CN105509339B - A kind of scope of freedom Opticai Concentrating System With Secondary Reflection efficiently changed for solar heat/electricity - Google Patents

Abstract

The invention relates to a free-surface secondary reflection concentrating system for efficient conversion of solar heat/electricity, and relates to a concentrating system for efficient conversion of solar heat/electricity. The present invention aims to solve the technical problem that the entrance area of the heat absorbing cavity of the traditional solar dish-type concentrating system is limited and cannot receive all the energy of the light spot, which will be intercepted, resulting in a waste of resources. The system of the present invention is made up of primary mirror, secondary mirror and receiver; Primary mirror, secondary mirror and receiver are all axisymmetric structures, and primary mirror, secondary mirror and receiver three are coaxial; Receiver is made up of The heat absorber, the concentrating photovoltaic panel and the flange are composed, and the concentrating photovoltaic panel is installed on the outside of the flange; the method of determining the free-form surface of the secondary mirror is as follows: 1. Discretization of the starting point and the target point; 2. Solve the discrete points of the secondary mirror free-form surface; 3. Draw the secondary mirror surface. The invention is applied in the field of solar energy.

Description

A Free Surface Secondary Reflection Concentrating System for Solar Thermal/Electrical Efficient Conversion

technical field

The invention relates to a light concentrating system for solar heat/electricity high-efficiency conversion.

Background technique

With the continuous development of precision machining technology and the arrival of new 3D printing technology, the design of advanced optical systems has become more efficient and flexible. Compared with traditional methods, free-form surfaces have higher design freedom and flexible space layout, making The design of the optical system is simplified, giving it the advantages of compact structure, high utilization rate and energy saving. Different from the traditional optical system, the free-surface optical system does not have a specific surface equation, and it cannot be defined by the equation formula. The free-form surface is often composed of many space points, and then the non-uniform rational B-spline (NURBS) curves or other methods for connection reconstruction to finally obtain the space surface. The technology has few applications in the solar field and remains to be developed. The Gaussian energy flow distribution obtained by the traditional solar dish concentrating system is characterized by a higher energy flow value closer to the center, and a significantly lower energy flow on the outer side. In practical applications, in order to ensure sealing and safety, the entrance area of the solar heat absorbing cavity is limited, and in many cases it cannot receive the energy of all the spots, so it will be intercepted, and the energy of the concentrated spots outside will be discarded, resulting in a waste of resources. waste.

Contents of the invention

The present invention aims to solve the technical problem that the entrance area of the heat-absorbing cavity of the traditional solar dish-type concentrating system is limited, and cannot receive all the energy of the light spot, which will be intercepted, resulting in waste of resources. A free-surface secondary reflection concentrating system for solar heat/electricity efficient conversion.

The free-surface secondary reflection and concentrating system for solar heat/electricity high-efficiency conversion of the present invention adopts a free-surface Cassegrain reflection and concentrating system, which is composed of a primary mirror, a secondary mirror and a receiver; the primary mirror, the secondary mirror and the The receivers are all axisymmetric structures, and the primary mirror, secondary mirror and receiver are coaxial; the primary mirror and the secondary mirror are connected by a bracket, the concave surface of the primary mirror faces the secondary mirror, the receiver is fixed on the bracket, and the bracket It is set on the axis of the primary mirror, secondary mirror and receiver; the receiver is composed of a heat absorber, a concentrated photovoltaic panel and a flange, and the flange is installed at the optical window end of the heat absorber. The battery board is installed on the outside of the flange, and the optical window of the heat sink faces the secondary mirror; the heat sink is cylindrical, and the concentrated photovoltaic battery board is a hollow ring;

The primary mirror adopts a traditional solar dish parabolic reflector, and the secondary mirror is a reflective mirror surface in the form of a free-form surface. The free-form surface of the secondary mirror is determined as follows:

1. Discrete start and target points:

To determine the size of the primary mirror and receiver, the calculation formula is as follows:

w(R _max ² -R _min ² )/C _G =(r _max ² -r _min ² ) (1),

w is the occupancy ratio of the CPV subsystem, C _G is the geometric concentration ratio of the CPV subsystem, R _max is the outer radius of the primary mirror, R _min is the inner radius of the primary mirror, and r _max is the receiver The radius of the outer ring of the concentrated photovoltaic panel, r _min is the radius of the inner circle of the concentrated photovoltaic panel in the receiver, R _min ≥ r _max , five of which are known quantities, and the sixth quantity can be obtained , to determine the dimensions of the primary mirror and receiver;

