Method and device for recognizing faults in a photovoltaic system

Abstract

The invention relates to a method and a device for recognizing faults in a photovoltaic system (1). A first output voltage (U0, UMPP) of the system (1) and/or a first parameter derived from the output voltage (U0, UMPP) is determined at a first point in time in a first operating state of the photovoltaic system (1). At a second point in time in a second operating state comparable to the first operating state, a second output voltage (U0, UMPP) and/or a second parameter of the system (1) derived from the output voltage (U0, UMPP) is determined. Finally, a deviation between the first and the second output voltage (U0, UMPP) and/or between the first and the second parameter is identified and a fault notification is output if the deviation exceeds a predeterminable threshold.

Claims

1. A method for recognizing faults in a photovoltaic system, comprising the steps: determining a first parameter derived from a first output voltage of the photovoltaic system at a first time point in a first operating state of the photovoltaic-system for determining a starting condition during an initialization process, determining a second parameter derived from a second output voltage of the photovoltaic system at a second time point, when a weather analysis for establishing a sun radiation above a threshold leads to a positive result and there is a second operating state comparable with the first operating state, wherein the weather analysis is performed by using output data from the inverter and without using a light sensitive sensor or a radiation sensor, and wherein the weather analysis is considered to be positive if a power output of the inverter is above 15% of the respective nominal power, determining a deviation between the first and second parameter and outputting an error message when the deviation exceeds a predeterminable threshold, wherein each of the first parameter and the second parameter is the ratio between the maximum power point voltage and the open circuit voltage of the photovoltaic system.

2. The method as claimed in claim 1, wherein the first parameter and the second parameter are determined at a radiation greater than 100 W/m.sup.2.

3. The method as claimed in claim 1, wherein the first parameter and the second parameter are determined at essentially the same radiation or the same power output.

4. The method as claimed in claim 1, wherein the first parameter and the second parameter are determined at essentially the same temperature.

5. The method as claimed in claim 1, wherein to determine the operating status of the photovoltaic system meteorological data is used from at least one of a weather station and a database.

6. The method as claimed in claim 1, wherein the first parameter and the second parameter are determined on different days at essentially the same time.

7. The method as claimed in claim 1, wherein the first parameter and the second parameter are determined on different days essentially at the same position of the sun.

8. The method as claimed in claim 1, wherein the first parameter and the second parameter are determined at essentially the same output power of the photovoltaic system.

9. A device for recognizing faults in a photovoltaic system, comprising: a determining device determining a first parameter derived from a first output voltage of the photovoltaic system at a first time point in a first operating state of the photovoltaic system and determining a second parameter derived from a second output voltage of the photovoltaic system at a second time point in a second operating state comparable with the first operating state when a weather analysis for establishing a sun radiation above a threshold leads to a positive result, wherein the weather analysis is performed by using output data from the inverter and without using a light sensitive sensor or a radiation sensor, and wherein the weather analysis is considered to be positive if a power output of the inverter is above 15% of the respective nominal power, a deviation determining device determining a deviation between the first and second parameter and an error message indicator issuing an error message when the deviation exceeds a predeterminable threshold, wherein each of the first parameter and the second parameter is the ratio between the maximum power point voltage and the open circuit voltage of the photovoltaic system.

10. An inverter for a photovoltaic system with DC voltage side and AC voltage side connections, wherein the inverter comprises the device for recognizing faults in a photovoltaic system as claimed in claim 9 wherein the device for recognizing faults in a photovoltaic system is connected to the DC voltage side connections.

11. A charging controller for a photovoltaic system, wherein the charging controller comprises the device for recognizing faults in a photovoltaic system according to claim 9 wherein the device for recognizing faults in a photovoltaic system is connected to input-side connections of the charging controller.

12. A photovoltaic system comprising one or more solar cells and/or one or more solar modules, wherein the photovoltaic system further comprises an inverter with DC voltage side connections connected to the device for recognizing faults in a photovoltaic system according to claim 9 and at least one of AC voltage side connections and a charging controller having input-side connections connected to said device.

