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wind turbine
WIND POWER

Description

Wind power refers to the use of wind to drive a turbine, generally to create electricity. The wind turbine is the descendent of the windmill, looking either like a giant propeller in the air or an eggbeater standing on its head. A row of wind turbines can be hypnotic as they turn slowly together.

The usefulness of wind turbines depends a great deal on location. Strong winds are obviously desirable, and gusts of higher speed produce most of the power. (Available power goes as the cube of wind speed.) Open areas where the wind flows smoothly are best, but the traditional Dutch image of a windmill on top of a house is still ok. Rows of wind turbines will capture a cross section of wind. Downwind rows should be set well back so as not to interfere with each other. This can be a problem when the wind direction varies. One solution is to put the turbines closer together and accept some inefficiency.

wind farm, west-central TX

Engineering

A wind turbine is basically a propeller on a pole, turning in a vertical plane. The whole rig will swivel like a weather vane to follow the wind. A brake prevents damage if the wind gets too strong. The spinning part is connected by gears to a generator and inverter (for AC current).

A field of wind turbines will be hooked together and into the local power grid – running power lines from the city to the wind turbine farm can be a major expense. The coupling into the power grid has to be carefully regulated, because power companies like constant and controllable sources. Irregular inputs, such as from wind, can drive dangerous oscillations in the power grid and cause blackouts.

Some property owners run a single wind turbine for supplemental power. (It can't provide all the power; wind speed isn't constant.) When the wind drops, the property draws power from the local grid. When the wind generates more power than needed, the turbine feeds power back into the grid, in many jurisdictions earning a credit for the owner.

As wind turbines are usually well separated and elevated, the land dedicated to wind power can often be used for other purposes as well, for example, agriculture.

classic rural windmill

Outlook

Wind energy is a small but growing fraction of the world total power generation. Usage as a percent of total energy needs is highest in Denmark at around 40%. The largest generators are the United States and China (below).

installed wind energy by country 2014

Maximum capacity (in the table, below) is what could be generated with sustained high winds; actual power generation averaged over the year tends to be around 20% of that number.

Year     World Wind
Power Capacity
(GWatt)
2005         59.1
2006         74.2
2007         93.8
2008         121
2010         197
2014         370


Wind energy is nonpolluting and sustainable. Operating costs and maintenance tend to be very small. The installation costs can be high, particularly as the best locations are far from population centers, sometimes even offshore. Government subsidies of "green" energy make the up-front costs more attractive to private investors.
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