JP2022112053A - Battery diagnosis method and battery diagnosis device - Google Patents

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

The present invention relates to technology for diagnosing solar cells.

More than seven years have passed since the start of FIT (Feed In Tariff), and there has been a noticeable increase in the number of photovoltaic power generation systems whose performance is ensured and those which are not. Under these circumstances, the need to evaluate the long-term value of power plants is increasing due to the activation of the secondary market. In such technical due diligence, it is important to estimate the lifetime of the solar cell module.

In recent years, attention has been focused on the deterioration of solar cell modules due to an increase in the moisture permeability of fillers and sealing materials that constitute solar cell modules. As the solar cell module deteriorates, the shunt resistance of the solar cell module decreases.

Patent Documents 1 and 2 below are known as prior art techniques for quantifying deterioration from the shunt resistance of a solar cell module. Patent Literature 1 describes a method of detecting a decrease in shunt resistance at an early stage using impedance diagnosis. Patent Literature 2 describes determining the end of life of a solar cell string when the shunt resistance value drops below a threshold value.

JP 2014-165232 A JP 2004-287787 A

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 the solar cell (module or string) based on the measurement result.

Patent Document 1 describes early detection of a decrease in shunt resistance using impedance, but does not mention to what extent the measured impedance correlates with the value of the shunt resistance. . Patent Literature 2 describes that when the measured shunt resistance is below a threshold, it is determined that the full life has been reached. However, the remaining life prediction is not mentioned.

The present invention has been made in view of the problems described above, and provides a technique that enables the remaining life of a solar cell to be determined with sufficient accuracy even when the calculation accuracy of the shunt resistance is insufficient. intended to

The battery diagnosis method according to the present invention distinguishes between a first period during which the shunt resistance decreases at a first decrease rate and a second period during which the shunt resistance decreases at a second decrease rate greater than the first decrease rate. The remaining life of the solar cell is estimated by calculating the time required for the state of deterioration of the solar cell to reach a reference value from the period or the period after the second period.

According to the battery diagnosis method of the present invention, even when 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 the above will become apparent from the following description of the embodiments.

1 is a side sectional view of a solar cell module; FIG. 1 is an equivalent circuit diagram of a solar cell string 1 and a solar cell module 1a. FIG. The results of an accelerated test performed on the solar cell module under a high temperature and high humidity environment of 85° C. and 85% are shown. It is a lineblock diagram of a photovoltaic power generation system. 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 photovoltaic power generation system is installed; FIG. 4 is an example of a current-voltage characteristic curve of the solar cell string 1. FIG. FIG. 4 is a diagram showing the relationship between shunt resistance and solar cell output; FIG. 4 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 under a high temperature and high humidity environment of 85° C. and 85%; 4 is a flow chart for explaining a procedure for estimating the remaining life of a solar cell module and a string; 4 is a flow chart for explaining a procedure for estimating the remaining life of a solar cell module and a string; FIG. 11 is a configuration diagram of a battery diagnosis device 100 according to Embodiment 3;

<Embodiment 1>
FIG. 1 is a side sectional view of a solar cell module. A plurality of photovoltaic cells 1a are connected by an interconnector 1b. The solar cell 1a is protected by the filler 1e between the glass plate 1c and the back sheet 1d. Further, a sealing material 1f is provided between the aluminum frame 1g and the glass plate 1c and between the aluminum frame 1g and the back sheet 1d to prevent moisture from entering the module. As the filler 1e, EVA (ethylene-vinyl acetate copolymer resin) is generally used. Butyl or silicon is generally used as the sealing material 1f.

FIG. 2 is an equivalent circuit diagram of the solar cell string 1 and the solar cell module 2. As shown in FIG. A solar cell string 1 is configured by arranging a plurality of solar cell modules 2 in series. The solar cell module 2 can be expressed as a plurality of solar cells 22a arranged in series and each solar cell 22a bypassed by a bypass diode 22b. An equivalent circuit of the photovoltaic 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.

