Power systems with high renewable energy sources: A review of inertia and frequency control strategies over time

Traditionally, inertia in power systems has been determined by considering all the rotating masses directly connected to the grid. During the last decade, the integration of renewable energy sources, mainly photovoltaic installations and wind power plants, has led to a significant dynamic characteristic change in power systems. This change is mainly due to the fact that most renewables have power electronics at the grid interface. The overall impact on stability and reliability analysis of power systems is very significant. The power systems become more dynamic and require a new set of strategies modifying traditional generation control algorithms. Indeed, renewable generation units are decoupled from the grid by electronic converters, decreasing the overall inertia of the grid. ‘Hidden inertia’, ‘synthetic inertia’ or ‘virtual inertia’ are terms currently used to represent artificial inertia created by converter control of the renewable sources. Alternative spinning reserves are then needed in the new power system with high penetration renewables, where the lack of rotating masses directly connected to the grid must be emulated to maintain an acceptable power system reliability. This paper reviews the inertia concept in terms of values and their evolution in the last decades, as well as the damping factor values. A comparison of the rotational grid inertia for traditional and current averaged generation mix scenarios is also carried out. In addition, an extensive discussion on wind and photovoltaic power plants and their contributions to inertia in terms of frequency control strategies is included in the paper.This work was supported by the Spanish Education, Culture and Sports Ministry [FPU16/04282]

Effects of the second virial coefficient on the adiabatic lapse rate of dry atmospheres

We study the effect of the second virial coefficient on the adiabatic lapse rate of a dry atmosphere. To this end, we compute the corresponding adiabatic curves, the internal energy, and the heat capacity, among other thermodynamic parameters. We apply these results to Earth, Mars, Venus, Titan, and the exoplanet G1 851d, considering three physically relevant virial coefficients in each case: the hard-sphere, van der Waals, and the square-well potential. These examples illustrate under which atmospheric conditions the effect of the second virial coefficient is relevant. Taking the latter into account yields corrections towards the experimental values of the lapse rates of Venus and Titan in some instances.Comment: 12 pages, 8 figures. Comments are welcom

Análisis de las motivaciones para la participación en la comunidad

En este artículo se describen y se analizan los tipos de motivación que conducen a los integrantes de una comunidad a participar en sus asociaciones. De una muestra de 274 estudiantes universitarios, 138 manifestaron pertenecer al menos a una asociación. Los participantes indicaron el nombre de la(s) asociación(es) y las incluyeron en diferentes categorías (política, cultural, asistencial, religiosa, deportiva, de ocio y otras). Cada participante expresó sus motivos para pertenecer a ella(s). Se realizó un análisis de contenido con sus respuestas, utilizando los diez tipos motivacionales de la teoría de los valores de Schwartz como categorías de codificación. Los resultados indican una diferente orientación por género para participar en las asociaciones. En general, los motivos colectivistas están más representados en la participación en la comunidad que los motivos individualistas.This paper aims to describe the motivation types driving people of a community to participate in its associations. Out of a sample of 274 university students, 138 reported they belonged to at least one association. Participants reported the name of the association(s) and included it/them in different categories (political, cultural, assistencial, religious, sporting, leisure and others). Every participant expressed his/her motives to participate there. A content analysis was made on their answers, using the ten motivational types of Schwartz's theory of values as coding categories. Results show a differential gender orientation to participate in different types of associations. In general, collectivist motives are more represented in community participation than individualist motives

Electrochemical study of platinum deposited by electron beam evaporation for application as fuel cell electrodes

Platinum is the most used catalyst in electrodes for fuel cells due to its high catalytic activity. Polymer electrolyte and direct methanol fuel cells usually include Pt as catalyst in their electrodes. In order to diminish the cost of such electrodes, different Pt deposition methods that permit lowering the metal load whilst maintaining their electroactivity, are being investigated. In this work, the behaviour of electron beam Pt (e-beam Pt) deposited electrodes for fuel cells is studied. Three different Pt loadings have been investigated. The electrochemical behaviour by cyclic voltammetry in H2SO4, HClO4 and in HClO4+MeOH before and after the Pt deposition on carbon cloth has been analysed. The Pt improves the electrochemical properties of the carbon support used. The electrochemical performance of e-beam Pt deposited electrodes was finally studied in a single direct methanol fuel cell (DMFC) and the obtained results indicate that this is a promising and adequate method to prepare fuel cell electrodes

