This Solar Power Meter Packs a Real Photovoltaic Panel for Accurate Field Measurements
Want to know how well a solar panel is likely to work in a given location? This handheld gadget is exactly what you need.
Pseudonymous maker "Green Energy Harvester," hereafter simply "Green," has released a guide to building a compact solar power meter — designed to make it easy to figure out where best to position and angle solar panels prior to installation.
"This project started with a simple frustration. Most professional solar irradiance meters available in the market are too expensive for regular field use, learning, or DIY projects," Green explains. "Even after investing in them, they often remain closed and non-customizable — you use them as they are, without understanding or improving how they work. While working with solar panels during site surveys and testing, I often needed a simple tool to quickly check sunlight conditions. Carrying an expensive instrument for every small task did not make sense, and low-cost alternatives based on generic light sensors were not reliable enough for real solar work."
Rather than keeping on trying disappointing or expensive off-the-shelf options, Green decided to build something from scratch. "The idea was to measure sunlight the same way a solar panel experiences it," the maker explains, "using a real silicon solar cell instead of a generic light sensor. Along with irradiance, I also wanted to understand how tilt and orientation (azimuth) affect the readings, because in real installations, orientation plays a major role in performance."
Inside the gadget's housing is a Seeed Studio XIAO ESP32C3, a compact development board built around Espressif's ESP32-C3 microcontroller. This is linked to a current sensor and tiny solar cell, a compass sensor, and an OLED display, plus a tactile switch and a circuit made up of a range of resistors, capacitors, and an N-channel MOSFET. Everything is powered by an integrated 18650 lithium battery, meaning it can operate in-the-field — though the solar panel is for measuring how well solar panels would work in the same position, rather than charging the battery.
"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," Green explains. "Unlike optical light sensors, this method closely represents the behavior of actual photovoltaic modules and therefore provides physically meaningful measurements for solar applications.
"Tilt and azimuth are shown so the user can make sure the device is properly aligned while taking measurements. This helps ensure that the measured irradiance truly represents the sunlight available to a correctly installed solar panel, making the readings more meaningful and closer to real-world solar installation conditions."
The project is documented in full, including a parts list and source code, on Instructables.