WO2013060587A1

WO2013060587A1 - Wind protection device for a solar collector assembly and a solar collector assembly with the wind protection device

Info

Publication number: WO2013060587A1
Application number: PCT/EP2012/070379
Authority: WO
Inventors: Daniel SUCH
Original assignee: Siemens Aktiengesellschaft; Siemens Concentrated Solar Power Ltd.
Priority date: 2011-10-24
Filing date: 2012-10-15
Publication date: 2013-05-02

Abstract

The invention relates to a wind protection device (10, 110) for a solar collector assembly (100) comprising a longitudinal structure with a first end and a second end, a leading edge (11), a trailing edge (12), a first surface (13, 113) and a second surface (14, 114), wherein the first surface (13, 113) is more curved than the second surface (14, 114) in order to generate a lifting force (125) perpendicular to the first surface (13, 113). The invention further relates to a solar collector assembly (100) with such a wind protection device (10, 110).

Description

Wind protection device for a solar collector assembly and a solar collector assembly with the wind protection device

The invention generally relates to solar power production, in particular to a wind protection device for a solar collector assembly and a solar collector assembly with such a wind protection device.

A conventional parabolic trough solar field consists of units for transferring the solar energy in to thermal power. The unit of the solar field is called a loop, comprising of a collection of receiver tubes (also called "solar receivers" or "vacuum air collectors") for absorbing solar energy and transferring absorbed energy to a heat transfer fluid which is located in the receiver tubes. Additional segments of the loop, reflector troughs (also called "focusing reflectors") are provided to focus the sun rays onto the receiver tubes. An assembly of a receiver tube and a respective reflector trough together with a supporting structure of the receiver tube and the reflector trough is called solar collector assembly (in the following also "SCA") . The SCA

conventionally comprises a metal framework designed to keep the receiver tube and the reflector trough suitably aligned. The SCA generally allows the tracking of the sun during the day in order to generate sufficient heat in the receiver tube. Another part of the SCA is a number of substantially vertical drive pylons for supporting the substantially horizontal parabolic framework of the SCAs . The drive pylons are generally vertical pylons having a driving mechanism for rotating the metal framework supporting the reflector

troughs . A basic arrangement of a conventional solar field unit is shown in Fig. 1. The solar field unit 1 comprises a cold header 3, a loop 4, and a hot header 5. The loop 4 consists of a plurality of SCAs 6 each comprising a parabolic reflector trough 8 and a receiver tube 9 in the focusing axis of the parabolic reflector trough 8. In this figure, the SCAs are arranged in a substantially horizontal manner, but it is also possible that the SCAs are arranged in a vertical direction. Between the hot header 5 and the cold header 3, thermal power is transmitted to heat exchangers used to transfer thermal energy from the heat transfer fluid system to a water steam cycle including a steam turbine for

converting thermal energy to electric energy.

A general problem of conventional solar field units is that most of them are installed in regions in which strong winds, e.g. thermal winds, occur. Due to the form and size of the focusing reflectors, the SCAs are susceptible for high loads acting on the metal framework and the drive pylons of the

SCAs caused by the wind force. Thus, wind fences or elements for moving the SCAs (e.g. the driving mechanisms in the drive pylons) are used to lower the wind effects in the SCAs. For example, the SCAs are moved into a position in which they are protected against the wind forces. This, however, lower the reflection of solar energy at the receiver tubes by worsening the tilt angle of the focusing reflectors to the sun. If fences are used, the focusing reflectors are shaded in some extent so that the effectiveness of the solar field unit is reduced as well.

Therefore, it is an object of the present application to solve the above problems and to provide an alternative wind protection device for solar collector assemblies and an improved solar collector assembly. More particularly, an object of the invention is to improve the effectiveness of a solar collector assembly during operation in a wide range of different wind conditions. This object is met by a wind protection device according to claim 1 and a solar collector assembly according to claim 5. The wind protection device according to the invention is adapted for the use in a solar collector assembly, especially in an SCA comprising a receiver tube, a reflector trough, and a framework of supports, a supporting structure, for the receiver tube and the reflector trough (also called "trough system") . The reflector trough can preferably have a

parabolic trough shape in order to focus the reflected sun rays in its longitudinal center of the trough, but any other shape permitting a respective focusing of the sun rays to the loop line is suitable as well. For simplification, reflector trough is used in the following description for any of those reflector shapes.

