Here are some of the basics for your BEAM Robot:
First you will need a simple elecronics curcuit a so called Solarengine, which is the heart of many solar-powered robots.
Type-1 Solar Engine-a voltage controlled trigger
The basic idea of a solar engine is, that the avaliable solarcells do not supply enough power to the robot motors. So the power is stored in a larger capacitor (C) until there will be enough energie to run the small motor(s). If there is light the system should operate continuously.
Here are another two simple Type-1 Solar Engine without the 1381 chip but with diodes:
Here you see the Panasonic BP-243318 solarcell
Size: 24×33 mm
Voltage: 3.45 V
Current: 16.4 mA
Note: These circuits are for Personal use only. Commercial usage is prohibited unless
arrangements are made with the patent holder Mark W. Tilden