Novel groove type concentrating solar heat collection system and design method thereof

Abstract

The invention discloses a novel groove type concentrating solar heat collection system, which is characterized in that a main reflector is a line focusing reflector, a secondary reflector is a cylindrical reflector, the secondary reflector is arranged between the vertex and the focus of the main reflector, the concentrating direction of the secondary reflector is vertical to the concentrating direction of the main reflector, the main reflector is arranged on a single-axis tracking device, and the single-axis tracking device is arranged on the base. The receiver is installed on a focus of the concentrating solar heat collection system and can move front and back to track focus position movement under different incident angles. The working temperature of the system is 550 DEG C, and the photo-thermal efficiency of the system can reach 63.3% and is close to the efficiency of a tower system, so that the performance of the system is quite excellent. According to the system, the receiver needs to be moved to receive focused solar rays under different incident angles, a second tracking device does not need to be provided for the main reflecting mirror, the large-scale and low-cost single-shaft horizontally-installed groove type system is kept, and the reliability of the system is improved.

Description

Technical Field

[0001] The invention relates to the technical field of solar energy heat collection systems, and in particular to a novel trough type concentrated solar energy heat collection system and a design method thereof. Background Art

[0002] Line focusing solar concentrators are usually designed as parabolic trough concentrators or linear Fresnel concentrators. These concentrators only need one axis rotation to track the sun, and their linear geometry is well matched to the receiving tube placed on the focal line, which converts light energy into heat energy and transmits energy through a liquid medium. Line focusing concentrators are one of the most widely used solar concentrators, however, the disadvantage of these linear focus concentrators is that their concentration ratio is limited. Since they can only focus sunlight in one direction, the maximum concentration ratio does not exceed the result of the following formula:

[0003]

[0004] Here θ is the acceptance half angle of the concentrator. For the common line-focusing parabolic trough concentrator, when using a tube receiver, the theoretical maximum concentration ratio is:

[0005]

[0006] Ideally, the interception half angle is equal to the half angle of view of the solar photosphere, which is 4.65 mrad. For a parabolic trough system using a tube receiver, the theoretical concentration ratio is 68.45. If atmospheric scattering, installation of the concentrator, tracking error, and optical error of the reflector are taken into account, the interception half angle is much larger. The geometric concentration ratio of the trough concentrator on the European market is only 26. 1 The product design is based on the system Gaussian distribution average error of about 8mrad, interception half angle of about 20mrad 2 ,The interception rate is only 90%, and coupled with the cosine factor loss, the system efficiency is low.

[0007] Since the radiation and convection heat loss of the concentrator is proportional to the light-passing area of ​​the receiver, increasing the concentration ratio of the line focusing concentrator, that is, reducing the light-passing area of ​​the receiver, is conducive to improving the efficiency of the system. Increasing the concentration ratio is one of the main measures to improve the efficiency of the system, and people have proposed many methods. Using a cavity or flat receiver instead of a tubular receiver, the theoretical concentration ratio can be increased to 107.53; adding a compound parabolic concentrator or a V-groove concentrator in front of the receiver can reduce the radius of the tubular receiver. 3 ; and similar secondary concentrators designed using the multi-surface method 4 wait.

[0008] In the field of astronomical optics, two reflectors are often used to form a telescope, which can also achieve the effect of focusing light. It can eliminate the field and coma at the same time to form a bright optical system. At this time, the image radius is reduced and the image quality is improved. This technical solution is also widely used in solar concentrators. 5 The latest technology has increased the concentration ratio of the line focusing trough system to 55. 6 However, these methods are all limited by the concentration ratio caused by the line focusing system that can only focus in one direction. Although there is some improvement in the geometric concentration ratio, adding a reflector not only increases the reflection loss, but also increases the divergence of the reflected light, and the overall efficiency does not necessarily increase, so it is rarely used in actual products.

[0009] Compared with the rotating parabola and other point focusing reflectors, which can focus sunlight in two directions, the theoretical concentration ratio is the square of the concentration ratio of the linear concentrator, which is theoretically 46248 times. The main measure to surpass the theoretical limitation of linear concentrators while maintaining the advantage of using only a single tracking device in the line focusing system is to introduce a concentrator in another direction to improve the concentration ratio. As far as we know, the earliest scheme 7 After the parabolic concentrator, a cylindrical lens is used to continue focusing the light. Experiments show that the geometric concentration ratio is as high as 1100X, and the interception rate is about 50%. However, this method requires dual-axis external tracking of the sun and requires a relatively large amount of reflection and refraction. Each reflection and refraction will reduce the efficiency.

