Capacity Value of Wind Power

Power systems are planned such that they have adequate generation capacity to meet the load, according to a defined reliability target. The increase in the penetration of wind generation in recent years has led to a number of challenges for the planning and operation of power systems. A key metric for generation system adequacy is the capacity value of generation. The capacity value of a generator is the contribution that a given generator makes to generation system adequacy. The variable and stochastic nature of wind sets it apart from conventional energy sources. As a result, the modeling of wind generation in the same manner as conventional generation for capacity value calculations is inappropriate. In this paper a preferred method for calculation of the capacity value of wind is described and a discussion of the pertinent issues surrounding it is given. Approximate methods for the calculation are also described with their limitations highlighted. The outcome of recent wind capacity value analyses in Europe and North America, along with some new analysis, are highlighted with a discussion of relevant issues also given

Polariton propagation in weak confinement quantum wells

Exciton-polariton propagation in a quantum well, under centre-of-mass quantization, is computed by a variational self-consistent microscopic theory. The Wannier exciton envelope functions basis set is given by the simple analytical model of ref. [1], based on pure states of the centre-of-mass wave vector, free from fitting parameters and "ad hoc" (the so called additional boundary conditions-ABCs) assumptions. In the present paper, the former analytical model is implemented in order to reproduce the centre-of-mass quantization in a large range of quantum well thicknesses (5a_B < L < inf.). The role of the dynamical transition layer at the well/barrier interfaces is discussed at variance of the classical Pekar's dead-layer and ABCs. The Wannier exciton eigenstates are computed, and compared with various theoretical models with different degrees of accuracy. Exciton-polariton transmission spectra in large quantum wells (L>> a_B) are computed and compared with experimental results of Schneider et al.\cite{Schneider} in high quality GaAs samples. The sound agreement between theory and experiment allows to unambiguously assign the exciton-polariton dips of the transmission spectrum to the pure states of the Wannier exciton center-of-mass quantization.Comment: 15 pages, 15 figures; will appear in Phys.Rev.

Elektronenmikroskopische Untersuchungen der Kernmembran während der Mitose mit Hilfe der Gefrierätzung und Ultradünnschnittserien

I.1 $\underline{PROBLEMSTELLUNG}$Gegenstand der vorliegenden Untersuchung war, mit Hilfe der angegebenen elektronenmikroskopischen Präparationsmethoden dasSchicksal der Kernhüllen im Verlauf der Mitose zu verfolgen. Dabei war von Interesse, welche Membransysteme an der Neubildungder Tochterkernhüllen beteiligt sind.I.2 $\underline{ZUSAMMENFASSUNG- DER- ERGEBNISSE}$Mit Hilfe der Ultradünnschnitt-Technik und der Gefrierätzmethode wurde das Verhalten der Kernmembranen während der Mitose verfolgt. Dabei wurden bekannte Vorstellung von der Ultrastruktur bestätigt; andere, neue Erkenntnisse während einzelner Mitosephasen konnten gefunden werden:1.) Kernmembranen aus I n t e r p h a s e k e r n e n sind Doppelmembranen (Dicke: 80 - 90 $\mathring{A}$), die durch eine wässrige Zwischenphase (Breite: 200 $\mathring{A}$) getrennt sind. Kernporen (Durchmesser etwa 80 nm) verbinden die äußere und innere Kernmembran. Beim Austreten der äußeren Kernmembran in das Cytoplasma sind Kernporen nicht mehr nachweisbar. 2.) In der mittleren und späten P r o p h a s e zerreißt die Kernhülle aufgrund der Chromosomenkontraktion. Die Kernmembranen als Doppelmembran mit Kernporenbesatz bleiben erhalten. 3.) In der M e t a p h a s e werden die Membranhüllenreste auf die Zellpole verteilt. Der Doppelmembrancharakter und Porenbesatz bleibt erhalten. 4.) In der A n a p h a s e läßt sich folgendes nachweisen:a.) In der Aequatorialebene setzt ein Membranwachstum ein, wobei die Natur des Endomembransystems unklar ist. b.) Die strukturelle Einheit der Kernmembranhülle bleibt in der Nähe der Zellpole erhalten. 5.) Zu Beginn der frühen T e l o p h a s e werden an das Karyoplasma grenzende ER-Membranen in die sich neubildende Kernhülle einbezogen. Die Kernhüllen der Tochterkerne besitzen Michcharakter: Es werden zu ihrem Aufbau Reste der Parentalkernhüllen einbezogen und ER-Membranen zusätzlich benötigt. Es konnte mit Hilfe der artefaktfreien Gefrierätzung gezeigt werden, daß - entgegen der herkömmlichen Vorstellung vom völligen Aubbau der Kernhülle während der Mitose - Teile der alten Kernmembran auf die Tochterkerne verteilt werden. Daraus ergeben sich unter dem Aspekt der Übertragung membrangebundener Enzyme, u. a. der DNA - Initiation, wichtige molekularbiologische Konsequenzen

Application of wind generation capacity credits in the Great Britain and Irish systems

The concept of capacity credit is widely used to quantify the contribution of renewable technologies to securing demand. This may be quantified in a number of ways; this paper recommends the use of Effective Load Carrying Capability (ELCC, the additional demand which the new generation can support without increasing system risk), with system risk being measured using Loss of Load Expectation (LOLE, this is calculated through direct use of historic time series for demand and wind load factor). The key benefit of this approach is that it automatically incorporates the available statistical information on the relationship between wind availability and demand during the hours of very high demand which are most relevant in assessing system adequacy risk. The underlying assumptions are discussed in detail, and a comparison is made with alternative calculation approaches; a theme running through the paper is the need to consider the assumptions carefully when presenting or interpreting risk assessment results. A range of applications of capacity credits from Great Britain and Ireland are presented; this includes presentation of effective plant margin, ensuring that the optimal plant mix secures peak demand in economic projection models, and the Irish capacity payments system. Finally, new results comparing capacity credit results from the Great Britain and Irish systems using the same wind data are presented. This allows the various factors which influence capacity credit results to be identified clearly. It is well known that increasing the wind load factor or demand level typically increases the calculated capacity credit, while increasing the installed wind capacity typically decreases its capacity credit (as a percentage of rated capacity). The new results also show that the width of the probability distribution for available conventional generating capacity, relative to the peak demand level, also has a strong influence on the results. This emphasises further that detailed understanding of risk model structures is vitally important in practical application