WO2004029521A1

WO2004029521A1 - Optical concentrating system

Info

Publication number: WO2004029521A1
Application number: PCT/BG2003/000036
Authority: WO
Inventors: Georgi Lukov Gushlekov
Original assignee: Individual
Current assignee: Individual
Priority date: 2002-09-25
Filing date: 2003-09-23
Publication date: 2004-04-08
Anticipated expiration: 2005-03-25
Also published as: AU2003266873A1; BG65247B1; BG107146A

Abstract

Modular optical concentrating system assembled by multiple equal or similar elements, composed of reflecting surfaces in the form of concentrating parabola (1) and functional curve, realized as collimating parabola (2) or concentrating hyperbola (3) . Additional dissipating area (4, 5) of appropriate shape could be added to the functional curve shape (2, 3) surface as to allow for the system to fold in stowed position.

Description

OPTICAL CONCENTRATING SYSTEM

TECHNICAL FIELD The present invention relates to a modular optical concentrating system intended for concentrating of parallel light rays applying several different approaches and will be used in solar energy devices and other optical system.

BACKGROUND OF THE INVENTION Large optical concentrating systems comprise the following main systems:

A fixed-dish, high-precision concentrator, composed of details with spherical or parabolic reflective surfaces to allow accurate aiming towar the focal point. An array of heliostasts (flat or a slightly concave surfaces) covering large surfaces, which redirects light to the dish. The disadvantages of this system arise from the necessity of sophisticated driving of the system, the big unemployment surface, and mutual overlapping of heliostats. It is difficult to maintain and protects from harsh weather and other environmental conditions due to the nature and size of the construction.

Another solution includes a large dish with a receiver located at its focal point, which transforms concentrated light into useful energy. Among major disadvantages we should mention the weight of the receiver, which must be driven simultaneously with the dish. Yet another is the fact that the receiver overshadows the concentrator, while flexible coupling is needed to supply high temperature working fluid. Moreover, protection from harsh environment conditions is far from being solved.

There have been several attempts to overcome the necessity of flexible coupling by fixing the receiver, while a large system of high- precision aimed heliostats redirect the light to the receiver. The problems here again derive from the requirements for a sophisticated driving system, high degree of unused surface, mutual overshadowing and difficult protection from harsh weather conditions. A design of collapsible and portable construction of optical concentrator was published in the U.S. Patent No 4,293,192 [Allen Bronstein]. A flexible sheet of highly reflecting material is wrapped tightly around two identical form members of identical parabolic surfaces, facing precisely one another. The form members are moved away from each other until the sheet is spread out to fit closely their surface over its full length. However, the convenience and applicability of this technology does not go beyond its initial assembly. The disadvantages already described in large optical concentrating systems have not been solved in this application either. In Russia Patent No 2 000 524 [Twerjanovich E. V.] has described a big optical concentrating system from equal sets of lenses and prisms, tilted under a fixed angle to the optical axis, which concentrate incident parallel light rays. The disadvantage of the system is that the redirected light rays are not parallel to one another, therefore, it is difficult to ensure the degree of concentration required in large optical concentrating systems.

In the U.S. Patent No 5,054,466 [John White et al] use paraboloidal surface to concentrate parallel light rays outside the limits of the paraboloid (offset reflector). The overshadowing caused by the receiver is thus avoided. The concentrating paraboloidal surface is made up of facets, whose reflective surfaces have the shape of different parts of the paraboloid. This example shows the difficulties of manufacturing large optical concentrating system out of one monolithic paraboloidal surface.

In the U.S. Patent No 4,439,020 [Saburo Maruko] has described an optical concentrating system comprising parabolic trough-shaped reflectors and collimating lenses with common focal lines. The outgoing light beam of concentrated parallel light rays can be redirected to a required direction through an array of flat reflectors. The problem of cooling all optical elements after the first one of this system is still difficult to solve.

In the U.S. Patent No 4,690,355 [Hernst Horning and Dietrich Rex] solar cells are arranged on the rear side of a concentrating parabolic trough-shaped reflector. These reflectors are attached by means of cables so that construction easily folds and unfolds. However, this method is inapplicable with large optical concentrating systems. In WO Patent No 97/13104 [Pak, Hwa Rang] used parabolic type mirrors with common focus (or focus line) to concentrate incident parallel light rays into outgoing light beam of parallel light rays. To deflect the outgoing light beam to any inclined direction, different from 0° and 90°, an additional flat plane type mirror is provided. In practice the space in front of the collimating parabola is unused, it needs cooling, as does the additional flat plate type mirror. Both parabolic surfaces are solid and it is very difficult to protect the system against harsh weather conditions.