According to the invention, the wind protection device comprises a longitudinal structure with a first end and a second end, a leading edge, a trailing edge, a first surface and a second surface, wherein the first surface (also called "upper surface") is more curved than the second surface in order to generate a lifting force perpendicular to the first surface. More particularly, the general shape of the wind protecting device is designed like an airfoil or a wing in order to provide the respective lifting force. In other words, the wind direction (the direction of the incoming wind and reflected wind, respectively) produces the lifting force that is perpendicular to its incoming direction and is in the direction of the curved surfaces.

The lifting force of each of the wind protection devices induces a moment which is directed in the opposite direction of the wind induced moment induced at the reflector troughs and the SCA by the incoming or attacking wind. The term

"moment" means a rotational moment throughout the text.

Hence, the loads from the drive pylons required for acting against those incoming wind induced moments on the reflector trough of SCAs in wind situations are preferably reduced by means of the wind protection device according to the

invention. The advantage is that the SCAs are protected from the wind induced moments by the counter moment generated. The counter moment is the sum of each of the moments generated by the wind protection devices according to the invention. It is possible that two or more such moments generated by the wind protection devices are in opposite directions and the counter moment is the remaining moment. According to the invention, the counter moment is, independently from the present wind condition, adjusted such that it is in opposite direction to the turning moment of the drive pylon, that means to the load induced via the wind on the reflector trough itself on the pivot axis between the reflector trough and the pylon (e.g. acts at the driving mechanism of the pylon) .

The moments are produced by the lifting force acting on the device and its distance and orientation towards the centre of rotation of the SCA.

An external wind shield like a fence or the movement of the trough system into a position where the wind induced loads and/or moments are lowered can be additionally used as auxiliary wind protection means. Consequently, the efficiency of a solar field unit or possible application in severe or varying wind conditions can be further improved.

In order to protect a solar field unit, especially the SCAs from higher loads acting on the drive pylons which are, for example, suitable to operate the SCAs in several different wind conditions, the above object is, in a further aspect of the invention, met by a solar collector assembly as described below. A solar collector assembly according to the invention comprises a receiver tube, a reflector trough, and a

framework of supports (also called supporting structure) for the receiver tube and the reflector trough, and a number of wind protection devices according to the invention. A number means that one wind protection device on the upper or the lower longitudinal edge of the reflector trough or a

plurality (i.e. two, three, four or even more) of such wind protection devices at the upper and/or lower edge of the reflector trough can be used. The size, especially the length, and the number of the wind protection devices depends on several parameters and especially is related to the wind induced forces which act on the SCA. Upper and lower are defined herein with regard to a horizontal reflector.

However, the reflectors can also be aligned in a

substantially vertical manner or an angular manner. In case of a vertical alignment, upper and lower longitudinal edges means the right-hand or left-hand longitudinal side of the reflector .

As described above, the wind protection device used has a shape substantially like an airfoil or wing and generates a counter rotating moment on the trough system in order to lower the load, especially from the drive pylons of an SCA. This is achieved by the specific shape of the wind protection device in the form of an airfoil or a wing so that it

