METHOD FOR MEASURING HELIOSTATS AND METHOD FOR CALIBRINGING HELIOSTATS

Description

[0001] The present invention relates to a method for measuring heliostats of a heliostat field comprising several heliostats of a solar tower power plant and to a method for calibrating such heliostats.

[0002] Solar tower power plants feature a heliostat field consisting of a multitude of heliostats, each heliostat having at least one reflector with a mirror surface through which solar radiation can be concentrated onto an absorber.

[0003] The heliostats are often arranged along curved paths around the solar tower. The distances between the heliostats and the tower / absorber can vary from several hundred meters to more than a kilometer, depending on the heliostat's position. Each reflector has a focal length that is adapted to the distance between the reflector and the absorber.

[0004] During operation, the heliostats track the sun's position. The characteristic parameters necessary for precise tracking of the heliostats are usually the following: two angles to describe the tilt (azimuth axis, elevation axis), offset for both the elevation and azimuth axes, two parameters describing the nonlinearity of the drives, an angle describing the 90° deviation between the elevation and azimuth axes, and the deviation between the optical axis defined by the mirrors and the optical axis as defined by the axis positions.

[0005] To achieve the most precise focusing of a heliostat on the absorber, the aforementioned offsets and parameters must be determined to enable calibration of the heliostat's control system. Furthermore, these offsets and parameters must also be checked during operation to allow for any necessary adjustments.

[0006] The known methods for determining the offset use the so-called camera-target method, in which a focal spot of the heliostat on a white, diffusely reflecting target is observed with a camera.

[0007] There are also approaches to performing a photometric evaluation of images of the mirror surface. These are described in EP 1 717 568 A2 and DE 10 2011 080 969 of the applicant. In these methods, reflections of a target on the mirror surface of the reflector are recorded and evaluated with a camera. These two known methods are optimized for measuring parabolic trough collectors.

[0008] The established flux density-based methods require a fixed hardware installation on the tower and are also dependent on the sun's position and the availability of direct sunlight. Individual calibration of heliostats takes a very long time due to the large number of heliostats.

[0009] From DE 10 2015 217 086 A1 it is known to fly an aircraft over a heliostat field and to record the image of the aircraft generated on the reflector of a heliostat in order to deduce the orientation of the heliostat by means of the position of the aircraft at the time of recording and the position of the image on the reflector.US 7,994,459 B2 discloses a method for measuring heliostats of a heliostat field comprising several heliostats of a solar tower power plant comprising a solar tower, wherein the heliostats each have at least one reflector having a mirror surface, comprising the steps of: providing a light source; aligning at least some of the heliostats to be measured to reflect light from the light source onto a predetermined target area where a camera is located; taking pictures of one or more of the heliostats to be measured with the camera at a predetermined time interval; evaluating the images; and determining a target vector of each of the heliostats to be measured and comparing it with a target value to determine a target-actual deviation; wherein at least steps a) to c) are performed at a time of low solar radiation or at night.

[0010] It is therefore an object of the present invention to provide a method for measuring heliostats that is independent of solar radiation and, moreover, can be carried out with minimal hardware requirements, with high accuracy, and very quickly. It is also an object of the present invention to provide a method for calibrating heliostats.

[0011] The invention is defined by the features of claim 1 as well as the features of claim 11 and claim 17.

[0012] The inventive method for measuring heliostats of a heliostat field comprising several heliostats of a solar tower power plant comprising a solar tower, wherein the heliostats each have at least one reflector having a mirror surface, provides the following steps: a) Providing a light source, wherein the light source is located in a reflection area of ​​at least some of the heliostats to be measured; b) Aligning at least some of the heliostats to be measured to reflect light from the light source onto a predetermined target point or target area in the sky or in the immediate vicinity of the solar tower; c) Moving an aircraft with at least one camera along a predetermined flight pattern around and over the target point or target area and simultaneously capturing images of one or more of the heliostats to be measured using the camera at predetermined time intervals; d) Evaluating the images, whereby for each of the heliostats to be measured, it is determined in at least some of the images whether light from the light source was reflected into the camera, and wherein a virtual target is calculated from the images using a previously determined or stored capture position of the corresponding image.wherein the focal point for each heliostat to be measured is determined on the virtual target, e) determining a target vector for each of the heliostats to be measured based on the focal point on the virtual target and comparing it with a setpoint to determine a target-actual deviation, wherein at least steps a) to c) are carried out at a time of low solar radiation or at night.

