Radiation collector and method of manufacture thereof

Abstract

Non-imaging radiation collecting and concentrating devices, and assemblies, are disclosed. The non-imaging radiation collecting and concentrating devices comprise an entrance aperture for receiving incoming radiation, an exit aperture located opposite to the entrance aperture for outputting concentrated radiation, and one or more concaved reflectors arranged between the entrance and exit apertures. The concaved reflectors define an acceptance angle of the device relative to an optical axis thereof and configured such that their optical focuses are located between edges of the exit aperture and the optical axis, thereby substantially preventing escape of the incoming radiation received in the entrance aperture within the acceptance angle and providing substantial uniform radiation collection at the exit aperture of the device.

Claims

1. A non-imaging radiation collecting and concentrating device comprising: an entrance aperture for receiving incoming radiation, an exit aperture located opposite to said entrance aperture for outputting concentrated radiation, and one or more concaved reflectors arranged between said entrance and exit apertures, said one or more concaved reflectors defining an acceptance angle of the device relative to an optical axis thereof and configured such that optical focuses thereof are located between an edge of said exit aperture and said optical axis, thereby substantially preventing escape of the incoming radiation received in the entrance aperture within said acceptance angle and providing substantial uniform radiation collection at the exit aperture of the device; wherein a distance between the optical focus of each of the one or more concaved reflectors and an edge of the exit aperture is such that the radiation concentrated by said one or more concave reflectors is focused to the exit aperture without hitting another concaved reflector of the device; wherein the distance between the optical focus of each of the one or more concaved reflectors and the opposite edge of the exit aperture is about 0.05 to 0.27 of a dimension of the exit aperture.

2. A method of constructing the radiation collector according to claim 1, the method comprising: providing one or more concaved reflectors, each of the one or more concaved reflectors configured to reflect and concentrate incident radiation onto a focal region thereof; and arranging said one or more concaved reflectors to define the entrance aperture for receiving the incident radiation, the exit aperture for outputting the radiation reflected and concentrated by said one or more concaved reflectors, and the optical axis extending along centers of said apertures, such that the focal region of each of the one or more concaved reflectors is obtained between the edge of the exit aperture and the optical axis.

3. The method of claim 2, further comprising configuring the one or more concaved reflectors for locating the focal regions thereof at a distance from an edge of the exit aperture such that the radiation concentrated by said one or more concaved reflectors is focused to the exit aperture without hitting another concaved reflector of the device.

4. The method of claim 3 wherein configuring the one or more concaved reflectors comprises adjusting a concave depth of the at least some of the reflectors.

5. The method of claim 3 wherein the one or more concaved reflectors are parabolic reflectors and wherein configuring of the one or more concaved reflectors comprises adjusting at least one of a parabolic focus, parabolic directrix, or parabolic vertex, of said parabolic reflectors.

6. The method of claim 2, further comprising using the radiation collector to collect solar radiation.

7. The method of claim 6, further comprising configuring at least some of the one or more concaved reflectors to define acceptance angle of the device of about 20° to 30°.

8. The method of claim 6, further comprising configuring at least some of the one or more concaved reflectors to obtain a concentration ratio of about 2 to 3.

9. The method of claim 2, further comprising adjusting heights of at least some of the one or more concaved reflectors to set a dimension of the entrance aperture.

10. The non-imaging radiation collecting and concentrating device of claim 1 wherein the incoming radiation is received from a solar radiation source.

11. The non-imaging radiation collecting and concentrating device of claim 10 wherein the acceptance angle of the device is about 20° to 30°.

12. The non-imaging radiation collecting and concentrating device of claim 10 wherein concentration ratio of the device is in the range of 2 to 3.

13. The non-imaging radiation collecting and concentrating device of claim 1 wherein the one or more concaved reflectors comprises two concaved reflectors symmetrically positioned one in front of the other.

14. A radiation collecting and concentrating device having a polygon funnel-shaped structure constructed by intersection of two or more of the non-imaging radiation collecting and concentrating devices of claim 13.

15. The non-imaging radiation collecting and concentrating device of claim 1 wherein the one or more concaved reflectors are configured such that the optical focus of each of the one or more concaved reflectors is located either within a region defined by the exit aperture, or above or below the exit aperture.

16. The non-imaging radiation collecting and concentrating device of claim 1, wherein the distance between the optical focus of each of the one or more concaved reflectors and the opposite edge of the exit aperture is about two tenths of a dimension of the exit aperture.

17. The non-imaging radiation collecting and concentrating device of claim 1 wherein a height of the non-imaging radiation collecting and concentrating device is adjusted to set dimension of the entrance aperture.

18. The radiation collecting and concentrating device of claim 1 wherein the one or more concaved reflectors are constructed as a surface revolution of a concaved curve about the optical axis of the device.

19. A lighting system, comprising an array of radiation collectors arranged for collection of radiation of a celestial radiation source throughout a predefined trajectory thereof, said array of radiation collectors comprising one or more of the non-imaging radiation collecting and concentrating devices according to claim 1.

20. A collector assembly, comprising: an array of the radiation collector according to claim 1, said array of radiation collectors configured to form an equilateral radiation collection front for efficiently transferring concentrated light outputted from said array of radiation collectors towards a corresponding equilateral output opening.

