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Artículos en revistas It is shown how a standard nonlinear programming approach can be applied to solve a sophisticated version of the static optimal mix problem in generation planning. The model presented includes technical minima of thermal capacity, detailed operating models of storage-hydro and pumped-hydro units, a realistic model of capital costs for hydro plants, operating reserve and minimum demand constraints, and capacity already in existence. The model formulation is in a format that can be directly handled by the well-known MINOS code and can be efficiently solved. The use of a general-purpose nonlinear optimization program results in a great flexibility, making it possible to modify the model formulation easily or to adapt it to the characteristics of a particular electric system. A realistic application to the Spanish generation system is presented info:eu-repo/semantics/publishedVersion

Capítulos en libros This paper describes a strategic information platform developed for the German electric utility Eon, to provide historical bidding analysis and medium-term forecasting of the Iberian Electricity Market. This platform, PLAMER, has three main modules: Initialization module, consisting of different sub-modules to define the electrical system structure and to organize the input data of the rest of modules, PLAMER-bids, to read, aggregate and visualize market historical bids and also to prepare them for their future forecasted values, and PLAMER-clearing, for market clearing emulation using forecasted bids. PLAMER-clearing models the Iberian market based on a bid clearing mechanism with an inherent market splitting procedure. This market splitting is built with a bi-nodal simplification, one node representing the Spanish System and the other the Portuguese one. Both are simply connected by a unique equivalent interconnection line. The medium term clearing model uses a generation portfolio per generation company in terms of technologies, for supplying monthly demand for different load levels, and labour and non-labour periods. Some technical constraints, such as minimum outputs and pumping energy balance, are also taking into account. The mathematical problem of PLAMER-clearing is a quadratic programming model solved using GAMS language and CPLEX optimizer. Finally, a real Iberian case study is detailed and some market splitting outputs are analyzed. info:eu-repo/semantics/publishedVersion

It is now environmentally desirable and legally mandatory to add renewable fuels such as ethanol or ethyl tert-butyl ether to gasoline. However, biofuels affect, among other properties, the distillation curve of gasoline, which is subject to strict regulations. This work presents a simple mathematical model capable of accurately predicting the influence that the addition of these oxygenates has on the distillation curve. In order to address this issue, it is essential to find a simple mathematical correlation between the boiling temperatures of the hydrocarbons present in gasoline and the properties (boiling temperature and volume or molar concentration of ethanol) of the corresponding azeotropic mixtures formed with ethanol. Power functions have been assumed to model the temperature composition diagrams of the vapour-liquid equilibrium. Experimental data previously published by these and other authors have been used to fit and validate the model. The results provided by the mathematical model can be of great interest to understand the process of fuel evaporation in spark-ignition engines or the adjustment of distillation cuts in refineries, in order to comply with the regulations, in terms of the distillation curve, after adding ethanol or ethyl tert-butyl ether.

Artículos en revistas There has been total unanimity about the vital importance of reliability of supply since the beginning of the electricity sector deregulation process. This paper describes the procedure proposed by Pérez-Arriaga et al. [2005. White paper for the reform of the regulatory scheme of the power generation in Spain. For the Ministry of Industry, Tourism and Trade of Spain (in Spanish)] to improve upon the current scheme to guarantee a reasonable reserve margin, the capacity payment mechanism. This alternative design introduces improvements aimed at guaranteeing at least a minimum capacity reserve margin, as well as at providing a strong incentive for generating units to be available when needed, namely, in situations when supply is likely to be insufficient to meet the total demand. info:eu-repo/semantics/publishedVersion

Abstract From the sustainable perspective, the optimum thickness calculations of the buildings envelope insulation materials published in scientific journals suffer a number of notable shortcomings. The most relevant are the short amortization time periods and the prevalence of economic criterion. The work presented shows that an increase from 20 to 50 years in the amortization time period involves, in some cases, to double the value of the optimum thickness. Moreover, the thicknesses calculated applying energetic or environmental criteria for the optimization give, in some cases, results 10 times higher than the ones obtained using the economic argument. The type of insulation materials (especially their different characteristics at the manufacturing stage) and the calculation conditions (e.g. Degree-Days zone) also affect optimum thicknesses determination.

This paper proposes a linear programming problem to find the optimal planning and operation of aggregated distributed energy resources (DER), managed by an aggregator that participates in the day-ahead wholesale electricity market as a price-maker agent. The proposed model analyzes the impact of the size of the aggregated resources and gives the optimal planning and management of DER systems, and the corresponding energy transactions in the wholesale day-ahead market. The results suggest that when the aggregated resources are large enough, DER systems can achieve up to 32% extra economic benefits depending on the market share, compared with a business-as-usual approach (not implementing DER systems). info:eu-repo/semantics/draft

Abstract Isobaric vapor–liquid (VLE) and vapor–liquid–liquid equilibria (VLLE) were measured for the ternary system water + ethanol + cyclohexane at 101.3 kPa. The experimental determination was carried out in a dynamic equilibrium still with circulation of both the vapor and liquid phases, equipped with an ultrasonic homogenizer. The experimental data demonstrated the existence of a ternary heterogeneous azeotrope at 335.6 K with a composition of 0.188, 0.292, 0.520 mole fraction of water, ethanol and cyclohexane, respectively. The experimental data were compared with those obtained using UNIFAC and NRTL models with parameters taken from literature.

Hot water heat stores with stratification are a common technology used in solar energy systems and reuse of waste heat. Adding a PCM module at the top of the water tank would give the system higher storage density, and compensate heat loss in the top layer. The work presented here includes experimental results and numerical simulation of the system using an explicit finite-difference method. Experiments and simulations were carried out using different cylindrical PCM modules. With only 1/16 of the volume of the store being PCM, 3/16 of water at the top of the store was held warm for 50% to 200% longer and the average energy density was increased by 20% to 45%. Furthermore, these 3/16 of water were reheated by the heat from the module after being cooled down in only 20 min.