Two different approaches to obtaining the time series of solar insolation and wind velocity data for engineering analyzes of power systems are considered. A stochastic model for obtaining solar insolation and wind velocity at daily sampling intervals based on monthly average parameters is described. A comparative analysis of calculating various combinations of complex power systems based on the use of photovoltaic converters (PVC), windmills, and fuel generators by applying different approaches to obtaining stochastic solar insolation and wind velocity data in the VizProRES software package is carried out. Based on the simulated data, a probabilistic assessment of systems with different equipment compositions is given. A comparison of the average costs of kWh obtained proceeding from long-term climatic data and generated based on the monthly averaged parameters has shown that the difference in the results for the “PVC + fuel generator” and “windmill + fuel generator” systems was less than one percent, and for the PVC + windmill + fuel generator was slightly more than 3%, which shows the possibility of using each approach for design analysis of power systems consisting of one or more probabilistic sources.