FIELD OF THE INVENTION
The present invention generally relates to photovoltaic power plant and, in particular, improving the longevity of the photovoltaic (PV) modules of the power plant by controlling potential-induced degradation in such modules. More particularly, the present invention relates to a method of detecting and mitigating the effect of potential induced degradation in photovoltaic modules of solar photovoltaic power plants.
BACKGROUND OF THE INVENTION
Background description includes information that may be useful in understanding the present subject matter. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed subject matter, or that any publication specifically or implicitly referenced is prior art.
Potential-induced degradation (PID) is one of the main reasons for power losses in PV power plants installed in last few years. PID is the phenomena where modules start to degrade in terms of power output. PID arises because of flow of leakage current from the active path of the modules to the grounded frame. This leakage current causes charged particles to migrate into the cells through stacking faults and cause shunting of the cells. This is the major cause of degradation for effected modules. Because of the nature of the migrating charge particles, such degradation is observed mainly on the modules facing the negative voltages in the circuit. However, several other leakage paths and PID mechanism have also been identified that lead to PID.

There are several methods available for confirming PID in case there is a power loss at the plant. The most common off-site method is applying high voltage under specific environmental conditions. This simulates the site conditions of high voltage in a PV string and the heat and the humidity that have been known to cause PID. Modules that show degradation during this test are marked PID-susceptible. This method requires dismounting of modules and transporting them off-site for testing.
Besides, there are some on-site methods without dismounting and transporting modules such as using aluminum sheets on the mounted modules. In this method, a conductive aluminum sheet is applied to a part of module and voltage corresponding to the system voltage in the field is applied to the module. This is another method of simulating the conditions that precipitate PID. Even though the dismounting of modules is not required, this also requires special tools and accessories to carry out the testing and only one module can be tested at a time. After detection, the mitigation of PID is another important issue. The mitigation of PID is possible with negative grounding of the inverters. During the negative grounding, the topology of the inverter is changed such that one terminal is at positive bias with one of the terminals held at zero potential. This avoids negative potential at the module level. There are several solutions available that implement different arrangements to implement negative grounding or similar solutions.
Several methods have been proposed to counter PID during the manufacturing such as WIPO publication WO/2014/047006 “Methods of reducing and/or eliminating potential induced degradation of photovoltaic cell modules” and WIPO

publication WO/2015/191699 “Controlling potential-induced degradation of photovoltaic modules” that propose changes in the structure and constitution of the module before it if installed as a part of PV system. Nonetheless, a module can only be called PID-resistant and not PID free and there is always a possibility of degradation due to PID at the system level. For example, patents CN203166494U “Device for solving potential induced degradation”, Publication CN103248007A “PID (Potential Induced Degradation)-resistant circuit and monitoring device thereof” and Publication CN107994861A “Method and system for solving potential induced degradation” describe methods to apply negative grounding or reducing the negative potential applied to PV string array. These methods do not describe repairing of PID affected modules.
Another solution for PID is to periodically (usually at night) apply a reverse potential to the PV array to offset the effects to active potential during the operating hours of the day. External apparatus, usually called the anti-PID kits are available to implement such solutions. Patents/Publication such as CN103944502B “Potential anti potential induced degradation photovoltaic systems, photovoltaic modules and inverters”, CN104201981B “An anti-inducing potential of a control method and control system attenuation” EP3340417A1 “Photovoltaic inverter system, potential induced degradation effect compensation method and device for the same”, WO/2018/171765 “Control device and control method having both pid effect suppression and reparation functions” and CN106505626 “A kind of photovoltaic inverting system and its PID effect compensation method and device” describe various methods of supplying such compensating voltages to the system using special circuit to tackle PID.

