Abstract:
Described herein are solar energy apparatus that overcome many of the disadvantages and shortcomings of conventional solar energy absorption structures. The solar energy apparatus may comprise inexpensive material and have smaller dimensions to reduce the overall cost of the apparatus. The apparatus may also have coatings which help to maximize the amount of solar energy absorbed and minimize the deterioration of the apparatus due to overheating. The apparatus may include a system for monitoring and controlling the temperature of the apparatus to prevent overheating.

Description:
[0001]    This application claims the benefit of priority to U.S. Provisional Application No. 60/901,063, filed Feb. 12, 2007, the entirety of which is incorporated by reference. 
     
    
     BACKGROUND 
       [0002]    Solar energy absorption structures or panels for absorbing solar energy are known in the art. Such conventional solar energy absorption structures typically include a body or frame and an energy absorption fluid flowing through the body. Many of these conventional solar energy absorption structures have various shortcomings. 
         [0003]    For example, conventional solar energy absorption structures are typically made of materials—such as optical glass, aluminum, or copper—which can result in structures that are often difficult to install, heavy and costly to manufacture. 
         [0004]    Further, many of the components of conventional solar panels have solid black absorbing surfaces that can often overheat, thereby resulting in extreme stress on the solar panels. More specifically, when exposed to the sun, a conventional solar panel can heat up to between 300° F. and 400° F. if energy absorption fluid has been drained from the panel, or if energy absorption fluid is not being continuously pumped through the panel, e.g., during fluid stagnation periods. In order to prevent damage to or extreme stress on the panels, conventional solar panels must be made of materials that are able to resist such high temperatures. Such materials are typically expensive. 
         [0005]    Another known shortcoming of conventional solar energy absorption structures is that energy absorption fluid has a propensity to overheat when exposed to sunlight during fluid stagnation periods. Also, in some climates, such as Northern climates, antifreeze is added to the energy absorption fluid to prevent damage. However, during fluid stagnation periods, the antifreeze can be heated to levels that can ruin or degrade the antifreeze. In the event the antifreeze becomes degraded, the fluid can become acidic and dissolve the components of the absorber and other parts of the system and piping, thereby requiring maintenance. Moreover, damage to a fluid can be difficult to detect unless checked by a professional. Accordingly, if the fluid is not checked regularly, just one instance of the fluid overheating can permanently damage the system. 
         [0006]    Another known shortcoming of conventional solar energy absorption structures is that many such structures cannot produce uniform heat transfer at low cost. 
       SUMMARY 
       [0007]    Described herein are various embodiments of solar energy apparatus that overcome many of the disadvantages and shortcomings of conventional solar energy absorption structures. 
         [0008]    In certain embodiments of the invention described herein, solar energy absorbers that may comprise transparent plastic material are disclosed. The dimensions of the solar energy absorbers may be minimized so as to reduce the amount of energy absorption fluid, such as black fluid, flowing through the solar energy absorber. Reflective coatings, selective coatings for improved absorption and reflectors may also be included in the solar energy absorbers. 
         [0009]    In other embodiments of the invention described herein, headers for solar energy absorbers that may comprise transparent plastic materials and reflective coatings are disclosed. 
         [0010]    In other embodiments of the invention described herein, housings for absorbers that may comprise foam or transparent plastic materials are disclosed. The housings may also include reflective coatings. The housings may also include elements for holding an absorber in position. 
         [0011]    In still other embodiments of the invention described herein, combined absorber and absorber housings are disclosed. The combined absorber and absorber housings may comprise transparent plastic material or foam. 
         [0012]    In yet another embodiment of the invention described herein, a solar absorptive fluid circulation system is disclosed. The solar absorptive fluid circulation system may include a monitoring system for monitoring the temperature of the system and valves that may be opened to drain the system of black fluid should the system exceed a predetermined temperature. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    Embodiments of the present disclosure are shown in the accompanying drawings. 
           [0014]      FIG. 1  is a perspective view of an absorber of a solar energy apparatus. 
           [0015]      FIG. 2  is a perspective view of an absorber of a solar energy apparatus. 
           [0016]      FIG. 3  is a bottom end view of an absorber of a solar energy apparatus. 
           [0017]      FIG. 3A  is a bottom end view of an absorber according to one embodiment. 
           [0018]      FIG. 3B  is a bottom end view of an absorber according to another embodiment. 
           [0019]      FIG. 3C  is a bottom end view of an absorber according to yet another embodiment. 
           [0020]      FIG. 4  is an end view of a center conductor of a solar energy apparatus according to one embodiment. 
           [0021]      FIG. 5  is an end view of the center conductor illustrated in  FIG. 4  but shown with energy absorption fluid flowing there through. 
           [0022]      FIG. 6  is a side view blowup of a section of an absorber portion of the of a coaxial solar energy apparatus. 
           [0023]      FIG. 7  is an end view blowup of a section of an absorber portion of the of a coaxial solar energy apparatus. 
           [0024]      FIG. 8  is an end view blowup of possible center conductor configurations in an absorber portion of a coaxial solar energy apparatus. 
           [0025]      FIG. 9  is an end view of possible reflector shapes in an absorber portion of a coaxial solar energy apparatus. 
           [0026]      FIG. 10  is the side view of an absorber portion of a coaxial solar energy apparatus. 
           [0027]      FIG. 11  is a blowup of the side view of the absorber portion of the coaxial solar energy apparatus. 
           [0028]      FIG. 12  is a three dimensional view of a coaxial solar energy apparatus. 
           [0029]      FIG. 13  is a side view of a coaxial solar energy apparatus with headers attached. 
           [0030]      FIG. 14  is a partial side view of a absorber of a solar energy apparatus shown with a header. 
           [0031]      FIG. 16  is a cross-sectional end view of a solar energy apparatus. 
           [0032]      FIG. 17  is a detailed view of the area inside the circle labeled Detail  17 - 17  in  FIG. 16 . 
           [0033]      FIG. 18  is an exploded perspective view of a solar energy apparatus according to one embodiment. 
           [0034]      FIG. 19  is an end view of the solar energy apparatus of  FIG. 18  shown with an end cap removed. 
           [0035]      FIG. 20  is a partial end view of the solar energy apparatus of  FIG. 18  shown with the end cap and a header removed. 
           [0036]      FIG. 21  is a 3D view of an absorber assembly. 
           [0037]      FIG. 21A  is an end view of an absorber portion of a solar energy apparatus. 
           [0038]      FIG. 22  is an end view of the shell portion of a solar energy apparatus. 
           [0039]      FIG. 23  is an end view blow up of a solar energy apparatus. 
           [0040]      FIG. 24  is an end view of a solar energy apparatus with end caps removed. 
           [0041]      FIG. 25  is a 3D view of the track and flexible beam. 
           [0042]      FIG. 26  is a top view of a solar energy apparatus. 
           [0043]      FIG. 27  is a side view of a solar energy apparatus. 
           [0044]      FIG. 28  is a three dimensional view of a solar energy apparatus. 
           [0045]      FIG. 29  is a perspective view of a solar energy apparatus having a top to bottom fluid flow according to one embodiment. 
           [0046]      FIG. 30  is a top view of the solar energy apparatus of  FIG. 29 . 
           [0047]      FIG. 31  is an end view of the solar energy apparatus of  FIG. 29  shown with an end wall removed. 
           [0048]      FIG. 32  is a cross-sectional side view (without headers) of the solar energy apparatus as shown in  FIG. 33  taken along the line  32 - 32  in  FIG. 33 . 
           [0049]      FIG. 33  is a perspective view of the solar energy apparatus of  FIG. 29  shown with energy absorption fluid in the absorber. 
           [0050]      FIG. 34  is an end view of an embodiment of a solar energy apparatus having a plurality of vacuum chambers. 
           [0051]      FIG. 35  is an exploded perspective view and an assembled perspective view of a modular solar energy apparatus according to one embodiment. 
           [0052]      FIG. 36  is an exploded side view and an assembled side view of the modular solar energy apparatus of  FIG. 34 . 
           [0053]      FIG. 37  is an exploded end view and an assembled end view of the modular solar energy apparatus of  FIG. 34 . 
           [0054]      FIG. 38  is a top plan view of the modular solar energy apparatus of  FIG. 34 . 
           [0055]      FIG. 39  is a perspective view of a plurality of modular solar energy apparatus coupled together. 
           [0056]      FIG. 40  is a perspective view of a solar energy apparatus according to one embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0057]    Described herein are embodiments of solar energy apparatus for collecting and distributing solar energy. The solar energy apparatus include a solar collector system through which a solar absorptive heat transfer fluid, such as black fluid, is allowed to flow. The solar energy collector system may include a solar energy collection portion and a solar energy transfer portion. As the solar absorption fluid flows through the solar energy collection portion, it contacts sun light and collects solar energy. The solar absorption fluid then flows through the solar energy transfer portion where the solar energy collected in the solar absorption fluid is utilized immediately or is transferred to a thermal energy storage system, such as a water heating or building heating system, via a thermal exchange element or a heat collection storage container. Continuing from the thermal energy transfer portion, the absorptive fluid returns to and again flows through the solar energy collection portion to restart the solar energy collection and distribution process in a closed loop. Accordingly, the solar energy apparatus provides continuous collection and distribution of solar energy. 
         [0058]    With reference to  FIG. 1 , an absorber  20  for collecting solar energy is illustrated. The absorber  20  includes a generally rectangular shaped front panel  22  spaced apart from and extending parallel to a corresponding generally rectangular shaped rear panel  24 . The front panel  22  and rear panel  24  are coupled to each other along their respective sides  26 ,  28  by edge members  30 . In a specific embodiment of the absorber, a light reflective layer  44  may be formed under the rear panel  24 . The absorber  20  has an overall length A. 
         [0059]    The absorber  20  also includes a bottom header  60  at the bottom end  38  of the absorber  20  having an open end  70  and a closed end  72  and a top header  62  at the top end  42  of the absorber  20  having an open end  70  and a closed end  72 . Closed ends  72  may be open if there are a plurality of absorbers  20  placed in series or in parallel so that fluid may flow between absorbers. Also, the closed end  72  of the top header  62  and the closed end  72  of the bottom header  60  do not need to be on the same side of the absorber. The closed ends  72  may be on opposite sides of the absorber so that flow goes in one side of the bottom header  60  and out the opposite side of the top header  62 , which creates more uniform fluid flow. 
         [0060]    The bottom header  60  and top header  62  are in fluid communication with the space between the front panel  22  and rear panel  24 . The bottom header  60  may include a fluid valve  113  and the top header may include an air valve  115 . 
         [0061]    In operation, energy absorptive fluid, such as black fluid, is flowed into the open end  70  of the bottom header  60 . The bottom header  60  fills with energy absorptive fluid and eventually begins to fill the space between the front panel  22  and the rear panel  24 . Once the fluid has reached the top end  42  of the absorber  20 , the fluid flows into the top header  62  and out the opening  70 . 
         [0062]    As shown in  FIG. 2 , solar absorptive heat transfer fluid  160  fills the absorber  20  when solar absorptive heat transfer fluid  160  flows into bottom header  60  and up the absorber  20  to the top header  62   
         [0063]    With reference to  FIG. 3 , the structure of the absorber  20  is illustrated in greater detail. The front panels  22  and rear panel  24  are coupled to each other along their respective sides  26 ,  28  by edge members  30  and along respective inward surfaces by a plurality of internal members  32 . Although not necessary, as shown in the illustrated embodiments, the edge members  30  and internal members  32  extend generally parallel to each other and the respective sides  26 ,  28  of the front panel and rear panel  24 . The edge members  30  are coupled, e.g., adhered, to the sides  26 ,  28  of the front panel  22  and rear panel  24 , and serve to seal the sides together. The internal members  32  are coupled to the inward surfaces of the front panel  22  and rear panel  24  to at least partially form a seal between respective internal members and the inward surfaces of the front panel  22  and rear panel  24  and to keep the front panels  22  and rear panel  24  from moving apart or together, such as when fluid between the panels is under pressure or suction relative to outside air. In certain implementations, the internal members  32  are coupled to the inward surfaces of the panels  22 ,  24  through use of any of various bonding techniques, such as, but not limited to, use of an adhesive. 
         [0064]    The absorber  20  includes a plurality of fluid chambers  34  in which a heat exchange medium, such as solar absorptive heat transfer fluid, is contained, absorbs sunlight, and is circulated. The fluid chambers  34  include the areas defined between the inward surfaces of the front and rear panels  22 ,  24  and either adjacent internal members  32  or an internal member  32  and an inward surface of an edge member  30 . The fluid chambers  34  each have an inlet opening  36  proximate the bottom end  38  shown in  FIG. 1 . The fluid chambers  34  also have an outlet opening (not shown) proximate the top end  42  of the absorber  20  shown in  FIG. 1 . The fluid chambers  34  extend generally parallel to the sides  26 ,  28  of the panels  22 ,  24  and generally perpendicular to the bottom and top ends  38 ,  42  shown in  FIG. 1 . 
         [0065]    The absorber  20  has an overall width B and overall depth C. The front panel  22  and rear panel  24  are spaced apart from each other a distance E, i.e., the fluid chambers  34  have a depth or height E. The edge members  30  can have the same general length A (see  FIG. 1 ) and depth C, respectively, of the absorber  20  and a width F. A first of the internal members  32  can be spaced a distance G away from an outer side of an edge member  30  and a second of the internal members  32 , i.e., the next adjacent internal member, can be spaced a distance H, or “2 times G”, away from the outer side of the same edge member  30 . In other words, each internal member  30  can be spaced a distance “n times H” away from an outer side of an edge member, where n is the number of internal members between the internal member in question (including itself) and the edge member  30 . In other embodiments, the internal members  30  can be spaced at any of various distances away from the outer side of the edge members  30  and relative to each other to form fluid chambers  34  having any of various widths S. In other words, each chamber can have a width S equal to the difference between the distance G and the width F of the edge members. 
         [0066]    The front panel  22  and rear panel  24  are each made from a clear material, such as optically transparent plastic, which permits energy emitted from the sun to pass through and heat the heat exchange medium. The plastic may have any or all of the characteristics of plastic as set forth in Table 1 below. 
         [0067]    The rear panel  24  includes a light reflective layer  44  positioned adjacent an outer surface of the rear panel. For example, in some implementations, the light reflective layer  44  is a metallic layer, such as a thin piece of sheet metal, or foil, coupled to, such as by being adhered to, or otherwise bonded to, the outer surface of the rear panel  24 . In some implementations, the reflective surface is spaced apart from the outer surface of the rear panel  24  such that an insulating layer of air can be positioned between the reflective surface and the rear panel. 
         [0068]    In one specific exemplary implementation, the overall length A is approximately 96 inches, the overall width B is approximately 48 inches and the overall depth C is approximately 0.13 inches. The thickness D of the front panels  22  and rear panel  24  is approximately 0.02 inches and the panels are spaced apart a distance E of approximately 0.09 inches. The distance G is approximately 0.5 inches and the distance H is approximately 1.0 inches. In this and other implementations, the weight of the absorber plus absorptive fluid is less than 30 pounds. 
         [0069]    In some implementations, the components of the absorber can be made using plastic extrusion processes. For example, one or more of the front and rear panels can be a polycarbonate panel, such as manufactured by Gallina USA, of Janesville, Wis. 
         [0070]      FIG. 3A  depicts an alternative exemplary implementation of an absorber  20 A similar to absorber  20 , but with a different overall depth C and chamber width S. The absorber  20 A has an overall depth C of approximately 0.25 inches and a width S of the chambers of approximately 0.25 inches. The absorber  20 A can hold approximately 5 gallons of absorptive fluid. 
         [0071]    Referring to  FIG. 3B , in another specific exemplary implementation of an absorber  20 B that is similar to absorber  20  and formed using a plastic extrusion process, the overall length A is approximately 96 inches, the overall width B is approximately 48 inches and the overall depth C is approximately 0.16 inches. The thickness D of the front panel  22  and rear panel  24  is approximately 0.01 inches and the panels are spaced apart a distance E of approximately 0.14 inches. The width S of each chamber is approximately 0.16 inches. The absorber of this specific implementation can hold approximately 3 gallons of absorptive fluid, e.g., black fluid, and weigh less than approximately 35 pounds excluding the black fluid. 
         [0072]    In  FIG. 3C , yet another exemplary implementation of an absorber  20 C that is similar to absorber  20  and formed using a plastic extrusion process is illustrated. The overall length A is approximately 96 inches, the overall width B is approximately 48 inches and the overall depth C is approximately 0.06 inches. The thickness D of each of the panels  22 ,  24  is approximately 0.01 inches and the panels are spaced apart a distance E of approximately 0.04 inches. The width S is approximately 0.25 inches. The absorber  20 C can hold approximately 1 gallon of solar absorptive heat transfer fluid and weigh less than approximately 18 pounds without fluid. 
         [0073]    In addition to fluid chambers formed between two plates to form a solar energy absorber as described above, the solar energy absorber may have other configurations. Referring to  FIGS. 4 and 5 , and according to another embodiment, a solar energy collector  300  includes a center conductor collection portion  310 . The center conductor  310  includes a generally cylindrical inner conduit  320  and a generally cylindrical outer conduit  330  coaxial with and surrounding the inner conduit. An inner surface of the inner conduit  320  defines an axially extending fluid passageway  322  having a generally circular cross-section and the inner surface of the outer conduit  330  defines an axially extending passageway  332  having a generally circular cross-section with a radius greater than that of the fluid passageway  322 . The outer conduit  330  can have a maximum diameter L that in some implementations is approximately 1.0 inches. 
         [0074]    The outer conduit  330  is coupled to the inner conduit  320  by posts  324  circumferentially spaced about and secured to an external surface of the inner conduit and an internal surface of the outer conduit. In some implementations, the posts  324  are elongate and extend a length of the center conductor  310 . In other implementations, the posts  324  are discrete spacers, such as columns or blocks, positioned at incremental locations along the length of the center conductor  310 . Although three posts  324  are shown in the illustrated embodiments, in other embodiments, more or less than three posts are used. 
         [0075]    In an alternative implementation, the posts  324  can be disks having a central hole with a diameter that is approximately equal to the outer diameter of the inner conduit and an outer diameter that is approximately equal to the inner diameter of the outer conduit such that the disks rest between the inner and outer conduits and maintain the inner and outer conduits in coaxial alignment. 
         [0076]    In one embodiment, the ratio of the length of each post  324  divided by the cross-sectional area of each post  324  is maximized in order to minimize heat lost through conduction as heat moves axially up the posts. 
         [0077]    The center conductor collection portion  310  includes a region  350  defined between the inner and outer conduits  320 ,  330  within which a vacuum is created to reduce convective heat losses. In some implementations, an infrared reflective coating may be applied to the interior surface of the outer conduit  330  to increase infrared reflection back into the fluid passageway  322  when visible and UV light is converted into heat inside fluid passageway  322 . With specific reference to  FIG. 4 , with no fluid present in the fluid passageway  322 , the conductor  310  does not absorb solar energy as sunlight is allowed to pass through the conductor and scatter. 
         [0078]    In some embodiments, a portion of the lower half of any of the surfaces may be coated with a light-reflecting surface so that light reflects back to sky rather than passing through center conductor  310  when heat absorptive fluid is absent. In certain implementations, one or more of the components of the center conductor  310  can be made of plastic, glass, plastic coated glass, or any combination thereof. 
