The European Green Deal frames Europe’s response to climate change challenges and commits to delivering net-zero greenhouse gas emissions at the EU level by 2050 and an EU-wide greenhouse gas (GHG) emissions reduction target of at least 55% for 2030 [1]. In line with EU ambition, the Programme for Government, ‘Our Shared Future,’ commits to achieving a 51% reduction in Ireland’s overall GHG emissions from 2021 to 2030 and to achieving net-zero emissions no later than 2050 [2].

A roadmap has been developed through Ireland’s Climate Action Plan 2021 to put Ireland on a low-carbon trajectory to meet future targets in 2030 and 2050. These are challenging targets, and Ireland has already missed targets for 2020.

According to the Environmental Protection Agency (EPA) report [3], since 2011, emissions have deviated upward, with an overall peak in 2018, despite a modest reduction from 2008 to 2011. EPA data also highlights agriculture as the top emitter in 2020, with 37% of Ireland’s emissions. Transport contributed 18%, while industry generated 15%.

Ireland’s national gas network provides almost a third of all primary energy, 40% of heating, and nearly half of Ireland’s electricity generation. It is among the safest and most modern gas networks in the EU [4] and can help significantly decrease emissions by facilitating a more sustainable and secure transition to a clean energy future.

Natural gas is a cleaner than oil and coal and can replace these fuels in heat and power generation in the short term. The network can also transport renewable gases, such as biomethane and hydrogen which were called out in the recent RePower EU announcement, for long-term energy sustainability.

Collaborative research has begun between Gas Networks Ireland and University College Dublin’s (UCD’s) Energy Institute to ensure the safety and operability of the Irish Gas Network when transporting a blend of hydrogen and methane.

Hydrogen and decarbonising the gas network

Hydrogen can be generated through electrolysis, and when renewable electricity is used, there are no GHG emissions making the hydrogen 'green'.

This power to hydrogen (P2H) process can capture excess renewable electricity that would be otherwise lost and increases the use of available renewable energy. Alternatively, low-carbon hydrogen can be obtained through methane reforming combined with carbon capture and storage.

Hydrogen is flammable and can be burned to produce heat for end users. It is widely accepted that hydrogen can be injected into the existing polyethene distribution pipelines at blends of up to 20% and used in post-1996 gas appliances with out any increased risk to the public or infrastructure. 

Green hydrogen production

Ireland has one of the best wind resources in Europe and has significant potential for wind generation – onshore and offshore –  which can be expected to exceed end users’ demands. With the current levels of wind generation on the island of Ireland, the electricity grid operators sometimes shed renewable power due to grid limits and constraints.

The long-term Irish target is to instal more wind farms, which will increase the surplus renewable power. Therefore, finding an alternative use for this excess electricity will increase the percentage of renewable energy throughout the energy system. Hydrogen production using electrolysers is a potential solution that provides a significant opportunity to convert this excess renewable power to green hydrogen, which can then be injected into the national gas network.

There are several projects now under way in Europe to investigate the use of gas networks for the delivery of clean hydrogen. The HyDeploy project was the UK’s first hydrogen blending project. HyDeploy 2, aims to help the UK reduce carbon emissions and reach the net-zero target by 2050 [5]. The French ANR project, blending hydrogen in Ameland island in the Netherlands, and the M/R HELLE project in Denmark are all testing hydrogen blends in gas networks. 

Flexible energy storage

The use of P2H can help increased energy system flexibility. Through storage of green hydrogen in pipelines, daily variations in electricity production and demand could be accommodated. While seasonal variations would require large dedicated storage facilities [6]. The gas network can play a key role in renewable energy storage by providing reliable and complementary backup to variable renewable power.

Modelling results

The results from modelling of the Irish gas network incorporating green hydrogen show that hydrogen blends can be mixed with natural gas through the transmission pipelines without considerable changes to their operational pressure and flow rates[7].

Following a case study, if the daily average curtailed wind in Ireland in 2018 was converted into green hydrogen, a significant emissions reduction of 400 metric tonnes of CO2 could be achieved, due to 2% less natural gas consumption of about 200,000 Nm3 [7]. There are limitations though in hydrogen levels accepted by different gas-based appliances and equipment.

Safe limits

The upper hydrogen limited operation of many devices has been evaluated based on the Wobbe index, material compatibility and safe allowable hydrogen concentration. Figure 1 shows the hydrogen limits of current end users’ equipment.

The gas distribution pipelines could convey up to 50% (even 100%) hydrogen concentration depending on the type of pipeline components and the designated standards. However, because of the end users' appliances, the allowable hydrogen concentration is likely to be at a maximum blend of 15%-20% in distribution networks.

