A trough type concentrating solar thermal system and tracking method with multi-mirror tracking

Abstract

The application provides a kind of multi-mirror tracking groove type concentrating collector system and tracking method, belongs to solar tracking field.To solve the problem of low precision, large area occupied by existing groove type concentrator using single-axis tracking and difficult to realize double-axis tracking technology, including main frame and four frame supports below, the main frame is provided with several crossbars, the crossbar is connected with plane mirror through first hinged component, the main frame below is provided with groove type concentrator, four corners of groove type concentrator are located in the same plane parallel to main frame, and four corners are connected with four frame supports or two corners are connected with frame telescopic support and other two corners are connected with frame support, and heat collecting tube is arranged on focal line of groove type concentrator.The position of groove type concentrator is controlled to the position of plane mirror and main frame, the control process does not occupy additional space, reduces the area occupied by groove type concentrator, reduces the control difficulty, which is beneficial to reduce the energy loss of groove type concentrator and improve its heat collecting efficiency.

Description

Technical Field

[0001] This invention relates to the field of solar energy tracking technology, and more specifically, to a multi-mirror tracking trough-type concentrating solar collector system and tracking method. Background Technology

[0002] Solar energy, as the cleanest energy source, has been widely used. However, due to problems such as low solar energy flux density and the constantly changing position of the sun, solar collectors must be equipped with concentrating tracking technology to obtain sufficient energy. Parabolic trough solar collectors are the most mature concentrating devices on the market. Their tracking methods are mainly of two types: north-south arrangement with east-west tracking, and east-west arrangement with north-south tracking. Both are single-axis tracking. Although the heat collection efficiency has been improved, there is still a significant energy loss compared to dual-axis tracking.

[0003] Existing patents, such as a trough-type solar concentrator tracking bracket (application number: CN202110754453.3), describe a bracket with adjustable lenses equipped with a set of wheels. These wheels, driven by a motor, move the bracket along an arc-shaped track, allowing the trough-type concentrator mounted on it to rotate according to the sun's position, thus reflecting sunlight onto the solar collector tubes from the most suitable direction. While the movement of the adjustable lens bracket avoids frequent movement of the solar collector tubes, controlling the rotating mirrors is difficult and costly. Furthermore, to avoid shading when rotating with the sunlight, the spacing between adjacent trough-type concentrators is relatively large, resulting in a large footprint and consequently affecting the heat collection efficiency.

[0004] An existing patent describes a compact tracking composite concentrating solar thermal system (application number: CN202011230946.9), comprising several parallel-arranged concentrating solar thermal units, a tracking transmission device connecting each unit, and a support frame. This compact tracking composite concentrating solar thermal system is easy to integrate with buildings and can be connected in series or parallel as needed to increase the system's heat collection temperature and heat capacity, meeting the thermal utilization requirements for medium and low temperatures (100~200℃). In contrast, connecting multiple trough concentrators in series also requires the mirrors to rotate, which is more difficult to control and does not solve the problem of a large footprint.

[0005] In summary, due to the high cost, difficulty in mirror control, and large footprint of parabolic trough solar collectors, dual-axis tracking is difficult to achieve. Specifically, the dual-axis tracking support structure is more complex and therefore more prone to failure, resulting in higher investment and maintenance costs. Moreover, the large rotation area of ​​the trough collector during dual-axis tracking would lead to an excessively large footprint if a large array dual-axis tracking were to be implemented.

[0006] Therefore, providing a tracking system with lower control difficulty and less energy loss has become an urgent problem to be solved. Summary of the Invention

[0007] The technical problem to be solved by this invention is:

[0008] To address the issues of low tracking accuracy and large footprint of existing trough concentrators using single-axis tracking technology, and the difficulty in implementing dual-axis tracking technology.

[0009] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:

[0010] This invention provides a multi-mirror tracking trough-type solar concentrator system, comprising a trough-type concentrator, a collector tube, a plane mirror, a crossbar, a frame support, a main frame, rollers, and a first hinged component.

