WO2019008206A1 - Autonomous system for recording solar irradiance - Google Patents

Abstract

Low-maintenance system to record solar irradiance comprising a pyranometer (1) with ventilation (4, 5), a shadowband (6) and a structure (18) with movable supports (7, 8, 9). The system is designed to operate autonomously with cleaning means to clean the sensor (1) by blowing compressed air (51, 52, 53, 54, 26) and brushing (28, 29); guiding means (10, 11, 20, 21) for the shadowband (6) and a protection arm (22); power supply means that include a battery (32) and a solar panel (16); control means with a control board (40) coupled to the guiding means to establish the position of the shadowband (6) relative to the sensor (1) and establish measurement intervals for the sun, shadow and inactivity according to the geographical position, calendar date, time of day and response time of the pyranometer (1). Acquisition means record the measurements taken and store them in a memory (46).

Description

 AUTONOMOUS SYSTEM TO REGISTER SOLAR IRRADIANCE

DESCRIPTION

Technical sector of the invention

The present invention belongs to the field of measurement of solar irradiance. Especially, the invention relates to a device for measuring and recording solar irradiance and other meteorological variables for use in places of difficult access, capable of operating autonomously and with low maintenance.

BACKGROUND OF THE INVENTION

Large-scale solar plant projects require prior knowledge of existing solar resources in areas where they can be implemented with a guarantee. This requires a historical data bank of the conditions of the solar irradiance of the place, that endorse the credits and helps necessary for the construction of the solar plants.

At present, there is a great lack of data on solar irradiation in large and large areas of the planet. For this reason, data taken from satellite are used in combination with field data to estimate interannual variability and long-term mean values. But this brings uncertainty because it is the measurements taken on land that have the greatest precision.

For this reason it is necessary to take data on land for years to know the potential of solar energy in different areas of the planet that may be attractive for the installation and operation of large-scale solar plants.

Solar concentration technologies require historical measurements of direct solar radiation, DNI (Direct Normal Irradiance) which, unfortunately, are very scarce and require specific instruments such as:

^* Pyrheliometers, permanently oriented to the sun by solar trackers specially designed for it. ^* Radiometers with rotating shadow band, RSR (Rotating Shadowband Radiometer),

In short, as indicated above, solar concentration technologies use direct solar irradiation, DNI, so that, through the use of mirrors, high concentrated solar energy flows can be obtained in order to produce, through thermal processes at high temperature, large amounts of electrical energy among others, efficiently. For this reason, it is necessary to know the historical levels of direct solar irradiance in the most important locations for its implantation, as well as its continuous measurement during the periods of their production.

For the accurate measurement of direct solar irradiance, DNI, very expensive instruments are commonly used, called as indicated above, pyrheliometers, as well as more or less sophisticated solar trackers that require continuous and complicated maintenance. These teams need to be permanently oriented to the sun with great precision by solar trackers in one or two axes that require at least one daily maintenance to ensure the aiming and cleaning, which complicates its continued use in remote areas or difficult to access. The followers in an axis are more economical and simple but the follow-up is not perfect and requires the presence of an operator, at least twice throughout the day, in order to adjust the score due to the daily variation of the solar declination and to condition the equipment cable that usually rolls when turning. Other tracking systems work in two axes achieving a much more precise aiming, requiring less maintenance and human presence, but they are much more expensive and sophisticated.

Other equipment used for the measurement of direct solar irradiance, DNI, are the Rotating Shadowband Radiometer, RSR, which are cheaper and require less care but are more inaccurate since they currently use a silicon photodiode whose response is limited to a small part of the solar spectrum, visible light and near infrared, and are very dependent on the ambient temperature. His insensitivity, apart from Solar spectrum, makes them inaccurate and dependent on atmospheric conditions determined by the presence of aerosols, moisture, CO2 and other components.

These devices use a single sensor for the measurement of the three components of solar irradiance (direct, global and diffuse), which obtains a measurement of horizontal irradiance in sun and shadow conditions, by rotating a band, which causes a shading to the passage of the sensor.

Depending on the denomination or type of sensor used, these devices are also called Rotating Shadowband Pyranometer, RSP, or Rotating Shadowband Irradiometer, RSI.

Through the knowledge of the horizontal global irradiance, GHI, obtained from the measurement of the sensor under sun conditions, and the horizontal diffuse irradiance, DHI, obtained in shaded conditions, the direct irradiance value, DNI, can be determined by means of the formula:

DNi = (GHI - DHI) / SINE (a); Where α is the solar height in radians.

Currently there are several devices / products on the market with similar characteristics that are called "Rotating Shadowband Radiometer", RSR. The best known are: · Model RSP-4G (Rotating Shadowband Pyranometer) of "Reichert GmbH"

• Model RSR-2 (Rotating Shadowband Radiometer) from "Irradiance, Inc."

