PowerPoint Slideshow about 'Hydroelectricity ' - zacharee-horn
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Hydroelectricity is electricity obtained from hydropower. Most hydroelectric power comes from the potential energy of dammed water driving a water turbine and generator, although less common variations use water's kinetic energy or dammed sources, such as tidal power. Hydroelectricity is a renewable energy source.
The energy extracted from water depends not only on the volume but on the difference in height between the source and the water's outflow. This height difference is called the head. The amount of potential energy in water is proportional to the head. To obtain very high head, water for a hydraulic turbine may be run through a large pipe called a penstock.
While many supply public electricity networks, some hydroelectric projects were created for private commercial purposes. For example, aluminium processing requires substantial amounts of electricity, and often dedicated hydroelectric projects are built to serve aluminium electrolytic plants. In the Scottish Highlands there are examples at Kinlochleven and Lochaber, constructed during the early years of the 20th century. In Suriname, the 'van Blommestein' lake, dam and power station were constructed to provide electricity for the Alcoa aluminum industry
Geothermal power is the use of geothermal heat to generate electricity. It is often referred to as a form of renewable energy, but because the heat at any location can eventually be depleted it is by definition not strictly renewable. Geothermal comes from the Greek words geo, meaning earth, and therme, meaning heat. Geothermal literally means "earth heat". Geothermal-generated electricity was first produced at Larderello, Italy, in 1904.
By the end of 2005 worldwide use of geothermal energy for electricity had reached 9.3 GWs, with an additional 28 GW used directly for heating . If heat recovered by ground source heat pumps is included, the non-electric use of geothermal energy is estimated at more than 100 GWt (gigawatts of thermal power) and is used commercially in over 70 countries .
During 2005 contracts were placed for an additional 0.5 GW of capacity in the United States, while there were also plants under construction in 11 other countries .