Low solidity wind turbine amiable

Abstract

A horizontal axis wind turbine, HAT wind turbine (151), for a bulk production of electricity from wind, comprising a tower (5), a nacelle (6), a generator, a rotor (152), and a blade (154), the rotor being rotatable about a rotor axis by the wind and having at least two blades, the rotor having a rotor solidity SOLrotor of maximally 0.05, the rotor configured to have a design tip speed ratio λdesign of at least 4, and an electric power coefficient CPE of at least 0.30, the rotor having a radius R and a diameter D which is at least 50m, the rotor further having an average radial solidity avgsol.25R in the radial range from 0.2R to 0.3R, and an average radial solidity avgsol.75R in the radial range from 0.7R to 0.8R, wherein the ratio between the average radial solidities avgsol.25R / avgsol.75R is one of: less than 2.00; less than 1.75; less than 1.50; less than 1.25; less than 1.00; less than 0.90; less than 0.75; less than 0.50; and less than 0.25.

Description

[0001] 19 / 09 / 2025

[0002] 1

[0003] LOW SOLIDITY WIND TURBINE AMIABLE

[0004] Field

[0005] The present invention relates to a horizontal axis wind turbine (HAT), a blade for a HAT, a rotor for a HAT, a control of a HAT, a method for adapting an existing HAT, a method for installing a HAT and a method for extraction of useful power from a HAT.

[0006] Background

[0007] Wind energy is increasingly contributing to the world energy production and has become one of the cheapest sources of clean and renewable energy. This success has led to the installation of many wind turbines all over the world. In particular in more densely populated areas, the implementation of HATs encounters the so-called “nimby” (i.e. , not in my backyard) problem: many people advocate clean energy from HATs but do not want the turbines nearby. Some people associate HATs with hindrance. Also because of the experienced hindrance, people sometimes oppose wind energy projects and thereby delay or even cancel its implementation. Environmental hindrance experienced from HATs typically includes acoustic and visual hindrance, although other forms of environmental hindrance may be perceived as well.

[0008] Visual hindrance may come in different forms. Some people are disturbed by the large moving rotor blades that may be visible up to a distance from the turbine of about 50 or even 100 times the diameter of the rotor, depending on the size of the HAT. This visibility of the moving rotors is often experienced as disturbing the tranquility of the landscape.

[0009] Another form of visual disturbance may occur closer to a HAT. Up to about 12 rotor diameters distance, depending on the position of the sun and the cloudiness of the sky, the solar light intensity may change as a result of a moving cast shadow, where HAT blades between the observer and the sun cast a repetitive shadow pattern. Cast shadow may also form a hindrance to solar farms (partial shadowing of panels may reduce yield) and crops, which are dependent on the amount of received sunlight.

[0010] Yet another form of visual hindrance may be caused by high intensity reflections of sunlight on blades. Such form of light hindrance is becoming less relevant nowadays though, since opal blade coatings are being applied to blades to reduce reflections.

[0011] Acoustic hindrance is typically caused by the rotating rotor blades. Known solutions to acoustic hindrance include the application of a serrated trailing blade edge to reduce the noise. Indeed, this solves acoustic hindrance to some extent, though usually not enough to take away the negative perception. Moreover, the application of serrations increases the cast shadow hindrance, which may be undesirable.

[0012] Another form of hindrance may be environmentally. I.e., that the blades usually are made of composite which is a material that cannot be recycled easily. 19 / 09 / 2025

[0013] 2

[0014] Most wind energy is harvested by turbines of the HAT type, typically including one rotor with three blades, although multiple rotors are possible. For example, a HAT may include a first rotor of 113m in diameter and a second concentric rotor of 40m in diameter. Such first rotor does not need blades with a large chord nearthe rotor center, because the second rotor, typically rotating at a higher rpm, can harvest energy in the rotor center efficiently. For several reasons, HATs with double rotors have not become common practice. Firstly, the two rotors run at different rotational speeds and therefore each require a mechanism to convert the mechanical energy to electricity. The double drive trains increase costs and complexity. This complexity may lead to more down time and subsequently reduces the yield of the HAT. Secondly, blade root bending moments of the large blades, the blade root being the part of the blade nearest to the hub, remain about the same compared to one rotor HATs. Because the blade root bending moments are about equal, the pitch bearing will be about equal. To lead through the large bending moments, preferably thick blade roots are used. Thus, the larger blades may have a reduced chord, but the total blade length and the thickness, and thus the amount of composite required, will be about similar to that of blades of a turbine without the second rotor. Thirdly, the typically thick blade roots of the larger rotor in the range of the second smaller rotor have a more or less cylindrical shape, which generates large aerodynamic drag and thus reduces the yield of the large rotor. Moreover, this drag reduces the wind for the small rotor and thus reduces the yield of the small rotor as well. Furthermore, the uneven air speed in the small rotor area induced by the blade roots of the large rotor causes additional noise and the relative position of the small rotor blades compared to the large blade roots determines noise reflections, which may lead to a more uneven noise level.

[0015] The efficiency of a HAT may be expressed as a yield per unit of cost. Reducing HAT hindrance at the cost of HAT efficiency is undesirable. Other factors to take into consideration when expressing the efficiency of a HAT may include the transport and installation of the typically large and heavy HAT components, which are already causing problems and which are preferably not further impaired. Finally, a factor is that the control of a HAT in certain wind conditions may lead to high loads, which increase the cost.

[0016] Summary of the Invention

[0017] The present disclosure aims to provide a wind turbine of the Horizontal Axis Turbine type (herein referred to as “HAT” or “HAT wind turbine”) that reduces one or more of the various hindrance aspects described throughout this disclosure, while maintaining or even improving the efficiency of the state-or-the-art HAT.

[0018] Wind power is one of the most important sources of renewable energy that enables the worldwide energy transition. To produce so much energy from wind that it becomes a significant fraction of the worldwide energy consumption, medium and large wind turbines, are required and in case of offshore wind energy, such large turbines may be considered as the only option. Regretfully wind turbines of this size also cause the most hindrance. In short it would be 19 / 09 / 2025

[0019] 3 advantageous if in particular the wind turbines of 50m diameter and in particular 100m or more, would cause less hindrance while maintaining or improving the yield over cost ratio. The expert in the art only considers two or three blades for horizontal axis wind turbines of this size. Therefore, it is a breakthrough thought that in contradiction to the conventional preference of a HAT including three and sometimes two blades with relatively large chords, according to the present disclosure it may be favorable to apply blades with lower chord ratios to such a HAT and possibly more of such blades to address any or more of the following sources of hindrance: (i) cast shadow; (ii) disturbance of the tranquil landscape; (Hi) reduction of yield of solar farms or crops (iv) average sound pressure; (v) sound amplitude modulation; (vi) infrasound; (vii) bird casualties and / or (iix) composite waste. In addition it has been found that embodiments of the present disclosure can improve the yield over cost ratio of the HAT for any one or more of the reasons: (i) reduced tip losses; (ii) less downtime because of less hindrance; (iii) a better ratio between yield and storm loads due to the lower solidity and / or a lower ratio of SOIO 25R / SOIO 75R; (iv) a higher efficiency because of the double rotor concept; (v) a cheaper rotor because of the truss structure and / or the stays and / or the outer blade parts being small compared to state-or-the-art blades; (vi) less manufacturing costs because of using pultruded blade sections and / or blades of reduced length and / or reduced chord; (vii) a control advantage during a storm; (viii) easier logistics, installation and blade production because of reduced blade length and or blade chord; (ix) less rotor unbalance during installation and (x) less composite waste at the end of the lifetime of the blades.

[0020] According to an aspect of the disclosure, a HAT for the bulk production of electricity from wind is proposed. The HAT may include a tower. The HAT may further include a nacelle. The HAT may further include a generator. The HAT may further include a rotor. The rotor may be rotatable about a rotor axis by the wind. The rotor may have a rotor solidity SOLrotor of maximally 0.05. The rotor has a radius R and a diameter D which may be at least 50m. The rotor may include a number of blades N, which may reach at least a radial position of 0.90R, wherein N may be at least 2. The rotor may be designed to have a tip speed ratio “Adesign“ of at least 4. The rotor may have an electric power coefficient CPE of at least 0.30. The rotor may further have an average radial solidity averaged over the radial range from 0.2R to 0.3R “avgsol 25R” and an average radial solidity averaged over the radial range from 0.7R to 0.8R “avgsoIjsR”, wherein avgsol 25R / avgsol 75R may be less than 2.00.

[0021] In an embodiment, avgsol 25R / avgsol 75R may be less than 1.75.

[0022] In an embodiment, avgsol 25R / avgsol 75R may be less than 1.50. In an embodiment, avgsol 25R / avgsol 75R may be less than 1.25. In an embodiment, avgsol 25R / avgsol 75R may be less than 1. In an embodiment, avgsol 25R / avgsol 75R may be less than 0.9. In an embodiment, avgsol 25R / avgsol 75R may be less than 0.75. In an embodiment, avgsol 25R / avgsol 75R may be less than 0.5. In an embodiment, avgsol 25R / avgsol 75R may be less than 0.25. 19 / 09 / 2025

[0023] 4

[0024] The rotor may further have an average radial solidity averaged over the radial range from 0.3R to 0.4R “avgsol 35R”.

[0025] In an embodiment, avgsol 3SR / avgsol 75R may be less than 2.00.

[0026] In an embodiment, avgsol 3SR / avgsol 75R may be less than 1.75.

[0027] In an embodiment, avgsol 3SR / avgsol 75R may be less than 1.50.

[0028] In an embodiment, avgsol 3SR / avgsol 75R may be less than 1.25.

[0029] In an embodiment, avgsol 3SR / avgsol 75R may be less than 1.

[0030] In an embodiment, avgsol 3SR / avgsol 75R may be and less than 0.9.

[0031] In an embodiment, avgsol 3SR / avgsol 75R may be less than 0.75.

[0032] In an embodiment, avgsol 3SR / avgsol 75R may be less than 0.5.

[0033] In an embodiment, avgsol 3SR / avgsol 75R may be less than 0.25.

[0034] In an embodiment, avgsol ssR, may be less than 0.030.

[0035] In an embodiment, avgsol ssR, may be less than 0.025.

[0036] In an embodiment, avgsol ssR, may be less than 0.020.

[0037] In an embodiment, avgsol ssR, may be less than 0.015.

[0038] In an embodiment, avgsol ssR, may be less than 0.010.

[0039] In an embodiment, avgsol ssR, may be less than 0.005.

[0040] In an embodiment of an offshore HAT, the rotor may have a solidity, SOLrotor, of less than 0.016.

[0041] In an embodiment of an offshore HAT, the rotor may have a solidity, SOLrotor, of less than 0.014.

[0042] In an embodiment of an offshore HAT, the rotor may have a solidity, SOLrotor, of less than 0.012.

[0043] In an embodiment of an offshore HAT, the rotor may have a solidity, SOLrotor, of less than 0.011.

[0044] In an embodiment of an offshore HAT, the rotor may have a solidity, SOLrotor, of less than 0.010.

[0045] In an embodiment of an offshore HAT, the rotor may have a solidity, SOLrotor, of less than 0.009.

[0046] In an embodiment of a large onshore HAT, the rotor may have a solidity, SOLrotor, of less than 0.018.

[0047] In an embodiment of a large onshore HAT, the rotor may have a solidity, SOLrotor, of less than 0.016.

[0048] In an embodiment of a large onshore HAT, the rotor may have a solidity, SOLrotor, of less than 0.014.

[0049] In an embodiment of a large onshore HAT, the rotor may have a solidity, SOLrotor, of less than 0.012.

[0050] In an embodiment of a large onshore HAT, the rotor may have a solidity, SOLrotor, of less than 0.011. 19 / 09 / 2025

[0051] In an embodiment of a large onshore HAT, the rotor may have a solidity, of less than 0.010.

[0052] In an embodiment of a medium onshore HAT, the rotor may have a solidity, of less than 0.030.

[0053] In an embodiment of a medium onshore HAT, the rotor may have a solidity, of less than 0.022.

[0054] In an embodiment of a medium onshore HAT, the rotor may have a solidity, of less than 0.017.

[0055] In an embodiment of a medium onshore HAT, the rotor may have a solidity, of less than 0.014.

[0056] In an embodiment of a medium onshore HAT, the rotor may have a solidity, SOLrotor, of less than 0.012.

[0057] In an embodiment the HAT may have a rotor solidity which may be less than with f1 being a factor which may be 1.4, or 1.3, preferably 1.2, more preferably 1.1 , and more preferably about 1.0.

[0058] In an embodiment SOLrotor is larger than

[0059] For example, when 7 and f1 =1 .4, it means that in an embodiment SOLrotor may be less than 1 ,4 / 72= 0.029 and more than 0.8 / 72= 0.016.

[0060] In an embodiment the average radial solidity for r = 0.35R, avgsolo 35R is less than a limit with f2 being a factor which may be 1.7, or 1.5, or 1.3, preferably 1.1 , more preferably 0.9, more preferably 0.7 and even more preferably 0.5.

[0061] For example, when 8 and f2 =1 .1 , it means that in an embodiment SOIO.3SR may be less than 1.1 / 82= 0.017.

[0062] It has been shown that in an embodiment the is reduced by deliberately using blades which have in a certain radial range a shorter chord than is needed to obtain maximum yield at a certain Also, in another embodiment SOLrotor may be reduced by using a second smaller coaxial rotor rotating at a higher rpm. Those measures may reduce the radial solidity in the range from 0.05R to 0.6R and thereby also reduce

[0063] The blades may have a distribution of a local chord crversus a radial position r, wherein the local chord crin the radial range from r = 15%R to R may be below 9%R.

[0064] In an embodiment, crmay be below 8%R, for r = 15%R to R.

[0065] In an embodiment, crmay be below 7%R, for r = 15%R to R.

[0066] In an embodiment, crmay be below 5.5%R, for r = 15%R to R.

[0067] In an embodiment, crmay be below 5%R, for r = 15%R to R.

[0068] In an embodiment, crmay be below 4.5%R, for r = 15%R to R.

[0069] In an embodiment, crmay be below 4%R, for r = 15%R to R.

[0070] In an embodiment, crmay be below 3.5%R, for r = 15%R to R.

[0071] In an embodiment, crmay be below 3%R, for r = 15%R to R.

[0072] In an embodiment, crmay be below 2.5%R, for r = 15%R to R. 19 / 09 / 2025

[0073] In an embodiment, crmay be below 2%R, for r = 15%R to R.

[0074] In an embodiment, crmay be below 1 ,5%R, for r = 15%R to R.

[0075] In an embodiment, crmay be below 5.5%R - 2.5 / 85*(r-15%R), for r = 15%R to R.

[0076] In an embodiment, crmay be below 5%R - 2 / 85*(r-15%R), for r = 15%R to R.

[0077] In an embodiment, crmay be below 4.5%R - 1 ,5 / 85*(r-15%R), for r = 15%R to R.

[0078] In an embodiment, crmay be below 4%R - 1 / 85*(r-15%R), for r = 15%R to R.

[0079] In an embodiment, crmay be below 3.5%R - 0.5 / 85*(r-15%R), for r = 15%R to R.

[0080] In an embodiment, crmay be below 5.5%R - 3.5 / 85*(r-15%R), for r = 15%R to R.

[0081] In an embodiment, crmay be below 5%R - 3 / 85*(r-15%R), for r = 15%R to R.

[0082] In an embodiment, crmay be below 4.5%R - 2.5 / 85*(r-15%R), for r = 15%R to R.

[0083] In an embodiment, crmay be below 4%R - 2 / 85*(r-15%R), for r = 15%R to R.

[0084] In an embodiment, crmay be below 3.5%R - 1 ,5 / 85*(r-15%R), for r = 15%R to R.

[0085] In an embodiment, crmay be below 3%R - 1 / 85*(r-15%R), for r = 15%R to R.

[0086] In an embodiment, crmay be below 2.5%R - 0.5 / 85*(r-15%R), for r = 15%R to R.

[0087] In an embodiment, crmay be below 5.5%R - 4.0 / 85*(r-15%R), for r = 15%R to R.

[0088] In an embodiment, crmay be below 5%R - 3.5 / 85*(r-15%R), for r = 15%R to R.

[0089] In an embodiment, crmay be below 4.5%R - 3.0 / 85*(r-15%R), for r = 15%R to R.

[0090] In an embodiment, crmay be below 4%R - 2.5 / 85*(r-15%R), for r = 15%R to R.

