Hydropower , hydraulic power or water power is power that is derived from the force or energy of moving water, which may be harnessed for useful purposes.
Prior to the widespread availability of commercial electric power, hydropower was used for irrigation, and operation of various machines, such as watermills, textile machines, sawmills, dock cranes, and domestic lifts.
Another method used a trompe, which produces compressed air from falling water, which could then be used to power other machinery at a distance from the water.
History
Early uses of water power date back to Mesopotamia and ancient Egypt, where irrigation has been used since the 6th millenium BC and water clocks had been used since the early 2nd millenium BC. Other early examples of water power include the Qanat system in ancient Persia and the Turpan water system in ancient China.
Waterwheels and mills
Hydropower has been used for hundreds of years. In India, water wheels and watermills were built; in Imperial Rome, water powered mills produced flour from grain, and were also used for sawing timber and stone; in China, watermills were widely used since the Han Dynasty. The power of a wave of water released from a tank was used for extraction of metal ores in a method known as hushing. Hushing was widely used in Britain in the Medieval and later periods to extract lead and tin ores. It later evolved into hydraulic mining when used during the California gold rush.
In China and the rest of the Far East, hydraulically operated "pot wheel" pumps raised water into irrigation canals. In the 1830s, at the peak of the canal-building era, hydropower was used to transport barge traffic up and down steep hills using inclined plane railroads. Direct mechanical power transmission required that industries using hydropower had to locate near the waterfall. For example, during the last half of the 19th century, many grist mills were built at Saint Anthony Falls, utilizing the 50-foot (15 m) drop in the Mississippi River. The mills contributed to the growth of Minneapolis.
Hydraulic power pipes
Hydraulic power networks also existed, using pipes carrying pressurized liquid to transmit mechanical power from a power source, such as a pump, to end users. These were extensive in Victorian cities in the United Kingdom. A hydraulic power network was also in use in Geneva, Switzerland. The world famous Jet d'Eau was originally only the over pressure valve of this network.
Natural manifestations
In hydrology, hydropower is manifested in the force of the water on the riverbed and banks of a river. It is particularly powerful when the river is in flood. The force of the water results in the removal of sediment and other materials from the riverbed and banks of the river, causing erosion and other alterations.
Modern usage
There are several forms of water power currently in use or development. Some are purely mechanical but many primarily generate electricity. Broad categories include:
- Waterwheels, used for hundreds of years to power mills and machinery
- Hydroelectricity, usually referring to hydroelectric dams, or run-of-the-river setups (e.g. hydroelectric-powered watermills)
- Damless hydro, which captures the kinetic energy in rivers, streams and oceans
- Vortex power, which creates vortices which can then be tapped for energy
- Tidal power, which captures energy from the tides in horizontal direction
- Tidal stream power, which does the same vertically
- Wave power, which uses the energy in waves
- Osmotic power, which channels river water into a container separated from sea water by a semipermeable membrane.
- Marine current power which captures the kinetic energy from marine currents.
- Ocean thermal energy conversion which exploits the temperature difference between deep and shallow waters.
Hydroelectric power now supplies about 715,000 megawatts or 19% of world electricity. Large dams are still being designed. The world's largest is the Three Gorges Dam on the third longest river in the world, the Yangtze River. Apart from a few countries with an abundance of hydro power, this energy source is normally applied to peak load demand, because it is readily stopped and started. It also provides a high-capacity, low-cost means of energy storage, known as "pumped storage".
Hydropower produces essentially no carbon dioxide or other harmful emissions, in contrast to burning fossil fuels, and is not a significant contributor to global warming through CO 2 .
Hydroelectric power can be far less expensive than electricity generated from fossil fuels or nuclear energy. Areas with abundant hydroelectric power attract industry. Environmental concerns about the effects of reservoirs may prohibit development of economic hydropower sources.
The chief advantage of hydroelectric dams is their ability to handle seasonal (as well as daily) high peak loads. When the electricity demands drop, the dam simply stores more water (which provides more flow when it releases). Some electricity generators use water dams to store excess energy (often during the night), by using the electricity to pump water up into a basin. Electricity can be generated when demand increases. In practice the utilization of stored water in river dams is sometimes complicated by demands for irrigation which may occur out of phase with peak electrical demands.
Not all hydroelectric power requires a dam; a run-of-river project only uses part of the stream flow and is a characteristic of small hydropower projects. A developing technology example is the Gorlov helical turbine.
Tidal power
Main article: Tidal powerHarnessing the tides in a bay or estuary has been achieved in France (since 1966), Canada and Russia, and could be achieved in other areas with a large tidal range. The trapped water turns turbines as it is released through the tidal barrage in either direction. A possible fault is that the system would generate electricity most efficiently in bursts every six hours (once every tide). This limits the applications of tidal energy; tidal power is highly predictable but not able to follow changing electrical demand.
Tidal stream power
Main article: Tidal powerA relatively new technology, tidal stream generators draw energy from currents in much the same way that wind generators do. The higher density of water means that a single generator can provide significant power. This technology is at the early stages of development and will require more research before it becomes a significant contributor. Several prototypes have shown promise.
Wave power
Main article: Wave powerHarnessing power from ocean surface wave motion might yield much more energy than tides. The feasibility of this has been investigated, particularly in Scotland in the UK. Generators either coupled to floating devices or turned by air displaced by waves in a hollow concrete structure would produce electricity. For countries with large coastlines and rough sea conditions, the energy of waves offers the possibility of generating electricity in utility volumes.
Small scale hydro power
Small scale hydro or micro-hydro power has been increasingly used as renewable energy source, especially in remote areas where other power sources are not viable. Small scale hydro power systems can be installed in small rivers or streams with little or no discernible environmental effect on things such as fish migration. Most small scale hydro power systems make no use of a dam or major water diversion, but rather use water wheels. Many areas of the North Eastern United States have locations along streams where water wheel driven mills once stood. Sites such as these can be renovated and used to generate electricity. Also, small scale hydro power plants can be combined with other energy sources as a supplement. For example a small scale hydro plant could be used along with a system of solar panels attached to a battery bank. While the solar panels may create more power during the day, when the majority of power is used, the hydro plant will create a smaller, constant flow of power, not dependent on the sunlight.
There are some considerations in a micro-hydro system installation. The amount of water flow available on a consistent basis, since lack of rain can affect plant operation. Head, or the amount of drop between the intake and the exit. The more head, the more power that can be generated. There can be legal and regulatory issues, since most countries, cities, and states have regulations about water rights and easements.
Over the last few years, the US Government has increased support for alternative power generation. Many resources such as grants, loans, and tax benefits are available for small scale hydro systems.
In poor areas, many remote communities have no electricity. Micro hydro power, with a capacity of 100 kW or less, allows communities to generate electricity. This form of power is supported by various organizations such as the UK's Practical Action.
Micro-hydro power can be used directly as "shaft power" for many industrial applications. Alternatively, the preferred option for domestic energy supply is to generate electricity with a generator or a reversed electric motor which, while
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