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posted by martyb on Tuesday September 05 2017, @12:16PM   Printer-friendly
from the will-it-cool-my-beer? dept.

New water-cooling solar panels could lower the cost of air conditioning by 20%

Most of us have heard of solar water heaters. Now there's a solar water cooler, and the technology may sharply lower the cost of industrial-scale air conditioning and refrigeration.

The new water coolers are panels that sit atop a roof, and they're made of three components. The first is a plastic layer topped with a silver coating that reflects nearly all incoming sunlight, keeping the panel from heating up in the summer sun. The plastic layer sits atop the second component, a snaking copper tube. Water is piped through the tube, where it sheds heat to the plastic. That heat is then radiated out by the plastic at a wavelength in the middle region of the infrared (IR) spectrum, which is not absorbed by the atmosphere and instead travels all the way to outer space. Finally, the whole panel is encased in a thermally insulating plastic housing that ensures nearly all the heat radiated away comes from the circulating water and not the surrounding air.

Researchers at Stanford University in Palo Alto, California, recently placed three water cooling panels—each 0.37 square meters—atop a building on campus and circulated water through them at a rate of 0.2 liters every minute. They report today in Nature Energy that their setup cooled the water as much as 5°C below the ambient temperature over 3 days of testing [DOI: 10.1038/nenergy.2017.143] [DX]. They then modeled how their panels would behave if integrated into a typical air conditioning unit for a two-story building in Las Vegas, Nevada. The results: Their setup would lower the building's air conditioning electrical demand by 21% over the summer.


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  • (Score: 1, Informative) by Anonymous Coward on Tuesday September 05 2017, @07:06PM (1 child)

    by Anonymous Coward on Tuesday September 05 2017, @07:06PM (#563876)

    It doesn't need power, and is not a perpetual motion device. It is a means of radiating heat to space, and works even though it is in full sunlight. Thus it provides the advantage of letting an air conditioning unit operate more efficiently than if it were rejecting heat to the ambient air. The best you can do in the way of using this for perpetual motion would be to operate a heat engine between the ambient air as a heat source and this device's cold side as a heat sink. The difference is only about 5 C, so it would not be very practical. It isn't perpetual in the theoretical sense because you will eventually run out of ambient heat or heat up the universe.

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  • (Score: 0) by Anonymous Coward on Tuesday September 05 2017, @09:59PM

    by Anonymous Coward on Tuesday September 05 2017, @09:59PM (#563940)

    The best you can do in the way of using this for perpetual motion would be to operate a heat engine between the ambient air as a heat source and this device's cold side as a heat sink. The difference is only about 5 C, so it would not be very practical.

    A 5°C difference is plenty enough to generate useful work. Looking at the first peltier device I could find which included this information in the datasheet (Marlow RC12-2.5) this should generate approximately 5mW at 0.2V, with physical dimensions about 30mm x 30mm. Not a lot, but if this device can really do this then we can build an array of these.

    Let's put 33 in series to get a nice 1m x 30mm row, producing a more useful ~6.6V, capable of outputting about 25mA. So we can put 33 of those in parallel to get a 1m x 1m panel, giving us about 0.8A maximum output -- around 5W. It'll be big and expensive but you can certainly run something off of that. Perhaps it would be useful for spacecraft. There may also be better peltier devices.

    A solar panel will do better (about 30x more power for the same area) but it is generally easier to point something away from the sun than towards it.