Managing seasonal and interannual variability of renewables

Renewables are growing rapidly in the electricity systems around the world as countries seek to improve their energy security, meet emission reduction targets and take advantage of cheaper electricity sources. Thanks to successful use of flexibility resources – from stronger grids and interconnections to demand-side measures, affordable storage and dispatchable power supply – many countries have already securely and efficiently integrated significant shares of variable renewables (VRE) in their electricity generation. As wind and solar continue to grow as a proportion of generation, system level surpluses and periods of lower generation will eventually expand beyond hour-to-hour or daily variations to seasonal timescales. Addressing seasonal variability of renewables means that flexibility resources will be needed to varying extents throughout the year, even on a week-to-week or month-to-month basis. The present study, produced in support of Japan’s G7 Presidency, explores the integration of VRE beyond 70% share of annual generation in future power systems, focussing on four different climatic regions: Temperate with hot summer, Tropical, cold Arid and Continental with warm summer. The study confirms that a mix of flexibility resources is needed to manage variability across all timescales and seasons. In particular, systems with very high level of VRE require seasonal flexibility services, which can be provided from existing thermal power capacities and from hydropower plants. Eventually, as energy systems transition towards net zero emissions, all flexibility services will need to be fully decarbonised.