FR3118363A1 - Method and system for estimating the electrical power supplied by a photovoltaic module - Google Patents

Abstract

The invention relates to a method for estimating the electrical power of a photovoltaic module, present among a group i of several photovoltaic modules, said method comprising the following steps: Acquisition of the following environmental parameters for the group i of photovoltaic modules: overall horizontal irradiance; : Ambient temperature ; : Wind speed ; Determination of a temperature of each photovoltaic module of group i of photovoltaic modules, Determination of the electrical power (delivered by group i of photovoltaic modules at the maximum power point, Determination of corrected environmental parameters for which each of the photovoltaic modules of group i of photovoltaic modules provides the corrected electrical power, Determination of the corrected electrical power of at least one target photovoltaic module belonging to the group i of photovoltaic modules from the corrected environmental parameters Figure to be published with the abstract: Figure 4

Description

Method and system for estimating the electrical power supplied by a photovoltaic module

Technical field of the invention

The present invention relates to a method and system for estimating the electrical power supplied by a photovoltaic module present in a photovoltaic power plant.

State of the art

A photovoltaic power plant generally comprises several chains of photovoltaic modules (also called photovoltaic panels or solar panels) connected in parallel.

In 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 chain of photovoltaic 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").

In the same plant, the photovoltaic 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 .

The operating state of each photovoltaic module in a chain must be monitored regularly in order to identify any faults that could cause a loss of production. Depending on the case, 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 photovoltaic module.

There are different solutions for monitoring the operating status of a photovoltaic module.

Some solutions use current and voltage sensors to verify the electrical behavior of the photovoltaic module. Document WO2015/118608 describes such a method based on the IV curve of a photovoltaic cell. This solution is however very expensive if it is desired to be installed on all the photovoltaic modules of an architecture.

Other solutions use temperature sensors. This is the case, for example, of the patent US6512458B1 and of the application US2011/088744A1 which describe solutions in which temperature sensors are intended to measure the temperature at the level of the bypass diodes in order to deduce therefrom a possible fault at the level of the bypassed cells. . 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.

Finally, other solutions use thermal cameras to identify any hot spots on the photovoltaic modules, after electrical stimulation.

Given the size of a photovoltaic plant, each maintenance operation can become costly. Some faults detected on a photovoltaic 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 photovoltaic 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.

This process is based in particular on the relationship below, which makes it possible to estimate the electrical power loss of a photovoltaic module, referenced k (equation (1)):

• is the thermal coefficient of the photovoltaic module;
• is the surface of the photovoltaic module;
• is the hot spot temperature;
• 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.

This technical solution relies in particular on electrical data acquired at the level of the photovoltaic module to refine the estimate and thus improve the reliability of the detection of a defective photovoltaic module.

This object is achieved by a method for estimating the electrical power of a photovoltaic module, present among a group of several photovoltaic modules of a photovoltaic power plant, referenced group i of photovoltaic modules, said method comprising the following steps:

• Acquisition of the following environmental parameters for group i of photovoltaic modules:
  • : global irradiance at the horizontal level;
  • : Ambient temperature ;
  • : Wind speed ;
• Determination of a temperature of each photovoltaic module of the group i of photovoltaic modules,
• Determination of the electrical power delivered by the group i of photovoltaic modules at the maximum power point,
• Determination of corrected environmental parameters for which each of the photovoltaic modules of group i of photovoltaic modules provides the corrected electrical power, taking into account constraints on the energy balance of the modules and on the electrical power delivered at the maximum power point by the group i of photovoltaic modules,
• Determination of the corrected electric power of at least one target photovoltaic module belonging to the group i of photovoltaic modules from the corrected environmental parameters.

According to one feature, the step of acquiring environmental parameters includes a step of measuring said parameters.

According to another feature, 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.

