Photovoltaic panel control system

Abstract

A control system 350 for a photovoltaic, PV, panel 190, the PV panel comprising a plurality of PV modules 185-n, wherein the control system comprises one or more processors configured to: receive an e

Description

TECHNICAL FIELD The present disclosure relates to a photovoltaic (PV) panel control system. Aspects of the invention relate to a control system for a photovoltaic (PV) panel, to a system, to a vehicle, and to a computer-implemented method for a photovoltaic (PV) panel. BACKGROUND It is known to provide photovoltaic panels which convert sunlight incident on the panels into electrical energy. Such panels may be installed, for example, on a building or on a vehicle. Different issues may arise which reduce the efficiency of the panel to convert sunlight to electricity, such as soiling / dirt, and electrical connection faults. It can be a challenge to identify when there is an issue, and what that issue is, and therefore how to remedy it (and whether an intervention is indeed useful or whether the issue is likely to remedy itself). It is an aim of the present invention to address one or more of the disadvantages associated with the prior art. SUMMARY OF THE INVENTION Aspects and embodiments of the invention provide a photovoltaic (PV) panel control system. Aspects of the invention relate to a control system for a photovoltaic (PV) panel, to a system, to a vehicle, and to a computer-implemented method for a photovoltaic (PV) panel, as claimed in the appended claims. According to an aspect of the present invention there is provided a control system for a photovoltaic, PV, panel, the PV panel comprising a plurality of PV modules, wherein the control system comprises one or more processors collectively configured to, for at least one PV module of the plurality of PV modules: receive a reference energy signal indicative of an amount of solar radiation incident on the PV module; determine a generation threshold indicative of an expected amount of electrical energy generated by the PV module in dependence on the reference energy signal; receive an energy signal indicative of an amount of electrical energy generated by the PV module; and if the amount of electrical energy generated by the PV module is below the generation threshold, output a PV panel status signal indicative of the operation status of the PV panel. Advantageously, unexpected electrical energy generation characteristics of a PV module in a PV panel comprising a plurality of PV modules can be determined and indicated. By considering the operation on a per module basis, determination of the operation status of the PV panel can be more intelligently made. Throughout this description, a PV panel may be understood to comprise a plurality of electrically connected PV modules, and each PV module may be understood to comprise a plurality of electrically connected PV cells. Each PV cell may be understood to be configured to convert light / solar energy into electrical energy. According to an aspect of the present invention there is provided a control system for a photovoltaic, PV, panel, the PV panel comprising a plurality of PV modules, wherein the control system comprises one or more processors collectively configured to, for at least one PV module of the plurality of PV modules: receive an energy signal from the PV module, the energy signal indicative of an amount of electrical energy generated by the PV module; receive a reference energy signal from a solar sensor, the reference energy signal indicative of an amount of solar radiation incident on the solar sensor; determine, in dependence on the reference energy signal, a generation threshold indicative of an expected amount of electrical energy generated by one or more of the plurality of PV modules; if the amount of electrical energy generated by the PV module is below the generation threshold, compare the amount of electrical energy generated by the PV module with an amount of electrical energy generated by at least one further PV module of the plurality of PV modules; determine an operation status of the PV panel in dependence on the comparison; and output a PV panel status signal indicative of the operation status of the PV panel. Advantageously, the PV modules can be compared to each other to determine the operation status of the PV panel per module, rather than simply considering the operation of the PV panel overall. By considering the operation on a per module basis, determination of the operation status of the PV panel can be more intelligently made. Typically electronic outputs, such as current and voltage outputs, are already present per module so these can be used for PV module monitoring on a per module basis without adaptation of the PV panel modules. 1 The generation threshold may equal the expected amount of electrical energy generated by one or more of the plurality of PV module in some examples. For example, this may be the case when comparing the electrical energy generation performance of a PV module with an expected amount of electrical energy generation for a PV module. The generation threshold may be equal to the expected amount of electrical energy generated by a PV module multiplied by a multiplier factor in some examples, for example, a multiplier factor associated with a plural number of PV modules being taken into account (in some examples, the plural number of PV modules may be all the PV modules of a PV panel). The control system may comprise one or more controllers collectively comprising at least one electronic processor having an electrical input for receiving an input signal; and at least one memory device electrically coupled to the at least one electronic processor and having instructions stored therein; and wherein the at least one electronic processor is configured to access the at least one memory device and execute the instructions thereon so as to: receive an energy signal from the PV module, the energy signal indicative of an amount of electrical energy generated by the PV module; receive a reference energy signal from a solar sensor, the reference energy signal indicative of an amount of solar radiation incident on the solar sensor; determine, in dependence on the reference energy signal, a generation threshold indicative of an expected amount of electrical energy generated by one or more of the plurality of PV modules; if the amount of electrical energy generated by the PV module is below the generation threshold, compare the amount of electrical energy generated by the PV module with an amount of electrical energy generated by at least one further PV module of the plurality of PV modules; determine an operation status of the PV panel in dependence on the comparison; and output a PV panel status signal indicative of the operation status of the PV panel. The control system may be configured to determine the operation status of the PV panel to be a single module operation fault status in dependence on the amount of electrical energy generated by the PV module being below a threshold proportion of the amount of electrical energy generated by at least one further PV module. The control system may be configured to determine the operation status of the PV panel to be a plural module operation fault status in dependence on the amount of electrical energy generated by the PV module and the amount of electrical energy generated by the at least one further PV module being below a threshold proportion of an amount of electrical energy obtainable from the PV module and the at least one further PV module, the amount of electrical energy obtainable from the PV module and the at least one further PV module determined in dependence on the amount of solar radiation incident on the solar sensor. Advantageously, a determination may be made whether there is a fault with a single PV module or plural PV modules and which PV modules are faulty. Rather than simply considering the operation of the PV panel overall, determination of the operation status of the PV panel can be more intelligently made on a per-PV module basis. If there is an error with a PV module this can be flagged to a user, otherwise a user may not be aware of an error with a particular module because the PV panel may not be readily visible. Also typically an error may be flagged in relation to operation of the overall PV panel, but here an issue with a specific module or modules of the PV panel may be provided to aid maintenance. The threshold proportion may be an amount between 0 and 1 times the total amount of electrical energy obtainable from the PV module. For example, the threshold proportion may be 0.95x, 0.9x, 0.8x, 0.75x, 0.6x, 0.5x, or another multiplier, multiplied by the total amount of electrical energy obtainable from the PV module. Advantageously, a fault may be