PORTABLE REFLECTOMETER AND METHOD FOR CHARACTERISING THE MIRRORS OF SOLAR THERMAL POWER PLANTS

• US 20130169950A1
• Filed: 07/20/2011
• Published: 07/04/2013
• Est. Priority Date: 07/21/2010
• Status: Active Grant

• Current Assignee: Abengoa Solar New Technologies S.A. (Abengoa SA)
• Original Assignee: Abengoa Solar New Technologies S.A. (Abengoa SA)
• Inventors: Heras Vila, Carlos, Alonso Esteban, Rafael, Villuendas Yuste, Francisco, Mainar Lpez, Marta, Izquierdo Nez, David, Salinas riz, Iigo, Asensio Prez-Ullivarri, Javier
• Granted Patent: US 9,746,418 B2
• Time in Patent Office: Days
• US Class Current: 356/51
• CPC Class Codes: G01M 11/005 Testing of reflective surfaces, e.g. mirrors
• CPC Class Codes: G01N 21/47 Scattering, i.e. diffuse reflection G01N21/25, G01N21/41 take precedence G01N21/55 takes precedence
• CPC Class Codes: G01N 21/55 Specular reflectivity
• CPC Class Codes: G01N 2201/0221 Portable; cableless; compact; hand-held
• CPC Class Codes: G01N 2201/0625 Modulated LED
• CPC Class Codes: G01N 2201/0627 Use of several LED's for spectral resolution

Abstract

The invention relates to a portable reflectometer and to a method for characterizing the collector mirrors used in solar power plants for the in-field characterization of reflection coefficients. The equipment includes all of the components required for this measurement, such as a module to measure the reflection coefficient of the mirror, an electronic data acquisition and processing system, a system for processing data and controlling the equipment, a system for storing the data of interest, a user interface system, and a system allowing communication between the aforementioned systems and an outer casing. The equipment can be used to characterize the specular reflection coefficient of flat or curved mirrors of different thicknesses, without requiring adjustments to be made to the equipment, minimizing the influence of diffuse reflection on the measurement.

Claims

1. Portable reflectometer for the characterization of mirrors of solar collectors (1) characterized in that it comprises at least the following elements:

A module that carries out the measurement of the coefficient of the reflection of the mirror (13);

An electronic system for acquiring and processing signals (12);

A data processing and equipment control system (14);

A system for storing relevant data (15);

A user interface system (23);

A system for the communication between the above systems (12, 13, 14, 15,23);

An exterior casing.

2. Portable reflectometer according to claim 1, characterized in that each one of the modules (13) that carry out the measurement of the coefficient of the reflection of the mirror comprises at least one light emitting diode (2) as optical source and two photodetectors (3, 4) sensitive to the appropriate wavelengths.

3. Portable reflectometer according to claim 2, characterized in that the photodetectors (3, 4) are followed in two steps of amplification (19) whose gain depends on the value of the resistances that they have.

4. Portable reflectometer according to claim 3, characterized in that at least one of the amplification steps may have a gain that can be varied at any moment via software commands.

5. Portable reflectometer according to claim 2, characterized in that the number of light emitting diodes is comprised between 1 and 24 within the spectral range between 300 and 2500 nm corresponding to the solar spectrum.

6. Portable reflectometer according to claim 2, characterized in that the arrangement of the emitters, they are placed in a linear configuration.

7. Portable reflectometer according to claim 2, characterized in that the arrangement of the emitters, they are placed in a circular configuration.

8. Portable reflectometer according to claim 2, characterized in that each emitter is placed oriented in such a way that the maximum emission direction of the light beam coincides with the optical axis of incidence of the system on the mirror.

9. Portable reflectometer according to claim 8, characterized in that the output light beam of the emitter and incident on the mirror is limited in size and aperture by a diaphragm (5) to ensure the size of the area illuminated on the mirror surface, thus limiting the contribution of diffuse reflection in the measurement.

10. Portable reflectometer according to claim 9, characterized in that a lens (6) is located after the specular reflection of the beam on the mirror, oriented according to the optical axis of the system and double the size of the size of the beam on this point, focusing the light beam on the photodetector (3) in order to obtain the signal of direct measurement of the reflected power.

11. Portable reflectometer according to claim 1, characterized in that the electronic acquisition and processing system of signals (12) includes:

a synchronous detection (16) that allows to carry out the measurements with a sufficient signal to noise ratio, even in conditions of intense ambient light, an analog-to-digital converter (17) and a modulation generator (18).

