  Many studies have shown that hydrogen could play a large role in the energy
transition for hard-to-electrify sectors, but previous modelling has not
included the necessary features to assess its role. They have either left out
important sectors of hydrogen demand, ignored the temporal variability in the
system or neglected the dynamics of learning effects. We address these
limitations and consider learning-by-doing for the full green hydrogen
production chain with different climate targets in a detailed European
sector-coupled model. Here, we show that in the next 10 years a faster scale-up
of electrolysis and renewable capacities than envisaged by the EU in the
REPowerEU Plan is cost-optimal in order to reach the +1.5{\deg}C target. This
reduces the costs for hydrogen production to 1.26 Eur/kg by 2050. Hydrogen
production switches from grey to green hydrogen, omitting the option of blue
hydrogen. If electrolysis costs are modelled without dynamic learning-by-doing,
then the electrolysis scale-up is significantly delayed, while total system
costs are overestimated by up to 13% and the levelised cost of hydrogen is
overestimated by 67%.