Further, US20180269688A1 “Method and device for recognising faults in a photovoltaic (pv) generator” describes a method of monitoring that detects faults including PID but it requires manipulating the operation of the inverter by the use of external circuits to achieve it.
Also, Publication CN107765094A “Photovoltaic cell panel PID restoration device” and US20190190272A1 “Recovery of degraded photovoltaic panel” use external devices such as switches, power supply etc., to apply the principles of bias voltages to exert repair and restoration of the modules.
Existing method make use of some kind of external devices for detection, elimination and/or recovery of PID. Further, none of the methods systematically identifies and isolates the faulty modules and distinguishes reversibly degraded modules from the modules that are irreversibly damaged and cannot be repaired on site.
There are several methods available for confirming PID in case there is a power loss at the plant including the most common off-site method of applying high voltage under specific environmental conditions and on-site methods like using aluminum sheets or using special electrical circuits without dismounting and transporting modules. Further, there are methods for halting or reversing PID using negative grounding, anti-PID kits and various biasing methods. All these methods make use of some kind of external devices for detection, elimination and/or recovery of PID. Further, none of the methods systematically identifies and isolates

the faulty modules and distinguishes reversibly degraded modules from the modules that are irreversibly damaged and cannot be repaired on site.
Thus, there remains a need for a method using system voltage bias, without the use of any external devices/circuits. Also there remains a need for detecting PID (Potential-induced degradation) and providing an improvement in system performance over negative grounding method by recovering modules. There remains a need for isolating irreversibly damaged modules.
OBJECTS OF THE INVENTION
In view of the foregoing limitations inherent in the state of the art, some of the objects of the present disclosure, which at least one embodiment herein satisfy, are listed below.
It is an object of the present disclosure to detect and mitigate the effect of PID ((Potential-induced degradation) of solar modules in order to restore the normal working conditions of a PV plant with decreasing power output.
Another object of the invention is to isolate the detected irreversibly damaged modules without dismounting the modules and without using special electrical or other accessories.
It is yet another object of the present disclosure to propose a method to measure PID and use PID mitigation including inverter grounding for the purpose of accurate detection.

It is still yet another object of the present disclosure to propose a method for PID detection and isolating irreversibly damaged modules and/or improving performance with inverter negative grounding.
It is another object of the present disclosure to propose a method to detect PID, improving plant performance and detecting faulty modules.
It is still yet another object of the present disclosure to propose a method for data collection involving system voltage available in the active power path to resolve the issues related to PID.
These and other objects and advantages of the present invention will be apparent to those skilled in the art after a consideration of the following detailed description taken in conjunction with the accompanying drawings in which a preferred form of the present invention is illustrated.
SUMMARY OF THE INVENTION
This summary is provided to introduce concepts related to detect potential-induced degradation (PID), improving plant performance and detecting faulty module by a specific way of data collection and polarity reversal of the photovoltaic module in a photovoltaic array in a solar photovoltaic (PV) plant. The concepts are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

The present disclosure relates to a method to detect and mitigate the effects of Potential-induced degradation (PID) in solar PV power plants. The method comprises recording an open circuit voltages (Voc) of the plurality of photovoltaic modules in the photovoltaic array of length L related to a position of a photovoltaic module in the photovoltaic array, wherein ‘1’ is a positive most module, ‘L’ is a negative-most module. Measuring the PID by plotting the relation between open circuit voltages (Voc) and the position of the photovoltaic module is defined by an equation and if low performance is determined, polarity reversal of the photovoltaic string is performed and replacing the damaged photovoltaic modules to provide improvement over negative grounding.
In one aspect, the method for controlling a potential-induced degradation (PID) in solar photovoltaic (PV) plant by providing an improvement over negative grounding by recovering damaged modules by polarity reversal of the photovoltaic string, and following the steps, Step 1: opening a plurality of the photovoltaic module connections. Step 2: recording the Voc of the modules with respect to position in the photovoltaic array from position ‘1’ to position ‘L’, Step 3: reversing the connections of the plurality of the photovoltaic modules so that first module ‘1’ of the photovoltaic array is connected to the negative terminal of the string monitoring box (SMB) and last module ‘L’ is connected to positive terminal of the string monitoring box (SMB). Step 4: monitor the performance of photovoltaic array within predetermined time of polarity reversal; and Step 5: moving low performing modules to positive bias in the photovoltaic array to recover all potential-induced degradation effected modules and remove non-recovered modules.