According to another feature, the step of determining the corrected environmental parameters is implemented by solving 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 :

• corresponds to the irradiance at the level of the plane of a photovoltaic module of the group i of photovoltaic modules;
• is the corrected absorption factor for group i of photovoltaic modules;
• is the corrected ambient temperature for group i of photovoltaic modules;
• is the corrected wind speed for group i of photovoltaic modules;
• is the corrected electrical power for each photovoltaic module of group i of photovoltaic modules;
• corresponds to the power delivered by group i of photovoltaic modules at the maximum power point;
• corresponds to the tolerance allowed with respect to the power ;

According to another feature, said weighting function f is as follows:

In which :

• are selected weighting factors;

According to another feature, the method comprises steps of:

• Selection of at least one reference photovoltaic module, distinct from said target photovoltaic module, from among the group i of photovoltaic modules, on the basis of the homogeneous character of its temperature, called reference temperature,
• Determination of a theoretical electrical power supplied by the reference photovoltaic module at the reference temperature,
• Determination of corrected environmental parameters taking into account the following additional constraint:

In which :

• corresponds to the theoretical electrical power supplied by the reference photovoltaic module;
• corresponds to the corrected electrical power of each photovoltaic module of group i of photovoltaic modules;
• corresponds to an accepted power tolerance for each photovoltaic module of the group i of photovoltaic modules;
• corresponds to the reference photovoltaic module(s) present in group i of photovoltaic modules;

According to another feature, the theoretical electrical power supplied by the reference photovoltaic module is determined from the following relationship:

In which :

• is a power loss factor as a function of temperature;
• is an aging factor of the photovoltaic plant;
• corresponds to the age of the photovoltaic plant in years;
• (W) is a reference electrical power delivered by a photovoltaic module under standard operating conditions;
• corresponds to a temperature equal to the temperature of the reference photovoltaic module;

According to another feature, the method comprises steps of:

• Determination of the current at the maximum power point which crosses the group i of photovoltaic modules and of the voltage at the maximum power point across the terminals of the group i of photovoltaic modules,
• Determination of the voltage at the terminals of each photovoltaic module of the group i of photovoltaic modules,
• Determination of the corrected electrical power delivered by each photovoltaic module of group i of photovoltaic modules,
• Use of the corrected electric power determined for each photovoltaic module of the group i of photovoltaic modules for the determination of the corrected environmental parameters.

According to another feature, the method comprises a step of determining the loss of electrical power of the target photovoltaic module.

According to another feature, the method comprises a step of determining the state of the target photovoltaic module by comparing said loss of electrical power determined for this module with a threshold value.

According to another particularity, the method includes 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 also relates to a system for estimating the electrical power of a photovoltaic module present among a group of several modules of a photovoltaic power plant, referenced group i of photovoltaic modules, said system comprising:

• A module for acquiring the following environmental parameters for group i of photovoltaic modules:
  • : global irradiance at the horizontal level;
  • : Ambient temperature ;
  • : Wind speed ;
• A module for determining a temperature of each photovoltaic module of the group i of photovoltaic modules,
• A module for determining the electrical power delivered by the group i of photovoltaic modules at the maximum power point,
• A module for determining corrected environmental parameters for which each of the photovoltaic modules of group i of photovoltaic modules provides the corrected electrical power, taking into account constraints on the energy balance of the modules and on the electrical power delivered at the maximum power point by the group i of photovoltaic modules,
• A module for determining the corrected electrical power of at least one so-called target photovoltaic module, belonging to the group i of photovoltaic modules, from the corrected environmental parameters.

According to one feature, the system includes means for measuring environmental parameters.

According to another feature, the system comprises a module for determining a temperature of each photovoltaic module, which is configured to determine the temperature of each photovoltaic module of the group i of photovoltaic modules from a thermal image acquired for each photovoltaic module of group i of modules.

According to another feature, the module for determining the corrected environmental parameters is configured to solve a nonlinear optimization problem defined by the following constraints:

In which :

• corresponds to the irradiance at the plane of the reference module;
• is the corrected absorption factor for group i of modules;
• is the corrected ambient temperature for group i of modules;
• is the corrected wind speed for group i of modules;
• is the corrected electrical power for each photovoltaic module of group i of photovoltaic modules;
• corresponds to the power delivered for group i of photovoltaic modules at the maximum power point;
• corresponds to the tolerance allowed with respect to the power ;

According to another feature, said weighting function f is as follows:

In which :

• are selected weighting factors;

According to another feature, the system comprises:

• A module for selecting at least one reference photovoltaic module, distinct from said target photovoltaic module, from among the group i of photovoltaic modules, on the basis of the homogeneous character of its temperature, called reference temperature,
• A module for determining a theoretical electrical power supplied by the reference photovoltaic module at the reference temperature,
• A module for determining the corrected environmental parameters taking into account the following additional constraint:

In which :

