A method and instrument for measuring the light transmittance of dust in solar photovoltaic panels

Abstract

This invention describes a method and instrument for measuring the light transmittance (shading) of a solar photovoltaic panel when it is dusty. The method utilizes a reference method, calculating the light transmittance (luminous flux Φ) of the solar photovoltaic panel before cleaning (in a dusty state). t The ratio of the light transmittance (luminous flux Φ0) on the photovoltaic panel to the light transmittance after cleaning (dust-free state) is used to assess the amount of accumulated dust on the panel (or the pollution index) and to determine the impact of dust on the photoelectric conversion efficiency. The calculation formula is: β = Φ t / Φ0, β is the dust transmittance coefficient. In addition, the present invention also describes the principle, structure and usage of the solar photovoltaic panel dust transmittance coefficient tester designed according to this reference method. This instrument is a miniaturized portable field tester, which mainly consists of two parts: the test host (1) and the external clamp probe assembly (2) (all integrated in one host box).

Description

Technical Field

[0001] This invention falls under the technical field of testing techniques and instruments related to solar energy development and utilization. This testing technology can be applied to various aspects of photovoltaic panel design, manufacturing, and subsequent maintenance. The promotion and application of this invention have significant economic and social benefits in ensuring the energy utilization rate of photovoltaic power generation systems, improving the economic efficiency of photovoltaic power plant operations, and reducing energy losses. Background Technology

[0002] After installation and commissioning, photovoltaic panels are exposed to the natural atmosphere for extended periods, constantly subjected to complex weather conditions such as wind, sun, and rain. Over time, sand and dust accumulate, becoming increasingly thick and abundant. A significant portion of the solar energy reaching the panels is reflected, while another portion is absorbed by the dust and stored as heat within these dust particles. Consequently, less and less solar energy reaches the silicon solar cells through the tempered glass, resulting in substantial waste. If this dust is not cleaned, the photovoltaic panels cannot achieve sufficient and effective photoelectric conversion. This not only leads to economic losses but also poses significant safety hazards, such as the potential for hot spots caused by severe dust accumulation, which can burn out the panels and even cause fires in the photovoltaic power station.

[0003] Therefore, real-time knowledge and quantitative measurement of the dust coverage (transmittance coefficient) of photovoltaic panels is an essential routine monitoring and maintenance task in the daily operation of photovoltaic power plants. This invention addresses the current market's lack of efficient and accurate online testing methods and instruments by developing a solar photovoltaic panel dust transmittance coefficient tester.

[0004] The following is combined with Figure 1 The physical structure of photovoltaic panels is analyzed, and several similar testing methods are compared.

[0005] Dust mass collection method A certain area (s, unit: square meters) of dust is collected manually or mechanically, and its mass (m, unit: grams) is measured. Then, the amount of dust per unit area, i.e., the dust density (m / s), is calculated. Based on the previously established relationship table (functional relationship) between power generation loss and dust density, the current solar energy loss is determined.

[0006] The drawbacks of this method are twofold. First, the process is cumbersome, requiring weighing with a balance and area measurement, which are difficult to automate. Second, when the pollution concentration is low (mild), although the concentration of pollutants already has a significant impact on photoelectric conversion efficiency, the pollutants are difficult to collect or are not collected completely, leading to large test deviations.

[0007] Dust flashover voltage measurement method Similar to flashover meters used in power transmission and distribution, these meters assess the degree of contamination on photovoltaic panels by measuring the critical flashover voltage of pollutants on the panel surface. However, because the flashover voltage is affected by multiple physical variables such as humidity, temperature, ash density, salt density, and leakage current, the measurement results do not have a direct physical linear correlation with the light transmittance of the photovoltaic panel, significantly reducing the accuracy and persuasiveness of the measured data.

[0008] Transmittance photometry Firstly, from Figure 1 Let's analyze the structure of a solar photovoltaic panel. A solar photovoltaic panel generally has a 5-layer structure. The top layer is a tempered glass layer (101), followed by an EVA layer (102), then the core component of the photovoltaic panel, the silicon crystal battery layer (103), then another EVA layer (104), and finally the backsheet layer (105).

[0009] from Figure 1 As can be seen, the tempered glass layer (101) is a high-transmittance material. It is made of white glass that has undergone high-temperature quenching, which greatly improves its hardness, bending strength, and tensile strength. The tempered glass layer has a very high visible light transmittance. The silicon crystal battery layer (103) is a bluish-gray silicon crystal layer (divided into monocrystalline silicon and polycrystalline silicon). Light in the visible light spectrum that can produce the photoelectric effect cannot penetrate the silicon crystal layer. The back sheet layer is generally made of tempered glass or polymer materials (such as polycarbonate), so the back sheet layer is colorless and transparent. The EVA layer is a transparent adhesive film layer, and its function is to bond the various materials together as a whole.

