Solar Reflection Apparatus

Abstract

A solar reflection apparatus (60) is disclosed comprising a rotatable reflection (assembly 20) and a drive mechanism (12) which is operable to drive rotation of the reflection assembly (20) at its axis of rotation. The reflection assembly (20) comprises a curved linear reflector (4) defining a focal axis F, a counter weight (17) operable to balance the self weight of the reflector (4), and a support structure (15) via which the reflector (4) and counter weight (17) are rotatably mounted at locations along the focal axis F of the reflector (4). A solar collection apparatus (2) is also disclosed comprising a solar reflection (apparatus 60) as disclosed above and a heat collecting element (6), fixedly mounted along the focal axis F of the reflector (4). Also disclosed is a method of reflecting solar radiation comprising forming a reflection assembly (20), mounting the reflection assembly (20) for rotation about the focal axis F of the reflector (4) and driving rotation of the reflection assembly (20) at its axis of rotation. The reflection assembly (20) comprises a linear curved reflector (4) that defines the focal axis F, a counter weight (17) operable substantially to balance the self weight of the reflector (4), and a support structure (15).

Description

The present invention relates to a solar reflection apparatus, a solar collection apparatus and a method of reflecting solar radiation, all of which may be appropriate for use in a solar thermal power plant.

BACKGROUND TO THE INVENTION

Concentrated Solar Power (CSP) systems use lenses or mirrors to focus large areas of sunlight onto a small target area. The focused light is used to heat a working fluid or heat transfer fluid (HTF) for use in a conventional power plant. Tracking systems are employed to orient the lenses or mirrors to focus the maximum amount of sunlight throughout the solar day.

One of the most efficient concentrating technologies is the parabolic trough, comprising a linear parabolic reflector which concentrates light on a heat collecting element positioned along the focal line of the reflector. The heat collecting element is generally a heat collecting pipe which may be filled with water for steam generation or with a HTF. The parabolic trough reflector is rotated during the solar day to remain oriented towards the sun. Conventional systems, examples of which are currently in operation in Europe and the United States, form the reflectors and heat collecting pipe as a unitary construction, rotating the entire construction about a designated axis during the solar day. These systems require rotation and may require translation of the central heat collecting pipe. They must therefore employ components such as flexible hoses or more usually swivel ball joints to connect the rotating heat collecting pipe to the stationary pipe work that will transport the heated fluid to the power generation section of an associated power plant.

There are several disadvantages associated with the use of swivel ball joints, chief among which are the associated costs, both capital cost in installation and maintenance costs associated with the smooth functioning of large fields of solar collectors. There are also issues of containment integrity associated with swivel ball joints. Leaks are known to occur at such joints and can cause a fire risk as well as resulting in the release of potentially hazardous liquids and associated fumes. A further issue associated with swivel joints is their stiffness. High stiffness is an inevitable consequence of attempting to ensure containment integrity, but high stiffness joints require high power for rotation and induce undesirable torsional stresses in the reflector, reducing reflector efficiency and increasing the parasitic load on the plant.

Certain systems have attempted to address the above issues by rotating the reflector independently of the heat collecting pipe, as in GB2235786. According to this system, the reflector is rotated via a bearing through which the heat collecting pipe passes; rotation is powered by a drive shaft that engages a toothed arcuate construction on the convex surface of the reflector. Unfortunately, such systems merely exchange the high costs and maintenance issues associated with swivel joints for comparable costs and issues associated with the more complex construction and drive system. There remains a need therefore for a solar collection system that addresses the above noted disadvantages of conventional systems.

Parabolic trough solar collectors are known to be susceptible to severe damage from high winds. In the event of high wind conditions, it is necessary to rotate the reflectors to a specific “high wind” position in which loads on the parabolic reflectors and their support structures are minimised. The majority of parabolic trough designs rely on hydraulic arms to rotate the reflectors and these must therefore be employed to place the reflectors in the high wind position when necessary. In the event of power failure, a portable hydraulic back up system must be employed. Such a system is transported to the location of, and then connected to, the existing hydraulic drive to place the reflectors in the high wind position. Owing to the vast scales on which solar collection plants operate, the number of reflectors to be rotated and the distances the back up system may be required to move can be very great. The process of placing an entire solar field into the high wind position in the event of a power failure can therefore be extremely time consuming.

