A method for measuring solar direct radiation spectrum

Abstract

A method for measuring the solar direct radiation spectrum belongs to the field of radiation spectrum measurement technology. To address the problems of current measurement systems that rely on expensive and complex dual-axis mobile tracking devices, resulting in high maintenance costs, multiple transmission links, and large errors, the invention includes the following steps: designing a framework for a polar-rotating solar direct radiation spectrum measurement system, optimizing the design of a PAR-SDNSIM, reconstructing spectral radiation intensity and evaluating solar spectrum measurement accuracy, and analyzing experimental results. The invention constructs a new PAR-SDNSIM architecture consisting of a SDRCFM and a SRMS, achieving direct solar radiation spectrum measurement without mobile tracking throughout the entire year and at all latitudes, further improving the theoretical system for direct solar radiation spectrum measurement.

Description

Technical Field

[0001] The present invention relates to the technical field of radiation spectrum measurement, and in particular to a method for measuring solar direct radiation spectrum. Background Art

[0002] Accurate measurements of direct solar radiation spectra are crucial for fields such as atmospheric science, climatology, agricultural science, and solar energy utilization. High-quality direct solar radiation spectral data are fundamental to these studies, while precise sun tracking and accurate spectral measurements are crucial for data accuracy.

[0003] Current measurement systems rely on expensive and complex dual-axis motion tracking devices, which have disadvantages such as high maintenance costs, multiple transmission links and large errors.

[0004] Aiming at the above problems, a method for measuring solar direct radiation spectrum is proposed. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for measuring the direct solar radiation spectrum, which uses this device to solve the problems of the measurement systems in the above background relying on expensive and complex dual-axis mobile tracking devices, with high maintenance costs, multiple transmission links and large errors.

[0006] To achieve the above object, the present invention provides the following technical solution: a method for measuring the direct solar radiation spectrum, comprising the following specific steps:

[0007] S1: Design a framework for a polar-rotating solar direct radiation spectrum measurement system;

[0008] S2: PAR-SDNSIM optimization design;

[0009] S3: Spectral radiation intensity reconstruction and solar spectrum measurement accuracy assessment;

[0010] S4: Analysis of experimental results.

[0011] Furthermore, the framework for designing a polar-axis rotation solar direct radiation spectrum measurement system described in S1 has the following specific steps:

[0012] S101: Build the overall architecture of PAR-SDNSIM;

[0013] S102: Discrete and Reconstruction of SDRCFM;

[0014] S103: Time-space scale spectral radiation intensity reconstruction link.

[0015] Furthermore, the PAR-SDNSIM optimization design described in S2 has the following specific steps:

[0016] S201: SDRCFM Design and Performance Evaluation;

[0017] S202: SRMS design and performance evaluation.

[0018] Furthermore, the spectral radiation intensity reconstruction and solar spectrum measurement accuracy evaluation described in S3 are specifically performed as follows:

[0019] S301: Spectral radiation intensity reconstruction matrix simulation;

[0020] S302: Accuracy assessment of direct solar radiation spectrum measurement.

[0021] Furthermore, the specific steps for constructing the PAR-SDNSIM overall architecture described in S101 are as follows:

[0022] S1011: Using a polar-axis rotation tracking device to offset changes in the solar azimuth angle, and designing a free-form surface that can reflect direct solar beams of varying incident angles into the SRMS, the overall architecture of the constructed PAR-SDNSIM is divided into two parts: the SDRCFM and the SRMS.

[0023] S1012: The direct sunlight beam at noon on the equinox day reflected by the SDRCFM is perpendicular to the incident beam at that time, and the reflected beam serves as the optical axis and rotation axis of the SDRCFM;

[0024] S1013: Analyze typical dispersion structures, and use a cross-type Czerny-Turner dispersion structure for SRMS;

[0025] S1014: The PAR-SDNSIM is tilted according to the latitude of its installation location, and the SDRCFM optical axis passes perpendicularly through the slit position of the SRMS. Light beams of different incident angles are reflected and modulated by the SDRCFM surface and converge on the light spot area at the slit position of the SRMS. After that, the light beams passing through the slit pass through the collimating reflector, diffraction grating, and focusing reflector of the SRMS, forming diffraction spectrum lines on the CCD detector, thereby obtaining the spectral distribution information of direct solar radiation.

[0026] Furthermore, the discretization and reconstruction of the SDRCFM described in S102 are specifically performed as follows:

[0027] S1021: SDRCFM controls the mirror slope of the free-form surface to regulate the path of the direct sunlight beam after reflection, so that the direct sunlight beam at noon of two to two minutes after reflection by SDRCFM converges to a point on the optical axis of SDRCFM, and establishes a mapping model between the incident angle of the direct sunlight beam and the mirror slope.

