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NETWORK / 12 / DECEMBER 2019 / JANUARY 2020 FLEXIBILIT Y Calculating storage and flexibility needs in a net-zero world Alex Buckman, networks and energy storage practice manager at the Energy Systems Catapult, describes its new Storage and Flexibility Model, a number- crunching tool that can calculate the future storage and renewable generation capacity needed to meet variable demand in a net-zero world. R eaching net zero means building an energy system radically differ - ent to what we have today, with storage and flex- ibility expected to play a much larger role. As demand for electricity rises, and intermittent renewables become more prevalent, storage technologies such as batteries and hot water tanks will help ensure that networks can cope, whilst allowing homes and busi - nesses to save money by avoiding times of peak demand. Until now, we have relied on carbon-based energy storage, such as gas and oil. These are generally kept in either large storage sites before being used in refineries, or independent storage sites before being sent to smaller storage tanks at petrol stations. Energy consumption in the UK is still incredibly reliant on fossil fuels (see chart, below), with gas and petroleum the incumbent giants. Coal has seen a dramatic reduction in recent years, and whilst this is welcome, it risks distracting us from the vital flexibility that natural gas and petroleum still provide to the energy system. Take three examples across different timescales: Season by season: The average daily gas demand on distri- bution networks in winter is approximately five times higher than in summer, balanced through a mix of imported gas and increasing gas extraction to above average demand. Hour by hour: When the so- called "Beast from the East" struck in 2018, electricity demand increased by 11 GW within three hours. In fact, 80% of the increase in total electric - ity demand was met by gas and coal – an energy volume of 28.8 GWh, equivalent to the output of 2.5 Dinorwig power stations. Any electrification of heat sup - ply would increase this energy volume substantially. Annual inland energy consumption by primary fuel in the UK (million tonnes of oil equivalent) Source: Digest of UK energy statistics (DUKES) 2018 Second by second: The electricity network requires real-time balancing to make sure that the frequency on the network remains within op- erational limits – this becomes more difficult with more re- newables in the energy system. The "balancing mechanism" is one of the ways we can procure flexibility to help balance the electricity system. In the year leading up to September 2019, however, it's worth noting that approximately 80% of the energy volume procured by the balancing mechanism was fossil fuel-based. Clearly, a net zero energy system will have profound im - pacts on the role of storage and flexibility, way beyond the well- known challenges of integrating high amounts of renewables. The flexible roles of natural gas and petroleum will need to be replaced, even if optimistic rates of carbon capture and storage can be achieved (which is far from guaranteed). Replacing their flexibility within our current system would be extremely difficult; replacing them in a net zero energy system will be nothing short of heroic. Low carbon supply technolo - gies are typically less flexible, whilst electrified demands do not benefit from the luxury of gas "linepack" – the volume of gas contained within the system – to reduce real-time balancing re - quirements. When you then add the volumes of seasonal energy storage supplied by fossil fuels, it becomes increasingly complex to find the most appropriate system design and storage mix. A net-zero energy system will need to be able to balance supply and demand across energy vec - tors, network levels and time- frames, but the exact role storage and flexibility will take is depend- ent on the system that emerges. A model future The Energy Systems Catapult has therefore launched the Storage and Flexibility Model (SFM), which provides a com - prehensive representation of the