What is a Savonius Wind Turbine : Design & Its Working

The origin of savonius wind turbine was initiated in the year 1922 by a Finnish scientist Savonius. Before the initiation of this wind turbine, Europeans had attempted to invent a vertical type of wind turbines having twisted blades. The initial discussion of this device was done by Czanad. He composed that there exists multiple vertical axis type of wind turbines having either V-designed or twisted blades. But these models had not reached the level of advancement. In his composition, it was indicated that he has a thought to develop a turbine which is the same as Flettner kind but has an auto rotational method. So, today let us have a detailed discussion on savonius wind turbine, its working principle, design, advantages, and disadvantages.

What is Savonius Wind Turbine?

The savonius wind turbine definition is that it is employed for the conversion of wind force into torque based on the rotational shift. The turbine is included with multiple aerofoils, but these are not every time placed on the rotational shaft, but also ground positioned or even these are airborne systems.

Savonius Wind Turbine Design

The design of the turbine can be done in two ways one is classic barrel type and the other is Icewind type.

Classic Barrel Design

The construction of a classic barrel savonius wind turbine is so streamlined as because the blades are in half-cylindrical shape and so the name is the barrel. These barrels will not have a meeting point at the axis, but they are away from each other. There are many parameters that define the shape of the barrel. Here, we will be following the below approach:

‘D0’ – external diameter of the rotor’s base

‘D’ – blade radius which is the distance that is in between the two blades

‘h’ – rotor height

In order to design the square-shaped turbine, a ratio of D:h is followed. The other proportion that is used in D0: D where defines how much away that the base is ahead of the blade.

The turbine’s base is required for structural reliability as this offers extensive support for the blades in opposing the dragging pressure of the wind thus pushing the rotor blades.

The design of the wind turbine is shown below:

Icewind Design

Mostly savonius wind turbines that are designed using Icewind type are used for household purposes like farms, houses and in cabins, and telecom towers. The designs are completely high-end, simple, reliable, and less cost and they also need less maintenance for the generation of energy.

They can provide nearly 1000 watts of energy when operated at 10 m/s and a smaller turbine can produce 300 watts at 10 meters/second. These both designs can deliver speeds in the range of 2 – 60 m/sec showing no mechanical issues or overheating. Few of the turbines those are designed using Icewind type are shown as below:

Working

The device in a similar way to a cup anemometer. The savonius wind turbine working principle can be easily explained because this is considered as the most streamlined turbine when compared with other turbines. This is a dragging kind of instrument where it consists of some 2 – 3 cups. From the above portion, when the rotor is seen, it appears in the shape of “S” in the form of a cross-section.

Due to this curvature shape, the cups will have minimal dragging when they move in the opposite direction of the wind, whereas they experience maximum drag while moving in the same direction of the wind. This variation in the dragging creates the spinning movement of the savonius turbine.

As these instruments are drag type, they grab minimal wind power when compared with that of other same sized lift kinds of turbines. Most of the brushed section of savonius rotor is close to the ground level when the device has minimal mount having no stretched post thus delivering low energy extraction because of the fewer wind speeds observed at lesser heights.

The cups in the savonius wind turbine will not have faster rotational speeds when compared with the wind speed and this creates a tip speed proportion of either one or less than one. This states that the device has minimal rotational speed but produces a higher amount of torque.

So, these instruments are not exactly suitable for the production of electricity as they require higher RPMs for the generation of higher current and voltage values. For this, a gearbox can be inserted to minimize the torque and enhance the generator RPM level, and this corresponds that the turbine does not hold the ability to start by itself.

This is the savonius wind turbine working.

Savonius Wind Turbine Power Output

As per Betz’s principle, the high range of power that is received by the rotor is

Pmax = (16/27) (1/2) . ρ. d. h. v³

Where ‘ρ’ corresponds to the density of the air

‘d’ and ‘h’ corresponds to the height and diameter of the rotor

‘v’ corresponds to the speed of the wind

Whereas in the practical scenarios, the received power is only half which is given by

Pmax = 0.18 kg/m-³ d. h. v³

Power output defines the higher power level which can be extricated from the airflow. Due to the mass and momentum conservation, there will be no complete energy extraction from the wind. With Betz’s law, it was demonstrated that the higher amount of kinetic energy that was received from the wind should not go beyond 60%.

So as per this principle, none of the turbines extracts the entire energy from wind. The below picture is the curve that is plotted against the turbine’s power coefficient to the ratio of before and after passage across the turbine. The Betz’s threshold is based on the wind turbine’s horizontal axis and is not directly applicable to the vertical kind of turbines.

A similar statement contends that the theoretical threshold might be enhanced by the application of a standard VAWT method. Though, it is stated that VAWT’s have minimal efficiency than that of HAWT’s and are less probable in the present state to move across the threshold for the turbine’s horizontal axis.

The curve which is plotted for power output shows the wind turbine’s efficiency at various speed levels. The plot represents the power output in relation to the wind speed and this provides a detailed thought regarding the lesser and higher levels of a wind turbine.

The generated power is minimal than that of the received kinetic energy because it has to pass through a gearbox, and generator and these have lesser performances. Each turbine will have its specific required speed level to function. These devices will not operate at higher speed levels so as to obstruct the mechanical damage.

Advantages and Disadvantages

The advantages and disadvantages of the savonius wind turbine are explained in the below section.

The advantages of Savonius Wind Turbine include the following.

• Operation of the device is regardless of the wind direction
• These don’t need any kind of yaw process which means that these are completely stable.
• The turbines are cost-effective and the operation is so streamlined
• Even suitable for minimal applications which have minimal electric loads also
• The blades in the turbine need no mechanism to alter the angles
• Provides minimal noise
• Integration is also so simple
• Simple maintenance

The disadvantages of Savonius Wind Turbine include the following.

• The equipment used for the installation is not desirable
• These are not suitable in locations where those are a high range of turbulent winds

And this is all about the concept of Vertical Axis Wind Turbine. This article provided an explanation of Savonius Wind Turbine working, design, working principle, efficiency, power, advantages, and drawbacks. It is even more crucial to know clearly about savonius wind turbine efficiency?