Abstract:
The invention teaches a family of flat concentrator PV panels wherein an array of enhanced light beam splitters coupling with a plurality of optical grooves efficiently collects light and transmits collected light substantially to the active surface(s) of an array of size-reduced PV cells with low aspect ratio.

Description:
REFERENCE TO RELATED APPLICATION 
       [0001]    The present application is a divisional application of the U.S. patent application Ser. No. 12/231,046 which is a non-provisional application based on the provisional Appl. Ser. No. 61/123,437. Thus the present application claims priority to the provisional Appl. Ser. No. 61/123,437 filed on Apr. 8, 2008, the entire content of which is hereby incorporated by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates in general to photovoltaic technology. More particularly, the invention relates to a flat concentrator PV panel in which an array of enhanced light beam splitters coupling with a plurality of optical grooves efficiently collects light and transmits collected light substantially to the active areas of an array of size-reduced photovoltaic cells with a low aspect ratio. 
       BACKGROUND OF THE INVENTION 
       [0003]    Flat plate Photovoltaic (PV) panel is a system that produces electricity by having sunlight directly strike PV cells made of expensive semiconductor material. 
         [0004]    To reduce the cost, concentrator PV panel which requires less PV cell consumption is being highlighted in today&#39;s market. Concentrator PV technologies use relatively inexpensive optics such as mirrors or lenses to concentrate or focus light from a relatively broad collection area onto a much smaller area of active semiconductor PV material. Conventional Concentrator PV systems must be pointed directly at the sun because they work by focusing sunlight onto a targeted area, and hence they require trackers which follow the sun&#39;s trajectory throughout the day. Since concentrator PV systems require less semiconductor material to capture a given amount of sunlight, it is still cost-effective to use more expensive and higher efficiency cells to increase the electricity generated from a given collection area. Indeed, concentrator PV approaches offer an effective, practical way to keep solar cell conversion efficiencies high while keeping semiconductor material costs down. 
         [0005]    Taking consideration that the incident angel of the sunlight various over one year, North to South is approximately 47° and East to West is approximately 180°, it is calculated that a linear concentrator PV panel with one dimensional concentration may be is best for terrestrial solar generation system application. 
         [0006]    Over the past twenty years, there have been various solutions in the field of concentrator PV panel with PV cells arranged in rows that look like a strip array of solar cells. In this type of PV panels, such as the PV panel illustrated in  FIG. 1 , which includes a cover glass  101 , a middle layer  103  and a back layer  104 . Some sunlight, such as  106 , directly impinges on an array of PV cell strips  102  which is embedded in the middle layer  103 . Some other sunlight, such as  107   a,  impinges on an array of reflective beam splitters, such as  105 , coupled in between two neighboring solar cell strips  102 . The reflected light  107   b,    107   c  from the reflective beam splitter  105  is then totally internally reflected ( 107   b  to  107   d,  and  107   c  to  107   e ) by the front surface  101   a  of the cover plate  101  to the nearest PV cell strips  102 . The magnification, i.e., the ratio of the pitch b 1  of the PV cell array and the width a 1  of the PV cell strip  102 , is about 2 usually. 
         [0007]    In U.S. Pat. No. 5,877,874, Glenn A. Rosenberg disclosed a holographic planar concentrator (HPC) as the beam splitter for collecting and concentrating optical radiation. The holographic planar concentrator comprises a planar highly transparent plate and at least one multiplexed holographic optical film mounted on a surface thereof. The multiplexed holographic optical film has recorded therein a plurality of diffractive structures having one or more regions which are angularly and spectrally multiplexed. Two or more of the regions may be configured to provide spatial multiplexing. The HPC is fabricated by: (a) recording the plurality of diffractive structures in the multiplexed holographic optical film employing angular, spectral, and, optionally, spatial multiplexing techniques; and (b) mounting the multiplexed holographic optical film on one surface of the highly transparent plate. The recording of the plurality of diffractive structures is tailored to the intended orientation of the holographic planar concentrator to solar energy. The HPC is mounted in the intended orientation for collecting solar energy and at least one solar energy-collecting device is mounted along at least one edge of the holographic planar concentrator. 
         [0008]    In U.S. Pat. No. 7,238,878, Ronald C. Gonsiorawski disclosed a PV panel with V-shaped grooves as a beam splitter running in at least two directions and coated with a light reflecting medium so as to provide light-reflecting facets that are aligned with the spaces between adjacent cells and oriented so as to reflect light falling in those spaces back toward the transparent front cover for further internal reflection onto the solar cells, whereby substantially all of the reflected light will be internally reflected from the cover sheet back to the PV cells, thereby increasing the current output of the module. 
