A base for a wind turbine, a wind turbine installed on a base, and a method for making a base for a wind turbine

Abstract

A base (10) for a wind turbine and a method for making a base is disclosed. The base comprises a side wall (11) enclosing an inner volume and having a circular cross-sectional shape. The side wall comprises a lower section (12) extending from a lower side towards an upper side, an upper section (14) extending from the upper side towards the lower side, and a centre section (13) extending from the lower section to the upper section, said centre section meeting the lower section in a first horizontal plane (P1) and meeting the upper section in a second horizontal plane (P2). The centre section has a first outer diameter (d1) at the first horizontal plane and a second outer diameter (d2) at the second horizontal plane, said first outer diameter being larger than said second outer diameter, and an outer pitch angle (α) of the centre section decreases in the height direction. The lower section, the centre section, and the upper section are made from concrete and integrally formed.

Description

[0001] Title of Invention

[0002] A base for a wind turbine, a wind turbine installed on a base, and a method for making a base for a wind turbine

[0003] Technical Field

[0004] The invention relates to the installation of wind turbines on-shore as well as off-shore and the provision of support for the wind turbines.

[0005] Background Art

[0006] With the increasing demand for sustainable energy, wind turbines have been optimised both with respect to power conversion and size. With an increased size the wings can become longer, which will increase the power production capacity, and it is also possible to reach levels, where wind speeds are high and there is less turbulence caused by landscape factors, such as hills, vegetation, and buildings. The need for transporting components from a production site to a site of installation has, however, set limits on the total size of wind turbines. Increasing the height has therefore necessitated still stronger towers and bigger foundations, which has added to the production costs.

[0007] Summary of Invention

[0008] With this background, it is an object of the invention to provide a means and a method by which it is possible to cost efficiently increase the height of a wind turbine.

[0009] In a first aspect of the invention this and further objects are achieved with a base for a wind turbine comprising a side wall extending in a height direction from a lower side to an upper side, enclosing an inner volume, and having a circular cross-sectional shape, where an inner side of the side wall faces the inner volume and an outer side of the side wall faces away from the inner volume; where said side wall comprises a lower section extending from the lower side towards the upper side, an upper section extending from the upper side towards the lower side, and a centre section extending from the lower section to the upper section, said centre section meeting the lower section in a first horizontal plane and meeting the upper section in a second horizontal plane; where said centre section has a first outer diameter at the first horizontal plane and a second outer diameter at the second horizontal plane, said first outer diameter being larger than said second outer diameter, and where an outer pitch angle of the centre section decreases in the height direction; and where of the lower section, the centre section, and the upper section are made from concrete and integrally formed.

[0010] With the outer pitch angle of the centre section decreasing in the height direction, the outer side becomes gradually steeper in the height direction, so that the centre section gets the shape of a trumpet, giving the base a relatively large footprint. This has several advantages, one being that with the trumpet shape concrete is applied where it is most needed from a structural point of view. Wind turbine towers experience large lateral loads from the turbine operation, and since they in principle act as a cantilever column under static and dynamic load, the sectional bending moment is largest at the tower bottom, i.e. in the base close to the lower side. With the large diameter at the lower side, the bending stress level in the side wall is reduced compared to a conical shape with a linear decrease in diameter from bottom to top, where the bending moment capacity is decreased at a slower rate than the decrease of the actual bending moment section force resulting from lateral loads.

[0011] Another advantage is that the trumpet shape, allows the loads of the wind turbine to be distributed over a large area, and by forming the base from concrete, it can be formed on the installation site, eliminating the need for transportation of components from a production site.

[0012] The use of concrete as compared to for example steel will in itself result in a thicker side wall which may also result in a relatively large footprint of the base and hence a good load distribution.

[0013] The use of concrete may also result in that the base is relatively heavy, which may contribute to a stabilization of the finished wind turbine.

[0014] The upper side and the lower side will typically be horizontal, when the wind turbine is to be installed off-shore or on a level terrain, but if the wind turbine is to be installed for example in a mountainous area, it may be advantageous that the base is capable of compensating for unevenness in the terrain, for example by the lower side being non-horizontal.

