Hello,

I was discussing this project with some of you on a different thread, but I figured I should create a separate thread so others can benefit from it. I am working on a simple solar tracker for a school project. The panel is not very big, it is roughly about 12'' x 55'', and I am guessing it weighs about 20 lbs or so. My initial design idea is a single axis tilted at the angle that will position the panel orthogonal to the sun's rays. The axis will be a rod or a pipe that will be positioned down the middle of the back side of the panel. The lower end of that pipe will rest on fixed surface, and the upper end will probably be attached to a DC motor, possible through a set of bike sprockets and a chain for gear reduction. I might use some wheel bearings to give the rod freedom of rotation.

My questions are:
1. would any DC motor work? I was advised to get a cheap used cordless drill and use its motor. I found a couple at the local pawn shop with voltages ranging between 9.6V and 18V. Would a drill with lower voltage rating like 9.6V do the trick?
2. What should I use to stop the panel from rotating too far and would the motor be able to prevent from rotating in the other direction if it wasn't balanced?
3. Any suggestions or is there anything that seems to be a problem in this design?

I'll post the circuit tomorrow from work. Any feedback will be appreciated.

Thanks.

 

You may want to consider elevation angle adjustment also. In the summer months the angle is lower than the winter months. I also think you will need some further gear reduction as the most the panel would move would be about 180 degrees from sun up to sun set, in a period of x hours.
If you monitor the output voltage of the panel that could be your control of the movement, but you might need some kind of timing to automatically point the panel east in the morning.

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(1) Certainly. You need enough torque (about 1/10 the stall torque) and enough speed (to run the full range in 12 hrs).
(2) Limit switches. If the gearing has enough reduction ratio, it will be difficult to drive it backwards. Your intensity sensors would normally move it towards optimum if a backwards movement actually happens.
(3) You would benefit greatly by reading up on state machines.

 

That is definitely something I consider. I thought however that since this is more of a project, and since the elevation angle won't change in a short period of time, I could just adjust it manually.

As far as the resetting the panel in the morning to face east, what is the best method to accomplish that?

 

I did a similar project my sophomore year. What I did was I used 2 photo resistors connected to a power source, i used an HC12 microcontroller as such:

main(){
VR1 = voltage photoresistor1 passes through (or does not pass through depends if your connection is sinking or rising sensitive)
VR2 = voltage photoresistor1 passes through(or does not pass through depends if your connection is sinking or rising sensitive)
tolerance = maximum voltage difference circuit can tolerate so the while loop doesnt jitter the motor from left to right constantly to get perfect equilibrium

while (VR1+VR2 == total power supplied)
{
if(VR1 - VR2 > tolerance)
turn to VR1
else if( VR2 - VR1 > tolerance)
turn to VR2
else
do nothing
}

turn to reset position
}

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have 2 photoresistors with a divider between them make the panel follow the brightest perhaps if its very sensitive put a delay restriction on rotation intervalls so that its not permenently on and using more power than its making. set a minimum brightness level so that at sunset it stops searching. in the morning it would possibly automatically turn back to the start following the most brightly lit sensor else create some kind of autoreset after brightness has gone down to a certain level at sunset. elevation could be ajusted manually say once a month

I also think that mirrios are being greatly overlooked as a way of increasing potential only problem is it makes the structure more complex as it needs to withstand wind but at the gain of 2X the power why no panels are rated at power produce on the equator at midday clearly most places get 1/2 or less the light the equator gets so if it was increased with mirrors you would get more bang for the buck !

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Instead if using old drill motors which can draw 3+ Amps why don't you use a satellite actuator. I have been using some, and my 24" actuator draws about 300 mA and my 18" actuator draws about 400 mA. An added bonus is that they come with adjustable limit switches and are weatherproof as well.

For a cheap tracker circuit look at http://pages.prodigy.net/rich_demartile/

Rick...

 

for the tracker, use 3 photosensors instead of 2. the unit will track the sun perfectly.. when the one on the right is getting more light the circuit moves the center one toward that one until the center one is getting the most light. The left one does the same thing, when it is getting more light the circuit moves to the center one toward that one.

In this manner, you will have optimum positioning of the panel at all times...

 

How does the unit backtrack in the morning? I think sensor placement will be pretty important.

If I were doing it, I'd use a small uC to only adjust the unit once every 10 minutes or so and then backtrack at the right point. Then as a bonus, it could do all sorts of reporting and monitoring of the output.