• Twin-RSI Model (Rotating Shadowband Irradiometer) from "CSP Services GmbH" · Model: SDR-1 (Single Detector Rotating Shadowband Radiometer) from "Yankee Environmental Systems, Inc."

All these devices use a photodiode as a sensor element, which is generally the LICOR-LI200 model. This type of sensors are characterized by their high sensitivity and small response time, which allows them to adapt to rapid and abrupt variations in solar irradiance. This feature is used to take measurements of solar irradiance in conditions of sun and shade before the passage of a narrow band that shadows the sensor during its rotating movement for a moment.

The band is a thin metallic arch that performs a rotating movement, describing a sphere in the center of which is the sensor. The arc rotates moved by an electric motor in a cyclic way, shading in its passage and for a moment the sensor in each described turn.

Usually the axis of rotation of the sphere is inclined at an angle to the horizontal, equal to the latitude of the place, so that the device is aligned with the Earth's equator. The sensor, in each round, takes a measurement in the periods of sun and shadow for the determination of the global and diffuse irradiance. The equipment has a timer to perform the measurements in the programmed times that usually range between 5 and 60 seconds.

The rapid response of the sensor, in the order of milliseconds, simplifies the system of movement of the shading band and limits it to a continuous rotation every time interval established. However, the sensor used in these devices has a limited response throughout the solar spectrum, being sensitive only to visible light and near infrared, which makes it inaccurate in the presence of elements in the atmosphere that absorb certain lengths of wave and alter the passage of solar radiation in non-sensitive areas by the sensor.

Dirt is a factor that must be avoided in order to measure the irradiance correctly, so daily maintenance of the same is necessary. The aforementioned equipment does not have active cleaning and self-protection systems.

Description of the invention

In view of the foregoing, it would be desirable to have a solution capable of recording the solar irradiance that would improve the limitations identified in the current state of the art. In particular, a sensor type RSR, which covers a wider spectrum of wavelengths and can operate reliably more time autonomously and without maintenance personnel reviews. The present invention is conceived to respond to these needs. We propose a system specially designed to work autonomously and to record solar irradiance using a thermal pyranometer sensor to measure the incident solar irradiance, with a shading band and a structure that includes movable supports to house components. The system has means of preventive cleaning, by forced ventilation, and active to clean the sensor by brushing and blowing with compressed air, means of protection against inclement weather and guidance means of the shading band and the pyranometer to make measurements in various conditions of shade and sun. A control unit governs the means of protection and cleaning to guarantee the safety and optimum conditions of measurement of the sensor, and the guidance means to fix the shading band with respect to the sensor and to establish cycles with shadow and with sun in accordance with the latitude and the moment of the day, where the duration of the cycles takes into account the response time of a thermal pyranometer.

To reduce the need for maintenance, scheduled and automatic cleanings and protection mechanisms against adverse meteorological agents and during the night period are contemplated.

The data acquisition unit allows you to record a large number of measurements obtained over long periods of time.

Although the thermal pyranometer has sensitivity to a large part of the solar spectrum, its response is slow. To solve this disadvantage, a more complex cyclic shading control has been developed that adapts the response time of the sensor to the periods of sun and shadow.

Preferably, the system has autonomous photovoltaic power, as well as cleaning means and protection means (eg for night), and a control unit and a data acquisition unit. All this allows you to measure the values of solar irradiance and other meteorological variables with great precision and record over long periods of time in isolated or inaccessible places. The system performs the reading and recording of solar irradiance values in its horizontal, horizontal and direct global components, by means of a "Rotating Shadowband Radiometei", RSR, which uses a thermal pyranometer, as a sensor element, and a rotating band driven by a special movement system which, knowing the date, time and geographical location, calculates the solar position to position the band so that its shadow falls on the sensor's eye. Shaded and sunny cycles are programmed to obtain measurements of solar irradiance in both conditions.

The rotation of the band, in the form of an arc, describes a sphere in the center of which the eye of the sensor is placed. The band turns, by means of a motor whose axis is inclined an angle equal to the latitude of the place, so that, the sensor is arranged like observer in the terrestrial equator. The calculation of the solar azimuth at the equator will determine the angular position of the band to cause the shadow on the sensor at each moment. Once the measurement of the horizontal global irradiance, GHI, taken under sun conditions and the horizontal diffuse irradiance, DHI, in shaded conditions, corrected by a band factor, FB, originated by the obstruction of the same on the surface, is known of the sphere, the direct normal irradiance, DNI, is determined by the equation:

DNI = ((GHI - (DHI ^* FB ^* FC) / SINE (a)) equation [1]

Being:

^* Solar height of the place in radians, α

^* The Band factor, FB, is minimal in the sunrise and sunset of the day and adopts a maximum value at noon. It varies throughout the day from 1 to 1, 10 depending on the constructive dimensions of the equipment, (radius of rotation of the sphere, dimensions of the band and latitude of the place) and the position of the band throughout the day. This factor is applied to the reading of horizontal diffuse irradiance, DHI, and corrects the obstruction of the band on the celestial hemisphere seen by the sensor at each moment.

