Deterioration factor estimation device, and deterioration factor diagnostic method

Abstract

To provide a diagnostic technology which can estimate local deterioration of series resistance provided in a solar cell.SOLUTION: A solar cell system concerning the present invention acquires series resistance of a solar cell when the solar cell restricts output under first solar radiation, acquires the series resistance of the solar cell when the solar cell follows the maximum power point, and diagnoses whether a deterioration factor of the solar cell is local increase of the series resistance or the overall increase of the series resistance by using the series resistance.SELECTED DRAWING: Figure 11

Description

Technical Field

[0001] The present invention relates to a technique for diagnosing the degradation factors of solar cells.

Background Art

[0002] As a degradation factor of solar cells, degradation of the shunt resistance is considered. By estimating the degradation of the shunt resistance, the degree of degradation of the solar cell can be estimated. Various methods have been proposed for estimating the degradation of the shunt resistance.

[0003] The following Patent Document 1 aims to "accurately grasp the degradation of the encapsulant of the solar cell module and the degradation of the solar cell itself by accurately obtaining the reduction in the shunt resistance from the IV characteristics of the solar cell affected by other factors such as solar radiation fluctuations and measurement instrument errors." For this purpose, it describes the technique that "the parallel resistance calculation device according to the present invention calculates the reverse saturation current of the diode portion of the solar cell using a provisional resistance value of the parallel resistance, and repeats the calculation while changing the provisional resistance value until the reverse saturation current matches a specified value." (See the abstract).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Conventional methods for estimating degradation factors, such as in Patent Document 1, estimate the degradation of a solar cell by estimating the degradation of the shunt resistance. However, among actual degradation cases of solar cells, the inventors have found that there are cases where the performance of the solar cell may be degraded due to local degradation of the series resistance provided in the solar cell. It is difficult to estimate local degradation of the series resistance using conventional methods that estimate degradation of the shunt resistance as in Patent Document 1.

[0006] The present invention has been made in view of the above problems, and an object thereof is to provide a diagnostic technique capable of estimating local degradation of the series resistance provided in a solar cell.

Means for Solving the Problems

[0007] The solar cell system according to the present invention acquires the series resistance of the solar cell when the solar cell is limiting its output under a first solar irradiance, and acquires the series resistance of the solar cell when the solar cell is tracking the maximum power point, and uses these series resistances to diagnose whether the degradation factor of the solar cell is a local increase in the series resistance or an overall increase in the series resistance.

Effects of the Invention

[0008] According to the solar cell system of the present invention, local degradation of the series resistance provided in the solar cell can be estimated. Other problems, configurations, effects, etc. will become clear from the description of the following embodiments.

Brief Description of the Drawings

[0009]

Figure 1A

Figure 1B

Figure 2

Figure 3A

Figure 3B

Figure 4A

Figure 4B

Figure 5A

Figure 5B

Figure 5C

Figure 6

Figure 7A

Figure 7B

Figure 7C

Figure 8A

Figure 8B

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Figure 15

Embodiments for Carrying Out the Invention

[0010] <Embodiment 1> FIGS. 1A to 1B show the configuration of the solar cell panel 1. The solar cell panel 1 is configured by arranging solar cell modules 12. The solar cell string 11 is configured by connecting the solar cell modules 12 in series and bypassing each solar cell 14 by a bypass diode 13. The solar cell module 12 is configured by connecting the solar cells 14 in series. The equivalent circuit of the solar cell 14 has a current source, a pn junction diode, a shunt resistance (parallel resistance), and a series resistance. The current source supplies a current proportional to the solar irradiance. When any one of the solar cells 14 in the solar cell module 12 fails, the failed solar cell module 12 is bypassed by the bypass diode 13.

[0011] FIG. 2 shows the current-voltage characteristics of the solar cell. Since the solar cell 14, the solar cell module 12, the solar cell string 11, and the solar cell panel 1 all exhibit similar characteristics, hereinafter, unless otherwise explicitly distinguished, they will simply be referred to as the solar cell.

