Due to humanity's huge scale of thermal energy consumption, any improvements in thermal energy management practices can significantly benefit the society. One key function in thermal energy ...management is thermal energy storage (TES). Following aspects of TES are presented in this review: (1) wide scope of thermal energy storage field is discussed. Role of TES in the contexts of different thermal energy sources and how TES unnecessitates fossil fuel burning are explained. Solar power generation, building thermal comfort and other niche applications of TES are presented. (2) Insight into classes of TES storage materials with details like their physical properties, cost, operational performance and suitability to application requirements is provided. (3) Insight into types of TES systems is presented. TES systems are classified using different types of criteria. Most common TES systems like seasonal TES systems, CSP plant TES systems, TES systems of domestic solar thermal applications, heat and cold storages of building HVAC systems etc are described. Active TES systems like thermocline, packed bed, fluidized bed, moving bed etc are analyzed. Passive TES systems implemented in buildings, textiles, automobiles etc are presented. TES systems operating in cold, low, medium and high temperature ranges are listed. Design parameters, operational issues and cost model of TES systems are discussed.
•Technology, material and research works in thermal energy storage were summarized.•Thermal properties of thermal energy storage materials were presented and analyzed.•Heat storage mechanism and applications based TES systems were shown in detail.•Performance parameters and operational issues based TES systems were discussed.
Column Sketches Hentschel, Brian; Kester, Michael S.; Idreos, Stratos
Proceedings of the 2018 International Conference on Management of Data,
05/2018
Conference Proceeding
Odprti dostop
While numerous indexing and storage schemes have been developed to address the core functionality of predicate evaluation in data systems, they all require specific workload properties (query ...selectivity, data distribution, data clustering) to provide good performance and fail in other cases. We present a new class of indexing scheme, termed a Column Sketch, which improves the performance of predicate evaluation independently of workload properties. Column Sketches work primarily through the use of lossy compression schemes which are designed so that the index ingests data quickly, evaluates any query performantly, and has small memory footprint. A Column Sketch works by applying this lossy compression on a value-by-value basis, mapping base data to a representation of smaller fixed width codes. Queries are evaluated affirmatively or negatively for the vast majority of values using the compressed data, and only if needed check the base data for the remaining values. Column Sketches work over column, row, and hybrid storage layouts.
We demonstrate that by using a Column Sketch, the select operator in modern analytic systems attains better CPU efficiency and less data movement than state-of-the-art storage and indexing schemes. Compared to standard scans, Column Sketches provide an improvement of 3x-6x for numerical attributes and 2.7x for categorical attributes. Compared to state-of-the-art scan accelerators such as Column Imprints and BitWeaving, Column Sketches perform 1.4 - 4.8× better.
bLSM Sears, Russell; Ramakrishnan, Raghu
Proceedings of the 2012 ACM SIGMOD International Conference on Management of Data,
05/2012
Conference Proceeding
Data management workloads are increasingly write-intensive and subject to strict latency SLAs. This presents a dilemma: Update in place systems have unmatched latency but poor write throughput. In ...contrast, existing log structured techniques improve write throughput but sacrifice read performance and exhibit unacceptable latency spikes.
We begin by presenting a new performance metric: read fanout, and argue that, with read and write amplification, it better characterizes real-world indexes than approaches such as asymptotic analysis and price/performance.
We then present bLSM, a Log Structured Merge (LSM) tree with the advantages of B-Trees and log structured approaches: (1) Unlike existing log structured trees, bLSM has near-optimal read and scan performance, and (2) its new "spring and gear" merge scheduler bounds write latency without impacting throughput or allowing merges to block writes for extended periods of time. It does this by ensuring merges at each level of the tree make steady progress without resorting to techniques that degrade read performance.
We use Bloom filters to improve index performance, and find a number of subtleties arise. First, we ensure reads can stop after finding one version of a record. Otherwise, frequently written items would incur multiple B-Tree lookups. Second, many applications check for existing values at insert. Avoiding the seek performed by the check is crucial.
Power generation systems are attracting a lot of interest from researchers and companies. Storage is becoming a component with high importance to ensure system reliability and economic profitability. ...A few experiences of storage components have taken place until the moment in solar power plants, most of them as research initiatives. In this paper, real experiences with active storage systems and passive storage systems are compiled, giving detailed information of advantages and disadvantages of each one. Also, a summary of different technologies and materials used in solar power plants with thermal storage systems existing in the world is presented.
