In this paper, two control strategies involving "continuous" and "ON/OFF" operation of the diesel generator in the solar photovoltaic-diesel-battery hybrid systems are modeled. The main purpose of these developed models is to minimize the hybrid system's operation cost while finding the optimal power flow considering the intermittent solar resource, the battery state of charge and the fluctuating load demand. The non-linearity of the load demand, the non-linearity of the diesel generator fuel consumption curve as well as the battery operation limits have been considered in the development of the models. The simulations have been performed using "fmincon" for the continuous operation and "intlinprog" for the ON/OFF operation strategy implemented in Matlab. These models have been applied to two test examples; the simulation results are analyzed and compared to the case where the diesel generator is used alone to supply the given load demand. The results show that using the developed photovoltaic-diesel-battery optimal operation control models, significant fuel saving can be achieved compared to the case where the diesel is used alone to supply the same load requirements. (C) 2015 Elsevier Ltd. All rights reserved.