Method for constituting photovoltaic power generation system

Abstract

To efficiently and properly supply electric power generated by a solar cell panel to storage battery side.SOLUTION: A method for constituting photovoltaic power generation system is for constituting a photovoltaic power generation system that supplies electric power generated by a plurality of solar battery panels constituting a solar battery to a storage battery, electric power system or load equipment via a semiconductor breaker without using a power conditioner, and includes determining the series number of solar battery panels meeting both the first condition that the open voltage of the solar battery is never below the full charge voltage of the storage battery and the second condition that the voltage of the storage battery is within a voltage range for attaining certain charging efficiency or higher.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] An embodiment of the present invention relates to a photovoltaic power generation system configuration method and a photovoltaic power generation system. [Background technology]

[0002] Generally, in a photovoltaic power generation system, the power generated by the solar panel is input to a power conditioner called a PCS (Power Conditioning System) or power conditioner, where it is converted from DC to AC in a DC / AC converter and supplied to load equipment and the power grid. In addition, the power required to operate the load equipment at night when no power is being generated is stored in a storage battery.

[0003] FIG. 28 shows an example of a typical solar power generation system.

[0004] As shown in Fig. 28, a power conditioner 100 is connected to a plurality of PV panels (solar battery panels) 11 constituting a solar cell 10, a storage battery 13, and also to load equipment and a power system (hereinafter referred to as "power system, etc.") not shown. The power conditioner 100 has three power converters. Specifically, it has a DC / DC converter 121 used for MPPT (Maximum Power Point Tracking) control, a DC / DC converter 131 used for charge / discharge control of the storage battery 13, and a DC / AC converter (inverter) 14 used for DC / AC conversion between the power system, etc.

[0005] The energy generated by the PV panel 11 undergoes multiple power conversions in the power conditioner 100, resulting in significant losses. In particular, when the power stored in the storage battery 13 is used on the power grid side, even if each power converter has an excellent efficiency of 0.95, the power will be converted four times by the three power converters in the power conditioner 100, and only about 80% of the energy can be used at best. In reality, each power converter often operates under light load, which significantly reduces the conversion efficiency. For this reason, the current situation is that only about 60% of the generated energy can actually be used. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 7304532 Summary of the Invention [Problem to be solved by the invention]

[0007] As mentioned above, because power conditioners cause large power losses, it is desirable to use the energy generated by the solar panel as efficiently as possible by some means or method that can replace the power conditioner. In such a case, it is also desirable to ensure that the power generated by the solar panel, whose current and voltage change depending on the amount of sunlight and temperature, is appropriately supplied to the storage battery.

[0008] The present invention has been made in consideration of the above circumstances, and aims to provide a method for configuring a solar power generation system and a solar power generation system that enable the power generated by a solar panel to be supplied to a storage battery efficiently and appropriately. [Means for solving the problem]

[0009] A method for configuring a solar power generation system according to an embodiment is a method for configuring a solar power generation system in which power generated by a plurality of solar cell panels constituting a solar cell is supplied to a storage battery, a power grid, or a load device via a semiconductor circuit breaker without using a power conditioner, and includes a step of determining the number of solar cell panels connected in series to satisfy both a first condition that the open circuit voltage of the solar cell does not fall below the fully charged voltage of the storage battery, and a second condition that the voltage of the storage battery falls within a voltage range that achieves a certain level of charging efficiency or higher. [Effects of the Invention]

[0010] According to the present invention, the power generated by the solar cell panel can be efficiently supplied to the storage battery by appropriately maintaining the relationship between the voltage of the solar cell panel and the voltage of the storage battery. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram showing an example of the configuration of a photovoltaic power generation system using a semiconductor circuit breaker according to an embodiment. [Figure 2] FIG. 2 is a diagram showing an example of a system configuration including a microgrid that realizes local production and consumption of electricity by interchange of DC power. [Figure 3] FIG. 3 is a diagram showing an example of a graph showing the characteristics of a typical PV panel under certain solar radiation conditions. [Figure 4] FIG. 4 is a diagram showing an example of a conditional expression indicating Condition 1. In FIG. [Figure 5] FIG. 5 is a diagram showing an example of a graph showing the relationship between the power and voltage obtained from a general solar cell under certain solar radiation conditions. [Figure 6] FIG. 6 shows the time variations of vlow and vhigh shown in FIG. 5 under certain solar radiation conditions, and is a diagram showing an example in which the voltage of the storage battery, which changes with charging, is within a voltage range determined by vlow and vhigh, achieving highly efficient charging. [Figure 7] FIG. 7 is a diagram showing an example of a processing procedure for appropriately combining solar cells and storage batteries. [Figure 8] FIG. 8 is a diagram showing an example of the processing included in steps S12 and S16 in FIG. [Figure 9] FIG. 9 shows an example of a graph showing the change over time of each physical quantity obtained by simulating charging operation on a clear day using the above-mentioned verification PV panel (400 W), simulator, and lithium-ion battery for the "number of series connections: 11." [Figure 10] Figure 10 is a graph (part 1) showing the characteristics of the PV panel (400W) used for verification. [Figure 11] Figure 11 is a graph (part 2) showing the characteristics of the PV panel (400W) used for verification. [Figure 12] FIG. 12 is a diagram showing the specifications (catalog values) of the PV panel (400 W) used for verification. [Figure 13] FIG. 13 shows an example of a graph showing the illuminance dependency of each physical quantity obtained by simulating charging operation using the above-mentioned verification PV panel (400 W), simulator, and lithium-ion battery for the "number of series: 12." [Figure 14] FIG. 14 is a diagram showing an example of the configuration of devices used for verification. [Figure 15] FIG. 15 is a graph showing the relationship between the number of PV panels connected in series and MPP efficiency when the SOC is 0[%]. [Figure 16] FIG. 16 is a diagram showing an example of a graph showing the relationship between the number of PV panels connected in series and MPP efficiency when the SOC is 60[%]. [Figure 17] FIG. 17 is a diagram showing an example of a graph showing the relationship between the number of PV panels connected in series and MPP efficiency when the SOC is 96%. [Figure 18] FIG. 18 is a diagram showing an example of the configuration of devices used for verifying the operation of a DC power converter. [Figure 19] FIG. 19 is a diagram showing an example of a graph showing the results of measuring the conversion efficiency and MPPT efficiency of a DC power converter using the devices shown in FIG. 18, with the "number of series connections being 9." [Figure 20] FIG. 20 is a diagram showing a modification of the conditional expression in FIG. [Figure 21] FIG. 21 is a diagram showing a modification of the conditional expression in FIG. [Figure 22] FIG. 22 is a diagram showing an example of a graph including vlow, vhigh, and vbattery. [Figure 23] FIG. 23 is a diagram showing an example of a graph showing maximum power generation Pmpp, 0.95*Pmpp, and Vhigh and Vlow corresponding to 0.95*Pmpp. [Figure 24] FIG. 24 shows the results of a simulation in which the number n of PV panels connected in series is set to 11. [Figure 25] FIG. 25 shows the results of a simulation in which the number n of PV panels connected in series is set to 12. [Figure 26] FIG. 26 shows the results of a simulation in which the number n of PV panels connected in series is set to 13. [Figure 27] FIG. 27 is a diagram conceptually showing the relationship between the battery voltage-charging current characteristics of a lithium ion battery and the power generation output-voltage characteristics of a solar cell. [Figure 28] FIG. 28 is a diagram showing an example of a general solar power generation system. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments will be described with reference to the drawings.

