Caveats of green hydrogen for decarbonisation of heating in buildings

Hydrogen (H2) has rapidly become a topic of great attention when discussing routes to net-zero carbon emissions. About 14% of CO2 emissions globally are directly associated with domestic heating in buildings. Replacing natural gas (NG) with H2 for heating has been highlighted as a rapid alternative for mitigating these emissions. To realise this, not only the production challenges but also potential obstacles in the transmission/distribution and combustion of H2 must be technically identified and discussed. This review, in addition to delineating the challenges of H2 in NG grid pipelines and H2 combustion, also collates the results of the state-of-the-art technologies in H2-based heating systems. We conclude that the sustainability of water and renewable electricity resources strongly depends on sizing, siting, service life of electrolysis plants, and post-electrolysis water disposal plans. 100% H2 in pipelines requires major infrastructure upgrades including production, transmission, pressure-reduction stations, distribution, and boiler rooms. H2 leakage instigates more environmental risks than economic ones. With optimised boilers, burning H2 could reduce GHG emissions and obtain an appropriate heating efficiency; more data from boiler manufacturers must be provided. Overall, green H2 is not the only solution to decarbonise heating in buildings, and it should be pursued abreast of other heating technologies.