generates a lifting force directed perpendicular to the first surface of the wind protection device. As the wind protection device is for example arranged in a position that the curved first surface is facing against the center, more particularly against the centerline, of the reflector trough (the through system) of the SCA, the lifting force is directed into the same direction. If the wind protection device is pointed with its curved surfaces in the opposite direction of the SCA center (focus) because of the incoming wind direction being from the opposite side, the lifting force faces away from the SCA center and as such counters the rotation of the SCA due to the wind load. More particularly, the wind protection device, which is arranged at the upper longitudinal edge of the reflector trough, is shaped in such a manner that it produces lift in the downward direction (i.e. facing substantially into the centerline of the preferably parabolic reflector trough) . Thus it produces a moment (i.e. a rotational moment) opposing the sail effect of the reflector trough (which may also be called "mirror") when wind is flowing into and/or around the reflector trough. At the lower longitudinal edge of the reflector trough, the loads and moments generally are

directed opposite to the loads and moments of the wind protection device mounted on the upper side of the reflector trough. Accordingly, independently of the place where the wind protection device is mounted, it lowers the load on the reflector trough and, thus, the turning moment required to hold the reflector trough (also called "parabola") at a correct position during wind conditions. Therefore, the use of the wind protection device facilitates either the lowering of the load on the drive pylon or an actuating means such as a motor arranged thereon or raising the maximal wind velocity (load) that the drive pylon or, more particularly the motor at the drive pylon, can withstand. Hence, the efficiency of the SCA can be improved and the range of use at locations with different wind conditions can be widened.

Particularly advantageous embodiments and features of the invention are given by the dependent claims, as revealed in the following description. Features of the embodiments may be combined as desired to arrive at further embodiments.

According to a preferred embodiment, the wind protection device can have a second surface which is substantially flat or dished. Thus, the device can be designed in either

symmetrical or non-symmetrical airfoil shape, which will be dictated by the relevant wind directions for the specific site. An asymmetric design improves the adjustment of the lifting force and especially increases the lift induced compared to a symmetrical airfoil.

In another embodiment, the wind protection device according to the invention comprises a mounting means adapted for mounting the wind protection device to an upper longitudinal end and/or a lower longitudinal end of a reflector trough of a solar collector assembly. In other words, the wind

protection device can be connected to the preferably

parabolic reflector through at both sides of the parabola, more particular to the framework of supports holding the mirrors of the trough. If wind protecting devices are

provided at both ends of the reflector trough, the counter force (or counter moment) resulting from any of the devices used can be calculated as the sum of the single forces (or moments) resulting from the lifting force of any of the devices. The counter force (or moment) is preferably adjusted such that is opposite to the force (or moment) induced by the wind at the drive pylon and, thus, lowers this force (or moment) respectively.

The wind protection device according to another preferred embodiment of the invention comprises a mounting means for supporting the wind protection device in its longitudinal axis from one end to the other end in a free floating manner. Free floating means that the device is freely rotatable, e.g. for the full 360° angle range, or is at least freely adjustable in a specific angle. Accordingly, the wind

protection device can be automatically forced in the right direction by the incoming wind, which is the sum of the direct incoming wind and wind reflected from the reflector trough. For the purpose of generating a respective counter moment which is opposite to the moment induced at the drive pylon by the incoming wind, the wind protection device is preferably held in a position that at least a part of the force induced by the lifting force is directed against the momentum induced by the incoming wind at the drive pylon. Preferably, the freely rotatable wind protection device can orient itself in such a manner that its leading edge faces towards the incoming wind.

Moreover, the wind protection devices are preferably designed in such a manner that they do not produce moment against their center of rotation. Wing type devices have an

aerodynamic center that acts as a force acting line of the lifting force and as such does not create moments between the centre of gravity and the aerodynamic center line. Thus the wind protection devices have a zero rotational moment of its own on its hinge line. The solar collector assembly according to the second aspect of the invention preferably comprises a mounting means for mounting the wind protection device to an upper longitudinal end and/or lower longitudinal end (or the respective edge) of the reflector trough. This position is suitable for producing the respective counter force (or moment, respectively) and being in a position that the wind protection device does not shade the reflector troughs, i.e. the mirrors, in a

substantial manner. The size of the wind protection device is preferably such that only minimal impact on the shading of the mirrors, i.e. the reflector troughs, is attained at one side, while on the other side the size is sufficient to provide a respective force (or moment) against the sail effect in wind conditions. The position at the end of the reflector trough, i.e. in prolongation of the reflector trough in its vertical direction, is advantageous for

avoiding shading and generating the respective force (or moment) .

