阅读说明：本技术 一种太阳能电池板无损检测方法 (Nondestructive testing method for solar cell panel ) 是由 陈婷 黄晶晶 于 2021-08-02 设计创作，主要内容包括：本发明公开一种太阳能电池板无损检测方法,包括以下骤,S1:利用红外热像仪测量太阳能电池板表面温度,每块太阳能电池板选取温度最高的部分为测量区域,其温度值为测量温度；S2:以步骤S1太阳能电池板的状态和测量温度为边界条件下,将太阳能电池板从外向内分为各个薄层,根据能量守恒定律和傅立叶定律建立温度场无内热源的一维导热微分方程。本发明的太阳能电池板无损检测方法根据太阳能电池板损坏后的温度比正常发电时温度有所上升,得到了太阳能电池板在损坏状态下红外辐射强度高于正常工作发电时红外辐射强度的结论,为对太阳能电池板进行红外无损检测提供理论支撑,同时根据不同时刻的温度比较确定哪组太阳能电池板发电情况。(The invention discloses a nondestructive testing method for solar panels, which comprises the following steps of S1, measuring the surface temperature of the solar panels by using a thermal infrared imager, wherein the part with the highest temperature is selected as a measuring area of each solar panel, and the temperature value is the measuring temperature; and S2, under the boundary condition of the state and the measured temperature of the solar panel in the step S1, dividing the solar panel into thin layers from outside to inside, and establishing a one-dimensional heat conduction differential equation of the temperature field without an internal heat source according to an energy conservation law and a Fourier law. According to the nondestructive testing method for the solar panel, the temperature of the damaged solar panel is increased compared with the temperature of the damaged solar panel during normal power generation, the conclusion that the infrared radiation intensity of the solar panel in the damaged state is higher than that of the solar panel during normal power generation is obtained, theoretical support is provided for infrared nondestructive testing of the solar panel, and meanwhile, the power generation condition of the solar panel is determined according to the temperature comparison at different moments.)

1. A nondestructive testing method for a solar panel is characterized by comprising the following steps:

s1, measuring the surface temperature of the solar cell panel by using a thermal infrared imager, wherein the part with the highest temperature is selected as a measurement area of each solar cell panel, and the temperature value is the measurement temperature;

s2, under the boundary condition of the state and the measured temperature of the solar panel in the step S1, the solar panel is divided into thin layers from outside to inside, and a one-dimensional heat conduction differential equation without an internal heat source in a temperature field is established according to the law of energy conservation and the Fourier law;

s3, obtaining a node equation by a one-dimensional heat conduction differential equation according to a numerical calculation method and a first-order backward difference method, then performing iterative solution on the differential equations of all nodes in a simultaneous manner to obtain a curve of the temperature of each thin layer changing along with time, and reserving the curve of the temperature value of the outer surface of the solar cell panel changing along with time so as to obtain the simulated temperature of each time on the solar cell panel;

s4, measuring the surface temperature of the solar cell panel by using the thermal infrared imager from the next moment, selecting the part with the highest temperature of each solar cell panel as a measurement area, and recording the temperature value at each moment as the actual measurement temperature;

and S5, comparing the actual measured temperature and the simulated temperature at each moment or comparing the extreme values of the actual measured temperature and the simulated temperature to judge whether the solar panel is in the power generation state.

2. The nondestructive testing method for the solar panel according to claim 1, characterized in that: in step S3, the solar panel region is discretized, and is divided into n thin layers from the outside to the inside, and if the total thickness is X, the thickness of the thin layer is Δ X — X/n, and if the calculation time T is k Δ τ, and k is 0,1,2, and 3 …, the central temperature of the ith thin layer at time T may be represented as T (k, i); for the initial conditions, the calculation starts in the morning when the temperature is considered to be approximately linearly distributed in the thickness direction, i.e.

In the formula, T₁And T₂Initial temperature values for the inner and outer surfaces, respectively.

