In a recent paper , published on Joule, Stanford University researchers are reporting the successful creation of a device that is able to generate electricity by exploiting the difference of temperature that can be established during the night between the surrounding air and the surface of the device that is cooling itself by emitting infrared radiations towards the night sky.
The possibility to generate electricity by exploiting thermal difference is not new, what is new here is the idea of creating a temperature difference by having part of the device radiating energy into the outer space,
As shown in the graphic, the device contains a thermoelectric generator, one side exposed to the air temperature and the other in contact with an aluminum plate. This plate, like a solar panel, actually an anti-solar panel, is facing the night sky and radiates thermal energy towards the sky. This lowers the temperature of the plate, some 2 centigrades less than the lower part of the device that has the same temperature of the air. How is it possible the the aluminum plate has not the same temperature of the air? Good question! Here is the trick. The aluminum plate is isolated from the ambient temperature with a transparent insulating panel that lets the radiating energy go through but blocks the heat exchange.
Two degrees of temperature difference is not that much and indeed the electricity produced by a one square meter of panel is around 25 mW (that could power a single LED). This is nowhere near the 100 W that modern solar panel can produce (out of the 1,350W received from the Sun). The researchers are confident that they will be able to increase the efficiency and reach 0.5W per square metre. That would be 0.5% of the yield of a solar panel but it could be enough to power an LED light in your living room at a time when the solar panel will not produce any electricity.
Not sure if this can find an application on my or your roof. However, it can be useful to power several IoT (ambient sensors), a new form of energy scavenging, and for that there could be a market in the coming decades. For sure I am impressed to see the ingenuity of researchers in finding new ways of solving problems that have seemed plainly impossible!