To determine the ability of the module to withstand the effects of high temperature and humidity followed by sub-zero temperatures. After the fabrication of a high power photovoltaic (PV) module, the most critical aspect is the duration for which the module can produce useful power. Reliability and lifetime of photo-voltaic (PV) modules are key factors to system performance and warranty and thus are extremely important as far as PV business is concerned. Outdoor field testing is an accurate method in estimating module lifetime. However, since PV modules commonly come with twenty five years of warranty, testing modules in field for that long period is not feasible. Thus, due to time constraints, many accelerating aging tests have been derived over the years for testing reliability of PV modules. The accelerated test protocols established by organizations like IEC and UL have been adopted worldwide as official tests to evaluate module quality and reliability standards.