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Energy Systems Integration Newsletter: March 2020

In this edition, a new video highlights how NREL is modernizing distribution systems, a Q&A with grid visionary Ben Kroposki, an NREL-developed technology continues to make a real-world impact, and more.

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New Video Highlights How NREL Is Modernizing Distribution Systems

Watch our latest video, which highlights NREL's advanced distribution management system (ADMS) test bed and how it's helping utilities bridge the gap between research and deployment. With more distributed energy resources being integrated onto the electric grid, utilities need improved management systems that allow for an affordable, reliable, and resilient grid of the future. The ADMS test bed allows industry partners to validate and optimize their management systems under real-world scenarios in the lab, reducing risk before deployment in the field.

Housed in the ESIF, the test bed combines a multi-timescale simulation environment with power- and controller-hardware-in-the-loop to simulate a utility distribution system and help utilities evaluate the performance of ADMS applications to monitor and coordinate renewable energy assets. With its ability to mirror a utility's unique circumstances, the test bed can help optimize the value of a specific ADMS application for a more efficient and secure grid.

In addition to the video, check out this fact sheet for more on the ADMS test bed.

Q&A with Ben Kroposki: A Grid Visionary

Ben Kroposki has an idea of where the electric grid is going. Throughout his career, he has worked at the innovative edge of renewable energy in power systems, leading to his current role at NREL as director of the Power Systems Engineering Center. In this Q&A, Kroposki shares his view of the future grid and how NREL and nearby universities are taking the lead.

NREL-Developed Technology Continues To Make Real-World Impact

Utilidata, an industry leader in grid edge optimization, recently announced that they have secured the rights to the NREL-developed Real-Time Optimal Power Flow (RT-OPF) technology. Developed in the ESIF with funding from DOE's Advanced Research Projects Agency-Energy (ARPA-E) Networked Optimized Distributed Energy Systems (NODES) program, RT-OPF enables highly localized load control, providing seamless integration of distributed energy resources.

"When our team at NREL first conceived of this technology and secured ARPA-E funding, our vision was that utilities would be able to take localized control of lots of different distributed devices without having to send the data to a centralized location," said Andrey Bernstein, senior researcher in NREL's Power Systems Engineering Center and one of the core developers of this technology. "Now that we've delivered on that vision, we look forward to working with Utilidata to bring our RT-OPF technology to market."

Utilidata plans to embed this technology, along with its existing voltage optimization technology and virtual power flow model, into smart meters, unlocking new potential for grid edge control.

NREL's work under the NODES program is already making a real-world impact. See how this technology helped Holy Cross Energy build a net-zero energy housing community.

The Measurable Value of Resilient Energy Systems

The resilience of energy systems is essential to utilities and communities, but how do we measure the benefits of resilience and how much they cost? Researchers at NREL created a framework to model resilience metrics and their quantitative values to demonstrate that investing in resilience strategies for the electric grid is smart planning for utilities and communities. For example, the number of hours customers are without power is one example of a resilience metric that has a measurable cost. Reducing those hours is a measurable resilience benefit.

Through a Laboratory Directed Research and Development project, NREL researchers published an article in the IEEE Systems Journal and an NREL technical report that show the value of measuring multiple resilience metrics and benefits over time and demonstrate examples of this framework in case studies, which include a grid-level operator and a campus- or building-level operator. This resilience framework can help decision makers make informed investments to protect the grid.

For more on this project and the article, check out this news article.

Newly Released: 2018 Renewable Energy Grid Integration Data Book

NREL, in conjunction with Lawrence Berkeley National Laboratory and on behalf of DOE's Office of Energy Efficiency and Renewable Energy, recently released the 2018 Renewable Energy Grid Integration Data Book. The report examines key trends in renewable grid integration and uncovered that "the share of variable renewable energy—mainly solar and wind—generation on U.S. regional power systems more than doubled on average from 2012 to 2018."

The data book also contains charts and data on renewable energy capacity and generation, wholesale and retail electricity markets, power system operations, transmission, and retail electricity markets.

Read the full article on the report here.

New Guidebook Informs Next Generation of Grid Integration

NREL's grid integration experts, with support from the U.S. Agency for International Development (USAID), shared the processes and best practices for high-quality grid integration studies in a new guidebook for practitioners across the globe. The guidebook, Variable Renewable Energy Grid Integration Studies: A Guidebook for Practitioners, synthesizes the past decade of lessons learned and approaches for conducting high-quality grid integration studies.

"This guidebook will inform the next generation of grid integration studies," said Ilya Chernyakhovskiy, NREL researcher and guidebook coauthor. "It will help teams and project leaders to build on NREL's experience delivering high-quality analysis and insights and to build consensus among in-country stakeholders around ambitious renewable energy targets."

Grid integration studies help power system planners understand the broad, system-level issues that might arise with increased variable renewable energy sources on the electric grid and the operational pathways that could support higher levels of renewable generation.

Read more about the guidebook and the USAID-NREL partnership's grid integration work.

NREL's High-Performance Computing Capabilities Drive Breakthrough Solar Panel Study

What if a solar panel could collect light on both sides of the panel while following the sunlight throughout the day?

