Patent Publication Number: US-2013234516-A1

Title: Electricity generation controller, electricity generation control system, and electricity generation control method

Description:
BACKGROUND 
     1. Technical Field 
     The present invention relates to an electricity generation controller, an electricity generation control system, and an electricity generation control method. 
     2. Background Art 
     Photo voltaic power generation for converting sunlight energy into electric energy by utilization of a photo voltaic panel. (PV panel) has hitherto become pervasive. In relation to photo voltaic power generation, waste materials, water discharge, noise, vibrations, or the like, do not occur during power generation, and utilizing photo voltaic power generation as an emergency power supply is also expected. For these reasons, photo voltaic power generation has particularly received attention in recent years. 
     PV panels are often installed outdoors, such as on a rooftop, in order to increase an electrical energy production. For this reason, the PV panels are vulnerable to direct influence of natural phenomena, like winds, rain, snow, and other factors. A longstanding buildup of the influence of natural phenomena and other factors sometimes causes a breakdown in the PV panels. 
     A technique described in connection with JP-A-2007-311487 has been known as a method for carrying out a fault diagnosis of the PV panels. JP-A-2007-311487 discloses measuring a current-voltage characteristic of the PV panels, converting the current-voltage characteristic into a base condition, and determining which one of a plurality of standard characteristics most closely resembles the base condition. The fault diagnosis of the PV panels can thereby be performed in detail. 
     However, according to the technique described in connection with JP-A-2007-311487, a worker must go to an installation site of the PV panels and conduct a fault diagnosis by directly connecting a characteristic evaluation apparatus to the PV panels, which involves consumption of much time In particular, in a case where the PV panels are installed on a rooftop, the diagnosis turns into high-lift, high-voltage work fraught with danger. Moreover, since the worker must go to the mount site of the PV panels, delay is likely to arise in finding a fault, which causes a loss in electrical energy production from the instant of occurrence of a fault up to the instant of finding the fault. 
     SUMMARY 
     The present invention provides an electricity generation controller, an electricity generation control system, and an electricity generation control method that make it possible to carry out an easy fault diagnosis of photo voltaic panels. 
     An aspect of the present invention provides an electricity generation controller for controlling an electrical energy production of a photo voltaic panel, the electricity generation controller including: a control section that controls an output of the photo voltaic panel within a first range; a signal processing section that processes a predetermined signal; and an output range change section that changes an output range of the photo voltaic panel controlled by the control section from the first range to a second range in accordance with the predetermined signal processed by the signal processing section, wherein the second range is broader than the first range. 
     Another aspect of the present invention provides an electricity generation control system including a plurality of electricity generation controllers for controlling electrical energy productions of a plurality of serial- or parallel-connected photo voltaic panels, wherein each of the electricity generation controllers includes: a control section that controls an output of the photo voltaic panel within a first range; a signal processing section that processes a predetermined signal; and an output range change section that changes an output range of the photo voltaic panel controlled by the control section from the first range to a second range in accordance with the predetermined signal processed by the signal processing section, wherein the second range is broader than the first range. 
     Still another aspect of the present invention provides an electricity generation control method for controlling an electrical energy production of a photo voltaic panel, the method including: controlling an output of the photo voltaic panel within a first range; processing a predetermined signal; and changing an output range of the photo voltaic panel from the first range to a second range in accordance with the processed predetermined signal, wherein the second range is broader than the first range. The present invention enables easy performance of fault diagnosis of a photo voltaic panel. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings: 
         FIG. 1  is a schematic block diagram showing a photo voltaic system according to embodiments of the present invention; 
         FIG. 2  is a block diagram showing an example of a configuration of a panel controller (a slave unit) according to the embodiments of the present invention; 
         FIG. 3  is a block diagram showing an example of a configuration of a power conditioner with a built-in panel controller (a master unit) according to the embodiments of the present invention; 
         FIG. 4  is a graph showing an example of an I-V characteristic of a PV panel achieved during MPPT control operation in the embodiments of the present invention; 
         FIG. 5  is a graph showing an example of an I-V characteristic of the PV panel achieved during fault diagnostic processing in the embodiments of the present invention; 
         FIG. 6  is a flowchart showing a first example of operation achieved during fault diagnostic processing performed by the panel controller (the slave unit) according to the first embodiment of the present invention; 
         FIG. 7  is a flowchart showing a second example of operation achieved during the fault diagnostic processing performed by the panel controller (the slave unit) according to the first embodiment of the present invention; 
         FIG. 8  is a flowchart showing an example of operation achieved during fault diagnostic processing performed by the panel controller (the master unit) according to the first embodiment of the present invention; 
         FIG. 9  is a sequence diagram showing an example of operation achieved during cooperative diagnostic processing performed in a photo voltaic system of a second embodiment of the present invention; and 
         FIG. 10  is an enlarged view of surroundings of a PV string in the photo voltaic system shown in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present invention are hereunder described by reference to the drawings. 
     First Embodiment 
       FIG. 1  is a schematic view of an example of a configuration of a photo voltaic system  1  according to a first embodiment of the present invention. The photo voltaic system  1  is equipped with photo voltaic (PV) panels  10 , panel controllers  20 , a junction box  30 , a power conditioner  40 , a panel controller  50 , and a server GO. The photo voltaic system is an example of a power generation control system. 
     The individual PV panel  10  is a panel that includes a photo voltaic battery that converts light energy into electric power by means of a photoelectric effect. The PV panel  10  can be also a photo voltaic cell that is a photo voltaic elementary substance or a photo voltaic battery module that is a combination of a plurality of photo voltaic batteries. The PV panels  10  are connected in series to a power line PL. A one-to-one correspondence exists between the PV panel  10  and the panel controller  20 . 
     In the embodiment shown in  FIG. 1 , the PV panels  10  are connected in series to each other by way of the power line FL, thereby making up a photo voltaic string (PV string)  11 . Further, the photo voltaic strings  11  are connected in shunt with each other in the junction box  30  by way of the power lines PL, thereby making up a photo voltaic array (PV array). Although the PV string is made by connecting four PV panels  10  in series, the number of PV panels is not limited to four. Further, although the PV array is constituted by connecting four PV strings in parallel, the number of PV strings is not limited to four. 
     The panel controller  20  controls an electrical energy production of the PV panel  10 . The panel controller  20  inputs generated electrical power of the corresponding PV panel  10  and controls in such a manner that the generated electrical power comes to desired electrical power. Desired electrical power is determined from a control signal pertinent to electrical power generation from the power conditioner  40  (the signal including information, such as a voltage and an electrical current). Desired electrical power sometimes varies from one panel controller  20  to another according to insolation conditions, and the like. Specifically, the panel controller  20  controls an electrical energy production of the PV panel  10 . Further, the panel controller  20  and the panel controller  50  communicate with each other by way of the power line PL. 
     Moreover, the panel controller  20  operates as a slave unit of the panel controller  50 . The panel controller  20  communicates with another panel controller  20  or the panel controller  50  by means of wired or wireless communication. Also, both wired and wireless communication can be used. In the case of wired communication, communication is established by use of for instance, the power line PL and by utilization of a communications frequency band of for instance, 2 to 30 MHz. In the case of wireless communication, a communications frequency band of for instance, 1.9 GHz, is utilized. 
