Medium-high temperature cavity type heat collector used in trough type heat collecting system

Abstract

The utility model discloses a medium-high temperature cavity type heat collector used in a groove type heat collecting system, which comprises a transparent outer cover pipe and a V-shaped metal groove heat collector, the center of the opening surface of the V-shaped metal groove is located at the center of the transparent outer cover pipe, the inner side or the outer side of the V-shaped metal groove is connected with a metal pipe, and the space between the inner pipe and the outer pipe is vacuumized or filled with gas. A reflecting layer is additionally arranged on the inner side or the outer side of the backlight surface of the transparent outer cover pipe, or an anti-radiation cover is additionally arranged on the backlight part between the transparent outer cover pipe and the heat collector; or a heat insulation layer is added to the backlight part on the outer side of the transparent outer cover pipe; or simultaneously, a heat insulation layer is arranged on the backlight part outside the transparent outer cover pipe. The V-shaped groove is used for replacing a round tube, incident light rays can be absorbed in the V-shaped groove for multiple times, the absorption rate is increased by 3% to 4% similar to that of a cavity absorber, and the defect that a tubular heat collector is low in absorption rate is overcome. The space between the V-shaped groove and the transparent outer cover pipe is vacuumized, a reflecting film or an anti-radiation film or / and a heat insulation layer is added to the backlight part, heat loss is reduced, and the heat loss is low.

Description

Technical Field

[0001] This utility model relates to the field of solar collector tube technology, and more particularly to a medium-high temperature cavity collector for use in a trough solar collector system. This utility model is applicable to trough concentrating solar collectors, replacing currently used vacuum collector tubes. Background Technology

[0002] Parabolic trough solar collectors are a key component of parabolic trough solar thermal power generation systems. They convert direct solar radiation focused by reflectors into heat energy, reaching temperatures up to 400°C. The most commonly used type is the vacuum collector tube, with an inner stainless steel tube and an outer glass tube with corrugated metal ends. The inner tube is coated with a selective absorption coating to maximize the absorption of direct solar radiation and minimize infrared re-emission. The glass-metal joints at both ends provide a sealed connection with the corrugated metal tubes, offering high-temperature protection and maintaining a vacuum within the sealed internal space. This reduces heat loss through convection and conduction, and the selective absorption coating further minimizes radiative heat loss. On the other side, the corrugated metal tubes connect to the inner absorber tubes. These flexible corrugated tubes compensate for the difference in thermal expansion and contraction between the inner metal tube and the outer glass tube during the heating and cooling of the absorber tubes. The focused direct solar radiation is converted into heat energy on the surface of the metal tubes, transferred to the heat transfer medium, and heated to over 400°C. The outer glass tube can serve as additional protection to prevent infrared wavelength energy from being re-radiated outward, thereby reducing heat loss. The outside of the glass tube is covered with an anti-reflective coating. The glass should be borosilicate glass, which can transmit short-wave radiation within 2.5 micrometers, while having a high absorption rate for long-wave radiation, reducing heat radiation loss. At the same time, it allows solar radiation energy to pass through the glass tube and be absorbed by the metal tube.

[0003] To improve the performance of vacuum heat exchange tubes, many improvement measures have been proposed. One approach is to add fins or other structures inside the absorber tube to reduce heat transfer resistance and decrease the temperature difference between the heat transfer fluid inside the tube and the outer surface, thereby reducing heat loss. Another approach is to add reflective or insulating films to the backlight side of the absorber tube to increase the interception rate and reduce heat loss; or to add an anti-reflective film to the light-facing side of the glass tube to increase transmittance. Relevant patents and literature include:

[0004] CN200820032619.0 adds a reflector between the absorption tube and the glass tube on the backlight side to increase the interception rate and reduce heat loss.

[0005] CN200820032620.3 Adds a reflective layer to the back surface of the glass tube to increase the interception rate and reduce heat loss.

