The thermal energy storage system (TES) installation provides the optimization of energy source, energy security supply, power plant operation and energy production flexibility. The aim of this research - evaluate the feasibility of thermal energy system installation at Riga TPP–2. The six modes were investigated: four for non–heating periods and two for heating periods. Different research methods were used: data statistic processing, data analysis, analogy, forecasting, financial method and correlation and regression method. In the end, the best mode was chosen – the increase of cogeneration unit efficiency during the summer.