EP4652369A1 - Efficient wind turbine amiable - Google Patents

Abstract

A HAT wind turbine (151 ) for the production of electricity from wind, comprising a tower (5), a nacelle (6), a generator and a rotor (152), the rotor being rotatable about a rotor axis by the wind, the rotor having a rotor solidity SOLrotor of maximally 0.10 and the rotor having a radius R, the rotor further having an average chord avgsol.25R in the radial range from 0.15R to 0.35R, and an average chord avgsol.?5R in the radial range from 0.65R to 0.85R, wherein the rotor comprises a number of blades (4, 23, 43, 44, 93, 1 13, 154, 183) N of at least 2, which reach at least a radial position of 0.90R, wherein the blades have a distribution of a local chord cr (9, 28, 94) versus a radial position r, wherein the local chord cr in 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%R; below 2%R; and below 1,5%R, and 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

EFFICIENT WIND TURBINE AMIABLE

Field The present invention relates to a horizontal axis wind turbine (HAT), a blade tor 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.

Background

Wind energy is increasingly contributing to the world energy production and has become one of the cheapest sour ces of clean and renewable energy . This success has led to the installation of many wind turbines al! 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. 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 ofthe rotor, depending on the size of the HAT. This visibility of the moving rotors is often experienced as disturbing the tranquility of the landscape.

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 and crops, which are dependent on the amount of received sunlight.

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.

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 salves 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.

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 targe chord near the 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, toe 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 'nub, remain about the same compared to one rotor HATs. Because the blade root banding 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, toe 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 mots of the large rotor causes additional noise and toe 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.

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.

Summary of the Invention

The present disclosure aims to provide a wind turbine of the Horizontal Axis Turbine type (hereinafter 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 (ha efficiency of the state-or-the-art HAT.

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, large wind turbines, with a rotor diameter of 100m or more, 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 advantageous if in particular the wind turbines of 100m diameter and more, would cause less hindrance. 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 shorter chords and possibly more of such blades to address the following sources of hindrance: (i) cast shadow; (ii) disturbance of the tranquil landscape; (iii) reduction of yield of solar farms or craps (iv) average sound pressure; (v) sound amplitude modulation; (vi) infrasound: and/or (vii) bird casualties. In addition, it may simplify the transportation and the Installation of a blade and may lead to a higher yield ever cost ratio of the wind turbine.

According to an aspect of the disclosure, a HAT for the 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 SOL_rotor of maximally 0.10. The rotor has a radius R and a diameter D. The diameter D may be 100m or more. The rotor may include a number of blades N, wherein N may be at least 4. The rotor may further include a largest chord of a blade, wherein this largest chord may be less than 12%R, or less than 11 %R, or less than 10%R, or less than 9%R or less than 8%R. According to an aspect of the disclosure, a HAT for toe production of electricity from wind is proposed. Ths 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 SOL_rotor of maximally 0.10. The rotor has a radius R, The rotor may include a number of blades N, which reach at least a radial position of 0.90R, wherein N may be at least 4. The blades may have a distribution of a local chord c_r versus a radial position r, wherein the local chord c_r In the radial range from r = 15%R to R may be below 5.5%R.

According to an aspect of the disclosure, a HAT for the 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 SOL_rotor of maximally 0.10. The rotor has a radius R, 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 blades may have a distribution of a local chord c_r versus a radial position r, wherein the local chord c_r in the radial range from r = 15%R to R may be below 9%R. The rotor may further have an average radial solidity averaged over the radial range from 0.15R to 0.35R “avgsoI_.25R” and an average radial solidity averaged over the radial range from 0.65R to 0.85R “avgsoI_.75R”, wherein avgsol_.25R /avgsoI_.75R may be less than 2,00.

The rotor may further have an average radial solidity averaged over the radial range from 0,15R to 0.35R “avgsoI_.25R” and an average radial solidity averaged over the radial range from 0.65R to 0.85R “avgsoI_.75R”

In an embodiment, avgsol_.25R /avgsoI_.75R may be less than 2.00.

In an embodiment, avgsol_.25R /avgsoI_.75R may be less than 1 .75.

In an embodiment, avgsol_.25R /avgsoI_.75R may be less than 1.50.

In an embodiment, avgsol_.25R /avgsoI_.75R may be less than 1,25. In an embodiment, avgsol_.25R /avgsoI_.75R may be less than 1 ,

In an embodiment, avgsol_.25R /avgsoI_.75R may be less than 0.9.

In an embodiment, avgsol_.25R /avgsoI_.75R may be less than 0,75, In an embodiment, avgsol_.25R /avgsoI_.75R may be less than 0.5. tn an embodiment, avgsol_.25R /avgsoI_.75R may be less than 0,25.

The rotor may further have an average radial solidity averaged over the radial range from 0.25R to 0.45R “avgsoI_.35R”.

In an embodiment, avgsoI_.35R /avgsoI_.75R may he less than 1 .75.

In an embodiment, avgsoI_.35R /avgsoI_.75R may be less than 1.50. In an embodiment, avgsoI_.35R /avgsoI_.75R may be less than 1.25. in an embodiment, avgsoI_.35R /avgsoI_.75R may be less than 1.

In an embodiment, avgsoI_.35R /avgsoI_.75R may be and less than 0.9. in an embodiment, avgsoI_.35R /avgsoI_.75R may be less than 0.75.

In an embodiment, avgsoI_.35R /avgsoI_.75R may be less than 0.5. In an embodiment, avgsoI_.35R /avgsoI_.75R may be less than 0.25.

The rotor may have a radial solidity at radial position 0.25R, sol_.25R and a radial solidity at a radial position 0.75R, sol_.75R. The ratio between those radial solidities may be expressed as sol_.25R/sol_.75R

In an exampie embodiment, sol_.25R/sol_.75R, may be less than 2.00, In an example embodiment, sol_.25R/sol_.75R, may be less than 1 .75.

In an example embodiment, sol_.25R/sol_.75R, may be less than 1.50.

In an exampie embodiment, sol_.25R/sol_.75R, may be less than 1 .25.

In an exampie embodiment, sol_.25R/sol_.75R, may be less than 1 .00.

In an example embodiment, sol_.25R/sol_.75R, may be less than 0.90. In an exampie embodiment, sol_.25R/sol_.75R, may be less than 0.75. in an example embodiment, sol_.25R/sol_.75R, may be less than 0.50.

In an example embodiment, sol_.25R/sol_.75R, may be less than 0.25.

In an embodiment, c_r may be below 8%R, for r = 15%R to R.

In an embodiment, c_r may be below 7%R, for r = 15%R to R. In ah embodiment, c_r may be below 5.5%R, for r = 15%R to R.

In an embodiment, c_r may be below 5%R, for r = 15%R to R, In an embodiment, c_r may be below 4.5%R, for r = 15%R to R. In an embodiment, c_r may be below 4%R, for r = 15%R to R, In an embodiment, c_r may be below 3%R, for r = 15%R to R. In an embodiment, c_r may be below 2%R, for r = 15%R to R.

In an embodiment, c_r may be below 1.5%R, for r = 15%R ta R. in an embodiment, c_r may be below 5.5%R - 2.5/85*(r-15%R), for r = 15%R to R.

In an embodiment, c_r may be below 5%R - 2/85*(r-15%R), for r = 15%R to R,

In an embodiment, c_r may be below 4,5%R - 1.5/85*(r-15%R), for r = 15%R to R, In an embodiment, c_r may be below 4%R - 1/85*(r-15%R), for r = 15%R to R.

In an embodiment, c_r may be below 3.5%R - 0.5/85*(r-15%R), for r = 15%R to R. in an embodiment, c_r may be below 5.5%R - 3,5/85*(r-15%R). for r = 15%R to R. In an embodiment, c_r may be below 5%R - 3/85*(r-15%R), for r = 15%R to R, In an embodiment, c_r may be below 4.5%R - 2.5/85*(r-1S%R), for r = 15%R to R.

In an embodiment, c_r may be below 4%R - 2/85*(r-15%R), for r = 15%R to R, in an embodiment, c_r may be below 3.5%R - 1.5/85*(r-15%R), for r = 15%R to R. In an embodiment, c_r may be below 3%R - 1/85*(r-15%R), for r = 15%R to R, In an embodiment, c_r may be below 2.5%R - 0.5/85*(r-15%R), for r = 15%R to R, In an embodiment, c_r may be below 5.5%R - 4.0/85*(r-15%R). for r = 15%R to R.

In an embodiment, c_r may be below 5%R - 3.5/85*(r-15%R), for r = 15%R to R. tn an embodiment, c_r may be below 4,S%R - 3.0/85*(r-15%R), for r = 15%R to R. In an embodiment, o_r may be below 4%R - 2,5/85*(r-15%R), for r = 15%R to R.

In an embodiment, c_r may be below 3.5%R - 2.0/85*(r-15%R), for r = 15%R to R, In an embodiment, c_r may be below 3%R - 1 .5/85*(r-15%R), for r = 15%R to R,

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

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

In an embodiment, the HAT may include at least S blades, which reach at least a radial position r of one of: 0.70R; and 0 90R.

In an embodiment, the HAT may include at least 7 blades, which reach at least a radial position r of one of; 0.70R; and 0.90R,

In an embodiment, the HAT may include at ieast 11 blades, which reach at least a radial position r of one of: 0.70R; and 0,90R. In an embodiment, the number of blades N may be maximally 7, which reach at ieast a radial position r of one of: 0.70R; and 0.90R,

In an embodiment, the number of blades N may be maximally 11 , which reach at least a radial position r of one of; 0.70R; and 0.90R. in an embodiment, the number of blades N may be maximally 17, which reach at least a radial position r of one of; 0.70R; and 0.90R. in an embodiment, the number of blades N may be maximally 43. which reach at least a radial position r of one of: 0.70R; and 0.90R. in an example embodiment, the number of blades N may equal a prime number at a radial position r of one of: 0.70R; and 0.90R, in an exampie embodiment, N may be 4. in another example embodiment, N may be 5. in another example embodiment, N may be 6. In another example embodiment, N may be 7, In an example embodiment N may be 11 .