3. The nondestructive testing method for the solar panel according to claim 1, characterized in that: the heat exchange between the surface of the solar cell panel and the external environment in the step S2 includes the radiant heat Q applied to the surface of the solar cell panel by the external environment_radiSelf-radiation Q of solar panel_radoAnd the sunConvection heat exchange Q between surface of battery plate and air_conv。

4. The nondestructive testing method for the solar panel according to claim 3, wherein the nondestructive testing method comprises the following steps: the external environment acts on the radiant heat Q on the surface of the solar cell panel_radiComprising solar radiation Q to which the surface of the solar panel is subjected_sunThe surface of the solar panel receives the radiation Q of the ground_groundAnd the surface of the solar panel receives the atmospheric radiation Q of the sky_sky。

5. The nondestructive testing method for the solar panel according to claim 4, wherein the nondestructive testing method comprises the following steps: the solar radiation Q received by the surface of the solar cell panel_sunDirect solar radiation Q including surface absorption of solar panels_sundirAnd the scattered radiation Q of the atmosphere absorbed by the surface of the solar cell panel to sunlight_sundisThe surface of the solar panel absorbs the reflected radiation Q of the ground_sunref。

6. The nondestructive testing method for the solar panel according to claim 5, wherein the nondestructive testing method comprises the following steps: according to the analysis of the heat exchange between the surface of the solar cell panel and the external environment, the outer boundary condition can be obtained as

Wherein k is a thermal conductivity coefficient; t is the temperature; n is the direction of the external normal at a certain position of the boundary surface; q_radiThe radiant heat energy acted on the surface of the solar cell panel for the external environment; q_radoRadiation of the solar panel itself; q_convThe convection heat exchange between the surface of the solar cell panel and the air is realized.

7. The nondestructive testing method for the solar panel according to claim 2, characterized in that: the heat conduction differential equation of step S2 is based on the law of conservation of energy and the fourier law, and is generally in the form of a rectangular coordinate system

Wherein ρ is density; t is the temperature; c is the specific heat capacity; τ is time; k is a thermal conductivity coefficient; phi_vHeating power in unit volume of infinitesimal element; for the solar cell panel without an internal heat source and with the plane size far larger than the thickness size, the basic equation of the temperature field can be simplified into a one-dimensional heat conduction differential equation without the internal heat source

Technical Field

The invention relates to a nondestructive testing method for a solar cell panel.

Background

The solar panel is a device which directly or indirectly converts solar radiation energy into electric energy through a photoelectric effect or a photochemical effect by absorbing sunlight; and the infrared characteristic is an important basis for target identification. The infrared radiation characteristic of the damaged solar cell panel is different from that of the solar cell panel in a normal working state.

Solar energy plays an increasing role in production and life as a new green energy source. However, the maintenance and repair of the solar cell are important problems which disturb the development of the solar cell at present, and as a starting point of energy supply, it is very critical that a part with a problem can be timely and accurately found when the problem occurs. However, due to the characteristics of large number of solar cells, large area and uniform shape, it is difficult to find problems from the surface. In practical application, however, due to the direct action of sunlight, the temperature characteristics of the solar cell may change during the use process, which can be used as an important basis for performing nondestructive testing on the solar cell.

When a large number of solar panels are used as devices for converting electric energy, whether one group of solar panels is in a normal power generation state or not is difficult to directly judge through naked eyes, the quality of the solar panels needs to be analyzed from the power generation amount, and the specific quality of the group of solar panels needs to be disassembled, so that infrared nondestructive detection on the solar panels is necessary; therefore, if people are familiar with the infrared radiation characteristics of the solar cell, the specific problem place can be quickly positioned by using the infrared detection equipment according to the working state of the solar cell, so that the problem finding speed is greatly improved.

Disclosure of Invention

The invention aims to solve the problems and provide a nondestructive testing method for the solar panel, which can perform infrared nondestructive testing on the solar panel.

