EP2449255A2

EP2449255A2 - Windmill

Info

Publication number: EP2449255A2
Application number: EP10712081A
Authority: EP
Inventors: Henning Sparre Solfeldt; Jakob Bejbro Andersen
Original assignee: Edgeflow APS
Current assignee: Edgeflow APS
Priority date: 2009-04-01
Filing date: 2010-03-31
Publication date: 2012-05-09
Also published as: WO2010115832A2; WO2010115832A4; WO2010115832A3

Abstract

A windmill which comprises a rotor and a frame for rotatably supporting the rotor for a rotation around an axis. The rotor defines opposite ends and comprises a number of blade sections which extend between the opposite ends and define a surface of rotation around the axis during the rotation of the rotor. The rotor further comprises a set of frame structures, and each frame structure of the set of frame structures interconnect the number of blade sections and form a node at each blade section.

Description

Windmill

The invention relates to a windmill with a rotor, which has a frame for carrying the rotor for rotation around a substantially horizontal axis, said rotor comprising a number of blade sections, which extend between the ends of the rotor and are adapted to define a surface of rotation around the axis of the rotor during the rotation of the rotor

Windmills of this type exist, which are suitable for mounting along the edge of a roof especially on larger buildings, such as industrial buildings, sports centres and administration buildings, which are located in an open area wherein the wind has free access to the building Especially due to the weight, such windmills are restricted with respect to length Accordingly, it can be difficult to adapt the length of the rotor so that the frames at the end of the rotor can be mounted on structural parts in an industrial building E g a length of 18 metres can be a possibility

An object of the invention is thus to provide a windmill, the rotor of which is relatively light and long.

Another object of the present invention is to obtain a favourable placement of windmills in an urban environment. A particular problem encountered in placing windmills in such an environment is that buildings or other constructions may obstruct the wind. A particular feature of the present invention is a placement of a windmill on a building taking advantage of the influence the building has on the wind direction around the building. This has the advantage that more power can be drawn from the wind. Another particular feature of the present invention is a rotor construction allowing for having a long and light rotor This has the advantage that the windmill can be placed on a building that only allows for a small additional load from the windmill, or on buildings with a wide spacing between its supporting structures

In addition to the above objects, the above features and the above advantages, numerous other objects, advantages and features will be evident from the descriptions given below The objects, advantages and features are according to a first aspect of the present invention obtained by a windmill comprising a rotor and a frame for rotatably supporting the rotor for a rotation around an axis, the rotor defining opposite ends and comprising a number of blade sections extending between the opposite ends and defining a surface of rotation around the axis during the rotation of the rotor, the rotor further comprising a set of frame structures, and each frame structure of the set of frame structures interconnecting the number of blade sections and forming a node at each blade section.

The rotor may be self-supporting when the axis is oriented horizontally and the rotor is connected to the frame at its opposite ends This has the effect that the rotor does not have to be supported at its middle when oriented horizontally, which has the advantage that the windmill is easier to install and requires less machinery to be mounted on the building upon which it is attached. Each frame structures of the set of frame structures may lay in a radial plane in relation to the axis This has the effect that the set of frame structures will present a narrow profile for a wind perpendicular to the axis of the rotor One advantage of this is that the set of frame structures wil! only have a smal! influence of the flow of air through the rotor for a wind perpendicular to the axis, i.e the wind for which it may function optimally

The axis may be substantialSy horizontal The substantially horizontal axis allows for an easy access to the rotor and to the parts of the frame that engages the opposite ends of the rotor, which makes service of the windmill easier Further, the substantially horizontal axis also allows for windmills that protrude less from buildings, Le they have less influence of the contours of the buildings This makes ft easier to fit the windmills between buildings Each node at a blade section of the number of blade sections may be connected with adjacent nodes on the adjacent frame structures and at other blade sections of the number of blade sections by means of thin pretensioned connecting elements. This has the effect that the rotor will have a more rigid structure, with a higher resonance frequency, which allows for longer rotors supported at their opposite ends only.. The connecting elements between nodes may comprise wires adapted to be fixed to the nodes The number of blade sections may be four, five, six, or preferably three

Each frame structure of the set of frame structures may be located between the opposite ends and may be made of poles extending between the number of biade sections. The poles extending between the number of blade sections may be hollow with a smooth outer surface This allows for light frame structures with good aerodynamic properties. Each frame structure of the set of frame structures may be located between the opposite ends and may be made of one single bent metal pipe The pipe ends of the metal pipe may be welded together and in the area around the nodes flattened to form bearing portions for mounting against the inside of a biade section of the number of blade sections This has the advantage of a simple technica! realisation of a rotor that is both light and strong

Each blade section of the number of blade sections may be twisted around the axis to define a first helix or a first portion of a helix This has the effect, with the wind coming from a random direction, that a blade section is more likely to present a portion efficiently driving the rotation at the given wind direction.. This has the advantage that the rotor more easily will start to rotate when standing still or pick up energy from an irregular gusty wind Each blade section of the number of blade sections may be twisted by the tension of the preteπstoned connecting elements This allows for simple technical realisation Each blade section of the number of blade sections may be linear and extend parallel to the axis Typically, the wind speed will be higher a few metres above or beside a building than at the surface of the building, This gradient in the wind speed will induce a paddle-wheel effect on the rotor. The linear blade sections are favourable for taking advantage of this effect

A first frame structure of the set of frame structures may be positioned at one of the opposite ends The rotor may further comprise a first hub centred on the axis, and the first hub may be connected to and at least partially support the first frame structure and/or the number of blade sections The first hub allows for a windmill without an axle going through the rotor, which means that the weight of the windmill may be lower, allowing for a mounting on buildings having weaker supporting structures A second frame structure of the set of frame structures may be positioned at the opposite side of the rotor from the first frame structure.. The rotor may further comprise a second hub centred on the axis and the second hub may be connected to the second frame structure and/or the number of blade sections The second hub in combination with the first hub allows for the rotor to be rotationally supported at its opposite ends only, which has the advantage of a lighter construction without any through-going axle. The first hub may be connected to each node formed by the first frame structure by at least two wires and these at least two wires may extend from the first hub from points spaced apart along the axis. The specified wires provide additional stabilisation against vibrations or movements of the rotor along the axis, without any significant increase in the weight of the rotor The first hub may be connected to the first frame structures by a first plate. This allows for simple technical realisation, in particular the mounting of a rotor onto the frame This has a particular advantage if the rotor is to be mounted at a location that is hard to access, e g on the roof or the wall of a building

A first blade section of the number of blade sections may have an aerofoii crosε- section with a leading edge and a trailing edge Each node formed at the first blade section may be located at a point between the leading edge and the trailing edge Each node formed at the first blade section may be located at a point between the centre of gravity and centre of pressure of the aerofoil cross-section The centre of pressure is the point at which the pitching moment is zero when the wind comes from the direction having the greatest effect on the blade section The specified positioning between the centre of gravity and the centre of pressure gives a low moment induced by the difference in the lift force from the wind and the centripetal force from the rotation

