I NTRODUCTI ON

The disclosure relates to a m ultirotor wind turbine comprising a tower extending in a vertical direction from a tower bottom to a tower top. The wind turbine further com prises a load carrying structure extending transverse to the vertical direction and arranged to carry at least two energy generating units, the load carrying structure being carried rotationally by the tower via a yaw

arrangement.

BACKGROUND OF THE I NVENTI ON Wind turbines norm ally comprise one or m ore energy generating units, each energy generating unit comprising a load carrying hub carrying one or m ore wind turbine blades. The wind acts on the wind turbine blades, thereby causing the load carrying hub to rotate. The rotational movements of the load carrying hub are transferred to a generator, either via a gear arrangem ent or directly, in the case that the wind turbine is of a so-called direct drive type. I n the generator, electrical energy is generated, which may be supplied to a power grid.

Some wind turbines are provided with two or more energy generating units in order to increase the total power produced by the wind turbine, without having to provide the wind turbine with one very large, and therefore heavy, energy generating unit. Such wind turbines are som etimes referred to as‘m ultirotor wind turbines’.

Traditional horizontal axis wind turbines sometim es utilise the roof of the energy generating unit as platform for hoisting spare parts to and from the energy generating unit. Som etimes, the roof is used also as a landing platform for a helicopter. Since the major part of the assem bly and service work on a wind turbine is carried out on the drive train and com ponents thereof, the roof of the energy generating unit is a natural choice for establishing access to the wind turbine for helicopters or drones or for hoisting spare parts to and from the wind turbine.

Not least on off-shore installations, such a platform m ay provide easy and safe access to the energy generating unit.

I n m ultirotor wind turbines the energy generating units m ay be carried by a load carrying structure which is, in turn, connected to a tower via a yaw bearing structure. I n such wind turbines, centre of gravity of the energy generating units is displaced with respect to a longitudinal, vertical axis defined by the tower.

Due to the displacement, the roof of the energy generating units m ay becom e unsuitable as a platform for hoisting or landing purpose.

DESCRI PTI ON

It is an object of em bodim ents of the invention to provide a m ultirotor wind turbine with im proved access for spare parts and personnel. It is a further object of em bodim ents to provide improved strength of a m ultirotor structure and to increase safety relative to helicopter operations near a wind turbine.

According to a first aspect, herein is disclosed a m ultirotor wind turbine com prising :

- a tower extending in a vertical direction from a tower bottom to a tower top;

- at least two energy generating units, each energy generating unit holding a rotor defining a rotor plane, and each energy generating unit com prising a drive train driven by the rotor, and

- a load carrying structure extending transverse to the vertical

direction and arranged to carry the at least two energy generating units (5) , the load carrying structure being carried rotationally by the tower via a yaw arrangement, the m ultirotor wind turbine further com prising a platform form ing an upwards facing plane working surface, particularly a platform being rem ote from the energy generating unit.

The working surface defines a working area where personnel can receive parts being lowered from a helicopter or from a drone, or it defines a working area where a helicopter or a drone can land.

I n the following, helicopters, drones, or any sim ilar flying objects configured for transport of personnel and/or parts to and from a platform is generally referred to as vehicle.

When the platform is remote from the energy generating unit, the risk of collision between the rotor and the vehicle is reduced. Further, the risk of fire, explosion, or other potentially hazardous m alfunctioning of the wind turbine is higher in, or near, the energy generating unit, and when the platform is rem ote from the energy generating unit, it increases the potential for the platform to be used during escape from a m alfunctioning or burning wind turbine.

The working surface may particularly be form ed as a receiving platform with an area which is at least 1 -2 square m eters large to enable receipt of parts which are lowered. Such a platform m ay have a surrounding fence

The working surface may alternatively be formed as a landing platform with an area of at least 10 square m eters and not having an upwards fence but rather an outwards or slightly downwards safety net surrounding the working surface.

The platform m ay also include a reconfigurable fence having at least a lowered and a raised configuration where the fence projects over the working surface in the raised configuration and is at or below the working surface in the lowered configuration. I n that way, the platform can change between being suitable as a working platform and being suitable as a landing platform . I n the present context the term‘m ultirotor wind turbine’ should be interpreted to mean a wind turbine com prising two or m ore energy generating units mounted on one tower.

