Secondary reflector design method based on non-imaging optics and condensation heat collector

Abstract

The invention relates to a secondary reflector design method based on non-imaging optics and a condensation heat collector, and belongs to the technical field of solar photo-thermal condensation. Comprising the following steps: S1, determining the type of a main reflector according to an engineering working condition, wherein the main reflector comprises a paraboloid groove type main reflector PTC or a compound paraboloid main reflector CPC; s2, dynamically determining the size and position of a heat absorption inner tube based on the type and parameters of the main reflector; and S3, assuming the end point position of the secondary reflector, then initializing the starting point position of the secondary reflector, and generating a plurality of sections of quasi-elliptical line curved surfaces through end point convergence verification according to the edge extreme light principle and the light isometric constraint condition. S4, analyzing the condensation effect of the secondary reflector, and optimizing the starting point position of the secondary reflector until the condensation effect of the secondary reflector reaches an expected target; and S5, according to the positions and the sizes of the second-stage reflecting mirror and the heat absorption inner pipe, the combination mode of the second-stage reflecting mirror and the vacuum heat collection pipe is selected. Aiming at the problems of small condensation ratio, light escape, non-uniform energy flux density distribution, remarkable thermal stress and the like of paraboloid groove type and compound paraboloid heat collectors, a dynamic design method of a secondary reflector consisting of a plurality of sections of quasi-elliptical lines is constructed to solve the problems in the prior art.

Description

Technical Field

[0001] The present invention relates to a design method of a secondary reflector based on non-imaging optics and a concentrating collector, belonging to the technical field of solar thermal concentrating technology. Background Art

[0002] In the global energy pattern, traditional fossil fuels have long dominated. However, with the rapid economic development and continuous population growth, they are facing the dual challenges of sharp decline in reserves and depletion crisis. At the same time, the environmental problems caused by burning fossil fuels are becoming increasingly serious. Greenhouse gas emissions lead to global warming, acid rain erodes the ecological environment, and air pollution threatens human health. These problems have prompted the world to actively seek clean and sustainable new energy alternatives.

[0003] As a clean energy source that is inexhaustible and renewable, solar energy plays a crucial role in the energy transformation process. Solar thermal conversion technology can convert solar radiant energy into useful thermal energy and is widely used in various fields such as hot water supply, building heating, industrial heating, and power generation, showing broad market prospects. Among them, the parabolic trough solar collector (PTC) and the compound parabolic solar collector (CPC) have attracted much attention in large-scale solar thermal utilization projects due to their excellent light concentration performance. They focus the sun's rays to increase the energy density, thereby improving the photothermal conversion efficiency.

[0004] However, in the actual application process, many problems that need to be solved urgently have gradually emerged in these two types of collectors.

[0005] For the CPC, although it does not need to accurately track the sun's position during operation, when the heat transfer working fluid needs to reach a higher working temperature, the acceptance half-angle must be reduced to increase the geometric concentration ratio, which will cause the height of its reflector to increase rapidly, forming a "tall and thin" structure. This structure will not only cause serious problems of mutual occlusion between devices, affecting light collection, but also greatly increase the material consumption of the reflector and raise the cost. Truncating the CPC can reduce the height and material consumption, but it is difficult to guarantee the geometric concentration ratio after truncation, resulting in the heat transfer working fluid being unable to reach the required working temperature.

[0006] For PTC, it is one of the most widely commercialized and stable solar thermal power generation technologies in the world. Its core principle is to reflect and focus sunlight onto high-temperature solar vacuum heat collectors located on the focal line through parabolic trough collectors, heating the fluid inside the tubes to achieve the conversion of solar energy into thermal energy. The optical-thermal conversion efficiency of the trough collector directly determines the power generation efficiency of the entire system. To improve the power generation efficiency and reduce the investment cost, it has become a current development trend to adopt trough concentrators with larger apertures. However, simply increasing the aperture width of the concentrator will result in an increase in the focal spot width, and some of the concentrated light spots will exceed the diameter of the metal inner tube of the vacuum heat collector, causing waste of solar radiation energy. In addition, increasing the operating temperature of the trough collector can significantly improve the power generation efficiency of the system. Currently, trough solar thermal power generation systems using 400°C high-pressure steam and 550°C molten salt as heat transfer working fluids have been applied. However, under high-temperature operating conditions, the thermal radiation loss of the metal inner tube increases sharply. Especially when the inner tube diameter increases, the heat dissipation area increases, and the heat loss increases significantly, resulting in a reduction in the power generation efficiency of the system. At the same time, due to the uneven distribution of the energy flux density on the surface of the vacuum heat collector, the circumferential temperature gradient of the metal inner tube is relatively large, generating large thermal stress and bending deformation, further affecting the safety and stability of the system.

[0007] To solve the above problems, setting up a secondary mirror has become an effective technical means. The secondary mirror can reflect the light spots that exceed the diameter of the vacuum heat collector back onto the vacuum heat collector again, reducing energy loss, increasing the concentration ratio and optical-thermal conversion efficiency of the concentrator. At the same time, the secondary mirror can homogenize the energy flux density distribution on the surface of the vacuum heat collector, reduce the temperature gradient and thermal stress, thereby reducing the risk of heat loss and bending deformation, and improving the safety and power generation efficiency of the system. To break through the development bottleneck, researchers have focused on the secondary mirror technology. By precisely designing its shape, position and optical characteristics, the concentration ratio of the collector has been significantly improved, the energy flux density distribution has been improved, and energy loss has been reduced. In-depth study of the adaptability of secondary mirrors in different types of collectors and the development of general and efficient design methods have important practical significance for expanding the application scenarios of PTC, improving stability, and helping CPC overcome limitations and enhance market competitiveness, and will inject strong impetus into the booming development of the solar thermal industry.

[0008] Currently, there have been related technological attempts for improvement. For example, in the patent application publication number: CN111238060A, a high-temperature solar heat collecting tube with a secondary concentrator, its trough-type collector, and in the patent application publication number: CN102762931A, a cylindrical solar collector with an optimal secondary concentrator and its design method add a secondary reflector in the vacuum heat collecting tube to optimize energy utilization. However, their technical principles are different from those of the present invention, and their applicable scopes are also different. The patent application publication number: CN103256724A, a solar concentrator and its design method, uses a light-homogenizing reflector to homogenize the energy flux density, focusing on solving the problem of uneven energy flux density distribution, and it cannot increase the concentration ratio and reduce energy loss. Summary of the Invention

[0009] The object of the present invention is to propose a design method for a secondary reflector and a concentrator based on non-imaging optics. Aiming at the problems existing in parabolic trough (PTC) and compound parabolic concentrator (CPC) collectors, such as insufficient concentration ratio, light escape, uneven energy distribution, and significant thermal stress, the present invention constructs a dynamic design method for a secondary reflector composed of multiple segments of quasi-elliptical lines.

