Secondary reflection receiver concentrating solar heat collection system and design method

Abstract

The invention relates to the technical field of solar photo-thermal utilization, in particular to a secondary reflection center receiver concentrating solar heat collection system and a design method thereof. The system is composed of a heliostat field composed of a plurality of heliostats which are symmetrically or approximately symmetrically arranged, an inclined plane secondary reflector installed on a high tower and a receiver which is obliquely installed close to the ground. Each heliostat is accurately controlled through a tracking system, and sunlight is reflected and focused to a common focus located at the high position of the right south of a heliostat field. Afterwards, the light rays are further reflected by the secondary reflector and guided to the receiver, and efficient light energy collection and heat energy conversion are achieved. Through accurate tracking and focusing of the heliostat and the guiding effect of the secondary reflector, the system can efficiently gather sunlight to the receiver, and the light energy collection efficiency is improved. The heliostat field is arranged symmetrically or approximately symmetrically, so that the heliostat field is attractive, shadow shielding can be effectively reduced, and the overall condensation effect is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of solar thermal utilization, and in particular to a secondary reflection receiver concentrating solar thermal collection system and a design method thereof. Background Art

[0002] Traditional solar thermal systems often face problems such as low light energy utilization, high system complexity, and high costs. The discontinuity and instability of solar energy also limit its large-scale application.

[0003] The secondary reflection central receiver system, also known as the secondary reflection tower system, consists of a heliostat field consisting of multiple heliostats, secondary reflectors installed on high towers, and a central receiver installed on the ground. It is to transfer the receiver in the ordinary central receiver system from the high tower to the ground, thereby reducing the cost of building the high tower and reducing the transmission distance of the high-temperature medium, thereby reducing costs and improving efficiency. The earliest form of this design is also called a solar furnace. As early as 1933, German scholar Straube developed a solar furnace consisting of a heliostat and a concentrator. i The French Odeil lo solar furnace, which was put into operation in 1969, consists of 63 6*7.5m planar heliostats and a 40*54m parabolic concentrator, focusing up to 1MW of energy on the focal plane. The secondary reflector is a parabolic concentrator, which is composed of 9,500 back-reflecting flat glass silver mirrors, with a focal length of 18 meters.

[0004] A solar furnace is an optical system that produces high-energy flux density solar radiation. This can generate very high temperatures. It is usually used for research and manufacturing. It mainly projects sunlight vertically onto a parabolic mirror through a heliostat, and the parabolic reflector focuses the sunlight near the focal point. The temperature at the focal point can reach up to 3500℃. This heat energy can be used to generate electricity, smelt steel, and make hydrogen fuel or nanomaterials. The largest solar furnace built by the Institute of Electrical Engineering of the Chinese Academy of Sciences has a parabolic concentrator area of ​​300 square meters. In 2009, Professor Chen Yingtian of USTC invented a heliostat with small aberration and developed a solar furnace with a higher concentration ratio for smelting high-purity silicon. This achievement was selected as one of the top ten scientific and technological advances in China in 2009.

[0005] The common solar furnace uses a flat reflector as a heliostat, which makes the central sun rays incident nearly vertically on the parabolic concentrator. The parabola is fixed vertically and the receiving surface is also vertical to the ground. The heliostat reflects the central sun rays nearly parallel to the ground, which is equivalent to a tower system with a central receiver installed on the ground and a tower height of 0. This will make the cosine factor smaller and the efficiency lower. The total light-transmitting area of ​​the heliostats of the French Odei l lo solar furnace is 2835 square meters, but the solar energy intercepted by the receiving surface is only 1000kW. The main purpose of the solar furnace is to obtain high temperature. The advantage of such a design is that the concentrator is fixedly installed, which can obtain a higher geometric concentration ratio and a large light-transmitting area at the same time. However, the incident angle of sunlight on the heliostat is large, especially when the solar altitude angle is large and the energy is large, the incident angle is larger, and the cosine factor is lower, resulting in lower daily and annual average efficiencies. Moreover, the light-transmitting area of ​​the concentrator used is equivalent to the area of ​​the heliostat, which means that two sets of mirror areas are required. The cost is much higher than that of the ordinary tower system, and it is not suitable for low-cost solar power generation.

[0006] The solar furnace uses a flat heliostat, which only changes the direction of sunlight, does not focus the sun, and allows the central ray of sunlight entering the solar furnace to be incident vertically, so that there is almost no difference between the sunlight entering the solar furnace concentrator and the sunlight coming from the sun. Therefore, the optical analysis of the solar furnace can be equivalent to a rotating parabolic dish system.