Establish a three-dimensional rectangular coordinate system (x, y, z), the origin O is the intersection point of the bracket and the primary mirror, the z-axis is the axis pointing from the origin to the secondary mirror along the bracket, and the y-axis is parallel to the concentrated photovoltaic in the receiver The radius of the battery panel and the axis pointing from the origin to the direction of the concentrated photovoltaic panel. The x-axis is the axis passing through the origin O and perpendicular to the plane where the z-axis and y-axis are located. Only the area where the z-axis and y-axis are positive numbers is used for calculation;

Take n points P _i,j-1 on the primary mirror, n is a positive integer, the difference between the y-axis coordinate values of all two adjacent points is equal, i is the serial number of n points, i is a positive integer, and the number 1 is The point on the primary mirror whose y-axis coordinate value is equal to R _max , and No. n is the point on the primary mirror whose y-axis coordinate value is equal to R _min . The serial number i gradually increases from No. 1 to No. n, and y _{i, j-1} is the n The coordinate value of a point on the y-axis, the calculation formula is as follows:

y _i,j-1 =y _1,j-1 -(i-1)×(y _1,j-1 -y _n,j-1 )/n (2);

The z-axis coordinates of point P _i,j-1 are calculated by the formula z=y ² /4f, where f is the focal length of the primary mirror;

Determine the splitting node P _k,j-1 on the primary mirror, and calculate its y-axis coordinate value y _k,j-1 , the calculation formula is as follows:

If the n points P _i,j-1 taken on the primary mirror do not contain the light splitting node P _k,j-1 , then find a y-axis coordinate value and y _k,j-1 among the n points on the primary mirror The closest point P _i,j-1 is used as the splitting node P _k,j-1 ;

Take m points P _i,j+1 on the receiver, m is a positive integer and m=n, the difference between the y-axis coordinates of all two adjacent points is equal, i is the serial number of m points, and i is a positive integer , No. 1 is the point on the receiver whose y-axis coordinate value is equal to r _max , and the serial number i gradually increases along No. 1 to m. y _{i, j+1} is the coordinate value of the m points on the y-axis, y _{k ,j+1} is the coordinate value of the point P _k,j+1 on the y-axis of the light splitting node P _k,j-1 on the receiver after secondary mirror reflection, y _k,j+1 is equal to r _min , and the rest The calculation formula of y _i,j+1 of m-1 points is as follows:

2. The solution of discrete points on the free-form surface of the quadratic mirror:

Set P _i,j as the point P _i,j-1 where the sunlight irradiates on the primary mirror reflects to the corresponding point on the secondary mirror, θ _i is the reflection half angle corresponding to P _i,j , the calculation method of θ _i is as follows :

with Represent vectors respectively and vector the unit vector of

is the normal vector of point P _i,j , Obtained by the following formula:

The matrix Rot(x,θ _i ) is:

The coordinates of point P _1,j are known quantities, and its normal vector It can also be obtained from this,

normal vector The reverse extension of is the vector Two adjacent normal vectors with Corresponding reverse extension line vector and vector The intersection point is C _i-1 , let the vector That is, the following formula:

t _i-1 and t _i are vectors respectively and vector , t _i is the length from point P _{i,j to} point C _i , and t _i-1 is the length from point P _{i-1,j to} point C _i-1 ;

P _i,j is represented by the following formula:

λ _i is a vector the mold;

Substituting formulas (5)(7)(9) into (6), we get Substituting the single-valued function with parameter λ _i into formula (8), taking t _i-1 and t _i as unknowns, the function is obtained:

The coordinates of point C _i-1 are:

Substituting formula (10) into (11) to obtain the coordinates of point C i- ₁ , and then substituting the coordinates of point C _i-1 and formula (9) into formula (12), the value of λ _i can be obtained. Substituting the value of λ _i into formula (9), the coordinates of P _i,j can be obtained;

3. Draw the quadratic mirror surface: connect and reconstruct the coordinates of P _{i, j} with non-uniform rational B-spline curves to obtain the quadratic mirror free curve, use the three-dimensional construction function of the drawing software to draw the quadratic mirror free curve, the primary mirror and The receiver rotates the curve around the z-axis to obtain a three-dimensional free-form surface.

