Battery diagnostic method and battery diagnostic device

Abstract

To provide a technique capable of grasping with sufficient accuracy the remaining life of a solar battery, even when the calculation accuracy of shunt resistance is insufficient.SOLUTION: A battery diagnosis method of the present invention discriminates a first period when shunt resistance drops with a first drop rate from a second period when it drops with a second drop rate larger than the first drop rate, and estimates the remaining life of a solar battery by calculating the time required for the deterioration state of the solar battery to reach a reference value from the second period or a period after the second period.SELECTED DRAWING: Figure 8

Description

[Technical field]

[0001] The present invention relates to a technique for diagnosing a solar cell. [Background technology]

[0002] More than seven years have passed since the start of the Feed In Tariff (FIT) system, and it is becoming clear that some solar power generation systems have guaranteed performance and others do not. In this situation, the need to evaluate the long-term value of power plants has become even higher due to the activation of the secondary market. In such technical due diligence, it is important to estimate the lifespan of solar cell modules.

[0003] In recent years, attention has been focused on deterioration of solar cell modules due to increased moisture permeability of the filler and sealing materials that make up the solar cell module. When a solar cell module deteriorates, the shunt resistance of the solar cell module decreases.

[0004] The following Patent Documents 1 and 2 are known as prior art for quantifying degradation from the shunt resistance of a solar cell module. Patent Document 1 describes a method for detecting a drop in shunt resistance at an early stage using impedance diagnosis. Patent Document 2 describes determining the lifespan of a solar cell string when the shunt resistance value drops below a threshold value. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2014-165232 A [Patent Document 2] JP 2004-287787 A Summary of the Invention [Problem to be solved by the invention]

[0006] Many methods for measuring the shunt resistance of solar cells have been proposed. However, the measurement of shunt resistance has a large error due to the influence of the exposure environment, so it is difficult to estimate the life of a solar cell (module or string) based on the measurement results.

[0007] Patent Document 1 describes the use of impedance to detect a drop in shunt resistance at an early stage, but does not mention the extent to which the measured impedance correlates with the value of the shunt resistance. Patent Document 2 describes that if the measured shunt resistance falls below a threshold, it is determined that the device has reached its full life. However, it does not mention remaining life prediction.

[0008] The present invention has been made in consideration of the above-mentioned problems, and aims to provide a technology that can grasp the remaining life of a solar cell with sufficient accuracy even when the calculation accuracy of the shunt resistance is insufficient. [Means for solving the problem]

[0009] The battery diagnosis method of the present invention distinguishes between a first period in which the shunt resistance decreases at a first rate and a second period in which the shunt resistance decreases at a second rate that is greater than the first rate, and estimates the remaining life of the solar cell by calculating the time required for the degradation state of the solar cell to reach a reference value from the second period or a period after the second period. Effect of the Invention

[0010] According to the battery diagnosis method of the present invention, even if the calculation accuracy of the shunt resistance is insufficient, the remaining life of the solar cell can be grasped with sufficient accuracy. Problems, configurations, effects, etc. other than those described above will become clear from the description of the following embodiments. [Brief description of the drawings]

[0011] [Figure 1] FIG. 2 is a side cross-sectional view of a solar cell module. [Diagram 2]2 is an equivalent circuit diagram of a solar cell string 1 and a solar cell module 1a. [Diagram 3] The results of accelerated testing of solar cell modules in a high-temperature, high-humidity environment of 85°C and 85% are shown. [Figure 4] FIG. 1 is a configuration diagram of a solar power generation system. [Diagram 5] 1 is a diagram showing a configuration for acquiring current-voltage characteristics of a solar cell string 1 via a junction box 41 at a power generation site where a solar power generation system is installed. [Figure 6] 2 is an example of a current-voltage characteristic curve of the solar cell string 1. [Figure 7] FIG. 13 is a diagram showing the relationship between shunt resistance and solar cell output. [Figure 8] 1 is a diagram showing the relationship between the decrease in cell output and the deterioration of shunt resistance when an accelerated test is performed on a solar cell module in a high-temperature and high-humidity environment of 85° C. and 85%. [Figure 9] 10 is a flowchart illustrating a procedure for estimating the remaining lifetime of a solar cell module and a string. [Figure 10] 10 is a flowchart illustrating a procedure for estimating the remaining lifetime of a solar cell module and a string. [Figure 11] FIG. 11 is a configuration diagram of a battery diagnosis device 100 according to a third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] <Embodiment 1> FIG. 1 is a side cross-sectional view of a solar cell module. A plurality of solar cells 1a are connected by interconnectors 1b. The solar cells 1a are protected by a filler 1e between a glass plate 1c and a back sheet 1d. Furthermore, a sealant 1f is provided between an aluminum frame 1g and the glass plate 1c and between the aluminum frame 1g and the back sheet 1d, thereby preventing moisture from entering the inside of the module. EVA (ethylene vinyl acetate copolymer resin) is generally used as the filler 1e. Butyl or silicone is generally used as the sealant 1f.

