(709b) Optimization of Combined Heat and Power Generation Using Electrical Energy Storage

Combined heat and power plants (short: CHP plants) simultaneously supply usable thermal and electrical energy. Since the demand for electricity and heat do not coincide over time, it is often not possible to totally use both, thermal and electrical energy. It is therefore necessary, to store the overshoot of energy. Storage for thermal energy is already integrated in state-of-the-art heat-controlled CHP plants. However, the storage of the electrical energy to improve the self-sufficiency and self-consumption rate is currently not implemented. Thus, this study aims at analyzing the potential of integrated electrical energy storage for heat-controlled CHP systems to achieve a higher degree of utilization of the electrical energy.

In this context of additional electrical energy storage systems, different battery types were investigated with respect to their suitability for their integration in heat-controlled CHP plants. Furthermore, a simulation tool was implemented to determine the optimal thermal and electrical energy storage capacity for a given CHP plant based on technical and economic aspects. To enable a detailed investigation of the storage system and its interaction with a heat-controlled CHP plant, the system was described with the help of block oriented models. For this purpose the CHP plant structure, its storage systems and its different control algorithms were modeled using MATLAB and MATLAB Simulink. To simulate the CHP plant model dynamically, load profiles for hot water, space heating and electrical energy demand were used with a resolution of one minute. Furthermore, the daily load profiles depending on weather data and climatic properties were expanded to an annual load profile. With the generated model, optimal storage sizes for thermal and electrical energy could be identified, depending on building type, number of inhabitants, motor characteristics and climatic regions. For this purpose, a conventional heat-controlled CHP plant without an electrical energy storage was examined and the results were compared with heat-controlled CHP plants each with a different additional electrical storage system. In every case, the impact of a variation of the storage size on the self-sufficiency and self-consumption rate was examined. As a result it could be shown that an additional electrical storage system is able to significantly increase the self-sufficiency and the self-consumption rate. Although the optimal storage size can already be determined with the self-sufficiency and the self-consumption rate, also the cost-effectiveness of an additional storage system for electrical energy in the form of a battery was calculated. It was shown that the optimal storage capacity given by the calculation of the cost-effectiveness does not coincide with the storage capacities given by the key figures self-sufficiency and self-consumption rate. Subsequently, the optimal storage size for electrical and also for thermal energy was determined with the help of the data of the electrical energy usage and the calculations of the cost-effectiveness, considering energetic and economic aspects.