Solar Tracker at Woodland Harvest Mountain Farm

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Odalys Benitez & Leon Santen

While living on a farm in the Appalachian Mountains of North Carolina, my friend Leon and I decided to upgrade our recently constructed solar array (meant to meet the electricity needs for 15 engineering students), and build a solar tracker. A solar tracker is meant to maximize the amount of power generated by the solar array by always pointing it in the direction where the sun is strongest. This was a great avenue for us to gain more robotics project experience, as well as contribute something to the farm that was so graciously deciding to host students for two pandemic semesters.

Before building and planning, we took the time to get acquainted with stakeholders who would be using the solar tracker during and long after we're gone. This mainly included the farm owners, and students. Through interviewing and conversations, we came away with some important findings.

Design Constraints

• Try our best to build the tracker with materials we can find on the farm, in an effort to make the tracker as sustainable as possible and in alignment with the farm owner's values.
• Build the tracker with consideration of the environment and climate. It should be resilient in the face of strong winds, rain, and changing terrain.
• Position the tracker in an ideal location where it will be easy to connect to the electrical system in the house, and where it will not obstruct any views of animals or gardens.
• Try our best to build the tracker in a way that will be easy to repair if anything goes wrong after we leave.

After grounding our project in user-centered principles, we set out to design, plan, and build. We designed the initial version of the solar tracker mount by taking inspiration from existing solar trackers. As we progressed in our design, we ran calculations on various things. We ensured that the hinges we picked to rotate the mount (pan/tilt) could sustain the load of the panels, and we ensured that the linear actuators we picked would enable the full range of motion for the solar tracker.

After we finalized the design and parts list, we began putting in the physical labor of love for such a large project. We dug post holes two meters down, debarked two huge tree trunks, drilled straight through locus posts, and cut through steel with only a jigsaw.

Electrical
System

As we built, we also designed the electrical system. We started by setting out requirements.

- Our goal is to optimize the solar power output by controlling the pan and tilt of the array.

- Furthermore, the system must be reliable, safe, and easily maintainable, as it needs to be used and cared for by everyone who lives on the farm in the future.

We picked an Arduino as the main controller, and then used a 12V power supply and a 5V supply to power the actuators and Arduino, respectively.
Each linear actuator (one for pan, one for tilt) was controlled by the Arduino through a motor driver, enabling smooth control.
In order to sense the pan/tilt of the array, we originally tried to incorporate rotary encoders into the design, however changes in the hinge mechanism meant we couldn't easily mount any sort of encoder there.
Instead, we thought outside the box, and mounted an accelerometer directly on the solar panel array. This way, we could always detect the panel's orientation relative to Earth's gravity
Using the motor drivers and the accelerometer, we created a PID loop on the Arduino to be able to easily move the panels to a commanded orientation.
Next, we added a pyranometer, which is a sensor that detects the sun's strength ("irradiance") at a given angle. Using these readings, we were able to implement functionality to "scan" with the panels to find the point of highest irradiance, corresponding to the highest solar panel energy output.
As well, we added a clock IC, which would precisely tell us the current date and time. Using a lookup table for sun inclinations, we were able to come up with an initial guess for the optimal panel orientation, then use the pyranometer to fine-tune.