SYSTEM FOR THE REAL-TIME HIGH PRECISION MEASUREMENT OF THE ATMOSPHERIC ATTENUATION OF ELECTROMAGNETIC RADIATION FROM AT LEAST ONE SOURCE AND METHOD FOR MEASUREMENT

Abstract

A system for measurement of monochromatic attenuation for each wavelength of the spectrum, understood as such the attenuation at a wavelength of the spectrum with the spectral width provided by the measurement equipment, of the spectral attenuation in the spectral range of measurement, understood as such the set of monochromatic attenuations at all the wavelengths throughout the spectral range of measurement, and the total attenuation, understood as such the attenuation calculated by the integration of the spectral attenuation in the spectral range of measurement weighted with the solar spectrum. A method for measurement, providing measurement of attenuation in the entire spectral range for the best energy system efficiency evaluation and for achieving a differential measurement of meteorological phenomena causing the attenuation, providing relevant information for the meteorological forecast in this specific field, which can be used for evaluating the attenuation phenomenon for solar plants site selection and for operating plants.

Claims

1.-17. (canceled)

18. A system for the real-time spectral width resolution measurement of the atmospheric attenuation spectrum of electromagnetic radiation, characterized in that it comprises: at least one electromagnetic radiation source, at least two reflective telescopes for the capture of a beam of the radiation from only said source which are located at different distances from said source, each telescope comprising a diaphragm between the telescopic objective and the eyepiece to limit the angle of acceptance of the telescope and avoid the capture of light that comes from outside the radiation source of the system, at least one system for optical alignment of each telescope with the source, at least one photodiode array spectrometer as real time detection and measurement device (23, 24), optically connected to each of the telescopes to provide of the radiation in the solar spectral range between 300 nm and 1650 nm, splitting means for splitting the beam of radiation after each eyepiece to take one part of the beam to the at least one array spectrometer and another part of the beam to the system for optical alignment of each telescope with the source, and at least one processor for the communication between the spectrometers; for analyzing the aforementioned measurements from the signals detected by the spectrometers; as well as for inferring the solar energy attenuation in the distance between the telescopes through the difference, in real-time, of the spectral energy that strikes in said telescopes; and for calculating, in said distance between the two telescopes: the monochromatic atmospheric attenuation for each wavelength of the spectrum, the relative spectral atmospheric attenuation, by comparing the spectral curves obtained from the measurements of each detection and measurement device (23, 24), the absolute spectral atmospheric attenuation, and the global attenuation from this attenuation spectrum, such that the global attenuation is calculated by the integration of the spectral attenuation in the spectral range of measurement weighted with the solar spectrum.

19. The system according to claim 18, characterized in that the beam captured by the telescopic optical device is split by the splitting means into as many beams as there are detection and measurement devices connected to the optical device, said beams being guided to and focused on said detection devices, each device covering a different region of the spectral range to be measured.

20. The system according to claim 19, characterized in that the beam is split by optical beam splitters.

21. The system according to claim 19, characterized in that the beam is split by multifibers.

22. The system according to claim 18, characterized in that the detection and measurement devices are monochromators.

23. The system according to claim 18, characterized in that the system for alignment comprises a digital camera to enable displaying the captured image of the source.

24. The system according to claim 18, characterized in that it comprises a reflective screen as a source which reflects the sunlight towards the telescopic optical capture devices.

25. The system according to claim 24, characterized in that it comprises an absorbing screen, located close to the reflective screen, for excluding the background light from the measurement.

26. The system according to claim 18, characterized in that the telescopic optical device comprises an angle of acceptance equal to or less than the angle subtended by the source on said device.

27. The system according to claim 24, characterized in that it comprises an heliostat that reflects the sunlight to the reflective screen and this one towards the telescopes.

