Solar photovoltaic module hot spot life evaluation method
By constructing a photovoltaic cell micro-unit model and an electro-thermal-structural coupled simulation model, the problem of inaccurate hot spot lifetime assessment of photovoltaic modules was solved, and accurate lifetime prediction was achieved, meeting the precision requirements of photovoltaic power plant operation and maintenance decision-making.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-30
- Publication Date
- 2026-04-10
AI Technical Summary
Existing technologies cannot accurately assess the hot spot effect of photovoltaic modules caused by partial shading or cell defects, resulting in a large deviation between the life prediction results and the actual operating conditions. They also lack multi-physics coupling and multi-factor dynamic correlation, which cannot meet the precision requirements of photovoltaic power plant operation and maintenance decision-making.
A photovoltaic cell micro-unit model was constructed, and the micro-cell unit and single diode equivalent circuit were connected in parallel. By combining MATLAB/SIMULINK and ANSYS software, an electro-thermal-structural coupled simulation model was established. Through iterative calculation, accurate coupled analysis of electrical performance, temperature field, and structural stress was achieved. A multi-factor lifetime assessment model was established and dynamically corrected by associating it with actual meteorological data.
It achieves accurate quantitative assessment of hot spot component lifetime, breaks through the limitations of traditional models, accurately simulates current distribution law, reflects the semiconductor negative temperature characteristics caused by hot spot high temperature and the deformation accumulation effect caused by temperature unevenness, and improves the accuracy of lifetime prediction and engineering adaptability.
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Abstract
Description
Technical Field
[0001] This invention relates to the field of solar photovoltaic technology, specifically a method for assessing the hot spot lifetime of solar photovoltaic modules. In particular, it addresses the hot spot effect caused by partial shading or cell defects by using an electro-thermal-structural coupling simulation model and a lifetime degradation factor to achieve accurate prediction of the photovoltaic module lifetime. Background Technology
[0002] With the large-scale promotion of the solar photovoltaic industry, the long-term reliability and accurate lifespan assessment of photovoltaic modules have become core technological requirements for industry development. During actual outdoor operation, photovoltaic modules are highly susceptible to hot spot effects due to localized shading (such as dust accumulation, tree shadows, or leaf cover) or manufacturing defects in the photovoltaic cells themselves. Specifically, this manifests as abnormally high temperatures in localized areas of the module due to current mismatch, leading to a decrease in module output power, uneven internal temperature distribution, and a significant increase in thermal strain, ultimately drastically shortening the overall lifespan of the module. In this invention, photovoltaic modules exhibiting the aforementioned hot spot effect are collectively referred to as hot spot modules, while photovoltaic modules without the hot spot effect are simply referred to as photovoltaic modules, and subsequent descriptions will follow this definition.
[0003] Currently, industry assessment methods for hot spot effects largely rely on single experimental tests or simplified simulation models. These methods generally neglect the coupling effects of multiple physical fields, including electrical, thermal, and structural mechanics, leading to significant discrepancies between predicted hot spot module lifetimes and actual operating conditions. This makes it difficult to meet the precision requirements of photovoltaic power plant operation and maintenance decisions. Specific technical shortcomings are as follows:
[0004] Oversimplification of Models: Unable to Reflect Microscopic Current Mismatch Characteristics; Existing Technologies Do Not Based on the Physical Structure of Photovoltaic Cells, and Construct Models Such as Figure 3 The parallel micro-battery unit model shown was not constructed as described. Figure 4 The micro-unit single-diode equivalent circuit shown only uses the overall battery equivalent model for electrical characteristic analysis. This simplified approach cannot accurately simulate the current distribution pattern inside the battery under partial shading, and it is difficult to reflect the microscopic mechanism of the sudden increase in current density in the unshaded area. This results in insufficient accuracy in predicting the thermal power and temperature extreme values of hot spots, and cannot provide accurate electrical parameter support for lifetime assessment.
[0005] Multi-physics coupling effect is missing: temperature and stress prediction deviation is significant The traditional evaluation scheme often analyzes the degradation of the electrical performance of the photovoltaic module or the single temperature change in isolation, without integrating the coupling relationship of electrical output, heat conduction and structural stress. On the one hand, the existing experimental platform usually only measures the output power or surface temperature of the photovoltaic module, lacks the configuration of strain gauges and strain testing systems, and cannot quantify the internal stress and strain distribution caused by hot spots; on the other hand, the simulation model simplifies the multi-layer composite structure of the photovoltaic module and the battery series-parallel topology, does not establish an iterative simulation process of electricity-heat-structure, and cannot reflect the weakening effect of the semiconductor negative temperature characteristic (NTC) on the photoelectric conversion efficiency caused by the high temperature of the hot spot, as well as the cumulative effect of local deformation caused by uneven temperature, resulting in distortion of the predicted results of temperature and stress in the hot spot area.
[0006] One-sided life evaluation system: lack of dynamic correlation of multiple factors In the existing life evaluation model, the photovoltaic module life degradation factor only considers the influence of a single environmental parameter, does not correlate with actual meteorological data (such as irradiance, wind speed, ambient temperature, relative humidity) for dynamic correction, and does not include multiple factors such as thermal stress cycle, hydrolysis, and ultraviolet degradation in the coupling formula of the degradation factor. At the same time, the existing life formula lacks empirical support, neither considers the influence of photovoltaic module topology on life, nor quantifies the differential influence of shading ratio, number and distribution of hot spot cells on life, resulting in the model being unable to accurately reflect the actual law of cooperative degradation of hot spot cells and normal cells.
[0007] In summary, the existing technology has not formed a comprehensive electricity-heat-structure coupling photovoltaic module hot spot life evaluation system, which cannot solve the industry pain point of insufficient accuracy of hot spot component life evaluation, and there is an urgent need for a full-link evaluation scheme that can integrate microcell model, multi-physics coupling simulation, and multiple factor life degradation correlation. SUMMARY
[0008] (1) Technical problems to be solved The present application aims to solve the problem of inaccurate photovoltaic module hot spot life evaluation in the prior art, including: Accurately quantify the influence of electricity-heat-structure coupling under hot spot effect; Establish a dynamic degradation model based on actual meteorological data.
