Patent Description:
Modern wind turbines are used for supplying electricity to the grid. A wind turbine generally includes a tower with a nacelle supported on top of the tower. A wind turbine rotor comprising a hub and a plurality of wind turbine blades may be rotatably mounted to the nacelle.

The wind turbine blades may be set in motion by wind. The hub of the wind turbine may be operatively coupled with a rotor of a generator. As the hub and blades rotate, the kinetic energy of the wind is converted to kinetic mechanical energy of the wind turbine rotor and ultimately to electrical energy or power in the generator. The generator may typically be arranged inside the nacelle.

The wind turbine rotor may be coupled directly to the generator rotor in so-called direct drive wind turbines. Or the wind turbine rotor may include a main rotor shaft (a so-called "low speed shaft") which leads to a gearbox. A high-speed shaft of the gearbox may then drive the generator. Regardless of the topology of the wind turbine, the electrical power output of the generator may be fed to an electric grid. The connection of the generator to the grid may include e.g. a converter, transformer, medium voltage line and other.

Elements like the gearbox, the generator, and converter, electrical power cables, cooling systems and structures (e.g. bedplate and frames) may be partly or completely housed in a nacelle. The nacelle provides a cover to protect such elements from the outside environment. The nacelle may comprise a structural frame made of e.g. steel beams and bars and a housing or enclosure made of a composite material such as glass fibre reinforced composites.

Throughout the lifetime of a wind turbine, it may be necessary to remove a component such as e.g. a gearbox from the nacelle for major repair or for substitution by a new component. It is known in the art to remove the roof the nacelle and lower the roof using a large crane. Access is thus provided to the nacelle from the top. The component that is to be removed or replaced can then be lifted out of the nacelle. A wind turbine comprising a hatch on the roof of a nacelle is disclosed in <CIT>. Further prior art is disclosed in <CIT>, <CIT>, and <CIT>.

Using a large crane mounted on the ground can be expensive and cumbersome. The present disclosure provides methods that avoid the use of such a large crane.

In a first aspect, a wind turbine nacelle according to claim <NUM> is provided.

In accordance with this aspect, a wind turbine nacelle is provided to which access can be provided from above the nacelle without the need for a ground mounted crane. A nacelle mounted crane may be erected or unfolded thanks to space created by removing the roof panel.

In a further aspect, a method for providing access to an inside of a wind turbine nacelle according to claim <NUM> is provided. The method comprises detaching a displaceable roof panel from other portions of a roof of the nacelle and lifting the displaceable roof panel from an inside of the nacelle. The method further comprises displacing the displaceable roof panel towards a front or a rear of the nacelle.

Reference now will be made in detail to embodiments of the disclosure, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation only, not as a limitation. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present disclosure without departing from the scope of the appended claims. Thus, it is intended that the present disclosure covers such modifications and variations as come within the scope of the appended claims.

In examples, the rotor blades <NUM> may have a length ranging from about <NUM> meters (m) to about <NUM> or more. Rotor blades <NUM> may have any suitable length that enables the wind turbine <NUM> to function as described herein. For example, non-limiting examples of blade lengths include <NUM> or less, <NUM>, <NUM>, <NUM>, <NUM> or a length that is greater than <NUM>. As wind strikes the rotor blades <NUM> from a wind direction <NUM>, the rotor <NUM> is rotated about a rotor axis <NUM>. As the rotor blades <NUM> are rotated and subjected to centrifugal forces, the rotor blades <NUM> are also subjected to various forces and moments. As such, the rotor blades <NUM> may deflect and/or rotate from a neutral, or non-deflected, position to a deflected position.

In the example, the wind turbine controller <NUM> is shown as being centralized within the nacelle <NUM>, however, the wind turbine controller <NUM> may be a distributed system throughout the wind turbine <NUM>, on the support system <NUM>, within a wind farm, and/or at a remote control center. The wind turbine controller <NUM> includes a processor <NUM> configured to perform the methods and/or steps described herein. Further, many of the other components described herein include a processor.