[0012] The upper part of FIG. 2 shows the current-voltage characteristics (characteristics of output current and output voltage) of a normal solar cell. The middle part of FIG. 2 shows the current-voltage characteristics when the series resistance increases overall due to deterioration. The plot near the maximum power point decreases overall compared to the normal state, resulting in a decrease in the maximum output. The lower part of FIG. 2 shows the current-voltage characteristics when the shunt resistance decreases due to deterioration. Similar to the middle part of FIG. 2, the plot near the maximum power point decreases overall compared to the normal state. Furthermore, the short-circuit current and the open-circuit voltage also decrease compared to the normal state.

[0013] Figure 3A shows the front and back views of a solar cell. On the front surface of the solar cell, bus bars 31 and fingers 32 are arranged. On the back surface of the solar cell, the back resistance is arranged in a planar manner.

[0014] Figure 3B is an equivalent circuit diagram of a solar cell module. The finger 32 can be represented as a series connection of the series resistances of the solar cells. Solar cells are arranged between the finger 32 on the front surface and the back resistance. The bus bar 31 extends in a direction orthogonal to the finger 32 at the contact point between the solar cell and the finger 32. In FIGS. 3A to 3B, an example with two bus bars 31 is shown.

[0015] Figures 4A to 4B show another configuration example of a solar cell module. Different from FIGS. 3A to 3B, three bus bars 31 are arranged on the front surface of the solar cell module. Other configurations are the same as those in FIGS. 3A to 3B.

[0016] Figures 5A to 5C show the process of replacing a solar cell module with an equivalent circuit for analyzing its operation. A terminal voltage V0 is connected to the solar cell module, and the portion enclosed by the dotted line frame in FIG. 5A is the analysis target. FIG. 5B is an equivalent circuit diagram of the portion within the dotted line frame in FIG. 5A. To simplify the analysis, as shown in FIG. 5C, the parallel connection of the diode and shunt resistance of the solar cell is replaced with a current source.

[0017] Figure 6 shows an example of decomposing the equivalent circuit in FIG. 5C by the principle of superposition. The upper part of FIG. 6 is the equivalent circuit in FIG. 5C. This equivalent circuit can be represented by the superposition of the current supplied from the power source on the left side and the current supplied from the power source on the right side (the principle of superposition). FIG. 6 schematically shows the state of superposing the operations of each partial circuit.

[0018] Figures 7A to 7C show the results of analyzing the operation of the equivalent circuit of the solar cell module. Here, the analysis was carried out using the superposition principle shown in Fig. 6. Fig. 7A is the equivalent circuit diagram in the upper part of Fig. 6. As shown in Fig. 7A, let the series resistances be R1 to R9 in order from the left side, and the potentials at both ends of the series resistances be V1 to V10 in order from the left side.

[0019] Fig. 7B exemplifies two deterioration patterns of the series resistance. The total resistance of the solar cell module is the same in any pattern. Pattern 1 is a deterioration pattern in which only R5 increases by a factor of 4 and R6 to R8 become 0, resulting in a locally increased series resistance. Pattern 2 is a pattern in which all series resistances increase (deteriorate) evenly.

[0020] Fig. 7C shows the results of analyzing the operation of the solar cell module in each of Pattern 1 and Pattern 2. As a result of the analysis, it was found that the potentials V1 to V10 are generally the same between Pattern 1 and Pattern 2, while a larger current flows through each diode in Pattern 1 than in Pattern 2.

[0021] Fig. 8A shows the vicinity of the maximum power point in the current-voltage characteristics of the solar cell. When the battery voltage is low, the diode in the equivalent circuit of the solar cell is turned off, and the voltage further decreases. Conversely, when the battery voltage increases, the diode transitions from off to on. The vicinity of the maximum power point corresponds to this voltage region. In other words, when the solar cell is operating near the maximum power point, random on / off of the diode may occur frequently with fluctuations in the battery voltage.