         [0079]    Referring to  FIG. 5 , in operation, solar absorptive heat transfer fluid  360  is introduced in and allowed to flow within the fluid passageway  322  by operation of a pump (not shown). With solar absorptive heat transfer fluid  360  present and circulating through the center conductor  310 , solar energy is collected by the solar absorptive heat transfer fluid  360  as thermal energy and transferred to a thermal storage mass (similar to thermal storage mass  152  in  FIG. 40  described in greater detail below) external to the center conductor  310 . 
         [0080]    In some embodiments, the collector  300  may be drained of fluid to reduce the overall temperature of the collection portion  310  in the event the overall temperature exceeds a predetermined threshold. For example, in one specific implementation, the system drawing heat from the collector  300  is a steam system and the thermal mass is a block of inexpensive metal. The solar absorptive heat transfer fluid can be a high temperature oil compound with T tm     —     max  set to 600° F. to provide sufficient heat for generating steam and T c     —     max  set to just above 600° F. When the overall temperature T c  of the collection portion  310  reaches T c     —     max , the pump turns off and the fluid is allowed to drain from the center conductor  310 . With no fluid being located within the conductor  310 , the collector is placed in the non-operative state and solar energy penetrating the conductor will pass through unabsorbed. 
         [0081]    Because the overall temperature of the collector  300  can be controlled, expensive high-temperature glass or plastics need not be used, and less expensive glass and plastic substitutes can be used. 
         [0082]    The inner conduit, outer conduit and posts may each be made of optically transparent plastic material. The plastic material may be, for example, polycarbonate plastic. The plastic may have any or all of the characteristics set forth in Table 1 below. 
         [0083]    According to another embodiment,  FIGS. 6 and 7  illustrate a side view and a cross-sectional view of an absorber assembly  801 . The absorber assembly  801  generally comprises an insulating tube  810 , at least one spacer  820 , a center conduit  830  and a reflector  840 . The insulating tube  810  and center conduit have a generally coaxial arrangement, wherein the spacer  820  centers the center conduit  830  within the insulating tube  810  and maintains a space between the center conduit  830  and the insulating tube  810 . The spacer  820  also matingly receives reflector elements  840  between each spacer  820 . The reflector  840  is generally positioned in the insulating tube  810  below the center conduit  830 . 
         [0084]    When in operation, solar absorptive heat transfer fluid flows through the center conduit  830  as described in greater detail below. Depending on the level of desired insulation within the assembly, the sealed space between center conductor  830  and insulating tube  810  may contain air, a noble or inert gas such as argon, or a vacuum. 
         [0085]    The insulating tube  810  and the center conductor  830  run the full length of the absorber  801 . In one embodiment, the diameter of the insulating tube  810 , I_d, equals twice the diameter, C_d, of the center conductor  830 . Incident solar energy enters the center conductor  830  directly or reflects off reflector  840  to enter the center conductor  830 . The placement of the reflector  840  directly below the center conductor  830  and with walls extending from the base of the insulating tube  810  to its median point at a 45 degree angle make possible the collection of nearly all incident rays, both direct and diffuse, from sunrise to sunset with solar absorptive heat transfer fluid present in the center conductor  830 . Absorptive materials cover only half the surface of the collector, yet the collector collects nearly all the incident solar energy. When no solar absorptive heat transfer fluid is present, the collector assembly reflects all incident solar energy. Reflector  840 , which reflects all incident solar energy, returns incident radiation back to sky. 
         [0086]    Referring to  FIG. 7 , outer coating  811  may be applied to the insulating tube  810  to block UV radiation or provide anti-reflective properties. The material forming the insulating tube  810  must allow the transmission of solar energy to either the center conduit  830  or the reflector  840  or both with little on no attenuation. Insulating tube  810  may be extruded from glass, plastic, or other suitable solar transmissive material. The plastic material may have any or all of the characteristics described in Table 1 below. Inner coating  813  coats the interior to reflect infrared radiation back to the center conduit  830  or to stop air from entering the structure when a vacuum is present on the interior of the absorber. Inner coating  813  prevents the escape of noble or inert gas such as argon, if present, to the outside air. 
         [0087]    Outer coating  831  may be applied to the center conduit  830  to decrease permeability to air or noble or inert gas, and to reduce the reflection of incident energy. The material forming the center conduit  830  must allow the transmission of solar energy to either the solar absorptive heat transfer fluid, when present, or to or from the reflector  840  with little on no attenuation. Center conduit  830  may be extruded from glass, plastic, or other suitable solar transmissive material. The plastic material may have any or all of the characteristics described in Table 1 below. Inner coating  833  must stop solar absorptive heat transfer fluid from entering the material of center conduit  830 . Without a coating, the solar absorptive heat transfer fluid flowing through the center conduit  830  may, over time, enter the material of the center conduit  830  and begin the discoloration process. As the center conduit  830  discolors, it absorbs incident solar energy even with no solar absorptive heat transfer fluid present. This effect causes the temperature of the center conduit  830  to rise with no solar absorptive heat transfer fluid present. With sufficient discoloration, the temperature of the center conduit  830  may rise to a point where the material fails. Coating  833  prevents or minimizes staining, and thereby prevents or minimizes material failure. 
         [0088]    Materials of similar or differing temperature coefficients of expansion may be utilized to form the insulating tube  810  and center conduit  830  depending on the application. 
         [0089]    The reflector  840  resides at the base of the assembly. It may be formed of a single piece of material either by cutting and bending, or it may be extruded. Surface  841  must be mirror-like to reflect all incident solar energy. Coating may be applied to surface  843  to block infrared radiation from escaping. Polished aluminum, plated plastic, or other suitable material may be used to form the reflector. 
         [0090]    The spacer  820  serves to position the center conductor  830  within the insulating tube  810 . It also matingly receives the reflector  840  in slots  823 . The spacer material may be plastic, or other suitable substance with high thermal resistance to minimize the conduction of heat from the center conductor  830  to the insulating tube  810  to ambient. The plastic material may have any or all of the characteristics described in Table 1 below. A coating  821  may be applied to the spacer  820  to reflect incident solar energy to either the reflector  840  or the center conduit  830 . Coating  821  may stop incident reflections to increase transmissivity through spacer  820 . 
         [0091]    As shown in  FIG. 8 , center conduit  830  may take on differing dimensions and shapes. Center conductor  830 . 1  maintains the circular shape and diameter C_d but blocks solar absorptive heat transfer fluid from entering the center of the cylinder. Fluid chambers  834 . 1  exist only at the perimeter of the structure. Center conductor  830 . 1  delivers the same solar absorptive properties of an open cylinder, but requires much less solar absorptive heat transfer fluid in the absorber. Likewise center conductors  830 . 2 ,  830 . 3 , and  830 . 4  function similarly optically, but do so with much less solar absorptive heat transfer fluid than that held by an equivalent cylinder. As the shape of the center conductor changes, so must the profile of the spacer  820 .  FIG. 8  illustrates both the shape of the center conductor and its respective spacer. 
         [0092]    As shown in  FIG. 9 , reflector  840  may take on differing dimensions and shapes  840 . 1 ,  840 . 2  and  840 . 3 . A differing shape may be utilized to optimize performance for a particular application. 
         [0093]    Referring now to  FIGS. 10 and 11 , the individual absorber assembly may also comprise end seals  827  and couplers  825 . End seals  827  seal the ends of the absorber  801  by creating a seal between the end of the insulating tube  810  and the center conduit  830 . The seal  827  can be attached with a suitable adhesive or other known connecting method. The seal  827  itself may contain gaskets, joints, welds, adhesives, bellows or other known flexible attachment methods to accept differing thermal expansion characteristics between the center conductor  830  and the insulating tube  810 . 
         [0094]    Coupler  825  attaches each absorber end to its respective header  860  or  861  shown in  FIGS. 12 and 13 . The coupler  825  can be attached with a suitable adhesive, mechanically, or using another known connecting method. Seals between the coupler  825  and header may contain gaskets, joints, bellows, clamps or other known flexible attachment methods to accept thermal expansion and contraction of the absorber assembly  801 . 
         [0095]    Still referring to  FIGS. 10 and 11 , each reflector  840  segment is approximately L_s in length. One end of the reflector  840  plugs into a spacer  820  and the remaining end plugs into a spacer  820  or an end seal  827 . The combination of spacer thickness and reflector length establishes dimension L_s. L_s is also the distance at which spacers  820  are spaced apart to accept differing rates of thermal expansion and contraction. With a vacuum present, the spacers  820  may be effectively locked into place to distribute stress along the length of the absorber instead of just concentrating stress just at the end seals  827 . Additionally, if a vacuum is present, a getter resides in the vacuum space. 
         [0096]    Referring to  FIGS. 12 and 13 , a collector assembly  800  includes N (the number of individual assemblies) absorber assemblies  801  connected to header assemblies  860  and  861 . The width of the absorber portion, W_abs, equals the diameter of an individual absorber assembly, I_d, multiplied by the number of absorber assemblies  801 , N, found in the collector, or in equation form: W_abs=N×I_d, when the absorber tubes touch each other. To minimize cost per BTU of solar energy collected, the absorber tubes may be spaced apart. Under this condition the W_abs becomes the sum of the number of absorbers utilized plus the sum of the spaces between each absorber. W_abs is slightly less than the overall width B. The length of the collector assembly  800  is slightly longer than the length of the absorber assembly L_abs. Headers  860  and  861 , which may be identical, may determine the maximum height H_abs. of the structure if their diameter exceeds I_d shown in  FIG. 8 . If the diameter of headers  860  and  861  is less than I_d, then I_d sets the maximum height of the structure. Absorber assemblies  801  connect to the headers  860  and  861  with their centers spaced I_d apart, or more. As such they may, or may not, contact each other. 
         [0097]    In operation, filling the center conduits of the absorber assemblies  801  with solar absorptive heat transfer fluid makes the collector solar absorptive. The solar absorptive heat transfer fluid enters through bottom header  861 , fills the absorber center conduits of the absorber assembly  801 , then exits through top header  860 . As noted previously, the solar absorptive heat transfer fluid flow direction may be reversed. 
         [0098]    In one specific exemplary implementation, the length A is approximately 96 inches; the width B is approximately 48 inches; the absorber thickness is approximately 0.02 inches; C_d is 0.5 inches: I_d is 1.0 inch; N is 48, and L_s is 12 inches. The collector assembly may weigh less than approximately 25 pounds, hold less than 5 gallons of fluid, operate with vacuum insulation, and be manufactured inexpensively. 
         [0099]    In another specific exemplary implementation, the length A is approximately 20 feet; the width B is approximately 10 feet; the absorber thickness is approximately 0.02 inches, C_d is 3 inches; I_d is 6 inches; N is 20; and L_s is 12 inches. The center conduit makes use of the configuration defined by  830 . 1 . This collector assembly, which collects solar energy over an approximate 200 square foot area, assembles in a modular fashion. The entire assembly may weigh less than 200 pounds, holds less than 20 gallons of fluid, operates with air as the insulator, and may be manufactured and installed inexpensively. 
         [0100]    Referring now to  FIG. 14 , headers  60  and  62  are described in greater detail. The bottom header  60  (being representative of the top header  62 ) includes a fluid reservoir portion  64  and an elongate absorber attachment portion  66  extending substantially the length of and forming a one-piece construction with the fluid reservoir portion. The bottom header  60  has a length that is at least the width of the absorber to which it is attached. In some embodiments, the header  60  can be formed of extruded plastic. The plastic may be optically transparent plastic. The plastic may be, for example, polycarbonate plastic. The plastic material may have any or all of the characteristics described in Table 1 below. 
         [0101]    The fluid reservoir portion  64  defines a generally circular fluid passageway  68  extending from an open end  70  to a closed end  72  (as shown in  FIG. 1 ) of the bottom header  60 . The fluid passageway  68  defined by the interior surface of the tubular shaped portion can have a radius I and the fluid reservoir portion  64  can have a cylindrical external surface with an overall radius J. 
         [0102]    The absorber attachment portion  66  extends away from the external surface of the fluid reservoir portion  64  and has a generally rectangular shape having a height K and a depth L. In some embodiments, the height K is approximately 1.0 inches and the depth L is approximately 0.5 inches. The absorber attachment portion  66  can have any of various other shapes, such as, for example, trapezoidal. 
         [0103]    An elongate slot  74  is formed, such as by milling or an intrinsic slot made by extrusion, in the absorber attachment portion  66  and penetrates an external surface of the absorber attachment portion. The slot  74  extends less than the length of the header  60  and is approximately equal to or slightly longer than the overall width B of the absorber  20 , has a width approximately equal to or slightly wider than the overall depth C of the absorber, and has a depth equal to or less than the depth L. In this manner, the slot  74  is configured to matingly receive the end of the absorber  20  within the absorber attachment portion  66 . The absorber can be retained within the elongate slot  74  through use of an adhesive or other known bonding technique. Absorber  20  may slide into attachment portion  66  which forms a seal with a gasket or other known “slip in” methods. When attached to each other, the absorber  20  and top and bottom headers  60 ,  62  can be referred to as an absorber assembly. 
         [0104]    In certain implementations, a fluid inlet feed slot  76  is formed in the header in fluid receiving communication with the fluid passageway  68  and fluid expelling communication with the fluid chambers of the absorber  20  when the absorber is received within the elongate slot  74 . In other words, the fluid inlet feet slot  76  provides a channel between the fluid passageway  68  and the fluid chambers of the absorber  20  through which solar absorptive heat transfer fluid is permitted to flow. The fluid inlet feed slot  76  slot extends a substantial portion of the elongate slot  74  such that each of the fluid chambers of the absorber  20  are in at least partial fluid receiving communication with the fluid inlet feed slot  76 . In the illustrated embodiment, the fluid inlet feed slot  76  is a single continuous slot. In other embodiments, the fluid inlet feed slot can be multiple slots spaced apart along the length of the elongate slot. 
         [0105]    In certain implementations, the top and bottom headers  60 ,  62  are plated with a reflective layer, such as a metallic layer, to reflect solar energy from the sun and prevent solar radiation from contacting any solar absorptive heat transfer fluid flowing through the headers or solar absorptive heat transfer fluid residually remaining within the headers in the event solar absorptive heat transfer fluid is drained or otherwise removed from the panels as will be described in more detail below. 
         [0106]    In certain applications, absorber assemblies such as those described above are placed in housings. Referring now to  FIGS. 16 and 17 , an embodiment of an absorber assembly housing is illustrated. In  FIGS. 16 and 17 , a body  100  includes a base  102  and a cover assembly  104 . The base  102  is an at least partially rigid structure having a bottom wall  106 , four side walls  108  extending transversely from the bottom wall and an open top end opposite the bottom wall. The bottom wall  106  and side walls  108  define a recess  109  within which the absorber assembly, including the headers, is positioned. In certain implementations, the absorber assembly is coupled to the base  102  such that absorber  20  lays relatively flat against the bottom wall  106  and the headers are matingly received within and extend through apertures formed in the side walls  108 . This can be accomplished by forming recesses in the bottom wall  106  for receiving at least a portion of the headers  60 ,  62 . When positioned within the recess  109 , the side walls  108  extend upwardly away from the bottom wall a distance substantially greater than the overall depth C of the absorber such that the upper surfaces of the side walls are elevated above that of the absorber and headers. 
         [0107]    In some implementations, the absorber  20  is attached to, such as adhesively bonded to, an upper surface of the bottom wall  106  such that the absorber and base  102  form a unified assembly. In other implementations, the absorber  20  is secured to the base  100  via the mating engagement between the sides  108  of the base  100  and the headers without any direct attachment of the absorber to the base. 
         [0108]    The base  102  acts as an insulator to reduce conductive, convective and radiated heat losses from the solar absorptive heat transfer fluid flowing through the absorber  20 . Moreover, the base  102  can provide structural support and rigidity for enduring the environmental conditions in which the collector portion will operate. Accordingly, in some embodiments, the base  102  is made from structural foam, such as polyurethane foam. The thickness of the bottom wall  106  and side walls  108  is determined based on the desired maximum heat loss through the absorber  20  and the R-Value of the foam. For example, in certain implementations, the bottom wall  106  or side walls  108  can be two-inch thick inexpensive polyurethane foam having an insulating value of R-3 or greater per inch. In one embodiment, the inexpensive foam has an R-10 insulation value. 
         [0109]    Typically, inexpensive foams such as polyurethane foam tend to melt at temperatures around 200° F. Accordingly, conventional solar collectors would require more expensive foams capable of operating at higher temperatures, or a “buffer insulation” between the absorber and the foam, commonly associated with such conventional collectors. As will be described in more detail below, the ability of the solar energy apparatus described herein to control operating temperatures allows for the use of lower cost foam materials relative to conventional solar collectors. 
         [0110]    In some embodiments, the portions of the base  102  and side walls  108  that may be exposed to solar radiation are plated or painted with a metallic layer to reflect the radiation and prevent UV damage to the base. 
         [0111]    The cover assembly  104  includes a cover  110  coupled to the top surfaces of the side walls  108  and cover supports  112  positioned within the recess  109  between the cover  110  and the absorber  20 . The cover  110  may hermetically seal off an insulation chamber  114  defined between the side walls  108 , bottom wall  106 , cover  110 , and absorber  20 . In some implementations, a seal or flexible adhesive is positioned between the cover  110  and the side walls  108  and cover supports  112  to attach the cover to the side wall and cover supports and to sealingly enclose the insulation chamber  114 . The insulation chamber  114  can include dead air or a noble or inert gas, such as Argon, to better insulate the absorber from the environment. The cover  110  can be sealed to the top surfaces of the side walls  108  with any of various adhesives or with other mechanical assemblies, such as an aluminum U-channel perimeter frame and gaskets. Such a U-channel can also provide an attachment point for coupling the collector to a mounting surface, such as a roof. 
         [0112]    Each cover support  112  can be an elongate beam, such as a plastic I-beam, having a first side attached to the cover  110  and a second side opposite the first side attached to or simply touching the absorber  20 . The cover supports  112  couple the cover  110  to the absorber  20  to provide structural support to the cover  110 . 
         [0113]    As described above, in some implementations, the absorber is coupled to the base  102  and the cover  110  via the cover supports  112  by an adhesive or other known method of attachment e to form an integrated structural solar energy connector capable of withstanding harsh environmental conditions. 
         [0114]    In specific implementations, the absorber  20 , cover  110 , cover supports  112  are made of a optically transparent plastic. The plastic can be any of various plastics characterized by any of various parameter values or performance characteristics depending on the desired application, manufacturing costs or other variables. Listed in Table 1 below are several clear plastic parameters, associated general descriptions of the parameter, parameter values according to various embodiments, and associated comments. The parameters, parameter descriptions, parameter values, and comments listed in Table 1 are associated with the characteristics of exemplary types of plastics that can be used to form the plastic components of some embodiments of the solar energy apparatus described herein. In other embodiments, the plastic components can be made of plastics having performance characteristics outside of the value ranges specified in Table 1. 
         [0000]    
       
