Classifications

• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02S—GENERATION OF ELECTRIC POWER BY CONVERSION OF INFRARED RADIATION, VISIBLE LIGHT OR ULTRAVIOLET LIGHT, e.g. USING PHOTOVOLTAIC [PV] MODULES
  • H02S50/00—Monitoring or testing of PV systems, e.g. load balancing or fault identification
  • H02S50/10—Testing of PV devices, e.g. of PV modules or single PV cells
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02S—GENERATION OF ELECTRIC POWER BY CONVERSION OF INFRARED RADIATION, VISIBLE LIGHT OR ULTRAVIOLET LIGHT, e.g. USING PHOTOVOLTAIC [PV] MODULES
  • H02S50/00—Monitoring or testing of PV systems, e.g. load balancing or fault identification
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E10/00—Energy generation through renewable energy sources
  • Y02E10/50—Photovoltaic [PV] energy

Definitions

• the present invention relates to a method and system for estimating the electrical power supplied by a photovoltaic module present in a photovoltaic power station.
• a photovoltaic power plant generally comprises several chains of photovoltaic modules (also called photovoltaic panels or solar panels) connected in parallel.
• each string the photovoltaic modules are connected in series.
• Each photovoltaic module comprises several photovoltaic cells connected in series, in the form of rows of cells.
• Each photovoltaic cell is intended to convert solar energy into electrical energy.
• the chains of photovoltaic modules are connected to a converter, for example an inverter. This converter converts the DC voltage supplied by each string of modules into an AC voltage. The role of the converter is also to determine an operating point for which the power delivered by a chain of photovoltaic modules is maximum (maximum operating point designated MPP for "Maximum Power Point").
• the modules can be arranged with different orientations to capture solar energy at different times of the day.
• a photovoltaic plant can extend over several km 2 .
• each photovoltaic module in a chain must be monitored regularly in order to identify any faults that could cause a loss of production.
• the defect may be of different natures, in particular permanent if it is a hardware problem, or temporary if it is for example the presence of shading or dust on the module.
• Patent application US2011/316343A1 describes for its part a photovoltaic module comprising several interconnected cells, in which each cell is associated with a control unit which comprises a power sensor and a temperature sensor to monitor the integrity of the cell.
• each maintenance operation can become costly. Some faults detected on a module may turn out to be serious, requiring intervention, while others are minor or even non-existent. It is therefore relevant to be able to estimate the loss of production caused by a fault on a module, in order to decide whether or not an intervention is necessary.
• Patent application WO2016/189052A1 describes in particular a method making it possible to estimate the loss of production of a photovoltaic module, from a thermal image of the module.
• a c is the surface of the photovoltaic module
• T k is the hot spot temperature
• T ref is a reference temperature
• This earlier solution may however lack precision, because it must be based on data provided by a weather station, often not present on the site, or on satellite data.
• the object of the invention is therefore to propose a method which makes it possible to estimate the electrical power loss of a photovoltaic module, in an accurate and reliable manner. Disclosure of Invention
• This object is achieved by a method for estimating the electrical power of a so-called target photovoltaic module, present among a group of several photovoltaic modules of a photovoltaic power plant, referenced group i of modules, said method comprising the following steps:
• the step of acquiring environmental parameters includes a step of measuring said parameters.
• the step of determining the temperature of each photovoltaic module of the group i of photovoltaic modules is carried out from a thermal image acquired for each photovoltaic module of said group i of photovoltaic modules.
• the theoretical electrical power supplied by the reference photovoltaic module is determined from the following relationship:
• P STC (W) is the reference power under standard conditions (1000W/m 2 , 25°C);
• T(i,j) corresponds to a temperature equal to the reference temperature of the reference photovoltaic module
• the step of determining the corrected environmental parameters is implemented by solving a nonlinear optimization problem defined by the following constraints:
• Tamb c (i) is the corrected ambient temperature for group i of photovoltaic modules
• T(i,f) is a temperature equal to the reference temperature of the reference photovoltaic module
• WindSpeed c (C) is the corrected wind speed for group i of modules
• Ref Modules (i) corresponds to the reference module(s) present in group i of modules;
• said weighting function f is as follows:
• said weighting function f is as follows:
• the method comprises a step of determining the loss of electrical power of the target photovoltaic module, distinct from the reference module.
• a step of determining the state of the target photovoltaic module by comparing said loss of electrical power determined for this target photovoltaic module with a threshold value.
• the target photovoltaic module comprises a step for carrying out diagnostics and/or maintenance of the target photovoltaic module when said determined electrical power loss is greater than said threshold value.
