Air

 

Primordial people saw wind as an invigorating breath, the soul and cosmic forces bringing the world back to life. According to ancient beliefs it also symbolized an invisible and incomprehensible, even demonic power. Cosmology classified wind as one of the four elements. Together with fire, it was identified with motion and activity, a masculine element. Many circles of culture considered air to be a primordial element that when compressed produced heat, fire, so it could bring life.

 

Already in ancient times wind was a perceptible symbol of life and a universal driving force. In Hindu mythology the personification of this life-giving although whimsical element was Vāyu. He was believed to have the power of giving life to any object. Vāyu was usually depicted as mounting a gazelle, holding a large banner or a fan which to this day has been perceived as an attribute of movement and air.

 

A very important figure in the pantheon of Sumerian deities was Enlil – the “Lord of the Wind” who was a personification of the third underlying force in the universe – air. On the other hand, Egyptians identified life-giving wind with Amun – the god of fertility, opulence, and harvest who was normally presented as a king wearing a crown with two feathers. Sometimes – in order to emphasize the significance of this deity – his skin was painted blue, which symbolized the sky and immortality. 

 


Ancient Greeks, personifying the universe identified the wind with directions of the world. They also distinguished between higher regions of air – aether and lower – air. With time the first of these elements was represented as the elemental fire that gave rise to the sun and the stars. In Greek mythology the aether was also the seat of the gods. According to Greek beliefs, Zephyrus was the west wind and its gentle, mild breeze was a sign of the coming spring. On the other hand, Apheliotes symbolized the east wind bringing storm. Boreas – a personification of the north wind, was dangerous to sailors in connection with its turbulent nature and penetrating coldness. The last of them – Notos was associated with the southern part of the world and symbolized a humid summer breeze. The descendants of Homer also believed that the deity responsible for air movement was not only Hermes but also Aeolus – the mythical ruler of the winds. He kept the wind deep in a cave and let it out very carefully, taking care not to cause detriment to the harvest. Aeolus closed all the adverse winds in a sack and gave it to Odysseus. Unfortunately, the ship’s crew was not able to control their curiosity, so they opened the sack and let the winds out, so the boats sailed away from the shore of Ithaca that they could already see on the horizon. 

 

Judeo-Christians saw wind as a divine epiphany. On the other hand, in Scandinavian mythology Wayland the Smith had a wind catching power. Germanic people who were not familiar with the actual reasons for this phenomenon considered Wayland a divine entity to which sacrifices had to be made. With time, Nordic mythology started associating the power over storms and winds with Wōden – Odin. According to the tradition of Persian Mazdaism, the main task of this element was to maintain the Universe and control its moral and physical balance. In the Muslim religion, the wind was the force lifting Allah’s throne up.

 

No muth  but it can blow, no wings  but it can fly...

 

Folk legends reflect a strong belief in the powerful, almost transcendental force of nature as a sacrum. Thus, the wind was identified with a volatile element, inspiration, an environment full of light, voice and smell or an element binding the sky and the earth. This element was perceived as both an ally and an enemy – similar ambivalence could be observed in relation to other forces of nature. Sometimes it was described as a refreshing sea breeze bringing relief on hot summer days and sometimes as a destructive whirlwind that ruined everything that entered its path.

 

Wind is just a movement of air, a mass surrounding the Earth, the place in which oxygen giving life to humans is accumulated. This indispensable natural component in folk legends – due to the fact that it is invisible – was often depicted as a diabolic power, unfriendly to any God’s creature. This was the explanation given to all damage and losses caused by a sudden blow of wind. This element was also associated with suicide by hanging. According to folk legends, a person committing suicide was immediately captured by evil forces and carried away to hell. At that time the wind was believed to be the result of wild dancing of the devil with the soul. High-pitched sounds accompanying air movements were identified with the moaning and groaning of people who died in tragic circumstances and were buried improperly. Thus, a wavy and whistling wind was to remind the living about the dead. At the same time, it was associated with requests for prayer, memory and compassion. According to folk culture, the sounds coming out from a home furnace were evidence that the soul of a deceased relative was suffering. In Poland it was also believed that the wind was the main reason for all diseases, including insanity, cold, paralysis and even the source of rash. Slavs associated the whirling of air masses with vertigo, insanity or swelling.

