Sustainable energy via temperature differences proposed by researchers at Harvard University. Two methods of using the difference in temperatures between the earth and space to produce clean, sustainable energy have been presented in a report by Harvard professor Federico Capasso. Both are reliant on the fact that a difference in temperature can be harnessed to do work on a very small-scale, but aim to use large-scale installations to produce enough energy to power the planet.
The first method involves a hot plate warmed by the infrared emissions of the planet placed near a second plate that is cooled to a specific temperature. The researchers found that there is enough radiation at any given place on Earth to generate 2.7 watts of direct current power per square meter over 24 hours, but this is a very small amount of power, meaning the device would have to be very efficient to be viable. Unfortunately, challenges in cooling the second plate sufficiently for power to be generated have proven this method will not work for generating electricity at an industrial scale.
The second method of harvesting sustainable energy via temperature differences proposed involves nano-scale rectifying antennas, or rectennas, to turn Earth’s natural electromagnetic radiation into direct current power and then emitting infrared radiation into space. This method is more likely to work, as despite the low amount of power generated in tests, efficiency could be increased by use of reflectors to focus a wide areas worth of radiation into a small space, increasing power generated by rectennas in the area. Rectifying antennas are in use now, generating small amounts of power as a by-product of large microwave dishes and safely transmitting radiation into the sky.
Both methods of emissive energy harvesting are still in the early research phase, but the concepts they employ have been shown to be scientifically sound. Although it is counterintuitive to think that energy can be harvested by emitting radiation, but the physics hold up on the nano-scale. Despite the current restrictions on both designs, the problems will likely be solvable with recent strides in nano-manufacturing and materials science.
The primary challenge of both methods is the that enough power must be generated for the components to behave as desired. As professor Capasso says “the more power that’s flowing through a single circuit, the easier it is to get the components to do what you want. If you’re harvesting energy from infrared emissions, the voltage will be relatively low.” There are ideas to smooth this wrinkle however, such as adding rectenna assemblies to solar cells, where a small portion of the solar energy harvested would go toward improving the efficiency of the electromagnetic harvesting. At night, the rectenna would take over for the solar cell and provide electricity during low solar input, increasing the efficiency of the entire setup.
However the challenges are overcome, the idea of sustainable energy via temperature differences proposed has a very nice ring to it, likely one that researchers and inventors will be hearing for until the idea is put to effective use.
By Daniel O’Brien