Here's an older article from the Loudoun County Aeromodelers Association in Virginia, US, describing in detail how they planned and installed a solar-powered charging station for their electric RC planes. Their calculations and decisions made for interesting reading, and the result seems thorough.

They're using a single solar panel, connected to four 6V / 220Ah golf cart batteries. On Saturdays and Sundays the club use the storage batteries as power source for charging their LiPo batteries for the plans. During the rest of the week, the storage battery is recharged by the solar panel.