Patent Description:
Radiometers, such as pyranometers and pyrheliometers, are used for determining incoming radiation from the sun. For proper operation and for determining the actual radiation at the location, originating from the sun, it is important that transparency of protective windows separating a detector from the outside is substantially continuous over time. However, pollutants in the air, either airborne, carried by means of precipitation or present in any other way, deposit on the protective windows. This affects transparency of the protective windows over time, in a not easy to predict way. This, in turn, affects accuracy of measurements. Cleaning is a good solution, but as the progress of soiling is very difficult to predict, cleaning is usually done rather too often than not. This is at a certain cost.

<CIT> relates to a fire alarm which consists of a housing in which sensors, a radiation source, and an optical window are disposed. A reflector protection basket or ring is disposed above the optical window. The basket or ring is suit-able for protecting the optical window against mechanical influences, allows UV and IR radiation to pass through to a sufficient degree, and reflects UV and IR radiation from the housing interior, on its inside. Monitoring of the contamination of the window, function monitoring of the sensors and of the signal processing electronics, as well as easy replaceability of the components in the fire alarm are provided.

<CIT> relates to a foreign-particle detection system for use with an optical instrument having a transmissive window with a first side and a second side. The detection system includes a radiation source to emit a radiation signal, a diffusing reflector to diffusively spread the radiation signal emitted by the radiation source over the first side of the transmissive window, a radiation detector to detect, at the second side of the transmissive window, the diffusively spread radiation signal transmitted by the transmissive window, and to generate a detected radiation signal based on the detected diffusively spread radiation signal, and a computation module communicatively coupled to the radiation detector to detect a presence of foreign particles on at least one of the first side or the second side of the transmissive window based on at least the detected radiation signal.

<CIT> relates to device for detecting soiling. The device comprises a light source, which emits a light beam, and an opaque layer having a first boundary surface and a second boundary surface, whereby the light beam emitted by the light source first impinges on the first boundary surface, and part of a light beam fraction, which is scattered at the second boundary surface, impinges on a receiver and forms a measuring signal, and hereby the first boundary surface is set up to scatter part of the incident light beam, and the part impinging on the receiver of the light beam, scattered at the first boundary surface, forms a reference signal, and the device is set up further to determine a measure for the soiling of the second boundary surface from the comparison of the reference signal and measuring signal.

Thus, according to an aspect, the problem relates to improving the detection of soiling of a shield.

This problem is solved by the subject-matter of the independent claims.

it is preferred to determine an amount of soiling on the protective window locally.

A first aspect provides a device for detecting solar irradiance. The device comprises a housing, a detector for receiving solar irradiance and for providing a detector signal providing an indication of an amount of solar irradiance received by the detector and a shield transparent to at least part of the solar irradiance to be detected, a shield connection body for connecting the device to the shield and the housing providing a detector space for housing at least part of the detector. The device further comprises a first light source for emitting light to the shield and a first light sensor arranged to receive light from the first light source, arranged to provide a first signal providing an indication for an amount of light received by the first light sensor. The device is arranged to be coupled to a processing unit arranged to compare a value of the first signal to a reference sensor value and arranged to generate a first warning signal if a difference between the sensed value of the sensor signal and the reference sensor value is above a first predetermined threshold. According to the invention, the processing unit is arranged to determine, based on the first signal, a transmission value related to a transmission factor of the shield for a range of electromagnetic waves and output the transmission.

Usually, if the shield is clean, the shield and in particular the inner wall thereof will reflect only a very small part of the light emitted by the light source. Most of the light emitted by the light sources will travel through the shield, to the outside of the device. However, particles, either solid or liquid - or both - will scatter light and reflect light back in to the detector space. The reflected light may be received by the light sensor. Hence, the magnitude of a signal generated by the light sensor in response to receive light is an indication for pollution of the outer wall of the shield. Therefore, a signal is generated if the difference between the signal received from the sensor and a reference signal value is too high, to warn for pollution.

Additionally to providing a warning signal, also another type of information signal based on the first signal may be provided. For example, a value indicating a loss of transmission due to pollution may be reported or a value indicating actual transmission of the shield. The value provided is determined based on the first signal and is provided for a frequency range of electromagnetic waves, in particular for the sunlight spectrum or a part thereof, including at least a part of visible light and, optionally, near infra-red and/or near ultra-violet. Alternatively or additionally, based on a calculated transmission loss due to pollution of the shield, an efficiency loss of a photovoltaic panel may be reported.

In an embodiment, the first light source is arranged for emitting a first light beam that coincides with the shield at a first angle relative to the shield and at a first incidence area on the shield, resulting in a first reflected beam, the first light sensor is arranged for sensing light originating from the first incidence area; and the first light sensor is provided out of the path of the first light beam and the path of the first reflected first light beam.

While measuring the scattered light and reducing or even preventing incidence of direct light or a directly reflected beam, pollution of the shield may be better determined. Reason for this is that in this setup, the first light sensor will predominantly receive light from the first light source that is scattered by pollutants on the outer side of the shield.

