Rapid Shutdown Device For Solar System: All You Need To Know

There are many reasons why solar PV systems can catch fire: DC arc faults, poor equipment and installation, etc. Globally, firefighters participate in an average of 2 solar-related fires per week. Even when the system is turned off, the solar panel still outputs power at high voltage. That’s why every solar PV roof should add module-level rapid shutdown device to keep firefighters and homeowners safe.

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<Fire risk in solar rooftop system>

What is rapid shutdown?

Rapid shutdown is an electrical safety requirement and regulation for rooftop solar panel system by the National Electrical Code (NEC) in USA.

A precaution to fast switch off the solar system DC conductors by mechanical. To reduce fire and improve firefighter safety on solar rooftops.

Why rapid shutdown is required?

The concept of PV systems rapid shutdown is proposed by the National Electrical Code (NEC or NFPA 70). The purpose of its issuance is to regulate electrical products and installations, avoid electrical risks, and protect the personal safety of firefighters. The NEC is revised every three years as technology evolves. In the U.S., most states are required to enforce NEC rapid shutdown requirements for PV systems.

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<National Electrical Code>

NEC 2014

NEC 2014 690.12 standard was released and made clear requirements for rapid shutdown: the solar panel should be installed with a rapid shutdown switch, and PV system voltage needs to drop below 30V within 10 seconds to provide the best system safety.

NEC 2017

NEC 2017 690.12 has made strict changes to the rapid shutdown requirements. Taking the distance to the PV matrix 305mm as the limit, within 30S after the rapid shutdown device is started, the voltage outside the limit range is reduced to below 30V, and the voltage within the boundary range is reduced to below 80V. Therefore it is required to achieve “Module-Level Rapid Shutdown”.

Module-level Rapid Shutdown can reduce the voltage to a range that can be tolerated by the human body. This change is undoubtedly more convenient for firefighters’ rescue work.

NEC 2020

In the latest NEC 2020, “PV hazard control systems” are proposed. The new standard requires the PV system to have a “PV hazard control systems”, so that the PV system can be in a controllable state in a critical situation, that is to say, the “PV hazard control systems” can be used to realize module-level rapid shutdown. Within 30S after the rapid shutdown is started, the voltage within the boundary range drops below 80V.

Why rapid shutdown is so important?

The rapid shutdown is essential to the roof-mounted solar system. Even if the conduit running from panel to panel is entirely secured, there are isolated cases where those conduits can get sun damaged.

If this occurs, anyone near the system can be exposed to live electricity and may result in a dangerous situation. But with the help of rapid shutdown function, the responders can quickly cut off the power from those conduits, providing them secure access to the location around the solar system.

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<BENY BFS-11 wiring diagram>

Can the inverter achieve rapid shutdown function?

  • MLPE

The first need to be clear is that according to NEC 2020, rapid shutdown requires module-level rapid shutdown. One that can meet this requirement is Module-Level Power Electronics (MLPE). MLPE mainly includes: rapid shutdown device, micro-inverter, power optimizer.

  • Inverter

Inverters are divided into central inverter, string inverter and micro-inverter.

①The traditional PV inverter method is to connect PV panels in series and parallel to form a PV array. Usually, the DC voltage after series and parallel is 600~1500V, then DC is converted into AC and connected to the grid through a central or string inverter. 

Micro-inverter is a PV inverter with module-level MPPT function. It’s a device that directly converts the DC generated by each module into AC and then connects to the grid.

Micro-inverter can avoid the DC high voltage problem existing in the string inverters, and realize the module-level rapid shutdown function. At the same time, it can also perform independent MPPT control on each module, which greatly improves the overall efficiency.

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<BENY Micro-inverter>

However, the current micro-inverter’s disadvantage is mainly due to the high cost per watt, which leads to its low market share. Therefore, the most popular rapid shutdown solution on the market is “string inverter + rapid shutdown”.

BENY Module-Level Rapid Shutdown Device

The module-level rapid shutdown solutions we are offering allow all types of solar modules can be communication cable version and Sunspec version:

*24VDC communication cable + emergency button switch RSD initiation

*PLC communication + RSD transmitter

Panels connected with BENY Electric RSDs will be reduced to 0V in microseconds, and the AC powered emergency switch or the RSD transmitter completes the RSD solution meets the NEC rapid shutdown solution.

  • BFS-11/BFS-12 is a module-level rapid shutdown device offers fire safety for solar rooftop and building, remains the rapid shutdown function period the solar PV system whole working life.

Emergency button switch is required to initiate the rapid shutdown operating, as a trigger place on the ground and easier to reach.

The communication cable on the rapid shutdown device should be connected in series and wire to the button switch. So the button switch can control the BFS rapid shutdown devices. A communication that is no cross-talk with the inverter or WiFi source.

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<BENY BFS-11&BFS-12&Emergency Button Switch >
  • BFS-21/BFS-22 is designed and developed as the most reliable module level rapid shutdown device for solar building fire safety and meeting the NEC requirements. BFS-21 operates SINGLE standard PV module (>=40V) or TWO modules (<40V), BFS-22 Operates TWO standard PV module (>=40V) or FOUR modules (<40V).

BFS-21/BFS-22 complies with NEC 2017&2020 690.12 rapid shutdown requirements when work with the SunSpec signal transmitter BFT-01 or an inverter with built-in transmitter, in non-interference with the inverter AFCI.

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<BENY BFS-21&BFS-22>

Conclusion

NEC is a US standard, and more countries will add rapid shutdown to the mandatory standard in the future. The number of countries mandating the installation of rapid shutdown for distributed PV is gradually increasing. At present, the United States, Canada, Australia, Germany, Italy, and the Philippines all use the mandatory installation of rapid shutdown to improve the safety of distributed PV rooftop . Thailand joined the ranks of high safety requirements this year. Other European countries are currently studying and imitating German safety standards.

BENY module-level rapid shutdown BFS-11/BFS-12 products are working with emergency button switch, which can shutdown panels to 0V at microseconds, comply with CE certification and NEC2017&2020 requirements; BFS-21/BFS-22 products have PLC control signal, comply with SunSpec certification and NEC2017&2020 requirements. BENY products can meet all the rapid shutdown needs, contact us now for product details and industry latest information.

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