Brazil's National Electric System Operator (ONS) released, on October 19, 2026, a set of technical notes with guidance for validating models of wind, photovoltaic and battery energy storage system (BESS) plants. The material is available for review by power sector agents, who may submit questions and comments to the operator until November 10, 2026. For those who develop, supply or build battery projects in Brazil, this is a reference document likely to directly influence the path from project to commercial operation.
What the ONS released
The technical notes address how the models representing the electrical behavior of these plants should be validated. In practice, the operator now sets out, in dedicated documents, the criteria and procedures it expects to see applied when an agent submits the models of its projects. The publication covers three technologies that share grid connection through power electronic inverters: wind generation, solar photovoltaic generation and battery storage.
The explicit inclusion of BESS alongside variable renewable sources is a relevant point. Storage systems have been gaining ground in sector planning, and having formal validation guidance aimed at them reduces the room for divergent interpretations among agents, suppliers and the operator itself.
- Who published: the ONS.
- When: October 19, 2026.
- What: technical notes with guidance for validating models of wind, photovoltaic and BESS plants.
- Deadline for questions: until November 10, 2026.
Why model validation matters
To plan and operate the interconnected system, the operator performs electrical studies that simulate how each facility responds to voltage and frequency variations and to grid disturbances such as short circuits and line outages. These simulations rely on mathematical models that represent the behavior of each plant, including inverter and plant controls.
Validating a model means demonstrating that it reproduces, with acceptable fidelity, the actual behavior of the equipment or plant. If the model is inaccurate, studies may underestimate or overestimate risks, affecting everything from the definition of operating limits to system security. In inverter-based resources, dynamic behavior is largely determined by software and control settings, which makes validation even more sensitive: two pieces of equipment with the same capacity can respond quite differently to the same event.
For batteries, the issue gains an additional layer, because the system can both inject and absorb power and switch rapidly between the two modes. Correctly representing these transitions, as well as the grid support functions a BESS can provide, requires well-built and proven models.
Deadline for contributions
The ONS has opened room for agents to review the content and submit questions until November 10, 2026. This is the window in which developers, manufacturers and consultancies can raise interpretation doubts, practical application difficulties or points that deserve clarification before the guidance becomes embedded in day-to-day processes with the operator.
Taking part in this stage is especially useful for those with projects already under development, as it allows the guidance to be tested against the reality of the equipment actually quoted and the schedules underway.
What this means for the Northeast
The publication addresses wind, solar and batteries in the same set of guidance, which resonates with a striking feature of the region: the proximity between connection points and renewable plants already in operation, a scenario that favors hybrid or co-located arrangements with storage. According to an ENLACE survey of Northeast substations eligible for LRCAP 2026, 22 substations in Ceará, 19 in Bahia and 8 in Piauí have wind or solar plants in operation nearby.
In projects combining batteries with existing or new generation, validation must look not only at each piece of equipment in isolation, but also at the interaction between controls of different technologies at the same connection point. For this reason, we believe guidance covering all three sources at once is likely to carry particular weight for those structuring hybrid projects in Ceará, Bahia and Piauí.
Our view
In our assessment, the publication signals that battery storage is being treated by the operator as a structural part of the system, not as an exception. Formal validation guidance is a step toward regulatory maturity: it gives investors predictability and reduces the risk of rework at advanced project stages, when adjustments tend to be more costly and time-consuming.
At the same time, we see points that still require clarification. How the guidance will be applied to projects already underway, the level of detail required from manufacturers when delivering models and compatibility with equipment of different origins are topics that may raise questions. If these issues are not properly addressed, there is a risk of bottlenecks in the verification phase, especially when the inverter or control system supplier does not closely follow Brazilian requirements.
In the coming weeks, the main milestone is the November 10, 2026 deadline for submitting questions to the ONS. We recommend following the responses and any adjustments the operator may release after this period, as they will indicate how the guidance will be interpreted in practice.
What changes in practice
For each link in the BESS chain, the publication brings concrete tasks:
- Developers: review the technical notes, map the impact on projects in the pipeline and submit questions to the ONS by November 10, 2026. It is worth including model validation in the schedule from the early phases.
- EPCs: factor validation requirements into commissioning and testing planning, aligning early with suppliers so the necessary data is available.
- Manufacturers: check whether inverter, power plant controller and battery system models meet the guidance and whether documentation is ready for processes in Brazil.
- Suppliers and integrators: provide contractually for the delivery of validated models and technical support during verification stages with the operator.
In short, model validation is no longer an end-of-project technical detail and becomes an item to be managed from conception. Those who act early are likely to face fewer surprises in the access and commissioning stages.
Original source: ONS — ONS publica novos documentos para validação de modelos de usinas eólicas, solares e sistemas de armazenamento (BESS)
Julio Martinez