[0009] (2) Technical solutions The present application realizes the quantitative evaluation of the life of photovoltaic module under hot spot working condition through two core links of multi-physics coupling simulation and life evaluation model establishment, and the specific steps are as follows: 1. Photovoltaic cell microcell model construction 1.1 Constructing a photovoltaic cell microcell model Crystalline silicon photovoltaic cells are essentially thin-film pn junctions with an asymmetric structure. To accurately analyze the microscopic effects of localized shading on the cell, its physical structure is equivalent to... Nu Parallel micro-battery units with identical area and physical characteristics, such as Figure 3 As shown; simultaneously, a single-diode equivalent circuit consisting of a photogenerated power source, a diode, a series resistor, and a parallel resistor is constructed for each micro-battery unit, as shown. Figure 4 As shown, the parallel resistance reflects the battery leakage level, while the series resistance mainly includes the metal body resistance and the contact resistance generated by the connection between the metal and the semiconductor. For the aforementioned micro-battery unit, its implicit equation is derived based on the photovoltaic power generation principle: (Formula 1) In the formula, The diode reverse saturation current (A); n u This is the diode ideality factor; T Battery temperature (K); K b Boltzmann's constant, K b =1.380×10 -23 J / K; q For electron charge, q =1.608×10 -19 C.
[0010] 1.2 Output the overall photovoltaic cell characteristic parameters based on Nu By analyzing the parallel connection of individual micro-cell units, the characteristic parameters of the overall photovoltaic cell can be derived: (Formula 2) In the formula, (A) (Photogenerated Current) (A) n c , (Ω) and (Ω) is a characteristic parameter of photovoltaic cells. N u This represents the number of micro-cells in a photovoltaic cell. This model provides the core theoretical foundation for calculating the electrical characteristics of subsequent hot spot module circuit simulations.
[0011] 2. Construction of an electro-thermal-structural coupling simulation model for hot spot components A multiphysics coupled simulation model of the hot spot component was established based on MATLAB / SIMULINK and ANSYS software. Accurate coupled analysis of electrical performance, temperature field, and structural stress and strain was achieved through iterative calculations. The specific iterative process is as follows: (1) Input initial parameters (wind speed, initial temperature of hot spot components, irradiance, surface shading ratio); (2) Construct an equivalent circuit model of the hot spot component based on SIMULINK and photovoltaic cell micro-unit model (i.e., the circuit simulation model of the hot spot component to be applied later) and calculate the output characteristics of the hot spot component; (3) Establish a heat transfer simulation model of hot spot component based on ANSYS heat transfer sub-model, take the heat power output by the equivalent circuit model of hot spot component as the heat source boundary condition in the heat transfer simulation model of hot spot component, and solve the temporary temperature field of hot spot component. (4) Feed the temporary temperature field obtained from the heat transfer simulation model of the hot spot component back to the equivalent circuit model of the hot spot component, and re-iterate the output characteristics of the hot spot component; (5) Repeat steps (3) and (4) for iterative calculation until the iteration error of parameters such as electric power, thermal power, and local maximum temperature of the hot spot component is less than 1%, then determine that steady state has been reached and output the temperature field and output characteristics of the hot spot component. (6) The steady-state temperature field of the hot spot assembly is used as the body load input into the structural simulation model of the hot spot assembly. At the same time, the contact points of the mounting holes on the two long sides of the aluminum frame are set as fixed constraints according to the actual installation method of the hot spot assembly. The stress and strain fields of each layer of the hot spot assembly are obtained by solving.
[0012] 2.1 Simulation Model of Hot Spot Component Circuit A hot spot module circuit simulation model based on MATLAB / SIMULINK and photovoltaic cell micro-unit models was established for the photovoltaic module topology used. For example... Figure 5 As shown, each photovoltaic cell string is modeled individually, and its electrical parameters are derived from the photovoltaic module. I-U Characteristic curve extraction (specific parameter is photocurrent) Reverse saturation current Diode ideality factor Series resistor Parallel resistors By adjusting the shading ratio, received irradiance, and operating temperature of each battery string, the actual operating conditions of the hot spot assembly are simulated, and the output of each battery string and the overall hot spot assembly is obtained. I-U , P-U characteristic.
[0013] 2.2 Heat Transfer Simulation Model of Hot Spot Component A three-dimensional thermal model of the hotspot module was built based on Ansys Workbench. The hotspot module consists of a glass cover, upper EVA, photovoltaic cells, lower EVA, TPT backsheet, and aluminum frame. Figure 6 As shown.
[0014] The three-dimensional thermal model of the hot spot component assumes the following conditions: ① The material properties of each layer of the hot spot assembly are independent of temperature and are isotropic; ②Ignore the contact thermal resistance between the layers of materials in the hot spot assembly; ③ Only consider the heat exchange between the upper and lower surfaces of the hot spot assembly and the outside environment, ignoring the heat exchange on the sides; ④ Treat the hot spot heating caused by current mismatch as an internal heat source, and import it into the Ansys Steady-state Thermal module as a volume heat source to solve the temperature field.
[0015] 2.3 Simulation Model of Hot Spot Component Structure A simulation model of the hot spot assembly structure was constructed based on the Ansys Static Structural module. The steady-state temperature field obtained from the heat transfer simulation model of the hot spot assembly was used as the volume load input to the simulation model. According to the actual installation method of the hot spot assembly, the contact points of the mounting holes on the two long sides of the aluminum frame of the hot spot assembly were set as fixed constraints, such as... Figure 7 As shown, the influence of the hot spot on the stress and strain of each layer of the hot spot assembly is analyzed. The focus is on key mechanical parameters such as the first principal stress, Von Mises stress, and shear stress.
[0016] 3. Establishment of a photovoltaic module life assessment model under hot spot conditions This invention uses the relative decline in power generation capacity of photovoltaic modules as an indicator of lifespan degradation, and establishes a photovoltaic module lifespan assessment model that considers hot spots, as detailed below: 3.1 Power Relationship Between Photovoltaic Modules and Photovoltaic Cells Based on the series-parallel topology of photovoltaic modules and the single-diode model of photovoltaic cells, the power relationship between photovoltaic modules and photovoltaic cells is derived:
[0017] (Formula 3) In the formula: For photovoltaic modules t Maximum output power (W) at any given time; , , Parallel units Battery string Photovoltaic cells (referred to as photovoltaic cell) m , s , c Output power (W), voltage (V), and current (A) of the device. Parallel unit The terminal voltage (V); Parallel unit The output current (a); To use parallel units Current (a) of the bypass diode; Parallel unit Medium battery string The terminal voltage (V); For diode ideality factor, Boltzmann's constant, For electron charge; Photovoltaic cells I-U The relationship can be derived from a single-diode model of a photovoltaic cell. Wherein, the photovoltaic cell... Photocurrent With the intensity of the radiation received and temperature related, For photovoltaic cells occlusion ratio, The temperature coefficient of photocurrent; For photovoltaic cells under standard test conditions (STC), , Photocurrent under ( ).
[0018] 3.2 Power Attenuation Model Photovoltaic modules are inevitably affected by factors such as high temperature, high humidity, and strong ultraviolet radiation during actual operation. The power generation capacity of photovoltaic modules decreases over time according to the following law: (Formula 4) In the formula, The maximum output power (W) of the photovoltaic module at the initial moment of commissioning; For power sensitivity parameters; For shape parameters; The lifespan degradation factor (% / year) of photovoltaic modules; This refers to the runtime.
[0019] 3.3 Multi-factor coupling relationship of photovoltaic module lifespan degradation factors Lifetime degradation factors of photovoltaic modules The coupling relationship with operating factors such as photovoltaic cell temperature, ambient humidity, and ultraviolet radiation intensity is as follows: (Formula 5) In the formula: The normalization constant for physical dimensions (1 / (% / year)) 2 ); , , These are the degradation rates (% / year) of photovoltaic modules caused by hydrolysis, ultraviolet degradation, and thermal stress. RH The average relative humidity is (%). UV The average ultraviolet intensity (taken as 5% of the incident solar irradiance POA, W / m) 2 ); , , Hydrolysis, UV degradation, and thermal stress coefficient, respectively; , , These are the degradation parameters for humidity, ultraviolet intensity, and operating temperature, respectively. , , These are the activation energies for photovoltaic module power degradation caused by hydrolysis, photodegradation, and thermal cycling, respectively. The number of thermal stress cycles (cycles / year) is the number of cycles. The operating temperature range (K) of the component; Boltzmann constant (8.26 × 10⁻⁶) -5 eV / K), The operating temperature (K) of the component. This represents the highest daily operating temperature (K) of the photovoltaic module. , These represent the photovoltaic module operating temperature and the ambient temperature (K), respectively. To receive solar irradiance (W / m²) on the array plane 2 ); Wind speed (m / s); a and b are model parameters.
[0020] 3.4 Calculation of hot spot component lifetime The lifetime of a photovoltaic module is defined as the time from commissioning to the degradation of its relative power generation capacity to a threshold (usually 0.8). Combining equation (4), we obtain the lifetime expression: (Formula 6) In the formula, This is the threshold value for the relative power generation capacity of photovoltaic modules (taken as 0.8).
[0021] (III) Beneficial Effects (1) Precise characterization of microscopic electrical properties, laying a solid foundation for lifetime assessment parameters: This invention overcomes the limitations of traditional overall battery equivalent models. Based on the physical structure of the pn junction of crystalline silicon photovoltaic cells, it constructs a parallel microcell unit model and an equivalent circuit of a single diode in the microcell unit, deriving the implicit equations of the microcell unit and the overall battery characteristic parameters (Equations 1 and 2). This model can accurately simulate the internal current distribution of the battery under partial shading, quantify the microscopic mechanism of the sudden increase in current density in the unshaded area, and provide core electrical parameter support for the accurate calculation of the thermal power and temperature extreme values of hot spot modules. It solves the problem of insufficient parameter prediction accuracy caused by neglecting microscopic current mismatch in traditional models.
[0022] (2) Multiphysics coupling simulation to realize the full-dimensional quantity of hot spot effect: This invention, based on MATLAB / SIMULINK and ANSYS software, establishes an electro-thermal-structural coupled simulation model of a hot spot module and designs an iterative process of "electrical characteristic calculation - temperature field solution - structural stress-strain analysis" (with iteration error converged to 1%), achieving accurate coupled analysis of electrical performance, temperature field, and structural stress. On one hand, the model uses the thermal power output from the equivalent circuit model of the hot spot module as the heat source within the heat transfer sub-model, while simultaneously feeding the temperature field back to the equivalent circuit model of the hot spot module to correct electrical parameters, reflecting the weakening effect of the negative temperature coefficient (NTC) of semiconductors on photoelectric conversion efficiency. On the other hand, the model solves the stress-strain field based on the actual installation constraints of the photovoltaic module, quantifying the cumulative effect of local deformation caused by temperature inhomogeneity, and solving the problem of temperature and stress prediction distortion caused by isolated analysis of single physical fields in traditional schemes.
[0023] (3) Multi-factor dynamic life assessment to improve the engineering adaptability of life prediction: This invention uses relative power generation capacity attenuation (threshold 0.8) as the lifetime degradation index and constructs a multi-factor coupled lifetime assessment model: First, based on the photovoltaic module topology, the power correlation formula between the photovoltaic module and the photovoltaic cell is derived (Formula 3); second, a lifetime degradation factor coupling formula including hydrolysis, ultraviolet degradation, and thermal stress is established (Formula 5), and actual meteorological data (irradiance, wind speed, temperature, humidity, etc.) is linked to achieve dynamic correction of degradation factors; finally, combined with the power attenuation model (Formula 4), the lifetime calculation formula for hot spot modules is derived (Formula 6). This model can quantify the differentiated impact of shading ratio, number and distribution of hot spot cells on lifetime, solving the problem that traditional lifetime assessment systems only consider a single environmental parameter and lack empirical support. Attached Figure Description
[0024] Figure 1 This is a flowchart of the method of the present invention.
[0025] Figure 2 shows a photovoltaic module partial shading test bench according to an embodiment of the present invention, wherein: (a) is a schematic diagram of the test bench, and (b) is the topology of the photovoltaic module.
[0026] The components are described as follows: photovoltaic module ①, DC electronic load ②, white insulating tape ③, patch thermocouple ④, thermocouple thermometer ⑤, irradiator ⑥, infrared thermal imaging camera ⑦, strain gauge ⑧, strain testing system ⑨, and computer ⑩.
[0027] Figure 3 Schematic diagram of a photovoltaic cell micro-unit model.
[0028] Figure 4 Photovoltaic cell microcell single diode model circuit diagram. Where: battery micro-unit, S represents photoelectric power source, and D is equivalent diode; The parallel resistor, in Ω, reflects the battery leakage level. For series resistance, Ω, it mainly includes the resistance of the metal body and the resistance generated by the connection between metal and semiconductor; Photocurrent, A; Let A be the current flowing through the equivalent diode; Let A be the current flowing through the parallel resistor; I u The output current of the microcell is in A; U u V is the output voltage of the microcell.
[0029] Figure 5 Simulation model of hot spot component circuit.
[0030] Figure 6 Schematic diagram of a multi-layered composite structure for a photovoltaic module.
[0031] Figure 7 Structural constraints of photovoltaic modules.
[0032] Figure 8. Meteorological data of Wuhan, China in 2024, where (a) is direct radiation, (b) is diffuse radiation, (c) is total radiation, (d) is air temperature, (e) is relative humidity, and (f) is wind speed.
[0033] Figure 9 The effect of shading ratio on hotspot battery temperature and thermal power.
[0034] Figure 10 The effect of the shading ratio on the reverse voltage and current of the battery.
[0035] Figure 11 shows the effect of hot spot cell distribution on cell temperature, where (a) is the hot spot cell distribution and (b) is the hot spot cell temperature.
[0036] Figure 12 shows the stress and strain of each layer of the photovoltaic module along the normal direction of the hot spot cell, where: (a) is the strain of each layer of the photovoltaic module, (b) is the first principal stress of each layer of the photovoltaic module, (c) is the Von Mises stress of each layer of the photovoltaic module, and (d) is the shear stress of each layer of the photovoltaic module.
[0037] Figure 13 Photovoltaic cell degradation factors.
[0038] Figure 14 Annual surface temperature of hot spot battery.
[0039] Figure 15 Lifetime degradation curves of photovoltaic cells and photovoltaic modules.
[0040] Figure 16 shows the impact of hot spot cells on the lifespan of photovoltaic modules. (a) shows the impact of the shading ratio of hot spot cells on the lifespan of hot spot modules, and (b) shows the impact of the number of hot spot cells in the same cell string on the lifespan of hot spot modules. =0.4). Detailed Implementation
[0041] To make the above-mentioned objectives, features, and advantages of the present invention more apparent and understandable, the specific implementation method of the solar photovoltaic module hot spot lifetime assessment method of the present invention will be described in detail below with reference to specific experimental data, simulation parameters, accompanying drawings, and formulas. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention. This embodiment is based on a 545W rated power monocrystalline half-cell photovoltaic module, whose topology is "6 cell strings + 3 bypass diodes", and the entire module consists of 144 photovoltaic cells connected in series and parallel. The specific execution flow is as follows: I. Construction and Parameter Calibration of Experimental Platform for Partial Shading of Photovoltaic Modules 1.1 Composition of the experimental platform A photovoltaic module partial shading experimental platform was constructed as shown in Figure 2. The core equipment included a 545W monocrystalline half-cell photovoltaic module, a DC electronic load, white insulating tape (for simulating partial shading), patch thermocouples, thermocouple thermometers, irradiators, infrared thermal imaging cameras, strain gauges, a strain testing system, and a computer. Among them, the patch thermocouples and strain gauges were precisely placed on the backsheet surface corresponding to the shaded cells to synchronously collect temperature and thermal strain data of the hot spot area. The internal topology of the photovoltaic module was "2 cell strings + 1 bypass diode" to form a parallel unit, and 3 of these parallel units were connected in series to form the overall output circuit.
[0042] 1.2 Experimental Parameter Settings The core electrical parameters of the photovoltaic cells used in the experiment were determined by the photovoltaic module. I-U The characteristic curve was extracted, and the specific parameters under the standard test conditions STC (irradiance 1000W / m², temperature 25℃) are: photocurrent. =6.965A, reverse saturation current =4.2364A, diode ideal factor =1.013, series resistance 0.0053611Ω, parallel resistance =240Ω).
[0043] During the experiment, the battery shading ratio was adjusted using white insulating tape, and experimental data were collected under different hot spot conditions under natural light.
[0044] II. Parameter Calculation of Photovoltaic Cell Micro-unit Model This section constructs a micro-unit model of a photovoltaic cell and sets its parameters, providing a theoretical basis for calculating its electrical characteristics.
[0045] 2.1 Solving the implicit equations of photovoltaic cell micro-units Equivalent to crystalline silicon photovoltaic cells Nu Parallel micro-battery units with identical area and physical characteristics (such as...) Figure 3 As shown), the single diode equivalent circuit of each microcell (e.g.) Figure 4 As shown), for the above micro-battery unit, the implicit equation satisfying Formula 1 is: (Formula 1) In the formula, The diode reverse saturation current (A); n u This is the diode ideality factor; T Battery temperature (K); K b =1.380×10 -23 J / K is the Boltzmann constant; q= 1.608×10 -19 C represents the electron charge.
[0046] Using the photovoltaic cell parameters under standard operating conditions as a benchmark, and substituting the Boltzmann constant and the electron charge constant, the photocurrent of a single photovoltaic cell microcell can be obtained. Diode current Parallel resistor leakage current Furthermore, by deriving the parallel relationship between the photovoltaic cell micro-units, the characteristic parameters of the overall photovoltaic cell are obtained (Formula 2).
[0047] (Formula 2) In the formula, (A) (Photogenerated Current) (A) n c , (Ω) and (Ω) is a characteristic parameter of photovoltaic cells. N u This refers to the number of micro-units in a photovoltaic cell.
[0048] III. Construction and Iterative Solution of the Electro-Thermal-Structure Coupled Simulation Model This section establishes a multiphysics coupled simulation model and achieves accurate electro-thermal-structural analysis through iterative calculations.
[0049] 3.1.1 Circuit Simulation Model: For the photovoltaic module topology used in the experiment shown in Figure 2, a hot spot module circuit simulation model based on MATLAB / SIMULINK and a photovoltaic cell micro-unit model was established. For example... Figure 5 As shown, each photovoltaic cell string is modeled individually, and its electrical parameters use the STC extracted values from the experimental parameter settings in Section 1.2 of this specific implementation method. The actual operating conditions of the hot spot assembly are simulated by adjusting the shading ratio, received irradiance, and operating temperature of each cell string, and the outputs of each cell string and the overall hot spot assembly are then presented. I-U , P-U characteristic.
[0050] 3.1.2 Heat transfer simulation model: A 3D thermal model of the hotspot module was built using Ansys Workbench. The 3D structure of the hotspot module includes a glass cover, upper EVA, photovoltaic cells, lower EVA, TPT backsheet, and aluminum frame (e.g., Figure 6 (As shown in Table 1). The overall dimensions of the hot spot module are 2279mm × 1134mm, and the dimensions of a single photovoltaic cell are 175mm × 94mm. The vertical spacing between each photovoltaic cell is 2mm, the horizontal spacing is 1mm, and the gaps are filled with EVA. The material properties of each layer are shown in Table 1.
[0051] Table 1
[0052] The three-dimensional thermal model of the hot spot component assumes the following conditions: ① The material properties of each layer of the hot spot assembly are independent of temperature and are isotropic; ②Ignore the contact thermal resistance between the layers of materials in the hot spot assembly; ③ Only consider the heat exchange between the upper and lower surfaces of the hot spot assembly and the outside environment, ignoring the heat exchange on the sides; ④ Treat the hot spot heating caused by current mismatch as an internal heat source, and import it into the Ansys Steady-state Thermal module as a volume heat source to solve the temperature field.
[0053] 3.1.3 Structural Simulation Model: Using the Ansys Static Structural module, the contact points of the mounting holes on the two long sides of the hot spot assembly aluminum frame are set as fixed constraints (e.g., Figure 7 As shown, the steady-state temperature field output by the heat transfer simulation model of the hot spot module is used as the body load input to the structural simulation model of the hot spot module to solve the first principal stress, Von Mises stress and shear stress of each layer of the photovoltaic module.
[0054] 3.2 Execution of Coupled Iterative Process (1) Initial parameter input: Based on typical operating conditions in Wuhan (irradiance 700W / m², ambient temperature 26℃, wind speed 2m / s, shading ratio) =0.4 is the initial boundary condition; (2) Calculate the output characteristics of the photovoltaic module using a hot spot module circuit simulation model; (3) Use the thermal power output by the equivalent circuit model of the hot spot component as the heat source boundary condition in the heat transfer simulation model of the hot spot component, and solve the temporary temperature field of the hot spot component. (4) Then feed the temporary temperature field obtained from the heat transfer simulation model of the hot spot component back to the equivalent circuit model of the hot spot component, and re-iterate the output characteristics of the hot spot component. (5) Repeat steps (3) and (4) for electrical-thermal iterative calculations until the iterative error of electrical power, thermal power, and local maximum temperature is less than 1%, and obtain the steady-state temperature field (the extreme temperature of the unshaded area of the hot spot battery is 141℃, the shaded area is 71.9℃, and the unshaded battery is 39.8℃, etc.). Figure 9 (as shown) (6) Thermal-structural coupling: The steady-state temperature field was input into the simulation model of the hot spot component structure to obtain the stress and strain distribution of each layer (as shown in Figure 12). The principal stress, Von Mises stress and shear stress of the hot spot battery were increased by 2.37, 13.77 and 13.11 times respectively compared with the case without hot spots. The relevant data need to be verified by subsequent experiments to verify its regularity.
[0055] IV. Photovoltaic module life assessment under hot spot conditions 4.1 Construction of Power Correlation and Lifetime Decay Model The photovoltaic module-based cell series-parallel topology (as shown in Figure 2(b)) includes... There are several parallel units, each consisting of... Each battery string is formed by connecting a battery string and a bypass diode in parallel. Based on the photovoltaic cell model (formed by connecting multiple photovoltaic cells in series) and the single diode model of the photovoltaic cell, the power relationship between the photovoltaic module and the photovoltaic cell is derived (Formula 3):
[0056] In formula 3 =0.045%1 / K, and the definitions of all other variables are the same as those in the invention. The degradation of photovoltaic module power generation capacity over time follows Formula 4: (Formula 4) In formula 4, The power sensitivity parameter is set to 0.35. The shape parameter is set to 0.44, and the definitions of the other variables are the same as those in the invention.
[0057] 4.2 Multi-factor calculation of lifespan degradation factor Based on the multi-factor coupling relationship in Formula 5, and substituting the meteorological data (annual average relative humidity) for Wuhan area in 2024... RH UV intensity UV Take 5% of POA, number of thermal stress cycles (etc.), calculate lifetime degradation factor under different shading ratios. .
[0058] (Formula 5) In formula 5: , , Hydrolysis, UV degradation, and thermal stress coefficient, respectively; , , These are the degradation parameters for humidity, ultraviolet intensity, and operating temperature, respectively. , , These are the activation energies for photovoltaic module power degradation caused by hydrolysis, photodegradation, and thermal cycling, respectively. The Boltzmann constant is 8.26 × 10⁻⁶. -5 eV / K; a=-3.47, b=-0.075; the definitions of the other variables are the same as those in the invention.
[0059] When there are no hot spots The annual fluctuation range is 0.009~1.094% / year, under hot spot conditions. =0.4 Peak rate reached 8.573% / year (e.g.) Figure 13 As shown in the figure, it is 7.8 times that of the hot spot-free condition.
[0060] 4.3 Quantitative Calculation of Hot Spot Module Lifetime Using a relative power generation capacity decay to 0.8 as the lifetime threshold, the lifetime of the hot spot module under different operating conditions is calculated using Formula 6: (Formula 6) The following service life data were calculated: The lifespan of photovoltaic modules under hot spot-free operating conditions is 33.46 years; At 0.4: the lifespan of a single-cell hot spot module is 15.27 years, the lifespan of a 3-cell hot spot module in the same cell string is 28.54 years, the lifespan of a single parallel unit 2-cell hot spot module is 7.75 years, and the lifespan of a 3-parallel unit 1-cell shading photovoltaic module is 33.46 years.
[0061] V. Experimental Verification and Simulation Analysis Experimental verification was conducted based on the aforementioned experimental platform. Simulation analysis was performed based on the 2024 Wuhan meteorological data provided by ECMWF (as shown in Figure 8) and the established coupled simulation and lifetime assessment model. The system verified the accuracy of the electro-thermal-structural coupled simulation model of the hot spot module and extracted the influence law of hot spots on the lifetime of photovoltaic modules, as detailed below: 5.1 Accuracy Validation of the Model Based on Occlusion Ratio A control experiment was conducted, using irradiance of 700 W / m², ambient temperature of 26℃, and wind speed of 2 m / s as boundary conditions, to investigate different shading ratios. The temperature data of the shielded battery was collected through an experimental platform under the hot spot conditions of (0, 0.2, 0.4, 0.6, 0.8, 1.0) and compared with the simulation results.
[0062] 5.1.1 Effects on temperature and heat output: When a photovoltaic cell develops a hot spot, both experimental and simulation results show (e.g.) Figure 9 As shown in the figure, the temperature and thermal power of the hot spot battery first increase and then decrease with the increase of the shading ratio.
[0063] (1) Unobstructed ( =0) The cell temperature is approximately 39.8℃; when When the coefficient of thermal conductivity is 0.4, the unshaded area of the hot spot cell in the hot spot assembly reaches the extreme temperature of 141℃, while the temperature of the shaded part rises to 71.9℃ due to the influence of heat conduction.
[0064] (2) When When the value is 0.2, the thermal power of the hot spot battery reaches its extreme value of 58.84W.
[0065] (3) Mechanism explanation: After partial shading, almost all the current of the hot spot cells in the entire hot spot assembly flows through the unshaded part, resulting in increased current density, increased heat power in the unshaded part, and a temperature rise to 141℃. The shaded part, because it does not receive solar radiation, hardly generates photocurrent, so this part of the cell does not generate a hot spot, but its temperature also rises slightly to 71.9℃ due to the heat conduction of the unshaded part of the cell.
[0066] When the hot spot cell in the hot spot module is shaded, it exhibits purely resistive characteristics, and its total heat power... It is the product of the reverse voltage across the battery and the magnitude of the current flowing through it. Figure 10 Simulations show that, in When the voltage is 0.2, the reverse voltage is -12.48V, the current is 4.71A, and the heat power reaches its maximum. With... As the shading ratio increases, the reverse voltage across the hot spot cell in the hot spot assembly increases, but the photocurrent generated by the unshaded portion decreases, resulting in the thermal power first increasing and then decreasing as the shading ratio increases.
[0067] The deviation between experimental and simulation data is less than 0.2%, which verifies the applicability of the electro-thermal-structural coupling simulation model under different shading ratios.
[0068] 5.1.2 Impact on lifespan: As shown in Figure 16(a), when only one cell in the photovoltaic module experiences a hot spot, the module lifespan first decreases and then increases with increasing shading ratio. f When the value is 0.4, the hot spot component lifetime drops to a minimum of 15.27 years. Table 2 shows the absence of hot spots ( f =0、 f When the value is 1.0, the maximum lifespan of the photovoltaic module is 33.46 years. f When the value is 0.4, the hot spot component lifespan drops to a minimum of 7.75 years.
[0069] Table 2
[0070] 5.2 Analysis of the effect of hot spot cell number on lifetime The number of hot spot photovoltaic cells within the same battery string is set as a variable (1, 2, 3 cells), while maintaining the shading ratio. f With other parameters remaining consistent (e.g., 0.4), multiple simulation scenarios were constructed. Figure 16(b) and Table 2 show that when the number of hot-spot cells in the same battery string increases from 1 to 2 or 3, the hot-spot module lifespan increases from 15.27 years to 23.99 years and 28.54 years, respectively. This is because multiple hot spots can distribute the reverse voltage of a single cell, reducing heat power and temperature. This verifies the adaptability of the electro-thermal-structural coupling simulation model of this invention to multi-hot-spot battery conditions.
[0071] 5.3 The Influence of Hot Spot Distribution on Module Lifespan 5.3.1 Hot Spot Distribution Design Based on the photovoltaic module topology of "6 cell strings + 3 bypass diodes" in Figure 2(b), design different hot spot distribution conditions, including hot spot distribution of two cell strings in a single parallel unit. ), 2 parallel units, each with 1 battery string hot spot Each of the three parallel units has a battery string hot spot. Types such as ) and uniformly set hot spot battery shading ratio =0.4.
[0072] (1) The effect of temperature distribution (Figure 11): At that time, the highest temperature of the hot spot cell in the hot spot module was 141.22℃.
[0073] At that time, the highest temperature of the hot spot cell in the hot spot module dropped to 135.82℃.
[0074] At that time, the temperature of each cell in the photovoltaic module was only 39.8℃, and no hot spot effect occurred. The reason is that the three parallel units are operating in the same state, there is no current mismatch, and the shaded cells are not reverse biased.
[0075] (2) Distribution and quantity affect lifespan (Table 2): When a hot spot occurs in two cell strings of a parallel unit, the current mismatch of the hot spot module is most severe, and the lifespan drops to 7.75 years, which is 76.84% less than the lifespan of a normal photovoltaic module (high-risk operating condition). When one cell in each of the three parallel units is shaded at the same time, the photovoltaic module has no current mismatch, no hot spot effect, and its lifespan remains at 33.46 years (risk-free operating condition).
[0076] 5.4 Degradation Mechanism of Hot Spots Throughout Their Life Cycle 5.4.1 Temperature field characteristics analysis: Using the meteorological data for Wuhan in 2024 in Figure 8 as boundary conditions, the annual temperature fluctuation range of the hot spot cell in the hot spot module is obtained through an electro-thermal-structural coupled simulation model. Figure 14 The results show that the annual temperature fluctuation range of the battery without hot spots is -0.27℃ to 61.4℃; when a battery develops a hot spot, the annual fluctuation range becomes 10.72℃ to 185.13℃; the temperature rise of the hot spot battery is positively correlated with the irradiation intensity and the ambient temperature, with the maximum temperature difference reaching 131.64℃ in summer and 105.56℃ in winter.
[0077] 5.4.2 Thermal stress characteristic analysis: The localized high temperatures caused by hot spots subject photovoltaic modules to cyclic thermal stress and strain. Simulation analysis was conducted on the shading ratio in hot spot modules. The impact of a hot spot cell with a value of 0.4 on each layer of the photovoltaic module is shown in Figure 12.
[0078] (1) Material differences: Glass, as a brittle material, does not bear much primary stress and strain, indicating that the influence of local high temperature on the glass layer by the hot spot is negligible; EVA and TPT are both composite materials with high yield strength, and the influence of thermal stress and thermal strain caused by local high temperature on the hot spot is negligible; As the core electronic component of photovoltaic modules, the battery is subjected to large local thermal stress and thermal strain by the local high temperature on the hot spot.
[0079] (2) The stress / strain of the solar cell increases dramatically: compared with the condition without hot spots, in Under the hot spot condition of -0.4 MPa, the hot spot caused the first principal stress, Von Mises stress, shear stress, and strain of the solar cells in the hot spot module to increase by 2.37, 13.77, 13.11, and 1.51 times, respectively. Although the peak value of the first principal stress (-0.13 MPa) is much lower than the bending strength of monocrystalline silicon (~57 MPa) and will not cause immediate breakage, long-term cyclic thermal stress will induce microcrack propagation and material degradation, reducing the lifespan of the photovoltaic module.
[0080] 5.4.3 Verification of the correlation between lifetime degradation factor and photovoltaic module lifetime (1) The occlusion ratio affects the degradation factor: Lifetime degradation factors under hot spot conditions were analyzed through simulation. Change characteristics: Figure 13 No hot spots were observed in the middle. =0、 When the radiation intensity is 1.0, the degradation factor of photovoltaic cells in photovoltaic modules fluctuates with the seasons. In summer, the radiation intensity is high, resulting in a large degradation factor. The annual fluctuation range of the cell degradation factor is 0.009-1.094% / a. After hot spots occur, The degradation factor of hot spot cells in the hot spot module under operating conditions of 0.2, 0.4, 0.6, and 0.8 increased to 0.889-7.580% / a, 0.102-8.573% / a, 0.065-5.893% / a, and 0.051-4.669% / a, respectively. =0.4 Under operating conditions, the degradation factor reaches its maximum value because the local temperature of the hot spot cell in the hot spot module is the highest.
[0081] (2) Correlation between degradation factor and component lifetime and model validation: Figure 15 When no hot spots are observed, all cells in the photovoltaic module degrade synchronously, and the lifespan of the photovoltaic module is the same as that of the photovoltaic cells, with a module lifespan of 33.46 years; when one photovoltaic cell continuously experiences... When the hot spot value is 0.4, the lifetime of the hot spot module is jointly determined by the degradation of the normal cell and the hot spot cell. The lifetime of the hot spot module is shortened to 15.27 years, a reduction of 54.36%. This correlation verifies the lifetime prediction logic of the simulation model.
[0082] In summary, the electro-thermal-structural coupling simulation model of the hot spot module in this invention is basically consistent with the experimental data, confirming that the hot spot accelerates the degradation of the photovoltaic module through local high temperature and mechanical stress. The degree of impact depends on the shading ratio, the number and distribution of hot spot cells, and the worst operating condition ( =0.4) and uneven distribution) The lifespan of hot spot modules decreased by more than 76%. Therefore, in the design and operation and maintenance of photovoltaic modules, it is necessary to avoid local shading and optimize the internal circuit structure to extend the lifespan of hot spot modules.
Claims
1. A method for assessing the hot spot lifetime of a solar photovoltaic module, characterized in that, Includes the following steps: S1 Constructs a micro-unit model of photovoltaic cells: Equivalent to crystalline silicon photovoltaic cells as... Nu Each microcell unit has the same area and physical characteristics. A single diode equivalent circuit is constructed for each microcell unit, which includes a photovoltaic power source, a diode, a series resistor, and a parallel resistor. The implicit equation of the microcell unit is derived based on the photovoltaic power generation principle, and the overall photovoltaic cell characteristic parameters are derived based on the parallel relationship. S2 establishes an electro-thermal-structural coupling simulation model for the hot spot component: Based on MATLAB / SIMULINK and ANSYS software, the initial parameters are first input, and then the output characteristics of the hot spot component are calculated through circuit simulation. The output thermal power is used as the heat source in the heat transfer simulation to solve the temporary temperature field. The temporary temperature field is fed back to the circuit simulation model for iterative calculation until the error is <1% to obtain the steady-state temperature field. The steady-state temperature field is then used as the body load input to the structural simulation model. The stress and strain field is solved with the mounting holes on the two long sides of the aluminum frame as fixed constraints. S3 establishes a hot spot module lifetime assessment model: Based on the photovoltaic module topology, the power relationship between the photovoltaic module and the photovoltaic cell is derived. Combining the power decay model and the lifetime degradation factor formula with multiple factors coupled, the lifetime of the hot spot module is calculated with the relative power generation capacity decaying to 0.8 as the threshold.