With the support of its high-performance computing (HPC) capabilities, NREL released early results of a three-year study aimed at answering this question. Using state-of-the-art computational modeling and predictive simulation capabilities, NREL researchers collected data from June 2019 to November 2019 that revealed up to a 9% gain in energy production using bifacial panels.

"We've drawn on the Eagle high-performance computer a lot recently," said Chris Deline, NREL researcher and principal investigator in the study. "We're completing one-year performance simulations that would take four or five days on a laptop in less than a minute on Eagle."

NREL researchers anticipate that new data will remove barriers to advancing the cutting-edge technology by providing information and best practices that increase installation efficiency, reduce costs, and improve durability.

Learn more about how NREL's HPC capabilities powered the bifacial solar study.

How Resilient Are Community Microgrids? NREL Researchers Develop a Holistic Assessment To Find Out

Microgrids can provide many benefits to cities, hospitals, universities, military bases, and even neighborhood communities, including reduced energy costs, less demand on the electric grid, and independent energy generation during grid disturbances. Although microgrids are nimbler than the large electric grid, they are still vulnerable to weather events and cyberattacks. To assess the resilience of microgrids, NREL researchers developed a holistic assessment that quantifiably measures the resilience factors of microgrids.

Published in Applied Energy, this article, titled “Microgrid Resilience: A Holistic Approach for Assessing Threats, Identifying Vulnerabilities, and Designing Corresponding Mitigation Strategies,” provides a scoring system that calculates the risk factors of both cyber and physical threats and prioritizes mitigation measures to increase a microgrid's resilience. This holistic approach is also a methodological framework that decision makers can use to determine the economic feasibility of technological and operational mitigation strategies that can best inform the development of microgrids. The authors present example applications of their framework in both cyber and physical scenarios. Future work will include the development of metrics that allow decision makers to weigh the costs and benefits of different microgrid resilience investments.

Residential Battery Study from NREL Compares Performance of Consumer Devices

Not all residential battery systems are the same, and neither are the customers who use them. How batteries are charged, where they are located, and their specific chemical designs all influence the lifetime of a battery energy system.

A recent study from NREL, "Analysis of Degradation in Residential Battery Energy Storage Systems for Rate-Based Use Cases," presents rigorous testing of residential batteries from various vendors and under broad climate and charging conditions. The results create much-needed information around residential batteries and their operation, helping stakeholders make the right choices for their communities.

Residential battery systems involve many siloed stakeholders, with little information to unite them—customers seeking inexpensive systems, installers unaware of optimal programming, and utilities developing appropriate rate structures. This study provides unbiased experimental data so that stakeholders have a common understanding of systems and how they will react across operational scenarios.

This research was performed in the ESIF on the laboratory's newly installed residential battery test bed. Users of the test bed can experiment on the full range of consumer devices, paired with other hardware such as PV, and within realistic environmental conditions.

Learn more about battery energy storage at NREL.

Publications Roundup

"Small-Signal Modeling and Design of Phase-Locked Loops Using Harmonic Signal-Flow Graphs"

The growth of power electronics on the grid, such as wind turbines and PV inverters, are causing a shift in the stability issues faced by the grid. Engineers are seeking new ways to model control interactions and resonances that appear with these new grid technologies. This paper, published in the IEEE Transactions on Energy Conversion, introduces a modeling technique named harmonic signal-flow graphs that can model the dynamic behavior of power electronics technologies in an organized and visual manner. The visual tool presented in this paper can support the development of high-fidelity models of power electronics technologies to understand the dynamic behavior of the grid.

"Submodular Optimization Problems and Greedy Strategies: A Survey"

Where power systems are becoming more complex, so is their management. Engineers are interested in optimizing such systems, but when the number of decisions and actors increase, reliable optimization algorithms are harder to come by. This paper, published in Discrete Event Dynamic Systems, surveys the application of the greedy optimization strategy to problems that can guarantee accurate solutions, a characteristic of so-called submodular problems. The greedy strategy, which makes the locally optimal choice at each stage, is easy to implement and guarantees constant-factor approximations for optimization problems with submodular structures. The method explored in this paper has applications in power systems, such as energy storage device placement design and islanding control for power system stability maintenance.

"Solar Irradiance Capturing in Cloudy Sky Days: A Convolutional Neural Network-Based Image Regression Approach"

Cloud cover presents the greatest challenge for forecasting solar energy and one value in particular: global horizontal irradiance (GHI). NREL has a legacy in improving algorithms that measure GHI, and this IEEE Access paper adds another to the list. The method described overcomes the costs of expensive measurement instruments and high-performance computers by using image recognition—direct photography of the sky—and a convolutional neural network algorithm to efficiently and effectively monitor cloud cover and GHI. With reliable data about solar energy incidence, communities can better plan their energy management.

Providing Ramping Service with Wind To Enhance Power System Operational Flexibility

This NREL technical report describes an approach to wield wind for mitigating the undesirable ramping effects of system net load from uncertain and variable renewable resources. In this report, the authors present resources and findings that can help grid operators to increase system operational flexibility with ramping capability and reduce the costs associated with wind integration. One major resource to come out of this project is an open-source, multi-timescale electricity market simulation tool, OpenSMEMS. This tool was used throughout the research, and in partnership with industry, to demonstrate the team's approach to model flexible ramping services from wind energy.