In an embodiment, the diameter D may be at least 5m.

In an embodiment, the diameter D may be at least 10m,

In an embodiment, the diameter D may be at least 20m.

In an embodiment, the diameter D may be at least 40m,

In an embodiment, the diameter D may be at least 70m,

In an embodiment, the diameter D may be at least 100m,

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

In an embodiment, the diameter D may be at ieast 200m. in an embodiment, the diameter D may be smaller than 40 m and at least 3m.

In an embodiment, the diameter D may be smaller than 40 m and at least 5m. in an embodiment, the diameter D may be smaller than 40 m and at least 10m.

In an embodiment, the diameter D may be smaller than 40 m and at least 25m.

In an embodiment, the rotor may be designed to have a C_P of at least 0.35.

In an embodiment, the rotor may be designed to have a C_P of at least 0,40,

In an embodiment, the rotor may be designed to have a C_P of at least 0.45.

In an embodiment, the rotor may be designed to have a C_PE of at least 0.35,

In an embodiment, the rotor may be designed to have a C_PE of at least 0.40.

In an embodiment, the rotor may be designed to have a C_PE of at least 0.45.

The values for C_P of some embodiments may be low compared to those of large state of the art HATs which have C_P values often above 0.45. This may be explained by the iow chords used by some embodiments so that less energy may be captured near the rotor center. The yield over cost ratio may be more relevant and may be higher versus that of large state of the art HATs. in an embodiment, the rotor may be configured for a maximum solidity, SOL_rotor, of 0.07.

In an embodiment, the rotor may be configured for a maximum solidity, SOL_rotor, of 0.05.

In an embodiment, the rotor may be configured for a maximum solidity, SOL_rotor, of 0.04.

In an embodiment, the rotor may be configured for a maximum solidity, SOL_rotor, of 0.035.

In an embodiment, the rotor may be configured for a maximum solidity, SOL_rotor, of 0.03.

In an embodiment, avgsol_.25R, may be less than 0.06,

In an embodiment, avgsol_.25R, may be less than 0.05.

In an embodiment, avgsol_.25R, may be less than 0.04.

In an embodiment, avgsol_.25R, may be less than 0.03.

In an embodiment, the rotor may be configured with a design tip speed ratio, λ_design= ωR/U, wherein λ_design of less than 9.

In an embodiment, the rotor may be configured with a λ_design of less than 8.

In an embodiment, the rotor may be configured with a λ_design of less than 7.

In an embodiment, the rotor may be configured with a λ_design of l ess than 6. In an embodiment, the rotor may be configured with a λ_design of less than 5.

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 at a radial position R3,

In an embodiment, one of the following may apply: R3 > 0.20R; R3 > 0.30R; R3 > 0.40R; or R3 > 0.45R.

In an embodiment, one of the following may apply: R3 < 080R; R3 < 0.7DR; R3 < 0.60R; or R3 < 0.50R.

In an embodiment, one of the following may apply: 0.20R < R3 < 0.80R; 0.30R < R3 < 0.70R; or 0.40R < R3 < 0.60R. In an embodiment, the HAT may further include a stay and a stay holder. A biade, the stay and the stay holder may be connected at a radial position between 0.25R and 0.85R. The stay holder may be connected to the blade in a pivotable manner at a joint so that the blade may pitch about the joint over at least 30º, Alternatively, the biade may pitch about the joint over at least 60°. Alternatively, the blade may pitch about the joint over at least 90°, In an embodiment, a truss structure in a center of the rotor may connect a blade to a hub.

The truss structure may include a blade joint and a hub joint which may be connected by one of. two compression members; a compression member and a stay. A pitchable blade may be connected to a pitch bearing at a blade joint. A blade joint may be connected to a blade joint of an adjacent blade by a compression member or by a stay, In an embodiment, the rotor blades may have no structural support outward of a radial position of 70%R, For example: there may not be structural support from compression members or stay beyond 70%R to the blade, ft has been found that support in this range decreases aerodynamic performance and thus is a disadvantage.

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.

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

In an embodiment, the pitch bearing may be located at a radial position of larger than 0.25R and less than 0.6R.

In an embodiment, the pitch bearing may be located at a radial position of larger than 0.3R and less than 0.8R,

In an embodiment, the pitch bearing may bo located at a radial position of larger than 0.35R and less than 0.6R, in an embodiment, the pitch bearing may be located at a radial position of larger than 0,4R and less than 0.6R.

In an embodiment, the pitch bearing may be located at a radial position of larger than 0.45R and less than 0.6R. 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.

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

In an embodiment, one of the following may apply: 0.25R < R2 < 0.70R; 0.30R < R2 < 0.80R: 0.35R < R2 < 0.55R: or 0.40R < R2 < 0.55R.

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.

In an embodiment, the second rotor may further be designed to have, when in use, an axial force coefficient, One of the following may apply to the second rotor when spinning freely:

In an embodiment the HAT has a blade including a pultruded aerodynamic profile with a length of one of: at least 50%R; at least 60%R; at least 70%R; and at least 80%R.

In an embodiment said pultruded airfoil may have twist, may have vortex generators and may have gurney flaps,

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.

In an embodiment, D may be larger than 1m and smaller than 50m. The HAT may include a tail vane surface to align the rotor with the wind. A part of the tail vane surface may be fixed in a hinged manner. The fixation of the part in a hinged manner may mean that the part may pivot relative to the nacelle depending on the wind forces on said part. The tail vane surface may be larger than πR²/10. Alternatively, the tail vane may be larger than πR²/5. Alternatively, the tai! vane may be larger than πR²/2. Alternatively, the tai! vane may be larger than Alternatively, the tail vane may be larger than ¾D². Alternatively, the tail vane may be larger than D². Alternatively, the tail vane may be larger than 1½D².

Irt an embodiment, the HAT may be an onshore turbine.

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

In an embodiment, the HAT may be grid connected. In an embodiment, the HAT may be stand alone.

In ah embodiment, the HAT may have exactly one rotor.

In an embodiment, the HAT may have exactly one largest rotor of radius R and exactly one second coaxial rotor of radius R2. in an embodiment the HAT may have two rotors which are coaxial arid which rotate in the same direction. 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 siender blades with the small chord vaiues 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.

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

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

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

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

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

In an embodiment, the generator may be using super conduction. In an embodiment, the rotor may drive a hydraulic transmission.

In an embodiment the mechanical power may be converted first into hydraulic power which subsequently may be converted to electric power.

In an embodiment, the rotor the rotor comprises a ring-shaped structure extending in radial direction to less than 20%R ; In another embodiment, the rotor may not comprise a ring-shaped structure. in an embodiment, the rotor may comprise an airfoil with a relative thickness t/c of 30% or more.

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

In an embodiment, a vortex generator may be attached to the rotor. In an embodiment, the rotor may comprise an airfoil with a design lift coefficient ci.design of

1.5 or larger.

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

In an embodiment, the rotor may be of the fast runner type and may be configured with a design tip speed ratio, λ_design, wherein λ_design may be more than 4.

In an embodiment, the rotor may be of the fast runner type and may be configured with a design tip speed ratio, λ_design, wherein λ_design may be more than 5. in an embodiment, the rotor may be of the fast runner type and may be configured with a design tip speed ratio, λ_design, wherein λ_design may be more than 6. in an embodiment the combined chord may be below 16.5%R.

In an embodiment, may be below 15%R, for r = 15%R to R. in an embodiment, may be below 13.5%R, for r = 15%R to R. in an embodiment, may be below 12.0%R, for r = 15%R to R.

In an embodiment, may be below 10.5%R, for r = 15%R to R. In an embodiment, may be below 9.0%R, for r = 15%R to R. to an embodiment, may be below 7.5%R, for r = 15%R to R. In an embodiment, may be below 6.0%R, for r = 15%R to R. to an embodiment, may be below 16.5%R - 7.5/85*(r-15%R), for r = 15%R to R. In an embodiment, may be below 15%R - 6.0/85*(r-15%R), for r = 15%R to R. to an embodiment, may be below 13.5%R - 4.5/85*(r-15%R), for r = 15%R to R. to an embodiment, may be below 12%R - 3.0/85*(r-15%R), for r = 15%R to R. in an embodiment, may be below 16.5%R - 10.5/85*(r-15%R), for r = 15%R to R.

In an embodiment, may be below 15%R - 9.0/85*(r-15%R), for r = 15%R to R. lo an embodiment, may be below 13.5%R - 7.5/85*(r-15%R), for r = 15%R to R.

In an embodiment, may be below 12.0%R - 6.0/85*(r-15%R), for r = 15%R to R. in an embodiment, may be below 10.5%R - 4.5/85*(r-15%R), for r = 15%R to R.

In an embodiment, may be below 9.0%R - 3.0/85*(r-15%R), for r = 15%R to R, In an embodiment. may be below 7.5%R - 1 .5/85*(r-15%R), for r = 15%R to R. In an embodiment, may be below 16.5%R - 12,0/85*(r-15%R), for r = 15%R to R.

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

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

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

In an embodiment, may be below 10.5%R - 6.0/85*(r-15%R), for r - 15%R to R. In an embodiment, may be below 9.0%R - 4.5/85*(r-15%R), for r = 15%R to R. in an embodiment, may be below 7.5%R- 3.0/85*(r-15%R), for r = 15%R to R. 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 limitfog line over a range of maximally 5%R. This may serve to compensate for, s.g., blade connections, which may lead to an Increase of the combined chord over less than 5% radial range.

According to an aspect of the disclosure, a blade may be proposed for use in a rotor of a HAT for extraction of useful power from wind. The blade may be rotatable around a shaft of the HAT by the wind. The blade may have a distribution of a local chord c_L versus a blade length position I from L=0 at the blade root to L=100% at a blade tip, wherein the local chord c_L for I = 15%L to L may be below 5,5%L. A ratio of a local chord at blade length position 0.25L, sol_0.25L, and a chord at blade length position 0.75L, sol_0.75L , expressed as sol_0.25L/ sol_0.75L , may be less than 2.00.