In this aspect the method for isolating damaged modules for overcoming a potential-induced degradation (PID) in solar photovoltaic (PV) plant by polarity reversal, recording performance before and after polarity reversal after a predetermined time, changing low performing modules to positive bias in the photovoltaic array, recovering the reversibly damaged modules and isolating the irreversibly damaged modules and replacing the irreversibly damaged photovoltaic modules to provide improvement over negative grounding.
In an aspect the predetermined time is after 1-2 weeks of polarity reversal. The presence of potential-induced degradation is measured by the high occurrence of low Voc towards the negative end of the photovoltaic array.
Other objects, features and advantages of the present disclosure will become apparent from the following detailed description. It should be understood, however, that the detailed description and the specific examples, while indicating specific embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter that is regarded as forming the present subject matter, it is believed that the present disclosure will be better understood from the following description taken in conjunction with the accompanying drawings, where like reference numerals designate like structural and other elements, in which:

FIG. 1A is a schematic arrangement of plurality of photovoltaic modules connections in a photovoltaic array before and after implementing polarity reversal in accordance with the present invention;
FIG. 1B is a block diagram of solar PV plant with plurality of PV arrays having plurality of photovoltaic modules before and after implementing polarity reversal in accordance with the present invention;
FIG. 2 is a flowchart for handling the plurality of photovoltaic module after polarity reversal for recovering from potential induced degradation in accordance with the present invention;
FIG. 3 shows a measurement of Voc of the plurality of photovoltaic module with respect to the position in the photovoltaic arrays showing various degrees of low performance in an embodiment of the present invention;
FIG. 4 shows an electroluminescence images of the plurality of photovoltaic module from solar photovoltaic power plant in an embodiment of the present invention;
FIG. 5 shows IV measurements for the plurality of photovoltaic module showing nominal as well as low Voc at solar photovoltaic power plant in an embodiment of the present invention;
FIG. 6 shows a measurement of the open circuit voltages (Voc) of photovoltaic module with respect to their position in the photovoltaic string in an embodiment of the present invention;
FIG. 7 shows a gain in photovoltaic string Voc observed after polarity reversal in an embodiment of the present invention;

FIG. 8 shows a generation data at solar photovoltaic power plant before and after implementing the polarity reversal and negative grounding of inverters in an embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
The detailed description of various exemplary embodiments of the disclosure is described herein with reference to the accompanying drawings. It should be noted that the embodiments are described herein in such details as to clearly communicate the disclosure. However, the amount of details provided herein is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.
It is also to be understood that various arrangements may be devised that, although not explicitly described or shown herein, embody the principles of the present disclosure. Moreover, all statements herein reciting principles, aspects, and embodiments of the present disclosure, as well as specific examples, are intended to encompass equivalents thereof.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a”, “an”, and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises”, “comprising”, “includes”, “consisting” and/or “including” when used herein, specify the presence of stated features,

integers, steps, operations, elements and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and/or groups thereof.
It should also be noted that in some alternative implementations, the functions/acts noted may occur out of the order noted in the figures. For example, two figures shown in succession may, in fact, be executed concurrently or may sometimes be executed in the reverse order, depending upon the functionality/acts involved.
Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which example embodiments belong. It will be further understood that terms, e.g., those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
Embodiments explained herein pertain to detect Potential-induced degradation (PID), improving plant performance and detecting faulty module by a specific way of data collection and polarity reversal of the photovoltaic modules 106. In a photovoltaic array 104 for detecting, mitigating and recovering potential-induced degradation (PID) in a solar photovoltaic (PV) plant 102. FIG. 1A is a schematic arrangement and FIG. 1B is a block diagram of plurality of photovoltaic modules 106 connections in a photovoltaic array 104 before and after implementing polarity reversal in accordance with the present invention. The plurality of photovoltaic modules 106 are positioned on the positive portion of the photovoltaic array 104 as

