Abstract:
A solar panel system includes a plurality of the panels connected together in one or more panel strings. An embodiment includes a signal generator module connected to the photovoltaic panel strings injecting a multiple radio frequency signal onto each of the strings and a detector module analyzing a frequency response echo from the panel strings. The signal generator may include a string coupling module communicating with a controller. The detector module analyzes the echo to obtain an analog fingerprint for each panel string and determine whether the fingerprint for each panel string is within an acceptable range. The detector module initiates an alarm when one of the fingerprints is outside the acceptable range. During night time, when no current is being produced by the photovoltaic cells, a DC or AC source may be connected to the panel strings to inject a signal onto the strings for the same purpose.

Description:
RELATED APPLICATIONS 
       [0001]    The present application claims the benefit of priority of U.S. Provisional Application Ser. No. 61/603,915, filed Feb. 27, 2012, and titled ENHANCED, MORE ROBUST ANTI-THEFT SYSTEM AND METHOD FOR LARGE SOLAR PANEL SYSTEMS, the disclosure of which is incorporated herein by reference in its entirety. 
     
    
     FIELD OF THE TECHNOLOGY 
       [0002]    This disclosure relates to photovoltaic systems in general, and more particularly but not limited to, improving the security of photovoltaic systems. 
       BACKGROUND 
       [0003]    Despite the use of anti-theft systems in solar installations, solar modules (also known as solar panels) are still very attractive to thieves because many installations, particularly the larger systems, are located in isolated or remote sites and utilize a large number of expensive modules. What is therefore needed is an enhanced system offering a greater degree of security and protection for solar panels from potential theft. 
       SUMMARY OF THE DESCRIPTION 
       [0004]    The present disclosure provides an enhanced system offering a greater degree of protection for solar panels from theft. In particular, a multi-modal system is provided, one that offers multiple theft detection and alarm systems within one system, thus enabling improved theft detection. In cases, only one mode might be implemented; in other cases, however, two or more modes could be combined for better protection. However, in any case, compared to systems currently available, the cost per panel would be lower and the installation would be easier. 
         [0005]    Systems and methods offering a greater degree of protection for solar panels from potential theft are disclosed herein. Some embodiments are summarized in this section. In some cases only one mode might be implemented. In other cases, however, two or more modes in accordance with the present disclosure could be combined for enhanced, robust protection. 
         [0006]    An embodiment of a solar panel system in accordance with the present disclosure includes a plurality of photovoltaic cells connected together in panels. A plurality of the panels is preferably connected together in one or more panel strings. The panel strings are connected to an inverter and in turn connected to an AC distribution grid. The anti-theft system includes a signal generator module connected to the one or more photovoltaic panel strings operable to produce and inject a multiple radio frequency signal onto each of the strings and a detector module operable to receive and analyze a frequency response echo from each of the panel strings to confirm integrity of the solar panel system. 
         [0007]    An exemplary signal generator comprises a string coupling module communicating with a system on a chip (SOC) controller. Preferably the string coupling module in the signal generator module injects an RF signal in a range of 1 khz to 100 khz. An exemplary detector module analyzes an echo of the injected RF signal to obtain an analog fingerprint for each panel string. This detector module determines whether the fingerprint for each panel string is within an acceptable range. The detector module initiates an alarm when one of the fingerprints is outside the acceptable range. 
         [0008]    A method of enhancing the anti-theft capability of a solar panel system in accordance with the present disclosure comprises providing a plurality of photovoltaic cells connected together in panels, and thence in one or more panel strings, connected to an inverter and in turn connected to an AC distribution grid; providing a signature generator module connected to the one or more panel strings; injecting a multiple radio frequency signal onto each of the strings via the signal generator module; receiving a frequency response echo from each of the panel strings; and analyzing the frequency response echo from each of the panel strings to confirm integrity of the solar panel system. 
