Abstract:
The invention relates to photovoltaic solar power systems and more specifically to solar photovoltaic systems which include concentrators of solar radiation. The invention includes application of single curvature and compound-curvature concentrators. A supporting member with an installed photovoltaic cell serves as an element in a heat sink unit and, at the same time, as a detail of a tracking mechanism. It allows to construct a cheap and reliable photovoltaic solar power system.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This invention relates to photovoltaic solar power systems and more specifically to solar photovoltaic systems, which include concentrators of solar radiation.  
         [0002]     It is known, that high cost of solar photovoltaic cells limits their wide application as renewable source of electrical energy. Usage of relatively cheap concentrators of solar radiation allows to diminish significantly the fraction of cost of a photovoltaic cell in the total cost of the photovoltaic solar power system and to achieve in such a way decrease of required investment per unit of generated power of this system.  
         [0003]     This approach provides some advantages to solar concentrating photovoltaic systems as compared to common photovoltaic flat-plate systems. The concentrators ensure higher efficiency of converting solar radiation into electricity by photovoltaic solar cells. At the same time, significant reducing the size of the solar cells gives possibility to apply more expensive solar cells with higher efficiency and improved stability of their output characteristics at high temperatures.  
         [0004]     On the other hand, there are some technical problems to be solved in using concentrators of solar radiation. These problems relate to design of a suitable tracking mechanism and dissipation of heat releasing on the photovoltaic cells.  
         [0005]     There are some US patents, which are related to the area of solar photovoltaic systems with application of concentrators of solar radiation. For example, it is possible to mention U.S. Pat. Nos. 4,056,405, 4,361,717, 4,604,494, 4,971,633 and 5,374,317.  
         [0006]     However, there is a necessity in technical solutions, which provide cheap and reliable constructions of solar photovoltaic power systems with application of concentrators of solar radiation.  
       BRIEF SUMMARY OF THE INVENTION  
       [0007]     This invention proposes some relatively simple and reliable constructions of modular solar photovoltaic power systems with application of the concentrators of solar radiation.  
         [0008]     In the case of application of single curvature tracking concentrators, such construction includes some main units:  
         [0009]     Posts with a bearing pipe installed on these posts; the bearing pipe serves for removal of heat released on photovoltaic solar cells by a liquid medium flowing in it and, in addition, this bearing pipe serves as an axle for tracking motion of a single curvature concentrator after the sun. The bearing pipe can be provided with a layer of thermal insulation. It allows to utilize better the heat releasing on the photovoltaic solar cells.  
         [0010]     A supporting member that is fabricated from metal with high thermal conductivity, this supporting member has a plane surface, which serves for installation of the photovoltaic cell, and an opposite concave cylindrical surface with radius nearly equal to the radius of the bearing pipe; the supporting member should be positioned on the bearing pipe and can be turned around it. In such a way, the supporting member and the bearing pipe constitute a cylindrical hinge.  
         [0011]     The solar photovoltaic cell itself that is installed with good thermal contact on the plane surface of the supporting member. The term “solar photovoltaic cell” implies in this invention solar cells themselves, solar cell modules and arrays of solar cell modules.  
         [0012]     The abovementioned single curvature concentrator of solar radiation in the form of a parabolic trough-wise mirror, this parabolic trough-wise mirror is provided with a frame, which is joined with the supporting member by some truss struts.  
         [0013]     A tracking mechanism, which causes turning the single curvature concentrator and the supporting member in such a way that solar radiation, which is reflected from this concentrator, comes mainly on the surface of the solar cell. This tracking mechanism includes a set of tracking rods joined with the frames of the single curvature concentrators, actuating units serving for displacement of the tracking rods and a control unit.  
         [0014]     It should be noted that several supporting members with associated solar cells and concentrators can be positioned on one bearing pipe.  
         [0015]     The proposed solar photovoltaic power system includes as well some auxiliary units: a system of cooling the liquid medium; a unit for conditioning electrical current generated by the array of the solar cells. The system of cooling the liquid medium can include units for utilization of heat accumulated by the liquid medium.  
         [0016]     The aforementioned cylindrical hinge can be provided with a liquid lubricant in order to diminish friction between the supporting member and the bearing pipe.  
         [0017]     There is an elastic element in the form of a Ω-wise flat spring (or springs), two extreme sections of this flat spring are installed on the supporting member and its middle section passes over the bearing pipe. In such a way, this Ω-wise flat spring ensures good mechanical and thermal contact between the bearing pipe and the supporting member.  
         [0018]     In addition, the cylindrical hinge can be protected by a longitudinal cap from above in order to minimize ingress of moisture and dust into this cylindrical hinge.  
         [0019]     The cylindrical surface of the supporting member, the outer surfaces of the bearing pipe and the internal surface of the Ω-wise flat spring can be provided with antifriction coatings.  
