The Importance of Rapid Shutdown in PV Systems

n recent years, the adoption of solar energy has surged due to its positive impact on the environment and economy. However, as with any electrical system, solar energy has its own set of risks. The power generated by photovoltaic (PV) systems can pose safety threats to people and property, particularly during installation, maintenance, or emergencies. In order to address these concerns, the National Electric Code (NEC) has introduced safety regulations for photovoltaic installations, which include the need for rapid shutdown. It is a crucial safety feature that can mitigate the potential hazards associated with PV systems. This article will explore the significance of rapid shutdown in PV systems and how it enhances safety. We will examine how it operates, the NEC's stipulations for rapid shutdown, and the advantages of implementing this safety measure.

Discovering solar rapid shutdown and its applications

So what exactly is rapid shutdown in the context of photovoltaics? Basically, it refers to a set of guidelines that mandate a solar panel system to have a quick and easy method of cutting off the electrical energy flowing through the system as a safety measure. The primary purpose of this requirement is to give firefighters a way to deactivate the power source in the event of a fire, ensuring their safety.

When exposed to sunlight, PV panel systems can become electrically charged, which makes a rapid shutdown necessary. Without this mechanism, there is no safe way to turn off the current flowing through the conductors. Merely turning off the inverter does not entirely cut off the power, as the solar panels would still generate electricity, and the electrical cables coming from them would still have live current. This creates a risk of electrocution for anyone who comes into contact with the solar panel system, including first responders who may need to access your roof in an emergency. By implementing rapid shutdown, the risk of electrocution for anyone accessing the roof can be mitigated as the solar system can be de-energized within a minute.

Components of a rapid shutdown system

Rapid Shutdown Device (RSD)

This type of module-level power electronics (MLPE) is mounted on the back of each solar module. RSDs are equipped with technology that enables them to reduce or turn off voltage output across the PV array.

Initiator

This component activates the rapid shutdown mechanism and typically comes in the form of an emergency stop button found on the inverter. This tool can be set off either manually or automatically, such as in case of a power failure.

Inverter

Besides converting the solar modules' electrical output into energy that can power your house, the inverter is also an essential element in the rapid shutdown solar system, with the rapid shutdown initiator frequently integrated into the inverter.

Legal obligations for rapid shutdown installation

Most states have requirements for the rapid shutdown of photovoltaic systems based on the current electrical code. The NEC updates its safety guidelines for electrical systems every three years, but it's up to each state to decide if and when to adopt them.

For example, if your state follows NEC 2014 regulations, conductors situated more than ten feet above a PV system need to be reduced to 30 volts and 240 amperes within ten seconds of turning on the rapid shutdown switch. Under NEC 2017, conductors located more than one foot above the ground must be de-energized and lowered to 80 volts within 30 seconds of turning on the rapid shutdown system within the array boundary.

Even though the NEC released its most recent update in 2020, fifteen states still adhere to the NEC 2017 standards. However, in reality, there are no major disparities in rapid shutdown solar requirements between NEC 2017 and NEC 2020. If you want to know the current status, visit the National Fire Protection Association's website.

Adding rapid shutdown to your solar setup

Different types of inverter systems have varying rapid shutdown capabilities, with some having the feature built-in while others require extra equipment to be installed. The two most commonly used inverter options for home PV systems in the United States are microinverters and power optimizers, such as Enphase and SolarEdge. These systems are conveniently located under each panel and already have built-in rapid shutdown features.

On the other hand, string inverter systems typically do not come with built-in rapid shutdown capabilities, meaning they must be equipped with rapid shutdown solar devices to meet regulatory requirements. Although some examples of string inverters come equipped with integrated rapid shutdown, it's not the typical configuration.

Note that for a ground-mounted solar system, the NEC doesn't mandate a rapid shutdown system, no matter which kind of inverter you are utilizing.

It is essential to hire a qualified installer to ensure that your solar system adheres to your state's current NEC rapid shutdown requirements. Experienced installers possess the necessary expertise to design your solar array while complying with these regulations.

If you've installed a solar panel before your state adopted NEC 2014, NEC 2017, or NEC 2020, any modifications you make to it must adhere to the current rules before the inspection. This means you'll need to install a rapid shutdown system as part of the upgrade.

Sources:

https://www.nfpa.org/NEC/