The Pros, Cons and Other Strategic Considerations of Battery-Electric Versus Hydrogen-Fuel Cell Electric Buses
By Doug Parker
DateMarch 14, 2022
In my last IBI Insights article, I provided a general overview on why the transition to bus fleet electrification is accelerating with mass transit agencies around the globe. I observed that this trend is being driven by the rapidly growing political will to take practical steps that combat climate change and reduce greenhouse gas (GHG) emissions.
For transit agencies faced with mapping out a transition strategy for electrified bus fleets, one of the biggest considerations is in deciding on the type of electrification technology to implement within their fleets. While there are various hybrid electric-diesel options available in the marketplace, transitioning to a true zero-emission fleet generally comes down to choosing between battery-electric bus (BEB) or fuel-cell electric bus (FCEB) technology.
As the name implies, BEB technology relies exclusively on battery power, to move buses as well as to keep the lights, heating, air conditioning, and other ancillary systems operating properly. Large capacity lithium-ion (Li-ion) battery systems are by far the most common type used in mass transit buses, offering some of the highest energy density and voltage delivery currently available in BEB solutions.
Overall, Li-ion battery systems offer many key benefits over fossil fuel energy when used for BEB applications. These include lower total life cycle cost, quieter vehicle operation, and superior reliability.
The weight and bulk of the Li-ion battery system required to reliably complete the conventional daily service of a bus had often been considered a major drawback in the past. But ongoing technological improvements have dramatically increased the on-route charge duration of Li-ion batteries relative to their weight and size, making them increasingly practical for use in transit bus fleets.
Major improvements in Li-ion battery density (Watt-hours per kilogram and Watt-hours per cubic metre) have increased their capacity by three to four times over just a few years ago, and researchers continue to improve vehicle battery technology. This can make a huge difference when planning how far and how long a bus can travel from when it leaves the garage until it returns to be recharged.
Indeed, the capital cost to convert an existing diesel fleet to BEBs and install the charging infrastructure to keep them running is significant. But as the global movement to vehicle electrification continues to accelerate, those upfront costs are steadily coming down.
Fuel-cell electric buses
Fuel-cell electric bus technology is based on combining a zero GHG emissions hydrogen fuel cell with a battery. The FCEB battery is of a much smaller capacity than a BEB battery and is constantly recharged through the fuel cell output. Its role is to provide a suitable range of power output.
Some key FCEB benefits include a longer driving range than BEBs before needing to refuel or recharge. FCEB refueling is also much faster than BEB recharging (i.e. Minutes to fill an empty hydrogen tank, versus three to four hours to recharge a depleted BEB battery).
There are, though, some inherent drawbacks to using FCEBs as a clean energy alternative to diesel buses.
For one, the cheapest and most common way to make hydrogen is through steam methane reformation, which in very simple terms converts natural gas into hydrogen. Because it relies on a fossil fuel source, this produces carbon monoxide and carbon dioxide as byproducts. The resulting fuel is referred to as grey hydrogen. If the carbon by-product can be captured and permanently sequestered, the produced fuel is instead called blue hydrogen.
Green hydrogen is the only variety of hydrogen production deemed climate neutral. It is made through electrolysis, which uses electricity to produce hydrogen from water with the by-product being oxygen. While green hydrogen involves zero-emission production, a significant amount of electricity is required to produce it, so green hydrogen still involves emissions unless this electricity is generated from a renewable source such as wind or solar.
Regardless of which type or combination of electric vehicle technology a transit agency chooses to convert its bus fleet to, the transition will require a great deal of pre-planning and analysis that goes beyond the vehicle selection.
From determining the type and number of charging stations to incrementally deploy throughout a phased fleet transition, to identifying where hydrogen refueling or on-route charging should occur, to the charging schedule for each bus in the fleet to minimize peaking in power demand, many critical decision points need to be factored in. Asset management, block scheduling adjustments, and specialized training for operators and maintenance staff are some other key considerations.
Fortunately, management of all these variables can be planned for through full optimization using data intelligence approaches designed specifically for this purpose. These involve modelling for block energy use and facility charging infrastructure operations. We’ll explore these in our next IBI Insights article on bus fleet electrification.
Doug Parker is a transportation systems engineer and planner, specializing in assisting public agencies with applying advanced technology. He is a recognized leader in transit technology consulting, working closely with the transit technology consulting practice across IBI Group. His 33 years of experience spans all public transit modes, including rail, fixed route bus, bus rapid transit, ferries, demand responsive transit, and rural transit. It also includes the full range of transit technologies, including those in support of planning, operations management, public information, revenue management, security, and business intelligence. Doug has been involved with numerous planning, research and evaluation efforts including regional deployment program development, architectures, evaluations, and several Transit Cooperative Research Program projects.
Doug Parker is a transportation systems engineer and planner, specializing in assisting public agencies with applying advanced technology. He is a recognized leader in transit technology consulting, working closely with the transit technology consulting practice across IBI Group.
His 33 years of experience spans all public transit modes, including rail, fixed route bus, bus rapid transit, ferries, demand responsive transit, and rural transit. It also includes the full range of transit technologies, including those in support of planning, operations management, public information, revenue management, security, and business intelligence.
Doug has been involved with numerous planning, research and evaluation efforts including regional deployment program development, architectures, evaluations, and several Transit Cooperative Research Program projects.