The premise behind gravity-driven energy production solutions is fairly simple, on paper. A large mass is lowered down a shaft. The cables attached to that weight spins a hoisting system that generates electricity via infrastructure above. The weight is lifted back to the top under renewable power when the sun is shining or the wind is blowing, or when traditional energy is cheaper, or by switching the hoisting system to a generator to help bring the weight back up.
The gravity solution can provide an immediate power boost to the grid. The deeper the shaft and the heavier the weight, the greater the power generated.
Best of all, it’s a system that uses empty mine shafts, infrastructure that is already in place and often resource-intensive to maintain, even in a disused state.
“Almost every country has old, abandoned mine sites where there’s a shaft,” says Paul Barclay, ABB’s Sales Manager Hoisting Solutions.
“Those shafts are on average between 500 and 1,200 metres deep. In South Africa and in some of the deeper gold mines in the US, they could be as deep as 2,000 metres, which could create a very nice period for regeneration.”
"Abandoned" shafts are typically under the care of mining companies, Barclay says. Those companies have to conduct maintenance to keep them in a safe condition, or plug them and shut them off, which includes rehabilitation.
“Either path requires a resource investment,” he says. “Or they can install a gravity regen solution on the shaft.”
Alongside the sustainability payoff, Barclay says, a regen retrofit could enable an otherwise-unused shaft to be classified as "operational", reducing closing charges, fees and penalties.
Perfecting the science of energy generation
The on-paper simplicity belies complex physics.
The generation of the maximum amount of electricity over the longest period of time requires a certain weight to be lowered down the available length of shaft, with a specific level of resistance provided by the hoisting system that acts as a generator.
“What the leading players are looking to do is find that place where they can have the object lowered as long as they can and regen as much as they can, without being in an environment where any person can be injured or damage something or the environment,” Barclay says.
Such a system can be set up to be fully automated and remotely managed, removing almost all human risk. But still, there are some optimisation challenges.
“The trick is the balance between the size of weight, the speed you lower it, and the amount of regen you want,” Barclay says. “You’re generating power as long as you’re lowering the weight – that period we call the ‘regen cycle’.” As it puts power into the grid immediately, it could represent an excellent solution during periods of peak demand when the mine site is connected to a grid serving a community.
On more remote sites, it can serve as a localized solution, providing for the unique energy needs of the mining business itself. “It solves a problem around what miners call ‘peak power shaving’, or controlling their costs when they suddenly need power during peak demand,” he says.
“That’s the beauty of this system. You can switch it on within minutes and put power straight into the grid. We’re talking about sufficient power to potentially run a small mining operation for a few hours if configured correctly.”
Advantages of gravity energy solutions
Among the numerous payoffs, there are challenges associated with gravity generation methods:
- The mine shaft must be structurally sound and, as abandoned shafts may have degraded over time, additional work may be required to shore up the shaft walls.
- The hoisting system must be capable of safely handling large weights – up to 100 tons – without failure.
- Advanced control systems must be put in place to enable safe and efficient distribution of energy.
The advantages over conventional energy generation and storage methods include:
- Minimal maintenance requirements: While other solutions such as batteries require regular replacement, gravity solutions can run for decades with relatively minimal maintenance.
- Gravity energy solutions rely purely on mechanical movement converted to electrical energy, so suffer no chemical degradation.
- Power generation is instantaneous, making it ideal for peak-demand scenarios and for reducing or negating the reliance on diesel or gas generators.
- Existing, disused infrastructure is utilised, saving costs and reducing environmental impacts.
Where are gravity solutions at now?
Currently, gravity energy production is in a pilot phase. Projects are underway around the world, including in Wollongong, NSW, to test and prove the process as a viable, sustainable energy alternative.
“The concept works, and the technology already exists,” Barclay says. “The regeneration, the mechanical hoists with their electrical drive train systems used to regen, the grid connection software – it’s all there. It can work today.
“There are so many mines globally interested in gravitational energy solutions, and ABB continues to work closely with our partners to ensure that they achieve maximum regeneration in a safe and sustainable way. They just need a customer to say ‘Do it on my site’: a customer willing to invest in a full-scale system together with our partners. Our partners can achieve this for them right now.”