The specific position of the receiver on the bracket of the present invention can be adjusted by itself according to actual needs, and adjusting the position change of the receiver will cause the free-form surface of the secondary mirror to be solved again.

Advantages of the present invention:

1. High total energy utilization and conversion efficiency

The principle of skewed light vector transmission adopted by the present invention can obtain the most suitable energy flow distribution according to the specific conditions of the energy flow receiving surface. The remaining part of the energy, and the optimized design of the secondary free mirror to obtain a uniform energy flow distribution, the connecting flange of the battery plate and the heat absorber will obtain the least energy, and this system enables as much energy as possible to be effectively converted ;

2. Low manufacturing and processing costs

The primary mirror of the present invention adopts a traditional dish-type concentrator, so it only needs to process and design a secondary mirror with a smaller area accordingly, which saves processing and manufacturing costs;

3. Strong safety and reliability

The concentrating photovoltaic system is often the joint utilization mode of solar heat/electricity, especially the weakest and most easily damaged link in the case of high-power concentrating. This method realizes the uniform energy flow distribution of the concentrating photovoltaic system, greatly improving the system safety and reliability;

4. High degree of design freedom

Based on the skewed light vector transmission design method proposed in the present invention, adaptive structural parameters can be obtained according to the specific needs of users, such as adapting to any receiving surface position, light splitting ratio, size and uniformity of concentrated energy flow, etc., to ensure system operation Optimum condition and great freedom of design.

This method is based on the incident light in the general sense, rather than the traditional way (the light vector that must be incident parallel to the optical axis) to solve. This method uses the basic vector relationship, that is, the law of mirror reflection and the normal vector matrix derivation relation. The solution has good universality and can adapt to many parameter requirements such as the position of the receiving surface, the splitting ratio, the size and uniformity of the concentrated energy flow, and so on.

Description of drawings

Fig. 1 is a schematic diagram of a free-surface secondary reflection concentrating system for solar heat/electricity efficient conversion in the second specific embodiment, 1 is a primary mirror, 2 is a secondary mirror, 4 is a heat absorber, and 3 is concentrated photovoltaics solar panels;

Fig. 2 is the bottom view of the receiver in the second specific embodiment, 4 is a heat absorber, and 3 is a concentrated photovoltaic panel;

Fig. 3 is the optical schematic diagram of the free-surface secondary reflection and concentrating system for solar thermal/electrical high-efficiency conversion in the second specific embodiment, 1 is a primary mirror, 2 is a secondary mirror, 4 is a heat absorber, and 3 is a concentrator. Photovoltaic panels;

Fig. 4 is the optical schematic diagram of the secondary mirror in the specific embodiment two, and 2 is the secondary mirror;

Fig. 5 is a light transmission path diagram of test 2, and 2 is a secondary mirror;

Fig. 6 is a light transmission path diagram of test three, and 2 is a secondary mirror;

Fig. 7 is a cloud diagram of the concentrated energy flow distribution of the receiver in Test 1, 3 is the concentrated photovoltaic panel, 4 is the heat absorber, and 6 is the center of the heat absorber.

detailed description

Specific Embodiment 1: This embodiment is a free-surface secondary reflection and concentrating system for solar thermal/electrical high-efficiency conversion, which adopts a free-surface Cassegrain reflection and concentrating system, consisting of a primary mirror 1, a secondary mirror 2 and The receiver is composed of; the primary mirror 1, the secondary mirror 2 and the receiver are all axisymmetric structures, and the primary mirror 1, the secondary mirror 2 and the receiver are coaxial; the primary mirror 1 and the secondary mirror 2 are connected by a bracket 5 , the concave surface of the primary mirror 1 faces the secondary mirror 2, the receiver is fixed on the bracket 5, and the bracket 5 is arranged on the axis of the primary mirror 1, the secondary mirror 2 and the receiver; the receiver is composed of the heat absorber 4 and The concentrating photovoltaic cell panel 3 is composed of a flange, the flange is installed on the optical window end of the heat absorber 4, the concentrating photovoltaic cell panel 3 is installed on the outside of the flange, and the optical window of the heat absorber 4 faces the secondary mirror 2; The heat absorber 4 is cylindrical, and the concentrated photovoltaic panel 3 is a hollow ring;