21. A method of modifying a non-imaging radiation collecting and concentrating device having one or more concaved radiation reflecting elements arrange about an optical axis of the device to define entrance and exit apertures thereof, the method comprising: adjusting a concave depth of the one or more radiation reflecting elements such that optical focuses thereof are shifted a predefined distance from edges of the exit aperture towards the optical axis of the non-imaging radiation collecting and concentrating device, to thereby prevent escape of incoming radiation received at the entrance aperture and provide a substantial uniform radiation collection profile; wherein a distance between the optical focus of each of the one or more concaved radiation reflecting elements and the edge of the exit aperture is such that the radiation concentrated by said one or more concave reflectors is focused to the exit aperture without hitting another concaved reflector of the device; wherein the distance between the optical focus of each of the one or more concaved reflectors and the opposite edge of the exit aperture is about 0.05 to 0.27 of a dimension of the exit aperture.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In order to understand the invention and to see how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings. Features shown in the drawings are meant to be illustrative of only some embodiments of the invention, unless otherwise implicitly indicated. In the drawings like reference numerals are used to indicate corresponding parts, and in which:

(2) FIGS. 1A and 1B schematically illustrate perspective and front views, respectively, of a classical two-dimensional CPC device;

(3) FIGS. 2A and 2B present a classical (full-height) CPC design having 25° acceptance angle and exit aperture of 300 mm, and simulations thereof, wherein FIG. 2A is a schematic illustration of the CPC device and FIG. 2B is a plot showing flux/radiation collection obtained in simulations of the CPC device of FIG. 2A for solar and point radiation sources;

(4) FIGS. 3A and 3B show the classical CPC design of FIG. 2A implemented using truncated parabolic reflectors, wherein FIG. 3A shows a schematic illustration of the truncated CPC device and FIG. 3B shows flux collection plots obtained in simulations of the full-height classical CPC device of FIG. 2A and of the truncated CPC device of FIG. 3A, with solar radiation sources;

(5) FIGS. 4A to 4C show illumination maps and ray tracing diagrams obtained in solar radiation source simulations of the truncated CPC device of FIG. 3A at 0°, 20° and 25°, illumination angles, respectively, and FIG. 4D shows illumination map and ray tracing diagram obtained in a point radiation source simulation of the truncated CPC device of FIG. 3A for a 25° illumination angle;

(6) FIGS. 5A and 5B present a simulation of a (full-height) classical CPC design having 30° acceptance angle and concentration ratio of 2, wherein FIG. 5A is a schematic illustration of the CPC device and FIG. 5B shows flux collection plots obtained in solar radiation source simulations of the CPC devices of FIGS. 2A and 5A;

(7) FIG. 6A and FIG. 6B schematically illustrate sectional and perspective views, respectively, of modified two-dimensional CPC devices according to some possible embodiments;

(8) FIGS. 7A and 7B present simulation of a truncated modified CPC design according to possible embodiments having 25° acceptance angle and concentration ratio of 2, wherein FIG. 7A is a schematic illustration of the truncated modified CPC device and FIG. 7B shows flux collection plots obtained in solar radiation source simulations of the CPC devices of FIGS. 2A, 5A and 7A;

(9) FIGS. 8A to 8D schematically illustrate modified three-dimensional CPC designs according to some possible embodiments, wherein FIGS. 8A and 8B respectively show perspective and top views of a three-dimensional CPC device having a rectangular funnel shape, FIG. 8C shows a top view of a three-dimensional CPC device having a hexagonal funnel shape, and FIG. 8D shows a skirt-shaped three-dimensional CPC device;

(10) FIG. 9 show flux collection plots obtained in solar radiation source simulations of classical CPC devices and of modified CPC devices according to possible embodiments;

(11) FIGS. 10A to 10C show simulation results of performance of various CPC designs disclosed herein as obtained for large ray divergence conditions (e.g., “cloudy” conditions), wherein FIG. 10A is a ray tracing diagram obtained for a truncated modified CPC device with the large ray divergence conditions, FIG. 10B is a ray tracing diagram obtained for a full-height non-modified CPC device having a 30° acceptance angle, with the large ray divergence conditions, and FIG. 10C shows plots of flux collection obtained in the simulations with 60° half angle radiation source;

(12) FIGS. 11A and 11B show comparison results between a full-height classical CPC design and a truncated modified CPC design, according to some possible embodiments, having about the same exit apertures and about the same acceptance angles, simulated with a solar radiation source, wherein FIG. 11A is a schematic illustration of the CPC devices used in the simulations and FIG. 11B show flux collection plots of solar radiation source simulations; and

(13) FIGS. 12A to 12 D show assemblies of radiation collectors array configured in some embodiments to form an equilateral radiation collection front, wherein FIG. 12A is a sectional side view of a radiation collection assembly comprising an array of radiation collectors, and FIGS. 12B, 12C, and 12D, respectively show side-sectional, top perspective, and bottom perspective, views of a radiation collection assembly comprising an array of radiation collectors having additional internal light reflectors.

DETAILED DESCRIPTION OF EMBODIMENTS

(14) One or more specific embodiments of the present application will be described below with reference to the drawings, which are to be considered in all aspects as illustrative only and not restrictive in any manner. In an effort to provide a concise description of these embodiments, not all features of an actual implementation are described in the specification. Elements illustrated in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the invention. Though dimensions are indicated for some elements in the figures, these dimensions are provided by way of example only, and the invention is of course not limited to these specific examples. This invention may be provided in other specific forms and embodiments without departing from the essential characteristics described herein.

