HYDROELECTRICITY basin is second in developed waterpower Significant Significant additional waterpower potential still exists in the Missouri and Ohio River basins and in the North and South Atlantic portions of the United States The largest hydroelectric power plant in the United States is the Grand Coulee which has a capacity of 7,600 megawatts Among water’s virtues as a source of power is the fact that it is renewable meaning that it can be used again after it supplies energy This contrasts with energy sources including fossil fuels such as coal petroleum and natural gas that are destroyed when they are used Hydroelectric installations also supply added benefits to a region For example a dam built to provide a head for water turbines usually creates a reservoir that can supply water for irrigation irrigation and drinking Potential sources of waterpower include the tides waves and currents of the ocean as well as the differences in temperature between the surface and the bottom of the ocean 8
Chapter One TYPES OF WATERPOWER The vast majority of the world’s hydroelectricity hydroelectricity is produced by the power of falling water Hydroelectric power plants are usually located in dams that are built across rivers In a dam water is collected at a higher elevation and is then led downward through large pipes to a lower elevation The falling water causes the water turbines to rotate producing electricity Oceans can also be used to create hydroelectricity hydroelectricity Those waterpower sources are known as tidal power and wave power Tidal power is created during the tide when the water level along the oceanic oceanic coast changes Wave power is harnessed by the up-and-down motion of waves 9
HYDROELECTRICITY HYDROELECTRIC PLANTS In the generation of hydroelectric power water is collected or stored at a higher elevation and led downward through large pipes or tunnels called penstocks to a lower elevation The difference in these two elevations is known as the head At the end of its passage down the pipes the falling water causes turbines to rotate The turbines in turn drive generators which convert the turbines mechanical energy into electricity Transformers are then used to convert the alternating voltage suitable for the generators generators to a higher voltage suitable for long-distance These engineers are inspecting one of the giant turbines inside a hydroelectric power station 10
TYPES OF WATERPOWER transmission The structure that houses the turbines and generators and into which the pipes or penstocks feed is called the powerhouse Hydroelectric power plants are usually located in dams that impound rivers thereby raising the level of the water behind the dam and creating as high a head as is feasible The potential power that can be derived from a volume of water is directly proportional to the working head so that a high-head installation requires a smaller volume of water than a low-head low-head installation to produce an equal amount of power some dams In the powerhouse is constructed on one flank of the dam part of the dam being used This diagram of the Hoover Dam shows the dam itself and part of the reservoir behind it The reservoir known as Lake Mead is one of the largest man-made 11 lakes in the world