13. A computer program product with a non-transitory computer program saved thereon, which can be loaded into the memory of the device for recognizing faults in a photovoltaic system according to claim 9 and/or an inverter with DC voltage side connections connected to said device and AC voltage side connections and/or a charging controller having input-side connections connected to said device and/or a computer, and executes a method for recognizing faults in a photovoltaic system when the computer program is implemented there, said method comprising the steps: determining a first parameter derived from a first output voltage of the photovoltaic system at a first time point in a first operating state of the photovoltaic system for determining a starting condition during an initialization process, determining a second parameter derived from a second output voltage of the photovoltaic system at a second time point, when a weather analysis for establishing a sun radiation above a threshold leads to a positive result and there is a second operating state comparable with the first operating state, wherein the weather analysis is performed by using output data from the inverter and without using a light sensitive sensor or a radiation sensor, and wherein the weather analysis is considered to be positive if a power output of the inverter is above 15% of the respective nominal power, determining a deviation between the first and second parameter and outputting an error message when the deviation exceeds a predeterminable threshold, wherein each of the first parameter and the second parameter is the ratio between the maximum power point voltage and the open circuit voltage of the photovoltaic system.

14. A method for recognizing module damage in a photovoltaic system, wherein an initialization process is performed for determining a starting condition of the system after installation, and wherein for determining measurement values for recognizing module damage with determined measurement values a weather analysis for detecting a solar radiation which is above a threshold is conducted, wherein with a positive weather analysis additional measurement values are recorded and compared with the starting condition, wherein the weather analysis is performed by using output data from the inverter and without using a light sensitive sensor or a radiation sensor, wherein the weather analysis is considered to be positive if a power output of the inverter is above 15% of the respective nominal power, and wherein the measurement values are of the ratio between the maximum power point voltage and the open circuit voltage of the photovoltaic system.

15. The method as claimed in claim 14, wherein with a negative weather analysis a new weather analysis is carried out at least at a later time point.

16. The method as claimed in claim 14, wherein to identify module damage a continuous assessment of the Udc voltage is performed, wherein from a change in the ratio of Mpp voltage to the open circuit voltage of the module a creeping and/or sudden instance of module damage is identified.

17. The method as claimed in claim 14, wherein the initializing process is started at predetermined time points, in particular at midday, or at a defined, set time point, or a manually activated measuring process is started for determining and recording the operating status of the system.

18. The method as claimed in claim 14, wherein at least one instance of module damage is identified and reported via a display element, wherein the at least one instance of module damage is selected from the group consisting of: high-impedance soldering points inside the modules, open soldering point on a cell, hotspots, shadowing, dirt, cell breakage, and high-impedance soldering point in the connection box.

19. The method as claimed in claim 14, wherein at a predetermined time point, a weather analysis is carried out, in which the supplied amount of energy or the inverter power is identified and compared with a predeterminable value to achieve a positive weather analysis.

20. The method as claimed in claim 14, wherein an evaluation for recognizing module damage is performed via a control device arranged in the inverter or an externally connected control device.

Description

(1) For a better understanding of the invention the latter is explained in more detail with reference to the following Figures.

(2) In a schematically much simplified representation the Figures show:

(3) FIG. 1 a schematic photovoltaic system;

(4) FIG. 2 a current-voltage diagram and a power-voltage diagram of a solar module;

(5) FIG. 3 a path of the open circuit voltage and the voltage at maximum power point as a function of the radiation output;

(6) FIG. 4 the effects of a breakdown of a solar module or a solar cell;

(7) FIG. 5 the time path of the voltage at the maximum power point;

(8) FIG. 6 a schematic view of a photovoltaic-system with an inverter according to the invention;

(9) FIG. 7 a schematic view of a photovoltaic system with a device according to the invention in the form of a measuring device.

(10) First of all, it should be noted that in the variously described exemplary embodiments the same parts have been given the same reference numerals and the same component names, whereby the disclosures contained throughout the entire description can be applied to the same parts with the same reference numerals and same component names. Also details relating to position used in the description, such as e.g. top, bottom, side etc. relate to the currently described and represented figure and in case of a change in position should be adjusted to the new position. Furthermore, also individual features or combinations of features from the various exemplary embodiments shown and described can represent in themselves independent or inventive solutions.

(11) The exemplary embodiments show possible embodiment variants of a device according to the invention, whereby it should be noted at this point that the invention is not restricted to the embodiment variants shown in particular, but rather various different combinations of the individual embodiment variants are also possible and this variability, due to the teaching on technical procedure, lies within the ability of a person skilled in the art in this technical field. Thus all conceivable embodiment variants, which are made possible by combining individual details of the embodiment variant shown and described, are also covered by the scope of protection.

