150 research outputs found
Transformation of polarons to bipolarons in disordered matter
The polaron to bipolaron transition in disordered media under the influence
of a broadband ac electric field is suggested: ac conductivity vs. frequency
measurements in disordered media with inhomogeneous disorder induce
spatio-temporal fluctuations of the density of polarons yielding polaron to
bipolaron transformation. The external field results in the transition,
alternatively to an increasing doping level. The assertion is confirmed by
performing successive complex impedance measurements in disordered media. A
systematic increase of the real part of the ac conductivity in the frequency
domain, followed by mutual reduction of the magnetic inductivity of conducting
polypyrrole, are explained.Comment: 8 pages plus 3 figures. Accepted for publication in Applied Physics
Letter
Electricity storage requirements to support the transition towards high renewable penetration levels: Application to the Greek power system
This paper investigates the electricity storage requirements to support the
transition towards a high renewable energy source (RES) penetration in a
cost-optimal manner. The achieved reduction of renewable energy curtailments
and the decrease in the total generation cost of the system are quantified
against a counterfactual scenario without storage. A methodology is presented
to determine the optimum mix of short- and medium-duration storage needed to
support system operation at increased RES penetration levels, using the mixed
integer linear programming mathematical optimization. The Greek power system
serves as a realistic study case, in its planned development for the year 2030,
with a targeted annual RES energy penetration in the order of 60%. Li-ion
batteries and pumped-hydro are selected as the representative technologies to
include in the storage mix, assuming energy-to-power ratios of up to 6 hours
for the former and 10 hours for the latter. It is shown that the introduction
of a suitable mixture of storage facilities may improve renewable energy
integration and, at the same time, reduce system cost to the extent that
entirely compensates for the full cost of storage, thus allowing for a net
economic benefit for the system. The optimum storage portfolio for the study
case system and the targeted RES penetration level combines 2-h batteries and
6-h pumped-hydro stations, with an aggregate capacity of new facilities between
1250 MW and 1750 MW, on top of the existing 700 MW of open-loop pumped hydro
plants. The optimum storage requirements vary with the targeted RES penetration
and with the balance of RES technologies in the generation mix, particularly
the level of PV integration.Comment: 28 pages, 19 figure
A comprehensive review of electricity storage applications in island systems
Electricity storage is crucial for power systems to achieve higher levels of
renewable energy penetration. This is especially significant for
non-interconnected island (NII) systems, which are electrically isolated and
vulnerable to the fluctuations of intermittent renewable generation. This paper
comprehensively reviews existing literature on electricity storage in island
systems, documenting relevant storage applications worldwide and emphasizing
the role of storage in transitioning NII towards a fossil-fuel-independent
electricity sector. On this topic, the literature review indicates that the
implementation of storage is a prerequisite for attaining renewable penetration
rates of over 50% due to the amplified requirements for system flexibility and
renewable energy arbitrage. The analysis also identifies potential storage
services and classifies applicable storage architectures for islands. Amongst
the available storage designs, two have emerged as particularly important for
further investigation; standalone, centrally managed storage stations and
storage combined with renewables to form a hybrid plant that operates
indivisibly in the market. For each design, the operating principles,
remuneration schemes, investment feasibility, and applications discussed in the
literature are presented in-depth, while possible implementation barriers are
acknowledged. The literature on hybrid power plants mainly focuses on
wind-powered pumped-hydro stations. However, recently, PV-powered battery-based
hybrid plants have gained momentum due to the decreasing cost of Li-ion
technology. On the other hand, standalone storage establishments rely heavily
on battery technology and are mainly used to provide flexibility to the island
grid. Nevertheless, these investments often suffer from insufficient
remunerating frameworks, making it challenging for storage projects to be
financially secure.Comment: 55 pages, 10 figure
Effect of composition on the dielectric relaxation of zeolite-conducting polyaniline blends
The complex permittivity of conducting polyaniline and zeolite - polyaniline
blends was measured in the frequency range 0.01 to 2000000 Hz from room
temperature to liquid nitrogen temperature. A loss peak is detected for 25, 35
and 50 wt % zeolite blends. Its position in the frequency domain, activation
energy and intensity is a function of composition. The experimental results are
interpreted through the competing multiple role of zeolite: as being less
conducting than polyaniline, it impedes the electric charge flow by dividing
large conducting polyaniline regions into smaller pieces, subsequently provides
short-range pathways and, moreover, enriches the blend in interfaces separating
zeolite from polyaniline.Comment: Accepted for publication in J. Appl. Phy
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