         
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                   
                 Exemplary 
               
               
                 Parameter 
                 Description 
                 Comment 
                 Value Range 
               
               
                   
               
             
             
               
                 Absorptivity to 
                 Ability to convert sunlight 
                 In some implementations, lower 
                 &lt;0.05 
               
               
                 visible + UV light 
                 into heat inside the material. 
                 values are desirable. 
               
               
                 Emissivity to 
                 Ability to emit infrared. 
                 In some implementations, lower 
                 &lt;0.2 
               
               
                 infrared light 
                   
                 values are desirable. Low values of 
               
               
                   
                   
                 emissivity reduce need for low 
               
               
                   
                   
                 emissivity values of the solar 
               
               
                   
                   
                 absorptive heat transfer fluid. 
               
               
                 Transmissivity to 
                 Ability to transmit sunlight 
                 In some implementations, higher 
                 &gt;0.9 
               
               
                 visible + UV light 
                 without attenuation. 
                 values are desirable, particularly as 
               
               
                   
                   
                 the number of layers of plastic 
               
               
                   
                   
                 between sun and solar absorptive 
               
               
                   
                   
                 heat transfer fluid increases. 
               
               
                 Reflectivity to 
                 Percentage of incident light 
                 In some implementations, lower 
                 &lt;0.05% 
               
               
                 visible + UV light 
                 reflecting off the surface of 
                 values are desirable, particularly as 
               
               
                   
                 the plastic. 
                 the number of layers of plastic 
               
               
                   
                   
                 between sun and solar absorptive 
               
               
                   
                   
                 heat transfer fluid increases. 
               
               
                 Thermal 
                 Ability of a substance to 
                 In some implementations, lower 
                 &lt;1.5 (BTU- 
               
               
                 Conductivity 
                 conduct heat per unit length 
                 values are desirable. Low 
                 in/hr-ft 2 -F.) 
               
               
                   
                 for a given cross-sectional 
                 conductivity can provide top layer 
               
               
                   
                 surface area. 
                 insulation. 
               
               
                 Operating Point 
                 Low temperature at which 
                 In some implementations, it is 
                 &lt;−40° F. 
               
               
                   
                 plastic begins to be 
                 advantageous for the plastic to 
               
               
                   
                 functionally unstable. 
                 operate in a cold environment. 
               
               
                 Plastic 
                 High temperature at which a 
                 In some implementations, higher 
                 &gt;220° F. 
               
               
                 Deformation 
                 plastic becomes structurally 
                 temperatures are desirable. 
               
               
                 Temperature 
                 unstable. 
               
               
                 Flammability 
                 Ability of plastic to support 
                 In some implementations, lower 
                 Low 
               
               
                   
                 combustion. 
                 flammability values are desirable. 
               
               
                 Fluid 
                 Ability of plastic to remain 
                 In some implementations, plastic is 
                 High 
               
               
                 Compatibility 
                 functionally operable when 
                 compatible with solar absorptive 
               
               
                   
                 in contact with fluid. 
                 heat transfer fluid for at least 30 
               
               
                   
                   
                 years. 
               
               
                 Cost 
                 Fair market value of plastic. 
                 Post-extrusion or post-molded. 
                 &lt;$2/Pound 
               
               
                 Lifetime 
                 Time period in which 
                 In some implementations, efficiency 
                 &gt;10 Years 
               
               
                   
                 plastic remains functionally 
                 may decrease by 20% after 30 years, 
               
               
                   
                 stable with similar physical 
                 and by 10% after 10 years. 
               
               
                   
                 and optical properties. 
               
               
                 Staining 
                 Ability of the plastic to 
                 Staining may result in the absorption 
                 High 
               
               
                   
                 resist staining. 
                 of heat &amp; fluid contact. In some 
               
               
                   
                   
                 implementations, small amounts of 
               
               
                   
                   
                 staining can be tolerated as internal 
               
               
                   
                   
                 stagnation temperature fluid may be 
               
               
                   
                   
                 increased as a result. Surface 
               
               
                   
                   
                 coatings can ameliorate this 
               
               
                   
                   
                 requirement. 
               
               
                 Permeability to 
                 Ability of liquid to diffuse 
                 In some implementations, fluid 
                 Low 
               
               
                 liquid 
                 through plastic. 
                 should not permeate through the 
               
               
                   
                   
                 plastic. 
               
               
                 Permeability to air 
                 Ability of air to diffuse 
                 In some implementations, gas 
                 Low 
               
               
                 and vapor 
                 through plastic 
                 permeation through the plastic 
               
               
                   
                   
                 should be minimal 
               
               
                 UV resistant 
                 Ability of plastic to resist 
                 In some implementations, as 
                 High 
               
               
                   
                 physical and optical damage 
                 transmissivity remains high, the 
               
               
                   
                 from UV rays over time. 
                 plastic is able to resist UV rays. 
               
               
                 Glue Adhesion 
                 Temperature at which 
                 In some implementations, glue stops 
                 ~250° F. 
               
               
                   
                 plastic loses ability to 
                 working when plastic starts to loose 
               
               
                   
                 remain adhesively bonded 
                 its properties. 
               
               
                   
                 to glue. 
               
               
                 Hardness 
                 Resistance of plastic to 
                 Environment can cause scratches on 
                 High 
               
               
                   
                 indentation under a static 
                 outer shell top surface. Such 
               
               
                   
                 load or to scratching 
                 scratches can undesirably cause 
               
               
                   
                   
                 some reflection and some absorption 
               
               
                   
                   
                 of solar energy. Hail, or objects 
               
               
                   
                   
                 hurled by the wind, may damage or 
               
               
                   
                   
                 ruin top surface. 
               
               
                 Tensile Strength 
                 Ability of plastic to resist 
                 In some implementations, the higher 
                 High 
               
               
                   
                 longitudinal stress without 
                 the tensile strength, the better so as 
               
               
                   
                 tearing apart. 
                 to resist environmental elements, 
               
               
                   
                   
                 such as wind suction, and to remain 
               
               
                   
                   
                 secured to the collection portion. 
               
               
                   
                   
                 This may reduce when exposed to 
               
               
                   
                   
                 UV light. 
               
               
                   
               
             
          
         
       
     
