AU2015264790A1 - Method and apparatus for detecting the type of shading on a photovoltaic system - Google Patents
Method and apparatus for detecting the type of shading on a photovoltaic system Download PDFInfo
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- H—ELECTRICITY
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- H02S—GENERATION OF ELECTRIC POWER BY CONVERSION OF INFRARED RADIATION, VISIBLE LIGHT OR ULTRAVIOLET LIGHT, e.g. USING PHOTOVOLTAIC [PV] MODULES
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Abstract
Abstract The invention relates to a method (440) for detecting the type of shading (132) on a photovoltaic system (100). The method comprises at least a step of determining 5 (442) at least a first kink (124; 224; 324) in a first characteristic curve (118; 218; 318) associated with the photovoltaic system (100), at a first point in time, and at least a second kink (126; 224; 324) in a second characteristic curve (120; 218; 318) associated with the photovoltaic system (100), at a second point in time, and a step of determining (444) the type of shading on the photovoltaic system (100) so as to 10 detect shading and/or soiling, using the first kink (124; 224; 324) and the second kink (126; 224; 324). The first characteristic curve (118; 218; 318) and the second characteristic curve (120; 218; 318) represent a characteristic curve (118, 120; 218; 318) that can be determined using an electric current and voltage generated by the operation of the photovoltaic system (100). 2476330v1 m CN m~ .Uj. (00 co co 001 001 ~co cI ~ I
Description
Method and Apparatus for Detecting the Type of Shading on a Photovoltaic
System
Prior Art
The present invention relates to: a method for detecting the type of shading on a photovoltaic system, a corresponding apparatus for detecting the type of shading on a photovoltaic system, and a corresponding computer program.
Local shading of a photovoltaic generator can result in considerable loss of output. There are various ways of detecting such loss of output. Currently, systems are used that determine the nominal output for the photovoltaic generator, using model-based approaches, and then compare this with the output measurements for the actual system. To determine the nominal output, either weather-data from satellites are evaluated, or insolation-values are measured directly on the photovoltaic generator. For each fault in a predefined list, the probability of this fault being present is estimated, based on the deviation (resolved cumulatively or temporally). Definite differentiation of faults is not possible. Due to measurement uncertainties, shading is only detectable in the case of reductions in output of about 5% or more. These methods require online access, for the satellite-based approach, or an additional irradiance sensor for offline devices.
The published patent application DE 10 2012 217 878 A1 describes a method and an apparatus for detecting at least one switching bypass diode in a photovoltaic system.
Disclosure of the Invention
Against this background, the approach presented here provides a method for detecting the type of shading on a photovoltaic system, an apparatus for detecting the type of shading on a photovoltaic system, said apparatus using said method, and a corresponding computer program, all as claimed in the independent claims. Advantageous forms of implementation will emerge from the respective dependent claims and from the description below.
Causes of shading can be identified by evaluating a photovoltaic generator’s characteristic curves. In a photovoltaic system, strings of cells can be bypassed, by means of e.g. a bypass diode, to prevent hotspots or other faults caused by shading. Each switching bypass diode in a photovoltaic system means a disconnected cell string — hence, a cell string providing no output. In the photovoltaic system’s inverter, a characteristic curve for the photovoltaic system can be recorded and used, e.g. in modern photovoltaic systems, to determine an operating point, for the entire string of modules, at which the photovoltaic module concerned is able to deliver the highest possible power output. The characteristic curve can therefore be prepared and utilised to conclude what type of shading a photovoltaic system is experiencing. In particular, it is possible to differentiate between at least soiling and local shading.
