The advantages of wind energy

Wind power is the conversion of wind energy intocube of the wind speed. The power of the example
more useful forms, usually electricity using windbreeze above through the example rotor would be
turbines. In 2005, worldwide capacity ofabout 2.5 megawatts.
wind-powered generators was 58,982 megawatts;As the wind turbine extracts energy from the air
although it currently produces less than 1% offlow, the air is slowed down, which causes it to
world-wide electricity use, it accounts for 23% ofspread out and diverts it around the wind turbine to
electricity use in Denmark, 4.3% in Germany andsome extent. Albert Betz, the German physicist,
approximately 8% in Spain. Globally, wind powerdetermined in 1919 that a wind turbine can extract at
generation more than quadrupled between 1999 andmost 59% of the energy that would otherwise flow
2005.through the turbine's cross section. The Betz limit
Most modern wind power is generated in the form ofapplies regardless of the design of the turbine. More
electricity by converting the rotation of turbine bladesrecent work by Gorlov shows a theoretical limit of
into electrical current by means of an electricalabout 30% for propeller-type turbines.[8] Actual
generator. In windmills (a much older technology)efficiencies range from 10% to 20% for
wind energy is used to turn mechanical machinery topropeller-type turbines, and are as high as 35% for
do physical work, like crushing grain or pumpingthree-dimensional vertical-axis turbines like Darrieus or
water.Gorlov turbines.
Wind power is used in large scale wind farms forDistribution of wind speed (red) and energy (blue) for
national electrical grids as well as in small individualall of 2002 at the Lee Ranch facility in Colorado. The
turbines for providing electricity to rural residences orhistogram shows measured data, while the curve is
grid-isolated locations.the Rayleigh model distribution for the same average
Wind energy is abundant, renewable, widelywind speed. Energy is the Betz limit through a 100
distributed, clean, and mitigates the greenhousemeter diameter circle facing directly into the wind.
effect if used to replace fossil-fuel-derived electricity.Total energy for the year through that circle was
Cost and growth15.4 gigawatt-hours.Windiness varies, and an average
The cost of wind-generated electric power hasvalue for a given location does not alone indicate the
dropped substantially. Since 2004, according to someamount of energy a wind turbine could produce
sources, the price in the United States is now lowerthere. To assess the climatology of wind speeds at a
than the cost of fuel-generated electric power, evenparticular location, a probability distribution function is
without taking externalities into account. In 2005,often fit to the observed data. Different locations will
wind energy cost one-fifth as much as it did in thehave different wind speed distributions. The
late 1990s, and that downward trend is expected todistribution model most frequently used to model
continue as larger multi-megawatt turbines arewind speed climatology is a two-parameter Weibull
mass-produced.[4] A British Wind Energy Associationdistribution because it is able to conform to a wide
report gives an average generation cost of onshorevariety of distribution shapes, from gaussian to
wind power of around 3.2 pence per kilowatt hour.[5]exponential. The Rayleigh model, an example of which
Wind power is growing quickly, at about 38% inis shown plotted against an actual measured dataset,
2003, up from 25% growth in 2002. In the Unitedis a specific form of the Weibull function in which the
States, as of 2003, wind power was the fastestshape parameter equals 2, and very closely mirrors
growing form of electricity generation on athe actual distribution of hourly wind speeds at many
percentage basis.locations.
Wind energyBecause so much power is generated by higher
An estimated 1 to 3% of energy from the Sun thatwindspeed, much of the average power available to
hits the earth is converted into wind energy. This isa windmill comes in short bursts. The 2002 Lee Ranch
about 50 to 100 times more energy than issample is telling: half of the energy available arrived in
converted into biomass by all the plants on earthjust 15% of the operating time. The consequence of
through photosynthesis. Most of this wind energy canthis is that wind energy is not dispatchable as for
be found at high altitudes where continuous windfuel-fired power plants; additional output cannot be
speeds of over 160 km/h (100 mph) occur.supplied in response to load demand. - - Since wind
Eventually, the wind energy is converted throughspeed is not constant, a wind generator's annual
friction into diffuse heat all through the earth'senergy production is never as much as its nameplate
surface and atmosphere.rating multiplied by the total hours in a year. The ratio
The origin of wind is simple. The earth is unevenlyof actual productivity in a year to this theoretical
heated by the sun resulting in the poles receiving lessmaximum is called the capacity factor. A well-sited
energy from the sun than the equator does. Also thewind generator will have a capacity factor of as
dry land heats up (and cools down) more quickly thanmuch as 35%. This compares to typical capacity
the seas do. The differential heating powers a globalfactors of 90% for nuclear plants, 70% for coal
atmospheric convection system reaching from theplants, and 30% for oil plants. When comparing the
earth's surface to the stratosphere which acts as asize of wind turbine plants to fueled power plants, it
virtual ceiling.is important to note that 1000 kW of wind-turbine
Wind variability and turbine powerpotential power would be expected to produce as
A Darrieus wind turbine.The power in the wind can bemuch energy in a year as approximately 500 kW of
extracted by allowing it to blow past moving wingscoal-fired generation. Though the short-term (hours
that exert torque on a rotor. The amount of poweror days) output of a wind-plant is not completely
transferred is directly proportional to the density ofpredictable, the annual output of energy tends to
the air, the area swept out by the rotor, and thevary only a few percent points between years. - -
cube of the wind speed.When storage, such as with pumped hydroelectric
The mass flow of air that travels through the sweptstorage, or other forms of generation are used to
area of a wind turbine varies with the wind speed"shape" wind power (by assuring constant delivery
and air density. As an example, on a coolreliability), commercial delivery represents a cost
15°Cincrease of about 25%, yielding viable commercial
(59°F) day at seaperformance. Electricity consumption can be adapted
level, air density is 1.225 kilograms per cubic metre (itto production variability to some extent with Energy
gets less dense with higher humidity). An 8 m/sDemand Management and smart meters that offer
breeze blowing through a 100 meter diameter rotorvariable market pricing over the course of the day.
would move almost 77,000 kilograms of air perFor example, municipal water pumps that feed a
second through the swept area.water tower do not need to operate continuously
The kinetic energy of a given mass varies with theand can be restricted to times when electricity is
square of its velocity. Because the mass flowplentiful and cheap. Consumers could choose when to
increases linearly with the wind speed, the windrun the dishwasher or charge an electric vehicle.
energy available to a wind turbine increases as the