The first blade section may have the same cross-section throughout its length Each frame structure may comprise a node portion defining an aperture in which the second blade section may be received and supported This has the advantage that the rotor is easy to assemble and that the rotor is strong and durable, which means that little service is necessary when operating the windmill This is particularly advantageous when mounting the windmill in a hard to access location, e g. on a building Each frame structure of the set of frame structures may comprise a first and a second elongated portion connected to the node portion at the leading and trailing edge, respectively, for supporting the second blade section This allows for a rotor construction that is light with frame structures having little air friction when the rotor is rotating

A first frame structure of the set of frame structures may have a circular outer rim centred on the axis The circular outer rim allows for additional connections to or supports of the rotor along its length The first frame structure of the set of frame structures may be a ring centred on the axis This has the effect that the air friction is reduced when rotating the rotor If each frame structure of the set of frame structures is laying in radial plane, the wing will not cleave the air when the rotor is rotating The first frame structure of the set of frame structures may be a toroid centred on the axis. This allows for a strong and light construction of the rotor The windmill may further comprise a rim connector engaging the circular outer rim under the rotation of the rotor This has the effect that the resonance frequency of the rotor is increased Generally, the resonance frequency of the rotor is lowered when the length of the rotor is increased Hence, the rim connector allows for windmills with longer rotors The rim connector may comprise an endless belt engaging and defining a loop around the circular outer rim. This has the effect that the rotor will be held in place by the belt The rim connector may comprise a wheel engaging the circular outer rim This has the advantage of a simple stabilising of the rotor by lowering the resonance frequency The circular outer rim may comprise teeth to define a sprocket and the rim connector may comprise an endless chain or connector sprocket engaging and cooperating with the sprocket This has the effect that the wind energy collected by the rotor can be efficiently transferred to auxiliary equipment connected with the rim connector

The windmill may further comprise a number of electrical generators or pumps coupled to the rotor A first electrical generator or pump of the number of electrical generators or pumps may be coupled to the rotor via the first hub A second electrical generator or pump of the number of electrical generators or pumps may be coupled to the rotor via the rim connector

A frame structure of the set of frame structures may twist around the axis to define a second helix or a second portion of a helix The helical frame structure has the effect that it can convey diagonal forces between the blade sections, which gives additional stiffness to the rotor This allows for the use of longer rotors A frame structure of the set of frame structures may twist around the axis to define a second helix or a second portion of a helix, the second helix or a second portion of a helix may twist around the axis in a direction opposite to the twisting of the first helix or the first portion of a helix This brings additional stiffness to the rotor The frame structure in question may intersect each blade section at the right angle, giving additional stiffness to the construction The helical frame structure may also have the advantage that it increases the resonance frequency of the rotor

The frame may be provided with dampeners for dampening the spreading of mechanical vibrations from the rotor to the supporting surroundings The dampeners are particularly advantageous when mounting the windmill on a building housing people that can be disturbed by the mechanical vibrations It also has the advantage that cyclic stresses induced by the mechanical vibrations from the rotor will be reduced, causing less fatigue damage on the structure of the building to which it is mounted.

The windmill may be adapted to be incorporated in a number of windmills in a windmill system, in which the number of windmills may be attached to a building

The objects, advantages and features are according to a second aspect of the present invention obtained by a windmill system comprising a number of windmills according to the first aspect of the present invention, wherein the number of windmills are mounted on and supported by said building This allows for the placement of windmills in an urban environment on locations that have favourable wind conditions it also allows the windmills to be attached to structures that are already present in an urban environment, i e no additional supporting structures need to be built.. The number of windmills may be greater than two and the number of windmills may have co-linear axes. The resonance frequency of the rotor generally decreases with an increased length of the rotor. Hence, in order to avoid low frequency resonances and at the same time take advantage of an horizontally extending building, a single windmill of a specific length can be replaced by two or more windmills with a combined length equal to the specific length. That the number of windmills has co-linear axes means that ail of the windmills have a rotor centred on a common axis

The building may have a first and a second surface portion connected by an edge or elongated edge portion. The edge and the number of windmills are attached to the building at the edge or edge portion The wind speeds and the local pressure of the wind are generally higher at an edge of a building. Thus, by the specified placement of the windmills, more wind energy can be collected The first and second surface portions may be planar The planar surface portions will give a sharp edge or edge portion between them, around which the wind speeds can be particularly high.

The number of windmills may be positioned with their respective axes extending in the same direction as the edge or elongated edge portion This has the advantage of an efficient use of the influence the building has on the wind direction Further, the wind speeds typically increase from a point close to the edge or edge portion to a point a few metres away from the edge or edge portion By the specified positioning, each blade section of each windmill will be subjected to the wind having approximately the same wind speed Thus, stresses due to different loads on each blade section are avoided or reduced, which can otherwise cause them to break

The rotors of the number of windmills may extend from both the first and second surface portions This has the effect that any wind running parallel to either the fs^'rst or the second surface portion having a wind component perpendicular to the edge or edge portion will be readily caught by the windmill The building may comprise a first and a second wall, and the first surface portion may be located on the first wall and the second surface portion may be located on the second wall By this positioning, wind channelled between buildings can be caught by the windmills This is aSso particuiariy favourable for tall and narrow buildings. The building may comprise a first wall and a second roof section, and the first surface portion may be located on the first wall and the second surface portion may be located on the second roof section. This particular positioning is advantageous for tali buildings extending vertically. The wind failing on a building generally has a strong horizontal component. Some of the wind will be forced upwards by the wall of the building, which means that the edge between the wall and the roof is a particularly advantageous position for a windmill, where the wind directed upward by the wall of the building can be caught

The building may comprise a first wali and a second roof section, and the first surface portion may be located on the first wall and the second surface portion may be located on the second roof section. This particular positioning and orientation of the rotor with respect to the building is advantageous for collecting the wind energy

The building may comprise a first roof section and a second roof section, and the first surface portion may be located on the first roof section and the second surface portion may be located on the second roof section. The resulting positioning of the windmills is particularly favourable if the roof sections define a pitched roof with a ridge defining the edge or edge portion The pitched roof also catches and channels horizontal wind components and redirects them towards the ridge. The building may have a protruding portion at which the number of windmills may be attached. The wind speed wili typically be higher around a protruding portion of a building, which functions to channel or redirect the wind. Hence, it is favourable to position windmills at this particular portion. The building may have a convex portion corresponding to a portion of a vertically extending cylinder, and the number of windmills may be positioned on the convex portion with their respective axes extending vertically This particular positioning is favourable for tall tower-like constructions, such as silos

