Temperature and irradiance have a considerable impact on the efficiency of a water-pumping photovoltaic system. Thus, a flexible and effective model is required to examine how to maximize its performance. This chapter details the development of an accurate mathematical model for the photovoltaic (PV) pumping system using a multi-model approach. The PV system's behavior under varying environmental conditions is reflected through a multi-model structure consisting of eight linear local models that use a convex polytopic transformation in conjunction with nonlinear weighting factors. Each local model represents the PV system in a precise zone of its operating domain. The fusion of these models, after being assigned corresponding weighting factors, results in an innovative modeling framework that facilitates the design of robust and real-time control strategies to effectively optimize Maximum Power Point Tracking and enhance system efficiency. Simulation results confirm the model's accuracy and its high capability to describe the behavior of the PV system under various climatic conditions of temperature and insolation.