Patent Publication Number: US-2015075518-A1

Title: Solar collector of fixed and concentrating flat panel type

Description:
REFERENCE TO RELATED APPLICATIONS 
     This application claims the priority benefit of Korean Patent Application No. 10-2013-111492 filed on Sep. 17, 2013, the entire contents of which are incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention relates to a fixed concentration type flat panel solar collector and, more particularly, to a solar collector of a fixed and concentrating flat panel type, wherein the structures of the reflection plate and absorption plates of the solar collector are optimized and a coating layer is formed on a surface of the absorption plate, thereby being capable of improving concentration efficiency. 
     BACKGROUND OF THE INVENTION 
     As well known, a solar collector is basically divided into a vacuum tube type solar collector and a flat panel type solar collector. Regarding the vacuum tube type solar collector, China produces a solar energy concentration area of 12 million m 2  or more per year based on the price competitiveness of a bore-silicated glass tube, sells the solar collectors in the domestic market, and also exports them to the European market. In particular, Himin and Linuo in Shandong province, Qinghua in Peking, SunRain in Jiangsu province, and Vantage in QUangdong province are leading export companies, and they are threatening the solar energy market of Korea after the second half of 2004. 
     A technical field using solar energy is gradually changed from a range of a relatively low temperature (about 60° C.) in the past to solar energy cooling fields and industrial process heat use fields, and thus a solar energy use temperature is also expanded to about 60 to 150° C. Regarding the temperature range of the solar collector required in the solar energy cooling field, a solar energy cooling system associated with an absorption type refrigerator requires about 95° C. In the dehumidification cooling field, water temperature of about 70° C. is required. There is a need to continue to develop new solar collectors suitable for purposes. 
     In order for a solar collector to be used in such middle and high temperature, the solar collector needs to have a very excellent thermal loss characteristic. A vacuum tube type solar collector and a CPC solar collector belong to such a solar collector. However, such solar collectors has many limits when a large amount of the solar collectors are installed because the solar collectors are expensive and limited in installation. 
     In 2005, with the necessity of researches on a middle-temperature solar collector, TASK 33/IV of IEA carried out researches on the development, performance improvement, and optimization of a middle-temperature solar collector (having a range of 80 to 250° C.). Companies which product such middle-temperature solar collectors include Solaire, SCHUCO, AoSol, Solarfocus, PARASOL, and SOLITEM. Such a solar collector has been developed to have a different structure and a concentrating type, thus having good high temperature efficiency. 
     An energy concentration type solar collector using middle and high temperatures may include a vacuum tube type, a Parabolic trough Concentrator (PTC), a Compound Parabolic Concentrator (CPC), a parabolic complex solar collector, and a parabolic dish depending on the geometric structure of a concentrating form. 
     The use of such an energy concentration type solar collector is gradually increased in advanced countries due to the development of process heat or solar energy cooling and solar energy in industrial sites because the energy density is very greater than that of a non-energy concentration type solar collector. 
     The CPC type solar collector is fixed without tracking the sun, and has a solar energy absorption area smaller than a solar energy incident area and is an energy concentration type solar collector capable of obtaining a range of a middle temperature (about 100 to 200° C.). The CPC type solar collector may have an energy concentration cost of 10 or less, and may obtain a desired temperature depending on selection. 
