ES2890455A1 - RADIOMETRY DEVICE AND PROCEDURE FOR THE MEASUREMENT OF SOLAR IRRADIANCE (Machine-translation by Google Translate, not legally binding) - Google Patents

Abstract

Radiometry device and procedure for measuring solar irradiance. In which the device (1) comprises an optical fiber (3), with a core (11) and a cover (12), and in which a beam of sunlight (2) falls on one end; an optical power meter module (4); and a signal processing module (5). The procedure comprises the steps of obtaining one or more measurements of optical power, {IMAGE-01}, obtaining the gross solar irradiance, {IMAGE-02} as a ratio between the optical power, {IMAGE-03} and the area of the surface of the core (11) of the optical fiber (3) exposed to the beam of sunlight (2), calculation of a correction factor, {IMAGE-04} and obtaining a measurement of solar irradiance, as the product between gross solar irradiance and correction factor. {IMAGE-05} (Machine-translation by Google Translate, not legally binding)

Description

DESCRIPTION

RADIOMETRY DEVICE AND PROCEDURE FOR THE MEASUREMENT OF

SOLAR IRRADIANCE

OBJECT OF THE INVENTION

The object of the invention falls within the Test and Measurement Instrumentation sector used in radiometry for the characterization of solar radiation, and in particular in the measurement of solar irradiance, this being the magnitude that represents the incident solar optical power on a given surface area.

Specifically, the object of the invention is a device and procedure consisting of the generalization of the pyrheliometer concept, which provides the measurement of the solar irradiance or optical flow of a beam of sunlight defined by an acceptance cone, which falls perpendicularly on a surface of a certain area.

BACKGROUND OF THE INVENTION

Solar radiation is an inexhaustible energy resource for planet Earth. The different levels of solar irradiance that affect the earth's surface are of special importance in the sectors of meteorology, astronomy, agriculture, and of extreme importance in the solar energy sector (both photovoltaic and solar thermal) for optimization, in terms of performance and efficiency of the energy production process.

In general, the solar radiation that falls on the surface of the atmosphere is characterized by its spectral density of optical flux or spectral irradiance, E ( A), with units of W • m_2 • Hz_1 (or W • m_2 • nm"1 ), which is distributed in a spectral range that goes from 300 nm to 4000 nm, approximately From E ( A) the solar irradiance, E, with units of W ■ m~2, is defined as the integral of the spectral irradiance throughout the entire spectrum, and therefore characterizes the intensity of solar radiation per unit area.The solar irradiance that reaches the surface of the atmosphere takes values of 1367 W • m~2 according to the WRC ( World Radiation Center ), 1373 W -m ~ 2 according to the WMO ( World Meteorological Organization ) and 1353 W ■ m ~ 2 according to NASA ( National Aeronautics and Space Administration).

However, the intensity of solar radiation that falls on the earth's surface is less as a result of the absorption and scattering processes that a beam of sunlight undergoes when passing through the atmosphere. In this sense, the solar irradiance that falls on each point on the earth's surface depends both on its geographical location and on the time instant of measurement, due to multiple factors such as: the distance from the Earth to the Sun, which varies along all year; the different atmospheric agents, such as clouds, which produce a dispersion of the beam of sunlight; the percentage of atmospheric humidity that determines a series of absorption bands in the solar spectrum; and, air pollution; among others; which together translates into a modification of the particular spectral irradiance for any location on the earth's surface and time of day.

Therefore, the solar irradiance incident on any point on the earth's surface varies over time and is denoted by E ( t). Depending on the origin and source of the incident sunlight beam at the measurement point, three types of measurement are defined for solar irradiance:

- Direct Normal Irradiance or DNI ( Direct Normal Irradiance ), for the beam of sunlight coming directly from the Sun and which is measured by a pyrheliometer mounted on a solar tracker.

- Diffuse Horizontal Irradiance or DHI (from the English Direct Horizontal Irradiance ), for the solar radiation coming from the entire sky except that which comes directly from the Sun (that is, the DNI), and which is measured by means of a pyranometer with a shadow band to eliminate the direct sunlight beam from the Sun.