In an embodiment, c_L for I = 15%L to L may be below 5%L

In an embodiment, c_L for I = 15%L to L may be below 4.5%L. in an embodiment, c_L for i = 15%L to L may be below 4%L tn an embodiment, c_L for I = 15%L to L may be below 3%L. in an embodiment, c_L for I = 15%L to L may be below 2%L.

In an embodiment, c_L for I = 15%L to L may be below 1 .5%L. in an embodiment, c_L for I = 15%L to I. may be below 5.5%L - 2.5/85*(l-15%L). In an embodiment, c_L for I = 15%t. to L may be below 5%L - 2/85*(l-15%L). in an embodiment, c_L for I = 15%L to L may be below 4.5%L - 1.5/85*(l-15%L). in an embodiment, c_L for I = 1 S%L to L may be below 4%L - 1 ,5/85*(l-15%L). in an embodiment, c_L for I = 15%L to L may be below 3.5%L - 0.5/85*(l-15%L). In an embodiment, c_L for I = 15%L to L may be below 5.5%L - 3.5/85*(l-15%L).

In an embodiment, c_L for I = 15%L to L may be below 5%L - 3/85*(l-15%L).

In an embodiment, c_L for I = 15%L to L may be below 4.5%L - 2,5/85*(I-15%L). tn an embodiment, c_L for I = 15%L to L may be bsiow 4%L - 2/85*(l*15%L).

In an embodiment, c_L for I = 15%L to L may be below 3.5% - 1.5/85*(l-15%L), In an embodiment, c_L for I = 15%L to L may be below 3%L - 1/85*(l-15%L).

In an embodiment, c_L for I = 15%L to L may be below 2.5%L - 0.5/85*(l-15%L). in an embodiment, c_L for i = 15%L to L may be below 2%L.

In an embodiment, c_L for I = 15%L to L may be below 5.5%L - 4.0/85*(l-15%L). in an embodiment, c_L for l = 15%L to L may be below 5%L - 3,5/85*(l-15%L). In an embodiment, c_L for I = 15%L to L may be below 4.5%L - 3.0/85*(l-15%L).

In an embodiment, c_L for I = 15%L to L may be below 4%L - 2.5/85*(l-15%L), In an embodiment, c_L for I = 15%L to L may be below 3.5%L - 2.0/85*(l-15%L). In an embodiment, c_L for I = 15%L to L may be below 3%L - 1.5/85*(l-15%L). In an embodiment, c_L for I = 15%L to L may be below 1.5%L. In an example embodiment, sol_0.25L/ sol_0.75L may be less than 1 ,75,

In an example embodiment, sol_0.25L/ sol_0.75L may be less than 1.50. In an example embodiment, sol_0.25L/ sol_0.75L may be less than 1 ,25, In an example embodiment, sol_0.25L/ sol_0.75L may be less than 1.00. In an example embodiment, sol_0.25L/ sol_0.75L may be less than 0,90. In one embodiment the blade according to the invention may be made out of one piece with a length of at least one of: 40m, 60m, 80m, 100m, The slenderness of such a blade may be advantageous because the shorter chord may ba easier to transport and the slenderness may make It more easy io bend.

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 dr more of the features described above.

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 shaft. The method may further Include converting torque from a rotor of the HAT Into electric energy using a generator of the HAT. in the following part of the description, embodiments of the present disclosure may be described, by way of example only. Brief Description of the Drawings

Some embodiments are illustrated by the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, in which: Fig, 1 shows an onshore upwind HAT with seven blades;

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

Fig, 3 shows an onshore upwind HAT with seven blades and seven shorter blades;

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

Fig. 5 shows a local chord distribution and limits of an embodiment; Fig. 6 shows an onshore HAT with seven blades and a second rotor with three blades;

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

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

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

Fig. 10 shows an offshore HAT with a large downwind rotor and a small upwind rotor; Fig. 11 shows a small onshore eleven bladed rotor with a large tail vane;

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

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

Fig, 14 shows a pultruded twisted airfoil section with integrated structural elements;

Fig. 15 shows a pultruded airfoil section with cuts to decrease torsion stiffness; Fig. 16 shows an airfoil with transparent serrations;

Fig. 17 shows an airfoil with a sharp trailing edge;

Fig. 18 shows an airfoil with vortex generators;

Fig. 19 shows an improved vortex generator pair;

Fig. 20 shows a local chord distribution and limits of an embodiment; Fig. 21 shows a tiltable HAT with five pultruded twisted blades.

Fig, 22 shows a combined chord and limits of an embodiment.

Fig. 23 shows a combined chord and limits of an embodiment. Fig. 24 shows a combined chord and limits of an embodiment.

Detailed Description

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. The figures and described embodiments are intended for illustrative purposes only, and do not serve as restriction of the scope of the protection as laid down by the claims. The drawings are not drawn to scale unless specifically Indicated,

The scope of the invention is indicated by the appended claims rather than by this detailed description. All changes within the meaning and range of equivalency of the claims are regarded to be covered by the claims.

Reference throughout this specification to features, advantages, or similar language does not imply that all the features and advantages that may be realized with the present invention should be or are in any single exampie of the invention. Rather, language referring to the features and advantages may be understood to mean that a specific feature, advantage, or characteristic described in connection with an embodiment may be included in at least one embodiment of the present invention. Thus, discussions of the features and advantages, and similar language, throughout this specification may, but do not necessarily, refer to the same example.

Furthermore, the described features, advantages, and characteristics of the invention may be combined in any suitable manner in an embodiment. One skilled in the relevant art will recognize, considering the description herein, that the invention can be practiced without one or more of the specific features or advantages of a particular embodiment. In other instances, additional features arid advantages may be recognized in certain embodiments that may not be present in all embodiments of the invention. Reference throughout this specification to "one embodiment," "an embodiment," or similar language means that a particular feature, structure, or characteristic described in connection with the indicated embodiment is included in at least one embodiment of the present invention. Thus, the phrases "in one embodiment," "in an embodiment," and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment

Used terminology

The faitowing tenminaiogy are used throughout the present disclosure.

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 radius R, which is designed to extract useful energy from the wind, which further is non-aifborne and which has a fixed foundation.

Air-borne 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.

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 and the 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; mobile devices can be toy like products to momentarily drive ieds 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 be have a fixed foundation. 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.

The HAT definition may further 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 30%R or 50%R or 70%R. Such ring-shaped structures are known and may be disadvantageous. There may be three types of such ring-shaped structures: ring-shaped structures with mainly a structural function; concentrator type rotors and direct drive generators. Also ring-shaped structures which are a combination of one or more of the three types may be disadvantageous and are excluded.

Ring-shaped structures with mainly a structural function and 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 one 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 ring-shaped 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 longitudinal direction. 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.

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 toads 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 should 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 (smaller than R/5 or smaller than R/10 or smaller than R/50). This has the advantage of obtaining a higher relative speed between the 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 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 more weight, larger transportation problems, more problems to maintain a narrow air gap and thus more costs.

A medium HAT may be defined as a HAT having a diameter larger than 40m, larger than 50m or larger than 70m.

A large HAT may be defined as a HAT having a diameter larger than 100m, larger than 140m or larger than 200m.

A small HAT may be defined as a HAT having a diameter smaller than a medium HAT and larger than 3m, forger than 5m, larger than 10m or larger than 25m.

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.

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.

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.

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, with R the radius of the largest rotor.

A number of blades “N” may be defined as the number of biades of a rotor. 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. The number of blades may be counted for each rotor independently. If, e.g,, a HAT includes a first rotor with a blade extending to position Ri and a second rotor with a blade extending to position Ra, which rotors may be designed to run at different rotation speeds, then the number of blades of each rotor is counted independently, if, e.g,, 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 (N_0.3R = 10) and five blades at 0.8R (N_0.8R = 5), while N for the rotor as a whole is 10, ih 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 360º/N +/- 360º/4N or 360º/N +/- 3º, For example, when N=7, the azimuth angle between adjacent blades is 51.4º +/- 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 aerodynamlcally more efficient, since an even azimuthal distribution of the blades leads to the smallest tip losses.

The direction of a longitudinal blade part may be given by a rotor azimuth angle φ with φ∈[0°,360°] and a polar angle 8 with the rotation axis with θ∈[0°, 180°]. If a rotor with N blades has multiple aerodynamicaliy shaped elongated parts which may be directed within 360º/4 N 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 360º/(4*7) = 12.9° difference In azimuth angle and within 30° difference in polar angle may be counted as one blade.

A blade may include a connection side where the blade connects to the hub of the rotor. A blade may be connected to a hub via an intermediate structure like a truss structure. The blade further includes a tip side. The radial position of the connection side may be smaller than the radial position of the tip side. Along the length of a blade, the blade may include stiffening connections to improve structural integrity. The aerodynamic part of a blade may include 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 may include a fixed inner part and a pitchable outer part or may have a pitchabie outer part only. A blade as a whole may be installed at a fixed pitch angle or may be installed to a pitch device and have a variable pitch angle.

A radial position "r" may be expressed as r = xR, with x∈[0,1] or x∈[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”. Similarly, “in the blade length range from M 5%L to L” = "for 1 = 15%L to L”.

A local chord “c_r“ 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 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 c_r may 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 oh the wind speed, e.g., when sails may be used, then the largest local chord at position r with fully extended 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 . 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 c_r may 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, which develop, in use, ho 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) at position r, may preferably be excluded from the local chord. The local chord may refer to a blade of the largest rotor.

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.

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 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.

The rotor solidity “SOL_rotor" may be the mathematical Integral over a radial length, e.g., from r = 0.15R to R, of the local chords c_r of all the blades N of a largest rotor, divided by the rotor swept area, using equation 1 below. Note that a spinner in the rotor center does not contribute to SOL_rotor.

The rotor solidity “SOLrotor may alternatively be the projected area of the rotor or of the coaxial rotors including the hub and/or spinner on a plane perpendicular to the rotor axis, wherein the blades are pitched so that the projected area is maximal, divided by the swept area of the (largest) rotor.

