Polar axis rotation type solar direct radiation spectrum measurement system and method

Abstract

The invention discloses a polar axis rotation type solar direct radiation spectrum measurement system and method, and belongs to the technical field of solar radiation measurement, the system comprises a solar direct radiation focusing free-form surface reflecting mirror and a solar spectrum measurement optical system, the effective reflection focusing half angle of the reflecting mirror is 2.5 degrees, and the effective reflection focusing half angle of the reflecting mirror is 2.5 degrees. A 52-degree * 5-degree field-of-view direct light beam can be converged to a system slit, and the system is constructed and optimized based on a polar axis principle, so that the irradiance uniformity and the light spot overlap ratio are ensured. The spectral measurement system adopts a crossed Czerny-Turner structure, the working spectrum band is 380-780 nm, and the spectral resolution is lt; the RMS radius is 1t, 2nm; 6 [mu] m; the system further comprises a self-adaptive sampling space-time spectrum radiation intensity reconstruction link, errors are compensated through uniform and dynamic sampling, the WMO requirement is met, the global latitude does not need to be frequently aligned and tracked all year round, the measurement precision is high, and the reliability is high.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of solar radiation measurement, in particular to a polar axis rotation type solar direct radiation spectrum measurement system and method. BACKGROUND

[0002] High-precision measurement of solar direct radiation spectrum is a scientific cornerstone for the study of surface energy budget and climate system, and its observation data has important application value in the fields of atmospheric composition analysis, climate change modeling, agricultural photosynthesis efficiency evaluation and solar energy resource development.

[0003] Early single-axis tracking devices are widely used due to their simple structure and low cost, but as the measurement accuracy requirements increase, the dual-axis tracking system, which can more accurately simulate the solar motion trajectory, has gradually become the mainstream. However, the dual-axis tracking system has problems such as high control difficulty, high maintenance cost and complex error transmission. The polar axis rotation tracking device has developed, such as the MS series of solar sunshine hour measurement systems of the EKO company in Japan, but it has defects such as limited working latitude interval and inability to accurately control the light spot using the diffuse reflection principle.

[0004] In the field of solar direct radiation spectrum measurement, although researchers have made certain achievements, such as the related systems developed by the CIMEL company in France, the PREDE company in Japan, the World Radiation Center (WRC) in Switzerland and some domestic research institutions, most of these systems cannot fully meet the requirement of the World Meteorological Organization (WMO) that a 2.5° solar half-opening angle should be considered in solar direct radiation measurement. Although some systems have improved the tracking method or optical design to some extent, there are still deficiencies in light spot control, integration with the spectrometer system and measurement accuracy, and they cannot achieve the measurement of solar direct radiation spectrum without frequent alignment tracking in the global latitude range required by WMO.

[0005] Therefore, there is an urgent need for a polar axis rotation type solar direct radiation spectrum measurement system and method that can meet the requirements of the World Meteorological Organization for a 2.5° solar half-opening angle, and has high measurement accuracy, wide latitude adaptability and does not require frequent alignment tracking. SUMMARY

[0006] The purpose of the present application is to provide a polar axis rotation type solar direct radiation spectrum measurement system and method, which solves the problem that the existing solar direct radiation spectrum measurement system cannot fully meet the requirements of the World Meteorological Organization for the solar opening angle, and the tracking method in the prior art is complex, the measurement accuracy is insufficient, and the integration with the spectrometer system is poor.

[0007] The present application solves the above technical problems by the following technical solutions: A polar-axis rotating solar direct radiation spectral measurement system is provided, comprising a solar direct-focusing freeform surface mirror and a solar spectral measurement optical system. The solar direct-focusing freeform surface mirror has an effective reflection and focusing angle range of 2.5° for direct solar light, which can reflect and converge a 52°×5° field of view of direct solar light to the slit position of the solar spectral measurement optical system. The solar spectral measurement optical system adopts a cross-type Czerny-Turner optical path structure for splitting and detecting the converged beam to obtain solar direct radiation spectral information.

