Study on thermo-electric-hydrogen conversion mechanisms and synergistic operation on hydrogen fuel cell and electrochemical battery in energy flexible buildings

The integration with electrochemical battery (high current and high power for fast power response) and H-2 (high energy density) in district buildings can mitigate grid power fluctuation, and provide energy flexibility for renewable supply and demand-side management, whereas the current literature provides few progresses on synergistic operation to stabilize clean power supply and sustainable transition. In this study, an integrated multi-energy system is formulated, consisting of district buildings, distributed renewable systems, a complementary battery-hydrogen storage, H-2 vehicles, and external energy infrastructures (such as power grid and H-2 station). Multiple energy interactions (e.g., renewable-to-vehicle, vehicle-to-building (V2B), grid-to-building (G2B) and etc.) are deployed to enhance renewable penetration, self-consumption, and mitigate grid dependence. A low-grade heat recovery system is proposed to improve the overall energy efficiency throughout the power-gas-power conversion process. Furthermore, a stack voltage model is applied to quantify real-time fuel cell (FC) degradation magnitudes for hydrogen vehicle (HV) transportation and V2B, which will then be equivalent to operational costs for economic feasibility analysis. After that, considering the four-stage prices of utility grid in Guangzhou, an off-power shifting strategy was proposed and implemented for cost saving, together with comparative analysis on charging/discharging priorities between hydrogen and battery. Results showed that the V2B and the off-peak power shifting strategy can improve the energy flexibility and mitigate the power grid dependence, i.e., the V2B and first charging/discharging priority on H2 systems will improve the off-peak renewable energy shifting from 30% to 35%, and the off-peak grid power shifting from 57% to 75%. Meanwhile, the V2B and the proposed grid power shifting strategy can also save the operating costs for HV owners from 14,375 to 7996 CNY/vehicle center dot a, by 44.4% and the whole energy system from 29.47 to 17.21 CNY/m(2)center dot a by 40.6%. Moreover, the application of off-peak power shifting can slow down the FC degradation by 2.35%, due to the deactivation of V2B process during the off-peak period. However, the low energy efficiency on power-H-2-power conversion will lead to a surge of equivalent CO2 emissions from 10.19 to 19.32 kg/m(2)center dot a by 88.22%. Research results can incentivise the stakeholders' participation in a hydrogen-based renewable-network-loadstorage framework with economic benefits, mitigation on fuel cell degradation, and promote the win-to-win collaborations.