How grid-forming inverters will enable continuing growth of solar and grid reliability​

A non-descript, boxy piece of connection equipment known as a grid-forming inverter could hold the key to restarting the grid after an outage. Like the difference between self-driving and conventional cars, grid-forming inverters are not physically different from their traditional grid-following counterparts. What sets the inverters apart are the controls inside.

Inverters with grid-forming controls can provide system support functions on power grids with very large amounts of renewable, inverter-based resources like solar, wind and batteries. Similar to the self-driving capability that can control and drive a car in response to traffic, grid-forming inverters can sense and respond to changes on the grid in real time. This ability makes it possible for a network of solar energy systems to designate a subset of its inverters to operate in grid-forming mode while the rest follow their lead. That means they’re able to maintain stable grid voltages and frequencies during disturbances and disruptions, which is critical to the reliability and resilience of the grid’s operation.

Grid-forming inverters can also restart a downed grid using inverter-based resources like solar, wind and batteries — a process known as black start. Traditional “grid-following” inverters, on the other hand, require normal grid voltage and frequency already be established, like through a natural gas power plant, before they can inject power into the grid.

The Biden-Harris Administration set an ambitious goal to decarbonize the grid by 2035, and the National Renewable Energy Laboratory (NREL) found that wind and solar energy could provide as much as 80% of generation on a 100% clean electricity grid. As more inverter-based resources are deployed, the grid will need to adapt to the new types of energy technologies.

The future grid has three main characteristics: lower inertia, more uncertainty and more distributed energy resources. DOE is investing in technology research, development and demonstration to support operating a power system with up to 80% of generation from wind and solar, which would have some periods of time with close to 100% inverter-based resources. These resources are already more prevalent in certain regions. Hawaiian islands like Kauai and Maui are routinely operating with over 80% inverter-based resources today.

DOE is funding research and innovation to support the integration of grid-forming inverters into electric grids of steadily increasing size and complexity. For example, DOE awarded $2.9 million to NREL to create and validate advanced grid models that can simulate dispatching and dynamic response behaviors of inverter-based resources. NREL found that implementing grid-forming controls on several inverters could help stabilize a 100% renewable energy system on Maui.

In 2021, DOE launched the Universal Interoperability for Grid-Forming Inverters (UNIFI) Consortium, a $25 million initiative with the goal of leading the industry to achieve the full potential of grid-forming technologies. NREL, University of Texas at Austin and the Electric Power Research Institute lead UNIFI and aim to develop a universal set of guidelines for the integration of inverter-based resources on the grid. UNIFI has developed guidelines and specifications for how companies should build grid-forming inverters and test them to see how they work together in a large power grid. UNIFI also includes activities in standards, commercialization, education, training and field demonstration.

In a related effort, in May 2023 DOE awarded $26 million for eight selected projects to support the development and demonstration of essential grid reliability services provided by large-scale wind, solar and energy storage facilities. One project, led by Portland General Electric, is demonstrating grid-forming inverters at the Wheatridge Renewable Energy Facility in Oregon, North America’s first energy center to combine wind, solar and energy storage systems in one location. If successful, this will be the first bulk power system-connected grid-forming hybrid power plant in the United States and will encourage utilities to consider including grid-forming capabilities in their own interconnection requirements.

Grid-forming inverters are just beginning to be deployed today. As the technology matures and the grid transitions to more renewable resources, these DOE-funded demonstrations will build the case for leveraging grid-forming inverters to maintain grid reliability. Over the next several years, grid-forming inverters will become a more prevalent and essential feature of the modern grid.

Dr. Becca Jones-Albertus is the Director of the U.S. Department of Energy (DOE) Solar Energy Technologies Office (SETO). SETO has an annual budget of over $300 million to advance solar technology and support an equitable transition to a decarbonized energy system. This includes innovative research on photovoltaic and concentrating solar-thermal power technologies, grid integration, and analysis and technical assistance to reduce soft costs and increase access to affordable solar energy. Dr. Jones-Albertus also works with DOE leadership and interagency partners on key issues such as supply chains, grid modernization, and workforce training.

Dr. Jones-Albertus has spent her career advancing solar technology and working to reduce regulatory barriers to solar deployment. Prior to joining the Energy Department, Dr. Jones-Albertus worked in the private sector, where she led efforts to develop solar cells that twice achieved world-record efficiencies. Dr. Jones-Albertus graduated magna cum laude from Princeton University and holds an M.S. and Ph.D. in materials science and engineering from the University of California, Berkeley. She has more than 10 patents and 40 technical publications.