Dropping a deadweight down an abandoned mineshaft sounds more like a scene from a murder movie than the concept for renewable energy generation. Yet, with technical assistance from SOTO Consulting Engineers, the concept of dropping weights down unused mineshafts is exactly what energy technology company Green Gravity is exploring to provide renewable energy. Minus the dead body, of course.

The renewable energy scene is dominated by projects involving wind and solar, with more than $17 billion invested into projects under construction or due to start, as of late 2021, according to Clean Energy Council figures. Other technologies barely rate a mention. 

Yet, while Green Gravity’s idea is based partly on developing new technology, it is also part of a circular economy where disused mine shafts are a critical piece of infrastructure. The idea behind Green Gravity’s proposal is to harness gravity and kinetic energy to generate and store power. 

By lifting and dropping a heavy weight down a mineshaft, the movement of mass releases kinetic energy that can be captured and directed to the grid. Pumped hydroelectricity is based on a similar idea: water is released from dams and flows downhill, where it spins turbines that convert motion into electrical energy. The water is then pumped back uphill to repeat the process. 

The beauty of Green Gravity’s concept is that it requires far less space, doesn’t need any additional resources, such as water, and provides a use for unused mineshafts that require extensive and costly rehabilitation. Green gravity cites a figure of about 85,000 inactive mine sites around Australia, which have been decommissioned and not in operation. Only 3,000 of those have been rehabilitated, highlighting the potentially massive liability problem ahead. 

Being an energy generation and storage solution, it can produce and dispatch energy on-demand, smoothing out the intermittency issues with wind and solar-based technologies. In addition, it doesn’t need water, chemicals, or destruction of land, and overall has a very small environmental footprint. 

“Here is thinking out of the box – gravity is potential energy, it’s freely available, and we should be able to harness it with the right thinking,” says SOTO Managing Director Frank Soto. “There is so much solar generation that they give power away for free in the middle of the day. But at 7pm the demand is much greater, and this is where the gap needs to be plugged. 

SOTO was introduced to Green Gravity in late 2021 to explore how the concept could move from drawing board to design and construction. 

“I looked at the references they provided and did my own calculations of potential energy due to gravity,” Mr Soto says. “The numbers spoke volumes to me, and I could see engineering problems that needed solutions – an engineer’s dream. The re-use of a legacy asset like a disused mine shaft is a stroke of genius in my opinion. There are more than 1000 mine shafts in NSW alone.”

SOTO produced 3D models of the concept, using proven and reliable mechanical and electrical engineering machinery. The firm currently has a project team working on solutions for taking the gravity unit and integrating it into a mineshaft to build a demonstration site. 

“We did some calculations and preliminary concepts to stress test the concept and compare to what was in the public domain in this space,” Mr Soto said. “No one has really done this sort of thing or commercialised the idea because what is great in theory does not always convert to the real world so easily. 

“The biggest hurdle may not be the engineering, but it will take a big investment and a lot of innovation to get it off the ground and construct a demonstration or commercial scale system to plug into the grid. Yet, how this system could be plugged into the future of power generation is very appealing.

“Green Gravity can and should be a player in the renewable energy space.”