Presented here is a method for detecting the type of shading on a photovoltaic system, said method comprising the steps of: - determining a first characteristic curve and a second characteristic curve, said first and second characteristic curves each representing a curve determined using a current and voltage generated by the operation of the photovoltaic system; - determining at least a first kink in a first characteristic curve associated with the photovoltaic system, at a first point in time; and at least a second kink in a second characteristic curve associated with the photovoltaic system, at a second point in time; - determining the type of shading on the photovoltaic system, so as to detect shading and/or soiling, using the first kink and the second kink; and - outputting a shading-signal representing the type of shading. A photovoltaic system may be understood as meaning a photovoltaic or PV power generation installation or plant, or part of such a power-generation installation or plant. By means of solar cells, a photovoltaic system is able to convert part of the incident solar radiation into electrical energy. The direct type of energy conversion occurring in a photovoltaic system can be referred to as photovoltaics. In a photovoltaic system, individual solar modules can be connected together in series, to form a so-called string. The solar modules of a photovoltaic system can be referred to as a solar generator. The photovoltaic system may have an inverter, in which the direct current produced in the solar modules can be converted into alternating current. The inverter can be designed to record and measure a characteristic curve for the photovoltaic system or a characteristic curve for a solar module and/or cell string. This characteristic curve is then associated with the photovoltaic module (for a particular time period). This characteristic curve may be a current-voltage (characteristic) curve or a power-voltage (characteristic) curve; and/or it may be a derived characteristic curve, i.e. a curve derived from those characteristic curves. A current-voltage characteristic curve can be referred to as an l-U (or l-V) curve. A power-voltage characteristic curve can be referred to as a P-U (or P-V) curve. In a power-voltage characteristic curve, the system power generated can be plotted as a function of the system voltage. The characteristic curve may be in the form of a current-voltage graph. The characteristic curve may be in the form of a power-voltage graph. The characteristic curve may also be a part or segment of a characteristic curve. A solar module and/or a cell string may have series-connected solar cells and/or parallel-connected solar cells. A solar module and/or a cell string can be characterised by at least one electrical characteristic curve. In the case of a plurality of series-connected solar modules and/or cell strings, a bypass diode may be connected in antiparallel to each solar module and/or cell string. A bypass diode can be referred to as a freewheeling diode (or flyback diode). The maximum current and the reverse voltage of the bypass diode can be akin to the electric-current values and voltage values of the solar module and/or cell string. With series-connected solar modules and/or cell strings, a bypass diode may be referred to as an active bypass diode if the current is flowing through the bypass diode of a solar module and/or cell string.
In the step of determining kinks, a characteristic curve derived from the characteristic curve is determined, for use to determine the kink. This derived characteristic curve may be the result of derivation, integration, or transformation of the current-voltage characteristic curve and/or the power-voltage characteristic curve. The derived characteristic curve (i.e. the curve derived from the characteristic curve that was determined) may be derived from the power-voltage characteristic curve. A derived characteristic curve may be understood as being one that has been subjected to differential calculus. For this, a derivative or differential quotient of the characteristic may be found. The derivative may be a first derivative, or alternatively a higher derivative such as a second derivative.
The resultant derived characteristic curve may be a current-voltage characteristic curve and/or a power-voltage characteristic curve, transformed into another parameter space. A characteristic curve transformed into another parameter space may be understood as meaning, for example, a Fourier-transformed characteristic curve. A transformed characteristic curve can be evaluated easily and efficiently. A kink is to be understood as meaning here a point on the characteristic curve or derived characteristic curve at which there is a jump, or at least a discontinuity in the slope. For example, within a predefined tolerance range around the kink, the sign of the slope of the characteristic curve or derived characteristic curve may change, and/or the slope of the characteristic curve or derived characteristic curve may change its absolute value by more than double.
In addition, in the outputting-step, a shading-signal representing the type of shading may be outputted to a user or to a control or information unit, e.g. to initiate the repositioning of the solar module to an orientation with greater insolation per unit of area, or to initiate notification to a cleaning service to clean the solar module.
In the step of determining the type of shading, the relationship of a parameter of the second kink to a parameter of the first kink can be determined, in order to determine the shading and/or soiling of the photovoltaic system. A relationship of this kind may be understood as being a change in the position (or in a parameter) of the kink in the second characteristic curve relative to the position (or a parameter) of the kink in the first characteristic curve. For this, it is possible, for instance, to relate a current/voltage value or power value of the photovoltaic system at the first kink, as a parameter, to a current/voltage value or power value of the photovoltaic system at the second kink. Such relating may also be understood as being the determining of a time-dynamic behaviour, although only two separately detected parameters are compared with each other. Thus, a dynamic behaviour of the kink that can be detected over a period of observation can indicate local shading. Soiling can be characterised by there being little or no dynamic behaviour of the kink over time.
