Photovoltaic inspection system and photovoltaic inspection method

A photovoltaic inspection system is provided, the photovoltaic inspection system detecting a failure by eliminating ON/OFF operation of a switch or others at the time of inspection or checkup as much as possible, reducing an influence of a temperature distribution as a whole with a small effort, and detecting a local deterioration in a photovoltaic module or string. According to a typical embodiment, in a photovoltaic system having a plurality of photovoltaic strings formed of one or a plurality of photovoltaic modules arranged to be aligned, a photovoltaic inspection system which detects the failure in the photovoltaic strings includes: a current detector which measures each of a first output current of a first photovoltaic string and a second output current of a second photovoltaic string; and a monitoring unit which calculates a second temperature property of the second photovoltaic string based on a value of the first output current and a value of the second output current and which determines whether the second photovoltaic string has the failure or not based on the second temperature property.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is entitled to the benefit of and incorporates by reference subject matter disclosed in International Patent Application No. PCT/JP2013/071860 filed Aug. 13, 2013.

TECHNICAL FIELD

The present invention relates to a photovoltaic technique, and, more particularly, the present invention relates to a technique effectively applied to a photovoltaic inspection system and photovoltaic inspection method of detecting a failure in a photovoltaic (PV) module or string.

BACKGROUND ART

In recent years, by the introduction of FIT (Feed-in Tariffs) or others, the market of a large-scale photovoltaic system which is so-called mega solar system or others having an output equal to or larger than 1 megawatt has been expanded. In the mega solar system, several thousands to several tens of thousands of sheets of a PV module whose class is 100 W to 200 W is arranged at one location in a PV power site.

As a method of detecting a failure in a PV module, there are methods such as inspecting a deterioration of a cell by visual inspection, a method of detecting the presence or absence of abnormal heat generation of a cell by a thermometer, and a method of inspecting electrical property such as current-voltage property by a tester. These inspections are normally performed to each of a PV module or PV string (hereinafter, simply referred to as a “PV module” in some cases).

As a technique related to this, for example, Japanese Patent Application Laid-Open Publication No. 2010-123880 describes a technique of determining whether a failure has occurred in the PV module or not by providing measuring means and communicating means for each PV module or string, transmitting a measured property value and an identification signal of the PV module to a control device, and comparing the transmitted result with a previously-set threshold.

Also, Japanese Patent Application Laid-Open Publication No. 2011-146472 describes a technique of determining a high-temperature portion on a surface of a PV array as failure by an imaging machine which performs infrared-ray imaging of the surface of the PV array, by a moving mechanism which moves the imaging machine, by an observation monitor which displays an image obtained by the infrared-ray imaging by the imaging machine moved by the moving mechanism, and by a control device which controls the infrared-ray imaging of the imaging machine and the movement of the moving mechanism.

SUMMARY

According to a conventional technique, the failure of the PV module in the PV system can be detected efficiently to some extent.

However, for example, the technique as described in Japanese Patent Application Laid-Open Publication No. 2010-123880 has a problem of high cost since it is required to provide the measuring means and the communicating means for each PV module or string. It is possible to take a method of sequentially performing the measurement while manually connecting the measuring means and the communicating means to the PV module as a measurement target, and then, switching the connection to another PV module. However, the method is inefficient in a large-scale system such as a mega solar system, and besides, has a risk such as switching error between ON and OFF of a switch at the time of the connection switching.

Furthermore, although a threshold setting method is not particularly mentioned, a failure may not be detected if the set threshold is too large. Conversely, if the set threshold is too small, there is a high possibility of occurrence of such erroneous detection that a failure is determined even through the state is normal, and therefore, accuracy of failure detection is decreased. Therefore, it is required to set an appropriate threshold. However, since the property of the PV module are changed by fluctuations in the amount of solar radiation and temperature, it is very difficult to set the appropriate threshold.

Still further, for example, the technique as described in Japanese Patent Application Laid-Open Publication No. 2011-146472 has a problem of high cost again since it is required to install a rail or others T the mega solar site as a moving mechanism which moves an imaging machine such as an infrared-ray camera. Still further, even if the failure portion becomes a high-temperature portion, the difference in temperature from a normal portion is about 5° C., and even the difference in temperature of about 5° C. can be detected by local observation. However, in the technique as described in Patent Document 2, particularly in the case of the large-scale PV module such as the mega solar system, such a difference may be hidden in a temperature distribution (which is generally about 40° C. to 90° C.) as a whole, and may not be detectable.

