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Comment by remcob | Hacker News Reader

> 45-50°C below the ambient air temperature

That's incredible! Isn't that enough to run a heat engine on? If so, does this allow you to extract (nearly) free energy out of the ambient heat?

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Have to consider the amount of heat moved, too. It's the same difference as between pressure and volume, or volts and amps. Perhaps it can't move a large volume of heat quickly, but can achieve a decent temperature difference given enough time?

And even if it can, I am reasonably confident (from my arm chair here) that this combination of relying on a narrow band of passive IR emissions to drive a heat engine will be less effective than a photovoltaic cell generating electricity directly from incoming visible radiation across a relatively broad frequency band.

Ah, but only one of those still operates in the dark.

50C is not much for heat engines your limited to under 15% effecency in the best theoretical case. So solar + battery is going to be a net win unless your thinking of flipping panels at night for ~1% more power over pure solar panels which is silly from a cost perspective.

I thought solar was widely favored long term, but it's going to be a long time before it establishes that position.

That differential could run a Sterling engine.

You can run a Stirling engine on much lower temperature differentials:

https://en.wikipedia.org/wiki/Applications_of_the_Stirling_e...

https://www.amazon.com/Three-Stirling-Engines-Without-Machin...

That differential was quoted for perfect insulation. Plugging in a heat engine is the opposite of insulation.

My god, that could be a great asset to communities in water-starved regions of the planet.

It all comes down to units of thermal rejection per area per unit lifetime cost. If either one of those values is less than desirable expectations will fall short.

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