JP2013168591A - Solar simulator and defect determination method of solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of determining the defect of solar cell by using that method in the output characteristic curves of a solar cell, and to provide a solar simulator which allows for that method.SOLUTION: The solar simulator includes a light source for irradiating a solar cell with pseudo sunlight, a characteristics acquisition unit for acquiring the I-V curve of current and voltage output from the solar cell by receiving the pseudo sunlight from the light source, a defect determination unit for determining defect of the solar cell from the shape of the I-V curve obtained by the characteristics acquisition unit, and a controller performing total control of the characteristics acquisition unit and defect determination unit.

Description

  The present invention relates to an apparatus for inspecting general performance of solar cells, such as solar cells, a string in which solar cells are connected in a row, and a solar cell panel in which a plurality of strings are arranged in parallel and connected in a panel shape.

  A solar cell is known as a method of using solar energy. In the production of solar cells, it is important to evaluate the performance of whether the solar cells have the desired power generation capability. In performance evaluation, output characteristics are usually measured.

  The output characteristic is performed as a photoelectric conversion characteristic for measuring the current-voltage characteristic of the solar cell under light irradiation. Solar light is desirable as the light source, but a solar simulator is used because the intensity changes depending on the weather. In the solar simulator, a xenon lamp, a metal halide lamp, or the like is used instead of sunlight. Further, when these light sources are turned on for a long time, the light amount changes due to a temperature rise or the like. Therefore, the output characteristic curve of the solar cell is obtained by plotting the collected data using the flash light of these lamps with the horizontal axis representing voltage and the vertical axis representing current (see, for example, Patent Document 1).

  As a method different from this, there is a method in which current is applied in the forward direction to the solar battery cell to cause the current to flow in the forward direction, causing an electroluminescence (EL) action, and determining the quality of the solar battery cell from the light emitting state. Yes (see Patent Document 2). However, since Patent Document 2 determines whether or not the light is good only by the brightness of the emitted light from the solar battery cell, even if there is a crack, it is determined that the product is non-defective if the brightness is a predetermined value or more. However, if there is a crack, the power generation capability of the solar cell may be suddenly reduced, so it should be determined as a defective product.

JP2007-88419 WO2006 / 059615

  In the solar cell inspection method of Patent Document 2 described above, a defect exhibiting a large-area dark area (dark area) as shown in FIG. 10 can be clearly and identified, but a thin linear crack as shown in FIG. It is difficult to identify. When a linear thin defect as shown in FIG. 11 is also operated as a solar cell, there is a possibility of causing a decrease in output in the future. The possibility that such a defect in FIG. 11 exists cannot be detected by the measurement technique taken by the solar simulator described in Patent Document 1.

  In general, a solar cell is provided by arranging a plurality of solar cell strings (a plurality of solar cells electrically connected in series) arranged in parallel in a plurality of rows and electrically connected in series. Therefore, when a problem occurs in one solar cell string, the performance of the solar cell as a whole is affected. For this reason, it is necessary to inspect for the presence of defects that will cause a significant decrease in output in the future.

  In order to solve the above-described problems, the present invention provides a method for determining a defect of a solar cell using an output characteristic curve, and a solar simulator using the method.

The solar simulator of the first invention for solving the above-mentioned problems is a light source that irradiates a solar cell with simulated sunlight, an IV curve of a current voltage that is received from the solar cell and is output from the solar cell. A characteristic acquisition unit that acquires the defect, a defect determination unit that determines a defect of a solar cell based on the shape of the IV curve obtained by the characteristic acquisition unit, and a control device that controls the entire characteristic acquisition unit and the defect determination unit It is characterized by including.
According to the solar simulator of the first invention, it is possible to determine the presence or absence of defects in the solar cell by acquiring the output characteristic curve of the solar cell. For this reason, when using the defect determination method using EL (electroluminescence), the accuracy can be further improved.

The solar simulator of the second invention is characterized in that, in the first invention, the presence or absence of the defect is determined by the differential value of the IV curve in the defect determination unit.
According to the solar simulator of the second invention, since the determination of the presence / absence of the defect is determined by the differential value of the IV curve in the defect determination unit, it is easy to perform data processing operation by using a computer such as a personal computer. Is possible.