SUMMARY OF THE INVENTION

According to the present invention, there is provided a solar reflection apparatus comprising a rotatable reflection assembly and a drive mechanism, operable to drive rotation of the reflection assembly at its axis of rotation; the reflection assembly comprising a curved linear reflector defining a focal axis, a counter weight operable substantially to balance the self weight of the reflector, and a support structure via which the reflector and counter weight are rotatably mounted at locations along the focal axis of the reflector.

Mounting the reflection assembly at the focal axis, about which the assembly is rotated, significantly simplifies construction of the apparatus and hence the capital cost of manufacture and installation. In addition, driving rotation at the axis of rotation enables a simplified drive mechanism to be employed, further reducing costs and increasing reliability of the apparatus. Fine control of rotation can be achieved with rotation driven at the axis, enabling accurate solar tracking and associated benefits in efficiency.

By balancing the self weight of the reflector with a counter weight, and thus forming a reflection assembly, the power required to drive rotation of the reflector is greatly reduced, saving energy and reducing induced torsional stresses in the reflector.

The mounting locations for the reflection assembly may for example be located at opposite ends of the reflection assembly. The drive mechanism may comprise a motor and direct gear transmission, which may for example employ both worm and toothed gears.

The drive mechanism may be mounted substantially on the focal axis of the reflector. Thus, at least a final driven gear of the drive mechanism may be mounted on or about the focal axis, with a power source and any other associated gearing being adjacent thereto. The drive mechanism may comprise an in line drive assembly mounted substantially on the focal axis of the reflector. Since the drive motor does not move with the reflector during rotation, there is no need for long, moving power cables to the motor, and further the weight of the motor is not added to the weight of the reflector assembly.

The reflection assembly may be rotatably mounted via bearings on a fixed frame. In embodiments of the invention, the bearings are mounted directly above the support legs of the frame, so that the loads exerted by the reflection assembly and counterweight are reliably carried.

In embodiments of the invention, the reflection assembly may be mounted in split Cooper® Bearings or other suitable bearing types.

The support structure of the reflection assembly may comprise a journal and a plurality of radiating arms, at least one of which extends to the reflector and at least another of which extends to the counter weight. In this manner, the reflector and counter weight may be supported by respective arms on opposed sides of the journal which is located at the focal axis of the reflector. The use of a journal which rotates with the reflector is expected to be easier to install than alternative arrangements. At least two arms may extend to the reflector, one to each extremity of the curved reflecting surface.

The reflector of the reflection assembly may be a parabolic trough reflector.

The counterweight of the reflection assembly may be operable to bias the reflection assembly to a predetermined rotational position. Such a position may for example be a “high wind” position in which external forces acting on the reflection assembly, and particularly the reflector, may be minimised.

The counterweight may be operable to cause the reflection assembly to adopt the predetermined rotational position under the action of gravity. For example, the counterweight may be constructed and mounted such that it creates a moment about the axis of rotation that is smaller by some predetermined amount than that created by the reflector. Thus, in the absence of other locking or rotational forces, the counterweight will cause the reflection assembly to assume a position under the action of gravity where the counterweight is at its furthest distance from the ground and the reflector is oriented directly below its focal axis.

In embodiments of all aspects of the invention, the counterweight may be composed of two or more separate portions supported at locations spaced along the length of the reflector assembly. For example, a counterweight may be located at each end of the reflector. This is distinct from an embodiment in which a single counterweight extends along the length of the reflector. Embodiments in which a counterweight is located at each end of the reflector may be advantageous over an embodiment in which a single counterweight extends along the length of the reflector, since the latter may be inclined to bend under its self-weight and induce bending and torsion forces in the supports supporting the counterweight. Further, separate counterweights located at opposite ends of the reflector assembly may be preferred for the reasons that they will create less shadow on the reflector than a counterweight extending along the length of the reflector.

The solar reflection assembly may further comprise a clutch mechanism operating between the drive mechanism and the reflection assembly. The clutch mechanism may be operable to engage or disengage the drive mechanism with the reflection assembly and may be configured for remote operation. For the purposes of this specification, the term “clutch mechanism” includes within its scope all components or devices which may act to connect a driven mechanism to a driving mechanism.

According to another aspect of the present invention, there is provided a solar reflection apparatus comprising a rotatable reflection assembly and a drive mechanism operable to apply rotational drive proximate an axis of rotation of the reflection assembly, the axis of rotation being substantially coincident with a focal axis of a reflector of the reflection assembly.

The drive mechanism may comprise a motor and direct gear transmission, which may for example employ both worm and toothed gears. The drive mechanism may be mounted substantially on the focal axis of the reflector. The drive mechanism may comprise an in line drive assembly that is mounted substantially on the focal axis of the reflector.

