Flat plate solar collector
BACKGROUND OF THE INVENTION 
     It is an object of the present invention to provide a modular high performance, low-cost and structurally strong collector which can be inexpensively and readily repaired. Another object of the present invention is to provide a high performance collector having improved efficiency coupled with high reliability as a result of the employment of a low-cost plastic flow channel plate. 
     SUMMARY OF THE INVENTION 
     In accordance with the aforementioned objects the present invention provides a modular flat plate solar collector having a top cover selectively coated for transmitting maximum solar radiation. A plurality of stacked, separate low-cost solar collector elements are maintained by fastening members in intimate contact with each other and with the top plate during operation thus providing a stacked, structurally strong unit. Removal of the fastening members permits inexpensive parts replacement. The performance of this modular flat plate solar collector is further improved by employing a flow channel plate having passages with an aspect ratio substantially in the range of 20 or greater. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates an exploded view in partial cross-section showing the modular configuration of the solar collector of the present invention. 
     FIG. 2 shows a partially broken away view of the convection suppressor employed in the present invention. 
     FIG. 3 is a perspective view, partially broken away, illustrating an assembled solar collector of the present invention. 
     FIG. 4 depicts performance curves illustrating the improved efficiency of the present solar collector employing the flow channel plate of the present invention compared against other collector configurations. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Now referring to FIG. 1, it illustrates a collector unit having a transparent glass cover 10 approximately 1/8  inch thick which is treated with an anti-reflective material in order to transmit the maximum amount of solar radiation and filter out ultra-violet radiation. The ultra-violet radiation tends to degrade many of the plastic type components employed in present low-cost collector units. A convection suppressor having a height of about 2 inches, generally shown at 12 and in greater detail in FIG. 2, is formed of a thin walled plastic material, approximately 0.005 inches thick, and operates to minimize radiation losses due to convection and conduction. The suppressor 12 contains a plurality of separate compartments 14 whose length and width dimensions in the preferred embodiment may vary anywhere between 1 and 1/2 inches so as to form either rectangular or square enclosures. Other shapes for the compartments, e.g., circular or multisided, are also suitable. The compartments 14 interrupt convection currents and they also trap air to form stagnant air pockets which act as insulators to minimize thermal losses. 
     An absorber sub-assembly or unit 16 is formed by depositing a thin, e.g., of the order of one micron, black chrome layer 18 on a thin, e.g., one to five mil aluminum foil layer 20. This structure results in an absorber having a solar absorbtivity figure of 0.95 or higher, and conversely an infra-red emissivity radiation loss figure of 0.05 or less. 
     A channel fluid flow plate 22 is formed by joining two thin plastic sheets each 25-100 mils thick. A lower plastic sheet 24 can be formed or contoured by using a thermal plastic material and vacuum or thermal molding techniques to form a plurality of corrugations or bumps 26 in order to define a plurality of passages 27. Ultrasonic or adhesive bonding techniques can then be employed to join the lower sheet 24 to an upper sheet 28. If thermal setting plastic sheets are used then the corrugations or bumps 26 are joined to the upper sheet by an adhesive as ultrasonic techniques are not suitable for thermal setting plastics. 
     The thin metal foil absorbing surface 16 is subsequently attached to the plastic flow channel plate 22 in a manner which minimizes the thermal impedance between the members. This attachment can be accomplished via known bonding techniques (e.g., adhesive bonding). 
     A low density solid block 30, such as plastic foam, two to 3 inches thick, provides insulation at the back of the plastic channel flow plate 22. The insulator 30 not only prevents heat losses but adds structural integrity and support to the overall unit. 
     When assembled, outer support member 32 and inner support member 34, having appropriately positioned fastening holes 36 and 38, are interlocked by screws (not shown) to engage the side of the collector elements, the transparent top cover 10, and a thin metal or plastic back cover 40 in order to maintain the collector elements in stacked and intimate contact with each other as represented by the dotted lines. It can be seen that this modular approach allows the collector unit to be readily assembled or disassembled for repair. Moreover, since each of the collector elements is separable, replacement costs are kept to a minimum. Only one half of the collector is shown for simplicity, and in the preferred embodiment a single panel is one by two meters in size. This unit is readily mounted on existing structures without requiring special reinforcing as it is extremely light, approximately 5 pounds per square foot for the materials described. 
     FIG. 3 illustrates an assembled collector unit and includes a transparent cover 50, convection suppressor 52, absorber plate 54, a partially broken away flow plate 56 to show a plurality of fluid passages generally shown at 58, and a low density insulating foam insulator block 60. These collector elements are supported by base plate 62 and held in stacked intimate relationship by interior and exterior mounting flanges 64 and 66, respectively. The fasteners for members 64 and 66 are not shown in this depiction. 
     Improved efficiency of this collector is obtained by the combination of the cited, or described, collector elements, minimizing the conductive losses within the flow channel plate 22, as best illustrated in FIG. 1. This is accomplished by minimizing the internal sidewall area within each of the channels 27 thus decreasing sidewall conduction losses. More of the radiation received by the absorber plate is available to heat the fluid within the individual passages 27. Fluid, such as water in the preferred embodiment is conveyed under pressure to the fluid passages 58 via inlet fitting 68. 
     In the preferred embodiment each of the channels depicted in FIG. 1 is one inch wide and 0.05 inches in height. Thus the aspect ratio, i.e., width over height is at least 20. Higher aspect ratio can be obtained within manufacturing and fluid frictional limitations so as to further reduce sidewall conduction and increase overall efficiency of the solar collector. Curve I in FIG. 4 illustrates the improved performance of the solar collector of the present invention compared against other solar collectors where the letter designation (A-I) for each curve coincides with the letter designation associated with the collector configurations characterized in the following chart. 
     
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             NUMBER OF                                                    
COLLECTOR    GLAZING ABSORBER PLATE                                       
CONFIGURATION                                                             
             LAYERS  ABSORPTANCE                                          
                              EMITTANCE                                   
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A.                                                                        
  Flat Black 1       .93      .93                                         
B.                                                                        
  Flat Black 2       .93      .93                                         
C.                                                                        
  Flat Black W/Soft                                                       
             1       .93      .93                                         
  Vacuum                                                                  
D.                                                                        
  Flat Black W/Soft                                                       
             2       .93      .93                                         
  Vacuum                                                                  
E.                                                                        
  Selective  2       .9       .1                                          
F.                                                                        
  Selective W/Soft                                                        
             1       .9       .1                                          
  Vacuum                                                                  
G.                                                                        
  Selective W/Soft                                                        
             2       .9       .1                                          
  Vacuum                                                                  
H.                                                                        
  Selective W/High                                                        
             1       .9       .1                                          
  Vacuum                                                                  
I.                                                                        
  High Convection                                                         
             1       .5       .05                                         
  Suppressant Anti-                                                       
  Reflection Treatment                                                    
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     It is noted that the present invention collector is more efficient than all of the other collector configurations therein represented with the exception of the selective high vacuum collector configuration. Of course this latter collector configuration is much more expensive than the collector configuration of the present invention.