         [0115]    Referring to  FIG. 17 , in some embodiments, the cover  110  is made of plastic that meets more performance characteristics, such as those described above, than the plastic of which the front panel  22  of the absorber  20  is made of. Similarly, in some embodiments, the plastic of the front panel  22  of the absorber  20  meets more performance characteristics, such as those described above, than the plastic of which the rear panel  24  of the absorber is made. In other words, in some embodiments, the requirements for the plastic of the cover  110  are more stringent than the requirements for the plastic of the front panel  22  of the absorber  20 , and the requirements for the plastic of the front panel  22  are more stringent than the requirements for the plastic of the rear panel  24  of the absorber. 
         [0116]    In some embodiments, the plastic components can be made from Lexan SLX2432T, manufactured by General Electric. In some embodiments, other plastics, such as polycarbonate and acrylic plastics, can be used. 
         [0117]    Prior to collecting solar energy, the collection portion does not contain solar absorptive heat transfer fluid. In this non-operational state, solar energy penetrates the cover  110 , front panel  22 , absorber chamber  34 , and rear panel  24  and is reflected by the reflective layer  44  to the atmosphere with minimal absorption. Further, solar energy is reflected off the reflective layers on the base  102  and bottom and top headers. Because little to no solar energy is absorbed in this non-operational state, the temperature of the components of the collection portion  12  and the overall temperature of the collection portion remains relatively unchanged, i.e., approximately equal to ambient temperature. 
         [0118]      FIGS. 18 ,  19  and  20  illustrate another embodiment of a housing for an absorber assembly. Referring to  FIG. 18 , an extruded collector assembly  500  includes at least three components: a shell  560 , headers  540 ,  550 , which may be identical, and end caps  510 ,  520 , which may be identical. An adhesive, or any other known bonding or coupling method, secures the components in the proper position. 
         [0119]    In the illustrated embodiment, the shell  560  includes a generally hollow, rectangular-shaped shell having spaced-apart front and rear walls  511 ,  512  and two side walls  515  positioned around opposite sides of and coupling the front and rear walls. The shell  560  includes spaced-apart top and bottom open ends  513 ,  514 , respectively. 
         [0120]    The end caps  510 ,  520  are coupled to the bottom and top ends  514 ,  513 , respectively, of the shell  560  to partially encapsulate the headers  540 ,  550 . The end caps  510 ,  520  can be attached to the ends of the shell  560  with a suitable adhesive or other known connecting method. For example, although not shown, in some implementations, the shell  560 , headers  540 ,  550  and end caps  510 ,  520  can be coupled together using flexible gaskets, joints, bellows, or other known flexible attachment method to seal and allow movement between the shell, headers, and end caps. Such a flexible attachment method can allow for independent movement between the shell  560  and an absorber housed therein, such as when the temperatures of the various components of the collector assembly  500  are different or changed relative to each other. 
         [0121]    As shown in  FIGS. 19 and 20 , the shell  560  also includes a plurality of spaced-apart absorber support members  563  positioned between the walls of the shell and extending transversely from the front wall  511  to the rear wall  512 . An absorber  562  is positioned within the shell  560  via the support members  563  as described in greater detail below. Insulation cavities  564 ,  565  are formed within the shell as described in greater detail below. 
         [0122]    As shown in  FIG. 20 , the support members  563  include absorber channels  570  within which an absorber, such as absorber  562 , is held in place and properly positioned with respect to the walls of the shell. The absorber  562  is similar to and includes the same general features as the absorbers  20 ,  20 A,  20 B,  20 C described above. Also, the support members  563  and side walls  515  can include recesses or cut-outs  561  for matingly receiving a respective one of the headers  540 ,  550  shown in  FIG. 18 . The headers can be secured within the cut-outs  561  with a suitable adhesive or other known connecting method. 
         [0123]    The shell  560  allows light to transmit through to an absorber  562  and, in some embodiments, is made primarily of a UV resistant plastic or glass. The plastic material may have any or all of the characteristics described in Table 1 above. As with the absorbers previously described, the absorber  562  contains solar absorptive heat transfer fluid when in a solar energy absorption mode and does not contain solar absorptive heat transfer fluid when in a solar energy reflection mode. 
         [0124]    The shell  560  includes upper and lower insulation cavities  564 ,  565 , respectively. The upper insulation cavities  564  are defined between the front wall  511  of the shell and the absorber  562  and the lower insulation cavities are defined between the rear wall  512  and the absorber. The cavities  564 ,  565  provide dead air insulation above and below the absorber  562 , respectively. In some embodiments, the lower insulation cavities  565  can be filled with an insulative material, such as foam beams or solid foam, to improve bottom insulation performance and strengthen the shell  560 . 
         [0125]    The front and rear panels of absorber  562  have a thickness D, which is defined above in relation to  FIG. 3 . Each support member  563  has a height that is substantially greater than its thickness. In certain implementations, the thickness of each support member  563  is smaller than the thickness D of the panels of the absorber  562 . The reduced thickness of the support members  563  can relieve stresses associated with thermal expansion of the absorber  562  when the absorber  562  contains hot circulating solar absorptive heat transfer fluid and the shell  560  is cold. Since a tall, but thin, member offers high thermal resistance per unit length, the ratio of the height of supports  563  divided by the width of the supports may be large to minimize conduction of heat from the absorber  562  to the outer shell  560 . As shown in  FIG. 20 , the support member  563  are spaced-apart a distance H from each other. 
         [0126]    In some implementations, the thickness of the shell walls is greater than the thickness D of the absorber front and rear panels. Such a configuration can improve the structural performance of the shell and allow the shell to better withstand adverse environmental conditions. 
         [0127]    As shown in  FIGS. 18 and 19 , the shell  560  has a length A, a width B, and a height L. In certain implementations, the length of the absorber  562  is slightly less than the length A of the shell  560  and the width of the absorber is slightly less than the width B of the shell. Configuring the absorber to be slightly shorter and narrower than the shell provides a space to attach the headers  510 ,  520  and provides space for horizontal and vertical thermal expansion when the headers are connected to absorber  562 . Like the absorber described above, absorber  562  has a plurality of fluid channels through which an absorptive fluid can flow. Each channel has a width S and a depth or height E. 
         [0128]    In one specific exemplary implementation, the length A is approximately 96 inches; the width B is approximately 48 inches; the thickness D is approximately 0.01 inches; the height E is approximately 0.10 inches; the width S is approximately 0.25 inches; the distance H is approximately 3.00 inches; and the height L is approximately 3.00 inches. The collector assembly  500  may weigh less than approximately 15 pounds, hold less than approximately 1.5 gallons of solar absorptive heat transfer fluid, and be manufactured inexpensively. 
         [0129]      FIGS. 21 through 28  illustrate still another embodiment of a housing for an absorber assembly. As shown in  FIGS. 21 ,  21 A and  22 , a shell  702  serves as a housing for a an absorber  701 . 
         [0130]    As shown in  FIG. 21 , the absorber  701  includes absorber panel  721 , headers  760 ,  761  at the ends of the absorber panel  721  and a plurality of flex beams  741  coupled to the absorber panel  721 , extending the length of the absorber panel and aligned perpendicularly to the headers  760 ,  761 .  FIG. 21A  illustrates a front view of the absorber assembly. The absorber  701  consists of the absorber panel to which header pipes  760  and  761  attach at each end using an adhesive or other suitable method. Flex beams  741 , spaced distance H apart, attach to the absorber panel  721  on the top and bottom surfaces using an adhesive or other suitable method. Distance L_abs must be less than A shown in  FIG. 27 . Distance W_abs must be less than B shown in  FIG. 22 . The height of the absorber must be less than L shown in  FIG. 22 . 
         [0131]    As shown in  FIG. 22 , the shell  702  includes a generally hollow, rectangular-shaped shell having spaced-apart top and bottom panels  711 ,  731  and two side panels  751  and  752  positioned on opposite sides of and connecting to the top and bottom panels using side connecting beams  750  in four locations. Tracks  740 , spaced H apart, attach to the top and bottom panels using an adhesive or other suitable method. 
         [0132]      FIGS. 23 and 24  illustrate an expanded front view of the left side of the collector assembly  700  with headers  760  and  761  removed and a front view of the collector assembly  700  with headers  760  and  761  removed, respectively. The top panel  711  passes solar energy to the absorber panel  721  while providing insulation and infrared reflectivity. The absorber panel  721  contains a solar absorptive heat transfer fluid when collecting solar energy. When not collecting solar energy, the absorber panel  721  contains no solar absorptive heat transfer fluid. The bottom panel  731  provides insulation and infrared energy reflectivity. Side panel  751  provides insulation and infrared energy reflectivity. Corner beams  750  connect the top panel  711  to the left side panel  751  and right side panel  752 . Corner beams  750  also connect the bottom panel  731  to the left side panel  751  and right side panel  752 . Shell tracks  740  attach, by adhesive or other suitable method, to the top panel  711  and bottom panel  731 . The distance H separates one track from the other. Absorber flex beams  741  attach, by adhesive or other suitable method, to the top and bottom surfaces of absorber  721 . The distance H separates one flex beam from the other. The track  740  matingly receives flex beam  741  to connect the shell assembly  702  to the absorber assembly  701  while providing movement within the structure to adapt to temperature change and environmental stress. 
         [0133]    Each flexible beam  741  has a length that is substantially greater than its thickness. Likewise, the length of the flexible beam  741 , because of its serpentine shape, significantly exceeds its height. In certain implementations, the thickness of each support member  741  may be made considerably less than the total length of the serpentine support member. Since a long, but thin, member offers high thermal resistance per unit length, the ratio of the length of flexible beam  741  divided by the material thickness of the supports may be large to minimize conduction of heat from the absorber  721  to the outer panels  711  and  731 . By intention, they form a very poor thermal connection to track  740 . 
         [0134]    While the flexible beam  741  is shown having a serpentine shape, any other flexible shape which accommodates lateral stress without failure may also be used for the flexible beam. For example, the flex beams may be comprised of two flexible beams opposing each other and bowing away from each other, like two opposing leaf springs. 
         [0135]      FIG. 25  illustrates the relationship between the top panel  711 , the absorber  721 , the bottom panel  731  and the tracks  740  and flex beams  741  in three dimensional detail. With solar absorptive heat transfer fluid present, the temperature of the absorber  721  rises when exposed to solar radiation. A rising temperature produces expansion of the absorber in all dimensions. To accommodate expansion in the length of the absorber, the flex beam  741  slides within the track  740 . The serpentine nature of the flex beam readily accepts changes in dimension of width and height. The compressive and expansive properties of the flex beam accept and adapt to ambient temperature variations, wind load, and impact from natural and man-made objects. 
         [0136]    Referring back to  FIGS. 23 and 24 , one embodiment uses coatings and additives upon and within panel  711  to optimize performance. An ultra violet, UV, blocker with antireflective properties coats the top surface  710  of the top panel  711 . This coating protects the top panel  711  and all components below from the harmful effects of UV radiation. The antireflective nature of the coating maximizes the amount of solar energy passing into the absorber panel  721 , when filled with solar absorptive heat transfer fluid, over a range of incident sun angles. An infrared coating may also be applied to the top surface  710 . 
         [0137]    An infrared reflective coating  712  may be used to stop heat from being radiated to outside space when the collector  700  collects solar energy. The coating  712  passes incident energy to the absorber  721  while reflecting infrared emitted from the absorber  721  back to the absorber. The bottom surface of the top panel  711  may also include an ultraviolet blocker. 
         [0138]    Specific coatings on the interior chambers, formed by E_shell and S_shell, of the top panel  711  determine part of the heat loss characteristics and thereby part of the insulation characteristics of the top panel  711 . An optically transmissive coating applied to the interior chambers allows the top panel  711  to be filled with a noble or inert gas, such as argon, or support a vacuum to increase the thermal resistance over air filling the chamber. The interior chambers may also be made from an optically transmissive material, thereby eliminating the need for a coating. One embodiment uses a coating which entraps a noble or inert gas in the top panel  711 . Significant increases in thermal resistivity occur under such a condition. A similar, or possibly different, coating may be applied to prevent gasses from entering the top panel  711 . This coating permits the creation of a vacuum. In case of a vacuum, a getter may be inserted inside chambers of the top panel  711  Very high thermal resistance exists with a vacuum present on the interior of the top panel  711 . Heat only conducts outward through the thin vertical support members of  711 , where the ratio of E_shell to the thickness, D is large. The top panel&#39;s thermal conductivity is small compared to conventional solar collector top glazing, which is frequently glass. The top panel material may be low thermal conductivity plastic. The interior chambers may also be coated with an anti-staining material. 
         [0139]    Coatings and additives upon and within bottom panel  731  optimize thermal performance. An infrared reflective coating  732  may be used to stop heat from being radiated to space when the collector  700  collects solar energy. The coating  732  returns infrared emitted from the absorber  721  back to the absorber. Coating  732  may also be an ultra violet, V, blocker with antireflective properties. 