In embodiments of all aspects of the invention, the use of worm and toothed gears provides may provide an advantage over other types of transmissions, such as hydraulic drives, since when not being driven to rotate the reflection assembly, it locks the position of the reflection assembly and acts to reduce or eliminate any drift without the need for break mechanisms or constant adjustment to maintain optimum focus of the solar energy. In a worm and toothed gear arrangement, the toothed gear may be axially aligned with and secured to the journal, and the worm gear connected to the motor drive. The worm gear may be biased by, for example, a spring or other resilient member so as to press the worm spiral element into contact with teeth of the toothed gear, and thus reduce any play or float in the toothed gear and therefore possible movement in the reflection assembly. The use of a worm and toothed gear arrangement may also require a smaller motor and gearbox than other arrangements.

According to another aspect of the present invention, there is provided a solar collection apparatus comprising: a solar reflection apparatus of the first or second aspects of the present invention, and a heat collecting element fixedly mounted along the focal axis of the reflector. The heat collecting element may be a heat collecting pipe.

Rotating the reflection assembly around a fixed heat collecting element such as a collector pipe eliminates the need for swivel joints, flexible piping or other adjustable components in connecting the heat collecting element to the static pipe work of a solar thermal power plant. Eliminating the need for swivel joints reduces capital and maintenance costs, solar collector down time and improves containment integrity of fluids being transferred through the heat collecting element. Eliminating swivel joints also reduces induced torsion and associated distortion of the reflector, improving solar tracking and concentration of solar energy. Without the stiff swivel joints, less power is required to rotate the reflector.

The heat collecting element may be suitable for transporting for example a working fluid such as water or a heat transfer fluid for use in a solar thermal power plant.

The heat collecting element is mounted on at least two fixed supports distributed along the focal axis of the reflector. The supports may be located at opposed ends of the reflection assembly. The fixed supports may be operatively connected to the fixed frame on which the reflection assembly is mounted, thus simplifying the overall construction of the solar collection apparatus.

The heat collecting element may extend through the gear transmission of the drive mechanism, further simplifying construction. For example, the heat collecting pipe may pass through the bearings at each end of the assembly, and may be spaced from the bearings, so as not to be in contact therewith. By spacing the heat collecting pipe from the bearings, it is possible to reduce deleterious heating of the bearing by fluid in the collector pipe, and thus improve reliability. In an embodiment, the space between the heat collecting pipe and the bearings may be a simple air gap. In another embodiment, an insulating material may be placed in the radial space between the collector pipe and the bearings though which the pipe passes. The radial gap between the collector pipe and the bearings may, for example, be greater than 25 mm, or may be greater than 50 mm or may be greater than 75 mm. The radial gap may, for example, be less than 200 mm or may be less than 100 mm.

The solar collection apparatus may further comprise at least one auxiliary support operable to support the self weight of the heat collecting element. The auxiliary support may be located along a region of the heat collecting element that spans the reflector. By supporting the self weight of the heat collecting element, a larger reflector span can be accommodated, increasing collector capacity and overall field efficiency when a plurality of solar collection apparatuses is assembled into an array.

The auxiliary support may be independent of the reflection assembly. For example, the apparatus may comprise a frame constructed around and above the reflector assembly, from which the heat collecting element may be suspended.

Alternatively, the auxiliary support may operatively connect the reflector and the heat collecting element. The auxiliary support may comprise a heat collecting element support arm, fixedly connected to a reflecting surface of the reflector and rotatably connected to the heat collecting element.

An auxiliary reflector may be provided, which is rotatably fixed with respect to the reflector and mounted about the axis of rotation to reflect solar energy from the main reflector unit which does not directly focus at the axis of rotation. Thereby, reflected solar energy from the main reflector which would otherwise not fall directly on the collecting element is reflected back towards the axis of rotation, where the collector unit is located. In this way, the efficiency of the apparatus may be improved.

According to a further aspect of the present invention, there is provided a solar collection array comprising a plurality of rows of solar collection apparatuses according to the present invention, each row comprising a plurality of solar collection apparatuses, arranged such that their focal axes are coincident, a single heat collecting element mounted along the coincident focal axes.

According to a further aspect of the present invention, there is provided a method of reflecting solar radiation comprising: forming a reflection assembly comprising a linear curved reflector that defines a focal axis, a counter weight operable to balance the self weight of the reflector, and a support structure; mounting the reflection assembly for rotation about the focal axis of the reflector; and driving rotation of the reflection assembly at its axis of rotation.

