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Energy Systems Integration Newsletter April 2019

Solar-Plus-Storage Pilot at NREL Leads to Hawaii Deployment, PRECISE Cuts Costs for Rooftop PV, and Kate Anderson Does 'Cool Job' Podcast Episode

Aerial view of homes with solar panels in Hawaii.

Solar-Plus-Storage Pilot at NREL Leads to Hawaii Deployment, Wins Award

The sun never sets in Kauai—at least as far as renewable energy is concerned. With the help of a successful pilot program that started at NREL, one of the world's largest solar-plus-storage systems now powers this Hawaiian island with around-the-clock solar energy.

Prior to this installation in Kauai, the plant's developer and operator, AES Distributed Energy Inc., teamed with NREL to design a test bed for understanding Kauai's power plant dynamics. The test bed was installed at NREL, where AES and NREL could test a smaller scale solar-battery system in a power-hardware-in-the-loop environment with a simulation of Kauai's electric grid. The test bed's 240-kW photovoltaic (PV) and 500-kWh battery energy storage system (BESS) was recently named the 2019 Best Storage Application of the Year by Colorado Solar & Storage Association.

The test bed was useful for de-risking a few components of AES' PV peaker plant in Kauai. Control decisions—such as when to charge and when to dispatch storage or when to dispatch combined solar and storage—benefitted from the trial before reaching Kauai's 65,000 customers. Less technical issues were also explored with the test bed, such as setting construction guidelines and defining component integration and lessons learned with specific hardware implementation.

NREL is a unique resource, worldwide, for this scale of testing. It is home to a controllable grid interface, which can simulate a range of grid conditions and provide test conditions that are similar to those of Kauai. Further, scientists at NREL can continuously monitor the test bed's data, allowing a deployment such as the PV peaker plant to be tuned to the needs of its customers.

Lessons learned from AES and NREL's efforts are important for similar solar-plus-storage designs. The Colorado Solar and Storage award notes that the test bed "is designed to ensure programmatic and technical success for solar PV + BESS." In particular, its infrastructure supports the exploration of future designs across global markets by mimicking varying rate schedules, fast frequency responses, black-start conditions, microgrid conditions, and utility grid conditions for both 50-Hz and 60-Hz frequencies.

The NREL team was led by David Corbus and included Vahan Gevorgian, Przemyslaw Koralewicz, Steve Nixon, and Robb Wallen. The next phase of research with AES extends to PV-battery systems that provide microgrid functionality and advanced grid services.

New Software Cuts Costs and Delays for Rooftop Photovoltaics

Across the world, residents are ready for solar PV, so much so that utilities need help—the number of new PV applications is outpacing the utilities' capacity to review and approve them. Utilities assign unique operational settings to each application, which can take days to determine, despite thousands of new applications per week. NREL has stepped forward with PRECISE, a software that automates the process: halving the review time while generating optimal settings for every customer's individual device.

"We couldn't staff up to the level that would be necessary to do a custom study that often takes two to three days for each rooftop PV system," says Dave Brown, an engineer at Sacramento Municipal Utility District.

Sacramento Municipal Utility District's customers are among the nation's highest in PV adoption. Moreover, California utilities mandate the use of "smart" inverters—devices that transform power for PV and can be programmed to help stabilize grid conditions, like voltage and frequency. With dozens of inverter settings that change values every second, utilities' job to configure these devices has gotten much harder.

"These systems can do a lot of things. Choosing what they should do is a hard question," says the principal investigator of PRECISE, Adarsh Nagarajan. "When a homeowner applies for a new interconnection request, a utility can put in the location of the PV in PRECISE, and PRECISE will mention what advanced inverter settings that PV should be taking."

Although mass-PV adoption is limited so far to a few states, PRECISE has potential to be scaled nationwide, and beyond. For any utility that is stepping up its share of residential PV, PRECISE can both speed up the interconnection process, and lower the interconnection costs.

To get the full story, watch this 3-minute video.

Q&A with Adarsh Nagarajan: Energy Storage as an Entity and Asset

Adarsh Nagarajan is the group manager for Power System Design and Planning at NREL. One of his specializations includes finding solutions and understanding grid integration challenges of various emerging technologies, such as solar, wind, and energy storage systems. Learn about Nagarajan's exciting new collaborations.

Powering Our Research with High-Performance Computing

High-performance computing (HPC) at NREL offers unparalleled resolution and a completely unique perspective on systems. The HPC Data Center is home to Eagle, the largest HPC system in the world exclusively dedicated to advancing renewable energy and energy-efficiency technologies. Learn more about the HPC capabilities at NREL and how our supercomputer has paved the way for exciting new breakthroughs.