The primary mirror adopts a traditional solar dish parabolic reflector, and the secondary mirror is a reflective mirror surface in the form of a free-form surface. The free-form surface of the secondary mirror is determined as follows:

1. Discrete start and target points:

To determine the size of the primary mirror and receiver, the calculation formula is as follows:

w(R _max ² -R _min ² )/C _G =(r _max ² -r _min ² ) (1),

w is the occupancy ratio of the CPV subsystem, C _G is the geometric concentration ratio of the CPV subsystem, R _max is the outer radius of the primary mirror, R _min is the inner radius of the primary mirror, and r _max is the receiver The radius of the outer ring of the concentrated photovoltaic panel, r _min is the radius of the inner circle of the concentrated photovoltaic panel in the receiver, R _min ≥ r _max , five of which are known quantities, and the sixth quantity can be obtained , to determine the dimensions of the primary mirror and receiver;

Establish a three-dimensional rectangular coordinate system (x, y, z), the origin O is the intersection point of the bracket and the primary mirror, the z-axis is the axis pointing from the origin to the secondary mirror along the bracket, and the y-axis is parallel to the concentrated photovoltaic in the receiver The radius of the battery panel and the axis pointing from the origin to the direction of the concentrated photovoltaic panel. The x-axis is the axis passing through the origin O and perpendicular to the plane where the z-axis and y-axis are located. Only the area where the z-axis and y-axis are positive numbers is used for calculation;

Take n points P _i,j-1 on the primary mirror, n is a positive integer, the difference between the y-axis coordinate values of all two adjacent points is equal, i is the serial number of n points, i is a positive integer, and the number 1 is The point on the primary mirror whose y-axis coordinate value is equal to R _max , and No. n is the point on the primary mirror whose y-axis coordinate value is equal to R _min . The serial number i gradually increases from No. 1 to No. n, and y _{i, j-1} is the n The coordinate value of a point on the y-axis, the calculation formula is as follows:

y _i,j-1 =y _1,j-1 -(i-1)×(y _1,j-1 -y _n,j-1 )/n (2);

The z-axis coordinates of point P _i,j-1 are calculated by the formula z=y ² /4f, where f is the focal length of the primary mirror;

Determine the splitting node P _k,j-1 on the primary mirror, and calculate its y-axis coordinate value y _k,j-1 , the calculation formula is as follows:

If the n points P _i,j-1 taken on the primary mirror do not contain the light splitting node P _k,j-1 , then find a y-axis coordinate value and y _k,j-1 among the n points on the primary mirror The closest point P _i,j-1 is used as the splitting node P _k,j-1 ;

Take m points P _i,j+1 on the receiver, m is a positive integer and m=n, the difference between the y-axis coordinates of all two adjacent points is equal, i is the serial number of m points, and i is a positive integer , No. 1 is the point on the receiver whose y-axis coordinate value is equal to r _max , and the serial number i gradually increases along No. 1 to m. y _{i, j+1} is the coordinate value of the m points on the y-axis, y _{k ,j+1} is the coordinate value of the point P _k,j+1 on the y-axis of the light splitting node P _k,j-1 on the receiver after secondary mirror reflection, y _k,j+1 is equal to r _min , and the rest The calculation formula of y _i,j+1 of m-1 points is as follows:

2. The solution of discrete points on the free-form surface of the quadratic mirror:

Set P _i,j as the point P _i,j-1 where the sunlight irradiates on the primary mirror reflects to the corresponding point on the secondary mirror, θ _i is the reflection half angle corresponding to P _i,j , the calculation method of θ _i is as follows :

with Represent vectors respectively and vector the unit vector of

is the normal vector of point P _i,j , Obtained by the following formula: The matrix Rot(x,θ _i ) is:

The coordinates of point P _1,j are known quantities, and its normal vector It can also be obtained from this,

normal vector The reverse extension of is the vector Two adjacent normal vectors with Corresponding reverse extension line vector and vector The intersection point is C _i-1 , let the vector That is, the following formula:

t _i-1 and t _i are vectors respectively and vector , t _i is the length from point P _{i,j to} point C _i , and t _i-1 is the length from point P _{i-1,j to} point C _i-1 ;

P _i,j is represented by the following formula:

λ _i is a vector the mold;

