1,720,985 research outputs found
Optimal offering of generation, energy storage, and flexible demand participants in electricity markets with block orders
No full textThe ongoing decarbonization of energy systems introduces challenges to the operation of deregulated day-ahead electricity markets, due to the intermittency of renewable energy sources. A main challenge refers to the short-term risk, that market participants are faced with, deriving from the highly uncertain spot prices. Due to this uncertainty, the scheduling of participants becomes cumbersome, especially when their portfolios comprise assets, exhibiting time-coupling and lumpy characteristics. The USA market paradigm inherently addresses this issue, as it prescribes the explicit declaration of participants' operational parameters to the market operator, hence transferring to the latter the responsibility of satisfying participants' operational constraints. However, the European market paradigm, traditionally invited participants to submit strictly economic hourly orders, rendering them responsible for satisfying their operational constraints and ill-equipped to sufficiently express their preferences. In order to allow participants to implicitly convey their operational characteristics to the market, and hedge the price uncertainty risk, European markets have introduced non-convex offering structures, the most prominent of which is block orders (BOs). BOs constitute intertemporal power offers, and are characterized by an all-or-nothing condition, implying that each BO is either accepted or rejected by the market in its entirety. This thesis proposes novel optimal offering models, which enable generation, energy storage, and flexible demand participants, to leverage both eligible offering structures of European markets, i.e., hourly orders and BOs. Moreover, it studies the suitability of different types of BOs towards implicitly encompassing the operational properties of each type of considered participants. Furthermore, it employs the proposed models in large-scale studies considering UK market data, showcasing their relevance and applicability, in that the associated computational cost is not prohibitive towards their employment. Finally, it focuses on both price-taking and strategic participant behaviour, investigating the implications of introducing BOs, on individual participants' welfare and social welfare.Open Acces
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
A two-stage modeling framework for the optimal utilization of load flexibility in energy and reserve markets
Get PDFFacilitating new businesses for retailers to unlock Demand Response (DR) services in electricity markets is key to enabling deep decarbonization. These new businesses will create additional revenue streams for retailers as well as enhance system flexibility. However, it will require retailers to appropriately manage their contracted flexible loads to be able to offer multiple services to the system. Therefore, this work proposes a two-stage modeling framework to determine the optimal operation of a retailer that provides DR services in energy and reserve markets. In the first stage, a data-driven estimation method based on Inverse Optimization (IO) is used to characterize consumer behavior for future operating scenarios. The results are inputted into the second stage, where the model optimizes retailers operations by formulating a bilevel optimization problem between the retailer and the reserve market in which the retailer is also constrained by loads optimization problems. Through several case studies based on the Chilean electricity market, we demonstrate the economic benefits of a multi-service approach by comparing it against the current approach of an actual retailer that only participates in the energy market. Additionally, we also demonstrate the benefits of enabling DR in reserve markets by quantifying reserve cost savings.FONDECYT N°1181928 e ISCI ANID PIA/Apoyo AFB180003Versión original del auto
A scalable cooperative game theoretic framework for coalitional energy management
Get PDFThe advances in distributed energy resources (DER) propelled power networks worldwide to transition from a unidirectional model to a bidirectional one, under which uncertain and intermittent renewable generation cause load balancing issues. Energy storage as flexible resources have the potential to mitigate the stress on the network, and local energy markets emerged in recent years to encourage efficient management of these resources. However, the formulation of a market scheme that incentivizes such operation by offering profit for all the participants remains an unresolved challenge. This thesis proposes the novel application of cooperative game theory to coalitional energy management, which extends existing cooperative theoretic frameworks to the energy storage operation. The proposed scheme is then proven to have a non-empty core, ensuring the existence of a payoff allocation that incentivizes participation in the grand coalition of all participants.
This thesis focuses on two main payoff allocations: the Shapley value and the nucleolus.
The Shapley value is a commonly used payoff allocation in cooperative game theory, but is highly computationally complex. This thesis proposes a novel multi-step sampling method based on optimal stratified sampling for estimating the Shapley value, and demonstrates its effectiveness to improve the scalability of the proposed scheme. It is shown, however, that the Shapley value is not necessarily stabilizing, meaning that given the payoffs based on the Shapley value, some participants may choose to defect from the grand coalition and form smaller coalitions for higher profits.
The nucleolus, albeit a less commonly used payoff allocation in cooperative game theory, is proven to be stabilizing, preventing defection from the grand coalition. Similarly, the computation time of the nucleolus increases exponentially with the number of participants, strictly limiting the size of this scheme. This thesis proposes a new strategy which incorporates clustering techniques to estimate the nucleolus at reduced computation times, where a novel marginal contribution profile is constructed as the clustering features. While maintaining a high estimation accuracy, it is shown to easily scale up the scheme from less than 15 participants to over 100, a well applicable number of load buses in a real distribution feeder
Modelling and analysing the impact of flexible technologies on market-based generation investment planning
Get PDFIn recent times, the value of flexibility potentials available at the demand side in addressing techno-economic challenges associated with the decarbonisation of power systems has attracted notable interest from governments, industry and academia. Notwithstanding these interests, its impacts on long-term power system planning has only been investigated using system cost minimisation models. Such models are inherited from the era of vertically integrated power utilities and cannot represent the profit-oriented decisions of the liberalised electricity industry. Available market-based generation investment planning models in technical literature neglect the time-coupling effects in their operational timescale and for this reason are inherently unable to integrate the operation of non-generating flexible technologies.
This thesis investigates the impacts of demand flexibility on the long-term investment decisions of a self-interested generation company under different market designs. The thesis proposes a novel time-coupling, bi-level optimisation model which accounts for the energy shifting flexibility of the demand side. This model is further enhanced to also incorporate the operation of reserve markets with demand side participation, thereby presenting a jointly cleared energy and reserves market. This model is solved using rigorous mathematical techniques involving the formulation of a Mathematical Program with Equilibrium Constraint (MPEC) problem and the transformation of the MPEC problem to a Mixed Integer Linear Program (MILP) problem.
Different case studies have been carried out to investigate the impact of demand flexibility participating in either only the energy market or in both the energy and reserves market. These case studies demonstrated the similarities in impact of different flexible technologies on the optimal generation investment decisions and enhancing the profit earned by the investing company. The thesis also investigates different scenarios regarding the flexibility of the demand side, market design options and strict carbon targets. The thesis findings show the dependence of the impact of demand flexibility on the optimal investment decisions of the examined generating company on: (i) the market(s) in which demand flexibility participates and (ii) the market design option considered.Open Acces
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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