Solar Tracker

Solar Tracker is an Arduino-based photovoltaic panel positioning system. It uses two LDR sensors, an irradiance input, a servo motor, a compass module, an RTC module, EEPROM persistence, and a browser-based Web Serial control interface to keep a solar panel aligned with the most favorable light direction during the configured operating window.

The project combines embedded control and a lightweight web dashboard. The Arduino firmware performs the real-time tracking logic, while the HTML interface allows the operator to connect through USB serial, set angles, sync the RTC, configure sunrise and sunset times, adjust magnetic declination, toggle operation modes, record calibration data, and export CSV files.

Project objective

The objective of this project is to maximize solar energy capture by orienting a photovoltaic panel toward the best available solar incidence angle throughout the day. The system is designed for small photovoltaic installations, educational experiments, solar-energy research, and prototypes that need low-cost automatic solar tracking.

The tracker uses LDR readings to compare light intensity on the east and west sides of the panel, an analog irradiance input to estimate solar incidence, an HMC5883L compass module to support orientation checks, and an RTC module to keep operation limited to a configured sunrise-to-sunset period. Configuration values are stored in EEPROM, allowing the system to keep important parameters after power cycling.

Main features

• Arduino firmware for UNO, NANO, MEGA, and compatible boards.
• Servo-based panel angle control from 30° to 150°.
• Active solar tracking based on LDR difference and PID control.
• Passive solar tracking based on time progression between sunrise and sunset.
• Manual positioning mode through the serial menu or web interface.
• Auto-calibration routine for finding the angle with maximum irradiance.
• RTC-based operating schedule.
• HMC5883L compass orientation check with magnetic declination compensation.
• EEPROM persistence for operating mode, schedule, magnetic declination, and filter state.
• Sudden-variation filter for reducing unstable movement caused by temporary shadows or fast irradiance disturbances.
• Buzzer alerts for startup, movement, confirmation, orientation errors, RTC errors, compass errors, and invalid input.
• Browser-based control panel using the Web Serial API.
• Real-time chart for irradiance versus panel angle using Chart.js.
• CSV export for calibration or experiment data.
• Included STL files for 3D-printed mechanical parts.

Repository structure

Solar-Tracker/
├── README.md
├── CHANGELOG.md
├── CONTRIBUTING.md
├── LICENSE
├── NOTICE.md
├── SECURITY.md
├── docs/
│   ├── ARDUINO_FIRMWARE.md
│   ├── HARDWARE_GUIDE.md
│   ├── OPERATING_GUIDE.md
│   ├── SERIAL_PROTOCOL.md
│   ├── WEB_APP.md
│   ├── TROUBLESHOOTING.md
│   └── ORIGINAL_README.md
├── hardware/
│   └── 3d-models/
│       ├── FanStBase.stl
│       ├── FanStGrille.stl
│       ├── FanStVert.stl
│       ├── Laser_Cradle_9mm_SG90.stl
│       ├── Servo_Box_3.stl
│       ├── arduino_uno_bottom.stl
│       └── arduino_uno_top.stl
└── src/
    ├── arduino/
    │   └── Solar_Tracker/
    │       └── Solar_Tracker.ino
    └── web/
        ├── index.html
        └── Solar Tracker.html

System overview

The firmware runs in a loop and reads the sensors once per second. During the configured operating interval, it chooses the appropriate behavior based on the current mode:

In active mode, the tracker compares the west and east LDR readings. The difference between these readings becomes the tracking error. The firmware applies a PID-style correction and moves the servo when the error exceeds the configured tolerance.

In passive mode, the tracker does not depend primarily on the LDR difference. Instead, it maps the current time between sunrise and sunset to the servo angle range. At sunrise, the servo approaches the minimum angle. At sunset, it approaches the maximum angle.

In manual mode, the operator defines the desired angle. The tracker keeps the servo at that manually configured angle until automatic behavior is restored.

Outside the configured operating time, the firmware returns the servo to a neutral position and detaches the servo to reduce unnecessary power consumption.

Hardware components

The project is designed around commonly available Arduino modules:

Component	Purpose
Arduino UNO/NANO/MEGA or compatible board	Main controller
Servo motor, such as SG90 or compatible	Moves the solar panel structure
2 × LDR sensors	Detect light imbalance between east and west sides
Irradiance sensor or analog light sensor	Measures solar irradiance through analog input A2
HMC5883L compass module	Provides magnetic orientation data
PCF8563 RTC module	Keeps date and time for operating schedule
Buzzer	Provides acoustic alerts
3D-printed parts	Mechanical support, servo mount, Arduino case, and structural parts
External servo power supply	Recommended for stable motion under load

Default pin mapping

Arduino pin	Connected device	Notes
A0	West LDR	Analog input
A1	East LDR	Analog input
A2	Irradiance sensor	Mapped from 0–5 V to 0–1000 W/m² in firmware
D3	Servo signal	PWM-capable output
D13	Buzzer	Tone alerts
SDA/SCL	RTC + compass	I2C bus

For Arduino UNO and NANO, the I2C pins are normally A4/SDA and A5/SCL. For Arduino MEGA, they are normally pins 20/SDA and 21/SCL. Always connect all grounds together, especially when using an external servo power supply.