DISCLOSURE OF THE INVENTION The aim of the invention is to create a modular optical concentrated system, referred to hereinafter "the system", which surmount the shortcomings of the system described above. Firstly, the concept includes the development and implementation of a construction, allowing the manufacture of systems comprising equal or similar elements that are technically easy to produce. Secondly, these elements should not be interfering among themselves. The third aim is to resolve the heating problems mentioned above. The final aim is to build a facility, easy to fold and unfold in working (erected) position, when it is necessary, without disturbing the optical properties and functions of the system.

In accordance with that goal, the system comprises multitude equal or similar elements, composed of reflective surfaces in the form of concentrating parabola and functional curve. In accordance with the invention, the reflective surface in the form of functional curve of each element is located on the rear side of the reflective surface in the form of a concentrating parabola in such a way, that the incident parallel light rays reach the concentrating parabolic surface freely and the outgoing light beams reach their final destination unhindered. In one embodiment of the invention the functional curve is a collimating parabola, which focus is identical with the one of its relevant concentrating parabola. Furthermore, both parabolic surfaces can be located in such a way, that the outgoing light beams be parallel to each other, one beside the other while being orthogonal to the incident ones. It is also possible to position both parabolic surfaces, so that the outgoing light beams are at an angle, different from 90°, to the incident ones.

In yet another embodiment, the concentrating and its relevant collimating parabolic surfaces are located in such a way, that the outgoing light beams are gathered aside or behind the system on a surface, whose size could be at least corresponding to the size of one outgoing light beam.

The collimating parabola could have such parameter and positioning that the area of the reflective surface of its shape be a function of the thermal energy it dissipates, provided the concentration ratio is maintained constant. Furthermore, the concentrating and its relevant oppositely located collimating parabolic surfaces can create a module.

Again in accordance with the invention the functional curve could be made as a part of hyperbola, and one of its foci coincide with the focus of its relevant concentrating parabola. The outgoing light rays are concentrated at its second focus, which is also common for the system and can be located aside or behind it.

Again, the parameters and location of the hyperbolically formed reflecting surface could be made in such a way that its area to be a function of the dissipated thermal energy, saving the ratio of concentration while its second focus is located aside or behind the system.

It is also provided that additional subsidiary dissipating area of shape, which allows the folding of the system, be added to reflective surfaces of functional curve shapes, realized as a collimating parabola or hyperbola. Moreover, the additional dissipating area and the areas shaped as functional curve and concentrating parabola, can form a module with closed space, which can serve for forced cooling.

The equal or similar elements described above, made up of reflective surfaces with the shape of concentrating parabola and functional curve, allow the system to fold and unfold while functioning. The working condition of the elements is ensured by supports located on carriers whose number equals the number of the elements.

BRIEF DESCRIPTION OF THE DRAWINGS In the figures presented herein, light rays are indicated by dotted lines; incident light rays come in from right to left. In all the figures the principles of the invention are illustrated by cross sectional views, which demonstrate the shape and location of the relevant reflective surfaces.

Fig. 1 and Fig. 2 show classical mirror system for concentrating incident parallel light rays of size a in outgoing light beam of concentrated parallel light rays (referred to as outgoing light beam for short) of size b. In Fig. 1 the outgoing light beam is orthogonal, in Fig 2 - parallel to the incident light rays and the collimating parabolic surface 2 is contrary arranged to the incident light rays. In Fig 3 and Fig. 4 typical assembly of reflectors of the Cassegrain type is presented. It consists of reflective surfaces in the forms of concentrating parabola 1 and hyperbola 3. One of the hyperbola's foci of the surface 3 coincides with the parabola 1 foci, and the other is common for the entire system F₀. In Fig. 4 the outgoing light rays are concentrated behind the system, while in Fig. 3 - aside to it. The incident parallel light rays of a dimension a are focused at the system's common focus F₀.

