GB2484107A

GB2484107A - Modular wind turbine blade for a vertical axis wind turbine

Info

Publication number: GB2484107A
Application number: GB1016390.5A
Authority: GB
Inventors: Frederic Silvert; Charles Smadja
Original assignee: Nenuphar SARL
Current assignee: Nenuphar SARL
Priority date: 2010-09-29
Filing date: 2010-09-29
Publication date: 2012-04-04
Also published as: WO2012041992A1; GB201016390D0

Abstract

A blade for a vertical axis wind turbine comprises two or more blade segments connected together by a connection arrangement 22a, b between adjacent blade segments. The connection arrangement comprises one or more rigid inserts 28a, b supported within the interior of each of the blade segments and each having a portion extending outwardly from the end of the blade segment towards the end of the adjacent blade segment and at least one connecting member or fishplate 30 between adjacent blade segments and connected to the outwardly extending portions of the one or more rigid inserts 28a, b. The fishplate may be bolted or welded to a blade support arm 16c and the joint covered by a composite material aerodynamic cover 32. The inserts may be a metal rod or plate of constant or varying thickness and may be partially embedded in the polymer (e.g. polyurethane) foam of an FRP covered single or multiple blade core. The blades may have reinforcing rims or webs and may be straight or curved to from a helix when assembled.

Description

MODULAR WIND TURBINE BLADE FOR A VERTICAL AXIS WIND TURBINE

The present invention relates to a modular blade having a novel means for connecting adjacent blade segments, and to a vertical axis wind turbine comprising one or more such modular blades.

Wind turbines and windmills have been used for centuries to harness the energy from the wind. Typically, conventional wind turbines have been of a horizontal axis type construction, with blades arranged around a horizontal shaft. However, vertical axis wind turbines (VAWTs) are also known. In wind turbines of a vertical axis construction, the blades are often arranged around a central, vertical mast and are connected to the mast by means of one or more support arms.

A number of different types of VAWT exist, each having a different arrangement and orientation of the blades. For example, in an H-type VAWT, the blades are typically arranged substantially vertically at an approximately constant distance from the central mast and the aerodynamic flow and associated angle of attack are almost constant along the length of the blade. Unlike with horizontal axis wind turbines (HAWTs), it is therefore possible to use blades for an H-type VAWT which have a substantially constant cross sectional shape and dimensions along the length of the blade. Other types of VAWT incorporate curved blades, for example, in an egg-beater' or troposkein formation, where the ends of each blade are typically mounted at the central mast.

With the development of increasingly large wind turbines, there is a demand for wind turbine components of increasing size. In particular, there is a need to continue increasing the size and length of the blades such that the conversion of wind energy to electrical energy can be optimised. However, as the dimensions of the wind turbine blades increases, it becomes more difficult to manufacture and transport the blades in a single piece and the associated costs increase significantly.

It has previously been proposed to provide a modular wind turbine blade for a horizontal axis wind turbine, formed of a number of blade modules which may be manufactured and transported separately before being assembled to form the wind turbine blade. For example, US-.A-2008/145231 and US-A-7,393,184 both disclose a modular blade construction for a horizontal axis wind turbine.

However, the use of connected modules to form a blade for a horizontal axis wind turbine can be problematic, since areas of stress concentration can be introduced in the region of the joint between adjacent modules, which can compromise the mechanical integrity of the blade. Furthermore, the mechanical connectors or fasteners typically required for connecting adjacent blade modules can significantly increase the overall weight of the blade, which in turn increases the loading on the blade components.

The blades used in vertical axis wind turbines are typically of an entirely different construction and shape to those used in horizontal axis wind turbines and the mechanical loading to which the blades are subjected during use are entirely different in each case.

Therefore it has generally not been appropriate to apply the proposed techniques of producing and joining blade segments to the manufacture of VAWT blades. Furthermore, a suitable modular construction that has been specifically designed for use in VAWT blades has not previously been proposed.

