Abstract:
A solar power generation system for providing operating power for a desired application, the system includes one or more solar-array modules, wherein each of the one or more solar-array modules includes a multiplicity of solar cells and a high efficiency DC to DC power converter. The multiplicity of solar cells is arranged in strings of serial-units electrically connected in parallel to form a crisscross matrix array of solar cells, which matrix allows currents to bypass malfunctioning cells, thereby improving the performance of the system. The power converter includes fast MOSFET transistors having duty cycle that is operationally constant and is almost 50%. Optionally, the power converter includes a plus conductive pad and a minus conductive pad, wherein each of the strings of serial-units is individually wired to the plus conductive pad and the minus conductive pad.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit under 35 USC  119 ( e ) from U.S. provisional application 61/297,747, filed on Jan. 23, 2010, which is hereby incorporated by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to a solar electric-power generation apparatus and more particularly, to a solar electric-power generation apparatus facilitated to maximize the power generation of a solar array, having a crisscross network configuration, wherein the solar cells are often subject to at least partial shading. 
       BACKGROUND OF THE INVENTION 
       [0003]    Photovoltaic cells have been widely used in a variety of applications to generate convenient electricity. Typically, a single solar cell produces an output voltage around 0.5V, and a plurality of cells, typically Silicon based, is conventionally connected in series to provide higher voltage levels. Referring to  FIG. 1   a , multiple solar cell  22  are conventionally connected in series to form a “serial-unit”  26  of solar cells  22 , wherein multiple serial-units  26  may be interconnected in series to form a string of serial-units  28 , in order to obtain the desired output voltage in a solar-array module  20 . Each serial-unit  26  may include one or more cells and is protected by a bypass diode  25  that is added to bypass local problems such as dirt, overcastting shades, other partial shading or otherwise malfunctioning cells. 
         [0004]    Solar cells  22 , being connected in series, suffer from the following setbacks:
       a) Solar cells  22  may be subject to at least a partial light occlusion due to shading and/or dirt accumulated on one or more modules. Electric power generated in partially shaded cells is greatly reduced. An electric current produced by the cell is reduced proportional to the light intensity decreasing. Bypass diodes  25  enable the flow of electric current but does not compensate for the lost power from the bypassed serial-unit  26 . Typically, the voltage drop on a diode  25  is about 0.25V.   b) Typically, solar array module  20  is sensitive to inverse breakdown voltage that may be developed in another solar-array module  20 . Diode  27  prevents the breakage of the solar-array module. Diode  27  also prevents a solar-array module output short circuit.   c) Inequality between solar cells  22  also yields a loss in power.       
 
         [0008]    In an exemplary arrangement, for a nominal 30 volt Silicon solar-array module generating system, about 60 cells are connected in series to produce a 30 volt output. Usually, bypass diodes are placed across groups of cells, for example, 5-20 cells per diode instead of one bypass diode per cell to lower the cost. Cells connected in series with bypass diodes have been proven to be effective in many photovoltaic applications. 
         [0009]    Reference is also made to  FIG. 1   b , which is a schematic block diagram showing the voltage drop on output protection series diodes of a conventional solar module  20 . Furthermore: 
         [0000]        V out= Vp−Vds[V]   (2)
 
         [0000]    where Vout is the total voltage produced by the module including voltage drop on series diode  27 . This voltage drop may be the reason for module additional power losses. 
         [0010]    Practically, two diodes electrically connected in series are used in order to avoid diode breakdown voltage. If a cell in a serial-unit  26  malfunctions for any reason, the power produced by the whole serial-unit  26  is lost. The power produced by the module is computed as follows: 
         [0000]    
       
         
           
             
               
                 
                   Pout 
                   = 
                   
                     
                       Pp 
                       ( 
                       
                         1 
                         - 
                         
                           xn 
                           m 
                         
                         - 
                         
                           
                             
                               2 
                               * 
                               Vds 
                             
                             + 
                             
                               n 
                               * 
                               Vdp 
                             
                           
                           
                             
                               Vp 
                               * 
                               
                                 ( 
                                 
                                   m 
                                   - 
                                   xn 
                                 
                                 ) 
                               
                             
                             m 
                           
                         
                       
                       ) 
                     
                      
                     
                         
                     
                     [ 
                     W 
                     ] 
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
         [0000]    where
   Pout is the total power produced by the module, including power loss on series diodes  27 .   Pp is the maximum power that solar-array module  20  produces Mien all cells  22   12  function,   x is the number of Cells  22  in a serial-unit  26 ,   n is the number of malfunctioning serial-units  26 ,   Vds is the voltage drop over a diode  27  electrically connected in series with solar-array module  20 ,   Vdp is the voltage drop over bypass diode  25  electrically connected in parallel with a serial-unit  26 , and   Vp is the voltage that solar-array module  20  produces when all cells  22  function.   
 