[0011] The main frame has a frame support at each of its four corners. The main frame includes several crossbars, each with a roller at both ends. The rollers are engaged in a groove on the side wall of the main frame and can slide along the extension direction of the groove. Each crossbar is connected to a plane mirror via a first hinge member. A trough-type concentrator is located below the main frame. The four corners of the trough-type concentrator are connected to the frame support and are located on the same plane parallel to the main frame. A heat collection tube is provided on the focal line of the trough-type concentrator. The two ends or the middle of the heat collection tube are fixed to the trough-type concentrator via a heat collection tube bracket.

[0012] This invention provides a multi-mirror tracking trough-type solar concentrator system, including a trough-type concentrator, a collector tube, a plane mirror, a crossbar, a frame support, a main frame, rollers, a first hinge member, a second hinge member, a third hinge member, a telescopic short rod, and a frame telescopic support.

[0013] The main frame includes several crossbars, each with rollers at both ends. The rollers are engaged in grooves on the side wall of the main frame and can slide along the extension direction of the grooves. Each crossbar is connected to a plane mirror via a first hinge member.

[0014] Two telescopic frame supports are provided on one side along the direction of the crossbar. The top of each telescopic frame support is hinged to the telescopic end of the telescopic short rod through a third hinge member. The other end of the telescopic short rod is connected to the main frame. On the opposite side of the telescopic frame supports is a frame support. The frame support is connected to the main frame through a second hinge member. A trough-type concentrator is provided below the main frame. The four corners of the trough-type concentrator are connected to the telescopic frame supports and the frame support, respectively, and are located on the same plane parallel to the main frame. A heat collection tube is provided on the focal line of the trough-type concentrator. The two ends or the middle of the heat collection tube are fixed to the trough-type concentrator through a heat collection tube bracket.

[0015] Furthermore, each crossbar is connected to the plane mirror via at least one first hinge member, and when the number of first hinge members is at least two, the first hinge members are evenly distributed.

[0016] Furthermore, each crossbar has a roller motor on one side of the roller, which drives the rotation of the roller. The first hinge member has a first hinge motor for driving the rotation of the plane mirror. The frame telescopic support is electrically driven or hydraulically driven.

[0017] Furthermore, it also includes a central controller and sensors. The input terminal of the central controller is connected to the sensors, and the output terminal of the central controller is connected to the roller motor, the first hinge motor, and the frame telescopic support column, respectively.

[0018] Furthermore, the sensor includes a rotation angle sensor for monitoring the rotation angle of the plane mirror and an infrared sensor for monitoring the distance between the crossbars.

[0019] This invention provides a tracking method for a multi-mirror tracking trough-type concentrating solar collector system, comprising the following steps:

[0020] Step 1: Determine the position and angle of the plane mirror. Arrange the system in a north-south direction, monitor the relevant signals of the sun's position in real time, and obtain the rotation angle of the plane mirror and the spacing of the crossbars through the above parameters.

[0021] Step 2: Adjustment of the plane mirror and the crossbar. Based on the position and angle results of the plane mirror obtained in Step 1, the central controller sends signals to the first control module and the second control module respectively. The first control module controls the first hinge motor to drive the plane mirror to rotate around the central axis of the first hinge component. The second control module controls the roller motor to adjust the roller to drive the crossbar to move horizontally in the east-west direction, changing the distance between adjacent plane mirrors.

[0022] This invention provides a tracking method for a multi-mirror tracking trough-type concentrating solar collector system, comprising the following steps:

[0023] Step 1: Determine the position and angle of the plane reflector and the angle of the main frame. Arrange the system in a north-south direction, monitor the relevant signals of the sun's position in real time, and combine the tilt angle of the main frame plane to obtain the rotation angle of the plane reflector, the spacing of the crossbars, and the height of the frame telescopic support through the above parameters.

[0024] Step 2: Adjustment of the plane mirror and crossbar. Based on the position and angle of the plane mirror obtained in Step 1, the central controller sends signals to the first control module and the second control module respectively. The first control module controls the first hinge motor to drive the plane mirror to rotate around the central axis of the first hinge component. The second control module controls the roller motor to adjust the roller to drive the crossbar to move along the east-west direction of the main frame plane, changing the distance between adjacent plane mirrors.

[0025] Step 3: Adjustment of the main frame. Based on the height of the frame telescopic support obtained in Step 1, the central controller sends a signal to the third control module. The third control module controls the frame telescopic support to change its telescopic height. The telescopic length of the telescopic short rod is adjusted in conjunction with the height of the frame telescopic support. The second hinge component rotates as the telescopic height changes.

