WO2017021548A1

WO2017021548A1 - Improved system, device and methods for regenerating solar panels

Info

Publication number: WO2017021548A1
Application number: PCT/EP2016/068811
Authority: WO
Inventors: Jo BEYEN; Davy VERHEYDEN
Original assignee: Innotech Bvba
Priority date: 2015-08-05
Filing date: 2016-08-05
Publication date: 2017-02-09
Also published as: BE1022976B1

Abstract

This invention concerns a method for regenerating solar panels, a system and a method for generating electricity from solar energy, a slave device for regenerating solar panels,and preferably controlled by a master device configured to control one or more of the slave devices. Furthermore, the invention concerns a method for installing the slave device.

Description

IMPROVED SYSTEM, DEVICE AND METHODS FOR

REGENERATING SOLAR PANELS

TECHNICAL DOMAIN The invention concerns a method, a device and a system for regenerating solar panels to retain or improve their efficiency by removing residual charges that accumulate in the solar cells.

STATE-OF-THE-ART

Solar panels lose their efficiency over time. This is due to a number of factors. One factor is the accumulation of residual charges in the solar cells, which is caused by a potential difference between a solar cell and the solar panel support structure, which houses the solar cell. This phenomenon is called potential induced degradation.

The term Potential Induced Degradation or PID is used to indicate the decrease in solar cell and solar panel efficiency, caused by parasitic currents, which, in practice, stem from a potential difference between a solar cell or solar panel terminals on the one hand and, on the other hand, the structure in which the solar cells or solar panels are assembled and connected to the grounding. This potential difference causes the number of residual charges in the solar cells to increase, leading to an efficiency reduction of the photovoltaic process. The PID problem was already identified in the 1970s, and became the focus of attention again between 2005 and 2010 due to the substantial reduction in production costs and sales prices.

S. Pingel et al., Proceedings of the 35th IEEE PVSC, 20-25 June 2010, pp. 2817- 2822, describes the PID problem in solar cells and solar panels as well as methods to prevent PID by applying, or restoring, an a nti- reflective coating. A method to restore the efficiency of solar panels that have been subject to PID is to apply a regeneration voltage across the panels, i.e. between the terminals and the support structure, enabling residual charges to be removed from the solar cells.

Documents WO2014191846A1 and BE 1 020 776 by Futech, describe a device and a method for restoring and/or preventing defects in solar panels, whereby a regeneration voltage is applied directly to and between the supporting structure on which the solar panels are assembled and solar panels' negative terminal, the positive terminal, or both terminals, in which case these are short circuited. The device is installed in series between the inverter and the panel on the inverter's conductor to the positive terminal as well as the inverter's conductor to the negative terminal of the solar panel. This means that in order to install the device on an existing solar panel system, each electric cable between an inverter and a solar panel or a set of solar panels will have to be interrupted. This leads to high installation costs and in many cases a loss of the guarantee that is provided by the solar panel system installer. Moreover, the electricity generated flows through the cables of the device, which creates a heavy load for these cables, particularly in the case of large systems and in the long term. The document also describes a device that has one or several switches for interrupting or establishing electrical connections. The presence of such switches may drastically reduce the lifespan of the device, particularly in the case of the existing application whereby the switches have to be able to cope with high currents and be capable of switching daily for a period of some 20 years. The document US 2001/040453 by Toyomura Fumitaka describes a method and apparatus for testing a solar panel, among others. However, the document does not mention PID, or offers any solution to the problem of PID. It only provides an apparatus (and accompanying method) for testing solar panels by applying a voltage between the solar panel and the outer housing of the panel, however this voltage is neither intended to regenerate the solar panel, nor is it suitable for doing so. As such, the document both doesn't describe the problem of PID with solar panels, nor does it disclose a method for regenerating solar panels.

In practice, a plurality of solar panels are connected in series to produce a higher DC voltage. A commercially obtainable solar panel can typically produce a voltage of 30 to 40 V during electricity generation. By connecting a plurality of solar panels in series, e.g. 14 to 17 panels, the voltage can be increased to approximately 400 to 700 V. Solar panels connected in series is also known as a 'string'. The power that is generated in one string is transmitted to an inverter which, for example, can convert the supplied DC current at a DC voltage from approximately 500 V (direct voltage or DC) to an alternating current at an alternating voltage of approximately 220-230 V or 380 V (alternating voltage or AC). Several strings are compiled at sites with larger solar panel systems, whereby, for example, 4 strings can be connected to one inverter, and various inverters from a site are connected to, for example, the power grid via a control box. The PID problem is particularly significant with large solar panel systems, in which many solar panels are connected in series, so that electricity can be generated with a high DC voltage. The problem with such strings is that the average potential difference between each solar cell and the grounded structure will increase. As an example: a solar panel with 60 solar cells can typically produce a potential difference of 35 V (direct voltage or DC) during photovoltaic electricity generation. When two such panels are connected in series, this produces a potential difference of 70 V (DC). This potential difference is measured between the positive and the negative terminal of the panels connected in series. However, the voltage across the positive terminal of the first panel may, for instance, be +20 V in relation to the (grounded) support structure, while the voltage across the negative terminal of the first panel and the positive terminal of the second panel is -15 V in relation to the support structure, and while the voltage across the negative terminal of the second panel is -50 V in relation to the support structure. This may cause the solar cells at the first panel to produce an average absolute potential difference of approx. 9 V with the support structure (roughly 4/7 of the solar cells will be on a positive voltage, i.e. average + 10 V, and the other 3/7 will be on a negative voltage, i.e. average -7.5 V in relation to the support structure) and at the second panel, the solar cells will produce an average absolute potential difference of 32.5 V with the support structure. It is clear that, if many more solar panels are connected in a string, for example, typically 14 to 17 panels, the average absolute potential difference between the solar cells in the panels and the support structure increases drastically. This also means that the PID problem in solar panel systems increases significantly with larger strings.

Furthermore, there is a need to provide a regeneration system that can be safely and easily implemented in existing solar panel systems, without the necessity of substantially disrupting the existing solar panel system, for instance by having to cut wiring and the likes. Also, it is desirable that the operating conditions of the regeneration system reduce danger for operators due to the high voltages and/or currents involved in the system.

The present invention aims to provide a solution for at least some of the abovementioned problems.