As used herein, the term "processor" is not limited to integrated circuits referred to in the art as a computer, but broadly refers to a controller, a microcontroller, a microcomputer, a programmable logic controller (PLC), an application specific, integrated circuit, and other programmable circuits, and these terms are used interchangeably herein. It should be understood that a processor and/or a control system can also include memory, input channels, and/or output channels.

<FIG> is an enlarged sectional view of a portion of the wind turbine <NUM>. In the example, the wind turbine <NUM> includes the nacelle <NUM> and the rotor <NUM> that is rotatably coupled to the nacelle <NUM>. More specifically, the hub <NUM> of the rotor <NUM> is rotatably coupled to an electric generator <NUM> positioned within the nacelle <NUM> by the main shaft <NUM>, a gearbox <NUM>, a high-speed shaft <NUM>, and a coupling <NUM>. In the example, the main shaft <NUM> is disposed at least partially coaxial to a longitudinal axis (not shown) of the nacelle <NUM>. A rotation of the main shaft <NUM> drives the gearbox <NUM> that subsequently drives the high-speed shaft <NUM> by translating the relatively slow rotational movement of the rotor <NUM> and of the main shaft <NUM> into a relatively fast rotational movement of the high-speed shaft <NUM>. The latter is connected to the generator <NUM> for generating electrical energy with the help of a coupling <NUM>. Furthermore, a transformer <NUM> and/or suitable electronics, switches, and/or inverters may be arranged in the nacelle <NUM> in order to transform electrical energy generated by the generator <NUM> having a voltage between 400V to <NUM> V into electrical energy having medium voltage (<NUM> - <NUM> KV) or higher voltage, e.g. 66kV. Said electrical energy is conducted via power cables <NUM> from the nacelle <NUM> into the tower <NUM>.

The gearbox <NUM>, generator <NUM> in transformer <NUM> may be supported by a main support structure frame of the nacelle <NUM>, optionally embodied as a main frame <NUM>. The gearbox <NUM> may include a gearbox housing that is connected to the main frame <NUM> by one or more torque arms <NUM>. In the example, the nacelle <NUM> also includes a main forward support bearing <NUM> and a main aft support bearing <NUM>. Furthermore, the generator <NUM> can be mounted to the main frame <NUM> by decoupling support means <NUM>, in particular in order to prevent vibrations of the generator <NUM> to be introduced into the main frame <NUM> and thereby causing a noise emission source.

For positioning the nacelle <NUM> appropriately with respect to the wind direction <NUM>, the nacelle <NUM> may also include at least one meteorological measurement system which may include a wind vane and anemometer. The meteorological measurement system <NUM> can provide information to the wind turbine controller <NUM> that may include wind direction <NUM> and/or wind speed. In the example, the pitch system <NUM> is at least partially arranged as a pitch assembly <NUM> in the hub <NUM>. The pitch assembly <NUM> includes one or more pitch drive systems <NUM> and at least one sensor <NUM>. Each pitch drive system <NUM> is coupled to a respective rotor blade <NUM> (shown in <FIG>) for modulating the pitch angel of a rotor blade <NUM> along the pitch axis <NUM>. Only one of three pitch drive systems <NUM> is shown in <FIG>.

In the example, the pitch assembly <NUM> includes at least one pitch bearing <NUM> coupled to hub <NUM> and to a respective rotor blade <NUM> (shown in <FIG>) for rotating the respective rotor blade <NUM> about the pitch axis <NUM>. The pitch drive system <NUM> includes a pitch drive motor <NUM>, a pitch drive gearbox <NUM>, and a pitch drive pinion <NUM>. The pitch drive motor <NUM> is coupled to the pitch drive gearbox <NUM> such that the pitch drive motor <NUM> imparts mechanical force to the pitch drive gearbox <NUM>. The pitch drive gearbox <NUM> is coupled to the pitch drive pinion <NUM> such that the pitch drive pinion <NUM> is rotated by the pitch drive gearbox <NUM>. The pitch bearing <NUM> is coupled to pitch drive pinion <NUM> such that the rotation of the pitch drive pinion <NUM> causes a rotation of the pitch bearing <NUM>.