(12) FIG. 1 shows schematically a photovoltaic system 1 consisting of a plurality of identically designed solar modules 2.sub.11 . . . 2.sub.mn. A plurality of solar modules 2.sub.11 . . . 2.sub.mn connected in series (and arranged here vertically below one another) form a string respectively. A plurality of strings connected in parallel (and arranged here horizontally next to one another) form the photovoltaic system 1. Of course, the local distribution of the solar modules 2.sub.11 . . . 2.sub.mn can also be different in a real system.

(13) A solar module 2.sub.11 . . . 2.sub.mn consists of a plurality of solar cells 3.sub.1 . . . 3.sub.x connected in series. In the shown example one solar module 2.sub.11 . . . 2.sub.mn consists only of a string of solar cells 3.sub.1 . . . 3.sub.x connected in series. However, it is also possible for one solar module 2.sub.11 . . . 2.sub.mn to consist of a plurality of parallel connected solar cells 3.sub.1 . . . 3.sub.x or strings. Lastly, one solar module 2.sub.11 . . . 2.sub.mn also comprises a bypass diode (also a free-wheeling diode) D.sub.B, here anti-parallel to all solar cells 3.sub.1 . . . 3.sub.x. It is also possiblealthough not usualthat each solar cell 3.sub.1 . . . 3.sub.x comprises its own bypass diode D.sub.B or one bypass diode D.sub.B is provided for several solar modules 2.sub.11 . . . 2.sub.mn. The bypass diode D.sub.B has in a known manner the purpose of maintaining the current flow and thereby the current generation of a string even when a solar module fails, for example because it is broken or it is in the shade. In this case the voltage generated by the other modules in the string means that the defect or shaded module is operated in reverse direction. Thus without the bypass diode D.sub.B the entire string would fail.

(14) In the following observations solar cells 3.sub.1 . . . 3.sub.x and solar modules 2.sub.11 . . . 2.sub.mn are considered to be equivalent. Although in the following reference is made to solar modules 2.sub.11 . . . 2.sub.mn, the same also applies equally to solar cells 3.sub.1 . . . 3.sub.x. Both are considered within the scope of the invention as elements which generate voltage and current with radiation.

(15) FIG. 2 shows a current-voltage diagram and a power voltage diagram of a solar module 2.sub.11 . . . 2.sub.mn. Here characteristic curves are represented with varying light radiation distinguished by the radiation power P.sub.11 . . . P.sub.15. It is shown clearly that with increasing light radiation both the short circuit current (i.e. the output current I at output voltage U=0) and the open circuit voltage (i.e. the output voltage U at initial current I=0) increase. From a certain level of light radiation (here in the curve for P.sub.13) only the short circuit current I rises noticeably, the open circuit voltage however remains more or less constant.

(16) Furthermore, for P.sub.14 the so-called maximum power point, (also referred to as the MPP-point), i.e. the operating point with the greatest output power of the solar module 2.sub.11 . . . 2.sub.mn, is entered. The associated voltage and the associated current are represented by dashed lines.

(17) The voltage at the maximum power point is denoted in this case by U.sub.MPP. The dotted line shows generally the path of the output power of the solar module 2.sub.11 . . . 2.sub.mn.

(18) FIG. 3 shows the path of the open circuit voltage U.sub.0 as well as the voltage at maximum power point U.sub.MPP as a function of the radiation output P.sub.1. It can be seen clearly that both the open circuit voltage U.sub.0 and the voltage U.sub.MPP remain constant from a certain radiation output P (here marked by a dashed line). In reality this value is at a radiation output of about 100 W/m.sup.2.

(19) FIG. 4 shows what happens if a solar module 2.sub.11 . . . 2.sub.mn (or a solar cell 3.sub.1 . . . 3.sub.x) no longer supplies electrical power for any reason. The solid lines show the characteristic curves already known from FIGS. 2 and 3 with the correct functioning of the solar module 2.sub.11 . . . 2.sub.mn. If one solar module 2.sub.11 . . . 2.sub.mn fails, the current flows through the assigned bypass diode D.sub.B. Since the voltage dropping at the bypass diode D.sub.B is much lower than the voltage produced by a solar module 2.sub.11 . . . 2.sub.mn this is associated with a drastic drop of voltage U.sub.MPP. The characteristic curves on the failure of a solar module 2.sub.11 . . . 2.sub.mn are shown by dashed lines in FIG. 4. The current/voltage characteristic lines are denoted by I/U, the power/voltage characteristic lines by P.sub.1/U. With an increasing number of branches connected in parallel in a photovoltaic system 1 the effect is naturally smaller. In a usual real photovoltaic system 1 the effect is therefore generally much less than is shown in FIG. 4.