I n the present context the term‘energy generating unit’ should be interpreted as a nacelle, a rotor with blades, and a drive train. The drive train may include a shaft connecting the rotor to a generator, and optionally also include a gearbox between the rotor and the generator. I n a direct driven wind turbine, the drive train may only be constituted by the rotor part of the generator. Parts of the drive train are typically inside the nacelle. According to the invention, at least a part of an energy generating unit is attached to the fram e. This part could e.g. be the nacelle including or excluding the drive train inside the nacelle, the rotor including or excluding the blades, or it could be the complete energy generating unit.

By definition herein, the direction facing the front of the rotor plane, i.e. the direction of the wind is called downstream direction, and the opposite direction from the nacelle towards the rear of the rotor plane is called upstream direction.

The energy generating unit could be configured to face the rotor plane against the wind, i.e. a so called upstream units or it could be configured to face the nacelle against the wind and the rotor away from the wind, i.e. a so called downstream units.

I n the present context, the term‘tower’ should be interpreted to m ean a substantially vertical structure, arranged to carry the energy generating units of the m ultirotor wind turbine via at least one load carrying structure.

I n addition to the claim ed load carrying structure with at least one energy generating unit, one or m ore additional energy generating units may be mounted directly on the tower. The tower m ay com prise a num ber of tower segm ents, which are assem bled to form the tower.

A single tower m ay carry one, two, or more load carrying structures. Each load carrying structure may be supported by one or more towers, e.g. arranged such that m ore towers are connected by a load carrying structure extending between the towers.

Each load carrying structure may carry at least two energy generating units, e.g. three, four, five or six energy generating units. For this purpose, the load carrying structure m ay e.g. have a triangular, quadrangular, pentagonal or hexagonal outer contour, or it m ay stretch out far from the tower in different directions and have several energy generating units attached in rows extending away from the tower.

The working surface could be offset in horizontal direction relative to the energy generating units in such a way that the energy generating unit is at least partly outside the outer contour of the platform when seen in a top view in the direction from the tower top to the tower bottom . Preferably the distance between the outer contour of the energy generating units and the platform is at least equal to the length of the blades of the energy generating units such that the distance between the outer contour of one energy generating unit and the platform is at least equal to the length of the blades of that energy generating unit. I n one em bodim ent, the distance between the outer contour of the energy generating units and the platform is at least equal to half of the distance between two energy generating units which are on opposite sides of the tower. This may particularly be an advantage when the platform is located above the tower top.

The platform could be placed in an altitude which is higher than the altitude of the energy generating units, e.g. at an altitude which is higher than the highest mounted energy generating unit. The vertical distance, defined as the difference in altitude of the highest m ounted energy generating unit and the platform could be at least equal to the length of the blades of the energy generating unit.

The working surface could also be offset in horizontal direction relative to the rotor planes of one or of all energy generating units in such a way that all rotor planes are at least partly outside the outer contour of the platform when seen in a top view in the direction from the tower top to the tower bottom . Even though this m ay not necessarily be a requirement for safe landing, e.g. if the platform is at a m uch higher altitude, it may increase safety further.

By“centre of the platform” is herein m eant the geom etrical centre. I f the platform is circular, the centre of the platform is the centre of circle. If the platform has other shapes, the centre is the arithm etic mean position of all the points in the two dim ensional shape of the working surface of the platform , i.e. the m ean position of all the points in in an XY-coordinate system in the plane of the working surface.

The platform could be arranged sym metrically between two rotor planes when seen in a top view in the direction from the tower top to the tower bottom . The sym m etry m eans that one rotor plane can be m irrored onto another rotor plane by a m irror plane through the centre of the platform .

The working surface could be offset in a horizontal plane relative to tower in such a way that the working surface is asym m etric relative to the tower top. By asym metric is herein meant that the geom etric centre of the working surface is offset relative to the geom etric centre of a cross section transverse to the tower at the tower top.

As a result of the asym metry, a front point of the outer periphery of the platform may be behind the corresponding front point of the periphery of the tower top cross section in the direction from the rotor plane along the rotor axes and rearwards away from the rotor planes. The distance between the front points in the rearward direction could be anything above zero such as 1 0, 20, 30, 40, 50, 60 or m ore percent of the largest dimension of the platform .

