Emerging Small Wind2008

Working paper No 7 (2008) Digital Time stamping

Emerging Small Wind Technology

Working Paper No 7 (2008) Emerging Small Wind Technology

©2008 The Applied Research Institute for Prospective Technologies 1

Contents

Small scale renewables ...................................................................................................................... 1

Small wind versus solar panels ................................................................................................... 3

Types of Small Wind Turbines ......................................................................................................... 5

Application areas .............................................................................................................................. 6

Main designs of small wind turbines ......................................................................................... 7

Main technical limitations of existing small wind turbines ............................................... 9

Emerging small wind technology.................................................................................................. 12

Magnus effect................................................................................................................................... 12

Magnus type wind turbine........................................................................................................... 16

Review: Patents on Magnus type wind turbine....................................................................... 17



Small scale renewables

The specific factors that drive the uptake of domestic scale grid-connected renewables are predominantly financial (61% of respondents identified the high cost of the technology as the most important barrier to overcome),1 which may be a factor in the limited take-up to date. For many end-users of electricity, there may be no move to small-scale renewable energy generation until the total cost to the end-user of using grid-supplied electricity (taking account of its retail price, any other expenses as an electricity consumer and convenience) exceeds the total cost of electricity generated from small-scale renewables. The utility of the electricity supply is generally similar (i.e. there are no specific advantages or disadvantages derived from the implementation of a grid-connected renewable electricity system). In general, it is cheaper and easier for a grid-connected consumer to purchase standard electricity via the grid. Notwithstanding this, take-up of domestic grid-connected renewable energy systems is observed to be increasing, mainly due to changes in awareness of climate change, and community desire to take direct action. Rising residential and commercial electricity price rises over the past seven years are also having a significant impact. Policy measures and incentive programs have also successfully stimulated development of the domestic and small scale renewable energy around the world. Some of these have led to high levels of grid-connected small-scale renewables (e.g. in Germany and Japan).

As well as factors that evenly influence the demand for all renewable technologies, there are those that only influence demand for particular technology – that are mainly competitive price of technology and the availability of resources, site dependence.

Small scale renewables for primary energy production (electricity generation not heat production) presently available are:

• Solar photovoltaic (PV) panels;

• Small wind turbines;

• Micro, small hydro turbines.

The comparison of these technologies is presented in the Table 1:

1 Cipcigan L.M., Taylor P.C., Trichakis P. Potential for Microgeneration Study and Analysis. Final Report. 2005



Table 1: Comparison of small scale renewables for primary energy production

Renewable technology

Pay-back period2

Costs

[Euro cents per

kWh]

Resource availability

Solar photovoltaic panels3

6 to 12 years for businesses

6 to 22 years for residential installations

25-65 Yearly sum of horizontal global irradiation varies from 800-1800 (kWh/m2/year)

Small wind turbines4

6 to 12 years for businesses

8 to 16 years for residential installations

4-12 Wind resources level at 50 m above ground varies from depending on topographic conditions (5-9 m/s in open area, 7-11.5 hills and ridges; 2-6 sheltered terrain - Weibull distribution).

Every EU-25 country have and exploitable wind resources.

Micro, small hydro turbines5

6-15 5-15 Extremely dependent on a country’s geography – the water drop height of 4 m is needed.

More than 82% of economically feasible potential has already been exploited in former EU15, presently target countries are New Member Stated and Accession Countries.

Small wind versus solar panels

Typical location for installation of small scale renewables are rural or suburban homes; “on-site” communities (schools and other public sector buildings); farms;

2 The figures reflect net-metering systems displacing energy that would otherwise be purchased from a utility company. The actual payback period depends on resource availability at the site, system efficiency and utility rates. Not taking into account the ongoing incentive programms.