positive modules 112 and on the negative side of photovoltaic array 104 as negative modules 116. The plurality of photovoltaic modules 106 and the photovoltaic array 104 performance in terms of Voc 108 and (Vop, Iop) 110 is recorded and the polarity reversal is carried out based on the requirement. After the polarity reversal, at least predetermined time such as 7 sunny days are given to the plurality of photovoltaic modules 106 for recovery. The performance of the photovoltaic array 104 is checked after recovery.
In one embodiment the method 100 for detecting and mitigating the effects of potential-induced degradation (PID) in a solar photovoltaic (PV) plant 102, the method 100 comprises a photovoltaic arrays 104; having a plurality of photovoltaic modules 106, of length L related to a position of the photovoltaic module 106 in the photovoltaic array 104, wherein ‘1 to L/2’ are positive modules 112 configured close to a positive terminal 114 and ‘L/2 + 1 to L’ are negative modules 116 configured close to a negative terminal 118 of string monitoring box (SMB), recording an open circuit voltages (Voc) 108 of the plurality of photovoltaic modules 106, measuring the potential-induced degradation (PID) by plotting the relation between open circuit voltages (Voc) 108 and the position of the photovoltaic module (106) in the photovoltaic array 104 defined by an equation Avg(Voc)1-L/2 > Avg(Voc)L/2-LPID,
or measuring the potential-induced degradation by another equation, (Vop * Iop)Post -reversal > (Vop * Iop)Pre - reversalPID; where Vop is the operating voltage and Iop is the operating current for the photovoltaic array 104 , post-reversal and pre-reversal are the readings after and before the polarity reversal, wherein if low

performance is determined, polarity reversal of the photovoltaic array 104 is performed and performance of photovoltaic array 104 is recorded in a specified interval of time under specific condition of sun.
FIG. 2 is a flowchart for handling the plurality of photovoltaic modules 106 after polarity reversal for recovering from potential induced degradation in accordance with the present invention. The plurality of photovoltaic modules 116 on the negative portion of the photovoltaic array 104 before the polarity reversal are referred to as ‘Pre- rev –’ and the plurality of photovoltaic modules 112 on the positive portion of the photovoltaic array 104 are referred to as ‘Pre- rev +’. Having different treatments for the plurality of photovoltaic modules 106 on the both ends of the photovoltaic array 104. Section (A) of FIG.2 shows scheme for the modules that were previously at negative side i.e., ‘Pre-rev – ‘.
‘Pre-rev-’ are the plurality of photovoltaic modules 112 after polarity reversal and will mostly recover under the healing influence of the positive potential after polarity reversal if the damage is due to potential induced degradation. But few of these modules may not recover and few are previously positive side referred as ‘Pre-rev+’ could degrade.
If the photovoltaic modules ‘Pre-rev-’ do not recover either the photovoltaic modules 112 have suffered irreversible damage or, the photovoltaic modules 116 at the other end might have degraded faster due to negative potential (i.e) due to symmetric topology of inverter and the overall photovoltaic array 104 Voc 108 is too

low to exert a healing effect. In this case, few of the plurality of photovoltaic modules 116 could be exchanged with other photovoltaic modules 116 at another good photovoltaic array 104 of PV plant 102 for recovery and the PID detection and mitigation procedure is repeated.
In one embodiment if further investigation is required to ascertain the cause of degradation and few of the plurality of photovoltaic module 112 are tagged for replacement. Specifically, if ‘Pre-rev+’ photovoltaic modules 116 have not degraded, ‘Pre-rev–’ photovoltaic modules 112 can be marked for replacement after polarity reversal and the said waiting period.
If photovoltaic modules 116 have degraded after polarity reversal, these particular modules shall be replaced with the photovoltaic modules 116 of the high performing photovoltaic array 104 of PV plant 102 and the aforementioned PID detection procedure is to be repeated.
Section (B) of FIG.2 shows the scheme for previously positive end of the string (Pre-rev +) i.e., 116 after polarity reversal. These photovoltaic modules 112 (as shown in FIG. 1A) may be susceptible to PID without showing any degradation as they were under positive voltage influence. In such case, these photovoltaic modules 116 start to degrade after polarity reversal, they have to be moved to the other good photovoltaic array 104 of PV plant 102. The procedure for moving modules to other strings (i.e., procedure for step 4a. and 3b. in sections (A) and (B) of FIG. 2) is followed. The degraded modules of ‘Pre-rev+’ could be exchanged with the negative side photovoltaic modules 116 of a good performing photovoltaic

