Power storage system, power supply system and control method

Abstract

To provide a power storage system, a power supply system and a control method which can maximize generated power depending on weather to improve economical efficiency.SOLUTION: A power storage system comprises: a power conversion unit which supplies generated power by a power generator to a load and a system; a charging unit which charges a storage battery by the generated power; and a control unit which controls the power conversion unit and the charging unit, wherein the control unit controls the charging unit to charge the storage battery by first surplus power exceeding power to be supplied to the load and the system of the generated power when the generated power is larger than a predetermined reference value, the generated power depends on weather, the maximum value of the generated power is larger than an upper limit value of power which can be supplied from the power conversion unit to the load and the system in system interconnection, and the reference value is equal to or less than the upper limit value.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present disclosure relates to a power storage system, a power supply system, and a control method. [Background technology]

[0002] Hybrid power storage systems are known. For example, Patent Document 1 below discloses a system that includes a solar cell, a storage battery, and a power conditioner. The power conditioner converts DC power generated by the solar cell into AC power and supplies it to a load, and also charges the storage battery with the power generated by the solar cell. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-161189 Summary of the Invention [Problem to be solved by the invention]

[0004] In a hybrid energy storage system, the power conditioner includes one DC / AC converter and one DC / DC converter for the battery, but may also include multiple DC / DC converter circuits for photovoltaic power generation. This is to control the power generation state of solar panels (hereinafter referred to as PV (photovoltaic) panels) mounted on roofs with multiple surfaces facing different directions, at their optimal operating points. Many energy storage systems sold in Japan are equipped with three- or four-circuit DC / DC converters for photovoltaic power generation, so that they can accommodate complex shapes such as hipped roofs.

[0005] 1 shows an example configuration of a hybrid power storage system 900. The power storage system 900 includes DC / DC converters 920 to 928, a DC / AC converter 930, a relay 932, and a relay 934. The DC / DC converter 920 and the DC / AC converter 930 have the function of converting power bidirectionally. Each of the DC / DC converters 920 to 928 is connected in parallel to the DC / AC converter 930. The power storage system 900, together with a storage battery 910 and PV strings 912 to 918, constitutes a power supply system.

[0006] Each of the PV strings 912 to 918 includes a plurality of PV modules (solar panels). The plurality of PV modules are connected in series with one another. A PV module is, for example, a module in which a plurality of PV cells (the smallest unit capable of receiving light (such as sunlight) and generating electricity) are connected in series, arranged on a flat surface, and sealed with tempered glass or the like. As described above, each of the PV strings 912 to 918 can be mounted on roofs with different facing surfaces.

[0007] The DC power generated by the PV strings 912 to 918 is boosted by the DC / DC converter 922 and DC / DC converter 928, input to the DC / AC converter 930, converted to AC power by the DC / AC converter 930, and output via the relays 932 and 934. Single-phase three-wire AC power is supplied from the relay 932 to the load via a distribution board (not shown) of the house in which the power storage system 900 is installed. The relay 934 is connected to the grid, and the power generated by the PV strings 912 to 918 is output to the grid (hereinafter referred to as power selling).

[0008] The storage battery 910 is a rechargeable secondary battery. The storage battery 910 is charged with DC power obtained by converting commercial AC power supplied from a grid via a relay 934 (hereinafter referred to as purchased power) into DC power by a DC / AC converter 930 and further converting it by a DC / DC converter 920. The storage battery 910 is also charged with DC power obtained by converting DC power generated by the PV strings 912 to 918 from the DC / DC converter 922 by a DC / DC converter 928 and the DC / DC converter 920.

[0009] Photovoltaic DC / DC converters incorporate the power generated by strings of several standard silicon-based power generation modules connected in series. This means a maximum short-circuit current of 10 to 15 A, a maximum voltage of 400 to 450 V, and a power generation capacity of 2 to 2.5 kW per circuit. The total power generation is 6 to 7.5 kW for three circuits and 8 to 10 kW for four circuits. Meanwhile, the maximum output of DC / AC converters is set to less than 6 kW to accommodate standard household power contracts. Specifically, most DC / AC converters have a maximum output of 4.4 kW, 5.5 kW, or 5.9 kW. Therefore, the maximum output of DC / AC converters is lower than the total maximum output of photovoltaic DC / DC converters. In recent years, with the decline in the price of photovoltaic modules, so-called overloading has become common, where strings with a larger capacity than the DC / AC converter's output are configured to generate more power even in weak sunlight. While this approach extends the time periods during which high power generation close to the maximum output of the photovoltaic DC / DC converter can be achieved, it is actually limited by the DC / AC output limit.

[0010] For example, consider a hybrid energy storage system with a maximum AC output of 6.0 kVA (5.7 kW at a power factor of 0.95) when connected to the grid, a maximum solar power input of 8.8 kW, and a maximum battery charge / discharge power of 6.0 kW. In a system with these specifications, it is possible to generate more than the AC output limit of 5.7 kW by charging part of the generated power into the battery. If the solar panels can be increased to 165% of the maximum input power, or 14.5 kW, and solar panels with a maximum capacity of 14.5 kW are connected, it will be possible to generate more than 5.7 kW as long as the solar radiation intensity is 40% or more of the rated value.

[0011] The hybrid energy storage system has two operating modes: a mode in which the surplus power remaining after subtracting the household's power consumption from the power generated is sold (hereinafter referred to as "power sell-priority mode"), and a mode in which the surplus power is charged into a storage battery and used for household consumption (hereinafter referred to as "green mode"). Figure 2 shows an example of daily power consumption in power sell-priority mode. The solid line graph shows the change in power consumption (power consumption) in a home where the system is installed. The dotted line graph, with varying spacing between dots, shows the change in power generated by the solar panels and the corresponding change in power generation capacity. The dashed line graph shows the charge / discharge of the storage battery, i.e., the change in the charge / discharge command value. The dashed line graph shows the change in the remaining battery capacity, and the double-dashed line graph shows the change in power sold / purchased. The dashed line graph, which is thinner than the dashed line representing the remaining battery capacity, shows the power generation loss, which is the difference between the actual power generated and the solar panel's power generation capacity. Figure 2 plots power (in kW) for each hour, with adjacent points connected by a straight line. The remaining capacity of the storage battery is expressed in terms of the amount of power (kWh), so the vertical axis represents the amount of power. The same display as in Figure 2 is used in Figure 3 and subsequent figures.