The building may comprise an energy-storage for storing wind power from the number of windmills in an urban environment the wind speeds tend to be more irregular and shifting than in rural areas, due to the presence of buildings or other constructions Thus, a windmill in an urban environment may have a varying energy production The energy storage allows the wind power to be stored as a buffer for a later use, or for smoothening the output from the system Naturaily₍ the wind energy, i e the kinetic energy of the wind, collected by the windmill may have to be converted into another energy form, such as electrical energy, before storage

Many buildings have a main grid adapted to a certain frequency standard, e g 50 hertz or 60 hertz Hence, it is an advantage if the varying frequency of the wind power output can be adapted to the standardised frequency of the building The wind power may be in the form of an alternating current, and the system according to the second aspect of the present invention may further comprise a frequency converter for changing the frequency of the alternating current

The wind energy is in the form of an electrical current, and the system may further comprise a rectifier for transforming the alternating current to a direct current, and the energy storage may comprise a battery for charging by the direct current and/or a hydrolyser for splitting water into hydrogen and oxygen by a hydrolysis driven by the direct current This enables storing of the wind energy without any emission or influence on the local environment The building may comprise an energy-conveyor for conveying wind power from the number of windmills within the building and/or to the outside of said building The wind power is in the form of an electrical current, and the energy-conveyor may comprise an electrical contact positioned within the building for tapping the electrical current

The object, advantages and features are according to a third aspect of the present invention obtained by a method of producing a windmill according to the first aspect of the present invention comprising the steps of. providing the frame, providing the number of blade sections, providing the set of frame structures, interconnecting the number of biade sections by the set of frame structures to form the rotor defining opposite ends and including the number of blade sections extending between the opposite ends, each frame structure forming a node at each blade section, and rotationally supporting the rotor by the frame for enabling the rotation around the axis The specified order of the steps of producing the windmill allows for the frame to be mounted on the building prior to the rotor being connected with the frame The produced windmill may have any of the features of the windmill according to the first aspect of the present invention

The step of providing the number of blade sections may comprise providing a blade by an extrusion or pultrusion, and cutting the biade into a blade section of the number of blade sections. This allows for a simple technical realisation of the method for producing a windmill, where the extrusion or pultrusion allows for lightweight and strong blade sections The blade may be twisted in the extrusion or pultrusion by a rotational extrusion or pultrusion, respectively, to define a helix or a portion of a helix. This allows for stiff blade sections that are both light and strong The step of providing the number of blade sections may comprise; providing a straight blade, cutting the blade into a blade section of the number of blade sections, and twisting the blade sections to define a helix or a portion of a helix This is a simple technical realisation of the method of producing a windmill according to the third aspect of the present invention

The method may further comprise, providing thin connecting elements, connecting adjacent nodes on adjacent frame structures and at adjacent blade sections by said thin connecting elements, and tensioning said connecting elements This allows for a light rotor that is stiff and self-supporting In tensioning the connecting elements each of the number of blade sections may be twisted to define a helix or a portion of a helix. This allows for the twisting of the blade sections to be made in situ when instating the windmill to adapt to local wind conditions.. Each blade section may have the same cross-section throughout its length, each frame structure may comprise a node portion defining an aperture for receiving a blade section of the number of blade sections, and the step of interconnecting the number of blade sections by the set of frame structures may comprise inserting a blade of the number of blades into the aperture. This has the advantage of an easier assembly of a windmill with a both strong and durable rotor.

According to a fourth aspect of the present invention, the object of providing a windmill, the rotor of which is relatively light and long is obtained by the aforementioned windmill being peculiar in that the blade sections are interconnected in substantially radial planes by means of an in each plane iaying frame arrangement, which connects adjacent blade sections and forms a node at respective blade sections and that each node at a blade section is connected with adjacent nodes on the adjacent frame arrangements at other blade sections by means of thin, prestensioned connecting elements

Thus it is obtained that the blade sections - instead of being fixed to structural elements as previously - now become structural elements themselves and thereby avoid other structural elements such as one through-going shaft By use of the frame arrangements and the thin, pretensioned connecting elements connected herewith, a rigid construction is obtained where force is absorbed by the blade sections and the frame arrangements Thus, the rotor can be manufactured with a minimum of materials consumption, and its length can be great compared to the diameter due to all constructive elements being light and located at the periphery. The length of the rotor is variable by changing the number of frame arrangements and/or the distance between these Thus, with a given diameter there is great freedom to vary the length according to the existing needs in a simple manner. The diameter of the rotor can also be changed if so desired

Particularly desirably, according to the invention the number of blade sections may equal three. Hereby the frame arrangements of course become triangular, which is statically advantageous

According to the invention at least the frame arrangements, which are located between the ends of the rotor viewed in axial direction, can be made of poles, which extend from blade section to blade section in the circumferential direction of the rotor.

In another preferred embodiment of the invention, at least the frame arrangements located between the ends of the rotor, viewed in axial direction, can each be made of one single bent metal pipe, the ends of which are welded together and in the area around the nodes are flattened to form bearing portions for mounting against the inside of the corresponding blade section

According to the invention, the connecting elements between the nodes of the frame arrangement may comprise wires, which are adapted to being fixed to the nodes Hereby an especially low weight of the rotor is achieved Especially practical, the blade sections can each extend in a substantially spiral course around the rotor This can be obtained by providing the connecting elements in each node with various lengths, whereby the basic type with parallel and straight biade sections can be changed to the rotor having a more or less varied twisted shape A torsion of 120° between the frame arrangements at the ends seems optimal, both functionally and visually Other degrees of torsion, such as 180°, are also an option It will be easier for a rotor with twisted blades to recommence rotation after calm in accordance with common prior art

According to the invention, the frame arrangements at the ends of the rotor can have a hub for rotational mounting of the rotor to the frame whereby the mounting to the frame becomes particularly simple A particularly light construction is obtained if the hub is connected to each of the corresponding frame arrangement nodes by means of at least two wires, which extend from the point, which are located at intervals, viewed in the rotor's axial direction

Brief description of the drawings

A multitude of embodiments of the different aspects of the present invention are depicted below, where.

