Abstract:
A tracking system for a solar collector assembly array where the tracking system includes a coplanar circular rim structure including multiple circular rims, where each circular rim is fitted around a respective solar collector and where each solar collector has a general shape of a sealed and inflated cylindrical tube housing having a longitudinal center axis and where each solar collector is in a horizontal planar array with respect to each other. The tracking system further includes a first elongated frame structure for supporting the circular rim structure such that all of the circular rims are generally vertically coplanar with one another. The tracking system further includes a cable serially wrapped around each of the respective circular rims to form a closed cable loop where the wrapped cable forms a series of a generally vertical coplanar loops with each loop contacting around a respective rim structure such that at least one generally complete gripping loop is formed on each respective rim. An actuator is attached to the frame structure such that actuator provides a controllable driving force to the closed cable loop to allow for controlled rotation of each solar collector assembly around its respective longitudinal axis.

Description:
FEDERALLY-SPONSORED RESEARCH AND DEVELOPMENT 
     This invention (Navy Case NC 100,711) is assigned to the United States Government and is available for licensing for commercial purposes. Licensing and technical inquiries may be directed to the Office of Research and Technical Applications, Space and Naval Warfare Systems Center, Pacific, Code 72120, San Diego, Calif., 92152; voice (619) 553-5118; email ssc_pac_t2@navy.mil 
    
    
     CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
     This application is related to application Ser. No. 13/017,154, filed Jan. 31, 2011, entitled “Lightweight Solar Collector Assembly and Array”, which is assigned to the same assignee as the present application and which is hereby incorporated by reference herein. 
     BACKGROUND OF THE INVENTION 
     This invention relates generally to apertures of radiant energy (e.g. electromagnetic radiation and sound) both for collecting and emitting. The aperture of the invention is particularly adaptable to the collection of solar energy for use in heating systems, thermal to electrical conversion systems and in photovoltaic conversions systems. The aperture is also particularly well suited to relatively low cost, labor saving methods for erecting and maintaining such solar energy systems. 
     Over the years a variety of systems have been devised for the collection and utilization of solar energy. While many of these systems are quite efficient in accomplishing the objective, i.e. collecting and storing solar energy to supplement or replace more expensive systems utilizing common sources of energy, one primary problem remains, the initial cost of making and installing an efficient solar energy collecting system. If a solar energy collecting system is very expensive to make and install, such high capital expenditure is undesirable, since the potential user must wait too long to amortize this cost before realizing any savings in energy expense. 
     It is well known that solar energy may be converted into other useful forms of energy by using proper techniques. For example, solar energy may be converted into electrical energy by a so-called solar cell. The most common solar cells are made of silicon, but cells made of other materials, e.g., cadmium sulfide and gallium arsenide, have also been developed and tested. The required voltage and/or amperage may be generated using an appropriate series-parallel matrix in an integrated array. 
     At the current state of the art, a principal obstacle to wide scale adoption of solar cell energy collector installations is that manufacturing and installation costs of solar cell arrays generally are substantially higher than the cost of conventional electrical energy generating installations. Another factor limiting wide spread adoption of solar panel cells is radiant heating of the cells which reduces cell efficiency. 
     While the cost of manufacturing the solar cells per se currently is the single largest cost factor in the manufacture of a solar cell energy collector installation, any technique which increases the overall efficiency of a solar cell energy collector, or which reduces the cost of manufacturing and/or installing a solar cell energy collection system may have significant commercial importance. 
     In addition to the photoelectric conversion technique just described, it is well known that solar energy may be converted to other more useful forms of energy through thermal conversion techniques. Typically thermal conversion techniques involve using sunlight to heat up a liquid or gas contained in a thermal converter enclosure and then utilizing the heated liquid or gas in an appropriate manner well known to one skilled in the art to generate power. 
     However, as in the case of solar cells, relatively low energy collection efficiency, relatively high cost of manufacturing and relatively high installation costs have presented a principal obstacle to wide scale adoption of solar thermal energy collectors. Thus, any technique which increases the overall efficiency of a solar thermal energy collector of which reduces the cost of manufacturing and/or installing a solar thermal energy collector system may have significant commercial importance. 
     One technique the art has developed to increase efficiency of solar cells and thermal converters is to collect and focus solar energy onto the solar cells or thermal converters by means of a so-called “solar concentrator”. Thus a typical solar energy collection system may include reflective or refractive devices which are designed to collect solar energy impinging upon a relatively large area and to focus the collected energy onto a relatively small area of utilization. While the use of solar concentrators result in economic savings by increasing the effective collection area of a solar cell or thermal converter, the prior art solar concentrators themselves are costly to manufacture, and also may add appreciably to the weight of the solar energy collector system. This latter consideration is particularly important in the case of solar cell or solar thermal energy collector systems which are to be used on buildings since the heavier a solar energy collector system is, the more costly the required supporting structure. 
     SUMMARY OF THE INVENTION 
     Accordingly, a primary object of this invention is to provide a solar energy concentrator which substantially overcomes or avoids a number of the aforesaid problems encountered in the manufacture and use of solar energy collector systems according to prior art. Another object is to provide a method of making solar energy concentrators which are especially light weight, and which can be manufactured using relatively inexpensive, commercially available materials. Yet other objects of the invention are (1) to provide solar energy concentrators which may be effectively and easily employed for the collection and utilization of solar energy, (2) to provide solar energy concentrators of the type described in combination with solar cells for increasing the intensity of radiation received by such cells and also for distributing the concentration of such radiation, and (3) to provide relatively low cost, labor saving methods for erecting and maintaining solar energy collectors of the type described. Still other objects are to provide solar cell collection systems with means for cooling the solar cell, and to provide solar energy concentrators of the type described in combination with solar thermal converters. 
