Open Concentrating PV Solar Tracker Controller

Achieve better than 0.1° sun tracking accuracy with a compass a tilt sensor and a shading beam sun sensor.

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Concentrating Photovaltic CPV systems have up to 35% efficiency but require highly precise dual axis tracking. This Arduino Uno based tracker controller is easy to build with detailed instructions, elaborate firmware and a user-friendly RS232 interface. Thanks to an integrated compass and sun sensor it works without encoders or end switches for astronomic tracking, requires minimal cabling and achieves better than 0.1° accuracy with a shading beam sun sensor. Safety features include a wind sensor with go to storm routine and a pull string interrupter when the tracker moves out of range. This control is made to track almost anything that runs with two DC motors configured with a wide range of EEPROM resident parameters (soft start/stop ramps, motor speeds, sensor sensitivity, overcurrent …). See


Typically, tracker controllers are control cabinets with cables running to limit switches and encoders which are notoriously unreliable as the cables degrade in the UV light or the sensors get flooded with rain. A failed sensor or encoder may make the tracker run beyond its limits and self-destruct. Furthermore, the control cabinet gets into the way of the moving generator. I have even seen trackers running on a central PC connected to two Siemens SPS or at least running on a one board PC. What a waste of money, resources and electric energy.

Now imagine what a “mature” solar tracker controller would look like. Think of the solar tracker as a dishwasher. There would be a small circuit board somewhere in the housing with not much more on it than a µC, some FETs and possibly some extra sensors. But this control didn’t exist. Someone had to make it, so I started this job. I had no idea about microcontrollers but I knew about solar trackers. Now I know about microcontrollers too, and it is great fun. Thank you, Arduino community. As I moved along, I learned about the MPU9250 9 axis compass and figured out that it would be perfect for the astronomic tracking. The real challenge was the self-calibration routine but I successfully solved this riddle. It even works on trackers with an extensive amount of magnetic steel as I confirmed when I was allowed to test one of the prototypes on a 10 m2 CPV tracker for a day.

Yet I don’t know about best practice circuit board design and I greatly thank Ermanno Antonelli for joining forces with me. He is a professional in electronic board design and we now have a board ready and working (with a few aspects of new chips to be sorted out - WIP). The somewhat bulky shading beam sensor is now replaced by a much more compact imaging sun sensor and 6 FETs with a FET driver replace the costly VNH5019 dual motor shield. We also replaced the MPU9250 (end of life) with latest generation sensor chips. Furthermore, we included RS485 communication because we want this board to be fit for application in a large tracker field where commands may come over a long distance from a central control cabinet. The board is not much bigger than a credit card and yet capable of controlling 8A at 50V. It is so flat that we can mold it in silicone on the backside of its mounting plate for encapsulation and thermal management. It is also designed to be EMC compliant.

This board is made for mass production and we may or may not decide to make it available open source. A mature tracker controller board as a product may actually have more impact on the energy transition than an open source project which is never adopted by a major manufacturer. We will choose the option that will allow us to make a real difference. 

This contest is a very welcome chance to generate some visibility. Other than that the project has been presented at the Concentrating Photovoltaics Conferences CPV-17 (2021, Freiburg) and CPV-18 (2022, Myiazaki). Preprints of the papers are available on request. 


Even so this is an electronics project, it is made to allow new kinds of mechanics. Up until now people believe that precise trackers will require precise mechanics. This is not true! The mechanics only need to be able to perform small steps and be stiff enough not to swing in the wind. If they are “wobbling” while they move, it doesn’t matter if you are doing the fine adjustment using a highly sensitive sun sensor. This control is actually made for my favorite tracker design: a three wheeled carriage that turns on spot and pulls up the generator against gravity with a winch. If the ground is somewhat uneven that’s fine. It may even be gravel. The winch is not exact, but it is made in such a way that the rope slips when the storm is shaking the generator. Thus the tracker will move to the safe “stow position” even without electrical power....

