Abstract:
A collector for concentrating light rays including a first conical segment having an inner reflective surface joined to or nested within a second conical segment having an inner reflective surface. A first embodiment consists of stacked reflective segments, where the upper conical segment is slightly diverging and the lower conical segment is converging in the direction of an input light ray. A second embodiment comprises an outer conical segment that converges in the direction of an input light ray and a nested inner conical segment that also converges in the direction of a light ray. In either embodiment, the present invention is capable of concentrating more energy when not aimed directly at an energy source than single cone collectors and thus simplifies the source tracking strategy.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS  
       [0001]    The present application claims priority to U.S. Provisional Application Ser. No. 60/451,403 of the same title, filed on Mar. 4, 2003, and hereby incorporated by reference. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of Invention  
           [0003]    The present invention relates to optical structures and methods for collecting and utilizing beams of light and, more specifically, to devices for the collection and concentration of beam sunlight for its conversion to electricity, heat, or lighting.  
           [0004]    2. Description of Prior Art  
           [0005]    The conical or funnel-shaped collection structure was known and patented in the nineteenth century for the practice of delivering natural light to the interior of buildings (see, e.g., U.S. Pat. Nos. 550,376, 585,770, and 668,404). The optical principles are simple. The larger of two apertures of a truncated cone points substantially towards the sky, collecting daylight. The smaller of the two apertures receives the collected light in concentrated form and releases it to a distribution system or other means for delivering it to the interior of a structure, such as a building. Conically shaped reflectors have a wide angle of acceptance of solar rays, typically over tens of degrees away from the principal optic axis. This feature contrasts with focusing types of concentrators like lenses and parabolic focus reflectors, which must be pointed at the sun to within a few degrees. A recent version of this optical structure has merely improved on the mounting and interface means for the truncated cone, see e.g., U.S. Pat. No. 5,648,873.  
           [0006]    Applications for the collection of sunlight may take one of two forms. The first is stationary, whereby the optical structures do not move over time. The second form tracks the apparent trajectory of the sun to maximize the collection of available solar power. The simplest of these structures remains stationary over time. One strategy uses a non-moving funnel-shaped collection structure, see, e.g., U.S. Pat. No. 4,052,976, but introduces the complication of a concentrated area of light that moves over time instead of aiming at a constant target aperture. U.S. Pat. No. 4,267,824 is directed to an inflatable conical structure, which merely makes the concentrating truncated cone provide light into a portable device.  
           [0007]    Other conical structures have good collection characteristics, but suffer from other complications. U.S. Pat. Nos. 4,266,858, 4,337,758, and 5,174,275 disclose conical segments in their optical networks but require axially elongated target regions instead of a simple fixed exit aperture for concentrated rays. In other inventions, a conical structure is a secondary element in an optical network, such as in U.S. Pat. No. 5,460,659.  
           [0008]    Another strategy for collecting light is based on a plurality of conical collectors, see, e.g., U.S. Pat. No. 4,309,079. These collectors are arranged in a semicircular fashion to receive the rays of the sun across its arc of trajectory. In the first embodiment, each conical collector has its own means of receiving concentrated solar radiation. In the second embodiment, the conical structures comprise a single collector. These embodiments do not take advantage of economy of scales, however, whereby a small number of cones may be combined to collect sunlight over an angular range greater than that of a single cone. The disclosed means for receiving concentrated sunlight are also not easy to interface to a distribution system like a reflective duct.  
           [0009]    There have been many inventions that actively point an optical network at the sun to enhance its collection capabilities. An example is U.S. Pat. No. 4,590,920, in which a conical reflector is found to be but a secondary element in an apparatus that tracks the sun.  
           [0010]    U.S. Pat. Nos. 4,080,221 and 4,223,174 teach the greatest economy and simplicity of implementation, but are limited to a truncated conical structure in its simplest form. The latter patent merely proposes an optical enhancement to the basic cone.  
