Recent findings from the National Laboratory of the Rockies (NLR) demonstrate that grid-forming inverters are essential for maintaining stable power grids as they transition to renewable energy. By analyzing real-world data from Kauaʻi Island, researchers discovered that switching from grid-following to grid-forming controls effectively eliminated frequency oscillations during generator failures. This technology provides synthetic inertia, successfully mimicking the mechanical stability of traditional fossil fuel plants. The study confirms that deploying large-scale batteries with these advanced controls is a critical step for ensuring long-term grid reliability and avoiding expensive infrastructure upgrades.
The investigation began following a 2021 incident on Kauaʻi, where an oil-fired generator unexpectedly tripped offline. While the island’s solar-plus-storage facilities responded within 50 milliseconds to stabilize the frequency, the system suffered from significant oscillations during the recovery phase. Analysts determined that the issue stemmed from the limitations of grid-following inverters, which rely on an external grid signal rather than actively stabilizing the network.
To address these vulnerabilities, the Kauaʻi Island Utility Cooperative partnered with the NLR to transition its solar-plus-storage assets to grid-forming controls. Unlike their predecessors, grid-forming inverters maintain a constant frequency and voltage, creating a digital version of the rotational inertia typically provided by heavy turbines in conventional power plants. This synthetic inertia allows the grid to remain resilient even when traditional generators fail.
The effectiveness of this transition was proven in 2023 when the same generator tripped again. Under the new grid-forming settings, the system maintained perfect stability with no recorded oscillations. Jin Tan, the project lead at NLR, noted that the comprehensive testing—which included computer modeling and physical grid re-creations—confirmed that these inverter-based resources significantly bolster grid strength.
These findings are now informing the work of the UNIFI Consortium, a group dedicated to standardizing grid-forming software across the industry. The consortium is currently developing a library of models and controls to streamline the adoption of this technology. Experts from the Energy Systems Integration Group (ESIG) have also weighed in, recommending that all new large-scale battery projects incorporate grid-forming capabilities to prevent the need for costly retrofits as the global energy mix continues to evolve.