[0091] In an embodiment, crmay be below 3.5%R - 2.0 / 85*(r-15%R), for r = 15%R to R.

[0092] In an embodiment, crmay be below 3%R - 1 ,5 / 85*(r-15%R), for r = 15%R to R.

[0093] In an embodiment, crmay be below 2.5%R - 1 ,0 / 85*(r-15%R), for r = 15%R to R.

[0094] In an embodiment, crmay be below 2%R - 0.5 / 85*(r-15%R), for r = 15%R to R.

[0095] In an embodiment, a rotor may include blades, which have a local chord for r = 15%R to R that may be less than a certain limiting line. In such cases, the chord may be larger than the prescribed limiting line over a range of maximally 5%R. This may serve to compensate for, e.g., blade connections, which may lead to an increase of the chord over less than 5% radial range.

[0096] In an embodiment, the largest HAT rotor may include exactly 2 blades, which reach at least a radial position r of one of: 0.70R; and 0.90R.

[0097] In an embodiment, the largest HAT rotor may include exactly 3 blades, which reach at least a radial position r of one of: 0.70R; and 0.90R.

[0098] In an embodiment, the largest HAT rotor may include exactly 4 blades, which reach at least a radial position r of one of: 0.70R; and 0.90R.

[0099] In an embodiment, the largest HAT rotor may include exactly 5 blades, which reach at least a radial position r of one of: 0.70R; and 0.90R.

[0100] In an embodiment, the largest HAT rotor may include exactly 6 blades, which reach at least a radial position r of one of: 0.70R; and 0.90R.

[0101] In an embodiment, the largest HAT rotor may include exactly 7 blades, which reach at least a radial position r of one of: 0.70R; and 0.90R. 19 / 09 / 2025

[0102] In an embodiment, the largest HAT rotor may include exactly 11 blades, which reach at least a radial position r of one of: 0.70R; and 0.90R.

[0103] In an embodiment, the largest HAT rotor may include at least 3 blades, which reach at least a radial position r of one of: 0.70R; and 0.90R.

[0104] In an embodiment, the largest HAT rotor may include at least 4 blades, which reach at least a radial position r of one of: 0.70R; and 0.90R.

[0105] In an embodiment, the largest HAT rotor may include at least 5 blades, which reach at least a radial position r of one of: 0.70R; and 0.90R.

[0106] In an embodiment, the largest HAT rotor may include at least 7 blades, which reach at least a radial position r of one of: 0.70R; and 0.90R.

[0107] In an embodiment, the largest HAT rotor may include at least 11 blades, which reach at least a radial position r of one of: 0.70R; and 0.90R.

[0108] In an embodiment, the number of blades N of the largest HAT rotor may be maximally 7, which reach at least a radial position r of one of: 0.70R; and 0.90R.

[0109] In an embodiment, the number of blades N of the largest HAT rotor may be maximally 11 , which reach at least a radial position r of one of: 0.70R; and 0.90R.

[0110] In an embodiment, the number of blades N of the largest HAT rotor may be maximally 17, which reach at least a radial position r of one of: 0.70R; and 0.90R.

[0111] In an embodiment, the number of blades N of the largest HAT rotor may be maximally 43, which reach at least a radial position r of one of: 0.70R; and 0.90R.

[0112] In an example embodiment, the number of blades N of the largest HAT rotor may equal a prime number at a radial position r of one of: 0.70R; and 0.90R.

[0113] In an embodiment, the diameter D may be at least 70m.

[0114] In an embodiment, the diameter D may be at least 100m.

[0115] In an embodiment, the diameter D may be at least 140m.

[0116] In an embodiment, the diameter D may be at least 200m.

[0117] In an embodiment, the diameter D may be at least 300m.

[0118] In an embodiment, the diameter D may be at least 450m.

[0119] In an embodiment, the blade may include an outer blade part. A truss structure in a center of the rotor may connect each outer blade part to a hub. The truss structure may include main rods connecting each of the outer blade parts to the hub. The truss structure may further include tangential connections connecting to two adjacent outer blade parts. The truss structure may further include forward rods connecting the hub to the outer blade parts in a forward direction. Herein, the forward direction is defined as a direction away from the plane of the blades and away from the nacelle. For each outer blade part said outer blade part, a main rod, a forward rod and the rotor axis may be arranged within a same plane.

[0120] In an embodiment, one or more of the main rods, the tangential connections and the forward rods may be aerodynamically shaped. 19 / 09 / 2025

[0121] 8

[0122] In an embodiment, the distance between a longitudinal axis of the main rods and a longitudinal axis of the tower may be less than 0.1 R, or less than 0.05R or preferably less than 0.03R.

[0123] In an embodiment, the HAT wind turbine may further include a second rotorthat is coaxially arranged with the rotor and has a smaller diameter R2. The small rotor may be rotatable about a further rotor axis by the wind and has at least two blades. The blades of the small rotor may cover an inner area of the rotor in a projection perpendicular to the rotor axis. The inner area may be the rotor area at a smaller radius than that of the outer blade parts.

[0124] In an embodiment, the truss structure may include a blade joint, a hub joint, and a compression member. The blade joint may be connected to the hub joint by two compression members or by one compression member and one stay or by one compression member and two stays. In an embodiment, a blade joint of a first blade may be connected to a blade joint of an adjacent second blade joint by a compression member or by a stay.

[0125] In an embodiment, the rotor blades may have no structural support outward of a radial position of 70%R. For example, in one embodiment a rotor may be used that does not include structural support from compression members or stay beyond 70%R to the blade. It has been found that support in this range decreases aerodynamic performance, thus is disadvantageous and may be omitted.

[0126] In an embodiment, the compression member and / or the stay may have an aerodynamic shape. The compression member and / or the stay may have such an aerodynamic shape that the compression member and / or the stay may generate aerodynamic lift which contributes to a rotor torque, when the HAT is in use.

[0127] In an embodiment, the rotor may include a first blade and a second blade. The first blade and the second blade may have a tangential connection in a radial range AR.

[0128] In an embodiment, one of the following may apply: AR > 0.20R; AR > 0.30R; AR > 0.40R; or AR > 0.45R.

[0129] In an embodiment, one of the following may apply: AR < 080R; AR < 0.70R; AR < 0.60R; or AR < 0.50R.

[0130] In an embodiment, one of the following may apply: 0.20R < AR < 0.80R; 0.30R < AR < 0.70R; or 0.40R < AR < 0.60R.

[0131] In an embodiment, a blade may be fixed to a pitch bearing.

[0132] In an embodiment, the pitch bearing may be located at a radial position larger than 0.25R. In an embodiment, the pitch bearing may be located at a radial position larger than 0.3R. In an embodiment, the pitch bearing may be located at a radial position larger than 0.35R. In an embodiment, the pitch bearing may be located at a radial position larger than OAR. In an embodiment, the pitch bearing may be located at a radial position larger than 0.45R. In an embodiment, the pitch bearing may be located at a radial position larger than 0.5R.

[0133] In an embodiment, the pitch bearing may be located at a radial position larger than 0.55R. In an embodiment, the pitch bearing may be located at a radial position of less than 0.6R. 19 / 09 / 2025

[0134] 9

[0135] In an embodiment, the pitch bearing may be located at a radial position of less than 0.7R.

[0136] In an embodiment, the HAT may include a first blade and a second blade. The first blade may be part of a first rotor and may reach to radial position R. The second blade may be part of a second rotor and may reach to radial position R2.

[0137] In an embodiment, one of the following may apply: : R2 < 0.80R; R2 < 0.70R; R2 < 0.60R; or R2 < 0.55R.

[0138] In an embodiment, one of the following may apply: R2 > 0.25R; R2 > 0.30R; R2 > 0.35R; R2 > 0.40R or R2 > 0.45R.

[0139] In an embodiment, one of the following may apply: 0.25R < R2 < 0.70R; 0.30R < R2 < 0.60R; 0.35R < R2 < 0.55R; 0.40R < R2 < 0.55R; or 0.55R < R2 < 0.75R.

[0140] In an embodiment, a second rotor with second blades may not produce energy directly by not being connected to a generator and may be designed to spin freely.

[0141] In an embodiment, the second rotor may further be designed to have, when in use, an axial force coefficient, CD, ax. One of the following may apply to the second rotor when spinning freely: CD, ax > 0.6; CD, ax > 1 .0; CD, ax > 1 .2; CD, ax > 1 .5; or CD, ax < 2.2.

[0142] In an embodiment, the HAT may be an onshore turbine.

[0143] In an embodiment, the HAT may be or an offshore turbine.

[0144] In an embodiment, the HAT may be grid connected.

[0145] In an embodiment, the HAT may be stand alone.

[0146] In an embodiment, the HAT may have exactly one rotor.

[0147] In an embodiment, the HAT may have exactly one largest rotor of radius R and exactly one second coaxial rotor of radius R2.

[0148] In an embodiment the HAT may have two rotors which are coaxial and which rotate in the same direction.

[0149] In an embodiment, the rotor may be downwind relative to the tower. This may be advantageous since it may save an active yaw mechanism. Another possible advantage may be that the slender blades with the small chord values according to an embodiment may have more space to bend in a downwind configuration wherein the loads may bend the blades away from the tower instead of towards the tower in the case of an upwind configuration.

[0150] In an embodiment, the rotor may be upwind relative to the tower.

[0151] In an embodiment, the rotor may be supported by a tower on both the upwind and the downwind side.

[0152] In an embodiment, the HAT may have an upwind rotor and a downwind rotor.

[0153] In an embodiment, the generator may be of the direct drive type.

[0154] In an embodiment, the generator may be of the geared type.

[0155] In an embodiment, the generator may be using super conduction.

[0156] In an embodiment, the rotor may drive a hydraulic transmission.

[0157] In an embodiment the mechanical power may be converted first into hydraulic power which subsequently may be converted to electric power. 19 / 09 / 2025

[0158] In an embodiment, the rotorthe rotor comprises a ring-shaped structure extending in radial direction to less than 20%R;

[0159] In another embodiment, the rotor may not comprise a ring-shaped structure.

[0160] In an embodiment, the rotor may comprise an airfoil with a relative thickness t / c of 30% or more.

[0161] In an embodiment, the rotor may have an airfoil with camber.

[0162] In an embodiment, a vortex generator may be attached to the rotor.

[0163] In an embodiment, the rotor may comprise an airfoil with a design lift coefficient &, design of 1 .5 or larger.

[0164] In an embodiment, the rotor may comprise a blade section a weight percentage of carbon fibers of 10% or more.

[0165] In an embodiment the largest rotor may have a combined chord Nrcrwhich may be below 16.5%R for r = 15%R to R.

[0166] In an embodiment, Nrcrmay be below 15%R, for r = 15%R to R.

[0167] In an embodiment, Nrcrmay be below 13.5%R, for r = 15%R to R.

[0168] In an embodiment, Nrcrmay be below 12.0%R, for r = 15%R to R.

[0169] In an embodiment, Nrcrmay be below 10.5%R, for r = 15%R to R.

[0170] In an embodiment, Nrcrmay be below 9.0%R, for r = 15%R to R.

[0171] In an embodiment, NrCr may be below 7.5%R, for r = 15%R to R.

[0172] In an embodiment, Nrcrmay be below 6.0%R, for r = 15%R to R.

[0173] In an embodiment, Nrcrmay be below 4.5%R, for r = 15%R to R.

[0174] In an embodiment, NrCr may be below 16.5%R - 7.5 / 85*(r-15%R), for r = 15%R to R.

[0175] In an embodiment, Nrcrmay be below 15%R - 6.0 / 85*(r-15%R), for r = 15%R to R.

[0176] In an embodiment, Nrcrmay be below 13.5%R - 4.5 / 85*(r-15%R), for r = 15%R to R.

[0177] In an embodiment, NrCr may be below 12%R - 3.0 / 85*(r-15%R), for r = 15%R to R.

[0178] In an embodiment, Nrcrmay be below 10.5%R - 1.5 / 85*(r-15%R), for r = 15%R to R.

[0179] In an embodiment, Nrcrmay be below 16.5%R - 10.5 / 85*(r-15%R), for r = 15%R to R.

[0180] In an embodiment, Nrcrmay be below 15%R - 9.0 / 85*(r-15%R), for r = 15%R to R.

[0181] In an embodiment, Nrcrmay be below 13.5%R - 7.5 / 85*(r-15%R), for r = 15%R to R.

[0182] In an embodiment, NrCr may be below 12.0%R - 6.0 / 85*(r-15%R), for r = 15%R to R.

[0183] In an embodiment, Nrcrmay be below 10.5%R - 4.5 / 85*(r-15%R), for r = 15%R to R.

[0184] In an embodiment, Nrcrmay be below 9.0%R - 3.0 / 85*(r-15%R), for r = 15%R to R.

[0185] In an embodiment, Nrcrmay be below 7.5%R - 1.5 / 85*(r-15%R), for r = 15%R to R.

[0186] In an embodiment, Nrcrmay be below 16.5%R - 12.0 / 85*(r-15%R), for r = 15%R to R.

[0187] In an embodiment, NrCr may be below 15%R - 10.5 / 85*(r-15%R), for r = 15%R to R.

[0188] In an embodiment, Nrcrmay be below 13.5%R - 9.0 / 85*(r-15%R), for r = 15%R to R.

[0189] In an embodiment, Nrcrmay be below 12%R - 7.5 / 85*(r-15%R), for r = 15%R to R.

[0190] In an embodiment, Nrcrmay be below 10.5%R - 6.0 / 85*(r-15%R), for r = 15%R to R.

[0191] In an embodiment, Nrcrmay be below 9.0%R - 4.5 / 85*(r-15%R), for r = 15%R to R. 19 / 09 / 2025

[0192] 11

[0193] In an embodiment, Nrcrmay be below 7.5%R - 3.0 / 85*(r-15%R), for r = 15%R to R.

[0194] In an embodiment, Nrcrmay be below 6.0%R - 1 ,5 / 85*(r-15%R), for r = 15%R to R.

[0195] In several embodiments, a rotor may have a combined chord for r = 15%R to R that may be less than a certain limiting line. In such cases, the combined chord may be larger than the prescribed limiting line over a range of maximally 5%R. This may serve to compensate for, e.g., blade connections, which may lead to an increase of the combined chord over less than 5% radial range.

[0196] In an embodiment the rotor of radius R has NO SR blades reaching a radial position of at least 0.9R and a second coaxial smaller rotor of radius R2, the second rotor having N2O SR2 blades reaching a radial position of 0.9R2.

[0197] In an embodiment NO SR is exactly 2 and N2O SR2 is exactly 2.

[0198] In an embodiment NO SR is exactly 2 and N2O SR2 is exactly 3.

[0199] In an embodiment NO SR is exactly 3 and N2O SR2 is exactly 2.

[0200] In an embodiment NO SR is exactly 3 and N2O SR2 is exactly 3.

[0201] In an embodiment NO SR is exactly 3 and N2O SR2 is exactly 5.

[0202] In an embodiment NO SR is exactly 5 and N2O SR2 is exactly 3.

[0203] In an embodiment NO SR is exactly 5 and N2O SR2 is exactly 5.

[0204] In an embodiment NO SR is exactly 7 and N2O SR2 is exactly 3.

[0205] In an embodiment NO SR is exactly 7 and N2O SR2 is exactly 7.

[0206] According to an aspect of the disclosure, a blade may be proposed for use in a rotor designed to be free spinning and to block the wind without producing a useful torque. The blade may be rotatable around a rotor axis of the HAT by the wind. In one embodiment the blade may be made out of one piece with a length of at least 10m or 20m or 50m or 70m or 100m and being designed to be used as second coaxial smaller rotor in the centre of a larger rotor of a medium or large HAT. The advantage may be that the second coaxial smaller rotor contributes to the yield of the HAT without having the complexity of an own drive train.

[0207] According to an aspect of the disclosure, a method may be proposed for adapting an existing HAT. The method may include removing a rotor from the existing HAT. The method may further include installing a new rotor so that the HAT becomes a HAT having one or more of the features described above.

[0208] According to an aspect of the disclosure, a method may be proposed for extraction of useful power from wind using a HAT having one or more of the features described above. The method may include causing the wind to rotate blades of the HAT around a rotor axis. The method may further include converting torque from a rotor of the HAT into electric energy using a generator of the HAT.

