The significance of interconnector counter-trading in a security constrained electricity market

Throughout the European Union there is an increasing amount of wind generation being dispatched-down due to the binding of power system operating constraints from high levels of wind generation. This paper examines the impact a system non-synchronous penetration limit has on the dispatch-down of wind and quantifies the significance of interconnector counter-trading to the priority dispatching of wind power. A fully coupled economic dispatch and security constrained unit commitment model of the Single Electricity Market of the Republic of Ireland and Northern Ireland and the British Electricity Trading and Transmission Arrangement was used in this study. The key finding was interconnector counter-trading reduces the impact the system non-synchronous penetration limit has on the dispatch-down of wind. The capability to counter-trade on the interconnectors and an increase in system non-synchronous penetration limit from 50% to 55% reduces the dispatch-down of wind by 311 GW h and decreases total electricity payments to the consumer by €1.72/MW h. In terms of the European Union electricity market integration, the results show the importance of developing individual electricity markets that allow system operators to counter-trade on interconnectors to ensure the priority dispatch of the increasing levels of wind generation.

Evaluation of thermochemical biomass conversion in fluidized bed

Dado o aumento acelerado dos preços dos combustíveis fósseis e as incertezas quanto à sua disponibilidade futura, tem surgido um novo interesse nas tecnologias da biomassa aplicadas à produção de calor, eletricidade ou combustíveis sintéticos. Não obstante, para a conversão termoquímica de uma partícula de biomassa sólida concorrem fenómenos bastante complexos que levam, em primeiro lugar, à secagem do combustível, depois à pirólise e finalmente à combustão ou gasificação propriamente ditas. Uma descrição relativamente incompleta de alguns desses estágios de conversão constitui ainda um obstáculo ao desenvolvimento das tecnologias que importa ultrapassar. Em particular, a presença de elevados conteúdos de matéria volátil na biomassa põe em evidência o interesse prático do estudo da pirólise. A importância da pirólise durante a combustão de biomassa foi evidenciada neste trabalho através de ensaios realizados num reator piloto de leito fluidizado borbulhante. Verificou-se que o processo ocorre em grande parte à superfície do leito com chamas de difusão devido à libertação de voláteis, o que dificulta o controlo da temperatura do reator acima do leito. No caso da gasificação de biomassa a pirólise pode inclusivamente determinar a eficiência química do processo. Isso foi mostrado neste trabalho durante ensaios de gasificação num reator de leito fluidizado de 2MWth, onde um novo método de medição permitiu fechar o balanço de massa ao gasificador e monitorizar o grau de conversão da biomassa. A partir destes resultados tornou-se clara a necessidade de descrever adequadamente a pirólise de biomassa com vista ao projeto e controlo dos processos. Em aplicações de engenharia há particular interesse na estequiometria e propriedades dos principais produtos pirolíticos. Neste trabalho procurou-se responder a esta necessidade, inicialmente através da estruturação de dados bibliográficos sobre rendimentos de carbonizado, líquidos pirolíticos e gases, assim como composições elementares e poderes caloríficos. O resultado traduziu-se num conjunto de parâmetros empíricos de interesse prático que permitiram elucidar o comportamento geral da pirólise de biomassa numa gama ampla de condições operatórias. Para além disso, propôs-se um modelo empírico para a composição dos voláteis que pode ser integrado em modelos compreensivos de reatores desde que os parâmetros usados sejam adequados ao combustível ensaiado. Esta abordagem despoletou um conjunto de ensaios de pirólise com várias biomassas, lenhina e celulose, e temperaturas entre os 600 e 975ºC. Elevadas taxas de aquecimento do combustível foram alcançadas em reatores laboratoriais de leito fluidizado borbulhante e leito fixo, ao passo que um sistema termo-gravimétrico permitiu estudar o efeito de taxas de aquecimento mais baixas. Os resultados mostram que, em condições típicas de processos de combustão e gasificação, a quantidade de voláteis libertada da biomassa é pouco influenciada pela temperatura do reator mas varia bastante entre combustíveis. Uma análise mais aprofundada deste assunto permitiu mostrar que o rendimento de carbonizado está intimamente relacionado com o rácio O/C do combustível original, sendo proposto um modelo simples para descrever esta relação. Embora a quantidade total de voláteis libertada seja estabelecida pela composição da biomassa, a respetiva composição química depende bastante da temperatura do reator. Rendimentos de espécies condensáveis (água e espécies orgânicas), CO2 e hidrocarbonetos leves descrevem um máximo relativamente à temperatura para dar lugar a CO e H2 às temperaturas mais altas. Não obstante, em certas gamas de temperatura, os rendimentos de algumas das principais espécies gasosas (e.g. CO, H2, CH4) estão bem correlacionados entre si, o que permitiu desenvolver modelos empíricos que minimizam o efeito das condições operatórias e, ao mesmo tempo, realçam o efeito do combustível na composição do gás. Em suma, os ensaios de pirólise realizados neste trabalho permitiram constatar que a estequiometria da pirólise de biomassa se relaciona de várias formas com a composição elementar do combustível original o que levanta várias possibilidades para a avaliação e projeto de processos de combustão e gasificação de biomassa.

Enabling solar electricity with electric vehicles in future energy systems

Tese de doutoramento, Sistemas Sustentáveis de Energia, Universidade de Lisboa, Faculdade de Ciências, 2015

Monetary policy, exchange rates and stock prices in the Middle East region

A structural vector autoregressive model is employed to investigate the impact of monetary policy and real exchange rate shocks on the stock market performance of Kuwait, Oman, Saudi Arabia, Egypt and Jordan. In order to identify the structural shocks both short run and long run restrictions are applied. Unlike previous literature the contemporaneous interdependence between the financial variables are left unrestricted to give a more accurate depiction of the relationships. The heterogeneity of the results reflect the different monetary policy frameworks and stock market characteristics of these countries. Mainly, monetary policy and the real exchange rate shocks have a significant short run impact on the stock prices of the countries that apply a relatively more independent monetary policy and flexible exchange rates.

