Tigo Energy rapid shutdown units installed on a solar awning.
Almost half of U.S. states have now adopted the 2020 National Electrical Code, which includes specific fire safety requirements for rooftop solar projects. If a fire should break out at a home or commercial building, the code ensures firefighters won’t be harmed by an energized solar array on the rooftop.
Installers now have multiple options to satisfy this measure in the code, including the use of module-level rapid shutdown devices and PV Hazard Control systems — listed as UL 3741.
To achieve PV Hazard Control certification under UL 3741, products must pass a series of tests designed to simulate situations firefighters may encounter on a solar rooftop. The testing analyzes what happens when first responders fall on damaged solar panels while wearing typical protective gear. There’s no prescribed combination of solar products to satisfy this new rating; the merits of each submitted product or product combination are scrutinized during testing.
Rapid shutdown devices are also certified by UL, but most units can work with numerous string inverter brands. Small units are affixed to either one or two solar panels to reduce the voltage to 80 V within 30 seconds once the shutdown switch is activated at the inverter, which the code-making body decided was a safe voltage for firefighters to work around.
An increasing number of manufacturers are bringing rapid shutdown devices to market, so installers now have multiple choices when it comes time to choose this small but important part of solar systems.
The main rapid shutdown devices on the market in 2022 include:
APsmart – APsystems
APsmart package includes the rapid shutdown receiver and inverter-agnostic transmitter
The rapid shutdown unit is small and can be buckled to the module frame or applied to module backsheet using adhesive
Works well in bifacial applications because it doesn’t block the underside of the module
SunSpec Rapid Shutdown System JMS-F – SMA America
SMA says the JMS-F device features up to 50% fewer internal components than alternatives, resulting in greater lifetime reliability
Uses the existing DC lines between the inverter and PV array for power line communications
Technical support available from SMA’s extensive O&M program
Inverter-agnostic
TS4 rapid shutdown suite – Tigo Energy
Tigo says its devices work with the largest network of inverters and module types
Tigo works closely with many inverter partners to integrate its Rapid Shutdown System Transmitters into their inverters, which simplifies installation
Tigo’s rapid shutdown suite gives customers the freedom to choose other features they need in module-level power electronics
Power Optimizer – SolarEdge
SolarEdge’s Power Optimizer is a DC/DC converter connected to each module with built-in SafeDC rapid shutdown feature
SafeDC automatically reduces module voltage to a safe level whenever the inverter or grid power is shut down
Only works with SolarEdge inverters
FireRaptor – IMO Automation
IMO Automation’s FireRaptor is a solid-state switch that doesn’t require powerline communications
Comes with a 20-year warranty and works with all inverter types
FireRaptor can automatically shut down if the temperature sensor on the device detects a rise above programmed trigger level