     An object of the present invention is to provide a method of making a solar reflector which is very economical because of the utilization of inexpensive materials. 
     Another object is to provide such a method wherein the steps for fabricating the few parts making up the assembly are simple and can be carried out inexpensively. 
     A further object of the invention is to provide such a method which involves very few steps to complete the assembly of the unit thereby reducing labor costs. 
     Another object of the invention is to provide such a method wherein the steps thereof can be carried out without utilization of expensive machinery, indeed one that can be accomplished with inexpensive standard tools. 
     Still another object is to provide an improved tracking system for a lightweight solar collector assembly and array. 
     Other objects, advantages and salient features of the present invention will become apparent from the following detailed description, which, taken in conjunction with the accompanying drawings discloses a preferred embodiment thereof. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be more fully described in connection with the annexed drawings, where like reference numerals designate like components, in which: 
         FIG. 1   a  is an end view of a solar energy collector utilizing the lightweight aperture of the invention; 
         FIG. 1   b  is a top view of the solar energy collector of  FIG. 1   a;    
         FIG. 2   a  is an end view of another embodiment a solar energy collector utilizing the lightweight aperture of the invention; 
         FIG. 2   b  is a top view of the solar energy collector of  FIG. 2   a;    
         FIG. 2   c  is a perspective or isometric view of the solar energy collector of  FIGS. 2   a  and  2   b;    
         FIG. 2   d  is a perspective view of a solar energy collector array. 
         FIG. 3   a  is a cross-section view of a vacuum-formed support rib; 
         FIG. 3   b  is a cross-section view of a high modulus support rib; 
         FIG. 4  is a cross-section view of a vacuum-formed support structure; 
         FIG. 5   a  is an end view of another embodiment a solar energy collector utilizing the lightweight aperture of the invention; 
         FIG. 5   b  is a top view of the solar energy collector of  FIG. 5   a;    
         FIG. 6   a  is an end view of another embodiment a solar energy collector utilizing the lightweight aperture of the invention; 
         FIG. 6   b  is a top view of the solar energy collector of  FIG. 6   a;    
         FIG. 7   a  is an end view of another embodiment a solar energy collector utilizing the lightweight aperture of the invention; 
         FIG. 7   b  is a top view of the solar energy collector of  FIG. 7   a;    
         FIG. 8   a  is an end view of another embodiment a solar energy collector utilizing the lightweight aperture of the invention; 
         FIG. 8   b  is a top view of the solar energy collector of  FIG. 8   a;    
         FIG. 9  is a blown-up end view of  FIG. 8 ; 
         FIG. 10   a  is a side view of a passive cooling loop of the invention; 
         FIG. 10   b  is a top view of the passive cooling loop of  FIG. 10   a;    
         FIG. 11   a  is a side view of field-replaceable module of the invention; 
         FIG. 11   b  is a side view of a second embodiment of a field-replaceable module; 
         FIG. 12   a  is a side view of a passive cooling plate of the invention; 
         FIG. 12   b  is an end view of the passive cooling plate of  FIG. 12   a;    
         FIG. 13   a  is a side view of a heat exchanger of the invention; 
         FIG. 13   b  is an end view of the heat exchanger of  FIG. 13   a;    
         FIG. 14   a  is a schematic end view of a rotation mechanism of the invention; 
         FIG. 14   b  is a schematic end view of a translation mechanism of the invention; 
         FIG. 15  is an end view of a translation mechanism capable of inverting a lightweight aperture 
         FIG. 16  shows a support frame which can be utilized with the embodiments shown in  FIGS. 2   a - 2   d;    
         FIG. 17  shows a tracking/drive system which can be utilized with the embodiments shown in  FIGS. 2   a - 2   d.    
         FIG. 18  shows an end, cross-sectional view of a portion of a drive/tracking system which can be utilized with the embodiments shown in  FIGS. 2   a - 2   d ,  16  and  17 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1   a  is an end view of a solar energy collector  101  utilizing the lightweight aperture of the invention.  FIG. 1   b  is a top view of the solar energy collector  101  of  FIG. 1   a , and can be either a complete collector or section of a longer collector. Solar energy collector  101  is an example of a concentrator. Solar energy collector  101  comprises a reflector  105  with a concentrating shape, which in this case is approximately the shape of a parabolic trough. The parabolic trough shape is a specific example of an approximately constant cross-section shape. The parabolic trough shape is a specific example of a surface with substantial curvature in only one dimension. Reflector  105  is held in place and in shape by trough  110  which is an example of a first support means for the reflector  105 . By itself, reflector  105  would not be able to maintain its shape against the force of gravity since it is very thin and hence very flexible. A preferred example of reflector  105  is a metallized (e.g. aluminum) polymer (e.g. polyester terephthalate (PET)) film with a thickness under 250 μm and more preferably with a thickness of about 50 μm. For added lifetime its is also preferred that reflector  105  also be protected by a thin topcoat of acrylic containing ultraviolet (UV) light blockers, stabilizers, or brighteners or the like as is well know in the art of sunlight stabilization of polymers. Solar energy collector  101  also comprises a receiver  115  which is an example of a receiving zone. 