3 Marcel Šúri, Thomas A. Hulda, Ewan D. Dunlopa, Heinz A. Ossenbrinka. Potential of solar electricity generation in the European Union member states and candidate countries. Solar Energy. Volume 81, Issue 10, October 2007, Pages 1295-1305

4 Wind Energy THE FACTS an analysis of wind energy in the EU-25. 2004

5 European Small Hydropower Association – small hydro power in figures < http://www.esha.be/index.php?id=50>



industries (with high energy consumption processes) and other (urban settings, off-grid battery systems – remote homed, telecom, marine). All technologies are site specific due to the nature of resources, especially hydropower (it mostly used for electrification of isolated sites).

PV growth during last years was mainly driven by government incentives. Although it is generally recognised that grant support cannot be a long term mechanism (cost effectiveness is not predicted to occur until 2030, however, a technology breakthrough could reduce capital costs and bring this forward towards 2020), when the break-even for small wind is predicted circa 2010 –2015, Figure 1.

Figure 1: Energy cost: domestic small wind (EEE - Energy Export Equivalence)1

Moreover, small wind turbines is more cost-effective solution to those homes, communities or businesses needing more than 1kW watts of generated power (which is in most cases,

Table 2) than PV. Unlike PV's, which stay at basically the same cost per watt independent of array size, wind turbines get less expensive with increasing system size. The cost of regulators and controls is essentially the same for PV and wind. Somewhat surprisingly, the cost of towers for the wind turbines is about the same as the cost of equivalent PV racks and trackers. The cost of wiring is usually higher for PV systems because of the large number of connections. A typical home consumes between 800-2,000 kWh of electricity per month and a 4-10 kW wind



turbine or PV system is about the right size to meet this demand. At this size wind turbines are much less expensive.

Table 2: Need of generated power depending on application area

Application Generated power (need)

Rural or suburban homes 1-25 kW

“On-site” communities (schools and other public sector buildings)

100kW-1MW

Farms 10-400kW

Industries (high energy consumption processes).

10-400 kW

Other (urban settings, off-grid battery systems – remote homed, telecom, marine)

0.1-60kW

Types of Small Wind Turbines

Small wind turbines are generally categorized as (Figure 2):

• Horizontal axis wind turbines (HAWT): in these models the shaft is parallel to the ground. Although they must self-align with the wind, HAWTs are mechanically simple and require a relatively small ‘footprint’ on the ground to mount and secure the tower. The majority of small and large turbines installed today are HAWTs.

• Vertical axis wind turbines (VAWT): in these models the shaft is perpendicular to the ground. These turbines typically require a relatively large ‘footprint’ on the ground to mount and secure the tower.



Horizontal axis wind turbine Darreius-type vertical axis wind turbine

Cycloturbine

Figure 2: Schematic views of different turbine concepts

Application areas

Small turbines were used mainly for remote power generation either alone or in conjunction with other energy sources and battery storage with presently emerging target to enter the urban or industrial areas. They can be divided into three categories: micro (up to 1 kW), mid-range (1-10kW) and mini-turbines (10-50kW). Typical applications are presented in

Table 3.



Table 3: Applications for Small wind turbine

Small Wind Turbine Category

Entitlement Battery Charging & light seasonal loads

Residential & heavy seasonal loads

Commercial, institutional, farms, and remote communities

Typical Power Rating

≤1 kW 1-10 kW 10-50 kW (and more)

Typical Grid Connectivity

Mostly off-grid, some on-grid

Mostly on-grid, some off-grid

On-grid, Isolated-grid, or off-grid

Typical Applications

• Mobile uses (sailboats, recreational vehicles, etc.)

• Seasonal applications (small cottages, hunting lodges, etc.)

• Rural & 'urban perimeter' residential homes (small loads)

• Specialty power sources (radar and telecomm devices, measurement instruments, cathodic protection, remote weather stations, etc.)

