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Energy Systems Integration News

A monthly recap of the latest happenings at the Energy Systems Integration Facility and developments in the energy systems integration (ESI) research at NREL and around the world.

August 2017

Read the latest ESI news from NREL.

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Follow the Installation of a Bioreactor at the ESIF

Last week, researchers at the ESIF installed a 25-foot tall bioreactor system just north of the facility, where large hydrogen compressors and hydrogen storage vessels already exist. As part of NREL’s collaboration with Southern California Gas Company to create and demonstrate a carbon-free, power-to-gas system, the bioreactor will be used to produce renewable natural gas from excess renewable electricity and a microorganism that converts hydrogen and carbon dioxide to methane. The power-to-gas technology, which will be demonstrated for the first time ever in the United States, could provide North America with a large-scale, cost-effective solution for storing excess energy produced from renewable sources in the existing natural gas network.

This pilot project will help determine if such an approach to energy storage is viable for megawatt-scale system designs. Learn more about the project on the Southern California Gas partner page.

Studying Microgrids, Forecast Uncertainty, and Voltage Estimation, Interns Establish Long-Term Relationships with NREL

The ESIF hosts a large cohort of interns each summer, some of which continue to work on NREL projects after they return to their universities.

Among interns from this summer’s Energy Systems Integration Summer Graduate Development Program, Richard Bryce is used to tackling many of his trickier research problems on his own. A PhD student at the University of Massachusetts, Bryce is studying hybrid microgrid design, exploring how photovoltaic panels can bring better affordability and reliability to microgrids. At the University of Massachusetts, his data is limited to the university’s campus and he can draw on a small set of microgrid experts.

When Bryce started an internship at NREL this summer, he discovered a new wealth of resources: data from a range of commercial and military microgrids and an entire floor of microgrid and power systems experts. “At NREL, you’re met with a genuine interest to collaborate,” he said, “By working in collaboration with field experts, my work is going to be dramatically elevated.” Bryce’s work from this summer is now being prepared for journal publication, and he hopes to apply the analytical tools and programming skills he developed to his own research.

Jose Daniel Lara, PhD student at the University of California Berkeley, is studying how to incorporate the probabilistic uncertainty of weather forecasts into power system operations. Like Bryce, Lara’s work so impressed members of the ESI team that he was asked to continue his research at NREL after he returns to school.

Andreas Schmitt spent hours this summer estimating grid voltage—under conditions when minimal information is available. He looked at matrix completion algorithms to recover and estimate missing data, allowing the team to get a better sense of the grid’s current state without needing to invest in significant infrastructure upgrades. While this research approach is different from his doctoral work in topology estimation at Virginia Tech, Schmitt was excited to be part of a project that is outside of his core research area.

“Energy systems integration combines a number of fields,” Schmitt said. “The exposure I got to all of these topics—and people with different backgrounds—has really been fantastic.”

Review Article Examines BESS Use in United States, China

ESI researchers Yingchen Zhang, Vahan Gevorgian, Ella Chou, and Rui Yang worked with Caixia Wang, Xuejiao Lei, Qionghui LI, and Liping Jiang of the State Grid Energy Research Institute in Beijing, China, to produce a review article that focuses primarily on utility-scale battery energy storage system (BESS) use in the United States and China. The article, "Grid-Level Application of Electrical Energy Storage: Example Use Cases in the United States and China," examines the experiences of grid-level BESS applications in both countries and summarizes the technical and institutional lessons from these experiences. It specifically examines U.S. installations in California, Hawaii, and Texas, as well as Chinese installations in Beijing, and Liaoning and Guangdong Provinces. The article notes that U.S. markets are better at compensating BESS systems for the grid services they provide, while better scheduling and control systems are being developed for system operators. Meanwhile, China is undergoing a market reform that could achieve similar outcomes.

NREL Researchers Evaluate the Value of Combined Photovoltaic and Energy Storage Systems

A recent NREL technical report examined the benefit of a battery energy storage system (BESS) when paired with a utility-scale solar photovoltaic (PV) system. The report examined both separately installed systems and systems that integrated the PV and BESS components to work together. Although the current high price of batteries causes all combinations with a BESS to have a lower benefit-to-cost ratio than a PV system alone, the best-performing choice is a direct-current system where the BESS is used only to store solar energy, thus qualifying for the investment tax credit. The report, titled "Evaluating the Technical and Economic Performance of PV Plus Storage Power Plants," by NREL's Paul Denholm, Josh Eichman, and Robert Margolis, also looks to the near future and finds that by 2020, a BESS will likely yield significant additional cost benefits to PV developers. The report was covered by Utility Dive and Greentech Media.

NREL and DOE Explore Effects of the Eclipse

While the nation studied the sky to catch a glimpse of the eclipse, NREL and the DOE kept an eye on the grid to see the effect of blacking out the sun during a period of typically high solar production. NREL engineers went live on Facebook August 15, to show a time-lapse of what the eclipse would look like on the U.S. grid, and to explain the importance of their solar eclipse grid impact study that was funded by DOE’s SunShot initiative. This research is especially important for helping utilities manage the variability of solar power to operate the electric grid reliably and at the lowest cost possible.

The DOE produced a pre-eclipse podcast that explains how the grid has changed since the last coast-to-coast eclipse 99 years ago, why an eclipse matters for solar, and what researchers hoped to accomplish with the eclipse grid impact study.

