Nowadays, energy companies operate in a highly competitive environment. To maintain the leader position, as a reaction to various changes energy companies must take appropriate steps in a timely manner. Correct assessment of the situation ensures implementation of adequate measures. The situation can be assessed correctly by using a complex approach and/or analysing it according to the specific circumstances. The complex approach also envisages designing of an appropriate model, which studies the impact of changes on the research object, while dealing with the object within a system and as part of the system. The article gives a theoretical background of the system dynamics model in order to evaluate the impact of integration of renewable energy sources (RES) on the operational efficiency of energy supply facilities (power and heat supply) on the national and regional levels, as well as provides the first modelling results.