[0022] Fig. 8B shows an example of the current-voltage characteristics when the series resistance increases locally. When the series resistance increases locally, unlike the case where the series resistance increases overall shown in the middle part of Fig. 2, the current-voltage characteristics are similar to those when the shunt resistance decreases shown in the lower part of Fig. 2. It is considered that this feature can be used to detect a local increase in the series resistance.

[0023] As described with reference to FIG. 7C, when the series resistance locally increases, the current flowing through the diode in the battery cell equivalent circuit increases as a whole, and as a result, the output current from the battery cell decreases. This is because the output current is obtained by subtracting the diode current from the output of the current source. Further, near the maximum power point, by flowing more current through the diode, the voltage across the diode tends to be insufficient, and as a result, the number of diodes that are turned off increases (see the explanation in FIG. 8A), and the current-voltage characteristic becomes a characteristic that is concave as a whole. As a result, near the maximum power point, the IV characteristic is as shown in the upper right part of FIG. 8B, and in other current regions, the IV characteristic shows a decrease in current as a whole.

[0024] FIG. 9 shows an example of the change over time of the output power of a solar cell. In principle, the output power of a solar cell increases as the solar irradiance increases. However, for example, in order to match a prior power generation plan, the output power may be intentionally suppressed. FIG. 9 illustrates the output power when such output suppression is implemented. In this example, the output suppression is performed twice, and the solar irradiance is larger in the latter case. In the following, a method for estimating the degradation factors of a solar cell will be described using the cell characteristics during these two output suppressions.

[0025] Near the maximum power point, as described above, the equivalent diode tends to repeatedly turn on and off randomly, so this region is not desirable for use in diagnosis. Therefore, a voltage region with more stable operation is used for diagnosis. Specifically, it is considered desirable to use the measured values when the battery is operating under the control of a device (e.g., a converter) that controls the battery (i.e., during output suppression). On the other hand, in a region where the battery voltage is low, since the voltage drop is small as shown in the middle and lower parts of FIG. 2, it is difficult to obtain data that can be used for diagnosis. As a result, in the present invention, the degradation factors are diagnosed using the measured values when the solar cell output is suppressed.

[0026] Figure 10 shows the current-voltage characteristics and the power-voltage characteristics when suppressing the output of the solar cell. When suppressing the output of the solar cell, the solar cell is operated in a negative voltage region where the value obtained by differentiating the power with respect to the voltage in the power-voltage characteristics is negative. This condition is set as ∂P / ∂V < a predetermined value 3. This voltage region corresponds to a voltage region where the value obtained by differentiating the current with respect to the voltage in the current-voltage characteristics is negative. This condition is set as ∂I / ∂V < a predetermined value 1. Further, the maximum power point corresponds to a voltage region where the value obtained by differentiating the power with respect to the voltage in the power-voltage characteristics is approximately 0 (within a predetermined range around 0).

[0027] Figure 11 is a flowchart for explaining the procedure for diagnosing the degradation factors of the solar cell. This flowchart can be implemented, for example, by a control device 100 (arithmetic unit 110) described later. Each step of FIG. 11 will be described below.

[0028] (FIG. 11: Step S1101) The control device 100 acquires the measured value of an arbitrary operating point (output voltage, output current) = (Va, Ia) and the measured value of the solar irradiance pa when the solar cell is implementing the output limit as shown in FIGS. 9 to 10 under the first solar irradiance. The power-voltage characteristics and the current-voltage characteristics when implementing the output limit are assumed to satisfy the conditions described in FIG. 10 respectively. The control device 100 calculates the first loss and the first series resistance R1 of the solar cell respectively by the procedure of FIG. 12 described later using the acquired measured values.