If the solar cell module is used for a long period of time in an exposed environment, the weather resistance performance of the filler and sealing material will also deteriorate, resulting in reduced adhesion and other factors that will allow moisture to permeate through and reduce the performance of the solar cell. .

FIG. 3 shows the results of an accelerated test of a solar cell module under a high temperature and high humidity environment of 85° C. and 85%. Since all solar cell modules have basically the same configuration, it is assumed that once moisture enters the module, the module performance will decline at the same rate, regardless of the materials used and manufacturing capacity. In FIG. 3, it can be seen that the three solar cell modules (represented by curves 3a, 3b, and 3c, respectively) have different deterioration start points, but have the same performance deterioration rate with respect to elapsed time.

FIG. 4 is a configuration diagram of a photovoltaic power generation system. The photovoltaic power generation system includes a junction box 41 for bundling a plurality of solar cell strings 1 , a current collection rack 42 for bundling the plurality of junction boxes 41 , a DC/DC converter 43 and an inverter 44 . The connection box 41 is equipped with a backflow prevention diode 41a for preventing current from flowing into the solar cell string, a circuit breaker 41b for interrupting the current path, a circuit breaker 41c, and the like. A total of a plurality of strings bundled by the junction box 41 is connected to the DC/DC converter 43 via the current collection rack 42 . A breaker 42a is also installed in the current collecting rack. A plurality of solar cell strings are collectively controlled by the DC/DC converter 43 . 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.

FIG. 5 is a diagram showing a configuration for acquiring the current-voltage characteristics of the solar cell string 1 via the junction box 41 at the power generation site where the photovoltaic power generation system is installed. A terminal of a measuring instrument 5 for measuring 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 the measurement is started, the load of the electronic load 53 in the measuring instrument 5 is varied, the current flowing from the solar cell string 1 is measured by the ammeter 51, and the voltage of the solar cell string 1 at that time is measured by the voltmeter 52. measure. Thereby, the current-voltage characteristics of the solar cell string 1 can be obtained. It goes without saying that the solar cell module 2 is similarly measured.

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

FIG. 7 is a diagram showing the relationship between shunt resistance and solar cell output. It can be seen that when the shunt resistance becomes less than 1Ω, a sudden change in the output finally becomes visible.

FIG. 8 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 under a high temperature and high humidity environment of 85° C. and 85%. The upper diagram in FIG. 8 and the lower diagram in FIG. 8 are described with the same time scale. As described in the explanation of FIG. 3, since the structure of the solar cell module is the same, many silicon crystal solar cell modules exhibit similar characteristics.

It can be seen that the sudden drop in output as shown in 8b is observed at an earlier stage than the sudden drop in output as shown in 8a. A state in which the shunt resistance is close to 1000Ω is defined as the first period (8c), a period in which the shunt resistance drops sharply from 1000Ω to about 1Ω is defined as the second period (8d), and then a period in which the shunt resistance gradually changes. is defined as the third period (8e). If the second period (8d) can be identified even under the exposure environment, it becomes easy to estimate in which period the solar cell is placed in the accelerated test even when the measurement accuracy of the shunt resistance is low. .

FIG. 9 is a flow chart explaining the procedure for estimating the remaining life of the solar cell module and the string. This flowchart can be executed by a device for diagnosing the remaining life of a solar cell. For example, devices such as the DC/DC converter 43 and the inverter 44 can implement this flowchart. Other devices may perform. It is assumed below that these battery diagnosis devices carry out this flow chart. The battery diagnosis device holds the results of the accelerated tests already performed on the solar cells, and uses the results to perform the following steps. The battery diagnostic device executes this flowchart periodically (for example, every month, every six months, every twelve months, etc.).

(Fig. 9: Step S901)
The battery diagnostic device calculates the shunt resistance of the solar cell module or string.

