Modern hydro-electric power stations:

Above - Itaipu Dam, built in 1983 in Brazil/Paraguay and generates up to 12,600MW.

Google Earth - Itaipu Dam, Paraguay

About 20 per cent of the world’s electricity is generated through the use of water. Today’s hydro-electric power station has a simpler design than a conventional coal-fired station. Basically, the hydro-electric plant consists of a water turbine which converts the energy from flowing water into mechanical energy. Then, an electric generator converts this mechanical energy into electrical energy. (See figure below.)

To enlarge view - click here.
Source: Pacific Power.

For more information about hydro-electric power plant, go to:
http://www.nationmaster.com/encyclopedia/Hydroelectricity

While a water turbine is much more sophisticated than the old water wheel, it is similar in operation. In both cases, blades are attached to a shaft and when flowing water presses against the blades, the shaft rotates. The effect is the same as wind pressing against the blades of a windmill. After the water has given up its energy to the turbine, it is discharged through drainage pipes or channels. These drainage pipes are known as the “tailrace” of the power station. The remaining water is used for irrigation or water supply purposes or, in some parts of the world, the water flows back into the ocean.

To view a diagram of a water turbine, go to:
http://www.nationmaster.com/encyclopedia/Water-turbine

Hydro-electricity is a renewable resource because it is continually produced by the movement of fresh water from rivers and lakes. Hydro-electric power stations are situated where they can take advantage of the greatest fall of a large quantity of water. This is normally at the bottom of a deep and steep-sided valley or gorge, or near the base of a dam. As discussed earlier, the amount of electrical energy that can be generated from a water source depends on two things; the distance that the water has to fall (the head) and the quantity of water flowing. Hydro-electric power stations usually require water storage schemes. It is necessary to store water to ensure a reliable supply of electricity can be generated from water energy whenever it is needed. These hydro-electric schemes address a basic problem with electricity: once it’s generated, it has to be used immediately and it can’t be stored. In hydro-electric schemes, the potential energy of water can be stored in dams or river systems and released to generate electricity as and when it’s required.

Originally, hydro-electric power stations were of a small size and they were set up at waterfalls in the vicinity of towns because it was not possible at that time to transmit electrical energy over great distances. The main reason why there is now a large-scale use of hydro-electric power is because it can now be transmitted inexpensively over hundreds of kilometres to its required destination, making hydro-power economically viable. Transmission over long distances is carried out by means of high voltage, overhead power lines. They are known as transmission lines and the electricity that can be transmitted is either alternating current or low-voltage direct current (DC).

^ back to top ^