Leveraging energy flexibilities for enhancing the cost-effectiveness and grid-responsiveness of net-zero-energy metro railway and station systems

The number of metro railway systems is rapidly increasing, and several projects are being implemented to install renewables and convert overhanging power line-based trains into battery-powered trains. This study comprehensively reveals the energy flexibility potential of a net-zero metro railway system. Various energy flexibility strategies, quantification, and crucial trade-offs are explored to reach high levels of techno-enviro-economic and grid-responsive performance. Energy flexibility strategies, such as forced shutdown, forced charging, peak shaving, valley filling, energy shifting, and synergic control, are implemented to accurately reduce the maximum demand power, increase the self-consumption of self-generated renewables, and limit the import of power from the grid. This study systematically proposes a set of energy flexibility solutions for improving the interchangeable battery-powered net-zero metro railway system without modifying the capital cost. It suggests a cost-effective energy flexibility solution for the case in which the restriction in the capital cost is removed. Swappable battery-powered railway systems without (reference-1) and with (reference-2) renewable energy are simulated as reference cases for energy flexibility analysis. The annual operational cost and net present value (NPV) of reference-2 are −0.9 × 10⁶ and 72.4 × 10⁶ HKD, respectively. These values indicate that the net-zero metro railway system is techno-economically feasible. Without changing the capital cost, the energy flexibility measures help to reduce the annual operational cost 10.3 % lesser and NPV 1.89 × 10⁶ HKD greater compared to those of reference-2. When implementing a few more energy flexibility strategies by incorporating a cost-effective energy flexibility source, the annual operational cost, NPV, and annual maximum grid imported power of the net-zero metro railway system were 26.1 % lesser, 3.9 × 10⁶ HKD greater, and 58.3 % less than those of reference-2. Moreover, the strategies proposed in this study are suitable for sector-coupled systems whether the vehicle demand is lower than or equal to or higher than the building demand.