Solar power is not free.

You can decide to not fix the panel that was being used to power a GPU.

Or you could sell the power back.

Or you could put it in a battery bank for when the sun is down.

Or, if none of those are the case and you just have excess power that's useless for anything but a GPU, then you prepaid for the GPU.

I love that we have solar panels, but we weren't gifted them. Using power has a cost.