In order to achieve the purpose, the invention is realized by the following technical scheme: a nondestructive testing method for a solar panel comprises the following steps:

s1, measuring the surface temperature of the solar cell panel by using a thermal infrared imager, wherein the part with the highest temperature is selected as a measurement area of each solar cell panel, and the temperature value is the measurement temperature;

s2, under the boundary condition of the state and the measured temperature of the solar panel in the step S1, the solar panel is divided into thin layers from outside to inside, and a one-dimensional heat conduction differential equation without an internal heat source in a temperature field is established according to the law of energy conservation and the Fourier law;

s3, obtaining a node equation by a one-dimensional heat conduction differential equation according to a numerical calculation method and a first-order backward difference method, then performing iterative solution on the differential equations of all nodes in a simultaneous manner to obtain a curve of the temperature of each thin layer changing along with time, and reserving the curve of the temperature value of the outer surface of the solar cell panel changing along with time so as to obtain the simulated temperature of each time on the solar cell panel;

s4, measuring the surface temperature of the solar cell panel by using the thermal infrared imager from the next moment, selecting the part with the highest temperature of each solar cell panel as a measurement area, and recording the temperature value at each moment as the actual measurement temperature;

s5 compares the actual measured temperature and the simulated temperature at each time or the extreme values of the actual measured temperature and the simulated temperature to determine whether the solar cell panel is in the power generation state.

Still further, in step S3, the solar panel region is discretized, and is divided into n thin layers from outside to inside, and if the total thickness is X, the thickness of the thin layer is Δ X ═ X/n, and if the calculation time T is k Δ τ and k is 0,1,2,3 …, the central temperature of the ith thin layer at time T can be represented as T (k, i); for the initial conditions, the calculation starts in the morning when the temperature is considered to be approximately linearly distributed in the thickness direction, i.e.

In the formula, T₁And T₂Initial temperature values for the inner and outer surfaces, respectively.

Further, the heat exchange between the surface of the solar cell panel and the external environment in the step S2 includes the radiant heat Q applied to the surface of the solar cell panel by the external environment_radiSelf-radiation Q of solar panel_radoAnd the convection heat exchange Q of the surface of the solar cell panel and the air_conv。

Furthermore, the radiation heat energy Q acted on the surface of the solar cell panel by the external environment_radiComprising solar radiation Q to which the surface of the solar panel is subjected_sunThe surface of the solar panel receives the radiation Q of the ground_groundAnd the surface of the solar panel receives the atmospheric radiation Q of the sky_{s ky}。

Further, the solar radiation Q received by the surface of the solar cell panel_sunDirect solar radiation Q including surface absorption of solar panels_sundirAnd the scattered radiation Q of the atmosphere absorbed by the surface of the solar cell panel to sunlight_sundisThe surface of the solar panel absorbs the reflected radiation Q of the ground_sunref。

In particular, according to the analysis of the heat exchange between the surface of the solar cell panel and the external environment, the outer boundary condition can be obtained as

Wherein k is a thermal conductivity coefficient; t is the temperature; n is the direction of the external normal at a certain position of the boundary surface; q_radiThe radiant heat energy acted on the surface of the solar cell panel for the external environment; q_radoRadiation of the solar panel itself; q_convThe convection heat exchange between the surface of the solar cell panel and the air is realized.

Still further, the heat conduction differential equation of step S2 is based on the law of conservation of energy and the fourier law, which is generally in the form of a rectangular coordinate system

Wherein ρ is density; t is the temperature; c is the specific heat capacity; τ is time; k is a thermal conductivity coefficient; phi is a_vHeating power in unit volume of infinitesimal element; for the solar cell panel without an internal heat source and with the plane size far larger than the thickness size, the basic equation of the temperature field can be simplified into one-dimensional heat conduction without the internal heat sourceDifferential equation

In conclusion, the invention has the following beneficial effects: according to the nondestructive testing method for the solar panel, the temperature of the damaged solar panel is increased compared with the temperature of the damaged solar panel during normal power generation, the infrared radiation characteristic of the solar panel is further verified on the basis of temperature calculation, the conclusion that the infrared radiation intensity of the solar panel in a damaged state is higher than that of the solar panel during normal power generation is obtained, theoretical support can be provided for infrared nondestructive testing of the solar panel, and meanwhile, the power generation condition of the solar panel is determined according to the temperature comparison at different moments.

