The article highlights the problems of distributed energy generation and focuses on solar-diesel hybrid power plant modelling and optimization. Designing power systems based on renewable energy sources includes a very relevant task of building mathematical models of such systems and their elements. The article presents an approach and definition of mathematical models describing photovoltaic-diesel (PV-D) hybrid power system elements used in decision making processes as a part of PV-D operation control. An overview of PV module output power, performance and temperature models is given. Along with the analysis of the specific fuel consumption dependencies on the operating power of the diesel generator, an example of diesel power plant unit commitment is shown.