[0010] The design method for a secondary reflector based on non-imaging optics described in the present invention includes the following steps:

[0011] S1: Determine the type of the primary reflector according to the engineering conditions, including a parabolic trough primary reflector PTC or a compound parabolic primary reflector CPC;

[0012] S2: Dynamically determine the size and position of the heat-absorbing inner tube based on the type and parameters of the primary reflector;

[0013] S3: Assume the endpoint position of the secondary reflector, then initialize the starting point position of the secondary reflector, and then, according to the marginal extreme ray principle and the ray equal-path constraint condition, iteratively calculate the trajectory coordinates of the secondary reflector point by point from the inside out, and generate a multi-segment quasi-elliptical line surface through endpoint convergence verification;

[0014] S4: Analyze the concentrating effect of the secondary reflector, and optimize the starting point position of the secondary reflector until the concentrating effect of the secondary reflector (3) reaches the expected target;

[0015] S5: According to the positions and sizes of the secondary reflector and the heat-absorbing inner tube, select the combination method of the secondary reflector and the vacuum heat collecting tube to realize the dynamic adaptation of the geometric parameters of the secondary reflector, the heat-absorbing inner tube, and the glass outer tube.

[0016] Preferably, when the primary reflector is a parabolic trough PTC, its parameters include the acceptance half-angle θ a , focal length F, opening width A a , edge angle φ e, the light source splitting factor K, calculates the size and position of the PTC heat-absorbing inner tube through the following formula:

[0017] The coordinate origin is set at the center of the parabola, and the trajectory equation of the PTC is:

[0018]

[0019] where F is the focal length of the parabolic trough collector PTC, which can be calculated through formula (2); φ is the angle between the line connecting any point on the PTC reflector and the focus and the negative direction of the Y-axis, and its value range is from -φ e to φ e ;

[0020]

[0021] The light source of the PTC is split into two sub-light sources: ΔS1 and ΔS2. The light source splitting factor K is introduced to control the relative sizes of the two sub-light sources. The light of the sub-light source ΔS1 can directly reach the heat-absorbing inner tube, while the light of the sub-light source ΔS2 needs to be reflected by the secondary reflector to reach the heat-absorbing inner tube. K can range from 0 to 1. When K = 0.5, both sub-light sources are equal to the acceptance half-angle θ of the concentrator a ;

[0022] The center of the circular tube absorber of the conventional concentrator is located at the coordinate origin, with a radius r o :

[0023]

[0024] In the formula: A ap is the size of the incident light aperture (light-collecting surface) of the PTC;

[0025] A small-sized heat-absorbing inner tube is used in combination with a secondary reflector to replace the circular tube absorber of the conventional concentrator. The radius r of the heat-absorbing inner tube is:

[0026] r = 0.5A ap (cot(φ e + θ a (2K - 1)) - cot(φ e + θ a K))sin(φ e + θ a (2K - 1)) (5)

[0027] The coordinates of the center of the heat-absorbing inner tube:

[0028]

[0029] Preferably, when the primary reflector is a compound parabolic concentrator (CPC), its parameters include the acceptance half-angle θ a and the truncation position φt , φ t is the maximum value that the parameter φ in formula (1) can take, the radius r of the absorber of the conventional concentrator's circular tube o , and the radius r of the heat-absorbing inner tube. The size and position of the CPC heat-absorbing inner tube are calculated by the following formula:

[0030] The center of the absorber of the conventional concentrator's circular tube is located at the origin of coordinates. The trajectory equation of the CPC:

[0031]

[0032] where φ is the angle between the line connecting any point on the CPC mirror and the origin of coordinates and the negative direction of the Y-axis, and its value range is from 0 to φ t ;

[0033] The center coordinates of the heat-absorbing inner tube 4:

[0034]

[0035] Preferably, step S3 specifically includes the following sub-steps:

[0036] S31: Assume the endpoint position Q n *:

[0037] Considering that the occlusion of the secondary mirror will affect its own geometric trajectory, and the endpoint position Q n of the secondary mirror is unknown, so a certain point at the extreme ray position needs to be assumed as its endpoint position in advance, denoted as Q n *;

[0038] For PTC, the equation of the extreme ray position:

[0039]

[0040] For CPC, the equation of the extreme ray position:

[0041] y = Y(φ t ) + tan(φ t )(x - X(φ t )) (10)

[0042] Preset the abscissa value of point Q n *, and calculate the ordinate value of point Q n * through formula (9) or formula (10);

[0043] S32: Initialize the starting point Q1 position of the secondary mirror:

[0044] For PTC, the starting point Q1 of the secondary mirror is initialized as the intersection of the extreme ray (9) and the Y-axis, obtained from formula (11):

[0045]

[0046] For the CPC, the starting point Q1 of the secondary mirror is initialized to the top end of the heat-absorbing inner tube and obtained from Equation (12):

[0047]

[0048] The starting point Q1 of the secondary mirror needs to be further optimized and adjusted according to the optical simulation results at a later stage;

[0049] S33: Use an iterative algorithm to recursively solve the subsequent coordinate sequence Q of the secondary mirror i (i = 2, 3, 4…n):

[0050] Determine the trajectory coordinates of all points sequentially by point-by-point calculation, that is, determine the position of point Q2 through point Q1, then determine the position of point Q3 through the position of point Q2, and so on, until the extreme ray position (7) where the secondary mirror extends is calculated. This point is the calculated endpoint Q n ;

[0051] S34: Endpoint convergence check:

[0052] Compare the assumed endpoint Q n * position with the actual position of the calculated Q n Revise the position of the assumed endpoint Q n Repeat steps S32, S33, and S34 until the horizontal coordinate error between the assumed endpoint and the calculated endpoint is less than the allowable error ε.

[0053] Preferably, the specific process of the iterative calculation in step S33 includes the following steps:

[0054] S331: Calculate the fixed focus P of the spatial point Q i (i = 1, 2, 3..n) i

[0055] As Figure 4 shown, when calculating the coordinates of point Q i through point Q i+1 , it is first necessary to calculate the fixed focus Pi of point Q i . There are multiple points on the primary mirror, and the incident light within the acceptance angle can reach the spatial point Q i after being reflected by these points. Select the leftmost P i point as the fixed focus of point Q i . The specific positioning process is as follows:

[0056] Find point P T , Q point and P TThe connection line of the points is tangent to the heat absorption inner tube (4), and the angle between the tangent point and the Y-axis is represented by φ c It is represented by;

[0057]

[0058] By solving the system of equations (13), the coordinates (X(φ T ), Y(φ PT )) of point P on the primary mirror can be determined. The fixed focus can only appear on the right side of point P. Otherwise, it will be intercepted by the heat absorption inner tube. Specifically, if the light within the acceptance angle (±θa) can reach the spatial point Q1 after being reflected by point P PT ), then the fixed focus can be directly selected as point P T without subsequent calculations; T T T T

[0059] The extreme ray is incident on point P n on the primary mirror at an incident angle of π / 2 - θa through the end point Q S * of the secondary mirror. The extreme ray is incident on point P n on the primary mirror at an incident angle of π / 2 + θa through the end point Q E * of the secondary mirror;

[0060]

[0061] By solving expression (14) and expression (15), the position parameters of points P S and P E can be determined;

[0062] Between point P S and point P ap , find point P A . The extreme ray is incident on point P A on the primary mirror at an incident angle of π / 2 + θa, and after reflection, it can reach point Q1 on the secondary mirror. The slope of the reflected light is represented by k A ;

[0063] Y Q1 - Y PA = k A (X Q1 - X PA ) max(X PS , X PT ) ≤ X PA ≤ X Pap (16)

[0064] Between point P E and point P ap , find point P B, The extreme light is incident on the primary mirror at an incident angle of π / 2 + θa at point P B and can reach point Q1 on the secondary mirror after reflection. The slope of the reflected light is represented by k B .

[0065] Y Q1 -Y PB = k B (X Q1 -X PB ) max(X PE , X PT ) ≤ X PB ≤ X Pap (17)

[0066] Find point P S between point P E and point P C such that, within the light source angle range, the light passing through the extreme light position Q n * is incident on point P3 on the primary mirror and can reach point Q on the secondary mirror after reflection. The slope of the reflected light is represented by k C . If P S , P E are both on the left side of P T , then there is no point P C that meets the requirements;

[0067] Y Q1 -Y PC = k C (X Q1 -X PC ) max(X PS , X PT ) ≤ X PC ≤ X PE (18)

[0068] Solve for the coordinates of P A , P B , P C according to formulas (16), (17), and (18). Select the leftmost point as the fixed focus of the spatial point Q i , denoted as P i . The extreme light is tangent to the heat-absorbing inner tube at point C i after being reflected by P i and Q i . Since the occlusion of the secondary mirror affects the value of the fixed focus and thus the geometric trajectory of the secondary mirror, this is the reason for first assuming the position of the endpoint Q n * of the secondary mirror;

[0069] S332: Calculate adjacent trajectory points Q i+1Coordinates:

[0070]

[0071] Regarding point P i as a point light source, the light rays within the acceptance angle (±θa) can all reach the heat absorption inner tube tangentially after being reflected by R i and Q i Q i+1 curve. The landing point on the heat absorption inner tube is called the moving focus. The moving focus moves along the heat absorption inner tube from point C i to point C i+1 . Therefore, the Q i Q i+1 curve is not a strict ellipse; it is a quasi-ellipse segment;

[0072] Solving for the coordinates of point Q i+1 based on formula (19), where v is a fixed value. For each v-degree movement of the moving focus, a quasi-ellipse segment is designed. The smaller the value of v, the more segments and the smaller the size of the secondary reflector, and the better the light concentration effect;

[0073] S333: Calculate the endpoints Q n of the secondary reflection point by point:

[0074] Repeat steps S331 and S332 until the secondary reflector extends to the extreme light position to obtain the calculated endpoint coordinates Q n .

[0075] Preferably, the value range of v in step S332 is 0.1° - 2°.

[0076] Preferably, the combination method of the secondary reflector and the vacuum heat collecting tube in step S5 includes:

[0077] Fully encapsulated built-in type: The secondary reflector is integrated into the internal space of the outer glass tube, and the environmental tolerance and structural stability are improved through a fully sealed structure design;

[0078] Externally attached independent type: The secondary reflector is modularly and independently encapsulated and externally installed on the outside of the vacuum heat collecting tube, which is compatible with the direct replacement of commercial vacuum tubes and reduces the engineering transformation cost;

[0079] Internal and external separated and optimized type: Based on optical simulation, the layout of the reflector segments is optimized, and some reflector units are placed outside the outer glass tube to balance the geometric size of the reflector and the utilization rate of the internal space of the outer glass tube.

[0080] A concentrating solar collector according to the present invention includes:

[0081] A main reflector; including a parabolic trough type main reflector PTC or a compound parabolic main reflector CPC;

[0082] An endothermic inner tube with a selective absorption coating on its surface, whose size and position are dynamically determined based on the parameters of the primary mirror;

[0083] A secondary mirror, composed of multiple segments of quasi-elliptical lines, generated by a secondary mirror design method based on non-imaging optics, for secondarily focusing the escaping light rays onto the surface of the endothermic inner tube;

[0084] A glass outer tube, adaptively installed with the secondary mirror, forming an externally attached independent type, fully encapsulated built-in type, or internal and external separated optimized type structure.

[0085] Preferably, the material of the secondary mirror is a high-reflectivity metal, coated glass, or a high-reflectivity coating.

[0086] The secondary mirror design method based on non-imaging optics and the concentrator collector of the present invention have the following beneficial effects:

[0087] (1) The light concentration efficiency is significantly improved, and the energy utilization rate is doubled.

[0088] The geometric concentration ratio is greatly increased:

[0089] PTC system: The geometric concentration ratio of Example 1 is increased from the conventional 35.92 to 86.18 (an increase of 139.87%), and the energy concentration ratio is increased from 32.361 to 72.735 (an increase of 124.8%).

[0090] CPC system: The geometric concentration ratio of Example 2 is increased from 1.57 to 2.59 (an increase of 65.47%), and the energy concentration ratio is increased from 1.442 to 2.055 (an increase of 42.51%).

[0091] (2) The uniformity of the energy flux distribution is optimized, and the risks of thermal stress and deformation are reduced.

[0092] The uniform energy distribution significantly reduces the risks of thermal stress and tube body bending deformation, and improves the system safety and long-term operation stability. The standard deviation of the circumferential local concentration ratio (LCR) of the endothermic inner tube in Example 1 is reduced from 27.419 to 12.128 (a decrease of 55.7%), effectively alleviating the circumferential temperature gradient problem caused by uneven energy flux.

[0093] (3) The light energy absorption rate is increased.

[0094] The average incident angle of the light rays reaching the endothermic inner tube (4) in Example 2 is reduced from 61.55° to 33.92°, increasing the light energy absorption rate of the selective absorption coating.

[0095] (4) Effectively solve the problem of light ray escape, reduce heat loss, and enhance the adaptability to high-temperature working conditions.

[0096] Secondary utilization of escaping light: The secondary mirror reflects the focal spot light beyond the diameter of the heat-absorbing inner tube to the tube surface for the second time, reducing energy waste caused by light escape, improving the photothermal conversion efficiency, and effectively reducing the sensitivity of the optical efficiency of the concentrator to tracking deviation.

[0097] Suppression of high-temperature thermal radiation: Under high-temperature conditions (300 - 550 °C), the small-size design of the heat-absorbing inner tube reduces the heat dissipation area, decreases the thermal radiation loss of the metal inner tube, and improves the power generation efficiency of the high-temperature system.

[0098] (4) Enhanced system compatibility and engineering adaptability

[0099] Flexible multi-mode installation: The secondary mirror and the heat-absorbing inner tube support three integration modes: externally attached independent type (compatible with direct replacement of commercial vacuum tubes), fully encapsulated built-in type (improving weather resistance), and internal and external separated optimized type (balancing space utilization and concentrating efficiency), to adapt to the requirements of different engineering scenarios.

[0100] Dynamic parametric modeling: The design method is based on the shape of the primary mirror (including but not limited to PTC / CPC), realizing the adaptive adjustment of the curvature and spatial pose of the secondary mirror, and achieving seamless adaptation with various primary mirror systems.

[0101] (5) Outstanding economic and environmental benefits

[0102] Reduction of material costs:

[0103] CPC system: By replacing the traditional "tall and thin" mirror structure with a secondary mirror, the height and material consumption of the mirror are reduced.

[0104] PTC system: The coordinated design of the small-size heat-absorbing inner tube and the optimized secondary mirror improves the solar photothermal conversion efficiency, reduces the dependence on fossil energy, and helps achieve the carbon neutrality goal. Description of the drawings

[0105] Figure 1 : Comparison between the PTC secondary concentrator applying the example of the present invention and the conventional PTC structure; in the figure, (a) is the PTC secondary concentrator applying the present invention; (b) is the conventional PTC.

[0106] Figure 2 : Comparison between the CPC secondary concentrator applying the example of the present invention and the conventional CPC structure; in the figure, (a) is the PTC secondary concentrator applying the present invention, (b) is the conventional PTC.

[0107] Figure 3 : Schematic diagram of the combination of three secondary mirrors and vacuum heat pipes; in the figure, (a) is the externally attached independent type, (b) is the fully encapsulated built-in type, (c) is the internal and external separated optimized type.

[0108] Figure 4 : The fixed focus P of point Q on the secondary reflector i ; i ;

[0109] Figure 5 : The light ray passes through the fixed focus P i and is reflected by the secondary reflector Q i Q i+1 and the optical path schematic diagram of the reflected light ray being tangent to the heat absorption inner tube;

[0110] Figure 6 : The position diagram of each point on the secondary reflector calculated point by point;

[0111] Figure 7 : The PTC ray tracing result of the application example of the present invention;

[0112] Figure 8 : The comparison of the circumferential LCR of the PTC heat absorption inner tube of the application example of the present invention with the conventional PTC;

[0113] Figure 9 : The CPC ray tracing result of the application example of the present invention.

[0114] Figure 10 : The comparison of the circumferential LCR of the CPC heat absorption inner tube of the application example of the present invention with the conventional CPC;

[0115] In the figure: 1. Parabolic trough primary reflector PTC; 2. Compound parabolic primary reflector CPC; 3. Secondary reflector; 4. Heat absorption inner tube; 5. Glass outer tube; 6. Conventional concentrator circular tube absorber; 7. Extreme light position; 8. The lowest extreme light ray of the sub-source ΔS1 at the edge of the PTC mirror; 9. The uppermost light ray of the sub-source ΔS1 at the edge of the PTC mirror; 10. The uppermost extreme light ray of the sub-source ΔS2 at the edge of the PTC mirror; 11. The extreme light ray passing through the assumed end point Qn* of the secondary reflector with an incident angle of π / 2 - θa; 12. The extreme light ray passing through the assumed end point Qn* of the secondary reflector with an incident angle of π / 2 + θa. Specific embodiments

[0116] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments.

[0117] Embodiment 1: PTC secondary concentrating collector (A ap = 5.647 m, θ a = 0.5°, K = 0.6)

[0118] Step 1: Definition of primary reflector parameters

[0119] As Figure 1 shown, the trajectory of the parabolic trough primary mirror PTC 1 is accurately determined by using the primary mirror parameters and their trajectory equations.

[0120] Primary mirror parameters: The selected opening width A ap is 5.647 m, the edge angle φ e is 80°, and the acceptance half-angle θa is 0.5°.

[0121] The light source splitting factor K = 0.6 (ΔS1 / ΔS2 = 2:3).

[0122] The coordinate origin is set at the center of the parabola. The trajectory equation of the PTC is:

[0123]

[0124] where F is the focal length of the parabolic trough primary mirror PTC 1, which can be calculated by formula (2); φ is the angle between the line connecting any point on the PTC mirror and the focus and the negative direction of the Y-axis, and its value range is -φ e to φ e .

[0125] where F is the focal length of the PTC:

[0126]

[0127] The light source splitting factor K (0 ≤ K ≤ 1) is introduced to regulate the relative sizes of the two sub-light sources (ΔS1 and ΔS2). When K = 0.5, both sub-light sources are equal to the acceptance half-angle θ of the concentrator a .

[0128]

[0129] When K = 0.6 (ΔS1 / ΔS2 = 2:3), ΔS1 = 0.4°, ΔS2 = 0.6°.

[0130] Step 2: The radius and the position of the center of the heat-absorbing inner tube 4

[0131] As Figure 1 shown in (a) below, the radius and the position of the center of the heat-absorbing inner tube 4 are determined by means of the lowest extreme ray 8 of the sub-light source ΔS1 at the edge of the PTC mirror tangent to the heat-absorbing inner tube 4 and the ray 9 of the sub-light source ΔS1 at the upper edge of the PTC mirror, and the specific values are calculated by using formula (5) and formula (6). It can be calculated by formula (5) that the radius r of the heat-absorbing inner tube 4 is 10 mm; the center coordinates of the heat-absorbing inner tube 4 are determined by formula (6) to be (0, 1667.413 mm).

[0132] The relevant mathematical model is as follows:

[0133] Radius r of the heat-absorbing inner tube 4:

[0134] r = 0.5A ap (cot(φ e + θ a (2K - 1)) - cot(φ e + θ a K))sin(φ e + θ a (2K - 1)) (5)

[0135] Core coordinates of the heat-absorbing inner tube 4:

[0136]

[0137] Step 3: Assume the endpoint Q n * coordinates

[0138] Q n * is the assumed endpoint of the secondary mirror 3, located on the extreme ray position 7. Set the abscissa of the secondary mirror endpoint to 100, and obtain the position Q n * of the assumed secondary mirror endpoint through formula (9), with coordinates (100, 1689.559) mm.

