Can we develop solar panels that work at night?
Posted by Alex Barrett on 18 May 2016 at 11:55 am
The main limitation of renewable energy technologies is their intermittency. At some times they produce more than enough energy to serve our needs, but this is very dependent on conditions of weather and light which are out of our control. These periods of intense energy production do not always match up with the times when we need the most power. In no case is this more pronounced than that of solar photovoltaic systems (Solar PV). Solar panels produce a lot of energy when the sun is shining, but do not work at night when we need power for lighting and space heating.
Various researchers are working on designing alternatives to solar panels that will produce power during the periods when it is needed most. Several different approaches have been taken to capturing a wider range of energy than is presently harvested by solar cells. While they are still at the early stages of development these technologies show a lot of potential once they are perfected.
One study [1, 2, 3] has demonstrated that highly efficient solar cells can be produced by printing nanoantennas onto sheets of flexible material. These are designed to absorb energy in the infrared region of the spectrum. By matching the size of the antenna to the wavelength of infrared radiation (around 1-100 μm) they can convert infrared radiation into electrical current. Infrared is a large component of sunlight, but is also emitted by any warm surface. Consequently the Earth continues to emit infrared radiation after the sun has set.
Another technology that may one day be used to harness this flow of infrared radiation is the emissive energy harvester (EEH) . The researchers developing this technology estimate that as much as 1017 W of energy is constantly emitted by the Earth in the form of infrared radiation. They describe a panel that would be pointed at the sky, emitting infrared radiation, in the range of wavelengths where the atmosphere is mostly transparent. Their study suggest that the “imbalance between incoming and outgoing radiation can be converted into an imbalance in electron motion, i.e. into useful electrical power.” 
EEH panels would require a clear sky, as low lying cloud would reduce the heat flow on which they rely, but the system would be able to work during the day or at night so long as there isn’t too much cloud. This system is still at the earliest stage of development, but has been shown to be thermodynamically possible. It will be a long time before we see these panels on our roofs, but they have the potential to revolutionise how renewable energy is generated.
- Kotter, D., Novack, S., Slafer, W., & Pinhero, P. (2010). Theory and Manufacturing Processes of Solar Nanoantenna Electromagnetic Collectors. ASME. J. Sol. Energy Eng., 132(1), 011014–011014. .
- Solar Power Authority
- Byrnes, S. J., Blanchard, R., & Capasso, F. (2014). Harvesting renewable energy from Earth’s mid-infrared emissions. Proceedings of the National Academy of Sciences of the United States of America, 111(11), 3927–3932.
Image Credit: Dept of Energy Solar Decathlon via Flickr
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