This is an analogue computer with a digital option. It is an elegant, unique idea for MPPT. I have some documentation videos and circuit inside the link. The circuit works but I never used it much because my wind turbine project stalled. I am back: April 2016.
This is using two LEDs to sense the sun and send +- or -+ logic signals to a full bridge motor driver like L298 or http:/www.redrok.com 3X schematic. I bought his. I recommend it. I changed the front end logic to 4060 and 4011 ICs here, for fun. You could use this circuit to turn on an irrigation motor for a very short time every few hours or days (just omit the sun sensor and select appropriate timing pins and much lower oscillation frequency for the 4060).
The project video shows a fridge timer which can be set to trigger during high battery voltage sunny days so the defrost cycle never uses valuable battery power. It is switchable to act like a regular defrost timer for long cloudy stretches of time, like winter.
The project video shows a way to power solar panel rotator motors from a solar panel, supplemented by a walladapter.