[0026] Compared with the prior art, the beneficial effects of the present invention are:

[0027] This invention discloses a multi-mirror tracking trough-type concentrating solar collector system and tracking method, comprising a main frame and four frame supports below it. The main frame is provided with several crossbars, which are connected to a plane mirror through a first hinge member. A trough-type concentrator is provided below the main frame. The four corners of the trough-type concentrator are located in the same plane parallel to the main frame and are respectively connected to the four frame supports or to the frame telescopic supports and the frame supports. The solar collector tube is arranged on the focal line of the trough-type concentrator.

[0028] This invention discloses a multi-mirror tracking trough-type solar concentrator system and tracking method. The plane mirrors are controlled by single-axis rotation control. The total size of all plane mirrors in the main frame is smaller than the size of the trough-type solar concentrator. The tilt of the main frame plane is controlled by telescopic control. Compared with the dual-axis tracking of the trough-type solar concentrator, the difficulty of adjusting the position of the plane mirrors and the main frame plane to track sunlight is significantly reduced, and the cost is also relatively low.

[0029] This invention provides a multi-mirror tracking trough-type concentrating solar collector system and tracking method. During the control process, the position changes of the plane mirror and the main frame will not occupy extra space. It does not need to consider the mutual occupancy of conventional trough-type concentrators during the tracking process, thus reducing the footprint of the concentrator and reducing the energy loss of the trough-type concentrator. The heat collection effect per unit area is relatively increased.

[0030] This invention discloses a multi-mirror tracking trough-type solar concentrator and tracking method. The plane mirrors track along the east-west direction, and the spacing between the plane mirrors is adjusted and controlled as the solar altitude angle changes. Compared with the single-axis tracking of conventional trough-type solar concentrators, this invention ensures that more light can fall vertically into the trough-type solar concentrator through reflection by the plane mirrors in high-latitude regions and when the sun is low. On the other hand, it can also reduce the impact of light blocking between the plane mirrors.

[0031] This invention discloses a multi-mirror tracking trough-type solar concentrating and heat collection system and tracking method. Based on the east-west tracking of the plane mirror and the adjustment of the mirror spacing, the tilt of the main frame plane is adjusted by controlling the height of the telescopic support of the frame, so that the entire plane can track the position of the sun's movement, further increasing the probability of sunlight falling into the plane mirror. Attached Figure Description

[0032] Figure 1 This is a three-dimensional structural schematic diagram of a multi-mirror tracking trough-type concentrating solar collector system according to Scheme 1 of the present invention;

[0033] Figure 2 This is a three-dimensional structural schematic diagram of a multi-mirror tracking trough-type concentrating solar collector system according to Scheme 2 of the present invention;

[0034] Figure 3 For the present invention Figure 2 A magnified view of a section at point A in the middle;

[0035] Figure 4 For the present invention Figure 2 A magnified view of a section at point B in the middle;

[0036] Figure 5 For the present invention Figure 2 A magnified view of a section at point C;

[0037] Figure 6 This is a target sunlight path diagram in this invention.

[0038] Explanation of reference numerals in the attached figures:

[0039] 1. Trough-type concentrator; 2. Heat collection tube; 3. Plane reflector; 4. Crossbar; 5. Frame support column; 6. Main frame; 7. Roller; 8. First hinge component; 9. Second hinge component; 10. Third hinge component; 11. Telescopic short rod; 12. Frame telescopic support column. Detailed Implementation

[0040] In the description of this invention, it should be noted that the terms used in the various embodiments, such as "upper," "lower," "front," "rear," "left," and "right," which indicate orientation, are only used to simplify the description of the positional relationships based on the accompanying drawings and do not mean that the components and devices referred to must be operated in accordance with the specific orientations and defined operations, methods, and structures in the specification. Such directional terms do not constitute a limitation of this invention.

[0041] In the description of this invention, it should be noted that the terms "first," "second," and "third" mentioned in the embodiments of this invention are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined with "first," "second," and "third" may explicitly or implicitly include one or more of that feature.

