P/00/009 Regulation 3.10 5 AUSTRALIA Patents Act 1990 10 COMPLETE SPECIFICATION 15 Invention Title: 20 PHOTOVOLTAIC ARRAY PROTECTION SYSTEM The invention is described in the following statement, including the best method 25 of performing it known to us: 30 35 40 45 Our Ref: 082023 50 -2 PHOTOVOLTAIC ARRAY PROTECTION SYSTEM The present invention relates to photovoltaic arrays and, more particularly, to the detection and protection of solar cell power generating arrays. 5 BACKGROUND Solar cell (photovoltaic) arrays for the generation of electrical power comprise individual cells connected together and fitted into a common housing to create a solar 10 module. Current technology typically provides modules with electrical output up to about 5A at 30VDC. Modules may be further assembled into large arrays to suit the needs of a particular renewable energy generation project. The working voltage of a large array may be 600V 15 or more depending on the number of modules connected in series. Large high voltage power sources present a number of possible hazards, including those of electric shock and fire. Either may result from electrical arcing in a solar 20 module array which may cause overheating, localized burning of wiring and components and eventually fire. Arcing faults are typically associated with electrical connections that have been badly installed, degraded over time or are the result of damage to associated insulation 25 material by insects, vermin or mechanical means.
- 3 Arcing faults are particularly hazardous in solar module arrays because the output of a solar module is inherently current limited, so that the fault does not escalate quickly to operate a fuse or circuit breaker in 5 the way that it might in a conventional electrical generation or distribution system. In addition the electrical output of a solar module array is direct current, so there is no opportunity for an arc to extinguish at a current zero as occurs in AC systems. 10 It is highly likely that any arc in a solar module will continue to burn until the sun goes down and the generation of electricity ceases. The arc may start again the next day if appropriate conditions continue to exist. An electric arc involves temperatures in the range of 3000 15 7000 degrees C, which is well capable of burning or melting most materials as well as producing droplets of molten material that may cause a fire wherever they fall. This is especially a problem for solar module arrays that are integrated with the structure of a building, such as when 20 typically mounted to a roof. It is an object of the present invention to address or at least ameliorate some of the above disadvantages, Notes 1. The term "comprising" (and grammatical variations 25 thereof) is used in this specification in the inclusive -4 sense of "having" or "including", and not in the exclusive sense of "consisting only of". 2. The above discussion of the prior art in the Background of the invention, is not an admission that any 5 information discussed therein is citable prior art or part of the common general knowledge of persons skilled in the art in any country. BRIEF DESCRIPTION OF INVENTION 1. Accordingly in one broad form of the invention there 10 is provided a photovoltaic array protection system for a photovoltaic array; said photovoltaic array including interconnected solar modules of solar cells; said system including at least one monitoring module for at least one solar module of said solar modules of 15 said array; said monitoring module operatively associated with a bypass module; said bypass module including a selectively actuable power switch; said bypass module operated so as to substantially short circuit or shunt said at least one solar module and 20 thereby to provide an alternative path for current from the solar modules of said array if said monitoring system detects an arcing condition associated with said at least one solar module of said solar modules of said array. 25 Preferably said bypass module remains in a closed condition even if said monitoring module detects cessation of said arcing condition when said bypass module is closed. 5 Preferably said monitoring module acts to periodically open the switch of the said bypass module if said arcing condition is detected to persist; said monitoring module acting according to a predetermined or random schedule. Preferably said at least one monitoring module is in 10 communication with a control module; said control module programmed to operate said bypass module to short circuit or shunt the output of said at least one of said solar modules and provide an alternative path for current from other modules if a said monitoring module detects an 15 arcing condition associated with said at least one of said solar modules monitored by said monitoring module. Preferably said photovoltaic array includes at least one array of in-series connected solar modules. Preferably said photovoltaic array includes at least two, 20 said in-series connected arrays of solar modules, connected in parallel. Preferably each of said solar modules comprises an array of interconnected solar cells mounted in a housing. Preferably each of said solar modules is provided with a 25 said bypass module; said bypass module connected across a -6 said solar module and interconnecting wiring between said solar module and adjoining said solar modules. Preferably a said monitoring module is adapted to detect broad spectrum noise current generated in said at least 5 one solar module or its interconnecting wiring. Preferably a said monitoring module is adapted to detect broad spectrum noise voltage generated in said at least one solar module or its interconnecting wiring. Preferably a said monitoring module is adapted to detect 10 a broad spectrum noise electromagnetic field generated- in said at least one solar module or its interconnecting wiring. Preferably said monitoring module includes radio receiver 15 technology; said radio receiver technology measuring signal power present in a sequence of small frequency ranges; said broad spectrum noise current detected in a broad range of frequencies representative of arcing' in said interconnecting wiring. 20 Preferably said monitoring module- includes a spectrum analyzer unit. The system of any previous claim wherein said monitoring module is provided with a transducer; said transducer coupling said broad spectrum noise from said solar module 25 connecting wiring, to said monitoring module. Preferably said transducer is a voltage transducer.