 

Harnessing the wind

 

For centuries the movement of air masses has been used as the source of energy to mill grains, pump water and irrigate fields. One of the oldest methods used by people to control the power of the wind was sail boats that appeared on the waters of the ancient Nile in the fourth millennium before Christ. The subordinates of the pharaohs equipped their ships with tetragonal sails that, when favourable northern winds blew, could sail upstream. To this end, Egyptians used the simplest square rigs. The sail was spread between two horizontal spars on the ship’s mast. In this way wind power drove the boats and allowed faster transport than by rowing. Thanks to this invention in the following millennium Egyptians started sailing to the east along the coast of the Mediterranean Sea until they reached the famous Lebanon cedar forests. The trunks of those trees have been preserved in the pyramid of the pharaoh Snefru in Dahshur. 

 

Talking about the potential of air, it is worth mentioning kites. According to a legend, kites were invented by a Chinese farmer who, wanting to avoid his hat being carried away by the wind, tied it by means of a rope. Other sources indicate that the kite was invented in the battle field around 2000 years before Christ when Han Xin of the Han dynasty, lifted it into the air to determine the distance to be travelled by his army to reach the city walls. From that time simple structures made of four slats covered with fabric were used in battle to transmit short messages to the commanders using a code – the colour, shape and movement of the kite.

 

 

With time merchants and sailors took that invention to Korea, Japan and the Malayan Archipelago. In the Cherry Blossom Country even more functions were ascribed to kites. One of them was, for instance, the symbolic driving away of evil spirits. Most likely it was Marco Polo who around the 13th century brought the flying structure to the Old Continent. It has various functions; depending on the needs it was used to communicate simple information or was used as a testing tool.

 

An invention that was very important to the development of mankind and enabled man to harness the nature of the wind was the windmill. Thus, wind power was the earliest exploited renewable energy. The masters of wind control were the inhabitants of Seistan who, as the Arabic geographer al-Istachri recounted in his writings dating back to the 10th century, were the first to build windmills with wheels rotated by air masses. Compared to European structures the windmills had a vertical axis of rotation and its structure resembled a revolving door. Archaeologists reconstructing the ancient inventions claim that from 6 to 12 canvas wings were attached in a radiant shape to the shaft on the end of which a moving millstone was mounted. To ensure faultless operation of the facility one side of the mill had to be shielded with a wall and thus the air flow came from one direction only. Soon technological modifications followed which did not require labour-consuming replacement of the wall. According to the records of al-Dimashqi dating back to the 13th /14th century the inhabitants of Seistan erected the building (of the height of minaret) composed of two parts one on top of the other. The upper part comprised the mill and the lower a device driven by the force of the wind. The revolving mechanisms also moved the millstones on the top and the whole structure operated irrespective of the direction of the wind. This was achieved by means of four special holes in the mill that were wider on the outside to ensure that wind could enter them unobstructed. The wind entered the mill through one of the gaps where – depending on the direction from which it was blowing – meeting on its way a machine with canvas-covered ribs that under the pressure was set in motion. In addition, the machine set in motion the millstones on the top that were grinding the grain. 

 

Scientists claim that it was not a coincidence that windmills were invented there. People living in that territory were mobilized by the absence of rivers or streams to drive water mills. There are theories that water wheels with a horizontal axis of rotation that were popular in mountainous areas contributed to the discovery of the mills. Another inspiration could be prayer wheels with a horizontal axis of rotation moved by the wind, famous in Central Asia. This type of mill, called the carrousel mill, was mainly propagated in Arab countries, although in the 12th century they were known as far as in China. In Egypt it was used to crush sugar cane.

 

 

Flour without torment

 

It is difficult to give a clear answer to the question whether European mills come from the carrousel models of Seistan or whether they came into being independently. The first windmills appeared in the Old Continent (in the territory of Belgium or France) at the beginning of the 12th century. In the following century the structures became popular throughout Europe. The first windmills, in contrast to carrousel models, had a horizontal axis of rotation, thus they were more efficient as the wind impacted the whole surface of the wooden vanes.

 

A post mill popular in Poland where it was called “koźlak” derives its name from “kozioł”, that is, a special base supporting a central vertical post around which the whole structure was rotated. Post mills were wooden, usually two-level buildings in the form of a rectangle which survived, without major structural changes until the 20th century. The mills had to be set adequately prior to putting them into operation. The whole structure was rotated to ensure that the wings were in the right position to the direction of the wind. 

 

Another variant of the windmill was the so-called Dutch mill – a brick tower mill with a fixed body and rotating roof “cap” with attached vanes rotated in the direction of the wind by means of special bearings. According to popular theories this model was designed by Leonardo da Vinci because in Mediterranean countries there were similar structures with wings formed by sails that were unfolded or folded depending on the wind force. Most likely they were created for saline works that already in ancient times produced salt by pumping between sea water pools. In turn, other researchers claim that the invention was designed in 1557 by a Dutch architect, Jan Adriaanszoon Leeghwater.

