The effects of changing mechanical loads exerted on PV modules in field conditions, for example by wind pressure, are currently being discussed in regard to their reliability as well as possible yield losses. This is also in view of the fact that PV modules with cells made of crystalline silicon may show or develop microcracks in some cases.
The oscillations and deflections that occurred on c-Si PV modules mounted on a fixed rack and on a uniaxial tracker at ZSW’s Widderstall outdoor testing facility were recorded by means of laser displacement sensors with high-resolution deflection and scanning intervals. At the same time, the wind speed was also recorded at the location. The modules selected for testing were shown to have individual cells with microcracks by electroluminescence (EL) imaging. The deflections of the module plane observed in the field investigation are in the range of a few millimetres around the rest position. This also applies to modules mounted on the uniaxial tracker, where a daily cycle of deflections caused by the rotation of the support frame is superimposed on the wind effects. In the laboratory, these modules show that the measured STC power is only slightly dependent on mechanical deflections of up to +/- 5 mm (see figure below). Since the deflections (-2/+4 mm intervals) observed in the field investigation during a one-year measuring period are below this critical threshold, it can be concluded that no relevant performance or yield reductions occur in modules damaged by microcracks during field operation.