Characterization of Silicon-Based Photovoltaic Cells Using Broadband Impedance Spectroscopy

The growth in photovoltaic (PV) installations makes characterization and condition monitoring essential. In this paper, broadband impedance spectroscopy is implemented for characterization and performance monitoring of silicon solar cells for near real-time operation. An optimized quasi-logarithmic broadband signal is designed to estimate the impedance response of the cells. Electrical equivalent circuits are then modeled from the obtained Nyquist plots and the cell parameters are extracted using complex nonlinear least squares. This procedure can be applied for direct estimation of the internal parameters of the silicon solar cells/module at different operating points. Results show that the implemented broadband characterization yields good correlation to the conventional electrochemical impedance spectroscopy (EIS) at significantly reduced equipment cost and signal acquisition time (of approximately 1s). Based on the variation of the parameters extracted, new models for n-connected series and parallel cells were proposed toward module or array monitoring. A new condition monitoring parameter was also explored, which is the use of the solar cell critical frequency. It is observed that, the determination of the critical frequencies at various operational conditions can be used to further reduce the frequency scanning range and time for easier online implementation using the PV system's associated converters.