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What is Wind Energy?

Or where does the wind come from?

Wind energy is converted sun energy. The sun radiates energy onto the earth at an hourly rate of 174,423,000,000,000 kW hours. The earth is heated unevenly by the sun - the atmosphere heats up much more quickly in the equator regions than in the rest of the globe and dry land heats up (and cools down) more quickly than the oceans do. This differential heating of the earth drives a global atmospheric convection system: warm air is lighter than cold air and rises to altitudes of approx. 10 km (6 miles); it then moves north- and southwards, while cold air moves underneath the warmed-up lighter air. Because of the earth’s rotation, the air streams do not move straight towards the north and south, but circulate in the northern and southern hemispheres, but spiral in opposite rotation directions (hot air clockwise, cold air counter clockwise on the northern hemisphere). Ground surfaces interfere with this air-flow, resulting in different air pressures. Wind is the movement of air between pressure systems as they try to balance out.

It is estimated that 1-2% of the sun’s energy on earth is converted naturally into wind energy. A research study conducted at Harvard University concluded that a global network of wind power stations could meet the power consumption of the entire world population.

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History of Wind Energy

Harnessing the wind is one of the oldest methods of generating energy. Since ancient times man has used the help of windmills to grind the harvest and to pump water. With the appearance of electricity at the end of the nineteenth century, the first prototypes of modern wind turbines were built, using technology based on the classical windmill. Since then it has been a long process until wind energy was accepted as a serious and commercially sound method to generate energy.

The oil crisis of the 70s, and even more the anti-nuclear power movement of the 80s, raised interest in alternative energies and the search for new ecologically and commercially viable ways of generating power intensified. The wind turbines built at that time were mainly for research, and extremely expensive. With the help of government financed international research and funding programs, as well as the creation of research institutes in the 80s, new methods of renewable power generation continued to be researched, developed and implemented.

Research institutes such as the German Wind Energy Institute (DEWI) and the Danish Research Institute Risø, as well as various research programmes and international co-operatives in the wind energy sector, were instrumental for the industrial and technological breakthroughs of professional wind energy pioneers. Thanks to close co-operation between the research institutes and the wind energy pioneers, international standards, strict regulation and increasingly efficient designs were developed and implemented to result in modern, commercially viable wind parks.

With the development of the 55 kW wind power station in 1981, the early high costs of wind energy were dramatically reduced. Wind energy is now one of the cheapest energy sources when all external costs (e.g. environmental damage) are taken into account.

Modern wind power stations increasingly generate a major proportion of global energy. Germany is one of the biggest wind energy markets, with the second largest amount of installed wind power capacity (23,903 MW in 2008) after the USA. Alongside Germany and the US, Spain, France, Denmark, China and India are the biggest users of wind energy to generate electricity.

The wind energy industry, with its continuously growing export volume, has become an important global growth market and economic factor.

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Future of Wind Energy

International climate and environmental experts agree that the atmosphere of our planet is warming up and that we are running short of resources. Furthermore, all power stations built in the 60s or 70s will soon have to be replaced. Political and economical requirements have changed dramatically since those stations were built; global environmental problems can no longer be ignored. International environmental treaties, such as the Kyoto Protocol, establish legally binding commitments for the reduction of greenhouse gas concentrations in the atmosphere and industrialised countries agreed to reduce their collective GHG (greenhouse gas) emissions. International, standardised applications for renewable energies, regardless of national regulations or climate conditions, are more and more likely to be put into place. The wind energy industry’s future looks optimistic.

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Chronology of Wind Energy Pioneers

Charles F. Brush (1849-1929), one of the founders of the US electrical industry. Brush constructed a machine in the winter of 1887-88, now considered to be the first automated wind turbine for electricity generation. The scale of it was gigantic, with a rotor diameter of 17 m (50 ft.) and 144 rotor blades made of cedar wood. The turbine ran for 20 years and charged the batteries for Brush’s mansion. Despite its size, the turbine generated only 12 kW of electricity.

Poul la Cour (1846-1908), Danish meteorologist. La Cour is considered to be the father of the modern wind industry. His first commercial wind turbine was installed after the First World War, during a general fuel shortage. He founded the first wind power research centre in Jütland, where he gave the first courses to wind power engineers, performed the first wind channel experiments, and published the first wind energy magazine.

Albert Betz (1885-1968), German physicist. As the head of the Aerodynamic Institute in Göttingen, he formulated the so-called Betz law, which states that, independent of the design of a wind turbine, only 16/27 (or 59%) of the kinetic energy of the wind can be converted to mechanical energy. His book Wind-Energie und ihre Ausnutzung durch Windmühlen (Wind Energy and its Use by Windmills), published in 1926, gives a good account of the understanding of wind energy and wind turbines at that period.

Palmer Cosslett Putnam (1910-1986), US engineer. Putnam developed the 1.25 MW Smith Putnam wind turbine in 1941. This turbine had a short life span and was shut down because of problems caused by inappropriate construction materials; the modern materials and quality standards now used had not yet been developed.

Ulrich W Hüttner (1910-1990), German/Austrian engineer. He developed the 100 kW StGW-34 wind turbine, a milestone for modern wind turbine technology. It was installed in 1957 on a test field in the Swabian Alps.

Johannes Juul (1887-1969), Danish engineer and student of Poul la Cour. He constructed the first 200 kW wind turbine in Denmark at Vester Egesborg in 1957. This turbine is the prototype of modern wind turbines.

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How to calculate Wind Energy?

Wind is made up of moving air molecules which have mass - though not much. Any moving object with mass carries Kinetic Energy in an amount which is expressed by the equation:

Kinetic Energy = 0.5 x Mass x Velocity2

Where the Mass is measured in kg, the Velocity in m/s, and the Kinetic Energy is given in joules.

Air has a known density (around 1.23 kg/m3 at sea level), so the mass of air hitting a wind turbine (which sweeps a known area) each second is given by the following equation:

Mass/sec (kg/s) = Velocity (m/s) x Area (m2) x Density (kg/m3)

Therefore, the power (i.e. energy per second) in the wind hitting a wind turbine with a certain swept area is given by simply inserting the Mass/sec calculation into the standard kinetic energy equation given above, resulting in the following vital equation:

Power = 0.5 x Swept Area x Air Density x Velocity3

Where Power is given in watts (i.e. joules/second), the Swept Area in square metres, the Air Density in kilograms per cubic metre, and the Velocity in metres per second.

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How to Calculate Air Density?

The evaluation of the air density is essential for wind measurements, as the air density varies largely on different levels and degrees. The air pressure difference between – 10° C and + 30 ° C  is 0.177 kg/m3.

Air Density is: 

In kg/m3; air pressure = p, Gaskonstante R, temperature in Kelvin = T

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What is the Measuring Unit for Wind Energy?

Wind energy is measured in kilowatt hours (kWh) or megawatt hours (MWh), plus the time period, e.g. per year and per hour.

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Literature


Literaturtipps

 

How to contact us


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