Virtual power plant models and electricity markets - A review

In recent years, the integration of distributed generation in power systems has been accompanied by new facility operations strategies. Thus, it has become increasingly important to enhance management capabilities regarding the aggregation of distributed electricity production and demand through different types of virtual power plants (VPPs). It is also important to exploit their ability to participate in electricity markets to maximize operating profits. This review article focuses on the classification and in-depth analysis of recent studies that propose VPP models including interactions with different types of energy markets. This classification is formulated according to the most important aspects to be considered for these VPPs. These include the formulation of the model, techniques for solving mathematical problems, participation in different types of markets, and the applicability of the proposed models to real case studies. From the analysis of the studies, it is concluded that the most recent models tend to be more complete and realistic in addition to featuring greater diversity in the types of electricity markets in which VPPs participate. The aim of this review is to identify the most profitable VPP scheme to be applied in each regulatory environment. It also highlights the challenges remaining in this field of study

Optimal short-term water-energy dispatch for pumping stations with grid-connected photovoltaic self-generation

Increases in the energy costs of irrigation water pumping facilities puts the economic sustainability of recent investments in the modernization of farms at risk. To address this problem, it is essential to apply renewable technologies for the production of electricity, and photovoltaic energy is particularly attractive due to its lower cost and recent technological advances. The aim of this research is to develop a mathematical techno-economic dispatch model that optimizes the hourly schedule of pumping equipment subject to electrical and hydraulic constraints to minimize the weekly operating costs of a real pumping station. The resulting model is formulated as a mixed-integer nonlinear programming problem that determines the optimal hourly combination of pumping equipment and available resources to meet water and energy needs. The proposed model comprises fixed and variable speed pumps, a grid-connected photovoltaic plant, and two water ponds for internal regulation and storage. The results verify that the combination of self-consumption photovoltaic facilities and variable speed drives make it possible to maximize the percentage of self-consumed energy up to 99.41% during the month with the highest demand for water. In this case, the pumping station reduces its energy costs by 21.56%, in addition to improving water management

Water-energy management for demand charges and energy cost optimization of a pumping stations system under a renewable virtual power plant model

The effects of climate change seriously affect agriculture at different latitudes of the planet because periods of drought are intensifying and the availability of water for agricultural irrigation is reducing. In addition, the energy cost associated with pumping water has increased notably in recent years due to, among other reasons, the maximum demand charges that are applied annually according to the contracted demand in each facility. Therefore, very efficient management of both water resources and energy resources is required. This article proposes the integration of water-energy management in a virtual power plant (VPP) model for the optimization of energy costs and maximum demand charges. For the development of the model, a problem related to the optimal operation of electricity generation and demand resources arises, which is formulated as a nonlinear mixed-integer programming model (MINLP). The objective is to maximize the annual operating profit of the VPP. It is worth mentioning that the model is applied to a large irrigation system using real data on consumption and power generation, exclusively renewable. In addition, different scenarios are analyzed to evaluate the variability of the operating profit of the VPP with and without intraday demand management as well as the influence of the wholesale electricity market price on the model. In view of the results obtained, the model that integrates the management of the water-energy binomial increases the self-consumption of renewable energy and saves electricity supply costs

Comparative assessment of different solar tracking systems in the optimal management of PV-operated pumping stations

The integration of photovoltaic energy in pumping systems is complex, and the technical constraints of hydraulic and pumping systems must be considered. Exploitation models that link energy management with water management are necessary to ensure the profitability of these investments. This research proposes the design and application of a mathematical model for optimal hourly operation of pumping equipment at the minimum cost for a pumping station with different configurations of self-consumption photovoltaic generation for one week, subsequently extended to an entire year. The proposed optimization problem is formulated as a mixed-integer nonlinear model. Findings of this paper indicate that a self-consumption photovoltaic plant with single-axis solar tracking can increase production by 33.4% and reduce operating costs by 28.9% compared to a fixed system. Therefore, more energy is self-consumed (81.6%), and a more efficient pumping operation is achieved. The use of a two-axis tracker improves photovoltaic production by 3.2% with economic savings of 4.8% compared to a single-axis tracker, but this difference is small considering its higher investment costs and technical complexity. As a result, the single-axis solar tracker is generally used in pumping stations to achieve efficient management and reduced operating costs

Optimizing survival outcomes with post-remission therapy in acute myeloid leukemia.

Optimization of post-remission therapies to maintain complete remission and prevent relapse is a major challenge in treating patients with acute myeloid leukemia (AML). Monitoring patients for measurable residual disease (MRD) is helpful to identify those at risk for relapse. Hypomethylating agents are being investigated as post-remission therapy. Identification of recurrent genetic alterations that drive disease progression has enabled the design of new, personalized approaches to therapy for patients with AML. Emerging data suggest that targeted post-remission therapy, alone or in combination with chemotherapy, may improve outcomes. Results of ongoing clinical trials will further define potential clinical benefits

La liberalidad hoy. Los contenidos básicos comunes de formación ética y ciudadana en la EGB en la reforma educativa argentina

La proliferación de conceptos éticos que observamos en la modernidad, junto con el aumento de la equivocidad entre muchos de ellos, no contribuyen a clarificar y orientar la acción moral, ni la educación encaminada a ella. En este artículo, en una primera parte, tratamos de precisar uno de esos conceptos, el de liberalidad y su posición respecto a términos próximos y concomitantes tales como la solidaridad, la generosidad, el respeto y la tolerancia. En la segunda parte, nos centramos en ver en qué medida está presente la promoción de esta virtud social —la liberalidad— en la propuesta de Formación Ética y Ciudadana que la reforma educativa argentina (1993), concretamente en los Contenidos Básicos Comunes, sugiere. Se concluye subrayando la necesidad de profundizar en un marco teórico adecuado en el que estén presentes las virtudes sociales aunque sin ninguna duda, la propuesta que la Ley Federal de Educación nos ofrece constituye una base aceptable de discusión e investigación presente y futura.---------------------The proliferation of ethical concepts that can be found in modem thinking, together with the increasing confusion between them, make no contribution for defining clear guide fines for moral action: nor moral education. The aim of this paper is to contribute to a more accurate definition of one of these concepts, liberality, and their relation to related notions such as solidarity, generosity, respect for others, and above all, tolerance. Then we focus on the presence of this social virtue within the project of Ethical and Civic Education in the 1993 Argentinian Education Bill. The conclusions underline the need for an adequate theoretical frame. In this regard, the "Ley Federal de Educacion" offers an interesting basis, for discussion and practical and research development

Time-delay and Doppler tests of the Lorentz symmetry of gravity

Modifications to the classic time-delay effect and Doppler shift in General Relativity (GR) are studied in the context of the Lorentz-violating Standard-Model Extension (SME). We derive the leading Lorentz-violating corrections to the time-delay and Doppler shift signals, for a light ray passing near a massive body. It is demonstrated that anisotropic coefficients for Lorentz violation control a time-dependent behavior of these signals that is qualitatively different from the conventional case in GR. Estimates of sensitivities to gravity-sector coefficients in the SME are given for current and future experiments, including the recent Cassini solar conjunction experiment.Comment: 13 pages, 4 figures, references added, matches PRD versio

A educación cívica nunha sociedade globalizada

El presente artículo pretende formular el sentido de la educación cívica o educación para la ciudadanía democrática. Se confía en la educación cívica como solución a muchos problemas políticos, sociales, de convivencia, etc. que se tienen formulados en las democracias occidentales. Surge así, la necesidad de una nueva educación para la ciudadanía que viene a solucionar las patentes dificultades relacionadas con la globalización, el multiculturalismo, los movimientos migratorios, las tecnologías de la información y comunicación, la violencia, la falta de compromiso cívico, etc. Tanto las propuestas de desarrollo como las experiencias habidas, reconocen la insuficiente claridad en su sentido, en sus contenidos y objetivos. El fenómeno de la globalización intensifica esta carencia, pues la educación cívica no puede plantearse con el mero alcance de la comunidad nacional o local, sino que debe tener un sentido globalizador. Hay unas grandes orientaciones educativas idóneas para la educación cívica en una sociedad globalizadora: prioridad a la acción ciudadana, rehabilitación de la educación estética, promoción de la educación de la afectividad y de la educación para la solidarida

A virtual power plant optimal dispatch model with large and small-scale distributed renewable generation

Volatility and sharp increases in the price of electricity are serious economic problems in the primary sector because they affect modernization investments for irrigation systems in Spain. This paper presents a new virtual power plant (VPP) model that integrates all available full-scale distributed renewable generation technologies. The proposed VPP operates as a single plant in the wholesale electricity market and aims to maximize profit from its operation to meet demand. Two levels of renewable energy integration in the VPP were considered: first, a wind farm and six hydroelectric power plants that inject the generated electricity directly to the distribution network, and second, on-site photovoltaic plants associated with each of the electricity supply points in the system that are designed to prioritize self-consumption. The proposed technical-economic dispatch model was developed as a mixed-integer optimization problem that determines the hourly operation of distributed large-scale renewable generation plants and on-site generation plants. The model was applied to real data from an irrigation system comprising a number of water pumping stations in Aragon (Spain). The results of the VPP model demonstrate the importance of the technical and economic management of all production facilities to significantly reduce grid dependence and final electricity costs

Techno-economic model and feasibility assessment of green hydrogen projects based on electrolysis supplied by photovoltaic PPAs

The use of hydrogen produced from renewable energy enables the reduction of greenhouse gas (GHG) emissions pursued in different international strategies. The use of power-purchase agreements (PPAs) to supply renewable electricity to hydrogen production plants is an approach that can improve the feasibility of projects. This paper presents a model applicable to hydrogen projects regarding the technical and economic perspective and applies it to the Spanish case, where pioneering projects are taking place via photovoltaic PPAs. The results show that PPAs are an enabling mechanism for sustaining green hydrogen projects