         [0009]    In U.S. Pat. No. 7,164,839, Eldon H. Nyhart, Jr., et al disclosed a radiation collector configured to collect incident radiation. The radiation collector includes a radiation directing component as a beam splitter configured to redirect the incident radiation, a buffer component configured to receive the radiation redirected by the radiation directing component, and a propagation component configured to receive the radiation from the buffer component and to propagate the radiation towards a first end of the propagation component. 
         [0010]    Those approaches fail to provide wide angle of view with sufficiently high concentration ratio and thus are much limited. What is desired is a flat concentrator PV panel in which an array of enhanced light beam splitters coupling with a plurality of optical grooves efficiently collects light and transmits collected light substantially to the active areas of an array of size-reduced photovoltaic cells with a low aspect ratio. 
       SUMMARY OF THE INVENTION 
       [0011]    The present invention teaches a concentrator PV panel with a small horizontal view angle not less than 40 degree and a large view angle equal to 180 degree, perpendicular to each other that satisfies a fixed ground solar generation system application criteria. The PV panel includes rows of PV cell or a linear array of PV cells connecting in series and/or in parallel, alternating with rows of optical reflective beam splitters. The PV cell rows and beam splitter rows completely covers the light-incident surface of the PV panel. The PV cell array is sandwiched in between a transparent cover plate and a back plate using an adhesive. The backside plate is insulating and humidity-proof. To reduce the optical length and increase concentration ratio, rows of grooves with flat or curved sidewalls are formed on the front surface of the transparent cover plate, each of which being parallel to and above of a PV cell row. A humidity protected mirror is attached on the back surface of the back plate. 
         [0012]    In another aspect, the PV cell array is sandwiched in between a transparent cover plate and a transmitting plate using a transparent and insulating adhesive. The PV cell array formed by a plurality of bifacial PV cell rows that are placed in parallel to each other separated by a space and are electrically connected in series or in parallel. An array of grooves for optical length reduction and an array of grooves for beam splitting enhancement are formed on the back surface of the transmitting plate. The beam splitting enhancement grooves are arranged alternate with the optical length reduction grooves. Each beam splitting enhancement groove and the adjacent optical length reduction groove are connected by a cylindrical surface. A humidity protected mirror is attached on the back surface of the transmitting plate. 
         [0013]    In one preferred embodiment, the concentrator PV panel includes (a) a light transparent cover plate with an anti-reflection flat front surface and a back surface; (b) a transmitting plate with a front surface and a grooved back surface; (c) a PV cell array which is sandwiched in between the light transparent cover plate and the transmitting plate using a transparent and insulating adhesive; (d) a reflector attached onto the back surface of the transmitting plate. 
         [0014]    In another implementation, the grooved back surface in the above described preferred embodiment has an array of optical length reduction grooves, each of which having a pair of bent symmetrical sidewalls. Every two optical length reduction grooves are connected to each other through a flat surface. The symmetrical sidewalls have flat or curved surfaces. For the curved surface, the cross sectional view of the curved surface can be parabolic, elliptical, spherical, or a step curve. 
         [0015]    Yet in another implementation, the grooved back surface in the above described embodiment has a plurality of optical length reduction grooves alternating with a plurality of beam splitting enhancement grooves on the back surface of the transmitting plate. Every two beam splitting enhancement grooves are connected to each other through either a flat surface or a circular surface having a diameter substantially equal to the thickness of the light transmitting plate. Each beam splitting enhancement groove has a pair of symmetrical flat sidewalls or a pair of symmetrical curved sidewalls, with a groove angle larger than 90 degree and a depth in the range between 0 and the thickness of the transmitting plate. 
         [0016]    In another preferred embodiment, the concentrator PV panel includes (a) a light transparent cover plate with a grooved front surface and a back surface; (b) a transmitting plate with a flat front surface and a grooved back surface; (c) a PV cell array which is sandwiched in between the light transparent cover plate and the transmitting plate using a transparent adhesive; and (d) a reflector attached onto the back surface of the transmitting plate. The grooved front surface has an array of total internal reflection (TIR) grooves, each of which having a pair of flat or curved sidewalls. The cross sectional view of the curved sidewall can be parabolic, elliptical, spherical, or a step curve. Every two TIR grooves are connected to each other through a flat surface. 