[0013] <Basic configuration> 1 is a diagram showing an example of the configuration of a solar power generation system using a semiconductor circuit breaker according to an embodiment. Elements common to those in FIG. 28 are given the same reference numerals.

[0014] The solar power generation system 1 shown in FIG. 1 includes a plurality of PV panels 11 constituting a solar cell 10, a semiconductor circuit breaker 12 that operates autonomously depending on the situation, a storage battery 13, and a DC / AC converter 14.

[0015] The semiconductor circuit breaker 12 enables the power generated by the PV panel 11 to be safely and efficiently supplied to the storage battery 13, a power system (not shown), or load equipment without using a power conditioner.

[0016] The semiconductor circuit breaker 12 is connected between the PV panel 11 and the storage battery 13. Specifically, the semiconductor circuit breaker 12 is composed of a plurality of semiconductor switching elements, each of which is configured to be turned on or off depending on the voltage of the storage battery 13 (the voltage of the entire storage battery) and the state of the current flowing through the internal circuit. Each semiconductor switching element can be configured as a MOSFET (Metal-Oxide-Semiconductor Field-Effect-Transistor), a bipolar transistor, an IGBT (Insulated Gate Bipolar Transistor), or a SiC-MOSFET.

[0017] The semiconductor circuit breaker 12 further includes a control unit that turns each semiconductor switching element on or off depending on the voltage, current, or temperature of a predetermined part of the circuit. This control unit monitors the voltage, current, temperature, remaining capacity (SOC) of the storage battery 13, and other conditions of each part through signals supplied from various instruments and the like arranged within the semiconductor circuit breaker 12, and controls the on / off of each semiconductor switching element depending on the conditions. The control unit can be configured with a microcontroller. The power source for the control unit may be configured to be obtained from the solar cell 10 or the storage battery 13.

[0018] The solar power generation system 1 shown in Fig. 1 uses only one power converter that generates power loss. That is, the only power converter is a DC / AC converter 14 that performs DC / AC conversion. This results in a very high energy efficiency of 0.95, unlike conventional power conditioners that have three power converters.

[0019] Although a DC / AC converter is illustrated here as an example of a power converter, the present invention is not limited to this example, and a DC / DC converter may be used instead. If a DC / DC converter is used, direct current power can be exchanged with other devices or systems via a microgrid or the like. In this case, depending on the situation, it may be possible to omit the installation of a DC / DC converter. If the solar power generation system 1 is connected to a microgrid or the like, it may be possible to realize local production and consumption of power in a specific area, for example, thereby reducing the cost of power.

[0020] <Example of system configuration including a microgrid that realizes local production and consumption> Figure 2 shows an example of a system configuration including a microgrid that realizes local production and consumption of electricity by interchange of DC power.

[0021] FIG. 2 shows an example in which a microgrid (local grid) 20 that enables DC power interchange is employed. The microgrid 20 has a DC bus (DC bus) that can supply DC power of, for example, 1500 V. Various devices or systems that can transmit and receive DC power are connected to the DC microgrid 20, including the semiconductor circuit breaker 12 described above. Here, an example is shown in which a plurality of semiconductor circuit breakers 12 are connected to the microgrid 20.

[0022] Each semiconductor circuit breaker 12 is connected to a PV panel 11 that constitutes a solar cell 10, a grid stabilization battery group 13A (a combination of an appropriate number of batteries 13 for stabilizing the power of the microgrid), and an EV charger / discharger (a charger / discharger for electric vehicles) 15.

[0023] In the microgrid 20, in addition to a plurality of semiconductor circuit breakers 12, a plurality of bidirectional DC / DC converters (power converters capable of performing bidirectional DC / DC conversion) 21 may be connected. Each bidirectional DC / DC converter is connected to a power-converterless DC power supply system (a DC power supply system not equipped with a power conditioner) 22, and further, devices or systems 23 such as PV panels, wind turbines, and EV chargers / dischargers are connected to each power-converterless DC power supply system.

