Gravitricity is an innovative gravity-based mechanical energy storage technology being developed by Gravitricity, an energy storage company based in Edinburgh, Scotland, UK. The novel energy storage system is based on the principle of raising and lowering a heavyweight to store and release electrical power.
It is believed that the technology if commercialised, will enable the storage of intermittent renewable energy, grid stabilisation, and rapid frequency response.
Gravitricity is piloting a 250kW energy storage demonstrator project based on this technology in Edinburg with the start of trial operations and grid-connection expected in 2021. The cost of Gravitricity’s 250kW energy storage demonstrator is estimated to be approximately £1m ($1.25m).
The Gravitricity demonstrator energy storage system will be an above-ground structure to be installed at the Port of Leith in Edinburg, Scotland, UK.
Gravitricity entered into a land lease agreement with Forth Ports, the operator of Port of Leith, in May 2020, to build the demonstrator on an industrial site at the Leith port. The port’s electrical network and grid connections will be utilised by the demonstrator.
Gravitricity energy storage concept
The system operating on Gravitricity technology consumes electric power to lift the weight and generates electric power when the weight is lowered.
A bunch of cables, with the help of a winch system, will suspend the weights weighing up to 5,000t in a shaft. Electrical drives will be used to control the winch system in order to keep the weight stable in the shaft. A tensioned guide wires system will prevent the weights from swinging and damaging the shaft.
The disused mineshafts or newly built shafts can be used for suspending weights. The depth of the shaft ranges from 1500m for disused mineshafts to 150m for purpose-built shafts.
The company claims the Gravitricity energy storage system can offer a 50-year design life and a round trip efficiency in the range of 80-90%. It is also believed to offer a cost-effective energy storage solution compared to lithium batteries.
Gravitricity 250kW energy storage demonstrator
The fabrication of the 250kW demonstrator commenced in August 2020. It will be an above-ground system with the rig height planned to be 16m. The demonstrator consists of two weights of 25t each suspended by steel cables. The length of the stroke will be 7m while the drop time for the full power of 250kW is expected to be 14s.
Gravitricity is planning a two-month test programme on the demonstrator system. It will perform a test by dropping two weights simultaneously for the generation of full power (250kW) and calculate the speed of response. The other tests include dropping one weight at a time to calculate energy output over a longer period.
The test will also validate the frequency response of the system. The test programme will provide inputs for the development of a full-scale 4MW project which is expected to be launched in 2021.
Gravitricity fundraise and grants
Gravitricity received approximately £1.5m ($2m) through crowdfunding. The company was also awarded a grant of approximately £300,000 ($373,000) under Innovate UK's Energy Catalyst programme in March 2020. The funds will be used for Gravitricity project feasibility work in South Africa in which consultancy firm RESA Energy is a partner.
Gravitricity was also earlier awarded a grant of approximately £650,000 ($907,000) from Innovate UK’s Infrastructure Systems Innovation competition in February 2018, apart from an initial grant of approximately £175,000.
Huisman, a Netherlands-based company specialised in lifting and drilling equipment, entered into a contract with Gravitricity to deliver a 250kW gravity-based grid stabilisation concept demonstrator in January 2020.
The fabrication of the energy storage demonstrator started at Huisman’s factory in the Czech Republic in August 2020. It is expected to be completed by the end of December 2020.
Kelvin Power, an engineering company, was contracted for the fabrication of a lattice tower for the 250kW demonstrator.