     In one embodiment, Trough  110  comprises foam. Depending on the desired usage requirements there are at least two general classes of foam which can be chosen for the foam; rigid and flexible. Rigid foam can be for example Styrofoam. Styrofoam is a trademark name for polystyrene thermal insulation material, manufactured by Dow Chemical Company. Its advantage is that relatively thin structures can support both their own weight and that of the reflector  105 . The disadvantage of using Styrofoam is that it can be somewhat brittle under large impact loading. Flexible foam can be for example polyethylene foam also known as packing foam. Polyethylene foam is readily available in a thickness of about 3.2 mm which is sufficient, when laminated with one or preferable two layers of PET film, to provide a stiff mechanical support to reflector  105 . 
     In another embodiment, trough  110  comprises a vacuum-formed/blow-formed structure. Such a vacuum-formed/blow-formed structure resembles a large version of a modern soda or water bottle (or “blister” packaging) and can be fabricated by well known vacuum and or blowing techniques starting from sheet or tube thin-wall polymer (e.g. PET). 
     Trough  110 , whether a foam or a vacuum-formed/blow-formed structure, can be further stiffened and strengthened by incorporating a thin layer of metal (e.g. aluminum) by lamination. 
     Solar energy collector  101  can optionally comprise a glaze tube  120 . Optional glazed tube  120  will sometimes be desirable when collector  101  is used to collect sunlight in the converted energy form called heat. 
       FIG. 2   a  is an end view of another embodiment a solar energy collector utilizing the lightweight aperture of the invention.  FIG. 2   b  is a top view of the solar energy collector of  FIG. 2   a . The length of the collector can be relatively short as illustrated or very much longer depending on particular application needs 
     Solar energy collector  201  comprises a reflector  205  with a concentrating shape, which in this case is approximately the shape of a section of a cylindrical tube. The cylindrical shape is a specific example of an approximately constant cross-section shape. The cylindrical shape is a specific example of a surface with substantial curvature in only one dimension. Reflector  205  is held in place and in shape by window sheet  210  which is an example of a first support means for the reflector  205 . By itself, reflector  205  would not be able to maintain its shape against the force of gravity since it is very thin and hence very flexible. The window sheet  210  is sealed against the long edges (lengthwise edges) of reflector to form a substantially leak-tight cylindrical structure  230  when pressurized within by a suitable gas (such as air). 
     To form a completely sealed vessel, the short ends (lateral edges) of the cylindrical structure  230  can be simply sealed (not illustrated), or sealed by attaching to seal end  240 , a first bulkhead and seal end  250 , a second bulkhead. The bulkheads can be constructed of thick and hence rigid materials (e.g. wood, plastic, metal etc.) or of thin flexible materials. Seal end  250  can also comprise an input port  260  to enable pressurization of the interior of the vessel  270 . Seal end  240  can also comprise a fluid input  280  and seal end  250  can also comprise a fluid output  290  to provide cooling fluid to receiver  215  which is an example of a receiving zone. 
     A preferred example of reflector  205  and window sheet  210  is polymer (e.g. polyester terephthalate (PET)) film with a thickness under 250 μm. For added lifetime its is also preferred that reflector  205  and window sheet  210  also be protected by a thin topcoat of acrylic containing ultraviolet (UV) light blockers, stabilizers, or brighteners or the like as are well know in the art of sunlight stabilization of polymers. To provide light reflecting characteristics to reflector  205  a metallized (e.g. aluminum) layer should be included. Solar energy collector  201  also comprises a receiver  215  which is an example of a receiving zone. 
     Solar energy collector  201  can optionally comprise a glazed tube  220 . Glazed tube  220  will sometimes be desirable when collector  201  is used to collect sunlight in the converted energy to form heat. 
       FIG. 2   c  shows a perspective or isometric view of the solar energy collector assembly  201 , which in one embodiment comprises a sealed and inflated cylindrical-tube shaped housing  201 . As shown in  FIG. 2   c , the solar collector assembly  201  comprises a sealed and inflated cylindrical-tube shaped housing. The tube housing includes a bottom cylindrically-trough shaped reflector portion having a reflection surface extending along a longitudinal length. The reflection surface preferably is made of a relatively thin and flexible metalized polymer film. 
     The assembly  201  further includes a top cylindrically-shaped transparent polymer film sheet portion made of a relatively thin and flexible polymer film. The top and bottom sheet portions form a pressure sealed cylindrical tube housing when the respective ends of the top and bottom films are sealed together and the tube housing is inflated with a gas via valve  230  so that the top transparent film portion passes solar energy to the reflection surface. The collector assembly shown in  FIG. 2   c  further includes a receiver tube disposed longitudinally above the reflection surface in a focal line or focal plane of the cylindrical-trough shaped reflector portion. The absorber tube extends along the longitudinal length of the reflection surface, and contains a heat transfer fluid for absorbing solar energy reflected from the reflection surface to the focal line or focal plane. 
     One embodiment of making the reflector tube of the instant invention is to start from thin polymer material that is produced in tubular form, rather than flat sheet or film form. It is well known in the art of plastics processing that tubular films can be produced, for example, by blowing a bubble in molten polymer in a process known as blown film extrusion. 
