  Renewable electricity sources such as wind and solar have shown a remarkable
development in terms of efficiency, costs and availability, but system
integration still remains a challenge. Realizing a fully renewable electricity
supply will require large scale storage technologies and flexible users to
overcome long periods of low power generation. At the same time, other sectors
such as mobility and industry must be electrified to replace fossil fuels.
Power-to-Methane is a promising technology as it enables large-scale energy
storage and sector coupling using existing infrastructures. In this work, we
analyze the co-transformation of the German electricity, mobility and industry
sector taking into account the recent decisions for coal phase out until 2038.
We evaluate the necessary capacities of renewables and storage sizes as well as
system costs and associated emissions using a techno-economic optimization
model with a high technological and temporal resolution in the open source
framework OSeMOSYS. We find three rather different stages of the transformation
driven by the decreasing emission gap and the coal phase out. Solar power is
expanded vastly until 2030, then coal is replaced mainly by fossil natural gas
until 2040. Emission caps become very challenging afterwards such that all
flexibility options are greatly expanded: Storage, curtailment and flexible
Power-to-Methane.