     The panel controller  20  also performs processing pertinent to Maximum Power Point Tracking (hereinafter also referred to simply as “MPPT control”). MPPT control is one for maximizing electrical power generated by means of photo voltaic power generation in the entire photo voltaic system  1 . The panel controller  20  also performs processing pertinent to fault diagnostic processing for determining if the PV panel  10  is faulty. 
     The junction box  30  collectively connects the power lines PL, each of which serves as wiring for a single PV string  11 . made by connecting the plurality of PV panels  10  in series, to the power conditioner  40 . The junction box  30  includes terminals for connections with the power lines PL, switches used for a check or maintenance, a lighting protection element, a blocking diode for inhibiting backflow of electricity, and others. 
     The junction box  30  can be also combined with the power conditioner  40  into a single unit. Alternatively, the junction box  30  can be omitted. 
     The power conditioner  40  converts, into AC power, DC power equivalent to generated electrical power of the individual PV panel  10  output from the panel controller  20 . The power conditioner  40  is connected to; for instance, a distribution board (not shown). 
     The power conditioner  40  performs processing pertinent to MPPT control. MPPT control is one for maximizing electrical power generated by means of photo voltaic power generation in the entire photo voltaic system  1 . The power conditioner  40  also performs processing pertinent to fault diagnostic processing for determining if the PV panel  10  is faulty. 
     The panel controller  50  operates as a master unit for the plurality of panel controllers  20 . The panel controller  50  also performs processing pertinent to fault diagnostic processing. The panel controller  50  receives; for instance, values measured by the panel controller  20  (e.g., a measured current value, a measured voltage value, and measured power) from the panel controller  20  and monitors the electrical energy production of the PV panel  10  at all times. 
     Specific restrictions are not imposed on the installation site of the panel controller  50 . For instance, the panel controller  50  can be installed in the power conditioner  40  or in the junction box  30  or can be connected to any arbitrary point on the power line PL. Furthermore, when wireless communication is established between the panel controller  50  and the panel controllers  20 , the essential requirement for the panel controller  50  is to be placed at any location connected to a communication line. By way of example, the panel controller  50  is accommodated in the power conditioner  40  in  FIG. 1 . 
     The server  60  communicates with another communication device, like the panel controller  50 , thereby acquiring, storing, and analyzing data. The panel controller  50  performs processing pertinent to faulty diagnostic processing. 
     The server  60  can be a server installed in a locale that is the property of an owner of the PV panels  10  or a server installed at a remote site that is a property of a manufacturer or a maintenance service provider of the PV panels  10 . 
     An example of a detailed configuration of the panel controller  20  is now described. 
       FIG. 2  is a block diagram showing an example of the configuration of the panel controller  20 . The panel controller  20  is equipped with an MPPT section  210 , a communication section  220 , a coil section  240 , and a coupler  250 . 
     The MPPT section  210  performs MPPT control. Further, the MPPT section  210  is also connected in series to the corresponding PV panel  10  and controls an inter-terminal voltage of the PV panel  10  in such a way that the electrical power generated by the PV panel  10  becomes maximum. A detailed configuration of the MPPT section  210  will be described later. 
     The MPPT section  210  performs fault diagnostic processing of the PV panel  10  connected to the panel controller  20 . Fault diagnostic processing will be described in detail later. 
     The communication section  220  is connected in parallel to the PV panel  10  and sends a communication of various information by way of the power line PL. For instance, the communication section  220  sends to the power conditioner  40  a communication of a control signal pertaining to electrical power generation of the PV panel  10 . A detailed configuration of the communication section  220  will be described later. 
     The coil section  240  is connected in series to the PV panel  10 , and coils  241  and  242  are provided for a pair of power lines PL, respectively. The coil section  240  acts as a first filter section that blocks a frequency band for transmission of a control signal and permits passage of a frequency band for transmission of DC power. The coil section  240  makes it possible to block a signal of a high frequency band which is a signal band, thereby preventing transmission of the control signal to the PV panel  10 . 
     The coupler  250  is connected in series to the communication section  220  and made up of a coil transformer  251  and coupling capacitors  252   a  and  252   b.  The coupler  250  acts as a second filter section that permits passage of a frequency band for transmission of a control signal and blocks a frequency band for transmission of DC power. 
     The coupler  250  makes it possible to prevent application of the DC voltage to the communication section  220  (i.e., cut DC components) and permit passage of a signal in a signal band for transmission of the control signal. 
     The coupling capacitors  252   a  and  252   b  also act as noise filters. Accordingly, noise transmitted from the PV panel  10  to the panel controller  20  and switching noise that occurs in a DC-DC converter  213  of the MPPT section  210  can be prevented from being transmitted to the communication section  220 . 
     The coupler  250  is exemplified as being made up of the capacitors and the transformer but can be embodied by another configuration. 
     When the panel controller  20  performs wireless communication, the coupler  250  is unnecessary. By way of example,  FIG. 2  shows a presumption that the panel controller  20  performs communication by way of the power line PL. 
     The MPPT section  210  is equipped with a first voltage sensor  211 , a current sensor  212 , the DC-DC converter  213 , a second voltage sensor  214 , and a microprocessor (MPU: Micro Processing Unit)  215 . 
     The first voltage sensor  211  detects a voltage (inter-terminal. voltage) output from the PV panel  10  connected to the panel controller  20 . A voltage detected by the first voltage sensor  211  is hereinbelow referred to also as a first detected voltage. 
     The current sensor  212  detects an electric current output from the PV panel  10  connected to the panel controller  20 . An electric current detected by the current sensor  212  is hereinbelow referred to also as a first detected current. 
     The DC-DC converter  213  is equipped with a switch section  213 S having a switching element for power conversion purpose. The switch section  2135  is toggled between ON and OFF at correct time, thereby controlling a power supply fed, as a power source, from the PV panel  10  by way of the power line PL. 
     The DC-DC converter  213  receives as an input a voltage output from the PV panel  10  connected to the panel controller  20  and transforms the input voltage by use of the switch section  2135 . Further, the switch section  213 S is controlled ON/OFF in accordance with a PWM (Pulse Width Modulation) signal from the MPU  215 . 
     The second voltage sensor  214  detects a voltage (a transformed voltage) output from the DC-DC converter  213 . A voltage detected by the second voltage sensor  214  is hereinbelow referred to also as a second detected voltage. 
     The MPU  215  controls the DC-DC converter  213  in such a way that the first detected voltage or the second detected voltage comes to a predetermined voltage value. For instance, the “predetermined voltage” is a voltage value that is indicated by a control signal received by the communication section  220 . Further, control of the DC-DC converter  213  is controlling a duty ratio of the switch section  2135  in the DC-DC converter  213 . 
     The communication section  220  is equipped with a main IC (Integrated Circuit)  221 , memory  228 , a low-pass filter (LPF)  229 , a band pass filter (BPF)  230 , and a driver IC  231 . 