[0015] Any reference to items being horizontal, vertical, upper, lower, or similar indications of direction used herein are to be understood as referring to the base in the installed use state.

[0016] In some embodiments, the total pitch angle of the base, i.e. the angle of a line extending from the outer side of the side wall at the lower side to the outer side of the side wall at an upper side relative to vertical, is 10-30 degrees, preferably at least 15 degrees.

[0017] It is presently considered advantageous that the lower section, the centre section, and the upper section are made by additive manufacturing, also called printing, each comprising a plurality of layers of concrete located on top of each other in the height direction. Printing provides a high degree of freedom with respect to the shape of the base and a base printed on-site may be giving any desired size, without needing to divide the base into sections of sizes suitable for transport as would be necessary with many traditional concrete disposition techniques. In a printed base the lower section, the centre section, and the upper section may thus be made in one continuous process, ensuring optimal coherence between them. Furthermore, printing on-site may allow a good cohesion with a foundation. Still further, locally available materials may be used in the concrete.

[0018] The layers printed may have different widths, but it is presently considered advantageous that the width of at least some of the printed layers is at least than 400 mm. This may provide a relatively large footprint and / or a good support for additional layers printed on top of the layer. The thickness of the side wall may be 300-500 mm. A side wall thickness of 450 mm has been tested and found to provide a good balance between footprint, load bearing capacity, and material consumption.

[0019] Each printed layer may be made with a different composition of the concrete, for example using a stronger concrete in layers, which will be subject to higher loads. As an example, the lower section may be printed using a stronger concrete than the concrete used for the centre section and / or the upper section. Depending on the width of each layer, the base may be made as a single-walled structure, but the side wall may also be a double-wall with an inner wall defining the inner side and an outer wall defining the outer side, or a single wall may be made by depositing two layers of concrete closely adjacent to each other.

[0020] In one embodiment, the lower section is conical with the outer side of the side wall extending at a first outer pitch angle, and the first outer pitch angle preferably corresponds to the outer pitch angle of the centre section at the first horizontal plane. In this way the lower section and the centre section extends in stepless continuation of each other with no unnecessary stress concentrations, and the lower section provides a bigger footprint of the base than the diameter of the centre section at the first horizontal layer.

[0021] In one embodiment, the upper section is cylindrical or substantially cylindrical. While the centre section, and possibly the lower section, provides a bigger footprint of the base than that of the tower of the wind turbine, the upper section will then simply increase the height of the base, thereby raising the nacelle of the wind turbine higher above the ground when using the same tower.

[0022] The transition between all sections should preferably be continuous and smooth to avoid unnecessary stress concentrations.

[0023] In one embodiment, the thickness of side walls decreases in the height direction. A bigger thickness is typically associated with a higher strength, making the base strongest at the bottom, but a bigger thickness at the lower side may also contribute to a bigger footprint. By combining thickness and properties of the concrete used, the base may be given different properties in different sections or within a section.

[0024] The base may comprise reinforcement chosen from the group comprising: rods, rings, or fibres. Fibres may be mixed into the concrete and may be made for example of steel, carbon, a polymer, or a mixture of polymers. Rods and rings will typically be made from steel, but the use of other materials is not excluded. Rods may be arranged to form a lattice as is known from traditional reinforced concrete structures made by casting. Rings may be arranged on top of printed layers and covered by the next printed layer. Depending on the width of the printed layers it is also possible to print two layers side by side and to arrange a ring between them.

[0025] When printing using concrete, fibres used for reinforcement tend orient themselves in the direction of printing, i.e. in a length direction of the printed layer, which will typically be horizontal, and tangentially when printing along a circular path. To compensate for this, supplemental reinforcement, such as rods, may be arranged to extend across the direction of printing, radially and / or in the height direction. Supplemental reinforcement in the height direction may also contribute to preventing any tendency towards layer separation resulting from the fact that fibres will generally not extend from one layer into another.

