Photovoltaic Modules Power Degradation and Lifetime Prediction under Accelerated Damp-heat Conditions Based on Gamma Process

The reliability and lifetime determine the levelized cost of energy (LOCE) of photovoltaic (PV) modules and effectiveness of PV system. Although this theme has attracted researchers attention in recent years, there still lack an effective method to model PV modules power degradation. Therefore, this paper put forward to adopt gamma process to establish the relationship between PV modules power degradation, and temperature, relative humidity (RH). And then PV modules service lifetime is predicted under accelerated damp-heat conditions. Firstly, accelerated damp-heat tests are carried out on three different temperature and RH levels. Based on Peck model, a data transformed method is proposed to obtain more power degradation data under other seven damp-heat conditions. Secondly, gamma process with an exponential transformation is applied to model PV modules power degradation under accelerated damp-heat conditions. The relationship between power degradation and temperature, RH is established by theoretical derivation and validated by experimental data. Then Expectation Maximum (EM) algorithm is proposed to estimate model's parameters. Finally, PV modules lifetime under several different damp-heat conditions is predicted. It is found that PV modules lifetime is approximate 20 to 25 years under (50 degrees C/45% RH) condition. But we also conclude that PV modules lifetime sharply decreases as the increment of temperature and RH. Hence, more factors or other test types are recommended to be considered in later accelerated tests.