Enhancing Grid Stability with Energy Storage & Grid-Forming Inverters

As the world races to meet ambitious climate targets as outlined by the Intergovernmental Panel on Climate Change (IPCC), accelerating the energy transition is an urgent priority. This acceleration hinges, in part, on the widespread deployment of renewable energy sources like wind and solar. However, the integration of wind and solar resources into the power grid presents challenges, including how to manage inherent intermittency and the associated impacts on grid instability.

As deployment and penetration of wind and solar increases, so does the complexity of grid operations. Traditional power systems were designed around centralized, predictable power generation; the grid must now adapt to a landscape where energy generation comes from more distributed and variable resources.

Adding to this complexity is the continued rise in electricity demand due to the ongoing electrification of buildings, transportation, and the rapid expansion of data centers. The increasing frequency and negative impacts of major weather events add additional volatility.

The role of BESS in grid reliability and resilience

In response to these challenges, battery energy storage systems (BESS) have emerged as a key technology for improving grid reliability and resilience. BESS can provide the flexibility needed to balance supply and demand in real time by storing excess energy when production is high and releasing it when production falls short. It also offers additional ancillary services such as fast frequency response, which can serve to further support the grid during more transient events.

Related:How LS Energy Solutions and Volvo Penta Drive Innovation in BESS

During recent and extended heatwaves in California and Texas—each leaders in the effort to deploy BESS at scale—both states were able to avoid blackouts by leveraging BESS and renewable energy resources.

“California’s power grid held up against prolonged record temperatures because of new clean energy resources, more battery storage, and enhanced coordination with state government – and the grid was also able to export energy to other states in need during this heat wave,” said Dede Subaki, VP of System Operations at the California Independent System Operator (CAISO).

And Pablo Vargas, CEO of the Electric Reliability Council of Texas (ERCOT) said, “We’ve seen significant additions of energy storage resources, solar resources and wind resources, with a few additions also on the gas side. All of that has helped to contribute to less scarcity conditions.”

Texas and California are exciting examples of how BESS mitigates the effects of extreme weather and prevents rolling blackouts from impacting customers. But, as additions of grid-scale batteries continue to grow, we still need to address the fact the inverter-based resources like wind, solar, and BESS, do not provide the grid stability that fossil-fuel-based resources do.

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The promise of grid-forming inverter-based resources

One promising area of research, development, and innovation involves grid-forming (GFM) inverter-based resources (IBRs). GFM IBRs will further support grid stability and resilience and enable even higher penetrations of BESS and renewable energy resources.

Today, the majority of BESS, solar, and wind resources utilize power conversion devices called inverters to convert output from these assets into electricity the grid can use. Inverters rely on the grid's voltage and frequency to operate and are referred to as “grid-following” because they passively adjust their output based on the grid’s frequency and voltage.

Synchronous generators (SG), on the other hand, are powered by a variety of fossil fuel-based sources like natural gas, coal, and diesel, as well as renewable sources like hydro and nuclear. Unlike grid-following inverters, SGs rotate at a constant speed which contributes to grid stability by providing inertia and voltage regulation.

Related:LG Energy Solution Shares Key BESS Growth Insights for 2024

When grid events occur, such as a frequency excursion caused by an imbalance of generation and load, grid-following inverters have limited ability to support the grid like SGs can. They can even exacerbate the problem by tripping offline when their generation is most needed.  

This is where grid-forming inverter-based resources (GFM IBRs) come in. Like SGs, GFM IBRs can actively establish and maintain grid voltage and frequency independently. This means GFM IBRs can supplement or, in cases such as microgrids, replace the role of SGs by providing fast and stable response to events, helping maintain system voltages and frequency, providing robust fault ride through, and even having black start capabilities.

The development and implementation of GFM IBR technology are being driven by several key working groups and consortiums. The Universal Grid Forming Inverter (UNIFI) Consortium, for example, is a collaborative effort that brings together researchers, industry stakeholders, and utilities to advance the understanding and deployment of grid-forming inverters. UNIFI is being led by the National Renewable Energy Laboratory (NREL), the University of Texas, Austin, and EPRI, and is supported by a wide network of vendors, system operators, system integrators, utilities, and other relevant agencies and entities. 

The consortium focuses on creating standardized testing procedures, developing new control strategies, and addressing the technical challenges associated with integrating GFM IBRs into existing grid infrastructure. The recent UNIFI Consortium Overview and Update from February 2024 and UNIFI Seminar Series are great resources for understanding the evolving GFM landscape.

Like the Unifi Consortium in the US, other counties like Australia and Great Britain have similar research and standardization efforts underway. For Great Britain, the National Grid ESO (NGESO) have their Great Britain Grid Forming (GBGF) Best Practice Guide. And the Australian Energy Market Operator (AEMO) have their Voluntary Specification for Grid-forming Inverters.

Black Start & Islanding Microgrids

Another promising capability of GFM IBRs, especially when coupled with BESS, is their potential to help manage and mitigate system outages via black start capabilities and the enabling of islanded microgrid systems.

For black start operations, GFM inverters are particularly promising because of their ability to limit transformer inrush currents during initial energization by smoothly ramping up voltages. Research continues to address some of inherent challenges facing IBRs in this context, such as handling the phase imbalances found in distribution feeders.

NREL demonstrated GFM IBRs, in conjunction with BESS, being utilized to manage the black start of a small local microgrid after an outage at the substation feeding their Flatiron campus and then sustaining microgrid operations for 24 hours.

Conclusion

Recent examples in California and Texas highlight the importance of BESS in preventing rolling blackouts and providing stable electricity from wind and solar resources. But the integration of more inverter-based resources into the grid presents challenges to grid stability. The good news is that cutting-edge research into grid-forming inverter-based resources help address these challenges. GFM IBRs give renewable energy resources similar grid-stabilizing capabilities as SGs, further enabling a larger penetration of renewable energy resources on the grid and accelerating our energy transition goals.