(20) According to the invention the output voltages of the photovoltaic system 1 and/or parameters derived from this output voltage are determined at different time points but in comparable operating conditions of the photovoltaic system 1. If there is a deviation between the output voltages or the derived parameters an error message is emitted. This can be performed for example optically or acoustically. For example, a message to a mobile phone is also possible. The voltages that are determined are for example the maximum power point voltage U.sub.MMP and/or the open circuit voltage U.sub.0 of the photovoltaic system 1. Also the ratio of the two is suitable for an evaluation. Although in the following observations the maximum power point voltage U.sub.MPP is mentioned, the explanations relate equally to the open circuit voltage U.sub.0 and the ratio between the voltage U.sub.MMP and the open circuit voltage U.sub.0.

(21) FIG. 5 now shows the time path of the voltage U.sub.MMP (continuous line) and their average value (indicated by a dashed line) of a photovoltaic system 1. It can be seen clearly that the voltage U.sub.MPP drops relatively quickly to a stable level after the first startup of the photovoltaic system 1, generally within the first 3 to 6 months. This is associated with ageing or a stabilization phase of a solar module 2.sub.11 . . . 2.sub.mn which have a relatively significant effect at the beginning of operation. Afterwards the voltage U.sub.MPP only drops slightly. The voltage U.sub.MMP oscillates to a greater or lesser extent about an average value, mainly because different temperatures have a comparatively strong influence on the said voltage U.sub.MMP. With an increasing temperature the voltage U.sub.MMP drops, whereas it increases with falling temperature (as already mentioned the open circuit voltage U.sub.0 is subject to the same effect, which is eliminated on the formation of the quotient between U.sub.MMP and U.sub.0). In the shown diagram at a specific time point a massive and relatively sudden drop in the voltage U.sub.MPP is established. According to the invention an error message is sent, as it is assumed that a fault has occurred in the photovoltaic system 1. The error can have different causes: in the photovoltaic system 1 (solar cell 3.sub.1 . . . 3.sub.x, solar module 2.sub.11 . . . 2.sub.mn, connection box) there is a high-impedance or even an open soldering point, welding point, clamping connection, etc. a solar cell 3.sub.1 . . . 3.sub.x or a solar module 2.sub.11 . . . 2.sub.mn is in the shade or dirty a solar cell 3.sub.1 . . . 3.sub.x or a solar module 2.sub.11 . . . 2.sub.mn is broken.

(22) Although shadowing or dirt are not actual defects they do lead to a reduction in output and are therefore still considered as faults in the photovoltaic system 1 in terms of the invention. For example, a tree may have grown in the vicinity of a photovoltaic system 1 over the years so that the latter is now in the shade. The operator of the photovoltaic system 1 can take appropriate steps in response to the error message.

(23) It should be noted at this point that the stabilizing phase shown in FIG. 5 does not occur in all types of solar cells, but as a rule only in certain thin layer cells. Unlike the representation in FIG. 5 the drop in voltage at the beginning of the operation of a photovoltaic system 1 may not occur. This means the voltage is more or less constant up to the occurrence of a fault.

(24) The voltage U.sub.MPP in FIG. 5 was determined on different days but at the same time of day. The voltage U.sub.MPP therefore fluctuates a relatively small amount from its average value. Of course, also measurement values can be determined during a specific time period on the day. Lastly, it is also possible to record the values over 24 h (this may be practical in polar regions for example). As a rule the voltage U.sub.MPP then fluctuates more strongly from an average value. Depending on the width of the fluctuation the values obtained should therefore be subjected to greater or lesser low pass filtering, sliding average value formation or the like, so that individual rogue measurements do not trigger a false alarm. It can also be observed whether the drop in voltage U.sub.MPP continues over a longer period, e.g. several days, and an error message is only sent then. Lastly, how long it needs to be waited before an error message is sent is relative to the tolerable loss of output. Lastly, it is also possible, in addition or alternatively to evaluate the rate of change of the voltage U.sub.MPP and for example to emit an error message if the rate of change exceeds a specific threshold.

(25) As an alternative to determining the voltage U.sub.MPP at the same time of day it can also be carried out at the same position of the sun. The above then applies by analogy.