There is a need for an improved device and method for regenerating solar panels that are or could be subject to PID. The device and method should have a better scalability than the existing technology to ensure that the PID problem can also be treated effectively in larger systems. There is therefore also a need for a device that can be installed easily and a method for installing it. There is also a need for an improved system for generating electricity from solar energy, whereby the PID problem can be significantly reduced. SUMMARY OF THE INVENTION

The invention concerns an easy-to-install device, whereby the existing electrical wiring between the inverter and solar panels can remain intact and which can be used for larger systems. The invention also concerns methods for regenerating solar panels and for installing the device, and also a system and method for generating electricity from solar energy. The scalability and lifespan of the device, the system and the methods of operating the present invention is exceptionally better than devices, systems or methods that are already available, among other things due to the easy to install device.

In a first aspect, the present invention concerns a method for regenerating solar panels that are connected in one or several strings, whereby at least one string is connected between an inverter's positive input terminal and negative input terminal for supplying a DC voltage generated by solar energy, whereby the method of operation comprises the following steps:

provide an input voltage to a slave device; the input voltage to the slave device is preferably provided by a master device;

generate a regeneration DC voltage in the slave device from the input voltage; supplying the regeneration DC voltage to a positive input terminal and/or a negative input terminal of the inverter.

In this context, 'the regeneration of solar panels' means that the efficiency of the solar panels will improve because the effects of PID, i.e. the increase in residual charges in the solar cells, will be counteracted or restored.

A 'string' contains one or several solar panels connected in series. Consequently, during energy production, a string can supply a direct current at a DC voltage that increases as the number of solar panels in the string increases. A string comprises a negative and a positive terminal that is connected to an inverter to convert the electricity generated from DC voltage to alternating voltage. Note that for the terminals of the solar panel, it will generally not be specified whether these are 'input' our 'output' as this depends on the regime under which they operate (input during regeneration, output during energy production), and the terms 'input' or Output' do not necessarily refer to different terminals of the solar panel. In the case of a small system, a string may only comprise one solar panel. However, a string preferably comprises two or more solar panels, e.g. 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 solar panels or more. More preferably a string comprises 10 to 20 solar panels; most preferably 14 - 17 solar panels.

Solar panels produce DC voltage from solar energy. Solar panels that are connected in a string supply DC voltage to an inverter that can convert the DC voltage into alternating voltage, preferably alternating voltage of 220-230 V or possibly about 380 V. The positive input terminal of the inverter is the terminal that is connected to the positive terminal of the solar panel string, i.e. the string's terminal that is connected to that side of the first solar panel in the string that has the highest electrical potential when the solar panels generate electricity via the photovoltaic effect in the solar cells. The negative input terminal of the inverter is therefore the terminal that is connected to the negative terminal of the solar panel string, i.e. the string's terminal that is connected to that side of the last solar panel in the string that has the lowest electrical potential when the solar panels generate electricity. The term 'inverter' as used in this application refers to a device capable of converting a DC voltage, as generated by a solar panel or a string of solar panels, into an alternating voltage, typically a commonly used mains voltage such as 220-230 V or 380 V alternating voltage. In a preferred embodiment an inverter comprises a number of positive and negative input terminals that can be connected respectively to the positive and negative terminals of a number of solar panel strings. In a further preferred embodiment the negative input terminals are at least partly and preferably fully, internally shorted in the inverter. Also in a preferred embodiment, the inverter comprises one or more maximal power point trackers (MPPTs), more preferably the inverter comprises two MPPTs.

A maximal power point tracker (MPPT), as used in this application, refers to a device that maximises the electrical power produced by the connected solar panels or strings. Solar cells have non-linear current-voltage characteristics. By adjusting, for example, a load that is placed across a solar cell, the current produced by a solar cell can be adjusted to maximise the power, i.e. the product of current (I) and voltage (V). The same applies to solar panels and strings that comprise a large number of connected solar cells. An inverter may comprise one or more, preferably two, MPPTs, to which one or more, preferably two or three, strings can be connected.

The term 'slave device' as used in this application refers to a device that is at least controlled by external signals and is consequently considered dependent or subservient to these external signals and possibly to the device that produces these external signals, i.e. a 'master device'. The external signals may include the delivery and/or stopping of the supply current or supply voltage, or may also comprise electronic control signals.

The term 'master device' refers to a device that is designed to control one or more slave devices through signals. Preferably, it is also designed to provide said slave device(s) power through a wired connection, possibly said providing of power also serving as signals to control and direct the slave device(s). Preferably, this master device also allows for a central point where the operation of the system can be controlled by an operator and settings can be adjusted or updated if necessary. Furthermore, data can be logged at this place for the entire system (typically at night). The advantages of the 'master-slave' configuration of the invention lie, amongst others, in the fact that it is easy to install, and safe to use. The slave devices receive input from the master device at relatively low voltages, while the slave devices then generate a higher regeneration voltage and apply this directly to an inverter, and thus to (a string of) solar panels, which allows a safe operation, as the high voltage is generated and applied locally, instead of provided over a length of wires. Furthermore, the system according to the invention only requires a single power source at a master device, instead of at each slave device (as is the case in prior art devices). Also, the invention preferably requires only a single connection to a functional earth, again at the master device, and not necessarily at each of the slave devices (which are grounded through the master device). A central master device can as said also allow central updates or adjustments to be made, instead of at each slave device, and a single location where data can be logged (typically at night, during regeneration). In a further improvement, the configuration of the system with master and slave devices allows an easy install for additional slave devices, which can be simply plugged in without much further trouble. Slave devices can be installed in a so-called daisy chain, over other slave devices, which reduces the amount of wiring necessary. The terms 'regeneration voltage' or 'regeneration DC voltage' as used in this application refer to a DC voltage from which the voltage is attuned to prevent the PID problem by removing residual charges in the solar cells under the effect of the applied voltage. The regeneration voltage is applied to the solar panels' or string's positive terminal, the negative terminal or both, creating a potential difference between the solar panel's solar cells on the one hand and the solar panel's support structure on the other hand. The voltage necessary for regenerating the solar panels depends on the number of solar panels in a string and/or the type of solar panels, i.e. either the layout or the type and number of solar cells. The literature states that PID typically occurs at potential differences of -160 V. In the case of small solar panel systems, a voltage of 160 V is already sufficient to visibly tackle the PID problem. However, a voltage of 400 V, 500 V or more appears appropriate for current commercial solar panels. The regeneration voltage is preferably between 400 V and 1500 V, more preferably between 500 V and 1000 V, most preferably between 500 V and 980 V. In one embodiment, the regeneration voltage is essentially constant during a period when the solar panels are not producing electricity, particularly during the night. In another embodiment, the regeneration voltage follows a predetermined profile during a period when the solar panels are not producing electricity, particularly during the night. This predetermined profile may be a constant profile, an incremental constant profile, a block profile, a repetitive profile, or a combination of these. The profile preferably comprises a period T during which the substantially constant or substantially incremental constant regeneration voltage is supplied, whereby the period T is preferably at least 80%, preferably at least 90%, more preferably at least 95%, yet more preferably at least 99%, most preferably about 100% of the period in which the solar panels are not producing electricity.

