An Australian storage start-up, Green Gravity, has announced the first test site for its gravity energy storage system (GESS) which will use up to 30-tonnes of steel coil lowered into vertical mine shafts.
Green Gravity and Yancoal have signed a Memorandum of Understanding (MoU) to run a pre-feasibility study looking at whether and how the technology might work in decommissioned ventilation shafts, starting with the closed Austar mine in NSW. The study is expected to finish in 2023.
The study will also consider the tech’s potential for working in the NSW grid as a long duration energy storage provider.
Led by former BHP executive Mark Swinnerton, Green Gravity is fresh from its first capital raise in May when it landed $1.4 million. It is currently raising $18 million.
“The potential for the system is in the hundreds of MWh,” Swinnerton told RenewEconomy.
“The Yancoal mineshafts are in the 400-500m depth range and we consider this depth to be supportive of commercial scale operations for the technology.”
In an earlier statement he said costs can be kept low by re-using mining assets and by using gravity as the fuel they don’t have to use and pay for land, water and chemicals that other storage technologies need.
“Successfully identifying the best method of fitting gravitational technology at the former Austar mine site will create a template for beneficial re-use of legacy mining sites for Yancoal, and for thousands of other mines around the country,” he said in the statement.
Yancoal Australia CEO David Moult says the company is “proactively exploring” renewable energy opportunities with a potential role in beneficial post-mining land use.
“This MOU with Green Gravity is a demonstration that we are serious in assessing potential renewable energy opportunities and in collaborating with innovative partners to progress our strategy and vision for Yancoal’s future,” he said.
Re-using mine shafts as gravity batteries
Green Gravity made a media splash earlier this year when it said it had 175 possible sites in mind that could generate a total of 3GWh of energy.
Swinnerton told RenewEconomy at the time the sites were across the country in places such as Illawarra, the Hunter region, Mt Isa in Queensland, and Tasmania, many of which are perfect for re-use: concrete-lined, premium shafts that are sitting idle.
Today he said they’d assessed dozens of sites “in a reasonable level of detail” and is confident “that there is a large number of potential host locations for the storage system”.
The demonstration plant will use excess renewable energy during the day to lift 30 tonne steel coils to the top of a mine shaft. When energy is needed in the evening it drops those weights which creates kinetic energy to spin a regenerative electrical motor, somewhat similar to what is used in the wind generation industry.
Green Gravity’s technology is similar to pumped hydro in that it uses gravity to generate power, but as yet it is untested at scale. It’s working with the University of Wollongong and Soto Engineering to develop the concept.
The rise of gravity storage
A number of different companies around the world are testing different GESS concepts.
The Long Duration Energy Council says Australia will build as much as 0.5-1 TWh of long duration storage systems, be it concentrated solar thermal, gravity, compressed air, pumped hydro or something else, between 2030 and 2040.
Swiss hopeful Energy Vault has struck a range of deals in Australia to test out its tech, which involves lifting blocks of purpose-made composite material up to 100 metres in the air.
Its backers include Saudi Aramco and Korea Zinc, and it has agreements with BHP and Italian company Enel Green Power. It has a pilot plant in Switzerland and it has a contract to build a 10MW system in China, although most of its recent deals have been centred on battery storage.
Other aspirants in the space include Gravitricity in the UK which also uses an underground weights design, and Heindl-Energy in Germany and Gravity Power in the US.
Both are pitching a system that pumps water under a giant underground rock or weight. ARES is building a 50MW plant in Nevada to test its system of pushing railcars downhill.
Swinnerton believes his technology has an advantage over other long duration technologies in that it can be designed to provide short duration power of two to four hours, as well as long duration power.