In the case of a ring-shaped wind concentrator, a chord of this concentrator multiplied by the circumference of the concentrator may be added to any of two above definitions for “SOL_rotor”. The radial solidity “sol_r" may be defined as the sum of the local chords c_r of all the blades N 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, The average radial solidity “avgsotr” may be defined as the average of the radial solidity of a rotor in a radial range from r-0.1 R to r+0.1R. Equation 3 defines as example “avgsol_.25R” as the average radial solidity between radial positions 0.15R and 0.35R, Analogously “avgsoI_.35R" may be the average radial solidity between 0.25R and 0.45R and “avgsol_.75R” may be the average radial solidity between 0.65R and 0.85R. It should be noted that radial solidity, the radial solidity ratios and the average solidity ratios may refer to the largest rotor.

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.

The power coefficient “C_P" may be defined as the ratio of the mechanical power “P_M“ 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 “C_PE“ 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). C_P may aiways be higher than or equal to C_PE when the turbine 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 the swept area of the largest rotor πR². In equation 4 and 5, p is an air density.

In the present disclosure, if the HAT includes two rotors, the axial force coefficient “Co_.ax" refers to a smaller rotor with radius R₂, typically referred to as a second rotor, and equals the ratio of the axial force “F_ax" exerted by the smaller rotor on the wind and a momentum flow of the undisturbed wind U through a rotor swept area mPa² of the smaller rotor (see equation 5 below).

The design tip speed ratio "Adestgn'' refers to the ratio of the angular rotor speed "ω” multiplied by the rotor radius R and the undisturbed wind speed U for which the rotor reaches its maximum value for C_P (see equation 6, left side, below). A ratio at another radial position than at the tip may be defined as the radial speed ratio λ_r = λ_design/R (see equation 6, right Side, below). Although a rotor typically has a highest yield at A^g*, HAT control may deviate from this optimum, e,g., to reduce leads or sound, to avoid eigenfrequencies or to avoid overpower. It should be noted that λ_design may refer to the iargest rotor,

A rotor may be designed using the known Blade Element Momentum (BEM) theory. It has been found that, based on BEM and for 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. in equation 7, may be a design lift coefficient, which is an airfoil property. The product 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.

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 ail direct sunlight is blocked, It should be noted that every HAT has a shaft which may be a part that may be required to enable the relative rotation of nacelle and rotor. The shaft may be fixed to the rotor or may be fixed to the nacelle, Overview

Environmental hindrance by a wind turbine, in particular from a wind turbine of the HAT type, may take different farms. The following types of hindrance will be discussed: (I) visual (or optical) hindrance; (ii) acoustic hindrance and (iii) hindrance to birds.

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 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.

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.

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 focal chord may be reduced to below an angle of 0,50°, the sun may be not folly covered by the blade and the core shadow may be removed.

The maximum of the local chord of a known, state-of-the-art blade may be typically 7%R, R indicating the radius of the rotor. 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, D indicating the diameter of the rotor. 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 care 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.

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.

Regarding the tranquility of the landscape, in particular large moving blades draw attention and may elicit a stress reaction 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 π(20D)² square 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 π(20D)² * 4400h = 7040000 - %πD²m²h.

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 • ¼πD² • 1500 m²h= 6000 • ¼πD²m²h, which is about 1200 times lower.

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.

Reducing the maximum chord and reducing the local chord in accordance with the present disclosure may be particularly advantageous tor medium and large HATs. Also, for small HATs reducing the maximum chord and iocal chord may be advantageous. 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. 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.

Ths 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 HAT s. Also, for small HATs increasing the number of blades may be advantageous.

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 a t least 0.35. Moreover, medium, large and small HATs may preferably be capable of surviving larger wind speeds, e.g., including extreme wind speeds of 40 m/s.

For state-of-the-art HATs there is genera! 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 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 doubted 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. 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; (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 audlbie 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 tor seven blades or more. This may be particularly true for medium and large HATs. but to a lesser extent also applies to small HATs, To a lesser extent since the rotation speed of small HATs may be so fast that individual blade noise may not de distinguishable.

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 oh 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,

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 and λ_r, the product of N and the local chord Ct preferably 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 biade 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, λ_r=3.2 and 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.

It may thus be favorable to reduce th® acoustic hindrance by a combination of reducing the tip speed, a reduction of the chord and an increase of the number of blades. Such combination minimizes visual and acoustic hindrance, while maintaining yield.

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 the air pressure impact near a rotating blade and second by the high velocities / air pressure drop in the vortices shod 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 tne inventor that this reduces the range around the blade wherein a certain air pressure may be induced by the biade and that the strength of the tip vortices may be reduced, resulting in a rotor becoming a lower hazard for birds.

The hazard to a bird for a rotor of diameter D with N blades may be expressed as follows. The bound vorticity may be considered linear to D and inversely proportional to N, so The hazardous space for a bird due to the N shed tip vortices of strength may be the space wherein the vortex induced velocities may be above a certain limit. In a plane perpendicular to the width and height of this space each may be proportional to and the length of the space, in the direction of may also be linear to Thus, the space and if we substitute herein we find wherein k, k₁ and k₂ are constants. The air pressure impact to the bird may be expressed as follows. The hazardous space

Sr is considered proportional to the square of the bound vorticity, proportional to the blade length, the latter being proportional to D, so If we again substitute we find S_P = cD³/N², with c and c₁ being constants. 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.

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. With a lower blade speed, in an embodiment a lower than conventional λ_design may be favorable. For a conventional offshore turbine, λ_design may typically be in the range from 9 to 10, In an embodiment λ_design ≤ 9, preferably λ_design ≤ 8, and more preferably λ_design is about 7. For a conventional onshore turbine. λ_design may typically be in the range of 8 to 9. In an embodiment for an onshore HAT, λ_design ≤ 8, preferably λ_design ≤ 7, more preferably λ_design ≤ 6, and more preferably λ_design ≤ 5.

To improve the visibility of the rotor swept area to a bird, in ah 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. On the other hand, rotors with two or three blades have large open areas in between the blades, which may 'invite' a bird td fly through those open areas, with a high collision risk, when the rotor is rotating.

T o avoid bird casualties, a lower rotation speed and/or a larger number of blades may thus be favorable. For a lower speed, a larger combined chord may be applied to keep the efficiency high, which may again be an argument for a larger number of blades. In an embodiment, the HAT may Include a control feature, which minimizes the shadow impact to crops or to a solar energy system like photovoltaic panels by yawing the HAT, turning the rotor and pitching the blades so that the shadow impact may be minimal, during periods of direct sunlight when the turbine cannot produce much energy, e.g., because of a low wind speed or malfunctioning. In those periods, the position of the yaw angle and/or the pitch angles of the blades independently if possible and/or the rotor azimuth angle may be adjusted, depending on the position of the sun, so that the shadowing of the producing units may be minimal and/or the cross section of the blades may ba minimal in the direction perpendicular to the sunlight.

In an embodiment, the solar panels in an area which may be shadowed by the HAT may be divided in groups, the panels being connected In series in a group and the group connected to an inverter with a maximum power point tracker wherein the panels within the same group may be installed in such a way that they, depending on the position of the sun, may be in the shade or out of the shade at the same time as far as possible. For exampie, it may be advantageous if all panels of the same group on the North side of the HAT may be located In a pie-shaped area around the tower and in particular at least 3 tower diameters from the tower.

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 weli with turbine size. And tow frequencies generally cause more problems titan high frequencies. Also, the whooshing effect from the individual blades increases with turbine size. For smaller turbines smaiier 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 40m 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 smaiier HATs may typically be reduced because buildings and trees may hide the smaller HAT.

In an embodiment, the HAT may be a medium HAT.

In another embodiment, the HAT may be a large HAT.

In an embodiment the HAT of the present disclosure may be made in serial production such that at least two exemplars of the same diameter and with the same radial solidity sob for r = 15%R to R may be produced.

The hazard for rare birds is typicaily regarded as more important than that of more common birds. The rare birds often may be predator 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.

Further Sxampfe Embodiments

In an embodiment, the HAT may have a design tip speed ratio λ_design, wherein the number of blades N at 60%R may be between N_0.6R,min = INT(100π/λ_design ² + 0.5) and N_0.6R,max = 2 · N_0.6R,min. Preferably, N is taken as a prime number or twice a prime number. For example, when λ_design = 7, then, e,g., N_0.6R,min = INT( 100π/7^a +0.5) = 6 and N_0.6R.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.

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 preferably more preferably more preferably more preferably For the design lift coefficient, the lift coefficient of an airfoil with the highest lift over drag ratio may be chosen . it has been found that instead of using the lift coefficient of maximum lift oyer 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 before the stall angle as design lift coefficient. The stalling angle may be the lowest positive angle of attack a where the derivative under 2D conditions. The advantage of using this latter design lift coefficient may be that may be higher so that blades with a shorter chord can be used to achieve the required lift which reduces optical hindrance and also may have load advantageous.

The airfoil properties may preferably be valid for the Reynolds number that corresponds to the design of the HAT under operational conditions of, e.g., 8 m/s wind speed.

In an embodiment, a HAT with low environmental hindrance may be realized having a maximum electric power coefficient, C_PE, measured behind the generator, which may be higher than 0.30, preferably higher than 0.35, more preferably higher than 0.40, more preferably higher than 0,45.

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.

Like the unexpected visual and acoustic advantages of embodiments of offshore turbines, those advantages also apply to anima! rich nature areas onshore, since also animals may be disturbed by noise, oast 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. The advantage is valid for all wind turbines with more than 3 blades according to certain embodiments. Since there often are many trees in nature rich areas, and thus only medium or large wind turbines are economically efficient because their swept areas usually are at higher altitude, above the height of the trees, the advantage is larger for medium wind turbines and may even be largest for largo wind turbines. The inventor found that using biades with a low chard possibly combined with rotors with more than 3 blades may not only reduce hindrances but also may increase the yield over cost ratio, which may be particularly important for medium size wind turbines and even more important for large wind turbines, 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 going further 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. Furthermore, state-of-the-art turbines sometimes need to be switched off because of hindrance. However, since the HAT according to the present disclosure causes less hindrance, the hindrance related down time may be less or none, which may add an estimated 1% to 2% to the yield.