         [0018]    It should be noted that equation (1) is an approximation and is suitable for x*n≦45. 
         [0019]    Reference is now made to FIG.  2 - a  block diagram, showing a prior art solar-array module  30 . Solar-array module  30  includes solar cells  22  electrically connected in series to form serial-units  26 . In the example shown in  FIG. 2 , each serial-unit  26  includes 4 solar cells  22 . The serial-units  26  are interconnected in parallel ( 32 ), to obtain a desired current producing capacity for solar array module  30 . The number of solar cells  22  that form a serial-unit  26  determines the voltage level provided by solar-array module  30 . The number of serial-units  26 , electrically connected in parallel, determines the current level provided by solar-array module  30 , to thereby obtain the predetermined electric power. 
         [0020]    For example, a solar module  30  includes 60 solar cells  22 , wherein each serial-unit  26  includes 4 solar cells  22  and wherein 15 serial-units  26  are electrically interconnected in parallel. For solar cells  22  that produce 0.5 Volt each, each serial-unit  26  produces 2 Volts. 
         [0021]    A power converter  34  is connected at the exit of the array of solar cells  22  of module  30 , which power converter  34  converts the input voltage level (2 Volts, in the afore mentioned example) to a significantly higher output voltage level, for example 30 Volts, in the afore mentioned example. Hence, when a solar cell  22  that is a member of a serial-unit  26  is defective, the module loses the power of the whole serial-unit  26 . 
         [0022]    Therefore, there is a need and it would be advantageous be able to prevent power loses of the whole serial-unit  26  as a result of a malfunction solar cell. 
         [0023]    Reference is also made to FIG.  3 - a  block diagram, showing a prior art solar-array module  40 . Solar-array module  40  is similar to solar array module  30 , except that each serial-unit  26  includes a single solar cell  22 . Solar module  40  is optimal in the sense that when a solar cell  22  malfunctions, the only power loss is the power of the serial-unit  26  containing the malfunctioning solar cell  22 . 
         [0024]    In an optimal solar module the power loses are very small. 
         [0025]    Typically, the voltage level of a conventional solar cell  22  is relatively low (about 0.5V). With this level of input voltage, the input current of power converter  44  for solar module, for example of 250 W, will be very high (more than 500 A), and power converter  44  efficiency is not high enough to provide such current level. Therefor, there is a need and it would be advantageous be able to provide a higher input voltage to power converter  44 . 
         [0026]    It should be noted that throughout the present disclosure, the invention is described using the text and related drawings. The equations are included only as a possible help to persons skilled in the art, and should not be considered as limiting the invention in any way. Various other equations may be used by persons skilled in the art. 
         [0027]    There is a need for and it would be advantageous to have an apparatus, system and method for solar electric power generation, wherein the apparatus facilitates maximization of the power generated by a solar-array module in which module one or more Silicon solar cells malfunction. 
       SUMMARY OF THE INVENTION 
       [0028]    By way of introduction, the principal intentions of the present invention include providing a solar-array system that includes one or more solar-array modules. Each solar-array module includes multiple solar cells. Groups of solar cells are electrically connected in series to form a serial-unit of cells. Multiple serial-units of cells are electrically connected in parallel to form an array of cells, wherein all solar cells are electrically interconnected to form a crisscross network of solar cells. That is, multiple serial-units may be further electrically interconnected in series to form a string of serial-units, wherein the strings of serial-units are also electrically interconnected in parallel, to form a crisscross matrix array of solar cells. 
         [0029]    The present invention includes providing a solar-array module, wherein all the solar cells are electrically interconnected in a crisscross configuration, to form a network of solar cells. Each solar-array module includes a power converter, which power converter is electrically connected at the exit of the array of solar cells, and which power converter is required to convert the input voltage level to a significantly higher output voltage level at the panel output. 
         [0030]    The power converter is facilitated of handling large values of input current. Such currents are required to supply a significant power at low voltage. For example, in a 250 Watt power converter with an input voltage of 2 Volt and an efficiency of 95%, the required input current is 132 Amp. 
         [0031]    If some of the light is prevented from illuminating a particular solar cell, the total power of the solar-array module will be reduced by the defective cell. All the remaining In cells in the string of serial-unit will continue to provide the produced power to the solar-array module. The total solar-array module power can be calculated by the follows formula, which formula generalizes formula (3): 
         [0000]        P out= P max(1 −xn/m )[ W]   (4)
 
         [0000]    where
   Pout is the total power produced by the solar-array module when one or more solar cells malfunction,   Pmax is the maximum power that the solar-array module produces when all solar cells function,   x is the number of solar cells in a serial-unit,   n is the number of malfunctioning serial-units,   m is the number of solar cells in the solar-array module,   η is the power converter&#39;s efficiency.   
 