         [0020]     It is possible to apply a single curvature Fresnel mirror instead of the single curvature parabolic mirror in the form of a trough.  
         [0021]     In addition, it is possible to apply two tilted mirrors in the form of strips installed on the edges of the photovoltaic solar cell; the aperture formed by these strips is covered by a plate of diffusing glass with high value of the light transmission coefficient. This allows to provide uniform distribution of the concentrated solar radiation on the surface of the photovoltaic solar cell.  
         [0022]     The photovoltaic solar power system itself comprises a number of the modules described above, where these modules are arranged in series and in parallel; the modules, which arranged in series, have the common bearing pipe and the modules arranged in parallel have the common tracking rods. It should be noted, that it is possible to apply tracking ropes instead of the tracking rods. This allows to use the tracking rods from material with very low coefficient of thermal expansion (for example, the ropes fabricated from quartz fibers). Application of such ropes provides high precision of tracking.  
         [0023]     In the case of application of compound-curvature concentrators in the form of dish-type mirrors, a module of the proposed system comprises a bearing pipe that is mounted on the vertical posts. The bearing pipe can be provided with a layer of thermal insulation. It allows to achieve better utilization of the heat releasing on the photovoltaic solar cells.  
         [0024]     Some T-pieces are built into the bearing pipe. The lower branch of each T-piece is sealed by a metal convex hemi-spherical cap.  
         [0025]     The upper side of a metal supporting member has the concave surface in the form of a spherical segment with the radius almost identical to that of metal convex hemi-spherical cap. In such a way, this pair: the hemi-spherical cap of the T-piece and the concave surface of the supporting member present a spherical joint.  
         [0026]     The supporting member is assembled with the bearing pipe by some springs; tension of these springs ensures tight mechanical and thermal contact between the hemi-spherical cap and the supporting member.  
         [0027]     A liquid lubricant can be used for diminishment of friction in this spherical joint.  
         [0028]     The contacting surfaces of this spherical joint can be provided with antifriction coatings.  
         [0029]     In addition, it is possible to apply a concave cap in the form of a spherical segment, which seals the lower branch of the T-piece, and a convex surface in the form of a hemi-sphere of the supporting member; this convex surface should be in tight mechanical and thermal contact with the concave surface of the cap.  
         [0030]     In such a way, the supporting member with all units installed on it can be turned with respect to the convex or concave surface of the cap.  
         [0031]     The lower side of the supporting member has a plane surface intended for installation of the photovoltaic solar cell.  
         [0032]     In addition, the supporting member is provided with the spring eyes, each spring eye serves for joining with one end of a spring, the other end of the spring is joined with an auxiliary detail mounted on the bearing pipe. There is the abovementioned compound-curvature concentrator of solar radiation in the form of a parabolic dish mirror and its frame; this frame is joined with the supporting member by some truss struts.  
         [0033]     It is possible to apply a compound-curvature Fresnel mirror instead of the compound-curvature parabolic dish mirror.  
         [0034]     The set of the modules with the compound-curvature concentrators is provided with a common mechanism of tracking, which includes tracking rods, mechanisms of actuation of the tracking rods and a control unit.  
         [0035]     In order to provide homogenous distribution of the concentrated solar radiation on the surface of the solar cell, it is possible to apply an auxiliary optical element, which allows to redistribute concentrated solar radiation that has a form of converging conical beam on a square solar cell. Operation of this auxiliary optical element can be based on principles of non-imaging optics. For example, the auxiliary optic element may be constructed as a funnel with reflecting inner walls; the wide opening of this funnel has the circular form which is deformed at the opposite opening of the funnel into the square form. In addition, the inner reflecting wall of the funnel can be provided with such waviness and roughness that it ensures more uniform distribution of the concentrated radiation on the solar cell. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
       [0036]      FIG. 1  shows is a cross-section of two adjacent photovoltaic concentrator modules arranged in parallel with a common tracking rod and with trough-wise parabolic concentrators.  
         [0037]      FIG. 2  demonstrates a top view of the photovoltaic concentrator module with the trough-wise parabolic concentrator.  
         [0038]      FIG. 3  shows a cross-section of a combined unit of a bearing pipe and a supporting member in the case of application of the trough-wise parabolic concentrator.  
         [0039]      FIG. 4  shows a cross-section of a photovoltaic concentrator module with a dish-type parabolic concentrator.  
         [0040]      FIG. 5  demonstrates a cross-section of a combined unit of the bearing pipe and the supporting member of the photovoltaic concentrator module with the dish-type parabolic concentrator.  
         [0041]      FIG. 6  shows a top view of the combined unit of the bearing pipe and the supporting member of the photovoltaic concentrator module with the dish-type parabolic concentrator. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0042]     Referring to the drawings and particularly to  FIG. 1 , this drawing demonstrates a cross-section of two adjacent photovoltaic concentrator modules arranged in parallel with a common tracking rod and trough-wise parabolic concentrators. It comprises posts  101  with bearing pipes  102 , supporting members  103  with solar cells  104  installed on their low surfaces, parabolic troughs  105  with frames  106 ; these frames  106  are joined with the supporting members  103  by truss struts  107 .  