 

The structure became popular mainly in Holland, so with time it became a characteristic landmark and the windmills alone were referred to as Dutch windmills. In 1750 this model was improved by the Scottish builder of farming machinery, Andrew Meikle. The engineer mounted a spinning fan (wind turbine) on the opposite side of the sail which, by means of gear transmission adjusted the position of the cap in relation to the wind.

 

The third type of windmills – a roller windmill called “paltrak”- combined the characteristics of the “koźlak” and tower windmill. The building itself was reminiscent of the post mill, whereas the working principle – sails rotated according to the direction of the wind – stems from the construction of a tower mill. The difference was the plane of rotation, since in this case the structure rotated above the wall base thanks to incorporated bearings facilitating free movement of the rest of the windmill.

 

 

For a long time windmills were used only for grinding grain to make flour, though sometimes they were also in use in salt works. In 1344 in Holland they were used for pumping water, and thus drying land and controlling the water level in lowlands. Those were ladle windmills erected on wet land that needed drying (in Poland they were situated in Żuławy – the alluvial delta of the Vistula). Post mills or tower mills were erected by canals with locks, and the rotating ladles pushed the water into a neighbouring water reservoir above the windmill level. Drying mills collected water from the low-situated parts into ditches situated at the right level. In low pressure areas, where the energy of windmills was used to drain water from the land, a considerable difference in height could be observed between respective levels. Then, a whole set of devices was used and their number depended on the absolute difference of levels in water reservoirs. This technology was called level drying. In Holland the structures were also used to drive dredges, saw mills, and oilers, although – according to some historians – the use of windmills in production plants was clearly objected to by workers who were afraid of unemployment, which often resulted in riots. 

 

With time the design of windmills was modified and in England it was even analyzed more thoroughly by scientists. John Smeaton (1724-1792) – an engineer experimenting with the performance of motors – found that windmills rarely generated more than 10 kW of power, although they were capable of producing as much as 20 kW.

 

American structures

 

We can talk about a real revolution in the power industry from 1888 when Charles Francis Brush built the first automatically operated wind turbine generator with 12 kW of power. The pioneer of the electrical engineering industry built a turbine with a diameter of 17 metres, with 144 cedar wood vanes that for 20 years charged batteries in his basement. At that time, many engineers and amateur inventors designed household wind turbines. Wind turbines generating electricity and driving water pumps were very popular on American farms. Only a Danish scientist, Poul la Cour, demonstrated that rotors with several vanes were much more efficient for electricity generation purposes. La Cour used the generated electricity to produce hydrogen in the process of electrolysis that was further used in gas lamps to light his school.

 

The intensive development of small wind turbines in the United States and in Europe was inhibited by the global economic crisis in the 1930s and World War II. It is true that the first 1250 kW wind power station, Grandpa’s Knob in Rutland (Vermont, USA), was put into operation in 1941 but the actual revival took place in the 1950s.

 


The contemporary wind turbine technology was developed in 1957 by one of la Cour’s students, a Danish engineer, Johannes Juul, who was the first to build a wind turbine with an alternating current generator. His design solutions used in a 200 kW wind power station built in 1959 in the seaside village of Gedser in Denmark, are considered modern to this date. The Gedser turbine operated faultlessly for 11 years. Next, after a failure in 1960 it was bought by NASA which used it for investigation into the development of innovative technologies. In 1960 more than one million wind power stations operated in the world.

 

Fuel crises in 1956 and after 1975 restored the interest in using wind for power generation purposes. The first was a result of war in Egypt, and the other was connected with the suspension of oil deliveries by most members of the Organization of the Petroleum Exporting Countries (OPEC).

 

The wind business

 

The 1980s saw the development of the wind power industry. In the United States, the federal government introduced wind power into the national programme for research and development. However, before the boom, for many years, teams of engineers worked to improve wind turbines, generators, automatic and mechanical elements. Thanks to the simultaneous development of materials engineering, the emergence of new technologies, and electrical engineering, the turbines that were produced were larger, more efficient and at the same time less prone to fault. Initially, their power output was 600 kW, then 800 kW, and soon it was more than 1 MW.

 

Currently, the generators achieve the power of several megawatts. Control systems in turbines are highly developed and cover automatic wind capturing to use the wind energy to the maximum extent, automatic smooth control of current generator voltage and frequency, and switching the wind turbine on and off. The achievements of the aviation industry are more and more often used in their construction. For example, in the Polish WE-10 turbine, designed by the Institute of Buildings, Mechanization and Electrification in Agriculture, the airfoils of the Mi2 helicopter were adapted into turbine vanes. Propellers are also built of various materials such as for example steel, composite, glass fibre etc.