[0139]

[0140] Step 4: Determine the coordinates of the starting point Q1 of the secondary mirror 3

[0141] Initialize the starting point Q1 of the secondary mirror as the intersection of the extreme ray R1 and the Y-axis, and obtain the coordinates of point Q1 as (0, 1677.56) mm through formula (11).

[0142]

[0143] Next, iteratively calculate the coordinates of the subsequent points Q i (i = 2, 3, 4..n).

[0144] Step 5: Calculate the fixed focus P i of point Q i (i = 1, 2, 3..n)

[0145] As Figure 4 shown, for the spatial point Q i , there are multiple points that can reach Q after being reflected by the primary mirror i , select the P i point with the smallest abscissa as its fixed focus.

[0146] As Figure 5 shown, find point PT , Q i point and P T The connecting line between the point and the heat absorption inner tube 4 is tangent, and the fixed focus can only appear on the right side of point P T , otherwise it will be intercepted by the heat absorption inner tube 4

[0147]

[0148] The coordinates of point P (X(φ T ), Y(φ PT )) on the primary mirror can be determined by solving the system of equations (13). The fixed focus can only appear on the right side of point P PT , otherwise it will be intercepted by the heat absorption inner tube 4 T

[0149] The light rays within the acceptance angle (±θa) can reach the spatial point Q1 after being reflected by point P T . The fixed focus can be directly selected as point P T , and no subsequent calculations are required. If this condition is not met, subsequent calculations are still needed

[0150] As Figure 5 shown, assume the extreme ray 11 with an incident angle of π / 2 - θa at the end point Q n * of the secondary mirror is incident on point P S on the primary mirror. Assume the extreme ray 12 with an incident angle of π / 2 + θa at the end point Q n * of the secondary mirror is incident on point P E on the primary mirror

[0151]

[0152] The position parameters of points P S and P E can be determined by solving expressions (14) and (15)

[0153] Between point P S and point P ap , find point P A . The extreme ray is incident on point P A on the primary mirror with an incident angle of π / 2 + θa and can reach point Q1 on the secondary mirror 3 after reflection. The slope of the reflected light is represented by k A

[0154] Y Q1 - Y PA = k A (X Q1 - X PA ) max(X PS , X PT ) ≤ X​​PA ≤X Pap (16)

[0155] At point P E and point P ap Find point P between them B , the extreme ray is incident on the primary mirror at point P with an incident angle of π / 2 + θa. After reflection, it can reach point Q1 on the secondary mirror 3. The slope of the reflected ray is represented by k B . B .

[0156] Y Q1 -Y PB =k B (X Q1 -X PB )max(X PE ,X PT )≤X PB ≤X Pap (17)

[0157] At point P S and point P E Find point P between them C , within the light source angle range, the ray passing through the extreme ray position Q n * is incident on point P3 on the primary mirror. After reflection, it can reach point Q on the secondary mirror 3. The slope of the reflected ray is represented by k C . If P S , P E are both on the left side of P T , then there is no point P C that meets the requirements.

[0158] Y Q1 -Y PC =k C (X Q1 -X PC )max(X PS ,X PT )≤X PC ≤X PE (18)

[0159] Solve for the coordinates of P A , P B , P C (not necessarily all have solutions) according to equations (16), (17), and (18). Select the leftmost point as the fixed focus of the spatial point Q i , represented by P i . The extreme ray R i is tangent to reach point C i on the heat absorption inner tube 4 after reflection by P i and Q i .

[0160] Step 6: Solve for Q based on the equal optical path constraint of formula (19). i+1 Point coordinates.

[0161] The light ray R1 is reflected by P1 and Q1 and then reaches point C1 on the heat absorption inner tube 4 tangentially. Fix the position of point P1, and rely on the equal optical path constraint to find point Q2 of the secondary mirror 3. After the light ray is reflected by point P1 and point Q2, it reaches point C2 on the heat absorption inner tube 4 tangentially.

[0162]

[0163] The coordinates of point Q2 are solved by formula (19) as (0.001 mm, 1677.567 mm), where v = 0.1°.

[0164] Step 7: Obtain the endpoint Q of the secondary mirror n coordinates

[0165] As Figure 6 shown, repeat step 5 and step 6, and obtain the subsequent coordinates of the secondary mirror 3 by point-by-point calculation until the secondary mirror 3 extends to the extreme light position 7. The uppermost extreme light ray 10 of the sub-light source ΔS2 at the edge of the PTC mirror surface follows the extreme light position 7 and then reaches the heat absorption inner tube 4 tangentially after being reflected by the secondary mirror 3, and the endpoint coordinates Q n (102.784 mm, 1689.043 mm) are obtained accordingly.

[0166] Step 8: Adjust the assumed endpoint Q n * position

[0167] Since the assumed endpoint Q n * falls on the left side of the calculated result Q n So move the assumed endpoint Q n * position to the right until the horizontal coordinate error between the assumed endpoint and the calculated endpoint is less than the convergence condition of the allowable error ε. Here, the allowable error ε = 1 mm.

[0168] After calculation, it is finally determined that when the endpoint Q of the secondary mirror n (102.707 mm, 1689.057 mm), the convergence condition that the horizontal coordinate error between the assumed endpoint and the calculated endpoint is less than the allowable error ε is satisfied.

[0169] Step 8: Optical performance analysis of the secondary mirror

[0170] After obtaining all the trajectory coordinates of the secondary mirror 3, a complete mirror surface can be generated by symmetric extension, and then the light condensing effect of the secondary mirror 3 can be analyzed.

[0171] Figure 7Shows the light path tracking results of the PTC secondary concentrator designed according to the present invention (θ a = 0.5°, φ e = 80°, K = 0.6 (ΔS1 / ΔS1 = 2 / 3)). Figure 8 Shows the local concentration ratio (Local concentration ratio, LCR) in the circumferential direction of the heat absorption inner tube 4. Compared with the conventional PTC, after using the secondary reflector designed by the present invention, the geometric concentration ratio increases by 139.87%, the energy concentration ratio increases by 129.7%, and at the same time, the uniformity of the circumferential energy distribution of the heat absorption inner tube 4 is improved.

[0172] Step 9: Adjust the position of the starting point Q1 of the secondary reflector

[0173] Since the concentrating effect is relatively ideal, the position of the starting point Q1 of the secondary reflector is no longer adjusted.