According to the invention a second light sensor is arranged for sensing light from the first beam or the first reflected beam. The value from the second sensor may be used to filter out any degradation of the first sensor, the second sensor and the light source.

An embodiment of the device comprises a second light source for emitting light to the shield and a second light sensor arranged to receive light from the second light source, arranged to provide a second sensor signal providing an indication for an amount of light received by the second light sensor. The device according to the invention works in conjunction with the processing unit that is further arranged to compare the first sensor signal to the second sensor signal and generate a second warning signal if a sensor signal difference between the first sensor signal and the second sensor signal is above a second predetermined threshold.

Different sensors and different light sources may be positioned at different locations around the detector. Hence, signals received by the different sensors provide an indication of pollution at different locations of the shield. A difference in values of the first sensor and the second sensor above a particular threshold indicates a difference in pollution at different areas of the shield. If signal values are substantially equal, pollution is homogeneous.

A further embodiment of the device works advantageously if the processing unit is further arranged to generate a third warning signal if a sensor signal difference between the first sensor signal and the second sensor signal is below a second predetermined threshold if the difference between the first sensor signal or the second sensor signal on one side and the reference sensor value on another side is above the first predetermined threshold.

This processing unit generates a signal in case of substantially homogeneous pollution of the shield. Signal distortion due to homogeneous pollution requires less processing power to compensate for.

In a further embodiment, the processing unit is arranged to obtain colour correction data related to colour characteristics of particles of surroundings of the device and the processing unit is arranged to adjust a value of the first signal or to adjust the reference value based on the colour information obtained. Different colour particles scatter light in a different way and may absorb a certain amount of light. Pollution of white particles an pollution of black particles provide different intensities of scattered light, even though they reduce transmission of light through the shield with substantially the same amount. This is because black particles usually absorb more light than white particles. this embodiment allows to compensate for the different signals and provide a signal that provides an uniform signal substantially the same for the amount of blocked light from outside, irrespective from the colour of the pollutants.

A second aspect provides a system for determining soiling of a shield for covering a detector for detecting solar irradiance, comprising the device according to any of the preceding claims and the processing unit.

A third aspect provides a solar panel. The solar panel comprises a laminate comprising a transparent shielding layer and a photovoltaic layer arranged for receiving solar irradiance transmitted through the shielding layer; and the device according to the first aspect. The device is provided such to receive solar irradiance transmitted through the shielding layer.

A fourth aspect provides a method of determining soiling of a shield for covering a detector for detecting solar irradiance in a device. The device comprises a housing, a detector for receiving solar irradiance and for providing a detector signal providing an indication of an amount of solar irradiance received by the detector, the shield, the shield and the housing providing a detector space for housing at least part of the detector. The device further comprises a first light source for emitting light to the shield and a first light sensor for providing a first signal providing an indication for an amount of light received by the first light sensor. The method comprises receiving the first signal, comparing a value of the first signal to a reference sensor value and generating a first warning signal if a difference between the sensed value of the sensor signal and the reference sensor value is above a first predetermined threshold. Additionally to comparing the method comprises, according to the invention, determining, based on the first signal, a transmission value related to a transmission factor of the shield for a range of electromagnetic waves and output the transmission value.

The claimed invention further comprises a computer programme product as defined in claim <NUM>.

The various aspects and embodiments thereof will now be discussed in further detail in conjunction with Figures. In the Figures,.

<FIG> shows a pyranometer <NUM> as a radiometer. The pyranometer <NUM> comprises a device housing <NUM> provided with holder cup <NUM> for receiving a detector housing module <NUM> which forms part of the device housing <NUM>. The holder cup <NUM> may be a through hole in the housing <NUM>. The device housing <NUM> further comprises an optional circular depression <NUM> for receiving a rim of a dome <NUM>. At the bottom of the circular depression <NUM>, an O-ring may be provided for providing a substantially watertight closure. The dome <NUM> is provided for protection of electrical and electronic elements held by the detector housing module <NUM>. The dome <NUM> acts as a shield to any pollution, yet it is transparent or at least largely transparent for a spectrum of solar irradiation the pyranometer <NUM> is intended to detect.

The detector housing module <NUM> comprises a detector <NUM> for receiving solar irradiation to detect. The detector <NUM> is arranged to generate a signal upon receiving solar irradiation. Preferably, the detector <NUM> comprises a thermocouple, though other types of detectors may be envisaged as well. The detector <NUM> is provided in the centre of the detector housing module <NUM> and in the centre of the dome <NUM>.

The detector housing module <NUM> further holds multiple LEDs <NUM>, indicated as circles, as light sources. Alternatively to LEDs, also other light sources may be used, including, but not limited to laser and laser diodes in particular, incandescent or fluorescent light sources, other, or a combination thereof. The LEDs <NUM> are preferably blue light LEDs, with a spectrum peak between <NUM> and <NUM>. An advantage of such light emitting diodes is that their operation is only to a small extent affected by temperature.

The detector housing module <NUM> also comprises photo sensors <NUM>, arranged for detecting light and for generating a signal, of which signal the value relates to an amount of light received. The photo sensors <NUM> are at least sensitive to a spectrum emitted by the LEDs <NUM>.