It would therefore be desirable to provide a novel modular blade construction which is suitable for use on a vertical axis wind turbine. It would be particularly desirable if such a modular construction could overcome the problems associated with the use of connected blade modules in horizontal axis wind turbines, such as the problems with increased mechanical loading on the blade components.

According to the present invention there is provided a blade for a vertical axis wind turbine wherein the blade is formed of two or more connected blade segments. The ends of adjacent blade segments are connected together by means of a connection arrangement provided between the adjacent blade segments and comprising: one or more rigid inserts supported within each blade segment and each having a portion extending outwardly from the end of the blade segment towards the end of the adjacent blade segment; and at least one connecting member between adjacent blade segments. The at least one connecting member is connected to the outwardly extending portions of the one or more inserts from each of the adjacent blade segments.

According to the present invention there is also provided a vertical axis wind turbine comprising a central mast and two or more blades according to the invention, as defined above. Each blade is connected to the central mast by means of one or more support arms and at least one support arm is connected to the blade through the connection arrangement between adjacent blade segments. The connection of the support arm to the blade is thereby advantageously integrated with the connection of the adjacent blade segments.

The present invention further provides an individual blade segment for forming a blade for a vertical axis wind turbine wherein the blade is formed of two or more connected blade segments. At one or both ends the blade segment further comprises one or more rigid inserts supported within the blade segment and having at least a portion extending outwardly from the end of the blade segment. Two or more such blade segments can be connected together to form a blade according to the invention.

The term "vertical axis wind turbine" (VAWT) is used to refer to a wind turbine for the conversion of wind energy to electrical energy in which the wind turbine blades are mounted for rotation around a central, vertical axis. This type of wind turbine would be known to the skilled person. Well known VAWT constructions include the H-type or "Darrieus" VAWT, which include vertical blades mounted around a central shaft. Other known types of VAWT incorporate a helical blade configuration, or a troposkein (egg beater") blade configuration.

The use of a modular blade is particularly suitable for the vertical axis construction of wind turbine, since in a VAWT the blade mechanical loading is more evenly distributed along the blade than in a horizontal axis wind turbine (HAWT). This is at least partly due to the different mounting arrangements of the blades in the different types of wind turbine.

In a HAWT, the blades are connected to the main rotor shaft at the blade root only * and the blade then extends away from the rotor shaft. Mechanical loading is highest at the blade root, since the root is subjected to the highest centrifugal and bending forces and must support the weight of the blade as well as the aerodynamic loads applied over the entire blade.

On the other hand, in a VAWT, the blades are typically connected to a central rotating shaft or mast by one or more support arms. The support arms transfer the torque from the blades to the central mast and must support not only the weight of the blade but also the centrifugal loading and the aerodynamic torque that drives the generator.

However, the arrangement of the support arms means that the mechanical loading is more evenly distributed along the blades and unlike in a modular HAVVT blade, the centrifugal and aerodynamic loading of each blade segment in a VAVVT blade is directly transferred to the central mast through the support arms, without increasing the loading of * any adjacent blade segments. It is therefore possible to manufacture the VAWT blades in several segments that withstand lower stress levels and reduce the overall weight of the blades.

The blades according to the present invention are modular blades formed of two or more connected blade segments, or modules, which are connected together by means of the connection arrangement provided between adjacent segments. In one preferred embodiment of the invention, the blade is formed of three connected segments, which are joined to each other using two connection arrangements.

Preferably, the segments of the blade are connected to each other in a longitudinal direction, so that the blade is segmented along its length. Where the blade is mounted substantially vertically, the blade segments will therefore be assembled one on top of each other. Preferably, the cross section of the ends of adjacent blade segments which are to be -4-.

connected together are similar or preferably substantially identical so that the only required connections are the connections between the blade segments in a longitudinal direction.

Each blade segment of the blades according to the present invention can be manufactured separately and since the blade segments will typically be significantly shorter in length than the overall blade, the production facility and in particular the mould for producing the blade segments can be kept relatively short. This makes the manufacture of the blade segments both simpler and more cost effective than the production of a one piece blade.

