Abstract:
A data collection device for photovoltaic power generation is provided. The data collection device according to an embodiment includes a receiver that receives data on an amount of photovoltaic power generation, a storage unit that stores a representative pattern of a graph for monitoring the amount of photovoltaic power generation, a control unit that extracts a graph for a first piece of data on the amount of photovoltaic power generation received by the receiver and compares the extracted graph with the representative pattern stored in the storage unit to extract a pattern comparison value, and a transmitter that transmits the first piece of data compared by the system control unit to an external device.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    Pursuant to 35 U.S.C. §119(a), this application claims the benefit of earlier filing date and right of priority to Korean Patent Application No. 10-2015-0014856, filed on Jan. 30, 2015 the contents of which are all hereby incorporated by reference herein in its entirety. 
       BACKGROUND 
       [0002]    The present disclosure relates to a photovoltaic device, and particularly to, a device that monitors a photovoltaic power generation result value. 
         [0003]    Due to worries about the exhaustion of fossil energy, such as oil and environmental pollution, interest in alternative energy increases. Among others, photovoltaic power generation that uses solar energy to produce electricity on a large scale by spreading, on a large scale, panels to which solar batteries are attached. The photovoltaic power generation has advantages in that there is no need to consume fuel costs and there is no air pollution or waste, because it uses unlimited, pollution-free solar energy. 
         [0004]    A solar energy power generation style includes an independent style and a system-associated style. In the system-associated style, a photovoltaic device is connected to a typical power system. When a photovoltaic system generates electricity in daytime, it transmits power and at night or when it rains, the photovoltaic power generation system receives electricity from a system. In order to efficiently use the system-associated photovoltaic system, a photovoltaic system has been introduced which stores idle power in a battery energy storage system (BESS) under a light load, and discharges the BESS to supply discharged power as well as photovoltaic power to the system under a heavy load. 
       SUMMARY 
       [0005]    Embodiments provide a photovoltaic device that delivers minimum data for making a graph to increase monitoring efficiency under the assumption that a daily power generation amount graph of photovoltaic power generation has a certain pattern. 
         [0006]    In one embodiment, a data collection device for photovoltaic power generation includes a receiver receiving data on an amount of photovoltaic power generation; a storage unit storing a representative pattern of a graph for monitoring the amount of photovoltaic power generation; a control unit making a graph for monitoring the amount of photovoltaic power generation based on a first piece of data on the amount of photovoltaic power generation received by the receiver and the representative pattern stored in the storage unit; and a transmitter transmitting the graph made by the control unit to an external device. 
         [0007]    The control unit may compare the first piece of data with the representative pattern, select a most similar representative pattern as a result of comparison, and make a graph. 
         [0008]    The control unit may make a graph based on a graph pattern selected when recently making a graph, when as a result of comparison, a selectable representative pattern is in plurality. 
         [0009]    The receiver may further receive a second piece of data on photovoltaic power generation, and 
         [0010]    the second piece of data may include an exceptional section start time, an exceptional section end time, and a minimum amount of power generation within an exceptional section. 
         [0011]    The control unit may compare the second piece of data with a second representative pattern stored in the storage unit ( 317 ) to modify an entire graph. 
         [0012]    The control unit may receive power generation amount data on all exceptional sections to make the entire graph, when the second piece of data is in plurality. 
         [0013]    The first piece of data may include a time at which power generation starts, a time at which power generation ends, and a maximum amount of power generation. 
         [0014]    In another embodiment, a photovoltaic system includes a photovoltaic device absorbing and converting solar energy into electrical energy and transmitting converted photovoltaic power generation amount and related data; and a solar data collection device comparing the photovoltaic power generation amount and related data received from the photovoltaic device and making a graph for monitoring photovoltaic power generation based on a result of comparison. 
         [0015]    The photovoltaic system may further include an external device that controls the solar data collection device and collects data from the photovoltaic device. 
         [0016]    The external device may make a graph for monitoring photovoltaic power generation based on the data collected from the photovoltaic device. 