determined with the electrical energy conversion capability of a PV module if the energy conversion capability is lower than a threshold expected value. For example, it may be undesirable to flag a fault if the PV module is operating at a sufficiently high electrical conversion rate (e.g. 98% of the total theoretically possible amount of energy conversion). In some examples, the PV panel may be attached to a vehicle. Advantageously, a PV panel on a vehicle may be monitored. This may be desirable because a PV panel on a vehicle is typically located on top of the roof where it is not readily visible to a user. Furthermore, factors affecting the operation of PV modules of the PV panel in a vehicle may relate to issues specific to a movable PV panel. The operation status and remedies for an error of operation of the PV panel may be tailored for a PV panel which may be moved (i.e. by the vehicle being driven). An example may be poor energy conversion by a PV module which has a leaf or other loose debris covering it. On the vehicle being driven, the leaf / loose debris is likely to be displaced, and the PV module able to operate as expected (i.e. to generate electrical energy from indecent solar energy), so there may be no need 2 to provide any indication of the temporary inability of that PV module to efficiency generate electrical energy. As another example, if the energy generated by a PV module is low and that of the neighbouring PV module is as expected, even after the vehicle has been driven, then a “local persistent soiling” error may be flagged. The control system may be configured to determine an operation status of a module connection error in dependence on the amount of electrical energy generated by the PV module being substantially zero, and the amount of electrical energy generated by the at least one further PV module being a non-zero amount. The control system may be configured to determine an operation status of a local soiling error in dependence on the amount of electrical energy generated by the PV module being lower than the amount of electrical energy generated by the at least one further PV module, wherein the at least one further PV module is directly neighbouring the PV module. The control system may be configured to determine an operation status of a general soiling error in dependence on the amount of electrical energy generated by the PV module, and the amount of electrical energy generated by the at least one further PV module directly adjacent to the PV module, each being below a threshold proportion of an amount of electrical energy obtainable from the PV module and the at least one further PV module, the amount of electrical energy obtainable from the PV module and the at least one further PV module determined in dependence on the amount of solar radiation incident on the solar sensor. Advantageously, different detected characteristics of the PV module may be processed by the control system which may then determine the type of error according to the detected characteristics. Typical errors which may occur for a PV module include an electrical connection fault for the module, a local soiling error (for example due to bird droppings on module), or a general soiling error (for example due to a buildup of dust or plant matter). The control system may be configured to determine a maintenance action in dependence on the operation status; and output a maintenance signal to an indicator apparatus to cause the indicator apparatus to indicate a suggested maintenance of the PV module. Examples include an operation status of a module connection error with a suggested maintenance of checking the electronic connections; an operation status of a local soiling error with a suggested maintenance of checking for and cleaning off local soiling such as bird droppings; and an operation status of general soiling error with a suggested maintenance of cleaning off general soiling, such as built-up dust covering the panel. Advantageously, alongside being able to determine the type of error present, the control system is able to suggest a maintenance action to remedy the problem. For example, the suggested maintenance in the event of detecting an electrical connection fault will be different to the situation where the detected error is determined to be a soiling issue. The energy signal may be derived from one or more of: a sensed current through the PV module, a sensed voltage across the PV module; a sensed temperature of the PV module, and a sensed resistance of the PV module. Advantageously, current and voltage are typically already obtainable for a PV module without additional adaptation of current PV panel hardware; resistance may be derived from current and voltage, and temperature sensors such as thermistors or thermocouples may be fitted to the PV panel to allow temperature monitoring to give a full picture of operation of the PV modules. The control system may be configured to, if the amount of electrical energy generated by the PV module is above the generation threshold, inhibit comparison of the amount of electrical energy generated by the PV module with an amount of electrical energy generated by at least one further PV module of the plurality of PV modules. Advantageously, if the overall PV panel is determined to be operating as expected, then the control system can inhibit analysing the operation per PV module, at least for a time to save processing effort and power. The control system may be configured to store, in a historical PV operation log, over an operational time period, historical PV module operating data comprising: the amount of electrical energy generated by the PV module, and one or more of: the amount of solar radiation incident on the solar sensor, and the amount of electrical energy generated by at least one further PV module, and determine the operation status of the PV panel further in dependence on the historical PV module operating data. Advantageously, the historical operation of the PV modules of the PV panel can be logged and used by the control system in analysing new data from the PV modules to help determine whether there is a fault. The control system may be configured to determine the operation status of the PV panel by adapting the expected amount of electrical energy generated by one or more of the plurality of PV modules according to a lifetime degradation factor arising from usage of the PV panel. The expected 3 amount of electrical energy generated may be the electrical energy by one or more of the plurality of PV modules, or all the PV modules of the PV panel, in which case the expected amount of electrical energy is that expected to be generated by the PV panel. Advantageously, account may be taken of the lifetime of the PV panel and PV modules, as typically it is expected that the efficiency of operation would reduce over time / usage. The control system may be configured to determine an indicator provision time at which the control system is to output the PV panel status signal in dependence on one or more of: a frequency of variation of the amount of electrical energy generated by the PV module compared with amount of solar radiation incident on the solar sensor; a time duration of a threshold difference between the amount of electrical energy generated by the PV module compared with the amount of solar radiation incident on the solar sensor; and the PV panel operation status indicative of a PV panel error status in a predetermined number of consecutive drive cycles (e.g. a key on / key-off event). Advantageously, the control system can intelligently determine an appropriate time to flag a potential error to a user, to find a balance between informing the user of an error early enough to remedy it (in some cases before additional or more permanent faults develop because the initial fault was not remedied) and avoiding flagging every fluctuation or temporary error to a user which is not useful and may be annoying to the user. The indicator apparatus to which the control system is configured to output the PV panel status signal may comprise one or more of: an in-vehicle output apparatus; a user portable personal electronic device; and a home output device. Advantageously there are different ways in which the user may be informed of the status of the PV modules. The control system may be configured to receive one or more environmental parameters indicative of an environmental factor of the PV panel, and determine the operation status of the PV module further in dependence on the one or more environmental factors. Advantageously the environment of the vehicle can be accounted for, for example to assist in providing relevant, timely and / or appropriate alerts regarding the operation of the PV panel. The one or more environmental factors may comprise one or more of: a speed