array 104 string because these photovoltaic modules 116 are least likely to have PID. Further, once PID affected modules are exchanged with good photovoltaic array 104 at position 116, the polarity of the new photovoltaic array 104 should be reversed so that this photovoltaic modules 116 could recover under positive bias and do not face negative voltages.
This process could be carried out repetitively depending upon the size of power plant and the manpower availability to accumulate the PID affected photovoltaic modules 106 on the positive side of the photovoltaic array 104 and separate out the photovoltaic modules 106 that have suffered non-reversible damages due to PID or any other issue. Along with negative grounding of the inverters 122 (As shown in FIG 1B), moving photovoltaic modules 106 and isolating permanently damaged photovoltaic modules 106, the solar plant could be brought back to benchmark performance with minimum cost.
FIG. 3 shows a measurement of Voc of the plurality of photovoltaic module 106 with respect to the position in the photovoltaic array 104 showing various degrees of low performance in an embodiment of the present invention. In a preferred embodiment highlights the data recording and polarity reversal for detecting potential-induced degradation (PID) and for the recovery of the photovoltaic module 106 is determined. It compares the plant performance before and after implementing the polarity reversal. In a preferred embodiment the solar photovoltaic power plant 102 showing significant generation loss is subjected to extensive analysis to analyze the root cause behind the generation loss. For example: the capacity of the plant was in 3-5 MWp range. Based on FIG. 3, the

preliminary assessment shows that considerable numbers of modules were showing low open circuit voltages (Voc). Total 7365 modules from across the plant are randomly measured under open circuit conditions and more than 18.6% were found to be having lower than benchmark Voc.
In one embodiment in order to assess the possibility of potential-induced
degradation (PID) effect, a study was carried out by selecting the lowest
performance sections of the solar photovoltaic power plant 102 in a site. For
example: 169 photovoltaic array 104 from lowest output inverter 122 are selected
for further analysis and open circuit voltages at photovoltaic array 104 level were
collected. Voc 108 loss of up to 250 V was measured for several photovoltaic array
104 with each array containing 24 modules. The photovoltaic array 104 showing
less than 700 V (nominal Voc ~800V) were selected for further analysis and Voc
values were recorded for each individual photovoltaic module 106 of the
photovoltaic array 104 with respect to the position of the photovoltaic module 106
in the photovoltaic array 104. Based on the study it was seen that the low
performing photovoltaic modules 106 are located on the negative side of the string.
Data for some of the photovoltaic arrays 104 are shown in FIG.3. Since potential-
induced degradation (PID) arises due to application of negative voltages to the
photovoltaic module 106, the trend is clearly indicative of potential-induced
degradation (PID) based on
Avg(Voc)1-L/2 > Avg(Voc)L/2-L PID------ (Equation 1)
FIG. 4 shows an electroluminescence images of the plurality of photovoltaic module 106 from solar photovoltaic power plant in an embodiment of the present invention.

The current-voltage (IV) results corresponding to each photovoltaic module 106 is identified by serial number in FIG. 5. Few affected photovoltaic modules 106 as well as good photovoltaic modules 106 were transported from the site for comparative studies. The photovoltaic modules 106 were tested for current-voltage (IV) and electroluminescence (EL) results. FIG. 4 shows different electroluminescence (EL) images of the photovoltaic module 106 showing shunt failures of the solar cells which produce dark areas in the images. The degradation in power and Rshunt is matching with the extent of damage visible in EL images in FIG. 4.
FIG. 5 shows IV measurement for the plurality of photovoltaic module 106 showing low Voc at solar photovoltaic power plant in an embodiment of the present invention. The results shows that the loss of power conversion efficiency shown in FIG. 5 matches well to the loss of shunt values detected in EL images confirming that the degradation is due to potential-induced degradation (PID). It could be seen that module C1495355 is showing worst EL pattern as shown in FIG. 1 and the lowest module efficiency of 1% as shown in FIG.5. On the other hand, for C14167582 the extent of degradation is minimum both in electroluminescence (EL) and current-voltage (IV) plots. The other modules fall in between these cases. This re-confirms that the degradation in solar photovoltaic power plant performance is on account of potential-induced degradation (PID).
FIG. 6 shows a measurement of the open circuit voltages (Voc) 108 of photovoltaic module 106 with respect to their position in the photovoltaic array 104 in an embodiment of the present invention. The color code for the range of Voc 108 is in the legend below the charts of FIG. 6. The string/array numbers on the x-axis are arbitrary. Y-axis shows the position of the module. P1 is most positive for (A)