-7 Preferably said transducer is a current transducer. Preferably said transducer is an electromagnetic transducer. 5 Preferably said monitoring module operates at one or more fixed frequencies. Preferably said monitoring module operates over a range of tunable frequencies. Preferably said tunable frequencies are varied 10 automatically over a monitoring cycle. Preferably said system further includes control logic; said control logic programmed to: (a) process electrical noise information received from any said monitoring module of said solar 15 modules, (b) tune said frequencies of any said monitoring module to eliminate false signals from external sources, (c) execute a "control algorithm correlating 20 presence or absence of broad spectrum noise current with the status of any one said bypass modules. 25 Preferably said control logic is further programmed to: -8 (d) determine if any bypass module activated due to detected arcing should remain in an activated state, (e) periodically deactivate an activated said 5 bypass module so as to determine if an arcing situation persists. Preferably said control logic is connected to a distributed communication network; said control logic communicating with a master control module. 10 Preferably said control logic is connected to an alarm signal generator; said alarm signal generator transmitting an alarm signal to said master control module. Preferably data transmitted between said control logic 15 and said master control module is encrypted. Preferably said control logic is implemented using a microprocessor. Preferably said control logic is implemented using discrete logic circuitry such as relays, logic gates and 20 logic gate arrays. In yet a further broad form of the invention there is provided a method of protecting a photovoltaic array from damage due to arcing in electrical connections of said 25 array; said array comprising in-series and in-parallel 9 connected solar modules; said method including the steps of: (f) providing at least one monitoring module for said solar modules, 5 (g) connecting a transducer to each said at least one monitoring module, (h) tuning each said monitoring module to be responsive to at least one broad spectrum noise current representative of arcing in connections 10 of a said solar module, (i) providing said solar modules with at least one bypass module; thereby to provide an alternative path for current from the solar modules of said array if said monitoring system 15 detects an arcing condition associated with said at least one solar module of said solar modules of said array. Preferably any one said bypass module is adapted to form a substantially short circuit or shunt across a 20 predetermined maximum number of said solar modules and provide an alternative path for current from other modules if said monitoring module detects said at least one broad spectrum noise current. Preferably said predetermined maximum number of said 25 solar modules is that number of solar modules which have a combined output of less than 40V, - 10 Preferably said predetermined maximum number of solar modules is one solar module. Preferably said array is provided with a control module; said control module in communication with each said at 5 least one monitoring module; said control module activating a said bypass module when said monitoring module communicates detection of a said broad spectrum noise current. In yet a further broad form of the invention there is 10 provided a method of preventing electric shock injury to personnel working on a photovoltaic array; said method including the steps of: (j) monitoring occurrences of arcing conditions in the solar modules or in interconnections 15 between solar modules of said array, (k) activating a bypass module connected across at least that said solar module with which a said arcing condition is associated, wherein said bypass module when activated forms a 20 substantially short circuit or shunt at least across said solar module with which said arcing condition is associated and provides an alternative path for current from other series connected modules. Preferably said array is provided with at least one 25 arcing condition monitoring module; said monitoring - 11 module communicating an arcing condition signal to a control module. Preferably said control module is in controlling communication with each bypass module of said array; said 5 control module activating said bypass module on receipt of a said arcing condition signal. Preferably a said bypass module is connected across a predetermined maximum number of solar modules; said maximum number limited to that number of solar modules 10 which are unlikely to generate a voltage sufficient to instigate arcing in said bypass module. In yet a further broad form of the invention there is provided a switched photovoltaic module array; said array comprising one or more solar modules electronically 15 interconnected to provide an aggregated module array electrical output; each solar module comprising an encapsulated array of solar cells; said solar cells electrically interconnected to provide an aggregated module electrical output; each solar module electrically 20 interconnected by a first module connecting conductor and a second module connecting conductor; each module having associated therewith a bypass module; said bypass module including a selectively actuable power switch in series with a bypass conductor link; said bypass conductor link 25 electrically connected across said solar module whereby when said selectively actuable power switch is actuated, - 12 a low resistance path is created across said solar module thereby to substantially shunt output from said solar