Field of Invention

This invention relates to the improvement of sail type horizontal axis wind turbine rotors for maximizing the wind energy conversion, suitable for rotors of all sizes and in particular to larger size rotors.

Background of the Invention

Wind power has been in use from the time humans put sails to power boats. A windmill is a prime mover that converts the energy of wind into rotational energy by means of vanes. Centuries ago, windmills were used to mill grain, pump water or both. The use of windmills was increasingly widespread until the early 19th century. Because of the development of steam power, internal-combustion engine their rapid demise became inevitable. However, electrical generation from wind power has given the windmills a new life in the form of wind turbines. Wind turbines come in several sizes ranging from a small roof top size of few hundred watts to a large utility scale size of few mega watts.

In an effort to evolve much better alternative energy devices using natural resources such as sun light, wind, sea waves, etc., researchers have been working throughout the world endlessly. The depletion or shortages of the fossil fuels like petroleum, coal, etc, pollution by burning fossil fuels, global warming, green earth initiatives are driving the renewable energy developments at its maximum pace. Among them wind is one of the best natural resources and is yet to be used at its maximum for our energy needs.

Horizontal-axis wind turbine (HAWT) and vertical-axis wind turbine (VAWT) are the two main types. Both of them have numerous configurations already in use, experimented ones and under development ones. The most common HAWTs have two or three bladed rotor or multi-bladed rotor where rotor frame or hub containing many vanes or blades. They operate in upwind or downwind formats. Upwind HAWT rotors generally have a wind aligning system which keeps them changing the facing direction in accordance with changing wind direction. Whereas downwind HAWT rotors are of self aligning type. The aligning system is known as yawing. Yaw control of smaller ones is generally by tail vanes and for larger turbines separate yaw drives are available. Whereas, VAWT rotors are like vertical cylinders that have a 360° face, don’t require a yawing system as wind blowing from any direction hit the same way.

Among the above two types the HAWT are found to be the best devices as they are generally simple, efficient and suitable for any size. Rotor, nacelle and tower are the three main parts of a HAWT. The rotor is the prime . component of a wind turbine of any type as it only harnesses the energy from the wind. Nacelle is for making use of that harnessed energy into useful purposes. It houses the rotor and generator assembly and control systems for speed, yawing, safety and all other kind for a wind turbine unit’s smooth operation. The tower supports the nacelle assembly on its top With the advancement in technology, the present day wind turbines especially the HAWTs of utility scale size are one of the most advanced engineering structures for their size and operating systems.

As the size increases the complications also increase in all respects for any equipment and wind turbines too are no exceptions. The size of a wind turbine unit is determined by the capacity specification in the following order. The rotor size is made to meet the capacity requirement and as per the rotor size the nacelle and tower are made. As we look into the most common present HAWTs, the smaller ones come with two to eight or even more bladed rotors and the larger ones come with two or three bladed rotors. Rotors with two or three blades are the most common ones.

It is a common practice that for a HAWT, the specification is based on the sweep area of its rotor. Meaning, the specification takes into account only the quantity of energy of a moving beam of wind of cross section equal to the rotor sweep area hitting over the sweep area for a unit time; and is given by the below formula.

E = 1/2pAV ³ . Where,

p - Density of beam of wind,

A - Cross sectional area of beam of wind (equal to the rotor sweep area) V - Velocity of wind (length of beam equal to the velocity of wind)

The same formula is used for wind energy calculations of a rotor or wind turbine specification irrespective of rotor’s configuration features like number of blades, area of blades, etc. and is given by below formula.

1/2pCAV ³ . Where, C is conversion co-efficient.

But practically the beam of wind will hit only on the blade area not on the sweep area. However, it is claimed that because of the rotational speed of rotors, the blades are almost forming a circular wall of sweep area size. Hence the sweep area based specification is justified.