     The main IC  221  is equipped with a CPU (Central Processing Unit)  222  and PLC-MAC (Power Line Communication Media Access Control layer) block  223 . In addition, the main IC  221  is equipped with a PLC-PHY (Power Line Communication-Physical layer) block  224  and a DA converter (DAC: DIA converter)  225 . The main IC  221  is equipped with an AD converter (ADC: AID converter)  226  and a variable amplifier (VAG: Variable Gain Amplifier)  227 . 
     The main IC  221  is an integrated circuit that functions as a control circuit for effecting a power line communication. The main IC  221  is connected to the MPU  215  of the MPPT section  210  and exchanges data by means of serial communication. 
     For instance, an 8-bit RISC (Reduced Instruction Set Compute) processor is implemented in the CPU  222 . The PLC-MAC block  223  manages a MAC layer (Media Access Control layer) of a transmission signal and that of a received signal. The PLC-PHY block  224  manages a PRY layer (Physical layer) of a transmission signal and that of a received signal. 
     The DA converter  225  converts a digital signal into an analogue signal. The AD converter  226  converts an analogue signal into a digital signal. The variable amplifier  227  amplifies a signal input from the BPF  230 . 
     The memory  228  is a semiconductor storage device, like RAM (Random Access Memory) and ROM (Read Only Memory). The LPF  229  permits transmission of a low frequency component of the signal input from the DA converter  225  and blocks the other components. The BPF  230  permits transmission of a predetermined frequency component of a signal input from the coupler  250  and blocks the other components. The diver IC  231  is an IC for activating predetermined equipment. 
     The CPU  222  controls operation of the PLC-MAC block  223  and operation of the PLC-PRY block  224  by utilization of data stored in the memory  228 , as well as controlling the entirety of the communication section  220 . 
     The communication section  220  generally performs communication as follows. Data to be transmitted, which are stored in the memory  228  or the like, are transmitted to the main IC  221 . The main IC  221  subjects the data to digital signal processing, thereby generating a digital transmission signal. The thus-generated digital transmission signal is converted into an analogue signal by the DA converter  225  and output to the power line PL by way of the low-pass filter  229 , the driver IC  231 , and the coupler  250 . 
     The signal received from the power line PL is delivered to the band pass filter  230  by way of the coupler  250 . After being subjected to gain control by the variable amplifier  227 , the signal is converted into a digital signal by the AD converter  226 . The thus-converted digital signal is subjected to digital signal processing, to thus be converted into digital data. The thus-converted digital data are stored in; for instance, the memory  228 . 
     An example of digital signal processing implemented by the main IC  221  is now described. The communication section  220  uses a single carrier signal as a transmission signal. The communication section  220  converts data to be transmitted into a single carrier transmission signal and outputs the thus-converted transmission signal. Further, the communication section  220  processes a single carrier received signal, to thus convert it into received data. Digital signal processing for these converting operations is primarily performed by the PLC-PHY block  224 . 
     An example of a detailed configuration of the power conditioner  40  is now described. 
       FIG. 3  is a block diagram showing an example of a configuration of the power conditioner  40 . The power conditioner  40  is equipped with an MPPT section  410 , a communication section  420 , a coil section  440 , a coupler  450 , and a DC-AC converter  460 . In the example shown in  FIG. 3 , the MPPT section  410  and the communication section  420  belong to the panel controller  50 . 
     Although the MPPT section  410  is different from its counterpart MPPT section  210  of the panel controller  20  by only reference numeral  200 , they have the same configuration and function, and therefore their explanations are omitted. A detailed internal configuration (e.g., an MPU  415 ) of the MPPT section  410  also differs from the detailed configuration (e.g., the MPU  215 ) of its counterpart MPPT section  210  of the panel controller  20  by only reference numeral  200 . However, since they have the same configuration and function, their explanations are omitted. 
     A voltage detected by a first voltage sensor  411  is hereinbelow referred to also as a third detected voltage. A voltage detected by a second, voltage sensor  414  is hereinbelow referred to also as a fourth detected voltage. Moreover, an electric current detected by a current sensor  412  is hereinbelow referred to also as a second detected current. 
     Although the communication section  420  is different from its counterpart communication section  220  of the panel controller  20  by only reference numeral  200 , they have the same configuration and function, and therefore their explanations are omitted. A detailed internal configuration (e.g., a CPU  422 ) of the communication section  420  also differs from the detailed configuration (e.g., the CPU  222 ) of its counterpart communication section  220  of the panel. controller  20  by a difference of only reference numeral  200 . However, since they have the same configuration and function, their explanations are omitted. 
     Although the coil section  440  is different from its counterpart coil section  240  of the panel controller  20  by only reference numeral  200 , they have the same configuration and function, and therefore their explanations are omitted. 
     Although the coupler  450  is different from its counterpart coupler  250  of the panel controller  20  by only reference numeral  200 , they have the same configuration and function, and therefore their explanations are omitted. 
     The DC-AC converter  460  converts, into AC power, DC power equivalent to generated electrical power of the individual PV panel  10  output from the panel controller  20 . 
     Incidentally, even when the power conditioner  40  is not accommodated in the panel controller  50 , the power conditioner  40  is equipped with the MPPT section  410  and the communication section  420 . 
     The server  60  is equipped with component parts analogous to component parts of a common server. For instance, the server  60  is equipped with a communication section having a wired or wireless communication function, and the server  60  communicates with another communications device, such as the panel controller  50 . 
     The server  60  has a memory, a CPU, and the like. The CPU exercises a program stored in the memory, whereby a predetermined function can be implemented. For instance, the server  60  determines, from information from the panel controller  20 , if the PV panel  10  is faulty. 
     An example of MPPT control of the photo voltaic system  1  is now described. 
     The panel controller  20  and the power conditioner  40  exchange data for MPPT control to each other by means of communication. 
     First, the communication section  420  of the power conditioner  40  receives from the panel controller  20  a control signal including voltage information and current information by way of the power line PL. The voltage information is information about the first detected voltage or the second detected voltage. The current information is information about the first detected current. 
     Subsequently, the communication section  420  of the power conditioner  40  calculates a voltage value and a current value that are optimum for the PV panel  10  from the voltage information and the current information about the panel controller  20 . The voltage value and the current value, which are optimum for MPPT control, correspond to a voltage value and a current value of the individual PV panel  10  at which overall electric power generated by the plurality of PV panels  10  becomes maximum. The optimum voltage value and the optimum current value are dependent on the orientation of the PV panel  10 , the installation site of the PV panel  10 , and the weather, and therefore sometimes vary from one PV panel  10  to another. 
     Subsequently, the communication section  420  of the power conditioner  40  generates a control signal by incorporating the thus-calculated voltage and current values for the PV panel  10  into optimum voltage information and optimum current information. The communication section  420  transmits the control signal to the panel controller  20  corresponding to the PV panel  10  by way of the power line PL. The communication section  420  can also calculate optimum electric power from the optimum voltage information and the optimum current information, incorporate the thus-calculated optimum electric power into the optimum current information, incorporate the optimum power information into the control signal, and transmit the control signal to the panel controller  20 . 