         [0017]    The external device may provide a user with the data collected from the photovoltaic device or the graph for monitoring photovoltaic power generation. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]      FIG. 1  is a block diagram of a system-associated photovoltaic device according to an embodiment. 
           [0019]      FIG. 2  is a block diagram of a small-capacity system-associated photovoltaic device according to an embodiment. 
           [0020]      FIG. 3  is a flowchart of the operation of a system-associated photovoltaic device according to an embodiment. 
           [0021]      FIG. 4  is a block diagram of a system-associated photovoltaic device according to another embodiment. 
           [0022]      FIG. 5  is a block diagram that represents the configuration of a photovoltaic system. 
           [0023]      FIG. 6  is a block diagram that represents the configuration of a data collection device. 
           [0024]      FIG. 7  is a diagram that represents a result of monitoring of photovoltaic power generation using a typical method. 
           [0025]      FIG. 8  is a flowchart of monitoring an amount of photovoltaic power generation according to an embodiment. 
           [0026]      FIG. 9  is a diagram that represents how to make a power generation graph based on a representative pattern. 
           [0027]      FIGS. 10 and 11  represent processes of monitoring when received data includes additional values other than a maximum amount of power generation. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0028]    Embodiments are described below in detail with reference to the accompanying drawings so that a person skilled in the art may easily practice the embodiments. However, the present disclosure may be implemented in many different forms and is not limited to embodiments that are described herein. In addition, parts irrelevant to descriptions are not provided in the drawings in order to make the present disclosure clear and similar parts throughout the disclosure have similar reference numerals. 
         [0029]    Also, when it is described that a part includes some components, it should be understood that it may not exclude but further include other components if there is no specific objection. 
         [0030]    In the following, a system-associated photovoltaic device according to an embodiment is described with reference to  FIGS. 1 to 3 . 
         [0031]      FIG. 1  is a block diagram of a system-associated photovoltaic device according to an embodiment. 
         [0032]    A system-associated photovoltaic device  100  according to an embodiment includes a solar battery array  101 , an inverter  103 , an alternating current (AC) filter  105 , an AC/AC converter  107 , a system  109 , a charging control unit  111 , a battery energy storage system  113 , and a system control unit  115 . 
         [0033]    The solar battery array  101  is obtained by coupling a plurality of solar battery modules. The solar battery module is a device in which a plurality of solar batteries is connected in series or parallel to convert solar energy into electrical energy to generate a certain voltage and current. Thus, the solar battery array  101  absorbs solar energy to convert it into electrical energy. 
         [0034]    The inverter  103  inverts direct current (DC) power into AC power. It receives the DC power supplied by the solar battery array  101  or the DC power discharged by the battery energy storage system  113  through the charging control unit  111  to invert them into AC power. 
         [0035]    The AC filter  105  filters the noise of power inverted into the AC power. 
         [0036]    The AC/AC converter  107  converts the size of a voltage of the AC power devoid of noise, and supplies the converted power to the system  109 . 
         [0037]    The system  109  is a system that incorporates many power stations, substations, power transmission and distribution cables, and loads to generate and use power. 
         [0038]    The charging control unit  111  controls the charging and discharging of the battery energy storage system  113 . When the system is a heavy load, the charging control unit  111  receives power from the battery energy storage system  113  and delivers it to the system. When the system is a light load, the charging control unit  111  receives power from the solar battery array  101  and delivers it to the battery energy storage system  113 . 
         [0039]    The battery energy storage system  113  receives electrical energy from the solar battery array  101  for charging and discharges the charged electrical energy according to the power supply and demand condition of the system  109 . In particular, in the case that the system  109  is a light load, the battery energy storage system  113  receives idle power from the solar battery array  101  for charging. When the system  109  is a heavy load, the battery energy storage system  113  discharges charged power to supply power to the system  109 . The power supply and demand condition of the system has a big difference according to the time zone. Thus, it is inefficient that the system-associated photovoltaic device  100  uniformly supplies the power supplied by the solar battery array  101  without consideration of the power supply and demand condition of the system  109 . Therefore, the system-associated photovoltaic device  100  uses the battery energy storage system  113  to adjust an amount of power supply according to the power supply and demand of the system  109 . Accordingly, the system-associated photovoltaic device  100  may efficiently supply power to the system  109 . 