• the invention relates to a system for estimating the electrical power of a photovoltaic module, called target, present among a group of several modules of a photovoltaic power plant, referenced group i of modules, said system comprising:
• o Gh global irradiance at the horizontal level
• o Tamb Ambient temperature
• o WindSpeed Wind speed
• the means for acquiring the environmental parameters comprise means for measuring said parameters.
• the determination module is configured to determine the temperature of each photovoltaic module of group i of photovoltaic modules from a thermal image acquired for each photovoltaic module of group i of modules.
• the theoretical electrical power supplied by the reference photovoltaic module is determined from the following relationship:
• P STC (W) is the reference power under standard conditions (1000W/m 2 , 25°C);
• T(i,j) corresponds to a temperature equal to the reference temperature of the reference photovoltaic module
• the second module for calculating the corrected environmental parameters is configured to solve a nonlinear optimization problem defined by the following constraints: And by minimizing a weighting function f on said corrected environmental parameters with respect to the acquired environmental parameters, in which:
• G p (j) corresponds to the irradiance at the plane of the reference photovoltaic module
• ⁇ c (i) is the corrected absorption factor for group i of photovoltaic modules
• Tamb c (l) is the corrected ambient temperature for group i of photovoltaic modules; • T(i,f) is a temperature equal to the reference temperature of the reference photovoltaic module;
• WindSpeed c (f) is the corrected wind speed for group i of photovoltaic modules
• Pelec c (i,j) is the corrected electrical power for the reference photovoltaic module
• Modules Ref (i) corresponds to all the reference photovoltaic modules present in group i of modules;
• said weighting function f is as follows:
• said weighting function f is as follows:
• the third calculation module is configured to determine the electrical power loss of the target photovoltaic module.
• the system comprises means for determining the state of the target photovoltaic module by comparing said loss of electrical power determined for this module with a threshold value.
• the system includes means for carrying out diagnostics and/or maintenance of said target photovoltaic module when its determined electrical power loss is greater than said threshold value.
• FIG. 1 schematically represents a conventional photovoltaic power station
• FIG. 2 schematically represents the architecture of a photovoltaic module
• FIG. 3 schematically represents the simplified structure of a photovoltaic module with which the estimation system of the invention is associated;
• FIG. 4 shows the different steps of the method of the invention and the different functional modules involved during the execution of this method
• a photovoltaic power plant typically has the following layout and operating features:
• photovoltaic modules also called photovoltaic panels or solar panels
• the photovoltaic modules are for example identical and arranged with the same orientation and with the same inclination.
• Each chain of photovoltaic modules comprises several photovoltaic modules connected in series.
• a photovoltaic module (generally referenced Mi ,j in the remainder of the text) comprises several photovoltaic cells (not shown) connected in series.
• the photovoltaic cells are distributed in several rows.
• a row can comprise one or more photovoltaic cells.
• Each photovoltaic cell is intended to convert solar energy into electrical energy.
• a converter for example an inverter 10, comprising several switching arms based on transistors, is intended to convert a direct voltage supplied by each chain of photovoltaic modules into an alternating voltage.
• Control means integrated or not in the converter, are able to control the inverter to perform the voltage conversion.
• Each module advantageously comprises anti-return diodes (not shown) positioned in a suitable manner, for example in series with the photovoltaic modules of each string.
• Each module advantageously comprises bypass diodes (called “bypass”) to bypass each a row of separate photovoltaic cells of a photovoltaic module if a cell of this row was faulty.
• bypass diodes called “bypass"
• FIG. 1 one bypass diode is shown per photovoltaic module.
• each photovoltaic module there is the following arrangement:
• the photovoltaic cells are organized in several rows or groups. In Figure 2 two columns of cells form a row of cells.
• a separate bypass diode is associated with each row of photovoltaic cells shown.
• a row of cells comprises several photovoltaic cells but it could only comprise a single photovoltaic cell.
• Each photovoltaic module has a surface or area, referenced A.
• each chain of photovoltaic modules represents, for example, a group i of distinct photovoltaic modules.
• each photovoltaic module is referenced j, with j ranging from 1 to M.
• the system of the invention is intended to estimate, ultimately, the loss of production or energy power of a photovoltaic module in operation of the photovoltaic power station, this module being potentially defective.
• the estimate can be made when the photovoltaic plant is in operation.
• in operation or “during operation”, it is meant that the photovoltaic module or the photovoltaic power plant is in the process of producing electrical energy, by conversion of incident light energy.