     Subsequently, the communication section  220  of the panel controller  20  receives the optimum voltage information and the optimum current information from the power conditioner  40 . The MPPT section  210  of the panel controller  20  controls ON/OFF the switch section  213 S of the DC-DC converter  213  such that a voltage value incorporated in the received optimum voltage information and a current value incorporated in the received optimum current information are acquired. 
     Specifically, the MPU  215  controls ON/OFF the switch section  2135  such that the first detected voltage or the second detected voltage comes to the voltage value incorporated in the optimum voltage information. The MPU  215  can also control ON/OFF the switch section  213 S such that the first detected current comes to the current value incorporated in the optimum current information. 
     Since an output side of the DC-DC converter  213  is presumed to be more affected by noise than is an input side of the DC-DC converter  213 , the first detected voltage is preferable as the optimum voltage. 
     The power conditioner  40  is herein presumed to provide the panel controller  20  with information about the optimum voltage and current. The MPU  215  of the panel controller  20  instead can also determine, for itself, optimum voltage information and optimum current information from the first detected voltage and the second detected voltage. Further, the power conditioner  40  can also perform MPPT control on the basis of the third detected voltage, the fourth detected current, or the second detected voltage, all of which have been detected by the power conditioner  40 . 
       FIG. 4  is a graph showing an example of an output voltage characteristic and an output current characteristic (an I-V characteristic) of the PV panel  10  achieved during MPPT control operation. The I-V characteristic of the PV panel  10  changes according to an amount of sunlight as indicated by lines L 1  to L 3  shown in  FIG. 4 . The lines ordered in increasing sequence of sunlight quantity are L 1 , L 2 , and L 3 . When performing MPPT control, the panel controller  20  or the power conditioner  40  controls the output voltage and the output current of the individual PV panel  10  such that the electric power becomes maximum according to the amount of sunlight. In  FIG. 4 , an operating point of a control result is designated by symbol D 1 . 
     Fault diagnostic processing of the photo voltaic system  1  is now described. 
     Fault diagnostic processing is performed by use of the MPPT section  210  of the panel controller  20  or the MPPT section  410  of the power conditioner  40 . During fault diagnostic processing, a determination is made, on the basis of the I-V characteristic acquired at the operating point of the PV panel  10 , as to whether or not the individual PV panel  10  is faulty. 
     The following two; for instance, are conceivable as a method for acquiring an I-V characteristic of the PV panel  10  used in fault diagnostic processing. During fault diagnostic processing, the MPPT section  210  of the panel controller  20  can broadly acquire various operating points other than the maximum operating point. 
     Under a first acquisition method, the MPPT section  210  of the panel controller  20  sequentially changes the operating point of the PV panel  10  to be diagnosed, thereby acquiring an I-V characteristic of the PV panel  10  at each operating point. 
     Under a second acquisition method, the MPPT section  410  of the power conditioner  40  sequentially changes an input voltage and an input current of the power conditioner  40 . Operating points of the respective PV panels  10  change in conjunction with the changes. The MPPT section  210  of the panel controller  20  acquires an I-V characteristic of the individual PV panel  10  at its operating point. 
     The output voltage or the output current of the PV panel  10  acquired by the panel controller  20  corresponds to the first detected voltage, the second detected voltage, or the first detected current. Moreover, the number of operating points controlled by the panel controller  20  is not particularly limited. A more accurate fault diagnosis can be practiced by acquisition of I-V characteristics at a larger number of operating points. 
     The panel controller  20  can also acquire the I-V characteristic of the PV panel a number of times by changing the date and time for acquiring the I-V characteristic and collect a statistic on the I-V characteristics. For instance, the panel controller  20  can also use an average of the plurality of thus-acquired I-V characteristics for fault diagnostic processing. The system can thereby address various insolation conditions and environmental conditions, such as a cloudy environment where the first characteristic was acquired, so that occurrence of an erroneous determination can be prevented. 
     The server  60  collects and stores the information about the I-V characteristics of the PV panels  10  acquired by the respective panel controllers  20  by way of the panel controller  50 . Specifically, voltage and current information stored in the server  60  include at least one of pieces of information about the first detected voltage, the second detected voltage, and the first detected current. 
     The server  60  determines, from the I-V characteristic of the PV panel  10  acquired from the panel controller  20 , whether or not the PV panel  10  is faulty. 
     The server  60  stores the I-V characteristic of the PV panel  10  on a per-panel basis and calculates a difference (e.g., a divergence) between the I-V characteristic of one predetermined PV panel  10  and the I-V characteristic of another PV panel  10 . When the thus-calculated difference is a predetermined level or more, the server  60  can determine that the PV panel is faulty. 
     For instance, the server  60  previously retains information about an I-V characteristic of the PV panel  10  owned by the manufacturer (i.e., information about an I-V characteristic acquired in normal conditions) and compares the I-V characteristic for the normal conditions with the I-V characteristic acquired from the panel controller  20 . If a comparison result shows a difference of predetermined level or more, the server  60  can determine that the PV panel is faulty. 
     For instance, the server  60  stores information about the I-V characteristic of the PV panel that was determined to be faulty in the past and compares the I-V characteristic with the I-V characteristic acquired from the panel controller  20 . When the comparison result shows a predetermined level of similarity or more, the server  60  can determine that the PV panel is faulty. 
     Further, the server  60  can also cause a display device for displaying stored data on a Web screen to display information about the I-V characteristic and a P (power)-V (voltage) characteristic of the PV panel  10 . The server  60  can calculate electric power from the first detected voltage or the second detected voltage and the first detected current. The server  60  can have the display device, or the display device can be a separate one. Visualizing the characteristics of the PV panels  10  further facilitate fault diagnosis. 
     When determining, on the basis of a result of fault diagnostic processing, that the PV panel  10  is faulty, the server  60  can report it to a user by use of the Web screen, an e-mail, voice, or the like. The user means the proprietor, manufacturer, or maintenance service provider of the PV panel  10  that is diagnosed as being faulty. 
     A specific example of fault diagnostic processing is now described. 
       FIG. 5  is a graph showing an example of the I-V characteristic of the PV panel  10  achieved during fault diagnostic processing.  FIG. 5  shows respective operating points sequentially changed by means of fault diagnostic processing. When compared with the I-V characteristic that is shown in  FIG. 4  and achieved during MPPT control, a distribution range of operating points D 3  and D 4  achieved during fault diagnostic processing can be understood to be broad. During fault diagnostic processing, the distribution range of the operating points can be intentionally broadened. 
     The sever  60  previously retains in its internal memory; for instance, information about an operating point distribution of the PV panel  10  achieved in normal conditions. When determining that a divergence of predetermined standard level or more exists between an operating point distribution D 2  achieved in normal conditions and the operating point distributions D 3  and D 4  acquired in fault diagnostic processing, the server  60  determines that the PV panel  10  is faulty. Fault diagnostic processing is carried out for each PV panel  10 . 