[0209] In the following part of the description, embodiments of the present disclosure may be described, by way of example only. 19 / 09 / 2025

[0210] 12

[0211] Brief Description of the Drawings

[0212] Embodiments of the present disclosure will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbol indicate corresponding parts, in which:

[0213] Fig. 1 shows an onshore upwind HAT with seven blades;

[0214] Fig. 2 shows an offshore upwind HAT with five blades;

[0215] Fig. 3 shows an onshore upwind HAT with seven blades and seven shorter blades;

[0216] Fig. 4 shows a local chord distribution and limits of an embodiment;

[0217] Fig. 5 shows a local chord distribution and limits of an embodiment;

[0218] Fig. 6 shows an onshore HAT with seven blades and a second rotor with three blades;

[0219] Fig. 7 shows an onshore HAT with seven blades with stay;

[0220] Fig. 8 shows a stay holder which allows blade pitching;

[0221] Fig. 9 shows an offshore HAT with a three bladed downwind rotor with stay;

[0222] Fig. 10 shows an offshore HAT with a large downwind rotor and a small upwind rotor;

[0223] Fig. 11 shows a small onshore eleven bladed rotor with a large tail vane;

[0224] Fig. 12 shows the shadow impact of the prior art and of an embodiment;

[0225] Fig. 13 shows AM sound by blade passages for different blade numbers;

[0226] Fig. 14 shows a local chord distribution and limits of an embodiment;

[0227] Fig. 15 shows a HAT with five pultruded twisted blades;

[0228] Fig. 16 shows a combined chord and limits of an embodiment;

[0229] Fig. 17 shows a combined chord and limits of an embodiment; and

[0230] Fig. 18 shows a combined chord and limits of an embodiment.

[0231] The figures are intended for illustrative purposes only, and do not serve as restriction of the scope of the protection as laid down by the claims.

[0232] Detailed Description

[0233] It will be readily understood that the components of the embodiments as generally described herein and / or are illustrated in the appended figures could be arranged and designed in a wide variety of different configurations. Thus, the following more detailed description of various embodiments, as represented in the figures, is not intended to limit the scope of the present disclosure but is merely representative of various embodiments.

[0234] Used terminology

[0235] The following terminology are used throughout the present disclosure.

[0236] We define the HAT wind turbine of the present disclosure “HAT”, as a wind turbine of the Horizontal Axis Turbine type with a largest rotor of a radius R, which is designed to extract useful energy from the wind, which further is non-airborne and which has a fixed foundation. Air-borne 19 / 09 / 2025

[0237] 13 devices are excluded for at least one of the following reasons: the hindrance mechanisms regarding shadow, noise and birds are incomparable to those of the HAT; the overall aerodynamic and / or structural optimization is incomparable.

[0238] Devices without a fixed foundation are excluded for at least one of the following reasons: devices without a fixed foundation, thus being mobile, have a different optimization. For example the structure does not need to withstand high survival wind speeds above 40 m / s, let alone above 50 m / s or above 60 m / s and such device should be easy to install and easy to break down; mobile devices have incomparable hindrance properties since in case of hindrance they can be moved and thus they do not permanently cause hindrance at the same location; mobile devices may be built less durable and are not meant for permanent power production, instead they may be meant to occasionally deliver power; mobile devices finally may be designed to be easy to carry and transport; and mobile devices can be toy like products to momentarily drive low-power devices, such as LEDs for decoration purposes, which are incomparable to devices meant for bulk power production. It should be noted that floating offshore wind turbines and horizontal axis wind turbines installed on a ship are regarded to have a fixed foundation.

[0239] In an embodiment the HAT turbine may have a tilt mechanism which can tilt the axis of the HAT turbine away from the horizontal position, sometimes even by 90 degrees, to control the loads and / or the power and / or to stop the rotor.

[0240] In an embodiment the HAT is meant for bulk energy production at a fixed position and should be capable of surviving wind speeds of one of: 40m / s; 60m / s; 72m / s and 80m / s.

[0241] In an embodiment the HAT of the present disclosure may be restricted to a HAT which does not include a ring-shaped structure concentric to the rotor and extending to a radial position larger than 20%R, or in another embodiment larger than 30%R, or in another embodiment larger than 50%R, or in another embodiment larger than 70%R. Ring-shaped structures st these radial positions are known and may be disadvantageous. Three types of such ring-shaped structures are known and may be used or combined: ring-shaped structures with mainly a structural function; concentrator type rotors and direct drive generators.

[0242] Ring-shaped structures with mainly a structural function and extending to a radial position larger than 20%R, 30%R, 40%R, 50%R or 70%R may be disadvantageous for one or more of the following reasons: ring-shaped structures connecting different blades are known but may be inefficient since the arc-like connections of the ring-shaped structure between blades cannot handle efficiently tension and / or compression forces between the blades, a straight connection would be more cost effective; ring-shaped structures are known with blades connected to the ringshaped structure without a direct connection from the blade root in blade longitudinal direction to the hub, so that the blade root bending moment may be captured fully by torsion of the ring-shaped structure which adds material and thus costs to the ring-shaped structure making the rotor inefficient. Therefore, in an embodiment every blade which reaches a radial position of 0.90R is directly connected to the hub by a straight structure following the blade’s longitudinal direction. 19 / 09 / 2025

[0243] 14

[0244] In the present disclosure, a HAT wind turbine rotor having straight tangential connections between the blades at a radius >0.2R or >0.3R or >0.4R or >0.5R, is not considered a HAT with a ring-shaped structure.

[0245] Concentrator type rotors with the aim to increase or decrease the air speed inside the concentrator ring which may be extending to a radial position larger than 20%R or 30%R or 40%R or 50%R or 70%R may be excluded for at least one of the following reasons: concentrator type rotors have a different aerodynamic and structural optimization; a concentrator ring may be connected to more than three blades to create multiple load carrying (moveable) supports to the ring-shaped concentrator, which argument for more than three blades vanishes without the concentrator ring; concentrator type rotors may have more than three blades to reduce the strength of the circulation per blade and so to reduce the disadvantageous aerodynamic interaction between the blade tips and the concentrator; wind turbines with a concentrator ring typically have a lower yield over cost ratio; the large concentrator attracts loads particularly at survival wind speed conditions; the concentrator causes much cast shadow and the concentrator may be costly.

[0246] Devices with a direct drive generator extending in the radial direction beyond 20%R or 30%R or 40%R or 50%R, may have a direct structural connection between the blades and the generator, thus not via the hub. This could be an argument to apply many blades since it leads to many structural supports for the generator giving a better distribution of the loads and less loads per support. However, the direct connection between the generator and the blades at a radial position of at least 10%R or 20%R or 30%R may not be favorable since the bending moments of the blades may deform the generator wherein a narrow air gap between the electromagnetic rotor and statorshould be maintained. Such devices may further have contra rotating rotors of which the blades pass each other in opposite direction at a small mutual distance (smallerthan R / 5 orsmaller than R / 10 or smaller than R / 50). This has the advantage of obtaining a higher relative speed between the electromagnetic rotor and ‘stator’ of the generator. However, the mutual blade passages of the close counter rotating rotors cause, in use, noise and aeroelastic excitation. To decrease the excitation and the noise, it could be suggested to increase the number of blades and / or to use different blade numbers for the different rotors. Even then, such devices are not favorable. The use of overlapping contra rotating rotors with approximately the same diameters (difference less than 30% or less than 20% or less than 10%) may further be inefficient regarding yield over cost ratio since a single rotor can already extract almost all energy. Compared to corotating rotors, counter rotating rotors have the further disadvantage of more disturbing the tranquility of the landscape and causing more ‘chaotic’ cast shadow which may cause more hindrance. Finally, a direct drive generator with a radius of more than 20%R may lead to various disadvantageous such as high weight, large transportation problems, more problems to maintain a narrow air gap and thus more costs.

[0247] A large HAT may be defined as a HAT having a diameter largerthan 100m.A medium HAT may be defined as a HAT having a diameter larger than 50m and smaller than a large HAT.

[0248] A small HAT may be defined as a HAT having a diameter smaller than a medium HAT. 19 / 09 / 2025

[0249] 15

[0250] Devices without a fixed foundation or mobile wind turbines are typically small wind turbines. Small wind turbines may have a fixed foundation, but such small wind turbines typically have different characteristics compared to medium HATs and large HATs, such as lower tip speeds, different blade designs, lower power coefficients, lower survival wind speeds, less optimization of performance.

[0251] The solution of the present disclosure may advantageously be applied to large HATs and medium HATs. The various hindrance aspects or optimizations described throughout this disclosure may not apply to small wind turbines orto a lesser extent, which small wind turbines are therefore outside of the scope of the present disclosure.

[0252] In the following, where reference is made to a HAT, this refers to a large HAT and / or a medium HAT.

[0253] A HAT may have one or more downwind and / or one or more upwind rotors. Different rotors of the same HAT may rotate at different speeds. The HAT may be onshore or offshore. The HAT may be installed on a ship. The HAT may have a single foundation with two towers, each tower having one or more rotors which in use have exclusive swept areas or have (partly) overlapping swept areas. The HAT may have a single tower or a tower which splits in one or more arms which each may be connected to a rotor.

[0254] A rotor may be a structure of parts which rotates in use about the same axis and with the same speed and in the same direction and is designed to decelerate the wind when in use.

[0255] A center of rotation of a rotor is a point on the rotation axis of the rotor which corresponds to an averaged axial position of the rotor swept area.

[0256] A HAT has coaxial horizontal axis rotors when the distance between the centers of rotation of the rotors is less than R / 2, or less than R / 4 or less than R / 10.

[0257] A number of blades “N” may referto the number of blades of a rotor which reaches at least a radial position of 0.9R or at least a radial position of 0.7R. The number of blades may be counted per rotor independently.

[0258] If a HAT includes a rotor with blades of different lengths, then the number of blades may be dependent on the radial position. E.g., a rotor with five long blades reaching from 0.1 R to R and five small blades reaching from 0.1 R to 0.6R has ten blades at 0.3R (N03R = 10) and five blades at 0.8R (NO.BR = 5).

[0259] If multiple aerodynamically shaped elongated parts of the same rotor extend along the same length axis, at the same side of the rotation axis, then those parts may be considered parts of the same blade, and those parts together may be counted as one blade.

[0260] The direction of a longitudinal blade part may be given by a rotor azimuth angle <p with <pe[0°,360o] and a polar angle 0 with the rotation axis with 0e[O°,18O0]. If a rotor with N blades has multiple aerodynamically shaped elongated parts which may be directed within 360° / 4N difference in azimuth angle and within 30° difference in polar angle, then those parts may be considered parts of the same blade and those parts together may be counted as one blade. For example, when a rotor has 7 blades, then aerodynamically shaped elongated parts which may be directed within 19 / 09 / 2025

[0261] 16

[0262] 360° / (4*7) = 12.9° difference in azimuth angle and within 30° difference in polar angle may be counted as one blade.

[0263] In some embodiments the blades may be assumed to be distributed evenly over the rotor azimuth: when the rotor has N blades, it means that an azimuth angle between adjacent blades may be 360° / N + / - 360° / 4N or 360° / N + / - 3°. For example, when N=7, the azimuth angle between adjacent blades is 51.4° + / - 12.9° or 51.4° + / - 3°, so that a minimum azimuth angle between adjacent blades is 38.6° or 48.4° and a maximum azimuth angle is 64.3° or 54.4°. This even distribution of the blades may have any of the following advantages: the rotor will be well balanced; the rotor swept area may appear more as a ‘closed’ inaccessible surface to birds, the even distribution avoids that blades may be installed so nearby each other that the cast shadow becomes deeper or may become core shadow and the rotor may be aerodynamically more efficient, since an even azimuthal distribution of the blades leads to the smallest tip losses.

[0264] A blade may exist of one piece or of multiple parts. A blade comprises an outer part which may be the only part. The outer part includes at one end a connection side where the blade connects to a hub of the rotor and at the other end a tip side. A blade part may be connected to the hub via an intermediate structure like a truss structure. Along the length of a blade, the blade may include stiffening connections to improve structural integrity. The blade may include an aerodynamic part which may have a leading edge and a trailing edge. Cross sections of the aerodynamic part of the blade may include airfoils. Away from stiffening connections, a blade may be adapted to improve aerodynamics. A blade part may be in a fixed position relative to the rotor or may be fixed to a pitch device and be pitchable.

[0265] A radial position “r” may be expressed as r = xR, with xe[0,1] or xe[0%,100%], and defines a position measured outwards from the rotational axis at a distance of x times the radius “R” of the largest rotor. The meaning of “in the radial range from r=15%R to R” = “for r = 15%R to R”.

[0266] A local chord “cr“ at a radial position r of a blade may be defined as the sum of the distances between the leading edge and the trailing edge of all the blade parts of the rotor at the radial position, which, in use, may contribute to the aerodynamic lift at the radial position. If the blade consists of one part at the radial position, then crmay be the distance between the leading edge and the trailing edge of that part at that radial position. Extensions of airfoils by serrations to reduce sound may not be considered as part of the local chord. If a blade has a variable local chord which depends on the wind speed, e.g., when sails may be used, then the smallest local chord at position r with fully retracted variable parts may be used. At the blade root where the blade shape often transforms from a more aerodynamic shape to a more cylindrical shape, the largest distance in a cross section of the transition part at the radial position may be taken as value for the local chord as long as the part may produce lift when in use. If a blade consists of multiple aerodynamically shaped parts such as e.g. without limitation radial stay and / or radial compression elements, connecting joints at different radial positions (larger than 10%R), which, in use, may contribute to the lift, then the local chord crmay be the sum of the chords of those multiple aerodynamically shaped parts at radial position r. Blade parts or rotor parts such as e.g. the hub and / or the spinner, 19 / 09 / 2025

[0267] 17 which develop, in use, no aerodynamic lift, may not contribute to the local chord. Tangential stay or tangential compression elements connecting adjacent blades at equal radial positions (equal within 5%R or within 10%R) at position r, may preferably be excluded from the local chord even when they may produce lift when in use.

[0268] The maximum chord of a blade may be the largest value of the local chord value along the blade length, typically for r = 15%R to R.

[0269] Several embodiments have a rotor with blades which have a local chord for r = 15%R to R which may be less than a certain limit. In such cases the local chord may be larger than the prescribed limit over maximally 5%R. This may serve to compensate for e.g. connections which lead to an increase of the chord over less than 5% radial range. Such local chord extensions may also be excluded from the maximum chord.

[0270] The rotor solidity “SOLrotor“ may be the mathematical integral over a radial length, e.g., from r = 0.15R to R, of the local chords cr, of all the blades of a largest rotor, divided by the rotor swept area, using equation 1 below.

[0271] SOLrotor— — 1 fR>-1

[0272] TtR crdr equation 1)

[0273] 0 15Kall blades

[0274] In the case of a ring-shaped wind concentrator, a chord of this concentrator multiplied by the circumference of the concentrator divided by the swept area TTR2may be added to the above definitions for “SOLrotor”.

[0275] The radial solidity “solr” may be defined as the sum of the local chords Cr, of all the blades of a rotor, at radial position r, divided by the rotor circumference at a radius R of the rotor (see equation 2 below). In case of coaxial rotors, the radial solidity is calculated for each rotor separately.

[0276] The average radial solidity “avgsolr” may be defined as the average of the radial solidity of a rotor in a radial range from r-0.05R to r+0.05R. Equation 3 defines as example “avgsol 25R” as the average radial solidity between radial positions 0.2R and 0.3R. Analogously “avgsol 35R” may be the average radial solidity between 0.3R and OAR and “avgsol 75R” may be the average radial solidity between 0.7R and 0.8R. It should be noted that radial solidity, the average radial solidity, the radial solidity ratios and the average solidity ratios may refer to the largest rotor.

[0277] The undisturbed wind speed “U” may be defined as the speed of wind through the rotor swept area in case that the wind is not disturbed by the HAT.

[0278] The power coefficient “Cp“ may be defined as the ratio of the mechanical power “PM“ produced by the HAT and the kinetic power in the undisturbed wind through the rotor swept area (see equation 4, left side). The electric power coefficient “CPE“ may be defined as the ratio of the electric power PE produced by the HAT and the kinetic power in the undisturbed wind through the rotor swept area (see equation 4, right side). Cp may always be higher than or equal to CPE when the turbine 19 / 09 / 2025

[0279] 18 extracts power from the wind. If a turbine has two rotors with overlapping swept areas, then the power coefficients follow from the ratio of the power of both rotors combined and an undisturbed kinetic wind power through the swept area of the largest rotor TTR2. In equation 4 and 5, p is an air density.