[0028] S1022: The incident angle of the direct sunlight beam at noon on the summer solstice and winter solstice is and The angle between the direct sunlight beam at noon on the summer solstice and the SDRCFM optical axis after reflection is and , the SDRCFM mirror slope corresponding to the summer solstice and winter solstice is and , the SDRCFM mirror slope corresponding to the two-equinox day is , and The equation is as follows:

[0029] ;

[0030] S1023: Set the incident angle range of the direct sunlight beam Bring in and The equation of can be used to obtain the mirror slope required by SDRCFM and establish the discrete and reconstruction model of SDRCFM;

[0031] S1024: SDRCFM diameter is , maximum working distance , the intersection of the two is the coordinate origin, and the length of the working part , the minimum axial working distance of the reflector is , SDRCFM is divided into Region, The coordinates of the discrete points are , each corresponding height is , the equation for SDRCFM is as follows:

[0032] ;

[0033] S1025: The free-form reflective mirror structure of direct sunlight focusing composed of discrete points is obtained through the SDRCFM equation, and a continuous and smooth SDRCFM surface is constructed through surface fitting.

[0034] Furthermore, the spatiotemporal scale spectral radiation intensity reconstruction link described in S103 has the following specific steps:

[0035] S1031: Take the incident angle of the direct sunlight beam as the spectral radiation intensity reconstruction benchmark in the time and space scales, and assume that the incident angle is , assuming that the peak wavelength of the discrete spectrum of the diffraction line collected by the CCD detector is , assuming that the spectrum distribution of direct solar beams at different incident angles is consistent, the solar direct radiation spectrum matrix is ,different The corresponding direct solar radiation spectrum matrix can be expressed as ,in At the incident angle In this case, the radiation flux corresponding to the peak wavelength of the diffraction line spectrum;

[0036] S1032: Assume that the incident angle that can be measured and resolved in SRMS is , the spectral distribution measurement matrix can be expressed as , the solar direct radiation spectrum matrix in the time and space scale can be expressed as ,Will Take the reciprocal of each element in and get the matrix , the equation of the spectral radiation intensity reconstruction matrix in the time and space scale is as follows:

[0037] ;

[0038] S1033: Perform regression analysis on the spectral radiation intensity reconstruction matrix at the time and space scales, and implement the spectral radiation intensity reconstruction link at the time and space scales.

[0039] Furthermore, the SDRCFM design and performance evaluation described in S201 has the following specific steps:

[0040] S2011: Select a light cone with an incident angle of ±23.5°, ±20°, ±16°, ±12°, ±8°, ±4° and 0° and a 5° apex angle as the sampling beam for SDRCFM design, and is 350mm, according to and The equations of and the equations of SDRCFM are used to iteratively obtain the initial structural parameters of SDRCFM;

[0041] S2012: The SDRCFM's ability to control direct solar beams at all latitudes was comprehensively evaluated using irradiance uniformity and spot overlap at both temporal and spatial scales. The specific equations are as follows:

[0042] ;

[0043] In the formula is the maximum irradiance of the light spot at each incident angle; is the minimum irradiance of the light spot at each incident angle; the minimum boundaries of the light spot at each incident angle on the x-axis and y-axis are and , the maximum boundary is and ;

[0044] S2013: By controlling the discrete number of incident angles of SDRCFM , XY polynomial is used to iteratively optimize and reconstruct SDRCFM, and the curvature radius of the optimized SDRCFM vertex is The cone coefficient is 0.008413. is -1.3201, and the resulting surface expression equation is as follows:

[0045] ;

[0046] In the formula for The coefficient of the term, superscript and Representing variables , The order of

[0047] The specific steps for SRMS design and performance evaluation described in S202 are as follows:

[0048] S2021: The wavelength of direct solar radiation covers 280nm-3000nm, of which 50% of the solar radiation energy is concentrated in the visible spectrum region of 380nm-780nm. The 380nm-780nm range is selected as the working spectrum for verification. The SRMS incident angle is set to 14°. The grating diffraction equation is as follows:

[0049] ;

[0050] S2022: Calculate the grating color resolution. The specific equation is as follows:

[0051] ;

[0052] Where d is the grating period, is the incident wavelength, m is the diffraction order of the grating diffraction equation, and are the incident angle and the diffraction angle of the corresponding diffraction order m, respectively, and N is the number of grating lines;

[0053] S2023: Select the grating line number 600l / mm and set the grating incident diffraction angle is 30°, and the grating incident angle is obtained based on the grating diffraction equation The grating diffraction angle is 25.74° It is 4.26°.

[0054] Furthermore, the spectral radiation intensity reconstruction matrix simulation described in S301 has the following specific steps:

[0055] S3011: Standard deviation of spectral radiant flux The spectral fluctuations at each incident angle are characterized by the following equations:

[0056] ;

[0057] In the formula The angle of incidence is When SRMS measures the spectral radiation flux corresponding to the wavelength, represents the mean spectral radiation flux at each incident angle, and n is the number of peak wavelengths measured by SRMS;

[0058] S3012: Reconstruct the matrix equation based on the spectral radiation intensity at the time and space scale in S1032 Based on the ,Through multiple regression analysis, the reconstruction rules of the ,spectral radiation intensity at each incident angle are obtained.

