This section covers the possibility of using hydrogen fuel cell vehicles in your fleet.  

As discussed in the options for powering a zero or ultra-low emission fleet page, hydrogen has the potential to make up for battery electric’s driving range constraints. This is because it offers a greater driving range and faster refuelling. 

However, there is a limited availability of hydrogen vehicles on the market and limited coverage of hydrogen refuelling stations in Scotland.  

This section aims to provide you with the information to consider whether hydrogen fuel cell vehicles may be a suitable option for some of your vehicles. There is still not enough information available for us to give specific vehicle options, and cost and emission 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 breaking water apart with electrical power (electrolysis) or cracking fossil fuels with steam (steam methane reforming). There are zero tailpipe emissions when using hydrogen in a fuel cell vehicle. This means hydrogen production is the biggest contributor to the total emissions.  Methods of creating hydrogen are listed below. 

Although hydrogen has the highest energy density on a weight basis, it is not highly energy dense by volume. This means that for storage and distribution, it must be stored either as a cryogenic liquid, or more commonly as a high-pressure gas. For use in vehicles, hydrogen is generally stored as a gas at either 350 or 700 bar pressure, in tanks.   

In a fuel cell, the hydrogen undergoes an electrochemical reaction, where its single proton and electron are split. The movement of the electrons through the circuit creates electricity, and the hydrogen proton, electron, and oxygen from the air are then combined to form water. As this is an electrochemical process, there are no by-products. The only output is the water produced. In a fuel cell electric vehicle (FCEV), there is an additional small battery, which the fuel cell recharges, and the battery directly controls the vehicle motors (and can make use of regenerative braking).   

Hydrogen can also be combusted like a fossil fuel. However, this process is highly inefficient and produces NOx as a by-product, which is an air pollutant. We wouldn’t recommend using hydrogen in this way for vehicle use.   

The main advantage of hydrogen over battery electric is the fuel energy density and the quick refuelling time. Together, these mean that with a developed refuelling system, FCEVs could overcome the range barrier in some applications.   

Producing hydrogen

The methods for hydrogen creation are often referred to by colour. However, there is no recognised standard for this colour coding, so it’s vital always to verify your hydrogen’s specific source and all the inputs used to produce it. For example, ‘green hydrogen’ generally refers to hydrogen produced by electrolysis, but the emissions produced will vary widely depending on the source of the electricity. We’ll refer to the creation process rather than a colour to avoid confusion. We’ve also listed some of the more common colours below, however this may not match other documents. 

Considerations when adopting FCEVs

The driving range of FCEVs are less of a constraint compared to BEVs. However, there is a limited variety of hydrogen vehicles compared to battery electric. This can only be resolved when the market matures.  

A key consideration is how your hydrogen will be produced. As covered in the section above, only hydrogen made through electrolysis powered by excess renewable electricity is truly zero emission. All other forms of producing hydrogen have varying (and sometimes high) levels of upstream emissions associated with their production.  

There are currently very few hydrogen refuelling stations in the UK, so you’ll likely have to store hydrogen for vehicles at your depots. You’ll have to decide whether to produce your own hydrogen on-site or have it delivered to your depot. Manufacturing hydrogen on-site using an electrolyser could be a viable option. However, there is around a 35% loss in energy during electrolysis. If you combine this with the further energy losses in the vehicle fuel cell and power train losses (outlined in table 16), you’d need over double the electricity to drive the same mileage compared to charging a BEV directly. Electrolysis requires approximately 15-30 litres of pure water per kg of hydrogen, so this would also either have to be sourced or purified on-site.  

Another consideration is that while hydrogen is very energy dense on a weight basis, allowing for greater driving range, the well-to-wheel efficiency is much lower than internal combustion engine (ICE) vehicles, BEVs and vehicles running on biofuels.

FCEV HDVs are four to six times less energy efficient than BEVs on a well-to-wheel basis (Zemo, 2021).  This means that, no matter how your hydrogen is produced, there will be a far greater energy loss compared to other methods of powering your fleet.  

This inefficiency, paired with the higher unit cost of hydrogen, makes it an expensive zero emission option (as outlined in table 16). This shows that the fuel cost of hydrogen makes it the most expensive fuel to travel an equivalent distance, compared with diesel or battery electric.  

Because of the energy loss well-to-wheel of FCEVs, and the greater maturity of the BEV market, we recommend adopting BEVs where possible. However, don’t rule out hydrogen for fleet segments that are harder to decarbonise. For example, if your fleet regularly covers longer driving ranges.