         [0040]    The system control unit  115  controls the operations of the charging control unit  111 , the inverter  103 , the AC filter  105 , and the AC/AC converter  107 . 
         [0041]    The sensor unit  116  senses other elements related to photovoltaic power generation. In this case, the sensor unit  116  may include any one of a sunshine sensor and a temperature sensor. In a particular embodiment, the sensor unit  116  may sense sunshine while photovoltaic power generation is performed. In another embodiment, the sensor unit  116  may sense temperature while photovoltaic power generation is performed. 
         [0042]      FIG. 2  is a block diagram of a small-capacity system-associated photovoltaic device according to an embodiment. 
         [0043]    A small-capacity system-associated photovoltaic device  200  according to an embodiment includes a solar battery array  101 , an inverter  103 , an AC filter  105 , an AC/AC converter  107 , a system  109 , a charging control unit  111 , a battery energy storage system  113 , a system control unit  115 , and a DC/DC converter  117 . 
         [0044]    The present embodiment is the same as the embodiment in  FIG. 1  but further includes the DC/DC converter  117 . The DC/DC converter  117  converts the voltage of DC power generated by the solar battery array  101 . The voltage of power produced by the solar battery array  101  in the small-capacity system-associated photovoltaic device  200  is low. Thus, there is a need to boost the voltage in order to input power supplied by the solar battery array  101  to the inverter. The DC/DC converter  117  converts the voltage of power produced by the solar battery array  101  into a voltage that may be input to the inverter  103 . 
         [0045]      FIG. 3  is a flowchart of the operation of a system-associated photovoltaic device according to an embodiment. 
         [0046]    The solar battery array  101  converts solar energy into electrical energy in step S 101 . 
         [0047]    The system control unit  115  determines whether there is a need to supply power to the system  109 , in step S 103 . Whether there is a need to supply power to the system  109  may be determined based on whether the system  109  is a heavy load or light load. 
         [0048]    When there is no need to supply power to the system  109 , the system control unit  115  controls the charging control unit  111  to charge the battery energy storage system  113 , in step S 105 . In particular, the system control unit  115  may generate a control signal that controls the charging control unit  111 . The charging control unit  111  may receive the control signal to charge the battery energy storage system  113 . 
         [0049]    The system control unit  115  determines whether there is a need to discharge the battery energy storage system  113 , in step S 107 . It is possible to determine whether there is a need to discharge the battery energy storage system  113  because electrical energy supplied by the solar battery array  101  fails to satisfy the power demand of the system  109 . Also, the system control unit  115  may determine whether the battery energy storage system  113  stores sufficient electrical energy to be discharged. 
         [0050]    When there is a need to discharge the battery energy storage system  113 , the system control unit  115  controls the charging control unit  111  to discharge the battery energy storage system  113 , in step S 109 . In particular, the system control unit  115  may generate a control signal that controls the charging control unit  111 . The charging control unit  111  may receive the control signal to discharge the battery energy storage system  113 . 
         [0051]    The inverter  103  inverts electrical energy discharged by the battery energy storage system  113  and electrical energy converted by the solar battery array  101  into AC, in step S 111 . In this case, the system-associated photovoltaic device  100  inverts both the electrical energy discharged by the battery energy storage system  113  and the electrical energy converted by the solar battery array  101  through a single inverter  103 . Each electric appliance has a limit in consumption power. The limit includes an instantaneous limit and a long-term limit, and maximum power that may be used without damage to a device for a long time is defined as rated power. In order to maximize the efficiency of the inverter  103 , there is a need to supply power so that the battery energy storage system  113  and the solar battery array  101  use power corresponding to 40% to 60% of the rated power. 
         [0052]    The AC filter  105  filters the noise of inverted power, in step S 113 . 
         [0053]    The AC/AC converter  107  converts the size of a voltage of the filtered AC power to supply the converted power to the system  109 , in step S 115 . 