The LEDs <NUM> and the photo sensors <NUM> are preferably arranged such that light emitted by any LED <NUM> and directly reflected by the inner wall of the dome <NUM> cannot reach a photo sensor <NUM>. Yet, light scattered by any particle, either solid or liquid, present on the inner wall or the outer wall of the dome <NUM>, may be received by any photo sensor <NUM>. Therefore, viewed from the top of the pyranometer <NUM>, the LEDs <NUM> and the photo sensors <NUM> are preferably not aligned on one line with the centre of the detector housing module <NUM> or with the detector <NUM>.

<FIG> provides a schematic representation of a system <NUM> for determining soiling of the pyranometer <NUM>. The system <NUM> comprises the pyranometer <NUM> with the components discussed above. Furthermore, <FIG> shows the pyranometer <NUM> to comprise an optional pyranometer signal processor <NUM>. The pyranometer signal processor <NUM> receives signals from the detector <NUM> and the photo sensors <NUM>, processes the signals and transmits the processed signals to a processing module <NUM>. The processing may include noise reduction, digitalisation, compression, amplification, filtering, other, or a combination thereof. The pyranometer signal processor <NUM> may also be arranged for controlling operation of the LEDs <NUM>.

The processing module <NUM> comprises a communication unit <NUM> for receiving signals from the pyranometer <NUM>, either processed or unprocessed. The received signals are provided to a general processing unit <NUM> for assessment of the signals. The processing module <NUM> may further comprises a storage module <NUM> for storing of data, including a computer programme product, like firmware, for programming the general processing unit <NUM> for executing operations as discussed above and below. The processing module <NUM> may be a separate entity or comprised by the pyranometer <NUM>.

The operation of the system <NUM> will now be discussed in further detail in conjunction with <FIG> and a flowchart <NUM> provided by <FIG>. The various parts of the flowchart are briefly summarised in the table below:.

The procedure starts in a terminator <NUM> and proceeds by checking for daylight conditions in step <NUM>. If daylight condition is determined, the procedure branches to step <NUM> for switching to AC - alternating current - mode and proceeds to step <NUM>. If no daylight condition is determined, the procedure does not branch to step <NUM> and proceeds to step <NUM> in DC mode.

In step <NUM>, a first LED is lit and in step <NUM>, a second LED is lit. Alternatively, more or less LEDs <NUM> are lit, yet in this embodiment, two LEDs <NUM> are lit. In DC mode, the LEDs <NUM> are preferably lit continuously for a pre-determined amount of time. In AC mode, the LEDs <NUM> are preferably lit intermittently for a pre-determined amount of time. As background light like daylight and also other regular light during night time, such as moonlight and street lighting, has a substantially continuous nature, intermittently emitted LED light may be differentiated from background light.

In step <NUM>, a first signal is received from a first photo sensor and a second signal is received from a second photo sensor <NUM> in step <NUM>. The first LED <NUM> and the second LED <NUM> may be activated over the same period or over different periods, either overlapping or complementary, in DC as well as in AC mode. So the second photo sensor <NUM> may receive light from the first LED <NUM> as well as from the second LED <NUM>. This applies to the first photo sensor <NUM> as well.

The signals received from the photo sensors <NUM> are generated by the photo sensors <NUM> in response to receiving light. That light may originate from the LEDs <NUM>, but also from background light such as sun, moon, street lighting, other, or a combination thereof. The AC mode is devised to compensate for light not originating from the LEDs <NUM>.

In the AC mode, the receiving of the signals includes determining an alternating component in the received signal, preferably a component alternating at the same frequency as at which the LEDS <NUM> intermittently emit their light. More in particular, an amplitude of the alternating component is determined as a signal value and a signal magnitude in particular for each of the signals provided by the photo sensors <NUM>.

In step <NUM>, the first signal and in particular a magnitude of the first signal is compared to a pre-defined threshold. Over normal operation of the pyranometer <NUM>, only a small amount of the light emitted by the LEDs <NUM> will be reflected by the inner wall of the dome <NUM> and most of the light will pass through the dome <NUM>. If the outer wall of the dome <NUM> is soiled, light passing through the dome <NUM> will be scattered and reflected towards the space inside the dome <NUM>. The scattered light is received by the photo sensors <NUM>. Hence, an increased amount of light received by the photo sensors <NUM> and an increased signal magnitude provide an indication of soiling of the outer wall of the dome <NUM>.

Therefore, if the magnitude of the first signal is below a first pre-determined threshold, the soiling of the outer wall of the dome <NUM> is determined to be below a per-determined threshold. This is implemented in step <NUM>: if the first signal is below the first pre-determined threshold, the process proceeds to step <NUM> in which the magnitude of the second signal is compared to a second pre-determined threshold. If the first signal is above the first pre-determined threshold, the process branches to step <NUM> in which a first warning signal is set, to indicate the outer wall of the dome <NUM> is soiled above a particular level - and action may need to be taken.

