Plumbing the depths.
Regarding the article "Renewables go underground," here are a few basic sums (Professional Engineering No 3, 2019).
One of the deepest mine shafts in the UK is at Astley Green in Lancashire, 814m deep and 6.4m diameter. If we take a concrete weight 6m diameter and 12m high, we have 340[m.sup.3] or 814te. To wind this weight the full height of the shaft consumes 6.5MJ, or 1.8MWh. Dinorwig pumped storage can deliver 288MW for five hours, 800 times as much.
I'd be very surprised if there were anything like that number of disused shafts that deep in the UK, and the winding gear required to lift 814 tonnes through 814m in one go will be quite something.
Duncan Webster, Warrington