of movement of the PV panel; a duration of movement of the PV panel; a current location of the PV panel; the presence of a barrier apparatus located to block solar energy from reaching at least part of the PV panel; and a current or recent weather condition in the location of the PV panel. Advantageously, the environment of the PV panel may be taken into account in the processing of the control system to determine whether there is an error with the PV module. For example if the PV panel is affixed to a vehicle, then a local soiling error may be monitored before, during, and after movement of the vehicle to determine whether the soiling was temporary, such as by a leaf resting on the panel, or more permanent, such as by bird droppings blocking sunlight from reaching the PV module. In an aspect there is provided a system comprising: any control system disclosed herein, and a PV panel comprising the plurality of PV modules. Advantageously, the control system and PV panel may be provided together as a system so the control panel can be connected to and operate with the PV panel. The system may further comprise a solar energy detection module configured to detect an amount of solar energy received by the PV panel. Advantageously, the solar energy detection module may also be provided with the system to allow for the control system to obtain the expected amount of solar energy of the PV module. The system may further comprise an indicator apparatus in some examples. In an aspect there is provided a vehicle comprising any control system disclosed herein, or any system disclosed herein. Advantageously, a vehicle comprising a control system and a PV panel may be provided so a user of the vehicle can be informed of the operation of the PV panel on a per module basis. In an aspect there is provided a computer-implemented method for a photovoltaic, PV, panel, the PV panel comprising a plurality of PV modules, the method comprising, for at least one PV module of the plurality of PV modules: receiving an energy signal from the PV module, the energy signal indicative of an amount of electrical energy generated by the PV module; receiving a reference energy signal from a solar sensor, the reference energy signal indicative of an amount of solar radiation incident on the solar sensor; determine, in dependence on the reference energy signal, a generation threshold indicative of an expected amount of electrical energy generated by one or more of the plurality of PV modules; if the amount of 4 electrical energy generated by the PV panel is below the generation threshold, comparing the amount of electrical energy generated by the PV module with an amount of electrical energy generated by at least one further PV module of the plurality of PV modules; determining an operation status of the PV module in dependence on the comparison; and outputting a PV panel status signal indicative of the operation status of the PV panel. Advantageously, a PV panel comprising a plurality of PV modules can be intelligently monitored for operation status and potential faults. In an aspect there are provided computer readable instructions which, when executed by one or more processors, cause the one or more processors to perform any method disclosed herein. Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and / or in the following description and drawings, and in particular the individual features thereof, may betaken independently or in any combination. That is, all embodiments and / or features of any embodiment can be combined in any way and / or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and / or incorporate any feature of any other claim although not originally claimed in that manner. BRIEF DESCRIPTION OF THE DRAWINGS One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a control system in accordance with embodiments of the invention; Figure 2 shows a PV panel comprising a plurality of PV modules; Figure 3A shows a method in accordance with embodiments of the invention; Figure 3B shows a system comprising a control system in accordance with embodiments of the invention; Figure 4 shows a method in accordance with embodiments of the invention; and Figure 5 shows a vehicle in accordance with embodiments of the invention. DETAILED DESCRIPTION With reference to Figure 1, there is illustrated a control system 100 for a photovoltaic (PV) panel, the PV panel comprising a plurality of PV modules. Throughout this description, a PV panel may be understood to comprise a plurality of electrically connected PV modules, and each PV module may be understood to comprise a plurality of electrically connected PV cells. Each PV cell may be understood to be configured to convert light / solar energy into electrical energy. An example is shown in Figure 2. The control system 100 comprises one or more controller 110. The control system 100 as illustrated in Figure 1 comprises one controller 110, although it will be appreciated that this is merely illustrative. The controller 110 comprises processing means 120 and memory means 1130. The processing means 120 may be one or more electronic processing device 120 which operably executes computer-readable instructions. The memory means 130 may be one or more memory device 130. The memory means 130 is electrically coupled to the processing means 120. The memory means 130 is configured to store instructions, and the processing means 120 is configured to access the memory means 130 and execute the instructions stored thereon. The controller 110 comprises an input means 140 and an output means 150. The input means 140 may comprise an electrical input 140 of the controller 110. The output means 150 may comprise an electrical output 150 of the controller 100. The control system 100 is configured to receive data from a PV module sensor 160 (e.g. a current sensor, a voltage sensor, or a temperature sensor) and determine an operation status of the PV module depending on the received data. The input 140 is arranged to receive a signal 165, indicative of the data from a PV module sensor 160, such as an energy signal 165 indicative of an amount of electrical energy generated by the PV module. The energy signal 165 is an electrical signal. The control system 100 is configured to output a control signal 155 to indicate the operation of the PV module (and therefore the PV panel of which the PV module is a part). The output 150 is arranged to output a PV panel status signal 155 which is indicative of the operation status of the PV panel. For example, the control system 100 may be configured to, for at least one PV module of the plurality of PV modules: receive an energy signal 165 from the PV module. The energy signal 165 is indicative of an amount of electrical energy generated by the PV module. The control system 100 may be configured to receive a reference energy signal 167 from a solar sensor 162. The reference energy signal 167 is indicative of an amount of solar radiation incident on the solar sensor. The control system 100 may be configured to determine a generation threshold indicative of an expected amount of electrical energy generated by the PV module 160 in dependence on the reference energy signal 167. The solar energy sensor 162 providing the reference energy signal 167 may be a light dependent resistor element 162 or similar solar energy sensor distinct from the PV modules of the PV panel. If the amount of electrical energy generated by the PV module is below the generation threshold, the control system 100 may be configured to compare the amount of electrical energy generated by the PV module with an amount of electrical energy generated by at least one further PV module of the plurality of PV modules, determine an operation status of the PV panel in dependence on the comparison, and output a PV panel status signal 155 indicative of the operation status of the PV panel (e.g. to an indicator device 170 such as a display screen). The operation status may indicate that there is an electrical energy generation inefficiency or error for a particular PV module. Advantageously, unexpected electrical energy generation characteristics of a PV module in a PV panel comprising a plurality of PV modules can be determined and indicated. The indicator apparatus to which the control system is configured to output the PV panel status signal 155 may comprise one or more of: an in-vehicle output apparatus (if the PV panel is located on a vehicle); a user portable personal electronic device such as smartphone or table computer; a home output device such as a desktop computer, and a home charger device for an electric vehicle. Advantageously there are different ways in which the user may be informed of the status of the PV modules. By considering the operation on a per module basis (and / or on a per-cell basis in some examples), determination