Construction of the prototype of a gravity-driven energy storage system that promises to operate at half the price of current market-leading lithium-ion (Li-ion) batteries is now underway, with plans to start testing the innovative technology in Scotland next spring.

A 250kW version of Edinburgh-based Gravitricity’s concept – which works by raising weights totalling up to 12,000 tonnes into a lattice tower and releasing them into a deep shaft to discharge energy as required – is being built by Dutch winch specialist Huisman and UK engineering firm Kelvin Power as part of a £1m ($1.3m) project.

“Our demonstrator will use two 25-tonnes weights suspended by steel cables. In one test we’ll drop the weights together to generate full power and verify our speed of response. We calculate we can go from zero to full power in less than a second – which can be extremely valuable in the frequency response and back-up power markets,” said Gravitricity lead engineer Miles Franklin.

“We’ll then run tests with the two single weights, dropping one after the other to verify smooth energy output over a longer period, alongside a programme of other tests to demonstrate and refine the full capabilities of the system.”

The two-month trials, which will be carried out with the system grid-connected, are expected to lead to development of a first full-scale 4MW model later in 2021.

Gravitricity, which has recently raised over £1.5m for technology development through a crowdfunding campaign and have also received a £640,000 grant from Innovate UK, the British government’s innovation agency, sees the technology being deployed in repurposed mineshafts around the world.

An earlier study from Imperial College London highlighted that the technology was well suited to a role in grid balancing and rapid frequency response services for electricity network operators given that in a frequency response scenario – requiring 700 cycles per year and a duration of 15 minutes at a power output of 4MW – the system had a predicted levellised cost of storage (LCOS) of $141/kW per year, “outperforming all alternatives”.

CGI of above-ground part of Gravitricity's gravity-based energy storage system Photo: Gravitricity

The report found that electricity released by a typical 10MW Li-ion battery would cost $367MWh over its lifetime compared with a cost of $171/MWh for electricity from a Gravitricity project.

Competition among next-generation energy storage technologies looking to depose Li-ion at the top of the energy storage market continues to hot up with liquid air ‘cryo-batteries’ – such as UK developer Highview Power’s, Canadian outfit Zinc8’s zinc-air design, and vanadium redox flow batteries – including Canadian-UK joint venture Invinity's – all claiming their technology will outclass Li-ion on long-term LCOS.

Li-ion batteries have come to monopolise a global energy storage sector forecaset by Bloomberg New Energy Finance to grow from 9GW/17GWh in 2018 to over 1TW/850GWh by 2040.

New battery chemistries were picked out alongside high-temperature heat pumps and green hydrogen by international energy consultancy DNV GL to lead the ‘second phase’ energy transition technologies that will build on the ongoing wind- and solar-powered shift.