METHOD AND DEVICE FOR MONITORING THE MAXIMUM POWER POINT AND MONITORING THE DEGRADATION OF A PHOTOVOLTAIC MODULE

Abstract

A method for monitoring the maximum power point of a photovoltaic module, comprising periodic measurements (120) of the module's I / V operating point and the positioning of said operating point at its maximum power point (MPP), and monitoring the degradation of said module, said monitoring comprising: - periodic measurements with n1>1 constant or variable, steps (130, 140) of measuring the I and V parameters of the module for voltage-shifted points VMPP+α and VMPP-β on the I(V) curve relative to the maximum power point (MPP), calculating the slope dI / dV+ at point VMPP+α and the slope dI / dV- at point VMPP-β, and storing said data as well as the MPP; - periodic measurements with n2 > n1, steps (160, 170) of measuring I and V values ​​by sweeping the I(V) curve and calculating parameters (Jsc; Voc ; FF ; Rs ; Rsh ; I0 ;n) of the module and storage of said parameters and values, - one or more steps (200) of calculation, plotting and display of curves of pairs of data from the p measured and calculated parameters, - one or more steps of degradation detection from said measured and calculated parameters. Figure of the abstract: 3;

Description

Title of the invention: METHOD AND DEVICE FOR MONITORING THE MAXIMUM POWER POINT AND MONITORING THE DEGRADATION OF A PHOTOVOLTAIC MODULE Technical field

[0001] This disclosure relates to the management and operation of photovoltaic modules such as photovoltaic panels or assemblies of photovoltaic panels. Previous technique

[0002] Maximum Power Point Trackers (MPPTs) are known to be used for single-junction or multi-junction photovoltaic modules. These MPPTs are used in photovoltaic installations such as solar farms, rooftops, and other applications. They are particularly well-suited to single-sided or bifacial photovoltaic modules.

[0003] It is also known that the materials constituting the different sub-cells of a single-junction or multi-junction module are prone to degrade over time.

[0004] To date, silicon cells are a mature technology that has benefited from decades of research to increase its reliability. However, such cells can now be combined with perovskite cells, for which one of the challenges remains the long-term stability of their constituent materials. It is therefore necessary to be able to monitor their degradation and understand the causes of this degradation and its distribution over time and frequency.

[0005] In the case of cells combining, for example, silicon junctions with perovskite junctions, it is particularly important to understand the causes of material degradation in the junctions that lead to a loss of module efficiency, and thus anticipate the necessary improvements to enhance these technologies. It is also desirable, within the context of photovoltaic module operation, to be able to perform early anomaly detection in order to anticipate the replacement of defective modules during a favorable period and thus avoid periods of downtime. The performance of modules under real-world conditions, whether in a photovoltaic field or on a rooftop, is particularly affected by these degradation mechanisms.Although monitoring the power output of modules is carried out to verify their performance throughout their lifespan, this monitoring does not allow for a real-time understanding of the degradation mechanism at play. This information is also valuable for module manufacturers to gain a better understanding of their technology and its evolution over time.

[0006] It is therefore not possible to foresee the necessary improvements or to perform early anomaly detection by anticipating the replacement of defective modules during a favorable period, since the solutions proposed in the state of the art allow monitoring of the power produced and therefore of the power degradation, but not identification of the causes. Summary

[0007] The present disclosure improves the situation and makes it possible to investigate the causes of reduced module performance and to improve the monitoring of the performance and degradation of such photovoltaic modules.

[0008] To this end, the present disclosure relates to a method for monitoring the maximum power point of at least one photovoltaic module, comprising, at intervals of 5t0, measurements of the operating point I / V of said module and positioning of said operating point at its maximum power point (MPP), and which includes monitoring the degradation of said module, said monitoring comprising: - according to a periodicity »i<5ï0 with ni>l constant or variable, measurement steps of the parameters I and V of said module for points offset in voltage VMPP+a and VMPP-[3 on the curve I(V) with respect to the maximum power point MPP, a calculation of the slope dI / dV+ at the point VMpp+a and of the slope dl / dV- at the point VMpp-|3 and storage of said data as well as the MPP, - according to a periodicity n2ôt0 with n2 ni > steps of measuring values ​​of I and V by sweeping the curve I(V) and calculating parameters (Jsc; Voc; FF; Rs; Rsh; 10; n) of the module and storing said parameters and values, - one or more steps of calculation, plotting and displaying curves according to / P\\2 / pairs of data from the p measured and calculated parameters, - one or more degradation detection steps based on said measured and calculated parameters.