of the operation status of the PV panel can be more intelligently made. The PV modules can be compared to each other to determine the operation status of the PV panel per module, rather than simply considering the operation of the PV panel overall. Typically electronic outputs, such as current and voltage outputs, are already present per module so these can be used for PV module monitoring on a per module basis without adaptation of the PV panel modules. Furthermore, the control system may initially check the electrical energy output of the overall PV panel is as expected, and then check for electrical energy generation on a per-PV module basis if the electrical energy generation of the overall PV panel is lower than expected. This is a processingefficient manner for determining the operation of the PV panel on a per-PV module basis, triggering the per-PV module checks if overall the PV panel is not operating as well as expected. The generation threshold may equal the expected amount of electrical energy generated by one or more of the plurality of PV modules, for example, if comparing the electrical energy generation performance of a PV module with an expected amount of electrical energy generation for a PV module. The generation threshold may equal the expected amount of electrical energy generated by a PV module multiplied by a multiplier factor in some examples, for example if comparing the electrical energy generated by one PV module to that generated by four neighbouring PV modules, the generation threshold considered for the single PV module under review may be one quarter of the total of the four neighbouring modules. Figure 2 illustrates a PV panel 190. The PV panel 190 comprises a plurality of PV modules 185, for example arranged in a row as shown (in other examples the PV modules may be arranged in a 2D grid to form the PV panel). Each PV module may be comprised of a plurality of PV cells 180, for example arranged in a grid as shown (other grid dimensions, geometries, and arrangements e.g. a linear collection of PV cells, are also possible). Each PV module 185 may have dedicated electrical connections and advantageously, the control systems 100 disclosed herein, such as that of Figure 1, can make use of the electrical parameters readable from each PV module 185 through the existing electrical connections to obtain information about the operation of the PV panel 190 on a per-PV module 185 basis. In some examples, each PV cell 180 may have dedicated electrical connections and advantageously, the control systems 100 disclosed herein, such as that of Figure 1, can make use of the electrical parameters readable from each PV cell 180 through the existing electrical connections to obtain information about the operation of the PV panel 190 on a per-PV cell 180 basis. While examples presented herein discuss managing a PV panel comprising PV modules by considering energy signals from PV modules to determine an operation status of a PV module, in some examples energy signals may be obtained from the PV cells on a cell-by-celI basis (as well as, or instead of, a module-by-module basis) to determine an operation status of a PV cell (and therefore of a PV panel comprising the PV cell(s)). In some examples, there may be a PV panel comprising a plurality of PV cells without arrangement of PV cells into a PV module or modules. This disclosure therefore covers examples considering operation of PV cells of a PV panel; PV cells of a PV module or modules of a PV panel, and PV modules of a PV panel. Discussions herein which relate to a PV module may in other examples relate to a PV cell, or to a PV cell and a PV module (i.e. for an approach which considers plural levels of modularity of the PV panel). The PV element (whether a PV cell, PV module, and / or PV panel), which is the subject of the examples discussed herein, may provide an energy signal indicative of an amount of electrical energy generated by the PV element to the control system which may determine a generation threshold indicative of an expected amount of electrical energy generated by one or more of the PV cells and / or PV modules (the PV elements). If the amount of electrical energy generated by the PV element is below the generation threshold, the control system may compare the amount of electrical energy generated by the PV element with an amount of electrical energy generated by at least one further PV element (e.g. a comparable element, such as another PV cell if the PV element under analysis is a PV cell) of the plurality of PV elements. The control system may then determine an operation status of the PV panel in dependence on the comparison, and output a PV panel status signal indicative of the operation status of the PV panel (based on the operation status determined of the PV element). Provided the PV element under analysis (e.g. a cell, a module) is able to provide an energy signal to the control system, then the operation of that PV element may be determined and used to report on the operation of the PV panel. Figure 3A illustrates a computer-implemented method 300 according to an embodiment of the invention. The method 300 is a method for a PV panel 190 comprising a plurality of PV modules 185. The PV panel 190 may be a PV panel of a vehicle 500, such as the vehicle 500 illustrated in Figure 5. The method 300 maybe performed by the control system 100 illustrated in Figure 1. In particular, the memory means 130 may comprise computer-readable instructions which, when executed by the processing means 120, perform the method 300 according to an embodiment of the invention. The method 300 may be performed for at least one PV module 185 of the plurality of PV modules of the PV panel 190. The method 300 comprises a step 302 of receiving an energy signal 310 from the PV module. The energy signal 310 is indicative of an amount of electrical energy generated by the PV module. The energy signal 310 may be derived from, for example, a sensed current through the PV module as measured by an ammeter of the PV module, and / or a sensed voltage across the PV module as measured by a voltmeter or potentiometer of the PV module. The energy signal may be derived from, for example, a sensed resistance of the PV module determined using a sensed current and voltage of a PV module. The energy signal may be derived from, for example, a sensed temperature of the PV module sensed by a thermistor or other thermal sensor in connection with the PV module. Current and voltage are typically already obtainable for a PV module 185 without additional adaptation of current PV panel hardware, and resistance may be derived from current and voltage, which allows for sensing of the operation of a PV module without additional hardware adaptation of the PV modules. Temperature sensors such as thermistors or thermocouples may befitted to the PV panel to allow temperature monitoring to give a full picture of operation of the PV modules. The method 300 comprises a step 304 of receiving a reference energy signal 312 from a solar sensor. The reference energy signal 312 is indicative of an amount of solar radiation incident on the solar sensor. For example, the solar sensor may be separate from the PV panel and may be exposed to solar energy similarly to the PV panel (for example, the solar sensor and PV panel may be located next to each other on a surface). By receiving sunlight at a separate solar sensor from the PV panel and obtaining an electrical signal representative of the received sunlight by the solar sensor, a reference is obtained with which to compare the energy received (and converted to electrical energy) by the PV modules 185 of the PV panel 190. The method 300 comprises a step 306 of determining, in dependence on the reference energy signal 312, a generation threshold 314 indicative of an expected amount of electrical energy generated by one or more of the plurality of PV modules. That is, by obtaining the reference level of sunlight to electrical energy conversion using the solar sensor, a threshold amount of electrical energy expected to be converted from sunlight by the PV module (in the absence of problems preventing operation of the PV module, such as dirt covering the PV module or connection errors) can be calculated. As a simplistic example, the reference energy signal 312 may indicate an amount of incident light energy per second reaching the solar sensor. A multiplier factor may be used to scale the amount of incident light reaching the solar sensor to an amount of incident light reaching the PV module per second (e.g. if the solar energy collector area of the PV module is 300 times larger than the solar energy collector area of the solar sensor, the multiplier factor is 300. The amount of solar energy received by the solar sensor may then be multiplied by 300 to obtain a