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The advantages of wind energy Wind power is the conversion of wind energy mass flow increases linearly with the wind into more useful forms, usually electricity speed, the wind energy available to a wind using wind turbines. In 2005, worldwide turbine increases as the cube of the wind capacity of wind-powered generators was speed. The power of the example breeze above 58,982 megawatts; although it currently through the example rotor would be about 2.5 produces less than 1% of world-wide megawatts. electricity use, it accounts for 23% of electricity use in Denmark, 4.3% in Germany As the wind turbine extracts energy from the and approximately 8% in Spain. Globally, wind air flow, the air is slowed down, which power generation more than quadrupled between causes it to spread out and diverts it around 1999  and  2005. the wind turbine to some extent. Albert Betz, the German physicist, determined in 1919 that Most modern wind power is generated in the a wind turbine can extract at most 59% of the form of electricity by converting the energy that would otherwise flow through the rotation of turbine blades into electrical turbine's cross section. The Betz limit current by means of an electrical generator. applies regardless of the design of the In windmills (a much older technology) wind turbine. More recent work by Gorlov shows a energy is used to turn mechanical machinery theoretical limit of about 30% for to do physical work, like crushing grain or propeller-type turbines.[8] Actual pumping  water. efficiencies range from 10% to 20% for propeller-type turbines, and are as high as Wind power is used in large scale wind farms 35% for three-dimensional vertical-axis for national electrical grids as well as in turbines  like  Darrieus  or Gorlov turbines. small individual turbines for providing electricity to rural residences or Distribution of wind speed (red) and energy grid-isolated  locations. (blue) for all of 2002 at the Lee Ranch facility in Colorado. The histogram shows Wind energy is abundant, renewable, widely measured data, while the curve is the distributed, clean, and mitigates the Rayleigh model distribution for the same greenhouse effect if used to replace average wind speed. Energy is the Betz limit fossil-fuel-derived  electricity. through a 100 meter diameter circle facing directly into the wind. Total energy for the Cost  and  growth year through that circle was 15.4 gigawatt-hours.Windiness varies, and an The cost of wind-generated electric power has average value for a given location does not dropped substantially. Since 2004, according alone indicate the amount of energy a wind to some sources, the price in the United turbine could produce there. To assess the States is now lower than the cost of climatology of wind speeds at a particular fuel-generated electric power, even without location, a probability distribution function taking externalities into account. In 2005, is often fit to the observed data. Different wind energy cost one-fifth as much as it did locations will have different wind speed in the late 1990s, and that downward trend is distributions. The distribution model most expected to continue as larger multi-megawatt frequently used to model wind speed turbines are mass-produced.[4] A British Wind climatology is a two-parameter Weibull Energy Association report gives an average distribution because it is able to conform to generation cost of onshore wind power of a wide variety of distribution shapes, from around 3.2 pence per kilowatt hour.[5] Wind gaussian to exponential. The Rayleigh model, power is growing quickly, at about 38% in an example of which is shown plotted against 2003, up from 25% growth in 2002. In the an actual measured dataset, is a specific United States, as of 2003, wind power was the form of the Weibull function in which the fastest growing form of electricity shape parameter equals 2, and very closely generation  on  a  percentage  basis. mirrors the actual distribution of hourly wind  speeds  at  many  locations. Wind  energy Because so much power is generated by higher An estimated 1 to 3% of energy from the Sun windspeed, much of the average power that hits the earth is converted into wind available to a windmill comes in short energy. This is about 50 to 100 times more bursts. The 2002 Lee Ranch sample is telling: energy than is converted into biomass by all half of the energy available arrived in just the plants on earth through photosynthesis. 15% of the operating time. The consequence of Most of this wind energy can be found at high this is that wind energy is not dispatchable altitudes where continuous wind speeds of as for fuel-fired power plants; additional over 160 km/h (100 mph) occur. Eventually, output cannot be supplied in response to load the wind energy is converted through friction demand. - - Since wind speed is not constant, into diffuse heat all through the earth's a wind generator's annual energy production surface  and  atmosphere. is never as much as its nameplate rating multiplied by the total hours in a year. The The origin of wind is simple. The earth is ratio of actual productivity in a year to unevenly heated by the sun resulting in the this theoretical maximum is called the poles receiving less energy from the sun than capacity factor. A well-sited wind generator the equator does. Also the dry land heats up will have a capacity factor of as much as (and cools down) more quickly than the seas 35%. This compares to typical capacity do. The differential heating powers a global factors of 90% for nuclear plants, 70% for atmospheric convection system reaching from coal plants, and 30% for oil plants. When the earth's surface to the stratosphere which comparing the size of wind turbine plants to acts  as  a  virtual  ceiling. fueled power plants, it is important to note that 1000 kW of wind-turbine potential power Wind  variability  and  turbine  power would be expected to produce as much energy in a year as approximately 500 kW of A Darrieus wind turbine.The power in the wind coal-fired generation. Though the short-term can be extracted by allowing it to blow past (hours or days) output of a wind-plant is not moving wings that exert torque on a rotor. completely predictable, the annual output of The amount of power transferred is directly energy tends to vary only a few percent proportional to the density of the air, the points between years. - - When storage, such area swept out by the rotor, and the cube of as with pumped hydroelectric storage, or the  wind  speed. other forms of generation are used to "shape" wind power (by assuring constant delivery The mass flow of air that travels through the reliability), commercial delivery represents swept area of a wind turbine varies with the a cost increase of about 25%, yielding viable wind speed and air density. As an example, on commercial performance. Electricity a cool 15°C consumption can be adapted to production (59°F) day at sea level, variability to some extent with Energy Demand air density is 1.225 kilograms per cubic Management and smart meters that offer metre (it gets less dense with higher variable market pricing over the course of humidity). An 8 m/s breeze blowing through a the day. For example, municipal water pumps 100 meter diameter rotor would move almost that feed a water tower do not need to 77,000 kilograms of air per second through operate continuously and can be restricted to the  swept  area. times when electricity is plentiful and cheap. Consumers could choose when to run the The kinetic energy of a given mass varies dishwasher or charge an electric vehicle. with the square of its velocity. Because the 1 A B C D E F 96 97 99 100 101 102 103 104 105 106 107 108 109 110 111 112 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137