         [0054]    The system-associated photovoltaic device  100  supplies converted power to the system in step S 117 . 
         [0055]    Since the system-associated photovoltaic device  100  according to the embodiments in  FIGS. 1 to 3  uses only a single inverter  103 , there are following limitations when the rated power of the inverter  103  is determined based on the capacity of the solar battery array  101  in order to design the system-associated photovoltaic device  100 . When the battery energy storage system  113  discharges electricity and thus supplies electrical energy along with the solar battery array  101 , it is difficult to maximize the efficiency of the inverter  103  because the inverter  103  uses power exceeding 40% to 60% of the rated power. Alternatively, when the battery energy storage system  113  discharges electricity and thus supplies electrical energy solely, it is difficult to maximize the efficiency of the inverter  103  because the inverter  103  uses power less than 40% to 60% of the rated power. Besides, when the battery energy storage system  101  supplies a little amount of electrical energy, it is difficult to maximize the efficiency of the inverter  103  because the inverter  103  uses power less than 40% to 60% of the rated power. In this case, the efficiency with which the system-associated photovoltaic device  100  converts solar energy into electrical energy decreases. Also, since the total harmonic distortion (THD) of power increases, the quality of power that the system-associated photovoltaic device  100  produces goes down. 
         [0056]      FIG. 4  is a block diagram of a system-associated photovoltaic device according to another embodiment. 
         [0057]    A system-associated photovoltaic device  500  according to another embodiment includes a solar battery array  501 , a first inverter  503 , an AC filter  505 , an AC/AC converter  507 , a system  509 , a control switch  511 , a charging control unit  513 , a battery energy storage system  515 , a system control unit  517 , and a second inverter  519 . Also, it is possible to further include a sensor unit  116 . 
         [0058]    The solar battery array  501  is obtained by coupling a plurality of solar battery modules. The solar battery module is a device in which a plurality of solar batteries is connected in series or parallel to convert solar energy into electrical energy to generate a certain voltage and current. Thus, the solar battery array  501  absorbs solar energy to convert it into electrical energy. 
         [0059]    The first inverter  503  inverts DC power into AC power. It receives the DC power supplied by the solar battery array  501  or the DC power discharged by the battery energy storage system  515  through the charging control unit  513  to invert them into AC power. 
         [0060]    The AC filter  505  filters the noise of power inverted into the AC power. 
         [0061]    In order to be capable of supplying AC power to the system, the AC/AC converter  507  converts the size of a voltage of the AC power devoid of noise and supplies the converted power to the system  509 . 
         [0062]    The system  509  is a system that incorporates many power stations, substations, power transmission and distribution cables, and loads to generate and use power. 
         [0063]    The control switch  511  adjusts the flow of power supply between the battery energy storage system  515  and the first inverter  503 . The control switch  511  receives a control signal from the system control unit  517  to operate according to the control signal. In particular, when the battery energy storage system  515  discharges electricity to supply power to the first inverter  503 , the system control unit  517  generates a control signal that connects the control switch  511  and the first inverter  503 . The control switch  511  receives the control signal to connect the charging control unit  513  and the first inverter  503 . When power is not supplied to the first inverter  503 , the system control unit  517  generates a control signal that disconnects the control switch  511  from the first inverter. The control switch  511  receives the control signal to be disconnected from the first inverter  503 . 
         [0064]    The charging control unit  513  controls the charging and discharging of the battery energy storage system  515 . When the system is a heavy load, the charging control unit  513  receives power from the battery energy storage system  515  and delivers it to the system. In this case, the charging control unit  513  may supply power to any one of the first inverter or the second inverter  519  or to both the first inverter  503  and the second inverter  519 . When the system is a light load, the charging control unit  513  receives power from the solar battery array  501  and delivers it to the battery energy storage system  515 . 
         [0065]    The battery energy storage system  515  receives idle power from the solar battery array  501  for charging, when the system is the light load. The battery energy storage system  515  discharges charged power to supply power to the system  509 , when the system is the heavy load. As described in the embodiments in  FIGS. 1 to 3 , the system-associated photovoltaic device  500  may use the battery energy storage system  515  to efficiently power to the system  509 . 