Exemplary lengths of SCAs are between about 20 to 150 meters, more preferably about 40 to 120 meters, in particularly about 60 to 100 meters. The wind protection devices are preferably arranged in about 50 to 100 %, more preferably in about 55 to 85 %, in particularly in about 60 to 70 % of the length of the SCA. Exemplary lengths of one or a series of wind

protection devices at one side of an SCA are about 40 to 110 meters, more preferably about 60 to 90 meters, in particular about 70 to 80 meters.

The wind protection devices generally have an elongated shape so that the width of them is much smaller than the length. This would also be advantageous because a substantially smaller width than length helps to avoid shading on the reflector trough. Exemplary widths are about 10 to 50 cm, preferably about 15 to 35 cm, more preferably about 17 to 23 cm. The general surface area provided mainly depends on the wind conditions at the solar unit and can be suitably adjusted at each SCA individually. Thus, different sizes of wind protection devices can be used in one solar field and, thus, the counter force can be specifically adjusted at each SCA.

In order to achieve the respective force or moment, it is preferred that the mounting means is a cantilever for holding the wind protection device at its free end in longitudinal direction. The cantilever preferably protrudes from the upper end and/or the lower end of the reflector trough, preferably at both longitudinal ends only, in order to define a gap between the reflector trough and the wind protection device. The gap allows a wind flow passing through it and generating the respective lifting force. The proposed gap is preferably dimensioned in such a manner to avoid any aerodynamic

interference between the SCA and the device. Therefore, the gap is preferably above one chord (i.e. the width) of the device above the SCA.

According to a further embodiment of the solar collector assembly according to the second aspect of the invention, the mounting means can preferably be connected to each

longitudinal end of the wind protection device in such a manner that the wind protection device is mounted in its longitudinal axis from one end to the other end in a free floating manner. As described above, due to the free floating arrangement, the wind protection device can be automatically forced in the right direction by the incoming wind.

Accordingly, the wind protection device is automatically arranged such, that the respective counter moment is

generated .

In another embodiment of the solar collector assembly

according to the invention, a number of wind protection devices are used which have a first surface and a second surface, wherein the first surface is, e.g., substantially faced against the center of the reflector trough and is more curved than the second surface in order to generate a lifting force perpendicular to the first surface. Thereby, a

respective lifting force ("lift") and resultant moment through the trough center of rotation in the opposite direction of the wind induced moments, i.e. the counter moment, is generated.

The solar collector assembly according to another preferred embodiment comprises a supporting structure comprising a number of substantially vertical drive pylons for supporting a framework of supports for the receiver tube and the reflector trough, wherein the drive pylons comprise an actuation means for tracking the sun on the horizon.

Optionally, the tracking of the sun during the day can also be carried out by means of a control system for tracking the sun by moving the SCA mounted on the drive pylons. In such a constitution, the wind induces a respective rotation moment at the connection between the drive pylons and the framework for the reflector trough. Thus, the use of the wind

protection devices allows a reducing of the force at the drive pylons by generating a counter force which acts on the drive pylons in opposite direction. Hence, the SCA can be used in a wider range of different wind conditions, e.g. stronger winds, varying wind directions, or others. Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for the purposes of illustration and not as a

definition of the limits of the invention.

Fig. 1 shows a solar field unit according to the prior art;

Fig. 2 shows a cross sectional view of a wind protecting device according to an embodiment of the invention; Fig. 3 shows a cross sectional view of a solar collector assembly according to an embodiment of the invention in a first wind direction; Fig. 4 shows a cross sectional view of the solar collector assembly according to Fig. 3 in a second wind direction;

Fig. 5 shows a schematic front view of an SCA member with a wind protection device mounted on its top;

Fig. 6 shows a schematic side view of the SCA member of Fig. 5.