     The line L 4  shown in  FIG. 5  designates an I-V characteristic of the PV panel  10  acquired at a predetermined amount of sunlight and in normal conditions (i.e., nonfaulty conditions). When the sever  60  acquires from the panel controller  20  information about operating points D 3  designated by solid triangles in  FIG. 5 , the respective operating points D 3  are aligned to the line L 4 . Accordingly, when acquiring information about the respective operating points D 3 , the server  60  determines that the PV panel  10  is nonfaulty. 
     In the meantime, when the server  60  acquired from the panel controller  20  the respective operating points D 4  designated by solid circles in  FIG. 5 , some of the operating points D 4  are away from the line L 4 . Therefore, when acquiring information about the respective operating points D 4  and when the line L 5  that is a locus passing through the respective operating points D 4  diverges from the line L 4  by a predetermined standard distance or more, the sever  60  determines that the PV panel  10  is faulty. 
     Explanations are now given to timing at which fault diagnostic processing is commenced. 
     Conceivable timing for commencing fault diagnostic processing is; for instance, manual initiation of fault diagnostic processing. Fault diagnostic processing thus commenced is also called manual diagnosis. In addition, for instance, another conceivable way is to commence fault diagnostic processing on the basis of preset information. Fault diagnostic processing thus commenced is also called automatic diagnosis. 
     In relation to manual diagnosis, the photo voltaic system  1  commences fault diagnostic processing by detection of for instance, pressing a physical diagnosis button provided on any of the devices or a diagnosis button displayed in the Web screen. For instance, the panel controller  50  detects pressing the diagnosis button and commands commencement of fault diagnostic processing. The device equipped with the physical diagnosis button includes; for instance, the panel controller  50 , the power conditioner  40 , or another dedicated terminal. 
     In relation to automatic diagnosis, for instance, any of the devices in the photo voltaic system  1  previously retains information about a time to commence fault diagnostic processing and commences fault diagnostic processing at the date and time corresponding to the time information. 
     For instance, the panel controller  20  retains scheduled information and commands commencement of fault diagnostic processing when an unillustrated timer detects a coincidence with, a scheduled date and time. The time information includes; for instance, a time interval at which fault diagnostic processing is performed and information about a date and time to perform fault diagnostic processing. 
     Moreover, in relation to automatic diagnosis, the photo voltaic system  1  commences fault diagnostic processing on the basis of for instance, information about power generation of the PV panel  10 . 
     For instance, when an electrical energy production of a predetermined PV panel  10  is continually lower than electrical energy productions of the other PV panels  10 , the photo voltaic system  1  commences fault diagnostic processing of the predetermined PV panel  10 . 
     Moreover, the electrical energy production of the PV panel  10  is stable or greater than a predetermined level, the photo voltaic system  1  commences fault diagnostic processing. A determination as to whether or not the electrical energy production is stable can be rendered by monitoring the first detected voltage, the second detected voltage, or the first detected current stored in the server  60  and on the basis of a determination as to whether or not a variation falls within a predetermined range. When the variation falls within the predetermined range, the electrical energy production is determined to be stable. Accuracy of fault diagnosis can thereby be enhanced. 
     Aside from manual diagnosis and automatic diagnosis, the photo voltaic system  1  can also commence fault diagnostic processing at initiation of the power conditioner  40 , the panel controller  50 , or the panel controller  20 . 
     When the power of the power conditioner  40  or the panel controller  20  is switched from OFF to ON, the power conditioner  40  or the panel controller  20  commands commencement of MPPT control in order to generate electric power at the maximum power operating point. During MPPT control, the operating point of the PV panel  10  is changed primarily to a point that is expected to be a maximum electrical power point. The operating point is usually changed in sequence from the maximum value side of the range of the voltage output from the PV panel  10  during MPPT control. Accordingly, as can be comprehended by reference to  FIG. 4 , the amount of shift in operating point of the PV panel  10  does not increase much. 
     When fault diagnostic processing is performed at initiation of the power conditioner  40  or the panel controller  20 , fault diagnostic processing is commenced along with MPPT control. Specifically, the panel controller  20  shifts the voltage from the maximum value side of the output voltage of the PV panel  10 , which is a target of fault diagnosis, not to a vicinity of the maximum electrical power operation point but further up to the minimum value side, thereby acquiring an I-V characteristic at respective operating points over the broad range of the PV panel  10 . 
     Such operation of the power conditioner  40 , the panel controller  50 , or the panel controller  20  at initiation is likewise applicable to a reset (i.e., a restart), as well. Resetting of the power conditioner  40  or the panel controller  20  is commanded by; for instance, the panel controller  50 . 
     The device that commanded commencement of manual diagnosis, automatic diagnosis, or fault diagnostic processing for initiation or reset generates a diagnostic operation request for requesting commencement of fault diagnostic processing. When the device is other than the panel controller  20 , a diagnostic operation request is transmitted to the panel controller  20  corresponding to the PV panel  10  that is a target of fault diagnosis. 
     Next, an example of operation of the fault diagnostic processing performed by the photo voltaic system  1  is described. 
       FIG. 6  is a flowchart showing a first example of operation achieved during fault diagnostic processing performed by the panel controller  20 .  FIG. 6  is presumed to perform fault diagnostic processing by utilization of respective operating points that shift during MPPT control. 
     First, the MPU  215  of the MPPT section  210  sets an initial value to each of variables (step S 101 ). Specifically, the MPU  215  sets an initial value (e.g., 50%) to a variable D 1  of a Duty value used for controlling the switch section  213 S of the DC-DC converter  213 . Further, the MPU  215  sets an initial value (e.g., one minute) to a variable t 1  of a transmission interval. Moreover, the MPU  215  sets an initial value (e.g., 100%/1024) to a variable Δd 1  of a change interval of a Duty value. The transmission interval represents an interval at which the panel controller  20  periodically transmits information about the I-V characteristic of the PV panel  10  to the panel controller  50 . The Duty value can be changed in; for instance, 1024 steps. 
     Subsequently, the first voltage sensor  211  or the second voltage sensor  214  measures (detects) a voltage V 1 . The current sensor  212  measures (detects) an electric current I 1  (step S 102 ). 
     Incidentally, since the output side of the DC-DC converter  213  is presumed to be more affected by noise than is the input side of the DC-DC converter  213 , the first detected voltage is preferable as a measured value. 
     The MPU  215  next calculates electric power P 1  from the thus-measured voltage V 1  and the thus-measured current I 1  (step S 103 ). The electric power P 1  can be also measured (detected) by separately providing an electric power sensor. 
     Subsequently, a determination is made as to whether or not the MPU  215  received the diagnostic operation request from the panel controller  50  (step S 104 ). The diagnostic operation request is received by the communication section  220 . For instance, the power conditioner  40  transmits a diagnostic operation request to the panel controller  50  at initiation or reset of the power conditioner  40 . The panel controller  50  transfers the diagnostic operation request to the panel controller  20 . 
     When received the diagnostic operation request from the communication section  220 , the panel controller  20  performs fault diagnostic processing (step S 105 ). Operation to be performed during fault diagnostic processing in response to the fault diagnosis commencement request will be described later by reference to  FIG. 7 . The diagnostic operation request is sometimes generated by the MPU  215  of the panel controller  20  for itself at predetermined timing. 
