A photovoltaic (PV) generator is internally a power limited non-linear current source having both constant current and voltage like properties depending on the operating point. This paper investigates the dynamic properties of a PV generator and demonstrates that it has a profound effect on the operation of the interfacing converter. The most important properties an input source should have in order to emulate a real PV generator are defined. These properties are important, since a power electronic substitute is often used in the validation process instead of a real PV generator. This paper also qualifies one commercial solar array simulator as an example in terms of the defined properties. Investigations are based on extensive practical measurements from dc-dc as well as three- and single-phase dc-ac converters.