[0024] In the example of FIG. 2, each individual semiconductor circuit breaker 12 is connected to the microgrid 20 without using a bidirectional DC / DC converter. In this case, there are advantages such as being less likely to cause momentary power outages and being able to construct the system at a low cost.

[0025] <Two conditions for appropriately supplying the generated power of the PV panel to the battery 13> In the present embodiment, in the photovoltaic power generation system 1 shown in FIG. 1, the generated power of the PV panel 11 whose current and voltage change depending on the sunshine amount and panel temperature is supplied to the battery 13 with high efficiency through the semiconductor circuit breaker 12. For this purpose, in the present embodiment, a first condition (Condition 1) for appropriately directly connecting the PV panel 11 and the battery 13 and a second condition (Condition 2) for efficiently storing the generated power in the battery 13 are considered respectively. In the consideration of Conditions 1 and 2, it is important to grasp the characteristics of the PV panel 11 and the characteristics of the battery 13 respectively. When combining the PV panel 11 and the battery 13, by matching the characteristics of the PV panel 11 (constant current - constant voltage characteristics, etc.) and the characteristics of the battery 13, it becomes possible to efficiently and appropriately supply the power generated by the PV panel 11 to the battery 13 side.

[0026] FIG. 3 shows an example of a graph representing the characteristics of a general PV panel under certain insolation conditions.

[0027] The graph in FIG. 3 shows the global solar irradiance intensity [kW / m for a PV panel with a rated output of 1.3 kW from 4 o'clock to 20 o'clock on a clear summer day. 2], air temperature [°C], panel temperature (or cell temperature) [°C], DC current [A], and DC voltage [V] over time. In the graph of Figure 3, the direction of the arrow attached to each physical quantity indicates the position of the scale (left or right side of the graph) to which the physical quantity should be referred.

[0028] As shown in the graph in Figure 3, PV panels have the characteristic that the DC current (output current) changes according to the global solar radiation intensity (or amount of solar radiation), and the DC voltage (output voltage) changes according to the panel temperature. In particular, from around 6:00 to around 18:00, the higher the panel temperature (cell temperature), the lower the DC power (generated power), and it can be seen that the drop is particularly large in range R centered around noon.

[0029] For this reason, if the voltage of the solar cell drops below the voltage of the storage battery, charging may become impossible. In this embodiment, focusing on this point, the first condition (condition 1) for appropriately directly connecting the PV panel 11 and the storage battery 13 is that the open circuit voltage of the solar cell 10 does not fall below the fully charged voltage of the storage battery 13 (maximum voltage of the storage battery 13).

[0030] Fig. 4 shows an example of a conditional expression that indicates Condition 1. However, the conditional expression shown in Fig. 4 is only an example, and is not limited to this example. Part of the conditional expression may be changed as appropriate.

[0031] In the conditional expression in Figure 4, V battery_max represents the fully charged voltage of the storage battery 13 (the maximum voltage of the storage battery 13). oc represents the open circuit voltage of the solar cell 10.

[0032] V oc is the open-circuit voltage (calculated from the product of a constant A, the panel temperature T, and a predetermined ln function) at the maximum solar irradiance (hereinafter referred to as "maximum solar irradiance") and the maximum cell temperature (hereinafter referred to as "maximum cell temperature") in the installation environment of one solar panel. oc_PV (S max ,T max) and the number of solar panels in series (number of solar panels connected in series N). The ln function includes the panel temperature T and illuminance (or solar radiation) S as variables. The 298 in the ln function is the Kelvin value equivalent to 25°C. The ln function also includes V oc The temperature dependence and illuminance dependence (or solar radiation dependence) of

[0033] The procedure for deriving the conditional expression in FIG. 4 is outlined below.

[0034] 1. The voltage-current characteristic equation of a solar cell (having a constant voltage region and a constant current region) is obtained from the equivalent circuit of the solar cell.

[0035] 2. The exact equations are complex and difficult to handle, so negligible terms are simplified.

[0036] 3. Use physical constants to further simplify the calculation formula.

[0037] 4. Obtain the relationship between current and voltage using illuminance (or solar radiation) S and panel temperature (or cell temperature) T as parameters.

[0038] Using the conditional expressions in FIG. 4 as described above, the panel temperature T and illuminance S in the environment in which the solar power generation system 1 is used, and the full charge voltage (maximum voltage) V of the storage battery 13 are calculated. battery_max After obtaining the values ​​of each of these, the number of PV panels in series that satisfies the conditional formula in Figure 4, i.e., the number of PV panels connected in series, N (N: integer), is selected to determine V oc V battery_max However, in the conditional expression of FIG. 4, V battery_max and V oc If the difference between V and V is too large, the loss increases and the efficiency decreases. battery_max and V oc It is desirable to select an integer N that minimizes the difference between this and the number of PV panels in series. In other words, it is desirable to select the smallest number of PV panels in series among multiple candidates that satisfy condition 1.

[0039] Next, a second condition (condition 2) for storing generated power in the storage battery 13 with high efficiency will be described.

[0040] In order to store electricity in the storage battery 13 with high efficiency, it is important to consider the efficiency of the power supplied from the solar cell 10 to the storage battery 13.

[0041] Figure 5 shows an example of a graph showing the relationship between the power and voltage obtained from a typical solar cell under certain solar radiation conditions. In the graph in Figure 5, the horizontal axis represents the voltage V of the solar cell, and the vertical axis represents the power P obtained from the solar cell.

[0042] The graph in Figure 5 shows a PV curve that shows the relationship between the power P and voltage V of a solar cell. ideal,Vmax ) indicates the power and voltage values ​​when the power is at its maximum. ideal *x" indicates the power obtained by MPPT control of the power conditioner. x represents the power conversion efficiency of the power conditioner. Here, x = 0.95. "P ideal *The lower of the two voltages corresponding to "x" is v low and the larger one is called v high It is called.