         [0140]    Coating  730  provides additional infrared reflectivity and may also have antireflective properties. Coating  730  and  732  may or may not be identical. 
         [0141]    Specific coatings on the interior chambers, formed by E_shell and S_shell, of the bottom panel  731  determine part of the heat loss characteristics and thereby part of the insulation characteristics of the bottom panel  731 . A coating applied to the interior chambers allows the bottom panel  731  to be filled with a noble or inert gas, such as argon, or support a vacuum to increase the thermal resistance over air filling the chamber. One embodiment uses a coating which entraps a noble or inert gas in the bottom panel  731 . Significant increases in thermal resistivity occur under such a condition. A similar, or possibly different, coating may be applied to prevent gasses from entering the bottom panel  731 . This coating permits the creation of a vacuum. In the case of a vacuum, a getter may be inserted inside chambers of bottom panel  731 . Very high thermal resistance exists with a vacuum present on the interior of the bottom panel  731 , heat only conducts outward through the thin vertical support members of  731 , where the ratio of E_shell to the thickness, D is large. The thermal conductivity of the bottom panel is comparable to the thermal conductivity of the insulation commonly used on the bottom sides of the conventional solar collectors. The bottom panel material may be low thermal conductivity plastic. The interior chambers may also be coated with an anti-staining material. 
         [0142]    The side panel  751 , while differing in dimension from the bottom panel  731 , uses similar coatings and exhibits similar performance. 
         [0143]    While not shown in any drawings, insulation (fiberglass, foam, or other suitable type) may be inserted in the spaces between the absorber  721  and the bottom panel  731  to further increase collector efficiency. This insulation must be expandable and compressible or allow enough space to not interfere with the operation of the flex beams  741 . Insulation may be applied outside of shell  702  on the bottom  731  and the sides  751  and  752  for additional heat loss reduction. 
         [0144]    Coatings and additives upon and within the absorber panel  721  optimize performance. The antireflective nature of the coating maximizes the amount of solar energy passing into the absorber panel  721 , when filled with solar absorptive heat transfer fluid, over a range of incident sun angles. A reflective coating  722  or reflective material applied by adhesive or other know means reflects the full spectrum of incident energy upwards back to sky with no solar absorptive heat transfer fluid present in the absorber  721 . The combination of solar absorptive heat transfer fluid and a bottom reflective surface make the absorber  721  either solar absorptive when the solar absorptive heat transfer fluid is present, or solar reflective when no solar absorptive heat transfer fluid exists in the absorber  721 . 
         [0145]    A coating on the interior chambers, formed by E_abs and S_abs, prevents the absorption of the solar absorptive heat transfer fluid into the materials that form the absorber  721 . Without any coating as the collector ages, the solar absorptive heat transfer fluid may enter the materials forming the absorber  721  and begin a discoloration process. As the absorber  721  discolors it absorbs incident solar energy even with no solar absorptive heat transfer fluid present. This effect causes the temperature of the absorber  721  to rise when exposed to solar radiation. With sufficient absorption of solar absorptive heat transfer fluid, the temperature of the absorber  721  may rise to a point where the materials forming the absorber  721  fail. The interior coating of the absorber  721  prevents staining and thereby material failure. 
         [0146]      FIGS. 26 ,  27  and  28  illustrate a top, side and three dimensional view of the complete assembly, respectively. Corner beams  750  couple together the sides of the shell and flex beams  741  mate with shell tracks  740  to position the absorber inside the shell. End caps  770 ,  771  are coupled to the bottom and top ends of the shell for the purpose of partially encapsulating the headers  760 ,  761 , and the entire absorber assembly. The end caps  770 ,  771  can be attached to the ends of the shell with a suitable adhesive or other known connecting method. For example, although not shown, in some implementations, the shell headers  760 ,  761  and end caps  770 ,  771  can be coupled together using flexible gaskets, joints, bellows, or other known flexible attachment method to seal and allow movement between the shell, headers, and end caps. Such a flexible attachment method can allow for independent movement between the shell and absorber, such as when the temperatures of the various components of the collector assembly are different or changed relative to each other. 
         [0147]    With specific reference to  FIG. 27 , openings  753  provide access to headers  760 , 761 . Connecting pipes with suitable couplers attach through these openings. In this manner, one collector assembly  700  may be connected to another collector assembly  700 , or headers  760  and  761  may be connected to their respective feed and return lines. With end caps  770  and  771  removed, the couplers may be attached to the headers by mechanical means, or by using an adhesive or other suitable method. 
         [0148]    As shown in  FIGS. 24 ,  26  and  28 , the collector  700  has a length A, a width B, and a height L. In all implementations, the length of the absorber  701  is slightly less than the length A of the shell  702  and the width of the absorber is slightly less than the width B of the shell. Configuring the absorber to be slightly shorter and narrower than the shell provides a space to attach the headers  760 ,  761  and provides space for horizontal and vertical thermal expansion when the headers are connected to absorber  721 . Like the absorber described above, absorber  721  has a plurality of fluid channels through which an absorptive fluid can flow. As shown in  FIG. 23 , each channel has a width S_abs and a depth or height E_abs. 
         [0149]    In one specific exemplary implementation, the length A is approximately 96 inches; the width B is approximately 48 inches; the material thickness D is approximately 0.01 inches; the height E_abs is approximately 0.16 inches; the width S_abs is approximately 0.16 inches; the width S_shell is approximately 0.50 inches and E_shell is approximately 0.50 inches; the distance H is approximately 12.00 inches; and the height L is approximately 3.00 inches. The collector assembly  700  may weigh less than approximately 25 pounds, hold less than approximately 3.0 gallons of solar absorptive heat transfer fluid, and be manufactured inexpensively. 
         [0150]    In other embodiments described herein, the absorber is built into the housing. Referring to  FIGS. 29 and 30 , a collector  200  having a collection portion  202  is shown. Collection portion  202  is similar to collection portion  12 , but is configured to circulate solar absorptive heat transfer fluid in a top to bottom direction rather than a bottom to top direction as with collector  10 . The collection portion  202  includes a body  210  having a foam base  212 , three large elongate foam ribs  214 , four small elongate foam ribs  215 , two large elongate foam side ribs  222 , and two small elongate foam side ribs  223 . The number of large elongate form ribs and small elongate foam ribs may be greater than or less than the stated numbers and other materials similar to foam may also be used. The surfaces of the foam components may also be coated with a material making the foam impermeable to circulating fluid. 
         [0151]    Base  212  is generally rectangular with a rear wall  216 , a top wall  217 , and a bottom wall  219  projecting transversely from the rear wall. An absorber recess  220  is defined between the rear wall  216  and the side walls  218  shown in  FIG. 30 . Top and bottom headers  242 ,  244  are located at the top and bottom end  230 ,  232 , respectively. Arrow  254 ,  255  and  256  indicate the direction of flow of solar absorptive heat transfer fluid when the collector is in operation. 
         [0152]    Referring to  FIG. 31 , the small elongate foam ribs  215  project transversely away from rear wall  216  and extend the length of the recess  220  from the top wall  217  at a top end  230  of the body  210  to the bottom wall  219  at a bottom end  232  of the body  210  as shown in  FIG. 29 . The small elongate foam ribs  215  extend generally parallel to each other and the side ribs  223  from the top end  230  to the bottom end  232  shown in  FIG. 29 . Each of the small elongate foam ribs  215  are spaced-apart from the side ribs  223  a distance “n times D 1 ” where n is the number of small elongate foam ribs between the foam rib in question (including itself) and a side rib  223 . 
         [0153]    The large elongate foam ribs  214  project transversely relative to the rear wall  216  and extend from the top end  230  to the bottom end  232  of the body  210  shown in  FIG. 29 . Each large elongate foam rib  214  is aligned with a small elongate foam rib  215 , positioned between two adjacent small elongate foam ribs  215 , and extends generally parallel to the adjacent small elongate foam ribs. Each of the large elongate foam ribs  214  are spaced-apart from the side ribs  222  a distance “n times D 2 ” where n is the number of large elongate foam ribs between the foam rib in question (including itself) and a side rib  222 . In the illustrated implementation, D 2  is greater than D 1 . 
         [0154]    Referring to  FIGS. 31 and 32 , the collection portion  202  includes an inner optical layer  240  supported by and attached to the small elongate foam ribs  215  and side ribs  223 . In the illustrated implementation, the inner optical layer  240  is positioned above the small ribs  215 ,  223  such that several fluid chambers  229  are defined between the base  216 , the inner optical layer  240  and adjacent small ribs  215 ,  223 . The fluid chambers  229  are in fluid receiving communication with the top header  242  and fluid expelling communication with the bottom header  244  shown in  FIG. 29 . 
         [0155]    The collection portion  202  also includes an outer optical layer  250  supported by and attached to the large elongate foam ribs  214  and side ribs  222 . The optical layer  250  and dead-air, or inert gas in some implementations, located within insulation chambers  252  defined between the inner optical layer  240 , the outer optical layer  250 , and adjacent large ribs act as an insulator in the same manner as the cover  110  and insulation chamber  114 . As with collection portion  12 , the inner and outer optical layers  240 ,  250 , which may be made of a plastic material having some or all of the characteristics described in Table 1 above, provide two layers of insulation between the environment and the solar absorptive heat transfer fluid circulating through the fluid chambers. The two layers of insulation assist in keeping heat stored in the solar absorptive heat transfer fluid from being lost via radiation, conduction, or convection into the outside environment. 
         [0156]    In some embodiments, the base  212 , large ribs  214 ,  222 , and small foam ribs  215 ,  223  are plated with a reflective layer or coating to reflect sunlight to keep the components of the collection portion  202  cool and, in some embodiments, keep ultraviolet light from damaging the plastic or insulation. Additionally, the reflective layer can enhance solar energy absorption by redirecting the sunlight striking the ribs into solar absorptive heat transfer fluid contained within the fluid chambers, thereby increasing the overall efficiency of the collector  200 . 
         [0157]    Referring to  FIG. 33 , in operation, solar absorption fluid, such black fluid  270 , enters the top header  242  as indicated by directional arrow  254  via a pump and lines much like the collector  10  as previously described. Once the header  242  is filled up to the level where its liquid meets the recess, fluid overflows from the header and into the fluid chambers. The fluid is then continuously gravity fed downward through the fluid chambers as indicated by directional arrows  255  from the top end  230  to the bottom end  232 , collecting solar energy along the way, until it collects in and exits from the bottom header  244  as indicated by directional arrow  256 . 
         [0158]      FIG. 34  illustrates another embodiment of a combined housing and absorber. As shown in  FIG. 34 , a solar energy collector  400  includes a collection portion  402  with four layers of extruded plastic or glass, e.g., a top layer  410 , bottom layer  412 , upper middle layer  414 , and lower middle layer  416 . The plastic material may have some or all of the characteristics described in Table 1 above. Additionally, the plastic may be coated with a material to make the plastic impermeable to vapor and air. 
         [0159]    The top layer  410  and upper middle layer  414 , and bottom layer  412  and lower middle layer  416 , can be coupled together in a spaced apart relationship via a plurality of spacers  420 . The spacers  420  can run a length of the collection portion  402  such that vacuum chambers  422  are formed between respective layers and spacers. The air within the vacuum chambers  422  can be vacated to form a vacuum within each of the vacuum chambers. Getters may be placed inside each vacuum chamber. The vacuum chambers may also be chambers filled with dead air, inert gas or noble gas, rather than a vacuum. 
         [0160]    The upper and lower middle layers  414 ,  416  are coupled together in a spaced apart relationship via absorption chamber spacers  424 . As with the spacers  420 , the absorption chamber spacers  424  can extend a length of the collection portion  402  such that fluid chambers  426  are defined between the upper and lower layers  414 ,  416  and respective spacers  424 . Although not shown, headers can be implemented at respective inlets and outlets to the chambers  426  and solar absorptive heat transfer fluid can be pumped into the chambers  426  via one header and out of the chambers via another header. Top and bottom headers may be recessed to allow only chamber  426  to connect to top and bottom headers. 
         [0161]    As the solar absorption fluid flows between the headers and through the fluid chambers  426 , it collects solar energy. The vacuum chambers  422  are vacated of air to create a vacuum that provides an insulating barrier for preventing conducted and convective heat losses from the solar absorptive heat transfer fluid as it flows through the fluid chambers  426 . 
         [0162]    In some implementations, the fluid chambers  426  have a depth of approximately 0.05 inches. 
         [0163]    The collection portion  402  has a width Q and an overall depth R. In some implementations, the width Q is approximately 6.0 inches and the depth R is approximately 0.5 inches. 
         [0164]    Although not specifically shown, in some implementations, the collection portion  402  may have foam insulation, e.g., a body, surrounding sides  430 , ends (not shown) and bottom layer  412  of the collection portion. Also, a reflective layer  432 , such as a plated metallic layer, may be coupled to the outer surface of the bottom layer  412  to reflect solar light when the fluid chambers  426  are not filled with solar absorption fluid. Further, although the implementation of the solar energy collector  400  illustrated in  FIG. 34  has four layers, in other implementations, the solar energy collector can have more or less than four layers. 