Substituting formulas (5)(7)(9) into (6), we get Substituting the single-valued function with parameter λ _i into formula (8), taking t _i-1 and t _i as unknowns, the function is obtained:

The coordinates of point C _i-1 are:

Substituting formula (10) into (11) to obtain the coordinates of point C i- ₁ , and then substituting the coordinates of point C _i-1 and formula (9) into formula (12), the value of λ _i can be obtained. Substituting the value of λ _i into formula (9), the coordinates of P _{i, j} can be obtained;

3. Draw the quadratic mirror surface: connect and reconstruct the coordinates of P _{i, j} with non-uniform rational B-spline curves to obtain the quadratic mirror free curve, use the three-dimensional construction function of the drawing software to draw the quadratic mirror free curve, the primary mirror and The receiver rotates the curve around the z-axis to obtain a three-dimensional free-form surface.

Embodiment 2: The difference between this embodiment and Embodiment 1 is that the receiver is installed at the intersection of the bracket 5 and the primary mirror 1 . Others are the same as the first embodiment.

Embodiment 3: The difference between this embodiment and Embodiment 1 or 2 is that the receiver is installed on the bracket 5 and the distance from the primary mirror 1 is 1/4 of the length of the bracket 5 . Others are the same as those in Embodiment 1 or 2.

Embodiment 4: The difference between this embodiment and Embodiments 1 to 3 is: the receiver is installed on the bracket 5 and the distance from the primary mirror 1 is 1/3 of the length of the bracket 5 . Others are the same as the specific embodiments 1 to 3.

Embodiment 5: The difference between this embodiment and Embodiments 1 to 4 is: the receiver is installed on the bracket 5 and the distance from the primary mirror 1 is 1/2 of the length of the bracket 5 . Others are the same as the specific embodiments 1 to 4.

Prove the beneficial effect of the present invention by following test:

Test 1: This test is a free-surface secondary reflection and concentrating system for solar thermal/electrical high-efficiency conversion, using a free-surface Cassegrain reflection and concentrating system, consisting of a primary mirror 1, a secondary mirror 2 and a receiver; The mirror 1, the secondary mirror 2 and the receiver are all axisymmetric structures, and the primary mirror 1, the secondary mirror 2 and the receiver are coaxial; the primary mirror 1 and the secondary mirror 2 are connected by a bracket 5, and the primary mirror 1 The concave surface faces the secondary mirror 2, the receiver is fixed on the support 5, and the support 5 is arranged on the axis of the primary mirror 1, the secondary mirror 2 and the receiver; the receiver is composed of the heat absorber 4 and the concentrated photovoltaic panel 3 and a flange, the flange is installed on the optical window end of the heat absorber 4, the concentrated photovoltaic panel 3 is installed on the outside of the flange, and the optical window of the heat absorber 4 faces the secondary mirror 2; the heat absorber 4 is Cylindrical, the concentrated photovoltaic panel 3 is a hollow ring;

The primary mirror adopts a traditional solar dish parabolic reflector, and the secondary mirror is a reflective mirror surface in the form of a free-form surface. The free-form surface of the secondary mirror is determined as follows:

1. Discrete start and target points:

To determine the size of the primary mirror and receiver, the calculation formula is as follows:

w(R _max ² -R _min ² )/C _G =(r _max ² -r _min ² ) (1),

w is the dominant ratio of the CPV subsystem, C _G is the geometric condensing ratio of the CPV subsystem, R _max is the outer radius of the primary mirror, R _min is the inner radius of the primary mirror, r _max is the receiving The radius of the outer ring of the concentrated photovoltaic panel in the receiver, r _min is the radius of the inner circle of the concentrated photovoltaic panel in the receiver, R _min ≥ r _max , five of them are known quantities, and the sixth one can be obtained The amount determines the size of the primary mirror and receiver;

Establish a three-dimensional rectangular coordinate system (x, y, z), the origin O is the intersection point of the bracket and the primary mirror, the z-axis is the axis pointing from the origin to the secondary mirror along the bracket, and the y-axis is parallel to the concentrated photovoltaic in the receiver The radius of the battery panel and the axis pointing from the origin to the direction of the concentrated photovoltaic panel. The x-axis is the axis passing through the origin O and perpendicular to the plane where the z-axis and y-axis are located. Only the area where the z-axis and y-axis are positive numbers is used for calculation;

