NL2021633B1

NL2021633B1 - A method for eliminating dangerous situations caused by photovoltaic systems.

Info

Publication number: NL2021633B1
Application number: NL2021633A
Authority: NL
Inventors: Bekker Misha; Otten Marald
Original assignee: Atlas Technologies Holding Bv
Priority date: 2018-09-14
Filing date: 2018-09-14
Publication date: 2020-05-06

Abstract

The invention relates to a method of eliminating dangerous situations occurring during an abnormal situation, the dangerous situations caused by a photovoltaic system (@), the system comprising multiple groups (100) of interconnected photovoltaic cells (102), the interconnected cells interconnected by interconnections (104), each of the groups capable of generating an open voltage when exposed to sunlight, at least two of the groups connected in series thereby forming a string (202) of photovoltaic cells, the open source voltage of each of the groups in full sunlight a safe voltage, the open source voltage of each of the strings in full sunlight a dangerous voltage, the method characterized in that each of the groups (100) is connected to an electronic circuit (402) associated to said group, each of the electronic circuits (302) has an enable input (304) for connecting to an enable signal (306), the enable signal generated by a controller (308), the electronic circuit (302) enabled when the enable signal is active, the electronic circuit disabled otherwise, each of the groups (100) shorted or at least having its maximum voltage reduced by the associated electronic circuit (302) when the associated electronic circuit is disabled, the voltage of each of the strings (202) a safe voltage when the groups (100) forming the string are shorted or at least have their maximum voltage reduced, and the enable signal (306) is not active when an abnormal condition is detected by the controller (308), or when a break in the connection between controller and enable input occurs. As in abnormal situations the maximum voltage over string and/or broken leads in the solar panel is limited to a safe voltage by the shorts, no dangerous situation occurs.

Description

A method for eliminating dangerous situations caused by photovoltaic systems.

Technical field of the invention.

[0001] The invention relates to a method of eliminating a dangerous situation occurring during an abnormal situation, the dangerous situation caused by a photovoltaic system, the system comprising multiple groups of interconnected photovoltaic cells, the interconnected cells interconnected by interconnections, each of the groups capable of generating an open voltage when exposed to sunlight, at least two of the groups connected in series thereby forming a string of photovoltaic cells, the open source voltage of each of the groups in full sunlight a safe voltage, the open source voltage of each of the strings in full sunlight a dangerous voltage.

[0002] The invention further relates to a photovoltaic system comprising multiple groups of interconnected photovoltaic cells, the interconnected cells interconnected by interconnections, each of the groups capable of generating an open voltage when exposed to sunlight, at least two of the groups connected in series thereby forming a string of photovoltaic cells, the open source voltage of each of the groups in full sunlight a safe voltage, the open source voltage of each of the strings in full sunlight a dangerous voltage.

Background of the invention.

[0003] Photovoltaic systems generate a direct current and voltage when exposed to sunlight. Such a system or solar panel comprises a multitude of photovoltaic cells, also named solar cells, each cell capable of generating a voltage of up to approximately 0.5 V. The maximum current of a cell is, amongst others, proportional to the amount of irradiation by the sun (or other lighting sources) and the surface area of the cell. Cells are grouped in groups of interconnected cells, with several cells in series (resulting in a higher voltage) and/or in parallel (resulting in a larger current).

[0004] The number of cells connected in series or parallel in a group is limited by the effect of shading of a cell: a shaded cell behaves as a high-ohmic resistance, and very little current can pass through it. When many cells are connected in series, the chance that one of the cells is shaded and blocks the current from the other cells increases. [0005] Often several groups of cells are connected in series thereby forming a string. Each group in the string is typically connected to a bypass diode. The bypass allows current of other groups in the string to pass through it when the current of one group is limited due to non-illumination of one (or more) cells.

[0006] Several such groups are often put in series forming a string. A string typically comprises a series diode to enable the parallelization of several such strings. Several such strings are normally arranged on a solar panel, that is the largest mechanical unit of photovoltaic cells in a photovoltaic system. A solar panel may have its own converter, or may be connected to a central converter.