The solar simulator of the third invention is the solar simulator according to the first invention, wherein the presence or absence of the defect in the defect determination unit is determined by the voltage value of the solar cell as the measured object of the IV curve being 0. 0 of the open circuit voltage (V _oc ). and judging the presence or absence of the step beyond the 0.01I _SC from 0.005I _SC of the short circuit current from 001V _OC with respect to the voltage width of 0.002V _{OC (I SC).}
According to the solar simulator of the third invention, the same effect as that of the first invention can be expressed by a simpler method.

A defect determination method for a solar cell according to a fourth aspect of the present invention for solving the above problems includes a step of acquiring an IV curve of the solar cell, a region where the acquired IV curve is not flat, or a stepped region. And a step of determining the presence or absence of defects in the solar cell based on the uneven or stepped region.
According to the present invention, the same effects as those of the first invention can be exhibited.

The defect determination method for a solar cell according to a fifth aspect of the present invention is characterized in that, in the fourth aspect, a region that is not flat or has a step is determined by a differential value of the IV curve.
According to the defect determination method for a solar cell of the fifth invention, the same effect as that of the second invention can be exhibited.

Defect determination method of a solar cell of the sixth invention, in the fourth invention, the presence or absence of the defect in the defect determination unit, the I-V voltage of the solar cell to be measured is the open-circuit voltage curve (V _OC ) and judging the presence or absence of the step beyond the 0.01I _SC from 0.005I _SC of the short circuit current from 0.001 V _OC with respect to the voltage width of 0.002 V _{OC (I SC)} of.
According to the defect determination method for a solar cell of the sixth invention, the same effect as that of the third invention can be exhibited.

The block diagram which shows schematic structure of the solar simulator by this invention. One example of a solar cell. The example of the IV curve of the solar cell which has a defect. The example of the IV curve of the solar cell which has a defect. The example of the IV curve of the solar cell which has a defect. The example of the IV curve of the solar cell which has a defect. The example of the IV curve of the solar cell without a defect. The flowchart of the defect determination method of the solar cell by this invention. Explanatory drawing of another example of the defect determination method of the solar cell by this invention. An example of the EL image of the photovoltaic cell which has a dark area as a defect. An example of the EL image of the photovoltaic cell which has a crack as a defect.

A solar simulator according to a first embodiment of the present invention will be described with reference to FIGS.
FIG. 1 is a block diagram showing a schematic configuration of a solar simulator according to the present invention. Light emitted from the flash light source 1 is irradiated onto a solar cell (including a solar battery cell) that is the object to be measured 2. The solar cell that is the device under test 2 generates power according to its own performance characteristics and outputs current and voltage. The characteristic acquisition unit 3 measures the current and voltage generated and output from the DUT 2. The measured power generation capacity is obtained as an output characteristic curve (hereinafter referred to as an IV curve). FIG. 7 is an IV curve in a state where the solar cell is not defective. The defect determination unit 4 determines the presence / absence of a solar cell defect or the type of defect based on the obtained IV curve. The overall control device 5 performs overall control of the solar simulator.

  The IV curve obtained from the characteristic acquisition unit 3 is affected by the state of cell defects in the solar battery. For example, if the power generation capacity varies depending on solar cells and strings (a plurality of solar cells electrically connected in series), the output characteristic curve is affected. When the solar cell or the string has a defect or the like, a region where the IV curve is not flat or a step is generated. The mechanism will be described below.

  FIG. 2 shows a solar cell 2 constituted by three rows of solar cell strings. Three strings A (11), string B (12), and string C (13) are electrically connected in series. Further, as shown in FIG. 2, bypass diodes 14, 15, and 16 are connected in the forward direction to the ends of the respective strings. When the power generation capacity differs for each string due to the bypass diode, the power generation amount of other strings is not affected. The situation where the cell has a defect and does not generate power is schematically the same as the following state. That is, it is the same as the state where the shaded cell 17 in FIG. At this time, the current output through irradiation with light flows through the bypass diode 14 without passing through the string A (11). Further, when there is a defect in the solar battery cell in the string A (11), a part of the shaded cell 17 in FIG. 2 is shielded from light. The power generation amount of the string A (11) is determined by the state of the defect of the solar battery cell in the string A (11). As a result, as shown in FIG. 3, one step portion X is generated on the IV curve of the solar cell obtained as a result. The present invention determines whether or not a cell in a solar cell has a defect based on the step shape appearing in the IV curve as described above.

