Enterprise N-ERGIE was found in 2000. It supplies heat energy, electricity, water and gas and provides energy efficiency service. N-ERGIE owns Sandreuth combined heat and power plant (CHP), where the largest heat storage tank (33000 m3) is installed in Europe. Before the heat accumulation system establishment the production of electricity was influenced by heat energy demand. The installation of heat storage tank decouples the production of heat energy and electricity at power plant. This gave an opportunity to increase the flexibility of Sandreuth CHP and adjust its operation modes to the volatile situation at electricity market and integrate variable renewable energy in the process of energy production. The construction of accumulation system was lasting almost two years. The costs of this project are approximately 12.4 millions €.