Secondary reflection center receiver concentrating solar heat collection system

Abstract

The utility model relates to the technical field of solar photo-thermal utilization, in particular to a secondary reflection center receiver concentrating solar heat collection system, which consists of a heliostat field consisting of a plurality of heliostats which are symmetrically or approximately symmetrically arranged, an inclined plane secondary reflector which is arranged on a high tower and a receiver which is obliquely arranged 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 utility model relates to the technical field of solar thermal utilization, in particular to a secondary reflection central receiver concentrating solar thermal collection system. 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 high-temperature media, 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 heliostats and concentrators. i The French Odeillo solar furnace, which began operating in 1969, consists of 63 flat heliostats with a light-through area of ​​6 x 7.5 meters and a parabolic concentrator with a light-through area of ​​40 x 54 meters. It focuses up to 1 MW of energy onto its focal plane. The secondary reflector is a parabolic concentrator made 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 generates high-energy flux and very high temperatures. It is typically used for research and manufacturing. It primarily uses heliostats to project sunlight vertically onto a parabolic reflector, which then focuses the sunlight near a focal point. Temperatures at the focal point can reach as high as 3,500°C. This heat energy can be used for power generation, steel smelting, hydrogen fuel production, or nanomaterials. The largest solar furnace built in China, at 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 the University of Science and Technology of China (USTC) developed a solar furnace with a higher concentration ratio using a new heliostat with low aberration, which is used to smelt high-purity silicon. This achievement was selected as one of China's Top Ten Scientific and Technological Advances of 2009.

[0005] Conventional solar furnaces use flat reflectors as heliostats, directing the sun's central rays nearly perpendicularly onto parabolic concentrators. The parabolic concentrators are fixed vertically, with the receiving surface also perpendicular to the ground. The heliostats reflect the sun's central rays nearly parallel to the ground, equivalent to a tower system with a zero-height tower and a central receiver mounted on the ground. This results in a small cosine factor and lower efficiency. The total light-transmitting area of ​​the heliostats in the French Odeillo solar furnace is 2,835 square meters, but only 1,000 kW of solar energy is intercepted by the receiving surface. The primary purpose of a solar furnace is to achieve high temperatures. The advantage of this design is the fixed installation of the concentrators, which allows for a high geometric concentration ratio and a large light-transmitting area. However, the incident angle of sunlight on the heliostats is relatively large, especially at high solar altitudes and high energy levels. This results in a low cosine factor, resulting in lower daily and annual average efficiencies. Furthermore, the light-transmitting area of ​​the concentrators is comparable to that of the heliostats, requiring two sets of mirrors. This significantly increases the cost compared to conventional tower systems, making it unsuitable for low-cost solar power generation.

[0006] The solar furnace uses a flat heliostat, which only changes the direction of sunlight but does not focus it. The central ray of sunlight entering the solar furnace is incident vertically, so that the sunlight entering the solar furnace's concentrator is almost indistinguishable from 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 low-aberration curved heliostats and spherical or paraboloidal concentrators. This allows for a much smaller concentrator area than the heliostat, allowing for a higher concentration ratio. While the principle is closer to a secondary concentrating disk system, its optical analysis is much more complex. Professor Chen's research group primarily studies aberrations and focal plane energy flux density distribution.

[0008] In 1976, Rabl proposed the use of a secondary reflective tower system, which uses reflectors on tall towers to reflect light to the ground, allowing solar receivers to be placed on the ground, rather than on top of tall towers as in most commercial central receiver concentrated solar power (CSP) plants today. Although pumping losses are smaller, high-temperature heat transfer pipes can be reduced, as well as the weight of the tower being borne, resulting in lower structural costs, which significantly reduces costs. In addition, the downward beam concentrator provides the opportunity to use a new type of top-irradiated receiver. However, compared to tower receivers, the optical constraints and costs associated with tower reflectors may result in a secondary reduction in the performance or increase in the cost of designing a tower system. These obvious problems ii Related to the extra reflections from the secondary reflector, which manifests as reflection losses, increased aberrations leading to reduced interception, and the need to use ideal hyperboloids, which increases costs iii. The secondary reflector needs to operate at a higher energy flux density, and due to the high optical error requirements, its lifespan is likely to be much shorter. 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 features a parabolic concentrator positioned horizontally at a height, with heliostats positioned directly below the concentrators. This allows sunlight from various directions to be incident perpendicularly on the concentrators, achieving a concentration ratio of up to 6000. Structurally, the secondary reflector tower system is similar to this solar furnace, but differs in that the heliostat's light-passing area is much larger than that of the secondary concentrator, and most sunlight reflected by the heliostats does not enter the concentrator perpendicularly. Because parabolic concentrators effectively concentrate parallel light, they also have a good effect on sunlight with very small distribution angles. However, for incident light with large distribution angles, according to 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. Consequently, the larger the heliostat area in the system, the larger the mirror field area required, the greater the angle of incidence entering the concentrator, and the larger the image spot radius, making the use of parabolic concentrators difficult.

