Electricity + Control October 2019

EARTHING + LIGHTNING PROTECTION

Lightning protection systems for rooftop solar PV installations

Trevor Manas, Director, Lightning Protection Concepts

Solar photovoltaic energy supply systems are being used increasingly throughout South Africa. Based on the facts that owner-generated electricity is cheaper and provides a high degree of independence from the national electrical grid, PV systems are fast becoming an integral part of localised electrical installations.

at a glance

• Lightning discharges cause field-based and conducted electrical in- terference and this effect increases in relation to cable lengths or conductor loops. • Whether or not a struc- tural lightning protection system is required, the in- stallation of a coordinated surge protection system for the PV installation is imperative. 1 2

M any of these systems are installed in exposed places such as on roof tops and will therefore be subjected to all weather conditions (including lightning) for decades. The cables of photovoltaic (PV) systems often enter the building and extend over long distances before they reach the electrical connection point. Lightning discharges cause field-based and conducted electrical interference and this effect increases in relation to cable lengths or conductor loops. Surges not only damage PV systems but can also damage the other devices inside the building. Most importantly, production facilities can easily be damaged, disrupting or halting production. The energy released by a lightning discharge is one of the most frequent causes of fire. Therefore the protection of personnel and the prevention of fire are paramount in the case of a direct lightning strike to a building. At the stage of designing a PV system, the building should be assessed to determine whether Lightning protection for rooftop installations

or not there is a lightning protection system in place, or, for new structures, whether or not lightning protection is required. The need for lightning protection for the PV system will relate to this assessment and will differ for a building without lightning protection and a building or structure that is or has to be equipped with a permanently effective lightning protection system. The installation of PV modules on a building does not increase the risk of a lightning strike. The need for lightning protection does not derive directly from the existence of a PV system. There may however be an increased danger for the electric facilities of the building in the event of a lightning strike. This is based on the fact that, due to the wiring of the PV lines inside the building in existing risers and cable runs, strong conducted and radiated interferences may result from lightning currents. It is therefore necessary to estimate the risk of lightning strikes according to SANS/IEC 62305 Part 2, and to take the results from this into account in designing the lightning protection system (LPS). Surge protection for PV systems Surges in PV systems are caused by inductive or capacitive voltages from lightning discharges and switching operations in the upstream ac system. Lightning surges in the PV system can damage PV modules and inverters. This can have serious consequences for the operation of the system: high repair costs of the inverter, for example, or system failure which will reduce power availability considerably. Surge protection devices (SPDs) installed to protect the ac, dc and data systems have proven to be effective in protecting the electrical systems from destructive over-voltages and surge currents.

Solar PV systems are often installed on rooftops and are therefore exposed to all weather conditions – including lightning – over decades.

26 Electricity + Control

OCTOBER 2019