In addition, the blade segments can be transported individually and assembled on site. Advantageously, this means that smaller and more cost effective transport means can be used and that smaller and lower capacity installation and handling equipment, such as cranes, are suitable.

The use of a modular blade also improves the efficiency and cost of maintenance of the blades, since in the case of blade failure or damage, it is possible to replace only the defective or damaged blade segment whilst retaining the other blade segments. As well as minimising the materials and parts required to provide a replacement segment, the amount of material to be scrapped is also minimised, thereby reducing the financial losses as well as the losses of time and material associated with the scrappage.

A modular blade construction additionally provides greater flexibility in the overall length of the blade, so that the blade can be adapted depending upon the environment and the energy requirements of the turbine. Different length blade segments can readily be manufactured and assembled in different configurations to achieve different lengths of blade and different positions of the joints.

The connection arrangement between adjacent blade segments provides a strong and stable connection which is capable of withstanding the loads to which the blades are subjected during use. The components of the connection arrangement can be easily manufactured and assembled. During assembly and maintenance of the blades according to the invention, the inserts can quickly and easily be connected to the at least one connecting member in order to join adjacent blade segments. The connection process requires neither specialist equipment nor skills and can therefore be carried out in an efficient and cost effective way. The same applies if disconnection of adjacent blade segments is required, for example in order to replace a defective segment. The connection arrangement advantageously avoids the need to drill hotes within the blade segment and thereby avoids stress concentrations around the arrangement. The mechanical integrity of the blade is therefore retained.

In particularly preferred embodiments of the present invention, the at least one connecting member of the connection arrangement between adjacent blade segments comprises attachment means for attaching the connection arrangement to the peripheral end of a blade support arm of a vertical axis wind turbine.

Similarly, in particularly preferred embodiments of the vertical axis wind turbine of the present invention, the peripheral end of the support arm is attached to the at least one connecting member of the connection arrangement of the blade. For example, the peripheral end of the support arm may be welded, bolted, or mechanically fastened to the at least one connecting member so that together the support arm and at least one connecting member form a one-piece structure.

The term "peripheral end" refers to the free end of the support arm that is furthest * from the central mast. The opposite end of the support arm will be attached to the central mast by suitable means.

In preferred embodiments in which the blades are formed of three connected blade segments connected by two connection arrangements, the at least one connecting member within each connection arrangement includes attachment means for attaching the connection arrangement to a support arm.

In addition to the support arm or arms attached to the blade through the connection arrangement, one or more additional support arms may be provided to support the blades, for example, towards the ends thereof. These additional support arms may be connected to the blade segments using an alternative attachment arrangement if the point of connection is located along the blade length and does not coincide with an end of the blade segments.

Alternatively, these additional support arms may be connected to the blade segments using the described connection arrangement if the point of connection coincides with the free end of the upper and/or lower blade segment. Suitable attachment arrangements for the additional support arms would be known to the skilled person.

Preferably, where additional support arms are incorporated towards the ends of the blade, the support arms are positioned a distance from the ends of the blades, rather than at the very ends. For example, the distance between an additional support arm and the end of the blade may be between one quarter and one half of the overall blade length and preferably around one third of the overall blade length.

By providing attachment means for attaching the support arms to the blade as part of the connection arrangement for connecting adjacent blade segments, the overall strength of the connection between the blade segments is significantly improved and in particular, the loading on the connection arrangement is minimised. Furthermore, the support arm can be connected to the blade without adversely affecting the mechanical integrity of the blade segment and without significantly penalising the aerodynamic efficiency of the blade.

Advantageously, the number, dimensions, altitudes and cross sections of the support arms in the vertical axis wind turbines according to the invention can be varied in order to optimise the performance and efficiency of the turbine. For example, the projected surface area of the support arms in the wind direction can be minimised in order to reduce the undesirable drag of the support arms as they rotate during use. Each support arm may be provided substantially horizontally, which advantageously minimises the wake effects in a standard horizontal air flow. Alternatively, each support arm may be provided at a different angle relative to a horizontal plane, in order to confer sound dynamic behaviour to the blade where necessary. Where a blade is supported by two or more support arms, the support * arms may be connected to the blade at the same angle relative to a horizontal plane, or at a different angle relative to a horizontal plane to each other.

