Tanygrisiau Reservoir

The culprit-- British Power's Tanygrisiau Reservoir. Vastly inconvenient though it was for the Ffestiniog Railway, the Tanygrisiau Reservoir formed part of a fascinating concept in national electric power management. During slack periods in power usage, water is pumped from Tanygrisiau through underground pipes uphill to a higher reservoir at Llyn Stwlan. When demand spikes, the water from Stwlan is flows back down through the pipes and turns turbines connected to generators, which in turn generate electricity to be fed back into the national grid. The water in the reservoirs thus functions as power bank, enabling British Power to meet times of peek power demand without building an overcapacity of straight generating plants.