METHOD AND DEVICE FOR DETERMINING A GLOBAL RADIATION INTENTION OF SOLAR RADIATION

Description

State of the art

[0001] The invention relates to a method and a device for determining a global irradiance of solar radiation and / or at least one of its components, in a horizontal plane and / or in a plane inclined to the horizontal plane, wherein the components comprise direct radiation, diffuse radiation, and radiation reflected from the ground.

[0002] For solar applications, e.g. with fixed or tracking flat plate collectors or photovoltaic modules, accurate measurements of global irradiance of solar radiation in arbitrary planes (GTI) and with high temporal resolution are of great interest.

[0003] Pyranometers can be used to measure the irradiance from the hemisphere above the sensor plane. Pyranometers provide fairly accurate measurements of the ground irradiance (GTI), but only for the plane used at the time of installation.

[0004] For example, US patent 20160334123 A1 discloses a device in which a pyranometer is used to measure the irradiance of solar radiation. Alternatively, the pyranometer is replaced by a camera.

[0005] Since radiation measurements are needed for planning purposes even before the construction of a solar power plant, and the ideal tilt angle or tracking mode of the collectors is not yet known at that time, inclined pyranometers alone are not sufficient.

[0006] Furthermore, for the accurate modeling of solar power plants or energy input into buildings, it is also useful to decompose the global irradiance in the inclined plane (GTI) into direct normal radiation (DNI) and diffuse irradiance in the inclined plane (DifTI). In practice, the GTI is therefore estimated from a measurement of the global irradiance in a horizontal plane (GHI) or from the DNI and GHI using transposition models. Measuring DNI and horizontal diffuse radiation (DHI) requires additional, complex, and maintenance-intensive measurement technology. A pyrheliometer tracking the sun measures the DNI. A pyranometer with a sun-tracking shadow ball measures the DHI. If only GHI is measured, DNI and DHI can be obtained using a decomposition model. The use of transposition and, in particular, decomposition models is associated with significant errors.

[0007] Cloud cameras were used to continuously determine the absolute radiation density or radiance distribution of the sky across all angular ranges and with high temporal resolution. Special laboratory setups with an additional tracker, shadow band, or a custom-built cloud camera were used for this purpose.

[0008] Beispielhaft werden folgende Publikationen genannt: López-Álvarez, M. A. et al., "Using a trichromatic CCD camera for spectral skylight estimation", Applied Optics, 2008, vol. 47(34), H31-H38.); Rossini, E. G., Krenzinger, A., "Maps of sky relative radiance and luminance distributions acquired with a monochromatic CCD camera", Solar Energy, 2007, vol. 81(11), 1323-1332; doi:10.1016 / j.solener.2007.06.013), Schade, N. H. et al., "Enhanced solar global irradiance during cloudy sky conditions", Meteorologische Zeitschrift, 2007, vol. 16(3), 295-303; Feister, U. et al., "Ground-based cloud images and sky radiances in the visible and near infrared region from whole sky imager measurements", EUMETSAT Satellite Application Facility Workshop, German Weather Service and World Meteorological Organization, 2000.

[0009] Radiance distributions of the sky were used as a reference for cloud detection, as described, for example, in the publication by Cazorla, A. et al., "Development of a sky imager for cloud cover assessment". JOSA A, 2008, vol. 25(1), 29-39.

[0010] Camera systems described in the literature can only determine the radiance distribution of the sky outside the solar disk. Various systems calculate the DNI from camera images. Machine learning has been used to derive DNI and DHI from camera images; see, for example, Schmidt, T., et al., "Retrieving direct and diffuse radiation with the use of sky imager pictures", 2015, EGU General Assembly Conference Abstracts.

[0011] The DHI was calculated from the radiance distribution of the sky, which is determined from the image of a specially constructed cloud camera, and the DNI was estimated from a "smearing" effect of the solar disk in the camera image, see for example Kurtz, B., Kleissl, J. "Measuring diffuse, direct, and global irradiance using a sky imager", Solar Energy, 2017, vol. 141, 311-322.

[0012] From both components together, a determination of the global irradiance in the horizontal plane (GHI) can be made. Disclosure of the invention

[0013] The object of the invention is to provide an improved method for determining a global irradiance of solar radiation and / or at least one of its components in a horizontal plane as well as in a plane inclined to the horizontal plane.

[0014] Another task is to create a device for carrying out such a procedure.

[0015] The problems are solved by the features of the independent claims. Favorable embodiments and advantages of the invention become apparent from the further claims, the description, and the drawings.

[0016] According to one aspect of the invention, a method is proposed for determining a global irradiance of solar radiation and / or at least one of its components in a horizontal plane and / or in a plane inclined to the horizontal plane, wherein the components comprise direct radiation, diffuse radiation, radiation reflected from the ground, with a device comprising at least one radiation sensor unit, a camera, and an evaluation unit which is provided for evaluating measurement data from the radiation sensor unit and / or the camera.

[0017] The global irradiance is calculated from the solar radiation irradiance of the radiation sensor unit and the angle-resolved radiation information of the camera and / or converted into one or more of its components in the horizontal plane and / or in a plane inclined to a horizontal plane.

[0018] Advantageously, the radiation sensor unit and the camera can detect the same area above the horizontal plane. The respective plane defines the boundary of the camera's and the radiation sensor unit's respective fields of view.

[0019] The radiation sensor unit and the camera can, for example, be arranged on an axis that is typically oriented in a north-south direction. In this case, the radiation sensor unit is located north of the camera in the northern hemisphere and south of the camera in the southern hemisphere.

[0020] A pyranometer, in particular a thermopile pyranometer, can advantageously be used as the radiation sensor unit, and a cloud camera, such as a Mobotix Q25 surveillance camera, can be used as the camera. In an advantageous embodiment, both instruments are arranged horizontally leveled and in close proximity to each other at the same height.

[0021] The red-green-blue (RGB) color channels of the camera image are weighted and summed. This weighting of the channels ensures the most uniform possible sensitivity of the camera in the visible wavelength range. This gray value is then multiplied by a broadband correction to account for radiation at wavelengths outside the camera's measurement range.

[0022] In this system, the radiation sensor unit is arranged in a plane, determining the irradiance of solar radiation within a 180° field of view above the plane. The camera is also arranged in a plane, capturing a 180° field of view above the plane. The radiation sensor unit and the camera are located at the same site. The irradiance of solar radiation is measured by the radiation sensor unit within the plane of the radiation sensor unit. The camera captures an image of the sky within the field of view, and the resulting image is an image of the sky containing RGB channels. A global irradiance of the solar radiation is measured and converted into the global irradiance and / or one or more of its components in the horizontal plane and / or in a plane inclined to a horizontal plane.This involves determining the diffuse radiation in the horizontal and / or inclined plane, in particular in the plane of the radiation sensor unit, using the following steps: . (i) Determining a broadband correction factor from the ratio of broadband radiation to the proportion registered by the camera using the daylight spectrum and the spectral sensitivity of the camera's RGB channels; (ii) Determining weights of the RGB channels according to the inverse sensitivity using the camera's recording settings; (iii) Summing the weighted RGB channels of the camera image; (iv) Multiplying the summed RGB channels by the broadband correction factor; (v) Assigning angular ranges of the sky to image pixels of the camera using internal and / or external calibration values ​​of the camera; (vi) Weighting the image areas according to the projection onto the horizontal and / or inclined plane; (vii) Determining the angular range of the field of view of the horizontal and / or inclined plane from its inclination and orientation as well as from the inclination and orientation of the camera's sensor; (viii) Determining the angular range of the sun disk from location and time;(ix) Excluding the angular range of the sun disk from the angular range of the field of view of the horizontal and / or inclined plane; (x) Integrating the image areas over the field of view; (xi) Determining the diffuse radiation in the horizontal and / or inclined plane, in particular in the plane of the radiation sensor unit (10), by multiplying it by a correction factor of the camera sensitivity. Advantageously, the radiation sensor unit and the camera can detect the same area above the horizontal plane. The respective plane represents the boundary of the respective field of view of the camera or the radiation sensor unit.

[0023] The radiation sensor unit and the camera can, for example, be arranged on an axis that is typically oriented in a north-south direction. In this case, the radiation sensor unit is located north of the camera in the northern hemisphere and south of the camera in the southern hemisphere.

