A series of short films exploring how we’re harnessing hydro power for a net-zero future.

Hydro power is Scotland’s original source of renewable energy and one which has an increasingly vital role to play in our path to achieving net zero carbon emissions by 2045.

As we move towards an electricity system with ever greater levels of more intermittent forms of renewable energy, hydro’s ability to store its main fuel source, water, and its flexibility to generate power when needed by the grid will be increasingly important.

To highlight hydro’s role in tackling climate change we’ve created a tour of our hydro business.

The tour explains the basics of hydro power generation, takes you inside some of our hydro power stations, looks at how we manage our environmental responsibilities and examines how the use of digital technology can help drive the next generation of hydro.

Film 1 : Introducing our virtual Hydro Tour

Find out what to expect from our series on Britain’s Biggest Battery.

Film 2 : The Basics of Hydro Power

Learn about the different forms of hydro power and how they work.

Film 3 : Inside our Hydro Power Stations

Take a trip inside four of our hydro power stations and see how they connect together to form Britain’s Biggest Battery

Film 4 : The Role of Hydro in Combating Climate Change

Hear how we safely manage our main fuel source, water, while also protecting the natural environment.

Hydro schemes and how they work

Find out more about how our Pumped, Storage and Run of River hydro schemes work by clicking below.

Storage Hydro Electric


Storage hydro electric (sometimes also known as ‘impounded power’) is a natural loch or man-made reservoir formed by draining a river which collects water draining from the surrounding area, which can be hundreds or even thousands of square kilometres in size. This creates a store of water situated at a higher altitude than the power station it supplies. The difference in height between the power station and the reservoir is called the ‘head’. The higher the head, the more energy there is in the water to drive the turbines and the more electricity it can produce. This is the same principle as the ‘header’ tanks in the lofts of houses that provide the water pressure for the hot water taps.

These schemes give power station operators much more control over when, and how much, electricity is generated in response to customers’ needs. Even so, the amount of water operators are allowed to extract from the reservoir is controlled, in order to prevent the water level falling so low that environment and wildlife are adversely affected.

This diagram shows how water is moved from an upper reservoir to a lower reservoir to generate electricity. When there is excess energy in the system, the process is reversed. Water is pumped from the lower reservoir to the upper reservoir.

Pumped Storage Hydro


Pumped storage schemes have two reservoirs to hold water, with one higher than the other. It works when water is released from the higher reservoir to drive the turbines in the power station below before passing into the lower reservoir. Then, when there is cheap surplus electricity available, the electricity generators are switched to become massive motors pumping water from the lower reservoir back to the higher one, where it's stored until needed to meet the next peak in demand.

Traditionally, pumped storage has been used when there is high demand for electricity. As we move to an electricity system with a higher proportion of intermittent renewable generation (such as wind power or solar) pumped storage will have an important role to play in ‘storing’ electricity when the UK is generating more than is needed and then using this electricity to meet demand when the demand for electricity is higher.

Pumped storage gives operators even greater control over when power stations run and can respond very quickly to meet unexpected high electricity demand. Typically, pumped storage can be operating in full output in under two minutes when called on to do so.

Our Foyers power station, on the south shore of Loch Ness, is one of only four pumped storage schemes in the UK.

Run of River Hydro


In the simplest run of river schemes, some of the water from a naturally fast-flowing river is diverted via a tunnel to drive a water turbine in a nearby power station. The turbine spins as the water flows, driving a shaft that is connected to the electricity generator. The water is then allowed to flow back in the river.

The main disadvantage of run of river schemes is that the amount of electricity and when it can be generated is almost entirely governed by how much water there is in the river at any given time. When permission is granted to build run of river schemes, there is usually a requirement that a set minimum amount of water must always be allowed to remain in the river to protect wildlife and habitat. So when the river is low, due to lack of rain, the power station may be starved of water and unable to generate any electricity at all.

Admittedly this doesn’t happen very often in Scotland – but it does sometimes.

Our hydro schemes in numbers

MW of conventional hydro
MW of flexible pumped storage
power stations
km of tunnels
Coire Glas Storage (GWh)