Assessment of the Thermal Energy Storage in Friedrichshafen District Energy Systems

The thermal energy storage (TES) of an actual district energy (DE) system is analyzed thermodynamically, using energy and exergy approaches. With a case study, the results for the TES of the DE system are verified with previous studies. The actual case considered is the Friedrichshafen DE system in Germany. This system is solar assisted, uses natural gas as a backup, and is equipped with a TES. The TES stores the surplus solar energy until is needed by thermal energy users of the system. Using solar energy allows the DE system to use significantly less fossil fuel than would otherwise be the case. Seasonal TES, which normally requires significant thermal insulation to adequately reduce thermal losses, is used in the DE system. The use and role of thermal storage in a district energy system is assessed considering the Friedrichshafen DE system. The results show the significant influence of the return temperature of the circulating media (water) from the DE system thermal network. Furthermore, the financial impact of the TES is not limited to a reduction of the operational cost of the DE system but also to an increase in the initial costs for the DE system.