Making more efficient devices is the most reasonable way to try to achieve SunShot goals,” Campbell said.
Campbell’s work focuses on thin film photovoltaic, or solar, cells in which a thin layer of a semiconductor is deposited on a layer of glass or stainless steel. Thin film cells are expected to overtake more expensive circular silicon wafers used in most of today’s solar arrays.
Campbell favors the high efficiency of what he calls “the champion of all the thin film technologies,” known by the acronym CIGS for its copper-indium-gallium-selenide composition.
CIGS-based solar cells have topped 20 percent efficiency in lab demonstrations — meaning they have converted 20 percent or more of the sun’s solar radiation into electricity. Manufacturers, Campbell said, today are producing CIGS cells that are up to 14 percent efficient, while the theoretical efficiency limit is close to 30 percent.
Campbell and other U researchers using a tandem solar cell structure, made up of two separate cells joined together, in hopes of making significant gains in efficiency. Studies elsewhere have found that a tandem structure raises the theoretical efficiency limit to close to 45 percent.
“This turns out to be a much more efficient way to harvest the energy that the sun is providing,” Campbell said.
To absorb more high-energy light, Campbell is adding another element — aluminum — to the CIGS recipe, now known as CIAGS.
To improve reliability, the tandem cells are covered with a moisture-protection barrier, developed at the U in collaboration with a sponsoring company that makes products that use CIGS-based solar cells, Campbell said. He declined to identify the company but said it was not 3M.
Changing properties of the materials that make up a solar cell to get more energy from it is a promising area of study, said William Shafarman, a scientist in the Institute of Energy Conversion at the University of Delaware who has done 25 years of research on thin film solar cells.
While he has worked with adding aluminum to CIGS-based cells, Shafarman said he most recently has replaced some of the copper with silver, which produced the best results he has seen.
“Efficiency and performance matter, but cost also matters,” Shafarman said. “The thin films have the potential for much lower cost. The critical issue is getting to large-scale manufacturing, which is what it will take to get the cost down.”
Written By: Todd Nelson
Source: Finance & Commerce