The Office for Low Emission Vehicles’ Hydrogen for Transport Programme will support 33 fuel cell electric buses for Aberdeen, Belfast and Liverpool. And the ultra-low-emission bus scheme will fund 20 in Crawley, West Sussex.
The issue isn’t as simple whether batteries or fuel cells are better; decarbonising public transport requires careful consideration of the impact on energy networks, among a host of other factors.
The downsides of batteries
Battery electric buses currently have a range of around 120 miles – not enough for a full day. Topping up batteries during a route is one option. For example, Milton Keynes has inductive wireless charging using equipment embedded in the road at bus stops.
Such on-street infrastructure is expensive, though, and can you imagine the demand on the local grid if three buses were to turn up at once expecting to charge? A large city bus station using three chargers simultaneously could need as much as 1.5MW. That’s a lot for the local grid to cope with, especially if it was never designed for such loads.
Currently, most electric buses are slow-charged overnight using 30-60kW chargers for three to four hours. So, creating a new depot in central London for 50 battery buses requires a 2.5MW connection – not easy to find in a city centre where the grid is already under pressure.
At WSP, we’re working with UK power distribution companies to strengthen electrical infrastructure so it can support widespread electric-vehicle charging as well as intelligently managing demand to make use of spare capacity at night. But arguably only cities that were previously home to energy-intensive industries would have the power networks to cope if every bus were to be converted to battery-electric tomorrow.
A role for hydrogen
With a range of 250 miles from one fill, enough for a full day’s work, hydrogen-powered fuel cell electric buses can address some of these problems. Where do they get this hydrogen from, though?
One option is electrolysis, which – unlike battery charging – places a relatively steady demand on the energy network throughout the day. It can also be co-located with greener energy generation. In Birmingham, for example, a redundant industrial area is now home to Tyseley Energy Park where a 9MW biomass power station consuming waste wood is co-located with a green vehicle fuelling facility. Its electrolysis units produce hydrogen for Birmingham’s 22 new fuel cell electric buses. WSP was the owner’s engineer for the construction of the biomass power plant.
Battery technology has had a head start and its lower cost reflects this. However, as the technology matures and production and distribution of hydrogen increases – if, for instance, it replaces methane for domestic heating– it could become an increasingly viable option for heavy-duty uses such as buses. Hydrogen propulsion, although currently expensive, avoids upgrades to the local grid or the installation of on-street infrastructure, both of which could be costly.
It’s about mobility, not just fuel
Hydrogen fuel cells and battery propulsion need to be viewed within the wider context of how we will all get around in the future. And this question needs to consider other factors – including what shape and form public transport will take.
Like other heavy-duty uses, such as road freight and the railways, hydrogen fuel cells for buses may well be part of the new mobility landscape – one where we can hope that emissions at point-of-use will be a thing of the past.
Co-authored by:
Giles Perkins: Head of Future Mobility for WSP in the UK
Mike Pickin: Associate Consultant, Energy for WSP in the UK (and lifelong bus enthusiast)
