A calculation method for the shading efficiency of heliostats in tower solar thermal mirror fields

Abstract

The present invention discloses a method for calculating the shading efficiency of heliostats in a tower solar thermal mirror field, comprising the following steps: obtaining heliostat coordinate information; calculating the sun's position and the sun's direction vector at a certain moment; calculating the normal vector of the heliostat at that moment; determining the heliostat that will be blocked; calculating the projected area of ​​the blocking heliostat on the mirror surface of the blocked heliostat; calculating the blocked area on the mirror surface of the blocked heliostat; and calculating the shading efficiency of the blocked heliostat. The method disclosed in the present invention sets a reasonable range for selecting heliostats that may be blocked, greatly reducing invalid operations and improving the overall calculation speed. At the same time, the projection operation is simplified by utilizing the principle that the vertical multiplication of two vectors equals zero. The method has simple logic, high calculation efficiency, and high calculation accuracy, thereby improving the accuracy of calculating the optical efficiency of the entire mirror field.

Description

Technical Field

[0001] The present invention relates to the field of solar thermal power generation, and in particular to a method for calculating the shading efficiency of heliostats in a tower-type solar thermal mirror field. Background Art

[0002] In recent years, solar thermal power generation technology has seen significant development. Compared to traditional photovoltaic power generation, it offers advantages in flexible energy storage and adjustable power generation. Tower-type solar thermal power generation has gradually gained popularity due to its high heat collection efficiency. In a solar thermal power plant, the mirror field is the device that collects solar energy, and its performance directly affects its absorption efficiency. Optical efficiency is a key indicator of field performance. It refers to the overall utilization rate of solar energy by the field. Improving optical efficiency is a key factor in improving the overall efficiency of a solar thermal power plant system. Optical efficiency includes cosine efficiency, shadowing efficiency, obstruction efficiency, atmospheric attenuation, and overflow efficiency. Shadowing and obstruction efficiency are the most difficult to calculate. When the sun's altitude is low, the shadowing loss occurs when the rear heliostats are blocked by the front heliostats when receiving solar rays. When the rear heliostats are blocked by the front heliostats when reflecting solar rays to the target point of the heat sink tower, this is called shadowing loss. Shadowing and obstruction efficiency are related to the sun's position, the height of the heat sink tower, and the position and shape of the heliostats. We need to calculate these efficiencies accurately and quickly, and then continuously optimize them to improve the efficiency of solar energy collection in the concentrating field of a solar thermal power station.

[0003] The main methods for calculating shadow and obstruction efficiency are plane projection and ray tracing. Among existing algorithms, plane projection suffers from large calculation errors and cannot accurately calculate the shadow and obstruction efficiency of multiple heliostats. When the number of heliostats is large and the field is large, the computational complexity of ray tracing increases significantly, making the calculations more time-consuming. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention provides a method for calculating the shading efficiency of heliostats in a tower solar thermal mirror field, so as to achieve the purpose of simple calculation and high accuracy.

[0005] To achieve the above object, the technical solution of the present invention is as follows:

[0006] A method for calculating the shading efficiency of heliostats in a tower solar thermal mirror field comprises the following steps:

[0007] Step 1: Obtain heliostat coordinate information based on the mirror field layout;

[0008] Step 2: Calculate the sun's position and direction vector at a certain moment based on the geographic latitude and longitude and altitude information of the mirror site, as well as local meteorological information;

[0009] Step 3, calculating the normal vector of the heliostat at that moment according to the direction vector of the sun and the direction vector of the target point;

[0010] Step 4: From the set of blocked heliostats A N Select a blocked heliostat A i , i is the serial number of the shaded heliostat, N is the number of all shaded heliostats in the mirror field; i Heliostat B that causes shading j range, blocking heliostat B j Composition set B M , M is the total number of heliostats in the front row that will face heliostat A i The number of heliostats that generate shading, j is the serial number of the shading heliostat;

[0011] Step 5: Block heliostat B j All vertices of the obscured heliostat A i Project the plane to find the heliostat B j In the blocked heliostat A i Projected area S on the mirror surface j ;

[0012] Step 6: Calculate the set B of all blocked heliostats M The blocking heliostat in the blocked heliostat A i The projected area on the mirror surface is summed up, and the overlapping part is calculated only once to obtain the blocked heliostat A. i The area S blocked on the mirror surface M ;

[0013] Step 7: Calculate the number of blocked heliostats A i The occlusion efficiency η:

[0014]

[0015] Among them, S i The blocked heliostat A i The mirror area;

[0016] Step 8: Repeat steps 4 to 7 to calculate the set of blocked heliostats A. N The shading efficiency of all shaded heliostats in .