[0024] A pyranometer, in particular a thermopile pyranometer, can advantageously be used as the radiation sensor unit, and a cloud camera, such as a Mobotix Q25 surveillance camera, can be used as the camera. In an advantageous embodiment, both instruments are arranged horizontally leveled and in close proximity to each other at the same height.

[0025] The red-green-blue (RGB) color channels of the camera image are weighted and summed. This weighting of the channels ensures the most uniform possible sensitivity of the camera in the visible wavelength range. This gray value is then multiplied by a broadband correction to account for radiation at wavelengths outside the camera's measurement range.

[0026] Using a geometric internal and external calibration standard for cloud cameras, a sky region (azimuth and zenith angle) is specified for each pixel of the camera image. This yields an estimate of the sky's radiance distribution.

[0027] Analogous to the radiance distribution, a luminance distribution is calculated. For this purpose, the RGB color channels are weighted according to the sensitivity of the human eye before summation. Integrating the luminance distribution over all angular ranges yields a measured illuminance. The illuminance output by the camera and the illuminance calculated from the camera image are compared. The radiance distribution is scaled according to the ratio of these two values ​​to compensate for the influence of the camera control on the camera's sensitivity.

[0028] The area of ​​the solar disk is masked. For an evaluated horizontal or inclined plane, each sky region in the radiance image is weighted according to a projection onto the plane. Integrating the radiance distribution over all sky regions that lie within the field of view of the inclined plane yields the diffuse irradiance of the respective plane originating from the sky.

[0029] The horizontal diffuse irradiance (DHI) is calculated accordingly. The diffuse irradiance in the plane of the pyranometer is also calculated accordingly. By comparing this to the global irradiance measured by the pyranometer and taking into account the current position of the sun, the direct normal radiation (DNI) is calculated.

[0030] In an advantageous embodiment, the pyranometer can be arranged horizontally. In this case, the pyranometer directly measures the global irradiance in the horizontal plane (GHI). Alternatively, GHI can be calculated analogously to the global irradiance in the inclined plane (GTI), based on the pyranometer measurement and the cloud camera image.

[0031] To correct for refractive effects in the camera lens, the first estimated DHI value, as well as all other calculated diffuse irradiances, especially the diffuse irradiance in the plane of the pyranometer, are reduced by a proportion of the DNI. The DNI is then recalculated.

[0032] The GTI in an evaluated plane is ultimately derived from a direct component, a diffuse component from the sky, and a component reflected from the ground. The DNI is projected onto the evaluated plane, thus yielding the direct component. The diffuse irradiance is calculated from the camera image for this plane as described above. The reflected component is obtained by multiplying the GHI by the albedo of the ground and the term 1 − cos Neigungswinkel der geneigten Ebene gegen die Horizontale / 2 .

[0033] According to a favorable embodiment of the method, the global irradiance of solar radiation determined by the radiation sensor unit in the plane of the radiation sensor unit can be converted into the global irradiance and / or into at least one of its components in the horizontal plane and / or in the plane i inclined to the horizontal plane, at least one of the quantities of radiation reflected from the ground, and / or diffuse radiation in the horizontal plane and / or in the plane inclined to the horizontal plane, in particular in the plane of the radiation sensor unit, and / or the position of the sun at the time of the radiation measurement, and / or a sensor-specific correction factor, which in particular includes lens parameters of the camera, can be used. Factors of the sun's position that influence the radiation measurement can be taken into account during the conversion.

[0034] In this way, the global irradiance and its components in a horizontal and / or inclined plane can be determined with high accuracy from the measurement data of the radiation sensor unit together with the measurement data of the camera.

[0035] According to a favorable embodiment of the method, at least one of the following quantities can be used to convert camera measurements: a ratio of broadband radiation to the proportion of radiation registered by the camera, and / or an internal and / or external calibration of the camera, and / or an inclination and orientation of the camera sensor, and / or an inclination and orientation of the inclined plane, and / or the position of the sun during radiation measurement, and / or a camera sensitivity determined from an illuminance of the camera and / or the spectral sensitivity of the RGB channels and / or recording settings and / or the RGB camera image and / or the internal and / or external calibration of the camera.

[0036] Factors influencing the radiation measurement, such as the sun's position, can be taken into account during the conversion process. In this way, the global irradiance and its components in the horizontal and / or inclined plane can be determined with high accuracy from the camera's measurement data combined with the measurement data from the radiation sensor unit.

[0037] In a favorable embodiment of the method, image information from the camera can be used to convert the global irradiance in the plane of the radiation sensor unit into the global irradiance and / or into at least one of its components in another horizontal and / or inclined plane. In particular, the combination of image information from the camera and measured values ​​from the radiation sensor unit can be used to reduce the uncertainty caused by image artifacts. This can increase the accuracy of the method.

[0038] With a favorable design of the method, the determination of direct solar radiation as a component of global irradiance in any plane can be carried out using the following steps: (i) Determining ground-reflected radiation using albedo, inclination and orientation of the inclined plane, and a measurement of global irradiance in the plane of the radiation sensor unit; (ii) Determining direct radiation in the plane of the radiation sensor unit by subtracting the measurement of diffuse radiation, evaluated for the plane of the radiation sensor unit, and the ground-reflected radiation, evaluated for the plane of the radiation sensor unit, from the global irradiance in the plane of the radiation sensor unit; (iii) Determining direct normal radiation by inverting the projection onto the plane of the radiation sensor unit using the sun's position calculated from location and time; (iv) Determining lens refraction correction by multiplying the direct normal radiation by a correction factor, which includes, in particular, lens parameters of the camera;(v) Determining the corrected direct radiation by adding the direct radiation in the plane of the radiation sensor unit and the lens refractive correction, and inverting the projection into the plane of the radiation sensor unit and projecting into the arbitrary plane.

[0039] With a favorable embodiment of the method, the diffuse radiation of solar radiation, as a component of the global irradiance, can be determined in any plane by the following steps: (i) Determining radiation reflected at ground level using albedo, inclination, and orientation of the inclined plane, as well as a measurement of the global irradiance in the plane of the radiation sensor unit; (ii) Determining the direct radiation in the plane of the radiation sensor unit by subtracting the measurement of diffuse radiation, evaluated for the plane of the radiation sensor unit, and the radiation reflected at ground level, evaluated for the plane of the radiation sensor unit, from the global irradiance in the plane of the radiation sensor unit; (iii) Determining direct normal radiation by inverting the projection onto the plane of the radiation sensor unit using the sun's position calculated from location and time;(iv) Determining a lens refraction correction by multiplying the direct normal radiation by a correction factor, which in particular includes lens parameters of the camera; (vi) Determining the corrected radiation in the arbitrary plane by subtracting the lens refraction correction from the diffuse radiation, evaluated for the arbitrary plane.;

[0040] With a favorable embodiment of the method, the global irradiance of solar radiation in the horizontal and / or inclined plane can be determined by the following steps: (i) Determining radiation reflected from the ground using albedo, inclination and orientation of the inclined plane, as well as a measurement of the global irradiance in the plane of the radiation sensor unit; (ii) Determining the direct radiation in the plane of the radiation sensor unit by subtracting the measurement of diffuse radiation, evaluated from the camera measurement data for the plane of the radiation sensor unit and the radiation reflected from the ground, evaluated for the plane of the radiation sensor unit, from the global irradiance in the plane of the radiation sensor unit; (iii) Determining direct normal radiation by inverting the projection onto the plane of the radiation sensor unit using the sun's position calculated from location and time;(iv) Determining a lens refraction correction by multiplying the direct normal radiation by a correction factor which includes lens parameters of the camera; (v) Adding the direct radiation in the plane of the radiation sensor unit and the lens refraction correction, and inverting the projection into the plane of the radiation sensor unit and projection into the horizontal and / or inclined plane; (vi) Subtracting the lens refraction correction from the diffuse radiation, evaluated for the horizontal and / or inclined plane;(vii) Determining the global irradiance in the horizontal and / or inclined plane by summing the radiation reflected from the ground, the direct radiation in the horizontal and / or inclined plane, and the diffuse radiation evaluated for the horizontal and / or inclined plane. This allows the global irradiance in a horizontal and / or inclined plane to be determined with high accuracy from the measurement data of the radiation sensor unit together with the measurement data of the camera.