(Fig. 9: Step S902)
The battery diagnostic device determines whether or not the solar battery has reached the second period described in FIG. For example, the determination procedure can be as follows. A time decrease rate 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 decrease rate calculated last time and the time decrease rate calculated this time is equal to or greater than the threshold, it can be determined that the shunt resistance is rapidly decreasing (that is, the second period has started). .

(Fig. 9: Step S902: Supplement)
This step assumes that the solar cell is in the second period when this flowchart is executed. However, even if the solar cell passes through the second period and reaches the third period, the following steps are the same. As for the procedure for distinguishing between the second period and the third period, the method described in the second embodiment can be used.

(Fig. 9: Step S903)
The battery diagnosis device obtains the acceleration in the accelerated test using the result of the accelerated test that has already been performed. Specifically, the time elapsed from the start of operation until the current performance of the solar cell was reached (that is, the time elapsed from the start of operation to the implementation of this step), and the Determine the ratio between the time elapsed to reach the point performance. This ratio can be used as the acceleration for acceleration tests.

(Fig. 9: Step S903: Calculation example)
At the time of performing this step, 9000 hours have passed since the start of operation of the solar cell, and the performance of the solar cell has deteriorated to 95% of that at the start of operation (that is, decreased by 5%). . In the accelerated test already performed, it is assumed that 3000 hours elapsed before the performance of the solar cell decreased to 95% of that at shipment. Then, the acceleration of the acceleration test is 9000/3000=3 times.

(Fig. 9: Step S903: Supplement)
In the above description, the ratio between the actual elapsed time and the elapsed time in the accelerated test was obtained based on the performance of the solar cell at the time of performing this step. It does not have to be the one at the time. For example, if the time elapsed for the solar cell performance to drop to 98% is known in advance for both the real time and the accelerated test time, the ratio of the times may be used.

(Fig. 9: Step S904)
The battery diagnosis device uses the acceleration of the acceleration test to calculate the remaining life of the solar battery. For example, it is defined that the solar cell reaches the end of its life (cannot be used any longer) when it reaches 80% of the performance at the time of shipment. The battery diagnosis device obtains from the result of the accelerated test the elapsed time during the accelerated test until the solar cell reaches 80% of the performance at the time of shipment from the performance at the time of this step. This corresponds to the remaining life in the accelerated test. The battery diagnosis device multiplies the remaining life in the acceleration test by the acceleration to estimate the actual time from the execution of this step to the life. This time is the remaining life of the solar cell.

(Fig. 9: Step S904: Supplement)
This step uses the time it takes for the solar cell to reach the end of life from the second period (or a subsequent period) in the accelerated test, and It is meaningful to estimate the time it takes to In other words, there is significance in estimating the remaining life of the solar cell using the data relating to the second period in particular among the results of the accelerated test.

<Embodiment 1: Summary>
The battery diagnosis device according to the present embodiment identifies the second period in which the rate of decrease over time of the shunt resistance increases sharply. The battery diagnosis device further estimates the actual remaining life of the solar cell using the elapsed time from the second period in the accelerated test to the end of life and the acceleration of the accelerated test. By estimating the remaining life using the second period in which the shunt resistance drops significantly, it is possible to estimate the remaining life with a certain degree of accuracy even when the shunt resistance measurement accuracy is not sufficient. Further, by using the data regarding the second period in the accelerated test, the remaining life can be estimated while maintaining the estimation accuracy and without actually consuming the solar cell.

<Embodiment 2>
In the first embodiment, the procedure for estimating the remaining life of the solar cell has been described using the data regarding the second period among the results of the accelerated tests that have already been performed. Embodiment 2 of the present invention describes a procedure for estimating the remaining life of a solar cell by using changes over time in the actual shunt resistance of the solar cell instead of using the results of the accelerated test.

FIG. 10 is a flow chart explaining the procedure for estimating the remaining life of the solar cell module and the string. This flow chart can be implemented by the battery diagnosis device, as in FIG. The battery diagnostic device executes this flowchart periodically (for example, every month, every six months, every twelve months, etc.).

