The Section 690.12 update to the 2017 National Electrical Code (NEC) calls for module-level rapid shutdown of solar systems instead of NEC 2014’s array-level shutdown requirement. Starting Jan. 1, 2019 when NEC 2017 goes into effect in certain jurisdictions, all conductors within an array’s 1-ft boundary have to be reduced to 80 V or less within 30 seconds of rapid shutdown initiation.
Smart modules, microinverters and other module-level power electronics (MLPEs) assist solar systems with module-level rapid shutdown. Here are the products that can bring solar projects installed after Jan. 1, 2019 to compliance with NEC 2017 module-level rapid shutdown.
Optimizers, smart modules and flexible MLPEs
Whether a panel comes pre-attached with optimizers or other MLPEs as a smart module or installers have to attach them in the field, these DC devices can be module-level rapid shutdown-compliant.
When rapid shutdown is required on systems with these DC products, the AC breaker is flipped, and the loss of power causes the module-level electronics to turn off and suspend voltage output.
The LG NeON R smart module solution, which consists of SolarEdge inverters, SolarEdge power optimizers and LG modules, is one example of a smart module in compliance with NEC 2017 rapid shutdown requirements. When the system loses AC power, the inverters turn off and the power optimizers start to safely draw down power.
Tigo is a seasoned power optimizer manufacturer, but the company’s solutions have evolved past just optimizing individual solar panels. The company’s TS4 platform offers many more module-level options, such as monitoring or fire safety. These flexible MLPE (Flex MLPE) products take the place of standard bypass diodes in the junction box and allow all types of modules—like Trina Solar’s TrinaSwitch—to meet module-level shutdown compliance without additional external boxes. Many inverters are also UL-listed to work with Tigo’s TS4 to be in compliance with NEC 2017.
SMA is one of those inverter companies. The SMA Sunny Boy inverters communicate with Tigo’s Cloud Connect Advanced (CCA) universal dataloggers to talk to the optimizers in the case of an emergency.
“The PV system rapid shutdown initiator is the main AC service breaker,” said Mike Mahon, solar academy trainer at SMA America. “The loss of communication at the TS4 devices in conjunction with the cessation of output power of the PV inverter triggers the TS4 devices to isolate their modules from the series string.”
When the AC circuit breaker is disconnected within a Tigo system, the loss of power from the grid causes the inverter and the CCA to turn off. When these two things shut off, the TS4 devices automatically enter rapid shutdown mode so output voltage and power turn off completely.
With all DC-based MLPEs assisting with rapid shutdown, the AC breaker is the only switch to flip. No extra button is needed to confirm that voltage is shut down for first responders or others wanting to turn off an array.
Microinverters and AC modules
Rapid shutdown occurs similarly for microinverters and optimizers: The AC breaker is the only switch to flip for the solar system to shut down.
“When the main breaker is shut off, all microinverters immediately shut off and all conductors and wiring are de-energized,” said Surya Potharaju, senior director of product management at microinverter manufacturer Enphase Energy. “Put another way, the UL 1741 inverter compliance requires that inverters cease operation whenever the utility parameters fall out range. Shutting off the main breaker places the utility voltage and frequency out of range.”
Microinverters ship rapid-shutdown-compliant and no additional components are needed. The same can be said about AC modules with microinverters already attached.
Having module-level devices like optimizers, microinverters and flexible MLPEs means nothing to the rapid shutdown conversation if they cannot communicate with the string inverter or main AC connection.
The SunSpec Alliance, a trade group formulating standards to enable plug-and-play systems, established the SunSpec Communication Signal for Rapid Shutdown Interoperability Specification that defines a communication protocol for module-level rapid shutdown. When modules, MLPEs and inverters achieve this specification, it is a guarantee to solar installers that the products will interact with each other to achieve shutdown when initiated.
Fronius was the first inverter company to announce its Symo Advanced inverter complied with the SunSpec guidelines for rapid shutdown communication over power lines. As long as the modules and/or MLPEs in the solar system are also SunSpec-certified, then the Fronius Symo Advanced inverter can assist with module-level rapid shutdown.
SMA and Tigo released a module-level rapid shutdown unit that is also SunSpec-certified. Tigo’s TS4-F (Fire Safety) device is purely a shutdown device and does not offer other optimizing features. SMA plans to bring all its U.S. string inverters in full compliance with the SunSpec rapid shutdown specification before Jan. 1, 2019.
ABB also has some of its products SunSpec-certified, and many other manufacturers are working to meet requirements before NEC 2017 goes into effect.