When it comes to solar energy, ensuring fire safety is of utmost importance.

Numerous countries have recognized the significance of implementing safety measures to ensure the secure operation of solar systems and facilitate the safe access of firefighters to the roof area. Rapid shutdown emerges as a crucial protocol in achieving this goal.

Let’s explore the 5 things solar owners need to know about rapid shutdown.

1) What Exactly Is Rapid Shutdown?

Rapid shutdown refers to an electrical safety mandate originally introduced by the United States National Electrical Code (NEC) for photovoltaic (PV) systems. It necessitates the inclusion of an “on or off” switch to de-energize or lower the voltage of solar modules on the roof.

2) Why Is Rapid Shutdown Crucial? 

Rapid shutdown provides a secure approach for firefighters and solar installers to deactivate or decrease the voltage and current from a PV array. This effectively prevents electrical hazards. By turning off or reducing the voltage at the module level, it significantly diminishes the risk of shock from high voltage originating from the solar modules.

3) Can Inverters Fulfill This Requirement? 

While inverters can shut off to prevent energy transmission from the modules, the modules continue to generate electricity as long as sunlight is available. Therefore, voltage and current are still present on the wires between the modules and the inverter.

As a result, most rapid shutdown codes mandate that the shutdown occurs at the module level. This has led to the widespread use of module-level power electronics (MLPE) or microinverters to meet this function.

The US National Electrical Code necessitates communication between the inverter and the module-level rapid shutdown device. Together, these components form a system referred to as PV Rapid Shutdown System (PVRSS).

4) Who Needs Rapid Shutdown?

If you have multiple sections of panels on your roof with a gap exceeding 2 meters (which is likely), it’s necessary to have rapid shutdown devices between them if they are sharing inverters. Even if you pass your DC cable through the attic without protection (which is actually worse), you need rapid shutdown devices to ensure the safety of emergency service workers and  contractors.

5) Components of a Rapid Shutdown System

A rapid shutdown system comprises several critical elements. Firstly, there is the Rapid Shutdown Device (RSD). RSDs are attached to solar modules. They have the capability to turn off or reduce voltage output across the entire solar system, ensuring compliance with PV Rapid Shutdown regulations.

Another important component is the initiator, typically in the form of an emergency stop (e-stop) button located within an inverter. This initiator triggers the rapid shutdown process, either manually by pressing the e-stop button or automatically in the event of a power loss from the grid.

A final essential element is the inverter itself. The inverter converts the electricity generated by the solar modules into usable energy for residential use. In many cases, the rapid shutdown initiator can be found within the inverter.

Collectively, these three components are known as Photovoltaic Rapid Shutdown Equipment (PVRSE). They are integral to a rapid shutdown system, ensuring that voltage levels are reduced to a safe level. Compliance with the US National Electrical Code requires PVRSE and PVRSS to be UL Listed for rapid shutdown purposes.

Conclusion

Electrical inspectors rarely climb sloped residential roofs due to safety concerns. This has resulted in some installers failing to correctly implement rapid shutdown regulations.

Make sure to talk to prospective installers about their rapid shutdown procedures before your next solar installation.

Image Source: Solar Dev, https://shorturl.at/bEV19