[0042] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0043] Specific Implementation Plan 1: Combining Figure 1 and Figure 3 As shown, the present invention provides a multi-mirror tracking trough-type concentrating solar thermal system, including a trough-type concentrator 1, a heat collection tube 2, a plane reflector 3, a crossbar 4, a frame support 5, a main frame 6, rollers 7, and a first hinge member 8.

[0044] The main frame 6 has a frame support 5 at each of its four corners. The main frame 6 includes several crossbars 4, and each crossbar 4 has a roller 7 at both ends. The roller 7 is engaged in a sliding groove on the side wall of the main frame 6 and can slide along the extension direction of the sliding groove. Each crossbar 4 is connected to a plane mirror 3 through a first hinge member 8. A trough-type concentrator 1 is provided below the main frame 6. The four corners of the trough-type concentrator 1 are connected to the frame support 5 and the four corners of the trough-type concentrator 1 are located on the same plane parallel to the main frame 6. A heat collection tube 2 is provided on the focal line of the trough-type concentrator 1. The two ends and the middle of the heat collection tube 2 are fixed to the trough-type concentrator 1 through a heat collection tube bracket.

[0045] Combination Figure 6 As shown, the angle of the plane mirror 3 is adjusted according to the change of sunlight, so that the incident sunlight is reflected by the plane mirror 3 and shines perpendicularly onto the trough concentrator 1 below. Through the reflection of the trough concentrator 1, the light is gathered onto the heat collection tube 2, where it is absorbed and converted into heat energy. When adjusting the angle of the plane mirror 3, the spacing of the crossbars 4 can be changed to avoid shading between two adjacent plane mirrors 3, which would affect the collection of sunlight.

[0046] Preferably, each crossbar 4 is connected to the plane mirror 3 through at least one first hinge member 8. When the number of first hinge members 8 is at least two, the first hinge members 8 are evenly distributed.

[0047] Specific Implementation Plan Two: Combining Figure 2 , Figure 4 and Figure 5 As shown, the two frame supports 5 on one side along the direction of the crossbar 4 are both frame telescopic supports 12. The top of each frame telescopic support 12 is hinged to the telescopic end of the telescopic short rod 11 through a third hinge member 10. The other end of the telescopic short rod 11 is connected to the main frame 6. The frame support 5 on the opposite side of the frame telescopic support 12 is connected to the main frame 6 through a second hinge member 9. At this time, the four corners of the trough-type concentrator 1 are connected to the frame telescopic support 12 and the frame support 5 respectively, and the trough-type concentrator 1 does not tilt with the extension and retraction of the frame telescopic support 12, and always remains in a horizontal state.

[0048] The other combinations and connections in this implementation scheme are the same as in Specific Implementation Scheme 1.

[0049] Preferably, each crossbar 4 has a roller motor on one side of the roller 7, the first hinge member 8 has a first hinge motor for driving the plane mirror to rotate, and the frame telescopic support 12 is electrically driven or hydraulically driven.

[0050] Preferably, it also includes a central controller and sensors. The input terminal of the central controller is connected to the sensors, and the output terminal of the central controller is connected to the roller motor, the first hinge motor, and the frame telescopic support 12, respectively.

[0051] Preferably, the sensors include a rotation angle sensor for monitoring the rotation angle of the plane reflector 3 and an infrared sensor for monitoring the distance between the crossbars 4. The rotation angle signal of the plane reflector 3 and the distance signal between the crossbars 4 are fed back to the central controller via the two sensors. The signals are compared with the real-time acquired rotation angle of the plane reflector 3 and distance between the crossbars 4. If there is a deviation, the rotation angle of the plane reflector 3 and the distance between the crossbars 4 are adjusted according to the real-time signal acquisition results, so that the main direction of the receiving surface of the plane reflector 3 is kept facing east in the morning, horizontal at noon, and west in the afternoon.

[0052] Specific Implementation Plan Three: Combining Figure 1 and Figure 3 As shown, the present invention provides a tracking method for a multi-mirror tracking trough-type concentrating solar collector system, comprising the following steps:

[0053] Step 1: Determine the position and angle of the plane mirror 3. Arrange the system in a north-south direction and monitor the relevant signals of the sun's position in real time. It can calculate the altitude angle, azimuth angle, declination angle, hour angle of the sun's position, and the angle between the plane mirror 3 and the incident light rays of the sun. The rotation angle and the distance between the plane mirror 3 are obtained through the above parameters.

