Photovoltaic panel temperature prediction method under steady-state thermal load effect

Abstract

The invention relates to the technical field of photovoltaic panels, in particular to a photovoltaic panel temperature prediction method under the steady-state thermal load effect, which comprises the following steps: measuring the thickness parameter of each layer of a photovoltaic panel and the surface temperature values of the upper and lower outer layers; and constructing a temperature prediction model of each layer of the photovoltaic panel, and performing temperature prediction on each layer by using the material heat conduction correction coefficient and the thickness parameter of each layer of the photovoltaic panel. The problem that effective prediction of the interlayer temperature of the photovoltaic panel is lacked in the prior art is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of photovoltaic panels, and in particular to a method for predicting the temperature of a photovoltaic panel under a steady-state heat load. Background Art

[0002] Photovoltaic panels are multi-layer "sandwich" structures, and generally include: a back panel layer, a first EVA layer, a silicon wafer layer, a second EVA layer and a tempered glass substrate layer. Photovoltaic panels also include photovoltaic panels with multiple silicon wafer layers, which are prepared by hot pressing to bond and solidify each layer of material.

[0003] During the heating preparation and service process of photovoltaic panels, the temperature will not change suddenly under normal circumstances. In each short time interval, it can be considered that the photovoltaic panels are subject to steady-state thermal loads. However, thermal loads will significantly affect the preparation and service performance of photovoltaic panels, such as the thermal curing effect of the EVA adhesive layer during the preparation process, the residual stress / deformation in the panel after the thermal load disappears, the electrical conversion efficiency affected by temperature during service, and the service life. Therefore, it is particularly necessary to measure and monitor the temperature of each layer of the photovoltaic panel.

[0004] Since photovoltaic panels are made of multiple layers of materials with different physical properties, the temperature of the exposed upper and lower surfaces is easy to measure directly, but the temperature of the material sealed inside is difficult to measure non-destructively. In addition, due to differences in material properties, interlayer thickness, etc., the temperature of each internal layer is not equal to the surface temperature of the photovoltaic panel. Therefore, it is urgent to develop a method to measure the interlayer temperature of photovoltaic panels. Summary of the invention

[0005] In view of the shortcomings of the existing methods, the present invention solves the problem of lack of effective prediction of the interlayer temperature of photovoltaic panels in the prior art.

[0006] The technical solution adopted by the present invention is: a method for predicting the temperature of a photovoltaic panel under a steady-state heat load comprises the following steps:

[0007] Step 1: Measure the thickness parameters of each layer of the photovoltaic panel and the surface temperature values ​​of the upper and lower outer layers of the photovoltaic panel;

[0008] As a preferred embodiment of the present invention, the layers of the photovoltaic panel include: a back panel layer, an EVA layer, a silicon sheet layer and a glass layer.

[0009] As a preferred embodiment of the present invention, the upper and lower outer layers are a back plate layer and a glass layer.

[0010] As a preferred embodiment of the present invention, the photovoltaic panel includes: a single-layer, a double-layer, or a plurality of-layer photovoltaic panels.

[0011] As a preferred embodiment of the present invention, the total number of layers of the single-layer photovoltaic panel is 5.

[0012] Step 2: Construct a temperature prediction model for each layer of the photovoltaic panel, and use the thermal conductivity correction coefficient and thickness parameters of each layer of the photovoltaic panel to predict the temperature of each layer;

[0013] As a preferred embodiment of the present invention, the formula of the temperature prediction model of each layer of the photovoltaic panel is:

[0014] T i =A i z+B i , z i-1 ≤z≤z i (1)

[0015] Among them, T i is the temperature distribution of the ith photovoltaic panel along the z direction, A i is the thermal conductivity correction coefficient of the i-th layer material, B i is the correlation coefficient with the thickness of the i-th layer of material, z i-1 、z i are the thickness coordinate values ​​of the lower and upper surfaces of the i-th layer of material respectively.

[0016] As a preferred embodiment of the present invention, the formula of the thermal conductivity correction coefficient is:

[0017]

[0018] Among them, λ i is the thermal conductivity of the i-th layer material; T1 is the lower surface temperature of the photovoltaic panel; T n is the upper surface temperature of the photovoltaic panel; n is the total number of photovoltaic panels; h i is the thickness of the i-th layer of material.

[0019] As a preferred embodiment of the present invention, the formula of the material thickness correlation coefficient is:

[0020]

[0021] Where T1 is the lower surface temperature of the photovoltaic panel; h j is the thickness of the j-th layer of material, A j is the thermal conductivity correction coefficient of the jth layer material, z i-1 is the z-direction coordinate value of the i-1th layer of material.