[0059] Furthermore, the solar direct radiation spectrum measurement accuracy assessment described in S302 includes the following specific steps:

[0060] S3021: Set the incident spectral distribution to the standard AM1.5G solar spectrum in the visible light range, and the radiant flux to a solar constant. The spectral distribution of direct solar radiation at each incident angle can be obtained after spectral radiation intensity reconstruction, and normalized according to the spectral integrated energy to obtain the normalized standard AM1.5G solar spectrum and the reconstructed direct solar radiation spectrum;

[0061] S3022: Spectral curve area error was established and spectral radiant flux error , the specific equation is as follows:

[0062] ;

[0063] ;

[0064] In the formula and They are the normalized standard AM1.5G and the reconstructed solar spectrum radiation flux;

[0065] S3023: Introducing the average error of the spectral curve area and the average error of spectral radiation flux , the specific equation is as follows:

[0066] .

[0067] Compared with the prior art, the present invention has the following beneficial effects:

[0068] 1. This invention abandons the traditional complex dual-axis mobile tracking mechanism and adopts advanced tracking principles to greatly simplify the system composition. It constructs a new PAR-SDNSIM architecture consisting of SDRCFM and SRMS, which realizes the measurement of direct solar radiation spectrum without mobile tracking in all latitudes throughout the year, further improving the theoretical system of direct solar radiation spectrum measurement.

[0069] 2. The present invention constructs a time-space scale spectral radiation intensity reconstruction link consisting of a solar direct radiation spectrum matrix, a spectral distribution measurement matrix, and a spectral radiation intensity reconstruction matrix at a time-space scale, providing a new theoretical basis and practical method for ensuring the accuracy of solar direct radiation spectrum measurement.

[0070] 3. Starting from the slit energy and the corresponding RFUS angle, the present invention deeply analyzes the coupling effect of SDRCFM and SRMS, and accordingly selects a slit size of 25μm. The SRMS is optimized to achieve a spectral resolution better than 2nm in the 380nm-780nm spectral range within the full field of view, providing measurement conditions and technical guarantees for the accurate measurement of the direct solar radiation spectrum. BRIEF DESCRIPTION OF THE DRAWINGS

[0071] Figure 1 It is a schematic diagram of the overall process of the present invention;

[0072] Figure 2 The overall architecture and measurement principle diagram of the PAR-SDNSIM of the present invention;

[0073] Figure 3 This is a model diagram of the mapping between the incident angle of the direct sunlight beam and the mirror slope of the present invention;

[0074] Figure 4 Schematic diagram of the discrete and reconstructed SDRCFM of the present invention;

[0075] Figure 5 Reconstructing the link graph of the spatiotemporal scale spectral radiation intensity of the present invention;

[0076] Figure 6 This is the initial structure diagram of the SDRCFM of the present invention;

[0077] Figure 7 SDRCFM coefficient diagram of the present invention;

[0078] Figure 8The working optical path diagram of each incident angle of the present invention is as follows;

[0079] Figure 9 is a graph showing the illuminance distribution at various incident angles according to the present invention;

[0080] Figure 10 This is the maximum spot boundary diagram for each incident angle of the present invention;

[0081] Figure 11 The light spot profile and superimposed energy distribution diagram for all incident angles of the present invention;

[0082] Figure 12 is a relationship diagram of the slit size, passing energy and RFUS of the present invention;

[0083] Figure 13 It is the system structure diagram and local point diagram of the present invention;

[0084] Figure 14 This is the PAR-SDNSIM simulation model diagram of the present invention;

[0085] Figure 15 The spectral distribution diagram of direct solar radiation at each incident angle measured by the SRMS of the present invention;

[0086] Figure 16 Schematic diagram of the mean and standard deviation of the spectral radiation flux at each incident angle of the present invention;

[0087] Figure 17 For the present invention Contour map;

[0088] Figure 18 For the present invention Contour map;

[0089] Figure 19 The normalized standard AM1.5G solar spectrum and the reconstructed solar direct radiation spectrum distribution diagram of the present invention;

[0090] Figure 20 For different incident angles of the present invention and Maximum value diagram;

[0091] Figure 21 For the present invention distribution map;

[0092] Figure 22 This is a schematic diagram of the measurement results of the solar direct radiation spectrum of the present invention;

[0093] Figure 23 Schematic diagram of typical peak and trough wavelength spectrum measurement errors of the present invention. DETAILED DESCRIPTION

[0094] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0095] In order to solve the technical problems that the current measurement systems rely on expensive and complex dual-axis motion tracking devices, which have high maintenance costs, many transmission links and large errors, such as Figure 1-Figure 23 As shown, the following preferred technical solutions are provided:

[0096] 1. Design framework of polar-axis rotation solar direct radiation spectrum measurement system: The principle of polar-axis rotation solar direct radiation spectrum measurement mainly includes the overall architecture construction of the polar-axis rotation solar direct radiation spectrum measurement system (PAR-SDNSIM), the SDRCFM discretization and reconstruction method, and the spatiotemporal scale spectral radiation intensity reconstruction link.