[0010] Therefore, when designing a secondary reflector tower system, the concentrators are primarily constructed using hyperboloids or ellipsoids. These surfaces exploit the light-gathering properties of these surfaces. By aiming incident light at one focal point on either surface, the reflected light will be focused at the other focal point. If the heliostat were a flat reflector, only one point on the heliostat could aim the reflected light at one focal point; all other reflected light would deviate from that focal point and thus be unable to focus at the other focal point. Using curved mirrors for heliostats reduces this deviation and improves the focusing effect. However, the direction of light entering the heliostat varies significantly due to changes in the sun's position, resulting in a corresponding change in the angle of incidence. This increased phase dispersion increases the direction of the reflected light, making it difficult to aim at the focal point of the concentrator, resulting in a larger image spot radius and a lower concentration ratio. Because the concentration ratio is significantly lower than that of conventional tower systems, even with limited scale, the optical efficiency of currently designed secondary reflector tower solar furnace systems is not very high, with a reported value of approximately 57%, significantly lower than that of conventional central receiver systems. Utility Model Content

[0011] The purpose of the utility model is to overcome the shortcomings of the prior art and provide a secondary reflection central receiver concentrated solar heat collection system to improve optical efficiency.

[0012] The technical solution of the utility model is as follows:

[0013] A secondary reflection central receiver concentrating solar thermal collection system comprises a heliostat field consisting of multiple heliostats, secondary reflectors mounted on high towers, and a receiver mounted near the ground. The system is characterized in that: the heliostat field is arranged symmetrically or nearly symmetrically, with the axis of symmetry arranged in a north-south direction; each heliostat is controlled by a tracking system to reflect and focus sunlight onto a common focal point located at a high point directly south of the field; the secondary reflectors are plane reflectors, mounted obliquely on the high towers, and located in the optical path between the heliostats and the common focal point; the receiver is mounted obliquely near the ground; sunlight received by the heliostats is reflected onto the secondary reflectors, and then reflected by the secondary reflectors to the receiver.

[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 is selected on the symmetry axis of the heliostat field, which is 0.6-0.8L away from the southernmost heliostat in the field. The center of the secondary reflector is arranged on a line connecting point A and 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 centered at point A is controlled by a tracking system to direct its reflected light toward the common focus, which is redirected by the secondary reflector and focused onto the center of the receiver, with the receiving opening 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 is 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*sinβ*α; the width of the heliostat field is W, and the width of the secondary reflector w≈W*α.

[0018] Preferably, the 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.

[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 mounted on an azimuth tracking device; all heliostats share the azimuth tracking device, and each row of heliostat reflectors is mounted on the same horizontal rotation axis and shares a height tracking device; the width of the heliostat field should not exceed one-half of the length, and the optimal design is about one-third;

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

[0022] Working principle:

[0023] Heliostat field layout and ray tracing:

[0024] The multiple heliostats in the system are precisely controlled by a tracking system to ensure they track the sun's position 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.

[0025] Each heliostat is designed to reflect and focus sunlight onto a common focal point, located directly south of the field, at a height between 1 / 5 and 1 / 4 of the field's north-south length, L. This layout ensures that light reflected from the heliostats in all directions converges to the same point.

[0026] The function of the secondary reflector:

[0027] The tower-mounted secondary reflector is a flat mirror strategically positioned on the tower, in the optical path between the heliostats and the common focus. Its primary function is to receive light from the heliostats and reflect it further to a receiver near the ground.

