For experimentation purposes, the sun is terrible. It doesn't have a fixed, standard output that allows reproducible measurements, you can't dim it to measure effectiveness at various radiation levels etc.

As a power source, it's not that bad: It does need storage and the output level fluctuates, but almost all other power sources need storage as well (fossil fuels before conversion to electricity, which makes things easier, but still) and it does need management. It's certainly harder to handle than other sources, but that's exactly what's being explored right now, even with that setup. Solar power does come with a few upsides as well though: Installations are comparatively easily transportable and independent, don't require grid connection and once in place require steady supplies and doesn't produce and waste .