[0010] The latest improvement measure is to use a second concentrator to focus in another direction, which is equivalent to using two line focusing concentrators to achieve point focusing function. Using a bidirectional V-groove or bidirectional compound parabolic concentrator does not require additional tracking equipment, and it is easiest to achieve focusing in another direction, and improve the original direction focusing, so that the concentration ratio can be greatly improved. Among them, the V-groove concentrator uses a flat reflector, which has a simple structure and low cost, but its disadvantage is that it needs to be reflected multiple times inside the concentrator. Since each reflection will lose energy, it has a high geometric concentration ratio, but the collection efficiency is reduced, and the energy concentration ratio is much lower, so it has no practical application value in the field of medium and high temperature concentrated solar energy. Even if 4 reflections are considered, the geometric concentration ratio is only 5.7 times. If an ordinary reflector is used, even if the reflectivity is as high as 94%, 22% of the energy will be lost due to multiple reflections; and the reflector area is large and consumes a lot of materials.

[0011] The compound parabolic concentrator uses two parabolic reflectors to replace the two flat reflectors in the V-groove concentrator. For the line-focusing compound parabolic concentrator, its theoretical concentration ratio is also 1 / sin0. As a solar concentrator, under ideal conditions, the theoretical value is 215.1, which is consistent with the V-groove concentrator. Due to the use of parabolas, the manufacturing difficulty increases, and the actual application value in the medium-temperature concentrated solar thermal utilization system is even smaller. The latest design is to use multiple flat reflectors to form a quasi-parabolic reflector. 8 .

[0012] Use a refractive compound parabola or V-groove concentrator, that is, a V-groove or compound parabola made of transparent material. 9 At this time, the reflection that occurs on the side is total reflection, and there is no reflection loss, but the path of the light in the internal refractive material is longer, and the absorption effect is relatively large, which also brings energy loss. However, at this time, the concentration ratio will increase by the square of the refractive index n of the reflective compound parabolic concentrator. Under the north-south axis tracking, a two-way compound parabolic concentrator is used. Even if it is fixedly installed and no second tracking device is added, the incident angle is within the range of plus or minus 23.5 degrees, and the concentration multiple can reach 7.6 times, and the overall system concentration multiple can reach 300 times. 10 .

[0013] When this secondary concentrator is fixed on the common north-south or east-west horizontal axis, the incident angle becomes very large. In many operating conditions, not only is there no focusing effect, but the incident light is prevented from reaching the receiver. At this time, it is necessary to add a rotating device to track the incident angle of sunlight, which can significantly increase the focusing multiple. The parabolic trough concentrator using a refractive compound parabolic secondary concentrator has an estimated theoretical focusing multiple of 6000 times, and the maximum focusing ratio of the design working at 20 degrees latitude is 1482 times. 11 However, when the secondary refraction concentrator of this scheme works under such a high energy flux density, the temperature will increase significantly, causing problems such as expansion of the refraction material, resulting in increased optical errors and reduced actual focusing multiples. In addition, the secondary concentrator consumes a lot of materials and is costly, which also hinders practical application.

[0014] The latest technical solution is to use a second curved mirror 12, focusing in another direction, thus avoiding the disadvantages of using the above-mentioned compound parabolic concentrator. This technical solution uses a variety of specially designed curved reflectors, which need to be moved to track sunlight at different incident angles. When the interception rate reaches 80% at an interception radius of 9mrad, the concentration ratio reaches 335. The disadvantage is that the system is very complicated, and special secondary concentrators need to be designed for reflectors with different edge angles in the linear parabolic concentrator. Although the concentration ratio can be increased to 1563, the types of secondary reflection concentrators that need to be specially designed and manufactured have also increased dramatically. Whether it has practical application value remains to be tested. Summary of the invention

[0015] The purpose of the present invention is to remedy the defects of the prior art and provide a novel trough-type concentrated solar thermal collection system and a design method thereof.