- Global Horizontal Irradiance or GHI ( Global Horizontal Irradiance English ), which considers all solar radiation from the sky and is generally measured with a Pyranometer with a horizontal sensor.

These measurements of solar irradiance are those used in meteorology applications, and their specific definitions are subject to the specifications of the International Organization for Standardization (ISO ) and the World Meteorological Organization (WMO or WMO).

On the other hand, the solar energy sector, both photovoltaic and solar thermal, makes use of these measurements (mainly the DNI) to monitor the solar irradiance that affects solar panels and heliostats. However, in concentrated solar applications, the measurement and monitoring of the concentrated solar flux is also very important in order to be able to operate the solar plant in the optimal conditions of maximum performance, efficiency and safety. In this sense, the measurements of solar irradiance from concentrated solar flux they are much more demanding both from the point of view of magnitude and dynamic range, as well as extreme operating and operating conditions.

The three key elements or components that make up a solar irradiance measurement device are: the structure or device that determines the acceptance cone for solar radiation; the surface or area of incidence of solar radiation; and, the detector for the measurement of the optical power incident on the surface of a determined area. These three elements are determined by the different configurations of the measuring device, which generally includes a solar radiation capture element and a detector. The most critical element is usually the detector, for which there are two alternatives in the state of the art:

- Thermal detectors or thermopiles, which convert the thermal energy captured from the beam of sunlight into electrical energy. They are normally made up of thermocouples connected in series or parallel that do not respond to an absolute temperature, but instead respond to a temperature gradient by generating a voltage. Their main advantage is that they present a measure of optical power with a wide spectral width and does not depend on the wavelength. The measurement can self-calibrate providing an accuracy of the order of 1%. As a drawback, it presents a very poor sensitivity (typically of the order of 10p,W).

- Semiconductor photodetectors, which capture optical radiation by converting photons into electron-hole pairs, and, therefore, converting optical power into electrical current. The main advantage of semiconductor photodetectors is their excellent sensitivity (even below 1pW), a wide dynamic range, an accuracy of around 2%, less complexity, less maintenance and lower cost. However, they have the drawback that the optical power measurement they provide depends on the wavelength and that semiconductors are not sensitive to the entire spectral range of solar radiation, that is, that the bandwidth of the semiconductor's responsivity it is less than the spectral width of the solar radiation to be measured, so the optical power measurement is less precise and requires a calibration process. The reverse-biased junction photodiode and the photovoltaic cell working in the region near the short circuit are used as semiconductor photodetectors.

In the meteorology sector, the most used instruments for measuring solar irradiance are:

- Thermopile pyranometer, designed for the measurement of solar radiation in a wide bandwidth thanks to the fact that the thermopile has a practically flat sensitivity in the spectral range between 300nm and 2800nm. They provide a very high precision measurement for GHI and DHI (if shadow band is included).

- Pyranometer based on photodiode, or also known as Silicon pyranometer (since Silicon is the semiconductor that presents the greatest responsiveness in the maximum solar spectral irradiance). Said pyranometer detects the portion of the spectrum between 400nm and 800nm for photovoltaic cell-based photodetectors, or between 350nm and 1100nm for reverse-biased junction photodiode-based photodetectors.

- Thermopile-based pyrheliometer for the measurement of the DNI, composed of a cavity responsible for capturing the beam of sunlight within an acceptance cone (generally an acceptance angle of 2.5° is established) that falls on a thermopile that converts thermal energy into a voltage difference.

In the concentrating solar energy sector, there are two sensors for measuring concentrated solar irradiance or concentrated solar flux: the Gardon radiometer and the HFM sensor. Both sensors base their operating principle on thermopiles and are characterized by having an incidence surface around 25mm in diameter and a dynamic range of measurement between 0 and 50 MW -m~2. They are very sensitive, they need a cooling circuit to be able to operate in very high temperature conditions and they have a very high cost.

In the state of the art of the technique, other instruments have been presented for the measurement of solar irradiance. An instrument for measuring the GHI is known, integrating an optical fiber together with a diffuser as a solar radiation capture element and a Silicon photodetector for measuring the optical power, with the purpose of placing the photodiode far from the point of measure and ensure controlled solar irradiance measurement conditions.

