Solar fields can encounter destructive pure lightning storms. Given the expansive ground coverage of solar panels, which are often exposed and isolated, surge protection is essential for maintaining their lifespan. Lightning is a discharge in the atmosphere. During a lightning strike, the release of energy can cause fires due to the high charge concentration in rain clouds, leading to air ionization. This ionization between the ground and the rain cloud results in a discharge from the cloud to the ground. The surges induced by these storms are the most significant.

Indirect lightning strikes are destructive. Uncontrolled observations on lightning activities often do not aptly indicate the overvoltage levels caused by lightning in photovoltaic arrays. Indirect lightning strikes can easily damage sensitive components inside PV devices, and the cost of repairing or replacing damaged components is usually high, affecting the reliability of the PV system. Overvoltage depends on each photovoltaic system and the wiring setup. Photovoltaic systems are exposed in vast open spaces, often in fields or atop buildings. Charged rain clouds accumulating over such open areas tend to discharge in the form of lightning. When this occurs, voltage surges are likely. The more expansive the field, the greater the potential for damage.

Standard for the Installation of Lightning

Surges can damage electronic equipment to catastrophic failure levels. If a person is present during a surge, it can also pose a threat to their safety. An indirect lightning strike can be fatal if a person is within 60 feet of the strike point. When a photovoltaic system is located in industrial settings, business operations and equipment are also at risk. Although inverters are costly, the downtime cost in industrial applications is even higher. When lightning strikes a solar photovoltaic system, it induces transient currents and voltages within the PV system circuitry. These transient currents and voltages appear at the equipment terminals and can lead to insulation and dielectric failures in the solar PV electrical and electronic components (such as PV solar panels, inverters, control, and communication equipment) and devices within buildings. Array boxes, inverters, and MPPT (Maximum Power Point Trackers) have the highest failure points. To prevent high energy from passing through electronic devices and causing high-voltage damage to the PV system, voltage surges must have a grounding path. All conductive surfaces should be grounded directly, and all lines entering and exiting the system (such as Ethernet cables and AC power) should be grounded through a surge protector. Every string group inside array boxes, combiner boxes, and DC disconnect switches needs a surge protector.

Classification of Surge Protectors:

Surge protectors prevent damage caused by surges. UL 1449 defines Type 1, Type 2, and Type 3 surge protectors:

  • Type 1: A one-port, permanently connected surge protector, designed for use between the secondary side of service transformers and the line side of service equipment overcurrent devices and the load side, including outside the meter socket enclosure, and encapsulated surge protectors that can be installed without an external overcurrent protection device. Type 1 surge protectors can be connected between the PV array and the main service disconnect switch in the PV system.
  • Type 2: A permanently connected surge protector designed for devices on the load side of service equipment overcurrent devices; includes surge protectors located at branch panels and encapsulated surge protectors. The Imax value is the maximum single discharge current the surge protector can support, represented by an 8/20µs waveform.
  • Type 3: Point of use surge protectors, installed with a minimum conductor length of 10 meters from the electrical service panel to the point of use, for example, power line connections, direct plug-ins, socket types, and surge protectors installed at the protected device’s location. No conductors supplied or used to connect the surge protector should be set within this distance (10 meters).

Type 1 surge protectors can protect against direct lightning strikes, characterized by a 10/350 µs current wave. Type 1 surge protectors are used for central inverters. Type 2 surge protectors can protect against indirect lightning strikes, characterized by an 8/20 µs waveform, representing a lightning strike with a rise time of 8 µs and a half-peak duration of 20 µs. They can prevent overvoltages from propagating into electrical devices and equipment and can also protect against the electromagnetic effects of lightning surges propagating within wires. Every MPPT, as well as string inverters and array boxes, should use Type 2 surge protectors. Boxes experiencing surges often get damaged due to indirect lightning strikes. Material, height, type, and shape all influence an object’s ability to attract lightning strikes. If a box’s shape or material has a tendency to attract lightning, Type 1 surge protectors or lightning rods should be used.

Height, sharp shapes, and isolation are primary characteristics determining lightning strike locations. The notion that metal attracts lightning is a myth. However, it’s crucial to understand that regardless of where a PV field is located or the shape of nearby objects, surge protectors are indispensable for every PV system due to their inherent vulnerability to direct and indirect lightning strikes.