Abstract:
A method for testing a photovoltaic panel connected to an electronic module. The electronic module has at least one input attached to the photovoltaic panel and at least one power output. The method of testing the photovoltaic panel begins with activating a bypass of the electronic module. The bypass is preferably activated by applying a magnetic or an electromagnetic field. The bypass provides a low impedance path between the input and output of the electronic module.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application benefits from U.S. applications 60/992589 filed 5 Dec. 2007 and 61/039050 filed 24 Mar. 2008 of the same inventors. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to production testing of photovoltaic panels, and more specifically to testing of photovoltaic panels which include integrated circuitry. 
       DESCRIPTION OF RELATED ART 
       [0003]    Current voltage (IV) characteristics of a conventional photovoltaic panel are measured using a flash tester. The flash tester measures electrical current characteristics of a photovoltaic panel during a single flash of light of duration typically within one millisecond emitted by the flash lamp. The measurement procedure is based on known properties of a reference photovoltaic panel which has been independently calibrated in an external laboratory. The external laboratory has determined accurately the short circuit current corresponding to standard test conditions (STC) using an AM1.5G spectrum. AM1.5G approximates a standard spectrum of sunlight at the Earth&#39;s surface at sea level at high noon in a clear sky as 1000 W/m 2 . “AM” stands for “air mass” radiation. The ‘G’ stands for “global” and includes both direct and diffuse radiation. The number “1.5” indicates that the length of the path of light through the atmosphere is 1.5 times that of the shorter path when the sun is directly overhead. During flash testing homogeneity of irradiance over the photovoltaic panel is obtained by a 6-meter distance between the flash lamp and the photovoltaic panel. 
         [0004]    Reference is now made to  FIG. 2  which illustrates a conventional flash tester  17 . Flash tester includes a flash lamp  16 , placed inside a closed lightproof cabin  19  which is painted black inside. Alternatively, black curtains minimize the intensity of reflections towards photovoltaic panel  10  from the interior surfaces of the cabin. The homogeneity of irradiance over area of photovoltaic panel  10  is measured by placing an irradiance sensor in various positions of the measurement plane. During the flash testing procedure, a flash tester  17  is connected to the output of photovoltaic panel  10 . The measurement procedure starts with a flash test of a reference photovoltaic panel. The short circuit current is measured during an irradiance corresponding to AM1.5G. The reference photovoltaic panel is then exchanged for the test photovoltaic panel. During a subsequent flash, the irradiance sensor triggers a current-voltage (IV) measurement procedure at the same irradiance as during the measurement of the reference photovoltaic panel. 
         [0005]    Conventional photovoltaic panels are typically connected together in series to form strings and the strings are optionally connected in parallel. The combined outputs of the connected photovoltaic panels are typically input to an inverter which converts the generated direct current voltage to alternating current of the grid. Recently, photovoltaic panels have been designed or proposed with integrated circuitry. 
         [0006]    Reference is now made to  FIG. 1  which illustrates schematically a photovoltaic system  14  with a circuit or electronic module  12  integrated with a photovoltaic panel  10 . The term “electronic module” as used herein refers to electronic circuitry integrated at the output of the photovoltaic panel. The “electronic module” itself may be of the prior art or not of the prior art. A representative reference (Cascade DC-DC Converter Connection of Photovoltaic Modules, G. R. Walker and P. C. Sernia,  Power Electronics Specialists Conference,  2002. ( PESC 02), Vol. 1 IEEE, Cairns, Australia, pp. 24-29) proposes use of DC-DC converters integrated with the photovoltaic panels. The DC-DC converter integrated with the photovoltaic panel is an example of an “electronic module”. Other examples of “electronic modules” include, but are not limited to, DC-AC inverters and other power conditioning electronics, as well as sensing and monitoring electronics. 
         [0007]    Another reference of the present inventors which describes an example of photovoltaic system  14  including photovoltaic panel  10  integrated with electronic module  12  is US20080143188, entitled “Distributed Power Harvesting Systems Using DC Power Sources”. 