[0043] As can be seen from the graph of FIG. 5, when the solar cell 10 and the storage battery 13 are connected, the operating point on the PV curve is ideal *x”, i.e., within the power range low Larger than v high If the solar cell 10 and the storage battery 13 are combined so that the total power consumption falls within a range smaller than the above, it can be said that the storage battery 13 can be charged more efficiently than when a power conditioner is used.

[0044] FIG. 6 is a graph showing the v low and v high The graph shows the time change under certain solar radiation conditions, and the voltage of the storage battery that changes with charging is v low and v highFIG. 10 is a diagram showing an example in which highly efficient charging is achieved within a voltage range determined by

[0045] In the graph of Figure 6, v low and v high The range Q between and is shown. Range Q represents the voltage range at each time that achieves highly efficient charging. battery represents the voltage of the storage battery, which changes over time. When charging of the storage battery begins, the voltage gradually increases as charging progresses, and charging ends when it reaches the full charge voltage.

[0046] As can be seen from the graph in FIG. 6, when the solar cell 10 and the storage battery 13 are connected, the v battery But, v low and v high If the solar cell 10 and the storage battery 13 are combined so that the total power consumption falls within the range Q between the two, it can be said that the storage battery 13 can be charged more efficiently than when a power conditioner is used.

[0047] In this embodiment, focusing on this point, the second condition (condition 2) for storing the generated power in the storage battery 13 with high efficiency is that the voltage of the storage battery 13 during a certain time period falls within a voltage range that achieves a certain level of charging efficiency or higher, that is, within a voltage range that achieves a higher efficiency than the efficiency achieved when MPPT control of the power conditioner is performed.

[0048] By combining the solar cells 10 and the storage batteries 13 (particularly by selecting the number of PV panels connected in series) so as to satisfy both the above-mentioned conditions 1 and 2, it becomes possible to efficiently and appropriately supply the power generated by the PV panels 11 to the storage batteries 13. Note that, in the above explanation, an example has been given in which the "number of PV panels connected in series" is selected so as to satisfy both conditions 1 and 2, but this is not limiting. For example, in order to satisfy condition 2, it is also possible to select not only the "number of PV panels connected in series" but also the "number of storage batteries connected in parallel."

[0049] <Example of processing procedure> Next, an example of a processing procedure for appropriately combining the solar cell 10 and the storage battery 13 will be described with reference to the flowcharts of Figures 7 and 8. These processes can be performed by a computer. However, the processing procedures shown here are only an example and are not limited to this example. Part of the processing may be modified as appropriate.

[0050] As shown in FIG. 7, first, various information such as the temperature and illuminance (or amount of solar radiation) of the PV panel required when combining the solar cell 10 and the storage battery 13, as well as various information indicating the respective characteristics of the solar cell 10 and the storage battery 13, are obtained (step S11).

[0051] Next, based on the acquired information, a combination of solar cell 10 and storage battery 13 is set (step S12).

[0052] The process of step S12 includes a process of selecting the number of PV panels in series so as to satisfy conditions 1 and 2. For example, as shown in FIG. 8, the minimum number of PV panels in series that satisfies condition 1 is selected (step S21), and after confirming that condition 2 is satisfied, a final decision is made to adopt the selected number of PV panels in series (step S22). However, the procedure shown here is merely an example and is not limited to this example. Some of the processes may be modified as appropriate.

[0053] Next, returning to FIG. 7, the solar power generation system 1 is operated in a state where the solar cell 10 and the storage battery 13 are connected via the semiconductor circuit breaker 12 (step S13).

[0054] During operation, it is monitored whether any malfunction has occurred, and it is confirmed whether the above combination needs to be reset (step S14).

[0055] If there is no need to reset the setting (branch to "No" in step S14), the process from step S13 is repeated.

[0056] On the other hand, if some malfunction occurs during operation and it becomes necessary to reset the above combination (branch to Yes in step S14), the process proceeds to step S15.

[0057] In step S15, similar to the processing in step S11 described above, various information such as the temperature and illuminance (or amount of solar radiation) of the required PV panel, as well as various information indicating the respective characteristics of the solar cell 10 and the storage battery 13, are acquired (step S15).

[0058] Next, the combination of solar cell 10 and storage battery 13 is reset (step S16).

[0059] The process of step S16 includes a process of reselecting the number of PV panels in series so as to satisfy conditions 1 and 2. For example, the same processes as steps S21 and S22 in Fig. 8 described above are performed. Note that the process of reselecting the number of PV panels in series may be achieved by manually removing or installing PV panels, or may be achieved by installing a switch capable of changing the number of PV panels in series in advance and operating the switch using a computer or the like.

[0060] After that, the process returns to FIG. 7 and the process from step S13 is repeated.

[0061] <Verification results> Hereinafter, the effectiveness of the photovoltaic power generation system 1 when the solar cell 10 and the storage battery 13 are electrically connected directly and charged without using a power conditioner will be described, based on the results of verification using a simulator or the like.

[0062] Details of the simulator specifications will be given later, but here we connected a simulator (600V, 16.7A) that mimics the operation of a PV panel (400W) to a lithium-ion battery (380V, 64Ah) equivalent to a storage battery via a diode, and verified the effectiveness of each of the four cases of 10 to 13 that had been previously selected as candidates for the number of PV panel series (hereinafter referred to as "number of series 10," "number of series 11," "number of series 12," and "number of series 13," respectively).

[0063] As an example, Figure 9 shows a graph illustrating the change over time in each physical quantity obtained by simulating charging operations on a clear day using the above-mentioned verification PV panel (400 W), simulator, and lithium-ion battery for an "11-series" system. In the graph in Figure 9, the horizontal axis represents elapsed time [hours], the vertical axis (left side) represents voltage [V], and the vertical axis (right side) represents charging current [A] or charging power [kW]. The direction of the arrow attached to each physical quantity indicates the position of the scale (left or right side of the graph) that should be referenced for that physical quantity.