[0016] The present invention is achieved through the following technical solutions:

[0017] A novel trough-type concentrated solar thermal collection system includes a main reflector, a secondary reflector, a receiver and a single-axis tracking device. The main reflector is a line focusing reflector, the secondary reflector is a cylindrical reflector, the secondary reflector is installed between the vertex and the focus of the main reflector, the focusing direction of the secondary reflector is perpendicular to the focusing direction of the main reflector, the main reflector is installed on the single-axis tracking device, the receiver is installed on the focus of the concentrated solar thermal collection system, and the receiver can move forward and backward to track the movement of the focus position under different incident angles.

[0018] The main reflector is a line-focusing parabolic reflector or is composed of a plurality of strip cylindrical reflectors. The centers of the plurality of strip cylindrical reflectors form a parabola, and the center normal vector of each strip cylindrical reflector is consistent with the parabola normal vector of its installation position.

[0019] The receiver is a cavity receiver or a flat panel receiver.

[0020] The edge angle of the primary reflector Between 30-60 degrees.

[0021] The position of the secondary reflector and the width of the main reflector in the focusing direction are determined by the shading ratio α of the secondary reflector, α is between 0.03 and 0.15, the width of the secondary reflector in the focusing direction of the main reflector = the width of the main reflector * shading ratio α, the distance from the vertex of the secondary reflector to the vertex of the main reflector = the focal length of the main reflector * (1-α) + the height of the secondary reflector h / 2; the half width w of the secondary reflector in the focusing direction y The spherical aberration θ generated in the focusing direction of the main reflector is x Determine, according to the following formula:

[0022]

[0023] is the edge angle of the main reflector, W is the half-width of the main reflector, and the spherical aberration θ x The smaller it is, the less impact it has on system performance.

[0024] The tracking axis of the concentrated solar thermal system is installed in the north-south direction.

[0025] The working location of the concentrated solar thermal system is within the Tropic of Cancer and the Tropic of Capricorn and is installed horizontally; in high-latitude areas outside the Tropic of Cancer and the Tropic of Capricorn, the tracking axis is parallel to the earth's axis.

[0026] A novel trough-type concentrated solar thermal collection system design method specifically includes the following steps:

[0027] The first step is to complete the preliminary design, including:

[0028] 1) Preliminary design of the main reflector, determine the half-width W of the main reflector according to the requirements; the edge angle of the main reflector The initial design selected 45 degrees; the vertex curvature radius of the primary reflector is calculated as follows:

[0029]

[0030] The initial design selects the main reflector as a parabola, e = 1, then r1,

[0031]

[0032] Then the focal length f 1 =r 1 / 2; y1 half width of the primary reflector, r 1 is the radius of curvature of the primary reflector;

[0033] 2) Preliminary design of the secondary reflector. The shading ratio of the secondary reflector is initially selected as α, then the half width of the secondary reflector in the x direction, that is, the focusing direction of the main reflector, is:

[0034] w x =W*α

[0035] The half width of the secondary reflector in another focusing direction is calculated as follows:

[0036]

[0037] θ x is the spherical aberration θ produced by the secondary reflector in the focusing direction of the primary reflector x , the initial design chooses 0.5mrad, and the focal length of the secondary reflector is calculated as follows:

[0038] f2 =f 1 *α+h / 2

[0039] h is the height of the secondary reflector, calculated as follows

[0040]

[0041] r 2 is the radius of curvature of the secondary reflector vertex, f1 is the focal length of the primary reflector, f1 = r1 / 2;

[0042] Secondary reflector installation position, distance between vertex and primary reflector vertex:

[0043] d=(1-α)*f 1 -h / 2

[0044] 3) Preliminary design of the receiver. The calculation formula for the half width in the x and y directions is:

[0045]

[0046] k x and k y are the receiver interception ratios in the x and y directions, σ t is the total error of the Gaussian distribution of reflected light intensity,

[0047] The initial design takes 3; the distance between the receiver and the vertex of the secondary reflector = the focal length of the secondary reflector = r 2 / 2;

[0048] The second step is to establish a ray tracing method system performance simulation calculation program;

[0049] In the third step, the net energy efficiency is taken as the goal, and the annual average incident angle of the trough system is used as the incident angle in the y direction to optimize the optimal design parameters under different working locations.