[0028] The mounting angle and position of the secondary reflector are critical to ensure it effectively directs light from the heliostats to the receiver. According to design requirements, the center of the secondary reflector should be located on a line connecting point A on the heliostat field's axis of symmetry (approximately 0.6-0.8L from the southernmost heliostat) to the common focal point, with its inclination angle at 45 degrees to this line.

[0029] Receiver design:

[0030] 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 possible and converted into heat energy.

[0031] 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.

[0032] Overall workflow:

[0033] When the sun rises, the tracking system automatically starts and controls each heliostat to adjust its angle to track the sun's position.

[0034] The heliostats reflect and focus sunlight onto a common focal point, where the rays are then received by secondary reflectors and reflected again to a receiver.

[0035] 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.

[0036] 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.

[0037] This new design utilizes a Newtonian telescope structure, using a flat reflector as the secondary mirror. This allows the heliostat to focus light, while the secondary mirror serves only to redirect light, as originally envisioned in the secondary reflector tower system. This design offers a novel approach to the secondary reflector tower system. The advantage of this design is that the secondary reflector allows the height of the receiving tower to be increased, thereby improving efficiency, without the expense of building a taller tower.

[0038] In the Newtonian reflecting telescope structure, the position and size of the secondary reflector are related. If a parallel-to-the-ground configuration is used, according to secondary reflection focusing theory, the drawback is that the key parameter, shading ratio α, needs to be large to allow the receiver to be farther from the secondary mirror, closer to the ground. This reduces the secondary mirror's height while maintaining the virtual primary focus at a higher position. This has the unfortunate effect of increasing the secondary mirror's area. If α = 0.5, and the receiving surface is placed on the ground, the virtual primary tower height will be twice that of the secondary mirror, but the secondary mirror's area will be one-quarter the field of view. A further problem is that, similar to using a curved mirror as the secondary mirror, this significantly limits the field of view.

[0039] This utility model, inspired by conventional solar furnace designs, incorporates a secondary reflector tower system with its main axis tilted toward the ground, while the secondary mirror forms a 45-degree angle with the main axis. This design employs a north-field approach, achieving higher efficiency and avoiding excessive heliostat angles of incidence that increase image aberrations. Placing the entire system on an azimuth tracking platform further enhances efficiency. This design reduces the secondary mirror's height from the ground compared to conventional towers and eliminates the need for a larger structure, thereby reducing its construction cost.

[0040] Ray tracing calculations show that, with the addition of a secondary reflector, the receiver's interception rate of the heliostats decreases slightly for more distant heliostats, while it increases for closer heliostats, remaining unchanged overall. Ray tracing calculations indicate that the photothermal efficiency can reach 64%, significantly higher than existing secondary reflection central receiver systems.

[0041] The position of the secondary reflector does not affect the interception rate. For a secondary reflector dish system, define the blockage rate α. Increasing α is equivalent to moving the secondary reflector away from its original focus, lowering the receiver's height above the ground, and increasing the secondary reflector area.

[0042] For the PS10 field, the distance from the center of the primary mirror to the bottom of the receiving tower is assumed to be half the field length, or 400 meters. When α = 0.18, the center of the receiver is 8.5 meters above the ground. Due to the tilt of the receiving surface, this is equivalent to being installed on the ground. Calculations show that the efficiency of far-field heliostats decreases slightly. For the farthest heliostat, for example, the heliostat at coordinates [300, 800], at an azimuth angle of 80 degrees and an elevation angle of 30 degrees, the interception rate without a secondary reflector is 84.72%. With the addition of a secondary reflector, the interception rate drops to 82.95%. For near-field heliostats, for example, the heliostat at coordinates [100, 50], the interception rates without and with a secondary reflector are 98.48% and 99.98%, respectively. Adding a secondary reflector actually increases the interception rate. This is because adding a secondary reflector increases the distance between the far-field heliostats and decreases the distance between the near-field heliostats. Therefore, if the secondary reflector uses a 45-degree plane turning mirror, the aberration will not increase and the optical performance will remain basically unchanged. This is consistent with the aberration theory of the Newtonian telescope with a 45-degree turning mirror.