Pitch drive system <NUM> is coupled to the wind turbine controller <NUM> for adjusting the pitch angle of a rotor blade <NUM> upon receipt of one or more signals from the wind turbine controller <NUM>. In the example, the pitch drive motor <NUM> is any suitable motor driven by electrical power and/or a hydraulic system that enables pitch assembly <NUM> to function as described herein. Alternatively, the pitch assembly <NUM> may include any suitable structure, configuration, arrangement, and/or components such as, but not limited to, hydraulic cylinders, springs, and/or servomechanisms. In certain embodiments, the pitch drive motor <NUM> is driven by energy extracted from a rotational inertia of hub <NUM> and/or a stored energy source (not shown) that supplies energy to components of the wind turbine <NUM>.

The pitch assembly <NUM> may also include one or more pitch control systems <NUM> for controlling the pitch drive system <NUM> according to control signals from the wind turbine controller <NUM>, in case of specific prioritized situations and/or during rotor <NUM> overspeed. In the example, the pitch assembly <NUM> includes at least one pitch control system <NUM> communicatively coupled to a respective pitch drive system <NUM> for controlling pitch drive system <NUM> independently from the wind turbine controller <NUM>. In the example, the pitch control system <NUM> is coupled to the pitch drive system <NUM> and to a sensor <NUM>. During normal operation of the wind turbine <NUM>, the wind turbine controller <NUM> may control the pitch drive system <NUM> to adjust a pitch angle of rotor blades <NUM>.

According to an embodiment, a power supply <NUM>, for example comprising a battery, electric capacitors hence letter or an electrical generator driven by the rotation of the hub <NUM>, is arranged at or within the hub <NUM> and is coupled to the sensor <NUM>, the pitch control system <NUM>, and to the pitch drive system <NUM> to provide a source of power to these components. In the example, the power supply <NUM> provides a continuing source of power to the pitch assembly <NUM> during operation of the wind turbine <NUM>. In an alternative embodiment, power supply <NUM> provides power to the pitch assembly <NUM> only during an electrical power loss event of the wind turbine <NUM>. The electrical power loss event may include power grid loss or dip, malfunctioning of an electrical system of the wind turbine <NUM>, and/or failure of the wind turbine controller <NUM>. During the electrical power loss event, the power supply <NUM> operates to provide electrical power to the pitch assembly <NUM> such that pitch assembly <NUM> can operate during the electrical power loss event.

In the example, the pitch drive system <NUM>, the sensor <NUM>, the pitch control system <NUM>, cables, and the power supply <NUM> are each positioned in a cavity <NUM> defined by an inner surface <NUM> of hub <NUM>. In an alternative embodiment, said components are positioned with respect to an outer surface of hub <NUM> and may be coupled, directly or indirectly, to outer surface.

<FIG> schematically illustrates an example of a wind turbine nacelle. In <FIG>, only an upper part of a housing of the nacelle is shown. The housing may be made up of a plurality of panels, which may be made of e.g. a fibre reinforced composite. Inside the housing, a (steel) structural frame may be provided. The frame may be attached to the housing such that the loads on the housing can be transmitted to the frame and to the wind turbine tower.

In a first aspect of the present disclosure, a wind turbine nacelle <NUM> is provided. The nacelle <NUM> comprises a housing including a front side <NUM>, and a rear side <NUM> separated from the front side along an axial direction x. The housing further comprises a first sidewall <NUM> and a second sidewall (not visible in this side view) extending from the front side <NUM> to the rear side <NUM>. The housing also comprises a roof. The roof comprises one or more roof panels <NUM>, <NUM>, <NUM>, <NUM>, and at least one of the roof panels <NUM>, <NUM>, <NUM>, <NUM> is a displaceable roof panel configured to be displaced along the axial direction x to provide access to the nacelle <NUM> from above. The displaceable roof panel can be displaced with respect to a part of the nacelle, i.e. not the whole nacelle roof is displaced.