• Commercial parks & camps

• Electric fencing

• Off-grid rural houses with large lot sizes (usually >1 acre)

• On-grid rural houses with large lot sizes (usually >1 acre) where DC appliances are driven by wind turbine/batteries or where some electricity is stored on the grid through Net Metering

• Larger cottages or hunting lodges with significant share of electricity from wind

• On-grid or isolated-grid large farms

• Off-grid small farms where small wind complements a diesel generator set and/or solar photovoltaics

• On- or off-grid commercial or institutional buildings

• Isolated-grid communities where wind is complemented by diesel generators and/or other sources

Main designs of small wind turbines

The main components of common wind turbine are presented in Figure 3.



Figure 3: Main components of typical small wind turbine

The main options in wind machine design and construction include:

• Number of blades (commonly two or three);

• Rotor orientation: downwind or upwind of tower;

• Blade material, construction method, and profile;

• Hub design: rigid, teetering or hinged;

• Power control via aerodynamic control (stall control) or variable pitch blades (pitch control);

• Fixed or variable rotor speed;

• Orientation by self aligning action (free yaw), or direct control (active yaw);

• Synchronous or induction generator;

• Gearbox or direct drive generator.

The most common small wind turbines in 10-50 kW category are 3-bladed, horizontal axis, up-wind machines with many designs available, having their own unique advantages and disadvantages. While most of these turbines employ direct-drive permanent magnet alternators, some use asynchronous induction generators and gearboxes (placed in the nacelle assembled with the rotor). Different electrical controls and power conditioning equipment packages are available depending on whether the turbines are intended for stand-alone battery charging or for grid-connected applications. Most of these wind turbines are variable speed machines that employ passive stall regulation and furling for overspeed control, although some use electrical controls to slow down the generator rotor. No turbines in this size range are known to use active (i.e. motorized) pitch control. Typical rotor diameters for these turbines range from 5 to 15 m while tower heights are usually



from 18 to 40 m. Because of the significant weight and loading of these turbines, special attention has to be paid to proper tower design and installation. The life expectancy of well-built and well-maintained wind turbines is generally expected to be over 20 years. This may vary significantly however depending on operating conditions (e.g. high turbulence winds, extreme dust or cold). Some non-integrated turbine designs allow for the replacement of virtually all major components, allowing the system’s life to be extended indefinitely.

The ideal wind turbine design is not dictated by technology alone, but by a combination of technology and economics: wind turbine manufacturers wish to optimise their machines, so that they deliver electricity at the lowest possible cost per kilowatt hour (kWh) of energy.

Main technical limitations of existing small wind turbines

The main technical limitations of existing small wind technology limiting deeper penetration of small wind turbines are:

• Low power coefficient:

The most important factors in how much power the wind turbine will produce are the rotor diameter and height of tower (Figure 4). Betz' law and average power coefficient of turbines (20-35%) limits the turbine output very much. The smaller in size the wind turbine is – the higher power coefficient is needed for achievement of required output and in cost-efficient way: each square metre of rotor area costs money, so it is necessary to harvest whatever energy is possible for pushing the costs per kWh down.



(a) (b)

Figure 4: (a) Theoretical power production for small wind turbines when the wind speed is 10 m/s; (b) Wind speeds increase with height6

The wind turbine rotor is the most complicated, important and almost always – the only component unique in the wind turbines system. The rotor's blades control all the energy capture and almost all the loads, and are therefore a primary target of R&D efforts. The challenge is to create the knowledge and engineering tools that enable blade designers to squeeze the most performance throughout a range of wind speeds sites that previously were considered as not cost effective.

• Power coefficient dependence form the wind speed (Figure 5) is also a very limiting parameter of the overall performance and cost-efficiency of wind turbine.

