Aneel’s new rule unifies renewable energy curtailment, gradually including hydroelectric plants.
Brazil’s National Electric Energy Agency (Aneel) has defined a new regulatory framework for curtailment, the system that manages the reduction of power generation during periods of oversupply in the National Interconnected System (SIN). The decision, approved by the board of directors on October 6, represents a significant shift by distributing the effects of curtailments among different renewable sources, with the progressive inclusion of hydroelectric plants with spillage that could be turbined (EVT).
This update, the result of the third and final phase of Public Consultation 45/2019, aims to optimize the management of the Brazilian electrical system, which has seen significant growth in wind and solar sources. Following a preparation period by the National Electric System Operator (ONS) and a one-year test period known as the “shadow period,” the new methodology will take full effect in 18 months.
Unified Sharing and Gradual Inclusion of Hydroelectric Plants
The main novelty lies in the unification of curtailment sharing for energy reasons. Currently, reductions are applied separately by source. Under the new rule, wind, solar, and hydroelectric plants with spillage capacity (EVT) will share these impacts. However, the inclusion of hydroelectric plants will not be immediate.
The model provides for a phased incorporation of hydroelectric plants’ participation. In the first cycle of the final rule, 25% of the eligible participation of hydro plants with EVT will be considered. This percentage will increase to 50% in the following cycle, 75% in the third, and reach 100% in the fourth cycle. This gradual transition was an important adjustment to allow the sector to adapt and mitigate potential abrupt impacts.
The concept of spillage that could be turbined (EVT) refers to water that could be used to generate electricity but is released without passing through the turbines. Hydroelectric participation in this sharing will occur specifically when there is EVT, distinguishing between situations where water is simply released and those where the plant reduces generation but manages to store it for future use.
One of the directors involved in the decision stated:
The gradual incorporation of hydro plants with EVT was a balanced solution to accommodate different perspectives within the agency and ensure a smoother transition for the electricity sector.
Preparation and Testing Period
The established schedule provides for a robust adaptation period. The ONS will have 180 days after the publication of the resolution to carry out the necessary operational and systemic adaptations. This will be followed by a 12-month shadow period, during which the results of the new methodology will be simulated and published without the actual application of penalties.
This testing phase will also serve to evaluate a differentiated treatment for wind and solar plants with reserve energy contracts. The simulation proposal is that energy curtailments targeting these sources be allocated first to plants without these contracts before impacting those with reserve commitments. This measure, however, was not approved as a final rule and is intended solely to gather data for future deliberations.
Other Important Definitions
Aneel‘s decision also addressed other crucial issues:
- Curtailment for Electrical Reasons: For reliability constraints and external outages, sharing will be done “ex post,” meaning after the operation, distributing the effects among eligible agents in a more equitable manner.
- Self-Generation: In self-generation ventures, curtailments for energy reasons will primarily affect only the portion of generation that exceeds local consumption at the time, avoiding unnecessary cuts in production directly tied to the manufacturing process.
- Transparency and Auditing: The requirement for an independent audit on the calculation of curtailment events was maintained, alongside the publication of data and reports to ensure process transparency.
This new guideline from Aneel signals an important step toward the maturity of the renewable energy sector in Brasil, seeking greater balance and efficiency in water resource management and the integration of diverse generation sources. The sector will closely monitor the implementation of these rules, which promise to shape the future of the country’s energy operations.