According to another aspect of the present invention, there is provided a solar reflection apparatus comprising a rotatable reflection assembly and a drive mechanism, operable to drive rotation of the rotatable reflection assembly, the reflection assembly comprising a curved linear reflector and a biasing means, the biasing means operable to bias the reflection assembly to a predetermined rotational position.

The biasing means may for example comprise a counterweight, operable to bias the reflection assembly into the predetermined position under the action of gravity. A clutch mechanism may operate between the drive mechanism and the reflection assembly, so as to engage or disengage the drive mechanism with the reflection assembly. The clutch mechanism may be configured for remote operation.

The aspects of the present invention contribute to an apparatus which is suited to large scale operations. For example, the apparatus of the invention is suited to accommodate reflector lengths of at least 20 meters, for example at least 50 metres, for example at least 75 meters, and even up to 100 metres. Prior art arrangements are less easily able to accommodate reflector systems of such magnitude.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:

FIG. 1 is a partial perspective view of a solar collection apparatus.

FIG. 2 is a partial perspective view of a reflection assembly.

FIG. 3 is a partial perspective view of a solar reflection apparatus.

FIG. 4 is a perspective view of a solar collection apparatus.

FIG. 5 is a partial sectional view illustrating further detail of the solar collection apparatus of FIG. 1.

FIG. 6 is a partial perspective view showing a collector pipe support arm.

FIGS. 7a to 7c illustrate details of a bearing arrangement shown in FIG. 6.

FIGS. 8a and 8b illustrate details of an arrangement comprising a further reflector unit.

DETAILED DESCRIPTION OF THE INVENTION

With reference to FIGS. 1 to 4, a solar collection apparatus 2 comprises a solar reflection apparatus 60 and a heat collecting element in the form of a collector pipe 6.

The solar reflection apparatus 60 (illustrated in FIG. 3) comprises a linear parabolic reflector 4, a counterweight 17 in the form of two counterweight units 8, 10 and a drive mechanism 12. The reflector 4 and counterweight units 8, 10 are connected via a support structure 15 in the form of two support units 22, 24 and together these elements constitute a solar reflection assembly 20 (illustrated in FIG. 2). The solar reflection assembly 20 is mounted for rotation about an axis of rotation, along which the collector pipe 6 extends.

The reflector 4 is a linear parabolic reflector, or parabolic trough, and extends linearly along an axis x from a first end 21 to a second end 23. The reflector 4 defines a focal axis F, onto which solar radiation approaching the reflector is focussed. The reflection assembly 20, including the reflector 4, is mounted such that its axis of rotation is coincident with the focal axis F of the reflector 4, enabling the reflection assembly to be rotated around the focal axis F of the reflector 4. The reflector 4 may be a single piece of coated silver, polished aluminium or mirrored glass but may also be a V-type parabolic trough, formed from two reflectors arranged at an angle to one another in a manner known to those skilled in the art. The counterweight units 8, 10 and support units 22, 24 are located at each end 21, 23 of the reflector 4, such that each end of the reflector 4 has an associated counterweight unit 8, 10 and support unit 22, 24.

With particular reference to FIGS. 1 and 5, each support unit 22, 24 comprises a journal 26 having an annular flange 28 protruding from a first end thereof and three or more support arms 30, 32, 34 extending radially from the journal 26 in a supporting plane that intersects the reflector 4 at or near an edge 21, 23 of the reflector 4. For the purpose of clarity, much of the following description refers to a first support unit 22 at a first end 21 of the reflector 4, but it will be appreciated that corresponding features are found on a second support unit 24 at a second end 23 of the reflector 4. The support arms 30, 32, 34 of the support unit 22 are connected to the journal 26 via bolts 36 that engage the support arms 30, 32, 34 and the annular flange 28 of the journal 26. Alternatively, the support arms 30, 32, 34 and journal 26 may be integrally formed. Two of the support arms 30, 32 extend towards and are connected to the first end 21 of the reflector 4. A first of the reflector support arms 30, 32 extends towards and is secured to an upper (as seen in FIG. 1) linear edge 38 of the reflector 4 and a second of the reflector support arms 30, 32 extends towards and is secured to a lower (as seen in FIG. 1) linear edge 40 of the reflector 4. A third support arm 34 extends from the journal 26 to the counterweight unit 8. As can be seen in FIG. 1, the support arms 30, 32, 34 are arranged such that the counterweight unit 8 and reflector 4 are on opposed sides of an axis of rotation of the journal 26. The support arms of both support units 22, 24 are dimensioned such that the axis of rotation of each of the journals 26 is coincident with the focal axis F of the reflector, enabling the reflector to be rotated about its focal axis.

