I have a 28w and 100w folding backpacking panels that I haven't used yet. The 28v is nearly identical to yours. What wattage does it produce(21w, 28w?) and how long does it take to charge your phone?
I wish you nothing but positive vibes on your journey. I'm interested to see how long you push it out.
21W. I've never thought to time, but my general impression is that it's fast.