An opposite asym m etry can also be applied, i.e. instead of the front point of the outer periphery of the platform being behind the corresponding front point of the periphery of the tower top cross section, the front point of the outer periphery of the platform could be in front of the corresponding front point of the periphery of the tower top cross section in the direction towards the rotor planes. The offset could particularly be to the extent where the tower top is at least partly outside the outer contour of the platform when seen in a top view in the direction from the tower top to the tower bottom . The offset could particularly be to the extent where the centre of the platform is outside the outer contour of the tower top.

The offset may enable improved access to the tower and prevent that the platform prevents access to the upper tower parts.

On a wind turbine with upstream units, the platform may be offset in the downstream direction, and on downstream units, the platform m ay be offset in the upstream direction to thereby bring the platform further away from rotor plane and thus increase safety.

To increase safety, the distance from the platform to the tower could be sm aller than a distance from the platform to the energy generating structures.

Particularly, the tower top could be at least partly within the outer contour of the platform when seen in a top view in the direction from the tower top to the tower bottom . I .e. the platform could be directly at the tower top.

The tower top could be at a higher altitude than at least a part of the energy generating units, e.g. at a higher altitude than the hub of the energy generating unit, herein referred to as hub-height. The platform could be at a higher altitude than the tower top, e.g. such that the platform defines the highest point of the wind turbine.

The platform may be integrated in structural com ponents of the tower. By structural components of the tower is herein m eant those parts of the tower which provides play a role in providing the structural rigidity and strength which is required for the tower. The tower com prises a plurality of such structural com ponents which are designed, engineered and m anufactured under controlled conditions for a specific purpose with respect to strength and rigidity and considering a specific load situation. The platform may e.g. be structurally connected to at least a part of the load carrying structure, and/or the platform m ay be structurally connected to the tower top.

The load carrying structure m ay com prise: - a load carrying hub rotationally carried by the tower via the yaw arrangement;

- a first load carrying arrangem ent extending outwards on a left side of the load carrying hub; and

- a second load carrying arrangement extending outwards on a right side of the load carrying hub; each load carrying arrangem ent may com prise a primary structure attached to the load carrying hub in a lower interface and extending between the lower interface and a corresponding one of the at least two energy generating units. Accordingly, each load carrying arrangement is arranged to handle the loads involved with carrying their respective energy generating unit(s) . Furtherm ore, the load carrying arrangem ents m ay advantageously be arranged on opposing sides of the tower, in order to balance forces and loads with respect to the tower.

Each load carrying arrangem ent may com prise a tension arrangem ent, the tension arrangem ent may com prise at least one secondary structure attached to the load carrying hub in an upper interface and extending above the prim ary structure between the upper interface and the corresponding one of the at least two energy generating units such that gravity acting on the energy generating units causes compression of the prim ary structure and tension in the at least one secondary structure.

Particularly, each load carrying arrangem ent m ay comprise a primary structure and at least two secondary structures, i.e. the tension arrangement may com prise: - a forward secondary structure attached to the load carrying hub in a forward point of the upper interface and extending above the prim ary structure between the forward point and the corresponding one of the at least two energy generating units, and

- a rearward secondary structure attached to the load carrying hub in a rearward point of the upper interface and extending above the prim ary structure between the rearward point and the corresponding one of the at least two energy generating units, where the forward point and rearward point are on opposite sides of the right side or left side of load . Preferably, the axes defined by the prim ary structure and the two secondary structures are not arranged in the sam e plane, thereby defining a three-dimensional carrying structure.

This design has the consequence, that when gravity acts on the energy generating unit, this causes push in the prim ary structures and pull in the secondary structures. This causes the secondary structures to be preloaded, due to gravity acting on the energy generating units. The preloading of the secondary structures ensures that these structures are capable of handling loads originating from thrust of the energy generating units. I n particular, since the secondary structures extend on opposing sides of the prim ary structure, i.e. the forward secondary structure on one side and the rearward secondary structure on the other side of the prim ary structure, thrust loads acting in one direction will increase the pull in a first secondary structure and decrease the pull in the second secondary structure, while thrust loads acting in an opposite direction will decrease the pull in the first secondary structure and increase the pull in the second secondary structure. However, the preload in the secondary structures ensures that a certain pull rem ains in each of the secondary structures, also when the pull is decreased, due to the thrust loads. The two opposing directions could, e.g. , be the direction of the incom ing wind and the opposite direction.