The front side <NUM> may be defined by the position of the wind turbine rotor upstream from the nacelle. The front side <NUM> of the nacelle may generally be the upstream side of the nacelle. The rear side <NUM> of the nacelle may generally be the downstream side of the nacelle.

One or more of the roof panels <NUM>, <NUM>, <NUM>, <NUM> may be displaceable along the x-direction. The roof panels may have different lengths. In examples, the length of the roof panels may be between <NUM> and <NUM> meters, and more particularly between <NUM>,<NUM> and <NUM>,<NUM> meters. In this particular example, four roof panels are shown, but it should be clear that in other examples, a different number of roof panels may be used, specifically between <NUM> and <NUM> panels.

In examples, the displaceable roof panel(s) may be configured to be displaced rearwards. Generally, there may be more available space at a downstream side of the nacelle, where the wind turbine rotor is not arranged.

<FIG> schematically illustrates an example in which a plurality of roof panels is displaceable. In the illustrated example, three roof panels <NUM>, <NUM>, <NUM> may be displaced rearwardly.

As will be illustrated in further detail, the first sidewall <NUM> and the second sidewall comprise first and second guiding elements <NUM>. And the displaceable roof panels <NUM>, <NUM>, <NUM> comprise a first and second guided elements (on the first and second sidewall respectively) configured to be guided by the first and second guiding elements <NUM> respectively.

An example of the guided and guiding elements is shown in <FIG>. The first sidewall <NUM> comprises a first side bracket <NUM> carrying one of the guiding elements <NUM>, and the second sidewall comprises a second side bracket carrying another one of the guiding elements (not shown). The displaceable roof panel <NUM> comprises a roof bracket <NUM>, wherein the guided element <NUM> is arranged at or near a lower end of the roof bracket <NUM>.

In this example, the first and second guiding elements <NUM> are rails. And the guided element may be sliders <NUM> (visible in <FIG>) configured to be received in the rails. The sliders <NUM> may be slid along the rails to displace the roof panel along the axial direction. Sliders may herein be regarded as components which allow a gliding, or sliding or even rolling of the roof (bracket) with respect to the sidewall (bracket). The sliders may include wheels, pads, friction reducing elements etc. as appropriate.

As may be seen in <FIG>, the side brackets may be mounted at a top of the side panel i.e. at a junction between the side panel and roof panel. The side bracket <NUM> may comprise a substantially U-shaped flange <NUM> to receive a top edge <NUM> of a sidewall. The roof bracket <NUM> may comprise a similarly U-shaped flange to receive a lower edge <NUM> of the roof panel.

Further shown in this particular example of <FIG> is a rear bracket <NUM>. The rear bracket <NUM> incorporates a part of a guiding element that forms a continuation of the guiding element of the sidewall brackets, i.e. rail <NUM>.

The rear bracket <NUM> in this particular example may be attached to a sidewall of the housing of the nacelle. The most rearward panel <NUM> may have been displaced forwards in order to create space for the mounting of the rear bracket.

The rear bracket <NUM> may be attached at an outside of the housing, either on the roof or on a sidewall of the nacelle housing. In other examples, such a rear bracket <NUM> may not be used.

In a further aspect of the present disclosure, a method for providing access to an inside of a wind turbine nacelle <NUM> is provided. The method comprises detaching a displaceable roof panel from other portions of a roof of the nacelle <NUM> and lifting the displaceable roof panel from an inside of the nacelle. The method then further comprises displacing the displaceable roof panel towards a front <NUM> or a rear <NUM> of the nacelle. Particularly, the displaceable roof panel may be displaced over other portions of the nacelle, e.g. other roof panels.

At least the panels that are configured to be detached from neighbouring portions of the nacelle may be removably mounted using e.g. a bolted connection. Lifting the displaceable roof panel(s) may comprise the use of a hydraulic lifting mechanism such as a hydraulic jack from an inside of the nacelle.

