Progressing Grid Interconnection Standards

Working closely with regulators, energy utilities and inverter manufacturers, UL is evolving the grid interconnection safety standards to keep pace with new power production applications, new product opportunities and new customers.


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Facilitating the safe connectivity of distributed generation to the grid system is one of the most important ways to enhance the viability of renewable energy sources.

One of the most important potential ways to enhance the viability of renewable energy sources and the evolution to smarter, more efficient energy grids is to facilitate the connectivity of distributed generation to the grid system. Distributed generation — or on-site, decentralized energy production that powers localized applications and connects to an electric grid via inverter technology — is already a reality that is continuing to expand because of its numerous benefits. Distributed generation supports more environmentally friendly power sources and promises to help reduce energy costs, add supplemental power sources when and where needed, and empower energy consumers to make more sustainable choices. Progressing utility grid interconnection standards is critical to help ensure that inverters connect on-site generation to grid systems in ways that are safe and secure without risking the stability of the grids. If implemented properly, distributed generation with advanced functionality and communications capability may even increase the reliability and stability of the grid.


Today, energy-related emissions are responsible for 60% of the world’s total greenhouse gases and 80% of carbon dioxide production.1 According to a 2013 study published by the Lawrence Livermore National Lab, the U.S. currently wastes 61% of its energy and 67% of its generated electricity.2 Given these statistics, it is clear that there is a need to improve the sustainability of energy across generation, transmission, distribution and usage, and that doing so promises environmental, efficiency and economic benefits.


Distributed generation enables businesses and communities to invest more directly in a transition to renewable energy. It does so by encouraging diversity in resources and scale, allowing for the installation of capacity based on business or community preference, and offering the potential to defray some of the costs of renewable energy by the sale of excess capacity to energy utilities.3 Distributed generation also reduces the amount of energy lost in transmitting electricity because power is generated near the point of consumption, often in the same building or facility.4


From the perspective of the energy utility industry, distributed generation has sometimes been viewed as a growing and potentially disruptive force that could weaken the traditional, centralized electric utility business model.5 However, a 2012 ZPryme/IEEE (Institute of Electrical and Electronics Engineers) survey of smart grid industry executives identified three key benefits of properly designed and implemented distributed generation to energy utilities: the ability to add supply where needed, reduced costs compared to larger-scale generation facilities and improved power reliability.6


In the U.S. and around the world, distributed generation is growing rapidly due to its many benefits.7 There are potential risks, however, and the effective mitigation of those risks is essential to fostering additional growth. Traditional utility electric power systems were designed to support a one-way power flow from the point of generation through a transmission system to distribution load levels.8 The integration on

The integration on the energy grid of distributed generation sources creates potential operational issues that can destabilize the grid or lead to system failure.

The integration on the energy grid
of distributed generation sources creates potential operational issues
that can destabilize the grid or lead
to system failure.

the energy grid of distributed generation sources creates potential operational issues that can result in undesirable operating conditions that destabilize the grid or lead to system failure.9 These developments require advanced control and protection schemes.10 It should not be surprising, then, that the most important consideration in developing and deploying distributed generation — cited by 94% of smart grid industry executives — is standards.11


UL had developed a standard for interconnection equipment, UL 1741, and contributed significantly to the IEEE 1547 interconnection system requirements. We then worked with the U.S. Department of Energy (DOE) and the National Renewable Energy Laboratory (NREL) to harmonize UL 1741 and IEEE 1547. This effort resulted in the revision of UL 1741 to require compliance with IEEE 1547 and IEEE 1547.1 (covering interconnection system testing). The combined safety and grid certification program addressed most electrical AHJ (authority having jurisdiction) and distributed generation interconnection needs and has delivered a solid safety and performance history in the U.S. and Canada.


Given the expansion of distributed generation technology innovations and providers in recent years, there is a growing need to update the existing IEEE 1547 grid interconnection standards, which define basic functionality with voltage and frequency ranges for operational and corresponding disconnect times. The continued growth of distributed generation also requires an evolution of these utility grid interconnection standards to help ensure that advanced renewable generation sources connect to the grid safely and securely.12 Advancing technology provides the mechanism for this evolution through so-called smart inverters.


UL is working closely with regulators, energy utilities and inverter manufacturers — each of which has its own perspectives and priorities — to evolve the Standard UL 1741 to include requirements for new and advanced inverter functions. Specifically, we are working with all the key stakeholders to expand and revise the existing single grid interconnection option to keep pace with new and emerging developments. To this end, we are developing new grid interconnection requirements and certification options.13


Our first concrete step was to develop a set of requirements that provides a means to certify products for special-purpose applications such as solar (PV) and wind power generation farms. These applications may have utility interconnection requirements that are different from those defined in IEEE 1547 or IEEE 1547.1, which necessitate a provision for different grid interconnection protection features, functions and operating parameters. The new requirements enable UL to test, rate and certify products for the special-purpose applications. We are fast-tracking the development of new requirements to UL 1741, which will go through the American National Standards Institute (ANSI) consensus standards process to ensure that the updated standard provides the safeguards regulators and utilities need along with the flexibility manufacturers want.14

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UL is working to advance utility grid interconnection standards to increase the safety of renewable energy while helping to ensure the stability and reliability of the electric grid.


UL has been participating in the revision and expansion of the standards IEEE 1547 and IEEE 1547.1. The updated IEEE 1547A incorporates clarifications for:

  • Voltage regulation, allowing stabilizing functions to be performed to enhance and maintain grid voltage (when agreed upon by grid and distributed resource operators).
  • Additional and alternative voltage and frequency trip limits and times at which an invertor ceases to energize its output when grid voltage or electric frequency extend beyond specified normal levels, including the ability to ride through longer periods of suboptimal voltage or frequency.

The IEEE 1547A standard is currently going through the consensus process, and we have begun work on IEEE 1547.1A, which incorporates test procedures for the new functionality defined in IEEE 1547A.15


We are also working closely with the state of California — the state at the forefront in incorporating distributed generation into its energy system — to expand its grid interconnection requirements as part of California Rule 21. Under UL 1741, we have developed a path for special-purpose grid interconnection requirements for utility-scale generation, and we are developing requirements for advanced invertor functionality to provide greater flexibility in the ways that distributed generation sources interact with and support the power grid.16 


UL’s work to advance utility grid interconnection standards is focused on increasing the safety of renewable energy while helping to ensure the stability and reliability of the electric grid. Our work has brought together energy utilities, manufacturers, government agencies, regulators and other interested parties to ensure that the installation codes, standards and certifications meet each group’s specific needs. The new requirements and forthcoming standards are designed to facilitate a streamlined process in which renewable energy equipment and systems can be designed, produced, evaluated, certified, sold, installed and operated in a way that is safe, efficient and beneficial to all stakeholders.17 


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