[0064] As can be seen from the graph in Figure 9, the battery voltage, charging current, and charging power initially continue to rise over time until about 4.5 hours have passed (corresponding to noon), after which they reach saturation (however, due to the characteristics of lithium batteries, the battery voltage will fluctuate slightly up and down).

[0065] 10, 11, and 12 show information indicating the characteristics of the PV panel (400 W) used for verification.

[0066] The graph in Figure 10 shows the current-voltage and power-voltage characteristics of the PV panel used for verification. The graph in Figure 10 shows how five different currents I1, I2, I3, I4, and I5 [A] each change according to voltage [V], and also how five different powers P1, P2, P3, P4, and P5 [W] each change according to voltage [V].

[0067] The graph in Figure 11 shows the normalized short-circuit current I sc [%], open circuit voltage V oc [%], maximum power generation P max The graph in Figure 10 shows the temperature dependence of I sc , V oc , P max It is shown that each of these changes depending on the cell body temperature [°C].

[0068] The graph in Figure 12 shows the specifications (catalog values) of the PV panel (400 W) used for verification.

[0069] For crystalline silicon solar cells, when the cell temperature rises by 1°C, the voltage drops by 0.28% and the generated power drops by 0.35%.

[0070] All catalog values ​​are at a temperature of 25°C.

[0071] In the summer in Japan, assuming the cell temperature reaches 65°C, the voltage and power will drop as shown below.

[0072] The voltage will decrease by (0.28[% / ℃] x (65[℃] - 25[℃]) = 11.2[%].

[0073] Power will decrease by (0.35[% / ℃] x (65[℃] - 25[℃]) = 14.0[%].

[0074] Therefore, the number of PV panels used will vary depending on the temperature.

[0075] As an example, Figure 13 shows a graph showing the illuminance dependency of each physical quantity obtained by simulating charging operation using the above-mentioned verification PV panel (400 W), simulator, and lithium-ion battery for "12 series number." In the graph in Figure 13, the horizontal axis is the amount of solar radiation [W / m 2The vertical axis (left side) represents voltage [V], and the vertical axis (right side) represents current [A] or temperature [℃]. The direction of the arrow attached to each physical quantity indicates the position of the scale (left or right side of the graph) that should be referenced for that physical quantity. I sc is the short circuit current, I mp is the operating current at maximum output, and V oc is the open circuit voltage, V mp indicates the operating voltage at maximum output.

[0076] The graph in Figure 13 shows the short-circuit current I sc and maximum output operating current I mp changes in proportion to the solar radiation intensity, while the open-circuit voltage V oc and maximum output operating voltage V mp is shown to decrease as the cell temperature increases.

[0077] FIG. 14 shows an example of the configuration of the equipment used for the verification.

[0078] 14 shows an example configuration in which a lithium ion battery 40 representing the aforementioned lithium ion battery (380 V, 64 Ah) and a simulator 41 representing the aforementioned simulator (600 V, 16.7 A) are connected via a diode 42. A voltmeter 43 for measuring voltage and an ammeter 44 for measuring current are installed on the line connecting the simulator 41 and the diode 42.

[0079] The simulation contents are as follows:

[0080] As mentioned above, the candidate numbers of PV panels in series were "10," "11," "12," and "13," and the simulation was performed under the following conditions.

[0081] Voltage dependence on cell temperature: -0.28[% / ℃] Output power dependence on cell temperature: -0.35[% / ℃] Solar radiation intensity: 0 to 1080 [W / m 2 ] Weather patterns: sunny, cloudy, rainy, etc. The evaluation items are as follows:

[0082] The system's power consumption was set at a maximum of 17W (heat generation by the diode).

[0083] MPP (Maximum Power Point) efficiency (%) was calculated by multiplying the actual power generated by the solar radiation by 100.

[0084] Below, we show the results of simulations conducted for "10 series connections," "11 series connections," "12 series connections," and "13 series connections," and calculated the MPP efficiency.

[0085] Fig. 15 shows an example of a graph representing the relationship between the number of PV panels connected in series and MPP efficiency when the SOC is 0%. Fig. 16 shows an example of a graph representing the relationship between the number of PV panels connected in series and MPP efficiency when the SOC is 60%. Fig. 17 shows an example of a graph representing the relationship between the number of PV panels connected in series and MPP efficiency when the SOC is 96%.

[0086] In each graph, the horizontal axis represents illuminance [W / m 2 ], and the vertical axis represents MPP efficiency [%].

[0087] In the graph of Figure 15 (SOC: 0[%]), in the case of "10 series connections", as the illuminance increases, the MPP efficiency drops below 95[%] and drops sharply. This is because as the illuminance increases, the cell temperature rises, the power output decreases, and the current flowing to the lithium battery decreases. In the case of "11 series connections", even if the illuminance changes, the MPP efficiency always exceeds 95[%]. This is because V battery_max and V oc This is because the difference between the two is small, and the loss is small, so high efficiency is maintained. In the case of "12 series" and "13 series", the MPP efficiency rarely exceeds 95%. This is because V battery_max and V oc This is because the difference between the two is large, resulting in large losses and a decrease in efficiency.

[0088] The graph in Figure 16 (SOC: 60%]) shows a similar trend to the graph in Figure 15. In particular, when the number of series is 12, the MPP efficiency approaches 100% over a wide range. The graph in Figure 17 (SOC: 96%]) also shows a similar trend to the graph in Figure 16.

[0089] Next, as another verification, the conversion efficiency and MPPT efficiency of the DC power converter were measured for comparison and the results are shown below. In this verification, the operation of the DC power converter was verified.

[0090] FIG. 18 shows an example of the configuration of the equipment used to verify the operation of the DC power converter.