         [0038]    According to the teachings of the present invention, there is provided a solar power generation system for providing operating power for a desired application, the desired application having a predetermined operating power level requirement and predetermined operating voltage level requirement. The system includes one or more solar-array modules, wherein each of the one or more solar-array modules includes a multiplicity of solar cells and a high efficiency DC to DC power converter. 
         [0039]    A preconfigured number of the solar cells are electrically connected in series to form a string of serial-units, which string of serial-units is facilitated to produce a first output voltage level, wherein the first output voltage level is insufficient to meet the desired application operating voltage level requirement. Also, a preconfigured number of the strings of serial-units are electrically connected in parallel to form an array of the solar cells, which array of the solar cells is facilitated to produce a first output power level. 
         [0040]    In each of the strings of serial-units, at least one selected solar cell of one of the strings of serial-units is also electrically connected in parallel to the respective solar cell of all other strings of serial-units, to form a crisscross matrix array of solar cells, wherein the crisscross matrix array of solar cells allows currents to bypass malfunctioning cells, thereby improving the performance of the system. 
         [0041]    The high efficiency DC to DC power converter is electrically connected to the crisscross matrix array of solar cells, the power converter configured to boost the first output voltage level to a second output voltage level higher than the first output voltage level. Preferably, the second output voltage level is substantially sufficient to meet the desired application operating voltage level requirement. 
         [0042]    Preferably, in each of the strings of serial-units, each solar cell is also electrically connected in parallel to the respective solar cell of all other strings of serial-units, to form the crisscross matrix array of solar cells. 
         [0043]    Preferably, each of the strings of serial-units consists of the same number of the solar cells electrically connected in series. 
         [0044]    Preferably, the power converter includes fast MOSFET transistors for alternately connecting the opposite sides in a primary of a transformer to a DC source, wherein the duty cycle of the fast MOSFET transistors is operationally constant and is almost 50%. 
         [0045]    Optionally, a preconfigured number of solar-array modules are electrically connected in series to form a string of solar-array modules, wherein the array of solar-array modules produces a third output voltage level, and wherein the third output voltage level is substantially sufficient to meet the desired application operating voltage level requirement. Optionally, a preconfigured number of the strings of solar-array modules are electrically connected in parallel, to form an array of solar-array modules, wherein the array of solar-array modules produces a third output power level, and wherein the third output power level is substantially sufficient to meet the desired application operating power level requirement. 
         [0046]    Optionally, the power converter includes a planar transformer, which transformer includes a ferromagnetic core, wherein two window openings are formed at the opposing ends of the ferromagnetic core, a primary coil, a secondary coil, input coil leads and output coil leads. The optional power converter further includes, an input printed circuit board, wherein receiving holes are formed in the input printed circuit, facilitating direct electrical connection to the input coil leads, and an output printed circuit board, wherein receiving holes are formed in the output printed circuit board, facilitating direct electrical connection to the output coil leads. The input printed circuit board and output printed circuit board are respectively disposed at the window openings of the ferromagnetic core, to thereby minimize the wiring length of wires from the primary coil and the secondary coil to the input printed circuit board and output printed circuit board, respectively. 
         [0047]    Optionally, the power converter includes a plus conductive pad and a minus conductive pad, wherein each of the strings of serial-units is individually wired to the plus conductive pad and the minus conductive pad. 
         [0048]    Optionally, each of the solar-array modules further includes a secondary, low power array of solar cells, used to start up the DC to DC power converter. 
         [0049]    Optionally, the solar power generation system of the present invention includes one or more solar-array modules, wherein each of the one or more solar-array modules includes a multiplicity of solar cells, a high efficiency DC to DC power converter and a start up device. A preconfigured number of the solar cells are electrically connected in series to form a string of serial-units, which string of serial-units is facilitated to produce a first output voltage level, wherein the first output voltage level is insufficient to meet the desired application operating voltage level requirement. Also, a preconfigured number of the strings of serial-units are electrically connected in parallel to form an array of the solar cells, which array of the solar cells is facilitated to produce a first output power level. 
         [0050]    Furthermore, in the optional solar power generation system, a preconfigured number of the solar cells are electrically connected in series to form a string of serial-units, the string of serial-units is facilitated to produce a first output voltage level; and a preconfigured number of the strings of serial-units are electrically connected in parallel to form an array of the solar cells, the array of the solar cells is facilitated to produce a first output power level. Furthermore, in the optional solar power generation system, a high efficiency DC to DC power converter electrically connected to the array of solar cells, the power converter configured to boost the first output voltage level to a second output voltage level higher than the first output voltage level, wherein the first output voltage level is insufficient to meet the desired application operating voltage level requirement, and wherein each of the solar-array modules includes a secondary, low power array of solar cells, used to start up the DC to DC power converter. 
         [0051]    These and further embodiments will be apparent from the detailed description and examples that follow. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0052]    The present invention will become fully understood from the detailed description given herein below and the accompanying drawings, which are given by way of illustration and example only, and thus not limiting in any way, wherein: 
           [0053]      FIG. 1   a  (prior art) is a schematic block diagram showing a conventional solar module with multiple cells electrically connected in series to form serial-units, wherein each serial-unit is protected by a bypass diode, wherein the serial-units may be interconnected in series to form a string of serial-units, and wherein each module is protected by a series diode; 
           [0054]      FIG. 1   b  (prior art) is a schematic block diagram showing the voltages across the module including voltage drop on series diode; 
           [0055]      FIG. 2  (prior art) is a schematic block diagram showing a solar array system including multiple serial-units electrically connected in parallel, according to embodiments of the present invention; 