Drawings

FIG. 1 is a graph showing temperature calculation and actual measurement curves for two states (power generation and no power generation) of a solar panel;

FIG. 2 is an infrared image of a solar panel in two states (power generation and no power generation);

fig. 3 is a graph of radiance calculations for two states of the solar panel (power generation and no power generation).

Detailed Description

The invention will be further described in detail with reference to examples of embodiments shown in the drawings to which, however, the invention is not restricted.

1. Simulation of heat exchange between surface of solar cell panel and external environment

The heat exchange between the surface of the solar cell panel and the external environment is mainly carried out in two modes of radiation and convection, and the conduction is mainly carried out between the insides of the solar cell panels. The surface of the solar panel receives radiation of the external environment mainly from the sun, the ground and the sky, and simultaneously the solar panel also radiates heat outwards;

1) radiation of the sun

During the day, the influence of solar radiation is dominant, and its radiation flux varies with the season, time, weather and geographical conditions. When dealing with solar radiation, it is generally divided into direct, diffuse and ground-reflected portions. The terms in the solar radiation can be determined by the following relation.

The solar panel surface absorbs direct solar radiation of

Q_sundir＝α_sunrE_sunp^mF_sun (1)

In the formula, alpha_sunIs the absorption coefficient of the solar panel surface to solar radiation; r is a correction value caused by the day-to-ground distance; e_sun＝1353W/m²Referred to as the solar constant; p is the atmospheric transparency coefficient, also known as atmospheric transparency; m is the mass of the atmosphere; p is a radical of^mIs the atmospheric transmittance, traditionally referred to as atmospheric transparency; f_sunIs the angular factor of the solar panel surface to the direct radiation of the sun.

Scattering is mainly caused by various gas molecules and aerosol molecules in the atmosphere, which attenuate the direct solar light and at the same time generate new radiation. The scattered radiation of the atmosphere on the sunlight absorbed by the surface of the solar cell panel is

In the formula, alpha_lThe absorption rate of the solar cell panel surface to the atmosphere scattered sunlight; h is the solar altitude; beta is the inclined angle of the inclined plane.

The reflected radiation of the ground facing the sun that the solar panel surface receives is related to the solar panel surface orientation. For the horizontal plane, only the reflection of the above-mentioned direct solar radiation and scattered solar radiation needs to be considered; for inclined surfaces, the reflected radiation from the ground must also be taken into account

In the formula, ρ_groundIs the solar reflectivity of the ground, epsilon refers to the emissivity.

The solar panel surface receives solar radiation of

Q_sun＝Q_sundir+Q_sundis+Q_sunref (4)

2) Radiation of the ground

The surface of the solar cell panel is also influenced by direct radiation from the ground, and for an object on a horizontal ground in an open area, the field angle of the ground to the object is close to 180 degrees, namely the ground can be approximate to an infinite horizontal gray body plane below, and the radiation from the ground received by the surface of the solar cell panel is

Wherein epsilon is emissivity and sigma is absorptivity; epsilon_groundEmissivity of the ground, and e_ground＝1-ρ_ground；T_groundThe ground temperature can be approximately replaced by the ambient atmospheric temperature; f_groundIs the angular factor of the solar panel surface to ground radiation.

3) Radiation of the sky atmosphere

The radiation of the sky atmosphere, which is mainly a long-wavelength radiation, is also a factor affecting the temperature of the solar panel. After absorbing a certain amount of solar heat and earth heat, the atmosphere has a certain temperature, and thus, the atmosphere also radiates to the solar cell panel. The atmospheric radiation of the sky can also be equivalent to an infinite large horizontal gray body plane positioned above, and the atmospheric radiation of the sky received by the surface of the solar cell panel is

In the formula, T_skyIs at atmospheric temperature; f_skyThe angle factor of the surface of the solar cell panel to the plane radiation of the atmosphere equivalent gray body; epsilon_skyIs the equivalent emissivity of the atmosphere.