value comparable to the expected value of solar energy converted to electrical energy by the PV module). An efficiency of the PV module solar energy conversion may be obtained based on a comparison of the solar energy received by the solar sensor and that detected as being received by the PV module. Of course this is a simple example and other considerations in determining the efficiency of solar energy conversion to electrical energy by PV modules may be accounted for. The generation threshold 314 may be determined and represents an acceptable minimum level of solar energy conversion to electrical energy. If the electrical energy produced by the PV module is above this generation threshold, this may be taken to indicate the PV module is working well enough, and that there is no issue which is causing a lower than expected level of energy conversion. Therefore, in some examples, the control system 100 may be configured to, if the amount of electrical energy generated by the PV module is above the generation threshold, inhibit comparison of the amount of electrical energy generated by the PV module with an amount of electrical energy generated by at least one further PV module of the plurality of PV modules. Advantageously, if the overall PV panel is determined to be operating as expected, then the control system 100 can inhibit analysing the operation per PV module, at least for a time to save processing effort and power. If the amount of electrical energy generated by the PV panel is at or above the generation threshold 314, this may be understood to indicate that there is no need to further check the operation of the PV module, because it is working as expected, and so the method may end at that point. However, if the amount of electrical energy generated by the PV module is below the generation threshold 314, the method 300 can take steps to determine why that may be, and provide a suitable indication of what a problem may be with the PV module(s) not performing as expected. The method 300 comprises, if the amount of electrical energy generated by the PV panel is below the generation threshold 314, a step 308 of comparing the amount of electrical energy generated by the PV module (which may be called the PV module under review), determined from the signal 310, with an amount of electrical energy generated by at least one further PV module of the plurality of PV modules. The at least one further PV module may be an immediately adjacent PV module to the PV module under review, may be plural PV modules immediately adjacent to the PV module under review, or may be one or more PV modules located separately from (i.e. not immediately adjacent to) the PV module under review. If the amount of electrical energy generated by the PV panel is below the generation threshold 314, then following the comparison step 308, the method 300 comprises a step 310 of determining an operation status of the PV module in dependence on the comparison of the amount of electrical energy generated by the PV module with the amount of electrical energy generated by at least one further PV module of the plurality of PV modules. The method 300 then comprises a step 320 of outputting a PV panel status signal 316 indicative of the operation status of the PV panel. For example, the control system 100 may be configured to determine the operation status of the PV panel to be a single module operation fault status in dependence on the amount of electrical energy generated by the PV module being below a threshold proportion of the amount of electrical energy generated by at least one further PV module. The output of a PV module is compared to that of another PV module of the PV panel to determine if its electrical energy output is lower than that of the further PV module. This may be the case, for example, if a bird dropping or other matter is attached to the PV module, blocking the path of sunlight to the PV module, but the soiling is localised on the PV module and is not present elsewhere on the PV panel. For example, the control system 100 may be configured to determine an operation status of a local soiling error in dependence on the amount of electrical energy generated by the PV module being lower than the amount of electrical energy generated by the at least one further PV module, wherein the at least one further PV module is directly neighbouring the PV module. As another example, the control system 100 may be configured to determine the operation status of the PV panel to be a plural module operation fault status in dependence on the amount of electrical energy generated by the PV module and the amount of electrical energy generated by the at least one further PV module being below a threshold proportion of an amount of electrical energy obtainable from the PV module and the at least one further PV module. The amount of electrical energy obtainable from the PV module and the at least one further PV module may be determined in 8 dependence on the amount of solar radiation incident on the solar sensor. As a simplistic example, for a PV panel of ten PV modules (labelled 0 to 9), there may be an expected electrical energy output of 10W from the PV panel as a whole, determined according to the solar energy being received by the solar sensor. Therefore, for a PV panel of 10 PV modules, an expected electrical energy output of 10W divided by 10 PV modules = 1W per PV module may be expected. If, however, the electrical energy output as a whole from the PV panel is less than 10W (for example, 8W), then each PV module may be considered individually and expected to provide around 1W. If PV modules 0 and 1 each provide less than 1W, then a plural module operation fault may be identified for PV modules 0 and 1. This may be due to, for example, dust gathering and blocking sunlight reaching panels 0 and 1. For example, the control system 100 may be configured to determine an operation status of a general soiling error in dependence on the amount of electrical energy generated by the PV module, and the amount of electrical energy generated by the at least one further PV module directly adjacent to the PV module, each being below a threshold proportion of an amount of electrical energy obtainable from the PV module and the at least one further PV module. As another example, the control system 100 may be configured to determine an operation status of a module connection error in dependence on the amount of electrical energy generated by the PV module being substantially zero, and the amount of electrical energy generated by the at least one further PV module being a non-zero amount. Such a fault may be due to a broken or disconnected electrical connection to the PV module. Advantageously, a determination may be made whether there is a fault with a single PV module or plural PV modules and which PV modules are faulty. Rather than simply considering the operation of the PV panel overall, determination of the operation status of the PV panel can be more intelligently made on a per-PV module basis. If there is an error with a PV module this can be flagged to a user, otherwise a user may not be aware of an error with a particular module because the PV panel may not be readily visible (for example, if the sunlight-exposed surface is not in a usual line of sight for a person, such as being located high up, facing towards the sky and / or otherwise positioned so the surface cannot easily be seen). Also, typically an error may be flagged in relation to operation of the overall PV panel, but here an issue with a specific module or modules of the PV panel may be provided to aid maintenance. Further, different detected characteristics of the PV module may be processed by the control system 100 which may then determine the type of error occurring according to the detected characteristics. Typical errors which may occur for a PV module include an electrical connection fault for the module, a local soiling error (for example due to bird droppings on module), or a general soiling error (for example due to a buildup of dust or plant matter). The threshold proportion below which an error may be determined to be present may be an amount between 0 and 1 times the total amount of electrical energy obtainable from the PV module. For example, the threshold proportion may be 0.95x, 0.9x, 0.8x, 0.75x, 0.6x, 0.5x, or another multiplier, multiplied by the total amount of electrical energy obtainable from the PV module. It may be undesirable to flag a fault if the PV module is operating at a sufficiently high electrical conversion rate as there is little detriment to the operation of the PV module. In some examples, the threshold proportion may be based on an amount of electrical energy obtainable from the PV module at the start of a monitoring period (for example, over a time period of e.g. a