       FIG. 2   d  is a perspective view of a solar energy collector array, in which four solar collector assemblies  201  are combined in an array configuration. The solar collector array shown in  FIG. 2   d  is supported by support frame  240  and can be moved by a suitable drive/tracking system  250 . Further details of the support frame are described in conjunction with  FIG. 16 , and further details of the drive/tracking system are described in conjunction with the  FIG. 17 . The array configuration shown in  FIG. 2   d  is suitable for mounting on a support structure, such as the roof of a building, a ground surface open area, or the like. Optional restraint line  231  is shown attached at two points of support frame  240 . The restraint line  231  can be used to ensure that collector assemblies  201  remain located atop support frame  240  even in the presence of strong winds. The restraint line  231  is preferably made of lightweight yet strong material (e.g. nylon rope or steel cable). 
       FIG. 3   a  is a cross-section view of a vacuum-formed support rib  301  which can be used to stiffen or strengthen (or both) the support means of the lightweight aperture of the invention (e.g. the solar collectors of  FIG. 1  and  FIG. 2 ). Such a vacuum-formed structure resembles a large version of a modern soda or water bottle (or “blister” packaging) and can be fabricated by well known vacuum and or blowing techniques starting from sheet or tube thin-wall polymer (e.g. PET). 
       FIG. 3   b  is a cross-section view of a high modulus support rib system  311  which can be used to stiffen or strengthen (or both) the support means of the lightweight aperture of the invention (e.g. the solar collectors of  FIG. 1  and  FIG. 2 ). High modulus support rib system  311  comprises a high modulus support rib  320 . If viewed from end on (not illustrated), the high modulus support rib  320  would look like a semi-circle or a parabola. Also show in  FIG. 3   b  is a vacuum-formed holder  325 . The illustrated arrow shows that high modulus support rib  320  is installed by sliding into the folds of the vacuum-formed holder  325 . The function performed by vacuum-formed holder  325  is to position the high modulus support rib  320  on the surface of the support means (e.g. on trough  110  of  FIG. 1 ) and resist forces which might otherwise tend to twist high modulus support rib  320  relative to the support means (which would otherwise defeat the reinforcing provided by high modulus support rib  320 ). 
       FIG. 4  is a cross-section view of a vacuum-formed support structure. The undulating shape generates a large amount of stiffness from a lightweight single part construction. 
       FIG. 5   a  is an end view of another embodiment a solar energy concentrator  501  utilizing the lightweight aperture of the invention.  FIG. 5   b  is a top view a single section of the solar energy concentrator  501  of  FIG. 5   a . Solar energy concentrator  501  is an example where the first support means comprises a super-atmospheric structure  510  and a sub-atmospheric pressure structure  520 . Solar energy concentrator  501  also comprises a reflector  505 . The layers are polymeric sheet as described earlier for the solar collectors of  FIG. 1  and  FIG. 2 . 
       FIG. 6   a  is an end view of another embodiment a solar energy concentrator  601  utilizing the lightweight aperture of the invention.  FIG. 6   b  is a top view a single section of the solar energy concentrator  601  of  FIG. 6   a . Solar energy concentrator  601  is an example where the first support means comprises a super-atmospheric structure  610  and a sub-atmospheric pressure structure  620 . Solar energy concentrator  601  also comprises a reflector  605 . The layers are polymeric sheets as described earlier for the solar collectors of  FIG. 1  and  FIG. 2 . It can be seen that the double tube version of super-atmospheric structure  610  enable  FIG. 6  to make more effective use of both film area and real estate regarding collector area. In other words, less film and real estate are needed per unit effective collector area in the design of  FIG. 6  than in the design of  FIG. 5 . 
     Referring back to  FIG. 1 , an example of a second means of support (i.e. second support means) is shown schematically as self-supporting means  130 . The self-supporting means  130  can be provided in a variety of manners. Examples of self-supporting means include a simple thick plate, a wheel with hub and spokes, an inflatable doughnut, a foam doughnut and a vacuum-formed doughnut. Additional examples of self-supporting means include foldable (or collapsible or inflatable) legs which attach to the receiver. The legs themselves are rigid enough to support both their own weight and in addition the weight of the receiver. The leg ends opposite to the attachment to the receiver can either attach to the first support means or simply touch the first support means. 
     Alternatively, a second example of a means of support can be provided by non-self-supporting means, in other words by tension members.  FIG. 2  illustrates tension members  212 ,  214 , and  216 , which may optionally additionally comprise means for tension adjustment, such as turn-buckles. Examples of tension members include strings, wires, cords, threads, filaments, ropes, chains and so on. For applications where the receiving zone may experience highly elevated temperatures, fiber glass filaments or rope may be preferred. Fiber glass is reasonably strong, has low thermal conductivity and reasonably affordable. Tension members can also contain more than one material. In other words two different strings could be attached (e.g. tied) to each other to make a 2-part tension member. For example fiber glass can be used in a potentially high temperature region near the receiver zone, while a polymer twine (e.g. nylon or polypropylene) could be used in a lower temperature zone near the first means of support. 
       FIG. 7   a  is an end view of another embodiment a solar energy collector utilizing the lightweight aperture of the invention.  FIG. 7   b  is a top view of the solar energy collector of  FIG. 7   a . The length of the collector can be relatively short as illustrated or very much longer depending on particular application needs. 
