Photovoltaic (PV) plants are becoming an ever more popular source of energy. While individual PV panels are quite resilient, failures do happen. Due to the arrangement of interconnections between multiple PV panels in an array and the maximum power point tracking mechanism, the failure of a single panel can influence the output of the whole ensemble. This paper estimates the impact of a single panel short-circuit failure on the output of a series–parallel array. Generally, the array power loss is larger than the contribution of the failed panel. The dependence of this increase on various factors such as the number of panels/strings, the shape of the current–voltage ( I–V ) curve of the panels, and the degree of panel inhomogeneities is investigated. This increase is found to depend most significantly on the shape of the I–V curve of the panel, and only weakly on a range of other parameters. It is, therefore, useful in estimating the impact of panel failures without the need to know many details about the system.