6 S. Clarke - Engineer, Rural Environment/OMAFRA. Electricity Generation Using Small Wind Turbines At Your Home Or Farm. 2003



0.20

0 5 10 15 20 m/s

Figure 5: Power coefficient dependence on the wind of typical Danish wind turbine per square metre of rotor area

Low efficiency of wind turbines in low speed wind sites leads to higher cost of energy generation (and longer pay-back period), Figure 6.7 The average annual wind speed is 4-4.5 m/s with wind resources level at 50 m above ground varying and depending on topographic conditions (5-9 m/s in open area, 7-11.5 hills and ridges; 2-6 sheltered terrain - Weibull distribution).8 Hence, quite a big share of time the wind turbine would operate not at the rate wind speed and with low power coefficient.

Figure 6: Calculated costs per kWh wind power as a function of the wind regime at the chosen site (number of full load hours)

7 Wind enerdy – THE FACTS. Volume 2: Costs & Prices, 2004

8 http://www.windpower.org/en/tour/wres/euromap.htm



• Very few small wind turbines have any blade pitch adjustment which means that they commonly experience very large angles of attack – leading to slow rotor acceleration. Passive control of turbine performance: passive control (furling or stalling) leads to a lower share of the energy in the wind will be running through the rotor area, hence this additionally limits the overall turbine efficiency.

• Blade rotational speed typically increases with decreasing size which results in the blade loading being dominated by centrifugal forces. Furthermore, the small blades can be difficult to make with high tolerances. When designing a wind turbine it is extremely important to calculate in advance how the different components will vibrate, both individually, and jointly. It is also important to calculate the forces involved in each bending or stretching of a component. Therefore the reliability and maintenance of the system are very important parameters, as the average annual maintenance costs of the typical wind turbine is around 2% of the original turbine investment, pushing up the costs of generated kWh.

• Sound pressure will increase with the fifth power of the speed of the blades relative to the surrounding air. The fast rotation common for small wind turbines generate noise pollution and what is much worse – infrasound vibrations (both affecting public health), what makes their sitting complex and highly inhibits penetration of the urban and industrial areas. Undesirable flickering is also mostly dependent on speed of rotor rotation.

• Big challenge with wind turbines has always been to convert a highly variable input – the wind impinging on the rotor – into a rock-steady alternating current output suitable for grid connection. Present, for the large turbines, the answer is to regulate blade pitch and power off-take so that the generator works at fixed speed in synchronism with the grid. But this is a waste available wind energy, and there is a need for variable speed drives when the generator/ turbine is allowed to be driven at varying speed, in line with the wind, and power electronics are used to render the alternating current output of the generator to direct current without efficiency losses.

Emerging small wind technology

Magnus effect

Magnus effect, as known as the movements of spinning balls in sport, especially tennis, golf, baseball, association football and cricket, is the physical phenomenon whereby an object's rotation affects its path through a fluid, in particular, air. It is a product of various phenomena including the Bernoulli effect and the formation of boundary layers in the medium around moving objects. In the runup to elucidation



of Magnus effect, side-force effect of the rotating bodies was noticed first time by an eminent English scientist Benjamin Roberts in 1742 during his investigations of spinning artillery projectiles using the swirling arm device. In the century later, German scientist Gustav Magnus explained this phenomenon as an aerodynamic effect. Further contribution came from Prandtl and his modification of Kutta-Jukowski theorem for bodies of rotation. Applied to aeronautics in experimental wingforms, the Magnus Theory states that if air is directed against smooth, revolving cylinder, whose circumferential speed is greater than that of the air current, a force is directed against one side of the cylinder - air compressed on one side and vacuum formed on the other - creating lift (Figure 7).

Figure 7: Schematic explanation of Magnus effect

The first qualitative explanation of lift force experienced by an aerodynamic shape was made possible by using Kutta–Jukowski theorem that assumes a specific flow behaviour in the near vicinity of the body with a sharp trailing edge. For an airfoil (the quintessential crosssection of a flying wing), the accepted solution is given by an application of this theorem that forces the flow to stagnate at the trailing edge. This theorem is not applicable for flow past bodies without sharp trailing edges – as in the case of a rotating cylinder. L. Prandtl explained the flow past a rotating cylinder heuristically by considering the flow to be inviscid and irrotational.



