POWER SUPPLY
The Dinorwig Power Station with a 9.1GWh output is well-concealed in the Welsh mountains.
taken from the grid and stored, to be released back into the grid at times of peak demand. The problem certainly existed during the fossil fuel era. An efficient method of tackling it has been stored hydro. Excess energy is used to pump water to top of a hill – the better option being a mountain. When demand outstrips supply, it is released to fall down the hill, passing through a turbine that turns a generator as it goes. Stored hydro is efficient, if costly, but has the disadvantage that it needs suitable geology – for instance, a mountain, which gets rained upon but is located reasonably near to the population that needs its energy. In the UK, the Dinorwig pumped hydro station has been operating since 1984 and can store 9.1GWh of electricity. There are alternatives though, and chemical
batteries are one of them. Large lithium batteries of up to 3,000MWh capacity have been built in California. But lithium is in huge demand for more portable batteries – most obviously for electric cars – and the energy stored in them leaks out over time. Another method has recently been put into commercial operation, which depends
34 | May 2025 |
www.hoistmagazine.com
entirely on the properties of electric hoists. It has been known since Victorian times that an electric motor is a consumer of electricity when it is working to turn something, and a generator of electricity when something is working to turn it. Regenerative braking has been used in cranes and hoists for many years. When the crane lifts a load, it consumes electricity, and when it lowers the load, the work is done by gravity – the ropes, therefore, turn the crane’s motor causing it to generate electricity that can be fed back into the grid. Electric cars use regenerative braking in the same way – their batteries get recharged when they brake.
Hence the gravity battery – by using peak electricity to power a hoist to lift a large weight, the weight is happily kept at that height for a while. Then, when demand for electricity spikes, the weight is slowly allowed to fall. The unwinding rope turns the hoist, which turns into a generator that feeds electricity back into the grid. Behold, you have stored electricity, which has been done very efficiently with minimal loss. All you need is a hoist, a heavy weight and a vertical distance through which the weight can move up and down.
That vertical distance is crucial – the bigger it is, the better. Disused redundant mineshafts have been investigated for the purpose, but Swiss company Energy Vault has produced the world’s first commercial-scale Gravity Energy Storage System (GESS) using above-ground lattice structures with hoists at the top of them. The 25MW/100MWh EVx Gravity Energy
Storage System (GESS) is in Rudong, Jiangsu Province, outside Shanghai in China and is currently being commissioned. It is directly adjacent to a wind farm and the national grid. The system is projected to achieve a round- trip efficiency exceeding 80% and to have a projected operational lifespan of 35 years. Peak power output is 25MW while the total energy stored is 100MWh, which can be released over a four-hour period – the length of time it takes the weights to fall. A second project, at Zhanguye City, is under construction. This will be slightly smaller at 175m, storing 68MWh of electricity that can be released at a peak rate of 17MW. The hoists of these projects need few unusual features as off-the-shelf models suffice. It is heartening to know that run-of-the-mill electric hoists might play a crucial part in saving the world.
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