Additionally to providing the first warning signal, the first value of the first signal may provided to a user, for example on a display. Alternatively, the first signal is processed to provide other useful information to a user. Such information may be a loss of transparency of the shield, an indication of a level of pollution of the shield, a level of production loss of a photovoltaic panel in the vicinity of the pyranometer, other, or a combination thereof.

After step <NUM>, the process continues to step <NUM>. In this step, if the magnitude or another value of the second signal is above the second pre-determined threshold, the process branches off to step <NUM> in which a second warning signal is set. If the magnitude or another value of the second signal is below the second pre-determined threshold, the process continues to step <NUM>. Also after step <NUM>, the process continues to step <NUM>. The second pre-determined threshold may be the same as the first pre-determined threshold - or different.

In step <NUM>, values of the first signal and the second signal are compared. Preferably, magnitudes of the signals are compared. As discussed above, photo sensors <NUM> and LEDs <NUM> are distributed along the detector and preferably at regularly distances. It is noted that preferably, a photo sensor <NUM>, the detector <NUM> and an LED <NUM> are not provided on one line. So each photo sensor receives light shattered by another particle at the outer wall of the dome <NUM> or shattered by multiple particles at particular areas of the outer wall of the dome <NUM>.

This means that, if the signal values compared are substantially equal - or differ by not more than a third pre-determined threshold, the soiling of the outer wall of the dome <NUM> is substantially homogeneous. If the signal values compared differ by more than the third pre-determined threshold, the soiling of the outer wall of the dome <NUM> is determined to be homogeneous.

If the soiling of the outer wall of the dome <NUM> is determined to be homogeneous, difference between the first signal and the first pre-determined threshold and/or difference between the second signal and the second pre-determined threshold may provide an indication for compensation of a detector signal generated by the detector <NUM> upon receiving irradiation. Homogeneous soiling affects the general sensitivity of the pyranometer <NUM> in general, which allows for determining a compensation. This will be discussed below in further detail.

Compensation may also be possible in case of inhomogeneous soiling, though this will be more difficult as it is difficult to determine the distribution of the soiling. In particular if the level of soiling is distributed randomly over the outer wall of the dome <NUM>, determining a way of compensating the detector signal to take the soiling into account is a tedious task. Whereas it may be possible, this embodiment will only compensate for soiling if substantial homogeneous soiling is determined.

Additionally or alternatively, providing compensation may comprise providing an accuracy estimator. The accuracy estimator may be provided as a percentage of a measurement value or a value of a signal provided by the detector <NUM>. Alternatively, it may be provided as an absolute value, to be added to or subtracted from a detected value.

A radiometer like the pyranometer <NUM> has an accuracy of about <NUM>%, out of manufacturing. However, soiling of the dome <NUM> of the pyranometer <NUM> may seriously affect the accuracy of the pyranometer <NUM> as not all light incident to the pyranometer <NUM> reaches the detector <NUM>. This may even be the case if homogeneous soiling has been determined. A decreased accuracy may be caused by randomness of soiling: even when homogeneous is detected, the soiling will have a random character. This random character means transparency of the dome <NUM> to radiation to be detected will also be affected in a random way.

The value with which accuracy is to be corrected due to soiling may be determined based on experimental data. Experiments may provide a link between a level of soiling, a level of homogeneity of the soiling, a signal level of a signal generated by the detector <NUM>, another factor or a combination thereof on one hand and the accuracy of the detector <NUM> under particular circumstances on the other hand. The corrected accuracy value may be used for correcting a signal level. Alternatively or additionally, the corrected accuracy level may be provided as such to an observer of the system <NUM> as shown by <FIG>.

In step <NUM>, the process branches to step <NUM> if the difference between the first signal and the second signal is above the third pre-determined threshold. In step <NUM>, a third warning signal is issued and the process branches to a terminator <NUM> and the process ends.

The process branches to step <NUM> from step <NUM> if the difference between the first signal and the second signal is below the third pre-determined threshold - and substantially homogeneous soiling is determined. In step <NUM>, a particular amount and, in case desired and available, a particular method of compensation is determined. It may be determined the detector value is only to be multiplied by a fixed amount. Alternatively or additionally, compensation may be made dependent on the time of the day.

A reason for doing so is that soiling of the outer wall of the dome <NUM> results in scattering of sunlight. This means that if the sun is very low, for example at an angle of less than five degrees with earth's surface, yet more light will be received by the detector <NUM> due to the scattering of particles. And if the sun is at a high position, around noon, the detector <NUM> will receive less radiation as certain radiation will be reflected away from the detector <NUM>, depending on distribution of particles or any other type of soiling.

The compensation may be made more accurate by providing a compensation curve comprising a compensation factor as a function of the time of day. Further accuracy may be obtained by providing calibrated curves per specific location. A reason for providing location dependent curves is that the nature of soiling particles and dust particles in particular vary per geographical location. The compensation value may be used for correcting the signal generated by the detector <NUM> or by correcting another value representing sun radiance intensity at a further step of processing the signal provided by the detector <NUM>.

