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FAEPAC - Fundación Axencia Enerxética Provincial da Coruña

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Small-scale hydraulic

Nowadays we make the distinction of these energies according to its size and power:

Medium and large Hydraulic, over 10 MW. Its environmental and social impact can be high. Ecologist groups do not consider it as a renewable source of energy.

Small-scale hydraulic, less than 10MW. Its environmental impact can be considered moderate. It is considered as a renewable source of energy in all aspects. It can be connected to existing electric networks or it can be used in independent applications.

It is highly respectful with the environment. The impact it may produce is small, it can be minimized and in many cases is totally avoidable (ladders for fish, ecologic flow, by-pass channelling below ground levels, vegetable screens, reforestation, etc.)

There are mainly two types of hydroelectric power stations:

  • Run-of-river facilities: Those power stations that use a certain facility to divert part of the flow and channel it towards the power station to reach the turbine. Afterwards, this flow is directed back to the river. These power plants have a constant head and a variable flow to reach the turbine, depending on hydrology. Therefore, in this type of power plant, the power capacity is directly related with the fluidity of water.

  • Hydroelectric dams: Those power facilities situated by dams built for hydroelectric purposes or other uses such as providing water to populated areas or irrigation. They can be used for power production, since they donít imply water volume consumption. They have the advantage of storing energy in order to use it whenever it is needed. They are the ones that regulatethe capacity of the power systems and its use is the best way to reach the balance consumption/production.

The structure of run-of-river facilities is formed by all or some of the following elements: a low dam, or diversion weir that diverts part of the flow through a channel towards a loading chamber. From the loading chamber parts a high pressure channelling system that drives water into the turbine. The turbine is situated in the power plant building as well as the electric generator and auxiliary elements. Finally a tail race will drive water back again to the river flow.

The power of a hydroelectric power station depends on the flow that can be turbined as well as on the head, that is, the difference in height between the entrance and way out of the facility. According to those parameters (head and flow), the most suitable turbine will be chosen. In order to know the characteristics of a certain facility, it is necessary to have all the data related to at least twenty hydrologic years.

Small-scale hydroelectric systems can supply energy for small villages. For example a 500kw station can provide power supply to 800 people. The energy source can be a stream, a channel or any other source of power that can supply the amount and water pressure needed, trough channelling to guarantee the working of the hydroelectric system.

Once channelled water gets into supply channelling it is transported to the turbine impeller at the other side. The turbine impels the generator and electric power is produced. There are three types of turbines:

Pelton turbine, used for big heads (more than 100 m).

Francis turbine, used for heads between 15 and 120 m.

Kaplan turbine, used for different heads between 1 and 20 m.

Turbines used in small scale hydraulic stations are divided into two types:

  • Action turbine: Is the one that uses the speed of water, that is its kinetic energy. The most common model is the Pelton turbine, it has a series of spoon-shaped buckets or blades mounted around the edge of a wheel. This type of turbine is used mainly for hydroelectric stations that have high heads and small flows of water.
  • Reaction turbine uses both water speed and pressure difference existing at between the water source and the water exit. The most common models are Francis Turbine and Kaplan turbine. They have four basic elements: the inlet, or scroll-shaped tube, distributor, runner and exit tube.


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