The entirety of the weight of the reflector 4 is carried via the support arms and journals of the two support units 22, 24, creating a moment arm about the axis of rotation of the journals 26. The counterweight units 8, 10 together constitute the counterweight 17, which is operable substantially to balance the moment arm of the reflector 4. The material and dimensions of the counterweight units 8, 10, together with the length and orientation of the counterweight unit support arms 34, are thus selected so as to balance out, as nearly as possible, the moment caused by the self weight of the reflector 4. It will be appreciated that precise equilibrium between the reflector 4 and the counterweight 17 is difficult to achieve. Thus, the counterweight 17 is designed and mounted substantially to balance the self weight of the reflector; the balance achieved is as near as is practicable. Such balance is sufficient to afford the desired advantages, substantially reducing the drive force required to rotate the reflector 4 and thus reducing the parasitic load on a plant in which the apparatus 2 is employed. An additional advantage afforded by the reduction in necessary drive force is that, in the event of power failure, the reflection assembly 20 can be rotated by hand. A hand crank (not shown) may be provided adjacent the drive mechanism 12 and can be used to rotate the reflection assembly 20 by providing manual drive to the drive mechanism 12.

In an alternative embodiment, the counterweight 17 is designed and mounted such that it substantially balances the weight of the reflector 4 and in addition, biases the reflection assembly 20 to a desired rotational position. For example, the counterweight 17 may be constructed and mounted to create a slightly smaller moment about the rotational axis than the reflector 4, such that under gravity, the counterweight 17 will cause the reflection assembly 20 to adopt a position with the counterweight 17 at its furthest distance from the ground and with the reflector disposed directly below the axis of rotation. The counterweight 17 may be structured to bias the reflection assembly 20 to any desired rotational position and in a preferred embodiment is operable to bias the reflection assembly 20 towards a high wind position in which wind loads on the reflector 4 are minimised. Such an arrangement has the additional advantage that, in the event of power loss, the reflection assembly 20 may assume the high wind position under gravity, relying only on the biasing effect of the counterweight 17 and not requiring any applied driving force.

The counterweight 17 is formed from a suitable material such as concrete or steel. The counterweight may be formed form an advantageous combination of concrete and steel. In a preferred embodiment, the counterweight 17 comprises two counterweight units 8, 10 mounted at opposite linear edges of the reflector 4. It is desirable for the majority of the load of the counterweight 17 to be carried at a ground contacting support, so as to allow the reflector 4 to rotate as freely as possible between supports. A plurality of smaller counterweight units may be employed between the reflector 4 edges in combination with more substantial counterweight units at the edges. However, it will be appreciated that other physical structures may be employed to form the counterweight 17. For example, in a less preferred embodiment, the counterweight 17 may comprise a single counterweight unit located near the linear centre of the reflector 4. Alternatively, a plurality of substantially equally sized counterweight units may be employed to balance the reflector self weight.

The reflector 4 and counterweight units 8, 10 are mounted via the support units 22, 24 on a static frame 15 which may be in the form of two U shaped legs 14, 16 as illustrated in the Figures. Each journal 26 of the support units 22, 24 is rotatably received in a bearing 42 which is mounted directly above the upper surface of the corresponding U shaped leg 14, 16, with the first ends of the journals 26, from which the flanges 28 and support arms 30, 32, 34 protrude, facing towards each other. The bearings 42 are preferably split Cooper® bearings but may be any other appropriate bearing type.