         [0066]    The system control unit  517  controls the operations of the charging control unit  513 , the first inverter  503 , the second inverter  519 , the AC filter  505 , and the AC/AC converter  507 . 
         [0067]    Unlike the embodiments in  FIGS. 1 to 3 , the embodiment in  FIG. 4  further includes the second inverter  519  that is connected to the battery energy storage system  515 . 
         [0068]    The second inverter  519  inverts DC power into AC power. It receives the DC power discharged by the battery energy storage system  515  through the charging control unit  513  and inverts the received DC power into AC power. By including the second inverter  519  besides the first inverter  503 , the first inverter or the second inverter selectively operates according to the size of power supplied by the system-associated photovoltaic device  500 . 
         [0069]      FIG. 5  is a block diagram that represents the configuration of a photovoltaic system  1 . 
         [0070]    Referring to  FIG. 5 , a solar inverter  103  may be included in the photovoltaic device  100 . Since the solar inverter  103  has been described above in detail, related descriptions are omitted in  FIG. 5 . The solar inverter  103  may exist in singularity or in plurality in the photovoltaic device  100 . The photovoltaic inverter  103  may deliver an amount of photovoltaic power generation to a data collection device  300 . 
         [0071]    The sensor unit  116  of the photovoltaic device  100  may deliver sensed data along with the amount of photovoltaic power generation to the data collection device  300 . In an embodiment, the sensed data may include at least one of sunshine, temperature, sunrise/sunset time, and a weather condition. The photovoltaic device may deliver power generation time information along with the above-described data to the data collection device  300 . 
         [0072]    The data collection device  300  receives and synthesizes data from a lower inverter  103  and the photovoltaic device  100 . The data collection device  300  may be a component in the photovoltaic device  100  or may be a separate component that is connected to a plurality of photovoltaic devices  100 . The data collection device  300  may provide the collected power generation information to users or clients for monitoring. Also, when there is a upper server  400  connected to the plurality of data collection devices  300 , it is possible to deliver the collected power generation information to the upper server  400 . 
         [0073]    In the following, the data collection device  300  is described in detail with reference to  FIG. 6 . 
         [0074]    The data collection device  300  may include a control unit  315 , a transceiver  316 , a storage unit  317 , and an output unit  318 , as shown in  FIG. 5 . However, the embodiment is not limited to components in  FIG. 5  and may further include other components as needed. 
         [0075]    The transceiver  316  receives photovoltaic power generation related data from the photovoltaic device  100  that includes the inverter  103  and various sensors (not shown). A reception method may include both wired and wireless communication methods. When the data collection device  300  is a component in the photovoltaic device  100 , it is possible to receive data through a circuit that is connected to between internal components. In particular, the transceiver  316  may receive an amount of photovoltaic power generation from the inverter  103  and deliver the received amount of power generation to the control unit  315 . 
         [0076]    Also, the transceiver  316  may transmit the collected photovoltaic power generation data to the upper server  400 . Likewise, it is possible to transmit the data to the upper server  400  through wired/wireless communication. 
         [0077]    Also, the transceiver  316  may also transmit the amount of photovoltaic power generation to users and clients. In particular, it is possible to transmit information for monitoring the amount of power generation to the owner of the photovoltaic device  100  or to an electricity dealer. 
         [0078]    Also, the transceiver  316  may also be divided into a transceiver and a receiver. 
         [0079]    The storage unit  317  stores the collected power generation data. Photovoltaic power generation is performed everyday, and the data collected by the data collection device  300  is stored in the storage unit  317  for the time being and transmitted to another place. The data stored in the storage unit  317  may be utilized for decreasing transmission data to be described below. 
         [0080]    Also, the storage unit  317  stores a representative pattern of a graph that may be referred to in order to make a graph for monitoring an amount of photovoltaic power generation. The stored representative pattern may be in singularity or in plurality with respect to each condition. 
