Microchannel systems could boost future of solar thermal electricity

Could lower costs and lead to a wider deployment of solar energy.

CORVALLIS, Ore. - Microchannel technology pioneered at Oregon State University has demonstrated in laboratory experiments that it can significantly improve the efficiency of solar thermal generation of electricity, which could lower costs and lead to a wider deployment of solar energy.

Based on this, and to help bring the technology to a practical test in the field, the U.S. Department of Energy SunShot Initiative today announced a $2.5 million award to OSU and five collaborating partners.

The recent findings are important, researchers say, because they could help make solar thermal electricity more cost-competitive with other forms of electricity generation and expand the number of locations able to host a solar thermal plant. The technology is also safe, long-lasting, friendly to the environment and produces no greenhouse gas emissions.

In contrast to conventional solar photovoltaic cells that produce electricity directly from sunlight, solar thermal generation of energy is developed as a large power plant in which acres of mirrors precisely reflect sunlight onto a solar receiver. At the solar receiver a fluid such as supercritical carbon dioxide is heated to a high temperature, which in turn is used as a heat source for an electricity generating facility.

Existing plants so far have been built in areas with the most consistent solar resource, such as the American Southwest. But if costs are lowered and efficiency improved, usage in general should expand, and other sunny areas in temperate or tropical zones around the world could develop such systems.

"Our advances could open the door to a significant, 15 percent higher efficiency for solar thermal technology," said Kevin Drost, an associate professor of mechanical engineering, now retired, at Oregon State University, which is leading the research consortium working to develop these systems.

"We're confident that this work will meet the goals being set by the Department of Energy," Drost said. "With their support we'll now move it beyond the laboratory toward a technology that could be commercialized."

A key to the advances is microchannel technology that has been developed at OSU in recent years, and is already finding applications in systems such as blood dialysis or advanced heat exchangers.

These microchannel systems use extremely small channels and a branching distribution system that speed the transfer process and improve efficiency. A microchannel lamination technology developed at OSU helps control cost, and short channels help control pressure.

"Solar thermal technology has to work at very high temperatures and very high pressures, which present special challenges," Drost said. "We are demonstrating that microchannel systems, as well as the use of supercritical carbon dioxide as a heat transfer fluid, should meet those challenges."

The use of supercritical carbon dioxide, the researchers said, is an important component of their system, in contrast to the molten salts now used for heat transfer. It can operate at 650-720 degrees centigrade, compared to 500 degrees for molten salt. The use of supercritical carbon dioxide will improve efficiency, use a much smaller turbine, and will help to eliminate the need for water cooling towers, a special concern in some of the sunny, dry locations where such energy plants are likely to be located.

The microchannel receiving panels using the supercritical carbon dioxide are also about four times smaller than existing technology, which reduces cost, loss of thermal energy and weight.

Collaborators on this project include Sandia National Laboratory, Pacific Northwest National Lab, the National Energy Technology Lab, University of California, Davis, and ECOKAP Technologies.

The U.S. Department of Energy SunShot Initiative is a collaborative national effort to make solar energy fully cost-competitive with traditional energy sources before the end of the decade.

Through SunShot, the Energy Department supports efforts by private companies, universities, and national laboratories to drive down the cost of solar electricity to $0.06, or six cents per kilowatt-hour.

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