         [0009]    The injecting preferably comprises generating and transmitting the radio frequency (RF) signal to a string coupling module which transfers the signal to the panel string. The RF signal is preferably in a range of 1 khz to 100 khz. The analyzing preferably includes obtaining an analog fingerprint for each panel string and determining whether the fingerprint for each panel string is within an acceptable range. If the fingerprint is outside the acceptable range, an alarm may be initiated. 
         [0010]    An apparatus for confirming integrity of a solar panel system in accordance with the present disclosure may include a plurality of photovoltaic cells connected together in panels, wherein the panels are connected together in panel strings. The apparatus preferably includes a signal generator module connected to the one or more photovoltaic panel strings operable to produce and inject a multiple radio frequency signal onto each of the strings. A detector module is operable to receive and analyze a frequency response echo from each of the panel strings to confirm integrity of the solar panel system. The signal generator module comprises a string coupling module communicating with a system on a chip (SOC) controller. The signal generator module injects an RF signal in a range of 1 khz to 100 khz onto each of the panel strings. The detector module analyzes an echo of the injected RF signal to obtain an analog fingerprint for each panel string, determines whether the fingerprint obtained for each panel string is within an acceptable range, and causes an alarm to be initiated when one of the fingerprints is outside the acceptable range. 
         [0011]    During night time operational mode, when no current is being produced by the photovoltaic cells, a DC or AC source may be connected to the panel strings to generate and inject a signal for the same purpose. This injected signal is then monitored to determine whether it is within an acceptable range and, if outside the acceptable range, the detector module may generate or trigger an alarm. 
         [0012]    The disclosure includes methods and apparatuses which perform these methods, including data processing systems which perform these methods, and computer readable media containing instructions which when executed on data processing systems cause the systems to perform these methods. 
         [0013]    Other features will be apparent from the accompanying drawings and from the detailed description that follows. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The embodiments are illustrated by way of example and not limitation in the figures of the accompanying drawings in which like references indicate similar elements. 
           [0015]      FIG. 1  is a simplified diagram of a typical solar panel system. 
           [0016]      FIG. 2  is simplified diagram of another typical solar panel system. 
           [0017]      FIG. 3  is a diagram of an exemplary enhanced anti-theft mode for a solar panel system in accordance with the present disclosure. 
           [0018]      FIG. 4  illustrates an alternate string configuration of PV cell/panels in accordance with the present disclosure utilized in the enhanced anti-theft solar panel system shown in  FIG. 3 . 
           [0019]      FIG. 5  illustrates another alternate string configuration of PV cell/panels in accordance with the present disclosure. 
           [0020]      FIG. 6  is a simplified block diagram of a solar power system in accordance with the present disclosure. 
           [0021]      FIG. 7  is a simplified diagram of a control system for the solar power system shown in  FIG. 3 . 
           [0022]      FIG. 8  is an operational flow diagram for the control system shown in  FIG. 7 . 
           [0023]      FIG. 9  is an alternative nighttime anti-theft mode for a solar panel system in accordance with the present disclosure. 
           [0024]      FIG. 10  is another alternative nighttime anti-theft mode for a solar panel configuration in accordance with the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0025]    The following description and drawings are illustrative and are not to be construed as limiting. Numerous specific details are described to provide a thorough understanding. However, in certain instances, well-known or conventional details are not described in order to avoid obscuring the description. References to one or an embodiment in the present disclosure are not necessarily references to the same embodiment; and, such references mean at least one. 
         [0026]    Reference in this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the disclosure. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. Moreover, various features are described which may be exhibited by some embodiments and not by others. Similarly, various requirements are described which may be requirements for some embodiments but not other embodiments. As a result, this specification represents a disclosure of all possible combinations of features described herein, except that certain combinations are excluded by reasons of mutually exclusive relationships in features, where the mutual exclusiveness is either explicitly identified in this specification or is apparent from the description of the respective features. 
         [0027]      FIG. 1  shows a high-level overview of an exemplary solar panel system  100  in accordance with the present disclosure. Within solar panel  101  are solar cells, shown here as diodes  102   a - n,  and by-pass diodes  103   a - c.  It is obvious that different panels may have different partition schemes, and the number of by-pass diodes may change accordingly. 
