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Published July 21, 2023 | Version v1
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D7.2 Concept of a conversion plan of a natural gas distribution network to hydrogen

  • 1. TNO
  • 2. DNV Netherlands


In work package 7 of HyDelta 2 “Conversion of natural gas distribution networks to hydrogen”, a model (i.e., a concept of a) conversion plan has been developed for the large-scale conversion of existing gas distribution networks to almost pure hydrogen. This model conversion plan is based on experiences and insights gained in hydrogen projects and conversion studies in the Netherlands and abroad. In order to understand in more detail what a conversion plan entails, two case studies have been developed for this project. The generic conversion plan offers regional network operators a basis for a specific conversion plan. Because each region and the gas distribution network located therein is unique, the generic conversion plan will have to be adapted to the specific characteristics of the gas distribution network.

Structure of the conversion plan

The model conversion plan contains a description of more than 50 activities to be carried out, divided into 3 phases and a total of 7 steps (to see the figure the reader is referred to the document). Alternatives are possible for some activities. The choice between alternatives depends, among other things, on the availability of devices/components and availability of suitably qualified personnel, or on the preference of the grid operator. Sometimes there are alternatives that require further investigation.

Time planning

Part of the conversion plan is a time schedule. Assumptions and preconditions apply to the time planning, such as the number of personnel to be deployed or the maximum duration of the gas interruption during the conversion. The lead time of the various steps and phases depends on the size of the distribution network and the number and types of end users. The lead time of steps and phases can be influenced by changes in assumptions and preconditions. During the execution phase of the conversion plan, the time schedule may have to be adjusted on the basis of the information obtained in the planning phase.

Tasks and responsibilities

A large number of parties will be involved in the implementation of the conversion plan: municipality(ies), distribution system operator, operators of the natural gas and hydrogen transport network, hydrogen suppliers, installers and end users. The model conversion plan indicates for each activity how the tasks and responsibilities can be divided. Because the conversion is a complex and time-consuming process, good coordination is essential. The municipality is the appropriate party to coordinate the conversion of the distribution network to hydrogen, because municipalities are designated to decide on and implement the energy transition at a local level. It has the necessary powers to do so, can make a broad assessment of interests and is supervised by a democratically elected council. The execution of work can be outsourced by the parties involved to contractors and consultants.

The parties involved will have to inform each other and good coordination is necessary for certain activities. The municipality is responsible for communication with the end users and will draw up a communication plan for this. Multiple communication forms and channels can be used. In addition, the municipality can set up an information point where end users can go with their questions during the entire conversion process.


This research has yielded the following insights:

