Thermal Energy Storage for District Heating

Abstract

Of the global energy demand, 20% can be allocated to residential energy demand. Most of this energy is produced by fossil fuels, which raises the importance of energy production in a more sustainable way. In order to do this on the level of residential heating applications, the Dutch government aims to make its residential neighborhoods natural gas-free. An often considered solution is making residential areas all-electric. However, when considering the heating of these households based on electricity, high peaks may occur in the electricity grid due to simultaneous heating at times of high demand. This could cause problems regarding the capacity of the electricity grid. Subsequently, the generation of electricity is nowadays associated with relatively high CO2 emissions, raising the awareness for alternative methods of heating. One of these methods is district heating coupled to (more) sustainable energy sources. A problem occurring with this combination is a possible discrepancy between the supply and demand of energy. Therefore, it could be beneficial to implement thermal energy storage in district heating. This research assesses the feasibility of different configurations of thermal energy storage integrated into district heating. For this research, a case study is conducted in which district heating for a residential area coupled with thermal energy storage is modeled. The model is based on the thermodynamic equilibrium of the network and is able to compute the required characteristics and key performance indicators of the district heating network. For the case study, multiple scenarios have been created which assess different distribution characteristics and heat sources. For reference, an all-electric scenario has been designed as well. The results of the case study show that the implementation of thermal energy storage in district heating is able to lower peak loads on the heat source by two-thirds. This implementation goes paired with an increase in levelized cost of energy of 10-16% and 8-73% higher CO2 emissions, compared to district heating without storage and depending on the characteristics of the district heating net and its heat source. However, for certain heat sources, the advantages of thermal energy storage outweigh the drawbacks or thermal energy storage might even be considered to be inevitable. This is especially the case for renewable heat sources, of which its share in the future energy market is considered to be substantial. Also, the results show that every scenario considering district heating performs better on levelized cost of energy and CO2 emissions than the all-electric scenario. When designing new DH projects, it is key that different available heat sources will be considered and that an accurate trade-off is made between the advantages and drawbacks of thermal energy storage. This research is based on the comparison of various scenarios for a case study. Therefore, it does not focus on finding the optimal parameters for either district heating or thermal energy storage. For finding these optimal parameters, future research must be conducted.