[0013] A time of low solar radiation could be, for example, a time during twilight or a time of heavy cloud cover, when solar radiation is not usually concentrated on the solar tower by means of the heliostats.

[0014] The "reflection area" of a heliostat refers to the area that is "visible" to the heliostat, i.e., the area from which something can be reflected by means of the mirror surface of the heliostat.

[0015] The light source is preferably located on a tower or the solar tower. However, it can also be located elsewhere or be movable, for example, on a second aircraft.

[0016] The method according to the invention has the particular advantage that a very large number of heliostats can be measured in a simple manner by photographing them during overflight with the aircraft and subsequently evaluating the images. For example, process steps b) to e) can also be repeated, taking different orientations of the heliostats to be measured. Data acquisition can thus be carried out in very short cycles for the different orientations of the heliostats. The method according to the invention thus advantageously enables, on the one hand, parallelized or nearly parallelized data acquisition by recording several heliostats simultaneously, and on the other hand, a high temporal density of measurement point acquisition.

[0017] Performing steps a) to c) at night has the distinct advantage that, due to the darkness, there is a high contrast between illuminated and unilluminated heliostats, and furthermore, ongoing daytime operations are not disrupted. The effort required for image analysis is also relatively low, as it only needs to be determined for each image and each heliostat to be measured whether light was reflected into the camera or not. Thus, only binary information per position along the flight path needs to be evaluated.

[0018] Furthermore, the variant of the inventive method in which the light source is arranged on a tower or the solar tower has the advantage that the concentrated light rays originate from the light source on the tower or the solar tower and thus from a stationary light source, so that, unlike when using, for example, the sun, the position of the heliostats does not have to be changed to adapt to the changing position of the light source.

[0019] The light source also eliminates the risk of damage to, for example, the aircraft due to excessive radiation, as could occur when using solar radiation.

[0020] The quality of the survey results can be improved by selecting the target point or area in the sky or in the immediate vicinity of the solar tower. For example, increasing the distance of the target point or area from the heliostats can enhance the resolution and stability of the method. Telephoto lenses can be used to ensure image quality even at greater distances.

[0021] The images recorded in step c) can also be recorded as a film sequence or sequences, for example.

[0022] The method according to the invention can provide that the light source is formed by a light spot generated on a target, the target being arranged on a tower, preferably a solar tower. The target is illuminated by an external light source to form the light spot, which is then reflected by the target, or the target is backlit by a light source to form the light spot. This has the advantage that targets already present on the solar tower can be used for carrying out the method according to the invention. Furthermore, the targets are usually arranged in close proximity to a receiver on the tower, ensuring that the heliostats to be measured can receive the light reflected from the target and are not obstructed by another heliostat.The light can, for example, be positioned on the ground, so that no additional technical equipment is required on the solar tower.

[0023] Additionally or alternatively, it may be provided that the light source is formed by one or more lights arranged on the solar tower.

[0024] Preferably, the size of the light spot or illuminating surface of the luminaire(s) is adapted to the size of the sun's reflection by at least one of the heliostats onto the solar tower, preferably onto the target. It can also be provided that the shape of the light spot or illuminating surface of the luminaire(s) is adapted to the shape of the sun's reflection by at least one of the heliostats onto the solar tower, preferably onto the target. When using multiple luminaires, the illuminating surface formed by the luminaires need not necessarily be completely illuminated; the luminaires can also be spaced apart and arranged according to the shape and / or size of the sun's reflection.

[0025] By adjusting the size and / or shape of the light spot or illuminating surface to match the image of the sun reflected onto the solar tower, the proportion used for reflection by a heliostat is comparable to the proportion used in normal heliostat operation. This results in high accuracy in heliostat measurements.