Furthermore, in the step of determining the type of shading, the relationship of the parameter can be determined using a change in the electric-current value at the second kink relative to the electric-current value at the first kink, and/or a change in the voltage level at the second kink relative to the voltage level at the first kink, and/or a change in the power at the second kink relative to the power at the first kink. Thus, the characteristic curve may be a current-voltage characteristic curve or a power-voltage characteristic curve. In this regard, the time-dynamic behaviour of the kink can be determined — in the type-of-shading determination step — using a value of the kink on the abscissa or ordinate of the characteristic curve.
It is also favourable if, in the step of determining the type of shading, a shaded area of the photovoltaic system and/or the degree of shading of the shaded area is determined using the first characteristic curve and the first kink and also a shaded area of the photovoltaic system and/or the degree of shading of the shaded area is determined using the second characteristic curve and the second kink and/or values derived therefrom, so as to determine the type of shading. Thus, a coordinate of the kink can represent a shaded area of the photovoltaic system or a degree of shading.
It is also advantageous if, in the step of determining kinks, at least a third kink, in at least a third characteristic curve associated with the photovoltaic system, is determined, at at least a third point in time. Said at least third point in time can be different from the first point in time and the second point in time. In the step of determining the type of shading, the type of shading can be determined using at least the third kink. Furthermore, in the kink-determination step, kinks can be determined in a multiplicity of characteristic curves associated with the photovoltaic system, with each characteristic curve of the multiplicity of characteristic curves being determined at a different point in time. In the step of determining the type of shading, the type of shading can be determined using the multiplicity of characteristic curves. In this way, a robust method can be created.
In the step of determining the type of shading, the variance and/or dispersion and/or deviation from a mean value, and/or deviation from a median, and/or a higher-order stochastic moment of the first kink, second kink, and at least the third kink, are determined; and the shading and/or soiling of the photovoltaic system is determined, using the variance and/or dispersion and/or deviation from the mean, and/or the deviation from the median, and/or the higher-order stochastic moment. In this way, the dynamic behaviour of the kink can be determined or evaluated overtime using various parameters.
In an additional kink-determining step, a fourth kink in a fourth characteristic curve associated with the photovoltaic system can be determined at a fourth point in time, and a fifth kink in a fifth characteristic curve associated with the photovoltaic system can be determined at a fifth point in time. Here, the fourth and fifth characteristic curves can each represent a characteristic curve determined using an electric current and voltage generated by the operation of the photovoltaic system. The additional kink-determination step can be performed after the kink-determination step. Alternatively, the additional kink-determination step can be performed in parallel with the kink-determination step. In an additional type-of-shading determination-step, an additional type of shading on the photovoltaic system can be determined, using the fourth and fifth kinks, in order to detect shading and/or soiling. Further, in a validation step following the additional type-of-shading determination step, the type of shading, determined in the type-of-shading determination step, and the additional type of shading determined in the additional type-of-shading determination step, are compared, in order to validate the type of shading. In this way, the type of shading can be further differentiated.
The approach presented here also provides an apparatus for detecting the type of shading on a photovoltaic system, said apparatus being designed to execute, control, or implement, in suitable equipment, the steps of a variant of a method presented here for detecting the type of shading on a photovoltaic system. This variant embodiment of the invention, in the form of an apparatus, likewise enables the objective of the invention to be achieved quickly and efficiently.
An apparatus for detecting the type of shading on a photovoltaic system can be understood as being a monitoring device. The apparatus may be integrated in an inverter forming part of the photovoltaic system. An apparatus can be understood as being an item of electrical equipment that processes sensor signals and, as a function thereof, outputs control signals and/or data signals. The apparatus may have an interface implemented as hardware and/or software. When implemented in hardware, the interfaces may for example be part of a so-called system ASIC containing all sorts of functions of the apparatus. However, the interfaces may also be separate, integrated circuits, or may consist at least partly of discrete components. When implemented in software, the interfaces can be software modules that are provided, along with other software modules, in e.g. a microcontroller.
Also advantageous is a computer program product or computer program with program code that can be stored on a machine-readable storage device or medium such as a semiconductor memory, hard disk, or optical storage and that serves to execute, implement, and/or control the steps of the method according to one of the forms of implementation described above, particularly when the program product is executed on a computer or an apparatus.
