  Degradation of backsheets (BS) and encapsulant polymer components of silicon
PV modules is recognized as one of the main reasons for losses in PV plant
performance and lifetime expectations. Here, we report first insights into the
correlation between BS composition of PV-modules and PV power station
performance by using a combination of lab- and field-imaging, as well as
spectroscopic and electrical characterizations. Using field-suitable
near-infrared absorption (NIRA) spectroscopy, the BS structure of 518
PV-modules, 2.5 percent of the PV-modules in a 5 MWp PV power station, was
identified on-site. The variance of the BS composition was found to be
heterogeneous across PV-modules of the same power class from the same
manufacturer. Polymaide-based BS cause in 10 out of 100 inverters ground
impedance values below 400 kOhm, which is a typical threshold for inverters
connecting to the grid. For primer-based BS this low value is reached 20 times.
We conclude these numbers best as possible from the available monitoring data
of inverters associated with BS-types from NIRA. Challenging is the
identification of degraded primer-based BSs, since visually they look healthy
and undistinguishable to well performing BSs. The present results demonstrate
that a deeper understanding of the relationship between bill-of-materials and
performance of PV-modules is necessary to avoid/minimize inverter shut-downs,
and that it can be achieved by using combinations of selected field and lab
characterization methods with monitoring data.