Summary
The demand of electric energy is increasing globally, and the fact remains that the major share of this energy is still being produced from the traditional generation technologies. However, ...the recent trends, for obvious reasons of environmental concerns, are indicating a paradigm shift towards distributed generation (DG) incorporating renewable energy resources (RERs). But there are associated challenges with high penetration of RERs as these resources are unpredictable and stochastic in nature, and as a result, it becomes difficult to provide immediate response to demand variations. This is where energy storage systems (ESSs) come to the rescue, and they not only can compensate the stochastic nature and sudden deficiencies of RERs but can also enhance the grid stability, reliability, and efficiency by providing services in power quality, bridging power, and energy management. This paper provides an extensive review of different ESSs, which have been in use and also the ones that are currently in developing stage, describing their working principles and giving a comparative analysis of important features and technical as well as economic characteristics. The wide range of storage technologies, with each ESS being different in terms of the scale of power, response time, energy/power density, discharge duration, and cost coupled with the complex characteristics matrices, makes it difficult to select a particular ESS for a specific application. The comparative analysis presented in this paper helps in this regard and provides a clear picture of the suitability of ESSs for different power system applications, categorized appropriately. The paper also brings out the associated challenges and suggests the future research directions.
In this manuscript, a comprehensive review is presented on different energy storage systems, their working principles, characteristics along with their applications in distributed generation power system. The novelty of the paper lies in the categorization of energy storage systems according to the power chain.
•Database based market analysis of stationary battery storage systems in Germany.•125,000 home storage systems with a cumulated battery capacity of 930 MWh in 2018.•59 large-scale storage systems ...with a cumulated battery capacity of 550 MWh in 2018.•Average specific storage prices reach from 800 €/kWh to 1,150 €/kWh in 2018.•Open access large-scale storage system database allows further individual analyzes.
The market for stationary battery storage systems (BSS) has been growing strongly around the world for several years. The areas of application for BSS range from ancillary services, to reductions in commercial power prices, to an increase in solar self-consumption in private homes. This wide range of applications, combined with the strong market growth, has led to significant research in the field of BSS. The central topics of these research activities include the simulation of BSS in renewable energy systems, the development of operating strategies and the economic evaluation of these. However, the young market lacks transparency and the underlying assumptions about prices and battery dimensions often do not correspond to reality. To address this issue, this paper provides detailed information about the markets of home storage systems (HSS), industrial storage systems (ISS), and large-scale storage systems (LSS) in Germany. We have been continuously building a database on the HSS and ISS market with accompanying research on subsidy programs and additional research. Furthermore, we have compiled the dataset on LSS in parallel through constant research and publish it with this paper. Our analyses show that by the end of 2018, a total of 125,000 HSS, with a battery power of about 415 MW and battery capacity of 930 MWh, had been installed in Germany. The current state of the ISS database, however, does not allow sharp estimates on the overall German ISS market, but shows the wide capacity and power ranges from some kW / kWh to nearly one MW / MWh for these systems. The 59 LSS have an accumulated power of 400 MW and a capacity of about 550 MWh. They operate mainly in the market of frequency containment reserve (FCR). Lithium-ion technologies dominate the HSS and LSS markets with high shares. The specific prices of this technology have fallen by more than 50% in recent years and were around 1,150 €/kWh in the HSS market and 800 €/kWh in the LSS market in 2018. Our results provide a solid basis for further research on the current and future status of BSS. Research from around the world can adapt the results pertaining to Germany as one of the pioneering markets to other countries.
Battery energy storage system with a fixed connection lacks the ability to meet various power and energy demands of the power grid. In this thread, Flexible Battery Energy Storage Systems (FBESS) ...with a highly controllable structure is proposed as a new path for future energy storage. With the increasing complexity of the battery system, an advanced strategy is needed from the control side to tune the multi-terminal of the FBESS. Especially, the FBESS, with a large number of switches, increases the dimension of the decision space, while the traditional control method can not well handle such a task. In addition, the control of the FBESS should consider both the working performance and the balance requirement of the cells. Thus, a Proximal Policy Optimization (PPO) based framework is proposed in this article to dynamically learn an optimal control strategy for FBESS. Utilizing the clipped surrogate objective, PPO can stably update the policy online through gradient descent. By utilizing its easy implementable property, the proposed method can efficiently control the high dimensional action space and synchronously improve the working time and the balancing performance. Experimental results with data collected from a real battery system prove the validation of the proposed framework.
