  Electricity transmission expansion has suffered many delays in Europe in
recent decades, despite its significance for integrating renewable electricity
into the energy system. A hydrogen network which reuses the existing fossil gas
network could not only help to supply demand for low-emission fuels, but could
also to balance variations in wind and solar energy across the continent and
thus avoid power grid expansion. We pursue this idea by varying the allowed
expansion of electricity and hydrogen grids in net-zero CO2 scenarios for a
sector-coupled and self-sufficient European energy system with high shares of
renewables. We cover the electricity, buildings, transport, agriculture, and
industry sectors across 181 regions and model every third hour of a year. With
this high spatio-temporal resolution, the model can capture bottlenecks in
transmission networks, the variability of demand and renewable supply, as well
as regional opportunities for the retrofitting of legacy gas infrastructure and
the development of geological hydrogen storage. Our results show consistent
system cost reductions with a pan-continental hydrogen network that connects
regions with low-cost and abundant renewable potentials to demand centres,
synthetic fuel production and cavern storage sites. Developing a hydrogen
network reduces system costs by up to 26 billion Euros per year (3.4%), with
the highest benefits when electricity grid reinforcements cannot be realised.
Between 64% and 69% of this network could be built from repurposed natural gas
pipelines. However, we find that hydrogen networks can only partially
substitute for power grid expansion. While the expansion of both networks
together can achieve the largest cost savings of 10%, the expansion of neither
is truly essential as long as higher costs can be accepted and regulatory
changes are made to manage grid bottlenecks.
