Silicon Photovoltaics on Metal Substrates: Investigating Cell Gap Changes in Modules With Aluminum Rear Cover

Abstract

New material combinations for photovoltaic (PV) modules are required for building-integrated photovoltaics (BIPV). In previous studies, it has been shown that PV modules with aluminum rear cover degrade heavily during thermal cycling due to interconnector fatigue. The mismatch in thermal expansion coefficients of the aluminum rear cover and the silicon solar cells was expected to induce a larger cell gap change in the solar cell strings under temperature change when compared to typical PV modules with glass covers. In this work, we confirm this effect by measuring and simulating the temperature-induced cell gap change in test modules with aluminum rear cover as well as with glass rear cover. For a module with glass rear cover, we measure and simulate only about 0.3 times the cell gap change as for a module with aluminum rear cover. Both measurement and simulation show increased cell gap changes for wider solar cells. Furthermore, we measure 20% less cell gap change for a 60% reduction in string length. All in all, we conclude that the (relative) cell gap change is the decisive parameter for controlling degradation due to thermal stress in future PV module designs with alternative material compositions.