SGN owns and operates the low-pressure gas network in Scotland. That means that as of 2020/21, it operates more than 44,000 miles of pipework and delivers gas to 5.9 million homes and businesses.
In response to a target from the Scottish Government to convert one million homes to low carbon heating by 2030, the gas distribution network (GDN) has examined the practicalities of converting millions of domestic customers on its network to receive 100% hydrogen through their pipes, in place of natural gas.
Work by other GDNs has so far found that the addition of hydrogen in domestic customers’ supply, up to around 20%, makes no difference to users and requires no changes to appliances or other equipment in the property. (Other types of customers’ requirements may be more prescriptive.)
A move to 100% hydrogen, as considered by SGN, is a different matter, with adjustments required to appliances (eg new burners for gas cookers) – and the assumption that gas boilers are ‘hydrogen ready’ or will be replaced with those that are.
SGN noted that conversion of an area from natural gas to 100% hydrogen requires it to engage with both business and domestic customers. Non-domestic customers are likely to have specific requirements.
First SGN would have to find areas of its network that can be ‘closed off’ from the remainder of its pipework, separating a hydrogen area from neighbouring, connected areas that continue to use natural gas. The hydrogen subsections would remain separate unless and until neighbouring subsections are switched to hydrogen in their turn.
SGN then identifies the necessary activities in converting a specific area, which it says might typically have 1000 connections. It would:
• Assess sensitivities of industrial and commercial plant in the area.
• Plan ‘sectorisation’ of a project area, so it could make additional connections and install strategically placed valves as needed, so as to minimise disruption and costs.
• Disconnect, isolate and purge the local natural gas system.
• Make additional network reinforcement or upgrades to district governors and remove or replace materials that are not suitable for hydrogen.
• In all properties convert burners and appliances to operate with 100% hydrogen.
• Make any additional changes to customers’ gas systems as required.
• Purge the pipework system
• Connect to the local (possibly temporary) hydrogen system.
The sectorisation plans would involve sub-sections of the network being supplied with a temporary hydrogen supply, and over time several sub-sectors that have been converted would be connected and commissioned as a complete sector.
SGN says customers will be without gas during the conversion process and it estimates the conversion process will require on average one person-day per customer.
With the framework for rollout above, SGN then considered the field requirements for a conversion that would meet the Scottish Government’s target to convert one million homes to low carbon heating by 2030 and then move on to the remainder.
It said the work would likely be carried out during periods of low demand (ie spring and summer). If the conversion process takes place from March to October over a period of 11 years (from 2024 to 2034):
• There will be 2,772 days available (assuming seven days a week and 4.5 weeks per month).
• Assuming one day per customer to convert, 649 customers can be converted per day.
• This would require a field workforce of approximately 1,300 dedicated to customer changeover, plus additional staff to support preparatory activities, and provide supervision and support.

Raising questions
SGN’s discussion usefully sets out an approach to the problem but, as might be expected, it immediately raises further questions to be examined.
Clearly, new gas meters will be required. BEIS Secretary of State Kwasi Kwarteng told a select committee meeting this year that, “We are developing prototype smart meters that can be installed to be adapted to hydrogen” but said nothing about when they will be available for a major rollout.
SGN has identified that business and organisational users will have specific and bespoke requirements and they may be complex. For the domestic part of the exchange, a key question is how much work will be required in each property. There should at least be some useful data from the smart meter rollout, a few percent of which have required visits from GDN staff to carry out enabling work or upgrades in properties concerned (assuming that data is available).
SGN has not allowed for detailed surveys in its list above, but that is surely the first step. It seems likely that in some cases domestic supply equipment (ie pipework) will have to be upgraded. One person-day per property may be optimistic, unless SGN has teams ready to address houses where more work is required.
Equally, the GDN will have to have a much better knowledge of the people in each area than it is likely to have now. Which households have people with special medical, social, cultural or other needs that will require specific support during the process?
Supplying hydrogen to converted subregions, potentially for long periods, is not a small matter. Even questions as simple as how much land will be required, in what may be a congested area, have to be addressed, not least because hydroegn storage is .
But even more important are political questions.
How ready will the people in each property be to accept the change? It is to be hoped that lessons were learned from the smart meter rollout – but that rollout was informed by the digital switchover and it was still the opposite of smooth. The numbers for each subsector discussed above are relatively small but the imposition is much greater than for meter installation. Fundamental questions arise about managing the costs?
Who pays for new appliances and other housing upgrades? Who pays for new meters? Crucially, who pays for the network changes and the general programme costs – is it gas customers or taxpayers? What happens to people who do not want to switch to hydrogen – if some customers decide to secede from the gas network instead, will electric alternative appliances be offered (and how much work will the local electricity distribution network operator have to do in parallel)? If several households secede, at what point does switching the subsection to hydrogen stop being cost effective?
Many projects are under way to investigate the feasibility and processes for switching gas customers to hydrogen and they have begun answering some technical questions.
Many more questions will be asked as the practicalities of a changeover of domestic are explored. It is to SGN’s credit that it has produced a document that prompts them.

Further reading
Towards 2032: costs rise to maintain aging gas transmission network
Towards 2032: NGESO details electricity system reinforcement needs