Author Topic: DIY single axis solar "tracker'"  (Read 520 times)

BruceM

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DIY single axis solar "tracker'"
« on: May 17, 2024, 07:49:42 PM »
Per Ade's request, here are some photos of my DIY single axis tracked arrays.

I have revised all my racks to (3) 2 inch, 0.10 thickness square tube rails for greater stiffness, having retired my original 800W rack and badly snail trailed 175W solar panels.  It was designed for seasonal tilt only with thinwall 1.5 inch rails and wasn't long enough for the 325 to 355 W surplus or used panels I can get locally for very cheap.

This is all part of my custom inverter upgrade, now with sufficient power to run my 1500W home cooler plus have enough power left over for all my other activities. The cooler works by chilling water for my in floor heat system, and that project was previously reported on here.

Under the solar panels you will see two aluminum boxes.  One of these is the Arduino Nano plus Accelerometer board for panel angle sensing, plus real time clock module and H-bridge board for driving the linear actuator.  The second box is unrelated to the tracker, and shorts out one of the 5 panels when there is excess voltage for the current load.  This pre-voltage regulator allows my simple custom linear PV current regulator to handle the new larger capacity input. The linear PV regulator uses 7 IGBT transistors, each with an op amp current sensing driver to evenly share the total current load.  My battery bank is nominal 125VDC, 10 100ah "marine" (lead calcium) batteries in series. 

The entire tracker system is powered by one very small 12V panel and a small AGM battery which is located 1.5 foot below grade in an 8 inch section of round galvanized duct with cap about 12 inches above grade.  The trackers are timed so that they all do their hourly movement staggered in time a couple minutes apart, keeping the max current demand to about 2 amps.  The real time clocks and tracker program of the Nano with specific data table for the individual array orientation are set via laptop and USB cable.  The manual motor drive cable can be used any time by just unplugging the 4 wire auto trailer plug at the Arduino tracker control box, and plugging in the manual cable.  Once the
Arduino is plugged in it checks current position versus table position for month and time of day, and motors the panel to the proper position.  The real time clock has a lithium cell to keep date and time when 12V power is removed.  As you can see in the photo of the tracker box internals, there is zero custom hardware, it is just wiring up of off the shelf components. There is no heat sink required for the H-bridge controller at the puny power levels (2A of 12V) required.  The Nano board provides the 12V to 5V linear regulation.  While the Nano is sleeping, power draw of the whole thing is < 5ma, if the Nano power indicator LEDs are clipped. 

The PV rack mechanicals are pretty simple and derived from older my seasonal tilt rack design.  I'm using 1/2 brass rods with steel split pins as the unlubed pivot points, with stainless steel washers to reduce pivot drag. Many here are very skilled in practical mechanical design  and will come up with there own solutions.  I am pleased with the results here.  It is very solid and does not bounce in the wind, and easily supports my weight and bouncing on the rack with very little movement.  I did all welding myself with my now 3 12V marine battery DC stick welder (with galvanized sheet strip resistor) and 3/32 6013 rods. It was a challenge but I did get the hang of it. MIG would be much better suited to the 0.10 inch wall square tube. 

At present to develop the data table needed for month, hour and position, I used a solar calculator service online to get the plots of sun azimuth and elevation for my location.  I built a scale model with digital inclinometer, and would set up the sun angle and azimuth pointing to the properly oriented scale solar rack, and then eyeball the best tilt angle of the array, reading the angle from the  inclinometer.  A very tedious process.  I then convert via table the angles to accelerometer units. 
A better solution would be to have a program which does this all for you given rack orientation and range of tilt, GPS coordinates and spits out the actual text data table to be inserted in the Arduino Nano program.  I have not done that as my programming skills are now quite diminished.

Having operated this for about a year, (the summer rack for a bit less) I am quite pleased with the cost, performance and reliability.  One design idea I have is to tilt up a version of the summer rack to say 45 degree inclination (I have a south facing hill handy) to do a "winter rack".  This would add to winter day performance but if the drive was changed to +- 90 degrees via gear motor and chain drive, it could also futher increase sunrise/sunset power all year.

I keep watching battery technology and may someday change to LFP or one of it's successors as prices continue to fall and performance continues to improve. 

Best Wishes,
Bruce M


 

BruceM

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Re: DIY single axis solar "tracker'"
« Reply #1 on: May 17, 2024, 08:09:02 PM »
More photos.

The geometry of the actuator mounts is a bit different for the +60 to -25 degree, SSW facing racks (pre-existing manual seasonal tilt), vs the new +-60 degree "summer" rack.  I prototyped these in wood in my shop to come up with the right geometry, and also to test the Arduino Nano, RTC, and accelerometer modules.  The accelerometer- ADXL345 is adequate in accuracy since a few degrees of error matters little for PV positioning.  I have the software repeatedly re-read and re-position as movement and stopping vibration causes errors.  Still, the hourly repositioning takes only a few seconds.  By not hunting and striving for perfection, the linear actuator life will be hugely extended.  I even intentionally avoid using the actuator's limit switches, since their life is limited as well.

Dark clouds mean nothing to this system-  it always has the panels in a reasonable position, waiting for the sun to peak out.  The overnight position can be whatever you prefer.  I choose a position that is suited for stormy high winds from the SW.  I have not added a very high wind sensor, yet, since that adds something to fail, and I think the existing mechanical design  is good for my situation. One issue I found was that using numbered drills to get very tight tolerance on the actuator pin holes was important to reduce play.

« Last Edit: May 18, 2024, 03:45:10 AM by BruceM »