[0017] In the above scheme, in step 2, the sun's position includes the sun's azimuth angle α and altitude angle β. The sun's direction vector u is calculated based on the sun's azimuth angle α and altitude angle β:

[0018]

[0019] In the above solution, in step 3, the normal vector n of the heliostat is calculated as follows:

[0020]

[0021] Where r is the direction vector from the center of the heliostat to the target point of the receiver.

[0022] In the above scheme, the specific method of step 4 is as follows:

[0023] For the case where all heliostats in the mirror field are rectangular, the blocked heliostat A i Center C b As the starting point, passing through the vertex D on the upper right side of the heliostat b Draw a straight line that intersects the upper edge of the front row heliostat at point D t , C b With D t The distance between them is h, C b and the midpoint C of the upper edge of the front row heliostat t The distance between the two rows of heliostats is k, the length of the heliostat is L, the width is W, the width of the aisle between the two rows of heliostats is LR, C b With D b The distance z between them is calculated as follows:

[0024]

[0025] therefore,

[0026]

[0027] From this, the distance h can be obtained:

[0028]

[0029] Where, k = LR + 1.5W;

[0030] Then, draw a semicircle with length h as radius. The heliostats in the front row that fall within the semicircle will be the heliostats that will be blocked. i The range of the obstructing heliostat where obstruction occurs.

[0031] In the above scheme, the specific method of step 5 is as follows:

[0032] Select blocking heliostat B j A vertex T1, from vertex T1 along the direction vector re in the blocked heliostat A i The projection point on the plane is BT1, and the direction vector re is from the target point to the blocked heliostat A i direction vector;

[0033] Coordinates of point BT1 The calculation is as follows:

[0034]

[0035] in, The coordinates of point T1 are known, and t is the distance from point T1 to point BT1 along the vector re. The calculation formula is as follows:

[0036]

[0037] in, The blocked heliostat A i The center point C b Coordinates, n A The blocked heliostat A i The normal vector of

[0038] According to formulas (7) and (8), the blocking heliostat B is obtained in turn. j Vertices T2, T3, and T4 are on the blocked heliostat A. i Projection points BT2, BT3, BT4 on the plane;

[0039] According to the coordinates of all projection points, use the shoelace formula to find the blocked heliostat B j In the blocked heliostat A i Projected area S on the mirror surface j ;

[0040] When a projection point falls on the blocked heliostat A i When the mirror is outside the mirror, it is necessary to calculate the blocking heliostat B j and the blocked heliostat A i Coordinates of the intersection points P1 and P2 of the mirror edges and Then, the coordinates of the projection points of the two intersection points are calculated according to formulas (7) and (8), and finally the shoelace formula is used to calculate the blocking heliostat B. j In the blocked heliostat A i Projected area S on the mirror surface j .

[0041] Through the above technical solution, the method for calculating the shading efficiency of heliostats in a tower solar thermal mirror field provided by the present invention has the following beneficial effects:

[0042] 1. The present invention uses a straight line method to calculate the shielding radius, setting a reasonable range for the selection of heliostats that may be shielded, greatly reducing invalid calculations and improving the overall calculation speed.

[0043] 2. The method of the present invention does not require complex calculations. It uses the principle that the vertical multiplication of two vectors is zero to simplify the projection operation. The logic is simple and easy to understand.

[0044] 3. The method of the present invention has high computational accuracy, which improves the accuracy of calculating the optical efficiency of the entire mirror field. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for describing the embodiments or the prior art.

[0046] Figure 1 Schematic diagram of the tower solar thermal solar vector, target point vector and heliostat normal vector;

[0047] Figure 2 Schematic diagram of solar altitude angle and azimuth angle;

[0048] Figure 3 Select a schematic diagram for the heliostat shading range;

[0049] Figure 4 This is a schematic diagram of the heliostat vertex projection calculation;

[0050] Figure 5 This is a schematic diagram showing that the projection of the vertex of the front heliostat does not fall within the range of the rear heliostat.

[0051] In the figure, 1. Heliostat; 2. Target point; 3. Heat absorption tower. DETAILED DESCRIPTION

[0052] The technical solutions in the embodiments of the present invention will be described clearly and completely below with reference to the accompanying drawings in the embodiments of the present invention.

