The role of long-term energy storage in investment planning of renewable power systems

The transition towards a decarbonized power system requires the integration of large shares of variable renewable energy sources. Their intermittent nature challenges the short-term ability of the power system to maintain the system balance, and its long-term ability to meet the peak demand. This results in an increased need for operational flexibility. Simultaneously, the availability of conventional dispatchable generation to provide such flexibility becomes less evident. Energy storage systems present an alternative source of flexibility. This paper focuses on the role of long-term storage, such as power-to-gas, which is able to also deal with seasonal variations in the output of renewables. It studies the impact of long-term storage on the investment planning of a conceptual power system following the integration of large shares of variable renewable generation. Simulations show that long-term storage reduces the need for installed renewable generation capacity to meet renewable objectives, and that it has a pivotal role in realising a fully renewable supply at a realistic cost. Results further show that the deployment of long-term storage depends greatly on the availability of biomass. If biomass is available, long-term storage investment only occurs at extremely high renewable penetrations.