It was in 1883 that Thomas Edison discovered this phenomenon but it was not until 1994 that Gerald Mahan published a rather pessimistic paper on the prospects for this form of refrigeration. It is based on an electrical device called a vacuum diode which goes under the name of the Cool Chip. It contains two thin films separated by a narrow vacuum layer. If a voltage is put across the gap the most energetic electrons on the negative side 'boil off', carrying their kinetic energy to the positive side of the chip. As the hottest electrons migrate, the negative side or cathode cools, opening up the prospect of chemical-free refrigeration. The extra energy in the electrons reaching the positive anode is merely dissipated as heat. This is the basis of thermionics.
A British company called Borealis is optimistic that this technology has considerable potential, offering 80% efficiency as against the 30-50% of a compressor refrigerator. A panel of 25 chips covering 5 cm2 would operate a typical domestic fridge using about 15 W of electricity. It has the advantage of being silent, with no moving parts and therefore virtually maintenance-free. It remains to be seen if the technology can be scaled up to provide cooling for buildings. Indirectly it has the potential for reducing the cooling load in buildings by cooling microprocessors and other electrical equipment that make a significant contribution to the heat build-up in offices.4
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The solar Stirling engine is progressively becoming a viable alternative to solar panels for its higher efficiency. Stirling engines might be the best way to harvest the power provided by the sun. This is an easy-to-understand explanation of how Stirling engines work, the different types, and why they are more efficient than steam engines.