94. Hydroelectric developments offer a clean source of electrical energy with a steady output, with no production of particulates or harmful gases. A scheme with a capacity of 100kW would typically supply enough electricity for about 150 homes. If this displaced electricity generated by currently operating fossil-fuel power stations, it would save the emissions of around 400 tonnes per year of carbon dioxide, as well as around 5 tonnes of sulphur dioxide and 2 tonnes of nitrogen oxides.

95. Major existing hydro schemes in Scotland are usually based on a dam and storage reservoir and currently generate about 11% of Scotland’s electricity. New hydro developments are likely to be much smaller and not require large storage reservoirs. The key aspects of the economics of hydro are the initial large capital outlays. However, this is mitigated by the long lifetime, high reliability and availability of plant, low running costs and no annual fuel costs.

96. Under the ROS, it is the intention to extend eligibility to include the output of refurbished hydroelectric plant of up to 20MW capacity and new hydro plant of any capacity. Very small hydro schemes (1.25MW DNC or less) will be eligible without the need to refurbish.

97. This section provides information on the technology and characteristics of hydroelectric developments and advice for handling these as planning and environmental issues in development plans and planning applications. It is concerned mainly with small-scale schemes often involving small-scale storage. It also includes advice on shoreline wave power developments as these fall within the control of the Planning Acts and are significantly different in character from offshore wave projects.

The Process

98. The process of harnessing waterpower is well established. Water flowing from a higher to a lower level is used to drive a wheel or turbine, producing mechanical energy. This energy may be used for a variety of purposes, including the generation of electricity. In simple terms, power output is related to the volume of water available, and the vertical distance through which it falls. Similar power can be obtained from a large quantity of water falling a small vertical distance, or from much less water falling a greater distance. In the first case a larger turbine is required; in the second case, the plant will be smaller. To provide sufficient depth of draw off the water, a natural pool is required or a headpond must be created with a weir. A conduit then conveys the water from the intake in the pool or headrace to the turbine. The conduit may be an enclosed pipe (or penstock) or an open channel, often called a headrace.

Characteristics

99. The essential elements in a typical hydroelectric scheme are discussed below. The scale and physical form of each of these elements will depend heavily upon local environmental conditions.

The Headworks

100. A reliable supply of water is clearly a pre-requisite for a viable hydro scheme. Rivers with large variations in flow will be unsuitable unless a holding reservoir is constructed to store water at times of excess. The water must also be sufficiently deep at source to enable the supply to be drawn off via an intake.

101. There are two principle types of headworks :

• Run-of-river - no (or negligible) water storage upstream of the weir i.e. the output from the turbine is proportional to the flow of the river.

• Storage - the intake structure is generally larger and is used to store water so that power from the turbine(s) can be timed to meet demand from consumers.

102. The intake normally comprises a trash screen of vertical or sloping bars to trap floating debris and a sluice gate to regulate the flow of water to the turbine. Some trash screens, which needs to be kept clear of debris on a regular basis, are designed to require virtually no maintenance through ‘passive’ design rather than automatic / active cleaning (e.g. over washed screens). A fine mesh screen may also be installed over the intake at certain times of the year to prevent fish being drawn into the supply pipe.

103. The intake structure is normally contained in a modest concrete housing set into the bank of the river. Where the water level needs to be raised in order to ensure a regular supply, the headworks will also include an artificial weir, usually of concrete or stone construction. As well as providing a water supply of suitable depth, the headpond behind the weir can help to sustain supplies to the turbine when the river is temporarily low.

The Headrace

104. Water is carried from the headrace to the turbine house by an enclosed pipe (penstock), an open channel (millrace, leat or lade), or by a combination of these. Depending on local circumstances, the distance between the headrace and the turbine house can vary from a few metres to one kilometre or more. New schemes using a high head of water will tend to use an enclosed or buried pipe. Some refurbishment schemes may use existing open channels.

105. A headrace pipe might be metal, plastic, concrete or made of a composite material. The range of diameter sizes for future run-of-river medium and high-head hydro schemes in Scotland is likely to be from 200 to 1500mm. A valve is incorporated close to the turbine house to enable the water supply to be regulated when required. The pipeline will be anchored securely to the ground, particularly at bends and junctions, and can be buried at places where it would otherwise limit access to land or cross areas of landscape sensitivity.

106. Open channels may be unlined, or lined with clay, concrete or plastic. They will usually incorporate a second sluice gate close to the turbine house, to divert or channel water back to the main stream when the turbine needs to be stopped.

107. The turbine house contains the turbine, the generator and associated electrical equipment. For a typical small-scale hydro scheme, the turbine house will be similar in size to a domestic double garage. The turbine will be sited to optimise the trade-off between the length of the headrace and the drop in water level, but there is a degree of locational flexibility. Where feasible, a turbine house may be partially buried. In order to minimise the length of the tailrace, the turbine house will normally be situated close to the watercourse. In visual terms the turbine house will often be the most prominent built element in a small-scale hydro scheme. Its design and location are thus significant planning considerations and are considered further below. (See paragraphs 116-120)

The Tailrace

108. After driving the turbine, water is returned to its natural course via the tailrace. Where the turbine house is close to the watercourse, the tailrace will take the form of a short open channel. In other cases it will be of similar construction to the headrace. As slow-moving water can impair the efficiency of the turbine, the tailrace should have a gradient sufficient to encourage a swift discharge of water.