[0041] Lens refraction causes an overestimation of diffuse radiation and thus an underestimation of direct radiation. This effect can be corrected by subtracting the overestimation from the diffuse radiation and adding it to the direct radiation.

[0042] According to the invention, the diffuse radiation in the horizontal and / or inclined plane, in particular in the plane of the radiation sensor unit, is determined by the following steps: (i) determining a broadband correction factor from the ratio of broadband radiation to the proportion registered by the camera using the daylight spectrum and the spectral sensitivity of RGB channels of the camera; (ii) determining weights of the RGB channels according to the inverse sensitivity using the camera's recording settings; (iii) summing the weighted RGB channels of the camera image; (iv) multiplying the summed RGB channels by the broadband correction factor; (v) assigning angular areas of the sky to image pixels of the camera using internal and / or external calibration values ​​of the camera; (vi) weighting the image areas according to the projection onto the horizontal and / or inclined plane;(vii) Determining the angular range of the field of view of the horizontal and / or inclined plane from its inclination and orientation, as well as from the inclination and orientation of the camera sensor; (viii) Determining the angular range of the sun disk from the location and time; (ix) Excluding the angular range of the sun disk from the angular range of the field of view of the horizontal and / or inclined plane; (x) Integrating the image areas over the field of view; (xi) Determining the diffuse radiation in the horizontal and / or inclined plane, in particular in the plane of the radiation sensor unit, by multiplying it by a correction factor for the camera sensitivity.

[0043] This allows the global irradiance, as well as the diffuse radiation in the horizontal and / or inclined plane and the direct radiation, to be determined with high accuracy from the measurement data of the radiation sensor unit together with the measurement data of the camera.

[0044] With a favorable embodiment of the method, the camera sensitivity correction factor can be determined by the following steps: (i) determining weights according to the sensitivity of each RGB channel of the camera using the spectral sensitivity of the RGB channels and the camera's recording settings; (ii) determining weights according to human perception; (iii) summing the weighted RGB channels from the RGB camera image; (iv) mapping angular areas of the sky to image pixels of the camera using the camera's internal and / or external calibration values; (v) integrating the weighted RGB channels over the hemisphere of the sky above the camera plane; (vi) determining the camera sensitivity correction factor by calculating the ratio of the camera's illuminance to the integrated weighted RGB camera image.This allows the global irradiance, as well as the diffuse radiation in the horizontal and / or inclined plane and the direct radiation, to be determined with high accuracy from the measurement data of the camera together with the measurement data of the radiation sensor unit.

[0045] According to a further aspect, a device is proposed for carrying out a method for determining a global irradiance of solar radiation and / or at least one of its components in a plane, in particular in a horizontal plane and / or in a plane inclined to the horizontal plane, wherein the components include direct radiation, diffuse radiation, radiation reflected from the ground, comprising at least one radiation sensor unit, a camera, and an evaluation unit which is provided for evaluating measurement data from the radiation sensor unit and / or the camera.

[0046] The radiation sensor unit is designed to determine the irradiance of solar radiation within a 180° field of view above a plane of the radiation sensor unit. The camera is designed to capture a 180° field of view above a plane of the camera. A combined measurement setup of the radiation sensor unit and camera is used at the same location.

[0047] The global irradiance of solar radiation is measured in a plane of the radiation sensor unit and converted into the global irradiance in a plane inclined to the plane of the radiation sensor unit and / or into one or more of the components of the global irradiance in the horizontal plane and / or in the plane inclined to the horizontal plane. Image information from the camera is used to convert the global irradiance in the plane of the radiation sensor unit into the global irradiance and / or into at least one of its components in this plane or in the horizontal plane and / or in the plane inclined to the horizontal plane from the measurement data of the radiation sensor unit. This conversion is achieved by using the intensity of RGB channels from the camera to convert the camera's measured values.

[0048] According to a further aspect of the invention, a device is proposed for carrying out a method for determining a global irradiance of solar radiation and / or at least one of its components in a plane, in particular in a horizontal plane and / or in a plane inclined to the horizontal plane, wherein the components comprise direct radiation, diffuse radiation, radiation reflected from the ground, comprising at least one radiation sensor unit, a camera, and an evaluation unit which is configured for evaluating measurement data from the radiation sensor unit and / or the camera. wherein the radiation sensor unit is arranged in a plane, wherein the radiation sensor unit determines the irradiance of solar radiation in a field of view of 180° above the plane, wherein the camera is arranged in a plane and the camera captures a field of view of 180° above the plane, wherein the radiation sensor unit and the camera are arranged in a combined measurement setup at the same location, wherein the irradiance of solar radiation is measured by means of the radiation sensor unit in the plane of the radiation sensor unit, wherein the camera captures an image of the sky in the field of view and the camera image is an image of the sky which has RGB channels, wherein the camera captures an image of the sky in the field of view and the camera image is an image of the sky which has RGB channels, wherein a determination of the diffuse radiation in the horizontal and / or inclined plane, in particular in the plane of the radiation sensor unit,with the steps, , (i) Determining a broadband correction factor from the ratio of broadband radiation to the proportion registered by the camera using the daylight spectrum and the spectral sensitivity of the camera's RGB channels; (ii) Determining weights of the RGB channels according to the inverse sensitivity using the camera's recording settings; (iii) Summing the weighted RGB channels of the camera image; (iv) Multiplying the summed RGB channels by the broadband correction factor; (v) Assigning angular ranges of the sky to image pixels of the camera using internal and / or external calibration values ​​of the camera; (vi) Weighting the image areas according to the projection onto the horizontal and / or inclined plane; (vii) Determining the angular range of the field of view of the horizontal and / or inclined plane from its inclination and orientation as well as from the inclination and orientation of the camera's sensor; (viii) Determining the angular range of the sun disk from location and time;(ix) Excluding the angular range of the sun disk from the angular range of the field of view of the horizontal and / or inclined plane; (x) Integrating the image areas over the field of view; (xi) Determining the diffuse radiation in the horizontal and / or inclined plane, in particular in the plane of the radiation sensor unit, by multiplying it by a correction factor of the camera sensitivity.

[0049] The radiation sensor unit is designed to determine the irradiance of solar radiation within a 180° field of view above a plane. The camera is designed to capture a 180° field of view above a plane.

[0050] The radiation sensor unit and the camera can advantageously be arranged along a north-south axis. In this case, the radiation sensor unit can be positioned north of the camera in the northern hemisphere and south of the camera in the southern hemisphere.

[0051] A pyranometer, particularly a thermopile pyranometer, can advantageously be used as the radiation sensor unit, and a cloud camera, such as a Mobotix Q25 surveillance camera, can be used as the camera. Both instruments are advantageously arranged horizontally leveled and in close proximity to each other at the same height. Additionally, the installation location should be chosen so that further obstacles in the fields of view of the radiation sensor unit and the camera are avoided.

[0052] According to the invention, the global irradiance of solar radiation (GTI) and the diffuse radiation in horizontal and / or inclined planes, as well as the direct radiation, can be determined using a fixed setup of the device, taking into account an image of the sky and the pyranometer. The GTI, the direct radiation, and the diffuse radiation can be determined for any number of tilt angles and azimuth orientations of the planes. Temporal changes of the angles are also possible in order to evaluate the planes of tracked receivers.

[0053] The image of the sky provides the real-time radiance distribution of the sky, excluding the solar disk. By adjusting the weighting and integrating the radiance distribution, the diffuse irradiance (DHI) in the horizontal plane and the component of the diffuse irradiance originating from the sky (DifTI) in any other plane can be determined. From the global irradiance measured by the pyranometer and the diffuse radiation calculated for that plane from the camera image, the DNI can be calculated using the known solar position. From this, the GTI can be determined. The direct component of the irradiance, DNI, is projected geometrically onto the desired plane. The diffuse component from the sky, DifTI, is obtained via the weighted integration described above. The component of the irradiance reflected from the ground into the inclined plane is determined by estimating the ground albedo and the known global irradiance, GHI.

[0054] Using the device according to the invention, the radiance distribution of the sky can be determined directly from the camera image. In contrast to the prior art, the device does not use any moving parts for the precise determination of the DNI and DHI, which makes the design significantly cheaper and more robust.

