DEVICE FOR MEASURING CONTAMINATION OF TRANSPARENT MATTER UNDER SOLAR RADIATION

Abstract

Measuring device (1) for measuring the contamination of material transparent to solar radiation, comprising a housing (3) with a longitudinal axis (A), wherein a support holds the housing (3) with its longitudinal axis (A) in a horizontal direction and the housing (3) is pivotably mounted on the support about the longitudinal axis (A), wherein the housing (3) has a wall (5) opaque to solar radiation which longitudinally encloses a space (7), wherein the wall (5) has at least one first opening (9) and at least one second opening (11), wherein the first opening (9) is closed with a disk (13) transparent to solar radiation and a cover device (15) for covering the second opening (11) is arranged at the second opening (11), and comprising at least one pyranometer (17) which is located in the space (7) at the first and second openings (9, 11) for measuring the contamination through the first and second openings (9, 11), respectively.the second opening (9, 11) can be positioned to allow solar radiation to penetrate, or with at least two pyranometers, wherein one of the pyranometers (17) is arranged at each of the first and second openings (9, 11) to measure solar radiation penetrating through the first and second openings (9, 11).

Description

[0001] The present invention relates to a measuring device for measuring the contamination of material transparent to solar radiation.

[0002] Solar power plants, especially solar thermal power plants, can experience performance losses due to soiling. Particularly in solar thermal power plants with concentrated solar power (CSP) technology, soiling of reflective surfaces is measured to determine maintenance intervals, for example. In parabolic trough power plants, solar radiation is concentrated onto an absorber tube via reflectors. The absorber tube is surrounded by a glass casing through which the solar radiation is transmitted before reaching the absorber tube. Therefore, in addition to the soiling of the reflective surfaces of the parabolic troughs, the soiling of the glass casing is also of particular interest. Other solar power plants also frequently use materials transparent to solar radiation, through which solar radiation is transmitted before reaching a radiation receiver.For example, in tower power plants, discs are known to be used in front of the entrance window of the radiation receiver.

[0003] The materials used in solar power plants that are transparent to solar radiation are exposed to the elements and become dirty with increasing exposure time.

[0004] To determine losses due to soiling, it is known to perform manual measurements using narrowband artificial LED light sources to measure the transmission in different wavelength ranges on the glass sheathing of absorber tubes. It is also known to expose samples of the material, which is transparent to solar radiation, to the elements and then measure them in the laboratory with regard to soiling.

[0005] The known measurement methods are quite labor-intensive, as a separate, technically trained person is required for operating the measuring device manually or for taking measurements in the laboratory. Furthermore, manual measurements use an artificial light source with a spectrum that differs from the solar spectrum, thus introducing measurement uncertainty. Laboratory measurements, for example using a spectrophotometer, can employ solar weighting to calculate the theoretical measurement result for a standard solar spectrum. However, a standard solar spectrum may not be representative of the spectrum present at the measurement site.

[0006] Furthermore, the angles of incidence in the previously known measurement methods are often not representative of the actual application.

[0007] It is therefore an object of the present invention to provide a measuring device with which the contamination measurement of materials transparent to solar radiation is improved.

[0008] The invention is defined by the features of claim 1.

[0009] The measuring device according to the invention for measuring the contamination of material transparent to solar radiation comprises a housing with a longitudinal axis, wherein a holder supports the housing with its longitudinal axis in a horizontal direction, and the housing is pivotably mounted on a holder about the longitudinal axis. The housing has a wall opaque to solar radiation, which encloses a space longitudinally, the wall having at least one first opening and at least one second opening. The first opening is closed with a disc transparent to solar radiation. At least one pyranometer can be placed in the space at the first and second openings for measuring solar radiation penetrating through the first and second openings, respectively.Alternatively, at least two pyranometers can be provided, with one pyranometer positioned at each of the first and second openings to measure solar radiation entering through those openings. A cover is provided at the second opening.