Figure 1: some of the ranges given are with modification to the end-user equipment (e.g. compressors, vehicles, turbines), while others are possible without necessarily any modification

Figure 2 shows the current limits of hydrogen concentration in pipelines, considering the Wobbe index and calorific value limits. According to this plot, provided by European standards, the red area relates to Common Business Practice (CBP), which is pointing to the gas quality criteria specification used in Europe for natural gas. The hydrogen content should not exceed 15–20% from a safety, metering and energy conversion perspective.

Figure 2 :The admissible hydrogen concentration in a natural gas network considering the blends’ Wobbe index and heat value (8)

Current research

A joint project between UCD Energy Institute and Gas Networks Ireland to test blended hydrogen, considering gas quality variations and end users’ limits on the gas network is currently under way. 

This study looks at the feasibility of different amounts of green hydrogen being added to the gas network and the impact on the operation of domestic appliances. UCD and Gas Networks Ireland see this as the first step to investigating the potential of gas networks for storing and transporting hydrogen so that end users can reduce their carbon emissions.

Gas Networks Ireland’s research and development facility in Citywest, Dublin, enables the safe testing of pipelines, meters and appliances off-network (Figure 3). Using this facility and the UCD laboratories in Belfield, Dublin (Figure 4), the team are carrying out the relevant investigations to understand the full potential of hydrogen and ensure Ireland’s pipelines are capable of safely transporting and storing this carbon-free gas.

This research investigates the operability of end-use appliances in the residential sector, including gas ovens, gas boilers and gas hobs with hydrogen blends from 2% to 20%. The test packages measure the gas blends’ operating pressure and flow rate variables. The research also includes gas flue analysis, flame temperature, leak and safety testing and Wobbe index testing (Figure 5).

Figure 3: the new testing facilities at Gas Networks Ireland’s research and development facility in Citywest, Dublin

Figure 4: Experimental pressure drop rig and leak test equipment in the UCD Energy lab

Figure 5 the scenarios for testing hydrogen blends at Gas Networks Ireland’s research and development facility in Citywest, Dublin

The outcome of this research will help inform the use and operation of Ireland’s gas distribution network to ensure that the hydrogen concentration meets the end users' limits and can be safe, secure and sustainable energy for use in the residential market.

Next phase and further end user research 

Science Foundation Ireland (SFI) Research and Development Industry Programme has awarded grant funding to support the next phase with additional support from Gas Networks Ireland.

This proposed research will investigate how consistent energy with differing gas types can be supplied to end users through the gas network when hydrogen is injected from multiple sources in varying quantities. The research will investigate the potential hydrogen injections locations and quantities, and how this will affect gas quality in the gas network given the end user limits.

Initially the project will focus on categorising end users into different groups: power plants, transportation, residential and agriculture. An overall categorisation of the end users will be devised based on the various end user equipment and installation compatibility considerations. 

As part of the categorisation process, this project will implement a national survey in Ireland to collect data about end users across the country to understand what current appliances and equipment are being used and what are their limitations for using a hydrogen blend. 

Authors: Ali Ekhtiari, Liam Nolan, Paul O’Dwyer, and Eoin Syron


1) Jim Scheer Matthew, Clancy Fiac Gaffney, 'Ireland’s Network Development Plan 2019,' SEAI Energy Modelling Group, Dublin, 2020.
2) Chiodi Alessandro, Gargiulo Maurizio, Rogan Fionn, Deane JP, Lavigne Denis, Rout Ullash K, 'Modelling the impacts of challenging 2050 European climate mitigation targets on Ireland’s energy system'.
3) EPA, 'Ireland's Environment – An integrated assessment,' epa, 2020.
4) GNI, 'Ireland's Gas Network – Delivering for Ireland,' Gas Networks Ireland, 2021.
5) HyDeploy, 'HyDeploy is a pioneering hydrogen energy project,' [Online]. Available: [Accessed March 2022].
6) I Power, 'Energy Storage Technologies,' ITM Power, March 2018. [Online]. Available: [Accessed March 2022].
7) Ali Ekhtiari, Damian Flynn, Eoin Syron, 'Investigation of the Multi-Point Injection of Green Hydrogen from Curtailed Renewable Power into a Gas Network,' Energies, vol. 13, no. 22, p. 6047, 2020.
8) Jacek Jaworski, Pawel Kuaga, and Tomasz Blacharski, 'Study of the effect of addition of hydrogen to natural gas on diaphragm gas meters,' Energies, vol. 13, p. 3006, 2020.
9) IDML ES Ali Ekhtiari, 'A novel approach to model a gas network,' Applied Sciences, vol. 9, no. 6, 2019.
10) DFE S Ali Ekhtiaria, 'Gas networks, energy storage and renewable power generation,' Chemical Engineering Transactions, vol. 76, 2019.