[0008] Furthermore, the solar direct-focusing freeform surface reflector includes an initial structural construction and performance optimization. The initial structural construction is based on the polar axis measurement principle, using an off-axis hyperbola with perfect aberration-free conjugate points as the base curve. Through segmented discretization and splicing, a solar direct-focusing base curve is constructed in the 52° field-of-view plane. This base curve is then rotated around a 5° field-of-view direction to extend it into three-dimensional space. The performance optimization focuses on the uniformity of solar direct irradiance at multiple angles. Overlap with the area of ​​direct sunlight spots from multiple angles The evaluation metrics are iteratively optimized.

[0009] Furthermore, the radius of curvature at the vertex of the optimized solar direct-focusing freeform surface mirror was further optimized. 2.34×10 -2 Conic coefficient The value is -1.28, and the face shape expression is... In the formula for The coefficients of the terms; the superscripts i and j indicate the order of the variables x and y.

[0010] Furthermore, the uniformity of the multi-angle direct solar irradiance The calculation formula is: ,in, The maximum irradiance of the light spot across all incident angles. The minimum irradiance of the light spot across all incident angles; the overlap of the areas of the multi-angle direct sunlight spot. The calculation formula is: ,in, This represents the area of ​​intersection of all incident light spots. This represents the area of ​​the union of all incident angle light spots.

[0011] Furthermore, the solar spectrum measurement optical system includes a slit and a collimating mirror arranged sequentially. Radiant grating Focusing mirror and CCD detector; the light beam reflected and converged by the solar direct focusing freeform surface mirror passes through the slit and then sequentially through the collimating mirror. Collimation, blazed grating Beam-splitting and focusing mirrors The light is focused, eventually forming diffraction lines on the CCD detector.

[0012] Furthermore, the working spectrum of the solar spectrum measurement optical system is 380nm-780nm, with a spectral resolution of less than 2nm. Throughout the entire working band, the RMS radius along the Y direction remains below 6μm, which is smaller than the single pixel size of the Toshiba TCD1304 linear CCD used, which is 8μm.

[0013] Furthermore, it also includes a spatiotemporal scale spectral radiance reconstruction link based on an adaptive sampling strategy, used to compensate for measurement errors in the direct solar radiation spectrum; The adaptive sampling strategy combines uniform sampling and dynamic sampling. Uniform sampling is performed first, and when the relative error of the radiation area of ​​the reconstructed spectrum exceeds a set threshold, dynamic encrypted sampling is performed in the low-precision region.

[0014] Furthermore, in the spatiotemporal scale spectral radiance reconstruction link based on the adaptive sampling strategy, let the incident angle of the direct beam be... , To sample the number of incident angles, the wavelength of the collected spectral peaks is... , The wavelength channel number is [value], and the multi-angle measurement spectral matrix is ​​[value]. Each column corresponds to the measured spectral data for one incident angle, and the corresponding standard AM1.5G direct solar radiation spectral vector is... Then the spectral reconstruction factor It can be represented as: Each wavelength The spectral reconstruction factor can be fitted as a k-th order polynomial: In the formula, If the coefficients are polynomials, then the reconstructed spectrum can be expressed as: The relative error of the radiative area of ​​the sampled reconstructed spectrum is: .

[0015] Furthermore, the adaptive sampling strategy includes uniform sampling at light source incident angles of ±23.5°, ±16°, ±8°, and 0°, evaluating errors at 2° intervals, and performing dynamic encrypted sampling in the range of -22° to -16° when the relative error of the radiant area of ​​the reconstructed spectrum exceeds ±1%.

[0016] Furthermore, a polar-axis rotating method for measuring direct solar radiation spectra is provided, comprising the following steps: S1: Receives a 52°×5° field of view of direct sunlight through a freeform surface mirror for direct solar focusing, and reflects and converges it to the slit position of the solar spectrum measurement optical system; S2: The converged beam enters the solar spectrum measurement optical system through the slit, and then passes through the collimating mirror in sequence. Radiant grating and focusing mirror Diffraction lines are formed on the CCD detector to obtain the initial solar direct radiation spectrum information; S3: The initial solar direct radiation spectrum information is processed by the spatiotemporal scale spectral radiance intensity reconstruction link based on an adaptive sampling strategy to compensate for measurement errors and obtain the final solar direct radiation spectrum.

[0017] Beneficial effects:

[0018] 1. In the polar axis rotating solar direct radiation spectral measurement system of the present invention, the solar direct focusing freeform surface reflector can meet the WMO requirement of 2.5° solar semi-open angle.

[0019] 2. This invention adopts a polar axis rotational architecture, which realizes direct solar radiation spectrum measurement without alignment and tracking throughout the year in a global latitude range. It is easy to operate and highly adaptable.

[0020] 3. The solar spectrum measurement optical system of the present invention adopts a cross-type Czerny-Turner optical path structure, with a working spectral range of 380nm-780nm and a spectral resolution of less than 2nm. The overall spectral measurement accuracy in the 380nm-780nm range is maintained between -0.98% and 0.29%, and the spectral measurement error corresponding to the wavelength is between -4.09% and 5.46%, indicating high measurement accuracy.

[0021] 4. The spatiotemporal scale spectral radiance reconstruction link based on the adaptive sampling strategy of this invention can effectively compensate for measurement errors and further improve the accuracy of spectral measurements.

[0022] 5. The solar direct radiation spectrum measured by this invention matches well with the typical peaks and troughs of the AM1.5G standard solar spectrum, with wavelength error controlled within ±3nm, demonstrating reliable performance. Attached Figure Description

[0023] Figure 1 This is a schematic diagram illustrating the overall architecture and measurement principle of the polar-axis rotating solar direct radiation spectral measurement system of the present invention; Figure 2 This is a schematic diagram of the basic curve construction model for direct solar focusing in this invention; Figure 3 This is a segmented discrete model diagram of the basic curve for direct solar focusing in this invention; Figure 4 This is a diagram of the optical path reconstruction model based on the solar direct focusing curve of the present invention; Figure 5 This is a model diagram of the splicing between micro-elements of the adjacent solar direct focusing basic curve of the present invention; Figure 6 This is a schematic diagram of the simulation results of the initial structure performance of the solar direct focusing freeform surface reflector of the present invention; Figure 7 This is a simulation result of the performance of the solar direct focusing freeform surface reflector of the present invention after the initial structural performance has been extended; Figure 8 The figure shows the simulation results of the optimized solar direct focusing freeform surface reflector of this invention. Figure 9 This is a schematic diagram of the solar spectrum measurement optical system of the present invention; Figure 10 This is a schematic diagram showing the relationship between the RMS spot size and wavelength in the Y direction of the solar spectrum measurement optical system of the present invention. Figure 11 This is a light trail diagram of the solar spectrum measurement optical system of the present invention; Figure 12 This is a schematic diagram illustrating the principle of spatiotemporal scale spectral radiance reconstruction based on an adaptive sampling strategy of the present invention. Figure 13 The diagram shows a simulation model of the solar direct radiation spectrum measurement system based on a freeform surface, which is used to reconstruct the uniform sampling spectrum of this invention. Figure 14 This is a schematic diagram illustrating the measurement accuracy of the uniform sampling spectral reconstruction results of the present invention; Figure 15 This is a scatter plot showing the distribution of spectral measurement errors corresponding to the wavelengths of direct solar radiation in this invention. Figure 16 The spectral measurement error distribution corresponding to the wavelength of direct solar radiation in this invention is for each solar incidence angle. A diagram illustrating the average and maximum values; Figure 17 This is a schematic diagram of the typical peak and trough wavelength spectral deviations of the present invention; Figure 18 This is a schematic diagram of the measurement results on the first day of this embodiment of the invention; Figure 19 This is a schematic diagram of the measurement results on the second day of an embodiment of the present invention; Figure 20 This is a schematic diagram of the measurement results on the third day of an embodiment of the present invention. Detailed Implementation

[0024] likeFigure 1 As shown, this embodiment provides a polar-axis rotating solar direct radiation spectral measurement system, which mainly consists of three parts: a solar direct-focusing freeform surface mirror, a solar spectral measurement optical system, and a spatiotemporal scale spectral radiance intensity reconstruction link based on an adaptive sampling strategy. The solar direct-focusing freeform surface mirror is responsible for receiving the solar direct beam within a 52°×5° field of view and focusing it onto a specific region; the solar spectral measurement optical system performs spectral dispersion and detection on the focused beam, outputting the original spectral signal; the reconstruction link processes the original signal to ultimately obtain high-precision solar direct radiation spectral data.

[0025] In this embodiment, the solar spectrum measurement optical system adopts a cross-type Czerny-Turner optical path structure. To ensure precise coupling between the solar direct-focusing freeform surface mirror and the solar spectrum measurement optical system, the incident beams at noon on the spring and autumn equinoxes must be perpendicular to the reflected beams from the solar direct-focusing freeform surface mirror, with the reflected beams serving as the optical axis and rotation axis of the freeform surface. The position and orientation of the solar direct-focusing freeform surface mirror are adjusted according to the latitude and longitude of the installation site, reflecting beams from different incident angles and converging them into a tiny spot area at the slit position of the solar spectrum measurement optical system. Subsequently, the beams passing through the slit sequentially pass through the collimating mirror of the solar spectrum measurement optical system. Radiant grating and focusing mirror The diffraction lines formed on the CCD detector are then used to obtain the direct solar radiation spectrum information.

[0026] The construction and optimization process of the solar direct-focusing freeform surface reflector in this application is based on the polar axis measurement principle. It uses an off-axis hyperbola with perfect, aberration-free conjugate points as the base curve. By segmenting, discretizing, and stitching the hyperbola into segments, the direct solar beam is converged and modulated on the 52° field-of-view plane, thus completing the construction of the basic solar direct-focusing curve (a two-dimensional curve). Based on this, the basic solar direct-focusing curve is rotated (extending from a two-dimensional plane to three-dimensional space) for a 5° field-of-view direction, reflecting and converging all the direct solar beams from the 52°×5° field of view onto the receiving surface, forming the initial structure of the solar direct-focusing freeform surface reflector.

[0027] Since the focused spot image from the freeform surface mirror is an irregular polygon, and considering the integration with the solar spectral measurement optical system and the influence of the time dimension, the evaluation metric for the optimization part is set as the uniformity of direct solar irradiance from multiple angles. Overlap with the area of ​​direct sunlight spots from multiple angles , and The specific formula is as follows: (1), (2), where the maximum and minimum irradiance of the light spot at all incident angles are respectively and . This represents the area of ​​intersection of all incident angle light spots; This represents the area of ​​the combined spot of all incident angle beams. Based on this, the initial structure of the solar direct focusing freeform surface mirror was further optimized to ensure that the solar direct focusing freeform surface mirror can reflect and converge all solar direct beams in a 52°×5° field of view to the solar spectral measurement optical system, thus completing the optimization of the solar direct focusing freeform surface mirror.

[0028] Therefore, the construction and optimization process of the solar direct-focusing freeform surface mirror can be divided into two parts: initial structure construction and performance optimization. The mathematical model of the solar direct-focusing basic curve is based on the basic hyperbola mathematical model but undergoes an off-axis transformation. To obtain the off-axis angle of the off-axis hyperbola, considering the symmetry of the freeform surface-based solar direct radiation spectral measurement system, we assume that the principal ray of the solar direct beam with an incident angle of 0° is perpendicular to its reflected ray and passes perpendicularly through the center of the slit. The reflected ray at this point is taken as the rotation axis of the solar direct-focusing freeform surface mirror. The angle between the real axis of the solar direct-focusing basic curve before and after the rotation is denoted as the off-axis angle of the off-axis hyperbola. , can be represented as (3) , in the formula It is the point where the direct sunlight converges, and it is always the first focus of the hyperbola before and after rotation; It is the second focus of the hyperbola before rotation; This is the second intersection point of the hyperbola after rotation; The point where the principal ray of the direct sunlight beam at 0° field of view intersects with the rotated hyperbola; Let be the optical axis and rotation axis of the freeform surface mirror that focuses direct sunlight. Let D be the working distance of the freeform surface reflector for direct solar focusing. Based on this, a basic curve construction model for direct solar focusing is constructed as follows: Figure 2 As shown. Figure 2 In the middle, the height of the freeform surface reflector for direct solar focusing Width of freeform surface reflector for direct solar focusing It can be represented as (4), in the formula, and These represent the vertical and horizontal distances between the principal ray of a direct solar beam with an incident angle of -23.5° to +23.5° and the intersection point of the rotated hyperbola, respectively. and These are the lengths of the reflected light rays corresponding to incident angles of -23.5° and +23.5°, respectively. and The corresponding receiving fields of view are -23.5° and +23.5° incident angles, respectively.

[0029] This invention divides the solar direct focus baseline curve into several micro-elements based on the field of view. Then, by changing the position and size of these micro-elements, a solar direct focus baseline curve with good spatiotemporal uniformity is constructed. A piecewise discrete model of the solar direct focus baseline curve is established as follows: Figure 3 As shown.

[0030] Figure 3 In the middle, the sequence 1~n corresponds to the principal rays of the direct sunlight with incident angles of -23.5°~+23.5°. Indicates the angle of direct sunlight; Indicates the angle between the incident ray and the reflected ray; The off-axis angle of the fundamental element of the direct solar focusing curve is the angle between the tangent at the center of the sub-mirror element and the optical axis; perpendicular to the angle... Normal; Let be the angle between the reflected ray and the optical axis, which is the receiving field of view of the sensor. The geometric relationship can be expressed as: (5) To ensure good spatiotemporal uniformity of the solar direct focusing baseline curve, the optical path lengths corresponding to each field of view should be as equal as possible. Based on this, an optical path reconstruction model for the solar direct focusing baseline curve should be established, such as... Figure 4 As shown. Figure 4 The optical path reconstruction model based on the fundamental curve of direct solar focusing, with the principal ray having the same optical path expression as follows: (6), in formula (6), The angle of incidence of direct solar radiation is . Incident optical path at time; The angle of incidence of direct solar radiation is . The output optical path at that time.

[0031] After equal optical path modulation, there will be some gaps and overlaps between adjacent solar direct focus base curve elements, as well as discontinuities and inconsistent slopes at the connection points. Therefore, using the solar direct focus base curve element corresponding to a field of view of 0° as the basic unit, the modulated solar direct focus base curve elements at each field of view are rotated and translated to complete the splicing between adjacent solar direct focus base curve elements, ultimately fusing them into a continuous and smooth solar direct focus base curve. The splicing model between adjacent solar direct focus base curve elements is as follows: Figure 5 As shown.

[0032] Figure 5 The image shows two adjacent field of view angles. and Corresponding solar direct focusing basic curve element and At this time, let's assume and The peak-to-valley value of the sag difference along the Y-axis is , express Center and and The distance between the intersections and the length of the overlapping area are denoted as... Then Rotate counterclockwise around its center Angle, then translate a distance along the direction of the principal ray of its incident beam. The new solar direct focusing fundamental curve micro-element was obtained. , and The corresponding angles between the principal ray of the incident beam and the reflected ray are respectively and Then the shift parameter can be expressed as (7), obtained according to formula (7) , and This allows for the splicing and fusion of the basic curves for direct sunlight focusing.

[0033] In this embodiment, light cones with incident angles of ±23.5°, ±22°, ±20°, ±18°, ±16°, ±14°, ±12°, ±10°, ±8°, ±6°, ±4°, ±2°, 0° and a cone apex angle of 5° are selected as the sampling beams for the design of the solar direct focusing freeform surface reflector. D is set to 350mm, and according to formulas (3)-(7), and with , To determine the performance indicators, the basic curve of direct solar focusing was segmented, discretized, and fused together to obtain the initial structural parameters of the freeform surface reflector for direct solar focusing, as shown in Table 1.

[0034]

[0035] Within the plane of the solar direct focusing baseline curve, a light cone with a 5° apex angle is used as the light source. The incident angles of the light source are ±23.5°, ±22°, ±20°, ±18°, ±16°, ±14°, ±12°, ±10°, ±8°, ±6°, ±4°, ±2°, and 0°. A simulation model for evaluating the performance of the solar direct focusing baseline curve is established, using an irradiance of 1... As the threshold for evaluating the performance of the solar direct focusing base curve, simulations were used to obtain the performance of the solar direct focusing base curve (irradiance at each angle, spot energy distribution, and spot boundary at each angle), as follows: Figure 6As shown. At this point, the direct solar radiation beams at each field of view are considered as light cones with a 5° apex angle. A freeform surface reflector for direct solar focusing is constructed by rotating and expanding the basic curve of direct solar focusing. Similarly, a 1... As a performance evaluation threshold, the simulation yielded the performance of the extended solar direct-focusing freeform surface mirror as follows: Figure 7 As shown. From Figure 6 The basic curve for direct solar focusing can be obtained. It is 100%, exhibiting good spatiotemporal homogeneity. The value is 55%. The light spot is symmetrical about the central axis of the irradiated surface in the X direction, while its coordinate gradually increases in the Y direction. This is because optimization is performed on the 52° field-of-view plane, resulting in a linear energy distribution across the field of view, with the spot width remaining constant while its length gradually increases. From Figure 7 It can be seen that the expanded freeform surface reflector for direct solar focusing has... It was 61.64%; The percentage is 28.96%, at which point the light spot is irregularly distributed relative to the origin.

[0036] Based on the expanded freeform surface reflector for direct solar focusing, continue to... , As an evaluation function, the freeform surface mirror for direct solar focusing is iteratively optimized, and the vertex curvature radius of the optimized freeform surface mirror for direct solar focusing is determined. 2.34×10 -2 Conic coefficient The value is -1.28, and the face shape expression is... (8), in formula (8) for The coefficients of the terms; the superscripts i and j indicate the order of variables x and y. The coefficients of the various terms of the solar direct-focusing freeform surface mirror are shown in Table 2. The performance of the optimized solar direct-focusing freeform surface mirror is as follows: Figure 8 As shown.

[0037]

[0038] Depend on Figure 8 Thus, the optimized freeform surface reflector for direct solar focusing is obtained. It is 99.98%. The overlap rate was 25.08%, although it was relatively low compared to... Figure 7 The light spot decreased, but at this point it was approximately symmetrically distributed relative to the origin, achieving the expected goal of converging and effectively controlling the energy of all incident angles.

[0039] In this embodiment, the solar spectrum measurement optical system is verified using the 380nm-780nm working spectrum band, and the sensor is a Toshiba TCD1304 linear CCD with an 8-pixel size. The effective length is 29mm, and the slit size is 25mm. ,according to Figure 8 The optimized solar direct-focusing freeform surface mirror has a maximum convergence angle of 5.58°. To ensure that the solar spectral measurement optical system can receive all the reflected beams from the solar direct-focusing freeform surface mirror, the incident angle of the mirror is set to 14°. The system structure diagram is shown below. Figure 9 As shown, after optimization, the line connecting the focal points of all rays across the entire spectral range lies on a single focal plane, representing the optimal image plane. The RMS radius and streak diagram for the entire Y-direction are shown below. Figure 10 and Figure 11 As shown. Throughout the entire operating wavelength range of the optical system, the RMS radius along the Y direction remains at 6. The following are cell sizes smaller than CCD: 8 Under all incident angles, the spectral resolution is better than 2 nm across the entire operating wavelength range.

[0040] Meanwhile, this embodiment proposes a spatiotemporal scale spectral radiance reconstruction link based on an adaptive sampling strategy. By using an adaptive sampling strategy that combines uniform sampling and dynamic sampling, high-precision reconstruction of spatiotemporal scale spectral radiance is achieved. The incident angle of the direct sunlight beam is used as the benchmark for spectral radiance reconstruction at the spatiotemporal scale, and the continuous change of the incident angle of the sun between -23.5° and +23.5° is observed.

[0041] Let the incident angle of the direct beam be... , m is the number of incident angles sampled, and the wavelength of the collected spectral peak is . Where n is the number of wavelength channels, and the multi-angle measurement spectral matrix is... Each column corresponds to the measured spectral data for one incident angle, and the corresponding standard AM1.5G direct solar radiation spectral vector is... Then the spectral reconstruction factor It can be represented as (9) Each wavelength The spectral reconstruction factor can be fitted to a K-order polynomial. (10), where, Let be the polynomial coefficients. Then the reconstructed spectrum can be expressed as: (11), the relative error of the radiative area of ​​the sampled reconstructed spectrum is (12) Set the measurement error threshold for the reconstructed spectrum of uniform sampling as follows: Mark low-precision areas as At this point, a dynamically encrypted sampling region is constructed based on the low-precision region. Continuing to use formulas (11) and (12), the reconstructed spectrum measurement error after the adaptive sampling strategy is obtained. The principle of spatiotemporal scale spectral radiance reconstruction based on the adaptive sampling strategy is as follows: Figure 12 As shown. In this embodiment, uniform sampling is first performed using light source incident angles of ±23.5°, ±16°, ±8°, and 0°, and the spectral measurement accuracy is evaluated at 2° intervals. The simulation model of the solar direct radiation spectrum measurement system based on freeform surfaces is set to be better than ±1%. Figure 13 As shown, the spectral measurement accuracy is as follows: Figure 14 As shown. According to Figures 13-14 It can be concluded that the angles of solar incidence are -20° and -18°. The values ​​are -1.15 and -1.10, respectively, exceeding ±1%. Therefore, dynamic sampling at 2° intervals was performed in the -22° and -16° ranges, resulting in a relative error of -0.98% to 0.29% for the reconstructed spectral radiant area. To evaluate the ability to measure the detail of direct solar radiation spectra, wavelength-corresponding spectral measurement errors were introduced. The expression is (13) The scattering interval of the direct solar radiation spectrum measurement is as follows: Figure 15 As shown, the angles of solar incidence are... The average and maximum values ​​are as follows Figure 16 As shown, the average value is distributed between -3.66% and 5.11%, and the maximum error is distributed between -4.09% and 5.46%.

[0042] Experimental environment and results of this embodiment: From May 9th to May 11th, 2025, a direct solar radiation spectrum measurement experiment under natural conditions was conducted in Changchun City, Jilin Province, China, from 8:00 AM to 4:00 PM. The measurement results are as follows: Figures 18-20 As shown. According to Figures 18-20 As can be seen, the polar-axis rotating solar direct radiation spectral measurement system designed in this paper can achieve solar direct radiation spectral measurement in the 380nm-780nm range without the need for tracking. The measurement results possess detailed characteristics of the solar direct radiation spectrum, and the spectral deviations at typical peak and trough wavelengths (392nm, 482nm, 688nm, and 760nm) that best reflect the details of the solar spectrum are as follows: Figure 17 As shown, although the measurement results are slightly different each time, the measured spectrum matches the typical peaks and troughs of the standard AM1.5G solar direct radiation spectrum, with a typical wavelength deviation of no more than ±3nm. This demonstrates that the polar axis rotating solar direct radiation spectrum measurement system of this invention has excellent measurement accuracy and reliability, and also proves the correctness and feasibility of the method proposed in this study.

[0043] Table 3 Comparison of Domestic and International Studies

[0044] While specific embodiments of the present invention have been described above, those skilled in the art should understand that these are merely illustrative examples, and the scope of protection of the present invention is defined by the appended claims. Those skilled in the art can make various changes or modifications to these embodiments without departing from the principles and essence of the present invention, but all such changes and modifications fall within the scope of protection of the present invention.

Claims

1. A polar-axis rotating solar direct radiation spectral measurement system, characterized in that, This includes a solar direct focusing freeform surface reflector and a solar spectrum measurement optical system; The freeform surface reflector for direct solar focusing has an effective reflection and focusing angle of 2.5° for direct solar light, which can reflect and converge a 52°×5° field of view of direct solar light to the slit position of the solar spectrum measurement optical system. The solar spectral measurement optical system employs a cross-type Czerny-Turner optical path structure to split and detect the converged beam in order to obtain direct solar radiation spectral information.

2. The system according to claim 1, characterized in that, The construction and optimization process of the solar direct focusing freeform surface reflector includes initial structural construction and performance optimization. The initial structure is constructed based on the principle of polar axis measurement, using an off-axis hyperbola with perfect aberration-free conjugate points as the base curve. By segmenting and splicing the hyperbola into segments, a solar direct focusing base curve is constructed in the local plane of a 52° field of view. The base curve is then rotated around the 5° field of view and extended into three-dimensional space. The performance optimization focuses on the uniformity of direct solar irradiance from multiple angles. Overlap with the area of ​​direct sunlight spots from multiple angles The evaluation metrics are iteratively optimized.

