The integration of photovoltaic (PV), energy storage systems, and increased levels of distributed generation requires that standards, codes and deployment guidelines improve and advance. This must happen in parallel with technological innovation and the increased demand for cleaner energy.

As PV systems become more intelligent and commonplace in electrical power systems, they must also become more adaptive to changing grid conditions and environmental stresses, and provide longer lifetime durations while remaining cost competitive with existing traditional power generation sources. In addition, PV systems are challenged to provide a safe environment for new technology both in new installation modes implemented in newly built PV plant and building applications, as well as when integrated with existing buildings and infrastructure. Inverters are as a result viewed as critical system elements because they act as the “brain” of the PV system due to the high level of computing power present and the control of power flow given their location in PV applications.

UL, an independent global safety science company, focuses on providing a path for national and international compliance in accordance with the harmonized international standards for PV power conversion products and electronic product safety.

SMA believes an updated UL Standard, UL 62109, represents a significant step forward in harmonizing power conversion equipment safety requirements with an international perspective. Utilities and authorities having jurisdiction (AHJs) require distributed generation that is reliable, safe, compatible with the requirements of the National Electrical Code (NEC), and has been tested and constructed to withstand the rigors of daily, full power operation without significant amounts of downtime.

Today, PV inverter manufacturers have the option of using either the existing UL 1741 Standard or the newer UL 62109 as the basis of their U.S. PV inverter product safety certifications.

UL 62109, Safety of power converters for use in photovoltaic power systems, was published on July 18, 2014. It is now the U.S. harmonized version of the international PV power conversion standard IEC 62109.

IEC 62109 is based on UL 1741 and was expanded and updated to address cutting-edge safety aspects of PV power conversion equipment. It’s being adopted around the world and is the basis for harmonized international safety certifications. UL 62109, like UL 1741, provides a means to determine that PV inverters and other PV electronics:

  • are constructed per common industry requirements;
  • can be installed in accordance with U.S. codes;
  • are operated per industry-specific required ratings;
  • perform safely under rated normal worst-case conditions;
  • perform safely under foreseeable abnormal operating conditions and failure modes.

While UL 1741 and UL 62109 may appear to be very different, they are actually quite similar and address the same types of hazards. .

IEC 62109 began in 1997 as a seedling draft of UL 1741, which UL authorized for IEC use to accelerate the IEC 62109 development. UL participates in the development of many IEC standards, with a heavy emphasis on participation on renewable energy technical committees, and this facilitates collaboration and standards development. While based on the foundation of UL 1741, IEC 62109 is somewhat different because IEC 62109 it was specifically developed to also address not only known gaps in UL 1741 but also the challenges of emerging PV power conversion technologies.

UL 62109 addresses hazard prevention at a more granular level, which allows for greater flexibility in inverter design. For these reasons, there are approximately 20% more tests in UL 62109 than in UL 1741.

UL 1741 was written to cover all forms of Distributed Energy (DE) / Distributed Generation (DG) source types, whereas UL 62109 was written specifically for PV applications (including specific requirements for battery based energy storage) while also anticipating and addressing the connection of other (non-PV) energy sources.

UL 62109 allows for a near harmonization with IEC 62109 for the evaluation of PV inverters. National deviations were established in UL 62109 to allow products evaluated under IEC 62109 to be brought into the U.S. market with as little redesign and retesting as possible, while still allowing compliance with U.S. NEC requirements for electrical power system compatibility.

UL 62109 addresses many of the same hazards as UL 1741, yet does so in a different manner. IEC 62109 and UL 62109 were based on the experience gained from applying multiple U.S. and international safety standards over the past 20 years. These newer standards benefit from the lessons learned and result in state-of-the-art sets of requirements.

UL 62109 evaluates for safety risks including from electric shock and fire. In the U.S., grid interactive inverters evaluated for shock and fire risks under the UL 62109 Standard need to additionally be evaluated to the utility interaction requirements in UL 1741 included in section 40 (including associated references to IEEE 1547 and IEEE 1547.1). There are also new requirements in UL 1741 Supplement SA for Grid Support Utility Interactive Inverters (often referred to as “advanced inverters”) that will be required in California effective September 7, 2017.

