Overview
ISO/TR 9901:2021 - Solar energy - Pyranometers - Recommended practice for use provides practical, state-of-the-art guidance for selecting, installing, operating and validating pyranometers in solar energy applications. The technical report covers outdoor and indoor measurements of plane of array (POA), global horizontal irradiance (GHI), diffuse and reflected irradiance, and use with solar simulators. It updates earlier guidance to reflect modern instrument classes (per ISO 9060:2018) and digital pyranometers with internal diagnostics.
Key topics and requirements
- Selection and accessories: guidance on choosing pyranometers and accessories (heating, ventilation, electronics, mounting) and on matching instruments to required accuracy classes.
- Installation and mounting: best practice for horizontal and inclined installations, diffusometers (pyranometers paired with shading devices) and reflected-radiation setups.
- Heating and ventilation: recommended measures to reduce dew, frost and contamination that bias readings.
- Inspection, maintenance and cleaning: schedules and procedures to preserve performance and minimize measurement drift.
- Data acquisition and storage: recommended sampling/recording practices, handling of digital outputs and internal diagnostics.
- Data quality control and correction: procedures for checking data integrity and applying corrections.
- Calibration and performance verification: procedures for laboratory calibration and on-site checks, including introduction of new sensitivity values.
- Uncertainty evaluation: guidance consistent with current practice (expanded uncertainty, coverage factor k = 2) and references to uncertainty standards.
- Indoor use: recommendations for pyranometer use with solar simulators and lab testing.
- Informative annexes: practical details on heating/ventilation systems and shading losses in reflected radiation measurements.
Applications
ISO/TR 9901:2021 is directly applicable to:
- PV plant performance monitoring and power-plant testing (including bifacial module assessment)
- Testing of PV modules and solar thermal collectors
- Laboratory measurements with solar simulators
- Resource assessment and performance ratio calculations where accurate irradiance is critical
Who should use it
- PV plant operators and O&M teams
- Test laboratories and calibration facilities
- Solar project engineers and system designers
- Instrument manufacturers and metrology specialists
- Researchers and standards bodies involved in solar measurement
Related standards
- ISO 9060:2018 (pyranometer specifications and classification)
- IEC 61724-1:2017 (PV system performance monitoring)
- ASTM G213-17, ASTM G183-15 (solar radiation and uncertainty guidance)
ISO/TR 9901:2021 is a practical reference to improve measurement reliability and reduce uncertainty when using pyranometers in solar energy projects.