     When the panel controller  20  commences fault diagnostic processing pertaining to step S 105 , the MPU  215  changes the output range of the PV panel  10  to a second range that is broader than a first range. The first range is a range of operating points used in a first example of operation shown in  FIG. 6 , and the second range is a range of operating points used in a second example of operation shown in  FIG. 7 . 
     In the meantime, when the communication section  220  has not received the diagnostic operation request, the MPU  215  adds Δd 1  to the Duty value D 1 . Specifically, D 1 ←D 1 +Δd 1  is generated (step S 106 ), where symbol “←” (“=” in  FIGS. 6 and 7 ) designates substitution. 
     The first voltage sensor  211  or the second voltage sensor  214  measures a voltage V 2  acquired after the Duty value D 1  was changed in step S 106 . The current sensor  212  measures a current I 2  acquired after the Duty value D 1  was changed in step S 106  (step S 107 ). 
     Subsequently, the MPU  215  calculates, from the thus-measured voltage V 2  and the thus-measured electric current I 2 , electric power P 2  acquired after the Duty value D 1  was changed in step S 106  (step S 108 ). Incidentally, the electric power P 2  can be also measured directly by additional provision of an electric power sensor. 
     The MPU  215  then determines whether or not the electric power P 2  is greater than the electric power P 1  (P 2 &gt;P 1 ) (step S 109 ). 
     When P 2 &gt;P 1  stands, the MPU  215  handles the information measured this time as preceding information (step S 110 ). For instance, the MPU  215  handles the electric power P 2  measured this time as preceding electric power. Specifically P 1 ←P 2  is adopted. The MPU  215  also handles the voltage V 2  measured this time as a preceding voltage. Specifically, V 1 ←V 2  is adopted. Furthermore, the MPU  215  handles the electric current I 2  measured this time as a preceding electric current. Specifically, I 1 ←I 2  is adopted. 
     Namely, when P 2 &gt;P 1  stands, the electric power P 1  measured last time is less than the electric power P 2  measured this time. Hence, the MPU  215  determines that the operating point is successfully approaching the maximum operating point and makes a preparation for the next measurement while the direction of transition of the operating point is kept in the same direction. 
     Meanwhile, when P 1 =P 2  stands, a positive or negative sign of the Duty change interval Δd 1  is inverted (step S 111 ). Specifically, Δd 1 ←−Δd 1  is adopted. Specifically, since the electric power P 1  measured last time is the electric power P 2  measured this time or more, the MPU  215  determines that the operating point passed by the maximum operating point, and changes the direction of transition of the operating point toward. the maximum operating point. 
     Subsequently, the MPU  215  adds the Δd 1  whose positive or negative sign is inverted to the Duty value D 1 . Namely, D 1 ←D 1 +Δd 1  is adopted (step S 112 ). 
     The communication section  220  transmits the value of the voltage V 1  and the value of the current I 1  to the panel controller  50  at each transmission interval t 1  (step S 113 ). The panel controller  50  can thereby manage information about the I-V characteristic in the neighborhood of the maximum operating point of the PV panel  10 . The I-V characteristic is used for the server  60  to determine if the PV panel  10  is faulty. 
     After processing pertaining to step S  113 , the panel controller  20  proceeds to step S 104 . 
     As shown in  FIG. 6 , when fault diagnostic processing is performed in conjunction with MPPT control, the shift range of the operating point is; for instance, a voltage range from 45(V) to 47(V) (a first range). The shift range is not limited to this range. 
     The fault diagnostic processing shown in  FIG. 6  enables performance of fault diagnosis of the PV panel  10  by mere performance of MPPT control. 
       FIG. 7  is a flowchart showing a second example of operation of the panel controller  20  achieved during fault diagnostic processing. In  FIG. 7 , fault diagnostic processing is presumed to be performed in a voltage range that is broader than the range of the respective operating points which shift during MPPT control.  FIG. 7  defines a voltage range in which the operating points are shifted. 
     First, the MPU  215  of the MPPT section  210  sets an initial value to each of the variables (step S 201 ). Specifically, the MPU  215  sets an initial value (e.g., 50%) to a variable D 2  of a Duty value. Further, the MPU  215  sets an initial value (e.g., 100%/1024) to a variable Δd 2  of the change interval. of the Duty value. Further, the MPU  215  sets an initial value (e.g., 10%) to a variable D_min of the Duty value. The MPU  215  also sets an initial value (e.g., 90%) to a variable D_max of the maximum Duty value. The MPU  215  also sets an initial value “0” to the variable Y 1 . 
     The first voltage sensor  211  or the second voltage sensor  214  measures (detects) a voltage V 3 . The current sensor  212  measures (detects) the electric current I 1  (step S 202 ). 
     Subsequently, the communication section  220  transmits a value of the measured voltage V 3  and a value of the measured electric current I 3  to the panel controller  50  (step S 203 ). Specifically, the communication section  220  transmits information about the I-V characteristic of the PV panel  10  acquired at an operating point of the voltage V 3 . Incidentally, the communication section  220  can also transmit the information with a smaller frequency rather than transmitting information each time the voltage V 3  and the electric current I 3  are measured. Moreover, the MPPT section  210  can also calculate an average of the voltages V 3  measured a number of times and an average of the electric currents I 3  measured a number of times, and the communication section  220  can transmit information about the averages. 
     The MPU  215  then adds Δd 2  to the Duty value D 2 . Specifically, D 2 ←D 2 +Δd 2  is adopted (step S 204 ). 
     The MPU  215  then determines if the Duty value D 2  is larger than the Duty minimum value D_min. (D 2 &gt;D_in) or if the Duty value D 2  is smaller than the Duty maximum value D_max (D 2 &lt;D_max) (step S 205 ). Specifically, the MPU  215  determines if the requirement for D_min&lt;D 2 &lt;D_max is fulfilled. 
     When the requirement for D_min&lt;D 2 &lt;D_max is fulfilled, the MPU  215  determines that the Duty value stays within the voltage range where the duty value is shifted and also determines whether or not the variable Y 1  is one (Y 1 =1) (step S 206 ). 
     When Y 1 =1 does not stand, the MPU  215  inverts the positive or negative sign of the Duty change interval Δd 2 . Further, the MPU  215  resets the Duty value D 2  to the initial value. The MPU  215  also adds one to the variable Y 1 . Specifically, Y 1 ←Y 1 +1 is adopted (step S 207 ). 
     Specifically, the MPU  215  determines that the Duty value first arrived at one end (either the Duty minimum value or the Duty maximum value) in the voltage range where the Duty value is shifted, and makes a preparation to change the Duty value to the other end. 
     After processing pertaining to step S 207 , the panel controller  20  proceeds to processing pertaining to step S 202 . 
     When Y 1 =1 stands, the panel controller  20  completes processing shown in  FIG. 7 . Specifically, the MPU  215  determines that the Duty value reached both the one end and the other end (both the Duty minimum value and the Duty maximum value) of the voltage range where the Duty value is shifted, and completes processing. 