28. A method for the real-time measurement of the atmospheric attenuation of electromagnetic radiation from a source by a system for measurement according to claim 18, characterized in that it comprises the following steps: a) aligning at least two telescopic optical devices, located at different distances from the source, towards the source of electromagnetic radiation, b) capturing a beam of electromagnetic radiation by means of each of the telescopic optical devices, c) detecting and taking monochromatic measurements in the various spectral regions covered by the captured detection and measurement devices, and d) calculating atmospheric attenuation in real-time by comparing monochromatic spectral measurements.

29. The method according to claim 28, characterized in that before aligning the devices towards the source of electromagnetic radiation, said devices are aligned with an absorbing screen to measure the background light and subsequently consider the excluding the background light from the measurement.

30. The method for measurement according to claim 28, characterized in that after calculating atmospheric attenuation, it comprises a step of applying spectral analysis and spectroscopic techniques to identify and discern the phenomena causing the previously calculated atmospheric attenuation.

31. The method according to claim 28, characterized in that before aligning the telescopic optical devices a calibration process is performed for the detection and measurement devices by locating the telescopic optical devices at the same distance from the source of electromagnetic radiation.

Description

DESCRIPTION OF THE DRAWINGS

[0055] The following drawings are attached to the present description and show a preferred embodiment of the invention in an illustrative and non-limiting manner:

[0056] FIG. 1 shows an extraterrestrial solar radiation spectrum (top curve) along with spectra at the terrestrial level for various concentrations of atmospheric water vapor. It also shows the water vapor transmittance in the upper right-hand part.

[0057] FIG. 2 shows a preferred diagram of an embodiment of the system for the measurement of the attenuation of solar radiation object of the invention.

[0058] FIG. 3 shows a second preferred diagram of an embodiment of the system for the measurement of the attenuation of solar radiation object of the invention in which an absorbing screen is included.

[0059] FIG. 4 shows a preferred diagram of a telescopic optical device for capturing a light beam.

[0060] FIG. 5 shows a preferred diagram of the detection and measurement device equipped with splitters.

[0061] FIG. 6 shows a preferred diagram of the detection and measurement device equipped with multifiber.

[0062] FIG. 7 shows the measurements spectroscopic taken by the reference device and the measurement device for calculating the spectral attenuation (intensity in arbitrary units, a.u., with respect to wavelengths).

[0063] FIG. 8 shows the variation between the two preceding measurements resulting in the existing spectral attenuation (variation in % with respect to wavelengths).

PREFERRED EMBODIMENT

[0064] As previously mentioned, the present invention relates to a system and method for the measurement of the atmospheric attenuation of electromagnetic radiation, in a differential and precise manner at each wavelength, i.e., in a spectral manner, allowing the characterization of the phenomena causing same, in the space comprised between various points.

[0065] The proposed system (FIGS. 2 and 3) is preferably made up of a useful source of emission 40 of electromagnetic radiation and at least two devices 10, 20 for capturing the radiation emitted by said source separated from one another and at different distances from the mentioned source 40. The useful source of emission of electromagnetic radiation can be both artificial and natural (the sun as both the direct and the reflected source). The optical devices 10, 20 for capturing electromagnetic radiation must be telescopic and assure the capture of electromagnetic radiation coming from only the mentioned source 40, which is achieved by adapting the angle of acceptance (maximum angle at which the incident light ray is trapped) to the geometric considerations of the system (size of the source and distance between the source 40 and the detecting devices 10, 20). Preferably the useful source will be a screen 40 which reflects the direct sunlight beam from the sun 60 or a light beam previously reflected by at least one heliostat 50. For example, the angle of acceptance (a) is 1 mrad, the angle of acceptance (a) being, as defined above, the largest angle at which the rays from an object or source strike the detection system and are detected by said detection system.

[0066] The reference telescopic optical device 10 and measurement device 20, each arranged at a different distance D from the source 40, preferably have a telescopic objective 11, followed by a field diaphragm 12 determining the focal length 1 of the device 10, 20, followed by an eyepiece 13 to amplify the signal and form the image (FIG. 4). After the eyepiece 13 either a beam splitter 15 (FIG. 5) or multifibers 25 (FIG. 6) can be used for splitting and directing the captured signal towards each detection and measurement device 23, 24.

