Wind farm

Abstract

A wind farm comprising a number of wind turbines arranged on a ground comprising a first ground portion having a first ground surface and an outer periphery and a second ground portion having a second ground surface and surrounding the first ground portion. The first ground portion is covered with a reflective artificial covering to provide a reflecting surface having an albedo higher than the albedo of the second ground portion and thereby generating a lower temperature and a higher pressure in the first ground portion than in the second ground portion and a wind having a speed in a direction from the first ground portion towards the second ground portion. Some of the wind turbines are arranged in the second ground portion in such a distance from the periphery of the first ground portion that they are subjected to the wind coming from the first ground portion.

Claims

1. A wind farm comprising: a plurality of wind turbines arranged on a ground, the ground comprising: a first ground portion having a first ground surface and an outer periphery; and a second ground portion having a second ground surface and surrounding wholly or partly the first ground portion, wherein the first ground portion is covered with a reflective first artificial covering configured to provide the first ground portion with a reflecting surface having an albedo higher than an albedo of the surrounding second ground portion and generate; a lower temperature and a higher pressure in the first ground portion than in the second ground portion, and a wind having a wind speed in a direction from the first ground portion towards the second ground portion; and wherein at least some of the wind turbines are arranged in the second ground portion in such a distance from the outer periphery of the first ground portion that they are subjected to the wind coming from the first ground portion.

2. The wind farm according to claim 1, wherein the reflective first artificial covering is formed by a liquid or granular coating applied to the first ground portion and is configured to provide the reflective surface.

3. The wind farm according to claim 1, wherein the reflective first artificial covering is formed by a plurality of flexible or rigid mirrors or mirror-like sheet elements arranged in the first ground portion.

4. The wind farm of claim 1, wherein the albedo of the reflective first artificial covering is at least between 50% and 90%.

5. The wind farm of claim 1, wherein a difference between the albedo of the first ground portion and the albedo of the second ground portion is at least between 30% and 80%.

6. The wind farm of claim 1, wherein the albedo of the reflecting surface is configured to cause a temperature difference of at least between 1 and 35 degrees Celsius between the first ground portion and the second ground portion.

7. The wind farm of claim 1, wherein an area of the reflective surface is at least between 0.3 and 50 km.sup.2.

8. The wind farm of claim 1, wherein an area of the first ground portion having the reflective first artificial surface and a difference in albedo between the first and the second ground portions is chosen such that a temperature difference of at least between 1 and 35 degrees Celsius occurs between the first ground portion and the second ground portion.

9. The wind farm of claim 1, wherein an area of the first ground portion having the reflective first artificial surface and a difference in albedo between the first and the second ground portions are chosen such that a temperature difference of at least between 1, and 35 degrees Celsius occurs between the first ground portion and the second ground portion when at least one of the wind turbines is subjected to a wind speed of at least between 2 m/s and 6 m/s.

10. The wind farm of claim 1, wherein the first ground portion is covered with a surface providing a Goldberg-Mohr friction coefficient k between said surface and a wind of less than between 0.1 and 0.03 s.sup.1.

11. The wind farm of claim 1, wherein the second ground portion is covered with a second artificial covering having an albedo lower than the albedo of the reflective first artificial coating.

12. The wind farm according to claim 11, wherein the second covering is formed by a granular or liquid coating applied to the second ground portion configured to provide the albedo lower than the albedo of the reflective first artificial coating.

13. The wind farm according to claim 11, wherein the second covering is formed by a plurality of flexible or rigid sheet elements arranged on the second ground portion.

14. The wind farm according to of claim 1, wherein the reflective first artificial covering is arranged on and/or supported on a leveled ground surface.

15. The wind farm of claim 1, wherein the second ground surface has a leveled ground surface.

16. The wind farm of claim 1, wherein at least some of the wind turbines are in the second ground portion and are arranged on a line being essentially parallel with the outer periphery of the first ground portion so as to be arranged essentially in the same distance from said outer periphery.

17. The wind farm of claim 1, wherein at least some of the wind turbines are, in the second ground portion and are arranged on a closed curve being essentially parallel with the outer periphery of the first ground portion so as to be arranged in essentially the same distance from said outer periphery.

18. The wind farm of claim 1, wherein at least some of the wind turbines are Danish type Horizontal Axis Wind Turbines (HAWT) comprising a tower and, on top of the tower, a nacelle with a rotor provided with three or fewer blades.

19. The wind farm of claim 1, wherein at least some of the wind turbines are Vertical Axis Wind Turbines (VAWT).

20. The wind farm of claim 1, wherein a wind barrier is provided between adjacent wind turbines of the plurality of wind turbines, said wind barrier being arranged so as to reduce an amount of wind leaving the first ground portion without passing an area covered by a rotor of one of the plurality of wind turbines.

21. The wind of claim 1, wherein the first ground portion with the reflecting surface has a shape with a high area to circumference ratio.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) Embodiments of the invention are described below with reference to the drawings in which:

(2) FIG. 1 illustrates the formation of a sea breeze circulation and a sea breeze,

(3) FIG. 2 illustrates the formation of air flow circulation and an essentially horizontal wind from a first to a second ground portion of a wind farm according to the invention as seen in a vertical sectional view of FIG. 3,

(4) FIG. 3 shows a perspective plan view of a wind farm according to the invention,

(5) FIG. 4 shows a sectional view of a mirror of which a plurality is arranged in the first ground portion so as to form a reflecting covering thereof,

(6) FIG. 5 shows a lateral view of a wind turbine of the Danish type arranged in the second ground portion, and

(7) FIG. 6 shows a lateral view of a modified wind turbine having an upwardly tilted nacelle and thereby an upwardly tilted rotor axis.

