Hydro Electricity

Originally, hydroelectric power stations were small, built next to waterfalls and close to towns because it was not possible to send the electrical energy over great distances. There is now large scale use of hydro electricity because improvements in electricity transmission means it can now be sent over hundreds of kilometres to where it is required. Hydropower is a proven and well advanced technology, with more than a century of experience. Modern power plants provide extremely efficient energy conversion.

Hydro Electric power is dependent on the amount of energy available from the water flowing and the height of the surface of the water above the turbine. This height is called the ‘head’ and the greater the head the more energy each cubic metre of water has available to spin a turbine, which in turn drives a generator which produces electricity. The greater the quantity of water the greater the number and size of turbines that may be spun and the greater the power output of the generators. Water is collected and stored in the dam above the power station for use when it is required. Some dams create a big lake behind the dam wall. Other dams simply block the river and divert the water through pipelines down to the power station. While a water turbine is much more sophisticated than the old water wheel it is similar in operation. In both cases flowing water rotates a shaft when flowing past the shaft blades. After the water has given up some of its energy to the turbine, it is discharged through drainage pipes or channels called the "tailrace". This is usually into the river downstream of the power station.

Microhydro systems operate by diverting part of the river flow through a penstock (or pipe) and a turbine, which drives a generator to produce electricity and the water flows back into the river. Microhydro systems are mostly "run of the river" systems, which allow the river flow to continue. This is preferable from an environmental point of view, as seasonal river flow patterns downstream are not affected and there is no flooding of valleys upstream of the system. As a cheap, renewable source of energy with negligible environmental impacts, microhydro power technologies have an important role to play in future energy supply, particularly in developing countries. It is an attractive alternative to diesel technologies in rural and remote areas of developing countries as a means of achieving rural electrification.

Hydro electric power is widespread in most countries where there is sufficient rainfall. Most hydro electric schemes are built as much as possible around the natural environment so as to minimise capital cost, these power stations tend to be smaller anywhere from a few hundred kilowatts to 20-30MW. The largest Hydro Electric scheme in the world is the Three Gorges Damn on the Yangtze River in China. The building of this project displaced 1 million Chinese, used 15m cubic meters of concrete and cost many $billion’s to construct.