AMS Institute, in collaboration with Amsterdam GVB and TU Delft’s public transport operators, has explored the integration of new electric bus chargers into the existing but underutilized energy infrastructure: the metro grid of the Noord-Zuidlijn in Amsterdam. The project devises a strategy to alleviate grid congestion, reduce greenhouse gas emissions, and minimize energy costs while ensuring no disruption to daily metro operations. Following encouraging results, GVB and AMS Institute are moving forward to establish a pilot test site for direct bus charging at Station Noord.
Congestion in energy grids
Given the congestion in energy grids, the options for electrifying public buses are constrained. Central to the energy transition is the shift toward electrification. Our energy generation is increasingly decentralized, with a growing reliance on solar panels and wind energy. However, this transition presents challenges for electricity grids, which struggle to cope with the heightened flow of decentralized energy while maintaining safety protocols. The limitations of the electric grid, designed with a fixed capacity decades ago, pose a significant obstacle to advancing today’s energy transition.
Could bus electrification and metro power be consolidated under a single power contract?
The designated site for the bus chargers sits opposite the Amsterdam Noord metro station, the terminal station of the new Noord-Zuid line. At such locations, transportation grid substations, which serve as power supply points, are typically oversized and underutilized to accommodate the very infrequent worst-case traffic scenarios. By linking the electric bus chargers to the metro substation, the demand for bus charging power could be integrated with the metro power demand and managed within the existing power contract.
Connecting the chargers to the third rail of the metro grid, which runs parallel to the metro grid and provides energy, would offer the most advantages. This setup would enable the bus chargers to draw energy from multiple substations across the Amsterdam Noord region, similar to metro vehicles. Consequently, the load demand would be distributed across various locations, preventing the occurrence of peak demand at a single substation, which could breach the power contract limit.
However, certain considerations must be addressed. Firstly, adding a new stationary load to the third rail would increase transmission losses, resulting in added energy costs. Secondly, there would be an increase in voltage drops on the third rail, which must remain above a certain threshold to ensure smooth metro operations and avoid disruptions in transport services.
Key findings
The results indicate that integrating bus chargers is feasible and profitable under various traffic scenarios. Despite a slight decrease in line voltage, it remained comfortably above the undervoltage threshold, ensuring no impact on daily metro operations. Moreover, the additional transmission losses were minimal, accounting for only about 5% of the daily consumption of the two bus chargers. These losses were offset by the harvesting of braking energy, equivalent to approximately 20% of the daily demand of the bus chargers. This translates to significant savings in energy costs.
The distribution of the bus charging load along the metro line ensured that no single substation bore the full burden alone. Instead, Noord supplied about 57% of the demand, Noorderpark 22%, and Amsterdam Centraal approximately 6%.
Despite utilizing 15% of braking energy for bus charging solutions, a significant portion (over 75%) of metro braking energy continues to be wasted. To address this issue, the implementation of energy storage systems could prove beneficial. This project also delved into the exploration of supercapacitors due to their ability to rapidly accept and discharge high levels of power. Aligned with the short, intense peaks of power associated with departing and arriving metro vehicles in the traction grid, supercapacitors are well-suited for capturing braking power peaks and supplying the power peaks required by accelerating metro vehicles.
Source: AMS Institute
Also check out: What can we learn from charging infrastructure collaboration at the Amsterdam Central Station?