Wind power

Wind power is the conversion of wind energy into more useful forms, usually electricity using wind turbines. At the end of 2006, worldwide capacity of wind-powered generators was 74,223 megawatts; although it currently produces less than 1% of world-wide electricity use, it accounts for approximately 20% of electricity use in Denmark, 9% in Spain, and 7% in Germany.
Globally, wind power generation more than quadrupled between 2000 and 2006.
Most modern wind power is generated in the form of electricity by converting the rotation of turbine blades into electrical current by means of an electrical generator. In windmills (a much older technology) wind energy is used to turn mechanical machinery to do physical work, like crushing grain or pumping water.
Wind power is used in large scale wind farms for national electrical grids as well as in small individual turbines for providing electricity to rural residences or grid-isolated locations.
Wind energy is ample, renewable, widely distributed, clean, and reduces toxic atmospheric and greenhouse gas emissions if used to replace fossil-fuel-derived electricity. The intermittency of wind seldom creates problems when using wind power at low to moderate penetration levels.

Growth and cost trends
Global Wind Energy Council (GWEC) figures show that 2006 recorded an increase of installed capacity of 15,197 megawatts (MW), taking the total installed wind energy capacity to 74,223 MW, up from 59,091 MW in 2005. Despite constraints facing supply chains for wind turbines, the annual market for wind continued to increase at an estimated rate of 32% following the 2005 record year, in which the market grew by 41%. In terms of economic value, the wind energy sector has become one of the important players in the energy markets, with the total value of new generating equipment installed in 2006 reaching €18 billion, or US$23 billion.
The countries with the highest total installed capacity are Germany (20,621 MW), Spain (11,615 MW), the USA (11,603 MW), India (6,270 MW) and Denmark (3,136). Thirteen countries around the world can now be counted among those with over 1000 MW of wind capacity. In terms of new installed capacity in 2006, the US lead with 2,454 MW, followed by Germany (2,233 MW), India (1,840 MW), Spain (1,587 MW), China (1,347 MW) and France (810 MW).
In 2004, wind energy cost one-fifth of what it did in the 1980s, and some expected that downward trend to continue as larger multi-megawatt turbines are mass-produced.However, installation costs have increased significantly in 2005 and 2006, and according to the major U.S. wind industry trade group, now average over 1600 U.S. dollars per kilowatt, compared to $1200/kW just a few years before. A British Wind Energy Association report gives an average generation cost of onshore wind power of around 3.2 pence per kilowatt hour (2005). Cost per unit of energy produced was estimated in 2006 to be comparable to the cost of new generating capacity in the United States for coal and natural gas: wind cost was estimated at $55.80 per MWh, coal at $53.10/MWh and natural gas at $52.50. Other sources in various studies have estimated wind to be more expensive than other sources (see Economics of new nuclear power plants, Clean coal, and Carbon capture and storage).
Most major forms of electricity generation are capital intensive, meaning that they require substantial investments at project inception, and low ongoing costs (generally for fuel and maintenance). This is particularly true for wind and hydro power, which have fuel costs close to zero and relatively low maintenance costs; in economic terms, wind power has an extremely low marginal cost and a high proportion of up-front capital costs. The estimated "cost" of wind energy per unit of production is generally based on average cost per unit, which incorporates the cost of construction, borrowed funds, return to investors (including cost of risk), estimated annual production, and other components. Since these costs are averaged over the projected useful life of the equipment, which may be in excess of twenty years, cost estimates per unit of generation are highly dependent on these assumptions. Figures for cost of wind energy per unit of production cited in various studies can therefore differ substantially. The cost of wind power also depends on several other factors, such as installation of power lines from the wind farm to the national grid and the frequency of wind at the site in question.
Estimates for cost of production use similar methodologies for other sources of electricity generation. Existing generation capacity represents sunk costs, and the decision to continue production will depend on marginal costs going forward, not estimated average costs at project inception. For example, the estimated cost of new wind power capacity may be lower than that for "new coal" (estimated average costs for new generation capacity) but higher than for "old coal" (marginal cost of production for existing capacity). Therefore, the choice to increase wind capacity by building new facilities will depend on more complex factors than cost estimates, including the profile of existing generation capacity.
Research from a wide variety of sources in various countries shows that support for wind power is consistently between 70 and 80 per cent amongst the general public.