The use of a slave device with a high voltage generator has a number of advantages in relation to the methods used in the state-of-the-art, particularly in the area of scalability and more specifically for large solar panel systems with a multitude of solar panels and a multitude of inverters. More specifically, the use of a slave device allows for providing one slave device for each inverter, which can be installed close to the inverter. A big advantage of this is that the high regeneration DC voltage will only have to be supplied over a short distance, which reduces both current loss and the safety risk. The power for the slave devices can in fact be supplied to said slave devices at a safe and low voltage by a central power source, for example, a master device. Furthermore, using a slave device provides a modular method for connecting a system for regenerating solar panels: if indeed a new string of solar panels is connected to an existing inverter, the slave device that was connected to that inverter can also be used for regenerating the solar panels in the new string, and this without additional wiring if, for example, the string is connected to an MPPT of the inverter that is already connected to the slave device, or just by connecting one or two wires; if one or more new strings of solar panels, coupled to a new inverter are connected to an existing solar panel system, a new slave device can be provided to regenerate the solar panels in the new string. This also minimises the amount of wiring necessary to supply a regeneration DC voltage. This is possible because the slave device can be connected to the negative and/or positive input terminals of the inverter, which connects the slave device in parallel across the inverter input terminals, which is both easier to execute, but is also less straining to the system, as opposed to prior art devices that provide the regeneration voltage (which are placed in between the inverter and the solar panels, thus requiring the currents to be conducted through the prior art device).

Electrically speaking, by placing the slave device in parallel over the inverter input terminals, this actually comes down to connecting the slave device in parallel across the string of solar panels, and thus providing the regeneration voltage to the string of solar panels. It is therefore unnecessary to interrupt the wires between the string and the inverter when installing the slave device, and the slave device can be connected with a minimum of work, time and risk, while also avoiding the stress of conducting high currents as in prior art devices.

In a further advantage with respect to prior art devices, there is no need for a disconnection of the electrical connection between the slave device and the inverter and/or the string of solar panels when not in regeneration mode. The devices of the prior art are all equipped with switches that actually physically disconnect the regeneration-providing device, said switches (or similar components) being prone to failure or errors. The system, specifically the slave device, according to the invention however does not require an actual disconnection from the inverter (and/or the string of solar panels), and is configured to stay connected even when the string of solar panels is in production mode. Furthermore, the methods, the device and the systems according to the present invention make it possible that during electricity production in the solar cells no generated electrical current runs through the slave device, which enables the slave device to be installed, restored or replaced during the production phase of the solar panels. This means a substantial simplification compared to existing systems and methods. It is also possible to connect the new slave device to the power source via another slave device, enabling different slave devices in a chain to be connected to one power source, i.e. one master device. Certainly in the case of large solar panel systems, this provides a substantial reduction in the amount of wiring needed to implement the regeneration method of the present invention.

A second aspect of the invention concerns a system for generating electricity from solar energy, comprising :

a plurality of solar panels that are connected in one or several strings, whereby at least one string is connected between an inverter's positive input terminal and the inverter's negative input terminal for supplying a DC voltage generated by the solar energy, whereby the inverter is configured to convert said DC voltage between the positive and negative input terminals into an alternating voltage and to provide said alternating voltage to the inverter's output terminals;

a slave device with a first output terminal connected to the inverter's positive input terminal and a second output terminal connected to the inverter's negative input terminal, whereby the slave device comprises a high voltage generator configured to generate a regeneration DC voltage from an input voltage, and whereby the slave device is configured to supply the regeneration DC voltage to the first and/or second output terminal;

- a master device that is connected to the slave device and configured to supply an input voltage to the slave device's high voltage generator.

The system for generating electricity from solar energy according to the present invention, allows for treating the solar panel PID problem in the system by placing a regeneration voltage across the solar panels, so that residual charges can be removed from the solar cells. The system allows the strings connected to an inverter to be connected to a slave device via their negative and positive terminal. The slave device should preferably be installed close to the inverter, as this increases safety (the high voltage generation happens close to the inverter, as opposed to prior art devices). By having a master device providing the slave device with an input voltage, the safety of use is increased, as well as reducing the scale for the slave devices, which no longer need to comprise all necessary components, as some components can be part of the master device which can be used for a plurality of slave devices at once.

A subsequent aspect of the invention concerns a method for generating electricity from solar energy with a system as described above and to be described in more detail further on in this document, comprising the following steps:

preventing the supply of a regeneration DC voltage to solar panel terminals during daytime, preferably by implementing one or several of the following steps: • interrupting the input voltage supply via the master device;

· interrupting the generation of regeneration DC voltage via the high voltage generator;

regenerating solar panels at night-time, preferably according to a method as described above or further on in this document. It is also possible to prevent the supply of the regeneration DC voltage in the daytime by interrupting the connection between the solar panel terminals on the one hand and the high voltage generator on the other hand.

The steps of daytime prevention of the regeneration DC voltage and the night-time regeneration can at least be partly implemented on the master device, whereby the master device stops the supply of an input voltage to all slave devices or a part thereof based on the time of actual sunrise and restart based on the actual sunset. For example, both the time and location of the solar panel system can be retrieved or calculated via information obtained via GPRS or GPS, and/or the actual sunrise and sunset for the location of the solar panel system can be retrieved or calculated. Alternatively or additionally, a sensor that can identify whether it is actually day or night based, for example, on a light intensity measure can also be set up at the location of the solar panel system. It is necessary to note here that it is important to avoid a regeneration voltage being supplied to solar panels during energy production. This is why preferably a safety margin is applied to the times of actual sunrise and sunset, ensuring the period of regeneration will only be at night-time.