(26) In a further alternative embodiment a measurement of the voltage U.sub.MPP is always activated at a specific level of radiation. For example, a timing element or timer can be AND connected to a light-sensitive sensor, so that for example every 15 minutes a measurement is recorded, provided that the radiation lies within a specific tolerance range. In addition, data can be evaluated from associated weather stations. The use of additional sensors and/or data from weather stations is however not obligatory for the invention.

(27) In a further alternative embodiment the output of the photovoltaic system 1 is used for triggering the determination of the measurement value. For example a timing element or timer can be AND connected to an output measuring device, so that for example every 15 minutes a measurement value is recorded, provided that the output power of the photovoltaic system 1 lies within a specific tolerance range. The value for the output power can originate from an inverter or charging controller connected to the photovoltaic system 1. It is particularly advantageous if the method according to the invention is performed directly in the inverter or charging controller.

(28) In the previous examples it was assumed that the measurement values are evaluated more or less at same time that they are determined, i.e. online. This is not absolutely necessary. An evaluation can also be performed offline.

(29) In a first example, measurement data as described above are determined and saved on a storage medium. For example a USB stick can be connected to a device according to the invention, an inverter according to the invention or a charging controller according to the invention. The data are then evaluated as described above on a PC with software which implements the method according to the invention.

(30) In an alternative embodiment the measurement data are transmitted for example by radio or the internet into an associated database, saved there and evaluated. For example, the producer of an inverter or charging controller according to the invention can ensure that from the latter the data are sent periodically to a specific database. In this way all photovoltaic systems 1, which are equipped with the inverters or charging controllers of the said producer, are monitored centrally. For example, an error message can prompt the manufacturer to offer the operator of the photovoltaic system 1 the services of a technician for checking the system, for example by phone or e-mail. The customer service can thus be designed to be particularly effective.

(31) In a further embodiment it is assumed that data on the voltage U.sub.MMP or the open circuit voltage U.sub.0 is available, but that the latter were not determined in comparable operating conditions of the photovoltaic system 1. To make the data usable for the method according to the invention said data are linked with historical data from a weather station or data from a meteorological institute. In this way values can be filtered out of the data of the photovoltaic system 1 which are relevant for the method according to the invention. In this way also historic values of a photovoltaic system 1, i.e. values which were taken prior to the present invention can also be made use of. Faulty photovoltaic systems 1 can thus also be detected in retrospect. The scope of the application of the invention is significantly increased by this method.

(32) With the use of external sensors it can also be advantageous to use the system power instead of the voltage, because it can generally be determined more easily and also more precisely.

(33) Lastly, FIG. 6 shows schematically a photovoltaic system 1, comprising a plurality of solar modules 2.sub.11 . . . 2.sub.mn, with an inverter 4 connected thereto. The inverter 4 comprises in this example an inverter circuit 5, a device according to the invention in the form of an analog-digital-converter 6 for detecting an output voltage of the photovoltaic system 1, a central computer unit 7 with connected memory 8 and a signal unit 9. In the memory 8 are the program steps and parameters necessary for performing the method according to the invention, which are read and executed or processed during the operation by the central computing unit 7. The memory 8 is also provided for saving measurement values. In the computer unit 7 it is checked whether two voltage values or two parameters derived therefrom differ from one another. If this is the case an error message is output via the signal unit 9. The signal unit 9 can consist of a signal lamp, a siren, a text display unit of the inverter 4, a radio transmitter or even a connection to the internet. Although the method according to the invention in this example is represented in software, of course a hardware representation is also possible, for example in the form of a corresponding integrated circuit.

(34) Lastly, FIG. 7 shows an arrangement in which the method according to the invention is performed offline. In this case the photovoltaic system 1 comprises an inverter circuit 5 connected thereto and a device according to the invention in the form of a measuring device 10 with an integrated data interface. By means of said data interface data are transmitted by cable or wireless connection to a database 12 located in the internet 11. By means of a PC 13 a person responsible for monitoring several photovoltaic systems 1 has access to this data and evaluates it with a program running on his PC 13, which performs the method according to the invention. In an alternative embodiment the method according to the invention is performed automatically at set times points on the PC 13, so that the intervention of an operator is only necessary when a defective photovoltaic system 1 is reported. In a further alternative embodiment the said program is executed directly in the database 10, which sends an error message to a previously determined e-mail address.