[0097] 1. Build the overall architecture of PAR-SDNSIM:

[0098] The sun's motion can be accurately described by the solar altitude and azimuth. The solar azimuth varies within a range of ±90°. At noon on the vernal and autumnal equinoxes, the direct solar beam is perpendicular to the Earth's surface, and the incident angle of the direct solar beam at this time is defined as 0°. Therefore, the angle between the direct solar beam and the direct solar beam on the equinoxes caused by changes in the solar altitude does not vary by more than ±23.5°. Based on this principle, while using a polar rotation tracking device to offset changes in the solar azimuth, a free-form surface design can effectively reflect direct solar beams at different incident angles (hereinafter referred to as incident angles) into the spectral radiation measurement system (SRMS). This enables year-round, global, and global latitudinal measurements of direct solar radiation without requiring mobile tracking. The PAR-SDNSIM architecture is therefore divided into two components: the SDRCFM and the SRMS.

[0099] Based on the alignment and coupling issues between SDRCFM and SRMS, this method requires that the direct solar beam reflected by SDRCFM at noon on the equinox day is perpendicular to the incident beam at that time, and the reflected beam is used as the optical axis and rotation axis of SDRCFM. After comprehensive analysis of typical dispersion structures, SRMS uses a cross-Czerny-Turner dispersion structure. In this case, the overall architecture of PAR-SDNSIM is as follows: Figure 2 shown.

[0100] The PAR-SDNSIM is tilted according to the latitude of its installation location, ensuring that the SDRCFM optical axis passes perpendicularly through the SRMS slit. Light beams of varying incident angles are reflected and modulated by the SDRCFM surface, converging precisely on a tiny spot at the SRMS slit. The light beams passing through the slit then pass through the SRMS's collimating mirrors, diffraction grating, and focusing mirrors, forming diffraction lines on the CCD detector, thereby obtaining the spectral distribution of direct solar radiation.

[0101] 2. Discrete and reconstruction of SDRCFM:

[0102] SDRCFM controls the path of the direct sunlight beam after reflection by controlling the mirror slope on the free-form surface, so that the direct sunlight beam at noon of two to two minutes after reflection by SDRCFM converges to a point on the optical axis of SDRCFM, and establishes a mapping model between the incident angle of the direct sunlight beam and the mirror slope, as shown in the following example: Figure 3 As shown in the figure is the optical axis of the reflector, and the incident angle of the direct sunlight beam at noon on the summer solstice and winter solstice is and The angle between the direct sunlight beam at noon on the summer solstice and the SDRCFM optical axis after reflection is and , the SDRCFM mirror slope corresponding to the summer solstice and winter solstice is and , the SDRCFM mirror slope corresponding to the two-equinox day is , at this time, according to the geometric relationship, we can know is 45°, and The equation is as follows:

[0103] ;

[0104] The incident angle range of the direct sunlight beam Bring in and The equation of can be used to obtain the mirror slope required by SDRCFM, and the discrete and reconstruction model of SDRCFM is established based on it, such as Figure 4 As shown in the figure, the diameter of SDRCFM is , maximum working distance , the intersection of the two is the coordinate origin, and the length of the working part , the minimum axial working distance of the reflector is , SDRCFM is divided into area, then The coordinates of the discrete points are , each corresponding height is , the equation for SDRCFM is as follows:

[0105] ;

[0106] According to the equation of SDRCFM, a free-form reflective mirror structure of direct sunlight focusing composed of discrete points can be obtained. Since there are multiple continuous and non-differentiable points, the energy of the light beam will change suddenly after reflection. Therefore, a continuous and smooth SDRCFM surface is constructed by surface fitting.

[0107] 3. Time-space scale spectral radiation intensity reconstruction link:

[0108] Because SRMS measures the spectrum of direct solar radiation throughout the entire year across global latitudes, a link must be established that can reconstruct spectral radiation intensity on a spatiotemporal scale to compensate for deviations that occur during SRMS measurements at different incident angles. Since SDRCFM utilizes the reflection principle to modulate energy only, it lacks spectral selectivity. Furthermore, according to the SRMS measurement principle, the peak wavelength positions of the diffraction spectra formed on the CCD detector at different incident angles of the direct solar beam are consistent, indicating that the peak wavelength distribution of the diffraction spectra is spatiotemporally consistent. Furthermore, the incident angle of the direct solar beam varies minimally throughout the day (0.13°), and changes in the incident angle can be ignored within a single-day measurement period. Therefore, this method uses the incident angle of the direct solar beam as the reference for reconstructing spectral radiation intensity on a spatiotemporal scale.

