While I'm not convinced by Tim's calculations the idea that there is no energetic free lunch is good to keep in mind. The last centuries have been characterised by the mistake of thinking 'oh we can do x and predict the consequences'.

I very much doubt our windmills will mess up global weather systems, or that solar power will starve the phytosphere.

However taking solar energy from outside of the planet to bring into the atmosphere is the same problem but in a different direction. Should be obvious really.

We are storing extra energy in the atmosphere due to greenhouse gasses. If human energy use is big enough to disrupt planetray systems, then sourcing it from the outside will cause more disruption, not less.

Same applies if we get 'limitless' fusion energy.