Photo: Bill Allsopp/Alamy
The switch to renewables is creating
its own challenges. Problematic and inefficient as it is, coal has one advantage over renewables: it stores energy. Lithium-ion (Li-on) batteries are increasingly used to store the excess energy generated by renewables, but while the cost of producing batteries has dropped like a stone over the past thirty years, there are environmental and ethical issues that still need to be addressed as they scale up. There is also a limit to how many times they can be charged and discharged per day, and they will degrade over time. Recently decommissioned coal mines could offer a more reliable alternative: kinetic batteries. Hydropower kinetic batteries are already the backbone of many energy networks, using cheaper off-peak or excess renewable energy to pump water into dams, ready to be released when needed. The same principle is used for what some are calling ‘gravity batteries’. There are different ways of implementing the technology, but all use
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the concept of storing potential energy by lifting a heavy weight. Kinetic energy is created by lowering the weight, which is converted into electricity by a generator. There are above-ground models in development, such as towers that raise and lower weights, but mineshafts offer a less obtrusive and ready-made solution. Former coal mines are already connected to the grid, have established road infrastructure and importantly, have local communities that are often in need of work. The deeper the shaft, the more electricity it will generate. One theoretical model uses containers full of sand instead of weights that could store up to 70 Terawatt hours – enough to power the whole world for 24 hours. Gravity batteries have the advantage
of being able to provide instantaneous power at different rates depending on the rate of descent. Scottish energy pioneer Graviticity estimates that their model could generate enough energy to power 13,000 homes for two hours on demand.
When it comes to large-scale
storage, it’s unlikely that gravity batteries will displace lithium batteries or hydropower. But with a potential lifespan of up to fifty years thanks to their repairability, gravity batteries could become an essential part of the UK’s energy mix, with the added benefit that, unlike Li-on batteries, they won’t short out, catch fire or leak. Gravity batteries are still in the
development stages, but mine water geothermal projects in former coal mines are already being used to generate heat for households and businesses. Deep coal mines are pumped to prevent them from flooding, so when a mine closes the pumps are switched off, and the mines fill with water. The further down you go the warmer it gets, which means that the mine water is naturally heated to between 10 and 20 degrees Celsius. In Gateshead, Northumberland, the
remnants of an industry that began in the 12th century and ended in the 1960s is again producing energy for its local community. The Gateshead Mine
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