• the estimation system comprises the following elements:
• the device for acquiring the temperature of a photovoltaic module can be formed by a device for acquiring thermal images and/or temperature sensors integrated in the photovoltaic module.
• the thermal image acquisition device is capable of taking thermal images of a photovoltaic module. It can be formed by a thermal camera 1 carried by an operator or by a drone, moving to scan each photovoltaic module of the plant.
• the environmental data acquisition means are intended to recover the weather data necessary for the implementation of the method of the invention.
• they can comprise sensors, installed at the level of the photovoltaic power station, for example thermal sensor 4 to measure the ambient temperature, irradiance sensor 2, anemometer 3 to measure the speed of the wind. They can also collect weather data available on remote servers, via a communication network.
• the computer 5 is intended to estimate the electric power of the photovoltaic module, potentially defective, of the group i of photovoltaic modules.
• the computer 5 comprises several functional software modules described below, which make it possible to carry out intermediate calculations necessary for estimating the electric power of the photovoltaic module.
• the thermal camera 1 and the means for acquiring environmental data are advantageously connected to the computer 5 in order to transmit their measurement data to it.
• the transfer of data to the computer 5 can be carried out automatically and/or by an operator using a suitable man-machine interface.
• the method of the invention firstly makes it possible to estimate the electrical power of a photovoltaic module, called the target photovoltaic module, of the group i of photovoltaic modules.
• This method can be executed for each photovoltaic module of the group i of photovoltaic modules. The process follows the steps described below.
• Step E0 Acquisition of environmental data
• the system acquires the data necessary for implementing the method. Depending on the means available, they are measured and/or retrieved on remote servers, for group i of photovoltaic modules. These data are transferred to the computer 5. These data are as follows:
• WindSpeed (m/s): Wind speed
• the computer 5 can determine the parameter:
• Step E1 Acquisition of temperature data at the level of each module and determination of the average temperature of each photovoltaic module
• the acquisition of temperature data is advantageously implemented using a thermal camera 1. It could be performed using data provided by temperature sensors integrated into each photovoltaic module.
• the data acquired for the group i of photovoltaic modules is then transferred to the computer 5 for processing.
• the acquisition of thermal images is carried out when the radiometric measurement conditions are satisfactory, with for example G greater than or equal to 600 W/m 2 and a stable wind speed less than or equal to 15 km/h.
• the conditions are specified in more detail in patent application WO2016/189052A1.
• each photovoltaic module of the group i of photovoltaic modules its thermal image is then divided or virtually segmented by the computer 5 into several temperature zones.
• Each temperature zone is characterized by its own temperature which is uniform or quasi-uniform over the entire zone.
• Two adjacent or contiguous thermal zones are considered distinct when they have between them a temperature difference greater than a predefined threshold value, for example equal to 10° C.
• a predefined threshold value for example equal to 10° C.
• a thermal zone, called hot is therefore a zone whose temperature exceeds the temperature of the other zones by the predefined threshold value.
• the computer 5 associates a determined temperature representative of the temperature of the zone.
• This temperature assigned to each zone can be an average temperature determined from all the temperatures of the zone.
• the computer 5 determines the average temperature of each photovoltaic module of the group i of photovoltaic modules. This temperature of the photovoltaic module j in the group i of photovoltaic modules is referenced (°C). Step E2 - Selection of a reference photovoltaic module
• the computer 5 selects at least one reference photovoltaic module (referenced Mref with Mref belonging to Module s Ref (j,y) in the group i of photovoltaic modules.
• a reference photovoltaic module is a photovoltaic module considered as healthy, distinct from the target photovoltaic module.
• the reference photovoltaic module Mref is a photovoltaic module analogous to the target photovoltaic module (that is to say with the same technical characteristics - located in the same string, with the same orientation and the same inclination) and not defective. It is part of the same group i of photovoltaic modules as the target photovoltaic module. It has a uniform temperature distribution over all of its zones. In other words, it does not include any hot thermal zone in the sense defined above during step E1.
• FIG. 3 two photovoltaic modules M1,1, M1,2 of group 1 of photovoltaic modules have been represented. One of the two is defective and the other photovoltaic module is healthy and can thus be chosen as the reference photovoltaic module Mref. All the reference photovoltaic modules of the same group i of photovoltaic modules are referenced Modules Ref (i)-
• Step E3 Estimation of the electrical power supplied by the reference photovoltaic module
• the computer 5 can estimate the theoretical electrical power that it would be able to supply.