           [0056]      FIG. 3  (prior art) is a schematic block diagram showing a optimal solar-array system as in  FIG. 3 , wherein each serial-units includes a single solar cell and thUs, serial-units are electrically connected in parallel; 
           [0057]      FIG. 4  is a schematic block diagram showing a solar-array module, wherein the cells are electrically interconnected in a crisscross matrix configuration, according to embodiments of the present invention, to allow currents to bypass malfunctioning solar cells; 
           [0058]      FIG. 5  is a schematic block diagram showing another solar-array module, wherein the cells are electrically connected in yet another exemplary crisscross matrix configuration, according to embodiments of the present invention; 
           [0059]      FIG. 6  is a schematic block diagram showing a solar array module as in  FIG. 2 , wherein the solar-array module further includes a secondary array of solar cells used to start up the convertor, according to embodiments of the present invention; 
           [0060]      FIG. 7  is a schematic block diagram showing a solar-array module as in  FIG. 3 , wherein the solar-array module further includes a secondary array of solar cells used to start up the convertor, according to embodiments of the present invention; 
           [0061]      FIG. 8  is a schematic block diagram showing a solar-array system including a multiplicity of solar-array modules, such as shown in  FIG. 4 , according to embodiments of the present invention; 
           [0062]      FIG. 9  is a schematic block diagram showing a solar-array system including a variety of solar-array modules, according to embodiments of the present invention; 
           [0063]      FIG. 10  (prior art) is an electric circuit diagram showing a DC to DC power converter using a Push-Pull topology design; 
           [0064]      FIG. 11  is an electric circuit diagram showing a DC to DC power converter without the output coil and in conjunction with solar-array modules, which use solar cells electrically connected in a crisscross matrix array; 
           [0065]      FIG. 12   a  is a diagram of switching times of a prior art power converter; 
           [0066]      FIG. 12   b  is a diagram of switching times of a power converter, in conjunction with solar-array modules which use solar cells electrically connected in series and/or in parallel; 
           [0067]      FIG. 13  is a perspective view of a structure of a DC to DC power converter, according to embodiments of the present invention; 
           [0068]      FIG. 12  is a schematic block diagram of a solar-array module having a secondary array of solar cells used to start up a solar-array module, according to variations of the present invention; 
           [0069]      FIG. 14  is a schematic block diagram of a solar-array module, wherein the strings of serial-units are electrically connected to each of the DC to DC power converter pads by single mutual line; 
           [0070]      FIG. 15  is a schematic block diagram of a solar-array module, wherein the strings of serial-units are individually electrically-connected to each of the DC to DC the power converter&#39;s pads. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0071]    The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided, so that this disclosure will be thorough and complete, and will fully convey the scope of the present invention to those skilled in the art. 
         [0072]    Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs. The methods and examples provided herein are illustrative only, and not intended to be limiting. 
         [0073]    By way of introduction, the principal intentions of the present invention include providing solar electric power generation apparatus and system that facilitates maximization of the power generated by a solar array module apparatus having one or more malfunctioning Silicon solar cells. 
         [0074]    Reference is now made to  FIG. 4 , which is a schematic block diagram showing a solar-array module  200 , wherein all solar cells are electrically interconnected in a crisscross matrix configuration, according to variations of the present invention, to allow currents to bypass malfunctioning solar cells. 
         [0075]    In solar-array module  200 , all solar cells  210  are electrically interconnected in a crisscross matrix configuration, to form a network  205  of solar cells  210 . Hence each individual serial-unit  222  includes just one solar cell  210 , whereby when a solar cell  210  malfunctions, the only power loss is that of that particular solar cell  210 . The extra lines  232  added to the array of solar cells  210  reduce the damage inflicted by a malfunctioning cell  210 , in the expense of cost and module area. Generally, solar-array module  200  can includes any number of serial-units  222 , electrically connected in series, to form a string of serial-units  220 . In the example shown in  FIG. 4 , Solar-array module  200  includes four serial-units  222  electrically connected in series to form a string of serial-units  220 . The voltage level of four serial-units  222  electrically connected in series is relatively high (about 2V). With this input voltage, the input current of power converter  250  will be four time less than the input current of power converter  44  ( FIG. 3 ), and power converter  250  efficiency is higher than the efficiency of power converter  44 . 
         [0076]    Reference is also made to  FIG. 5 , which is a schematic block diagram showing another solar-array module  300 , according to other variations of the present invention. In solar-array module  300 , the electrically interconnectivity of solar cells  310  in the array of solar cells  310  is a compromise between solar-array module  30  (see  FIG. 2 ) and solar-array module  200 , for reducing costs. Hence, when a solar cell  22  that is a member of a serial-unit  26  is defective, the module loses the power of the whole serial-unit  26 . When a solar cell  310  that is a member of a serial-unit  322   b  is defective, the module loses the power of the whole serial-unit  322   b . When a solar cell  310  that is a member of a serial-unit  322   a  is defective, the module loses the power of that particular defective solar cell to  310 . Solar-array module  300  can include any number of serial-units  322  electrically connected in series to form a string of serial-units  320 . 
         [0077]    The suggested solution (as shown in  FIG. 4  and  FIG. 5 ) solves the problem of high current at the power converter ( 34 ,  44 ,  250  or  350 ) entrance on the one hand, and the problem of losses of power due to a defective solar serial-units ( 26 ,  222  or  322 ), on the other hand. The suggested solution provides a general solution and gives flexibility in solar-array module designing. An appropriate solar-array module design can be selected to provide the proper solution for a selected application. 
         [0078]    When for example, a solar cell ( 210  or  310 ) malfunctions (“defective solar cell”), the solar serial-unit ( 222  or  322 ), to which the defective solar cell belongs, becomes a “defective serial-units”, the string of serial-unit ( 220  or  320 ), to which the defective solar serial-unit ( 222  or  322 ) belongs, becomes a “defective string of serial-unit ( 220  or  320 ). The other solar cells ( 210  or  310 ) of the defective string of serial-units ( 220  or  320 ) continue producing power and are able to output their current I Σ  through the parallel electrically connected functioning solar string of serial-units ( 220  or  320 ), all electrically connected in a crisscross matrix network, as described before. A portion of current I Σ  that flows through the parallel electrically connected functioning solar string of serial-units ( 22 ,  220  or  320 ) is a current I u : 
         [0000]    
       