A two or three bladed rotor of a small roof top HAWT that generally rotates at 400 - 800RPM may justify this claim. But for larger ones that rotate at much lower RPM would never justify this claim. Means, most of the wind is lost between the blade gaps. Following statements are given for a clear understanding of this fact. A three bladed rotor that rotates at 20RPM will get hit by the wind only the three blade area in one second. This is just a fraction of the sweep area. Thus in one second, most of the wind between the blade gaps is lost. For example, if a three bladed rotor with blades area of 6% of sweep area rotates at 20RPM means, 94% of wind gets lost in one second.

The options available to overcome this issue of a bladed rotor are; increasing the number of blades or area of blades or RPM of rotor or combination of all the options. For smaller rotors, all the three options are possible to some extent but in the case of a larger turbine this becomes almost impossible because of the robustness of blades. Any attempt to implement these options would certainly end up in a massive rotor weight that again will lead to massive supporting structures like rotor housing, gear box, control systems, tower, etc. and subsequently an expensive unit by all means. Manufacturing, handling, transporting, erecting, servicing and maintaining also becomes tough and expensive jobs then. Other problems of these bladed rotors particularly in larger rotors are such as danger of blade breakage and danger from broken blades; noise and dangerous blade vibrations particularly during gusts may be harmful to whole unit, danger to birds, etc.

It is understandable that if a smaller rotor can meet the capacity specification of a wind turbine, the whole unit size will come down proportionally and thus the difficulties and cost too. Therefore it becomes inevitable to develop a high performing rotor for the HAWT so that its size can be considerably small for maximum benefits. A clear understanding of all these problems, disadvantages and limitations of the bladed rotors and finding solutions would definitely lead to achieve the high performing rotor for the HAWT. After careful studies, using sails as an alternative to blades found to be a promising one. There exists a wide configuration of sail type HAWT rotors developed by researchers, few of them are in use but many are failed due to one or more of the conceptual or configuration mistakes that varies from a crude concept to a complicated configuration. Their general problems are such as overweight, in-efficient element, flappable sails, weak structures, etc.

Improving the sail type wind turbine with an aerodynamic sail structure and a rigid rotor frame structure in a way to eliminate all issues associated with the prior arts would result in a high performing HAWT rotor of simple, cost effective and sound structural integrity.

Below are some of the prior art of patent references of significance.

1 : US6402472B1 , Allan Curtis Hogue and Jeanette Diane Hogue, 2002- 06-11 : A sail-type windmill wheel in which the area of the wheel facing into the wind is adjusted by an automatic variation of the blade angle of the sails.

2. US2050142A, White Allen, 1936-08-04: This invention relates to a propeller and more specifically to self-regulating wind wheels or propellers.

3. US508009A, issued to A.F. George on 1893-1 1-07: This invention shows two wind turbines of horizontal and vertical axis types. The horizontal axis type has two rotors of different size in one axis one after other. The two are separate rotors.

4. US10066597B2, issued to Richard K. Sutz and Peter E. Jenkins on 2018-09-04: This invention shows horizontal axis type wind turbine that has two rotors of different size in one axis one after other. The two rotors are having separate shroud / diffuser.

5. US4065225A, issued to Allison William D on 1977-12-27: A multivane windmill having a plurality of pairs of diametrically opposed vanes mounted for rotation about a horizontal axis in alignment with the wind.

6. US2633921A issued to Monney Charles and Roger on 1953-04-07: A very conventional sail rotor and is adjustable too.

7. US7985052B2, issued to Sharolyn Vettese on 2011-07-26: A new concept curved blade for wind turbines is described.

8. US16943A, issued to J. C. Wilson and T. G. Wilson on 1857-03-31 : A sail type wind wheel with self adjusting sails.

Below are some of the prior art of non patent references of significance.

1. Max Velocity or Max-V Turbine by World Harmony - Describes a new concept highlighting the significance of rotor’s actual wind hitting area.

Ref: http://world-harmony.com/max-velocity-turbine/

2. “Vetrolov” wind turbine by vetronet.com - Describes a new concept sail type wind turbine which folds and unfolds like an umbrella at high winds. Generally group of smaller windmills as an alternative to the expensive modern wind turbines.