module, thereby to substantially reduce voltage across said solar module between said first module connecting 5 conductor and said second module connecting conductor. Preferably said bypass module is connected directly across a said one of said solar modules. Preferably said bypass module is connected across a said one of said solar modules and at least a portion of 10 conductors connected to the input and output of said one of said solar modules. Preferably said bypass module is connected across a said one of said solar modules and is integrated into the structure of said one of said solar modules, 15 Preferably said bypass module is electrically discrete from the solar module with which it is associated. Preferably said bypass module is mechanically discrete from solar module with which it is associated. Preferably said selectively actuable power switch is 20 remotely controllable whereby individual ones of said solar modules in a said photovoltaic module array can be shunted for a predetermined period of time by activating its associated bypass module for said predetermined period of time. 25 Preferably an arc detector is associated with said switched photovoltaic module array.
- 13 Preferably a module arc detector is associated with each said solar module. Preferably said arc detector is in communication with said bypass module. 5 Preferably said arc detector activates said bypass module when it detects an arc condition in the associated solar module with which both said arc detector and said bypass module are associated. In yet a further broad form of the invention there is 10 provided a A solar module within an array of solar modules; said solar module having associated therewith a bypass module; said bypass module including a selectively actuable power switch; said bypass module actuable so as to substantially short circuit or shunt 15 the output of said solar module and provide an alternative path for current of modules within said array into and out of the module; thereby to provide an alternative path for current from the solar modules of said array when said power switch is activated. 20 In yet a further broad form of the invention there is provided a method of shutting down selectively 25 portions of a solar module unit which is made up of electrically interconnected solar modules; said method - 14 utilising low capacity shunt switches; said shunt switches connected across elements within said solar module unit which match with the switching capacity of said low capacity shunt switches thereby to be able to 5 shut down selected portions of said solar module unit; thereby to provide an alternative path for current from the solar modules of said unit if a switch is activated. 10 Preferably a said shunt switch is connected across a predetermined maximum number of elements; said maximum number limited to that number of elements which are 15 unlikely to generate a voltage sufficient to instigate arcing in said shunt switch, BRIEF DESCRIPTION OF DRAWINGS Embodiments of the present invention will now be 20 described with reference to the accompanying drawings wherein: Figure 1 is a perspective view of a photovoltaic array comprising a number of interconnected solar modules, Figure 2 is a schematic of the photovoltaic array of 25 Figure 1 showing in-series and in-parallel arrangements of solar modules, -15 Figure 3 is a schematic of a number of in-series connected solar modules and controlling power switches in accordance with an embodiment of the present invention, Figure 4 is a block diagram showing the principle 5 components of an arc detector according to the invention, Figure 5 is a flow diagram showing the principle logic steps in the detection of an arcing situation according to an embodiment of the invention. 'Figure 6 is a circuit diagram of an arc detection 10 arrangement implemented using a voltage transducer arrangement in accordance with a further embodiment of the present invention, Figure 7 is a circuit diagram of components for use in association with a power switch incorporated in the 15 embodiment in figure 6, Figure 8 is a circuit diagram of an arc detection arrangement incorporating a current transducer in accordance with a further embodiment of the present invention, 20 Figure 9 is a circuit diagram of components of a power switch associated with the embodiment of figure 8, DETAILED DESCRIPTION OF PREFERRED EMBODIM4ENTS 25 In one form the present invention provides the ability to selectively switch (or 'shunt' ) either individual solar - 16 modules or interconnected groups of solar mod-les in a Photovoltaic array 10 of the type illustrated in Fig 1. In a further particular form an arc detection arrangement is described for use in association with the 5 Photovoltaic array 10 of the type illustrated in Fig 1 In yet a further particular form the electric arc detection arrangement is utilised to selectively activate the shunting arrangements on detection of an arcing condition in the Photovoltaic array 10 of the type 10 illustrated in Fig 1. Definitions and the ambit of concepts covered in this specification are as follows: 15 Photovoltaic system this is applied to: A single solar module or a series connected group of modules of sufficient voltage or current capability to sustain an arc between any of the electrical connections. Purpose of this system: To provide protection against the 20 risk of fire and other damage due to arcing taking place within the external wiring and internal interconnections of solar modules and to provide a means of shutting down a solar module array in response to safety and operational requirements, 25 Additional purpose: To provide an alarm signal to indicate that arcing is taking place.