           [0011]    3. Objects and Advantages  
           [0012]    It is a principal object and advantage of the present invention to widen the angle of acceptance of a collector.  
           [0013]    It is an additional object and advantage of the present invention to extend the number of useful hours of daily operation of a collector.  
           [0014]    It is a further object and advantage of the present invention to reduce the accuracy and cost needed for the mechanical tracking of the motion of the sun while providing maximal collection of available power.  
           [0015]    It is an additional object and advantage of the present invention to provide lens-less projection of rays along selected angles.  
           [0016]    Other objects and advantages of the present invention will in part be obvious, and in part appear hereinafter.  
         SUMMARY OF THE INVENTION  
         [0017]    The present invention comprises variations on a conical reflector for use in three different types of applications. In one embodiment, the collector comprises an upper segment having a reflective interior surface connected to a lower segment having a reflective interior surface along a common juncture, where the upper and lower segments taper away from said juncture to corresponding entrance and exit apertures. In other embodiment, the collector comprises an inner segment having a reflective interior surface and a reflective exterior surface that is surrounded by a first outer segment having a reflective interior surface and a second outer segment having a reflective interior surface connected to said first outer segment and positioned around said inner segment, where all segments taper toward said exit aperture.  
           [0018]    The first application of the present invention is for the collection and utilization of sunlight for conversion to electricity or heat. The second application collects sunlight for the illumination of buildings. The third application uses conical reflectors as a means for projecting the rays of various lighting sources. The present invention accomplishes the third application by placing the source or radiant light or energy at the smaller aperture of an enhanced conical reflector that selectively releases rays through its larger aperture. Applications for the present invention include novelty, merchandise display, and theatrical lighting fixtures. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]    [0019]FIG. 1 is a schematic representation of the path of light rays in a prior art collector having a reflective interior.  
         [0020]    [0020]FIG. 2 is a schematic representation of the path of light rays in another prior art collector having a reflective interior.  
         [0021]    [0021]FIG. 3 is a schematic representation of the path of light rays in a collector according to the present invention.  
         [0022]    [0022]FIGS. 4A and 4B are cross-sectional diagrams of a collector according to the present invention.  
         [0023]    [0023]FIG. 5 is a cross-sectional diagram of an alternate embodiment of a collector according to the present invention.  
         [0024]    [0024]FIG. 6 is a diagram of a test performed on a collector according to the present invention.  
         [0025]    [0025]FIG. 7 is a chart of the results of a test performed on a collector according to the present invention.  
         [0026]    [0026]FIG. 8 is perspective view of an alternate embodiment of a collector according to the present invention.  
         [0027]    [0027]FIG. 9A is a top view of an alternate embodiment of a collector according to the present invention.  
         [0028]    [0028]FIG. 9B is a cross-sectional view of an alternate embodiment of a collector according to the present invention.  
         [0029]    [0029]FIG. 9C is a schematic representation of an alternate embodiment of a collector according to the present invention.  
         [0030]    [0030]FIG. 10 is a cross-sectional, side view of a system including collectors according to the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0031]    Referring now to the drawings wherein like numerals refer to like parts throughout, there is seen in FIG. 1 a diagram of longitudinal cross-section of a prior art collector  10  comprising a truncated cone having a reflective interior. An input light ray  12  enters the top of collector  10  through an entrance aperture  14 , a portion of which is reflected through collector  10  and exits from a bottom aperture  16 . A target that makes use of the concentrated light, such as a photovoltaic cell (PV) may be placed below bottom aperture  16 .  
         [0032]    There are several key design parameters for collector  10 . A first parameter is the size of the target device, such as a photovoltaic (PV) cell, which determines the cross-sectional extent of bottom aperture  16 . A second parameter is the desired concentration ratio, which is one factor in specifying the cross-sectional extent of entrance aperture  14 . A third parameter is the vertical height of collector  10 . These parameters help define the requisite cone angle  18 , seen in FIG. 1 as the angle between the wall  20  that forms the cone of collector  10  and vertical reference axis  22 . Vertical reference axis  22  is parallel to the central longitudinal axis, or the optic axis, of collector  10 .  