[0026] In some embodiments, the base is tensioned by cables and / or rods extending through the inner volume and / or between an inner wall and an outer wall. Such cables and / or rods may extend from the lower section to the upper section or from a foundation on which the base rests to the tower of a wind turbine installed on the base. Pre- or post-tensioning may also contribute to preventing layer separation.

[0027] In some embodiments, the base comprises an inner support structure, which may for example comprise one or more transversal wall or transversal beams, flanges extending from the side wall, and / or a lattice extending along the inner side of the side wall. Such an inner support structure may be made by printing and / or may be integral with the side wall.

[0028] As the base has a relatively large footprint and will distribute the loads of the wind turbine over a relatively large area, the requirement for a foundation for supporting the base is different from those for a traditional window turbine foundation. The use of a strip foundation is presently considered advantageous as it will require less material than a traditional shallow mat foundation.

[0029] The base may alternatively be supported by, possibly integrated in, a floating foundation. A floating foundation may have a bottom plate and may be upwards open.

[0030] In some embodiments, the foundation comprises a plurality of curved portions connected to the base by straight walls, and where the curved portions together from an outer side wall of the foundation enclosing the base, giving the foundation the overall shape of a flower. Such a foundation is well suited for withstanding external horizontal loads, such as water pressure if the foundation is a floating foundation or earth pressure if the foundation is used on-shore or resting on a sea bed. An interior circular wall surrounding the base and interconnecting the straight walls of the foundation may provide additional strength and stiffness by hindering deflection of the straight walls and possibly also a bottom plate.

[0031] The base may be provided with local reinforcement where it meets the straight walls of the foundation to allow a distribution of pressure.

[0032] The base may be formed integrally with the foundation. This is particularly advantageous when making both the base and the foundation by printing.

[0033] In a second aspect of the invention the above and further objects are achieved with a method for making a base for a wind turbine where concrete is deposited along a circular path thereby forming a side wall extending in a height direction from a lower side to an upper side, enclosing an inner volume, and having an inner side of the side wall faces the inner volume and an outer side of the side wall faces away from the inner volume, said method comprising the following steps: I) Depositing concrete on a support surface thereby forming a lower section of the base, where a top of the lower section defines a first horizontal plane, II) Depositing concrete on the top of the lower section thereby forming a centre section of the base, where a top of the centre section defines a second horizontal plane, and III) Depositing concrete on the top of the centre section thereby forming an upper section of the base; where the lower section, the centre section, and the upper section are integrally formed; where a diameter of the circular path is gradually reduced during step II); and where a rate reduction of the diameter of the circular path is gradually decreased during step II).

[0034] Gradually reducing the diameter of the circular path at a gradually decreasing rate of reduction during will result in a centre section having an outer pitch angle decreasing in the height direction and hence the shape of a trumpet as explained above with reference to the first aspect of the invention. Embodiments and advantages described with reference to the first aspect also apply to the second aspect and vice versa, unless otherwise stated.

[0035] Brief Description of Drawings

[0036] In the following description embodiments of the invention will be described with reference to the schematic drawings, in which

[0037] Fig. 1 is a perspective view of an embodiment of a base;

[0038] Fig. 2 is a cross-sectional front view of an embodiment of a base in an installed state;

[0039] Fig. 3 is a front view of an embodiment of a base in an installed state;

[0040] Fig. 4 is a cross-sectional perspective view of an embodiment of a base;

[0041] Fig. 5 is a cross-sectional front view of an embodiment of a base in an installed state;

[0042] Fig. 6 is a perspective view of an embodiment of a base in an installed state;

[0043] Fig. 7 is a perspective view of an embodiment of a base in an installed state;

[0044] Fig. 8 is a perspective view of an embodiment of a base in an installed state,

[0045] Fig. 9 is a perspective view of an additive manufacturing system,

[0046] Fig. 10 is a sketch of cross-sections of three different wind turbine towers, and

[0047] Fig. 11 is a diagram comparing section modulus and cumulated material volume for the three structures in Fig. 10.

[0048] Description of Embodiments

[0049] In the following a detailed description of embodiments of the invention will be given with reference to the accompanying drawings. It should be noted that features having the same reference numerals have the same function. A feature in one embodiment could thus be exchanged for a feature from another embodiment having the same reference numeral unless clearly contradictory.