• corresponds to the theoretical electrical power supplied by the reference photovoltaic module;
• corresponds to the corrected electrical power of each photovoltaic module of group i of photovoltaic modules;
• corresponds to an accepted power tolerance for each photovoltaic module of the group i of photovoltaic modules;
• corresponds to the reference photovoltaic module(s) present in group i of photovoltaic modules;

According to another feature, the theoretical electrical power supplied by the reference photovoltaic module is determined from the following relationship:

In which :

• is a power loss factor as a function of temperature;
• is an aging factor of the photovoltaic plant;
• corresponds to the age of the photovoltaic plant in years;
• (W) is a reference electrical power delivered by a photovoltaic module under standard operating conditions;
• corresponds to a temperature equal to the temperature of the reference photovoltaic module;

According to another feature, the system comprises:

• A module for determining the current at the maximum power point which crosses the group i of photovoltaic modules and the voltage at the maximum power point across the terminals of the group i of photovoltaic modules,
• A module for determining the voltage at the terminals of each photovoltaic module of the group i of photovoltaic modules,
• A module for determining the corrected electrical power delivered by each photovoltaic module of the group i of photovoltaic modules,
• A module for injecting the corrected electrical power determined for each photovoltaic module of the group i of photovoltaic modules into the module for determining the corrected environmental parameters.

According to another feature, the system comprises a module for determining the loss of electrical power of the target photovoltaic module.

According to another feature, the system comprises a module for 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.

According to another feature, the system comprises means for carrying out diagnostics and/or maintenance of the target photovoltaic module when said determined electrical power loss is greater than said threshold value.

Brief description of figures

Other characteristics and advantages will appear in the detailed description which follows given with regard to the appended drawings in which:

• 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 software modules involved during the execution of this method;

Detailed description of at least one embodiment

With reference to the , a photovoltaic power plant typically has the following layout and operating features:

• Several strings of photovoltaic modules (also called photovoltaic panels or solar panels) are connected in parallel (two strings in Figure 1). In the same chain, the photovoltaic modules are for example identical and arranged with the same orientation and with the same inclination.
• Each string of photovoltaic modules comprises several photovoltaic modules connected in series.
• A photovoltaic module of a group i of photovoltaic modules (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 modules of each chain.
• Each photovoltaic module advantageously comprises bypass diodes (called "bypass") to each bypass a row of separate cells of a module if a cell of this row were faulty. In Figure 1, one bypass diode is shown per photovoltaic module.

With reference to the , in 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.
• In Figure 2, a separate bypass diode is associated with each row of cells shown. In FIG. 2, a row of cells comprises several cells but it could only comprise one cell.
• Each photovoltaic module has a surface or area, referenced A.

For the rest of the description, the photovoltaic modules Mi,j are referenced, with:

• i ranging from 1 to N and representing a group of several photovoltaic modules of the plant. In the same group i of photovoltaic modules, the photovoltaic modules belong to the same chain, are identical in architecture and have the same orientation and inclination. In FIG. 1, in a nonlimiting manner, each chain of photovoltaic modules represents for example a distinct group i of photovoltaic modules.
• In each group i of modules, each photovoltaic module is referenced j, with j ranging from 1 to M.
• Each photovoltaic module Mi,ja has a thermal image denoted Im _i,j .

On the , the plant is represented with N=2 groups of photovoltaic modules and M=3 photovoltaic modules per group of photovoltaic modules.

The system of the invention is intended to estimate, ultimately, the loss of production or energy power of a photovoltaic module that is defective in operation. The estimate can be made when the photovoltaic plant is in operation. By the terms “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.

No defective module, this request will mean a photovoltaic module having an electrical production lower than the production that it should normally provide under the conditions in which it is found.

With reference to the , the estimation system consists of the following elements:

• A device for acquiring the temperature of each photovoltaic module of the group i of photovoltaic modules;
• Means of acquiring environmental data, at the level of the plant or its nearby geography, in particular the ambient temperature, the irradiance (that is to say the power of an incident luminous flux), the speed of the wind ;
• Means for acquiring electrical data at the level of each photovoltaic module of the group i of photovoltaic modules;
• A calculator;

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. In a non-limiting way, 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 a photovoltaic module, called target, potentially defective. 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 electrical data acquisition means comprise means for determining the power delivered at the maximum power point for all the photovoltaic modules of the group i of photovoltaic modules. These determination means are activated in a synchronized manner with the device for acquiring the temperature of each photovoltaic module of the group i of photovoltaic modules, with a view to directly correlating the power delivered with the acquired temperature.

