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Your Quick Guide To Rapid Shutdown For Solar Systems


When you’re researching solar power systems for your home, the rapid shutdown feature might not be at the top of your list. That’s fair enough, but rapid shutdown is an important fire safety capability for a rooftop solar array.

How concerned do you need to be about rapid shutdown? Let’s delve deeper into the topic of rapid shutdown to understand how it works, where the government stands on it and how manufacturers approach fire safety with solar systems.

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What Is Rapid Shutdown In A Solar Array?

Rapid shutdown features two components – a piece of equipment in your array and an electrical safety code. Here’s what you should know about each part of the rapid shutdown conversation.

Rapid Shutdown Switch For A Solar PV System

Rapid shutdown is a method of quickly deenergizing a photovoltaic (PV) system to protect utility line workers during a power outage. If a solar energy system continues sending high-voltage power into the grid during an outage, that energy could injure workers trying to restore power. A rapid disconnect switch can prevent serious injuries.

NEC Code For Solar Installations

Rapid shutdown is also part of the National Electrical Code (NEC) in the United States. It became part of the NEC in 2014 to allow firefighters and other first responders to make solar panel systems safe during an emergency situation. Since then, the National Fire Protection Association has refined the guidelines as part of NEC 2017 and NEC 2020.

How Does Rapid Shutdown Work?

A rapid shutdown system works according to the type of solar inverter your solar system uses. No matter the solar inverter, though, the goal is to reduce your system’s power output to a safe level in 60 seconds or less. Firefighters can trigger this with a physical shutdown initiation switch on your system.

String Inverter Solar Rapid Shutdown

If your system has a string inverter, it’s live and producing electricity if the sun is shining. If your system includes power optimizers, your system is likely NEC-compliant. If not, you may need to install module-level power electronics (MLPE) to make rapid shutdown possible. There are string inverters that include rapid shutdown capabilities, though, and these have been even more prevalent since more states adopted the NEC 2017 guidelines. Check with your installer if you have questions about whether your solar panel system is prepared for rapid shutdown.

Microinverters Are Inherently Rapid Shutdown-Capable

Solar systems that use microinverters have built-in module-level rapid shutdown functions along with other panel-level capabilities such as real-time solar monitoring and performance data. This means you’re unlikely to need any additional rapid shutdown devices (RSDs) to comply with NEC guidelines. Your installer will assist you with any questions and help your system meet any necessary requirements.

Installers May Use Different Types Of Rapid Shutdown

Some installers may favor string inverters over microinverters, or vice versa. Others may use either option, depending on location, customer goals or other factors. Palmetto, for example, sometimes installs Enphase microinverters, or SolarEdge inverters equipped with power optimizers.

Is Rapid Shutdown Required By Law?

You’re likely to see rapid shutdown described as an NEC requirement. However, it’s not a federal law. Each state can adopt the NEC as it deems necessary. Arizona, Illinois, Mississippi and Missouri haven’t adopted the NEC rapid shutdown guidelines, although some municipalities in these states may opt to require the NEC guidance.

Some states may implement state-specific rapid shutdown requirements as well.

FAQs: Solar Rapid Shutdown For Solar Energy Systems

Here are common questions about the rapid shutdown requirement for PV systems.

Does my older solar system need a rapid shutdown device?

Homeowners living in states that have adopted the NEC guidelines must comply with the requirements enacted before their system was built. For example, a system installed in 2011 won’t have to meet the requirements set in place by NEC 2014, 2017 or 2020. A system installed in 2019 needs to comply with NEC 2014 and 2017.

If you plan to modify your system enough to require an inspection, though, you might need to comply with the current NEC guidelines. This could include adding a rapid shutdown switch.

Is rapid shutdown required for ground-mounted solar panels?

The NEC guidelines only apply to roof-mounted solar arrays. They don’t apply to ground-mounted PV arrays, so currently you won’t need a rapid shutdown solution if your solar array is on the ground.

The Bottom Line: Rapid Shutdown Is An Important Safety Feature

Homeowners would be wise to read up on the rapid shutdown requirements in their state or municipality. This can help you when discussing system design with an installer. Plus, if you already have solar modules, it’s always a good idea to know the requirements. This way, you can update your system to make it safer, or you can be prepared for any system expansion you’ve planned.

Learn more about the approach Rocket Solar uses for safe solar panel systems.Talk To A Solar Advisor today.

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