[0013] 2 is an equivalent circuit diagram of a solar cell string 1 and a solar cell module 2. The solar cell string 1 is formed by arranging a plurality of solar cell modules 2 in series. The solar cell module 2 can be expressed as a plurality of solar cell cells 22a arranged in series, each of which is bypassed by a bypass diode 22b. The equivalent circuit of the solar cell 22a has a current source 22c, a pn junction diode 22e, a shunt resistor 22f (parallel resistor), and a series resistor 22g. The current source 22c supplies a current proportional to the amount of solar radiation.

[0014] When solar cell modules are used for long periods in exposed environments, the weather resistance of the fillers and sealants deteriorates, causing a decrease in adhesion ability, allowing moisture to penetrate and reducing the performance of the solar cells.

[0015] Figure 3 shows the results of accelerated testing of solar cell modules in a high-temperature, high-humidity environment of 85°C and 85% humidity. In principle, the structure of all solar cell modules is the same, so although there are differences in the materials used and manufacturing capabilities, it is expected that once moisture penetrates the inside of the module, the module performance will degrade at a similar rate. In Figure 3, the three solar cell modules (represented by curves 3a, 3b, and 3c, respectively) start to degrade at different times, but it can be seen that the rate of performance degradation over time is the same.

[0016] FIG. 4 is a configuration diagram of a photovoltaic power generation system. The photovoltaic power generation system is composed of a junction box 41 bundling a plurality of photovoltaic strings 1, a current collecting rack 42 bundling a plurality of junction boxes 41, a DC-DC converter 43, and an inverter 44. The junction box 41 is equipped with a backflow prevention diode 41a for preventing current from flowing into the photovoltaic string, a circuit breaker 41b for cutting off the current path, an overall breaker 41c, and the like. The sum of the plurality of strings bundled by the junction box 41 is connected to a DC-DC converter 43 via a current collecting rack 42. A breaker 42a is also installed inside the current collecting rack. The DC-DC converter 43 controls the plurality of photovoltaic strings collectively. The DC voltage and DC current stepped up and down by the DC-DC converter 43 are converted to AC by the inverter 44 and connected to the system.

[0017] 5 is a diagram showing a configuration for acquiring the current-voltage characteristics of the solar cell string 1 via a junction box 41 at a power generation site where a solar power generation system is installed. A terminal of a measuring instrument 5 for measuring the current-voltage characteristics is connected to the p-side of the solar cell string 1, and the other terminal is connected to the n-side of the solar cell string 1. When measurement is started, the load of the electronic load 53 in the measuring instrument 5 is varied, the current flowing in from the solar cell string 1 is measured by an ammeter 51, and the voltage of the solar cell string 1 at that time is measured by a voltmeter 52. In this way, the current-voltage characteristics of the solar cell string 1 can be obtained. It goes without saying that the solar cell module 2 is also measured in the same way.

[0018] FIG. 6 is an example of a current-voltage characteristic curve of the solar cell string 1. When the performance of the solar cell string 1 is degraded, the graph becomes inclined in the region 6a. The shunt resistance is generally calculated from the change in voltage and current in the region 6a. However, the region 6a is susceptible to not only the decrease in shunt resistance but also to the influence of solar radiation fluctuations and partial shading during measurement. In addition, the region 6a is required to be in a state close to a short circuit, and a large current flows from the solar cell string 1, so that the influence of measurement errors is likely to occur. Furthermore, even if the bypass diode 22b is degraded, the slope of the region 6a fluctuates. In other words, due to these factors, it is difficult to accurately measure the shunt resistance based only on the current-voltage characteristic, and therefore it is difficult to estimate the remaining life of the solar cell from the measured shunt resistance value.