[0174] Step 10: Select the combination method of the secondary reflector 3 and the vacuum heat collecting tube

[0175] Since the secondary reflector 3 is large in size, with a length of 232.703, which is much larger than the radius of the heat absorption inner tube 4, which is 10 mm, and the gap between the secondary reflector 3 and the heat absorption inner tube 4 is only 0.151 mm, the internal and external separated optimization type (as shown in Figure 3 (c)) is selected, that is, the secondary reflection part is placed inside the glass outer tube 5 and part is placed outside the glass outer tube 5, and the radius of the glass outer tube 5 is set to 18 mm.

[0176] Comparative Example 1: Conventional parabolic trough solar collector (PTC) ((A ap = 5.647 m, θ a = 0.5°, φ e = 80°)

[0177] As shown in Figure 1 (b), using the main reflector parameters and its trajectory equation (1), to accurately determine the trajectory of the parabolic trough main reflector PTC 1.

[0178] Main reflector parameters: The selected opening width A ap is 5.647 m, the edge angle φ e is 80°, and the acceptance half angle θa is 0.5°.

[0179] Trajectory equation of PTC:

[0180]

[0181] where F is the focal length of the PTC, which can be calculated by formula (2); φ is the angle between the line connecting any point on the PTC reflector and the focus and the negative direction of the Y axis, and its value range is -φe to φ e 。

[0182]

[0183] For the conventional concentrator circular tube absorber 6, the center of the tube is located at the origin of coordinates, and the radius is r o :

[0184]

[0185] Example 2:

[0186] Compound parabolic concentrator (CPC) 2 secondary mirror design (θ a = 5°, φ t = 175°, r o = 30 mm, r = 10 mm)

[0187] Step 1: Definition of the primary mirror parameters

[0188] As shown in (a) of Figure 2 , use the primary mirror parameters and its trajectory equation (7) to accurately determine the trajectory of the compound parabolic concentrator (CPC) 2.

[0189] CPC mirror parameters: acceptance half-angle θ a = 5°, truncation position parameter φ t = 175°, radius r of the conventional concentrator circular tube absorber 6 o = 30 mm, and the center of the tube is located at the origin of coordinates.

[0190] Trajectory equation of CPC:

[0191]

[0192] Step 2: Radius and center position of the heat-absorbing inner tube 4

[0193] As shown in (a) of Figure 2 , the center coordinates of the heat-absorbing inner tube 4 are obtained as (0, -20) through formula (8).

[0194] In this patent, a small-sized heat-absorbing inner tube 4 is used in combination with a secondary mirror 3 to replace the heat-absorbing inner tube 4 of the conventional concentrator circular tube absorber 6, with a radius r = 10 mm (self-set). According to formula (8), the center coordinates are initialized as (0, -10 mm):

[0195]

[0196] Step 3: Assume the coordinates of the endpoint Q of the secondary mirror 3 n * coordinates

[0197] Set the abscissa of the endpoint of the secondary mirror to 60. Combining with the extreme ray position 7, the assumed endpoint position Q of the secondary mirror is obtained through formula (9). n *Coordinates (60, 24.865) mm.

[0198] y = Y(φ t ) + tan(φ t )(x - X(φ t )) (10)

[0199] Step 4: Determine the coordinates of the starting point Q1 of the secondary mirror 3

[0200] The starting point Q1 of the secondary mirror is initialized as the vertex of the heat absorption inner tube 4, and the coordinates of point Q1 are (0, -10) mm.

[0201]

[0202] Step 5: Calculate the coordinates of the subsequent points of the secondary mirror point by point

[0203] The coordinates of the subsequent points Q on the secondary mirror are calculated point by point i (i = 2, 3, 4..n) The process is the same as steps 5 - 7 of Embodiment 1. The finally calculated endpoint Q of the secondary mirror n The coordinates are (65.973, 21.951).

[0204] Step 6: Adjust the assumed endpoint Q n *Position

[0205] Since the assumed endpoint Q n *falls on the left side of the calculated result Q n So move the assumed endpoint Q n *position until the abscissa error between the assumed endpoint and the calculated endpoint is less than the convergence condition of the allowable error ε. Here, the allowable error ε = 1 mm.

[0206] After calculation, the endpoint Q of the secondary mirror is finally determined n (67.577 mm, 24.202 mm) satisfies the convergence condition that the abscissa error between the assumed endpoint and the calculated endpoint is less than the allowable error ε.

[0207] Step 8: Optical performance analysis of the secondary mirror

[0208] After adopting the secondary mirror designed by the present invention, compared with the conventional CPC (Comparative Example 2), the geometric concentration ratio (2.55) of the concentrating collector increases by 62.73%, and the energy concentration ratio (2.018) increases by 39.9%.

[0209] Step 9: Adjust the position of the starting point Q1 of the secondary mirror

[0210] Since the gap between the secondary reflector 3 and the heat-absorbing inner tube 4 is 0 mm, after adjusting the starting position Q1 of the secondary reflector upward to (0, -7.5 mm), compared with the conventional CPC (Comparative Example 2), the geometric concentration ratio increases by 62.73% before adjustment and 65.48% after adjustment. The gap between the secondary reflector 3 and the heat-absorbing inner tube 4 increases to 2.5 mm. This adjustment not only improves the concentration ratio but also places the secondary reflector 3 outside the vacuum heat pipe.

[0211] The detailed data after adjusting the starting position of the secondary reflector are shown in Table 1.

[0212] Figure 9 The light trace tracking results of the CPC secondary concentrator after adjusting the starting position of the secondary reflector are shown. Figure 10 is the local concentration ratio (LCR) in the circumferential direction of the heat-absorbing inner tube 4. Compared with the conventional CPC, after using the secondary reflector designed by the present invention, the geometric concentration ratio of the concentrator increases by 65.47% and the energy concentration ratio increases by 42.51%.

[0213] Step 10: Select the combination method of the secondary reflector 3 and the vacuum heat pipe

[0214] After adjusting the starting point of the secondary reflector 3, the gap between the secondary reflector 3 and the heat-absorbing inner tube 4 increases to 2.5 mm. Select the externally attached independent combination method (as shown in (b) of Figure 3 ), encapsulate the secondary reflector 3 completely outside the glass outer tube 5. The vacuum heat pipe can be selected as a commercial vacuum heat pipe. The radius of the glass outer tube 5 is taken as 12 mm, and the tube center position is the same as that of the heat-absorbing inner tube 4.

[0215] Comparative Example 2: Design of the secondary reflector of a conventional compound parabolic concentrator CPC (θ a = 5°, φ t = 175°, r o = 30 mm)

[0216] As shown in (b) of Figure 2 , use the main reflector parameters and its trajectory equation (7) to accurately determine the trajectory of the conventional compound parabolic main reflector 2.

