parts u'll need :

-USB extention cable

-plastic casing

-battery holder for 4 AA batteries

8V Solar panel with less then 200 mA

2 5V (or higher) diods

some wire

tools u'll need:

soldering iron

solder

electronic pliers

hot glue gun

Step 1:

cut the USB extension cable in two and isolate the wires from each other

Step 2:

solder one diod to the red wire so no electricity can pass from the USB side of the cable

solder the green and white wire together and isolate em with some tape

solder the negativ side of the battery pack to the black USB wire and the red one to the positiv side

solder the second diod to the red wire so no electricity can pass from the battery to the solar panel

make a knot in the Usb wire and cut a hole in the side of the plastic cable, and another one in the top of the casing.

solder the negativ side of the solar panel to the black wire and the positiv to the diod on the red cable

glue the solar panel on top odf the box and lead the cables through the hole u cut before

and ur done :)