[0010] The covering device can, for example, be a flap covering the opening from the outside. The measuring device according to the invention allows the disc, which is transparent to solar radiation, to be exposed to the elements. The covering device prevents contaminants from entering the room and from reaching the pyranometer(s) while the disc is exposed to the elements. The housing's mounting and pivotable bearing allow the transparent disc to be aligned in the same way as a solar-transparent material in a solar power plant would be in normal use. For example, in a parabolic trough power plant, the majority of the radiation is reflected by the parabolic trough reflectors and transmitted through the glass casing of a tubular absorber on the side of the absorber tube facing the reflector.The section of the absorber tube containing the glass sheath that is of particular interest is therefore the section facing the reflector. Using the measuring device according to the invention, the solar-transparent disc can now be aligned to mimic the movement of a parabolic trough collector tracking the sun. The disc is thus positioned on the side of the housing facing away from the sun. During this movement, the transparent disc is exposed to the elements. After a predetermined period, the housing is pivoted so that the disc is exposed to solar radiation. The cover can then be removed from the second opening, and a comparative measurement can be taken between the solar radiation passing unhindered through the second opening and the direct solar radiation transmitted through the solar-transparent disc.In this way, a particularly simple and advantageous method for measuring the soiling of the disc, which is transparent to solar radiation, is possible. The opaque wall of the housing ensures that when measuring direct solar radiation via the pyranometer, essentially only radiation that passes through the transparent disc or the second opening into the room is measured.

[0011] In the context of the present invention, "transparent to solar radiation" means that the disk or material has a hemispherical solar (AM 1.5) transparency of at least 85%. In the context of the present invention, "opaque to solar radiation" means that the wall has a hemispherical solar (AM 1.5) transparency of less than 3%.

[0012] The characteristic that the wall encloses the space lengthwise means that it is parallel to the longitudinal axis and surrounds the longitudinal axis at a distance.

[0013] In the embodiment where a pyranometer is provided, when measuring the incident direct solar radiation using a pyranometer, the pyranometer can be positioned first under the first opening to measure the solar radiation transmitted through the transparent disc, and then under the second opening. For this purpose, the pyrometer can be mounted on a guide rail so that it can be moved from one position to the other. However, since the radiation intensity can change during the successive measurements, measurement errors can occur.

[0014] Preferably, the housing is tubular in shape. The housing can have a circular cross-section. This allows the housing to be advantageously pivoted about its longitudinal axis. Furthermore, the shape of the housing is advantageously adapted to the shape of an absorber tube with a glass sheath. The housing can have a diameter corresponding to the diameter of a glass sheath of a parabolic trough power plant. For example, the housing can have a diameter between 10 cm and 20 cm.

[0015] In one embodiment of the measuring device, a ventilation system may be provided to ventilate the room. Since the housing is exposed to solar radiation during the day and has a wall opaque to solar radiation, the space inside the housing can heat up. To ensure the correct functioning of the pyranometer(s) located in the room, cool outside air can be introduced into the room via the ventilation system as needed.

[0016] The housing can be designed so that its front is closed by plates, with ventilation openings arranged in at least one of the plates for supply and exhaust air from the ventilation device. In this way, the ventilation device can advantageously draw cool outside air into the room.

[0017] It may also be provided that the ventilation device has several fans and that ventilation openings are arranged on both end plates.

[0018] Preferably, a thermostat is provided in the room to monitor the room temperature. Using the data determined by the thermostat, it can be ascertained whether the room temperature, measured by pyranometers, falls within a predetermined range when measuring the incident direct solar radiation.

[0019] It is also possible for the ventilation system to be controlled via data received from the thermostat. In other words, if the temperature in the room is too high, the ventilation system can start automatically and draw in cool outside air.

[0020] Preferably, a drive device is provided to drive the housing for the pivoting movement about the longitudinal axis. This enables automatic operation of the measuring device. The drive device can be arranged within the space.