         
           
             
               
                 
                   Iu 
                   = 
                   
                     
                       I 
                       Σ 
                     
                     
                       ( 
                       
                         
                           m 
                           x 
                         
                         - 
                         n 
                       
                       ) 
                     
                   
                 
               
               
                 
                   ( 
                   5 
                   ) 
                 
               
             
           
         
       
     
         [0000]    where
   m is the number of solar cells in the module.   x is the number of solar cells in a string of serial-units,   n the number of defective strings of serial-units.   
 
         [0082]    In a solar-array module  300 , for example, a 250 W solar-array module  300 , having 60 solar cells  310  arranged in 15 strings of serial-units  320 , wherein some serial-unit  322  includes 2 solar cells  310 , 15 serial-units  322  are electrically connected in parallel, and two other functioning solar cells  310  are electrically connected in series to each serial-unit  322 , all of which solar cells  310  are electrically interconnected in a crisscross matrix structure, as illustrated in  FIG. 5 . If a single solar cell  310  is defective, the whole serial-unit  322  that includes the defective cell becomes defective as well. The remaining two functioning solar cell  310 , electrically connected in series to the defective serial-unit  322 , continue to provide the produced current through parallel electrically connected solar string of serial-units  320 . 
         [0083]    Similarly, in a solar-array module  200  for example, in a 250 W solar-array module  200 , having 80 solar cells  210  arranged in 20 strings of serial-units  220 , wherein each serial-unit includes 1 solar cells  210  and 20 serial-units  222  are electrically connected in parallel and series, all of which solar cells  210  are electrically interconnected in a crisscross matrix structure, as illustrated in  FIG. 4 . If a single solar cell  210  is defective, that is single serial-unit  222  is defective, the remaining solar cells  210  of the defective string of serial-units  220  continues to provide produced current through parallel electrically connected solar cells  210 . 
         [0084]    An optional aspect of the present invention is to provide a start-up device ( 240  or  340 ) to provide the high voltage needed to operate the controller ( 252  or  352 ) of the power converter ( 250  or  350 ) of a solar-array module ( 200  or  300 ). A start-up device is required to generate the supply voltage for the controller ( 252  or  352 ) of the power converter ( 250  or  350 ). The start-up device ( 240  or  340 ) includes a multiplicity of small area, low power solar cells ( 245  or  345 ) electrically connected in series to form at least one string of solar cells ( 242  or  342 ). Optionally, several start-up devices ( 240  or  340 ) are dispersed inside the module ( 200  or  300 ), to reduce partial shading effect. Optionally, all start-up devices are electrically connected to in parallel. The array of start-up devices ( 240  or  340 ) is electrically connected to the power converter ( 250  or  350 ). It should be noted that the number of cells in each string of cells may vary according to the solar-array module ( 200  or  300 ) and/or power converter ( 250  or  350 ) specifications. 
       Example 
       [0085]    For a prior art solar module having 60 solar cells  22  electrically connected in series, whereas for each 6 solar cells  22  there is a bypass diode  25  electrically connected in parallel, to form a unit string. Now the prior art solar module is compare to a solar module of the present invention, with the same number of cells, but all cells are electrically interconnected in a net structure as described  FIG. 5 . Both modules are designed to produce 250 W of electric power. 
         [0000]    
       