- 17 Power switch connection: To short circuit a single solar module or more than one solar module connected in parallel Or to short circuit a single solar module or more than one solar module connected in series 5 Or to short circuit a single solar module or more than one solar module connected in a series parallel arrangement Power switch type: Normally open or Normally closed, Power switch purpose: To apply a short circuit to one or more solar modules in order to reduce the electrical output 10 below that required to sustain an electrical arc or To apply a near short circuit to one or more solar modules in order to reduce the electrical output below that required to sustain an electrical arc while allowing sufficient terminal voltage at the solar module(s) to provide 15 electrical power for the monitoring module and circuits associated with the power switch. Control of the power switch: Controlled by the associated monitoring module or Controlled manually by a master control module via a communications means or Controlled 20 manually by a master control module via a communications means. Monitoring module signal source: By measurement of the high frequency noise current, voltage, electromagnetic field or a combination of these directly or By measurement of the 25 high frequency noise current, voltage, electromagnetic field or a combination of these via a transducer.
- 18 Monitoring module arc detection technology: Monitoring module includes radio receiver technology to detect broad frequency range representative of arcing (superheterodyne, tuned radio frequency or direct conversion) or Monitoring 5 module includes a spectrum analyser unit. Frequencies used for arc detection: Monitoring module operates at one or more fixed frequencies or Monitoring module operates over a range of tuneable frequencies or Monitoring module has automatic variation of tuneable 10 frequencies. Monitoring module logic implementation: Monitoring modules includes any of microprocessor, logic functions implemented with logic gates or logic gate arrays, logic implemented with discrete components, logic implemented with 15 electromechanical devices such as relays. Monitoring module control algorithm: Major features that could be included in any combination: * Monitoring system includes logic to process electrical noise information 20 e Monitoring system includes logic to tune said frequencies to eliminate false signals e Monitoring system includes logic to correlate high frequency noise with the status of any power switch - 19 " Monitoring system includes logic such that the power switch remains closed if the monitoring module detects cessation of arcing when the switch is closed " Monitoring system includes logic to periodically or 5 randomly close power switch if arcing condition persists " Monitoring system includes logic to determine if any power switch should remain activated and periodically deactivate any power switch to determine if arcing 10 situation persists e Monitoring module receives commands from a central control module or from other monitoring modules to open or close the associated power switch 15 Monitoring module communications: No communications or communications with a master control module or communications with a distributed network without a master control module. Communications security: Communications are not encrypted 20. or communications are encrypted for security. Communications media: Wire connection or Fibre optics or Wireless (radio). 25 - 20 Electric arcs produce electrical noise over a very wide range of frequencies. The arc detector of at least some embodiments of the present invention is intended to detect this electrical noise and further validate the 5 assumption that it is the characteristic electrical noise from an electric arc by checking that the noise is occurring over a range of frequencies and preferably also that it is relatively continuous. These checks are intended to reject false detections caused by man made emissions 10 such as radio and television transmitters as well as other natural sources of electromagnetic emissions such as electrical storm activity. In a preferred form the presence of an electric arc is detected by monitoring the wideband electrical noise 15 associated with the electric arc. The electrical noise may be coupled to the input of the detection device by means of a voltage transducer, a current transducer, electromagnetic radiation or some combination thereof. It is desirable that the arc detection device does not 20 confuse natural or man-made electrical noise and signals that may be present in the local environment with those emitted by an actual arcing fault in the solar cell array and associated wiring and equipment. The present invention provides for the protection of a 25 photovoltaic array 10 of solar modules 12, as shown in Figure 1, from damage resulting from arcing of connections - 21 between the modules or within the modules. Typically as shown in Figure 2, an array 10 of solar modules 12 may be arranged with individual modules connected in series to form a column 14 of modules 12, and with columns of in 5 series connected modules interconnected in parallel. Each solar module in the array is typically 30VDC with a current output of 5A. Each column 14 is provided with a blocking diode 16 to prevent internal current circulation. With reference now to Figure 3, in-series connected 10 solar modules 12 are provided in preferred forms of the present invention with an arcing monitoring module 18. Preferably, each solar module 12 of the array 10 is provided with such a monitoring module as shown in Figure 3. 