         [0017]    In an alternative implementation, the grooved back surface in the above described preferred embodiment has a plurality of optical length reduction grooves alternating with a plurality of beam splitting enhancement grooves. Every two nearest adjacent beam splitting enhancement grooves are connected to each other through a pair of circular curved surfaces having a diameter equal to the thickness of the light transmitting plate. Each of the optical length reduction grooves has a pair of symmetrical flat or curved sidewalls connecting each other through a flat surface with groove angle larger than 90 degree and depth in the range from 0 to the thickness of the transmitting plate. 
         [0018]    Yet in another alternative implementation, each of the beam splitting enhancement grooves has a pair of symmetrical planar sidewalls spaced by a planar beam splitter. The angle between the symmetrical sidewalls is large than 90 degree. The planar beam splitter can be any of: a mirror coated V-shape groove, a diffuser, a hologram grating, a Bragg Grating, and an array of micro V-shape grooves. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0019]    For a more succinct understanding of the nature and objects of the present invention, reference should be directed to the following detailed description taken in connection with the accompanying drawings in which: 
           [0020]      FIG. 1  is a schematic fragmentary diagram illustrating a sectional view of a flat plate PV panel according to the prior arts; 
           [0021]      FIG. 2  is a schematic fragmentary diagram illustrating a sectional view of a flat concentration plate PV panel according to one preferred embodiment of the present invention; 
           [0022]      FIG. 3  is a schematic fragmentary diagram illustrating a sectional view of a flat concentration plate PV panel according to another preferred embodiment of the present invention; 
           [0023]      FIG. 4  is a schematic fragmentary diagram illustrating a sectional view of a flat concentration plate PV panel according to another preferred embodiment of the present invention; 
           [0024]      FIG. 5  is a schematic fragmentary diagram illustrating a sectional view of a flat plate concentration PV panel according to another preferred embodiment of the present invention; 
           [0025]      FIG. 6  is a schematic fragmentary diagram illustrating a sectional view of a flat plate concentration PV panel according to another preferred embodiment of the present invention; and 
           [0026]      FIG. 7  is a schematic diagram illustrating a cross sectional view of a beam splitter which is used in the embodiments illustrated in  FIGS. 2-6 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0027]    While the present invention may be embodied in many different forms, designs or configurations, for the purpose of promoting an understanding of the principles of the invention, reference will be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended. Any alterations and further implementations of the principles of the invention as described herein are contemplated as would normally occur to one skilled in the art to which the invention relates. 
         [0028]    Referring to  FIG. 1 , which is a schematic fragmentary diagram illustrating a sectional view of a flat plate PV panel according to the prior art, the PV panel includes a cover glass  101 , a water proof back plate  104 , and an array of PV cells, such as  102 , which is sandwiched between the cover glass  101  and the water proof back plate  104  by a transparent and insulative adhesive layer  103 , and an array of planar reflective beam splitters such as  105 . The PV cell rows  102  are spaced evenly. Each reflective beam splitter strip  105  is locating between two nearest adjacent PV cell rows  102 . Except partial of light  106  impinging to PV cells  102  directly, other light is refracted at front surface  101   a  of the cover plate  101  and transmits in the cover plate into the refraction light  107   a.  The reflective beam splitter  105  splits the refraction light  107   a  into two beams  107   b  and  107   c  which are reflected onto the nearest PV cells  102  through TIR of the front surface  101   a  of the cover plate  101 . The reflective beam splitter  105  can be a diffuser, a grating, or a micro V groove array. Due to the function of the reflective beam splitter  105 , the pitch b 1  of PV cell array can be larger than the width a 1  of the PV cell  102 . The concentration ratio is dependent on the ratio of b 2 /a 2 . To reduce the loss of reflective light, the front surface  101   a  contains an anti-reflection coating or includes an anti-reflection pattern structure. 
         [0029]    The preferred embodiments of the present invention illustrated below have substantially improved the prior arts. 
         [0030]      FIG. 2  is a schematic fragmentary diagram illustrating a cross sectional view of a flat plate concentrator PV panel according to one preferred embodiment of the present invention. The concentrator PV panel includes a cover plate  201 , which is made of a light transparent optical medium, such as optical glass, having an array of grooves such as  208  on the front surface, an array of PV cell strips such as  202  which may be crystalline silicon PV cell, a back plate  204 , and an array of reflective beam splitters such as  205 . The PV cell array and the reflective beam splitter array are sandwiched between the cover plate  201  and the water proof back plate  204  by a transparent electrical insulative adhesive  203 . The cover plate  201  has an anti-reflection layer on the front outer surface. In a typical implementation, the anti-reflection layer may be a dielectric coating or a micro V groove array with pitch size approximately 0.2˜2 mm. The micro V groove&#39;s inner angle between its two sidewalls is less than 90 degree. The micro V groove array and the TIR groove array are perpendicular to each other. 
