What is blue, green and grey hydrogen? And how can it be used to tackle climate change?

What is blue hydrogen? What is green hydrogen? And how to explain carbon capture? The experts from the Saudi Green Initiative explain the concepts that could prove key to lowering the planet’s emissions

Green hydrogen energy could be a major outlet to reaching net zero (AFP via Getty Images)

When fossil fuels are burnt, by coal-powered factories for example or during petrol refining, carbon turns into carbon dioxide, which is released into the atmosphere amplifying the greenhouse effect and contributing to global warming.

What is carbon capture?

Advances in technology mean carbon can be captured before it is released into the atmosphere. It’s then compressed into a liquid state before being stored underground. The latest advances advocate a system that “reduces, reuses, recycles and removes” carbon. Harmful gases are not only stored, but can be cycled as alternative fuel sources, or as new products such as chemicals or building materials.

Although carbon capture is a relatively new concept, it is gaining momentum as an effective tool to achieve net-zero targets. This week, Saudi Arabia’s Crown Prince Muhammed bin Salman announced that his country will create one of the biggest carbon capture hubs in the world, designed to capture 44 million tons of CO2 by 2035.

The hydrogen rainbow

Hydrogen is one of the most abundantly available elements in the universe and produces much more energy per litre than batteries without releasing any C02.

However, in order to be effectively used hydrogen must be separated from other elements in water and fossil fuels - and here is where it gets a little complicated.

Not all hydrogen is created equal or is equally sustainable. Most of the hydrogen used in plants and factories is grey hydrogen made from natural gas or methane and manufactured using an energy-intensive process which releases significant CO2 emissions.

Blue and green hydrogen, however, are more promising.

What’s the concept?

Like grey hydrogen, blue hydrogen is made from natural gas, but what makes it cleaner is that the CO2 released during the manufacturing process is captured and stored. What results is low-carbon hydrogen that releases no CO2.

Blue hydrogen is currently being produced at industrial scales and could be a sustainable alternative for parts of the heavy industry such as steel manufacturing. However, technology is not there yet, and there are other issues that need to be considered, such as the cost of production and storage, its energy intensive manufacturing process and more recently questions the lifetime viability of carbon storage.

Which brings us to green hydrogen. Less developed than its blue cousin, it could in the long have more potential. Green hydrogen is extracted from water. Only when this process is done using renewable energy or a low-carbon source to split water molecules into hydrogen and oxygen, can it be called green hydrogen.

Green hydrogen can be stored in tanks before being channelled into fuel cells that produce electricity with no harmful emissions. Already in use to power cars, green hydrogen remains a small player on the global hydrogen stage primarily due to cost, but much like renewables, this is likely to drop as it becomes more widely used.

A joint venture signed in 2020 between the Saudi ACWA Power and the Neom company will construct the biggest hydrogen plant in the world. The primary driver behind Saudi Arabia’s green initiatives is the Public Investment Fund, the $500bn sovereign wealth fund chaired by crown prince Mohammed bin Salman.

Find out more about the MGI summit and SGI forum here: greeninitiatives.gov.sa