Fig. 5 shows system of two equal elements, arranged in such a way that incident parallel light rays of 2a size are transformed into outgoing light beam of 2b size.

Fig. 6 represents an embodiment of the system from Fig. 5, in which the outgoing light beams are again parallel to each other, but are turned on at an angle, different from 90°, to the incident ones. The incident parallel light rays of 2a size are converted again into outgoing light beam of 2b size.

Fig. 7 is yet another embodiment of a Fig. 6, but the outgoing light beams converges to one place. In such a way the incident parallel light rays of 2a size (or bigger) are concentrated to a place of a size of one particular outgoing light beam b. Fig. 8 is an embodiment of a Fig. 7, but the outgoing light beams are gathered behind the system and the collimating parabolic surfaces 2 are situated oppositely to the incident light rays. The incident parallel light rays of 2a size (or bigger) are concentrated to a place of a size b.

Fig. 9 is functionally analogous to Fig. 1, but the collimating parabolic surface 2 has an area, commensurate to the aperture a of the concentrating parabolic surface 1. The incident parallel light rays of size a are narrowed to outgoing light beam of size b.

Fig. 10 shows a system, composed of elements, shown in Fig. 9, which transforms the incident parallel light rays of a size 2a into outgoing light beam of a size 2b.

Fig. 11 is similar to Fig. 10 with the only difference that the angle of deflection of the outgoing light beams is different from 90°. The incident parallel light rays of size 2a are transformed into outgoing light beam of size 2b.

Fig. 12 refers to Fig. 11, but bigger concentration of outgoing light beams is achieved: the incident parallel light rays of size 2a (or bigger) are concentrated to an area of size b.

Fig. 13 is a system of elements, comprising of parabolic 1 and hyperbolic 3 reflective surfaces, sharing a common focus (focal line) of concentration F₀, without mutual blockage, and the heat load of hyperbolic part 3 is accepted by the much more bigger surface of the covering parabolic part 1.

Fig. 14 refers to Fig. 4, but the surface of the hyperbolic reflective surface 3 is commensurate with the aperture a of the concentrating parabolic one 1.

Fig. 15 is a system composed of elements, shown in Fig. 14, sharing a common focus F₀ for the entire system.

Fig. 16 shows how the problem of precise positioning in working

(erected) position is resolved and what the system looks like in folded (safe) position.

DETAILED DESCRIPTION OF SEVERAL EMBODIMENTS The classical optical concentrating system in the art, as shown in Fig. 1 and Fig. 2, comprises concentrating parabolic surface 1 with a focus (focal line, in case of cylindrical surfaces) F coinciding with the focus of the collimating parabola 2. The incident parallel light rays of size a in Fig. 1 fall upon the reflective surface of the concentrating parabola 1 and are concentrated at the focus (focal line) F. The concentrating ratio a/b to the outgoing collimated light beam can be changed by varying the parameter of the collimating parabola 2. By rotating the collimating parabolic reflective surface 2 around the focus (focal line) F, the outgoing light beam changes only its path, without changing the concentration of the collimated light rays. The problems of this widely known system are two: the first one is the need of cooling the collimating surface 2, which, as a rule, is much smaller than the concentrating one 1. It can be resolved without applying forced cooling by thermally coupling the collimating 2 to the concentrating 1 parabolic surface as well as by ensuring additional cooling surface 4, as shown in Fig. 6. The problem can also be resolved by enlarging the area of the collimating surface 2 to allow for maintaining the heating within permissible limits, as is shown in Fig. 9÷12. The other problem is the overshadowing of a portion of the concentrating parabolic surface 1 and a portion of useful incident light rays is lost while the collimated surface 2 heats additionally. As shown in the explanation hereinafter, this problem can also be resolved.

Fig. 5 shows a system comprising of two identical pairs of parabolas with coinciding foci (focal lines) Fj. The collimating parabolic surface 2 with focus (focal line) Fi is mounted on the rear side (invisible for incident light rays) of the concentrating parabolic surface 1 with a focus (focal line) F₂: This type of positioning provides for greater space and size of the collimating parabolic surface 2 (respectively, the hyperbolic 3), as well as for adding of additional dissipating surfaces. The outgoing light beams are parallel to each other and practically touch each other, i.e. they are summed up. In this way the incident light rays of size 2a are transformed into the outgoing light beam of size 2b. The heat, that had to be dissipated by the small collimating parabolic surface 2, is accepted by the much bigger area of the concentrating parabolic surface 1. As shown in this figure, it is possible that the dissipation area be enlarged (for example, by section 4, shown in Fig. 6), without disturbing the system's functionality. Furthermore, it is possible to create a module with a closed space 6, which provides for forced cooling if needed (for example, additional concentrating of beams of concentrated yet parallel light rays).