The approach presented here will be described in more detail below, byway of example, with reference being made to the accompanying drawings, in which:
Fig. 1 is a schematic representation of a photovoltaic system with an apparatus for detecting the type of shading on a photovoltaic system, in an embodiment of the present invention;
Fig. 2 is a graph showing an example of a current-voltage characteristic curve of a photovoltaic system in an embodiment of the present invention;
Fig. 3 is a graph showing an example of a power-voltage characteristic curve of a photovoltaic system in an embodiment of the present invention;
Fig. 4 is a flowchart of a method implementing the present invention; and
Fig. 5 is another flow diagram of a method implementing the present invention.
In the following description of examples of favourable implementations of the present invention, elements shown in the various Figures that work similarly will be given the same or similar reference numbers, and no repeated descriptions of them will be given.
Fig. 1 is a schematic representation of a photovoltaic system 100, in an embodiment of the present invention. The photovoltaic system 100 comprises two solar modules 102 and an inverter 104. A solar module 102 has two cell strings 106 with series-connected solar cells 108, each string 106 having an antiparallel-connected bypass diode 110. The inverter 104 is designed to convert the DC voltage produced in the solar modules 102 into AC voltage. The inverter 104 has an interface for connecting the DC voltage from the solar modules 102. The interface is designed to detect the DC voltage present, and to produce a characteristic curve. The inverter 104 also comprises an apparatus 112 for detecting the type of shading on the photovoltaic system 100. If, during normal operation of the photovoltaic system 100, at least one bypass diode 110 is active, this can be detected from its switching during the recording of a characteristic curve. A switching bypass diode leads to a kink in the recorded curve. The characteristic curve can be recorded during an analysis process on the photovoltaic system 100, as the characteristic curve is proceeded along. The inverter comprises an additional interface 114, designed to provide AC voltage. In another embodiment, the additional interface 114 is designed to provide a message as to the type of shading that has been detected in the apparatus 112 for detecting the type of shading on the photovoltaic system 100.
The apparatus 112 for detecting the type of shading on a photovoltaic system 100 is designed to execute, in suitable devices, a method for detecting the type of shading on the photovoltaic system 100, as described in more detail with reference to Fig. 4. The apparatus 112 for detecting the type of shading on a photovoltaic system 100 comprises, in the embodiment shown in Fig. 1: an interface 116 for reading-in a first characteristic curve 118 related to or associated with the photovoltaic system 100, and for reading-in a second characteristic curve 120 related to or associated with the photovoltaic system 100; a device 122 for determining a first kink 124 in the first characteristic curve 118 at a first point in time, and for determining a second kink 126 in the second characteristic curve 120 at a second point in time; and a device 128 for determining the type of shading on the photovoltaic system 100, so as to detect shading and/or soiling, using the first kink 124 and the second kink 126. The first curve 118 and second curve 120 each represent a characteristic curve that is determined using a current and voltage produced by the operation of the photovoltaic system 100. In addition, the apparatus 112 in the embodiment shown in Fig. 1 has an interface 130 for providing the type of shading 132.
The characteristic curves 118, 120 are: a current-voltage characteristic curve; a power-voltage characteristic curve; or alternatively, characteristic curves based on said characteristic curves. Examples of characteristic curves are shown in Figs. 2 and 3.
One aspect of the concept presented here is the ability to differentiate soiling from shading caused by objects casting shadows. The basis for achieving this is provided by a method for detecting shading in general, by means of the resultant kinks in the power-voltage characteristic curve (P-U curve) and the current-voltage characteristic curve (l-U curve) of a shaded photovoltaic generator 100. Depending on the embodiment, the methods will be implemented autonomously on an inverter 104 or on separate diagnostic equipment. Alternatively, online evaluation may be employed.
When shading in general is detected, the kink in the power characteristic curve is further evaluated with respect to its ordinate, its abscissa, and the resulting properties, degree of shading, and area affected. The cause is then communicated to a user, who can initiate any corrective action to restore the full power production capacity of the photovoltaic generator 100.
Shading may be caused by shadows cast by a geometric object situated in the vicinity of the photovoltaic generator 100, or by soiling of the generator’s surface. In both cases there occurs, in the P-U curve or l-U curve, a kink whose ordinate is essentially dependent on the degree of shading and whose abscissa depends on the area affected by shading.
