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Return home6.2. Hydrogen fuel cell electric vehicles
Discover hydrogen fuel cell electric vehicles, producing hydrogen, electrolysis hydrogen, chlor-alkali hydrogen, SMR hydrogen, SMR-CCS hydrogen, coal or lignite hydrogen, and pyrolysis hydrogen, and explore the considerations when adopting FCEVs.
This section explores the potential role of hydrogen fuel cell vehicles (FCEVs) within your fleet.
As discussed in the options for powering a zero or ultra-low emission fleet, hydrogen has the potential to address some of the range limitations associated with battery electric vehicles. Hydrogen fuel cell vehicles can offer longer driving ranges and faster refuelling times.
However, there are currently relatively few hydrogen vehicles available on the market, and the network of hydrogen refuelling stations in Scotland remains limited.
This section provides information to help you assess whether hydrogen fuel cell vehicles may be suitable for parts of your fleet. Due to the limited availability of vehicle models and supporting infrastructure, it is not currently possible to provide comprehensive vehicle comparisons or reliable estimates of costs and emissions savings.
Hydrogen as a power source for vehicles
Hydrogen is the lightest and most abundant element in the universe and contains more energy per unit of weight than any fossil fuel. It can be produced by splitting water using electricity (electrolysis) or by extracting hydrogen from fossil fuels through steam methane reforming. Hydrogen fuel cell vehicles produce zero tailpipe emissions, meaning the environmental impact of hydrogen depends largely on how the hydrogen is produced. Common hydrogen production methods are outlined below.
Although hydrogen has a high energy density by weight, it has a low energy density by volume. As a result, it must be stored either as a cryogenic liquid or, more commonly, as a high-pressure gas. In vehicles, hydrogen is typically stored in tanks at pressures of either 350 or 700 bar.
In a fuel cell, hydrogen undergoes an electrochemical reaction that separates protons and electrons. The flow of electrons generates electricity, while the hydrogen protons, electrons and oxygen from the air combine to produce water. As this is an electrochemical process, there are no harmful tailpipe emissions. The only direct by-product is water. Fuel cell electric vehicles (FCEVs) also include a small battery that stores energy from the fuel cell and powers the electric motor. This battery can also capture energy through regenerative braking.
Hydrogen can also be burned in an internal combustion engine. However, this approach is relatively inefficient and produces nitrogen oxides (NOx), which contribute to air pollution. For this reason, hydrogen combustion is generally not considered the preferred option for vehicle applications.
The main advantage of hydrogen compared with battery electric vehicles is its high energy density and rapid refuelling time. Together, these characteristics could help fuel cell electric vehicles overcome some range and operational constraints in applications where battery electric vehicles may be less suitable.
Producing hydrogen
Hydrogen production methods are often described using colour-based terms. However, there is no universally recognised standard for this colour coding, so it is important to understand exactly how the hydrogen has been produced and the energy sources used in the process. For example, ‘green hydrogen’ generally refers to hydrogen produced through electrolysis, but the associated emissions can vary significantly depending on the source of the electricity used.
To avoid confusion, we refer to hydrogen by its production method rather than by its colour classification. However, some of the most commonly used colour terms are outlined below. Be aware that definitions may differ between organisations and publications.
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Electrolysis uses electricity to split water into hydrogen and oxygen. A direct electrical current passes between two electrodes in water, triggering an electrochemical reaction that produces hydrogen and oxygen gases.
The sustainability of hydrogen produced through electrolysis depends largely on the source of electricity used. In many cases, this may be electricity from the national grid. As with battery electric vehicles (BEVs), hydrogen produced using renewable electricity can be a zero emission fuel. The lowest-carbon hydrogen is typically produced using renewable energy sources such as wind power.
Electrolysis is currently an energy-intensive process, with energy losses of around 30% to 35%, and it requires significant volumes of purified water, typically between 15 and 30 litres per kilogram of hydrogen produced (Kumar & Himabindu, 2019). Although improvements in efficiency are being developed, many of these technologies have not yet been deployed at scale.
Despite these challenges, electrolysis remains one of the most sustainable methods of hydrogen production and has the potential to produce hydrogen
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Chlor-alkali hydrogen is produced through the electrolysis of a sodium chloride (NaCl) solution, typically brine. The primary purpose of this process is to produce chlorine (Cl2), but hydrogen (H2) and sodium hydroxide (NaOH) are also generated as by-products.
The chlor-alkali industry produces more than 250,000 tonnes of hydrogen each year as a by-product of chlorine production. However, around 10% to 15% of this hydrogen is currently unused (Euro Chlor, 2021). The scale of production is largely determined by demand for chlorine, although the use of by-product hydrogen could increase if hydrogen becomes more economically valuable.
As chlor-alkali hydrogen is produced using electrolysis, it has similar sustainability considerations to hydrogen produced through water electrolysis. Its environmental impact depends largely on the source of electricity used. Additional energy is required to process and separate the hydrogen and other outputs, but this production route is generally considered more sustainable and less energy intensive than steam methane reforming (SMR) (Lee et al., 2018).
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Steam methane reforming (SMR) is a process in which methane, typically from natural gas, is heated with steam to produce hydrogen and carbon dioxide. Similar processes can also use other hydrocarbon fuels, such as ethanol, propane or gasoline.
SMR remains one of the most common and cost-effective methods of producing hydrogen. More than 95% of global hydrogen production is currently derived from fossil-fuel-based processes such as SMR. However, the process is carbon intensive, producing approximately 9 to 10 tonnes of CO2 for every tonne of hydrogen generated (Rapier, 2020).