whereas P24 is most positive for (B) and (C). Modules were rated for nominal Voc 108 of 37 V. Several photovoltaic arrays 104 were subjected to the polarity reversal and their performance was tracked over several days. FIG. 6 shows color plot of Voc 108 for a collection of photovoltaic arrays 104 before and after carrying out the reversal over a period of time so that all photovoltaic arrays 104 performances could be compared clearly. Figure 6 (A) shows that the photovoltaic arrays 104 were showing the potential-induced degradation (PID) with low voltage modules occurring on the negative side. After recording the Voc 108 values, the polarity of the photovoltaic arrays 104 was reversed and the Voc 108 data was collected over a period of three weeks. Figure 6B and 6C show the process of improvement after the polarity reversal. It was observed that after one week, most of the photovoltaic arrays 104 had recovered and were showing improved performance as shown in FIG. 6B. After two more weeks, the photovoltaic arrays 104 that performed better after week one had further recovered. But the potential-induced degradation (PID) related degradation started to show off on the previously positive side of some of the other photovoltaic arrays 104. FIG. 6C shows the situation after 03 weeks. It could be seen that the only few photovoltaic arrays 104 had potential-induced degradation (PID) -susceptible modules on both sides of the photovoltaic array 104 for example String 156 in FIG. 6 and FIG. 7.
In one embodiment for example taken for the study shows the average monthly horizontal global radiance was 5.34 kWh/m2.day and average ambience temperature was 28°C during the implementation of polarity reversal scheme. It took about 35 hours of exposure and maximum reverse voltage of about 400 V for >95% recovery of the potential-induced degradation (PID) effected photovoltaic

arrays 104. The photovoltaic arrays 104 recover almost completely in one weeks’ times and before changing inverters topology.
FIG. 7 shows a gain in photovoltaic string Voc 108 observed after polarity reversal in an embodiment of the present invention. In FIG. 7 the lines show Voc 108 after week one, two and three. The bars show change in Voc 108 from before reversal to week 3. FIG. 7 shows the precise, quantitative effect of the reversal. Most of the strings show improvement of 100V to 200V after three weeks of polarity reversal. Here only photovoltaic array 104 Voc 108 was compared as potential-induced degradation (PID) was seen prominent. For detecting power loss due to degradation of shunt as in case of start of potential-induced degradation (PID), operating voltage and current could be measured as per equation show below and could be used to detect milder to severe cases of PID.
(Vop * Iop)Post - reversal > (Vop * Iop)Pre - reversalPID (Equation 2)
FIG. 8 shows a generation data at solar photovoltaic power plant before and after implementing the polarity reversal and negative grounding of inverters 122 in an embodiment of the present invention. Initial data collection was collected in the solar photovoltaic power plant. After that, negative grounding of the inverters 122 was carried out. An improvement in the performance could be seen as the polarity reversal was in progress. After the completion of complete activities and change in inverters 122 for negative grounding, a significant improvement in the performance was observed as shown in FIG. 8.
In one embodiment the photovoltaic array 104, Voc 108 has reduced in only one case. Such cases could be assigned to potential-induced degradation (PID) by