         [0008]    The “electronic module” herein may have electrical functionality, for instance for improving the electrical conversion efficiency of photovoltaic system  14 . Alternatively, “electronic module” as used herein may have another functionality unrelated to electrical performance. For instance in a co-pending patent application entitled, “Theft detection and Prevention in a Power Generation System”, the function of electronic module  12  is to protect photovoltaic system  12  from theft. 
         [0009]    Since a standard flash test cannot typically be performed on panel  10  after integration with electronic module  12 , for instance because the presence of module  12  affects the results of the standard test, it would be advantageous to have a system and method for flash testing of photovoltaic system 
         [0010]    The term “photovoltaic panel” as used herein includes any of: one or more solar cells, cells of multiple semiconductor junctions, solar cells connected in different ways (e.g. serial, parallel, serial/parallel), of thin film and/or bulk material, and/or of different materials. 
       BRIEF SUMMARY 
       [0011]    According to aspects of the present invention there are provided a method for flash testing a photovoltaic panel connected to an electronic module. The electronic module has at least one input attached to the photovoltaic panel and at least one power output. The method of flash testing the photovoltaic panel begins by activating a bypass of the electronic module. The bypass is activated by applying (preferably externally)a magnetic field or an electromagnetic field. The bypass provides a low impedance path between the input and output of the electronic module. The electronic module is typically permanently attached to the photovoltaic panel. The electronic module optionally performs DC to DC conversion or DC to AC conversion. The electronic module optionally performs maximum power point tracking at either the input or the output of the electronic module. The bypass circuit may include a reed switch, or a reed relay switch, a solid state switch or a fuse. After flash testing, the bypass of the electronic module is typically de-activated, by for instance communicating with the electronic module. The bypass may be permanently deactivated, or have an option for re-activation. Re-activation may be beneficial in such scenarios as electronics malfunction (such as disconnect), in which case re-activating the bypass will allow for connection of the photovoltaic panel directly to the output and continued power harvesting. According to aspects of the present invention there is provided a device for flash testing a photovoltaic panel connected to an electronic module. The electronic module has at least one input attached to the photovoltaic panel and at least one power output. A bypass provides a low impedance path between the input and output of the electronic module. The bypass includes a switch between the input and output of the electronic module. The switch may be a magnetically activated reed switch, an electromagnetically activated reed relay or a solid state switch. The electronic module may be, but is not limited to, a DC to DC converter, a DC to AC converter, or a maximum power point tracking module. The bypass includes a fuse and a parallel-connected switch. The parallel-connected switch is disposed between and connected in parallel with the photovoltaic panel and the electronic module. A power supply unit is connected across the output of the electronic module. The parallel-connected switch is closed to provide a low impedance path across the fuse to blow the fuse. The parallel-connected switch includes a silicon controlled rectifier, reed switch, solid state switch, or reed relay. Alternatively, a power supply is connected directly across said fuse and the current flow of the power supply de-activates the bypass by blowing of the fuse. The bypass may include a solid state switch. The bypass is deactivated either permanently (for instance in the case of a blown fuse) or the bypass may be reactivated as required (in the case of a switch. 
         [0012]    According to still other aspects of the present invention there is provided a device for flash testing a photovoltaic panel connected to an electronic module. The electronic module has at least one input attached to the photovoltaic panel and at least one power output. A bypass applied to the electronic module has two single pole double throw (SPDT) switches and a single pole single throw (SPST) switch. The output node of the photovoltaic panel is connected to the first SPDT switch common. The first output node of the first SPDT is connected to the input node of the electronic module. The second output node of the first SPDT switch is connected to the input node of the SPST switch. The output node of the SPST switch is connected to a first input node of a second SPDT switch. The output node of the electronic module is connected to the second input node of the second SPDT switch. The output node of the second SPDT switch is connected to enclosure output which may be connected to the flash tester. 
         [0013]    The foregoing and/or other aspects will become apparent from the following detailed description when considered in conjunction with the accompanying drawing figures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The invention is herein described, by way of example only, with reference to the accompanying drawings, wherein: 
           [0015]      FIG. 1  illustrates an electrical power generation system including a photovoltaic panel and electronic module. 
