Security of power supply in hydrothermal systems: Assessing minimum storage requisites for hydroelectric plants

Abstract

Unfavorable hydrological conditions experienced from 2014 to 2019 led to the depletion of main reservoir systems in Brazil, causing an increase of thermal energy dispatch. However, an important share of the observed thermal generation was out of economic merit, commanded by government entities which risk perception relies mainly on experts’ tacit knowledge. Despite the common sense that storage in reservoirs is intrinsically linked to system security, the metrics employed so far failed to compute the system’s real needs in terms of required stored energy in hydroelectric plants. This work proposes a new method to evaluate the security of power supply in systems with predominance of hydroelectricity, by the development of an optimization model that assesses the minimum secure levels for hydroelectric plants operation in each month, from a nonlinear-backward simulation of 88 historical streamflow series (1931–2018). In addition, based on the simulation results, two reference curves were suggested for the continuous monitoring of the reservoirs operation, with the purpose of subsidizing Brazilian government entities decisions on unorthodox thermal generation dispatch. The monitoring of the proposed reference curves is expected to represent a more robust criterion for decisions on out-of-merit thermal generation in Brazilian power system.