[0050] The advantages of the present invention are: the operating temperature of the system of the present invention is 550 degrees, and the system's photothermal efficiency can reach 63.3%, which is close to the efficiency of the tower system, indicating that the system of the present invention has excellent performance even when working at high temperatures. The system of the present invention does not need to install a second tracking device for the main reflector, thereby simplifying the system design and improving the system reliability. The system requires a mobile receiver to receive focused sunlight at different incident angles. Compared with the dish system, the main advantage is that it does not need to provide a second tracking device for the main reflector, maintaining the scale and low cost characteristics of the single-axis horizontal installation trough system. The present invention only uses commonly used industrial products, cylindrical reflectors, and can achieve a 400-fold point focusing effect for the line focusing trough system at a low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1This is a stereoscopic diagram of the installation of the primary reflector and the secondary reflector of the present invention;

[0052] Figure 2 This is a side view of the installation of the primary reflector and the secondary reflector of the present invention;

[0053] Figure 3 A side view of another direction of installing the primary reflector and the secondary reflector of the present invention;

[0054] Figure 4 A schematic diagram of spherical aberration produced by a bidirectional focusing parabolic trough system composed of two mirrors of the present invention;

[0055] Figure 5 This is a graph showing the impact of incident angle on system performance. DETAILED DESCRIPTION

[0056] like Figure 1-3 As shown, a novel trough-type concentrated solar thermal collection system includes a main reflector 1, a secondary reflector 2, a receiver and a single-axis tracking device. The main reflector 1 is a line focusing reflector, the secondary reflector 2 is a cylindrical reflector, the secondary reflector 2 is installed between the vertex and the focus of the main reflector 1, the focusing direction of the secondary reflector 2 is perpendicular to the focusing direction of the main reflector 1, the main reflector 1 is installed on the single-axis tracking device, the receiver is installed at the focus of the concentrated solar thermal collection system, and the receiver can move forward and backward to track the movement of the focus position under different incident angles.

[0057] The main reflector 1 is a line-focusing parabolic reflector or is composed of a plurality of strip cylindrical reflectors. The centers of the plurality of strip cylindrical reflectors form a parabola, and the center normal vector of each strip cylindrical reflector is consistent with the parabola normal vector of its installation position.

[0058] The receiver is a cavity receiver or a flat panel receiver.

[0059] The edge angle of the main reflector 1 Between 30-60 degrees.

[0060] The position of the secondary reflector 2 and the width of the primary reflector 1 in the focusing direction are determined by the shading ratio α of the secondary reflector 2, α is between 0.03 and 0.15, the width of the secondary reflector 2 in the focusing direction of the primary reflector 1 = the width of the primary reflector 1 * the shading ratio α, the distance from the vertex of the secondary reflector 2 to the vertex of the primary reflector 1 = the focal length of the primary reflector 1 * (1-α) + the height of the secondary reflector 2 h / 2; the half width w of the secondary reflector 2 in the focusing direction y The spherical aberration θ generated by the main reflector 1 in the focusing direction is x Determine, according to the following formula:

[0061]

[0062] is the edge angle of the primary reflector 1, W is the half-width of the primary reflector 1, where the spherical aberration θ x The smaller it is, the less impact it has on system performance.

[0063] The tracking axis of the concentrated solar thermal system is installed in the north-south direction.

[0064] The working location of the concentrated solar thermal system is within the Tropic of Cancer and the Tropic of Capricorn and is installed horizontally; in high-latitude areas outside the Tropic of Cancer and the Tropic of Capricorn, the tracking axis is parallel to the earth's axis.