[0091] FIG. 18 shows an example configuration in which a lithium ion battery 50 equivalent to the aforementioned lithium ion battery (380 V, 64 Ah) and a simulator 51 equivalent to the aforementioned simulator (600 V, 16.7 A) are connected via a bidirectional DC / CD converter (5 kW) 52, and a 24 V power supply 53 and a computer (PC) 54 for MPPT control are connected to the bidirectional DC / CD converter 52.

[0092] Furthermore, a diode 55, an ammeter 56, and a voltmeter 57 are installed between the simulator 51 and the bidirectional DC / CD converter 52, and an ammeter 58 and a voltmeter 59 are installed between the bidirectional DC / CD converter 52 and the lithium-ion battery 50. Furthermore, an ammeter 60 is installed between the bidirectional DC / CD converter 52 and the 24V power supply 53.

[0093] The simulation contents are as follows:

[0094] The number of PV panels in series was chosen as "9 in series" and the simulation was performed under the following conditions.

[0095] Voltage dependence on cell temperature: -0.28[% / ℃] Output power dependence on cell temperature: -0.35[% / ℃] Solar radiation intensity: 150, 200, 400, 600, 800, 1000 [W / m 2 ] The evaluation items are as follows:

[0096] ·Conversion efficiency is η=P out [W] / (P in [W]+24[V]×I AUX [A])

[0097] MPP efficiency [%] was calculated by {(actual generated power) / (maximum point power (Ir,t))}×100.

[0098] Fig. 19 shows an example of a graph showing the results of measuring the conversion efficiency and MPPT efficiency of a DC power converter with a "series number of 9" and using the devices shown in Fig. 18. In the graph of Fig. 19, the horizontal axis represents the load current [A] (= charging current), and the vertical axis represents the efficiency [%].

[0099] The graph in Figure 19 shows that while the MPPT efficiency is 96% or higher across the entire range, the DC / CD conversion efficiency shows a large drop in the range where the load current is small.

[0100] From the above verification results, the following could be confirmed:

[0101] When the number of PV panels in series is 11 (V battery_max and V oc The efficiency was highest when the difference between the SOC and the solar radiation intensity was smallest, and the MPP efficiency was extremely high at over 98% even when the SOC and the solar radiation intensity were changed.

[0102] Generates power even in low light conditions.

[0103] · Although a power conditioner was not used, the MPP efficiency was equivalent to that of a power conditioner.

[0104] <Summary of the embodiment> From the above, according to the embodiment, the following effects can be obtained.

[0105] By optimizing the configuration of the PV panels and storage battery, even a simple configuration in which the two are electrically connected in series can achieve MPP efficiency equal to or higher than that of systems using current power conditioners.

[0106] Parallel connection of PV panels does not need to exceed the maximum charging current of the storage battery. For larger scales, you can use multiple pairs of PV panels and storage batteries to expand the scale.

[0107] -System efficiency can be significantly improved from the previous approximately 65% ​​to 95%.

[0108] If the storage battery is 380V, the number of PV panels in series will be 11. If the power generation capacity of each PV panel is 400W, the power generation capacity will be 4.4kW, which is suitable for general household use.

[0109] A more specific example will be described below.

[0110] Example 1 First, the first embodiment will be described. In the first embodiment, a specific example of a method for determining the optimum number of PV panels connected in series will be described.

[0111] The following may be adopted as a specific procedure for determining the number of PV panels in series.

[0112] Step 1. The specifications of the storage battery must be decided first, as there is little flexibility in the battery capacity (number of series or parallel connections).

[0113] Step 2. Determine the V of the solar cell you are using. oc_PV (S max ,T max ) to check.

[0114] Step 3. Determine the minimum number of PV panels in series, N, that satisfies the conditional formula shown in Figure 20. s_pv(an integer). This conditional expression is different from the conditional expression in Figure 4 above in that it is based on the wiring resistance R se The conditional equation in Figure 20 is based on the maximum power generation current I pv_mpp is the full charge voltage V battery_max The conditions under which the signal will flow are shown below. Details will be explained later.

[0115] Step 4. Adjust the number of parallel solar panels (called strings) connected in series.

[0116] In step 2 above, V oc_PV (S max ,T max ) calculates the open circuit voltage of a PV panel at the maximum solar radiation intensity and maximum cell temperature under the conditions of use. There are two ways to do this:

[0117] Method 1:V oc_PV (S max ,T max ) is found from the derived equation.

[0118] Method 2: V from the PV panel datasheet oc Check the temperature dependence of V oc The data (usually 25°C) is corrected to the actual cell temperature.

[0119] In addition, in the above-mentioned step 3, the minimum number of PV panels in series N that satisfies the conditional expression in FIG. 20 is s_pv To find the integer, the value of each element in the conditional expression is calculated as follows: V battery_max Regarding the maximum charging voltage, check the battery datasheet and calculate I pv_mpp Regarding the maximum output operating current I from the solar cell datasheet, mp Check out R se For this, enter the wiring resistance from the solar panel to the storage battery.

[0120] Next, the above-mentioned steps 1, 2, and 3 will be described in more detail.

[0121] Step 1. The specifications of the storage battery, etc. shall be as follows:

[0122] Iron phosphate lithium-ion battery Operating voltage range: 320V~401V Maximum charge / discharge current: ±50A Solar panels Silicon polycrystalline PV panel (390W) Open circuit voltage (V oc ): 43.75V, short circuit current (I sc ):11.39A (at 25℃) Maximum output operating current (I mp ):10.67A Temperature dependency: Voltage -0.28[% / ℃], Power -0.35[% / ℃] PV cell maximum temperature setting: 65[℃] Maximum solar radiation intensity: 1000 [W / m 2 ] Step 2. If you use Method 1, V oc_pv When using Method 2, calculate V from the catalog value. oc_pv This gives the following result, for example:

[0123] V oc_pv =-V oc ×(100[%]-0.28[% / ℃]×ΔT) =43.75[V]×(100-0.28×40) / 100=38.85V I in the conditional expression in Figure 20 pv_mpp As shown in the conditional expression in Figure 21, mp Then, enter values ​​into each element of the conditional expression in Figure 21. mp Since temperature dependency is small, use the data sheet value.