In this way optical concentrating systems of similar components can be assembled without restrictions as to the size. The system can fold down when necessary, as shown in Fig. 16. This approach remains the same with all other suggested constructions. Fig. 6 shows an embodiment of the system in Fig, 5, in which the pairs of concentrating 1 and collimating 2 parabolic reflective surfaces with common foci (focal lines) F_i? are located by pairs on one axis, but the collimating parabolic reflective surfaces 2 are turned around their relevant foci (focal lines) at a precisely determined angle to this axis. In this way deflection of the outgoing light beams at angles, different from 0° or 90°, is realized. The collimating parabolic reflective surface 2 is hidden again behind the big concentrating parabolic surface 1 and is connected to it. The outgoing light beams are also parallel to each other and practically touch each other, i.e. they are summed up. But they can also converge to various degrees depending on the needed concentration. The maximum is shown in Fig. 7. In this case, the outgoing light beams from the entire system are converged in an area of size b, which is the size of one separate outgoing light beam. In this construction the parabolas of the concentrating surfaces 1 have equal parameters, as well as the parabolas of the collimating surfaces 2, but they are turned round their relevant foci Fj at different angles. The other possibilities, set forth above, are also available. Fig. 9 is an embodiment of Fig. 1, but the collimating parabolic surface 2 has the area of size a, commensurate to the aperture of the concentrating parabolic surface 1. In this case, to realize the same concentration of incident light rays, as in Fig. 1, the parameter of the collimating parabola of the surface 2 should be much smaller than that in Fig. 1. In this way the heating of the collimating parabolic surface 2 is practically commensurate to that of the concentrating parabolic surface 1 from Fig. 1. If needed, the area of the collimating parabolic surface 2 can be enlarged depending on the needed dissipated heat power. The increased capacity of heat dissipation and the possibility of utilizing it in systems, using total internal reflection, can be added to the advantages described above. This construction allows such positioning of the collimating parabolic surface 2 so that it is located at a sufficient distance from the caustic point (line) F. In case the collimating parabolic surface 2 is located opposite to the incident light rays both parabolic surfaces could be manufactured as a module. In this way the preciseness of the mutual location of both parabolic surfaces is guaranteed in the process of manufacturing. Furthermore, it is possible to create a closed space 7 (Fig. 12), which gives opportunity for forced cooling if needed. As with all constructions described above, in this way it is possible to assemble a system, which can be folded down when needed. Fig. 10 shows a system, analogous to the system in Fig. 5, but comprising the elements, described in Fig. 9. Collimating parabolic surfaces 2 do not interfere with concentrating ones 1 and the outgoing light beams. The advantages of the system, configured in this way, as compared to the one described in Fig. 5, are: 1. The collimating parabolic surface 2 do not load additionally thermally the concentrating parabolic surface 1; 2. The preciseness of the mutual location of both parabolic reflective surfaces can be achieved much more easily in the process of manufacturing.

For Fig. 11 and Fig. 12 the same advantages can be listed as for the systems in Fig. 9 and Fig. 10.

Fig. 13 shows much greater concentration in the point (line) F₀, outside the scope of the accepting construction. The well-known Cassegrain configuration, shown in Fig. 3 and Fig. 4, has a monolithic construction. In our case the hyperbolic reflective surface 3 is mounted on the rear side (unreachable for the incident light rays) of the concentrating parabolic surface 1 from the previously described parabola-hyperbola pair. In this way it is quite possible to assemble a big concentrating optical system according to purpose of the invention with all the advantages, mentioned above. The cost of the larger concentration is due to the different parameters of the hyperbolas 3. In Fig. 14 the heating of hyperbolic surface 3 is commensurate to that of the concentrating parabolic surface 1 from Fig. 4. Fig. 15 demonstrates the possibility of assembling a big optical concentrating system from elements, shown in Fig. 14, in which the concentrating parabolas 1 are of equal parameters, while the hyperbolas 3 have different parameters, so that all the incident light rays are focused in point F₀.

