# Electric grid in Brazil — structure and bottlenecks

The SIN links Brazil's four subsystems; the roles of MME, EPE, ANEEL, and ONS; and why Mato Grosso's bottleneck is local delivery, not lack of generation.

Author: NiLu
Locale: en
Published: 2026-08-09
Updated: 2026-08-09
Canonical: https://blog.nilu.pro/en/blog/electric-grid-brazil/
Markdown: https://blog.nilu.pro/en/blog/electric-grid-brazil.md
JSON: https://blog.nilu.pro/en/blog/electric-grid-brazil.json

## Article summary

- The SIN interconnects four subsystems — South, Southeast/Midwest, Northeast, and most of the North —, which allows transferring energy between regions and exploiting hydrological diversity.
- The MME grants, the EPE plans, ANEEL regulates, the ONS operates the SIN, and distribution utilities connect loads: distinct roles, documented in law and decree, not in market convention.
- The SIN's load grew 1,6% cumulatively in 2025 (ONS); the remaining generation-evacuation capacity (ONS/ANEEL/EPE technical note) measures something else: headroom for new generation projects, not load service.
- In Mato Grosso, the EPE diagnosis for the GET Centro-Oeste points to loading constraints tied to nighttime irrigation loads, with named corridors and substations — not a national shortage of generation.

## Contents

- [What is the SIN](#what-is-the-sin)
- [Who does what](#who-does-what)
- [System load vs. generation-evacuation capacity](#system-load-vs-generation-evacuation-capacity)
- [Two access tracks](#two-access-tracks)
- [Mato Grosso: what the EPE diagnosis shows](#mato-grosso-what-the-epe-diagnosis-shows)
- [Goiás and the "pent-up demand"](#goias-and-the-pent-up-demand)
- [Concession renewal: the legal calendar](#concession-renewal-the-legal-calendar)
- [Uncertainties](#uncertainties)

<a id="what-is-the-sin"></a>

## What is the SIN

The Operador Nacional do Sistema Elétrico (National Electric System Operator, ONS) defines the Sistema Interligado Nacional (National Interconnected System, SIN) as Brazil's large power-generation and transmission system — hydro, thermal, and wind, with hydroelectric predominance and multiple agents —, made up of four subsystems: South, Southeast/Midwest, Northeast, and most of the North, interconnected by the transmission network. This interconnection is what allows transferring energy between subsystems and exploiting hydrological diversity between regions of the country. [[1]](#ref-1)

The ONS is a private, non-profit civil association authorized to coordinate and control the operation of the SIN's generation and transmission facilities — as well as load forecasting and operational planning for isolated systems —, under ANEEL's supervision and regulation. It was created on August 26, 1998 (Law No. 9.648, as amended by Law No. 10.848/2004) and regulated by Decree No. 5.081/2004. [[2]](#ref-2) [[3]](#ref-3)

<a id="who-does-what"></a>

## Who does what

The rest of the institutional arrangement is also described in primary texts, not in market convention. Law No. 9.427/1996 establishes ANEEL and governs the concession regime for public electricity services; among its powers are implementing federal policies for the electricity sector, holding tenders for generation, transmission, and distribution concessions by delegation, and executing and overseeing the corresponding contracts. [[4]](#ref-4) Law No. 10.847/2004 authorizes the creation of the Empresa de Pesquisa Energética (Energy Research Company, EPE) as a federal public company linked to the Ministry of Mines and Energy (MME), tasked with providing study and research services that support energy-sector planning — electricity, oil and gas, coal, renewables, energy efficiency, among others. [[5]](#ref-5)

Putting these pieces together: the MME, as the granting authority, decides sector policy and grants or extends concessions; the EPE produces planning studies (such as the Ten-Year Energy Expansion Plan and the Transmission Study Group diagnostics); ANEEL regulates and oversees, including PRODIST and contracts under delegated rules; the ONS coordinates the operation of the SIN's generation and transmission and conducts Rede Básica access studies; and distribution utilities, as concessionaires of the public distribution service, handle load connection under ANEEL Normative Resolution No. 1.000/2021 and PRODIST Module 3. [[6]](#ref-6) [[7]](#ref-7)