Figure 8: Inviscid irrotational flow past a rotating cylinder for (a) zero, (b) subcritical, (c) critical and (d) supercritical rotation rates9

The maximum lift a rotating cylinder experiences when the rotation rate is increased beyond a critical limit. This can be readily explained with the help of Figure 8. If one defines a nondimensional rotation rate by Ω = Ω *D/2U∞, where the cylinder of diameter D rotates at Ω* while being placed in a uniform stream of velocity U∞, then one can define a non-dimensional number, called the Reynolds number, by Re = U∞D/ν for this flow field. In Figure 8 a, the steady inviscid irrotational flow field is depicted when the cylinder does not rotate and one can note a top-down and fore-aft symmetry of the flow field. In Figure 8 b, a case is depicted for Ω < 2, where both the front and rear stagnation points (halfsaddle points) are deflected downwards, causing the flow to exert an upward force on the cylinder. With increase of Ω to 2, these stagnation points move towards each other and merge at the lowermost point on the cylinder, as shown in Figure 8 c. For this location of stagnation point, it is easy to show that the corresponding nondimensional lift value is given by the coefficient CLmax = 4π. Prandtl heuristically reasoned this lift as maximum, because with further increase in Ω, the half-saddle point of Figure 8 c would move in the flow as a full saddle-point on a closed streamline that demarcates the flow field into two parts, as shown in Figure

9 Tapan K. Sengupta and Srikanth B. Talla. Robins–Magnus effect: A continuing saga. CURRENT SCIENCE, VOL.

86, NO. 7, 10 APRIL 2004



8 d. The region inside the closed streamline is insulated from the region outside permanently for steady inviscid flow. This fixes the vorticity at the critical rotation rate for the case of Figure 8 c. In a real flow, vorticity created at the solid wall is convected and diffused according to the governing Navier–Stokes equation. A steady flow model, presupposes equilibrium between the creation of vorticity and its viscous diffusion for all rotation rates. It was argued by Prandtl that the equilibrium at Ω = 2, decides the lift value when the rotation rate is increased further. This model appeared realistic in the absence of any counter-examples and is used in textbooks to explain lift generation and limiting mechanism. However, some recent experimental and numerical observations provide counter-examples where lift is found to exceed Prandtl’s maximum (8–10). Tokumaru and Dimotakis have observed that the maximum lift limit was violated by 20% for Re = 3800 and Ω = 10. The authors considered diffusion, unsteady flow processes as the main contributor in violating the maximum limit, while three-dimensional end-effects will tend to reduce the mean spanwise lift. For Ω > 2, the vorticity will be generated at a larger rate at the solid wall than it is dissipated by viscous action, thereby showing a monotonic increase in lift value, if the vorticity remains confined within the recirculating streamline. The role of diffusion is thus to peg the net circulation at a lower level. However, the viscous diffusion also plays a subtle role in supporting enhanced lift when it interferes with physical instability processes. This is clearly seen in computations that use excessive numerical dissipation to stabilize computations. It should be noted that for super-critical rotation rates, threedimensionality of the flow is suppressed due to Coriolis force predominating over convection and viscous diffusion. Thus, it is instructive to compute the flow by solving time dependent two-dimensional Navier–Stokes equation. The numerical results apart from validating experimental observation, also provide detailed time accurate account of the physical events, that is otherwise difficult to track experimentally. In doing so, the computational results also revealed a new physical instability that limits the monotonically increasing lift in an aperiodic manner.

The experimental observations for this flow are visual: in one case for the instability and uses an analytical model in the other case to arrive at the supposed violation of maximum lift. In contrast, the computational evidences are based on the full governing equations and show the instability and violation of maximum lift at high Reynolds number and high rotation rates, simultaneously. The physical instabilities in real flows are triggered by ambient noise. It shows the need to study and develop models for the actual background noise that is present in experiments. A realistic noise model with very high accuracy computational algorithms – that preserves fundamental physical principles – would provide conclusive evidence of this and many other problems of instabilities.