When a shadow is being cast, the area affected by the shading, and the corresponding degree of shading, exhibit dynamic behaviour over time. Furthermore, the formation of the shadow depends on the amount of direct insolation and thus exhibits random behaviour.
Soiling, on the other hand, exhibits relatively constant behaviour over the time of its existence, with respect to these variables. The area affected hardly changes over the time that the soiling exists, and does not depend on the amount of direct insolation.
One aspect is therefore the evaluation of the time dynamics of one or more of the following variables: - existence of a kink in the P-U curve or l-U curve - ordinate of the kink - abscissa of the kink - affected area calculated from the abscissa - degree of shading calculated from the ordinate
The apparatus 112 may be used on photovoltaic generators 100 of all sizes (photovoltaic generators of different string lengths), configurations (serial or parallel), and any technology (crystalline or thin film).
Advantages over the prior art are: higher accuracy of detection (detection being possible at > 2% reduction in power output), the possibility of pinpointing the cause of the fault, and eliminating the need to measure the insolation with an irradiance sensor or by satellite. In this way, the user can be informed directly of the reason for the power reduction, without having to undertake burdensome diagnosis of the photovoltaic generator. In addition, the values detected for evaluation are based solely on evaluation of the power curve. It is not necessary to collect any additional measurement values, and no online connection is required.
In the case of shading, two operating ranges occur — due to the reduced irradiance on part of the photovoltaic generator 100 — in which the photovoltaic generator 110 can be operated. In this regard, the bypass diodes 110 that are installed in photovoltaic modules 102 to protect the cells 108 play a major role. Due to the decreased insolation that it is experiencing, the shaded area can no longer provide full current. So that the affected cells 108 are not subjected to full current (hotspot fire hazard) when the plant 100 is in operation, bypass diodes 110 are connected in antiparallel, bypassing the affected cells 108. This results in two regions in the characteristic curve: a first region with higher current at lower voltage (in Figs. 2 and 3: first part of curve; bypass diodes active), and a second region with higher voltage and lower current (in Figs. 2 and 3: second, i.e. last part of the curve; bypass diodes inactive).
Fig. 2 shows, byway of example, a graphical representation of a current-voltage characteristic curve 218 of a photovoltaic system in an embodiment of the present invention. The current-voltage characteristic curve 218 may be a schematic representation of a characteristic curve 218 with the use of an embodiment of an apparatus 112, shown in Fig. 1, for detecting the type of shading on a photovoltaic system: the photovoltaic system may, for example, be the photovoltaic system 100 shown in Fig. 1. In this case, the characteristic curve 218 may have been determined by the apparatus 112 for detecting the type of shading on the photovoltaic system 100. In a Cartesian coordinate system, voltage U is plotted in volts V on the abscissa, and current I is plotted in amps A on the ordinate. Fig. 2 shows a current-voltage characteristic curve. This curve 218 represents a case of shading, in which a bypass diode in the photovoltaic system is switching. The characteristic curve 218 has a kink 224 in it. Thus, the amperage decreases in a region just below 10 V, from about 8 A to about 5 A. In a region between 10 V and about 30 V, the amperage is stable within a tolerance range, then drops away to the open circuit voltage. Thus, it can be seen that, in a case of shading, the characteristic curve 218 shown in Fig. 2 clearly forms two different regions.
Fig. 3 shows, byway of example, a graphical representation of a power-voltage characteristic curve 318 of a photovoltaic system in an embodiment of the present invention. The power-voltage characteristic curve 318 may be a schematic representation of a characteristic curve 318 occurring with the use of an embodiment of an apparatus 112, shown in Fig. 1, for detecting the type of shading in a photovoltaic system such as the photovoltaic system 100 shown in Fig. 1. In this case, the characteristic curve 318 may have been recorded by the apparatus 112 for detecting the type of shading in the photovoltaic system 100. In a Cartesian coordinate system, voltage U is plotted in volts V on the abscissa, and power P is plotted in watts W on the ordinate. Fig. 3 shows a power-voltage characteristic curve. This curve 318 represents a case of shading, in which a bypass diode in the photovoltaic system is switching. The characteristic curve 318 has a kink 324 in it.