In step <NUM>, the compensation determined in step <NUM> is applied to the detector signal. Subsequently, the process ends in the terminator <NUM>.

The processing of the signals, from the photo sensors <NUM> and from the detector <NUM>, is handled by the general processing unit <NUM>. In the embodiments discussed above, the general processing unit <NUM> is comprised by the processing module <NUM>. Alternatively, the general processing unit <NUM> is comprised by the housing <NUM> of the pyranometer <NUM>.

<FIG> show a particular configuration of the pyranometer <NUM> and the dome <NUM>, the LEDs <NUM> and the photo sensors <NUM> in particular. In the embodiments shown by <FIG>, the LEDs <NUM> and the photo sensors <NUM> are provided in a single plane, with the LEDs <NUM> and the photo sensors <NUM> provided in a concentric circle around the detector <NUM>. Furthermore, the LEDs <NUM> and the photo sensors <NUM> are provided in one space, defined by the housing <NUM> and the detector housing module <NUM> in particular on one side and the dome <NUM> on the other hand.

<FIG> shows another embodiment, in which the LED <NUM> is arranged to couple light into the material of the dome <NUM>. At another position at the rim of the dome <NUM>, the photo sensor <NUM> is provided for receiving - more or less - light emitted by the LED <NUM>. Soiling of the outer wall of the dome <NUM> provides particles at the dome having a particular refractive index. This may result in light emitted by the LED <NUM> to be coupled out of the dome <NUM>. And, in turn, this results in less light received by the photo sensor <NUM>, resulting in a change of signal strength provided by the photo sensor <NUM>.

<FIG> shows a further embodiment of the pyranometer <NUM>. Pyranometers are not uncommonly provided with two domes. <FIG> B shows the pyranometer having two domes, an outer dome <NUM> and an inner dome <NUM>. Within the inner dome <NUM>, the detector <NUM> is provided. In space defined by the housing <NUM>, the outside of the inner dome <NUM> and the inner wall of the outer dome <NUM>, the LEDs <NUM> and the photo sensors <NUM> are provided. The pyranometer <NUM> as shown by <FIG> has a working principle equivalent to that of the pyranometer shown by <FIG>.

<FIG> shows a yet another embodiment, a radiometer <NUM> having a flat window <NUM> as a shield for shielding the detector <NUM>. The radiometer <NUM> is not designed as a common pyranometer, though it may be used for other measurement with respect to intensity and/or radiation of the sun. For example, the radiometer <NUM> as depicted by <FIG> may be embodied as a pyrheliometer. Also the radiometer <NUM> shown by <FIG> C comprises a housing <NUM> and a space defined between the housing <NUM> and the shield <NUM> for housing the detector <NUM>, one or more LEDs <NUM> and one or more photo sensors <NUM>.

In yet another alternative, the LED <NUM> and the photo sensor are provided at opposite sides of the dome <NUM> or the shield <NUM>. <FIG> D shows a detector device <NUM> as again another embodiment. The detector device <NUM> shown by <FIG> may have the same construction as the radiometer <NUM> shown by <FIG>, though without the detector <NUM>. The detector device <NUM> is primarily intended for detecting soiling of the shield <NUM>. The shield <NUM> may be directly comprised by the detector device. Alternatively or additionally, the shield of which the soiling is to be detected is a window of a building, like a greenhouse, or a cover of a photovoltaic laminate. According to an example outside the claimed invention, the detector device <NUM> may be provided without shield of its own; a transparent part of the building, like a window, fulfils the function of the shield. In such an example, the detector device <NUM> comprises a shield connection member for connecting the detector device <NUM> to a panel of which the soiling is to be determined. The shield connection member may be embodied as a ridge as shown by <FIG>, at the outer perimeter of the detector device <NUM>. Alternatively or additionally, adhesive elements may be provided, like glue, suction cups, other, or a combination thereof. Yet, providing the detector device <NUM> with some shielding is preferred for protection of the components. Such shield of the device itself does not play a role in detection of soiling of a window or other transparent panel of the building.

According to an example outside of the claimed invention, the soiling detection is not limited to the shield comprised by the detector device, it may also be used for detecting soiling of a further shield like a window. In that case, the shield <NUM> of the detector device <NUM> is place in close vicinity or even in contact with the window. Between the window and the shield <NUM>, a substance may be provided for adaptation of refractive indexes to prevent unwanted reflections at interfaces of shield, window and air.

Whereas it is preferred that the LED <NUM> and the photo sensor <NUM> are provided within one and the same housing <NUM>, examples outside the claimed invention may be envisaged in which the photo sensor <NUM> and the LED <NUM> are placed on either side of a transparent surface of which soiling is to be detected.

The detector device <NUM> may be embodied in various ways, of which examples are provided below. <FIG> shows the detector device <NUM> provided in a photovoltaic panel <NUM>. The photovoltaic panel <NUM> comprises a transparent front layer <NUM>, a photovoltaic active layer <NUM> and a support layer <NUM>. The transparent front layer <NUM> may be provided in glass, an organic polymer, other, or a combination thereof and is transparent for at least a part of the spectrum of electromagnetic radiation to which the active layer <NUM> is sensitive. The transparent front layer <NUM> may be provided with an anti-reflective coating.