This specific layout and the load handling supported thereby is advantageous in connection with the platform . When the platform is structurally connected to at least a part of the load carrying structure, the platform m ay provide increased strength e.g. by increasing the distance between the forward and rearward secondary structures. The platform could be connected to at least one of the primary structures, it could be connected to at least one of the secondary structures, or the platform could form part of an upper interface connecting the at least one secondary structure to the load carrying hub The load carrying structure m ay advantageously be designed in such a m anner that collisions between the wind turbine blades of the energy generating units on the one hand, and the primary and secondary structures and the tower, on the other hand, are avoided. For instance, the prim ary structures may extend from the tower in a slightly forward direction, i.e. into the incom ing wind, thereby positioning the wind turbine blades in front of the tower. This also allows the secondary structures, extending on opposing sides of the prim ary structures, to be attached to the tower at a position behind the position of the wind turbine blades. At the sam e tim e, this will position the platform away from the rotor planes if it is placed between forward and rearward secondary structures. Accordingly, the platform may be closer to one of the forward secondary structure and rearward secondary structure than to the other one of the forward secondary structure and rearward secondary structure.

One of the forward secondary structure and rearward secondary structure could be connected to the platform and the other one of the forward secondary structure and rearward secondary structure could be connected to the load carrying hub.

I n one embodiment, the platform is connected to both the forward secondary structure and to the rearward secondary structure.

Accordingly, the platform may extend between the forward and the rearward secondary structures and thus provide an increased distance between the forward and the rearward secondary structure.

It is not ruled out that a single tower may have two or m ore load carrying structures of the kind described above mounted thereon. I n this case the load carrying structures m ay advantageously be arranged one above the other along the length of the tower.

Each primary structure m ay be in the form of one or more com pression bars. Com pression bars are suitable for receiving push. The compression bars could, e.g. , be in the form of tubes, rods, beams, such as I -beams, etc.

At least the working surface of the platform could be m ovable relative to the load carrying structure and fixed relative to the tower such that the working surface becomes fixed and does not rotate with the yaw movement of the wind turbine. This m ay enable a m ore stable working platform and im prove the conditions for landing with a vehicle.

Alternatively, at least the working surface of the platform is fixed relative to the load carrying structure and movable relative to the tower. That m ay enable steady conditions on the working surface with respect to the wind direction, i.e. the wind direction is always from the sam e direction relative to the working surface.

To facilitate access between the working surface and other areas of the wind turbine, the wind turbine m ay com prise an elevator, e.g. an elevator driving in the tower between different points of access. One point of access could be at a hatch at the tower bottom , one point of access could be at the place where the load carrying structure interface the tower, and one point of access could be at the platform , e.g. at the working surface.

If the platform is offset relative to the tower, the point of access at the working surface could be at the edge of the working surface. If the platform is directly above the tower top, the point of access at the working surface could be through a hole in the working surface.

The wind turbine may comprise a working passage extending from the working surface to the energy generating unit and allowing personnel to m ove between the nacelle and the working surface in a protected m anner. The working passage may include passage sections extending inside the tower and/or inside the prim ary structure to allow further protection during use of the passage.

The wind turbine m ay com prise a hoisting device located at the platform and configured for hoisting and lowering of item s from the working surface to and from a lower location of the wind turbine. Particularly, the hoisting device m ay be configured for moving items from the working surface to at least one of the energy generating units. The hoisting device may e.g. be in the form of a crane, e.g. a tower crane, and it m ay have an outrigger arm which is extendable to allow movement of the handled item in a direction being perpendicular to the vertical direction of the tower.

The wind turbine m ay comprise switchgear, power converter, and sim ilar electrical components configured for connecting the generators of the energy generating units to a power grid. Herein the term“electrical connection equipment incudes converters, transform ers, inverters, switch gear and peripheral equipm ent e.g. for cooling the aforementioned components.

