With its potential as an energy carrier that supports an increasingly renewable electricity grid, hydrogen can complement and accelerate other technologies required to deliver net-zero by 2050. Incorporated into the decarbonisation strategies of the UK and other major emitters, hydrogen is gathering momentum as a key pillar of the global green energy transition and has the potential to play an important role in ensuring decarbonisation targets are met.
Blue and green hydrogen
There are two current methods widely considered for large-scale generation of decarbonised hydrogen. Green (zero-carbon) hydrogen is produced either by water electrolysis driven by renewable electricity or directly from solar light by photocatalytic processes (a combined photoelectrocatalytic approach, in which the energy required to split water is provided by both electricity and solar irradiation, is also possible). Blue (low-carbon) hydrogen is derived from natural gas in combination with carbon capture, utilisation and storage (CCUS) technologies. However, there is a fierce dichotomy of opinions within the scientific, industrial, and political communities on the role of blue and green hydrogen in a decarbonised economy. For example, can the “green industrial revolution” pledged by Boris Johnson truly be achieved using a “twin track” approach of both blue and green hydrogen? Whilst blue hydrogen is often maligned as a distraction from decarbonisation efforts, discouraging corporate investment in “clean” technologies by perpetuating fossil fuel use, others consider it a crucial interim measure to facilitate a future hydrogen economy.
Even though we acknowledge that our ultimate goal should be to use green hydrogen produced from renewable-powered electrolysis, this is currently too expensive. This is not just because of the price of renewable electricity, which is rapidly becoming cost-competitive with other energy sources, but rather from the current cost of electrolysers themselves. Photocatalytic water splitting is a low-cost process, but its low efficiency renders it currently economically unviable. According to the International Renewable Energy Agency (IRENA), green hydrogen is projected to become cost-competitive with blue by 2030 (~2.5 USD/kg) and become significantly cheaper by 2040 (<1 USD/kg). In the meantime, lower generation costs and opportunities to repurpose existing infrastructure, could stimulate a rapid scale-up in trade of blue hydrogen in the short-term. If compatible with a sustainable energy system, this presents an opportunity to establish a hydrogen economy that can commence a phased transition from low to zero-carbon generation.
Why blue hydrogen should not be dismissed
Some experts have condemned blue hydrogen as wholly incompatible with a decarbonised energy future. They consider methane emissions in the natural gas supply chain and CO2 emissions from the hydrogen plant as fundamental and beyond any solution. Claiming to present a “best-case” scenario, they go on to suggest the greenhouse gas footprint of blue hydrogen is more than 20% greater than burning natural gas and imply that development is being driven by the self-interest of the Oil & Gas industry. Other experts have challenged those conclusions, which are based on data from a first-of-its-kind steam methane reforming plant with CO2 capture, designed to demonstrate technical feasibility rather than optimise efficiency. They think the original findings lack scientific rigour and present an unrealistic picture and are potentially misleading. Instead, they demonstrate that the climate impacts associated with blue hydrogen can be mitigated by ensuring low methane emissions and high CO2 capture rates. Additional research supports this conclusion and presents blue hydrogen as an attractive bridging technology with similar climate change impacts to green hydrogen, compatible with low-carbon economies.
Another concern of experts is the continued reliance on fossil fuels, which exposes price and supply to market volatility, thereby failing to support the goal of increased energy security. However, as a short-term solution, the benefits of driving investment in and deployment of CCUS technologies arguably outweighs the temporary delay in giving up fossil fuels altogether.
Blue hydrogen in a decarbonised energy future
As with any emerging technology, the need for strict policy is particularly important in the case of blue hydrogen. Meaningful thresholds for methane emissions and carbon capture rates are crucial for ensuring blue hydrogen makes a positive contribution to decarbonisation – indeed to define the criteria that should confer the label of blue hydrogen. If these can be met, blue hydrogen has a pivotal role to play in scaling-up hydrogen volumes in the short-term and driving commercial development of associated infrastructure and technologies along the value chain. For reference, just over 100 megatons (Mt) of hydrogen are produced annually, 1% of which is blue and 0.1% is green. Until commercial-scale green hydrogen production is successfully deployed and becomes cost-competitive, blue hydrogen, which is currently 2-3 times cheaper, offers an attractive bridging technology that, under rigorous regulation, can have a positive environmental impact and support the transition to a decarbonised energy system.
This article drew upon the following reference material:
UNFCCC, Transformational Action Needed for Paris Agreement Targets. 2020, United Nations Framework Convention on Climate Change.
DIT, Hydrogen Investor Roadmap. 2022, Department for International Trade.
IRENA, Geopolitics of the Energy Transformation: The Hydrogen Factor. 2022, International Renewable Energy Agency: Abu Dhabi.
IRENA, Green Hydrogen Cost Reduction: Scaling up Electrolysers to Meet the 1.5⁰C Climate Goal. 2020, International Renewable Energy Agency: Abu Dhabi.
Howarth, R.W. and M.Z. Jacobson, How green is blue hydrogen? Energy Science & Engineering, 2021. 9(10): p. 1676-1687.
Romano, M.C., et al., Comment on “How green is blue hydrogen?”. Energy Science & Engineering, 2022. n/a(n/a).
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IEA, Global Hydrogen Review 2021. 2021, International Energy Agency.
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