         
               
               
               
             
           
               
                   
               
               
                 Number of defective 
                 Prior art solar-array 
                 Innovative solar-array 
               
               
                 units 
                 module total power 
                 module total power 
               
               
                   
               
             
             
               
                 1 
                 218 
                 232 
               
               
                 3 
                 160 
                 216 
               
               
                   
               
             
          
         
       
     
         [0086]    Reference is also made to FIG.  6 —a schematic block diagram showing a solar-array module  400 , which is similar to solar-array module  30 , shown in  FIG. 2 , wherein solar-array module  400  further includes a start-up device  440 , used to start up a convertor  450 , according to embodiments of the present invention. The start-up device  440  includes a secondary array  442  of solar cells  445 . Reference is also made to FIG.  7 —a schematic block diagram showing a solar-array module  500 , which is similar to solar-array module  40 , shown in  FIG. 3 , wherein solar-array module  500  further includes a start-up device  540 , used to start up a convertor  550 , according to embodiments of the present invention. The start-up device  540  includes a secondary array  542  of solar cells  545 . A start-up device is required to generate the supply voltage for the controller ( 452  or  552 ) of the power converter ( 450  or  550 ). 
         [0087]    An aspect of the present invention is to provide a solar-array system for generating electric power, composed of multiple solar-array modules. Reference is made to FIG.  8 —a block diagram showing a solar-array system  600  that includes a multiplicity (in this example—4) of solar-array modules  200 , according to embodiments of the present invention. Solar-array modules  200  are electrically connected in series through the respective power converter  250  of each solar-array module  200 , to form a string of solar-array modules  620 . The voltage produced by solar-array system  600  is the sum of voltages provided by the power converters  250  of a string of solar-array modules  620 . 
         [0088]    Solar-array system  600  further include one or a plurality of similar strings of solar-array modules  620 , which strings of solar-array modules  620  are electrically connected in parallel ( 630 ), to provide the total power desired via a single voltage output (DC Vout) of solar-array system  600 . 
         [0089]    Optionally, the output voltage, DC Vout, of system  600 , is provided to an inverter  650  that is configured to convert the DC output of system  600  to an AC output, which is preferably electrically connected to the public electric grid. 
         [0090]    Reference is also to FIG.  9 —a block diagram showing an solar-array system  700  that includes a multiplicity (in this example—4) of a variety of solar-array modules ( 200 ,  300 ,  400  and  480 ), according to embodiments of the present invention. Solar-array modules  200 ,  300 ,  400 ,  480  and other configurations of solar-array modules  740  are electrically connected in series through the respective power converter ( 250 ,  350 ,  450  and  550 ) of each solar-array module ( 200 ,  300 ,  400 ,  480  and  740 ), to form a string of solar-array modules  720 . The voltage produced by solar-array system  700  is the sum of voltages provided by the respective power converter ( 250 ,  350 ,  450  and  550 ) of a string of solar-array modules  720 . 
         [0091]    Solar-array system  700  further include one or a plurality of similar strings of solar-array modules  720 , which strings of solar-array modules  720  are electrically connected in parallel ( 730 ), to provide the total power desired via a single voltage output (DC Vout) of solar-array system  700 . 
         [0092]    Optionally, the output voltage, DC Vout, of system  700 , is provided to an inverter  750  configured to convert the DC output of system  700  to an AC output, which is preferably electrically connected to the public electric grid. 
         [0093]    Reference is now made to FIG.  10 —an electric circuit diagram  60  showing an example of a DC to DC power converter using a Push-Pull topology, as known in the art. The switching transistors  76 ,  72  alternately connect opposite ends of the primary coil of the transformer  62  to the (−) side of a DC power source  66 , while the center of the primary coil is fixedly connected to the (+) side of DC power source  66 . Transistors  76 ,  72  are activated into their ON, OFF states by the respective input control voltages  78 ,  74 . 
         [0094]      FIG. 11  details the electric circuit diagram  800  of a DC to DC Push-Pull power converter according to the present invention. The output coil  64  (see  FIG. 10 ) was removed, as it is no longer necessary. The input capacitor  868  can have a smaller value or may be removed altogether. The output capacitor  865  can have a smaller value or may be removed altogether. 
         [0095]      FIG. 12A  details switching times of the prior art Push-Pull power converter  60 , showing the control voltage for MOSFET transistors  76  and  72  vs. time  735 . In prior art, the duty cycle of these pulses is significantly smaller than 50% and is not constant. That is, the ON state time  732  is significantly shorter than half the period time  731 . It should note that a MOSFET transistor is given by way of example only, and other types of transistor, suitable to the application, may be used within the scope of the present invention. 