[0022] As a preferred embodiment of the present invention, a photovoltaic panel temperature prediction system under steady-state thermal load includes: a memory for storing instructions executable by a processor; and a processor for executing instructions to implement a photovoltaic panel temperature prediction method under steady-state thermal load.

[0023] As a preferred embodiment of the present invention, a computer readable medium stores a computer program code, and when the computer program code is executed by a processor, a method for predicting the temperature of a photovoltaic panel under a steady-state thermal load is implemented.

[0024] Beneficial effects of the present invention:

[0025] 1. The temperature prediction model of each layer of the photovoltaic panel constructed by the present invention is simple. By measuring the temperature and thickness parameters of the photovoltaic panel and combining the thermal conductivity of each layer material, the temperature value corresponding to the coordinates of each layer can be accurately predicted;

[0026] 2. The predicted temperature value of the present invention can be used to evaluate indicators such as electrical conversion efficiency and service life of photovoltaic panels during their service life. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a flow chart of a method for predicting the temperature of a photovoltaic panel under a steady-state heat load of the present invention;

[0028] Figure 2 It is a schematic diagram of the structure of each layer of the photovoltaic panel of the present invention;

[0029] Figure 3 It is a schematic diagram of the coordinates of each layer of the photovoltaic panel of the present invention;

[0030] Figure 4 It is the numerical simulation photovoltaic panel temperature cloud map of the present invention;

[0031] Figure 5 It is a comparison chart of the numerical simulation and model analytical calculation results of the present invention. DETAILED DESCRIPTION

[0032] The present invention is further described below in conjunction with the accompanying drawings and embodiments. This figure is a simplified schematic diagram, which only illustrates the basic structure of the present invention in a schematic manner, and therefore it only shows the components related to the present invention.

[0033] like Figure 1 As shown, a method for predicting the temperature of a photovoltaic panel under a steady-state heat load includes the following steps:

[0034] Step 1: Measure the thickness parameters of each layer of the photovoltaic panel and the surface temperature values ​​of the upper and lower outer layers.

[0035] Each layer of the photovoltaic panel includes: a backplane layer, an EVA layer, a silicon wafer layer and a glass layer; usually the number of EVA layers is the number of silicon wafer layers + 1; for example, a single-layer photovoltaic panel includes: a backplane layer, a first EVA layer, a silicon wafer layer, a second EVA layer and a glass layer; a double-layer photovoltaic panel includes: a backplane layer, a first EVA layer, a first silicon wafer layer, a second EVA layer, a second silicon wafer layer, a third EVA layer and a glass layer; a three-layer photovoltaic panel includes: a backplane layer, a first EVA layer, a first silicon wafer layer, a second EVA layer, a second silicon wafer layer, a third EVA layer, a third silicon wafer layer, a fourth EVA layer and a glass layer, and so on. The temperature prediction of each layer of the photovoltaic panel using the method of the present invention is within the protection scope of the present invention.

[0036] like Figure 2 As shown, taking the back panel layer as the reference, the upper and lower outer layers are the glass layer and the back panel layer. Conversely, if the glass layer is taken as the reference, the upper and lower outer layers are the back panel layer and the glass layer.

[0037] Step 2: Construct a temperature prediction model for each layer of the photovoltaic panel, and use the thermal conductivity correction coefficient and thickness parameters of each layer of the photovoltaic panel to predict the temperature of each layer;

[0038] The formula for the temperature prediction model of each layer of the photovoltaic panel is:

[0039] T i =A i z+B i , z i-1 ≤z≤z i (1)

[0040] Among them, T i A is the temperature distribution of the ith photovoltaic panel along the z direction. Taking the lower surface of the photovoltaic panel as the reference, a coordinate system OZ representing the material thickness is established perpendicular to the upper surface direction, that is, the z direction. In this embodiment, the upper surface is the glass layer and the lower surface is the backplane layer. i is the thermal conductivity correction coefficient of the i-th layer material, B i is the correlation coefficient with the thickness of the i-th layer of material, z i-1 、z i are the thickness coordinate values ​​of the lower and upper surfaces of the i-th layer of material respectively.

[0041] like Figure 2 and 3 As shown, taking a single-layer photovoltaic panel as an example, the thickness of each layer is h1 to h5, the z0 of the backplane layer is 0, and z1 is h1; the coordinate value of the z1 of the lower surface of the first EVA layer is h1, and the coordinate value of the z2 of the upper surface of the first EVA layer is h1+h2, and so on.

