{"id":81587,"date":"2022-04-25T09:34:22","date_gmt":"2022-04-25T07:34:22","guid":{"rendered":"https:\/\/www.sonnenseite.com\/?p=81587"},"modified":"2022-04-25T09:34:23","modified_gmt":"2022-04-25T07:34:23","slug":"stanford-engineers-invent-a-solar-panel-that-generates-electricity-at-night","status":"publish","type":"post","link":"https:\/\/www.sonnenseite.com\/en\/science\/stanford-engineers-invent-a-solar-panel-that-generates-electricity-at-night\/","title":{"rendered":"Stanford engineers invent a solar panel that generates electricity at night"},"content":{"rendered":"\n

Radiative cooling might reduce the need for costly batteries in some applications<\/p>\n\n\n\n

The skies above Stanford, California, were unusually clear for several nights last October.<\/p>\n\n\n\n

That was good news for researcher Sid Assawaworrarit<\/a> and his colleagues. Those conditions were “probably the best of the year,” he tells IE.<\/em><\/p>\n\n\n\n

Assaworrarit isn’t an astronomer grateful that clouds didn’t block starlight from traveling through the atmosphere and reaching the mirror of his telescope. An electrical engineer, he welcomed the cloudless nights for an entirely different reason: a clear night means infrared light from the surface of solar panels can freely radiate out into space.<\/p>\n\n\n\n

That flow of energy enables the device Assaworrarit and his colleagues created \u2014 an ordinary solar panel outfitted with a thermoelectric generator \u2014 to generate a small amount of electricity from the slight difference in temperature between the ambient air and the surface of a solar panel pointed deep into space.<\/p>\n\n\n\n

At night, solar panels turn the table and emit photons<\/h5>\n\n\n\n

The new technology takes advantage of a surprising fact about solar panels.<\/p>\n\n\n\n

\u201cDuring 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,\u201d Assawaworrarit says. <\/p>\n\n\n\n

That\u2019s because solar panels \u2014 like everything warmer than absolute zero \u2014 emit infrared radiation. <\/p>\n\n\n\n

\u201cThere\u2019s 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,\u201d he says. <\/p>\n\n\n\n

As those photons leave the skyward surface of the solar panel, they cary heat with them. That means that on a clear night \u2014 when there are no clouds to reflect infrared light back toward the Earth \u2014 the surface of a solar panel will be a few degrees cooler than the air around it. That temperature differential is what Assawaworrarit and his colleagues are taking advantage of. A device called a thermoelectric generator can capture some of the heat flowing from the warmer air to the cooler solar panel and convert it into electricity.<\/p>\n\n\n\n

On a clear night, the device Assawaworrarit tested on the Stanford rooftop generates roughly fifty milliwatts for every square meter of solar panel (50 mW\/m2<\/sup>). <\/p>\n\n\n\n

\u201cI think that\u2019s probably a record number,\u201d he says. But Assawaworrarit and his team aren\u2019t stopping there. He says that with a couple of improvements (and in a good location) such a device could generate twice that amount of electricity. <\/p>\n\n\n\n

\u201cThe theoretical limit is probably about one or two watts per square meter,\u201d he says. \u201cThat\u2019s not a huge number, but there are a lot of applications\u201d where that kind of energy at night would come in handy. <\/p>\n\n\n\n

For instance, a large fraction of the world\u2019s population \u2014 roughly a billion people \u2014 don\u2019t have access to an electrical grid<\/a>. People living in that situation \u201ccan rely on solar during the day, but at night there\u2019s that not much they can do,\u201d he says. Unlike batteries that degrade substantially after a few thousand charge cycles, the kind of thermoelectric generators used in these solar panels are solid state, \u201cso the lifetime is pretty much forever,\u201d he says.<\/p>\n\n\n\n

Another good use for the technology is powering the immense network of environmental sensors researchers use to keep tabs on everything from weather conditions to invasive species in far-flung corners of the globe. Again, solar panels that generate a small amount of electricity at night could reduce the need for batteries \u2014 and the maintenance and replacement costs they incur. <\/p>\n\n\n\n

\u201cIf you can get up to a watt per square meter, it would be very attractive from a cost perspective,\u201d Assawaworrarit says.<\/p>\n\n\n\n

Read more <\/a><\/p>\n\n\n\n