The ONS (National Electric System Operator) presented last Thursday (26) a balance of the operation of the SIN (National Interconnected System) in the first half of 2025 and pointed out the main measures planned for the coming months.
The announcement took place during the July PMO (Monthly Operation Program) meeting, held in a hybrid format, with in-person meetings at the Operator's headquarters in Rio de Janeiro, something that had not happened since 2020.
One of the main highlights of the meeting was the announcement of a provisional solution for the new configuration of the SEP (Special Protection System) at the Xingu substation, in the North of the country.
The measure, according to the general director of ONS, Marcio Rea, will allow an increase of up to 1.500 MW in the nighttime flow of non-hydro renewable energy, such as wind and solar, from the Northeast to the Southeast/Central-West (900 MW) and North (600 MW) subsystems.
The increase, which will come into operation this Saturday (28), could reduce the need to activate thermoelectric plants during times of greatest power demand. In addition, the reinforcement in the transmission grid should benefit the so-called “wind harvest” of 2025, which begins in July, by expanding the capacity to transport wind energy generated in the Northeast.
By the end of July, the ONS also expects to implement a second adjustment to the SEP of the Xingu Bipoles, focusing on the wet season. The expectation is that, together with four other transmission works planned for this year, these measures will mitigate restrictions on renewable generation and enable more efficient operations.
The Operator also indicated that, with a new database of wind and photovoltaic models, it will be possible to reassess the exchange limits between regions and study new gains also for the daytime period.
Hydrological conditions
The balance of the first half of 2025 also brought a detailed analysis of the hydrological conditions faced by the National Interconnected System. According to the ONS, the wet season 2024/2025 was marked by irregular and below-average rainfall, requiring strategic action to preserve the reservoirs.
Despite the adversities, the Southeast/Central-West, Northeast and North subsystems ended June with storage levels higher than those recorded in January, which strengthens the security of energy supply during the dry period.
The South region, however, required special attention. It was the subsystem that faced the lowest inflows, impacting both the management of its reservoirs and the supply of the load. In June, partial recovery occurred with the arrival of heavier rainfall, but the ONS reinforces the importance of the South's role in meeting the night peak – especially between September and December, when the need for dispatchable and fast-response sources increases.
According to Alexandre Zucarato, ONS Planning Director, this context makes hydroelectric plants in the South essential to guarantee the stability of the system during this period.
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