Ref. http://vetronet.com/new-features-in-the-design-of-vetrolov-w ind- turbine/

It is evident from the above citations, although all of the prior arts are aimed to improve the wind turbine for maximizing the output; none of them seem to coincide with the present invention as claimed.

Summary of Invention:

New sail type wind turbine rotor, an inventive rotor configuration using improved fixed sail structure for maximizing the output and minimizing the cost of rotor of all sizes. As per the present invention, is provided with a fixed sail structure for use on HAWT rotors, comprises a sail cloth in the shape of a radially cut segment of an annular ring in the front view; two straight sail holders at the leading and trailing radial edges of sail; two profiled sail formers at the outer and inner circular edges that gives the sail a predefined shape of a boat sail in top view; and a plurality of sail stiffeners at the sail body running between the leading and trailing edges, resemble the sail formers in shape, ensures the sail a rigid and stiff surface and shape throughout In effect, the profiled sail formers shift the sail holders at the leading and trailing radial edges to front and back respectively and slope them outwardly as they run from the inner to outer sail formers in the side view.

The said fixed sail structure is dimensionally optimized and circularly arrayed to cover the. maximum sweep area of a cylindrical box type rotor frame comprising a centre wheel with shaft for load coupling and a plurality set of dual rings of front and back rings connected by cross bars for mounting the sails in single to a plurality of stages. The centre wheel and the set of dual rings are connected by separate front and back slanting spokes or by slanting sail holders itself depending on the size of rotor. For very large rotors, annular wind passages without sail elements are provided between each sail stages for easy throw of exit wind out of sails. These rotors are suitable for all sizes of HAWT in upwind or downwind formats.

It is accordingly a principal object of the present invention to provide a high performance sail type HAWT rotor in which the said fixed sail structure is firmly fixed and the sail surface is formed to a improved dual curve boat sail shape and made rigid and stiff throughout with sail stiffeners for making an efficient wind energy converter element. It is another primary object of the invention to provide a sail type HAWT rotor with a plurality of stages suitable for larger size turbines which is economical to build and operate.

It is also another primary object of the invention to increase the element area to sweep area ratio of rotor for maximum wind contact for maximum energy conversion. Also the majority of element area is at the peripheral sails resulting in higher torque.

It is yet another primary object of the invention to use light weight sail cloth for maximum element area to rotor weight ratio, stronger element, simple manufacturing, ^' easy of handling, transporting, assembling, keeping, replacing, etc.

It is a further primary object of the invention to implement boat sail shaped sails as the HAWT rotors are naturally in beam reach point of sailing, a course of sailing that is perpendicular to the wind. Beam reach is the fastest and most powerful point of sailing resulting in higher RPM and torque.

It is one more primary object of the invention to use a cylindrical box type rotor frame structure instead of single layer ring rotor. The box structure formed with front and back dual rings offer extraordinary structural rigidity.

It is an object of the invention, in the side view, both the front and back sail holders and spoke bars of rotor are made to slant outwardly, ensures the structural rigidity to withstand stronger winds and gusts. It is another object of the invention to optimize the sail width and sail length within and around 3m for any size of rotor for maximum benefits.

It is also another object of the invention to provide the sail array without gap and over lapping in the front view for free flow of exit wind by avoiding clashing of exit wind with free passing incoming wind and to minimize material respectively.

It is yet another object of the invention to provide the outer most rings and cross bars of rotor frame with controlled weight for controlling the flywheel effect.

It is further object of the invention to provide the rotor frame light in weight by using extruded sections, preferably hollow metal sections. Using spring steel rods for sail holders, sail formers, sail stiffeners, dual rings, cross bars, spoke bars, etc. add to enormous strength and light weight of rotor.

These and other characterizing features of this invention will be more clearly understood from the following detailed description and reference drawings.

