Consider this: Based on the number of existing bus charging stations in the United States, it would take about four years to fully charge every bus currently in use should they all be converted to electric overnight. With a rising number of transportation companies seeking ways to convert their fleets to electric, the issue of finding the most effective charging approach is fast coming to the forefront.
Discovering the ideal charging solution for your company means understanding a wide variety of factors. Only from this position can you land on a charging approach that effectively serves your fleet and your customers.
Scheduling Philosophies
Schedulers rely on a couple of philosophies for public transportation. The first is to leave time between routes for a bus to begin the next route. That way, if it’s late on a route for some reason, be it weather or an accident, it has time to get started or catch up on whatever the next route is.
In many cases this scheduling approach gives the company a chance to change drivers or allows a driver to grab a coffee, use the bathroom, etc. Additionally, the more variability in a route, typically the longer time a schedule leaves between routes. This is time that can be used for charging. The slack between routes may have to be expanded for some routes to add enough energy to the bus. This is known as between-route charging. Between-route charging typically happens off-road but does not necessarily mean a bus must return to the depot. Instead, the charger may be located in the corner of a parking lot associated with a commercial complex.
The second philosophy is especially true for longer, circular bus routes. In this approach, a company picks points along the route where the bus is likely to be mostly empty, allowing it to wait at that location and charge. This is known as in-route charging.
Both types of charging are valid and useful, but each typically requires different charging infrastructure and different ways of thinking about the route.
Another form of charging, depot charging, is a common methodology. While this method is not the focus of this post, it is certainly a valid, important option to consider.
Understanding the Choice
Both of these philosophies are being challenged by real-time tracking. This technological advancement has forced public transportation companies to strategically place buses based on where the potential problems through the course of the day are, offering flexibility to switch buses in and out on routes in order to catch up and meet the schedule.
So the choice in charging solutions is not a question of between-route or in-route charging. Instead, it’s more about finding a way to fit the charging to the scheduling and routing choices of the company.
For example, between-route charging may appear easier from a charging point of view, because, theoretically, if there is enough time between routes buses can travel to the various charging locations. A company may be able to support more infrastructure at these locations, and to service and maintain it. But the bigger picture may reveal that real estate is not available for all routes, or that some buses may have to travel a significant time to charge and then return to a route. In-route charging may also be required to accommodate an entire transportation system where space is constrained.
Considering the Options
As a company considers charging options, it may encounter schedule risk as it plans out where to locate chargers. It is possible to spend more money than is realistic, especially in cities where between-route charging locations may be difficult to develop. In some situations, digging up the bus stop or pull-off lane to put in a charging solution causes less impairment to the route and requires less space.
Take, for example, inductive or in-road charging. These systems are built into the actual road surface and then paved over. To charge, a bus stops over the place and lowers its own inductive charging plate, minimizing the difference between the two and allowing the charge to take place. This system requires no physical connection but does create small amounts of loss that are not seen in pantograph or direct connecting charging. Additionally, this system limits the amount of power that can be broadcast from the plate to the bus, resulting in smaller amounts of charge per second than with connected charging that is typically used for between-route charging.
Inductive charging means a bus does not have to cover the miles required for between-route charging and a driver doesn’t have to worry about another bus being on its plate when the bus needs a charge. Between-route systems can mean waiting for an available charging station, creating a more complicated schedule. This can especially hold true on cold days when more energy is used to heat the bus than to travel the route.
This type of system is not necessarily better than others, but it does highlight the fact that some systems are more applicable to a certain situation than others. The implementation of these options depends on how you build your routes, the space available and the infrastructure in place.
Considering Detroit
In Detroit, there are four transportation providers. This is a large area with a relatively sparse population for an urban core, and the main routes that the buses use are busy avenues. Buses pull over in the curbside lane for pickup and drop-off, and during rush hour this creates backups behind the buses.
If you start by considering in-route charging in this situation, you find that it may increase the existing traffic delays, which may result in negative reactions from pedestrians and commuters. For Detroit, these routes are probably best-suited for between-route charging, as there are several parallel routes that are a mile or so apart. In this route layout, between-route charging locations might be able to serve six to eight buses from a single charge location, especially on north-south and east-west oriented routes.
For bus routes that are not oriented on straight lines, but are aligned as a fan of routes, it might make more sense to use in-route charging, as routes may have dedicated stops for buses, such as pull-off lanes.
In these situations, picking a single strategy could be detrimental. Instead, a city like Detroit would benefit from considering individual charging strategies based on each route and the built environment.
Conclusion
There is no one-size-fits-all solution for any transportation company — instead, the solution could be a combination for each.
It’s about coming up with the optimal plan for routes and schedules. What’s the frequency of on-time buses? How does a route affect traffic? How does weather affect a route? How does weather affect your bus energy usage? How far do the buses go daily? Do they need enough energy to get back to the yard, or just enough to reach the next charger?
Based on the answers to these questions, as well as an understanding of the charging options available, a transportation company can decide what type of charging is right for each situation.
Curious how transit authorities can electrify? Face the challenges with a comprehensive electrification road map.