     Solar energy collector  701  comprises a plurality of water tubes  702 . The water tubes  702  form an example of a localization means. A localization means keeps the collector  701  in a relatively constrained location in spite of environmental forces such a strong winds or heavy precipitation. A localization means can also tend to maintain the collector  701  in a specific orientation. For example for an east-west aligned collector  701 , a localization means could be used to maintain a certain pointing angle relative to zenith for the collector  701  in spite of a strong wind. The water tube  702  can perform the localization function by having at least one tube filled at least partially with water. The weight of water tends to hold the collector  701  in place. By properly adjusting the filling of the water tubes with water and air, one can orient the pointing angle of the collector  701  relative to zenith. 
     The water tubes  702  can also form an example of a tracking means. A tracking means is capable of tracking the collector  701  to maintain an alignment with respect to the sun location whether on a seasonal basis or more preferably on a diurnal basis. With solar collector  701  aligned in a north-south orientation, it is possible to use the water tubes  702  to rotate the collector  701  throughout each day to track the sun. This tracking is accomplished by sequentially filling with water at least one, but preferably two or more tubes amongst the water tubes  702  with coordinated timing to match the movement of the sun across the sky. 
     The water tubes  702  can also participate in a stowage maneuver for the collector  701 . Such stowage is highly desirable to survive a high wind situation (say above 50 kph). To accomplish such stowage one can substantially fill many of the tubes amongst the water tubes  702  with water while simultaneously partially deflating the collector  701 . When this maneuver is performed, the collector  701  will assume a very much flattened appearing profile with corresponding low aerodynamic drag coefficient and foreshortened height. The combination of these two factors can reduce the drag per unit length of the collector  701  by about an order of magnitude and hence very substantially improve the collector&#39;s probability of surviving an extraordinarily high wind event. 
     The remainder of the description of the collector  701  is a repeat of the description of for collector  201  stated earlier. Solar energy collector  701  also comprises a reflector  705  with a concentrating shape, which in this case is approximately the shape of a section of a cylindrical tube. The cylindrical shape is a specific example of an approximately constant cross-section shape. The cylindrical shape is a specific example of a surface with substantial curvature in only one dimension. Reflector  705  is held in place and in shape by window sheet  710  which is an example of a first support means for the reflector  705 . By itself, reflector  705  would not be able to maintain its shape against the force of gravity since it is very thin and hence very flexible. The window sheet  710  is sealed against the long edges of reflector to form a substantially leak-tight cylindrical structure  730  when pressurize within. To form a completely sealed vessel, the short ends of the cylindrical structure  730  can be simply sealed (not illustrated), or preferably sealed by attaching to seal ends  740  and  750 . Seal end  750  also comprises an input port  760  to enable pressurization of the interior of the vessel  770 . 
     A preferred example of reflector  705  and window sheet  710  is polymer (e.g. polyester terephthalate (PET)) film with a thickness under 750 μm. For added lifetime its is also preferred that reflector  705  and window sheet  710  also be protected by a thin topcoat of acrylic containing ultraviolet (UV) light blocker, stabilizer, or brighteners or the like as is well know in the art of sunlight stabilization of polymers. To provide light reflecting characteristics to reflector  705  a metallized (e.g. aluminum) layer should be included. Solar energy collector  701  also comprises a receiver  715  which is an example of a receiving zone. 
     Solar energy collector  701  can optionally comprise a glaze tube  720 . Optional glazed tube  720  will sometimes be desirable when collector  701  is used to collect sunlight in the form of heat. 
       FIG. 8   a  is an end view of a solar energy collector  801  utilizing the lightweight aperture of the invention.  FIG. 8   b  is a top view of the solar energy collector  801  of  FIG. 8   a , and can be either a complete collector or section of a longer collector. The collector  801  is similar to collector  101  described above, but additionally comprises a secondary reflector  820 , an example of a receiving zone. 
     The collector  801  comprises trough  810 , and tension members  812 ,  814 ,  816  and  818 , which locate secondary reflector  820  relative to the trough  810 . Due to the addition of the secondary reflector  820 , a backplane zone  815  may be included and located, in this example, near the bottom of the trough  810 . In this example, second means of support for the receive zone  815  can be any sort of attachment method to the trough  810  such a fasteners, tape, bolts etc. As for the method of locating the secondary reflector  820  it is clear that other methods can be employed including a simple thick plate, a wheel with hub and spokes, an inflatable doughnut, a foam doughnut a vacuum-formed doughnut and so on. Solar energy collector  801  can optionally comprise a glaze tube (not illustrated) which may be desirable for thermal collection, but will generally not be desirable to photovoltaic-only systems. 
     Backplane zone  815  may optionally comprised a photovoltaic module (not illustrated) and passive cooling system which is better seen by referring to  FIG. 9 . 
       FIG. 9  is a blown-up end view of  FIG. 8 . Collector  801  may optionally comprise a passive cooling system  860  shown in this example in the shape of a wall approximately following the shape of trough  810 . The passive cooling system  860  can simply be a solid metal (e.g. aluminum) wall, or more preferably a partially hollowed wall, a specific example of which is illustrated in  FIG. 10 . 