         [0043]     The tracking rod  108  is joined with frames  106  through cylindrical hinges  108  and  109 . Ω-wise spring elements  110  hold the supporting members  103  with all other elements installed on these supporting members; in such a way, this Ω-wise spring elements  110  ensure good thermal contact between the bearing pipes  101  and the supporting members  103 .  
         [0044]      FIG. 2  demonstrates a top view of the photovoltaic concentrator module with the trough-wise parabolic concentrator. It comprises a bearing pipe  201 , a supporting member  202 , Ω-wise spring elements  203 , frame  204  of a trough-wise parabolic reflector  205 , truss struts  206  and tracking rods  207 .  
         [0045]      FIG. 3  shows a cross-section of a combined unit of a bearing pipe and a supporting member in the case of application of the trough-wise parabolic concentrator or another type of a single curvature concentrator. It includes: a bearing pipe  301 ; a supporting member  302  that is installed on this bearing pipe by a Ω-wise spring element  303 . A solar cell  304  is situated on the lower side of the supporting member  302 .  
         [0046]     The lateral walls  305  of the supporting member  302  are joined with truss struts  306 .  
         [0047]     A thin layer  307  of lubricant with good thermal conductivity is situated in the gap between the supporting member  302  and the bearing pipe  301 . The bearing pipe  301  is supported by post  308 .  
         [0048]      FIG. 4  shows a cross-section of a photovoltaic concentrator module with a dish-type parabolic concentrator. It comprises posts  401 , which support a bearing pipe  402  with an external envelope  403  and a thermal insulation layer  404 . In addition, the bearing pipe  402  and the external envelope  403  are provided with flexible joints  405  and  406 . The bearing pipe  402  incorporates a central T-piece  407 . The lower branch of this T-piece is sealed with a hemi-spherical cap  408 . A supporting member  409  has an upper depression  410  with the surface of a spherical segment, the radius of this depression conforms the radius of the hemi-spherical cap  408 .  
         [0000]     The lower side of the supporting member  409  has a planar surface  411 , it serves for installation of a photovoltaic solar cell  412 .  
         [0049]     In addition, the supporting member  409  serves for mounting frame  413  with a dish-type reflector  414  by truss struts  415 . Funnel  416  has the reflecting inner surface, the circular lower aperture and the square upper aperture. This funnel is installed on the supporting member  409  and it serves for transformation of converging conical light beam into the light that is incident on the square surface of the photovoltaic solar cell  412 .  
         [0050]     Tracking rods  417  and  418  perform tracking the dish-type reflector  414  in two directions; these tracking rods are joined with frame  413  of the dish-type reflector  414  through cylindrical hinges  419 ,  420 ,  421  and  422 .  
         [0051]     The supporting member  409  is held by springs  423  with respect to the bearing pipe  402 .  
         [0052]      FIG. 5  demonstrates a cross-section of a combined unit of the bearing pipe and the supporting member of the photovoltaic concentrator module with the dish-type parabolic concentrator. It comprises: a bearing pipe  501  with an external envelope  502  and a thermal insulation layer  503 ; a T-piece  504 , the lower branch of this T-piece  504  is sealed by a hemi-spherical cap  505 . A supporting member  506  has an upper depression with the surface of a spherical segment, the radius of this depression conforms the radius of the hemi-spherical cap  505 .  
         [0053]     The lower side of the supporting member  506  has a planar surface; it serves for installation of a photovoltaic solar cell.  
         [0054]     Funnel  507  has the reflecting inner surface, the circular lower aperture and the square upper aperture. This funnel is installed on the supporting member  506  and it serves for transformation of converging conical light beam into the light that is incident on the square surface of the photovoltaic solar cell.  
         [0055]     The supporting member  506  is held by springs  508  with respect to the bearing pipe  501 .  
         [0056]      FIG. 6  shows a top view of the combined unit of the bearing pipe and the supporting member of the photovoltaic concentrator module with the dish-type parabolic concentrator. It comprises a bearing pipe  601  with an external envelope  602  and a thermal insulation layer  603 ; a T-piece  604 , the lower branch of this T-piece is sealed by a hemi-spherical cap  605 . A supporting member  606  has an upper depression with the surface of a spherical segment, the radius of this depression conforms the radius of the hemi-spherical cap  605 .  
         [0057]     The lower side of the supporting member  606  has a planar surface that serves for installation of a photovoltaic solar cell  607 . In addition, there are funnel  609 , which transforms converging conical light beam into the light that is incident on the square surface of the photovoltaic solar cell  607 , and truss struts  608 .  
         [0058]     The supporting member  606  is held by springs  610  with respect to the external envelope  602 .