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.