         [0033]    There are at least two limiting conditions for collecting and concentrating light rays through a conical collector  10 . For a given cone angle  18 , referred to as α cone , there are orientations of input rays  12  that, upon a second reflection, will reflect back out through entrance aperture  14 . The angle of input ray  12  at which reflection back begins is defined as α reject  and seen in FIG. 1 as angle  26 . The relationship between these two angles is:  
         α reject =−3α cone +90°, 0&lt;α reject &lt;90°  (Equation 1)  
         [0034]    The second limiting condition occurs for input rays  12  that reflect too many times through the cone of collector  10  of a given vertical height. Such rays  12  will eventually reflect back through the entrance aperture  14 . For solar optic applications, these limiting conditions influence both the instantaneous power output and the ongoing energy production from collector  10  of a given size, cone angle  18 , and orientation relative to the apparent trajectory of the sun.  
         [0035]    As seen in FIG. 2, attempts to overcome these deficiencies in a prior art cone  28  include the introduction of an addition of upper conical segment  30  to entrance aperture  14 . Upper segment  30  defines an upper wall angle  32  relative to vertical reference axis  22  that is in the preferred range of 9°-11°. A lower conical segment  34  forms a lower wall angle  36  in the preferred range of 13°-17°. Additional conical segment  30  collects parallel, spatially adjacent rays after first reflection and transports them via vertical displacements to avoid the problem of too many reflections that will ultimately reject the rays, thus only the second limiting condition described above.  
         [0036]    As shown in FIG. 2, collector  28  does not extend the useful range of input rays  12 . Input rays  12  strike the upper conical wall segment at an input angle α 0  and have a first reflection at an angle α 1  relative to vertical reference axis  22 . Assuming an upper conical wall angle  30  of 10°, the relationship between the two angles is quantified in the first two columns of Table 1.  
                           TABLE 1                                   α 0  (in degrees)   α 1  (in degrees).                           30   50           35   55           40   60           45   65           50   70                      
 
         [0037]    If lower conical wall angle  36  is about 15°, the geometry shown in FIG. 2 will not enhance the range of collectable angles. The reflected rays in the selected range are greater than 45° and are therefore rejected by lower conical segment  34 .  
         [0038]    Referring now to FIG. 3, one embodiment of the present invention comprises double conical collector  40  having an upper conical segment  42  defined by an upper cone wall  44  having a slope in the opposite sense of a lower conical segment  46  defined by a lower cone wall  48 . Referring to FIGS. 4A and 4B, the upper and lower segments  42  and  46 , respectively, are positioned in a stacked arrangement along optic axis  54  and connected structurally along a common juncture.  
         [0039]    If the upper and lower angles  50  and  52  formed by upper and lower walls  44  and  48 , respectively, are at angles of 15° on either side of vertical reference axis  22 , input and output ray angles α 0  and α 1 , will be listed in Table 2.  
                                         TABLE 2                                   α 0  (in degrees)   α 1  (in degrees).                                        30   0           35   5           40   10           45   15           50   20                      
 
         [0040]    Upper conical segment  42  therefore extends the range of useful angles (&lt;45°) for double conical collector  40  well beyond that collectors  10  and  28  shown in FIGS. 1 and 2, respectively.  
         [0041]    The embodiment of the present invention shown in FIG. 3 may be modified to mimic the functionality of prior art collector  28 . Table 3 below lists the input and output ray angles α 0  and α 1 , respectively, if upper wall angle  44  is 10°. Output rays reflected from upper conical segment  42  become less slanted for lower segment  46 . This effect enhances the ray collection capabilities of the present invention below the limiting case of 45°. As a result, the preferred embodiment of the present invention improves the ray-passing capabilities of a three-dimensional structure.  
