Is it really limitless if both generating and consuming energy produces heat? Or is that too small of an effect even despite the heat inefficiency of fusion?
Earth gets multiple orders of magnitude more heat from the Sun than humans can ever hope to generate. In concrete terms, Earths gets 153 PW of energy in terms of solar radiation. It also radiates as much. In comparison, humanity uses something like 20 TW in total (that includes not only electricity, but also transportation etc). So, we could increase our energy use 100 times, and still be only around 1% of what we get from the Sun.
So that's between 150 and 250 years with the 2.5% energy consumption grows, then that much again for us to produce more energy than the sun shines on Earth.