[0065] The present invention only uses a commonly used industrial product, a cylindrical reflector, to enable the line focusing trough system to achieve a 400-fold point focusing effect at a low cost. Another line focusing reflector is used as a secondary concentrator to focus light in another direction, thereby achieving a point focusing effect. In the field of astronomical optics, two reflectors are often used to eliminate the field and coma aberrations at the same time to form a bright optical system. At this time, the image radius is reduced and the imaging quality is improved. This technical solution can also be applied to the line focusing system 13 , the main reflector can also use a linear Fresnel system 14 , only focusing in one direction. Although there is some improvement in the geometric focusing ratio, adding a reflector not only increases the reflection loss, but also increases the divergence of the reflected light. The overall efficiency does not necessarily increase, so it is less used. The added secondary focusing reflector is mainly used to focus light in another direction, which can greatly increase the focusing multiple. The disadvantage is that a tracking device must be added so that the secondary line focusing concentrator can focus light. However, the light in the focusing direction of the main reflector is also reflected by the secondary reflector, which may cause divergence due to the secondary being a curved surface. Therefore, the curved surface of the secondary reflector must consider the negative impact on the focusing direction of the main reflector. The simplest design is a plane in the direction of the main reflector, that is, the secondary reflector is a cylinder, and the simplest cylinder is a cylindrical surface. This article introduces a reduced design scheme based on this. The main reflector is a parabolic trough reflector, and the tracking axis is installed in the north-south direction. With the trough half-width W of 4 meters, the edge angle of 30 degrees, and the focal length According to the design of the secondary reflector focusing system, the secondary reflector is a plane mirror. If α = 0.1, the distance between the secondary reflector and the vertex of the primary reflector is (1-α)f, and the distance between the receiving surface and the vertex of the primary reflector is (1-2α)f. If the secondary reflector is a circular surface in another direction, it is actually a cylindrical surface. If its half width in the vertical (y direction) is w y , the radius is r, then its height is This causes the light reflected by the secondary reflector to change in the focusing direction of the primary reflector, increasing the image spot width. To reduce the image spot size, a smaller w should be selected; at the same time, the vertex should be (1-α)f+0.5*h away from the vertex of the primary reflector to minimize the influence of the cylindrical surface curvature. At this time, the focus of the cylindrical secondary reflector is on the receiving surface of the primary reflector, such as Figure 4 As shown, we have:

[0066] F2=αf1+0.5*h=0.5*r

[0067] From this we get:

[0068]

[0069] The half width of the cylinder in the x direction is w x , can be calculated as follows:

[0070]

[0071] At this time, the spherical aberration caused by the marginal light focused by the main reflector is:

[0072]

[0073] Convert to angle:

[0074]

[0075] If the longitudinal width of the secondary reflector is 0.2 meters, the spherical aberration is 1.2 mrad, and the average spherical aberration can be integrated to obtain one third of it, that is, 0.4 mrad. If the edge angle of the primary reflector is increased to 45 degrees, the maximum spherical aberration is 2.07 mrad and the average spherical aberration is 0.69 mrad. From this, the following formula can be obtained to calculate the width of the secondary reflector in the focusing direction (perpendicular to the focusing direction of the primary reflector):

[0076]

[0077] Assuming the parabola slope error is 2.5mrad, the cylindrical slope error is 1mrad, the solar image spot Gaussian radius is 3.0mrad, and other optical errors are 1mrad, the total error is 6.285mrad. The receiver x-direction half width can be approximately calculated as 3 times the image spot width produced by the total error. The receiver y-direction half width can be calculated as 5 times the image spot width produced by the total error.

[0078] Ray tracing calculations show that when using one-way tracking, the system performance changes with the incident angle in the other direction and drops rapidly. The best case is to install a tracking device on the receiver and use geocentric tracking. When the incident angle is at an intermediate value, the optimized design photothermal efficiency can reach 57.6%, but when the incident angle is 0 and the maximum 23.5 degrees, the efficiency drops to 52.7% and 47.3%. The system should use dual-axis tracking, or geocentric tracking, but the geocentric inclination needs to be adjusted every day. The receiver is installed on the tracking device, and the performance can be kept at the best state at all times, reaching 66.9%. The secondary reflector uses a cylindrical reflector, which has significantly better performance than a parabolic reflector. This is because the parabolic reflector has a large error, but even if the errors of the two are the same, their performance is almost the same.

[0079] With net energy efficiency as the goal, the receiver is installed on the tracking device, the reflectivity of the primary and secondary reflectors are 0.93 and 0.96 respectively; the slope error of the spherical mirror is 1mrad, the slope error of the parabolic reflector is 2.5mrad, the other errors are 1mrad, and the average error deviation of the Gaussian distribution of solar intensity is 3mrad. A cavity receiver is used, the operating temperature is 550℃, the heat loss coefficient is 35., the absorption rate is 0.98, and 5% other losses are considered. The width of the primary reflector is 8 meters, and the spherical aberration of the secondary reflector is increased. With 1mrad as the goal, the following are the optimized design parameters:

[0080]

[0081] like Figure 5 The figure shows the effect of the incident angle of the system on the interception rate and photothermal efficiency of the system when both the receiver and the secondary reflector are fixedly installed. When the incident angle is only 0.1 to 0.2 degrees, the system performance remains almost unchanged, but when it increases to 1 degree, the interception rate drops to 70% and the photothermal efficiency drops to 47.0%, both of which are much lower than vertical incidence. When using the geo-axis tracking system, the inclination angle of the tracking axis changes by 47 degrees in a year, with an average change of 0.129 degrees per day. In other words, the geo-axis tracking system can be used, and the inclination angle only needs to be adjusted once a day to maintain system performance.

