Step 1: Get supplies
1 Gameboy Advance (the original one not the SP or Micro)
1 Solar Panel (from garden lights)
1 Switch (optional yet recomended)
1 Diode (definatly NOT optional)
1 Voltage Regulator (only optional if your solar panel can't give out more than 6 volts)
A little bit of spare wire
Step 2: Put the small parts together
Switch -> Diode (make sure electricty flows from the switch to the regulator) -> Voltage Regulator
Step 3: Attach the new series to positive terminals
Next, connect the end with the voltage regulator to the Gameboy.
Make sure both are on positive terminals
Solder works best!
Step 4: Connect grounds
Step 5: Insert batteries
Step 6: Let your Gameboy charge in the sun
Congrats, your all done (and I just finished my first instructable). Go and celebrate.