Understanding Line Pack Is Key in a Hydrogen Future

At the heart of managing any energy system is the ability to balance supply and demand. In the UK, electricity network rebalancing occurs every 30 minutes, while the gas network does so once a day. Daily rebalancing allows suppliers and offtakers to input and draw gas instantaneously, which is key to achieving energy market liquidity and price harmonization across the network. This keeps end-user costs down and provides security of supply, with gas always available at the desired flow rate and pressure, despite moving through the pipelines at a walking speed. The instant availability of gas is enabled by intrinsic storage in the network infrastructure itself—an undervalued yet critical service called line pack.

Line Pack Is Crucial for Energy Security

Line pack is simply the volume of gas packed into the pipelines of the transmission system. It can be conceptualized as a buffer—just as extra water may be contained in a hose to ensure a steady flow when turning the tap on, line pack ensures there is always enough natural gas supply to meet demand despite unpredictable within-day fluctuations. Line pack can “swing” throughout the day, with a minimum value enabling gas distribution networks to run safely and meet demand, and a maximum value allowing a feasible route for incoming supply and ensuring infrastructure safety and integrity.

An average gas day in the winter of 2023/2024 saw a line pack swing of 26 million cubic meters, equivalent to 282 GWh—enough energy to power 97,000 UK homes for an entire year. Incredibly, line pack swing reached double this value in 2021. Analysis by the University of Birmingham revealed that the UK benefits from approximately 100 TWh of cumulative daily line pack flexibility from its natural gas system each year. Hypothetically, a service priced at 1p/kWh would value this at £1 billion, highlighting the economic benefits of the energy system flexibility currently provided by line pack. But what role will line pack play in a net-zero future when natural gas is no longer the primary energy vector?

Line Pack in a Hydrogen Future

Amid global efforts to transition to carbon neutrality, hydrogen has been identified as a key enabler for reducing reliance on fossil fuels. The European Hydrogen Backbone initiative aims to accelerate hydrogen adoption to support decarbonization and increase energy security, envisioning five Pan-European hydrogen corridors and a 20.6 million ton European hydrogen market by 2030. As outlined in its 2023 Energy Security Plan, the UK is also backing hydrogen as a key energy vector, with a £240 million Net Zero Hydrogen Fund and a low carbon hydrogen capacity ambition of 10 GW by 2030.

However, adding hydrogen to the pipeline network poses an array of challenges around system flexibility and the future role of line pack.

• Transportation: As hydrogen contains only one-third of the energy content of natural gas, greater volumes of hydrogen will be required to provide the same amount of energy. Furthermore, green hydrogen production relies on renewable energy sources, which are inherently intermittent and thus increase the burden of flexibility on line pack.
• Infrastructure: Continually fluctuating amounts of gas within a pipeline can negatively affect pipeline conditions, and cracks in pipelines exposed to hydrogen can grow approximately 10 times faster than those exposed to natural gas under similar pressure changes. Mitigating these challenges may not be possible with existing natural gas infrastructure, underscoring the importance of research on hydrogen line pack in validating the requirements for new pipeline development.
• Storage: To deal with increased supply-demand disparity, short-, medium-, and long-term storage will become increasingly important. Like today, the pipeline storage provided by line pack can play a key role in meeting the within-day flexibility needs of hydrogen producers and consumers.

Line pack management, which is becoming more complex with the increasing use of renewable feedstock, is critical to ensuring the reliability and safety of networks. This will only grow in importance for hydrogen networks. A research article published in the International Journal of Hydrogen Energy analyzed different line pack conditions in a simulated future gas network and revealed a key management tradeoff: high line pack scenarios led to smaller pressure losses, but maintaining low line pack reduced the risk of hydrogen embrittlement and shortened recovery times to a steady state in the pipeline.

As we navigate the transition to hydrogen, stakeholders relying on line pack flexibility—ranging from power stations to storage operators—will find themselves at the forefront of a transformative period in energy supply management. The scale of flexibility currently provided by natural gas line pack highlights a major energy transition challenge: how to provide low cost flexibility to future energy systems where hydrogen is a key player. Research into the impact of hydrogen on line pack will be key to addressing this challenge.