Drives & Controls July / August 2022

42 n CLEAN ENERGY July/August 2022 www.drivesncontrols.com Gravity-based energy storage is poised to lift off A Scottish engineering company has secured a £912,000 grant from the Department of Business Energy & Industrial Strategy to develop plans to build a gravity-based energy storage system on a brownfield site in the UK. Edinburgh-based Gravitricity will work with the control and simulation expert Industrial Systems and Control (ISC) and the winch supplier Huisman and Careys Civil Engineering to design a 4MWh-capacity system to be installed in a custom-built shaft, possibly at Knapton Energy Park in Yorkshire. The idea is simple. At times when electricity demand and prices are low, massive weights would be winched to the top of the shaft. When demand is high, the weights would be allowed to descend, generating power as they drop. Dropping a 500-tonne weight 800m could generate 1MWh. Gravitricity demonstrated the concept last year in a 250kW pilot plant using two 25- tonne weights in Leith, Edinburgh. It is also planning to build a full-scale project in a disused mineshaft somewhere in mainland Europe starting later this year. “Finding low-cost, long-life ways to store renewable power will be crucial in the world’s journey to net-zero,” says Gravitricity’s managing director, Charlie Blair. “Our multi- weight concept has been proven by our Leith demonstrator where two 25-tonne weights were configured to run independently, delivering smooth continuous output when lowered one after the other. We were able to demonstrate a round-trip efficiency of more than 80% and the ability to ramp up to full import or export power in less than a second. “A Gravitricity system with multiple weights offers a lower cost per MWh of energy stored – more weights give more mass (or MWh) – whilst the number of hoisting systems (which forms a substantial part of asset cost) does not increase,” he adds. “This project will demonstrate multi- weight use and control using a single set of hoisting equipment and will pave the way to custom projects which can be built wherever they are required.” Gravity-based energy storage has several potential advantages compared to other forms of large-scale energy storage, such as batteries or pumped storage hydroelectric schemes. It can reach full power in less than 1s and can release energy whenever it is needed, either in short bursts or over long periods of time. Full-scale projects could operate with efficiencies of up to 80%. Unlike batteries which degrade over time, gravity-based storage plants could operate reliably for periods of 50 years or possibly longer. They could be used to store energy from intermittent sources such as solar or wind power, and release it when needed to balance demand. They could also be used to power industrial processes that need short intense bursts of energy. Analysts at Imperial College have calculated that multi-weight gravity stores will offer long-duration energy storage at a lower cost than alternative technologies such as large-scale batteries or compressed air. They estimate that a 10MW/24.4MWh peak-shaving gravity-based installation operating for 25 years, would have a levelised storage cost of $171/MWh – less Energy storage systems that lift and lower large weights to store and release energy, are about to go commercial. They offer many potential benefits over other large-scale storage technologies – including much lower costs. Gravitricity’s proposed 4MWh gravity energy store could be built at Knapton in Yorkshire