Brief Description of the drawings:

Embodiments of the present application will now be described, by way of example only, with reference to the attached figures, wherein

• FIG - 1 shows the front, right, top & perspective views of an embodiment of the fixed sail structure in accordance with the present invention with all the parts and basic dimensional features marked; • FIG - 2 shows the perspective view of a first embodiment of a larger size rotor with four stages of sail array with only one sail per stage loaded;

• FIG - 3 shows the front, right & top views of the first embodiment shown in FIG - 2 with only one sail per stage loaded;

• FIG - 4 shows the perspective view of the first embodiment shown in FIG - 2 with all the sails loaded;

• FIG - 5 shows the front, right & top views of a second embodiment of a smaller size rotor with two stages of sail array;

• FIG - 6 shows the perspective view of the second embodiment shown in FIG - 5.

• FIG - 7 shows the border pipes of sail from leading edge.

• FIG - 8 shows the border pipes of sail from trailing edge.

Reference numerals and symbols in drawings

• Sail Structure (FIG - 1):

1 Sail

2 Outer sail former

3 Inner sail former

4 Front sail holder

5 Back sail holder

6 Sail stiffener

7 Sail stiffener

8 Tying wire

9 Fixed sail structure

W Sail width

L Sail length

X° Leading sail angle . Y° Trailing sail angle

A ⁰ Included angle of radial cut B° Depth angle of sail

• Larger size rotor (FIG 2 - 4)

9a Fixed sail structure of stage 1 9b Fixed sail structure of stage 2 9c Fixed sail structure of stage 3 9d Fixed sail structure of stage 4

11 Outer most set.of dual ring

12 Cross bars of larger rotor 13a Inner .most set of dual ring 13b First set of dual ring

13c Second set of dual ring 13d Third set of dual ring

13e Fourth set of dual ring 13f Fifth set of dual ring

13g Sixth set of dual ring

14 Larger rotor frame

15 Spoke bar

16 Centre wheel

17 Centre shaft

18 Larger rotor

• Smaller size rotor (FIG 5 - 6)

9e Fixed sail structure of stage 1 9d Fixed sail structure of stage 2 21 Outer set of dual ring 22 Cross bars of smaller rotor

23 Middle set of dual ring

24 Inner set of dual ring

25 Centre shaft

26 Centre wheel

27 Smaller rotor frame

28 Smaller rotor

• Sail detail (FIG 7 - 8)

31 Leading edge of sail

32 Trailing edge of sail

33 Outer circular edge of sail

Detailed description of the invention and preferred embodiments: Reference has to be given to my own co-pending Indian patent application.“Low cost high efficiency windmill rotor using sails” filed on 18/06/2013 (2637/CHE/2013), wherein four configurations of sail type rotor for HAWT described. After making significant research studies through prototype developments and testing of the same, understood the merits of the concept and shortfalls of the configurations. As a result, I developed the present improved new sail type wind turbine rotor configurations with a newer fixed sail structure that has a modified sail shape with sail stiffeners, a cylindrical box type rotor frame constructed with a set of dual front and back rings, both front and back slanting spokes and multi stage rotor configurations particularly suitable for larger wind turbines, making the present invention further more efficient, simpler, stronger, lighter and economically cheaper than the prior arts. In the fixed sail structured) shown in FIG -1 , the sail(1 ) is a sheet of wind proof fabric in the shape of a radially cut segment of an annular ring in the front view, has two straight front and back sail holders(4, 5) for mounting at the leading and trailing radial edges respectively, two profiled outer and inner sail formers(2, 3) at the outer and inner circular edges that give the sail a predefined shape of a boat sail in top view and profiled sail stiffeners (6, 7) at the sail body running between the leading and trailing radial edges, resemble the sail formers in shape, ensures the sail a rigid and stiff surface and shape throughout. In effect, the profiled sail formers(2, 3) shift the sail holders(4, 5) at the leading and trailing radial edges to front and back respectively and slope them outwardly as they run from the inner sail fdrmer(3) to the outer sail former(2) in the side view.