(Fig. 10: Step S1001)
The battery diagnosis device assumes that the solar cell has reached the first period or the second period described in FIG.

(Fig. 10: Steps S1002-S1003)
The battery diagnosis device calculates the shunt resistance value of the solar battery (S1002). The battery diagnosis device obtains the rate of decrease over time of the shunt resistance (S1003), as in S902.

(Fig. 10: Steps S1004-S1005)
When the time decrease rate of the shunt resistance calculated in S1002 is updated to the maximum value so far (S1004: Yes), the battery diagnosis device updates the maximum value so far by the value calculated in S1002 (S1005). , to S1010. If the maximum value has not been updated (S1004: No), the process proceeds to S1006.

(Fig. 10: Step S1006)
The battery diagnosis device determines whether or not the solar cell has reached the third period described in FIG. 8 (that is, determines whether or not S1008 has been passed). If it has reached, the process proceeds to S1009, and if it has not reached, the process proceeds to S1007.

(Fig. 10: Steps S1007-S1008)
The battery diagnostic device determines whether the time rate of decrease in shunt resistance is less than a predetermined amount compared to the current maximum value. For example, it is determined whether the temporal decrease rate calculated in S1002 is less than 50% of the current maximum value. This is for determining whether or not the sudden drop in shunt resistance has ended. If the temporal decrease rate is less than the predetermined amount compared to the maximum value (S1007: Yes), it is determined that the solar cell has reached the third period (S1008), and the process proceeds to S1010. Otherwise, skip to S1010 while assuming that the solar cell is in the first period or the second period.

(Fig. 10: Step S1009)
The battery diagnosis device estimates the remaining life of the solar cell by utilizing the fact that the temporal decrease rate of the shunt resistance in the third period is substantially constant. For example, if the current performance is 90% of the performance at the time of shipment, and it is specified that the life has expired when the performance reaches 80% of the performance at the time of shipment, the difference between the two (90%-80%) is the time deterioration rate. Remaining life can be estimated by dividing by .

(Fig. 10: Step S1010)
Based on S1009, the battery diagnosis device determines whether the solar battery has reached the end of its life or has reached the prescribed number of years of use. The battery diagnosis device outputs the determination result.

<Embodiment 2: Summary>
The battery diagnostic apparatus according to this embodiment identifies a third period in which the rate of decrease in shunt resistance over time is slower than that in the second period, and estimates the remaining life using the rate of decrease over time in the third period. As a result, the remaining life can be estimated even if the results of the accelerated test are not held.

In the battery diagnosis device according to the present embodiment, after the rate of decrease in shunt resistance with time reaches the second period, the rate of decrease in time with respect to the second period reaches a ratio of less than a predetermined value, so that the determine that it has been reached. This allows the boundary between the second period and the third period to be identified. That is, it is possible to estimate the remaining life without using the results of the accelerated test, while maintaining the estimation accuracy by identifying the significant rate of deterioration over time in the second period.

<Embodiment 3>
FIG. 11 is a configuration diagram of a battery diagnosis device 100 according to Embodiment 3 of the present invention. The battery diagnosis device 100 includes a calculation section 110 and a storage section 120 . The calculation unit 110 implements the flowchart of FIG. 9 or 10 . The storage unit 120 is a storage device that stores data used by the calculation unit 110 (for example, data describing results of accelerated tests). The arithmetic unit 110 can be configured by hardware such as a circuit device implementing the flowchart of FIG. 9 or FIG. 10, or by executing software implementing this by an arithmetic device such as a processor. .

<Regarding Modifications of the Present Invention>
In the above-described embodiment, the battery diagnostic device 100 may present in which of the first to third periods the flowchart of FIG. 9 or 10 was performed, together with the remaining life. Whether the solar cell is in the first period to the third period can be determined according to the temporal decrease rate of the shunt resistance, as described with reference to FIG. 9 or FIG. As for the output format, any format can be used, such as displaying on a screen or outputting data describing remaining life (and implementation period).

