EP4111506A1

EP4111506A1 - Architecture of photovoltaic installations

Info

Publication number: EP4111506A1
Application number: EP21703461.0A
Authority: EP
Inventors: Djamel HADBI
Original assignee: Electricite de France SA
Current assignee: Electricite de France SA
Priority date: 2020-02-24
Filing date: 2021-02-05
Publication date: 2023-01-04
Also published as: WO2021170371A1; FR3107625A1; FR3107625B1; CN115136325A; US20230074235A1

Abstract

A photovoltaic system comprising an output inverter (11) for a connection to a third-party network (1000), and at least one string, each string including at least one tandem module (1) of photovoltaic cells, each module having a first and a second pair of connectors. The modules of a string are connected in series by way of their first pair of connectors. The strings are connected to the output inverter in parallel with one another by way of connectors of each string from among the first pairs of connectors. Several modules are connected in parallel via their second pairs of connectors so as to form a first group coupled, via said second pairs of connectors, upstream of the output inverter, to a second group of module(s) made up of a single module or of a series of modules connected in series with one another by their first pairs of connectors.

Description

Title: Architecture of photovoltaic installations

Technical area

The invention relates to the field of energy production by a set of at least one photovoltaic module.

Prior art

A photovoltaic module (or panel) comprises a plurality of photovoltaic cells, for example 60 or 72 cells. Recently, a new type of photovoltaic cells has appeared: tandem cells. The tandem cells have a theoretical yield of more than 30% compared to 22% of conventional industrial PERC cells (PERC for “Passivated Emitter and Rear Cell”).

[0003] Tandem cells are composed of a stack of layers of different semiconductor materials, each P-N junction forming a sub-cell and therefore exhibiting different properties. The optimal operating conditions for energy conversion are different depending on the nature of said layers. In other words, tandem cells allow the cell as a whole to be efficient over a wider variety of operating conditions, making installations more flexible in terms of weather conditions, including light spectrum ranges, intensity of light. illumination and temperature.

When several types of PN junctions are present, each cell can have two terminals (or electrical terminals). The sub-cells are then connected in series. Such cells can then be connected in a conventional manner to the rest of the installation, in place of usual cells such as PERC cells. However, in practice, the efficiency of each cell is limited by the lower current of all the junctions. In other cases, each cell may have a number of terminals equal to twice the number of types of junctions. For example, each cell has four terminals (or independent electrical terminals (one pair per junction). As indicated in US 2017/0040557, and as for the other elements of photovoltaic installations, it is theoretically possible to associate a converter with each sub-cell. This makes it possible to decouple the operation of the sub-cells and therefore to make their efficiency independent of each other. In practice, it remains necessary to (at least) duplicate the other components of the installation (connectors, cabling, inverters, etc.), which significantly increases the risk of malfunctions and costs. In addition, converters are bulky and sensitive to heat due to solar radiation, which further reduces the practicality of such a system in practice.

Abstract

The present disclosure improves the situation.

A photovoltaic system is proposed comprising an output inverter for connection to a third-party network, and at least one string, each string including at least one module of tandem photovoltaic cells, each module having a first pair of connectors and a second pair of connectors, the modules of a string being connected in series to each other by means of their first pair of connectors, the strings being connected to the output inverter in parallel with each other by through connectors of each chain among the first pairs of connectors, several modules being further connected in parallel via their second pairs of connectors so as to form a first group, said first group being further coupled, via said second pairs of connectors. connectors, upstream of the output inverter, to a second group of module (s) consisting of a single module or of a series of modules connected in series with each other by their first pairs of connectors.

[0007] The characteristics set out in the following paragraphs can optionally be implemented. They can be implemented independently of each other or in combination with each other:

[0008] Each module includes a converter. Each first pair of connectors of a module is coupled to the second pair of connectors of said module through said converter. The converter is driven by means of an SPMP peak power point tracking algorithm so that the power subtracted through the second pair of connectors is made independent of the operating conditions of the first pair of connectors.

The converter is mounted on a face of the module opposite to the operational face of the photovoltaic cells, so that the converter is protected from solar radiation.

The first group and the second group each comprise a number of modules different from each other, so that the ratio between these two numbers can be chosen to correspond at least approximately to the voltage or current ratio of unitary operation of each of the two sub-cells constituting the tandem photovoltaic cells.

The first group and the second group include the same modules. The modules in a chain are assembled in series via their first pair of connectors on the one hand and via their second pairs of connectors on the other hand. Each string further includes a converter disposed in series or parallel between the string formed via the first pairs of connectors and the string formed via the second pairs of connectors. Each converter is driven using an SPMP peak power point tracking algorithm so that the power subtracted through the second pair of connectors is made independent of the operating conditions of the first pair of connectors.

The converter, arranged in series or in parallel between the chain formed via the first pairs of connectors and the chain formed via the second pairs of connectors, consists of two power switches. The output inverter includes a modular inverter with multiple inputs, said inverter being controlled by means of independent MPP maximum power point tracking algorithms on each input so that the power subtracted via the second pairs of connectors is made independent of the operating conditions of the first pairs of connectors.

Brief description of the drawings

[0014] Other features, details and advantages will become apparent on reading the detailed description below, and on analyzing the accompanying drawings, in which:

Fig. 1

[0015] [Fig. 1] illustrates the current or power characteristics as a function of the voltage of a conventional module for different operating conditions.

Fig. 2

[0016] [Fig. 2] shows a chain of tandem photovoltaic cells with two terminals.

Fig. 3

[0017] [Fig. 3] shows a detail of a two-terminal tandem photovoltaic cell.

Fig. 4

[0018] [Fig. 4] shows a chain of tandem photovoltaic cells with four terminals.

Fig. 5

[0019] [Fig. 5] shows a detail of a four-terminal tandem photovoltaic cell.

Fig. 6

[0020] [Fig. 6] shows a string of tandem photovoltaic cells with three terminals. Fig. 7

[0021] [Fig. 7] shows a detail of a three-terminal tandem photovoltaic cell.

Fig. 8 [0022] [Fig. 8] shows a two terminal photovoltaic module.

Fig. 9

[0023] [Fig. 9] illustrates current characteristics as a function of the voltage of the module of the preceding figure.

Fig. [0024] [Fig. 10] shows a photovoltaic module with four terminals.

Fig. 11

[0025] [Fig. 11] illustrates current characteristics as a function of the voltage of the module of the preceding figure.

Fig. 12 [0026] [Fig. 12] shows a two terminal module photovoltaic system.

Fig. 13

[0027] [Fig. 13] represents a photovoltaic system with four terminal modules (connectors, cables and split inverter). Fig. 14

[0028] [Fig. 14] represents a photovoltaic module with four terminals, the outputs of which are connected in series.

Fig. 15

[0029] [Fig. 15] illustrates current characteristics as a function of the voltage of the module of the preceding figure. Fig. 16

[0030] [Fig. 16] represents a photovoltaic module with four terminals, the outputs of which are connected in parallel.

Fig. 17 [0031] [Fig. 17] illustrates current characteristics as a function of the voltage of the module of the preceding figure.

Fig. 18

[0032] [Fig. 18] shows a four-terminal photovoltaic module whose outputs are coupled according to an example of an embodiment A. Fig. 19

[0033] [Fig. 19] illustrates current characteristics as a function of the voltage of the module of the preceding figure.

Fig. 20

[0034] [Fig. 20] shows a four terminal module photovoltaic system whose outputs are coupled according to an example of embodiment B.

Fig. 21

[0035] [Fig. 21] shows a four terminal module photovoltaic system whose outputs are coupled according to an example of an embodiment C1.

Fig. 22

[0036] [Fig. 22] shows a four terminal module photovoltaic system whose outputs are coupled according to an example of an embodiment C2. Fig. 23

RECTIFIED SHEET (RULE 91) ISA / EP [0037] [Fig. 23] shows a four terminal module photovoltaic system whose outputs are coupled according to an example of an embodiment D.

[0038] The drawings and the description below contain, for the most part, elements of a certain nature. They can therefore not only serve to better understand this disclosure, but also contribute to its definition, if applicable.

In the following, it is considered that:

- a "system" designates a photovoltaic installation as a whole, such as an electrical energy production plant including a plurality of photovoltaic "modules";

- a "module" designates what is commonly called a photovoltaic panel and including a plurality of photovoltaic "cells" (here tandem cells; usually 60 or 72 cells per module);

- a tandem "cell" designates the union of several "sub-cells", generally in the form of a stack of layers;

- a "sub-cell" refers to the combination of two layers of different materials forming a P-N junction and at the origin of the physical phenomenon of electricity generation under the effect of lighting.

Physical principles

For a good performance of a photovoltaic system (typically a production plant, or "photovoltaic farm"), the efficiency of the elementary components is one of the keys. Tandem cells theoretically show a good yield.

In particular, as for conventional photovoltaic cells (non-tandem), the characteristics (voltage and current) of the sub-cells are different from each other. Each sub-cell, each cell, each photovoltaic module, each string and each system has a theoretical maximum production point (or MPP for “Maximum Power Point”) defined by current and operating voltage conditions. This MPP varies from element to another. The MPP depends in particular on:

- intrinsic properties of the elements, which may be different depending on the manufacturing conditions, even between two theoretically identical models, and which are intentionally different between two sub-cells of a tandem cell,

- aging,

- dirt,

- lighting (exposed to sun or shade),

- of the temperature.

Reference is now made to [Fig. 1] By way of example, it shows the dependence of the characteristics of current, voltage, power, temperature and illumination of a module based on non-tandem cells (a single P-N junction per cell). Roughly speaking, we can consider that the light irradiation mainly influences the current produced while the voltage varies little in comparison. On the contrary, the temperature influences the voltage more, the current differences being smaller.

In conventional installations, the characteristics of certain elements are controlled via inverters controlled by means of an MPPT ("Maximum Power Point Tracker") algorithm which makes it possible to be placed as close as possible to a maximum power point in imposing current or voltage.

Replacing conventional cells with tandem cells in existing systems leads to limiting the yield of each tandem cell to the lower yield of the sub-cells which compose it. Likewise, this leads to limiting the efficiency of each tandem cell module to the lowest efficiency of the cells which compose it. The actual overall efficiency of the system is thereby limited. The difference between the real efficiency and the theoretical efficiency is all the more degraded as the power of the light spectrum is reduced or as the average photon energy (or APE for "Average Photon Energy") is low, for example less than 1, 78eV, which corresponds to frequent winter sunshine conditions in mainland France. In combination with the use of tandem cells, it is therefore preferable to use the energy available in each sub-cell regardless of the weather conditions by decoupling the heterogeneous sub-cells from one another. Optimizing the immediate environment of the cells is therefore also one of the keys to good energy performance: the entire conversion chain must be adapted to preserve the efficiency gain allowed by the tandem cells, from the PN layers. from sub-cells to the connection node to the transmission or distribution network.

Each element of the system has an MPP which is specific to it at each moment. It is therefore possible to provide controlled converters which make it possible to vary the operating conditions (current and voltage) of the elements with which they are associated.

In theory, it is possible to operate each of the elements under individually controlled current and voltage conditions by equipping each element with an inverter controlled by means of an MPPT algorithm. However, the number of optimizers and the properties of optimizers suitable for large powers make installation and maintenance costs prohibitive, especially for high power installations.

Description of the embodiments

In the following, the photovoltaic cells are tandem cells, that is to say comprising a plurality of sub-cells (two sub-cells in the examples shown). Within a tandem cell, referenced 1 below, the two sub-cells are of different physical nature from each other, which gives them different behaviors and properties under the effect of lighting. Therefore, in operation under similar illumination, the voltage and current across each of the sub-cells are generally different for each of the sub-cells.

Reference is now made to [Fig. 2] and [Fig. 3] A chain 101 of cells 1 connected in series to one another is shown therein. In this example, the subcells are connected in series with each other. So the cell 1 has only two terminals T1 and T2 (or connection terminals). In this simplified example, the single 101 chain can be seen as a module on its own. Such a module then presents itself only two terminals T1 and T2 (at the top in [FIG. 2]). Such cells are then compatible with existing infrastructures of modules accommodating cells with two connectors. Such modules are then compatible with existing infrastructures of systems accommodating modules with two connectors. The simplification and backward compatibility is improved to the detriment of the energy efficiency which is limited by the lower current of the two sub-cells (or of the two PN junctions).

Each chain and / or module can further include a diode arranged between the two terminals T1 and T2. This prevents the reverse current and therefore the string and / or the module consume electricity from the external network to which he / she is connected.

Reference is now made to [Fig. 4] and [Fig. 5] The sub-cells are similar to those of [Fig. 2] and [Fig. 3] In contrast, the sub-cells are not connected to each other in series but remain independent of each other. Thus, cell 1 has four terminals, ie two pairs: T 1 and T2 on the one hand and T3 and T4 on the other hand. In this simplified example, a first chain 101 similar to that of [Fig. 2] and [Fig. 3] corresponds to the serialization of cells 1 via their first pair of terminals T1 and T2. The chain 101 then also has two terminals T1 and T2 (at the top in [Fig. 4]). In addition, a second chain 102 similar to the first corresponds to the serialization of cells 1 via their second pair of terminals T3 and T4. The chain 102 then also has two terminals T3 and T4 (below in [Fig. 4]). Although the two sub-cells are physically integral with each other within each cell 1, the currents from each of the two types of sub-cells are dissociated at the output of cell 1. Two sets of specific connections to each of the two types of sub-cells are implemented.

Electrically, each of the two outputs T1-T2 and T3-T4 of the assembly shown in [Fig. 4] can be seen as a photovoltaic sub-module independent of each other. It therefore becomes possible, at least in theory, extract a maximum of power for each sub-cell (each junction) as a function of its nature and in particular of the semiconductor material used. For this, independent networks (electrically isolated from each other) can be provided downstream. This implies, for the cases of tandem cells with two subcells, doubling the cables, doubling the contacts, doubling the inverters and doubling the control components compared to existing installations with conventional cells (non-tandem). This further increases the risk of malfunction and costs both for installation and maintenance. In addition, such cells are often incompatible with the existing infrastructure of modules and systems with two connectors. The theoretical efficiency, which is no longer limited by the lower current of the two sub-cells (or of the two PN junctions), is improved to the detriment of backward compatibility and reliability.

Reference is now made to [Fig. 6] and [Fig. 7] This example can be seen as a hybrid solution of the previous two. By comparison with the example of [Fig. 4] and [Fig. 5], a common potential is created between the two sub-cells. A current pull line on one of the two sub-cells is created to prevent equalization of the current flowing through the two sub-cells (the two junctions). This theoretically makes it possible to achieve efficiencies similar to those of the previous architecture ([Fig. 6] and [Fig. 7]) by reducing the output to only three connectors instead of four. Such an architecture is particularly suitable for silicon-based cells having an interdigitated back contact structure (or IBC for “interdigitated back contact”), in particular because their contacts are entirely transferred to one of their face. Such cells nevertheless remain complex (and therefore expensive) to manufacture.

In the following, embodiments which make it possible to improve the situation with respect to the examples of the embodiment of [Fig. 2] These embodiments, in particular combined with the four terminal (or 4T) architectures of [Fig. 4] and / or to three terminals (or 3T) of [Fig. 6] allow both a decoupling of the sub-cells of the tandem cells, downstream of the cells themselves, so as to benefit in practice from the good theoretical yield of the cells. tandem cells while avoiding the multiplication of connections, wiring and electrical components.

In a tandem module, the performance of each junction is different because of the different characteristics of the semiconductor materials. In addition, these physical characteristics (such as bandgap energy or temperature coefficients) evolve differently with respect to solar irradiation and temperature.

Reference is now made to [Fig. 8], [Fig. 9], [Fig. 10] and [Fig. 11] [Fig. 8] illustrates a module with two terminals T1 and T2 while [Fig. 9] illustrates the characteristics of the module with two terminals T1 and T2. The larger the curve (constant current for a wide range of voltages), the greater the power developed by a module. The [Fig. 10] illustrates a module with four terminals T1 to T4 while [Fig. 11] illustrates the characteristics of the module with four terminals T1 to T4. The current-voltage characteristic of the two-terminal module T1-T2 is unique while each pair T1-T2 and T3-T4 of the four-terminal module has its own current-voltage characteristic which depends on the architecture of the modules ( band gap energy and intermediate transmission) but also the climatic conditions undergone by the module (temperature and light irradiation).

Reference is now made to [Fig. 12] [Fig. 12] shows a photovoltaic system. The system 10 comprises an output inverter 11. The system 10 is connected at the output to a third party network 1000 via the output inverter 11. The system 10 further comprises a plurality of strings each bearing an index i, i being a positive integer ranging from 1 to I where I is the number of chains. Each chain includes a plurality of modules 1 of tandem photovoltaic cells. Each module 1 jj carries the index i of the chain to which it belongs and an index j identifying it within the chain, j being a positive integer ranging from 1 to J where J is the number of modules 1 of the chain .

In an installation with modules 1 with a single pair of T1-T2 connectors (for example as shown in [Fig. 2], [Fig. 3], [Fig. 8] and [Fig. 9]) the modules are connected in series in order to achieve a level of voltage that can be used by medium power converters, for example between 800 V and 1,500 V. The strings are connected in parallel with each other in order to add their currents and achieve a high power level. The simplest architecture comprises a single output inverter 11 to which all the chains of modules are connected. The output inverter 11 is connected, at the output, to the third-party network 1000. Such an architecture is particularly suitable for very high power plants because it is particularly reliable and economical: a single converter is sufficient and inexpensive in relation to the quantity of The energy supplied to the third-party network 1000. A set of sensors and a control-command and monitoring subsystem is sufficient.

Reference is now made to [Fig. 13] Each module 1 jj has a first pair of connectors T 1 jj, T2jj and a second pair of connectors T3i, T4ij, the indices corresponding to those of module 1 jj. The 1 jj modules are connected via their first pair of connectors T 1 jj, T2jj in an identical manner to what has been described above for [Fig. 12] The modules 1 are further connected to it via their second pair of connectors T3i, T4ij in an identical manner to what has been described above for [Fig. 12] but by means of separate wiring from those used for the first pairs of connectors T 1 jj, T2jj. Likewise, a second output inverter 11 is arranged between the second wiring and the third-party network 1000.

Such an architecture is therefore obtained by doubling the connection and conversion equipment. Although the modules are based on tandem cells, each pair of terminals behaves like an independent module: terminals of the same type are connected in series in order to reach an exploitable voltage level (for example between 800 V and 1500 V ), especially if you want to use the same type of inverters for both networks. Alternatively, the two types of terminals may correspond to different voltages from each other. Different output inverters can then be implemented.

In such an architecture, the two networks are split, which doubles the complexity, the risk of failure, the cost of equipment, installation and maintenance compared to the architecture of [Fig. 12] Embodiments A

Reference is now made to [Fig. 14] and [Fig. 15] The T2 and T3 terminals are connected to each other so that the module goes from four terminals to two terminals (in series). As shown in [Fig. 15], placing the outputs in series requires that the current flowing through the two outputs is limited by the lower current. The resulting characteristic is less than the sum of the characteristics of the two independent outputs (T1-T2 and T3-T4). In addition, as soon as the characteristic T3-T4 goes down in current (due to underperformance in particular due to a decrease in illuminance), it will pull the resulting characteristic T1-T4 down as well.

Reference is now made to [Fig. 16] and [Fig. 17] The terminals T2 and T4 are connected to each other so as to be equipotential, the terminals T1 and T3 also being connected to each other for the same reason, the module passing from four terminals with two terminals (connection in parallel). As shown in [Fig. 17], paralleling requires that the resulting characteristic is less than the sum of the characteristics of the two independent outputs. In addition, as soon as the characteristic T3-T4 is pulled to the left, that is to say a current maintained for a smaller voltage range (due to underperformance, in particular due to an increase in the temperature), the resulting characteristic will also be pulled to the left.

