Testing Tool Ensures Renewables and the Grid Are In Tune

Late one summer afternoon in 2019, lightning struck a transmission circuit about 50 miles north of London. As electricity system disruptions go, the strike itself wasn't a major event—but it became one, unexpectedly knocking out power to more than 1 million people for 45 minutes. The culprit: electrical oscillations, or swings in frequency caused by sudden electrical events, that caused an offshore wind farm's output to drop abruptly, among other effects, creating systemwide instability. 

Worldwide, electric grids are becoming cleaner thanks to renewable energy, but they are also more complex than ever. The combination of wind and solar energy, batteries, electric vehicle stations, and new grid hardware can create new and unpredictable electrical interactions. After the outage in the United Kingdom, the country's Office of Gas and Electricity Markets concluded, "The incident has underlined the importance of the [electricity system operator] adapting to the complex and changing world it operates in." 

With support from the U.S. Department of Energy’s Wind Energy Technologies Office, the National Renewable Energy Laboratory (NREL) is helping grid operators and equipment manufacturers successfully adapt to the energy transition. The Grid Impedance Scan Tool (GIST) makes it possible to identify and avert potentially disruptive electrical oscillations. This capability is essential in the effort to integrate more clean energy resources while maintaining grid reliability. 

 "Power systems are very dynamic. The addition of renewable resources like wind and solar, along with battery storage systems, can result in electrical vibrations that risk creating chaos," said Shahil Shah, NREL principal engineer and GIST project lead.  

 GIST was a 2023 finalist for an R&D 100 award. Using digital models of devices and the surrounding electrical system, GIST software measures the impedance, or electrical resistance, of devices at their point of grid interconnection to evaluate system stability. In addition to software-only scans, GIST can also evaluate actual hardware such as battery storage on-site at the lab. 

 "GIST is the most advanced impedance scan technology in the world," Shah said. "And NREL is the only lab that can do this type of testing at megawatt scale in a comprehensive manner."   

Cacophony on the Grid 

Mechanical engineers have learned to account for physical forces like the winds that both drive turbines for energy and cause bridges and buildings to sway. Wind turbine blades are tested to ensure strong air currents don't cause so much wobbling that they damage the blade. Electrical oscillations can cause similarly damaging effects that may not be seen or heard—until the lights go out. 

 The consequences of electrical oscillations are not confined to power outages. In Australia, electricity oscillations that appeared on the power system in 2019 and 2020 caused the Australian Energy Market Operator (AEMO) to constrain the output of five solar power plants while it worked on determining a cause.  

Later, when intermittent oscillations in the same area of Australia raised concerns about the reliability of the larger Australian power system, authorities there turned to GIST for answers.  

"GIST was able to identify the devices and controls causing the instability problems under certain operating conditions, which narrowed down the source of the oscillations and enabled AEMO and network operators to explore appropriately targeted solutions with generators,” said Michael Gatt, AEMO's chief operating officer. 

AEMO is using GIST to conduct follow-up analyses of its system to integrate more renewable energy devices into its power system and meet a national goal of net-zero emissions by 2050. 

"GIST doesn't require you to break up the system—you don't have to test devices in parts," Shah explains. "It enables testing of a full power system as it is, without breaking it." 

Helping Manufacturers Meet Clean Energy System Needs 

NREL has partnerships with renewable energy hardware makers such as General Electric (GE) Vernova and SMA. When using GIST, neither partners nor grid operators need to share any protected information about the device design or control algorithms. They can use the software either alone or in conjunction with on-site hardware tests at NREL to see how their products will perform in different scenarios.  

GE and NREL have used GIST to demonstrate the ability of the company's Type III wind turbines to run in grid-forming mode, where the generating facility could set grid voltage and frequency and operate without power from the electric grid if needed.  

GIST is available for licensing from NREL, and Shah says the team has noticed a lot of interest both in the United States and internationally as the world plans for a future with modern grids that integrate more and more renewable resources. He adds that the team is working to scale the technology for real-time application by leveraging existing sensors on the grid. 

"We are exploring ways to extract information directly from the field, so that we can also gauge the reliability of electric grids in real time to help power system operators take corrective actions before an impending disruption," he said.