  FIG. 3 is an IV curve when the string A (11) has some defect. FIG. 4 is an IV curve when each of the solar cells of the string A (11) and the string B (12) has a defect. FIG. 5 is an IV curve in the case where each of the string A (11), the string B (12), and the string C (13) has a defect in the solar battery cell. FIG. 6 is an IV curve in the case of the situation of FIG. 4 where the defect situations of the string A (11) and the string B (12) are different. FIG. 7 is an IV curve when there is no defect. FIG. 4 is an IV curve in the case where the string A (11) and the string B (12) have a defect that causes the same reduction in power generation amount, and FIG. 5 shows the string A (11) and the string B (12). , String C (13) is an IV curve when there is a defect that causes the same decrease in power generation amount.

  It is rare that the IV curve becomes the situation shown in FIGS. Since the state of the defect of each string or cell is different, the decrease in the amount of power generation is different, and the IV curve is generally as shown in FIG. In any case, if each string and each cell is defective and the amount of power generation is abnormal, the IV curve takes a form as shown in FIGS. In FIG. 3, a step X or a non-flat portion X occurs at a position where the current value of the IV curve is high.

  FIG. 6 is an output characteristic curve when the power generation amounts of the string A (11), the string B (12), and the string C (13) are all different. This results in two steps or non-flat portions Y and Z. This indicates that there is no defect in one string and the remaining two strings have different power generation amounts, or that all three strings have different power generation amounts. FIG. 7 is an IV curve when there is no defect. The IV curve has a region M including a portion where the output current is at the maximum position and the slope of the curve is large. The portion with the large inclination is generated by the resistance of the connection portion between the DUT 2 and the characteristic acquisition unit 3, and is not generated by a cell defect in the solar cell.

  According to the above description, using the output characteristic curve obtained from the characteristic acquisition unit 3, the defect determination unit 4 extracts a step or a portion that is not flat, and determines that there is some defect if there is this. it can. When the IV curve is as shown in FIG. 6, it can be seen that at least the solar cells in the two strings are defective. When the IV curve is as shown in FIG. 5, it can be seen that there are defects in the solar cells in the three strings. In addition, the larger the step, the larger the defect area and the larger the area where power cannot be generated. Although the IV curve in FIG. 7 may be expressed together with other patterns of IV curves, this is a problem of the above-described connection between the solar simulator and the solar cell 2 to be measured, and can be ignored. . In the case of FIG. 3, it is possible to determine the presence or absence of a defect by using a decrease in the output of the entire solar cell with respect to an output determined in advance according to the material and size of the solar cell. Steps or non-flat portions can be identified using various IV curve analysis methods. For example, determination of a sudden change in the slope of the output characteristic curve and determination of continuity of the curve are used.

  FIG. 8 is a flowchart of the solar cell defect determination method of the present invention. The solar cell defect determination method according to the present invention uses the slope of the output characteristic curve. The procedure will be described below.

  When the solar cell 2 that is the object to be measured is set in the solar simulator and pseudo sunlight is emitted from the light source lamp, current and voltage are output from the solar cell. As a result, the characteristic acquisition unit 3 acquires an IV curve (S1). The inclination is acquired from the acquired IV curve (S2). As the inclination, a differential value of an IV curve is adopted. The IV curve is displayed in FIG. 3 to FIG. 7 and their composites. In the present invention, the defect is determined using the slope of the IV curve of the solar cell. The inclination changes according to a change in the current value or voltage value of the IV curve. If there is a step in the IV curve, it appears to change rapidly with a negative value. Therefore, a negative threshold value K of the inclination (differential value) is set. A region L (for example, FIGS. 3 to 6) exceeding the threshold value K is extracted (S3). The extracted region L having a large inclination includes a region that is not related to a defect like the region M in FIG. 7, and the region having a large Voc is not a defect, but has a large inclination like the region N. There is also an area. Therefore, a region where the degree of inclination largely does not depend on the defect, such as a region M and a region N between the start point and end point of the IV curve, is deleted (S4). In the region where the region M and the region N of the IV curve are deleted, a portion exceeding the threshold value K of the negative value of the slope (differential value) is determined as a defect (S5).

