This exercise lets children directly feel the energy in sunlight.
A dowel shaft can be attached to a motor with a piece of tubing slid onto a motor shaft bushing (or the motor pulley mounted backwards, as shown here). Hold the motor and shaft loosely in your upturned palm, with the tubing slightly bent. With your other hand aim the attached solar panel toward the Sun.
The motor and shaft assembly will vibrate in the open palm of your hand – a primitive sun-drum.
Consider that the solar panel is about 12 – 15% (1/8) efficient, and the motor is about 50% (1/2) efficient…so only about 1/8 x 1/2 = 1/16 of the total received solar energy is transformed into vibrating mechanical energy.
If solar cells were 100% efficient, and the motor 100% efficient, you would need a panel only 1/16 this size to produce the energy you feel in your hand.
That is to say, the energy you feel in your hand is the energy in a small postage-stamp area of sunlight.