[0055] Using the camera and pyranometer, the global irradiance in the plane of the pyranometer can be determined directly via the pyranometer. In the case of a horizontally oriented pyranometer, it directly measures the GHI. The camera image is used to determine the diffuse irradiance in any desired plane.

[0056] The global radiation measured by pyranometer can thus be converted with high accuracy into the irradiance in any given plane. The calculation of the GTI, and for this purpose the diffuse radiation in inclined planes, is carried out by an adapted integration of the radiance distribution.

[0057] A standard pyranometer and an inexpensive fisheye surveillance camera can be advantageously used for the measuring system. To use such a camera for measuring the radiance distribution of the sky, the camera's exposure control can be specifically adjusted. A suitable set of camera control parameters ensures that image properties relevant to the measurement remain largely constant, regardless of the observed scene. Instead of requiring an additional individual radiometric calibration for each cloud camera, this measuring system compares a diagnostic illuminance value output by the camera with a value calculated from the camera image during operation. This corrects the camera's sensitivity in real time. A correction for the camera image gain is applied during the calculation.

[0058] The measuring system described here uses a combined measuring setup of pyranometer and camera at the same location.

[0059] This arrangement uses the radiance distribution of the sky solely for conversion between GHI, GTI in different planes, and the respective components of global radiation: direct radiation, diffuse radiation, and radiation reflected from the ground. This ensures that the accuracy of the GTI measurement for small tilt angles of the plane under consideration approaches the measurement accuracy of the pyranometer.

[0060] Cloud cameras are poorly suited to determining the radiance distribution simultaneously in the area of ​​the sun disk and in the rest of the sky due to their limited dynamic range.

[0061] The combined setup, however, advantageously allows the solar disk to be excluded from the analysis. The DNI used in the analysis can be calculated from the measurement of the global irradiance and the diffuse radiation determined from the radiance distribution (excluding the solar disk).

[0062] The measurement setup is designed to achieve high accuracy in radiation measurements. For lower accuracy requirements, modifications to the setup and data analysis can be made.

[0063] Instead of a thermopile pyranometer, other measuring devices capable of providing a measurement of global irradiance can optionally be used, e.g., a photodiode or photovoltaic reference cell. Instead of a Mobotix Q25 surveillance camera, another weatherproof fisheye camera with a 180° field of view, comparable recording settings, and illuminance measurement capability can be used.

[0064] The evaluation can optionally omit the calculation of correction factors, such as camera sensitivity via comparison of illuminance, scattering effects depending on the direct normal radiation.

[0065] According to a favorable embodiment of the device, at least one sensor of the radiation sensor unit and at least one sensor of the camera can each be arranged in the horizontal plane such that the field of view of both sensors lies above the horizontal plane and is flush with the horizontal plane.

[0066] This allows the solar radiation in the hemisphere above the horizontal plane to be measured in a suitable way, in order to then determine the global irradiance as well as the diffuse radiation in the horizontal and / or inclined plane and the direct radiation.

[0067] According to a favorable embodiment of the device, the distance between the radiation sensor unit and the camera can be set or adjusted such that the sensor of the radiation sensor unit is visible in the field of view of the camera 20 at an elevation of at most 10°, preferably at most 5°. This sufficiently limits the portion of the sky obscured by the sensor of the radiation sensor unit for the camera, thus enabling the global irradiance in an inclined plane to be determined with sufficient accuracy.

[0068] With a favorable design of the device, the radiation sensor unit and the camera can be coupled, so that measurement data acquisition by the radiation sensor unit and camera is time-synchronized. This allows the measurement data to be suitablely correlated during evaluation for determining the global irradiance, the diffuse radiation in the horizontal and / or inclined plane, and the direct radiation.

[0069] According to a favorable embodiment of the device, the camera can be designed to have at least the following properties: a single image can be captured at fixed time intervals, in particular every half and full minute; the at least one sensor of the camera can have a constant color temperature; the camera can have a constant exposure time for each individual image.

[0070] For exposure control of the camera, a predetermined minimum value of medium image brightness can be set, whereby the exposure time remains unchanged at a higher image brightness.

[0071] In particular, the specified minimum value for average image brightness can preferably be at most 10%, more preferably at most 8%, and most preferably at least 5%. This allows for high accuracy in determining the global irradiance as well as the diffuse radiation in the horizontal and / or inclined plane and the direct radiation.

[0072] With a favorable design, the camera can be configured to capture the sky within its field of view. The sky image can provide a real-time radiance distribution of the sky, excluding the sun's disk. By appropriately weighting and integrating the radiance distribution, the diffuse irradiance (DHI) in the horizontal plane and the component of the diffuse irradiance originating from the sky (DifTI) in any other plane can be determined.

[0073] According to a favorable embodiment of the device, the radiation sensor unit can comprise at least one of a pyranometer, in particular a thermopile pyranometer, a photodiode, or a photovoltaic reference cell.

[0074] Depending on the required accuracy for determining the global irradiance in an inclined plane, a compromise can be found between the effort required for the measurement technology and the costs.

[0075] In a favorable embodiment of the device, the radiation sensor unit can be configured to acquire measurement data with high temporal resolution, in particular with a temporal resolution of less than 10 seconds, preferably less than 5 seconds, and most preferably less than or equal to 1 second. This provides sufficient temporal resolution for determining solar radiation under varying radiation conditions.

[0076] With a favorable design of the device, the radiation sensor unit can be configured to detect solar radiation in a wavelength range from 0.3 µm to 3 µm. This wavelength range is of particular interest for the design of photovoltaic systems and extends from the lower limit of visible light to the short-wavelength part of the infrared range.

[0077] With a favorable design, the camera can be configured to capture the entire field of view in a single image. In particular, the camera can be configured as a surveillance camera and / or a fisheye camera. Such a camera allows for the simple recording of the entire half-space above a plane without any mechanically moving parts. Furthermore, such cameras with varying resolutions are readily available at affordable prices. drawing

[0078] Further advantages will become apparent from the following description of the drawings. The figures illustrate exemplary embodiments of the invention. The figures, the description, and the claims contain numerous features in combination. A person skilled in the art will expediently consider the features individually and combine them into meaningful further combinations. They show, for example:

[0079] Fig. 1 shows a schematic diagram of a device for determining the global irradiance of solar radiation and its components (direct radiation, diffuse radiation, radiation reflected from the ground) in a horizontal and / or inclined plane according to an embodiment of the invention in a side view; Fig. 2 shows the structure of the device according to Figure 1 in an alternative configuration in which the planes of the radiation sensor unit and the camera are inclined to the horizontal plane; Fig. 3 shows the setup of the device according to Figure 1in a top view; Fig. 4 a flowchart of the method for determining the irradiance of solar radiation and its components direct radiation, diffuse radiation, radiation reflected from the ground in a horizontal and / or inclined plane according to an embodiment of the invention; Fig. 5 a flowchart for determining the diffuse irradiance originating from the sky in a plane; Fig. 6 a flowchart for calculating the correction factor of the camera sensitivity based on a comparison of the illuminance output by the camera and calculated; and Fig. 7 a photograph of the sky taken with a device according to an embodiment of the invention. Embodiments of the invention

[0080] In the figures, similar or equivalent components are numbered with the same reference symbols. The figures merely show examples and are not to be understood as limiting.

[0081] The directional terminology used below, including terms like "left," "right," "above," "below," "in front," "behind," "after," and the like, serves only to improve the understanding of the figures and is in no way intended to limit their generality. The components and elements depicted, their interpretation, and their use may vary according to the considerations of a person skilled in the art and be adapted to the specific applications.

[0082] Figure 1 Figure 500 shows a schematic setup of the device 500 for determining a global irradiance of solar radiation and its components direct radiation, diffuse radiation and radiation reflected at the ground in a horizontal plane 40 and / or in a plane inclined to a horizontal plane 40 according to an embodiment of the invention in a side view.

[0083] In Figure 2 The structure of the device 500 is according to Figure 1shown in an alternative setup in which planes 44, 46 of the radiation sensor unit 10 and the camera 20 are inclined against the horizontal plane 40.

[0084] In Figure 3 The structure of device 500 is shown in a top view.

[0085] The device 500 comprises a radiation sensor unit 10, a camera 20, and an evaluation unit 32 (in Figure 3 (shown), which is intended for evaluating measurement data from the radiation sensor unit 10 and / or the camera 20. The radiation sensor unit 10 is intended for determining the irradiance of solar radiation in a field of view 16 of 180°, i.e., the half-space above the plane 44, and the camera 20 is also intended for capturing a field of view 26 of 180°, i.e., the half-space above a plane 46.

[0086] At the in Figure 1In the illustrated arrangement of the device 500, the two planes 44, 46 are aligned in the horizontal plane 40 and coincide with the horizontal plane 40.

[0087] At the in Figure 2 In the illustrated arrangement of the device 500, the planes 44, 46 of the radiation sensor unit 10 and the camera 20 are each inclined at an angle 45, 47 to the horizontal plane 40. The angle 45, 47 can be adjusted between 0° and 90°.

[0088] In this embodiment, the radiation sensor unit 10 and the camera 20 are arranged, for example, on a north-south axis 42, with the radiation sensor unit 10 located on the northern hemisphere north of the camera 20, as shown in Figure 3 The arrangement is shown. On the southern hemisphere, the radiation sensor unit 10 would be located south of the camera 20.

[0089] The radiation sensor unit 10, which can be designed, for example, as a pyranometer, in particular a thermopile pyranometer, comprises a housing 12 above which the sensor 14 is arranged to detect the upper hemisphere with a field of view 16 of 180°.

[0090] The radiation sensor unit 10 is designed to detect solar radiation in a wavelength range of 0.3 µm to 3 µm.

[0091] The radiation sensor unit 10 can alternatively be designed as a photodiode or photovoltaic reference cell if lower requirements are placed on the accuracy of the determination of the global irradiance.

[0092] The camera 20, which can be configured, for example, as a fisheye surveillance camera, in particular as a Mobotix Q25 surveillance camera or as a cloud camera, comprises a housing 22 above which the sensor 24 is arranged to capture the upper hemisphere with a field of view 16 of 180°. The camera 20 is preferably configured to record the sky within the field of view 26.

[0093] The camera 20 is advantageously designed so that it can capture the entire field of view 26 in a single shot without the need for mechanically moving parts.

[0094] Both instruments are advantageously arranged horizontally leveled and in close proximity to each other at the same height. Additionally, the installation location is appropriately chosen to avoid any further obstacles in the fields of view of the radiation sensor unit and the camera.

[0095] In the advantageous embodiment shown here, the sensor 14 of the radiation sensor unit 10 and the sensor 24 of the camera 20 are each arranged in the horizontal plane 40 such that the field of view 16, 26 of the two sensors 14, 24 is located above the horizontal plane 40 and is flush with the horizontal plane 40.

[0096] The distance 30 between the radiation sensor unit 10 and the camera 20 is set so that the sensor 14 of the radiation sensor unit 10 is visible in the field of view 26 of the camera 20 with an elevation 28 of at most 10°.

[0097] The radiation sensor unit 10 and the camera 20 are coupled in such a way that measurement data acquisition by the radiation sensor unit 10 and camera 20 is synchronized in time. The measurement data is conveniently evaluated in the evaluation unit 32.

[0098] The measurement data acquisition of the radiation sensor unit 10 is carried out with high temporal resolution, in particular with a temporal resolution of less than 10 sec, preferably less than 5 sec, especially preferably less than or equal to 1 sec.

[0099] The camera 20 can be advantageously configured to capture a single image at fixed intervals, in particular every half and full minute. Advantageously, the at least one sensor 24 of the camera 20 can have a constant color temperature. The camera 20 can also advantageously have a constant exposure time for each individual image. For exposure control of the camera 20, a predetermined minimum value for average image brightness can be set, whereby the exposure time remains unchanged at higher image brightness levels.

[0100] In particular, the specified minimum value of an average image brightness can preferably be at most 10%, more preferably at most 8%, and most preferably at least 5%.

[0101] The image from camera 20 provides the real-time radiance distribution of the sky, excluding the solar disk. By adjusting the weighting and integrating the radiance distribution, the diffuse irradiance (DHI) in the horizontal plane 40 and the component of the diffuse irradiance originating from the sky (DifTl) in any other plane can be determined. From the global irradiance measured by the radiation sensor unit 10 (designed as a pyranometer) in plane 44 of the pyranometer and the diffuse radiation calculated from the camera image in this plane 44, the DNI can be calculated using the known position of the sun. From this, the GTI can be determined: The direct component of the irradiance DNI is projected geometrically onto the required plane. The diffuse component from the sky, DifTl, is obtained via the weighted integration described above.The proportion of irradiance reflected from the ground into the inclined plane is determined by estimating the albedo of the ground and the global radiation GHI determined via the pyranometer and the camera in the horizontal plane.

[0102] Using the described device, the radiance distribution of the sky can be determined directly via the camera image.

[0103] By means of the in the Figures 1 to 3 With the described device consisting of camera 20 and radiation sensor unit 10, in particular in the form of a pyranometer, the global radiation in the plane 44 of the radiation sensor unit 10 can be determined directly via the radiation sensor unit 10, which is designed, for example, as a pyranometer. The camera image is used to determine the diffuse irradiance in arbitrary planes instead of only in the horizontal plane.

[0104] Additionally, the direct radiation is determined by comparing the global radiation measured by the radiation sensor unit 10 (e.g., configured as a pyranometer) with the diffuse radiation from the camera image, evaluated for plane 44 of the pyranometer. The global radiation measured by the radiation sensor unit 10 (e.g., configured as a pyranometer) can thus be converted with high accuracy into the irradiance in any given plane. The calculation of the global irradiance index (GTI) and, for this purpose, the diffuse radiation in inclined planes, is performed via an adapted integration of the radiance distribution.

[0105] The in the Figures 1 to 3The described device utilizes a commercially available pyranometer and an inexpensive fisheye surveillance camera. To enable the use of such a camera for measuring the radiance distribution of the sky, the camera's exposure control can be specifically adjusted. A suitable set of camera control parameters ensures that image properties relevant to the measurement remain largely constant, regardless of the observed scene. Instead of performing an additional individual radiometric calibration for each camera 20, the present measuring system compares a diagnostic illuminance value output by the camera 20 with a value calculated from the camera image during operation. This corrects the camera's sensitivity in real time. A correction for the camera image gain is applied during the calculation.

[0106] The in the Figures 1 to 3The described device uses a combined measurement setup of a radiation sensor unit 10 and a camera 20 at the same location. This arrangement utilizes the radiance distribution of the sky for conversion between global radiation measurements from the pyranometer 10 and GHI, GTI, as well as between these quantities and their respective components: direct radiation, diffuse radiation, and radiation reflected from the ground.

[0107] This ensures that the accuracy of the GTI measurement for small inclination angles of the considered plane approaches the measurement accuracy of the pyranometer. The combined setup makes it possible to exclude the area of ​​the solar disk from the evaluation. The DNI used in the evaluation can be calculated from the measurement of global radiation and the diffuse radiation determined from the radiance distribution (excluding the solar disk).

[0108] The in the Figures 1 to 3The described device serves to achieve high accuracy in radiation measurement. For lower accuracy requirements, modifications to the setup and data evaluation can be made.

[0109] Instead of a thermopile pyranometer, other measuring devices capable of providing a GHI measurement can optionally be used, e.g., a photodiode or a photovoltaic reference cell. Instead of a Mobotix Q25 surveillance camera, another weatherproof fisheye camera with a 180° field of view, comparable recording settings, and illuminance measurement capability can be used.

[0110] The evaluation can then optionally omit the calculation of correction factors, such as camera sensitivity via comparison of illuminance, scattering effects depending on the direct normal radiation.

[0111] Figure 4Figure 1 shows a flowchart of the method for determining the irradiance of solar radiation in a plane inclined to a horizontal plane 40 according to an embodiment of the invention. A device with a radiation sensor unit 10, a camera 20, and an evaluation unit 32 is used, as shown in the following. Figures 1 to 3 The method is shown. It determines the global irradiance of solar radiation in a plane inclined to the horizontal plane 40. Furthermore, the method provides the DNI and the diffuse radiation in any given plane. The method can also be used to calculate either of these quantities.

