EPE and ONS update grid-connection note for battery storage projects

The Energy Research Office (EPE) and Brazil’s National System Operator (ONS) revised their joint technical note on October 22 setting minimum requirements for connecting battery energy storage systems to the transmission network. EPE said the requirements apply to solutions submitted for the 2026 Capacity Reserve Auction for Storage. The revision is not an auction award or an announcement of installed battery capacity; it provides a technical framework for project design and system integration.

The document updates a joint ONS/EPE technical note first issued in 2025. EPE and ONS said the revision includes clarifications and permits mathematical models of electromechanical transients to be provided in either ORGANON or ANATEM format, at the bidder’s choice. That flexibility concerns the model-submission format; it does not remove the grid-connection criteria or eliminate the need to model system behavior where required.

The note covers supervision, control, protection and telecommunications for connections to transmission facilities. It also specifies functions for battery power converters, including voltage and frequency control, alongside requirements for grid-forming operation. These provisions address how converter-based resources interact with grid voltage and frequency during design and validation. The announcement reports no measured performance or cost result for a particular battery technology.

The underlying technical document applies to battery storage systems connected individually or in shared arrangements and describes connections to the main grid, other transmission facilities and certain shared generation connections. It expects project proponents to assess their installation’s effects on the interconnected system and provide model data used in the studies. As a result, the requirements address electrical behavior at the connection point as well as the storage asset’s energy capacity.

Grid-forming criteria concern an inverter’s ability to support voltage-source behavior rather than only follow an existing grid waveform as a current source. The note treats response to voltage and frequency changes, active and reactive power control, fault response and model validation as distinct technical subjects. These details help define the behavior storage resources need to demonstrate if they are to support variable generation and system operations.

Auction rules and connection requirements are separate layers. EPE says the revision follows guidance in the Energy Ministry’s Normative Ordinance 136/2026; the technical note focuses on the characteristics needed for projects connecting to transmission facilities. Eligibility, awards and commercial service depend on the auction documents. The October 22 update should therefore be understood as a revision clarifying technical expectations for battery projects, not as new procurement volume or a policy target.