         [0165]    In some embodiments, one or more collection portions can be arranged in series or parallel and coupled to each other directly or via common headers to effectively provide a wider solar energy absorption area. 
         [0166]    Referring now to  FIGS. 35-39 , a modular solar collection system  600  according to one embodiment is shown. Similar to the collection systems described above, modular solar collection system  600  collects energy through use of a circulating or absorptive fluid, such as black fluid. The modular solar collection system  600  is configured to be easily connectable to adjacent collection systems as will be described in more detail below. 
         [0167]    Referring to  FIG. 35 , the collector assembly is shown with each component of the assembly separated and also with each component stacked together into the collector assembly. Collector assembly  600  includes an absorber assembly  610 , frame assembly  620 , foam assembly  630 , gasket  640 , clear top cover assembly  650 , and top retainers  660 . 
         [0168]    Referring now to  FIGS. 36 ,  37  and  38 , illustrating a side, front and top view of the collector assembly, the absorber assembly  610  is similar to the absorbers  20 ,  20 A,  20 B,  20 C described above. Generally, the absorber assembly includes an absorber  613  coupled to two headers  611 ,  612  using adhesive or other known coupling techniques. The absorber  613  can be made of a clear extruded material, such as UV protected polycarbonate plastic having characteristics as described in Table 1 above, and have an overall thickness C. In some instances, the thickness C can be approximately 0.25 inches, and in other instances, the thickness C can be less than or greater than 0.25 inches. The absorber assembly  610  includes one or more fluid chambers (not shown) such as described above. In certain implementations, the fluid chambers of the absorber assembly  610  can contain approximately one gallon of solar absorptive heat transfer fluid. 
         [0169]    The frame assembly  620  includes a right side beam  622 , left side beam  626 , top beam  627 , bottom beam  621 , header mounting apertures  623 , and top cover assembly supports  624 . The header mounting apertures  623  receive the headers of the absorber assembly  610  and allow access to the headers from a location external to the collection system  600 . The top cover assembly supports  624  are spaced-apart along the right and left side beams  622 ,  626  at appropriate intervals to align with mating structures on the top cover assembly as will be described in more detail below. 
         [0170]    The foam assembly  630  comprises a generally rectangular sheet of foam  631  having a thickness that can be approximately half a total thickness R of the collector assembly  600 . In some implementations, sealant materials can be applied to the surfaces of the sheet of foam  631  to reduce out gassing and enhance collector performance. In some implementations, the foam is encapsulated inside a high permeability substance such as plastic. The top surface of the sheet of foam  631  can also be coated with a reflective material  635  to reflect incident solar energy to the sky when fluid is not present in the absorber assembly  610  such that the internal temperature of the collector  600  is near ambient temperature. When fluid is present in the absorber assembly  610 , the reflective material  635  can, in some implementations, effectively increase the absorption path length through the fluid by a factor of two. More specifically, incident solar energy that enters the fluid, but is not absorbed, reflects off the reflective material  635  and passes through the fluid a second time for reabsorption. 
         [0171]    In some implementations, a moisture barrier  636  can be coated on the bottom of the sheet of foam  631  and right and left side beams  622  and  626  to prevent moisture from entering the foam and the assembly  600 . The foam assembly  630  can have stepped ends or recesses  632 ,  633  for receiving the headers of the absorber assembly  610  and allowing for thermal expansion and contraction of the absorber as it heats up and cools down. 
         [0172]    The frame assembly  620  is coupled to the foam assembly  630  and extends about a periphery of the foam assembly. In certain implementations, adhesives secure the frame assembly  620  to the foam assembly  630  to increase the overall strength of the collection assembly  600  and provide a seal between the frame assembly and the foam assembly. 
         [0173]    In the illustrated implementation, the absorber assembly  610  rests upon, but is not attached to, the foam assembly  630 . The foam assembly  630  vertically centers the absorber assembly  610  within the frame assembly  620 . The absorber assembly  610 , e.g., the absorber  613  and attached headers  611 ,  612 , has a length less than the length A of the collector assembly  600  and a width less than the width B of the collector assembly such that the absorber assembly can fit into and float within the frame assembly  620 . The floating nature of the absorber assembly  610  accommodates the thermal expansion and contraction of the absorber as hot solar absorptive heat transfer fluid is either added (expansion) or removed (contraction). 
         [0174]    The top cover assembly  650  comprises a generally rectangular plastic sheet having a front wall  654 , a top wall  652 , and a bottom wall  651 . In some implementations, the plastic may be polycarbonate and may have some or all of the characteristics described in Table 1 above. The top cover assembly  650  also includes beams  653  secured to an inner surface of the front wall  654  and extending parallel to the top and bottom walls  652 ,  651 . The beams  653  can be secured to the front wall  654  by an adhesive or other known fastening method. The beams  653  are sized and shaped to be matingly received and laterally secured in slots formed in the top cover assembly supports  624  of the frame assembly  620 . The top and bottom walls  652 ,  651  can, in some implementations, provide a weather seal and function as an end beam as well. 
         [0175]    The collector assembly  600  includes a pair of top retainers or brackets  660  that at least partially secure the top cover assembly  650  to the frame assembly  620 . In certain implementations, the top retainers  660  each include a central portion that extends lengthwise across the top cover assembly  650  between the top wall  652  and the bottom wall  651  and tabs that extend perpendicularly from the central portion and overlap the top and bottom walls. The tabs can be secured to the frame assembly  620  through use of a fastener or other coupling technique. When secured to the frame assembly  620 , the top retainers  660  secure the top cover assembly  650  in compression. Accordingly, the top retainers  660  prevent front to rear motion of the top cover assembly  650  relative to the frame assembly  620  and the mating engagement between the support beam  653  and the cover assembly supports  624  prevents side to side motion of the top cover assembly relative to the frame assembly. In this manner, the top cover assembly  650  can maintain its structural integrity during severe weather conditions and not make contact with the absorber assembly  610 . 
         [0176]    As has been described above, the foam assembly  630  seals a bottom of the collector assembly  600 , frame  620  seals the sides of the collector assembly, and the top 650 in conjunction with a gasket  640  seals the top of the assembly. Top retainers  660  compress the top 650 into the gasket  640  to form a complete perimeter seal. 
         [0177]    In an exemplary implementation, the length A is approximately 102 inches; the width B is approximately 52 inches; the thickness C is approximately 0.16 inches; and the depth R is approximately 4 inches. The beams of the frame assembly  620  can have a thickness of approximately 1 inch and a height of approximately 4 inches. The support beams  653  can have a thickness of approximately 0.25 inches and a height of approximately 1.25 inches. The collector assembly  600  according to this exemplary implementation, can weigh less than approximately 30 pounds and may hold less than 3 gallons of solar absorptive heat transfer fluid. 
         [0178]    In another exemplary implementation, the length A is approximately 106 inches; the width B is approximately 52 inches; the thickness C is approximately 0.25 inches; and the depth R is approximately 3.5 inches. The beams of the frame assembly  620  can have a thickness of approximately 1 inch and a height of approximately 4 inches. The foam assembly  630  is approximately 1.5 inches thick and the frame  620  is made from 1.0 inch by 3.5 inch PVC foam board. The absorber fluid chambers have a height E of approximately 0.25 inches and a width S of approximately 0.25 inches such that the absorber holds approximately 5 gallons of fluid. 
         [0179]    In some embodiments, the collector assembly  600  provides several advantages. For example, collector assembly  600  is made of inexpensive materials such that the collector assembly is light, strong, weather-proof, easily installed, and aesthetically appealing. The extensive use of plastics and foam in the collector assembly reduces the weight of the assembly, which can lend to easy installation versus heavier collectors. Employing securing structures extending in the directions of dimensions A and B, as well as securing many of the components together using adhesives and fasteners, results in a structurally strong and long-lasting collector assembly. The full perimeter gasket, folded down top cover assembly, and the use of sealant adhesives produce weather tight seals. Additionally, the configuration of the collector assembly  600  resists rain, snow, sleet, and ice build-up by providing smooth top surfaces on which accumulation will readily slide. Also, as described above, the floating nature of the absorber facilitates connecting adjacent units (as will be described below) using simple flexible pipe. Aesthetically, there are no visible components other than the case top and sides. For example, all pipes, connectors, and roof mounts remain out of sight under the top cover assembly  650 . 
         [0180]    As shown in  FIG. 39 , in certain implementations, the modular solar collection system  600  is connectable, such as in parallel, to other collector assemblies. In one specific implementation, such as shown in  FIG. 38 , three collection systems  600  are connected in parallel. Although three collection systems interconnected are shown, in other implementations, fewer or more than three collection systems can be connected together in parallel or otherwise. Flexible couplers (not shown) extending through holes  623  connect one collector assembly  600  to another connector assembly  600 . In some implementations, ten or more collector assemblies can be connected together. In some instances, on-site assembly of a collector assembly array can be accomplished in less than a day by a crew of two. In the event an additional collector assembly is needed, such as when more solar surface area coverage to capture more energy is desired, one or more additional collector assemblies can be easily connected in any of various configurations known in the art. 
         [0181]    The collector assembly  600  provides a combination of excellent energy collection performance, low manufacturing cost, and low installation cost. Accordingly, the collector assembly  600  can provide a considerable benefit to heat energy consumers. 
         [0182]    Turning now to  FIG. 40 , and according to one embodiment of a drainback system with a fluid reservoir  154  contained within the thermal storage mass  152 , a solar energy apparatus, e.g., solar energy collector, or collection system,  10 , includes a solar energy collection portion  12 . The collection portion  12  includes an absorber  20 , a bottom header  60 , a top header  62 , and a frame  100 . The solar energy collection portion  12  has a generally rectangular configuration although any other suitable geometry could be used. 
         [0183]    The collector  10  includes a solar energy distribution system  14 . The solar energy distribution system  14  includes a fluid pump  150 , thermal storage mass  152  and fluid reservoir  154  in thermal communication with each other via heat exchanger  158 . In some implementations, lines, as used herein, can be insulated conduits or pipes. 
         [0184]    In operation, solar absorptive fluid, e.g., black fluid, which is stored in the reservoir  154 , is pumped via lines  156  by pump  150  into the bottom header  60  at the open end  70  as indicated by directional arrow  161 . Black fluid entering the bottom header  60  flows through the fluid passageway of the header and is initially contained within the header by the closed end  72  of the header. The fluid passageway of header  60  fills with black liquid until the fluid reaches the level of the infeed slot  76  shown in  FIG. 14 . Further pumping of fluid into the fluid passageway of the header causes fluid to flow through the slot  76  and into the absorber chambers. As pumping continues, fluid flows upward in the direction indicated by directional arrow  163  from the bottom end  38  of the absorber to the top end  42  until the entire absorber fills with black fluid as shown in  FIG. 2 . 
         [0185]    Once the absorber chambers are filled, further pumping causes fluid to enter the top header  62  via an outfeed slot (not shown) similar to the infeed slot  76 . The fluid passageway of the top header  62  fills with fluid in the same manner as the bottom header  60  until the passageway is at least partially full and fluid exits the top header via its open end  70  in a direction indicated by directional arrow  165 . From the open end  70  of the top header  62 , the fluid enters fluid line  157  and flows into heat exchanger  158 , then returns to the reservoir  154 . Storage mass  152 , which can be any thermal mass commonly known in the art, stores heat for use by other devices (not shown) attached to the system. 
         [0186]    Although  FIG. 40  shows operation with only one collector assembly  12 , in other embodiments, several collector assemblies may be connected in series or in parallel. 
         [0187]    In operation, the pump  150  cyclically pumps fluid through the system such that fluid continuously flows upward through the absorber chambers. As black fluid flows through the absorber  20 , solar energy from the sun is absorbed in the black fluid as thermal energy. The thermal energy is then transferred to the thermal energy storage mass  152  via header  62  and transport pipe  157 , and heat exchanger  158 . 
         [0188]    The black, or sufficiently high absorptivity, fluid can have any of various properties or performance characteristics depending on the application or the structure of the collector, such as the depth of the absorber chambers. For example, listed in Table 2 below are several solar absorptive heat transfer fluid parameters, associated general descriptions of the parameters, parameter values according to various embodiments, and associated comments. The parameters, values, and comments listed in Table 2 are merely examples of parameters and parameter value ranges of implementations of solar absorptive heat transfer fluid that can be used in the solar energy apparatus described herein. In other embodiments, the solar absorptive heat transfer fluid can have performance characteristics that are not listed in Table 2 or fall outside of the value ranges specified in Table 2. 
         [0000]    
       