           [0016]      FIG. 2  illustrates a flash test module of the prior art. 
           [0017]      FIG. 3  illustrates a general equivalent circuit, representing the electronic module shown in  FIGS. 1 and 2  with a bypass applied, according to a feature of the present invention. 
           [0018]      FIG. 4  shows a flow chart of a method to flash test a photovoltaic panel according to an embodiment of the present invention. 
           [0019]      FIG. 5  is an activated bypass circuit, according to an embodiment of the present invention, of an electronic module connected to a photovoltaic panel and test module. 
           [0020]      FIG. 6  is a de-activated bypass circuit, according to an embodiment of the present invention of an electronic module connected to a photovoltaic panel. 
           [0021]      FIG. 7  is an activated bypass circuit, according to another embodiment of the present invention, of an electronic module connected to a photovoltaic panel and test module. 
           [0022]      FIG. 8  is a de-activated bypass circuit, according to another embodiment of the present invention of an electronic module connected to a photovoltaic panel. 
           [0023]      FIG. 8   a  is a de-activated bypass circuit using a fuse and power supply, according to another embodiment of the present invention of an electronic module connected to a photovoltaic panel. 
           [0024]      FIG. 8   b  is a de-activated bypass circuit using a fuse, power supply and silicone controlled rectifier (SCR), according to yet another embodiment of the present invention of an electronic module connected to a photovoltaic panel. 
           [0025]      FIG. 9  is an activated bypass circuit, according to yet another embodiment of the present invention, of an electronic module connected to a photovoltaic panel and test module. 
           [0026]      FIG. 10  is a de-activated bypass circuit, according to yet another embodiment of the present invention of an electronic module connected to a photovoltaic panel. 
           [0027]      FIG. 11  illustrates yet another way in which to de-activate bypass once a flash test has been performed according to a feature of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0028]    Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings; wherein like reference numerals refer to the like elements throughout. The embodiments are described below to explain the present invention by referring to the figures. 
         [0029]    Reference is now made back to  FIG. 1  which illustrates electrical power generation system  14 , including photovoltaic panel  10  connected to electronic module  12 . In some embodiments of the present invention, electronic module  12  is “permanently attached” to photovoltaic panel  10 . In other embodiments of the present invention, electronic module is integrated with photovoltaic panel  10  but is not “permanently attached” to photovoltaic panel  10 . The term “permanently attached” as used herein refers to a method or device for attachment such that physical removal or attempt thereof, e.g. of electronic module  12  from photovoltaic panel  10 , would result in damage, e.g. to electronic module  12  and/or panel  10 . Any mechanism known in the art for “permanently attaching” may be applied in different embodiments of the present invention. When electronic module  12  is permanently attached to the photovoltaic panel  10 , the operation of photovoltaic panel  10  ceases or connections thereof are broken on attempting to remove electronic module  12  from photovoltaic panel  10 . One such mechanism for permanently attaching uses a thermoset adhesive, e.g. epoxy based resin, and hardener. 
         [0030]    Referring to  FIG. 3 , an example of electronic module  12  is illustrated in more detail. Electronic module  12  connects photovoltaic panel  10  and test module  20 . Impedance Z 1  is the series equivalent impedance of electronic module  12 . Impedance Z 2  is the equivalent input impedance of electronic module  12 . Impedance Z 3  is the equivalent output impedance of electronic module  12 . Bypass link  40  when applied between the output of photovoltaic panel  10  and the input of test module  20  eliminates the effects of series equivalent impedance Z 1  during a flash test. With bypass link  40  applied, impedances Z 2  and Z 3  are connected in parallel with resulting shunt impedance Z T  given in Eq. 1. 
         [0000]    
       
         
           
             
               
                 
                   
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         [0000]    Where impedances Z 2  and Z 3  are both high in value, Z T  will have an insignificant effect upon a flash test of photovoltaic panel  10 . 