The term 'actual sunrise' refers to the time at which the sun comes into a position whereby it is possible that at least one of the solar panels or solar cells of a solar panel system at one site will produce electrical current via the photovoltaic effect. The term 'actual sunset' refers to the time at which the sun comes into a position whereby it is impossible that at least one of the solar panels or solar cells of a solar panel system at one site will produces electrical current via the photovoltaic effect. The terms 'actual day' and 'daytime' refer to the period between actual sunrise and actual sunset and the terms 'actual night' and 'night-time' refer to the period between actual sunset and actual sunrise.

A significant advantage of the above method is that only the master device needs to be provided with the information on the actual sunrise and actual sunset and therefore whether or not the input voltage can be supplied to the slave devices, or alternatively a command can be given to the slave devices whether or not to supply the regeneration DC voltage to the solar panel strings. This means that it can be arranged in a centralised manner that the panel regeneration fully occurs overnight, and not only, for example, for a short part of a twenty-four hour period during which it is definitely still night-time. It is clear that the centralised method offers significant advantages in terms of solar panel system scalability.

The steps for interrupting the supply of the input voltage by the master device and/or interrupting the generation of the regeneration DC voltage by the high voltage generator can be executed separately or in combination, and the interruption can be effected automatically, i.e. electrically or electronically controlled.

A subsequent aspect of the invention concerns the slave device for regenerating solar panels that are connected in one or several strings, whereby at least one string is connected between an inverter's positive input terminal and negative input terminal for supplying a DC voltage generated by solar energy; the slave device comprises: - a positive input terminal and a negative input terminal for receiving electricity by an input voltage between the positive and negative input terminal;

a first output terminal suitable for being connected to the negative input terminal of the inverter and/or a positive terminal of a string, and a second output terminal suitable for being connected to a positive input terminal of the inverter and/or a positive terminal of a string, the first and second output terminal configured for supplying electricity for a regeneration DC voltage;

a high voltage generator that comprises a negative input generator terminal connected to the negative input terminal and a positive input generator terminator connected to the positive input terminal and which is configured to convert the input voltage between the negative and positive input terminal into a regeneration DC voltage between a negative output generator terminal and a positive output generator terminal, whereby the positive output generator terminal is or can be connected via an electrical circuit to the first output terminal and/or the second output terminal for supplying the regeneration DC voltage, and preferably whereby the negative output generator terminal is or can be connected with a grounding, preferably a physical grounding.

Preferably, a control circuit or control mechanism is present in the slave device which compares the physical grounding to a grounding of a power source for the high voltage generator. If the difference between these values is above a predetermined threshold difference, the system can take actions. Possible actions include: notifying a user of said difference being too high (audio, visual and/or other signs), disabling the high voltage generator so no regeneration voltage is supplied, and/or other actions. This reduces the risk of accidents by the high voltage present at the connection/wiring for the physical grounding of the system if not actually connected to the grounding, as this situation could be dangerous for users and/or system.

The term 'physical grounding' as used in this document concerns an electrical reference potential that may, but does not necessarily have to, be equal to the electrical potential of the grounding. Within the context of this document, the term 'physical grounding' is used to indicate the potential of the solar panel construction, i.e. a support structure potential. The term 'physical ground' is also used in this document to indicate a conductive object, for instance a conducting wire, which is on the reference potential. The slave device preferably comprises a positive input terminal and a negative input terminal for receiving electricity by an DC input voltage between the positive and negative input terminal, a DC-DC converter connected to the negative and positive input terminal for converting the DC input voltage's electricity into electricity with DC output voltage at an output terminal whereby the magnitude of the DC output voltage is higher than the magnitude of the DC input voltage, preferably whereby the magnitude of the DC output voltage is at least 160 V, more preferably at least 200 V, yet more preferably at least 300 V, even more preferably at least 400 V and yet more preferably at least 500V, and preferably between 500 V and 1500 V, such as 500 V, 525 V, 550 V, 575 V, 600 V, 625 V, 650 V, 675 V, 700 V, 725 V, 750 V, 775 V, 800 V, 825 V, 850 V, 875 V, 900 V, 925 V, 950 V, 975 V, 1000 V, 1025 V, 1050 V, 1075 V, 1100 V, 1125 V, 1150 V, 1175 V, 1200 V, 1225 V, 1250 V, 1275 V, 1300 V, 1325 V, 1350 V, 1375 V, 1400 V, 1425 V, 1450 V, 1475 V, 1500 V or values in between.

Another subsequent aspect of the invention concerns a method for installing a slave device, comprising the following steps:

providing a slave device according to the present invention;

connecting a negative and a positive input terminal of the slave device to an input voltage source, preferably a master device;

connecting a first output terminal of the slave device to a negative (input) terminal of a solar panel, a string of solar panels, an inverter and/or a maximum power point tracker (MPPT) to which a string of solar panels may be connected; connecting a first output terminal of the slave device to a negative (input) terminal of a solar panel, a string of solar panels, an inverter and/or a maximal power point tracker (MPPT) to which a string of solar panels may be connected ;

- preferably connecting the slave device to a grounding, a physical grounding or a solar panel support structure. The physical grounding for the slave device is preferably provided via the master device.

The slave device, and particularly its input terminals and the optional physical grounding, can be directly connected to the master device, i.e. the first slave device that is installed. It is also possible to connect a slave device to another slave device, thereby forming a chain of slave devices.

DESCRIPTION OF THE FIGURES

Figure 1 illustrates a version of a master device - slave device configuration according to the present invention.

Figure 2 illustrates a version of the slave device according to the present invention. DETAILED DESCRIPTION

The invention concerns a method for regenerating solar panels, a system and a method for generating electricity from solar energy, a slave device for regenerating solar panels and a method for installing the slave device as described in the conclusions, and as further described in this document. Unless defined otherwise, all terms that are used in the description of the invention, technical as well as scientific terms, have the meaning as generally understood by the professional in the technical field of the invention. For a better assessment of the description of the invention, the following terms are explicitly explained.