[0124] This gives the following result:

[0125] (401[V]+11.4[A]×2[Ω])<(N s_pv ×38.85[V]) As a result, Ns>10.9, and the smallest integer that satisfies the condition is 11.

[0126] Next, operation check by charging simulation will be described with reference to FIGS.

[0127] In outdoor verification, it is impossible to repeatedly check the solar radiation intensity and cell temperature under the same conditions, so a comparison was made using a simulation. In addition, actual solar radiation data and cell temperature data on a clear day, data on PV panels from a specified manufacturer, and V-Ah characteristic data for the storage battery were used.

[0128] In Figure 22, v low and v high and v battery 22 shows an example of a graph including the above. In the graph of Fig. 22, the horizontal axis represents elapsed time [sec], and the vertical axis represents the voltage [V] of the solar cell.

[0129] The simulation period was set to 12 hours (from 6:00 to 18:00) as shown in FIG.

[0130] Next, V oc_pv The solar radiation intensity S and the cell and temperature T data for each hour are input into the mathematical formula to create the IV characteristics and PV characteristics for each hour, and the maximum power generation P mpp asked for.

[0131] Figure 23 shows the maximum power generation P mpp , 0.95*P mpp , and the said 0.95*P mpp V corresponding to high ,V low An example of a graph showing

[0132] As shown in Figure 23, when a conventional power converter with 95% efficiency is connected, the conversion output value is 0.95*P mmp and V at the two intersections of the P-V characteristic curves. high and V low The value of was calculated and plotted. The simulation was performed every second, and every second was reflected in the V-Ah characteristics of the battery.

[0133] Figure 22 shows the V battery V high and V low The existence of this gap indicates that charging was possible with an energy efficiency of over 95%.

[0134] Next, with reference to the graphs of FIGS. 24, 25, and 26, the results of a simulation in which the number n of PV panels connected in series is changed to 11, 12, and 13 will be shown.

[0135] In the graph of Figure 24, when the number of PV panels in series is 11, the battery voltage V battery In most of the time, V low and V high It is located between the two, indicating that highly efficient charging is possible.

[0136] In the graph of Figure 25, when the number of PV panels in series is 12, the voltage of the solar cells becomes large, so the storage battery voltage V battery In the morning, V low It can be seen that it is below .

[0137] In the graph of Figure 26, when the number of PV panels in series is 13, the voltage of the solar cells becomes even larger, so the battery voltage V battery In the evening, V low In this case, the efficiency drops and the number of PV panels in series is not optimal.

[0138] <Example 2> Next, a second embodiment will be described.

[0139] In Example 2, a specific example of a method for determining the optimal number of PV panels in series will be described from a different perspective than in Example 1. Here, the optimal number of PV panels in series is calculated based on two calculation policies.

[0140] The first calculation policy (calculation policy 1) is to use the conditional expression in FIG. 21, which was introduced as one of the conditional expressions showing the above-mentioned condition 1.

[0141] The second calculation policy (Calculation Policy 2) is to accurately calculate v within the range Q in Figure 6, which was introduced as a measure of Condition 2. battery The purpose of this is to utilize the constant voltage characteristics in the constant voltage region when charging the storage battery 13 with a constant current constant voltage charging method (a charging method typified by lithium ion batteries, etc.) so that the operating point of (1) is located at the same position as the voltage at which the cell temperature of the solar cell 11 is at its highest and the output is at its maximum, and the voltage at which the battery voltage becomes flat when the storage battery 13 is supplied with a constant current are made equal.

[0142] 27(a) and (b) conceptually show the relationship between the battery voltage-charging current characteristics of a lithium ion battery and the power output-voltage characteristics of a solar cell.

[0143] As shown in FIG. 27(a), when charging a lithium-ion battery, there is a region where the voltage becomes flat. Specifically, there is a constant current / constant voltage region U where the SOC is between about 25% and about 75% and the current and voltage are constant. In this example, the voltage in this region U and the voltage at maximum output when the cell temperature of the solar cell 11 is at its highest, that is, the generated power W shown in FIG. 27(b), mp_Tmax Voltage V mp_Tmax This will cause the solar cell 10 to charge the storage battery 13 at maximum output in the voltage range where the storage battery 13 should be most charged. When the voltage of the storage battery 13 reaches SOC 75% or higher, the voltage will rise. As the voltage of the solar cell 10 also rises, the charging current of the solar cell 10 will decrease. In other words, the charging current will decrease and be automatically controlled in a safe direction. However, because overcharging cannot be completely prevented, a separate physical means will be provided to open the charging circuit and stop charging if the charging voltage is about to exceed the full charge voltage.

[0144] The specific specifications of the solar cells and storage batteries are as follows:

[0145] Solar panel (390W) Maximum output operating voltage (V mp ):36.49[V], Operating current at maximum output (I mp ):10.69[A] Open circuit voltage (V oc ): 43.75 [V], short circuit current (I sc ):11.39[A](at 25℃) Temperature coefficient: V oc The characteristic is -0.28[% / ℃],P max The characteristic is -0.34[% / ℃] Lithium-ion battery Operating voltage range: 350~384V Plateau voltage (= open-circuit voltage in the plateau region between SOC 25% and SOC 75%): 375 V In addition, the maximum output operating voltage V when the maximum temperature of the solar cell in Tokyo is 65°C mp V oc and V mp It is known that the ratio of is almost the same even when temperature and illuminance change.

