The Glyn Rhonwy pumped storage scheme has apparently received the go-ahead, overcoming objections to any development like this in a National Park. It uses a disused slate quarry for the upper reservoir, which should make the overall development cheaper, and limit any new environmental impact.
Pumped hydro storage is efficient and good value for money so it’s a shame that the best places to do it tend to be wild uplands where we are most uncomfortable about industrial intrusions of this type.
Here’s an idea for a pumped storage scheme using abandoned coal mine workings. It could offer even greater capacity than Glyn Rhonwy, with even less environmental disturbance. If it could be made to work, it should be readily reproducible elsewhere in Wales.