Search

Severe droughts, water-use conflicts, and minimum outflow requirements have caused infeasibilities in modeling large-scale complex hydrothermal systems. This paper presents and discusses a new formulation of objective function and constraints to better represent multiple water uses and deal with infeasibilities in the HIDROTERM model, a nonlinear programming (NLP) model developed to optimize the operation of the Brazilian interconnected hydrothermal system. The system is one of the largest in the world. In the last 10 years, approximately 72% of electricity consumed in Brazil has been supplied by hydropower plants, but with increasing shares from thermal, wind, and, more recently, solar power generation. Because of hydrological changes in recent years and the additional operational constraints imposed by environmental agencies, the use of models for decision making, such as HIDROTERM, frequently encounters the problem of infeasibility. To avoid this problem, a new objective function is proposed in HIDROTERM that incorporates economic penalties when the preset requirements are not met. Based on economic considerations, some hard constraints are removed from the constraint set and added to the objective function as penalty terms. These constraints are tightly linked with multiple water uses, including environmental protection, flood control, consumptive uses, and navigation purposes. The proposed change in the objective function and constraints avoids the problem of infeasibilities and makes it possible to apply the model to extreme conditions. Additionally, this formulation helps identify and minimize the risk, duration, and intensity of unavoidable non-compliance occurrences related to multiple water uses. The presented new version of the HIDROTERM model can be used to study and support decision making in the management and operation of large-scale hydrothermal systems. These systems can be formed by a set of hydraulically connected individual hydropower plants and reservoirs, located within a set of electrically connected subsystems. Each subsystem contains demands and other power plants, including thermal, wind, nuclear, and solar plants, and exchanges. The model has been developed with continued improvements since 2008 and applied to large systems such as the Brazilian Interconnected Power System (BIPS) with over 150 reservoirs. A graphical user interface is provided. The objective function is to minimize the total costs of additional thermal dispatch and exchanges, as well as avoid or minimize deficits in energy supply in subsystems, minimum releases, consumptive uses, and minimum storages in reservoirs. The decision variables are the power and nonpower releases for each hydropower plant and the thermal dispatches and exchanges for each subsystem. Some typical applications include (1) monthly planning operation of the system, considering a planning horizon from 3 to 5 years; (2) diagnostic studies about reliability and resilience of existing systems, processing the same system configuration to a set of different hydrological or energy demand scenarios; (3) impact analysis of changes in operational rules and constraints related to multiple uses of water; and (4) planning and evaluation of expansion alternatives. The model can be applied to a complete hydrothermal system or subsets of it, including subsystems, basins, cascades, or a single hydropower plant. [ABSTRACT FROM AUTHOR]

The power system long-term expansion planning is a computer-intensive problem as demands a varied set of studies especially considering the increasing deployment of intermittent renewables. In the case of the Brazilian power sector planning, the responsible institutions mostly use proprietary software. This paper presents the multiyear two-stage academic generation and transmission expansion planning software, called CARTHER, developed by the authors in order to provide the academy an open-source and non-commercial software, with a friendly interface and with several applications for expansion planning of hydrothermal systems with high intermittent renewables penetration. CARTHER is then calibrated for a case study in the Brazilian power sector, considering the most recent governmental goals for renewable energies for the horizons of 2030, 2040, 2050 and 2060. The results demonstrate the functionality and the qualitative capacity of CARTHER optimization under the expansion's criteria of flexibility and reliability in the face of the intermittent renewables penetration. [ABSTRACT FROM AUTHOR]

This work presents the evolution of the main interarea modes of the Brazilian Interconnected Power System (BIPS) in the 2020–2024 horizon with high levels of wind and solar generation in the Northeast region of Brazil. The software PacDyn is chosen for the simulations using the Dominant Pole Spectrum Eigensolver algorithm to help identify the modes of interest. Besides that, the impacts of the expansion of BIPS's interconnections on the interarea modes are studied. The results showed that the main interarea modes of the BIPS are sufficiently damped. [ABSTRACT FROM AUTHOR]

Brazil is a case of the achievement of a high share of wind energy integration to an interconnected power system in an emerging market. A series of successful energy supply programmes and a strong renewable-oriented finance framework implemented since 2002, have promoted alternative renewables – wind installed capacity increased over 22-fold from 927 MW in 2011 to 21 GW in 2022, reaching 11.77% of total procured power. From this, about 90% are concentrated in Brazil's least developed region, the Northeast, where wind investment should create jobs and propel socioeconomic development. Despite that, there is no studies specific assessing the regional and economy-wide effects of those programmes, gap that this paper aims to fill by applying the regional Computable General Equilibrium (CGE) model TERM-BR10. We assess that by modelling an alternative scenario for the period 2010-19 based on an official electricity matrix built in 2010, that projected 3.4 additional GW of wind power while not considering all the success of renewable policies, against the observed installed capacity expansion, where wind power was 3.7 times higher than what had been planned. Our results show that in the absence of renewable policies, Brazil would have faced economic losses such as GDP (−0.27%) and investment (−4.76%). The Northeast region would have been the most impacted in terms of GDP (−1.3%), real wage (−2.99%) and employment creation (−0.1%). We propose that such socioeconomic co-benefits are incorporated in energy planning, which could promote regional equality through renewable energy expansion. • Wind power capacity increased over 20-fold from 2011 to 2022. • 90% are in the poorest region where policies propel development and job creation. • Policy absence would entail a GDP loss of 0.27% nationally and of 1.3% in the region. • Negative impacts to labour market are mostly over skilled jobs. [ABSTRACT FROM AUTHOR]