[0007] Typically, the voltage of a group of interconnected cells is not a dangerous voltage at any illumination, (less than, for example, 60 Vdc), while the voltage of a string or solar panel can be a dangerous voltage (more than, for example, 60 Vdc), depending on the number of cells and the illumination.

[0008] Normally a high string voltage will not be a problem as the system is designed for it, but in some abnormal instances electrocution or other dangerous situations (for example spark and fire risks) may occur.

Such a dangerous situation may occur when the solar panel is part of (the roof of) a solar driven car, that is: a car that is equipped with solar panels, the solar panels used for charging electric batteries that are used for powering the car. After a crash of such a solar car, firefighters may need to free passengers by cutting the roof from the rest of the car. Cables from the main part of the vehicle to the solar panel are likely the run through one of the pillars of the car, and while cutting the roof from the car the firefighters might cut through the cable that connects the solar panel with the rest of the car, with the risk of exposure to the open source voltage of the solar panel on the roof.

A similar dangerous situation may occur when fighting a fire of a house, where firefighters need to break through solar panels to get access to the heart of the fire.

Another such instance may occur when cracks in the solar panel may make certain parts of the solar panel accessible, or an interconnection between cells may be exposed, said parts normally covered. For roofs of houses such cracks may be caused be hail, and in vehicles either by hail or by a crash of the vehicle.

Yet another such instance occurs when servicing a photovoltaic system. Here as well service personnel may be exposed to the open source voltage of the solar panel when light falls upon the solar panel. As mentioned before the open source voltage of a panel can be a dangerous voltage.

[0009] It is noted that the use of a dangerous voltage is the result of a demand to higher efficiency: often the output voltage of a solar panel is fed to a DC/DC converter via a diode. Typically the DC/DC converter and the diode have a higher efficiency when the current is lower, and for the same power this implies a higher voltage.

[0010] In international application publication WO14085468A1 a system is described for reducing the electric potential in a photovoltaic system. It describes that groups of cells are grouped to form a panel. The system comprises a controller that detects the presence of a ‘continuity’ signal. When the continuity signal is interrupted a normally closed switch shorts the panel, thereby avoiding a dangerous voltage over the (shorted) panel connections.

[0011] A residual problem of this solution is that, when an abnormal condition occurs, the output of the solar system is shorted, but dangerous voltages between these shorted parts and parts halfway the solar panel may occur, to which persons may be exposed through, for example, a crack in the solar panel. The publication is silent about the maximum voltage of a group of photovoltaic cells. Therefore, even when such a fault condition interrupts the continuity signal, and results in a short of the panel, the parts within a group can have a dangerously high voltage, and, when exposed, the dangerous situation( for example the risk of electrocution), although reduced, is still present. The publication is further silent about the relative position of the short and the solar parts of the panel that are shorted. Therefore, it is well possible that a break of the panel not only leaves dangerous voltages accessible, but also disables the short as the leads for shorting the panel are broken.

[0012] In international application publication WO16163304A1 a safety device is provided that is inserted between the output terminals of a DC power system to safely and simply short-circuit/release the output from a DC power system generating high voltage, such as a solar cell string wherein many solar cell modules are connected in series.

[0013] Here as well a residual problem of this solution occurs when a fault condition occurs, for example a break in the solar panel, exposing a solar cell, or the interconnection between two cells. Even when such a fault condition interrupts the continuity signal, and results in a short of the panel, the exposed parts can have a dangerously high voltage, and the dangerous situation (e.g. the risk of electrocution), although reduced, is still present.

Summary of the invention.

[0014] To solve the residual problems of the above presented solutions the present invention provides a method to overcome this problem.

[0015] To that end the method according to the invention is characterized in that • each of the groups is connected to an electronic circuit associated to said group, • each of the electronic circuits has an enable input for connecting to an enable signal, the enable signal generated by a controller, the electronic circuit enabled when the enable signal is active, the electronic circuit disabled otherwise, • each of the groups shorted or at least having its maximum voltage reduced by the associated electronic circuit when the associated electronic circuit is disabled, • the voltage of each of the strings a safe voltage when the groups forming the string are shorted or at least have their maximum voltage reduced, • the enable signal is not active when an abnormal condition is detected by the controller, or when a break in the connection between controller and enable input occurs.