Regarding the production and transportation 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.

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, it will be show 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 Nc_r/(2πr) may be calculated at two radial positions, e.g., at r= 0.3R and r = 0.9R. By substituting and using equation 7, we find Nc_r/(2πr)_r=0,3R = 0.104 and Nc_r/(2πr)_r=0,9R = 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 airfail 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 ioads 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 load ratio. The inventor realized that it may be better 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, white the yield over cost ratio of the wind turbine may increase. Using a lower blade area for the blade at the root further means that the rotor solidity may be reduced, which has the additional advantage that the yield of crops and solar panels which may be located in the shadow of the rotor may be less impaired. The chord reduction at the root furthermore had the advantage of Sees cast shadow and iess impairment of the tranquility of the landscape. 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 is advantageous. Using those arguments, 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 solo.2snfsolo.75si, 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. The advantages regarding efficiency may also be realized for a HAT with exactly two or exactly three blades which reach a radial position of 0.99R and in particular for a HAT with exactly two blades which blades have a maximum chord of below 9%R or 8%R or 7%R, since blades with such low maximum chords may also have less optical hindrance and may have easier production and may have easier transportation.

In ah embodiment the HAT comprises a rotor with exactly two blades reaching a radial position of 0.90R and have a maximum chord of below 9%R.

In an embodiment the HAT comprises a rotor with exactly two blades reaching a radial position of 0.90R and have a maximum chord of below 8%R.

In an embodiment the HAT comprises a rotor with exactly two blades reaching a radial position of 0.90R and have a maximum chord of below 7%R. 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^R/solarsR 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. solo.zWsoIc.rsR even may be 0. This may be favorable as is explained above. Also, it may be favorable for embodiments having a coaxial second smaller rotor, designed for a higher rpm, which may be more efficient at 0.25R, with R being the radius of the larger rotor. in an embodiment, analogously to the ratio sol_0.25R/ sol_0.75R , also the average solidity ratios avgsol_.25Rfavgsol_.75R and avgsoI_.35R/avgsoI_.75R 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.

For example, the radial solidity of the rotor at 0.25R divided by the radial solidity of the rotor at 0.75R may be below 2.0. For example, sol_0.25R/ sol_0.75R may be equal to 1 .9, 1.7, 0.8 or 0.1 .

As a result of reducing the radial solidity near the root at a radial position below 0.6R, in an embodiment, the HAT may have a rotor solidity SOL_rotor which may be less than f/λ_design ², with f being a factor which may be less than 2.0, preferably less than 1 ,8, more preferably less than 1.8, and more preferably equals about 1.35.

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. Therefore, in an embodiment we propose a HAT with a rotor of which the average radial solidity at r=0.25R, avgsol_.25, is less than 0.07. In an embodiment avgsol_.25 is less than 0.06. In an embodiment avgsol_.25 is less than 0.05. In an embodiment avgsol_.25 is less than 0.04. in an embodiment avgsol.25 is less than 0.03. For offshore turbines the yield over cost ratio may he more important than the hindrance reduction. Therefore, in an embodiment, a HAT may have a rotor with two blades or more reaching a radius of R, which may be at least 70m. The ratio of the radial solidity at radial position 0.25R of the rotor and the radial solidity at a radial position 0 75R of the sama rotor, expressed as soio ssR/solo.rm. may be less than 2.0, preferable less than 1.75, more preferably less than 1 .5, and more preferably less than 1.25. In an embodiment, such offshore HAT may have five blades reaching a radius of R.

For onshore HATs both the yield over cost ratio and hindrance reduction may be important. Therefore, in an embodiment, a HAT may have a rotor with five blades or more reaching a radius of R. The ratio sol_0.25R/ sol_0.75R , may be less than 2.0, preferably less than 1.75, more preferably less than 1.5, more preferably less than 1.25. In an embodiment, such onshore HAT may have seven blades reaching a radius of R.

In an embodiment, at least one of the blades may include a blade section. If such a section has differences in its cross section over its length, then it may have a variable cross section. Such a variable cross section may be composed of a pultruded airfoil section integrated with one or more separately produced structural elements.

A potential problem which may occur with pultruded blade sections; pultruded products may have a constant cross section in the direction of pultrusion while the desired properties of a HAT blade may be a changing aerodynamic shape and a changing bending stiffness in the length direction of the blade. By installing structural elements of different lengths in the voids in the pultruded airfoil sections, the cross-section changes in the length direction of the blade and the bending stiffness may change accordingly. If a void in a pultruded airfoil section has a cylindrical shape with the same axis as the twist axis, then cylindrical structural elements of different length may be inserted into the voids and cured so that a pultruded airfoil section may be created with a bending stiffness that varies in the length direction of the blade. An advantage of using pultruded airfoil sections may be that with a pultrusion process fibers may be cured without wrinkles so that the composite may be used more efficiently leading to weight and cost saving. Furthermore, the pultrusion process may be controlled better (han a process wherein a blade may be made in one piece in a mold. Such better control may lead to less production uncertainty and thus requires less over dimensioning. Furthermore, the airfoil shape and the surface quality may be betterwhen using pultrusion and therefore may increase the yield compared to the process of making a blade in one piece in a large mold.

In an embodiment, the blade section may include a cylindrical void of which the axis coincides with a twist axis of the pultruded twisted airfoil section. The separately integrated structural element may be a cylindrical element which fits in the cylindrical void. The cylindrical element may be pultruded.

In an embodiment the pultruded airfoil section may be twisted by counter-rotating the cylindrical structural element and the pultruded airfoil section and connecting them under pretension.

In an embodiment, blades with a reduced chord may include blade sections that include a pultruded twisted aerodynamic section, which may lead to a more optimal use of composite and/or to a better surface quality and/or avoids the need of a large mold to make a blade In one piece.

In an embodiment, a section of at least one of the blades may be injection molded or 3D printed. Said section may include a tip of the blade. Alternatively, said section may include a transient from a blade section to another blade section with a different chord length. in an embodiment, one or more of the blades may indude a vortex generator with a cambered fin. The fin may have a fin thickness at about 95% of the height of the fin, wherein the thickness of the fin may be at least 0.5mm, Alternatively, the thickness of the fin may be at least 0.7mm, Alternatively, the thickness of the fin may be at least 1 mm. Alternatively, the thickness of the fin may be and at least 2mm.

In an embodiment, one or more of the blades may include a vortex generator with a baseplate and a cambered fin. The fin may extend under an angle with the normal to the base, wherein the angle may be larger than 0.5°. Alternatively, the angle may be larger than 1°. Alternatively, the angle may be more than 3°, Alternatively, the angle may be more than 10°. Alternatively, the angle may be about 15°. Alternatively, the angle may be less than 50°,

In an embodiment, at least one of the blades may include a vortex generator pair having at least two mirrored fins designed to generate counter rotating vortices, Each of the fins of the vortex generator pair may have its own baseplate so that the fins may be attached to the blade independently and the distance between the fins may be controlled.

In an embodiment, at least one of the blades may include vortex generators at the suction side of the blade, The vortex generators may be installed at a radial position larger than 60%R and at a chordwise position of more than 80% of the local chord. Alternatively, the chordwise position may be more than 70% of the local chord. Alternatively, the chordwise position may be more than 80% of the local chord. Alternatively, the chordwise position may be more than 90% of the local chord. Advantageously, such vortex generator(s) may further reduce the trailing edge sound of rotating HAT blades.

Equation 6 shows that using a higher design lift coefficient may reduce the combined chord and thus advantageously reduces hindrance. It is a new insight to use a high a.design to reduce hindrance To obtain a high assign it may be advantageous to apply optimized vortex generators. tn an embodiment, a HAT may have a blade including a pultruded aerodynamic section which extends over more than 50%R, preferably more than 60%R, more preferably more than 70%R. A pultruded blade section may include features to increase the design lift coefficient with increasing distance to the blade tip, which features may include the use of vortex generators and/or gurney flaps. The blade in this example may include precisely one pultruded blade section. This has the advantage that there may not be connections needed between pultruded sections so that the blade can be simple, cheap, accurate regarding shape and it has a high yield over cost ratio. The blade of this example may be designed for a five bladed rotor of diameter D and has the advantage that the blade can be extended by a factor 7/5 by increasing the length of the pultruded section, so that the blade becomes suitable for a 7 bladed rotor with a diameter of 7/5D, vice versa the blade length can be reduced by a factor 3/5, so that the shorter blade can be used for a 3 bladed rotor with a diameter of 3/5D. The pultruded blade section in this example may be twisted during the pultrusion process or afterwards. In the case wherein the same pultrusion mold may be used to produce blades for different rotors, the twist per unit of blade length may be increased of decreases so that the twist per %R remains about the same. Twist rate adaptations may be made by exerting a torque on the blade during the pultrusion process. Those embodiments have the advantage of a cheap and high quality pultruded aerodynamic section and by designing the rotor so that it may have about optimum aerodynamic efficiency at about 80%R or 90%R, while this efficiency decreases towards the main axis. The design uses the effect explained above that the tip harvests more energy per unit of blade area than the blade range close to the rotor center, so that the yield over load ratio improves and the optical hindrance reduces because of the low radial solidity at smaller radial positions and the overall low rotor solidity. In an embodiment, a pultruded blade section may include a prefab trailing edge which may be fed through the pultrusion mold so that it may be integrated in the pultruded section. The advantage may be a better shaped and thinner trailing edge which may be less sensitive to damage.

In an embodiment, at least one of the blades may include a strip attached to a blade trailing edge. The strip may have a trailing edge thickness of less than 2.0mm or less than 1.0mm over 50%R. Alternatively, the strip may have a trailing edge thickness of less than 1.0mm or less than 0.5mm over 25%R. Alternatively, the strip may have a trailing edge thickness of less than 0.5mm or less than 0.3mm over 10%R. Such a trailing edge strip may have the advantage of reducing the trailing edge noise of a HAT blade and may improve the structural integrity of the trailing edge of the blade.

