Much of the focus of energy infrastructure upgrades in the UK over the past few years has been on new electricity transmission infrastructure, such as the ‘great grid upgrade’. But also seeing huge investment has been the gas network, which today provides 700 TWh of power, double the energy value of the electricity network, and at a 99.9958% reliability rate, according to James Earl, CEO of gas trade association Future Energy Networks.

Over the past two decades, metallic pipework prone to corrosion and leaks has been replaced with plastic pipe underneath thousands of UK roads, as part of the so-called Iron Mains Replacement Programme. It is expected to wind up in the next five years, ensuring operation long past Clean Power 2030.

The capacity of the gas network is three to four times that of electricity supply at peak times. And providing capacity at peak times is one of its principal roles now. That is because gas generation has the advantage of being dispatchable, pointed out RWE Head of Corporate Affairs Alice Barrs. That means it plays a crucial role for security of supply, filling in gaps in the energy mix during, for example, times of low sun and low wind. RWE currently operates 7 GW of gas generation, including six combined cycle gas turbines (CCGTs) such as the UK’s largest, the 2.2 GWe Pembroke power station. She noted that even the Net Zero 2050 plans make some allowance for gas; batteries are limited in duration, sources of flexibility slide, and even ambitious plans for investment in new pumped storage capacity don’t completely remove need for some gas – around 40 GW in 2050.

Perhaps the most familiar use of natural gas is in domestic heating and cooking; 22 million connections in total, according to NESO. But, as extensive as that is – and Angela Needle, Director of Strategy at central England distributor Cadent Gas described the gas network as both ‘invisible’ and ‘everywhere’ – it is still too narrow. For example, in the city of Liverpool alone, there are 250,000 domestic connections, 4,180 industrial sites, five hospitals, a prison, a gas-fired power station and a university. UK-wide, the network extends to connect 67,000 industrial sites and 460,000 commercial ones (such as schools, hospitals and restaurants), according to Earl.

In addition to supplying power, the gas network provides benefits to the electricity network in terms of backup, and offers energy storage in the form of nightly top-up of high-pressure gas lines called ‘line pack’. However, electricity ratepayers don’t contribute to this service – only gas customers do, complained Needle.

Earl went on to suggest that the gas and electricity networks should be considered together, in a more holistic way than currently. For example, he referred to a recent Dutch study of hybrid gas/electric heat pumps, which showed an average saving of €1,000/y (£880/y) compared to having a gas boiler, because of the ability to switch between gas and electricity depending on conditions. Needle, agreeing, lamented the fact that UK utilities are separated into gas and electric, while in Europe they are in many cases integrated.

Hydrogen
Just as renewables are inserting renewable electrons into the electricity transmission and distribution grid, the gas system also can carry low-carbon molecules, such as hydrogen, whose combustion is carbon-free. A fraction of the methane flowing in the natural gas grid could be replaced by blending in hydrogen, such as for domestic heating. The government hydrogen blending consultation which closed in September proposed a 2% ratio, which was down from the previous government’s proposed fraction of 20% in 2023, due to concerns about potential costs, infrastructure modifications and variability of supply for users, especially at higher concentrations. (As of time of writing, a governmental decision about hydrogen blending is still being awaited.)

Hydrogen is held back by its high production costs, poor geographical availability and scale of supply. If used nationally, switching to a significant fraction of hydrogen in the gas supply would also require appliance changes at the user level, whether domestic, commercial or industrial.

But at least it is possible. ‘We have demonstrated you can put hydrogen in the gas network,’ said Needle. ‘You can convert the gas network to 100% hydrogen, that you can do it safely, and that you can have hydrogen boilers. We’ve done some [research] that shows that if you can get hydrogen cheap enough, then you can convert [the network]. I think the issue will ultimately come down to hydrogen will probably never be cheap enough to enable roll-out at scale.’

Instead of running hydrogen through existing natural gas pipes, both Needle and Earl predicted that it might instead be distributed through a separate network. And it would be much simpler to deploy a hydrogen network within the confines of small geographical areas – such as industrial clusters. And Needle agreed that it’s true that industrial clusters are where the biggest carbon emissions are. On the other hand, there are industrial and commercial connections spread throughout the Cadent gas network, and assuming that those customers would follow their energy source into a cluster is challenging, she added. Lots do location-specific work, such as kilns near clay deposits. And not every industrial use of gas can easily be electrified, which raises the question of how they could be weaned off of gas.

