When I lived up in North Wales I went to a hydroelectric plant with a school tour. The place in question is called "Dinorwig" and was, when commissioned, considered to be a technical marvel. It's built inside the mountain (and has earned the nickname the "electric mountain" for this reason) and can go from total shutdown, to 1800 MW output in only 16 seconds. <br>It is also a "pumped storage" facility, during off peak times, when less energy is in use but extra may be being produced, it uses that excess to pump water into the lake at the mountain top, then, when demand rises, the valves are opened and the lake drains through the turbines and into the bottom lake. If my memory serves me correctly, with the top lake at full capacity, they can generate power for 5-7 hours. <br>These days it is usually used to provide short term generation during sudden demand surges. (Tv ad breaks etc.) or if another power station goes offline and is also designed to be a "restart" facility should the national grid go dark.<br>It's an intriguing place, and the main hall is terrifying but awe inspiring. You can still take a minibus tour deep into the heart of the plant and the mountain and see how it works.<br>Dinorwig is on Wikipedia if anyone would like to know more.   <br>And I'm probably terribly sad for still finding that place amazing, and having fond memories of that school trip a good 20 years on. ,(reply>), I don't think they can run it for ~6 hours at full chat. 6 minutes maybe. But it can probably cover 6 hours worth of variable peaking demand over a period where the grid is always in slight deficit and the high momentum steam turbine plants are run so as to always be just very slightly off the pace to avoid too much overvoltage / increased frequency when demand suddenly drops, until needing to be refilled using surplus energy once the peak period is over.,(reply>), Did they still have the electric Leyland Sherpa tour bus?