Fig 1A is a perspective view of a preferred embodiment of a windmill system comprising a windmill mounted on a building,

Fig 1B is a sectional side view of the rotor of the windmill of Fig 1A showing its intended rotational direction,

Fig 2A is a perspective view of an alternative embodiment of a windmill system comprising a windmiil mounted on a building,

Fig 2B is a sectional side view of the rotor of the windmill of Fig 2A showing its intended rotational direction,

Fig 3A is a perspective view of an alternative embodiment of a windmill system comprising a windmill mounted on a building, Fig 3B is a sectional side view of the rotor of the windmill of Fig..3A showing its intended rotational direction,

Fig 4A is a perspective view of an alternative embodiment of a windmill system comprising a windmill mounted on a building,

Fig..4B is a sectional side view of the rotor of the windmill of Fig 4A showing its intended rotational direction,

Fig 5A is a perspective view of an alternative embodiment of a windmill system comprising a windmill mounted on a building,

Fig SB is a sectional side view of the rotor of the windmill of Fig..5A showing its intended rotational direction,

Fig.6 shows a perspective view of a rotor for a windmill according an alternative embodiment or aspect of the invention,

Fig 7 shows the area around a triangular frame arrangement's connection with a blade section in the rotor shown in Fig 6, viewed on a larger scale and furthermore in a perspective view,

Fig.8 shows the in Fig 6 shown rotor viewed in the area around one of the ends of the rotor, viewed on a larger scale and furthermore in a perspective view,

Figs.9a, b and c show schematically different embodiments of the rotor in different twisted states,

Fig 10 is a schematic illustration of a complete windmill system,

Fig 1 1A-E illustrate different positions of windmills on buildings relative to a predominant wind direction, and

Fig.12 illustrates a complete windmill system in an urban energy distribution Detailed description

Fig 1A is a perspective view of a preferred embodiment of a windmill system 100 comprising a windmill 102 mounted on a building 104. The windmill 102 comprises a frame 106 having two separate arms placing the rotor 1 10 of the windmill 102 at a distance from the building 104 One of the arms of the frame 106 engages the rotor 1 10 at one end 1 12 of the rotor 1 10, while the other arm of the frame 106 engages the rotor 1 10 at the opposite end 1 14 of the rotor 1 10 by its opposite ends 1 14

The rotor has three blade sections 1 16 that are interconnected by five frame structures 1 18 One of the frame structures 1 18 is positioned at one of the ends 1 12 of the rotor 110, while another of the frame structures 1 18 is positioned at the opposite end 114 of the rotor 1 10 The frame structures 1 18 are positioned with regular intervals between them. Each of the frame structures 1 18 forms a node 120 at each blade section 1 16 Further, each frame structure 1 16 comprises three poles 122 with a circular cross section defining a triangle when the rotor 1 10 is viewed from the side The nodes 120 are at the corners of the triangle

The rotor 1 10 further comprises a first hub 124 at one of its ends 1 12, and a second hub 126 at its opposite end 1 14. Each of the hubs comprises a hub axle 138 and a circular hub disc 140 centred on and connected to the middle of the hub axle 138 The first hub 124 connects to the frame structure 1 18 at one of the ends 1 12 of the rotor 1 10 via nine wires 128 One wire 128 extends from the end of the hub axie 138 to a node 120, while two wires extend from the hub disc to the same node 120 The two wires 128 extending from the hub disc 140 connect to the hub disc 140 with a spacing between them Thus, the three wires 128 connecting to the same node 120 together define a tetrahedron AIi nodes 120 at the ends of the rotor 1 10 are engaged similarly by wires 128 The second hub 126 connects to the frame at one of the other end 1 14 in the same way as the first hub 124 connects to the rotor 1 10

The first hub 124 and the second hub 126 are rotatabiy connected to the frame 106, thereby defining an axis around which the rotor 1 10 rotates All of the frame structures 118 lay in radial planes in relation to the axis, i e the axis is perpendicular to these radial planes The sectional view of Fig 1B corresponds to a cut in a radial plane The three blade sections 116 twist around the axis of rotation of the rotor 110 Further, the blade sections have the same cross-sectional shape throughout their respective lengths

A generator supported by the frame 106 is connected to the first hub 124 via a generator belt 132 Thus, when the rotor 110 rotates around its axis, the electrical generator 130 produces electrical power.

The frame 106 is connected to and supported by a horizontal and planar roof section 136 of the building The windmill 102 is further positioned close to an edge 142 between the planar roof section 136 and a vertical and planar wall 134. The frame 106 extends diagonally outward from the straight edge 142, so that the rotor is completely above the planar roof section 136 and partially outside of the planar wall 134 The windmill is oriented so that the axis of rotation of the rotor 1 10 is parallel to the straight edge 142.

Fig 2A is a perspective view of an alternative embodiment of a windmill system 100' comprising a windmill 102' mounted on a building 104' Features having similar or related functions as in Fig 1A have been given the same number indexing, but distinguished by priming instead. The windmill of Figs 2A and B differs from the windmill of Figs. iA and B mainly in that the frame structures 118', the first hub 122" and the second hub 124' hub have different constructions Features of this particular embodiment that are not explicitly mention, but regarded as present and identical to those of the preferred embodiment, have been indicated in Figs 2A and B.

The rotor 110' has three blade sections 1 16' that are interconnected by five frame structures 1 18' One of the frame structures 1 18^* is positioned at one of the ends 1 12' of the rotor 1 10, while another of the frame structures 118' is positioned at the opposite end 114' of the rotor 110' The frame structures 1 18' are positioned with regular intervals between them. Each of the frame structures 1 18' forms a node 120' at the outside of each blade section 1 16' Further, each frame structure 1 18' comprises three node portions at the nodes 120' Each of the node portions 144' has an aperture 146' receiving and supporting a blade section 1 16' The node portions 144' are interconnected by elongated portions 148' having square cross-sections. This means that each node portion 144' is connected to a first and a second elongated portion 148' and the frame structure defines a triangle with rounded corners at the nodes 120' when the rotor 1 10' is viewed from the side The first elongated portion 148' connects to the node portion 144' at the leading edge 156' of the blade section 1 16', while the second elongated portion 148' connects to the node portion 144' at the trailing edge 158' of the blade section 116'

The rotor 110' further comprises a first hub 124" at one of its ends 1 12', and a second hub 126' at its opposite end 114' Each of the hubs comprises a hub axle 138' and a circular hub disc 140' centred on and connected to an end of the hub axle 138' The hub axle 138' and the hub disc 140' of the first hub 124' connects to the frame structure 1 18' at one of the ends 1 12' of the rotor 1 10' via a first plate 150' laying in the same radial plane as the frame structure 1 18'. Similarly, the hub axie and the hub disc of the second hub 126' connects to the frame structure 118' at the opposite end 114^! of the rotor 1 10' via a second plate 152' laying in the same radial plane as the frame structure 1 18' The electrical generator 130' is coupled directly to the rotor 110'

Further, the frame 106' is connected to and supported by a vertical and planar wall 134' of the building 104' The windmill 102' is further positioned close to an edge 142' between the planar wall 134' and a horizontal roof section 136' The frame 106' extends diagonally outward from the straight edge 142', so that the rotor is completely outside the planar wail 134' and partially above the planar roof section 136' The windmill is oriented so that the axis of rotation of the rotor 1 10' is parallel to the straight edge 142'.