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 tangential stay can be effective without causing much aerodynamic drag. Tangential stay refers to a connection from one blade at a certain radial position to an adjacent blade at about the same radial position. In an embodiment, the HAT may have a first and a second blade, both being part of the same rotor, wherein the blades may have a tangential connection at a radial position R3 wherein R3 > 0.20R, preferably R3 > 0.30R, more preferably R3 > 0.40R, more preferably R3 > 0.45R. Additionally or alternatively, R3 < 0.8R, more preferably R3 < 0.70R, more preferably R3 < 0.60R, and more preferably R3 < 0.50R. in an embodiments 0.20R < R3 < 0.80R. preferably 0.30R < R3 < 0.70R and more preferably 0.40R < R3 < 0.60R.

In an embodiments, 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, which may make it easier to 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. 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 conventional pitch bearing installed at a radial position of less than 0,2R. A calculation revealed that a rotor with blades with, e.g., a length of 0.7R, ranging from 0.4R to 1.1R produces 7% more energy and has tower 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 0,4R to 1 .1 R may also be cheaper than 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. 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°.

In an embodiment with a rotor of more than 100m diameter with a truss structure and/or with blades of a reduced length and/or with more than 3 blades, there may be further advantage during the rotor installation. The weight and/or the blade length of a blade may be less compared to state-of-the-art rotors with 2 or 3 blades and therefore a blade can be lifted more easily. For the same reason, 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 er 3 blades Is installed. It may be, with just 1 blade installed, easier to turn the rotor to 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.

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 cut- out 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 ftp 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 consequents of pitching an entire biade as one piece over its full length with the blade root attached close to the center of rotation and the tip reaching R.

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 biade 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. in an embodiment, the HAT may have a diameter larger than 1m diameter and smaller than 50m diameter. Such HAT may have a tail vane to align the turbine io the wind, wherein a tail vane surface may be fixed In a hinged manner to the tail and the surface being larger than πR²/10; larger than πR²/5; larger than πR²/2; larger than ½D²; larger than ¾D²; larger than D²; and larger than 1½D².

In an embodiment, the HAT may have a blade that includes a pultruded airfoil section, possibly with twist. 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 sol_0.25R/ sol_0.75R ; (iv) a higher efficiency because of the double rotor concept; (v) a cheaper rotor because of the truss structure and/or the stays; (vi) less manufacturing costs because of using pultruded biade sections and/or blades of reduced length and/or reduced chord; (vii) a control advantage during a storm; (viii) easier logistics and installation because of reduced blade length and er blade chord and (six) less rotor unbalance during Installation when more than 3 blades may be applied.

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 higher solidity ratio, such as avgsol_.25R /avgsoI_.75R or avgsoI_.35R /avgsoI_.75R, since this implies a reduction of the local chord near the rotor center and thus less cast shadow. A higher λ_design leads less cast shadow since SOL_ROTOR will reduce because with increasing λ_design 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 λ_design and/or a larger N. A consequence of a lower λ_design may be, e.g, following equation 7 with an increase of the combined chord A larger combined chord may be solved by a larger N ('larger Other example hindrances, measures and consequences can be read from table 1.

Table 1: solutions to address one, multrp/e or all indicated sources of hindrance From table 1 it can be seen that certain measures are in contradiction. For example, a lower λ_design will reduce the sound pressure level but simultaneously increases the cast shadow, so it depends on the situation what the designer will chose.

An insight of the Inventor is that increasing the number of blades N may be advantageous for most or even all listed hindrances. And this insight may imply, assuming that λ_design remains about the same and thus that the combined chord is about the same, that a reduced chord is also advantageous regarding hindrance. Therefore some embodiments prescribe a chord below a certain limit.

Obviously, table 1 refers to wind turbines with the same diameter D and reducing the diameter is not a meaningful measure to reduce hindrance since the yield would reduce approximately with the square of the diameter. This emphasizes that the disclosure is important for all size wind turbines and particularly for middle size wind turbines and large size wind turbines.

A larger number of blades may add about 1% to 1,5% to the yield because of lower tip losses. The reduced hindrance may lead to a reduced hindrance cost downtime and may add another 1% or 2% to the yield. So remarkably, solutions of the present disclosure may result in more yield,

A reduced chord may result in reduced production, handling and transportation problems, but may also lead to less building height of the blade structure near the root and therefore may lead, at first sight, to more material In the root range of the blade to lead through the bending moments. The tip typically harvests more energy per unit of blade area than the blade range close to the rotor center. Therefore, the reduced chord may have a positive effect on the yield over storm load ratio and thus has advantage and save material In e.g., the tower or the foundation.

Description of the Drawings 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. An example of cross section l-l is shown In figures 16-18.

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, white 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-printing, 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 . An example of cross section IMS Is shown in figures 14-15.

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 is relatively high; in this case there are seven large blades 43 and seven shorter blades 44 in the same rotor 42, 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 large number of blades may reduce the probability of collision with birds.

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 c_limit = 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 c_limit = 5%R - 3/85(r-15%R), c_limit = 4.5%R - 2.5/85(r- 15%R), c_limit = 4%R - 2.0/85(r-15%R), c_limit = 3.5%R - 1 ,5/85(r-15%R), c_limit = 3.0%R - 1/85(r-

15%R), c_limit = 2.5%R - 0.5/85(r-15%R) and c_limit = 2.0%R.

Analogous to an embodiment explained by fig 4, in an embodiment, c_r may be below 5.5%R - 2.5/85*(r-15%R), for r = 15%R to R. in an embodiment, c_r may be below 5%R - 2,0/85*(r- 15%R). for r = 15%R to R, In an embodiment, c_r may be below 4.5%R - 1 .5/85*(r-15%R), for r = 15%R to R. In an embodiment, c_r may be below 4%R - 1.0/85*(r-15%R), for r = 15%R to R. In an embodiment, c_r may be below 3.5%R - 0.5/85*(r -15%R), for r = 15%R to R.

Fig. 5 shows another graph of a conventional distribution 60 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 61 wherein c_limit = 5.5%R -4.0/85(r-15%R), with the remark that the local chord may ba 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 c_limit = 5,0%R 3,5/85(r-15%R), c_limit = 4.5%R - 3.0/85(r-15%R), c_limit = 4.0%R - 2.5/85(r-15%R), c_limit = 3.5%R - 2.0/85(r-15%R), c_limit = 3.6%R - 1.5/85(r-15%R), c_limit = 2.5%R - 1.0/85(r-15%R), ), c_limit = 2.0%R - 0.5/85(r-15%R) and c_limit = 1,5%R.

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 S4 and a maximum chord 95. In this example, for the blade of the first rotor pointing vertically upward, an inner pultruded part 100, outboard puitruded pail 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. 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 also a conventional one, In an embodiment, the second rotor may directly generate energy via a connection to a generator.

In an embodiment, the second rotor may be designed to spin freely and to not produce a useful torque, so that C_P 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, In operation the second 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. The second rotor may include a brake so that it may be stopped in case of high wind speeds. This may reduce the loading on the HAT. For example, with increasing wind speed 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. When the maximum power of the HAT is approached, the second rotor may be hatted using the brake. 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 How 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. This embodiment has the advantages of a dual rotor system without the complexity of a drive train to capture the energy from the torque of the second rotor, 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. Preferably, the number of blades of the second rotor may be three and that of the first rotor may be at least five. Both the first rotor and the second may include pitch-controlled blades. The part of the first rotor 'covered' by the swept area of the second rotor may be optimized structurally to minimize loads and to only hold the part of the blades which is hot covered by the second rotor, Because of this the first rotor may have a much lower solidity below r=R2 and therefore has lower storm loads and may be controlled more easily. The captured energy may be about equal, even when the second rotor does not directly produce useful energy, because the first rotor harvests most of the energy in the wind which would flow through the swept area of the second rotor if it would not disturb er even block the flow.

Fig. 7 shows an embodiment of an onshore HAT 111 with a rotor with stay 112. In this example, the rotor has seven blades 113 which may be connected to the hub 7. In this example avgsol_.25R/avgsol_.75R and avgsoI_.35R /avgsol_.75R may be about 1 ± 30%. The bending moments on the blades may be ted efficiently to the hub via one or more stays. In an embodiment, the blades may be interconnected with tangential stays 114. In an embodiment, each blade may be fixed to the hub in forward direction with a stay 115. In an embodiment, each blade may be fixed in backward direction with a stay 116. The stay 115 and 116 may be radial stays. In an embodiment, the stays may come together at one point 117 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-Ill including a stay holder is shown in Fig. 8.

Fig. 8 shows an example of the cross section Ill-Ill of blade 113 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 bearing 134 from work position 131 to vane position 133. The stay holder may be connected to the tangential stays 114, to the forward stay 115 and to the backstay 116, and may include a shock absorber 136 to avoid damage to the biade. Fig. 9 shows an embodiment of an offshore HAT 151 with a downwind three bladed large rotor 152. In this example avgsol_.25R /avgsol_.75R and avgsoI_.35R /avgsol_.75R may be about 0 assuming the truss structure is not aerodynamicaliy shaped. The large rotor includes blades 154; one of the blades is shown cut-off at position 155 for illustration purposes. In this example, the blades may Include puitruded sections of four different sizes, from the tip to the root the sections 155, 156, 157 and 158 have a stepwise increasing chord. The large rotor may have a truss structure at its inside with tangential rods or tangential connections 156, forward rods 157 and rods 160 in the length direction of the blades. The latter may be fixed at one end to the hub 7 and at the other end to the blade 154. A pitch mechanism may be installed at connection point 159 or in the hub and may drive the blades via the rods 160. All rods may have an aerodynamic shape, in particular tire radial connections 160 and 157 may be designed to contribute to the aerodynamic lift. The rods may be compression elements, which can be loaded with compression and tension.

