Exponential, it fits the curve very nicely. I can give you the python code if you want to. I got 2 decades for all energy usage, not only electricity, which is only one sixth of that.
I just took the numbers for the whole world, that’s easier to find and in the end the only thing that matters.
The next few years are going to be interesting in my opinion. If we can make efuels cheaper than fossil fuels (look up Prometheus Fuels and Terraform Industries), we’re going to jump even harder on solar and if production can keep up it will even grow faster.