[0007] Professor Chen uses a low-aberration curved heliostat, and a spherical or rotating paraboloid as the concentrator. The concentrator area can be much smaller than the heliostat area, so a higher concentration ratio can be designed. In principle, it is closer to a secondary concentrating disk system, and its optical analysis is much more complicated. Professor Chen's research group mainly studied the aberration and focal plane energy flux density distribution.

[0008] In 1976, Rabl proposed the use of a secondary reflective tower system, which uses mirrors on tall towers to reflect light to the ground, allowing the solar receiver to be placed on the ground instead of on top of a tall tower as in most commercial central receiver concentrated solar power (CSP) plants today. Although pumping losses are smaller, high-temperature heat transfer piping can be reduced, as well as reducing the weight of the tower, making the structure cost lower, thereby significantly reducing costs. In addition, the downward beam concentrator provides the opportunity to use a new type of top-irradiated receiver. However, the optical constraints and costs associated with tower reflectors relative to tower receivers may result in reduced performance or increased costs of the designed tower system. These obvious problems ii Related to the extra reflections from the secondary reflectors, which manifests as reflection losses, decreased interception due to increased aberrations, and the need to use ideal hyperbolic surfaces, which increases costs iii. The secondary reflector needs to operate at a higher energy flux density, and due to the high optical error requirements, the life span may be much lower. In order to reduce the surface energy flux density, it is necessary to increase the area of ​​the secondary reflector, increase the shielding of the heliostat field, and may generate greater wind loads than similar tower receivers, increasing costs. Despite these difficulties, downward beam concentrators have proven useful in research. By 2021, the world's first commercialized secondary reflection tower solar power generation system has officially been put into operation in China. It is a secondary reflection tower system in the 50MW secondary reflection tower solar thermal power plant built in Yumen, my country.

[0009] The new solar furnace design is to arrange the parabolic concentrator horizontally at a high place, and the heliostat is arranged directly below the concentrator, so that the sunlight from different directions is incident vertically on the concentrator, and the concentration ratio can reach 6000. From a structural point of view, the secondary reflection tower system is similar to this solar furnace. The difference is that the light-transmitting area of ​​the heliostat is much larger than that of the secondary concentrator. Most of the sunlight reflected by the heliostat is not vertically incident on the concentrator. Since the parabolic concentrator can well concentrate parallel light, it also has a good focusing effect on sunlight with a very small distribution angle. However, for incident light with a large distribution angle, according to the aberration theory, the image spot radius is greater than the product of the distance from the reflection point to the focal plane intersection and the tangent of the incident angle. This inevitably leads to that the larger the area of ​​the system heliostat, the larger the mirror field area required, the larger the incident angle entering the concentrator, and the larger the image spot radius, making it difficult to use parabolic concentrators.

[0010] Therefore, when designing a secondary reflection tower system, the concentrator mainly uses a hyperboloid or an ellipsoidal surface, and uses the focusing performance of light on these two surfaces to aim the incident light at one focus on the two surfaces, so that the light reflected by the curved surface will be focused on the other focus. If the heliostat is a plane reflector, at most only one point on the heliostat can aim the reflected light at one focus of the concentrator, and the directions of other reflected light will deviate from the focus and cannot be focused on another focus. Using a curved mirror that can focus light as a heliostat will reduce the deviation and improve the focusing effect, but due to changes in the position of the sun, the direction of the light entering the heliostat changes greatly, and the incident angle changes accordingly. As the incident angle increases, the phase dispersion will increase, resulting in an increase in the deviation of the reflected light direction, making it difficult to aim at the focus of the concentrator, resulting in a large image spot radius and reducing the concentration ratio. Since the concentration ratio is much lower than that of the ordinary tower, even if the scale is limited, the optical efficiency of the currently designed secondary reflection tower solar furnace system is not very high, with a reported value of about 57%, which is significantly lower than that of the ordinary central receiver system. Summary of the invention

[0011] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a secondary reflection central receiver concentrated solar thermal collection system and a design method to improve optical efficiency.