<a id="system-load-vs-generation-evacuation-capacity"></a>

## System load vs. generation-evacuation capacity

This is where two frequently confused metrics need to be separated. The first is the system's load (demand): according to the ONS's October 2025 Monthly Load Bulletin, the SIN's load grew 1,6% cumulatively in 2025 relative to the same period of 2024, reaching 81.142 average MW; for the month, verified load fell 0,2% relative to October 2024, with a +1,4% variation over 12 months. Broken down by subsystem, the Southeast/Midwest recorded 45.612 average MW for the year to date (+0,5%), the South 14.038 average MW (+2,8%), and the Northeast 13.309 average MW (+1,7%) — numbers at the subsystem grain, which do not isolate Mato Grosso as a state. [[8]](#ref-8)

The second metric is something else: the SIN's remaining capacity for generation evacuation. Technical Note ONS DPL 0038/2025, released jointly with ANEEL and the EPE in the context of the New Energy Auction (LEN) A-5/2025, publishes figures for this remaining capacity — a headroom for injection by new generation projects, not a measure of load service or of connection refusal. [[9]](#ref-9) Treating the tables in this technical note as evidence of "lack of energy" for consumers — agricultural or of any other kind — conflates two different questions: how much new generation the grid can still evacuate is not the same question as whether a delivery constraint exists in a specific region.

<a id="two-access-tracks"></a>

## Two access tracks

Connecting a load to the grid and obtaining access to the Rede Básica transmission network follow distinct regulatory tracks, with their own deadlines. For distribution connection, ANEEL Normative Resolution No. 956/2021 establishes PRODIST (Modules I to XI), in force since the 1st of January 2022; its Article Five refers to Module 3 — Connection to the Distribution System —, which details procedures complementary to Normative Resolution No. 1.000/2021 (rules for providing the public distribution service, in force since January 3, 2022). [[6]](#ref-6) [[7]](#ref-7)

For permanent access to the transmission system, the ONS documents a different path: a request via the SGAcesso computer system, with the opinion issued in order of filing priority and capacity reservation tied to the signed usage contract (CUST). The Access Opinion is valid for 90 days; issuance deadlines, when there is no blocking pending issue, range from up to 30 days (no expansion, reinforcement, or improvement) to up to 120 days (with reinforcements or improvements) and up to 1 year (with expansions). [[11]](#ref-11)

<a id="mato-grosso-what-the-epe-diagnosis-shows"></a>

## Mato Grosso: what the EPE diagnosis shows

The Regional Diagnosis of the PDE 2034 for the Grupo de Estudos de Transmissão (Transmission Study Group, GET) Centro-Oeste, prepared by the EPE (EPE-DEE-RE-026-2025-rev0), covers the 2028-to-2039 horizon for Acre, Rondônia, Mato Grosso, Goiás, and the Distrito Federal, and identifies loading and voltage constraints in the region's transmission network — a planning diagnosis, distinct from the generation-evacuation-capacity metric cited above. [[10]](#ref-10)

For Mato Grosso specifically, the diagnosis links the growth of irrigation loads — largely concentrated in the nighttime period — to the intensification of grid loading, especially during the dry season, in what the study calls the non-coincident nighttime peak (scenario 2b). Among the relevant constraints already in the early years of the horizon is the loss of the 500 kV Cuiabá–Ribeirãozinho transmission line under high import/export; the most critical point is the dry-season nighttime peak combined with the wet-season daytime minimum, with a noted need for structural reinforcement on the 500 kV Jauru–Rio Verde Norte axis. The study's recommendations include completing a load-service study for the central MT region specifically targeting high irrigation loads, and scheduling reinforcement of the 500 kV Cuiabá–Ribeirãozinho–Rio Verde Norte axis. [[10]](#ref-10)