[0006] CN201520809847.4 An arc-shaped heat shield with a reflective coating is added to the back side between the metal tube and the glass tube to reflect sunlight onto the heat absorber tube a second time, increasing the interception rate and reducing heat loss; the outer surface is coated with a solar selective absorption coating to increase the absorption of sunlight.

[0007] CN201610143318.4 Install plane reflectors on both sides of the metal collector tube to reflect light a second time and improve the interception rate.

[0008] CN201611107912.4 modifies the light-facing and back-facing surfaces of the metal absorption tube to be flat, while the two sides remain curved. A flat heat shield is inserted between the two tubes on the back-facing side to reduce heat loss.

[0009] CN201621162534.5 applies a reflective and heat-insulating film layer to the back side of the outer glass cover tube to reduce radiative heat loss and increase the interception of incident sunlight.

[0010] CN201620288427.0 also adds a reflective coating to the backlight side of the glass tube, but the difference is that the coverage is less than 0.5, which can be used in larger edge corner slot systems.

[0011] CN201710564830.0 uses a metal heat absorber with arc-shaped fins to expand the interception surface and increase the interception rate. However, since its convex surface faces the incident light, the incident angle effect increases, and the absorption rate will decrease compared to using a metal tube.

[0012] CN201810459840.2 involves adding an anti-reflective layer to the light-facing side of the glass to increase the transmittance of the glass tube; and adding a reflective film to the back-facing side to increase the interception rate while reducing heat loss.

[0013] CN201980036407.0 also involves adding a reflective layer to the back surface of the glass tube to intercept reflected light, thereby improving the interception rate.

[0014] CN202210616703.1 involves adding a plane reflector to the backlight surface between the two tubes to increase the interception rate.

[0015] CN202420092343.4 adds a heat-absorbing coating to the light-facing side of the glass tube to reduce radiative heat loss from the light-transmitting side.

[0016] Another approach is to add an insulation layer to the outside of the glass tube on the side facing away from the light to reduce heat loss. See: Ramchandra G. P, Sudhir V. P, Jyeshtharaj B. J, et al. Alternative designs of evacuated receiver for parabolic trough collector. Energy; 2018, 155: 66–76.

[0017] Since incident sunlight is concentrated at the center of the sun, the heat collection tube usually blocks most of the sunlight, and the efficiency improvement by increasing the interception rate is minimal. Similarly, the glass tube itself has very low transmittance in terms of long-wave radiation, and adding a reflective film or heat shield only reduces heat loss slightly and contributes little to improving performance.

[0018] On the other hand, the efficiency of the collector tube is directly proportional to the transmittance of the glass tube and the absorptivity of the metal absorber tube. The methods mentioned above all ignore the improvement of the transmittance of the outer tube and the absorptivity of the inner tube. However, due to the incident angle effect, a large portion of the incident light is lost due to reflection by the inner and outer circular tubes currently used in vacuum collector tubes. We used ray tracing to simulate the surface, and the outer glass tube and the inner metal tube increase the reflection by about 4% to 8%, thereby reducing the transmittance and absorptivity, and reducing the efficiency by up to 8%. Utility Model Content

[0019] The purpose of this invention is to overcome the shortcomings of existing technologies where the incident angle has a significant impact on the transmittance of the glass tube and the absorption rate of the absorption tube, and to provide a medium-to-high temperature cavity collector for use in a trough-type heat collection system. This collector can improve the transmittance of the outer glass tube and the absorption rate of the metal absorption tube, thereby improving the efficiency and performance of the heat collection tube.

[0020] This utility model is achieved through the following technical solution:

[0021] A medium-high temperature cavity collector for a trough-type solar collector system includes a transparent glass outer tube and a V-shaped metal trough collector. A vacuum is evacuated or gas is introduced between the transparent glass outer tube and the V-shaped metal trough collector. The V-shaped metal trough collector is located inside the transparent glass outer tube. The V-shaped metal trough collector includes a metal tube with two metal fins connected to it. The two metal fins form a V-shaped opening, and the metal tube is connected to the inside of the V-shaped opening. The center of the opening surface of the V-shaped metal trough collector is at the center of the transparent glass outer tube.