[0026] The flight pattern along which the aircraft moves can include a meandering or spiral shape. This advantageously allows a large area to be covered. The aircraft could, for example, be a drone.

[0027] Preferably, the flight pattern is arranged in a plane containing the predetermined target point or target area. This avoids the need for conversions of the captured images with respect to the plane containing the target area or target point. It can also be provided that the flight pattern follows a virtual sphere, which has the advantage that each heliostat has the same inclination to a surface formed by the flight pattern.

[0028] Steps d) and e) can be performed offline by the aircraft after step c) has been completed. In other words, the images can be transmitted from the aircraft to a central computer, which can then process the images independently of steps a) to c). Of course, image processing can also begin while the aircraft is still in flight.

[0029] The method according to the invention can provide for several markers in the heliostat field, wherein in step d) individual heliostats to be measured can be identified in the images based on the markers. This ensures that a heliostat can be uniquely identified in each image, so that it can be determined for this heliostat whether light is reflected into the camera or not.

[0030] To identify individual heliostats to be measured, a simulation containing the position of at least some of the heliostats and markers can be used, and the simulation can be compared with the images. This allows a pixel in the image to be easily assigned to a heliostat.

[0031] Another method for measuring heliostats of a heliostat field comprising several heliostats of a solar tower power plant comprising a solar tower, wherein the heliostats each have at least one reflector having a mirror surface, comprising the following steps: a) Providing a movable light source and moving the light source through a reflection area of ​​at least some heliostats to be measured, b) Determining the position of the light source at different times, c) Aligning at least some heliostats to be measured to reflect light from the light source onto a target surface, wherein a plurality of cameras are arranged in a grid on the target surface, d) Recording images of one or more of the heliostats to be measured using the cameras at a predetermined time interval, e) Evaluating the images, whereby for each of the heliostats to be measured, it is determined in at least some of the images whether light from the light source was reflected into one of the cameras, and wherein, from the images, the focus point for each heliostat to be measured on the target surface is determined using the previously determined position of the light source.f) Determining a target vector for each of the heliostats to be measured based on the focal point on the target surface and comparing it with a target value to determine a target-actual deviation, , where at least steps a) to d) are carried out at a time of low solar radiation or at night.

[0032] A further variant of the method according to the invention is essentially a reversal of the method described above. Therefore, the advantages described above also apply to this variant of the method. Instead of a stationary light source and a movable camera, this variant provides a movable light source and a grid of stationary cameras. However, it would also be conceivable to arrange one or more movable cameras on the target surface, which can be positioned at different measuring points corresponding to the grid points. For example, one or more cameras could be moved along rails and take pictures at the measuring points.

[0033] The camera(s) may each have a fisheye lens, or two cameras directed in different directions may be arranged or arranged at each measuring point. This allows a particularly large area to be captured at each measuring point.

[0034] The light source can be moved using an aircraft.

[0035] The position of the light source can be determined by tracking the light source using a tachymeter.

[0036] The light source can be a balloon illuminated from within.

[0037] The light source is moved along a trajectory adapted to the different solar paths along which the sun moves throughout the year. This allows measurements to be taken independently of the sun's position, enabling data to be recorded virtually at any time, even for measurement points corresponding to solar positions that occur only briefly during the year. Furthermore, a large number of data points can be acquired in a very short time, resulting in a high temporal density of data points.

[0038] The method according to the invention can provide for several markers in the heliostat field, wherein in step e) individual heliostats to be measured can be identified in the images based on the markers. This ensures that a heliostat can be uniquely identified in each image, so that it can be determined for this heliostat whether light is reflected into the camera or cameras or not.

[0039] The invention further provides a method for calibrating heliostats. The method according to the invention can be carried out in this process. Subsequently, the heliostats to be measured can be calibrated using the target-actual deviation.

[0040] The invention will now be explained in more detail with reference to the following figures.

[0041] The single figure shows a schematic representation of a solar tower power plant 10, by means of which a variant of the method according to the invention is described.

[0042] The method according to the invention serves to measure heliostats 1 of a heliostat field 3 comprising several heliostats 1 of a solar tower power plant 10 comprising a solar tower 7. The heliostats 1 each have a reflector with at least one mirror surface.