[0217] CPC reflector parameters: acceptance half-angle θ a = 5°, truncation position parameter φ t = 175°. The radius ro of the circular tube absorber 6 of the conventional concentrator is 30 mm, and the tube center is located at the origin of coordinates.

[0218] Trajectory equation of CPC:

[0219]

[0220] The circular tube absorber of the conventional CPC, with a radius r o = 30 mm, and the tube center is located at the origin of coordinates.

[0221] Through non-imaging optical principles and dynamic point-by-point calculations, the present invention realizes the precise design and efficient adaptation of the secondary mirror, significantly improves the concentration ratio and energy flux uniformity, while reducing material consumption and heat loss. The embodiments verify its wide applicability in PTC, CPC and variant systems, providing reliable technical support for the efficient operation of solar thermal systems. Table 1 lists the specific parameters of two embodiments.

[0222] Table 1 Specific parameter values of two embodiments

[0223]

[0224] The above embodiments are only examples, and the parameters can be adjusted according to specific requirements in actual applications. Such variants should all be covered within the protection scope of the present invention.

[0225] As described above, it is only the preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and should all be covered within the protection scope of the present invention.

Claims

1. A design method for a secondary mirror based on non-imaging optics, characterized in that, It includes the following steps: S1: Determine the type of the primary reflector according to the engineering conditions, including the parabolic trough primary reflector PTC (1) or the compound parabolic concentrator CPC (2); S2: Dynamically determine the size and position of the heat-absorbing inner tube (4) based on the type and parameters of the primary reflector; S3: Assume the endpoint position of the secondary reflector (3), then initialize the starting point position of the secondary reflector (3), and then calculate the trajectory coordinates of the secondary reflector (3) point by point from the inside out according to the marginal extreme ray principle and the ray equal optical path constraint conditions, and generate a multi-segment quasi-elliptical line surface through endpoint convergence verification; S4: Analyze the light concentration effect of the secondary reflector (3), and optimize the starting point position of the secondary reflector (3) until the light concentration effect of the secondary reflector (3) reaches the expected goal; S5: According to the positions and sizes of the secondary reflector (3) and the heat-absorbing inner tube (4), select the combination method of the secondary reflector (3) and the vacuum heat collection tube to achieve the dynamic adaptation of the geometric parameters of the secondary reflector (3), the heat-absorbing inner tube (4) and the glass outer tube (5).

2. A design method of a secondary mirror based on non-imaging optics according to claim 1, characterized in that, When the main reflector is a parabolic trough type main reflector PTC(1), its parameters include the acceptance half-angle θ a , focal length F, opening width A a , edge angle φ e , light source division factor K, and the size and position of the heat absorption inner tube (4) are calculated through the following formula: The coordinate origin is set at the center of the parabola, and the trajectory equation of the PTC: Among them, F is the focal length of the parabolic trough type main reflector PTC (1), which can be calculated by formula (2); φ is the angle between the line connecting any point on the parabolic trough type main reflector PTC (1) and the focus and the negative direction of the Y-axis, and its value range is -φ e to φ e ; The light source of the parabolic trough type main reflector PTC (1) is divided into two sub-light sources: ΔS1 and ΔS2. A light source division factor K is introduced to control the relative sizes of the two sub-light sources. The light rays of the sub-light source ΔS1 can directly reach the heat absorption inner tube (4), while the light rays of the sub-light source ΔS2 need to be reflected by the secondary reflector (3) to reach the heat absorption inner tube (4). K can range from 0 to 1. When K = 0.5, both sub-light sources are equal to the acceptance half-angle θ of the concentrator. a ; The center of the tube of the conventional concentrator circular tube absorber 6 is located at the origin of coordinates, and the radius is r o : Where: A ap is the size of the incident light aperture of the PTC; Replace the conventional concentrator circular tube absorber (6) with the heat-absorbing inner tube (4) and the secondary reflector (3), and the radius r of the heat-absorbing inner tube (4): r = 0.5A ap (cot(φ e + θ a (2K - 1)) - cot(φ e + θ a K))sin(φ e + θ a (2K - 1)) (5) The tube center coordinates of the heat-absorbing inner tube (4):

3. A method for designing a secondary mirror based on non-imaging optics according to claim 2, characterized in that, When it comes to the compound parabolic concentrator (CPC) main reflector (2), its parameters include the acceptance half-angle θ a , the truncation position φ t , φ t is the maximum value that the parameter φ in formula (1) can take, the radius r o of the conventional concentrator circular tube absorber (6), and the radius r of the heat-absorbing inner tube (4). The size and position of the CPC heat-absorbing inner tube (4) are calculated by the following formula: The tube center of the conventional concentrator circular tube absorber (6) is located at the coordinate origin, and the trajectory equation of the compound parabolic concentrator CPC (2): where φ is the angle between the line connecting any point on the compound parabolic concentrator (CPC) main reflector (2) and the origin of coordinates and the negative direction of the Y-axis, and its value range is from 0 to φ t ; The tube center coordinates of the heat-absorbing inner tube (4):