[0112] Advantageously, a pyranometer, in particular a thermopile pyranometer, can be used as the radiation sensor unit 10, as described above, and a cloud camera, such as a Mobotix Q25 surveillance camera, can be used as the camera 20. Both instruments are advantageously arranged horizontally leveled and in close proximity to each other at the same height.

[0113] The red-green-blue (RGB) color channels of the sky image are weighted and summed. This weighting of the channels ensures the most uniform possible sensitivity of camera 20 in the visible wavelength range. This gray value is then multiplied by a broadband correction to account for radiation at wavelengths outside the measurement range of camera 20.

[0114] Using a geometric internal and external calibration standard for cloud cameras, a sky region (azimuth and zenith angle) is specified for each pixel of the camera image. This yields an estimate of the sky's radiance distribution.

[0115] Analogous to the radiance distribution, a luminance distribution is calculated. For this purpose, the RGB color channels are weighted according to the sensitivity of the human eye before summation. Integrating the luminance distribution over all angular ranges yields a measured illuminance. The illuminance output by camera 20 and the illuminance calculated from the camera image are compared. The radiance distribution is scaled according to the ratio of these two values ​​to compensate for any influence of the camera control on the sensitivity of camera 20.

[0116] The area of ​​the sun's disk is masked. For each evaluated sensor plane, every sky region in the radiance image is weighted according to a projection onto the plane. Integrating the radiance distribution over all sky regions within the field of view of the inclined plane yields the diffuse irradiance of the respective plane originating from the sky.

[0117] The horizontal diffuse irradiance in plane 44 of the radiation sensor unit 10 is calculated accordingly. The direct normal radiation (DNI) is calculated by comparing this to the horizontal global irradiance measured by pyranometer and taking into account the current position of the sun.

[0118] To correct for refraction effects in the lens of camera 20, the first estimated value of the diffuse radiation in plane 44 of the radiation sensor unit 10, as well as all other calculated diffuse irradiances, are reduced by a proportion of the DNI (lens refraction correction). The correction is then added to the direct radiation in plane 44 of the radiation sensor unit 10. The DNI is then recalculated.

[0119] The GTI in an evaluated plane is ultimately derived from a direct component, a diffuse component from the sky, and a component reflected from the ground. The DNI is projected onto the evaluated plane, thus yielding the direct component. The diffuse irradiance is calculated from the camera image for this plane as described above. The reflected component is obtained by multiplying the GHI by the albedo of the ground and the term 1 − cos Neigungswinkel der geneigten Ebene gegen die Horizontale / 2 .

[0120] According to the specified procedure, the global irradiance of solar radiation determined by the radiation sensor unit 10 in the plane 44 of the radiation sensor unit 10 can be converted into the irradiance 120 and / or its respective components, direct radiation 250, diffuse radiation 260, radiation reflected from the ground, in the horizontal plane 40 and / or in the plane inclined to the horizontal plane 40, by at least one of the quantities of radiation reflected from the ground, and / or diffuse radiation 220, and / or the position of the sun at the time of the radiation measurement, and / or a sensor-specific correction factor, which in particular includes lens parameters of the camera 20. Factors of the sun's position that influence the radiation measurement can be taken into account during the conversion.

[0121] Furthermore, according to the specified procedure for converting measured values ​​of camera 20, at least one of the following quantities can be used: a ratio 210 of broadband radiation to the proportion of radiation registered by camera 20, and / or a spectral intensity 202 of RGB channels of camera 20, and / or an internal and / or external calibration 208 of camera 20, and / or an inclination and orientation 102 of sensor 24 of camera 20, and / or the position of the sun during radiation measurement, and / or a camera sensitivity determined from an illuminance 300 of camera 20, and / or the spectral sensitivity 202 of the RGB channels, and / or recording settings 204, and / or the RGB camera image 206, and / or the internal and / or external calibration 208 of camera 20. Factors influencing the radiation measurement, such as the position of the sun, can be taken into account during the conversion.

[0122] In Figure 4The individual steps for determining the global irradiance 120 of solar radiation and / or its respective components, direct radiation 250, diffuse radiation 260, radiation reflected at ground level, in the horizontal plane 40 and in the plane inclined to the horizontal plane 40 are described.

[0123] In step S100, the radiation reflected at the ground is determined using albedo 100, inclination and orientation 102 of the inclined plane, as well as a measured value 104 of the global irradiance in the plane 44 of the radiation sensor unit 10.

[0124] In step S102, the direct radiation 108 in plane 44 of the radiation sensor unit 10 is determined by subtracting S102 from the measured value of the diffuse radiation 220, evaluated for plane 44 of the radiation sensor unit 10, from the global irradiance in plane 44 of the radiation sensor unit 10. The diffuse radiation 220 in plane 44 of the radiation sensor unit 10 is previously determined in module S200, described in Figure 5 , certainly.

[0125] The direct normal radiation 110 is then determined by reversing the projection in step S104 into the plane 44 of the radiation sensor unit 10 using the location and time 106 calculated in step S103 as the position of the sun.

[0126] In step S106, the direct normal radiation 110 is multiplied by a correction factor, which includes, in particular, lens parameters of the camera 20. This results in a lens refraction correction.

[0127] In step S108, the direct radiation 108 in plane 44 of the radiation sensor unit 10 and the lens refraction correction are added. In step S110, the projection onto plane 44 of the radiation sensor unit 10 is reversed, taking into account the sun's position calculated in step S103. Then, in step S112, this direct normal radiation 108 is projected onto the horizontal and / or inclined plane, taking into account its inclination and orientation 102, to obtain the corrected measurement of the direct radiation 250 in that plane.

[0128] In step S116, the lens refraction correction of the diffuse radiation 220 is evaluated for the inclined or horizontal plane, which is in module S200, as in Figure 5 The described value is determined and subtracted. This yields a corrected measurement of the diffuse radiation 260 in the relevant inclined or horizontal plane.

[0129] Then, in step S114, the global irradiance 120 in the horizontal and / or inclined plane can be determined by summing the radiation reflected at the ground from step S100, the direct radiation 250 as a component of the global irradiance 120 in the horizontal and / or inclined plane from step S112, and the diffuse radiation 260 as a component of the global irradiance 120, evaluated for the horizontal and / or inclined plane, corrected in step S116.

[0130] In Figure 5 A flowchart for determining the diffuse irradiance 220 originating from the sky in the horizontal or inclined plane, in particular in the plane 44 of the radiation sensor unit 10 using the module S200, is shown.

[0131] In step S202, a broadband correction factor 210 is first determined from the ratio of broadband radiation to the proportion registered by the camera 20 using the daylight spectrum 200 and the spectral sensitivity 202 of RGB channels of the camera 20.

[0132] In step S204, weights of the RGB channels are determined according to the inverse sensitivity using the recording settings 204 of camera 20.

[0133] This allows the weighted RGB channels of camera image 206 to be summed in step S206.

[0134] In step S208, the summed RGB channels are multiplied by the broadband correction factor 210.

[0135] This allows, in step S210, angular ranges of the sky to be assigned to image pixels of camera 20 using internal and / or external calibration values ​​208 of camera 20.

[0136] Then, in step S212, these image areas are weighted according to the projection into the horizontal and / or inclined plane.

[0137] In parallel, in step S216, the angular range of the field of view of the horizontal and / or inclined plane is determined from the inclination and orientation 102 of this plane, while in step S220, the angular range of the sun disk is determined from the location and time 106.

[0138] This allows the angular range of the sun disk to be excluded from the angular range of the field of view 26 of the horizontal and / or inclined plane in step S218.

[0139] Subsequently, in step S214, the image areas from step S212 are integrated across the field of view of the horizontal or inclined plane.

[0140] The diffuse radiation 220 in the horizontal or inclined plane, in particular in the plane 44 of the radiation sensor unit 10, can then be calculated in step S222 by multiplication with the correction factor 212 of the camera sensitivity, which was previously determined using the module S300.

[0141] In the illustrated embodiment in Figure 5 The diffuse radiation 220 is determined in the horizontal or inclined plane, in particular in plane 44 of the radiation sensor unit 10. Using the S200 module, the diffuse radiation 220 can be determined in any horizontal and / or inclined plane.

