Hydrogen and leakage in the future energy system – UK studies report

A new study for the UK government estimates the global warming potential of hydrogen at over double previously published estimates.

With hydrogen anticipated to be a major component of the future energy mix, this, in turn, has impacts on infrastructure and in particular the need for preventing leakage at any stage in the supply chain.

The study from scientists at the universities of Cambridge and Reading and the National Centre for Atmospheric Science states that hydrogen is not itself a greenhouse gas but has global warming potential due to its impact on the major greenhouse gases methane, water vapour and ozone at different levels in the atmosphere.

For example, leakage of hydrogen into the atmosphere would decrease the concentration of hydroxyl radicals (OH) in the troposphere (the lowest level in the atmosphere) and thereby increase the atmospheric lifetime of methane and its impact on climate, the study states.

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In addition, the tropospheric ozone would be increased, while there could be decreases in ozone mixing ratios in the upper stratosphere (the second level in the atmosphere).

Moreover, hydrogen leakage would lead to increases in water vapour throughout the atmosphere, with potentially significant increases in the stratosphere.

Global warming potential

Considering a range of scenarios with leakages of up to as high as 20%, the scientists estimate the global warming potential for a 100 year time horizon at 11 ± 5, “which is more than 100% larger than previously published calculations”.

The two previous estimates for the global warming potential were 5 ± 1 and 3.3 ± 1.4.

The study states that much of the difference arises from the inclusion of the stratospheric response, which was not considered in the previous studies, with approximately one third of the global warming potential arising from the changes in stratospheric water vapour.

The majority of the uncertainty arises from uncertainty in the magnitude of the soil sink for hydrogen.

The scientists conclude that leakage of hydrogen into the atmosphere during production, storage, distribution and use will partially offset some of the benefits of a hydrogen-based economy, but the minimisation of leaks needs to be a priority if hydrogen is adopted as a major energy source.

Further, the use of hydrogen provides an opportunity to reduce emissions of species which might be co-emitted during the production of carbon dioxide, such as methane, carbon monoxide, volatile organic compounds and oxides of nitrogen. Maximising these reductions should be a further policy priority.

The study was undertaken for the UK government’s Department of Business, Energy and Industrial Strategy (BEIS).

Hydrogen leakage

A second study for the government from Frazer-Nash Consultancy investigates fugitive hydrogen emissions in a 2050 economy.

Based on a production of 12,000kt/y (476TWh/y), the study finds that emissions could reach 174kt/y, with transport and storage the largest contributor accounting for more than half of the total (the other sectors being production and end uses).

As technologies can be implemented to reduce the key emissions from production and end-users, the dominant emission source is likely to be the gas distribution network repurposed for the transport of 100% hydrogen, due to the magnitude of the throughput in that network, the study concludes.