On January 20 the 2023 version of the ISO 9847 standard "Solar energy — Calibration of pyranometers by comparison to a reference pyranometer" was published.
Project leader and CEO of Hukseflux, Kees VAN DEN BOS says:
"My earliest record of the process of revision is from March 2019. We took about 4 years in total. A worldwide group of experts participated, both from manufacturers and government institutes. Really a nice joint effort. The main changes: more focus on indoor calibration, which is now the standard for the vast majority of solar industry. Also much improved content from the point of view of uncertainty evaluation and metrological vocabulary.
Pyranometer calibration is very relevant to application and finance of the solar energy industry. My estimate is that worldwide yearly over 15 000 high-end indoor calibrations are performed (new instruments plus recalibrations of instruments used in the field). Outdoor calibration? Maybe around 400 per year? Outdoor calibration is less popular because you need a clear day for a calibration, and the uncertainty is unpredictable; it varies with outdoor conditions and with solar elevation (which depends on the season)."