Solar panels are more popular the closer you are to the equator, so states like Hawaii and Arizona already have a lot of investment in solar. For the colder states, its financially a bad investment due to lack of enough sun throught longer periods of the year.

In population hotspots for example, in Socal, Solar is skyrocketing, but I wouldnt say they same for places like NYC.

I dont speak for other countries though, and wonder why some countries that should have it, havent invested enough in it (e.g latin countries, india) which receive a lot of sunlight.

Already this year, as it seems to me. Then next year, suddenly lots of 'buffer/unknown' - so where's that?

Because that's what solar installs have been doing so far this year, apparently:

https://cleantechnica.com/2023/08/11/solar-is-king-2023-50-global-growth-predicted/

China’s solar industry is operating at a 93.6% annual growth rate, looked at through the 12-month rolling average – or if you compare the first six months of 2023 to H1 2022, then the pace of installations has more than doubled, accelerating 154%