Fig 3A is a perspective view of an alternative embodiment of a windmill system 100" comprising a windmill 102" mounted on a building 104" Features having similar or related functions as in Fig 1A have been given the same number indexing, but distinguished by double priming instead The windmill of Figs 3A and B differs from the windmill of Figs 1A and B mainly in that the frame structures 1 18", the first hub 122" and the second hub 124" hub have different constructions Features of this particular embodiment that are not explicitly mentioned, but regarded as present and identical to those of the preferred embodiment, have also been indicated in Figs 3A and B

The rotor has three blade sections 1 16" that are interconnected by five frame structures 1 18" One of the frame structures 1 18" is positioned at one of the ends 1 12" of the rotor 1 10", while another of the frame structures 1 18" is positioned at the opposite end 1 14" of the rotor 1 10" The frame structures 1 18" are positioned with regular intervals between them Each of the frame structures 1 18" is a ring connecting to the insides of the blade sections 1 16", thereby defining nodes 120" at the connecting points to the blade sections 1 16" The rings of the frame structures 1 18" have a circular cross section

The rotor 1 10" further comprises a first hub 124" at one of its ends 1 12", and a second hub 126" at its opposite end 1 14". Each of the hubs comprises a hub axle 138" and a circular hub disc 140" centred on and connected to an end of the hub axle 138" The first hub 124" connects to the frame structure 1 18" at one of the ends 1 12" of the rotor 1 10" via tangentially iaced spokes 160" extending from the hub disc 140" to the frame structure 1 18" The second hub 126" connects to the frame at the other end 114 of the rotor 1 10 "in the same way as the first hub 124" connects to the rotor 1 10"

Further, the frame 106" is connected to and supported by a vertical and planar wall 134" of the building 104" The windmill 102" is further positioned close to an edge 142" between the planar wall 134" and a second planar wall 154". The frame 106" extends diagonally outward from the straight edge 142", so that the rotor is completely outside the planar wall 134' and partially outside the second planar wall 154". The windmill is oriented so that the axis of rotation of the rotor 110" is parallel to the straight edge 142"

Fig.4A is a perspective view of an alternative embodiment of a windmill system 100"' comprising a windmill 102'" mounted on a building 104"'. Features having similar or related functions as in Fig. IA have been given the same number indexing, but distinguished by triple priming instead.. The windmill of Figs 4A and B differs from the windmill of Figs.1 A and B mainly in that the there are no hubs at the ends of the rotor 1 10'" Features of this particular embodiment that are not explicitly mentioned, but regarded as present and identical to those of the preferred embodiment, have also been indicated in Figs 4A and B

The rotor 1 10'" has three blade sections 1 16'" that are interconnected by five frame structures 1 18'".. One of the frame structures 118"' is positioned at one of the ends 112'" of the rotor 1 10'", while another of the frame structures 1 18"' is positioned at the opposite end 1 14'" of the rotor 110'" The frame structures 118'" are positioned with regular intervals between them Each of the frame structures 1 18'" is a ring connecting to the outsides of the bSade sections 1 16'", thereby defining nodes 120'" at the connecting points to the blade sections 1 16"'. The frame 106'" comprises five support forks 162'", each supporting one of the five frame structure 1 18'" by four wheels 166'" engaging an arc of the lower side of its circular outer rim 168"' The frame structure 1 18'" is afso held in place by an endless belt 164'" engaging the upper side of its circular outer rim 168"' and pressing the frame structure 1 18'" towards the wheels 166^!" by way of also engaging a fork axle 170'" on the support fork 162'" beneath. Each of the two outermost support forks 162'" supports an electrical generator and coupled to and driven by the rotor 1 10'" via the endless belts 164'" Two of the other support forks 162'" support a break 172'" coupled to the rotor 1 10"' via the endless belts 164'" for enabling a reduction of the rotational speed of the rotor 1 10'"

The five support forks 162'" of the frame 106'" are connected to and supported by a horizontal and planar roof section 136'" of the building The windmill 102'" is further positioned at an edge 142'" between the planar roof section 136'" and a vertical and pianar wall 134'" The frame 106'" extends upwards from the planar roof section 136'" and the windmill is oriented so that the axis of rotation of the rotor 1 10'" is parallel to the straight edge 142'"

It is contemplated that, in an alternative embodiment, there are some frame structures 1 18'" supported by four wheels 166"' only and not held in place by an endless belt 164"'. Further, it is also contemplated that the rotor 1 10"' may comprise a plurality of individual rotor sections, each comprising a number of blade portions The rotor sections are adapted to be joined together by their blade portions to define the rotor 1 10'". The rotor sections may be defined by dividing the number of blade sections 1 16'" between two neighbouring frame structures 1 18"' of the rotor 1 10'" It is contemplated that in all the described embodiments the rotor can be similarly divided into rotor sections

Fig.δA is a perspective view of an alternative embodiment of a windmill system 100"" comprising a windmill 102"" mounted on a building 104"".. Features having similar or related functions as in Fig 1A have been given the same number indexing, but distinguished by quadruple priming instead The windmill of Figs 5A and B differs from the windmiil of Figs.iA and B mainly in that the frame structures 1 18"", the first 122"" hub and the second hub 124"" hub have different constructions. Features of this particular embodiment that are not explicitly mentioned, but regarded as present and identical to those of the preferred embodiment, have been indicated in Figs 5A and B.

The rotor 110"" has three blade sections 116"" that are interconnected by three frame structures 118"" One of the frame structures 1 18"" is positioned at one of the ends

1 12"" of the rotor 110"", while another of the frame structures 1 18"" is positioned at the opposite end 1 14"" of the rotor 1 10"". Both of these frame structures 118"" are ring shaped and lay in radial planes with respect to the axis of rotation of the rotor

1 10"" The third frame structure 1 18"" defines a helix connecting the first two frame structures 1 18"".. All of the frame structures 118"" connect to the insides of the blade sections 1 16"" and form nodes 120"" at the points of connection

The rotor 110' further comprises a first hub 124"" at one of its ends 1 12"", and a second hub 126"" at its opposite end 1 14"". Each of the hubs comprises a hub axle 138"" and a circular hub disc 140"" centred on and connected to an end of the hub axle 138"" The hub axle 138"" and the hub disc 140"" of the first hub 124"" connects to the frame structure 1 18"" at one of the ends 1 12"" of the rotor 1 10"" via a first plate 150'"' laying in the same radial plane as the frame structure 1 18"" Similarly, the hub axle and the hub disc of the second hub 126"" connects to the frame structure 1 18"" at the opposite end 1 14"" of the rotor 110"" via a second plate 152'"' laying in the same radial plane as the frame structure 118""

The frame 106"" is connected to and supported by a horizontal and planar roof section 136"" of the building The windmϋ! 102"" is further positioned close to an edge 142"" between the planar roof section 136"" and a vertical and planar wal! 134"" The frame 106"" extends diagonally outward from the straight edge 142"", so that the rotor is completely above the planar roof section 136"" and partially outside of the planar wall 134"" The windmill is oriented so that the axis of rotation of the rotor 1 10"" is parallel to the straight edge 142""

