Greater utility familiarity with smart inverters, as well as the further evolution of guiding standards and grid codes, are likely to enable the gradual emergence of optimal electric utility rollout strategies.
Rolling Out Smart Inverters
Ryan Edge, Ben York, Nadav Enbar | Solar Electric Power Association
THE WIDESPREAD DEPLOYMENT of solar photovoltaics (PV) in the United States has spurred interest in new inverter technology with enhanced grid support functionality. These advanced inverters, also known as “smart” inverters, are primed for widespread commercial rollout over the next 5-10 years. For electric utilities, the inverter technology promises grid reliability and efficiency benefits needed to manage growing PV penetration. While the technical capabilities of smart inverters are reasonably well understood, practical methods to configure and deploy the devices are not.
Today, a handful of electric utilities are introducing smart inverters with PV applications. This white paper, a collaboration between the Solar Electric Power Association (SEPA) and the Electric Power Research Institute (EPRI), explores these leading-edge utility smart inverter adoption strategies. It also examines the underlying rationales and value propositions to identify new concepts and strategies that industry peers may consider when developing their own smart inverter deployment plans. 1
Learning from the recent example of Germany’s necessary and costly retrofit of more than 300,000 solar inverters to enable grid supporting functions, utilities in the U.S. are beginning to turn to the technology to ensure grid reliability. Safety and grid interconnection standards (UL 1741 and IEEE 1547 respectively) are still being updated for advanced inverter functionality, so most U.S. utilities have yet to implement these functions to date. However, a select few utilities in service territories with high solar penetration are leading the way forward. This report profiles four utilities with individual approaches to smart inverter rollouts, including: Hawaiian Electric Companies, Arizona Public Service, Pacific Gas & Electric, and Salt River Project. The table on the previous page highlights key aspects of each rollout strategy.
Four common themes emerged among the case studies illustrated in this white paper that also apply to the industry at-large. These include:
1. EQUIPMENT STANDARDS ARE NOT KEEPING PACE WITH TECHNOLOGY ADVANCEMENT
UL 1741 and IEEE 1547 standards, as well as state grid codes such as California’s Rule 21, are in various stages of review and approval processes. Although electric utilities are not prevented from advanced inverter deployment before the standards are finalized, the potential legal liability resulting from an equipment malfunction may hinder adoption.
2. AUTONOMOUS GRID SUPPORT FUNCTIONALITY CAN BE READILY DEPLOYED AT LOW COST
All four of the utility implementation strategies include autonomous behavior of advanced inverters for frequency and voltage ride-through, ramp rate control, and fixed power factor functions. These low cost functions hold significant operational benefits for utilities, and UL 1741 and IEEE 1547 updates are expected to facilitate their deployment.
3. COMMUNICATIONS-BASED FUNCTIONALITY REMAINS A TRADEOFF BETWEEN INVERTER CAPABILITIES AND IMPLEMENTATION COST
Distribution optimization is being considered through the integration of inverter hardware with utility SCADA and other control software, such as distribution management systems (DMS) or distributed energy resource management systems (DERMS). Major challenges include utility access to inverter data and the analytical capability to process the data and update communication settings to alter distributed generation assets. Communications bandwidth will be required to interconnect and manage distributed energy resources. Current utility rollouts have either delayed communications capabilities or limited their deployment to targeted locations where benefits could be maximized.
4. INVERTER RETROFITS CAN BE EFFECTIVELY MANAGED
Thus far, utilities in the U.S. have avoided costly distributed generation issues that would necessitate smart inverter retrofits. Sufficient time remains, even in areas with the greatest grid penetration, to implement a deployment strategy. Even in Hawaii, where feeder penetrations are highest, Hawaiian Electric has worked with stakeholders to ensure that inverters deployed on its system can support the grid during modeled disturbances.
Greater utility familiarity with smart inverters, as well as the further evolution of guiding standards and grid codes, are likely to enable the gradual emergence of optimal electric utility rollout strategies. Absent a national grid code in the U.S., however, no single approach is likely to be viable. Research from EPRI, SEPA, and others will continue to evaluate the efficacy of smart inverter technologies as it relates to individual markets and utility business models. The promise of smart inverter technology is likely to spur further pilot and full-scale rollout of the technology by electric utilities in the near future. With experimentation and “learning by doing” we expect viable pathways forward to be clarified.
You can download the Executive Summary at:
1 This white paper builds on the 2014 SEPA report, Unlocking Advanced Inverter Functionality: Roadmap to a Future of Utility Engagement and Ownership, and the 2013 EPRI report, Utility Ownership of Distributed Inverters.
About Solar Electric Power Association
SEPA is an educational non-profit that enables the transition to a clean energy economy by facilitating utility integration and deployment of solar, demand response, other distributed energy resources, and supporting technologies onto the grid. Founded in 1992, SEPA has almost 25 years of experience working with electric utilities and companies offering solar, storage, demand response and other technologies that are part of the evolution of the grid. From research reports to educational events to advisory services, SEPA is the go-to resource for unbiased solar and distributed energy resource intelligence and collaborative dialogue between utilities and companies working in these emerging industries.
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