1,720,987 research outputs found
Validation of Energy Hub Solutions Through Simulation and Testing in a Lab Environment and Real World
No full textRenewables are currently playing, and they will play in the future as well, a crucial role in achieving the goal of decarbonizing the planet: just to give an idea, the “green” electricity grew by almost 7% in 2020 that has been produced mainly by wind and solar photovoltaics (PVs) (almost 60% of the globally produced electricity). The share of renewables in the global electricity generation reached almost 29% in 2020, a record annual increase of 2% points; moreover, the main path to decarbonize all the “hard-to-abate” sectors is their electrifications and use of efficient energy conversion technologies to provide also thermal and cooling energy by using “green” electricity. However, the way to produce energy has to be changed as well, moving from a “centralized” production to the local one. In this regard, energy hubs (EHs) are currently being developed as an architectural and operational solution for coupling multiple energy carriers at different scales. Indeed, EHs are multigeneration systems involving different energy carriers for different energy needs to meet the energy consumptions optimally by using local energy resources, numerous energy infrastructure, flexibility, and sustainable energy systems. EH is a candidate architecture for the emerging actors in the electricity market such as aggregators and local energy communities. However, they need to be tested and validated with real-world testing to assess their reliability and be more affordable. This chapter presents the application of EH solutions in lab environment and in real world together with an overview of the current deployment of local energy communities at the European level
Techno-economic analysis of a Liquid Air Energy Storage (LAES) for cooling application in hot climates
Full text linkThis work investigates the technical and economic feasibility of a Liquid Air Energy Storage (LAES) for building demand management applications. The thermodynamics and processes of the LAES configuration, as well as the description of the daily cooling energy demand profile, are described in details and the assumptions and constrains are pointed out. The quantitative analysis has been carried out for a daily cooling energy demand of an existing office building, located in Singapore, locality characterized by a typical hot climate. A thermodynamic analysis has been carried out for LAES configuration by means of the Aspen HYSYS® process simulation code. Under the technical assumptions formulated, LAES achieves an overall round trip efficiency of 45% with a specific consumption of 0.20 kWh/kgLA. The exergy analysis shows that LAES is characterized by an exergy efficiency of 84% and 67% for the liquefaction and the discharge processes, respectively; the compressor and the power turbines account for the highest exergy losses. Finally, the economic results show that under the actual condition of peak tariff and off-peak tariff in Singapore, the investment proposed is not convenient but in case of high values of LAES round trip efficiency and lower OPT the investment may be attractive. However, future works have to deal with the limitations introduced in the analysis, such as neglecting LAES operation costs, and the uncertainty related to capital costs figures.</p
Innovative cryogenic phase change material (PCM) based cold thermal energy storage for liquid air energy storage (LAES) – numerical dynamic modelling and experimental study of a packed bed unit
No full textElectrical energy storage represents a necessary link between sustainability goals and the enhancement of intermittent renewable energy sources penetration in electricity grids. Liquid air energy storage (LAES) is a promising large scale thermo-mechanical energy storage system whose round trip efficiency is largely affected by the performance of the sub-thermal energy storages. The high grade cold storage (HGCS) is by far the most important due to the crucial thermodynamic recovery of the waste cold stream released by the liquid air regasification process. LAES pilot plant and pre-commercial demonstrator, as well as the vast majority of the theoretical and experimental analysis found in literature studies, currently design to store that exergetically valuable cold source in sensible heat (SH) thermal energy storage, economically efficient but low energy density solution. Conversely, phase change material (PCM) has the potential to store a larger amount of energy using the same amount of storage volume. The objective of the present work is to numerically and experimentally investigate the thermal behaviour of a novel cryogenic HGCS packed bed filled by PCM and determine how the novelty introduced affects the LAES thermodynamic and economic performance compared to the SH configuration. To this end, a simplified transient one-dimensional numerical model to simulate the charging and discharging phase of the HGCS system has been developed and successfully validated against experimental results