Fig. 1 shows a conventional solar field unit 1 comprising a cold header 3, a loop 4, and a hot header 5. The loop 4 consists of a plurality of SCAs 6 each comprising a parabolic reflector trough 8 and a receiver tube 9 in the focusing axis of the reflector trough 8. Between the hot header 5 and the cold header 3, a generator unit (not shown) is typically arranged to generate electric power. The invention uses a similar general layout of a solar filed unit. The same general configuration of a solar field unit can be used according to the invention, but with SCAs specifically constructed in line with the principle of the invention as described below.

In Fig. 2 a cross sectional view of a wind protecting device 10 according to an embodiment of the invention is shown. The wind protection device has a general structure like an air foil or wing with a leading edge 11, a trailing edge 12, a first (upper) surface 13 and a second surface 14. The first surface 13 is curved in a specific manner, wherein the specific curvature is usually defined as camber. The second surface 14 is not curved or is, as it is shown in this figure, slightly dished. Therefore, the typical air flows around the curved first and the second surface as used for generating sufficient amount of lift in an airplane are used in the wind protecting devices of the invention. The general outline is a longitudinal element having substantially the same cross section as shown in the figure all over its length . In Fig. 3 a cross sectional view of a solar collector

assembly 100 according to an embodiment of the invention is shown in a first wind direction 150. The SCA 100 comprises a supporting structure 103 with a drive pylon 102, a framework 104 for holding the reflector trough 106, a mirror as the reflector trough 106 having a focus point (not shown) in its centreline, and at each of its lower and upper longitudinal ends (107, 108) a wind protection device 110. The receiver tube in the SCA' s centreline is not shown for simplification of the figure.

Each wind protection device 110 is mounted at the upper longitudinal end 107 or at the lower longitudinal end 108 of the reflector trough 106 with a cantilever-like mounting means 109. The free end 119 of each of the cantilevers mounted at or on the reflector trough is connected to a longitudinal end of the wind protection device 110 to hold it in a freely rotating position.

The form of the wind protection device 110 is the same as has been shown in Fig. 2. During operation in wind conditions, the incoming wind flow 120 and the reflected wind flow 130 flow around the wind protection device 110 and especially through the gap 118 between the reflector trough 106 and the wind protection device 110. Thereby, the wind protection device 110 is automatically oriented such that the first surface 113, the curved surface, is substantially directed to the centre of the reflector trough 106, while the second surface 114 is substantially facing outwards of the SCA. ue to the different flow speeds around the wind protection device 110, a lifting force 125 is generated which is

substantially facing against or directed to the centre of the reflector trough 106. The lifting force 125 and the drag 135 generated by the wind protection device 110 are responsible for a respective moment 145.

The moment 145 from the upper wind protection device 110 and the moment 145 from the lower wind protection device 110 are substantially opposite to each other and a total moment can be calculated from both values. This resulting total moment is called counter moment (not shown) and is directed opposite to the moment 155 induced by the incoming wind at the drive pylon 102. Accordingly, the moment 155 is lowered by the counter moment resulting from the sum of the respective moments 145. Thereby the load on the drive pylon is lowered, when wind protection devices as shown in the figure are used. Fig. 4 shows a cross sectional view of the solar collector assembly according to Fig. 3 in a second wind direction. As the wind is now coming from the opposite direction 150 compared to the situation shown in Fig. 3, the wind

protection devices 110 have been rotated such that the curved surface are now directed away from the SCA. Therefore the resulting moments 145 are directed into the opposite

direction as in the situation of Fig. 3 and, thus generating a moment acting against the moment induces by the wind direction 150 at the drive pylon 102.