New Report on Landscape of Distributed Energy Resources Interconnection Today

As the deployment of distributed energy resources continues to grow, the interconnection of these resources has become increasingly important and complex. To provide an overview of the current state of distributed energy resource  interconnection, NREL, the Interstate Renewable Energy Council, the Electric Power Research Institute, Florida International University, and the Smart Electric Power Alliance have compiled a report to act as a point of reference for strategic planners within utilities. An Overview of Distributed Energy Resource Interconnection: Current Practices and Emerging Solutions is intended to complement existing resources by providing a broad perspective and offering some forward-looking information not contained in the interconnection handbooks provided by some utilities.

New Tool Examines Jobs and Economic Impacts of Clean Energy Around the World

The USAID-NREL Partnership has launched the new International Jobs and Economic Development Impacts (I-JEDI) Model website, which houses the I-JEDI tool. I-JEDI can estimate the potential economic impacts of wind, solar, biomass, and geothermal energy projects. Countries represented in the I-JEDI tool include Colombia, Mexico, the Philippines, South Africa, and Zambia. It can be used by industry, governments, and other stakeholders to assess potential economic impacts of transitioning to clean energy. To learn more about the tool, read an NREL news story. 

Listen to Kate Anderson's "Cool Job" Podcast Episode

NREL Engineer Kate Anderson recently got the chance to help inspire students to pursue careers in renewable energy. On "You Have a Cool Job"—a podcast that highlights people who have taken their profession in a unique direction—Anderson explained the world of renewable energy, sharing trends in the field and major projects she works on. She also discussed the combination of technical work, leadership, and consulting her job requires as modeling and analysis group manager. 

NREL Engineer Elected to Energy Systems Integration Group Board of Directors

Bethany Frew, an engineer and member of the Economics and Forecasting Group in the Strategic Energy Analysis Center at NREL, was recently elected to the board of directors for the Energy Systems Integration Group (ESIG).

ESIG is a nonprofit educational association that focuses on providing resources and education to engineers, researchers, technologists, and policymakers for the evolving electric grid. With Frew's expertise in linear programming and energy systems modeling and analysis, her knowledge will provide a vital asset in fulfilling the group's mission to chart the future of energy systems integration with a total systems approach. Frew joined NREL in 2014 as a postdoctoral researcher. As both a graduate student and a researcher at NREL, Frew built and used computational models to analyze the power system for nearly 10 years. Frew will serve with the rest of the board of directors to oversee the association's plan for operations and strategic growth.

To learn more about Frew's election, see the ESIG website.

Video about Giving Customers More Control with NREL’s Grid-Edge Research

From electric vehicles, transactive energy, and rooftop solar, to battery storage, smart homes, and smart cities; our environment and technologies are merging, and customers want to shape what that looks like. At NREL’s Energy Systems Integration Facility, we’re working on testing and developing new grid-edge technologies that give customers what they want. And that also happen to be technically feasible and financially viable for utilities. To learn how NREL is bringing control to customers with projects like PRECISE, watch this video.

New Energy Systems Integration Publications

Transient Stability Assessment of Multi-Machine, Multi-Converter Power Systems: Recent wildfires in Southern California induced transmission faults, ultimately leading to more than 2,000 MW of lost PV generation. The disconnection of PV, however, could have been mitigated with higher fidelity transient analysis of renewable assets. This paper, published in IEEE Transactions on Power Systems, proposes a model for the transient dynamics of a PV power plant. The authors' model is unique for not relying on computationally expensive electromagnetic transient studies. The framework can also be tailored to study PV converter control strategies and is useful for modeling other converter-based technologies, such as batteries, variable-speed pump stations, flywheels, and compressed air.

Integrated Distribution System and Urban District Planning with High Renewable Penetrations: Sustainable, smart districts are on the rise, but their development is rarely coordinated with the local utility. This new paper, published in WIRES: Energy and Environment, reviews current practices in sustainable district planning and presents advances in modeling and design tools for incorporating power systems within the district planning process. The authors discuss planning resources such as optimization strategies for sustainable districts to coordinate with multi-energy systems. Finally, the authors review relevant building-to-grid modeling tools that can facilitate coordinated district and power system design with utility involvement.

Including Operational Aspects in the Planning of Power Systems with Large Amounts of Variable Generation: A Review of Modeling Approaches: Also published in WIRES: Energy and Environment, this review categorizes studies for energy system planning and investigates the impacts of methods used for modeling the integration of variable generation. The authors find that (1) greater temporal resolution is needed to accurately depict the optimal generation portfolio from variable generation (a few representative days will not suffice for modeling) and (2) that operational details are important factors for estimating realistic costs and predicting the optimal generation portfolio. Accounting for various policy constraints, for example, can have unexpected impacts on variable generation planning. This study can help guide modeling efforts that will improve decision-making for policy and investments in the power sector.