Non-contact photovoltaic module power generation efficiency evaluation method

Abstract

The invention discloses a non-contact photovoltaic module power generation efficiency evaluation method, which comprises the following steps: acquiring an infrared image of a photovoltaic module, and extracting a temperature matrix on the surface of the photovoltaic module; calculating solar energy absorbed by the photovoltaic module according to the irradiance of the surface of the photovoltaic module; calculating heat transfer between the photovoltaic module and the ambient environment according to the ambient temperature; calculating the electric power of the photovoltaic module according to the law of conservation of energy; and normalizing the electric power of the photovoltaic module, and evaluating the power generation efficiency and electric energy attenuation ratio of the photovoltaic module. Aiming at the problems of high cost and low efficiency of contact type electrical data acquisition of the photovoltaic module, non-contact type power generation efficiency evaluation of the photovoltaic module is realized. According to the invention, an unmanned aerial vehicle autonomous inspection technology and a fault diagnosis technology and a health assessment technology of the photovoltaic module can be combined, and an important basis is provided for intelligent operation and maintenance of a photovoltaic power station.

Description

Technical Field

[0001] The present invention relates to a non-contact photovoltaic module power generation efficiency evaluation technology, belonging to the technical field of intelligent inspection and smart operation and maintenance of photovoltaic systems. Background Art

[0002] In recent years, photovoltaic power generation has played an increasingly important role in the energy structure. As the basic unit of the photovoltaic power generation system, the photovoltaic module has a life cycle of 20-25 years. During this process, defects, failures, aging and other problems may occur. In order to ensure the stability, safety and power generation efficiency of the photovoltaic system, it is necessary to detect problematic photovoltaic modules in a timely manner. Output power is an important basis for judging the health of photovoltaic modules. Existing methods obtain the electrical characteristics of photovoltaic modules through IV testing and evaluate the output power.

[0003] However, IV testing is a contact measurement method. Every time a photovoltaic module is checked, the operation and maintenance personnel need to operate its connector to temporarily put it offline. This method consumes a lot of time and labor costs, and is very impractical for large-scale photovoltaic power stations. In addition to IV testing, currently commonly used photovoltaic module inspection methods include: visual observation, EL testing, infrared thermal imaging, etc. Among them, infrared thermal imaging can not only realize non-contact data collection, but also is an important way to analyze the temperature characteristics of photovoltaic modules.

[0004] The International Energy Agency has summarized the types of temperature anomalies in photovoltaic modules. Existing technologies have achieved hot spot detection and temperature anomaly classification of photovoltaic modules through infrared images. However, existing technologies have not yet solved the problem of non-contact evaluation of photovoltaic module power generation efficiency. The solar energy absorbed by photovoltaic modules is converted into electrical energy and thermal energy, which means that its output power has a certain correlation with temperature distribution. How to calculate the electric power of photovoltaic modules through infrared images to achieve non-contact evaluation of photovoltaic module power generation efficiency is an important issue that needs to be considered in the intelligent inspection and intelligent operation and maintenance of photovoltaic systems. Summary of the invention

[0005] Technical problem: The present invention aims to solve the deficiencies in the prior art by analyzing the heat transfer between photovoltaic modules and the surrounding environment based on infrared images, calculating the electric power of photovoltaic modules according to the law of conservation of energy, and providing a non-contact method for evaluating the power generation efficiency of photovoltaic modules.

[0006] Technical solution: A non-contact photovoltaic module power generation efficiency evaluation method of the present invention comprises the following steps in sequence:

[0007] S1: Collect infrared images of photovoltaic modules and extract the temperature matrix of the photovoltaic module surface;

[0008] S2: Calculate the solar energy absorbed by the photovoltaic module based on the irradiance on the surface of the photovoltaic module;

[0009] S3: Calculate the heat transfer between the photovoltaic module and the surrounding environment according to the ambient temperature;

[0010] S4: Calculate the electric power of the photovoltaic module according to the law of conservation of energy;

[0011] S5: Normalize the electric power of the PV module and evaluate the power generation efficiency and electric energy attenuation ratio of the PV module.

[0012] Furthermore, in step S1, on a sunny day with a light breeze and an irradiance of not less than 600 W / m 2 , collect infrared images of photovoltaic modules while avoiding reflections; the angle between the optical axis of the infrared camera and the surface of the photovoltaic module is not less than 60°, and the surface of the photovoltaic module is 2 The area occupies at least one pixel in the infrared image; the radial distortion of the infrared image and the perspective deformation of the photovoltaic module are corrected, and the temperature matrix F of the photovoltaic module surface is extracted.