[0280] In the present disclosure, if the HAT includes two rotors, the axial force coefficient “CD,ax“ refers to a smaller rotor with radius R2, typically referred to as a second rotor, and equals the ratio of the axial force “Fax“ exerted by the smaller rotor on the wind and a momentum flow of the undisturbed wind U through a rotor swept area TTR22of the smaller rotor (see equation 5 below).

[0281] A tip speed ratio “A“ refers to the ratio of an angular rotor speed “co” multiplied by the rotor radius R and the undisturbed wind speed U. A design tip speed ratio “Adesign” may be the tip speed ratio for which the rotor reaches its maximum value for Cp. A ratio at another radial position than at the tip may be defined as the radial speed ratio Ar= Adesign / R. Although a rotor typically may have the highest yield at Adesign, HAT control may deviate from this optimum, e.g., to reduce loads or sound, to avoid eigenfrequencies orto avoid overpower. Therefore, Adesign may also be the tip speed ratio applied by the control in the wind speed range between 8m / s and 10m / s “Acontroi”. Equation 6 shows the relations.

[0282] A rotor may be designed using the known Blade Element Momentum (BEM) theory. It has been found that, based on BEM and for Ar> 2, to extract much of the energy from the wind, an approximation to determine a local chord at a radial position r may be calculated as shown in equation 7 below.

[0283] - Nrcrr = - 1.8TT c — (equation 7) l, designer

[0284] In equation 7, ci, design may be a design lift coefficient, which is an airfoil property. The product NrCr may be called a combined local chord or “combined chord", which is a function of the radial position and is a rotor property that may apply to the largest rotor.

[0285] In the case of a free spinning rotor with radius R2 and rotating with a speed 102, a freespin tip speed Afreespin is the ratio between the tip speed W2R2 and U when the rotor reaches a power coefficient CP2 =0.

[0286] Cast shadow refers to the shadow of moving HAT blades. Core shadow refers to cast shadow at locations where the sun is fully covered by the moving blades, so that substantially all direct sunlight is blocked. 19 / 09 / 2025

[0287] 19

[0288] Overview

[0289] Environmental hindrance by a wind turbine, in particular from a wind turbine of the HAT type, may take different forms. The following types of hindrance will be discussed: (i) visual (or optical) hindrance; (ii) acoustic hindrance; (iii) hindrance to birds and (iv) composite waste.

[0290] Visual hindrance may be categorized as, e.g., direct cast shadow hindrance, indirect cast shadow hindrance resulting in reduction of yield of solar farms or crops, and / or hindrance impacting optically the tranquil landscape. Cast shadow may be the shadow created by the blades moving through the sunlight. The impact to the tranquil landscape may be caused by seeing the moving blades. Larger blades typically result in a larger visual hindrance.

[0291] Known solutions to visible hindrance typically involve a design process wherein mathematical algorithms may be used to calculate or measure when too much cast shadow occurs and subsequently determine when to switch-off the turbine. The general idea of experts in the field is that when wind energy needs to be harvested, the cast shadow of the large rotor blades may be inevitable. Applying transparent blades would not help since refraction of the light would cause light rays to change direction resulting in a cast shadow to still be formed. Moreover, the inner structure of HAT blades is typically made of fibers, which may be difficult to make transparent.

[0292] The present disclosure proposes that by reducing a local chord to the extent that visually the blade would no longer cover the sun completely, the core shadow vanishes. Conventionally, the sun is often assumed to be a point source of light, however the inventor realized that the sun is visible under an angle of about 0.50° on the horizon, and therefore when the local chord may be reduced to below an angle of 0.50°, the sun may be not fully covered by the blade and the core shadow may be removed.

[0293] The maximum of the local chord of a known, state-of-the-art blade may be typically 7%R. Applying trigonometry learns that such a chord may be visible under 0.50° from a distance of 0.07R / tan(0.50°) = 8R or 4D. Thus, with known HATs, up to 4D a blade will throw a core shadow. Lowering the maximum chord as proposed in embodiments of the present disclosure, e.g., by halving the known maximum chord to 3.5%R, results, in this example, in the core shadow to only reach a distance of 0.035R / tan(0.50°) = 4R or 2D. This means that in an important range of 2D to 12D from the HAT, i.e. , the range where visual hindrance may mostly be perceived, core shadow no longer occurs. Cast shadow hindrance typically involves both core shadow and partial shadow. Also, the partial shadow may be minimized, i.e., become half as ‘deep’ for the given example. Advantageously, the present disclosure may thus achieve a reduction in visual hindrance by a factor of about 2 or more by reducing the state-of-the-art maximum chord, e.g., by a factor of 2 in the above example.

[0294] An additional advantage of less deep shadows or less core shadow by the wind turbine involves the yield of photovoltaic solar panels which are located in the shadowed area: the power of certain solar systems, which consists of a string of solar panels in series, may be about linear to the power of the panel with the lowest yield, thus the panel in the deepest shadow, so that reduction of the depth of the shadow is advantageous. 19 / 09 / 2025

[0295] 20

[0296] Regarding the tranquility of the landscape, in particular large moving blades draw attention and may elicit a stress reaction for humans and animals, because motion may be perceived as danger. This type of hindrance may be often experienced as less disturbing than cast shadow, however the frequency of occurrence may be larger: it has impact during most of the daylight time and in case of a clear sky it may be disturbing up to 50 diameters distance from the HAT. Different from cast shadow hindrance, this type of hindrance may be not limited to the shadow area, but instead it affects about the entire surrounding of the turbine up to 10 to 50 diameters distance from the HAT. The hindrance may be estimated to, on average, reach a visual distance of about 20D, so that the circular area around the turbine wherein hindrance may occur may be about TT(20D)2square meter in size. Assuming that this hindrance occurs during about 50% of the time (e.g., excluding night time), which may be about 4400 hours per year, the hindrance frequency of the impact to the tranquility of the landscape may be about TT(20D)2■ 4400h = 7040000 ■ KTTD2m2h per annum.

[0297] In comparison, the cast shadow hindrance may typically be limited to an area of about 4 times the swept area (assuming the sun is 15° above the horizon) and it occurs only during direct sunlight, which occurs e.g., about 1500 per annum in The Netherlands. So, for the cast shadow we calculate a frequency of 4 ■ KTTD2■ 1500 m2h= 6000 ■ KTTD2m2h per annum, which is about 1200 times lower.

[0298] It is an insight of the inventor that by reducing the maximum chord by a factor of two, the distance at which the blades visually disappear in the background becomes about half. This may optically be understood since the angle whereunder the half-maximum chord is visible at half the distance may be equal to that of the full-maximum chord blade at the full distance. So, the visual hindrance may be reduced in distance by a factor of two and thus the hindrance area and the hindrance frequency may be reduced by a factor of four. Although the above-described embodiment may be based on the maximum chord, a similar logic may be applied to the local chord.

[0299] Reducing the maximum chord and reducing the local chord in accordance with the present disclosure may be particularly advantageous for medium and large HATs.

[0300] Bird related hindrance includes bird casualties caused by direct collision between the HAT and a bird. Also, it may be caused by a contactless overloading of a bird by first an air pressure impact near a rotating blade and second by the high velocities I an air pressure drop in the vortices shed from blade tips. If the number of blades applied in a HAT rotor increases and the chord is reduced, e.g., according to equation 7, then the lift per blade may be reduced. It is an insight of the inventor that this reduces the range around the blade wherein a certain air pressure may be induced by the blade and that the strength of the tip vortices may be reduced, resulting in a rotor becoming a lower hazard for birds.

[0301] The hazard to a bird for a rotor of diameter D with N blades may be expressed as follows. A bound vorticity T” may be considered linear to D and inversely proportional to N, so r = kiD / N. A hazardous space Sr for a bird due to the N shed tip vortices of strength r may be the space 19 / 09 / 2025

[0302] 21 wherein the vortex induced velocities may be above a certain limit. In a plane perpendicular to F, the width and height of this space each may be proportional to F and the length of the space, in the direction of F, may also be linear to F. Thus, the space Sr = k2N r3, and if we substitute herein F = kiD / N, we find Sr= k2N(kiD / N)3= k3D3 / N2, wherein k, ki and k2 are constants.

[0303] The air pressure impact to the bird may be expressed as follows. The hazardous space SP is considered proportional to the square of the bound vorticity, proportional to the blade length, the latter being proportional to D, so Sp = c1 DH. If we again substitute F = kiD / N, we find Sp = cD3 / N2, with c and m being constants.

[0304] It is an insight of the inventor that the vortex and / or pressure related hazardous space for birds by a rotor of diameter D may be decreasing with the number of blades, and in particular decreases with the square of the number of blades N.

[0305] Bird casualties by collisions with blades may occur less frequent when the entire swept area of the rotor is better visible to the bird and when the blades move at a lower speed. A lower blade speed gives a bird more time to react and avoid a collision with the blade, and in case of a collision the impact is less severe. In an embodiment a lower than conventional Adesign may be favorable. For a conventional offshore turbine, Adesign may typically be in the range from 9 to 10. For a conventional onshore turbine, Adesign may typically be in the range of 8 to 9.

[0306] In an embodiment, the rotor may be configured with a design tip speed ratio, Adesign = coR / U, wherein Adesign of less than 9.

[0307] In an embodiment, the rotor may be configured with a Adesign of less than 8.

[0308] In an embodiment, the rotor may be configured with a Adesign of less than 7.

[0309] In an embodiment, the rotor may be configured with a Adesign of less than 6.

[0310] In an embodiment, the rotor may be configured with a Adesign of less than 5.

[0311] For a lower tip speed ratio, a larger combined chord Nrcrmay be applied to keep the efficiency high (see equation 7), which may again be an argument for a larger number of blades.

[0312] Rotors with two or three blades have large open areas in between the blades, which may ‘invite’ a bird to fly through those open areas, with a high collision risk, when the rotor is rotating. Therefore to improve the visibility of the rotor swept area to a bird, in an embodiment it may be favorable to have at least four or five blades and preferably at least six or seven blades, because with more blades the rotor may appear more as a ‘closed’ inaccessible surface to the bird.

[0313] Also, when sight of birds is bad, e.g. at night or in dense fog, bird casualties may be about proportional to the projected area of a wind turbine rotor, so that reducing the chord at the root and thus reducing the rotor solidity SOLROTOR is advantageous.

[0314] Reducing Adesign has the above advantages, however it also leads to a larger solidity which is a disadvantage for the yield over cost ratio inter alia because of the larger required chords to capture the wind energy. Therefore, the HAT may have also a minimum Adesign.

[0315] In an embodiment, the rotor may be of the fast runner type and may be configured with a design tip speed ratio, Adesign, wherein Adesign may be more than 4. 19 / 09 / 2025

[0316] 22

[0317] In an embodiment, the rotor may be of the fast runner type and may be configured with a design tip speed ratio, Adesign, wherein design may be more than 5.

[0318] In an embodiment, the rotor may be of the fast runner type and may be configured with a design tip speed ratio, Adesign, wherein Adesign may be more than 6.

[0319] The turbine diameter may play an important role in all sources of hindrance. The rotor area exposed to direct or indirect sunlight, the total sound pressure level and the area wherein birds may be at risk approximately proportional to the square of the diameter. The contribution of the low frequencies in the sound of a HAT increases as well with turbine size. And low frequencies generally cause more problems than high frequencies. Also, the whooshing effect from the individual blades increases with turbine size. For smaller turbines smaller than 5m diameter this effect may be almost non-existent: such turbines rotate so fast that the individual blade sound cannot be heard. For medium of more than 50m diameter and even more for larger wind turbines of more than 100m diameter the rotor speed may be less and the individual blades of two or three bladed turbines may be distinguishable. Furthermore, the visual impact of smaller HATs may typically be reduced because buildings and trees may hide the smaller HAT.

[0320] In an embodiment, the HAT may be a medium HAT.

[0321] In another embodiment, the HAT may be a large HAT.

[0322] The hazard for rare birds is typically regarded as more important than that of more common birds. The rare birds may be predator birds or migratory birds, which usually fly at a higher altitude, which may be the altitude of medium and large HATs. Therefore, the larger the turbine the more important the different hindrances become, and therefore the present disclosure may be particularly relevant to medium and large HATs.

[0323] Regarding acoustic hindrance by a wind turbine, it is known that the aerodynamic sound pressure level may be approximately proportional to the fifth power of the tip speed of the blade, and thus reducing the tip speed may reduce noise from a rotating blade. However, since the aerodynamic lift generated by a HAT blade is about proportional to the square of the tip speed, a reduction of the tip speed would require a squared increase of the blade chord to maintain the required lift, see equation 7. The blade chord would thus increase, with all kinds of problems such as increased visual hindrance, transportation size and production issues because of the larger chord. Therefore, solutions to reduce the tip speed may be undesirable.

[0324] The inventor had the insight that to reduce noise, contrary to conventional knowledge, the chords may be decreased rather than increased. It has been found that the decreased chords and / or the reduced tip speed may be compensated for by, e.g., increasing the number of blades. Increasing the number of blades may be particularly advantageous for medium and large HATs.

[0325] For state-of-the-art HATs there is general consensus that the optimum number of blades is three or possibly two for medium or large electricity producing HATs. Other numbers of blades may typically not be considered for medium or large HATs aiming at electricity production and the person skilled in the art would typically not consider increasing the number of blades for HATs. Known arguments to favor three blades over more than three blades include that with more than 19 / 09 / 2025

[0326] 23 three blades the power coefficient is not getting much better (perhaps 1 %). Furthermore, every additional blade requires additional handling during transportation, hoisting and maintenance. Furthermore, there may be an argument concerning blade loads comparing a rotor with three blades to another rotor with more blades, e.g., six blades, wherein each blade of a three bladed rotor has twice the loading, also twice the chord and twice the thickness, compared to a blade of a six bladed rotor. Because of the double loading, the bending moments may be doubled too, however a structure of double thickness has a fourfold higher bending stiffness when the same amount of material may be used. Hence, having three blades with double loading blades requires less material than, e.g., six blades with single loading, because of which known HATs favor having three blades over more blades. So, this is an argument to use a low number of blades: typically 2 or 3.

[0327] It was an insight of the inventor that having more than three blades may impact acoustics positively. Generally, three sources of potential sound hindrance may be distinguished: (i) the total sound pressure level (SPL); (ii) Amplitude Modulation (AM); and (iii) infrasound. AM means that the sound of a HAT is not constant, but the individual blade passages may be audible as a disturbing repetitive ‘whooshing’ noise. It has been found that using more than three blades reduces AM sound. E.g., AM may be reduced by about a factor of 5 by changing from three to five blades. A further AM reduction to an almost constant sound pressure level may be achieved for seven blades or more. This may be particularly true for medium and large HATs.

[0328] Regarding infrasound, it was found that by changing a rotor design from the classic three chord blades to a larger number of short chord blades, the sound frequency distribution may shift to higher frequencies. This reduces the share of the infrasound and increases that of higher frequency sound. The shorter local chord of a blade leads to less built up of the boundary layer on the blade surface and thus to a thinner boundary layer which on its turn leads to higher frequency noise. Additionally, the shorter chord blade passes faster through the pressure field around the tower and thus also this source of sound shifts to higher frequencies. Advantageously, higher frequencies may be better damped in the atmosphere while low frequencies may be not, so that, the shift to higher frequency’s may be perceived as less disturbing at a distance from the wind turbine. Also, this type of hindrance is in particular valid for large HATs and to a less extent for medium HATs. Infrasound is rarely a problem for small HATs.

[0329] As shown in equation 7 above, chord reduction and the increase of the number of blades are related. From equation 7 it follows that, for a given &, design and Ar, the product of N and the local chord crpreferably meets a certain value. A chord reduction may be compensated by an increase of the number of blades and vice versa, as will be further explained below. Say an observer is at a distance of 3 diameters (3D = 6R) behind a turbine and we want the visibility of the blade to be limited to under 50% of the solar angle of about 0.5°, thus under about 0.25°, then the blade chord may be about tan(0.25°)*6R = 0.026R. If we substitute this in equation 7, it follows that by assuming r=0.4R, Ar=3.2 and ci, design =1 .5, the estimated number of blades N may be 5.2, so that in practice five or six blades may be used instead of the conventional three. 19 / 09 / 2025

[0330] 24

[0331] It may thus be favorable to reduce the acoustic hindrance for medium and large HATs by one or more of the following measures: (i) reducing the tip speed, (ii) chord reduction and (iii) an increase of the number of blades.

