US-12618590-B2 - Method for measuring heliostats, and method for calibrating heliostats

US12618590B2US 12618590 B2US12618590 B2US 12618590B2US-12618590-B2

Abstract

A method for measuring heliostats including: 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 or target area in the sky or in the vicinity of the solar tower; c) moving a flying apparatus 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 the camera at a predefined time interval; d) evaluating the images wherein a virtual target is calculated from the images by a previously determined or stored capturing position of the corresponding image; e) determining, by 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.

Inventors

Vincent Nettelroth
Moritz Leibauer

Assignees

Deutsches Zentrum für Luft- und Raumfahrt e.V.

Dates

Publication Date: 20260505
Application Date: 20221216
Priority Date: 20211217

Claims (17)

1 . A method for measuring heliostats in a heliostat field that has a plurality of heliostats and is part of a solar tower power plant that has a solar tower, the heliostats 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 or target area in the sky or in the vicinity of the solar tower; c) moving a flying apparatus 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 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 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; and e) determining, by 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.
2 . The method according to claim 1 , wherein the light source is formed by a light spot formed on a target, the target being arranged on a tower, and the target being irradiated by an external light 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.
3 . The method according to claim 2 , wherein 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.
4 . The method according to claim 2 , wherein 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.
5 . The method according to claim 1 , wherein the light source is formed by one or more lights arranged on the solar tower.
6 . The method according to claim 1 , wherein the flight pattern includes a meander or spiral shape.
7 . The method according to claim 1 , wherein the flight pattern is arranged in a plane in which the preset target point or the target area is located.
8 . The method according to claim 1 , wherein steps d) and e) can be performed offline of the flying apparatus after the end of step c).
9 . The method according to claim 1 , wherein several markers are provided in the heliostat field, wherein in step d) individual heliostats to be measured can be identified by the markers in the images.
10 . The method according to claim 9 , wherein 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.
11 . A method for calibrating heliostats in a heliostat field that has a plurality of heliostats and is part of a solar tower power plant that has a solar tower, the heliostats each having at least one reflector having a mirror surface, said method comprising the following steps: I) performing the method according to claim 1 ; and II) calibrating the heliostats to be measured using the target/actual deviation.
12 . A method for measuring heliostats in a heliostat field that has a plurality of heliostats and is part of a solar tower power plant that has a solar tower, the heliostats 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 the previously determined position of the light source; and f) determining, by 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.
13 . The method according to claim 12 , wherein the cameras each have a fisheye lens or that two cameras are arranged per measuring point, which are directed in different directions.
14 . The method according to claim 12 , wherein the light source is moved by a flying apparatus.
15 . The method according to claim 12 , wherein the position of the light source is determined by tracking the light source using a tachymeter.
16 . The method according to claim 12 , wherein the light source is an internally lit balloon.
17 . The method according to claim 12 , wherein 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.

Description

FIELD The present invention relates to a method for measuring heliostats of a heliostat field of a solar tower power plant, which heliostat field comprises a plurality of heliostats, as well as to a method for calibrating heliostats. BACKGROUND Solar tower power plants comprise a heliostat field of a plurality of heliostats, each heliostat including at least one reflector with a mirror surface, via which solar radiation can be concentrated onto an absorber. The heliostats are often arranged along curved paths around the solar tower. The distances of the heliostats to the tower/absorber may vary between several hundred meters and more than one kilometer, depending on the position of the heliostat. Each reflector has a focal length adapted to the distance of the reflector to the absorber. In operation, the heliostats track the position of the sun. The characterizing parameters that are necessary for precise tracking of the heliostats are usually the following: two angles to describe the tilt (azimuth axis, elevation axis), offset for the elevation and azimuth axes respectively, two parameters that describe the non-linearity of the drives, an angle that describes the deviation of 90° between the elevation and azimuth axes, as well as the deviation between the optical axis defined by the mirrors and the optical axis as actually defined by the position of the axes. In order to achieve the most accurate focusing of a heliostat on the absorber, the offsets and parameters mentioned must be determined to enable calibration of the heliostat control. Furthermore, the offsets and parameters must also be checked during operation in order to make necessary adjustments. 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. There are also approaches for 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 with a camera and evaluated. These two known methods are optimized for the measurement of parabolic trough collectors. The known flux density-based methods require a fixed hardware installation on the tower and are also dependent on the position of the sun or the availability of direct solar radiation. Individual calibration of heliostats takes a very long time due to the large number of heliostats. It is known from DE 10 2015 217 086 A1 to fly a flying apparatus over a heliostat field and to record the image of the flying apparatus generated on the reflector of a heliostat in order to deduce the orientation of the heliostat by means of the position of the flying apparatus at the time of recording and the position of the image on the reflector. SUMMARY Thus, it is an object of the present invention to provide a method for measuring heliostats which is independent of solar irradiation and can be performed with little hardware-related technical effort, as well as very precisely and very quickly. Further, it is another object of the present invention to provide a method for calibrating heliostats. The method for measuring heliostats of a heliostat field with a plurality of heliostats of a solar tower power plant comprising a solar tower, the heliostats each comprising at least one reflector having a mirror surface, provides the following steps: a) providing a light source, wherein the light source is arranged in a reflection area of at least some heliostats to be measured,b) aligning at least some heliostats to be measured in order to reflect light from the light source onto a predefined target point or target area in the sky or in the vicinity of the solar tower,c) moving a flying apparatus 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, 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. A time with low solar radiation may be, for example, a time during the dawn of a day or a time with heavy clouds at which usually no solar