I'm not convinced that hydrogen as an alternative to methane is ever going to happen.  There are problems with distributing it - it leaks easier than methane, and any old steel pipes still in use will be embrittled if they are used with hydrogen.  All older gas appliances would have to be converted or replaced.

Then there's the problem of energy density.  Taking figures from https://www.engineeringtoolbox.com/fossil-fuels-energy-content-d_1298.html,

Methane has an energy density of 54.0 MJ/kg, whereas hydrogen is 142.2 MJ/kg.  Yay for hydrogen.

But we measure the delivery of gas by the cubic metre.  I cubic metre of methane gives 40.34 MJ.  But a cubic metre of hydrogen is only 12.79 MJ.

So we'd be using gas over 3 times as fast if we switched to hydrogen.  That's an awful lot of hydrogen to keep pumping into the gas mains.

I'm not convinced that hydrogen as an alternative to methane is ever going to happen.  There are problems with distributing it - it leaks easier than methane, and any old steel pipes still in use will be embrittled if they are used with hydrogen.  All older gas appliances would have to be converted or replaced.

Then there's the problem of energy density.  Taking figures from https://www.engineeringtoolbox.com/fossil-fuels-energy-content-d_1298.html,

Methane has an energy density of 54.0 MJ/kg, whereas hydrogen is 142.2 MJ/kg.  Yay for hydrogen.

But we measure the delivery of gas by the cubic metre.  I cubic metre of methane gives 40.34 MJ.  But a cubic metre of hydrogen is only 12.79 MJ.

So we'd be using gas over 3 times as fast if we switched to hydrogen.  That's an awful lot of hydrogen to keep pumping into the gas mains.

Yes, We haven't enough electricity to spare to supply power for the electrolysis of water to produce the green hydrogen gas. Producing brown gas may be possible but CO2 is still produced then.

Another problem is how are you going to store the hydrogen gas at low pressure as the old  gasometers would hardly be useful?

CliveS said:

Producing brown gas may be possible

Nitrogen dioxide??? 

Brown gas - is this credible? if so why aren't more talking of it?

really?

We are in the fortunate position in the UK of having undergone a significant distribution system upgrade over the last 12 years. More than a decade ago, the UK gas networks supported by OFGEM embarked upon a programme of work known as the Mains Replacement Programme (MRP), whose intention was to replace cast iron and steel distribution mains with polyethylene pipe (the yellow pipes you may see being installed in roadworks).  Since that time, 85% of the UK distribution network has been replaced with PE which is 100% hydrogen compatible.  The remaining MRP is planned to have completed this programme before 2030.  Independent research and testing on representative gas distribution pipework was commissioned by BEIS and OFGEM in 2020.  This work was conducted by the UK HSE and DNV under the H21 and Hy4Heat programmes and concluded that if existing distribution pipework was leak free with methane, it would also be leak free with hydrogen.    The National Gas Transmission Network is steel, but mainly low strength steels, that do not suffer hydrogen embrittlement.  Nevertheless, a current research programme called FutureGrid for National Grid (as was) is building a large testing facility with decommissioned sections of the National Transmission System (NTS) at the DNV Spadeadam Research site.  That facility will test a number of hydrogen blends, plus 100% hydrogen to determine the suitability of the NTS for hydrogen.  That work is being monitored by the UK HSE.

The differences in energy density are an issue which is currently being addressed through significant network modelling to establish if the changes in pressures and flowrates will cause any issues.  It should always be borne in mind that the gas networks are "overdesigned" in that they are designed to carry the amount of energy needed for a 1 in 20 year extreme weather event.  The introduction of condensing boilers in the UK have also significantly reduced existing gas demand so there is significant flow headroom in the system today.