Energy-storage technologies and electricity generation

As the contribution of electricity generated from renewable sources (wind, wave, solar) grows, the inherent intermittency of supply from such generating technologies must be addressed by a step-change in energy storage. Furthermore, the continuously developing demands of contemporary applications require the design of versatile energy-storage/power-supply systems offering wide ranges of power density and energy density. As no single energy-storage technology has this capability, systems will comprise of combinations of technologies such as electrochemical supercapacitors, flow batteries, Lithium-ion batteries, superconducting magnetic energy storage (SMES) and kinetic energy storage. The evolution of the electrochemical supercapacitor is largely dependent on the development of optimised electrode materials (tailored to the chosen electrolyte) and electrolytes. Similarly, the development of Lithium-ion battery technology requires fundamental research in materials science aimed at delivering new electrodes and electrolytes; Lithium-ion technology has significant potential and a step-change is required in order to promote the technology from the portable electronics market into high-duty applications. Flow-battery development is largely concerned with safety and operability. However, opportunities exist to improve electrode technology yielding larger power densities. The main barriers to overcome in terms of the development of SMES technology are those related to high-temperature superconductors in terms of their granular, anisotropic nature. Materials development is essential for the successful evolution of flywheel technology. Given the appropriate research effort, the key scientific advances required in order to successfully develop energy-storage technologies generally represent realistic goals which may be achieved by 2050

Energy storage : the route to liberation from the fossil fuel economy?

If a low-carbon energy strategy is to be developed up to 2050, renewable energy sources will need to be deployed on a large scale against a scenario of increasing global energy demand. Renewables will vary from large-scale regional wind and marine clusters to more localised 'micro' generation. If a low-carbon strategy is to be successful, automotive transport will also need to be linked to the renewable infrastructure. Both of these need the development of efficient and viable energy storage

The control of porosity at nano scale in resorcinol formaldehyde carbon aerogels

Organic aerogels were synthesized by sol-gel polymerization of resorcinol (R) with formaldehyde (F) catalyzed by sodium carbonate (C) followed by vacuum drying. The influence of the resorcinol/sodium carbonate ratio (R/C) on the porous structure of the resultant aerogels was investigated. The nitrogen adsorption-desorption measurements show that the aerogels possess a well developed porous structure and mesoporosity was found to increase with increasing the R/C ratio. Carbon aerogels were obtained by carbonization of RF aerogels. The carbonization temperature impacts the microstructure of the aerogels by pore transformations during carbonization probably due to the formation of micropores and shrinkage of the gel structure. The results showed that a temperature of 1073 K is more effective in the development of the pore structure of the gel. Activated carbon aerogels were obtained from the CO2 activation of carbon aerogels. Activation results in an increase in the number of both micropores and mesopores, indicative of pore creation in the structure of the carbon. Activation at higher temperatures results in a higher degree of burn off and increases the pore volume and the surface area remarkably without change of the basic porous structure, pore size, and pore size distribution. separation [1, 2], electrode materials for energy storage [3-5], catalyst supports [6], packing materials for chromatography [7], host materials for gas storage[8], thermal and/or phonic insulators [9, 10], etc. For many advanced applications such as double layer supercapacitors the control of porosity at nano-level is very essential. Resorcinol formaldehyde (RF) aerogels are special type of highly cross-linked aromatic polymers with a high pore volume (0.25-1.25 cm3/g) [11], low density (0.06-0.103 g/cm3) [12], large specific surface area (400-1000 m2/g) [13], and mostly amorphous structure [14]. The morphology of RF aerogels can be modified as a function of different synthesis parameters. This characteristic allows the tailoring of the internal structure of these porous materials on a nanometer scale and makes them particularly well suited for a variety of applications. RF aerogels can be used as precursors for the preparation of porous carbons with similar appearance and macrostructure, but having slight differences in microstructure

An Improved Method for Bandwidth Selection when Estimating ROC Curves

The receiver operating characteristic (ROC) curve is used to describe the performance of a diagnostic test which classifies observations into two groups. We introduce a new method for selecting bandwidths when computing kernel estimates of ROC curves. Our technique allows for interaction between the distributions of each group of observations and gives substantial improvement in MISE over other proposed methods, especially when the two distributions are very different.Bandwidth selection; binary classification; kernel estimator; ROC curve

Energy storage in the UK electrical network : estimation of the scale and review of technology options

This paper aims to clarify the difference between stores of energy in the form of non-rechargeable stores of energy such as fossil-fuels, and the storage of electricity by devices that are rechargeable. The existing scale of these two distinct types of storage is considered in the UK context, followed by a review of rechargeable technology options. The storage is found to be overwhelmingly contained within the fossil-fuel stores of conventional generators, but their scale is thought to be determined by the risks associated with long supply chains and price variability. The paper also aims to add to the debate regarding the need to have more flexible supply and demand available within the UK electrical network in order to balance the expected increase of wind derived generation. We conclude that the decarbonisation challenge facing the UK electricity sector should be seen not only as a supply and demand challenge but also as a storage challenge. (c) 2010 Elsevier Ltd. All rights reserved

Unexpected properties of bandwidth choice when smoothing discrete data for constructing a functional data classifier