[0029] (FIG. 11: Step S1102) The control device 100 acquires the measured value of an arbitrary operating point (output voltage, output current) = (Vb, Ib) and the measured value of the solar irradiance pb when the solar cell is implementing the output limit as shown in FIGS. 9 to 10 under the second solar irradiance which is larger than the first solar irradiance. The power-voltage characteristics and the current-voltage characteristics when implementing the output limit are assumed to satisfy the conditions described in FIG. 10 respectively. The control device 100 calculates the second loss and the second series resistance R2 of the solar cell respectively by the procedure of FIG. 12 described later using the acquired measured values.

[0030] (Figure 11: Steps S1103 - S1104) When the second loss is less than or equal to the first loss (S1103: No), the control device 100 diagnoses that the degradation factor of the solar cell is not due to an increase in the series resistance (S1104). When the second loss is greater than the first loss, it proceeds to S1105.

[0031] (Figure 11: Step S1105) The control device 100 acquires the measured value of an arbitrary operating point (output voltage, output current) = (Vc, Ic) near the maximum power point and the measured value of the solar irradiance pc, respectively. The power - voltage characteristic of the maximum power point is assumed to satisfy the conditions described in Figure 10. The control device 100 calculates the maximum power point resistance R3 of the solar cell by the procedure of Figure 12 described later using the acquired measured values. R3 is the series resistance when the solar cell is operating to follow the maximum power point.

[0032] (Figure 11: Steps S1106 - S1108) When R3 is greater than R1 and R3 is greater than R2 (S1106: Yes), the control device 100 diagnoses that the local increase in the series resistance of the solar cell is the degradation factor (S1107). Otherwise, it is estimated that the overall uniform increase in the series resistance of the solar cell is the degradation factor (S1108).

[0033] (Figure 11: Steps S1106 - S1108: Supplementary) In these steps, it is determined whether R3 > R1 and R3 > R2 are satisfied. However, when only one of R3 > R1 or R3 > R2 is satisfied, the same diagnosis as in S1107 - S1108 may be performed. This is because R1 and R2 often have values close to each other. However, it is considered that the diagnostic accuracy is higher when both R3 > R1 and R3 > R2 are satisfied.

[0034] FIG. 12 is a flowchart for explaining the procedure of calculating the first series resistor R1 and the first loss. The second series resistor R2, the second loss, and the maximum power point resistor R3 can also be calculated by the same procedure. This flowchart can be implemented, for example, by a control device 100 (calculation unit 110) described later. Each step of FIG. 12 will be described below.

[0035] (FIG. 12: Step S1200) The control device 100 acquires the measured value of the operating point (Va, Ib) and the measured value of the solar irradiance pa, respectively. The control device 100 further acquires specification data describing the specification values of the solar cell. The specification data describes the following specification values: (a) short-circuit current I SC_ST , (b) open-circuit voltage V OC_ST , (c) optimum operating current I OP_ST , (d) optimum operating voltage V OP_ST , and (e) coefficients α and β in the calculation formula described later. α is the temperature characteristic [% / °C] of the short-circuit current, and β is the temperature characteristic [mV / °C] of the operating voltage. The specification data may be acquired, for example, from a power conditioner that drives the solar cell, or may be stored in advance in a storage device provided in the control device 100. It may also be acquired by other appropriate means.

[0036] (FIG. 12: Step S1200: Supplementary) Regarding the specification data, (c) optimum operating current I OP_ST , (d) optimum operating voltage V OP_ST can be described in advance in the data for each operating point j described later. Alternatively, these values may be obtained by calculation for each operating point j. These values at the operating point j are described as follows: (c) optimum operating current I OP_ST_j , (d) optimum operating voltage V OP_ST_j .

[0037] (FIG. 12: Step S1201) The control device 100 calculates the short-circuit current I SC as I SC_ST ·pa.