Reference is now made to [Fig. 18] and [Fig. 19] A DC-DC (direct current-direct current) converter 12 is arranged between the first pair of connectors T1-T2 and the second pair of connectors T3-T4. The converter 12 can be, for example, a simple “boost” converter (or parallel chopper). It can be composed in particular of two semiconductor switches: a transistor and a diode. The control of the converter 12 may include implementing an MPPT algorithm to optimize the power withdrawn from the second pair of connectors T3-T4 regardless of the operating point of the first pair of connectors T1-T2. Thus, thanks to the converter 12, the electrical decoupling of the two tandem outputs is ensured and the output characteristic of the tandem module is wider. Structurally, the converter 12 can be integrated into the tandem module, so that the output of the module downstream of the converter 12 is equivalent to a module with two connectors, which makes it possible to adapt such a module to existing conventional architectures.

Such a solution allows permanent optimization of the power produced whatever the operating conditions (solar irradiation and temperature). It requires a single converter 12 per module (and not one per cell). Compared to modules in which each cell is equipped with a converter, the cost and the risk of failure are drastically reduced: one converter per module is sufficient instead of 60 or 72 in known modules.

Preferably, the converter 12 is arranged on the back of the module (on the side of the module not exposed to the sun). By being protected from direct sunlight and high temperature, the risk of the converter overheating is limited.

Embodiments B

Reference is now made to [Fig. 20] corresponding to embodiment B.

In embodiment B, a plurality of modules 1 are put in parallel via their second pair T3-T4 to achieve a current range equivalent to that of a single module 1 via its first pair T1-T2. To avoid overloading the figure, a single paralleling is shown in [Fig. 20] In practice, several parallelings are applied on the system 10. To determine the number of modules to be put in parallel via the second pair of connectors T3-T4, the ratio b of the currents between the two pairs is calculated (ITI- T2 / lT3-T4 = b). b being the whole number (rounded) of modules 1 to be put in parallel. In [Fig. 20], an example with b = 3 is shown.

Embodiment B and its variants make it possible, with a relatively low cost (connection and cables), to connect pairs of connectors having different characteristics. The operating point remains limited by the lowest voltage which limits the production of each pair in particular when the operating point changes due to a change in solar irradiation or temperature.

Embodiments C

Reference is now made to [Fig. 21] and [Fig. 22] corresponding respectively to embodiments C1 and C2. In these two embodiments, the converters 12 are mutualized by comparison with the embodiment A. The second pairs of connectors T3-T4 are connected in groups each to a first pair of connectors T1-T2 by means of a common converter 12. This is relevant because the tandem outputs of the same chain generally experience the same operating conditions. For modules of the same type, the factory characteristics are very similar and remain so during their useful life. It is therefore reasonable to consider that their MPP is similar in operation.

In the embodiment C1 ([Fig. 21]), the second connectors T3- T4 are connected in parallel with the first connectors T1-T2 on the main bus via the converter 12. The second connectors T3- T4 form a secondary bus while the first connectors T1 -T2 form the main bus. The two buses are connected to each other in parallel, each via a converter 11, 12. In the embodiment C2 ([Fig. 22]), the second connectors T3-T4 are connected in series with the first connectors. T1-T2 on the main bus via converter 12. The two buses are connected to each other in series, each via output inverter 11 and converter 12.

[0073] A combination of embodiments B and C can achieve a good cost-complexity compromise. For example, modes C1 or C2 (converters shared on several modules) make it possible to smooth out any remaining differences at the output.

Embodiments D

Reference is now made to [Fig. 23] corresponding to embodiment D. In this embodiment, converter 13 is particular. The converter 13 includes a central modular inverter of type CHB or MMC (CHB for “Cascaded H Bridge” and MMC for “Multilevel Modular Converter”). The converter 13 makes it possible to connect second pairs T3-T4 (placed in series and / or in parallel) directly at the level of one or more submodules. The function of optimizing the second pairs T3-T4 can then be integrated into the controller of the converter 13, here forming a central inverter. The modular central inverter then also performs the function of decoupling between the first and second pairs T1-T2 and T3-T4 which have different characteristics. No additional DC-DC converter is required.