Included angle of radial cut(A°) forming the annular segment depends on the optimized sail width(W) of maximum three meters for any size of rotor. Accordingly the number of sail per stage occurs. Depth angle of sail(B°) of around 5° in the side view makes the sail holders(4, 5) to slope outwardly that ensures the rigidity of rotor to withstand wind gusts. Sail length(L) can also be optimized to maximum three meters for any size of rotor. In exceptional cases, any excess in breadth and width of sail would need additional sail stiffeners.

The said boat sail shaped sail(1 ) has the leading edge at the front and the trailing edge at the back. Sail formers(2, 3) with a combination of two tangential curves of different radius forms the boat sail shape. A smaller radius curve forming the shorter leading side (in general around one third of the sail width) and a larger radius curve forming the longer trailing side (in general, a ratio of 1 : 2 of the sail width). A leading sail angle(X°) at the leading edge is optimized between 45° - 70° for the sail to cruise forward easily, then the sail angle is quickly reduced by the smaller radius curve of the shorter leading side that run towards the trailing side, makes the wind to exert maximum thrust over the sails in the forward direction and again the sail angle is reduced more gradually until the trailing edge by the larger radius curve of the longer trailing side, ending with a trailing sail angle(Y°) of around 6°. The lesser sail angle makes the wind to take a much faster cut towards the trailing edge to escape out of sail at its maximum possible velocity at the trailing edge, making the sail structure propelled in the opposite direction which is favoring the forward movement of rotor. The combination of smaller radius curve of smaller sail width and larger radius curve of larger sail width ensures impact kind of thrust initially and higher speed of propulsion respectively. Sail angles ( X° and Y° ) can be optimized for individual rotor based on the average wind conditions in a particular site.

For a single stage rotor or for the inner most stage of a multi stage rotor where the sail is substantially triangular shape in front view, the leading and trailing sail angles (X° and Y°) are preferably varied throughout the sail length(L) with minimum and maximum values at the outer and inner sail formers(2, 3) respectively because of the reducing sail width(W) of these sails towards the inner edge where length of leading and trailing sides are considerably small.

The sail formers(2, 3) are adjustable on the sail holders(4, 5) for sail(1 ) tightening particularly at the leading and trailing ends; and are further pulled off preferably at the junction of two sail curves by tying wire(8) from the nearest cross bars of rotor frame or adjacent sail formers of next stage. Further to sail formers(2, 3) tightening, the real stiffness of the sail surface is achieved by sail stiffeners(6, 7) that makes the sail a rigid kind of sail element and is done by the same tying wire(8) by pushing them against the sail surface when pulled from the sail formers(2, 3). For this reason, the sail stiffeners(6, 7) are made slightly extra length. The sail stiffeners(6, 7) are fitted last on the sail structure over the sail holders with suitable fixing brackets (not shown) for each end. For larger sails, two rows of tying wires can be used.

Referring now to FIG 2 - 4, shown for exemplary purpose is a larger size rotor(18) configuration, has four stages with optimized fixed sail structures(9a - 9d) for each stage, circularly arrayed to cover the maximum sweep area of rotor. The rotor frame( 14) is a cylindrical box type structure constructed with a plurality set of dual rings(1 1 , 13a - 13g) for supporting the fixed sail structure’s top and bottom. Said set of dual rings(1 1 , 13a - 13g) have a front and back ring connected by cross bars(12) for rotor strength, sail mounting and also for tying sail formers(2, 3) in the outer and inner most dual rings. Each stage is separated by an annular gap without sails for the wind to pass freely that eases the flow of exit wind away from rotor. The rotor frame has a centre wheel structure(16) comprising a set of dual ring(13a) with cross bars of its own connected by its own spokes to a centre shaft(17) with flange for connecting to a load. The spokes of centre wheel are slanting opposite direction to that of main spoke bars. Means, from the centre shaft(17) they slope inwardly to dual ring( 13a).

