A design method for a free-form reflector array of a solar concentrator

Abstract

This invention discloses a design method for a freeform surface reflector array of a solar concentrator. The solar concentrator includes a freeform surface reflector array, a multi-junction solar photovoltaic cell, and a supporting structure. The multi-junction solar photovoltaic cell is mounted on the supporting structure with its photosensitive surface facing the reflective surface of the freeform surface. Several freeform surface reflectors, each with a rectangular aperture, are closely arranged to form a reflector array. A ray mapping method is used to collaboratively design each freeform surface, and each freeform surface reflector independently controls the incident light beam, generating a rectangular light spot with uniform energy distribution at the same spatial position. Parallel incident sunlight is focused onto the multi-junction solar photovoltaic cell after passing through all the freeform surface reflectors, forming a rectangular light spot with uniform illuminance distribution. The size and dimensions of the light spot are consistent with the size and dimensions of the photosensitive surface of the solar photovoltaic cell, thereby improving the uniformity and concentration ratio of light concentration.

Description

Technical Field

[0001] The present invention belongs to the field of solar energy concentration, and more specifically, relates to a design method for a free-form surface reflector array of a solar energy concentration device. Background Art

[0002] With the increasing global energy crisis and environmental pollution, the development and utilization of new renewable clean energy has become an urgent need for people's production, life and the maintenance of sustainable social development. Solar energy has an irreplaceable position in the new energy structure due to its advantages such as cleanliness and no greenhouse effect. The effective use of solar energy is considered to be one of the important ways to solve the energy crisis. Among them, Concentrating Photovoltaic (CPV) power generation technology has been recognized as one of the most promising ground-based power generation technologies due to its unique advantages, such as high photoelectric conversion efficiency and low power generation cost.

[0003] However, the high cost of multi-junction solar cells has become the main obstacle to their large-scale use. As an important component of the CPV system, the concentrating optical device can focus a large area of ​​sunlight onto a small area of ​​multi-junction solar cells, reducing the use area of ​​expensive multi-junction solar photovoltaic cells, thereby significantly reducing the cost of power generation. A CPV concentrating device with superior performance needs to meet the following requirements at the same time: 1) Uniform distribution of light intensity to ensure uniform heating of the photovoltaic cells, improve photoelectric conversion efficiency, and extend service life; 2) Matching the shape of the light spot with the shape of the photovoltaic cell to improve the effective utilization rate of the photovoltaic cell; 3) Low dispersion to ensure that the ultra-wide solar spectrum can be effectively received by the photovoltaic cell; 4) Small F / # value, a smaller F / # is conducive to reducing the volume of the concentrating optical system; 5) High concentration ratio to reduce the use area of ​​expensive multi-junction photovoltaic cells. The design of the concentrating optical system is an important research content and direction in the current CPV power generation technology, and it has very important research significance and application value in the application of new energy. Summary of the invention

[0004] In view of the above defects or improvement needs of the prior art, the present invention provides a free-form surface reflector array design method for a solar concentrating device. The free-form surface reflector array designed by this method can produce a uniform focusing spot and improve the photoelectric conversion efficiency of solar photovoltaic cells.

[0005] To achieve the above object, according to a first aspect of the present invention, a method for designing a free-form surface reflector array of a solar energy concentrator is provided, wherein the solar energy concentrator comprises a multi-junction solar cell, a support structure, and a reflector array comprising m*n free-form surface reflectors; the multi-junction solar cell and the reflector array are respectively arranged at the top and the bottom of the support structure, and the reflective surface of the reflector array faces the photosensitive surface of the multi-junction solar cell, and the method comprises:

[0006] 1) Taking the center point of the photosensitive area of ​​the multi-junction solar cell as the coordinate origin and the direction perpendicular to the photosensitive surface as the Z axis, a coordinate system is established; taking the projection of the reflector array on the XY plane as the full light source space SW and the photosensitive area of ​​the multi-junction solar cell as the target space T; and evenly dividing the target space T into (p+1)*(q+1) target grid points;

[0007] 2) The area of ​​the full light source space SW in any quadrant is uniformly gridded to obtain m / 2*n / 2 grids, and the grid k is regarded as the sub-light source space S k According to S k The light mapping relationship between the target space T and S is constructed. k The corresponding free surface point cloud; and S k Evenly divide into p*q grids, and obtain (p+1)*(q+1) preset grid points;

[0008] 3) According to the normal vector field N' of the free-form surface, the actual grid points formed by the light rays starting from each preset grid point in the target space T are calculated by the ray tracing method;

[0009] 4) Compare the actual grid points with the target grid points one by one and calculate the root mean square error;

[0010] 5) If the root mean square error is less than the threshold, the distribution of the target grid points is adjusted to form a new target space, and the process returns to step 2); otherwise, the process proceeds to step 6);

[0011] 6) Mirroring the free-form surface point clouds corresponding to all sub-light source spaces in any quadrant to obtain the point cloud of the reflector array, and performing three-dimensional modeling on the free-form surface point clouds to obtain the reflector array.

[0012] According to a second aspect of the present invention, there is provided a solar concentrating device, comprising a free-form surface reflector array obtained by the method described in the first aspect, a multi-junction solar cell, and a supporting structure; the multi-junction solar cell and the reflector array are respectively arranged at the top and bottom of the supporting structure, and the reflective surface of the reflector array faces the photosensitive surface of the multi-junction solar cell.

[0013] According to a third aspect of the present invention, there is provided a free-form surface reflector array design system for a solar concentrator, comprising: a computer-readable storage medium and a processor;

[0014] The computer-readable storage medium is used to store executable instructions;

[0015] The processor is used to read the executable instructions stored in the computer-readable storage medium and execute the method as described in the first aspect.

[0016] In general, compared with the prior art, the above technical solution conceived by the present invention can achieve the following beneficial effects.

[0017] 1. The invention provides a free-form surface reflector array design method for a solar concentrator, which uses a free-form surface optical solution to design the concentrating system in CPV. Compared with traditional optical surfaces (spherical surfaces, parabolic surfaces, etc.), free-form surfaces have higher optical design freedom and more flexible spatial layout capabilities. Applying them to solar concentrating systems is expected to achieve efficient concentrating performance. The incident sunlight is regulated by a free-form surface reflector array to generate a rectangular light spot with uniform energy distribution on a multi-junction solar photovoltaic cell.

[0018] 2. Each free-form surface reflector in the free-form surface reflector array obtained by the design method provided by the present invention can produce a concentrated light spot with uniform illumination distribution on the solar photovoltaic cell after focusing the incident sunlight, and the shape and size of the light spot are consistent with the shape and size of the photosensitive area of ​​the solar photovoltaic cell, which can improve the focusing uniformity and concentration ratio, thereby improving the photoelectric conversion efficiency of the solar photovoltaic cell and extending the service life of the photovoltaic cell; in addition, a higher concentration ratio is conducive to saving the use of multi-junction solar cells, thereby reducing the manufacturing cost of concentrated photovoltaic products and ultimately improving the economic benefits of green energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 One of the structural schematic diagrams of the CPV system provided in the embodiment of the present invention;

[0020] Figure 2 The second structural diagram of the CPV system provided by the embodiment of the present invention;

[0021] Figure 3 A schematic diagram of the light mapping principle between the full light source space SW and the target space T provided by an embodiment of the present invention;

[0022] Figure 4 A diagram showing a design example of a CPV system based on a free-form surface reflector array provided in an embodiment of the present invention;

[0023] Figure 5The light energy density received by the solar photovoltaic cell in the CPV system is simulated using optical simulation software. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0025] The embodiment of the present invention provides a method for designing a free-form surface reflector array of a solar concentrator device, such as Figure 1-2 As shown, the solar concentrating device comprises a multi-junction solar cell, a reflector array comprising m*n free-form surface reflectors, and a supporting structure; the multi-junction solar cell and the reflector array are respectively arranged at the top and bottom of the supporting structure, and the reflective surface of the reflector array faces the photosensitive surface of the multi-junction solar cell, and the method comprises:

[0026] 1) Establishing a coordinate system with the center point of the photosensitive area of ​​the multi-junction solar cell as the coordinate origin and the direction perpendicular to the photosensitive surface as the Z axis; taking the projection of the reflector array on the XY plane as the full light source space SW and the photosensitive area of ​​the multi-junction solar cell as the target space T; and evenly dividing the target space T into (p+1)*(q+1) target grid points;