[0010] from Figure 2 As you can see, due to manufacturing limitations, individual silicon crystal cells cannot be made as large as a complete photovoltaic panel; they must be assembled from small pieces. The cells are relatively small, with each side measuring only 100-200mm. A complete photovoltaic panel module has several transverse gaps (202) along its width. These gaps are not covered by silicon crystal cells and are therefore transparent and light-transmitting. The width of these gaps is approximately 6±2mm. Near the aluminum alloy frame, the length of the gaps is approximately 180±30mm.

[0011] Therefore, for the vast majority of photovoltaic panel structures, this 6mm x 180mm area is the best area for us to conduct light transmittance tests.

[0012] In addition, we assume that the dust and dirt cover on the entire photovoltaic panel (whether it is the light-transmitting seam area or the opaque silicon crystal covered area) is uniform. Measuring the light transmittance (or shading) of the light-transmitting seam is equivalent to measuring the light transmittance of the entire photovoltaic panel.

[0013] As mentioned above, by selecting a suitable light-transmitting area on the photovoltaic panel, the light-blocking effect of dust content can be utilized to measure the change in light transmittance under dust-containing and dust-free conditions, thus allowing for a relatively accurate calculation of the photovoltaic panel's light transmittance coefficient.

[0014] Moreover, the mathematical relationship between the amount of dust and light transmittance is highly linear before the dust saturates the photovoltaic panel (i.e., before the photovoltaic panel still produces a small amount of electricity).

[0015] In summary, among the three methods mentioned above, the third method, which uses the transmittance photometric method of active light source irradiation of photovoltaic panels, can directly and objectively evaluate the dust pollution index of photovoltaic power generation efficiency, making it the optimal evaluation and testing method. Summary of the Invention

[0016] The following is combined with Figure 3 This paper will provide a detailed explanation of the dust transmittance coefficient tester for solar photovoltaic panels designed based on the reference method principle.

[0017] The specific steps of the reference method are as follows: To assess the impact of dust on the power generation efficiency of photovoltaic panels, it is necessary to measure the luminous flux under two different conditions: a clean state and a dusty state. An active light source is used to illuminate the transverse gap (202) of the silicon cell array of the photovoltaic panel, and a photodetector is placed behind the transverse gap to receive the energy transmitted from the light source. The energy value is first measured with dust, and the luminous flux value is recorded as Φ. t After cleaning the dust from the gaps, measure the dust removal energy value again, and record the photometric value as Φ0. Here, Φ0 ≥ Φ t Through Φ t The ratio of β to Φ0 can accurately determine the current dust pollution level of the photovoltaic panel. β=Φ t / Φ0, β is defined here as light transmittance. The value of β is between 0 and 1. β is 1, which means that there is very little dust and almost no dust. β is 0, which means that there is a lot of dust and the photovoltaic panel is saturated, and there is almost no power output.

[0018] The solar photovoltaic panel dust transmittance coefficient tester mainly consists of two parts: the test host (1) and the external clamp probe assembly (2). The flexible cable end of the clamp probe assembly is soldered with an aviation plug, which can be connected to the host as one unit. The light transmitter module (306) is connected to the small socket (15) on the host panel with the connecting cable A (3); the light receiver module (311) is connected to the large socket (14) on the host panel with the connecting cable B (4). The light source electronic system module (303) receives the instructions sent from the CPU core control board module (301), and after precise calculation and modulation processing, generates a high-precision alternating high-frequency test signal that meets the test requirements.

[0019] The light emitter module (306) is a cylindrical component containing a point light source (315) and a collimating lens (316), among other devices. The light receiver module (311) is also a cylindrical component with the same diameter as the light emitter module (306), containing a photoelectric conversion sensor (312) and other devices.

[0020] When the upper clamp (309) and the lower clamp (310) are clamped on the photovoltaic panel, the center of the point light source (315), the center of the collimating lens (316), and the center of the photoelectric conversion sensor (312) are on a straight line, thus forming the optical axis (318).

[0021] Because a miniature light source is used, the light emitted from the collimating lens (316) reaches the test spot (6) formed by the transverse gap (12) of the photovoltaic panel. The diameter is only about 3.0 mm. The spot size is smaller than the minimum width of the transverse gap (12) of 6±2 mm, ensuring that the signal light passes through the photovoltaic panel under test vertically without side leakage.

[0022] The light path is as follows: signal light emitted from point light source (315) → collimating lens (316) → vertically incident photovoltaic panel (10) → photoelectric conversion sensor (312). Since the entire optical path is about 20mm, the distance is short. In addition, the divergence angle of the collimated beam is only 1°. Therefore, the diameter of the light spot does not change much from the light outlet to the sensitive surface of the photoelectric conversion sensor (312) within the entire optical path. This ensures that all the test light reaches the receiving sensitive surface of the photoelectric conversion sensor (312) and at the same time ensures the accuracy of the test.

