SAFETY
SOLARPOWER
“The 2014 NEC was non-specific about several points in rapid shutdown, such as how the rapid shutdown would be initiated, how the array was to be isolated, etc.,” Hamon said. “It indicated what had to happen, when and at what point, but the rest was left up to the AHJ and installer to decide how to implement.” When setting up a solar array, installers have to incorporate PV circuit conductors within 5 ft of entering a building or within 10 ft of the array. During rapid shutdown, solar arrays have 10 seconds to limit voltages to no more than 30 V (considered touchsafe in wet locations). Most of these requirements are easily met by inverters and optimizers currently on the market. If not, rapidshutdown controllers and/or combiner boxes are often where first responders can find shutdown devices.
NEC 20 17 AN D MO DULE-LEVEL S H UT D OW N While PV shutdown requirements in NEC 2014 were essentially vague, proposed revisions to NEC 2017 are much more detailed—expanding from less than 150 words to more than 1,100. Module-level shutdown becomes law of the land with a new section enforcing an 80-V limit within the solar array boundary, essentially mandating the use of module-level power electronics (MLPEs). Many firefighters are advocates of the new revisions. Even those who don’t completely understand its technicalities think “module-level shutdown” sounds a lot safer than “rapid shutdown.” Module-level shutdown can be accomplished using microinverters, DC optimizers, smart modules, AC modules and other MLPEs, which have all been on the market for some time. MLPE manufacturers obviously support the new code because their products inherently meet it. Though string inverters are not built for module-level shutdown, manufacturers are coming out with innovative solutions to meet the code such as incorporating optimizers. Other in-array shutdown devices may also be coming to market. “Module-level shutdown requires module-level electronics and remote control,” Hamon said. “While the overall safety will be improved, it would be hard to overlook that the additional components might reduce the reliability of the system.” However, many MLPE manufacturers argue that their products actually provide more system uptime than string inverters, though they come at an initially higher cost. The effects of NEC 2017 have yet to be seen, and with a louder outcry from the anti-module-level-shutdown crowd, it will be interesting to see how AHJs handle future solar installations.
By Kelly Pickerel Associate editor, SPW
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SOLAR POWER WORLD — 2017 RENEWABLE ENERGY HANDBOOK
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solarpowerworldonline.com
12/19/16 7:57 AM