Freiburg, Germany A joint programme from the Fraunhofer Center for Sustainable Energy Systems CSE in Boston, U.S., and the Fraunhofer Institute for Solar Energy Systems ISE in Freiburg, Germany, has published the first report from their PV Durability Initiative (PVDI).
In this first round of testing, five of the top ten Si-crystalline module producers were selected to be tested over approximately six months. Among them, for example, were modules from manufacturer SunPower.
Dr Harry Wirth, Director Division Photovoltaic Modules, Systems and Reliability at the Fraunhofer ISE, explained to REW that the six-monthly reports could include thin-film technologies, although other technologies differ in their testing requirements or may not yet be mature enough.
According to Fraunhofer, the results so far show a substantial spread in thermal cycling durability, while all of the tested module types proved to have very good stability in the damp heat/UV test sequence.
Modules are subjected to accelerated stress testing and are rated for both performance and safety. The programme partners say that existing IEC and UL protocols address the question of early field failure and safety of solar PV modules, but do not yet yield information about durability or the rate of degradation of power output.
Fraunhofer ISE and Fraunhofer CSE cooperated to develop the programme and tests can be carried out at both locations, Wirth said.
With a robust testing protocol, PVDI generates scores of zero to five that enable what the partners claim is a credible rating of PV modules based on their likelihood to perform reliably under different kinds of stress.
Fraunhofer says that its PVDI testing exceeds the demands of IEC standard module certification with extended accelerated testing, UV irradiation, damp-heat with positive and negative voltage bias as well as dynamic and static mechanical stresses at different temperatures. Also included are typical stresses such as temperature cycling, humidity-freeze, and damp-heat, which have been extended in order to come closer to the actual stress on a module.
In parallel with the accelerated tests, modules are subjected to long-term outdoor exposure while the correlation between the accelerated tests and operation in the field will be determined over time. Where possible, commercial modules are purchased on the open market, to avoid selection bias in the testing process.
Furthermore, Wirth said: “For us it is more important to adapt the test sequence to newest findings than to have comparability to older module types.”
The research is designed to provide solar PV financiers, developers and other industry players with the first widely available quantitative dataset to assess long-term durability, the authors added. For manufacturers, the data also encourages continuous improvements toward more durable modules.
Geoffrey Kinsey, Director of PV Technologies at Fraunhofer CSE, commented: “The potential for PV modules to fail in advance of their intended service life is a key factor that increases the perceived risk, and therefore the cost, of funding PV installations. PVDI addresses this issue“.
Fraunhofer Center for Sustainable Energy Systems CSE and the Fraunhofer Institute for Solar Energy Systems ISE invite PV module manufacturers, system developers, and financiers to participate in the PVDI program. Participants have access to more detailed data, since they finance the programme, Wirth explained.
Image: Courtesy Fraunhofer ISE