Converting wind energy is one way to get cheap electricity. There are many designs of wind generators. Some of them are designed for maximum efficiency, others are unpretentious in use. The Savonius rotor, created about 100 years ago, belongs to the second group; it is still successfully used to solve various technical problems.
History of creation
Sigurd Johannes Savonius (1884 - 1931) - an inventor from Finland, gained fame for his work in physics related to the study of wind energy. Over his life, he received several patents that are used not only for creating wind generators, but also in shipbuilding, as well as in ventilation systems of modern railway cars and buses.
Another inventor from Germany - Anton Flettner (1888 - 1861) at the beginning of the last century, came up with an alternative to the classic sail, creating the so-called Flettner rotor. The essence of the invention was as follows: a rotating cylinder, blown by the wind, received a directional force in the horizontal direction, exceeding 50 times the force of the air flow. Thanks to this discovery, several marine vessels were built using wind power for movement. Unlike ordinary sailboats, these vessels were not completely non-volatile. To rotate the rotor needed motors.
Reflecting on the Flettner sail, Savonius concluded that wind power could also be used to rotate it. In 1926, he developed and patented the design of an open cylinder with oppositely directed vanes inside.
A bit of physics
First, a little theory. Everyone noticed that when riding a bicycle, air creates significant resistance to movement. And the higher the speed, the higher this value. The second factor affecting the resistance is the cross-sectional area of the body, which is affected by the air flow. But there is still a third quantity, which is associated with the geometry of the body. It is precisely the designers of automobile bodies who try to reduce it when it comes to aerodynamics.
For example, we can say that three plates with the same cross-sectional area, but having different shapes: concave, straight and convex, will have a very different resistance coefficient. In the convex form, it will be 0.34, in the straight - 1.1, in the concave - 1.33. It was the concave shape that was taken for the blades of the Savonius rotor. It is recognized as the most efficiently receiving wind energy.
The principle of operation of the Savonius rotor
Unlike the Flettner sail, Savonius proposed dividing the cylinder into two halves and shifting them relative to each other to make the blades and the space between them. The essence of the idea of Savonius was that the air stream, beating in one blade, did not just go away after that, but, passing through the axial gap, redirected to the second blade, which greatly enhanced the effect of the wind.
This principle of operation allows the Savonius rotor to work even in light winds.
There are several profile options:
- The blades are fixed on the axis in such a way that there is no air gap between them. This is the simplest of the many descriptions of the Savonius rotor.
- The base of one blade is brought into the base of the other. A significant gap remains along the axis line. This option allows the wind from one half of the rotor to move to the other. More effective profile.
- The same as in the second embodiment, only the cross-sectional area of the blades is increased by adding a straight plate on the inside.
Scope of application
In the 60s of the last century, Savonius rotors were used in ventilation systems of railway transport. They were installed on the roofs of cars. During movement, the rotor began to spin up and pump air from the street into the room. Similar systems were installed on buses.
Today, the rotor finds its main application in wind generators with a vertical axis. There are a number of similar designs that combine two factors:
- vertical axis of rotation;
- unpretentiousness to the direction of a wind stream.
In addition to vertical wind generators, there are devices with a horizontal axis. They are distinguished by high returns with the same wind strength. Structurally, they resemble the blades of aircraft propellers located on a horizontal axis and having a guide tail for alignment with the wind.
Advantages of the Savonius wind generator
Despite the fact that vertically axial rotors of wind generators lose in efficiency horizontally axial, they still have a number of indisputable advantages:
- Work in any climatic zone. Due to the small transverse area, they are not afraid of hurricane winds.
- They do not require additional devices for their launch. Due to the concave shape of the blades, the start occurs at minimum winds of 0.3 m / s. The generator achieves optimal values at an air flow rate of 5 m / s.
- Due to the low noise level of up to 20 dB, the windmill can be installed in close proximity to the housing, which is important for low-power electricity generation and loss of current in the wires.
- Do not require a specific wind direction. They begin to work from the air flow going at any angle.
- Simple design reduces maintenance costs.
- Not dangerous for birds that perceive the structure as a whole and do not try to fly through the blades.
The disadvantages of vertical wind generators include relatively low efficiency, higher costs of building materials, large sizes that are required to achieve the required power.
How to make a do-it-yourself wind generator
It seems unlikely to make a device that would provide the country house with full electricity. However, to make a small windmill to generate free electricity, ensuring the operation of low-power devices (irrigation pump, street lighting in front of the house, opening an automatic gate), is affordable for any craftsman. This will require:
- 3 aluminum sheets with a side length of 33 cm, a thickness of about 1 mm;
- a drainpipe with a diameter of 15 cm and a length of 60 cm;
- water pipe with a diameter of 4 cm;
- electric generator (you can use a car);
- accessories (steel corners, self-tapping screws, nuts, bolts).
Manufacturing instruction
To make a simple Savonius rotor, you need:
- Cut 3 discs with a diameter of 33 cm from aluminum sheets.
- Cut the water pipe with a diameter of 15 cm along the axis to get 2 blanks for the blades. Then cut each part across in the middle. Thus, we get 4 identical blades of 30 cm in length.
- Drill a hole in the center of the discs through which you can insert a 4 cm diameter water pipe.
- Connect all three discs with a pipe, and insert blades between them. Two between two disks. The blades must be oriented so that the angle between their axes is 90 degrees. This will allow even a slight wind to spin the generator.
- Using the corners and screws, fix the blades on the aluminum discs.
- Press the generator shaft into the bottom of the pipe, which is the axis.
The wind generator is ready. It remains only to choose an installation location that would be open enough for air flow. If there is not enough wind, then you can make a high mast, on top of which to place a generator.
Factory-made vertical wind generators
With the development of alternative energy, there is an increasing demand for autonomous power supply products. Currently, there are Russian-made wind generators on the market, the price of which starts at 60 thousand rubles.
Such installations can be used in the private sector, satisfying electricity needs from 250 W to 250 kW.