[0016] By grouping the cells into groups which have a maximum open source voltage that is a safe voltage, and by associating each of the groups with its own associated electronics that short the group when not expressly enabled, an abnormal situation detected by the controller (resulting in a shorting of the groups), or a failure of the wiring between controller and electronic circuit, results in a reduction of voltage to a safe voltage for all voltages in the photovoltaic system. Even a fault in one of the electronics or a fault caused by cracks in the solar panel (thereby exposing a solar cell or an interconnection between two solar cells) will result in an exposed part with a safe voltage, and not result in a dangerous situation

[0017] It is noted that in many areas of engineering a DC voltage of more than 60 Vdc is considered a dangerous voltage, and a DC voltage below 60 Vdc is considered a safe voltage. However, different values are used in different areas. It is noted that for an AC voltage other margins are used. Also, the definition of dangerous is not limited to electrocution, but may include fire hazards due to arcing, explosions in dusty environments, etc.

[0018] In an embodiment of the method according to the invention the photovoltaic cells, the interconnections and the electronic circuits are mounted on a common substrate, and each of the groups occupies an area on the substrate, and the electronic circuit and interconnections associated with each group are mounted on the area occupied by the associated group.

[0019] Preferably solar cells and the electronic circuit comprising the circuitry to short the groups are mounted on a common substrate. The substrate can be a flexible foil with a conductor pattern on it, on which the components are mounted by soldering, by an adhesive such as a conductive glue, or such like. Also (part of) the connection between controller and electronic circuits can be formed on the substrate, for example in the form of a PCB trace. Damage to the board or foil then results in a disconnect and thus a disable of the electronic circuits. As the area occupied by the group and the associated electronic circuit overlaps, a disconnect of only the shorting wires is less likely.

[0020] In another embodiment of the method according to the invention the shorting or reducing the maximum voltage is performed by an electronic circuit (402) comprising a normally closed relay or a semiconductor device from the group of transistors, Darlington transistors, enhancement FETs and depletion FETs.

[0021] A normally closed relay is well suited to short a group. In a suitable circuit, with addition of, for example, a resistor as safety critical component, also the semiconductor devices can perform this function well. For example enhancement FETS with an ON” resistance of less 10 mQ and capable of withstanding a voltage of 60 Vdc are easily selected and take up little space. Depending on current in the string, number of groups, and voltage of the groups, the proper maximum resistance of the FET can be chosen.

[0022] In still another embodiment of the method according to the invention the method is performed while the photovoltaic system is part of a vehicle.

[0023] Recently not only electric vehicles are commercially available, but also vehicles with a solar panel. The current generated by such a panel can attribute to a large degree of the energy use of such a car. Such cars are already known from the Solar Challenge races in Australia, and are developed for commercial use by, for example, applicant (Atlas Technologies B.V., Helmond, the Netherlands, see https://lightyear.one/).

[0024] In a further embodiment of the method according to the invention the controller (308) ceases to send an enable signal (306) when an abnormal condition occurs from the group of the detection of: the inflation of an airbag, damage of a connection from a DC/DC converter to the solar panel, damage of the photovoltaic system, overheating of the batteries, or not properly receiving or processing of a watchdog signal.

[0025] When an abnormal situation occurs, other problems may be eminent. To avoid direct or indirect risks, such as overheating of the batteries, sparking, electrocution, etc. it is preferred to switch off power generation by the solar panel until the abnormal situation ends.

it is noted that this is a non-exhaustive list of abnormal conditions that may be used to cease sending an enable signal.

[0026] In another embodiment of the method according to the invention the enable signal is a loop signal, and the enable input of each of the electronic circuits comprises one or more optocouplers or transformers through which the enable signal runs, the enable inputs of each of the electronic circuits connected in series

[0027] By passing the enable signal in a loop signal through all electronic circuits, any disconnect results in a disabling of all electronic circuits. Optocouplers, also known as opto-isolators or photo-couplers, are well suited for use in a current loop with a DC loop current flowing though the diode of the optocoupler. However, also transformers can be used, in which case the loop current can for example be an AC loop current.