[0012] The technical solution of the present invention is as follows:

[0013] A secondary reflection central receiver concentrated solar energy heat collection system comprises a heliostat field composed of a plurality of heliostats, a secondary reflector mounted on a high tower and a receiver mounted near the ground, and is characterized in that: the heliostat field is arranged symmetrically or nearly symmetrically, the axis of symmetry is arranged in the north-south direction, each heliostat is controlled by a tracking system to reflect and focus sunlight onto a common focus, and the common focus is set at a high point due south of the mirror field; the secondary reflector is a plane reflector, which is installed obliquely on the high tower and is located on the optical path between the heliostat and the common focus; the receiver is installed obliquely near the ground; the sunlight received by the heliostat is reflected onto the secondary reflector, and then reflected by the secondary reflector to the receiver for reception.

[0014] Preferably, if the north-south length of the heliostat field is L, the height of the common focus is about L / 5 to L / 4.

[0015] Preferably, a point A on the symmetry axis of the heliostat field is selected, the point is 0.6-0.8L away from the southernmost heliostat in the field, the center of the secondary reflector is arranged on the line from point A to the common focus, and the secondary reflector is tilted so that the angle between it and the line is 45 degrees; the heliostat whose center is installed at point A controls its reflected light to point to the common focus through a tracking system, is changed in direction by the secondary reflector, and is focused to the center of the receiver, receiving an opening surface thereof perpendicular to the reflected light.

[0016] Preferably, the distance from the secondary reflector to the common focus is equal to the distance from the secondary reflector to the center of the receiver; the ratio of the distance from the secondary reflector to the common focus to the distance from the common focus to the point A is α, which should be 0.03 to 0.3, so that the receiver can be installed on the ground or close to the ground.

[0017] Preferably, the angle between the line connecting the secondary reflector to the common focus and the horizontal plane is β=atan(H / d), where d is the distance from point A to the common focus in the horizontal direction, which is approximately 0.8*L; the height of the secondary reflector h≈L*s inβ*α; the width of the heliostat field is W, and the width of the secondary reflector w≈W*α.

[0018] Preferably, the radius of curvature of each heliostat in the heliostat field is equal to twice the distance from the center of the heliostat to the common focus.

[0019] Preferably, the width of the heliostat field does not exceed the length.

[0020] Preferably, the secondary reflection central receiver concentrated solar thermal system is installed on an azimuth tracking device; all heliostats share the azimuth tracking device, and each row of heliostat reflectors are installed on the same horizontal rotation axis and share a height tracking device; the width of the heliostat field should not exceed one-half of the length, and the optimized design is about one-third;

[0021] Preferably, the receiver is a cavity solar receiver.

[0022] The design method of the secondary reflection central receiver concentrated solar thermal collection system is characterized by comprising the following steps:

[0023] S1: First complete the preliminary design, including:

[0024] 1) Determine the length and width of the heliostat field according to demand. If the total thermal power required is P, the heliostat field area S = P*4 square meters, and the heliostat field length L = (P*12) 0.5 ; Heliostat field width W = (P*12) 0.5 / 3;

[0025] 2) Determine the height of the heliostat h h and width w h ; The initial recommendations are 6 meters and 8 meters respectively;

[0026] 3) Determine the common focus position, which is 0.1*L due south of the heliostat field and has a height of H=0.25L;

[0027] 4) Determine the inclination angle of the secondary reflector, the angle between the line connecting point A to the common focus F and the horizontal plane is β=atan(H / (0.8*L)), and the inclination angle between the secondary reflector and the ground=π / 4 degrees-β radians;

[0028] 5) Determine α, calculated according to the following formula:

[0029] H*(1-α)-0.8L*α*cos(45-β)=h h *s inβ+h';

[0030] Here h' is the distance between the edge of the receiver and the ground, and the receiving surface has an inclination angle of β on the horizontal plane;

[0031] 6) Determine the position of the secondary reflector, the horizontal distance from the common focus is α*0.8L; the height distance from the ground = H*(1-α);

[0032] 7) Determine the center position of the receiver: located below the secondary reflector, the horizontal distance from the secondary reflector = 0.08L*s in(45-β); the vertical distance from the secondary reflector = 0.08L*cos(45-β), that is, the distance from the ground = H*(1-α)-0.08L*cos(45-β);

[0033] 8) Determine the size of the secondary reflector: the height of the secondary reflector h = L*s inβ*α; the width of the heliostat field is W, and the width of the secondary reflector w = W*α; the secondary reflector adopts a plane reflector;

[0034] 9) Determining the curvature radius of the heliostat: the optimal curvature radius of each heliostat in the heliostat field is equal to twice the distance from the center of the heliostat to the common focus;

[0035] S2: Establish a performance and cost simulation calculation program, determine the main design parameters based on the installation location, with the maximum annual average efficiency or minimum cost as the optimization goal, and then recalculate other parameters.

