The accelerated tests currently carried out on PV modules reduce the infant mortality as well as improve the production techniques during the manufacture of PV modules. However, they do not completely duplicate the real world operating conditions of PV modules. Hence it is essential to deploy PV modules in the field for extended period of time in order to estimate the degradation, if any, as well as to elucidate the degradation mechanisms. Moreover, PV modules should be tested by specially designed tests in harsh climates. In this paper some of the results obtained on a-Si:H modules from various US companies is discussed.