Small-scale hydro

Small-scale hydro facilities work by capturing a proportion of the energy contained within a unit of flowing water. This energy is usually converted directly to electricity where it is either stored in batteries, directly supplies the demand of a building or is fed onto the grid. The potential for small-scale hydro to directly supply the electrical demand of most buildings is simply not feasible as a suitable resource is required. Most resource will tend to be found in more remote location such as paper mills or distilleries. Where a suitable resource does exist small-scale hydro has the potential to provide a clean and secure supply of electricity, this is perhaps the biggest benefit of obtaining electricity from a suitable river.

Small-scale hydro facilities are generally regarded as those facilities which produce less than 20 MW of electricity annually.

The amount of energy that can be obtained from a small-scale hydro is subject to three main parameters. 1) The volume of water passing through the turbine 2) The change in elevation of water before passing through the turbine 3) The efficiency of the turbine.

The main component parts of a small-scale hydro facility are the intake where a flow of water is diverted from the main flow and into the feeder canal. The intake is usually protected by a grid to prevent the flow of large objects such as logs which may damage the turbines. The feeder canal is usually made of concrete. The forebay is a simply a tank whose job is to hold a sufficient body of water to ensure that the penstock is always fully submerged to prevent suction of air through the turbine. The penstock is simply a connecting device/tube between the water at the forebay level and the powerhouse. The water contained within the feedstock will be subject to some pressure thus it is often made from high-density steel. The powerhouse protects the turbines and the generator from the elements. The tailrace is simply the return of water back to the river from which it was taken. A salmon ladder is a device which is composed of several levels each of which are elevated such that salmon are able to migrate back up stream. The turbines in a small scale hydro facility are usually fitted with variable inlet vanes, these are necessary to ensure that the amount of work being received by the generator related to the frequency, voltage and power characteristics of the electrical equipment which is receiving the power from the generator. Gearing is used in order that the generator runs efficiently, this means high speeds. Generators simply supply the convert work to electricity. The main component parts of a turbine are the blades or vanes which cause the drive shaft to rotate as water is forced through nozzle which pressurizes the flow before passing onto the blades.

During the use phase the emissions from a small-scale hydro plant will be minimal. It during the construction phase where there is significant emissions associated with the materials processing and component manufacture.