Photovoltaic (PV) modules are commonly used in off-grid systems and are becoming the default choice of energy conversion technology in such applications. This is primarily driven by falling costs and the above average sunlight in Sub-Saharan Africa and South Asia, where electrification rates are the lowest. Whereas relatively few energy-impoverished communities are in locations whose climate and terrain can support wind- or hydro-based generation, most have enough sunlight for PV-based generation to be practical. This chapter describes the basic operating principles of PV arrays. Circuit models are presented. Methods for estimating the power output under different irradiance, shading, and temperature scenarios are given. Economic, environmental, and social considerations of the use of PV for off-grid electrification are discussed.