In this document, 'a/an' and 'the' refer to both the singular and plural unless the context clearly presupposes otherwise. For example, 'a segment' means one or more than one segment. When 'approximately' or 'about' are used in this document for a measurable quantity, a parameter, a duration or time, and the like, this refers to variations of +/-20% or less, preferably +/-10% or less, more preferably +/-5% or less, yet more preferably +/-1% or less, and even more preferably +/-0.1% or less than and of the cited value, insofar as such variations apply to the described invention. However, it should be understood here that the value of the quantity for which the term 'approximately' or 'about' is used, will itself be specifically disclosed.

The terms 'comprise', 'comprising', 'consist of, 'consisting of, 'equipped with', 'contain', 'containing', 'comprehend', 'comprehending', 'include' and 'including' are synonyms and are inclusive or open terms that indicate the presence of what follows, and do not exclude or preclude the presence of other components, characteristics, elements, members, steps, known from or described in the state-of-the-art.

The citing of numeric intervals by the end points comprises all whole numbers, fractions and/or real numbers between the end points, these end points included.

In a preferred embodiment of the invention, the input voltage is a DC voltage, preferably a safety DC voltage, more preferably a safety voltage of 80 V maximum, yet more preferably 70 V maximum, and even more preferably 60 V maximum, most preferably about 48 V. This allows for an easy and safe wiring between the master device and one or more slave devices. It should be noted here that the wiring of the solar panel system is usually exposed to extreme environmental factors (humidity, rain, exceptionally low and high temperatures, freezing, wind, hail, lightning, etc.) and that powering the slave devices with a (safety) DC voltage is an improvement in terms of sustainability and safety in relation to power supplied with an alternating voltage, for example, a power supply of 220-230 V or 380 V alternating voltage. Furthermore, it is to be stressed that the wiring from the master device to the slave device operates at very low voltages (ELV), while the only wirings at higher voltages are those from a source (net) to the master device. However, these need not be very long, or even exposed to external influences and can easily be shielded from human interaction.

In a preferred embodiment of the invention, the regeneration DC voltage is at least 160 V, more preferably at least 200 V, yet more preferably at least 300 V, even more preferably at least 400 V, and yet more preferably at least 500 V, and preferably between 500 V and 1500 V, such as 500 V, 600 V, 700 V, 800 V, 900 V, 1000 V, 1100 V, 1200 V, 1300 V, 1400 V, 1500 V or all values in between, 500 V, 525 V, 550 V, 575 V, 600 V, 625 V, 650 V, 675 V, 700 V, 725 V, 750 V, 775 V, 800 V, 825 V, 850 V, 875 V, 900 V, 925 V, 950 V, 975 V, 1000 V, 1025 V, 1050 V, 1075 V, 1100 V, 1125 V, 1150 V, 1175 V, 1200 V, 1225 V, 1250 V, 1275 V, 1300 V, 1325 V, 1350 V, 1375 V, 1400 V, 1425 V, 1450 V, 1475 V, 1500 V, more preferably between 500 V and 1000 V. As already mentioned, the voltage necessary for regenerating the solar panels depends on the number of solar panels in a string and/or the type of solar panels, i.e. either the layout or the type and number of solar cells. In the case of small solar panel systems, a voltage of 160 V is already sufficient to visibly tackle the PID problem. However, a voltage of 500 V or more appears appropriate for current commercial solar panels. The regeneration voltage is preferably between 500 V and 1000 V, most preferably between 900 V and 1200 V.

In a preferred embodiment, the regeneration voltage that is generated by the high voltage generator is only supplied to an inverter's positive input terminal, whereby the voltage to the inverter's negative input terminal is substantially lower than the voltage to the positive input terminal, i.e. substantially lower than the regeneration voltage. In this case, there is no short circuit between the inverter's negative and positive input terminal when the regeneration voltage is being supplied and no short circuit between the first and second output terminal of the slave device. The inverter's negative input terminal and the first connected output terminal of the slave device have a lower voltage because of the low voltage generated, for example, by moonlight or current loss. To give an example: when the regeneration voltage is about 900 V, the voltage on the inverter's negative input terminal is about 875 V. In a preferred embodiment of the slave device, there is a highly resistant internal connection between the first and second output terminal, which preferably comprises one or several diodes. Yet more preferably, this internal connection comprises an optical diode to measure the potential difference between the first and second output terminal. In a preferred embodiment, the input voltage is supplied to two or more slave devices. These two or more slave devices are preferably connected in parallel to the input voltage. This improves the scalability of the methods and systems of the present invention. In this case, the two or more slave devices are preferably simultaneously supplied with an input voltage. This provides an easy way to ensure that all slave devices are simultaneously prevented from supplying regeneration voltage to the solar panels, e.g. during the day. In a preferred embodiment, the supply of the input voltage is therefore interrupted at daytime.

In a preferred embodiment, the method for regenerating solar panels comprises the following steps:

measuring the voltage between the positive and the negative input terminals of the inverter. The measured voltage indicates whether the solar panels in the string that are connected to the inverter's negative and positive input terminals, are in an electricity producing phase. If this is the case, the measured voltage will be substantially different from zero, and no regeneration voltage can be supplied to the solar panels. In practice, there will also be a low voltage across a string of panels at night, for example, due to the moonlight. A typical voltage across a string of, for example, 17 panels is 25 V. The measured voltage should therefore drop below a predetermined first threshold before a regeneration voltage can be supplied. That is why the method should also include the following step:

preventing the supply of regeneration DC voltage to the positive and/or negative input terminal of the inverter if the measured voltage is higher than the first predetermined threshold, and preferably the supply of the regeneration DC voltage to the positive and/or negative input terminal of the inverter if the measured voltage is lower than a second predetermined threshold.

The second threshold may be the same as the first one, but is preferably higher than the first threshold to increase the certainty that generation only occurs during non- producing moments.

The first threshold is preferably between 50 V and 160 V, more preferably between 55 V and 140 V, most preferably about 60 V, and/or the second threshold is between 70 V and 200 V, preferably between 80 V and 160 V, most preferably about 90 V.

