Consider this: a) at some point our energy budget will exceed total Sun radiation reaching Earth, and b) indefinite "re-usage" of energy is impossible (entropy).
I actually considered this, making a disclaimer at the beginning and the end of the post :)
My point was that the timeframe would likely be quite different, e.g. millennia instead of centuries. From theoretical perspective doesn't change anything, but perhaps makes the argument a bit less dramatic.
What he did was to take the economists golden calf, the 3% growth pr annum, and run with it in physical terms. Demonstrating how, if economists managed to maintain that growth curve, the energy requirements would be staggering.
My point was that the timeframe would likely be quite different, e.g. millennia instead of centuries. From theoretical perspective doesn't change anything, but perhaps makes the argument a bit less dramatic.