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Reverse solar trap

  1. Jun 11, 2012 #1
    I've been thinking about this on and off for awhile now. It first started with the idea of a solar trap.

    Solar trap being something like having a solar collector focusing light on a container of water, having an infra red barrier around the container, and a black body at the centre. Incoming solar energy passes by the IR reflector, absorbed by the black body and re-emitted as radiation which is reflected by the IR reflector.

    I was pleasantly surprised some form of this technique is used in the high efficiency solar water heaters.

    So what stops one doing this in reverse? having a visible reflector, IR transmitting layer.

    Could this allow solar cooling during the day? It would of course depend on the net flux of radiation, perhaps looking at natural sunlight spectrum there maybe a band strongly absorbed by the atmosphere that is within the range put out by a black body.
     
  2. jcsd
  3. Jun 11, 2012 #2

    Bobbywhy

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  4. Jun 11, 2012 #3
    found this

    http://www.ispoptics.com/Images/MaterialChart.gif

    Germanium seems a good candidate, for a better view

    http://rmico.com/technical-notes/bk7-quartz-ge-si [Broken]

    in particular

    Germanium.gif


    based on this calculator
    http://www.calctool.org/CALC/phys/p_thermo/wien

    peak radiance of a 300 K object is 10 μm

    Atmospheric_Transmission.png

    there's some absorbance around that wavelength
     
    Last edited by a moderator: May 6, 2017
  5. Jun 11, 2012 #4
    So, after a bt of googling. This turns out to exist.

    A cold mirror

    http://en.wikipedia.org/wiki/Cold_mirror

    Although, they don't quite cover the spectrum that would be optimal, the limit currently for commerical mirrors is up to 2500nm,This is usually layered dialectric coatings.

    really want that to be transmissive between 2500nm and 15000nm.

    Germanium does a good job, although the ROI would be terrible, silicon, which does about 1600-7000nm would be ok, though im guessing cost wise it wouldn't be much better.
     
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