ISO 9846:2025

Overview

ISO 9846:2025 - Solar energy - Calibration of a pyranometer using a pyrheliometer - defines standardized laboratory and field procedures to calibrate a pyranometer by direct comparison to a reference pyrheliometer. This second edition updates ISO 9846:1993, adds a collimation tube method, refines data-treatment recommendations, and aligns terminology with related ISO guidance. The outcome of a calibration is the instrument sensitivity (responsivity) of the test pyranometer accompanied by an evaluated uncertainty.

Key topics and requirements

• Three approved calibration methods
  • Alternating sun-and-shade method: uses a shading disc to alternately expose and shade the test pyranometer while comparing to a tracking pyrheliometer. The test instrument may be horizontal, fixed-tilt or tracker-mounted.
  • Continuous sun-and-shade method: employs a shaded calibrated reference pyranometer in addition to the reference pyrheliometer; the reference pyranometer must lie in the same plane as the test device.
  • Collimation tube method: mounts the test pyranometer on a solar tracker with a collimation tube so both instruments share equivalent geometric fields of view for direct comparison.
• Apparatus and installation: specifies use of pyranometers, pyrheliometers, solar trackers, shade devices/collars, collimation tubes and data-acquisition systems, plus site and alignment requirements.
• Measurement procedures: preparatory steps, measurement sequencing, sampling and data-filtering approaches, and calculation of individual and combined sensitivity values.
• Uncertainty evaluation: guidance and suggestions for estimating calibration uncertainty; special attention to spectral effects for non‑spectrally‑flat pyranometers, where sensitivity depends on solar spectrum and limits calibration validity.
• Reporting: requirement to provide the sensitivity value with its uncertainty on the calibration certificate.

Applications and users

• Practical uses:
  • Calibration services and test laboratories validating pyranometers for PV performance testing, meteorology, climate monitoring and solar resource assessment.