In the connection arrangement of blades according to the present invention, the one or more rigid inserts are supported within the blade segment so that there is a fixed, strong connection between the rigid inserts and a part of the blade segment. The form of the connection will depend upon the construction of the blade segment.

In one preferred embodiment, the blade segment comprises an outer shell formed of one or more layers of a composite material and the one or more rigid inserts within the blade segment are connected to the outer shell by means of an internal composite supporting structure comprising one or more reinforcement rims, webs or other supporting structures of a composite material extending between the one or more rigid inserts and the internal surface of the outer shell. The one or more rigid inserts are thereby supported by the internal composite reinforcement structure provided by the one or more reinforcement rims, webs or other composite supporting structures.

The one or more reinforcement rims, webs or other composite supporting structures may be put into place within the blade segment prior to the moulding process. During heating of the blade segment within the mould, the internal reinforcement structure and the outer shell will then cure together and form a one-piece composite structure that provides increased reinforcement in the region of the rigid inserts. Alternatively, with certain blade constructions it may be more convenient to mould and cure the internal composite reinforcement structure separately from the components of the blade segment and to incorporate the one or more reinforcement rims, webs or other composite supporting structures into the blade segment when the blade outer shell is being formed or after the blade outer shell has been formed. In this case, the internal reinforcement structure may be glued or bonded to the outer shell using any suitable adhesive or other bonding means.

Preferably, each of the one or more rigid inserts comprises an outer layer of a composite material. For example, a layer of composite material may be wrapped around each of the rigid inserts. Where the rigid insert is formed of a non-composite material, such as a metal, the surface of the rigid insert is preferably provided with teeth or grooves to facilitate the wrapping of an outer composite layer around the insert and to facilitate the bonding of the rigid insert to the internal composite reinforcement structure, where present.

In addition1 the presence of the teeth or grooves in the outer surface of the rigid insert allows the level of stress transmitted by the rigid insert to the structure of the blade segment to be progressively decreased.

This outer layer of composite material is particularly advantageous in embodiments comprising internal reinforcement ribs, since it can improve the connection between the rigid inserts and the internal composite reinforcement structure. The outer layer of composite material around the rigid inserts, the reinforcement rims, webs or other internal composite structure and the outer shell of the blade segment may be glued or bonded together to form a connected composite structure which supports the rigid inserts within the blade segment.

In certain embodiments, the composite components may be cured together to form an integral composite structure within the blade segment.

The blade of the present invention may be of a known construction comprising an outer shell and an inner, longitudinal beam or spar which is connected to the inner surface of the outer shell. In this construction, the outer shell of each blade segment is typically formed of two shell parts that are formed separately and subsequently connected together to form the complete outer shell. The outer shell parts are usually connected along the trailing and leading edges of the blade by means of a suitable adhesive. Alternatively, the blade may be formed of an integral structure that has been moulded in one piece.

In blades according to the present invention having this construction of an outer shell and an inner spar, the one or more rigid inserts in a blade segment are preferably connected to the outer shell of each blade segment by means of the internal composite reinforcement structures described above, which extend between the rigid inserts and the inner surface of the outer shell.

The outer shell is preferably formed of composite material comprising reinforcement fibres, such as glass fibres, impregnated with a resin matrix, such as epoxy. Preferably, the outer shell is formed of pre-impregnated composite materials. Other suitable examples of composite materials include materials integrating carbon fibres and/or polyester resins.

Preferably, the outer shell is formed of between three and six layers of a composite material for blades having a length of between 10 m and 15 m, although this may be higher for larger blades. The number of layers in the outer shell may vary along the length of the blade or blade segment as well as possibly along the blade chord, to account for the different strain at different parts along the length and chord of the blade or blade segment during use. This may be particularly advantageous in longer blades or blade segments.