(15) The present invention provides novel stationary radiation collection device configurations designed to provide substantially uniform radiation collection within a predetermined angular span of the device and throughout a trajectory of a moving radiation source. The classical CPC designs commonly used nowadays in non-imaging applications are optimized to maximize collection of diffused and direct radiation emitted from a moving celestial source and concentrate it onto an area of minimum size. During experimentation and simulation of such classical CPC designs, using a realistic finite sized Solar Source, the inventors hereof surprisingly realized that these designs are not capable of providing uniform collection of radiation across the angular span of the device, particularly due to abrupt collection drop occurring at edge regions of their acceptance ranges. For these and other reasons it was understood that the classical CPC designs are not suitable for lighting applications, which initiated further research and experimentations in attempt to resolve these deficiencies.

(16) Although the following disclosure relates to radiation collection techniques and devices employing parabolic reflectors/surfaces, and particularly to modified CPC designs, it should be understood that the invention is not limited to such parabolic reflectors/surfaces and CPC designs, and that other types of curved/concaved reflectors/surfaces may be similarly used to provide radiation collecting devices providing substantially uniform radiation collection profiles, using the techniques and configurations described hereinabove and hereinbelow.

(17) A short discussion about the classical CPC designs exemplified in FIGS. 1A and 1B will be appropriate for better understanding of the CPC devices typically used nowadays in non-imaging applications. The classical CPC device 10 shown in FIG. 1A consists of two elongated parallel parabolic reflectors, 11a and 11b, symmetrically positioned (about the xz plane) one in front of the other with their reflective surfaces facing each other. The distance W.sub.A between the upper edges, 13a and 13b, of the parabolic reflectors, 11a and 11b, defines the width of the elongated entrance aperture 13 of the device 10, and the distance W.sub.a between their lower edges, 14a and 14b, defines the width of the elongated exit aperture 14 of the device. The distance between the surfaces of the parabolic reflectors 11a and 11b is progressively reduced towards the exit aperture 14 forming a tapering profile of the device.

(18) In classical CPC designs 10, in order to maximize the total radiation collection of the device, the parabolic focus of the parabolic reflectors must pass through the opposite edges of the exit aperture 14, and the parabola axis of each parabolic reflector must be tilted at an angle θ.sub.c with respect the optical axis 10s of the device, that is equal to the half angle of the angular span of the device, within which incident radiation received at the entrance aperture 13 cannot escape out of the device 10. Particularly, as shown in FIG. 1B, the parabola axis 12b of the parabolic reflector 11b passes through the lower edge 14a of the parabolic reflector 11a, thereby defining the focal point/line of the parabolic reflector 11b at the opposite edge 14a of the exit aperture 14. Similarly, the parabola axis 12a of the parabolic reflector 11a passes through the lower edge 14b of the parabolic reflector 11b, thereby defining the focal point/line of the parabolic reflector 11a at the opposite edge 14b of the exit aperture 14.

(19) The angle θ.sub.c between each of the parabola axes 12a and 12b of the parabolic reflectors and the optical axis 10s of the device equals to half of the angle defined between the lines 10v bounding the incident radiation, and defines the acceptance angle of the CPC device 10. The concentration value of the CPC device 10 is defined by the ratio between the widths of the entrance and exit apertures (W.sub.A/W.sub.a). It is noted that though the classical CPC device 10 as a three-dimensional structure, it is sometimes referred to as a two-dimensional CPC since it is constructed from two symmetrically positioned parabolic reflectors. The height H of the classical CPC device (also referred to herein as full-height) is typically determined by the following equation:
H=0.5.Math.W.sub.a.Math.Cot θ.sub.c.Math.(1+1/Sin θ.sub.c).  (1)
Such classical CPC devices are generally oriented in East-West direction for allowing effective collection of solar radiation throughout the day-time trajectory of the sun in the sky.

(20) FIGS. 2A and 2B present simulations of the classical CPC collector device 10 shown in FIG. 2A, having a 25° acceptance angle (θ.sub.c) and a concentration ratio of 709.9/300=2.36. The height H of the CPC device 10 simulated in this non-limiting example is the full-height of classical CPC design obtained by equation (1), 1082.80 mm. The graphical plots in FIG. 2B show flux collection vs radiation source angle as obtained in simulations of the classical CPC device 10 of FIG. 2A, for a solar radiation source (plot 21b) and a point radiation source (plot 21a). Surprisingly, the plot 21b evaluating the performance of the classical CPC collector 10 with a solar radiation source shows a noticeable decline (of about 30%) towards the end of the theoretical acceptance angle. As also seen in FIG. 2B, the plot 21a obtained in the evaluation of the classical CPC collector 10 with the theoretical point source does not display this phenomenon. However, as the simulated solar source represents the sun more accurately, taking into account its finite size in the sky of 32 minutes of arc (0.5334°), the flux collection plot 21b obtained for a solar radiation source is more realistic and relevant to non-imaging applications requiring uniform radiation collection profiles. Particularly, in the solar source simulation (plot 21b) the solar source rays are slightly diverging, compared to the fully collimated rays simulated with the point source (plot 21a), and this difference accounts for the performance loss seen in FIG. 2B.

(21) It is noted that although the plots shown in FIG. 2B were obtained for two-dimensional prismatic CPCs, the same principles are evenly applicable for three-dimensional CPC configurations e.g., having cylindrical symmetry or polygon funnel-shape.