[0042] Among them, the formula for the thermal conductivity correction coefficient and the material thickness correlation coefficient is:

[0043]

[0044] Among them, λ i is the thermal conductivity of the i-th layer material; T1 is the lower surface temperature of the photovoltaic panel; T n is the surface temperature of the photovoltaic panel; n is the total number of photovoltaic panels, in this example n = 5; h i is the thickness of the i-th layer of material, h i =z i -z i-1 , z i-1 is the z-direction coordinate value of the i-1th layer of material.

[0045] The thermal conductivity is determined by the material of each layer. For example, Table 1 shows the parameter values ​​of the thermal conductivity of a certain type of glass plate, a certain material EVA, a certain type of silicon wafer and a certain type of backplane. The thermal conductivity is determined by the model or material.

[0046] Table 1 Thermal conductivity values ​​of each layer of a certain type of photovoltaic panel

[0047] Thermal conductivity glass plate Silicon Wafer EVA Back Plate λ(W / m*K) 6 24 0.22 0.26

[0048] The measured values ​​of the thickness of each layer of a certain type of single-layer photovoltaic panel are shown in Table 2. The thickness of the two EVA layers is the same.

[0049] Table 2 Thickness values ​​of each layer of a certain type of photovoltaic panel

[0050] parameter glass plate Silicon Wafer EVA Back Plate Thickness h(mm) 3.2 0.3 0.4 0.17 Specific embodiment:

[0052] Using the data in Table 1 and Table 2 as measurement parameters, the temperature value of each layer is obtained using the temperature prediction model of each layer of the photovoltaic panel.

[0053] The total number of layers n = 5, calculate is a fixed value. For the convenience of subsequent description, Measure a certain time T n+1 -T1=65-25=40℃, calculate the temperature of each layer separately.

[0054] 1. Backplane layer:

[0055]

[0056] It is found that: T1 = 31.8124z + 25, 0 ≤ z ≤ 0.17;

[0057] 2. The first EVA layer:

[0058]

[0059] It is found that: T2 = 37.5965z + 24.0167, 0.17 ≤ z ≤ 0.57;

[0060] 3. Silicon wafer layer:

[0061]

[0062] It is found that: T3 = 0.3446z + 45.2503, 0.57 ≤ z ≤ 0.87;

[0063] 4. Second EVA layer:

[0064]

[0065]

[0066] It is found that: T4 = 37.5965z + 12.8412, 0.87 ≤ z ≤ 1.27;

[0067] 5. Glass layer:

[0068]

[0069] It is found that: T5 = 1.3785z + 58.8379, 1.27 ≤ z ≤ 4.47;

[0070] Through the above-mentioned model of temperature distribution of each layer of material, the temperature of each interface layer of the photovoltaic panel can be further obtained by substituting the specific thickness value z:

[0071] z=0, i.e. the lower surface of the backplane, corresponding to temperature: T=25℃;

[0072] z = 0.17, that is, the temperature corresponding to the interface between the back sheet and the first EVA layer: T = 30.4081 ° C;

[0073] z = 0.57, that is, the temperature at the interface between the first EVA layer and the silicon wafer layer is T = 45.4467°C;

[0074] z = 0.87, that is, the temperature at the interface between the silicon wafer layer and the second EVA layer is T = 45.5501°C;

[0075] z=1.27, that is, the interface temperature between the second EVA layer and the glass layer: T=60.5887℃

[0076] z=4.47, i.e. the upper surface of the glass layer, corresponding temperature: T=64.9998℃.

[0077] Since the internal temperature of photovoltaic panels cannot be detected non-destructively during the actual manufacturing or service process, that is, detection after destruction is meaningless, or additional hot spots may be generated to affect and change the performance of the photovoltaic panels, this verification scheme uses a numerical simulation method to directly extract the temperature of the observation point through a software platform, and uses the same condition parameters as the numerical simulation to substitute into the prediction model described in the present invention for analytical calculation, and then compares the simulation with the analytical calculation results to verify the effectiveness of the method of the present invention.

[0078] Numerical simulation: Assuming that the upper surface temperature of the photovoltaic panel is maintained at 65°C and the lower surface temperature is maintained at 25°C, the parameters in Tables 1 and 2 are used to simulate the temperature field using Abaqus finite element software. The temperature distribution cloud diagram is shown in the figure. Figure 4 As shown, the horizontal black is used as the interface of each layer, and the order of the layers of materials is Figure 2 Similarly, the software extracts the temperatures of the upper and lower surfaces of the entire photovoltaic panel and the interfaces of each layer of material as shown in Table 3.

[0079] The interface temperature calculated by the analytical model of the present invention is compared with the corresponding layer temperature calculated by numerical simulation through automatic calculation by simple software programming. The results are shown in Table 3 and Figure 5 As shown, the maximum error between the model prediction result and the numerical simulation result is 0.7075° C., and the maximum relative error is 2.33%. It can be seen that the temperature prediction method provided by the present invention has sufficient accuracy.

[0080] Table 3 Comparison of numerical simulation and predicted temperature of the model of the present invention

[0081]

[0082] The temperature prediction model for each layer of the photovoltaic panel constructed by the present invention is simple. By measuring the temperature and thickness parameters of the photovoltaic panel and combining the thermal conductivity of each layer material, the temperature value corresponding to the coordinates of each layer can be accurately predicted; the predicted temperature value can be used to evaluate indicators such as electrical conversion efficiency and service life during the service of the photovoltaic panel.

[0083] Based on the above ideal embodiments of the present invention, the relevant staff can make various changes and modifications without departing from the technical concept of the present invention through the above description. The technical scope of the present invention is not limited to the contents of the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. A method for predicting the temperature of a photovoltaic panel under a steady-state heat load, characterized in that: The following steps are involved: Step 1: Measure the thickness parameters of each layer of the photovoltaic panel and the surface temperature values ​​of the upper and lower outer layers; Step 2: Construct a temperature prediction model for each layer of the photovoltaic panel, and use the thermal conductivity correction coefficient and thickness parameters of each layer of the photovoltaic panel to predict the temperature of each layer.

2. The method for predicting the temperature of a photovoltaic panel under a steady-state heat load according to claim 1, characterized in that: The formula for the temperature prediction model of each layer of the photovoltaic panel is: T i =A i z+B i , z i-1 ≤z≤z i (1) Among them, T i is the temperature distribution of the ith photovoltaic panel along the z direction, A i is the thermal conductivity correction coefficient of the i-th layer material, B i is the correlation coefficient with the thickness of the i-th layer of material, z i-1 、z i are the thickness coordinate values ​​of the lower and upper surfaces of the i-th layer of material respectively.

3. The method for predicting the temperature of a photovoltaic panel under a steady-state heat load according to claim 2, characterized in that: The formula for the thermal conductivity correction factor is: Among them, λ i is the thermal conductivity of the i-th layer material; T1 is the lower surface temperature of the photovoltaic panel; T n is the upper surface temperature of the photovoltaic panel; n is the total number of photovoltaic panels; h i is the thickness of the i-th layer of material.

4. The method for predicting the temperature of a photovoltaic panel under a steady-state heat load according to claim 2, characterized in that: The formula for the material thickness correlation coefficient is: Where T1 is the lower surface temperature of the photovoltaic panel; h j is the thickness of the j-th layer of material; A j is the thermal conductivity correction coefficient of the jth layer material; z i-1 is the z-direction coordinate value of the i-1th layer of material.

5. The method for predicting the temperature of a photovoltaic panel under a steady-state heat load according to claim 1, characterized in that: The layers of a photovoltaic panel include: a backplane layer, an EVA layer, a silicon wafer layer, and a glass layer.

6. The method for predicting the temperature of a photovoltaic panel under a steady-state heat load according to claim 1, characterized in that: The upper and lower outer layers are the back panel layer and the glass layer.

7. The method for predicting the temperature of a photovoltaic panel under a steady-state heat load according to claim 1, characterized in that: Photovoltaic panels include: Single-layer, double-layer, or several-layer photovoltaic panels.

8. The method for predicting the temperature of a photovoltaic panel under a steady-state heat load according to claim 7, characterized in that: The total number of layers of a single-layer photovoltaic panel is 5.

9. Photovoltaic panel temperature prediction system under steady-state heat load, characterized in that: include: a memory for storing instructions executable by a processor; A processor, used to execute instructions to implement the photovoltaic panel temperature prediction method under steady-state heat load as described in any one of claims 1-8.

10. A computer readable medium storing computer program code, characterized in that: The computer program code, when executed by a processor, implements the method for predicting the temperature of a photovoltaic panel under a steady-state heat load as described in any one of claims 1 to 8.

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