Accurate measurement of solar irradiance is one of the most critical steps in solar photovoltaic system design, performance evaluation, and educational experimentation. Solar irradiance directly determines how much electrical power a solar panel can generate at a given location, tilt, and orientation. While professional irradiance meters and pyranometers provide high accuracy, they are often expensive, bulky, and inaccessible to students, hobbyists, and small-scale solar installers.

The DIY Solar Power Meter was developed to address this gap by offering a compact, low cost, and portable solution that can be used for quick field measurements, educational demonstrations, and experimental solar studies. The project focuses on practicality rather than laboratory-grade precision, providing sufficiently accurate readings for comparative analysis, panel alignment, and real-world learning.

This device combines a calibrated solar cell for irradiance estimation with orientation sensing for tilt and azimuth, all integrated into a handheld, battery-powered unit with a real-time OLED display. The complete system is built using widely available components and programmed using the Arduino platform, making it easy to understand, modify, and reproduce.

System Overview:

The DIY Solar Power Meter is built around an ESP32 microcontroller, which serves as the central processing unit for sensor data acquisition, calculations, and display control. The ESP32 was selected for its low power consumption, strong processing capability, and wide support within the Arduino ecosystem.

A precision current and voltage monitoring IC measures the electrical output of the solar cell. The short-circuit current is calculated from these measurements and converted into an irradiance value using a calibration constant derived from real outdoor testing.

To support proper solar panel alignment, the system also includes a combined accelerometer and magnetometer module. This sensor provides real-time tilt and azimuth readings, allowing the user to orient the device toward the sun or align solar panels accurately.

All data is displayed on a compact OLED screen, ensuring excellent readability even under bright outdoor conditions. A single button interface allows the user to navigate between display modes, keeping the user interaction simple and intuitive.

Solar Irradiance Measurement

This irradiance meter works on the short-circuit current (Isc) principle.

A silicon solar cell produces current proportional to the sunlight falling on it. At Standard Test Conditions (STC), 1000 W/m² of irradiance produces a known short-circuit current.

The irradiance is calculated using:

Irradiance (W/m²) = (Measured Isc / Rated Isc) × 1000

Because this method directly uses a solar cell, it naturally:

• Matches the solar spectrum
• Exhibits good cosine response
• Correlates well with actual PV performance

In this irradiance meter, a silicon solar cell is used as the primary sensing element to measure solar irradiance by exploiting the direct relationship between incident sunlight and the short-circuit current generated by the cell. Unlike optical light sensors, this method closely represents the behavior of actual photovoltaic modules and therefore provides physically meaningful measurements for solar applications.

The solar cell is operated under controlled short-circuit conditions using a MOSFET-based switching arrangement. The MOSFET is placed in the current path between the solar cell and the current sensing circuit, allowing the microcontroller to electrically connect or disconnect the solar cell as required. When the MOSFET is turned ON, the solar cell terminals are effectively shorted through the shunt resistor and the INA226 current measurement input, enabling accurate measurement of the short-circuit current. When the MOSFET is turned OFF, the solar cell is electrically isolated, preventing unnecessary current flow and reducing idle power consumption.

The generated short-circuit current flows through the INA226 current sensor and send to MCU for further processing. The electrical connection of the solar cell, MOSFET, and INA226 is shown in the schematic.

At Standard Test Conditions (STC), an irradiance of 1000 W/m² corresponds to the rated short-circuit current of the solar cell. By comparing the measured short-circuit current with the rated Isc value, the incident irradiance is computed in firmware.