The displaceable roof panel may be detached from neighbouring portions of the roof, but also from neighbouring portions of other parts of the housing such as the sidewalls.

After lifting the roof panels, a first side bracket <NUM> is mounted to a first sidewall <NUM> of the nacelle, and similarly a second side bracket is mounted to a second sidewall of the nacelle. The first sidewall and second sidewall may correspond to the two sides (left and right) of the nacelle. A sidewall may be composed of a single sidewall panel, or of multiple sidewall panels. The first and second side brackets comprise guiding elements <NUM> to guide the displaceable roof panel.

As illustrated before, the first and second brackets may be mounted to a top <NUM> of the first and second sidewalls. Sufficient vertical space may herewith be created to displace a roof panel over a neighbouring roof panel which may stay in place.

The method further comprises mounting a first and a second roof bracket <NUM> to the displaceable roof panel <NUM>, the first and second roof brackets <NUM> comprising a slider <NUM> configured to be guided by the guiding elements <NUM> of the first and second side brackets <NUM>.

In examples, displacing the displaceable roof panel may further comprise manually pushing the displaceable roof panel. an operator in the nacelle can simply push the displace roof panels in the axial direction. In other examples, pushing or pulling mechanism may be installed in the nacelle to replace or aid the manual pushing by the operator.

In examples, once one or more roof panels have been displaced, sufficient space may have been created for maintenance tasks which may involve erecting or unfolding a crane inside the nacelle. A crane mounted nacelle may be used to lift heavy components inside the nacelle, like a gearbox, generator or converter.

<FIG> schematically illustrates a further example of a nacelle with displaceable roof panels. According to an aspect of the present disclosure, a nacelle <NUM> for a wind turbine is provided, which comprises a housing including a front side, and a rear side separated from the front side along an axial direction, a roof, a first sidewall, and a second sidewall. The roof comprises a plurality of roof panels, and wherein one or more of the roof panels are displaceable roof panels <NUM>, <NUM> configured to be detached from neighbouring roof panels and from the first and second sidewalls. The nacelle is further configured to guide the displaceable roof panels <NUM>, <NUM> in the axial direction.

The example of <FIG> generally functions similarly as the example of <FIG>. However, the example of <FIG> is different from the example of <FIG> in that the roof bracket comprises a hinge allowing tilting of an upper part of the roof bracket with respect to a lower part of the roof bracket. This is illustrated in more detail in in <FIG>.

The displaceable roof panels may comprise a first and second slider <NUM> as before, and the sliders may be arranged at or near a bottom of the roof brackets to mate with a guide or rails <NUM> of the side brackets.

The roof bracket <NUM> comprises an upper part <NUM> which comprises a U-shaped flange <NUM> to receive a bottom edge of a roof panel. The roof bracket <NUM> of this example further comprises a lower part <NUM>. The upper part <NUM> is hingedly connected to the lower part <NUM> such that the upper part <NUM> can tilt with respect to the lower part.

In examples, the displaceable roof panels do not follow a linear (horizontal) path completely supported by rails. Rather, due to the shape of the nacelle, the path of the displaceable roof panels may have portions that are at an angle with neighbouring portions.

In examples, one of the displaceable roof panels comprises a first and second slider <NUM>, and wherein the first sidewall comprise a first rail <NUM> to guide the first slider <NUM>, and the second sidewall comprises a second rail to guide the second slider. The slider <NUM> may be configured to rotate with respect to the displaceable roof panel.

A hinge <NUM> between the upper and lower parts <NUM>, <NUM> of the roof bracket allows the slider <NUM> to tilt or rotate with respect to the roof panel and adjust for differing inclinations along its path.

In examples, a limited amount of rotation of e.g. less than 25º in either direction is allowed, and specifically less than 20º. Stoppers may be provided to limit the amount of rotation in either direction.