At the asset level, the same diagnosis points to overloads on the 230 kV Sinop–UTE Sorriso–Sorriso and Barra do Peixe–Rondonópolis lines, and on Rede Básica transformers at Ribeirãozinho and Sinop (500/230 kV); at the border with distribution, it cites as critical the substations at Brasnorte (230/138 kV), Lucas do Rio Verde (230/138 kV), Nova Mutum (230/69 kV), Rondonópolis (230/138 kV), and Sorriso (230/69 kV), plus loading and voltage issues in the Primavera region. In specific irrigation scenarios, the study projects overload at Brasnorte starting in 2028 (under a Juína contingency) and infeasible operation without reinforcements from 2032; at Lucas do Rio Verde, emergency overload from 2029 and under normal conditions from 2030; at Rondonópolis, from 2033; and it flags a need for reinforcement in the Primavera, Nova Ubiratã, and Boa Esperança regions as well. [[10]](#ref-10)

These are points and dates from a grid-planning study — named corridors, substations, and transformers, with scenario years —, not a public measurement of the volume of connection requests denied or pending in the local distribution utility's area; that specific data point remains a gap (see Uncertainties).

<a id="goias-and-the-pent-up-demand"></a>

## Goiás and the "pent-up demand"

The same EPE diagnosis volume covers Goiás: constraints on the 230 kV Itumbiara–Rondonópolis axis appear starting in 2028, and there is overload risk at border transformers — Itapaci (2028), Barro Alto (2029), Serra da Mesa (2031), and Águas Lindas (2032). In its recommendations for the state, the study records a "pent-up demand" in Northwest Goiás, information attributed by the EPE to the distribution utility Equatorial GO within the GET process itself — a service constraint reported in the diagnosis, again distinct from the generation-evacuation capacity measured by the ONS/ANEEL/EPE technical note. The share of agro-industrial loads specifically within that pent-up demand is not broken out in the available data. [[10]](#ref-10)

<a id="concession-renewal-the-legal-calendar"></a>

## Concession renewal: the legal calendar

The renewal of distribution concessions follows a calendar defined by law and decree — a matter of dates. Law No. 9.074/1995 establishes that, for transmission and distribution concessions contracted under its regime and that of Law No. 8.987/1995, the term must be that necessary for investment amortization, limited to 30 years, extendable once for an equal period at the discretion of the granting authority under the contract; the extension request must be made by the concessionaire up to 36 months before the contract ends, and the granting authority's decision must occur up to 18 months before that end date. [[13]](#ref-13)

Decree No. 12.068/2024 regulates this process for distribution: ANEEL must send its recommendation to the MME with at least 21 months' notice before the contract ends; the MME's decision — extend or open a tender — must be published up to 18 months before the end; and, if the decision is to extend, ANEEL presents a draft amendment that the concessionaire must sign within 90 days of notification, with the MME then executing the amendment. [[12]](#ref-12)

This same framework earlier gave rise to Public Consultation No. 152/2023 by the MME (Ordinance No. 737/GM/MME, of June 22, 2023), opened to discuss guidelines for extending 20 distribution concessions expiring between 2025 and 2031 — an administrative process by the granting authority to set general rules, and not, by itself, a decision on any specific concession. [[14]](#ref-14)

<a id="uncertainties"></a>

## Uncertainties

- There is no public volume, among the sources consulted, (in MW or number of opinions) of large loads pending or denied in the areas of Energisa Mato Grosso, Equatorial Goiás, or Energisa Mato Grosso do Sul — including irrigation MUST.
- It is not possible, with the sources available, to confirm the exact operating deadlines of PRODIST Module 3 (current version) for the load access opinion, beyond the module's existence and REN No. 1.000/2021.
- In the diagnosis consulted, there is no sectoral breakdown separating how much of the "pent-up demand" in Northwest Goiás is agro-industrial versus other uses.
- It was not possible, in this cycle, to confirm whether recent ONS operational reports on Southeast/Midwest constraints change the reading of the EPE's planning diagnosis for Mato Grosso.