(22) Optionally, and in some embodiments preferably, the height of the parabolic reflectors of the CPC device are reduced to about half of the full-height given by equation (1) hereinabove. Though the radiation collection of such reduced height CPC implementations (also referred to herein as truncated CPC devices) is somewhat reduced (˜7%), this reduction in the flux collection is considered acceptable since the reflective surface areas of the device are substantially reduced, resulting in a substantially smaller CPC device, which simplifies its production and reduces costs.

(23) FIG. 3A show a truncated CPC implementation 10* of the classical CPC device 10 shown in FIG. 2A. In this non-limiting example the height H* of the truncated CPC is about a half of the full-height H of the classical the CPC device 10 i.e., H*=H/2. As seen in FIG. 3B, showing plot 23b of the radiation collection of the truncated CPC device 10* compared to the radiation collection of the full-height classical CPC design 10 shown in plot 21b, the reduction in radiation collection of the truncated CPC device 10* is about 7%, for a 50% height reduction. Therefore, in some embodiments, the height of the CPC device is reduced to about 0.5 of the height of the classical CPC device having the same exit aperture W.sub.a and the same acceptance angle θ.sub.c.

(24) FIGS. 4A to 4C show (i) illumination maps and (ii) ray tracing diagrams, obtained in solar radiation source simulations of the truncated classical CPC collector 10* of FIG. 3A, at 0°, 20° and 25°, illumination angles, respectively. In FIG. 4A the location of the solar source forms a 0° angle with the optical axis 10s of the CPC device 10*, and the solar source's radiation rays are not fully collimated such that diverging rays are obtained and maximal radiation collection is obtained along two strips at about 100 millimeters to the right and to the left of the centerline of the exit aperture i.e., removed from the edges 14a and 14b of the exit aperture 14 by about 50 millimeters.

(25) In FIG. 4B the solar source is translated towards the edge 14b of the exit aperture 14 forming a 20° angle with the optical axis 10s of the CPC collector 10* and in this state the maximal radiation collection is obtained concentrated along a single strip removed from the edge 14b by about 75 millimeters (more or less centered between the edge 14b and centerline of the exit aperture 14).

(26) In FIG. 4C the solar source is further translated towards the edge 14b of the exit aperture 14, forming a 25° angle with the optical axis 10s of the CPC collector 10* (i.e., exactly at the acceptance angle of the CPC collector 10), and maximal radiation collection is obtained concentrated along a single strip located on the edge 14b, such that part of the concentrated radiation strip is obtained outside of the exit aperture 14. In this state part of the concentrated radiation falls on a lower section of the parabolic reflector 11b and reflected therefrom onto the opposing parabolic reflector 11a, and therefrom it is ejected outside from the classical CPC collector 10* (as shown by the dashed arrowed lines 22), and therefore lost. The same radiation loss phenomena of course occur at the opposite state, when a −25° angle is formed between the incoming radiation and the optical axis 10s of the CPC collector 10*.

(27) FIG. 4D shows an illumination map (i) and a ray tracing diagram (ii) obtained for a point radiation source simulation of the truncated CPC collector device 10* of FIG. 3A with similar illumination conditions as in FIG. 4C i.e., a 25° illumination angle of the point source being equal to the acceptance angle θ.sub.c of the device. As seen, the maximal collected radiation is well concentrated along a slender strip adjacent the edge 14b. In such ideal/theoretical conditions (obtained for a point source) no light gets ejected from the CPC device 10 even at the maximal illumination angle of the device. Particularly, in case of an ideal/theoretical point source the incoming radiation rays are truly collimated, and the CPC device 10 concentrates them to a nearly perfect line (with minimal thickness and higher concentration values), which thus theoretically enables utilizing the full angular potential of the classical CPC collector 10.

(28) In static solar lighting applications, which strongly rely on uniform light collection across angular design acceptance angles of their CPC collectors, the decreased radiation collection obtained near the edge of the acceptance angle (as shown in FIG. 4C) causes severely reduced performance at seasonal extremities, and whenever the location of the radiation source cause illumination angles that are near the angular spans edge of the CPC device.

(29) It is evident from the simulation results provided in FIG. 4A to 4D that a single parabolic reflector may be used to effectively collect incident radiation received at angles between 0° and +θ.sub.c, while losing most of the incident radiation received at angles between 0° and −θ.sub.c (or wise versa). Accordingly, in possible embodiments a single reflector element configured according to principles of the invention may be used in the radiation collection devices. However, as will be described hereinbelow, a single reflector element may be designed as a revolution object configured according to principles of the invention to effectively collect incident radiation received at angles between −θ.sub.c and +θ.sub.c.

(30) The present application aims to provide CPC collector designs suitable for static solar lighting applications. Design considerations for such applications includes, inter alia, maintaining a substantially constant radiation collection acceptance properties across the designed angular span (i.e., between −θ.sub.c and +θ.sub.c), obtaining minimal overall collection loss (integrated over the angular span).

(31) In addition, an important practical consideration in some embodiments is keeping a minimal height H of the CPC collector, since higher CPC troughs perform poorly in cloudy diffused conditions. The full-height CPC trough-shaped devices also entail larger reflector areas, cost and weight.

(32) A possible solution to the above is, in some embodiments, the use of a CPC collector designed for a wider angular span. For example, a CPC collector requiring uniform radiation collection within some predetermined angular span (e.g., 25°), may be designed to provide a somewhat greater angular span (e.g., 30°), so as to move the diminished collection zone out of the effective working angle of the device.