[0009] According to this method, the parameters measured during a lifetime period of the monitored module(s) allow, by comparison with degradation models, the determination of the type of degradation in progress and the informing of the status of these modules.

[0010] At least some of the parameters p are derived from a calculation of derivatives d[X] / d[Y] with X=[performance and degradation indicator] and Y=[local meteorological data], said performance and degradation indicator comprising Efficiency, Jsc, Voc, Impp, Vmpp, FF, Rs, Rsh, dFdV+, dl / dV-, said “meteorological data” comprising: humidity, ambient and module temperature, wind speed, pressure, UV index, Irradiance by means of dedicated meteorological sensors com- communicants and the display of said derivatives.

[0011] This type of calculation makes it possible to take into account meteorological data to refine the detection of defects.

[0012] The values ​​of a and [3 are advantageously adjusted according to the number of cells of the module or modules taken into account by the said measurement steps.

[0013] This allows monitoring of simple multi-cell modules or sets of modules in series or in series parallel connected to a single monitoring device.

[0014] The process may involve a modification of the values ​​of ni and / or n2 during said monitoring.

[0015] In particular, the values ​​of ni and / or n2 are reduced when a degradation is detected and in the absence of detection of evolution of the degradation, the values ​​of ni and / or n2 are increased at each loop of the algorithm.

[0016] This allows the periodicity of measurements to be adapted when a degradation appears.

[0017] The method may include one or more steps of selecting said data, parameters and values, to retain said data, parameters and values ​​corresponding to meteorological conditions set by the user.

[0018] This makes it possible to detect degradations whose appearance is dependent on temperature conditions, for example.

[0019] At least some of the p parameters can be derived from a calculation of the ratio of the time integral of the power at MPP by the product of the efficiency by the time integral of the perceived irradiance according to daily cycles.

[0020] This calculation makes it possible to provide parameters smoothed over a day.

[0021] At least some of the calculation, plotting and display steps include plotting curves of the slope dl / dV- as a function of the slope dI / dV+ for the points measured along said measurement steps.

[0022] The method may include a step of searching for degradation of the module and in case of degradation, a step of searching for a cause of degradation, for which said search is done by comparing the difference of a set of curves modeled for different modes of degradation with a curve obtained by measurements.

[0023] The method may include a step of displaying the cause of degradation.

[0024] The method may include comparing one or more parameter curves measured with a degradation limit indicator beyond which an anomaly detection alert is sent to an operator.

[0025] This disclosure further relates to a maximum power point tracking device of a photovoltaic module comprising a housing equipped with a display screen and a processor and configured to implement the disclosed method and display the curves obtained.

[0026] Said housing is interposed between one or more modules and a current converter direct current / alternating current.

[0027] Said box may include a communication module with external link to a remote computer of a monitoring system configured to program in particular in the digital processor the types of measurements and the periodicity of these measurements or to retrieve measurement data made by said box and to transmit to an operator information on the status of the modules and alerts on detection of anomalies.

[0028] This disclosure further relates to a computer program comprising instructions for implementing the process described above when this program is executed by a digital processor.

[0029] Finally, this disclosure relates to a non-transient recording medium readable by a computer on which a program is recorded for the implementation of the process when this program is executed by a digital processor. Brief description of the drawings

[0030] Other features, details and advantages will become apparent upon reading the detailed description below, and upon analysis of the accompanying drawings, on which:

[0031] [Fig-1] represents a traditional J(V) curve of a photovoltaic cell;

[0032] [Fig.2] represents the curve of [Fig.1] with measurement points according to one aspect of the present disclosure.

