Humanity has utilised energy from wind for transportation, in the form of sailing, for thousands of years. In fact, people have been able to sail longer than they have been able to write, with the earliest known image of a vessel under sail to be found on a piece of Egyptian pottery dating from 3100 BC.
Wind has also been harnessed for grinding grain, pumping water and even sawing wood, through the technology of windmills. The first windmills were invented in Persia around 600 AD and used only to grind grain. It is believed that this windmill technology spread back to Europe via the crusades and by the 1100's, windmills could be found throughout Europe. By 1400, there were around 10,000 windmills in England alone.
Towards the end of the 19th century, a number of factors combined to cause a decline in the use of windmills. Rural areas were depopulating as people moved to towns, and steam power, electricity and the internal combustion engine inventions were increasingly being used as alternatives. In England, there were only 350 working mills by the end of World War I, this decreased to 50 by the end of World War II. Today, of the 90 windmills still in existence in England, very few are still in working order.
The ability to generate electricity from the wind was developed in the 1860's by Moses Farmer. Windmills began to be used to generate electricity in the early 20th Century but it was the oil shocks of the 1970's that spurred serious modern interest in wind power as an alternative energy source.
Wind power is a clean, abundant, safe and low cost form of renewable energy. The wind power industry is currently growing very rapidly worldwide, with Europe taking a lead role. Many environmentalists now see it as the form of renewable energy most likely to replace 'conventional' generating methods.
Electricity from wind
The energy of wind is captured and converted into electricity by devices called wind turbines. There are two major types of turbine: vertical axis or horizontal axis.
Horizontal-axis wind turbines:
The horizontal-axis turbine is by far the most common type and generally resembles a gigantic propeller mounted on a tower. The components of this type of turbine are:
The blades are mounted perpendicular to the wind. The design of the blades is such that wind is forced to pass more quickly over the upper surface thus creating an area of lower air pressure and the force of 'lift'. The combination of lift and drag causes the rotor to spin, which in turn spins the shaft and the generator in order to produce electricity.
The rotor is mounted high on to a tower in order to utilise winds that are stronger, more stable and constant, than the winds which may be found closer to the ground.
Vertical-axis wind turbines:
This type of turbine is rarely used to generate electricity. It is difficult to mount vertical-axis turbines on to a tower and therefore, they are forced to utilise the less productive and more turbulent winds that are found closer to the ground. The Darrieus machine, which was patented in France in 1927, is the most often used type of vertical-axis turbine in terms of producing electricity. It can resemble an eggbeater or whisk and the blades are mounted parallel to the wind. Like the horizontal-axis turbine, as the blades rotate they spin a shaft which is connected to a gearbox and generator.
For both types of turbines, a certain minimum wind speed is required before the turbine is able to produce electricity. This minimum wind speed may differ from turbine to turbine, but has generally decreased over time due to technological advances. Conversely, high winds may overload and damage the generator. To prevent such damage, the turbine may be fitted with a limiter, or the gearbox and generator may disengage when the wind speed exceeds a safe maximum.
It is common to see several wind turbines grouped together in 'wind farms' for economic and practical reasons.
Decreasing cost of electricity generation
Historically, wind turbines have been expensive to build and were able to produce only small amounts of electricity. This prevented wind power from becoming a major source of energy. However, massive advances in research and development since the 1980's have resulted in a drop of about 85% in the cost of generating electricity from the wind. The cost per kilowatt hour (kWh) of wind generated electricity was approximately US 5 cents in 2001, down from US 30 cents in 1980. This makes wind power comparable in cost to electricity generated from coal or gas and cheaper than nuclear generated electricity.
The wind power market
As of 31st December 2001, the total worldwide installed capacity of wind power was approximately 24,000 Megawatts. More than 70% of this generating capacity was located in Europe. The worldwide total installed capacity of wind power has grown by roughly 30% each year over the five years to 2001.
See table below for the top five wind-energy markets (by installed capacity in Megawatts) as at the end of 2001:
Denmark currently derives 15% of all its electricity from the wind power. The wind power industry is worth about US $1 billion a year to Denmark, with wind turbines being a major export item. The Danish government has, in the past, provided tax incentives and subsidies to support the industry.
Germany derives about 3.5% of its electricity from the wind. However, it is the world leader in terms of installed capacity, with 11,500 wind turbines providing a total capacity of 8,750 Megawatts.
The United Kingdom derives about 0.37% of its electricity from wind and has a total installed capacity of 473.6 Megawatts. However, thirteen offshore wind farms are planned for the near future, each with a potential capacity of at least 1,000 Megawatts.
The USA, as at the end of 2001, is able to generate sufficient electricity for 1 million average American households from the wind.
The following table is taken from the March 2002 edition of 'wind directions' (which is available on the 'ewea' website) and demonstrates the installed capacity of wind power in various European nations.
Wind Energy Capacity Installed in Europe, in Megawatts(MW)
Environmental and other benefits of wind power
Wind turbines do not produce any air pollutants or greenhouse gases during the generation of electricity. Some pollutants are produced during the construction of a turbine but these are far less than 1% of the amount produced by a coal-fired power plant generating the equivalent amount of electricity, over the lifetime of a wind turbine.
As an example, wind power in the USA provides sufficient electricity for 1 million average American households which effectively prevents the emission of 6.8 million tonnes of carbon dioxide. Wind power in Europe provides sufficient electricity for 10 million average European households and thus prevents the emission of 24 million tonnes of carbon dioxide.
The construction of wind farms and wind turbines can create many jobs, with obvious flow on benefits for an economy. For example, the wind industry provides employment for about 35,000 people in Germany and more than 12,000 in Denmark. Wind farms can also be a source of income to the owners of the land on which they are built, through rental fees.
Generating electricity from the wind increases energy diversity, reducing reliance on fossil fuels. This is important given the rising cost and decreasing availability of fossil fuels and makes the technology especially attractive to developing nations.
The table below demonstrates the amount of pollutants and greenhouse gases produced by a coal fired power plant in comparison to a typical 750 Kilowatt wind turbine, over a period of 25 years.
Acknowledgment: This table is taken from the webpage: www.awea.org/faq/bal.html
Environmental and other drawbacks of wind power
There are a number of common concerns voiced by environmentalists and the general public regarding wind power:
To address some of these issues, Denmark has developed larger and more efficient wind turbines so that fewer are required in a wind farm. Denmark has also built the world's first offshore wind farm, which has the added advantage of better wind conditions and is therefore able to produce 60% more electricity than an onshore equivalent.
Wind power is now the world's fastest growing energy source and the installed capacity is expected to reach 30,000 Megawatts by the end of 2002. The capacity is predicted to grow by around 20% per year over the next few years. Investments in wind power of US $3 billion are planned in the USA for the immediate future. Brazil has approved 20 projects of more than 1,000 Megawatts each for future construction. The UK has approved plans for large offshore wind farms while other European countries and India, have plans to substantially increase their wind power capacity.