[0332] The present disclosure may not be limited to onshore HATs. Special benefit may be reached by the present disclosure for offshore HATs as well. One should realize that visual and noise hindrance may also apply to certain species of marine or freshwater animals and / or people working or recreating on water. Furthermore, offshore turbines may sometimes be seen from the shore and may cause the earlier mentioned disturbance of the tranquil landscape or of the tranquil sea view. So, in contradiction to conventional opinion, also offshore turbines may be sources of environmental hindrance. Furthermore, it has been explained that certain embodiments have a higher yield over cost ratio. Therefore, in an embodiment, the HAT may be an onshore turbine or an offshore turbine.

[0333] Like the unexpected visual and acoustic advantages of embodiments of offshore turbines, those advantages also apply to animal rich nature areas onshore, since not only humans but also animals may be disturbed by noise, cast shadow, impairment of the tranquil landscape and / or bird casualties. Additionally in nature areas usually more birds are flying around so that wind turbines with less casualties according to certain embodiments are in favor.

[0334] Since there often are many trees in nature rich areas, only medium or large wind turbines are economically efficient because theirswept areas usually are at higheraltitude, above the height of the trees, therefore the advantage is larger for medium wind turbines and may even be largest for large wind turbines.

[0335] Further Example Embodiments

[0336] In an embodiment, a required lift may be produced by airfoils with high design lift coefficients so that the radial solidity may be kept minimal. In an embodiment, the HAT applies an airfoil, which may have vortex generators, in any of the positions 0.5R, 0.7R and 0.9R, with a design lift coefficient &, design > 1.4, preferably ci, design > 1.6, more preferably ci, design > 1.8, more preferably ci, design > 2.0, more preferably ci, design > 2.2. For the design lift coefficient, the lift coefficient of an airfoil with the highest lift over drag ratio may be chosen.

[0337] In one embodiment an airfoil with a trailing edge flap or with an leading edge slat is applied so that a design lift coefficient ci, design > 2.4 can be applied.

[0338] In one embodiment of the rotor having a truss structure having a compression element, the compression element having the shape of an airfoil with a slat or flap and / or the compression element being cylindrical and rotating so that, in use, it develops lift using the Magnus effect.

[0339] It has been found that instead of using the lift coefficient of maximum lift over drag ratio as design lift coefficient, it may be advantageous to apply the lift coefficient & at an angle of attack between 4 and 9 degrees or between 5 and 8 degrees below the stall angle of attack as design lift coefficient. The stalling angle may be the lowest positive angle of attack a where the derivative dci / da = 0 under 2D conditions. The advantage of using this latter design lift coefficient may be that 19 / 09 / 2025

[0340] 25 it may be higher than the that at maximum lift over drag ratio, so that blades with a shorter chord can be used to achieve the required lift. The shorter chord may have less optical hindrance, lower storm loads and may also have other load advantageous according the known slender blade technology.

[0341] The airfoil properties may preferably be valid for the Reynolds number that corresponds to the Reynolds number of the airfoil when the HAT is operated at Acontroi at 9 m / s wind speed.

[0342] Where the skilled person typically focusses on high yield per unit of swept rotor area, the present disclosure focusses on parameters as yield over cost ratio or total avoided CO2 emissions or circularity.

[0343] Remarkably, for some embodiments in which the number of blades increases from, e.g., three to five blades, the yield may increase by about 1 %, and when going from three to seven blades, the yield may increase by about 1 .5%. For four or six blades the yield increase may be in between these values. For more than seven blades the further yield increase may be small. A reason of this yield increase may be that the tip-losses, often accounted by the ‘Prandtl tip correction’ may be less for more blades.

[0344] Furthermore, state-of-the-art turbines sometimes need to be switched off because of hindrance. However, since the HAT according to the present disclosure with more than 3 blades causes less hindrance, the hindrance related down time may be less or none, which may add an estimated 1 % to 2% to the yield.

[0345] In some embodiments the yield over cost ratio may increase while the power coefficient Cp decrease. This becomes clear by showing that the blade range close to the tip harvests more energy per unit of blade area than the blade range close to the rotor center. The solidity Ncr / (2irr) may be calculated at two radial positions, e.g., at r=0.3R and r=0.9R. By substituting (ci=1 .5, and Adesign=8) and using equation 7, we find Ncr / (2Trr)r=o 3R = 0.104 and Ncr / (2nr)r-o gR = 0.0116. So, at the root of the blade the required blade surface may be about a factor of 0.104 / 0.0116 = 9 more per unit of swept area than at the tip. And since the energy captured may be about proportional to the swept area, the airfoil at the root captures about 9 times less energy per unit of chord length, than that at the tip. At hurricane wind speeds, when the HAT may be halted to avoid damage, the loads by the blades on the tower bottom may be about linear to the blade area. Accordingly, the blade root causes high storm loads but harvests relatively low energy, while the blade tip may perform about the factor 9 better regarding yield over storm load ratio. The inventor realized that it may be better in terms of yield over cost to accept that the rotor produces less power near the rotor center so that the ratio between yield and loads increases. Therefore, in an embodiment, the blade area at the blade root may be less than what may be needed to obtain the maximum power extraction (the Lanchester Betz limit). The power extraction in the root range (below 0.35R of even below 0.45R) may drop to below 50% or even below 25% of the optimum or even approach 0, while the yield over cost ratio of the wind turbine may increase. Using a lower blade area for the blade, means that the rotor solidity may be reduced, which has the additional advantage that the 19 / 09 / 2025

[0346] 26 yield of crops and solar panels which may be located in the shadow of the rotor may be less impaired.

[0347] Therefore, in an embodiment, the radial solidity near the rotor center may be reduced relative to that near the tip. The ratio of the radial solidity at radial position 0.25R of a rotor and the radial solidity at a radial position 0.75R of the same rotor, expressed as SOIO 25R / SOIO ?5R, may be less than 2.0, preferably less than 1.75, more preferably less than 1.5, and more preferably less than 1.25 and more preferably less than 1 .0 and more preferably less than 0.90 and more preferably less than 0.75, and more preferably less than 0.50, and more preferably less than 0.25.

[0348] In an embodiment, at a radial position of 0.25R the aerodynamic blade section may be partly or fully replaced by structural elements, so that SOIO 25R / SOIO 75R may even become less than 0.75 or less than 0.50. In the extreme case of an embodiment wherein there may only be structural elements at 0.25R, which do not have an aerodynamic shape which contributes to the lift, SOIO 25R / SOIO 75R even may be 0.

[0349] Also, it may be favorable for embodiments having a smaller coaxial second rotor, designed for a higher rpm, which may be more efficient at 0.25R. Because of the higher rpm of the second rotor, the blades of the second rotor will have a higher speed than the blades of the largest rotor at the same radial position. And since the aerodynamic lift force is proportional to the square of the speed between the blade and the air, the second rotor can develop more lift per unit of chord length and thus can develop the optimum lift at a shorter chord.

[0350] In an embodiment, a rotor may be applied with low solidity near the rotor center since in this range the ratio between yield and storm loads may not be beneficial in the case of state-of- the-art HATs.

[0351] The maximum power coefficient may be lower than certain state of the art wind turbines, however the yield over cost ratio of an embodiment may be higher.

[0352] The values for Cp of some embodiments may be low compared to those of large state of the art HATs which have Cp values often above 0.45. This may be explained by the low chords used by some embodiments so that less energy may be captured near the rotor center. The low chords reduce the rotor solidity and this may reduce the loads and the cost. Also, in some embodiments the length of the blades is reduced while the rotor radius remains the same which also reduces cost. The yield over cost ratio may be more relevant and may be higher versus that of large state-of-the-art HATs.

[0353] In the present disclosure, HATs may be considered to be optimized for yield or yield over cost ratio or total avoided CO2 emissions or circularity, e.g., having a power coefficient of at least 0.30.

[0354] In an embodiment, the rotor may be designed to have a Cp of at least 0.30.

[0355] In an embodiment, the rotor may be designed to have a Cp of at least 0.35.

[0356] In an embodiment, the rotor may be designed to have a Cp of at least 0.40.

[0357] In an embodiment, the rotor may be designed to have a CPE of at least 0.30.

[0358] In an embodiment, the rotor may be designed to have a CPE of at least 0.35. 19 / 09 / 2025

[0359] 27

[0360] In an embodiment, the rotor may be designed to have a CPE of at least 0.40.

[0361] Advantages regarding efficiency and / or hindrance may also be realized for a HAT with the rotor having exactly two, exactly three, exactly five or exactly seven blades which reach a radial position of 0.90R and having a low ratio SOIO.25R / SOIO.75R as disclosed herein. The hindrance advantages become larger with increasing number of blades because the local blade chord will be smaller with increasing blade number. The efficiency advantage comes from the reduced rotor solidity. In an embodiment SOIO TSR will be designed so that the blades at 0.75R may be operated near the Lanchester-Betz optimum (axial induction factor at 0.75R between 0.25 and 0.33 using Blade Element Momentum theory). The low solidity ratios SOIO 25R / SOIO ?5R cause the rotor to have a below state-of-the-art solidity near 0.25R, so that the rotor solidity will be less, which will reduce loads and in particular storm loads and it will save on blade costs and on composite waste.

[0362] In an embodiment the first rotor of the HAT has exactly 2, exactly, 3, exactly 5 or exactly 7 blades and a truss structure in the rotor centre without having a second rotor.

[0363] In an embodiment the first rotor of the HAT has exactly 2, exactly, 3, exactly 5 or exactly 7 blades and the smaller coaxial second rotor has the same number of blades as the first rotor, which is advantageous for reducing storm loads by parking the first and the second rotor so that their blades have the same azimuth angles and the projected area on a plane perpendicularto the rotor axis is minimal.

[0364] In an alternative embodiment the first rotor of the HAT has exactly 2, exactly, 3, exactly 5 or exactly 7 blades and the smaller coaxial second rotor is unequal to that of the first rotor, which is advantageous since equal blade numbers may cause a higher excitation of vibrations.

[0365] In an embodiment, the HAT may have a design tip speed ratio Adesign, wherein the number of blades N at 60%R may be between No 6R.min = INT(100ir / Adesign2+ 0.5) and NO SR .max—2 ■ No 6R.min. Preferably, N is taken as a prime number or twice a prime number. For example, when Adesign = 7, then, e.g., No 6R.min = INT(100TT / 72+0.5) = 6 and No 6R,max = 12. Herein, the INT function returns an integer value, i.e., the number without its fractional part. If the blade number is a prime, then the lowest rotor eigenfrequency may correspond to the reciprocal of the rotor revolution period and the next eigenfrequency may be a factor N higher and it may be favorable to have the rotor eigenfrequencies far apart.

[0366] In an embodiment, the number of blades of the first rotor and the number of blades of the second rotor, both are prime numbers, e.g.: 2, 3, 5, 7, or 11.

[0367] To reduce the blade bending moments and in particular the bending moments with a direction vector mainly in rotor axial direction, the inventor realized that a tangential stay or a tangential compression element can be effective without causing much aerodynamic drag. Tangential stay refers to a guy-wire connection from one blade at a certain radial position to an adjacent blade in a certain radial range. In an embodiment, the HAT may have a first and an adjacent second blade, both being part of the same rotor, wherein the blades may have a tangential connection in a radial range AR wherein AR > 0.20R, preferably AR > 0.30R, more preferably AR > 0.40R, more preferably AR > 0.45R. Additionally or alternatively, AR < 0.80R, more preferably 19 / 09 / 2025

[0368] 28

[0369] AR < 0.70R, more preferably AR < 0.60R, and more preferably AR < 0.50R. In an embodiment 0.20R < AR < 0.80R, preferably 0.30R < AR < 0.70R and more preferably 0.40R < AR < 0.60R.

[0370] In an embodiment, the blade may include a pitchable outer part, which part may not be fixed near the center of rotation at r<0.20R and instead may be fixed at a radial position of 0.25R or larger. This has advantages: the pitchable outer part becomes shorter in length and possibly also in chord direction compared to a state-of-the-art blade ranging from about 0.05R to R. The pitchable outer part will be easier to produce, handle and transport. Also, the closer to the rotor center, the higher the bending moments exerted by the blade and having the outer blade part fixed at a larger relative radial position may take out the part with largest bending moments which may be the most expensive part and the part containing most composite. If the outer blade part may be fixed to a pitch bearing which may be installed at a larger radial position, then the pitch bearing may be loaded less and may be cheaper compared to a state-of-the-art pitch bearing installed at a radial position of less than 0.2R.

[0371] To reduce the flapwise bending moments caused by the aerodynamic forces on the blades, the inventor realized that a truss structure in the center of the rotor may connect each blade to the hub. In one embodiment the truss structure comprises a main rod and a forward rod between the hub and the pitchable outer blade part. In an embodiment the main and / orthe forward rod may be aerodynamically shaped so that the aerodynamic drag is low.

[0372] In an embodiment a distance, “d”, between a position of centre of the main rod where it is connected to the hub and a position of the centre of the forward rod where it is connected to the hub is at least 4%R, preferably at least 6%R and more preferably at least 8%R. In an embodiment the distance d is less than 20%R and preferably less than 15%R and more preferably less than 12%R. A distance d of more than 4%R and less than 20%R, e.g. of 10%R is advantageous since the root of large state-of-the-art wind turbine blades is approximately 3%R, so that a distance of 10%R provides already more than a factor of 3 building height so that flapwise bending moments can be resisted with approximately a factor of 3 less material, which saves costs.

[0373] In one embodiment there may be smaller rods connecting the main rod and the forward rod to add resistance to buckling.

[0374] In an embodiment the main rod and the forward rod are made of steel and preferably of high tension steel. It is an insight of the inventor that steel for said rods in the truss structure is advantageous when combined with tangential stay or rods between the joints of the outer blade parts. The stay effectively absorbs the additional bending moments which would appear due to the higher weight of steel compared to composite. The use of steel has the advantages of lower cost and better recyclability.

[0375] A calculation revealed that a rotor with blades with, e.g., a length of 0.7R, ranging from OAR to 1 .1 R produces 7% more energy and has lower costs of the blades and of the pitch bearings, compared to a rotor with blades of 0.95R length, ranging from 0.05R to R, where R refers to the radius of the latter conventional rotor. A blade ranging from OAR to 1 .1 R may also be cheaperthan 19 / 09 / 2025

[0376] 29 a blade ranging from 0.05R to R. The structure needed to replace the ‘taken out’ blade root between about .05R and 0.4R in this example, may be cheaper than the ‘taken out’ blade root.

[0377] In an embodiment, a HAT includes a rotor, wherein the bending induced forces by the blade may be reduced by the application of stay. In an embodiment a stay and a blade may be connected by a stay holder at a radial position between 0.25R and 0.65R, the stay holder preferably being fixed to the blade in a pivotable manner, which allows the blade to pitch over at least 30°, preferably at least 60°, more preferably by at least 90°.

[0378] Regarding the production, transportation and installation of blades, problems tend to get bigger with increasing turbine sizes and sometimes it can be practically impossible to reach certain HAT sides. Advantageously, in an embodiment, using a larger number of blades with a shorter chord and / or using blades with a shorter length may be less expensive compared to the smaller number of traditional blades with larger chords and / or longer length.

[0379] In an embodiment with a rotor with a truss structure and with blades of a reduced length, there may be further advantage during the rotor installation and during the production and transportation of the blades. The outer blade parts of the present disclosure may have less weight less length and easier and cheaper production compared to state-of-the-art blades.

[0380] In an embodiment of a rotor with more than three blades, when 1 blade of a rotor with more than 3 blades is installed, the rotor unbalance may be less than when 1 blade of a rotor with 2 or 3 blades is installed. It may be, with just 1 blade installed, easierto turn the rotorto an azimuth position wherein a next blade can be installed. With a three bladed rotor it is a problem to turn the rotor with two of the three blades installed to a favorable position to install the third blade due to the rotor unbalance. This problem may be reduced with a rotor with more than 3 blades. If for example a rotor has five blades, with positions 1 to 5 e.g. with increasing azimuth angle, the first blade being installed at position 1 , then the next blade can be installed at position 3, so that again the unbalance may be less compared to the situation when 2 blades may be installed of a 3 bladed rotor. In a method of installing a HAT with more than 3 blades, after the first blade is installed to the rotor, a second blade is installed at a rotor position which is not adjacent to the already installed first blade.