[0033] [Fig.3] shows a flowchart describing steps in embodiments of the present disclosure.

[0034] [Fig.4] represents theoretical degradation curves according to several degradation mechanisms and a measured degradation curve for a module;

[0035] [Fig.5] represents an example of an embodiment of a housing for implementing the process of the present disclosure. Description of the implementation methods

[0036] The maximum power point tracking with degradation monitoring device of this disclosure, referred to as MPPT-DM (for Maximum Power Point Tracking with Degradation Monitoring), is designed to monitor the degradation of photovoltaic modules in situ and in real time, and to identify the mechanisms involved in order to anticipate necessary improvements or to perform early anomaly detection by anticipating the replacement of defective modules during a favorable period and thus avoiding periods of unavailability. This applies both at the cell and module levels, with associated mechanisms.

[0037] Currently, new technologies such as perovskite cells, which can be coupled or not to other cells such as silicon, are in full development Development. Since it relies on materials different from silicon cells, it is crucial to monitor degradation under real-world conditions and, more specifically, to understand its causes in order to intervene or anticipate future module installations. Such monitoring ultimately allows for better prediction of the installation's lifespan and production.

[0038] During the lifetime of a module, its maximum power point evolves continuously. In order to optimize production, maximum power point tracking (MPPT) devices are conventionally used to continuously search for the optimal operating point of the module, thereby maximizing energy production.

[0039] In the case of normal prior art operation, curve 1 in [Fig. 1] represents the current density J2 as a function of the voltage V3 of a cell. The tracking devices continuously seek to maintain the power at the maximum power point (MPP) for the cells and modules. It is also known, equivalently, to use the current / voltage curve of a module to perform the MPP tracking function, and in the case of tracking one or more modules, according to this disclosure, the current / voltage curve I(V) is used for the calculations.

[0040] The monitoring device of the present invention is designed both to obtain the MPP and to regularly analyze the evolution of various electrical parameters associated with the current-voltage characteristic of the modules. To this end, the module will be specifically controlled by its monitoring device in order to retrieve the current-voltage parameters necessary to identify the ongoing degradation path and the underlying mechanisms. These parameters are measured by specific scanning of the current-voltage characteristic at defined times during the module's lifetime and allow the degradation paths and their causes to be deduced by comparison with modeled data of the same module in terms of mechanism. To this end, the present disclosure proposes a specific algorithm for controlling a monitoring device (or MPP tracker) for a photovoltaic module.

[0041] The solution and the different steps are detailed below:

[0042] In a traditional manner, according to regular time steps ôtQ, for example every 10 seconds, the tracking device performs measurements around the MPP in order to follow this point of maximum power continuously and maximize the power produced.

[0043] However, according to this disclosure, measurements are taken around the MPP by the tracking device, which will offset the operating point from the maximum power point. These measurements can be taken at intervals Δf; = «i^o, n being chosen, for example, between 100 and 10000 or more, or even variable depending on the age of the module, for example, decreasing with the age of the module. These Simple measurements allow us to identify an estimate of the slopes of the current / voltage curve around the maximum power point (MPP). Figure 2 shows these measurements around MPP 4 for a current / voltage density curve J(V) 1, again in the case of a single cell to maintain consistency with Figure 1. In this example, in addition to measuring the MPP, an initial measurement is taken by shifting the cell's operating point to a voltage VMPP-a, for example, VMPP- 50 mV at point 5, and to VMPP+[3, for example, VMPP + 50 mV at point 6. This gives, respectively, a tangent slope of 7 dJ / dV- for the point at VMPP- 50 mV and a tangent slope of 8 dJ / dV+ for the point at VMPP+ 50 mV. This interval around the maximum power point can be adjusted for a given photovoltaic installation, depending on the module technology. For example, points at VMPP- 100 mV and VmpP+ 50 mV or points at VMPP- 100 mV and VMPP + 100 mV can be chosen.Again, in the case of one or more modules as described in this disclosure, measurements are taken on the I(V) curve, where V is the module voltage and I is the module current, a homothetic curve of the J(V) curve where V is the cell voltage and J is the cell current density. In this case, VMpp, a and [3 will be adapted to the number of cells connected in series.

[0044] Subsequently, at a time step ôt2 = «2^0 ^1, chosen so as to impact For example, if electrical production is low, such as measurements taken once a day or less, a greater number of points on the current-voltage curve are acquired on the I(V) curve, possibly with points distributed across the entire voltage range [0; Voc], in order to generate sufficient information to obtain the parameters Jsc: short-circuit current density (or short-circuit current for multiple cells), Voc: open-circuit voltage, FF: form factor describing the shape of the curve. Then, by comparison to a model, for example a diode model, the parameters Rs: series resistance, Rsh: parallel resistance of the module, 10: diode saturation current, and N: ideality factor are obtained.

[0045] The number of points measured over the voltage range [0;Voc] is evaluated in a specific way to allow sufficient information to feed the model while minimizing acquisition time and impact on production.

[0046] Thus a data set El= [MPP ; dI / dV+ or dJ / dV+; dl / dV- or dJ / dV-] are obtained at regular time intervals 5 / 1 and another data set E2 = [Js ; Voc ; FF ; Rs ; Rsh ; 10 ; N] are obtained at regular time intervals Ôt2.

[0047] The collected data may optionally be subjected to pre-processing to select those measured under meteorological conditions specified by the user (temperature, irradiance, etc.). For example, only measurements taken under conditions close to the STC standard data (1000 Wm-2, 25°C) may be extracted.

[0048] Alternatively, a step of normalizing the data collected under Different weather conditions can be implemented to still use this data. This second method, for which no prior data selection is necessary, consists of calculating for each daily cycle the ratio of the time integral of the power at MPP to the product of the efficiency and the time integral of the perceived irradiance.

[0049] Finally, the acquired data can be compared with simulation results, which, knowing the characteristics of the module (spectral response, electrical, optical, and thermal behavior), and using physical models known as drift-diffusion models, allow the behavior to be determined in the presence of different degradation mechanisms. A more refined optimization of this analysis can be performed by, for example, adjusting a, P, θh, or 8t². The procedure described above is summarized in [Fig. 3].

[0050] In steps 100 and 110 the traditional operating point and positioning measurements at the MPP are carried out.

[0051] At step 120, a test is performed to check if the time ôt} = nv8t0 has been reached.

[0052] If not, a return to waiting for a time increment of 90 is performed.

[0053] If the instant ôtl = n}6t0 is reached, a measurement of the parameters I and V is performed for points offset on the curve I(V) above and below the point MPP and the data MPP; dI / dV+; dl / dV- are stored in step 140.

[0054] At step 150 a test is carried out to determine if the instant 8t2 = n2ôt0 is reached.

[0055] If this is not the case, a return to a time increment wait of 90 is performed.

[0056] If so, a complete measurement of the I and V values ​​over the entire I(V) curve, as well as the calculation of the parameters Jsc; Voc; FF; Rs; Rsh; 10; N, are carried out in step 160, and the measurements are then stored. In addition, the following parameters can also be measured and then used for degradation analysis (in the form of derivatives): [[performance indicator and degradation] [local meteorological data]. For example, the following data could be used for "performance indicator and degradation": Efficiency, Jsc, Voc, Impp, Vmpp, FF, Rs, Rsh, dl / dV+, dl / dV-, and the following data could be used for "meteorological data" via dedicated meteorological sensors within the system: humidity, ambient and module temperature, wind speed, pressure, UV index, irradiance.

[0057] The process is repeated by resetting the time counter and fixing the values ​​of ni and n2.

[0058] In step 225, for example, the values ​​of ni and / or n2 can be modified during said monitoring to take into account any degradation of the panel being monitored. These values ​​can, in particular, be reduced when degradation is detected or increased when no change in degradation is detected. The values ​​of ni and / or n2 can, in particular, be variable at each loop of the algorithm.

[0059] In parallel, data values ​​are selected in step 190, for example to retain measurements corresponding to fixed weather conditions, then data curves (up to f P \ for p measured parameters) are plotted with \ 2 / superposition of measured and calculated data to compare the characteristics of the module in real time with theoretical behaviors in the case of the presence of different degradation mechanisms.

