An important action in addressing environmental challenges is the intelligent and efficient use of energy, including reducing and/or reusing waste energy and using low carbon fuels to reduce GHG emissions. District energy (DE) is a beneficial method of using energy efficiently and effectively at the societal level. Integrating other beneficial energy technologies with a district energy system can considerably improve the efficiency of the combined system. Here, advantages of using thermal energy storage (TES) as a complementary system for solar energy collectors is examined, within the context of the Friedrichshafen district heating system, which utilizes renewable energy. The TES in the Friedrichshafen district energy system enhances its performance. Specifically, TES improves the performance of the solar energy system, reducing annual natural gas consumption and annual fuel costs by 30%.