[0012] Figure 2 shows the calculation results for remaining battery capacity, power sold and purchased, and power generation losses, assuming daily power consumption and power generation. Charging and discharging are assumed to occur between midnight and 6:00, and discharge between 16:00 and 24:00. In Figure 2, the storage battery is fully charged using overnight power, and as the downward white arrow indicates, the storage battery cannot be charged, so the solar power generation is limited to a maximum AC output of 5.7kW. In the example in Figure 2, the loss is 12.8kWh, which is about 22% of the original daily power generation capacity, and at a power sales price of 16 yen / kWh, a loss of 205 yen is incurred.

[0013] An example of power fluctuations over one day in green mode is shown in Figure 3. As shown in Figure 3, in green mode, surplus power is charged into the storage battery, making it possible to generate power that exceeds the maximum value of the grid-connected output. However, because all of the surplus power is charged into the storage battery, it quickly reaches full charge, and thereafter, just like in power sales priority mode, the input power of the solar power generation is limited to the maximum AC output of 5.7kW. In the example in Figure 3, the loss is 9.5kWh, which is about 17% of the original power generation capacity, and at a power sales price of 16 yen / kWh, a loss of 152 yen.

[0014] As mentioned above, in both the power sales priority mode and the green mode, even if the solar radiation conditions are such that power generation exceeds the maximum AC output of 5.7 kW, if the storage battery is fully charged, power generation will be limited to 5.7 kW, resulting in a power generation loss. The power generation loss increases as the capacity of the connected solar panels increases and the intensity of the solar radiation increases.

[0015] Therefore, an object of the present disclosure is to provide a power storage system, a power supply system, and a control method that can maximize weather-dependent generated power and improve economic efficiency. [Means for solving the problem]

[0016] According to one aspect of the present disclosure, there is provided a power storage system including a power conversion unit that supplies power generated by a power generation device to a load and a grid, a charging unit that charges a storage battery with the generated power, and a control unit that controls the power conversion unit and the charging unit, wherein if the generated power is greater than a predetermined reference value, the control unit controls the charging unit to charge the storage battery with first surplus power of the generated power that exceeds the power supplied to the load and the grid, the generated power depends on the weather, the maximum value of the generated power is greater than the upper limit value of the power that can be supplied from the power conversion unit to the load and the grid when connected to the grid, and the reference value is equal to or less than the upper limit value. [Effects of the Invention]

[0017] According to the present disclosure, it is possible to provide a power storage system, a power supply system, and a control method that can improve economic efficiency by maximizing weather-dependent generated power. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a block diagram showing the configuration of the power storage system. [Figure 2] FIG. 2 is a graph showing a change in power consumption in one day when the power storage system shown in FIG. 1 operates in the power sale priority mode. [Figure 3] FIG. 3 is a graph showing a change in power consumption in one day when the power storage system shown in FIG. 1 is operating in the green mode. [Figure 4] FIG. 4 is a block diagram showing the configuration of a power storage system according to an embodiment of the present disclosure. [Figure 5] FIG. 5 is a flowchart showing the operation of the control unit of the power storage system shown in FIG. [Figure 6] FIG. 6 is a graph showing the change in power consumption in one day as a result of the control operation shown in FIG. 4 being executed. [Figure 7] FIG. 7 is a graph showing the change in power in one day when the control operation shown in FIG. 4 is executed in a case where the amount of power generated by solar power generation is small. [Figure 8]FIG. 8 is a graph showing the change in power consumption in one day when the green mode is executed in a case where the amount of power generated by solar power generation is the same as that in FIG. [Figure 9] FIG. 9 is a graph showing the change in power in one day when the control operation shown in FIG. 4 is executed in a case where the amount of power generated by solar power generation is about medium. [Figure 10] FIG. 10 is a graph showing the change in power consumption in one day when the green mode is executed in a case where the amount of power generated by solar power generation is the same as that in FIG. [Figure 11] FIG. 11 is a flowchart showing the operation of the control unit of the power storage system according to the first modification of the present disclosure. [Figure 12] FIG. 12 is a flowchart showing the reference value update process shown in FIG. [Figure 13] FIG. 13 is a flowchart showing the first charge / discharge control shown in FIG. [Figure 14] FIG. 14 is a flowchart showing the second charge / discharge control shown in FIG. [Figure 15] FIG. 15 is a graph showing the change in power in one day when the control operation shown in FIG. 11 is executed in a case where the amount of power generated by solar power generation is about the same intermediate level as in FIG. [Figure 16] FIG. 16 is a graph showing the change in power in one day when the control operation shown in FIG. 11 is executed when the amount of power generated by solar power generation is the same as that in FIG. 15 and an electric vehicle is being charged. [Figure 17] FIG. 17 is a flowchart showing the operation of the control unit of the power storage system according to the second modification of the present disclosure. [Figure 18] FIG. 18 is a flowchart showing the overnight charging process shown in FIG. [Figure 19] FIG. 19 is a graph showing the change in power in one day when the control operation shown in FIG. 17 is executed in a case where the amount of power generated by solar power generation is smaller. DETAILED DESCRIPTION OF THE INVENTION

[0019] [Description of the embodiments of the present disclosure] The contents of the embodiments of the present disclosure will be listed and explained below. At least some of the embodiments described below may be combined in any combination.

[0020] (1) A power storage system according to a first aspect of the present disclosure includes a power conversion unit that supplies power generated by a power generation device to a load and a grid, a charging unit that charges a storage battery with the generated power, and a control unit that controls the power conversion unit and the charging unit, wherein the control unit controls the charging unit to charge the storage battery with first surplus power of the generated power that exceeds the power supplied to the load and the grid if the generated power is greater than a predetermined reference value, the generated power depends on the weather, the maximum value of the generated power is greater than an upper limit value of power that can be supplied from the power conversion unit to the load and the grid when connected to the grid, and the reference value is equal to or less than the upper limit value. This makes it possible to maximize the generated power of a power generation device (e.g., a solar power generation device or a wind power generation device) whose amount of generated power (hereinafter referred to as power generation amount) fluctuates depending on the weather, thereby improving economic efficiency.

[0021] (2) In the above (1), the power generation device may be a solar power generation device, thereby maximizing the power generated by the solar power generation device.

[0022] (3) In the above (1) or (2), the control unit may predict the power generation amount for a target day, which is a day corresponding to a weather forecast for the installation location of the power generation device, based on the weather forecast for the installation location of the power generation device, and may determine whether to change the reference value based on the predicted power generation amount, or may change the reference value in response to a determination that the reference value should be changed. This allows the power generation amount of the power generation device to be maximized with greater accuracy.

