This paper presents a simple method for evaluating the influence of wiring on the operating conditions of the direct current components in a photovoltaic system design. This method uses electrical circuit theory, electrical resistance modeling, and an iterative calculation approach to address the causality dilemma that exists when estimating voltage reductions in the wires that connect photovoltaic modules to power inverters. This method can be used to estimate the voltage, current output, and power output of each photovoltaic module in a system, and the corresponding total power available at the inverter, given current-voltage (I-V) models for the photovoltaic modules, and the lengths and thicknesses of the corresponding interconnection wiring. This paper uses this method to illustrate the influence that wiring can have on the direct current operating voltage that is needed at the power inverter to achieve maximum power performance for the system. The goal is that this method would be incorporated into software that analyzes the power performance and energy output of photovoltaic systems. (C) 2012 Elsevier Ltd. All rights reserved.