[0067] Should be pointed out the use of reflecting telescopes (which make use of mirrors instead of lenses for focusing the light and imaging), which prevent the angle of acceptance (α) from changing with the wavelengths. The telescopic optical devices 10, 20 could use a refracting type telescope.

[0068] The electromagnetic radiation coming from the source 40 captured by the telescopic optical devices 10, 20 will be conducted to at least one real-time detection and measurement device 23, 24 associated with each telescopic optical device 10, 20 (FIGS. 2 to 6), which will provide simultaneous real-time measurements of the spectrum thereof and in a spectral range that is broad enough for the considered application, preferably between 300 nm and 1650 nm (see FIG. 7). The comparison of the spectral curves obtained from the measurements of each detection and measurement device 23, 24 will provide as a result the relative spectral atmospheric attenuation of the electromagnetic radiation considered (see FIG. 8). Performing a prior calibration between both optical devices 10, 20 allows obtaining the absolute measurement of spectral attenuation.

[0069] According to a preferred embodiment (FIG. 2), and as discussed, as a source of emission of electromagnetic radiation the invention proposes the actual sunlight 60 reflected in a hemispherical manner by a light diffusing white screen 40 located at the maximum height at which the measurement of the attenuation will be taken along with a telescopic optical light device 10 close to the source and acting as a reference measurement of the light signal located at the level of the ground and to a telescopic optical device 20 located farther away from the source and acting as a measurement of the attenuated light signal by the atmosphere also located at the level of the ground. Additionally, the energy reflected by said screen 40 can be increased, causing solar energy reflected by one or more heliostats 50 to strike it. According to said preferred embodiment, the screen 40 is located at the height of the receiver of a concentrating central receiver (or tower 30) solar power plant, and the telescopic optical devices 10, 20 associated with their detection and measurement devices 23, 24 for detecting and measuring the attenuated light signal are located at two distances with respect to the central receiver in the solar field, for example at 300 meters (reference device 10) and 1600 meters (measurement device 20) from the source 40. These distances can vary depending on the size of the solar field or other conditioning factors.

[0070] Using the sun 60 as a light source simplifies the optical system and assures a spectral distribution and range suitable for modeling the attenuation phenomenon at the actual site (or any other site), for purposes of both prediction and resource estimation in the absence of recorded data.

[0071] It should be pointed out that the preferably circular or rectangular screen 40, though other geometric shapes are possible, must possess hemispherical reflectance to avoid the presence of privileged directions in reflection and thereby having a spatially uniform source. Likewise, this screen 40 must have a large enough size to assure that the telescopic optical device 20 of the attenuated light signal, the one farthest away, only captures light coming from the screen 40 and thereby avoid variable background signals which would entail uncertainties in the measurement. The size of the screen (T) must be related to the angle of acceptance (a) or inlet aperture of the optical system for the measurement 20 of the light signal and the distance (D) existing between said system 20 and the screen 40, according to the following equation:

T≥D*tan(α)

[0072] Specifically, for a distance of 1600 m and an aperture of 1 mrad, the size of the source has to be larger than a circle having a diameter of about 1.6 meters. The value of the inlet aperture of the optical system for the measurement of the light signal is determined by the focal length of the objective 11 and the field diaphragm 12. The preferred embodiment proposes that once the light signal is captured by the reference optical device 10 and by the optical measurement device 20 for measuring the attenuated light signal, they are transmitted by optical means, preferably optical fiber 21, 22 to a photodiode array spectrometer 23, 24 for the real-time measurement of the spectrum thereof simultaneously by both telescopic devices 10, 20.

[0073] To cover a sufficient spectral range in the case of sunlight, said preferred embodiment proposes the use as detection and measurement devices 23, 24 of two photodiode array spectrometers: one preferably being a silicon detector array 23 in the range of 300 nm to 1050 nm, and the other one preferably being an InGaAs detector array 24 in the range of 900 nm to 1650 nm. To enable the real-time measurement of both spectral ranges, the beam captured by each telescopic optical device 10, 20 must be split, preferably with a beam splitter 15, thought it is also possible by multifibers 25, and be focused on the optical means 23, 24, preferably the optical fiber 21, 22, 25, by means of focusing lenses 16, 18.