The drive mechanism 12 is mounted on the U shaped leg 14 of the frame 15 immediately adjacent the bearing 42 and journal 26. According to an alternative embodiment, the drive mechanism may be mounted on a dedicated stand or frame, separate from the U shaped leg 14 that supports the reflection assembly 20. The drive mechanism 12 comprises a motor 44, a drive shaft 45, a worm 46 and a worm gear 48. The motor 44, drive shaft 45 and worm 46 are arranged along an axis that is orthogonal to the axis of rotation of the reflection assembly 20. The motor 44 drives rotation of the worm 46 via the drive shaft 45. The worm 46 meshes with the worm gear 48 to drive rotation of the worm gear 48 about an axis that is coincident with the axis of rotation of the reflection assembly 20. The worm gear 48 is mounted about and secured to a second end of the journal 26 on which the reflector 4 and counterweight unit 8 are supported. The worm gear 48, journal 26, supporting arms 30, 32, 34, reflector 4 and counterweight unit 8 thus rotate as a single entity, with fixed connections between the individual elements. Rotation of the reflection assembly 20 (comprising the reflector 4, the support units 22, 24 and the counterweight units 8, 10) is thus driven by the action of the motor 44 via the worm 46 and worm gear 48. According to a preferred embodiment, rotation of the entire reflection assembly 20 is driven by a single drive mechanism 12, which may be positioned at a first or a second end of the reflection assembly. In an alternative embodiment, coordinated rotation is driven at both ends of the reflector 4 by two identical drive mechanisms 12 operating together, each end 21, 23 of the reflector having an associated drive mechanism 12 communicating with the adjacent support unit 22, 24. The two drive mechanisms 12 are synchronised, so as to reduce the incidence of torsional stresses in the reflector 4.

It will be appreciated that, via the worm 46 and worm gear 48, fine control in bidirectional rotation of the reflection assembly 20 can be achieved and positional stability is ensured by the locking action of the worm 46 in a stationary position. In addition, owing to the balancing action of the counterweight 17, relatively small forces are required to drive rotation of the reflection assembly 20 and a single drive mechanism 12, having relatively low power requirements, can be employed to drive rotation of the reflection assembly 20. It is an advantage of the invention that the drive mechanism 12 is an inherently reliable and simple mechanical arrangement, well suited to large scale operation and requiring minimal maintenance. Alternative embodiments of the arrangement may be envisaged employing alternative configurations of drive mechanism 12 that provide a similar level of simplicity of construction and reliability in operation. It is a further advantage of the drive mechanism 12 that backlash and associated losses in driving rotation of the reflection assembly are minimal, ensuring maximum efficiency of the solar collection apparatus 2 as a whole.

A clutch mechanism (not shown) may operate between the drive mechanism 12 and the reflection assembly 20, so as to engage or disengage the drive mechanism 12 and reflection assembly 20. According to preferred embodiments, a battery powered solenoid or small motor is used to disengage a drive pin, key, spline or other mechanical clutch so as to isolate the reflection assembly 20 from the drive mechanism 12. The disengagement may be triggered by a remote signal from an operator. Once disengaged from the drive mechanism 12, the reflection assembly 20 may be rotated, for example to assume a high wind position, under the action of a hand crank, which may engage a socket on an end of the drive shaft, or under a biasing action of the counterweight 17, as discussed above.

In an alternative embodiment (not shown) the drive mechanism may comprise an in line drive assembly with the motor 44 and drive shaft 45 located substantially on the focal axis of the reflector 4.

Referring again to FIG. 1, the collector pipe 6 is fixedly mounted along the focal axis F of the reflector 4, which is also the axis of rotation of the reflection assembly 20 as discussed above. The collector pipe 6 thus extends through the journals 26, on which the reflector 4 and counterweight units 8, 10 are supported, and through the worm gear 48 to rest upon dedicated support legs 50. According to embodiments of the invention, the collector pipe 6 comprises a plurality of operative sections of coated steel tube surrounded by an evacuated glass tube. These operative sections are joined together by sections of piping in a manner known to persons skilled in the art. Three or four operative sections may be employed to span a single reflector 4, with pipe sections extending from either side of the span to pass through the journals 26. These pipe sections are coated with appropriate insulation to protect the journals 26 from the heated liquid that flows through the collector pipe 6 and to ensure smooth rotation of the journals 26 about the collector pipe 6. Alternative embodiments of collector pipe may also be envisaged, for example without the evacuated glass tube.

As illustrated in FIG. 4, the collector pipe 6 is mounted on support legs 50 at either end of the reflector 4. Additional support may be given to the collector pipe in the form of collector pipe support arms 72, 74 that extend from a concave, reflecting surface 70 of the reflector 4. The collector pipe support arms 72, 74 are rigidly connected to the reflector 4 and extend towards the collector pipe 6 to encircle the collector pipe 6 in a rotatable manner. Thus, the collector pipe support arms 72, 74 lend support and stability to the collector pipe 6 and yet may be freely rotated around the circumference of the collector pipe 6, for example through the use of appropriate bearing connections. Detail of the collector pipe support arms 72, 74 and their interaction with the collector pipe 6 is illustrated in FIGS. 6 and 7. The collector pipe support arms 72, 74 comprise light weight support columns that are fixedly mounted to the parabolic reflector 4. The support arms 72, 74 support the collector pipe 6 via bearing connections 80. The bearing connections 80 each comprise a guide collar 84, formed from a suitable high temperature rated material, within which is received a split sleeve bearing 84. A preferred material for the split bearing 84 is carbon, owing to its high temperature performance, capability as a dry running bearing material and relatively low cost. The bearing 84 is held in place within the guide collar 82 by a split two piece steel retaining ring 86. A clearance 88 is provided between the collector pipe 6 and the split bearing 84 to allow for axial and rotational movement and for different amounts of thermal expansion in the various components. The split nature of the retaining ring 86 and bearing 84 ensure that these components can be removed and replaced without disturbing the collector pipe 6.