In summary, the radiation heat energy applied to the surface of the solar cell panel by the external environment is

Q_radi＝Q_sun+Q_ground+Q_sky (7)

4) Radiation of solar panel itself

The heat energy radiated and lost to the external space on the surface of the solar cell panel can be obtained by Stefan-Boltzmann law

Q_rado＝εσT⁴ (8)

5) Convection current

The energy entering the solar cell panel due to the heat convection between the surface of the solar cell panel and the air is

Q_conv＝H(T_air-T) (9)

In the formula, H is the convection heat transfer coefficient of the outer surface, and the value of H is related to the wind speed and the movement speed of the solar panel; t is_airIs the air temperature;

2. establishment of heat conduction differential equation

The distribution state of the temperature of the solar cell panel along with space and time under the action of a certain boundary condition can be solved by utilizing a heat conduction differential equation, so that the temperature distribution state of the surface of the solar cell panel and the change of the temperature distribution state along with the time can be obtained. The heat conduction differential equation is based on the law of conservation of energy and the Fourier law, and the general form of the heat conduction differential equation in a rectangular coordinate system is

Wherein ρ is density; c is the specific heat capacity; τ is time; k is a thermal conductivity coefficient; phi_vIs the heating power of a unit volume of a infinitesimal element.

When the internal heat source is not available and the plane size is far larger than the thickness size, the three-dimensional heat conduction can be processed as one-dimensional heat conduction. For the solar cell panel, the condition is mostly met, the basic equation of the temperature field can be simplified into a one-dimensional heat conduction differential equation without an internal heat source

3 establishment of boundary conditions

Boundary conditions guide the connection or interaction of the thermal object with respect to heat exchange between its boundary surface and the external environment. For unsteady state heat conduction, it is often the external driving force that allows the process to take place and develop. From the analysis of the heat exchange between the front solar panel surface and the external environment, the outer boundary condition can be obtained as

In the formula, n is the direction of the outer normal at a certain position of the boundary surface. The left side of the above equation represents the heat lost by conduction from the surface of the solar panel to the interior, and the right side represents the heat gained by the surface of the solar panel due to the combined effects of radiation and convection.

4. Numerical calculation method

The heat conduction problem is solved by a numerical method, and firstly, a solving area is discretized. In the solar cell panel, n thin layers can be divided from the outside to the inside, and if the total thickness is X, the thickness of the thin layer is X/n, and if the calculation time T is k Δ τ and k is 0,1,2, and 3 …, the central temperature of the ith thin layer at time T can be represented as T (k, i).

For the differential equation of heat conduction, using the backward difference format, the dispersion result is

The above situation in which the node equation can be obtained by substituting the basic differential format into the thermal conduction differential equation is limited to the inner node. For the boundary nodes, the node equation needs to be derived by using an energy balance method. Equation of boundary nodes of outer surface of solar cell panel when power is not generated

Equation of boundary nodes of outer surface of solar cell panel during power generation

In the formula, eta is the generating efficiency of the solar cell panel; whereinRespectively referring to the heat energy value at the next moment;

for the initial conditions, the calculation is usually started in the early morning, when the temperature can be considered to be approximately linearly distributed in the thickness direction, i.e.

In the formula, T₁And T₂Initial temperature values for the inner and outer surfaces, respectively.

The differential equations of all the nodes are simultaneously subjected to iterative solution, so that a curve of the temperature of each thin layer changing along with time can be obtained, the most concerned is the outer surface temperature value from the aim of researching the infrared characteristics of the solar panel, and T (k,0) is the outer surface temperature value to be finally solved.

5. Simulation results and conclusions

The calculation and test results of the solar panel temperature are shown in fig. 1. The calculation and test results of fig. 1 show that the theoretical calculation value is basically consistent with the measured value, and the error between the calculation value and the measured value is mostly about 2K, which illustrates the rationality of the theoretical model. The error is caused because the atmospheric transparency is an estimated value and has a certain error with the actual value; secondly, a small error exists between the temperature analog value and the measured value; third, there is some error between the real change influence of the surrounding environment, such as ground radiation, etc., and the theoretical calculation, but their influence is very small compared with the sun during the day, but it is obvious when there is no sun at night. The figure also shows that the calculation error is smaller when the sun exists in the daytime than at night, which is mainly because the sun is mainly the result of the action of the sun, and the radiation of the sun to the solar panel can be calculated more accurately;

