[jessriedel]

What's the advantage over direct thermoelectric conversion?

[curtis]

> What's the advantage over direct thermoelectric conversion?

Stirling engines can approach 50% efficiency [1], whereas thermocouples are usually less than 10% [2].

[1] https://en.wikipedia.org/wiki/Stirling_engine

[2] https://en.wikipedia.org/wiki/Thermoelectric_generator#Effic...

[jessriedel]

Cool, thanks! It's really surprising to me that inserting a mechanical intermediary has such a large efficiency advantage.

[brians]

Why does mechanical stuff suck? Because of friction of moving parts. Too much energy is lost to heat. For a thermal engine, if you can arrange to put the moving parts mostly on the hot side, that’s no longer loss.

[nickhalfasleep]

An RTG uses the Seebeck effect, which gets you microvolts per degree kelvin. A Stirling engine can theoretically extract many times more energy from the same temperature differential, but with a larger complexity.

[jessriedel]

Actually, when I mentioned thermoelectric conversion I wasn't referring to an RTG (which is just nuclear decay) but rather to the true nuclear reactors that the Soviets put in space:

https://en.wikipedia.org/wiki/Romashka_reactor https://en.wikipedia.org/wiki/TOPAZ_nuclear_reactor

They used thermoelectric conversion rather than a Sterling engine with moving parts (although I guess TOPAZ is technically "thermionc coversion").