provided by literature for SH medium and an experimental campaign carried out on a novel lab scale HGCS at TESLAB@NTU for PCM, representing a unicum in literature for both PCM and LAES applications. The numerical results have shown that the introduction of a PCM in the HGCS mitigates the thermocline effect shown in SH configuration ensuring: a) longer discharge phase by means of the thermal buffer phenomena triggered by the phase change process and b) lower specific consumption compared to SH configuration (0.272 vs 0.330 kWhe/kgLA) due to a lower time average outlet temperature of the heat transfer fluid during the HGCS discharge, corresponding to LAES charge phase. From an economic perspective, the decrease of the time average specific consumptions results in a notable payback period inferior to 3 years, making the economic investment considerably attractive.This work was partially funded by the Ministerio de Ciencia, Innovacion y Universidades de Espana (RTI2018-093849-B-C31 - MCIU/AEI/FEDER, UE) and by the Ministerio de Ciencia, Innovacion y Universidades - Agencia Estatal de Investigacion (AEI) (RED2018- 102431-T). This work is partially supported by ICREA under the ICREA Academia programme
Liquid Air Energy Storage performance enhancement by means of Organic Rankine Cycle and Absorption Chiller
No full textIn this paper, the potential of improving the round trip efficiency of Liquid Air Energy Storage was investigated through modelling and simulations using the numerical software EES-Engineering Equation Solver. Liquid Air Energy Storage is a novel energy storage concept whose performance is actually limited both by the inefficiencies of the charging (liquefaction cycle) and discharging (regasification and expansion) leading to a low value of round trip efficiency when compared to other energy storage solutions. In order to further improve the round trip efficiency, the opportunity to recover the waste heat released during the compression has been considered in this paper. Different integrated energy systems consisting Organic Rankine Cycle and/or Absorption Chiller were compared against a stand-alone Liquid Air Energy Storage used as a baseline. The integrated systems are compared in terms of different performance indices such as electric power output, ORC efficiency, round trip and overall efficiency of the stand-alone and integrated systems and utilization factor of the waste heat recovery systems. The results show that a tight integration between Liquid Air Energy Storage and Organic Rankine Cycle allows to significantly improve the round trip efficiency (up to 20%). Although the introduction of the absorption chiller decreases the specific consumption, the round trip efficiency is not improved due to the lower quality of waste heat available at the LAES discharge phase. The most remarkable results are achieved when the LAES is operated in trigenerative configuration: the introduction of both Organic Rankine Cycle and Absorption Chiller in combination with Liquid Air Energy Storage was found to improve the round trip efficiency by 30% due to a better utilization of the available waste heat
Improving liquefaction process of microgrid scale Liquid Air Energy Storage (LAES) through waste heat recovery (WHR) and absorption chiller
No full textLiquid air energy storage systems (LAES) store liquid air produced by a liquefaction cycle and convert it into electric/cooling power when needed. A small-scale Liquid air energy storage system represents a sustainable solution in microgrid and distributed generation, where small energy storage capacities are required. The main drawback of these systems though, is the low round trip efficiency due to a high specific consumption of the liquefaction cycle. In this work, a single-effect absorption chiller using a Water-Lithium Bromide solution is integrated with a small air liquefier with a liquid air production capacity of 0.834 t/h. In the proposed solution, the waste heat of the compression phase of the liquefaction cycle is recovered and used to drive the absorption cycle, where the resulting cooling power is used to decrease the specific consumption and improving the exergy efficiency of the system. The operative parameters of the absorption chiller reflect the specifications of the most common commercial models available in the market and the size has been selected to maximize the heat power recovered. The results of simulation of the absorption chiller integration show a reduction of the specific consumption of around 10% (537 kWh/t to 478 kWh/t) and an increase of exergy efficiency of around 11.5%
Preliminary assessment of waste heat recovery solution (ORC) to enhance the performance of Liquid Air Energy Storage system
Full text linkLiquid Air Energy Storage (LAES) is a novel energy storage system that stocks up energy by means of air liquefaction and recovers the cryogenic energy when required. The performance of LAES is actually limited both by the inefficiencies of liquefaction and discharge section leading to lower value of round trip efficiency compared to other energy storage solutions.
