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Case Study: The H21 series of projects shows how the U.K. could switch from natural gas to hydrogen

Arij van Berkel, Ph.D., Vice President, Research
November 4, 2021

The average household in the U.K. consumes 12,000 kWh of natural gas annually for cooking, heating, and hot tap water. This leads to annual emissions of 62 million tons of CO2 or 17% of the country's total greenhouse gas emissions in 2019. Decarbonizing the built environment is a difficult problem to solve in most European countries, where natural gas is the staple energy carrier for households. At the very least, it requires replacing all of the heating and cooking equipment in all households. The available choices are either full electrification or replacing natural gas with hydrogen, or extensive use of district heating networks. All of these choices involve major investments in the energy infrastructure, either by tripling the capacity of the electric grid, by converting the natural gas network to carry hydrogen, or by building new district heating networks and securing the heat sources needed for it.

In 2015, a consortium of U.K. regional gas distribution system operators set out to investigate the feasibility of converting the entire U.K. natural gas distribution network to hydrogen and converting all U.K. household gas consumption to hydrogen. This led to the H21 series of projects, conducted with the Leeds Beckett University. The series of projects is one of the main inputs into the U.K. hydrogen strategy launched in the summer of 2021.


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The H21 series of projects aims to find practicable solutions for the conversion of the entire gas distribution grid in the U.K. The first project in the series is the Leeds City Gate project. The results of this project were presented to the U.K. parliament in July 2016. This study essentially is a very detailed plan to convert the entire city of Leeds from natural gas to hydrogen. The report proposes dividing the city into blocks of approximately 2,500 gas connections (i.e., buildings). Each block can be converted in one week. The block will be disconnected from the gas grid at the start of the week, a workforce of about 1,000 people will enter the block and convert all appliances, and the block will be reconnected to the grid, which is now a hydrogen grid, by the end of the week. The report describes detailed solutions for converting the low-pressure gas grid to hydrogen block by block and provides detailed analyses of the hydrogen supply, the capacity of the converted grid, and the conversion process itself. The table below illustrates the level of detail in the entire study. This is Table 5.2 in the report, showing the planning for the appliance conversion per block.

Table 5.2 from the Leeds City gate report

The main conclusions of the Leeds City Gate project are:

  • It is possible to convert the distribution grid in Leeds from natural gas to hydrogen with minimal changes to the grid itself; moreover, the grid capacity will still be sufficient even though hydrogen has a lower volumetric energy density than natural gas.
  • Sufficient hydrogen can be provided by constructing 1 GW of steam methane reforming capacity connected to carbon capture and storage (CCS) in the Teesside area.
  • The total cost of the conversion for Leeds, including steam methane reforming, all infrastructure, and conversion of appliances but excluding the CCS infrastructure, would be 4 billion GBP ($5.4 billion). This would result in a 7% average increase in the gas bill per household.
  • A total of 1.5 million tons of CO2 would be sequestered annually.

After completing the City Gate project, the H21 consortium proceeded to conduct a series of projects in two general directions. One category of projects expands the concept of the gas grid conversion beyond Leeds to the rest of the U.K. by conducting detailed studies of conversion scenarios, hydrogen supply, and social acceptance of hydrogen. The other category of projects aims to develop "details" of the conversion, such as hydrogen gas detectors for households, to replace natural detectors, and hydrogen gas meters.


The H21 series of projects is the most extensive and detailed study of converting an entire country to hydrogen. The study provides a thorough analysis of the feasibility and detailed planning and costs analyses down to the household level. The findings show that it is possible and affordable to convert a country's entire gas grid to hydrogen. They also show how this can be affordable. As such, the H21 program is an impressive feat, and clients should follow these projects, which will help provide a deep understanding of the possibilities and difficulties of a complete switch to hydrogen.

At the same time, clients should exercise caution when looking at these studies. The entire series assumes that the sources of hydrogen will be blue hydrogen: steam-reformed methane with CCS. As long as natural gas prices are low enough and CCS is available (i.e., there is sufficient capacity for sequestration), blue hydrogen provides an alternative to natural gas at a small price premium. This may make hydrogen an economically attractive alternative to natural gas for the built environment. However, if the source of hydrogen is assumed to be green hydrogen, it is almost certain that hydrogen is a much more expensive alternative than electrification or district heating. The entire U.K. conversion strategy thus hinges on the availability and social acceptance of blue hydrogen.


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