Accelerated life tests (ALTs) are among destructive tests in which a product is subjected to an overrated parameter condition that leads failing of the product in a short amount of time. The test results of an ALT can be used for estimating the service life time of the product under normal condition and to determine the reliability information of the product. In the process of an ALT, the test units of a product are subjected to higher than normal levels of one or more accelerating parameters such as stress, voltage, temperature and so on. Then, thefailure rate and the reliability of the test units is determined and based on extrapolation methods, the normal service life and reliability of the product is obtained. This needs the lifetime models as functions of the accelerating parameters. Available standards in this fieldare often established based on qualitative procedures in the framework of pass/fail tests. These standards usually do not deal with lifetime of the product based on mathematical and quantitative models. This thesis investigates the degradation in performance of PV cells based on ALT using mathematical and physical models. To obtain the performance criteria and dominate factors in aging of the PV cells, various standards and existing test results are investigated. Then, a few test procedures are developed and proposed to perform ALT for the PV cells in order to estimate the lifetime and reliability function of the cells using mathematical Log-linear, hazard function models, and the physical model based o Eyring models. For preparing testing conditions, an experimental test setup including a controllable heat chamber with uniform heat distribution is designed and developed. The test results are used for the estimation of reliability, mean time to failure, and hazard function for the PV cells samples. Keywords : Accelerated Life Test; Aging of PV cells; Eyring Generalized Model; Hazard function; Log Linear Relationship; Photovoltaic; Proportional hazard; Reliability function.