Sources - Small Scale Hydro

Worldwide there remains vast potential from unexploited hydro resource ranging between 400-500 GW. Small scale hydro-power has great potential as a renewable energy source. Unlike large scale hydro projects, such as the Aswan Dam in Egypt, small scale-hydro power requires a limited amount of physical construction and therefore avoids the environmental and sociological problems associated with their development. Other advantages include:

  • Hydro is a concentrated energy source, so small systems can create relatively large amounts of energy.
  • Water turbine technology is highly efficient, in the region of 80-90%.
  • Hydro power can provide a high availability of power throughout the year and variations are seasonably predictable.
  • Small hydro projects have minimal visual and noise impacts.

In the Thames Valley such projects are limited to the availability of running water. It is a misconception that a requirement for hydro-electric power is a large volume river with a large velocity. Although these rivers have the potential for a greater amount of energy production, such projects are possible on smaller, slower water courses. For example, the River Thames has 44 weirs which potentially could generate hydro-electric power (studies indicate between 5-25MW capacity). Old mills, sluices and dams in the Thames Valley area, also have a great potential to generate electricity.

The principles of operating small-scale and large-scale hydro schemes are essentially the same. They require:

  • A suitable rainfall catchment area.
  • A hydraulic "head" (i.e. vertical distance from the reservoir or river to the turbine).
  • A water intake placed above a weir or behind a dam.
  • A pipeline or channel to transport the water from the reservoir or river to the turbine.
  • A flow control system.
  • A turbine, a generator, associated buildings and grid connection.
  • An outflow, where the water returns to the main water course.

Hydro Basics

The energy present in moving water is used to turn a turbine which generates electricity, which, depending on the scale of the system can either be exported to the local grid or used to charge batteries for local use. The following tables illustrates the varying scales of hydro-power and suggests a suitable turbine for each category.

Height Turbine types:
High head (above 100m) Pelton, Turgo, High head Francis.
Medium Head (20m to 100m) Francis, Cross Flow.
Low Head (5m to 20m) Cross Flow, Propeller, Kaplan.
Ultra Low Head (below 5m) Propeller, Kaplan, Water wheel

Environmental Issues

The principal environmental issues for small-scale hydro are:

  • Visual intrusion of the water intake, the dam or weir, and the turbine buildings.
  • The ecological impact of diverting water flow and the need to maintain sufficient flow through normal river channels.
  • Any damage to fish and other organisms passing through hydro turbines.
  • The impact of a scheme's construction phase when temporary dams may be necessary; there is also a risk of disturbing the sediment on the river bed and/or depositing construction materials in the water.
  • Any change in groundwater levels caused by the dam or weir.

Small Hydro Case Studies

Aberdulais Hydro-station

Water WheelIt is not always necessary to install new infrastructure for small scale hydro stations. The water wheel installed at Aberdulais (West Glamorgan) replaced one which was demolished in the 1830's and is now used to generate electricity. The project includes what is believed to be Europe's largest 20th century water wheel, measuring 8.2m in diameter and 2.8m wide. It generates 25kW of power, enough for around 40 houses. Hidden within the site is an electronically controlled 200kW Kaplan hydro turbine which adapts to changes in river flow. A fish pass was built through the powerhouse in order to allow migratory salmon to move up stream to spawn. The fish-pass has a viewing screen to cater for tourist interest.


The capital costs of small hydro schemes are within in the region of £3,000-£6,000 per kW capacity. Higher output sites tend to have a lower cost per kilowatt of capacity. All hydro installations have low ongoing maintenance costs and have long working lives. The feed-in tariffs means that that the economics are even better. The following fixed unit rates are payable from April 2010, for accredited hydro systems installed after July 2009:

Type Cost (pence/ kW)
Micro hydro (<15kW) 19.9 p/kWh
Micro hydro (15k-100kW) 19.9 p/kWh
Small hydro (100-2,000 kW) 11.0/pkWh

Links & Further Information

BABFO (British Association of Bio Fuels and Oils)

Attention: Peter Clery
Curlew Court
Guy's Head
Sutton Bridge
PE12 9QQ

Tel: 01406 350848
Fax: 01406 351791

British Hydropower Association

Unit 12
Riverside Park
Station Road
BH21 1QU

Tel: 44 (0)1202 886622
Fax: 44 (0)1202 886609

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