15 Arcing in low voltage DC connections, such as obtains between solar modules which typically operate up to about 5A at 30VDC, generates characteristic identifiable broad spectrum noise. In one preferred form the proposed arc detector of the 20 present invention uses radio receiver technology to measure the signal power present in a small frequency range. So as to avoid the possibility of concluding that a signal present in this small preferred frequency range relates to an electric arc when in fact it is associated with some man 25 made source such as a local broadcast or television station, the arc detector is automatically re-tuned in 22 accordance with a search algorithm to a different small predefined frequency range in an attempt to avoid the frequency of the man made source. In the event that the signal is from an electric arc, 5 it will occupy a broad range of frequencies and therefore the algorithm will be unable to find a small frequency range that is free of signals or where the signals are below some threshold value and it will be reasonable to conclude that the signal source is an electric arc. The 10 algorithm may be extended to ignore signals that cover a broad frequency range, but only occur for a short time such as those associated with lightning and electrical atmospheric events. The arc detector 18 can use any of the well-known 15 radio receiver topologies for the detection and measurement of signals over a small band of frequencies such as "tuned radio frequency", "superheterodyne" and "direct conversion". Preferably, in the present invention, the 20 superheterodyne or frequency conversion topology is used because this allows the convenient tuning across a range of frequencies. Figure 4 is a block diagram of one possible arrangement for an arc detector 100. 25 The input to the arc detector is a current or voltage signal that may be coupled directly from the solar module - 23 12 or via an aerial of some kind. The transducer 101 provides the appropriate electrical interface for the desired signal coupling arrangement. The output of the transducer will be signals covering a broad range of 5 frequencies, with only incidental selectivity with respect to frequency being preset in the transducer block 101. The signal is then . amplified or attenuated by amplifier/attenuator 102 in order to adjust the signal amplitudes so that they may be conveniently processed by 10 the following stages. The amplification or attenuation of this tage may optionally be controlled by control logic 108 so that the signal amplitudes fed to the following stages may be adjusted automatically to suit the particular conditions 15 pertaining at the particular time and place of the installation site. The measurement frequency filter (103) passes the total range of frequencies that the arc detector has been designed for and provides some, but not necessarily great, attenuation for frequencies outside this 20 range. The frequency mixer 104 combines the broad range of frequencies (measurement frequencies) present at the output of the measurement frequency filter 103 with the oscillator 107 such that output of the mixer will consist principally 25 of measurement frequency signals that have been translated to another frequency that is higher or lower than the - 24 original frequency by an amount that is the frequency of the oscillator 107. The stage following the mixer is the intermediate frequency amplifier. and filter 105 which is designed to pass only a narrow range of frequencies centred 5 around a fixed frequency referred to here as the intermediate frequency. Signals that were originally. within the range of measurement frequencies that are close to the oscillator frequency plus the intermediate frequency as well as 10 signals that were originally close to the oscillator frequency minus the intermediate frequency will be translated to frequencies close to the intermediate frequency and pass through the intermediate frequency amplifier and filter 105. Signals originally at other 15 frequencies will be translated to frequencies substantially different to the intermediate frequency and attenuated by the frequency selective nature of the intermediate frequency amplifier and filter. Where this scheme is used for the purpose of radio 20 signal reception, it is usual to arrange the various frequencies and frequency selective components such that one of either the oscillator frequency plus the intermediate frequency or the oscillator frequency minus the intermediate frequency is strongly attenuated by the 25 measurement frequency filter, so that signals of two different frequencies are not received at the same time. In - 25 the application of this technique as an arc detector, this feature is of lesser importance and the system will still be useful even if signals of two different frequency ranges are received at the same time. By this frequency mixing 5 process the combination of the fixed intermediate frequency and the frequency of the oscillator 107 determine the particular predominant narrow range of original signal frequencies that will be measured by the arc detector. The oscillator (107) frequency is controlled over whatever 10 range of frequencies is desirable in the particular application by the control logic 108. The amplitude of the signal at the output of the intermediate frequency amplifier 105 is measured by the power measurement 106 stage and the