         [0031]    Reference is made to  FIGS. 4 ,  5  and  6  which illustrate embodiments of the present invention.  FIG. 4  illustrates a flowchart for a method for flash testing a photovoltaic panel  10  by bypassing an electronic module  12  according to embodiments of the present invention.  FIGS. 5 and 6  are corresponding system drawings according to embodiments of the present invention of electrical power generation system  14 .  FIG. 5  illustrates bypass  40  when bypass  40  is activated. With reference to  FIG. 5 , a single pole single throw (SPST) switch  50  activated by magnetic field of magnet  52  connects the output of photovoltaic panel  10  and the input of test module  20  to bypass electronic module  12  during a flash test of photovoltaic panel  10 . SPST switch  50  in an embodiment of the present invention is a reed switch (for example, Part no: HYR 2031-1, Aleph America Corporation NV USA) or a reed relay, or a solid state switch. Bypass  40  of electronic module  12  is activated (step  201 ) by applying a magnetic field  52  to SPST switch  50  causing SPST switch  50  to close as shown in  FIG. 5 . The flash test is performed (step  203 ) using flash test module  20 . After the flash test of photovoltaic panel  10 , bypass  40  of electronic module  12  is de-activated by the removal of magnetic field  52  to SPST switch  50  (step  205 ).  FIG. 6  illustrates photovoltaic panel  10  connected to the input of electronic module  12 , with SPST switch  50  bypass de-activated (step  205 ). 
         [0032]    Reference is made to  FIGS. 7 and 8  which illustrate another embodiment of the present invention.  FIG. 7  illustrates bypass  40 . With reference to  FIG. 7 , a fuse  50   a  connects the output of photovoltaic panel  10  and the input of test module  20  to bypass electronic module  12  during a flash test of photovoltaic panel  10 . Referring back to  FIG. 4 , bypass  40  of electronic module  12  is activated (step  201 ) by virtue of fuse  50   a  being in an un-blown state as shown in  FIG. 7  and SPST switch  5   b  being open circuit. SPST switch  5   b  in an embodiment of the present invention is a reed switch (for example, Part no: HYR 2031-1, Aleph America Corporation NV USA) or a reed relay, or a solid state switch. The flash test is performed (step  203 ) using flash test module  20 . After the flash test of photovoltaic panel  10 , bypass  40  of electronic module  12  is de-activated (step  205 ).  FIG. 8  shows bypass  40  being de-activated (step  205 ).  FIG. 8  shows photovoltaic panel  10  connected to the input of electronic module  12  and a power supply unit (PSU)  13  applied across the output of electronic module  12 . SPST switch  5   b  is in a closed position because of the application of magnetic field  52 . 
         [0033]    Reference now made to  FIG. 11  which illustrates yet another way in which to de-activate bypass  40  (step  205 ) once a flash test has been performed (step  203 ) according to a feature of the present invention. Photovoltaic panel  10  is connected to the input of buck boost converter  12   a.  The output of buck boost converter  12   a  is connected to PSU  13 . During deactivation of bypass  40  (step  205 ), a power line communication superimposed on the output of buck boost converter  12   a  via PSU  13 , a wireless signal applied in the vicinity of buck boost converter  12   a , or based on some logic circuitry—i.e. a specific supply voltage applied by PSU  13  causes MOSFETS G C  and G A  to turn on. MOSFETS G C  and G A  turned on causes a short circuit current I SC  to flow from PSU  13  and through fuse  50   a.  The short circuit I SC  current blows fuse  50   a  making fuse  50   a  open circuit and bypass  40  is de-activated (step  205 ). 
         [0034]    The closure of SPST switch  5   b  and application of PSU  13  applied across the output of electronic module  12 , causes a short circuit current I SC  to flow from PSU  13  through fuse  50   a  and SPST switch  5   b.  The short circuit I SC  current blows fuse  50   a  making fuse  50   a  open circuit and the removal of magnetic field  52  de-activates bypass  40  (step  205 ). 
         [0035]    An alternative way of de-activating bypass  40  (step  205 ) is shown in  FIG. 8   a.    FIG. 8   a  shows photovoltaic panel  10  connected to the input of electronic module  12  and a power supply unit (PSU)  13  applied across fuse  50   a.  The application of PSU  13  across fuse  50   a,  causes a short circuit current I SC  to flow from PSU  13  and through fuse  50   a.  The short circuit I SC  current blows fuse  50   a  making fuse  50   a  open circuit and bypass  40  is de-activated (step  205 ). 