(33) By way of a non-limiting example, FIGS. 5A and 5B show simulation of a full-height classical CPC design 10′ having a 30° acceptance angle and concentration value of 2, designed for collection of radiation within a 25° angular span i.e., the acceptance angle is increased by 20%. As seen in FIG. 5A, showing the full-height CPC device 10′, the height H of the CPC device 10′ is almost twice (˜44% greater) the height H* of the classical (50%) truncated CPC device 10 shown in FIG. 3A. FIG. 5B respectively shows plots 21c and 21b of the flux collection obtained in solar radiation source simulations of the CPC device 10′ of FIG. 5A and of the classical (full-height) CPC device 10 of FIG. 2A. As seen, a 94% overall efficiency is obtained in this non-limiting example within the desired angular range/span (−25° to +25°). Though performance wise this may appear to be an acceptable compromise, the substantial increase in the height of the CPC device 10′ by 189% compared to the height of the classical 0.5 truncated CPC device 10, render this approach as a costly solution in terms of reflective area surfaces, device weight and construction burden.

(34) In order to resolve the above-mentioned deficiencies, in preferred embodiments modified CPC collectors are designed such that the parabolic focuses of their parabolic surfaces is shifted inwardly towards the centerline of the exit aperture of the device. As the rays of the solar sources are concentrated to a strip centered about the parabola focuses of the parabolic surfaces, moving their parabola focuses inwardly into the exit aperture ensures that all of the radiation received at the entrance aperture within the angular span of the device is trapped and cannot escape out of the device, and thus concentrated and hits the target (not shown) of the device. In this way, when the illumination angles of the incoming radiation are near, or equal to, the acceptance angle of the modified CPC device, the collected radiation is concentrated along a strip shifted inwardly towards the centerline of the exit aperture of the device, which prevents the escape of portions of the incoming radiation out of the device (exemplified in FIG. 2C).

(35) FIG. 6A and FIG. 6B schematically illustrate sectional and perspective views, respectively, of a modified two-dimensional CPC device 30, according to some possible embodiments, in which the focuses f.sub.a and f.sub.b of the parabolic surfaces 31a and 31b are shifted towards the centerline 14c of the exit aperture 14. As will be exemplified hereinbelow, designs of the modified CPC device 30 can provide collector structures having substantially the acceptance angle θ.sub.c and concentration ratio (W.sub.A/W.sub.a) as of the classical CPC design 10 shown in FIGS. 1 and 2A, but with substantially improved radiation collection uniformity throughout the angular span of the device and in certain embodiments with somewhat increased device height H.

(36) It is now understood that for concentration ratios of about 2 the shift distance q of the focuses f.sub.a and f.sub.b of the parabolic surfaces 31a and 31b towards the centerline 14c of the exit aperture 14 can be set up to 0.27 of the width W.sub.a of the exit aperture 14. Optionally, and in some embodiments preferably, the shift distance q of the focuses f.sub.a and f.sub.b of the parabolic surfaces 31a and 31b towards the centerline 14c of the exit aperture 14 is about 0.2 of the width W.sub.a of the exit aperture (i.e., q/W.sub.a≅0.2).

(37) FIGS. 7A and 7B present simulation of a modified truncated CPC design 30 according to possible embodiments having 25° acceptance angle and concentration value of 2. In this non-limiting example the shift distance q of the focus points (f.sub.b) of the parabolic reflectors is one tenth (0.1) of the width of the exit aperture 14 of the modified CPC device 30 (i.e., q=30, q/W.sub.a=0.1), which thus translates the parabola axis (12b) of the classical CPC design towards the optical axis 10s, at the 32b.

(38) As seen in FIG. 7A, showing a schematic illustration of the modified truncated CPC device 30, the height H′ of the modified truncated CPC design 30 is 456.36 mm. In this specific and non-limiting example the height of the device has been adjusted to maintain a concentration ratio of 2. More particularly, in order to move the optical focuses f.sub.b towards the optical axis 10s, as obtained in modified CPC device 30, curvature of the reflectors has been modified, thus resulting in different parabolic curves (different concave depth) of the reflective surfaces of the device. Thus, in order to maintaining the desired concentration ratio, the height of the reflectors has been adjusted for setting an entrance aperture width that provides the needed concentration ratio (W.sub.A=600 mm).

(39) FIG. 7B respectively shows plots 21b, 21c and 21d, of the flux collection obtained in solar radiation source simulations of the CPC devices 10 and 10′ of FIGS. 2A and 7A, respectively, and with the modified CPC device 30 of FIG. 7A. As seen, the radiation collection of the modified CPC device 30 over its 25° acceptance angle, as presented by plot 21d, is nearly uniform across the angular span, and substantially more uniform than the radiation collection of the CPC devices 10 and 10′ presented in the plots 21b and 21c.

(40) FIGS. 8A to 8D schematically illustrate modified three-dimensional CPC designs according to some possible embodiments. FIG. 8A shows a rectangular funnel-shaped modified CPC device 60 constructed from four parabolic reflectors 61 positioned to form a generally rectangular sectional shape, and designed to provide focal regions (f.sub.r, shown in FIG. 8B) inwardly displaced from the edges of the exit aperture 64 of the modified CPC device 60 towards the focal axis 60s of the device. The funnel-shaped modified CPC device 60 can be constructed from two modified two-dimensional CPC devices 30 of FIGS. 6A and 6B, by properly mounting the parabolic reflectors 31a and 31b of one modified two-dimensional CPC device 30 at the lateral sides (parallel to the yz plane) of the other modified two-dimensional CPC device 30.

