Centralized heat supply systems are well developed in Latvia, and 75 % of heat is produced in cogeneration mode, which is received by 69.5 % of the population. When cogeneration plants operate in the conditions of a free electricity market, it becomes problematic to balance the electricity and heat demand schedules. In the Thesis, the author analyses the application of heat accumulator in order to achieve more flexible operation of cogeneration plants in market conditions. This will significantly increase the number of calculation functions, which creates more uncertainty for making correct production decisions. The author offers a complex calculation methodology using real data in order to evaluate the operating parameters of heat accumulation at different modes. In addition, this methodology is integrated into the decision-making algorithm of the cogeneration plant.