• the calculator is based on the following formula (equation (2)):
• P STC (W) is the reference power delivered by a photovoltaic module under standard conditions (1000W/m 2 , 25°C);
• T(i,j) corresponds in this case to the average temperature of the reference photovoltaic module
• P elec (i,j) thus corresponds to the electrical power that the reference photovoltaic module Mref should theoretically supply, at its measured temperature T(i,j).
• this heat exchange coefficient of the photovoltaic module can be expressed by the following relationship (equation (4)):
• equation (3) is not respected for all healthy photovoltaic modules. This can be for several reasons:
• Wind speed and ambient temperature may vary locally, from one photovoltaic module to another; In the same group i of modules, these two parameters can be considered as identical from one photovoltaic module to another of the group;
• Tamb c (f) is the corrected ambient temperature for group i of photovoltaic modules
• WindSpeed c (f) is the corrected wind speed for group i of photovoltaic modules
• Pelec c i,j is the corrected electrical power supplied by each photovoltaic module of group i of photovoltaic modules
• One of the principles of the invention consists in determining corrected environmental parameters taking into account constraints on the energy balance of the reference photovoltaic module and a weighting function applied to the environmental parameters initially acquired during step E0.
• the computer 5 is thus led to determine the three parameters a c (i), Tamb c (C), WindSpeed c (C) which make it possible to verify the energy balance equation. For this, the computer 5 takes into account the following constraints: (equation (6))
• the computer 5 is also required to minimize a weighting function f of the three corrected parameters a c (j), Tamb c (C), WindSpeed c (i), with respect to the parameters initially acquired during the step E0. For each parameter, a distinct weighting coefficient is applied, according to the influence of this parameter.
• the expression of the function f can be the following:
• the calculator can also rely on the following expression f: With :
• AP which corresponds to an accepted power tolerance for the reference photovoltaic module.
• AP 10%.
• Modules Ref (i) which corresponds to the reference photovoltaic module(s), ie healthy, present in the group i of modules.
• P elecc (i,j) corresponds to the electrical power supplied by the reference photovoltaic module, determined in step E3.
• the computer 5 is required to solve the optimization problem mentioned above. This is a non-linear optimization problem that can be solved with "fmincon" type solvers.
• the computer 5 can estimate the power loss PowerLoss(ij) of each module compared to the average power of the reference photovoltaic modules of the same group of photovoltaic modules, by the following relationship:
• the computer 5 By determining this power loss for each photovoltaic module, the computer 5 is able to identify, within a group of several photovoltaic modules, the photovoltaic modules which are defective, for example by comparing the power loss calculated for the photovoltaic module with a stored threshold value. Each photovoltaic module declared as defective may be subject to specific diagnostic and/or maintenance actions.
• the step EO is implemented by the environmental data acquisition means of the system. This means, for example, measuring wind speed, ambient temperature and irradiance. This data can also be retrieved by the computer by connecting to a remote weather server.
• a remote weather server in a non-limiting manner, we have represented the various sensors 2, 3, 4 necessary for taking these measurements.
• Step E1 is implemented both by the temperature data acquisition device and by a processing module MT of the computer 5, responsible for processing the measurement data to assign an average temperature to each photovoltaic module.
• the data acquisition is carried out by the thermal camera 1 .
• Step E2 is implemented by a selection module MS of computer 5, the latter being responsible for selecting a reference photovoltaic module Mref.
• Step E3 is implemented by a first calculation module MC1 of computer 5, intended to calculate the theoretical electrical power P eiec i,j) supplied by the reference photovoltaic module Mref at its temperature.
• Step E4 is implemented by a second calculation module MC2 of the computer, intended to solve the optimization problem with a view to determining the three environmental parameters sought.
• Step E5 is implemented by a third calculation module MC3 of the computer, intended to estimate the actual electrical power Pelec c i,j) supplied by each photovoltaic module M i,j , in particular that of the target photovoltaic module, and the PowerLoss power loss i ) of each photovoltaic module.
• the computer can advantageously embed means for determining the state of each photovoltaic module by comparing said loss of electrical power determined for this photovoltaic module with a threshold value. If the photovoltaic module is considered defective (i.e. when its determined electrical power loss is greater than said threshold value), the computer 5 can be configured to activate means for diagnostics and/or maintenance of this photovoltaic module.
• the invention described above is therefore a particularly simple and reliable solution for determining the electrical power supplied by each module and possibly deducing a loss of power from a defective module in a photovoltaic power station. It could for example be used to identify within a group of photovoltaic modules certain photovoltaic modules which will be considered as defective due to a loss of power greater than a certain threshold. These photovoltaic modules can then be the subject of specific diagnostic or maintenance actions.

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