Magnus type wind turbine

Magnus wind turbine (Figure 9) can be described as a wind turbine equipped with cylinders, which consist of rotating end and non-rotating root parts and additional structures – turbulators. Rotation of the wheel is provided by Magnus force, which arises on the rotating cylinders with presence of the wind. Additional structures (spirals) create the driving force, which ensures an aerodynamic self-starting of the wheel and wind turbine operation at high and storm velocities of the wind exceeding permissible ones for the traditional blade wind turbines.

Figure 9: Magnus wind turbine: rotating cylinders (1), end plates (2), rotor body (3), tower (4), F is the rotor driving force10

Magnus type wind turbines can overcome most of limitations of traditional blade turbines which are presently in use. The major of them is their low efficiency at the most repeatable wind velocities V < 6 to 7 m/s that is due to small lift coefficient of a blade. Under such conditions, the power coefficient of wind turbines drops rapidly to zero at about V = 4 m/s (Figure 5). On the other hand, the Magnus wind turbines can be exploited in a wide range of wind velocities, that is, from 2 to 40 m/s instead of 5 to 25 m/s acceptable for the blade turbines. A reduced rotation velocity of the Magnus cylinder-rotor which is 2 – 3 times lower comparing to the blade one ensures its high ecological and operational safety. Also, an advantage of the Magnus wind turbine is aerodynamic self-regulation of the cylinder-rotor rotation preventing from its excessive spinup and destruction due to centrifugal forces. In particular, at wind velocities higher than about 35 m/s, the self-regulation results in diminution of the Magnus force with the cylinder-rotor self-braking.

10 N.M. Bychkov, A.V. Dovgal, V.V Kozlov. Magnus wind turbines as an alternative to the blade ones. Journal of Physics: Conference Series 75 (2007) 012004



Review: Patents on Magnus type wind turbine

The possibility to employ Magnus effect for the increase of wind turbine efficiency and cost-effectiveness, as revealed the patent search (Table 4), is known from the end of last century, although the working wind turbine prototypes making only the first steps.

Table 4: Patents related to Magnus type wind turbines

Title Patent Number Inventor/assignee Date

Issued Short description

Magnus type wind power generator

Magnus wind turbine device

US 2007/0046029 A1

WO/2007/017930

Nobuhiro Murakami, Akita (Japan)

1 March 2007

A Magnus type wind power generator (A) comprising a horizontal rotary shaft (3) for transmitting torque to a power generating mechanism (2), rotary column (5) disposed radially of the horizontal rotary shaft, driving motors (15) for rotatively driving the respective action between rotation of each rotary column and wind produces Magnus lift, which rotatesthe horizontal rotary shaft so as to drive power generationmechanism, wherein an air flow means (6) is installed forproducing air flows on the outer peripheral surfaces of rotarycolumns so as to increase the Magnus lift.



Magnus effect horizontal axis wind turbine

Magnus effect wind turbine

US6.375.424 B1

EP0886728

Paolo Scarpa (Rome,Italy)

23 April 2002

16 June 2004

A turbine and method which employ kinetic and potential energy of fluid to obtain mechanical and/or electric energy, is founded on the use of bulb shaped rotating blades that interact with a fluid, such as water or air. Each rotating blade rotates around its own axis and in the radial direction of fluid itself.

Wind generator using Magnus-effects

WO 02/42640 A1 David Terracina (Italy)

30 May 2002

This invention concerns a wind generator to obtain mechanical energy, and particularly alsi its use for the propulsion of naval means, characterized in that it provides at least two blades (2), rotating about their own axis, and provided also of rotation about their own axis perpendicular to their own axis, and provided also of rotation about their own axis, each one of said blases (2) providing, on asubstantially distal part (3), a plurality of projecting fins (4),said fins having suitable profile and inclination in function ofthe specific use.