[0050] Referring initially to Fig. 1 and 2, a perspective view of a base 10 for a wind turbine 1 is shown. The base 10 has a side wall 11 extending in a height direction H from a lower side L to an upper side U, enclosing an inner volume V. An inner side 112 of the side wall 11 faces the inner volume V and an outer side 113 of the side wall 11 faces away from the inner volume V. The side wall 11 side wall has a lower section 12 extending from the lower side L towards the upper side U, an upper section 14 extending from the upper side towards the lower side, and a centre section 13 extending from the lower section 12 to the upper section 14 The sections of the base 10 meet in horizontal planes. The centre section 13 meets the lower section 12 in a first horizontal plane P1 , and the centre section 13 has a first outer diameter d1 in the first horizontal plane P1. The centre section 13 meets the upper section 14 in a second horizontal plane P2 and has a second outer diameter d2 in the second horizontal plane P2. The first outer diameter is larger than the second outer diameter.

[0051] The base 10 is constructed in such a way that concrete is deposited along a circular path on a support surface 20, thereby forming the side wall 11 , which has a circular cross-sectional shape over the entire height of the base 10 in the height direction H. The lower section 12 is formed first, and the top of the lower section 12 defines the first horizontal plane P1 . The centre section 13 is then formed by depositing concrete on top of the lower section 12. The top of the centre section 12 defines the second horizontal plane P2. The upper section 14 is formed in top of the centre section 13 by deposition of concrete. A diameter of the circular path is gradually reduced. In this embodiment, the diameter of the centre section 13 is larger than the diameter of the upper section 14, however in some embodiments the diameter of the centre section 13 is equal to the diameter of the upper section 14. The diameter of the circular path is gradually decreased in the centre section 13. A preferred way of constructing the base 10 is by printing.

[0052] In the installed state shown in Fig. 2, a wind turbine 1 is installed on the base 10, and they meet at a transition portion 2. Here only, a tower of the wind turbine 1 is shown, however the wind turbine 1 also comprises not shown rotor blades and a nacelle.

[0053] Fig. 1 and Fig. 2 shown an on-shore installation where the base 10 is supported by a strip foundation 20 located underneath the ground surface 50. A part of the base 10 is also located underneath the ground surface 50. In some embodiments, only the foundation 20 is located underneath the ground surface 50.

[0054] In the embodiment shown in Fig. 3, the foundation 20 is a mat foundation, and the foundation and the base 10 are both located above the ground surface 50.

[0055] In Fig. 4, a cross sectional perspective view of the base shows that the side wall 11 has a constant thickness. In some embodiments the thickness of the side wall 11 decreases in the height direction H.

[0056] In the embodiment in Figs 1 -4, the lower section 12, the centre section 13, and the upper section 14 are all having an outer pitch angle a, which decreases in the height direction H so that the outer side 113 becomes gradually steeper in the height direction, giving the entire base 10 the shape of a trumpet. The total pitch angle [3 of the base, i.e. the angle of a line extending from the outer side of the side wall at the lower side to the outer side of the side wall at an upper side relative to vertical, is 20 degrees.

[0057] In the embodiment in Fig. 5, the outer pitch angle a of the centre section 13 also decreases in the height direction H, but the lower section 12 is conical with the outer side 113 of the side wall 11 extending at a constant outer pitch angle a1. The outer pitch angle of the centre section 13 at the first horizontal plane P1 corresponds to the first outer pitch angle a1 of the lower section 12 so that there is a smooth transition from the lower section to the centre section. In the embodiment in Fig. 5 only an upper part 141 and a lower part 142 of the upper section 14 is shown, and it is to be understood that this upper section is much higher than the lower section and the centre section. The upper section has a very small constant pitch angle a2, so that the upper part and the lower part are almost cylindrical. The upper section 14 could also be shorter and entirely cylindrical corresponding approximately to what is shown in the lower half of Fig. 5, i.e. having a pitch angle of zero. The total pitch angle is then 15 degrees.