(35) In the following the detailed sequence of the method for recognizing module damage is described, which can be applied to the FIGS. 1 to 7 described above or the embodiments.

(36) During the installation of a photovoltaic system 1 it is ensured during the assembly and startup that the system 1 is built to be fully functional. It is also ensured that the surrounding buildings and trees do not cast a shadow on the solar modules at midday, when the best possible radiation is normally available. Thus at the time of installing the system 1 it is possible to conclude and determine when the best radiation output is available. This can be defined for example in the inverter 5 by entering a time. Usually the best radiation occurs at midday, so that the inverter 5 is preset for measurements in this range. However, if the system is not aligned to the south, butas is frequently the caseis in an east-west alignment, by inputting a time for example the presetting of the measurements can be transposed.

(37) After the first startup of the system a one-off initializing process is started, in which a measuring process is performed for determining and recording the operating status of the system 1 at preset time points (e.g. at midday) or a defined, set time point, or is performed by manual activation. For this for example the open circuit voltage and the MPP point are determined and saved as reference values. Preferably, the initializing process is only started on a cloudless day, so that there is optimal radiation and thus an optimal operating status can be recorded. Thus after completing the installation an operating assessment is performed in very goodif not always the best possibleconditions, wherein said recorded measurement values are then saved as reference values for additional subsequent measurements.

(38) Once the initializing process is complete the inverter 5 can begin operation. The inverter 5 determines in running feed operation the relevant system parameters and recognizes automatically output-reducing damage in the photovoltaic system 1. In addition, at defined time points or time windows the ratio of MPP voltage to open circuit voltage is formed by the inverter 5. If this ratio worsens continually or abruptly then the solar generator is damaged. A database is created by the inverter 5, in which one or more of the following parameters are detected: Udc [V], inverter output at a time point [W], time and possible date, and preferably the open circuit voltage Uoc [V]. From this data the following module damage can be recognized: high-impedance soldering points in the modules, open soldering point on a cell, hotspots, shadowing, dirt, cell breakage, high-impedance soldering point in the connection box, etc., which can be reported via a display element. The created database can be saved in the inverter 5. With several inverters 5 connected together it is also possible that only one inverter 5 contains this database and the additional inverters 5 transmit the data, in particular measurement data, via WLAN or another network to the inverter 5 with the database to save it there. Of course it is also possible to arrange the database externally.

(39) In order to record data the conditions should be almost always be the same, but there is no need for externally connected sensors, such as for example a radiation sensor. This has the advantage that costs can be reduced and at the same time one source of error can be excluded. The inverter 5 can estimate the weather situation on the basis of recorded data so that only data is determined during permitted weather situations, i.e. on the basis of the recorded data first of all a so-called weather analysis is performed and the data is only saved and used on a successful weather analysis or further data are recorded. The weather analysis is repeated with a negative output at specific intervals which can be predefined, until the weather analysis is classed as positive. Thus data is determined at a later time point. The repetition is performed for example hourly from the beginning of the measurement. With a positive weather analysis the inverter 5 determines the remaining measurements and then does not perform any more new measurements that day. It is of course possible to set the inverter 5 so that the latter performs the measurements several times a day but this is not absolutely necessary.

(40) Preferably, such a weather analysis is performed at a predetermined time point (e.g. midday), whereby the inverter 5 checks whether there is sufficient sun radiation, for which reason the supplied amount of power or the inverter output is determined and compared with a predeterminable value. If this corresponds to a predefinable percentage, for example 50% of the respective maximum value, the inverter 5 decides that the weather analysis was performed positively, i.e. sufficient sun radiation was available. If this percentage is set to be relatively high, only very few or no clouds should be in the sky. The inverter 5 is then set to be very sensitive to the weather analysis.

(41) Once the weather analysis has been performed positively, further measurements are performed by the inverter 5, by means of which the inverter 5 or the control device connected therein or externally can perform an evaluation for recognizing module damage. The individual Udc voltage values are determined by the inverter 5.

(42) The open circuit voltage Uoc is preferably determined in such a way that the inverter 5 remains connected to the grid, but the latter does not take power from the modules for 2.sub.11 . . . 2.sub.mn, for a brief period so that it can measure the open circuit voltage Uoc.

(43) Of course, it is also possible to measure the open circuit voltage, such that the inverter 5 is briefly disconnected from the grid or the connected loads are switched off so that there are no longer any loads on the inverter 5.