Fig. 5 shows a schematic front view of an SCA member 106 with a wind protection device 110 mounted on its top. The SCA is supported at both sides and from its back (not shown) on a framework 104 directly connected to the drive pylons (not shown) . The wind protection device 110 is mounted at the framework 104 via mounting means wind protection device supports 112 and mounting means 109 holding the wind

protection device at its hinge portion which is directly positioned in the aerodynamic center (not shown) . Between the SCA 106 and the wind protection device 110, a gap of at least one chord is provided to allow a free rotation of the wind protection device around its hinge portion. Fig. 6 shows a schematic side view of the connection between the wind protection device support 112 and the wind

protection device 110 of Fig. 5. The wind protection device support is based behind the SCA 106 in order to avoid

shadowing at the mirrors of the SCA 106. The wind protection device support holds the wind protection device via mounting means 109 which are directed to the aerodynamic center 111 of the wind protection device 110. Thereby a hinge portion is provided allowing the wind protection device to freely rotate around the hinge angel in the aerodynamic center 111. Thus, the first surface 113 being curved and the second surface 114 can be arranged dependent on the incoming wind direction and provide a respective lifting action as described beforehand. Although the present invention has been disclosed in the form of preferred embodiments and variations thereof, it will be understood that numerous additional modifications and

variations could be made thereto without departing from the scope of the invention. While the invention has been

described with reference to wind protection devices for a solar collector assembly, other assemblies having a sailing effect may also be protected by the devices according to the invention. For the sake of clarity, it is to be understood that the use of "a" or "an" throughout this application does not exclude a plurality, and "comprising" does not exclude other steps or elements. A "means", "device" or "element" can comprise a number of separate means, devices or elements, unless otherwise stated.

Claims

Patent claims

1. Wind protection device (10, 110) for a solar collector assembly (100), comprising a longitudinal structure with a first end and a second end, a leading edge (11), a trailing edge (12), a first surface (13, 113) and a second surface (14, 114), wherein the first surface (13, 113) is more curved than the second surface (14, 114) in order to generate a lifting force (125) perpendicular to the first surface (13, 113) .

2. Wind protection device according to claim 1, wherein the second surface (13, 113) is substantially flat or dished.

3. Wind protection device according to claim 1 or 2, with a mounting means (109) adapted for mounting the wind protection device (10, 110) to an upper end (107) and/or a lower end (108) of a reflector trough (106) of a solar collector assembly (100) .

4. Wind protection device according to claim 3, wherein the mounting means (109) supports the wind protection device (10, 110) in its longitudinal axis from one end to the other end in a free floating manner.

5. Solar collector assembly (100) comprising a receiver tube (9), a reflector trough (106), and a framework (104) of supports for the receiver tube (9) and the reflector trough (106), wherein the solar collector assembly (100) further comprises a number of wind protection devices (10, 110) according to any one of the claims 1 to 5.

6. Solar collector assembly according to claim 5, comprising a mounting means (109) for mounting the wind protection device (10, 110) to an upper end (107) and/or lower end (108) of the reflector trough (106) .

7. Solar collector assembly according to claim 6, wherein the mounting means (109) is a cantilever for holding the wind protection device (10, 110) at its free end (...), wherein the cantilever protrudes from the upper end (107) and/or the lower end (108) of the reflector trough (106) in order to define a gap (118) between the reflector trough (106) and the wind protection device (10, 110) for a wind flow passing through the gap (118) .

8. Solar collector assembly according to claims 6 or 7, wherein the mounting means (109) is connected to each

longitudinal end of the wind protection device (10, 110) in such a manner that the wind protection device (10, 110) is mounted in its longitudinal axis from one end to the other end in a free floating manner.

9. Solar collector assembly according to any one of claims 5 to 8, having a wind protection device (10, 110) with a first surface (13) and a second surface (14), wherein the first surface (13) is substantially facing to the center of the reflector trough (106) and is more curved than the second surface (14) in order to generate a lifting force (125) perpendicular to the first surface (13) .

10. Solar collector assembly according to any one of claims 5 to 9, wherein the supporting structure (103) comprises a number of substantially vertical drive pylons (102) for supporting a framework (104) of supports for the receiver tube (9) and the reflector trough (108), wherein the drive pylons comprise an actuation means for tracking the sun on the horizon.