Decoupling of perovskite solar cells in the dark

Abstract

The invention relates to a method for operating a photovoltaic module (10). The photovoltaic module (10) has at least one perovskite solar cell (11). The method comprises operating the photovoltaic module (10) at least temporarily at the maximum power point by means of a regulating device (20) connected to the photovoltaic module (10), wherein the extraction of electrical energy is interrupted when the irradiation intensity of the electromagnetic radiation (2) impinging on the photovoltaic module (10) does not exceed a predetermined threshold value. The invention also relates to a photovoltaic device (1) comprising a photovoltaic module (10) having at least one perovskite solar cell (11) and a regulating device (20) connected to the photovoltaic module (10).

Description

Technical Field

[0001] This invention relates to a method for operating a photovoltaic module having at least one perovskite solar cell. The invention also relates to a photovoltaic device comprising a photovoltaic module having at least one perovskite solar cell and a regulating device connected to the photovoltaic module. Background Technology

[0002] In photovoltaic (PV) installations, PV modules are typically operated using Maximum Power Point Tracking (MPPT). This is an electronic method where the electrical load of the PV module is adjusted to extract maximum power from it. The optimal operating point of a PV module is not constant over time but is related to parameters such as irradiance, irradiance spectrum, and the temperature of the PV module's solar cells. The type of solar cells used (e.g., monocrystalline / polycrystalline / amorphous silicon) also affects where the optimal operating point is located. The optimal operating point is usually continuously readjusted.

[0003] For photovoltaic modules with crystalline silicon solar cells, maximum power point tracking is a method developed to maximize the extracted power.

[0004] To implement maximum power point tracking (MPPT) methods for photovoltaic (PV) modules, a regulating device is typically connected to the PV module (or a series of PV modules). The regulating device is pre-loaded with a resistor, also known as a load resistor. This load resistor is set such that it corresponds to the internal resistance of the PV module, where the PV module's power is at its maximum. In this configuration, the PV module operates under power adjustment by the regulating device.

[0005] The challenge of the MPPT method lies in reliably determining the optimal operating point with the least possible energy consumption. This is not easy, for example, when a photovoltaic device is partially shaded, because in this case, only the local power maximum of the regulating device may be determined instead of the global power maximum. For example, corresponding solutions for reliably determining the global power maximum of a photovoltaic module or photovoltaic device are disclosed in patent documents EP 1 750 193B1 or EP 2 360 546B1.

[0006] However, under all circumstances, the photovoltaic (PV) modules must remain continuously connected to the regulation unit to extract maximum power even when solar radiation is diffusely distributed on them, such as during cloudy or twilight conditions. At night, the PV modules remain connected to the regulation unit even when power cannot be extracted from them in complete darkness.

[0007] In recent years, the applicability of perovskites, such as CH3NH3PbI3, in solar cells has been studied. Due to the photoelectric properties of perovskites, they, in principle, allow for the efficient conversion of electromagnetic radiation energy into electrical energy. Perovskite-based solar cells, also referred to below as perovskite solar cells, are characterized by their relatively low manufacturing cost. Furthermore, perovskite solar cells are an attractive and important alternative to conventional silicon-based solar cells because the rapid progress made in recent years in terms of the efficiency of said perovskite solar cells, from a few percent to over 25% today, demonstrates that efficiencies significantly exceeding those of conventional solar cells can be achieved. It is possible to consider operating perovskite solar cells alone, or in combination with tandem photovoltaic modules, such as crystalline silicon solar cells.

[0008] Photovoltaic modules with perovskite solar cells are currently not commercially available. Correspondingly, there is no knowledge regarding the optimal operation of photovoltaic modules with perovskite solar cells.

[0009] WO 2016 / 164718 describes a control device for a PV facility, in which radiation values ​​are determined. A threshold value is also defined. Below the threshold, the PV system can be isolated from the electrical load. Monitoring / prediction of the PV facility's output power is performed, i.e., monitoring changes (in the series resistance). For this measurement, the battery must provide power and a corresponding incident radiation is required.

[0010] A control device for a perovskite PV cell is also known from US 2018 / 259990 A1. Summary of the Invention

[0011] In this context, the present invention aims to develop a concept and an efficient operating method for operating a photovoltaic module comprising one or more perovskite solar cells.

[0012] Within the scope of the applicant's own research, it has been surprisingly determined that perovskite solar cells degrade strongly when loaded with MPPT under no-light conditions, such as at night during the principal's hours. Degradation was also measured in some cases even under only low-intensity lighting.

[0013] The causes of degradation in photovoltaic modules containing one or more perovskite solar cells that operate with maximum power point tracking in low-light or no-light conditions remain unclear. The physical / chemical effects leading to the observed degradation have not yet been definitively elucidated.

[0014] However, according to the present invention, a significantly improved method for operating a photovoltaic module comprising one or more perovskite solar cells includes the following method: the method involves operating the photovoltaic module at its maximum power point, at least temporarily, by means of a regulating device connected to the photovoltaic module. Here, the extraction of electrical energy is interrupted when the intensity of electromagnetic radiation incident on the photovoltaic module does not exceed a predetermined threshold.

[0015] Clearly, perovskite photovoltaic modules typically have more than one perovskite solar cell, i.e., multiple perovskite solar cells. Perovskite solar cells can also be part of a series cell constructed from a perovskite solar cell and another solar cell, such as a conventional silicon solar cell. For such series solar cells, an impressive 28% efficiency has recently been achieved in laboratory standards.

[0016] In particular, the photovoltaic module is operated at the maximum power point by means of a regulating device for almost the entire period of time during which the irradiation intensity exceeds a predetermined threshold.

[0017] This means that when the irradiation intensity exceeds a predetermined threshold, the photovoltaic module can be advantageously operated at the maximum power point by means of the regulating device, and when the irradiation intensity does not exceed the predetermined threshold, energy extraction is interrupted.

[0018] The regulating device, in particular, is the inverter associated with the photovoltaic module, which is especially equipped with a configurable load resistor. In this case, the inverter can be associated with a single photovoltaic module (also known in technical terms as a micro-inverter) or with an entire string of photovoltaic modules. Theoretically, it is also possible to consider an individual inverter for each solar cell.

[0019] Because the load of the photovoltaic module is set according to the load voltage, and the output voltage of the regulating device should be approximately constant, a DC-DC converter is typically used to set the voltage difference, thereby enabling the setting of the solar cell load. Continuous readjustment of the photovoltaic module's optimal operating point (i.e., operation of the photovoltaic module at its maximum power point) is advantageously performed by a microcontroller or digital signal processor. Here, the required measurement data from the analog-to-digital converter can be provided to the processor. The analog-to-digital converter can then perform the necessary calculations and transmit the results to the DC-DC converter by means of pulse width modulation.

[0020] Regulation devices can also be found in so-called "power optimizers" associated with photovoltaic modules.

[0021] According to the present invention, when the intensity of electromagnetic radiation incident on the photovoltaic module does not exceed a predetermined threshold, the extraction of electrical energy is interrupted. The extraction of electrical energy is understood as extracting electrical energy from the photovoltaic module. When an adjustment device is connected, the extraction is controlled by the adjustment device, more precisely, so that the amount of energy extracted is always as large as possible under ideal conditions.

[0022] When the predetermined threshold of irradiance intensity is not exceeded, the photovoltaic module is electrically decoupled from the regulating device. Accordingly, the current loop with the photovoltaic module is open, and an open circuit voltage is applied to the photovoltaic module.

[0023] In practice, the decoupling or separation of the photovoltaic module from the regulation device can be easily achieved by separating the electrical contacts of the regulation device from the photovoltaic module (in other words, electrical insulation). For this purpose, the temporary separation of the photovoltaic module from the regulation device can be done electronically, for example, by means of a transistor controlled in a high-ohmic manner. If, for example, a metal-oxide-semiconductor field-effect transistor (MOSFET) is used, then significant energy need not be consumed in controlling the transistor. Compared to using a mechanical switch, using a transistor has the advantages of not involving moving parts, thus the transistor is maintenance-free and durable. Because no voltage can be extracted from the photovoltaic module when the switch / transistor is activated, the electrical power (or correspondingly, the extractable electrical energy) from the photovoltaic module is also zero.

[0024] According to the present invention, when the irradiation intensity is less than a predetermined threshold, the extraction of electrical energy is interrupted. The threshold is particularly located at 2 W / m². 2 and 20W / m 2 Between, preferably at 5W / m 2 and 15W / m 2 Within the range of and particularly preferably 10 W / m 2 Based on the applicant's own measurements specifically at the perovskite solar cells, it has been surprisingly shown that the perovskite solar cells, even at several W / m², exhibit performance characteristics. 2 It works very well and without degradation even under certain conditions. The threshold within one range corresponds to weak or very weak illumination of (multiple) perovskite solar cells. Therefore, it is advantageous to specify the threshold within one range, because degradation of perovskite solar cells, particularly a decrease in efficiency, has been observed, precisely under conditions of no illumination or (very) weak illumination, in conjunction with the connected MPPT adjustment device.

[0025] Preferably, the photovoltaic module is electrically short-circuited when the irradiation intensity does not exceed a predetermined threshold. This can also be achieved by a corresponding switch, relay, or transistor, in which case the switch, relay, or transistor is conductively connected to the two electrical contacts (front contact and rear contact or p / n contact) of the photovoltaic module. Because no current can be extracted from the photovoltaic module in this case, the extractable electrical power (or correspondingly, electrical energy) is also zero.

[0026] Irradiance intensity can be understood as the total power of electromagnetic energy incident on a surface with respect to the size of the surface. In other words, irradiance intensity is the radiant flux passing through the irradiated surface. This irradiance intensity is also called radiant flux density or irradiance.

[0027] For example, the photocurrent generated by the photovoltaic module can be used as a measure of the intensity of electromagnetic radiation incident on the photovoltaic module. This has the advantage that the photocurrent is generally detectable in measurement techniques and is therefore suitable as a regulating variable regarding the separation or electrical connection of the regulating device and the photovoltaic module. It is also possible (when the module efficiency is known and time-stability is stable) to use the output line of the photovoltaic module instead of the photocurrent as a measure of the intensity of radiation.

[0028] Alternatively, the irradiation intensity can also be determined by the impedance spectrum at one or more perovskite solar cells in the photovoltaic module (if any).

[0029] In the case of impedance spectroscopy, particularly electrochemical impedance spectroscopy, an alternating voltage is applied to a perovskite solar cell, and the resulting current is measured at different frequencies of the alternating voltage. Based on the measurement results appropriately plotted, for example, in so-called Bode or Nyquist plots, the internal parameters of the perovskite solar cell, such as carrier transport or carrier recombination rate, can then be deduced. The irradiation intensity of the solar cell under study can also be deduced, in particular, by using appropriate values ​​of these internal parameters.

[0030] Another feasible method for determining the intensity of electromagnetic radiation incident on a photovoltaic module is to install additional photovoltaic cells, using these cells to determine the intensity. Specifically, in this case, the intensity can be determined, for example, by means of the photocurrent generated by the additional photovoltaic cells.

[0031] The additional photovoltaic cells can be relatively small in size (e.g., l × l cm). 2 Furthermore, the additional photovoltaic cells can be advantageously integrated into the photovoltaic module. For example, the additional photovoltaic cells can be integrated into the frame, i.e., at the edge of the photovoltaic module.

[0032] Another feasible method for estimating the intensity of solar radiation hitting a photovoltaic (PV) module is to rely on meteorological data. The sunrise and sunset times for a specific location on Earth throughout the year (i.e., every day) are known, and this can be programmed into the regulating device, for example, once the location of the PV module is known. This has the advantage that it eliminates the need to generate and process measurement data for adjustments in the separation or connection of the regulating device. However, this method is less precise because it cannot detect and account for cloud cover or the shadow cast by the PV module or a portion thereof.

[0033] Finally, the inventive concept can also be realized in a photovoltaic device. The photovoltaic device includes a photovoltaic module having at least one perovskite solar cell and a regulating device connected to the photovoltaic module. The regulating device is designed to operate the photovoltaic module at its maximum power point, at least temporarily, but to interrupt energy extraction when the intensity of electromagnetic radiation incident on the photovoltaic module does not exceed a predetermined threshold. Attached Figure Description

[0034] The invention is described below with reference to the accompanying drawings.

[0035] The attached diagram shows:

[0036] Figure 1 The diagram shows a photovoltaic module that is electrically decoupled from the regulating device, thereby interrupting the extraction of electrical energy.

[0037] Figure 2 The same photovoltaic module is shown, which is now electrically connected to a regulating device, enabling the photovoltaic module to operate at its maximum power point.

[0038] Figure 3 The same photovoltaic module is shown, which is now short-circuited.

[0039] Figure 4 The efficiency of two perovskite solar cells is shown to progress over time. Detailed Implementation

[0040] Appendix Figure 1 To be continued Figure 3 (also known as) Figures 1 to 3 This illustrates an embodiment of a photovoltaic device 1 according to the present invention. The photovoltaic device 1 has a photovoltaic module 10 having a plurality of perovskite solar cells 11. For overview purposes, see attached... Figure 1Only one perovskite solar cell is shown in the diagram. Each perovskite solar cell 11 has an electron-conducting layer, a light-absorbing layer (also called an "absorber"), and a hole-conducting layer. The absorber contains perovskite with the general structural formula ABX3, where, for example, A = CH3NH3, B = Pb, and X = I3. Furthermore, the solar cell has a front contact 111 and a rear contact 112. The front contact 111 is preferably transparent to electromagnetic radiation in the specific wavelength range for which the solar cell is designed. The rear contact can be designed to be entirely opaque (e.g., including aluminum alloy). The perovskite solar cell 11 is embedded in a glass sheet, which should, for example, protect the perovskite solar cell from contamination and damage.

[0041] Appendix Figure 1 To be continued Figure 3 The image also shows solar electromagnetic radiation 2, also known as "solar radiation", which is directed onto the front side of the photovoltaic module 10 and thus onto the front side of the perovskite solar cell 11.

[0042] In the appendix Figure 1 The front and rear contacts 111 and 112 of the solar cell 11 shown are electrically connected to the regulating device 20. That is, the photovoltaic module 10 can be electrically connected to or decoupled from the regulating device 20 by means of the switch 30. Additionally, the photovoltaic module 10 can also be short-circuited by means of the switch 30.

[0043] In the appendix Figure 1 The diagram briefly shows the first position 301 of switch 30. In the first position 301, the switch is open, and the photovoltaic module 10 is electrically disconnected from the regulating device 20. Therefore, an open-circuit voltage is applied to the photovoltaic module 10. No energy is extracted from the photovoltaic module 10.

[0044] In the appendix Figure 2 The second position 302 of switch 30 is shown in a simplified diagram. In the second position 302, the switch is closed, and an electrical connection is established between the photovoltaic module 10 and the regulating device 20. The regulating device 20 is able to extract maximum power (or correspondingly, maximum energy) from the photovoltaic module by matching its load resistance to the current internal resistance of the photovoltaic module.

[0045] In the appendix Figure 3 The diagram briefly shows the third position 303 of the switch 30. In the third position 303, the switch connects the front contact 111 and the rear contact 112 of the photovoltaic module 10, thereby short-circuiting the photovoltaic module 10. The corresponding short-circuit current flows at the photovoltaic module 10, and no energy can be extracted from the photovoltaic module 10.

[0046] Specifically, the control device 20 itself can place the switch 30 in corresponding positions 301, 302, and 303. Under sufficiently high irradiance, the switch is closed (position 302), and maximum power point tracking (MPPT) of the photovoltaic module 10 is performed. However, if the irradiance does not exceed a predetermined threshold, the photovoltaic module 10 is either decoupled from the regulating device (position 301) or short-circuited. In both cases, the result is that MPPT of the photovoltaic module can no longer be performed by means of the regulating device 20, thereby preventing or at least reducing the degradation of the perovskite solar cells 11 of the photovoltaic module 10.

[0047] Appendix Figure 4 (also known as) Figure 4 The diagram shows the time-varying efficiency curves of the first perovskite solar cell 53 and the second perovskite solar cell 54. Time, in hours, is plotted on the horizontal axis 51, and normalized efficiency is plotted on the vertical axis 52. The efficiency is normalized, meaning that at the start of the measurement, the efficiency for both solar cells is set to a relative value of 1.0. The two solar cells are similar in construction, materials, and power. Both solar cells were artificially illuminated for six hours each, interrupted by six-hour periods of darkness. This should concisely simulate the day / night cycle in time. The illumination intensity and spectrum exemplarily correspond to real sunlight illumination.

[0048] During the entire 100-hour measurement period (approximately 8 day-night cycles), the first solar cell was connected to a conventional regulating device, known as a "maximum power point tracking regulator," used to operate the solar cell at its maximum power point. In particular, the solar cell was connected to or "loaded" by the aforementioned regulator even during the dark period.

[0049] As a result, this caused a significant degradation in the efficiency of the solar cells studied. At the end of the 100-hour measurement period, the efficiency of the solar cells was only about a quarter of the value at the beginning of the study.

[0050] During the period when the battery was exposed to darkness (8 × 6 hours), the second solar cell was disconnected from the "maximum power point tracking regulator." Here, a certain degree of efficiency degradation was observed both during the bright phase and during the dark phase. However, the degradation was significantly less compared to the first solar cell, which was permanently connected to the regulator. At the end of the 100-hour measurement period, the solar cell's efficiency was at least approximately three-quarters of its initial value.

[0051] Therefore, separating the photovoltaic module with perovskite solar cells from the MPPT conditioning device during darkness (or weak lighting) can at least mitigate the degradation of the perovskite solar cells, and may also completely eliminate or at least limit the degradation of the perovskite solar cells.

[0052] List of reference numerals

[0053] 1. Photovoltaic devices

[0054] 2 Electromagnetic radiation

[0055] 10 Photovoltaic Modules

[0056] 11 Perovskite Solar Cells

[0057] 111 Front contact area

[0058] 112 Rear contact area

[0059] 20 Adjustment device

[0060] 30 Switches

[0061] 301 First Position

[0062] 302 Second position

[0063] 303 Third position

[0064] 51 x-axis

[0065] 52. Vertical axis

[0066] 53 Efficiency of the first perovskite solar cell

[0067] 54. Efficiency of the second perovskite solar cell

Claims

1. A method for operating a photovoltaic module (10) having at least one perovskite solar cell (11), the method comprising operating the photovoltaic module (10) at a maximum power point at least temporarily by means of an adjustment device (20) connected to the photovoltaic module (10), wherein the extraction of electrical energy is interrupted when the intensity of electromagnetic radiation (2) incident on the photovoltaic module (10) does not exceed a predetermined threshold, wherein when the predetermined threshold of the intensity of the radiation is not exceeded, the photovoltaic module (10) is electrically decoupled from the adjustment device (20) by means of a transistor, and wherein the predetermined threshold is at 2 W / m 2 and 20W / m 2 Within the range between.

2. The method according to claim 1, The predetermined threshold is 5W / m 2 and 15W / m 2 Within the range between.

3. The method according to claim 1, The predetermined threshold is 10W / m 2 .

4. The method according to claim 1, The photovoltaic module (10) is operated at the maximum power point by means of the regulating device (20) during the entire time period when the irradiation intensity exceeds the predetermined threshold.

5. The method according to any one of claims 1 to 4, The photovoltaic module (10) is short-circuited when the irradiation intensity does not exceed a predetermined threshold.

6. The method according to any one of claims 1 to 4, The photocurrent generated by the photovoltaic module (10) is used as a measure of the intensity of the electromagnetic radiation (2) incident on the photovoltaic module (10).

7. The method according to any one of claims 1 to 4, The intensity of electromagnetic radiation (2) incident on the photovoltaic module (10) is determined by means of the impedance spectrum at one or more perovskite solar cells (11) of the photovoltaic module (10).

8. The method according to any one of claims 1 to 4, The photovoltaic module (10) has an additional photocell, and the intensity of electromagnetic radiation (2) incident on the photovoltaic module (10) is determined by means of the additional photocell.

9. The method according to claim 8, The irradiation intensity is determined by means of the photocurrent generated by the additional photocell.

10. The method according to any one of claims 1 to 4, The intensity of electromagnetic radiation (2) hitting the photovoltaic module (10) is estimated based on meteorological data.

11. The method according to any one of claims 1 to 4, The regulating device (20) is an inverter associated with the photovoltaic module (10).

12. The method according to claim 11, The regulating device (20) is a micro inverter.

13. The method according to any one of claims 1 to 4, The regulating device (20) is a power optimizer associated with the photovoltaic module (10).

14. A photovoltaic device (1) comprising a photovoltaic module (10) having at least one perovskite solar cell (11) and an adjustment device (20) connected to the photovoltaic module (10), wherein the adjustment device (20) is designed to operate the photovoltaic module (10) at least temporarily at its maximum power point, but interrupting energy extraction when the intensity of electromagnetic radiation (2) incident on the photovoltaic module (10) does not exceed a predetermined threshold, wherein the photovoltaic module (10) is electrically decoupled from the adjustment device (20) when the predetermined threshold of the intensity of the radiation is not exceeded, and wherein the predetermined threshold is at 2 W / m 2 and 20W / m 2 Within the range between.

15. The photovoltaic device (1) according to claim 14, wherein the predetermined threshold is at 5W / m 2 and 15W / m 2 Within the range between.

16. The photovoltaic device (1) according to claim 14, wherein the predetermined threshold is 10 W / m 2 .

Images