Wind energy
Main article: Wind
An estimated 1% to 3% of energy from the Sun that hits the earth is converted into wind energy. This is about 50 to 100 times more energy than is converted into biomass by all the plants on Earth through photosynthesis.[citation needed] Most of this wind energy can be found at high altitudes where continuous wind speeds of over 160 km/h (100 mph) occur. Eventually, the wind energy is converted through friction into diffuse heat throughout the Earth's surface and the atmosphere.
The origin of wind is complex. The Earth is unevenly heated by the sun resulting in the poles receiving less energy from the sun than the equator does. Also the dry land heats up (and cools down) more quickly than the seas do. The differential heating powers a global atmospheric convection system reaching from the Earth's surface to the stratosphere which acts as a virtual ceiling.

Turbine siting

Map of available wind power over the United States. Color codes indicate wind power density class.
As a general rule, wind generators are practical where the average wind speed is 10 mph (16 km/h or 4.5 m/s) or greater. Usually sites are pre-selected on basis of a wind atlas, and validated with wind measurements. Obviously, meteorology plays an important part in determining possible locations for wind parks, though it has great accuracy limitations. Meteorological wind data is not usually sufficient for accurate siting of a large wind power project. An 'ideal' location would have a near constant flow of non-turbulent wind throughout the year and would not suffer too many sudden powerful bursts of wind. An important turbine siting factor is access to local demand or transmission capacity.
The wind blows faster at higher altitudes because of the reduced influence of drag of the surface (sea or land) and the reduced viscosity of the air. The increase in velocity with altitude is most dramatic near the surface and is affected by topography, surface roughness, and upwind obstacles such as trees or buildings. Typically, the increase of wind speeds with increasing height follows a logarithmic profile that can be reasonably approximated by the wind profile power law, using an exponent of 1/7th, which predicts that wind speed rises proportionally to the seventh root of altitude. Doubling the altitude of a turbine, then, increases the expected wind speeds by 10% and the expected power by 34% (calculation: increase in power = (2.0) ^(3/7) – 1 = 34%).
Wind farms or wind parks often have many turbines installed. Since each turbine extracts some of the energy of the wind, it is important to provide adequate spacing between turbines to avoid excess energy loss. Where land area is sufficient, turbines are spaced three to five rotor diameters apart perpendicular to the prevailing wind, and five to ten rotor diameters apart in the direction of the prevailing wind, to minimize efficiency loss. The "wind park effect" loss can be as low as 2% of the combined nameplate rating of the turbines.
Utility-scale wind turbine generators have minimum temperature operating limits which restrict the application in areas that routinely experience temperatures less than −20°C. Wind turbines must be protected from ice accumulation, which can make anemometer readings inaccurate and which can cause high structure loads and damage. Some turbine manufacturers offer low-temperature packages at a few percent extra cost, which include internal heaters, different lubricants, and different alloys for structural elements, to make it possible to operate the turbines at lower temperatures. If the low-temperature interval is combined with a low-wind condition, the wind turbine will require station service power, equivalent to a few percent of its output rating, to maintain internal temperatures during the cold snap. For example, the St. Leon, Manitoba project has a total rating of 99 MW and is estimated to need up to 3 MW (around 3% of capacity) of station service power a few days a year for temperatures down to −30°C. This factor affects the economics of wind turbine operation in cold climates.[citation needed]

Onshore
Onshore turbine installations in hilly or mountainous regions tend to be on ridgelines generally three kilometers or more inland from the nearest shoreline. This is done to exploit the so-called topographic acceleration. The hill or ridge causes the wind to accelerate as it is forced over it. The additional wind speeds gained in this way make large differences to the amount of energy that is produced. Great attention must be paid to the exact positions of the turbines (a process known as micro-siting) because a difference of 30 m can sometimes mean a doubling in output. Local winds are often monitored for a year or more with anemometers and detailed wind maps constructed before wind generators are installed.
For smaller installations where such data collection is too expensive or time consuming, the normal way of prospecting for wind-power sites is to directly look for trees or vegetation that are permanently "cast" or deformed by the prevailing winds. Another way is to use a wind-speed survey map, or historical data from a nearby meteorological station, although these methods are less reliable.
Wind farm siting can sometimes be highly controversial, particularly as the hilltop, often coastal sites preferred are often picturesque and environmentally sensitive (for instance, having substantial bird life). Local residents in a number of potential sites have strongly opposed the installation of wind farms, and political support has resulted in the blocking of construction of some installations.[11]