         [0028]      FIG. 2  shows a high level overview of an alternative exemplary solar panel system  120 , which, in this example, is a three-section panel, in accordance with the present disclosure that is configured as a 144-cell panel with 72-volt output voltage over output wires  108  and  109  from panel  101 . Another common configuration is 60 to 80 cells yielding 30 to 54 volts, but still with three bypass diodes D 5 , D 10 , and D 15  as shown in  FIG. 2 . In many cases an optional local optimization unit, referred to herein and throughout as local management unit (LMU)  104 , may be integrated into the system. 
         [0029]    Typically, LMU  104  would include an output capacitor  105  between the wires  108  and  109  connecting to the string (of panels). An LMU may or may not be present in the system in all cases. In those cases where no LMU is present, an additional capacitor, typically in the 1-10 μF range with sufficient voltage, may be added such as alternate capacitor  106  (shown in dashed lines in  FIG. 2 ). Also, some LMU designs may not include an output capacitor  105 . In those cases an alternate capacitor  106  would be required. Behind capacitor  106 , the two wires  108  and  109  continue to be connected in a string. 
         [0030]      FIG. 3  illustrates a photovoltaic system  200  according to one embodiment utilizing enhanced theft management in accordance with the present disclosure. System  200  contains strings  204   a - n.  In each string  204   a - n  are multiple panels, of which exemplary panels  205 aa-an are shown in detail, each with a capacitor  206   aa - an  at the string in the manner shown in  FIGS. 1-2 . It is clear that the other strings have similar features, but not all strings are shown, for reasons of clarity and simplicity. Alternative embodiments of strings  204   x  are shown in  FIG. 4 , and, in  FIG. 5 . 
         [0031]    Turning back to  FIG. 3 , the system  200  includes a string coupling module  207   a,  exemplary of modules  207   a - n  for each of the strings  204   a - n,  others of which are not shown in detail, again, for reasons of clarity and simplicity. Module  207   a  contains two drivers  210  and  211 , one of which is inverted and the other of which is not inverted; two impedance-matching resistors,  212  and  213 ; a common-mode suppression inductor  214 ; and a coupling transformer  215 , which does a down transformation into the low impedance of the line. Typically, the transformation ratio is in the 10:1 range down, to better enable injection of the AC signal used to measure frequency response, etc. In some cases the down transformation may be a little as 1:1, while in other cases it may be 100:1 or even 1000:1. 
         [0032]    In system  200 , analog-to-digital converter (ADC)  216  connects to the microprocessor unit (MPU) discussed further below with reference to  FIG. 7 , typically a system-on-a-chip type, via MPU connector C 2 . In some other cases, to reduce costs, instead of placing an ADC  216  in each local unit  207 , there is an analog converter with analog multiplexer at the MPU/SOC, and only two wires, or even a single wire, can be brought into the system main controller, which is described below. 
         [0033]    This approach is possible due in part to the common-mode suppression inductor  214 . String decoupling capacitors  208 , typically in the 1-10 μF range with sufficient voltage, close each string into a separate loop, so the system  200  can measure the impedance and other behavior of each loop separately, at multiple frequencies. In some cases, inverter  202  may have an input capacitor, or combiner box  201  may contain circuitry with capacitors, but because these capacitors are not always present in these components, it is advisable, but not always required, to have, at or in module  207   a,  a string decoupling capacitor  208   a.    
         [0034]      FIG. 6  illustrates an overview of an exemplary photovoltaic system  600  with anti-theft system management in accordance with the present disclosure. The photovoltaic system  600  includes photovoltaic modules  601   a,    601   b,  . . . ,  601   n,  local management unit units  602 a,  602   b,  . . . ,  602   n,  an inverter  603 , and a system management unit  604 . In one embodiment, the system management unit  604  may be part of the inverter  603 . In other embodiments, the system management unit  604  may be integrated into the combiner box  606 , one of the local management units, or it may be a stand-alone unit. 