[0023] (4) In the above (3), the control unit may determine whether to change the reference value by determining whether the predicted power generation is within a predetermined range that is smaller than the reference value, and may decrease the reference value if the predicted power generation is within the predetermined range. This allows the storage battery to be charged with the generated power even when the power generation of the power generation device is at an intermediate level, thereby maximizing the generated power.

[0024] (5) In (3) above, upon determining that the reference value should be changed, the control unit may identify a peak time during the next power generation period by the power generation device, which is the time when the generated power is at its maximum, and may identify a reversal time, which is the first time after the peak time when the generated power is less than the power consumed by the load. The control unit may also change the reference value so that the storage battery is fully charged during a predetermined time period including the reversal time. This allows the storage battery to be fully charged or nearly fully charged using the generated power. Then, the storage battery can be discharged to supply power to the load, making it more economical.

[0025] (6) In the above (3), if the predicted power generation is equal to or less than a first threshold value that is smaller than a reference value, the control unit may control the charging unit to charge the storage battery with second surplus power, which is the power generation power that exceeds the power supplied to the load. This makes it possible to reduce economic losses due to power buying and selling.

[0026] (7) In the above (3), the control unit may predict the power generation on the target day using, in addition to the weather forecast, actual values ​​of power generation and power consumption by the load from the past target day. This allows for more accurate maximization of the power generation of the power generation device.

[0027] (8) In the above (6), the control unit may control the charging unit so that the storage battery is charged to a predetermined capacity with power supplied from the grid at night if the predicted power generation is equal to or less than a second threshold value that is smaller than the first threshold value. This allows the storage battery to be charged with inexpensive nighttime power when a lower power generation is predicted, and the discharged power of the storage battery can be supplied to the load during the day, which is more economical.

[0028] (9) A power supply system according to a second aspect of the present disclosure includes a storage battery and the power storage system described in (1) or (2) above. This maximizes the power generated by a power generation device (e.g., a solar power generation device or a wind power generation device) whose power generation amount varies depending on the weather, thereby improving economic efficiency.

[0029] (10) A control method according to a third aspect of the present disclosure includes a power conversion step of supplying power generated by a power generation device to a load and a grid, and a charging step of charging a storage battery with surplus power of the generated power that exceeds the power supplied to the load and the grid if the generated power is greater than a predetermined reference value, wherein the generated power depends on the weather, the maximum value of the generated power is greater than the upper limit of power that can be supplied from the power conversion unit to the load and the grid when connected to the grid, and the reference value is equal to or less than the upper limit. This makes it possible to maximize the generated power of a power generation device (e.g., a solar power generation device or a wind power generation device) whose power generation amount fluctuates depending on the weather, thereby improving economic efficiency.

[0030] [Details of the embodiments of the present disclosure] In the following embodiments, the same components are denoted by the same reference numerals, and their names and functions are also the same, so detailed descriptions thereof will not be repeated.

[0031] (System Configuration) Referring to FIG. 4 , the power storage system 100 according to the embodiment of the present disclosure includes DC / DC converters 120 to 128, a DC / AC converter 130, and relays 132 and 134. The power storage system 100 further includes a control unit 140, a storage unit 142, a timer 144, a communication unit 146, and a bus 148. The DC / DC converter 120 and the DC / AC converter 130 have a function of converting power bidirectionally. Each of the DC / DC converters 120 to 128 is connected in parallel to the DC / AC converter 130. Two wires at the connection point (see dashed line box) form a DC bus, and a capacitor (not shown) connecting the two wires is disposed. The power storage system 100 is a hybrid power storage system. The power storage system 100, together with the storage battery 110 and the PV strings 112 to 118, constitutes a power supply system 102. The power storage system 100 includes an operation unit (not shown) such as a remote controller for a user to input settings for the power storage system 100.

[0032] Each of the PV strings 112 to 118 includes a plurality of PV modules (solar panels). The plurality of PV modules are connected in series to one another. A PV module is, for example, a module in which a plurality of PV cells are connected in series, arranged on a flat surface, and sealed with tempered glass or the like. Each of the PV strings 112 to 118 can be mounted on roofs facing different directions.

[0033] The DC power generated by the PV strings 112 to 118 is boosted by the DC / DC converters 122 to 128, respectively, and input to the DC / AC converter 130, where it is converted to AC power by the DC / AC converter 130 and output via the relays 132 and 134. Single-phase three-wire AC power is supplied from the relay 132 to the load via a distribution board (not shown) of the house in which the power storage system 100 is installed. The relay 134 is connected to the grid, and the power generated by the PV strings 112 to 118 is output to the grid (power sale).

[0034] The storage battery 110 is a rechargeable secondary battery, such as a lithium-ion secondary battery. The storage battery 110 is charged with DC power obtained by converting commercial AC power supplied (purchased) from a grid via a relay 134 into DC power by a DC / AC converter 130 and further converting the DC power by a DC / DC converter 120. The storage battery 110 is also charged with DC power obtained by converting DC power generated by the PV strings 112 and 118 from the DC / DC converter 122 by a DC / DC converter 128 and the DC / DC converter 120.

[0035] A switch for turning on and off the connection between the storage battery 110 and the DC / DC converter 120, and a filter may be provided between the storage battery 110 and the DC / DC converter 120. The filter prevents noise, such as a ripple current generated by switching of the switching elements constituting the DC / DC converter 120, from being transmitted to the storage battery 110. The same applies to the PV strings 112 to 118 and the DC / DC converter 122 to 128. A filter may also be provided between the DC / AC converter 130 and the relays 132 and 134. The filter prevents noise, such as a ripple current generated by switching of the switching elements constituting the DC / AC converter 130, from being transmitted to the relays 132 and 134 and output to the load and the grid.

[0036] The control unit 140 generates and outputs a control signal 150 for controlling the operation of the power storage system 100. That is, the control unit 140 generates a control signal for causing each of the DC / DC converters 120 to 128 and the DC / AC converter 130 to function as a converter, and outputs the control signal to each converter. The control unit 140 also generates a control signal for operating (i.e., opening and closing) each of the relays 132 and 134, and outputs the control signal to the relays 132 and 134. The control unit 140 is, for example, a CPU (Central Processing Unit). The storage unit 142 is, for example, a rewritable nonvolatile semiconductor memory, and stores a computer program (hereinafter simply referred to as a program) executed by the control unit 140. The control unit 140 also uses the storage unit 142 as a work memory for executing processes, and stores the results of the executed processes in the storage unit 142 as appropriate. The functions of the power storage system 100 are realized by the control unit 140 reading and executing a program stored in the storage unit 142.

