Hydrogen fuel cells: All your questions answered

| 12 min
There is a lot of buzz around hydrogen and whether it might replace diesel in the future. But how does the technology work? What are the pros and cons of hydrogen? How does it stack up against electric trucks? Here are the answers to some of the most common questions about hydrogen fuel cells.

What is hydrogen and why is there so much excitement about it?

Hydrogen is a chemical element that is part of many naturally occurring compounds, including water. The hydrogen (H2) used in vehicles is an odourless gas and is normally produced by extracting hydrogen from water or natural gas.

Though there might be much hype today, hydrogen technology is nothing new. In fact hydrogen has been used for a long time to power spacecraft. But we are seeing a renewed interest thanks to a push to decarbonise the transport industry, falling cost of renewables and more detailed strategies from governments around the world to develop the technology further.

How is hydrogen fuel produced?

Steam methane reforming, or SMR, is the most common method for producing hydrogen at large industrial scales. In this process methane in natural gas reacts with steam, producing hydrogen and carbon monoxide. The carbon monoxide undergoes further reactions, generating more hydrogen. Hydrogen can also come from water through a process called electrolysis where water is split into hydrogen and oxygen with electricity.

There are also other sources of hydrogen such as biomass gasification—where plant matter is heated and reacted to produce hydrogen and carbon dioxide—and fermentation, where certain types of bacteria generate hydrogen as part of their metabolism. Hydrogen can also be produced by splitting water in solar cells submerged in water.  

How does hydrogen fuel get distributed?

Though it is possible to distribute hydrogen through pipelines used for natural gas, most of the hydrogen used for fuel today is produced at large plants and then transported with special liquid hydrogen trailers. Hydrogen can also be generated at refuelling stations through SMR or electrolysis. But this approach is generally less effective and costly.

How does a hydrogen fuel cell work?

A fuel cell vehicle works a bit like an internal-combustion engine except that the system doesn’t burn the hydrogen that it draws from a pressurized tank but fuses it with oxygen to produce electricity to power an electric motor. The process takes place in a PEM (Polymer electrolyte membrane) fuel cell made up of sets of thin plates, separated by membranes.

How is being hydrogen used in trucks?

Hydrogen can be used to fuel an internal combustion engine, which is similar to a Compressed Natural Gas (CNG) engine. Another solution is to use hydrogen in a fuel cell where it generates electricity to power the vehicle. Hydrogen can also be used as an auxiliary fuel cell to extend range on a battery-powered electric vehicle.

What are some of the pros of hydrogen fuel?

When hydrogen is used to power a fuel cell, the only by products are water and heat—no pollutants or greenhouse gases. Depending on how the hydrogen is produced it can be an extremely clean alternative to diesel. Hydrogen also packs a punch: 80 kg of hydrogen can deliver enough energy for a truck to cover 800 km! The fueling process for hydrogen vehicles is also quick and easy.

The propulsion in hydrogen fuel cell vehicles is electric. This means the driving experience feels similar to driving an electric truck; no engine noise, a fast start and the possibility to recover braking energy.

What are some of the cons of hydrogen fuel?

Hydrogen is very reactive, so it tends to erode other materials and it’s also highly flammable – factors that make it difficult and costly to transport. Another major problem is the lack of and high cost of building hydrogen infrastructure. Today there are only 337 hydrogen fuelling stations around the world, most of it in Germany and Japan. Although it’s been shown that existing CNG infrastructure can be used to transport and store hydrogen, this is not a good solution for fuel cells which must run on very clean hydrogen.

Hydrogen fuel cells are also expensive to manufacture as production is still small in scale and involves manual processes. Another key cost component is the hydrogen tank which is big and takes up a lot of space. Finally there is the cost of hydrogen fuel which is significantly higher than diesel.

How environmentally friendly is hydrogen?

When hydrogen reacts with oxygen in a fuel cell, the only output is water. So, when a truck is powered by a fuel cell there are no harmful tailpipe emissions. But any measure of climate impact  also has to take into account the production process for hydrogen which is very energy intensive. Most hydrogen today is produced using coal or natural gas. But if the electricity used for production comes from renewable energy sources, the hydrogen fuel can have a close to neutral carbon footprint (this is known as ‘green hyrogen’). Another way to reduce the footprint of hydrogen is Carbon Capture Storage (CCS) which is the process by which CO2 emissions from SMR are captured, transported and permanently sequestered deep underground.

Hydrogen vs. electric trucks, how do they compare?

For any alternative to diesel to succeed it must offer a clear advantage when it comes to cost, range and availability of infrastructure.  Here is how hydrogen fuel cells stack up against electric vehicles:

Cost: Both hydrogen fuel cells and lithium-ion batteries are both more expensive than diesel. The cost of lithium ion batteries however is coming down quickly. Bloomberg predicts that the crossover point — when electric vehicles become cheaper than their combustion engine equivalents — could be as soon as 2022. Because the development and roll-out of hydrogen vehicles has been limited it is difficult to measure similar gains.

Range: Hydrogen fuel cells have greater energy density than batteries, and therefore provide greater range to a vehicle. In fact the energy to weight ratio of a 700 bar hydrogen tank is ten times higher than a battery. Hydrogen fuel cells are also lighter than batteries, which means that hydrogen vehicles can manage a higher payload.

Infrastructure: The development and production of lithium-ion batteries has progressed far further than hydrogen fuel-cells. Electric trucks have proven to be commercially viable, particularly in urban transport. The fueling infrastructure for electric vehicles has also come much further. In the United States for instance there were 20.000 electric charging stations in 2018 and less than 45 hydrogen refilling stations.

Will hydrogen replace diesel or electric trucks?

Hydrogen is gaining a lot of momentum. Most major car and truck companies, including Volvo Trucks, are researching, working on solutions and forming partnerships to develop the technology. But it’s not just the automotive industry that’s waking up to the potential of hydrogen.

With growing concerns about climate change and demands for a ‘green recovery’ from COVID-19, governments are showing greater interest (and investment!) in hydrogen. Just this past May, the EU revealed a €750 billion recovery plan to fund green transport and industries. The plan, which is centred on The European Green Deal, highlights hydrogen as a priority with plans to develop the technology through an investment agenda and free cross-border trade of hydrogen. A European Clean Hydrogen Alliance that brings together investors with governmental, institutional and industrial partners was also announced earlier this year.

Though these developments all speak well for the future of hydrogen in trucking, there are still many hurdles to it making a meaningful climate or economic contribution. One area where hydrogen shows a lot of promise though is in heavy and demanding long-haul transport where it can be used to fuel an electric driveline. This means that rather than replacing electric trucks, which are more suitable for distribution and regional haulage, both technologies can work together to build a more sustainable transport system.

On the question of whether hydrogen might replace the diesel engine; the push for more sustainable transport means that hydrogen will probably replace some diesel vehicles. Particularly if there is a clear business case and competitive advantage to do so.

Alternative fuels: Assessing the pros and cons

Hydrogen fuel cells, electric trucks, biofuels, bio-LNG…the list of different alternatives to diesel just seems to be growing. As a transport operator it can be difficult to understand and navigate the alternative fuel landscape. To help you, I have prepared a guide that gives an overview of how each technology works and the pros and cons they carry. 

Lars Mårtensson

Lars Mårtensson works as Environment and Innovation Director at Volvo Trucks.

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