109. A proposal to construct or operate a hydro-electric station with a capacity of more than 1 MW must be submitted to the Scottish Ministers for consent under section 36 of the Electricity Act 1989. Before applying, an applicant must consult the Fisheries Committee, which advises on possible damage to fisheries or fish stocks. The current Scottish Executive intention, under "Proposals for Abolition or Reform of Public Bodies", is that the Fisheries Committee be abolished and its functions passed to the Inspector of Salmon and Freshwater Fisheries. Since this Committee is appointed by statute under the Electricity Act 1989, abolition will require a change of legislation when the legislative timetable allows.

110. The risk to all fish can be minimised by careful design and adjustment of the seasonal operating schedule of the plant. Some types of turbine (such as low to medium head crossflow designs) can oxygenate the river water and may thereby benefit the fish population. Where necessary, dams and weirs should include structures which allow the free passage of migratory fish and afford fish and other freshwater animals protection from the turbines.

"The Salmon (Fish Passes and Screens) (Scotland) Regulations 1994".

SI 1994/2524.

111. The Salmon (Fish Passes and Screens) (Scotland) Regulations 1994 require dams to have an adequate fish pass and all off-takes, whether or not associated with a dam, to be screened to protect the passage of salmon (and sea trout). The Scottish Office Agriculture and Fisheries Department issued non-statutory guidance notes, to accompany the Fish Pass Regulations, to assist owners of dams and weirs on the practical aspects of their implementation. It should be noted that while the Regulations apply to proposals dealt with by planning authorities, they do not apply to dams or off-takes which are authorised by the Scottish Ministers under Acts which provide that they can have regard to the arrangements for the safe passage of salmon and sea trout when authorising the scheme e.g. under the Electricity Act 1989.

"Rivers, Lochs, Coasts : The Future for Scotland’s Waters".

Scottish Executive Consultation Paper June 2001.

Siting in the Landscape and Design Considerations

116. As with several renewable sources of energy, it is usually only possible to exploit hydropower resources where technically the potential exists. Hydro schemes do however enjoy a limited locational flexibility to the extent that the precise siting of the headworks and, in particular, the turbine house, can sometimes be influenced by non-operational factors, including local landscape characteristics.

117. In general terms, it will be desirable to choose a location for the development where the built elements can be integrated into the landscape. Where rivers are lined with trees, for instance, it will be relatively simple to conceal the hydropower facilities, particularly if the existing woodland cover is supplemented by new planting. Where the development is taking place in a more open location, built elements should either be designed to be as small as possible, having regard to operational considerations, or should be designed to contribute positively to the landscape. In the case of schemes proposed for hillsides or other prominent locations, the landscape impact of the development, in close and distant views, should be appraised.

118. In some cases, the visual impact of the development can be minimised by siting the turbine house away from the headworks. However, the greater this separation is, the longer and potentially more prominent will be the headrace connection between the two. There will also be significant cost implications. The remote siting of a turbine house will rarely be justified by landscape considerations alone, and can become self-defeating if the headrace pipe or channel becomes a visually obtrusive feature in its own right. In many cases it will be advantageous to underground pipelines from the intake to the turbine house but careful restoration of the ground is necessary. Preferably, access tracks to weirs should be reinstated once the construction stage has been completed.

119. Although the foreseeable hydro developments will generally be small scale, their waterside location will, in some cases, place them in areas valued for their natural and/or cultural significance. Such schemes can operate for many decades, and their principal built elements will often become permanent additions to the landscape. In some circumstances, weirs, fish ladders and headrace channels can become features of interest in their own right, attracting visitors.

120. For these reasons, planning authorities may reasonably insist on a high standard of design. Particular attention may be required to the architectural quality of built elements, the choice of building materials and the manner in which the development is integrated with its surroundings. Measures to minimise the visual impact of headrace pipes and power lines should be considered carefully at the design and planning application stages.

Aquatic Habitats and Species

121. In designing a hydro scheme, account needs to be taken of the fact that different species will be affected in different ways and that some species, such as the freshwater pearl mussel, are protected under the EC Habitats Directive. Discussions with SNH will provide guidance on the species which require to be considered in a particular location. Experience has shown that by careful design it is possible to reconcile hydro schemes with conservation of the natural heritage.

Construction Disturbance

122. In general, the construction impact of a hydropower scheme will be no different to that of other developments of similar size. However, construction in or beside a river or loch may cause the water to become clouded with silt or mud. Before granting planning permission for a hydro project, the planning authority may, in consultation with SEPA and SNH, request that the developer specifies the site management measures that will be adopted to minimise this problem.

123. Additional to conventional hydroelectric power, the interface between the sea and the land has considerable energy generation potential. It does however differ from offshore wave and tidal in that it is within the land use planning regime. The main device deployed world-wide is the Oscillating Water Column (OWC). This consists of a partially submerged, hollow structure that is open to the sea below the water line. This encloses a column of air on top of a column of water. Waves cause the water column to rise and fall, which alternatively compresses and depressurises the air column. This trapped air is allowed to flow to and from the atmosphere via a Wells turbine, which has the ability to rotate in the same direction regardless of the direction of the airflow. The rotation of the turbine is used to generate electricity.