## References

1. <a id="ref-1"></a>[ONS — O que é o SIN](https://www.ons.org.br/paginas/sobre-o-sin/o-que-e-o-sin). ONS. Accessed August 09, 2026.
2. <a id="ref-2"></a>[ONS — O que é o ONS](https://www.ons.org.br/paginas/sobre-o-ons/o-que-e-ons). ONS. Accessed August 09, 2026.
3. <a id="ref-3"></a>[Decreto nº 5.081/2004 — regula o ONS](http://www.planalto.gov.br/ccivil_03/_ato2004-2006/2004/decreto/d5081.htm). Planalto. Accessed August 09, 2026.
4. <a id="ref-4"></a>[Lei nº 9.427/1996 — cria a ANEEL](https://www.planalto.gov.br/ccivil_03/leis/l9427compilada.htm). Planalto. Accessed August 09, 2026.
5. <a id="ref-5"></a>[Lei nº 10.847/2004 — autoriza a criação da EPE](https://www.planalto.gov.br/ccivil_03/_ato2004-2006/2004/lei/l10.847.htm). Planalto. Accessed August 09, 2026.
6. <a id="ref-6"></a>[REN ANEEL nº 956/2021 — institui o PRODIST](https://www2.aneel.gov.br/cedoc/ren2021956.html). ANEEL. Accessed August 09, 2026.
7. <a id="ref-7"></a>[PRODIST — hub de procedimentos regulatórios (incl. REN nº 1.000/2021)](https://www.gov.br/aneel/pt-br/centrais-de-conteudos/procedimentos-regulatorios/prodist). ANEEL. Accessed August 09, 2026.
8. <a id="ref-8"></a>[ONS — Boletim Mensal de Carga, outubro/2025](https://www.ons.org.br/AcervoDigitalDocumentosEPublicacoes/BoletimMensalCarga_outubro25.pdf). ONS. Accessed August 09, 2026.
9. <a id="ref-9"></a>[NT ONS DPL 0038/2025 — capacidade remanescente do SIN para escoamento de geração (LEN A-5/2025)](https://www.gov.br/aneel/pt-br/assuntos/noticias/2025/aneel-ons-e-epe-divulgam-nota-tecnica-com-os-quantitativos-da-capacidade-do-sin-para-escoamento-de-geracao/nt-ons-dpl-0038-2025-len-a-5-2025.pdf). ONS / ANEEL / EPE. Accessed August 09, 2026.
10. <a id="ref-10"></a>[EPE — Diagnóstico Regional PDE 2034, GET Centro-Oeste (EPE-DEE-RE-026-2025-rev0)](https://www.epe.gov.br/sites-pt/areas-de-atuacao/energia-eletrica/ArquivosGrupoEstudosTransmissao/3.3%20EPE-DEE-RE-026-2025-rev0%20-%20Diagn%C3%B3stico%20-%20PDE%202034%20-%20GET%20Centro%20Oeste.pdf). EPE. Accessed August 09, 2026.
11. <a id="ref-11"></a>[ONS — Acesso ao Sistema de Transmissão em 10 passos](https://www.ons.org.br/sites/multimidia/Documentos%20Compartilhados/acesso_conexao/arquivos/AcessoaoSistemadeTransmissaoem10passos.pdf). ONS. Accessed August 09, 2026.
12. <a id="ref-12"></a>[Decreto nº 12.068/2024 — licitação e prorrogação de concessões de distribuição](https://www.gov.br/mme/pt-br/acesso-a-informacao/legislacao/decretos/2024/decreto-n-12-068-2024.pdf). MME. Accessed August 09, 2026.
13. <a id="ref-13"></a>[Lei nº 9.074/1995 — outorga e prorrogação de concessões do setor elétrico](http://legis.senado.leg.br/norma/550950/publicacao/16418616). Senado Federal. Accessed August 09, 2026.
14. <a id="ref-14"></a>[Portaria MME nº 737/GM/MME (22/06/2023) — Consulta Pública nº 152/2023](https://antigo.mme.gov.br/c/document_library/get_file?groupId=436859&uuid=23d00b1e-4b9a-f827-6dcc-5e11287d7f92). MME. Accessed August 09, 2026.