In a preferred embodiment, the system for generating electricity from solar energy comprises two or more slave devices, whereby the master device is connected to said slave devices, preferably in such a way that the slave devices are connected in parallel to the input voltage supplied by the master device (or from a different perspective, whereby the slave devices are connected to the master device in parallel with the input voltage supplied by the master device). In this case, each of the slave devices are connected to a separate inverter, a separate MPPT, and separate string and/or separate solar panel. In a preferred embodiment of a system with a master device and two or more slave devices that are connected in parallel to the master device, the slave devices are connected to each other in a chain. This ensures that when connecting the second or further slave devices, the wiring, the feed wires in particular and the optional ground wire, will only have to bridge the distance to the nearest slave device. In a preferred embodiment, slave devices may therefore also be equipped with one or more connection contacts with terminals that are connected to the input terminals and optionally the physical grounding of the slave device.

In a preferred embodiment, the master device is configured to supply DC voltage to the high voltage generator of the slave device, and whereby the high voltage generator comprises a DC-DC converter for converting the DC voltage (input voltage) the master device supplies to the regeneration DC voltage, preferably whereby the DC voltage supplied by the master device is a safety DC voltage, more preferably a safety voltage of 80 V maximum, yet more preferably 70 V maximum, and yet more preferably 60 V maximum, most preferably about 48 V. In a preferred embodiment, the master device is configured to stop the supply of DC voltage to the high voltage generator during daytime and preferably to enable supply of DC voltage at night.

The master device is preferably connected to the slave device with two or more electrically conductive power wires to enable the supply of the input voltage. Preferably, the master device is separably connected to the slave device.

In a preferred embodiment, the system comprises a physical grounding, whereby the slave device is connected to the physical grounding and whereby the high voltage generator is preferably configured to generate the regeneration DC voltage with respect to the physical grounding. The slave device is preferably connected to the physical grounding via one or several electrically conductive grounding wires between the slave device and the master device. The connection between the slave device and the physical grounding is preferably interrupted in the master device at daytime.

In a preferred embodiment, the physical grounding is the potential of a solar panel support structure, and the physical grounding is supplied to the master device by a conductive cable connected to said support structure. The physical grounding can be therefore be further supplied to the slave device via the master device, or via another slave device if several slave devices are connected to the master device in a chain. This simplifies the setup for the slave devices, which do not need to separately be connected to the physical grounding, but can be grounded through the master device.

In a preferred embodiment the one or more ground wires and the two or more power wires between the master device and the slave device are located in the same casing.

In a preferred embodiment, the slave device comprises an electrical circuit that is connected to the first and second output terminals of the slave device and optionally to one or several additional output terminals of the slave device, whereby the high voltage generator is configured to supply the regeneration DC voltage to the first and/or second output terminal and/or optionally to one or several additional output terminals. The electrical circuit preferably comprises a high resistance connection, e.g. via one or several diodes, between the first and second output terminal. In a special preferred embodiment, the electrical circuit is switch-free.

In an alternative version, the electrical circuit is configured to prevent internal short circuiting between the first and second output terminal, optionally between at least two of the output terminals and preferably between each pair of output terminals, if there is a potential difference between these output terminals. The electrical circuit makes it possible whether or not to interrupt the supply of regeneration voltage to the inverter, MPPT, string or solar panel, and then specifically when there is a potential difference between the negative and the positive input terminal of the inverter connected to the first and second output terminal of the slave device. This electrical circuit can be implemented switch-free, which will substantially increase the service life of the device and the system. A switch-free circuit can, for example, utilise a high resistance internal connection between the first and second output terminal, whereby the potential difference between the first and second output terminal is preferably measured with an optical diode.

In an alternative version, the electrical circuit is configured to effectively make a short circuit between the negative and the positive input terminal of the inverter when no potential difference exists or is measured between the terminals.

In a preferred embodiment there are one or more additional output terminals to the slave device, whereby each of the additional output terminals is preferably connected to a positive input terminal of an additional inverter, an additional MPPT, an additional string or an additional solar panel, while the negative input terminal of said additional inverter, additional MPPT, additional string or additional solar panel is connected to the first output terminal of the slave device. This means that one slave device can supply a regeneration voltage to several inverters, MPPTs, strings or solar panels. One slave device is preferably provided for one inverter, whereby the inverter may comprise one or more MPPTs, preferably two MPPTs, whereby the slave device can supply each of the MPPTs of the inverter with regeneration voltage. This also enables all strings connected to the same MPPT or the same inverter to be provided with the regeneration voltage supplied by the same slave device.

In a preferred embodiment, the slave device comprises a safety circuit configured to prevent the supply of regeneration DC voltage to the first and/or second output terminal of the slave device, whereby the safety circuit preferably comprises a voltmeter that is configured to measure the voltage between the first and second output terminals and whereby the safety circuit is configured to prevent the supply of regeneration DC voltage to the first and/or the second output terminal of the slave device if the voltage measured between the first and second terminal is substantially different from zero, preferably the supply of regeneration DC voltage is permitted so long as the voltage measured between the first and second output terminals above a first predetermined threshold has dropped and the supply of regeneration DC voltage is prevented when the voltage measured between the first and second output terminals has exceed a second predetermined threshold. As indicated earlier on, the first threshold is preferably lower than the second threshold, the first threshold is preferably about 60 V and the second threshold is about 90 V. In a preferred embodiment, the methods of the present invention comprise the step for determining whether it is night or day by calculating an actual sunrise and/or sunset based on a determination of time and position (for instance via GPS and/or GPRS) of the system.

In a preferred embodiment of the slave device, the input voltage is a DC input voltage and the high voltage generator is configured to convert the DC input voltage into the regeneration DC voltage, preferably whereby the DC input voltage is a safety DC voltage, more preferably a safety voltage of 80 V maximum, yet more preferably 70 V maximum, and even more preferably 60 V maximum, most preferably about 48 V, and preferably whereby the regeneration DC voltage is at least 500 V. In a preferred embodiment, the slave device comprises:

a sensor for measuring the voltage between the first and second output terminals;

an electrical circuit that is connected to the first and second output terminals of the slave device and optionally to one or several additional output terminals of the slave device, whereby the high voltage generator is configured to supply the regeneration DC voltage to the first and/or second output terminals and/or optionally to one or several additional output terminals by means of the electrical circuit. The electrical circuit preferably comprises a high resistance connection, e.g. via one or several diodes, between the first and second output terminal. In a special preferred embodiment, the electrical circuit is switch-free.

In an alternative version, the electrical circuit is configured to prevent internal short circuiting between the first and second output terminals, optionally between at least two of the output terminals and preferably between each pair of output terminals, if the voltage measured by the sensor is substantially different from zero.

