This paper presents an approach, based on the harmonic domain (HD), to compute steady-state of single- and three-phase grid-connected photovoltaic (PV) systems. The PV generator component, assumed at maximum power point (MPP) operating point, is represented as Thévenin equivalent which is calculated based on its physical and electrical characteristics. Power electronic converters are modeled via the HD switching matrix concept. The rest of (linear) elements, i.e., filter, transformer, and AC grid, are represented in the HD via simple matrix/vector HD linear relations. The complete PV system is iteratively resolved to match the assumed MPP via a perturbed and observe (P&O)-type technique. The resultant HD model can be used for power quality applications and steady-state initialization. Two case studies are presented.