The reliability of solder joints in the solar cell metallization-interconnect system influences the lifetime of photovoltaic modules. Two field-aged modules - one with Sn62Pb36Ag2 solder at the solder joints (Solarex MSX 60), and the other with the standard Sn60Pb40 solder (Siemens M55) - were subjected to a modified thermal cycling (TC) test of IEC 61215. Three sections in each module were maintained at 85°C, 95°C, and 105°C during the 15-minute high temperature dwell time. Current equivalent to the module short-circuit current was injected through the module when the chamber temperature was above 25°C to simulate regular field operation. This novel approach aims to induce thermomechanical fatigue (TMF) at the solder joints and intermetallic compound (IMC) formation at the metal/solder interfaces. The activation energy (Ea) for solder bond degradation was calculated based on the series resistance (Rs) increase in TC testing rather than power drop to avoid the effect of confounding variables. Module-level Rs increase in MSX 60 module after TC800 cycles and in M55 module after TC400 cycles was 1.22% and 183.7%, respectively. The Ea determined for the module with 2wt% Ag is 0.24 eV and for that with the standard solder is 0.27 eV. The solder bond degradation seems to have been driven by TMF rather than IMC formation for both modules.