[0037] In response to a request from the control unit 140, the timer 144 outputs information indicating the current time (hereinafter simply referred to as the current time) to the control unit 140. The communication unit 146 has a function of communicating with the outside of the power storage system 100, i.e., with a communication network (hereinafter simply referred to as the network) 200. The communication unit 146 enables the control unit 140 to communicate with a server computer (hereinafter simply referred to as the server) 202 via the network 200. Data transmission between the control unit 140, the storage unit 142, the timer 144, and the communication unit 146 is performed via a bus 148. The communication between the communication unit 146 and the network 200 may be wireless communication via a wireless router (e.g., a Wi-Fi router), for example.

[0038] The server 202 has a function for providing weather forecasts. The server 202 maintains a weather forecast database and returns weather forecasts in response to external requests. The server 202 is, for example, a server installed at the Japan Meteorological Agency, and publishes weather forecasts for each forecast region across Japan. "Publishing" means being ready to provide the latest weather forecast in response to an external weather forecast request. A "forecast region" refers to, for example, an area determined by dividing each prefecture into multiple regions. A "weather forecast" includes weather information for a specified period (e.g., three hours) from the time of publication to the following day. Weather refers to the atmospheric condition, which combines weather-related factors such as temperature, humidity, wind, cloud cover, visibility, rain, snow, and thunder. "Weather information" is expressed in five categories, for example, "clear," "cloudy," "rain," "rain or snow," and "snow." The power generated by the PV strings 112 to 118 depends on the weather and decreases in the following order: clear, cloudy, rain, rain or snow, and snow.

[0039] (operation) The operation of the power storage system 100 will be described in detail with reference to FIG. 5. The process shown in FIG. 5 is implemented by the control unit 140 reading and executing a predetermined program stored in the storage unit 142. In parallel with this program, the control unit 140 also executes a program for monitoring the power generation states of the PV strings 112 to 118 and the power consumption states of the load. That is, the control unit 140 stores the total amount of power generated by the PV strings 112 to 118 and the power consumption by the load in the storage unit 142. This operation is repeatedly executed, for example, at predetermined intervals, based on information from the timer 144. The storage battery 110 is not charged with commercial power at night (hereinafter also referred to as "nighttime charging"), and instead supplies power to the load by discharging the storage battery 110 to reduce power purchases. Therefore, the charge amount (i.e., remaining battery power) of the storage battery 110 is at its lowest level around the time (dawn) when the PV strings 112 to 118 start generating power.

[0040] In step 300, the control unit 140 sets a reference value. The reference value is stored in advance in the storage unit 142. The reference value is, for example, an upper limit value Th of the grid-connected output, e.g., Th=5.7 (kW). The grid-connected output means the power (power consumption and power sold) supplied from the DC / AC converter 130 to the load and the grid when connected to the grid.

[0041] In step 302, the control unit 140 determines whether the latest power generation amount stored in the storage unit 142 is greater than the reference value set in step 300. If it is determined that it is greater, the control proceeds to step 304. If not, the control proceeds to step 306.

[0042] In step 304, the control unit 140 controls the DC / DC converters 120, 128, and 130 so that the power generated by the PV strings 112 and 118 is supplied to the load, sold up to the upper limit Th of the grid-connected output, and the storage battery 110 is charged with the surplus power. Here, the surplus power (first surplus power) means the power remaining after subtracting the power consumed by the load and the power sold from the power generated by the PV strings. If there is no surplus power, the storage battery 110 is not charged. Then, the control proceeds to step 312.

[0043] If the determination result in step 302 is NO, in step 306, the control unit 140 compares the latest power generation amount with the latest power consumption stored in the storage unit 142, and determines whether the power generation amount is greater than the power consumption. If it is determined that the power generation amount is greater than the power consumption, the control proceeds to step 308. If not, the control proceeds to step 310.

[0044] In step 308, the control unit 140 supplies the generated power to the load and sells the surplus power. Therefore, the storage battery 110 is not charged with the generated power. Here, the surplus power (second surplus power) means the remaining power after subtracting the power consumed by the load from the power generated by the PV string. Then, the control proceeds to step 312.

[0045] If the determination result in step 306 is NO, in step 310, the control unit 140 supplies the generated power and the discharged power of the storage battery 110 to the load. If the generated power and the discharged power of the storage battery 110 are smaller than the power consumption of the load, the control unit 140 supplies purchased power from the grid to the load. Thereafter, the control proceeds to step 312.

[0046] In step 312, the control unit 140 determines whether an instruction to terminate has been received. If it is determined that an instruction to terminate has been received, the program terminates. If not, control returns to step 302, and the above-described processing is repeated. The instruction to terminate is given, for example, by turning off the power supply to the power storage system 100.

[0047] As described above, in the power storage system 100, when the power generated by the PV strings 112 to 118 is greater than a reference value (for example, the upper limit value Th of the grid-connected output), the power storage system 100 can charge the storage battery 110 with surplus power (i.e., first surplus power). That is, when the weather is fine and the amount of power generation is large, the time when charging of the storage battery 110 with the generated power starts can be delayed, and a situation in which the storage battery 110 becomes fully charged and photovoltaic power generation must be restricted can be avoided. Therefore, it is possible to avoid losses in the power generated by the PV strings 112 to 118. That is, it is possible to maximize the power generated by a photovoltaic power generation device, the amount of power generation of which fluctuates depending on the weather, and improve economic efficiency.

[0048] A specific example will be shown with reference to FIG. 6. In FIG. 6, the same patterns of power generation and power consumption as those in FIGS. 2 and 3 are assumed. As indicated by the dotted line, power generation begins and increases around 6:00 a.m. Accordingly, the power sold and purchased, i.e., the power sold, indicated by the two-dot chain line, increases, but no charging or discharging occurs (charge / discharge command value = 0). Thereafter, the power generation peaks around 10:00 a.m. and remains at the peak until around 1:00 p.m. Accordingly, the power sold and purchased reaches an upper limit, charging begins (the charge / discharge command value increases), the storage battery 110 is charged with the surplus power of the generated power (first surplus power), and the remaining battery capacity increases. Thereafter, from around 1:00 p.m., the power generation begins to decrease from its peak. Around this time, the storage battery 110 is fully charged. Because the reference value is set to 5.7 kW, the generated power exceeding 5.7 kW is charged to the storage battery 110. If the maximum input power of solar power generation is 8.8 kW, the maximum charging of the storage battery 110 is 3.1 kW, which is the difference between the grid-connected maximum output of 5.7 kW. Even if charging of the storage battery 110 starts from 0%, it takes more than four hours to fully charge, which prevents loss of power generation.