Thus, an object of the present invention is to provide a PV inspection system and a PV inspection method of detecting a failure by eliminating the ON/OFF operation of the switch or others in the inspection or checkup as much as possible, reducing an influence of a temperature distribution as a whole with a small effort, and detecting a local deterioration in a PV module or string.

The above and other object and novel characteristics of the present invention will be apparent from the description of the present specification and the accompanying drawings.

The typical summary of the inventions disclosed in the present application will be briefly described as follows.

In a PV system having such a structure that a plurality of PV strings formed of one or a plurality of series-connected PV modules are arranged to be connected in parallel to each other, a PV inspection system according to a typical embodiment of the present invention is a PV inspection system which detects a failure in the PV strings, and has: a current detector which measures each of a first output current of a first PV string and a second output current of a second PV string; and a monitoring unit which calculates a second temperature property of the second PV string based on a value of the first output current and a value of the second output current and which determines whether the second PV string has a failure or not based on the second temperature property.

The effects obtained by typical aspects of the present invention will be briefly described below.

That is, according to the typical embodiment of the present invention, a failure can be detected by eliminating the ON/OFF operation of the switch or others in the inspection or checkup as much as possible, reducing an influence of a temperature distribution as a whole with a small effort, and detecting a local deterioration in a PV module or string.

DETAILED DESCRIPTION

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Note that components having the same function are denoted by the same reference symbols throughout the drawings for describing the embodiment, and the repetitive description thereof will be omitted.

FIG. 13is a diagram showing a general outline about an example of structure of a general PV system. A PV system1′ has such a structure that one or more PV strings31having a plurality of series-connected PV modules310are connected in parallel to each other via wire connection in a connection box20, are further integrated, and are connected to an electric power system43via a DC/DC converter41and an inverter42or a PCS (Power Conditioning System) including them although not shown. In this manner, electric power generated by each PV string31can be outputted to the electric power system43. The plurality of parallel-connected PV strings31may be arranged to configure a PV array30, and the connection box20may be provided for each PV array30. In the connection box20, note that a backflow preventing diode21is connected in order to prevent backflow of the current generated in each PV string31.

FIG. 14is a diagram showing a general outline about an example of structure of the general PV string31. The PV string31shown on the right side in the drawing has such a structure that the plurality of PV modules310are connected in series as described above. Each PV module310has such a structure that a plurality of PV cells311are connected in series, and besides, that a bypass diode312used in the failure or others is connected in parallel to the PV cells. Each PV cell311is formed of a semiconductor element or others which converts sunlight into electric power, and is expressed by an equivalent circuit as shown on the left side in the drawing as a so-called PV (PhotoVoltaic) cell model.

FIG. 15is a diagram showing a general outline about an example of a mechanism which detects a failure in each PV string31in the general PV system1′ in the conventional technique. The example ofFIG. 15shows such a that a current-voltage property is measured for each PV string31by sequentially connecting a current-voltage property measuring device50having electronic load, an ammeter and a voltmeter connected as shown in the drawing to a terminal corresponding to the respective PV strings31in the connection box20. As described above, the conventional technique takes such a mechanism that a failure is detected based on a difference state from a normal state by obtaining a current-voltage property by measuring a current and a voltage for each PV string31.

FIG. 16is a diagram showing a general outline about an example of the current-voltage property of the PV string in the general PV system1′. A plurality of property curves in the drawing indicate differences in property depending on temperature. The vertical line shown on a voltage axis indicates a measurement reference voltage. This reference voltage can be set as, for example, an operating voltage in the PV string31. Here, curves of solid-lines having intersection points with the vertical line indicating the reference voltage as represented by white circles1to3indicate a pattern of the current-voltage property at normal time. In this case, current values in a range indicated by the white circles1to3at the reference voltage can be regarded as current values in a normal range.

