Interesting calculation and I did not read your assumption carefully.
"keep up the current growth in energy use "
But this was not what I was talking about at all.
Energy comes to earth via sun, whether we use it, or not. For all our practical matters, it will be plenty to recycle all of our solar panels.
Because human population growth won't continue, like it did after industrialisation moved the limits of growth.
Discovering (allmost) speed of life travel would again moved those limits.
Till then humans will mate, as long as they see a future for their babies. As long as there is food and space. If there isn't, they largely won't reproduce. It is a common effect, can also be studied in rat populations in a lab. Self regulation.
"Have you seen what happens to slime molds once they run out of resources?"
They try to find a better habitat. Some succed, some fail.
https://dothemath.ucsd.edu/2011/07/galactic-scale-energy/ by a Professor of Physics, Astronomy & Astrophysics at the University of California, San Diego.
> Like any life. It grows until it runs out of ressources.
Citation needed. Show me any other species that managed to increase the extinction rate of other species by 1000x in 50 years.
> Then it stagnates.
Have you seen what happens to slime molds once they run out of resources?