I n one em bodim ent, the m ultirotor wind turbine com prises one or m ore sets of electrical connection equipm ent at the tower top beneath the platform . The m ultirotor wind turbine m ay e.g. comprise one set of electrical connection equipment for each energy generating unit, or it m ay com prise one m utual set of electrical connection equipm ent for all energy generating units.

The electrical connection equipm ent can be located in the tower below the working surface, or the electrical connection equipm ent can be located outside the tower, e.g. suspended on the side of the tower, beneath the platform .

The electrical connection equipm ent may particularly be accessible through the working surface. For that purpose, the working surface may com prise an opening through which the electrical connection equipm ent can be accessed.

The location of the electrical connection equipment beneath the platform facilitates easy access to service and replacement by use of flying vehicles, and the location at the top of the tower may increase safety and allow rescue of personal to the ground in case of fire in the electrical connection equipm ent. Further, the location of the electrical connection equipment at the tower top may reduce electrical loss and provide a m ore efficient energy production.

Additionally, the location at the tower top below the platform m ay increase balance in the tower and reduce the com plexity and dim ensions of the load carrying structure.

The electrical connection equipm ent referred to herein could particularly be for 33, 66 or 132 KVolt.

The rotor of the m ultirotor wind turbine m ay particularly comprise a set of rotor blades, particularly three blades. The m ultirotor wind turbine may further com prise a rotor locking structure configured to lock rotation of the rotor in a position where one blade extends in a direction from the energy generating unit towards a lower surface of the platform e.g. pointing in a horizontal direction.

The m ultirotor wind turbine m ay particularly com prise a coordinating locking structure configured to operate on two adjacent energy generating units to lock the rotor of both units such that at least one blade of each unit points towards a blade of the other unit. This may particularly be a position where both blades are horizontal.

I n a second aspect, a method of suspending a platform on a m ultirotor wind turbine is disclosed. The m ethod relates to a wind turbine com prising

- a tower extending in a vertical direction from a tower bottom to a tower top;

- a load carrying structure extending transverse to the vertical

direction and arranged to carry at least two energy generating units, the load carrying structure being carried rotat ion ally by the tower via a yaw arrangem ent.

According to the m ethod, the platform is arranged offset in a direction

perpendicular to the vertical direction relative to the energy generating units. The load carrying structure could be provided in accordance with the wind turbine of the first aspect of the invention, and the platform could be connected to at least one of the secondary structures. Particularly, it could be placed between the rearward and forward secondary structure to thereby increase the distance between these structures and improve the strength and stability of the load carrying structure. The m ethod according to the second aspect m ay im ply the use of any of the structures disclosed relative to the first aspect of the disclosure.

I n a third aspect, the invention provides a m ethod for bringing spare parts and personnel to and from a m ultirotor wind turbine according to claim 1 , the method comprising landing a flying vehicle on the working surface.

The m ethod may particularly be used for rescue of persons from the m ultirotor wind turbine, e.g. in case of fire etc.

Further, the method may particularly be applied for servicing or replacem ent of electrical connection equipment.

BRI EF DESCRI PTI ON OF THE DRAWI NGS

The invention will now be described in further detail with reference to the accompanying drawings in which :

Fig. 1 is a front view of a m ultirotor wind turbine comprising two load carrying structures according to an embodiment of the invention,

Fig. 2 is a side view of the m ultirotor wind turbine of Fig. 1 ,

Fig. 3 is a top view of the m ultirotor wind turbine of Figs. 1 and 2,

Figs. 4-7 show details of different em bodim ents of the m ultirotor wind turbine,

Fig. 8 illustrates that the rotor planes are outside the contour of the platform , and Figs. 9- 10 illustrate different properties of asym m etry between the platform and the tower top cross section.

DETAI LED DESCRI PTI ON OF THE DRAW I NGS

Fig. 1 is a front view of a m ultirotor wind turbine 1 com prising a tower 2 carrying two load carrying structures 3 according to an embodim ent of the invention. The load carrying structures 3 are arranged, one above the other, along the length of the tower 2.

Each load carrying structure 3 comprises two load carrying arrangements 4, extending away from the tower 2 on opposite sides of the tower 2, as seen from the viewing angle of Fig. 1 . Each load carrying arrangement 4 carries an energy generating unit 5, and each energy generating unit 5 com prises a nacelle 6 and a rotor 7 carrying three wind turbine blades 8.