                                         TABLE 3                                   α 0  (in degrees)   α 1  (in degrees).                                        20   0           25   5           30   10           35   15           40   20                      
 
         [0042]    As seen in FIG. 5, another embodiment of the present invention comprises double cone segments arranged into a nested collector  60  having separate inner and outer cones  62  and  64 , respectively, supported in the nested configuration by way of thin struts (not shown) or other supports that do not shadow a substantial portion of the rays passing through. Alternatively, nested collector  60  may have interior partitions that reflect light.  
         [0043]    With regard to either stacked collector  40  or nested collector  60 , there is a common entrance aperture  14  for all input rays  12 . There is also a common exit aperture  16  for input rays  12  passing through and impact a target device, such as a PV. As seen in FIGS. 4B and 5, the geometry of stacked collector  40  or nested collector  60  can be expressed by radii, r i , defining the distance from optic axis  54  to the edge of a given segment of cone a corresponding number of separation distances, d i , or heights. The radius of common exit aperture  16  may be defined as r 0 , and all successive radii are numbered sequentially therefrom. Nests of simple truncated cones may be also described as a list of r i  and d i . As seen in FIG. 5, it is necessary to designate which of the r i  are associated with each other in a given conical segment. Further refinement of these conventions need not be pursued further and will be understood by those skilled in geometrical optics.  
         [0044]    The innermost cone of nested collected  60  may be reflective on both sides to facilitate the passage of rays collected between radii r 3  and r 4 . Curved segments may be defined as functions of the form r i =r i (d a ,d b ), where d b &gt;d a  in a range beginning at d a  and ending at d b .  
         [0045]    The advantage of the poly-conical configurations of the present invention is that input rays  14  of orientations that are rejected in one part of collector  40  or  60  may be re-collected or passed independently through the optical system by another location.  
         [0046]    The poly-conical configuration of the present invention includes a few limits and trade-offs in order to optimize collection capabilities. For example, the upper portions of collector  40  and  60  may cast shadows across common exit aperture  16  at certain input ray  12  orientations. This problem may be partially solved by using transparent sections of upper or inner segments  42  or  62  respectively.  
         [0047]    Injudicious placement of changes in radius may result in light traps within the optical system. There are diminishing returns to an increase in collectors, as increasing the number of collectors  40  or  60  beyond a certain limit will produce no angular or other advantages and will degrade overall system performance.  
         [0048]    Collectors  40  or  60  may reflect light at least two physical mechanisms. One is by the use of a specular reflecting surface. The second is by Fresnel reflectivity of a transparent material supplied as the reflecting surface. The latter occurs when rays almost parallel to the structure&#39;s surface glance off with very little transmission through it. This may be readily envisioned for the top section of stacked collector  40  in FIG. 3. The advantage of a transparent upper section  42  is that it does not impede diffuse rays from entering the optical system under hazy sky conditions.  
         [0049]    As seen in FIGS. 6 and 7, a test comparison between a prior art, single cone collector  10  and double cone collector  40  of the present invention yielded favorable results. Collector  40  made from silver mylar, cardboard frustrum templates, and ad hoc fastening techniques having specification of r 0 =1 inch, r 1 =2.5 inches, r 2 =2 inches; d 1 =5 inches, d 2 =7.5 inches was compared to a prior art collector  10  lacking upper segment  42 . The entire inner surfaces of both segments were covered with reflective mylar. A target 1.4×1.2 in 2  buried contact photovoltaic (PV) cell obtained from the University of New South Wales, Australia target was positioned under exit aperture  16 . The area of the PV cell was thus 1.68 in 2  (0.011667 ft 2 , 10.83869 cm 2 , or 0.001084 m 2 ) and fit within the circular boundary of the common exit aperture. The PV cell&#39;s solid-state construction allowed it to increase output power in direct proportion to level of concentration of sunlight up to a concentration ratio of at least 10×. Thus, concentrating sunlight optically onto the cell by 2× doubles its power output compared with un-concentrated sunlight.  