[0036] Working principle:

[0037] Heliostat field layout and ray tracing:

[0038] The multiple heliostats in the system are precisely controlled by a tracking system to ensure that they can track the position of the sun in real time. These heliostats are arranged in a symmetrical or nearly symmetrical shape with the axis of symmetry along the north-south direction to maximize the efficiency of receiving sunlight.

[0039] Each heliostat is designed to reflect and focus sunlight to a common focal point, which is set high in the south of the mirror field, at a height of about 1 / 5 to 1 / 4 of the north-south length of the mirror field, L. This layout ensures that the light reflected from the heliostats in all directions can converge to the same point.

[0040] The role of the secondary reflector:

[0041] The tower mounted secondary reflector is a flat reflector that is strategically placed on the tower in the optical path between the heliostats and the common focus. The main function of the secondary reflector is to receive the light from the heliostats and further reflect it to a receiver near the ground.

[0042] The installation angle and position of the secondary reflector are critical to ensure that it can effectively direct the light from the heliostat to the receiver. According to the design requirements, the center of the secondary reflector should be arranged on the line from a point A on the symmetry axis of the heliostat field (about 0.6-0.8L from the southernmost heliostat) to the common focus, and its inclination angle is 45 degrees to the line.

[0043] Receiver design:

[0044] The receiver is installed at an angle close to the ground, with its opening perpendicular to the light reflected from the secondary reflector. This design ensures that the light can be captured by the receiver to the maximum extent and converted into heat energy.

[0045] The receiver is usually filled with a heat-absorbing medium (such as water, oil, etc.) to absorb and store the heat energy converted from sunlight.

[0046] Overall workflow:

[0047] When the sun rises, the tracking system automatically starts and controls each heliostat to adjust its angle to track the sun's position.

[0048] The heliostats reflect and focus the sunlight onto a common focal point, which is then received by secondary reflectors and reflected again to a receiver.

[0049] The receiver captures this light and converts it into heat, which can then be used for heating, power generation or other heat utilization purposes through a heat exchange system.

[0050] Through this series of sophisticated designs and automatic control systems, the system achieves efficient and stable solar energy collection and thermal energy conversion, providing an effective solution for the application of renewable energy.

[0051] The present invention proposes to adopt the Newtonian telescope structure and use a plane reflector as a secondary mirror, so that the heliostat can complete the focusing function, and the secondary mirror only plays the role of changing the direction originally envisioned by the secondary reflection tower system. It can be said that it is a new type of secondary reflection tower system. The advantage of this design is that with the help of the secondary reflector, the height of the receiving tower in the original design is increased, thereby improving efficiency; but it does not need to invest in the construction cost of the original high tower.

[0052] From the perspective of the structure of the Newtonian reflecting telescope, the position and size of the secondary reflector are related. If a parallel-to-the-ground configuration is used, according to the secondary reflection focusing theory, the disadvantage is that the key parameter shading rate α needs to be larger in order to allow the receiver to be farther away from the secondary mirror and closer to the ground, thereby lowering the height of the secondary mirror while keeping the virtual original focus at a higher position. The adverse effect is that the area of ​​the secondary mirror increases. If α = 0.5, if the receiving surface is placed on the ground, the virtual original tower height is twice the height of the secondary mirror tower, but the area of ​​the secondary mirror will reach one-fourth of the mirror field area. The bigger problem is that it is the same principle as using a curved mirror as a secondary mirror, which greatly limits the scope of the mirror field.

[0053] The present invention refers to the solar furnace of ordinary design, and the main axis of the designed secondary reflection tower system is tilted to the ground, and the secondary mirror is at a 45-degree angle to the main axis. In other words, the mirror field adopts the north field solution, which has higher efficiency and avoids excessive incident angle of the heliostat, which increases the aberration. The efficiency can be further improved by arranging the entire system on an azimuth tracking platform. With this design, the height of the secondary mirror from the ground will be lower than that of the original tower, and it does not need to be very large, thereby reducing the construction cost of the secondary mirror.

[0054] Ray tracing calculations show that, under the same design, with the addition of a secondary reflector, the receiver's interception rate of the heliostats is slightly lower for farther heliostats and higher for closer heliostats, but remains unchanged overall. Ray tracing calculation results show that the photothermal efficiency can reach 64%, which is significantly higher than the existing secondary reflection central receiver system.