     When fault diagnostic processing shown in  FIG. 7  is performed, the shift range of the operating point is; for instance, a range from 20(V) to 55(V) (a second range). However, the shift range is not limited to this range. 
     By means of the fault diagnostic processing shown in  FIG. 7 , the I-V characteristics for respective operating points of the PV panel  10  can be acquired in a predetermined voltage range that is broader than the voltage range acquired when MPPT control is performed. Further, since information about the I-V characteristic is transmitted to the panel controller  50 , the panel controller  50  can manage information about the I-V characteristic of the PV panel  10  belonging to the predetermined voltage range. 
       FIGS. 6 and 7  illustrate that the MPPT section  210  of the panel controller  20  performs both operations; namely, changing the operating point and sensor measurement. The power conditioner  40  can change the operating point instead, and the MPPT section  210  of the panel controller  20  can perform sensor measurement instead. 
       FIG. 8  is a flowchart showing an example of operation achieved during fault diagnostic operation performed by the panel controller  50 . In  FIG. 8 , the CPU  422  of the communication section  420  of the panel controller  50  monitors communications conditions. 
     The CPU  422  of the communication section  420  determines whether or not the diagnostic operation request is received from the server  60  (step S 301 ). When the diagnostic operation request is received, the communication section  420  transfers the diagnosis request operation to the panel controller  20  (step S 302 ). 
     The CPU  422  determines whether or not data are received from the panel controller  20  (step S 303 ). The data include, for instance, information about the I-V characteristic of the PV panel  10  acquired by the panel controller  20  during MPPT control or fault diagnostic processing. When the data are received from the panel controller  20 , the communication section  220  transfers the data to the server  60  (step S 304 ). 
     As above, in the panel controller  20  according to the embodiment, the MPPT section  210  has a function as a control section for controlling the output of the PV panel  10  within the first range. Moreover, the MPPT section  210  has a function of serving as an output range section that changes the range of the output of the PV panel  10  to the second range that is broader than the first range. 
     The output characteristic of the PV panel  10  can be searched over the output range of the PV panel  10  which is broader than that employed during MPPT control. Accordingly, fault diagnosis of the PV panel  10  can be easily performed. Further, fault diagnosis involves neither high-lift work nor risk. Further, fault diagnosis can be carried out by use of the module that performs common MPPT control, and hence a device specifically designed for fault diagnosis becomes obviated. 
     Second Embodiment 
     A second embodiment provides an explanation about fault diagnostic processing (cooperative diagnostic processing) that is performed in a cooperative manner by the PV panels  10  belonging to the PV string  11 . Since the photo voltaic system  1  according to the second embodiment is the same as that described in connection with the first embodiment in terms of a configuration, its explanations are omitted. 
     When one panel controller  20  in the PV string  11  performs fault diagnostic processing of a corresponding PV panel  10 , output voltages of all of the panel controllers  20  in the PV string  11  are controlled so as to become constant during cooperative diagnostic processing. Although making the output voltages constant is exemplified in the embodiment, the output currents can be also made constant instead. 
       FIG. 9  is a sequence diagram showing an example of operation achieved during cooperative diagnostic processing performed in the photo voltaic system  1 . In  FIG. 9 , performing cooperative diagnostic processing as fault diagnostic processing is presumed to be previously set.  FIG. 10  is an enlarged view of surroundings of the PV string  11  shown in  FIG. 1 . 
     First, the CPU  422  of the communication section  420  of the panel controller  50  is assumed to detect a predetermined cooperative diagnostic operation and detect a diagnostic operation request for a PV panel  10 A. The communication section  420  of the panel controller  50  transmits an output voltage value fixing command to all of the panel controllers  20  ( 20 A to  20 D) corresponding to the PV panels  10  ( 10 A to  10 D) in the PV string  11  to which the PV panel  10 A belongs (step S 401 ). The output voltage value fixing command is a control signal for the purpose of making the output voltages of all of the panel controllers  20  constant. 
     In the respective panel controllers  20  ( 20 A to  20 D), when the communication section  220  receives the output voltage value fixing command from the panel controller  50 , the MPPT section  210  performs output voltage value fixing operation (step S 402 ). Specifically, in order to make the output voltage of the panel controller  20  constant, the MPU  215  monitors the output value of the second voltage sensor and performs control so as to make the second detected voltage constant. Even when the second detected voltage is maintained constant, the first detected voltage and the second detected voltage are variable. The output voltage value fixing operation is performed not only in connection with the panel controller  20 A but also in connection with the other panel controls  20 B to  20 D, as well. 
     Subsequently, in the panel controller  20 A, the first voltage sensor  211  measures the first detected voltage at the first operating point of the PV panel  10 A, and the current sensor  212  also measures the first detected current (step S 403 ). The first operating point is determined from; for instance, the initial value of the Duty value employed by the MPU  215  in  FIGS. 6 and 7 . 
     The communication section  220  of the panel controller  20 A next transmits information about the measured voltage value and the measured current value (the measured values) to the panel controller  50  (step S 404 ). The measured values are equivalent to information about the I-V characteristic acquired at the first operating point of the PV panel  10 . 
     The communication section  420  of the panel controller  50  transfers the information about the measured values from the panel controller  20 A to the server  60  (step S 405 ). The server  60  receives the information about the measured values from the panel controller  50  and stores the information in itself. 
     After having completed measurement at the previous operating point (e.g., measurement pertaining to step S 403 ), the panel controller  20 A changes the operating point to the next operating point. Specifically, the MPU  215  changes the Duty value, thereby changing the input voltage and the input current for the panel controller  20 A (step S 406 ). 
     In the panel controller  20 A, the first voltage sensor  211  measures the first detected voltage at the changed operating point of the PV panel  10 A, and the current sensor  212  also measures the first detected current (step S 407 ). 
     The communication section  220  of the panel controller  20 A transmits information about the measured voltage value and the measured current value (measured values) to the panel controller  50  (step S 408 ). The measured values are equivalent to information about the I-V characteristic of the PV panel  10  acquired at the changed operation point. 
     The communication section  420  of the panel controller  50  transfer the information about the measured values from the panel controller  20 A to the server  60  (step S 409 ). The server  60  receives the information about the measured values from the panel controller  50  and stores the information in itself. 
     Processing pertaining to steps S 406  to S 409  is iterated in subsequent operation. The server  60  can thereby store information about the I-V characteristics of the PV panel  10 A at the respective operation points. The server  60  therefore can determine if the PV panel  10 A is faulty. 
     As above, the MPPT section  210  of the panel controller  20  controls the outputs of the PV panel  10  while the DC output of the DC-DC converter  213  is controlled so as to stay constant. Further, the panel controller  20  performs in cooperation with the other panel controllers  20  such that the DC outputs of the DC-DC converters  213  of all of the panel controllers  20  become identical with each other. 
     According to cooperative diagnostic processing shown in  FIG. 9 , even when the operating point is changed during fault diagnostic processing of the PV panel  10 A, electrical loads imposed on the other PV panels  10 B to  10 D belonging to the PV string  11  become constant. Consequently, fault diagnostic processing can be performed without electrically affecting the other PV panels  10 B to  10 D. 
