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The many colours of hydrogen

On 16 December 2021, Northern Ireland’s Economy Minister, Gordon Lyons launched ‘The Path to Net Zero Energy’ – setting three targets in energy efficiency, renewables and the green economy.

The strategy raises ambition on energy efficiency, heat decarbonisation and renewable electricity. It makes an important commitment to making energy more affordable as Northern Ireland transitions to a low carbon society.  

The strategy notably places a significant emphasis on hydrogen as well as heat pumps as low carbon technologies vital to the decarbonisation of heating in homes. It mentions our modern gas network that has the potential to be hydrogen ready. However, one of the questions we should be asking policy makers is what kind of hydrogen is going to be used? And is it going to be better for the planet that fossil fuels, or worse?

How green is Hydrogen?

Mooted as a key energy source for the future, the real question is what type of hydrogen will be used and where will it come from? A recent report warns against using blue hydrogen stating, 'Northern Ireland is not suited for such a transitional journey'. (Source: Hydrogen – Exploring opportunities in the Northern Ireland Energy Transition). 

Analysis carried out by Frontier Economics’ in the report ‘Hydrogen options for Northern Ireland found green hydrogen is the optimal and most likely option for hydrogen production in Northern Ireland.

Currently most hydrogen is produced by steam reforming of methane in natural gas (“grey hydrogen”), with high carbon dioxide emissions. Carbon capture and storage can be used to reduce these emissions, producing so-called “blue hydrogen,” frequently promoted as being a 'low emission' energy source.

However, lifecycle greenhouse gas emissions of blue hydrogen account for emissions of both carbon dioxide and unburned fugitive methane. Far from being low carbon, greenhouse gas emissions from the production of blue hydrogen are surprisingly high, due to the release of fugitive methane. In fact, the greenhouse gas footprint of blue hydrogen is more than 20% greater than burning natural gas or coal for heat and some 60% greater than burning oil for heat (Source: How green is blue hydrogen?). 

Hydrogen production has many colours, just like the old Jason Donovan song. So let's find out what the key differences are between different forms of hydrogen and why it so important in the context of the energy transition.

What is green hydrogen?

In the kaleidoscope of hydrogen colours, green hydrogen is the one produced with no harmful greenhouse gas emissions. Green hydrogen is made by using clean electricity from surplus renewable energy sources, such as solar or wind power, to electrolyse water. Electrolysers use an electrochemical reaction to split water into its components of hydrogen and oxygen, emitting zero-carbon dioxide in the process.

Green hydrogen currently makes up a small percentage of the overall hydrogen because production is expensive. Just as energy from wind power has reduced in price, green hydrogen will come down in price as it becomes more common.

What is blue hydrogen?

Blue hydrogen is produced mainly from natural gas, using a process called steam reforming, which brings together natural gas and heated water in the form of steam. The output is hydrogen – but also carbon dioxide as a by-product. That means carbon capture and storage (CCS) is essential to trap and store this carbon.

Blue hydrogen is sometimes described as ‘low-carbon hydrogen’ as the steam reforming process doesn’t avoid the creation of greenhouse gases.

What is grey hydrogen?

Currently, this is the most common form of hydrogen production. Grey hydrogen is created from natural gas, or methane, using steam methane reformation but without capturing the greenhouse gases made in the process.

What is black and brown hydrogen?

Using black coal or lignite (brown coal) in the hydrogen-making process, these black and brown hydrogen are the absolute opposite of green hydrogen in the hydrogen spectrum and the most environmentally damaging.

Just to confuse things, any hydrogen made from fossil fuels through the process of ‘gasification’ is sometimes called black or brown hydrogen interchangeably.

Japan and Australia announced a new brown coal-to-hydrogen project recently. This project will use brown coal in Australia to produce liquefied hydrogen, which will then be shipped to Japan for low-emission use.

What is pink hydrogen?

Pink hydrogen is generated through electrolysis powered by nuclear energy. Nuclear-produced hydrogen can also be referred to as purple hydrogen or red hydrogen.

In addition, the very high temperatures from nuclear reactors could be used in other hydrogen productions by producing steam for more efficient electrolysis or fossil gas-based steam methane reforming.

What is turquoise hydrogen?

This is a new entry in the hydrogen colour charts and production has yet to be proven at scale. Turquoise hydrogen is made using a process called methane pyrolysis to produce hydrogen and solid carbon. In the future, turquoise hydrogen may be valued as low-emission hydrogen, dependent on the thermal process being powered with renewable energy and the carbon being permanently stored or used.

What is yellow hydrogen?

Yellow hydrogen is a relatively new phrase for hydrogen made through electrolysis using solar power.

What is white hydrogen?

White hydrogen is naturally occurring geological hydrogen found in underground deposits and created through fracking. There are no strategies to exploit this hydrogen at present.

Source: National Grid

As with all choices, the devil lies in the detail. We all have a responsibility to hold government and the energy industry to account on the promises they have made to deliver a Net Zero future and make sure we move as quickly as possible to the cleanest and greenest sources of energy available.