resulting measurement, 15 being indicative of the signal amplitude of the signals of a narrow range of frequencies around the measurement frequency, is connected to the control logic 108. In the foregoing description, stages that are described as having an amplifying function may instead have 20 attenuation function and those described as having and attenuating function may have an amplifying function as may be convenient for controlling the signal amplitudes at the various stages. The particular amounts of amplification or attenuation may be set at the time of design or may be set 25 by the control logic (108) so that the system may adapt - 26 itself automatically to the circumstances of a particular installation, The control logic 108 executes an algorithm intended to determine if there is an electrical arc present. One 5 possible algorithm is shown in Figure, 5 and may be executed at preset intervals of time, for example, once every 20 seconds. Embodiments of the system of the present invention 10 further provide for a number of power switches 22 distributed through the photovoltaic array 10. A power switch 22 may be connected across a number of in-series connected solar modules, but more preferably, each solar module 12 will be provided with a power switch 22 15 incorporated in a monitoring module 18 as shown in Figure 3. Power switches 22 are preferably solid state (MOSFET etc) or electro-mechanical, and in one preferred form .are normally open, that is, open in the non-actuated condition. In an alternative preferred form they may be normally 20 closed (that is, require actuation to go open circuit). Switches 22 are connected in such a way by bypass conductors 24 and 26, as to effectively bypass a given module 12 and the modules connecting conductors 20 to adjoining modules. 25 Each switch 22, when activated into its closed condition, effectively short circuits or "shunts" the - 27 output of the solar module 12 and can provide an alternative path for current from the modules and its connecting conductors across which they are connected. As will be understood by those skilled in the art, this is an 5 acceptable way of stopping the electrical output of a solar module, Preferably, the present system provides for a "partial" short circuit by means of a low resistance load provided in the switch circuit, This allows some power for internal functions of the monitoring module 18 to remain 10 available. The system further includes some provision of power arrangements for the normal operation of the monitoring and control devices of the system, In one preferred embodiment, each power switch of the system is operatively connected to the monitoring module 15 for the one or more solar modules being monitored. When the monitoring module detects an arcing condition, it closes the power switch. If this closing of the switch and effective substantial short circuiting or shunting of the solar module or modules across which it is connected is 20 successful in arresting the arcing condition, the monitoring module maintains the power switch in its closed condition for a predominant period of time. If unsuccessful, the monitoring module may re-try periodically according to a predetermined schedule or randomly. 25 In another preferred embodiment, the monitoring modules 18 and power switches 22 are connected to, or in - 28 communication with, a control module 28 (referring to figure 3) provided with a microprocessor or similar. The microprocessor 29 may be programmed to fulfil the following functions: 5 (a) process the electrical noise information received from a monitoring module 18, (b) tune monitoring module 18 arcing detector to various frequencies to eliminate false signals from outside sources, 10 (c) control the power switch(es) 22, (d) execute a control algorithm that involves correlating the presence of absence of broad spectrum noise currents with the status of the various power switches 22, 15 (e) determine which, if any, of the power switches 22 should remain closed to prevent further arcing fault activity until appropriate maintenance activity can take place, 20 (f) attempt to restore the array 10 to complete or partial function by checking that arcing still recurs when one of more power switches 22 are reopened, (g) communicate data to and from other similar 25 control devices or a master control device. This data may include present status, - 29 commands to operate power switches 22 in the local or other monitoring modules 18, and may include data not directly related to the arcing fault control processes, such as 5 voltage, current, power, temperature and other parameters associated with the various solar modules 12. The communication means may include a data carrier interface, for example a radio receiver/transmitter, or 10 alternatively, wire, optical fibre or optical system, (h) provide security functions, data encryption etc. to prevent tampering with the system through the communication means. 15 In Use Although preferably one monitoring module 18 is provided for each solar module one monitoring module may service a predetermined maximum number of solar modules. An preferred practical limit is that the total voltage that 20 can be generated by the solar modules 12 controlled by any one power switch should not be high enough to initiate and sustain an arc under practical conditions. This is to ensure that the shorting switch 22 of each monitoring module 18 is not exposed to a condition that may cause it 25 to arc under normal operating conditions.
