Thermoelectric generators have been used for decades to power deep space probes like the Pioneers or Voyagers. They work, they aren't very efficient, they need a source of heat (decay of plutonium or warmed-up Earth surface) and cloudless sky to radiate IR into.
If you want to detect clouds, just point an IR thermometer at the sky. It actually is more or less the same thing internally, but made for less power output and more precision, go figure.
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And I suspect that the power harvested by this device would otherwise get radiated into space during night, so that's a second day in a row we get a thread about some "eco" energy source that actually contributes to global warming