I found a solar tracker article in Home Power Magazine.
A solar tracker is essentially a sensor, control electronics combined with an electric motor to position the solar panel in the most at the most optimum position throughout the day. As the sun travels across the sky, the panel will track it; always being at the right compass heading. This will ensure that your panel is always facing the sun. Some estimates indicate that by tracking the sun, this will increase your panel energy output by as much as 30%!!
The circuit is simple and straight forward.