UL 62109 also includes state-of-the-art requirements for items such as electrical spacings / insulation coordination, excessive temperature hazards, chemical hazards and sonic pressure hazards. These requirements allow products designed for the international market to more easily enter the U.S. markets, while simultaneously helping manufacturers deliver safer products that meet 21st century distributed energy generation challenges.

UL 62109-1 was first published in July 2014 and since then the UL 62109-2 Harmonization Committee has been working on developing the U.S. national differences for the adoption and publication of UL 62109-2. This work includes significant revisions to the U.S. PV ground fault protection requirements to address technology and NEC code changes. Other national differences include references to UL 1741 for grid interactive product requirements and expansion of the requirements for multi-mode products that operate both grid-tied and stand-alone.

Once UL 62109-2 is published, UL is planning to revise UL 1741 correspondingly, to replace the PV equipment requirements with a reference to the UL 62109 standard. UL 1741 will retain the requirements for grid interactive products, including the linkage and references to the IEEE 1547 series of standards. UL 1741 will also continue to be used to evaluate non-PV power conversion equipment such as microturbines, generators, wind turbines, fuel cells, and the like. The UL 1741 Standards Technical Panel (STP) will work through the cross references between UL 62109 and UL 1741 going forward.

The UL certification of SMA’s products made use of a combined certification approach, in which commonalities between UL 1741 and UL 62109 – where overlaps existed – allowed for combined testing and evaluation. This approach also included areas of refinement for both construction and testing requirements present in UL 62109, which UL 1741 had not previously addressed. The result was an evaluation addressing the classic safety challenges addressed in UL 1741, with the additional evaluation of new risks for inverters and distributed generation products through the application of a modern, streamlined methodology.

Some electrical and electric utility authorities having jurisdiction (AHJs) have been involved in the development of the UL 62109 national differences, and knowledge about – and application of – this standard is growing.

There are multiple notable advantages for manufacturers that certify their inverters to UL 62109. These include greater scope of design validation, safety enhancements and alignment of standards with the latest approaches for ground fault protection. For example, UL 62109 is the most widely accepted international PV power conversion standard and corresponding certifications help to future-proof inverter designs.

SMA is the first inverter manufacturer to have a product on the market with a 1500V, UL 62109-1certification. As stated earlier, UL 62109 is a standard written for PV inverters only, which benefits customers because it means that inverters are now undergoing more testing to help ensure safety, reliability and functionality.

Some examples of the types of inverter features that are tested include:

  • Touch temperatures of user-operated devices (knobs, handles, switches, displays)
  • Short circuit tests for housekeeping and auxiliary transformers
  • Requirements for over-temperature protection devices (in the choke, for instance) to shut off the inverter if limit is exceeded
  • Backfeed voltage protection to ensure energy is not present on the terminals of each source
  • Durability of markings and labeling to help assure safety of service personnel for the lifetime of the system

UL 62109 specifies more than 50 different tests, which is significantly more than specified by UL 1741. To compare, UL 1741 specifies approximately 20 different tests and they are not all obligatory (since this standard was written to address all forms of DG), nor are they necessarily related to PV application.

In addition to the harmonization of both standards, IEC 62109 and UL 62109 have major positive cost impacts for international inverter manufacturers. A number of tests used during IEC testing can also be applied for the UL standard, and test reports can be easily generated for both IEC conformity assessments and UL certification. This fundamentally reduces the test efforts and the project cycling time. The end result is that the inverter can be brought to market more quickly with a lower cost of production.

SMA had one major obstacle to overcome in obtaining the UL 62109-1 certification. Since UL 62109-2 has not been released, an alternative had to be identified. UL supported SMA’s goals by allowing SMA to adapt the not-yet-released content of UL 62109-2 (isolation monitoring and ground fault detection) with the appropriated counterparts of UL 1741, chapters 31 and CRD6.

