With coal mining becoming a thing-of-the-past, the world will be left with a lot of empty mine shafts. However, a group of entrepreneurs in the UK has come up with an idea that would breathe life back into coal mining communities.
The newly formed energy company, Gravitricity, has a patented technology to make old mine shafts generate energy using a giant weight system. Gravitricity has secured a £650,000 grant from Innovate UK, the government innovation agency to undertake the development of the sub-system design and deploying a 250kW concept demonstrator. The company aims to trial the first full-scale prototype in 2019 or 2020 at a disused mine in the UK.
The idea behind stored energy
As more and more electricity is generated from intermittent renewable energy sources, there is a growing need for technologies which can capture and store energy during periods of low demand and release it rapidly when required. Gravitricity looked at the problem and came up with an energy storage solution that uses the best characteristics of lithium batteries and pumped storage.
The company claims the technology is ideally suited to network-constrained users and operators, distribution networks and major power users, the technology operates in the 1MW to 20 MW power range and enables existing grid infrastructure to go further in a renewable energy world.
Pumped-storage hydroelectricity allows energy from intermittent sources (such as solar, wind) and other renewables, or excess electricity from continuous base-load sources (such as coal or nuclear) to be saved for periods of higher demand.
Many recently proposed projects avoid highly sensitive or scenic areas, and some, like the 2012 study by the European Renewable Energy Network propose to take advantage of “brownfield” locations such as disused mines.
Basically, Gravitricity’s patented technology uses a simple principal – What goes up must come down, or in this case, raising and lowering a heavy weight to store energy. In practice, it has similar advantages to pumped storage for networks up to 33kV, but without the need for a nearby mountain with a lake or loch at the top. And that is the good part of the plan.
Gravitricity’s technology and how it works
Gravitricity managing director Charlie Blair explained the system: “A cylindrical weight of up to 3000 tonnes is suspended in a deep shaft by a number of synthetic ropes each of which is engaged with a winch capable of lifting its share of the weight.” It appears that electrical power is absorbed or generated by simply lowering and raising the weight.
The weight is guided by a system of tensioned guide wires (patents applied for) to prevent it from swinging and damaging the shaft. The winch system can be accurately controlled through the electrical drives to keep the weight stable in the hole.
Blair said, “The winches become generators, producing either a large burst of electricity quickly, or releasing it more slowly depending on what is needed. When there is excess electricity, for example on a windy day, the weight is winched to the top of the shaft ready to generate power.”
“This weight can then be released when required, in less than a second, and the winches become generators, producing either a large burst of electricity quickly, or releasing it more slowly depending on what is needed, Blair adds.
The company claims the system has a work life of 50 years and is 80 to 90 percent efficient. And besides being versatile, it is also simple to operate and cost-effective when compared to lithium-ion batteries. Bottom line? All you need is a deep hole in the ground.