From the Editor: The blue hydrogen option – is it climate friendly? [Gas in Transition]

European countries are at the forefront of the energy transition in terms of the installation of renewable energy capacity and in formulation of clear targets, policies and support mechanisms.

The proportion of renewable energy in power generation regularly breaks records, the latest being in the UK, where, in the few days after Christmas, no coal was burned and natural gas use fell to just 6%, reducing the country’s fossil fuel use to the lowest level yet, according to data from UK generator Drax.

While this is a milestone to be celebrated, a windy, warm day at a period of low demand does not represent the demands of the electricity system over a year nor its seasonal and daily variations.

Renewables generated 127.8 TWh of power in the UK in 2020, the highest level ever, and an impressive 40% of total annual generation. But this was still only 17.4% of primary energy demand in a year in which renewables contribution was flattered by depressed demand as a result of the Covid-19 pandemic. While renewables’ contribution is growing fast in the power sector, it remains very low in other sectors of the economy, where the decarbonisation options are more expensive and harder to realise.

Hydrogen requirements

Renewable energy needs to expand rapidly not just to fully decarbonise the power sector, but to create the additional capacity needed to generate green hydrogen. German thinktank Agora Energiewende, in a recent report called 12 Insights on Hydrogen, estimated that 1 GW of electrolysis capacity requires 4,000 full load hours of renewable electricity, which in turn implies between 1-4 GW of renewable energy capacity, depending on the technology employed.

The low end represents offshore wind, which has a high capacity factor, while the high end reflects full dependence on solar PV, which has a much lower capacity factor. 

The UK’s 2030 target of 5 GW of low carbon hydrogen capacity would therefore mean an additional 5-20 GW of renewable energy capacity over and above its power sector requirements, if the push for hydrogen were to depend on green hydrogen alone.

The transitional option, and one to which most European hydrogen strategies remain open, is blue hydrogen produced from the steam reformation of natural gas combined with carbon capture and storage (CCS). In the European context this will almost certainly employ imported gas via pipeline or as LNG, whether used directly or indirectly to make up in other areas for the diversion of declining domestic supplies to blue hydrogen supply chains.

But the economic advantages of blue hydrogen production are clear; it is a proven technology; it is cheap compared with green hydrogen, providing the opportunity to blend blue and green hydrogen streams to provide consumers with a lower cost fuel early on; and it can be done at scale at the same time that renewable energy capacity is being expanded.

But a fundamental question remains – is blue hydrogen genuinely climate friendly?

Key parameters

A new study, On the Climate Impacts of Blue Hydrogen Production published in the journal Sustainable Energy & Fuels suggests that it is, albeit with some important provisos.

The study was undertaken specifically to address the full life cycle impact of blue hydrogen and notes that neither current blue nor green hydrogen production pathways render fully ‘net-zero’ hydrogen without additional CO₂ removal.

It finds that three parameters in particular are of critical importance: the blue hydrogen production technology employed, which determines the carbon capture rate; methane emissions from the natural gas supply chain; and the choice of metric for quantifying the climate impacts. 

Primary finding

The primary finding is that “if methane emissions from the natural gas supply chain are low and CO₂ removal rates are high, the climate impacts of blue hydrogen are similar to those at the upper end of the range of climate impacts caused by green hydrogen.”

But the bar is high. To compete on climate impacts with green hydrogen, blue hydrogen needs a life cycle greenhouse gas (GHG) footprint of no more than 2-3.5 kg CO₂-equivalent/kg. This requires a high CO₂ removal rate and supply chain methane emissions rates below about 1% based on a greenhouse warming potential (GWP) of 100 years and 0.3% if the GWP is 20 years.

As a result, “best-in-class natural gas supply chain management in combination with high CO₂ capture rates is vital for blue hydrogen to be a viable option,” the study argues.

The need for low supply chain emissions puts huge onus on emissions monitoring and measurement, around which there are many methodological and practical uncertainties.

It is also clear for LNG suppliers that to be part of a blue hydrogen supply chain they will need to double down on the minimisation of methane and carbon emissions not just from their own liquefaction operations but from their supply chains, which may require the cooperation of midstream and upstream companies. There are lots of gaps in mid-and upstream methane emissions data and a wide variety in the assessed levels of emissions.

A second essential is that the blue hydrogen plant employs the best technology to maximise the carbon capture rate. The study says carbon capture technology is sufficiently mature to allow long-term removal rates above 90% and that capture rates close to 99% are technically feasible but have yet to be demonstrated at scale.

Steam reforming natural gas lends itself well to carbon capture because in all reformation processes a hydrogen-rich syngas is produced from which the CO₂ can be easily separated with high purity. The study says that oxygen-based technologies with internal heating (autothermal reformers) offer good economies of scale and that their higher natural gas conversion rates should result in more energy efficient and less costly processes, leading to higher capture rates. 

In addition, hydrogen production and CO₂ capture must be integrated to minimise additional energy demand for the latter, for example by employing waste heat from the reformation process to regenerate solvent used in the capture process. Any net electricity import needs to be met by a low carbon energy source.

A further factor is that hydrogen itself exhibits a GWP of 5 over 100 years, the study says, which means that fugitive hydrogen emissions will play a role in determining the full life-cycle climate impact whether from blue or green hydrogen production chains.

The requirements become tougher if a shorter term GWP is used. In policy terms this would reflect an arguably already evident shift in priorities from long-term warming to GHG reductions needed in the next two decades.

In the European context, where domestic gas supply is in decline and import dependency is rising, sourcing gas from countries with low emissions rates and good monitoring practices is likely to become essential in terms of establishing blue hydrogen production chains. If, for example in the US, similar criteria are applied for domestic gas supply chains, low emissions rates and best practice in monitoring will become essential for domestic and export markets alike.

It is clear, however, that blue hydrogen can not be fully climate neutral, owing to supply chain emissions, even if reduced to residual levels, and because capture rates will fall short of 100%. As a result, the paper concludes that “the future of blue hydrogen in a climate-neutral world therefore depends strongly on the extent to which residual emissions can be avoided or compensated for via [additional] CO₂ removal and the availability of geological CO₂ storage sites.”