Monitoring outdoor performance and photodegradation of a-Si:H modules by evaluation of continuously measured I-V curves

The performance of a-Si:H modules is frequently and continuously monitored during outdoor operation. The simple constant field approximation (three parameters) is applied to fit the I-V curves. Indoor measurements demonstrate the sensitivity of the proposed method to monitor photodegradation. The evaluation of outdoor measurements proves that, with the proposed method, the effect of degradation can be isolated from the effects of temperature and irradiance dependent outdoor behavior of the a-Si:H module. The proposed method relates the overall defect density in the module with its outdoor performance and degradation state.