Motor JP19980317602 19981109

Kawai Hiroyoshi (Japan)

26 May 2000

To improve the power generation efficiency without an intense flow by arranging a means for increasing the flow velocity or a flow rate of fluid butting a rotor in a motor including the rotor rotated by receiving the fluid and a generator converting the rotating force of the rotary vane into an electric energy. When an introduced wind is blown in from a take-in window in front of a take-in box, a fan 2 is rotated and the shaft of the fan 2 penetratedthrough a partition board 18 and connected to a drum 1rotates a hollow drum 1. When the introduction wind is blownfrom the take-in window in front of the take-in box 8, it acts onthe rotating drum 1 to accelerate the flow velocity of theintroduction wind in the lower part of the drum 1 by Magnuseffect and causes a pressure reducing phenomenon. On theother hand, a suction wind is energetically sucked from abottom suction hole in the bottom of the take-in box 8 to blowtherethrough as an exhaust wind. The suction wind applies arotating force to a rotor in the entrance of the suction windduct linked with the bottom of the take-in box 8 and convertsit into an electric energy by the interlinked motor.



Magnus air turbine system

US4366386 Thomas F. Hanson (US)

28 December 1982

A Magnus effect windmill for generating electrical power is disclosed. A large nacelle-hub mounted pivotally (in Azimuth) atop a support tower carries, in the example disclosed, three elongated barrels arranged in a vertical plane and extending symmetrically radially outwardly from the nacelle. The system provides spin energy to the barrels by internal mechanical coupling in the proper sense to cause, in reaction to anincident wind, a rotational torque of a predetermined sense onthe hub. The rotating hub carries a set of power take-off rollerswhich ride on a stationary circular track in the nacelle. Shaftscarry the power, given to the rollers by the wind driven hub, toa central collector or accumulator gear assembly whose outputis divided to drive the spin mechanism for the Magnus barrelsand the main electric generator. A planetary gear assembly isinterposed between the collector gears and the spinmechanism functioning as a differential which is also connectedto an auxiliary electric motor whereby power to the spinmechanism may selectively be provided by the motor.Generally, the motor provides initial spin to the barrels forstart-up after which the motor is broken and the spinmechanism is driven as though by a fixed ratio coupling fromthe rotor hub. During high wind or other unusual conditions,the auxiliary motor may be unbroken and excess spin powermay be used to operate the motor as a generator of additionalelectrical output. Interposed between the collector gears of therotating hub and the main electric generator is a novel variable



speed drive-fly wheel system which is driven by the variablespeed of the wind driven rotor and which, in turn, drives themain electric generator at constant angular speed. Reference ismade to the complete specification for disclosure of other novelaspects of the system such as, for example, the aerodynamicand structural aspects of the novel Magnus barrels as well asnovel gearing and other power coupling combination apparatusof the invention. A reading of the complete specification isrecommended for a full understanding of the principles andfeatures of the disclosed system.

Wind turbine having a shaft arranged perpendicularly with respect to the wind direction on a vertical axis and Flettener rotors parallel to the shaft

WO/1981/000435 19 February 1981

The wind turbine comprises a shaft (1) arranged perpendicularly with respect to the wind direction according to a vertical, horizontal or inclined axis. Flettner rotors (2) are fixed on the spokes (3) or along the periphery (4) of wind turbines. These Flettner rotors transform from transverse generated by the Magnus effect into a rotation force of thewind turbine. The Flettner rotors which are provided preferablywith end disks, are driven by electrical motors or by Savoniusrotors. On the leeward of the wind turbine, the Magnus effectis eliminated by stopping the rotation of Flettner rotors or bytaking them away from the action of the wind by mask (5) orby other means. Thereby is provided a wind turbine which mayoperate with small wind speeds of which the number ofrevolutions is easily adjustable to a large extent and which hasa high efficiency due to the magnitute of the Magnus effect.

Emerging Small Wind2008

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