ESI Researchers Evaluate Gas-Turbine Power Source for the Naval Surface Warfare Center

The Naval Surface Warfare Center (NSWC) is evaluating the use of a gas turbine to power some of its loads, and ESI researchers are helping. NREL researchers Hugo Villegas, Ed Muljadi, and Vahan Gevorgian are driving the effort to develop an integrated model of a system with a gas turbine and a power processing unit that was designed by NSWC. The NSWC has developed models of both the gas turbine and the power processing unit, and Muljadi's team will first verify the performance of the gas turbine model under a variety of load conditions, and then will integrate the two models. The ESI team will use the integrated model to assess the performance of the system under a variety of load conditions, which will be defined by the NSWC.

Two NREL Reports Reinforce HECO’s Proposed Interconnection Tariff Changes

NREL's ESI researchers have performed a large body of work for the Hawaiian Electric Companies (HECO) over the past several years, most of which was geared toward allowing greater penetrations of solar photovoltaic (PV) systems on its distribution feeders. NREL's key recommendation was to require advanced inverters that could provide greater grid support and help maintain normal grid voltages. Now two recent NREL reports examine the impact of using such advanced inverters for voltage support and also consider the benefits of using advanced inverters to help mitigate frequency events using the frequency-watt function. HECO filed both reports with the Hawaii Public Utilities Commission as technical support for their proposed update to their interconnection tariff, Rule 14H, which will require several new grid support functions that are not yet required anywhere in the United States.

The first report, "Simulation of Hawaiian Electric Companies Feeder Operations with Advanced Inverters and Analysis of Annual Photovoltaic Energy Curtailment," written by NREL's Julieta Giraldez, Adarsh Nagarajan, Peter Gotseff, Venkat Krishnan, and Andy Hoke, as well as by HECO's Reid Ueda, Jon Shindo, Marc Asano, and Earle Ifuku, examines the use of advanced inverters that can "ride through" voltage disturbances and adapt their output to support grid voltage. This is in contrast to the inverters on HECO's system today, which operate at a fixed output of 95% real power and 5% reactive power with no ride-through capability. The analysis looked at both recent PV penetrations and those projected for the future and examined how the inverters operated with four separate automated response mechanisms.

The study found that increasing penetrations of advanced inverters actually helped with voltage control, and that inverters using volt-var control—in which real power is supplemented with reactive power to control voltage—had less of their energy curtailed while they resulted in a lower feeder demand for reactive power. Activating volt-watt control in combination with volt-var in the near-term PV-penetration cases resulted in annual energy curtailments of less than 0.5% per customer for 95% of the customers and less than 5% for the remaining 5% of the customers. This is the first known study to quantify the impacts of inverter-based voltage regulation using detailed annual simulations of full real-world feeder models including entire distribution secondary circuits.

The second report, "The Frequency-Watt Function: Simulation and Testing for the Hawaiian Electric Companies," prepared for the U.S. Department of Energy's Grid Modernization Laboratory Consortium, examines the use of frequency-watt control for advanced inverters. Frequency-watt control is an autonomous inverter function in which the inverter regulates its power output based on the grid frequency measured at its terminals. The report is based on an analysis by NREL and Sandia National Laboratories and ESIF power hardware-in-the-loop verification of the ability of real hardware inverters to respond to overfrequency events by rapidly reducing their output power, and it found that such inverters do help to mitigate overfrequency events. The report recommends the response be achieved in less than two seconds, regardless of the magnitude of the frequency change, using a response curve that matches that of conventional generators for proportional sharing of the response to the disturbance. The report was written by NREL's Andy Hoke, Austin Nelson, Jin Tan, Rasel Mahmud, and Vahan Gevorgian, as well as Mohamed Elkhatib, Jay Johnson, Jason Neely, Chris Antonio, Dean Arakawa, and Ken Fong.

Partner with NREL by September 15 to Advance Hydrogen at Scale Research

Through NREL, the U.S. Department of Energy’s Fuel Cell Technologies Office is offering up to $6 million in funding for collaborative projects to address key challenges associated with wide-scale production and use of hydrogen. The funding is part of the Hydrogen at Scale (H2@Scale) national laboratories consortium, which aims to develop and enable the deployment of transformational technologies that reduce the cost of hydrogen production and distribution. Proposals to participate in a cooperative research and development agreement (CRADA) project are due by September 15, 2017.

ESI Engineers Help Kazakhstan Run Its Grid With More Renewables

ESI engineers Barry Mather and Michael Coddington held a two-day training for the Kazakhstan Electricity Grid Operating Company on June 12 and 13 to address the best ways to integrate renewables into the power grid. The training focused primarily on codes and standards that will make it easier for renewables to interconnect with the grid. It was in support of an NREL project for the U.S. Agency for International Development (USAID) aimed at promoting the greater use of renewables in Central Asia, including the countries of Kazakhstan, the Kyrgyz Republic, Tajikistan, Turkmenistan, and Uzbekistan.

The grid operating company of Kazakhstan is drafting a solar and wind interconnection grid code and was so eager for NREL's input that they had the document translated into English for the ESI team. This caused the second day of the training to transition into a discussion of the proposed code, with the ESI team suggesting ways to modify the code to make it easier for projects of different sizes and different solar and wind technologies to interconnect with the national grid. For instance, Mather and Coddington noted that a zero-voltage ride-through requirement would be difficult to meet for some types of wind turbines, and a slightly relaxed requirement could open the market to all models of wind turbines.

Seeing the value in the discussion of the proposed grid interconnection code, the Kazakhstan Electricity Grid Operating Company has requested that NREL perform a detailed review of it, which is now proceeding as part of the USAID project. The next phase of the project will be a full-blown grid integration study for the Kazakhstan grid to evaluate any reliability impacts of higher penetrations of renewable energy. This study is being carried out specifically for Kazakhstan because the country leads the region in its plans for renewable energy deployment.