The characteristic curve 318 rises from the origin of the Cartesian coordinate system to a value of about 80 W at a voltage of about 9 V, then drops to a kink 324, with steadily increasing voltage, to a power level of approximately 60 W; and, from about 11 V, it rises steadily again until the power drops back to 0 W shortly before the open circuit voltage.
The characteristic curve 318 in Fig. 3 shows distinctly the formation of the two regions of a characteristic curve in the case of shading. The formation of the two power ranges of the characteristic curve 318 results in a distinct kink in the power curve 318. This property of the characteristic curve 318 is used, by an existing method, to detect shading in general. The basic idea is to evaluate two properties of this kink 324 over time, to identify the cause of the shading. In one example of implementing the invention, the area affected by the shading is evaluated, as the first property. This can be estimated using the abscissa of the kink:
In one step, a dynamic is calculated. In a different way of implementing the method, the ratio between the number of characteristic-curve measurements with shading (Nsh) and the total number of characteristic-curve measurements in a fixed time window (one day, for example) is determined:
If the trend of the affected area A exhibits low dynamics, with the ratio □ over the period under consideration being « 1, then the cause is soiling. As to the opposite conclusion, all cases to which this condition does not apply must be due to shading. Exceptions to this are brief effects. Brief effects are effects that only shade the photovoltaic generator for a few hours (bird). Given the short time they apply, the dynamics of these cases are very low. The ratio of the number of measurements with shading (Nsh) to the total number of measurements (Nmeas) is very low. Therefore, a brief effect exhibits the same behaviour as a shadow that, due to the insolation conditions, was only observable for a few hours. Further differentiation of these cases occurs using further measurement of curves (characteristics) and their re-evaluation.
Fig. 4 is a flowchart of a method 440 in one way of implementing the present invention. The photovoltaic system here may be an embodiment of a photovoltaic system 100 shown in Fig. 1. The method 440 here comprises at least one step 441 of detecting a first characteristic curve and a second characteristic curve, said first and second characteristic curves each representing a characteristic curve determined using the current and voltage generated by the operation of the photovoltaic system 100. In addition, the method 400 comprises a step 442 of determining a first kink and a second kink; and a step 444 of determining the type of shading on the photovoltaic system, said step 444 serving to detect shading and/or soiling, using at least the first kink and the second kink. In the kinkdetermining step 442, the first kink is determined, in a first characteristic curve associated with the photovoltaic system; and the second kink is determined, in a second characteristic curve associated with the photovoltaic system. Said first and second characteristic curves are two characteristic curves determined at two different times, using a current and voltage generated by the operation of the photovoltaic system.
In an optional implementation, the time behaviour of the kink is determined in step 444 (the step for determining the type of shading). Here, the temporal (dynamic) behaviour is determined between the two kinks, using: the change in the current overtime (i.e. comparing the change in current at the first and second kinks), the change in voltage overtime (i.e., comparing the change in voltage at the first and second kinks), or the change in power over time (i.e. comparing the change in power at the first and second kinks).
Optionally, a shaded area of the photovoltaic system, or the degree of shading of the shaded area, is determined in step 444, using the characteristic curves and kinks, in order to determine the type of shading.
In one example of implementing the inventive method, at least a third kink may optionally be determined — in the kink-determination step 442 — in at least a third characteristic curve, at a third point in time; said third point in time on the third characteristic curve being different to the first point in time on the first characteristic curve and the second point in time on the second characteristic curve. In this case, the type of shading may optionally be determined, in the type-of-shading determination step, using at least the third kink as well.
In an outputting step 445, a shading signal representing the type of shading can be outputted, for example to a user or to a control or information unit, to initiate re-adjustment of the photovoltaic module or photovoltaic generator, and/or cleaning of the surface of the solar module or photovoltaic generator.
