Savonius wind turbine with concentrator for low to medium wind sites – An Innovation by Dr. A. Jagadeesh , Wind Energy Expert
Savonius wind turbines are a type of vertical-axis wind turbine (VAWT), used for converting the force of the wind into torque on a rotating shaft. The turbine consists of a number of aerofoils, usually - but not always - vertically mounted on a rotating shaft or framework, either ground stationed or tethered in airborne systems.
The Savonius wind turbine was invented by the Finnish engineer Sigurd Johannes Savonius in 1922. However, Europeans had been experimenting with curved blades on vertical wind turbines for many decades before this. The earliest mention is by the Italian Bishop of Czanad, who was also an engineer. He wrote in his 1616 book Machinae novae about several vertical axis wind turbines with curved or V-shaped blades. None of his or any other earlier examples reached the state of development made by Savonius. In his Finnish biography there is mention of his intention to develop a turbine-type similar to the Flettner-type, but autorotationary. He experimented with his rotor on small rowing vessels on lakes in his country. There are no results of his particular investigation known, but Magnus-Effect is confirmed by König.
Schematic drawing of a two-scoop Savonius turbine The Savonius turbine is one of the simplest turbines. Aerodynamically, it is a drag-type device, consisting of two or three scoops. Looking down on the rotor from above, a two-scoop machine would look like an "S" shape in cross section. Because of the curvature, the scoops experience less drag when moving against the wind than when moving with the wind. The differential drag causes the Savonius turbine to spin. Because they are drag-type devices, Savonius turbines extract much less of the wind's power than other similarly-sized lift-type turbines. Much of the swept area of a Savonius rotor may be near the ground, if it has a small mount without an extended post, making the overall energy extraction less effective due to the lower wind speeds found at lower heights.
The Savonius Rotor
Advantages of the Savonius Rotor over the Conventional Airfoil:
1. Relative ease of construction.
2. Readily available materials for construction (for smaller units). Requires no unusual materials and can be made from many materials including metal, wood, or plastic.
3. Materials last longer.
4. Specifications are less stringent.
5. Easily reversible. The airfoil is made to operate one way only, but the Savonius Rotor can be switched to operate in the opposite direction.
6. The unit is unidirectional. This means:
• No need for a vane to direct it into the wind
• No torquing problems
• Possibility of direct drive down the tower, meaning there are no slips rings or directional gearing necessary (also, the generator or power application unit can be located at the base of the tower)
• Can be used for more applications. Airfoils are generally limited to electrical generation
• Much safer operation (the sharp edge is the trailing edge)
• Can more easily be made into a multiple unit on the same drive train, whereas the airfoil is solitary.
• Heavier construction provides the advantage of a flywheel effect.
1. Difficult to balance (although balance is less critical).
2. Less efficient than a conventional airfoil.
3. Requires a tower extension.
4. Slower operating speed
Origin of Wind Concentrator:
When we stand on a hill or on a dam, we experience high winds. Why? One is due to the height and another due to the slope. Taking a clue from nature, we conducted number of wind tunnel tests on models simulating dams (Escarpment) and measured the wind speeds at different heights with the model and with out the model. It has been found a 30 degrees slope increases the wind speed by a factor of 1.5 times at half the height of the top of the model. Since power is cube of velocity, power gain is 1.5 cubed = 3.34 This principle has been incorporated in the design of the concentrator (30 degrees over and below the rotor) The generator is the automobile generator with change of windings to reduce RPM.
This Wind rotor can be used for battery charging and will be a boon in rural areas with even moderate wind speeds as roof mounted device. It can be mounted on a big oil drum with pebbles out in the bottom of the drum to give stability.
Savonius Rotor with Concentrator designed by Dr.A.Jagadeesh
Urban wind turbines face an up-hill battle, as many people feel they are too big, too expensive, and potential eyesores. However McCamley just unveiled a prototype for a new vertical-axis turbine with a revolutionary design that allows it to overcome many of the issues associated with large horizontal-axis turbines. The company just installed its first prototype of the McCamley MT01 Mk2 in the UK at Keele University.
The new vertical-axis turbine has been installed at Keele University Science and Business Park by McCamley UK Ltd as part of a plan to transform how cities generate renewable energy. Whereas most turbines rely on a steady wind speed, McCamley’s vertical-axis turbine can cope with stronger, more turbulent gusts that are often found in urban environments. Also, whereas standard turbines draw power from the electrical grid to restart themselves whenever the wind drops below a certain level, the McCamley turbine is a self-starting wind turbine.
It is also easy to build as it is produced using ‘flat-pack’ storable parts and can be easily retrofitted and installed onto a roof without a supporting mast. The turbine is also effective on farms and related rural areas.
Dr Scott Elliott, CEO of McCamley UK Ltd said of the revolutionary turbine: “We’re pleased to be bringing our prototype to the UK for the first time. Wind energy has huge potential in the UK, but the traditional wind farm models are just not effective and are certainly not suitable for urban environments. This leaves a huge gap in the market where businesses, residential blocks and other organisations could be benefiting from clean energy. We believe that this design has the potential to be the new face of wind energy and is completely scalable, from 12kW designs to larger megawatt designs.”
“Our location at Keele University Business and Science Park has led to a real partnership where we’ve been able to utilise academic interest in the area to turn our expertise into commercial reality. We are really looking forward to working towards our microgeneration certification over the coming months and realising the potential of the prototype.”
The Cal-ePower 10 kW turbine technology has solved many of the problems faced by both vertical-axis turbines (VAWTs) and horizontal-axis turbines (HAWTs).
VAWTs have been known for their low efficiencies. One of the main reasons VAWTs are inefficient (<20%) is that the same wind that is driving the turbine is also impeding the returning blades. In other words, most VAWTs have to fight against their own design in order to produce power.
Another problem faced by VAWTs is poor start-up torque. Our concentrator technology solves both of these problems by providing a two-fold benefit for the turbine: It increases the wind speed and pressure on the drive-side of the blades, thus increasing torque and RPM, while blocking wind from impeding the returning blades.
HAWTs have problems due to their need for laminar (non-turbulent) airflow: To reach heights that have steady, strong less turbulent winds, HAWT manufacturers continue to build taller and taller machines (now over 300 ft at hub height). These huge sizes in turn are the cause of the other problems associated with HAWTs: Interference with RADAR, wildlife fatalities, noise production, obscuring the view, and human safety concerns associated with ice throw and blade loss. These problems have caused government and the public to slow or stop the development of dozens of wind power projects.
What is needed now is a solution in wind that can provide substantial amounts of power (up to 10 MW) without causing the problems associated with large HAWT wind farms. California Energy & Power provides this solution.
Below you can read other interesting materials about vertical turbines: