Grounding is one of the most important safety factors of any electrical system. Earthing (Grounding) facilitates the efficient and quick operation of protective relays in case of any earth fault and provides safety to costly equipment as well as working personnel. When a PV module generates electricity its surface area becomes charged and acts like a capacitor. This capacitance known as parasitic capacitance, has an undesirable effect i.e. Leakage current, also known as matrix residual current, is caused by parasitic capacitance between the photovoltaic system and the ground. This leakage current is not dangerous, however, it superimposes possible residual current that could occur through touching a live line through damaged insulation and can seriously pose a threat for working personnel as well as solar PV systems. Hence, the grounding of SPV modules and inverter becomes very important.

This paper gives an overview of the solar PV system and provides insight into the methods of grounding solar PV systems adopted internationally and being used in India. Besides the above this paper also provides an overview of Codes and Regulations w.r.t earthing of solar PV systems. Keywords: Earthing (Grounding), System Earthing, Protective Earth (PE), Step & Touch Potential, Solar PV, Lightning Protection, Inverter, Combining Box (CB).

 

1.0 INTRODUCTION

Grounding/ Earthing means making a connection to the general mass of earth. The use of grounding is so widespread in an electric system that at practically every point in the system, from the generators to the consumers’ equipment, earth

connections are made.

Earlier, the design criterion was to achieve lowest earth resistance, However, the modern design criterion for grounding system is to achieve low earth resistance and also to achieve safe’ steppotential’, ‘touch potential’ and voltage gradient during an earth fault between conductor and any of the earthed bodies in the substation.

 

The Objectives of Neutral Grounding are:

1. To preserve security of the electric system by ensuring that the potential on each conductor is restricted to such a value as it is consistent with the insulation applied.

2. To ensure efficient and fast operation of protective gear in case of earth faults. 

 

The objectives of General Grounding system include :

1. To provides a low resistance return path for fault current which further protect both working staff (freedom from dangerous electric shock voltage) and equipment installed in the substation.

2. To provide current carrying capability, both in magnitude and duration, adequate to accept the earth fault current permitted by the over current protective system without creating a fire or explosive hazard to building or contents.

3. To prevents dangerous GPR with respect to remote ground during fault condition.

4. To provide uniform potential bonding /zone of conductive objects within substation to the grounding system to avoid development of any dangerous potential between objects (and earth).

5. To prevent building up of electrostatic charge and discharge within the substation, which may results in sparks.

6. To allow sufficient current to flow safely for satisfactory operation (better performance) of protection system.

7. Providing a safe path for discharge directly to the earth if lightning strikes. 

 

Grounding of electronic equipment is necessary for the safety of personnel and equipment (Protectiv Earthing) and for proper functioning of the equipment (Functional Earthing). Usual methods of grounding of various metallic structures and housing of equipment in the substation for the safety of personnel are also applicable to grounding of cabinets and housings of the electronic equipment.

 

Grounding of the electronic equipment minimizes unwanted electrical signals (Electromagnetic Interference or EMI) that might interfere with the functioning of the equipment and cause component damage. It also prevents accumulation of static charge on the equipment by providing a low impedance leakage path to the earth for the same.

 

2.0 SOLAR PV SYSTEM & MAIN PARTS

Solar panels, made up of photovoltaic (PV) cells, capture sunlight particles or photons. Using a semiconducting material such as silicon, the PV cells convert the sunlight into useable direct current (DC) electricity. The main parts of solar PV. Solar Panel (Multi / Poly Crystalline) receives energy from solar radiation during the day. Photovoltaic effect of semiconductor cells converts solar energy to electrical energy. This electrical energy is stored in Battery Bank or Goes to grid. Since there is variation in electrical flow from solar panels due to variation in reception of solar energy, battery will have fluctuation in charging and discharging. This may lead to degradation of battery life. To protect, Charge Controller is used for smooth functioning of battery. The Maximum Power Point Tracking (MPPT) function of charge controller provides optimum charging and utilisation of solar power generated. In case load (i.e. lights) is suitable to function on AC, Inverter is used to convert battery’s electrical energy from DC to AC. Once the batteries are discharged, the system shifts automatically to the existing power from grid guided by auto switch-over. The load data & generation etc. is measured & is monitored through a computer & suitable software. Solar sensor is used to check the energy levels & control operations and switch over functions through a Programmable Logic Controller PLC.

 

1. PV Cell: Most elementary device that exhibits the photovoltaic effect, i.e. the direct nonthermal conversion of radiant energy into electrical energy

2. Solar Panel/ PV module: Complete and environmentally protected assembly of interconnected photovoltaic cells

3. PV Array: Assembly of electrically interconnected PV modules, PV strings or PV sub-arrays 

 

2.2 Types of Solar Plants:

1. Solar Rooftop System: Solar rooftop plant is mainly installed on roof of our home, building, shop etc. this plant generally in KW capacity 2. ON Grid Solar Plant : it is mainly installed for large scale power generation. These plants are in MW rating. On-Grid Systems are solar PV systems

that only generate power when the utility power grid is available. They must connect to the grid to function. They can send excess power generated back to the grid when you are overproducing.  3. Off Grid Plant: it is used for provide electricity

for those area where conventional power grid is not possible. Specifically for isolated area village. This plant also in KW capacities.  

 

4. The hybrid means combination of solar and wind or solar thermal with battery, the plant depends on available source on grid or off grid

 

3.0 SOLAR PV EARTHING (GROUNDING) Prime objective of Earthing is to provide a Zero Potential Surface in and around and under the area where the electrical equipment is installed or erected. To achieve this objective the non-current carrying parts of the electrical equipment is connected to the general mass of the Earth which prevents the appearance of dangerous voltage on the enclosures and helps to provide safety to working safety to working staff and public.

 

PV Plant Earthing may be divided into four 1. DC Earthing in PV: MMS Earthing should be Copper flat/GI flat (Rigid Material). Add 25% as extra while calculating the proper size of the earth flat material for the MMS. Generally for the 1MW PV Plant, Maximum Six to Eight earth pits for the DC Area (PV Area) are used as per Indian practice. The earth pits should be covered the PV Area as a rectangular format. SMB Earthing should be strengthened by connecting directly to earth pit, instead of connection with MMS.

2. AC Earthing : For the PV Plant based on the Short Circuit level of the System. Each Central Inverter should be earthed with two individual earth pits which is bonded with other earthing systems .

3. Special Earthing is nothing but, Earthing for the SCADA, CCTV & Weather Monitoring Station which is needed Copper Plate Earthing. It should be combined with main earthing.

4. AC EHV EARTHING: If PV Plant is more than 5MW, then power evacuation system is adapted with Switchyard. We known well Switchyard Earthing is taking to cater Touch voltage, Step voltage & Mesh Voltage. Earthing should done with Earth Mat which is common method used worldwide. For Switchyard Earthing, IEEE 80 is most preferable guide global wide.

 

4.0 METHODS OF EARTHING OF SOLAR PV SYSTEM

When it comes to Renewable Energy (RE) system earthing, a DC to AC inverter is unique in that it is exposed to both the AC and DC sides of the system. Thus, attention to its grounding requires special consideration. The point is that, when it comes to earthing the inverter, there are risks in treating an inverter like any other metal box.

 

However we need to look at the range of fault conditions that can occur inside an inverter, which is something like:

a. DC short

b. AC short

c. a DC positive to chassis earth fault

d. an AC hot to chassis earth fault

e. DC positive to AC hot short.

 

1.SEPARATE AND BONDED : Section 690.47(C) (1), a separate dc grounding-electrode system can be installed, provided it is bonded to the ac grounding-electrode system. The ac and dc GECs must be sized based on their respective NEC sections, and the grounding electrodes must be bonded using a conductor no smaller than the larger of the ac or dc GECs. Note that the dc GEC and/or the bonding conductor between the grounding electrodes cannot replace the required EGCs.

 

2. COMMON GROUNDING ELECTRODE : NEC Section 690.47(C)(2) allows for a common grounding electrode (or grounding-electrode system) to serve both the ac and dc systems, The dc GEC cannot replace the required ac EGC. In the event that the ac grounding electrode is not accessible, the dc GEC can connect directly to the ac GEC per Section 250.64(C)(1), which allows for irreversibly crimped or exothermically welded-connections. This method is widely employed for a variety of PV system types, from residential to utility-scale systems. For example, a ground ring around an inverter and transformer pad can serve as both the ac and the dc grounding electrode. The allowance for connecting to the ac GEC is helpful when the existing grounding electrode is accessible. Be aware, however, that if an existing ac grounding electrode is inaccessible, then there may be no way to verify that the resistance to ground is less than or equal to 25 ohm, as required in Section 250.53(A)(2).

 

3.COMBINED GROUNDING CONDUCTOR : A combined grounding conductor can serve as both the dc GEC and the ac EGC, as shown in Option 3, Figure 10. While Section 250.121 specifies that an EGC cannot be used as a GEC, Section 690.47(C) (3) amends this general Code requirement and provides an allowance exclusively for PV systems. On the face of it, installing one conductor instead of two seems like the simplest and least expensive method. In practice, the requirements associated with installing a combined grounding conductor may complicate things. Since the combined grounding conductor serves two functions—dc GEC and ac EGC—it must be sized according to the function that requires the largest conductor: The size of the ac EGC is determined based on NEC Table 250.122, and the size of the dc GEC is determined based on Section 250.166. Further, the combined conductor must either run unspliced or irreversibly spliced from the inverter to the grounding busbar in the associated ac equipment. While the option to use a combi ed grounding conductor is applicable to all PV system types, it is most common on systems that use micro inverters with an internal dc system bonding jumper.

 

5.0 LIGHTNING PROTECTION OF SOLAR PV

Solar arrays, like all electronic devices, are prone to surges in voltage that can harm components and increase downtime. Surge protection devices can help keep systems running and profitable. The lightning protection zone for solar PV system A power surge, also called a transient voltage, is a generally short increase in voltage that’s well above normal levels. For example, the standard voltage for a home or office is 220 V. Voltage can be thought of as electrical pressure. So just as too much water pressure will burst a garden hose, too high a voltage could damage electronics.  

 

Solar arrays are also electronic devices and so are subject to the same potential for damage from surges. Solar panels are especially prone to lightning strikes due to their large surface area and placement in exposed locations, such as on rooftops or ground-mounted in open spaces. Lightning is about 50,000°F—five times hotter than the sun—so it’s not surprising it can be detrimental to solar equipment. “If the solar panels are struck directly, lightning can burn holes in the equipment or even cause explosions, and the entire system is destroyed.” But the effects of lighting and other over voltages aren’t always so strikingly apparent, the secondary effects of these events can not only affect major components such as modules and inverters, but also monitoring systems, tracker controls and weather stations. The LA installation method Because all electrical equipment is susceptible to surges, SPDs are available for all solar array components. The industrial versions of these devices also use metal oxide varistors (MOV) in combination with other sophisticated equipment to conduct surge over voltages to grounding. Therefore, SPDs are generally installed after a stable grounding system is in place. A SPD network should be installed throughout the solar array’s AC and DC power distribution to protect critical circuits. SPDs should be installed on both the DC inputs and AC outputs of the system’s inverter(s) and be deployed with reference to ground on both the positive and negative DC lines. 

