Scientists Generate Power At Night By Passively Beaming Heat into Outer Space. It's "Like Solar Cells in Reverse"

That's pretty cool. Scientists have refined what's known as a Stirling engine - one that captures heat dissipation to generate power - to collect heat that's being released from the earth at night. 

They're calling it a sort of reverse solar cell. 

https://www.zmescience.com/future/scientists-generate-power-at-night-by-passively-beaming-heat-into-outer-space-its-like-solar-cells-in-reverse/