[0109] Assume the incident angle is , assuming that the peak wavelength of the discrete spectrum of the diffraction line collected by the CCD detector is For the sake of convenience, it is assumed that the spectrum distribution of direct solar beams at different incident angles is consistent, then the direct solar radiation spectrum matrix is , this time is different The corresponding direct solar radiation spectrum matrix can be expressed as ,in At the incident angle In this case, the radiation flux corresponding to the peak wavelength of the diffraction line spectrum.

[0110] Assume that the incident angle that can be measured and resolved in SRMS is , then the spectral distribution measurement matrix can be expressed as , the solar direct radiation spectrum matrix in the time and space scale can be expressed as , in order to facilitate the characterization of Take the reciprocal of each element in and get the matrix , at this time, the equation of the spectral radiation intensity reconstruction matrix in the time and space scale is:

[0111] ;

[0112] According to the matrix data form and regression analysis, the spectral radiation intensity reconstruction of continuous incident angles is obtained, thereby realizing the spatiotemporal scale spectral radiation intensity reconstruction link. The specific situation is as follows Figure 5 shown.

[0113] 2. PAR-SDNSIM Optimization Design:

[0114] 1. SDRCFM design and performance evaluation:

[0115] Since free-form surfaces do not fully comply with the edge ray principle in the field of traditional non-imaging optics, and the World Meteorological Organization stipulates that the semi-opening angle for direct solar radiation measurement is 2.5°, a light cone with an incident angle of ±23.5°, ±20°, ±16°, ±12°, ±8°, ±4° and 0° and a cone vertex angle of 5° is selected as the sampling beam in the design of SDRCFM. Since SRMS requires that the field of view of the incident beam should not be too large, SDRCFM needs to maintain a suitable working distance from SRMS. For this purpose, Set to 350mm, according to and The equations of and SDRCFM are used to iteratively obtain the initial structural parameters of SDRCFM. The specific parameters are as follows Figure 6 shown.

[0116] This method proposes a set of performance evaluation criteria for comprehensively evaluating the SDRCFM's ability to control direct solar beams at all latitudes based on radiative flux uniformity at spatiotemporal-scales (RFUS) and spot overlap degree (SOD). The specific equations are as follows:

[0117] ;

[0118] The maximum and minimum irradiance of the spot at each incident angle are: and , the minimum boundaries of the light spot at each incident angle on the x-axis and y-axis are and , the maximum boundary is and .

[0119] By controlling the incident angle of SDRCFM, the discrete number , sampling XY polynomial to iteratively optimize and reconstruct SDRCFM, the optimized SDRCFM vertex curvature radius The cone coefficient is 0.008413. is -1.3201, and the face expression equation is as follows:

[0120] ;

[0121] In the formula for The coefficient of the term, superscript and Representing variables , The order of SDRCFM is as follows: Figure 7 shown.

[0122] The optimized SDRCFM reflected beam path, the illumination distribution at each incident angle after reflection, the spot shape profile, the maximum spot boundary, the spot shape at each incident angle after reflection and the superimposed energy distribution are as follows: Figures 8-11 As shown in Figure 2, the maximum convergence angle of the reflected beam of the optimized SDRCFM is 8.567°, and the RFUS is 85.03%. is 25.12%. Although the overlap is average, Figure 11 It can be clearly seen that the reflected light beams at all incident angles have an obvious spot area intersection and energy concentration area, so it is possible to achieve the function of converging light beams at all incident angles.

[0123] 2. SRMS design and performance evaluation:

[0124] SDRCFM has modulated the incident angles of all direct solar beams together. In order to achieve efficient coupling between SRMS and SDRCFM, this method simulates the energy entering the slit and the corresponding RFUS by changing the slit width, and selects the slit width based on this. The simulation results are shown in Figure 2. Figure 12 As shown in the figure, it can be obtained that the slit width is positively correlated with the passing energy. There is a more obvious slope mutation when the width is 25μm, and then the energy increase effect brought by the increase in slit width is weakened. The slit width is negatively correlated with RFUS. As the slit width increases, the RFUS weakening effect gradually weakens. Due to the influence of the slit width on the contrast and spectral resolution of SRMS, the slit width is set to 25μm.

[0125] The 380nm-780nm operating spectrum was selected to validate this method. The sensor used was a TCD1304 linear array CCD with an effective image plane size of 29.184mm. To ensure that the SRMS could receive the entire SDRCFM reflected beam, the SRMS incident angle was set at 14°. The grating diffraction equation is as follows:

[0126] , m=0, ±1, ±2..., N-1;

[0127] Where d is the grating period, is the incident wavelength, m is the diffraction order of the grating diffraction equation, and are the incident angle and the diffraction angle of the corresponding diffraction order m, N is the number of grating lines, and the expression equation of the grating color resolution is as follows:

[0128] ;

[0129] In order to achieve that the center of the diffraction order of two different wavelengths is larger than the half-width angle of the grating diffraction order, the grating line number is selected to be 600l / mm, and the grating incident diffraction angle is set to The grating incident angle is 30°, and the grating equation solution is used to obtain the grating incident angle. The grating diffraction angle is 25.74° is 4.26°, and the performance indicators of the optimized SRMS system are as follows Figure 13 As shown in Figure 3, the spectral resolution of SRMS is better than 2 nm at all incident angles.