The roof bracket <NUM> may further comprise mounting holes <NUM> for removably mounting slider <NUM>. If the slider <NUM> needs to be replaced or repaired, it may easily be removed. Furthermore, in this example, roof bracket <NUM> comprises a possibility to adjust a preload on the sliders or e.g. the wheels of the sliders. Holes <NUM> provided in this example in the lower part <NUM> of roof bracket <NUM> at a height at which the slider <NUM> may be mounted. In the shown examples, bolts extending through holes <NUM> may be used to adjust a preload. Adjusting a preloading may be useful e.g. when a rail <NUM> or raceway is substituted or changed for another.

<FIG> further illustrates the attachment of side bracket <NUM> with rail <NUM> and a how a U-shaped flange <NUM> may receive a top edge <NUM> of a sidewall of the housing of the nacelle. <FIG> further illustrates the mounting of the roof bracket and the hinge <NUM> allowing tilting of the upper part <NUM> of the roof bracket with respect to a lower part <NUM> of the roof bracket.

A further difference between the example of <FIG> and the example of <FIG> is that a displaceable roof panel in the example of <FIG> may comprise an additional support at or near an end of the roof panel. In the example illustrated in <FIG>, the additional support may include one or more wheels which allow the displaceable roof panel to roll over neighbouring roof panels. the weight of the roof panel is supported in the rails and side brackets, but also by the additional support.

<FIG> schematically illustrates an alternative example of a mechanism for displacing roof panels. <FIG> shows an alternative example of a roof bracket <NUM> which may be attached to a displaceable roof panel. The bottom part <NUM> of the roof bracket <NUM> may incorporate a guided element such as a slider. The upper part <NUM> of the roof bracket <NUM> may again be configured to be attached to the displaceable roof panel and to support the roof panel.

As in the example of <FIG>, the upper part <NUM> of the roof bracket allows tilting with respect to the lower part <NUM> of the roof bracket <NUM> or vice versa. An alternative hinge <NUM> is herein provided comprising a scissor like structure including legs that are connected at a central point. Each of the legs comprises a slot like structure along which the central connection point may be displaced to allow for tilting.

<FIG> schematically illustrates a further example of a nacelle. In <FIG> and <FIG>, examples have been shown in which multiple displaceable roof panels are displaced along the same axial direction. In examples, such as the ones illustrated in <FIG> and <FIG>, first and second displaceable roof panels may be displaced as a unit. between them they remain attached.

In the example of <FIG>, a first displaceable roof panel <NUM> is configured to be displaced forwards, and the second displaceable roof panel <NUM> is configured to be displaced rearwards. In the illustrated example, roof panel <NUM> rests over a neighbouring front roof panel <NUM> in its most forward position, and roof panel <NUM> rests over a neighbouring rear roof panel <NUM> in its most rearward position.

In non-illustrated examples, first and second displaceable roof panels may be displaced in the same axial direction (particularly rearwards) but move independently from one another. The first displaceable roof panel may be placed over the second displaceable roof panel when both roof panels have been displaced to their rest positions e.g. their most rearward positions.

<FIG> schematically illustrates a further example of a wind turbine nacelle. The nacelle <NUM> once again includes sidewalls, of which a first sidewall <NUM> is visible this side view, a front or upstream side <NUM> and a rear or downstream side <NUM>. The housing of the nacelle <NUM> further comprises a plurality of roof panels, <NUM>, <NUM>, <NUM> and <NUM>. In this example, roof panels <NUM>, <NUM>, <NUM> are displaceable roof panels and they may be displaced along an axial direction, and more particularly they may be displaced rearwards.

In this example, displaceable roof panels <NUM>, <NUM>, <NUM> may be displaced as a unit, i.e. they remain attached to each other at all times. In order to displace them, the roof panels <NUM>,<NUM>, <NUM> may be detached from neighbouring portions of the nacelle and lifted. A rail may be attached to the nacelle, and particularly to the sidewalls of the nacelle housing. Roof brackets may be attached as herein before illustrated and these roof brackets may include sliders or alternatively rolling elements configured to be received in the rail.

