Arduino 2-axis servo solar tracker

What is a solar tracker?

A solar tracker can increase the efficiency of a solar panel by up to 100%! It does this by always keeping the panel perpendicular to the incoming rays of sunlight.

here's an equation to prove this:

P = AW sin θ

P = power generated by the solar panel

A = Area of the solar panel

W = is the solar constant, which is equal to 1340 watts per square meter

θ = the angle of the incoming light

Since sin(90) = 1  you get the best performance out of the panel when it is totally perpendicular.

Materials:

1 - Arduino Uno w/ ability to program it
1 - Breadboard
1 - 2 axis tracking mechanism (i used a magnifying mirror that swiveled up and down)
2 - 360 deg continuous rotation servos
1 - ball bearing tilt switch
5 - 10k resistors
1 - 5V breadboard power supply
3 - cadmium sulfide light sensitive resistors
wires
solder
soldering iron
vice (optional)

 

Step 1 The Y-axis

Depending on what you use as a tracking mechanism, yours might be a little different than mine.

I picked up a magnifying mirror from Shoppers normally used for shaving or applying makeup. It had a base and a swivel to tilt the mirror up and down.

I cut off one side of the swivel bracket and replaced it with a servo. I measured so that the shaft of the servo would line up with the swivel point of the mirror. I then had to drill a hole for the servo shaft to fit into.

I used hot glue and zip ties to secure the servo to the base and then the servo shaft inside the hole I had drilled.

Comments

[244 Jake]

Well a solar tracker, yes, but if you wanted to use what I see, a small mirror, and focus its light on water tank, all day long. That would most kool. A group of small mirrors could be grouped to all reflect the Suns heat to tank, all day long.

Reed switches could be used with magnets to define stop points.

Jake

[Graver]

Hi, I have put together your sun tracker. I could not find a ball bearing tilt switch so I substuted mercury switches not having luck with them as limit switches. I munted one up and one down at the axes line may be they should be out from closed to center. They don't stop the Y axes from rolling. I don't undersand how you arrived at the values for bsense = 1.05 and trsense = 1.03. What values should I see in ambient light and in direct sun light? What do you think about using 180 degree servos instead of continuous servos?
Fun project.

[aplavins]

I tested the 3 sensors from a single light source after they were mounted. the bottom sensor and top right sensor were giving me values that were lower than the top left sensor. This is probably due to some small variation in its manufacturing. The values 1.03 and 1.05 are ratios that the read analog value are multiplied by. I arrived at these values by powering up the tracker indoors where it would track the light on the ceiling. I used trial and error on the values until the mirror pointed the reflection of the light straight back at it.

Using 180 degree servos would be totally possible but would require major modification to the code. 360 degree servos use no feedback system and the pulse value you send to it represents a speed. With 180 degree servos, the pulse value represents a position.

Hope this helps!

[Graver]

Hi Apiavins: Still have a problem with the 1.03 and 1.05 numbers. Tried changing the 1.03 and 1.05 numbers to calabrate the sensors but they didn't seem to change. Did notice that bsense = bsense * 1.05 and trsense = trsende * 1.03 were commented out. I guess I don't understand were the calabration takes place. I have noticed that the sensor platforn does hunt a lot once it faces the light source. Think you said that sensitivity will take care of that. I will send you a photo of my tracker

[aplavins]

by default, the program doesn't change the values of bsense and trsense. you will have to uncomment the lines that multiply those values. you can also add a line to modify tlsense if you think that's more appropriate.

Increasing the value of sensitivity will reduce the amount of hunting.

nice pic, hope this helps!

[maewert]

Adam,

Cool project!  Great for an all-purpose tracker.  For a specific purpose (solar) tracker you may wish to consider using a polar mount instead of an alt-az mount.  This will mean that only one motor would move to track the sun throughout the day.  Since the position of the sun is predictable, you could compute its position and not rely on sensors. (This might mean that you might need to change to steppers instead of servos and power off the motors when they don't need to move maybe using a worm gear drive which holds its position after the motors are unpowered.) 

Your solution could generate some electricity even from moonlight since it would track the brightest object and not necessarily only Mr. Sun however!  You might need an algorithm to determine if it is worth the electricity spent in the motors to eek out the most current (I'd hate to see a bank of solar cells track the headlights from a passing car at night!)  Actually I WOULD like to see that!  It would make me back up a few times!

Very nice instructable.  Best Wishes.

[aplavins]

Thanks for the comment, I agree that a "polar mount" might be better for tracking the sun. I'm going to make one of those next. I want to be able to move it to different locations though. I'll probably need a gps sensor, compass, 3-axis accelerometer and an eeprom to store the sun's movement data.

An improvement I could make to this project would be to sense the ambient light and tell it not to track at night.