In a preferred embodiment, the slave device comprises one or more additional output terminals, whereby the slave device preferably comprises one or more sensors for measuring the voltages between the first output terminals on the one hand and each of the one or more additional output terminals on the other hand.

The following gives a description of the invention based on non-exhaustive examples that illustrate the invention, and which are not intended or may not be interpreted to limit the scope of the invention. EXAMPLES

EXAMPLE 1 :

An example of a version of the present invention is shown in figure 1.

The part to right of the dotted line in figure 1 shows a solar panel system, or 'PV (Photovoltaic) System', connection. The existing PV system may comprise a number of inverters (SOI), two of which are illustrated here. An inverter (SOI) may comprise two MPPTs (TZ1, TZ2). A plurality of solar panels (S03) that are connected in series form a string (S02) and are connected to an inverter (SOI) MPPT (TZ2). Several strings may be connected for each MPPT (TZ2), in this case 3 strings. The part left of the dotted line in figure 1 and the connections to the existing PV system illustrate a version of the present invention. More specifically, a slave device (S05) will be provided for each inverter (SOI), whereby the slave device will be separately connected to each of the MPPTs (TZ1, TZ2) of the inverter (SOI) for supplying the regeneration voltage to the positive and/or negative terminals of the MPPTs. The slave device (S05) is connected in parallel to the MPPT terminals in relation to the strings that are connected to the MPPTs. This way having to interrupt the connections between the MPPTs and the string to connect the slave device to an existing PV system can be avoided. Moreover, this also ensures that during the production phase of the solar panels (S03), the electricity produced does not run through the slave device (S05) or its internal circuits. Each slave device (S05) is equipped with a power supply and other control signals can be optionally provided via a master device (S04). The master device (S04) can supply or disrupt the power depending on whether it is day or night or can transmit control signals to the slave devices (S05), if necessary to each slave device individually, to stop or start the regeneration of the solar panels.

EXAMPLE 2 :

An example of a version of the slave device (S05) according to the present invention is shown in figure 2.

The slave device (S05) comprises:

-a positive input terminal (21) and a negative input terminal (22) for receiving electricity from an input voltage between the positive and negative input terminal. In this case, the input voltage is a direct voltage of about 48 V;

- a first output terminal (23) that can be connected to a negative input terminal of an inverter, an MPPT, a string and/or a solar panel, and a second output terminal (24) that can be connected to a positive input terminal of an inverter, the MPPT, string and/or solar panel. An additional output terminal (25) is also available that can be connected to a positive input terminal of an additional inverter, an additional MPPT (preferably a second MPPT of the same inverter), an additional string and/or an additional solar panel;

- a high voltage generator (26) that comprises a negative input generator terminal (28) connected to the negative input terminal (22) and a positive input generator terminator (27) connected to the positive input terminal (21) and which is configured to convert the input voltage between the negative (22) and positive (21) input terminal into a regeneration DC voltage between a negative output generator terminal (29) and a positive output generator terminal (30). The positive output generator terminal (30) is connected, in this case via an electrical circuit (31) to the first output terminal (23) and the second output terminal (24) as well as to the additional output terminal (25) for supplying the regeneration DC voltage. The negative output generator terminal (29) is connected to a grounding, in this case a physical grounding (PE). The electrical circuit (31) is connected to the first output terminal (23) and the second output terminal (24) of the slave device (S05) and one additional output terminal (25). The high voltage generator (26) is configured to supply the regeneration DC voltage to the first and second output terminal and the additional output terminal via the electrical circuit (31) Here the electrical circuit (31) is equipped with diodes (32, 33, 34, 35) that effectively short circuit the first output terminal (23) and the second output terminal (24), as well as the additional output terminal (25) if there is no potential difference (V) between the first (23) and second (24) output terminals. This potential difference (V) can be measured by a sensor (36). The sensor (36) preferably has a high internal electrical resistance, so that the current produced by the solar panels during the production phase, which flows through the sensor, is insignificant. If the solar panels are in the production phase, i.e. producing electricity by photovoltaic effect, diodes 32 and 33 ensure that a short circuit cannot occur between the first output terminal (23) connected to the negative input terminal of an inverter, MPPT, string or solar panel on the one hand and the second output terminal (24) or the additional output terminal (25) connected to the positive input terminals of the inverter, MPPT, string or solar panel on the other hand. Diode (34) and diode (35) ensure that the second output terminal (24) and the additional output terminal (25) are not effectively short circuited during the electricity producing phase of the solar panels. This enables the second output terminal (24) and the additional output terminal (25) to be connected to different inverters, different MPPTs, different strings and/or different solar panels.

The slave device (S05) also comprises a safety circuit configured to prevent the supply of regeneration DC voltage to the first output terminal (23) and the second output terminal (24) as well as the additional output terminal (25) of the slave device (S05). To this end, the safety circuit comprises a voltmeter (36), e.g. based on an optical diode, which is configured to measure the voltage (V) between the first output terminal (23) and the second output terminal (24). The safety circuit is configured to prevent the supply of regeneration DC voltage to the output terminals (23, 24, 25) if the measured voltage (V) exceeds a threshold voltage, e.g. above 160 V, by switching off the high voltage generator (26). If the voltage (V) that is measured, drops below a threshold voltage, e.g. below 120 V, the functioning of the high voltage generator will be enabled.

It is assumed that the present invention is not limited to the versions described above and that some adjustments or modifications to the described examples can be added without reassessing the added conclusions. For example, the present invention was described with reference to a first output terminal that is or can be connected to a negative input terminal of an inverter, MPPT or string of solar panels, but it is clear that a slave device can be equipped with different output terminals that are configured to be connected to a negative input terminal of an inverter, MPPT or string of solar panels. The different output terminals that can be connected to the negative input terminal of an inverter can be connected internally or can be separated. It is also possible that duplicate components are removed from the slave device, particularly from the output terminals.

Claims

CONCLUSIONS

1. A method for regenerating solar panels which are connected in one or several strings, whereby at least one string is connected between an inverter's positive input terminal and the inverter's negative input terminal for supplying a DC voltage generated by solar energy, whereby the method comprises the following steps:

supplying an input voltage to a slave device, whereby said input voltage is at most a 80 V DC voltage;

- generating a regeneration DC voltage in the slave device from the input voltage, preferably whereby said regeneration DC voltage is at least 500 V; supplying the regeneration DC voltage to a positive input terminal and/or a negative input terminal of the inverter.

