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BATTERY STORAGE NETWORK / 22 / NOVEMBER 2019 Pumped hydro Over 96 per cent of the world's energy storage is in the form of pumped-storage hydropower, according to the International Hydropower Association (IHA). It provides peak-load supply, using water cycled between a lower and upper reservoir. The water is pumped using surplus energy from the system during low demand conditions (see diagram, right). When electricity demand is high, water is released back to the lower reservoir through turbines to produce electricity. Last year, research published by the IHA estimated that an additional 78,000MW in clean energy storage will come online by 2030 from hydropower reservoirs fitted with pumped storage technology. According to the research, the benefits of pumped hydropower storage include lifetime cost, levels of sustainability and scale, as well as significantly longer discharge durations than many battery solutions. Despite its dominance in the market, pumped hydropower storage does have its drawbacks. As the process requires two reservoirs to be suitably spaced, there are clear geographical constraints. As well as specific design and construction requirements, there is also a perceived lack of flexibility when compared to solutions like battery storage. "Most batteries can be 'instant-on' so therefore can provide the right level of service to help with balancing," says Nick Kitchin, CEO, Cumulus Energy Storage. "Pumped hydro doesn't offer the same instant response times, which is often inadequate for much of the energy that the market requires. Most pumped-storage hydropower projects were built between the 1960s and 1980s, the best known UK example, Dinorwig Power Station in Snowdonia, north Wales, was completed in 1984. A proposed new 50 MW pumped storage facility at nearby Glyn Rhonwy in disused slate pits (below), was approved in 2013, at an expected cost of £120m. By 2019, this project had reached the "detailed engineering design" stage under its promoter, the Quarry Battery Company. According to the project's website, it will offer 100MW of power generation and 700 MWh of storage capacity, with a response time of 12 seconds from start to full power. Efficiency is estimated at around 81%, and the project would have a lifespan of 125 years. The Quarry Battery Company website also says that it is looking for partners and investors to help deliver the project.