Hydroelectric energy

Hydroelectric energy is generated by harnessing the energy contained in a mass of water located at a certain height. The force of the water causes one or more turbines to rotate, and these in turn move one or more electric generators.

The great advantage of this type of energy is that it can meet energy needs without using up exhaustible natural resources and it has only a limited environmental impact. It does not emit pollutant gases, nor does it generate solid waste that is hard to treat. It simply borrows some water and then returns it intact to the river.

Small hydro stations

Depending on the way they make use of waterfalls, small hydro stations are classified into two types:

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  Run of river

  The water is taken from the river flow, and once it has been used it is returned to the river downstream.
• 

  Dam

  The water is stored behind a dam and is subsequently used to generate electricity.

Components of a hydro station

Civil engineering is needed to channel and lead the water to the power station and to return it to the river after use.

To maintain the balance of the water ecosystem, an ecologically suitable water flow is maintained in the river and fish ladders are built.

1. Weirs and dams

   These constructions hold back the water and reroute it towards the channel.

2. Intake or Headgate

   Reroutes the water towards the headrace channel that carries it to the power stations. Has a net to prevent fish and solid waste getting through.

3. Headrace

   Channel fitted with hatches for cleaning and emptying.

4. Forebay tank

   Storage tank situated at the end of the headrace and from which the penstock leads. It is an essential part of the system, since it prevents air getting into the penstock.

5. Penstock

   Normally made of steel. It carries water to the turbine.

6. Tailrace

   Channel through which the water is returned to the river intact.

Equipment in a hydro station

Power house

This is the building that houses the turbine, the power generator and other auxiliary systems.

1. Turbines

Machines which transform the energy from the water into mechanical energy.

2. Electric generators

Machines which produce electricity out of the rotating mechanical energy in the turbines.

3. Transformers

During transport of the electricity from the place where it is produced to the final consumption site, a certain amount of energy is lost. The transformers increase the voltage, thus minimising this loss.

4. Auxiliary equipment

Necessary for proper operation of the power stations:

• Hatches
• Grilles and grille-cleaning systems
• Fire prevention system
• Lighting
• Flowmeter

5. Power line

Power line Transports the energy produced in the station to the place where it is to be used.

The turbines

These are the machines that transform the energy from the water into mechanical energy. The force of the water turns the turbine - which is shaped like a propeller. Because the turbines are connected to a generator, this rotation makes the generator produce electricity.

Turbines are classed into two groups:

Impulse turbines

These use the speed of the water to generate energy

PELTON turbine

Recommended for high falls (50 - 400m) and relatively low flows of water.

Reaction turbines

These use both the pressure and the speed of the water to generate energy.

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  KAPLAN turbine

  Adapted for use with small falls (normally less than 30m), but with large flows.
• 

  FRANCS turbine

  Used in medium-sized falls (5-100m).