[0381] In an embodiment the pitch mechanism of the outer blade part has two pitch bearing per blade, the pitch bearings at a mutual distance in blade longitudinal direction so that the blade bending moments can be transferred with a low building height which is aerodynamically advantageous. In an embodiment the diameter of the pitch bearing of the outer blade part is less than 1 %R, preferably less than 0.75%R and more preferably less than 0.5%R.

[0382] The rotation speed of the second rotor is, when in use, designed to be higher than that of the first rotor. The first rotor may be any rotor for a HAT turbine. The second rotor may be any rotor for a HAT turbine, for example a conventional one.

[0383] In the centre of the rotor, the second rotor can capture the wind energy with a lower solidity than the rotor if it has a higher rotation speed. E.g. when the second rotor reaches to 0.5R and has double the rotation speed of the rotor, then, according to equation 7, the needed combined chord 19 / 09 / 2025

[0384] 30 is about a quarter compared to the needed combined chord of the rotor. So, by using a faster rotating smaller second rotor in the rotor centre, the SOLrotor can be reduced which may have several advantages such as inter alia: lower storm loads, reduced blade length, less composite needed.

[0385] In an embodiment, the second rotor may directly generate energy via a connection to a generator.

[0386] In an embodiment, the second rotor may be designed to spin freely and to not produce a useful torque, so that Cp may be about 0. In an embodiment the second rotor is designed to have, in use, an axial force coefficient higher than 0.6, preferably higher than 1.0, more preferably higher than 1.2, more preferably higher than 1.5 and preferably lower than 2.2.

[0387] In operation the second free spinning rotor only decelerates the wind or even blocks it almost completely, so that the wind is forced to flow around the swept area of the second rotor and thus into that of the larger first rotor. The first rotor may be optimized for capturing maximum energy in combination with the blocking properties of the second rotor. So also the swept area of the second rotor contributes to the energy production. The captured energy may be about equal to a state-of-the-art turbine, even when the second rotor does not directly produce useful energy. The second rotor may include a brake and / or the blades may be pitch controlled, so that it may be stopped in case of high wind speeds.

[0388] In an embodiment the control of the HAT may be as follows: At cut-in wind speed, both rotors may start, the first rotor produces energy and the second rotor spins freely with an axial force coefficient larger than 0.6. The second rotor may deliver torque to a generator or may be free spinning. When the maximum power of the HAT is approached, the second rotor may be halted using the brake and / or the pitch drives. The second rotor no longer blocks the wind and no longer directs wind into about the radial range between R2 and R of the first rotor, so the power by the first rotor is reduced. The wind can flow with little obstruction through the swept area of the second rotor. Because the first rotor is still decelerating the wind, it may cause an increase of the air flow through the rotor center or through the swept area of the second rotor. At the cut-out wind speed also the first rotor may be stopped.

[0389] In one embodiment the dual rotor system has advantages without the complexity of a drive train to capture the energy from the torque of the second rotor.

[0390] In an embodiment the number of blades of the second rotor may be not equal to that of the large rotor, which has the advantages of less resonance and / or less sound.

[0391] In an embodiment the first rotor has two blades and the second three blades.

[0392] Both the first rotor and the smaller second may include pitch-controlled blades. The center of the first rotor may be ‘covered’ by the swept area of the second rotor and therefore does not need a certain chord lengths to capture wind power. Therefore, the center of the first rotor can be optimized structurally to minimize bending moments and to only provide for the fixation of the blades. A truss structure may be used. Since it rotating when in use, it should be shaped so that 19 / 09 / 2025

[0393] 31 the aerodynamic drag is low. Because of this the first rotor may have a lower solidity below r=R2 and therefore has lower storm loads and may be controlled more easily.

[0394] In an embodiment, a control problem with state-of-the-art rotors may be addressed. A control problem may occur in the wind speed range in between the rated wind speed and the cutout wind speed. In this range the rotor blades may typically be pitched to vane to control the power not to exceed a maximum power of the generator and / or not to exceed certain maximum load levels. Just before the cut-out wind speed the blades may typically be pitched to vane such that the blade tips have negative lift and accelerate the wind and absorb power or in other words produce negative power. The more inward blade range may produce more power than the maximum allowable. The total power then equals the sum of the power produced by the more inward blade part and the negative power by the tips, which may be the maximum power that the generator absorbs. This situation may be load dimensioning: the tip may be bended in the opposite direction compared to operation below the rated wind speed and the tips may even get stalled causing high loads. This negative effect may be the consequence of pitching an entire blade as one piece over its full length with the blade root attached close to the center of rotation and the tip reaching R.

[0395] In an embodiment, the above control problem may be reduced by a HAT including at least a first blade which may be member of a first rotor and a second blade which may be member of a second rotor, wherein the first blade reaches to radial position R and the second blade reaches to radial position R2. The first blade may be designed for a first range of rotation speeds and the second blade may be designed for a second range of rotation speeds. Advantageously, in these embodiments the first and the second blades may be controlled independently, so that the above control problem may be reduced. The first rotor may be optimized to extract energy from the flow in the range from radial position R2 to radial position R, while the second rotor may be designed to extract wind energy in the radial range below R2. The first and the second rotor may rotate about the same axis.

[0396] In an embodiment wherein the rotor the above control problem is reduced since the inward blade range will produce less power due to the low solidity ratio.

[0397] In an embodiment wherein the rotor has pitchable outer blade parts and a second smaller rotor in the rotor centre, the above control problem is reduced since the second rotor will be halted and / or controlled do that is will not produce overpower.

[0398] In an example embodiment the rotor with blades extending to 0.90R may have variable speed stall control. The low chords and low chord ratios reduce the rotor solidity and therefore reduce survival wind speed loads. This advantage may be used to use variable speed stall to control the rotor and to avoid overloading and / or overpowering and leads to the additional advantage of not needing pitch control and thus saving the pitch mechanism and maintenance thereof.

[0399] An advantage of pultruded tower sections is that they can be stiff while light in weight. As a result, the tower sections can be relatively thin, resulting in less shadow and thus lower visibility, 19 / 09 / 2025

[0400] 32 i.e. , it may contribute to reducing environmental hindrance. Another advantage of using pultruded tower sections is that it may influence wind to a lesser extent, resulting in a slight increase in the yield of the turbine. Moreover, the sound impact due to the blades crossing the pressure I velocity field around the tower sections may be reduced. Yet another advantage of pultruded tower sections is that when the tower is tilted to the ground, e.g., for maintenance purposes, then the weight of the tower, in particular the weight at high altitude, may be reduced.

[0401] In an embodiment the HAT wind turbine may have a tower which has a towertop diameter of less than 3.5%R, preferably less than 3.0%R, preferably less than 2.5%R and more preferably less than 2.0%R.

[0402] Thus, it has been found that the present disclosure provides even more advantages. Embodiments of the present disclosure can remarkably and advantageously contribute to addressing multiple sources of environmental hindrance while improving the yield over cost ratio of the HAT for any one or more of the reasons: (i) reduced tip losses; (ii) less downtime because of less hindrance; (iii) a better ratio between yield and storm loads due to the lower solidity and / or a lower ratio of SOIO 25R / SOIO 7SR; (iv) a higher efficiency because of the double rotor concept; (v) a cheaper rotor because of the truss structure and / or the stays and / or the outer blade parts being small compared to state-or-the-art blades; (vi) less manufacturing costs because of using pultruded blade sections and / or blades of reduced length and / or reduced chord; (vii) a control advantage during a storm; (viii) easier logistics, installation and blade production because of reduced blade length and or blade chord; (ix) less rotor unbalance during installation and (x) less composite waste at the end of the lifetime of the blades.

[0403] Table 1 below shows example types of environmental hindrance in the column ‘Hindrance’. In the column ‘Measure’, measures are given that may attenuate the specified type of hindrance. The measure may have a consequential impact on the HAT design, examples of which are presented in the column ‘Consequence’. For example, cast shadow hindrance may be attenuated by using blades with a reduced chord (measure: ‘shorter chord’), with as consequence that the number of blades N is preferably increased (‘larger N’) to keep the HAT efficiency high, based on, e.g. equation 7. The cast shadow hindrance also is reduced by a lower solidity ratio, such as avgsol 25R / avgsol 75R or avgsol 35R / avgsol 75R, since this implies a reduction of the local chord near at respectively the radial positions 0.25R and 0.35R and thus reduces cast shadow. A higher Adesign leads less cast shadow since SOLROTOR will reduce because with increasing Adesign the combined chord reduces according to equations 6 and 7. Another example concerns the hindrance of bird casualties, which may be attenuated by the measures: lower Adesign and / or a larger N. A consequence of a lower Adesign may be, e.g. following equation 7 with Ar= Adesign- r / R, an increase of the combined chord NrCr (‘larger NrCr‘). A larger combined chord may be solved by a larger N (‘larger Nrcr— > larger N’). Other example hindrances, measures and consequences can be read from table 1.

[0404] Hindrance Measure Consequence 19 / 09 / 2025 cast shadow shorter chord larger N lower solidity ratio lower SOLrotor higher Adesign lower N impairment of tranquil landscape shorter chord larger Nrcrlower solidity ratio lower SOLrotor yield of crops or solar plants Lower SOLRotor lower solidity ratio, higher Adesign shorter chord larger N noise sound pressure level SPL lower Adesign larger NrCr — > larger N noise AM larger N shorter chord noise infrasound shorter chord larger N bird casualties lower Adesign larger Nrcr—> larger N larger N lower SOLrotor lower solidity ratio composite waste of blades lower solidity ratio lower SOLrotor truss structure in center second smaller rotor coaxial rotors

[0405] Table 1: insights of the inventor regarding hindrance and efficiency.

[0406] From table 1 it can be seen that certain measures are in contradiction. For example, a lower design will reduce the sound pressure level but simultaneously increases the cast shadow, so it depends on the situation what design to choose.

[0407] An amazing conclusion of the inventor is that reducing the solidity ratio may be advantageous for most listed hindrances. And this insight may imply, assuming that Adesign remains about the same.

[0408] It has been found that reducing the diameter D of a conventional wind turbine is not a meaningful measure to reduce hindrance since the yield would reduce approximately with the square of the diameter. Therefore, the present disclosure aims to improve large sized HAT wind turbines and medium sized HAT wind turbines.

[0409] In an embodiment, the blade includes a pitchable outer part which is not fixed near the center of rotation at r < 0.05R or r < 0.20R, but instead at a radial position of 0.075R or larger. By removing or significantly reducing the innermost blade part, which normally exhibits the largest chord and experiences the highest root bending moments, this portion may be eliminated or reduced in size. As a result, the loads transmitted through the pitch bearing may be reduced, allowing the bearing to be lighter and less costly. The pitchable outer part may also become shorter in both length and chord, which may simplify production, handling and transport and may reduce the use of composite material, thereby reducing composite waste.

[0410] This measure may also reduce the solidity ratio sol0.25R / sol0.75R, which in conventional turbines is relatively high due to the large chord at 0.25R. A lower ratio indicates that the inner blade contributes less solidity compared to the outer blade region. Such a reduction in solidity may lead to improved survival behaviour under storm conditions and may diminish the risk of bird casualties, since storm loads and bird casualties are partly proportional to rotor solidity. The corresponding reduction in yield near the root may be marginal, as most power is harvested at larger radii, whereas the reduction in loads and cost may be substantial, thereby improving the yield-to-cost ratio. 19 / 09 / 2025

[0411] 34

[0412] In another embodiment, the rotor is equipped with more than three blades, each with a reduced chord compared to conventional three-bladed rotors. This design may distribute the aerodynamic loading more evenly around the azimuth. The shorter chords may generate thinner boundary layers which may shift the noise spectrum towards higher frequencies, which do attenuate faster in the atmosphere so that the sound pressure level may reduce. Furthermore, the noise emission may become more even around the azimuth, which may reduce amplitude modulation (“whooshing”). Because the blades are more slender, they may cover less of the sun, which may result in reduced cast shadow. The blades may appear in the landscape under a smaller observer angle and may disappear from sight at a shorter observer distance, leading to less visual impact. The increased blade count may make the swept area appear as a more continuous surface to birds, which may discourage flight through the rotor plane. The combined effect may be a rotor that is quieter, safer for birds, and structurally more balanced. Also the strength of tip vortices may be less with a higher blade count, which may further reduces bird casualties.

[0413] A principle insight of the inventor is that optimizing the energy capture of the parts of the blades which have a low speed (close to the rotor axis) is disadvantageous and that accepting a dsign further away from the optimum axial induction of 0.3 may be advantageous any of the following reasons: reduced storm loads and improved survival in extreme wind events, lower composite consumption, cheaper pitch bearings, easier transport and installation due to shorter, lighter blades, reduced visual hindrance and fewer bird collisions. Description of the Drawings

[0414] Fig. 1 shows an embodiment of an onshore HAT 1 with a rotor 2 designed to minimize environmental hindrance, e.g., by reducing noise and / or reducing cast shadow, while achieving a high yield over cost ratio. In this example, the rotor has a radius 3 and seven blades 4, a tower 5, a nacelle 6 and a hub 7. Each blade has length L 8, local chord 9 and maximum chord 10. The direction wherein the rotor turns is indicated by arrow 11 . The onshore turbine may be fixed to the ground 12 by any state-of-the-art foundation, which is not drawn.

[0415] Fig. 2 shows an embodiment of an offshore HAT 21 with an upwind rotor 22 with five blades 23 and a diameter D 33. The rotor may be designed to minimize environmental hindrance, e.g., by generating low noise and low cast shadow, while achieving a high yield over cost ratio. A blade 23 may include a pultruded aerodynamic inner part 24, which in this example also has the maximum chord 29, a pultruded middle part 25, a pultruded outer part 26 and a tip 27. The parts of the blade 23 may be made by injection molding or by 3D-pri nting , or by any conventional method. The offshore turbine may be positioned on a tower 5 which crosses the seawater surface 30 and continues as monopile foundation 32 which is fixed in the seabed 31 .

[0416] Fig. 3 shows an embodiment of an onshore HAT 41 with a rotor 42 designed for operating at a relatively low tip speed ratio A, so that the number of blades may be relatively high; in this case there are seven large blades 43 and seven shorter blades 44 in the same rotor 42. So NO SR=7 and NO 3R=14. For one large blade and one small blade it is indicated that there may be a pultruded inner part 45, a pultruded middle part 46 and a tip 47. In this example, the lower tip speed ratio may reduce the noise level of the turbine even further. Also, the lower tip speed and the relatively 19 / 09 / 2025

[0417] 35 large number of blades may reduce the probability of collision with birds. Also, the larger number of blades may reduce the noise: it may reduce the low frequency noise and it may reduce AM noise.

[0418] Fig. 4 shows a graph of a conventional distribution 50 of the local chord versus radial position and several limit lines for the local chord in an embodiment. In an embodiment, the local chord distribution of a blade stays under limit line 51 , wherein ciimit = 5.5%R -3.5 / 85(r-15%R), with the remark that the local chord may be above the line over a radial length of maximally 5%R. All shown limit lines may be valid for r = 15%R to R. Other limit lines 52, 53, 54, 55, 56, 57, 58 are respectively corresponding to the equations ciimit = 5%R - 3 / 85(r-15%R), ciimit = 4.5%R - 2.5 / 85(r- 15%R), ciimit = 4%R - 2.0 / 85(r-15%R), ciimit = 3.5%R - 1 ,5 / 85(r-15%R), Ciimit = 3.0%R - 1 / 85(r- 15%R), ciimit = 2.5%R - 0.5 / 85(r-15%R) and ciimit = 2.0%R.

[0419] Analogous to an embodiment explained by fig 4, in an embodiment, crmay be below 5.5%R - 2.5 / 85*(r-15%R), for r = 15%R to R. In an embodiment, crmay be below 5%R - 2.0 / 85*(r- 15%R), for r = 15%R to R. In an embodiment, crmay be below 4.5%R - 1 ,5 / 85*(r-15%R), for r = 15%R to R. In an embodiment, crmay be below 4%R - 1 ,0 / 85*(r-15%R), for r = 15%R to R. In an embodiment, crmay be below 3.5%R - 0.5 / 85*(r-15%R), for r = 15%R to R.