         
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                   
                   
                   
                 Exemplary 
               
               
                 Parameter 
                 Description 
                 Comment 
                 Value Range 
               
               
                   
               
             
             
               
                 Absorptivity 
                 A measure of the ability to 
                 In some implementations, higher 
                 &gt;0.95 
               
               
                   
                 convert sunlight into heat. 
                 absorptivity is desired. 
               
               
                 Emissivity 
                 Ability to emit infrared. 
                 In some implementations, lower 
                 &lt;0.90 
               
               
                   
                   
                 emissivity is desired. 
               
               
                 Evaporation 
                 The relative amount of 
                 Evaporation can degrade optical 
                 Very Low 
               
               
                   
                 energy required to convert 
                 performance. Moreover, evaporated 
               
               
                   
                 a liquid into a vapor per 
                 gases may escape and result in fluid 
               
               
                   
                 unit mass. 
                 loss. In some implementations, 
               
               
                   
                   
                 evaporation is minimal. 
               
               
                 Pigments or 
                 Materials with high 
                 In some implementations, higher 
                 Highly 
               
               
                 Dyes 
                 absorptivity that dissolve 
                 absorptivity is desired. Moreover, 
                 Absorptive 
               
               
                   
                 or stay in suspension 
                 pigments and dies should be selected 
               
               
                   
                 within a liquid 
                 that do not evaporate, adhere to 
               
               
                   
                   
                 surfaces, or hamper circulation. 
               
               
                 Liquid Abrasion 
                 Ability of fluid to 
                 Generally, the liquid should not 
                 Very Low 
               
               
                   
                 frictionally wear down 
                 significantly wear out fluid 
               
               
                   
                 other materials through 
                 containing structures or the pigments 
               
               
                   
                 fluid flow. 
                 or dyes. 
               
               
                 Specific Heat 
                 Heat capacity per unit 
                 In some implementations, higher 
                 &gt;0.4 
               
               
                   
                 mass 
                 values for specific heat are desired. 
                 BTU/Pound- 
               
               
                   
                   
                   
                 deg F. 
               
               
                 Density 
                 Unit mass or weight of a 
                 Not directly a performance measure 
                 Not applicable 
               
               
                   
                 material (in this case a 
               
               
                   
                 liquid) per unit volume. 
               
               
                 Density - 
                 A measure of the heat 
                 In some implementations, high 
                 &lt;50 
               
               
                 Specific Heat 
                 energy added per unit 
                 “Density times Specific Heat” is 
                 BTU/cubic 
               
               
                 Product 
                 volume of a material to 
                 desirable because it directly effects 
                 foot of 
               
               
                   
                 raise its temperature 1 
                 the required flow rate and thereby the 
                 substance 
               
               
                   
                 degree F. 
                 resulting pump size. 
               
               
                 Thermal 
                 Ability of a fluid to 
                 In some implementations, high 
                 &gt;4.0 (BTU- 
               
               
                 Conductivity 
                 conduct heat-per unit 
                 thermal conductivity is desired, such 
                 in/hr-ft 2 -F.) 
               
               
                   
                 length for a given cross- 
                 as proximate a thermal mass. 
               
               
                   
                 sectional surface area. 
               
               
                 Freezing Point 
                 Temperature at which fluid 
                 In some implementations, a low 
                 &lt;−40° F. 
               
               
                   
                 freezes. 
                 freezing point is desired for various 
               
               
                   
                   
                 reasons, such as freezing problems 
               
               
                   
                   
                 which break pipes. 
               
               
                 Boiling Point 
                 Temperature at which fluid 
                 In some implementations, higher 
                 &gt;200° F. 
               
               
                   
                 boils. 
                 boiling points are preferred to reduce 
               
               
                   
                   
                 danger, increase safety and prolong 
               
               
                   
                   
                 operability of the collector. 
               
