University of Ljubljana uses Eternalsun Spire flasher for accurate IV measurements to track PV module degradation


The University of Ljubljana is the largest University of Slovenia comprising many faculties from diverse scientific fields. Part of the University of Ljubljana is the Laboratory of Photovoltaics and optoelectronics (LPVO) within the Faculty of Electrical Engineering. It has the largest PV lab in Slovenia focusing on the exploitation of abundant solar energy with photovoltaics. As such, one of the key research interests is to evaluate how PV modules perform and degrade while being exposed to outdoor conditions.

spire flasher solar simulator

LPVO outdoor monitoring system for PV modules

LPVO outdoor monitoring system for PV modules is recognized worldwide due to its accuracy and versatility.

  • Key strong points are:
    • Modular and scalable design in configuration of multiple of 16 channels
    • Selectable individual operating point of the modules (Open/Short circuit, MPP)
    • Bias voltage for PID testing
    • Accurate IV curve measurement via four wire connection, simultaneous irradiance measurements with spectrally matched reference sensors
    • Windows control software with SQL database data storage for post analyses
    • Grid connection for energy recuperation
  • Reference institutions that use LPVO monitoring system for PV modules in their outdoor test facilities:
    • École polytechnique fédérale de Lausanne (EPFL)
    • Technische Universiteit Delft (TU Delft)
    • Helmholtz-Zentrum Berlin (HZB)
    • Faculteit Bèta Sciences and Technology (ZUYD)

Outdoor exposure requires accurate and stable indoor measurements

To measure the performance and even the tiniest degradation of PV modules while being exposed to outdoor conditions, LPVO requires both highly accurate and stable-over-time indoor PV module performance measurements. For this purpose it is working for over a year now with the Eternalsun Spire Long Pulse xenon flasher. For accuracy, the flasher has a long pulse, wide 300-1200nm spectrum with >99% Spectral Coverage (SPC), and high resolution uniformity according to the latest IEC 60904-9, edition 3.0, PRVD, publication date September 18, 2020. Stable measurements are of extreme importance for LPVO to make sure that tiny PV module degradations can be contributed to PV module degradation, not caused by the instability over time of the flasher. Spire flashers have proven to keep their specifications during their system lifetime, which is very difficult to achieve by LED based performance flashers.

pv modules outdoor testing university of of Ljubljana

  • If you aim to set up your own PV module outdoor exposure facilities and want to learn more about how to achieve this, contact Dr. Marko Jankovec of LPVO at 
  • If you aim to set up your own PV module indoor testing lab, and want to learn more about the requirements for accurate and stable PV indoor PV module measurements, contact Evangelia Miliou of Eternalsun Spire at