Meanwhile, curves of dotted lines having intersection points with the vertical line indicating the reference voltage as represented by black circles “a” to “c” indicate a pattern of the current-voltage property in failure, anomaly, deterioration, or others (hereinafter, collectively referred to as a “failure” in some cases). Here, in the curves corresponding to the black circles “b” and “c”, current values at the reference voltage largely differ and decrease from the current values in the normal range indicated by the above-described white circles1to3. In such a clear case, the failure can be easily detected by simple comparison between the current values. However, in the curve corresponding to the black circle “a”, in spite of the failure, the current value at the reference voltage does not differ from the current values in the normal range indicated by the above-described white circles1to3, and therefore, the curve indicates that it is difficult to detect the failure from the measurement of the current-voltage property.

This is because the temperature affects the current-voltage property, that is, because the current-voltage property has a temperature property, and a large-scale system with a very large area such as a mega solar system has a possibility of a large difference in temperature distribution depending on the location, and therefore, this shows that the failure cannot be accurately detected unless the influence of the temperature distribution is cancelled. However, for example, in such a method as keeping the current-voltage property at normal time for each temperature, process are complexed, and the required data amount increases.

Thus, the PV inspection system of one embodiment of the present invention determines the failure by, for example, for each PV string31of the PV system, obtaining a difference in the temperature property between another string adjacent or close to the string, calculating a temperature property of each PV string31based on this obtained difference, and comparing the temperature property and an assumed temperature property. Between the PV strings31adjacent or close to each other, the difference in temperature is small, and the difference can be ignored. Therefore, even in the large-scale system such as the mega solar system, the influence of the difference in temperature distribution depending on the location can be cancelled. Also, as described later, since a difference in temperature property between the PV strings31adjacent or close to each other can be calculated only from the current of each PV string31, the voltage measurement is not required, so that the accuracy of failure detection can be improved while measurement is facilitated to reduce the cost.

FIG. 1is a diagram showing a general outline about an example of structure of a PV system having a PV inspection system according to a first embodiment of the present invention. In the structure of the general PV system1′ shown inFIG. 13, a PV system1of the present embodiment has, for example, a string monitor10which measures and collects a current of each PV string31inside the connection box20. This string monitor10is a device configuring a part or entire of the PV inspection system, and may be fixedly installed inside the connection box20or may be configured so as to be attachable to the inside of the connection box20at the time of process of failure detection as a portable type.

The string monitor10has current detectors11each which measures an output current of each PV string31, a sampling processing unit12which obtains the output current measured at each current detector11at every constant time, a signal conversion transmission device13which converts a signal indicating the current value obtained by the sampling processing unit12into predetermined output information and outputs the signal, and a memory14which records the information about the current value transmitted from the signal conversion transmission device13.

The information about the current value of each PV string31recorded in the memory14can be taken out, for example, via an external terminal such as a USB (Universal Serial Bus) terminal included in the string monitor10but not shown to an external storage device such as a USB memory. Then, data is taken from the external storage device into a monitoring device or monitoring unit configured of a PC (Personal Computer), a server device, or others but not shown, so that it can be determined whether the failure has occurred or not by a method as described later. It is also possible to make such a structure as directly transmitting the data by the communicating means to the monitoring device or the monitoring unit not via the memory14. Also, the failure can be determined on the string monitor10by, for example, providing a CPU (Central Processing Unit) and a program on the string monitor10or by using a microcomputer or others to configure a monitoring unit not shown.

FIG. 2is a diagram showing a general outline about an example of structure of the current detector11. The current detector11can be configured by using, for example, a clamp-type circuit such as a general CT (Current Transformer) sensor formed of a circuit as shown in the drawing, and can measure the current without requiring a connection operation of opening a line from each PV string31.

FIG. 3is a diagram schematically showing a general outline about a specific example of structure at the time of inspection. Inside the connection box20, backflow preventing diodes21and MCCBs (wiring breakers)22are installed to wirings from the respective PV strings31, and the current detectors11such as CT sensors which measure output currents I1to Infrom the respective PV strings31are installed thereto. Furthermore, a MCCB23for the PV array30is also installed. The string monitor10collects current values measured by the respective current detectors11, and outputs data to, for example, a monitoring device17such as a PC. In the monitoring device17, the failure is detected based on the taken data by a method described later.

The following explanation is made about a method of detecting the failure from the current value of each PV string31measured by the string monitor10. As described above, in the present embodiment, the temperature property of each PV string31is obtained based on the difference in temperature property between the PV strings31adjacent or close to each other among the plurality of PV strings31arranged to be aligned, and it is determined whether the failure has occurred or not based on the temperature property.