[0130] 3. Spectral radiation intensity reconstruction and solar spectrum measurement accuracy assessment:

[0131] 1. Spectral radiation intensity reconstruction matrix simulation:

[0132] According to the design results of SDRCFM and SRMS, a complete PAR-SDNSIM simulation model is established to obtain ,like Figure 14 As shown in the figure, each incident angle has the same spectral distribution (equal energy spectrum) and radiation flux (10W). Using the Monte Carlo ray tracing method, the relative error of the simulation is within 2% when each incident angle reaches 5 million. At this time, the spectral distribution of direct solar radiation at each incident angle measured by SRMS is as follows: Figure 15 As shown in the figure, the spectral distribution of each incident angle has slight fluctuations and differences, and the trend is similar to the isoenergetic spectrum, but the energy value has a large difference. This is because the spot distribution on the SRMS slit is not completely consistent at different incident angles of the direct solar beam. Therefore, the standard deviation of the spectral radiation flux can be used. The spectral fluctuations at each incident angle are characterized by the following formula:

[0133] ;

[0134] Where, The angle of incidence is When SRMS measures the spectral radiation flux corresponding to the wavelength, The mean and standard deviation of the spectral radiant flux at each incident angle are as follows: Figure 16 As shown in the figure, the mean and standard deviation of the spectral radiation flux at each incident angle are different, and there is no obvious statistical regularity. It is difficult to obtain the reconstruction regularity for each incident angle based on a specific parameter or a simple mathematical model. Therefore, in order to ensure the measurement accuracy of the spectral radiation intensity of SDRCFM, this method is based on the spectral radiation intensity reconstruction matrix equation under the time and space scale, and then the spectral radiation intensity reconstruction regularity for each incident angle is obtained through multiple regression analysis. and The contour map of Figure 17 and Figure 18 shown.

[0135] 2. Accuracy assessment of direct solar radiation spectrum measurement:

[0136] The incident spectrum distribution in the PAR-SDNSIM working scenario simulation model is set to the standard AM1.5G solar spectrum in the visible light range, and the radiation flux is set to a solar constant (1367W). The spectral distribution of direct solar radiation at each incident angle after spectral radiation intensity reconstruction can be obtained. In order to facilitate the evaluation of the measurement error of the direct solar radiation spectrum, it is normalized according to the spectral integrated energy to obtain the normalized standard AM1.5G solar spectrum and the reconstructed direct solar radiation spectrum distribution as shown in the figure. Figure 19 shown.

[0137] according to Figure 19 It can be seen that the spectral distribution after reconstruction at each incident angle is very close to the standard AM1.5G solar spectrum distribution, but the overall area and details are different. In order to evaluate the measurement error of the direct solar radiation spectrum, the spectral curve area error is developed. and spectral radiant flux error , the specific formula is as follows:

[0138] ;

[0139] ;

[0140] Where, and They are the normalized standard AM1.5G and the reconstructed solar spectrum radiation flux. The maximum value of the sum of different solar direct beam incident angles is as follows: Figure 20 As shown, it can be seen that the The distribution ranges from 0.68% to 1.22%. The reconstructed solar direct radiation spectrum is basically consistent with the standard AM1.5G solar spectrum. The maximum value is 9.16% and the minimum value is -6.6%, which occur at incident angles of 23.5° and -23.5°, indicating that the edge field measurement performance of PAR-SDNSIM is slightly poor.

[0141] In order to evaluate the measurement results throughout the year, the average error of the spectral curve area is introduced and the average error of spectral radiation flux , the formula is as follows:

[0142] ;

[0143] according to Figure 20 It can be seen that is 0.95%. Figure 21 As shown, it can be seen that the 95% probability is between -0.17% and 2.07%, and the 90% probability is between -0.11% and 1.93%. The average errors of 404nm, 408nm and 532nm are -0.63%, 2.59% and 2.54% respectively.

[0144] 4. Analysis of experimental results:

[0145] according to Figure 22 As shown in Figure 2, the PAR-SDNSIM designed by this method can measure the direct solar radiation spectrum of 380nm-780nm without mobile tracking, and the measurement results have detailed characteristics of the direct solar radiation spectrum, such as Figure 23 As shown in the figure, the spectral measurement errors of the typical peak and trough wavelengths (392nm, 482nm, 506nm, 518nm, 540nm, 590nm, 656nm, 688nm, 720nm and 760nm) that can reflect the details of the solar spectrum are as follows. Although the weather is changeable, cloud thickness and aerosols will affect the changes in the direct solar radiation spectrum, resulting in slight differences in each measurement result, the above measurement method makes the measurement results consistent with the typical peaks and troughs of the standard AM1.5G solar spectrum, and the wavelength error does not exceed ±4nm, indicating that the designed PAR-SDNSIM has good spectral measurement accuracy and detail measurement capabilities. Figure 23 In the Chinese, 7-29 refers to July 29; 7-30 refers to July 30; and 7-31 refers to July 31.