[0053] like Figure 1 As shown, in a solar thermal power station, heliostats 1 track solar rays in real time and reflect them to the absorber target point 2 on the absorption tower 3. During this process, due to changes in the sun's position, the front heliostats may block the rear heliostats in the incident (shadow) or reflected (blocking) direction, thereby affecting the system's efficiency in collecting solar energy. The present invention uses rectangular heliostats as an example to provide a method for calculating the blocking efficiency of heliostats in a tower-type solar thermal mirror field, including the following steps:

[0054] Step 1: Obtain the coordinate information of each heliostat according to the mirror field layout;

[0055] Step 2: Calculate the sun's position and direction vector at a given moment using the Solar Position Algorithm (SPA) method developed by the National Renewable Energy Laboratory (NREL) based on the geographic latitude, longitude, and altitude of the mirror field, as well as local meteorological information.

[0056] like Figure 2 As shown, the sun's position includes the sun's azimuth angle α and altitude angle β. The sun's direction vector u is calculated based on the sun's azimuth angle α and altitude angle β:

[0057]

[0058] Step 3, calculating the normal vector of the heliostat at that moment according to the direction vector of the sun and the direction vector of the target point;

[0059] The normal vector n of the heliostat is calculated as follows:

[0060]

[0061] Where r is the direction vector from the center of the heliostat to the target point of the receiver.

[0062] Step 4: From the set of blocked heliostats A N Select a blocked heliostat A i , i is the serial number of the shaded heliostat, N is the number of all shaded heliostats in the mirror field; i Heliostat B that causes shading j range, blocking heliostat B j Composition set B M , M is the total number of heliostats in the front row that will face heliostat A i The number of heliostats that generate shading, j is the serial number of the shading heliostat;

[0063] like Figure 3 As shown, the blocked heliostat A i Center C b As the starting point, passing through the vertex D on the upper right side of the heliostat b Draw a straight line that intersects the upper edge of the front row heliostat at point D t , C b With D t The distance between them is h, C b and the midpoint C of the upper edge of the front row heliostat t The distance between the two rows of heliostats is k, the length of the heliostat is L, the width is W, the width of the aisle between the two rows of heliostats is LR, C b With D b The distance z between them is calculated as follows:

[0064]

[0065] therefore,

[0066]

[0067] From this, the distance h can be obtained:

[0068]

[0069] Where, k = LR + 1.5W;

[0070] Then, draw a semicircle with length h as radius. The heliostats in the front row that fall within the semicircle will be the heliostats that will be blocked. i The range of the obstructing heliostat where obstruction occurs.

[0071] According to the above method, all heliostats that may be blocked are screened in turn. The heliostats in the first row are not blocked by other heliostats and therefore can be excluded from the calculation.

[0072] Step 5: Block heliostat B j All vertices of the obscured heliostat A i Project the plane of the obstructing heliostat B on the obstructed heliostat A. i Projected area S on the mirror surface j ;

[0073] The specific method is as follows:

[0074] like Figure 4 As shown, select the blocking heliostat B j A vertex T1, from vertex T1 along the direction vector re in the blocked heliostat A i The projection point on the plane is BT1, and the direction vector re is from the target point to the blocked heliostat A i direction vector;

[0075] Coordinates of point BT1 The calculation is as follows:

[0076]

[0077] in, The coordinates of point T1 are known, and t is the distance from point T1 to point BT1 along the vector re. The calculation formula is as follows:

[0078]

[0079] in, The blocked heliostat A i The center point C b Coordinates, nA The blocked heliostat A i The normal vector of

[0080] According to formulas (7) and (8), the blocking heliostat B is obtained in turn. j Vertices T2, T3, and T4 are on the blocked heliostat A. i Projection points BT2, BT3, BT4 on the plane;

[0081] According to the coordinates of all projection points, use the shoelace formula to find the blocked heliostat B j In the blocked heliostat A i Projected area S on the mirror surface j ;

[0082] When a projection point falls on the blocked heliostat A i When the mirror is outside the mirror, it is necessary to calculate the blocking heliostat B j and the blocked heliostat A i Coordinates of the intersection points P1 and P2 of the mirror edges and like Figure 5 As shown, it is assumed that only the projection point of point T1 falls on the blocked heliostat A i In the mirror plane, the projection points of points T2, T3, and T4 are all outside the mirror plane. At this time, the coordinates of the intersection points P1 and P2 are and The calculation formula is as follows:

[0083]

[0084]

[0085] in, is the coordinate of point T2, is the coordinate of point T4.

[0086] Then according to the coordinates of the two intersection points P1 and P2 and Use formulas (7) and (8) to calculate the coordinates of the projection points of the intersection points P1 and P2, and finally use the shoelace formula to find the blocked heliostat B j In the blocked heliostat A i Projected area S on the mirror surface j .