[0043] When the secondary reflector is a hyperbolic surface, the equation should be:

[0044] x 2 +z 2 =2ry-(1-e 2 )y 2

[0045] The distances from the upper and lower focal points 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:

[0046]

[0047]

[0048] From this we get:

[0049]

[0050] The optical axis of the system in this solution should be perpendicular to the ground or slightly tilted. If used in a 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, making it 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 is

[0051] =βf0*tanθ, f0 is the focal length of the primary mirror, θ is the angle of incidence; 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.

[0052] In summary, this new system builds upon the North Field tower system by adding a flat reflector, shifting the focus of light from the center of the receiving tower to the ground. This system maintains the optical performance of the original tower system without changing the system's aberrations. By moving the receiver from the tower to the ground, the heat energy transmission distance is shortened. The secondary mirror area is also significantly reduced, significantly lowering the cost of the mounting tower. The secondary mirror uses a flat reflector, making it easier to manufacture and significantly improving light and heat efficiency, far superior to secondary reflective tower systems using curved mirrors.

[0053] Advantages of this utility model:

[0054] 1. Efficient light energy collection and conversion

[0055] Symmetrical arrangement of the heliostat field: Through the symmetrical or nearly symmetrical arrangement of the heliostat field and the precise tracking control of each heliostat, the system ensures that sunlight is efficiently reflected and focused onto a common focal point. This design improves the efficiency of light collection, allowing more sunlight to be converted into heat.

[0056] The introduction of secondary reflectors: As a key component in the optical path, secondary reflectors further enhance the concentration of light energy. They reflect light from the heliostats and direct it toward the receiver, thereby improving the receiver's heat collection efficiency.

[0057] 2. Optimized system layout and structural design

[0058] 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.

[0059] Tilted installation of the secondary reflector: The secondary reflector is tilted and installed on the tower at a 45-degree angle to the line connecting point A and 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.

[0060] Receiver tilt installation: The receiver is tilted and installed close to the ground, with its opening perpendicular to the reflected light. This design ensures that the receiver can receive the maximum amount of light from the secondary reflector and minimize light energy loss.

[0061] 3. Reduce costs and improve maintenance convenience

[0062] Lower equipment costs: Compared to traditional tower solar systems, this system reduces equipment costs by building secondary reflectors instead of the more expensive tower structure. Furthermore, since the receiver and heat transfer system are located on the ground, operation and maintenance costs are also reduced.

[0063] Improved maintenance convenience: The ground-mounted receiver and heat transfer system make maintenance and repair more convenient. Operators can complete most maintenance tasks without having to climb high, which improves work efficiency and reduces safety risks. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Figure 1 This is a working principle diagram of the utility model.

[0065] Numbers in the figure: 1: heliostat; 2: secondary reflector; 3: receiver; F: common focus F; F': actual focus; DETAILED DESCRIPTION

[0066] Example 1

[0067] A secondary reflection central receiver concentrating solar thermal collection system includes a heliostat field consisting of multiple heliostats. The heliostat field is composed of multiple heliostats 1 arranged in an array, secondary reflectors 2 mounted on high towers, and a receiver 3 mounted near the ground. The heliostat field is symmetrically arranged with the axis of symmetry 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, which is located at a high point directly south of the heliostat field. The secondary reflectors 2 are plane reflectors, mounted at an angle on the high tower, and located on the optical path between the heliostats 1 and the common focus F. The receiver 3 is mounted at an angle near the ground. The sunlight received by the heliostats 1 is reflected onto the secondary reflectors 2, and then reflected by the secondary reflectors 2 to the receiver 3 for reception.

[0068] 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.

[0069] A point A is selected on the symmetry axis of the heliostat field, 0.6-0.8L away from the southernmost heliostat in the heliostat field. The center of the secondary reflector 2 is arranged on a line connecting point A and the common focus F, and the secondary reflector 2 is tilted so that the angle between the secondary reflector 2 and the line is 45 degrees. The heliostat 1, which is centered at point A, is controlled by a tracking system to direct its reflected light toward the common focus F. The reflected light is redirected by the secondary reflector 2 and focused onto the center of the receiver 3, whose aperture is perpendicular to the reflected light.

[0070] 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.

[0071] The angle between the line connecting the secondary reflector 2 and the common focus F and the horizontal plane is β = atan(H / d), where d is the horizontal distance from point A to the common focus F, approximately 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.

[0072] The curvature radius 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.