[0420] Fig. 5 shows anothergraph of a conventional distribution 60 ofthe local chord versus radial position and several limit lines for the local chord in an embodiment. In an embodiment, the local chord distribution of a blade stays under limit line 61 wherein ciimit = 5.5%R -4.0 / 85(r-15%R), with the remark that the local chord may be above the line over a radial length of maximally 5%R. All shown limit lines may be valid for r = 15%R to R. Other limit lines 62, 63, 64, 65, 66, 67, 68, 69 are respectively corresponding to the equations ciimit = 5.0%R - 3.5 / 85(r-15%R), ciimit = 4.5%R - 3.0 / 85(r-15%R), ciimit = 4.0%R - 2.5 / 85(r-15%R), ciimit = 3.5%R - 2.0 / 85(r-15%R), ciimit = 3.0%R - 1.5 / 85(r-15%R), ciimit = 2.5%R - 1 ,0 / 85(r-15%R), ), Ciimit = 2.0%R - 0.5 / 85(r-15%R) and ciimit = 1 ,5%R.

[0421] Fig .6 shows an embodiment of an onshore HAT 91 with a dual rotor 92. In this example, the dual rotor includes a first rotor of radius R with seven blades 93 and a second rotor of radius R2 96 with three blades 97. The first rotor blades have a local chord 94 and a maximum chord 95. In this example, for the blade of the first rotor pointing vertically upward, an inner pultruded part 100, outboard pultruded part 101 and tip 102 are indicated. The smaller rotor blade of the second rotor may be connected to hub 98 and may rotate in direction 99.

[0422] Fig. 7 shows an embodiment of an onshore HAT 1 11 with a rotor with stay 112. In this example, the rotor has seven blades 113 which may be connected to the hub 7. There may be any other number of blades 113, e.g., two, three or five blades. In this example avgsol 25R / avgsol 75R and avgsol 35R / avgsol 75R may be about 1 + 30%. The bending moments on the blades may lead efficiently to the hub via one or more stays. In an embodiment, the blades may be interconnected with tangential stays 114, the tangential stays 114 being arranged substantially within the same plane as the blades 113 of the rotor. In an embodiment, each blade may be fixed to the hub in forward direction with a stay 115. Herein, the forward direction is defined as the direction away 19 / 09 / 2025

[0423] 36 from the plane of the blades 113 and away from the nacelle 6. The hub 7 may include a rod shaped element extending in the forward direction for fixing the stay 115 in the forward direction. In an embodiment, each blade may be fixed in backward direction with a stay 116. Herein, the backward direction is defined as the direction away from the plane of the blades 113 and towards the nacelle 6. The stay 115 and 116 may be radial stays, meaning that the extend mainly in radial direction. In an embodiment, the stays to a blade may come together at one point 1 17, also called a blade joint, where they may be fixed to the blade with a stay holder. Such stay holder may be designed such that the blade may pitch over at least 30 degrees, preferably at least 60 degrees and more preferably at least 90 degrees. An example of cross section Ill-Il l including a stay holder is shown in Fig. 8.

[0424] In the embodiment of Fig. 7, the blades 113 are preferably fixed to the hub at a close distance to the nacelle 6, e.g., within 0.1 R distance from the nacelle 6. A larger distance between the fixation points of the blades 113 at the hub 7 and the nacelle 6 may result in stress on the hub 7 due to the weight of the rotor and blades 113. Consequently, the stays 1 15 are preferably fixed to the hub 7 in the forward direction, as described above.

[0425] In an embodiment the HAT 111 may have blades 1 13 which comprise an inner part between the hub and the radial position of the tangential stay and an outer part with a radial range outside of the tangential stay 114. The outer part could be fixed to a pitch bearing near the radial position of the tangential stay.

[0426] Fig. 8 shows an example of the cross section Ill-Ill of blade 1 13 in Fig. 7. Fig. 8 shows an airfoil 131 in work position. With fixation point 132 it is fixed to the stay holder 135 in a manner such that it may rotate around axis 134 from work position 131 to vane position 133. The stay holder may be connected to the tangential stays 1 14, to the forward stay 115 and to the backstay 1 16, and may include a shock absorber 136 to avoid damage to the blade.

[0427] Fig. 9 shows an embodiment of a large HAT or a medium HAT, in this example an offshore HAT 151 , with a downwind three bladed large rotor 152. There may be any other number of blades, e.g., two, five or seven blades. In this example avgsol 25R / avgsol 75R and avgsol 35R / avgsol 75R may be about 0.5. The large rotor includes blades 154; one of the blades is shown cut-off at position

[0428] 155 for illustration purposes. In this example, the blades may include pultruded sections of four different sizes, from the tip to the root the sections 155, 156, 157 and 158 have a stepwise increasing chord, although other configurations of the blades are possible. The rotor 152 may have a truss structure at its inside with tangential connections 156, forward rods 157 and main rods 160. The truss structure connects the outer blade parts 154 to the hub 7. The tangential connections

[0429] 156 are arranged between the outer blade parts 154 of the rotor 152. The hub 7 may include a rod shaped element extending in the forward direction forfixing the forward rods 157. The forward rods

[0430] 157 may connect the hub 7 to the outer blade parts 154 in the forward direction. Herein, the forward direction is defined as the direction away from the plane of the blades 154 and away from the nacelle 6. The main rods 160 may be connected at one end to the hub 7 and at the other end to 19 / 09 / 2025

[0431] 37 the outer blade part 154. For each blade 154, the outer blade 154, a main rod 160 and a forward rod 157 and the rotation axis are preferably arranged within a same plane.

[0432] The tangential connections 156 may be implemented as tangential rods, such as shown in Fig. 9. Alternatively, the tangential connections 156 may be implemented as tangential stays 114, such as shown in Fig. 7.

[0433] A pitch mechanism may be installed at connection points 159, also called blade joints, or in the hub and may drive the blades via the main rods 160 or via a cylinder inside the main rods 160.

[0434] In an embodiment, one or more of the rods of the truss structure may have a cross section with an aerodynamic shape to, when in use, reduce drag, in particular the radial connections, e.g., the main rods 160 and / or the forward rods 157, may be designed to contribute to the aerodynamic lift. The contribution to the aerodynamic lift by the aerodynamically shaped rods of the truss structure is designed to be limited in accordance with the solutions provided by the present disclosure. E.g., the rotor 152 including the truss structure may have an average radial solidity avgsol 25R in the radial range from 0.2R to 0.3R and an average radial solidity avgsol 75R in the radial range from 0.7R to 0.8R, such that the ratio between the average radial solidities avgsol 25R / avgsol 75R is one of: less than 2.00; less than 1 .75; less than 1 .50; less than 1 .25; less than 1 .00; less than 0.90; less than 0.75; less than 0.50; and less than 0.25. Herein, the radial range from 0.2R to 0.3R is within the truss structure while the range from 0.7R to 0.8R is within the area covered by the outer blade parts 154. The rods may be compression elements, which can be loaded with compression and tension.

[0435] In an embodiment, one or more rods (157, 160) of the truss structure may have an aerodynamic cross-section so that they may contribute to lift and power generation of the rotor (152). These aerodynamic rods may either be fixed to operate in stall control or may include pitch control, while the outer blade parts have independent pitch control. Stall control of the inboard truss section may be advantageous because it avoids the need for pitch devices in this region and may improve survival behaviour. In survival wind conditions, the truss airfoils may remain fixed in a stalled position while the outboard blade parts are pitched to vane, ensuring that the inboard and outboard regions do not develop maximum lift or maximum drag simultaneously, which may reduce dimensioning load cases and thus saves cost. The rods (157, 160) may themselves have an aerodynamic cross-section, or they may be provided with a cover that gives them an aerodynamic cross-section.

[0436] In the embodiment of Fig. 9, the longitudinal axis of the main rods 160 is within a distance of 0.1 R and preferably 0.05R and more preferably 0.03R of the longitudinal axis of the tower 5, which is advantageous since a larger distance may result to higher loads on the main shaft and / or to the yaw bearings due to the larger overhang of the weight of the rotor and blades 1 13. The forward rods 157 are preferably fixed to the hub 7 in the forward direction, as described above.

[0437] In an embodiment, the rotor may include an outer blade part (154), which may be the only part of that blade. A truss structure in a center of the rotor may connect each outer blade part to a 19 / 09 / 2025

[0438] 38 hub (7). The truss structure may include main rods (160) connecting each of the outer blade parts to the hub. The truss structure may further include tangential connections (156) between ends of the truss structure, wherein said tangential connections do not connect the outer blade parts to each other, so as not to impede pitching of the outer blade parts. The main rods may be made so that they enable access through the rods to the pitch bearings

[0439] The blades 154 may be pre-bent, so that with increasing distance from the fixation point, the blade bends away from the tower, when it is in work position below rated wind speed.

[0440] Advantageously, the truss structure of the HAT 151 of Fig. 9 allows the rotor area contributing to the wind yield to be large, i.e . , resulting in a large HAT or medium HAT, while the blades 154 are relatively short. I.e., the blades 154 only start at the edge of the truss structure, leaving an, relatively small, aerodynamic gap in the area covered by the truss structure.

[0441] Note that a small wind turbine would not benefit from a truss structure as shown in Fig. 9, as weight of the rotor, tip speed or hindrance is less of an issue with small wind turbines.

[0442] In an embodiment the smaller second rotor can be installed to the hub 7 of the rotor, outside of the forward rods 157.

[0443] Fig. 10 shows another embodiment of a large HAT or a medium HAT, e.g., an offshore HAT 151 similar to Fig. 9. In this embodiment however it also includes an upwind small second rotor 153, in this example a three-bladed small rotor 153, however any other number of blades may be used on the small rotor 153. In this example, the small rotor 153 has blades 161 , which may be made of one or more pultruded sections 162, 163, 164, 165, 166 and 167, although other configurations of the blades 161 are possible. The blades 161 may be fixed to the hub 7 or to a second hub 168, wherein a pitch mechanism may be placed as well as a brake. Small rotor 153 may be designed to contribute to the generated power directly via a mechanical link to a generator and possibly to the generator of the large rotor. In a non-limiting preferred embodiment, the small rotor only serves to close the aerodynamic gap in the center of the large rotor 152, e.g., covering or partially covering the truss structure area of the rotor 152., by exerting an axial force blocking the wind. The small rotor 153 may be designed to have a high blockage by free spinning. Fig. 1 1 shows an embodiment of an onshore HAT 181 with a rotor 182 with eleven blades 183. The blades may include two pultruded sections: an inward section 185 and an outward section 184. The HAT 181 may be designed for a relatively low tip speed ratio of e.g., 6, such that it has a low sound level and may have a low risk for bird collisions.

[0444] Fig. 12 shows an example graph of cast shadow by a conventional blade passage 191 compared to that of the passage of a blade in an embodiment 192 at a distance of about 2D behind the wind turbine. On the y-axis is the ratio of the light intensity in the shadow over that without shadow. The conventional blade passage reaches core shadow when the intensity ratio becomes l / lo = 0.1 , equal to the indirect sunlight intensity ratio. On the x-axis the position of the passing blade is expressed in unit of the solar angle of 0.50°. In an embodiment, the cast shadow of the blade may be about half as wide and half as deep. The local chord of the conventional blade which passes the sun is about 10%R and the local chord of the blade in the embodiment is about 3.5%R. 19 / 09 / 2025

[0445] 39

[0446] Fig. 13 shows an example graph of the variation of SPL caused by individual blade passages. Curve 194 is the variation for a conventional HAT with three blades and shows an amplitude of about 6dB. In an embodiment, the number of blades of the HAT may be five and a reduced amplitude modulation may follow curve 195. In another embodiment, the number of blades may be seven and the amplitude modulation may almost vanish as shown by curve 196.

[0447] Fig. 14 shows another graph of a conventional distribution 250 of a local chord versus radial position and several limit lines 251-258 for a local chord in an embodiment. In an embodiment, the local chord distribution of a blade stays under limit line 251 , wh with the remark that the local chord may be above the line over a radial length All shown limit lines may be valid for r = 15%R to R. Limit lines 251 , 252, 253, 258 are respectively corresponding to the equations 4.5

[0448] Fig. 15 shows an embodiment of an onshore HAT 271 with a rotor 272 with five blades 273. In this example, each blade includes one pultruded twisted aerodynamic section which extends over at least 60%R. A blade 273 may optionally be equipped with lift coefficient increasing devices such as vortex generators and / or chord extensions and / or a gurney flap. In the example of Fig. 21 , the tower 274 may include one or more pultruded sections 275 which may exists of carbon fiber. The figure also shows the sun 276, which is only covered for a small fraction, and thus the cast shadow will be reduced, thanks to the slender blades 273.

[0449] Fig. 16 shows of a conventional distribution 280 of a combined chord Nrcrversus radial position and several limit lines 281 -288 for a local combined chord in an embodiment. For example, in an embodiment, the local combined chord distribution of a blade stays under limit line 281 , wherein NrCiimit = 16.5%R. All shown limit lines may be valid for r = 15%R to R. Limit lines 282, 283, 284, 285, 286, 287 and 288 are respectively corresponding to the 15.0%R, 6.0%R. For example, when a HAT has a largest rotor of 200m diameter with 7 blades reaching 0.9R and which blades have a local chord of 2m overthe full span, then Nrcr= 7 x 2m = 14m, which corresponds to 14%R, so that the design is below limit lines 181 and above limit lines 282-288.

[0450] Fig. 17 shows of a conventional distribution 290 of a combined chord Nrcrversus radial position and several limit lines 291 -298 for a local combined chord in an embodiment. For example, in an embodiment, the local combined chord distribution of a blade stays under limit line 291 , Nciimit = 16.5%R -10.5 / 85(r-15%R). All shown limit lines may be valid for r = 15%R to R. Other limit lines 292, 293, 294, 295, 296, 297 and 298 are respectively corresponding to the equations

[0451] Fig. 18 shows of a conventional distribution 300 of a combined chord Nrcrversus radial position and several limit lines 301 -309 for a local combined chord in an embodiment. For example, in an embodiment, the local combined chord distribution of a blade stays under limit line 301 , 19 / 09 / 2025

[0452] 40

[0453] = 16.5%R -12 / 85(r-15%R). All shown limit lines may be valid for r = 15%R to R. Other limit lines 302, 303, 304, 305, 306, 307 and 308 are respectively corresponding to the equations 15%R) and NrCiimit = 4.5%R. For example, when a HAT has a largest rotor of 200m diameter, which rotor has 5 blades reaching 0.9R and which blades have a local chord of 1 m at R linearly increasing to 3m at 0.15R, then at 0.75R the local chord is found by linear interpolation and is (Nrcr= 5 x 1.59m = 7.9m, which corresponds to 7.9%R, so that the design is below limit lines 301 and 302 and above limit lines 303-309.

[0454] The combined chord limits imply that crreduces by increasing Nrand since it has been explained that reducing crleads inter alia to less optical hindrance, the combined chord limit is a useful parameter.

[0455] Where in the above example embodiments a blade is described to include one or more pultruded sections, it is to be understood that a blade may alternatively be made as a conventional blade in one piece, and vice versa.

[0456] In the description above, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of implementations of the disclosed technology. It will be apparent, however, to one skilled in the art that embodiments of the disclosed technology may be practiced without some of these specific details.

[0457] Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope thereof.

[0458] Gustave Paul Corten, Msc nuclear engineering and PhD wind turbine aerodynamics is the author, illustrator and inventor of this disclosure. Considered names of a HAT according to the invention may be AmiWind or Ami Wind Turbine or Wind Turbine Amiable or Corten Wnd Turbine or wind turbine with a Corten rotor or CINIC Wind Turbine, CINIC being an abbreviation for Corten no Noise no Cast shadow.

[0459] In certain embodiments of an offshore HAT, the rotor may have a SOLrotor of less than 0.030, for example less than 0.025, 0.016, 0.014, 0.012, 0.011 . 0.010, 0.009, 0.008, 0.007, or less than 0.006.

[0460] In certain embodiments of a large onshore HAT, the rotor may have a of less than 0.030, for example less than 0.025, 0.018, 0.016, 0.014, 0.012, 0.011 , 0.010, 0.009, 0.008, or less than 0.007.

[0461] In certain embodiments of a medium onshore HAT, the rotor may have a of less than 0.030, for example less than 0.025, 0.022, 0.017, 0.016, 0.014, 0.012, 0.011 , 0.010 and 0.009. 19 / 09 / 2025

[0462] 41

[0463] The low SOLrotor can be obtained by using a design higherthan for example 6, 7, 8 or 9, by further using airfoils with a high &, design of above for example 1 .2, 1 .4, 1 .6, 1 .8 or above 2.0 and by reducing the chord of the largest rotor at radial positions below for example 0.3R, OAR, 0.5R or 0.6R to far below the chord needed for maximum energy extraction, thus to designs with an axial induction factor far below the optimum of 0.33.

