Is all the talk about green hydrogen just hot air?
In recent months, there’s been a palpable buzz within the energy sector and other industries about low carbon hydrogen—be it blue, pink or green.
In this article, we’ll focus on and define green hydrogen, talk about the associated benefits and risks, and explain how it can support net zero. We’ll also look at other kinds of hydrogen (H2) production, which have their own associated colour.
What’s green hydrogen – and how does it compare to grey and blue H2?
It’s possible to divide water into its constituent gases – oxygen (O) and H2 – by passing an electric current through the liquid using electrolysers. If renewable energy powers these devices, you’re effectively producing hydrogen without any greenhouse gas (GHG) emissions – giving rise to the term ‘green hydrogen’.
This means it’s theoretically possible to use green hydrogen as the bridge between renewable electricity and a range of applications or uses where few or no climate-neutral alternatives exist. For example, green hydrogen – as well as derived fuels such as green ammonia – could allow wind power to transform into a transportation fuel for container ships. Or solar power could become a feedstock in industrial processes.
This all sounds very encouraging – but doesn’t reflect the reality of most hydrogen production happening today. To understand this, we need to go ‘over the rainbow’.
The hydrogen rainbow
The world’s current rate of hydrogen production – 75 million tons each year – relies upon burning fossil fuels like coal to isolate the gas. Or, it involves splitting methane (CH4) into carbon dioxide (CO2) and hydrogen.
Either way, the carbon-intensive nature of these hydrogen production processes means that the output is generally referred to as grey (or brown or black – depending on the source) hydrogen.
Blue hydrogen represents an improvement upon these types. Although it involves the same process, the CO2 emissions resulting from production are captured and stored by using carbon capture, utilisation and storage (CCUS) technology.
It’s worth noting that removing carbon via CCUS is vital to tackling the climate crisis, according to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC). It states: “The deployment of carbon dioxide removals to counterbalance hard-to-abate residual emissions is unavoidable if net zero… emissions are to be achieved.”
Drax Power Station is at the forefront of developing and running trials with such technology. The plant uses sustainable biomass to generate renewable electricity in a process called bioenergy with carbon capture and storage (BECCS). And a newly-launched, US-based and wholly-owned subsidiary of Drax – called Elimini – is now developing new-build BECCS projects in the United States and beyond.
With regards to green hydrogen production involving renewable power sources, the CO2 emissions at the point of generation are zero.
The benefits and risks of green hydrogen
Research into hydrogen combustion suggests it can generate nitrous oxide (NO ) emissions – a harmful air pollutant. If the scale of hydrogen production rises, producers will need to be vigilant and ensure that NO levels don’t breach international rules restricting air pollution. There’s also a risk of hydrogen leaking into the atmosphere and interacting with other GHGs to increase the potential for global warming, so this is another area where producers will need to be diligent and compliant.
Another consideration regarding green hydrogen production through electrolysis is the availability of both the water and the renewable energy sources. If resources are limited, there’s a risk that the renewable power demands of household and small-scale commercial consumers will be superseded by those of large-scale hydrogen production plants. Similarly, scarce water resources will need to be managed – especially given research that suggests producing a kilogram of green hydrogen requires nine kilograms of water. To summarise:
Green hydrogen and net zero
The International Energy Agency (IEA) has modelling that implies that, to stay on track for net zero, around half of global hydrogen production will need to be clean by 2030. What’s more, two-thirds of this will have to come from green hydrogen, and the remaining third from blue hydrogen.
However, this seems unlikely to happen given the current state of play with green and blue hydrogen production (in terms of scale, risks and cost). On the other hand, it’s possible that investment and development will take place in the sectors where the decarbonisation benefits will be most marked.
The Carbon Trust highlights four areas where this might happen:
1. Greening some existing hydrogen production
High-emitting processes such as oil refining and chemical production often use carbon-intensive (grey or black) hydrogen production methods. However, given that H2 remains the only feasible feedstock for now, these sectors need to work on switching to green hydrogen when and where they can. And do so as quickly as possible.
2. Using green H2 for industrial heat
Processes such as steel manufacturing burn fossil fuels to generate heat, which is then used for melting and vaporising materials, or creating chemical reactions. It’s possible that green hydrogen that relies upon solar or wind power, for example, would be a viable, cleaner option.
3. Improving grid flexibility
Most nations recognise the need to decarbonise their energy systems – a task that, at times when demand exceeds the supply of renewable power, is likely to rely upon stored H2. This hydrogen can be created when production costs less in the context of the wider energy system, and then re-electrified when it’s needed – providing the flexibility required.
4. Tackling hard to abate sectors
Some industries – like shipping and aviation – have a high level of emissions that are hard to reverse or even reduce. In addition, storage technology isn’t advanced enough yet to apply to these sectors. Given these factors, hydrogen (and fuels derived from it) may be able to play a role – although there’s work needed in terms of reducing costs and achieving the scale necessary.
To answer our original question about the value of green hydrogen justifying the hype, it’s fair to say the chatter’s not just hot air. However, industry needs to take care of the potential risks around the creation of green hydrogen. And strive to eliminate the darkest shades of H2 that still dominate production processes.
