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10 | JUNE 2021 | UTILITY WEEK Speical report on storage Analysis The state of storage We need storage on the system to balance intermittent reneweables – and lots of it – but what technologies are currently available, are they yet commercially viable and can they scale up? Tom Grimwood talks to leading storage technology companies. R enewables such as wind and solar have already proved their ability to match and even beat fossil fuels on a cost per megawatt-hour basis. However, they are also intermittent, with their output determined by the UK's famously capricious weather. Building a zero-carbon energy system with renewables as the back- bone will require storage – and lots of it. Lithium-ion batteries are the most prominent stor- age technology at the moment and the yardstick against which others are measured. They have a number of strengths, including a high round-trip efficiency that ranges between 80 and 97 per cent depending on the use-case, according to Lazard's Levelised Cost of Storage report for 2020. However, they also have several limitations, which will mean they alone will not be enough to take us all the way to a decarbonised energy system. Lithium-ion batteries suffer from degradation between cycles, requiring careful management to retain their capacity. Production is currently constrained by supplies of lithium which, despite its natural abun- dance, remain limited. There are environmental con- cerns about some mining practices and ethical concerns over the mining of other constituent elements such as cobalt. These resource requirements mean that, despite falling costs, they are unlikely to ever be cheap enough to provide large-scale, long-duration storage. With this in mind, Utility Week takes a look at some of the many other storage technologies on offer. Flow batteries Matt Harper, chief commercial officer at Invinity Energy, says that in lithium-ion batteries the storage and delivery of energy are "tightly wound up" within the cell. In flow batteries, these capabilities are separated, with energy stored in tanks of liquid electrolyte and power generated in cell stacks through which the liquid is flowed – hence the name. ITM Power's new Gigafactory at Bessemer Park in Sheffield