Determination of electricity consumers’ load profiles via weighted evidence accumulation clustering using subsampling

With the electricity market liberalization, the distribution and retail companies are looking for better market strategies based on adequate information upon the consumption patterns of its electricity consumers. A fair insight on the consumers’ behavior will permit the definition of specific contract aspects based on the different consumption patterns. In order to form the different consumers’ classes, and find a set of representative consumption patterns we use electricity consumption data from a utility client’s database and two approaches: Two-step clustering algorithm and the WEACS approach based on evidence accumulation (EAC) for combining partitions in a clustering ensemble. While EAC uses a voting mechanism to produce a co-association matrix based on the pairwise associations obtained from N partitions and where each partition has equal weight in the combination process, the WEACS approach uses subsampling and weights differently the partitions. As a complementary step to the WEACS approach, we combine the partitions obtained in the WEACS approach with the ALL clustering ensemble construction method and we use the Ward Link algorithm to obtain the final data partition. The characterization of the obtained consumers’ clusters was performed using the C5.0 classification algorithm. Experiment results showed that the WEACS approach leads to better results than many other clustering approaches.

A congestion management and transmission price simulator for competitive electricity markets

In a liberalized electricity market, the Transmission System Operator (TSO) plays a crucial role in power system operation. Among many other tasks, TSO detects congestion situations and allocates the payments of electricity transmission. This paper presents a software tool for congestion management and transmission price determination in electricity markets. The congestion management is based on a reformulated Optimal Power Flow (OPF), whose main goal is to obtain a feasible solution for the re-dispatch minimizing the changes in the dispatch proposed by the market operator. The transmission price computation considers the physical impact caused by the market agents in the transmission network. The final tariff includes existing system costs and also costs due to the initial congestion situation and losses costs. The paper includes a case study for the IEEE 30 bus power system.

Data mining contributions to characterize MV consumers and to improve the suppliers-consumers settlements

This paper deals with the establishment of a characterization methodology of electric power profiles of medium voltage (MV) consumers. The characterization is supported on the data base knowledge discovery process (KDD). Data Mining techniques are used with the purpose of obtaining typical load profiles of MV customers and specific knowledge of their customers’ consumption habits. In order to form the different customers’ classes and to find a set of representative consumption patterns, a hierarchical clustering algorithm and a clustering ensemble combination approach (WEACS) are used. Taking into account the typical consumption profile of the class to which the customers belong, new tariff options were defined and new energy coefficients prices were proposed. Finally, and with the results obtained, the consequences that these will have in the interaction between customer and electric power suppliers are analyzed.

VPPs information needs for effective operation in competitive electricity markets

The large increase of renewable energy sources and Distributed Generation (DG) of electricity gives place to the Virtual Power Producer (VPP) concept. VPPs may turn electricity generation by renewable sources valuable in electricity markets. Information availability and adequate decision-support tools are crucial for achieving VPPs’ goals. This involves information concerning associated producers and market operation. This paper presents ViProd, a simulation tool that allows simulating VPPs operation, focusing mainly in the information requirements for adequate decision making.

Intelligent decision making in electricity markets: simulated annealing Q-Learning

Electricity markets are complex environments, involving a large number of different entities, playing in a dynamic scene to obtain the best advantages and profits. MASCEM is a multi-agent electricity market simulator to model market players and simulate their operation in the market. Market players are entities with specific characteristics and objectives, making their decisions and interacting with other players. MASCEM is integrated with ALBidS, a system that provides several dynamic strategies for agents’ behavior. This paper presents a method that aims at enhancing ALBidS competence in endowing market players with adequate strategic bidding capabilities, allowing them to obtain the higher possible gains out of the market. This method uses a reinforcement learning algorithm to learn from experience how to choose the best from a set of possible actions. These actions are defined accordingly to the most probable points of bidding success. With the purpose of accelerating the convergence process, a simulated annealing based algorithm is included.

Balancing market integration in MASCEM electricity market simulator

With the restructuring of the energy sector in industrialized countries there is an increased complexity in market players’ interactions along with emerging problems and new issues to be addressed. Decision support tools that facilitate the study and understanding of these markets are extremely useful to provide players with competitive advantage. In this context arises MASCEM, a multi-agent simulator for competitive electricity markets. It is essential to reinforce MASCEM with the ability to recreate electricity markets reality in the fullest possible extent, making it able to simulate as many types of markets models and players as possible. This paper presents the development of the Balancing Market in MASCEM. A key module to the study of competitive electricity markets, as it has well defined and distinct characteristics previously implemented.

Study of distribution network demand response events in the Portuguese system

In competitive electricity markets with deep concerns for the efficiency level, demand response programs gain considerable significance. As demand response levels have decreased after the introduction of competition in the power industry, new approaches are required to take full advantage of demand response opportunities. Grid operators and utilities are taking new initiatives, recognizing the value of demand response for grid reliability and for the enhancement of organized spot markets’ efficiency. This paper proposes a methodology for the selection of the consumers that participate in an event, which is the responsibility of the Portuguese transmission network operator. The proposed method is intended to be applied in the interruptibility service implemented in Portugal, in convergence with Spain, in the context of the Iberian electricity market. This method is based on the calculation of locational marginal prices (LMP) which are used to support the decision concerning the consumers to be schedule for participation. The proposed method has been computationally implemented and its application is illustrated in this paper using a 937 bus distribution network with more than 20,000 consumers.