Other low-carbon molecules
Earl complained that too few options are being considered for future scenarios. ‘I do think it has become this rather polarised debate over the last few years between “we electrify nearly everything” or “we use hydrogen as much as we possibly can”. That hasn't been helpful, and I don't think it has led to progress, frankly, which is why I think it could well be time to think about this in a slightly different way.’

He continued: ‘I like to call it a whole systems model, where we are, yes, trying to electrify where we possibly can, but also using a mixture of renewable gases in the mix as well; not just hydrogen, but [also] biomethane, fossil gas with CCS [carbon capture and storage] being a low-carbon gas as well, potentially other low-carbon gases like synthetic methane as well. And importantly, trying to get the systems to really work better together.’

He added that today the equivalent of one million homes can be heated by the quantity of biomethane currently produced from anaerobic digestion, which amounts to 11 TWh of power. He cited a recent report by the Green Gas Taskforce which proposes that up to 120 TWh of sustainable biomethane production is possible by 2050.

Needle amplified those views with her own reflections on biomethane. She said that as a source of green energy molecules, it is disadvantaged compared to renewable energy sources producing green electrons, for three reasons. First, although green electricity tariffs are now commonplace, there are no green gas contracts available in the market. Second, the UK Emissions Trading Scheme (UK ETS) doesn’t currently recognise biomethane as offering a carbon reduction compared to fossil natural gas. And third, an important subsidy for biomethane producers, The Green Gas Support Scheme, runs out relatively soon in March 2028.

Decommissioning
Needle confirmed that at Cadent, demand for shut-off is so slight that there is no disconnection team, despite the growth of heat pump installations. For her, the key question is how much of a gas network will be needed in a decarbonised energy system, and what will it be needed for? She cited NESO’s Future Energy Scenarios’ projections of dropping to 300 TWh at 2050. ‘What we don’t know is where it [the 300 TWh capacity] needs to be.’

Similar uncertainties are the bane of operations for gas power station operators such as RWE, said Barr, which intended that the fleet of CCGTs it invested in would be operated as always-on baseload production, but because of renewables deployments is now having to run as peaking plant at half the load factor (30%).

Barrs reported that RWE is now expecting load factors to decline even further, although it doesn’t (and can’t) know by how much. Lacking that information, the utility’s operational strategy for the CCGTs is limited to decarbonising them by fitting CCS or blending in hydrogen gas, refurbishing them to keep them going, or running them to close without refurbishment, to optimise the number of hours left. To improve operational efficiency, RWE has rebuilt the Staythorpe, Linconshire, power plant control room to be able to remotely operate four other CCGTs from the fleet. It is also building CCS plants at four sites: Staythorpe, Pembroke, Great Yarmouth and at a new site near the Humber (all to be submitted to Track 2, Phase 2 CCS cluster sequencing).

Turning to the actual process of gas network shut-down, Earl also pointed out that just because demand falls due to electrification doesn’t necessarily mean that the gas assets can be reduced by that proportion; it would need all of the demand to disappear to be able to get rid of it.

Still, that time of disconnection seems a long way off, particularly when faced by the great interest from energy-hungry data centres at this moment. ‘Gas networks have had close to 100 connection requests from data centres that are struggling to connect to the electricity network and want gas to produce electricity on site. This is the reality of the world in which we’re operating at the moment,’ observed Earl.

While adding that gas turbines for combined heat and power are nothing new, Needle agreed that the type of enquiry from some industrial customers has changed. What used to be backup power is now a request for primary energy because they can’t get a grid connection fast enough.

The consensus of the panel seemed to be that, notwithstanding Net Zero 2050 commitments, natural gas is not disappearing any time soon.

• Further reading: ‘US utility trials 50-50 hydrogen/natural gas mix in CCGT’. Georgia Power and Mitsubishi Power have completed trials blending hydrogen and natural gas fuels at both partial and full load on a combined-cycle gas turbine at a power plant near Atlanta, Georgia. They say the demonstration project is the first to validate 50% hydrogen fuel blending on an advanced class gas turbine, and is the largest test of this kind in the world to date.
• Find out how decarbonising heat can support the UK energy transition.