Arduino dependencies

Install these libraries in the Arduino IDE before compiling:

• RTClib
• Servo
• Adafruit HMC5883 Unified
• Adafruit Unified Sensor, required by the HMC5883 library
• Wire, included with the Arduino core
• EEPROM, included with the Arduino core

Getting started

1. Clone or download this repository.
2. Open src/arduino/Solar_Tracker/Solar_Tracker.ino in the Arduino IDE.
3. Install the required libraries from the Arduino Library Manager.
4. Select the correct board and serial port.
5. Upload the firmware to the Arduino.
6. Assemble the LDR sensors, irradiance input, compass, RTC, servo motor, and buzzer according to the pin mapping.
7. Open src/web/index.html in a browser that supports the Web Serial API.
8. Connect to the Arduino using the Connect to Arduino button.
9. Configure time, sunrise/sunset, magnetic declination, and operation mode.
10. Test the servo movement without a heavy panel before installing the final mechanical load.

Web control interface

The web app is a single HTML file that communicates with the Arduino through USB serial. It provides modules for serial connection, manual angle setting, automatic mode restoration, RTC synchronization, schedule configuration, magnetic declination, active/passive mode switching, sudden-variation filter control, data recording, CSV export, compass display, and an irradiance-versus-angle chart.

The interface sends the same menu commands expected by the Arduino serial menu. For example, the manual angle command sends option 7, followed by the desired angle.

Serial menu commands

The firmware exposes a simple text-based serial menu at 9600 baud:

Option	Action	Expected follow-up input
1	Adjust system date and time	YYYY MM DD HH MM SS
2	Adjust sunrise time	HH MM
3	Adjust sunset time	HH MM
4	Toggle sudden variation filter	None
5	Adjust magnetic declination	Decimal value in degrees
6	Toggle active/passive operation mode	None
7	Enter manual positioning mode	Angle from 30 to 150; invalid value returns to automatic mode

The web app uses these commands internally, so both the browser interface and the Arduino Serial Monitor can control the same firmware.

Operation modes

Active mode

Active mode uses the two LDR sensors as the main feedback source. The panel moves when the west/east light difference exceeds the tolerance threshold. A PID-style correction is applied using the configured constants in the firmware:

float Kp = 0.5, Ki = 0.1, Kd = 0.05;

Passive mode

Passive mode uses the configured sunrise and sunset times to calculate a time ratio. The firmware maps the current time to the servo range from 30° to 150°. This mode is useful when LDR readings are noisy, the sky is partially cloudy, or the mechanical structure requires predictable movement.

Manual mode

Manual mode allows the operator to set a fixed angle. This is useful for testing, calibration, inspection, or experiments that require a known panel position.

Auto-calibration

When active operation is enabled, the firmware can scan the servo range, measure irradiance at each angle, and store the best angle found during that scan. This routine helps identify the angle with the highest measured solar incidence at calibration time.

Data recording and CSV export

The web interface can record values received from the Arduino and export them as a semicolon-separated CSV file named Solar_Tracker.csv. The exported columns are:

Date/Time;Angle (°);Irradiance (W/m²);Compass (°)

This is useful for testing panel performance, validating the calibration routine, and comparing irradiance values at different angles.

3D models

The repository includes STL files for mechanical prototyping:

File	Description
FanStBase.stl	Base structure
FanStGrille.stl	Grille/support element
FanStVert.stl	Vertical support structure
Laser_Cradle_9mm_SG90.stl	SG90 servo cradle / small actuator support
Servo_Box_3.stl	Servo box
arduino_uno_bottom.stl	Bottom half of Arduino UNO enclosure
arduino_uno_top.stl	Top half of Arduino UNO enclosure

Review part dimensions, orientation, infill, and material selection according to the final panel weight and operating environment.

Recommended workflow

Start with the electronics on a bench before installing the complete mechanical system. Confirm that the RTC is recognized, the compass is working, LDR values change correctly, the irradiance input is within the expected 0–5 V range, and the servo can move across the allowed range without obstruction. After the bench test, assemble the mechanical structure, set the local magnetic declination, align the panel axis, and perform calibration under real sunlight.

Safety notes

Do not power the servo motor directly from the Arduino 5 V pin when moving a real panel or a heavy mechanism. Use an external regulated supply suitable for the servo current and connect the grounds together. Avoid mechanical end-stop collisions by testing the 30° and 150° limits before attaching the final load.

Potential expansions

• Add meteorological sensors to account for cloudy or unstable conditions.
• Replace the servo with a stepper motor and lead screw for larger photovoltaic panels.
• Add current, voltage, and power monitoring for real energy-yield evaluation.
• Add SD-card logging for offline data collection.
• Add Wi-Fi, Ethernet, MQTT, or Modbus communication for remote monitoring.
• Add a more complete calibration routine for compass hard-iron and soft-iron correction.
• Add enclosure protection for outdoor operation.

Documentation

More detailed documentation is available in the docs/ folder:

• docs/HARDWARE_GUIDE.md
• docs/ARDUINO_FIRMWARE.md
• docs/WEB_APP.md
• docs/SERIAL_PROTOCOL.md
• docs/OPERATING_GUIDE.md
• docs/TROUBLESHOOTING.md