Alternatively, the blade of the present invention may be formed of an inner core that has been wrapped or covered with one or more layers of composite material that form an outer shell. In this construction, the one or more rigid inserts are preferably embedded within the inner core at each end of the blade segment which is to be connected to an adjacent blade segment in the assembled blade. The inserts are preferably put in place within the core during manufacture of the blade segments, so that the expansion of the core during the moulding process also fixes the inserts in place. However, alternatively the inserts may be inserted into the inner core after the blade segment has been formed. The inserts may be embedded at the end of the blade segment only, or may extend through the entire blade segment.

The rigid inserts are supported within the blade segment by means of being embedded within the inner core material. In addition, the rigid inserts may be connected to the outer shell by means of one or more composite reinforcement ribs that are incorporated into the inner core and which extend through the inner core between the one or more rigid inserts and the inner surface of the outer shell.

Where the blade segment comprises an inner core, the inner core may be formed of any material having suitable density and compressibility characteristics, but is preferably formed of a foam material. Suitable materials for forming the inner core include polyurethane foam or any other polymer foam presenting similar density and compressibility ranges and ratios. The foam material may be obtained from two monomer precursors, which form a foam upon mixing. ln this case, the foaming mixture can be poured into a closed mould such that the foam takes the shape of the mould as it forms. Alternatively, the core may be assembled from pre-forrned or machined foam blocks.

The inner core may comprise a single piece of core material, or may be formed of multiple cores that have been compacted and glued together, for example, by the resin from the outer layers of composite material during the blade manufacturing process.

The outer shell surrounding the inner core may be formed of the same material and construction as described above in relation to blades having an inner spar.

During manufacture of the blade segments comprising an inner core, one or more layers of composite material are typically wrapped around the rigid, inner core material and the combined materials are placed in a mould and heated. During heating, the rigid core may expand to fill the mould, for example where a foam material, is used, thereby compressing the outer layers of composite materials and forming the desired airfoil shape of the blade or blade segment. in addition, the outer layers of the composite materials cure and the resin within the layers infuses into the inner core to bond the outer layers and the core, as well as bonding any separate sections of the core that may be present.

Where a blade segment requires the inserts at both ends, Ic. where the blade segment is an internal blade segment which is connected to adjacent blade segments at both ends, rather than a tip end blade segment which is connected to only one blade segment, separate blade inserts may be provided at both ends, or alternatively, one or more blade inserts may be provided which extend all of the way through the blade segments and outwardly extend from both ends.

The extent to which the inserts are required to outwardly extend beyond the end of the blade segments will depend upon the construction of the at least one connecting member to which the inserts are connected. A sufficient length must be provided beyond the end of the blade segment so that a secure connection can be made with the at least one connecting member.

Preferably, the inserts are provided in a direction which is substantially parallel to the longitudinal axis of the blade. A single insert may be provided at the end of a blade segment to be connected to an adjacent blade segment, or alternatively, two or more inserts may be spaced apart within the blade segment.

The rigid inserts may be formed of any suitable rigid material which is capable of withstanding the loading to which the insert will be subjected during use and which is capable of providing a secure connection to the at least one connecting member.

Preferably, the rigid inserts are formed of a metallic material.

The rigid inserts may be elongate in form, such as a rod or a beam, or may be in the form of a plate. The cross sectional shape and size of the insert will depend upon the construction of the at least one connecting member and the nature of the connection between the insert and the at least one connecting member. Suitable cross sectional shapes for a rigid beam include I-shaped or H-shaped beams.

Where two or more rigid inserts are incorporated into the connection arrangement, the rigid inserts may be of the same form as each other, or a combination of different forms of insert may be used.

Preferably the thickness of each of the inserts decreases towards at least one of its outer edges. This is particularly preferable at the outer edges of the portion of the insert that is supported or integrated within the blade segment as well as the outer edges of the portion of the insert that is in contact with the at least one connecting member. The reduction in thickness at the outer edges may be particularly desirable when the insert is in the form of a plate or beam. The reduction in thickness may be provided by a gradual reduction from the centre of the insert to the edges thereof, Alternatively, the insert may have a substantially constant thickness across the majority of its area, apart from at the outer edges where the reduction of thickness is provided. For example, the outer edges of the insert may be bevelled.