The photovoltaic active layer <NUM> preferably comprises a semiconductor material like silicon, germanium, gallium arsenide, other, or a combination thereof. The active layer <NUM> comprising one or more junctions between areas that have opposite conductivity types. The support layer <NUM> comprises a material suitable to provide rigidity to the photovoltaic panel <NUM>.

The detector device <NUM> is in this embodiment integrated in the photovoltaic panel <NUM>. For integration in the photovoltaic panel <NUM>, the active layer <NUM> and the support layer <NUM> are locally omitted or removed for accommodating the detector device <NUM>. Whereas this constitutes a preferred embodiment, the detector devices <NUM> presented in the various examples may also be provided as stand-alone devices as presented by <FIG>. Otherwise, the detector device may be provided at the inside of a glass panel of a greenhouse or another building.

In this embodiment, the detector device comprises a first light emitting diode - LED - <NUM> as a light source. The first LED <NUM> has a focussed beam. The focussing may be enabled by providing the first LED <NUM> with a lens, a collimator, another optical beam forming element, or a combination thereof. The beam of the first LED <NUM> is directed towards the front layer <NUM> of the photovoltaic panel <NUM>, which front layer <NUM> acts as a shield for the detector device <NUM>. More in particular, the beam of the first LED <NUM> is directed to the front layer <NUM> under a first angle and projects the beam on a first area of incidence <NUM>. The area of incidence is in this embodiment defined at the outer side of the front layer <NUM>.

The detector device further comprises a first light sensor <NUM> that may be embodied as a photodiode or any other suitable device or devices. The first light sensor <NUM> is arranged in the detector device <NUM> to detect light in a small area, thus detected within a relatively narrow first sensor beam indicated by the dotted line in <FIG>. The first sensor beam coincides with the outer side of the front layer <NUM> at a first detection area <NUM>.

The first detection area <NUM> is in this embodiment provided within the first area of incidence <NUM>. In another embodiment the two areas may have the same size, one may be larger than the other or the other way around; most important is that the two areas at least partially overlap. In yet another embodiment, the first light sensor is arranged to sense light at a wide angle, resulting in a large detection area.

Particles on the outside of the front layer <NUM> - dust, sand, pollen, soot, other, or a combination thereof - reflect light emitted by the first LED <NUM> in a scattered fashion. The amount of light scattered provides an indication of an amount of pollution on the outside of the front layer <NUM>.

To properly determine an amount of scattered light, it is advantageous that the first light sensor <NUM> does not receive any direct light emitted by the first LED or light within the reflected first beam. The reflected first beam may be a beam reflected by the inside of the front layer <NUM>, the outside of the front layer or a beam provided by both reflections. The reflected first beam extends from the front layer under the same angle as under which the first beam is incident to the front layer.

To prevent or at least reduce incidence of direct light of the first beam or the first reflected beam, the first light sensor <NUM> is, according to the invention, provided such that it is located out of the light path of the first beam or the first reflected beam. Additionally, the first light sensor <NUM> is provided with a lens, a collimator or another optical element for reducing a detection angle of the first light sensor.

As depicted by <FIG>, the first sensor beam is provided under an angle different from the angle under which the first beam is incident to the front layer <NUM>. Either the angle under which the first sensor beam is provided, the location of the first light sensor <NUM> within the detector device <NUM> or both parameters may both be tweaked to ensure in particular light scattered by potential particles on top of the front layer <NUM> arrives at the first light sensor <NUM>. In the same way, a minimum amount or at most a very small amount of light of the first beam or the reflected first beam arrives at the first light sensor <NUM>. This allows for accurate determination of scattered light. And if a proper position is picked, the angle under which the first light sensor <NUM> is provided may be the same as the angle under which the first LED <NUM> is provided.

The scattered light detected by the first light sensor <NUM> is processed by means of a signal processor <NUM> which is arranged to amplify, filter, encode, decrypt, compress or digitise the signal or provide a combination of these and/or other processing. The processed or unprocessed signal is provided to the a processing module <NUM>. The processing module <NUM> comprises a communication unit <NUM> for communicating with the detector device <NUM>.

The communication unit <NUM> may be arranged for processing the signal in accordance with processing performed by the signal processor <NUM>; the received signal may for example be decompressed. The signal processed by the communication unit <NUM> is provided to the processing unit <NUM>. The processing unit <NUM> may provide further processing of the signal, for example determining an average value, a derivative of the signal value over time, other, or a combination thereof.

The processing unit <NUM> is further arranged to compare the processed signal value, the instantaneous signal value or a combination thereof to one or more pre-determined values stored in a storage module <NUM> comprised by the processing module <NUM>. Based on that comparison, a warning signal is presented if the amount of scattered light sensed is too high, as this may be an indication of pollution of the front layer <NUM>. And if the front layer <NUM> is polluted, less light will reach the active layer <NUM> and less energy may be generated.