[0146] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus.

[0147] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for measuring direct solar radiation spectrum, characterized in that: The specific steps are as follows: S1: Design a framework for a polar-rotating solar direct radiation spectrum measurement system; S2: PAR-SDNSIM optimization design; S3: Spectral radiation intensity reconstruction and solar spectrum measurement accuracy assessment; S4: Experimental results analysis; The framework for designing a polar-rotating solar direct radiation spectrum measurement system as described in S1 is as follows: S101: Build the overall architecture of PAR-SDNSIM; S102: Discretization and reconstruction of SDRCFM; S103: Time and space scale spectral radiation intensity reconstruction link; The specific steps for building the PAR-SDNSIM overall architecture described in S101 are as follows: S1011: Using a polar-axis rotation tracking device to offset changes in the solar azimuth angle, and designing a free-form surface that can reflect direct solar beams of varying incident angles into the SRMS, the overall architecture of the constructed PAR-SDNSIM is divided into two parts: the SDRCFM and the SRMS. S1012: The direct sunlight beam at noon on the equinox day reflected by the SDRCFM is perpendicular to the incident beam at that time, and the reflected beam serves as the optical axis and rotation axis of the SDRCFM; S1013: Analyze typical dispersion structures, and use a cross-type Czerny-Turner dispersion structure for SRMS; S1014: The PAR-SDNSIM is tilted according to the latitude of its installation location, and the SDRCFM optical axis passes perpendicularly through the slit position of the SRMS. Light beams of different incident angles are reflected and modulated by the SDRCFM surface and converge on the light spot area at the slit position of the SRMS. After that, the light beams passing through the slit pass through the collimating reflector, diffraction grating, and focusing reflector of the SRMS, forming diffraction spectrum lines on the CCD detector, thereby obtaining the spectral distribution information of direct solar radiation.

2. A method for measuring direct solar radiation spectrum according to claim 1, characterized in that: The PAR-SDNSIM optimization design described in S2 is as follows: S201: SDRCFM Design and Performance Evaluation; S202: SRMS design and performance evaluation.

3. A method for measuring direct solar radiation spectrum according to claim 2, characterized in that: The specific steps of spectral radiation intensity reconstruction and solar spectrum measurement accuracy evaluation described in S3 are as follows: S301: Spectral radiation intensity reconstruction matrix simulation; S302: Accuracy assessment of direct solar radiation spectrum measurement.

4. A method for measuring direct solar radiation spectrum according to claim 3, characterized in that: The specific steps for the discretization and reconstruction of SDRCFM described in S102 are as follows: S1021: SDRCFM controls the mirror slope of the free-form surface to regulate the path of the direct sunlight beam after reflection, so that the direct sunlight beam at noon of two to two minutes after reflection by SDRCFM converges to a point on the optical axis of SDRCFM, and establishes a mapping model between the incident angle of the direct sunlight beam and the mirror slope. S1022: The incident angle of the direct sunlight beam at noon on the summer solstice and winter solstice is α S and α N The angle between the direct sunlight beam at noon on the summer solstice and the SDRCFM optical axis after reflection is θ S and θ N , the SDRCFM mirror slope corresponding to the summer solstice and winter solstice is γ S and γ N , the SDRCFM mirror slope corresponding to the two-equinox day is γ O , γ S and γ N The equation is as follows: S1023: Set the incident angle range of the direct sunlight beam to [-α S ,α N ]Substitute into γ S and γ N The equation of can be used to obtain the mirror slope required by SDRCFM and establish the discrete and reconstruction model of SDRCFM; S1024: The diameter of SDRCFM is D, the maximum working distance is L, the intersection of the two is O as the coordinate origin, the length of the working part is L1, the minimum axial working distance of the reflector is L2, the SDRCFM is divided into m areas according to the direct solar radiation incident angle range, and the coordinates of the i-th discrete point are I i (x i ,y i ), each corresponding height is d i , the equation for SDRCFM is as follows: S1025: The free-form reflective mirror structure of direct sunlight focusing composed of discrete points is obtained through the SDRCFM equation, and a continuous and smooth SDRCFM surface is constructed through surface fitting.

