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Solar Energy: Capturing Infrared Radiation to Make Nighttime Solar Possible

By Dick Weisinger

Solar energy by definition is energy produced from the sun. Max production is possible on sunny days and can drop to as much as only 10-25 percent of their maximum output on cloudy days.

Both the predictability and the non-predictability of hours of light per day and the occurrence of clouds and storms has been a serious drawback of the technology. It means that solr energy primarily supplements traditional energy sources. Or it means the limitations need to be worked around by building infrastructure like massive batteries to store electricity for use during low production hours.

Some researchers are working on another option that doesn’t seem possible: the production of solar energy in the dark. One approach investigated by researchers at UNSW is the capture of heat from the earth as infrared light as the earth cools when no longer exposed to the sun.

Ned Ekins-Daukes, associate professor at UNSW, said that “using thermal imaging cameras you can see how much radiation there is at night, but just in the infrared rather than the visible wavelengths. What we have done is make a device that can generate electrical power from the emission of infrared thermal radiation.”

A somewhat similar thermo-electric approach is also being investigated at Stanford in a group led by Shanhui Fan.

Sid Assawaworrarit, a member of the Stanford team, said that “during the day, there’s a light coming in from the Sun and hitting the solar cell, but during the night, something of a reverse happens. That’s because solar panels — like everything warmer than absolute zero — emit infrared radiation. There’s actually light going out from the solar panel, and we use that to generate electricity at night. The photons going out into the night sky actually cool down the solar cell.”

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