Wind Energy

Wind is air in horizontal motion across the Earth’s surface. Wind is caused by differences in pressure, where the air is accelerated from higher to lower pressure. Wind is a product of sunlight – pure solar energy.

Wind power comes from the conversion of wind energy (the kinetic energy of air in motion) into an useful form of energy, such as using wind turbines to make electricity, windmills for mechanical power, wind pumps for water pumping or sails to propel ships.

To convert kinetic energy of the wind into mechanical energy (e.g. to produce electricity) a device called wind turbine is used. Wind turbines have blades, which are rotated by the power of wind. These turbines can rotate about horizontal or vertical axis. The horizontal-axis wind turbines look like huge but slim windmills and have an electric generator with blades mounted on top of a tower. Wind towers need to be very high to catch the wind with the highest velocity. Vertical axis turbines have two or three blades that spin around a vertical, or upright, shaft. Key advantage of vertical wind turbine is the fact that it does not need to be pointed into the wind to be effective. Vertical axis turbines produce less electricity than horizontal axis turbines because blades are closer to the ground where the wind is slowed down by obstacles, such as trees.

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Figure 1. Anatomy of a wind generator. A wind turbine consists of blades attached to a hub. They form the rotor. The rotor in this drawing is attached via a shaft to the rotor of the alternator. When it spins, it produces electricity.

The sizes of wind turbines vary greatly – from tiny turbines for powering one building to huge wind machines. A group of wind turbines in the same location is usually called a wind farm.

A wind farm may be located offshore and onshore. Higher energy yield is possible on offshore farms and their localization is less troublesome for human population centers. On the other hand, connection of offshore farm to the grid is more complicated.

FACTS: The largest operational wind farms on land are located in the USA. The largest offshore wind farm in the world with the capacity of 367 MW is the Walney Wind Farm in the United Kingdom. The world's largest floating wind turbine is operating 10 kilometres offshore in 220-meter-deep water, southwest of Karmøy, Norway. It began operating in September 2009 and utilizes a 2.3 MW turbine. Another "big" example is Denmark which gets almost 20% of its electricity from wind  - this is the largest share of any country.

Small Wind Power Plants

Small-scale wind power is the name given to wind generation systems with the capacity to produce up to 50 kW of electrical power.

In contrast to large wind turbines, small wind power plans can be used where there are less favorable wind conditions. They do not need large amount of undeveloped land and do not emit noise nuisance, which blade tips of large wind generators produce. They can be installed for example in a city on lamp posts or roofs of buildings.

Applications of Small Wind Power Plants

Small wind turbines are widely used to power standalone telecommunication and navigation systems, holdings and summer houses, pumping, lighting standalone facilities and many other remote systems separated from the grid. Small wind power plants often cooperate in hybrid systems with photovoltaic modules. Such combination is a reliable and optimum solution to meet local energy demand.


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Figure 2. Applications of small wind power plants

 Why use wind turbines?

Wind is an abundant and reliable source of energy.

There is only one-time installation cost for setting up a wind generator - afterwards the electricity produced by the wind turbine is free.

Wind turbines use an extremely robust technology, which is designed for both local and remote operation and requires only periodic maintenance.

The use of wind energy has fewer environmental impacts than using many other energy sources. It does not cause emission of greenhouse gases or other pollutants. A wind turbine has a small physical footprint relative to the amount of electricity it can produce.

Where to use wind turbines?

As a rule, wind speed increases with altitude and over open areas that have no windbreaks. Good sites for wind plants are the tops of smooth, rounded hills, open plains or shorelines, and mountain gaps that produce wind funneling. Wind speed changes during the day and in different months and seasons. Study of wind conditions in a specific area consists of the identification of two of its main characteristics: speed and direction.

The base for construction of wind power plant is a credible wind feasibility study. This is a detailed study into all of the key issues that determine whether a site is suitable for wind development. It includes among other things estimation of the minimum energy that a plant set on a mast of a given height and at a given place can produce. Wind measurement (12 month period is recommended) is carried out with a survey mast of a given height.

The image below shows how wind obstructions may act and the way to avoid them.

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Figure 3.  Wind turbines location


Wind power plants usually use wind speeds in the 4 to 25 m/s range. Wind power at speeds lower than 4 m/s is considered small. At speeds greater than 25 m/s wind power plant is stopped due to safety reasons.

In case of small wind power plants wind measurement is carried out at the place chosen for the location of small wind turbine. The measurements take no less than three months and are finished if results are consistent with the general trend of wind conditions in the study area.

FACTS: Wind turbines produce from less than 1 MW to around 5 MW per unit in commercial models. Nuclear reactors used for power production range from around 600 MW to around 1300 MW. Assuming that wind turbine produces average 2MW, 433 wind turbines is needed  to equal the nuclear plant's capacity if the wind is to blow 24 hours a day 7 days a week.

What are potential obstacles?

The main limitation of wind power is that no electricity is produced when the wind is not blowing. Moreover, wind energy plants (like solar collectors) require massive amounts of land. It takes 20 times as much land to produce each kilowatt of electricity on a wind farm as it does in a conventional natural gas or coal-fired power plant.

Wind turbines are noisy. Each one can generate the same level of noise as a family car traveling. The blades of wind turbines can hit birds who attempt to fly between them.

Wind power is a relatively difficult environmental integration that can affect aesthetics of landscape.

 

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