FIGS. 8a and 8b illustrate a modification of the apparatus to allow additional solar energy to be collected. A further arcuate reflector 100 is closely spaced from the collector pipe 6, and is adapted to reflect solar energy which has been reflected by reflector 4 but which does not focus on to the collector pipe 6. The further reflector 100 is concentric with reflector 4 and is mounted on the support arms 72 and rotates with the reflector 4.

In an alternative embodiment (not illustrated), the collector pipe 6 may be supported via a framework constructed around and substantially above the reflection assembly 20. For example, the collector pipe 6 may be suspended from arms mounted on a suitable framework located immediately above the reflection assembly 20. The support for the collector pipe 6 may thus be entirely independent of the remaining components of the solar collection apparatus 2.

In use, the solar collection apparatus 2 is assembled at an appropriate site in accordance with the Figures. Solar radiation is focused by the reflector 4 onto the collector pipe 6 mounted at the focal axis F of the reflector 4. Fluid flows through the collector pipe 6 and is heated by the concentrated solar radiation focused by the reflector 4. A sensor (not shown) senses the position of the sun relative to the reflector 4 and sends a signal to the motor or motors 44 to rotate the reflection assembly 20 such that the reflector 4 is oriented toward the greatest available concentration of solar radiation. The motors 44 transmit rotational force via the worms 46 and worm gears 48 to the journals 26, causing the reflection assembly 20 to rotate such that the reflector 4 tracks the position of the sun in the sky. The weight of the reflector 4 is balanced by the counterweight units 8, 10, ensuring that minimal power is required to drive rotation of the reflection assembly 20. The worms 46 and worm gears 48 of the drive mechanisms 12 assist in ensuring that fine control of the position of the reflection assembly 20 can be achieved, maintaining the reflection assembly at the correct orientation for maximum concentration of solar radiation.

It will be appreciated that the reflection assembly 20, comprising the reflector 4, counterweight units 8, 10 and support structure 15, rotates around the stationary collector pipe 6. Independent rotation of the reflection assembly 20 ensures that the collector pipe 6 may be fixedly connected to other static pipe work without the need for swivel ball joints or other adjustable connectors that permit rotational movement.

Eliminating the need for such adjustable connectors ensures excellent containment integrity in the pipe system, increasing the range of fluids which may be heated by the apparatus. It is a further advantage of the apparatus of the present invention that the line of incidence of the concentrated solar radiation on the collector pipe 6 rotates around the circumference of the stationary collector pipe 6 as the reflector 4 rotates around the collector pipe 6 during the solar day. In this manner, the generation of a single hot spot or “hot line” along the collector pipe 6, and consequent degradation of the pipe surface along this line, is avoided.

The present invention thus also provides an advantageous method of reflecting and collecting solar radiation, involving driving rotation of a reflection assembly 20 at its axis of rotation, rather than at a location distant from the axis of rotation, and causing that rotation to take place about a stationary collector pipe 6.

The solar collection apparatus 2 of the present invention is particularly suited for use in a solar thermal power plant. In such plants, solar energy is used to generate heat for the production of super heated steam. This steam is then used to drive the production of electricity in a known manner. Large fields of solar thermal collectors are employed to heat either a working fluid such as water or a heat transfer fluid such as a silicon oil. Static piping conveys the heated fluid to the power generation facility of the plant. Solar collection on a significant scale, involving large numbers of individual collectors, is required to provide the necessary heat to fuel a solar thermal plant. At such scales, issues of capital cost, maintenance and reliability become paramount. The present invention provides a solar collection apparatus that is inherently suited to such large scale production.