[0082] The operating temperature of the above-designed system is 550 degrees, which belongs to the application range of high-temperature power generation. The system's secondary reflector plus tracking system can achieve a photothermal efficiency of 66.9%, and the system efficiency exceeds that of the tower type. The system should use dual-axis tracking, but it can also use geocentric tracking. By adjusting the geocentric inclination every day, there is no need to install a second tracking device for the main reflector, thereby simplifying the system design and improving the system reliability. Compared with the dish system, the main advantage is that there is no need to provide a second tracking device for the main reflector, maintaining the low cost characteristics of the single-axis installation trough system.

[0083] The documents cited in the present invention are as follows:

[0084] 1.M.Geyer,E.Lüpfert,R.Osuna,A.Esteban,W.Schiel,A.Schweitzer,E.Zarza,P.Nava,J.Langenkamp,and E.Mandelberg,“EUROTROUGH-Parabolic Trough CollectorDeveloped for Cost Efficient Solar Power Generation,”Proceedings of the11thInternational Symposium on Concentrating Solar Power and Chemical EnergyTechnologies p.7(2002).

[0085] 2.Bendt P,Rabl A,Gaul H W,et al.Optical analysis and optimization ofline focus solar collectors.Report of Solar Energy Research Institute,1979,29(9):568.https: / / doi.org / 10.2172 / 5746400

[0086] 3.M.Collares-Pereira,J.M.Gordon,A.Rabl,and R.Winston,“Highconcentration two-stage optics for parabolic trough solar collectors withtubular absorber and large rim angle,”Sol.Energy 47(6),457–466(1991)

[0087] 4.P.Benítez,R.García,and J.C.Mi nano,“Contactless efficient two-stagesolar concentrator for tubular absorber,”Appl.Opt.36(28),7119–7124(1997)

[0088] 5.Jeffrey M.Gordon, Aplanatic optics for solar concentration, Opt.Express18(S1)A41-A52(2010)

[0089] 6. Leonardo FLde Souza, Naum Fraidenraich, and Jeffrey M.Gordon, Aplanatic solar concentrators for tubular absorbers, Optics Letters Vol.49, Issue 6, pp.1441-1444 (2024)

[0090] 7.N.Davidson, L.Khaykovich, and E.Hasman, "Anamorphic concentration of solar radiation beyond the one-dimensional thermodynamic limit," Appl.Opt.39(22),3963–3967(2000)

[0091] 8. Chen Fei. Principles and Applications of Non-imaging Solar Concentration[M]. Beijing: Science Press, 2021.12.pp148

[0092] 9. Winston, & Roland. (2005). Nonimaging optics. Elsevier Academic Press, pp69

[0093] 10.Brunotte,M.,Goetzberger,A.,&Blieske,U..(1996).Two-stageconcentrator permitting concentration factors up to 300x with one-axistracking.Solar Energy,56(3),pp285-300.

[0094] 11.Cooper,T.,Ambrosetti,G.,Pedretti,A.,&Steinfeld,A..(2013).Theoryand design of line-to-point focus solar concentrators with tracking secondaryoptics.Appl Opt,52(35),pp8586-8616

[0095] 12. J.D.Johnsen,et al.Line-focus solar concentration 10timeshigher than the 2D thermodynamic limit,Opt.Express 30(14)pp24362-24374(2022)

[0096] 13.M.Collares-Pereira,J.M.Gordon,A.Rabl,and R.Winston,“Highconcentration two-stage optics for parabolic trough solar collectors withtubularabsorber and large rim angle,”Sol.Energy 47,457–466(1991).L.F.L.deSouza,N.Fraidenraich,and J.M.Gordon,Aplanatic solar concentrators for tubularabsorbers,Optics Letters Vol.49(6),pp.1441-1444(2024) https: / / doi.org / 10.1364 / OL.517874

[0097] 14.L.F.L.de Souza,N.Fraidenraich,C.Tiba,et al.,Analytic opticalevaluationof linear aplanatic solar Fresnel reflectors,Sol.Energy 249(2023),107-121。

Claims

1. A new type of trough-type concentrated solar thermal system, characterized by: The invention comprises a main reflector, a secondary reflector, a receiver and a single-axis tracking device. The main reflector is a line focusing reflector, the secondary reflector is a cylindrical reflector, the secondary reflector is installed between the vertex and the focus of the main reflector, the focusing direction of the secondary reflector is perpendicular to the focusing direction of the main reflector, the main reflector is installed on the single-axis tracking device, the receiver is installed on the focus of the concentrated solar thermal collection system, and the receiver can move forward and backward to track the movement of the focus position under different incident angles.