       FIG. 10   a  is a side view of a passive cooling loop  1001  of the invention.  FIG. 10   b  is a top view of the passive cooling loop  1001  of  FIG. 10   a . A cooling loop cell  1007  is shown in  FIG. 10   a  and within the dashed box in  FIG. 10   b  which represents a portion of the passive cooling system  860  referred to in  FIG. 9 . The cooling loop cell  1007  is substantially filled with a heat transfer fluid, for example water. Heat enters the cooling loop cell  1007  at the bottom of  FIG. 10   a  and through an inner wall  1020  of  FIG. 10   b . Since heated fluid typically expands becoming lighter, it thereafter rises as indicated by the block arrows on the left side of  FIG. 10   a  and by the circle-dot symbols of  FIG. 10   b . Upon reaching the top of the cell  1007 , the fluid cools becoming denser and travels downward as indicated by the block arrows on the right side of  FIG. 10   a  and by the circle-X symbol of  FIG. 10   b . The fluid also cools as it travels downward by transferring heat through outer wall  1030 . Examination of fluidynamic flow equations shows that for flow channels that are of the order of 2 mm thick or thicker, significant water flow and hence significant heat transfer can be supported using this approach. 
     Wall blocks  1040  and  1050  can be made from, for example, foamed insulating polymers (e.g. Styrofoam, polyethylene, or polypropylene foam). The inner wall  1020  and the outer wall  1030  can be made from, for example, metal (e.g. aluminum) foil with a thickness as small as the order of 10 μm to 50 μm. Metal wall material will enhance the lateral transfer of heat as well as the through wall transfer. Optionally, the inner wall  1020  and the outer wall  1030  can each comprise a thin polymer layer (e.g. PET) to provide toughness to the walls. Alternatively, inner wall  1020  and the outer wall  1030  can each simply comprise polymer film (e.g. PET) with a thickness as small as the order of 50 μm. 
       FIG. 11   a  is a side view of a field-replaceable module  1101  of the invention. Receiving zones as described above (whether including a secondary reflector or not) can comprise a photovoltaic unit. Furthermore a photovoltaic unit can comprise a field-replaceable unit as exemplified by the field-replaceable module  1101 . The field-replaceable module  1101  comprises solar cell layer  1110 , a splitable heat transfer layer  1120 , a highly thermally conductive (e.g. metal) layer  1130 , and a heat removal layer  1140  (which may be either actively or passively cooled). An example of a splitable heat layer is a layer of viscous heat transfer liquid. A second example of a splitable heat layer is a split block of metal wherein the inner surfaces of the two sides of the split block have very closely matched contours which enable high heat transfer when the surfaces are put in contact. A third example of a splitable layer is a solid but pliant (via either elastic or inelastic deformation) layer. 
       FIG. 11   b  is a side view of a second embodiment of a field-replaceable module  1102 . The field-replaceable module  1101  comprises solar cell layer  1150  bonded directly to a highly thermally conductive (e.g. metal) upper layer  1160 , a splitable heat transfer layer  1170 , a highly thermally conductive (e.g. metal) lower layer  1180 , and a heat removal layer  1190  (which may be either actively or passively cooled). 
       FIG. 12   a  is a side view of a passive cooling plate  1201  of the invention.  FIG. 12   b  is an end view of the passive cooling plate  1201  of  FIG. 12   a . The passive cooling plate  1201  comprises a plurality of fluid-filled fins  1210 , a highly thermally conductive (e.g. metal) layer  1220 , and a photovoltaic cell containing layer  1230 . Each fluid-filled fin amongst the plurality of fluid-filled fins  1210  comprises a thin-layer shell (of thickness roughly 50 μm to 250 μm) comprising either a polymer layer (e.g. PET) or a metal layer (e.g. aluminum foil) or both in a laminated combination. The thin-layer shell can optionally comprise additional polymer layers (e.g. polypropylene) which aid in the melt-sealing assembly of the fluid-filled fins  1210 . 
     Still other optional layers may include, for example a protective acrylic topcoat of containing ultraviolet (UV) light blockers, stabilizers, or brighteners or the like as is well know in the art of sunlight stabilization of polymers. Yet an addition outer layer can comprise a selective emitter (i.e. a “white” appearing surface which substantially reflects sunlight, but is a good emitter of infrared heat radiation). The fluid which fills the fins  1210  should have high specific heat capacity, good thermal conductivity and reasonably low viscosity. A preferred fluid is water due too its good heat transfer properties, safe nature and extremely low cost. 
     Examination of fluidynamic flow equations shows that for fluid-filled fins  1210 , with at least partially hollow cross-sections on the order of 2 mm thick or thicker, significant water flow and hence significant heat transfer can be supported by natural convection in a manner similar to that described earlier for a passive cooling loop. In this example as well as the prior example, it is not necessary to drive the flow around a particular circuit, but rather, the natural convection process can establish its own natural convective cells. This will occur simply by virtue of the fact that heat will be applied to the lower portion of passive cooling plate  1201  and heat will be removed by natural convection in the air between the fins  1210  (and similarly so in the prior example). 
       FIG. 13   a  is a side view of a heat exchanger  1301  of the invention.  FIG. 13   b  is an end view of the heat exchanger  1301  of  FIG. 13   a . The passive cooling plate  1301  comprises a plurality of highly thermally conductive (e.g. metal) fins  1310 , a highly thermally conductive (e.g. metal) layer  1320 , and a photovoltaic cell containing layer  1330 . 
     Examination of aerodynamic flow equations shows that for fins  1310  that contain air separations on the order of 2 mm thick or thicker, significant air flow and hence significant heat transfer can be supported by natural convection. This will occur simply by virtue of the fact that heat will be applied to the lower portion of passive cooling plate  1301  and heat will be removed by natural convection in the air between the fins  1310 . 
