Bypass concentrating photovoltaic photo-thermal system integrated with hybrid optical filter and numerical simulation method

Abstract

The invention relates to a bypass concentrating photovoltaic photo-thermal system integrated with a hybrid optical filter and a numerical simulation method. The bypass concentrating photovoltaic photo-thermal system comprises a glass substrate, an upper bypass channel, a phase change material layer, a photovoltaic cell and a lower bypass channel which are arranged in sequence, the upper bypass channel and the lower bypass channel are communicated and internally provided with heat conduction fluid. The upper bypass channel functioning as a selective liquid filter and the phase change material layer integrate a hybrid optical filter. According to the invention, the selective liquid light filter and the phase change material are integrated into the mixed optical light filter in two channels, so that the overall efficiency of a spectrum beam splitting and concentrating photovoltaic photo-thermal system can be effectively improved.

Description

Technical Field

[0001] The invention relates to a bypass concentrating photovoltaic thermal system with an integrated hybrid optical filter and a numerical simulation method, belonging to the field of concentrating photovoltaic thermal. Background Art

[0002] By combining photovoltaic and thermal technologies, the concentrated photovoltaic and thermal systems significantly alleviate the efficiency attenuation problem caused by heat accumulation in traditional photovoltaic systems, while greatly improving the comprehensive utilization efficiency of solar energy and the applicability of the system. However, in order to balance the electrical output and thermal output, the heat sink configuration of the concentrated photovoltaic and thermal systems is more complicated, and the thermal load of the photovoltaic layer will also increase. To solve this problem, spectral beam splitting concentrated photovoltaic / thermal technology (SBS-CPV / T) came into being. This technology optimizes the spectrum, converts short-wavelength photons into electrical energy, and directs long-wavelength photons to the heat sink to generate thermal energy. By reducing the thermal load of photovoltaic modules and maintaining the optimal temperature with the assistance of heat sinks, the spectral beam splitting concentrated photovoltaic / thermal system improves the ability to separate electricity and heat, enhances the temperature adaptability of the collector, and expands the potential for thermal energy application. Among them, the selective liquid filter is based on the principle of spectral beam splitting technology, and its thermal and optical properties can effectively improve the overall efficiency of the system.

[0003] At present, there are many types of spectral beam splitters (SBS), among which selective liquid filters have the function of heat transfer fluid and can be used safely in hot and sunny climates. They are non-flammable, easy to obtain, reasonably priced, and resistant to degradation. However, their optical structure is relatively complex, and the optimization method of using selective liquid filters to improve the overall efficiency of spectral beam splitting concentrated photovoltaic / photothermal systems requires further research to ensure consistency with the spectral response of the selected photovoltaic laminate.

[0004] At present, some researchers are considering integrating phase change materials (PCM) into spectral beam splitters to further improve the solar energy conversion efficiency of concentrated photovoltaic and thermal systems. This is because phase change materials have significant advantages in reducing temperature fluctuations of heat transfer fluids and storing heat efficiently. In addition, due to their phase change mechanism, phase change materials can absorb and store thermal energy more effectively than traditional heat-sensitive energy storage materials. However, existing research mainly focuses on adding phase change material layers to concentrated photovoltaic and thermal systems or using encapsulated phase change materials for cooling and energy storage. The application of phase change materials as components of filtering units in spectral beam splitting concentrated photovoltaic / thermal systems is not mature enough, resulting in a low performance improvement in the final system. Summary of the invention

[0005] The present invention provides a bypass concentrating photovoltaic / thermal system and a numerical simulation method integrated with a hybrid optical filter, aiming to solve at least one of the technical problems existing in the prior art. To this end, the present invention proposes a bypass concentrating photovoltaic / thermal system and a numerical simulation method integrated with a hybrid optical filter, which can effectively improve the overall efficiency of the spectral beam splitting concentrating photovoltaic / thermal system.

[0006] On the one hand, the technical solution of the present invention relates to a bypass concentrating photovoltaic thermal system, comprising: a glass substrate, an upper bypass channel, a phase change material layer, a photovoltaic cell and a lower bypass channel arranged in sequence; the upper bypass channel and the lower bypass channel are connected and have a heat transfer fluid built in; the upper bypass channel that acts as a selective liquid filter and the phase change material layer integrate a hybrid optical filter.