The rail <NUM> in this example may be substantially completely linear and horizontal. The rail <NUM> may be supported through a plurality of side brackets attached to the sidewalls of the housing, particularly along portions of the sidewall where the roof panels have been lifted.

The rail may further be supported at supports <NUM>, <NUM> on a rear portion of the nacelle. These supports may be attached at an outside of the nacelle, contrary to the side brackets arranged along the more forward parts of the nacelle.

In the illustrated example, as may be seen in the figure, the rail <NUM> extends beyond the rear end of the nacelle in a manner such that the roof panels <NUM>, <NUM>, <NUM> may be moved in a rearwards direction such that at least roof panel <NUM> reaches beyond a rear end of the nacelle. In the illustrated example, the roof panels <NUM>, <NUM>, <NUM> may be displaced rearwardly to an extent that the roof of the nacelle is open along the entire length of the panels <NUM>, <NUM>, <NUM>.

Although in this particular example, a rail was mentioned as a guiding element, it should be clear that in other examples, other guiding elements might be used including e.g. bearings, raceways, bushings or other.

<FIG> schematically illustrates a wind turbine nacelle according to a further example. The nacelle <NUM> includes a telescopic mechanism. The telescopic mechanism may comprise a guiding element (e.g. a base rail <NUM>) and a guided element, e.g. further rail portions <NUM>, <NUM>. One of the further rail portions <NUM> may be attached to a displaceable roof panel.

In normal operation, the telescopic mechanism may be partially of fully extended in a first direction (e.g. towards a front of the nacelle), and a base of the telescopic mechanism may be attached to a sidewall <NUM> of the housing of the nacelle. To provide access from above, the displaceable roof panel(s) <NUM> may be separated from other portions of the housing and the telescopic mechanism may be extended in an opposite direction (e.g. in a rearwards direction of the nacelle) to displace the displaceable roof panel along the axial direction.

<FIG> illustrates yet a further example of a nacelle <NUM>. The nacelle <NUM> in this example comprises roof panels <NUM>, <NUM>, <NUM>, <NUM>. The displaceable roof panel <NUM> can be lifted and displaced in an axial direction x. In this particular example, the displaceable roof panel <NUM> may be displaced in a forward direction.

The roof panel <NUM> which is neighbouring to displaceable roof panel <NUM> may comprise a plurality of rollers <NUM>. The roof panel <NUM> may be lifted from an inside of the nacelle. A hydraulic jack like a hydraulic scissor jack <NUM> may be used. In examples, the hydraulic jack may include a roller or wheel. After lifting the displaceable roof panel <NUM>, the roof panel may be pushed in the axial direction and further slide over rollers <NUM> incorporated in a neighbouring panel.

Claim 1:
A wind turbine nacelle (<NUM>), comprising:
a housing including a front side (<NUM>), and a rear side (<NUM>) separated from the front side along an axial direction (x), first and second sidewalls (<NUM>) extending from the front side to the rear side and a roof, wherein
the roof comprises one or more roof panels (<NUM>, <NUM>, <NUM>, <NUM>), and wherein
at least one of the roof panels is a displaceable roof panel configured to be displaced along the axial direction (x) with respect to another part of the roof to provide access to the nacelle (<NUM>) from above, wherein
the first and second sidewalls (<NUM>) comprise first and second guiding elements (<NUM>), and wherein the displaceable roof panel comprises first and second guided elements (<NUM>) configured to be guided by the first and second guiding elements (<NUM>) respectively, wherein
the first sidewall (<NUM>) comprises a first side bracket (<NUM>) carrying one of the guiding elements (<NUM>), and the second sidewall comprises a second side bracket carrying another one of the guiding elements, and the displaceable roof panel comprises a roof bracket (<NUM>), wherein the guided element is arranged at or near a lower end of the roof bracket, and wherein the roof bracket (<NUM>) comprises a hinge (<NUM>) allowing tilting of an upper part (<NUM>) of the roof bracket with respect to a lower part (<NUM>) of the roof bracket.