> Do you happen to know the weight and full sun power output of your solar cell?
Sorry, no. Never bothered measuring.
I found it was able to recharge the two Tenergy CR123R batteries I use with my Steripen in maybe 4 - 6 hours, depending on the sky, after I had treated two litres of water. That took 1 amp for 2*90 seconds.
So ... Steripen power consumption of 180 seconds at 1 amp draw at 6 V nominal: about 1,000 watt-seconds. Assume 50% recharge efficiency: 2,000 watt-seconds required. Spread that over 5 hours or 18,000 seconds: 0.11 watt output required (which is not all that much).
Assume 1 kW per squ metre sun power. The cell is about 0.13 m x 0.06 m or 0.0078 sq m. It should 'see' about 7.8 W under perfect conditions. Assume that the angle of the cell with respect to the sun, my movement, etc, gives 20% solar interception efficiency: about 1.56 W of sun power available. Assume a solar cell efficiency of about 7%: power output of 0.11 W. Matches requirement.
OK, the assumed efficiencies have been slightly fudged, but the numbers are quite realistic.
On the last trip I also used the same solar cell to recharge my mobile phone battery. I used the phone to ring ahead to Refuges a few times - I could have done just as well by taking one spare fully charged phone battery, but the weight of the adapter I made was extremely small.
This works for me. But I do not lug around all sorts of electronic devices when we are walking. I am quite capable of surviving without them - actually I don't own them anyhow. (Yeah - super-techie but no devices!). I have a log book - Rite in the Rain paper.