     A high-efficiency CPC solar collector basically includes a reflection plate, an absorption plate, a heat transfer pipe, and a frame. The high-efficiency CPC solar collector is chiefly developed and used in association with the vacuum tube type solar collector. 
     Such a CPC solar collector may be chiefly used in a solar energy cooling system for an industrial process that requires high-temperature energy of 70 to 150° C. and a solar energy cooling system that uses a high temperature of about 95° C. because the solar collector may obtain a higher temperature by concentrating energy through the concentration of light. 
     Most of CPC solar collectors have relatively good performance because they have been developed in the form of a vacuum tube type solar collector, but are expensive. Furthermore, the CPC solar collector has many disadvantages compared to a conventional flat panel type solar collector because a high installation cost is required when installing a large-scale commercial system because vacuum tubes must be assembled and the design is complicated. 
     Recent researches on the CPC solar collector is chiefly focused on a scheme for increasing an energy concentration cost according to a change in the shape of a reflection mirror, the design of an absorber, and a scheme for improving performance through grafting with the vacuum tube type solar collector. In such researches, localization researches have been partially carried out by some research institutes, and some products associated with the vacuum tube type solar collector have been developed. However, the research and development and commercialization of solar collector products having a flat panel type solar collector form are yet incomplete. 
     EXEMPLARY REFERENCES 
     Korean Patent No. 10-0692950 entitled “Flat-Plate Solar Collector using Channel Type Absorber Plate (Mar. 3, 2007) 
     Korean Patent No. 10-0993809 entitled “Solar Collector Module and System” (Nov. 5, 2010) 
     Korean Patent Application Publication No. 20-2002-0047766 entitled “Plat Type of Solar Absorber System Comprising Atransparent Insulator” (Jun. 22, 2002) 
     Korean Patent No. 10-0388044 entitled “Panel of Solar Collector and Apparatus for Manufacturing the Same (Jun. 4, 2003) 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a solar collector of a fixed and concentrating flat panel type, which is capable of maximizing a solar energy absorption ratio by optimizing the structures of the reflection plate and absorption plates of the solar collector. 
     Another object of the present invention is to provide a solar collector of a fixed and concentrating flat panel type, which is capable of improving concentration efficiency by forming a coating layer on a surface of an absorption plate. 
     In accordance with an aspect of the present invention, a solar collector of a fixed and concentrating flat panel type configured to comprise a hollow frame  28 , a cover  12 , and a transmission body  20 , and hollow absorption pipes  22  and rises  24  for supplying an external thermal medium and to have an insulator  14 , a reflection plate  16 , and absorption plates  18  sequentially disposed within the solar collector, wherein the reflection plate  16  is configured to have an elliptical symmetry structure and to reflect solar energy toward the absorption plates  18  as much as possible with respect to an incident angle of the solar energy that varies according to each time zone. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram illustrating the configuration of a solar collector of a fixed and concentrating flat panel type in accordance with an embodiment of the present invention; 
         FIG. 2  is an exploded view of the technical configuration of the solar collector of a fixed and concentrating flat panel type illustrated in  FIG. 1 ; 
         FIG. 3  is an enlarged view of the technical configuration of the solar collector of a fixed and concentrating flat panel type illustrated in  FIG. 1 ; 
         FIG. 4  is a cross-sectional view of an absorption plate  18  illustrated in  FIG. 3 ; and 
         FIG. 5  is a graph illustrating a change of reflectance and a radiation factor according to an NaOH ratio after the surface pre-processing of the absorption plate  18  in accordance with an embodiment of the present invention. 
     