(41) FIG. 8B shows a top view of the funnel-shaped modified CPC device 60 constructed by intersecting two modified two-dimensional CPC devices 30a and 30b (e.g., each device being a modified truncated two-dimensional CPC device 30 of FIGS. 6A and 6B) which centerlines 14c cross each other perpendicularly. In this specific and non-limiting example a square funnel-shaped modified CPC device is obtained, which focal regions f.sub.r fall of (and/or within) a square within, and concentric with, the edges of the exit aperture 64 of the device 60.

(42) Of course, the intersecting of more than two modified two-dimensional CPC devices 30 may be used to construct other polygon-shaped funnel-shaped modified truncated (or full-height) CPC devices. For example, and without being limiting, FIG. 8C shows a top view of a modified truncated (or full-height) three-dimensional CPC device 65 having a hexagonal funnel shape constructed by intersecting three modified truncated (or full-height) two-dimensional CPC devices 30a, 30b and 30c, which centerlines 14c cross each other at 120° angles. Similarly, the focal regions f.sub.r of the modified CPC device 65 fall on (and/or within) a hexagon within, and concentric with, the edges of the exit aperture 66 of the device 65.

(43) FIG. 8D shows a sectional view of a skirt-shaped modified truncated (or full-height) three-dimensional CPC device 67 designed as a revolution object obtained by revolving a modified parabolic curve of the reflectors described herein about the optical axis 67s of the device 67. In this way, a circular funnel-shaped reflector is obtained having circular concentric entrance aperture 69i with radius r.sub.A, and a circular exit aperture 69o with radius r.sub.a. Accordingly, the width W.sub.A of the entrance aperture 69i of the cylindrical funnel-shaped reflector 67 is defined by the diameter (2.Math.r.sub.A) of its upper opening, and the width W.sub.a of its exit aperture 69o is defined by the diameter (2.Math.r.sub.a) of its bottom opening. The focal regions f.sub.r of the circular funnel-shaped reflector 67 fall on (and/or within) a circle obtained within, and concentric with, the edges of the exit aperture 69o.

(44) FIG. 8D further shows a cylindrical target object 68 (e.g., light guide) configured to receive the collected light concentrated at the exit aperture 69o and transfer it to a desired location for use (e.g., lighting, heating, conversion, etc.). In this non-limiting example the diameter of the cylindrical target object 68 is configured to substantially match the width W.sub.a of the exit aperture 69o of the device 67.

(45) It is noted that similar target objects (not necessarily of cylindrical shape) can be used at the exit aperture of any of the modified (truncated or full-height) CPC devices described herein, to receive the collected radiation and deliver it to a predetermined location/facility. The shift distance q of the focus of the parabolic surfaces of the different modified CPC devices described herein is in some embodiments about 0.02 to 0.27 of the width W.sub.a of the exit aperture of the respective CPC device, optionally about 0.2 of the width W.sub.a of the exit aperture (i.e., q/W.sub.a≅0.2).

(46) The radiation collectors, and modified (truncated or full-height) CPC devices, described herein, may be fabricated from any good quality mirrors for the collected wavelength, such as, but not limited to, metallic, polymer or glass mirrors. Such radiation collectors may also be constructed using total internal reflection (TIR) effect, by creating a high refractive index volume, contained within the following surfaces: input and output plains, symmetrical concave (parabolic or other) converging/tapering surfaces, that are being immersed in a relatively lower refractive index medium. A TIR CPC would be an effective solution in relatively smaller CPCs due to weight considerations. Possible production methods may include, but not limited to: sheet-metal forming including curve approximation by division into flat segments, composite materials lamination, vacuum formed thermo-polymers, cold molding of flexible sheets, and spatial positioning of discreet mirrored facets combined to form the aforementioned converging/tapering concave reflective surfaces.

(47) One or more reflective layers (e.g., silver, gold, aluminum or any other reflective substance, such as, but not limited to reflective polymer) may be applied (e.g., by sputtering, electroplating or painting) at least on the inner surfaces of the reflectors. The concentration ratio (W.sub.A/W.sub.a) of the modified CPC devices can effectively be in the range of 1 to the maximal possible concentration (for a 2D CPC in air would being about 1/sin(θ.sub.c) or up to 1/sin.sup.2(θ.sub.c) in case of a surface revolution 3D CPC).

(48) As discussed and exemplified hereinabove, while the height of some embodiments of the modified CPC device is somewhat increased in comparison to the height of the classical CPC design having the same exit aperture and same acceptance angle (also referred to herein as the counterpart classical CPC design), but the increase in the height of the modified CPC devices described herein is relatively small (about 0.1 to 0.31 of the height of the counterpart classical CPC design).

