Hi All!
I'm on my third year with a pair of these Joos Solar chargers. I only require one on my tours, but was so pleased with the first one I purchased, I bought a second using a dividend from REI co-op:
http://solarjoos.com/Tech specs here:
http://solarjoos.com/tech-specsPre-read summary:
They are not perfect, but have worked well and reliably in my use with a relatively high charging rate compared to other units I've tried. I wish they were much lighter, had larger-capacity storage batteries for the weight, ready-made mounts for touring bicycles, and would fill more than 90% from a mains charger (sun exposure is required for the remaining 10% charge).
=====
The Solar Joos has a power gauge (LED blinks...takes awhile to become familiar with it, but it works to show both state and rate of charge), a PC app if desired for finer understanding of battery health and charge rates/levels, and the 20Wh – 5,400 mAh Li-po battery is user-replaceable. It will (has) charge(d) while fully submerged under water and also charges on cloudy days and inside my tent, albeit much more slowly (ref Rualaxander's comment above). It takes about 18-20 hours total in continuous *bright* sunshine for the accumulator battery to go from flat to full, hence my purchase of a second for extended periods "away" when not riding my dyno-charger equipped bicycles. The accumulator battery is also replaceable,and holds at least 80% charge for a year in my use. It is*heavy* (battery and steel heat sink/backing plate), but tough as nails and reliable as houses for me in my use, a major plus. It can also be physically locked to the bike while Away (using a cable or smallish chain), ensuring it will still be there upon return. If removed, it fits neatly under the lid-cap of my size Large Ortlieb handlebar bag.
Mine has been dropped face down on gravel and rocks by me and on the corner of a scanner table by airport security personnel, drowned in days of rain, scarred by a dropped crankarm across the face, and has survived sustained high temps of 45.5°C in operation and managed a couple of days/nights very sluggishly at -23.3°C. I made some web straps to attach and mount mine atop my tent on the rear rack.
The trick if to never, ever charge from it during the day, instead using daylight to charge its own accumulator battery, then drawing from it to charge other gadgets (primarily my phone and Eneloop AA/AAA batteries in an Eneloop USB charger) while in camp overnight. Output is 5vdc at up to 1.0A. For continued use, I tried to draw no more than 50-66% power from its total capacity overnight to ensure I could recharge it fully the next day. Going past that, you'll find yourself in debt as there may not be enough sunshine on continued rainy/heavily overcast days to keep up, a limitation I've found with all solar chargers used on continued non-sunny days.
When I did my double-crossing of Europe, the bike AndyBG loaned me had no dynohub-charger, so I used one of these instead, augmented by a 20,000mAh pile that was rechargeable only from mains power. The Joos did most of the job alone, but needed help when demand was high and there were sustained cloudy/rainy days. In those conditions, I think a second unit might have completely substituted for the reserve pile but would have totaled more weight then I wanted to carry. For more sustained requirements (i.e. continuous GPS tracking throughout each day's travel), I would prefer a dyno-charger or other setup that ensured a steady charging rate provided I rode long enough at the required pace. All these on-bike gadgets have their limitations, and charging requirements can become a lifestyle of sorts successfully balance demand/replenishment.
Early model Joos Solar chargers suffered from problems with the charging cord/socket that resulted in many poor reviews. Mine were not problematic but were among those listed as affected, so the company sent me replacement cords for free.
Best,
Dan.
