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How effective are solar modules?

New measuring facility for the performance testing of solar modules

PTBnews 2.2023
Especially interesting for

the photovoltaics industry

testing and calibration laboratories

At PTB’s Competence Center for Photovoltaics, a new measuring facility has been developed with which the performance of solar modules under standard test conditions can be determined with much greater accuracy compared to previous methods.

Solar Module Cube with its front side directed towards the sun during a measurement

Photovoltaics is one of the main pillars of the energy transition as we move towards carbon-free energy production. In Germany, the government’s coalition agreement calls for a total of 200 gigawatts of PV capacity to be installed by 2030. As the business volume associated with this expansion will amount to hundreds of billions of euros, each percent of measurement uncertainty corresponds to a financial equivalent of approximately one billion euros. Against this background, PTB with its Competence Center for Photovoltaics has set itself the objective of extending the traceability chain from the solar cell to the solar module and validating it metrologically. This will serve to reduce the uncertainties resulting from the size and technology leap from cells to modules.

PTB’s new measuring facility is unique in the world. It allows the performance of solar modules to be determined under standard testing conditions with much greater accuracy than was possible with previous methods. To test their efficiency, solar modules are installed inside the Solar Module Cube, a facility with a mass of 9000 kg and a heigth of 9 meters. It is located on rails so that it can be easily moved outside with its open side aligned to face the sun during testing. The front opening can be opened within a few seconds and closed again just as quickly after the measurement data has been recorded. The temperature thus remains stable, and virtually no diffuse solar radiation or ground-reflected solar radiation strikes the module.

The measuring facility combines the advantages of various previous laboratory and free-field measurement methods. Initial measurements were carried out in the autumn of 2022. Apart from determining the electrical parameters of the solar module at vertical light incidence, its reflection behavior was also determined by varying the angle of incidence. This is an important input quantity for calculating the yield of solar systems. For this purpose, the Solar Module Cube was tracked to follow the sun, and the solar module was rotated in 5° steps to attain inclination angles ranging from −95° to +95° relative to the sun. Initial results relating to the electrical properties showed that they very closely matched the values determined in the laboratory on the solar simulator. The measurements relating to the reflection behavior will be compared with the results from other laboratories over the course of 2023.The measuring facility allows PTB to offer the world’s lowest measurement uncertainty for solar modules, helping to improve investment security along the photovoltaics value chain.


Stefan Riechelmann
Department 4.5, Applied Radiometry
Phone: +49 531 592-4149
Opens local program for sending emailstefan.riechelmann(at)ptb.de

Scientific publication

S. Riechelmann et al.: Primary calibration of solar modules with direct sunlight. 39th European Photovoltaic Solar Energy Conference and Exhibition, submitted