(44) In order that module damage can be determined it is necessary that a continuous detection of the Udc-voltage is performed for recognizing the module damage. By changing the ratio of MPP voltage to the open circuit voltage of the modules 2.sub.11 . . . 2.sub.mn creeping or sudden module damage can be recognized.

(45) For this the following data are determined and saved:

(46) Udc (start)=average value of detected Udc values over a defined start period,

(47) Uoc (start)=average value of detected Uoc values over a defined start period,

(48) Udc (current)=average value of detected Udc values over a defined current time period,

(49) Uoc (current)=average value of detected Uoc values over a defined current time period,

(50) Ratio (start)=Udc (start)/Uoc (start)

(51) Ratio (current)=Udc (current)/Uoc (current)

(52) Module damage can be recognized from a deviation of the ratio (current) to the ratio (start). Here the (start) values correspond to the detected measurement values during the initialization process on the installation of the system 1, whereas the (current) values correspond to the currently determined measurement values. Udc (start) or Udc (current) are formed by an average value of 50 (input option) detected day values.

(53) In order to record individual Udc voltages for continuous ratio formation, in an advantageous variant of the invention the following conditions have to be met: sufficient radiation available (supplied amount of energy or the inverter output between two data logger entries corresponds on average to at least 50% (input option) of the inverter nominal power or the photovoltaic system 1), determining the individual Udc voltage values about midday (input option, assumption: at midday the system should not be affected by shadowing from the assembly site), each day only one value (average value of all Udc voltage values determined on this day) is recorded for calculating Udc (current).

(54) The following, further conditions have to be met in this variant, so that the individually determined Udc voltage value can be used for further calculation: recording a new individual Udc voltage for determining a Udc daily average value is only performed, if the latter deviates from the Udc (current) by not more than 20% (input option). on recording a new Udc daily average value for Udc (current) the oldest Udc daily value is dropped. The Udc (current) is always only formed from a number of Udc daily values, as defined above (shift register, FIFO).

(55) Module damage can be recognized if the quotients (as described above) differ from one another, wherein with a corresponding deviation a defect is reported or the last 20 (input option) consecutively individually detected Udc voltage values (i.e. radiation ok, time period ok) lay outside the bandwidth for inclusion in the Udc daily average value and an error message is sent.

(56) Furthermore, it is of course possible that the detected values can also be used for other error messages, i.e. a fault in the system can be established for example if the deviation from predetermined values, in particular the Udc voltage, is too great.

(57) It is possible to say that a method of recognizing module damage or generator damage is performed in a photovoltaic system 1, in which an initializing process is performed for determining the output condition of the system 1 after installation, and for determining measurement values to determine module damage first of all a weather analysis is performed, wherein with a positive weather analysis further measurement values are recorded, but with a negative weather analysis at a later time point a new weather analysis is performed. To recognize module damage a continuous measurement of the Udc voltage is performed, whereby from a change in the ratio of MPP voltage to open circuit voltage of the module 2.sub.11 . . . 2.sub.mn creeping and/or sudden module damage is recognized.

(58) It should be noted at this point that the variants shown only represent a portion of the possible ways of implementing the idea according to the invention. In particular, the implementations of the invention shown in FIG. 6 and FIG. 7 can differ or be combined with one another. A person skilled in the art can easily adapt the predefined information to his requirements.

(59) Finally, as a point of formality, it should be noted that for a better understanding of the structure of the device according to the invention, the latter and its components have only been shown in schematic form in part. Of course, the devices shown may contain additional, not shown component groups or components.

(60) The problem addressed by the independent solutions according to the invention can be taken from the description.

(61) Mainly the individual embodiments shown in FIGS. 6 and 7 can form the subject matter of independent solutions according to the invention. The objectives and solutions according to the invention relating thereto can be taken from the detailed descriptions of these figures.

LIST OF REFERENCE NUMERALS

(62) 1 Photovoltaic system 2.sub.11 . . . 2.sub.mn Solar module 3.sub.1 . . . 3.sub.x Solar cells 4 Inverter 5 Inverter circuit 6 Analog-digital-converter 7 Central processing unit 8 Memory 9 Signal unit 10 Measuring device 11 Internet 12 Database 13 PC I Current P.sub.1, P.sub.11 . . . P.sub.15 Radiated output t Time U Voltage U.sub.0 Open circuit voltage U.sub.MPP Voltage Maximum Power Point