[0027] 2) The area of ​​the full light source space SW in any quadrant is uniformly gridded to obtain m / 2*n / 2 grids, and the grid k is regarded as the sub-light source space S k According to S k The light mapping relationship between the target space T and S is constructed. k The corresponding free surface point cloud; and S k Evenly divided into p*q grids, (p+1)*(q+1) preset grid points are obtained; where m and n are

[0028] 3) According to the normal vector field N' of the free-form surface, the actual grid points formed by the light rays starting from each preset grid point in the target space T are calculated by the ray tracing method;

[0029] 4) Compare the actual grid points with the target grid points one by one and calculate the root mean square error;

[0030] 5) If the root mean square error is less than the threshold, the distribution of the target grid points is adjusted to form a new target space, and the process returns to step 2); otherwise, the process proceeds to step 6);

[0031] 6) Mirroring the free-form surface point clouds corresponding to all sub-light source spaces in any quadrant to obtain the point cloud of the reflector array, and performing three-dimensional modeling on the free-form surface point clouds to obtain the reflector array.

[0032] Furthermore, S k The light mapping m between the target space T satisfies the following formula:

[0033]

[0034]

[0035] N·(▽×N)=0;

[0036] Among them, det(▽m) represents the determinant of the Jacobian matrix ▽m of mapping m, and Respectively represent S k and T, N represents S k The normal vector of the corresponding free-form surface.

[0037] Furthermore, in step 5), the area of ​​the target space T is kept unchanged, and the distribution of the target grid points is adjusted using the least squares method or the symplectic transformation method.

[0038] Furthermore, the root mean square error Where t and t' represent the target grid point and the actual grid point respectively.

[0039] Furthermore, the light aperture of each free-form surface reflector is rectangular, which is used to reflect and focus the incident sunlight onto the photosensitive surface of the multi-junction solar cell, and the shape and size of the light spot are the same as those of the multi-junction solar photovoltaic cell.

[0040] Further, the free-form surface reflectors have the same size;

[0041] Alternatively, the m*n free-form surface reflectors have multiple sizes, and the sizes are proportional to each other.

[0042] Specifically, Figure 1As shown, the solar concentrating device mainly includes: a free-form surface reflector array, a multi-junction solar photovoltaic cell, and a supporting structure. The multi-junction solar cell 3 is located directly above the center of the free-form surface reflector array 1 and is fixed on the supporting structure 2. The photosensitive surface of the multi-junction solar cell 3 faces the reflective surface of the free-form surface reflector array 1. The supporting structure is installed on an equatorial device, which is used to align the sun so that the sunlight always enters the reflector array vertically. The free-form surface reflector is fixed at the bottom of the supporting structure, and the reflective surface of the reflector faces the photosensitive surface of the multi-junction solar photovoltaic cell. The solar photovoltaic cell is installed on the top of the supporting structure. The solar cell and the free-form surface reflector array are arranged symmetrically about the X-axis and the Y-axis. The solar cell and the free-form surface reflector array are completely symmetrically distributed in the four quadrants in the XY plane. The center position of the solar photovoltaic cell is regarded as the coordinate origin of the Cartesian coordinate system, and the Z axis is perpendicular to the photosensitive surface of the photovoltaic cell. The free-form surface reflector array is symmetrical about the XZ plane and the YZ plane. Each free-form surface reflector is closely arranged on the XY projection plane, and the projection of the free-form surface reflector array in the XY plane is symmetrically distributed about the X axis and the Y axis.

[0043] The light aperture of each reflector is rectangular, which can reflect and focus the incident sunlight onto the photosensitive area of ​​the solar photovoltaic cell. The shape and size of the light spot are consistent with the shape and size of the photosensitive area of ​​the solar photovoltaic cell, and the energy distribution of the light spot is uniform.

[0044] Refer to the following Figure 3 , the optical design method of the free-form surface reflector array is described in detail, the method comprising:

[0045] S1: Set the design parameters, including the number of reflector arrays, the overall aperture size, the photosensitive surface size of the photocell, and the distance between the photocell and the free-form surface along the z-axis. Set the CPV system to be symmetrical about the XZ plane and YZ plane.

