Electricity will meet an increasing fraction of the world’s growing energy needs as fossil fuels are phased out. In Great Britain most will be provided by wind and solar. To match wind and solar, which are volatile, with demand, which is variable, they must be complemented by using wind and solar generated electricity that has been stored when there is an excess, and/or supply from large-scale flexible low-carbon sources, of which there are very few. Chris’s talk will describe the findings of a study (which can be found at royalsociety.org/electricity-storage) of options that can provide reliable electricity when wind and solar generation is unable to meet demand directly (with or without steady baseload supply). The long-term variability of wind speeds requires some very long-term large-scale storage, which would best be provided by hydrogen. The cost appears to be acceptable, but new market mechanisms will be needed to attract the investment that will be needed.