Upon reading the BBC
's report that UK city Milton Keynes is piloting an electric bus (built by Wrightbus
), I began to wonder, again, about the practicality of this technology.
Here's a video about the Milton Keynes trial below:
Some may recall I wrote about this for Future Cities last year (see Still Waiting for the (Electric) Bus): What it comes down to is a bus's unique duty cycle -- that is, once a bus leaves a depot in the morning it runs a whole lot more than it does not run. For contrast, a car being driven inside a city will alternate periods of running with equal, if not longer, periods of halt. Since the charging happens when the vehicle is not running, a bus presents a unique challenge.
So, with this Milton Keynes news, is the electric bus technology on a roll? Will we all be riding electric buses before long? The answer to these questions will depend on what part of the world we are talking about. Not only because of greater and lesser government support, subsidies, etc. -- which makes a big difference, of course -- but also because of the varying nature of human habitation.
Various technologies converge in making it possible for a city bus to run for 16 hours after a single extended charge. I have ridden Sunwin buses in Shanghai that charge ultracapacitors on their roof very rapidly -- in the 45 seconds that the bus is "dwelling" (taking on and dropping off passengers at a stop). I have also ridden a Proterra bus in San Francisco that, like the Milton Keynes bus, charges only at each terminus and therefore needs about 10 minutes for a top-up charge.
The Wrightbus engages the power source via an induction connection that it makes with a coil embedded in the street. The Sunwin bus does the same via an overhead pantograph that engages with two electric rails suspended above the point where the bus comes to a halt. Storage technologies vary too. The Chinese example uses ultra-capacitors, which are remarkable for the rapidity with which they can charge and discharge. Many other buses -- Wrightbus and Proterra, included -- use batteries. Batteries have become much quicker to charge, but they still lag capacitors in the rapidity of charging and discharging.
In general, dense European and Asian cities are better for electric buses. Unlike American buses, which often have to run very long distances between stops, including on highways and freeways, buses in denser urban centers run shorter distances. They are able to alternate charging opportunities with shorter runs. For the companies that construct power and maintain charging stations, denser areas are also preferable. Density typically translates to shorter runs for cables, as well as easier logistics to send crews to, etc.
All of this sets up a very interesting virtuous cycle: As electric buses become more commonplace, they are more likely to be deployed in areas which are denser, and therefore likely to have higher utilization and ridership.
On the other hand, there's America, where renewed oil and gas exploration/extraction, existing infrastructure for Compressed Natural Gas buses (CNG), and sparsely populated suburbs, will all continue to present a huge challenge to the deployment of electric bus technology.
— Projjal K. Dutta, New York's Metropolitan Transportation Authority's Director of Sustainability Initiatives. (The views reflected in this blog are his personal views and do not reflect those of the MTA. Find him on Twitter: @projjal.)