International Spectroradiometer Intercomparison 2025
Final report
The International Spectroradiometer Intercomparison (ISRC) is a metrological event in the field of solar radiation measurements. The ISRC is managed by the European Solar Test Installation (ESTI) laboratories of the European Commission Joint Research Centre on an annual basis. The 13th edition was held in June 2025 at the Joint Research Centre site of Ispra, Italy.
The event consisted of a week of uninterrupted measurements of the solar radiation by the instruments of different participants, with the ESTI instrumentation acting as reference for the performance evaluation of spectroradiometers and pyranometers. Spectroradiometers were assessed also using the artificial light source of Apollo, a large area steady state solar simulator of ESTI, and a QTH standard lamp on a spectroradiometer calibration bench.
Starting in 2011, the first ISRC focused primarily on photovoltaic research and applications. Over the years, the range of interested participants has gradually expanded, encompassing not only laboratories in the PV field, but also space agencies, national metrological institutes (NMI), university and research groups, manufacturers of measurement equipment operating in the fields of climatology and meteorology.
The physical quantities measured during the campaign were the broadband solar irradiance and the spectrally resolved spectral irradiance (direct and global normal).
The present report summarizes the results of the Intercomparison, divided in different sections: in the first section the broadband irradiance sensors are presented; the second, third and fourth are dedicated to the performance indicators of the spectroradiometers in outdoor conditions using natural sunlight, indoor using the Apollo solar simulator and indoor against the QTH standard lamp; the fifth contains a summary of the prototype instruments present at the Intercomparison.
Prototype instruments were not comparable directly with the reference instruments; their interest in participating at the ISRC was mainly to collect data for further development of the instruments or validation of mathematical models.
PAVANELLO Diego;
ALESSANDRINI Stefano;
TOME Davide;
THIEL Christian;
2026-02-03
Publications Office of the European Union
JRC145057
978-92-68-36570-0 (online),
1831-9424 (online),
EUR 40620,
OP KJ-01-26-044-EN-N (online),
https://publications.jrc.ec.europa.eu/repository/handle/JRC145057,
10.2760/5390543 (online),
Additional supporting files
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