[0023] Electrical signal transmission link: The photoelectric conversion sensor (312) converts the light intensity transmitted through the photovoltaic panel (10) into a voltage signal. This voltage signal is transmitted to the receiving light signal processing module (305) via the connecting cable B (4). After a series of signal processing steps such as modulation and demodulation, the processed signal is transmitted to the CPU core control board module (301). The CPU integrates an analog-to-digital converter, which converts the voltage signal into a digital signal through AD conversion, thus obtaining luminous flux values ​​of different intensities.

[0024] The power supply system module (302) is responsible for providing power to the entire test system, including the CPU core control board module (301), the light source system power supply module (303), the touch display system module (304), the light signal receiving and processing module (305), and the power supply system module (303), totaling five modules. This power supply capability is reflected in multiple voltage ranges, such as the 3.3V required by the CPU core control board module (301) and the 12V required by the touch display system module (304).

[0025] The touch display system module (304) is a human-computer interaction interface component. It adopts the specifications of a 7-inch color capacitive touch screen and is mainly used to display the calculation results output by the core board. It is also a two-in-one functional component that serves as an input device for users when operating the interface.

[0026] The CPU core control board module (301) is the command and control center of the entire test system. In addition to converting photometric signals from analog to digital, it also has multiple functions such as data storage, test report generation, and document printing.

[0027] Regarding the clamping and positioning of the clamp probe assembly (2), the positioning plate (5) is made of 5 mm thick transparent plexiglass. The plate has a parallel sliding groove (9), which is cut through and hollowed out. The lower part of the light emitter lens barrel (306) can move left and right within the groove to select a positioning point. The diameter of the lens barrel is the same as the width of the groove, and their fit tolerance is a precision sliding clearance. Figure 3 As can be seen in the (AA view), there are laser-engraved scale lines on the left side of the positioning plate (5). These scale lines are used to align and correct the left seam line (7) and right seam line (8) on the photovoltaic panel. After alignment, the center line of the positioning plate (5) coincides with the center line of the transverse gap seam (202) of the silicon cell assembly. Attached Figure Description

[0028] Figure 1 A cross-sectional view of the 5-layer structure of a solar photovoltaic panel.

[0029] Figure 2 Selection of test area for light transmittance of solar photovoltaic panels

[0030] Figure 3 Overall schematic diagram of the photovoltaic panel dust transmittance coefficient testing system In the picture: 101-Tempered glass layer, 102-EVA layer, 103-Silicon crystal cell layer, 104-EVA layer, 105-Backsheet layer, 201-Aluminum alloy frame, 202-Transverse gap of silicon cell assembly, 203-Silicon crystal wafer, 1-Test host, 2-Clamp probe assembly, 3-Connecting cable A, 4-Connecting cable B, 5-Positioning plate, 6-Test spot, 7-Left seam line, 8-Right seam line, 9-Parallel sliding groove, 10-5-layer photovoltaic panel assembly, 11-Clamp, 13-Scale center line on positioning plate, 14-Gap alignment scale line, 15-Horizontal scale line of sliding groove, 16-Small socket, 17-Large socket, 301-CPU core control board module, 302-Power supply system module, 303-Light source electronic system module, 304-Touch display system module, 305-Receiver signal processing module, 306-Light emitter lens barrel, 307-Pin, 308-Torsion spring, 309-Upper clamping plate, 310-Lower clamping plate, 311-Light receiver lens barrel, 312-Photoelectric conversion sensor, 313-Lower barrel sealing ring, 314-Upper barrel sealing ring, 315-Point light source, 316-Collimating lens, 317-Rotating pin, 318-Optical axis Detailed Implementation

[0031] (1) Select the test area Locate the transverse gap (202) of the silicon cell array in the photovoltaic panel to be tested, and place the positioning plate (5) in this area. Visually observe and ensure that the center line of the scale on the positioning plate is located at the bisector of the transverse gap (202), that is, the value of the left line (7) of the gap is basically equal to the scale value of the right line (8) of the gap. Then, use two clips (11) to fix the positioning plate (5) firmly on the photovoltaic panel.

[0032] (2) Mounting the probe assembly Remove the clamp probe assembly (2) from the main unit. Clamp the light emitter lens (306) and light receiver lens (311) of the clamp probe assembly (2) into the parallel sliding slot (9) of the positioning plate (5). Since the two lens tubes are applied to the photovoltaic panel by the spring torque of the torsion spring (308), when you release your hand, the two lens tubes are still well clamped to the photovoltaic panel and will not loosen or shift. Then observe whether the sealing rings (313 and 314) at the end faces of the two lens tubes are tightly connected to the upper and lower surfaces of the photovoltaic panel. If there is any gap in the seal, move the position slightly.

