New solar tech collects energy at night

Gold nano-antennas set this solar energy-collecting technology apart from the rest. Using cheap, flexible materials, researchers at Idaho National Laboratory, a branch of the U.S. Department of Energy, hope to create mass-produced plastic sheets with billions of nano-scale antennas to collect energy.

The tiny antennas are designed to target heat rather than light, in the form of the lower-energy infrared rays continually emitted by Earth. The sun radiates a lot of infrared energy, some of which is absorbed by Earth and re-released after the sun sets. Traditional solar cells only collect visible light, which is why they become useless at night. By collecting infrared instead, this new solar material should be able to collect energy after dark. In addition, placing a strip of this material near any source of infrared radiation – say, an engine’s exhaust pipe or any industrial process – would allow it to capture the waste heat. 

Each nano-antenna is a tiny gold spiral or square treated in polyethylene, a material used in plastic bags. They’ve built and tested a few prototypes of the material by stamping the metal antennas onto plastic sheets. Initial experiments seem to show that the antennas capture about half of the energy available to it.

But a substantial technical hurdle still remains – transforming the captured energy into useable electricity. The infrared rays create very fast alternating currents in the antennas, which would need to be converted to direct current to be used by everyday appliances. Current technology for converting ac to dc can’t handle the high frequencies seen here, so the researchers still need to devise some workaround. For the technology to gain a foothold and eventually compete with established solar materials, the researchers will have to find a very inexpensive way to do so.

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