[0038] (FIG. 12: Step S1202) The solar radiation amount pa is the short circuit current I SC_ST The current operating current at the current level of radiation is Ia, so the short circuit current at the current level of radiation can be defined as Ia / j. Therefore, the radiation level pa is expressed as (short circuit current at the current level of radiation) / I SC_ST That is, it is expressed by the following formula: pa = (Ia / j) / I SC_ST Transform this equation to j=(Ia / pa) / I SC_ST Furthermore, by substituting the formula in S1201, we get j=(Ia) / I SC Considering the number of solar cell strings, j = (Ia / number of strings) / I SC The control device 100 implements the operating point j through the above procedure.

[0039] (FIG. 12: Step S1203) The control device 100 calculates the solar radiation amount pa and the operating voltage V at the battery temperature T=298K using kT / q=0.026 at 298K. P is calculated according to the following formula: T: absolute temperature of the solar cell [K], k: Boltzmann constant, q: charge of electron [C], nf: junction constant, number of cells: N cell , is.

[0040] (Figure 12: Step S1203: Calculation formula) V p =n f 0.026 N cell ln(pa)+V op_ST_j

[0041] (Figure 12: Step S1204) Rs1 is the series resistance per cell. The control device 100 calculates the voltage drop V'p due to Rs1 by the following formula: V'p=Vp+Ia·Rs1·Ncell. The meaning of V'p will be explained in S1205.

[0042] (Figure 12: Step S1205) The control device 100 calculates the assumed temperature T of the solar cell according to the following formula. β is generally the temperature characteristic of silicon and is about -2mV / K. V'p is the assumed series resistance Rs1 replaced by the voltage drop based on this (assumed voltage drop). In other words, the following formula calculates the assumed temperature T based on the difference between the measured voltage Va and the assumed voltage drop.

[0043] (Figure 12: Step S1205: Calculation formula) T = 298 + (V PE - V') p ) / (N cell ·β)

[0044] (Figure 12: Step S1206) The control device 100 updates the short - circuit current I SC_ST according to the following formula.

[0045] (Figure 12: Step S1206: Calculation formula) I SC_ST = I SC_ST ·{1+(α·(T - 298)) / 100}

[0046] (Figure 12: Step S1207) When the control device 100 repeats S1202 - S1206 more than a predetermined number of times (for example, 3 times), it skips to step S1208. When it is not repeating, after performing S1206, it returns to S1202.

[0047] (Figure 12: Step S1208) The control device 100 converts the operating current Ia into the value (I P0 ) under the standard solar irradiance and standard temperature (STC: Standard Condition) according to the following formula.

[0048] (Figure 12: Step S1208: Calculation formula) I P0 ={(Ia / number of strings / j) / pa·(1 + α·(298 - T) / 100)}·j

[0049] (Figure 12: Steps S1209 - S1211) The control device 100 calculates the difference delta_I between the I calculated in S1208 P0 and the standard operating current I OP_ST_j . If delta_I is small enough, it skips to S1212; otherwise, it increments Rs1 (e.g., increases by 0.0001) and returns to S1202.

[0050] (Figure 12: Step S1212) The control device 100 calculates the first loss = (V'p - Vp) / Vp.

[0051] <Embodiment 1: Derivation process of the calculation formula in S1203> The solar cell can be represented by the following formula (1). I = Isc·p - Is·{exp((q·(V / N cell )) / (n f ·k·T))}···(1) In formula (1), I SC = I SC_ST , kT / q = 0.026 at 298K, and using I = I SC_ST ·p·j, V p can be represented by the following formula (3). V p = n f ·0.026·ln(((1 - j)·I SC_ST ·p) / Is)···(3) The standard operating voltage V OP_ST when p = 1.0 is represented by the following formula (4). V OP_ST = n f ·0.026·ln(((1 - j)·I SC_ST ) / Is)···(4) Subtracting formula (4) from formula (3) to calculate the voltage difference, we obtain the following formula (5). V p - V OP_ST = n f ·0.026·ln(p)···(5) Therefore, the following formula (6) can be derived. Formula (6) is used in S1203. V p=(V p -V OP_ST )+V OP_ST =n f ·0.026·ln(p)+V OP_ST ···(6)