[0033] (3) Aviation plug for connecting cables Connect the optical transmitter module (306) to the small socket (15) on the host using connecting cable A (3), and connect the optical receiver module (311) to the small socket (14) on the host using connecting cable B (4).

[0034] (4) Turn on the main unit power and perform a dust-laden photometric value test. Turn on the power switch of the dust transmittance tester. The touch screen of the touch display system module (304) will light up. Click the button on the screen to start the dust-bearing photometric value test and obtain the dust-bearing photometric value Φ. t (Energy value E) t ).

[0035] (5) Wipe off the dust on the photovoltaic panel and perform a dust removal photometric value test. Remove the clamp probe assembly (2) from the photovoltaic panel and wipe the dust in the area of ​​the parallel sliding groove (9) inside the positioning plate (5) with an alcohol swab (Note: you can wipe it multiple times until there is no visible dust or stains). Clamp the clamp probe assembly (2) again at the groove position that was just tested, and click the button on the touch screen to start the dust removal photometric value test and obtain the dust removal photometric value Φ0 (energy value E0).

[0036] Based on the two tests (photometric value Φ with dust), t The issue of the test point for the dust removal photometric value Φ0 not coinciding needs to be explained here. Because the physical material of the entire transverse gap (12) is uniform, the cleanliness of the entire parallel sliding groove is also uniform after wiping away dust. Therefore, the photometric value measured will be the same whether the test point is slightly to the left or slightly to the right within the parallel sliding groove. However, a transverse scale line (15) is still made at the slot of the positioning plate (5) for the convenience of the tester to make a rough reference.

[0037] (6) Calculate the dust transmittance coefficient β of the test results. Click the [Calculate] button on the touch screen, and the CPU core control board module (301) will press β=Φ t The formula for / Φ0 is used to calculate the dust transmittance coefficient of the photovoltaic panel and to determine the corresponding pollution level.

[0038] (7) Other functions of the software Clicking the "Generate Test Report" button in the software will save the relevant test parameters to the instrument's memory.

[0039] (8) End the test After the operation is complete, turn off the instrument power and put the clamp probe assembly (2) back into the main unit. The test is over.

Claims

1. This invention discloses a method and instrument for evaluating and measuring the light transmittance of dust on solar photovoltaic panels, characterized in that, The evaluation employed a reference method, using the light transmittance (Φ0) after dust removal as a benchmark. β was used to assess the degree of dust obstruction. That is, the light transmittance (luminous flux Φ) with dust was used as the reference. t Divide by Φ0. The calculation formula is as follows: β = Φ t / Φ 0。 2. The method and instrument for measuring the dust transmittance of a solar photovoltaic panel as described in claim 1, characterized in that, The light-transmitting area is selected at the transverse gap of the silicon solar cell assembly (12), or the light-transmitting area can be selected at the light-transmitting edge without silicon crystal layer.

3. The method and instrument for measuring the dust transmittance of a solar photovoltaic panel as described in claim 1, characterized in that, The instrument consists of two parts: the test host (1) and the external clamp probe assembly (2). The two are connected by a flexible cable more than 2 meters long. This design makes operation convenient. During the test, the test host (1) can be placed on the ground or platform, freeing up the hands. One person only needs to move the clamp probe assembly (2) to complete the test.

4. The method and instrument for measuring the dust transmittance of a solar photovoltaic panel as described in claim 1, characterized in that, The clamping structure uses a caliper: the upper part of the caliper is the light transmitter module (306), and the lower part of the caliper is the light receiver module (311). The clamping force of the caliper comes from the torsion spring (308) at the pivot of the upper and lower clamping plates. Of course, top springs or tension springs can also be installed at the front and rear of the pivot to achieve the same clamping effect.

5. The method and instrument for measuring the dust transmittance of solar photovoltaic panels as described in claim 1 do not use lasers. The light source is a miniature semiconductor point light source with a white light emission spectrum (300nm~950nm), rather than a laser-emitted light source with a specific wavelength.

6. The method and instrument for measuring the dust transmittance of a solar photovoltaic panel as described in claim 1, further characterized in that, The beam was collimated and shaped at the exit port of the lens tube.

7. The method and instrument for measuring the dust transmittance of a solar photovoltaic panel as described in claim 1, further characterized in that, In terms of operating mode, the optical signal is processed by modulation and coupling to output an alternating high-frequency mode.

8. The method and instrument for measuring the dust transmittance coefficient of a solar photovoltaic panel as described in claim 1 do not require disassembly or modification of the existing structure or circuit components of the photovoltaic panel during testing, nor do they require interruption of the photovoltaic panel's operation. Electrically, it is a completely independent instrument system.

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