       FIG. 14   a  is a schematic end view of a rotation mechanism  1401  of the invention. The rotation mechanism  1401  comprises an axis of rotation  1410  driven, for example by an electric motor (not illustrated) via a gear reduction box (also not illustrated). The point of  FIG. 14   a  is to show that if large rotation angles need to be accommodated (as is typically required to track the sun throughout a day) then the axis of rotation  1410  must necessarily be a substantial distance above the mounting plane  1420  (which can be the surface of the earth or some suitable platform including a mobile platform). Examples of the need for such large angles include pointing to the east for collecting sunlight during early morning, pointing to the west for collecting sunlight during the late afternoon and completely inverting the collector  1430  to protect it during hail or high wind events. The rotation mechanism  1401  will be preferred for systems which include thermal collection (both thermal only systems and photovoltaic/thermal combination systems) since this approach makes for a simple way of running a fluid line through the collector. 
       FIG. 14   b  is a schematic end view of a translation mechanism  1402  of the invention. The translation mechanism  1402  comprises a drive mechanism  1450  shown schematically in  FIG. 14   b . The point of  FIG. 14   b  is to show that if large rotation angles need to be accommodated, then the drive mechanism  1450  may be a relatively short distance above the mounting plane  1420 . The utility of this approach is mounting hardware (not illustrated) for the drive mechanism  1450  can be much shorter than the mounting hardware for rotation mechanism  1401  of  FIG. 14   a . To better understand the translation mechanism  1402  the next figure expands on a detailed example. 
       FIG. 15  is an end view of an example of a translation mechanism  1501  for a lightweight aperture. The translation mechanism  1501  comprises a mount  1505 , a motor-driven pulley  1510  (e.g. drive gear), a first corresponding pinch pulley  1515 , an idler pulley  1520  and a second corresponding pinch pulley  1525 . Taken together; the motor-driven pulley  1510  (e.g. drive gear), the first corresponding pinch pulley  1515 , the idler pulley  1520  and the second corresponding pinch pulley  1525  correspond to an example of a means of rotation. Note that this means of rotation is also connected to a trough track  1527 , which in this case is an example of at least a portion of a first support means. Also note that the mount  1505  is attached to a platform  1530 . Examples of the platform  1530  can include a surface of the earth, a building, a structure, a vehicle, a water-going vessel, or even an airborne or space borne craft among others. 
     The mechanism as described so far works by translating the trough track  1527  when the motor-driven pulley  1510  is rotated. Since the trough track  1527  is curved, when it is moved through the translation mechanism  1501 , the orientation of the trough track  1527  is thereby rotated. Thus tracking of a solar collector or more generally an aperture can be accomplished. The idler pulley  1520  and the second corresponding pinch pulley  1525  serve to “lock” in (i.e. stiffen against rotation by environmental forces, e.g. wind) the entire system. 
     By adding another level of sophistication, this mechanism can be made capable of inverting the solar collector. To do this the idler pulley  1520  and the second corresponding pinch pulley  1525  are now mounted so that they may be either fixed (relative to the location of the motor-driven pulley  1510  and the first corresponding pinch pulley  1515 ) or selectively translated. What is meant by selectively translated is that relative motion can be accommodated upon “selection”. This relative motion is necessary to enable the trough track  1527  to be driven “around the relatively sharp corner” that can be seen in the upper left and upper right portions in  FIG. 15 . So when translating the trough track  1527  nears the sharp corners, this flexibility can be “selected.” By contrast, when it is desired is to rotate the system (rather than invert it), this flexibility can be “un-selected.” 
       FIG. 16  shows a support frame  1601  which can be utilized with the embodiments shown in  FIGS. 2   a - 2   d . Frame  1601 , is preferable built up from rigid elongated members  1605 ,  1610 ,  1615 ,  1620 ,  1625 ,  1630 ,  1635 ,  1640 ,  1645 ,  1650 ,  1655 ,  1660 , and  1665 . Rigid elongated members  1605 ,  1610 ,  1615 ,  1620 ,  1625  form a first end frame  1626  which supports a solar tracking drive system illustrated and later detailed in  FIG. 17 . Furthermore, first end frame  1626  provides mechanical support against gravity, wind and other environmental loads for optical reflecting units on a first end. Similarly, rigid elongated members  1635 ,  1640 ,  1645 ,  1650 , and  1655  form a second end frame  1656 , which supports the optical reflecting units on their opposite end. Rigid elongated members  1660 , and  1665  serve to maintain proper spacing between (and vertical support for) first end frame  1626  and second end frame  1656 . Additional structural integrity and rigidity can be provided by rigid elongated members  1670  and  1675 . Elongated members can take many forms though tubular (e.g. cylindrical) will be suitable in many cases. Another form for elongated member that will generally suitable is extruded angle (e.g. “angle iron”). 
     Elongated members have been successfully built and tested which in one example are made of plastic (e.g. ABS plastic, or more specifically water drainage pipe nominal 2″ diameter). In such a construction example, joints between elongated members are provided by water drainage pipe joints and assemblies are fastened together with cement as is common in the plumbing art. Elongated members have also been successfully built and tested which are made of metal (e.g. steel, or more specifically EMT electrical conduit nominal ½″ diameter). 
