When it comes to buses, will hydrogen or electricity win?
Finding new ways to power vehicles around the world has long been a vital part of tackling the climate crisis. When it comes to small passenger vehicles, there is no doubt that the future belongs to battery-electric cars, rather than those powered by hydrogen fuel cells, the other viable alternative. However, as the size of a vehicle increases, hydrogen can become an increasingly attractive option. For buses, some argue that hydrogen power offers several key advantages over their battery-electric counterparts. Which of them will eventually become the main technology in buses could also have an influence on other forms of transport.
Battery electric and hydrogen fuel cell vehicles have similar propulsion systems. Both store energy to power an electric motor. However, in the latter case, the energy stored in the form of hydrogen is converted into electricity by the fuel cell, rather than being stored in a rechargeable battery.
Electric car sales reaches 3 million in 2020, up 40% from 2019, with some 10 million electric cars now on the world’s roads. Hydrogen car registrations remain three orders of magnitude below this figure, and there are only 26,000 on the road globally, concentrated in three countries: Korea, the United States (mainly California) and Japan. Although there are still several hydrogen fuel cell cars available on the market, made by Toyota and Hyundai, they tend to be more expensive than battery electric cars and can currently be difficult to power: hydrogen is expensive for purchase, and there are far fewer refueling stations than charging points in most places.
But when it comes to larger vehicles, the picture isn’t as clear. As vehicles get bigger, it becomes more difficult to electrify them, with ever larger batteries required. For energy-intensive applications such as long-haul trucks, some experts say hydrogen may be the best option.
Buses fall somewhere between cars and trucks on this spectrum. “The big problem is the mass of the buses,” says James Dixon, a researcher in energy and transport systems modeling at the University of Oxford. “Batteries have a relatively low energy density: the energy density is about 1/40th the energy density of a liquid hydrocarbon fuel, such as gasoline or diesel.” Hydrogen also has a relatively low energy density (the amount of energy that can be stored per unit density or surface area) – about four to five times lower than petroleum fuels, but much higher than electric batteries. , he adds.
China already has approximately 5,300 hydrogen fuel cells buses on its routes, the vast majority of the world’s fleet, but other countries are investing in technology. Neil Collins, managing director of Northern Ireland-based bus maker Wrightbus, said his company was technology-independent and made both battery-powered and hydrogen fuel-cell electric buses. It integrates trip data from its bus operator customers into a tool to model different driving cycles for its vehicles, to help them find the best technical solution for that particular route.
The benefits of hydrogen include shorter refueling times and often longer tank range. But hydrogen technology and infrastructure are more expensive, Collins says, while industry competence for using electric buses is also likely higher than for hydrogen. Dixon also notes that one of the concerns about hydrogen has always been its safety. “It has fairly wide flammability limits and is notoriously difficult to store in a pressurized container without leaking,” he says. “In terms of infrastructure, electricity is much easier because you don’t need liquid fuel trucks driving around.”
Still, hydrogen may be a better option in a city with lots of hills, like Hong Kong, where it’s also very hot and humid, Collins says. “That’s going to be a problem for electric buses, because the cooling and the hills will just drain the batteries,” he says. “But if the city is relatively flat, and travel times are relatively short, and it’s not very hot or very cold, battery power can do a pretty good job.”