How do Hydrogen Buses Work? Are They Fuel Efficient?

Back in June 2021, the Mayor of London, Sadiq Khan, introduced the newest additions to the London bus fleet. A total of 20 new double-decker units have been added to London’s “route 7” bus line, which runs between East Acton and Oxford Circus in the nation’s capital. They are the first buses of their kind to be launched in England, but not the first in the UK. The first in the UK, and the world, was launched in the northeastern Scottish city of Aberdeen.

But why all the fanfare about these hydrogen buses? What makes them so special, anyway? In today’s blog, we’re looking at hydrogen buses; what they are, how they work and what advantages they bring to the landscape of public transport. More broadly, we also want to understand what benefits this technology has and if it could really be the big fuel of the future.

How do Hydrogen Buses Work?

The buses currently being supplied to the UK are wholly made within the country, with the hydrogen element coming from Luxfer, a company based in Nottingham. As Luxfer explains, their hydrogen gas cylinder concept is fairly straightforward, as well as efficient, producing no harmful waste or emissions:

They do call it “the future of transport,” but is their claim justified?

The principal components of Luxfer’s system include:

  • Motor
  • Gas cylinders
  • Battery pack
  • Fuel cells

In the gas cylinders — which are loaded at the front of the bus in the roof — is stored pure hydrogen gas. It is kept at high pressure in its impact-resistant, leak-proof reinforced cylinders. When hydrogen is needed for the fuel cell, the tank regulates the pressure, lowering it, and thus allowing the hydrogen to flow safely from the tank towards the fuel cells which are at the back of the bus.

Once the hydrogen reaches the fuel cells, it passes along the surface of the fuel cell membrane, which splits it into protons and electrons. The result of this is an electric current, after which the hydrogen combines with oxygen from atmospheric air that is blown across the other side of the membrane. The result of that combination, as you might expect, is water.

 The electrical energy produced is then channeled into the battery pack, which charges up and stores the energy to use for vehicle propulsion. This battery pack is very similar in design to those you would see on a regular battery electric vehicle (BEV) like electric cars from Tesla, for instance. Drawing on the electric power from the battery is an electric motor, which in turn sends torque to the wheels to drive the bus forward.

The only by-products of this process are heat and water, so hydrogen power in buses also means we are cutting emissions to zero. The hydrogen bus motor also doesn’t need to run when the bus is idling, which makes it very efficient, too. The bus can also take advantage of additional energy-saving technologies such as regenerative braking, which recycles power back to the battery for an extra boost. This additional power is very useful for adding some much-needed acceleration, especially when the bus has to tackle steep inclines.

Refueling

A hydrogen refuelling station in Seoul South Korea
A hydrogen refuelling station in Seoul South Korea

From the above information we can see that these hydrogen buses essentially work a lot like electric vehicles do in that they rely on stored energy within a battery, which feeds an electric motor that propels the vehicle forward. All of that is very familiar to those who are already au fait with electric vehicle technology, but there is clearly one critical difference between the two. A regular EV doesn’t have a set of hydrogen tanks installed anywhere about its structure, but the hydrogen bus does.

Hydrogen buses rely on electrical power for propulsion, but they are not refueled by plugging them into an EV charging station. They do rely on specialist infrastructure, but in many ways it’s more similar to the traditional refueling experience. When a hydrogen bus needs refueling, it will pull up to a hydrogen dispenser, which on the surface looks in many ways like a regular gasoline pump. There are some differences, of course, since it’s dispensing a gas, not a liquid, but many of the same principles apply.

The bus has a refueling port to which a nozzle from the dispenser is connected. Once the nozzle is sealed in place, hydrogen is simply pumped into the bus and stored in the special tanks. The whole process only takes about as long or a tiny bit longer than regular gasoline fueling. It’s certainly a lot faster than electric charging.