[0013] Furthermore, in step S2, G represents the irradiance on the surface of the photovoltaic module, S represents the area of ​​the surface of the photovoltaic module, and N represents the number of material layers of the photovoltaic module; the solar energy absorbed by the photovoltaic module is calculated as follows:

[0014]

[0015]

[0016] Among them, Q k represents the solar energy absorbed by the kth layer of the photovoltaic module, α k represents the absorption rate of the kth layer material of the photovoltaic module, k=1,…,N; when q=0, τ q =1; when 1≤q≤k-1, τ q It represents the transmittance of the qth layer of material in the photovoltaic module; Q represents the solar energy absorbed by the entire photovoltaic module.

[0017] Furthermore, in step S3, T a Indicates the air temperature, T s Indicates the sky temperature, F i,j The elements in the temperature matrix F representing the surface of the PV module are used to calculate the heat transfer between the surface of the PV module and the surrounding environment as follows:

[0018]

[0019]

[0020] Among them, Φ fRepresents the heat convection between the PV panel surface and the surrounding environment, Ψ f Represents the thermal radiation between the surface of the photovoltaic module and the surrounding environment, δ f represents the area of ​​the surface of the photovoltaic module corresponding to each element in the temperature matrix F, σ represents the Stefan-Boltzmann constant, ε f Represents the emissivity of the photovoltaic module surface, ε s represents the radiance of the sky, h f Represents the convective heat transfer coefficient on the surface of the photovoltaic module.

[0021] Furthermore, in step S3, T g Indicates the ground temperature, B i,j The element in the temperature matrix B representing the back side of the photovoltaic module, Δ b Represents the temperature difference between the back and surface of the PV module. The heat transfer between the back of the PV module and the surrounding environment is calculated as follows:

[0022] B i,j =F i,j +Δ b

[0023]

[0024]

[0025] Among them, Φ b Represents the heat convection between the back of the photovoltaic module and the surrounding environment, Ψ b Represents the thermal radiation between the back of the photovoltaic module and the surrounding environment, δ b Indicates that each element in the temperature matrix B corresponds to the area of ​​the back of the photovoltaic module, ε b Represents the emissivity of the back side of the photovoltaic module, ε g represents the emissivity of the ground, h b Indicates the convective heat transfer coefficient on the back of the PV module.

[0026] Furthermore, in step S4, the solar energy absorbed by the photovoltaic module is converted into heat energy and electrical energy, and the electrical power of the photovoltaic module is calculated as follows:

[0027] P=Q-Φ f -Ψ f -Φ b -Ψ b

[0028] Where P represents the electrical power of the photovoltaic module.

[0029] Furthermore, in step S5, the normalized irradiance is G0, the normalized cell temperature is T0, the temperature coefficient of the photovoltaic module power is β, and the normalized photovoltaic module power is as follows:

[0030]

[0031] Where P0 represents the normalized photovoltaic module power, Represents the average value of each element in the PV panel surface temperature matrix F, Δ c Indicates the temperature difference between the cells inside the photovoltaic module and the surface.

[0032] Furthermore, in step S5, the ideal electric power of the photovoltaic module under normalized environmental conditions is P m , the power generation efficiency and power attenuation ratio of photovoltaic modules are evaluated as follows:

[0033]

[0034]

[0035]

[0036] Among them, η represents the power generation efficiency of the photovoltaic module under actual environmental conditions, η0 represents the power generation efficiency of the photovoltaic module under normalized environmental conditions, and γ represents the power attenuation ratio of the photovoltaic module.

[0037] Beneficial effects: In order to solve the problem of high cost and low efficiency of contact electrical data collection of photovoltaic modules, the present invention provides a non-contact photovoltaic module power generation efficiency evaluation method, which analyzes the heat transfer between the photovoltaic module and the surrounding environment based on infrared images, calculates the electric power of the photovoltaic module according to the law of conservation of energy, and realizes non-contact photovoltaic module power generation efficiency and electric energy attenuation evaluation. This method can be combined with autonomous drone inspection technology, as well as photovoltaic module fault diagnosis technology and health assessment technology, to provide an important basis for the intelligent operation and maintenance of photovoltaic power stations. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a schematic diagram of the overall process of the embodiment;

[0039] Figure 2 Schematic diagram of photovoltaic modules absorbing solar energy;

[0040] Figure 3 Schematic diagram of heat transfer between photovoltaic modules and the surrounding environment. DETAILED DESCRIPTION

[0041] The specific implementation modes of the present invention will be further described in detail below in conjunction with the accompanying drawings, but the protection scope of the present invention is not limited to the embodiments. Figure 1 As shown, a non-contact photovoltaic module power generation efficiency evaluation method of this embodiment includes the following steps in sequence:

[0042] S1: Collect infrared images of photovoltaic modules and extract the temperature matrix of the photovoltaic module surface.

[0043] In this embodiment, on a sunny day, with a light breeze and an irradiance of no less than 600 W / m 2 , collect infrared images of photovoltaic modules while avoiding reflections; the angle between the optical axis of the infrared camera and the surface of the photovoltaic module is not less than 60°, and the surface of the photovoltaic module is 2 The area occupies at least one pixel in the infrared image; the radial distortion of the infrared image and the perspective deformation of the photovoltaic module are corrected, and the temperature matrix F of the photovoltaic module surface is extracted.

[0044] S2: Calculate the solar energy absorbed by the PV module based on the irradiance on the surface of the PV module.

[0045] In this embodiment, Figure 2 The figure is a schematic diagram of photovoltaic modules absorbing solar energy. G represents the irradiance on the surface of the photovoltaic module, S represents the surface area of ​​the photovoltaic module, and N represents the number of material layers of the photovoltaic module. The calculation of the solar energy absorbed by the photovoltaic module is as follows:

[0046]

[0047]

[0048] Among them, Q k represents the solar energy absorbed by the kth layer of the photovoltaic module, α k represents the absorption rate of the kth layer material of the photovoltaic module, k=1,…,N; when q=0, τ q =1; when 1≤q≤k-1, τ q It represents the transmittance of the qth layer of material in the photovoltaic module; Q represents the solar energy absorbed by the entire photovoltaic module.

[0049] S3: Calculate the heat transfer between the photovoltaic module and the surrounding environment based on the ambient temperature.

[0050] In this embodiment, Figure 3 Schematic diagram of heat transfer between photovoltaic modules and the surrounding environment. a Indicates the air temperature, T s Indicates the sky temperature, F i,j The elements in the temperature matrix F representing the surface of the PV module are used to calculate the heat transfer between the surface of the PV module and the surrounding environment as follows:

[0051]

[0052]

[0053] Among them, Φ fRepresents the heat convection between the PV panel surface and the surrounding environment, Ψ f Represents the thermal radiation between the surface of the photovoltaic module and the surrounding environment, δ f represents the area of ​​the surface of the photovoltaic module corresponding to each element in the temperature matrix F, σ represents the Stefan-Boltzmann constant, ε f Represents the emissivity of the photovoltaic module surface, ε s represents the radiance of the sky, h f Represents the convective heat transfer coefficient on the surface of the photovoltaic module.

[0054] T g Indicates the ground temperature, B i,j The element in the temperature matrix B representing the back side of the photovoltaic module, Δ b Represents the temperature difference between the back and surface of the PV module. The heat transfer between the back of the PV module and the surrounding environment is calculated as follows:

[0055] B i,j =F i,j +Δ b

[0056]

[0057]

[0058] Among them, Φ b Represents the heat convection between the back of the photovoltaic module and the surrounding environment, Ψ b Represents the thermal radiation between the back of the photovoltaic module and the surrounding environment, δ b Indicates that each element in the temperature matrix B corresponds to the area of ​​the back of the photovoltaic module, ε b Represents the emissivity of the back side of the photovoltaic module, ε g represents the emissivity of the ground, h b Indicates the convective heat transfer coefficient on the back of the PV module.

[0059] S4: According to the law of conservation of energy, calculate the electric power of the photovoltaic module.

[0060] In this embodiment, the solar energy absorbed by the photovoltaic module is converted into heat energy and electrical energy. The electrical power of the photovoltaic module is calculated as follows: P = Q - Φ f -Ψ f -Φ b -Ψ b

[0061] Where P represents the electrical power of the photovoltaic module.

[0062] S5: Normalize the electric power of the PV module and evaluate the power generation efficiency and electric energy attenuation ratio of the PV module.

[0063] In this embodiment, the normalized irradiance is G0, the normalized cell temperature is T0, the temperature coefficient of the photovoltaic module power is β, and the normalized photovoltaic module power is as follows:

[0064]

[0065] Where P0 represents the normalized photovoltaic module power, Represents the average value of each element in the PV panel surface temperature matrix F, Δ c Indicates the temperature difference between the cells inside the photovoltaic module and the surface.

[0066] The ideal electric power of a photovoltaic module under normalized environmental conditions is P m , the power generation efficiency and power attenuation ratio of photovoltaic modules are evaluated as follows:

[0067]

[0068]

[0069]

[0070] Among them, η represents the power generation efficiency of the photovoltaic module under actual environmental conditions, η0 represents the power generation efficiency of the photovoltaic module under normalized environmental conditions, and γ represents the power attenuation ratio of the photovoltaic module.