[0049] (First Modification) The control method shown in FIG. 5 can avoid power generation losses on sunny days as described above, but is not necessarily effective when the amount of power generation is relatively low, such as on cloudy days. When the amount of power generation is low on cloudy days (when the generated power is below a reference value (e.g., 5.7 kW)), if the charge / discharge of the storage battery 110 is controlled using the control method shown in FIG. 5, the storage battery 110 is not charged with the generated power, and all surplus power (i.e., second surplus power) is sold. Then, power purchases occur during time periods when the power consumption by the load exceeds the generated power. As a specific example, FIG. 7 shows a pattern when the amount of power generation is 50% of the amount of power generation shown in FIG. 6. In this example, step 306 shown in FIG. 5 is executed during power generation from 7:00 to around 16:00 (see the dotted line graph), and step 310 shown in FIG. 5 is executed after 16:00. As a result, 19 kWh of power is sold during the daytime. After that, 13.3 kWh of power is purchased (see the dotted oval region). If the selling price of electricity is 16 yen / kWh and the purchasing price is 30 yen / kWh, the difference between the selling price and the purchasing price will result in an expenditure of 95 yen.

[0050] Figure 8 shows the pattern when operating in green mode with the same power consumption and power generation as Figure 7. In this case, the power sold is 6.2 kWh and the power purchased is 0.75 kWh. As above, if the power selling price is 16 yen / kWh and the power purchasing price is 30 yen / kWh, the difference between the power selling price and the power purchasing price will result in an income of 77 yen. Therefore, compared to the case of Figure 7, where the control method of Figure 5 was implemented, operating in green mode will result in a profit of 172 yen.

[0051] FIG. 9 shows a pattern when the charge / discharge of the storage battery 110 is controlled by the control method shown in FIG. 5 when the amount of power generation is at an intermediate level, for example, 70% of the amount of power generation shown in FIG. 6. Referring to FIG. 9, step 304 of FIG. 5 is executed between about 10:00 and about 13:00, and the amount of power generation exceeding the reference value (5.7 kW) is charged to the storage battery. Therefore, no power generation loss occurs. However, because the storage battery 110 is only charged to about 6% (see the dashed-dotted line graph between about 10:00 and about 13:00), power purchase from the grid occurs during the night (see the dotted oval area). FIG. 10 also shows a pattern when, assuming the same amount of power generation as above, 70%, all surplus power is charged to the storage battery 110 instead of the control method of FIG. 5. In this case, the storage battery 110 is charged to 100%, so no power purchase from the grid occurs. However, the storage battery 110 becomes fully charged in the morning, charging ends, and power generation loss occurs. That is, in the dotted elliptical region, there is a period in which the actual generated power is smaller than the power generation capacity.

[0052] As a first modification, a control method for avoiding the above-described power generation loss during fine weather and further avoiding the above-described situation when the amount of power generation is below an intermediate level will be described. The control method according to the first modification is shown in FIG. 11 . The system configuration is the same as that of the power storage system 100 and the power supply system 102 shown in FIG. 4 . That is, the process shown in FIG. 11 is realized by the control unit 140 reading and executing a predetermined program stored in the storage unit 142. In parallel with this program, the control unit 140 executes a program for monitoring the power generation status of the PV strings 112 to 118 and the power consumption status of the load. That is, the control unit 140 stores the power generation amounts of the PV strings 112 to 118 and the power consumption by the load in the storage unit 142. This operation is repeatedly executed, for example, at predetermined intervals, based on information from the timer 144. Note that the storage battery 110 is not charged overnight, and instead supplies power to the load by discharging the storage battery 110 to reduce power purchases. Therefore, the charge amount (i.e., remaining battery power) of the storage battery 110 is at its lowest level around the time (before dawn) when the PV strings 112 to 118 start generating power.

[0053] In step 400, the control unit 140 sets a reference value. The reference value is stored in advance in the storage unit 142. The reference value can be updated as described below, so the value set here is an initial value of the reference value. The reference value is, for example, the upper limit value Th of the grid-connected output, e.g., Th=5.7 (kW).

[0054] In step 402, the control unit 140 determines whether a predetermined time has arrived. Specifically, the control unit 140 reads out the predetermined time stored in the storage unit 142, obtains the current time from the timer 144, and compares them to determine whether the predetermined time has arrived. If it is determined that the predetermined time has arrived, control proceeds to step 404. Otherwise, control proceeds to step 412. The predetermined time refers to the time at which a process to change the reference value, which will be described later, is executed, and is set to, for example, the time before power generation by the PV strings 112 and 118 starts.

[0055] In step 404, the control unit 140 predicts the amount of power generation by the PV strings 112 to 118 during the next daytime (between sunrise and sunset). For example, the control unit 140 stores weather forecast information provided by the server 202 in the storage unit 142, reads the weather forecast for the area where the power storage system 100 is installed from the most recent stored weather forecast, and predicts the amount of power generation during the next daytime. The control unit 140 can predict the amount of sunshine from the weather forecast, and can predict the amount of power generation by photovoltaic power generation. As described above, the control unit 140 executes a program that monitors the power generation states of the PV strings 112 to 118 and the power consumption states of the loads. If this data is stored in the storage unit 142 as historical data, the control unit 140 may predict the amount of power generation using the historical data in addition to the weather forecast. After that, the control proceeds to step 406.

[0056] In step 406, the control unit 140 determines whether the power generation amount predicted in step 404 is at an intermediate level. If it is determined to be at an intermediate level, control proceeds to step 410. Otherwise, control proceeds to step 408. The intermediate level is, for example, a range greater than 60% and equal to or less than 80% of the power generation capacity of the PV strings 112 to 118. Note that a range different from this range may also be defined as the intermediate level.

[0057] In step 408, the control unit 140 resets the reference value, which has been updated as described below, to its initial value. If the reference value has not been changed and remains the initial value, the initial value is maintained. Then, control proceeds to step 412.

[0058] If the determination result in step 406 is YES, the control unit 140 executes a reference value update process in step 410. Thereafter, the control proceeds to step 412. The reference value update process is shown in FIG.

[0059] 12, in step 440, control unit 140 predicts the operating state for the next daytime based on the most recent weather forecast stored in memory unit 142 and actual data on past power generation and power consumption. For example, control unit 140 creates patterns such as those shown in FIGS. 6 to 10, taking into account the current remaining battery power of storage battery 110. Thereafter, control proceeds to step 442.

[0060] In step 442, the control unit 140 identifies the time when the generated power is at its maximum (hereinafter referred to as the peak time) in the pattern created in step 440. Thereafter, the control proceeds to step 444.

