Seasonal, Daily, and Hourly Optimal Reservoir Operations of the Brazilian Hydro–Wind–Solar–Thermal Power System

In the last 12 months, from July 2023 to June 2024, 65.5% of the Brazilian effective electric generation was produced by hydropower, 14.1% by wind power, 9.3% by solar, 9.0% by thermal, and 2.1% by nuclear. Although the interconnected power system remains predominantly hydroelectric, with over 150 large hydropower plants and reservoirs, there has been a significant increase in participation of thermal, wind, and solar power plants in the last 12 years. Before 2012, contributions from wind power and solar generations were insignificant. However, after 2012, the increase in wind and solar becomes significant and the former hydro–thermal power system evolved to the current hydro–wind–solar–thermal power system. The seasonal, daily, and hourly variations in demand as well as the difference in time scale of wind power and solar generations must be balanced by the dispatch of hydropower and thermal plants as well as exchanges between different regions of the country. HIDROTERM is a nonlinear programming optimization model previously developed for planning the operation of the Brazilian hydrothermal system. In this study, we use the HIDROTERM model to compare system operations of 2012 versus 2024 using different hydrological scenarios to study how the recent significant changes in the system affected optimal reservoir operations in different time scales and what new solution methods must be developed to adequately improve the planning of system operation.