[0054] The spacing of the plane mirrors 3 can be observed through the spacing of the crossbars 4;

[0055] Step 2: Adjustment of the crossbar 4 and the plane mirror 3. Based on the position and angle results of the plane mirror 3 obtained in Step 1, the central controller sends signals to the first control module and the second control module respectively. The first control module controls the first hinge motor to drive the plane mirror 3 to rotate around the central axis of the first hinge member 8. The second control module controls the roller motor to adjust the roller 7 to drive the crossbar 4 to move horizontally in the east-west direction, changing the distance between adjacent plane mirrors 3, so as to ensure that as much sunlight as possible can be reflected by the plane mirror 3 and then incident perpendicularly on the surface of the trough concentrator 1.

[0056] The other combinations and connections in this implementation scheme are the same as in Specific Implementation Scheme 1.

[0057] This invention reduces the energy loss of conventional east-west single-axis tracking of the trough concentrator 1 by controlling the rotation angle of the plane mirror 3 and the spacing between adjacent plane mirrors 3. On the one hand, it ensures that more light can fall vertically onto the surface of the trough concentrator 1 through reflection by the plane mirrors 3 when the sun is low in high latitude regions. On the other hand, adjusting the spacing of the plane mirrors 3 ensures that the shading effect between the plane mirrors 3 is minimized when the sun is at different altitudes, which is beneficial to increasing the solar energy received by the surface of the trough concentrator 1. Moreover, the size of the plane mirror 3 in this application is smaller than the size of the trough concentrator 1, which reduces the difficulty of control and drive. The position change of the plane mirror 3 during the control process will not occupy additional space, and there is no need to consider the mutual shading effect of the conventional trough concentrator 1 during the tracking process, thus reducing the footprint of the trough concentrator 1.

[0058] Specific Implementation Plan Four: Combining Figure 2 , Figure 4 and Figure 5 As shown, the present invention provides a tracking method for a multi-mirror tracking trough-type concentrating solar collector system, comprising the following steps:

[0059] Step 1: Determine the position and angle of the plane reflector 3 and the angle of the main frame 6. Monitor the relevant signals of the sun's position in real time. Calculate the altitude angle, azimuth angle, declination angle, hour angle of the sun, and the angle between the plane reflector 3 and the incident sunlight. Combine this with the tilt angle of the main frame 6 to achieve the goal of receiving as much solar energy as possible. Obtain the rotation angle of the plane reflector 3, the spacing of the plane reflectors 3, and the height of the frame telescopic support column 12 through the above parameters.

[0060] Step 2: Based on the rotation angle of the plane mirror 3, the spacing of the plane mirror 3, and the height of the frame telescopic support 12 obtained in Step 1, the central controller transmits signals to the first control module, the second control module, and the third control module respectively. The first control module controls the first hinge motor to drive the plane mirror 3 to rotate around the central axis of the first hinge member 8. The second control module controls the roller motor to adjust the roller 7 to drive the crossbar 4 to move horizontally in the east-west direction, changing the distance between adjacent plane mirrors 3. The third control module controls the frame telescopic support 12 to adjust the telescopic height of the frame telescopic support 12. The telescopic length of the telescopic short rod 11 is adjusted in conjunction with the height of the frame telescopic support 12. The second hinge member 9 also rotates with the change in telescopic height, thereby realizing the adjustment of the tilt of the plane of the main frame 6, ensuring that as much sunlight as possible can be reflected by the plane mirror 3 and then incident perpendicularly on the surface of the trough concentrator 1.

[0061] The other combinations and connections in this implementation scheme are the same as in Specific Implementation Scheme Two.

[0062] Based on the first specific implementation scheme, this invention adds the adjustment of the tilt angle of the main frame 6 plane to ensure that the entire main frame 6 plane tracks the position of the sun's movement, further increasing the probability that sunlight falls into the trough concentrator 1 after being reflected by the plane mirror 3. Compared with single-axis tracking technology, it further reduces energy loss. Moreover, the control of the tilt angle of the main frame 6 plane is achieved through telescopic control, which is less difficult to control. Furthermore, the position change of the main frame 6 during the control process will not occupy extra space.

