But you need a lot of fluid or gas to move the heat in that radiator system, whereas solar has the benefit of extremely efficiently moving power around at great distances through wiring or integrated bus bars.

And you need to get the heat away from the central point to the extremities of the radiator as much as possible. So you can maximize how much energy can be radiated away.

Seems like the weight of the system would be an issue with whatever gas or liquid you used to fill those radiators, but maybe I'm wrong...