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NETWORK / 22 / NOVEMBER 2018 DEMAND RESPONSE & ENERGY STORAGE L ast month, environmentalists welcomed an update to the Smart Systems and Flexibility Plan issued by Ofgem that con - firmed that 15 of the 29 actions recommended in the original plan had already taken place. Measures include avoiding overpayments for energy storage and developing new licence condi - tions to ensure DNOs and DSOs cannot operate storage without Ofgem's consent – a move intended to ensure competitiveness in the market. "[It's] good progress for those companies looking to develop low-carbon projects, aggregate demand, store electricity and develop smart EV charging facilities," James Court, policy and external affairs director at the Renewable Energy Association (REA), said in October. But what types of storage project are being developed, or could be developed, in the UK? Some are stalwarts of the industry, such as pumped hydro, in which water is pumped up a hill at times of electricity sur - plus and released downhill through a tur- bine when demand is high. Pumped hydro is the most common global energy storage technology, with about 168GW of capacity installed. It's a well-understood, utility- scale technology, with four operational pumped hydro plants in the UK delivering 2,828MW capacity (24GWh of energy stor - age), according to the British Hydropower Association. Although pumped hydro is a traditional technology – there have not been any new developments in the industry in Britain since 1984 – it has the potential to deliver 1.75GW of additional capacity, says a report by Scottish Renewables. But potential pumped hydro projects are thin on the ground in Britain. One option may be to enhance existing systems. For example, Scottish Power has completed a two-year feasibility study to determine Smart storage The launch last year of the Government-backed Smart Systems and Flexibility Plan was a milestone on the road to a smarter energy system in the UK. The plan outlined the way in which continued decarbonisation of the economy and greater adoption of renewable energy could be supported by energy storage and demand side response (DSR) services. Ben Hargreaves reports. whether it is possible to expand the 440MW Cruachan pumped-storage hydro plant near Oban, Scotland to 600MW in 2016. There are also plans for new schemes. Snowdonia Pumped Hydro's proposed new 100MW plant at Glyn Rhonwy, north Wales, is in the detailed engineering design phase. It was awarded a Development Consent Order by BEIS last year as a "nationally significant" infrastructure project. With such schemes, the high capital cost of development and environmental impact of projects are poten - tial barriers. Other technology Compressed air technologies also have the potential to be used at a very large, regional scale for energy storage. Compressed air energy storage (CAES) plants convert electri - cal energy into high-pressure compressed air that can be released at a later time to drive a turbine, producing electricity. The first two CAES plants were established in Huntorf, Germany in 1978 (321MW) and McI - ntosh, Alabama, US, (110MW) in 1991. Both plants provide grid balancing services and store their air in subterranean salt caverns. As with pumped hydro, there haven't been new utility-scale CAES facilities built for some time. According to Storelectric, there is the potential for the development of 5GW of compressed air energy storage in the UK. Another energy storage technology with big potential is liquid air. What is said to be the largest liquid air energy storage project in the UK, run by Highview Power, became operational in Bury, near Manchester, this year. Liquid air energy storage use elec - tricity to cool air until it liquefies, stores the liquid air in a tank, brings the liquid air back to a gaseous state by exposure to ambient air or with waste heat from an industrial process, and uses that gas to turn a turbine and generate electricity. Highview Power's founders claim their technology has The Plessey Kiwi Power installation in Plymouth.