Mario T. L. Barros

Optimization of Large-Scale Hydrothermal System Operation

This paper presents the development of a mathematical model to optimize the management and operation of the Brazilian hydrothermal system. The system consists of a large set of individual hydropower plants and a set of aggregated thermal plants. The energy generated in the system is interconnected by a transmission network so it can be transmitted to centers of consumption throughout the country. The optimization model offered is capable of handling different types of constraints, such as interbasin water transfers, water supply for various purposes, and environmental requirements. Its overall objective is to produce energy to meet the country’s demand at a minimum cost. Called HIDROTERM, the model integrates a database with basic hydrological and technical information to run the optimization model, and provides an interface to manage the input and output data. The optimization model uses the General Algebraic Modeling System (GAMS) package and can invoke different linear as well as nonlinear programming ...

Trade-Off Analysis among Multiple Water Uses in a Hydropower System: Case of São Francisco River Basin, Brazil

AbstractThis paper evaluates the impacts of multiple water uses on the operation of a system of existing reservoirs that originally were designed for hydropower generation. The research reported in this paper utilizes a nonlinear optimization model, developed to optimize hydropower production for a system of interconnected reservoirs. This model was modified to include water withdrawals for consumptive uses. The formulated multiobjective optimization problem is solved by employing the weighting method. The formulation considers water allocation policy for consumptive uses and individual hydropower plants. By parametrically varying the weighting coefficients, the tradeoff relationship (Pareto front) between hydropower generation and water demand for consumptive uses was traced out. The modified model is applied to the Sao Francisco River Basin in Brazil, where there are several hydropower plants in operation with a total installed capacity of 10.7 GW. The river basin is an important agricultural land that ...

Planning and Operation of Large-Scale Water Distribution System with Hedging Rules

One of the most critical problems that all megacities (cities with more than 10 million people) face today is the shortage of water supply. Finding a solution to this problem presents a great challenge to hydrologists, urban planners and environmentalists. This paper describes the development of an optimization model for planning and operation of a large-scale water supply distribution system. An important characteristic of the model is that it considers the hedging rules during a dry period when water supply is insufficient to meet the planned demand and water shortage occurs. The water distribution system is formulated as a network flow model in terms of nodes and links and solved by the GAMS language, which has access to several linear and nonlinear algorithms. A user friendly interface is developed to facilitate the manipulation of a large amount of data and to generate graphs and tables for analysis for decision makers. The developed methodology has been implemented for the Sao Paulo Metropolitan Area Water Distribution System that supplies water to 18 million people. Some preliminary results obtained show good performance of the model.

Brazilian Hydrothermal System Operation: Interconnected Large System or Isolated Subsystems?

Hydrothermal systems are formed by hydropower plants and different types of thermal power plants, i.e., plants that use different types of fuel. Thermal power plants are very versatile to meet energy demand; therefore, they can be dispatched at any time, with the exception of certain plants, such as nuclear, that are operated on a demand basis. Hydropower plants are also versatile, but exhibit a serious operational constraint, which is water availability. It is clear, therefore, the importance of planning the operation, especially in large hydrothermal systems. In countries where a high percentage of the energy consumed is produced by hydropower, there is a need to determine the degree of connection of the hydro system to increase its effectiveness and efficiency. A large interconnected hydro system can be better managed considering the hydrological diversity occurring in different watersheds. On the other hand, isolated subsystems of smaller sizes, may possibly be able to operate with greater safety. This paper discusses the issue of the energy gain of a hydrothermal system in view of its size. The case study is the national interconnected hydrothermal system in Brazil. The analysis employs an optimization model, HIDROTERM, which has been developed for the optimal planning and operation of the Brazilian hydrothermal system. A comparative analysis is made comparing the Brazilian system operated in a fully interconnected scheme and with some isolated subsystems operating independently. The results can be used to determine the optimal configuration of the hydrothermal system.

The São Francisco River Water Transfer System: An Optimization Model for Planning Operation

Brazil’s poorest region, located in the country’s northeast, suffers mainly because of its dry climate and limited water resources. The demand for water and irrigation is very high, and shifts in Brazilian water resources policy can minimize drought social impacts. The most important source of water supply is the Sao Francisco river basin. Many years ago a water transfer system was designed in order to address the planned irrigation demand in the dry area. At that time the main conflict was between irrigation demand and the hydroelectrical impacts on the Sao Francisco hydropower system. The project changed its basic objectives and today the main water uses are irrigation and water supply in many cities located in the dry areas. Today the quantity of water planned to be transferred from the Sao Francisco river to the semi-arid area of the northeast region known as the “Drought Polygon” is small compared to the originally proposed amount, so the impacts on hydropower production are minimized. Despite this the project is still very controversial due mainly to its negative environmental impacts related to water quality in the Sao Francisco river. In order to minimize these impacts it is necessary to develop a highly efficient model to plan the operation of the system. The SISAGUA model developed by Barros et al. (2005) is a very convenient tool to accomplish this goal. This paper presents the application of SISAGUA to the optimal operation of the Sao Francisco river water transfer system and some very interesting results related to environmental impacts.