[0028] It is noted that the enable signal can be a simple DC or AC current, but may also be more intricate, for example a signal (a current) derived from a watchdog signal or a signature watchdog signal.

[0029] In an aspect of the invention the photovoltaic system is characterized in that each of the groups is connected to an electronic circuit associated to said group, • each of the electronic circuits has an enable input for connecting to an enable signal, the enable signal generated by a controller, the electronic circuit enabled when the enable signal is active, the electronic circuit disabled otherwise, • each of the groups shorted or at least has its maximum voltage reduced by the associated electronic circuit when the associated electronic circuit is disabled, • the voltage of each of the strings a safe voltage when the groups forming the string are shorted or at least have their maximum voltage reduced, • the enable signal is not active when an abnormal condition is detected by the controller, or when a break in the connection between controller and enable input occurs.

[0030] By grouping the cells into groups which have a maximum open source voltage that is a safe voltage, and by associating each of the groups with its own associated electronics that short the group of photovoltaic cells when not expressly enabled, even a fault in one of the electronics or a fault caused by cracks in the solar panel (thereby exposing a solar cell or an interconnection between two solar cells) will result in an exposed part with a safe voltage, and not result in a dangerous situation. By using a current loop (or an optical loop) with all loop inputs in series, an interrupt of the current loop results in all electronic circuit being disabled. As a result not only the output of the solar panel is at a safe voltage (as in the prior art), but also all interconnects, even when exposed due to a break of the panel.

[0031] In an embodiment of the photovoltaic system according to the invention the photovoltaic cells, interconnections and electronic circuits are mounted on a common substrate, and each of the groups occupies an area on the substrate, and the electronic circuit associated with each group is mounted on the area occupied by the associated group.

[0032] Preferably solar cells and the electronic circuit comprising the circuitry to short the groups are mounted on a common substrate. The substrate can be a flexible foil with a conductor pattern on it, on which the components are mounted by soldering, by an adhesive such as a conductive glue, or such like. Also (part of) the connection between controller and electronic circuits can be formed on the substrate, for example in the form of a PCB trace. Damage to the board or foil then results in a disconnect and thus a disable of the electronic circuits. As the area occupied by the group and the associated electronic circuit overlaps, a disconnect of only the shorting wires is less likely.

[0033] In another embodiment of the photovoltaic system according to the invention the shorting or reducing the maximum voltage is performed by an electronic circuit comprising a normally closed relay or a semiconductor device from the group of transistors, Darlington transistors, enhancement FETs and depletion FETs.

[0034] A normally closed relay is well suited to short a group. In a suitable circuit, with addition of, for example, a resistor as safety critical component, also the semiconductor devices can perform this function well. For example enhancement FETS with an “ON” resistance of less 10 mQ and capable of withstanding a voltage of 60 Vdc are easily selected and take up little space.

[0035] In yet another embodiment of the photovoltaic system according to the invention photovoltaic system is part of a vehicle.

[0036] Recently not only electric vehicles are commercially available, but also vehicles with a solar panel. The current generated by such a panel can attribute to a large degree of the energy use of such a car. Such cars are already known from the Solar Challenge races in Australia, and are developed for commercial use by, for example, applicant (Atlas Technologies B.V., Helmond, the Netherlands, see https://lightyear.one/).

[0037] In a further embodiment of the photovoltaic system according to the invention the controller ceases to send an enable signal when an abnormal condition occurs from the group of detection of: the inflation of an airbag, damage of a connection from a DC/DC converter to the solar panel, damage of the photovoltaic system, overheating of the batteries, or not properly receiving or processing of a watchdog signal.

[0038] When an abnormal situation occurs, other problems may be eminent. To avoid direct or indirect risks, such as overheating of the batteries, sparking, electrocution, etc. it is preferred to switch off power generation by the solar panel until the abnormal situation ends.

[0039] In yet another embodiment of the photovoltaic system according to the invention the enable signal is a loop signal, and the enable input of each of the electronic circuits comprises one or more optocouplers or transformers through which the enable signal runs, the enable inputs of each of the electronic circuits connected in series.

