33,180 research outputs found
Alpha Entanglement Codes: Practical Erasure Codes to Archive Data in Unreliable Environments
Data centres that use consumer-grade disks drives and distributed
peer-to-peer systems are unreliable environments to archive data without enough
redundancy. Most redundancy schemes are not completely effective for providing
high availability, durability and integrity in the long-term. We propose alpha
entanglement codes, a mechanism that creates a virtual layer of highly
interconnected storage devices to propagate redundant information across a
large scale storage system. Our motivation is to design flexible and practical
erasure codes with high fault-tolerance to improve data durability and
availability even in catastrophic scenarios. By flexible and practical, we mean
code settings that can be adapted to future requirements and practical
implementations with reasonable trade-offs between security, resource usage and
performance. The codes have three parameters. Alpha increases storage overhead
linearly but increases the possible paths to recover data exponentially. Two
other parameters increase fault-tolerance even further without the need of
additional storage. As a result, an entangled storage system can provide high
availability, durability and offer additional integrity: it is more difficult
to modify data undetectably. We evaluate how several redundancy schemes perform
in unreliable environments and show that alpha entanglement codes are flexible
and practical codes. Remarkably, they excel at code locality, hence, they
reduce repair costs and become less dependent on storage locations with poor
availability. Our solution outperforms Reed-Solomon codes in many disaster
recovery scenarios.Comment: The publication has 12 pages and 13 figures. This work was partially
supported by Swiss National Science Foundation SNSF Doc.Mobility 162014, 2018
48th Annual IEEE/IFIP International Conference on Dependable Systems and
Networks (DSN
A review on the complementarity of renewable energy sources: concept, metrics, application and future research directions
It is expected, and regionally observed, that energy demand will soon be
covered by a widespread deployment of renewable energy sources. However, the
weather and climate driven energy sources are characterized by a significant
spatial and temporal variability. One of the commonly mentioned solutions to
overcome the mismatch between demand and supply provided by renewable
generation is a hybridization of two or more energy sources in a single power
station (like wind-solar, solar-hydro or solar-wind-hydro). The operation of
hybrid energy sources is based on the complementary nature of renewable
sources. Considering the growing importance of such systems and increasing
number of research activities in this area this paper presents a comprehensive
review of studies which investigated, analyzed, quantified and utilized the
effect of temporal, spatial and spatio-temporal complementarity between
renewable energy sources. The review starts with a brief overview of available
research papers, formulates detailed definition of major concepts, summarizes
current research directions and ends with prospective future research
activities. The review provides a chronological and spatial information with
regard to the studies on the complementarity concept.Comment: 34 pages 7 figures 3 table
Energy recovery from solid waste. Volume 2: Technical report
A systems analysis of energy recovery from solid waste demonstrates the feasibility of several current processes for converting solid waste to an energy form. The social, legal, environmental, and political factors are considered in depth with recommendations made in regard to new legislation and policy. Biodegradation and thermal decomposition are the two areas of disposal that are considered with emphasis on thermal decomposition. A technical and economic evaluation of a number of available and developing energy-recovery processes is given. Based on present technical capabilities, use of prepared solid waste as a fuel supplemental to coal seems to be the most economic process by which to recover energy from solid waste. Markets are considered in detail with suggestions given for improving market conditions and for developing market stability. A decision procedure is given to aid a community in deciding on its options in dealing with solid waste, and a new pyrolysis process is suggested. An application of the methods of this study are applied to Houston, Texas
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Wind Power Capacity Value Metrics and Variability: A Study in New England
Capacity value is the contribution of a power plant to the ability of the power system to meet high demand. As wind power penetration in New England, and worldwide, increases so does the importance of identifying the capacity contribution made by wind power plants. It is critical to accurately characterize the capacity value of these wind power plants and the variability of the capacity value over the long term. This is important in order to avoid the cost of keeping extra power plants operational while still being able to cover the demand for power reliably. This capacity value calculation is particularly interesting because wind power output and demand for electricity are not statistically independent. They are both driven by the weather.
This dissertation describes a model of the New England power system in the presence of increasing wind power penetration, used to achieve three major ends: To evaluate the magnitude of the contribution that wind power would make to resource adequacy in the New England Power system at various levels of penetration (up to 50%). To characterize the inter-annual variability in that contribution To assess various capacity value metrics with regard to their ability to predict the long term capacity value of wind power plants, especially based on limited data To characterize the interaction of wind power plants and energy storage with respect to capacity value
These ends were achieved by completing three studies: a long-term study based on measured wind data, a high-penetration study based on synthesized data, and an investigation of the effect of grid-scale energy storage. While the methods used in these studies are generally applicable, New England is used as a consistent example since many of these phenomena are strongly affected by the regional wind and power system characteristics.
The results of this work show that wind power capacity value is relatively high at low penetration and decreases substantially as penetration increases to 50% and that this is not significantly improved by the inclusion of grid-scale (daily load-shifting) energy storage. Also, the capacity value of this energy storage, considered separately is relatively high, and not strongly dependent on wind energy penetration level. In future power systems with higher wind penetrations than 50% or those relying on longer-term storage (which could be necessary to reach very high levels of renewable penetration), new metrics of capacity value may be necessary to ensure system adequac
Intermittency and the Value of Renewable Energy
A key problem with renewable energy is intermittency. This paper develops a method to quantify the social costs of large-scale renewable energy generation. The method is based on a theoretical model of electricity system operations that allows for endogenous choices of generation capacity investment, reserve operations, and demand-side management. We estimate the model using generator characteristics, solar output, electricity demand, and weather forecasts for an electric utility in southeastern Arizona. The estimated welfare loss associated with a 20% solar photovoltaic mandate is 11% higher than the average cost difference between solar generation and natural gas generation. Unforecastable intermittency yields welfare loss equal to 3% of the average cost of solar. Eliminating a mandate provision requiring a minimum percentage of distributed solar generation increases welfare. With a $21/ton social cost of CO2 this mandate is welfare neutral if solar capacity costs decrease by 65%.
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