         [0031]    The TIR grooves such as  208 , the rows of PV cells such as  202 , and the strips of reflective beam splitters such as  205  are parallel to each other. Each TIR groove of the TIR groove array is designed in such a manner that it is located directly above the relative PV cell row of the PV cell array. 
         [0032]    Each TIR groove  208  has two sidewalls  209   a  and  209   b  which are symmetrical to the central line  211 . The bottom  210  of the TIR groove  208  can be flat or curved. The depth d 2  of the TIR groove  208  and the thickness c 2  of the cover plate  201  are determined for the most effective TIR purpose in accordance with the geometrical properties of the sidewalls  209   a  and  209   b.  Typically, d 2  is in a range of  0 . 5 - 10 mm. The longitudinal axis of the TIR groove  208  is parallel to the longitudinal axis of the PV cell row  202 , but the cross section of the TIR groove  208  at a right angle to its longitudinal direction and the cross section of the nearest PV cell row  202  at a right angle to its longitudinal direction share a same central line  211 . 
         [0033]    The reflective beam splitters  205  can be optical diffusers, a gratings, or micro V grooves. As an example, the incident light  206  is refracted on the front surface  201   a  and transmitted through the cover plate  201  as light  207   a.  The light  207   a  impinging on the reflective beam splitter  205  is then split into two light beams  207   b  and  207   c.  The lights  207   b  and  207   c  are totally reflected on the inner surface of the front surface  201   a  of the cover plate  201 . The reflected lights  207   d  and  207   e  ultimately substantially travel backwards to two nearest PV cells  202 . 
         [0034]    Due to the innovative design as illustrated in  FIG. 2 , relatively less PV cells are required for a same size PV panel. For example, in a same size implementation, the pitch b 2  for the PV cell rows in  FIG. 2  is the same as the pitch b 1  of the PV cell rows in  FIG. 1 , but the required width a 2  for the PV cell rows in  FIG. 2  is much less than the required width a 1  for the PV cell rows in the PV panel illustrated in  FIG. 1 . Thus, the magnification is higher and the light energy is used more effectively in the present embodiment of the invention. 
         [0035]      FIG. 3  is a schematic fragmentary diagram illustrating a flat plate concentrator PV panel according to another preferred embodiment of the present invention. The concentrator PV panel includes a cover plate  301  made of a light transparent optical medium such as optical glass. The cover plate  301  has a flat front anti-reflection surface  301   a  and a grooved back surface  311 . A number of trapezoidal grooves, such as  321  and  322 , are evenly spaced in parallel and are located on the back surface  311  of the cover plate  301 . Here, “front surface” refers to the side of the concentrator PV panel facing the light source such as sun, and “back surface” refers to the side of the PV panel backing the light source. The back surface is usually mounted to a support structure such as a frame. 
         [0036]    Various strips of reflective beam splitters, such as  305 , are evenly spaced in parallel with a spacing b 3  which is in the range between 1 mm to 100 mm. Each trapezoidal groove  321  has a flat top surface  313  and a pair of sidewalls  312   a  and  312   b  which are symmetrical to a central line  308  at a right angle to a longitudinal direction of the trapezoidal groove and has a groove angle α 1  between the symmetrical sidewalls larger than 90 degrees and a depth d 3  in the range between 0 and the thickness c 3  of the cover plate  301 . Typically, angle α 1  is in a range of 90-160 degrees. The groove depth d 3  and the cover plate thickness c 3  are determined for the most effective TIR purpose in accordance with the geometrical properties of the sidewalls  323   a  and  323   b.  Typically, d 3  is in a range of 0.5-50 mm. 
         [0037]    In a typical implementation, every trapezoidal groove  321  is connected to two nearest adjacent trapezoidal grooves through a PV cell row such as  302 . The PV cell rows are evenly spaced in parallel and are coupled in the layer  303  and in the areas near the bottom plane  304  between two adjacent trapezoidal grooves. The PV cell rows  302 , the trapezoidal grooves  321  and the reflective beam splitter strips  313  are in parallel to each other. 
