Two types of crystalline silicon (c-Si) photovoltaic (PV) modules have been tested in the cold-dry climate of the Gobi Desert of Mongolia, from 2002 to 2012, to verify the preliminary estimation of PV power generation. This study mainly focuses on the analysis of the long-term performance of the PV modules using indices such as energy yield, reference yield, performance ratio (PR), and characterization indices of the main electrical parameters as well as degradation rate. Average annual energy yields were 1880 h for Module 1 and 1789 h for Module 2. Thus, PRs were 0.85 and 0.80, while the average annual reference yield was 2223 h. On the other hand, degradation rates of Modules 1 and 2 were −1.28 and −0.86%/year, respectively. The electrical degradation observed in both modules was due to the loss of short-circuit current as open-circuit voltage reduction was not considered in this field test.