‘Where it’s most effective’ == places that use their energy during the day, e.g, any place close-ish to the equator that needs daytime cooling.

Solar farms can be deployed at large scale in less than three years. Here’s India adding 7 MW in that timeframe: https://www.greenlaunches.com/alternative-energy/less-three-...

We do have lots of solar panels and lots of solar panel manufacturing capacity. I don’t think we have the nuclear resources we need to produce as fast.