Research on economy and energy flexibility optimization for existing buildings based on thermal and electrical energy storage

Building energy system retrofits is an effective solution to address the rapid urban development and clean energy system reform in the future. The economic benefits and energy flexibility potential from existing building energy system retrofits are substantial due to large amounts of existing buildings. To improve economy and energy flexibility of existing buildings, a study on building energy system retrofits was carried out. Two retrofit solutions were primarily proposed, respectively the photovoltaic with thermal energy storage (PV-TES) system and photovoltaic with hybrid energy storage (PV-HES) system. Then, a mixed-integer linear programming (MILP) model was developed to simultaneously optimize the capacity and operation of energy storage systems to minimize the annual total cost (ATC). A comparative evaluation of retrofit solutions was presented based on economy, environment, and energy flexibility. Furthermore, an analysis of key factors was conducted for the PV-HES system. The results showed that the PV-HES system performed better in economic efficiency and energy flexibility compared to the PV-TES system. While the PV-HES system exhibited poor environmental efficiency. The optimal capacity of the battery was affected by time-of-use (TOU) tariffs, PV generation, and battery cost. The findings of this study have offered a guidance to existing building energy system retrofits.