This paper proposes a simple behavioural model for photovoltaic modules. This model can be used to characterise current–voltage and power–voltage outputs of photovoltaic modules as a function of solar module temperature and solar radiation intensity. Such a model cannot only serve as a tool to study the I–V curve and its maximum power point characteristics but also to design photovoltaic power systems and power converters used for PV applications. It can also be used for performance rating. This model has first been developed to study the maximum power point characteristics by exploring the existing similarity between the photovoltaic module I–V characteristic and the step response of a first-order system. It has the advantage to use only parameters that are available on the data sheet. To construct the proposed model, measured I–V curves at different working conditions (solar radiation intensity and ambient temperature) were used, then other I–V characteristics corresponding to different working conditions have been used to validate it. The obtained results show a high degree of correspondence between the real outdoor measured I–V characteristics and those given by the developed model.