In the previous article, we have defined some environmental factors that solar installers are stressed over. During the rainy season, installers are concerned about the storms and lightning impacts as they are the major calamitous failure of the solar panel system. The time and cost incurred in repairing the damage due to the indirect and direct strikes are high, hence prior protection against these damages is worth the investment. The article below describes some of the easy techniques that one can implement to protect against these damages.

Lightning strikes are mostly classified as direct and indirect strikes.

Direct Strikes are severe but rare, it leads to melting of the panels and damage to the inverter, fuses, and cable. It induces high current into the system, thus causing overheating and damage to the system. An indirect strike occurs more often, it creates electromagnetic induction that generates high voltage into the solar system and house. The generated high voltage passes through the system wiring to the components, thus damaging the conductor, solar panels, inverter, and other components connected. But don’t worry! We take steps to help avoid lightning damages to the PV system. Risk analysis and protection against lightning must be done according to the IEC standard (we have further described the IEC standards for protection against lightning strikes) at the designing stage.

Two main solutions to protect against the lightning strike:

1. Grounding 2. Lightning arrestor

Grounding:

Grounding is one of the basic techniques used to divert the path of lightning from the component straight to the ground. For places with occasional lightning strokes, the grounding technique is enough to protect the PV system from lightning and surges (without adding any other protection equipment). Good grounding is very necessary, even if we use lightning arrestors and surge protectors it will work effectively only with proper grounding.

For proper grounding one needs to follow the following points:

1. Check the resistivity of the ground: Electricity flow handling capacity. Article 250 (the article specifies the requirement of grounding and bonding) and article 690.41 (the article specifies solar PV electrical energy system) of the National electrical code (NEC) specify grounding requirements. 2. Interconnect all the PV panels, inverter, controller, and all the other components to the common ground along with the house grounding system to the common earthing point. We need to install one earth pit for the DC side (solar panels, DC distribution box) and one for the lightning arrestor and AC side (inverter, AC Distribution Box). 3. For proper and effective grounding, the use of copper / Aluminium wire / GI strip is highly recommended. The wire/strip used should be free from sharp bends and twists and should be buried in a way such that most of the area comes in contact with moist soil.

Do we need to install other protective equipment to protect against lightning?

Adding protective equipment depends on the location and environmental condition. It is recommended to install additional lightning protective devices under the following circumstances: 1. If the solar panel is installed in the lightning prone location 2. Presence of heavy metal objects such as water tanks, solar thermal heaters, satellite antennas, etc. 3. Length of wire larger than 100m 5. Dry soil with poor conductivity Let us check the lightning protection system in detail. The lightning Protection system is categorised as follows:

External protection systems

External protection systems are used to protect the solar rooftop system from direct lightning strikes. This type of protection system gets activated only when lightning strikes over the solar system, thus protecting solar panels and other equipment associated with it.

1. Air termination system

An air termination system is installed to protect the building from uncontrolled lightning strikes. The system consists of cables, spanned wires, and conductors. A correct design, dimension with more attention towards the corners and edges allows better protection against lightning. Design methods commonly used for air termination systems are: Mesh Method – It is used for the flat roof structure Rolling Sphere – It is the universally used method for all types of structure Protection Angle Method – It is preferred for single masts and finials type structures. For solar energy systems, the protection angle method is recommended.

2. Down conductors

The down conductor act as a conductive connector between air and earth termination systems. It allows the passage of lightning current to the earth termination system and provides the shortest and least resistant path to the current. For proper protection, down conductors should match the following guidelines: The down conductor should offer several short distances parallel current paths. A high voltage insulated down conductor is installed to ensure proper protection and separation distance from other conductive components. Conductors should be evenly distributed. The number of conductors required depends on the rooftop external edges area, so a proper calculation must be done.

3. Earthing termination system

Earthing termination system is installed to avoid voltage-rise in the earthing system, it helps in discharging the surge current to the earth. For effective discharging, it is recommended to use a low-frequency electrode offering a low resistance path to the earth and resistance to corrosion.

Internal Lightning Protection System(LPS)

To protect the building structure against indirect strikes, internal LPS is used. It is done in the following ways:

1. Lightning equipotential bonding –

It reduces the voltage difference by connecting the different isolated parts of the system using conductors or surge protection devices with the help of IEC 60364-4-41 standard(It defines the essential requirements related to protection against electric shock, direct and indirect contact of persons and livestock) Dangerous sparking is prevented by keeping an appropriate distance between the electrical conducting components and lightning protection equipment.

2. Surge (Lightning) protection device –

Surge protection devices are a part of the lightning protection system. The primary function of SPD is to limit transient overvoltages of atmospheric origin below the set hazardous value and divert current waves to the earth to protect the electrical installation system. In solar energy systems, SPDs are installed in ACDBs (AC distribution box) and are inbuilt in Inverters as well. Lightning rods are placed on the building top and are connected to the ground, they help in preventing the surrounding atmosphere from the static charges. In the case of lightning, the developed high current will pass to the ground directly.

IEC standards for lightning protection

The International Electrotechnical Commission (IEC) defines guidelines for all electrical, electronic and other similar technologies. BS EN/IEC 62305 defines guidelines in consideration of lightning protection, it is divided into four major parts: 1. General principle 2. Risk management 3. Physical damage to the structures and life hazard 4. Electrical and electronic systems

Lightning protection for residential rooftop solar consumer – key points

The following points should be taken into consideration while building a lightning protection system for rooftop solar models: 1. Install lightning rod at the topmost point in the location where the solar energy system is installed. 2. The DC connection of the PV system should be kept at a reasonable distance from the metal components on the roof. 3. Ensure AC distribution box and inverter consists of a surge protection device. 4. Make sure down conductors are not rusted(as it increases the resistivity) and earthed properly.