Schematic for Solar Collector Sun Tracking

Richard Gideon shares his knowledge

April 2005

Ken, I just noticed in your November article you mentioned you were planning to develop an electronic circuit to enable your solar collector to track the sun. Well I have been there and done that. (See attached files) I designed this circuit a couple years ago to position a photoelectric panel that I have. The circuit has been working without any problems BUT the drive motor does need to be sealed from the weather, I am on my third attempt at trying to keep it dry.

Basically I am using two photo resistive cells as sensors. They are mounted in a plastic box about 1 ½" apart with a 5" vertical light barrier between them. Similar to a sundial. When aligned in an East-West manner and pointed directly at the sun both cells will see the same amount of light. As the sun moves, assuming we are working with the flat earth theory, the vertical barrier will cause a shadow to be cast on one of the photocells. This imbalance is detected by the circuitry and a relay is closed starting the drive motor to reposition the collector panel.

At the end of the day when the sun sets into a puddle of black, muddy, hot water, as believed by some, the circuitry senses this and returns the collector to the east for the start of the next day. Also the circuit is not affected by changes in light intensity and does not require any exotic parts to build. A "Radio Shack" could probably supply all parts needed minus the drive motor.

If you wish feel free to use this circuit anyway you choose.

Sincerely

Richard Gideon

Attachment: PCB Wizard - SUN TRACKER.pdf (23K)

Operation of Sun Tracker Circuit.

With the photocells mounted on the solar collector and in bright sunlight and correctly aimed at the sun each photocell should produce about 3000 ohms of resistance. This value can be obtained by placing different pieces of translucent plastic over the cells; this is not a critical value. The plastic will also protect the cells from the weather.

With both photocells seeing the same amount of light trimpot VR1 is adjusted to drive the output of voltage comparator IC1a low this is indicated by LED 2 turning off. As long as both cells see the same amount of light the circuit will not respond, even if a cloud has the nerve to pass between your solar collector and the sun.

Now as the sun moves and the vertical barrier causes a shadow to be cast on the west photocell IC1a senses this change and its output will go high, turning on LED 2, and begins the slow charging of C3 through R5. 

After C3 has charged to the value determined by voltage divider R6 & R7, IC1b’s output goes high this turns on transistor Q1 that in turn energizes relay RL1 causing the drive motor to start. The motor then runs turning the collector until the west cell again sees the full light of the sun, this returns the circuit to its initial state and the motor stops. The circuit then waits for the sun to move again and the whole process repeats.

The purpose of the time delay provided by R5, C3 & D1 (D1 is used to discharge C3 at end of cycle) was because I designed the circuit to be used with a photoelectric panel and precise alignment to the sun is not required. After building the circuit it soon became apparent that if I did not wish the joy of having to listen to the sound of the drive motor start and run briefly every few seconds, then this time delay was necessary.

So now at the end of the day after the sun has been turned off, the west photocell has one more duty to perform. It sends a voltage to IC1c and when compared with the voltage set by trimpot VR2 its output will go high turning on LED 1 and to transistor Q2 that energizes relay RL2 causing the motor to run in reverse, driving the collector back to the east for the start of the next day. Also the output of IC1c goes to IC1d, this turns on the output of IC1d that in turn prevents the possibility of transistor Q1 from being turned on. This then keeps relay RL1 from being energized and prevents lots of smoke and fire that would occur if both relays were allowed to be energized at the same time.

Finally there are two switches SW1 & 2. These are limit switches mounted on the collector to control the maximum amount of rotation in the east and west directions.