How did wind turbines develop?
The Bush machine

The world’s first wind turbine was built in 1888 by Charles F. Bush. The machine itself was a generator mounted on a windmill. The turbine consisted of a disk - with many blades and of a diameter of 17 m - and of a tail. A 1:50 gear transmission was connected to the axis. The generator made circa 500 rotations per minute and generated direct current. Its performance was about 12 kW/hs which is fairly low compared to the 70-100 kWs of modern turbines with the same size. It was used for 20 years.

Small systems

These small machines consisted of a little generator and a number of redone propellers. American farms used them for running household appliances and for pumping out water from the wells. They could generate around 3kW of electricity. Because the electric network spread in the country their use became needless, but in Africa or Australia they are still popular.

Big turbines

The ancestor of all big turbines was the Russian Balacava wind turbine. It was functioning for 2 years and during this period generated 200,000 kW energy. Seeing its success, America, Denmark, France and Great Britain also started using such equipments.

How did big turbines develop?

The F. L. Smith turbine

F. L. Smith was a Danish company that built turbines. Their turbines had two or three blades but only the three-bladed models got the “Danish concept” naming. These turbines could produce direct current.

The Gedser turbine
The first Gedser turbine was built in 1956 by the Danish Johannes Juul. It gained its name from the shore it was built on. The turbine could generate 200 kW current and included many innovations. The turbine had three blades which were connected with guy wires. The nacelle was turned by an electro mechanic apparatus, and contained an asynchronous alternator. An aerodynamic brake was introduced – for the first time – which, in case of too high winds, protected the turbine from overspinning. This turbine was the biggest at its time and was functioning for 11 years.
What are modern wind turbines like?
As mills, wind turbines can also be divided into two groups: vertical and horizontal axis turbines.
The horizontal axis turbine
The rotor and the generator are placed on the top of the tower. The rotor has to face the wind, therefore by smaller turbines a wane, while by bigger ones a servo motor connected to a wind speed sensor is mounted. Most of them have a gear-box so as to increase the blade’s revolutions. The blades are rigid and placed to a small distance from the tower, to avoid their impact. They are slanted a bit upwards. The most common is the three-bladed turbine but there are also two- and even one-bladed models. Usually three-bladed turbines are used to generate electricity. The efficiency of these turbines is higher than that of the horizontal axis, it can reach 45%.
The vertical axis turbines
The Darrieus turbine
The Darrieus wind turbine consists of two or three airfoils which are situated around the axis like by an eggbeater. It has both advantages and disadvantages: the advantage is that the mechanical parts are closer to the ground, while its disadvantage is that it can’t start on its own, only if it is pushed a little. Its efficiency is around 37%. They are not widely used because of their high prices.

The Giromill or H-bar

It developed from the Darrieus turbine and differs from it in the shape of the blades. Its blades are not arch-shaped but vertical ones in H setting. A new, alternating field generator was developed for this kind of rotor.

The Savonius wind turbines

The Finnish engineer, S. J. Savonius invented this kind of turbine in 1922. He completed the Darrieus rotor with a turbine equipped with two half drums. These drums helped the turbine gain the optimal speed for the start. In its simplest form it is two cups or half drums fixed to a central shaft in opposing directions. Each drum catches the wind and so turns the shaft, bringing the opposing cup/drum into the flow of the wind. This cup then repeats the process, so causing the shaft to rotate further, thus completing a full rotation. This process continues all the time the wind blows and the turning of the shaft is used to drive a pump or a small generator. Modern Savonius machines have evolved into fluted bladed devices, which have a higher efficiency and less pulsation than the older twin drum machines. Although its efficiency is not more than 23%, they have a long “life”.
The present and future of wind turbines

In developed countries, wind energy is the most promising of all renewed energy sources. Europe stands in the first place concerning the use of the power of wind to generate electricity. 12% of the electric current used in Denmark is produced by wind turbines.

What are the advantages of wind turbines?

-Maybe their most important advantage is that they are environmentally safe. While producing electric current, no harmful substances are released into the air.
-Contrary to nuclear power plants, their use is safe.
-They are powered by a secure, free and unfailing energy source and this is what assured their development during the energy crisis.
-Their low cost can compete with the cost of the nuclear energy, coal or petrol.
-They are easily mounted.
-The changes in the price of the fuel don’t influence theirs.
-They can be installed wherever the wind blows adequately.
-They don’t endanger or chase away wild animals

What are the disadvantages of wind turbines?

-They can’t be used in lull or low wind
-The energy produced can be stored partly or not at all
-Due to their high price they are not competitive
-Wind doesn’t contain much energy if we compare it with the energy of burning of coal
-Many think that they occupy much space and do not fit into the environment
-They are noisy
-They are dangerous to birds: it is estimated that in 1991 the 1731 MW American wind farm killed 10thousand birds in one year’s time.

What are the future plans?

According to the EWEA (European Wind Energy Association) by the year 2020, 12% of the world’s energy need will be generated by wind turbines, assuming that the world’s energy need will be twice as high as it is now. This has practically no obstacles. In Denmark for instance, in the windy period 50% of the country’s needs is covered by wind turbines. The benefits of the project are that 1475 new workplaces will be established, 11768 million tons of carbon-dioxide will not be sent out, 1261000 MW of energy will be generated, which would cover Europe’s energy needs for a whole year.