Understanding field failure and degradation modes in solar photovoltaic (PV) modules is very important for various reasons especially for this widely used technology. The University of Applied Sciences Ostwestfalen-Lippe in Höxter owns photovoltaic-modules of different cell types, sizes and operation periods in German weather conditions. This paper presents a detailed degradation investigation and performance parameters analysis for chosen samples of polycrystalline, monocrystalline and thin film modules in the laboratory and outdoor test conditions after 10 years of exposure. The obtained measurements were standardized and then compared with the warranted values of the manufacturer’s datasheets for each module type. The real outdoor measurements for the larger units show that the maximum power Pmax after 10 years of exposure for polycrystalline, monocrystalline and amorphous thin film modules had declined by: 8.47%, 37.67%, and 19.05% respectively, which translates to an annual linear degradation rates of 0.652%, 3.67%, and 1.465% for each type respectively. While the maximum power output of the smaller units had declined by 19.05%, 19.36%, and 21.75% for polycrystalline, monocrystalline and amorphous thin film modules respectively, which also translated to annual linear degradation rates of 1.48%, 1.67%, and 0.6% for each type respectively. On the other hand, the laboratory tests for these modules show that there is a clear variation with the obtained outdoor results, where the Pmax for the same larger units had declined by 39.6%, 57.4%, and 82.5% for polycrystalline, monocrystalline and thin film modules respectively, While the Pmax output of smaller units had declined by 51.2%, 39.38%, and 9.39% for polycrystalline, monocrystalline and thin film modules respectively, The comparison of the efficiency and fill factor parameters for the obtained results with the manufacturer’s data shows that the outdoor measurements introduce close results than the laboratory results. The discoloration of the encapsulant is the most frequently occurring visually observable defects on the modules.