         [0081]    The output unit  318  may display data for monitoring the amount of photovoltaic power generation. The output unit may include a display unit that visually displays data, and a speaker that auditorily outputs data. 
         [0082]    The control unit  315  controls the operations of the above-described transceiver  316 , storage unit  317 , and output unit  318 . Furthermore, the control unit  315  may process the received data to generate difference data. How to process the data is described below in detail. 
         [0083]    Refer back to  FIG. 5 . 
         [0084]    The photovoltaic system  1  may include the upper server  400  to which the plurality of data collection devices  300  are connected. The upper server  400  may synthesize and collect photovoltaic power generation information that is delivered from the plurality of data collection devices  300 . In a small-scale photovoltaic system  1 , the upper server  400  may not separately exist and the data collection device  300  may also function as the upper server. 
         [0085]    An administrator may efficiently manage and control a corresponding system, when operating a large-scale photovoltaic system through the upper server  400 . The upper server  400  may control both the lower data collection device  300  and the photovoltaic device  100 , and by collecting data from a plurality of photovoltaic devices, it is possible to compare amounts of power generation of the power generation devices  100  and control malfunction. Also, the upper server  400  may provide the data received from the photovoltaic device  100  or the data collection device  300  and a graph for monitoring to users. For example, the upper server  400  may provide the amount of photovoltaic power generation and related data received from the data collection device  300  to users. Also, the upper server  400  may provide users with the graph for monitoring that is received from the data collection device  300 . Also, the upper server  400  may make the graph for monitoring based on the amount of photovoltaic power generation and related data that is received from the data collection device  300 , and provide the graph to users. 
         [0086]      FIG. 7  is a diagram that represents a result of monitoring of photovoltaic power generation using a typical method. 
         [0087]    For the monitoring of the photovoltaic power generation, the data collection device  300  has typically collected data needed for monitoring from a solar inverter and various sensors. In addition, the control unit  315  of the data collection device  300  may provide users with a result of monitoring that is based on the collected data, or deliver the result of monitoring to the upper server. 
         [0088]    However, the data collection device  300  has typically collected an amount of photovoltaic power generation at a certain time interval (e.g., every five minutes) to monitor the amount of photovoltaic power generation, as shown in  FIG. 7 . When a typical method is used, there is an advantage in accuracy because an amount of power generation is continuously received at a short interval. 
         [0089]    According to the typical method, a transmission data amount increases because all amounts of power generation are transmitted at intervals. Thus, communication charge increases in proportion to the increased data amount. Also, in the case of transmission using wireless communication, there are limitations in that a situation in which it is difficult to transmit data occurs or extra money is needed to install an amplifier in order to supplement low communication quality, when transmission is performed in a region where communication quality is low. 
         [0090]    In the following, a photovoltaic device that supplements typical limitations is described with reference to  FIGS. 8 to 11 . 
         [0091]      FIG. 8  is a flowchart of monitoring an amount of photovoltaic power generation according to an embodiment. 
         [0092]    The transceiver  316  of the data collection device  300  receives only specific partial data on photovoltaic power generation from the inverter  103  of the photovoltaic device  100 , in step S 301 . The specific data may be a time at which power generation starts, a time at which power generation ends, and a maximum amount of power generation. Furthermore, it is also possible to receive position information on the photovoltaic device. The position information may be latitude and longitude information. By receiving only minimum data and not entire data on an amount of photovoltaic power generation, it is possible to reduce communication charge for data delivery. Also, even when communication quality is low, it is possible to reduce the burden of data delivery because there is a little amount of data. 
         [0093]    In another embodiment, the transceiver  316  may also receive only a maximum amount of power generation. In particular, the times at which power generation starts and ends may be found based on previously input position data on the photovoltaic device. Since photovoltaic power generation is directly concerned in sunrise and sunset times, it is possible to find sunrise and sunset times according to the position data to infer the time at which power generation starts and ends. 