[0061] In step 444, the control unit 140 identifies the time (hereinafter referred to as the reversal time) at which the generated power becomes smaller than the power consumed by the load after the peak time in the pattern created in step 440. Thereafter, the control proceeds to step 446.

[0062] In step 446, the control unit 140 specifies a reference value so that the storage battery 110 will be fully charged around the reversal time specified in step 444. Specifically, the control unit 140 changes the reference value based on the patterns of generated power and power consumption predicted in step 440, and simulates the remaining battery capacity of the storage battery 110 when charged with generated power. This allows the control unit 140 to specify the reference value that will result in full charge at the reversal time. Then, control proceeds to step 448.

[0063] In step 448, the control unit 140 updates the current reference value with the reference value determined in step 446. Control then returns to step 412 in the flowchart of FIG.

[0064] In step 412, the control unit 140 determines whether the amount of power generation predicted in step 404 is at a low level. If it is determined to be at a low level, control proceeds to step 416. Otherwise, control proceeds to step 414. A low level refers to a power generation amount equal to or less than a first threshold, for example, a range of 60% or less of the power generation capacity of the PV strings 112 to 118. Note that a range different from this range may also be defined as the low level. Note that, as described above, when step 410 is executed, the amount of power generation is at an intermediate level, so the determination result in step 412 is NO, and step 414 is executed.

[0065] In step 414, control unit 140 executes the first charge / discharge control. Thereafter, control proceeds to step 418. A specific example of the first charge / discharge control is shown in FIG. 13. The flowchart shown in FIG. 13 is obtained by deleting step 300 and step 312 from the flowchart shown in FIG. 5. Steps denoted with the same reference numerals in FIG. 13 and FIG. 5 are the same. Therefore, the following description will not be repeated and will focus mainly on the differences. The difference is that, as described above, when step 414 is executed after step 410 has been executed and the reference value has been updated, the updated reference value is used in step 302 of FIG. 13. After step 304, step 308, or step 310 has been executed, control returns to the flowchart of FIG. 11 and proceeds to step 418.

[0066] If the determination result in step 412 is YES, in step 416, the control unit 140 executes second charge / discharge control. Thereafter, control proceeds to step 418. A specific example of the second charge / discharge control is shown in FIG. 14. The flowchart shown in FIG. 14 corresponds to the green mode, and is the same as the flowchart shown in FIG. 5 in that steps 300, 306, and 312 are deleted and step 304 is replaced by steps 460 and 462. In FIG. 14 and FIG. 5, steps with the same reference numerals are the same. Therefore, the following description will not be repeated and will mainly focus on the differences.

[0067] 14, if the determination result in step 302 is NO, step 310 is executed. On the other hand, if the determination result in step 302 is YES, in step 460, control unit 140 determines whether storage battery 110 is chargeable. Specifically, control unit 140 determines that storage battery 110 is chargeable if it is not fully charged. Otherwise (fully charged), control unit 140 determines that storage battery 110 is not chargeable. If it is determined that storage battery 110 is chargeable, control proceeds to step 462. Otherwise, control proceeds to step 308.

[0068] In step 462, control unit 140 controls DC / DC converter 120, DC / DC converter 128, and DC / AC converter 130 so as to supply power generated by PV strings 112 and 118 to the load and use the surplus power (second surplus power) to charge storage battery 110. After step 462, step 308, or step 310 has been executed, control returns to the flowchart in FIG. 11 and proceeds to step 418.

[0069] In step 418, the control unit 140 determines whether or not an instruction to terminate has been received. If it is determined that an instruction to terminate has been received, the program terminates. If not, the control proceeds to step 420. The instruction to terminate is given, for example, by the user operating the operation unit of the power storage system 100 to stop the operation of the power storage system 100.

[0070] In step 420, the control unit 140 determines whether or not a predetermined time has arrived, similar to step 402. If it is determined that the predetermined time has arrived, control returns to step 404. If not, control proceeds to step 422.

[0071] In step 422, the control unit 140 determines whether the power generation amount predicted in step 404 is at a low level, similar to step 412. If it is determined to be at a low level, control returns to step 416. If not, control returns to step 414.

[0072] The processing from step 404 onwards is repeated until an instruction to end is given in step 418, step 420 and step 422. Then, step 414 or step 416 is repeated depending on the amount of power generation predicted in step 404 until the predetermined time for updating the reference value arrives.

[0073] As described above, when the power generated by the PV strings 112 to 118 is greater than a reference value (for example, the upper limit value Th of the grid-connected output), the power storage system 100 can charge the storage battery 110 with surplus power (first surplus power) in the same way as the control shown in Fig. 5 (see step 414). That is, when the weather is fine and the amount of power generation is large, the time when charging of the storage battery 110 with the generated power starts can be delayed, thereby avoiding a situation in which the storage battery 110 becomes fully charged and photovoltaic power generation must be restricted. Therefore, it is possible to avoid the occurrence of losses in the power generated by the PV strings 112 to 118.

[0074] Furthermore, when the power generated by the PV strings 112 to 118 is at an intermediate level, the power storage system 100 updates the reference value (see step 410) and changes the reference value to a value smaller than the initial value, thereby enabling the storage battery 110 to be charged with the surplus power (first surplus power) (see step 414). Therefore, as described above with reference to Figures 9 and 10, it is possible to avoid the purchase of power from the grid at night and the occurrence of power generation loss due to the inability to charge the storage battery 110 with the surplus power. Therefore, even when the amount of power generated by the power generation device is at an intermediate level, the storage battery can be charged with the generated power, and the generated power can be maximized.

[0075] As described above, the power generation amount for the target day, which is the day corresponding to the weather forecast, is predicted based on the weather forecast for the installation location of the power storage system 100, and it is determined whether to change the reference value based on the predicted power generation amount. This makes it possible to more accurately maximize the power generation amount of the power generation device.

[0076] As described above, the control unit 140 predicts the power generation amount for the target day using the weather forecast as well as actual data on power generation amount and power consumption by the load from the past target day, thereby maximizing the power generation amount of the power generation device with higher accuracy.

[0077] As described above, when the control unit 140 determines to change the reference value, it identifies the peak time, which is the time when the generated power is at its maximum during the next power generation period by the power generation device, and identifies the reversal time, which is the first time after the peak time when the generated power is less than the power consumed by the load.The control unit 140 then changes the reference value so that the storage battery is fully charged during a predetermined time period including the reversal time.This allows the storage battery to be fully charged or nearly fully charged using the generated power.After that, it becomes more economical to supply power to the load by discharging the storage battery.

