do you mean to like charge a capacitor with a solar panel, then use a voltage detector to trigger a release from the capacitor into either a battery or motor?
If so, the voltage detector ensures that there is enough power to drive a motor, usually there isnt enough power coming directly from a small solar panel to drive a motor, so the power is stored up in a capacitor until it reaches a level that can drive the motor. If you cant get the relevant voltage detector (samples maxim-ic) you may be able to do something with transistors.