following equation 1. Further, systematic approach as described in FIG. 2 could categorize low performing modules into reversibly damaged suitable for recovery and irreversibly damaged modules.
In a preferred embodiment for mitigation of potential-induced degradation (PID) could be applied for symmetric topology of solar inverters. Similar approaches could be applied for inverters with negative grounding or with photovoltaic power powers with different kind of counter-PID accessory in operation such as anti-PID kit. Also, it could be used to improve the solar photovoltaic power plant 102 in all cases and to check the effectiveness of the counter- potential-induced degradation (PID) measure in place.
In one embodiment the Avg(Voc)1-L/2 is a module Voc averaged over modules from 1 to L/2. In a preferred embodiment the Avg(Voc)L/2-L is a module Voc averaged over modules from L/2+1 to L. The specific condition of sun is 30 – 50 hrs of time interval and sunshine measured at 5 kWh.m2/day. The solar photovoltaic (PV) panel is symmetric topology of solar inverters.
In a preferred embodiment the method 100 for controlling a potential-induced degradation (PID) in solar photovoltaic (PV) panel 102 by providing an improvement over negative grounding by recovering damaged modules by polarity reversal of the photovoltaic array 104 and following the steps, Step 1: opening a plurality of the photovoltaic modules 106 connections. Step 2: Recording the Voc of the modules with respect to position in the photovoltaic array from position ‘1’ to position ‘L’, Step 3: reversing the connections of the plurality of the photovoltaic

modules so that first module ‘1’ of the photovoltaic array is connected to the negative terminal of the string monitoring box (SMB) and last module ‘L’ is connected to positive terminal of the string monitoring box (SMB). Step 4: monitor the performance of photovoltaic array within predetermined time of polarity reversal; and Step 5: moving low performing modules to positive bias in the photovoltaic array to recover all potential-induced degradation effected modules and remove non-recovered modules.
In a preferred embodiment the predetermined time is 1-2 weeks of polarity reversal.
In one embodiment the method 100 for isolating damaged modules for overcoming a potential-induced degradation (PID) in solar photovoltaic (PV) plant 102 by polarity reversal , recording performance of photovoltaic modules 106 before and after polarity reversal after a predetermined time, changing low performing modules to positive bias in the photovoltaic array 104 for recovery, isolating the irreversibly damaged modules and replacing the damaged photovoltaic modules to provide improvement over negative grounding.
In a preferred embodiment the predetermined time is after 1-2 weeks of polarity reversal. The presence of potential-induced degradation is measured by the high occurrence of low Voc 108 towards the negative end of the photovoltaic array 104.
In a preferred embodiment using this method 100 for detecting and mitigating the effects of potential-induced degradation (PID) in a solar photovoltaic (PV) plant

102. The solar photovoltaic (PV) plant 102 investor could arrest and reverse the loss due to PID and bring the power plant back to normal working condition within 1-2 weeks. Using this method 100, issues of onsite detection without the use of dismounting or using special apparatus are addressed. The method 100 also reduces the mitigation of the problem which is to be used associated with the negative grounding of the inverters. The individual modules affected by reversible as well as irreversible degradation could be separately distinguished using the methods 100 described in the invention.
TECHNICAL ADVANTAGE
The present disclosure proposes a specific way of data collection and polarity reversal of the PV module in a PV string as an inventive method for detecting, mitigating and recovering PID.
The present disclosure proposes a method for mitigation of PID that could be applied for symmetric topology of solar inverters.
The present disclosure proposes a method that could be applied for inverters with negative grounding or with photovoltaic power powers with counter-PID accessory in operation such as anti-PID kit.
The present disclosure proposes a method to improve the plant performance in all cases and to check the effectiveness of the counter-PID measure in place.
Furthermore, each of the appended claims defines a separate invention, which for infringement purposes is recognized as including equivalents to the various elements or limitations specified in the claims. Depending on the context, all

references below to the “invention” may in some cases refer to certain specific embodiments only. In other cases, it will be recognized that references to the “invention” will refer to subject matter recited in one or more, but not necessarily all, of the claims.
Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description of all groups used in the appended claims.
Furthermore, those skilled in the art can appreciate that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. It will be appreciated that several of the above-disclosed and other features and functions, or alternatives thereof, may be combined into other systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may subsequently be made by those skilled in the art without departing from the scope of the present disclosure as encompassed by the following claims.
The claims, as originally presented and as they may be amended, encompass variations, alternatives, modifications, improvements, equivalents, and substantial

equivalents of the embodiments and teachings disclosed herein, including those that are presently unforeseen or unappreciated, and that, for example, may arise from applicants/patentees and others.
While the foregoing describes various embodiments of the present disclosure, other and further embodiments of the present disclosure may be devised without departing from the basic scope thereof. The scope of the present disclosure is determined by the claims that follow. The present disclosure is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.