[0055] The location of the secondary plane reflector does not affect the interception rate. Referring to the secondary reflector dish system, the blocking rate α is defined. Increasing α is equivalent to moving the secondary plane reflector away from the original focus, while lowering the height of the receiver from the ground; increasing the area of ​​the secondary reflector.

[0056] For the PS10 mirror field, the distance from the center of the main mirror to the bottom of the receiving tower is half the length of the mirror field, that is, 400 meters. When α = 0.18, the height of the receiver center from the ground is 8.5 meters. Due to the tilt of the receiving surface, it is equivalent to being installed on the ground. Calculations show that the efficiency of the far-field heliostat is slightly reduced. For the farthest heliostat, for example, the heliostat with a coordinate position of [300,800], when the azimuth angle is 80 degrees and the elevation angle is 30 degrees, the interception rate without a secondary reflector is 84.72%, and when a secondary reflector is added, the interception rate drops to 82.95%; for the near-field heliostat, for example, the heliostat with a coordinate position of [100,50], the interception rates without and with a secondary reflector are 98.48% and 99.98% respectively. Adding a secondary reflector increases the interception rate. This is because adding a secondary reflector increases the distance of the far-field heliostat and reduces the distance of the near-field heliostat. Therefore, when the secondary reflector uses a 45-degree plane turning mirror, the aberration will not increase and the optical performance remains basically unchanged. This is consistent with the aberration theory of the Newtonian telescope with a 45-degree turning mirror.

[0057] When the secondary reflector is a hyperbolic surface, the equation should be:

[0058] x 2 +z 2 =2ry-(1-e 2 )y 2

[0059] The distances from the upper and lower foci to the vertex are r / (e+1) and r / (e-1) respectively. If the height of the receiving surface from the ground is hx, and the height of the original receiver center from the ground is ht, then:

[0060]

[0061] From this we get:

[0062]

[0063] The optical axis of the system in this scheme should be perpendicular to the ground or slightly tilted. If it is used in the North Field Tower System, the optical axis of the system is tilted at a small angle to the ground, and the focus moves mainly in the horizontal direction. The height of the receiving surface can only be slowly lowered, and it is difficult to achieve the purpose of moving the receiving surface to the ground. If the receiver is set on the ground or close to the ground, the receiver is far away from the secondary mirror. According to the aberration theory of secondary reflection optical system, the image spot radius

[0064] =βf0*tanθ, f0 is the focal length of the primary mirror, θ is the incident angle; β is the magnification of the secondary mirror, which is equal to the ratio of the two focal points f2 / f1, which is consistent with the phenomenon observed in the literature.

[0065] In general, the present invention adds a plane reflector to the North Field tower system technology, changes the light focused on the center of the receiving tower, and focuses it on the ground. It does not change the system aberration, and maintains the optical performance of the original tower system; the receiver is moved from the high tower to the ground, which shortens the heat energy transmission distance; the secondary mirror area is also greatly reduced, and the structural cost of the installation tower is also greatly reduced. The secondary mirror uses a plane reflector, which is easy to manufacture, and the light and heat efficiency is significantly improved, which is far superior to the secondary reflection tower system composed of curved mirrors.

[0066] Advantages of the present invention:

[0067] 1. Efficient light energy collection and conversion

[0068] Symmetrical arrangement of heliostat field: Through the symmetrical or nearly symmetrical arrangement of the heliostat field and the precise tracking control of each heliostat, the system can ensure that sunlight is efficiently reflected and focused to a common focus. This design improves the efficiency of light energy collection and allows more sunlight energy to be converted into heat energy.

[0069] Introduction of secondary reflectors: As a key component in the optical path, the secondary reflector further enhances the light energy collection effect. It reflects the light from the heliostat and directs it to the receiver, thereby improving the receiver's heat collection efficiency.

[0070] 2. Optimized system layout and structural design

[0071] Height design of the common focus: The common focus is set at a high point due south of the mirror field, and the height is approximately between 1 / 5 and 1 / 4 of the length L of the mirror field in the north-south direction. This design helps to reduce the loss of light during propagation and enables the light to be focused more accurately on the receiver.

[0072] Tilt installation of secondary reflector: The secondary reflector is tilted and installed on the high tower, and forms a 45-degree angle with the line from point A to the common focus. This design not only helps to accurately guide the reflected light, but also enhances the stability and wind resistance of the system.

[0073] Receiver tilt installation: The receiver is tilted and installed close to the ground, with its opening surface perpendicular to the reflected light. This design ensures that the receiver can receive the maximum amount of light from the secondary reflector and reduce the loss of light energy.