[0043] A target 9 is arranged below a receiver 12 on the solar tower 7. This target 9 can be the same one used in prior art methods for calibrating the heliostats 1. The target 9 is illuminated by an external light 11, so that a light spot 13 is formed on the target 9. The light spot 13 forms the light source used for the method according to the invention.

[0044] The method according to the invention is carried out at a time of low solar radiation, for example at night. First, some or all of the heliostats 1 are aligned to reflect the light from the light source 13 onto a predetermined target point 15. The target point 15 can, for example, be a point in the sky.

[0045] Using a flying device 17, which carries at least one camera, a predetermined flight pattern is flown around and over the target point 15, while images of the heliostats 1 are simultaneously taken using the camera.

[0046] The images are then evaluated, with each image being analyzed to determine whether or not light reflected from the light source by a heliostat 1 is visible. A virtual target 19 is then calculated from the images based on the previously determined or stored acquisition position of the corresponding image. Using the information on whether light reflected from the light source by a heliostat 1 is visible in the images, the focal point 23 of the corresponding heliostat 1 on the virtual target 19 can be determined.

[0047] Subsequently, a target vector can be determined for each heliostat 1 based on its focus points 23 on the virtual target 19. This target vector can be compared with a setpoint for the target vector, which was determined, for example, from the design of the solar tower power plant or through a simulation. By comparing it with the setpoint, a target-actual deviation can be determined. In the figure, the endpoint of the setpoint for the target vector is shown as the target focus point 25.

[0048] The target-actual deviation can be used, for example, for the calibration of the corresponding heliostat 1.

[0049] The luminaire 11 can be designed such that the size and shape of the generated light spot 13 on the target 9 corresponds to the size and shape of a light spot generated by reflection of sunlight on the target 9.

[0050] To enable the identification of individual heliostats 1 during image analysis, markers 21 can be provided in the heliostat field 3. These markers 21 can be identified in the captured images, and their position simplifies the identification of individual heliostats 1. Alternatively, a simulation of the heliostat field 3, containing the heliostats 1 and the markers 21, can be used to compare the simulation with the images and thus enable identification of the heliostats 1.

[0051] The inventive method for measuring heliostats 1 can serve to calibrate the heliostats 1 by using the determined target-actual deviation for the calibration of the heliostats 1.

[0052] The method according to the invention has the advantage that the measurement and calibration of the heliostats 1 can be carried out at a time when the solar tower power plant 10 is not in operation, namely at night. The measurement can be performed independently of the sun's position, whereby data can be recorded virtually at any time for measurement points corresponding to a sun position that occurs only briefly during the course of a year. Furthermore, a large number of data points can be recorded in a very short time, i.e., with a high temporal density of data points.

[0053] Furthermore, a large number of heliostats 1 can be measured simultaneously, since a multitude of images, including many or even all heliostats 1, can be captured in a very short time while flying over the heliostat field 3. Because it only needs to be determined whether a heliostat 1 has reflected light from the light source into the camera, so that the light from the corresponding heliostat 1 is visible in the image, the amount of data to be processed is comparatively small, allowing the procedure to be carried out in a relatively short time.

[0054] Thus, the method according to the invention enables time-saving measurement and calibration of heliostats 1, whereby the equipment-related effort can be kept very low. Reference symbol list

[0055] 1 Heliostat 3 Heliostat field 7 Solar tower 9 Target 10 Solar tower power plant 11 External light 12 Receiver 13 Spot of light 15 Target point 17 Aircraft 19 Virtual target 21 Marker 23 Focus point