[0019] Figure 7 shows the relationship between the shunt resistance and the solar cell output. It can be seen that when the shunt resistance becomes less than 1 Ω, a sudden change in output finally becomes visible.

[0020] Figure 8 shows the relationship between the decrease in cell output and the deterioration of shunt resistance when an accelerated test was performed on a solar cell module in a high-temperature and high-humidity environment of 85°C and 85% humidity. The upper and lower figures in Figure 8 are depicted on the same time scale. As mentioned in the explanation of Figure 3, the structure of the solar cell module is the same, so many silicon crystalline solar cell modules show similar characteristics.

[0021] It can be seen that the sudden drop in output as shown in 8b occurs at an earlier stage than the sudden drop in output as shown in 8a. The state in which the shunt resistance is close to 1000 Ω is defined as the first period (8c), the period in which the shunt resistance suddenly drops from 1000 Ω to about 1 Ω is defined as the second period (8d), and the period after which the change in shunt resistance becomes gradual is defined as the third period (8e). If the second period (8d) can be identified even in an exposed environment, it will be easy to estimate in which period of the accelerated test the solar cell is placed, even if the measurement accuracy of the shunt resistance is low.

[0022] FIG. 9 is a flowchart explaining the procedure for estimating the remaining life of a solar cell module and a string. This flowchart can be executed by a device that diagnoses the remaining life of a solar cell. For example, this flowchart can be executed by devices such as the DC-DC converter 43 and the inverter 44. Other devices may also execute this flowchart. In the following, it is assumed that these battery diagnostic devices execute this flowchart. The battery diagnostic device holds the results of accelerated tests that have already been performed on the solar cells, and uses those results to execute each of the following steps. The battery diagnostic device executes this flowchart periodically (for example, once a month, every six months, every twelve months, etc.).

[0023] (Figure 9: Step S901) The battery diagnostic device calculates the shunt resistance of a solar cell module or string.

[0024] (Figure 9: Step S902) The battery diagnostic device judges whether the solar cell has reached the second period described in Fig. 8. The judgment procedure can be, for example, as follows. The time rate of decrease of the shunt resistance is obtained according to the difference between the previous calculation of the shunt resistance and the current calculation. If the difference between the time rate of decrease in the previous calculation and the time rate of decrease in the current calculation is equal to or greater than a threshold value, it can be judged that the shunt resistance has suddenly decreased (i.e., entered the second period).

[0025] (Figure 9: Step S902: Supplement) This step is based on the assumption that the solar cell is in the second period when this flowchart is carried out. However, even if the solar cell has passed the second period and reached the third period, the following steps are the same. The procedure for distinguishing between the second period and the third period can be the same as that described in the second embodiment.

[0026] (Figure 9: Step S903) The battery diagnostic device uses the results of the accelerated test that has already been performed to determine the acceleration in the accelerated test. Specifically, the device determines the ratio between the time that has elapsed since the start of operation of the solar cell until it reaches its current performance (i.e., the time that has elapsed from the start of operation until this step is performed) and the time that has elapsed from the performance at the time of shipment until it reaches the performance at the time of this step in the accelerated test. This ratio can be used as the acceleration in the accelerated test.

[0027] (Figure 9: Step S903: Calculation example) At the time this step is carried out, 9000 hours have passed since the solar cell began operation, and the solar cell's performance has decreased to 95% of what it was at the beginning of operation (i.e., a 5% decrease). In the accelerated test already carried out, it was assumed that 3000 hours had passed before the solar cell's performance had decreased to 95% of what it was at the time of shipment. In this case, the acceleration of the accelerated test is 9000 / 3000=3 times.

