Editor’s Note: With the proliferation of ACPV systems in the United States, installers today must know how to tell the difference between true AC modules and DC modules with field-attached microinverters. As is often the case in the solar industry, the devil is in the details — so here’s a quick overview of the regulatory, testing and manufacturing distinctions that make a true AC module.
AC modules are defined in the U.S. National Electric Code (NEC) as “a complete, environmentally protected unit consisting of solar cells, optics, inverter and other components, exclusive of tracker, designed to generate AC power when exposed to sunlight.” The NEC Article 690 requires equipment such as AC modules to be listed for the application. Manufacturers and authorities having jurisdiction (AHJ’s) typically rely on Nationally Recognized Testing Laboratories (NRTLs) for this evaluation and Listing/Certification. A true AC module will be Listed/Certified as an AC module by a Nationally Recognized Testing Laboratory (NRTL).
The evaluation and listing of the AC module requires the use of two UL standards, UL1741 and UL1703. UL1741 contains the requirements for the combination of the inverter with the PV module and also references some tests from UL1703 depending on the mounting arrangement of the microinverter to the PV module. The components that make up the AC module assembly may also be individually evaluated and listed to these standards or requirements from these standards combined with requirements from other appropriate UL standards. For example, the PV module is evaluated to UL1703 and the microinverter is evaluated to UL1741 (including IEEE1547 to be identified as utility interactive) along with some of the environmental requirements from UL1703. UL has also recently released an outline of investigation for the AC connectors that combine connector requirements from other UL connector standards with UL1703 environmental tests.
The SolarBridge Pantheon microinverter was evaluated and certified by Canadian Standards Association (CSA), a U.S. NRTL, to UL 1741 2nd Edition (including IEEE1547) as a component for use with listed AC modules. Additionally, the SolarBridge Pantheon microinverter is tested to environmental protection requirements from UL 1703 such as:
Humidity Freeze, 10 cycles (HF10), followed by wet insulation resistance and dielectric strengthThermal Cycle 200 (TC200), followed by wet insulation resistance and dielectric strength Sequential TC200 and HF10 followed by dielectric and Ground Continuity test.
Assembly of an AC module should be performed in a factory under follow-up inspection control of the NRTL that performed the evaluation/listing. Factory assembly with dedicated quality control is critical to ACPV reliability and allows for the AC module to maintain UL1741 listing. This is a major advantage over field-assembled ACPV systems consisting of PV modules and separate microinverters installed underneath or non-listed assemblies as discussed later in this article.
AC Module Cables
AC modules with factory-integrated SolarBridge microinverters include SolarBridge special-use AC cables evaluated to various parts of UL’s AC Connector Standards and UL 1703 for use in outdoor PV applications.
The AC Connectors are locking type, suitable for disconnection under load and are designed to withstand extreme outdoor conditions. They will not deform at high temperatures that can be encountered in ACPV applications, can tolerate complete immersion in water without failure and will withstand UL-standard impact tests at temperatures as low as -35°C.
The jacketed multiconductor AC cables used are XLPE designated as Tray Cable-Extended Run (“TC-ER”) type, outdoor rated and designed for wiring in free air and/or for management within standard AC wiring components such as exterior wire tray. Clips are provided for neat and secure cable management using the AC module frame.
AC modules are connected together to form an ACPV system, and if the ACPV system is constructed using listed AC modules evaluated for the application, installers can look to Section 690.6 of the U.S. NEC for installation requirements. There are other installation designs, however, that can be called ACPV systems. These include designs where the microinverter is installed near the PV module (a “detached” microinverter) or, in some cases, bolted to the frame of the PV module at an assembly location off-site, or on-site just before installation (non-listed).
Section 690.6 (A) states “the requirements of Article 690 pertaining to PV source circuits (i.e. DC circuits) shall not apply to AC modules.” However, installers must follow all guidance provided throughout Article 690 when installing ACPV systems using detached microinverters or non-listed assemblies where the microinverter is bolted onto the PV module frame on-site or at some facility unassociated with the PV module manufacturer. This means that the installer will need to consider requirements such as: DC ground fault detection and interrupt, DC cable management, DC disconnecting means and DC grounding as well as the AC equipment grounding conductor to the inverter.
Not Quite AC Modules
Installers should be especially cautious with AC modules without any certification markings to support the assembled product. Look for the NRTL Listing or Certification mark along with identification that it is an AC module evaluated to UL1741. The markings will include AC ratings and the term “utility interactive,” which identifies compliance to IEEE1547. AC modules will have at least one ratings/nameplate label with the AC module NRTL mark and AC ratings, but also may be provided with the DC PV module listing label and ratings.
PV modules that have inverters attached without an AC module evaluation by a NRTL may violate the original listing of the PV module and even void the warranty of the module.
AC modules powered by SolarBridge microinverters are covered by one warranty from the module manufacturer. SolarBridge works closely with the module manufacturers to assure product safety requirements are met, the AC module is listed and the microinverter is paired correctly with the module (ratings and mounting). This includes evaluations to assure the PV module will pass rated loads after the inverter is attached. Improper mounting could impact the PV module rails or result in damage to the PV module back sheet material.
If the assembly is not evaluated and listed by a NRTL or constructed outside the PV-module factory, installers could be liable for installing unwarranted products that may not be safe and/or may not qualify for state or federal rebate/incentive programs. Installers and inspectors should always check the manufacturer’s product documentation and look for the AC module label on the back of the unit.
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