At the LEEE-TISO Test Centre, the most commonly sold modules on the market undergo a series of tests in order to examine their quality and reliability in terms of energy production (Wh/W) and power degradation over time. The Nominal Power of PV module (Pn) measured at STC, the only standard parameter stated by the manufacturers, only partially describes module performance and does not give any information about energy production; in fact two modules with equal power may have dissimilar energy production. The most important aspect of the tests is to compare energy output of modules exposed in identical real outdoor conditions. The aim of these tests is to answer the questions which need to be posed when planning a PV plant. During the eighth test cycle, carried out in 2001-2, the results confirmed the observations of the previous cycles. The testing procedures we developed over the years were slightly modified at the beginning of cycle 8 in order to evaluate the initial degradation of silicon crystalline module. Keywords: Qualification and testing - 1: PV Module - 2: Degradation - 3: