阅读说明：本技术 光伏设备 (Photovoltaic device ) 是由 M.弗莱舍尔 A.施内特勒 于 2018-03-06 设计创作，主要内容包括：本发明涉及具有不同电池单元类型的两个PV电池单元(11、21)的串联PV电池单元组(1)。单独的功率电子单元(31、32)被指派给每个PV电池单元,使得在相应PV电池单元中生成的电压或对应电流产量可以被供应给所指派的功率电子单元。功率电子单元可以借助调节设备(40)彼此独立地运行,使得每个PV子系统都在其最佳工作点工作,每个PV子系统分别具有PV电池单元之一和指派给相应PV电池单元的功率电子单元。为此,调节设备可以工作使得在运行每个PV子系统的功率电子单元期间,指派给相应功率电子单元的PV电池单元的电流产量和电池单元电压的乘积最大。(the invention relates to a series PV-cell stack (1) with two PV-cells (11, 21) of different cell types. A separate power electronic unit (31, 32) is assigned to each PV cell unit, so that the voltage generated in the respective PV cell unit or the corresponding current production can be supplied to the assigned power electronic unit. The power electronic units can be operated independently of one another by means of the regulating device (40) such that each PV subsystem, each having one of the PV cells and a power electronic unit assigned to the respective PV cell, operates at its optimum operating point. To this end, the conditioning apparatus may be operated such that, during operation of the power electronic units of each PV subsystem, the product of the current production and the cell voltage of the PV cells assigned to the respective power electronic unit is maximized.)

1. A PV installation (100) having

A multi-PV cell group (1) having at least one first PV cell (11) of a first cell type and a second PV cell (21) of a second cell type, wherein the first and second cell types are different from each other, and wherein each of the PV cells (11, 21) provides a cell voltage U1, U2 when light is incident on the respective PV cell (11, 21),

A power electronic device (30) having a separate first power electronic device unit (31) assigned to the first PV cell (11) and a separate second power electronic device unit (32) assigned to the second PV cell (22), wherein the cell voltages U1, U2 and the corresponding current productions I1, I2 generated in the respective PV cell (11, 21) are feedable to the separate power electronic device unit (31, 32) assigned to the respective PV cell (11, 21),

-a regulating device (40) for regulating the power electronics (30),

Wherein

-the first power electronics unit (31) and the second power electronics unit (32) are operable independently of each other by means of the regulating device (40) such that each PV subsystem (10, 20) having one of the PV cell units (11, 21) and the power electronics unit (31, 32) assigned to the respective PV cell unit (11, 21), respectively, operates at its optimal operating point.

2. The PV installation (100) according to claim 1, characterised in that the regulating device (40) is designed to regulate the respective power electronics unit (31, 32) during operation of the power electronics unit (31, 32) of each PV subsystem (10, 20) such that the product of the current yield I1, I2 and the cell voltage U1, U2 assigned to the PV cell (11, 21) of the respective power electronics unit (31, 32) is maximal.

3. The PV installation (100) according to claim 2, characterised in that the regulating device (40) is designed, when regulating the power electronics units (31, 32), to adjust the input resistance of the respective power electronics unit (31, 32) such that the product of the current yield I1, I2 and the cell voltage U1, U2 of the PV cell (11, 21) assigned to the respective power electronics unit (31, 32) is maximized.

4. PV installation (100) according to one of the claims 1 to 3, characterised by a sensor installation (50) having

-a device (51) for determining the temperature of the PV-cell units (11, 21) and/or for determining the ambient temperature of the multi-PV-cell stack (1), wherein one or more parameters describing the temperature and/or the ambient temperature are fed to the regulating device (40) as input variables, and/or

-a device (52) for determining the intensity of light incident on the PV device (100), in particular on the first PV cell unit (11), wherein a parameter describing the light intensity is fed to the adjusting device (40) as an input variable, and/or

-a device (53) for determining the spectrum of light incident on the PV device (100), in particular on the first PV cell (11), wherein parameters describing the spectrum are fed to the adjusting device (40) as input variables,

Wherein

-the regulating device (40) is designed to regulate the power electronics unit (31, 32) based on one or more input variables fed thereto.

5. The PV installation (100) according to claim 4, characterised in that the regulation device (40) is designed to carry out the regulation, in particular on the basis of a look-up table or in a model-based manner, such that the input resistance is determined and set as a function of one or more input variables of each power electronics unit (31, 32) such that the product of the current yield I and the cell voltage U of the PV cell (11, 21) assigned to the respective power electronics unit (31, 32) is maximal.

6. The PV device (100) according to one of the claims 1 to 5, characterised in that the first and second battery cell types are selected such that their PCE maxima lie in different spectral ranges.

7. The PV arrangement (100) according to one of claims 1 to 6, characterised in that the first PV cell unit (11) is a perovskite-based PV cell unit and/or the second PV cell unit (21) is a silicon-based PV cell unit.

8. The PV installation (100) according to claim 7, characterised in that the regulating device (40) is designed to regulate the power electronics unit (31) assigned to the first perovskite-based PV cell (11) such that the hysteresis of the output variables of the first PV cell (11), in particular the cell voltage U1 and the current yield I1, is compensated.

9. The PV installation according to one of claims 1 to 8, characterised in that the regulating device (40) is designed to carry out a regulation of the power electronics units (31, 32) such that ageing of the respective PV cell units (11, 21) and/or soiling of the group of multi-PV cells (1) is compensated.

10. a method for operating a PV installation (100), the PV installation (100) having

A multi-PV cell group (1) having at least one first PV cell (11) of a first cell type and a second PV cell (21) of a second cell type, wherein the first and second cell types are different from each other, and wherein each of the PV cells (11, 21) provides a cell voltage U1, U2 when light is incident on the respective PV cell (11, 21),

a power electronic device (30) having a separate first power electronic device unit (31) assigned to the first PV cell (11) and a separate second power electronic device unit (32) assigned to the second PV cell (22), wherein the cell voltages U1, U2 and the corresponding current productions I1, I2 generated in the respective PV cell (11, 21) are fed to the separate power electronic device unit (31, 32) assigned to the respective PV cell (11, 21),

-a regulating device (40) for regulating the power electronics (30),

Wherein

-the first power electronics unit (31) and the second power electronics unit (32) are operated independently of each other by means of the regulating device (40) such that each PV subsystem (10, 20) having one of the PV cell units (11, 21) and the power electronics unit (31, 32) assigned to the respective PV cell unit (11, 21), respectively, operates at its optimal operating point.

11. the method according to claim 10, characterized in that the respective power electronics unit (31, 32) is adjusted during operation of the power electronics unit (31, 32) of each PV subsystem (10, 20) such that the product of the current yield I1, I2 and the cell voltage U1, U2 assigned to the PV cell (11, 21) of the respective power electronics unit (31, 32) is maximized.

12. The method according to claim 11, characterized in that the input resistance of the respective power electronics unit (31, 32) is adjusted when adjusting the respective power electronics unit (31, 32) such that the product of the cell voltage U1, U2 and the current yield I1, I2 of the PV cell (11, 21) assigned to the respective power electronics unit (31, 32) is maximized.

13. The method according to one of claims 10 to 12, wherein the PV device (100) comprises a sensor device (50), the sensor device (50) having

-a device (51) for determining the temperature of the PV-cell units (11, 21) and/or for determining the ambient temperature of the multi-PV-cell stack (1), wherein one or more parameters describing the temperature and/or the ambient temperature are fed to the regulating device (40) as input variables, and/or

-a device (52) for determining the intensity of light incident on the PV device (100), in particular on the first PV cell unit (11), wherein a parameter describing the light intensity is fed to the adjusting device (40) as an input variable, and/or

-a device (53) for determining the spectrum of light incident on the PV device (100), in particular on the first PV cell (11), wherein parameters describing the spectrum are fed to the adjusting device (40) as input variables,

Wherein the power electronics unit (31, 32) is regulated based on one or more input variables fed to the regulating device (40).

14. The method according to claim 13, characterized in that the adjustment is carried out in particular on the basis of a look-up table or in a model-based manner such that the input resistance is determined and set in dependence on one or more input variables of each power electronics unit (31, 32) such that the product of the current yield I and the cell voltage U of the PV cell (11, 21) assigned to the respective power electronics unit (31, 32) is maximal.

15. The method according to one of claims 10 to 14, characterized in that the power electronics units (31, 32) are adjusted such that the influence caused by aging of the respective PV cell units and/or the influence caused by soiling of the group of multi-PV cells (1) is compensated.

Technical Field

The present invention relates to a photovoltaic device having two or more individual solar cells.

Background

Solar power generation using Photovoltaic (PV) devices is contributing to electricity production to a rapidly growing extent, both from the environment and also from an increasing economic factor (e.g., in central europe). However, this renewable energy source must also be competitive, and in particular compared to conventional energy sources, for which reason it is sought to drive the PV power generation costs lower than those of conventional, in particular fossil energy production, even in areas with moderate intensity solar radiation, such as germany.

The cost of PV installations is largely determined by system costs, such as for overall panel, wiring, power electronics, and other structural costs. Although so-called perovskite materials, such as CH3NH3PbI3 (or more generally, (CH3NH3) MX3-xYx (where M = Pb or Sn, and X, Y = I, Br or Cl))) have gained increased attention in recent years and promised the effect of reducing operating costs, the use of such new inexpensive solar cells alone is still insufficient, due to their photovoltaic properties, to allow efficient conversion of electromagnetic radiation energy into electrical energy. In contrast, it is necessary to further increase the efficiency of the solar cell unit.

One solution to increase efficiency is to use a so-called series PV cell stack, in which two or even more light-sensitive PV cell units or layers are arranged on top of each other. The individual battery cells are ideally different in their spectral sensitivity, that is to say the different battery cells have their respective maximum efficiency for different spectral ranges of the sunlight. This results in: the series stack of cells as a whole provides high efficiency over a wide spectral range.

Such a series stack of battery cells may have, for example, conventional silicon-based PV cells on which further, for example perovskite-based PV cells are applied. Perovskite materials have a larger band gap than silicon-based materials, and thus perovskite-based PV cells have higher absorption components in the blue or short wavelength spectral range and pass longer wavelengths of light. The silicon-based PV cell absorbs more strongly in the longer wavelength spectral range so that light passing from the perovskite cell or layer, or at least a portion thereof, is absorbed by the silicon cell.

fig. 1 shows a side view of such a known series PV cell stack 1. The upper cell 11 of the series cell stack 1, that is to say the cell facing the light source or the sun, not shown, is a PV cell made of a first material having the greatest efficiency in the first spectral range S1. The lower cell 21 is a PV cell made of a second material having the greatest efficiency in a second spectral range S2, wherein the spectral ranges S1, S2 and the materials are different. Such a series-connected cell group operates in principle according to the concept that the current I generated under light incidence L flows successively through the two battery cells 11, 21, that is, the battery cells 11, 21 are electrically connected in series. However, in this case, there arises a problem in that, for a case where currents of significantly different magnitudes are generated in the two battery cells 11, 21, the battery cell 11, 21 generating a low current is flowed by a large current of the other battery cell 21, 11, which may cause damage. Furthermore, the following applies: ideally, both cells 11, 21 deliver the same current per photosensitive surface area. However, this is not generally the case due to the different properties of the materials used in the different battery cells 11, 21. This has the following effect: the efficiency of the series stack of PV cells 1 as a whole is significantly lower than would be theoretically possible or would be expected based on individual efficiencies.

In principle, this problem can be solved by a solution called "current matching" in that the individual battery cells 11, 21 are designed such that they deliver the same large current. To achieve this, the photosensitive regions 12, 22 of the two PV cells 11, 21, which generate current under the respective illumination, can be coordinated with one another, wherein the region 12 in the first cell 11 consists of a first material and the region 22 in the second cell 21 consists of a second material. It is assumed here that: the current generated in the regions 12, 22 is proportional to the surface area of the respective region 12, 22. Accordingly, the surface area and the number of regions 12, 22 can be selected differently as indicated in fig. 2, so that both battery cells 11, 21 ultimately carry the same large current. The size and number to be selected for this purpose for the surface area depend in this case on the respective material. However, differently formed superimposed structures have proven to be technically problematic in this context.

Fig. 2 shows a view in the y direction in the plane indicated by the dashed line in fig. 1, wherein the illustration in fig. 2 is selected as if the battery cells 1 of fig. 1 were turned over one above the other, so that the two layers 11, 21 are now side by side. It is to be explained that the surface area of the region 12 of the first battery cell 11 is larger than the surface area of the region 22 of the second battery cell 21. Here, for the sake of clarity, only a few of the respective regions 12, 22 are provided with reference numerals. For each PV cell unit 11, 21, the following applies: the regions 12, 22 of the respective battery cells 11, 21 are connected in series into respective region groups 13, 23. Furthermore, the two zone groups 13, 23 are also connected electrically in succession, that is to say in series.

Although the concept of matching the surface area of the photosensitive regions 12, 22 theoretically provides a solution to the problem. It has proven practical, however, that the efficiency of a series PV cell stack 1 constructed in this manner continues to remain below theoretically possible values on average. This is related to the fact that: the light intensity is not in fact constant in time but is subject to fluctuations of greater or lesser intensity during the day, which have different magnitudes of influence on the voltage or current generated by the different battery cells. Therefore, silicon-based PV cells (Si cells) operate with particularly high efficiency at high light intensities, that is to say, for example, in full sunlight. However, at weaker light, the efficiency of such Si cells drops below that of, for example, organic PV cells, which have relatively high efficiencies, especially under diffuse and weak light. Furthermore, it is assumed that different battery cells are subjected to different aging influences and temperature change processes. Therefore, the solution with matching surface areas of the photosensitive regions illustrated in fig. 2 is not ultimately the main objective.

Disclosure of Invention

it is therefore an object of the present invention to illustrate an alternative for a high efficiency photovoltaic cell.

This object is achieved by a PV system as described in claim 1 and by a method of operation as explained in claim 10. The dependent claims describe advantageous embodiments.

The PV device according to the invention has a multi-PV-cell stack with at least a first PV cell of a first cell type and a second PV cell of a second cell type, wherein the first and second cell types are different from each other, and wherein each of the PV cells provides a cell voltage U1, U2 when light is incident on the respective PV cell. Furthermore, a power electronic device is provided, which has a separate first power electronic device unit assigned to the first PV cell unit and a separate second power electronic device unit assigned to the second PV cell unit. The electrical cell voltages U1, U2 and the corresponding current productions I1, I2 generated in the respective PV cell units can be fed to the individual power electronics units assigned to the respective PV cell units, for example via suitable electrical connections. The PV system further has a control device for controlling the power electronics. The first and second power electronics units can now be operated independently of one another by means of the regulating device, so that each PV subsystem, which each has one of the PV cell units and the power electronics unit assigned to the respective PV cell unit, is operated at its optimum operating point. In other words, the PV system has at least one first PV subsystem and a second PV subsystem, wherein the first PV subsystem has a first PV cell unit and a first power electronics unit, and the second PV subsystem has a second PV cell unit and a second power electronics unit.

For the design of the high efficiency multi-PV cell stack proposed here, which does not lose its high efficiency even at variable illumination intensities, the "current matching" scheme described above can be dispensed with. A series PV cell stack has two galvanically isolated PV cells that are neither connected in series nor otherwise directly electrically connected. More precisely, the voltages generated by the PV cells of the cell stack under illumination and thus the corresponding currents are fed to the individual power electronics units, respectively. This is achieved by using separate power electronics units for different PV cell units: each PV cell unit can be operated at an optimal operating point.

The regulating device is designed to regulate the respective power electronics unit during operation of the power electronics unit of each PV subsystem such that the product of the current yield I1, I2 of the PV cell unit assigned to the respective power electronics unit and the cell voltage U1, U2 is maximized. In this case, it is of course assumed here and hereafter: the expression that the product should be "maximum" does not necessarily mean, or may not necessarily mean, the exact point at which the product reaches its maximum absolute value at any point in time. This is also technically not possible so far, since the value fed to the regulating device is in fact constantly changing within a certain range, so that the theoretical actual maximum at time T1 is no longer the theoretical maximum at the next time T2. Accordingly, the expression that the respective product should be "maximum" means: within the scope of the regulation, the power electronics units are each adjusted continuously in such a way that the respective current-voltage product changes toward the instantaneous theoretically possible maximum value. In fact, the adjustment is made such that the current-voltage product considered in the determined period of time does not become smaller. That is, for the case where the theoretically possible maximum has been reached, the product should become larger or may remain constant.

The regulating device may be operated for this purpose such that the input resistance of the respective power electronics unit can be regulated when regulating the respective power electronics unit, so that the product of the current yield I1, I2 and the cell voltage U1, U2 of the PV cell assigned to the respective power electronics unit is maximal.

In particular, the regulating device is designed to regulate the power electronics units independently of one another. For this purpose, the regulating device can have a number of regulators corresponding to the number of PV subsystems, for example. These regulators can be designed, for example, as so-called PID regulators.

Alternatively or additionally, the PV system has a sensor system with a system for determining the temperature of the PV cell units and/or for determining the ambient temperature of the multi-PV-cell stack, wherein one or more parameters describing the temperature and/or the ambient temperature are fed to the regulating system as input variables. Additionally or alternatively, the sensor device may have a device for determining the intensity of light incident on the PV device (in particular on the first PV cell unit), wherein a parameter describing the intensity of light is fed to the adjusting device as an input variable. Also additionally or alternatively, the sensor device may have a device for determining the spectrum of the light incident on the PV device (in particular on the first PV cell unit), wherein the parameters describing the spectrum are fed to the adjusting device as input variables. The regulating device is now designed to regulate the power electronics unit based on one or more input variables fed to it.

The control device is designed in particular to carry out the control, in particular on the basis of a look-up table or in a model-based manner, such that the input resistance is determined and set as a function of one or more input variables of each power electronics unit, such that the product of the current yield I of the PV cell assigned to the respective power electronics unit and the cell voltage U is maximal.

The first and second battery cell types are preferably selected such that their PCE maxima (PCE = power conversion efficiency) lie in different spectral ranges.

For the second PV cell, the cell type is specifically chosen such that its PCE maximum lies in the spectral range in which the first PV cell is substantially transparent. "substantially transparent" shall mean in this case that the first PV cell unit absorbs this particular spectral range significantly less than other spectral ranges. It must of course be assumed that the first PV cell unit in principle has a certain degree of absorption in each spectral range relevant for the present application, but it may equally be assumed that the degree of absorption is relatively low within a certain range of the spectrum and is therefore "substantially transparent".

For example, the first PV cell may be a perovskite-based PV cell and/or the second PV cell may be a silicon-based PV cell.

In this case, the regulating device is designed to regulate the power electronics unit assigned to the first perovskite-based PV cell unit such that a hysteresis of the output variable of the first PV cell unit is compensated. This compensation is achieved by correspondingly adjusting the operating parameters of the regulator (e.g., PID parameters).

Furthermore, the regulating device is designed to carry out a regulation of the power electronics units such that ageing of the respective PV cell units and/or soiling of the groups of multiple PV cell units or of the individual PV cell units is compensated. Here, it is again sought to optimize the product of the current yield I assigned to the respective power electronics unit and the battery cell voltage U, wherein the input resistances of the power electronics units are also set here independently of one another.

in a method according to the invention for operating such a PV system with a multi-PV-cell stack, power electronics and a control device of the type mentioned at the outset, the first and second power electronics units are operated independently of one another by means of the control device, so that each PV subsystem, which each has one of the PV cells and the power electronics unit assigned to it, respectively, is operated at its optimum operating point.

In operating the power electronics units of each PV subsystem, the respective power electronics unit is adjusted such that the product of the current yield I1, I2 of the PV cell assigned to the respective power electronics unit and the cell voltage U1, U2 is maximized.

When adjusting the respective power electronics unit, the input resistance of the respective power electronics unit is adjusted such that the product of the current yield I1, I2 of the PV cell assigned to the respective power electronics unit and the cell voltage U1, U2 is maximized.

The regulating devices preferably regulate the power electronics units independently of one another.

Also for the case of PV installations with sensor installations of the aforementioned type, the power electronics unit is regulated on the basis of one or more input variables fed to the regulating installation.

The adjustment is carried out in particular on the basis of a look-up table or in a model-based manner such that an input resistance with which the product of the current yield I and the cell voltage U of the PV cell assigned to the respective power electronics unit is maximized is determined and set as a function of one or more input variables of each power electronics unit. Here, the aging curve for the cell case may also be stored in a look-up table.

For each power electronic device, the voltage and current levels are thus adjusted such that the maximum energy yield of the respective PV cell is achieved, that is to say that each PV cell operates with the power electronic device assigned to it at its optimum operating point.

This adjustment may be made, for example, by adjusting the input resistance of the respective power electronics, wherein adjusting the input resistance has an effect on the current yield I in case the cell voltage U of the PV cell connected to the power electronics depends on the illumination. The product of the voltage U and the corresponding current I generated by a PV cell under illumination describes the energy yield of the PV cell.

By the individual adjustment possible by means of separate power electronics units, this can be achieved with significantly lower losses than in the case of PV cells with electrically fixed couplings, in which one cell type is in fact always operated in a suboptimal manner. The concept is therefore based on a shift away from the hitherto ubiquitous paradigm of conventional series connection of individual battery cells of a multi-PV-cell stack with common electronics towards a parallelization concept of individual PV battery cells in which two PV cell units can be operated under optimum conditions with separate main electronics and useful energy can be superimposed on the electronics level.

By this solution the explained disadvantages of different current carrying capacities of different PV cell units are eliminated. At the same time, each PV cell of the cell stack can be operated at its optimum operating point, that is to say both PV cells can be operated continuously at their respective optimum operating points by providing separate power electronics for them.

The proposed solution also addresses another problematic aspect of multiple PV cell stacks: PV cells typically undergo an aging process. In a conventional series connection of the battery cells of a battery cell stack according to the prior art, this inevitably leads to a coordinated detuning of the individual battery cells. This effect no longer plays a role in the solution according to the invention.

In addition, a wide degree of design freedom for the individual battery cells results by eliminating "current matching". Thus, for example, the surface areas of the two PV cells of the cell stack can be selected as freely as possible, i.e. cell surface areas optimally adapted to the respective technology can be used in each case. Of course, stacked PV cells of the same size may be used as well. This is particularly advantageous in using thin film systems for individual PV cells, in which the layer boundaries and corresponding steps often constitute a technical obstacle for the layers deposited thereon.

By splitting the cell stack into individual battery cells and in particular using separate independent power electronics as described above, electronics optimized for the respective PV cell can be used. According to the invention, due to the individual electronics, in addition to the adjustment of the respective optimum operating point, the problematic subject matter which occurs in particular in novel perovskite-based PV cell units can also be solved. For example, hysteresis of the output characteristic value of the battery cell is exhibited in the perovskite-based battery cell, that is, the output characteristic of the battery cell is changed according to the previous operation of the battery cell. This can be compensated for, for example, by adjusting the PID parameters of a PID regulator integrated in the power electronics of the perovskite-based PV cell.

In contrast to conventional PV cells, perovskite-based PV cells furthermore often exhibit a so-called starting effect, in which the maximum efficiency of the cell, often referred to as "power conversion efficiency" (PCE), is achieved under constant illumination only after a certain delay time after the cell has started to operate. Unlike perovskite-based cells, the PCE of silicon-based PV cells is reached almost immediately after the start of operation. And both subsystems can operate at the optimum operating point due to separate power electronics units and individual regulation of the different PV subsystems. Although the energy yield of the perovskite-based battery cell is reduced compared to the yield of other battery cells during the influence of the start-up effect, it is still optimal for the present case due to the possibility of individual regulation.

The concept can be applied not only in the case of a combination of perovskite-based and silicon-based cells, but in principle also with any combination with other PV cell types such as thin-film solar cells or with III/V semiconductor cells.

Further advantages and embodiments result from the figures and the corresponding description.

Drawings

the invention and exemplary embodiments are explained in more detail below with reference to the drawings. Where identical components in different figures are identified using the same reference numerals.

Wherein:

Figure 1 shows a series stack of PV cells according to the prior art,

Figure 2 shows a cross-section of a series PV cell stack according to the prior art,

Figure 3 shows a PV installation according to the invention,

Figure 4 shows the relationship between current production I and cell voltage U in the case of a typical PV cell,

figure 5 shows a PV device according to a first variant of the invention,

Fig. 6 shows a PV device according to a second variant of the invention.

Like reference symbols in the various drawings indicate like elements.

Detailed Description

Fig. 3 shows a PV device 100 with a multi-PV cell stack 1, the multi-PV cell stack 1 having a first PV cell 11 of a first cell type (that is to say having one or more first photoactive regions 12 made of a first material that provide a voltage U1 under illumination) and a second PV cell 21 of a second cell type (that is to say having one or more second (not shown) photoactive regions 22 made of a second material that also provide a voltage U2 under illumination). The multi-PV cell stack 1 with two PV cells 11, 21 is thus a series PV cell stack. For the sake of simplicity, the expression that the respective PV cell units generate voltages (or the like) is generally used below, however this means that these voltages are generated by the respective photoactive regions of the cell units.

The cell stack 1 is arranged during operation such that the first PV cell unit 11 faces a light source, for example the sun. The light L emitted by the light source and incident on the cell stack 1 therefore first encounters the first PV cell 11, which in a known manner leads to the first PV cell 11 or its photoactive region 12 made of the first material generating a first cell voltage U1. After passing through the first PV cell 11, the corresponding residual light falls on the second PV cell 21, which likewise in a known manner leads to the second PV cell 21 or its photoactive region 22 made of the second material generating a second cell voltage U2.

Advantageously, the two battery cell types are selected such that the maximum efficiency, also referred to as "power conversion efficiency" (PCE), of the different battery cells 11, 21 lies in different spectral ranges. In particular, for the second PV cell 21, the cell type is selected such that its PCE maximum lies in the spectral range in which the first PV cell 11 is substantially transparent. By "substantially transparent" should here be meant that the first PV cell unit 11 absorbs this particular spectral range significantly less than other spectral ranges. It must of course be assumed that: the first PV cell 11 in principle has a certain degree of absorption in each spectral range relevant for the present application, but it can equally be assumed that the degree of absorption is relatively low in a certain range of the spectrum and that the cell 11 is thus "substantially transparent" to this spectral range.

In the example shown, the first PV cell 11 is a perovskite-based PV cell, that is to say the photoactive region 12 of the first PV cell 11 has a perovskite material. And the second PV cell unit 21 is a silicon-based PV cell unit. Perovskite materials have a larger band gap than silicon-based materials, and thus perovskite-based PV cells 11 have a higher absorption component in the blue or short wavelength spectral range and pass longer wavelengths of light. The silicon-based PV cell 21 absorbs more strongly in the longer wavelength spectral range so that light passing from the perovskite cell 11, or at least a portion thereof, may be absorbed by the silicon cell 21.

The PV system 100 has a power electronics unit 30, the power electronics unit 30 having a first power electronics unit 31 and a second power electronics unit 32, the power electronics units 31, 32 operating separately and independently of one another. The first power electronics unit 31 is assigned to the first PV cell unit 11 and the second power electronics unit 32 is assigned to the second PV cell unit 21. Here, the first PV cell unit 11 and the first power electronics unit 31 form the first PV subsystem 10 of the cell stack 1. Likewise, the second PV cell unit 21 and the second power electronics unit 32 form a second PV subsystem 20 of the cell stack 1. The cell voltages U1, U2 generated by the PV cells 11, 21 under illumination are fed to the respective power electronics units 31, 32 via the respective electrical connections 14, 24. The corresponding current yields I1, I2 are derived from the respective input resistances of the power electronics units 31, 32.

the PV system 1 furthermore has a regulating system 40, which regulating system 40 is designed to regulate the respective power electronics unit 31, 32 during the operation of the power electronics unit 31, 32 of each PV subsystem 10, 20 such that the product of the current yield I1 or I2 of the PV cell 11, 21 assigned to the respective power electronics unit 31, 32 and the cell voltage U1 or U2 is maximized. This results in a maximum energy yield of the respective PV subsystem 10, 20, wherein the key point is to reach an optimal operating point for the PV subsystems 10, 20 individually and independently of each other.

In this context and in order to explain the way in which the regulating device 40 works, fig. 4 shows the relation between the current production I and the cell voltage U at constant illumination for a typical PV cell. The optimal operating point with the maximum energy production or optimal energy production is located at the point identified by MAX in the graph, at which the product of the cell voltage U and the current production I is the largest. In variable use conditions, that is to say for example in varying light conditions, it is inevitable that at least one of the PV cells 11, 21 is no longer operating at the optimum operating point due to the different properties of the PV cells 11, 21 of the cell stack 1, which different properties of the PV cells 11, 21 typically respond differently to changes in light intensity, temperature, etc. For the entire cell stack 1 this means that it as a whole cannot be used at the optimum operating point. It is only possible to operate the cell stack 1 at the optimal operating point when the individual PV cells 11, 21 or PV subsystems 10, 20 forming the cell stack 1 are each themselves operated at the optimal operating point. To achieve this, separate power electronics 31, 32 are used, since the separate and independent use of power electronics allows for individually optimizing the operating parameters for each PV cell 11, 21 or for each PV subsystem 10, 30.

The regulating device 40 is now designed to regulate the input resistance of the respective power electronics unit 31, 32 and thus the current yield I in the respective PV subsystem 10, 20 when regulating the respective power electronics unit 31, 32, such that the product of the current yield I1 or I2 and the cell voltage U1 or U2 is maximal for the PV cells 11, 21 assigned to the respective power electronics unit 31, 32, wherein the regulating device 40 regulates the power electronics units 31, 32 in particular independently of one another. In this regard, the conditioning installation 40 can have a number of conditioners 41, 42, for example corresponding to the number of PV subsystems 10, 20, wherein each power electronics unit 31, 32 or each PV subsystem 10, 20 is assigned a conditioner 41, 42. These regulators 41, 42 can be designed, for example, as so-called PID regulators.

the regulating device 40 or the respective regulators 41, 42 for example operate such that for each PV subsystem 10, 20 its current production I1 or I2 and the cell voltage U1 or U2 are measured individually. In particular, for example, the first regulator 41 may vary the input resistance of the first power electronics unit 31 based on the values of I1 and U1 fed to said first regulator, and here monitor the current yield I1 and the cell voltage U1 or the product of these measurements. The input resistance is then set such that, as already mentioned, the product of the current production I1 and the cell voltage U1 is maximized, with a maximum energy production of the first PV subsystem 10. The regulator 42 of the second PV subsystem 42 operates in the same manner by varying the input resistance of the second power electronics unit 32 such that the product of the current production I2 and the cell voltage U2 of the second PV subsystem 20 is maximized, with a concomitant maximum energy production of the second PV subsystem 20. By means of the electrical connections 43, 44 between the power electronics units 31, 32 and the regulators 41, 42, indicated by double arrows, the interconnected components 31, 41 or 32, 42 thus interact in such a way that the regulators 41, 42 are supplied with current and voltage values I1, I2, U1, U2, and the regulators 41, 42 influence the power electronics units 31, 32 in terms of regulating the input resistance of the power electronics units on the basis of these values.

In addition to or instead of the current and voltage measurement based approach explained above, the regulating device 40 may be fed with data from the sensor device 50. The sensor device 50 has a device 51 for determining the temperature of the PV cells 11, 21 and/or for determining the ambient temperature of the series PV cell stack 1. One or possibly more parameters describing the temperature and/or the ambient temperature are fed to the regulating device 40 and the individual regulators 41, 42 as input variables. Alternatively or additionally, the sensor device 50 may have a device 52 for determining the intensity of light incident on the multi-PV-cell stack 1 and in particular on the first PV cell 11, wherein a parameter describing the intensity of light is fed to the regulating device 40 or the regulators 41, 42 as an input variable. Furthermore, the sensor device 50 may have a device 53 for determining the spectrum of the light incident on the multi-PV cell stack 1 and in particular on the first PV cell 11, wherein the parameters describing the spectrum are fed to the regulating device 40 or the regulators 41, 42 as input variables. The regulating device 40 is now designed to regulate the power electronics units 31, 32 on the basis of one or more input variables fed thereto such that the product of the current yield I and the cell voltage U of the PV cells 11, 21 assigned to the respective power electronics unit 31, 32 is maximized. This can in turn be achieved by correspondingly adjusting the input resistance of the respective power electronics unit 31, 32. The target value to which the input resistance is set in this case may be determined, for example, in a model-based manner or from a look-up table, such that the product of the current yield I and the cell voltage U of the PV cell 11, 21 assigned to the respective power electronics unit 31, 32 is maximal, by determining and setting the input resistance from the corresponding look-up table depending on one or more input variables of each power electronics unit 31, 32.

Furthermore, aging processes of the battery cells 11, 21 can also be observed and, if necessary, taken into account by means of the control device 40. If the effectiveness of finding the optimal operating point is monitored in both power electronics units 31, 32, a warning about degradation of one of the battery cells may be output or the aging state may be monitored.

The following generally applies: fouling of solar cells, particularly in arid desert regions, occurs due to the deposition of dust and is often enhanced by salt-containing aerosols. In wet and natural areas, fouling occurs due to (green) cell transplantation, and in industrial areas fouling occurs due to the deposition of particles such as smoke. The dust deposits and green cells have clearly discernable colors and thus change the spectral composition of the light reaching the actual PV cell. In the case of soot deposits which at first sight appear colourless (that is to say substantially black), it becomes clear from a more precise observation that the dark soot particles also have a spectrally dependent light absorption. In the case of mechanical changes of the surface, for example a matt surface due to sand grains, scattering of the light occurs without the spectral shift taking place first. In the case of a change in the spectral composition of the light due to soiling, there is inevitably a detuning of the current generation of the two spectrally different PV individual cells 11, 21 of the series-connected cell 1. The only possibility to be able to operate the two battery cells 11, 21 stably as before despite an insult is to control the two battery cells separately or to adjust the two PV subsystems 10, 20 independently and separately according to the above-described scheme in which the respective power electronics unit 31, 32 is adjusted for each subsystem 10, 20 such that the deposition of the cell voltage U and the current yield I of the PV battery cell 11, 21 assigned to the respective power electronics unit 31, 32 is maximized. Furthermore, in applications in which it is possible to compensate for soiling of the PV cell units 11, 21 and in the same way for possible ageing of the PV cell units 11, 21, the adjustment is based on the setting of the input resistance of the respective power electronics unit 31, 32 such that the product is maximal.

the solution proposed here is therefore suitable for compensating for a wide variety of situations or environmental conditions, with the key point being to adjust the PV subsystems 10, 20 or the power electronics units 31, 32 independently of one another.

Fig. 5 shows an embodiment of a PV system 100 in which the wiring effort between the cell stack 1 and the power electronics 40 is reduced. For this purpose, the battery cells 11, 21 are set to a common potential or connected to one another, so that only 3 lines have to be routed to the power electronics 40.

The embodiment shown in fig. 6 results in: it is possible to minimize the overall occurring voltage of the individual battery cells 11, 21 and thus minimize the requirement for wiring insulation. For this reason, the two battery cells 11, 21 are arranged such that their voltages U1, U2 are opposite to each other. This is of course not justified in the case of conventional series PV cell stacks, but may be advantageously applied here. It is also optionally expedient to place the mutually opposite terminals of the battery cells 11, 21 at a common potential, as in the embodiment illustrated in fig. 5.