This power is called (KW) and is measured at the PV module string level. In known manner, a so-called MPPT (for “Maximum Power Point Tracking”) regulator regularly scans the electrical voltage produced by the photovoltaic module with a view to finding the maximum current output point. In a photovoltaic module, the maximum possible intensity is dependent on the light power received by the photovoltaic module. As long as the load does not exceed the capacity of the photovoltaic module, the electrical intensity is maximized by the sunshine received. When the load increases too much, the voltage drops, down to zero. In this case, the output power is also zero. To maximize the power, the MPPT regulator will vary the voltage circulating in the photovoltaic module, in order to reach the highest possible voltage without lowering the electrical intensity.

Optionally, the acquisition means can also be configured to acquire the electric current supplied by each photovoltaic module of the group i of photovoltaic modules at the maximum power point, referenced (A), and the voltage at the terminals of each photovoltaic module of group i of photovoltaic modules at the point of maximum power, referenced (V).

Starting from this architecture, the method of the invention firstly makes it possible to estimate the electrical power of a photovoltaic module present in a group i of photovoltaic modules. The process follows the steps described below.

Stage E0 – Acquisition environmental data

Thanks to the means of acquisition of environmental data, the system acquires the data necessary for the implementation of the method. Depending on the means available, they are measured and/or retrieved from remote servers. This data is transferred to the computer. These data are as follows:

• : global irradiance at the horizontal level;
• : Ambient temperature ;
• : Wind speed ;

Furthermore, as the inclination and orientation of the photovoltaic modules in each group i of photovoltaic modules are known, the computer 5 can determine the parameter:

• which corresponds to the irradiance at the plane of the photovoltaic module;

Step E 1 – Acquisition of data from temperature at the level of each module photovoltaic and determining the average temperature of each module photovoltaic

The acquisition of temperature data is advantageously implemented using a thermal camera 1. It could be carried out using data supplied by temperature sensors integrated into the photovoltaic module. The acquired data 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 .

For each photovoltaic module, its thermal image is then virtually cut or 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. By quasi-uniform, it is meant that the temperature can vary from one point to another in the thermal zone, but that the temperature difference between two points in the same zone always remains below said predefined threshold value. A thermal zone, called hot, is therefore a zone whose temperature exceeds the temperature of the other zones by the predefined threshold value.

With each thermal zone, the computer 5 then 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 then determines the average temperature of each photovoltaic module. The calculator assigns this average temperature as the temperature of the photovoltaic module j in the group i of photovoltaic modules, referenced .

Step E2 – Acquisition of electrical data

As indicated above, the computer 5 acquires the electrical data relating to each group i of modules comprising the photovoltaic modules to be evaluated. The groups i can thus correspond to chains of modules of the PV plant, connected to inverters providing these measurements. The acquisition of these data is synchronized with that of the temperature of each photovoltaic module of the group i of photovoltaic modules. These electrical data are as follows:

• (KW): Power delivered by group i of photovoltaic modules at the maximum power point;
• (A) – optional acquisition: Current delivered by group i of photovoltaic modules at the maximum power point;
• (V) – optional acquisition: Voltage at the terminals of group i of photovoltaic modules at the maximum power point;

Stage E 3 optional – Selecting a module photovoltaic reference

During this optional step, the computer 5 can select at least one reference photovoltaic module (referenced Mref) from a group i of modules. A reference photovoltaic module is a module considered to be healthy. In the remainder of the description, reference will also be made indiscriminately to a photovoltaic module or to a healthy photovoltaic module. This step is optional and may not be executed by computer 5.

The reference module Mref is a photovoltaic module analogous to the monitored and targeted photovoltaic module (ie with the same technical characteristics – with the same orientation and the same inclination) and not defective. It is part of the same group i of photovoltaic modules as the monitored 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.

On the , two modules M1.1, M1.2 of group 1 of photovoltaic modules have been shown. 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 of the reference photovoltaic modules of the same group i of photovoltaic modules is referenced The same chain of photovoltaic modules can in fact comprise several healthy photovoltaic modules.