               
                 Viscosity 
                 Ability of fluid to resist its 
                 In some implementations, low 
                 Low 
               
               
                   
                 own flowing. 
                 viscosity values are desirable. Higher 
               
               
                   
                   
                 values may require a larger pump. 
               
               
                   
                   
                 Generally, aging and liquid 
               
               
                   
                   
                 temperature are factors that 
               
               
                   
                   
                 determine the viscosity of the fluid. 
               
               
                 Surface Tension 
                 Ability of fluid to form 
                 Low surface tension allows the fluid 
                 Low 
               
               
                   
                 tension on its surface that 
                 to fully drain from the absorber, 
               
               
                   
                 holds itself together. 
                 results in less capillary action and 
               
               
                   
                   
                 wicking. This reduces problems of 
               
               
                   
                   
                 pipes breaking during freezing. 
               
               
                 Flammability 
                 Ability of fluid to support 
                 In some implementations, lower 
                 Low 
               
               
                   
                 combustion. 
                 flammability values are desirable. 
               
               
                 Plastic 
                 Ability of fluid to remain 
                 In some implementations, plastic is 
                 High 
               
               
                 Compatibility 
                 functionally operable 
                 compatible with solar absorptive heat 
               
               
                   
                 when in contact with 
                 transfer fluid for at least 30 years. 
               
               
                   
                 plastic. 
               
               
                 Cost 
                 Fair market value of fluid. 
                 In some implementations, lower fluid 
                 &lt;$10/gallon 
               
               
                   
                   
                 cost is desirable. 
               
               
                 Lifetime 
                 Time period in which fluid 
                 In some implementations, the fluid is 
                 &gt;3 Years 
               
               
                   
                 remains functionally stable 
                 replaced once every three years. In 
               
               
                   
                   
                 certain implementations, the 
               
               
                   
                   
                 controller includes a computer that 
               
               
                   
                   
                 provides a notification to replace the 
               
               
                   
                   
                 fluid. 
               
               
                 Staining 
                 Propensity of the fluid to 
                 Staining may result in the absorption 
                 Low 
               
               
                   
                 stain. 
                 of heat during stagnation which may 
               
               
                   
                   
                 cause plastic to break over a period of 
               
               
                   
                   
                 time. 
               
               
                 Permeability 
                 Ability of fluid to 
                 In some implementations, the 
                 Low 
               
               
                   
                 permeate through plastic. 
                 permeability of the fluid is desirably 
               
               
                   
                   
                 low. This is a function of the fluid 
               
               
                   
                   
                 and the plastic of Table 1 together. 
               
               
                 Resistant to O 2   
                 Ability of fluid to resist 
                 In some implementations, fluid is 
                 High 
               
               
                 and UV 
                 oxidization and UV 
                 generally resistant to oxidization and 
               
               
                   
                 damage. 
                 UV damage. 
               
               
                 Eco-friendly 
                 Measure of negative 
                 Generally desirable to reduce long- 
                 Low 
               
               
                   
                 impact on environment. 
                 and short-term harm to environment. 
               
               
                 Future 
                 Ability to change fluids as 
                 In some implementations, selecting a 
                 Medium 
               
               
                 Expandable 
                 better ones are developed. 
                 fluid that resists staining and lowers 
               
               
                   
                   
                 permeability allows future fluids to 
               
               
                   
                   
                 be compatible with the original 
               
               
                   
                   
                 absorber with perhaps higher 
               
               
                   
                   
                 performance since past residues will 
               
               
                   
                   
                 be minimized. 
               
               
                   
               
             
          
         
       
     
         [0189]    In some embodiments, the solar absorptive heat transfer fluid can be automotive automatic transmission fluid or propylene glycol, and the pigments or dyes can be conventional printing inks known in the art, carbon black, or other high absorbtivity substance, in powder form. 
         [0190]    In some implementations, one or more of the surfaces of the base  102  defining the insulation chamber  114  shown in  FIGS. 16 and 17  can be coated with a low permeability coating. Further, in some implementations, the insulation chamber  114  is in gas vapor flow communication with a low permeability bladder bag  103  external to the structure or an expansion tank known in the art. By coating the base  102  with a low permeability coating and using a low permeability bladder bag  103  or expansion tank to supply and maintain gas in the insulation chamber  114 , the rate at which gas permeates through the base  102  may be sufficiently reduced to economically contain a noble or inert gas, such as Argon or Nitrogen, within the insulation chamber. 
         [0191]    In some embodiments, the solar energy collection system  10  can be operated to reduce the overall temperature of the system in the event the temperature of the absorber exceeds a predetermined threshold. As the solar absorptive heat transfer fluid circulates through the system, the thermal storage mass  152  will increase in temperature if the current energy taken out of the system, either directly or through a thermal heat exchange element or heat exchanger (not shown) in energy transfer communication with the thermal storage mass  152 , is less than the current sun input that is converted into heat. 
         [0192]    More specifically, the temperature of the fluid exiting the thermal storage mass  152  and entering the absorber  20  is approximately the same as the temperature of the thermal storage mass. The temperature of the fluid flowing through the absorber  20  increases to a new temperature greater than the temperature of the thermal storage mass  152  as it absorbs energy from the sun. The fluid exits the absorber at the new higher temperature and comes into heat exchange contact with the thermal storage mass, which causes the temperature of the thermal storage mass to increase. If energy is not transferred from the system, the fluid exits the thermal storage mass at a temperature greater than when it exited the thermal mass in the previous cycle. In other words, the temperatures of the components around the solar energy collection system loop can increase in tandem. Without some mechanism to reduce the sun input converted to heat or increase the current energy consumption, the temperature of one or more of the components around the loop may become dangerously high and cause long-term damage to some or all of the components including but not limited to any plastic, foam or fluid materials. 
         [0193]    Based on the properties of the solar absorptive heat transfer fluid, plastic components and insulator components of the solar energy apparatus described herein, a predetermined maximum operating temperatures of the thermal storage mass T tm     —     max  and the collection portion T c     —     max  may be selected where T c     —     max  is slightly above T tm     —     m . For example, in one specific implementation, the thermal mass can be water, T tm     —     max  can be set to 180° F. (sufficiently below the boiling point of water), and T c     —     max  can be set to 195° F., which is somewhat below the boiling point of water or a composite liquid. The collector will continuously pump fluid through the absorber and transfer thermal energy to the thermal mass until the overall temperature T c  of the collection portion reaches T c     —     max , at which time the pump will shut off and a fluid valve  113  located in the bottom header  60  and an air valve  115  located in the top header  62  will open. The fluid is then allowed to drain out of the absorber  20  and into the fluid reservoir  154  via the fluid valve  113  and the line  162 . As the fluid drains, air entering through the air valve  115  replaces the fluid. With no fluid being located within the absorber  20 , the collector is placed in the non-operative state and solar energy penetrating the absorber will be reflected by the reflective layer  44  shown in  FIG. 1 . Since solar energy is being reflected, rather than absorbed, the overall temperature T c  of the collection portion will not exceed T c     —     max  and can be maintained below a safe operating limit. 
         [0194]    In some embodiments, a control system, such as system  167 , is included. The system  167  may include a microcomputer that monitors temperature at one or more locations within the solar energy collection system  10  and opens the valve described above when the temperature at the one or more locations reaches a predetermined limit. 
         [0195]    In some embodiments, the solar energy collection system can include an additional safety mechanism to prevent overheating of the collection system in the event the control system fails. The additional safety mechanism includes a snap switch, as commonly known in the art, which forces the fluid to drain from the absorber if the control system fails to open the valve. For example, in some implementations, the microcomputer of the control system can be programmed to open the valve at a T c     —     max  limit of 160° F. and the backup snap switch could have a temperature threshold of 160° F. If the microcomputer or its interfacing components fail, the snap switch will shut off at 160° F., thus draining the fluid from the absorber. The use of a snap switch, or other similar device, provides a simple and reliable safety backup to the control system. 
         [0196]    After the fluid has drained from the absorber  20 , the temperature of the collection system will decrease. Once the temperature of the solar energy collection system dips below a predetermined minimum temperature, the control system can close the fluid valve  113  and pump  150  can again circulate solar absorptive heat transfer fluid through the absorber  20 , which causes the air within the absorber exit the absorber through the air valve  115 . Once the absorber  20  is full, the air valve  115  can close. 
         [0197]    In view of the many possible embodiments to which the principles of the disclosed solar energy apparatus may be applied, it should be recognized that the illustrated embodiments are only examples and should not be taken as limiting the scope of the disclosure. 
         [0198]    It can thus be seen that at least certain of solar energy absorption apparatus embodiments set forth above can provide the following advantages among others:
   1. Reduction in the cost of manufacturing due to, among other things, the ability to make the apparatus with inexpensive materials that, in some instances, can be extruded. For example, traditional solar panels use an absorber made of metal and a top surface made of a different material that allows light to pass through. Accordingly, the absorber and top surface of traditional solar panels cannot be extruded as one piece. In contrast, the use of solar absorptive heat transfer fluid in the solar energy apparatus described herein allows for the top layer and the absorber to be made of the same material. Therefore, in some implementations, the top surface and the absorber can formed as a single extruded part, which lowers manufacturing cost.   2. Reduction in the size, thickness, and weight due to, among other things, a reduced volume and depth of absorptive fluid flowing through the collection portion of the apparatus. For example, the amount of solar absorptive heat transfer fluid to heat a typical home may go from 100 gallons to 20 gallons, saving up to $20 per month in operating costs over the life of the system.   3. Reduced apparatus cost for each Joule (BTU) collected due to, among other things, the reduced volume of absorptive fluid, the unique composition of the absorptive fluid and plastic components.   4. Prolonged operating life due to, among other things, a construction made of plastic with particular optical and UV characteristics and the use of reflective materials, layers, or coatings for protecting underlying structures.   5. Enhanced temperature control to prevent overheating and prolong the life of the absorptive fluid and structural components of the apparatus. For example, as one instance of overheating can cause deleterious long-term effects on the components of an apparatus, effectively eliminating such overheating by reflecting light back to the sky promotes system reliability in a natural and reliable way.   6. Potential for increased efficiency. The efficiency of the collector is a direct function of the absorptivity of the solar absorptive heat transfer fluid to visible and UV light. As such, as better fluids become a reality, the efficiency of existing systems can be increased by simply changing the fluid.   7. Reduction in the cost of system and operation. By using less solar absorptive heat transfer fluid, the cost of the system is reduced. Additionally, the size, and thereby the cost, of the drain back storage tank can be reduced, which results in less insulation required to insulate the storage tank and a lower overall system insulation cost.   8. Uniform heat transfer to absorptive fluid. Since heat transport is ubiquitous over the entire surface of the absorber, uniform heat transfer is achieved at no additional cost. This ubiquity of heat transfer completely obviates the economic trade-off between conventional absorber thickness and riser pipe spacing.   9. Quicker and easier installation compared to conventional solar energy collectors.   10. Increased efficiency due to, among other things, the ability to construct vacuum insulation inexpensively to eliminate convective and conductive heat losses from the absorber to the ambient air. In some implementations, the vacuum insulation exists in panel form, while in others the insulation exists within a cylinder.   11. Reduced overheating, thereby allowing for use of inexpensive materials and eliminating damage to circulation fluid.   12. Increased efficiency due to shapes and configurations that capture nearly 100% of the incident solar energy at any incident sun angle.   13. Increased efficiency due to utilization of infrared radiation retention coatings.   14. Increased safety due to control of the maximum operating temperature of the device, thereby reducing effects of scalding and eliminating steam.   15. Increased design flexibility, as structural dimensions, structural materials, fluid composition, maximum operating temperature, stagnation temperature, environmental effects and insulation properties remain controllable and predictable while using common, low cost, materials and processes.   16. Elimination of heat pipes and pipes that heat to a condenser which has a glass-metal interface connecting to the top header. When the header flow stops (stagnates), the glass-metal interface goes up in temperature and can damage the evacuated tube since the tiniest crack will let air in and ruin the vacuum. Coaxial solar absorptive heat transfer fluid collectors eliminate this problem by having no dissimilar materials that get hot and heat collection goes away during stagnation because the black fluid drains out of the tubes.   17. Increase in collection of more diffuse solar energy, possibly up to 2 times more.   18. Lower maintenance costs since components are limited to temperatures that do not cause them long-term damage and cannot cause heat transport fluid to become an agent of chemical attack upon components that come in contact with the fluid.