FIG. 4is a diagram showing an example of obtaining the temperature property of the current-voltage property of the plurality of PV strings31arranged to be aligned. For the plurality of PV strings31arranged to be aligned, when the current values of the respective strings are set to I1, I2, I3, . . . , when the voltage values thereof are set to V1, V2, V3, . . . , and when the temperatures thereof are set to T1, T2, T3, . . . , sequentially from a left end in the drawing, it has been known that a temperature property of a current-voltage property for each PV string31and an i-th PV string31can be expressed by the following formulas.

In the formulas for the above-described i-th PV string31, terms Vi, Ii, Ti, and Isiare a voltage of the i-th PV string31, a current thereof, a temperature thereof, and a saturation current thereof in a reverse direction, respectively. Also, a term Ncellis the number of PV cells311included in the PV string31, and terms n, k, and q are constants. Furthermore, a term Iscis a standard short-circuit current, and a term pais a solar radiation amount. The solar radiation amount pacan be presumptively calculated from the following formula.

In the above-described formula, a term Iopis an operating current, a term ISCis a short-circuit current, and a ratio j therebetween is constant. Therefore, if a term Iop_twhich is a total current of the respective PV strings31as a whole can be obtained, an assumed solar radiation amount pacan be calculated.

Here, consideration is made for the difference in temperature property of the current-voltage property expressed by the Mathematical Formula 1 between the i-th PV string31and its adjacent i+1-th PV string31. In this case, as shown inFIG. 4, while the temperature distributions (T1, T2, T3, . . . ) for the respective PV strings31are not uniform, the temperature differences (T2−T1, T3−T2, T4−T3, . . . Ti+1−Ti) between the PV strings31adjacent to each other can be regarded as being small as much as being ignored, and therefore, are regarded as 0, so that the difference in temperature property is approximately expressed by the following formulas.

The formula expressed on the right side of the above-described formula does not include the voltage and the temperature as parameters, and can be obtained only from the current values of the i-th and i+1-th PV strings31. This value, that is, a difference in temperature property expressed on the left side of the above-described formula becomes approximately 0 if each of the i-th and i+1-th PV strings31is normal.

Meanwhile, when one of the adjacent PV strings31includes a PV module310with the failure, a voltage higher than that at the normal state is detected in the PV string31with the failure, and therefore, the value of the difference in temperature property expressed on the left side of the above-described formula is not 0. That is, the value obtained by substituting the current value detected in the PV string31with the failure into the Mathematical Formula 3 is not 0. Therefore, when the value obtained from the Mathematical Formula 3 is not 0, it can be considered that at least one of the i-th and i+1-th PV strings31has the failure so that the temperature property is abnormal.

Therefore, based on this deviation in temperature property, a degree of the deviation in temperature property is calculated by calculating a temperature property in a unit of the PV cell311for each of the i-th and i+1-th PV strings31by using the method as described later, and comparing this calculated result with an assumed temperature property in a unit of the PV cell311. When this degree of the deviation is equal to or larger than a predetermined threshold, it can be estimated that the failure has occurred in any PV module310or PV cell311of this PV string31. Note that the i+1-th PV string31is not necessarily adjacent to the i-th PV string31, and may be a PV string31distant away from the PV string by a plurality of strings as long as the temperature difference can be ignored.

FIG. 5is a diagram showing a general outline about an example of the method of detecting the failure in the above-described PV strings31. On a first row from the top of the drawing, six PV strings31from No. 1 to No. 6 counted from an end in arrangement of the plurality of PV strings31are exemplarily illustrated. Among them, it is presumed that the failure has occurred in a part of the PV cells311of the PV string31of No. 3.

Here, a second row shows the results obtained by calculating values of difference in the temperature property of the current-voltage property between the adjacent PV strings31based on the formula expressed in the above-described Mathematical Formula 3 from the current values measured in the respective PV strings31with i=1 to 6. The example ofFIG. 5shows that a difference between No. 2 and No. 3 (−3 [V/T]) and a difference between No. 3 and No. 4 (+3 [V/T]) are not in a state of 0.