The rotor shown in Fig 6-8 comprises three bfade sections 1, 2 and 3 with a commonly known symmetrica! shape These blade sections 1 , 2 and 3 are fixed to a number of triangular frame arrangements 4-10, which extend perpendicular to the rotor's axis of rotation The triangular frame arrangements' 4- 10 corners each form a node 1 1-31 together with the corresponding blade section Each node is connected with the node of the adjacent triangular frame arrangement 1 1-31 at the two other blade sections 1-3 by means of a wire 32-67, which by means of a suitable not shown tension device is pretensioned so that the entire rotor constitutes a rigid construction

Fig. 7 shows on a larger scale the area around the node 25 at the connection between the triangular frame arrangement 8 and the blade section 3. The triangular frame arrangement 8 is made of a bent metal pipe with a diameter in the region of 30-40 mm In the area around the node 25 the frame arrangement has been flattened to ease the mounting on the blade section 2

The rotor has a hub 70, 71 at each end, which is used for mounting of the rotor in a commonly known manner to a not further illustrated frame. By means of this mounting, the rotor may also in a commonly known manner be connected to a generator. Fig 8 shows the hub and thus the triangular frame arrangement 10 at the end on a larger scale The hub 70 is connected to each node 29, 30 and 31 in the frame arrangement 10 by means of two wires 72-77, as the wires to each node 29 are connected to the hub 70 at points, which are located at intervals in the axial direction of the hub Hereby the hub 70 is secured in the same manner as the hub in a bicycle wheel.. Hereby the construction becomes particularly light and simple

Fig.. 9a-c show three different embodiments of the rotor according to the invention For the sake of clarity, no reference numbers have been included apart from the reference numbers for the three blade sections From Fig. 9a it can be seen that the blade sections extend parallel to each other and the rotor's axis of rotation In Fig. 9b the blade sections 1-3 follow a slightly spiral course so that their at one end is located 120° from the location at the other end In fig 9c they follow a more spiral course, as they extend with a torsion of 180° from one end to the other. This twisted state is obtained relatively easily by varying the length of the wires, which connect the respective nodes

As mentioned, both sections have a symmetrical profile, which is in the region of 25-30 cm long and 4-6 cm tall at a rotor diameter of 2 0-2.5 m

The invention has been described with reference to preferred embodiments Of course many changes can be made without hereby diverging from the scope of the invention Instead of wires flat irons or stays may be used, which of course are better at absorbing any existing force Furthermore, the number of blade sections may be different than the mentioned three, whereby the frame arrangements of course are adjusted hereto The frame arrangements may also be made of composite material or wood

The windmill described is suitable for use especially along oblong zones around the roof edges of buildings (and side edges on taller buildings) These areas have the most wind energy due to the wind speed accelerating during the passage around the building, Apart from the mentioned rotor being adaptable to the interval between the load-bearing constructions of the buiϊding, the further interval between the points of support on the building mean fewer supports and thus further savings

Fig 10 is a schematic illustration of a preferred embodiment of a complete windmill system 200 The system 200 comprises windmills positioned on a building 232 with the axis of rotation of their rotors oriented either horizontally 204 or vertically 206 Some of the windmills are positioned on the roof section 208, and some of the windmills are positioned on a wall 210 The building has a protruding vertically extending cylindrical portion 234. Some windmills are positioned at the protruding portion 212, and some windmills are positioned on the protruding portion 214.. Some of the windmills are positioned in a row with co-linear rotational axes 216 All the windmills produce electrical power and are connected to an energy conveyor 218 in the form of an interna! grid in the building A frequency converter 220 and a rectifier 222 are coupled to the energy conveyer 218 A battery 224 and a hydrolyser 226 are coupled to the rectifier 222 A hydrogen tank 228 and an oxygen tank 230 are coupled to the hydrolyser 226

Fig..1 1A-E illustrate different preferred positions of windmills on buildings 232 relative to a predominant wind direction 240 The buildings 242 have a roof 242, and a wall 244 or side 246 facing the predominant wind direction 240 In Fig 6A the windmills 250 are positioned horizontally on the roof 242 and in a row at and along the edge between the roof 242 and the wall 244 facing the predominant wind direction 240.. in Fig 6B the windmills 250 are positioned horizontally on the wall 244 facing the predominant wind direction 240 and in a row at and along the edge between the roof 242 and the wall 244 facing the predominant wind direction 240. In Fig.6C the windmills 252 are positioned vertically on a side wall 254 and in a row at and along the edge between the side wall 254 and the wall 244 facing the predominant wind direction 240. Windmills 252 are also positioned similarly on the other side of the building 232 In Fig 6D the windmills 252 are positioned vertically in a row at and along the edge between the side 246 facing the predominant wind direction 240 and the side 256 facing away from the predominant wind direction of a circular-cylindrical building 232 Windmills 252 are also positioned similarly on the other side of the building 232. In Fig 6E the windmills 252 are positioned horizontally at and along the ridge 248 of a pitched roof 242, where the ridge is between a roof portion 258 facing the predominant wind direction 240 and a roof portion 260 facing away from the predominant wind direction

The predominant wind direction may be defined by the natural causes due to global weather phenomena or regional or locai weather phenomena. Examples of global weather phenomena are the westerlies at north mid-latitude, north-easterly trade winds north of the equator, south-easterly trade winds south of the equator, and westerlies at south mid-latitudes An example of a regional weather phenomena is the Mistral wind in south-eastern France coming from the north, northwest, or west Examples of local weather phenomena are the Foehn wind on dry down-slope side in the lee of a mountain range and the sea or land breezes in coastal regions On even smaller scales, the predominant wind direction at a building may be defined by the surrounding buildings or structures.

Fig 12 illustrates a complete windmill system in an urban energy distribution The electrical-power generating windmill 266 is positioned on the roof 264 of a building 262 An electrical energy conveyor 268 leads the electrical power to ground level, where a distributer/rectifier/frequency-converter 270 distributes an alternating current having the local grid frequency to an electrical car 272, to a heater in a water tank 274, and to the local electrical grid 282. The distributer/rectifier/frequency-converter 270 also distributes a direct current to an electrolyser 276 producing hydrogen and oxygen by splitting water. The produced hydrogen is stored in a hydrogen tank 278 and the produced oxygen is stored in an oxygen tank 280

Further points characterizing the invention.

