Hydrogen: Clearing Up the Colours

From green hydrogen to black — what hydrogen colours mean for the climate

September 30, 2020

At Enapter, we get out of bed every day to do what we can to solve climate change. Our approach: creating scalable electrolysers that use water electrolysis to replace fossil fuels with green hydrogen. But what exactly is green hydrogen, if hydrogen is a colourless gas?

We’ll come back to the ‘green’ part later, but industry players use colour codes like ‘green hydrogen’ to distinguish between the different types of technology used to produce H₂ gas. Right now, there’s a huge buzz around hydrogen’s potential to become a key element of the transition to a climate-neutral economy, and this discussion comes with an equally extravagant colour spectrum of hydrogen names. (If you’ve never heard of pink hydrogen, you’re not the only one!) Although hydrogen colours may seem to be a rather beige topic, it’s one that strikes at the heart of the value that a hydrogen economy can offer. So we decided to put things into context and elaborate on what the different colours mean — because even though the gas is colourless, its hue has vivid implications for our planet.

Cracking the hydrogen colour code

Although there is no universal naming convention for hydrogen, almost everyone can agree on the fact that the majority of today’s H₂ production is either green, blue or grey. Let’s start with the most beautiful part of the hydrogen rainbow: 

Green hydrogen, simply put, is hydrogen made with renewable electricity via electrolysis. We believe it’s the oil of the 21st century and the only way to decarbonise society’s liquid and gaseous fuel needs. Electrolysers use an electrochemical reaction to split water into its components of hydrogen and oxygen, emitting zero carbon dioxide in the process. Water electrolysis has been widely used since the 1920s, first with alkaline technology (TA) hydrolysers, followed in the 1960s by proton exchange membrane (PEM) systems, and now, our highly-efficient anion exchange membrane (AEM) electrolysers. Green hydrogen currently makes up less than 1% of overall hydrogen production, but we’re planning to help change that very soon with scaled-up production of our game-changing AEM technology.

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 and carbon dioxide, with the latter then caught through industrial Carbon Capture, Utilisation and Storage (CCUS) projects. CCUS projects seek to make blue hydrogen production climate-neutral by moving the captured CO₂ to underground cavities like spent gas and oil reservoirs or finding industrial uses for the captured gas. However, blue hydrogen can perhaps be better described as ‘low-CO₂ hydrogen’ as the steam reforming process doesn’t actually avoid the creation of greenhouse gases.

Grey hydrogen is essentially any hydrogen created from fossil fuels without capturing the greenhouse gases made in the process. This is where things start to get a bit more complicated — depending on the hydrocarbon used and how much carbon dioxide it releases, it can also be known as brown hydrogen or black hydrogen. If it’s made from lignite (brown coal), it’s most likely brown hydrogen, and black hydrogen if it comes from black coal, although some people call any hydrogen made from fossil fuels either black or brown hydrogen. Hydrogen has been made from coal through the process of ‘gasification’ for more than 200 years. Grey hydrogen from steam reformed natural gas without CCUS accounts for around 71% of all hydrogen production today, while coal gasification makes up the majority of the rest.

Beyond green, blue and grey

As with many things in life, the hydrogen world is not as simple as it first appears. We also have turquoise hydrogen. Turquoise hydrogen is a by-product of methane pyrolysis, which splits methane into hydrogen gas and solid carbon. Some consider that this makes turquoise hydrogen a low-emission hydrogen choice — but this depends on the energy-hungry thermal process being powered with renewable energy and the carbon being permanently stored.

After this, the colours start to get a bit blurred. Pink hydrogen also finds its place in the spectrum, referring to hydrogen generated through electrolysis powered by nuclear energy. Yellow hydrogen is used by some to refer to hydrogen made through electrolysis with solar power, while confusingly, others consider it as electrolysed hydrogen made using power of mixed origin — i.e. the mix of renewable and fossil power actually flowing through the grid.

Finally, white hydrogen is naturally-occurring geological hydrogen found in underground deposits and created through fracking, although there aren’t viable exploitation strategies.

But even if we know what each colour can stand for, one particularly hairy question remains: Which hydrogen colour or colours can help us transition to a climate-neutral economy? 

