A simple solar tracker can be built using some common radio shack parts, to upgrade this project to full size, you would simply use a heavier duty motor and relays which would be dependent on the size of your panels and how much energy is needed to rotate them.

Parts List:
3 x LDR
1 x 33 R Resistor
1 x 75 R Resistor
1 x 100 R Resistor
1 x 10K Resistor
1 x 20K Resistor
1 x 2N4401 Transistor
1 x TIP120 Darlington pair
1 x 9v Relay
1 x 5v Motor

With the schematic laid out, you can see it is a very simple design. The position of the sensors is what allows this system to track the sun.

Sensor #3 is located in an inverted enclosure so that the light will only hit it when its facing directly at the sun. When the sun leaves photoresistor #3, its resistance increases switching on the Darlington pair which interns switches on the relay that drives the motor. When sun hits the photoresistor it’s resistance decreases disabling the Darlington pair and in turn stopping the motor.

Now you may ask what happens when the sun goes down or is hidden behind a cloudy sky? Does this tracker aimlessly scan the sky? well this is where photoresistor #2 comes in, Flush mounted this little guy can see the entire sky. When photoresistor #2 senses the sun is out it drives the NPN transistor low. If the sun should disappear for the evening, the lack of sun will raise the resistance which brings the NPN transistor base high turning the darlington pair to low and disabling the tracker. Sensor #1 is mounted to the east, which will sense the sun rising in the morning.

I hope this tutorial on building a solar tracker has inspired you to build your own! If you build your own large scale tracker be sure to post what you used for a motor and any upgrades to this system.