Here, when the temperature property for each PV string31shown on a third row in the drawing is obtained, a difference in temperature property as a reference value is set to 0 [V/T], and the temperature property of the PV string31of No. 1 at the end is temporarily set to a reference value (0 [V/T]), and besides, based on the temperature property, temporal values of the temperature property for the other PV strings31are sequentially obtained. For example, for the PV string31of No. 2 in the drawing, the temporal value of the temperature property of the PV string31of No. 2 is 0 [V/° C.] since the temporal value of the temperature property of the PV string31of No. 1 is 0 [V/° C.] and the difference in temperature property between the PV strings31of No. 1 and No. 2 is 0 [V/° C.].

Furthermore, for the PV string31of No. 3, the temporal value of the temperature property of the PV string31of No. 3 is −3 [V/° C.] since the temporal value of the temperature property of the PV string31of No. 2 is 0 [V/° C.] and the difference in temperature property between the PV strings31of No. 2 and No. 3 is −3 [V/° C.]. Also, for the PV string31of No. 4, the temporal value of the temperature property of the PV string31of No. 4 is 0 [V/° C.] since the temporal value of the temperature property of the PV string31of No. 3 is −3 [V/° C.] and the difference in temperature property between the PV strings31of No. 3 and No. 4 is +3 [V/° C.]. In the following, a temporal temperature property value of each PV string31can be obtained with a similar procedure.

A temperature property value in a unit of the PV cell311as shown on a fifth row in the drawing is calculated by dividing the temporal temperature property value for each PV string31obtained by such a procedure as described above by the number of PV cells311included in the PV string31, calculating a temporal temperature property value ([mV/° C.]) in a unit of the PV cell311as shown on a fourth row in the drawing, and further adding the assumed temperature property value in the PV cell311to the calculated value. Note that the assumed temperature property in the PV cell311can be obtained by the following Mathematical Formula.

In the above-described formula, a term Vocis an open-circuit voltage of the PV string31, and a term Voc/Ncellis obtained by dividing the open-circuit voltage by the number of PV cells311included in the PV string31. Also, a term Ego/q is a bandgap reference voltage, and is set to about 1.25 V in the present embodiment. Since the value of the open-circuit voltage Vocat normal temperature (298 [K]) and the value of the number Ncellof the PV cells311included in the PV string31are known from the specification of the PV module or others, the assumed temperature property in the PV cell311can be previously calculated as a constant value, and is a value such as −2.0 [mV/° C.] in the present embodiment.

The temperature property value for each PV string31and the assumed temperature property value in the PV cell311obtained from the above-described procedure are compared with each other, so that it can be detected that the PV string31includes the PV module310with the failure when the deviation is equal to or larger than the predetermined threshold. The predetermined threshold can be set to a value such as 10% of an absolute value of the assumed temperature property in the PV cell311although not particularly limited thereto.

In this manner, by making the difference in the temperature property of the current-voltage property between the PV strings31adjacent or close to each other, the difference in the temperature distribution at the location in the large-scale system such as the mega solar system can be cancelled. Also, since the difference in the temperature property can be calculated only from current measurement values, it is not required to measure the voltage, so that a work and a facility cost for the measurement can be reduced, and the decrease in the accuracy of detection due to the requirement of the measurement for many parameters can be suppressed.

FIG. 6is a flowchart showing a general outline about an example of a process flow used when the failure detection method for the PV strings31described above is performed. First, by the current detector11of the string monitor10, based on an instruction from the sampling processing unit12, the current of each PV string31is measured (S01). The measured current value is recorded in the memory14via the signal conversion transmission device13.

Then, in the monitoring device or others, the current value recorded in the memory14is obtained via an external storage device or others or via communication, and it is determined whether the PV string31has the failure or not by the procedure described later based on the current value. As described above, not the monitoring device or others but the string monitor10itself may perform the process by using a CPU or others. Here, first, the current values for the respective PV strings31are totalized to calculate a total current (S02). Next, based on the total current value, an assumed solar radiation amount is calculated based on the formula expressed in the above-described Mathematical Formula 2 (S03).

Then, for each of the PV strings31arranged to be aligned, based on the formula expressed in the above-described Mathematical Formula 3, each difference in temperature property of the current-voltage property between the adjacent PV strings31is calculated (S04). As described above, the calculation may be made not only for the adjacent PV strings but also, for example, the PV strings31close to each other intermittently extracted every several ones.

Then, a loop process of sequentially repeating a process for all PV strings31as failure detection targets is started. The PV strings31as the targets here are the PV strings31to which the string monitor10is connected, and may not include all PV strings31in the PV system1.

