March 7, 2014
Harvesting The Infrared
In our search for new sources of energy, we may have been overlooking one that has been right in front of us for years. Do not worry, it is easy to miss and it requires you to think a little backwards in order to understand how to make use of it. I am referring to the infrared emissions our planet gives off every day — the heat that is expelled into the cold recesses of space. Thanks to new technological advances and a bit of thinking outside the proverbial box by the physicists at the Harvard School of Engineering and Applied Sciences (SEAS), the imbalance between our home planet and the cold emptiness that surrounds her could soon be turned into a direct-current source of power, one that has yet to be tapped into. It is weird to think about being able to generate power via emitting rather than absorbing, but it is doable. Less efficient, but still doable.
In order to accomplish this, the research team has suggested using two different kinds of emissive energy harvesters. One that would be analogous to a solar thermal generator while the other would be analogous to a photovoltaic cell. The trick to it is that both of them would be run backwards. For the first harvester, you would have a “hot” plate at the temperature of the Earth and air, with a “cold” plate on top of that one. The cold plate, made of a highly emissive material that cools by radiating heat upwards, would face the sky. The heat difference between the two plates would generate power. Now much, but a few watts per square meter every day all day and night. The difficult part of it comes from keeping the “cold” plate cold, namely cooler than the ambient temperature around it. The second device would focus on more the differences in temperature between nanoscale diodes and antennas relying on what is called “electrical noise.” When a diode is hotter than its resistor, it pushes its current in a single direction, which produces a positive voltage. Using a microscopic antenna as the resistor, it could efficiently emit the Earth’s infrared radiation towards the sky, cooling the electronics in only that part of the circuit, which would cause the diodes to run hotter, as desired. According to the study, a single flat device could be coated in lots of these tiny little circuits, all pointed up at the sky, so they could be constantly generating power.
One proposed idea is that these devices could be linked up to presently existing solar cells so that they continue to draw in power, even at night, with no real extra installation cost. The greatest problem facing the team on this advancement is the relatively low voltage they would be working with. At higher voltages, it would be a more simple matter to do what they want it to. With such low voltages, it would be difficult to successfully create an infrared diode that will do what they need it to. The teams are already considering what new types of diodes might handle these lower voltages, such as tunnel and ballistic diodes. Another option is to increase the impedance of the circuit components, which would raise the voltage to a more easy to work with level. Presently, they have not yet come up with a reliable fix to this problem, but having identified the problems they are facing, it is only a matter of time before they find a solution.
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