         [0050]    [0050]FIG. 7 is a plot of the unloaded output power as a function of solar input angle for the single and double collectors,  10  and  40 , respectively. In the conventions of the solar energy industry, unloaded power is a rating for PV performance and is a function of open circuit voltage and short-circuit current. Open circuit voltage is measured when a volt-meter is the only electrical device across the PV cell terminals. Short-circuit current is measured when an ammeter of sufficiently low internal impedance is the only device across the cell&#39;s terminals. The unloaded output power is then taken as the product of the open circuit voltage and the short-circuit current. The results, expressed in units of watts, are plotted in FIG. 7 with their estimates of measurement precision shown as error bars.  
         [0051]    The graph in FIG. 7 shows that from 0° to 30° of solar input angle, the power output of the prior art collector  10  was slightly higher than that of the double cone (although the data is within mutual measurement error). This is expected due to the slight shading of input aperture  14  by the opaque regions of upper segment  42  of the double cone collector  40 . The most noteworthy difference appeared in the range of angular incidence from 30°-50°. As the graph in FIG. 7 shows, the PV cell&#39;s power output under single cone  10  vanishes in that range. Over the same range, however, the power output under double cone collector  40  remains constant at a significant level. The double cone collector  40  thus extends the useful range of solar input.  
         [0052]    Referring to FIG. 8, there is seen an alternate embodiment of upper segment  42 . Transparent areas  66  are provided to reduce the shading effects when solar incidence is in the range of 0°-30°. These light-admitting areas  66  may also be simple cut-outs of the material comprising upper conical segment  42 . Opaque regions  68  with reflective inner linings are on the eastern and western “wings” of upper segment  42 . The reflective wing region  68  collect light when the sun is at its eastern and western extremes of trajectory relative to entrance aperture  14  of collector  40 .  
         [0053]    Another embodiment of the present invention for increasing the amount of luminous power delivered to the exit aperture when multiple prior art conical collectors  10  are positioned in an array is seen in FIG. 9A-9C. As seen in FIG. 9A, entrance aperture  14  is substantially circular and creates square region  70  when a plurality of collectors  10  are placed side-by-side in an array, circular entrance apertures  14 . Light-collecting structures  72  in the corners of nearest-neighbor squares  70  make use of space that is normally unused in optical collecting devices. As seen in FIGS. 9B and 9C, light collected from the corners is piped by substantially vertical guides  74  from nearby entrance aperture  14  to nearby exit aperture  16 . As seen in FIG. 9B, light guides  74  terminate near a light-transmissive section  76  where the sidewall silvering ends near the bottom of collector  40 . The light in guides  74  is then preferentially released onto a PV cell  78  positioned at the bottom of collector  40 .  
         [0054]    Light guides  74  depicted in FIGS. 9A-9C may operate by the principles of total internal reflection or by specular reflection. As FIG. 9C shows, input rays  80  released from light guides  74  are obliquely disposed onto a PV cell  78 . This embodiment requires a PV cell  78  that can accept rays  80  at such angles. One example is the PV cell available from the University of New South Wales used to generate the data contained in FIG. 7.  
         [0055]    The minimum combination of this embodiment consists of a simple conical collector  10  and light guides  74 . Light guides  74  provide more luminous power to exit aperture  16  than collector  10  would otherwise, especially at ray angles near zero degrees. When light guides  74  are used with stacked and nested collectors  40  and  60 , respectively, light guides  74  compensate for loss of power due to shadowing effects.  
         [0056]    There is seen in FIG. 10 a standard commercial panel unit  82  in the solar electric industry is a panel-like package that holds, supports, encloses, positions, and protects the working components and allows for easy installation. Panel  82  includes a weatherproof cover  84  above collectors  40  and may be glued, epoxied, caulked, or otherwise adhered to upper segments  42 . If two or more collectors  40  are included in each panel  82 , a structural support member  86  may be provided for securing them together. A screw-in holder, glue, epoxy, caulk, or other similar attachment method may attach a PV cell  88  to exit aperture  16  of each optical unit  82 . The bottom of individual collectors  40  should be at some minimum distance from whatever supports  86  to protect the PV assemblies  88  during installation and to help absorb mechanical perturbations should panel  82  be dropped.  