In the loop process, first, for the PV string31as a process target, a temporal temperature property value is calculated based on a temporal temperature property value obtained by a process as described later for an immediately-previous-target PV string31and on the value of the difference in temperature property from the immediately-previous-target PV string31(S05).

Specifically, as shown inFIG. 5, the temporal temperature property value for the process-target PV string31is calculated by adding the value of the difference in temperature property from the immediately-previous-target PV string31to the temporal temperature property value for the immediately-previous-target PV string31. Note that, when the process-target PV string31is a beginning PV string31, as described above, the value of the reference value for the temporal temperature property (0 [V/° C.] in the present embodiment) is set as a temporal temperature property value of the beginning PV string31.

Next, a temporal temperature property value per the PV cell311is calculated (S06) by dividing the temporal temperature property value calculated for the process-target PV string31at step S05by the number of PV cells311included in the process-target PV string31. Furthermore, a non-temporal temperature property value per the PV cell311is calculated (S07) by adding the assumed temperature property value (−2.0 [mV/° C.] in the present embodiment) of the PV cell311calculated based on the formula expressed in the above-described Mathematical Formula 4 to the temporal temperature property value per the PV cell311.

Then, a difference between the temperature property value per the PV cell311calculated at step S07and the assumed temperature property value (−2.0 [mV/° C.] in the present embodiment) calculated based on the formula expressed in the above-described Mathematical Formula 4 is calculated (S08), and it is determined whether the difference value is smaller than a predetermined threshold or not (S09). When the value is smaller than the predetermined threshold, the process proceeds to a process for a next PV string31in the loop process without doing anything.

On the other hand, when the value is equal to or larger than the predetermined threshold, an alarm notifying of this is outputted (S10). An output form of the alarm is not particularly limited, and can, for example, display a notification message on a screen of the monitoring device, or can transmit the notification message to a predetermined E-mail address. The form may notify of this via voice or others. When the alarm output is completed, the process proceeds to a process for the next PV string31in the loop process. After the process is repeated for all PV strings31in the loop process, the failure detection process ends. Note that the above-described series of processes is desirably performed periodically with, for example, an instruction from the sampling processing unit12of the string monitor10or others as a trigger.

As described above, the PV inspection system having the string monitor10of the first embodiment of the present invention determines the failure by, for example, obtaining a difference in temperature property of the current-voltage property between those adjacent or close to each other for each PV string31, calculating a temperature property of each PV string31based on this difference, and comparing this calculated result and an assumed temperature property. In this manner, even in the large-scale system such as the mega solar system, the influence of the difference in temperature distribution depending on the location can be cancelled. Also, since the value of the difference in temperature property can be calculated only from the current of each PV string31, it is not required to measure the voltage, so that the accuracy of failure detection can be improved while the measurement is facilitated to reduce the cost.

The PV inspection system of the first embodiment described above obtains the solar radiation amount pa, which is a parameter required to calculate the difference in temperature property of the current-voltage property between the PV strings31adjacent or close to each other as an assumed solar radiation amount calculated based on the total current Iop_t, which is a total of currents of the respective PV strings31by the formula expressed in the above-described Mathematical Formula 2.

By contrast, a PV inspection system of a second embodiment of the present invention practically measures and obtains the solar radiation amount paby an actinometer or others in order to reduce the influence of the difference in the distribution of the solar radiation amount depending on the location on the mega solar system and to more improve the accuracy of failure determination.

FIG. 7is a diagram showing a general outline of an example of structure of a PV system1having a PV inspection system of the second embodiment of the present invention. In addition to the structure of the PV system1of the first embodiment shown inFIG. 1, the string monitor10of the present embodiment further has an I/O unit15which inputs/outputs a signal to/from an external device and an actinometer16connected thereto. In this manner, information about the solar radiation amount measured by the actinometer16can be used at the time of the process of failure detection.

FIG. 8is a flowchart showing an example of a process flow used when the failure detection method for the PV strings31in the present embodiment is performed. Here, the processes at steps S02and S03in the process procedure of the first embodiment shown inFIG. 6, that is, the process of calculating the total current which is the total of currents of all the target PV strings31and the process of calculating the assumed solar radiation amount pabased on the total current are replaced by a process of practically measuring and obtaining the solar radiation amount paby the actinometer16(S20). The other processes (S01and S04to S10) are similar to the process procedure of the first embodiment shown inFIG. 6, and therefore, repetitive description thereof is omitted.