[0007] On the other hand, the technical solution of the present invention relates to a numerical simulation method based on computational fluid dynamics for simulating spectral beam splitting concentrated photovoltaic thermal systems, which is applied to the bypass concentrated photovoltaic thermal system of the above-mentioned embodiment; the method includes the following steps: S100, constructing an optical model to obtain the relationship between the optical properties of the phase change material and the wavelength and temperature; S200, constructing a thermoelectric model to obtain the coupling of thermophotoelectricity; S300, solving the constructed computational fluid dynamics model to obtain the multi-physical field coupling of optics, thermal and electrical integration.

[0008] Further, the step S100 includes: S110, calculating the size and optical parameters of the RT25 phase change material to obtain the optical properties of the phase change material in the semi-solid phase; S120, constructing a user-defined function UDF1 to calculate the changes in absorption and scattering coefficients by averaging the optical properties of seven bands; S130, simulating temperature dependence by fitting the data to eight separate second-order polynomial equations for each band.

[0009] Further, a user defined function UDF2 is constructed to calculate the power generated by the photovoltaic cell by the number of photons transmitted within the spectral response (SR) band of the silicon cell.

[0010] Further, the step S300 includes: S310, using a non-grey discrete coordinate model to solve the radiation transfer equation, capturing the changes in the solar spectrum, the optical properties of embedded materials, and the spectral response of silicon cells according to seven spectral bands; S320, by solving the radiation transfer equation and the conservation equations of mass, momentum and energy, the pressure, velocity, temperature and radiation heat transfer field in the proposed system module are obtained.

[0011] Furthermore, according to the phase change of phase change materials being numerically expressed as the change of stored or released energy, the melting and solidification processes are modeled using the enthalpy hole method to obtain the energy change.

[0012] The beneficial effects of the present invention are as follows.

[0013] The bypass concentrating photovoltaic and solar thermal system with integrated hybrid optical filter of the embodiment of the present invention proposes an innovative design of integrating a selective liquid filter (SLF) and a phase change material (PCM) into a hybrid optical filter in a dual channel, thereby significantly improving the absorption and conversion efficiency of light energy in the concentrating photovoltaic system, enhancing the power generation capacity of the system, effectively optimizing thermal energy management, and improving the overall system performance and economic benefits.

[0014] Based on the proposed innovative design system, a more efficient and accurate method was developed numerically, which constructed a comprehensive numerical model in a computational fluid dynamics (CFD) environment to simulate the spectral beam splitting concentrated photovoltaic / photothermal system, fully integrating optical, thermal and electrical modeling while utilizing a non-grey discrete coordinate (DO) model. The present invention can obtain key performance parameters at different Reynolds numbers (800, 1700, 2300) and concentration ratios (5, 15, 25), and optimize the performance of the spectral beam splitting concentrated photovoltaic / photothermal (SBS-CPV / T) system by analyzing the changes in the thickness of the phase change material (PCM) and the selective liquid filter (SLF) and adjusting the flow rate of the heat transfer fluid (HTF). BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0016] Figure 1 Schematic diagram of the structure of a bypass concentrating photovoltaic thermal system according to an embodiment of the present invention.

[0017] Figure 2 1 is a graph of optical constants of liquid RT25 material obtained by calculation according to the embodiment, wherein (a) represents the extinction coefficient and the refractive index; (b) represents the solid-state scattering coefficient; and (c) represents the enthalpy-temperature curve in the heating mode.

[0018] Figure 3 The reliability of the calculation is verified according to the embodiment, and the transmittance of the RT25 phase change material in the liquid and solid states measured in the experiment and the calculation model is shown.

[0019] Figure 4 1 is the effect of temperature on the optical properties of the phase change material obtained by fitting the data of the embodiment, (a) represents the absorption coefficient; (b) represents the scattering coefficient; (c) represents the extinction coefficient of different phases in the broadband of sunlight.

[0020] Figure 53 is a reliability test diagram of the CFD model according to an embodiment of the present invention, wherein (a) represents the transmittance of the phase change material in different bands (taking into account the temperature dependence of the semi-solid phase); and (b) represents the temperature and liquid fraction of the phase change material that change with time.

[0021] Figure 6 It is a diagram of evaluation results of various performance parameters of the system under set parameter conditions according to an embodiment.

[0022] Figures 7 to 13 It is a diagram of evaluation results of the influence of different concentrations and Reynolds numbers on various performance parameters of the system according to an embodiment of the present invention. DETAILED DESCRIPTION

[0023] The following will be combined with the embodiments and drawings to clearly and completely describe the concept, specific structure and technical effects of the present invention, so as to fully understand the purpose, scheme and effect of the present invention. It should be noted that, in the absence of conflict, the embodiments in this application and the features in the embodiments can be combined with each other. It should be noted that, unless otherwise specified, when a feature is referred to as "fixed" or "connected" to another feature, it can be directly fixed or connected to another feature, or it can be indirectly fixed or connected to another feature. In addition, the descriptions of upper, lower, left, right, top, bottom, etc. used in the present invention are only relative to the relative positional relationship of the components of the present invention in the drawings. In addition, unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by technicians in this field. The terms used in this specification are only for describing specific embodiments, not for limiting the present invention. The term "and / or" used herein includes any combination of one or more related listed items. It should be understood that although the terms first, second, third, etc. may be used in the present disclosure to describe various elements, these elements should not be limited to these terms. These terms are only used to distinguish elements of the same type from each other. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of the present disclosure.

[0024] See also Figures 1 to 5 The bypass concentrating photovoltaic / thermal (CPV / T) system of the integrated hybrid optical filter of the technical solution of the present invention comprises a glass substrate, an upper bypass channel, a phase change material layer, an air gap layer, a photovoltaic cell and a lower bypass channel arranged in sequence; the upper bypass channel and the lower bypass channel are connected, and the upper bypass channel which acts as a selective liquid filter is integrated with the phase change material layer into a hybrid optical filter.

[0025] Specifically, see Figure 1The upper glass substrate (Glass substrate) disposed on the top of the present invention plays a protective role and has light transmittance, and the concentrated solar spectrum (Concentrated Solar spectrum) is directly irradiated on the upper glass substrate.

[0026] Furthermore, in the upper and lower bypass channels of the present invention, the heat transfer fluid initially enters from the fluid inlet (FluidInlet), flows through the lower bypass channel located below the photovoltaic cell (PV cell) to maintain the temperature of the photovoltaic cell within the optimal operating range, and then, the heat transfer fluid passes through the upper bypass channel located above the phase change material layer (PCM) and flows out from the fluid outlet (FluidOutlet), wherein the upper bypass channel located above the phase change material layer (PCM) also acts as a selective liquid filter (Liquid filter).

[0027] Furthermore, the phase change material layer (PCM) of the present invention can use RT25 phase change material, thereby utilizing the RT25 phase change material to have sufficient optical clarity, transparency and non-scattering properties in the liquid phase. The phase change material layer divides the incident light into a thermal band and a photovoltaic band, thereby optimizing the spectral response of the silicon cell. The hybrid optical filter integrated with the phase change material and the selective filter layer used in the present invention can improve the thermal mass of the selective liquid filter and its absorption of the thermal spectrum, reduce heat loss, and enhance the thermal decoupling between the heat absorber and the photovoltaic cell.

[0028] Furthermore, the air gap layer (Air Gap) of the present invention is used to separate the photovoltaic cell (PV cell) and the phase change material layer, thereby preventing the heat of the hybrid optical filter at the upper part from being transferred to the photovoltaic cell panel, which is beneficial to ensure that the hybrid optical filter can operate at a much higher temperature than the photovoltaic cell.

[0029] In some application embodiments, specific parameter settings of the bypass concentrated photovoltaic thermal (CPV / T) system of the integrated hybrid optical filter of the present invention are shown in Table 1.

[0030] Table 1:

[0031] See also Figures 1 to 5The numerical simulation method for simulating spectral beam splitting concentrated photovoltaic / thermal system based on computational fluid dynamics of the technical solution of the present invention is applied to the bypass concentrated photovoltaic / thermal system of the embodiment of the present invention, and the method includes at least the following steps: S100, constructing an optical model to obtain the relationship between the optical properties of the phase change material and the wavelength and temperature; S200, constructing a thermoelectric model to obtain the coupling parameters of thermophotoelectricity; S300, solving the constructed computational fluid dynamics model to obtain the multi-physical field coupling parameters of optical, thermal and electrical integration. Specifically, the present invention constructs a comprehensive numerical model in a computational fluid dynamics (CFD) environment to simulate the spectral beam splitting concentrated photovoltaic / thermal system, and the numerical simulation method adopts a bidirectional coupling method, that is, a multi-physical field coupling method that integrates optical, thermal and electrical models.

[0032] In some embodiments, the optical modeling of the present invention obtains the relationship between the optical properties of the phase change material and the wavelength and temperature. Figure 2 First, the transmittance, absorptivity and reflectivity of the RT25 phase change material in solid and liquid states can be calculated based on its refractive index (n-RT25) and extinction coefficient (k-RT25).

[0033] Among them, the transmittance in liquid state , reflectivity and absorption rate The calculation is as follows: ; ; ; In the formula, It represents the reflectivity when light is incident from the glass interface to the phase change material interface. It represents the reflectivity when light is incident from the phase change material to the glass interface. Represents the overall transmittance of the phase change material (considering the reflection loss at the incident and exit interfaces); The transmittance inside the phase change material (not considering the loss of interface reflection), represents the reflectivity inside the phase change material; where,

[0034] ; ; ; In the formula, represents the refractive index of the phase change material, represents the refractive index of glass, It indicates the transmittance of phase change material at a certain wavelength. represents the extinction coefficient of the phase change material, is the thickness of the phase change layer, represents the extinction coefficient at a certain wavelength, is the absorption coefficient, is the scattering coefficient; The calculation is as follows:

[0035] ; Among them, the transmittance in the solid state , reflectivity and absorption rate The calculation is as follows: ; ; ; In the formula, represents the optical thickness of the phase change material, represents the diffuse interface reflectivity between glass and phase change material, represents the diffuse interface reflectivity between glass and air, represents the diffuse component of radiation; represents the transmittance of the glass; where ; ; ; In the formula, It represents the extinction coefficient of phase change material at a certain wavelength. represents the diffuse reflection interface reflectivity from medium i to medium j, It represents the ratio of the adjacent high refractive index layer to the low refractive index layer; represents the diffuse radiation intensity, represents the single scattering albedo, represents the internal transmittance of the glass, is the incident radiation intensity, are orthogonal weights, are the direction cosines, represents the dynamic viscosity of the phase change material, and It is derived from the boundary conditions; the parameters The calculation is as follows: , See also Figure 3By comparing the experimental results with the calculation results, the reliability of the calculation method of the present invention can be proved. Then, the obtained solid and liquid optical properties are applied to the subsequent method to further consider the dependence of the optical properties of the phase change material in the semi-solid phase on temperature.

[0036] As the liquid fraction As the phase change material tends to liquidify, the rate of change of the extinction coefficient also increases. Therefore, the present invention assumes that the extinction coefficient is inversely proportional to the liquid fraction, and the specific formula is as follows: ; In the formula, represents the extinction coefficient of the phase change material in the semi-solid phase, represents the extinction coefficient of phase change material in liquid phase, represents the extinction coefficient of the phase change material in the solid phase, represents the liquid fraction, Indicates temperature, represents the scattering coefficient of the phase change material in the semi-solid phase, is the physical thickness of the phase change material, is the optical thickness, is the extinction coefficient of the phase change material in the semi-solid phase; where the transmittance fraction when the phase change material changes between liquid and solid The change is represented by: ; In the formula, It indicates the transmittance of the phase change material at a certain wavelength when it is in liquid state. It indicates the transmittance of the phase change material at a certain wavelength when it is in the solid state.

[0037] See also Figure 4 , showing the variations of different absorption coefficients, scattering coefficients and extinction coefficients with wavelength and temperature, verifying that the method applied in the present invention can effectively capture the changes in the optical properties of phase change materials at different wavelengths and temperatures, thereby accurately simulating their optical properties in the CFD domain.

[0038] Then, a new user-defined function (UDF1) is constructed, which defines the optical properties of the phase change material as a common function of temperature and wavelength. The UDF1 function calculates the changes in absorption and scattering coefficients by averaging the optical properties of seven bands, and accurately models the temperature dependence by fitting the data to eight separate second-order polynomial equations for each band.

[0039] In some embodiments, in the thermoelectric modeling of the present invention, in order to achieve thermophotovoltaic coupling, a user-defined function (UDF2) is also developed, that is, the electric power generated by the photovoltaic cell is defined as a function of the number of photons that pass through the hybrid filter and are within the spectral response (SR) band of the silicon cell.

[0040] In some embodiments, in the numerical model solution of the present invention, the constructed CFD model uses a non-grey discrete coordinate model to solve the radiation transfer equation, and uses seven spectral bands to capture the changes in the solar spectrum, the optical properties of embedded materials (such as pure water and RT25PCM), and the spectral response of silicon cells. Then, by solving the radiation transfer equation and the mass, momentum and energy conservation equations, the pressure, velocity, temperature and radiation heat transfer field in the proposed system module are obtained. In addition, for the modeling of phase change materials, since the phase change is numerically represented as a change in stored or released energy, the enthalpy hole method is used in ANSYS Fluent to model the melting and solidification processes. Specifically, its calculation process is expressed as follows:

[0041] The radiative transfer equation is expressed as follows:

[0042] ; In the formula, It represents the radiation intensity at a specific direction and position, r represents a Cartesian coordinate point in space, and s represents the direction unit vector. The second term represents the amount of radiation absorbed by the medium, represents the scattering coefficient, represents the absorption coefficient, n represents the refractive index, represents the Stefan Boltzmann constant, Indicates temperature, represents the scattering phase function, represents the solid angle; The mass conservation equation is expressed as follows: Selective Liquid Filters: ; Phase change materials: ; The momentum equation is expressed as follows: Solid components and selective liquid filters: ; Phase change materials: ; The energy equation is expressed as follows: Optical Filters: ; Phase change materials: ; Silicon wafer: ; other: ; In the formula, is equal to the energy emitted within the control volume minus the absorbed incident radiation, i.e. the net radiation loss, is the heat source term, which is used to calculate the volumetric electric power generated by the photovoltaic panel, represents dynamic viscosity, g represents gravitational acceleration, represents thermal conductivity, represents density, Indicates speed, Indicates pressure, is the coefficient of thermal expansion, represents the momentum source term, Indicates time; s Subscripts denote solids, represents the thermal conductivity of the solid, Represents the solid temperature.

[0043] When a phase change material undergoes a phase change, its thermophysical properties also change. In order to capture its changes, a model that takes into account the fact that the properties of the phase change material change. The change in thermal conductivity of the phase change material during the phase change process is expressed as follows:

[0044] ; In the formula, represents the current temperature of the phase change material, represents the solidus temperature of the phase change material, represents the liquidus temperature of the phase change material; represents thermal conductivity, represents the liquid phase thermal conductivity of the phase change material, Represents the solid phase thermal conductivity of the phase change material.

[0045] Photovoltaic panels generate electricity, and the heat transfer fluid (pure water) absorbs heat as heat output, achieving photovoltaic-thermal coupling. To evaluate system performance, the thermal conversion efficiency and photoelectric conversion efficiency Determined by the following formula: ; In the formula, represents the heat conversion efficiency, represents the thermal power obtained by the system, represents the top surface area of ​​the photovoltaic panel, represents the concentration ratio, represents the specific heat capacity of the working fluid, represents the fluid mass flow rate, and denote the inlet and outlet fluid temperatures, Represents the solar irradiance per unit area.

[0046] ; In the formula, represents the photoelectric conversion efficiency, Represents the output power of the photovoltaic panel, Indicates the photovoltaic panel temperature, represents the open circuit voltage, Indicates the short-circuit current, represents the filling factor, represents the battery efficiency temperature coefficient, represents the reference temperature, Indicates the reference photoelectric conversion efficiency. Further, the present invention adopts a 5 W single crystal silicon cell (270 mA), the temperature coefficient is 0.45% / °C, and the reference efficiency is 23%. In addition, the present invention comprehensively proposes the main energy-saving efficiency as follows:

[0047] ;

[0048] In the formula, represents the Rankine cycle efficiency, It represents an indicator for evaluating the energy-saving efficiency of concentrated photovoltaic systems.

[0049] In addition, the economic feasibility of the present invention can be expressed by the following value function: To evaluate:

[0050] ; Wherein, W is a value factor, which is calculated by comparing the relative market value of heat energy and electricity, and further in the present invention, W=3; is the electrical power of the photovoltaic panel without a thermal absorber.

[0051] In the model parameter setting section, the sides of all layers and the back of the lower fluid channel are assumed to be adiabatic and opaque, and the effect of thermal contact resistance is not considered. The upper surface of the top glass layer is defined by mixed boundary conditions, the ambient temperature is 298 K, and the local wind speed is 3.5 m / s. The convective heat transfer coefficient of the air flowing through the top glass substrate is Determined by the following formula:

[0052] ;

[0053] In the formula, Indicates air flow rate.

[0054] The fluid domain uses a velocity inlet boundary condition at the inlet with a Reynolds number range of 800-2300, and a pressure outlet boundary condition at the outlet with zero gauge pressure.

[0055] Finally, see Figure 5 and Table 2, the reliability analysis of the numerical model CFD was carried out.

[0056] To ensure the accuracy and effectiveness of the model, the solar irradiance was 892W / m 2 The grid independence test was performed with the concentration ratio set to 15, the Reynolds number set to 1700, the inlet fluid temperature set to 298.15K, the filter thickness set to 5mm, and the phase change material thickness set to 2mm. On this basis, the present invention selected a grid containing 439,952 elements for subsequent analysis.

[0057] Table 2, grid independence test:

[0058]

[0059] After model validation, an in-depth performance analysis was conducted to investigate the effects of various operating conditions, including concentration ratio and Reynolds number of the selectivity filter, as well as key design parameters, such as thickness.

[0060] See also Figure 6 After analyzing the overall performance, the entire system was first evaluated using numerical simulation under the conditions of 5 mm filter thickness, 2 mm phase change material thickness, 40 concentration ratio and 120 Reynolds number to determine the impact of various performance parameters on the analysis. Specifically, they include: the impact on the liquid fraction of the phase change material used, the impact on the radiative heat flux transmitted by the photovoltaic surface, the impact on the outlet temperature of the photovoltaic cell and the selective liquid filter, the impact on the power generation and heat gain in the CPV system, the impact on the time-varying electrical efficiency, thermal efficiency and total primary efficiency of the CPV system, and the impact on the total effective energy efficiency and value function of the CPV system.

[0061] In some embodiments, the present invention can evaluate various performance parameters of the spectral beam splitting concentrated photovoltaic / photothermal (SBS-CPV / T) system under constant parameter conditions. These parameters include radiative heat transfer at different levels (thermal band and photovoltaic band), temperature (volume average temperature of the photovoltaic layer and phase change material layer, and area weighted average temperature of the outlet surface), liquid volume fraction, thermal power and electrical power, and efficiency (electrical efficiency, thermal efficiency and main energy saving efficiency).

[0062] In some embodiments, the present invention can obtain the influence on system performance under different Reynolds numbers and concentration ratios, including: the influence on the liquid fraction of the phase change material used, the influence on the radiation heat flux transmitted by the photovoltaic surface, the influence on the outlet temperature of the photovoltaic cell and the selective liquid filter, the influence on the power generation and heat gain in the concentrated photovoltaic system, the influence on the electrical efficiency, thermal efficiency and total primary efficiency of the concentrated photovoltaic system over time, and the influence on the total effective energy efficiency and value function of the concentrated photovoltaic system.

[0063] See also Figures 7 to 13 , the effects on various performance parameters were studied for three different concentrations (5, 15 and 25) and three Reynolds number values ​​(800, 1700, 2300).

[0064] In some embodiments, the present invention can study the impact on system performance by adjusting the thickness of the phase change material layer (1 mm, 2 mm and 3 mm) and the pure water layer (2 mm, 5 mm and 7 mm), and the Reynolds number (800, 1700, 2300), including evaluating their impact on power generation and heat energy, total energy and effective energy efficiency.

[0065] In some embodiments, the present invention can study the impact on system performance by adjusting the thickness of the phase change layer and the pure water heat transfer fluid, including evaluating their impact on power generation and heat energy, total energy and effective energy efficiency.

[0066] In some embodiments, the present invention can optimize the system to maximize power output, improve total primary efficiency and increase merit function (MF) by adjusting design parameters, combining numerical calculation and priority sorting. During the optimization process, each input parameter is set within the target range, and the factors are prioritized by importance scale (such as 1 to 5) and weight (such as 0.1 to 10), among which power output, efficiency and MF are given the highest priority (+++++), followed by heat gain and total enthalpy efficiency. According to the optimization results, the optimal design parameters are spectral filter layer (SLF) thickness of 5.905mm, Reynolds number of 800, and phase change material (PCM) film thickness of 1mm. This optimization method effectively balances thermal and electrical performance, ensures the maximization of the overall performance of the system, and promotes the overall progress of economy, environment and technology.

