Wind is simple air in motion. It is caused by the uneven heating of the earth’s surface by the sun. Since the earth’s surface is made of very different types of land and water, it absorbs the sun’s heat at different rates.

 

During the day, the air above the land heats up more quickly than the air over water. The warm air over the land expands and rises, and the heavier, cooler air rushes in to take its place, creating winds. At night, the winds are reversed because the air cools more rapidly over land than over water.

 

In the same way, the large atmospheric winds that circle the earth are created because the land near the earth's equator is heated more by the sun than the land near the North and South Poles.

 

Today, wind energy is mainly used to generate electricity. Wind is called a renewable energy source because the wind will blow as long as the sun shines.

 

Like old fashioned windmills, today’s wind machines use blades to collect the wind’s kinetic energy. Windmills work because they slow down the speed of the wind. The wind flows over the airfoil shaped blades causing lift, like the effect on airplane wings, causing them to turn. The blades are connected to a drive shaft that turns an electric generator to produce electricity.  The electricity is sent through transmission and distribution lines to a substation, then on to homes, business and schools.

 

Operating a wind power plant is not as simple as just building a windmill in a windy place. Wind plant owners must carefully plan where to locate their machines. One important thing to consider is how fast and how much the wind blows.  Wind speed increases with altitude and over open areas with no windbreaks. Good sites for wind plants are the tops of smooth, rounded hills, open plains or shorelines, and mountain gaps that produce wind funneling.

 

Wind turbines start operating at wind speeds of about 10 miles per hour and reach maximum power output at around 33 miles per hour.  At very high wind speeds over 50 miles per hour, wind turbines may shut down.  To be commercially viable wind farms need to operate at an annual average wind speed of over 14.5 miles per hour. 

 

Although various designs and configurations exist, wind turbines are generally grouped into two types used today based on the direction of the rotating shaft (axis): horizontal–axis wind machines and vertical-axis wind machines.

 

KID’S PAGE

By Trish Penny