A Postage Stamp of Sunlight
This exercise lets children directly feel the energy in sunlight.

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.