Edinburgh, Scotland startup Gravitricity has harnessed the potential energy of unused mineshafts as part of its low-cost energy-storage system that could disrupt the renewable energy storage sector.
The system calls for a large weight (2,000 metric tons) to be suspended in a vertical mineshaft. When the system has excess electricity—on a windy or sunny day, for example—the weight would be winched to the top of the shaft, creating potential energy. When energy is needed, operators would let the weight fall, releasing the stored energy and using it to power generators.
The system has been called straightforward and compared to existing systems in which water is pumped uphill and then released when energy is low.
In April, Gravitricity commissioned an independent assessment of the technology by researchers at Imperial College London’s Centre for Environmental Policy to produce a cost assessment of their solution to the energy storage problem. (Gravitricity’s managing director and lead engineer are also graduates of Imperial College.)
Despite significant upfront costs, the report found that in the long run, the Gravitricity technology showed compelling results. Researchers found that the system could provide a lower cost of energy storage than all alternatives, including lithium-ion batteries. This is in part due to factors, such as operating costs, potential degradation and changes to the cost of energy. For example, the system beat out lithium-ion batteries, which degrade over time, because of its zero degradation and potential for multiple daily cycles.
Initial projects are expected to utilize existing mine shafts. With a £650,000 grant (roughly $880,000) from Innovate UK, the company has signed a research and development agreement with Huisman, a Dutch manufacturing company specializing in lifting and drilling, to develop a 250-kilowatt concept demonstrator and test it in the Netherlands and Scotland in early 2019.
One concern is the stabilization of the land surrounding the mines. These areas have multiple mineshafts and tunnels running in various directions, which can result in sub-surface movement. Work would have to be done to ensure that the land is stabilized, and the surface can hold the significant weight.
Another potential pitfall could turn into a positive. Mines are often in remote places, which raises questions about how well these deep mine shafts are connected to the grid or what it would cost to extend the grid to these areas. If Gravitricity’s system were to launch, however, it could bring jobs and opportunities areas that have been particularly hurt by the decline in mining that has occurred as alternative renewable-energy systems have been adopted.