[0022] A reflective film is attached to the backlight side of the inner side of the transparent glass outer casing tube.

[0023] A radiation shield is provided in the backlight section between the transparent glass outer casing tube and the V-shaped metal trough collector; the radiation shield is an arc-shaped plate, with a reflective film attached to the side of the arc-shaped plate facing the V-shaped metal trough collector, and a low infrared emissivity material coating on the other side.

[0024] An insulation layer is provided on the backlit portion of the outer side of the transparent glass outer casing tube.

[0025] A medium-high temperature cavity collector for a trough-type solar collector system includes a transparent glass outer tube and a V-shaped metal trough collector. A vacuum is evacuated or gas is introduced between the transparent glass outer tube and the V-shaped metal trough collector. The V-shaped metal trough collector is located inside the transparent glass outer tube. The V-shaped metal trough collector includes two V-shaped grooves and a metal tube. Each V-shaped groove is a V-shaped opening formed by two metal fins. The two V-shaped grooves are arranged side-by-side, and the metal tube connects between the two V-shaped grooves. The adjacent ends of the two V-shaped grooves are connected, with the connection point at the center of the transparent glass outer tube. A reflective film is affixed to the inner, backlit side of the transparent glass outer tube.

[0026] A medium-high temperature cavity collector for a trough-type solar collector system includes a transparent glass outer tube and a V-shaped metal trough collector. A vacuum is evacuated or gas is filled between the transparent glass outer tube and the V-shaped metal trough collector. The V-shaped metal trough collector is located inside the transparent glass outer tube. The V-shaped metal trough collector is a V-shaped structure composed of two flat tubes, or multiple V-shaped structures composed of multiple round tubes, or a star-shaped structure composed of multiple flat tubes, or composed of 4 to 10 metal fins connected to a metal tube. Each metal fin points towards the center of the metal tube. The center of the metal tube coincides with the center of the transparent glass outer tube. A radiation shield is provided on the backlight portion between the transparent glass outer tube and the V-shaped metal trough collector.

[0027] A selective radiation absorption coating is provided on the inner surface of the V-shaped metal trough collector.

[0028] The light-facing surface of the transparent glass outer casing tube is covered with an anti-reflective coating.

[0029] A medium-high temperature cavity collector for a trough-type solar collector system includes a rectangular outer casing tube and a V-shaped metal trough collector. The light-facing side of the rectangular outer casing tube is a V-shaped glass surface, and the remaining part is an open rectangle composed of three metal plates. A vacuum is evacuated or gas is filled between the rectangular outer casing tube and the V-shaped metal trough collector. The V-shaped metal trough collector includes a metal tube with two metal fins connected to it, forming a V-shaped opening. The metal tube is connected inside the V-shaped opening, and the opening surface of the V-shaped metal trough collector is parallel to the V-shaped opening of the rectangular outer casing tube, with a distance greater than or equal to 0 between the two opening surfaces. This design overcomes the stringent vacuum requirements of traditional vacuum tubes, has a simple structure, and significantly reduces manufacturing costs. It eliminates the need to consider metal sealing issues, greatly improving system stability. The V-shaped opening of the outer casing glass allows some reflected light to enter the transparent glass, increasing transmittance. It is primarily suitable for trough-type systems with an edge angle of 45 degrees, small optical errors, and a large light-gathering ratio.

[0030] An insulation layer is provided on the outside of the rectangular outer casing tube.

[0031] The heat transfer fluid flows inside the metal tube, delivering solar energy absorbed and converted by the inner surface of the V-groove.

[0032] The advantages of this utility model are: 1) This utility model uses a V-shaped groove instead of a round tube. The incident light will be absorbed multiple times in the V-shaped groove, similar to a cavity absorber. The absorption rate increases by 3% to 4%, which is close to the complete absorption of the cavity receiver, thus overcoming the disadvantage of low absorption rate of tubular collectors.

