Not to be pedantic, but it's not really "free". Energy is conserved (First law of Thermodynamics). But anyway, I got ya. I think it's cool. Never got too deep into it, but a good buddy of mine does a lot with solar panels. We go camping and can charge batteries that charge phones, run other electronics, etc. Last year, the house he was renting got a "surprise" remodel. It was such a mess that he ended up moving out into the backyard temporarily, living in a tent. Ran lights and the TV off of solar-charged batteries.
There are several repeaters (GMRS and 2m/70cm) around here that are running solar.