         [0096]    These waveforms cause ripple in the circuit, which require relatively large values of the input capacitor  68 ; output coil  64  and output capacitor  65 . Such large values result in a costly implementation and bulky components. Input capacitor  68  rated for high currents may be very expensive. 
         [0097]    Moreover, the large currents in the capacitors  68  and  65 , and the resistance of the large coil  64 , result in significant ohmic losses, thus reducing the converter&#39;s efficiency. Therefore, this prior art power converter may be expensive, bulky and with a low efficiency. 
         [0098]    It is the intention of present invention to provide an innovative power converter that is an efficient and low cost power converter, in conjunction with, crisscross matrix of solar cells arrays of solar-array modules and solar-array systems (see for example,  FIG. 4 ,  FIG. 5 ,  FIG. 8  and  FIG. 9 ). 
         [0099]      FIG. 12B  details switching times of a power converter  800 , showing the control voltage for the MOSFET transistors  876  and  872  vs. time  735 . 
         [0100]    The ON time  741  of the MOSFET transistors in  FIG. 12B  is almost 50%. The OFF time  742  of the MOSFET transistors in  FIG. 12B  is almost 50% also. Hence, the operational duty cycle of the MOSFET transistors  876  and  872  is constant and is just less than 50% (almost 50%), wherein the duty cycle is defined as: 
         [0000]      Duty cycle=ON time(741)/ T (731). 
         [0101]    The “dead” time  743  between the switching time ON to OFF of one MOSFET transistor, and the switching OFF to ON of the other MOSFET transistor is a very, very small time relating to the ON and OFF time periods, this to prevent both MOSFET transistors  876 ,  872  from conducting simultaneously. The same consideration applies to the “dead” time  744 . Through transformer  862  in diagram  800  flows a current which is only interrupted just in very small “dead” time intervals  743  and  744 . The power converter operates almost like a DC/DC transformer with small input voltage and high output voltage. Thus very small current interrupt for “dead” time intervals  743  and  744 , greatly reducing the ripple in the power converter input and output circuits. Significantly smaller values or may be completely deleting of the input capacitor  868 , output coil  864  and output capacitor  865  can be used, to reduce costs, as well as the weight and volume of the power converter and to increase the power converter&#39;s efficiency. 
         [0102]      FIG. 13  details the structure of a DC to DC power converter, according to variations of the present invention, with a planar transformer  900 . The transformer  900  includes a ferromagnetic core  910  and coils, input coil leads  912  and output coil leads (not shown on the down side of transformer  900 ). Ferromagnetic core  910  includes two window openings formed at the opposing ends of ferromagnetic core  910 . 
         [0103]    Only the structure of the circuit to the primary coil is detailed, because here we have a high current due to the low voltage; the secondary has a higher voltage thus a lower current, so losses in the wiring are much lower. 
         [0104]    The leads  912  of the transformer&#39;s primary coil are connected to an input printed circuit  920  and the leads of the transformer&#39;s secondary coil are connected to an output printed circuit  930 , respectively. To connect the wires as required, there are receiving holes  922 , formed in input printed circuit  920 , facilitating direct electrical connection input coil leads  912  and holes  924  for wires  1010  of strings of serial-units, in the input printed circuit  920 . The output printed circuit  930  has receiving holes  932  for output coil leads (not shown) and holes for the power converter&#39;s output wires  954 . 
         [0105]    The input printed boards  920  and a output printed board  930  placed very tightly to planar transformers  900 , onto windows  962  and  964 , respectively. 
         [0106]    The input and output switching circuits are divided into two small printed boards  920  and  930 , each mounted close to one of the two openings formed at the opposing ends of ferromagnetic core  910 . Thus, the leads  912  of the primary and secondary coils of the transformer will reach directly, in the shortest path possible, to the switching circuits. This structure minimizes the length of the wires and the dimensions of the power converter. 
         [0107]    Structure  900  reduces copper losses in the wiring and improves the efficiency of the power converter. The overall current flows in printed circuits  920  and  930 , which printed circuits are so designed as to have a very small resistance. Only very short wiring is required from input printed circuit  920 , to the primary coil in the transformer  910  and only very short wiring is required from output printed circuit  930 , to the secondary coil in the transformer  910 . 
         [0108]    Moreover, shortens switching lines decreases the area of the loop for RFI in the switching input and output electrical circuits, thus reducing Radio Frequency Interference (RFI). 
         [0109]    Preferably, printed circuits  920 ,  930  are implemented as a multilayer printed circuit board (PCB), with a grounded shielding surface; this further contributes to avoid electromagnetic radiation. Furthermore, the transformer is contained in a ferromagnetic structure, made for example of ferrite; this also contributes to avoid electromagnetic radiation and to reduce RFI to the environment. Thus structure operates as FARADY enclosure. An “environmentally green” product is thus achieved. 