[0033] 2) The present invention draws a vacuum between the V-groove and the transparent outer cover tube, adds a reflective film or anti-radiation film to the backlight part, or adds an insulation layer at the same time to reduce heat loss and achieve low heat loss.

[0034] 3) One of the solutions of this utility model uses a V-groove transparent outer cover solution, which not only overcomes the stringent vacuum requirements of traditional vacuum tubes, but also has a simple structure and greatly reduces manufacturing costs; it also eliminates the need to consider the problem of metal sealing, which greatly improves the stability of the system; and it forms a V-groove structure, which greatly increases the transmittance, and is mainly suitable for groove systems with a large light concentration ratio.

[0035] 4) Pure copper is required as the fin material to ensure that heat can be transferred from the fins to the inner tube; flat tubes or multiple round tubes arranged in parallel are used to replace the finned inner tube. The heat transfer fluid flows inside the tube to transfer heat energy. The thermal resistance is small. Stainless steel or carbon steel materials can be used, and it is easy to manufacture. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the structure of Embodiment 1 of the present utility model;

[0037] Figure 2 This is a schematic diagram of the structure of Embodiment 2 of the present invention;

[0038] Figure 3 This is a schematic diagram of the structure of Embodiment 3 of this utility model;

[0039] Figure 4 This is a schematic diagram of the structure of Embodiment 4 of this utility model;

[0040] Figure 5 This is a schematic diagram of the structure of Embodiment 5 of the present invention;

[0041] Figure 6 This is a schematic diagram of the structure of Embodiment 5 of this utility model, which uses a flat tube instead of a round tube with fins.

[0042] Figure 7 This is a schematic diagram of the structure of Embodiment 6 of the present invention;

[0043] Figure 8 This is a schematic diagram of the structure of Embodiment 7 of this utility model;

[0044] Figure 9 This is a schematic diagram of the structure of Embodiment 8 of this utility model;

[0045] Figure 10 This is a schematic diagram of the overall design of this utility model. Detailed Implementation

[0046] like Figure 10 As shown, this invention uses ray tracing to simulate and calculate the absorption rate of shortwave radiation by the solar collector. For a vacuum chamber solar collector, it is assumed that the heat loss per unit area of ​​the opening surface is equal to the heat loss per unit outer surface area of ​​the inner tube of the vacuum collector tube, and the heat dissipation area is approximately equal to the area of ​​the V-groove opening surface. Ray tracing is used to directly calculate the concentrator interception rate and optical performance, thereby establishing a system performance simulation model. With the goal of maximizing the annual average photothermal efficiency, the main design parameters of the solar collector are determined through optimization calculations, including the V-groove opening area, the V-groove depth (distance from the apex to the opening surface), and the outer casing radius; for the V-shaped glass outer casing, the depth of the V-shaped glass outer casing is determined. One of the conclusions obtained from the optimization is that the ratio of the half-width to the height of the V-groove opening surface is between 1:1 and 1:3, which will not be described in detail below. Example 5 is used for a trough system with an edge angle of approximately 90 degrees; the other schemes are used for trough systems with an edge angle of approximately 45 degrees. In practical applications, the transparent glass tube cover 1 and the two ends of the V-shaped metal trough collector 2 are connected by a metal-glass connector 9, which can be a metal corrugated pipe.

[0047] Example 1: A medium-high temperature cavity collector for use in a trough-type solar collector system, such as... Figure 1As shown, the device includes a transparent glass tube outer cover 1 and a V-shaped metal groove collector 2. The center of the opening of the V-shaped groove is located at the center of the transparent glass tube outer cover 1, and a metal tube 3 is connected to its inner side. The inner side of the transparent glass tube outer cover 1 is either evacuated or filled with gas. A radiation shield 4 is added to the backlighting portion between the transparent glass tube outer cover 1 and the V-shaped metal groove collector 2. The radiation shield 4 is constructed by adding a reflective film to the side of the curved steel plate facing the collector tube and adding a low infrared emissivity material to the other side.

[0048] The transparent glass tube outer casing allows sunlight to enter the interior of the V-shaped metal trough collector. Its shape and design help focus sunlight onto the V-shaped metal trough collector, improving light collection efficiency.