         [0094]    In an embodiment, the control unit  315  of the data collection device  300  may use pre-stored position information to find the times at which power generation starts and ends with reference to a table related to sunrise and sunset. Since data on sunrise and sunset is already accumulated for each region, it is possible to put and use the data into a table. The table may be stored in the storage unit  317 . In this case, the data collection device  300  may receive, along with power generation amount information, information for identifying a power generation device transmitting the power generation amount information and the control unit  315  may obtain position information on the photovoltaic device  100  based on identification information. 
         [0095]    In another embodiment, the control unit  315  may calculate sunrise and sunset times based on position information. The control unit  315  may find times at which photovoltaic power generation starts and ends by using an algorithm that calculates sunrise and sunset according to latitude, longitude, and a date. 
         [0096]    The control unit  315  calls a representative pattern of a photovoltaic power generation amount graph from the storage unit  121 , in step S 311 . This process is described in more detail with reference to  FIG. 9 . 
         [0097]      FIG. 9  is a diagram that represents how to make a power generation amount graph based on a representative pattern. 
         [0098]    Referring to  FIG. 9 , a pattern A, a pattern B, and a pattern C may be stored in the storage unit as representative patterns in an embodiment. Regarding the number of stored patterns, a relatively large number of patterns may be stored in a region where climate frequently varies (e.g., Korea) and a relatively small number of patterns may be stored in a region where climate rarely varies (e.g., desert). Corresponding patterns may be stored upon the initial system design or may be newly stored according to a position at which the photovoltaic device is installed, during operation. 
         [0099]    The pattern A is a pattern in which a time at which power generation starts is earliest and values close to a maximum amount of power generation are maintained for a long time. A corresponding pattern may be a power generation amount pattern that corresponding to summer in which there is a lot of sunshine and day is relatively long. The pattern C is a pattern in which the time at which power generation starts is latest and values close to a maximum amount of power generation are short. A corresponding pattern may be a power generation amount pattern that corresponding to winter in which there is less sunshine and day is relatively short. 
         [0100]    Since an amount of photovoltaic power generation fundamentally varies according to sunshine, it is possible to empirically perceive that daily power generation amount has almost the same pattern. Thus, it is possible to store representative patterns in the storage unit  317 , receive only representative values that may select patterns, and select patterns closest to the received representative values to make a graph for monitoring. 
         [0101]    Refer back to  FIG. 8 . 
         [0102]    The control unit  315  compares the received time at which power generation starts, the received time at which power generation ends, and the received maximum amount of power generation with a graph called from the storage unit  317 , in step S 321 . In particular, since each stored pattern has times at which power generation starts and ends as characteristics, it is possible to compare the received data with stored patterns to select the most similar pattern. For example, when the times at which power generation starts and ends have smallest differences from the pattern A, the control unit  315  may select the pattern A. 
         [0103]    In another embodiment, the control unit  315  may preferentially select a graph that has been selected most recently, when received data has a difference difficult to distinguish from two or more patterns. For example, when the currently received data has an intermediate value between the patterns A and B and thus it is difficult to select, it is possible to select the pattern B as a result of comparison if a graph for monitoring is made based on the pattern B for the past one week. 
         [0104]    The control unit  315  makes a graph for monitoring base don a result of comparing the received specific data with a graph pattern called from the storage unit  317 , in step S 331 . In an embodiment, a corresponding graph may be made in the photovoltaic device  100 . In another embodiment, the corresponding graph may be made through a higher server. In the latter case, the photovoltaic device  100  may transmit the made graph, and it may transmit only specific data for making the graph and the higher server may select a graph pattern to make the graph. 
         [0105]      FIGS. 10 and 11  represent processes of monitoring when received data includes additional values other than a maximum amount of power generation. 
         [0106]    In the process in which the control unit  315  compares the received data with a graph in step S 321  in  FIG. 8 , it is determined whether there are values other than the maximum amount of power generation in data, in step S 322 . Since an amount of photovoltaic power generation fundamentally has almost a constant pattern, it is possible to make a rough graph if there is data on a maximum amount of power generation, and there may be sections that represent accidental values according to a climate condition. For example, in the case that it has rained from 9 AM to 11 AM, sunshine decreases while it rains and thus an amount of power generation has no choice but to decrease in proportion thereto. In this case, since there are sections that have different values from stored patterns, there may be a need to make a graph to reflect it. 