  • Coordination, responsibilities and communication:
    • A large number of parties are involved in the implementation of the conversion plan. It is essential to make good agreements about the responsibilities of the tasks to be executed.
    • Because the conversion is a complex and time-consuming process, good coordination is essential. The municipality is the appropriate party to coordinate and communicate about the conversion of the distribution network to hydrogen.
    • Parties involved will have to inform each other optimally and good coordination is required for certain activities.
    • Support by the end-user is an essential precondition. This concerns the public acceptance that the energy supply with natural gas can no longer continue to exist, that hydrogen is a good replacement for natural gas, i.e., safe, affordable (compared to alternatives such as all-electric) and security of supply is guaranteed.
    • The municipality is responsible for communication with the end users and will have to draw up a communication plan for this.
  • Duration of the conversion plan:
    • The conversion of a part of the gas distribution grid (from planning phase to implementation phase) can take several years. In the two cases studied, this varies from about 3 years (3,700 connections) to more than 6 years (30,000 connections).
    • If a different choice is made for replacing natural gas, such as for a heat network (construction of a new network) or for all-electric (grid reinforcement), a plan will also have to be drawn up and implemented. The activities are partly comparable to those of the conversion plan to hydrogen and will also entail a considerable lead time. However, no comparison has been made.
    • The duration of the conversion plan is determined by the size of the distribution network (i.e., the number of connections and the required number of qualified personnel) or by new Hydrogen Distribution Station(s) (HDS) to be realized and expansion/upgrading of the distribution network, including the lead time of permit granting. The latter requires a joint planning by the national and regional gas network operator.
    • The implementation phase (preparatory work and conversion operation) takes up more than 70-80% of the total time.
    • The duration of the conversion operation, during which the gas supply to end users is interrupted, can be limited by carrying out as much work as possible (such as replacing the existing central heating boiler with an H2-ready boiler) during the preparatory work. Even if this saves little time in total, this shift does provide more flexibility in the implementation.
    • The physical conversion (last step of the conversion plan) can be shortened considerably if a dual-fuel boiler and dual-fuel gas meter can be used and flushing the gas pipes with nitrogen can be omitted. This makes the conversion process less complex, shortens the total lead time of the conversion plan and can lead to cost savings.
    • Most technically trained personnel are required for inspection of the installations at the end users (planning phase) and replacing the gas installations (execution phase). By deploying more personnel, the lead time can be reduced.
  • Dividing the distribution network into sections:
    • For the conversion, the gas distribution network will be divided into sections. The number and size of these sections depends on two preconditions: the duration of the gas interruption and the number of installers to be deployed to convert the gas equipment at the end users.
    • If dual-fuel devices/components can be used (such as gas meter, central heating boiler), the sections can be larger or no sectioning is required at all.
    • The order in which the sections are converted from natural gas to hydrogen depends on the position of the hydrogen and natural gas feed-in points in the grid. It may be necessary to use a temporary feed-in point (for example a tube trailer with hydrogen or natural gas or via an additional pipeline to be installed).
  • Security of supply:
    • Because existing gas infrastructure is used and adjacent areas have to be supplied with natural gas in addition to the area being supplied with hydrogen, it is often impossible to maintain the security of supply of the hydrogen distribution network at the same level as in the situation when natural gas was still being distributed. The risk of an interruption of the hydrogen supply to end users will then have to be dealt with in a different way.
  • Alternatives:
    • Replacing the central heating boiler with an H2-ready boiler or with a dual-fuel boiler (if available) during the preparatory work: A dual-fuel boiler saves time during the conversion operation. The lead time for the preparatory work remains the same as for replacement by an H2-ready boiler.
    • Whether or not to flush the distribution pipe, connection pipe and/or indoor pipe with nitrogen: If flushing with nitrogen can be skipped, this simplifies the work during the conversion operation.
    • Whether or not to use gas stoppers at every customer: These are now being used for new connections, but they are not present for existing connections.
    • Temporary gas supply from the existing gas network or with tube trailers: During the conversion, end users who have not yet been supplied with hydrogen will still have to be supplied with natural gas. This is possible if the distribution network that is being converted still has a city gate station that is connected to an RTL on natural gas or is connected to a gas distribution network that remains on natural gas. Alternatively, a tube trailer can be used for the temporary supply of natural gas or hydrogen.


This research leads to the following recommendations:

  • Lessons learned from current pilots: various pilot projects will be carried out in the coming years. The experiences and insights gained (also with regard to coordination, responsibilities and communication) can form an important input for the further development of the model conversion plan.
  • Acceleration of permit procedures: the lead time of permit procedures can have a major impact on the lead time of the whole conversion plan (e.g., the permit procedure for the HDS). It is recommended to investigate how the lead time of permit procedures can be shortened.
  • Remediation: for gas distribution networks that are being converted to hydrogen, it is recommended to replace old pipe sections, including cast iron, in the coming years.
  • Suitability of valves: insufficient research has been carried out into the leak-tightness (both internal and external leakage) of valves running on hydrogen. Further research into this is recommended.
  • Inerting indoor pipelines: the extent to which the inner pipeline should be inertized with nitrogen is still under discussion. It is therefore recommended to conduct additional (practical) research into this.
  • Filling the gas network with hydrogen: research must show how a meshed network can be safely filled with hydrogen.
  • H2-ready boiler: the use of an H2-ready boiler is decisive for the implementation of the conversion. However, a good definition or standardization of an H2-ready boiler is still lacking. It is recommended to set this up.
  • Dual-fuel components: availability of dual-fuel boiler and gas meters greatly simplifies and accelerates the physical conversion. It is recommended to have a dual-fuel boiler developed or market parties to encouraged to do so. More clarity is also needed about the suitability of gas meters for both natural gas and hydrogen.
  • Security of supply: compared to natural gas distribution, the security of supply of hydrogen distribution cannot always be maintained at the same level due to a smaller number of feed-in points and/or less meshing of the grid. It is recommended that research be carried out into the risk of interruption of the hydrogen supply and how this can be mitigated.
  • Increasing conversion efficiency: the costs of the conversion have not been mapped out in this study. A better insight into the conversion costs can be helpful in improving the cost efficiency of the conversion process. In addition, the conversion to hydrogen may be simplified, for example by performing activities more efficiently or limiting the number of actions. Research could be carried out into this.
  • Availability of affordable hydrogen: whether it is attractive for end users to switch to a hydrogen-based gas supply depends on the future availability and affordability of hydrogen. This is an important precondition for converting the gas distribution network. It is recommended that developments with regard to the hydrogen supply be followed closely.


Dit project is medegefinancierd door TKI Nieuw Gas | Topsector Energie uit de PPS-toeslag onder referentienummer TKI2022-HyDelta.



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