Characterizing the capacitance of different c-Si PV cell technologies using impedance spectroscopy

Abstract

In conditions of partial shading, the deployment of sub-module maximum power point tracking is known to increase the energy yield of crystalline silicon (c-Si) based photovoltaic (PV) modules. To facilitate PV module designs endowed with an increasing granularity of sub-module power converters, it could be advantageous to exploit the impedance of the c-Si PV cells. For example, it is well known that c-Si PV cells exhibit capacitive effects. However, for such applications, it is critical that the self-capacitance of the PV cells is large enough. As of yet, there are no reports that give a clear overview of the self-capacitance that can be expected for modern industrial c-Si cell technologies. In this work, we report the capacitance of four different industrial c-Si PV cell technologies, namely Al-BSF, PERC, IBC, and SHJ. These capacitance values are obtained by fitting a dynamic model of the solar cell to measurements obtained using impedance spectroscopy in dark conditions. It was found that depending on the cell technology, capacitances in the range of 0.5-6 mF/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> can be expected for operation at maximum power point. Our results show that there is a high potential to remove the input capacitors from sub-module power converters in PV applications, due to the fact that the ripple voltage at the input of the converter is naturally suppressed by the PV self-capacitance.