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UL Launches Advanced Inverter Testing and Certification Program

September 8, 2016

UL Tests and Certifies Inverters & Other Utility Interconnected DG Equipment for Grid Support Functions Using the New UL 1741 Supplement A

NORTHBROOK, Ill., September 8, 2016 UL a global safety science organization, announces its new Advanced Inverter Testing and Certification Program. As electric utilities continue to modernize their grids through the use of larger amounts of distributed generation and renewable energy sources, the UL service portfolio expands to meet the ever-changing needs for safety, performance and grid support functionality. This new program utilizes the new UL 1741 Supplement A (SA) to test and certify inverters and other utility interconnected distributed generation (DG) equipment for grid support functions enabling smarter, safer, reactive grid interconnection.

"Brownouts or blackouts have demonstrated the far-reaching impacts of utility grid instabilities," said Jeff Smidt, vice president and general manager, UL Energy and Power Technologies division. "We are pleased to now publish the latest updates via UL 1741 SA for grid support utility interactive inverters to meet the current market need for a more stable utility grid.”

Advanced inverter testing is smart, reactive control of DG for support of ongoing modernization of grids utilizing increasing levels of DG and renewable energy resources. Traditional utility interconnection requirements (IEEE 1547) require DG devices to disconnect when the grid is experiencing stability issues. The UL 1741 SA specifies the test methods needed to build the foundation enabling DG devices to stay online and adapt their output and overall behavior to stabilize the grid during abnormal operation rather than simply disconnecting.

The State of California has announced that inverters installed in the state will be required to comply with the Rule 21 grid interconnection requirements within one year of publication of the UL 1741 SA. Other states are considering adopting similar installation requirements, especially in areas with high levels of DG and solar penetration.

Rule 21 is the inverter-related revision to the State of California Electric Tariff Rule 21 made by the California Public Utility Commission (CPUC). Rule 21 is a Source Requirement Document (SRD) to be used with the UL 1741 SA. SRDs set the specific parameter settings to be used with the test methods of the UL 1741 SA. Other SRDs may also be used with the UL 1741 SA as other markets look to build smart grid functionality into the modernization of their electrical power system.

UL has taken the lead working with industry to develop the UL 1741 SA to set the guidelines for modern smart grid interconnection. Additionally, UL has built two state of the art inverter testing laboratories for advanced inverters. These labs utilize automation to minimize time to market, reducing average test times to less than 3 weeks. Alternatively, UL has a well versed engineering staff which can witness testing at client’s facilities already equipped with laboratory facilities able to run the required test plan.

For more information, visit us at SPI - Booth #W525, The Battery Show - Booth #1621, register for a free webinar on October 6, 2016 at 10-11am CST: Advanced Inverters UL 1741 SA (, or visit For product testing, evaluation or certification questions, email