[0078] In this way, when the amount of power generation is medium, the reference value of the power generation to be charged is set to a value smaller than the initial value (for example, 5.7 kW) and the charging of the storage battery 110 is increased, thereby maximizing both power generation and self-consumption. However, since charging in excess of the surplus power results in power purchases and losses, if the power generation exceeding the reference value becomes greater than the surplus power, only the surplus power is charged. The method for determining the charge / discharge command value for the storage battery 110 at each time (for example, every hour) can be expressed mathematically as shown in (Equation 1) to (Equation 3) below. (Equation 1) Pb1 = Ppv - Pth; Ppv > Pth =0; Ppv≦Pth (Formula 2)Pb2=Ppv-Pc (Formula 3)Pb=Min(Pb1,Pb2)

[0079] In (Equation 1) to (Equation 3), the charge / discharge command value for the storage battery 110 is Pb (charge if positive, discharge if negative), the photovoltaic power generation power is Ppv, the lower limit (i.e., reference value) of the photovoltaic power generation power at which charging of the storage battery starts is Pth, and the load power consumption is Pc. Pb1 and Pb2 are determined by (Equation 1) and (Equation 2), respectively, and the smaller of Pb1 and Pb2 is determined as the charge / discharge command value Pb by (Equation 3). Note that (Equation 1) means that if Ppv > Pth (i.e., the photovoltaic power generation power exceeds the reference value), Pb1 is set to Ppv - Pth (i.e., first surplus power), and if Ppv ≦ Pth (i.e., the photovoltaic power generation power is equal to or less than the reference value), P1 is set to 0.

[0080] Furthermore, the power storage system 100 operates in the green mode when the power generated by the PV strings 112 to 118 is at a low level (see step 416). Therefore, as described above with reference to Figures 7 and 8, it is possible to suppress economic losses due to power buying and selling.

[0081] A specific example where the amount of power generation is at an intermediate level will be shown with reference to Figures 15 and 16. In Figure 15, the same patterns of power generation and power consumption as in Figure 9 are assumed. That is, the amount of power generation is 70% of the amount of power generation shown in Figure 6. In step 410 described above, the reference value is changed from the initial value (e.g., 5.7 kW) to, for example, 3.3 kW (see the horizontal line in Figure 15).

[0082] Referring to FIG. 15, power generation begins at approximately 6:00 and increases (see the dotted line graph). At approximately 8:00, the power generation exceeds the power consumption, resulting in surplus power, but charging of the storage battery 110 is not performed (charge / discharge command value Pb=0). At approximately 9:00, the power generation exceeds the reference value of 3.3 kW, and charging of the storage battery 110 begins with the power generation exceeding the reference value (charge / discharge command value Pb=Ppv-Pth). This makes it possible to delay the time when the storage battery 110 is fully charged. This makes it possible to avoid power generation losses caused by suppression of power generation, as shown in FIG. 10. Furthermore, in FIG. 15, the amount of power purchased and sold after 6:00 PM is 0, which makes it possible to avoid purchasing power from the grid, as shown by the dotted oval in FIG. 9.

[0083] FIG. 16 shows a case where an electric vehicle is charged with 3 kW of power from 2:00 PM to 3:00 PM when the same reference value (3.3 kW) as in FIG. 15 is set. At 2:00 PM, the generated power is 4.5 kW, and the power that exceeds the reference value (3.3 kW) is 1.2 kW. However, because the power consumption by the load, including the electric vehicle, is 4 kW, the storage battery 110 is charged with only the surplus of 0.5 kW after subtracting the power consumption of the load. In FIG. 16, too, it is possible to avoid the generation loss caused by the suppression of generated power as shown in FIG. 10, and it is also possible to avoid the purchase of power from the grid as shown by the dotted oval in FIG. 9.

[0084] (Second Modification) In the first modification, if the amount of power generation is small, the storage battery may not be fully charged even if all the surplus power is used to charge it (see step 416 in FIG. 11 (specifically, step 462 in FIG. 14)). In such a case, depending on the amount of power consumed by the load, the storage battery may not be able to supply enough power to the load, resulting in the need to purchase power. The control method according to the second modification can achieve the same purpose as the first modification and is also designed to deal with such situations.

[0085] A control method according to the second modification is shown in Fig. 17. The system configuration is the same as that of the power storage system 100 and the power supply system 102 shown in Fig. 4. That is, the process shown in Fig. 17 is realized by the control unit 140 reading and executing a predetermined program stored in the storage unit 142. In parallel with this program, the control unit 140 executes a program for monitoring the power generation states of the PV strings 112 to 118 and the power consumption state of the load. That is, the control unit 140 stores the power generation amounts of the PV strings 112 to 118 and the power consumption by the load in the storage unit 142. This operation is executed repeatedly, for example, at predetermined intervals, based on information from the timer 144.

[0086] The flowchart shown in Fig. 17 is obtained by adding step 500 and step 502 to the flowchart shown in Fig. 11. Steps with the same reference numerals are the same in Fig. 11 and Fig. 17. Therefore, the following description will not be repeated and will focus mainly on the differences.

[0087] As will be described later, in the second modification, overnight charging of the storage battery may be performed according to the predicted amount of power generation. Therefore, the process of predicting the amount of power generation (step 404) needs to be performed before the overnight charging starts. For example, if the time to start the overnight charging is midnight, the predetermined time to be determined in step 402 may be set to, for example, 11:00 PM.

[0088] After step 408 or step 410 is performed, in step 500, the control unit 140 determines whether the power generation amount predicted in step 404 is at an extremely low level. If it is determined to be at an extremely low level, control proceeds to step 502. Otherwise, control proceeds to step 412. The extremely low level refers to a power generation amount below a second threshold, e.g., a range of 30% or less of the power generation capacity of the PV strings 112 to 118. Note that a range different from this range may be defined as the extremely low level depending on the power consumption. As described above, the occurrence of a state in which the storage battery 110 cannot supply sufficient power to the load, i.e., the need for overnight charging, depends not only on the amount of power generation but also on the power consumption by the load. As described above, the control unit 140 stores the power generation amount of the PV strings 112 to 118 and the power consumption by the load in the storage unit 142. Therefore, an appropriate extremely low level can be set taking into account the actual power consumption.

[0089] In step 502, the control unit 140 executes overnight charging. Then, the control proceeds to step 416. A specific example of overnight charging is shown in FIG.