         [0038]    Here, “trapezoidal groove” refers to a 3-dimensional structure in which any cross section view at a right angle to its longitudinal axis is a trapezoid with two parallel sides of different length and a pair of symmetrical unparallel sides of identical length. Its top surface refers to the plane where the trapezoid&#39;s narrow side resides. Its bottom plane refers to the plane where the trapezoid&#39;s wide side resides. 
         [0039]    The reflective beam splitter  305  can be an optical diffuser, a grating, or an array of micro V shape grooves. As an example, the refractive light  307   a  of light  306  impinges on the reflective beam splitter  305 , and is split into reflective lights  307   b  and  307   c,  which are further reflected upwardly to the inner surface of the front surface  301   a.  Upon TIR, reflective lights  307   d  and  307   e  travel ultimately substantially to the active area of the PV cell  302 . The geometry of symmetrical sidewalls  323   a  and  323   b  of the trapezoidal groove  321  is such that the light impinging on the sidewall  323   a  or  323   b  is substantially reflected to the front surface  301   a  and ultimately substantially backwards toward the surface of the PV cell  302 . Because of this geometrical design, relatively less PV cells are required for a PV panel. 
         [0040]    Note that the reflective beam splitters  305  and the concentrator PV cell rows  302  are located on different planes. By placing the reflective beam splitter  305  on the top plane  313  of the trapezoidal groove  321  for beam splitting enhancement, low aspect ratio As=c 3 /b 3  can be achieved in 1.5-4 at very low cost. 
         [0041]    Now referring to  FIG. 4  which is a schematic fragmentary diagram illustrating a sectional view of a flat plate concentrator PV panel according to another preferred embodiment of the present invention. This embodiment is a combination of the embodiment illustrated in  FIG. 2  and the embodiment illustrated in  FIG. 3 . The concentrator PV panel includes a cover plate  401  made of a light transparent optical medium, such as optical glass, having an array of V shape TIR grooves such as  406  in the front surface  401   a,  an array of PV cell rows such as  402  in the bottom surface areas  408  connecting the neighboring trapezoidal grooves  403 , an array of reflection beam splitters such as  405  in the top surface area  410  of the trapezoidal groove  403 , and a back cover mirror  404 . Here, “front surface” refers the surface of the cover plate facing the source of the incident light. The cover plate  401  in  FIG. 4  is similar to the cover plate  201  in  FIG. 2 . The back cover mirror  404  can be a single layer mirror or a multi-layer mirror with identical optical properties. The two-layer description herein is for illustration only. Single layer or multi-layer implementations depend on cost effectiveness for manufacturing. 
         [0042]    Each TIR groove, such as  406 , of the TIR groove array is located directly above the relative PV cell row such as  402 . With a pitch range b 4  which is approximately 5 mm-100 mm, each TIR groove in the front surface has two sidewalls  407   a  and  407   b  symmetrical to the central line  412 , and a bottom surface  411  which is parallel to the relative PV cell row  402 . The symmetrical sidewalls can be either flat or curved surfaces. For a pair of symmetrical curved surfaces, the cross sectional view of a surface can be parabolic, elliptical, spherical, or step curve. The geometrical properties of the sidewalls are designed according to such a calculation that they, with TIR properties, redirect the reflected light from each reflective beam splitter such as  405  of the reflective beam splitter array, substantially to the active areas of two nearest adjacent PV cell rows such as  402 . In other words, the sidewalls  407   a  and  407   b  of the TIR groove  406  totally internally reflect substantially all the light from the reflective beam splitter  405  to the PV cell rows  402 . The PV cell rows  402  are evenly spaced in parallel to form an array with a pitch b 4 . 
         [0043]    The back surface of the cover plate  401  includes an array of trapezoidal grooves such as  403  with a pitch b 4 . Typically, the depth d 4  of the trapezoidal groove is in a range of 0.5-50 mm. Each of the trapezoidal grooves has a pair of symmetrical planar sidewalls such as  409   a  and  409   b.  The reflective beam splitter strips, such as  405 , are evenly spaced in parallel to form an array with a pitch b 4 . The PV cell rows such as  402 , the trapezoidal grooves such as  403 , the reflective beam splitters such as  405 , and the TIR grooves such as  406  are in parallel to each other. Here, “trapezoidal groove” refers to a structure in which any cross sectional view on its longitudinal axis is a trapezoid with two parallel sides of different length and a pair of symmetrical unparallel sides of identical length. 