[0040] By passing the enable signal in a loop signal through all electronic circuits, any disconnect results in a disabling of all electronic circuits. Optocouplers, also known as opto-isolators or photo-couplers, are well suited for use in a current loop with a DC loop current flowing though the diode of the optocoupler. However, also transformers can be used, in which case the loop current can for example be an AC loop current.

[0041] It is noted that the enable signal can be a simple DC or AC current, but may also be more intricate, for example a signal (a current) derived from a watchdog signal or a signature watchdog signal.

Brief description of the figures.

[0042] The invention is now elucidated using figures, in which identical reference signs indicate corresponding features. To that end:

Figure 1 schematically shows a group of interconnected photovoltaic cells,

Figure 2 schematically shows a prior art photovoltaic system,

Figure 3 schematically shows a photovoltaic system according to the invention,

Figure 4 schematically shows a loop signal, and

Figure 5A - 5D schematically show several electronic circuits for shorting.

Detailed description of the invention.

[0043] Figure 1 schematically shows a group 100 of interconnected photovoltaic cells 102, the interconnected photovoltaic cells interconnected by interconnections 104.

A photovoltaic cell, also named a solar cell, is often a mono- or polycrystalline wafer of doped silicon. It produces, when illuminated, an open source voltage of up to approximately 0.7 V. However, this voltage is the open source voltage, i.e. at a load current of 0 A. Maximum power is delivered at a lower voltage, due to the internal resistance of the cell. Effectively a maximum voltage of approximately 0.5 - 0.6 V is delivered at maximum power.

[0044] A solar cell has a very low open source voltage. A higher voltage is preferred for efficient transport. Also, the system into which it feeds (often the grid or mains voltage, or the voltage of the battery of an electric car) is much higher, and for a converter (either a DC/AC converter or a DC/DC converter), much higher voltages than 0.5 V are preferred. Therefore, several cells are connected in series. Such a group of cells, typically 10 to 30, are interconnected.

[0045] Figure 2 schematically shows a prior art photovoltaic system 200.

Several groups of solar cells 100 are connected in series to form a string 202.

If a cell 102 is not illuminated, no current will pass through it. Only a small leakage current will pass, so the non-illuminated cell behaves in first approximately as a high ohmic resistance. This is a reason not to connect too many cells in series. Several groups are connected in series, and to minimize the effect of a group with a non-illuminated cell (not passing current) a bypass diode 204 bridges each group.

[0046] It is noted that ideally every cell is bridged by a bypass diode, but this involves too many interconnections, and thus a compromise in the number of interconnections and a loss of voltage/power is sought. Typically, between 10 and 30 cells are connected in series to form a group.

[0047] In this figure 2 it is shown that two groups are connected in series, but a larger number of groups, for example four, can be connected in series. On the top of the string a series diode 208 is shown to avoid current from other strings to be shorted into another string, in case the voltage of a string differs from another. Variation of string voltage can be caused by differences in illumination, defect cells, etc. The person skilled in the art will recognize that this series diode need not be placed on top of the string but can be placed between any group forming the string.

[0048] Several strings are connected in parallel (here two strings in parallel are shown, but this number may differ), thereby forming a solar panel. This series diode may be eliminated when no strings are connected in parallel.

[0049] To minimize the chance of hazardous situations international application publication WO14085468A1 describes that a switch 210 shorts the outputs of the interconnected strings when a controller 212 detects that a ‘continuity signal’ 214 is discontinued (‘broken’). Due to this short the output voltage is a non-dangerous voltage. [0050] The output signal is typically fed to a converter (not shown), either a DC/DC converter (when fed to a battery system) or a DC/AC converter (when fed to e.g. a grid connected system) to change the final output voltage to the final output voltage demanded.

[0051] It is noted that, although each group 100 has a safe maximum voltage, a string 202 has a dangerous maximum voltage.

It is noted that a dangerous voltage is often defined as a (DC) voltage in excess of 60 Vdc, although in certain areas of application different voltages may be used.

Therefore, when a break between groups occurs, the short over the string formed by these groups results in a dangerous voltage at the break, especially in those cases where no series diode is present.

[0052] Figure 3 schematically shows a photovoltaic system 300 according to the invention.