[0058] The transitions between all sections should preferably be smooth to avoid weak zones of the base 10 and unnecessary stress concentrations.

[0059] The base 10 may comprise a not shown inner support structure 15. The inner support structure 15 may be located on inside the side wall 11 of the base 10, or it may be located on the inner 112 or outer side 112 of the side wall 11. The inner support structure 15 may be lattices, flanges, pre- or posttensioning, grids, or beams. The inner support structure 15 may also be made by printing, preferably additive manufacturing. Experiments have shown that pre- or post-tensioning resulting in a pre-stressing force of 100-150 MN provides good results.

[0060] In Fig. 5, the base 10 is provided with pre- or post-tensioned cables 15 extending through the inner volume V. The cables 15 extend from the foundation 20 to the transition portion 2. Such cables 15 or rods may also extend from the lower section 12 to the upper section 14.

[0061] Additionally, or alternatively, the base 10 may comprise reinforcement in form of for example rods, rings, fibres, or a combination and is not considered as part of the concrete itself.

[0062] In Fig. 6, the base 10 is formed integrally with a floating foundation 200 intended for offshore uses. The foundation 200 has curved portions 201 arranged in a flower shape, and the curved portions 201 are connected to the base 10 by straight walls 202. The curvature of the curved portions 201 allow them to withstand water pressure from the exterior and transfer it to the straight walls. The base 10 may be provided with local reinforcement where it meets the straight walls 202 to be able to take up forces originating from exterior water pressure.

[0063] In the embodiment shown, the curved portions 201 have a smooth curved shape, however they may also be sharp, pointy, having rounded comers, or a combination. The foundation 20 further comprises an interior curved wall 203 in the shape of a circle, to provide additional stability.

[0064] In Fig. 7, another embodiment of the floating foundation 200 is shown, in which the size of the curved portions 201 vary. This foundation as well as the one in Fig. 6 has a bottom 204 allowing it to float. The straight walls 202, the curved portions 201 , and the interior curved wall 203 may contribute to supporting the bottom against water pressure from below.

[0065] Fig. 8 shows the base 10 and the floating foundation 200 with anchor beams 30. A proximal end 31 connected to the foundation 20, and in a distal end 32 is connected to cables 33 or chains, which are in turn attached to anchors blocks (not shown) at a bottom of the sea. The anchor beams 30 and cables 33 prevent the base 10 and foundation 20 from floating unintentionally. In this embodiment, there are three anchor beams 30, however there may alternatively be less or more.

[0066] The foundations shown in Fig. 6 and Fig. 7 may also be used on-shore or on a sea bed. In those cases, the interior spaces between the curved portions 201 and the straight walls 202 may be filled, for example with rocks, gravel, or water.

[0067] Fig. 9 shows an embodiment of an additive manufacturing system 2000 with a printing unit 2001 mounted on a gantry system 2002 configured for moving the printing unit in a three-dimensional space defined by axes X, Y, and Z corresponding to the longitudinal direction D1 , width direction D2 and height D3. The printing unit 2001 is mounted to be moveable along a first horizontal beam 2003 in a horizontal direction along the X-axis, the first horizontal beam is mounted to be moveable along a set of second horizontal beams 2004 in a horizontal direction along the Y-axis, and the second set of horizontal beams are mounted to be moveable along four uprights 2005 in a vertical direction along the Z-axis.

[0068] The position and extend of the four uprights 2005 thus delimit the space in which the printing unit 2001 can move. The movement of the beams 2003, 2004 is here achieved by the use of motors built into attachments blocks 2006 and the printing unit 2001 is moved by a chain drive (not visible) driven by a motor built into attachments blocks 2006 of the first horizontal beam. Each of the four uprights 2005 of the gantry system 2002 rest on a foundation 2007 provided on the surface 5000 on which a construction is to be printed. The surface 5000 may for example be a ground surface, a foundation, or an upper surface of an existing construction, such a bottom plate 204.

