In the craggy highlands of north Wales an energy mountain is being created. When completed in two years, it will be Europe's largest pumped storage electric power plant, and the world's most modern facility for dealing with grid failures and other large-scale electrical emergencies.
The project at Dinorwic has already involved excavation of 1.3 Million cubic yards of rock and earth. When it begins operating, it will enable water to be pumped up the mountain into a huge reservoir, then run down again through turbines into another.
Engineers faced with sudden power-station breakdowns will be able to produce 13 million watts of electricity at 10 seconds' notice, and sustain output at that level for five hours. Dinorwic's response time will be faster than any comparable facility in the world.
Pumped storage plants have three main uses. They can deal with peaks in demand for electric power, stabilize the flow of alternating current, and act as a standby power supply for times when conventional or nuclear power stations in a power grid must be shut down.
The last function will be Dinorwic's specialty, though its more mundane contribution to predictable power supplies is important, too.
When generators or transformers fail, there is always an urgent need to switch on power from an alternative source. Dinorwic will provide an option of stunning size and flexibility.
If whole communities are blacked out because of a grid failure, the energy mountain will be mobilized.
Also, a decision to begin pumping Dinorwic electricity into a complex power network at a moment of failure could help prevent chain-reaction faults elsewhere in the system.
The method to be used is simple. Water will be pumped up through the mountain, using electricity at off-peak times to fuel the pumps. Then, when the resources of the energy mountain are needed, switches will be thrown and the water will begin flooding through tunnels with built-in turbines.
Dinorwic is particularly suitable for use in a grid with a number of nuclear power stations. These operate most economically if their generating output can be kept constant.
At normal times power from Dinorwic will be fed into the grid as and when required, leaving nuclear stations to keep on chugging at a steady rate of power generation.
The Dinorwic planners at first met opposition from Welsh environmentalists, who objected to the unsightly terrain scars usually associated with pumped storage projects. Engineers answered the objections by digging huge holes in the ground and burying most of the station equipment, including about six miles of cable linking Dinorwic to a grid feeder point.
The two reservoirs, one at the top of the energy mountain the other at the bottom, are more than a mile apart. Water will fall 1,600 vertical feet on its power-generating journey.
Later, pumped storage plants may be even less offensive to the eye than Dinorwic, because engineers believe they have found a way of burying the huge reservoirs, too.