A plurality set of outwardly slanting spoke bars(15) at front and back connect all the set of dual rings(11 , 13a - 13f) with the dual ring(13a) of center wheel(16) to form a larger rotor frame(14). Once all the fixed sail structures(9a - 9d) are fully loaded, the larger rotor(18) structure becomes very strong for use as a horizontal axis wind turbine rotor in upwind or downwind format. The outer and inner most set of dual rings(1 1 , 13a) can have a heavier section as compared to other sets (13a - 13f ). The example model is a 30m diameter downwind type rotor of four stage configuration with 12, 24, 36 & 36 number of sails in 1 st, 2nd, 3rd & 4th stages respectively and it rotates the load clockwise. For a upwind rotor, either the flange on the centre shaft(17) or the fixed sail structure(9a - 9d) mounting direction of front and back should be reversed and it will rotate the load counter clockwise.

Referring now to FIG 5 & 6, shown for exemplary purpose is a smaller size rotor configuration^), has two stages with optimized fixed sail structures(9e, 9f) for each stage, circularly arrayed to cover the maximum sweep area of rotor. The rotor frame(27) is a cylindrical box type structure constructed with three set of dual rings, namely; outer(21 ), middle(23) and inner(24) ones for supporting the fixed sail structure’s top and bottom. The dual rings(21 , 23 & 24) that have a front and back ring are connected by cross bars(22) for rotor strength, sail mounting and also for tying sail formers(2, 3) in the outer and inner dual rings. The rotor frame has a centre wheel structure(26) comprising a set of dual ring(24) with cross bars of its own connected by its own spokes to a centre shaft(25) with flange for connecting to a load.

As the rotor size is small, there is no separate spoke bars for the rotor frame. Instead, the sail holders(4, 5) of fixed sail structures(9e, 9f) will function as spokes for independent stages. Once all the fixed sail structures(9e, 9f) are fully . loaded, the smaller rotor(28) structure becomes very strong for use as a horizontal axis wind turbine rotor in upwind or downwind format. The outer and inner set of dual rings(21 , 24) can have a heavier section as compared to middle set(23). The example model is a 6m diameter downwind type rotor of two stage configuration with 12 & 18 sails in the 1 st and 2nd stages respectively and it rotates the load clockwise. For a upwind rotor, either the flange on the centre shaft(25) or the fixed sail structure(9e, 9f) mounting direction of front and back should be reversed and it will rotate the load counter clockwise.

The sails are preferably made with border pipes as shown in FIG 7 & 8 for inserting the sail formefs(2, 3) and sail holders (4, 5); and are formed by stitching, heat sealing and gluing depending on the sail material: FIG - 7 shows the symmetric border pipe for leading edge(31 ), outer circular edge(33) and inner circular edge (not shown). Unlike the other edges, the trailing edge(32) of sail should have asymmetric border pipe for smooth trailing end with no projecting surface obstructing the exit wind as shown in FIG - 8. The sail formers(2, 3) preferably have detachable (generally by internal or external threading) eye rings of two different types suitable for leading and trailing ends for mounting at the end of sail holders(4, 5) allow to have smaller size border pipes on sails to save on material.

Materials and methods of construction

* The sail material to be used are generally of outdoor types with high resistance to stretch, wear and tear, environmental stresses, UV, etc. and of higher breaking strength, longevity and cost effective. The quality parameters required are very much dependant on the sail size and rotor size. Synthetic fibers of nylon, polyester in a variety of woven, spun and molded textiles with coatings of PVC, PU, etc. are the best suitable. Fabrics of aramids, carbon fibers and branded sail fabrics including laminated ones can also be used for very large turbines for long life provided the cost is compromised.

• The sail holders, cross bars and separate spoke bars are in general bolted with their corresponding parts. They are preferably made up of pipes with ends having inner threads or welded nuts; or rods with welded end pipes with inner threads or welded nuts. They have spanner holding flats at each of their end. The bolts of sail holders have lock nuts for locking them in right position.