WE CLAIM:
1. A method 100 for detecting and mitigating the effects of potential-induced degradation (PID) in a solar photovoltaic (PV) plant (102) having a plurality of photovoltaic arrays 104, the method comprising:
a. providing a low performing photovoltaic array (104) of length L having a
plurality of photovoltaic modules (106);
b. opening a plurality of the photovoltaic module (106) connections;
c. recording an open circuit voltages (Voc) (108) of the plurality of photovoltaic
modules (106) related to a position of the photovoltaic module (106) in the
photovoltaic array 104, wherein ‘1 to L/2’ are positive modules (112) configured
close to a positive terminal (114) and ‘L/2+1 to L’ are negative modules (116)
configured close to a negative terminal (118) of SMB (String Monitoring Box);
iii. measuring the potential-induced degradation (PID) by plotting the relation
between open circuit voltages (Voc) (108) and the position of the photovoltaic
module (106) in the photovoltaic array 104 defined by an equation Avg(Voc)1-L/2
> Avg(Voc)L/2-LPID, wherein
when low performance is experienced in case equation (Avg(Voc)1-L/2 > Avg(Voc)L/2-L  PID) is not met, polarity reversal of the photovoltaic array 104 is performed and the photovoltaic array 104 performance is recorded in a specified interval of time under specific condition of sun and the potential-induced degradation is measured based on the equation, (Vop * Iop)Post - reversal
> (Vop * Iop)Pre-reversalPID; where Vop is an operating voltage and Iop is a

current voltage for the photovoltaic string (110) , and post-reversal and pre-reversal are the readings after and before the polarity reversal.
2. The method as claimed in claim 1, wherein the Avg(Voc)1-L/2 is a module Voc averaged over modules from 1 to L/2.
3. The method as claimed in claim 1, wherein the Avg(Voc)L/2-L is a module Voc averaged over modules from L/2+1 to L.
4. The method as claimed in claim 1, wherein the specific condition of sun is 30 –
50 hrs. of time interval and sunshine measured at 5 kWh.m2/day.
5. The method as claimed in claim 1, wherein the solar photovoltaic (PV) plant
(102) has symmetric topology of solar inverters.
6. The method 100 for controlling a potential-induced degradation (PID) in solar
photovoltaic (PV) panel (102), the method comprising:
(i) recovering the damaged modules by polarity reversal of the array 104 and following the steps:
a) providing a low performing photovoltaic arrays (104) of length L having a plurality of photovoltaic modules (106);
b) determining potential induced degradation as per Claim 1. c;
c) moving low performing modules to positive bias in the photovoltaic array 104 to recover all potential-induced degradation effected modules;

d) monitoring the photovoltaic array 104 within predetermined time of polarity reversal;
e) performing negative grounding of the inverters 122 with 1-2 weeks of polarity reversal

7. The method as claimed in claim 6, wherein the predetermined time is 1-2 weeks of polarity reversal.
8. The method 100 for isolating damaged modules for overcoming a potential-induced degradation (PID) in solar photovoltaic (PV) panel (102), the method comprising:
a. determining the polarity reversal and recording performance after a
predetermined time;
b. changing low performing modules to positive bias in the photovoltaic array
104;
c. measuring the plurality of the photovoltaic modules (106) which reaches the
damaged state attaining degraded irreversibly;
d. isolating the irreversibly damaged modules; and
e. replacing the damaged photovoltaic modules (106) to provide improvement
over negative grounding.
9. The method as claimed in claim 8, wherein the predetermined time is after 1-2
weeks of polarity reversal.

10.The method as claimed in claim 1 or 6 or 8, wherein presence of potential-induced degradation is measured by the high occurrence of low Voc (108) towards the negative end of the photovoltaic array 104.