[0087] Step 6: Calculate the set B of all blocked heliostats M The blocking heliostat in the blocked heliostat A i The projected area on the mirror surface is summed up, and the overlapping part is calculated only once to obtain the blocked heliostat A. i The area S blocked on the mirror surface M ;

[0088] Step 7: Calculate the number of blocked heliostats A i The occlusion efficiency η i :

[0089]

[0090] Among them, S i The blocked heliostat A i The mirror area;

[0091] Step 8: Repeat steps 4 to 7 to calculate the set of blocked heliostats A. N The shading efficiency of all shaded heliostats in .

[0092] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for calculating the shading efficiency of heliostats in a tower solar thermal mirror field, characterized in that: The steps include: Step 1: Obtain heliostat coordinate information based on the mirror field layout; Step 2: Calculate the sun's position and direction vector at a certain moment based on the geographic latitude and longitude and altitude information of the mirror site, as well as local meteorological information; Step 3, calculating the normal vector of the heliostat at that moment according to the direction vector of the sun and the direction vector of the target point; Step 4: From the set of blocked heliostats A N Select a blocked heliostat A i , i is the serial number of the shaded heliostat, N is the number of all shaded heliostats in the mirror field; i The range of heliostat B that produces shading, shading heliostat B j Composition set B M , M is the total number of heliostats in the front row that will face heliostat A i The number of heliostats that generate shading, j is the serial number of the shading heliostat; Step 5: Block heliostat B j All vertices of the obscured heliostat A i Project the plane of the obstructing heliostat B on the obstructed heliostat A. i Projected area S on the mirror surface j ; Step 6: Calculate the set B of all blocked heliostats M The blocking heliostat in the blocked heliostat A i The projected area on the mirror surface is summed up, and the overlapping part is calculated only once to obtain the blocked heliostat A. i The area S blocked on the mirror surface M ; Step 7: Calculate the number of blocked heliostats A i The occlusion efficiency η i : Among them, S i The blocked heliostat A i The mirror area; Step 8: Repeat steps 4 to 7 to calculate the set of blocked heliostats A. N The shading efficiency of all the shading heliostats in ; The specific method of step 5 is as follows: Select blocking heliostat B j A vertex T1, from vertex T1 along the direction vector re in the blocked heliostat A i The projection point on the plane is BT1, and the direction vector re is from the target point to the blocked heliostat A i direction vector; Coordinates of point BT1 The calculation is as follows: in, The coordinates of point T1 are known, and t is the distance from point T1 to point BT1 along the vector re. The calculation formula is as follows: in, The blocked heliostat A i The center point C b Coordinates, n A The blocked heliostat A i The normal vector of According to formulas (7) and (8), the blocking heliostat B is obtained in turn. j Vertices T2, T3, and T4 are on the blocked heliostat A. i Projection points BT2, BT3, BT4 on the plane; According to the coordinates of all projection points, use the shoelace formula to find the blocked heliostat B j In the blocked heliostat A i Projected area S on the mirror surface j ; When a projection point falls on the blocked heliostat A i When the mirror is outside the mirror, it is necessary to calculate the blocking heliostat B j Coordinates of the intersection points P1 and P2 with the edge of the obscured heliostat A and Then, the coordinates of the projection points of the two intersection points are calculated according to formulas (7) and (8), and finally the shoelace formula is used to calculate the blocking heliostat B. j In the blocked heliostat A i Projected area S on the mirror surface j .

2. The method for calculating the shading efficiency of a heliostat in a tower solar thermal mirror field according to claim 1, wherein: In step 2, the sun's position includes the sun's azimuth angle α and altitude angle β. The sun's direction vector u is calculated based on the sun's azimuth angle α and altitude angle β:

3. The method for calculating the shading efficiency of a heliostat in a tower solar thermal mirror field according to claim 2, wherein: In step 3, the normal vector n of the heliostat is calculated as follows: Where r is the direction vector from the center of the heliostat to the target point of the receiver.

4. The method for calculating the shading efficiency of a heliostat in a tower solar thermal mirror field according to claim 1, wherein: The specific method of step 4 is as follows: For the case where all heliostats in the mirror field are rectangular, the blocked heliostat A i Center C b As the starting point, passing through the vertex D on the upper right side of the heliostat b Draw a straight line that intersects the upper edge of the front row heliostat at point D t , C b With D t The distance between them is h, C b and the midpoint C of the upper edge of the front row heliostat t The distance between the two rows of heliostats is k, the length of the heliostat is L, the width is W, the width of the aisle between the two rows of heliostats is LR, C b With D b The distance z between them is calculated as follows: therefore, From this, the distance h can be obtained: Where, k = LR + 1.5W; Then, draw a semicircle with length h as radius. The heliostats in the front row that fall within the semicircle will be the heliostats that will be blocked. i The range of the obstructing heliostat where obstruction occurs.

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