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Crystalline silicon PV modules has been in use for long time in many PV applications. It was not expected that PV modules of old technology will last for twenty years. A PV system which was installed in 1979 in the Libyan Desert is still running with a little decrease in the output power and small changes in its designed parameters. The crystalline silicon PV modules have proved of given an acceptable range of its nominal power rating for thirty one years of work According to that, the life time of the crystalline silicon PV modules can be extended for more than forty years, and this will convince module manufacturers to give a PV module warranty for more than 30 years. PV Modules of front glass cover which has been in work for more than thirty years were tested and its IV curves were measured. A measurement setup for outdoor and indoor measurements of PV modules characteristics is used to evaluate the PV modules parameters. This paper presents the measuring results of outdoor and indoor measurements on the PV models which were in work for more than 30 years. A comparison of the current results with the initial designed parameters was made, and the power degradation after this long period of work was measured.