A reduction of thickness of one or more of the outer edges of the insert reduces the stiffness of the insert at those edges and ensures that the integration of the insert within the blade segment does not generate high shear stresses and does not affect the mechanical integrity of the outer shell or the reinforcement rims, webs or other internal composite structures, where present. In addition, the reduction of thickness of the outer edges of the portion of the insert in contact with the at least one connecting member helps to reduce the levels of stress in the region of the connection.

* In addition or alternatively to the reduction in thickness of the insert at the outer edges of the portion of the insert that is supported within the blade segment, this portion of the insert may comprise a plurality of teeth or lugs extending from at least one edge thereof.

The insert is preferably provided with teeth on the edge that is perpendicular to the blade segment longitudinal axis, or on the two opposed edges that are parallel to the blade segment longitudinal axis, or on all edges of the portion of the insert that is supported within the blade segment. The provision of teeth advantageously improves the load distribution at the edges of the insert so that the shear stress levels in the inner core or in the reinforcement structure accommodating the insert within the blade segment can be reduced in the region in which the insert is embedded.

The at least one connecting member of the blades according to the invention is provided between adjacent blade segments and is connected against or around the rigid inserts extending from the ends of the adjacent segments. Suitable constructions for the at least one connecting member would be known to the skilled person. In preferred embodiments, the at least one connecting member comprises at least one connecting plate and/or connecting beam, which is fixed or attached to the rigid inserts extending from the ends of the blade segments to be connected together. In a particularly preferred embodiment, the at least one connecting member comprises at least one metal fishplate.

The connection between the at least one connecting member and the rigid inserts may be achieved through any conventional means. For example, the rigid inserts may be welded to the at least one connecting member or more preferably, the connection arrangement may further comprise one or more mechanical fasteners, such as nut and bolt fasteners, for connecting or clamping the rigid inserts to the support member. This enables the blade segments to be easily assembled and dissembled, for installation, repair and maintenance operations.

In certain preferred embodiments, the connection arrangement comprises a pair of opposed connecting members connected to opposed sides of the rigid inserts. With this arrangement, the rigid inserts are securely fixed between the opposed connecting members.

In certain cases, it may be appropriate to use a larger number of connecting members, for example, three or four connecting members clamping the rigid inserts between them.

In addition to the reinforcement ribs described above, the blade segment may be provided with additional internal, reinforced rims or webs or other internal composite structures which extend transversely across the blade segment cross section to provide additional reinforcement. The rims or webs or other internal composite structures may be provided along a part or all of the length of the blade segment. For example, additional rims can be added locally to avoid blade shell buckling in specific regions where the blade experiences local large deflections while bending.

Preferably, the blades according to the present invention further comprise one or more aerodynamic covers arranged over and around the connection arrangement in order to maintain a substantially continuous airfoil surface in combination with the outer surfaces of the blade segments.

The nature of the connection arrangement and its position between the blade segments typically means that there will be a gap between the ends of the outer surface layers of adjacent blade segments and therefore a discontinuity in the airfoil surface of the blade. In certain cases, during use of the blades on a VAWT, this discontinuity may result in aerodynamic perturbations, such as induced drag loads and wakes, which potentially reduce the aerodynamic performance of the turbine. The inclusion of the aerodynamic covers will therefore typically be advantageous to the performance of the turbine, since the covers are placed over the connection arrangement and are adapted to maintain the continuous airfoil surface of the blade as much as possible, thereby avoiding or reducing the aerodynamic impact of the connection arrangement. The aerodynamic covers may also provide the additional function of protecting the connection arrangement from the external environment.

The aerodynamic covers may be fixed to the connection arrangement, or the outer surface layers at the ends of the connected blades segments, or both. The aerodynamic covers may be formed of a composite material that provides a similar surface finish to the outer surface layers of the blade segments. Alternatively, the aerodynamic covers may be formed of metallic plates that have been shaped to fit around the connection arrangement.