2. A method according to the preceding conclusion 1, whereby the input voltage is supplied parallel and essentially simultaneously to two or more slave devices that are connected to each other in a chain.

3. A method according to any one of the preceding conclusions 1 or 2, comprising :

measuring the voltage between the positive and the negative input terminals of the inverter;

supplying the regeneration DC voltage to the positive and/or negative input terminal of the inverter if the measured voltage is essentially zero, and preventing the supply of the regeneration DC voltage to the positive and/or negative input terminal of the inverter if the measured voltage is substantially different from zero.

4. A system for generating electricity from solar energy, comprising :

a plurality of solar panels that are connected in one or several strings, whereby at least one string is connected between an inverter's positive input terminal and the inverter's negative input terminal for supplying a DC voltage generated by the solar energy, whereby the inverter is configured to convert said DC voltage between the positive and negative input terminals into an alternating voltage, and to provide said alternating voltage to output terminals of the inverter;

a slave device with a first output terminal connected to the inverter's positive input terminal and a second output terminal connected to the inverter's negative input terminal, whereby the slave device comprises a high voltage generator, whereby said high voltage generator is configured to generate a regeneration DC voltage from an input voltage, and whereby the slave device is configured to supply the regeneration DC voltage to the first and/or second output terminal of the slave device, preferably whereby the high voltage generator comprises a DC-DC converter for converting the input voltage to the regeneration DC voltage;

a master device that is connected to the slave device and configured to supply the input voltage to the slave device's high voltage generator, whereby said input voltage is at most a 80 V DC voltage.

A system according to the preceding conclusion 4, comprising two or more slave devices, whereby said slave devices are connected to the master device in parallel with respect to the input voltage supplied by the master device. A system according to any one of the preceding conclusions 4 or 5, further comprising a physical grounding, whereby the slave device is connected to the physical grounding via the master device and whereby the high voltage generator is configured to generate the regeneration DC voltage with respect to the physical grounding.

A system according to any one of the preceding conclusions 4 to 6, whereby the slave device comprises an electrical circuit that is connected to the first and second output terminals of the slave device and optionally to one or several additional output terminals of the slave device, whereby the high voltage generator is configured to supply the regeneration DC voltage to the first and/or second output terminals and/or optionally to one or several additional output terminals via the electric circuit, whereby the electrical circuit is configured to prevent an internal short circuit out between the first and the second output terminal of the slave device, optionally between at least two of the output terminals and preferably between each pair of output terminals if a potential difference is present between these output terminals. A system according to any one of the preceding conclusions 4 to 7, whereby the slave device comprises a safety circuit configured to prevent the supply of the regeneration DC voltage to the first and/or second output terminals of the slave device, whereby the safety circuit comprises a voltmeter that is configured to measure the voltage between the first and second output terminal and whereby the safety circuit is configured to prevent the supply of regeneration DC voltage to the first and/or the second output terminal of the slave device if the voltage measured between the first and second terminal is substantially different from zero.

9. A method for generating electricity from solar energy with a system according to any one of the preceding conclusions 4 to 8, comprising the steps:

preventing the supply of a regeneration DC voltage to solar panel terminals during daytime by implementing one or several of the following steps:

· interrupting the supply of the input voltage by the master device, whereby said input voltage is at most a 80 V DC voltage;

• interrupting the generation of the regeneration DC voltage via the high voltage generator;

regenerating solar panels at night-time according to a method according to any one of the preceding conclusions 1 to 3.

10. A method according to the preceding conclusion 9, comprising the step of determining whether it is day or night by calculating an effective sunrise and/or sunset based on a determination of time and position of the system.

11. A slave device for regenerating solar panels that are connected in one or several strings, whereby at least one string is connected between an inverter's positive input terminal and the inverter's negative input terminal for supplying a DC voltage generated by solar energy, the slave device comprising :

a positive input terminal and a negative input terminal for receiving electricity by an input voltage between the positive and negative input terminal;

- a first output terminal suitable for being connected to the negative input terminal of the inverter and/or a string, and a second output terminal suitable for being connected to a positive input terminal of the inverter and/or a string, the first and second output terminal configured for supplying electricity for a regeneration DC voltage;

- a high voltage generator that comprises a negative input generator terminal connected to the negative input terminal and a positive input generator terminal connected to the positive input terminal and which is configured to convert the input voltage between the negative and positive input terminals into a regeneration DC voltage between a negative output generator terminal and a positive output generator terminal,

whereby the positive output generator terminal is or can be connected via an electrical circuit to the first output terminal and/or the second output terminal for supplying the regeneration DC voltage.

12. A slave device according to the preceding conclusion 11, whereby the input voltage is at most 80 V DC, and the high voltage generator is configured to convert the DC input voltage into the regeneration DC voltage of at least 500 V.

13. A slave device according to any one of the preceding conclusions 11 or 12, further comprising :

a sensor for measuring the voltage between the first output terminal and the second output terminal.

an electrical circuit that is connected to the first and second output terminals of the slave device and optionally to one or several additional output terminals of the slave device, whereby the high voltage generator is configured to supply the regeneration DC voltage to the first and/or second output terminal and/or optionally to the one or several additional output terminals via the electrical circuit, whereby the electrical circuit is preferably configured to prevent internal short circuiting between the first and second output terminals, optionally between at least two of the output terminals and preferably between each pair of the output terminals if the voltage measured by the sensor is substantially different from zero.

14. A slave device according to any one of the preceding conclusions 11 to 13, comprising one or more sensors for measuring the voltages between the first output terminal on the one hand and the second and optionally one or more additional output terminals on the other hand.

15. A method for installing a slave device, consisting of the steps:

providing a slave device according to any one of the preceding conclusions 11 to 14;

connecting a negative and a positive input terminal of the slave device to an input voltage source;

connecting the first output terminal of the slave device to a negative terminal of a solar panel, a string of solar panels, an inverter to which a string of panels can be optionally connected, and/or a maximum power point tracker (MPPT) to which a string of solar panels can be optionally connected;

connecting the second output terminal of the slave device to a positive terminal of a solar panel, a string of solar panels, an inverter to which a string of solar panels can be optionally connected, and/or a maximal power point tracker (MPPT) to which a string of solar panels can be optionally connected.