4. A design method of a secondary mirror based on non-imaging optics according to claim 1, characterized in that, The specific steps of the step S3 specifically include the following sub-steps: S31: Assume the endpoint position Q of the secondary mirror (3) n *: Since the occlusion of the secondary mirror (3) will affect its own geometric trajectory, and the position Q of the end point of the secondary mirror (3) n is unknown, it is necessary to assume a point on the extreme ray position (7) as its end point position in advance, denoted as Q n *; For the parabolic trough primary reflector PTC (1), the equation of the extreme ray position (7): For the compound parabolic concentrator CPC (2), the equation of the extreme ray position (7): y = Y(φ t ) + tan(φ t )(x - X(φ t )) (10) Preset Q n *The abscissa value of the point, calculate Q through formula (9) or formula (10) n *The ordinate value of the point; S32: Initialize the starting point Q1 position of the secondary reflector (3): For the parabolic trough primary reflector PTC (1), the starting point Q1 of the secondary reflector (3) is initialized as the intersection of the extreme ray (9) and the Y-axis, and is obtained by the formula (11): For the compound parabolic concentrator CPC (2), the starting point Q1 of the secondary reflector (3) is initialized as the top end of the heat-absorbing inner tube (4), and is obtained by the formula (12): The starting point Q1 of the secondary reflector (3) needs to be further optimized and adjusted according to the optical simulation situation later; S33: Use an iterative algorithm to recursively solve the subsequent coordinate sequence Q of the secondary mirror (3) i (i = 2, 3, 4... n): The trajectory coordinates of all points are determined sequentially by point-by-point calculation, that is, the position of point Q2 is determined by point Q1, and then the position of point Q3 is determined by the position of point Q2, and so on, until the extreme ray position (7) extended by the secondary mirror (3) is calculated, and this point is the endpoint Q obtained by calculation n ; S34: Endpoint convergence verification: Compare the assumed endpoint Q n *Position with the calculated Q n For the actual position, revise the position of the assumed endpoint Q n Repeat steps S32, S33, and S34 until the abscissa error between the assumed endpoint and the calculated endpoint is less than the allowable error ε 5. A design method of a secondary mirror based on non-imaging optics according to claim 4, characterized in that, The specific process of the iterative calculation in the step S33 includes the following steps: S331: Calculate the spatial point Q i The fixed foci P of (i = 1, 2, 3..n) i Through Q i Calculate Q at point i+1 When calculating the Q i point coordinates, it is first necessary to calculate the fixed focus Pi of the Q point. There are multiple points on the primary mirror, and the incident light within the acceptance angle can reach the spatial point Q after being reflected by these points i , select the leftmost P i point as the fixed focus of the Q i point, and the specific positioning process is as follows: Find point P T , the line connecting point Q and P T is tangent to the heat-absorbing inner tube (4), and the angle between the tangent point and the Y-axis is represented by φ c ; The coordinates (X(φ T ), Y(φ PT )) of point P on the primary mirror can be determined by solving the system of equations (13). The fixed focus can only appear on the right side of point P, otherwise it will be intercepted by the heat-absorbing inner tube (4). If the light within the acceptance angle (±θa) can reach the spatial point Q1 after being reflected by point P PT ), the fixed focus can be directly selected as point P T without subsequent calculations; T If the light within the acceptance angle (±θa) can reach the spatial point Q1 after being reflected by point P T ), the fixed focus can be directly selected as point P without subsequent calculations; Through the secondary mirror assuming the end point Q n * And the extreme ray (11) with an incident angle of π / 2 - θa is incident on the main mirror at point P S Through the secondary mirror assuming the end point Q n * And the extreme ray (12) with an incident angle of π / 2 + θa is incident on the main mirror at point P E point; The position parameters of P can be determined by solving Expression (14) and Expression (15). S and P E can be obtained. At point P S and point P ap Find point P between A , assuming endpoint Q through the secondary mirror n * and the extreme ray (12) with an incident angle of π / 2 + θa is incident on the primary mirror at point P A Point, and after reflection, it can reach point Q1 on the secondary mirror. The slope of the reflected light is represented by k A Indicated; Y Q1 -Y PA =k A (X Q1 -X PA ) max(X PS , X PT ) ≤ X PA ≤ X Pap (16) At point P E and point P ap Find point P B between them. Assume that the extreme ray (12) with an incident angle of π / 2 + θa at the end point Qn* is incident on the primary mirror at point P B and can reach point Q1 on the secondary mirror after reflection. The slope of the reflected light is represented by k B ; Y Q1 -Y PB =k B (X Q1 -X PB ) max(X PE , X PT ) ≤ X PB ≤ X Pap (17) At point P S and point P E Find point P C between them. Within the light source angle range, the light passing through the extreme ray position Q n * is incident on point P3 of the main reflector and can reach point Q on the secondary reflector (3) after reflection. The slope of the reflected light is represented by k C . If P S and P E are both on the left side of P T , then there is no P C point that meets the requirements; Y Q1 -Y PC =k C (X Q1 -X PC ) max(X PS , X PT ) ≤ X PC ≤ X PE (18) Solve for P according to formulas (16), (17), and (18). A , P B , P C coordinates, and select the leftmost point as the spatial point Q i 's fixed focus, denoted by P i , and the extreme ray is tangent to the heat-absorbing inner tube (4) at point C after reflection by P i and Q i ; i point S332: Calculate the adjacent trajectory point Q through the equal optical path constraint formula i+1 Coordinates: Regarding point P i as a point light source, the light rays within the acceptance angle (±θa) can all reach the heat absorption inner tube (4) tangentially after being reflected by R i and Q i Q i+1 curve. The landing point on the heat absorption inner tube (4) is called the moving focus, and the moving focus moves along the heat absorption inner tube (4) from point C i to point C i+1 . Therefore, the Q i Q i+1 curve is a section of a quasi-ellipse; Solve for Q based on Equation (19) i+1 Point coordinates, where v is a fixed value. For each v-degree movement of the moving focus, a section of the quasi-elliptical line is designed. The smaller the value of v, the more segments and the smaller the size of the secondary mirror, and the better the light-gathering effect. S333: Calculate the endpoint Q of the secondary mirror (3) point by point n : Repeat steps S331 and S332 until the secondary mirror (3) extends to the extreme ray position (7) to obtain the calculated endpoint coordinates Q n .

6. A design method of a secondary mirror based on non-imaging optics according to claim 5, characterized in that In the step S332, the value range of v is 0.1° - 2°.

7. A design method of a secondary mirror based on non-imaging optics according to claim 1, characterized in that The combination methods of the secondary reflector (3) and the vacuum heat collection tube in the step S5 include: Full encapsulation built-in type: The secondary reflector (3) is integrated into the internal space of the glass outer tube (5), and the environmental tolerance and structural stability are improved through a fully sealed structure design; External attached independent type: The secondary reflector (3) is modularly independently encapsulated and externally installed on the outside of the vacuum heat collection tube, which is compatible with the direct replacement of commercial vacuum tubes and reduces the engineering transformation cost; Internal and external separation optimization type: Optimize the segmented layout of the reflector based on optical simulation. Some reflector units are placed outside the outer glass tube (5) to balance the geometric size of the secondary reflector (3) and the utilization rate of the internal space of the outer glass tube (5).

8. A concentrating collector, characterized in that, It includes: The primary reflector, including a parabolic trough primary reflector PTC (1) or a compound parabolic primary reflector CPC (2); The heat-absorbing inner tube (4), with a selective absorption coating on its surface, and its size and position are dynamically determined based on the parameters of the primary reflector; The secondary reflector (3), composed of multiple segments of quasi-elliptical lines, is generated by a method for designing a secondary reflector based on non-imaging optics described in any one of claims 1-7, and is used to secondarily focus the escaping light onto the surface of the heat-absorbing inner tube (4); The outer glass tube (5), which is adaptively installed with the secondary reflector (3), includes an externally attached independent type, a fully encapsulated built-in type, or an internal and external separation optimization type structure.

9. A concentrating collector according to claim 8, wherein, The material of the secondary reflector (3) is a high-reflectivity metal, coated glass, or a high-reflectivity coating.

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