Engineering Fundamentals: An Introduction to Engineering, 4th ed.c

are classified as crystalline, polycrystalline silicon, and amorphous silicon. Examples of

photovoltaic cells are shown in Figure 13.31.

Wind Energy

Wind energy is a form of solar energy. As you all know, because of earth’s tilt and orbit, sun

heats the earth and its atmosphere at different rates. You also know that hot air rises and

cold air sinks to replace it. As the air moves, it has kinetic energy. Part of this kinetic energy

can then be converted into mechanical energy and into electricity. A U.S. wind resource

map is shown in Figure 13.32. As shown in this figure, the potential for generating elec-

tricity from wind is categorized as marginal to superb based on wind speeds. Two types of

wind turbines are used to extract the energy from the wind, a vertical axis turbine, and a

13.6 Energy Sources, Generation, Consumption 405

■Figure 13.30

The Alamosa photovoltaic plant

in Colorado.

Source:Courtesy of DOE /NREL

■Figure 13.31

Examples of photovoltaic materials.

Source:Courtesy of DOE /NREL

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