The advancement of renewable energy in Brazil, particularly intermittent sources, has been driving an accelerated transformation of the Brazilian electricity grid. This growth has exposed the system's structural fragility, particularly with regard to the flow of intermittent generation.
This effect is evidenced through a disturbance analysis, carried out on August 15, 2023, by the ONS (National Electric System Operator), on the Quixadá Transmission Line (LT) (LT 500 kV Quixadá), located in Ceará; which shows that with the increase in the active power flow in the LT, there is a cascade shutdown of several lines and loads, affecting the Northeast and part of the North and Southeast of the country.
According to the Operator, in subsequent analysis, one of the explanations for the disturbance in the system was the increase in photovoltaic and wind generation in the SIN (National Interconnected System).
The event highlighted significant vulnerabilities, such as the high concentration of renewable generation (wind and solar) in regions with limited transmission infrastructure, such as some states in the Northeast and northern Minas Gerais; the lack of adequate voltage and frequency control in some renewable power plants; and systemic risk during periods of high renewable generation and low local demand.
Therefore, measures were adopted to maintain the stability of the SIN, such as conservative operating limits, with the aim of preserving the security of the system and avoiding the dispatch of renewable plants in areas with saturated transmission grids.
Furthermore, a significant increase in renewable generation curtailments was observed, especially in the Northeast region of the country. According to the ONS, this effect is called constrained-off or curtailment. Normative Resolution No. 1.073 of September 2023 defines operational restriction events due to constrained-off according to the following reasons:
According to the National Electric System Operator, this effect is called constrained-off or curtailment. Normative Resolution No. 1073 of September 2023 defines operating restriction events due to constrained-off according to the following reasons:
I. Reason for external unavailability: motivated by unavailability in facilities external to the respective Photovoltaic Generating Plants or sets of Photovoltaic Generating Plants as defined in art. 20-A.
II – Reason for meeting electrical reliability requirements: motivated by reasons of electrical reliability of equipment belonging to installations external to the respective Photovoltaic Generating Plants or sets of Photovoltaic Generating Plants as defined in art.20-A and which do not originate from unavailability of the respective equipment.
III – Energy reason: motivated by the impossibility of allocating energy generation to the load.
As a result, renewable plants (solar and wind) began to be notified by the ONS in order to reduce their generation.
Therefore, curtailment has become an almost daily occurrence, especially in the states of Bahia, Piauí, and Minas Gerais, where there is a high concentration of renewable generators and lower relative consumption. According to ONS data, more than 1,2 TWh were lost between September 2023 and June 2024 due to generation curtailment.
Thus, the constrained-off, that is, the reduction of electricity generation in plants, within the Brazilian context, is linked to factors such as: saturation of transmission capacity, operational limitations in the interconnected system, excess generation compared to local demand and, to a lesser extent, energy security criteria.
In addition to the growing volume, it is noteworthy that the generation cut has affected plants with signed contracts, including in the ACR (Regulated Contracting Environment), which compromises the economic predictability of the projects.
The EpowerBay study showed that in July 2025, Brazil experienced significant generation outages in four Brazilian states, reaching losses exceeding 50%. The graphs below show the constrained-off ranking and the loss percentage for each set.
Graph 1 – Losses (%) per set – constrained-off ranking
As can be seen in Graph 02, in general, the state of Bahia had the largest generation cuts in June 2025.
Chart 2 – Losses (%) states
When compared to the international scenario, generation cuts are handled with advance planning, encouraging flexibility and generally with compensation.
Germany, for example, has the capacity to export through interconnections with Poland, France, and the Netherlands, reducing saturation and providing full compensation for renewable generation cuts.
China, on the other hand, recorded curtailment of over 20%, and after investments in complementary electrical systems, such as energy storage, this number fell to less than 6% in 2023.
The phenomenon of curtailment is a symptom of an electrical system in transition; its occurrence has been aggravated by the lack of integration between generation and transmission, contractual rigidity and the absence of flexibility mechanisms.
At the same time that the country expands its installed capacity with renewable sources, especially solar and wind, systemic barriers emerge that prevent the full use of this clean energy.
Some tools can be used to mitigate constrained-off, but it requires a coordinated response between public and private agents, involving not only investments, but also structural reforms in the regulatory and commercial model.
One of these tools is the expansion of Transmission, reinforcing the transportation infrastructure. Delays in strategic projects, such as the Northeast-Southeast Project lines, have directly contributed to increased operational constraints.
Electric energy storage is one of the most promising tools for mitigating the effects of curtailment in systems with high penetration of intermittent sources, such as solar photovoltaic and wind power.
In these cases, the power generation cut can be reduced through the use of storage systems, allowing the energy that, momentarily, cannot be injected into the electrical grid to be stored, instead of being reduced or having its generation interrupted.
Another essential point is operational modernization, with investment in technologies that increase the flexibility and operability of the SIN.
The creation of new flexibility products, such as capacity reservations and ancillary services, will allow for more efficient use of available resources, valuing those who can modulate their supply or demand.
Brazil has the potential to lead the global energy transition, but for this to happen, renewable energy needs to not only be generated, but fully utilized.
The opinions and information expressed are the sole responsibility of the author and do not necessarily represent the official position of the author. Canal Solar.