Fig. 10 shows another embodiment of an offshore HAT 151 , in this case however it also includes an upwind three-bladed small rotor 153, The smaller rotor has blades 161, which may be made of one or more puitruded sections 162, 163, 164, 165, 166 and 167, The blades may be fixed to a second hub 168, wherein a pitch mechanism may be placed as well as a brake. Rotor 153 may be designed to contribute to the generated power directly via a mechanical link to a generator and possibly via a gear to the generator of the large rotor, tn a non-limiting preferred embodiment, the small rotor only serves to close the aerodynamic gap in the center of the large rotor by exerting an axial force blocking the wind. The small rotor may be designed to have a high blockage by free spinning. The wind will then be directed around the small rotor into the blades of the large rotor so that the small rotor indirectly, via the large rotor, contributes to the generation of power. The small rotor may be equipped with a brake such that the small rotor may be halted at a certain wind speed. Fig. 11 shows an embodiment of an onshore HAT 181 with a rotor 182 with eleven blades 183, The blades may include two puitruded sections: an inward section 185 and an outward section

184. Ths turbine may be directed to the wind by a large tail vane 189. Such tail vane is particularly advantageous for smaller HATs. 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. The vane may be stiffened by a support structure 186 and typically has a large surface that may be divided in a fixed surface 190 and multiple smaller hinged surfaces 187. Each of the surfaces 187 may be fixed by hinges 188 to the support 186. An advantage of such design is that at low wind speeds the vane is large enough to align the rotor to the wind, while at high wind speeds, when the wind direction changes suddenly, the vane will not exert a high alignment force to the HAT, because surfaces 187 will hinge into a more horizontal position and so reduce the alignment force. This avoids fast yaw motions which cause high gyroscopic tilt moments which overload the HAT, It has been found that alignment of a HAT with a tail vane in this embodiment may be effective, as the large vane provides enough alignment force at near cut-in wind speeds to align the HAT. Also, when the turbine operates at low wind speeds of, e.g., 3 to 6 m/s, and the vane may be in the wake, where the wind speed may be decelerated to about 1/3 of an undisturbed wind speed by the energy extraction of the rotor, the vane has enough cross section to align the HAT to the wind. Advantageously, the large surface of such taii vane may also be suitable for advertisement, e.g., to place a logo.

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. On the y-axis is the ratio of the light intensity in the shadow over that without shadow. The conventional biade passage reaches core shadow when the intensity ratio becomes l/l₀ = 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 biade which passes the sun is about 10%R and the iocai chord of the biade in the embodiment is about 3.5%R.

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 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,

Fig, 14 shows an example of a puitruded twisted airfoil section 200 with leading edge 202 and trailing edge 203 and the direction of pultrusion 201, which may be parallel to the blade length axis. The section ends with chord 205 corresponds to cross section ll-ll of Fig. 2. The chord 205 at one end may be twisted during the pultrusion process with respect to the chord 206 at the other end by an angle 207. The puitruded airfoil section may include voids 208, 209 which may be tilled with separately produced structural elements 210. which may be cured in void 208 over a length 211 so that the section obtains a larger bending stiffness over length 211. For illustrative reasons, void 208 is shown to have only separately produced structural elements at one side of the void, although in practice the structural elements may also be cured at the opposite side or other sides in the void or in the other voids, and the structural elements may have different lengths.

Fig 15. shows an example of a blade section 212 which has been puitruded without twist. Cuts 213, 214 may be made during the pultrusion or afterwards. The cuts may reduce the torsion stiffness of the section. Therefore, the section may be twisted easily after production and the cuts may be cured again, fixing the blade section in twisted position. Such produced blade section may also be considered as a puitruded twisted airfoil section. The puitruded airfoil section may have a circular void 215 such that, e.g., a separately produced structural element in the shape of stiffening cylinder 216 may be installed in the circular void. The axis of the circular void may coincide with the twist axis. The stiffening cylinder may be installed over a length 217 in the puitruded airfoil section such that the stiffness of the combination varies in blade length direction.

Fig 16. shows an example of a blade section 220 with optional serrations 221 and cross section 222, which corresponds to cross section ll-ll of Fig. 1, As shown in Fig. 16, the serrations 221 need not be part of the local chord. In an embodiment, the serrations may be made of transparent flat plates to reduce the cast shadow. Preferably, the serration surfaces may be optically coated such that the fraction of reflected fight is minimized,

Fig. 17 shows another example of a blade section 220 with an optional thin plate 203 attached to the trailing edge. The piate 203 may be made of a stiff materia!, e.g,, a composite, end sticks out with respect to the trailing edge 203 such that a sharp extended trailing edge 223 is obtained, The thickness of the extended trailing edge is, e.g;, 0,5mm or less. The thin plate may be transparent and/or may be optically coated to reduce cast shadow.

Fig, 18 shows an example of a blade section 230 with, near the trailing edge, optional vortex generator pairs 232. Each vortex generator pair may have a baseplate 239 and two fins 231 which may be designed to generate counterrotating vortices. The distance between the pressure sides of the fins 233 may be fixed and that between the suction sides 234 may be varied. In an embodiment, the vortex generators may be installed near the trailing edge, e.g., beyond a chordwise position of 60%c or even beyond 80%c. The chordwise position is counted from 0%c at the leading edge to 100%c at the trailing edge and the reference for the position of a vortex generator is the front of the fin of a vortex generator. The vortex generators near the trailing edge serve to reduce the thickness of the boundary layer and thereby to reduce the noise generated by the airfoil. The airfoil section may aiso have vortex generators installed at about 20%c to 40%c. Here, also vortex generators pairs like 235 may be used or vortex generators with separate fins 236, which may not be connected via a base plate. The advantage of the latter vortex generators is that both the distance between the pressure side 237 and the distance between the suction sides 238 may be varied, such vortex generators may be used at the trailing edge as well. This may lead to a higher aerodynamic efficiency and to the need of a smaller amount of vortex generator pairs. An example of cross section IV-IV is shewn in Fig. 19.

Fig. 19 shows an example of an optimized vortex generator pair 232, such as shown in Fig. 18, attached using tape 243 to the airfoil surface 241 . In an embodiment, the fins 242 of the vortex generator pair may not be extending perpendicular to the baseplate 239 instead they have an angle 240 which is at least 0.5 degree In particular at least 1 degree and more in particular at least 2 degrees and preferably about 10-15 degrees. An advantage of the vortex generator pair 232 as shown in Fig. 19 is that the vortex generators have a slightly higher performance, apply a smaller baseplate 239, may be stapled and may be injection molded more easily because the product may be loosened easily in a two-part mold because of the angle 240. In an embodiment, the thickness of the fins (247) measured at 95% (245) of the total fin height (246) is at least 0.5mm, or at least 0,7mm, or at least 1mm, or at least 2mm, In an embodiment the edges of the vg-fins 244 may be rounded instead of sharp, which has the advantage that they have better erosion resistance and the round edges may be causing less damage when touching other objects or less Injuries to service personnel or may cause less risk for cutting ropes of abseilers doing blade maintenance.

Fig. 20 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 , wherein with the remark that the local chord may be above the line over a radial length of maximally 5%R. Al! shown limit lines may be valid for r = 15%R to R. Limit lines 251 , 252, 253, 254, 255, 256, 257, 258 are respectively corresponding to the equations

Fig, 21 shows an embodiment of an onshore HAT 271 With a rotor 272 with five blades 273. In this example, each blade includes one puitruded 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 fiap. In the example of Fig, 21 , the tower 274 may include one or more puitruded sections 275 which may exists of carbon liber. An advantage of puitruded 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, i.e., it may contribute to reducing environmental hindrance. Another advantage of using puitruded 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 / velocity field around the tower sections may be reduced. Yet another advantage of puitruded 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. The figure also shows the sun 276, which Is only covered for small fraction, and thus the cast shadow will be reduced, thanks to the slender blades 273.

Fig. 22 shows of a conventional distribution 280 of a combined chord versus 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 All shown limit lines may be valid for r = 15%R to R. Limit lines 282, 252, 283, 284, 285, 286, 287 and 288 are respectively corresponding to the equations

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 focal chord of 2m over the full span, then Nc_r = 7 x 2m = 14m, which corresponds to 14%R, so that the design is below limit lines 181 and 282 and above limit lines 282- 288.

Fig, 23 shows of a conventional distribution 290 of a combined chord versus 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 , = 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, 298, 297 and 298 are respectively corresponding to the equations Fig, 24 shows of a conventional distribution 300 of a combined chord Nm.- versus 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, = 16.5%R -12/85(r-15%R). All shown limit fines 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 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 iocal chord of 1m at R linearly increasing to 5m at 0.15R, then at 0.75R the local chord is found by linear interpolation and is (Nc_r = 7 x 2m = 14m, which corresponds to 14%R, so that the design is below limit lines 181 and 282 and above limit Sines 282-288.

The combined chord limits imply that c_r reduces by increasing N_r and since it has been explained that reducing c_r leads inter alia to less optical hindrance, the combined chord limit is a useful parameters.

Where in the above exampie 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,

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.

Gustave Paul Codec, Mac nuclear engineering and PhD wind turbine aerodynamics is the author, illustrator and inventor of this disclosure. Considered names of a turbine according to the invention may be AmiWind or Ami Wind Turbine or Wind Turbine Amiable or Corten Wind Turbine or CINIC Wind Turbine. CINIC being ah abbreviation for Corten no Noise no Cast shadow.

Claims

Claims

1. A HAT wind turbine (1, 21, 41, 91 , 111, 151 , 181 ) for the production of electricity from wind, comprising a tower (5), a nacelle (6), a generator and a rotor (2, 22, 42, 92, 112, 152, 182), the rotor being rotatable about a rotor axis by the wind, the rotor having a rotor solidity SOL_rotor of maximally 0.10 and the rotor having a radius R (3), the rotor further having an average chord avgsol_.25R in the radial range from 0.15R to 0.35R, and an average chord avgsol_.75R in the radial range from 0.65R to 0.85R, wherein the rotor comprises a number of blades (4, 23, 43, 44, 93, 113, 154, 183) N of at least 2, which reach at least a radial position of 0,90R, wherein the blades have a distribution of a local chord c_r (9, 28, 94) versus a radial position r, wherein the local chord c_r in 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%R; beiow 2%R; and below 1,5%R, and wherein the ratio between the average radial solidities avgsol_.25R /avgsoI_.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 them 0.25.

