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Wind Power Fact Sheet

Wind power has been used for thousands of years as an important energy source. It has been harnessed for over one thousand years to pump water, to grind grain and to provide motive power for other activities. Wind is the product of the movement of air. Air has a certain density and surrounds the earth for a layer of approximately 64km in altitude. Air exerts a downward pressure, which is referred to as atmospheric pressure. The pressure on the earth's surface is one atmosphere, or one "bar", at sea level (mean absolute sea level/masl). Air pressure is measured with a barometer.

As the Earth rotates on its axis, gravity forces this relatively "heavy" air near the Earth's surface to spin round with it. However, the air higher up is less affected. The difference between the speed at which air moves close to the surface and the speed of air higher up forms vortexes or whirlpools. This mixing causes variations in air speed, and, consequently, "wind" is generated at the earth's surface.

Additionally, the sun warms the earth and the atmosphere. Heating is greater at the equator than at the earth's poles. Warm air is less dense (weighs less) than cold air. Warm air rises while cold air sinks. Therefore, there is always a series of pressure differentials in the air caused, 1) by the earth's rotation; and 2) by differential temperature on the earth's surface. These two factors account for the earth's "wind".

Wind and Energy

Air moves (i.e., wind), and this accounts for its "kinetic energy". The energy contained within wind can be harnessed to generate force for transport (sails), for mechanical energy (windmills) and for electrical energy (wind turbines). Fans or blades are fixed to a shaft on a wind mill or wind turbine. They are set at an angle such that the air striking them forces them to turn. This turns the shaft, which can then either push a piston (to pump water), turn a series of shafts (e.g., to grind grain) or to turn a turbine to generate electricity.

 Wind mills and turbines must be designed to take advantage of the slowest wind speeds (in order to generate energy during periods of relative calm), while at the same time be controlled in order not to turn too quickly during periods of high wind speeds. This range of powering for a generator gives it its "rated power".

History of Wind Use

Wind has been harnessed for energy for thousands of years. The first sailing ships used wind at least five thousand years ago. Records show Babylonians using wind for powering grinding mills nearly five thousand years ago. Windmills were introduced into Europe from the Middle East during the early Middle Ages. This technology quickly spread all over the continent to the extent that by 1750 over 5,000 windmills were recorded in use in England. Windmills were used extensively by the Dutch from the 16th Century into the 20th Century to pump water to prevent flooding (as the Dutch reclaimed so much land from the sea).

Ancient windmills were big, inefficient and clumsy affairs (but suited to the needs of the times). The first "modern" windmills were developed in the 19th century for livestock and agricultural use in Australia and the United States, and quickly spread to other places, particularly Africa, in the 20th Century. These "new" windmills were made primarily of metal, mounted on relatively light towers, and easily assembled and disassembled. It is recorded that there were over 5 million of these in use in the United States by the 1930s. There were another 500,000 in Australia, and perhaps a quarter that number in South Africa, the rest of Southern Africa and East Africa, with over a million in use in Latin America. Their primary uses were for water pumping for livestock, for small-scale irrigation, and for domestic uses.

Small "dynamos" or electric generators were often connected to these mills to generate direct current (DC) to charge car batteries for household lighting and radios. This was in widespread use in the United States, Latin America, South Africa and Australia until after the Second World War.

Modern Wind Energy

Wind energy has undergone a revolution over the past century. The Danes developed the world's first large wind electrical turbines during the 1930s. These were in widespread use during the Second World War when imported petroleum was scarce, and Denmark needed all the electricity it could get. As with virtually all renewable energy sources (except large-scale hydropower), wind fell into general disuse with the large-scale production and distribution of inexpensive petroleum following the Second World War. This had a major effect of changing water pumping patterns all over the world, to such an extent that by 1970, fewer than 50,000 windmills were in use in the United States, and windmills for pumping fell into almost total disuse in Africa and Latin America.

However, the petroleum price "shocks" of the 1970s and the world's growing concern for the environment had the effect of stimulating new research, development, testing and production of windmills and wind turbines. Even as petroleum prices slid back to historical levels during the 1980s, the Danes persisted with their work in the field of wind turbine design and production. Conscious effort on the part of government, industry, academic and research institutions, and local Danish communities not only kept the wind industry alive during the 1980s, but helped to install more wind electricity generating capacity than anywhere outside the United States. Today, 75% of all wind turbines exported in the world are Danish-made.

Wind turbines are characterised by their range and diversity. The smallest wind turbines can generate several hundred watts (mainly for recreational uses, but increasingly of interest for charging batteries in the developing world). At the other end of the spectrum, pilot tests in New Zealand have produced 3 MW turbines, and the Danes are in the process of pilot testing turbines of 2 MW for off-shore wind electricity generation.

Germany has installed over 2 GW of wind electricity since 1994, making it the world's largest wind electricity generator (installation proceeds at over 100 MW per month at present). The UK, The Netherlands and Denmark are pioneering large off-shore wind "farms" with designs for hundreds of megawatts of capacity for the next five years. Meanwhile, the USA is ready to re-embark upon another major wind energy programme, the Indians have installed more wind electricity than any country in the developing world, and wind electricity is of growing interest all over the world.

Table 1 - Projected Global Wind Installation Rate

Installation Rate (MW per year)

1995

2000

2005

EU

610

1,620

1,030

Other Europe

18

170

200

North America

175

750

500

South America

23

250

500

China

50

275

500

India

300

400

500

Other

35

250

450

Total

1,210

3,715

3,680

Source: ESD

Meanwhile, wind pumping continues to develop, although at a slower pace, and with much less international interest. Wind pumps suffer from two important disadvantages relative to wind turbines, which can be, and are, used for water pumping. Wind pumps must be sited over or very near their water sources. This reduces the areas where they can be used, as, obviously, not every area on or near water has good wind "regimes" (wind speeds, frequency of good winds, etc.). Second, wind pumps have only one application, water pumping. A wind turbine, on the other hand, can be sited in an area with good wind, and an electric cable can then be laid to the borehole, well, stream or river to pump the water to the desired location. When the electricity is not being used for pumping, it can be used for other purposes such as lighting homes, providing storage electricity for refrigerators, computers, etc.

Given the wide range of wind turbines available today, and the extensive research and development of wider "niche" applications, it seems that wind generated electricity may replace windmills for pumping water in all but a few locations.

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