- 30 A photovoltaic array 10 equipped with the monitoring modules 18, control module/s and communication means of the present invention, may be shut down at will; that is, the output voltage and all the internal voltages of the solar 5 module array 10 reduced to a safe to touch voltage, even if the array is in partly faulty condition. Thus the present system overcomes the problem that in a conventionally arranged solar module array, the array can only be shut down by short circuiting the output of the 10 whole array. In the event that there are ineffective connections, or faults within a solar module in parts of the array, such as is associated with an arcing situation, dangerous voltages can remain. This has serious occupational health and safety implications for maintenance 15 and emergency service personnel. In effect conventional systems are akin to small power stations with a semi functional "off" button. Voltage Sensing Embodiment 20 With reference to Figures 6 and 7 there is illustrated a further detailed embodiment which is to be read in conjunction with Figure 3 and where in like components are numbered as for the embodiment of Figure 3. In this instance, a bypass module in the form of power 25 switch 22 is arranged to be able to selectively shunt solar module 12. The bypass module shunts, in this instance, not - 31 only the solar module 12 but also a first module connecting conductor 50 and a second module connecting conductor 51. It will be observed that first module connecting conductor 50 includes a connection to a separate bypass module in the 5 form of a separate power switch 22a intended to shunt solar module 12a. Similarly, second module connecting conductor 51 includes a connection to a bypass module in the form of power switch 22b which is arranged to shunt solar module 10 12b in this instance arc detector 52 is connected across solar module 12 and the associated first module connecting conductor and second module connecting conductor so as to primarily sense or be sensitive to voltage. As illustrated in Figure 7, in a preferred form, the power switch 22 15 additionally includes a series connected resistor or shunt type voltage regulating device 53 and a series connected inductor 54. The resistor or shunt type voltage regulating device 53 allows a small voltage at the solar module terminals when the power switch is closed (in bypass mode). 20 This small voltage may be used to power the arc detector 52 even while shunting of solar module 12 is taking place. Similarly, series conductor 54 is used to block broad spectrum signals and allow the arc detector 52 to function with the power switch 22 closed (in shunt mode). 25 - 32 Current sensing embodiment With reference to figures 3, 8 and 9 there is illustrated a detailed embodiment wherein a current sensing-based arc detector is utilized. Like components 5 are numbered as for the embodiment of Figs 6 and 7. In this instance the arc detector is placed in series with the first module connecting conductor (outside of its connection to any other bypass module)-suitable locations are labeled X,Y and Z respectively in figure 8. 10 Supporting circuitry for this current sensing embodiment is illustrated in figure 9. The supporting circuitry can include a resistor connected in series with a power switch 22 in conjunction with a parallel connected 15 capacitor 54 connected across the series connected power switch and a resistor 53 as illustrated in figure 9. The resistor 53 allows a small voltage at the solar module terminals when the power switch is closed (in shunt 20 mode). This voltage may be used to power the arc detector (located at one or more locations X,Y,Z). The shunt capacitor 54 is utilized to pass high frequency signals so as to allow arc detection to function whilst the power switch is open (not in bypass mode). 25 33 The above describes only some embodiments of the present invention and modifications, obvious to those skilled in the art, can be made thereto without departing from the scope of the present invention. 5 In particular it is to be noted that the bypass module may be connected directly across the solar module which it is intended to protect or otherwise be associated with. Indeed in some embodiments the bypass module may be built into the solar module itself. 10 In alternative forms, the bypass module may be connected across the solar module and at least some of the input and output conductors of the solar module so that shorting or shunting includes shorting or shunting of part of the input and output conductors as well as the solar 15 module itself.