2. The HAT according to any of the preceding claims, the rotor further having an average radial solidity avgsol_.25R in the radial range from 0.15R to 0.35R, and an average radial solidityavgsoI_.75R in the radial range from 0.65R to 0.85R, wherein the ratio between those average radial solidities, avgsol_.25R /avgsoI_.75R is one of: less than 1.75; less than 1 .50: less than 1.25; less than 1.00; fess than 0.90; fess than 0.75; less than 0.50; and less than 0,25.

3. The HAT wind turbine according to any of the preceding claims, the rotor further having an average radial solidity avgsoI_.35R in the radial range from 0.25R to 0.45R and an average radial solidity avgsoI_.75R in the radial range from 0.65R to 0.85R, wherein the ratio between those average radial solidities, avgsoI_.35R /avgsoI_.75R is one of: 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.

4. The HAT wind turbine according to any of the preceding claims, wherein the blades have a distribution of a local chord c_r (9, 28, 94) versus a radial position r, wherein the fecal chord c_r in 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%R; below 2%R; and below 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); and below 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 - V85*(r-15%R); below 2.5%R - 0.5/85*(r-15%R); and below 2%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.S%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); below 3%R - 1.5/85*(r-15%R); and below 1.5%R.

5. The HAT wind turbine according to any of the preceding claims, wherein the number of blades N is one of: at least 3 blades; at least 4 blades: at least 5 blades; ad least 7 blades; and at least 11 blades, which blades reach at least a radial position of one of: 0.70R; and 0.90R.

6. Ths HAT 'Wind turbine according to any one of the preceding claims, wherein the number of blades N is one of: maximally 7 blades; maximally 11 blades; maximally 17 blades; and maximally 43 blades, which blades reach at least a radial position of one of: 0.70R; and 0.90R.

7. The HAT wind turbine according to any one of the preceding claims, wherein the diameter D is one of: at least 5m; at least 10m; at least 20m; at least 40m; at least 70m; at least 100m; at least 140m; at least 200m.

8. The HAT wind turbine according to any one of the preceding claims, wherein the diameter D is smaller than 40m and one of: at least 3m; at least 5m; at least 10m; at least 25m.

9. The HAT wind turbine according to any one of the preceding claims, wherein the rotor is designed to have a maximum power coefficient C_P of at least one of: 0.35; 0.40 and 0.45 and in particular wherein the rotor is designed to have a maximum electric power coefficient C_PE of at least one of: 0,35; 0.40 and 0.45,

10, The HAT wind turbine according to any one of the preceding claims, wherein the rotor is configured for a maximum solidity, SOL_rotor, of one of; 0,07; 0.05; 0.04; 0.035; and 0,03,

11. The HAT wind turbine according to any one of the preceding claims, wherein an average radial solidity of the rotor at r=0,25R, avgsol_.25R, is one of: less than 0.06; less than 0.05; less than 0,04; and less than 0.03 and in particular wherein avgsol_.25R refers to a largest rotor.

12. The HAT wind turbine according to any one of toe preceding claims, wherein the rotor is configured with a design tip speed ratio, λ_design, and wherein λ_design is one of: less than 9; less than 8; fess than 7; less than 6; and fess than 5.

13. 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 R3, wherein: one of: R3 > 0.20R; R3 > 0.30R; R3 > 0.40R; and R3 > 0.45R, and/or one of: R3 < 080R; R3 < 0.70R; R3 < 0.60R; and R3 < 0.50R, and/or one of: 0.20R < R3 < 0.80R; 0.30R < R3 < 0.70R; and 0.40R < R3 < 0.60R.

14. The HAT wind turbine according to any one of the preceding claims, further comprising a stay (115, 1 16, 117) and a stay holder (135), wherein a blade, the stay and the stay holder are connected at a radial position between 0.25R and 0.65R, the stay holder being connected to the blade in a pivotable manner at a joint so that the blade may pitch about the joint over one of: at least 30°; at least 60°; and at least 90°.

15. The HAT wind turbine according to any one of the preceding claims, wherein a truss structure in a center of the rotor connects a blade to a hub, the truss structure comprising a blade joint, a hub joint, and one of: a compression member; a stay, wherein a blade joint is connected to a hub joint by two compression members (156, 157, 160) or by one compression member and one stay 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 stay .

16. The HAT wind turbine according to any one of the preceding claims, wherein a blade is fixed to a pitch bearing (159), wherein the pitch bearing is located at a radial position of one of: larger than 0.25R; larger than 0.3R; larger than 0.35R: larger than 0.4R; larger than 0.45R, and less than 0.6R.

17. 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 a first rotor and reaches to radial position R and the second blade is part of a second rotor and reaches to radial position R2, wherein: one of: R2 < 0.70R; R2 < 0.60R; and R2 < 0.55R, and/or one of: R2 > 0.25R; R2. > 0.30R; R2 > 0.35R; and R2 > 0.40R, and/or one of: 0.25R < R2 < 0.70R; 0.30R < R2 < 0.60R; 0.35R < R2 < 0.55R: and 0.40R < R2 < 0.55R.

18. The HAT wind turbine according to ciaim 19, wherein the second rotor is designed to spin freely and to not produce a useful torque, so that C_P is about 0, and is further designed to have, when in use, an axial force coefficient, Co,_ax, being one of:

19. The HAT wind turbine according to any of the preceding claims comprising a blade, wherein the blade comprised a pultruded aerodynamic profile with a length of one of; at least 50%R; at least 60%R; at least 70%R; and at least 80%R, and optionally wherein the pultruded aerodynamic profile comprises twist and/or vortex generators and/or gurney flaps,

20. The HAT wind turbine according to any one of the preceding claims, wherein D is larger than 3m and smaller than 50m, and further comprising a tail vane surface (186, 187, 190) to align the rotor with the wind, wherein the tail vane surface is one of: larger than πR²/10: larger than πR²/5; larger than πR²/2; larger than ½D²; larger than ¾D²; larger than D²; and larger than 1½D² and in particular wherein a part of the tail vane surface (187) is fixed in a hinged manner.

21. 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 or downwind 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 rind shaped structure; the generator is using super conduction: the rotor drives a hydraulic transmission; the rotor comprises an airfoil with a relative thickness tto 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 o! of 1.5 or larger: and the rotor comprises a blade section a weight percentage of carbon fibers of 10% or more.

22. The HAT wind turbine according to any one of the preceding claims, where in the rotor is of the fast-runner type, wherein λ_design is one off: more than 4; more than 5 and more than 6.

23. The HAT wind turbine according to any of the preceding claims, wherein a largest rotor has a distribution of a combined chord (9, 28, 94) versus a radial position r, wherein the combined chord in the radial range from r = 15%R to R is one of: below 15,0%R; beiow 13.5%R; below 12.0%R; below 10.5%R; below 9,0%R; below 7.5%R; and below 6,0%R or 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); and beiow 10.S%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 - 7,5785*(r-15%R); beiow 12.0%R - 6,0/85*(r-15%R); below 10,5%R - 4.5785*(r-15%R); below 9,0%R - 3.0/85*(r-15%R); and below 7.5%R - 1.5/85*(r-15%R), or one of: below 16.5%R - 12.0/85*(r-15%R); below 1S.0%R - 10.5/85*(r-15%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); beiow 9,0%R -4.5/85*(r-15%R): below 7.5%R - 3,0/85*(r-15%R): and below 6.5%R - 1.5/85*(r-15%R).

24. A blade (4, 23, 43, 44, 93, 113, 154, 183) for use in a rotor of a HAT wind turbine (1 , 21, 41, 91 , 111 , 151 , 181 ) for extraction of useful power from wind, the blade being rotatable around a shaft of the HAT wind turbine by the wind, the blade having a distribution of a local chord c_L, (9, 28, 94) versus a blade length position I from L=0 at the blade root to L=100% at a blade tip, wherein the value of the local chord c_L in the blade length range from l= 15%L to L is one of : below 5,5%L below 5%L; below 4.5%L: below 4%L; below 3%L; below 2%L: and below 1.5%L, or one of: below 5.5%L - 2.5/85*(l-15%L); below 5%L - 2/85*(l-15%L); below 4.5%L - 1.5/85*(l-15%L); below 4%L - 1.5/85*(l-15%L); and below 3.5%L - 0.6/85*(l-15%L), or one of: below 5.5%L - 3.5/85*(l-15%L); below 5%L - 3/85*(l-15%L); below 4.5%L - 2.5/85*(l-15%L); below 4%L - 2/85*(l-15%L); below 3.5% - 1 ,5/85*(l-15%l); below 3%L - 1/85*(I-15%L) and: below 2.5%L - 0.5/85*(l-15%L), or one of: below 5.5%L - 4.0/85*(l-15%L); below 5%L - 3,5/85*(l-15%L); below 4,5%L - 3.0/85*(l-15%i); below 4%L - 2.5/85*(l-15%L); below 3,5%L - 2.0/85*(l-15%L); and below 3%L - 1 .5/85*0-15%L),

25. The blade according to claim 24, out of one piece with a length of at least one of: 40m, 60m, 80m, 100m.

26. A method for adapting an existing HAT wind turbine, the method comprising: removing a rotor from the existing HAT wind turbine; and installing a new rotor so that the wind turbine becomes a wind turbine (1, 21, 41 , 91 , 111 151 , 181) according to any one of the claims 1 -25,

27. A method for extraction of useful power from wind using a HAT wind turbine according to any one of the ciaims 1-25, the method comprising: causing the wind to rotate blades of the HAT wind turbine around a shaft; and converting torque from a rotor of the HAT wind turbine into electric energy using a generator of the HAT wind turbine.