Stage E 4 optional – Estimation of the electrical power supplied by THE module photovoltaic reference

The computer 5 can estimate the theoretical electrical power that a healthy photovoltaic module, that is to say the reference module, would be able to supply. The calculator is based on the following formula (equation (2)):

In which :

• is a power loss factor of the photovoltaic module as a function of temperature;
• is an aging factor of the photovoltaic plant;
• corresponds to the age of the photovoltaic plant in years;
• (W) is a reference electrical power delivered by a photovoltaic module under standard operating conditions (1000W/m², 25°C);
• corresponds to the temperature of the reference photovoltaic module, determined during step E1;

It will be understood that the computer 5 relies in particular on pre-stored data, linked to the aging of the module and of the plant.

thus corresponds to the electrical power that a healthy photovoltaic module should theoretically provide, at its temperature measured.

Step E5

In a known manner, the energy balance equation of a photovoltaic module is as follows (equation (3)):

In which :

• is the absorption factor of the photovoltaic module, its theoretical value is between [0.8-0.9];
• (W/°C/m²) is the thermal exchange coefficient of the photovoltaic module;

In a known manner, this heat exchange coefficient of the photovoltaic module can be expressed by the following relationship (equation (4)):

However, we observe that equation (3) above is not respected for all the healthy photovoltaic modules of a group i of photovoltaic modules. This can be for several reasons:

• Inhomogeneous aging or soiling that affects the absorption factor of the photovoltaic module;
• Wind speed and ambient temperature may vary locally, from one photovoltaic module to another; On the same group i of photovoltaic modules, these two parameters can however be considered as identical from one photovoltaic module to another of the group;

It is therefore relevant to ensure that the energy balance relationship is respected. For this, it is necessary to consider the following corrected parameters:

• is the corrected absorption factor for each photovoltaic module of group i of photovoltaic modules; it is possible to choose a coefficient valid for group i of photovoltaic modules;
• is the corrected ambient temperature for each photovoltaic module of group i of photovoltaic modules; it is possible to choose a temperature valid for group i of photovoltaic modules;
• is the corrected wind speed for group i of photovoltaic modules;
• is the corrected electrical power for each photovoltaic module of group i of photovoltaic modules;

These settings , , are considered as the corrected environmental parameters of the modules.

Step E5.1

Computer 5 must then determine the three parameters , , which make it possible to verify the energy balance equation. For this, the computer 5 must take into account the following constraints:

(equation (5))

(equation (6))

(equation (7))

(equation (8))

The computer 5 is also required to minimize a weighting function f of the three corrected parameters , , , with respect to the parameters acquired initially during step E0. For each parameter, a distinct weighting coefficient is applied, according to the influence of this parameter.

By way of example, the expression of the function f can be the following (equation (9)):

As a variant, the calculator can also rely on the following expression f:

With :

• which corresponds to the corrected electric power of each photovoltaic module of the group i of photovoltaic modules;
• which corresponds to an accepted power tolerance for each photovoltaic module of the group i of photovoltaic modules. For example, we can choose ;
• which are the weighting factors. By way of example, one can choose C1=100, C2=C3=1. The absorption factor varies very little compared to ambient temperature and wind speed;
• which corresponds to the tolerance allowed with respect to the power acquired during step E2. For example, the tolerance can be set at 3%;
• which corresponds to the reference photovoltaic module(s) present in the group i of photovoltaic modules (if selection of a reference photovoltaic module in step E3);
• which corresponds to the theoretical electrical power supplied by a healthy photovoltaic module, determined beforehand in step E4 (if a reference photovoltaic module is selected in step E3).

Optionally, it can be considered that the ambient temperature is homogeneous for all the photovoltaic modules of the group i of photovoltaic modules. We then have (equation 10):

Step E5.2 optional

As indicated above, during step E2, in an improved version, it is possible to have measurements of the current which crosses the entire chain of photovoltaic modules (i.e. group i) and of the voltage at the terminals of group i of photovoltaic modules.

These measurements make it possible in particular to be able to identify problems associated with bypass diodes used in photovoltaic modules.

For the group i of photovoltaic modules which constitute in this example a chain of modules in series connected to an inverter allowing the electrical measurement, we therefore have at the level of the individual modules Mi,j:

(equation (11))

(equation (12))

Depending on the electrical connection architecture of the modules within the measurement groups, equations (11) and (12) above may vary, while remaining within the principle of the invention.

It is thus possible to formulate the expression of the tension at the terminals of a healthy photovoltaic module. This expression is the following (equation (13)):

With :

• which is the MPPT voltage at standard conditions (STC = 25°C, 1000W/m²); this is constructor data;
• which is the MPPT voltage variation factor, also given by the manufacturer;
• D1, D2 which are parameters of the empirical functions which are extracted thanks to the simulation data;
• And with (equation (14)):

• G(i) being the measured or estimated irradiance, respectively on a photovoltaic module of the group i of photovoltaic modules.

Knowing the voltage at the terminals of a healthy photovoltaic module, the computer 5 will estimate the voltage at the terminals of each other photovoltaic module of the group i of photovoltaic modules. For each photovoltaic module of group i of photovoltaic modules, it must be taken into account that its voltage may be reduced depending on the number of active bypass diodes. We can therefore add a variable which corresponds to the number of diodes activated for each photovoltaic module, referenced . is the total number of diodes in the photovoltaic module. A continuous degradation factor is also added: . This factor makes it possible to take into account the level of aging of each module, which may vary from one module to another.

We then obtain the expression of the voltage at the terminals of a photovoltaic module:

Finally we get:

This expression is added to the constraints defined above in step E5.1 above and makes it possible to make the determination of the corrected parameters more precise.

Step E5.3

The computer 5 is required to solve the optimization problem mentioned above (step 5.1 and step 5.2 if executed). This is a non-linear optimization problem that can be solved with "fmincon" type solvers.

Step E6

Once the three corrected parameters obtained ( , ) by solving the optimization problem, it is possible to determine the electric power provided by each photovoltaic module Mi,j based on relation (5) above.

Subsequently, the computer 5 can estimate the loss of power of each photovoltaic module compared to the average power of the reference photovoltaic modules of the same group of photovoltaic modules, by the following relationship:

In the absence of determination of a reference photovoltaic module in step E3, the expression in the denominator can be replaced by a theoretical reference power, such as that determined in step E4.

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.

As illustrated by the , the architecture of the estimation system of the invention can be described as follows:

• Step E0 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. In FIG. 4, 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. In FIG. 4, in a non-limiting manner, the data acquisition is carried out by the thermal camera 1.
• Step E2 is implemented thanks to the inverter 6 responsible for transmitting the electrical data of the group i of photovoltaic modules and to a module for acquiring the electrical data relating to the group i of photovoltaic modules, this acquisition module being integrated into the calculator. It is a question of acquiring the electric power (KW) at the maximum power point, and possibly the current (A) delivered at maximum power point and voltage (V) supplied at maximum power point.
• The optional step E3 is implemented by a selection module MS of the computer 5, the latter being responsible for selecting at least one reference photovoltaic module Mref.
• The optional step E4 is implemented by a first calculation module MC1 of the computer 5, intended to calculate the electrical power theoretical provided a healthy photovoltaic module.
• Step E5 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. During step E5.2, the MC2 module can in particular use the current measurements (A) voltage (V) at the level of group i of photovoltaic modules and estimate the corrected electrical power in order to facilitate obtaining the desired environmental parameters.
• Step E6 is implemented by a third calculation module MC3 of the computer, intended to estimate the actual electrical power supplied by each photovoltaic module Mi,j and the power loss of each photovoltaic module.

The computer can advantageously embed means for determining the state of the target photovoltaic module by comparing said loss of electrical power determined for this photovoltaic module with a threshold value. If the photovoltaic module is considered to be defective (that is to say when its determined electrical power loss is greater than said threshold value), the computer 5 can be configured to activate diagnostic and/or maintenance means of this photovoltaic module.

It should be noted that the invention described above remains applicable in the case where so-called bifacial photovoltaic modules, that is to say with their two active faces, are used within the plant. In this particular case, the equation (2) of electrical power supplied by a healthy photovoltaic module is as follows:

With

• which is the solar irradiance received by the front face of the photovoltaic module;
• which is the solar irradiance received by the rear face of the photovoltaic module; It can come from a measurement or an estimate from a model;
• which is the bifacial factor coming from the data of the manufacturer of the photovoltaic module;

Equation (5) becomes for its part:

The remainder of the process of the invention applies in an identical manner.