[0049] The center of the opening of the V-shaped metal trough solar collector is aligned with the center of the transparent glass tube outer casing. This design allows sunlight to be effectively reflected and focused onto the inner metal tube of the collector. The V-shaped structure maximizes the reception of sunlight and its conversion into heat energy.

[0050] Metal tubes typically have good thermal conductivity, enabling them to quickly transfer absorbed heat to where it is needed.

[0051] By evacuating or filling the space between the inner and outer tubes, a vacuum environment can effectively reduce heat conduction and convection, thereby improving the heat preservation performance of the collector. This design also reduces the possibility of heat loss to the surrounding environment through the outer casing.

[0052] The radiation shield is constructed of curved steel plates, with a reflective film on the side facing the heat collector tubes and a low-infrared emissivity material on the other side. The reflective film reflects heat from the backlighting area, reducing heat loss; the low-infrared emissivity material reduces heat loss through radiation.

[0053] Example 2: A medium-high temperature cavity collector for use in a trough-type solar collector system, such as... Figure 2 As shown, it includes a transparent glass tube outer cover 1 and a V-shaped metal groove collector 2. The center of the opening surface of the V-shaped groove is on the center of the glass tube, and a metal tube 3 is connected to the inside. The inside of the transparent glass tube outer cover 1 is evacuated or filled with gas, and a reflective film 5 is added to the backlight part of the glass tube.

[0054] Example 3: A medium-high temperature cavity collector for use in a trough-type solar collector system, such as... Figure 3 As shown, the device includes a transparent glass tube outer cover 1 and a V-shaped metal groove collector 2. The center of the opening of the V-shaped groove is located at the center of the glass tube, and a metal tube 3 is connected to its inner side. The inner side of the transparent glass tube outer cover 1 is evacuated or filled with gas. A radiation shield 4 is added to the backlighting portion between the glass tube and the collector. The radiation shield 4 is constructed by adding a reflective film to the side of the curved steel plate facing the collector tube and adding a low infrared emissivity material to the other side. A heat insulation layer 6 is added to the backlighting portion of the outer side of the glass tube outer cover.

[0055] Example 4: A medium-high temperature cavity collector for use in a trough-type solar collector system, such as... Figure 4 As shown, it includes a transparent glass tube outer cover 1 and a V-shaped metal groove collector 2. The V-shaped metal groove collector 2 consists of two V-shaped grooves and a metal tube 3. Both V-shaped grooves are connected to the metal tube 3. The center of the opening surface of the V-shaped groove is on the center of the glass tube, and the outer side is connected to the metal tube 3. The inner side of the transparent glass tube outer cover 1 is evacuated or filled with gas. A reflective film 5 is added to the backlight part of the glass tube.

[0056] Example 5: A medium-high temperature cavity collector for use in a trough-type solar collector system, such as... Figure 5 As shown, it includes a transparent glass tube outer cover 1 and a V-shaped metal trough collector 2. The V-shaped metal trough collector 2 is composed of a metal tube 3 with 6 metal fins evenly connected on it. Each fin points to the center of the metal tube. The center of the metal tube coincides with the center of the transparent glass tube outer cover 1. The inside of the transparent glass tube outer cover 1 is evacuated or filled with gas and a radiation shield 4 is added.

[0057] Multiple flat tubes 10 can be used to form a star-shaped structure, replacing the round tube with finned design. Other designs can also be replaced in the same way, such as... Figure 6 As shown, the heat transfer fluid flows inside the tube, directly transferring heat energy to the wall surface. This significantly reduces thermal resistance and improves heat transfer efficiency. Carbon steel or stainless steel tubes can easily meet the heat transfer requirements. Using this collector instead of traditional vacuum collector tubes, ray tracing calculations show that the optimized design increases the photothermal efficiency from 55% to 65%.

[0058] The V-shaped metal trough solar collector consists of six metal fins evenly connected to a metal tube, with each fin pointing towards the center of the tube. This design allows incident light to be absorbed multiple times by the wall surface, similar to a cavity receiver, thus improving the absorption efficiency of sunlight.