    
    
     Description of reference numerals of principal elements in the drawings 
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 10: solar collector 
                 12: cover 
               
               
                   
                 14: insulator 
                 16: reflection plate 
               
               
                   
                 18: absorption plate 
                 20: transmission body 
               
               
                   
                 22: absorption pipe 
                 24: rise 
               
               
                   
                 26: pipe connection body 
                 28: frame 
               
               
                   
                 30a, 30b: coating layer 
               
               
                   
                   
               
            
           
         
       
     
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, embodiments of the present invention are described with reference to the accompanying drawings. In the following detailed description, some representative embodiments of the present invention for achieving the aforementioned objects are described below. Furthermore, other embodiments that may be proposed by the present invention are replaced with descriptions in the configuration of the present invention. 
     In an embodiment of the present invention, absorption plates of a V-band form in which coating layers are formed on both sides within a solar collector fabricated in a flat panel type are installed at regular intervals, and a reflection plate configured to reflect solar energy toward the absorption plates and to have an elliptical and symmetrical structure are disposed under the absorption plates. Accordingly, a solar collector of a fixed and concentrating flat panel type which is capable of maximizing a solar energy absorption ratio and improving concentration efficiency may be implemented. 
       FIGS. 1 to 3  are diagrams illustrating a solar collector of a fixed and concentrating flat panel type in accordance with an embodiment of the present invention. The solar collector  10  in accordance with an embodiment of the present invention includes a hollow frame  28 , a cover  12 , and a transmission body  20  that form a frame of a square form. The solar collector   10  includes an insulator  14 , a reflection plate  16  having an elliptical and symmetrical structure, and absorption plates  18  of a V-band type which are sequentially installed within the solar collector  10 . The solar collector  10  further includes hollow absorption pipes  22  and rises  24  for supplying an external thermal medium. 
     The reflection plate  16  and the absorption plates  18  correspond to essential elements of the present invention. The solar collector  10  is configured to increase an absorption ratio for solar energy and improve concentration efficiency. This may be easily understood by the following detailed description. 
     Referring to  FIGS. 1 to 3 , the frame  28  that forms an outskirt square frame of the solar collector  10  is chiefly fabricated by extruding aluminum. In order to increase insulation performance, a hollow layer  28   a  is formed at the central part of the frame  28 . Furthermore, a groove for fixing the transmission body  20  on a front surface is formed in the frame  28 . The transmission body  20  is shaped using transparent materials or semi-transparent materials, and is made of glass materials. 
     The cover  12  is disposed in the rear of the frame  28 , more specifically, at a point that faces the transmission body  20 . The insulator  14 , the reflection plate  16 , and the absorption plates  18  are disposed between the transmission body  20  and the cover  12 . In this case, the hollow absorption pipes  22  are disposed inside the frame  28  at both ends thereof, and a plurality of rises  24  is connected to the respective absorption pipes  22 . Connection pipes  26 , that is, paths through which an externally supplied thermal medium flows, are disposed at both ends of the absorption pipes  22  in the absorption pipes  22  and the rises  24 . Such a configuration corresponds to a common technical configuration in configuring the solar collector  10 , and a detailed description thereof is omitted. 
     The reflection plate  16 , that is, one of the essential elements of the present invention, is disposed at the top of the insulator  14  as shown in  FIG. 3 . The reflection plate  16  is configured to increase an absorption ratio for solar energy and to improve concentration efficiency. That is, the reflection plate  16  is configured to have an elliptical symmetry structure in order to improve reflection efficiency as much as possible. As shown in  FIG. 3 , the lower part of a shape, such as an alphabetic letter “W”, rounded, and such shapes are connected to form the reflection plate  16 . In such a configuration, the reflection plate  16  may reflect solar energy toward the absorption plates  18  as much as possible with respect to an incident angle of the sun that is varied depending on the time zone. Furthermore, reflection coating processing has been performed on the front surface (i.e., a top surface in  FIG. 3 ) of the reflection plate  16  so that solar energy may be reflected. 
     As shown in  FIGS. 3 and 4 , the absorption plate  18  is configured in an alphabetic letter “V” form. More specifically, the absorption plate  18  is configured to have a V-band type structure and to absorb solar energy (or reflection light) reflected by the reflection plate  16  and directly incident solar energy. As described above, the absorption plate  18  is configured to have the 
     V-band structure so that it is less changed as much as possible with respect to modification in the length direction. Furthermore, the rises  24  are arranged at the bottoms of the corners of the absorption plates  18  in the middle of each of the absorption plates  18 , as shown in  FIG. 4 . 
     In particular, coating layers  30   a  and  30   b  are formed on the front and rear surfaces of the absorption plates  18  so that solar energy may be absorbed as much as possible. The coating layers  30   a  and  30   b  may be selectively coated on both surfaces of or one surface of the absorption plates   18 . The coating layers  30   a  and  30   b  are formed using a coating method and a composition to be described later. 
     The solar collector  10  configured as above according to an embodiment of the present invention has been implemented to have an optimum structure based on a light absorption ratio according to each incident angle for solar energy through computation analysis. The reflection plate  16  has the elliptical symmetry structure, and the absorption plate  18  has the V-band type structure. If the reflection plate  16  and the absorption plates  18  were applied to the solar collector  10 , solar energy absorption ratios were 100%, 95.7%, 85.6%, 81.8%, and 89% at respective incident angles 0°, 15°, 30°, 45°, and 60°. It was revealed that a light loss was small and the solar collector  10  had a sufficient function. Furthermore, an energy concentration cost was 2.4, that is, a relatively high level. Accordingly, the solar collector  10  is a fixed energy concentration type solar collector of a flat panel type through such an energy concentration cost. 
     Table 1 below illustrates light absorption ratios according to incident angles for solar energy through solar energy computation analysis. 