as can be seen from fig. 1, in the daytime, the temperature of the solar panel when the solar panel does not generate electricity is higher than the temperature of the solar panel when the solar panel generates electricity, and the infrared radiation of the solar panel when the solar panel does not generate electricity is also higher than the infrared radiation of the solar panel when the solar panel generates electricity. FIG. 2 shows infrared images of the solar panel in two states of normal power generation and no power generation, and the correctness of the temperature calculation model is also verified;

based on the conclusion and the fact that the infrared radiation of the solar panel when the solar panel does not generate electricity is higher than the infrared radiation of the solar panel when the solar panel generates electricity, the nondestructive testing method for the solar panel is designed, and comprises the following steps:

s1, measuring the surface temperature of the solar cell panel by using a thermal infrared imager, wherein the part with the highest temperature is selected as a measurement area of each solar cell panel, and the temperature value is the measurement temperature;

s2, under the boundary condition of the state and the measured temperature of the solar panel in the step S1, the solar panel is divided into thin layers from outside to inside, and a one-dimensional heat conduction differential equation without an internal heat source in a temperature field is established according to the law of energy conservation and the Fourier law;

s3, obtaining a node equation by a one-dimensional heat conduction differential equation according to a numerical calculation method and a first-order backward difference method, then performing iterative solution on the differential equations of all nodes in a simultaneous manner to obtain a curve of the temperature of each thin layer changing along with time, and reserving the curve of the temperature value of the outer surface of the solar cell panel changing along with time so as to obtain the simulated temperature of each time on the solar cell panel;

s4, measuring the surface temperature of the solar cell panel by using the thermal infrared imager from the next moment, selecting the part with the highest temperature of each solar cell panel as a measurement area, and recording the temperature value at each moment as the actual measurement temperature;

s5 compares the actual measured temperature and the simulated temperature at each time or the extreme values of the actual measured temperature and the simulated temperature to determine whether the solar cell panel is in the power generation state.

6. Verification of a simulation

The infrared radiation of the solar panel mainly consists of two parts, namely the infrared radiation emitted by the solar panel and the reflected ambient infrared radiation. The solar panel can be generally considered as a diffusive gray body. Because the calculation of the radiant quantity of any diffusion gray body can be obtained by calculating the radiant brightness, the infrared radiation characteristic of the solar panel can be obtained after the radiant brightness is calculated.

1) Self-radiation

After the surface temperature of the solar cell panel is calculated, if the surface temperature is in a full electromagnetic wave band, the total radiation emittance is

M＝εσT⁴ (17)

The radiance of a solar panel can be derived from the radiance characteristics of a diffuse source

If the spectral characteristics of the solar panel are considered, the spectral characteristics can be calculated according to Planck's law, wherein the spectral characteristics are lambda at delta lambda₁～λ₂Radiation emittance of the wavelength band of

In the formula c₁、c₂Is the spectral emissivity.

2) Reflected radiation

The solar cell panel reflects radiation to the environment

M_r＝ρ_eQ_r (20)

In the formula, ρ_eIs the equivalent reflection coefficient; q_rThe total radiation quantity of the outside to the solar cell panel. The brightness of the radiation reflected by the solar panel can be obtained by the radiation characteristic of the diffuse reflection source

In summary, the total radiance of the solar cell panel is

L＝L_s+L_r (22)

3) Calculation results

Fig. 3 shows the profile of the radiance of a solar panel over 24 hours a day. As can be seen from fig. 3, the infrared radiation of the solar panel changes in the day substantially in accordance with the change trend of the temperature of the corresponding azimuth in the day. And the radiation brightness of the solar panel during normal power generation is smaller than that during no power generation, and the characteristic difference can be used as an important basis for carrying out infrared nondestructive detection on the solar panel and is also used for verifying the temperature simulation under the two solar states (power generation and no power generation).

The above-mentioned embodiments are only for convenience of description, and are not intended to limit the present invention in any way, and those skilled in the art will understand that the technical features of the present invention can be modified or changed by other equivalent embodiments without departing from the scope of the present invention.