[0046] Determine the number of free-form surface reflectors in the array m*n (m in the horizontal direction and n in the vertical direction; or n in the horizontal direction and m in the vertical direction), the overall aperture size L*W; the photosensitive surface size a*b of the solar photovoltaic cell, the distance between the solar photovoltaic cell and the vertex of the free-form surface reflector along the z-axis is h, the number of free-form surface reflectors in each quadrant is m / 2*n / 2, the plane space z=0 is defined as the full light source space SW, and the photosensitizing area of ​​the solar photovoltaic cell is defined as the target space T.

[0047] S2: The first quadrant area of ​​the whole light source space SW is uniformly divided into grids, the number of grids is m / 2*n / 2, and each grid is regarded as a sub-light source space S.

[0048] S3: Take a grid in step S2, that is, the sub-light source space S, and the energy density distribution in the light source space is E s(u,v), the energy density distribution of the target space T is E t (m i,j (u,v)), where m i,j is the light mapping relationship between the sub-light source space S and the target space T, and is the quantity to be determined. The sub-light source space S is meshed again, and the number of sub-grids divided is p*q, and the shape and size of each sub-grid are consistent.

[0049] S4: Assume that all the energy in the light source space S taken in S3 reaches the target space T, and thus construct the mathematical relationship of energy conservation:

[0050]

[0051] Among them, det(▽m) represents the determinant of the Jacobian matrix ▽m of mapping m.

[0052] Assuming that the energy at the edge of the light source space S reaches the edge of the target space T, the boundary conditions in the light mapping process are constructed:

[0053]

[0054] in, and Represent the boundaries of S and T respectively.

[0055] The free surface normal vector field determined by the light mapping relationship also needs to satisfy the integrability condition, that is,

[0056] N·(▽×N)=0,

[0057] Where N represents the normal vector, which is obtained by the reflection theorem under the premise that the information of the incident light and the outgoing light is known.

[0058] S4.1: Grid the target space T, the number of grids is p*q, and (p+1)*(q+1) grid points are obtained, and the shape and size of each sub-grid are consistent. Since the light source space has been gridded in step S3, the initial light mapping relationship m0 between the sub-light source space S and the target space T can be determined, and based on the mapping relationship m0, the free-form surface reflector point cloud is constructed.

[0059] Among them, any method in the prior art can be used to construct a free-form surface reflector point cloud based on the mapping relationship m0, for example: using the least squares method provided in the article "Freeform illumination optics construction following an optimal transport map", "Applied Optics", Vol.55, Issue 16, pp. 4301-4306 (2016), to construct a free-form surface reflector point cloud based on the mapping relationship m0.

[0060] S4.2: Based on the reflection theorem, calculate the normal vector field N' of the free surface, and use the ray tracing method to calculate the actual grid points formed by the light rays starting from each grid point in the light source space S and reaching the target space T (that is, the distribution of (p+1)*(q+1) actual grid points). Calculate the RMS error between the actual grid point distribution and the target grid point distribution (one-to-one comparison of each point), Where t and t' represent the target grid point and the actual grid point respectively.

[0061] S4.3: Use the least squares method or symplectic transformation method to perform area-preserving transformation (in-plane transformation) to adjust the target grid point distribution t in the target space, regain the light mapping relationship, and construct a new free-form surface reflector point cloud.

[0062] S4.4: Repeat steps S4.2-S4.3 until the error between the actual grid distribution and the target grid distribution is lower than a threshold.

[0063] S5: Repeat steps S2-S4 to complete the construction of all free-form surface reflectors in the first quadrant, perform a mirror operation to obtain a free-form surface reflector array, and the number of reflectors is m*n. Use 3D modeling software to construct the reflector array as a solid and connect it to the support structure.

[0064] All free-form reflectors are fixed at the bottom of the supporting structure to form a whole, with the reflective surface facing the solar photovoltaic cell. Parallel incident sunlight is reflected and focused by the reflector array to the photovoltaic cell, forming a uniform energy spot on the photovoltaic cell with the same shape and size as the photosensitive surface of the photovoltaic cell, and finally converted into electrical energy through photoelectric conversion.

[0065] The free-form surface reflector may have different sizes and aspect ratios.

[0066] Reference Figure 4The design example shown in the figure has the following design parameters: the overall aperture of the reflector array is 1000mm*1000mm, the photosensitive area of ​​the solar photovoltaic cell is 20mm*20mm, the distance between the solar photovoltaic cell and the reflector along the Z axis is 1600mm, and the number of reflectors is 4*4. After completing the design of the free-form surface reflector array through the above steps, Figure 5 As shown, the focusing performance of the CPV system is simulated in the optical simulation software, and the uniformity of the energy received on the photovoltaic cell is obtained to be 0.88, and the energy utilization efficiency is 98.07%.