Industrial applications

[0075] Embodiments A are applicable to all photovoltaic installations. A module with four connectors according to embodiment A behaves like a conventional module with better efficiency. It can therefore be used in small domestic installations, on the roofs of buildings and in photovoltaic power plants. This solution can therefore be applied to new installations as well as to the renovation of existing installations.

[0076] Embodiments B and C are applicable to all photovoltaic installations having at least one chain of modules.

Embodiment D is particularly suitable for large-scale installations and can advantageously replace existing solutions based on inverters of the "string" type or of the "central" type.

[0078] The present disclosure is not limited to the examples of systems described above, only by way of example, but it encompasses all the variants that a person skilled in the art may envisage in the context of the protection sought. In particular, the different embodiments can be combined with each other, in particular at different levels of the systems (cells, submodules, modules, chains, bus, system).

List of reference signs

[0079] - 1: Module;

- 10: System; - 11: Output inverter;

- 12: Converter;

- 13: Converter + output inverter; - 101, 102: chain; - 1000: Third party network.

Claims

[Claim 1] Photovoltaic system comprising an output inverter (11, 13) for connection to a third party grid (1000), and at least one string (i), each string including at least one module (1 jj) of photovoltaic cells tandem, each module having a first pair of connectors (T 1 jj, T2jj) and a second pair of connectors (T3jj, T4jj), the modules of a chain being connected in series to each other via their first pair of connectors, the strings being connected to the output inverter in parallel with each other via connectors (T1i, i, T2i, j) of each string among the first pairs of connectors, several modules being further connected in parallel via their second pairs of connectors so as to form a first group, said first group being further coupled, via said second pairs of connectors, upstream of the output inverter, to a second group of modules (s) consisting of a modu the only one or a series of modules connected in series with each other by their first pairs of connectors.

[Claim 2] System according to the preceding claim, in which each module comprises a converter, each first pair of connectors (T 1 jj, T2 jj) of a module is coupled to the second pair of connectors (T3 i, T4 ij) of said module via said converter, said converter being controlled by means of an algorithm for tracking the maximum power point SPMP so that the power subtracted via the second pair of connectors (T3 ij, T4 ij) is made independent of the operating conditions of the first pair of connectors (T 1 jj, T2 u).

[Claim 3] System according to the preceding claim, in which the converter is mounted on a face of the module opposite to the operational face of the photovoltaic cells, so that the converter is protected from solar radiation.

[Claim 4] A system according to one of the preceding claims, wherein the first group and the second group each comprise a number of modules different from each other, so that the ratio between these two numbers can be chosen to correspond at least approximately to the unit operating voltage or current ratio of each of the two sub-cells constituting the tandem photovoltaic cells.

[Claim 5] System according to one of the preceding claims, in which the first group and the second group comprise the same modules, the modules of a chain being assembled in series via their first pair of connectors (T 1 jj, T2jj) on the one hand and via their second pairs of connectors (T3ij, T4i) on the other hand, each chain further including a converter arranged in series or in parallel between the chain formed via the first pairs of connectors (T 1 u, T2jj ) and the chain formed via the second pairs of connectors (T3ij, T4i), each converter being driven by means of an algorithm for tracking the maximum power point SPMP so that the power subtracted via the second pair of connectors (T3jj, T4jj) is made independent of the operating conditions of the first pair of connectors (T 1 jj, T2jj).

[Claim 6] System according to the preceding claim, in which said converter, arranged in series or in parallel between the chain formed via the first pairs of connectors (T1i, j, T2i, j) and the chain formed via the second pairs of connectors (T3i, j, T4i, j), consists of two power switches.

[Claim 7] The system according to one of the preceding claims, wherein the output inverter includes a modular inverter with multiple inputs, said inverter being driven by means of independent MPP maximum power point tracking algorithms on each input of so that the power subtracted via the second pairs of connectors (T3jj, T4jj) is made independent of the operating conditions of the first pairs of connectors (T 1 jj, T2jj).