Range and Fuel Efficiency

We’ll cover more about efficiency in the next section on the pros and cons of hydrogen fuel technology, but let’s consider the range first of all. The buses being used in London can manage between 200 and 250 miles when factoring in a full load of 90 passengers. To add some perspective, getting 200-250 miles from a current consumer electric car such as the Nissan Leaf is about the standard for a “decent” long-range EV. There are some EVs that do far better of course, such as Tesla models offering up to nearly 400 miles, but these are small units with little payload. That a large double-decker bus with 90 people on-board can manage 250 miles is very impressive.

Consumer-focused hydrogen technology like that used in the Toyota Mirai, for instance, can typically offer 300 miles or more range.

What are the Pros and Cons of Hydrogen Technology?

A hydrogen fuel cell bus
A hydrogen fuel cell bus

So now we can see how it is that hydrogen fuel technology works on these buses. Let’s now turn to look at the various pros and cons of its use for public buses, and even more broadly.

Pro – Clean Technology with Zero Emissions

Even though cities like London have been working hard to reduce emissions of their bus fleets, it’s hard to compete with a technology that eliminates harmful emissions altogether. Hydrogen is really a very genuinely clean technology because the hydrogen gas doesn’t depend on fossil fuels for its production.

This stands in contrast to traditional BEV buses and cars, which emit no harmful emissions but rely on electrical power to recharge, and how that electrical power is generated causes some controversy over how “green” the technology really is. If the local electrical grid relies heavily on coal power, for instance, then more reliance on coal power as a result of buses and other vehicles going electric isn’t going to help with air pollution, water pollution and other environmental concerns.

In this sense, hydrogen is a smart move because it’s easy to see how hydrogen reduces the carbon footprint of the bus, even when you factor the production of the bus into the equation. As it only emits water and heat, then air pollution in cities can be greatly improved. London has about 9,000 buses in its fleet, which before a major retrofit completed in 2021 still contained about 15 percent nitrogen oxide emissions in its fumes. That has now been reduced to just 4  percent. Once again, though, it’s hard to compete with zero, and that’s why hydrogen delivers.

Pro – Reduced Noise

Since these hydrogen buses are running on electrical energy and don’t feature noisy clanking diesel engines, they are much, much quieter. The average diesel bus makes noise from 80 to 95 decibels depending on whether it’s idling or accelerating. When you apply that to a fleet of 9,000 units running all over the city, that makes a lot of noise. A hydrogen bus can reduce that noise level by at least half, especially when the bus is at a standstill, there will be almost no noise at all when idling.

Reduced noise isn’t just good news for those residents living near bus routes who can now enjoy life with the windows open a bit more, but also for those riding the bus itself. The interior noise on the bus is very low, and the smooth operation of the electric motor also reduces shaking, vibrations and jostling/jerking that is characteristic of regular bus travel.

Pro – Efficiency is Ideal for Urban Use

The range and efficiency of hydrogen buses is ideal when thinking about applying it to an urban space as you would with buses. Such technology is most efficient when used at lower speeds, and city buses only operate within the confines of the city limits. No highway or high-speed driving means that hydrogen-powered technology works at its most efficient rate, all the time. Combine that with the facts about emissions and noise, and you get a nice combination of factors that seem to make these hydrogen buses an ideal choice.

Pro – Fast Refueling

Finally, one big pro that these buses have, especially when compared to conventional electric buses that rely on charging stations, is that the fueling process is much faster and more efficient. Bus terminals can have hydrogen pumps installed into them easily enough which allows for buses to be refueled and ready to go in minutes. This reduces the burden on the number of vehicles required, too. Instead of having certain vehicles out of action for hours at a time while they are properly recharged (even with fast charging), you can refuel in a much faster time.

Con – Cost

The first problem is cost, particularly the cost of the hydrogen fuel. In California, the average price has been as high as $16.51 per kilogram, with 1 kilogram representing about the same amount of energy as a gallon of gasoline. Using a commercial car as an example, the Hyundai Nexo, it can hold about 6.3kg of hydrogen and gets about 60 miles per kilogram. That’s about 360 miles of range, give or take, and it costs $100 to fill up.