Additionally to providing the first warning signal, the first value of the first signal may provided to a user, for example on a display. Alternatively, the first signal is processed to provide other useful information to a user. Such information may be a loss of transparency of the shield, an indication of a level of pollution of the shield, a level of production loss of a photovoltaic panel in the vicinity of the detector device <NUM> or in which the detector device <NUM> is provided, other, or a combination thereof.

Performance of LEDs is known to degrade over time. Some LEDs have a performance degradation already in the first active hour, typical LEDs lose a few percent of their performance after <NUM> to <NUM> hours and even half their performance after approximately <NUM> hours. Degradation of the performance of the first LED <NUM> results the processing module <NUM> being able to determine an amount of pollution in a less accurate way. If the first LED <NUM> produces less light, less light will be reflected by the same amount of particles on the outside of the front layer <NUM> and the signal value generated by the first light sensor <NUM> will be less, with the same amount of pollution. Without correction for the degradation, the processing module <NUM> will report less pollution than is present in reality.

<FIG> provides the same photovoltaic panel <NUM> with the detector device <NUM> as shown by <FIG>. In addition to the detector device shown by <FIG> shows the detector device <NUM> comprising a second light sensor <NUM>. Other than the first light sensor <NUM>, the second light sensor <NUM> is arranged to receive light directly from the first beam or from the reflected first beam. Receiving light directly from the first beam is preferred over measurement on the reflected first beam, as the intensity of the reflected beam may be influenced by scattering by particles at the outside of the shield. The signal generated by the second light sensor <NUM> in response to receiving the direct light is processed and subsequently evaluated for the signal value by the processing module <NUM>.

By assessing pollution of the front layer <NUM> based on a quotient of a first value of the first signal provided by the first light sensor <NUM> on one hand and a second value of the second signal provided by the second light sensor <NUM>, the factor of the degradation of the first LED <NUM> is filtered out as a factor that may influence the determined amount of pollution. It is noted that should there be question of degradation of the light sensors, such degradation is also filtered out. According to the invention, the first value of the first signal provided by the first light sensor <NUM> is divided by the first value plus the second value. This is particularly preferred if the directly reflected signal is measured by the second light sensor <NUM>, rather than the direct beam provided by the first LED <NUM>.

The amount of light scattered by polluting particles depends on characteristics of the particles. Colour of the particles is a relevant factor in this aspect, apart from other aspects like state of the particle - liquid or solid - material of the particle, smoothness of the particles (rounded vs. sharp edges), other, or a combination thereof. The colour of a particle is an important factor in the amount of light scattered. With the same amount of polluting particles or with the same amount of the front layer <NUM> covered with polluting particles, white pollution and highly reflective pollution will provide more scattered light than black pollution or mat pollution. It is preferred to correct a signal value received from the first sensor to adjust for this effect.

Information on adjustment may be provided by storing once or periodically, with updates, correction information comprising a correction factor, in the storage module <NUM>. Additionally or alternatively, the colour of the pollution may be determined automatically. The configuration shown by <FIG> is arrange to provide a correction factor to compensate to at least some extent for differences in colour of pollution.

In the configuration shown by <FIG>, the detector device comprises a second LED <NUM> as a second light source. The second LED <NUM> emits light in a second spectrum, that is different from the first spectrum at which the first LED <NUM> emits light. More in particular, the first spectrum as a part that has no overlap with the second spectrum and the second spectrum has a part that does not overlap with the first spectrum. For example, the first spectrum covers red to yellow and the second spectrum covers yellow to blue. And the first light sensor <NUM> is arranged to be sensitive to the total of the first spectrum and the second spectrum - or at least the largest part of the combined spectrum, including the nonoverlapping parts.

The first LED <NUM> and the second LED <NUM> are operated one after the other. Depending on a first signal value with the first LED <NUM> switched on and a second signal value with the second LED <NUM> switched on, the colour of the scattered light, collected by the first light sensor, may be determined. If the first signal value is higher with the first LED <NUM> switched on compared to the second signal value with the second LED <NUM> switched on, it is likely the colour of the particles is reddish, this may indicate the particles comprise sand. If it is the other way around, the particles may be greenish, indicating presence of algae. The processing of the signals received, as well as the method for controlling the LEDs may be executed by the processing module <NUM> and the processing unit <NUM> in particular.

<FIG> shows another embodiment, in which the detector device <NUM> comprises the first LED <NUM>, the first light sensor <NUM> and a third light sensor <NUM>. Like the first light sensor <NUM>, the third light sensor <NUM> is arranged to capture light scattered by particles at the outer side of the front layer <NUM>, rather than a beam of light provided by the first LED <NUM>.

Whereas the embodiment discussed in conjunction with <FIG> makes use of a wide band sensor and two narrow band light sources, the embodiment shown by <FIG> makes use of a wide band light source and two narrow band light sensors. More in particular, the first LED <NUM> is in this embodiment arranged to emit light over a large part of the visible spectrum. To this purpose, the first LED <NUM> may be an LED module, comprising LEDs emitting light at different narrow spectra. Alternatively or additionally, the first LED <NUM> is a white LED, i.e. a blue light LED covered with a layer breaking down blue light into light with multiple longer wavelengths or lower frequencies.