[0059] Example 6: A medium-high temperature cavity collector for use in a trough-type solar collector system, such as... Figure 7 As shown, it includes a rectangular outer casing tube and a V-shaped metal trough collector 2. The light-facing side of the rectangular outer casing tube is a V-shaped glass surface 8, and the remaining part is an open rectangle composed of three metal plates 7. Gas is filled between the rectangular outer casing tube and the V-shaped metal trough collector 2. The V-shaped trough collector is connected to the metal tube 3, and its opening surface is parallel to the opening of the V-shaped surface of the glass tube and the distance is very small. An insulation layer 6 is added to the outside of the rectangular outer casing.

[0060] The collector employs a rectangular outer casing with a V-shaped glass surface facing the light, allowing for multiple reflections and increasing light transmittance. The remaining portion consists of three metal plates. This design optimizes the collector's shape, making it more suitable for specific installation environments, and further improves collection efficiency through this optimized shape.

[0061] Highly efficient sunlight collection;

[0062] Example 7: A medium-high temperature cavity collector for use in a trough-type solar collector system, such as... Figure 8 As shown, it includes a transparent glass tube outer cover 1 and a V-shaped metal trough collector 2. The V-shaped metal trough collector 2 is composed of multiple V-shaped structures formed by multiple circular tubes. The inner side of the transparent glass tube outer cover 1 is evacuated or filled with gas and a radiation shield 4 is added.

[0063] Example 8: A medium-high temperature cavity collector for use in a trough-type solar collector system, such as... Figure 9 As shown, it includes a transparent glass tube outer cover 1 and a V-shaped metal trough collector 2. The V-shaped metal trough collector 2 is a V-shaped structure composed of two flat tubes 10. The inside of the transparent glass tube outer cover 1 is evacuated or filled with gas and a radiation shield 4 is added.

[0064] The combination of the transparent glass tube cover and the V-shaped metal groove collector in this invention can maximize the collection and focusing of sunlight, thereby improving the light collection efficiency.

[0065] The V-shaped structure design of this invention allows sunlight to be effectively reflected and focused onto the inner metal tube of the collector, further improving the heat collection efficiency. This invention uses a V-shaped groove instead of a circular tube, causing the incident light to be absorbed multiple times within the V-shaped groove, similar to a cavity absorber. This increases the absorption rate by 3% to 4%, approaching the complete absorption of a cavity receiver, overcoming the low absorption rate of tubular collectors.

[0066] This invention reduces heat loss by using vacuum or gas filling, effectively reducing the possibility of heat being lost to the surrounding environment through the outer cover.

[0067] The design of the radiation shield, reflective film, and insulation layer of this utility model further reduces heat loss through radiation and conduction, thereby improving the heat preservation performance of the solar collector.

[0068] The metal fin structure of this invention increases the surface area of ​​the collector and improves the heat absorption efficiency, making it suitable for scenarios requiring high heat output.

[0069] The design of the rectangular outer casing tube of this utility model optimizes the shape of the solar collector, making it more suitable for specific installation environments. At the same time, by optimizing the shape, the solar collection efficiency is further improved.

[0070] This utility model provides various structural designs in different embodiments, allowing for the selection of a suitable structure based on different application scenarios and requirements. For example, embodiments 1 and 3 are suitable for scenarios requiring high thermal insulation performance; embodiments 2 and 4 are suitable for scenarios with simple structures and low costs; and embodiments 5 and 6 are suitable for scenarios requiring high heat output or specific installation environments.

[0071] This invention achieves efficient solar energy collection, excellent thermal insulation, and efficient heat energy utilization. Different embodiments offer diverse structural options to meet various application scenarios and requirements.

