Australian start-up eyes disused mine shafts for giga-scale gravity energy storage | RenewEconomy

A newly launched Australian start-up has unveiled its own take on gravitational energy storage technology that will use super-heavy weights in legacy mine shafts to capture and release energy, with around 3GWh of potential storage capacity already identified for development.

The company, called Green Gravity, is headed up by ex-BHP executive Mark Swinnerton, who has led the engineering of the technology from Wollongong in New South Wales, and is working with universities and engineering partners – including the University of Wollongong and Soto Engineering – to develop it further.

The new company and technology launch comes as Swiss outfit Energy Vault gathers huge interest and numerous deep-pocketed investors in its “gigawatt-scale” kinetic energy based energy storage solution inspired by pumped hydro, but using blocks of solid material instead of water.

So far, the Swiss energy storage company has attracted interest from such giants of industry as Korea Zinc, Enel Green Power, Saudi Arabia’s Aramco and Swinnerton’s former employer, BHP.

Even Andrew Forrest’s Fortescue Future Industries is proposing to use gravity to charge the batteries in its “infinity train”, that will feature trains laden with iron ore charging as they come down the hills from mines to the port, injecting enough energy into the batteries to take the empty trains back to the starting port.

And, of course, pumped hydro operates on the same principal, Charging, or pushing water up to a higher resevoir, and then letting the water flow downwards to spin the generator when needed.

Green Gravity wants to use the potential gravitational energy of large masses, but Swinnerton says there are a few key differences to his company’s technology – some of which promise to make it cheaper and easier to build and more flexible in its applications.

The first key difference is in the use of proven mechanical parts and disused mine shafts – the latter of which exist in “bucketloads” around the country, Swinnerton told RenewEconomy on Monday. He puts the number at nearly 100,000.

Not all of these are suitable, of course, but Green Gravity has so far identified 175 mine shafts profiled across about 80 mines that it believes are very highly suited to housing the technology and would require minimal work to be converted for energy storage purposes.

“We’ve got about 3GWh of capacity already identified as really highly suited to our technology” said Swinnerton.

“This is real capacity that … is spread across the [National Electricity Market] and usually already connected to, or right next to existing transmission infrastructure.

“These first 175 [sites] are in all sorts of places, including Illawarra, the Hunter region, Mt Isa in Queensland, in Tasmania; and many of them are concrete-lined, premium shafts that are no longer required for mining operations and sitting there idle.

“Many of these shafts require minimal work to get them ready. …And then there’s another 3GWh after that that will be in slightly more difficult conditions, but we’ll figure out how to use more and more mine sites as we get more experience.”

Another key difference to the value proposition for Green Gravity, Swinnerton points out, is in the flexibility of the energy storage solution. While some gravitation energy technologies are focused on offering long-duration storage, Swinnerton says his company’s technology promises more variability.

“This technology is highly flexible. We can configure it for very short duration, where it can assist with local grid stability for distributed energy storage. But we also think there’s an opportunity in the two- to four-hour end of the spectrum as well. And then, of course, the longer duration, too.”

Given the basic physics of the technology, what each Green Gravity system offers will depend somewhat on the size and depth of the existing mine shaft, as well as the weight and density of the mass used to capture and release the energy.

Some of the multitude of smaller disused mine shafts scattered, for example, throughout country Victoria, could prove valuable as a source of community renewables energy storage for regional communities, Swinnerton points out.

That said, to make the most of the spaces and depths the mine shafts offer, Green Gravity’s technology will initially use “super, super heavy” weights made from steel, and possibly also iron ore.

On the financial side of the equation, Swinnerton says the company has so far been backed by a number of private investors, but is talking with the federal government and with the NSW state government about the possibilities of grant funding.

The company has also “started conversations” with venture capitalists and is aiming to conduct a fund-raising round in the next few months. And there’s lots of interest from miners, too.

“We’re really encouraged about the reception we’re getting across the full spectrum of mining houses. It’s very attractive for many of them, as both an energy storage solution and in terms of mine rehabilitation.

According to Green Gravity’s head of business development, Fionna Millikan, of the roughly 85,000 decommissioned legacy mine sites around Australia, and of that number only 3,000 have been rehabilitated, which adds up to a “large liability” for industry and government.

“Green Gravity’s concept of using the potential energy in a mass in a vertical mine shaft has a lot of advantages,” says David Whittle, a senior research fellow at Monash University and expert in mine planning.

“The environmental footprint of such an operation is very, very small. Even compared to things like lithium batteries. …So this has got to be one of the lowest environmental footprint renewable energy storage concepts there is,” he said.

“By reusing the existing infrastructure of disused mines, Green Gravity is developing sustainable energy storage infrastructure at a very competitive cost,” Swinnerton added.

“In the coming years our technology will offer a viable and scalable alternative to lithium-ion solutions.

“Green Gravity is working with multiple large energy, manufacturing and mining companies to rapidly develop a demonstration plant at a mining site.”