(49) FIG. 9 shows the flux/radiation collection plots 21b, 21c and 21d, obtain in the solar radiation source simulations of the classical and modified CPC designs described hereinabove, together with a flux/radiation collection plots 21e and 21f obtained for solar radiation source simulations of a modified CPC design with acceptance angles θ.sub.c=25° and focus shifts q from the edges of the exit aperture of 0.2.Math.W.sub.a and 0.27.Math.W.sub.a, respectively. As seen, the flux collection plots 21e (obtained for θ.sub.c=25° and 0.2.Math.W.sub.a focus shift) and 21f (obtained for θ.sub.c=25° and 0.27.Math.W.sub.a focus shift) are nearly uniform across the angular span. It is noted that the 0.27.Math.W.sub.a focus shift is considered to be the geometrical limit for possible focus shifts of the modified CPC design that enables maintaining the desired concentration ratio (i.e., as of the classical CPC design). It should be therefore understood that while focus shifts greater than 0.27.Math.W.sub.a from the edge of the exit aperture are possible, such implementations results in a significant change of the CPC design, which will typically impose a change in the concentration ratio of the device.

(50) The following table presents various results obtained in the solar radiation source simulations of the various modified truncated CPC designs described hereinabove:

(51) TABLE-US-00001 1 - 2 - 3 - Modified 4 - Modified 5 - Modified Classical Classical θ.sub.c = 25°, focus θ.sub.c = 25°, focus θ.sub.c = 25°, focus CPC type θ.sub.c = 25° θ.sub.c = 30° shift of 0.1 .Math. W.sub.a shift of 0.2 .Math. W.sub.a shift of 0.27 .Math. W.sub.a Total flux 328,941 310,797 306,684 309,455 314,774 Collected (lux) Total [%] 100% 94% 93% 94% 96% compared to type 1 Min/Max [%]  64% 89% 89% 89% 94% at 0~25° CPC Height 412.5 779.4 456.4 541 746.3 [mm] Height [%] 100% 189%  111%  131%  181%  compared to type 1

(52) The concentration ratios of all CPC devices/types in the above table are W.sub.A/W.sub.a=2. As seen from the above results, the modified CPC design of type 3 or 4 (θ.sub.c=25°, focus shift of 0.1.Math.W.sub.a or 0.2.Math.W.sub.a) appears to provide good results with relatively small increase in the height of the device and somewhat reduced flux collection performance.

(53) FIGS. 10A and 10B show ray tracing diagrams of a truncated CPC design having acceptance angle of θ.sub.c=25°, and a full-height CPC design having acceptance angle of θ.sub.c=30°, respectively, obtained for large ray divergence conditions (e.g., simulating dispersed “cloudy” conditions). As seen in FIG. 10A, wide acceptance angle is achieved in the ray tracing diagram of solar source simulation obtained for the truncated modified CPC device with the acceptance angles of θ.sub.c=25°. On the other hand, in the simulation of the full-height classical CPC design with acceptance angle of θ.sub.c=30°, shown in FIG. 10B, the ray tracing diagram present narrow acceptance angle. Comparison of the various CPC designs described herein show that in cloudy conditions angular deviations become much smaller, but the full-height CPC designs perform poorly in such large ray divergence conditions.

(54) FIG. 10C shows plots of flux/radiation collection obtained over the angular span in the large ray divergence conditions simulations, wherein plot 41a shows the flux collection obtained with the classical 50% truncated CPC design with θ.sub.c=25° (shown in FIG. 3A), plot 41b shows the flux collection obtained with the classical 50% truncated CPC design with θ.sub.c=30° (shown in FIG. 5A), plot 41c shows the flux collection obtained with the truncated modified CPC design with θ.sub.c=25° and 0.1.Math.W.sub.a focus shift (shown in FIG. 7A), plot 41d shows the flux collection obtained with the modified truncated CPC design with θ.sub.c=25° and 0.2.Math.W.sub.a focus shift (shown in FIG. 11A), and plot 41e shows the flux collection obtained with the truncated modified CPC design with θ.sub.c=25° and 0.27.Math.W.sub.a focus shift. As seen, good radiation collection is obtained in the large ray divergence conditions simulations for the truncated modified CPC designs having acceptance angle θ.sub.c=25° and focus shifts of 0.1.Math.W.sub.a and 0.2.Math.W.sub.a. The radiation collection of the truncated modified CPC designs having acceptance angle θ.sub.c=25° and focus shifts of 0.27.Math.W.sub.a the large ray divergence conditions simulation is also acceptable, although somewhat reduced (due to the relatively larger CPC height, which is detrimental in these conditions).

(55) FIGS. 11A and 11B provide another non-limiting comparative example between radiation collection performance of the full-height CPC design having acceptance angle of θ.sub.c=25° (shown in FIG. 2A) and a non-truncated modified CPC design 70 having acceptance angle of θ.sub.c=25° and focus shift 0.2.Math.W.sub.a, shown in FIG. 11A. As seen, in the truncated modified CPC device 70 the parabolic focuses f.sub.b are shifted (q=60) from the parabola axes 12b of the classical CPC design to the new parabola axes 72b of the modified parabolic reflector 71b. In addition, the height H** of the non-truncated modified CPC device 70 was reduced (to 866.2 mm) due to mathematical limitations imposed by the shifting of the focal point 0.2.Math.W.sub.a towards the optical axis 10s (i.e., for the parabolic reflector to be parallel to the symmetry/optical axis 10s at the entrance aperture 13).

(56) In FIG. 11B the radiation collection (solar source) simulation result of the non-truncated modified CPC design 70 of FIG. 11A shown in plot 23c is compared to the radiation collection simulation of the full-height classical CPC design of FIG. 2A shown in plot 23a. As seen, a noticeably improved angular uniformity is obtained in the radiation collection curve 23c simulated for the non-truncated modified CPC design 70. It is also interesting to note that the improved performance is very similar in this case to the results obtained with the truncated modified CPC designs, but giving an overall collection reduction of only 5%, while achieving excellent angular uniformity across the full collection range.