[0052] <Derivation process of the calculation formula in Embodiment 1: S1208> Isc at temperature T is represented by the following formula 13. Isc=(I PE / j) / p···(13) When Isc is returned to Isc0 at room temperature, the following formula 14 is obtained. Isc0=((I PE / j) / p)·(1 + α·(298 - T) / 100)···(14) Therefore, I P0 is represented by the following formula 15. This formula 15 is used in S1208. I P0 =Isc0·j = j·((I PE / j) / p)·(1 + α·(298 - T) / 100)···(15)

[0053] Figure 13 is a flowchart for explaining the procedure of the control device 100 to rank the quality of the solar cell based on the diagnosis result of the solar cell. If Rs1 is less than or equal to the first threshold and RS3 / Rs1 is less than or equal to the second threshold, it is determined to be normal or uniformly deteriorated. If Rs1 is less than or equal to the first threshold and Rs3 / Rs1 exceeds the second threshold, it is determined that the series resistance is locally slightly increased. If Rs1 exceeds the first threshold and Rs3 / Rs1 is greater than or equal to the third threshold, it is determined that the series resistance is locally increased. If Rs1 exceeds the first threshold and Rs3 / Rs1 is less than the third threshold, recycling is recommended.

[0054] In Figure 13, instead of Rs3 / Rs1, the difference obtained by subtracting Rs1 from Rs3 may be used, or for example, if Rs1 and Rs2 are approximately the same value, Rs2 may be used instead of Rs1.

[0055] <Embodiment 2> FIG. 14 is a configuration diagram of a solar cell system according to Embodiment 2 of the present invention. The solar cell system is configured by driving one or more solar cells with a power conditioner. The control device 100 (deterioration factor estimation device) controls the solar cells through controlling the power conditioner. The control device 100 can be configured by, for example, a computer. The control device 100 includes an arithmetic unit 110. The arithmetic unit 110 performs the procedure for estimating the deterioration factors of the solar cells described in the above embodiments.

[0056] FIG. 15 is an example of a screen of a user interface provided by the control device 100. The user interface can present, for example, the change over time of the solar cell output, the diagnostic results and ranking results described in Embodiment 1, and the like.

[0057] <Regarding Modifications of the Present Invention> The present invention is not limited to the above-described embodiments and includes various modifications. For example, the above-described embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described. Also, part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Further, for part of the configuration of each embodiment, addition, deletion, or replacement with other configurations is possible.

[0058] In the above embodiments, the arithmetic unit 110 can be configured by hardware such as a circuit device that implements its function, or can be configured by a software that implements its function being executed by an arithmetic device such as a CPU (Central Processing Unit).

Description of Reference Numerals

[0059] 11: Solar cell string 12: Solar cell module 14: Solar cell 100: Control device 110: Arithmetic unit

Claims

1. A degradation factor estimation device for estimating the degradation factors of a solar cell, comprising: an arithmetic unit for estimating the degradation factors of the solar cell; the arithmetic unit acquires a first series resistance of the solar cell when the solar cell is limiting its output under a first solar irradiance; the arithmetic unit acquires the series resistance of the solar cell when the solar cell is tracking the maximum power point as the maximum power point resistance; the arithmetic unit uses the first series resistance and the maximum power point resistance to diagnose whether the degradation factor of the solar cell is a local increase in the series resistance or an overall increase in the series resistance; A degradation factor estimation device characterized by the above.

2. the arithmetic unit acquires a first loss of the solar cell when the solar cell is limiting its output under the first solar irradiance; the arithmetic unit acquires a second loss of the solar cell when the solar cell is limiting its output under a second solar irradiance greater than the first solar irradiance; when the second loss is greater than the first loss, the arithmetic unit diagnoses that the degradation factor of the solar cell is due to an increase in the series resistance; when the second loss is less than or equal to the first loss, the arithmetic unit diagnoses that the degradation factor of the solar cell is not due to an increase in the series resistance; The degradation factor estimation device according to claim 1, characterized by the above.

