This is a foldable multi-page solar panel based on inexpensive 100mmx69mm epoxy covered solar panels which can be bought on eBay for less than $3 a piece. One of these panels delivers 5.5V @ 150mA under optimal conditions (full sunshine at noon). So combining 5 of them in parallel, will result in a power source that easily delivers 500mA over most sunshine hours during the entire day. That power can be used directly via an USB cable to drive or charge any of your USB powered mobile devices or alternatively to "collect" the sun's energy in a Li-Ion USB power pack used from which you can charge your mobile devices later on.
The challenge in this project was to combine several such solar panels in a foldable compact stack, so that I can take it along easily on all my trips.
The STL files provided here are for a pack of 5 panels, but the SCAD file is parametrized to allow for any (reasonable!) number of panels in the pack. Also, it is of course possible to use solar panels with a different voltage and/or wire them differently in order to get a foldable solar panel for other purposes.
_Update 2014-11-08: I just uploaded a new version of this foldable solar panel which uses larger 150x130mm solar cells that deliver 500mA at 5V each.__
The solar panels are mounted by sliding them under the two triangular corner that are included in the frame structure. Then the panels are fixated with 2 of the separately printed triangles, which are glued to the other 2 corners of the inner frame (I just "glue" them using acetone on my ABS prints). This is illustrated in the last photo.
Two adjacent printed frames are attached via two M3x10 screws that serve as axes of the hinges.
The panels are wired by connecting the plus poles of all pages together and then to pin 1 of the USB socket. Then all the minus poles are tied together and are connected to pin 4 of the USB socket. There are holes on each side of the frame through which wires are led through. When soldering the wires, make sure to leave enough (but not too much!) spare wire between the pages to allow proper folding.
The USB type a socket is soldered on a little piece of prototyping PCB (18x24mm) and slit into the USB socket box on the last (outermost) panel.