Next, a solar simulator according to the second embodiment will be described. In the solar simulator of the present embodiment, a method for determining whether or not a solar cell has a defect from the IV curve will be described with reference to FIG. FIG. 9 is an explanatory diagram of an example applied to the case where the number of strings of the solar cell shown in FIG. 2 is three (strings 11 (A), 12 (B), and 13 (C) in FIG. 2). . In Example 1, the slope (differential value) of the curve was calculated from the IV curve, and the presence or absence of defects was determined based on the result. Voltage value width of the voltage value and (2/3) 0.002 V _OC from 0.001 V _OC in the vicinity of the voltage value of the Example 2, the open circuit voltage as shown in FIG. 9 _{(V OC) (1/3)} Check the difference in current value with respect to. Since this is a case where the number of strings is three, if there is an abnormality such as a defect in the solar battery cell, the voltage value in the vicinity of the voltage value of (1/3) and (2/3) of the open circuit voltage (V _OC ) A step in the current value is likely to occur. The step of the current value is ΔI1 and ΔI2. The ΔI1 and ΔI2 is, it is determined whether the defect determination in the solar cell by detecting the presence or absence of the step which exceeds the 0.01I _SC from 0.005I _SC. As in the first embodiment, determination can be made by data processing using a personal computer or the like. Since the gradient (differential value) is not used, data processing and determination can be easily performed.

In the description of the present embodiment, the number of strings of solar cells is three, but the number of current value step differences is increased or decreased depending on the number of strings. When the number of strings is T, the voltage value at both ends in the voltage value range from (1 / T) Voc to {(T-1) / T} Voc of the open circuit voltage (V _OC ) and (1 / T) What is necessary is just to detect the presence or absence of a step in the current value in the vicinity of the voltage value for each Voc.

  Such a determination method is effective in the following cases. Before being formed as a solar battery, the solar battery cell constituting the solar battery is used by checking its output with an inspection device called a cell tester. However, the accuracy of output selection with a cell tester is 1% to 2% (± 0.5% to ± 1%). Therefore, even if graded, there is a possibility that a slightly different output is mixed in the solar cell. If a grade with a slightly different output is mixed, the output of the solar cell is similarly reduced by about 1% to 2%. Further, when a cell having a small number of outputs is mixed, the output of the solar battery further decreases.

  According to the determination method of the present embodiment, the state of mixing of solar cells having different grades can be confirmed and fed back to the previous process, and the output of the solar cell can be stabilized.

  As described above, according to the present invention, it is possible to determine the presence / absence of a cell defect in a solar cell by measuring and acquiring the IV curve of the solar cell with a solar simulator and analyzing the shape of the IV curve. Become. As another means for determining the presence or absence of defects in solar cells, there is an inspection means using an EL (electroluminescence) phenomenon. A defect missed by the EL method can be confirmed by the present inspection method. Thereby, the accuracy of the determination method of the presence or absence of a defect can be improved. In addition, it is possible to confirm that the solar cells having different output grades are mixed in the solar cell, and the output of the solar cell can be stabilized.

1 Light source 2 Object to be measured (solar cell)
3 Characteristic acquisition unit 4 Defect determination unit 5 Overall control device

Claims (6)

A light source that irradiates a solar cell with simulated sunlight, a pseudo-sunlight received from the light source, a characteristic acquisition unit that acquires an IV curve of a current voltage output from the solar cell, and the characteristic acquisition unit A defect determination unit that determines a defect of a solar cell according to a shape of an IV curve, and a control device that controls the entire characteristic acquisition unit and the defect determination unit. Solar simulator.   The solar simulator according to claim 1, wherein the defect determination unit determines whether or not the defect exists based on a differential value of the IV curve. In the defect determination unit, existence of the defect, compared voltage value width of 0.002 V _OC from 0.001 V _OC of the I-V curve of the voltage value open-circuit voltage of the solar cell to be measured _{(V OC)} solar simulator according to claim 1, wherein the determining by the presence or absence of 0.005I _SC of the step beyond the 0.01I _SC of the short-circuit current _{(I SC)} Te. The step of acquiring the IV curve of the solar cell, the step of grasping the region where the acquired IV curve is not flat, or the stepped region, and the defect of the solar cell by the region which is not flat or stepped A method for determining a defect of a solar cell, comprising the step of determining the presence or absence of a solar cell.   The method for determining a defect in a solar cell according to claim 4, wherein an area that is not flat or has a step is determined by a differential value of the IV curve. In the defect determination unit, existence of the defect, compared voltage value width of 0.002 V _OC from 0.001 V _OC of the I-V curve of the voltage value open-circuit voltage of the solar cell to be measured _{(V OC)} defect determination process of solar cell according to claim 4, characterized in that to determine the presence or absence of the step beyond the 0.01I _SC from 0.005I _SC of the short-circuit current _{(I SC)} Te.

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