This work investigates the thermodynamic feasibility of an integrated energy system consisting of a LAES system and Organic Rankine Cycle (ORC) in order to recover the waste heat released by the compression phase. To further improve the round trip efficiency of LAES, different integrated LAES-ORC system configurations have been modelled by means of the numerical software EES-Engineering Equation Solver v.10, which allows to compute the thermo-physical properties of the working fluids throughout the whole cycles. The LAES-ORC integrated systems are compared in terms of different performance indices such electric power output, round trip efficiency of stand-alone and integrated systems and recover efficiency of ORC. Moreover, since the potential benefits of waste heat recovery by means of ORC introduces a new capital and operative cost, an economic analysis has been carried out in order to determine the impact of ORC introduction in LAES economy. The results show that a tight integration between LAES and ORC allows to significantly improve the round efficiency (up to 20%) and reduce the pay-back period of stand-alone LAES as high as 6 %
Liquid air energy storage for combined cooling, heating and power : techno-economic performance enhancement through waste heat & cold recovery
No full textLarge scale or grid scale Electrical Energy Storage systems (EESs) represent one of the most viable solutions to address some of the issues related with the integration of large portion of renewables into the future grid and to facilitate their further penetration guaranteeing the required flexibility and reliability of the electrical grid. Besides mitigating grid instability, large scale EESs also allow decoupling demand and supply, hence offering the opportunity to be operated as peak-shavers during peak demand hours.
Concurrently, another global pressing issue is represented by the constant increase of cooling demand arising by the global warming and rapid development of emerging countries, usually located in the warmer areas of the world. Indeed, using conventional cooling technologies might be not sustainable putting at stake the reliability of existing electrical networks and dramatically increasing the greenhouse gas emissions. As a consequence, new thinking on how to efficiently integrate and recover cold into the wider energy system becomes necessary.
Liquid Air Energy Storage (LAES) is one of the most promising large scale energy storage concept that stores electricity in the form of liquefied air/nitrogen discharging electric power back to the grid by means of liquid air regasification and expansion in power producing devices. LAES has recently attracted significant attention in research and industry due to several advantages among which viable capital costs, high energy density and no geographical/geological constrains. In particular, due to its intrinsic thermo-mechanical nature, it is capable to be integrated with other valuable high exergy energy carriers (e.g. waste heat/cold from industrial process/ Liquefied Natural Gas regasification) and to simultaneously produce both electricity and free cooling energy being configured an ideal technology bridge between enhancement of RES exploitation and the necessity to face the booming of cooling demand. Beside those benefits, the main LAES drawback has been identified in the low value of the round-trip efficiency, estimated around 50-60 % for large scale systems, mainly due to the low exergy efficiencies during the air liquefaction and power recovery processes.
This thesis aims at contributing at the broader field of large scale energy storage by adopting a novel system perspective which puts a special focus on interactions within the system in order to seek the optimal operation conditions and the best route for performance enhancement of LAES system. In particular, the thesis proposes a novel and systematic methodology for LAES system (plant based) design in order to investigate LAES performance and identify potential areas of improvements.
To this end, a steady state model has been developed and used then to simulate the performance of different system architectures. Based on a comprehensive sensitivity analysis carried out on different LAES operative parameters, a methodology for the LAES design is progressively developed and integrated in a well defined procedure. The novel methodology incorporates new parametric performance maps as a unique and user-friendly tool for LAES design under operative parameters variation for different configurations. The optimized LAES system have been environmentally analyzed by means of LCA methodology: among three large scale EESs assessed LAES has proved to deliver the lowest environmental impact.
Once defined the main areas of opportunity based on the outcomes of the previous technical analysis, the thesis aims to develop and assess, from a techno-economic perspective, novel LAES architectures either operating in the conventional full electric configuration or providing both electricity and cooling energy in the novel polygeneration configuration. Indeed, the second part of the thesis proposes different and novel technology solutions to enhance both the thermodynamic and economic performances of LAES by a more efficient utilization of the thermal energy (heat and cold) streams during LAES operation.
Firstly, waste heat recovery concept is proposed and efficiently integrated in LAES. Indeed, the most remarkable results are achieved by LAES in polygeneration configuration where the Organic Rankine Cycle technology allows to improve the LAES round trip efficiency by 20 % decreasing at the same time the Levelized Cost of Storage by 10 %. Finally, to effectively recover the waste cold discharged by liquid air regasification, a Phase Change Material-based (PCM) High Grade Cold Storage (HGCS) is proposed. Two different configurations (single and cascade PCM) have been modeled and compared with a baseline case configuration where Sensible Heat material is implemented. For this purpose, a numerical model of the HGCS has been developed and successfully validate against experimental data to increase the confidence on the results. The techno-economic analysis has shown that, due to its ability to act as thermal buffer, PCM implementation guarantees a decrease of LAES specific consumption up to 10 % with a remarkable payback period inferior to 5 years.Doctor of Philosoph
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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