       FIG. 17  shows a tracking/drive system  1701  which can be utilized with the embodiments shown in  FIGS. 2   a - 2   d . Tracking/drive system  1701  uses cable loop  1705  to couple the driving force of linear actuator  1710  to rotate one or more rims exemplified by rims  1715 ,  1720 ,  1725  and  1730 . Cable loop  1705  can couple to rims in wide variety of circuit configurations, but  FIG. 17  shows a preferred circuit. It can be seen that the cable wraps around each of the rims  1715 ,  1720 ,  1725  and  1730  in turn. This full loop of wrapping around each rim (as opposed to simply wrapping around a small fraction of the circumference of each rim) ensures a tight and self-cinching grip which results in a high level of friction and thereby minimizes, if not completely eliminates, slip between the driving cable and the rotating rims. 
     To properly manage the motion of the cable, the cable loop  1705  is wrapped around of a set of pulleys  1735 ,  1740 ,  1745 ,  1750 , and  1755  which are affixed to a frame (not shown in this figure). The rims  1715 ,  1720 ,  1725  and  1730  are preferably located at the ends of collector tubes (not shown in this figure) and more preferable a north end (assuming that the collectors tubes are oriented along a north-south axis and the system is in the northern hemisphere on the Earth), though they may also be located midway along such collector tubes (or any other location along the collector tubes for that matter). 
     There are two main reasons for preferring an end location for the rims  1715 ,  1720 ,  1725  and  1730 . The first reason is that an end location gives easy access for maintenance of all of the parts of the tracking/drive system. The second reason is that locating the rims at the north end minimizes shadows cast by the rims (assuming that the collector&#39;s tubes are oriented along a north-south axis and the system is in the northern hemisphere on the Earth). In some situations, a central location for the rims along the collector tubes may be preferred. This preference would correspond to systems which have very long collector tubes and would be chosen to optimize the transfer of torque along the very long collector tubes. 
     Cable loop  1705  is attached to a movement arm  1760  of linear actuator  1710 , for example by a nut and bolt (not illustrated). Linear actuator  1710  is also affixed to a frame (not shown in this figure) and can be any linear actuator as is commonly available in the solar tracking industry. Linear actuator  1710  is preferably affixed to an upper portion or top of a frame to ease maintenance and to avoid being submerged when heavy rains might flood where the tracking/drive system  1701  is located. A turnbuckle (not shown) could be utilized to provide tightening of the cable loop  1705  by suitable adjustment. 
     To assure that the forces applied to the rims result in essentially pure rotation (i.e. with no significant translation), the rims  1715 ,  1720 ,  1725  and  1730  are supported and translationally constrained by casters  1762 ,  1763 ,  1764 ,  1765 ,  1766 ,  1767 ,  1768 ,  1769 ,  1772 ,  1773 ,  1774 ,  1775 ,  1776 ,  1777 ,  1778  and  1779 . The rims are preferably shaped like typical bicycle rims and can actually be bicycle rims. The casters preferably have wheels that are narrow enough to fit within the circumferential trough of the rims (i.e. the circumferential region around bicycle rims where bicycle tires are normally gripped by the rims). 
       FIG. 18  shows details of a tracking/drive system and more particularly,  FIG. 18  shows an end, cross-sectional view of a portion of a drive/tracking system which can be utilized with the embodiments shown in  FIGS. 2   a - 2   d ,  16  and  17 . 
     In  FIG. 18 , a rim  1815  is supported on rollers  1820  and  1830 . The rim  1815  is in contact with the sealed and inflated cylindrical tube housing  1808 . The rollers  1820  and  1830  are parts of a first set of casters  1825  and  1835  respectively and supported by axels  1822  and  1832  respectively. Note that cable loop  1805  wraps around the rim  1815  and under both axels  1822  and  1832 . This preferred routing of the cable loop  1805  ensures that rim  1815  will remain located (held down) during a high wind gust. The first set of casters  1825 ,  1835  are affixed to the top portion of elongated support member  1803 . A second set of casters (not shown in  FIG. 18 ) could be affixed at the top of rim  1815  with another elongated support member (not shown) to provide still further support. It should be understood that the cable loop  1805  is completely wrapped around the rim  1815  to provide a gripping action, which enables controlled rotation of the rim  1815  (and the cylindrical housing  1808 ), thereby minimizing or eliminating translational movement. 
     Other embodiments of the present invention for solar collectors could be for when a single collector housing is utilized, or for when two tracking systems are desired for both ends of, for example, a solar collector array where the sealed and inflated cylindrical tube housings each have an extended horizontal length. Other embodiments of the present invention for tracking can apply to solar collectors of a broad range of configurations and are not restricted to those comprising sealed and inflated cylindrical tube housings. 
     While the invention has been described in terms of a collector of solar energy for both thermal and photovoltaic (and combination) energy systems, it is important to explicitly state that this lightweight aperture can be used for other systems as well. One such system is radio frequency technology where the aperture can be used for transmission, or reception or both. The radio frequency band of primary interest extends from a few tens of MHz up to several hundred GHZ. This range can even extend through the THz bands for either short range (e.g. radar) applications within the earth&#39;s atmosphere or to long range application in outer space. 
     The aperture of the invention need not be restricted to electromagnetic radiation. With suitable wall materials (to assure good reflectivity) the aperture can be used for acoustic applications. Examples would include sensitive listening systems in the air and a multitude of underwater sound-based devices. 
     Once given the above disclosure, therefore, various other modifications, features or improvements will become apparent to the skilled artisan. Such other features, modifications, and improvements are thus considered a part of this invention, the scope of which is to be determined by the following claims.