How much storage do we need?
The increasing penetration of low-carbon generation capacity requires more power system flexibility. Figure 1 compares the findings of 30 studies across the US, EU, Germany, and Great Britain (GB), regarding the required electricity storage energy capacity and power capacity in low-carbon power systems with increasing shares of variable renewable energy (VRE). The energy capacity and power capacity requirements are displayed relative to annual electricity and peak power demand respectively. Most studies appear to agree that for up to a VRE penetration of 50%, a power market requires less than 0.02% energy storage capacity and 20% power capacity. Taking Great Britain as an example with ~50 GW peak and 300 TWh annual demand, this would amount to 10 GW and 60 GWh of electricity storage capacity.
Storage requirements increase exponentially at higher levels of VRE penetration. Moving to 80% and 90% penetration, the energy capacity requirement increases to 0.03–0.1% and 0.05–0.2% respectively (60–300 GWh and 150–600 GWh in the example of GB). Power capacity requirements increase to 20–50% and 25–75% (10–25 GW and 12.5–37.5 GW). There is substantial variation between the findings of different studies, especially in terms of energy storage capacity, as the studies in Figure 1 cover several geographies and make their own differing assumptions about the mix of technologies which provide flexibility (i.e. storage vs interconnection, flexible generation, and DSR).
Figure 1 - (a) Electricity storage energy capacity and (b) electricity storage power capacity requirements as a function of variable renewable energy penetration. Capacity requirements are displayed relative to annual electricity or peak power demand. Data based on a literature review of 30 studies modelling electricity storage requirements in low-carbon power systems in the US, Great Britain, Germany, and the EU, in part compiled by Zerrahn et al., 2018 in "On the economics of electrical storage for variable renewable energy sources." Budischak scenarios: GIV—Grid-integrated vehicles, National Grid scenarios: CR—Community Renewables, TD—Two Degrees, SP—Slow Progress, CE—Consumer Evolution. Repenning scenarios: KS 80/95–80%/95% emission reduction.
Incorporating low shares of VRE is relatively easy as their variability can be accommodated by slight alterations in the dispatch of conventional power stations. As VRE share increases further it becomes increasingly difficult to manage the balance between supply and demand. Exponentially increasing power capacity is needed to consume the increasing amounts of excess renewable energy for later discharge in most cost-efficient low-carbon energy systems. The combined impact of additional variable power capacity and the time it is supposed to generate electricity means that energy capacity requirements increase at an even higher exponential rate to ensure sufficient electricity is available at all times. Not only is more backup power needed but it is also needed for longer periods of time. The table below quantifies energy and power capacity need of energy storage for various levels of VRE penetration.
Schmidt, O., & Staffell, I. Monetizing Energy Storage - A toolkit to assess future cost and value. Oxford University Press. 2023.