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The company had toyed with the idea of using only thermoelectric modules hooked up to PV panels. In a thermoelectric module, voltage applied across a thermoelectric material sandwiched between two ceramic plates makes one side hot and the other cold. However, existing thermoelectrics (which are used in temperature-controlled car seats, lasers, and portable picnic coolers), typically bismuth or lead telluride, are not efficient enough for large refrigerators.
Gang Chen, a professor of mechanical engineering at MIT, says that the efficiency of a cooling unit depends on its size. "As you shrink the size to a hotel refrigerator, the compressor itself becomes less efficient," he says. "In those cases, thermoelectric becomes increasingly more attractive." Promethean's approach to combining thermoelectrics with compressors sounds like a logical argument to increase cooling efficiency in commercial-scale systems, Chen says.
The company's 60-liter prototype used bismuth-telluride modules from Dallas-based Marlow Industries. That is the most efficient cooling material known so far, says Boston College physics professor Zhifeng Ren. But there is still room for improvement, and Grama says that the company is on the lookout for new, possibly more-efficient materials.
The startup company might be in luck. Many advances in thermoelectric materials have come out of laboratories recently. MIT's Chen, for one, has increased the efficiency of bismuth antimony telluride by 40 percent by using nanocrystalline materials. Researchers are also tinkering with lead telluride and are starting to use silicon nanowires and silicon-germanium composites. Chen and Ren have founded a company called GMZ Energy, headquartered in Newton, MA, to commercialize their nanocomposite material, and they're expecting commercial thermoelectric modules within one year.
Nanomaterials could be used for lower-emission cars and solar panels.
Sometimes it appears necessary to invest more checking third world simple solutions, before going sophisticated. There is a beautiful –no moving parts- heat exchanger capable of cooling a large house refrigerator silently, with a flame the size of large candle. It can work for decades I used it myself. I reckon it can be easily adapted to solar or any other kind of heat, compressed or liquid natural gas, or a mix of them, inexpensively.
Those off-grid villages should be connected to grid on the first place. Such connection is relatively cheep and will let them to use "of the shelf" efficient refrigerators that are already in mass production. Plus electricity mean education(computers/Internet) and electric light and gazillion other things that define quality of life. Plus, such connection will be there sooner or later. Compare to custom made temporal fix of narrow problem...
What needs to be considered, here, is that solutions that are developed keeping rural areas of India in mind can potentially have a much deeper impact due to depth of rural india as well as wider impact through technology transfers into other developing nations. Africa, for one, is in dire need of solutions of these kinds. 20% saving does amount to significant saving in terms of PV modules / batteries and other Balance Of System (BOS) components that are required to drive these chillers. Interestingly, the solution brings two technologies into one system with a seeming dedicated control gear, cost of which may circumvent the savings.
Off Grid dont you think if they could get on a grid they would?We plan to move to an island there is no power for 10 miles maybe you can pay to run a line in for us? this is about living off grid and i dont believe the indains here in panama have a choice.guess you think they should have fiberglass boats w/ outboards too
$12,000!? There have got to be cheaper ways to refrigerate. Evaporative cooling is one way. The Sun's energy can also be used to evaporate a refrigerant and thereby drive a cooling process using the condensation of the refrigerant. Lastly, fairly simple modifications can be made to existing technology to improve efficiencies and these changes can be made at a very low cost. I have been using a chest freezer modified with a heating thermostat and relay switch to run as a refrigerator. The unit uses 0.-0.2 kwh a day. With power consumption that low, you only need a small pv panel and battery to keep it going. I have posted the details of the project here: http://practicallyoffthegrid.com/2010/02/how-to-make-your-own-high-efficiency-refrigerator/
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20 Comments
House fridge efficiency
Can thermocouples be used to increase efficiency of existing refrigerators/ AC economically?
As a bridge, I mean. I assume that truly high efficiency thermocouple devices would eventually be configured to eliminate compressors entirely (much to be desired!).
I understand many TC units are currently experimental and hard to "price", but in a transition period could they produce electricity from the waste heat of compressor? Of course there would have to be a storage device/battery, and maybe a DC refrigerator. Which takes us back to off-grid niches, I suppose. It's just that all that exhaust heat in a heat exchanger seems such a waste.
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