The Colours of Hydrogen

Grey, Blue or Green; what’s your favourite colour?

Hydrogen is the lightest and most abundant atom in the universe, accounting for about 88% of all atoms. It is a vital atom; hydrogen is burnt in the core of our Sun, providing us with ample light and warmth for life on Earth.

Despite its abundance, hydrogen is very difficult to produce in its pure form; all those pesky hydrogen atoms keep wanting to combine with other atoms and molecules. For example, in combination with oxygen it forms water, another vital part of life on our planet.

You might have heard that Aberdeen and the North East of Scotland is getting serious about a new hydrogen economy. The idea certainly has a lot of potential. Hydrogen can be used as a very clean and climate-friendly alternative for fossil fuels including transport, domestic and commercial heating, batteries for long-term storage of mains power, energy intensive industries such as steel making, turbines for electrical power, even as a substitute fuel for jet engines. So, hydrogen has a lot going for it.

 The controversy comes when you consider how best to produce the hydrogen. There are three methods of making hydrogen, corresponding to the three colours: grey, blue and green.

Grey Hydrogen

The most popular, and the cheapest, method of producing pure hydrogen is through a process called steam reforming. This is usually done at a chemical plant, applying vast amounts of steam to natural gas (methane) or some other hydrocarbon fuel. The result is, more or less, pure hydrogen and carbon dioxide.

Rather than try to explain all the whys and wherefores of the process, I’m going to refer you to the excellent team at Real Engineering on YouTube:

Blue Hydrogen

This method of producing hydrogen is, put simply, the Grey Hydrogen method but the carbon dioxide is captured as part of the process and put back (sequestered) into the ground. This process is an example of Carbon Capture, Use and Storage (CCUS). Note that this method has not yet been demonstrated anywhere at a scale sufficient to make a difference. You may have heard of the Acorn project here in NE Scotland; this is an attempt to demonstrate the method by returning small quantities of carbon dioxide into exhausted offshore reservoirs under the North Sea. Again, the demonstration will not capture sufficient carbon dioxide to make a significant impact. The earliest demonstration of Acorn will be in 2024. As you can imagine, the cost of Blue Hydrogen is still unknown since it relies on unproven technology.

Green Hydrogen

This method relies on the process of electrolysis. It involves passing an electric current through water which separates the two atoms, hydrogen and oxygen. Each can be captured separately and used in other industrial processes. Note that no carbon dioxide is released in the process so carbon capture is not needed. At this time, Green Hydrogen is a very simple and proven process but relatively expensive compared to Grey Hydrogen. The main expense comes from the cost of electricity. The power industry is exploring ways of routing ‘surplus’ renewable electricity (wind, solar, hydro) to electrolysis plants; such electricity would be very cheap. The economics of this are uncertain and would require careful consideration.

As a Climate Action group, ACA supports the development of Green Hydrogen as the most sustainable option in the long term. I’ve no doubt we will return to this topic again.