Claims

1. A method for measuring heliostats (1) in a heliostat field (3) that has a plurality of heliostats (1) and is part of a solar tower power plant (10) that has a solar tower (7), the heliostats (1) each having at least one reflector having a mirror surface, said method comprising the following steps: a) providing a light source, b) aligning at least some heliostats to be measured in order to reflect light from the light source onto a predefined target point (15) or target area in the sky or in the vicinity of the solar tower, c) moving a flying apparatus (17) having at least one camera along a predefined flight pattern around and over the target point or target area, and simultaneously capturing images of one of the one or more heliostats to be measured by means of the camera at a predefined time interval, d) evaluating the images, wherein, for each of the heliostats to be measured in at least some of the images, it is determined whether light from the light source has been reflected into the camera, and wherein a virtual target is calculated from the images by means of a previously determined or stored capturing position of the corresponding image, wherein the focal point for each heliostat to be measured is determined on the virtual target, e) determining, by means of the focal point on the virtual target (19), a target vector of each of the heliostats to be measured and comparing it with a target value in order to determine a target / actual deviation, wherein at least steps a) to c) are carried out at a time with low solar radiation or at night.

2. Method according to claim 1, characterized in that the light source is formed by a light spot (13) formed on a target (9), the target (9) being arranged on a tower, and the target being irradiated by an external light (11) to form the light spot and reflecting the radiation that forms the light spot, or the target being backlit by a light to form the light spot (13).

3. Method according to claim 1, characterized in that the light source is formed by one or more lights arranged on the solar tower.

4. Method according to claim 2 or 3, characterized in that the size of the light spot or a lighting area of the light or the lights is adapted to the size of a reflection of the sun by at least one of the heliostats onto the solar tower, preferably on the target.

5. Method according to one of claims 2 to 4, characterized in that the shape of the light spot or a lighting area of the light or the lights is adapted to the shape of a reflection of the sun by at least one of the heliostats onto the solar tower, preferably on the target.

6. Method according to any of claims 1 to 5, characterized in that the flight pattern includes a meander or spiral shape and / or the flight pattern is arranged in a plane in which the preset target point or the target area is located.

7. Method according to one of claims 1 to 6, characterized in that steps d) and e) can be performed offline of the flying apparatus after the end of step c).

8. Method according to one of claims 1 to 7, characterized in that several markers (21) are provided in the heliostat field (3), wherein in step d) individual heliostats to be measured can be identified by means of the markers in the images.

9. Method according to claim 8, characterized in that for identifying individual heliostats to be measured, a simulation including the position of at least some of the heliostats and the markers is used and the simulation is compared to the images.

10. A method for measuring heliostats (1) in a heliostat field (3) that has a plurality of heliostats (1) and is part of a solar tower power plant (10) that has a solar tower (7), the heliostats (1) each having at least one reflector having a mirror surface, said method comprising the following steps: a) providing a movable light source and moving the light source through a reflection are of at least some heliostats to be measured, b) determine the position of the light source at different times, c) aligning at least some heliostats to be measured in order to reflect light from the light source onto a target surface, wherein a plurality of cameras is arranged in a grid on the target surface, d) capturing images of one or more of the heliostats to be measured using the cameras at a specified time interval, e) evaluating the images, wherein for each of the heliostats to be measured it is determined in at least some of the images whether light from the light source has been reflected into one of the cameras, and wherein the focal point for each heliostat to be measured on the target surface is determined from the images by means of the previously determined position of the light source, f) determining, by means of the focal point on the virtual target, a target vector of each of the heliostats to be measured and comparing it with a target value in order to determine a target / actual deviation, wherein at least steps a) to c) are carried out at a time with low solar radiation or at night.

11. Method according to claim 10, characterized in that the cameras each have a fisheye lens or that two cameras are arranged per measuring point, which are directed in different directions.

12. Method according to claim 10 or 11, characterized in that the light source is moved by means of a flying apparatus.

13. Method according to one of claims 10 to 12, characterized in that the position of the light source is determined by tracking the light source using a tachymeter, wherein the light source preferably is an internally lit balloon.

14. Method according to one of claims 11 to 13, characterized in that the light source is moved along a trajectory which is adapted to different sun orbits along which the sun moves in the course of a year.

15. A method for calibrating heliostats (1) in a heliostat field that has a plurality of heliostats (1) and is part of a solar tower power plant that has a solar tower, the heliostats (1) each having at least one reflector having a mirror surface, said method comprising the following steps: I) performing the method according to one of claims 1 to 14, II) calibrating the heliostats to be measured using the target / actual deviation.