gbw - Stwlan dam

Stwlan Dam impounds the upper storage reservoir for the Tan-y-Grisiau pumped storage hydro-electricity scheme, also known as the Ffestiniog Power Station, which was commissioned in 1963. This type of station can respond to a sudden peak demand in seconds and the power required to "recharge" the system evens out the base load demand overnight. Full output is 360 MW and operates at 72% efficiency - the missing percentage represents the use of electricity to pump water back up to Llyn Stwlan, at times of otherwise low demand - such as overnight.