This paper presents an evaluation of the performance degradation of photovoltaic modules after twelve operation years in a steppe region environment in Algeria. The objective is to understand the different degradation modes of the photovoltaic modules and associated factors and their impact on the electrical properties (V-oc, I-sc, V-max, I-max, P-max and FF) using the degradation tests of IEC 61215 qualification standard and the electroluminescence test. The experimental results show that yearly degradation rates of the maximum power output P-max present the highest possible loss, ranging from 2.08% to 5.2%. Additionally, the results show that the short-circuit current I-sc comes second with yearly degradation rates spanning from 2.75% to 2.84%. Finally the open-circuit voltage V-oc is the least affected, with yearly degradation occurring from 0.01% to 4.25%.