[0074] 3. Reduce costs and improve maintenance convenience

[0075] Lower equipment costs: Compared with traditional tower solar systems, this system reduces equipment costs by building secondary reflectors instead of more expensive tower construction. At the same time, since the receiver and heat transfer system are located on the ground, it also reduces operation and maintenance costs.

[0076] Improved maintenance convenience: Ground-mounted receivers and heat transfer systems make maintenance and repair work more convenient. Operators can complete most maintenance tasks without having to climb to a height, which improves work efficiency and reduces safety risks. BRIEF DESCRIPTION OF THE DRAWINGS

[0077] Figure 1 This is a working principle diagram of the present invention.

[0078] Numbers in the figure: 1: heliostat; 2: secondary reflector; 3: receiver; F: common focus F; F': actual focus; DETAILED DESCRIPTION

[0079] Example 1

[0080] A secondary reflection central receiver concentrated solar energy heat collection system comprises a heliostat field composed of a plurality of heliostats, the heliostat field is composed of a plurality of heliostats 1 arranged in an array, a secondary reflector 2 installed on a high tower and a receiver 3 installed close to the ground, the heliostat field is symmetrically arranged, and the axis of symmetry is arranged in the north-south direction, each heliostat 1 is controlled by a tracking system to reflect and focus sunlight onto a common focus F, and the common focus F is set at a high point due south of the heliostat field; the secondary reflector 2 is a plane reflector, which is obliquely installed on the high tower and is located on the optical path between the heliostat 1 and the common focus F; the receiver 3 is obliquely installed close to the ground; the sunlight received by the heliostat 1 is reflected onto the secondary reflector 2, and then reflected by the secondary reflector 2 to the receiver 3 for reception.

[0081] The length of the heliostat field in the north-south direction is L, and the common focus F is about L / 5 to L / 4 high.

[0082] A point A on the symmetry axis of the heliostat field is selected, and the distance between the point A and the southernmost heliostat in the heliostat field is 0.6-0.8L. The center of the secondary reflector 2 is arranged on the line from point A to the common focus F, and the secondary reflector 2 is tilted so that the angle between it and the line is 45 degrees. The heliostat 1 with its center installed at point A is controlled by a tracking system to point its reflected light to the common focus F, and the secondary reflector 2 changes its direction and focuses it to the center of the receiver 3, and the opening surface of the receiver 3 is perpendicular to the reflected light.

[0083] The distance from the secondary reflector 2 to the common focus F is equal to the distance from the secondary reflector 2 to the center of the receiver 3; the ratio of the distance from the secondary reflector 2 to the common focus F to the distance from the common focus F to the point A is α, which should be 0.03 to 0.3, so that the receiver 3 is installed on the ground or close to the ground.

[0084] The angle between the line connecting the secondary reflector 2 to the common focus F and the horizontal plane is β=atan(H / d), where d is the distance from point A to the common focus F in the horizontal direction, which is approximately 0.8*L; the height of the secondary reflector h≈L*s inβ*α; the width of the heliostat field is W, and the width of the secondary reflector w≈W*α.

[0085] The radius of curvature of each heliostat 1 in the heliostat field is equal to twice the distance from the center of the heliostat 1 to the common focus F.

[0086] The secondary reflection central receiver concentrated solar thermal system is installed on an azimuth tracking device; all heliostats 1 share the azimuth tracking device, and each row of heliostats 1 reflectors are installed on the same horizontal rotation axis and share a height tracking device; the width of the heliostat field should not exceed one-half of the length, and the optimized design is about one-third;

[0087] Receiver 3 is a cavity solar receiver.

[0088] A plurality of heliostats 1 are arranged symmetrically on the heliostat field, with the axis of symmetry being located in the north-south direction. Each heliostat is equipped with a tracking system capable of tracking the position of the sun in real time.

[0089] When sunlight hits the heliostat, the heliostat reflects and focuses the light onto a common focus F through its curvature design. Due to the symmetrical arrangement of the heliostat field and the precise control of the tracking system, sunlight from different directions

[0090] The secondary reflector 2 is a plane reflector, which is installed on a high tower at an angle and is located on the optical path between the heliostat 1 and the common focus F. Its center is arranged on the line from a point A on the symmetry axis of the heliostat field to the common focus F, and forms an angle of 45 degrees with the line.

