Scaling Up Battery Swapping Services in Cities
Electrification of urban transportation is at the heart of burgeoning smart-city transformations. Electric vehicles run on batteries and electric motors, and therefore offer the prospect of benefits such as reducing carbon emissions. These anticipated benefits have pushed governments around the world to aggressively incentivize the adoption of electric vehicles. For example, the UK and France plan to ban the sale of new internal-combustion vehicles by 2035 and 2040, respectively. Chinese megacities ration more electric vehicle sales than fossil-fuel car sales by capping the numbers of issued licence plates. Given these trends, over 500 million passenger vehicles on the road, or 30% of the entire fleet, are expected to be electric by 2040.
As electric vehicles thrive, battery swapping is reviving. Battery swapping is an alternative to plugging in cars for battery charging: it refers to refuelling an electric vehicle by replacing the depleted battery on board with a charged one. The revival of battery swapping is driven by its three advantages over plug-in charging: 1) Speed: The swap process takes only 3-5 minutes, whereas using even Telsa's supercharger takes more than 30 minutes to charge a battery to 80%. 2) Compactness: The short service time allows a swapping station to occupy much less space than a plug-in charging station in order to achieve the same service level. 3) Safety: Compared with vehicle owners, service providers can more efficiently charge and maintain batteries. Therefore, battery swapping is widely believed likely to prevail, especially in large cities.
Nevertheless, electric vehicle companies and municipalities are now facing major challenges when they try to scale up battery swapping services in cities:
- Demand Uncertainty and Service Proximity: The infrastructure deployment needs to be dense so that random swapping demands are able to access a swapping station without much detour. The resulting urban swapping station networks are highly decentralized and thus difficult to operate.
- Battery Availability: Swapping stations also need to ensure a high availability of charged batteries in stock to satisfy swapping demands and to avoid queueing. This operational challenge is exacerbated by the decentralized layout of swapping stations, since swapping demands are more variable when disaggregated than when pooled. Consequently, the service provider has to build up massive battery inventories, which are expensive and environmentally detrimental.
- Grid Accessibility: Finally, charging depleted batteries at swapping stations may overload or even destabilize local low-voltage power distribution grids. These "last-mile" grids were often built without allocating enough capacity for electric vehicle charging. Upgrading existing distribution grids would be prohibitive, if not infeasible.
For years, GERAD's researchers have been working on operations research problems concerning greening our urban transportation systems under uncertainty. In particular, Wei Qi and his collaborators within and outside of GERAD have been working on providing deeper understanding of how to scale up citywide battery swapping services in order to cope with the aforementioned challenges. For example, these researchers are examining a "swap locally, charge centrally" network setting where batteries are locally swapped at decentralized swapping stations, and transported to and charged at more centralized charging stations that are connected to grids of sufficient capacity (which are typically of higher-voltage levels or near a substation). They have built models that analytically characterize the intertwined and stochastic operations of stocking, swapping, charging, and circulating batteries between a centralized charging station and decentralized swapping stations. They have also developed a new algorithmic framework combining constraint-generation and parameter-search techniques to solve intricate joint infrastructure planning and operations problems.