12. Portable reflectometer according to claim 11 characterized in that the synchronous detection (16) is analog.

13. Portable reflectometer according to claim 12 characterized in that the modulation generator (18) is a local oscillator.

14. Portable reflectometer according to claim 12 characterized in that the analog-to-digital conversion (17) is performed with a data acquisition board DAQ or with a microcontroller.

15. Portable reflectometer according to claim 11 characterized in that the synchronous detection (16) is digital.

16. Portable reflectometer according to claim 15 characterized in that the modulation generator (18) sea a local oscillator.

17. Portable reflectometer according to claim 15 characterized in that the modulation generator (18) is any digital processing system such as a DSP (digital signal processor), an FPGA (Field Programmable Gate Array), a microcontroller capable of digital signal processing or a computer.

18. Portable reflectometer according to claim 11 characterized in that the process of the signal is performed with any digital processing system such as a DSP (digital signal processor), an FPGA (Field Programmable Gate Array), a microcontroller capable of digital signal processing or a computer.

19. Portable reflectometer according to claim 11 characterized in that the digital processing system used in the synchronous detection (16) and in the modulation generator (18) are the same.

20. Portable reflectometer according to claim 1 characterized in that the data processing and equipment control system (14) is a computer external to the portable reflectometer.

21. Portable reflectometer according to claim 20 characterized in that the communication between the equipment and the external computer is carried out via wireless means or cable.

22. Portable reflectometer according to claim 20 characterized in that the data storage system (15) is located in the computer external to the portable reflectometer.

23. Portable reflectometer according to claim 20 characterized in that the user interface system (23) is located in the computer external to the portable reflectometer.

24. Portable reflectometer according to claim 1 characterized in that the data processing and equipment control system (14) is a system built into the equipment itself.

25. Portable reflectometer according to claim 24 characterized in that the system built into the equipment itself replaces at least one of the components used also in the system processes for acquisition and processing of the signal (12), these components being the synchronous detector (16), the analog-to-digital converter (17) and the modulation generator (18), as well as those of the storage system (15) and those of the user interface system (23).

26. Portable reflectometer according to claim 24 characterized in that the system built into the equipment itself replaces the storage system (15) and/or the user interface system (23) carrying out their functions.

27. Method of characterization of mirrors of solar thermal power plants making use of the portable reflectometer of the previous claims characterized in that the measurement of the coefficient of the reflection of the mirrors comprises the following steps:

1. Position the equipment a way in which it is stably supported on the mirror.

2. Turn on the equipment emitters.

3. In a consecutive way, each one of the LED emitters is modulated to the measurement frequency.

4. This output LED emitter beam in the direction of the mirror is limited in numerical aperture by a diaphragm (5) in order to ensure the size of the beam on the mirror surface.

5. The beam generated by the LED emitter (2) is specularly reflected in the mirror surface.

6. The specular reflection of the beam on the mirror is collected by the lens (6) of double the size of the beam at this point. This lens (6) is oriented according to the optical axis of the system, and focuses the light beam on the direct light measurement detector (3).

7. On the other hand, the system obtains a reference signal from the measurement of the part of light emitted by the LED in the other different direction, by means of the detector (4).

8. The data obtained in the reflection detector corresponding to the modulated LED is normalized with its reference signal, in order to eliminate the influence of variations in the intensity of emission of each LED.

9. Subsequently, the coefficient of the reflection of the mirror for each wavelength is obtained. This final value of the coefficient is obtained also by a known standard reference.

10. The values corresponding to the standard are stored in the equipment after a prior calibration, which requires the use of a mirror with known reflection coefficients. This calibration is performed following the first eight steps of this procedure itself.

11. Subsequent processing of the acquired information, basically consisting in obtaining the values of the reflection coefficient for each of the wavelengths from the relation between the direct signal and the reference signal prior to calibration using standard.

12. Obtaining the overall values of reflectance by weighting the values obtained in each wavelength with the weight corresponding to said wavelength in the solar spectrum.

28. Method of characterization of mirrors according to claim 27 characterized in that the light beam reflected on the mirror is collected directly by the photodetector (3) without making use of the lens (6) in order to obtain the signal of direct measurement of the reflected power.

29. Method of characterization of mirrors according to claim 27 characterized in that the measurements of reference signal and y reflected signal are measured simultaneously for each wavelength.