Most states have adopted the 2017 update of the National Electrical Code, and some have even graduated to the 2020 version. In both, module-level rapid shutdown is required for any solar project on a building. In the past year, many manufacturers have introduced their own rapid shutdown devices with different features and price points.
“Having multiple different manufacturers or technologies in the market for that allows flexibility and actually allows a lot of forward compatibility,” said Michael Mills-Price, head of inverter and energy storage business at PVEL.
Along with longtime RSD manufacturer Tigo Energy, installers can now choose among a number of brands, from APsystems to Generac, that are now offering their proprietary rapid shutdown tools.
Some devices on the market are compatible with any brand of string inverter. For example, APsystems produces the rapid shutdown package called APsmart, a small device that can either be buckled to the module frame or applied to the backsheet using adhesive. The company says its device works well for bifacial applications due to its compact size and tucked-away installation option.
ZERUN makes a similar product called the ZERUN Rapid Shutdown Solution. The devices are duration-tested before shipment to ensure longevity and can also be mounted on the module frame or backsheet.
IMO Automation makes the FireRaptor, a device that comes with a 20-year warranty and doesn’t require powerline communications. The FireRaptor can automatically shut down if the temperature sensor detects a rise above the programmed trigger level.
Other rapid shutdown devices only work with one brand of inverter. Generac’s PWRzone system comes with an optimizer and small rapid shutdown switch, but it only works with the company’s PWRcell inverters. Similarly, SolarEdge offers a power optimizer with built-in rapid shutdown functionality, but only works with SolarEdge inverters.
As a final option, installers can choose to use microinverters to satisfy rapid shutdown requirements without having to install both a string inverter and RSD. Microinverters are often seen as inherently compliant with rapid shutdown rules because they convert high-voltage DC power to lower-voltage, safer AC power that can drop down to 80 V within 30 seconds. However, the 2017 NEC does not specifically identify microinverters as a way to satisfy the rapid shutdown requirement.
Module-level rapid shutdown has added cost and time to installations, but also brings important protection to first responders in case of a fire. Although rapid shutdown devices can vary widely, installers should review test reports like those from PVEL to ensure rapid shutdown functionality before choosing which of these important devices to use.