Wind Power

Wind is simply the movement of air caused by the heating of the earth’s surface by the sun. The heating is uneven due to the different types of land and water that causes the sun's heat to be absorbed at different rates.

Wind power is the conversion of wind energy into a useful form. Historically wind energy has been directly used for sailing boats or it has been converted into mechanical energy using windmills for pumping water or grinding grain. Today the main application of wind power is the generation of electricity using wind turbines. Wind is called a renewable energy source because the wind will blow as long as the sun shines.

Wind farms that are used for large scale operation are usually connected to local electric networks. They also have smaller turbines to provide electric power to isolated areas. When utilities buy back electricity that is not being used by smaller household turbines it is called net metering. This is happening at an increasing rate.

Environmentalists favor wind energy as an alternative to fossil fuels for power because it is plentiful, renewable, widely distributed, clean and produces lower greenhouse gas emmissions. But wind farms are not welcomed by everyone due to the visual impact of the farms and other effects this constuction has on the environment. The fact that the wind is intermittant does not creat a problem when wind power is a small percentage of the total demand. When wind power is used for a smaller part of the demand, the cost for the extra power is considered to be moderate. There is a study that indicates that using wind for 70% of usage is possible at the current power prices by combining wind farms together with an High Voltage direct Current (HVDC) supergrid.

Today there are two kinds of wind turbines used based on the direction of the rotating shaft or axis: horizontal-axis and vertical-axis. They vary widely in size due to their usage. Smaller turbines are used for homes and businesses and can have a capacity of less than 100 kilowatts. Larger commercial sized turbines may have a capacity of 5 million watts, or 5 megawatts. The larger machines can be put together into wind farms that provide power to the electrical grid.

Horizontal-axis
The horizontal-axis type is used most today. Their blades are similar to airplane propellers. They can stand as tall as a 20-story building and have three blades that are 200 feet across. These types of wind machines are tall and wide to capture more wind. The largest wind turbines have blades longer that a football field.

Vertical-axis
The blades of the vertical-axis machine go from top to bottom. The Darrieus wind turbine is the most common and is similiar to a large two-bladed egg beater. These are typically stand 100 feet tall and 50 feet wide. They make up a small percentage of the wind turbines in use today.

The Wind Amplified Rotor Platform (WARP) is different than the other two kinds of wind systems and is designed to be more efficient and use less land than typical wind systems. The WARP does not use large blades; instead, it looks like a stack of wheel rims. Each of these modules have two small, high capacity turbines that are mounted to both of its concave wind amplifier module channel surfaces. The concave surfaces direct the wind toward the turbines, which amplifies the wind speeds by 50 percent or more. Eneco, the company that designed WARP, plans to market the technology to power offshore oil platforms and wireless telecommunications systems.

Savonius wind turbines are another type of vertical-axis wind turbine, used for converting wind power into torque on a rotating shaft. The Savonius wind turbins were invented by Finnish engineer Sigurd J. Savonius in 1922.
Savonius turbines are one of the simplest turbines. They are drag-type devices, that consist of two or three scoops. Looking down, a two-scoop machine would look like an "S" shape in cross section. Because of the curvature, the scoops use less drag when moving against the wind than when moving with the wind. The difference in drag is what causes the Savonius turbine to spin. Because they are drag-type machines, Savonius turbines extract much less of the wind's power than other like-sized lift-type wind turbines. Much of the swept area of a Savonius rotor is near the ground, making the overall energy extraction less effective due to lower wind speed at lower heights.

Savonius turbines are typically used when cost is more important than efficiency. For example, most anemometers are Savonius turbines, because efficiency is not as important for that application. Larger Savonius turbines have been used to create electric power on deep-water bouys, which need small amounts of power and little maintenance is required. Design is simplified because, unlike horizontal-axis turbines, no pointing mechanism is needed for changeing wind direction and the turbine starts by its self. Savonius and other vertical-axis machines are not usually connected to electric power grids. They can sometimes have long helical scoops, to give smooth torque.