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Energy Systems Integration News

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

May 2017

Read the latest ESI news from NREL.

Aerial view of the National Wind Technology Center

NREL's National Wind Technology Center Evaluates Utility-Scale Energy Storage System

NREL recently began evaluating a 1-MW, RESolve energy storage system to assist in research that aims to optimize the grid for wind and solar power plants. NREL is partnering with Renewable Energy Systems Americas—the system's manufacturer—to test advanced controls for integrating battery energy storage with renewable energy systems. The system was installed at NREL's National Wind Technology Center (NWTC) in late-March.

As part of that testing, the storage system will be connected directly to the electric grid through the NWTC's controllable grid interface. It will also be integrated with a nearby 400-kW photovoltaic system to evaluate its ability to ensure consistent energy output.

NREL researchers will use the RESolve system to interpret a range of information—from analyzing the performance of individual battery cells to understanding how storage can be controlled at the grid level. Testing frequency regulation, renewable energy integration, and seamless grid-to-island transitions will lay the groundwork for a large-scale rollout of the technology.

Report Examines How to Power More of the World with Photovoltaics

There's a huge disconnect when it comes to solar energy: although the amount of usable sunlight illuminating the Earth far exceeds the world's total energy production, the production of power from solar photovoltaic (PV) systems is currently only approximately 1% of global power production. What barriers need to be overcome for PV power to achieve more of its potential?

A new paper, published in Science Magazine on April 14, attempts to answer that question by examining the technical, infrastructure, economic, and policy barriers to greater adoption of PV power. The paper, Terawatt-Scale Photovoltaics: Trajectories and Challenges, was co-authored by 21 PV experts from around the world, including 8 from NREL. The paper is based on input from 57 experts who met in Germany in March 2016 for the first “Terawatt Workshop” gathering, organized by the Global Alliance of Solar Energy Research Institutes.

The group determined that current trajectories should reach approximately 3 TW of PV capacity by 2030 and that 5–10 TW could be in place by then if the following advances occur:

  • A continued reduction in the cost of PV systems while also improving the performance of solar modules
  • A drop in the cost and time required to expand manufacturing and installation capacity
  • A move to more flexible grids that can handle high levels of PV power through increased load shifting, energy storage, or transmission
  • An increase in demand for electricity by using more for transportation (in electric vehicles and plug-in hybrids) and heating and cooling (using heat pumps, for instance)
  • Continued progress in energy storage.

Nancy Haegel, director of NREL's Material Science Center, was the lead author on the paper. Benjamin Kroposki, director of NREL's Power Systems Engineering Center, was a contributing author. See the NREL press release for more information. 

NREL and Caterpillar Assess New Grid-Stabilizing Inverter

Caterpillar Inc. partnered with NREL to assess their 300-kVA-amp bi-directional power inverter, designed to stabilize utility grids and microgrids by integrating energy storage. The high-power testing subjected the inverter to precise and very rapid changes in grid voltage and frequency to rigorously test the ride-through and grid support functions of the inverter. As part of the testing, the inverter endured 200% overload for 13 seconds, after which power slowly curtailed automatically to keep the inverter online.

The testing successfully validated the inverter's capability to stay online and provide twice its rated power to help stabilize the grid, while simultaneously managing the temperatures of its power electronics to ensure longevity. The inverter maintained good efficiency even under very high and very low loads, allowing the system to maintain efficiency for energy storage applications.

Ground-Based Solar Radiation Measurements Verify NREL's Solar Database

Achieving higher penetrations of solar energy on the grid and reducing system integration costs requires accurate knowledge of the available solar radiation resource; however, ground-based measurements are expensive, so most solar radiation data are generated from satellite-based observations. The National Solar Radiation Database (NSRDB), maintained by ESI researchers, uses satellite data to generate a serially complete collection of the three most common measurements of solar radiation: global horizontal, direct normal, and diffuse horizontal irradiance.

"These satellite-based observations help us estimate surface radiation for long periods of time at a relatively low cost," said Manajit Sengupta, an NSRDB team member.

To ensure the accuracy of this approach, however, the NSRDB team—Sengupta, Aron Habte, and Anthony Lopez—recently conducted a validation study on the newest NSRDB data set, which includes data from 1998-2015. The team compared the satellite-derived data in the NSRDB to ground-based data and found statistically similar outcomes.

"The validation study basically quantifies the accuracy of the solar radiation data," said Habte, the principal investigator on the validation study. "We compared our NSRDB data to high-quality, real-world ground measurements that represented various climatic regions around the country."

Supported by the U.S. Department of Energy's SunShot Initiative, the NSRDB helps quantify intra-hour, inter-hour, seasonal, and inter-annual variability of solar resources—essential information for accurately designing utility-scale solar energy projects. It also includes meteorological data such as temperature, humidity, surface pressure, dew point, and wind speed. This combination equals a powerful tool that provides essential information to policymakers, financiers, project developers, and analysts.

Ibrahim to Speak on Cybersecurity at This Year's American Renewable Energy Day Summit

The American Renewable Energy Day (AREday) Summit, held annually by Aspen's American Renewable Institute, brings together more than 100 cross-sector speakers each year. Among presenters at this year's event from June 19-22, NREL's Erfan Ibrahim, director of Cyber Physical Systems Security & Resilience Center, will provide critical discussion on cybersecurity for distributed energy resources as they become increasingly integrated to the grid.