The data functions that are studied in the course of functional data analysis are assembled from discrete data, and the level of smoothing that is used is generally that which is appropriate for accurate approximation of the conceptually smooth functions that were not actually observed. Existing literature shows that this approach is effective, and even optimal, when using functional data methods for prediction or hypothesis testing. However, in the present paper we show that this approach is not effective in classification problems. There a useful rule of thumb is that undersmoothing is often desirable, but there are several surprising qualifications to that approach. First, the effect of smoothing the training data can be more significant than that of smoothing the new data set to be classified; second, undersmoothing is not always the right approach, and in fact in some cases using a relatively large bandwidth can be more effective; and third, these perverse results are the consequence of very unusual properties of error rates, expressed as functions of smoothing parameters. For example, the orders of magnitude of optimal smoothing parameter choices depend on the signs and sizes of terms in an expansion of error rate, and those signs and sizes can vary dramatically from one setting to another, even for the same classifier.Comment: Published in at http://dx.doi.org/10.1214/13-AOS1158 the Annals of Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical Statistics (http://www.imstat.org

Preparation of controlled porosity carbon aerogels for energy storage in rechargeable lithium oxygen batteries

Porous carbon aerogels are prepared by polycondensation of resorcinol and formaldehyde catalyzed by sodium carbonate followed by carbonization of the resultant aerogels in an inert atmosphere. Pore structure of carbon aerogels is adjusted by changing the molar ratio of resorcinol to catalyst during gel preparation and also pyrolysis under Ar and activation under CO2 atmosphere at different temperatures. The prepared carbons are used as active materials in fabrication of composite carbon electrodes. The electrochemical performance of the electrodes has been tested in a Li/O2 cell. Through the galvanostatic charge/discharge measurements, it is found that the cell performance (i.e. discharge capacity and discharge voltage) depends on the morphology of carbon and a combined effect of pore volume, pore size and surface area of carbon affects the storage capacity. A Li/O2 cell using the carbon with the largest pore volume (2.195 cm3/g) and a wide pore size (14.23 nm) showed a specific capacity of 1290 mA h g−1

Mixed signals: central bank independence, coordinated wage bargaining, and European Monetary Union

Plans for European Monetary Union are based on the conventional postulate that increasing the independence of the central bank can reduce inflation without any real economic effects. However, the theoretical and empirical bases for this claim rest onmodels of the economy that make unrealistic information assumptions and omitinstitutional variables other than the central bank. When the signaling problems between the central bank and other actors in the political economy are considered,we find that the character of wage bargaining conditions the impact of central bankindependence by rendering the signals between the bank and the bargainers moreor less effective. Greater independence can reduce inflation without majoremployment effects where bargaining is coordinated, but it brings higher levels ofunemployment where bargaining is uncoordinated. Thus, currency unions like the EMU may require higher levels of unemployment to control inflation than their proponents envisage; they will have costs as well as benefits, costs which will bedistributed unevenly among and within the member nations based on the changesinduced in the status of the bank and of wage coordination -- Die Konzepte für die Europäische Währungsunion basieren auf dem allgemeinvertretenen Postulat, daß mit größerer Unabhängigkeit der Zentralbank die Inflationohne reale ökonomische Effekte verringert werden kann. Allerdings beruht die theoretische wie empirische Basis für diesen Anspruch auf Modellvorstellungen einer Volkswirtschaft, die auf unrealistischen Annahmen der Bedeutung von Informationen beruhen und institutionelle Variable - mit Ausnahme der Zentralbank - außer acht lassen. Wird allerdings die wechselseitige Wahrnehmung und Interpretation vonInformationen (signaling problems) zwischen Zentralbank und den anderenAkteuren in der politischen Ökonomie in die Analyse einbezogen, dann ist festzustellen, daß die Art der Lohnfindung die Intensität der Auswirkungen derZentralbankunabhängigkeit beeinflußt je nachdem, wie wirksam die wechselseitige Wahrnehmung und Interpretation von Informationen zwischen der Zentralbank und den Tarifpartnern vermittelt ist.Im Falle koordinierter Tarifverhandlungen kann eine größere Unabhängigkeit derZentralbank die Inflation in der Tat ohne größere Beschäftigungseffekte vermindern,im Falle unkoordinierter Tarifverhandlungen führt dies allerdings zu einem höherenNiveau der Arbeitslosigkeit. Daraus leitet sich die Überlegung ab, daß eineWährungsunion vom Typ Europäische Währungsunion ein höheres Maß an Arbeitslosigkeit erfordert, um die Inflation unter Kontrolle zu halten, als es ihre Befürworter erwarten. Bei den sich dann einstellenden Vor- und Nachteilen werden die Nachteile zwischen und innerhalb der Mitgliedstaaten ungleich verteilt sein, abhängig von dem letztendlich verwirklichten Grad der Unabhängigkeit derZentralbank und der Form der Lohnfindung.

Grid-connected renewables, storage and the UK electricity market

This article is a critical counterpoint to an article by published by Swift-Hook in the journal of Renewable Energy entitled "Grid-connected intermittent renewables are the last to be stored". In contrast to Swift-Hook we found evidence that "grid-connected intermittent renewables" have been, and will continue to be stored when it suits the "UK market" to do so.  This article is important to policy makers as energy storage (through EV battery demand side management for example) may well have an important role to play in facilitating the integration of high wind penetrations

Non Parametric Confidence Intervals for Receiver Operating Characteristic Curves

We study methods for constructing confidence intervals, and confidence bands, for estimators of receiver operating characteristics. Particular emphasis is placed on the way in which smoothing should be implemented, when estimating either the characteristic itself or its variance. We show that substantial undersmoothing is necessary if coverage properties are not to be impaired. A theoretical analysis of the problem suggests an empirical, plug-in rule for bandwidth choice, optimising the coverage accuracy of interval estimators. The performance of this approach is explored. Our preferred technique is based on asymptotic approximation, rather than a more sophisticated approach using the bootstrap, since the latter requires a multiplicity of smoothing parameters all of which must be chosen in nonstandard ways. It is shown that the asymptotic method can give very good performance.Bandwidth selection, binary classification, kernel estimator, receiver operating characteristic curve.