         [0044]    Each reflective beam splitter of the reflective beam splitter array can be an optical diffuser, a grating, or an array of micro V grooves. The light impinging on a reflective beam splitter such as  405  is reflected upwardly into the sidewalls  407   a  or  407   b  or bottom surface  411  of the nearest TIR groove  406  and ultimately substantially backwards toward the active surface of the related PV cell rows  402 . The geometry of the symmetrical sidewalls  407   a  and  407   b  or bottom surface  411  of the TIR groove  406  is such that the reflected light from the reflective beam splitters  405  is reflected to the active areas of the PV cell rows  402 . Because of this geometrical design, relatively less PV cells are required for a same size PV panel. Thus, light energy is used more effectively and efficiently. By placing each reflective beam splitter of the reflective beam splitter array  405  in the top surface areas  410  of the related trapezoidal groove  403  of the beam splitter enhancement trapezoidal groove array, the width a 4  of the PV cell row  402  is much less than the pitch b 4  of PV cell array. The larger concentration M=(1+b/a) and low aspect ratio As=U(a+b) can be achieved. 
         [0045]      FIG. 5  is a schematic fragmentary diagram illustrating a cross sectional view of a flat plate concentrator PV panel according to another preferred embodiment of the present invention. The concentrator PV panel includes a cover plate  501  and a back plate  504  as a transmitting plate with an array of reflection grooves such as  508  and an array of trapezoidal reflection grooves such as  506  wherein the reflective beam splitter  505  are coupled on the top surface of the trapezoidal groove  506 . An array of bifacial PV cell rows such as  502  is sandwiched by the cover plate  501  and back plate  504  through a transparent adhesive layer  503 . The cover plate  501  is made of a light transparent optical medium, such as optical glass, with a flat front surface  501   a.  Both the front and back surfaces of bifacial PV cell row  502  are active with photovoltaic properties. The back plate  504  includes an array of trapezoidal grooves such as  506  which are evenly spaced in parallel and are located on the backside of the back plate  504 , and an array of inverted reflection grooves such as  507  which are evenly spaced in parallel and are located on the backside of the back plate  504 . The trapezoidal groove  506  includes a top plane  512  and a pair of symmetrical sidewalls  511   a  and  511   b.  The inverted reflection groove  508  includes a top plane  514  and a pair of symmetrical sidewalls  513   a  and  513   b.  The cover plate&#39;s “front surface” refers to the surface of the concentrator PV panel directly facing the light source such as sunlight. The back plate&#39;s “backside” refers to the opposite side of the front surface of the concentrator PV panel. Trapezoidal groove refers to a structure in which any cross section view at a right angle to its longitudinal axis is a trapezoid with two parallel sides of different length and a pair of symmetrical unparallel sides of identical length. The trapezoidal groove&#39;s “top plane” refers to the planar area where the trapezoid&#39;s narrow side resides. The “inverted reflection groove” refers to a structure in which any cross sectional view at a right angle to its longitudinal axis is an inverted V shape with a pair of symmetrical sides. 
         [0046]    The back plate  504  includes an array of reflective beam splitters such as  505  which are evenly spaced in parallel and are coupled in the areas immediately above the top plane  512  of the trapezoidal groove  506 . The array of PV cell rows such as  502  are evenly spaced in parallel and in the areas between two adjacent trapezoidal grooves, such as  506  and  507 , and facing the inverted reflection groove  508  which is also between the trapezoidal grooves  506  and  507 . 
         [0047]    Each of the inverted reflection grooves  508  is located between two trapezoidal grooves  506  and  507 , and has a pair of sidewalls  513   a  and  513   b  symmetrical to the middle line  510 . The inverted reflection groove  508  is for optical length reduction. Its sidewalls  513   a  and  513   b  can be flat or curved surfaces having reflection properties. For a pair of symmetrical curved surfaces, the cross sectional view of a surface can be parabolic, elliptical, spherical, or a step curve. The upper planar surface  514  of the inverted reflection groove  508  and the PV cell row  502  have the same central line  510 . The “upper planar surface” means the planar area facing the backside of the PV cell  502 . The geometry of symmetrical sidewalls  513   a  and  513   b  of the inverted reflection groove  508  is such that the light impinging on the sidewalls  513   a  and  513   b  is substantially reflected to the active area on the back surface of the PV cell row  502 . Here, “back surface” refers to the surface facing the inverted reflection groove  508 . 
         [0048]    In the preferred implementation, the width of the space between two adjacent PV cell rows is substantially same as the width of the wider side of the trapezoid  506 , as marked “c 5 ” in  FIG. 5 , and the width of the PV cell row  502  is substantially same as the width of the space between two adjacent trapezoidal grooves’ bottom sides, as marked “a 5 ” in  FIG. 5 . 
