Modern Mechanix, astute as always, asks this question about this solar-powered radio from 1956, said to operate in the dark for up to eight months without recharging: "If they have a battery that powers the radio for eight months why would the solar cells be necessary?"
I just think it's neat that there were solar-powered units in the '50s. I have no reason to think otherwise, mind you, I just didn't realize the tech was mature enough at the time to be seen in working products. I tend to think of solar as the power source of the '80s.
Sun-Powered Receiver (Apr, 1956) [ModernMechanix.com]