[0069] Next to the gantry system 2002 a printing material supply facility 3000 is shown, and a tubing system 4000 connects the printing material supply facility to the printing unit 2001 , serving as a printing material supply line. The printing material supply facility 3000 may comprise a mixing unit and / or a buffer unit for receiving printing material produced elsewhere. The printing material is concrete consisting of cement, aggregate and water and may be made in the printing material supply facility or supplied from an external manufacturing site. It is also possible to modify a material supplied from an external manufacturing site in the printing material supply facility, for example by admixing one or more additives, aggregates, or fibres.

[0070] A material pump 3001 is used for pushing the printing material from the printing material supply facility 3000 through the tubing system 4000 to the printing unit 2001 . In the embodiment shown, the material pump is integrated in the printing material supply facility 3000, but it could also be a separate unit. Likewise, it is to be understood that the material pump 3001 could be replaced by or supplemented with a material pump arranged at or on the gantry system 2002, and that such a material pump might be a suction pump. At present it is considered advantageous to use a piston pump, which is well suited for moving high viscosity material. This applies regardless of how other parts of the additive manufacturing system 2000 are embodied.

[0071] The tubing system 4000 is here composed of flexible tubes allowing the tubing system to follow the movement of the gantry system 2002 and the printing unit 2001 so that a continuous and reliable supply of printing material is ensured. The tubing system may also comprise pipes. One or more additive supply lines (not shown) may be integrated in the tubing system 4000. In the embodiment shown, a control unit 3002 for controlling the supply of printing material to the printing unit 2001 is built into the printing material supply facility. The control unit 3002 could alternative be located elsewhere, including on or at the printing unit 2001 or on or at the gantry system 2002.

[0072] In Fig. 9 the printing of two curved portions of a flower shaped foundation 200 as shown in Fig. 6 and Fig. 7 have been initiated, but it is to be understood that a printing operation may begin with the printing of a base and that the printing path followed by the printer will usually be longer than just two curved portion and that the gantry system will often be larger than shown.

[0073] As described with reference to Fig. 5 the base may be considerably taller than what is shown in Fig. 1 -4 and may potentially eliminate the need for a tower. In such cases the tower may be considered as being integrated in the base. In Fig. 10 and Fig. 11 such a base with an integrated tower, which will hereafter be referred to as a trumpet tower 4 for ease of reference, is compared to two different embodiments 5, 6 of conical wind turbine towers made from concrete. The trumpet tower 4 is shown to the left in Fig. 10. The conical concrete tower 5 shown at the centre of Fig. 10 has the same diameter both at the lower side and at the upper side as the trumpet tower 4, and the conical concrete tower 6 shown to the right in Fig. 10 has the same diameter at the upper side as the base 4 but a smaller diameter at the lower side, corresponding to the shape of a traditional wind turbine tower. The centre tower in Fig. 10 will hereafter be referred to as the wide conical tower and the righthand tower in Fig. 10 will hereafter be referred to as the slim conical tower.

[0074] Fig. 11 shows the cumulated concrete volume and the section modulus affecting each of the three tower structures in Fig. 10 as a function of the height above the ground. In this example, all three towers have a height of 120 meters, a side wall thickness of 450 mm, and a diameter at the upper side of 3.4 meters. The trumpet tower 4 and the wide conical tower 5 have a diameter at the lower side of 14.5 meters and the slim conical tower 6 has a diameter at the lower side of 8 meters.

[0075] As is seen from graphs 41 , 51 , 61 , showing the cumulated concrete volume for towers 4, 5 and 6, respectively, the material consumption is considerably larger for the wide conical tower 5 than for the two other towers, and as seen from graphs 42, 52, 62 showing the section modulus for the ... the material consumption is considerably larger for the conical tower 5 having the same diameters at the upper and lower sides as the trumpet tower 4

[0076] As explained above, wind turbine towers experience large lateral loads from the turbine operation, and the sectional bending moment is largest at the bottom, i.e. close to the lower side. Increasing the diameter at the lower side reduces the bending stress levels. From linear elastic theory of beams the bending stress is given by Navier’s formula, and with section modulus depending on the tower diameter cubed. With the linear decrease in tower diameter from bottom to top seen in the conical towers 5, 6 the bending moment capacity is decreased at a slower rate than the decrease of the actual bending moment section force resulting from lateral loads. With the trumpet tower on the other hand, the section modulus only decreases much more quickly as illustrated by graphs 42, 52, and 62 in Fig. 11 . In other words, with the trumpet tower concrete is applied where it is more need from a structural point of view.