[0060] In the event that degradation is detected in test 230, a process of analyzing said curves to search for a cause of degradation is carried out in step 210 and its result is displayed in step 220.

[0061] Test 230 can be a comparison of the calculated curves with theoretical curves of degradation types.

[0062] An illustrative example of determining the degradation path for a perovskite module (mono junctions) is shown in Figure 4. In this example, the curve dl / dV- (the slope in Vmpp-a) is plotted against dI / dV+ (the slope in Vmpp+ / i). The measurement points 11 taken at given intervals throughout the use of the panel are superimposed on curves of possible degradations according to various causes of degradation: Me1, degradation of the hole-extracting layer ("HTL degradation" in English), Me2, degradation of the interface between the hole-extracting layer and the perovskite ("PVK / HTL interface defects" in English), Me3, degradation of the perovskite layer ("PVK defects" in English), Me4, degradation of the interface between the electron-extracting layer and the perovskite ("PVK / ETL interface defects" in English), Me5, degradation of the electron-extracting layer ("ETL degradation" in English).

[0063] This determination remains generalizable to any type of module.

[0064] Similar curves representing other parameters as a function of each other obtained from the measured and calculated datasets can be plotted and used (up to f P for P measured parameters). The comparison of the gap of the set \ 2 / modeling curves for different modes of degradation with the set of curves obtained from measurements then allows us to deduce the mechanisms at stake.

[0065] Once the degradation modes have been determined, the process may include comparing 240 one or more degradation mechanisms with a degradation limit indicator beyond which an early anomaly detection alert 250 is sent to an operator.

[0066] The collected data can be analyzed according to distinct and / or chosen time periods; the analysis can then make it possible to determine the mechanism responsible of the degradation during these periods. For example, one can imagine that a mechanism degrading performance in winter is not activated by weather conditions in summer, and that another mechanism is then decisive. The analysis will therefore be different for these periods.

[0067] The data collected and analyses made can be applied to the entire photovoltaic installation, or a distinction can be made between the chains connected to the different inputs of the monitoring device(s).

[0068] It is possible to consider certain sets of parameters such as El, E2, E3=[Jsc, Voc, FF] or even E1+E3, alone or cumulatively.

[0069] The tracking system referred to as the "MPPT-DM tracker" of this disclosure, which enables the tracking of degradation mechanisms, is shown in [Fig. 5] in the form of a box 12. In this example, two panels 15 are each connected to a box 12 of this disclosure, the two boxes being connected to a DC / AC converter 16 connected to a network 21.

[0070] The box 12 which replaces a traditional MPP monitoring box has power inputs 23 for connection to the panel and power outputs 22 to the converter and includes an electronic board 17 provided with a digital processor 18, such as a microcontroller with digital and analog inputs / outputs for example, its associated memory 19, also provided with a display 13 for viewing the results, optionally a keyboard 14 and / or a communication module 20 with external link 25 to a remote computer 24 configured for example to program in particular in the digital processor 18 the types of measurements and the periodicity of these measurements or to retrieve measurement data made by said box and to transmit to an operator information on the status of the modules and alerts on detection of anomalies.

[0071] The digital processor 18 and its memory are configured to implement the method for monitoring the maximum power of the module(s) and the steps of the method described in this disclosure. This system is adaptable to any type of photovoltaic module.

[0072] The housing is inserted, as shown in the example, between photovoltaic modules such as photovoltaic panels and a direct current / alternating current (DC / AC) converter, which is itself connected to an alternating current network. Alternatively, the monitoring device can be integrated into the inverter housing and included in a "photovoltaic inverter" package.

[0073] The monitoring device can also be used with or without the degradation analysis function.

[0074] This disclosure may apply to different types of modules regardless of their technology, silicon and perovskite technologies being mentioned in This is a non-limiting example and may concern a photovoltaic field comprising more than two panels and in particular may include several rows of panels each connected to an MPPT-DM device as described.