[0028] (Figure 9: Step S903: Supplement) In the above explanation, the ratio between the actual elapsed time and the elapsed time in the accelerated test is calculated based on the performance of the solar cell at the time of performing this step, but the performance of the solar cell used as the reference does not necessarily have to be that at the time of performing this step. For example, if the time elapsed until the performance of the solar cell drops to 98% is known in advance, both the actual time and the accelerated test time, the ratio of those times may be used.

[0029] (Figure 9: Step S904) The battery diagnostic device calculates the remaining life of the solar cell using the acceleration of the accelerated test. For example, it is specified that the solar cell reaches the end of its life (cannot be used any further) when it reaches 80% of its performance at the time of shipment. From the results of the accelerated test, the battery diagnostic device obtains the elapsed time in the accelerated test from when the solar cell's performance at the time of performing this step to when it reaches 80% of its performance at the time of shipment during the accelerated test. This corresponds to the remaining life in the accelerated test. The battery diagnostic device estimates the actual time from when the present step is performed until the end of its life by multiplying the remaining life in the accelerated test by the acceleration. This time becomes the remaining life of the solar cell.

[0030] (Figure 9: Step S904: Supplement) This step is significant in that it estimates the time it will take for the solar cell to reach its end of life in an actual environment from the second period (or a subsequent period) using the time it will take from the second period (or a subsequent period) to reach its end of life in the accelerated test. In other words, it is significant to estimate the remaining life of the solar cell using data on the accelerated test, particularly data on the second period.

[0031] <First embodiment: Summary> The battery diagnostic device according to the present embodiment identifies a second period during which the rate of decrease of the shunt resistance over time increases rapidly. The battery diagnostic device further estimates the actual remaining life of the solar cell using the elapsed time from the second period to the end of life in the accelerated test and the acceleration of the accelerated test. By estimating the remaining life using the second period during which the shunt resistance decreases significantly, the remaining life can be estimated with a certain degree of accuracy even when the measurement accuracy of the shunt resistance is insufficient. Furthermore, by using data related to the second period in the accelerated test, the remaining life can be estimated without actually wearing out the solar cell while maintaining the estimation accuracy.

[0032] <Embodiment 2> In the first embodiment, a procedure for estimating the remaining life of a solar cell is described using data related to the second period from the results of the accelerated test that has already been performed. In the second embodiment of the present invention, a procedure for estimating the remaining life of a solar cell is described using a change over time in the actual shunt resistance of the solar cell instead of using the results of the accelerated test.

[0033] Fig. 10 is a flowchart explaining the procedure for estimating the remaining lifespan of a solar cell module and a string. This flowchart can be executed by a battery diagnostic device similar to that of Fig. 9. The battery diagnostic device executes this flowchart periodically (for example, once a month, once every six months, once every twelve months, etc.).

[0034] (Figure 10: Step S1001) The battery diagnostic device assumes that the solar cell has reached the first period or the second period described in FIG.

[0035] (FIG. 10: Steps S1002 to S1003) The battery diagnostic device calculates the shunt resistance value of the solar cell (S1002). The battery diagnostic device obtains the time decrease rate of the shunt resistance in the same manner as in S902 (S1003).

[0036] (FIG. 10: Steps S1004 to S1005) If the time rate of decrease in shunt resistance calculated in S1002 has updated the maximum value up to that point (S1004: Yes), the battery diagnostic device updates the maximum value up to that point with the value calculated in S1002 (S1005) and proceeds to S1010. If the maximum value has not been updated (S1004: No), the battery diagnostic device proceeds to S1006.

[0037] (Figure 10: Step S1006) The battery diagnosis device judges whether or not the solar cell has reached the third period described in Fig. 8 (i.e., judges whether or not it has passed through S1008). If it has reached the third period, the process proceeds to S1009, and if it has not reached the third period, the process proceeds to S1007.

[0038] (FIG. 10: Steps S1007 to S1008) The battery diagnostic device judges whether the time rate of decrease of the shunt resistance is less than a predetermined amount compared to the current maximum value. For example, it judges whether the time rate of decrease calculated in S1002 is less than 50% of the current maximum value. This is for judging whether the rapid decrease of the shunt resistance has ended. If the time rate of decrease is less than a predetermined amount compared to the maximum value (S1007: Yes), it is judged that the solar cell has reached the third period (S1008) and proceeds to S1010. Otherwise, it is assumed that the solar cell is in the first or second period and skips to S1010.