Preferably, blades according to the invention have a substantially constant cross section along the length thereof, providing a substantially constant aerodynamic airfoil profile and chord. Each of the blade segments making up the blades therefore also has a substantially constant cross section along its length and a cross section which is substantially the same as that of the other blade segments. This makes the production and assembly of the blades more straightforward than for a HAWT blade, where a varying aerodynamic profile and chord is necessary along the length.

The blade segments may be substantially straight, whereby a straight wind turbine blade is formed upon connection of the blade segments. Alternatively, one or more of the blade segments forming the blade may be curved or twisted in order to provide the blade with a non-straight configuration, such as a curved or helical configuration.

The blade segments forming the blade may be connected such that the longitudinal axes of the blade segment are aligned. This arrangement may be suitable, for example, for a substantially vertical blade. Alternatively, one or more of the blade segments forming the blade may be connected such that the longitudinal axes of adjacent blade segments are at * an angle to each other. With this configuration, it is possible to produce blades that extend around the central mast of the wind turbine rather than extending substantially vertically.

The invention will be further described, by way of example only, with reference to the following figures in which: Figure 1 shows a schematic representation of an H-shaped vertical axis wind turbine according to the invention; Figure 2 shows a schematic cross-sectional view of the connection arrangement between two blade segments forming the blade of the turbine of Figure 1; and Figure 3 shows a schematic cross-sectional view of an alternative connection arrangement between two blade segments forming a blade according to the invention.

The wind turbine 10 shown schematically in Figure 1 is a vertical axis wind turbine comprising a central, rotating mast 12 and two vertical blades 14. The blades 14 are positioned opposite to each other to provide an "H" configuration and each blade is connected to the central, rotating mast 12 by four, spaced apart support arms 16a,b,c,d.

The support arms 16a,b,c,d extend substantially horizontally from the central rotating mast and the blades are mounted vertically on the ends of the support arms 16a,b,c,d. The uppermost support arm I 6a is provided at the top of the mast 12 and the blades 14 extend a short distance above the mast 12.

During use, the incident wind causes the blades 14 to rotate about the central mast 12 in the direction shown by the arrow A in Figure 1 and the aerodynamic torque is transmitted to the central mast 12 through the support arms 16a,b,c,d. The central mast 12 is mounted in a base portion 18 of the turbine which includes a generator (not shown). The rotation of the central mast 12 is transferred directly to the rotor of the generator in a known manner.

Each blade 14 is formed of three connected blade segments; an upper blade segment 20a, a middle blade segment 20b and a lower blade segment 20c. The blade segments 20a,b,c are of a similar length and cross section to each other and are assembled in a longitudinal, vertical direction. The blade segments 20a,b,c are each formed of an inner foam core 24 formed of a polyurethane foam and a number of overlying, outer layers 26 of a glass reinforced epoxy resin composite material.

Adjacent blade segments are connected together by a connection arrangement, 22a,b. A first connection arrangement 22a is provided between the ends of the upper 20a and the middle 20b blade segments whilst a second connection arrangement 22b is provided between the ends of the middle 20b and the lower 20c blade segments. The first 22a and second 22b connection arrangements are of the same construction as each other and the description of connection arrangement 22a below applies equally to the connection arrangement 22b.

Figure 2 shows a schematic cross-sectional view of the connection arrangement 22a between the upper blade segment 20a and the middle blade segment 20b. The connection arrangement 22a comprises a first metal insert 28a extending from the lower end of the upper blade segment 20a, a second metal insert 28b extending from the upper end of the middle blade segment 20b and a metal fishplate 30 connecting the ends of the elongate metal beams 28a,28b. Each of the metal inserts 28a,28b is in the form of a metal rod or plate which is embedded in the foam core at the end of the corresponding blade segment 20a or 20b and extends a short distance beyond the end of the blade segment. The extending ends of the metal inserts 28a,28b are bolted to the fishplate 30.