5. A method for measuring direct solar radiation spectrum according to claim 4, characterized in that: The specific steps of the spatiotemporal scale spectral radiation intensity reconstruction link described in S103 are as follows: S1031: Using the incident angle of the direct solar beam as the reference for reconstructing the spectral radiation intensity in time and space, let the incident angle be α, and let the peak wavelengths of the discrete spectrum of the diffraction line collected by the CCD detector be λ1, λ2...λ n , assuming that the spectrum distribution of direct solar beams at different incident angles is consistent, the solar direct radiation spectrum matrix is The solar direct radiation spectrum matrix corresponding to different α can be expressed as in is the radiation flux corresponding to the peak wavelength of the diffraction line spectrum at the incident angle α; S1032: Assume that the incident angles that can be measured and resolved in SRMS are α1, α2, ..., α m , the spectral distribution measurement matrix can be expressed as Φ spatio-temporal =[Φ(α1) Φ(α2) … Φ(α m )] n×m , the solar direct radiation spectrum matrix in the time and space scale can be expressed as S spatio-temporal =[SS … S] n×m , S spatio-temporal Take the reciprocal of each element in and get the matrix S spatio-temporal-inverse , the equation of the spectral radiation intensity reconstruction matrix in the time and space scale is as follows: M spatio-temporal =Φ spatio-temporal ⊙S spatio-temporal-inverse ; S1033: Perform regression analysis on the spectral radiation intensity reconstruction matrix at the time and space scales, and implement the spectral radiation intensity reconstruction link at the time and space scales.

6. A method for measuring direct solar radiation spectrum according to claim 5, characterized in that: The specific steps for SDRCFM design and performance evaluation described in S201 are as follows: S2011: Select the light cone with incident angles of ±23.5°, ±20°, ±16°, ±12°, ±8°, ±4° and 0° and a 5° apex angle as the sampling beam for SDRCFM design, and L is 350mm. According to γ S and γ N The equations of and the equations of SDRCFM are used to iteratively obtain the initial structural parameters of SDRCFM; S2012: The SDRCFM's ability to control direct solar beams at all latitudes was comprehensively evaluated using irradiance uniformity and spot overlap at both temporal and spatial scales. The specific equations are as follows: Where E max is the maximum irradiance of the light spot at each incident angle; E min is the minimum irradiance of the light spot at each incident angle; the minimum boundary of the light spot at each incident angle on the x-axis and y-axis is r x-min and r y-min , the maximum boundary is r x-max and r y-max ; S2013: By controlling the discrete number m of incident angles of SDRCFM, the XY polynomial is used to iteratively optimize and reconstruct the SDRCFM. After optimization, the vertex curvature radius c of the SDRCFM is 0.008413, and the cone coefficient k is -1.3201. The obtained surface expression equation is as follows: Where B i,j is x i y j The coefficient of the term, superscript i and j indicate the order of the variables x and y; The specific steps for SRMS design and performance evaluation described in S202 are as follows: S2021: The wavelength of direct solar radiation covers 280nm-3000nm, of which 50% of the solar radiation energy is concentrated in the visible spectrum region of 380nm-780nm. The 380nm-780nm range is selected as the working spectrum for verification. The SRMS incident angle is set to 14°. The grating diffraction equation is as follows: d(sinθ i ±sinθ d )=mλ; S2022: Calculate the grating color resolution. The specific equation is as follows: Where d is the grating period, λ is the incident wavelength, m is the diffraction order of the grating diffraction equation, and θ i and θ d are the incident angle and the diffraction angle of the corresponding diffraction order m, respectively, and N is the number of grating lines; S2023: Select the grating line number 600l / mm, set the grating incident diffraction angle φ to 30°, and obtain the grating incident angle θ based on the grating diffraction equation i is 25.74°, and the grating diffraction angle θ d It is 4.26°.

7. A method for measuring direct solar radiation spectrum according to claim 6, characterized in that: The specific steps of the spectral radiation intensity reconstruction matrix simulation described in S301 are as follows: S3011: Use the standard deviation σ of the spectral radiation flux wavelength (α) Characterizes the spectral fluctuations at each incident angle. The specific equation is as follows: Where E(α, λ i ) is the spectral radiation flux corresponding to the wavelength measured by SRMS when the incident angle is α, represents the mean spectral radiation flux at each incident angle, and n is the number of peak wavelengths measured by SRMS; S3012: Reconstruct the matrix equation of spectral radiation intensity based on the time and space scale in S1032 spatio-temporal Based on the M spatio-temporal ,Through multiple regression analysis, the reconstruction rules of the ,spectral radiation intensity at each incident angle are obtained.

8. The method for measuring direct solar radiation spectrum according to claim 7, characterized in that: The specific steps for evaluating the solar direct radiation spectrum measurement accuracy described in S302 are as follows: S3021: Set the incident spectral distribution to the standard AM1.5G solar spectrum in the visible light range, and the radiant flux to a solar constant. spatio-temporal The spectral distribution of direct solar radiation at each incident angle can be obtained after spectral radiation intensity reconstruction, and normalized according to the spectral integrated energy to obtain the normalized standard AM1.5G solar spectrum and the reconstructed direct solar radiation spectrum; S3022: Spectral curve area error RSE is established area and spectral radiation flux error RSE wavelength , the specific equation is as follows: Where E Standard-AM1.5G (λ i ) and E Post-Reconstruction-AM1.5G (α, λ i ) are respectively the normalized standard AM1.5G and the reconstructed solar spectrum radiation flux; S3023: Introducing the spectral curve area average error RSEA area and the average error of spectral radiation flux RSEA wavelength , the specific equation is as follows:

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