In replt to M6HBS:
I bought one of the small 1.5 Watt solar panels from Maplin designed to be left on a car dashboard to trickle charge the car battery, which is sufficient to charge a 7Ah Slab in reasonable daylight & of course much better in good sunshine.
It takes several hours to bring a partially discharged SLAB back to full charge, but using a small radio such as an FT817, I could see it being useful if I was away on an extended trip away from a mains / vehicle charging option, & it may keep a SLAB from discharging too much if used while operating.
Although Solar panels have come a very long way in the past few years, they aren’t yet at the stage where you could power a 100 Watt HF radio from a panel the size of a QSL card. HI!
I wouldn’t carry the suitcase sized item described earlier up a summit myself, but it may be interesting to see how much more time, if any, a small solar panel would give when using it to trickle charge a SLAB while in use. Certainly the current drain on TX would drain the battery as usual, but a few watts from a large enough solar panel should compensate for any current drain on receive.
How many Amps does the radio draw on receive? How many Watts does the panel produce @ 13.8V? A simple bit of Ohms law should let you know if it is worthwhile.
Good luck in any case