● The front and back ring of dual rings are in general separated into a number of segments and assembled during rotor assembly. Depending on the size of rotor, the number of segments for each ring can be done in a way that all segments are geometrically same. The maximum length of a segment should be well within the capacity range of storage, transport, manufacturing, handling, etc.

● Centre wheel is generally a single welded structure for strength with centre shaft provided with flange, coupling, etc. for connecting to a load. Centre loading is the best option. It is preferable to have the spokes of centre wheel in reverse slope as that of separate spoke bars of rotor frame or sail holders.

● Due care in rotor configuration with respect to upwind, downwind and rotational direction must be taken for loads dependant on rotational direction and pulling direction of shaft.

● Providing intermittent wind gaps by orderly removing few sails in each stage may help the flow of exit wind.

● Proper rust proofing of metal parts and water proofing for pipe made parts are important quality aspect.

● Central conical wind deflector at the centre of rotor is suggested for wind concentration over the sails only for smaller rotors of diameter within 4m.

● Central conical wind deflector for larger rotors, shrouding the outer and inner dual rings of each stage, adding diffuser or concentrator between stages can be done with the sail material itself. But are recommended only as optional features as these will only complicate the rotor structure. Instead, going for a slightly bigger rotor could be a better choice. ● Other methods of fixing for the sail and rotor assembly parts, like quick acting clamps for mounting cross bars and spoke bars and swivel brackets for mounting angular sails holders, etc. can be used but involve additional costs and weight.

● Extending centre shaft ends preferably on both sides of rotor and connecting the ends with dual rings or spoke bars of rotor by means of tying wires (not shown) can be done for larger rotor wheels or for additional strength in small rotor structures when very thin sections are used for light weight.

Operation

As these rotors are using specific boat sail shaped sails operating in the beam reach point of sail, the speed of fixed sail structures could reach as high as six times that of wind and even more because of the nature of these rotor constructions. Unlike the sail boats that have floating, tilting and wavy movements acting against energy conversion and generally looser sails as compared with the present invention rotors that have fixed sails of very stiff surface and are steady and firm running ones with best control systems, enable them maximum wind energy conversion in the form of rotor speed and torque. Generally upwind rotors are easier to control.

• Rotor control with respect to wind facing direction, speed and safety are by external means like gear box, tail vane, tail vane furling, electric yaw drive, etc.

• Safety can be achieved by tail vane furling for small rotors and electric yawing for larger rotors.

• According to the varying wind velocity, the rotor direction facing the wind can be adjusted by external drives so as to control the speed. Also, advanced generator, gear box and control systems are useful in exploiting the varying wind conditions. Applications and advantages

It can be very well understood from the above described features, present invention not only maximize the energy conversion but minimize the cost also to a greater extent. Apart from normal wind turbine or windmill kind of applications, these rotors can be used as an underwater turbine.

Below are some of the advantages of implementing these rotors.

● Can produce three to six times more power than the existing rotors of same size depending on the size: Larger the rotor larger will be the output gain. In other words a smaller size rotor is enough to produce same amount of power of a larger existing rotor. Therefore,

● Lower tower is enough.

● More number of turbines in a same wind farm as it requires smaller space.

● More than one rotor also is possible in a single tower with suitable fixtures.

● Very much suitable for areas with limited wind velocity.

● Apart from use on new wind machines, these rotors can be retrofitted to existing machines as a replacement to old rotors.

● Cost saving can go to the tune of one tenth of the existing rotor cost or even less as the size increases.

It is obvious from the above description, a new sail type HAWT of high performing nature has been revealed to overcome the limitations of prior arts. The present invention also offers a very reliable and cost saving solution for the rotors of modern use suitable for all wind conditions and sizes. Implementing changes and altering to further advantages may readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the sole embodiments and specific details of above description but encompasses any and all embodiments within the scope of the present invention and following claims.