[0053] Figure can be thought to be derived from figure 2. However, instead of having a short over the strings, each group 100 has its own shorting circuit 302, each with its own enable input 304. This implies that, in abnormal situations, each group is shorted, even though the voltage of a group is always safe (the maximum voltage of a group is always lower than a dangerous voltage). This in turn implies that each string has a safe voltage, and when a break occurs in a string, no dangerous voltage occurs over this break. Only a break in a group would result in a voltage over the break, but this is always a safe voltage. The controller 308 stops sending and enable signal 306 when one of several abnormal situations 310 is detected.

[0054] It is noted that a short of the electronic circuits is, for safety, equivalent to a reduced voltage, as long as the addition of all reduced voltages in a string are a safe voltage. For optimum safety the sum of the reduced voltages plus the voltage of a group should be a safe voltage, as, when a break in a group occurs, the voltage over the break can be as high as the addition of all groups in the string plus the group voltage.

[0055] It is further noted that when the enable inputs take the form of a loop signal is a loop signal (that is: a signal that loops through each enable input).

[0056] Figure 4 schematically shows a loop signal. Loop signals are known and have a special added value in the enable signal of the photovoltaic system described here. In a loop signal a current is passed through the input of an apparatus, the input comprising of two contacts (304a, 304b) together forming the input. Especially if the input is a photocoupler or a transformer, this is easily implemented. An advantage of a loop signal is that a break or disconnect in the signal wiring is easily detected. The signal can for example be a DC current, to be detected by an optocoupler or a differential amplifier, an AC current, to be detected by an optocoupler, a differential amplifier or a transformer, or a signal derived from e.g. a signature watchdog.

[0057] The multitude of electronic circuit described here do not operate at the same electric ground, as the groups they short have different electric levels. The use of optocouplers and transformers enable the working of input and output at different electric levels.

[0058] Figure 5A - 5D schematically show several electronic circuits for shorting.

[0059] Figure 5A schematically shows a normally closed relay. When no current flows through the coil, the contacts are connected. Hereby the relay can short the group, the coils of all relays can be connected in series, thereby forming a loop input to receive a loop signal. Even when used otherwise, there is a galvanic insulation between coil and contact, enabling a potential difference between the coil and the contact.

[0060] Figure 5E3 schematically shows a depletion FET. A depletion FET conducts when no (or little) gate voltage is applied and enters a non-conducting state when the gate voltage exceeds a limit. This means that the FET is normally conducting, as is needed in this application. As a side-benefit such a FET also shows an integrated diode between drain and source that allows elimination of the bypass diode 204.

[0061] Figure 5C schematically shows an enhancement FET. Contrary to the working of a depletion FET, an enhancement FET is normally not conductive and only becomes conductive when the gate voltage rises above a certain level. In this circuit the resistor pulls the gate up, and only a current through the transistor can bring the gate down (thus enabling the electronic circuit). As a side-benefit such a FET also shows an integrated diode between drain and source that allows elimination of the bypass diode 204.

[0062] It is mentioned that the transistor can be part of an optocoupler, thereby enabling galvanic insulation and a potential difference between the source of the FET and the input signal.

[0063] Figure 5D schematically shows a Darlington transistor. Figure 5D can be thought to be derived from figure 5C. However, instead of a FET a Darlington transistor is used. This implies that the integrated diode is not present and that bypass diode 204 is still needed. If the current of the group is not too large, also a unipolar transistor can be used instead of a Darlington transistor.

[0064] It will be recognized that the above electronic examples form a non-exhaustive list and that the skilled artisan can design and costruct many other circuits to reach the same goal: shorting or at least reducing the output voltage of a group of photovoltaic cells.

[0065] It is noted that each electronic circuit can comprise an optimizer, enabling the efficient addition of power of each group of solar cells. As an alternative each string can use one optimizer, or each panel.

Claims

Conclusions.

