Rafael de Sa Ferreira

Time-of-Use Tariff Design Under Uncertainty in Price-Elasticities of Electricity Demand: A Stochastic Optimization Approach

Time-of-use (ToU) electricity tariffs are currently employed or considered for implementation in many jurisdictions around the world. In ToU modalities, a set of different tariffs for different hours of the day and/or seasons of the year is defined at the beginning of a given horizon, and then kept constant until its end. While designing ToU tariffs, one of the most significant sources of uncertainty to be considered relates to price-elasticities of demand. We propose an approach for ToU tariff design based in quadratically constrained quadratic programming and stochastic optimization techniques, addressing these uncertainties and dealing with various aspects of tariff design from the point of view of the regulator/regulated utility.

A Flexible Mixed-Integer Linear Programming Approach to the AC Optimal Power Flow in Distribution Systems

In this paper, we propose a flexible mixed-integer linear programming formulation of the AC OPF problem for distribution systems, using convexification and linearization techniques. The proposed formulation allows the representation of discrete decisions via integer decision variables, captures the nonlinear behavior of the electrical network via approximations of controllable accuracy, and can be solved to global optimality with commercial optimization solvers. The formulation is based on conventional variables that describe network behavior, which ensures its flexibility and the possibility of application to various distribution system problems, as we indicate with case studies.

Time-of-use tariffs in Brazil: Design and implementation issues

In late 2011, the Brazilian Electricity Regulatory Agency approved a new tariff structure for distribution services. This included the creation of the White Tariff, a time-of-use (Toll) tariff modality for retail consumers connected to low-voltage distribution grids. Brazil is currently conducting an ambitions smart meter roll-out plan, and consumers will be able to opt for Toll tariffs in the coming years. In preparation for that, the regulator has started the definition of the economic signals embedded in Toll tariffs for several distribution utilities, at the occasion of their multi-annual Tariff Review processes. This has been done despite of the fact that virtually no country-specific data on demand response to electricity prices is currently available, which brings additional difficulties to the process. In this paper, we discuss the design and implementation of Toll tariffs in Brazil, highlighting lessons learned so far and coming challenges, from an economic and regulatory perspective.

Energy tariff and demand response in Brazil: An analysis of recent proposals from the regulator

The development of the smart grid has received growing attention from various institutions of the Brazilian electricity sector since 2009. Recent Public Hearings held by the Brazilian Electricity Regulatory Agency (ANEEL) aimed at presenting proposals for smart grid related regulation, and gathering contributions of different stakeholders regarding the issues discussed. The objective of this paper is to analyze some of the topics discussed in Public Hearing #120/2010, in which ANEEL proposed mechanisms to incorporate economic signals to the energy tariffs of regulated consumers supplied by distribution companies. These measures may be interpreted as efforts to begin the gradual advance of smart grid enabled demand response programs. As will be discussed in the paper, special attention should be given to the conciliation between the proposed measures and the particularities of the Brazilian electricity sector regulation, in order to implement such proposals in a smooth way.

Transmission expansion in fast growing economies and the challenges of renewables integration

Transmission expansion in fast growing economies imposes severe challenges to electricity markets, given the need for planning and executing major midterm investments in an environment of uncertainty in load growth and generation expansion, coupled to the arrival of distributed renewable energy resources. This paper describes the approaches of two countries, Brazil and Chile, to tackle the challenges of transmission expansion, focusing on treatment of uncertainties, schemes for implementing expansion plans, and problems currently faced by different stakeholders. Renewable energy projects have experienced a significant development in the two countries, despite of difficulties faced by project developers with regard to financing, contracting, and, particularly, grid connection. We discuss solutions adopted or currently under consideration for the integration of renewables to the transmission system.

Distribution network reconfiguration under modeling of AC optimal power flow equations: A mixed-integer programming approach

One of the most common applications of the AC optimal power flow (ACOPF) in distribution systems is the network reconfiguration problem, which consists of altering the topology of the network in order to optimize a given objective function - usually, minimizing ohmic losses. We propose a mixed-integer linear programming reformulation of the network reconfiguration problem for distribution systems, under full modeling of the ACOPF equations. The proposed formulation captures the non-linear behavior of the electrical network via approximations of arbitrary accuracy, allows the representation of discrete decisions via integer decision variables, and can be solved to global optimality with commercially available optimization solvers. The applicability of the proposed formulation is indicated with help of case studies.

Flexible Connections: Solutions and Challenges for the Integration of Renewables in South America

Feed-in tariffs, quota systems, and auction schemes are all used to stimulate NCRE growth in South America. These methods present common challenges in terms of development, operation, and transmission. Common solutions to these challenges are being developed, and Brazil is leading the way with its rapid incorporation of NCRE. The existing market, commercial, and regulatory frameworks may present barriers to the timely and cost-effective connection of renewable generation, as they may not be flexible and agile enough to allow for the connection of smaller, dispersed generators with short construction times. This has led to the revision of network tariff arrangements, including the review of network operating and design practices, security standards, access regimes, investment incentives, cost recovery, and rates. The experiences presented in this article illustrate some of the key initiatives and solutions being proposed to address the challenge of unlocking the doorway for renewables. Further concerns need to be addressed, however, with a broader vision that seeks convergence to an efficient, 21st-century, low-carbon energy system through more cooperative development of renewables and the required transmission assets.

The Expansion of Transmission: The Challenges Faced in South America

Transmission system expansion boomed in several South American countries in the 2000s and the early 2010s. Network capacity additions were required to cope with fast-growing electricity demand, prompted by average gross domestic product growth rates of around 5% per year in 2003?2008 and 3% per year in 2008-2013. Following a trend verified in most infrastructure segments, private sector participation in transmission investments increased significantly in the period, which was the result of reforms in the electricity industry that had initiated in the 1990s.

Facilitating the Integration of Renewables in Latin America: The Role of Hydropower Generation and Other Energy Storage Technologies

It is well known that storage facilities can provide value to various electricity sectors through several services, which we group into five main classes.

A non-linear programming approach to maintenance budgeting for multi-component systems

Maintenance budgeting refers to optimally allocating monetary resources so as to minimize the sum of (deterministic) preventive maintenance and (stochastic) corrective maintenance and unavailability costs. We propose a non-linear programming formulation for this problem, for a complex, multi-component system. Results of a case study for a combined cycle thermal power plant indicate the applicability of the proposed approach.