The ITAIPU dam is a binational hydroelectric project located in the Paraná River basin, on the border between Brazil and Paraguay. Currently, it is responsible for serving about 7% and 85% of the energy demand of these countries, respectively. In this context, Itaipu Binacional has been recognized as a world leader in clean and renewable energy production, having produced approximately 2.85 billion MWh since it began operating in 1984. The plant has an installed capacity of 14 GW with 20 generating units of 700 MW, distributed in two sectors with 10 generating units each, one operating at 50Hz and the other at 60Hz.

In the Paraná River basin, 56 hydroelectric power plants are located upstream of ITAIPU, representing just over half (53%) of Brazil's storage capacity. The Brazilian power system is centrally operated by the National Electric System Operator of Brazil- ONS, which determines the operating policies to be applied to these hydroelectric power plants. The resulting water discharges from these plants will make up the portion of the regularized inflow to ITAIPU, which, added to the flow of the incremental basin, will make up the total inflow to the plant. The Paraguayan power system is operated by the National Electricity Administration of Paraguay- ANDE, responsible for providing electricity services in the country.

ITAIPU's water discharge is coordinated between the plant operators and the system operators of both countries to meet each country's energy needs while meeting constraints associated with the plant's operation. Both the Brazilian and Paraguayan power systems are mainly composed of hydroelectric power plants, which has led to a significant dependence on weather conditions, mainly related to the rainy periods.

In recent years, the amount of rainfall observed in some of the main river basins of these countries has been significantly below the historical average. As a result, the accumulated rainfall deficit over the last 10 years in some basins reaches a higher value than the total precipitation that occurs on average in a year in these regions. As a result, the inflows to power plants in these basins have also remained below the historical average. In the case of ITAIPU, 2021 had the worst inflow series of all time. Thus, the plant's energy production has followed the trend imposed by the atypical below average inflow values, with a gradual decrease in its total discharge, which has reached minimum values in 2021.

The persistent low inflow values gradually led to the worst energy scenario seen in the last 91 years. As a result, ONS needed to adopt exceptional measures to preserve stored resources to ensure the security of Brazil's electric power supply. In Paraguay, the consequences were mostly felt in terms of the navigability of the Paraná River. This paper will present and discuss the key measures adopted by ITAIPU during 2021, which helped the Paraguayan and Brazilian interconnected systems in a scenario of water scarcity, highlighting the productivity record achieved this year.

Keywords: Itaipu Binacional, Hydroelectric plants, reservoir operation, atypical drought conditions, planning and operation of electrical power systems.

Biographies:

R.E. Oviedo-Sanabria was born in Foz do Iguaçu, Brazil, in 1984. He received a B.Sc. degree in Electrical Engineering from the FP - UNE, Ciudad del Este, Paraguay; and finished 2019 the MBA in the Electric Sector of Brazil from the Fundação Getúlio Vargas -FGV. Since 2012, he has been working in the Statistics and Programming Division of the System Operation Department of Itaipu Binacional, Hernandarias, Paraguay.

R.J. de Andrade was born in Curitiba, Brazil, in 1982. He received a B.Sc. Physics degree from Federal University of Paraná, Brazil, 2004; the Electrical Engineering degree from Technological Federal University of Paraná, Brazil, 2007; and finished in 2019 the MBA of the Electric Sector of Brazil from the Fundação Getúlio Vargas - FGV. Since 2013, he has been working in the Statistics and Programming Division of the System Operation Department of Itaipu Binacional, Brazil.

R.A. González-Fernandez was born in Asunción, Paraguay, in 1985. He received the B.Sc. degree from the State University of São Paulo-UNESP, Guaratinguetá, SP, Brazil, in 2007, and the M.Sc. and Ph.D. degrees from the Federal University of Itajubá, UNIFEI, Brazil, in 2009 and 2012, respectively. Since 2012, he has been working in the Statistics and Programming Division of the System Operation Department of Itaipu Binacional, Paraguay. In 2011, he received the IEEE PES Technical Committee (PSACE) Prize Paper Award.