Leveraging building flexibility and regional complementarity to achieve urban zero-carbon power systems: Evidence from Hong Kong and Guangdong

Carbon neutrality accelerates profound green transitions in high-density cities, where building flexibility and regional coordination emerge as promising enablers. However, existing research only assesses flexibility potentials of single buildings or clusters, ignoring its synergistic value across the urban grid or regional cooperation. To address this gap, this study develops a power system planning and operation framework integrating building flexibility and regional cooperation, with Hong Kong and Guangdong’s power grids as a case study. The results reveal that Hong Kong’s building flexibility capacity in load-shifting ranges from 126.48 to 1207.24 MW, positively correlated with load levels but negatively correlated with load fluctuation rates. Residential buildings contribute 54.5% of the total flexibility potential, while office and retail buildings collectively account for 25.8%, with distinct temporal complementarity. Relying on Guangdong’s green power imports enables Hong Kong to realize carbon neutrality at a baseline cost of 53.38 billion USD. The activation of local building flexibility further reduces the cost by 470 million USD and cuts energy storage demand by 60%. Regional cooperation magnifies the value of building flexibility, lowering Hong Kong’s total system cost by an additional 4.8% (2.59 billion USD) and reducing Guangdong’s annual average peak load by 831.74 GWh. Sensitivity analysis reveals that building flexibility participation is strongly negatively correlated with demand response costs within the range of 0–71.43 USD/MWh, and participation saturates once the peak-shaving subsidy hits 214.29 USD/MWh. This work is expected to provide reliable technical support for power system decarbonization in high-density cities and surrounding regions globally.