Claims

1. A medium-to-high temperature cavity collector for use in a trough-type solar collector system, characterized in that: It includes a transparent glass outer casing tube and a V-shaped metal trough collector. A vacuum is drawn or gas is filled between the transparent glass outer casing tube and the V-shaped metal trough collector. The V-shaped metal trough collector is located inside the transparent glass outer casing tube. The V-shaped metal trough collector includes a metal tube with two metal fins connected to it. The two metal fins form a V-shaped opening. The metal tube is connected to the inside of the V-shaped opening. The center of the opening surface of the V-shaped metal trough collector is at the center of the transparent glass outer casing tube.

2. A medium-high temperature cavity collector for a trough-type solar collector system according to claim 1, characterized in that: A reflective film is attached to the backlight side of the inner side of the transparent glass outer casing tube.

3. A medium-high temperature cavity collector for a trough-type solar collector system according to claim 1, characterized in that: A radiation shield is provided in the backlight section between the transparent glass outer casing tube and the V-shaped metal trough collector; the radiation shield includes an arc-shaped plate, on the side of the arc-shaped plate facing the V-shaped metal trough collector, a reflective film is attached, and the other side is coated with a low infrared emissivity material coating.

4. A medium-high temperature cavity collector for a trough-type solar collector system according to claim 1, characterized in that: An insulation layer is provided on the backlit portion of the outer side of the transparent glass outer casing tube.

5. A medium-to-high temperature cavity collector for use in a trough-type solar collector system, characterized in that: The device includes a transparent glass outer tube and a V-shaped metal trough collector. A vacuum is drawn or gas is filled between the transparent glass outer tube and the V-shaped metal trough collector. The V-shaped metal trough collector is located inside the transparent glass outer tube. The V-shaped metal trough collector includes two V-shaped grooves and a metal tube. The V-shaped grooves are V-shaped opening grooves formed by two metal fins. The two V-shaped grooves are arranged side by side. The metal tube is connected between the two V-shaped grooves. The two adjacent ends of the two V-shaped grooves are connected. The connection point is at the center of the transparent glass outer tube. A reflective film is attached to the inner backlight side of the transparent glass outer tube.

6. A medium-to-high temperature cavity collector for use in a trough-type solar collector system, characterized in that: It includes a transparent glass outer casing tube and a V-shaped metal trough collector. A vacuum is drawn or gas is filled between the transparent glass outer casing tube and the V-shaped metal trough collector. The V-shaped metal trough collector is located inside the transparent glass outer casing tube. The V-shaped metal trough collector is a V-shaped structure composed of two flat tubes, or multiple V-shaped structures composed of multiple round tubes, or a star-shaped structure composed of multiple flat tubes, or composed of 4 to 10 metal fins connected to a metal tube. Each metal fin points to the center of the metal tube. The center of the metal tube coincides with the center of the transparent glass outer casing tube. A radiation shield is provided in the backlight section between the transparent glass outer casing tube and the V-shaped metal trough collector.

7. A medium-high temperature cavity collector for a parabolic trough solar collector system according to any one of claims 1-6, characterized in that: A selective radiation absorption coating is provided on the inner surface of the V-shaped metal trough collector.

8. A medium-high temperature cavity collector for a parabolic trough solar collector system according to any one of claims 1-6, characterized in that: The light-facing surface of the transparent glass outer casing tube is covered with an anti-reflective coating.

9. A medium-to-high temperature cavity collector for use in a trough-type solar collector system, characterized in that: The device includes a rectangular outer casing tube and a V-shaped metal trough collector. The light-facing side of the rectangular outer casing tube is a V-shaped glass surface, and the remaining part is an open rectangle composed of three metal plates. A vacuum is drawn or gas is filled between the rectangular outer casing tube and the V-shaped metal trough collector. The V-shaped metal trough collector includes a metal tube with two metal fins connected to it, forming a V-shaped opening. The metal tube is connected to the inside of the V-shaped opening, and the opening surface of the V-shaped metal trough collector is parallel to the V-shaped opening surface of the rectangular outer casing tube.

10. A medium-high temperature cavity collector for a trough-type solar collector system according to claim 9, characterized in that: An insulation layer is provided on the outside of the rectangular outer casing tube.

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