Optionally, in one form of implementation of the invention, the method 440 for detecting the type of shading on a photovoltaic system has an additional kink-determination step 446, an additional type-of-shading determination step 448, and a validating step 450. In the additional kink-determination step 446, at least two additional kinks are determined in at least two additional characteristic curves, that is, there is one additional kink per additional characteristic curve, with the additional characteristic curves relating to other points in time that are different from the first two points in time. In the additional type-of-shading determination step 448, an additional type of shading on the photovoltaic system is determined, in order to detect shading or soiling, using the additional kinks. In the final step 450, the shading determined in step 444 and the additional shading determined in additional step 448 are compared, in order to validate the type of shading or to further differentiate it. Here too, in a corresponding step 445, the (now validated or differentiated) type of shading is suitably outputted.
In a particular form of implementation, the above-described optional variants of kink-determination step 442 and type-of-shading determination step 444 are similarly applied to the optional additional kink-determination step 446 and the optional additional type-of-shading determination step 448.
Fig. 5 is another flowchart of a method 440 in an example of implementing the present invention. The method 440 may be a variant of a method 440 shown in Fig. 4 for detecting the type of shading on a photovoltaic system. The photovoltaic system concerned may be an embodiment of a photovoltaic system 100 shown in Fig. 1. The method 440 starts with a step 552 of determining a multiplicity of characteristic curves, each of the curves being determined at a different time. Thus, in step 552, a set of characteristic curves for a defined period of time is determined. The next step 554 comprises the kink-determination step 442 and the type-of-shading determination step 444 described with reference to Fig. 4. Then comes a decision step 556, in which it is decided whether a first dynamic determined in step 554 (said first dynamic being the absolute value of a change in the observed parameters of the first and second kink) is less than a first threshold value. If the outcome of decision step 556 is Yes, then the left-hand path marked J is taken, in which, in step 558, the additional kink-determination step 446 and additional type-of-shading determination step 448 described with respect to Fig. 4 are performed, so as to determine a second dynamic. If the outcome of decision step 556 is No, then the right-hand path marked N is taken, in which, in another step 560, the additional kink-determination step 446 and additional type-of-shading determination step 448 described for Fig. 4 are performed, to determine a third dynamic. Depending on the outcome of decision-step 556, one of the two steps 558, 560 is performed. This is then followed, in either case, by a validation-step 450. If a second dynamic, calculated in step 558, is greater than a second threshold value, then the type of shading is detected as being soiling on the photovoltaic system. If a third dynamic, calculated in step 560, is greater than a third threshold value, then the type of shading is detected as being a shadow causing a reduction in power output. If, in either path, the dynamic concerned is found in step 450 to be not greater than a predetermined threshold value, then shading or a brief effect is detected, and the method is started again with characteristic-curve determination step 552.
As one aspect of the invention, Fig. 5 provides a flowchart of the cause-identifying method 440. This involves using further variables to evaluate and obtain further dynamics, depending on the example: - the abscissa and the ordinate of the kink - the degree of shading of the shaded area, which can be estimated using the ordinate of the kink:
- dynamic functions: variance, dispersion, deviation from the mean; deviation from the median; higher-order stochastic moments...
In the examples of the inventive concept described, P-U and l-U curves are used for detecting and differentiating between soiling and shading. In this regard, a dynamic for the area affected and a dynamic for the degree of shading can be determined. Alternatively or additionally, the dynamic of the existence of kinks is evaluated. This provides a method 440 for identifying the causes of instances of shading.
The forms of implementation of the invention that are described and shown in the Figures are chosen only by way of example. Different implementations may be combined in whole or in part. In the latter case, individual features of different implementations may be combined, or one implementation may be supplemented with features of another implementation.
Furthermore, the steps presented here can be repeated, and can be executed in a different order to that described.
If an example includes an “and/or” relation between a first feature and a second feature, then this is to be read as meaning that, in one form of implementation, the example has both the first feature and the second feature, and in another form of implementation, it has either the first feature or the second feature but not both.
Claims (10)
- Claims:1. A method for detecting the type of shading on a photovoltaic system, said method including the steps of: - determining a first characteristic curve and a second characteristic curve, said first and second characteristic curves each representing a curve determined using a current and voltage generated by the operation of the photovoltaic system; - determining at least a first kink in a first characteristic curve associated with the photovoltaic system, at a first point in time; and at least a second kink in a second characteristic curve associated with the photovoltaic system, at a second point in time; - determining the type of shading on the photovoltaic system so as to detect shading and/or soiling, using the first kink and the second kink; and - outputting a shading-signal representing the type of shading.