High penetration of renewable energy resources in the power system results in various new challenges for power system operators. One of the promising solutions to sustain the quality and reliability ...of the power system is the integration of energy storage systems (ESSs). This article investigates the current and emerging trends and technologies for grid-connected ESSs. Different technologies of ESSs categorized as mechanical, electrical, electrochemical, chemical, and thermal are briefly explained. Especially, a detailed review of battery ESSs (BESSs) is provided as they are attracting much attention owing, in part, to the ongoing electrification of transportation. Then, the services that grid-connected ESSs provide to the grid are discussed. Grid connection of the BESSs requires power electronic converters. Therefore, a survey of popular power converter topologies, including transformer-based, transformerless with distributed or common dc-link, and hybrid systems, along with some discussions for implementing advanced grid support functionalities in the BESS control, is presented. Furthermore, the requirements of new standards and grid codes for grid-connected BESSs are reviewed for several countries around the globe. Finally, emerging technologies, including flexible power control of photovoltaic systems, hydrogen, and second-life batteries from electric vehicles, are discussed in this article.
•Optimization of Photovoltaic/micro-wind turbine energy systems with hydrogen and battery.•Techno-economic assessment of various Solar Photovoltaic sun tracking configurations.•Battery autonomy and ...hydrogen tank autonomy is considered.•Sensitivity evaluation of the feasible systems is considered.
The residential application of renewable energy is on the rise in sub-Saharan Africa with many of these systems using battery storage systems as back-ups; however, the adoption of hydrogen storage systems in household energy system applications has attracted few research attentions. Since the environmental impact attributed to hydrogen storage devices is small, it can serve as a complementary or alternative storage device. Using the hybrid optimisation model for electric renewables software, this study presents a techno-economic and sensitivity modelling of a solar photovoltaic (PV)/micro wind turbine/ fuel cell (FC) energy system backed up with both battery and hydrogen storage devices, under seven solar photovoltaic tracking orientations. Because of their strategic status in sub-Saharan Africa, one location each in South Africa and Nigeria were selected for the implementation of the study. The results show that the optimal energy system for the Nigerian scenario is a PV/FC/electrolyzer/battery/hydrogen storage system operated in the daily adjusted horizontal axis mode; the total net present cost and the cost of energy for this system is $9421 and $0.754/kWh respectively. As for the South African scenario, the optimal system is also a PV/FC/electrolyzer/battery/hydrogen storage system operated in the dual axis mode; its total net present cost and the cost of energy for the system is $8771 and $0.701/kWh respectively. Overall, the results show that the addition of a hydrogen storage system is technically feasible for most of the sun tracking configurations in both locations of study. Finally, the economic viability of hydrogen storage systems will be increased if the capital costs associated with the hydrogen sub-system is reduced.
Pors Juels, Ari; Kaliski, Burton S.
Conference on Computer and Communications Security: Proceedings of the 14th ACM conference on Computer and communications security; 28-31 Oct. 2007,
10/2007
Conference Proceeding
In this paper, we define and explore proofs of retrievability (PORs). A POR scheme enables an archive or back-up service (prover) to produce a concise proof that a user (verifier) can retrieve a ...target file F, that is, that the archive retains and reliably transmits file data sufficient for the user to recover F in its entirety.
A POR may be viewed as a kind of cryptographic proof of knowledge (POK), but one specially designed to handle a large file (or bitstring) F. We explore POR protocols here in which the communication costs, number of memory accesses for the prover, and storage requirements of the user (verifier) are small parameters essentially independent of the length of F. In addition to proposing new, practical POR constructions, we explore implementation considerations and optimizations that bear on previously explored, related schemes.
In a POR, unlike a POK, neither the prover nor the verifier need actually have knowledge of F. PORs give rise to a new and unusual security definition whose formulation is another contribution of our work.
We view PORs as an important tool for semi-trusted online archives. Existing cryptographic techniques help users ensure the privacy and integrity of files they retrieve. It is also natural, however, for users to want to verify that archives do not delete or modify files prior to retrieval. The goal of a POR is to accomplish these checks without users having to download the files themselves. A POR can also provide quality-of-service guarantees, i.e., show that a file is retrievable within a certain time bound.
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