1 Windmill with a rotor, which has a frame for carrying the rotor for rotation around a substantially horizontal axis, said rotor comprising a number of blade sections ( 1-3), which extend between the ends of the rotor and are adapted to denote a surface of rotation around the axis of the rotor during the rotation of the rotor, wherein the blade sections (1-3) are interconnected in substantially radial planes by means of an in each piane laying frame arrangement (4-10), which connects adjacent blade sections (1-3) and forms a node (1 1-31) at the respective blade sections (1-3) and that each node (1 1-31) at a blade section (1-3) is connected with adjacent nodes ( 1 1-31) on the adjacent frame arrangements (4-10) at other blade sections (1-3) by means of thin pretensioned connecting elements (32-67)

2 Windmill according to point 1, wherein the number of blade sections (1-3) is three

3 Windmiil according to point 1 or 2, wherein at least the frame arrangements (5-9), which are located between the ends of the rotor viewed in axial distance, are made of poles, which extends from biade section (1-3) to blade section (1-3) in the circumferentia! direction of the rotor

4 Windmill according to point 1 , 2 or 3, wherein at least the frame arrangements (5-9) located between the ends of the rotor, viewed in axial direction, each are made of one single bent metal pipe, the ends of which are welded together and in the area around the nodes (14-28) are flattened to form bearing portions for mounting against the inside of the corresponding blade section (1-3)

5 Windmill according to point 1 , 2, 3 or 4, wherein the connecting elements

(32-67) between the frame arrangements' (4-10) nodes comprise wires, which are adapted to being fixed to the nodes (1 1-31)

6 Windmil! according to one or more of the points 1-5, wherein the blade sections (1-3) each extend in a substantially spiral course around the rotor

7 Windmill according to one or more of the points 1-5, wherein the blade sections (1-3) extend in linear courses parallel to the rotor's axis of rotation

8 Windmill according to point 6, wherein the blade sections (1-3) are located in a substantially spiral course by regulation of the length and/or tension of the wires (32»67) 9 Windmill according to one or more of the points 1-8, wherein the frame arrangements (4, 10) at the ends of the rotor have a hub for rotational mounting of the rotor to the frame

10 Windmiil according to one or more of the points 1-9, wherein the hub

(70, 71 ) is connected to each of the corresponding frame arrangements¹ (4, 10) nodes {1 1- 13, 29-31) by means of at ieast two wires (72-76), which extend from points, which are located at intervals, viewed in the rotor's axia! direction

Item list

100 windmill system

102 windmill

104 building 106 frame

1 10 rotor

1 12 end of rotor

1 14 opposite end of rotor

1 16 blade section 1 18 frame structure

120 node

122 poles

124 first hub

126 second hub 128 wire

130 electrical generator

132 generator belt

134 wall

136 roof section 138 hub axle

140 hub disc

142 edge

144 node portion

146 aperture 148 elongated portion

150 first plate 152 second plate

154 second wall

156 leading edge

158 trailing edge 160 spoke

162 support fork

164 endless beit

166 wheel

168 outer rim 170 fork axle

172 break

200 windmill system

204 windmill with horizontal axis

206 windmill with vertical axis 208 windmill on roof section

210 windmill on wall

212 windmill at protruding portion

214 windmill on a convex portion

216 windmills with co-linear axes 218 energy conveyor

220 frequency converter

222 rectifier

224 battery

226 hydrolyser 228 hydrogen tank

230 oxygen tank

232 building

234 protruding vertically extending cylindrical portion

238 pitched roof building 240 predominant wind direction

242 roof

244 wail facing predominant wind direction

246 side facing predominant wind direction

248 ridge 250 horizontal windmills

252 vertical windmills 254 sidewalf

256 side facing away from predominant wind direction

258 roof facing predominant wind direction

260 roof facing away from predominant wind direction 262 building

264 roof

266 windmill

268 energy conveyor

270 distributer/rectifier/frequency-converter 272 electrical car

274 heater

276 electrolyser

278 hydrogen tank

280 oxygen tank 282 local grid

Claims

1 A windmill comprising a rotor and a frame for rotatably supporting said rotor for a rotation around an axis, said rotor defining opposite ends and comprising a number of blade sections extending between said opposite ends and defining a surface of rotation around said axis during said rotation of said rotor, said rotor further comprising a set of frame structures, and each frame structure of said set of frame structures interconnecting said number of blade sections and forming a node at each blade section

2 The windmiil according to claim 1 , wherein each frame structures of said set of frame structures is laying in a radial plane in relation to said axis

3 The windmill according to any of the claims 1 to 2, wherein said axis is substantially horizontal

4 The windmill according to any of the claims 1 to 3, wherein each node at a blade section of said number of blade sections is connected with adjacent nodes on the adjacent frame structures and at other blade sections of said number of blade sections by means of thin pretensioned connecting elements

5 The windmill according to claim 4, wherein said connecting elements between nodes comprise wires adapted to be fixed to the nodes

6 The windmill according to any of the claims 1 to 5 wherein the number of blade sections is four, five, six, or preferably three

7 The windmill according to any of the claims 1 to 6, wherein each frame structure of said set of frame structures is located between said opposite ends and is made of poles extending between said number of blade sections

8 The windmill according to any of the claims 1 to 7, wherein each frame structure of said set of frame structures is located between said opposite ends and is made of one single bent metal pipe, the pipe ends of said metal pipe is welded together and in the area around the nodes flattened to form bearing portions for mounting against the inside of a blade section of said number of blade sections

9. The windmϋi according to any of the claims 1 to 7, wherein each blade section of said number of blade sections is twisted around said axis to define a first helix or a first portion of a heϋx

10 The windmill according to claim 9, wherein each blade section of said number of blade sections is twisted by the tension of said pretensioned connecting elements

11 The windmill according to any of the claims 1 to 8, wherein each blade section of said number of blade sections is linear and extends parallel to said axis

12 The windmill according to any of the claims 1 to 11 , wherein a first frame structure of said set of frame structures is positioned at one of said opposite ends, said rotor further comprising a first hub centred on said axis, and said first hub is connected to and at least partially supporting said first frame structure and/or said number of blade sections

13 The windmill according to claim 12, wherein a second frame structure of said set of frame structures is positioned at the opposite side of said rotor from said first frame structure, said rotor further comprising a second hub centred on said axis, said second hub being connected to said second frame structure and/or said number of blade sections

14. The windmill according to any of the claims 12 to 13, wherein said first hub is connected to each node formed by said first frame structure by at least two wires, said at least two wires extend from said first hub from points spaced apart along said axis.