[0067] It should be noted that traditional research mainly focuses on adding phase change material layers to concentrated photovoltaic thermal systems or using encapsulated phase change materials for cooling and energy storage, which ignores the unique advantage of phase change materials with adjustable optical properties, which can be flexibly adjusted to selectively transmit different parts of the solar spectrum. In addition, the integration of spectral beam splitters and phase change materials in traditional research on concentrated photovoltaic thermal systems usually only considers the correlation between the optical properties of phase change materials and wavelength, while ignoring the dependence of optical properties on temperature. In other words, traditional technology does not fully utilize the relationship between the optical properties of phase change materials and temperature, that is, the optical properties of phase change materials in the solid, liquid and semi-solid phases are greatly related to temperature, especially in the semi-solid phase.

[0068] The above is only a preferred embodiment of the present invention. The present invention is not limited to the above implementation. As long as the technical effect of the present invention is achieved by the same means, any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present disclosure shall be included in the scope of protection of the present disclosure. All should belong to the protection scope of the present invention. Within the protection scope of the present invention, its technical scheme and / or implementation method can have various modifications and changes.

Claims

1. A bypass concentrated photovoltaic thermal system, characterized in that: include: A glass substrate, an upper bypass channel, a phase change material layer, a photovoltaic cell and a lower bypass channel are sequentially arranged; The upper bypass channel is connected to the lower bypass channel and contains a heat transfer fluid; the upper bypass channel, which acts as a selective liquid filter, integrates a hybrid optical filter with the phase change material layer.

2. The bypass concentrated photovoltaic thermal system according to claim 1, characterized in that: The phase change material layer is made of RT25 phase change material to divide incident light into a thermal band and a photovoltaic band.

3. The bypass concentrated photovoltaic thermal system according to claim 1, characterized in that: The heat transfer fluid enters from the fluid inlet, passes through the lower bypass channel and the upper bypass channel in sequence, and then flows out from the fluid outlet to maintain the temperature of the photovoltaic cell within a set working range.

4. The bypass concentrated photovoltaic thermal system according to claim 1, characterized in that: The invention also includes an air gap layer, wherein the air gap layer is arranged between the phase change material layer and the photovoltaic cell.

5. The bypass concentrated photovoltaic thermal system according to claim 1, characterized in that: It also includes an aluminum film layer, which is arranged between the photovoltaic cell and the lower bypass channel.

6. A numerical simulation method for simulating spectral beam splitting and concentrating photovoltaic and thermal systems based on computational fluid dynamics, characterized in that: A bypass concentrating photovoltaic thermal system applied to any one of claims 1 to 5; The method comprises the following steps: S100, constructing an optical model to obtain the relationship between the optical properties of the phase change material and the wavelength and temperature; S200, constructing a thermoelectric model to obtain thermophotoelectric coupling parameters; S300, solving the constructed computational fluid dynamics model to obtain multi-physics field coupling parameters of optical, thermal and electrical integration.

7. The method according to claim 6, characterized in that The step S100 includes: S110, calculating the transmittance, absorptivity and reflectivity of the RT25 phase change material in solid and liquid states according to the refractive index and extinction coefficient; Among them, the transmittance in liquid state , reflectivity and absorption rate The calculation is as follows: ； ； ； In the formula, It represents the reflectivity when light is incident from the glass interface to the phase change material interface. It represents the reflectivity when light is incident from the phase change material to the glass interface. represents the overall transmittance of the phase change material; The transmittance inside the phase change material, represents the reflectivity inside the phase change material; where, ； ； ； In the formula, represents the refractive index of the phase change material, represents the refractive index of glass, It indicates the transmittance of phase change material at a certain wavelength. represents the extinction coefficient of the phase change material, is the thickness of the phase change layer, represents the extinction coefficient at a certain wavelength, is the absorption coefficient, is the scattering coefficient; The calculation is as follows: ； Among them, the transmittance in the solid state , reflectivity and absorption rate The calculation is as follows: ； ； ； In the formula, represents the optical thickness of the phase change material, represents the diffuse interface reflectivity between glass and phase change material, represents the diffuse interface reflectivity between glass and air, represents the diffuse component of radiation; represents the transmittance of the glass; where ； ； ； In the formula, It represents the extinction coefficient of phase change material at a certain wavelength. represents the diffuse reflection interface reflectivity from medium i to medium j, It represents the ratio of the adjacent high refractive index layer to the low refractive index layer; represents the diffuse radiation intensity, represents the single scattering albedo, represents the internal transmittance of the glass, is the incident radiation intensity, are orthogonal weights, are the direction cosines, represents the dynamic viscosity of the phase change material, and It is derived from the boundary conditions; the parameters The calculation is as follows: ， In which, assuming that the extinction coefficient is inversely proportional to the liquid fraction, it is expressed as: ； in ; ； ； ； In the formula, represents the extinction coefficient of the phase change material in the semi-solid phase, represents the extinction coefficient of phase change material in liquid phase, represents the extinction coefficient of the phase change material in the solid phase, represents the liquid fraction, Indicates temperature, represents the scattering coefficient of the phase change material in the semi-solid phase, is the physical thickness of the phase change material, is the optical thickness, is the extinction coefficient of the phase change material in the semi-solid phase; where the transmittance fraction when the phase change material changes between liquid and solid The change is represented by: ； In the formula, It indicates the transmittance of the phase change material at a certain wavelength when it is in liquid state. It indicates the transmittance of the phase change material at a certain wavelength when it is in the solid state; S120, constructing a user-defined function UDF1 to calculate changes in absorption and scattering coefficients by averaging optical properties of seven bands; S130. The temperature dependence was simulated by fitting the data to eight separate second-order polynomial equations for each band.

