- Could we build a very efficient heat engine in outer space because of the avaialability of a very cold reservoir.
I have a question about building efficient heat engines in outer space. In theory you could have a hot reservoir heated by the sun that was several hundred degrees C, and a cold reservoir that was very cold - maybe 50K - 100K or even colder. Thus, theoretically at least, a heat engine could be very efficient, much more efficent than photovoltaics. Is this practical, or would the radiator required to cool the cold reservoir be prohibitively large? If you did try to build something like this, what working fluid would be best?