     The present invention is not limited to the configuration according to the embodiment. Any configurations can be applied to the present invention, so long as the functions described in connection with claims or the functions yielded by the configurations described in connection with the embodiments can be accomplished. 
     In the embodiment, the power conditioner  40  and the panel controller  50  can be also provided as separate devices. In this case, when the MPPT section  410  of the power conditioner  40  is not used for MPPT control and the fault diagnostic processing, the MPPT section  410  can be omitted. The configuration of the power conditioner  40  can thereby be simplified. 
     In the embodiment, the plurality of PV panels  10  can be also connected in parallel to each other, to thus make up the PV string. As a result, even when the generated electric current is decreased under influence of a shade of the predetermined PV panel  10 , influence on the other PV panels  10  can be prevented. 
     In the embodiment, a battery can be also set in place of the power conditioner  40 . Generated electrical power can be temporarily stored rather than being provided indoors instantly. 
     In the embodiment, the panel controller  20  can be also equipped with a DC-AC converter in a stage subsequent to the MPPT section  210  and convert generated electrical power into AC electrical power. The power conditioner  40  that performs DC-AC conversion can thereby be omitted, and the configuration of the photo voltaic system  1  can be simplified correspondingly. Moreover, AC power is transmitted through the power lines PI, a power loss can be diminished. 
     In the embodiment, the panel controller  50  can store information about fault diagnostic processing and determine if the PV panel  10  is faulty in place of the server  60 . 
     A first aspect provides an electricity generation controller for controlling an electrical energy production of a photo voltaic panel, the electricity generation controller including: a control section that controls an output of the photo voltaic panel within a first range; a signal processing section that processes a predetermined signal; and an output range change section that changes an output range of the photo voltaic panel controlled by the control section from the first range to a second range in accordance with the predetermined signal processed by the signal processing section, wherein the second range is broader than the first range. 
     The configuration makes it possible to search for an output characteristic of the photo voltaic panel in an output range of the photo voltaic panel which is broader than that achieved during normal operation (e.g., operation of Maximum Power Point Tracking (MPPT control)). Accordingly, a fault diagnosis of the photo voltaic panel can be readily performed. Moreover, fault diagnosis involves neither high-lift work nor danger. Further, fault diagnosis can be carried out by use of for instance, the control section that performs MPPT control, and hence a device specifically designed for fault diagnosis becomes obviated. 
     The electricity generation controller may be configured so that the output of the photo voltaic panel includes at least one of an output voltage and an output current of the photo voltaic panel. 
     The configuration makes it possible to easily perform fault diagnosis on the basis of the output voltage or the output current of the photo voltaic panel. 
     The electricity generation controller may further include: a voltage measurement section that measures the output voltage of the photo voltaic panel; a current measurement section that measures the output current of the photo voltaic panel; and a transmission section that transmits power generation information on the photo voltaic panel in accordance with a measurement result of the voltage measurement section and the current measurement section. 
     The configuration enables; for instance, another device, to store and analyze power generation information on the photo voltaic panel. Therefore, the other device can determine if the photo voltaic panel is faulty. 
     The electricity generation controller may be also configured so that the control section includes a DC conversion section that receives the output of the photo voltaic panel as a DC input, subject the input to DC conversion, and produces a DC output, and the control section controls the output of the photo voltaic panel in a state where the DC output of the DC conversion section is controlled to be constant. 
     The configuration makes it possible to easily perform fault diagnosis without electrically affecting another PV panel. 
     The electricity generation controller may be also configured so that the output of the DC conversion section includes at least one of an output voltage and an output current of the DC conversion section. 
     The configuration makes it possible to perform fault diagnosis of the photo voltaic panel while at least either the output voltage or the output current of the DC conversion section is made constant. 
     The electricity generation controller may be also configured so that the control section controls the DC output of the DC conversion section to be constant and identical with a DC output of a DC conversion section provided in another electricity generation controller that controls an electrical energy production of another photo voltaic panel that is different from the photo voltaic panel of the electricity generation controller. 
     The configuration enables the electricity generation controller and another electricity generation controller to perform fault diagnosis in a cooperative manner without electrically affecting each other. Accordingly, accuracy of fault diagnosis is enhanced. 
     The electricity generation controller may be also configured so that the predetermined signal includes a diagnostic operation request signal for requesting diagnostic operation for determining if the photo voltaic panel, is faulty. 
     The configuration makes it possible to perform fault diagnosis in response to; for instance, user&#39;s actuation of the electricity generation controller with a button, scheduling of diagnostic operation, or a diagnostic operation request from another device. 
     A second aspect provides an electricity generation control system including a plurality of electricity generation controllers for controlling electrical energy productions of a plurality of serial- or parallel-connected photo voltaic panels, wherein each of the electricity generation controllers includes: a control section that controls an output of the photo voltaic panel within a first range; a signal processing section that processes a predetermined signal; and an output range change section that changes an output range of the photo voltaic panel controlled by the control section from the first range to a second range in accordance with the predetermined signal processed by the signal processing section, wherein the second range is broader than the first range. 
     The configuration makes it possible to search for an output characteristic of the photo voltaic panel in an output range of the photo voltaic panel which is broader than that achieved during normal operation (e.g., operation of Maximum Power Point Tracking (MDPT control)). Accordingly, a fault diagnosis of the photo voltaic panel can be readily performed. Moreover, fault diagnosis involves neither high-lift work nor danger. Further, fault diagnosis can be carried out by use of for instance, the control section that performs MPPT control, and hence a device specifically designed for fault diagnosis becomes obviated. 
     The electricity generation control system may be configured so that the control section of each of the electricity generation controllers includes a DC conversion section that receives the output of the photo voltaic panel as a DC input, subjects the input to DC conversion, and produces a DC output, and the control section of each of the electricity generation controllers controls the output of the photo voltaic panel while controlling the DC output of the DC conversion section to be constant and identical with the DC output of the DC conversion section of other electricity generation controller. 
     The configuration enables the electricity generation controllers in the electricity generation system to perform fault diagnosis in a cooperative manner without electrically affecting each other. Accordingly, accuracy of fault diagnosis is enhanced. 
     A third aspect provides an electricity generation control method for controlling an electrical energy production of a photo voltaic panel, the method including: controlling an output of the photo voltaic panel within a first range; processing a predetermined signal; and changing an output range of the photo voltaic panel from the first range to a second range in accordance with the processed predetermined signal, wherein the second range is broader than the first range. 
     The method makes it possible to search for an output characteristic of the photo voltaic panel in an output range of the photo voltaic panel which is broader than that achieved during normal operation (e.g., operation of Maximum Power Point Tracking (MPPT control)). Accordingly, a fault diagnosis of the photo voltaic panel can be readily performed. Moreover, fault diagnosis involves neither high-lift work nor danger. Further, fault diagnosis can be carried out by use of; for instance, the control section that performs MPPT control, and hence a device specifically designed for fault diagnosis becomes obviated. 
     The present application is based upon and claims the benefit of Japanese patent application No. 2012-053534 filed on Mar. 9, 2012, the contents of which are incorporated by reference in its entirety.