Heating homes with clean hydrogen by converting natural-gas networks to run on pure H2 is a terrible idea — far more difficult, expensive and inefficient than simply using electric heat pumps, according to an independent report released today.
Using green hydrogen to heat buildings via boilers would be almost six times less energy efficient than heat pumps powered by renewable energy and require a 150% increase in primary energy generation, and clean H2 would increase heating costs and require the conversion of largely concealed pipework in millions of homes and buildings, said the UK-focused study, Hydrogen: A decarbonisation route for heat in buildings?, by the London Energy Transformation Initiative (LETI)*.
“Of note, we have found that the public discourse on hydrogen appears severely unbalanced, with [the] gas supply industry in particular over-selling ‘green-gas’ to policy makers in order to protect their interests,” the report says.
“The lack of tangible benefits… casts serious doubts on the practicality of a gas switch over.”
Expecting governments or investors to fund a national gas grid upgrade that would require new infrastructure technology unproven at scale “seems unlikely when viewed alongside the alternative of rapidly falling renewable electricity costs (such as wind farms)” it adds. “Expecting consumers to pay will unduly penalise those in society least able to pay.”
The study points out that green hydrogen for heating has an energy efficiency of 46% — in other words, for every 100kWh of renewable energy used to produce green H2, only 46kWh of buildings heat is produced, due to energy losses in the production, storage and transportation of the gas. By contrast, heat pumps produce an energy efficiency of 270%, meaning that for every 100kWh of renewable energy, 270kWh of heat is produced.
Blue hydrogen — produced via methane with carbon capture and storage (CCS) — would be slightly more energy efficient than green, resulting in 58% of the energy in natural gas being used for heating buildings. But blue H2, which is advocated by the gas industry, is not a zero-emission technology.
“This process does however emit CO2 as well as having upstream methane greenhouse gas leakages,” the report says. “Large-scale CCS technology is proposed to capture some 90% of these CO2 emissions. Additional bio-sequestration [eg, bioenergy with CCS] or similar would also be required to remove the remaining 10% of CO2 for ‘blue’ hydrogen to become zero carbon.”
The natural-gas industry says that 95-99% of emissions from methane-based hydrogen production could be captured and stored.
But the LETI report suggests that biggest, most insurmountable challenge of using hydrogen for heating is the gas pipework inside buildings — much of which is hidden inside walls and under floors — that would need to be upgraded to handle smaller hydrogen molecules. Existing gas boilers and cookers would also have to be replaced.
“The building side of a gas grid switch over [to 100% hydrogen] is in the hands of millions of building occupier owners… therefore, decisions by them to permit a switch over, or not, are likely to be made using non-energy/carbon rationale (eg, cost, amenity, expectations and disruption),” says the study.
“However, the new manufactured hydrogen is expected to cost more than natural gas, particularly if the cost of building pipework and appliance conversion is amortised within it. Issues like responsibility for disruption, redecoration and liability for re-purposing dwelling pipework are unresolved.
“LETI concludes it is unlikely that zero-carbon hydrogen supplied via a re-purposed gas mains network will be available for the vast majority of buildings, for the foreseeable future.”
However, the report does concede that “there does seem to be a sounder logic of fewer high-intensity gas users connecting to a smaller network”. These users include gas peaker plants, heavy industry requiring high-temperature heat, aviation and long-distance haulage.
The study does not point out that when hydrogen is combusted, it reacts with nitrogen in the air to produces nitrogen oxides that are greenhouse gases.
*LETI is a UK-based voluntary network consisting of more than 1,000 developers, engineers, housing associations, architects, planners, academics, sustainability professionals, contractors and facilities managers.