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Hydro energy from pumped storage

Hydro energy from pumped storagePumped storage reservoirs provide a place to store energy until it's needed.

There are fluctuations in demand for electricity throughout the day. For example when a popular TV programme finishes, many people go and put the kettle on, causing a peak in demand for electrical power.

When electricity is suddenly demanded, we need a way of producing power which can go from producing no power to full power immediately, and keep generating power for half an hour or so until other power stations can catch up with the demand for energy. This is why pumped storage reservoirs are so useful.

How does it work?

A pumped storage plant has two separate reservoirs, an upper and a lower one. When electricity is in low demand, for example at night, water is pumped into the upper reservoir.

When there is a sudden demand for power, giant taps known as the headgates are opened.
This allows water from the upper reservoir to flow through pipes, powering a turbine, into the lower reservoir.

The movement of the turbine turns a generator which creates electricity. The electricity is created in the generator by using powerful magnets and coils of wire. When the coils are spun quickly inside the magnets, they produce electricity.

Water exiting from the pipe flows into the lower reservoir rather than re-entering a river and flowing downstream. At night, the water in the lower reservoir can be pumped back up into the upper reservoir to be used again.

In terms of how pumped storage and dammed water generate electricity, the methods are the same. The difference is that in pumped storage, the water is continually reused, whereas in hydroelectric dams, the water which generates electricity continues flowing downriver after use.


  • Pumped storage is a way we can generate electricity instantly and quickly
  • No pollution or waste is created
  • There is little effect on the landscape, as typically pumped storage plants are made from existing lakes in mountains


  • Expensive to build
  • Once the pumped storage plant is used, it cannot be used again until the water is pumped back to the upper reservoir

Pumped storage in the UK

Most pumped storage plants are located in Scotland, except the largest of all, Dinorwig, which is in North Wales. Dinorwig, built in 1984, produces 1,728 MW (megawatts). This is enough electricity to power nearly 7 million desktop computers. Dinorwig has the fastest "response time" of any pumped storage plant in the world - it can provide 1320 MW in 12 seconds.

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