 
     In an embodiment of the present invention, the coating layers  30   a  and  30   b  are formed on both surfaces of the absorption plates  18  as shown in  FIG. 4 . An absorption ratio for solar energy may be maximized because the coating layers  30   a  and  30   b  are formed. A light function wet surface processing method for the absorption plates  18  is described in detail below. 
     Various types of oxidization layers, such as Cu2O and cupric oxide (CuO), may be formed on a surface of the absorption plate  18  made of copper (Cu) depending on thermal and chemical oxidization conditions. CuO, that is, black copper oxides, is a substance capable of functioning as a solar energy absorbent. In an embodiment of the present invention, the copper oxidization layer is made of potassium persulfate (KPS, K2S2O8), sodium hydroxide (NaOH), and sodium carbonate (SC, Na2CO3). A reaction generated in an oxidization solution is expressed in Chemical Equation 1 below. 
     KPS/NaOH processing process 
       Cu+S 2 O 8   2− ═CuSO 4 +SO 4   2− 
 
       CuSO 4 +2NaOH═Cu(OH) 2 (s)+Na 2 SO 4 (aq)
 
       Cu(OH) 2 (s)═CuO(s)+H 2 O( I )  (1)
 
     An SC processing process is a process of additionally processing unreacted CuSO4 into CuO in the KPS/NaOH processing process. 
       2CuSO 4 +H 2 O+2Na 2 CO 3═Cu   2 (OH) 2 CO 3 +2Na 2 SO 4 +CO 2   
       Cu2(OH) 2 CO 3 ═2CuO+CO 2 +H 2 O( I )
 
     A process of determining a CuO structure is chiefly performed in the KPS/NaOH processing process. As may be seen from the above chemical reaction mechanism, the structure and thickness of the oxidization layer are controlled by a ratio and processing time of KPS and NaOH. In general, the formed CuO oxidization layer has a needle and layer form of a nano to micro size. As the thickness of the oxidization layer increases, the oxidization layer gradually becomes dark and has a higher light absorption ratio. 
     In such a case, an increase of the heat radiation factor inevitably appears according to an increase of light absorption. Accordingly, the application of the oxidization layer to the absorption plates of a solar collector is limited because most of absorbed solar heat is lost in an infrared form. In an embodiment of the present invention, an oxidization layer having an excellent absorption ratio may be fabricated while having the radiation factor as much as possible by optimizing the structure and thickness of the oxidization layer. To this end, hydrogen peroxide may be used to form the structure of the oxidization layer capable of lowering reflectance and the radiation factor through surface pre-processing. It was monitored that the CuO formation reaction within the KPS/NaOH solution was significantly delayed. Accordingly, optimum conditions were deduced by increasing the content and oxidization time of NaOH. Compared to reflectance and the radiation factor of 15 and 15% in the initial product, excellent results in which reflectance and the radiation factor value were 10 and 10% were secured under the optimum conditions as absorption plates for solar energy after such surface processing. Meanwhile,  FIG. 5  is a graph illustrating a change of reflectance and the radiation factor according to NaOH ratios after the surface pre-processing of the absorption plates  18 . 
     In accordance with the present invention, the V-band type absorption plates each having both sides coated are disposed within the flat panel type solar collector, and the reflection plate configured to have the elliptical symmetry structure and to reflect solar energy toward the absorption plates is disposed under the absorption plates. Accordingly, there are advantages in that solar energy that is incident at all angles can be efficiently absorbed and the absorption ratio of the solar collector can be maximized. 
     Furthermore, the present invention is advantageous in that the concentration of solar energy is high compared to the 1:1 concentration of a conventional solar collector through an energy concentration cost of 2.4, a radiation loss area can be reduced through the front surfaces of the absorption plates, and a heat loss ratio of the solar collector can be significantly improved. Furthermore, the absorption plate of the present invention is advantageous in that it can improve concentration efficiency because the coating layers are formed on both sides of the absorption plate in order to properly absorb direct light and reflection light. 
     Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.