Each load carrying arrangem ent 4 comprises a primary structure 9, in the form of a tube, and two secondary structures 10, in the form of double wires. I n Fig. 1 , only one of the secondary structures 10 for each load carrying arrangem ent 4 is visible.

The primary structures 9 extend away from the tower 2 along a direction which form s an acute angle with respect to a substantially vertical longitudinal axis defined by the tower 2. Thereby the prim ary structures 9 extend away from the tower 2 along an inclined upwards direction.

The secondary structures 1 0 extend away from the tower 2 along a direction which is substantially perpendicular to the substantially vertical longitudinal axis defined by the tower 2. Thereby the secondary structures 10 extend away from the tower 2 along a substantially horizontal direction. Accordingly, an angle is defined between the direction in which primary structure 9 of a given load carrying arrangement 4 extends, and the plane in which the secondary

structures 10 of the load carrying arrangement 4 extend. The primary structures 9 and the secondary structures 10 are attached to the tower 2 via a yaw arrangement 1 1 , allowing the entire load carrying structure 3 to perform yawing m ovements with respect to the tower 2 in order to direct the rotors 7 into the incom ing wind. The m ultirotor wind turbine further com prising a platform 12 form ing an upwards facing plane working surface

The primary structures 9 of a given load carrying structure 3 and the secondary structures 10 of the load carrying structure 3 are attached to the tower 2 at separate positions along the length of the tower 2. When gravity acts on the energy generating units 5, the m utual positions of the prim ary structures 9 and the secondary structures 1 0 causes push in the prim ary structures 9 and pull in the secondary structures 10. Thereby a preload is introduced in the secondary structures 10, due to the gravity acting on the energy generating units 5. During operation of the m ultirotor wind turbine 1 , thrust forces will act on the energy generating units 5, in the direction of the incom ing wind or in the opposite direction. When this occurs, the pull in one of the secondary structures 10 of each of the load carrying arrangements 4 is decreased while the pull in the other secondary structure 10 is increased. However, the preload introduced in the secondary structures 10, due to gravity acting on the energy generating units 5, is sufficiently high to ensure that the secondary structure 10, in which the pull is decreased, rem ains tight. Accordingly, the load carrying structure 1 is capable of handling the thrust forces introduced during operation of the m ultirotor wind turbine 1 . Fig. 2 is a side view of the m ultirotor wind turbine 1 of Fig. 1 . It can be seen in Fig. 2 that the prim ary structures 9 extend from a position behind the tower 2 to a position in front of the tower 2, thereby positioning the rotors 7 of the energy generating units 5 in front of the tower 2, and facing the incom ing wind. It can further be seen that one of the secondary structures 10 of each load carrying arrangem ent 4 extends from an attachm ent point behind the tower 2 to the position of the energy generating unit 5. This will be described in further detail below with reference to Fig. 3.

Fig. 3 is a top view of the m ultirotor wind turbine 1 of Figs. 1 and 2. I n Fig. 3 it can be seen that the platform 12 is offset in horizontal direction relative to the rotor planes 19, i.e. it is located at a distance behind the rotor planes.

Each load carrying arrangem ent 4 comprises two secondary structures 10’, 10”extending on opposing sides of the prim ary structure 9 from the position of the energy generating unit 5 to respective attachment points at the tower 2. This, combined with the fact that the prim ary structures 9 extend in an inclined upwards direction, as described above with reference to Fig. 1 , has the consequence that the primary structure 9 and the secondary structures 10 of each load carrying arrangem ent 4 form a three-dimensional structure, which ensures that an appropriate preload is introduced in the secondary structures 10, due to gravity acting on the energy generating unit 5.

The working surface 17 of the platform 12 is made with an open structure allowing wind to blow through the surface. This improves the landing conditions for a vehicle.