^* The Clarity factor, FC, is minimum on clear days and maximum on days with heavy fog. This factor is applied to the reading of the horizontal diffuse irradiance, and corrects the obstruction of the band of part of the circumsolar irradiance This depends on the clarity index and the diffuse fraction at the test site.

Once a sun and shadow cycle has been performed, the equipment stores the data in a permanent ROM record. These cycles must allow periods of sun and shade, with times longer than the response time of the sensor used, which can vary between 5 and 30 seconds. For a commercial sensor, such as the pyranometer model CM1 1 from the manufacturer Zipp & Zonen, this is 15 seconds for a response of 95% and only 5 seconds for a CM22 from the same manufacturer and for the same conditions. Due to the response times of the pyranometers used, and to guarantee the stability in the measure, the sunny and shaded times should oscillate between 10 and 30 seconds.

The measures adopted correspond to the point value taken at the end of each period, so that, in days with variable irradiance, the data obtained may contain an error due to the variability and non-simultaneity of the measurements, made under sun and shade conditions, out of phase in time up to 30 seconds. This effect is also observed in the first and last hours of the day, where the solar irradiance varies more rapidly, due to the strong variation of solar ascension. To obtain more precise measurements of the pyranometer, it remains ventilated and its measurements are adjusted due to the dependence of its sensitivity with the ambient temperature and with the variation of the irradiance.

The ventilation of the equipment prevents the deposition of dust particles on the sensor glass, which keeps it cleaner during the day. A protection device is stationed on the sensor during night periods or adverse weather conditions such as rain, hail, snow or strong wind protecting it from them and avoiding deterioration or dirtiness of it.

This protection device has an active system of cleaning, by blowing air under pressure on the glass and brushing it by means of a roller / brush driven by an electric motor, which is activated at the beginning of the day to ensure the cleaning of the sensor glass during the measurement day. Thanks to the above, the system requires low maintenance and ensures protection and cleanliness. It has autonomous power, preferably by means of a photovoltaic panel, a charger and an electric battery that, together with the previous characteristics, allow it to work in places of difficult access, without assistance and for long periods of time. This is also possible since it has a permanent storage in ROM memory, which is able to keep the data obtained from irradiance and other meteorological variables for long periods of time.

BRIEF DESCRIPTION OF THE DRAWINGS

To complement the description made, and in order to help a better understanding of the characteristics of the invention, a detailed description of a preferred embodiment will be made based on a set of drawings that are attached to this specification and where , with merely illustrative and not limitative character, the following has been represented:

Figures 1 and 2 show in a general way the constructive concept of the shading device indicating the axes, movements and degrees of freedom in profile and plant view.

Figure 3 shows a perspective view of a preferred application indicating the main elements.

Figures 4 and 5 show the constructive design of a preferred application of the shading device and of the protection system in profile and plant view respectively.

Figures 6 and 7 show the construction design of a preferred application of the cleaning device in profile and plant view respectively.

Figure 8 shows a block diagram of the control cabinet of the equipment indicating its most important components.

Description of a preferred application For a better understanding of the invention, a preferred embodiment of the invention will be described in detail and based on the drawings.

As shown in figures 1 and 2, the shading device consists of a special structure, consisting of a table 18, on which several mobile supports (7, 8 and 9) are arranged, which allow several movements (A, B, C , D, E and F) and degrees of freedom in order to be able to adjust and position the eye of a sensor 1 in the center of the sphere described by a metal band 6, in the shape of an arc and painted in black, which rotates according to a inclined axis. A gearmotor 10, whose axis is inclined at an angle (C) equal to the latitude of the place, displaces the band 6 so that, when turning (F), it describes a sphere with center in the eye of the sensor 1.

Figures 1 and 2 show the conceptual and dimensional design, in profile and plan view, of the shading device that conforms to the dimensions of a sensor 1 consisting of a pyranometer of the firm KlPP & Zonen model CMP22 for a latitude of 37 ° N . Band 6, in the form of an arc, when rotating (F), describes a sphere that has a radius of 175mm. This band 6 has a width of 40 mm and a length of 125 ° of arc from the axis of rotation, being able to adjust this by means of the displacement (E), by the surface of the sphere. As shown in figures 1 and 2, table 18, which contains the whole assembly, is arranged outdoors in a sunny place, without shadows throughout the day and on a level horizontal plane (14 and 19), so that , the axis of rotation is arranged to the south and aligned with the sensor 1 in the North / South direction.

With the sunny device, the band 6, when turning (F), projects its shadow on the horizontal plane where the eye of the sensor 1 is located so that, at an angular position of the determined band 6, and at a specific time of the day , the shadow projected by band 6, will intercept the eye of sensor 1 so that it is hidden from the solar disk. Once the band 6 reaches this angular position, it must remain in that position for a time in order for the sensor 1 to adapt to the new light conditions and perform a measurement of the solar irradiance in shadow. After this time, band 6 will hide under sensor 1 for a while to allow it to be measured in sunny conditions. Figure 3 shows a perspective drawing of a preferred application made as a prototype of the invention incorporating a table 18, leveled by four adjustable legs 19 and a spirit level 14, in which a shading device as indicated above is arranged (1 to 13) and a protection and cleaning device (20 to 29). On the south face of the table 18 is placed a support 15, adjustable in inclination by means of hinges and a pin with flap 17, to house a photovoltaic panel 16 of 12 Vdc and on the north face of the table 18 is placed a watertight cabinet control 30.

Figures 4 and 5 show a profile and plan drawing of the prototype indicating all the most important elements, as well as the actual dimensions and dimensions, once the table is leveled and all the supports are adjusted (A, B, C, D, E and I), to achieve placing the eye of sensor 1 in the center of the sphere with an inclination of the axis of rotation of the band at 37 ° N, which corresponds to the latitude of the test site. As can be seen in both figures, the sensor 1 is housed in a cylindrical container or container 3, on which there is a conical cap 2, which exposes the double transparent and spherical window of the sensor 1. This cap 2, is removable for accessing the body of the sensor 1 and having an opening of a diameter greater than the window of the sensor 1, in order to allow the ascending passage of air, around said window, driven by three small fans 4 located in the rear part of the container 3. The air driven by the fans 4 passes through a filter 5 that retains the dust and solid particles, cools the body of the sensor 1 and exits to the outside through the mouth of the cap 2, so as to avoid deposition of dust and other Elements on the sensor window 1.

Figures 6 and 7 show a profile and plan drawing of the prototype cleaning system.

At the beginning of the day, at sunrise, the control system contained in the cabinet 30, will proceed to the loading of the lung 51 by operating the air compressor 52, until reaching the pressure level set in the pressure transducer / pressure switch 53 Once the lung 51 is loaded, at the established pressure, the eye of sensor 1 will be cleaned, for which it will be produced simultaneously: - an oscillating up / down movement of the protection arm 22, by controlling the position 21 of the motor of the protection system 20, forcing the brush 29 to withdraw and approach the window of the sensor 1 during a certain number of cycles, - a rotary movement of the brush 29, driven by the cleaning motor 28, to produce a sweep over the entire surface of the sensor glass 1 during the oscillating movement,

- the activation of the solenoid valve 54 to produce a blow of air that exits with force, through small holes of the blow ring 26, to incite circularly, in a horizontal plane, on the base of the sensor glass 1.

Once the blowing and brushing is done, the protective container 23 will be removed, leaving the sensor 1 uncovered. For this, the gearmotor 20 will be operated, moving the arm 22 until reaching the rest position, thanks to the control of the angular position measured by the incremental encoder 21 and a reference position switch 25. Once the sensor 1 is discovered, and the arm 22 is positioned at its other end, the fans 4 will be activated and the process of controlled and programmed movements (F) will begin. the cyclic operation of a gearmotor 10, which positions the band 6, thanks to the reading of an incremental encoder 11 coupled on its axis and of a proximity sensor 12 that detects the presence of a magnet 13, integral with the band 6, in order to obtain an absolute reference of position of the same. The operating and movement cycles are controlled and programmed in the control card 40, located inside the cabinet 30, to cause alternate sun and shadow intervals on the eye of the sensor 1, with times longer than the response time thereof. , in order to perform the measurement of solar irradiance in both conditions.

At sunset, the band 6 will be retracted to its resting position located in the lower part of the sensor 1, remaining there until a new sunrise, the fans 4 will be deactivated and the gearmotor 20 will be activated, to position the protective container 23 on the sensor 1, thanks to the movement (G) of the arm 22 and to the movement (H) of the rocker arm that holds the container 23. As shown in Figure 8, the control card 40 manages the movement of two motors (10 and 20), through two servos 35, and all the functionality of the equipment being fed by a safe and autonomous power supply to 12Vdc composed of a photovoltaic solar panel 16, a charge regulator 31, a battery 32 and an electrical protection by means of a magnetothermic 33.

The electronic control board 40 is powered at 5Vdc, by means of a DC / DC converter 42 that efficiently transforms the 12Vdc from the autonomous power supply system, and is governed by two microcontrollers (41a and 41b), each one of them with ROM memory to host the firmware, work RAM and EEPROM memory to store parameters and variables. One of them, the master microcontroller 41a, performs all the operational functions and precise calculation of the solar vector by using a powerful astronomical algorithm, with better accuracies of +20 arc seconds in both axes, as well as the processes and operational strategies measurement, protection, ventilation and cleaning, programmed shading / sunny cycles, reading, processing and storage of measurement data and calculation of band position 6.

The master microcontroller 41a, during the day and every 6 seconds, calculates the solar azimuth at the terrestrial equator, to determine the angular position of the band 6 to produce the shading, and the instantaneous solar elevation, a, at the location of the equipment with Corrections by atmospheric refraction.

For this, the master microcontroller 41a has a real-time clock 43 maintained with battery, for the knowledge of the day and the time, and is assisted, through an SPI bus, of another slave microcontroller 41 b, of a converter ADC 44 digital analog and an SD 46 storage card.

The slave microcontroller 41 b performs, according to the instructions received from the master 41a via SPI, the functions of controlling the position of the motors (10 and 20) and of the reading and activation of digital input and output signals. For this purpose, it performs the reading of the limits and position detectors (12 and 25), the reading of the states of the servos 35, as well as the activation, by means of solid state relays 34, of elements such as fans 4 and orders to protection and cleaning systems. In the same way, this microcontroller 41 b determines the angular position of the axes of the gearmotors (10 and 20), by reading the signals A and B of incremental encoders (11 and 21), as well as controls the operation of two servos of direct current 35 by means of the technique of modulation in pulse width, PWM. All this, in order to achieve precise control of the position of the axes of the engines (10 and 20) with different speeds between allowed positions defined by detectors and limits.

An analog / digital converter, ADC, 44 is used that has a voltmeter of 24 bits of resolution and 8 channels, with configurable ranges and gain. Due to the low sensitivity in the electrical output signal of sensor 1, thermal pyranometer, which usually does not exceed 10mV, the assigned channel, for the measurement of the output signal of sensor 1, is programmed with the maximum gain in the lower voltmeter range that is 78, 125mV, with a resolution of 1, 2 V and a linearity error of + -0.001%. Due to the low voltage to be measured, and to minimize errors in the measurement, calibration and zero correction techniques are used, offsets, in order to measure solar irradiance with an error of less than 0.2%.

Once the electrical signal of the sensor 1 is measured, a correction is made to it due to the influence of the temperature and in accordance with the law provided by the manufacturer of the equipment, for which the reading of the temperature of the body of the sensor 1, by means of a platinum resistance thermometer of the type PT100 disposed in its interior. To perform this measurement, a constant current source 45 of 1 mA is used. Once the measurement is corrected, it is converted to engineering units, W / m2, applying the sensor calibration factor 1 given by the equipment manufacturer or from the last registered calibration.

Once the irradiance values have been obtained in sun and shade conditions, equation [1] is applied to determine the direct irradiance considering the solar elevation of the moment and applying the Band factor, FB, and the Clarity factor, FC.

The band factor is calculated by an equation that determines the factor of concealment of the band 6 on the celestial vault and is a function of the position angular of the band 6, the geographical position and the dimensional design of the equipment.

The Clarity factor, FC, is a function of the conditions of clarity and the atmospheric characteristics of the site and is calculated experimentally, obtaining a law that relates it directly to the diffuse fraction, the relationship between diffuse and global irradiance, and the content of aerosols. and other components in the atmosphere.

The channels of the ADC 44 converter are read every second and, in each measurement cycle, the values converted to engineering units of the eight channels in their minimum, medium and maximum values are recorded.

The data assigned to these channels are the following:

• ChO. Irradiance sensor 1

• Ch1. Irradiance additional sensor (reserve)

• Ch2. Sensor temperature 1 (PT100) · Ch3. Additional sensor temperature (PT100)

• Ch4. Autonomous power system voltage

• Ch5. Total electrical consumption of the equipment

• Ch6. Air pressure lung

• Ch7. Reservation The measurement cycle is configurable, establishing the sunny and shading time of sensor 1. If we consider a time of 30 seconds of sunshine and 30 seconds of shading, 128 bytes of data will be recorded every minute on the microSD card 46, which is assumed about 185Kb each day. This, with a maximum of 32Gb of capacity and with a cycle of one minute of recording, will allow a storage period of 182 days.

The control card 40 has a local control 47 that allows, by means of switches arranged on the card itself, local control of the movement of the band in order to carry out maintenance, adjustment or start-up work. The master microcontroller 41 a has a serial communications port that can operate under the RS232 48, RS422 or RS485 49 two or four wire standards, using the MODBUS RTU protocol.

Using the RS232 48 port it is possible to connect a field console 50 or a laptop, from which the programming and configuration of the equipment is carried out, as well as the saving of the stored data of the microSD card 46. However, other techniques and mechanisms can be implemented to transfer this information. For example, through a wireless communications module (e.g. based on mobile telephone technology).

Using the RS485 49 port it is possible to communicate the equipment with other devices for the exchange of data through a bus with MODBUS RTU protocol via wired or wireless lineThe unit can act as a bus master to collect data from Climate sensors and exchange data with other devices.

In order to enrich the meteorological information and to be able to determine emergency situations due to conditions that could contaminate the sensor or jeopardize the operation of the equipment, it communicates, through the RS485 port 49, by MODBUS RTU protocol, with a sensor US climate of the range 49200.00.000 from the manufacturer Thies Clima, obtaining from it, every 4 seconds, the following information:

• Wind speed and direction

• Air temperature and inside of the equipment • Relative humidity and dew point

• Absolute and relative air pressure at sea level

• State of rain and intensity

• Accumulated of daily rain and type of meteor (rain, snow, hail)

• Absolute and relative uncorrected humidity · Magnetic north and solar brightness This data is stored, each measurement cycle, in the microSD card 46 together with the average, minimum and maximum data of the eight channels of the ADC 44 converter, in addition to others such as the day, time, operating mode, angular position of the band at the time of shading and the band factor, the elevation and solar azimuth, the gross values of the irradiances measured, converted and calculated (global horizontal, diffuse and direct). In total, 64 registers (128bytes) are stored in each measurement cycle.

The data from the Climate sensor are used, in addition to its registration and enrichment of the database, for the determination of dangerous situations and to allow the team to protect themselves by moving the arm to the protection position. Among others, the conditions that have been incorporated in the prototype are:

• Wind speed higher than 15m / s (adjustable)

• Detection of rain, snow or hail and humidity · Low battery voltage

Method of operation and start-up.

This section describes the process of operation and operation of the equipment, indicating the different adjustment, maintenance and start-up processes. one . The equipment, thus conceived, can work in places of difficult access, where human presence is not frequent, so it must be adjusted and configured previously according to the selected site. This site must be chosen taking into account that the equipment must be placed on solid and stable ground, in a sunny place, without shadows throughout the day and without obstacles or nearby objects, that can intercept or reflect the sun's rays (such as buildings, industrial buildings, towers, masts, mirrors or reflective surfaces). The place should be fenced or bounded to prevent free access to people or animals. 2. As indicated in figure 1, first adjust the position of the support 9 to an inclination (C), corresponding to the latitude of the place already a height (D), so that the band 6 can turn without obstacles. Then, the positions of the rest of the supports (7 and 8) and movements (A, B, D and E) must be adjusted, so that the eye of the sensor 1, is in the center of the sphere formed by the band 6 when turning (F). Place the table 18 in the final place and orientate it so that the gearmotor 10 and the eye of the sensor 1, are aligned with the north-south line. A simple method for this is to place, on its south side and on the table 18, a rod, arranged vertically to the plane thereof of sufficient length and rigidity, and wait to mark the shadow projected just at solar noon. Once the table 18 has been aligned, it will have to be leveled by the four adjustable legs 19, aided by the spirit level 14. Remove the cap 2 to check the internal leveling of the sensor 1, inside the container 3, aided by the spirit level it has the sensor 1 itself and check the good state of cleaning of the air filter 5. It will be necessary to adjust the screw 17 so that the photovoltaic panel 16 is inclined at a favorable angle, for a greater uptake of energy. As a general rule, this inclination should be about 10 ° higher than the latitude of the place to favor a greater catch in winter, although this will depend on the geographic and climatic conditions of the place. Check that the autonomous power system has enough power in the battery 32, energize the equipment 33 and move the band 6 locally, by means of the local control switches 47, arranged in the control card 40, to verify that it rotates without obstacles. During the rotation, adjust the support of the proximity sensor 12, until it approaches a distance close to the magnet 13, which transports and is integral with the band 6, so that detection occurs. In room 47, move the arm 22 of the protection system and adjust the position (I) of the support, so that the container 23, is well seated in its resting position. Also check the correct seating of the container 23 on the sensor window 1 by adjusting the tilt axis 24 to the correct arm distance. Connect to the serial port RS232 48, the field console 50 and, from it, configure the most important parameters of the equipment such as, among others: the time and day, the geographical position of the place and the desired cycle times, indicating the periods of shadow and sun in seconds, as well as the desired mode of operation and the law that defines the correction FB (according to equation [1]) according to the new location. In order to perform a correction by atmospheric refraction of the solar elevation at the first and last hour of the day, the ambient temperatures and the average monthly atmospheric pressures of the new site must be entered, as well as all the configuration parameters of the ADC converter 44 indicating ranges , earnings and conversion formulas to engineering units of the 8 available channels. It is usual to arrange the first channel for the measurement of the signal from sensor 1, the second to use it for use in techniques of zero correction or a second sensor / pyranometer and the third and fourth for measurements of body temperature of the sensors. The rest of the channels are connected to other variables such as: battery voltage 32, power consumption, lung air pressure 53 and other external sensors. It will also be necessary to indicate the emergency limits of the meteorological variables obtained from the Climate sensor. This information will be important to determine the activation of the protection and cleaning system in order to safeguard the sensor 1 from the inclement weather. Once the system parameters have been configured, we must choose a mode of operation from among the following: a) local mode, with action through the switches 47 b) defense mode. It is used for a protection of the sensor 1 while remaining safe from adverse conditions. c) cleaning mode. It is used to start a cleaning process by brushing and blowing. d) mode with band 6 lowered without movement. It is used to have two independent pyranometers always in the sun in the first two channels. e) mode with band 6 always in shadow. It is used to have two pyranometers, one always in shade and the other always in sunlight. Band 6 performs continuous monitoring throughout the day. f) mode with band 6 with sun and shadow cycles. It is used to have a single pyranometer 1 that performs the measurements under sun and shade conditions due to the alternate cycles of movement of the band 6. Under normal conditions, the mode of operation will be the operation of the band 6 with cycles of sun and shade using a single sensor 1. Once the desired mode of operation has been selected, the measurement process begins with the protective container 23 being removed to its resting position exposing the sensor window 1, the fans 4 are activated and the they record the data obtained in each measurement cycle. At sunset, the defense mode is activated and the band 6 is collected in the lower part of the sensor 1, staying there all night, the fans 4 are stopped and the protection system is activated, positioning the container 23 on the window of sensor 1, protecting it during the night period. During this period the data continues to be registered with the established cycle periods. At the beginning of the day, at sunrise, the control will activate the cleaning and protection system by charging the air lung 51, the oscillating movement of the protection arm 22, the blowing (52, 54) and the sweep of the brush 29 on the sensor window 1. Once the cleaning is done, the container 23 of the sensor 1 will be removed, the fans 4 will be activated and the cycle of movement of the band 6 will start, according to the selected operating mode . In order to protect the sensor window 1 from dirt, moisture and external agents such as wind, abrasion, snow, hail, rain, etc., the team will decide the activation of the cleaning and protection system when necessary thanks to the data provided by the Climate sensor communicated via MODBUS, RTU 49.

