Accurate field assessment of modules power in large-scale photovoltaic plants using modified sampling and power compensation

Accurately assessing the whole capacity of modules in large-scale PV plants remains challenging due to the huge number of modules and the uneven working temperature of encapsulated cells in modules. In this paper, a new methodology for accurately assessing the whole module power of large-scale PV plants in the field was proposed. First, a representative 400-module sample was selected from a 20,000-module plant following ISO-2859–1:1999. Their I-V characteristics were measured in the field, and corrected to STC according to IEC-60891:2021. Based on the proposed modified sampling method, the 400-module sample was distilled to the 25-module sample. The robustness and advantages of the modified sampling method over traditional sampling were then verified through the comparative experiments. Second, a fine power compensation model, considering temperature differences between p-n junction and backsheet as well as power loss caused by cells’ mismatch, was built to reduce the error in STC-corrected power obtained outdoors. In order to examine its validity and reliability, the modified-sampling-based sample was transported indoors for accurate measurement. After compensation, the modules power along with their distributions obtained outdoors agree well with the indoor-measured results. Compared with uncompensated data, the errors in STC-corrected power obtained outdoors have decreased by more than 73 %. The obtained results demonstrate that the accurate and cost-effective module power assessment for large-scale PV plants can be realized in the field by using modified sampling and power compensation.