Method for eliminating dangerous situations during an abnormal condition, the dangerous situations caused by a photovoltaic system (300), the system containing multiple groups (100) of interconnected photovoltaic cells (102), the interconnected cells interconnected interconnections (104), each of the groups able to generate a voltage when exposed to sunlight, at least two of the groups connected in series thereby forming a strand (202) of photovoltaic cells, the open voltage of each group in full sunlight a safe voltage, the open voltage of each of the strands in full sunlight forming a dangerous voltage, the method characterized in that • Each of the groups (100) is connected to an electronic circuit (302) associated with said group, • Each of the electronic circuits (302 ) has an enable input (304) to connect to an enable signal (306), the enable signal formed by a controller (308) , the electronic circuit (302) enabled when the enable signal is active and not enabled in all other cases, • Each of the groups (100) shorted or at least having a reduced maximum voltage through intervention of the electronic circuit (302) associated with said group when the electronic circuit is not enabled, • The voltage of each of the strands (202) is a safe voltage when the groups forming the strand are shorted or at least have a reduced maximum voltage, • The enable signal (306) is not active when a abnormal condition is detected by the controller, or when a break in the connection between controller and enable input occurs.

The method of claim 1 wherein photovoltaic cells (102), connections (104) and electronic circuits (302) are mounted on a common substrate, and each of the groups (100) occupies an area on the substrate, and the electronic circuit and the compounds associated with said group occupy the same area.

The method according to any one of the preceding claims, wherein the short-circuiting or at least reduction of the maximum voltage is effected by an electronic circuit comprising a normally closed relay or a semiconductor from the group of transistors, Darlington transistors, enhancement FETs and depetion FETs.

The method according to any of the preceding claims taking place while the photovoltaic system (300) is part of a vehicle.

The method of claim 4 wherein the controller (308) ceases to transmit an enable signal (306) when an abnormal condition occurs from the group of: detecting an airbag inflating, damaging the DC / DC connection spark to the photovoltaic system, battery overheating, or incorrect processing of a watchdog signal.

The method of any preceding claim wherein the enable signal (306) is a loop signal, and the enable input (304) of each of the electronic circuits (302) includes an optocoupler or a transformer through which the enable signal passes, the enable signal of all electronic circuits connected in series.

Photovoltaic system (300) containing multiple groups (100) of interconnected photovoltaic cells (102), the interconnected cells interconnected by connections (104), each of the groups capable of generating a voltage when exposed to sunlight, at least two of the groups connected in series thereby forming a strand (202) of photovoltaic cells, the open voltage of each group in full sunlight a safe voltage, the open voltage of each of the strands in full sunlight forming a dangerous voltage, characterized in that • Each of the groups (100) is connected to an electronic circuit (302) associated with said group, • Each of the electronic circuits (302) has an enable input (304) to connect to an enable signal (306), the enable signal by a controller (308), the electronic circuit (302) enabled when the enable signal is active and not enabled in all other cases, • Each of the groups (100) shorted o f having at least a reduced maximum voltage through intervention of the electronic circuit (302) associated with said group when the electronic circuit is not enabled, • The voltage of each of the strands (202) is a safe voltage when the groups forming the strand are shorted or have at least a reduced maximum voltage, • The enable signal (306) not being active when an abnormal condition is detected by the controller, or when a break in the connection between controller and enable input occurs.

The photovoltaic system according to claim 7, wherein the photovoltaic cells (102), connections (104) and electronic circuits (302) are mounted on a common substrate, and each of the groups (100) occupies an area on the substrate, and the electronic circuit and the connections associated with said group occupy the same area.

The photovoltaic system according to any one of claims 7-8, wherein the shorting or at least reducing the maximum voltage is effected by an electronic circuit comprising a normally closed relay or a semiconductor from the group of transistors, Darlington transistors, enhancement FETs and depetion FETs .

The photovoltaic system according to any one of claims 7-9, wherein the photovoltaic system (300) is part of a vehicle.

The photovoltaic system of claim 10 wherein the controller (308) ceases to transmit an enable signal (306) when an abnormal condition occurs from the group of: detection of an air bag inflating, damage to the junction of a DC / DC inverter to the photovoltaic system, battery overheating, or incorrect processing of a watchdog signal.

The photovoltaic system of any one of claims 7-11, wherein the enable signal (306) is a loop signal, and the enable input (304) of each of the electronic circuits (302) includes an optocoupler or transformer through which the enable signal running, it enable