Quantification of System-Level Mismatch Losses using PVMismatch

Differences in the current-voltage characteristics of photovoltaic (PV) modules connected in series and parallel combinations lead to a loss in the system level power referred to as “electrical mismatch”. As a result of electrical mismatch, the power at the maximum operating point of the PV system is less than the sum of the power outputs of the modules if they were acting independently. In this study, the PVM is match python package was used to model PV modules from two representative flash test datasets. Randomly sampling from that dataset, a variety of PV systems configurations were simulated using the Monte Carlo technique to arrive at distributions of potential configuration-specific mismatch losses. Further, this method was extended to simulate annual energy loss due to mismatch for a sample location. The method provides a framework to quantify electrical mismatch losses for accurate performance modeling of PV systems and enables sensitivity analyses to adopt effective binning strategies for reducing system level mismatch losses.

I. Introduction

Differences in the current-voltage characteristics of photovoltaic (PV) modules connected in series and parallel combinations lead to a loss in the system level power referred to as “electrical mismatch”. The electrical mismatch has been studied in literature [1]–[5] primarily by using one of two methods: (1) synthesizing system level current-voltage (I-V) curves by progressively summing I-V curves of PV modules in series-parallel combinations, as per the system design requirements; and (2) estimating electrical mismatch loss in PV systems composed of modules with known or statistically generated characteristics, as per Bucciarelli etal [1], as summarized by Webber et. al [6]. For a PV system composed of newly fabricated cells, the system level electrical mismatch losses are estimated to be less than 0.01% [5] using Bucciarelli's model. For 1MW PV array mismatch loss is % Kaplanet. al [7]. MacAlpine et. al [8] suggest the commonly used mismatch loss figure of 1-2% should have adequate accuracy for most simulations. With such a wide range of mismatch loss figures found in the literature, we find there is a need for a method to quickly estimate case specific (system size, PV module type, binning size) mismatch loss from the manufacturer flash test dataset for accurate modeling of PV systems energy production.