[0039] (Figure 10: Step S1009) The battery diagnostic device estimates the remaining life of the solar cell by utilizing the fact that the rate of decrease in the shunt resistance over time is approximately constant during the third period. For example, if the current performance is 90% of the performance at the time of shipment and the end of the life is defined as when the performance reaches 80% of the performance at the time of shipment, the remaining life can be estimated by dividing the difference between the two (90%-80%) by the rate of decrease over time.

[0040] (FIG. 10: Step S1010) The battery diagnostic device judges whether the solar cell has reached the end of its life or whether the solar cell has reached a specified number of years of use based on S1009, and outputs the judgment result.

[0041] <Embodiment 2: Summary> The battery diagnostic device according to the present embodiment identifies a third period in which the time rate of decrease in shunt resistance is gentler than that in the second period, and estimates the remaining life using the time rate of decrease in the third period. This makes it possible to estimate the remaining life even when the results of the accelerated test are not stored.

[0042] The battery diagnostic device according to the present embodiment determines that the third period has been reached when the time rate of decline of the shunt resistance reaches a ratio of the second period that is less than a predetermined value after the time rate of decline reaches the second period. This makes it possible to identify the boundary between the second period and the third period. In other words, by identifying a significant time rate of decline in the second period, it is possible to estimate the remaining life without using the results of an accelerated test while maintaining the estimation accuracy.

[0043] <Embodiment 3> Fig. 11 is a configuration diagram of a battery diagnostic device 100 according to a third embodiment of the present invention. The battery diagnostic device 100 includes a calculation unit 110 and a storage unit 120. The calculation unit 110 executes the flowchart of Fig. 9 or Fig. 10. The storage unit 120 is a storage device that stores data used by the calculation unit 110 (e.g., data describing the results of an accelerated test). The calculation unit 110 can be configured by hardware such as a circuit device that implements the flowchart of Fig. 9 or Fig. 10, or can be configured by a calculation device such as a processor executing software that implements this.

[0044] <Modifications of the present invention> In the above embodiment, the battery diagnosis device 100 may present whether the flow chart of Fig. 9 or Fig. 10 was performed in the first period, the second period, or the third period, together with the remaining life. Whether the solar cell is in the first period, the second period, or the third period can be determined according to the time rate of decrease in the shunt resistance, as described in Fig. 9 or Fig. 10. The output format may be any format, such as displaying the information on a screen or outputting data describing the remaining life (and the implementation period).

[0045] In the above embodiment, the remaining life of a solar cell is estimated using the deterioration of the solar cell's performance. The performance here refers to a performance parameter that can represent the deterioration of the solar cell, such as the output power of the solar cell.

[0046] In the above embodiments, the value of the shunt resistor can be calculated, for example, by any of the following methods.

[0047] (Calculation method 1) The current-voltage characteristics of the solar cell are measured, for example, after the operation of the solar cell is stopped. The value of the shunt resistance is calculated using the obtained current-voltage characteristics and a known calculation method. For example, a calculation method that takes into account the battery temperature is generally known. Since this is a known method, details will be omitted here.

[0048] (Calculation method 2) Calculate the shunt resistance by substituting the output current and output voltage obtained from the solar cell control device (e.g. DC / DC converter) into the formula that expresses the relationship between the output current and output voltage in the solar cell equivalent circuit. This formula is commonly known, so details will be omitted. [Explanation of symbols]

[0049] 1: Solar cell string 2: Solar cell module 100: Battery diagnostic device 110: Arithmetic section 120: Storage section

Claims

1. A battery diagnostic method for diagnosing a solar cell, comprising the steps of: acquiring a change over time in a shunt resistance of the solar cell; identifying a first period during which the shunt resistance decreases at a first rate of decrease in the change over time and a second period during which the shunt resistance decreases at a second rate of decrease in the change over time, the second rate of decrease being greater than the first rate of decrease; estimating a remaining life of the solar cell by calculating a time required for the performance of the solar cell to reach a reference value from the second period or a period after the second period; having In the step of identifying the second period, a third period is identified in which the shunt resistance decreases at a third decrease rate that is smaller than the second decrease rate after the second period. A battery diagnostic method comprising:

2. A battery diagnostic method for diagnosing a solar cell, comprising the steps of: acquiring a change over time in a shunt resistance of the solar cell; identifying a first period during which the shunt resistance decreases at a first rate of decrease in the change over time and a second period during which the shunt resistance decreases at a second rate of decrease in the change over time, the second rate of decrease being greater than the first rate of decrease; estimating a remaining life of the solar cell by calculating a time required for the performance of the solar cell to reach a reference value from a period after the second period; having The battery diagnosis method further includes identifying a third period after the second period during which the shunt resistance decreases at a third rate of decrease that is smaller than the second rate of decrease; In the step of estimating the remaining life, a time required for the shunt resistance to decrease to a reference value is calculated in accordance with the third decrease rate, thereby estimating the remaining life of the solar cell. A battery diagnostic method comprising:

3. the battery diagnosis method is performed using a result obtained when the solar cell reaches the second period during an accelerated test of the solar cell, The step of estimating remaining life includes: calculating, as an acceleration in the accelerated test, a ratio between a time required for the performance of the solar cell to decrease to a current value after the solar cell is started to be used and a time required for the performance degradation of the solar cell to decrease to the current value in the accelerated test; A step of obtaining an accelerated remaining life of the solar cell by calculating a time required for the performance of the solar cell to reach a reference value in the accelerated test of the solar cell; A step of estimating an actual remaining life of the solar cell by multiplying the accelerated remaining life of the solar cell in the accelerated test by the acceleration. have 3. The battery diagnostic method according to claim 1 or 2.

4. The battery diagnostic method further includes a step of indicating whether the solar cell is in the first period, the second period, or a period after the second period.

3. The battery diagnostic method according to claim 1 or 2.

5. The step of identifying the third period of time comprises: acquiring a rate of decrease in the shunt resistance over time; comparing the acquired decrease rate with the second decrease rate; determining that the solar cell has reached the third period when the acquired rate of decline is a ratio of the second rate of decline to a predetermined value or less; have 3. The battery diagnostic method according to claim 2.

6. The battery diagnosis method includes a step of calculating the shunt resistance from a current-voltage characteristic of the solar cell.

3. The battery diagnostic method according to claim 1 or 2.

7. The battery diagnosis method includes: acquiring an output current and an output voltage of the solar cell from a control device that controls the solar cell; calculating the shunt resistance using the output current and the output voltage; have 3. The battery diagnostic method according to claim 1 or 2.

8. A battery diagnostic device for diagnosing a solar cell, comprising: A calculation unit that estimates a remaining life of the solar cell, The calculation unit is acquiring a change over time in a shunt resistance of the solar cell; identifying a first period during which the shunt resistance decreases at a first rate of decrease in the change over time and a second period during which the shunt resistance decreases at a second rate of decrease in the change over time, the second rate of decrease being greater than the first rate of decrease; estimating a remaining life of the solar cell by calculating a time required for the performance of the solar cell to reach a reference value from the second period or a period after the second period; Implemented the following: In the step of identifying the second period, the calculation unit identifies a third period in which the shunt resistance decreases at a third decrease rate that is smaller than the second decrease rate after the second period. A battery diagnostic device comprising:

9. A battery diagnostic device for diagnosing a solar cell, comprising: A calculation unit that estimates a remaining life of the solar cell, The calculation unit is acquiring a change over time in a shunt resistance of the solar cell; identifying a first period during which the shunt resistance decreases at a first rate of decrease in the change over time and a second period during which the shunt resistance decreases at a second rate of decrease in the change over time, the second rate of decrease being greater than the first rate of decrease; estimating a remaining life of the solar cell by calculating a time required for the performance of the solar cell to reach a reference value from a period after the second period; Implemented the following: The computing unit further performs a step of identifying a third time period, after the second time period, in which the shunt resistance decreases at a third decrease rate that is smaller than the second decrease rate; In the step of estimating the remaining life, the calculation unit estimates the remaining life of the solar cell by calculating a time required for the shunt resistance to decrease to a reference value in accordance with the third decrease rate. A battery diagnostic device comprising:

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