 

AC protection should be deployed on each power conductor to the ground. Combiner circuits should also be protected, as should all control circuits and even tracking and monitoring systems to prevent interference and data loss. When it comes to commercial and utility-scale systems, the 10-m rule should be used. For installations with DC cable lengths under 10 m (33 ft), DC solar surge protection should be installed at a convenient point such as at inverters, combiner boxes or closer to the solar modules. For installations with DC cabling over 10 m, surge protection should be installed at both the inverter and module ends of the cables. Residential solar systems with micro inverters have very short DC cabling, but longer AC cables. An SPD installed at the combiner box can protect the home from array surges. An SPD on the main panel can protect the home from array surges as well, in addition to those from utility power and other internal equipment. Additional steps, such as adding lightning air terminals, can be taken to further protect a solar array specifically from lighting. “Solar arrays are expected to operate with a known failure rate during 25 years or more.” “Random failures due to surges and transients lower the financial return. Loss of reliability reduces the value of solar power generation to grid operators.

 

6.0 GROUNDING OF SOLAR PV IN INDIA- PRACTICES

In India solar PV system installation has grow exponentially. Unfortunately there are no clear cut guidelines or methodology for grounding of PV solar system. The solar installations are being carried out as per the drawings approved by the consultant or OEM Generally for the 1MW PV Plant, Maximum Six to Eight earth pits for the DC Area (PV Area) are used as per Indian practice. The earth pits should be covered the PV Area as a rectangular format

 

7.0 GROUNDING OF SOLAR PVREGULATIONS & CODES

First of all, let us start with CEA safety regulation 2023 Chapter X i.e. Additional Safety Requirements for Renewable Generating Stations

 

7.1 Safety Requirements for Solar Installations The Following Earthing Requirements for Solar Installations Shall be Ensured, Namely: –

i. solar earthing shall be as per the relevant standard;

ii. the frame of inverter cabinet shall be connected with the earthing bus bar through the earthing terminals using flexible braided copper wire;

iii. all metal casing and shielding of the plant, each array structure of the photovoltaic yard, equipment, inverters and control systems shall be earthed through proper earthing;

iv. earthing system shall connect all non-current carrying metal receptacles, electrical boxes, appliance frames, chasis and photovoltaic module mounting structures in one long run and the earth strips shall be interconnected by proper welding and shall not be bolted;

v. there shall be adequate number of interconnected earth pits provided in each location and minimum required gap shall be provided in between earth pits as per relevant standard.

 

7.2 National Electrical Code of India (Part 8) : 

covers essential requirements for electrical installations for power supply systems based on the solar photovoltaic (PV) energy including PV modules, PV array circuits, inverters, controllers and balance of system components used for such systems. These systems may be interactive with electric power utility or other electrical power production sources, such as diesel generator (DG) or may be stand-alone, with or without electrical energy storage, such as batteries. These systems may have A.C. or D.C. output for utilization. The objective of this document is to address the design, installation, safety and quality requirements arising from the characteristics specific of PV installations.

 

The scope of this Part of the Code includes following:

a. General safety procedures and practices in Solar PV Installations, both rooftop and utility scale.

b. General characteristics of solar PV components and installations, both rooftop and utility scale.

c. Requirements and recommendations in wiring and earthing of rooftop PV installations on buildings or industrial structures.

d. Requirements and recommendations in electrical safety protection of solar PV systems, both rooftop and utility scale.

 

1. EARTHING (Clause 7 page -736) TN-S system with separate protective conductor shall be used as below in the a.c. side. For d.c. side various configurations are explained in TABLE 1 BELOW. However in all systems, separate protective conductor is necessary. PV array configuration shall be permitted with and without functional (Active) d.c. earthing. NOTES 1. TN-C system shall not be used.

2. TT system if used on a.c. side shall be protected with an RCD of 30 mA at origin of installation.

 

Earthing of one of the live conductors of the d.c. side is permitted if there is at least simple separation between the a.c. side and the d.c. side. Some PV module types require functional earthing of one of the current carrying poles of the PV array for proper operation. Thin film modules typically need to be negatively earthed, to prevent ‘bargraph’ corrosion inside the module. Back-contact modules need to be positively earthed to achieve their rated efficiency. Functional PV module earth is useful to bleed charge away from the PV cells and mitigate PID of cells. Negative pole of crystalline silicon PV

 

