In research, solar collectors and photovoltaic systems (PV/T) are considered, which are one of the most promising systems of renewable energy sources. Electricity, which is produced by photovoltaic panels, has great potential, but there may be technological shortcomings, which do not give maximum efficiency. The main goal of our research is to develop a universal model of heat exchange processes for optimizing the design features of PV/T systems at the stages of design and variability, which allows us to increase the term of service of such systems and their efficiency. The expanded model allows you to change more practical parameters for two coordinates of a flat collector, such as to change the consumption of thermal energy, thermal support of the absorber plate, heat exchange, operating temperature, etc. The results of model investigations correlate with the experimental data. On the basis of the proposed model, a software product for the modeling of PV/T systems was developed and tested on the experimental results of those ready-towear PV/T systems. In the course of carrying out the expansions, depending on the basic parameters, the heating was removed when one segment of the collector was passed by approximately 1.5 °C. The designated increase in temperature was reached at a heat transfer rate of 0.6 m/s, which allows high rates to be achieved. The most optimal will be the heating when passing through the collector by 5 °C, which will allow to reduce the heat transfer rate to 0.2 m/s and significantly reduce the amount of electricity consumed by the pump. The variation of the expanded model allows to implement a wide range of optimization tasks at the stages of designing and optimizing solar collectors and PV/T systems, to take the optimal design parameters to achieve the greatest efficiency and minimum occupancy.