[0071] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents, and any modifications or equivalent replacements that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A non-contact photovoltaic module power generation efficiency evaluation method, characterized by: The following steps are included in sequence: S1: Collect infrared images of photovoltaic modules and extract the temperature matrix of the photovoltaic module surface; S2: Calculate the solar energy absorbed by the photovoltaic module based on the irradiance on the surface of the photovoltaic module; S3: Calculate the heat transfer between the photovoltaic module and the surrounding environment according to the ambient temperature; S4: Calculate the electric power of the photovoltaic module according to the law of conservation of energy; S5: Normalize the electric power of the PV module and evaluate the power generation efficiency and electric energy attenuation ratio of the PV module.

2. A non-contact photovoltaic module power generation efficiency evaluation method according to claim 1, characterized in that: In step S1, on a sunny day, with a light breeze and an irradiance of not less than 600 W / m 2 , collect infrared images of photovoltaic modules while avoiding reflections; the angle between the optical axis of the infrared camera and the surface of the photovoltaic module is not less than 60°, and the surface of the photovoltaic module is 2 The area occupies at least one pixel in the infrared image; the radial distortion of the infrared image and the perspective deformation of the photovoltaic module are corrected, and the temperature matrix F of the photovoltaic module surface is extracted.

3. A non-contact photovoltaic module power generation efficiency evaluation method according to claim 2, characterized in that: In step S2, G represents the irradiance on the surface of the photovoltaic module, S represents the area of ​​the surface of the photovoltaic module, and N represents the number of material layers of the photovoltaic module; the solar energy absorbed by the photovoltaic module is calculated as follows: Among them, Q k represents the solar energy absorbed by the kth layer of the photovoltaic module, α k represents the absorption rate of the kth layer material of the photovoltaic module, k=1,…,N; when q=0, τ q =1; when 1≤q≤k-1, τ q It represents the transmittance of the qth layer material of the photovoltaic module; Q represents the solar energy absorbed by the entire photovoltaic module.

4. A non-contact photovoltaic module power generation efficiency evaluation method according to claim 3, characterized in that: In step S3, T a Indicates the air temperature, T s Indicates the sky temperature, F i,j The elements in the temperature matrix F representing the surface of the PV module are used to calculate the heat transfer between the surface of the PV module and the surrounding environment as follows: Among them, Φ f Represents the heat convection between the PV panel surface and the surrounding environment, Ψ f Represents the thermal radiation between the surface of the photovoltaic module and the surrounding environment, δ f represents the area of ​​the surface of the photovoltaic module corresponding to each element in the temperature matrix F, σ represents the Stefan-Boltzmann constant, ε f Represents the emissivity of the photovoltaic module surface, ε s represents the radiance of the sky, h f Represents the convective heat transfer coefficient on the surface of the photovoltaic module.

5. A non-contact photovoltaic module power generation efficiency evaluation method according to claim 4, characterized in that: In step S3, T g Indicates the ground temperature, B i,j The element in the temperature matrix B representing the back side of the photovoltaic module, Δ b Represents the temperature difference between the back and surface of the PV module. The heat transfer between the back of the PV module and the surrounding environment is calculated as follows: B i,j =F i,j +D b Among them, Φ b Represents the heat convection between the back of the photovoltaic module and the surrounding environment, Ψ b Represents the thermal radiation between the back of the photovoltaic module and the surrounding environment, δ b Indicates that each element in the temperature matrix B corresponds to the area of ​​the back of the photovoltaic module, ε b Represents the emissivity of the back side of the photovoltaic module, ε g represents the emissivity of the ground, h b Indicates the convective heat transfer coefficient on the back of the PV module.

6. A non-contact photovoltaic module power generation efficiency evaluation method according to claim 5, characterized in that: In step S4, the solar energy absorbed by the photovoltaic module is converted into heat energy and electrical energy, and the electrical power of the photovoltaic module is calculated as follows: P=Q-Φ f -P f -F b -P b Wherein, P represents the electrical power of the photovoltaic module.

7. A non-contact photovoltaic module power generation efficiency evaluation method according to claim 6, characterized in that: In step S5, the normalized irradiance is G0, the normalized cell temperature is T0, the temperature coefficient of the photovoltaic module power is β, and the normalized photovoltaic module power is as follows: Where P0 represents the normalized photovoltaic module power, Represents the average value of each element in the PV panel surface temperature matrix F, Δ c Indicates the temperature difference between the cells inside the photovoltaic module and the surface.

8. A non-contact photovoltaic module power generation efficiency evaluation method according to claim 7, characterized in that: In step S5, the ideal electric power of the photovoltaic module under normalized environmental conditions is P m , the power generation efficiency and power attenuation ratio of photovoltaic modules are evaluated as follows: Among them, η represents the power generation efficiency of the photovoltaic module under actual environmental conditions, η0 represents the power generation efficiency of the photovoltaic module under normalized environmental conditions, and γ represents the power attenuation ratio of the photovoltaic module.

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