I've always thought solar was kind of cool, especially if the panel is small and lightweight. The only two things I personally would need it for would be the battery for my headlight and my cell phone.
What I chose to do several years ago was to carry a battery charger for each of those. I also carry a small outlet tester (the cheap one with two leads and an LED). You would be surprised at how many parks and shelter houses have electricity.
Is it ethical? Probably not. I've asked permission to plug in many times. No one has turned me down.
I do like the solar panel idea alot. I may look into it this year again. I'm sure the technology has come a long way in the last few years.
Jerry H