The solar collection apparatus 2 of the present invention is comparatively simple to construct, reducing capital expenditure on new plant construction. The drive mechanism 12 is simple to manufacture and assemble and is inherently reliable and easy to maintain, thus reducing both planned and unplanned downtime of the solar collection field. Rotating the reflection assembly at the axis of rotation eliminates complicated drive and support mechanisms, reducing the number of component parts that require manufacture and maintenance. By balancing the weight of the reflector 4 with the counterweight 17, the amount of power required to drive rotation of the reflector 4 is reduced, reducing the parasitic load on the plant. In addition, torsional stresses, and consequent distortion of the reflector 4, are minimised.

The solar collection apparatus 2 of the present invention also addresses issues associated with placing solar reflectors into an appropriate high wind position. The balancing effect of the counterweight 17 ensures that the reflector 4 can be rotated using a hand crank or other hand tool, thus eliminating the need for a portable hydraulic back up system. In addition, if the counterweight 17 is configured to bias the reflection assembly to the high wind position, the reflector 4 can be placed in the high wind position simply by remotely disengaging the drive mechanism and allowing the assembly to move under gravity.

Claims

1. A solar reflection apparatus comprising: the reflection assembly comprising a curved linear reflector defining a focal axis, a counter weight operable substantially to balance the self weight of the reflector, and a support structure via which the reflector and counter weight are rotatably mounted at locations along the focal axis of the reflector.

a rotatable reflection assembly; and

a drive mechanism operable to drive rotation of the reflection assembly at its axis of rotation;

2. A solar reflection apparatus as claimed in claim 1, wherein the drive mechanism comprises a motor and direct gear transmission.

3. A solar reflection apparatus as claimed in claim 1, wherein the drive mechanism is mounted substantially on the focal axis of the reflector.

4. A solar reflection apparatus as claimed in claim 1, wherein the reflection assembly is rotatably mounted via bearings on a fixed frame.

5. A solar reflection apparatus as claimed in claim 1, wherein the support structure comprises a journal and a plurality of radiating arms, at least one of which extends to the reflector and at least another of which extends to the counter weight.

6. A solar reflection apparatus as claimed in claim 1, wherein the reflector is a parabolic trough reflector.

7. A solar reflection apparatus as claimed in claim 1, wherein the counter weight is operable to bias the reflection assembly to a predetermined rotational position.

8. A solar reflection apparatus as claimed in claim 7, wherein the counter weight is operable to cause the reflection assembly to adopt the predetermined rotational position under the action of gravity.

9. A solar reflection apparatus as claimed in claim 7, further comprising a clutch mechanism operating between the drive mechanism and the reflection assembly.

10. A solar collection apparatus comprising:

a solar reflection apparatus as claimed in claim 1, and a heat collecting element fixedly mounted along the focal axis of the reflector.

11. A solar collection apparatus as claimed in claim 10, wherein the heat collecting element comprises a heat collecting pipe.

12. A solar collection apparatus as claimed in claim 10, wherein the heat collecting element is mounted on least two fixed supports distributed along the focal axis of the reflector.

13. A solar collection apparatus as claimed in claim 12, wherein the fixed supports are operatively connected to a fixed frame on which the reflection assembly is mounted.

14. A solar collection apparatus as claimed in claim 10, wherein the heat collecting element extends through a gear transmission of the drive mechanism.

15. A solar collection apparatus as claimed in claim 14, wherein a clearance gap is provided between the heat collecting element and the gear transmission.

16. A solar collection apparatus as claimed in claim 10, further comprising at least one auxiliary support operable to support the self weight of the heat collecting element.

17. A solar collection apparatus as claimed in claim 16, wherein the auxiliary support is located along a region of the heat collecting element that spans the reflector.

18. A solar collection apparatus as claimed in claim 16, wherein the auxiliary support is independent of the reflection assembly.

19. A solar collection apparatus as claimed in claim 16, wherein the auxiliary support operatively connects the reflector and the heat collecting element.

20. A solar collection apparatus as claimed in claim 19, wherein the auxiliary support comprises a heat collecting element support arm fixedly connected to a reflecting surface of the reflector and rotatably connected to the heat collecting element.

21. A solar collection array comprising a plurality of rows of solar collection apparatuses as claimed in claim 10, wherein each row comprises a plurality of solar collection apparatuses, arranged such that their focal axes are coincident, and a single heat collecting element mounted along the coincident focal axes.

22. A method of reflecting solar radiation comprising:

forming a reflection assembly comprising a linear curved reflector that defines a focal axis, a counter weight operable to balance the self weight of the reflector, and a support structure;

mounting the reflection assembly for rotation about the focal axis of the reflector; and

driving rotation of the reflection assembly at its axis of rotation.

23. (canceled)