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