7.3 NATIONAL PORTAL FOR ROOFTOP SOLAR

Hon’ble Prime Minister of India, Shri Narendra Modi launched the National Portal for Rooftop Solar on 30/07/2022. Shri R. K. Singh, Union Minister for Power and NRE and Shri Krishan Pal Gurjar, MoS, Power and Heavy Industries were present. Shri Bhagwanth Khuba, MoS, MNRE joined virtually. This portal provides the Technical specifications for rooftop solar plants installed under simplified procedure as under:

1. Roof Top Solar (RTS) Photo Voltaic (PV)

Earthing Protection (clause 7.1)

i. The earthing shall be done in accordance with latest Standards.

ii. Each array structure of the PV yard, Low Tension (LT) power system, earthing grid for switchyard, all electrical equipment, inverter, all junction boxes, etc. shall be grounded properly as per IS 3043-2018.

iii. All metal casing/ shielding of the plant shall be thoroughly grounded in accordance with CEA Safety Regulation 2010. In addition, the lightning arrester/masts should also be earthed inside the array field.

iv. Earth resistance should be as low as possible and shall never be higher than 5 ohms.

v. For 10 KW and above systems, separate three earth pits shall be provided for individual three earthing viz.: DC side earthing, AC side earthing and lightning arrestor earthing.

2. Lightning Protection (clause 7.2)

i. The SPV power plants shall be provided with lightning & over voltage protection, if required. The main aim in this protection shall be to reduce the overvoltage to a tolerable value before it reaches the PV or other sub system components. The source of over voltage can be lightning, atmosphere disturbances etc. Lightning arrestor shall not be installed on the mounting structure.

ii. The entire space occupying the SPV array shall be suitably protected against Lightning by deploying required number of Lightning Arrestors (LAs). Lightning protection should be provided as per NFC17-102:2011/IEC 62305 standard.

iii. The protection against induced high-voltages shall be provided by the use of Metal Oxide Varistors (MOVs)/Franklin Rod type LA/Early streamer type LA.

iv. The current carrying cable from lightning arrestor to the earth pit should have sufficient current carrying capacity according to IEC 62305. According to standard, the minimum requirement for a lightning protection system designed for class of LPS III is a 6 mm2 copper/ 16 mm2 aluminum or GI strip bearing size 25*3 mm thick). Separate pipe for running earth wires of Lightning Arrestor shall be used.

 

8.0 CONCLUSION:

Grounding procedure of solar PV system for safety of personnel and equipment, called protective grounding, is same as being applied for grounding of other metallic housings and structures in the power station. Functional grounding is important for proper functioning of the equipment. It stabilizes circuit reference potential, protects the circuit against static charge and over- voltages, and minimizes interference from unwanted signals (noise). Various methods of grounding of solar PV have been discussed. Adequate designing of grounding system will help in mitigating or eliminating the danger of shock as well as failure of solar PV system.

Importance of providing protection against over voltage should not be ignored and adequate designing must be done to safeguard our solar system against over voltage in the system. Last but not the least there is acute need to follow guidelines for grounding of solar PV system as discussed in section 7 in the article.

 

REFERENCES

1. IEEE Std. 80-2013, IEEE Guide for Safety in AC Substation Grounding, New York, NY: IEEE

2. NEC (SP30) National Electrical Code 2023

3. Manual on,” Grounding of A C Power Systems,” Publication No 339, C.B.I.P. New Delhi, 2017

4. IS 3043-2018 Indian Standard Code of Practice for Earthing.

5. CEA ‘Measures relating to Safety and Electric Supply’ 2023

6. IEC 62738 :Ground Mounted PV Power Plants

7. IEC 62548: PV Arrays- Design Requirements

8. IEC 60364-7-712: Requirement for Special Installation- Solar PV Power Supply System

9. IEC 60364-5-54: Selection and Erection of Electrical Equipment, Earthing Arrangements , Protective Conductors and Protective Bonding Conductor

10. Article 250 and 690 of NEC

11. IEC 62305- Protection Against Lightning

12. Photovoltaic System Grounding – American Board for Codes and S tandards.