The AREday 2017 theme is “Protecting America's Greatness: The Business of Innovation, Climate Leadership and Resilient Communities” and will feature thought leaders from across the country in the renewable energy space. Ibrahim's talk will cover cybersecurity practices developed by NREL researchers, addressing the fast-changing threat landscape from hackers, system errors, and natural disasters that are crucial to mitigate for the sustainability of a 21st-century electric grid.

NREL and iUnit Open the Door to Grid-Integrated, Multifamily Construction

ESIF researchers showcased one of their key partner projects on May 4, 2017. Nearly 30 industry partners, representing 25 companies, visited a 380-ft2 modular studio prototype apartment created by Denver developer iUnit and now located in the ESIF. Open-house participants were able to tour the unit in person and learn about the partnership between iUnit and NREL, which employs the ESIF's hardware-in-the-loop research capabilities and energy modeling tools to examine the performance of the apartments in combination with energy storage and energy management tools. Learn more about the project.

Microgrid Controller Competitive Procurement Letters of Interest are Due June 2

Don't forget to submit letters of interest for NREL's dual-staged competitive procurement for a microgrid controller technology by 3 p.m. MT (5 p.m. ET) on June 2. This unique opportunity calls for a microgrid controller technology where up to five respondents will compete on state-of-the-art testbeds at the ESIF between June and December, 2017. The top performer will have the opportunity for its microgrid controller to be purchased and made part of a permanent microgrid research testbed available to NREL researchers and other users of the ESIF. 

ESIF Webinar on PV Grid Support Inspires Greentech Media Article

NREL, the California Independent System Operator (CAISO), and First Solar recently completed a project in which a 300-MW photovoltaic (PV) power plant within the CAISO service area was controlled to contribute to system-wide reliability. The results of that project are presented in a technical report, Demonstration of Essential Reliability Services by a 300-MW Solar Photovoltaic Power Plant, and formed the basis of a webinar held on April 27, 2017. That webinar, in turn, led Senior Editor Jeff St. John of Greentech Media to publish an article titled, "More Data on How First Solar and NREL Are Balancing the Grid With Utility-Scale Solar."

Today's utility-scale solar inverters have speedy response characteristics, making them "more akin to batteries and other fast-responding assets" than competing natural-gas-fired generators, making them more valuable to utilities.

The article notes that providing such grid support means "deliberately holding back a certain amount of solar generation—say, 10 percent or so—in order to be able to move production up and down in line with grid operator market signals" and warns that it's hard to determine the value of doing so. However, if the solar power plant's output is being curtailed anyway, this is a way to potentially recover some revenue. The article also notes that today's utility-scale solar inverters have speedy response characteristics, making them "more akin to batteries and other fast-responding assets" than competing natural-gas-fired generators, making them more valuable to utilities. Operating independently of the PV plant, the inverters can even offer frequency and voltage support at night through their interactions with the grid.

The article concludes with a look ahead to the future, when PV penetrations increase to the point that a decreasing number of spinning generators will be providing the essential reliability services and inertia that help stabilize the grid. To compensate, utility-scale PV plants may employ their power electronics and software controls in a way to provide similar types of services and "synthetic inertia" to the grid.

Hannegan to Leave NREL for Holy Cross Energy

Bryan Hannegan is leaving NREL to take a new position as president and chief executive officer of Holy Cross Energy. Hannegan has served as NREL's associate laboratory director for the Energy Systems Integration directorate since August 2013. Under his leadership, the ESIF was opened and commissioned. With more than 125 academic and commercial partners and many high-profile projects, the ESIF stands out as one of his most visible accomplishments.

Hannegan also built the organization, staff, and operations of the ESI directorate and developed NREL's grid integration program. Additionally, when the U.S. Department of Energy was looking for "big ideas" that cut across disciplines and offered substantial energy benefits to the country as a whole, Hannegan co-led the "big idea" that resulted in DOE's Grid Modernization Laboratory Consortium, a $220 million, three-year investment to advance the fundamental technologies needed for a reliable and sustainable future electric grid.

In his new role as a utility company executive, Hannegan looks forward to taking grid modernization from the lab and putting it into practice. Holy Cross Energy has a 78-year history of providing electric power to its members, who are located primarily in Eagle, Garfield, and Pitkin counties in Colorado, including the towns of Aspen, Glenwood Springs, and Vail.

Hannegan started his career as a staff scientist on the U.S. Senate's Committee on Energy and Natural Resources. He next moved to the Council on Environmental Quality, serving as the primary policy advisor to President George W. Bush on domestic energy policy issues, as well as the deputy environmental policy advisor to the president. Hannegan then served nearly seven years as the vice president of environment and renewable energy at the Electric Power Research Institute before coming to NREL.

Juan Torres has been named the new associate lab director for ESI and joins NREL from Sandia National Laboratories, where he most recently served as deputy to the vice president for energy and climate programs. Torres starts on June 5, and Hannegan will stay on board until June 23 to assist with the transition.

In Case You Missed It: Greening the Grid Webinar

As part of Greening the Grid's webinar series, the Clean Energy Solutions Center, U.S. Agency for International Development , and NREL hosted a webinar on power purchase agreements (PPAs) as a mechanism for utilities to procure variable renewable energy from independent power producers. ESIF Grid Integration Manager Barbara O'Neill shared her expertise as a presenter, discussing how PPA provisions can enable wind and solar technologies to enhance grid stability and power system flexibility.  Learn more by viewing the May 9 webinar and presentation slides on the Clean Energy Solutions Center website.