Take 100 points P _i,j-1 on the primary mirror, n is a positive integer, the difference between the y-axis coordinate values of all two adjacent points is equal, i is the serial number of n points, i is a positive integer, and the number 1 is The point on the primary mirror whose y-axis coordinate value is equal to R _max , and No. n is the point on the primary mirror whose y-axis coordinate value is equal to R _min . The serial number i gradually increases from No. 1 to No. n, and y _{i, j-1} is the n The coordinate value of a point on the y-axis, the calculation formula is as follows:

y _i,j-1 =y _1,j-1 -(i-1)×(y _1,j-1 -y _n,j-1 )/n (2);

The z-axis coordinates of point P _i,j-1 are calculated by the formula z=y ² /4f, where f is the focal length of the primary mirror;

Determine the splitting node P _k,j-1 on the primary mirror, and calculate its y-axis coordinate value y _k,j-1 , the calculation formula is as follows:

The 100 points P _i,j-1 taken on the primary mirror do not include the light splitting node P _k,j-1 , find a y-axis coordinate value closest to y _k,j-1 among the 100 points on the primary mirror The point P _50,j-1 is used as the splitting node P _k,j-1 ;

Take 100 points P _i,j+1 on the receiver, the difference between the y-axis coordinates of all two adjacent points is equal, i is the serial number of 100 points, i is a positive integer, and number 1 is y on the receiver The point whose axis coordinate value is equal to r _max , the serial number i gradually increases from No. 1 to No. 100, y _{i, j+1} is the coordinate value of the y-axis among these 100 points, and y _{k, j+1} is the splitting node P The coordinate value of point P _k,j+1 on the receiver on the y-axis after _k,j-1 is reflected by the secondary mirror, y _k,j+1 is equal to r _min , and y _i,j of the remaining 99 points ₊₁ calculation formula is as follows:

2. The solution of discrete points on the free-form surface of the quadratic mirror:

Set P _i,j as the point P _i,j-1 where the sunlight irradiates on the primary mirror reflects to the corresponding point on the secondary mirror, θ _i is the reflection half angle corresponding to P _i,j , the calculation method of θ _i is as follows :

with Represent vectors respectively and vector the unit vector of

is the normal vector of point P _i,j , Obtained by the following formula:

The matrix Rot(x,θ _i ) is:

The coordinates of point P _1,j are known quantities, and its normal vector It can also be obtained from this,

normal vector The reverse extension of is the vector Two adjacent normal vectors with Corresponding reverse extension line vector and vector The intersection point is C _i-1 , let the vector That is, the following formula:

t _i-1 and t _i are vectors respectively and vector , t _i is the length from point P _{i,j to} point C _i , and t _i-1 is the length from point P _{i-1,j to} point C _i-1 ;

P _i,j is represented by the following formula:

λ _i is a vector the mold;

Substituting formulas (5)(7)(9) into (6), we get Substituting the single-valued function with parameter λ _i into formula (8), taking t _i-1 and t _i as unknowns, the function is obtained:

The coordinates of point C _i-1 are:

Substituting formula (10) into (11) to obtain the coordinates of point C i- ₁ , and then substituting the coordinates of point C _i-1 and formula (9) into formula (12), the value of λ _i can be obtained. Substituting the value of λ _i into formula (9), the coordinates of P _i,j can be obtained;

Table 1 is the relevant parameters of the primary mirror, secondary mirror and receiver in Test 1,

Table 1

According to the formula 1, the radius r _max of the outer ring of the concentrated photovoltaic panel is 0.5m.

The coordinates of 100 points on the secondary mirror are finally obtained through the above formula, as shown in Table 2:

Table 2

3. Draw the quadratic mirror surface: connect and reconstruct the coordinates of P _{i, j} with non-uniform rational B-spline curves to obtain the quadratic mirror free curve, use the three-dimensional construction function of the drawing software to draw the quadratic mirror free curve, the primary mirror and The receiver rotates the curve around the z-axis to obtain a three-dimensional free-form surface.

Experiment 2: The difference between this experiment and Experiment 1 is that the geometric concentration ratio of the CPV subsystem is 60suns, and other known quantities are the same.

Test 3: The difference between this test and test 2 is that the distance between the receiver and the primary mirror is 3m, and other known quantities are the same.