[0021] It may be provided that a retaining device engages the cover, and that the cover can be opened or closed by pivoting the housing about its longitudinal axis. In other words, the retaining device holds the cover in place when the housing pivots about its longitudinal axis, thereby opening, for example, the second opening. The retaining device may be attached to the housing's mounting bracket, for example, in the form of a steel cable arranged parallel to the housing. Alternatively, the cover may be provided with a locking mechanism, for example, in the form of one or more springs, to hold the cover in its open or closed position.

[0022] Alternatively, the cover device can be provided with a separate drive for opening and closing. This allows the opening and closing of the cover device to occur independently of the pivoting movement of the housing.

[0023] Both the retaining device and the drive of the cover device advantageously enable the automatic operation of the measuring device according to the invention.

[0024] The measuring device according to the invention can further include a curved plate arranged at a distance from the housing. The curved plate advantageously simulates a parabolic reflector, thereby making it particularly realistic to reproduce the tendency of the transparent disc to become soiled.

[0025] When using the measuring device according to the invention, it can also be provided that the housing is pivoted throughout the day during the phase in which the transparent disc is exposed to the weather. In particular, it can be provided that the transparent disc is tracked with a 180° offset relative to the sun, following its position. This type of tracking replicates the positioning in a real parabolic trough collector and thereby produces a soiling characteristic similar to that which would occur in power plant operation.

[0026] During the measurement of directly incident radiation using at least one pyranometer, the angle of incidence relative to the sun can also be recorded. This allows the transmittance of the transparent disk to be determined as a function of the angle of incidence.

[0027] Using the measuring device according to the invention, it is possible to determine the soiling load of transparent materials used in solar power plants and thus improve the yield forecasting for power plant projects. Cleaning activities can also be optimized in operating solar power plants.

[0028] The invention will be explained in more detail below with reference to the single figure. The figure shows: Fig. 1 a schematic view of the measuring device according to the invention for measuring the contamination of material transparent to solar radiation and Fig. 2 a schematic sectional view of the measuring device according to the invention.

[0029] The measuring device 1 according to the invention Fig. 1The housing 3 has a longitudinal axis A. The housing 3 is held by a support (not shown) with its longitudinal axis in the horizontal direction, the housing being supported on the support about the longitudinal axis A.

[0030] The housing 3 has a wall 5 that is opaque to solar radiation and encloses a space 7 lengthwise.

[0031] The wall 5 has a first opening 9 and a second opening 11. The first opening 9 is closed by a disk 13 that is transparent to solar radiation.

[0032] A cover device 15 is arranged at the second opening 11 for covering the second opening 11.

[0033] How best to Figure 2 , a schematic sectional view of the measuring device according to the invention Figure 1As can be seen, in chamber 7, a pyranometer 17 is arranged at each of the first and second openings 9, 11, by means of which the solar radiation penetrating through the first and second openings can be measured. The pyranometers 17 are arranged such that they are aligned with the first or second opening 9, 11.

[0034] The housing 3 is closed at the end with plates 19, 19a. Ventilation openings 21 are arranged in plate 19a, which serve for the supply and exhaust air of a ventilation device 23. The ventilation device 23 consists of fans 25, which are arranged at the ventilation openings 21 and supply fresh air to room 7 and / or exhaust air from room 7 to the outside.

[0035] In room 7 a thermostat 27 is also provided, which registers the temperature of room 7 and controls the ventilation device 23, so that the temperature in room 7 can be advantageously regulated in order to ensure the correct function of the pyranometers 17.

[0036] Furthermore, a drive device 29 is arranged in space 7, via which the housing 3 is driven for the pivoting movement about the longitudinal axis A. The housing 3 can thus be automatically pivoted about its longitudinal axis.

[0037] A retaining device (not shown) is attached to the mounting bracket of axis A (not shown) at a distance slightly greater than the radius of the housing 3. This device allows the cover 15 to be opened and closed by means of the pivoting movement of the housing 3. The retaining device can, for example, be a steel cable attached to the mounting bracket of the measuring device (not shown) and arranged parallel to the housing. To ensure that the cover remains in the closed or open position, it can incorporate a spring mechanism that acts in the direction of the assumed position of the cover 15. The position of the cover is changed by the fixed retaining device as the measuring device passes by. To open the cover, the steel cable engages in the eyelet 16 near the suspension point of the closed cover 15 and opens it when moved away from the opening 11.The cover device 15 is closed when the device 3 moves past the steel cable in the opposite direction with the cover device 15 open.

