By Sergio Cortizo*, special for the column
A study by the National System Operator (ONS) points out that Brazil should go through blackouts before December this year. In other words, the question is no longer whether there will be a power outage, but when and for how long.
On August 25, the ONS published a technical note (NT-ONS DGL 0093/2021), assessing the situation of the National Interconnected System (SIN) until the end of November this year. The document adopts realistic assumptions regarding river flows in the coming months. See the first chart.
The ONS study analyzes two scenarios for meeting energy demand, called cases A and B. The difference between them is that case A works with the real conditions of generation, while case B has a counterfactual character: it estimates how much additional energy the country should be able to generate to avoid shortages before the end of November.
In case A, the conclusion is that there will be a shortage of energy even with all the emergency measures adopted:
“Even with the depletion of the main hydraulic resources in the Southeast/Midwest, with the reaching of the restriction range of the plants in the São Francisco basin, with full thermal dispatch, and with maximization of energy transfer from the North/Northeast to the Southeast considering flexible transmission limits according to the N-1 criterion, the resources are insufficient to meet the energy market, resulting in deficits of 3,824 MWmonth in October and 3,746 MWmonth in November”, says the technical note.
And, in case B, she assesses that “in order to ensure energy service, it is essential to increase supply by about 5.5 GW med between September/21 and November/2021, totaling 16.5 GW per month”.
Therefore, the ONS has already warned, in the stars of the technical note, that a blackout should happen before the end of November this year.
To understand the ONS numbers, it is important to know the difference between two types of blackouts, known in electrotechnical jargon as “energy crisis” and “power crisis”.
In the system, electricity is produced at the same moment it is consumed, that is, electricity must be generated in the same second it will be used, exactly in the amount demanded by consumers, in addition to the inevitable losses during transmission and distribution . Hence the expression “demand service”, meaning that, in each second, the demand is defined by the electricity consumers, and the system operator is responsible for generating exactly the quantity demanded in real time.
In order to meet demand, some form of energy is converted to electricity at the time of “generation”. This original energy source can be hydraulic, thermal, nuclear, solar, biomass or some other source not used in the SIN.
Some of these energy sources can be stored to be converted to electricity when needed, while others cannot.
Typically, hydraulic, thermal and nuclear sources can be stored, while wind and solar sources cannot. Thus, the first three are called “dispatchables” in electrotechnical jargon. Under the current conditions of the SIN, nuclear, wind and solar sources supply a small portion of the demand (approximately 15%), with most of the load being supplied by additional orders from hydroelectric and thermoelectric plants.
a power crisis it occurs when, at a given moment, the system operator is unable to meet the instantaneous demand for electrical energy, thus being forced to immediately turn off a part of the network or even the entire network, in order to avoid more serious problems. It may happen that there is even energy stored, but the system is not capable of converting it into electricity with the necessary speed to meet the demand at that critical moment.
On the other hand, an energy crisis it happens when non-storable energy sources are insufficient to meet demand and there is no longer dispatchable energy to complement the service. This is when the system does not have additional sources of stored energy. Normally, this occurs when the reservoirs of hydroelectric plants are empty or there is no fuel in the thermoelectric plants.
There is a lack of energy equivalent to a week of total SIN generation before we arrive in December
In practice, the two types of seizures can be confused, as the conditions under which they occur are often similar. For example, the yield of hydroelectric power plants depends on the level of their reservoir: the lower, the lower the yield. Thus, when many hydroelectric plants have empty reservoirs, the system’s instantaneous generation capacity decreases, creating the risk of a power crisis.
Empty reservoirs also mean little stored hydro energy, meaning the system could be close to an energy crisis. However, the two types of crisis are conceptually distinct and, in general, are considered separately when planning the operation of the electricity system.
In the case of Brazil in 2021, it was initially thought that the depletion of reservoirs could lead to power crises for the SIN (due to the drop in the yield of hydroelectric plants). In the first half, projections indicated that there might be enough water to avoid an energy crisis in the system. However, the rains expected for the middle of the year in the southern region of the country did not materialize, and thus, the technical note published by the ONS at the end of August already indicated that the situation had worsened.
The ONS study estimates that 7.6 GWmonth of energy is needed to avoid an energy crisis before December (case A) and 16.5 GWmonth to also avoid a power crisis (case B).
In other words, there is an amount of energy in the order of one week of total generation from the SIN to supply the country by the end of November 2021.
Sérgio Cortizo is a physicist and has worked for the federal government with climate change and energy since 2009