[0090] 18, in step 510, control unit 140 determines a target value for charging. The target value is determined as the remaining battery capacity of storage battery 110 at the time when charging ends (hereinafter referred to as the end time). Control unit 140 can determine the target value based on the amount of power generation predicted in step 404 and the predicted value of power consumption. The predicted value of power consumption can be determined based on past performance data.

[0091] In step 512, the control unit 140 charges the storage battery 110 with grid power. Then, the control proceeds to step 514.

[0092] In step 514, the control unit 140 determines whether or not to terminate charging. Specifically, the control unit 140 determines whether the termination time has arrived and whether or not the remaining battery capacity of the storage battery 110 has reached the target value determined in step 510, and if it is determined that either of these conditions has been met, it determines to terminate charging. The termination time is the time before the daytime rate starts to be applied (for example, from 7:00 to 24:00), and is set to, for example, 6:00 AM. If it is determined that charging should be terminated, control returns to the flowchart shown in FIG. 17. Otherwise, control proceeds to step 516.

[0093] In step 516, control unit 140 determines whether an instruction to terminate charging has been received, similar to step 418. If it is determined that an instruction to terminate charging has been received, control returns to the flowchart shown in Fig. 17. Otherwise, control returns to step 512. As a result, step 512 is executed until it is determined that charging should be terminated.

[0094] As described above, if you have a contract with an electric power company for time-based rates and can use inexpensive nighttime electricity, and it is predicted that the amount of power generated will be extremely low, you can charge the storage battery 110 in advance during the upcoming nighttime to make up for the power shortage. This can save on electricity bills and is more economical.

[0095] As a specific example of when the amount of power generation is at an extremely low level, Fig. 19 shows a pattern in which the predicted amount of power generation is 20% of the amount of power generation shown in Fig. 6, and the storage battery is charged to 58% using nighttime power from midnight to 6:00. During the time period when daytime rates are applied, from 7:00 to midnight, the power stored in the storage battery 110 during the night and the power generated by solar power generation are used, making it possible to avoid purchasing power. In other words, the two-dot chain line in the graph is 0 after 7:00.

[0096] As described above, power generation and power consumption can be predicted from past performance data. The accuracy of the predicted values ​​can be improved by comparing them with the performance data daily and correcting them. However, the weather on that day must be taken into consideration. For example, the weather can be ranked based on the weather forecast and used to predict power generation and power consumption. Furthermore, more accurate predictions can be achieved by processing the performance data separately for weekdays and holidays. By comparing the predicted values ​​with the performance data daily and correcting them, seasonal fluctuations can be reflected to some extent in the predicted values.

[0097] In the above, the case where the power supply system 102 includes photovoltaic power generation devices (i.e., PV strings 112 to 118) has been described, but the present invention is not limited to this. The power supply system 102 may include a power generation device whose power generation amount varies depending on the weather, and may include a wind power generation device instead of a photovoltaic power generation device. Furthermore, the power supply system 102 may include a wind power generation device in addition to the photovoltaic power generation device. In such a system, the power generation amount of the power generation device whose power generation amount varies depending on the weather can be maximized to improve economic efficiency.

[0098] Although the present disclosure has been described above by explaining the embodiments, the above-described embodiments are merely examples, and the present disclosure is not limited to only the above-described embodiments. The scope of the present disclosure is defined by the claims in the claims, taking into consideration the description of the detailed description of the invention, and includes all modifications within the meaning and scope equivalent to the wordings described therein. [Explanation of symbols]

[0099] 100, 900 Energy storage system 102 Power Supply System 110, 910 storage battery 112, 114, 116, 118, 912, 914, 916, 918 PV strings 120, 122, 124, 126, 128, 920, 922, 924, 926, 928 DC / DC converters 130, 930 DC / AC converter 132, 134, 932, 934 relays 140 Control Unit 142 Storage section 144 Timer 146 Communications Department 148 Bus 150 Control Signal 200 Network 202 Server

Claims

1. a power conversion unit that supplies power generated by the power generation device to a load and a power grid; a charging unit that charges a storage battery with the generated power; a control unit that controls the power conversion unit and the charging unit, the control unit controls the charging unit to charge the storage battery with first surplus power of the generated power that exceeds power supplied to the load and the grid when the generated power is greater than a predetermined reference value; The generated power depends on the weather, the maximum value of the generated power is greater than an upper limit value of power that can be supplied from the power conversion unit to the load and the grid during grid interconnection; The reference value is equal to or less than the upper limit value.

2. The power storage system according to claim 1 , wherein the power generation device is a solar power generation device.

3. The control unit predicting the power generation amount for a target day, which is a day corresponding to a weather forecast for a location where the power generation device is installed, based on the weather forecast; determining whether to change the reference value based on the predicted power generation result; The power storage system according to claim 1 or 2, wherein the reference value is changed in response to a determination that the reference value should be changed.

4. The control unit determining whether or not the predicted power generation is within a predetermined range that is smaller than the reference value, thereby determining whether or not to change the reference value; The power storage system according to claim 3 , wherein the reference value is reduced if the predicted generated power falls within the predetermined range.

5. The control unit In response to the determination that the reference value is to be changed, a peak time is identified, which is a time when the generated power is at a maximum in a next power generation period by the power generation device; identifying a reversal time, which is the first time after the peak time that the generated power becomes smaller than the power consumed by the load; The power storage system according to claim 3 , wherein the reference value is changed so that the storage battery is fully charged in a predetermined time period that includes the inversion time.

6. 4. The power storage system according to claim 3, wherein, when the predicted power generation is equal to or less than a first threshold value that is smaller than the reference value, the control unit controls the charging unit to charge the storage battery with second surplus power of the generated power that exceeds the power supplied to the load.

7. 4. The power storage system according to claim 3, wherein the control unit predicts the generated power on the target day using, in addition to the weather forecast, actual values ​​of the generated power and power consumption by the load in the past before the target day.

8. 7. The power storage system according to claim 6, wherein, if the predicted power generation is equal to or less than a second threshold value that is smaller than the first threshold value, the control unit controls the charging unit so that the storage battery is charged to a predetermined capacity with power supplied from the grid during the night.

9. A storage battery and A power supply system comprising the power storage system according to claim 1 or 2.

10. a power conversion step of supplying power generated by the power generation device to a load and a grid; a charging step of charging a storage battery with surplus power of the generated power that exceeds the power supplied to the load and the grid if the generated power is greater than a predetermined reference value; The generated power depends on the weather, the maximum value of the generated power is greater than an upper limit value of power that can be supplied from the power conversion unit to the load and the grid during grid interconnection; The control method, wherein the reference value is equal to or less than the upper limit value.

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