Harnessing hydroelectric power

How hydroelectric power works, regional schemes and information on installing your own micro-hydro scheme.


The UK currently (2011) generates about 1.5% of its electricity from hydroelectric schemes. Although further large-scale development potential is limited, there is scope for exploiting our remaining small-scale hydro resources in a sustainable way.

Understanding hydroelectric power

Hydroelectric power is the energy derived from flowing water. This can be from rivers or man-made installations, where water flows from a high-level reservoir down through a tunnel and away from a dam.

Turbines placed within the flow of water extract its kinetic energy and convert it to mechanical energy. This causes the turbines to rotate at high speed, driving a generator that converts the mechanical energy into electrical energy.

The amount of hydroelectric power generated depends on the water flow and the vertical distance (known as ‘head’) the water falls through.

Types of hydroelectric schemes

There are 3 main types of hydroelectric schemes in use in the UK:

Storage schemes

In storage schemes, a dam impounds water in a reservoir that feeds the turbine and generator that are usually located within the dam itself.

Run-of-river schemes

Run-of-river schemes use the natural flow of a river, where a weir can enhance the continuity of the flow. Both storage and run-of-river schemes can be diversion schemes, where water is channelled from a river, lake or dammed reservoir to a remote powerhouse containing the turbine and generator.

Pumped storage

Pumped storage incorporates two reservoirs. At times of low demand, generally at night, electricity is used to pump water from the lower to the upper basin. This water is then released to create power at a time when demand, and therefore price, is high. Although not considered a renewable energy (because of its reliance on electricity), pumped storage is very good for improving overall energy efficiency.

UK use of hydroelectricity

There are 3 main categories used to define the output from hydroelectric power:

  • large-scale capacity: hydro plant producing more than 5 megawatts (MW)

  • small-scale capacity: hydro plant producing less than 5 megawatts

  • micro-scale capacity: hydro plant producing less than 50 kilowatts

The total hydroelectric installed capacity in the UK at the end of 2011 was approximately 1676 megawatts, which is around 1.9% of the current total UK generating capacity and 14% of renewable electricity generation capacity.

Hydroelectric power’s contribution to our renewables targets

The UK currently (2011) generates about 1.5% (5,700 Gwh) of its electricity from hydroelectric schemes - most of which are large-scale schemes in the Scottish Highlands.

Hydroelectric energy uses proven and efficient technology; the most modern plants have energy conversion efficiencies of 90% and above. Hydro has a typical load factor of 35 to 40%.

Future development

It is unlikely we will see again the scale of development witnessed in the UK in the 1950s and 1960s. Opportunities to use this technology on a large scale are now limited, not only because of environmental concerns but also because many of the most economically attractive sites for schemes have already been used. However, it is important we exploit our remaining small-scale hydro resources in a sustainable way.

Some old watermills are also being refurbished and brought back into the energy supply network.

Recent studies estimate there is a remaining viable hydro potential of 850 to 1550 megawatts in the UK. This represents approximately 1 to 2% of current UK generating capacity and so would make a modest but useful contribution to UK renewable energy and emission reduction targets. There are a number of steps that have to be considered before a scheme can be built, eg scheme economics, environmental permits, planning consent and connection to the local electricity network.

Installing a micro-hydro scheme on your property

A number of people have already installed micro-hydro schemes. In general, even small-scale schemes provide enough power for a number of houses or a small community.

Although upfront costs for hydropower are high, installations should last for decades. Low head installations can generate renewable energy 24 hours a day.

Feed-in Tariffs (FITs), available since April 2010 to reward renewable electricity generation, provide a further incentive but installers must consider issues such as protecting wildlife and fish - which may mean including additional features in the scheme design.

Contact the Energy Saving Trust on 0800 512 012 for more information. You can also find more details about micro-hydro installations on the Energy Saving Trust website and the Environment Agency’s run-of-river hydropower guidance.

Planning permission for hydro schemes

Hydro developers should contact the relevant local authority for specialist advice at the earliest stage before undertaking a feasibility study.

Developers will also require environmental permits from the Environment Agency (England), Natural Resources Wales, the Scottish Environmental Protection Agency or the Northern Ireland Environment Agency.

Finding an approved installer

The Microgeneration Certification Scheme’s (MCS) full micro-hydro standards are still under development. In the meantime, MCS transitional lists for installers and products are available. MCS is linked to eligibility for FITs less than 50kWs. FITs also reward the generation of hydro electricity less than 5MW.

Hydro scheme developments in your area

The British Hydropower Association can tell you more about developments in your area.

Published 22 January 2013