The objective pursued by this instrument is not to expose the photodiode directly to solar radiation, and for this it uses an optical fiber to conduct the solar radiation from the measurement point to the laboratory facilities where the photodiode is located with stable working conditions. . The end of the optical fiber located at the measurement point incorporates a diffuser to approximate a cosine law response to incident solar radiation and protects it from atmospheric conditions by means of a glass bulb. In this way, a measurement of the GHI is carried out using a measurement method using calibration factors that depend on the different masses of air that the beam of sunlight passes through.

However, this proposal does not use the properties of the optical fiber defined by the numerical aperture that characterizes an acceptance cone and, therefore, capable of being used for the measurement of the DNI. In this work, the problems of the spectral selectivity of the silicon photodetector, which does not cover the entire spectral range of the light, becoming a source of error, as well as the variations in the spectral irradiance of the light due to the location, are indicated. altitude and atmospheric conditions.

Other proposals related to the measurement of irradiance that separate the solar radiation capture element and the photodetector are the patent application for the measurement of the angle of incidence of solar radiation ES2597982 and for the detection of incident radiation in a solar receiver W02016/ 110606A1. Both proposals present a system and method for detecting solar radiation based on a radiation capture element consisting of a quartz rod with a diameter between 1 mm and 4 mm as an optical waveguide.

The objectives of these two proposals are: one, the measurement of the angle of incidence of the light radiation in the capture element from the circular crown that is obtained at the output of the quartz rod; and two, the detection of concentrated solar flux in the tower receiver of a solar thermal power plant by placing the quartz rod through the solar receiver panels in the area exposed to concentrated solar radiation (withstanding operating temperatures of up to 1000°C ), with the purpose of conducting said radiation towards the rear area of the solar receiver, already with lower temperatures, where a measurement module for guided radiation is located. The measurement module contemplates the options of using either a photodetector, an array of photodetectors, or a CCD matrix.

However, the system and method contemplated in these proposals do not show the procedure for obtaining a quantitative measure of the irradiance of the incident light beam. Obtaining a quantitative measure of solar irradiance ( W ■ m~2) is not direct or immediate since it will depend on the spectral irradiance of the incident radiation, the surface of incidence, the losses that the radiation may suffer in its guided to the optical detection module, and the spectral response of the optical detection module.

On the other hand, these proposals consider the possibility of using optical fiber as an optical waveguide to conduct optical radiation from the sensor element to the optical power measurement module, although its use is neither direct nor obvious due to the intrinsic considerations that fiber presents. optics in terms of its core and shell construction characteristics (refractive indices necessary to ensure the principle of total reflection internal), different dimensions of the core and cover (and therefore, different incidence surfaces, as well as the possible single-mode or multimode behavior), and numerical aperture characteristic that translates into a certain cone of acceptance for the incident radiation.

DESCRIPTION OF THE INVENTION

The object of the present invention is a radiometry device and method for measuring the solar irradiance of a light beam. The device comprises an optical fiber, with a first end on which a light beam is incident. The optical fiber comprises a core, a jacket and optionally a coating. The light beam falls on the surface delimited by the nucleus and within the acceptance cone that delimits its numerical aperture. Solar radiation coupled to the optical fiber within these specifications (acceptance cone and fiber core area) is taken to the opposite end of the fiber where the optical power is measured by an optical power meter module, which it will preferably comprise a semiconductor photodiode.

A first approximation of the measurement procedure for solar irradiance at the measurement point (end of the optical fiber exposed to the beam of sunlight) is the ratio between the optical power measured by the measuring module and the area of the optical fiber core. ( W ■ m~2). The advantages of this proposal lie in the fact that the different designs of the optical fiber allow controlling both the cone of acceptance of solar radiation from the numerical aperture characteristic of the optical fiber and the incidence surface through the core area.

Making use of geometric optics, all the light rays contained within the acceptance cone that strike the core area of the optical fiber exposed to solar radiation are guided by it to its other end with very low losses, to measure its optical power using the meter module.

The advantages of using an optical power meter module's semiconductor photodiode lie in its stability, linearity, low maintenance, and low cost, as well as its excellent sensitivity in adapting to low optical power levels coupled to the fiber optic core of dimensions micrometric. On the other hand, the reduced dimensions of the optical fiber allow it to be integrated into the solar receivers of solar thermal power plants. of concentration whenever special optical fibers are used to work at high temperatures.

Therefore, the radiometry device for the generic measurement of solar irradiance comprises:

- an optical fiber as a radiation capture element to take advantage of its small size characteristics, definition of an acceptance cone based on its numerical aperture, definition of the radiation incidence surface based on the core area, optical guidance properties of very low losses, and versatility of different designs and configurations,

- as a solar radiation detector element, an optical power meter module preferably comprising a semiconductor photodiode, which provides characteristics and properties of high sensitivity compatible with the low levels of optical power coupled to the optical fiber due to the reduced size of the core , low cost, linearity and stability, low maintenance, and fast response time, and - additionally, the device may comprise a processing module, connected to the measuring module and configured to process and send the measurements obtained by the module to an external equipment measurer.

The present invention also defines a measurement procedure based on obtaining the quotient between the optical power measured by the optical power meter module and the area of the optical fiber core, thus obtaining, in a first approximation, a measurement of optical irradiance ( W ■ m~2).

Specifically, the procedure takes as input, in a first stage, the optical power value measured by the measuring module and the processing module, and the area of the optical fiber core, and calculates a first approximation of the solar irradiance as the quotient of the optical power measured by the surface area of the nucleus.

In a second stage to this first approximation of the Solar Irradiance, a correction or calibration factor is calculated that takes into account the limited spectral response of the semiconductor photodiode, the pattern of the spectral distribution of the incident solar radiation, and the losses that introduces the optical fiber in the optical radiation guide from the point of measurement or fiber coupling to the semiconductor photodiode (or optical power meter module).

In a third stage of the procedure, the calibration process is carried out by correcting the first approximation of the solar irradiance by means of the correction or calibration factor (calculated in the second stage), thus obtaining the measurement of the final solar irradiance.

The invention therefore consists of a complementary measurement device and measurement procedure that, while maintaining levels of simplicity of assembly and maintenance, achieve an improvement in the performance of current products, such as very fast response dynamics, versatility and flexibility. in the design of the acceptance cone for solar radiation, greater dynamic range associated with the possibility of working with different sizes of the optical fiber core, greater sensitivity thanks to the use of semiconductor photodiodes, less complexity, and lower cost.

DESCRIPTION OF THE DRAWINGS

To complement the description that is being made and in order to help a better understanding of the characteristics of the invention, according to a preferred example of its practical embodiment, a set of drawings is attached as an integral part of said description. where, by way of illustration and not limitation, the following has been represented:

Figure 1.- Shows a block diagram of the device object of the invention.

Figure 2.- Shows a detail of the end of the optical fiber exposed to the beam of sunlight, in which the definition of the acceptance cone (determined by the numerical aperture) and the surface area of the fiber core are graphically represented.

Figure 3.- Shows an example of embodiment of the device.

Figure 4.- Shows an example of the stages of the procedure for measuring the DNI throughout a day, represented by means of a flow chart.

PREFERRED EMBODIMENT OF THE INVENTION

A preferred embodiment of the present invention is described below, with the help of figures 1 to 4, which defines a procedure and a measuring device, both for the Obtaining the solar irradiance that characterizes the intensity or magnitude of solar radiation that falls on a certain point.

Figure 1 shows the block diagram of the device (1) for obtaining the solar irradiance from a beam of sunlight (2), which strikes the end of an optical fiber (3). The beam of sunlight (2) is fully characterized by its spectral irradiance E ( A) and will vary depending on the geographical location of the measurement point, as well as the instant or moment in time of the measurement (season of the year, month, day). and hour).

The device (1) therefore comprises an optical fiber (3), an optical power meter module (4) connected to the optical fiber (3), and a signal processing module (5), connected to the power meter module optics (4).

The optical fiber (3) is characterized by its dimensions 2a/2b, core (11) and cover (12) diameters respectively and represented in detail in Figure 2, the refractive indices of the core (11) and cover (12) , n1 and n2, respectively, its attenuation coefficient per unit length a ( A), and its length L.

These parameters, represented in Figure 2, determine:

- the acceptance cone for the solar light beam (2) that is coupled to the inside of the optical fiber (3) coming from the outside (air) from its numerical aperture defined as AN = sin ( 9a) = Jnf - n \, where Qa is the acceptance angle;

- the surface area of the core (11) of the optical fiber (3), Acore = n ■ a2, through which the beam of sunlight (2) enters, and is coupled, to the interior of the optical fiber (3) ; Y

- the losses suffered by the optical radiation coupled to the optical fiber (3) in its propagation along its entire length. The optical fiber (3) captures the portion of the solar light beam (2) contained within the acceptance cone determined by the optical fiber (3) and conducts it to the opposite end of the optical fiber (3) located at a distance L (suffering losses per length unit characterized by a(A)), which is directly connected to the optical power meter module (4).

The optical power meter module (4) comprises, as shown in Figure 1, a semiconductor photodetector (6) characterized by its response function called responsiveness R ( A). The semiconductor photodetector (6) provides an electrical current proportional to the optical radiation that reaches it. This electrical current is amplified and converted in voltage through a transimpedance amplifier (7) which is subsequently digitized in an analog-digital converter (8).

The optical power meter module (4) provides at its output a measure of optical power proportional to the magnitude of optical radiation that has reached its input through the optical fiber (3), said measure depending on the selected wavelength to fix the value of the responsivity^(l), which determines a conversion factor of photogenerated electrical current to incident optical power. Consequently, the optical power measured by the optical power meter (4) will be equal to:

where Amin and Amax represent the minimum and maximum values of the spectral range in which the spectral irradiance of the incident sunlight beam extends (2).

Finally, the device (1) comprises a signal processing module (5) which in turn comprises, as shown in Figure 1, a microprocessor (9) responsible for implementing the operating principle and the calibration process. of the measurement, and a data acquisition module (10) in order to be able to continuously take and store the measurements over time. The signal processing module (5) houses software that develops the steps of the measurement procedure and of the acquisition and storage of the measurements over time with a certain sampling rate.

Once obtained by the signal processing module (5) the measurement of the optical power P0 xi corresponding to the beam of sunlight (2), which within the acceptance cone of the optical fiber (3) is coupled to the core (11 ) of the same, the measurement procedure used by the measurement device (1) already described is described below, and which allows the measurement of solar irradiance to be obtained at the measurement point (end of the optical fiber (3 ) exposed to the beam of sunlight (2)).

The measurement procedure comprises three basic stages, which are described below:

- Starting data. The optical power measurement provided by the optical power meter module (4), that is, P0 xi, is taken as input data.

- Stage 1: Obtaining the gross Solar Irradiance, 0gross,xi■ Knowing the surface area of the core (11) of the optical fiber (3) exposed to the light beam, Acore , which is the coupling surface of the solar light beam (2) inside the optical fiber (3), as shown in figure 2, it is immediate to obtain a first approximation of the Solar Irradiance at the measurement point, and which is denoted as Gross solar irradiance (also gross solar flux):

- Stage 2: Calibration of the measurement - Calculation of the correction factor, FC X.. The Correction Factor necessary to calibrate the raw Solar Irradiance value takes into account three factors: one, the limited spectral response of the semiconductor photodetector ( 6) that in principle it does not cover the entire spectral range of the incident solar radiation; two, the spectral distribution of solar radiation within its total spectral range; and three, the losses suffered by the optical radiation in its propagation through the optical fiber (3) from the measurement point to its entry into the optical power meter module (4).

Considering E ( A) the spectral irradiance pattern corresponding to the beam of sunlight (2), R ( A) the responsivity function of the semiconductor photodetector (6), At the wavelength selected in the optical power meter module ( 4) for the conversion of electrical current to optical power, at ( A) the attenuation coefficient per unit length of the optical fiber (3), and L the length of the optical fiber (3), the correction factor is obtained for the calibration of the optical irradiance measurement as:

- Stage 3: Obtaining the measurement of solar irradiance, 0measurement ■ Once the calibration factor FCX has been obtained. In the measurement calibration stage, the value of the solar irradiance measurement is obtained as the product of the gross solar irradiance times said correction factor, as follows:

^{^ gross meas 0 ,X i} ■FCXi (400)

This measurement procedure can be implemented directly in the microprocessor (9) of the signal processing module (5) of the device (1), to work in real time, or indirectly through a software algorithm on a computer or external computer.

The present invention therefore combines a measurement device (1) with a complementary measurement procedure to obtain the measurement of the solar irradiance that falls on a certain measurement point defined by the fraction of solar radiation contained within the cone acceptance determined by the numerical aperture of an optical fiber (3).

An example of a specific embodiment of the present invention for the measurement of direct solar irradiance or DNI throughout a day, or full day, is presented in figures 3 and 4. Figure 3 presents an implementation of the device ( 1) of measurement of the present invention, while figure 4 shows a flow diagram of the measurement procedure that makes use of the device (1) of figure 3.

The implementation of the device (1) shown in Figure 3 comprises the optical fiber (3), the optical power meter module (4), and the signal processor module (5). The optical fiber (3) is a jumping optical fiber with a dimension index of 50/125 p,m (core (11) and cover (12) diameters, respectively), numerical aperture 0.22, which translates into an acceptance angle 12.70° (this angle defines the acceptance cone for the coupling of the solar light beam (2) inside the optical fiber (3), as shown in figure 2), attenuation coefficient per unit length a ( A), and fiber length equal to 20m.

The end of the optical fiber (3) exposed to the beam of sunlight (2) is mounted on a solar tracker (13), as shown in figure 3, in order to maintain the surface of the end of the optical fiber. (3) in a position perpendicular to the direction of incidence of the beam of sunlight (2) throughout the day, and thus ensure the condition of direct normal incidence.

The beam of sunlight (2) is characterized by its spectral irradiance pattern that determines the distribution of optical power throughout the spectrum (in this embodiment Amin is considered equal to 300nm and Amax equal to 4000nm), and which generally depends of the geographical location of the measurement point as well as the moment and instant in which the measurement is made (season of the year, month, day and hour).

The beam of sunlight (2) falls perpendicularly on the end of the optical fiber (3) exposed to the Sun, coupling a certain amount of optical radiation to its interior. This optical radiation coupled to the interior of the optical fiber (3) propagates through it, suffering optical power losses characterized by the attenuation coefficient per unit length a ( A) and the length of optical fiber (3) traveled.

The optical radiation propagated by the optical fiber (3) reaches the opposite end of the optical fiber (3), which is connected to the optical power meter module (4) responsible for measuring the incident optical power that reaches its input. .

The optical power meter module (4) comprises a Silicon photodetector (6), characterized by its responsiveness function ^ (2), a transimpedance amplifier (7) to increase the signal level, and an analog-digital converter (8 ) to digitize the measurement.

For the conversion of the photogenerated electrical current into optical power, it is necessary to introduce in the optical power meter module (4) the value of the responsivity for a specific wavelength (in this embodiment it is taken equal to 635nm), and from there that the value of the optical power measurement provided by the optical power meter module (4), PoA., depends on the selected value. The optical power value P 0 provided by the optical power meter (4) is entered as input to the signal processor module (5) in order to obtain the value of the solar irradiance measurement, which with this particular configuration of the device (1), corresponds to the DNI.

The signal processor block (5) houses software that executes the steps of the measurement procedure in its microprocessor (9), implementing the measurement operation principle and the correction factor calculation procedure for its calibration. Likewise, the data acquisition module (10) is in charge of taking the DNI measurement over time with a determined sampling rate and storing it.

The measurement procedure object of the invention is graphically represented in Figure 4, showing the three stages of which it is composed by means of a flow diagram. The measurement procedure is implemented in the signal processing module (5) in order to be able to work in real time.

The measurement procedure takes as input data the optical power measurement provided by the optical power meter module (4) continuously over time, Po A.(í), as indicated in the block diagram of flow of Figure 4, labeled “MEASURE”. A detail of the measurements carried out throughout a day is represented inside this block to indicate the magnitudes of optical power (y axis) acquired and the temporal resolution (x axis).