         [0107]    In an embodiment, when it is determined that there are no values other than a maximum amount of power generation, the control unit  315  returns to step S 331  to make a graph. 
         [0108]    In another embodiment, the control unit  315  determines that there are values other than the maximum amount of power generation, a graph model for an exceptional situation is called from the storage unit  317 , in step S 323 . For example, the graph for the exceptional situation may be a pattern for a rainy situation or a cloudy situation. The storage unit  317  may store a representative pattern for each weather situation based on accumulated data. 
         [0109]    The control unit  315  compares another of the received values with the graph for the exceptional situation that is called from the storage unit  317 , in step S 314 . In an embodiment, the received data may be data on from a time at which power generation starts to a time at which an amount of power generation decreases before reaching the maximum amount of power generation. Also, it may be data on a time at which the amount of power generation recovers since a time at which the amount of power generation decreases. In addition, it may be data on a minimum amount of power generation in each exceptional situation section. 
         [0110]    The system control unit  315  may compare information on a section where there is a variation in amount of power generation, with the data on the minimum amount of power generation to select a closest pattern. 
         [0111]    In an embodiment, when data on the exceptional section matches with a representative pattern, a corresponding pattern is selected to modify the graph of the exceptional section in step S 325 . In particular, it is possible to apply a minimum value to the received exceptional section to employ a matching graph pattern to modify the entire graph. 
         [0112]    The above steps are described in more detail with reference to  FIG. 11 . 
         [0113]    As shown in  FIG. 11 , a section #1 at which an amount of photovoltaic power generation varies may be represented in an embodiment according to a weather condition. In this case, the control unit  315  may receive data on the start time of #1, the end time of #1, and the minimum amount of power generation of #1 through the transceiver  316 . The control unit  315  may call a graph pattern for an exceptional situation from the storage unit as described above, and make a power generation amount graph for monitoring according to the most similar pattern. 
         [0114]    In another embodiment, there may be no matching patterns as a result of comparing a value for the exceptional section with a representative pattern for the exceptional situation. For example, there may be a case where it is difficult to accurately make a graph with only a minimum power generation value because the exceptional section has a significant variation in amount of power generation. In this case, the control unit  315  receives all data on the exceptional section through the transceiver  316  in step S 326 . 
         [0115]    In particular, referring to  FIG. 11 , the control unit  315  receives data on an entire amount of power generation from the start time of #1 to the end time of #1 through the transceiver  316 . In this case, there is a burden to have to receive more data than when referring to a representative pattern of a graph, but by receiving only data on some sections without receiving data on all sections in a typical manner, it is possible to make a graph almost matching with actual data by using relatively less data. 
         [0116]    Referring back to  FIG. 10 , data on an exceptional section is received to modify the entire graph in the same manner in step S 325 . The process of making the graph in  FIG. 10  may also be performed within the photovoltaic device  100  or by a higher server. 
         [0117]    The data monitoring method as described above may be used for all data that has a constant pattern, such as sunshine or temperature, as well as an amount of photovoltaic power generation. 
         [0118]    When delivering data on the amount of photovoltaic power generation, it is possible to roughly monitor an amount of power generation even without delivering all data, thereby reducing communication charge and efficiently performing monitoring in a region where communication is not easily allowed. 
         [0119]    The characteristics, structures, and effects described in the embodiments above are included in at least one embodiment but are not limited to one embodiment. Furthermore, the characteristic, structure, and effect illustrated in each embodiment may be combined or modified for other embodiments by a person skilled in the art. Thus, it would be construed that contents related to such a combination and such a variation are included in the scope of embodiments. 
         [0120]    Embodiments are mostly described above. However, they are only examples and do not limit the present disclosure. A person skilled in the art may appreciate that many variations and applications not presented above may be implemented without departing from the essential characteristic of embodiments. For example, each component particularly represented in embodiments may vary. In addition, it should be construed that differences related to such a variation and such an application are included in the scope of the present disclosure defined in the following claims.