2. A novel trough type concentrated solar thermal system according to claim 1, characterized in that: The main reflector is a line-focusing parabolic reflector or is composed of a plurality of strip cylindrical reflectors. The centers of the plurality of strip cylindrical reflectors form a parabola, and the center normal vector of each strip cylindrical reflector is consistent with the parabola normal vector of its installation position.

3. A novel trough-type concentrated solar thermal collection system according to claim 1, characterized in that: The receiver is a cavity receiver or a flat panel receiver.

4. A novel trough type concentrated solar thermal collection system according to claim 1, characterized in that: The edge angle of the primary reflector Between 30-60 degrees.

5. A novel trough type concentrated solar thermal collection system according to claim 4, characterized in that: The position of the secondary reflector and the width of the main reflector in the focusing direction are determined by the shading ratio α of the secondary reflector, which is between 0.03 and 0.

15. The width of the secondary reflector in the focusing direction of the main reflector = the width of the main reflector * the shading ratio α. The distance from the vertex of the secondary reflector to the vertex of the main reflector = the focal length of the main reflector * (1-α) + the height of the secondary reflector h / 2; the half width w of the secondary reflector in the focusing direction y The spherical aberration θ generated in the focusing direction of the main reflector is x Determine, according to the following formula: is the edge angle of the main reflector, W is the half-width of the main reflector, and the spherical aberration θ x The smaller it is, the less impact it has on system performance.

6. A novel trough type concentrated solar thermal collection system according to claim 1, characterized in that: The tracking axis of the concentrated solar thermal system is installed in the north-south direction.

7. A novel trough type concentrated solar thermal collection system according to claim 6, characterized in that: The working location of the concentrated solar thermal system is within the Tropic of Cancer and the Tropic of Capricorn and is installed horizontally; in high-latitude areas outside the Tropic of Cancer and the Tropic of Capricorn, the tracking axis is parallel to the earth's axis.

8. A novel trough-type concentrated solar thermal system design method, characterized in that: The specific steps include: The first step is to complete the preliminary design, including: 1) Preliminary design of the main reflector, determine the half-width W of the main reflector according to the requirements; the edge angle of the main reflector The initial design selected 45 degrees; the vertex curvature radius of the primary reflector is calculated as follows: The preliminary design selects the main reflector as a parabola, e = 1, then r1, Then the focal length f1 = r1 / 2, y1 is the half width of the main reflector, and r1 is the radius of curvature of the main reflector; 2) Preliminary design of the secondary reflector. The shading ratio of the secondary reflector is initially selected as α, then the half width of the secondary reflector in the x direction, that is, the focusing direction of the main reflector, is: w x =W*a The half width of the secondary reflector in the other focusing direction is calculated as follows: θ x is the spherical aberration θ produced by the secondary reflector in the focusing direction of the primary reflector x , the initial design chooses 0.5mrad, and the focal length of the secondary reflector is calculated as follows: f2=f1*α+h / 2 h is the height of the secondary reflector, calculated as follows r2 is the radius of curvature of the secondary reflector vertex, f1 is the focal length of the primary reflector, f1 = r1 / 2; Secondary reflector installation position, distance between vertex and primary reflector vertex: d=(1-α)*f1-h / 2 3) Preliminary design of the receiver. The calculation formula for the half width in the x and y directions is: k x and k y are the receiver interception ratios in the x and y directions, σ t is the total error of Gaussian distribution of reflected light intensity; The distance between the receiver and the vertex of the secondary reflector = the focal length of the secondary reflector = r2 / 2; The second step is to establish a ray tracing method system performance simulation calculation program; In the third step, the net energy efficiency is taken as the goal, and the annual average incident angle of the trough system is used as the incident angle in the y direction to optimize the optimal design parameters under different working locations.

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