week, a month, six months, a year, or over a period of use e.g. in the context of a PV panel located on a vehicle, the monitoring period may be over 5, 10, 50 or 100 drive cycles, over 100, 200, 500 or 1000 miles travelled). In this way, a gradual decrease in performance of the PV module(s) may be monitored over time so a steady decline in performance may be detected e.g. due to a gradual build-up of dust on at least part of the PV panel. This approach may also be advantageous to help avoid flagging an issue which is temporary and likely to resolve itself without intervention. For example, if a leaf or loose debris is present on a PV module on a vehicle, thereby blocking sunlight for reaching thePV module, this may not be flagged as an issue immediately on detection if, after a drive cycle of the vehicle, the leaf has been dislodged by vehicle movement and no intervention has been required to remedy the issue. Figure 3B illustrates a system 350 according to an embodiment of the invention. The system 350 comprises a PV panel 190 comprising a plurality of PV modules 185-1 to 185-n and is configured to receive energy signals 352 from the PV modules, for example electrical current through a PV module and / or voltage across the PV module. The PV module 190 is located on a vehicle in this example. The control system 100 of Figure 1 is represented by the control module 356 which is configured to receive inputs 352, 360, 364 from the PV modules 185-1 to 185-n. In this example, the control module 356 is configured to receive data 360 from a solar sensor 358 (as described above, to provide a reference reading of the solar energy reaching the PV panel 190) as well as data 352 from the PV modules 185-1 to 185-n. In this example, the control module 356 is configured to receive data 364 from one or more vehicle modules 362. The one or more vehicle modules 362 may comprise, for example, a key on / off module (which may be called a drive cycle module, to indicate when the vehicle is in use or is stationary and not in use), a vehicle speed module (to indicate movement of the vehicle), and / or a weather module (to indicate the weather conditions in the location of the vehicle). Other modules may be envisaged which are able to provide data to be accounted for in determining reporting operation of the PV modules and possible also a suggested remedy to an identified PV module operating problem. For example, a PV module which is stationary and which is indicating poor energy conversion performance may not be indicated as an error in case the issue is loose debris resting on the PV panel. If the same poor energy conversion continues following movement of the vehicle, the issue may then be flagged for a user to take action (e.g. check the PV module and clean off any dirt present). That is, the control module may be configured to receive one or more environmental parameters indicative of an environmental factor of the PV panel, and determine the operation status of the PV module further in dependence on the one or more environmental factors. The one or more environmental factors may comprise one or more of: a speed of movement of the PV panel; a duration of movement of the PV panel; a current location of the PV panel; the presence of a barrier apparatus located to block solar energy from reaching at least part of the PV panel; and a current or recent weather condition in the location of the PV panel. The control module 356 can then make a determination of an operation status 366 of a PV module 185-1 to 185-n, based on the operating parameters 352 of the PV module 185-1 to 185-n, the data 360 from the solar sensor 358, and data 364 from one or more vehicle modules 362, and output the operation status 366. As well as being able to indicate an operation status or potential fault of a PV module on a module-by-module basis, in some examples the control system 100 may be configured to determine a maintenance action in dependence on the operation status, and output a maintenance signal to an indicator apparatus to cause the indicator apparatus to indicate a suggested maintenance of the PV module. For example, a module connection error may be indicated with a suggested maintenance of checking the electronic connections of the PV module showing an error. For example, an operation status of a local soiling error may be indicated with a suggested maintenance of checking for and cleaning off local soiling such as bird droppings. For example, an operation status of a general soiling error may be indicated with a suggested maintenance of cleaning off general soiling, such as built-up dust covering the panel. The control system / control module 100, 356 in some examples may be configured to store 368, in a historical PV operation log, over an operational time period, historical PV module operating data comprising: the amount of electrical energy generated by the PV module, and one or more of: the amount of solar radiation incident on the solar sensor, and the amount of electrical energy generated by at least one further PV module. The control system 100 may be configured to determine the operation status of the PV panel further in dependence on the historical PV module operating data. Advantageously, the historical operation of the PV modules of the PV panel can be logged and used by the control system in analysing new data from the PV modules to help determine whether there is a fault. For example, the control system may log performance of the PV modules over time and in relation to one or more other factors, such as weather conditions, time of day, period of operation, any maintenance actions performed such as cleaning or resetting, and make a determination as to the operation status of a PV module in dependence on the historical performance of the PV module as well as current operating parameters. The control system I control module 100, 356 may be configured in some examples to determine the operation status of the PV panel by adapting the expected amount of electrical energy generated by one or more of the plurality of PV modules according to a lifetime degradation factor arising from usage of the PV panel (discussed later in relation to Figure 4 and element 406). The expected amount of electrical energy generated may be the electrical energy generated by one or more of the plurality of PV modules, or all the PV modules of the PV panel, in which case the expected amount of electrical energy is that expected to be generated by the PV panel. Advantageously, account may be taken of the lifetime of the PV panel and PV modules, as typically it is expected that the efficiency of operation of the PV modules would reduce over time / usage. By accounting for this expected behaviour, the control system may improve operation status reporting by, for example, not flagging an operational issue with a suggestion of cleaning the overall PV panel if the reduction in performance compared to an expected performance is more likely due to the long lifetime of use of the PV panel rather than a soiling issue, and instead providing a suggestion for an overall maintenance procedure to be performed (e.g. checking and replacing wiring or electrical components, performing a factory reset type procedure or annual service type procedure) due to the length of use of the PV panel. Figure 4 illustrates an example method 400 of operation of a control system 100 according to an embodiment of the invention. In particular, the method 400 is a method for a PV panel comprising a plurality of PV modules. The PV panel in this example is a PV panel mounted on a vehicle. In particular, the memory means 130 may comprise computer-readable instructions which, when executed by the processing means 120 of the control system 100, perform the method 400. Step 408 is a key-on step whereby the vehicle engine is powered on, which triggers the control system 100 to begin operation in receiving data relating to the PV panel operation and determination of the operation status of the PV modules of the PV panel. In step 410, the energy output of a PV module (in this example this PV module under inspection may be termed the nth PV module) is compared to a reference expected energy generation value, for example based on solar sensor data. This comparison may use data such as the solar loading 402 (e.g. in W / m2) of the PV module, the PV module power 404 (e.g. in W), and / or the expected minimum reference performance 406 of the PV module, which may be determined based on PV module manufacturing tolerances, a PV module lifetime degradation factor, and / or a standard deviation or error margin. In step 412 a comparison is made to determine if the energy output of the PV module is at least equal to, or greater than, an expected reference energy output performance. If it is, then no flag or output may be provided