. The equipment thus installed, can work autonomously without interruption for long periods of time, being necessary only human presence at times to check the operation and perform maintenance tasks that will consist of: a) Check and adjust the time of the clock 43 b ) Check the autonomous power system and perform a deep cleaning of the photovoltaic panel 16 adjusting, if necessary, the inclination of the same 17 and check the state of charge of the battery 32. c) Download the data contained and stored in the microSD card

 46 or proceed to replace it with a new one. d) Check, clean or replace the air filter 5, thoroughly clean the inside of the container 3 and the window of the sensor 1 as well as the cleaning brush 29 and check the correct operation of the fans 4 and of the shading systems, of protection and cleaning. e) Proceed to a general cleaning of the equipment and put it back into operation.

As a compilation, the system described here has the following advantages and characteristics:

one . Use a thermal sensor instead of, as the equipment indicated above, use a silicon photodiode. The sensor used is a pyranometer ventilated and corrected in temperature with secondary standard quality, which, although it has a slow response, is, unlike photodiodes, sensitive to a large part of the solar spectrum and is more stable against changes in ambient temperature . This gives it a better measurement of irradiance, more precise, more reliable and more immune to changes in ambient temperature and atmospheric conditions.

2. It has an integrated means of cleaning and automatic protection during night or climatologically adverse periods, which enables it to work without assistance for long periods of time.

3. It is autonomous by means of photovoltaic power supply, together with an integrated data acquisition system, datalogger, provided with a 24-bit voltmeter that allows the accurate measurement, recording and storage, in a microSD memory card, of the data during long periods of time, make this equipment can be used in isolated places or difficult to access where there is no electricity supply and human presence.

4. It integrates a control unit assisted by a real-time clock, which uses a powerful astronomical calculation algorithm that allows to control the shading of the sensor by means of the movement of a rotating band that is positioned accurately, performing alternative shading cycles and sunny for programmed periods of time according to the response time of the sensor.

5. It is versatile. Registers the value of the diffuse irradiance, measured in each shading cycle, corrected by the actual obstruction of the band according to the adopted position. It also records the horizontal global irradiance value measured during the sunny periods and the direct irradiance calculated and corrected using the antennal measurements and the solar elevation of the instant considered. 6. In addition, it incorporates other meteorological sensors in order to record other data to complete the meteorological information and determine adverse weather conditions to ensure the cleanliness, protection and safety of the equipment.