Claims

Claims1 . A base for a wind turbine comprising a side wall extending in a height direction from a lower side to an upper side, enclosing an inner volume, and having a circular cross- sectional shape, where an inner side of the side wall faces the inner volume and an outer side of the side wall faces away from the inner volume, where said side wall comprises a lower section extending from the lower side towards the upper side, an upper section extending from the upper side towards the lower side, and a centre section extending from the lower section to the upper section, said centre section meeting the lower section in a first horizontal plane and meeting the upper section in a second horizontal plane, where said centre section has a first outer diameter at the first horizontal plane and a second outer diameter at the second horizontal plane, said first outer diameter being larger than said second outer diameter, and where an outer pitch angle of the centre section decreases in the height direction, and where of the lower section, the centre section, and the upper section are made from concrete and integrally formed.

2. A base for a wind turbine according to claim 1 , where a total pitch angle of the base is 10-30 degrees, preferably at least 15 degrees.

3. A base for a wind turbine according to claim 1 or 2, where the lower section, the centre section, and the upper section are made by printing, each comprising a plurality of layers of concrete located on top of each other in the height direction.

4. A base for a wind turbine according to one or more of the preceding claims, where the lower section is conical with the outer side of the side wall extending at a first outer pitch angle.

5. A base for a wind turbine according to one or more of the preceding claims, where the upper section is cylindrical.

6. A base for a wind turbine according to one or more of the preceding claims, where the thickness of side walls decreases in the height direction.

7. A base for a wind turbine according to one or more of the preceding claims, further comprising reinforcement chosen from the group comprising: rods, rings, or fibres.

8. A base for a wind turbine according to one or more of the preceding claims, further comprising an inner support structure.

9. A wind turbine installed on a base according to one or more of claims 1 -8, said wind turbine comprising a rotor blades, a nacelle, and a tower, where the tower is supported by the base, and where the base is supported by a foundation.

10. A wind turbine according to claim 9, where reinforcement elements having two ends are attached to the tower at one end and to the foundation at the other end, and where the reinforcement elements extend through the inner volume of the base.11 . A wind turbine according to claim 9 or 10, where the foundation is a strip foundation.

12. A wind turbine according to claim 9 or 10, where the foundation is a floating foundation.

13. A wind turbine according to claim 9, 10 or 12, where the foundation comprises a plurality of curved portions connected to the base by straight walls, and where the curved portions together from an outer side wall of thefoundation enclosing the base.

14. A wind turbine according to claim 13, where the foundation further comprises an interior circular wall surrounding the base and interconnecting the straight walls.

15. A wind turbine according to claim 13 or 14, where the base is provided with local reinforcement where it meets the straight walls of the foundation.

16. A wind turbine according to one or more of claims 9-15, where the base is formed integrally with the foundation.

17. A method for making a base for a wind turbine where concrete is deposited along a circular path thereby forming a side wall extending in a height direction from a lower side to an upper side, enclosing an inner volume, and having an inner side of the side wall faces the inner volume and an outer side of the side wall faces away from the inner volume, said method comprising the following steps:I) Depositing concrete on a support surface thereby forming a lower section of the base, where a top of the lower section defines a first horizontal plane,II) Depositing concrete on the top of the lower section thereby forming a centre section of the base, where a top of the centre section defines a second horizontal plane, andIII) Depositing concrete on the top of the centre section thereby forming an upper section of the base. where the lower section, the centre section, and the upper section are integrally formed, where a diameter of the circular path is gradually reduced during step II), and where a rate reduction of the diameter of the circular path is gradually decreased during step II).

18. A method according to claim 17, where the base is made by printing.

19. A method according to claim 17 or 18, where the base is formed integrally with a foundation.

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