         [0036]    Another way of de-activating bypass  40  (step  205 ) is shown in  FIG. 8   b.    FIG. 8   b  shows photovoltaic panel  10  connected to the input of electronic module  12  and a power supply unit (PSU)  13  applied across the output of electronic module  12 . The anode and cathode of a silicon controlled rectifier (SCR)  15  is connected in parallel across the output of photovoltaic panel  10  and the input of electronic module  12 . The gate of an SCR  15  is connected inside electronic module  12  in such a way that the application of PSU  13  across the output of electronic module  12  causes a gate signal to be applied to the gate of SCR. A gate pulse applied to SCR  15  switches SCR  15  on. Alternative ways to get a pulse to the gate of SCR  15  include, power line communication superimposed on the output of electronic module  12  via PSU  13 , a wireless signal applied in the vicinity of electronic module  12 , or based on some logic circuitry—i.e. a specific supply voltage applied by PSU  13  causes a gate signal to be applied to SCR  15 . A gate signal applied to SCR  15  and application of PSU  13  applied across the output of electronic module  12 , causes a short circuit current I SC  to flow from PSU  13  through fuse  50   a  and SCR  15 . The short circuit I SC  current blows fuse  50   a  making fuse  50   a  open circuit and bypass  40  is de-activated (step  205 ). 
         [0037]    Reference is now made to  FIGS. 4 ,  9  and  10  which illustrate another embodiment of the present invention of electrical power generation system  14 , particularly applicable in cases when the resulting shunt impedance ZT is small enough to disrupt the results of the flash test, such as being less than 1 Mega Ohm in electronic module  12 . Referring back to  FIG. 4 ,  FIG. 4  illustrates a flowchart for a method for flash testing a photovoltaic panel  10  by bypassing an electronic module  12  according to embodiments of the present invention.  FIG. 4  includes step  201  of activating a bypass, step  203  performing the flash and de-activating the bypass, step  205 . 
         [0038]      FIG. 9  illustrates bypass  40  when bypass  40  is activated. With reference to  FIG. 9 , a single pole double throw (SPDT) switch  70 , SPST switch  72  and SPDT switch  74 , activated by magnetic field of magnet  52 , connects the output of photovoltaic panel  10  and the input of test module  20  to perform the function of bypassing electronic module  12  during a flash test of photovoltaic panel  10 . SPDT switches  70  and  74  in an embodiment of the present invention is a reed switch (for example, Part no: HYR-1555-form-C, Aleph America Corporation Reno, Nev. USA) or a reed relay, or a solid state switch. SPDT switches  70  and  74  when activated by magnetic field  52  provide open circuit impedance in place of shunt impedance ZT when electronic module  12  is being bypassed during a flash test of photovoltaic panel  10 . The bypass  40  of electronic module  12  is activated (step  201 ) by applying a magnetic field  52  to SPST switch  72  and SPDT switches  70  and  74  causing switch positions shown in  FIG. 9 . Next the flash test is performed (step  203 ) using flash test module  20 . After the flash test of photovoltaic panel  10 , the bypass of electronic module  12  is de-activated by the removal of magnetic field  52  to SPST switch  50  and SPDT switches  70  and  74  (step  205 ).  FIG. 10  shows photovoltaic panel  10  connected to electronic module  12  with SPST switch  50  and SPDT switches  70  and  74  de-activated (step  205 ). 
         [0039]    During operation of electrical power generation system  14 , DC power is produced by photovoltaic panel  10  and transferred to the input of electronic module  12 . Electronic module  12  is typically a buck-boost converter circuit to perform DC to DC conversion or an inverter converting DC to AC or a circuit performing maximum power point tracking (MPPT). 
         [0040]    While the invention has been described with respect to a limited number of embodiments, it will be appreciated that many variations, modifications and other applications of the invention may be made.