Tackling emissions from road, rail, aviation and marine transport is critical if the world is to meet the obligations of the Paris Agreement.

In past features we’ve written about the potential of hydrogen and the production scale-up and technologies required to realise this potential. Now we focus on one of the sectors where hydrogen can play a major role.

Significant progress has already been made in many countries to decarbonise electricity generation through renewable energy. These efforts, however, represent merely the initial steps in our collective effort to decarbonise. The transportation sector poses one of the most significant challenges to decarbonisation goals, in part, to the inherent need to store energy for use at another time or location.

In the UK alone, transport accounted for 33% of total carbon-dioxide equivalent emissions in 2018 at 121 tonnes of carbon dioxide equivalent - nearly double that emitted by power stations for energy supply[1]. Progress to decarbonise the UK’s transport sector has been stagnant, with road transport emissions alone up on 1990 levels[2].

Transport emissions account for 33% of UK emissions

Is hydrogen a solution?

Hydrogen may offer the transport sector a route to decarbonisation through large-scale technology expansion. If produced via renewable energy powered electrolysis, steam reformation of methane with carbon capture, or steam reformation of biomass, hydrogen can be utilised as a carbon-free transport fuel. When utilized through a hydrogen fuel cell, it offers opportunity for a variety of transport modes and the only by-products are heat and water vapor. This brings a substantial additional benefit of avoiding local air pollution which is affecting the health of millions of people worldwide.

A diffuse gas in ambient conditions, hydrogen must be compressed in order to minimise the volume of storage required onboard any vehicle. It has an impressive energy density of three times that of hydrocarbon fuels such as diesel and it is this energy density that is appealing to advocates and could lend itself particularly well to heavy and long-range transport applications such as heavy goods vehicles, trains, ships and planes. Furthermore, hydrogen refuelling can be around 15 times faster than electric charging, with four hydrogen dispensers able to do the job of 60 fast charger stations [3].

In addition to looking at hydrogen as a fuel source in its own right, hydrogen-based fuels can also be created and used in much the same way as biofuels.

A sustainable mix to fuel the future

A focus of efforts to decarbonise transport has been electrification via battery electric vehicles (BEVs) such as cars, buses, planes, trains and boats. In addition, railways and train lines operate from a continuous supply of electricity fed via overhead lines.

Electric vehicles, of course, can only claim to be as green as the source electricity used to power them, coupled with the carbon intensity of the vehicle manufacturing process. Additional challenges can include lengthy charging times, limited range, poor comparable energy density, self-discharge and degradation issues, materials expense, and weight penalties. These challenges are being overcome as technology improves, but mainly for smaller and lighter vehicles and less so for large vehicles and/or longer-range applications. This is where hydrogen may have a pivotal role to play.

Biofuels such as biomethane, ethanol and biodiesel also offer the opportunity to provide a store of energy suitable for use in transport applications. Though liquid biofuels can offer many of the advantages of existing hydrocarbon fuels in terms of application and solve many of the limitations experienced by battery electric vehicles, their uptake as a transport fuel has been slow due to supply limitations and socio-environmental issues.

How the decarbonisation of the transport sector will unfold will be a complex interaction between the technical suitability of the technologies and the economics which ultimately govern the price of fuels to consumers. It is likely that no one green technology will become dominant in the transport sector.  An ecosystem of technologies can be expected, which will also interface and couple with other energy sectors, with hydrogen and hydrogen-based fuels playing a crucial role as energy transition gathers pace.

Adam Frew
Renewable energy consultant

Adam is a renewable energy consultant with our clean energy business specialising in renewable hydrogen projects. He has project managed a number of hydrogen projects, including investigating renewable hydrogen for application in marine transport and the feasibility of battery and hydrogen storage technologies.