Hydrogen: where is low-carbon fuel most useful for decarbonisation?

Is hydrogen the lifeblood of a low-carbon future, or an overhyped distraction from real solutions?

One thing is certain – the coal, oil and natural gas which currently power much of daily life must be phased out within coming decades. From the cars we drive to the energy that heats our homes, these fossil fuels are deeply embedded in society and the global economy. But is the best solution in all cases to swap them with hydrogen – a fuel which only produces water vapour, and not CO₂, when burned?

Answering that question are six experts in engineering, physics and chemistry.

Road and rail

Hu Li, Associate Professor of Energy Engineering, University of Leeds

Transport became the UK’s largest source of greenhouse gas emissions in 2016, contributing about 28% of the country’s total.

Replacing the internal combustion engines of passenger cars and light-duty vehicles with batteries could accelerate the process of decarbonising road transport, but electrification isn’t such a good option for heavy-duty vehicles such as lorries and buses. Compared to gasoline and diesel fuels, the energy density (measured in megajoules per kilogram) of a battery is just 1%. For a 40-tonne truck, just over four tonnes of lithium-ion battery cells are needed for a range of 800 kilometres, compared to just 220 kilograms of diesel.

With the UK government set to ban fossil fuel vehicles from 2035, hydrogen fuel cells could do much of the heavy lifting in decarbonising freight and public transport, where 80% of hydrogen demand in transport is likely to come from.

A fuel cell generates electricity through a chemical reaction between the stored hydrogen and oxygen, producing water and hot air as a byproduct. Vehicles powered by hydrogen fuel cells have a similar driving range and can be refuelled about as quickly as internal combustion engine vehicles, another reason they’re useful for long-haul and heavy-duty transport.

Hydrogen fuel can be transported as liquid or compressed gas by existing natural gas pipelines, which will save millions on infrastructure and speed up its deployment. Even existing internal combustion engines can use hydrogen, but there are problems with fuel injection, reduced power output, onboard storage and emissions of nitrogen oxides (NOₓ), which can react in the lower atmosphere to form ozone – a greenhouse gas. The goal should be to eventually replace internal combustion engines with hydrogen fuel cells in vehicles that are too large for lithium-ion batteries. But in the meantime, blending with other fuels or using a diesel-hydrogen hybrid could help lower emissions.

It’s very important to consider where the hydrogen comes from though. Hydrogen can be produced by splitting water with electricity in a process called electrolysis. If the electricity was generated by renewable sources such as solar and wind, the resulting fuel is called green hydrogen. It can be used in the form of compressed gas or liquid and converted to methane, methanol, ammonia and other synthetic liquid fuels.

But nearly all of the 27 terawatt-hours (TWh) of hydrogen currently used in the UK is produced by reforming fossil fuels, which generates nine tonnes of CO₂ for every tonne of hydrogen. This is currently the cheapest option, though some experts predict that green hydrogen will be cost-competitive by 2030. In the meantime, governments will need to ramp up the production of vehicles with hydrogen fuel cells and storage tanks and build lots of refuelling points.

Hydrogen can play a key role in decarbonising rail travel too, alongside other low-carbon fuels, such as biofuels. In the UK, 6,049 kilometres of mainline routes run on electricity – that’s 38% of the total. Trains powered by hydrogen fuel cells offer a zero-emission alternative to diesel trains.

The Coradia iLint, which entered commercial service in Germany in 2018, is the world’s first hydrogen-powered train. The UK recently launched mainline testing of its own hydrogen-powered train, though the UK trial aims to retrofit existing diesel trains rather than design and build entirely new ones.

This article is republished from The Conversation under a Creative Commons license. Read the rest of the original article, which includes a look at aviation, heating, electricity and energy storage, and heavy industry.

Header image by FrankHH/Shutterstock