Draft PPS18: Renewable Energy
Annex 1 Small Hydro Technology
E2. The technology for harnessing waterpower is well established. Water flowing from a higher to a lower level is used to drive a turbine, which produces mechanical energy. This mechanical energy is usually turned into electrical energy by a generator, or more rarely to drive a useful mechanical device.
E3. The energy produced is directly proportional to the volume of water and the vertical distance it falls. Thus, a similar amount of energy could be produced from a small volume of water falling over a long vertical distance (high head), as from a larger amount of water falling a much shorter vertical distance (low head).
E4. The majority of schemes will be ‘run of river’, where water is taken from a river from behind a low weir, with no facility for water storage, and returned to the same watercourse after passing through the turbine. In addition, there is some potential for small hydro installed on existing reservoirs, but these may also be treated as ‘run of river’, as they do not involve the construction of a new impounding structure.
E5. Pumped storage schemes are capable of being used in conjunction with more intermittent forms of renewable energy to smooth out the intermittency by providing an element of energy storage. During periods of low demand, but when the prime resource is available, excess energy is used to pump water from a lower level to a higher level reservoir. During periods when demand is high and the prime resource availability is low, the water from the higher reservoir is released via a turbine to the lower reservoir to generate electricity. Such schemes may require the construction of two new reservoirs, but apart from this, the technology employed, and the implications for the planning system, are similar to those outlined in this section. However, because of the cost involved, pumped storage schemes of less than 1MW are likely to be extremely rare.
The essential elements of a hydro scheme are as follows:
- a source of water that will provide a reasonably constant supply. Sufficient depth of water is required at the point at which water is taken from the watercourse, and this is achieved by building a low weir (typically around 2 metres high) across the watercourse. This is called the ‘intake’;
- a pipeline, often known as a penstock, to connect the intake to the turbine. A short open ‘headrace’ channel may be required between the intake and the pipeline, but long headrace channels are rare due to environmental and economic constraints;
- a building housing the turbine, generator and ancillary equipment – the ‘turbine house’.
- a ‘tailrace’ returning the water to the watercourse; and,
- a link to the electricity network, or the user’s premises.
This section contains the following sub-categories: