Hydroelectricity, or hydroelectric power, is a form of hydropower that uses the energy released as a result of water falling, or flowing downhill or by wave-differences, under the influence of gravity to produce electricity. Specifically, the mechanical energy of the flowing or waving water is converted to electrical energy by a Water turbine and generator. Hydroelectric power is usually generated at dams or other places where water descends from a height like coasts with a high tides difference. Hydroelectricity is a renewable energy source, since the water that flows in rivers has come from precipitation such as rain or snow and waves in the sea, or even ocean, are moon related.
The energy that may be extracted from water depends not only on the volume but on the difference in height between the water impoundment (or source) and the water outflow. This height difference is called the head. The amount of potential energy in water is directly proportional to the head. For this reason, it is advantageous to build dams as a high as possible to produce the maximum electrical energy.
The waters of Llyn Stwlan, the upper reservoir of the Ffestiniog Pumped Storage Scheme in north Wales, can just be glimpsed on the right. The lower power station has four water turbines which can generate 360 megawatts of electricity within 60 seconds of the need arising
While many hydroelectric schemes supply public electricity networks, some projects were created for private commercial purposes. For example, aluminium processing requires substantial amounts of electricity, and in Britain's Scottish Highlands there are examples at Kinlochleven and Lochaber, designed and constructed during the early years of the 20th century. Similarly, the 'van Blommestein' lake, dam and power station were constructed in Suriname to provide electricity for the Alcoa aluminium industry.
Hydroelectric power, using the potential energy of rivers, now supplies 19% of world electricity. Iceland produces 83% of its electricity from Hydro (2004). Apart from a few countries with an abundance of it, hydro capacity is normally applied to peak-load demand, because it is so readily stopped and started. It is not a major option for the future in the developed countries because most major sites in these countries having potential for harnessing gravity in this way are either being exploited already or are unavailable for other reasons such as environmental considerations.
Advantages and disadvantages
The chief advantage of hydro systems is their capacity to handle seasonal (as well as daily) high peak loads. In practice the utilisation of stored water is sometimes complicated by demands for irrigation which may occur out of phase with peak electrical demands. Times of drought can cause severe problems, since water replenishment rates may not keep up with desired usage rates.
Concerns have been raised that large hydroelectric projects might be disruptive to the surrounding ecosystem. For instance, studies have shown that dams along the Atlantic and Pacific coasts of North America have reduced salmon populations by preventing access to spawning grounds upstream.