The main issue is lack of demand currently, which means there’s no mass production of hydrogen like there is of gasoline. Experts predict that if hydrogen production and distribution were to match that of gasoline, then prices would be lower for hydrogen. On paper, there are many reasons to believe that hydrogen should be cheaper as a fuel. Right now, however, the costs are prohibitively high.

When you apply that to buses, therefore, that’s a big downside because it makes the cost of running the bus fleet greater. That means a greater chunk of the city budget is needed to subsidize them, or that ticket prices have to go up to meet the shortfall.

Con – Refueling Scarcity

Toyotas Fuel Cell Bus going around its designated route in Ginza street at night
Toyotas Fuel Cell Bus going around its designated route in Ginza street at night

Another issue concerning fuel is scarcity of infrastructure. For public transportation applications, this perhaps isn’t a great concern because bus terminals can install their own units and therefore ensure that buses will always get fuel when needed. The problem more broadly however is that fueling infrastructure remains scarce. Looking at California as an example, many eager buyers of the Toyota Mirai were glad to see the introduction of a smartphone app that connected with their car and guided them to the nearest hydrogen fueling station, but then disappointed to find that they were notoriously unreliable.

Many were inactive when drivers arrived, forcing them to go further afield and very far out of the way, which in turn also wastes fuel. Until the hydrogen station is as ubiquitous as the regular gasoline station — or, increasingly, the EV charging station — then it doesn’t stand much chance of competing as a viable alternative to existing fuels.

Con – Safety Issues

Hydrogen technology works, and is improving with new technologies such as those used in the London buses which feature lighter gas tanks that reduce the overall weight of the vehicle, but it can’t be called a “mature” technology just yet. There are many advantages that are apparent, but the unknowns about safety are cause for concern.

For example, hydrogen is a very explosive gas, even more so than gasoline is flammable. An exploding hydrogen tank or multiple tanks on a bus would be a very violent blast that could do serious injury and damage. Even if you ensure the safety of the gas, there are also concerns on noise, especially with buses. The advantage of a noisy bus is that you can always hear it coming, even if you’re hard of hearing. So, we either have silent killers on the road, or we make them noisy, which puts us back close to square 1 when it comes to noise reduction.

Conclusion: Would BEV Buses Not Be Better?

When looking at hydrogen technology, people easily compare it directly to BEV technology that we are increasingly familiar with: we charge the vehicle on a plug-in charging unit, and then let the electrical energy of the battery turn the motors which drive the car. Is the use of hydrogen really an advantage, or more of a hindrance?

On one hand, using hydrogen does mean we are using a more genuinely clean energy source, wherever we apply it. There’s no need to charge up over 1 or more hours, and we get the same additional benefits such as zero emissions and reduced noise levels. On the other hand, hydrogen just feels more complicated to many people, and it feels simpler to make use of more of our existing (and growing) electrical infrastructure.

In addition, we already know that BEV technology is cheaper to run than gasoline, whereas hydrogen is currently more expensive. Even if all the buses in the country were using it, it wouldn’t be enough of a demand to drive down prices of hydrogen to the levels where gasoline is, and then ordinary electric power for cars is even cheaper than that gasoline. With DC fast charging improving on charge times, it may well be better to keep developing the electric infrastructure and technology rather than changing lanes to accommodate hydrogen. Time will tell, of course, but otherwise it’s quite clear that BEV technology is winning the race.

About Tristan Perry

Tristan is a software developer who is passionate about eco-friendly lifestyles - and products, such as green cars! He has loved seeing Nissan and Tesla sell loads of quality EVs over the last decade - with every other car manufacturer finally following suit.

EV adoption seems to be at a tipping point now, with 'ordinary folk' starting to order them too. This is naturally aided by very expensive gas prices, but also a genuine desire for people to try and improve the environment.

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