If you are considering the adoption of hydrogen vehicles, it is important to understand how the hydrogen is produced. Hydrogen generated through SMR without carbon capture and storage (CCS) has a significant carbon footprint and may not provide the emissions reductions required to support decarbonisation objectives.
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Steam methane reforming with carbon capture and storage (SMR-CCS) produces hydrogen using the steam methane reforming process, with carbon dioxide emissions captured and stored after production.
The sustainability of hydrogen produced through SMR-CCS depends largely on the proportion of carbon emissions that are successfully captured and permanently stored. It is important to note that not all CO2 emissions can be captured. The Committee on Climate Change (2018) states that more than 95% of CO2 emissions would need to be captured and stored for SMR-CCS hydrogen to be considered a low-carbon fuel.
However, there are currently no large-scale SMR-CCS facilities operating at this level of performance. For example, Shell’s Quest facility in Alberta, Canada, one of the largest SMR-CCS plants in operation, has been reported to capture around 48% of total stack emissions (Global Witness, 2022).
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Hydrogen produced from coal and lignite is generated through a gasification process and is among the most carbon-intensive methods of hydrogen production.
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Pyrolysis hydrogen is a relatively new technology and has not yet been deployed at scale. It produces hydrogen from methane, often sourced from biogas, while generating solid carbon rather than carbon dioxide as a by-product. This removes the need for carbon capture and storage (CCS).
As a result, pyrolysis has the potential to offer emissions performance comparable to hydrogen produced through steam methane reforming with carbon capture and storage (SMR-CCS).
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Naturally occurring hydrogen can be found in underground geological reservoirs. However, these resources are relatively rare and can be difficult to locate and extract economically.
Considerations when adopting FCEVs
The driving range of fuel cell electric vehicles (FCEVs) is generally less of a constraint than that of battery electric vehicles (BEVs). However, the range of hydrogen-powered vehicles available on the market remains limited compared with battery electric alternatives. This is likely to improve as the market matures.
A key consideration is how the hydrogen is produced. As outlined above, only hydrogen produced through electrolysis using surplus renewable electricity has the potential to be a near-zero emission fuel. Other hydrogen production methods are associated with varying, and in some cases significant, upstream greenhouse gas emissions.
There are currently very few hydrogen refuelling stations in the UK, meaning organisations may need to store hydrogen at their own depots. This requires consideration of whether hydrogen should be produced on-site or delivered by a supplier. Producing hydrogen on-site using an electrolyser may be an option, but electrolysis typically involves energy losses of around 35%. When combined with losses in the fuel cell and vehicle powertrain, more than twice as much electricity may be required to deliver the same vehicle mileage as charging a BEV directly. Electrolysis also requires approximately 15 to 30 litres of purified water for every kilogram of hydrogen produced.
Another important consideration is efficiency. While hydrogen has a high energy density by weight, enabling longer driving ranges, the overall well-to-wheel efficiency of FCEVs is significantly lower than that of BEVs and can also be lower than vehicles powered by biofuels.
Studies have found that fuel cell heavy goods vehicles can be four to six times less energy efficient on a well-to-wheel basis than equivalent battery electric vehicles (Zemo, 2021). As a result, substantially more energy is required to power a vehicle using hydrogen than with direct electrification.
This lower efficiency, combined with the relatively high cost of hydrogen, means that FCEVs can be an expensive zero emission option. As shown in Table 16, hydrogen is typically one of the most expensive fuels when comparing the cost of travelling an equivalent distance.
Given the lower well-to-wheel efficiency of FCEVs and the greater maturity of the BEV market, we recommend adopting battery electric vehicles wherever they are operationally suitable. However, hydrogen should not be ruled out for fleet segments that are more difficult to decarbonise, particularly those requiring longer ranges, rapid refuelling or specific operational capabilities.
Table 16 - Cost comparison of different fuels
| Fuel type | Units | Cost/unit | Cost | Fuel kWh | Fuel cell loss | Power train loss | Wheel kWh |
|---|---|---|---|---|---|---|---|
| Hydrogen | kg | £12.50 (1) | £12.50 | 33 | 30% | 8% | 20 |
| Diesel | litres | £1.46 (2) | £8.12 | 58 | - | 65% | 20 |
| Electricity | kWh | £0.22 (3) | £5.27 | 24 | - | 16% | 20 |
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- Hydrogen costs are based on a median UK hydrogen price of £10 to £15 per kilogram.
- Diesel fuel costs are based on AA fuel prices for April 2022 (175p per litre, with 20% VAT deducted) (AA, 2022).
- Electricity prices are based on UK Government data.
Table 16: Cost comparison of different fuels. This table compares 1kg of hydrogen (equivalent to approximately 33kWh of energy) with the cost of delivering the same amount of usable energy to the wheels using diesel or battery electric power. After accounting for losses within the fuel cell and vehicle powertrain, around 20kWh of the original 33kWh stored as hydrogen reaches the wheels.
The 20kWh delivered to the wheels is equivalent to approximately 65 miles of driving in a passenger car or 11 miles in a heavy-duty vehicle (HDV). By working back from this figure using the efficiency of battery electric and diesel vehicles, the amount of fuel energy required can be calculated. Applying the relevant fuel costs then allows the relative cost of travelling the same distance using each fuel type to be compared.