The invention described above is therefore a particularly simple and reliable solution for determining the electrical power supplied by each photovoltaic module and possibly deducing therefrom a power loss of a defective photovoltaic module in a photovoltaic power station. It can for example be used to identify, within a group of photovoltaic modules, certain photovoltaic modules which will be considered defective due to a loss of power above a certain threshold. These photovoltaic modules can then be the subject of specific diagnostic or maintenance actions.

Claims (22)

Method for estimating the electrical power of a photovoltaic module, present among a group of several photovoltaic modules of a photovoltaic power plant, referenced group i of photovoltaic modules, characterized in that it comprises the following steps:

• Acquisition of the following environmental parameters for group i of photovoltaic modules:
  • : global irradiance at the horizontal level;
  • : Ambient temperature ;
  • : Wind speed ;

• Determination of a temperature of each photovoltaic module of the group i of photovoltaic modules,
• Determination of electrical power ( delivered by group i of photovoltaic modules at the maximum power point,
• Determination of corrected environmental parameters for which each of the photovoltaic modules of group i of photovoltaic modules provides the corrected electrical power, taking into account constraints on the energy balance of the modules and on the electrical power ( delivered at the maximum power point by group i of photovoltaic modules,
• Determination of corrected electrical power of at least one target photovoltaic module belonging to the group i of photovoltaic modules from the corrected environmental parameters.

Method according to claim 1, characterized in that the step of acquiring environmental parameters includes a step of measuring said parameters. Method according to claim 1 or 2, characterized in that the step of determining the temperature ( of each photovoltaic module of group i of photovoltaic modules is produced from a thermal image acquired for each photovoltaic module of said group i of photovoltaic modules. Method according to one of Claims 1 to 3, characterized in that the step of determining the corrected environmental parameters is implemented by solving 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 :

• corresponds to the irradiance at the level of the plane of a photovoltaic module of the group i of photovoltaic modules;
• is the corrected absorption factor for group i of photovoltaic modules;
• is the corrected ambient temperature for group i of photovoltaic modules;
• is the corrected wind speed for group i of photovoltaic modules;
• is the corrected electrical power for each photovoltaic module of group i of photovoltaic modules;
• corresponds to the power delivered by group i of photovoltaic modules at the maximum power point;
• corresponds to the tolerance allowed with respect to the power ;

Method according to Claim 4, characterized in that the said weighting function f is the following:

In which :

• are selected weighting factors;

Method according to claim 4 or 5, characterized in that it comprises steps of:

• Selection of at least one reference photovoltaic module (Mref), distinct from said target photovoltaic module, from among the group i of photovoltaic modules, on the basis of the homogeneous character of its temperature, called reference temperature,
• Determination of an electric power ( theoretical supplied by the reference photovoltaic module at the reference temperature,
• Determination of the corrected environmental parameters taking into account the following additional constraint:

In which :

• corresponds to the theoretical electrical power supplied by the reference photovoltaic module;
• corresponds to the corrected electrical power of each photovoltaic module of group i of photovoltaic modules;
• corresponds to an accepted power tolerance for each photovoltaic module of the group i of photovoltaic modules;
• corresponds to the reference photovoltaic module(s) present in group i of photovoltaic modules;

Method according to Claim 6, characterized in that the theoretical electrical power supplied by the reference photovoltaic module is determined from the following relationship:

In which :

• is a power loss factor as a function of temperature;
• is an aging factor of the photovoltaic plant;
• corresponds to the age of the photovoltaic plant in years;
• (W) is a reference electrical power delivered by a photovoltaic module under standard operating conditions;
• corresponds to a temperature equal to the temperature of the reference photovoltaic module;

Method according to claim 6 or 7, characterized in that it comprises steps of:

• Current determination ( ) at the maximum power point that crosses the group i of photovoltaic modules and the voltage ( ) at the maximum power point at the terminals of group i of photovoltaic modules,
• Determination of the voltage at the terminals of each photovoltaic module of the group i of photovoltaic modules,
• Determination of the corrected electrical power ( ) delivered by each photovoltaic module of group i of photovoltaic modules,
• Use of the corrected electrical power determined for each photovoltaic module of the group i of photovoltaic modules for determining the corrected environmental parameters.

