All the electricity we generate becomes waste heat in the atmoshpere. Global energy use is currently ~0.1% of Sun power hitting the Earth. USA uses ~10x more electricity per person than India does, assume bringing everyone up to USA levels means we'll be around 1% of Sun power. Grow the population from ~8Bn to predicted ~12Bn and we'll be around 1.5%.

And then everyone gets "too cheap to meter" fusion power? There is not a /lot/ of headroom there, we surely can't go to outputting as much waste heat again as the planet gets from The Sun - and before you say "solar", you already said "fusion".