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California Smart Inverter Integration Needs Standards Development

As the deployment of solar power increases in California, so too has the sense of urgency to revise the state’s regulations and relevant national standards governing how these distributed generation resources interconnect and communicate with the grid. To achieve the kind of advanced grid functionality (AGF) required to accommodate these higher levels of solar energy, the utilities insist that inverters play a larger role, to be “smarter” and incorporate a range of automated control capabilities that will help smooth out potential grid fluctuations. Enphase shares this vision and is working with other industry stakeholders in the development of the necessary national standards and regulatory compliance testing protocols that will help ensure the transition to an advanced, stable grid.

At the forefront of these regulatory efforts is the Smart Inverter Working Group (SIWG), which will soon present its updated recommendations for revising Rule 21 to the California Public Utilities Commission and California Energy Commission. The current Rule 21 statute, which governs the technical requirements that distributed-generation resources must meet in order to interconnect to the California grid, has become outdated as solar technology has improved and PV deployment has accelerated. Although Rule 21 only applies to the California system, it has a large influence on the regulations governing renewables interconnection in the rest of the United States because of the state’s leadership role in deploying solar, wind, and other alternative energy sources.

The SIWG’s technical recommendations focus on a range of autonomous and remotely commanded grid-stabilizing functions that the utilities see as necessary to deal with the challenge of ever-growing penetration of distributed solar in the power mix. Inverters play a key role as the “brains” of photovoltaic systems, and will be expected to provide integration and communication capabilities. Fault ride-through, reactive power control, and other advanced inverter features will deal with momentary disturbances, supporting the utility’s efforts to operate the grid and making it possible to deploy much more solar in a safe and reliable way. 

On the national level, ongoing activities are also progressing on amending the UL/ANSI 1741 and IEEE 1547 standards that will facilitate the implementation of these advanced capabilities. Any changes to Rule 21 must be harmonized with the regimen of testing and certification procedures that will be called for in those amended standards, so the clock is ticking on updating these protocols. Before any inverter is certified in the United States, it must be third-party tested at a National Research Testing Laboratory (NRTL), but the labs can’t move forward until the new standards are approved. Any customer-owned facility that tries to install an unlisted inverter would be in violation of the National Electrical Code, but the UL listing process can’t take place until the testing procedures for the new functions — some of which are prohibited in the current version of IEEE 1547 — are included in the revised standards. 

The UL 1741 revision process has been moving along more quickly than its IEEE counterpart, so the SIWG has set a goal of developing the first draft of test protocols by the beginning of the year and submitting them to the UL technical panel for review. After the review process and the addition of other suggested changes, the revised 1741 document will go out for ballot; if it passes, UL believes the standard could go into effect in late spring of 2014.  

In the early days of the SIWG, there was a fundamental lack of understanding among representatives from certain European manufacturers participating in the group about how the regulatory process works in the U.S., including the realities of standards development and other North American compliance issues. This misunderstanding led to early drafts that did not incorporate the proper standards certification steps and necessary timelines for standards development. For manufacturers that recognize the critical importance of grid safety, there were also concerns about certain proposed inverter functions that could have a negative impact on one of the key safety requirements of any photovoltaic system — anti-islanding. This is the capability that ensures that inverters remain disconnected during downtimes and do not accidentally re-energize the grid and potentially electrocute a line-worker.  

Whether it’s testing for anti-islanding or one of the advanced functionality features, it will take time for Sandia National Labs, UL, and other NRTLs to assess and certify the new inverter products. The labs are limited in number and have finite engineering bandwidth. One must consider how long it will take to get every inverter model from every manufacturer certified or recertified to the new U.S. standards—let alone the time it will take the companies themselves to redesign and re-qualify these feature-rich inverters. Even on an accelerated timeline, the testing process is likely to take months.

The recognition by the working group of these mitigating factors has led to a prudent restructuring of the Rule 21 recommendations. An aggressive but reasonable timeline still allows for the start of pilot testing by utilities of the advanced inverters in coordination with each other and with existing utility control equipment by mid-2014. If the field-testing goes according to plan, the new inverter standard would become mandatory for all new grid-connected systems in California in October 2015. 

Included in this recommended timeline is a placeholder of 15 months for the adoption period, which will ultimately be set by the UL standards technical panel. This would allow manufacturers time to make any needed changes to their equipment and, more importantly, to provide enough time for the NRTLs to test those products in need of requalification. Historically, the UL adoption period for similar changes has been 18-24 months, so the abbreviated — and aggressive — time-frame recognizes the urgency acknowledged by the Rule 21 stakeholders.

Although the solar companies, industry associations, and investor-owned utilities agree on the necessity of advanced grid management capabilities as part of the updated Rule 21, there has been some debate about how to proceed. The issue is not with inverters themselves, as many suppliers have no inherent technical or practical limitations that would prevent cost-effective implementation of existing requirements or new smart device functionality. Capabilities such as a single point of bidirectional communication and automated control embedded in devices that can be networked and scaled to virtually any system size will provide the intelligence necessary to support a robust and reliable next-generation grid. 

Lead image: Solar maintenance via Shutterstock

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