         [0110]      FIG. 14  details regular electrical connections from solar cells  210  to the converter&#39;s pads  920  and  930 .  FIG. 14  is a schematic block diagram of a solar-array module  202 , wherein the solar cells string of serial-units  220  are electrically connected to each of the DC to DC power converter pads  920  and  930  by single mutual line  204  and  206 , respectively. 
         [0111]    A possible problem with low voltage solar cells is ohmic losses in the wiring from string of serial-units  220  to the DC to DC power converter  250 . For example, assuming a 250 Watt solar array module, having 60 solar cells  210 , wherein every 4 solar cells  210  are electrically connected in series to form a string of serial-units  220  of solar cells  210 , and the string of serial-units  220  are also electrically interconnected in parallel, to form crisscross matrix having 15 strings of serial-units  220  each including 4 solar cells (see for example  FIG. 14 ); in such configuration: 
         [0000]    The input voltage to power converter  250  is about 2 Volt (each solar cell  210  generates about 0.5 Volt, and there are 4 solar cells in series). The total input current to power converter  250  will be more of 125 Amp, according to the efficiency of power converter  250 . 
         [0112]    The current of one string of serial-units  220  of solar cells  210  (about 8.3 Amp) is multiplied by the 15 of string of serial-units  220  in parallel to yield the total current flowing in the wires  204  and  206  from the string of serial-units  220  to power converter  250 . Thus, the total current may exceed values of 125 Amp. 
         [0113]    For example: the solar-array module is about 0.9 meter wide. For copper wires  204  and  206  of 1 mm thickness and 10 mm width, in a conventional embodiment, the ohmic losses in the wires is approximately 26.5 Watt. This is a loss of 10.6% for a power converter of 250 Watt, a quite unacceptable value. 
         [0114]    If thicker wires are used, the ohmic losses decrease. For example: for wires  204  and  206  of a 15 mm by 10 mm cross section, the losses will be about 1.8 Watt. 
         [0115]    This is a reasonable value, however, thicker wires  204  and  206  are rigid and have a large size, weight and cost, a quite unacceptable value. 
         [0116]      FIG. 15  details electrical connections from the solar cells to the power converter pads, according to the present invention.  FIG. 15  is a schematic block diagram of a solar-array module  1000 , wherein the strings of serial-units  220  are individually electrically-connected to each of the DC to DC power converter pads  920 ,  930 . Throughout the present disclosure, a string is defined as a plurality of solar cells connected in series, and a string of serial-units  220  is defined as a plurality of solar cells  210  electrically connected in series as well as the of solar cells  210  parallel electrically connected to the respective solar cells  210  in the adjacent strings of serial units  220 . In the present example, each string of serial-units  220  includes four solar cells. 
         [0117]    A solar-array module includes a plurality of strings of serial-units  220  and one DC to DC power converter  250 . The (+) side of each string of serial-units  220  is electrically connected to the (+) pad  920  of the power converter. The (+) pad  920  of power converter  250  is implemented as a wide and large area pad, which is mounted close to the power converter  250  input, in order to reduce copper losses. The (−) side of each strings of serial-units  220  is electrically connected to the (−) pad  930  of power converter  250 , which is also implemented as a wide and large area pad, mounted close to the power converter  250  input, in order to reduce copper losses. 
         [0118]    In the above example, the matrix array of solar-array module  1000  (for example of 250 Watts) includes 15 strings of serial-units  220 , the current in each string of serial-units will be about 8.3 Amp. Through each string of serial-units  220  flows a maximal electric current as large as each solar cell  210  can generate, in our example about 8.3 Amp. This is a relatively low current, resulting in low copper losses (lower than in prior art solar arrays). A large electric current only flows in the large (+) and (−) input pads  920  and  930  of power converter  250 . The current reaching pads  920  and  930 , is the sum of the currents generated by all the strings of serial-units  220 . In this example, the total sum current may be about 125 Amp. 
         [0119]    In solar-array module  1000 , each string of serial-units  220  is separately electrically-connected to the large (+) and (−) input pads  920  and  930  of the power converter  250 . The ohmic losses will be about 2.3 Watt or 0.92% of the total output power 250 Watt. Such reduced losses are achieved with an innovative wiring schemes uses separate wires  1010 , thus reducing ohmic losses in the wiring. The wiring scheme presented in the example solar-array module  1000 , results in a substantial reduction in Ohmic losses, compared with prior art wiring, having the same type of wires:
       In a conventional wiring scheme: Ohmic losses=21.25%.   In the present novel wiring scheme: Ohmic losses=0.92%.       
 
         [0122]    Hence, the present novel wiring scheme significantly reduces ohmic losses, while allowing utilizing relatively thin wires—1 mm thickness and 10 mm width, for example. 
         [0123]    The present invention being thus described in terms of several embodiments and examples, it will be appreciated that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are contemplated.