Modeling and Analysis of Carbon Flow for Zero-Carbon Buildings：a Case Study of Power Supply Stations

[Objective] To address the challenges of accurate monitoring and accounting of carbon flows in current building-level energy system carbon emission indices and optimization analysis，this paper proposes a modeling and analysis method for carbon flows in zero-carbon power supply stations. [Methods] First，the connection principles between the load of the power supply station’s load and the upstream power grid，as well as the access method for the DC load of power supply stations，are defined，establishing typical application scenarios for zero-carbon power supply stations. Next，based on the basic network structure of power supply to the station via the transformer area + DC microgrid，a method for calculating the carbon potential at the building-level busbar is proposed. This method comprehensively accounts for factors such as power flow between busbars，renewable energy generation，and the charging and discharging states of energy storage equipment. A model is then developed for allocating and calculating system losses and load carbon flow rates in zero-carbon power supply stations. Based on the measured power at various points and the corresponding busbar carbon potential，carbon flow rates are allocated to system losses and loads according to established principles. The models consider both scenarios of insufficient and surplus renewable energy generation，as well as the impact of energy storage charging and discharging states on carbon potential calculations. Finally，a specific case is presented to demonstrate the detailed process of calculating and allocating the busbar carbon potential and load carbon flow rates in the power supply station. [Conclusions] The calculation results show that when there is insufficient new energy generation，the carbon potential of the AC busbar remains at a maximum of 0.451 kg/kWh； When there is an excess of new energy generation，the carbon potential of the AC busbar drops to a minimum of 0.042 kg/kWh. In addition，energy storage discharge is considered as a power source and has a significant impact on the carbon potential of the DC busbar. [Conclusions] This paper provides theoretical and methodological support for carbon flow analysis in zero-carbon power supply stations，contributing to the advancement of low-carbon operation and energy optimization management in future power supply service centers.