The measurement of current–voltage (J–V) characteristics is one of the most straightforward methods for the characterization of solar cells. Consequently, an accurate knowledge of its meaning is of high relevance for the comprehension and technological feedback of these devices. The internal series resistance is one limiting parameter of the fill factor and the efficiency of these devices. A second limiting parameter is the p-n junction space charge region recombination. In this paper, we present a method to determine the lumped series resistance by combining the J–V characteristics in the dark and under 1-sun illumination. As a first approximation, the lumped series resistance under illuminated conditions is used for the dark J–V characteristic at small currents. Based on this, we present a method to quantify resistive losses and space charge region recombination only from the dark and illuminated J–V curves so that a simple separation of both losses becomes possible with all inline cell testers.