I started this project, because I wanted to create something useful and also because I had some spare small solar panel. I wanted to check my designing as well as programming skills also I thought it would be fun and interesting.
So first of all I undid some mounts of my solar panel and started measuring its dimensions. Then I created precise 3D model of my solar panel using Fusion 360. I knew I would need only horizontal rotation so I also created model of small but sufficient servo.
To have a solar panel which can track position of the sun and rotate accordingly you need some way of telling the system where the sun is. I used 3 simple and cheap photoresistors which are just resistors which change its resistance accordingly to amount of sun shine they get. Then you just read voltage values.
I used 3, one is oriented on the sun, the other two track relative position of the sun to the middle photoresistor. And with those basic rules you can create some reliable sun tracker. Of course there are many ways to arrange photoresistors so it’s more precise, more reliable but I decided it was enough.
I continued to create mount for panel, mount for photoresistors with adjustable tilt and cover for servo. Both servo and photoresistors were on the rotating side of the system. Then I just created small mount in which I could secure the rotor of servo and also screw the system on a wooden plank.
As a brain of the system I was using small Arduino Nano, which was powered by a phone charger (5V 1A), but it can also be powered by USB port. Power consumption of Arduino Nano was pretty small. Also small servo wasn’t moving too often and servos don’t drain electricity while not moving.
I soldered all connections on the Arduino and created small case for it too. And case itself was placed inside another plastic case which was mounted to a wooden plank next to solar panel. I hooked up the power cable from solar panel to a small water fountain few meters next to it.
I printed all parts from Fusion 360 on my 3D printer using ABS plastic and also sprayed it black.
The system worked flawlessly for 3 months, but due to strong winds and rains and insufficient isolation, motor got wet. Arduino and photoresistors were still working. Also one time I had to replace one photoresistor because the glue I used to isolate its connection got on the photo-sensible side and over time it blackened.
If I were to do this again I would put a lot more dedication to isolation and more smooth movement. And I would also recommend to hide photoresistors because over time they could get a little dirty.