An estimated 427 GW of battery storage capacity was in the interconnection queues around the U.S. as of the end of 2021. In the absence of any incentives or requirements for more advanced control capabilities, all of these resources are being planned with conventional grid-following (GFL) controls. Some of these batteries will be built in weak grid areas already dominated by GFL inverter-based resources (wind, solar, battery storage), areas that are already strained due to stability constraints. The integration of additional inverter-based resources (IBRs) in such areas is likely to further reduce stability margins and may even result in new stability constraints. This will lead to a reduction of low-cost generation export from existing IBRs in these areas, driving up overall energy costs. To relieve these constraints, additional transmission assets such as synchronous condensers or transmission lines will be needed, thus also driving transmission costs higher.
Batteries with new advanced controls, termed grid forming (GFM), can provide stability services that are inherently delivered by conventional synchronous generators today. The advantage of implementing GFM controls in newly planned batteries is that the stability can be provided by the resources themselves as they are added to the system. Thus, the integration of these new resources with GFM controls can both maintain stable and reliable operation and be achieved more efficiently and at lower cost, as it does not require addition of new transmission assets.
At the ESIG Special Topic Grid-Forming Workshop, held June 6-9, 2022, Andrew Isaacs from Electranix discussed how the Hawaiian Islands, as they approach levels of IBRs nearing 90% in the coming year, are faced with the acute need to install GFM batteries and rely on them for maintaining grid stability and preventing blackouts. The rest of the U.S., where IBR penetration levels are moderate and existing synchronous machines are still providing reliability services, has a unique window of opportunity to procure, test, and gain experience with GFM technology in a “safe environment,” before the need for IBRs to contribute to grid stability becomes acute.
GFM Batteries Are Low-Hanging Fruit
GFM controls can potentially be implemented on any type of IBR, including new solar and wind plants, but batteries are particularly low-hanging fruit for the implementation of these controls. GFM behavior requires a certain amount of energy buffer, which for wind and solar resources means continuous operation below their maximum power production. In addition, for wind turbines, GFM operation may result in greater and more frequent mechanical stress, which needs to be accounted for in the wind turbine design. But the battery is the energy buffer, hence only software modifications to a battery’s controls are needed to make the battery a GFM resource.
Several grid-connected GFM projects have been deployed around the world, and further development is happening at unprecedented speed. Australia leads the way with three large-scale GFM batteries already in operation and two large projects under construction. On December 17, 2022, the Australian Renewable Energy Agency (ARENA) announced co-funding of eight large scale GFM batteries across Australia with total project capacity of 2 GW/4.2 GWh, to be operational by 2025. In Great Britain five new large grid-connected GFM batteries will be deployed between 2024 and 2026. Large equipment manufacturers such as SMA, Tesla, and Hitachi already have commercial offerings of GFM controls in battery storage.
Independent system operators (ISOs), regional transmission organizations (RTOs), utilities, and their stakeholders can draw from interconnection requirements already proposed or approved around the world to draft the specifications for GFM capability for new batteries in their systems. For example, the National Grid Electricity System Operator (NGESO) in Great Britain has already included non-mandatory requirements for GFM capability in its grid code, while the European Union–funded project OSMOSE recommended the inclusion of GFM capability requirements for all new transmission-connected batteries in European grid codes. The association of European Transmission System Operators is currently in the process of developing these requirements.
Even in the absence of requirements for GFM capability, developers can be proactive and procure new batteries with GFM capability today, given that only software modifications to the battery’s controls are needed compared to GFL. The developer (as well as owners of other resources in the area, and a region overall) would benefit from less curtailment of IBR resources in the area including these new batteries.
Testing and Demonstration of Services Can Be Done Ahead of Requirements
We don’t need to wait for GFM functionality to be required in order to begin testing and implementing these controls. Capabilities to provide grid services have been tested on existing plants in the absence of interconnection requirements. In 2017-2018, First Solar and the National Renewable Energy Laboratory tested several existing projects in California, Arizona, Texas, and Puerto Rico to demonstrate that solar resources can provide essential reliability services (such as regulation, primary and fast frequency response, and voltage support) with similar or superior performance compared to conventional thermal generators. Following the successful demonstration, some of these plants are currently providing reliability services in their respective areas.
Similarly, GFM capability can be deployed in RTO/ISO/utility areas through pilot projects involving a number of newly built batteries with GFM controls. A pilot involving several plants concentrated in one geographical area, for example, weak grid area in the Texas Panhandle, would allow testing of the interoperability of GFM IBRs from different inverter manufacturers with different GFM control strategies. In parallel with the pilots and in collaboration with the manufacturers involved (to obtain manufacturer-specific models of GFM IBRs), ISOs/RTOs/utilities can carry out simulation studies and explore the broader benefits and grid impacts of GFM batteries. These two initiatives would provide a solid basis for moving forward with the necessary interconnection requirements, performance specifications, and modeling requirements for GFM capability in batteries.
While GFM capability in batteries can be delivered at relatively low (or even zero) cost, there still may be some cost burden associated with the development of a project with this relatively new technology. Depending on the outcomes of the benefits study, some market-based mechanisms can be considered to incentivize GFM capability rather than implementing it through an interconnection requirement.
The Cost of Inaction: Continued Curtailment, Instability, and Higher Costs
This is a moment in the industry when a need is becoming fully understood and an effective, low-cost solution has emerged. Deploying GFM capability in batteries is the clear solution to the weak grid issues that increasingly are the cause of wind and solar curtailments. But ISOs’/RTOs’/utilities’ opportunity to utilize this low-cost solution may soon pass—while only a relatively small number of batteries are installed in the U.S. today, a significant amount of battery capacity will likely be developed in the next few years. Without specifications and the appropriate incentives or requirements, much or all of this capacity will likely lack GFM capability, resulting in continued stability challenges, continued solar and wind curtailment, and the need for costly supplemental stabilizing equipment. In contrast, with specifications and the appropriate incentives or requirements, this capacity can be installed with GFM capability and result in increased grid stability, less curtailment, and little or no need for additional costly stabilizing equipment.
ISOs/RTOs/utilities can work with stakeholders to carry out studies of the implementation of GFM technology in weak grid areas and then act quickly to implement pilot projects in a fashion similar to how the provision of ancillary services from GFL IBRs has been tested in the past. Experience from installations around the world, particularly in Hawaii, Australia, and Great Britain, can be used as a guide.
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