I think that the idea here is toproduce some current while grabbing the remainder of the energy (over ninetypercent of incoming) to produce hot water. Thus the reason for 200C. Thebottom of the thermal cycle will be never higher than 100C while the top end ispushed to 200C.
The actual heat differential isplausibly enough to drive a reverse Rankin cycle engine able to produce 75%brake horsepower.
This all suggests that the wholepackage is capable of been cleverly engineered into a highly efficient heat andpower generation package although complex enough to give Rube Goldberg anheadache.
In the meantime Rossi Focardi areending all this effort by making it completely obsolete which was already trueand why it has never gained much traction.
Solar power, with a side of hot running water
by David L. Chandler
MIT News Office
Doctoral student Daniel Kraemer, right, and Professor Gang Chen displaya prototype of a flat-panel solar-thermoelectric generating device. Photo:Melanie Gonick
MIT researchers and their collaborators have come up with an unusual, highperformance and possibly less expensive way of turning the sun's heat intoelectricity.
Their system, described in a paper published online in the journalNature Materials, produces power with an efficiency roughly eight times higherthan ever previously reported for a solar thermoelectric device - one thatproduces electricity from solar heat.
It does so by generating andharnessing a temperature difference of about 200 degrees Celsius between theinterior of the device and the ambient air.
The concept "is very radical," says Gang Chen, MIT's CarlRichard Soderberg Professor in Power Engineering and director of the PappalardoMicro and Nano Engineering Laboratories, who co-authored the new paper with MITdoctoral student Daniel Kraemer and collaborators from Boston College Solar-Thermal Energy Conversion Center , an Energy Frontier Research Center at the U.S.
While solar thermal electricitysystems aren't a new idea, they typically involve vast arrays of movablemirrors that track the sun and focus its rays on a small area. The new approachuses flat, stationary panels similar to traditional solar panels, eliminatingthe need for tracking systems.
Like the silicon photovoltaic cells thatproduce electricity when struck by sunlight, Chen's system is a solid-statedevice with no moving parts. A thermoelectric generator, placed inside a vacuumchamber made of glass, is covered with a black plate of copper that absorbssunlight but does not re-radiate it as heat. The other side of the generator isin contact with ambient temperatures. Placed in the sun, the entire unit heatsup quickly, even without facing the sun directly.
The device requires much less material than conventional photovoltaicpanels, and could therefore be much less expensive to produce. It can also beintegrated into solar hot water systems,allowing the expenses of the structure and installation to serve two functionsat once. Such solar waterheaters arerarely 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 aswell.
The materials used to build such solar thermoelectric generators, madethrough a nanostructured process, were developed jointly a few years ago inChen's lab at MIT and in co-author Zhifeng Ren's lab at Boston College. Theirteams have continued to work on improving these materials and integrating theminto complete systems.
Chen points out that the U.S. Department of Energy has programs todevelop thermoelectric systems, mostly geared toward harnessing waste heat fromcar and truck engines. He says that solar applications for such devices alsocan "have an important role to play" in reducing carbon emissions."Hopefully we can prove that," he adds.
Li Shi, associate professor of mechanical engineering at the Universityof Texas at Austin, says this approach to solar power is "very novel,simple, and easy for low-cost implementation." The efficiency level theyhave demonstrated so far, at 4.6 percent, is "already quite impressive,"he says.
"With the use of other or new thermoelectric materials that canoperate at a higher temperature," Shi adds, "the efficiency may beimproved further to be competitive with that for state-of-the-art amorphoussilicon solar cells. This can potentially provide a different approach torealizing the $1-per-watt goal for solar-electricity conversion."
The new system wouldn't be a substitute for solar photovoltaics,Chen says, but offers "another way" of tapping into the enormousamount of solar energy that bathes the Earth every day. And because it can bepiggybacked onto the existing solar hot-waterindustry, the thermoelectric device could be a relatively inexpensive addition,with "no subsidies required," Chen suggests. "It can be agame-changing thing," he says.
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