and the process ends in step 414, because there does not appear to be any error or issue in performance of the PV module. This may be considered to be a step of, if the amount of electrical energy generated by the PV module is above the generation threshold, inhibition of comparison of the amount of electrical energy generated by the PV module with an amount of electrical energy generated by at least one further PV module of the plurality of PV modules (as discussed below in relation to step 424). If the energy output is less than the expected output, the process moves to step 416 where the energy output of the PV module is checked compared to the energy output of another PV module of the PV panel, such as a neighbouring PV module. Again this maybe determined in dependence on the expected minimum reference performance 406 of the PV module, and on the PV module power (e.g. in W) of the PV module 420 (which may be labelled the nth module), the PV module power of a PV module 418 neighbouring to one side of the PV module (i.e. the n-1 th module) and / or the PV module power of a PV module 422 neighbouring to another side of the PV module (i.e. the n+1 th module). In step 424 a comparison is made to determine if the energy output of the PV module 420 against the energy outputs of the n-1 th and / or n+1 th PV modules 418, 422. If the energy output appears to be comparable between the nth and the n-1th and / or n+1th PV modules, then a “multiple PV module” issue may be flagged 426 because the nth PV module was found to show a different energy output to an expected value determined from an independent reference in step 412, and a similar (anomalous) energy output to another n+1thPV module in the same PV panel. If the energy output is not comparable between the nth and the n-1th and / or n+1 th PV modules, then a “single PV module” issue may be flagged 428, because the nth PV module was found to show a different energy output to an expected value determined from an independent reference in step 412, and a different (anomalous) energy output to another (the n-1 th and n+1th PV modules) in the same PV panel. Whether a single PV module issue or multiple PV module issue is determined, in step 430, the control system 100 may be configured to perform one or more further determinations in order to better narrow down the potential issue, and / or identify one or more suggested remedies to the issue. Possible further considerations made in step 430 include: • Does the single or multiple PV module issue stop after one (or more than one) “x” km / h driving event (where “x” km / h is a threshold velocity which is a predetermined speed at which loose debris on the PV panel is expected to be dislodged, such as 20kph). Similar checks may be checking if the issue stops after an acceleration of “y” km / h2 (where “y” km / h2 is a threshold acceleration which is a predetermined acceleration at which loose debris on the PV panel is expected to be dislodged). If so, then a diagnosis of loose debris on the PV panel (now dislodged) may be made, and this may not be necessarily flagged in an output since the issue has been remedied by the vehicle moving. • Does single or multiple module issue remain after multiple key on / off (i.e. drive cycle) events? If so, this suggests an issue spot soiling, for example due to bird droppings on the PV module(s). • Does the multiple module issue remain after several key on / off events? If so, this suggests general dirt / soiling being present across the multiple PV modules. • Isa roof rack and / or a roof box detected on the vehicle? For example this may be detected by a force, pressure or connection sensor on the roof bars of the vehicle, and / or entered as an input by a user, and provided to the control system. If so, and this causes the PV module or PV panel to be shielded from the sun, then the PV module detection process may be inhibited while the roof rack and / or roof box remain present, to avoid unnecessary processing. Following these one or more further checks, the control system 100 may move to step 432, wherein, depending on the output of the method performed as discussed above, if an issue is determined, and in some examples if a suggested remedial action is identified, these are output, for example to a display device to display a message to a user. The message may be, for example, “Solar panel performance is degraded, please check for debris” message. The message may be displayed on an in-vehicle display, sent to a user device such as a smartphone, sent to a vehicle apparatus such as a supply equipment (home charger) and displayed on a screen of the equipment, or otherwise notified to a user. If the problem persists (e.g. after remedial action) the user may take their vehicle to a dealer or repair facility. In some examples, the control system 100 may be configured to determine an indicator provision time at which the control system 100 is to output the PV panel status signal. This allows for intelligent notifications to be made, in order to inform a user of a potential fault and / or suggested remedy for an identified issue at a reasonable time. This may mean that the user is not inundated with indications too often, which may be annoying, and also is not left uninformed for a long time while the PV panel is not operating as well as it could be. The control system 100 may determine the indicator provision time in dependence on a frequency of variation of the amount of electrical energy generated by the PV module compared with amount of solar radiation incident on the solar sensor. That is, the indicator may be output based on a rolling average of the electrical energy generated, on a threshold frequency of the energy generated being below an acceptable threshold, or other dependence on a time variation factor to avoid outputting too many indications to the user. The control system 100 may determine the indicator provision time in dependence on a time duration of a threshold difference between the amount of electrical energy generated by the PV module compared with the amount of solar radiation incident on the solar sensor. That is, unless the energy generation is below an acceptable amount for a predetermined period of time, the indication may not be provided to avoid outputting an indication for a temporary issue, such as a leaf or loose debris resting temporarily on the PV panel. The period of time may be a single continuous time period (e.g. a single period of at least 15 minutes), or an accumulated period over a particular time window (e.g. for at least 20 minutes in a 60 minute window). The control system 100 may determine the indicator provision time in dependence on the PV panel operation status indicative of a PV panel error status in a predetermined number of consecutive drive cycles. For example, indication of a possible error after a single drive cycle may be annoying for a user and may be overly cautious (for example, if the issue is due to dust, and there is rainfall after one drive cycle which washes the rain away, then no user cleaning may be needed to remedy the issue), but providing the indication if the issue persists for at least a plural number of drive cycles (e.g. 3, 5,10, or another number) then this may be an indication that the issue can be remedied with some user intervention but not by leaving the problem to remedy itself. Advantageously, the control system can intelligently determine an appropriate time to flag a potential error to a user, to find a balance between informing the user of an error early enough to remedy it (in some cases before additional or more permanent faults develop because the initial fault was not remedied) and avoiding flagging every fluctuation or temporary error to a user which is not useful and may be annoying to the user. The control system may therefore intelligently determine when an issue is likely to be an issue which the user should be informed of so that it can be remedied, and when issue is likely to be temporary or inconsequential, for example a lower than expected solar energy receipts due to a temporary solar barrier such as a leaf resting on PV panel which is likely to blow away when the PV panel moves or wind blows over the PV panel. A vehicle 500 in accordance with an embodiment of the present invention is described herein with reference to the accompanying Figure 5. The vehicle 500 comprises a PV panel 190 and control system (not shown) as disclosed herein. Advantageously, the vehicle 500 comprising a control system and a PV panel 190 may be provided so a user of the vehicle can be informed of the operation of the PV panel on a per PV module basis as discussed above. It will be appreciated that various changes and modifications can be made to the present invention without departing from the scope of the present application.