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MIT license

text/plain - 1.08 kB - 05/01/2022 at 12:41



A slightly modified version of the presentation I have given at the CPV-18 conference with annotations concerning the pictures which are also used in the conference paper and which will be published through AIP (public access).

Adobe Portable Document Format - 1.35 MB - 04/29/2022 at 16:18



Detailed description of how to build and operate the tracker controller.

Adobe Portable Document Format - 2.61 MB - 04/28/2022 at 16:40


  • 1 × See list of components in ...Full_description.pdf

  • Ermanno joined the project

    Ruediger F. Loeckenhoff06/10/2022 at 14:48 0 comments

    Ermanno Antonelli now officially joined the team! Thank you so much, Ermanno. This is going to be great!

  • Done! Ready for the contest.

    Ruediger F. Loeckenhoff05/01/2022 at 11:49 0 comments

    May 1st 2022:

    Thank god I am living in Europe. I needed to add a video and these project logs to make the submission complete. I have two hours left Phew. The video is online now. I hope the link works. I also added the shading beam 3D-file to my GitHub repository. I am kind of greatfull that hackaday forced me to make a video. This will greatly add to our visibility.

  • Hackaday Contest

    Ruediger F. Loeckenhoff05/01/2022 at 11:45 0 comments

    April 27th 2022:

    I am swapping through my emails and I am learning about the hackaday contest. Oh dear, only a few days left.

  • CPV-18 conference

    Ruediger F. Loeckenhoff05/01/2022 at 11:43 0 comments

    April 25th 2022:

    I am presenting this work at the CPV18 conference as an online talk. This is my first conference talk and paper as a private person.

  • A great partner

    Ruediger F. Loeckenhoff05/01/2022 at 11:41 0 comments

    October 2021: I got Ermanno Antonelli interested, a real expert on DCB board design. This started a fruitfull cooperation to make an all in one control board reality.

  • Go live at GitHub

    Ruediger F. Loeckenhoff05/01/2022 at 11:39 0 comments

    Aug. 7th 2021:

    After years of work the project has gone live on From this time, there have been refinements mainly on the assembly instructions and comments in the code. The first version has already been fully functional.

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  • 1
    Step 1

    See assembly and operating instructions in ...Full_description.pdf

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Ruediger F. Loeckenhoff wrote 05/08/2022 at 19:22 point

I feel that I should add some more to my answer because it might have a somewhat frustrated undertone. We are working so hard to make CPV big scale reality and we are constantly so close to just making it. We already achieve a much higher efficiency than silicone flat plate PV and if we got the chance to move down the learning curve we would quickly be better in terms of Cent/kWh. This is basically a no brainer because the efficiency is higher and the material consumption is lower. I guess up until now we were just too slow and we let the flat plate industry run away. Yet I strongly believe that we can still catch up. We all had our learning curves on the side of CPV solar cell and CPV solar system development and I believe we came up with great products. Yet there is more too be done and I believe that the tracker controller is the lowest hanging fruit. With the “credit card sized board” we have moved 80% of the way in terms of cost reduction and I hope that this will help and give confidence in other fields such as solar tracker development. Putting CPV solar modules onto a tracker requires unnecessary material for the frame so the tracker and the module need to be integrated. This is actually another relatively low hanging fruit. Valldoreix Green Power has shown how this works. Getting rid of the foundation is yet another topic. I have shown one option with the three wheeled tracker with a winch. I believe this solution can be very cost effective, reliable and easy to repair. Yet there will be other options – show them to me!

In terms of the modules automatic assembly is the key. That requires investments and the first automatic production line requires a lot of development. A multiple replication of that line comes much cheaper. Then these lines need to run 24/7 to pay for themselves.
If you buy low quantities you are restricted to the most common materials and processes. If you can buy large you can get exactly what you need from one place at a low price without shipping stuff around.
… I got carried away. In the end there is one point I want to make:
Soitec has proven that CPV works and can be very cost efficient and reliable. Unfortunately, they were let down by there partners in the worst possible moment after having built up three production lines and the projects these lines were built up for where suddenly cancelled. That was a great tragedy.

