Sizing and optimizing the operation of thermal energy storage units in combined heat and power plants: An integrated modeling approach

Thermal energy storage technologies are of great importance for the power and heating sector. They have received much recent attention due to the essential role that combined heat and power plants with thermal stores will play in the transition from conventional district heating systems to 4th and 5th generation district heating systems. This paper presents a novel decision support method for sizing and optimizing the operation of thermal energy storage units in combined heat and power plants. To achieve this goal, the method in this paper comprises three steps. The first step provides an approximation of the storage capacity based on the characterization of the thermal load. The second step extends the applicability of the method by enabling the evaluation of the hourly operation of the combined heat and power plant with thermal storage. The third step evaluates the long-term economic effects of retrofitting the combined heat and power plant with a heat storage option. The applicability of the method is illustrated using the example of a coal-fired combined heat and power plant and the study of two scenarios. The analysis of the scenarios shows that the utilization of the energy storage enhances the operational flexibility of the system by increasing the number of hours in which the combined heat and power plant operates at its maximum electrical output and, at the same time, reduces the thermal contribution of the heat-only boilers. The method developed in this work can be applied to carry out the financial analysis of an energy storage project.