Claims

Demands

1. A method for monitoring the maximum power point of at least one photovoltaic module, comprising, at intervals of 5t0, measurements (120) of the operating point I / V of said module and positioning of said operating point at its maximum power point (MPP), characterized in that it comprises monitoring the degradation of said module, said monitoring comprising: - at intervals with n1 constant or variable, steps (130, 140) of measuring the parameters I and V of said module for points offset in voltage and VMPP-3 on the I(V) curve relative to the maximum power point (MPP), a calculation of the slope dV / dV+ at the point VMPP+a and of the slope d1 / dV- at the point VMPP-3 and storage of said data as well as the MPP, - at intervals of 2t0 with n2 - n1, steps (160, 170) of measuring values ​​of I and V by sweeping the curve I(V) and parameter calculation (Jsc; Voc; FF; Rs; Rsh; 10;N) said module and storage of said parameters and values, - one or more steps (200) of calculation, plotting and display of IPX curves of pairs of data from the p parameters measured ' 7 / and calculated, - one or more steps of degradation detection from said parameters measured and calculated.;

2. A method according to claim 1 wherein at least some of the parameters p are derived from a calculation of derivatives d[X] / d[Y]) with X=[performance and degradation indicator] and Y=[local weather data], said performance and degradation indicator comprising: Efficiency, Jsc, Voc, Impp, Vmpp, FF, Rs, Rsh, dVdV+, dl / dV-, said "weather data" comprising: humidity, ambient and module temperature, wind speed, pressure, UV index, irradiance by means of dedicated communicating weather sensors and the display of said derivatives.

3. Method according to claim 1 or 2 wherein the values ​​of a and [3 are adjusted according to the number of cells of said module taken into account by said measurement steps.

4. A method according to claim 1, 2 or 3 comprising a modification (225) of the values ​​of ni and / or n2 throughout said monitoring.

5. A method according to claim 4 wherein the values ​​of ni and / or n2 are reduced upon detection of degradation and wherein, in the absence of detection of evolution of degradation, the values ​​of ni and / or n2 are increased at each loop of the algorithm.

6. A method according to any one of the preceding claims comprising one or more steps (190) of selecting said data, parameters and values, to store said data, parameters and values ​​corresponding to meteorological conditions set by the user.

7. A method according to any one of the preceding claims wherein at least some of the p parameters are derived from a calculation of the ratio of the time integral of the power at MPP by the product of the efficiency by the time integral of the perceived irradiance according to daily cycles.

8. A method according to any one of the preceding claims wherein at least some of the calculation, plotting and display steps (200) include plotting curves of the slope dl / dV- as a function of the slope dI / dV+ for the points measured along said measurement steps.

9. A method according to any one of the preceding claims comprising a step (230) of searching for module degradation and, in the event of degradation, a step (210) of searching for a cause of degradation, wherein said search is done by comparing the deviation of a set of modeled curves (Mel, Me2, Me3, Me4, Me5) for different modes of degradation with a curve obtained by measurements.

10. Method according to claim 9 comprising a step of displaying cause of degradation.

11. Method according to claim 9 or 10 comprising comparing (240) one or more curves of measured parameters with a degradation limit indicator beyond which an anomaly detection alert (250) is sent to an operator.

12. Maximum power point tracking device of a photovoltaic module comprising a housing 12 equipped with a display screen 13, a processor and configured to implement the method of any one of claims 1 to 11 and display the curves obtained.

13. Device according to claim 12, wherein said housing is interposed between one or more modules and a DC / AC converter.

14. Device according to claim 12 or 13 wherein said housing comprises a communication module (20) with external link (25) to a remote computer (24) of a monitoring system configured to program in particular in the digital processor (18) the types of measurements and the periodicity of these measurements or to retrieve measurement data made by said housing and to transmit to an operator information on the status of the modules and alerts on detection of anomalies.

15. Computer program comprising instructions for carrying out the method according to any one of claims 1 to 11 when this program is executed by a digital processor.

16. A non-transient, computer-readable recording medium on which a program is recorded for the implementation of the method according to any one of claims 1 to 11 when this program is executed by a digital processor.

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