8. The method according to claim 6, characterized in that In the step S200, a user defined function UDF2 is constructed to calculate the power generated by the photovoltaic cell by the number of photons transmitted within the spectral response band of the silicon cell; Among them, the thermal conversion efficiency and photoelectric conversion efficiency Determined by the following formula: ； In the formula, represents the heat conversion efficiency, represents the thermal power obtained by the system, represents the top surface area of ​​the photovoltaic panel, represents the concentration ratio, represents the specific heat capacity of the working fluid, represents the fluid mass flow rate, and denote the inlet and outlet fluid temperatures, It represents the solar irradiance per unit area; ； In the formula, represents the photoelectric conversion efficiency, Represents the output power of the photovoltaic panel, Indicates the photovoltaic panel temperature, represents the open circuit voltage, Indicates the short-circuit current, represents the filling factor, represents the battery efficiency temperature coefficient, represents the reference temperature, Represents the reference photoelectric conversion efficiency.

9. The method according to claim 6, characterized in that The step S300 includes: S310, using a non-grey discrete coordinate model to solve the radiative transfer equation, capturing the variations in the solar spectrum, the optical properties of embedded materials, and the spectral response of silicon cells according to seven spectral bands; S320, by solving the radiation transfer equation and the mass, momentum and energy conservation equations, the pressure, velocity, temperature and radiation heat transfer field in the proposed system module are obtained; wherein, The radiative transfer equation is expressed as follows: ； In the formula, It represents the radiation intensity at a specific direction and position, r represents a Cartesian coordinate point in space, s represents the direction unit vector, and the second term represents the amount of radiation absorbed by the medium. represents the scattering coefficient, represents the absorption coefficient, n represents the refractive index, represents the Stefan Boltzmann constant, Indicates temperature, represents the scattering phase function, represents the solid angle; The mass conservation equation is expressed as follows: Selective Liquid Filters: ； Phase change materials: ； The momentum equation is expressed as follows: Solid components and selective liquid filters: ; Phase change materials: ； The energy equation is expressed as follows: Optical Filters: ; Phase change materials: ; Silicon wafer: ; other: ; In the formula, is equal to the energy emitted within the control volume minus the absorbed incident radiation, i.e. the net radiation loss, is the heat source term, which is used to calculate the volumetric electric power generated by the photovoltaic panel, represents dynamic viscosity, g represents gravitational acceleration, represents thermal conductivity, represents density, Indicates speed, Indicates pressure, is the coefficient of thermal expansion, represents the momentum source term, Indicates time; s Subscripts denote solids, represents the thermal conductivity of the solid, Represents the solid temperature.

10. The method according to claim 9, characterized in that According to the phase change of phase change materials, which is numerically expressed as the energy change stored or released, the melting and solidification processes are modeled using the enthalpy hole method to obtain the energy change; Among them, the change of thermal conductivity of the phase change material during the phase change process is expressed as follows: ； In the formula, represents the current temperature of the phase change material, represents the solidus temperature of the phase change material, represents the liquidus temperature of the phase change material; represents the liquid phase thermal conductivity of the phase change material, Represents the solid phase thermal conductivity of the phase change material.

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