Partial Shade-Mitigating Effects of Ideal Bypass Diode Insertion in Residential-Scale PV Systems

Abstract

This study focuses on the partial shade-mitigating effects related to the insertion of additional ideal by-pass diodes in residential-scale photovoltaic (PV) systems. For this purpose, quantification of the resulting energy yield benefits is carried out in a representative residential environment. Similar studies addressed the effects of partial shading on PV system output. It is widely recognized that partial shading inflicts disproportional losses to the energy output of PV systems. By-pass diodes are perceived as a potentially promising measure to increase the shade-tolerance of photovoltaic devices. However, most of the similar work either applied time-independent shading characteristics in their analysis or neglected the effects of by-pass diode insertion. The research presented here uses a novel and flexible energy yield model that is based on the physical description of PV systems. In this model the amount of by-pass diodes is incrementally increased from 3 to 5, 10, 12, 30 and 60 per module of 60 cells. The three considered PV system architectures include a central string inverter, per-module power optimizers and per-module micro-inverters. In the main model simulation run, the PV system is located in Eindhoven, The Netherlands and oriented southward with a tilt of 40°. A sensitivity analysis includes various roof orientation directions and various geographic locations in Europe.

The results of this work show that up to 60% of the shade-induced system output losses occurring in the reference case of 3 by-pass diodes are recoverable in the case of 60 by-pass diodes per module depending on the chosen system architecture. Overall the output of the central string-inverter-based PV system is most beneficially affected by the implementation of additional by-pass diodes. Furthermore the validation results of the energy yield model used here show good agreement with a yield model applied in former work. Another observed trend is the profound degree of consistency related to the recoverable fraction of shade-induced system output losses throughout the sensitivity simulations. This means that increasing the amount of by-pass diodes gives way to PV system efficiency improvements in a wide range of partial shading conditions. Consequently, if the economic benefits of increased PV system energy output related to by-pass diode insertion turn out to exceed the associated implementation costs, a widespread sales market for PV systems containing high amounts of by-pass diodes may develop in the future. Therefore economic cost-benefit assessments are recommended to be the focus of interest in future research efforts.