On first thought, the idea of folding and unfolding in working (erected) position such construction may seem heretical. But as shown in Fig. 16, this problem can be resolved in principle, especially where trough-shaped surfaces are concerned. The elements, which has the reflective surfaces with the shape of the concentrating 1 and collimating 2 parabolas, are attached to the moving part 9, which can be moved away freely along the slide-ways 8. Positioning can be performed with greatest precision by supports 10 and 11. Supports 10 and 11 are located on carriers 13 at the right places with the required precision and it is maintained during the positioning of the relevant elements. When the relevant element needs to be appropriately positioned, it has simply to be pressed to its relevant support with the appropriate force and the required precision of positioning will be achieved. Bumpers 12 protect the construction against impact. The reflective surface components having the shape of all other couples of curves, described above, can also be located in this way.

Claims

1. Optical concentrating system, comprising multitude equal or similar elements, composed of reflecting surfaces in the form of concentrating parabola (1) and of a functional curve, which is characterized in that the surface in the form of functional curve is located on the rear side of the reflecting surface in the form of concentrating parabola (1) in such a way, that the parallel incident light rays reach the concentrating parabola (1) freely while the formed outgoing light beams reach their final destination undisturbed.

2. Optical concentrating system as defined in claim 1, which is characterized in that the functional curve is a collimating parabola (2), having a common focus with its relevant concentrating parabola (2).

3. Optical concentrating system as defined in claim 2, which is characterized in that the concentrating parabola (1) and its relevant collimating parabola (2) are located in such a way that the outgoing light beams are parallel to each other, one beside the other and orthogonally cross the incident light rays.

4. Optical concentrating system as defined in claim 3, which is characterized in that the outgoing light beams are at angle, different from 90 degree to the incident light rays.

5. Optical concentrating system as defined in claim 2, which is characterized in that the concentrating parabola (1) and its relevant collimating parabola (2) are located in such a way, that the outgoing light beams are gathered aside or behind the system at a space, which minimum is of the order of the space of one elementary light beam.

6. Optical concentrating system defined in any of claims 3, 4 and 5, which is characterized in that the collimating parabola (2) is made of such parameter and location that the area of the reflective surface, having its shape, is a function of the dissipated thermal energy, simultaneously maintaining the concentration ratio.

7. Optical concentrating system as defined in claim 6, which is characterized in that the concentrating parabola and its relevant contrary located collimating parabola (2) create a module.

8. Optical concentrating system as defined in claim 1, which is characterized in that the functional curve is a part of hyperbola (3), one of which foci coincides with the focus of its relevant concentrating parabola (1), while the outgoing light beams are concentrated at its second focus (F₀), which is common for the whole system and can be located aside or behind it.

9. Optical concentrating system as defined in claim 8, whose major characteristic is that the hyperbola (3) is made of such parameters and location, that the area of the reflective surface having its shape is a function of the dissipated thermal energy, maintaining the same concentration ratio.

10. Optical concentrating system defined in any of claims 2, 3, 4, 5 and 8, which is characterized in that additional dissipating area (4) is added to the functional curve (2, 3).

11. Optical concentrating system as defined in claim 10, which is characterized in that the additional area of dissipation (4) is of shape, which allows folding down of the system in stowed position.

12. Optical concentrating system defined in any of claims 2, 3, 4, 5, 8 and 9, which is characterized in that the surfaces of the concentrating parabola and the functional curve shape, the functional curve thermally connected to the concentrating parabola, and the additional area (5) create a closed space module, that serves for forced cooling, saving simultaneously all the remaining functions of the system.

13. Optical concentrating system as defined in claim 7, which is characterized in that additional dissipating area of analogous shape is added to the module, thus creating a closed space, that serves for forced cooling, saving simultaneously all the remaining functions of the system.

14. Optical concentrating system as defined in claim 1, which is characterized in that it is assembled by multiple equal or similar elements, composed of reflecting surfaces (1, 2 and 3), which allows for the system to fold down in save position and unfold in working position.

15. Optical concentrating system as defined in claim 14, which is characterized in that the positioning of the reflective surfaces (1, 2 and 3) in working position is ensured by supports (10 and 11) located upon the carriers (13).