[0091] The light reflected by the heliostat first irradiates the secondary reflector, and then is reflected again by the secondary reflector, changes direction and focuses on the receiver 3. The tilt angle and position design of the secondary reflector ensure that the light can be accurately directed to the receiver.

[0092] Receiver 3 is a cavity solar receiver, which is installed at an angle close to the ground, with its opening surface perpendicular to the reflected light from the secondary reflector to ensure maximum light energy reception.

[0093] When sunlight is focused onto the receiver through the secondary reflector, the heat-absorbing material in the receiver absorbs the light energy and converts it into heat energy. The heat energy is then transferred to the working medium (such as water or steam) through the heat exchange system for subsequent applications such as power generation or heating.

[0094] Example 2

[0095] See also Figure 1 The design method of the secondary reflection central receiver concentrated solar thermal collection system specifically includes the following steps:

[0096] S1: First complete the preliminary design, including:

[0097] 1) Determine the length and width of the heliostat field according to demand. If the total thermal power required is P, the heliostat field area S = P*4 square meters, and the heliostat field length L = (P*12) 0.5 ; Heliostat field width W = (P*12) 0.5 / 3;

[0098] 2) Determine the height of the heliostat h h and width w h ; The initial recommendations are 6 meters and 8 meters respectively;

[0099] 3) Determine the common focus position, which is 0.1*L due south of the heliostat field and has a height of H=0.25L;

[0100] 4) Determine the inclination angle of the secondary reflector, the angle between the line connecting point A to the common focus F and the horizontal plane is β=atan(H / (0.8*L)), and the inclination angle between the secondary reflector and the ground=π / 4 degrees-β radians;

[0101] 5) Determine α, calculated according to the following formula:

[0102] H*(1-α)-0.8L*α*cos(45-β)=h h *s inβ+h';

[0103] Here h' is the distance between the edge of the receiver and the ground, and the receiving surface has an inclination angle of β on the horizontal plane;

[0104] 6) Determine the position of the secondary reflector, the horizontal distance from the common focus is α*0.8L; the height distance from the ground = H*(1-α);

[0105] 7) Determine the center position of the receiver: located below the secondary reflector, the horizontal distance from the secondary reflector = 0.08L*s in(45-β); the vertical distance from the secondary reflector = 0.08L*cos(45-β), that is, the distance from the ground = H*(1-α)-0.08L*cos(45-β);

[0106] 8) Determine the size of the secondary reflector: the height of the secondary reflector h = L*s inβ*α; the width of the heliostat field is W, and the width of the secondary reflector w = W*α; the secondary reflector adopts a plane reflector;

[0107] 9) Determining the curvature radius of the heliostat: the optimal curvature radius of each heliostat in the heliostat field is equal to twice the distance from the center of the heliostat to the common focus;

[0108] S2: Establish a performance and cost simulation calculation program, determine the main design parameters based on the installation location, with the maximum annual average efficiency or minimum cost as the optimization goal, and then recalculate other parameters.

[0109] The system works on the principle of precise reflection and focusing of light. Sunlight is reflected to a common focus by a field of heliostats, and then a secondary reflector directs the light to a receiver near the ground. The receiver converts the collected light energy into heat energy for subsequent use. The entire system achieves efficient light energy collection and heat energy conversion by precisely controlling the angles and positions of the heliostats and secondary reflectors and the arrangement of the receivers.

[0110] Through the above design method, it can be ensured that the secondary reflection receiver concentrated solar thermal system has high efficiency and economy in the design stage. Through accurate calculation and optimization of design parameters, the system can collect solar radiation to the maximum extent during operation and convert it into thermal energy, providing reliable energy support for subsequent power generation or heating applications.

Claims

1. A secondary reflective central receiver concentrated solar thermal collection system, comprising a heliostat field consisting of a plurality of heliostats, a secondary reflector mounted on a high tower and a receiver mounted near the ground, characterized in that: The heliostat field is arranged symmetrically or nearly symmetrically, with the axis of symmetry arranged in the north-south direction. Each heliostat is controlled by a tracking system to reflect and focus the sunlight onto a common focus, which is located at a high point due south of the field. The secondary reflector is a flat reflector, which is installed obliquely on a high tower and is located on the optical path between the heliostat and the common focus. The receiver is installed at an angle close to the ground; the sunlight received by the heliostat is reflected onto the secondary reflector, and then reflected to the receiver via the secondary reflector.

2. The secondary reflection central receiver concentrated solar thermal collection system according to claim 1, characterized in that: If the north-south length of the heliostat field is L, the common focus is about L / 5 to L / 4 high.