[0146] Here, the open circuit voltage V at 65°C oc_65 the open circuit voltage V oc The value of (43.75[V]) and V oc Calculate using the following formula, using the temperature coefficient value (-0.28 [% / ℃]) related to the characteristics.

[0147] V oc_65 =V oc ×(100[%]-0.28[% / ℃x](65[℃]-25[℃])) / 100=V oc ×0.916=43.75[V]×0.916=40.0[V] Next, the maximum output operating voltage V at 65°C mp_65 The calculated V oc_65 The value of (40.0 [V]) and the operating voltage V at maximum output shown in the specifications mp value (36.49[V]) and open circuit voltage V oc Using the value of (43.75 [V]), calculate using the following formula.

[0148] V mp_65 =V oc_65 ×(V mp / V oc )=40.0V×(36.49[V] / 43.75[V])=33.36[V] Next, the number of PV panels in series Ns is calculated based on the maximum output operating voltage V at 65°C. mp_65 The voltage (33.36 [V]) is calculated using the value of the plateau voltage (i.e., the plateau voltage of the lithium-ion battery) shown in the specifications (375 [V]) using the following formula.

[0149] Ns = (Lithium-ion battery plateau voltage) / V mp_65 =375[V] / 33.36[V]=11.24 When this decimal point-including number "11.24" is expressed as an integer, Ns=11.

[0150] In other words, the result is that the number of PV panels in series Ns=11.

[0151] Here, it is confirmed whether the calculated Ns=11 satisfies the conditional expression shown in calculation policy 1 (the conditional expression in FIG. 21).

[0152] In the conditional expression of FIG. 21, the calculated Ns=11 is used as N s_pv Also, substitute the calculated V oc_65 Change the value (40.0[V]) to "V oc_PV (S max ,T max )

[0153] Furthermore, the maximum value of the operating voltage range (384[V]) shown in the specifications is V battery_max and calculate the maximum output operating current I mp The value of (10.69[A]) is I mp Also, the value of the wiring resistance (1 [Ω]) from the PV panel to the storage battery is R se Substitute into

[0154] As a result, the conditional expressions in FIG. 21 become as follows:

[0155] (384[V]+10.69[A]×1[Ω])<(11[sheets]×40.0[V]) In other words, 394.7[V]<440[V], and it was confirmed that the condition was met.

[0156] As described above in detail, according to the embodiment, the power generated by the solar cell panel can be efficiently and appropriately supplied to the storage battery.

[0157] The present invention is not limited to the above-described embodiments, and the components can be modified and embodied in practice without departing from the spirit of the invention. Furthermore, various inventions can be created by appropriately combining multiple components disclosed in the above-described embodiments. For example, some components may be omitted from all the components shown in the embodiments. Furthermore, components from different embodiments may be appropriately combined. [Explanation of symbols]

[0158] 1...Photovoltaic power generation system, 10...Solar cell, 11...PV panel (solar panel), 12...Semiconductor circuit breaker, 13...Storage battery, 13A...Grid stabilization storage battery group, 14...DC / AC converter, 15...EV charger / discharger, 20...Microgrid, 21...Bidirectional DC / DC converter, 22...Power conditioner-less DC power supply system, 23...Equipment or system such as PV panel, wind turbine, EV charger / discharger, 40,50...Lithium-ion battery, 41,51...Simulator, 52...Bidirectional DC / DC converter, 42,55...Diode, 43,57,59...Voltmeter, 44,56,58,60...Ammeter, 53...24V power supply, 54...Computer (PC).

Claims

1. A method for configuring a solar power generation system that supplies power generated by a plurality of solar cell panels constituting a solar cell to a storage battery, a power system, or a load device via a semiconductor circuit breaker without using a power conditioner, comprising: determining the number of solar cell panels connected in series to satisfy both a first condition that the open circuit voltage of the solar cell does not become equal to or lower than a fully charged voltage of the storage battery and a second condition that the voltage of the storage battery falls within a voltage range that achieves a certain level of charging efficiency, A method for configuring a solar power generation system.

2. In the step, the smallest number of serially connected solar cell panels is selected from among a plurality of candidates for the number of serially connected solar cell panels that satisfy the first condition. The method for configuring a photovoltaic power generation system according to claim 1 .

3. The open-circuit voltage of the solar cell is calculated by multiplying the open-circuit voltage at the maximum solar radiation intensity and the maximum cell temperature in the installation environment of one solar cell panel by the number of solar cell panels connected in series. The method for configuring a photovoltaic power generation system according to claim 1 .

4. The open-circuit voltage of the one solar cell panel is calculated from a function including the temperature of the solar cell panel and the illuminance or the amount of solar radiation. The method for configuring a photovoltaic power generation system according to claim 3 .

5. The voltage range in which a certain level of charging efficiency is achieved is a voltage range in which a higher efficiency than that achieved when MPPT (Maximum Power Point Tracking) control is performed is achieved. The method for configuring a photovoltaic power generation system according to claim 1 .

6. In the step, the voltage when the cell temperature of the solar cell is at its highest and the output is at its maximum is made equal to the voltage in a voltage region where the battery voltage is flat when the storage battery is supplied with a constant current. The method for configuring a photovoltaic power generation system according to claim 1 .

7. A solar power generation system that supplies power generated by a plurality of solar cell panels constituting a solar cell to a storage battery, a power system, or a load device via a semiconductor circuit breaker without using a power conditioner, the number of solar cell panels connected in series is set so as to satisfy both a first condition that the open circuit voltage of the solar cell does not become equal to or lower than the fully charged voltage of the storage battery, and a second condition that the voltage of the storage battery falls within a voltage range that achieves a certain level of charging efficiency or higher; Solar power generation system.

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