(57) It is thus appreciated that the modified (focus shifted, truncated or non-truncated) CPC designs disclosed herein, provide optimal performance suited to static solar lighting system. In particular, these modified CPC designs provide: substantially uniform light collection across the designed angular span with a realistic finite sized Solar source; relatively high efficiency overall performance (minimal loss when compared to classic CPC designs); good performance in clear and cloudy conditions; and minimal cost, size, and weight, due to relatively low height parabolic reflectors of the modified CPC designs.

(58) FIG. 12A shows a side sectional view of a radiation collector assembly 80 comprising an array of elongated radiation collectors arranged side by side and oriented so as to maximize radiation collection from a (stellar) radiation source (not shown). The radiation collector assembly 80 further comprises a specially designed radiation guiding structure 85 configured to receive in a large-tilted opening 85t thereof the light radiation collected by the radiation collectors, and direct the received light towards a small-horizontal opening 85p. Optionally, and in some embodiments preferably, the large-tilted opening 85t and the small-horizontal opening 85p have substantially the same shape, but different dimensions and orientations.

(59) In this specific and non-limiting example the radiation collectors array of assembly 80 comprises four elongated radiation collectors, 81, 82, 83 and 84, aligned side by side one parallel to the other, and tilted such that their light collecting openings substantially face the radiation source. Each of the radiation collectors comprises a radiation guiding portion 77 configured to direct and concentrate the collected radiation towards an output opening thereof. The large-tilted opening 85t of the radiation guiding structure 85 is configured to receive the concentrated radiation from the radiation guiding portions 77 of the radiation collectors.

(60) The radiation guiding structure 85 comprises a major (large) reflector 85r portion having a curved/arced shape facing the output openings of the radiation guiding portions 77 of the radiation collectors, 81, 82, 83 and 84, and a minor (small) reflector 85s portion having a flat or slightly curved shape. The major reflector 85r is configured to direct the light received from the output openings of the radiation guiding portions 77 towards the small-horizontal opening 85p and/or the minor reflector 85r, and the minor reflector 85r is configured to direct internally reflected rays towards the small-horizontal opening 85p and/or the major reflector 85r.

(61) Optionally, and in some embodiments preferably, each radiation guiding portion 77 of the radiation collectors comprises a relatively short anterior reflector portion 77s, a relatively longer posterior reflector portion 77g, and a tilted reflector portion 77r connecting between the anterior and posterior reflector portions, 77s 77g, of adjacently located radiation reflectors. The tilted reflector portions 77r are configured to direct internally reflected rays towards the small-horizontal opening 85p and/or the major reflector 85r.

(62) This configuration of the radiation collector assembly 80 provides a substantially stable collector structure that can be easily and readily installed on roofs of buildings, or any flat horizontal surface, per design needs. The radiation collector assembly 80 can advantageously arrange an array of radiation collectors to form a substantially equilateral radiation receiving front 88 i.e., having an equilateral polygonal cross-section shape, allowing to efficiently transfer the concentrated radiation via corresponding equilateral openings, 85t and 85p, of the radiation guiding structure 85. This configuration further simplifies the interfacing between the equilateral output opening 85p of the radiation guiding structure 85 and a radiation guiding element having a circular cross-section shape (not shown), as ordinarily used in solar applications, and minimize radiation losses associated therewith. For improved efficiency, the internal light/radiation reflecting faces of the radiation guiding structure 85 also has a substantially corresponding equilateral polygonal cross-sectional shape tapering from the large-tilted opening 85t towards the small-horizontal opening 85p.

(63) In this specific and non-limiting example four elongated radiation collectors, 81 82 83 and 84, are arranged side by side in parallel to form a substantially square radiation receiving front 88 to efficiently concentrate and transfer collected radiation to the radiation guiding structure 85 having substantially square openings, 85t and 85p, and a substantially square cross-sectional shape formed by its internal reflecting faces. it is noted that the radiation collectors, 81 82 83 and 84, can be implemented by any one of the CPC devices disclosed herein or known in the art.

(64) Optionally, and in some embodiments preferably the radiation collectors, 81 82 83 and 84, are implemented by any one of the radiation collection apparatuses described in international patent application No. PCT/IL2017/050024, of the same applicant hereof, the disclosure of which is incorporated herein by reference. FIGS. 12B, 12C and 12D, respectively show side sectional, top and bottom perspective views, of a radiation collector assembly 80′ implemented using a specific radiation collector apparatus (20) having additional internal reflecting surfaces.

(65) The modified CPC/radiation collector designs disclosed herein can be used in a great variety of solar applications, such as, but not limited to, passive and active solar heating, space heating and hot water production, heat pumps and sorption cooling, air conditioning, and refrigeration systems, industrial air and water systems for process heat, desalination, and solar chemical systems for thermal power systems.

(66) As described hereinabove and shown in the associated figures, embodiments of the present invention provides modified CPC/radiation collector designs optimized for substantially uniform radiation collection at the price of slightly enlarged device dimensions and somewhat reduced flux collection. While particular embodiments of the invention have been described, it will be understood, however, that the invention is not limited thereto, since modifications may be made by those skilled in the art, particularly in light of the foregoing teachings. As will be appreciated by the skilled person, the invention can be carried out in a great variety of ways, employing more than one technique from those described above, all without exceeding the scope of the invention.