Industrial application This invention may be used in universities, public and private research organizations, meteorological stations, plants, fields or solar farms and, especially, in remote areas where a historical record of solar irradiation data and other meteorological data is required. The historical record of measurements on the ground of solar irradiance in its three components, direct, global and diffuse, is of vital importance in sectors such as meteorological, agricultural and energy sector within solar technology.

Numerical References

In the figures described, the numerical references correspond to the following parts and elements:

one . Sensor. Kipp & Zonen pyranometer model CMP22 with PT100 sensor

2. Protective cap

3. Container

 4. Fans

 5. Air filter

 6. Shading band

 7. Horizontal mobile support

8. Vertical mobile support

 9. Mobile support with turn

 10. Gearmotor for shading system

 eleven . Angular encoder ncremental

 12. Magnetic proximity detector

13. Magnet

 14. Spirit level

 15. Hinged support of the solar panel

 16. Solar photovoltaic panel

 17. Angle adjustment rod

18. Table

 19. Table levelers

 20. Gearmotor for protection system

twenty-one . Angular encoder ncremental 22. Protection arm

 23. Protection and cleaning container

24. Tilting axis

 25. Position detector

 26. Ring blowing

 27. Tilting support

 28. Cleaning gearmotor

 29. Cleaning brush

 30. Waterproof control cabinet

 31 Battery charge regulator

 32. Battery

 33. Magnetothermic

 34. Solid state relays

 35. Motor control cards or servos

40. Control card

 41 Microcontrollers

 42. Direct current DC / DC converter

43. RTC clock with NVRAM memory

44. Digital analog converter, ADC

45. Source of intensity

 46. microSD memory card

 47. Local command

 48. RS232 port

 49. RS485 port, MODBUS RTU protocol

50. Field console

 51 Air lung

 52. Air compressor

 53. Pressure transducer

 54. Blowing solenoid valve.

Claims

 Claims 1. Autonomous system for recording the solar irradiance comprising a thermal sensor of incident solar radiation, a shading band (6) and a structure (18) comprising movable supports (7,8,9), characterized in that the thermal sensor is a pyranometer (1) and because the system also includes: - cleaning means (4,5,28,29,52,54) configured to cool and keep the sensor clean by means of ventilation, blowing compressed air and brushing; - protection means (22, 23) comprising a container (23) configured to be positioned on the sensor (1) depending on the established type of interval, or adverse conditions; - guiding means (10, 11, 20, 21) configured to guide the shading band (6) and the protection means (22, 23); - feeding means comprising an electric battery (32) and a photovoltaic solar panel (16); - control means comprising a control card (40), coupled with the guidance means, configured to establish the position of the shading band (6) with respect to the sensor (1) and to establish: measurement intervals with sun, measurement intervals with shadow, and inactivity intervals, based on at least the following parameters: latitude and longitude, date of the calendar, time of day, and response time of the pyranometer (one ); - means of acquisition to record the measurements made by the pyranometer (1) and other meteorological variables such as, at least, wind and precipitation conditions, in each measurement interval and store them in a permanent memory (46). 2. Autonomous system according to claim 1, wherein the cleaning means comprise a compressor (52) associated with a lung (51) and a transducer of pressure (53) with a valve (54) that releases the stored compressed air to produce the blow over the pyranometer (1). 3. Autonomous system according to claim 2, wherein the cleaning means comprise a brush (29) or roller configured to rotate coupled to an engine (28) and move to brush the pyranometer window (1). 4. Autonomous system according to claim 3, wherein the valve (54) is configured to release compressed air and produce the blowing on the window of the pyranometer (1) simultaneously with the brushing. 5. Autonomous system according to claim 4, wherein the cleaning means comprise a fan (4) that is activated to cool the pyranometer (1) and avoid depositions during the measurement periods. 6. Autonomous system according to any one of the preceding claims 1 to 5, wherein the cleaning means are managed by the control means according to the inactivity, emergency and measurement intervals. 7. Autonomous system according to claim 6, wherein the emergency interval is defined as a function of the detection of precipitation and / or of a wind speed greater than a threshold. 8. Autonomous system according to any one of the preceding claims 1 to 7, wherein the readings of the pyranometer (1) are corrected by the control unit as a function of temperature. 9. Autonomous system according to any one of the preceding claims 1 to 8, wherein the control unit further comprises an interface of communications (48,49) to transfer the information stored in the permanent memory (46) to another device in a wired way. 10. Autonomous system according to any one of the preceding claims 1 to 8, wherein the control unit further comprises a communications module for transferring the information stored in the permanent memory (46) to another device wirelessly. Autonomous system according to any one of the preceding claims 1 to 10, wherein the structure with movable supports (7, 8, 9) is a table (18) with adjustable legs (19) and a spirit level (14). 12. Autonomous system according to any one of the preceding claims 1 to 1 wherein the support (15) of the table is tiltable and is configured to house the photovoltaic panel (16).