So here's the skinny on how the whole setup worked in the Canyon! Good to Great! The sun is fairly low this time of year, and I found that I had between about 9AM and 3PM where I had enough power to charge my iPhone 4S in .5A mode. I already knew the panel wouldn't support 1A mode, so I didn't try.
I was down for 6 days, and because of poor planning, I only had about 60% charge as I headed down from the South Rim. Basically I found about two 20 minute opportunities to charge each day. Breakfast time wasn't sunny enough yet, so I got about 20 minutes when I sat down for lunch, and another 20-40 minutes when I got to camp. Because the sun was so low, I couldn't lay the panel flat on the ground most times, so I often had to prop in up on a pretty steep angle on some rocks especially in the evenings. I was able to charge it up by about 40% each day, but I used about 50% a day (amazingly, since I use airplane mode). So each day, i ended up with a bit less charge than I started with. Turns out that taking videos and pictures all day (and looking at them) takes a drain on the battery! My 4th day, I was able to get into camp early enough to get a full 1.5hr charge on my phone and go from 8% to 100%! That was prodigious since the last two days were quite cloudy and that was the last opportunity I got to charge my phone!
The 'supervisory' circuit did a great job of minimizing oscillations in low light, but there was still a period of time where it would (as George has described) come on and off about every 10 seconds when the light was bright enough to reach 12V when unloaded, but dropped below 8 V when the phone started charging. That on-off cycling, although significantly slowed by the supervisory circuit, does drain the battery a bit as the screen keeps coming on and off with each cycle. I'm sure the amount of drain that the causes will be different for other types of phones.
We did see one other guy who had a solar panel and hung it off of his backpack, he had a goal zero one Nomad 7, but at 12 oz, that's 3X the weight with only 40% more power, so I could add almost 3 more slimmed down 5W powerfilms for that weight and be at 20W for 4+3.2+3.2+3.2 or 13.6 oz! (or course folded out side would be much larger too) I don't know how well his worked, or what he thought of it. However, based on the way the fall sun is and the switchbacks, I think it hanging it off the backpack is very inefficient in the canyon, so I had no inclination to try it.
I have to say, I seriously enjoyed the music each day and the lightweight photo/video capability that my iPhone provided! I got some GREAT pics, and was able to send some text messages from Indian Gardens Campground and the North Rim. This was a fantastic solution for me!
George, glad that last post could shed some light on your issue! Any more progess on the 6W panels? I got a chance to get my hand on a Brunton Solar Panel (very heavy!) at Grand Canyon Village and they use the brittle panels as well. But for the weight, I'd rather use two modified 5W Solarfilm Flexible Panels. Can't wait to hear what your final solution is!