2. The method for assessing the hot spot lifetime of a solar photovoltaic module according to claim 1, characterized in that, The implicit equation of the micro-battery unit in step S1 is: (Official 1) In the formula, The diode reverse saturation current (A); n u This is the diode ideality factor; T Battery temperature (K); K b Boltzmann's constant, K b =1.380×10 -23 J / K; q For electron charge, q =1.608×10 -19 C.
3. The method for assessing the hot spot lifetime of a solar photovoltaic module according to claim 2, characterized in that, The derivation formulas for the overall photovoltaic cell characteristic parameters in step S1 are as follows: (Official 2) In the formula, (A) (Photogenerated Current) (A) n c , (Ω) and (Ω) is a characteristic parameter of photovoltaic cells. N u This refers to the number of micro-units in a photovoltaic cell.
4. The method for assessing the hot spot lifetime of a solar photovoltaic module according to claim 1, characterized in that, The initial parameters mentioned in step S2 include wind speed, initial temperature of the photovoltaic module, irradiance, and surface shading ratio; the electrical parameters of the photovoltaic cells in the circuit simulation model are derived from the photovoltaic module. IU Characteristic curve extraction.
5. The method for assessing the hot spot lifetime of a solar photovoltaic module according to claim 1, characterized in that, The photovoltaic module three-dimensional structure of the heat transfer simulation model described in step S2 includes a glass cover, upper EVA, photovoltaic cells, lower EVA, TPT backsheet, and aluminum frame. The model sets the following assumptions: ① The material properties of each layer are independent of temperature and are isotropic; ② Interlayer contact thermal resistance is ignored; ③ Only heat exchange between the upper and lower surfaces and the outside is considered; ④ Current mismatch heating is regarded as an internal heat source and imported into the Ansys Steady-state Thermal module.
6. The method for assessing the hot spot lifetime of a solar photovoltaic module according to claim 1, characterized in that, The power relationship between the photovoltaic module and the battery mentioned in step S3 is shown in Formula 3. In the formula: For photovoltaic modules t Maximum output power (W) at any given time; , , Parallel units Battery string Photovoltaic cells (referred to as photovoltaic cell) m , s , c The output power (W), voltage (V), and current (A) of the device. Parallel unit The terminal voltage (V); Parallel unit The output current (A); To use parallel units The current (A) of the bypass diode; Parallel unit Medium battery string The terminal voltage (V); For diode ideality factor, Boltzmann's constant, For electron charge; photovoltaic cells IU The relationship can be derived from the single-diode model of a photovoltaic cell; photovoltaic cell Photocurrent With the intensity of the radiation received and temperature related, For photovoltaic cells occlusion ratio, The temperature coefficient of photocurrent; For photovoltaic cells under standard test conditions ( , Photocurrent under ( ).
7. The method for assessing the hot spot lifetime of a solar photovoltaic module according to claim 1, characterized in that, The power attenuation model mentioned in step S3 is as follows: (Official 4) In the formula, The maximum output power (W) of the photovoltaic module at the initial moment of commissioning; For power sensitivity parameters; For shape parameters; The lifespan degradation factor (% / year) of photovoltaic modules; This refers to the runtime.
8. The method for assessing the hot spot lifetime of a solar photovoltaic module according to claim 7, characterized in that, The multi-factor coupling relationship of the life degradation factor mentioned in step S3 is given by formula 5: In the formula: The normalization constant for physical dimensions (1 / (% / year)) 2 ); , , These are the degradation rates (% / year) of photovoltaic modules caused by hydrolysis, ultraviolet degradation, and thermal stress. RH The average relative humidity is (%). UV The average ultraviolet intensity (taken as 5% of the incident solar irradiance POA, W / m) 2 ); , , Hydrolysis, UV degradation, and thermal stress coefficient, respectively; , , These are the degradation parameters for humidity, ultraviolet intensity, and operating temperature, respectively. , , These are the activation energies for photovoltaic module power degradation caused by hydrolysis, photodegradation, and thermal cycling, respectively. The number of thermal stress cycles (cycles / year) is the number of cycles. The operating temperature range (K) of the component; Boltzmann constant (8.26 × 10⁻⁶) -5 eV / K), The operating temperature (K) of the component. This represents the highest daily operating temperature (K) of the photovoltaic module. , These represent the photovoltaic module operating temperature and the ambient temperature (K), respectively. To receive solar irradiance (W / m²) on the array plane 2 ); denoted as wind speed (m / s); a and b are model parameters.
9. The method for assessing the hot spot lifetime of a solar photovoltaic module according to claim 1, characterized in that, The formula for calculating the lifetime of the hot spot component in step S3 is as follows: (Official 6) In the formula, This is the threshold value for the relative power generation capacity of photovoltaic modules (taken as 0.8).
10. The method for assessing the hot spot lifetime of a solar photovoltaic module according to claim 1, characterized in that, In the implementation method based on meteorological data of Wuhan City in 2024, the power sensitivity parameter The value is 0.35, shape parameter The value is 0.44, and the hydrolysis coefficient is... The value is 1.97, the ultraviolet degradation coefficient. The value is 35.1, and the thermal stress coefficient is... The value is 0.001, representing the humidity degradation parameter. The value is 4.00, representing the ultraviolet intensity degradation parameter. The value is 1.05, representing the operating temperature degradation parameter. The value is 1.002, which is the activation energy for hydrolysis. The value is 0.49 eV, the activation energy for photodegradation. The value is 1.20 eV, and the activation energy for thermal cycling is... The value is 0.50 eV, and the model parameters a and b are -3.47 and -0.075 respectively.