Earlier quoted context omitted.
> My theory is that its darkness is down to the fact that the civilisation there has figured out a way to harness solar energy to near 100% capacity, along the lines of a Dyson sphere [1]. Very unlikely, in light of the fact that "the air of this planet is as hot as lava".
Isn’t that the expected outcome when energy production eventually outpaces the planet’s ability to dissipate energy into space?
The problem with an atmosphere hotter than lava is that very few materials are solid at those temperatures, and it's hard to imagine how a civilization could build an energy harvester without solid materials.