In step 1 of the measurement procedure, the measurement operation principle is implemented to obtain a first raw estimate of direct solar irradiance, denoted as DNlbrutaXi ( t), using the PoA.(t) measurement provided by the optical power meter module (4), and the surface of the core (11) of the end of the optical fiber (3) exposed to the beam of sunlight, A core, which in this case is equal to 1.9635 • 10-9 m2 . In the block labeled "1" (Block 1) of Figure 4, this magnitude is represented throughout the entire daylight hours of a specific day.

In step 2 of the measurement procedure, the correction factor necessary for the calibration of the magnitude of the gross direct solar irradiance, calculated in the previous step, is numerically obtained. To calculate this correction factor FC¿., the spectral irradiance pattern of the solar light beam (2), the attenuation coefficient per unit length and the length of the optical fiber (3), the characteristic responsivity curve of the Silicon photodetector (6), and the wavelength, 2¿, selected in the optical power meter module (4) for the measurement of the optical power P0 xi.

Using expression (300), in Block 2 of the measurement method, the correction factor FC X. is calculated, which in this embodiment of the invention remains constant for the entire measurement day and is equal to 1.2997.

Step 3 of the measurement procedure takes as input the value of the gross direct solar irradiance provided by Block 1, DNIbrutaX. ( t), and using the correction factor FCX. obtained in Block 2, calculates the value of the measurement of direct solar irradiance DNI ( t) through the calibration procedure given by expression (400). Therefore, at the end of Block 3 of the measurement procedure, represented in Figure 4, the measurement of the direct solar irradiance function is obtained, 0measured ( .t) or DNI ( t), throughout the entire day of a specific day.

The embodiment of the present invention that combines the measurement device (1) of Figure 3 with the measurement procedure of Figure 4 provides the measurement of the direct solar irradiance of the beam of sunlight (2) throughout the entire sunny day of a specific day. Said measurement provides the absolute value of the magnitude of the DNI, as well as its variations over time, with a temporal resolution that allows detecting atmospheric changes such as the passage of clouds or the like, with an immediate response time thanks to the optical nature of the device operating principle.

Claims (8)

Radiometry device (1) for measuring solar irradiance comprising: - an optical fiber (3), comprising a core (11), and in which a beam of sunlight (2) falls on one end, - an optical power meter module (4), connected to the optical fiber (3) at an end opposite the end on which the beam of sunlight (2) falls, and - a signal processing module (5), connected to the optical power meter module (4). 2. - The device (1) of claim 1, wherein the optical power meter module (4) comprises a photodetector (6) configured to provide an electric current proportional to optical radiation received from the optical fiber (3) . 3. - The device (1) of claim 2, wherein the optical power meter module further comprises a transimpedance amplifier (7) connected to the photodetector (6) configured to convert the electrical current generated by the photodetector (6). 4. - The device (1) of claim 3, further comprising an analog-digital converter (8) connected to the transimpedance amplifier (7) and configured to digitize the voltage signal generated in the transimpedance amplifier (7). 5. - The device (1) of claim 1, wherein the signal processing module (5) further comprises a microprocessor (9). 6. - The device (1) of claim 1, further comprising a data acquisition module (10) connected to the optical power meter module (4) and configured to continuously take and store optical power measurements and results , over time. 7. - Radiometry procedure for the measurement of solar irradiance, which includes the stages of: - obtaining one or more measurements of optical power, Po Xi of a beam of sunlight (2) incident on one end of an optical fiber (3) with a core (11) defining a surface area exposed to the beam sunlight (2), - conversion, by means of a photodetector (6), of the optical power, P0xi , into an electric current proportional to the optical power, - obtaining a gross solar irradiance, 0gross,M > as a quotient between the optical power, P0 xi and the area of the exposed surface of the core (11) of the optical fiber (3), A core, according to the equation: 0,Aj 0 _gross,Ai A, - calculation of a correction factor, FQ. , - Obtaining a measurement of solar irradiance, 0measured, as a product between the gross solar irradiance and the correction factor, according to the equation:

8. The method of claim 7, wherein the correction factor is obtained according to the equation:

where E(A) is a spectral irradiance pattern corresponding to the beam of sunlight (2), ^(A) is a function of the photodetector's responsiveness (6), A¡ is a wavelength selected for the conversion of electrical current to optical power , a(A) an attenuation coefficient per unit length of the optical fiber (3), and L the length of the optical fiber (3).