For each load carrying arrangem ent 4, one of the secondary structures 10’, 10” is attached to the tower 2 at a rearward point via the spacer 13 and via the platform 12 to which the spacer 13 is attached. I n the illustrated em bodim ent, the platform is displaced rearward relative to the tower and it increases the distance from the tower 2 to the rearward secondary structure 10”. The other, forward, secondary structure 10’ is attached to the tower 2 via a forward point on the platform 12 at a position in front of the tower 2 and closer to the tower 2 than the rearward secondary structure 10”. As described above with reference to Fig. 2, the primary structure 9 extends from a position behind the tower 2 to a position in front of the tower 2. This allows the rotor 7 of each of the energy generating units 5 to be arranged in front of the tower 2, and in front of the prim ary structure 9 and both of the secondary structures 10. Thereby the wind turbine blades 8 are kept clear from not only the load carrying structure 3 but also from the platform 12, and the risk of collision is m inim ised.

Fig. 4 illustrates in further details the forward and rearward attachm ent points via the platform 12 to thereby provide an increased distance between the forward and rearward secondary structures 10’, 10”. The illustrated platform is plane had form s an outwards, and slightly downwards fence 14 m aking the working surface suitable for landing with a vehicle.

Fig. 5 illustrates an alternative em bodim ent of the wind turbine, where the platform includes an upwards fence 15 making the working surface suitable for personnel to work and receive objects which are hoisted down from a vehicle above the wind turbine. Again, the rearward secondary structure 10” is attached to the tower 2 via a spacer 13 and via the platform 12, and the forward secondary structure 10’ is attached to the tower 2 via the platform 12.

Fig. 6 illustrates an alternative em bodim ent, wherein the working surface forms a landing surface for a vehicle. I n this embodiment, the working surface is asym metric relative to the tower top, i.e. it has a geometric centre which is offset in horizontal direction relative to tower. I n the illustrated em bodim ent, the offset has a size whereby in such a way that the tower top is com pletely outside the outer contour of the working surface when seen in a top view in the direction from the tower top to the tower bottom . I n this em bodim ent, the rearward secondary structure 10” is fixed to, and extends below the working surface. The illustrated platform 12 includes a passage bridge 16 allowing access for personnel between the interior of the tower 2 and the working surface 17.

Fig. 7 illustrates further details of the passage bridge 16 and the entrance opening 18 allowing entrance from the access bridge 16 into the tower 2.

Fig. 8 illustrates a top view of an em bodim ent where the working surface 17 is offset in horizontal direction relative to the rotor planes 19 of the energy generating units 5 such that all rotor planes are at least partly outside the outer contour of the platform . Figs. 9 and 1 0 illustrate details of asym m etry between the tower cross section and the platform . Both Fig. 9 and Fig. 10 illustrate the wind turbine seen from above and Fig. 8 illustrates an em bodim ent where the contour of the platform 12 overlaps the contour of the tower top 2”. Fig. 9 illustrates an embodiment where the contour of the platform 12 does not overlap the contour of the tower top 2”.

The illustrated wind turbine has blades form ing a rotor plane 20 by rotation of blades around the rotor axes 21 , and in both em bodiments the platform 12 is asym metric in the direction away from the rotor planes 20, and in both em bodim ents, the platform 12 is com pletely within the borders defined on right and left sides by the rotor exes 21 .

The platform 12 is asym m etric relative to the tower top 2” which m eans that the geom etrical centre of the platform 12 is shifted relative to the geometric centre of the cross section of the tower top.

I n both Fig. 9 and 1 0, a front point 22 of the outer periphery of the platform 12 is behind the corresponding front point 23 of the periphery of the tower top cross section in the direction of the arrow 24, i.e. in the direction from the rotor plane 20 along the rotor axes 21 and rearwards. The distance between the front points 22 and 23 in the direction of the arrow 24 could be anything above zero such as 10, 20, 30, 40, 50, 60 or m ore percent of the largest dim ension of the platform .

An opposite asym m etry can also be applied, i.e. instead of the front point 22 of the outer periphery of the platform 12 being behind the corresponding front point 23 of the periphery of the tower top cross section in the direction of the arrow 24, the front point 22 of the outer periphery of the platform 12 is in front of the corresponding front point 23 of the periphery of the tower top cross section in the direction opposite the arrow 24. Again, the distance between the front points 22 and 23 in the direction opposite the arrow 24 could be anything above zero such as 10, 20, 30, 40, 50, 60 or m ore percent of the largest dimension of the platform .