         [0035]    The solar modules  601   a,    601   b,  . . .  601   n  are connected in parallel to the local management unit units  602   a,    602   b,  . . . ,  602   n  respectively, which are connected in series to form a string bus  605 , which eventually is connected to an inverter  603  and the system management unit  604 . The string bus  605  can be can be one of many connected to the inverter  603  directly or as part of a mesh network or combiner boxes or fuse boxes (not shown). An isolated local management unit can be used as a combiner box  606  to adjust all voltages before connecting to the inverter  606 ; or, a single or multi-string inverter can be used. To limit the changes in the voltage of the bus, the system management unit  704  may assign a different phase for each of the local management units ( 602   a,    602   b,  . . . ,  602   n ). Furthermore, the system management unit  604 , can communicate with LMUs and other components in the system wirelessly so as to monitor and direct phase and duty cycle operational instructions to the appropriate local management units and other system components. The string bus  605 , string combiner  606 , and inverter  603 , correspond to strings  204   a - n,  combiner  201  and inverter  202  respectively shown in  FIG. 3 . 
         [0036]      FIG. 7  shows an exemplary control system  700 , according to one aspect of the system and method disclosed herein. Typically, controller  701  would be a system-on-a-chip (SOC) type, such as, for example, STM 32F4 microcontroller by ST Micro-Electronics, which is very suitable for this type of system. Connections  702   a - n  connect to the MPU Cl and C 2  contacts, shown in  FIG. 3 , of all the strings in the solar panel system. Typically, one SOC controller  701  can easily handle up to 12 strings, and because a typical combiner box, such as box  701 , typically has up to  12  strings, this approach creates a good match. SOC controller  701  would contain all the features needed for the control system, such as, for example, output pins that can drive the inverting and non-inverting drivers  210  and  211 , as well as the ADC  216 , in some cases with analog multiplexer to take in the measurements shown in  FIG. 3 . An SOC controller  701  also contains some program storage and some RAM, as well as software instances  704   a - n,  which include software for chip operations; for communicating, via any of the various wired or wireless communication methods over line  703  with the system management unit (SMU)  604  described below for generating a sweep across a wide range of frequencies, typically around 1-100 kHz; and the algorithms required to analyze the echo, including but not limited to impedance over frequency (looking for distinct peaks), FFTs, etc. 
         [0037]      FIG. 8  shows an exemplary process  800  for implementation of the enhanced anti-theft system according to one example of the system and method disclosed herein. This process is typically executed on the above-mentioned MPU in the SOC controller  301 , but other suitable configurations can be used instead, without departing from the spirit of the system described herein. In step  801  the system on a chip (SOC) controller  801  is initialized. In step  802 , the system checks in with the SMU  604  via communication line  703 , to verify that the SMU  604  is present and able to communicate, and thus not stolen. 
         [0038]    In step  803 , the system sets up a number representing the number of loops, such as strings  204   a - n,  in the system, with n=1 to start with. In step  804 , the system determines whether n is greater than the maximum number programmed for the loops. If yes, the process moves to step  805 , where it waits for interval t l  and then loops back to step  802  to start over again. In step  804 , if n is not greater than the preprogrammed maximum number of process loops, in step  806 , the system sends a sweep of radio frequency signals from f 10 →f hi  on string n, and in step  807 , the system analyzes the frequency response. In practice, these two steps happen concurrently, or closely interleaved, where a few (as little as  1 ) pulses of a specific frequency are sent, and the resulting response is analyzed. Said response is an “analog fingerprint” of the specific loop (i.e., string  204   x ). It may vary somewhat with daylight (energy produced by solar calls changes their impedance) as well as somewhat with weather (e.g., rain can change stray capacities, thus modify the fingerprint somewhat), but it will change dramatically if a panel or wiring are removed. In step  808 , the system checks to determine whether this fingerprint is within an acceptable range. If no, in step  809  the system sends an alarm to the main unit, and then the process continues to step  810 , where n is incremented to n+1, and then the process loops back to step  804 . If, in step  808 , the system finds that the frequency is within an acceptable range, the process continues directly to step  810 , without sending an alarm, and thence back to step  804 . In some cases, the system may be programmed to send an OK status (not shown) when moving directly from step  808  to  810 . 
