Hydrogen for heating: the facts

Hydrogen doesn’t naturally occur so has to be produced either from electrolysis of water or by steam-methane reformation and carbon capture. As we decarbonise then it would more likely be from electrolysis. End to end electrolysis is about 50% efficient meaning for each 1 kWh of electricity consumed about 0.5kWh of heat is produced when that Hydrogen is burned. If we consider that an air source heat pump has an efficiency of 300% and higher (meaning 1 kWh of electricity provides 3kWh of heat) then the same 1 kWh of electricity is 6x more useful when heating with a heat pump than producing and burning Hydrogen.

Hydrogen flame speed is up to 10x faster than Methane.

I described Flame Speed as an issue in the video. If you have a volume of leaked gas in your kitchen, flame speed is the time it takes to burn from one end of the kitchen to the other.

Hydrogen flame speed is up to 10x faster than Methane. That means Methane gives more of a cloud of orange flame that spreads across the room - it’s still pretty quick though. But Hydrogen burns so fast that it’s almost instant at burning all that gas in the kitchen and that’s what makes it more like an explosion.

An analogy is if you fill the sink from the tap fully or slowly. You can get the same volume of water in the sink. In the same way the amount of energy is the same but it was delivered quicker when the flame speed is higher.

Hydrogen catches fire much easier. Both Methane and Hydrogen don’t easily burn on their own but need to be mixed with oxygen in the air. This is the fuel to air mix ratio. Methane has the range of 7% air to 20% air. Hence the advice to open the windows if you have a gas leak. If the mix is diluted to 50% then it’s much less likely to catch fire. Hydrogen will burn with a mix between 4% and 75% air so it’s more likely to catch fire even if you have plenty of ventilation.

Hydrogen is the smallest molecule which means it leaks more easily than Methane.

Hydrogen, through the interaction with Methane in the atmosphere, has a greenhouse gas effect 11x greater than carbon dioxide emissions and there’s uncertainty how much Methane escapes from the national gas grid today with quite a wide range of values. This is worrying. By volume of gas, Hydrogen leaks from 1.2 to 2.8 times as much volume as Methane.

Hydrogen has a much lower energy density by volume.

If you imagine a cubic meter of gas in your kitchen, then there’s about 1/3rd the energy in the cubic meter of Hydrogen compared to that of Methane. In the video we had to place Hydrogen in the kitchen cabinets so we had about the same amount of energy as the Methane example where the Methane was just in the boiler. In fact even long distance transport of Hydrogen is a significant problem.