Method according to one of Claims 1 to 8, characterized in that it comprises a step of determining the loss of electrical power of the target photovoltaic module. Method according to Claim 9, characterized in that it comprises a step of determining the state of the target photovoltaic module by comparing the said loss of electrical power determined for this module with a threshold value. Method according to claim 10, characterized in that it includes a step of carrying out diagnostics and/or maintenance of the target photovoltaic module when said determined electrical power loss is greater than said threshold value. System for estimating the electrical power of a photovoltaic module present among a group of several modules of a photovoltaic power plant, referenced group i of photovoltaic modules, characterized in that it comprises:

• A module for acquiring the following environmental parameters for group i of photovoltaic modules:
  • : global irradiance at the horizontal level;
  • : Ambient temperature ;
  • : Wind speed ;
• A module for determining a temperature of each photovoltaic module of group i of photovoltaic modules,
• A module for determining the electrical power ( delivered by group i of photovoltaic modules at the maximum power point,
• A module for determining corrected environmental parameters for which each of the photovoltaic modules of group i of photovoltaic modules provides the corrected electrical power, taking into account constraints on the energy balance of the modules and on the electrical power ( delivered to the maximum power point by group i of photovoltaic modules,
• A module for determining the corrected electrical power of at least one so-called target photovoltaic module, belonging to the group i of photovoltaic modules, from the corrected environmental parameters.

System according to Claim 12, characterized in that it comprises means for measuring the environmental parameters. System according to Claim 12 or 13, characterized in that it comprises a module for determining a temperature (MT) of each photovoltaic module, which is configured to determine the temperature of each photovoltaic module of the group i of photovoltaic modules from of a thermal image acquired for each photovoltaic module of the group i of modules. System according to one of Claims 12 to 14, characterized in that the module for determining the corrected environmental parameters is configured to solve a nonlinear optimization problem defined by the following constraints:



In which :

• corresponds to the irradiance at the plane of the reference module;
• is the corrected absorption factor for group i of modules;
• is the corrected ambient temperature for group i of modules;
• is the corrected wind speed for group i of modules;
• is the corrected electrical power for each photovoltaic module of group i of photovoltaic modules;
• corresponds to the power delivered for group i of photovoltaic modules at the maximum power point;
• corresponds to the tolerance allowed with respect to the power ;

System according to Claim 15, characterized in that the said weighting function f is the following:

In which :

• are selected weighting factors;

System according to claim 15 or 16, characterized in that it comprises:

• A module for selecting at least one reference photovoltaic module (Mref), distinct from said target photovoltaic module, from among the group i of photovoltaic modules, on the basis of the homogeneous character of its temperature, called reference temperature,
• A module for determining an electrical power ( theoretical supplied by the reference photovoltaic module at the reference temperature,
• A module for determining the corrected environmental parameters taking into account the following additional constraint:

In which :

• corresponds to the theoretical electrical power supplied by the reference photovoltaic module;
• corresponds to the corrected electrical power of each photovoltaic module of group i of photovoltaic modules;
• corresponds to an accepted power tolerance for each photovoltaic module of the group i of photovoltaic modules;
• corresponds to the reference photovoltaic module(s) present in group i of photovoltaic modules;

System according to Claim 17, characterized in that the theoretical electrical power supplied by the reference photovoltaic module is determined from the following relationship:

In which :

• is a power loss factor as a function of temperature;
• is an aging factor of the photovoltaic plant;
• corresponds to the age of the photovoltaic plant in years;
• (W) is a reference electrical power delivered by a photovoltaic module under standard operating conditions;
• corresponds to a temperature equal to the temperature of the reference photovoltaic module;

System according to claim 17 or 18, characterized in that it comprises:

• A current determination module ( ) at the maximum power point that crosses the group i of photovoltaic modules and the voltage ( ) at the maximum power point at the terminals of group i of photovoltaic modules,
• A module for determining the voltage at the terminals of each photovoltaic module of the group i of photovoltaic modules,
• A module for determining the corrected electrical power ( ) delivered by each photovoltaic module of group i of photovoltaic modules,
• A module for injecting the corrected electrical power determined for each photovoltaic module of the group i of photovoltaic modules into the module for determining the corrected environmental parameters.

System according to one of Claims 12 to 19, characterized in that it comprises a module for determining the loss of electrical power of the target photovoltaic module. System according to Claim 20, characterized in that it comprises a module for determining the state of the target photovoltaic module by comparing the said loss of electrical power determined for this target photovoltaic module with a threshold value. System according to Claim 21, characterized in that it comprises means for carrying out diagnostics and/or maintenance of the target photovoltaic module when the said determined electrical power loss is greater than the said threshold value.