3. The secondary reflection central receiver concentrated solar thermal collection system according to claim 1 or 2, characterized in that: A point A on the symmetry axis of the heliostat field is selected, and the distance between the point A and the southernmost heliostat in the field is 0.6-0.8L. The center of the secondary reflector is arranged on the line from point A to the common focus, and the secondary reflector is tilted so that the angle between the secondary reflector and the line is 45 degrees. The heliostat centrally installed at point A controls its reflected light to point to the common focus through a tracking system, and is changed in direction by the secondary reflector and focused to the center of a receiver, receiving an opening surface thereof perpendicular to the reflected light.

4. The secondary reflection central receiver concentrated solar thermal collection system according to claim 1 or 2, characterized in that: The distance from the secondary reflector to the common focus is equal to the distance from the secondary reflector to the center of the receiver; the ratio of the distance from the secondary reflector to the common focus to the distance from the common focus to the point A is α, which should be 0.03 to 0.3, so that the receiver can be installed on the ground or close to the ground.

5. The secondary reflection central receiver concentrated solar thermal collection system according to claim 1 or 2, characterized in that: The angle between the secondary reflector and the common focus and the horizontal plane is β=atan(H / d), d It is the distance from point A to the common focus in the horizontal direction, which is about 0.8*L; the height of the secondary reflector h≈L*sinβ*α; the width of the heliostat field is W, and the width of the secondary reflector w≈W*α.

6. The secondary reflection central receiver concentrated solar thermal collection system according to claim 1 or 2, characterized in that : The radius of curvature of each heliostat in the heliostat field is equal to twice the distance from the center of the heliostat to the common focus.

7. The secondary reflection central receiver concentrated solar thermal collection system according to claim 1 or 2, characterized in that: The width of the heliostat field does not exceed the length.

8. The secondary reflection central receiver concentrated solar thermal collection system according to claim 1 or 2, characterized in that: The secondary reflection central receiver concentrated solar thermal collection system is installed on an azimuth tracking device; all heliostats share the azimuth tracking device, and each row of heliostat reflectors are installed on the same horizontal rotation axis and share a height tracking device; the width of the heliostat field should not exceed half of the length.

9. The secondary reflection central receiver concentrated solar thermal collection system according to claim 1 or 2, characterized in that: The receiver is a cavity solar receiver.

10. A design method for a secondary reflection central receiver concentrated solar thermal collection system, characterized in that: The specific steps include: S1: First complete the preliminary design, including: 1) Determine the length and width of the heliostat field according to demand. If the total thermal power required is P, the heliostat field area S = P*4 square meters, and the heliostat field length L = (P*12) 0.5 ; Heliostat field width W = (P*12) 0.5 / 3; 2) Determine the height h of the heliostat h and width w h ; The initial recommendations are 6 meters and 8 meters respectively; 3) Determine the common focus position, which is 0.1*L due south of the heliostat field and has a height of H=0.25L; 4) Determine the inclination angle of the secondary reflector, the angle between the line connecting point A to the common focus F and the horizontal plane is β=atan(H / (0.8*L)), and the inclination angle between the secondary reflector and the ground=π / 4 degrees-β radians; 5) Determine α, calculated according to the following formula: H*(1-α)-0.8L*α*cos(45-β)=h h *sinβ+h'; Here h' is the distance between the edge of the receiver and the ground, and the receiving surface has an inclination angle of β on the horizontal plane; 6) Determine the position of the secondary reflector, the horizontal distance from the common focus is α*0.8L; the height distance from the ground = H*(1-α); 7) Determine the center position of the receiver: located below the secondary reflector, the horizontal distance from the secondary reflector = 0.08L*sin(45-β); the vertical distance from the secondary reflector = 0.08L*cos(45-β), that is, the distance from the ground = H*(1-α)-0.08L*cos(45-β); 8) Determine the size of the secondary reflector: the height of the secondary reflector h = L*sinβ*α; the width of the heliostat field is W, and the width of the secondary reflector w = W*α; the secondary reflector adopts a plane reflector; 9) Determining the curvature radius of the heliostat: the optimal curvature radius of each heliostat in the heliostat field is equal to twice the distance from the center of the heliostat to the common focus; S2: Establish a performance and cost simulation calculation program, determine the main design parameters based on the installation location, with the maximum annual average efficiency or minimum cost as the optimization goal, and then recalculate other parameters.

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