The relevance of independent power testing for PV modules has increased in recent years. Since 2017, the discrepancy between the power ratings of many PV module manufacturers and the measurement results of Fraunhofer ISE has been growing, rising to a median negative deviation of 1.4 percent in 2025. A research team at Fraunhofer ISE evaluated more than 70,000 power measurements on photovoltaic modules that had been carried out in the institute's calibration laboratory, CalLab PV Modules, since 2012.

"Engineering, procurement, and construction (EPC) service providers, in particular, rely on the most accurate, independent power measurements available when selecting PV modules, not least to protect their investments. A stable, traceable calibration level at our accredited calibration laboratory serves as the absolute foundation for a reliable assessment of module quality as well as the power and energy efficiency of purchased modules," explains Martin Kaiser, head of CalLab PV Modules at Fraunhofer ISE. "The annual ring comparisons with the PTB are one of the most important indicators for us as to whether we are on the right track here." In the most recent measurement comparison, conducted in December 2025, the Federal Institute and calibration laboratory achieved a deviation of less than 0.15 percent on the determined power (Pmpp).

Regular round robin comparisons are regarded as one of the most essential forms of quality assurance for accredited testing and calibration laboratories. As a result, measurement programs have been ongoing for many years between the PTB and Fraunhofer ISE at both the solar cell and PV module levels to ensure quality and validate calibration levels. For the comparison, both institutes assess the same PV modules and solar cells independently under different test settings and then compare the results.

About the Physikalisch-Technische Bundesanstalt

As the national metrology institute, the Physikalisch-Technische Bundesanstalt is the highest authority for various measurement variables in Germany. As the second-largest metrology institute in the world, it enjoys an excellent international reputation in research relating to units and accurate measurement. It is a service provider for science, industry, and society, as reliable measurements are essential in all these areas. It advises the German federal government on all matters relating to metrology. Organizationally, it is a departmental research institution and higher authority within the remit of the German Federal Ministry for Economic Affairs and Climate Action (BMWK).

Contact for further information at Physikalisch-Technische Bundesanstalt (PTB):

Dr. Stefan Riechelmann

Phone +49 531 592-0

Stefan.Riechelmann@ptb.de