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MIT’s unique new solar heat system

MIT “’ the
Massachusetts Institute
of Technology
Cambridge, Massachusetts, United States — ESI-AFRICA.COM — 06 May 2011 – Researchers and their collaborators at MIT “’ the Massachusetts Institute of Technology “’ have come up with an unusual, high performance and possibly less expensive way of turning the sun’s heat into electricity.

Their system “’ described in a paper published online in the journal ‘Nature Materials’ this month, produces power with an efficiency roughly eight times higher than ever previously reported for a solar thermo-electric device — one that produces electricity from solar heat. It does so by generating and harnessing a temperature difference of about 200 degrees Celsius between the interior of the device and the ambient air.

“The concept is very radical,” says Gang Chen, MIT’s Carl Richard Soderberg Professor in Power Engineering, who co-authored the new paper with MIT doctoral student Daniel Kraemer and collaborators from Boston College and GMZ Energy. The work is funded by the Solid-State Solar-Thermal Energy Conversion Centre, an Energy Frontier Research Centre at the U.S. Department of Energy.

While solar thermal electricity systems aren’t a new idea, they typically involve vast arrays of movable mirrors that track the sun and focus its rays on a small area. The new approach uses flat, stationary panels similar to traditional solar panels, eliminating the need for tracking systems.

Like the silicon photovoltaic cells that produce electricity when struck by sunlight, Chen’s system is a solid-state device with no moving parts. A thermo-electric generator, placed inside a vacuum chamber made of glass, is covered with a black plate of copper that absorbs sunlight but does not re-radiate it as heat. The other side of the generator is in contact with ambient temperatures. Placed in the sun, the entire unit heats up quickly even without facing the sun directly.

The device requires much less material than conventional photovoltaic panels, and could therefore be much less expensive to produce. It can also be integrated into solar hot water systems, allowing the expenses of the structure and installation to serve two functions at once.

Such solar water heaters are rarely seen in the United States, but are already a highly successful mass-market product in China and Europe, where they provide households with hot water and in some cases space heating as well.
The materials used to build such solar thermo-electric generators were developed jointly a few years ago in Chen’s lab at MIT, and in co-author Zhifeng Ren’s lab at Boston College. Their teams have continued to work on improving these materials and integrating them into complete systems.

Chen points out that the U.S. Department of Energy has programmes to develop thermo-electric systems, mostly geared toward harnessing waste heat from car and truck engines. He says that solar applications for such devices also can have an important role to play in reducing carbon emissions. “Hopefully we can prove that,” he adds.

“The new system wouldn’t be a substitute for solar photovoltaics,” Chen says, “but offers another way of tapping into the enormous amount of solar energy that bathes the Earth every day. And because it can be piggybacked onto the existing solar hot-water industry, the thermo-electric device could be a relatively inexpensive addition, with no subsidies required, Chen suggests. “It can be a game-changing thing,” he says.