3. The system according to claim 2, characterized in that, Optimized vertex curvature radius of the freeform surface reflector for direct solar focusing 2.34×10 -2 Conic coefficient The value is -1.28, and the face shape expression is... , In the formula for Coefficient of the term; superscript and Representing variables , The order of.

4. The system according to claim 2, characterized in that, The uniformity of direct solar irradiance from multiple angles The calculation formula is: ,in, The maximum irradiance of the light spot across all incident angles. The minimum irradiance of the light spot across all incident angles; the overlap of the areas of the multi-angle direct sunlight spot. The calculation formula is: ,in, This represents the area of ​​intersection of all incident light spots. This represents the area of ​​the union of all incident angle light spots.

5. The system according to claim 1, characterized in that, The solar spectrum measurement optical system includes a slit and a collimating mirror arranged sequentially. Radiant grating Focusing mirror and CCD detector; The light beam, reflected and converged by the solar direct focusing freeform mirror, passes through the slit and then sequentially through the collimating mirror. Collimation, blazed grating Beam-splitting and focusing mirrors The light is focused, eventually forming diffraction lines on the CCD detector.

6. The system according to claim 5, characterized in that, The working spectral band of the solar spectral measurement optical system is 380nm-780nm, with a spectral resolution of less than 2nm. Throughout the entire working band, the RMS radius along the Y direction remains below 6μm, which is smaller than the single pixel size of the Toshiba TCD1304 linear CCD used, which is 8μm.

7. The system according to claim 1, characterized in that, It also includes a spatiotemporal scale spectral radiance reconstruction link based on an adaptive sampling strategy, used to compensate for measurement errors in the solar direct radiation spectrum; the adaptive sampling strategy adopts a combination of uniform sampling and dynamic sampling, first performing uniform sampling, and when the relative error of the radiance area of ​​the reconstructed spectrum exceeds a set threshold, performing dynamic encrypted sampling in the low-precision region.

8. The system according to claim 7, characterized in that, In the spatiotemporal scale spectral radiance reconstruction link based on the adaptive sampling strategy, let the incident angle of the direct beam be... , To sample the number of incident angles, the wavelength of the collected spectral peaks is... , The wavelength channel number is [value], and the multi-angle measurement spectral matrix is ​​[value]. Each column corresponds to the measured spectral data for one incident angle, and the corresponding standard AM1.5G direct solar radiation spectral vector is... Then the spectral reconstruction factor It can be represented as: Each wavelength The spectral reconstruction factor can be fitted as... order polynomial: , In the formula, If the coefficients are polynomials, then the reconstructed spectrum can be expressed as: , The relative error of the radiative area of ​​the sampled reconstructed spectrum is: 。 9. The system according to claim 7, characterized in that, The adaptive sampling strategy includes uniform sampling at light source incident angles of ±23.5°, ±16°, ±8°, and 0°, evaluating errors at 2° intervals, and dynamically encrypted sampling in the range of -22° to -16° when the relative error of the radiant area of ​​the reconstructed spectrum exceeds ±1%.

10. A polar-axis rotating method for measuring direct solar radiation spectra, characterized in that, The polar-axis rotating solar direct radiation spectral measurement system as described in any one of claims 1-9 includes the following steps: S1: Receives a 52°×5° field of view of direct sunlight through a freeform surface mirror for direct solar focusing, and reflects and converges it to the slit position of the solar spectrum measurement optical system; S2: The converged beam enters the solar spectrum measurement optical system through the slit, and then passes through the collimating mirror in sequence. Radiant grating and focusing mirror Diffraction lines are formed on the CCD detector to obtain the initial solar direct radiation spectrum information; S3: The initial solar direct radiation spectrum information is processed by the spatiotemporal scale spectral radiance intensity reconstruction link based on an adaptive sampling strategy to compensate for measurement errors and obtain the final solar direct radiation spectrum.

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