[0074] Furthermore, a system is needed which allows aligning telescopic systems with the screen, said system including both optical and mechanical components. This alignment requires splitting 14 the beam, before that described, to enable displaying the captured image in a digital camera 17 (preferably CCD). In a preferred embodiment, it is proposed that the telescopic systems 10, 20 are aligned towards the screen manually.

[0075] The described diagrams of both the telescopic optical device 10, 20 and the detection and measurement device 23, 24 together form the reference system and the system for the measurement of the attenuated light signal. Each of said devices provides a measurement of the spectral curve of the sunlight reflected by the screen in the range of 300 nm to 1650 nm, with a spectral width resolution of 0.5 nm, for example.

[0076] As mentioned, a possible measurement device 23, 24 is made up of the photodiode array spectrometers in which the sensors are clustered in an array, or monochromators which, from the refraction or scattering phenomenon, spatially separate the different wavelengths present in the signal. The system will thereby provide measurements of the light signal for each wavelength of the specified spectral range, that is, spectral curves of the intensity of the light signal (FIG. 7).

[0077] By the direct comparison of said curves, monochromatic atmospheric attenuation (FIG. 8) is obtained for each wavelength between 300 nm and 1650 nm with the spectral resolution of 0.5 nm of the electromagnetic radiation considered from the screen to the system for measurement. The set of all the monochromatic attenuations provide the values of the curve of the spectral attenuation of the electromagnetic radiation considered between 300 nm and 1650 nm. The values of the curve of said spectral attenuation, weighted with the spectrum of the electromagnetic radiation, provide the value of the global attenuation in the range of 300 nm to 1650 nm.

[0078] For obtaining an absolute measurement, the prior calibration between the measurements obtained by the reference system and the system for measurement must be assured, and the difference of distance traveled between the reference systems and the screen must be considered.

[0079] It should be pointed out that both the reference and the measurement signals can be contaminated by the light scattered by the atmospheric components present between the screen and the telescopic systems (for example, aerosols), defined as background light.

[0080] To characterize said background light, in another preferred embodiment (FIG. 3), the system object of the invention contemplates that the telescopic optical devices can be aligned towards an absorbing screen 45, i.e., it has a very low reflectivity (as close as possible to 0%), and particularly, much lower than that of the screen with hemispherical reflectance 40 described above (with a reflectively as close to 100% as possible) and used to provide reflected radiation to the telescopic optical devices. Therefore, the signal measured by the telescopic systems aligned towards the absorbing screen 45 can be taken into account to quantify and model the attenuation phenomenon.

[0081] The operating method of the preceding systems has the following steps: [0082] aligning at least two telescopic optical devices 10, 20, located at different distances from the source 40, towards the source of electromagnetic radiation 40, [0083] capturing a beam of electromagnetic radiation reflected in the source 40 by means of each of the telescopic optical devices 10, 20, [0084] detecting and taking monochromatic measurements in the various spectral regions covered by the detection and measurement devices 23, 24 for detecting and measuring the captured radiation (FIG. 7), and [0085] calculating atmospheric attenuation in real-time by comparing the monochromatic spectral measurements (FIG. 8).

[0086] The method preferably comprises a prior step before aligning the devices 10, 20 towards the source of electromagnetic radiation, in which the devices 10, 20 are aligned with an absorbing screen (FIG. 3) to measure the background light and subsequently consider the excluding the background light from the measurement.

[0087] Likewise, after the calculation of the atmospheric attenuation the method comprises a step of applying spectral analysis and spectroscopic techniques to identify and discern the phenomena causing the previously calculated atmospheric attenuation. Preferably also, before aligning the telescopic optical devices 10, 20, a calibration process is performed for the detection and measurement devices 23, 24 by locating the telescopic optical devices 10, 20 at the same distance from the source 40 of electromagnetic radiation.