If you do CPV right and you have enough financial impact to get good prices for the raw materials and you do have the projects to pay for the investments in fully automatic production lines, then CPV can quickly become one of the most important contributions to the energy transition – in particular in combination with storage. Fusion Fuel and RayGen seem to be on a very good way and I have great hopes that they will make it.

The great thrill of CPV for hackers is the chance to really contribute to the development. There is no chance to make a better solar cell in your garage, but you can make a better solar tracker if you have just the right idea. And this may then become a standard solution. Wouldn’t that be cool?

  Are you sure? yes | no

Ruediger F. Loeckenhoff wrote 05/08/2022 at 06:37 point

Written in Word, copied to the chat, formatting messed up.

  Are you sure? yes | no

Ruediger F. Loeckenhoff wrote 05/08/2022 at 06:33 point

Hi James,

Wow, you are asking the hard questions. In the residential scale CPV solar tracking is for enthusiasts. You might
buy some Soitec CX-M400, build up the tracker mechanics on your garage roof – and preferably come up with a new or refined solution, to contribute to the development buy the few components that my electronic circuit requires or – when we are done – buy our circuit board make it work and adjust the modules
Now wait for your friends to come by and show them a really cool gadget that even saves you 25% of your electricity costs.

This is hackaday after all. I believe this would be great fun for many. Because it is so visible. Cooler than a Tesla, because there are so many around already. And if you already do have a Tesla, you can charge it with CPV.

Now, these are my hopes why “you guys here” will get involved.

The next part of the question is about the economic chances of CPV. If we do have a chance, it is in solar plant scale. If you look at the components involved and the efficiencies we achieve (45% cell level, 33% module level, low thermal coefficients) we should be very well able to compete. After all those silicone flat plate PV guys need to cover the whole area with the same kind of material that microprocessors are made of. Insane, isn’t it? Unfortunately (or fortunately from an ecologic point of view) they are so far advanced that scale more than evens out these disadvantages. Fortunately – for us – there are niche markets to get started. Fusion Fuel uses the heat of the CPV receivers to make hydrogen electrolysis more efficient. And hydrogen will likely be a real megatrend. RayGen uses the heat of their big receiver to feed it into a storage system that involves heat pumps and rancine cycle turbines between huge hot/cold water basins. That’s really thermodynamics at its best.

In both cases, the advantages of CPV come together with heat – from the CPV receiver – and storage.

Yet, clearly CPV needs to advance or it will become irrelevant. This project is meant to be such an advance since it reduces a control box that may cost several hundred $ to a single printed circuit board that may be “extremely cost effective” with only a few non-expensive parts involved.

Yet I have to face the possibility that my work on CPV may not contribute to the energy transition. In that case this control board is also the most effective way to run a PV solar tracker. This may be one axis or two axis. In the latter case you don’t even need a sun sensor because gravity is pretty reliable (as any toddler struggles hard to find out). I.e. you can run a one axis tracker on a 3-axis accelerometer alone with high precision and there should be a cost-effective board made for Arduino code for this purpose.

Finally, there may be other applications for this board. It has a magnetic compass, an accelerometer and a 3-half bridge motor controller as well as an RTC. More I2C devices can be connected externally. For instance, you have a single Arduino-compatible board with a powerful three phase motor driver. Doesn’t that call for hacks?

If you are one of the enthusiasts that wants to show off with a CPV solar tracker on his garage roof, let me know and we can discuss solutions.

All the best


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James Newton wrote 05/07/2022 at 23:00 point

Do you have any public sources for these CPV type panels? And for the tracking mounts? What I can find for those so far appear to be very very expensive, and don't seem to justify the extra cost vs the energy produced. E.g. unless the size of the installation is the limiting factor, it would seem to be better to just buy more of the lower cost, non-moving, standard solar panels and spread them out over a larger area. I'm assuming this solution is targeted at installations where the space IS constrained, although I'm not sure I can think of a valid example... Perhaps this system would allow someone renting an apartment or condo to run internal lights off their balcony? Or perhaps for camping / wilderness survival where the weight might be less?

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