After being underwhelmed by commercial solar chargers (expensive + slow-to-charge + heavy) I decided to hack together something that delivered more power for less weight.

The easiest way to shed weight was to forgo any kind of battery storage - this will be a direct-charging device.

To make my Thing I obtained a cheap 6-Volt / 2-Watt solar panel + a 12-Volt USB car charger. I disassembled the USB charger, removed (desoldered) the cigarette socket components, and wired it to my solar panel. Even though it's made for a nominal 12-Volt input, the charger will work down to anything just over 5-Volts.

The Thing files attached are a surround / bumper for the finished device - mainly to protect and strengthen it. The parts are joined with double-sided sticky tape (and perhaps spin-welded). The panel is attached on one side with VHB foam tape. The charger is attached onto the other with hot glue or Sugru.

Misc Notes:

• the result is not water-proof! It can, however be used inside a clear polythene bag, with maybe a 20% drop in power output.
• The box slots on the sides are meant to hold Popsicle sticks (in order to hold the panel at an angle). I didn't have any to hand, so my photo demonstrates the idea with bamboo skewers. Popsicle sticks are recommended.
• The tabs on the tapered end are for attaching the device to a backpack (should you find yourself in need of juice whilst walking with the sun behind you).
• The Thing files attached assume a solar panel that is around 136mm x 110mm (which was a pretty common size when I was sourcing mine).
• The resulting device charges my phone roughly twice as fast as my friend's store-bought charger.

UPDATE: The Thing you see here has just come back from New Zealand's Te Araroa Trail where it performed perfectly, and survived the entire 3000km journey.