While solar cells are an efficient source of renewable energy during the day, currently there is no similar renewable approach to generating power at night. Solar lights can be outfitted with batteries to store energy produced in daylight hours for night-time use, but the addition drives up costs. 

With that in mind, researchers at Stanford University and the University of California-Los Angeles developed a low-cost device that can generate electricity and power tiny LED lights simply by harnessing the cold nighttime air. The novel technology sidesteps the limitations of solar power by taking advantage of the good old thermoelectric effect. As the device releases heat, it does so unevenly, the top side cooling more than the bottom. It then converts the difference in heat into electricity. 

At its best, the device generated around 0.8 milliwatts of power, corresponding to 25 milliwatts of power per square meter. That might just be…
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