3. when the maximum power point resistance is greater than the first series resistance, the arithmetic unit diagnoses that the degradation factor of the solar cell is due to a local increase in the series resistance; when the maximum power point resistance is less than or equal to the first series resistance, the arithmetic unit diagnoses that the degradation factor of the solar cell is due to an overall increase in the series resistance; The degradation factor estimation device according to claim 1, characterized by the above.

4. the arithmetic unit acquires a second series resistance of the solar cell when the solar cell is limiting its output under a second solar irradiance greater than the first solar irradiance; when the maximum power point resistance is greater than the first series resistance and the maximum power point resistance is greater than the second series resistance, the arithmetic unit diagnoses that the degradation factor of the solar cell is due to a local increase in the series resistance; when at least one of the maximum power point resistance is less than or equal to the first series resistance or the maximum power point resistance is less than or equal to the second series resistance holds, the arithmetic unit diagnoses that the degradation factor of the solar cell is due to an overall increase in the series resistance; The deterioration factor estimation device according to claim 1, characterized in that...

5. Based on the result of comparing the first series resistance and the maximum power point resistance, the calculation unit diagnoses the quality rank of the solar cell The deterioration factor estimation device according to claim 1, characterized in that...

6. The calculation unit wherein the first series resistance is greater than a first threshold value, and the ratio of the maximum power point resistance to the first series resistance, or the difference obtained by subtracting the first series resistance from the maximum power point resistance, is smaller than a second threshold value, in which case, a diagnostic result recommending recycling of the solar cell is output The deterioration factor estimation device according to claim 1, characterized in that...

7. The calculation unit acquires the second series resistance of the solar cell when the output of the solar cell is restricted under a second solar irradiance greater than the first solar irradiance, The calculation unit wherein the second series resistance is greater than a third threshold value, and the ratio of the maximum power point resistance to the second series resistance, or the difference obtained by subtracting the second series resistance from the maximum power point resistance, is smaller than a fourth threshold value, in which case, a diagnostic result recommending recycling of the solar cell is output The deterioration factor estimation device according to claim 1, characterized in that...

8. The calculation unit obtains the series resistance of the solar cell in a voltage region where the value obtained by differentiating the output current of the solar cell with respect to the output voltage of the solar cell is negative and the value obtained by differentiating the output power of the solar cell with respect to the output voltage is negative, as the first series resistance The deterioration factor estimation device according to claim 1, characterized in that...

9. The calculation unit obtains the series resistance of the solar cell in a voltage region where the value obtained by differentiating the output current of the solar cell with respect to the output voltage of the solar cell is negative and the value obtained by differentiating the output power of the solar cell with respect to the output voltage is within a predetermined range around 0, as the maximum power point resistance The deterioration factor estimation device according to claim 1, characterized in that...

10. Using the assumed value of the first series resistance, the calculation unit converts the output current and output voltage of the solar cell into converted standard voltage and converted standard current, which are the values when it is assumed that the solar cell is operating under standard temperature The calculation unit repeats the conversion while changing the assumed value of the first series resistance until the difference between the standard current when the solar cell operates under the standard solar irradiance and the standard temperature and the converted standard current converges, thereby calculating the first series resistance. The degradation factor estimation device according to claim 1, characterized in that.

11. A method for estimating a degradation factor of a solar cell, comprising: obtaining a first series resistance of the solar cell when the output of the solar cell is limited under a first solar irradiance; obtaining, as a maximum power point resistance, a series resistance of the solar cell when the solar cell is tracking the maximum power point; diagnosing, using the first series resistance and the maximum power point resistance, whether the degradation factor of the solar cell is a local increase in the series resistance or an overall increase in the series resistance; having A degradation factor estimation method, characterized in that.

Images