15. The windmill according to any of the claims 12 to 14, wherein said first hub is connected to said first frame structures by a first plate

16 The windmill according to any of the claims 1 to 15, wherein a first blade section of said number of blade sections has an aerofoil cross-section with a leading edge and a trailing edge

17 The windmill according to claim 16, wherein each node formed at said first blade section is located at a point between said leading edge and said trailing edge

18 The windrniil according to any of the ciaims 16 to 17, wherein each node formed at said first blade section is located at a point between the centre of gravity and centre of pressure of said aerofoil cross-section

19 The windmill according to any of the claims 16 to 18, wherein said first blade section has the same cross-section throughout its length

20 The windmill according to claim 19, wherein each frame structure comprises a node portion defining an aperture in which said second blade section is received and supported

21 The windmill according to claim 20, wherein each frame structure of said set of frame structures comprises a first and a second elongated portion connected to said node portion at said leading and trailing edge, respectively, for supporting said second blade section

22 The windmill according to any of the claims 1 to 21 , wherein a first frame structure of said set of frame structures has a circular outer rim centred on said axis

23 The windmill according to claim 22, wherein said first frame structure of said set of frame structures is a ring centred on said axis

24 The windmill according to claim 22, wherein said first frame structure of said set of frame structures is a toroid centred on said axis

25 The windmill according to any of the claims 22 to 24 further comprising a rim connector engaging said circular outer rim under said rotation of said rotor

26 The windmill according to claim 25, wherein said rim connector comprises an endless belt engaging and defining a loop around said circular outer rim

27. The windmill according to any of the claims 25 to 26, wherein said rim connector comprises a wheel engaging said circular outer rim

28 The windmill according to claim 25, wherein said circular outer rim comprises teeth to define a sprocket and said rim connector comprises an endless chain or connector sprocket engaging and cooperating with said sprocket

29.. The windmill according to any of the claims 1 to 28 further comprising a number of electrical generators or pumps coupled to said rotor

30 The wtndmiii according to claim 29, wherein a first electrical generator or pump of said number of electrical generators or pumps is coupled to said rotor via said first hub

31 The windmill according to any of the claims 29 to 30, wherein a second electrical generator or pump of said number of electrical generators or pumps is coupled to said rotor via said rim connector

32 The windmifi according to any of the claims 1 to 31 , wherein a frame structure of said set of frame structures twists around said axis to define a second heiix or a second portion of a heiix.

33 The windmill according to any of the ciaims 9 to 31 , wherein a frame structure of said set of frame structures twists around said axis to define a second heiix or a second portion of a helix, said second helix or a second portion of a helix twisting around said axis in a direction opposite to the twisting of said first heiix or said first portion of a helix

34 The windmii! according to any of the claims 1 to 33, wherein said frame is provided with dampeners for dampening the spreading of mechanical vibrations from said rotor to the supporting surroundings..

35. The windmill according to any of the claims 1 to 34, wherein said windmill is adapted to be incorporated in a number of windmills in a windmili system, in which said number of windmiiis are attached to a building..

36 A windmill system comprising a number of windmills according to any of the claims 1 to 35 and a building, wherein said number of windmiils are mounted on and supported by said building

37 The windmill system according to claim 36, wherein said number of windmills is greater than two and said number of windmills has co-linear axes

38 The windmill system according to any of the claims 36 to 37, wherein said building has a first and a second surface portion connected by an edge or elongated edge portion, said edge and said number of windmills are attached to said building at said edge or edge portion

39 The windmill system according to claim 38, wherein said first and second surface portions are planar

40 The windmill system according to any of the claims 38 to 39, wherein said number of windmills are positioned with their respective axes extending in the same direction as said edge or elongated edge portion

41 The windmill system according to any of the claims 38 to 40, wherein said rotors of said number of windmills extend from both of said first and second surface portions

42 The windmill system according to any of the claims 38 to 41 , wherein said building comprises a first and a second wall, and said first surface portion is located on said first wall and said second surface portion is located on said second wall

43 The windmill system according to any of the claims 38 to 41 , wherein said building comprises a first wall and a second roof section, and said first surface portion is located on said first wall and said second surface portion is located on said second roof section

44 The windmill according to claim 43, wherein a rotor of each of said number of windmills has a wing section of said number of wing sections having an aerofoil cross-section with a leading edge and a trailing edge, said wing section has a position of highest elevation in a rotation of said rotor around said axis and is oriented to position said leading edge upwind from said trailing edge with respect to a horizontal wind component perpendicular to said edge or edge portion

45 The windmill system according to any of the claims 38 to 41 , wherein said building comprises a first roof section and a second roof section, and said first surface portion is located on said first roof section and said second surface portion is located on said second roof section

46 The windmill system according to any of the claims 36 to 45, wherein said building has a protruding portion at which said number of windmills are attached

47 The windmill system according to any of the claims 36 to 37, wherein said building has a convex portion corresponding to a portion of a vertically extending cylinder, and said number of windmills are positioned on said convex portion with their respective axes extending vertically.

48 The windmill system according to any of the claims 35 to 47, wherein said building comprises an energy-storage for storing wind power from said number of windmills

49 The windmill system according to claim 48, wherein said wind power is in the form of an alternating current, said system further comprising a frequency converter for changing the frequency of said alternating current

50 The windmill system according to any of the claims 48 and 49, wherein said wind energy is in the form of an electrical current, and said system further comprises a rectifier for transforming said alternating current to a direct current, and said energy storage comprising a battery for being charged by said direct current and/or a hydrolyser for splitting water into hydrogen and oxygen by a hydrolysis driven by said direct current

51 The windmill system according to any of the claims 35 to 50, wherein said building comprises an energy-conveyor for conveying wind power from said number of windmills within said building and/or to the outside of said building.

52 The windmϋl system according to claim 51, wherein said wind power is in the form of an electrical current, and said energy-conveyor comprises an electrical contact positioned within said building for tapping said electrical current

53 A method of producing a windmill according to any of the claims 1 to 35 comprising. providing said frame, providing said number of blade sections, providing said set of frame structures, interconnecting said number of blade sections by said set of frame structures to form said rotor defining opposite ends and including said number of blade sections extending between said opposite ends, each frame structure forming a node at each blade section, and rotationally supporting said rotor by said frame for enabling said rotation around said axis

54 The method according to claim 53, wherein said step of providing said number of blade sections comprises. providing a blade by an extrusion or puitrusion, and cutting said blade into a blade section of said number of blade sections

55 The method according to claim 54, wherein said blade is twisted in said extrusion or puitrusion by a rotational extrusion or puitrusion, respectively, to define a helix or a portion of a helix

56 The method according to ciaim 53, wherein said step of providing said number of blade sections comprises. providing a straight blade, cutting said blade into a blade section of said number of blade sections, and twisting said blade sections to define a helix or a portion of a helix

57 The method according to claim 53 further comprising, providing thin connecting elements, connecting adjacent nodes on adjacent frame structures and at adjacent blade sections by said thin connecting elements, and tensioning said connecting elements

58. The method according to claim 57 wherein in tensioning said connecting elements each of said number of blade sections is twisted to define a helix or a portion of a helix

59 The method according to claim 53, wherein each blade section has the same cross-section throughout its length, each frame structure comprises a node portion defining an aperture for receiving a blade section of said number of blade sections, and said step of interconnecting said number of blade sections by said set of frame structures comprising: inserting a blade of said number of blades into said aperture