In the above embodiments, it has been described that the remaining life is estimated by using the performance degradation of the solar cell. The performance here is a performance parameter that can express the deterioration of the solar cell, such as the output power of the solar cell.

In the above embodiments, the value of the shunt resistance can be calculated, for example, by any of the following.

(Calculation method 1) The current-voltage characteristics of the solar cell are measured, for example, after temporarily stopping the operation of the solar cell. 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 considers the battery temperature is generally known. Since this is a well-known method, details are omitted here.

(Calculation method 2) Substituting the output current and output voltage obtained from the solar cell control device (for example, DC/DC converter) into the formula representing the relationship between the output current and the output voltage in the equivalent circuit of the solar cell. Calculate the shunt resistance by Since this formula is generally known, the details are omitted.

1: Solar cell string 2: Solar cell module 100: Battery diagnosis device 110: Computing unit 120: Storage unit

Claims (9)

A battery diagnostic method for diagnosing a solar cell,
a step of obtaining a change over time of the shunt resistance provided in the solar cell;
Identifying a first period during which the shunt resistance decreases at a first decrease rate over time and a second period during which the shunt resistance decreases at a second decrease rate greater than the first decrease rate over time. step,
estimating the remaining life of the solar cell by calculating the time required for the deterioration state of the solar cell to reach a reference value from the second period or a period after the second period;
A method for diagnosing a battery, comprising: The battery diagnosis method is performed using a result obtained by the solar cell reaching the second period in an accelerated test on the solar cell,
The step of estimating the remaining life includes:
Between the time required for the performance of the solar cell to decrease to the current value after the start of use of the solar cell and the time required for the performance degradation of the solar cell to decrease to the current value in the accelerated test A step of calculating the ratio of as the acceleration in the acceleration test,
obtaining an accelerated life expectancy in the accelerated test of the solar cell;
estimating the actual life expectancy of the solar cell by multiplying the life expectancy accelerated in the accelerated test of the solar cell by the acceleration;
The battery diagnosis method according to claim 1, characterized by comprising: In the step of identifying the second period, between the first period and a third period in which the shunt resistance decreases at a third decrease rate smaller than the second decrease rate after the second period 2. The battery diagnostic method according to claim 1, wherein the period of is identified as the second period. The battery diagnostic method further comprises the step of presenting in which of the first period, the second period, or a period after the second period, the battery diagnostic method is performed. Item 2. The method for diagnosing a battery according to item 1. The battery diagnostic method includes identifying a third period after the second period in which the shunt resistance decreases at a third decrease rate smaller than the second decrease rate,
In the step of estimating the remaining life, the remaining life of the solar cell is estimated by calculating the time required for the shunt resistance to decrease to the reference value according to the third rate of decrease. The method for diagnosing a battery according to claim 1. Identifying the third time period comprises:
obtaining a decrease rate of the shunt resistance over time;
comparing the obtained decrease rate and the second decrease rate;
Deeming that the solar cell has reached the third period when the acquired rate of decrease is a rate equal to or less than a predetermined value with respect to the second rate of decrease;
The battery diagnosis method according to claim 5, characterized by comprising: 2. The battery diagnostic method according to claim 1, further comprising: calculating the shunt resistance from the current-voltage characteristics of the solar cell. The battery diagnostic method includes:
obtaining the output current of the solar cell and the 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;
The battery diagnosis method according to claim 1, characterized by comprising: A battery diagnostic device for diagnosing a solar cell,
A computing unit for estimating the remaining life of the solar cell,
The calculation unit is
a step of obtaining a change over time of the shunt resistance provided in the solar cell;
Identifying a first period during which the shunt resistance decreases at a first decrease rate over time and a second period during which the shunt resistance decreases at a second decrease rate greater than the first decrease rate over time. step,
estimating the remaining life of the solar cell by calculating the time required for the deterioration state of the solar cell to reach a reference value from the second period or a period after the second period;
A battery diagnostic device characterized by:

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