Figure 5 is the light transmission path diagram of Test 2, 2 is the secondary mirror, Figure 6 is the light transmission path diagram of Test 3, 2 is the secondary mirror, and the concave-convexity of the free-form surface of the secondary mirror can be seen from the figure It mainly depends on the height of the receiver. After being reflected by the free-form surface of the secondary mirror, the collected light is divided into two parts, one part is gathered at the center point for high-temperature heat conversion, and the other part is evenly distributed around the receiver for gathering. Photovoltaic conversion, as the height of the receiver increases, the free surface mirror of the secondary mirror gradually changes from downward convex to upward concave. In addition, due to the fixed size of the CPV panels, as the height of the receiver increases, the light-splitting transition region becomes more obvious.

Figure 7 is the cloud diagram of the concentrated energy flow distribution of the receiver in Test 1, 3 is the concentrated photovoltaic panel, 4 is the heat absorber, 6 is the center of the heat absorber, the light-colored part is the area with strong energy flow, and the black is the energy flow area. In the area with weak flow, it can be seen from the figure that all light vector distributions coincide with the set target vector, that is, the energy flow gathered in the center converges at the origin of the heat sink, and the energy flow distribution obtained by the concentrated photovoltaic panels is completely uniform. Since all absorber target receiving vectors will converge exactly on the dot, the peak value of its central energy flow is very high.

Due to the deviation of the normal vector of the secondary free mirror in the transition area, even for point light sources, the light splitting transition area on the receiving surface will still receive part of the light, but the loss of this part is not large and can be ignored.

Claims (5)