[0063] While the present invention has been disclosed above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention, and all such changes and modifications will fall within the scope of protection of the present invention.

Claims

1. A multi-mirror tracking trough-type concentrating solar thermal system, characterized in that: It includes a trough concentrator (1), a heat collection tube (2), a plane mirror (3), a crossbar (4), a frame support (5), a main frame (6), rollers (7), a first hinge member (8), a second hinge member (9), a third hinge member (10), a telescopic short rod (11), and a frame telescopic support (12). The main frame (6) includes several crossbars (4), and each of the two ends of the crossbars (4) is provided with rollers (7). The rollers (7) are engaged in the grooves opened on the side wall of the main frame (6) and can slide along the extension direction of the grooves. Each crossbar (4) is connected to a plane mirror (3) through a first hinge member (8). Two frame telescopic support columns (12) are provided on one side along the direction of the horizontal bar (4). The top of each frame telescopic support column (12) is hinged to the telescopic end of the telescopic short rod (11) through the third hinge member (10). The other end of the telescopic short rod (11) is connected to the main frame (6). The side opposite to the frame telescopic support column (12) is the frame support column (5). The frame support column (5) is connected to the main frame (6) through the second hinge member (9). A trough concentrator (1) is provided below the main frame (6). The four corners of the trough concentrator (1) are connected to the frame telescopic support column (12) and the frame support column (5) respectively and are located on the same plane parallel to the main frame (6). A heat collection tube (2) is provided on the focal line of the trough concentrator (1). The two ends or the middle of the heat collection tube (2) are fixed to the trough concentrator (1) through the heat collection tube bracket.

2. The multi-mirror tracking trough-type concentrating solar collector system according to claim 1, characterized in that: Each crossbar (4) is connected to the plane mirror (3) by at least one first hinge member (8). When the number of first hinge members (8) is at least two, the first hinge members (8) are evenly distributed.

3. The multi-mirror tracking trough-type concentrating solar collector system according to claim 2, characterized in that: Each crossbar (4) has a roller motor on one side of the roller (7), which is used to drive the rotation of the roller (7). The first hinge member (8) is equipped with a first hinge motor for driving the plane mirror to rotate. The frame telescopic support (12) is electrically driven or hydraulically driven.

4. The multi-mirror tracking trough-type concentrating solar collector system according to claim 3, characterized in that: It also includes a central controller and sensors. The input of the central controller is connected to the sensors, and the output of the central controller is connected to the roller motor, the first hinge motor and the frame telescopic support (12).

5. A trough-type concentrating solar collector system with multi-mirror tracking according to claim 4, characterized in that: The sensors include a rotation angle sensor for monitoring the rotation angle of the plane mirror (3) and an infrared sensor for monitoring the distance between the crossbars (4).

6. A tracking method for a trough-type concentrating solar collector system with multi-mirror tracking according to any one of claims 1-5, characterized in that, Includes the following steps: Step 1: Determine the position and angle of the plane mirror (3) and the angle of the main frame (6). Arrange the system in a north-south direction, monitor the relevant signals of the sun's position in real time, and combine the tilt angle of the plane of the main frame (6) to obtain the rotation angle of the plane mirror (3), the spacing of the crossbars (4), and the height of the frame telescopic support (12) through the above parameters. Step 2: Adjustment of the plane mirror (3) and the crossbar (4). Based on the position and angle of the plane mirror (3) obtained in Step 1, the central controller sends signals to the first control module and the second control module respectively. The first control module controls the first hinge motor to drive the plane mirror (3) to rotate around the central axis of the first hinge member (8). The second control module controls the roller motor to adjust the roller (7) to drive the crossbar (4) to move along the east-west direction of the main frame (6) plane, changing the distance between adjacent plane mirrors (3). Step 3: Adjustment of the main frame (6). Based on the height result of the frame telescopic support (12) obtained in Step 1, the signal is sent to the third control module through the central controller. The third control module controls the frame telescopic support (12) to change its telescopic height. The telescopic length of the telescopic short rod (11) is adjusted in accordance with the height of the frame telescopic support (12). The second hinge component (9) rotates with the change of telescopic height.

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