Why Are Surge Protectors Indispensable for PV Energy Storage Systems?

The core components of these systems, including inverters, energy storage batteries, power conversion systems (PCS), and monitoring systems, consist of mostly precision electronic components whose insulation tolerance is poor. These precision electronic components are susceptible to two main types of surge events experienced while the system is operating:

1. Lightning surge events: Because outdoor PV arrays are designed to be unprotected from lightning strikes, the arrays are exposed to both direct lightning strikes as well as lightning-induced surges from nearby strikes. These lightning surges cause an instantaneous high voltage to surge through the components and can easily destroy the core equipment in your system.

2. Operational surges: When any of the systems experience events such as charging or discharging, starting and stopping inverters, or connecting or disconnecting to the grid, instantaneous voltage spikes can happen.

When connected to power grids, PV systemsproduce an electric current that is typically steady and smooth. However, conditions such as switching actions made to connect or disconnect from the power grid, 

spikes in current that occur from natural sources like lightning strikes or when thunderstorms or strong winds hit the system, or sudden shifts (greatly increased current levels) due to faults in the distribution network, if not properly protected with surge protective devices (SPDs), can result in very large surges of current being conducted through circuits, (typically resulting in large amounts of equipment damage or associated wear) and reduce the life of those systems.

Core Protective Functions of SPDs

The core protective function of SPDs is to shunt surge voltages to ground very quickly (within a few nanoseconds of the occurrence of voltage spike conditions), to shunt the surge current to ground, and to clamp (limit) the voltage to the equipment to within the acceptable range for that equipment to protect it from damage. SPDs protect the entire system. There are two types of SPDs used in PV systems; those located in combiner boxes or inverter DC input terminals that protect against surges generated by the PV arrays on the DC side of these systems, and those SPDs installed in grid-connected distribution cabinets to protect the connection of the grid and system on the AC side of the system from bi-directional surges. Signal side SPDs are also used to protect the “brain” components; that is, monitoring systems from signal interference and other factors that will lead to equipment malfunction.

Severe Consequences of Not Installing SPDs

Failure to install SPDs on a PV system will result in several key losses; most importantly, significant economic losses. Core component maintenance & repair costs are high, and the power generation revenues lost while the system is down, will be much higher than the actual investment in SPDs. Secondly, there are serious safety hazards associated with surges which can short circuit electrical equipment and cause DC arcs that may start fires - resulting in risk to personal and property safety. Thirdly, the use of SPDs is a requirement of most current standards and codes for PV energy storage systems. Not using SPDs will result in failure to meet electrical safety requirements for passing fire acceptance inspections and ultimately, will result in failure of insurance claims.

Key Selection and Installation Considerations for SPDs

To ensure the correct selection of an SPD, it is important that the SPD be appropriate for the configuration of the system in terms of: (i) voltage, (ii) protection performance, and (iii) operating environmental conditions. All applications require that SPDs be installed so that they are positioned accurately and that the SPD is connected to the ground with standard industry grounding techniques; this will allow surge current to be shunted to the ground as effectively as possible. It is also critical for the owner/operator to understand that SPDs are considered a consumable component (which means that eventually they will fail and will require replacement for ongoing protection) and, therefore, they must have a scheduled maintenance plan (which requires that the SPD is inspected and tested on a regular basis) and that a plan is in place to replace the SPD when it fails to ensure long term effectiveness of surge protection.

FAQs About Surge Protectors for PV Systems

1. Do all PV systems need surge protection?
Yes. All PV systems, regardless of size, are susceptible to surges, particularly from lightning and fluctuations in the utility grid, and therefore they will be exposed to significant amounts of surge current whether connected to a utility grid, or standalone.

2. How often will I need to replace SPDs?
Every manufacturer has defined the expected useful life of their SPDs; however, the actual life of an SPD may vary significantly because of the frequency and magnitude of surge events. Routine inspections can help the owner/operator determine when an SPD needs to be replaced.

3. Can I install SPDs?
It is always recommended that installation of an SPD be performed by a qualified installer. Improper installation could void the warranty of the SPD and could also create an increased risk of damaging the system.

Conclusion

SPDs have long been recognized to be one of the most important safety barriers for PV energy storage systems. By recognizing the importance of surge protection, selecting the right SPD product, and performing a standard installation and a routine maintenance program, the owners/operators can effectively eliminate the risks associated with surges and maintain the long term, stable operation of their systems and maximize their return on investment by utilizing PV energy storage systems in a safe, code compliant and efficient manner.