- 2. A method as claimed in claim 1, wherein, in the type-of-shading determination step, the relationship of a parameter of the second kink to a parameter of the first kink is determined, in order to determine the shading and/or soiling of the photovoltaic system.
- 3. A method as claimed in 2, wherein, in the type-of-shading determination step, the relationship of the parameter is determined using a change in the electric-current value at the second kink relative to the electric-current value at the first kink, and/or a change in the voltage level at the second kink relative to the voltage level at the first kink, and/or a change in the power at the second kink relative to the power at the first kink.
- 4. A method as claimed in any one of the preceding claims, wherein, in the type-of-shading determination step, a shaded area of the photovoltaic system and/or the degree of shading of the shaded area are determined using the first characteristic curve and the first kink, and/or the second characteristic curve and the second kink, and/or variables derived therefrom, so as to determine the type of shading.
- 5. A method as claimed in any one of the preceding claims, wherein, in the kink-determination step, at least a third kink is determined, in at least a third characteristic curve associated with the photovoltaic system, at least a third point in time; said at least third point in time being different from the first point in time and the second point in time; and the type of shading being determined, in the type-of-shading determination step, using at least the third kink.
- 6. A method as claimed in 5, wherein, in the type-of-shading determination step, the variance and/or dispersion and/or deviation from a mean, and/or deviation from a median, and/or a higher-order stochastic moment of the first kink, second kink, and at least the third kink, are determined; and the shading and/or soiling of the photovoltaic system is determined, using the variance and/or dispersion and/or deviation from the mean, and/or the deviation from the median, and/or the higher-order stochastic moment.
- 7. A method as claimed in any one of the preceding claims, further including: - an additional step of determining a fourth kink in a fourth characteristic curve associated with the photovoltaic system, at a fourth point in time, and a fifth kink in a fifth characteristic curve associated with the photovoltaic system, at a fifth point in time; said fourth characteristic curve and fifth characteristic curve each representing a characteristic curve determined using an electric current and voltage generated by the operation of the photovoltaic system; and said additional kink-determination step being performed after the kink-determination step; and - an additional step of determining an additional type of shading on the photovoltaic system so as to detect shading and/or soiling, using the fourth kink and the fifth kink; and - a validation step, in which the type of shading determined in the type-of-shading determination-step, and the additional type of shading determined in the additional type-of-shading determination-step, are compared, in order to validate the type of shading.
- 8. An apparatus including devices that are adapted to perform the steps of the method as claimed in any one of the preceding claims.
- 9. A computer program that is adapted to perform the steps of the method as claimed in any one of claims 1 to 7.
- 10. A machine-readable storage medium, with a computer program as claimed in claim 9 stored on it.
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| DE102014224486.2 | 2014-12-01 | ||
| DE102014224486.2A DE102014224486A1 (en) | 2014-12-01 | 2014-12-01 | Method and device for detecting a type of shading of a photovoltaic system |
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| AU2015264790A Abandoned AU2015264790A1 (en) | 2014-12-01 | 2015-12-01 | Method and apparatus for detecting the type of shading on a photovoltaic system |
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| AU (1) | AU2015264790A1 (en) |
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| CN108090315A (en) * | 2018-02-27 | 2018-05-29 | 南昌航空大学 | The analogy method of photovoltaic module Current Voltage output characteristic under the conditions of a kind of local shading |
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| JP5162737B2 (en) * | 2006-05-17 | 2013-03-13 | 英弘精機株式会社 | Solar cell characteristics evaluation system |
| JP5723611B2 (en) * | 2011-01-27 | 2015-05-27 | 株式会社日立製作所 | Solar power generation system, abnormality detection method, and abnormality detection system |
| JP5462821B2 (en) * | 2011-03-08 | 2014-04-02 | 株式会社日立パワーソリューションズ | Solar cell abnormality determination device and solar cell abnormality determination method |
| DE102012217878A1 (en) | 2012-10-01 | 2014-01-30 | Robert Bosch Gmbh | Method for recognizing switching bypass diode in photovoltaic system, involves reading characteristic curve of photovoltaic system with respect to detected current voltage characteristic and/or achievement voltage characteristic |
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| ITUB20155968A1 (en) | 2017-05-27 |
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