A while back, a Discover Circuits visitor wanted a simply way to demonstrate how electricity could be generated from the up and down movement of ocean waves. The system was to be part of a science fair project, showing different renewable energy sources.  I gave this some thought and came up with the system shown below. It uses a simple plastic foam float attached to a lever arm, which is connected to the shaft of an inexpensive stepper motor, available from www.jameco.com. The AC voltage output of the stepper motor was connected to a few Schottky diodes to convert the signal to DC.  When properly mounted in a tank of water, the motion of a wave in the tank causes the shaft of the stepper motor to move. That movement produces enough electricity to turn on the visible red LED.