Near-Shore
Near-Shore turbine installations are generally considered to be inside a zone that is on land within three kilometers of a shoreline and on water within ten kilometers of land. Wind speeds in these zones share wind speed characteristics of both onshore wind and offshore wind depending on the prevailing wind direction. Common issues that are shared within Near-shore wind development zones are aviary (including bird migration and nesting), aquatic habitat, transportation (including shipping and boating) and visual aesthetics amongst several others.
Sea shores also tend to be windy areas and good sites for turbine installation, because a primary source of wind is convection from the differential heating and cooling of land and sea over the course of day and night. Winds at sea level carry somewhat more energy than winds of the same speed in mountainous areas because the air at sea level is more dense.
Near-shore wind farm siting can sometimes be highly controversial as coastal sites are often picturesque and environmentally sensitive (for instance, having substantial bird life). Local residents in a number of potential sites have strongly opposed the installation of wind farms due to visual aesthetic concerns.

Offshore

Offshore wind turbines near Copenhagen
Offshore wind development zones are generally considered to be ten kilometers or more from land. Offshore wind turbines are less obtrusive than turbines on land, as their apparent size and noise can be mitigated by distance. Because water has less surface roughness than land (especially deeper water), the average wind speed is usually considerably higher over open water. Capacity factors (utilisation rates) are considerably higher than for onshore and near-shore locations which allows offshore turbines to use shorter towers, making them less visible.
In stormy areas with extended shallow continental shelves (such as Denmark), turbines are practical to install — Denmark's wind generation provides about 18% of total electricity demand in the country, with many offshore windfarms. Denmark plans to increase wind energy's contribution to as much as half of its electrical supply.
Locations have begun to be developed in the Great Lakes - with one project by Trillium Power approximately 20 km from shore and over 700 MW in size. Ontario is aggressively pursuing wind power development and has many onshore wind farms and several proposed near-shore locations but presently only one offshore development.
In most cases offshore environment is more expensive than onshore. Offshore towers are generally taller than onshore towers once the submerged height is included, and offshore foundations are more difficult to build and more expensive. Power transmission from offshore turbines is generally through undersea cable, which is more expensive to install than cables on land, and may use high voltage direct current operation if significant distance is to be covered — which then requires yet more equipment. Offshore saltwater environments can also raise maintenance costs by corroding the towers, but fresh-water locations such as the Great Lakes do not. Repairs and maintenance are usually much more difficult, and generally more costly, than on onshore turbines. Offshore saltwater wind turbines are outfitted with extensive corrosion protection measures like coatings and cathodic protection, which may not be required in fresh water locations.
While there is a significant market for small land-based windmills, offshore wind turbines have recently been and will probably continue to be the largest wind turbines in operation, because larger turbines allow for the spread of the high fixed costs involved in offshore operation over a greater quantity of generation, reducing the average cost. For similar reasons, offshore wind farms tend to be quite large—often involving over 100 turbines—as opposed to onshore wind farms which can operate competitively even with much smaller installations.

Airborne
Main article: Airborne wind turbine
Wind turbines might also be flown in high speed winds at altitude,[12] although no such systems currently exist in the marketplace. An Ontario (Canada) company, Magenn Power, Inc., is attempting to commercialize tethered aerial turbines suspended with helium[13]
The Italian project called "Kitegen" uses a prototype vertical-axis wind turbine. It is an innovative plan (still in the construction phase) that consists of one wind farm with a vertical spin axis, and employs kites to exploit high-altitude winds. The Kite Wind Generator (KWG) or KiteGen is claimed to eliminate all the static and dynamic problems that prevent the increase of the power (in terms of dimensions) obtainable from the traditional horizontal-axis wind turbine generators. A number of other designs for vertical-axis turbines have been developed or proposed, including small scale commercial or pilot installations. However, vertical-axis turbines remain a commercially unproven technology.

From wikipedia