         [0039]    During the daytime when the solar panels  101 ,  120 ,  204   a - n,    204   a - x  are producing power as above described, the system  300  effectively operates to monitor against theft. However, at night, when there is no current being produced by the photovoltaic panels, another mechanism, or mode, is preferably implemented to provide an effective anti theft system. During the night time hours, a separate DC current power supply  500 ,  900  or  1000  as shown in  FIGS. 5 ,  9 , and  10  may be connected to the strings of panels  204   x.    
         [0040]    The configuration shown in  FIG. 5  illustrates a DC power source  500  connected between one or more of the panels  100  or  120  and across wires  108  and  109  described above. This DC source is preferably disconnected from the panels during daytime operation. The configuration shown in  FIG. 9  shows a DC power source  910  connected again across positive and negative lead wires  108  and  109 , but this time, in the inverter  202 . The configuration shown in  FIG. 10  shows a low frequency AC power source  1010  in the inverter  202  connected again across the equivalent of wires  108  and  109 . In these configurations, for example, as shown in  FIGS. 5 , and  9 , a DC current may be connected and sent at night, and the sum of the reverse diodes and/or the solar cells&#39; inherent diodes (opposite direction) voltage may be measured. Depending on the lengths of the strings, such a process may require voltages such as, for example, between 25 and 1000V. If both should be measured, a low frequency signal may be injected and the current&#39;s non-linear behavior may be used to determine numbers for diodes each way, enabling the system  300 , in effect, to count panels, even if they don&#39;t each have an LMU  602 . These two approaches may require each string to be temporarily to be disconnected from the string combiner  206  shown in  FIG. 3 . In another approach, as shown in  FIG. 10 , AC current may be injected, enabling both forward and reverse diode measurement in one operation. 
         [0041]    In some cases, the system could tap a string containing maximizers so that it could apply a voltage somewhere along the string to forward bias k units and inverse bias the remaining n-k units (so that (n-k)Vt=k*Vmin_max_on. Such as approach yields a DC system that uses relatively little power but wakes up k maximizers, which in turn could directly communicate additional status information. 
         [0042]    Further, the system and method disclosed herein can be also used to monitor a string of solar modules  204   x  during the day in order to detect abnormalities such as in the occurrence of arcing. If the transformer  215  is modified to present soft saturation, it may also be possible to measure the current. Simple additions to the circuitry could allow for monitoring DC currents with a shunt/hall effect or magneto-resistive sensor plus monitor the voltage and other environmental variables such as temperature, etc. 
         [0043]    In addition, other modes of theft deterrence may be employed, such as, but not limited to, using cameras, IR/Thermal sensing or imaging, motion sensors, or simple mechanical methods such as complicated “anchoring” or attaching a tensioned string or simple extra wire whose continuity can be monitored in a straightforward way (as, for example, the ground wire that already is required by code). Another approach is the use of unique codes to enable only authorized users to turn the panels on. All these approaches should have some means of communication with a monitoring site. By combining one or more of these strategies, a far more secure approach can be taken, at low to moderate cost. 
         [0044]    It is clear that many modifications and variations of the system and method disclosed herein may be made by one skilled in the art without departing from the spirit of the novel art of this disclosure. These modifications and variations do not depart from its broader spirit and scope, and the examples cited here are to be regarded in an illustrative rather than a restrictive sense. 
         [0045]    In the foregoing specification, the disclosure has been described with reference to specific exemplary embodiments thereof. It will be evident that various modifications can be made thereto without departing from the broader spirit and scope as set forth in the following claims. The specification and drawings are, accordingly, to be regarded in an illustrative sense rather than a restrictive sense.