[0464] In an embodiment, the blade may include a pitchable outer part, which part may not be fixed near the center of rotation at r<0.05R and instead may be fixed at a radial position larger than 0.05R, for example 0.075R, 0.10R, 0.15R or largerthan 0.20R. Positioning the pitch bearing further outward reduces bearing loads and shortens the blade, with minimal impact on yield. Any minor yield loss can be offset by extending the blade at the tip.

[0465] In one embodiment, one or more tension members are arranged in the truss structure to reduce structural loading. The tension members may be realized as cables made from materials of high specific strength and fatigue resistance. Suitable examples include carbon fiber reinforced polymer (CFRP), aramid fibers (e.g., Kevlar® or Twaron®), and ultra-high molecular weight polyethylene (UHMWPE, e.g., Dyneema®). Alternatively, high-grade steel may be employed, for example in the form of a locked-coil cable or spiral strand.

[0466] The cable may be provided with a protective sheath of polymer material such as polyethylene (PE) or polyurethane (PU), configured to protect against ultraviolet radiation, moisture ingress, and erosion. The sheath may further comprise aerodynamic shaping or surface features, such as a streamlined fairing, helical strakes, or hydrophobic surface treatment, for reducing wind- induced vibrations including vortex-induced vibrations (VIV) and rain-wind vibrations (RWIV).

[0467] To ensure structural reliability, the cable may be pre-tensioned such that a positive tensile force remains across a complete rotor revolution. The system may further comprise a compliance element or load-limiting device arranged in-line with the cable to accommodate cyclic tension variations arising from blade gravity and rotor dynamics, thereby maintaining a tension-tension load regime. When the cables are anchored to steel structural members, a thermal-expansion compensation device and / or an adjustable tensioning mechanism may be provided to maintain the cable force within prescribed limits across temperature variations.

[0468] Each cable may be terminated in a socket configured to transfer axial loads without inducing bending. In one embodiment, the socket comprises a conical anchoring section extending over a multiple of the cable diameter, and a spherical articulation arranged in series with the socket to accommodate angular misalignment. The termination may be realized as a bonded (potted) cone, a wedge-type cone with a compliant liner, or, in the case of steel cables, a spelter socket or swaged fitting. Sealing features may be incorporated to prevent moisture ingress, and dielectric isolation layers may be provided to avoid galvanic interaction between composite cables and adjacent steel components.

[0469] A tensioning device, such as a screw turnbuckle or a hydraulic jack with locking collar, may be arranged in series with the cable termination to set and re-adjust pre-tension. In some 19 / 09 / 2025

[0470] 42 embodiments, a compliance or damping element, for example a visco-elastic cartridge or tuned mass damper, may be integrated in-line with the cable or arranged adjacent to the termination.

[0471] The cable system may further include a lightning conduction facility integrated in or along the cable, for example in the form of an electrically conductive strand or parallel conductor connected to ground. Embedded monitoring means, such as fiber-optic strain sensors or electrical load sensors, may be provided within the cable or termination for continuous measurement of tension and strain during operation.

Claims

AMENDED CLAIMSreceived by the International Bureau on 18 May 2026 (18.05.2026).

1. [Amended] A horizontal axis wind turbine, HAT wind turbine (1 , 21 , 41 , 91 , 111 , 151 , 181), for a bulk production of electricity from wind, comprising a tower (5), a nacelle (6), a generator, a rotor (2, 22, 42, 92, 112, 152, 182), and a blade (4, 23, 43, 93, 113, 154, 183), the rotor being rotatable about a rotor axis by the wind and having at least two blades, the rotor having a rotor solidity SOLrotor of maximally 0.05, the rotor configured to have a design tip speed ratio design of at least 4, and an electric power coefficient CPE of at least 0.30, the rotor having a radius R (3) and a diameter D (33) which is at least 50m, the rotor further having an average radial solidity avgsol 25R in the radial range from 0.2R to 0.3R, and an average radial solidity avgsol 75R in the radial range from 0.7R to 0.8R, wherein the ratio between the average radial solidities avgsol 25R / avgsol75R is one of:less than 1.50;less than 1.25;less than 1.00;less than 0.90;less than 0.75;less than 0.50; andless than 0.25.

2. [Original] The HAT wind turbine according to claim 1 , the rotor further having an average radial solidity avgsol35R in the radial range from 0.3R to OAR, wherein the ratio between the average radial solidities avgsol 35R and avgsoksR, avgsohsR / avgsoksR is one of:less than 2.00;less than 1.75;less than 1.50;less than 1.25;less than 1.00;less than 0.90;less than 0.75;less than 0.50; andless than 0.25.

3. [Original] The HAT wind turbine according to any one of the preceding claims, wherein an average radial solidity of the rotor at r=0.35R, avgsol 35R, is one of: less than 0.030; less than 0.025; less than 0.020; less than 0.015; less than 0.010 and less than 0.005.

4. [Original] The HAT wind turbine according to any one of the preceding claims, the rotor having a rotor solidity, SOLrotor, which is less than,in case of an offshore HAT one of: 0.016; 0.014; 0.012; 0.011 ; 0.010; 0.009; 0.008; 0.007; and 0.006, orin case of a large onshore HAT one of: 0.018; 0.016; 0.014; 0.012; 0.011 ; 0.010; 0.009; 0.008; and 0.007, orin case of a medium HAT one of: 0.030; 0.022; 0.017; 0.014; 0.012; 0.011 and 0.010.

5. [Original] The HAT wind turbine according to any of the preceding claims, the rotor having a design tip speed ratio, Adesign, and a rotor solidity SOLrotor, which is less than a limit f1 / Adesign2, wherein a factor f1 is one of:1.4;1.3;1.2;1.1 ; and1.0,and / or wherein SOLrotor is large r th an f1 / Adesign2with f1=0.8.

6. [Original] The HAT wind turbine according to any one of the preceding claims, the rotor having a design tip speed ratio, Adesign, and an average radial solidity at r=0.35R, avgsol 35R of less than a limit f2 / Adesign2,wherein a factor f2 is one of:1.7;1.5;1 3;1.1 ;0.9;0.7; and7. [Original] The HAT wind turbine according to any one of the preceding claims, the blade having a distribution of a local chord cr(9, 28, 94) versus a radial position r, wherein the local chord crin the radial range from r = 15%R to R is one of:below 9%R;below 8%R;below 7%R;below 5.5%R;below 5%R;below 4.5%R;below 4%R;below 3.5%R;below 3%R;below 2.5%R;below 2%R; andbelow 1 ,5%R,or one of:below 5.5%R - 2.5 / 85*(r-15%R);below 5%R - 2 / 85*(r-15%R);below 4.5%R - 1 ,5 / 85*(r-15%R);below 4%R - 1 / 85*(r-15%R); andbelow 3.5%R - 0.5 / 85*(r-15%R),or one of:below 5.5%R - 3.5 / 85*(r-15%R);below 5%R - 3 / 85*(r-15%R);below 4.5%R - 2.5 / 85*(r-15%R);below 4%R - 2 / 85*(r-15%R);below 3.5%R - 1 ,5 / 85*(r-15%R);below 3%R - 1 / 85*(r-15%R); andbelow 2.5%R - 0.5 / 85*(r-15%R),or one of:below 5.5%R - 4.0 / 85*(r-15%R);below 5%R - 3.5 / 85*(r-15%R);below 4.5%R - 3.0 / 85*(r-15%R);below 4%R - 2.5 / 85*(r-15%R);below 3.5%R - 2.0 / 85*(r-15%R); andbelow 3%R - 1 ,5 / 85*(r-15%R).below 2.5%R - 1 ,0 / 85*(r-15%R).below 2%R - 0.5 / 85*(r-15%R).

8. [Original] The HAT wind turbine according to any one of the preceding claims, wherein the number of blades of the rotor, which blades reach at least a radial position of one of: 0.70R; and 0.90R is one of: exactly 2 blades; exactly 3 blades; exactly 4 blades; exactly 5 blades; exactly 6 blades; exactly 7 blades; exactly 11 blades; at least 3 blades; at least 4 blades; at least 5 blades; at least 7 blades; and at least 11 blades and / or one of: maximally 7 blades; maximally 11 blades; maximally 17 blades; and maximally 43 blades.

9. [Original] The HAT wind turbine according to any one of the preceding claims, the rotor having a diameter D = 2R, the diameter being one of: at least 70m; at least 100m; at least 140m; at least 200m; at least 300m and at least 450m.

10. [Original] The HAT wind turbine (151) according to any one of the preceding claims, wherein the blade comprises an outer blade part and wherein a truss structure in a center of the rotor (152) connects each outer blade part (154) to a hub (7), the truss structure comprising: main rods (160) connecting each of the outer blade parts (154) to the hub (7); tangential connections (114, 156) connecting to two adjacent outer blade parts (154); and forward rods (157) connecting the hub (7) to the outer blade parts (156) in a forward direction, the forward direction being defined as a direction away from the plane of the blades (154) and away from the nacelle (6),wherein for each outer blade part (154) said outer blade part (154), a main rod (160) and a forward rod (157) and the rotor axis are arranged within a same plane.

11. [Original] The HAT wind turbine (151) according to claim 10,wherein one or more of the main rods (160), the tangential connections (156) and the forward rods (157) are aerodynamically shaped.

12. [Original] The HAT wind turbine (151) according to claim 10 or claim 11, wherein the distance between the longitudinal axis of the main rods (160) and the longitudinal axis of the tower (5) are at a distance of less than 0.1R and preferably less than 0.05R and more preferably less than 0.03R.

13. [Original] The HAT wind turbine (151) according to any one of the claims 10-12, further comprising a small rotor (153) coaxially arranged with the rotor (152), the small rotor (153) being rotatable about a further rotor axis by the wind and having at least two blades (161), wherein the blades (161) of the small rotor (153) cover an inner area of the rotor (152) in a projection perpendicular to the rotor axis.

14. [Original] The HAT wind turbine according to any one of the claims 10-13, wherein the truss structure comprises a blade joint, a hub joint, and one of: a compression member, wherein ablade joint is connected to a hub joint by two compression members (156, 157, 160) or by one compression member and one stay rod and in particular wherein a blade joint of a first blade is connected to a blade joint of an adjacent second blade joint by a compression member or by a rod.

15. [Original] The HAT wind turbine according to any one of the preceding claims, wherein the rotor comprises a first blade and a second blade, wherein the first blade and the second blade have a tangential connection (114, 156) at a radial position AR, wherein:one of: AR > 0.20R; AR > 0.30R; AR > 0.40R; and AR > 0.45R, and / orone of: AR < 080R; AR < 0.70R; AR < 0.60R; and AR < 0.50R, and / orone of: 0.20R < AR < 0.80R; 0.30R < AR < 0.70R; and 0.40R < AR < 0.60R.

16. [Original] The HAT wind turbine according to any one of the preceding claims, wherein a part of the blade is fixed to a pitch bearing (159), wherein the pitch bearing is located at a radial position largerthan one of: 0.05R; 0.075R; 0.10R; 0.15R; 0.20R; 0.25R; 0.3R; 0.35R; OAR; 0.45R, 0.5R; and 0.55R,and / or smaller than one of: 0.6R; and 0.7R.

17. [Original] The HAT wind turbine according to any one of the preceding claims, comprising a first blade and a second blade, wherein the first blade is part of the rotor and reaches to radial position R and the second blade is part of a second coaxial rotor and reaches to radial position R2, wherein:one of: R2 < 0.80R; R2 < 0.70R; R2 < 0.60R; and R2 < 0.55R, and / orone of: R2 > 0.25R; R2 > 0.30R; R2 > 0.35R; R2 > 0.40R; and R2 > 0.45 and / or one of: 0.25R < R2< 0.80R; 0.30R < R2< 0.70R; 0.35R < R2< 0.60R; 0.40R < R2< 0.55R; and 0.55R < R2 < 0.75R.

18. [Original] The HAT wind turbine according to claim 17, wherein the second rotor is designed to spin freely and to not produce a useful torque, so that Cp is about 0, and is further designed to have, when in use, an axial force coefficient, CD, ax, being one of: CD, ax > 0.6; CD, ax > 1.0; CD, ax > 1.2; CD, ax > 1.5; CD, ax < 2.2.

19. [Original] The HAT wind turbine according to any one of the preceding claims, wherein one or more of:the HAT wind turbine is an onshore turbine or an offshore turbine;the HAT wind turbine is grid connected or is stand alone;the HAT wind turbine has exactly one rotor;the HAT wind turbine has exactly one largest rotor of radius R and exactly one second coaxial rotor of radius R2;the HAT has two rotors which are coaxial and which rotate in the same direction;the rotor may be upwind ordownwind relative to the tower;the generator is of the direct drive type or of the geared type;the rotor comprises a ring-shaped structure extending in radial direction to less than 20%R; the rotor does not comprise a ring shaped structure;the generator is using super conduction;the rotor drives a hydraulic transmission;the rotor comprises an airfoil with a relative thickness t / c of 30% or more;the rotor comprises an airfoil with camber;the rotor comprises vortex generators;the rotor comprises an airfoil with a design lift coefficient cl of 1.5 or larger; and the rotor comprises a blade section having a weight percentage of carbon fibers of 10% or more.

20. [Original] The HAT wind turbine according to any one of the preceding claims, wherein the rotor with radius R has a distribution of a combined chord Nrcr(9, 28, 94) versus a radial position r, wherein the combined chord Nrcrin the radial range from r = 15%R to R is one of:below 16.5%R;below 15.0%R;below 13.5%R;below 12.0%R;below 10.5%R;below 9.0%R;below 7.5%R;below 6.0%R; andbelow 4.5%Ror one of:below 16.5%R - 7.5 / 85*(r-15%R);below 15.0%R - 6.0 / 85*(r-15%R);below 13.5%R - 4.5 / 85*(r-15%R);below 12.0%R - 3.0 / 85*(r-15%R); andb<IMG file=null he=null id=imgf000006_0001 img-content=null img-format=null inline=null orientation=null wi=null>elow 10.5%R - 1 ,5 / 85*(r-15%R),or one of:below 16.5%R - 10.5 / 85*(r-15%R);below 15.0%R - 9.0 / 85*(r-15%R);below 13.5%R - 7.5 / 85*(r-15%R);below 12.0%R - 6.0 / 85*(r-15%R);below 10.5%R - 4.5 / 85*(r-15%R);below 9.0%R - 3.0 / 85*(r-15%R); andb<IMG file=null he=null id=imgf000006_0002 img-content=null img-format=null inline=null orientation=null wi=null>elow 7.5%R - 1 ,5 / 85*(r-15%R),or one of:below 16.5%R - 12.0 / 85*(M5%R);below 15.0%R - 10.5 / 85*(M5%R);below 13.5%R - 9.0 / 85*(r-15%R);below 12.0%R - 7.5 / 85*(r-15%R);below 10.5%R - 6.0 / 85*(r-15%R);below 9.0%R - 4.5 / 85*(r-15%R);below 7.5%R - 3.0 / 85*(r-15%R); andb<IMG file=null he=null id=imgf000007_0001 img-content=null img-format=null inline=null orientation=null wi=null>elow 6.0%R - 1 ,5 / 85*(r-15%R).

21. [Original] The HAT wind turbine according to any one of the preceding claims, the rotor having N blades reaching a radial position of at least 0.9R, the HAT wind turbine further having a second rotor of radius R2, the second rotor being smaller and coaxial with the rotor, the second rotor having N2 blades reaching a radial position of O.9R2,wherein the number of blades N of the rotor and N2 of the second rotor is respectively one of:N=2 and N2=3;N=3 and N2=2;N=3 and N2=5;N=5 and N2=3; andN=7 and N2=3.

22. [Original] A blade (97, 161) designed for free spinning to block the wind without producing a useful torque, the blade having a length of at least one of: 10m; 20m; 50m; 70m; and 100m and in particular wherein the blade is designed to be applied fora HAT wind turbine (91, 151).

23. [Original] A method for adapting an existing horizontal axis wind turbine, HAT wind turbine, the method comprising:removing a rotor from the existing HAT wind turbine; andinstalling a new rotor so that the wind turbine becomes the HAT wind turbine (1, 21, 41, 91 , 111 , 151 , 181) according to any one of the claims 1-21.

24. [Original] A method for extraction of useful power from wind using the HAT wind turbine according to any one of the claims 1-21, the method comprising:causing the wind to rotate the rotor of the HAT wind turbine around a rotor axis; and converting torque from the rotor of the HAT wind turbine into electric energy using the generator of the HAT wind turbine.

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