1. A free-surface secondary reflection concentrating system for solar heat/electricity efficient conversion, characterized in that the free-surface secondary reflection concentrating system for solar heat/electricity efficient conversion adopts free-surface Cassegrain reflection The gathering system is composed of a primary mirror (1), a secondary mirror (2) and a receiver; the primary mirror (1), the secondary mirror (2) and the receiver are all axisymmetric structures, and the primary mirror (1), the secondary The secondary mirror (2) and the receiver are coaxial; the primary mirror (1) and the secondary mirror (2) are connected by a bracket (5), the concave surface of the primary mirror (1) faces the secondary mirror (2), and the receiver is fixed On the support (5), the support (5) is arranged on the axis of the primary mirror (1), the secondary mirror (2) and the receiver; (3) is composed of a flange, the flange is installed at the optical window end of the heat absorber (4), the concentrator photovoltaic panel (3) is installed on the outside of the flange, and the optical window of the heat absorber (4) faces the secondary The mirror (2); the heat absorber (4) is cylindrical, and the concentrating photovoltaic panel (3) is a hollow ring; The primary mirror adopts a traditional solar dish parabolic reflector, and the secondary mirror is a reflective mirror surface in the form of a free-form surface. The free-form surface of the secondary mirror is determined as follows: 1. Discrete start and target points: To determine the size of the primary mirror and receiver, the calculation formula is as follows: w(R _max ² -R _min ² )/C _G =(r _max ² -r _min ² ) (1), w is the occupancy ratio of the CPV subsystem, C _G is the geometric concentration ratio of the CPV subsystem, R _max is the outer radius of the primary mirror, R _min is the inner radius of the primary mirror, and r _max is the receiver The radius of the outer ring of the concentrated photovoltaic panel, r _min is the radius of the inner circle of the concentrated photovoltaic panel in the receiver, R _min ≥ r _max , five of which are known quantities, and the sixth quantity can be obtained , to determine the dimensions of the primary mirror and receiver; Establish a three-dimensional rectangular coordinate system (x, y, z), the origin O is the intersection point of the bracket and the primary mirror, the z-axis is the axis pointing from the origin to the secondary mirror along the bracket, and the y-axis is parallel to the concentrated photovoltaic in the receiver The radius of the battery panel and the axis pointing from the origin to the direction of the concentrated photovoltaic panel. The x-axis is the axis passing through the origin O and perpendicular to the plane where the z-axis and y-axis are located. Only the area where the z-axis and y-axis are positive numbers is used for calculation; Take n points P _i,j-1 on the primary mirror, n is a positive integer, the difference between the y-axis coordinate values of all two adjacent points is equal, i is the serial number of n points, i is a positive integer, and the number 1 is The point on the primary mirror whose y-axis coordinate value is equal to R _max , and No. n is the point on the primary mirror whose y-axis coordinate value is equal to R _min . The serial number i gradually increases from No. 1 to No. n, and y _{i, j-1} is the n The coordinate value of a point on the y-axis, the calculation formula is as follows: y _i,j-1 =y _1,j-1 -(i-1)×(y _1,j-1 -y _n,j-1 )/n (2); The z-axis coordinates of point P _i,j-1 are calculated by the formula z=y ² /4f, where f is the focal length of the primary mirror; Determine the splitting node P _k,j-1 on the primary mirror, and calculate its y-axis coordinate value y _k,j-1 , the calculation formula is as follows: n>k>1, If the n points P _i,j-1 taken on the primary mirror do not contain the light splitting node P _k,j-1 , then find a y-axis coordinate value and y _k,j-1 among the n points on the primary mirror The closest point P _i,j-1 is used as the splitting node P _k,j-1 ; Take m points P _i,j+1 on the receiver, m is a positive integer and m=n, the difference between the y-axis coordinates of all two adjacent points is equal, i is the serial number of m points, and i is a positive integer , No. 1 is the point on the receiver whose y-axis coordinate value is equal to r _max , and the serial number i gradually increases along No. 1 to m. y _{i, j+1} is the coordinate value of the m points on the y-axis, y _{k ,j+1} is the coordinate value of the point P _k,j+1 on the y-axis of the light splitting node P _k,j-1 on the receiver after secondary mirror reflection, y _k,j+1 is equal to r _min , and the rest The calculation formula of y _i,j+1 of m-1 points is as follows: 2. The solution of discrete points on the free-form surface of the quadratic mirror: Set P _i,j as the point P _i,j-1 where the sunlight irradiates on the primary mirror reflects to the corresponding point on the secondary mirror, θ _i is the reflection half angle corresponding to P _i,j , the calculation method of θ _i is as follows : with Represent vectors respectively and vector the unit vector of is the normal vector of point P _i,j , Obtained by the following formula: The matrix Rot(x,θ _i ) is: The coordinates of point P _1,j are known quantities, and its normal vector It can also be obtained from this, normal vector The reverse extension of is the vector Two adjacent normal vectors with Corresponding reverse extension line vector and vector The intersection point is C _i-1 , let the vector = vector That is, the following formula: t _i-1 and t _i are vectors respectively and vector , t _i is the length from point P _{i,j to} point C _i , and t _i-1 is the length from point P _{i-1,j to} point C _i-1 ; P _i,j is represented by the following formula: λ _i is a vector the mold; Substituting formulas (5)(7)(9) into (6), we get Substituting the single-valued function with parameter λ _i into formula (8), taking t _i-1 and t _i as unknowns, the function is obtained: The coordinates of point C _i-1 are: Substituting formula (10) into (11) to obtain the coordinates of point C i- ₁ , and then substituting the coordinates of point C _i-1 and formula (9) into formula (12), the value of λ _i can be obtained. Substituting the value of λ _i into formula (9), the coordinates of P _i,j can be obtained; 3. Draw the quadratic mirror surface: connect and reconstruct the coordinates of P _{i, j} with non-uniform rational B-spline curves to obtain the quadratic mirror free curve, use the three-dimensional construction function of the drawing software to draw the quadratic mirror free curve, the primary mirror and The receiver rotates the curve around the z-axis to obtain a three-dimensional free-form surface. 2. A free-surface secondary reflection concentrating system for solar heat/electricity efficient conversion according to claim 1, characterized in that the receiver is installed on the bracket (5) and the primary mirror (1) intersection. 3. A free-surface secondary reflection concentrating system for solar thermal/electrical high-efficiency conversion according to claim 1, characterized in that said receiver is installed on the support (5) with the primary mirror (1) The distance is 1/4 of the length of the support (5). 4. A free-surface secondary reflection concentrating system for solar thermal/electrical high-efficiency conversion according to claim 1, characterized in that the receiver is installed on the bracket (5) with the primary mirror (1) Distance is 1/3 place of support (5) length. 5. A free-surface secondary reflection concentrating system for solar thermal/electrical high-efficiency conversion according to claim 1, characterized in that said receiver is installed on the support (5) and the primary mirror (1) Distance is 1/2 place of support (5) length.