[0073] 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 the reflectors of each row of heliostats 1 are installed on the same horizontal rotation axis and share the height tracking device; the width of the heliostat field should not exceed one-third of the length;

[0074] Receiver 3 is a cavity solar receiver.

[0075] A plurality of heliostats 1 are arranged symmetrically on a heliostat field, with the axis of symmetry located in the north-south direction. Each heliostat is equipped with a tracking system that can track the position of the sun in real time.

[0076] When sunlight strikes a heliostat, its curvature reflects and focuses the light onto a common focal point, F. Due to the symmetrical arrangement of the heliostat field and the precise control of the tracking system, the secondary reflectors 2, which are plane reflectors, are tilted and mounted on high towers, located in the optical path between heliostat 1 and the common focal point, F. Their centers lie on a line connecting point A on the heliostat field's axis of symmetry and the common focal point, F, at a 45-degree angle.

[0077] The light reflected by the heliostat first hits the secondary reflector, 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.

[0078] Receiver 3 is a cavity solar receiver, which is installed tilted near the ground. Its opening surface is perpendicular to the reflected light from the secondary reflector to ensure maximum light energy reception.

[0079] When sunlight is focused onto a receiver via a secondary reflector, the heat-absorbing material within the receiver absorbs the light energy and converts it into heat. This heat energy is then transferred to a working medium (such as water or steam) through a heat exchange system for subsequent applications such as power generation or heating.

[0080] Example 2

[0081] See also Figure 1 The design method of the secondary reflection central receiver concentrated solar thermal collection system specifically includes the following steps:

[0082] S1: First complete the preliminary design, including:

[0083] 1) Determine the length and width of the heliostat field based on demand. If the total thermal power required is P, then 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;

[0084] 2) Determine the heliostat height h h and width w h ; The initial recommendations are 6 meters and 8 meters respectively;

[0085] 3) Determine the common focus position, which is 0.1*L due south of the heliostat field and at a height of H=0.25L;

[0086] 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;

[0087] 5) Determine α, calculated according to the following formula:

[0088] H*(1-α)-0.8L*α*cos(45-β)=h h *sinβ+h';

[0089] 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;

[0090] 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 is H*(1-α);

[0091] 7) Determine the center position of the receiver: located below the secondary reflector, horizontal distance from the secondary reflector = 0.08L*sin(45-β); vertical distance from the secondary reflector = 0.08L*cos(45-β), that is, distance from the ground = H*(1-α)-0.08L*cos(45-β);

[0092] 8) Determine the size of the secondary reflector: secondary reflector height h = L * sin β * α; heliostat field width W, secondary reflector width w = W * α; the secondary reflector is a plane reflector;

[0093] 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;

[0094] S2: Establish a performance and cost simulation calculation program. Based on the installation location, take maximum annual average efficiency or minimum cost as the optimization goal, determine the main design parameters, and then recalculate other parameters.

[0095] The system operates based on the precise reflection and focusing of light. A field of heliostats reflects sunlight to a common focal point, where secondary reflectors direct the light to receivers near the ground. The receivers convert the collected light energy into heat for subsequent use. The entire system achieves efficient light collection and heat conversion by precisely controlling the angles and positions of the heliostats and secondary reflectors, as well as the arrangement of the receivers.

[0096] The above design approach ensures that the secondary reflector central receiver concentrated solar thermal system is highly efficient and economical from the outset. By accurately calculating and optimizing design parameters, the system maximizes the collection of solar radiation and converts it into thermal energy during operation, providing reliable energy support for subsequent applications such as power generation and heating.

Claims

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

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

3. The secondary reflection central receiver concentrated solar thermal 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 a line connecting point A and the common focal point, and the secondary reflector is tilted so that the angle between the secondary reflector and the line is 45 degrees. The heliostat centered at point A is controlled by a tracking system to direct its reflected light toward the common focal point, which is then redirected by the secondary reflector and focused onto the center of a receiver, with its aperture receiving the reflected light perpendicular to the receiver.

4. The secondary reflection central receiver concentrated solar thermal system according to claim 3, 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 is installed on the ground or close to the ground.

5. The secondary reflection central receiver concentrated solar thermal system according to claim 1 or 2, characterized in that: The angle between the line connecting the secondary reflector to the common focus and the horizontal plane is β=atan(H / d), 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*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 system according to claim 1 or 2, characterized in that The 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.

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

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

Images