[0038] To measure the soiling of the transparent disc 13, the measuring device 1 is first pivoted into an exposure position in which the transparent disc 13 is facing downwards. Preferably, the transparent disc 13 is offset by 180° from the sun. It can then be provided that, during the day, the housing 3 is moved by the drive device 29 to follow the sun at this 180° offset. During the exposure phase, the cover device 15 is in its closed position, so that the opening 11 and thus the underlying pyranometer 17 are covered to minimize soiling.

[0039] During a measurement phase, the housing 3 is pivoted so that the first opening 9 is in direct sunlight. As the housing 3 is pivoted into the measurement position, the cover 15 is opened by the retaining device. The sun now shines directly into the first and second openings 9 and 11, and the radiation power can be measured using the pyranometer 17 located below. The solar radiation transmitted through the transparent disk 13 can be compared with the solar radiation striking the pyranometer 17 directly below the second opening 11. This yields the transmittance of the transparent disk 13. The angle of incidence of the sun is also recorded during the measurement, so that after several measurements, the transmittance can be determined as a function of the angle of incidence.

[0040] Since the transmittance of the transparent disk 13 changes with increasing soiling, and soiling of both pyranometers is simultaneously prevented, the soiling behavior of the disk 13 can be recorded maintenance-free even over periods of several weeks. The resulting soiling rates can be used to determine yield losses of a solar power plant or the need for cleaning.

Claims

1. Measuring device (1) for measuring the contamination of material transparent to solar radiation, comprising a housing (3) with a longitudinal axis (A), wherein a support holds the housing (3) with its longitudinal axis (A) in a horizontal direction and the housing (3) is pivotably mounted on the support about the longitudinal axis (A), wherein the housing (3) has a wall (5) opaque to solar radiation which longitudinally encloses a space (7), wherein the wall (5) has at least one first opening (9) and at least one second opening (11), wherein the first opening (9) is closed with a disk (13) transparent to solar radiation and a cover (15) for covering the second opening (11) is arranged at the second opening (11), and comprising at least one pyranometer (17) which is located in the space (7) at the first and second openings (9, 11) for measuring the contamination through the first and second openings (9, 11), respectively.the second opening (9, 11) can be positioned to receive solar radiation or with at least two pyranometers, wherein one of the pyranometers (17) is arranged at each of the first and second openings (9, 11) to measure solar radiation entering through the first and second openings (9, 11).

2. Measuring device according to claim 1, characterized by the fact that the housing (3) is tubular in shape.

3. Measuring device according to claim 1 or 2, characterized by a ventilation device (23) for ventilating the room (7).

4. Measuring device according to claim 3, characterized by the fact that the housing (3) is closed at the front by means of plates (19, 19a), wherein ventilation openings (21) are arranged in at least one of the plates (19a) for supply air and exhaust air of the ventilation device (23).

5. Measuring device according to one of claims 1 to 4, characterized by the fact that A thermostat (27) is arranged in the room (7) to monitor the temperature of the room (7).

6. Measuring device according to claim 5, characterized by the fact that The ventilation device (23) can be controlled via data received from the thermostat (27).

7. Measuring device according to one of claims 1 to 6, characterized by a drive device (29) by which the housing (3) can be driven for pivoting about the longitudinal axis (A).

8. Measuring device according to one of claims 1 to 7, characterized by the fact that a retaining device is attached to the mounting of the housing (3) which engages the cover device (15), wherein the cover device (15) can be opened or closed by pivoting the housing (3) about the longitudinal axis (A).

9. Measuring device according to one of claims 1 to 8, characterized by the fact that the cover device (15) has a locking mechanism for holding the open or closed position of the cover device (15).

10. Measuring device according to one of claims 1 to 7, characterized by the fact thatthe cover device (15) has a drive for opening and closing.