         [0049]    Note that the reflective beam splitter  505  and the PV cell row  502  are located on different planes. The PV cell row  502 , the trapezoid groove  506 , the reflective beam splitter strip  505 , and the inverted reflection groove  508  are all in parallel to each other. 
         [0050]    The reflective beam splitter  505  can be an optical diffuser, a grating, or an array of micro V-shape grooves. As an example, the light  515  impinging on the reflective beam splitter  505  is substantially reflected upwardly into the inner surface of the front surface  501   a  of cover plate  501  and is ultimately substantially reflected back to the active areas of the PV cell  502 . The geometry of symmetrical sidewalls  511   a  and  511   b  of the trapezoidal groove  506  is such that the light impinging on the sidewalls  511   a  and  511   b  is substantially reflected to the active areas on the back surface of the PV cell  502 . Because of this geometrical design, the width a 5  of the PV cell  502  is much less than the pitch b 5  of PV cell array. Therefore, relatively less PV cells are required for a same size PV panel and light energy is used more effectively and efficiently. 
         [0051]      FIG. 6  is a schematic fragmentary diagram illustrating a cross sectional view of a flat plate concentrator PV panel according to another preferred embodiment of the present invention. This embodiment is a combination of the embodiment illustrated in  FIG. 4  and the embodiment illustrated in  FIG. 5 . The concentrator PV panel includes a cover plate  601 , which is similar to the cover plate  401  in  FIG. 4 , and a back plate  604  as a transmitting plate wherein the reflective beam splitters such as  605  are coupled. 
         [0052]    The cover plate  601  is made of a light transparent optical medium, such as optical glass, having an array of TIR grooves, such as  615 , which are evenly spaced in parallel and are located above the bifacial PV cell rows, such as  602 . The TIR groove  615  is located directly against the PV cell row  602 . In other words, the longitudinal axis of the TIR groove  615  is parallel to the longitudinal axis of the PV cell row  602 , but the cross section of the TIR groove  615  and the cross section of the PV cell row  602  share a same central line  610  which is at a right angle to the longitudinal axis of the PV cell row  602 . The two sidewalls  616   a  and  616   b  of the TIR groove  615 , symmetrical to the central line  610 , can be flat or curved surfaces. For a pair of symmetrical curved surfaces, the cross sectional view of a surface can be parabolic, elliptical, spherical, or a step curve. The geometrical properties of the sidewalls are designed according to such a calculation that each of the sidewalls has TIR properties to the reflected light from the reflective beam splitter  605  coupled in the back plate  604 . In other words, the sidewalls  616   a  and  616   b  of the TIR groove  615  totally internally reflect substantially all the light from the reflective beam splitter  605  to the active areas on the front surface of the PV cell row  602 . 
         [0053]    The back plate  604  includes an array of trapezoidal grooves, such as  606  and  607 , which are evenly spaced in parallel and are located on the backside of the back plate  604 , and an array of inverted reflection grooves, such as  608 , which are evenly spaced in parallel and are located on the backside of the back plate  604 . The trapezoidal groove  606  includes a top plane  612  and a pair of symmetrical sidewalls  611   a  and  611   b.  The inverted reflection groove  608  includes a top plane  614  and a pair of symmetrical sidewalls  613   a  and  613   b.  The trapezoidal groves and the inverted reflection grooves are alternately arranged. 
         [0054]    Incorporated in the back plate  604  is an array of planer reflective beam splitter strips, such as  605 , which are evenly spaced in parallel and are coupled in the areas immediately above the top plane  612  of the trapezoid groove  606 . The bifacial PV cell rows, such as  602 , are evenly spaced in parallel and are sandwiched by the cover plate  601  and the back plate  604  by the transmission polymer  603 . 
         [0055]    Each of the inverted reflection grooves, such as  608 , located between two adjacent trapezoidal grooves  606  and  607 , has a upper planar surface  614  and a pair of symmetrical sidewalls  613   a  and  613   b.  The reflection groove  608  is for optical length reduction. Its sidewalls  613   a  and  613   b  can be flat or curved surfaces. For a pair of symmetrical curved surfaces, the cross sectional view of a surface can be parabolic, elliptical, spherical, or a step curve. The geometry of symmetrical sidewalls  613   a  and  613   b  of the inverted reflection groove  608  is such that the light impinging on the sidewalls  613   a  and  613   b  is substantially reflected to the back surface of the bifacial PV cell row  602 . The “back surface” refers to the surface facing the inverted reflection groove  608 . The upper planar surface  614  of the inverted reflection groove  608 , the bottom planar surface  617  of the TIR groove  615 , and the PV cell row  602  have the same central line  610 . In other words, the inverted reflection groove  608 , the TIR groove  615 , and the PV cell row  602  are respectively symmetrical to the central line  610  at a right angle to their longitudinal direction. 