In this manner, in place of the assumed solar radiation amount pacalculated from the total current of the PV strings31, by using the solar radiation amount practically measured by the actinometer16as the solar radiation amount pafor the PV strings31, the accuracy of failure detection can be improved. Note that the number of actinometers16is not limited to one, and a plurality of actinometers16may be set so as to correspond to the respective regions of the PV strings31. In this case, the solar radiation amount measured by each actinometer16can be used as the solar radiation amount pafor the PV string31in the corresponding region.

In the PV inspection systems of the first and second embodiments described above, a current value of each PV string31is measured by the fixed or portable string monitor10, and the difference in temperature property of the current-voltage property between the PV strings31adjacent or close to each other is calculated based on the measurement result. However, this case requires the current detector11for measuring the current values of all PV strings31in the target PV array30. Therefore, in the case of the fixedly setting to the connection box20, a setting space is required. Moreover, even in the case of the portable type, since the size of the string monitor10is increased and since many current detectors11are simultaneously set at the time of measurement, setting error tends to occur.

Thus, a PV inspection system of a third embodiment of the present invention has the string monitor10of the portable type, and has only two current detectors11such as CT sensors. In the present embodiment, the current values of a pair of the PV strings31adjacent or close to each other are each measured by the two current detectors11, and the difference in temperature property of the current-voltage property in this pair is calculated by the method described above. Then, an operator shifts the pair of the measurement-target PV strings31one by one, and performs the similar measurement thereto. By sequentially performing this operation to all the measurement-target PV strings31, processes equivalent to the processes up to step S04inFIG. 6orFIG. 8described above can be performed. Thereafter, the failure can be detected by processes similar to those at step S05inFIG. 6orFIG. 8and subsequent steps.

FIG. 9andFIG. 10are diagrams each showing a general outline of an example of structure of a PV system having the PV inspection system of the third embodiment of the present invention. A difference from the PV system inFIG. 1in the above-described first embodiment is that the string monitor10has only two current measuring devices11. The example ofFIG. 9shows the state in which two current values (I1and I2) named sequentially from the left side are measured among the PV strings31of the PV array30. The example ofFIG. 10shows the state in which current values (I2and I3) are measured by shifting the pair of the measurement-target PV strings31by one from the example ofFIG. 9.FIG. 11andFIG. 12are diagrams corresponding to the examples ofFIG. 9andFIG. 10, respectively, and each schematically showing a general outline of a specific example of structure at the time of inspection.

In this manner, the operator sequentially shifts the pair of the measurement-target PV strings31to measure the current values, and calculates the difference in temperature property of the current-voltage property, so that the results functionally similar to those of the first and second embodiments can be obtained. Also, in the present embodiment, by using the portable string monitor10having only two current measuring devices11, the setting space of the string monitor10can be reduced, so that the PV system can be configured as being compact.

In the foregoing, the invention made by the inventors of the present invention has been concretely described based on the embodiments. However, it is needless to say that the present invention is not limited to the foregoing embodiments and various modifications and alterations can be made within the scope of the present invention. For example, the above-described embodiments have been explained for easily understanding the present invention, but are not always limited to the ones including all structures explained above. Also, a part of the structure of one embodiment can be replaced with the structure of the other embodiment, and besides, the structure of the other embodiment can be added to the structure of one embodiment. Further, the other structure can be added to/eliminated from/replaced with a part of the structure of each embodiment.

Also, each structure, function, processing unit, processing means, and others described above may be partially or entirely achieved by hardware by, for example, designing as an integrated circuit. Also, each structure, function, and others described above may be achieved by such a software as causing a processor to interpret and execute a program which achieves each function. Information about the program, a table, a file, and others achieving each function can be placed on a recording device such as a memory, a hard disk, or an SSD (Solid State Drive), or on a recording medium such as an IC card, an SD card, or a DVD.

Furthermore, each of the above-described drawings shows a control line and an information line considered as being required for description, and all control lines and information lines for the performance are not always shown. Practically, almost all structures may be considered as being connected to each other.

The present invention can be used in a PV inspection system and a PV inspection method of detecting a failure of a PV module or string.