SMA found the opportunity to have this technical guidance to be a unique benefit of working directly with UL instead of another third-party certifier. Due to SMA’s long-established relationship with UL, the coordination process moves more smoothly and efficiently, and specific requests can be clarified more easily given the direct relationship to the developer of the standard itself. All of these factors result in less project coordination time and ultimately, a faster product launch.

SMA is also part of the UL Standard Technical Panel (STP), and plays a role in the creation and modification of new or existing UL standards. As an active STP participant, SMA is continuously involved in STP discussions and works in close cooperation with UL on new standards. For instance, SMA has weighed in on new requirements for UL 62109-2. In particular, SMA helped develop the requirement for current measurement in combination with the ground fault detecter interrupter (GFDI), which provides additional safety aspects for the detection of ground faults, while an increasing leakage current can be detected and monitored much earlier.

SMA believes that UL 62109 will become a new go-to standard in the U.S. PV industry soon, with the main initiator being the release of the second part of the standard. As an industry leader, SMA’s pursuit of UL 62109 certification is a significant opportunity for future risk reduction due to the PV-specific nature and the value it adds for its customers.

UL is an IEC 62109-1 and 62109-2 Certified Body Testing Laboratory (CBTL) for PV inverter and other PV electronic products. Under this internationally recognized testing accreditation, UL can provide globally accepted evaluation reports, known as a Certification Body (CB) report, to inverter manufacturers. These products can be evaluated to the standard for the U.S. and/or other market(s) under one project. The UL Mark can then be applied to the certified product and it can be sold in the U.S. and/or a CB report can be created and delivered for product needing certifications for markets outside of the U.S. This allows for certifications to the necessary safety testing and/or testing for grid interconnections to specified national requirements.

Key benefits of choosing UL include

  • One international base document offers much more consistent certifications
  • National differences are easier to address than national standards
  • Fewer revisions to track and comply with
  • Reduced engineering time to prepare for certifications
  • Reduced certification time to reduce product time to market
  • Significant certification cost savings

Manufacturers who plan to sell their inverter products in the U.S., European and other international markets can choose to have their product evaluated and certified in compliance with the IEC 62109-1 and -2 standards through UL. They can then apply the well-known UL Mark for the U.S. and also supply the needed CB report for the European and other non-U.S. markets. The need for only one project to complete product evaluation, testing and certification to the 62109 standard maximizes the coverage of certification budgets and accelerates product market entry.

UL certifications assess not only the safety performance of an end product through testing, they also review and validate the design via a thorough assessment of the safety-critical components used in the end-product design and provide guidance if some components are not acceptable because of ratings or limitations within the certifications they have received. In the end-product application, UL Recognized Components may sometimes need additional evaluation to function correctly and safely due to the environment in which they reside.

UL certification also concentrates on the overall design and construction of the end product to be able to evaluate items such as suitability of enclosures to contain risk of shock or fire, environmental protection, electrical spacings, ground fault protection, presence of proper insulation between hazardous circuits and users / accessible circuits, and overall compatibility of the product to be installed in accordance with the U.S. National Electric Code.

In summary, achieving UL certifications to product safety standards help manufacturers like SMA demonstrate that a product operates more safely with expected normal use, as well as under foreseeable abnormal conditions.

The UL Mark is one of the most recognized, accepted and trusted certification marks on the planet, appearing on nearly 22 billion products worldwide. Products carrying the mark have successfully met UL’s stringent standards after rigorous testing and extensive evaluation of representative samples. UL is the only certification organization in the world authorized to issue UL Marks.

Furthermore, SMA finds great value in UL’s pursuit of global research and standards to continually advance and meet ever-evolving product safety, performance and interoperability needs. The organization’s global network of technical experts and state-of-the-art facilities, along with their longstanding relationships with regulatory authorities, partner laboratories and industry technical leaders, helps manufacturers like SMA gain the compliance credentials they need to compete in a more complex global supply chain.

With UL, SMA has gained global reach and access. The company’s network of expert engineers provides knowledge about the various national and global requirements for specific market application of SMA products.

Lastly, UL acted as a single source provider and met all of SMA’s compliance needs. Bundling safety, performance and interoperability services results in savings of both time and money.

For SMA, choosing UL meant choosing speed, efficiency and success.