For anyone interested, eventually I figured out where the error is (also thanks to this site: http://tierneylab.blogs.nytimes.com/2010/03/05/the-second-law-strikes-back/).
The assumption that for a sufficiently large ellipsoid all the energy from one energy hits the other is wrong. No matter...
Hey Guys,
so I had a longish discussion with colleagues and on reddit about thermal equilibrium and the sun and how you cannot heat up anything above the surface temperature of the sun using clever mirrors and stuff.
However, somebody came up with Napkin calculations of the Stefan Boltzmann...