SolverSIN: A Practical Model for Large Hydrothermal System Analysis

Almost 90% of the electrical energy in Brazil is produced by hydropower plants, but in order to cover national demand and to ensure production during dry periods the system operates in conjunction with a set of thermal power plants. The Brazilian hydrothermal system is completely linked together and the main purpose of operation is to minimize the cost of energy production considering a long term horizon, generally five years. Therefore the complexity of the planning operation involves a large set of variables and many decisions have to be made in order to ensure maximum efficiency. Today the Brazilian National System Operator (ONS) runs a set of models to define the dispatch and the marginal cost of the energy in different parts of the country in a weekly time step. These models are very complex and are not practical to support basic information for the electrical agents in a short time. For this reason a very practical Decision Support System called SolverSIN was developed. This paper describes the SolverSIN model and shows its performance in dealing with a very complex hydrothermal systems analysis. The model was prepared to run with the Brazilian system considering its equivalent energy reservoirs scheme but its methodology can be adapted for any system. The main variables of the planning operation are estimated in a very short time and different situations can be explored to conduct sensitivity analysis of the main ones. Another important SolverSIN characteristic is its applicability to run different hydrological scenarios in order to evaluate the impacts on dispatches and energy costs. This is very important considering that the greater the safe thermal energy production of the system, the lower the electrical costs and the greater the protection to the environment due to minimization of oil consumption.

A Stochastic Hydrothermal Decision Support System for Planning Operation: New Developments for the HIDROTERM Model

The Brazilian hydrothermal system consists of a completely linked network of 143 medium and large hydropower plants, 888 small hydropower plants, and 1602 thermal and 82 wind power plants, with a total installed capacity of 128,570 MW. The hydropower plants produce, on average, 91% of the total electricity consumed in the country, while the complementary thermal system is dispatched mainly during periods of drought. In our previous studies, we developed a nonlinear programming model, HIDROTERM, to optimize the management and operation of the hydrothermal system, considering individual hydropower plants, thermal generation and exchange, multiple uses of the water, and system expansion. The model is deterministic. In this paper, we develop a new version of HIDROTERM to incorporate the stochasticity of the inflows in the formulation. Additionally, hourly load variation is represented by three levels: peak, base, and low. The proposed approach is based on a two-stage stochastic programming with recourse. In the first stage (first time period) the system passes from its initial state to the final state based on deterministic inflow forecasts. From the second time period on (the second stage), the state of the system branches out according to inflow scenarios. The branching can be scaled up gradually until the end of the planning horizon. New developments are made in the formulation, interface, database and the underlying simulation model. The newly developed integrated decision support system is being tested on the entire Brazilian hydrothermal system. 1 Assistant Professor, University of Sao Paulo; e-mail: rczambon@usp.br; ASCE/EWRI Member 2 Professor, University of Sao Paulo, Brazil; e-mail: mtbarros@usp.br; ASCE Member 3 Professor, University of Campinas; e-mail: franco@fec.unicamp.br 4 Assistant Professor, University of Campinas; e-mail: francato@fec.unicamp.br 5 Consulting Engineer; e-mail: jelopes1@gmail.com 6 Engineer, Companhia Energetica de Sao Paulo; e-mail: luis.nogueira@cesp.com.br 7 Distinguished Professor, UCLA; e-mail: williamy@seas.ucla.edu; ASCE Honorary Member 1563 World Environmental and Water Resources Congress 2013: Showcasing the Future

Water Conflicts in Hydrothermal System Operation: The São Francisco River, Brazil

There are many conflicts involved in the operation of a hydrothermal system mainly due to competitive uses of water. That is the case of Sao Francisco River located in the northeast region in Brazil. The hydro system in this region has an installed capacity of 10.7 GW and supports 13% of the Brazilian hydro electrical power. Due to the scarcity of water in this region the operation of this system has been questioned in the last few years. The competitive uses of water in this region are water supply, irrigation, animal raising and environmental protection. These demands can be attended by a proposed large water transfer system from Sao Francisco river to other watersheds in the region. The electrical sector is planning to review the reservoir operation rules in order to attend these demands. This paper presents results from a study conducted to evaluate the impacts of the hydro production caused by the multipurpose uses of water in the Sao Francisco River. The study was conducted by applying the HIDROTERM model, which is an optimization model that maximizes hydropower production and minimizes thermo production based on fossil fuels. A new objective function was added to the HIDROTERM model in order to evaluate the proposed water transfer system. The trade-offs among energy, water supply, irrigation and environment protection are presented, along with other relevant discussions.

Metrics and Risk Criteria Acceptance for Flood Control in Valleys Downstream Hydropower Plants

Given the importance of controlling floods in valleys and their impacts on the operation planning of hydropower plants, this research work aims at developing a contribution for finding a systematic metrics and risk criteria acceptance. It is assumed that each hydropower plant has a maximum flow constraint at downstream valley, thus requiring protection through operational procedures of the spillway and turbines. The decision about which risk level is acceptable for protection against flooding in the corresponding valleys should consider the nature, the complexity for control and the magnitude of the consequences of flooding. In general terms, high impacts will require low acceptable risk levels and, high complexity for flood control operation will require low acceptable risk levels. In order to describe the magnitude of consequences under flooding beyond the threshold level (maximum flow constraint), six severity descriptors were defined based on social impacts, possible fatalities, economic damages, operational damages, environmental damages and reputation losses to the image of the generation company. The severity descriptors are measured by using qualitative scales (low, moderate, high, catastrophic) with detailed instructions about the situations that leads to each position in the several scale levels. Similarly, five complexity operational flood control descriptors are also defined, with the corresponding qualitative scales. The proposed methodology is applied on a system of hydropower plants of the power generation company Companhia Energetica de Sao Paulo (CESP). This case study was developed with the collaboration of the technical staff of CESP, including professionals of different branches of the company. The results exhibits consistency, thus revealing the proposed methodology as an useful tool for supporting decision about risk criteria acceptance.