[0067] An embodiment of the present invention provides a solar concentrating device, comprising a free-form surface reflector array, a multi-junction solar cell, and a supporting structure obtained by a method as described in any of the above embodiments; the multi-junction solar cell and the reflector array are respectively arranged at the top and bottom of the supporting structure, and the reflective surface of the reflector array faces the photosensitive surface of the multi-junction solar cell.

[0068] An embodiment of the present invention provides a free-form surface reflector array design system for a solar concentrator, comprising: a computer-readable storage medium and a processor;

[0069] The computer-readable storage medium is used to store executable instructions;

[0070] The processor is used to read the executable instructions stored in the computer-readable storage medium and execute the method described in any of the above embodiments.

[0071] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for designing a free-form surface reflector array of a solar concentrator, wherein the solar concentrator comprises a multi-junction solar cell, a support structure, and a reflector array comprising m*n free-form surface reflectors, characterized in that: The method comprises: 1) Taking the center point of the photosensitive area of ​​the multi-junction solar cell as the coordinate origin and the direction perpendicular to the photosensitive surface of the multi-junction solar cell as the Z axis, a coordinate system is established; taking the projection of the reflector array on the XY plane as the full light source space, and taking the photosensitive area of ​​the multi-junction solar cell as the target space T; evenly dividing the target space T into p*q grids to obtain (p+1)*(q+1) target grid points; 2) The area of ​​the full light source space in any quadrant is uniformly gridded to obtain m / 2*n / 2 grids, and the grid k is regarded as the sub-light source space S k According to S k The light mapping relationship between the target space T and S is constructed. k The corresponding free surface point cloud; and S k Evenly divide into p*q grids, and obtain (p+1)*(q+1) preset grid points; 3) According to the normal vector field of the free-form surface, the actual grid points formed by the light rays starting from each preset grid point in the target space T are calculated by the ray tracing method; 4) Compare the actual grid points with the target grid points one by one and calculate the root mean square error; 5) If the root mean square error is less than the threshold, the distribution of the target grid points is adjusted to form a new target space, and the process returns to step 2); otherwise, the process proceeds to step 6); 6) Mirroring the free-form surface point clouds corresponding to all sub-light source spaces in any quadrant to obtain the point cloud of the reflector array, and performing three-dimensional modeling on the free-form surface point clouds to obtain the reflector array.

2. The method according to claim 1, characterized in that S k The light mapping m between the target space T satisfies the following formula: N·(▽×N)=0; Among them, det(▽m) represents the determinant of the Jacobian matrix ▽m of mapping m, and Respectively represent S k and T, N represents S k The normal vector of the corresponding free-form surface.

3. The method according to claim 1 or 2, characterized in that In step 5), the area of ​​the target space T is kept unchanged, and the distribution of the target grid points is adjusted using the least squares method or the symplectic transformation method.

4. The method according to claim 1, characterized in that The root mean square error Where t and t' represent the target grid point and the actual grid point respectively.

5. The method according to claim 1, characterized in that The light aperture of each free-form surface reflector is rectangular, and is used to reflect and focus incident sunlight to the photosensitive area of ​​the multi-junction solar cell, and the shape and size of the light spot are the same as those of the multi-junction solar cell.

6. The method according to claim 1, characterized in that The dimensions of each free-form reflector are the same; Alternatively, the m*n free-form surface reflectors have multiple sizes, and the sizes are proportional to each other.

7. A solar concentrating device, characterized in that: include: A multi-junction solar cell, a supporting structure, and a free-form surface reflector array obtained by the method described in any one of claims 1 to 6; The multi-junction solar cell and the reflector array are respectively arranged on the top and bottom of the support structure, and the reflective surface of the reflector array faces the photosensitive surface of the multi-junction solar cell.

8. A free-form surface reflector array design system for a solar concentrator, characterized in that: include: A computer readable storage medium and a processor; The computer-readable storage medium is used to store executable instructions; The processor is used to read the executable instructions stored in the computer-readable storage medium and execute the method according to any one of claims 1 to 6.

Images