Article published in the 16th edition of the Magazine Canal Solar
This article presents the evolution of the transmission network in Brazil, the way it has been planned and operated, the challenges of decarbonization with renewable sources, and finally the impact of DG (distributed generation) on the current development of this network.
Unlike what occurs in countries in the northern hemisphere with a predominance of thermal generation, Brazil developed its generating park through hydroelectric plants.
The first plants were built close to load centers, but due to the continuous increase in demand, it was necessary to look for facilities that were increasingly distant.
To achieve this, there was a need to build long-distance transmission systems to connect this generation, which does not occur in thermal systems. A pioneering example was the construction of the 750 kV alternating current system and the 600 kV direct current system to transport energy from the Itaipu plant in the XNUMXs.
All this development took place in a centralized state model coordinated by Eletrobrás. The expansion and operation of the network was carried out by the Eletrobrás group through GCPS and GCOI respectively.
From the 1990s onwards, with the restructuring of infrastructure sectors around the world, where greater efficiency was sought through the introduction of market models, the electricity sector separated production from energy transport.
This was necessary due to the natural monopoly characteristic of electricity transmission networks that could not be incorporated into the free market.
To this end, there was a need for laws to guarantee free access to networks by any agent as well as economic regulation to define transport tariffs today known as TUST (Tariff for the Use of Electrical Transmission Systems) and TUSD (Tariff for Use of Electrical Distribution Systems).
The deverticalization of companies that jointly planned generation and transmission, coordinating their implementations, ended up causing a certain disconnect between these activities.
In this new context, the planning of the Brazilian transmission system known as SIN (National Interconnected System) carried out in Brazil by the MME (Ministry of Mines and Energy) through the EPE (Energy Research Company) has been using as input data the generations contracted in the ACR (Regulated Contracting Environment) auctions and information on quantities to be sold in the ACL (Free Contracting Environment).
Everything was going well when wind generation appeared at the beginning of the 2010s and then solar generation from 2015 onwards with the incentive given as the discount on TUST and TUSD to these renewable sources due to the global urgency in decarbonizing production chains.
Despite being recent technologies, these uses appear to have much shorter execution times than the hydraulic (five years) and even thermal (three years) uses that prevailed in previous decades.
It is therefore possible to set up a wind generation project (two to three years) and a solar project (one to two years) in much less time than transmission projects (three to five years) which in turn have increased due to environmental and land issues.
This already raises the need for more active expansion planning, envisioning future opportunities for locations with potential for increased generation to minimize problems with the flow of this new energy.
The probability of finding regions with excess transmission capacity and others with significant restrictions ends up increasing due to this new condition.
This situation worsened when the government withdrew the discount on the transmission tariff for renewables in February 2022. Applications for concessions exploded and ANEEL (National Electric Energy Agency) ends up accepting without analyzing compliance with the transmission system.
Although most of these projects, which practically double the current generation capacity across the country, do not get off the ground, they cause great uncertainty in transmission planning.
The mismatch between the expansion of generation and transmission ends up bringing restrictions to the network that interfere with the operation of the SIN.
Furthermore, solar and wind plants have no control over dispatch, causing ramps and power fluctuations. Measures are adopted to overcome these problems, but often without economic support, such as:
- Limitation of generation dispatch during periods of network restriction. In many cases this period can last days or even months. As the decision to cut generation can affect different agents differently, the government chose to hold transmission capacity auctions to establish rights over the use of the network;
- The establishment of ancillary services for frequency control, voltage control, power reserve, load follower, to address the non-dispatchability of renewables. The way these services are allocated among agents and priced represents a major challenge and today these services are not satisfactorily remunerated.
These questions refer to the offer connected to the SIN, that is, related to centralized generation. Another point of uncertainty is in relation to demand at the interface points with distributors.
The load growth rate has varied over recent years due to uncertainty in the economy, the pandemic experienced in 2020 and 2021 and recently due to the growth in distributed generation.
The latter had a significant increase from 2015 onwards, reducing the net load observed at the interface substations between the transmission network (basic network) and the distribution network.
Although this generation is quite dispersed and represented basically by solar sources, the total has already reached more than 20 GW of power, that is, more than 10% of the country's total generation capacity.
Despite being located in the distribution network and individually representing a very small portion, the set of all DGs can affect the transmission network in several ways.
Recently, the ONS (National Electric System Operator) changed the way it forecasts load to include the effect of solar generation.
In regions where penetration is high and in many cases accompanied by the penetration of centralized generation, the effect of intermittency, for example, has brought some inconveniences, as is the case in the northern region of Minas Gerais.
It is important to list the main problems and benefits that DG can affect the distribution network and indirectly the transmission network. Below are some more representative points.
Network expansion
As DG with a predominance of solar sources that only generates during the day, it ends up relieving distribution networks and even transmission during this period.
Unlike countries in the northern hemisphere where the peak of consumption is greater in winter and at night, in tropical countries such as Brazil, the peak of the system is in summer and during the day due to the air conditioning load.
This climatic characteristic means that DG brings a benefit to the electricity grid, where the peak occurs around 14 pm. As the heavy load determines the need for network expansion, we can say that DG helps to minimize the need for additional capacity in the distribution and transmission networks.
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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.
An answer
Prof Marangon's comments are perfect