Brazil's electricity market is the largest in Latin America and the ninth largest in the world. It has been implemented as a mixed market in which regulated and deregulated contracting environments coexist. The volume of transactions in the deregulated market has experienced steep growth over the last few years and is expected to surpass the regulated market. Different programs to diversify the country's energy matrix have been devised, especially by integrating intermittent renewable sources to address the deregulated market expansion. Consequently, such an energy policy path has prompted the need to increase the granularity of the Brazilian deregulated market's spot price, namely the Difference Settlement Price (DSP). The DSP had been weekly defined accounting for three loading levels and four submarkets, and, as of 2021, it has been hourly defined accounting for four submarkets; the weekly DSP is inefficient in actually signaling prices based on ex-ante marginal cost of operation of the interconnected Brazilian power system. Besides such granularity alteration, Brazil has also undergone a severe hydrological crisis in 2021 that led to significantly lower water inflows into major hydrographic watersheds and, as a result, most hydroelectric power plant reservoirs hit a 91-year low. The described scenario is relevant in utility policies and energy economics since it depicts a significant paradigm shift experience in such a large electricity market. This study presents the first hourly DSP behavior analysis since its implementation in the Brazilian electricity market and explores its statistical characteristics and relationships with exogenous variables throughout 2021. Additionally, we discuss the hourly DSP's volatility observed in the year 2021 and how it has resulted in price spikes. At last, we compare the behavior of the Brazilian hourly DSP with the energy prices of five other countries' electricity markets. Despite being a significant market improvement, the DSP granularity increase per se could not accurately represent the actual marginal cost of operation over the year 2021 since, besides instabilities observed in the hourly DSP, market intervention mechanisms had to be applied by Brazilian regulatory agencies to minimize the hydrological crisis' impacts. • A new format for the electricity price publication has been implemented in the Brazilian deregulated market in 2021. • Brazil in 2021 has faced its worst hydrological crisis in 91 years. • Regime switch Markov analysis was able to characterize the moment of the hydrological crisis in the electricity price. • Specific patterns in the reserve margin and availability of generation source behaviors preceded the price spikes. • The set of variables influencing the electricity price may be more diverse and broad than the ones regarding only the power system operation conditions. [ABSTRACT FROM AUTHOR]

• A new Angle Difference Controller to adapt the power order of embedded HVDC links. • Simulations with the proposed ADC in the official Brazilian Power System model. • Performance comparison of the ADC implemented in LCC HVDC link and VSC HVDC link. • A tutorial example to make it clear the appearance of loop flows in AC-DC systems. This paper discusses the power flow control of embedded HVDC links in the Brazilian grid, with special attention to the requirements of intermittent energy sources where frequent load changes are needed, including power reversal, and automated action is called for. Recently two North-South bipoles, 4000 MW each, ±800 kV, have entered into service, these being embedded in the grid and with separate receiving end converter stations. In this case "reverse" power flow is foreseen, but only on a seasonal basis when water flow is low at the North region. The increasing capacity in wind and solar energy, especially in the Northeast region and the possibility of a new embedded HVDC link to carry the surplus power from this region, call for an adaptable power setpoint in the DC links in order to avoid adverse effects as loop flows and increased losses. The paper investigates the use of angle difference control and proposes a new controller to mitigate those adverse effects. [ABSTRACT FROM AUTHOR]

Abstract: This study is intended to attain preliminary estimates on the potential for carbon credits for Small hydropower (SHP) projects in the Brazilian overview, which was divided into two phases. In Phase I, a comparative analysis was conducted of accumulated CO2 emission values by the expansion of gross annual sources of coal and the accumulated CO2 emission values from the expansion of the gross annual installed capacity of SHP for two scenarios, Scenario 1 and Scenario 2. The results demonstrated the advantages of using SHP as an energy source, with regards to greenhouse gases (GHG) emissions, despite the uncertainty of the values of GHG emission factors. Phase II presents a case study based on data from a real time series for a station located in southern Minas Gerais State with an arbitrary value for the design head of the venture. The calculation of Permanency Power, Energy Curve, and values of Optimum Hydraulic Power Available (MW) and Optimum Flow Available (m3/s) was made possible by the Microsoft ® Excel ® spreadsheet from CERPCH . The calculation of net income derived from carbon credit for SHP projects was done through the Microsoft ® Excel ® spreadsheet from Michellis Junior , based on the CDM guidelines as recommended in the UN Convention on Climate Change, Ministry of Science and Technology. The results showed that the net revenues obtained for carbon credits in SHP projects located in the Isolated System were well above those obtained in the National Interconnected System. [Copyright &y& Elsevier]

We consider the inclusion of commitment of thermal generation units in the optimal management of the Brazilian power system. By means of Lagrangian relaxation we decompose the problem and obtain a nondifferentiable dual function that is separable. We solve the dual problem with a bundle method. Our purpose is twofold: first, bundle methods are the methods of choice in nonsmooth optimization when it comes to solve large-scale problems with high precision. Second, they give good starting points for recovering primal solutions. We use an inexact augmented Lagrangian technique to find a near-optimal primal feasible solution. We assess our approach with numerical results. [ABSTRACT FROM AUTHOR]