[0142] Figure 6 This shows a flowchart for calculating the correction factor 212 of the camera sensitivity based on a comparison of the illuminance output by the camera and calculated using the S300 module.

[0143] First, in step S302, weights are determined according to the sensitivity of each RGB channel of the camera 20 using the spectral sensitivity 202 of the RGB channels and the recording settings 204 of the camera 20.

[0144] Subsequently, in step S304, weights are determined according to human perception.

[0145] Using these weights, RGB channels from the RGB camera image 206 can then be weighted and summed in step S306.

[0146] In parallel, in step S310, angular ranges of the sky are assigned to image pixels of camera 20 using the internal and / or external calibration values ​​208 of camera 20.

[0147] Then, in step S308, the weighted RGB channels from step S306 are integrated across the hemisphere of the sky.

[0148] This allows the correction factor 212 of the camera sensitivity to be determined in step S312 by calculating the ratio of the illuminance 300 of the camera 20 and the integrated weighted RGB camera image.

[0149] Figure 7 Figure 1 shows a photograph of the sky with clouds, taken with a camera 20 of a device 500 according to an embodiment of the invention. The image is a typical photograph taken with a fisheye lens, offering a 180° field of view in the hemisphere above the horizontal. Near the zenith, the luminous, unspecified solar disk is visible, while at the edge of the image, closer to the horizon, unspecified clouds are visible. Reference sign

[0150] 10 Radiation sensor unit 12 Housing 14 Sensor 16 Field of view 20 Camera 22 Housing 24 Sensor 26 Field of view 28 Elevation 30 Distance 32 Evaluation unit 40 Horizontal plane 42 North-south axis 44 Plane of radiation sensor unit 45 Tilt angle 46 Plane of camera 47 Tilt angle 100 Albedo 102 Tilt, orientation of the sensor 104 Measured value global irradiance in horizontal plane 106 Location, time 108 Direct radiation in horizontal plane 110 Direct normal radiation 120 Global irradiance in inclined plane 200 Daylight spectrum 202 Spectral sensitivity of the RGB channels 204 Camera recording settings 206 RGB camera image 208 Camera calibration 210 Broadband correction factor 212 Correction factor Camera sensitivity 220 Diffuse radiation in sensor plane 250 Direct radiation in any plane 260 Diffuse radiation in any plane 300 Camera illuminance 500 Device

Claims

1. Method for determining a global irradiance (120) of solar radiation and / or at least one of its components, in a horizontal plane (40) and / or in a plane tilted with respect to the horizontal plane (40), wherein the components comprise direct radiation (250), diffuse radiation (220, 260), radiation reflected off the ground, with a device (500), comprising at least one radiation sensor unit (10), a camera (20), and an evaluation unit (32), which is configured for evaluating measurement data from the radiation sensor unit (10) and / or from the camera (20), wherein the radiation sensor unit (10) is arranged in a plane (44), wherein the radiation sensor unit (10) determines the irradiance of solar radiation in a field of view (16) of 180° over the plane (44), wherein the camera (20) is arranged in a plane (46), wherein the camera (20) captures a field of view (26) of 180° over the plane (46), wherein the radiation sensor unit (10) and the camera (20) are arranged in a combined measurement set-up at the same location, the camera image is an image of the sky, which has RGB channels; wherein a global irradiance of the solar radiation is measured and converted into the global irradiance (120) and / or into one or more of its components in the horizontal plane (40) and / or in the plane tilted with respect to the horizontal plane (40), wherein a determination (S200) of the diffuse radiation (220) in the horizontal and / or tilted plane, in particular in the plane (44) of the radiation sensor unit (10), is carried out comprising the steps of: (i) determining (S202) a broadband correction factor (210) from the ratio of broadband radiation to the portion registered by the camera (20) by means of the daylight spectrum (200) and the spectral sensitivity (202) of RGB channels of the camera (20); (ii) determining (S204) weights of the RGB channels according to the inverse sensitivity by means of the recording settings (204) of the camera (20); (iii) summing (S206) the weighted RGB channels of the camera image (206); (iv) multiplying (S208) the summed RGB channels by the broadband correction factor (210); (v) assigning (S210) angular ranges of the sky to image pixels of the camera (20) by means of internal and / or external calibration values (208) of the camera (20); (vi) weighting (S212) the image areas according to the projection into the horizontal and / or tilted plane; (vii) determining (S216) the angular range of the field of view of the horizontal and / or tilted plane from the tilt and orientation thereof and from the tilt and orientation of the sensor (24) of the camera (20); (viii)determining (S220) the angular range of the solar disc from location and time of day (106); (ix) excluding (S218) the angular range of the solar disc from the angular range of the field of view of the horizontal and / or tilted plane; (x) integrating (S214) the image areas over the field of view; (xi) determining the diffuse radiation (220) in the horizontal and / or tilted plane, in particular in the plane (44) of the radiation sensor unit (10), by multiplication (S222) by a correction factor (212) of the camera sensitivity.

2. Method according to Claim 1, wherein for converting the irradiance of the solar radiation in the plane (44) of the radiation sensor unit (10), said irradiance having been determined by the radiation sensor unit (10), into the global irradiance (120) and / or into at least one of its components in the horizontal and / or tilted plane, at least one of the variables of radiation reflected off the ground, and / or diffuse radiation (220) in the in the horizontal and / or tilted plane, in particular in the plane (44) of the radiation sensor unit (10), and / or the position of the sun in the radiation measurement, and / or a sensor-specific correction factor, which comprises in particular lens parameters of the camera (20), is used.

3. Method according to Claim 1 or 2, wherein for converting measured values of the camera (20), at least one of the variables of a ratio (210) of a broadband radiation to the portion of the radiation registered by the camera (20), and / or an intensity (202) of RGB channels of the camera (20), and / or an internal and / or external calibration (208) of the camera (20), and / or a tilt and an orientation (102) of the sensor (24) of the camera (20), and / or a tilt and an orientation of the tilted plane, and / or the position of the sun in the radiation measurement, and / or a camera sensitivity, which is determined from an illuminance (300) of the camera (20) and / or the spectral sensitivity (202) of the RGB channels and / or recording settings (204) and / or the RGB camera image (206) and / or the internal and / or external calibration (208) of the camera (20), is used.

4. Method according to any of the preceding claims, wherein the method includes image information of the camera (20) for converting the global irradiance (120) in the plane (44) of the radiation sensor unit (10) into the global irradiance (120) and / or into at least one of its components in this or some other horizontal and / or tilted plane, in particular wherein the combination of the image information of the camera (20) and / or measured values of the radiation sensor unit (10) is used to reduce the measurement errors caused by image artifacts.

5. Method according to any of the preceding claims, wherein the determination of the direct radiation (250) as a component of the global irradiance (120) in an arbitrary plane is carried out comprising the steps of: (i) determining (S100) a radiation reflected off the ground by means of albedo (100), tilt and orientation (102) of the tilted plane, and a measured value (104) of the global irradiance in the plane (44) of the radiation sensor unit (10); (ii) determining the direct radiation (108) in the plane (44) of the radiation sensor unit (10) by subtraction (S102) of the measured value of the diffuse radiation, evaluated for the plane (44) of the radiation sensor unit (10), and the radiation reflected off the ground, evaluated for the plane (44) of the radiation sensor unit (10), from the global irradiance (120) in the plane (44) of the radiation sensor unit (10); (iii) determining a direct normal radiation (110) by reversing the projection (S104) into the plane (44) of the radiation sensor unit (10) by means of the position of the sun calculated from location and time of day (106); (iv) determining a lens refraction correction by multiplying (S106) the direct normal radiation (110) by a correction factor, which comprises in particular lens parameters of the camera (20); (v) determining the corrected direct radiation (250) by adding (S108) the direct radiation (108) in the plane (44) of the radiation sensor unit (10) and the lens refraction correction, and reversing the projection (S110) into the plane (44) of the radiation sensor unit (10) and projection (S112) into the arbitrary plane.

6. Method according to any of the preceding claims, wherein the determination of the diffuse radiation (260) as a component of the global irradiance (120) in an arbitrary plane is carried out comprising the steps of: (i) determining (S100) a radiation reflected off the ground by means of albedo (100), tilt and orientation (102) of the tilted plane, and a measured value (104) of the global irradiance in the plane (44) of the radiation sensor unit (10); (ii) determining the direct radiation (108) in the plane (44) of the radiation sensor unit (10) by subtraction (S102) of the measured value of the diffuse radiation, evaluated for the plane (44) of the radiation sensor unit (10), and the radiation reflected off the ground, evaluated for the plane (44) of the radiation sensor unit (10), from the global irradiance in the plane (40) of the radiation sensor unit (10); (iii) determining a direct normal radiation (110) by reversing the projection (S104) into the plane (44) of the radiation sensor unit (10) by means of the position of the sun calculated from location and time of day (106); (iv) determining a lens refraction correction by multiplying (S106) the direct normal radiation (110) by a correction factor, which comprises in particular lens parameters of the camera (20); (v) determining the corrected diffuse radiation (260) by subtracting the lens refraction correction (S116) from the diffuse radiation (220), evaluated for the arbitrary plane.

7. Method according to any of the preceding claims, wherein the determination of the global irradiance (120) of the solar radiation in the horizontal and / or tilted plane is carried out comprising the steps of: (i) determining (S100) a radiation reflected off the ground by means of albedo (100), tilt and orientation (102) of the tilted plane, and a measured value (104) of the global irradiance in the plane (44) of the radiation sensor unit (10); (ii) determining the direct radiation (108) in the plane (44) of the radiation sensor unit (10) by subtraction (S102) of the measured value of the diffuse radiation, evaluated for the plane (44) of the radiation sensor unit (10), and the radiation reflected off the ground, evaluated for the plane (44) of the radiation sensor unit (10), from the global irradiance in the plane (44) of the radiation sensor unit (10); (iii) determining a direct normal radiation (110) by reversing the projection (S104) into the plane (44) of the radiation sensor unit (10) by means of the position of the sun calculated from location and time of day (106); (iv) determining a lens refraction correction by multiplying (S106) the direct normal radiation (110) by a correction factor, which comprises in particular lens parameters of the camera (20); (v) adding (S108) the direct radiation (108) in the plane (44) of the radiation sensor unit (10) and the lens refraction correction, and reversing the projection (S110) into the plane (44) of the radiation sensor unit (10) and projection (S112) into the horizontal and / or tilted plane; (vi) subtracting the lens refraction correction (S116) from the diffuse radiation, evaluated for the horizontal plane (40) and / or the tilted plane; (vii) determining the global irradiance (120) in the horizontal and / or tilted plane by summing (S114) the radiation reflected off the ground, the direct radiation (250) in the horizontal and / or tilted plane, and the diffuse radiation (260), evaluated for the horizontal and / or tilted plane.

8. Method according to any of the preceding claims, wherein a determination (S300) of the correction factor (212) of the camera sensitivity is carried out comprising the steps of: (i) determining (S302) weights according to the sensitivity of each RGB channel of the camera (20) by means of the spectral sensitivity (202) of the RGB channels and the recording settings (204) of the camera (20); (ii) determining (S304) weights according to human perception; (iii) summing (S306) the weighted RGB channels from the RGB camera image (206); (iv) assigning (S310) angular ranges of the sky to image pixels of the camera (20) by means of the internal and / or external calibration values (208) of the camera (20); (v) integrating (S308) the weighted RGB channels over the hemisphere of the sky above the plane (46) of the camera (20); (vi) determining the correction factor (212) of the camera sensitivity by calculation (S312) of the ratio of the illuminance (300) of the camera (20) and the integrated weighted RGB camera image.

9. Device (500) for carrying out a method according to any of the preceding claims, comprising at least one radiation sensor unit (10), a camera (20), and an evaluation unit (32), which is configured for evaluating measurement data from the radiation sensor unit (10) and / or from the camera (20), wherein the radiation sensor unit (10) is arranged in a plane (44), wherein the radiation sensor unit (10) determines the irradiance of solar radiation in a field of view (16) of 180° over the plane (44), wherein the camera (20) is arranged in a plane (46), wherein the camera (20) captures a field of view (26) of 180° over the plane (46), wherein the radiation sensor unit (10) and the camera (20) are arranged in a combined measurement set-up at the same location, wherein the irradiance of solar radiation is measured by means of the radiation sensor unit (10) in the plane (44) of the radiation sensor unit (10), wherein the camera captures a recording of the sky in the field of view (26) and the camera image is an image of the sky, which has RGB channels, wherein the evaluation unit is configured to carry out a determination (S200) of the diffuse radiation (220) in the horizontal and / or tilted plane, in particular in the plane (44) of the radiation sensor unit (10), comprising the steps of: (i) determining (S202) a broadband correction factor (210) from the ratio of broadband radiation to the portion registered by the camera (20) by means of the daylight spectrum (200) and the spectral sensitivity (202) of RGB channels of the camera (20); (ii) determining (S204) weights of the RGB channels according to the inverse sensitivity by means of the recording settings (204) of the camera (20); (iii) summing (S206) the weighted RGB channels of the camera image (206); (iv) multiplying (S208) the summed RGB channels by the broadband correction factor (210); (v) assigning (S210) angular ranges of the sky to image pixels of the camera (20) by means of internal and / or external calibration values (208) of the camera (20); (vi) weighting (S212) the image areas according to the projection into the horizontal and / or tilted plane; (vii) determining (S216) the angular range of the field of view of the horizontal and / or tilted plane from the tilt and orientation thereof and from the tilt and orientation of the sensor (24) of the camera (20); (viii)determining (S220) the angular range of the solar disc from location and time of day (106); (ix) excluding (S218) the angular range of the solar disc from the angular range of the field of view of the horizontal and / or tilted plane; (x) integrating (S214) the image areas over the field of view; (xi) determining the diffuse radiation (220) in the horizontal and / or tilted plane, in particular in the plane (44) of the radiation sensor unit (10), by multiplication (S222) by a correction factor (212) of the camera sensitivity.

10. Device according to Claim 9, wherein at least one sensor (14) of the radiation sensor unit (10) and at least one sensor (24) of the camera (20) are each arranged in the horizontal plane (40) in such a way that the field of view (16, 26) of the two sensors (14, 24) in each case is above the horizontal plane (40) and terminates with the horizontal plane (40).

11. Device according to Claim 9 or 10, wherein a distance (30) between the radiation sensor unit (10) and the camera (20) is set or settable in such a way that the sensor (14) of the radiation sensor unit (10) is visible in the field of view (26) of the camera (20) with an elevation (28) of at most 10°, preferably of at most 5°.

12. Device according to any of Claims 9 to 11, wherein the radiation sensor unit (10) and the camera (20) are coupled, such that measurement data are recorded by radiation sensor unit (10) and camera (20) in a manner synchronized over time.

13. Device according to any of Claims 9 to 12, wherein the camera (20) is designed to the effect that at least the following properties are present: - an individual image is recorded in a fixed time frame, in particular every half minute and full minute; - the at least one sensor (24) of the camera (20) has a constant colour temperature; - the camera (20) has a constant exposure duration for each individual image; - for an exposure control of the camera (20), a predefined minimum value of an average image brightness is set, wherein the exposure duration remains unchanged at a higher image brightness, in particular wherein the predefined minimum value of an average image brightness is preferably at most 10%, particularly preferably at most 8%, very particularly preferably at least 5%.

14. Device according to any of Claims 9 to 13, wherein the camera (20) is designed to record the sky in the field of view (26).

15. Device according to any of Claims 9 to 14, wherein the radiation sensor unit (10) has at least one out of pyranometer, in particular thermopile pyranometer, photodiode, photovoltaic reference cell.

16. Device according to any of Claims 9 to 15, wherein the radiation sensor unit (10) is designed to the effect that measurement data are recorded by the radiation sensor unit (10) with high temporal resolution, in particular with a temporal resolution of less than 10 sec, preferably less than 5 sec, particularly preferably less than or equal to 1 sec.

17. Device according to any of Claims 9 to 16, wherein the radiation sensor unit (10) is designed to capture solar radiation in a wavelength range of 0.3 µm to 3 µm.

18. Device according to any of Claims 9 to 17, wherein the camera (20) is designed to capture the entire field of view (26) in one recording, in particular wherein the camera (20) is designed as a surveillance camera and / or as a fisheye camera.