Electrochemical study of platinum deposited by electron beam evaporation for application as fuel cell electrodes

Platinum is the most used catalyst in electrodes for fuel cells due to its high catalytic activity. Polymer electrolyte and direct methanol fuel cells usually include Pt as catalyst in their electrodes. In order to diminish the cost of such electrodes, different Pt deposition methods that permit lowering the metal load whilst maintaining their electroactivity, are being investigated. In this work, the behaviour of electron beam Pt (e-beam Pt) deposited electrodes for fuel cells is studied. Three different Pt loadings have been investigated. The electrochemical behaviour by cyclic voltammetry in H2SO4, HClO4 and in HClO4+MeOH before and after the Pt deposition on carbon cloth has been analysed. The Pt improves the electrochemical properties of the carbon support used. The electrochemical performance of e-beam Pt deposited electrodes was finally studied in a single direct methanol fuel cell (DMFC) and the obtained results indicate that this is a promising and adequate method to prepare fuel cell electrodes

La clase Pino-Juniperetea en la provincia de León

Se ha realizado un estudio fitosociológico tanto de los sabinares montanos, como de los enebrales rastreros subalpinos y oromediterraneos, en la provincia de León, describiéndose cuatro nuevas subasociaciones: Juniperetum sabino-thuriferae quercetosum fagineae, Genisto sanabrensis-Juniperetum nanae echinospartetosum iberici y vaccinietosum uliginosi y Vaccinio myrtilli-Juniperetum nanae jasionetosum brevisepalae.In this paper a phytosociological study about montanous savin forets and, subalpine and oromediterranean creeping juniper shrubs in Leon province (NW Spain) is made.Four new subassociations are described: Juniperetum sahino-thunferae quercetosum fagineae, Gen isto sanabrensis-Juniperetum nanae echinospartetosum iberici and vaccinietosum uliginosi and Vaccinio myrtilli-Juniperetum nanae jasionetosumbrevisepalae

Vertical wind profile characterization and identification of patterns based on a shape clustering algorithm

Wind power plants are becoming a generally accepted resource in the generation mix of many utilities. At the same time, the size and the power rating of individual wind turbines have increased considerably. Under these circumstances, the sector is increasingly demanding an accurate characterization of vertical wind speed profiles to estimate properly the incoming wind speed at the rotor swept area and, consequently, assess the potential for a wind power plant site. The present paper describes a shape-based clustering characterization and visualization of real vertical wind speed data. The proposed solution allows us to identify the most likely vertical wind speed patterns for a specific location based on real wind speed measurements. Moreover, this clustering approach also provides characterization and classification of such vertical wind profiles. This solution is highly suitable for a large amount of data collected by remote sensing equipment, where wind speed values at different heights within the rotor swept area are available for subsequent analysis. The methodology is based on z-normalization, shape-based distance metric solution and the Ward-hierarchical clustering method. Real vertical wind speed profile data corresponding to a Spanish wind power plant and collected by using a commercialWindcube equipment during several months are used to assess the proposed characterization and clustering process, involving more than 100000 wind speed data values. All analyses have been implemented using open-source R-software. From the results, at least four different vertical wind speed patterns are identified to characterize properly over 90% of the collected wind speed data along the day. Therefore, alternative analytical function criteria should be subsequently proposed for vertical wind speed characterization purposes.The authors are grateful for the financial support from the Spanish Ministry of the Economy and Competitiveness and the European Union —ENE2016-78214-C2-2-R—and the Spanish Education, Culture and Sport Ministry —FPU16/042

El registro funerario cardial valenciano: dataciones radiocarbónicas

Se analiza el conjunto de dataciones sobre hueso humano disponible para el País Valenciano entre el final del Paleolítico y el Neolítico medio, y más concretamente las correspondientes a individuos del Neolítico antiguo con el fin de caracterizar de forma más precisa el ritual de enterramiento de esta etapa entre los ríos Xúquer y Vinalopó. La distribución geográfica de los yacimientos que contienen restos humanos y cerámica cardial señala la presencia de diferentes comunidades neolíticas que, ya desde un inicio, ocupan de forma ordenada el territorio. Por el momento, vista la información global en secuencia cronológica, se detectan tanto coincidencias como divergencias en la elección de los lugares de enterramiento en las etapas anteriores y posteriores a la aparición y el colapso del modelo de comunidades neolíticas cardiales