Fraunhofer ISE, PTB reports only 0.15% uncertainty in PV module yield measurements

The CalLab PV modules from Fraunhofer Institute for Solar Energy Systems ISE and the Physikalisch-Technische Bundesanstalt (PTB), the leading German authority on various measurement variables, have found that their power measurements of photovoltaic modules deviate on average by less than 0.15% from the reference value.

The two organizations have been conducting interlaboratory measurement programs at both solar cell and module levels for many years to validate calibration levels.

This work involves both institutes independently assessing the same PV modules and solar cells under different test settings and then comparing the results. Their last measurement comparison, completed in December, achieved a deviation of less than 0.15% from the determined power.

Martin Kaiser, head of CalLab PV Modules at Fraunhofer ISE, said the annual ring comparison with PTB “is one of the most important indicators for us to determine whether we are on the right track here.”

The discrepancy between the power of many PV module manufacturers and the measurement results of Fraunhofer ISE has grown to a median negative deviation of 1.4% in 2025, according to a statement from the institute.

Last March, Fraunhofer published the results of one longitudinal research project More than 70,000 solar panels were tested, with a negative trend becoming visible since 2017 between performance data from PV module manufacturers and the institute’s performance measurement of the modules.

Kaiser explained that engineering, procurement and construction service providers rely on the most accurate, independent power measurements available when selecting PV modules. “A stable, traceable level of calibration in our accredited calibration laboratory is the absolute basis for a reliable assessment of module quality and the power and energy efficiency of purchased modules,” he added.

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