DETAILED DESCRIPTION OF THE INVENTION

(8) As illustrated in FIG. 1 and described previously, a sea breeze circulation may be formed during a sunny day, and thereby a sea breeze from the sea to the land.

(9) An embodiment of a wind farm according to the invention is now described with reference to FIG. 2 to FIG. 6.

(10) As shown in FIGS. 2 and 3, the wind farm comprises a ground comprising a first ground portion 16 and a second ground portion 15 surrounding the first ground portion 16. The first ground portion 16 has a first ground surface 18 and a periphery 19 and is covered with a reflecting first artificial covering 20 so as to provide the first ground portion 16 with a reflecting surface having an albedo higher than the albedo of the surrounding second ground portion 15 having a second ground surface 22. Thereby and as described previously, the temperature in the first ground portion 16 will be lower than in the second ground portion 15 on a sunny day, and the temperature difference between the mentioned two ground portions will increase over time as the first ground portion not heated so much due to sunlight. As a result and as described previously, the result is the generation of air circulation comprising a wind 13 at low altitude having a wind speed in a direction from the colder first ground portion 16 to the warmer second ground portion 15.

(11) The wind farm according to the invention further comprises a plurality of wind turbines 17 arranged in the second ground portion. They are arranged in such a distance from the periphery of the first ground that they are subjected to the wind 13 coming from the first ground portion, as shown in FIGS. 2 and 3.

(12) In the embodiment shown, the reflecting first covering 20 is formed by a plurality of mirrors 23 arranged on the first ground surface 18. The first ground surface has, if necessary, been leveled in order to provide a smooth surface.

(13) As shown in FIG. 4, each mirror 23 comprises an upper highly transparent upper layer 24, preferably a glass layer or a polymer layer, a subjacent highly reflecting layer 25, such as an aluminum layer in the form of an aluminum foil or sheet or a metallization layer, and a lower protecting layer 26, such as a polymer sheet. Finally, a bottom layer 27 in the form of an insulating layer, such as a sheet of a foamed polymer is attached to the lower surface of the lower layer. The size of the mirrors can as an example be 1 m2 m for convenient handling.

(14) In the embodiment shown, the wind turbines 17 are of the so-called Danish type comprising a tower 28 and on top of the tower a nacelle 29 with a rotor 30 provided with three blades 31 and supported by a rotor axis 32 as shown in FIG. 5.

(15) The reflecting first artificial covering of the first ground portion 16 formed by the mirrors 23 will on a sunny day reflect up to 86-95% of the energy back to space while the surface of the surrounding second ground portion 15 will reflect about 26-29% of the energy back to space when the site of the wind farm is a desert.

(16) The large difference in albedo will over time cause a large difference in the temperature in the air above the first and the second ground portion. Assuming that the temperature above the first ground portion 16 is 15 degrees and above the second ground portion 15 is 35 degrees and the area of the first ground portion 15, i.e. the reflecting surface 21, is 1 km.sup.2, then the wind speed of the wind from the first to the second ground portion and to which the wind turbines 17 are subjected can be estimated to be as a maximum 26 m/s, as it appears from the previous example. Even though the wind speed in practice will be lower than 26 m/s, it is expected that the wind speed will be at such a level that the wind turbines work efficiently. Additionally, it should be noted that at present it is expected that the wind speed increases with an increasing area of the reflecting surface of the first ground portion.

(17) With the same assumptions as in the previous example the theoretical maximum wind speed from the first to the second ground portion will be 59.5 m/s if the area of the reflecting surface of the first ground portion is 5 km.sup.2. However, as mentioned in practice, the wind speed will be somewhat lower.

(18) The wind coming from the first ground portion 16 may not be parallel with the ground surface. It is believed that the wind 12 flowing downwardly towards the first ground portion 16 may gradually change into an essentially horizontal wind. It can therefore be advantageous that the rotor axis and preferably also the nacelle of the wind turbines are tilted upwardly so that it is essentially parallel with the wind coming from the first ground portion, as shown in FIG. 6.

(19) The tilt of the axis can be highest for the wind turbines closest to the periphery of the first ground portion and decrease with increasing distance from the periphery of the first ground portion. The tilt can be at least 5, 10, 15, 20, 25 or 30 degrees.

LIST OF REFERENCE NUMERALS

(20) 1 Rising air 2 Descending air 3 Sea breeze 4 Return flow 5 Land 6 Sea 11 Rising air flow 12 Descending air flow 13 horizontal wind 14 Return air flow 15 Second ground portion 16 First ground portion 17 Wind turbines 18 First ground surface 19 Periphery 20 Reflecting first covering 21 Reflecting surface 22 Second ground surface 23 Mirrors 24 Upper layer 25 Subjacent layer 26 Lower layer 27 Bottom layer 28 Tower 29 Nacelle 30 Rotor 31 Blades 32 Rotor axis HI High pressure at low altitude Hh High pressure at low altitude LI Low pressure at low altitude Lh High pressure at high altitude a Distance