Forecasting mismatch losses: An empirical study investigating module level inverter- and string inverter systems

Abstract: The purpose of this thesis is to investigate the correlation between irradiance and power output for a system with a module level inverter and a string inverter, respectively. An empirical study has been conducted and inverters in photovoltaic systems will be discussed and divided into two types; module level and string inverters. Different sources of mismatch such as degradation, partial shading and manufacturing issues are also part of the study.    The predicted mismatch for the string inverter system is 2,6 %, based on flash test data for fresh cells, although that value is likely to be underrated due to aging effects not accounted for in the model.   The system equipped with module level inverters generated 6,1 % more energy during the measured period. Although the period of measuring is short and the number of systems compared is small, this study has identified multiple sources that explain why the string inverter system is inferior and is outperformed by the module level inverter system regarding power output.