Central gas injection – the biomethane gift horse the government must stop looking in the mouth 

On Thursday 4 September, the Government in the House of Commons committed to making on-farm AD more affordable.

On Thursday 4 September the government in the House of Commons committed to making on-farm AD more affordable. On the same day, MPs, local politicians and key players in the industry gathered at Three Maids Hill for the official unveiling of Winchester’s first biogas plant. Developed by Acorn Bioenergy the plant takes advantage of a hybrid centralisation model known as ‘CGI hubbing’ (central gas injection), which is being adopted across Europe but faces challenges in the UK.  

Fortunately, the man who came up with the cost-cutting concept was there, Head of Biomethane Projects at Scotia Gas Networks Alan Midwinter. Jon Hughes grabbed him to find out more.

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JH: What is CGI hubbing? 

AM: At its most basic, it is a simple centralisation model. Rather than each individual operator having to invest in their own gas injection unit, a central one is developed. Then biomethane is simply delivered by virtual pipeline [trucks] and injected into the grid. Think of it like fuel being delivered to a filling station.  

JH: With the greatest respect, that hardly seems like the ‘lightbulb’ moment that has the industry so excited. That sounds like a standard hub and spoke model, as pursued in Denmark. What makes CGI hubbing different? 

AM: One of the challenges that needs to be overcome for the industry to reach its full potential is cutting the cost of grid injection. That was the problem I set out to solve back in 2014. How could we change the financials? The lightbulb solution was location.  

We found that by injecting biomethane into the grid at critical junctions, where the high-pressure national transmission line connects with a local distribution zone, there is no need to enrich the biomethane with propane because of the fast flow and volume of gas in the network. The lower calorific value (CV) of biomethane is not enough to dilute the total CV in the network. By doing this we calculated we could cut both CapEx and OpEx.  

JH: Can you quantify by how much this cuts CapEx and OpEx? 

AM: Sure, a fixed pipeline network injection unit would in today’s money add in the region of £1.5m in capital outlay. In terms of OpEx, for an individual operator injecting into the gas grid it can cost in the region of up to £300,000 a year on a 500m3 plant to enrich the biomethane with propane to raise its CV to ‘grid quality’.  

JH: That’s gamechanging in terms of making AD available, particularly to farmers, which is what the government recently said it is working to achieve? 

AM: It certainly is. And not just farmers, but also the wastewater treatment industry. For farmers it means they can install a modular upgrader – a one box solution – and cut both their input costs, in terms of outlay on energy and fertiliser, cut associated greenhouse gas emissions in line with NFU and government decarbonisation targets from treating manures and crop residues, and benefit from a fixed income stream from the sale of biomethane, fed into the national grid by a virtual pipeline.  

The same applies to WWT plants. Most people envisage these as being large scale facilities, but the truth of the matter is, most WWT plants in the UK are small. This would be an ideal solution for them to cut costs and benefit from a new revenue stream.  

JH: Portsdown Hill is the realisation of this CGI hubbing concept and where Acorn Energy will be sending its biomethane, about 30 miles away. Tell us about the facility? 

AM:  After we modelled the concept, we developed Portsdown Hill on the local national transmission junction, just outside Portsmouth. The facility has five injection points that can operate 24/7, each capable of delivering 1,200m3 of biomethane an hour. That equates to 144,000m3 a day, around 1million m3 a week. Once operating at full capacity, the site will supply low carbon energy to meet the annual heat demand for 27,000 customers in the local Havant and Portsmouth areas. 

The site has arrangements in place with five on-farm AD sites within a 90-minute radius of the facility. That is one of the additional great benefits of the site – making accessible grid entry to remote operators who would be otherwise prevented from doing so by their location.  

Incidentally, all the tankers delivering to Portsdown Hill will run on biomethane. The site can currently facilitate tankers with a 5,000-litre capacity but is being adapted to accommodate tankers of twice the size – cutting the need for deliveries by 50%. It is just one of a number of upgrades being considered. 

JH: In terms of capturing the energy from the currently untreated 100m tonnes plus of manures and slurries and wastewater, this has huge potential. Have you quantified how big it can be? 

AM: When we came up with the solution, SGN mapped the UK and identified a further potential 350 sites that share the same characteristics as Portsdown Hill. If each were restricted to serving five remote AD operators -and that wouldn’t necessarily be the case, we learnt a lot from building the prototype – that would enable 1,750 AD facilities to connect to the grid.  

JH: Based on Portsdown Hill capacity, that would equate to in the region of 350 million m3 of biomethane a week, on a path to meeting in the region of 8% of gas demand on current usage – all the while addressing farm decarbonisation, energy security, jobs and rural resilience? 

AM: That’s about the size of it.  

JH: Presumably, there are plans for central gas injection hubs to be deployed everywhere? 

AM: Not quite. Gas Networks Ireland is constructing a major new Central Grid Injection (CGI) facility in Mitchelstown, a key component of their strategy to increase biomethane injection into the national gas network. It will have capacity to inject up to 700 GWh of renewable biomethane gas annually, contributing approximately 12% of the Government’s 2030 biomethane target. 

Acorn Bio Energy are constructing further plants in the United Kingdom, their next hub site will be near Banbury, but I would love to see more ambition within the UK for this technology. We’ve had lots of delegations from Europe visit Portsdown Hill and they are adopting the method. 

In France [where the biomethane industry is turbocharged by government targets and support] injection portée (CGI hub/virtual pipeline) is emerging. In 2024 Methagora and Renera established the first site in France, aggregating biomethane output from several farms within ~100 km radius into one injection hub.  

So, while most French biomethane is still injected on-site, centrally pooled/virtual-pipeline injection is permitted and now operational in France in hub configurations when geography or grid access make individual connections uneconomic. 

Aside from that it is being explored as a future model across Europe.  

JH: I sense from your answer that while Europe is running with the model, the UK has yet to? Given it was a concept developed here in the UK, by you, why aren’t we in the fast lane when it comes to deployment?  

AM: When we developed Portsdown Hill, CGI hubbing was undertaken within RHI scheme. It remains the case under the GGSS but it is less clear. A producer needs to declare production and injection points and they don’t have to be the same place. However, reporting and verification requirements to accredit the volumes are quite onerous and this adds complexity for network operators. As the model is not explicitly recognised in the scheme developers are often unaware of its potential so don’t consider it with network operators. These issues have hampered uptake of the model. So, while across Europe it is being embraced to optimise energy and mineral recovery from organic waste, the model has stalled somewhat in the UK.  

JH: What a waste. Given what the government said on Thursday about making on-farm AD more economic, if the government could grant you one wish, what would it be? 

AM: Specifically, for CGI injection to be explicitly recognised in the GGSS replacement scheme. More generally, to make biomethane practical and cost effective, there needs to be confidence for investors to support growth in AD sector, therefore my wish list would be, early clarity on GGSS replacement, a commitment on resolving ETS anomaly [where biomethane injected into the gas grid is treated the same as fossil gas] and an extension to the RTFO scheme. 

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Last Word – ADBA analysis 

There are plenty of sites around the UK where there is feedstock, be that agricultural residues or even commercial and domestic food wastes, that can be captured effectively but are not close to a high-pressure grid line or indeed any gas grid connection. The potential to inject without the addition of propane can save not only the ~£7/MWh, but also avoids the fossil carbon emissions associated with this. So, it will not only cut the operational cost of biomethane injection but also improve the environmental impact of the supported gas. The long-term solution is to adjust the regulations that require propanation on any part of the grid but until then this CGI initiative is the best solution to getting higher degrees of decarbonisation on the UK gas grid.