Hydro is nowadays a mature technology and has been developed all around the world. In countries blessed with large rivers hydro plays a major role in the generation of electrical energy. The Itaipú hydroelectric power plant in Brazil has a generating capacity of 14000 MW. Manitoba Hydro in Canada has a total generating capacity of 5200 MW. The Three Gorges in China   have an installed capacity of 22500 MW, Baithetan has a capacity of 16000 MW, Xiluodu 14000 MW, Wudongde 10000 MW. These are the larger hydropower plants and the abundant hydropower resources in southwest China will be exploited on a large scale during the next decades. A number of large hydropower projects will be completed during this period. China ranks first in the world of hydro resources with a potential of 680 GW. An estimated 370 GW can be developed to provide electric energy production of 1900 TWh per year. Exploitable hydro- power resources in southwestern China account for 53 % of China’s total.

The running costs of hydropower plants are very low as energy is free, but the civil engineer- ing component of the capital cost is very high. The type of water turbine used depends on the head of water available. The energy is extracted from the water falling through the available head. The lower the head the larger the quantity of water necessary for a given turbine rating. High-head turbines operate with low water volumes and low-head turbines with high water volumes.

There are three basic types of water turbines. The Kaplan turbine has variable pitch blades that can be adjusted for optimum regulation. This type of turbine has been built for heads up to 60 m and is applied in river and pondage stations.

In the Francis turbine the guide and runner blades are designed for higher heads up to 500 m and the regulation is done by adjustment of the guide vanes at the water inlet.

The third type is the Pelton wheel, a turbine suitable for high heads and small quantities of water. The water is injected through one or more nozzles on the buckets on the turbine wheel. The regulation is done by means of needle valves on the nozzles and jet deflectors at the water inlet.

In comparison with a thermal power plant, a hydro power plant has the advantage of quick starting and effectively meet an abrupt increase in load demand. When water supplies are not available a pump storage scheme provides the advantages of a hydro plant. A pump storage scheme has two reservoirs at different heights, with the hydro plant situated at the level of the lower reservoir. During periods of low demand, usually at night, water is pumped from the lower to the higher reservoir using the cheap electricity from the thermal power plants. The generators act as motors and drive the turbines which act as pumps. During periods of peak demand, usually in day time, the water turbine drives the generator in the normal manner. The overall efficiency of the operation is not very high, in the order of 65 %. One of the larger pump storage plants in Europe is located in Vianden in Luxembourg.