Claims

1. A control system for a photovoltaic, PV, panel, the PV panel comprising a plurality of PV modules, wherein the control system comprisesone or more processors collectively configured to, for at least one PV module of the plurality of PV modules:receive an energy signal from the PV module, the energy signal indicative of an amount of electrical energy generated by the PV module;receive a reference energy signal from a solar sensor, the reference energy signal indicative of an amount of solar radiation incident on the solar sensor;determine, in dependence on the reference energy signal, a generation threshold indicative of an expected amount of electrical energy generated by one or more of the plurality of PV modules;if the amount of electrical energy generated by the PV module is below the generation threshold, compare the amount of electrical energy generated by the PV module with an amount of electrical energy generated by at least one further PV module of the plurality of PV modules;determine an operation status of the PV panel in dependence on the comparison; andoutput a PV panel status signal indicative of the operation status of the PV panel.

2. The control system of claim 1, where the control system is configured to:determine the operation status of the PV panel to be a single module operation fault status in dependence on the amount of electrical energy generated by the PV module being below a threshold proportion of the amount of electrical energy generated by at least one further PV module; anddetermine the operation status of the PV panel to be a plural module operation fault status in dependence on the amount of electrical energy generated by the PV module and the amount of electrical energy generated by the at least one further PV module being below a threshold proportion of an amount of electrical energy obtainable from the PV module and the at least one further PV module, the amount of electrical energy obtainable from the PV module and the at least one further PV module determined in dependence on the amount of solar radiation incident on the solar sensor.

3. The control system of any preceding claim, wherein the PV panel is attached to a vehicle.

4. The control system of any preceding claim, wherein the control system is configured to determine:an operation status of a module connection error in dependence on the amount of electrical energy generated by the PV module being substantially zero, and the amount of electrical energy generated by the at least one further PV module being a non-zero amount;an operation status of a local soiling error in dependence on the amount of electrical energy generated by the PV module being lower than the amount of electrical energy generated by the at least one further PV module, wherein the at least one further PV module is directly neighbouring the PV module; andan operation status of a general soiling error in dependence on the amount of electrical energy generated by the PV module, and the amount of electrical energy generated by the at least one further PV module directly adjacent to the PV module, each being below a threshold proportion of an amount of electrical energy obtainable from the PV module and the at least one further PV module, the amount of electrical energy obtainable from the PV module and the at least one further PV module determined in dependence on the amount of solar radiation incident on the solar sensor.

5. The control system of claim 4, wherein the control system is configured to:determine a maintenance action in dependence on the operation status; andoutput a maintenance signal to an indicator apparatus to cause the indicator apparatus to indicate a suggested maintenance of the PV module.

6. The control system of any preceding claim, wherein the energy signal is derived from one or more of: a sensed current through the PV module, a sensed voltage across the PV module; a sensed temperature of the PV module, and a sensed resistance of the PV module.

7. The control system any preceding claim, wherein the control system is configured to, if the amount of electrical energy generated by thePV module is above the generation threshold:inhibit comparison of the amount of electrical energy generated by the PV module with an amount of electrical energy generated by at least one further PV module of the plurality of PV modules.

8. The control system of any preceding claim, wherein the control system is configured to:store, in a historical PV operation log, over an operational time period, historical PV module operating data comprising:the amount of electrical energy generated by the PV module,and one or more of:the amount of solar radiation incident on the solar sensor, andthe amount of electrical energy generated by at least one further PV module, anddetermine the operation status of the PV panel further in dependence on the historical PV module operating data.

9. The control system of any preceding claim, wherein the control system is configured to determine the operation status of the PV panel by adapting the expected amount of electrical energy generated by one or more of the plurality of PV modules according to a lifetime degradation factor arising from usage of the PV panel.

10. The control system of any preceding claim, wherein the control system is configured to determine an indicator provision time at which the control system is to output the PV panel status signal in dependence on one or more of:a frequency of variation of the amount of electrical energy generated by the PV module compared with amount of solar radiation incident on the solar sensor;a time duration of a threshold difference between the amount of electrical energy generated by the PV module compared with the amount of solar radiation incident on the solar sensor; andthe PV panel operation status indicative of a PV panel error status in a predetermined number of consecutive drive cycles.

11. The control system of any preceding claim, wherein the control system is configured to receive one or more environmental parameters indicative of an environmental factor of the PV panel; and determine the operation status of the PV module further in dependence on the one or more environmental factors.

12. The control system of claim 11, wherein the one or more environmental factors comprises one or more of:a speed of movement of the PV panel;a duration of movement of the PV panel;a current location of the PV panel;the presence of a barrier apparatus located to block solar energy from reaching at least part of the PV panel; anda current or recent weather condition in the location of the PV panel.

13. A system comprising:the control system of any preceding claim; andthe PV panel comprising the plurality of PV modules.

14. A vehicle comprising the control system of any of claims 1 to 12, or the system of claim 13.

15. A computer-implemented method for a photovoltaic, PV, panel, the PV panel comprising a plurality of PV modules, the methodcomprising, for at least one PV module of the plurality of PV modules:receiving an energy signal from the PV module, the energy signal indicative of an amount of electrical energy generated by the PV module;receiving a reference energy signal from a solar sensor, the reference energy signal indicative of an amount of solar radiation incident on the solar sensor;determine, in dependence on the reference energy signal, a generation threshold indicative of an expected amount of electrical energy generated by one or more of the plurality of PV modules;5 if the amount of electrical energy generated by the PV panel is below the generation threshold, comparing the amount of electricalenergy generated by the PV module with an amount of electrical energy generated by at least one further PV module of the plurality of PV modules;determining an operation status of the PV module in dependence on the comparison; andoutputting a PV panel status signal indicative of the operation status of the PV panel.16

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