Pyranometers

A pyranometer is an instrument for measuring solar irradiance on a plane surface, most often on horizontal ground. It is used to quantify global horizontal irradiance (GHI) and, with additional methods, diffuse irradiance (DHI) and direct normal irradiance (DNI) for solar energy assessment, climatology, and meteorology.

Most pyranometers rely on a thermopile sensor paired with a glass or quartz dome that collects radiant energy from nearly the full sky. The dome shields the sensor from rapid ambient temperature changes while allowing exposure to shortwave and near-infrared radiation. The radiant flux absorbed by the sensor is converted into a voltage or current that is proportional to the incident irradiance. The device is designed to have a cosine response, meaning it aims to measure irradiance consistently across different sun angles.

Types and configurations vary, but the thermopile-based pyranometer is the most common in field measurements. Some devices use photodiode-based sensors or additional filtering for specific spectral characteristics. Many pyranometers include temperature compensation and require regular calibration to maintain accuracy.

Standards and calibration procedures are established to ensure data quality. ISO 9060 defines performance criteria and classification for pyranometers, including spectral response, temperature dependence, and angular response. Calibrations are traceable to the World Radiometric Reference (WRR), and data from well-maintained instruments are widely used in networks such as the Baseline Surface Radiation Network (BSRN) and in solar resource assessments.

Common applications include weather monitoring, climate research, solar energy resource assessment, and performance verification for photovoltaic systems. Proper installation, cleaning of the dome, ventilation considerations, and shielding from shadows or debris are important for reliable measurements.