What hydrogen colours get us to the world we need?

It’s perhaps easiest to start with the colours that will not get us to a world where greenhouse gas emissions are cut to a level that allows us and future generations to live safe and fulfilling lives. Given that the EU is aiming to be net-zero carbon across all sectors by 2050 — including tricky-to-electrify ones like freight and industry — only carbon-neutral or truly low-carbon hydrogen colours have a role to play.

That eliminates grey, brown or black hydrogen. The world’s economies urgently need to make drastic cuts to their CO₂ emissions. Even if grey hydrogen usage might help build hydrogen economy infrastructure, this is worthless if the scaling up of grey hydrogen pushes us further into destructive climate change feedback loops we can’t get out of.

Yellow hydrogen from mixed-origin grid energy can be ruled out for the same reasons as grey hydrogen — it still involves the burning of fossil fuels — while the feasibility and sense of pink hydrogen depend on your (and your country’s) stance on nuclear power. We can also dismiss white hydrogen for now since its extraction is not viable. 

Blue hydrogen appears to be an option, at least on the surface. If carbon capture and storage/utilisation were able to be safely implemented on a large scale, blue hydrogen could play a significant role in helping us transition to a clean hydrogen economy. However, those are some big ifs: CCUS has so far only enjoyed limited commercial success, with the economics and huge CCUS capacity required for wide-scale implementation of blue hydrogen not yet existing. Such technologies can capture more than 90% of greenhouse gas emissions, although, for many projects, it is less. And even if we assume that blue hydrogen production is low-carbon, we must consider the greenhouse gas emissions that come from leaks in natural gas pipelines. Then, just as with nuclear waste, there are potential issues with pushing the problem down the line; there is no certainty that it won’t leak out and little idea of who will be responsible if it does. Blue is, unfortunately, perhaps not so green.

Turquoise hydrogen overcomes some of the technical CCUS difficulties faced by blue hydrogen since it creates a solid carbon by-product, seemingly making this a contender for ‘carbon-neutral’ hydrogen. However, permanently storing carbon at an industrial scale is still an unknown quantity. On top of this, methane pyrolysis is much less efficient than steam reformation for blue hydrogen and is today only carried out at a small scale. 

That leaves green hydrogen

All of this seems to make one thing clear: Only green hydrogen has the climate impact we need, and it is the only true ‘climate-neutral’ solution on offer. But at what cost, you may ask? 

The rather eye-watering price of green hydrogen production (today, €3.50 to more than €10/kg, compared to €1.5/kg for grey hydrogen) has led to many dismissing large-scale water electrolysis using renewable energy as a costly dream. And these doubts may once have been well-founded — but that is no longer the case.  

With the plummeting cost of renewable energy production, rapid improvements in electrolyser efficiencies and the expected cost benefits of scaled-up production, we foresee that our modular electrolysers could produce green hydrogen with a lifetime cost on par with grey hydrogen by 2025. (Read about our green hydrogen pricing assessment here).  

Although this assumes falling power prices, it doesn’t take other possible positive influences into account. These include the introduction of carbon taxes, gas price volatility and gas price rises projected by the IEA, which would take grey and blue hydrogen prices along for the ride. Or the potential to produce green hydrogen in sun and wind-rich areas such as North Africa or the Middle East, and ship this just as fossil fuels are currently transported. 

We also need to consider the unique properties and flexibility of modular green hydrogen production; it lets us create energy storage solutions for efficient use of solar and wind energy, remote microgrids or flexible on-site power-to-gas production — delivered exactly where it’s needed, even away from centralised production of fossil-fuel-based hydrogens. In short, it’s the hydrogen colour that can deliver decarbonisation in both decentralised and large-scale applications, and the only option we can consider as the world faces the burning need to decouple our economies from fossil fuels and protect our environmental systems.  

The hydrogen transition in different parts of the world has already started with an approach that spans the hydrogen colour palette. At this critical stage, we need to be careful that the hype around hydrogen doesn’t let decision-makers sign on to just any colour of hydrogen — because we’re increasingly seeing that only green hydrogen is golden. 


by Joe Dodgshun.