Wind Power, energy present in a moving mass of air (wind), harnessed and converted into a useful form of power, usually electricity. As with all renewable energy sources (except tidal and geothermal), the energy in the wind comes from the Sun. One or two per cent of the energy absorbed by the Earth from the Sun is converted into wind via the mechanisms of convection and Coriolis forces. There are extensive sites around the world where the prevailing wind conditions could provide significant wind energy.
There are currently about 10 gigawatts (GW, or billion watts) of installed wind power extracting devices in the world, with Germany and Denmark leading the way in Europe, and the United States accounting for 1. 7 GW. By far the most common wind turbines are horizontal axis machines that look much like a traditional windmill, but there have been many novel designs of both horizontal and vertical axis machines.
Wind turbine blades operate in a similar way to an aeroplane wing and use a lift rather than a drag mechanism, which means they are much more efficient than their windmill predecessors. Efficiencies of up to 40 per cent are quoted, but there is a theoretical maximum efficiency of 67 per cent, as proved by the German physicist Albert Betz in 1919. In addition, a turbine may, on average, only generate 30 per cent of the time in a given location, due to seasonal and daily wind variations (see “Windmill”.
The Columbia Encyclopedia, Sixth Edition, 2004). Wind turbines today are typically rated at between 750 kilowatts (kW) to 1 megawatt (MW), with 2 MW machines now in production. The main components of a wind turbine are a rotor that drives a gearbox. The gearbox increases the rotational speed by approximately 50 times before driving an electrical generator. The highly variable nature of the wind means that, depending on the application, the power generated may be rectified and smoothed before being sold to the grid, or used in a nearby facility.
The wind turbine also has sophisticated hydraulic and blade-feathering systems to ensure optimum and safe operation. Designing a device to withstand all wind conditions is a complex engineering problem. Wind turbines are by necessity large structures and are therefore subject to large forces. The power available in the wind is proportional to the cube of the wind speed. This means that as the wind speed doubles, the energy in the wind goes up 23, or 8 times.
In addition, the rotor area increases by the square of the radius, so doubling the diameter increases the available power by 4 (see “Windmill”. The Columbia Encyclopedia, Sixth Edition, 2004). Unfortunately, these cube and square laws mean that the output of a wind turbine is extremely sensitive to wind speed, and subject to very large forces during periods of unusually high winds. III. Conclusion Governments are increasingly looking towards wind power and other renewable energy sources to combat increasing greenhouse gases and global warming.
During its operating life, a typical wind turbine can produce 80 times the energy used to build, operate, and dismantle it. Public opinion is broadly in favor of wind power, but the environmental impact of wind farms could be a barrier to future developments.
1. “Wind Mills”. Grolier Encyclopedia of Knowledge, pp. 678-681. vol. 18. 2. “Windmill: Uses and Improvements”. New Standard Encyclopedia, pp. 645-668, vol. 19. 3. “Windmill”. The Columbia Encyclopedia, Sixth Edition, 2004. Columbia University Press.