You can look at a world heat map plot of solar irradiance. That's one factor. The other factor is seasonal variability, which is a harder problem to solve than

You can look at a world heat map plot of solar irradiance. That's one factor. The other factor is seasonal variability, which is a harder problem to solve than low irradiance. Low irradiance can be solved by installing more panels, which will automatically be solved with future price declines.