         [0056]    In the preferred implementation, the width of the space between two adjacent PV cell rows, as marked “c 6 ” in  FIG. 6 , is substantially same as the width of the wider side of the trapezoid  606 , and the width of the PV cell row  602 , as marked “a 6 ” in  FIG. 6 , is substantially same as the width of the space between two adjacent trapezoidal grooves&#39; bottom sides. 
         [0057]    Note that the reflective beam splitters  605  and the PV cell rows  602  are located on different planes. The TIR grooves such as  615 , the PV cell rows such as  602 , the trapezoidal grooves such as  606 , the reflective beam splitter strips such as  605 , and the inverted reflection grooves such as  608  are all in parallel to each other horizontally. 
         [0058]    The reflective beam splitter  605  can be an optical diffuser, a grating, or an array of micro V-shape grooves. The light impinging on the reflective beam splitter  605  is reflected upwardly into the inner surface of the front surface  601   a  of the cover plate  601  or the sidewalls  616   a / 616   b  of the TIR groove  615  and is reflected ultimately substantially backward to the active areas on the front surface of the PV cell  602 . The geometry of symmetrical sidewalls  611   a / 611   b  of the trapezoidal groove  606  is such that the light impinging on the sidewalls  611   a  or  611   b  is reflected substantially to the active area on the back surface of the PV cell  602 . 
         [0059]    The sidewalls  616   a / 616   b  of the TIR groove  615 , the sidewalls  611   a / 611   b  of the trapezoidal groove  606 , and the sidewalls  613   a / 613   b  of the inverted reflection groove  608  can be flat or curves surfaces satisfying the maximal reflection or concentration of light to the active areas of the PV cells. 
         [0060]    Because of the geometrical designs of the TIR grooves, the inverted reflection grooves and the trapezoidal grooves as described above, the width a 6  of the PV cell  602  is much less than the pitch b 6  of PV cell array, and much less PV cells are required for a same size PV panel. Thus, light energy is used more effectively and efficiently. 
         [0061]      FIG. 7  is a schematic diagram illustrating a cross sectional view of a reflective beam splitter  700  which is used in the embodiments illustrated in  FIGS. 2-6 . The reflective beam splitter  700  has an array of micro V shape grooves G 1 -Gn located on the backside with a groove angle β (between the two sidewalls  701 / 702  of the micro V shape groove) depending on the refractive index of the optical transparent materials used for the reflective beam splitter and on the refractive index of the optical transparent materials used for the cover plate. As an example, the light  703   a  is changed to light  703   b;  the light  704   a  is changed to light  704   b.  In this manner, the parallel beam  703   a / 704   a  is split into unparallel beams  703   b  and  704   b.  In the typical embodiments of this invention, the angle β ranges in 100˜140 degrees. The depth L 7  of the micro V groove ranges in 0.01 to 50 mm. 
         [0062]    In the above described preferred embodiments, the beam splitter can be formed on the tope of the trapezoidal grooves directly or formed as thin film and laminated to the tope plane of the trapezoidal grooves. The non-transparent sidewalls of the trapezoidal groove and the reflective beam splitters can be coated with a multilayer dielectric coating mirror or a humidity-protected metal mirror such as, but not limited to, Silicon Dioxide coated metal foil or metal coating, metal coated polyethylene terephthalate (PET) film and metal coated polyvinyl fluoride (PVF) film. The adhesive used for fixing the PV cell array between the light transparent cover plate and the transmitting plate includes, but not limited to optical epoxies, ethylene vinyl acetate (EVA) and polyurethanes. The PV cell array includes a plurality of rows of PV cells with rectangular active area. The PV cell can be, but not limited to, monolithic PV cell and PV cell linear array electrically coupled to each other in series or in parallel. The concentrator PV panel according to the present invention can be incorporated in a square, rectangular, or any other shape of frame. Because of the innovative structures of the PV panels according to the present invention, sunlight tracking systems are not required for normal operation. 
         [0063]    While one or more embodiments of the present invention have been illustrated in detail, the skilled artisan will appreciate that modifications and adoptions to those embodiments may be made without departing from the scope and spirit of the present invention as set forth in the following claims.