As shown in Figure 2, the support arm lOb is also connected to the fishplate 30 by means of additional attachment bolts (not shown) or a welded joint. The support arm 16c is similarly connected to a fishplate in the connection arrangement 22b. The upper 16a and lower 16d support arms are connected to the upper 20a and lower 20c blade segments at a position away from the joints between the adjacent segments and for these support arms, a different form of attachment arrangement is used.

An aerodynamic cover 32 is provided around the connection arrangement. The cover 32 provides a bridge between the outer surface layers of the adjacent blade segments so that the outer, airfoil surface of the blade 14 remains as continuous as possible and the connection arrangement 22a,b is covered. The portion of the aerodynamic cover 32 in the region of the support arm 16 is curved outwardly towards the support arm 16, in order to integrate more gradually with the surface thereof.

Figure 3 shows an alternative connection arrangement 122 for connecting two adjacent blade segments 120a,b which is similar to the arrangement shown in Figure 2 but without the attachment of a support arm 16 to the connection arrangement 122.

Furthermore, in the arrangement 122 a pair of opposed fishplates 130 is provided in place of the single fishplate 30 in the embodiment of Figure 1. As shown in Figure 3, the extending portions of the metal inserts 128a,b are bolted between the fishplates 130 and an aerodynamic cover 132 is provided around the fishplates 130.

Claims

CLAIMS1. A blade for a vertical axis wind turbine wherein the blade is formed of two or more connected blade segments, wherein the ends of adjacent blade segments are connected together by means of a connection arrangement provided between the adjacent blade segments, the connection arrangement comprising: one or more rigid inserts supported within the interior of each of the blade segments and each having a portion extending outwardly from the end of the blade segment towards the end of the adjacent blade segment; and at least one connecting member between adjacent blade segments and connected to the outwardly extending portions of the one or more rigid inserts.
2. A blade according to claim I wherein the at least one connecting member comprises attachment means for attaching the connection arrangement to a support arm of a vertical axis wind turbine.
3. A blade according to claim 1 or 2 wherein each blade segment comprises an outer shell formed of one or more layers of a composite material and wherein the one or more rigid inserts are connected to the outer shell by means of one or more reinforcement rims, webs or internal structures made of composite material extending between the one or more rigid inserts and the internal surface of the outer shell.
4. A blade according to claim 1, 2 or 3 wherein each blade segment comprises an inner core and wherein the one or more rigid inserts are embedded within the inner core.
5. A blade according to any preceding claim wherein each of the one or more rigid inserts is a metal rod, beam or plate supported within the blade segment in a direction substantially parallel to the blade longitudinal axis.
6. A blade according to any preceding claim wherein each of the one or more rigid inserts comprises an outer layer of a composite material.
7. A blade according to any preceding claim wherein the at least one connecting member comprises at least one connecting plate or beam connected to the outwardly extending portions of the one or more rigid inserts.
8. A blade according to any preceding claim wherein the one or more rigid inserts are connected to the at least one connecting member by means of one or more mechanical fasteners, preferably one or more nut and bolt fasteners.
9. A blade according to any preceding claim wherein the connection arrangement comprises two opposed connecting members connected to opposed sides of the rigid inserts.
10. A blade according to any preceding claim further comprising one or more aerodynamic covers arranged over the connection arrangement in order to maintain a substantially continuous airfoil surface in combination with the outer surfaces of the blade segments.
11. A blade according to any preceding claim wherein the thickness of the one or more rigid inserts decreases towards at least one of the outer edges thereof.
12. A vertical axis wind turbine comprising a central mast and two or more blades according to any preceding claim, wherein each blade is connected to the central mast by means of one or more support arms and wherein at least one support arm is connected to the blade through the connection arrangement between adjacent blade segments.
13. A blade segment for forming a blade for a vertical axis wind turbine wherein the blade is formed of two or more connected blade segments, wherein the blade segment comprises one or more rigid inserts supported within the interior of the blade segment and having at least a portion extending outwardly from an end of the blade segment.