Likewise, the first light sensor <NUM> is arranged to cover a lower part of the spectrum emitted by the first LED <NUM> and the third light sensor <NUM> is arranged to be sensitive to a higher part of the spectrum emitted by the first LED <NUM>. For obtaining at least some colour information on particles on the outer side of the front layer <NUM>, the first LED <NUM> is switched on and signal values of signals provided by the light sensors are compared. If a first signal value provided by the first light sensor <NUM> is higher than a third signal value provided by the third light sensor <NUM>, the particles probably have a reddish colour and if the first signal value is lower than the third signal value, the particles probably have a greenish colour.

The embodiments discussed in conjunction with <FIG> may be extended with more LEDs, light sensors, or both for more accurate detection of the colours of particles polluting the front layer <NUM>. An issue that may not be directly addressed at this point is an amount of absorption of the particles; pure black particles will provide the same frequency response on sensors are pure white particles. However, pure white particles will provide higher signal values as they reflect more light than black particles. Black particles will absorb more light.

To address this issue, the intensity of light directly emitted by the light sources may be measured and the intensity of the light of light in the beam reflected by the front layer <NUM> may be measured and both values are compared. These values, optionally together with a value indicating an amount of received scattered light, may provide an indication of an amount of light absorbed by the particles. And the amount of absorption may provide a further indication on characteristics of the particles, which, in turn, may contribute to providing a correction factor.

<FIG> shows another embodiment for determining colour of particles on the front layer <NUM> or in the surroundings of the photovoltaic panel <NUM>. The configuration shown by <FIG> is based on the configuration discussed in conjunction with <FIG>. In addition to the configuration discussed in conjunction with <FIG>, at least one of a first colour sensor <NUM> and a second colour sensor <NUM> may be added to the system. The first colour sensor <NUM> is provided in the detector device <NUM>, preferably close to or in contact with the front layer <NUM>. This allows the first colour sensor <NUM> to gather information on colour or colours of particles present at the outside of the front layer <NUM>. This information may be used to look up a correction factor in a correction factor database <NUM> stored on the storage module <NUM>.

The second colour sensor <NUM> is provided apart from the photovoltaic panel <NUM>. This allows the second colour sensor <NUM> to collect information on colour within the surroundings of the photovoltaic panel. This information may be used to look up a correction factor in a correction factor database <NUM> stored on the storage module <NUM>.

Expressions such as "comprise", "include", "incorporate", "contain", "is" and "have" are to be construed in a non-exclusive manner when interpreting the description and its associated claims, namely construed to allow for other items or components which are not explicitly defined also to be present. Reference to the singular is also to be construed in be a reference to the plural and vice versa.

In the description above, it will be understood that when an element such as layer, region or substrate is referred to as being "on" or "onto" another element, the element is either directly on the other element, or intervening elements may also be present.

Furthermore, the invention may also be embodied with less components than provided in the embodiments described here, wherein one component carries out multiple functions. Just as well may the invention be embodied using more elements than depicted in the Figures, wherein functions carried out by one component in the embodiment provided are distributed over multiple components.

Claim 1:
A device (<NUM>) for detecting soiling of a shield (<NUM>), the device (<NUM>) comprising:
a housing (<NUM>);
a shield connection body for connecting the device (<NUM>) to the shield (<NUM>);
a first light source (<NUM>) for emitting light to the shield (<NUM>), wherein the first light source (<NUM>) is arranged for emitting a first light beam that coincides with the shield (<NUM>) at a first angle relative to the shield (<NUM>) and at a first incidence area (<NUM>) on the shield (<NUM>), resulting in a first reflected beam, the first reflected beam extending from the shield (<NUM>) under the same angle as under which the first light beam is incident on the shield (<NUM>);
a first light sensor (<NUM>) arranged to receive light from the first light source (<NUM>) and arranged to provide a first signal providing an indication for an amount of light received by the first light sensor (<NUM>),
wherein the first light sensor (<NUM>) is arranged for sensing light originating from the first incidence area (<NUM>),
wherein the first light sensor (<NUM>) is provided out of the path of the first light beam and the path of the first reflected beam, and
wherein the shield (<NUM>) and the housing (<NUM>) provide a sensor space for housing the first light source (<NUM>) and the first light sensor (<NUM>);
a second light sensor (<NUM>) arranged for receiving light directly from the first light beam or the first reflected beam and arranged to generate a second signal in response to receiving the light; and
a processing unit (<NUM>), the processing unit (<NUM>) being arranged to perform the following:
compare a value of the first signal to a reference sensor value;
generate a first warning signal if a difference between the sensed value of the first signal and the reference sensor value is above a first predetermined threshold;
determine, based on the first signal, a transmission value related to a transmission factor of the shield (<NUM>) for a range of electromagnetic waves and output the transmission value;
determine a ratio between the value of the first signal and a value representative of the second signal; and
generate a second warning signal if the ratio is above a second predetermined threshold.