         [0057]    To preserve the optical integrity of the system, a water-tight seal must be maintained at the transparent cover, across all junctures of segments in the optical units, and whatever device occupies the common exit aperture of each unit. In the case of PV cells  88 , a heat sink  90  should be in good thermal contact to draw away the unwanted effects of optical concentration. A more complicated panel structure may employ a circulating fluid to collect the excess heat for use with a thermal application. Panel  82  may also include protective sheathing  92  having ventilation apertures  94 . If PV cells  88  are to be wired in series, a common practice for achieving industry-standard output voltages, structural support members  86  must electrically isolate heat sinks  90  from each other. Members  86  may be supplied in the form of struts that link to form a supportive lattice on the underside of the panel.  
         [0058]    As certain implementations require the protection of the optics from moisture, dust, and vermin infestations, individual upper segments  42  should be sealed to a transparent cover. In embodiments that include a PV cell  88 , the cell should be on a heat sink  90  sealed to exit aperture  16 . In solar lighting implementations in which entrance apertures  14  are exposed to the atmosphere, a transparent cover  84  should be used to seal the opening into the building or other structure must be provided. Reflective optics above this transparent cover  86  may be cleaned by rain or by washing, in which case weep holes should be provided along the perimeter between the conical structures and the transparent barrier to the interior of the building. Alternatively, a transparent dome can enclose the entire structure and its penetration into a building.  
         [0059]    If the optic axes of collectors  40  or  60  can be kept within about 20° of aiming straight at the sun, the major benefits of optical concentration will occur. For applications where a plurality of optical panels  82  track the sun, energy output increases with increasing frequency of change in panel orientation. This situation may be controlled by something as simple as a timer set for the requirements of a given geological latitude of installation and thus does not require sensors, comparator and control logic, and continuously variable mechanical positioning devices required by prior art systems.  
         [0060]    Each of the optical configurations of the present invention may be combined with an appropriate mounting and positioning strategy to define specific commercial products. For electrical peak demand reduction where a panel-like structure is preferred, the stacked or nested configuration may be used, with some portion of the upper or interior conical segment(s)  42  and  62 , respectively, oriented to face west or southwest in a stationary structure. The mounting means may be onto the side of a building, or on panel-supporting means with the orientation of panel  82  about the vertical tilt axis defined by construction or fixed permanently at installation. One such embodiment is for stationary PV panels mounted facing an advantageous direction for the purpose of augmenting the electric power supply during certain times of the year. One example is during summer months when the demand for electricity reaches a maximum due to increased loads imposed by air conditioning. This application of PV technology is called peak demand reduction in the field of electric utility services.  
         [0061]    On-site installations where a panel-like structure is preferred, as in many residential and commercial applications, either the stacked or nested configuration may be used, with some portion of the upper or interior conical segments(s)  42  or  62 , respectively, transparent and mounted with one axis of freedom. To obtain the maximum energy production throughout a year, the vertical tilt angle of panels  82  may be adjusted periodically over weeks or months as the seasons change. This may be accomplished manually or via a pre-set control timer and means for mechanical actuation.  
         [0062]    Lighting applications, where collected and concentrated sunlight enters an interior lighting fixture through the wall or roof of a building, may use any of the embodiments of the present invention mounted to a weatherproof interface with a light-conveying means, such as a reflective duct or channel through the building envelope.  
         [0063]    Lighting displays with beams directed along selected directions may use any of the configurations, with a source of light placed at the smaller of the two apertures of the system of elements, and the larger of the two apertures pointed towards one or more objects on display. If mounted on a means for providing motion, these fixtures may track an object, such as an actor on a stage, or may serially illuminate a number of objects in a collection as during a sales presentation.