• Energy Research

Currently, energy storage systems are considered a key solution when mismatch occurs between energy supply and demand, allowing a more efficient energy deployment and use. The present paper is focused on the study of a latent heat thermal energy storage (LHTES) system based on a packed bed of encapsulated phase change material (PCM) of spherical shape, conceived as an auxiliary component of a micro-grid to be built in a Research Center located in southwestern Sardinia (Italy). The main purpose of this work was to perform numerical simulations for predicting the performance of the TES system, designed to store the surplus thermal energy produced during the weekend by a heat pump fed by a photovoltaic (PV) plant. The stored energy would then be utilized during the weekdays to integrate the air-conditioning system supply. The numerical simulations were based on a one-dimensional (1-D) two-equation transient model, able to return the thermocline profile of the water and the PCM separately. The behavior of the LHTES device during charge and discharge phases was reproduced, as well as during the standby periods. Finally, two characteristic indexes of the PV system were evaluated, to investigate the effect of TES on grid interchanges, self-consumption, and self-sufficiency.

This book contains the successful invited submissions [...]

AbstractThis work relates the study of system performance in operational conditions for an isolated micro-grid powered by a photovoltaic system and a wind turbine. The electricity produced and not used by the user will be accumulated in two different storage systems: a battery bank and a hydrogen storage system composed of two PEM electrolyzers, four pressurized tanks and a PEM fuel cell.One of the main problems to be solved in the development of isolated micro-grids is the management of the various devices and energy flows to optimize their functioning, in particular in relation to the load profile and power produced by renewable energy systems depending on weather conditions. For this reason, through the development and implementation of a specific simulation program, three different energy management systems were studied to evaluate the best strategy for effectively satisfying user requirements and optimizing overall system efficiency.

This study is aimed at comparing the environmental performance of a solar-only and hybrid solar-biomass organic Rankine cycle (ORC) plant using the exergoenvironmental method. The system studied adopts the design features of a real ORC plant currently running at Ottana, Italy, rated nominally at about 630 kW. Established procedures of the exergoenvironmental methods were applied, which integrate the principles of exergy and life cycle analyses. The method quantifies the yearly environmental impact rates of each of the plant components. The eco indicator-99 impact assessment method was adopted to quantify impact rates. Results showed that implementing the biomass hybridization scheme would improve the annualized exergetic efficiency of the existing solar ORC plant by about 3 percentage points, from about 7% with solar-only to about 10% with hybrid solar-biomass heat sources, although a small increase in the relative irreversibility rate is observed (from 49% to 51%). It would as well improve the capacity factor of the plant. However, the environmental impacts would be impacted negatively. Particularly, the specific exergoenvironmental impact rates were obtained as 27.4 Pts/MWh for the hybrid solar-biomass ORC plant, as against 20.3 Pts/MWh obtained for the solar-only plant, implying that the hybridization strategy would increase impact rate by about 35%. Similarly, it was obtained that biomass hybridization would increase the overall exergoenvironmental impact rates of the ORC plant by about 92,000 Pts/year, due majorly to increased exergy destruction in the plant components and the polluting emissions of the combustor.

This paper concerns a performance evaluation of advanced zero emissions (NOx, SOx, CO and particulate, but also CO2), coal gasification integrated power plants with hydrogen combustion (ZE-IGHC). In ZE-IGHC power plants the hydrogen is produced through CO shift conversion and subsequent CO2 separation. The hydrogen is burned using pure oxygen in an internal combustion steam power plant with double combustion and thermodynamic regeneration. As a result of raw gas cleaning, CO2 separation and hydrogen combustion with oxygen, the ZE-IGHC power plant eliminates pollutant and greenhouse gas emissions. A comparative study of ZE-IGHC plant configurations based on different gasifiers and raw gas cooling options indicated that net efficiencies of up to about 50% can be achieved by resorting to configurations based on dry-feed gasifiers and raw gas cooling heat recovery with steam production. The simpler and cheaper plant configurations based on wet-feed gasifiers and raw gas quench systems give an efficiency penalty of about 3-4 % points. The ZE-IGHC power plant presented here can be a very attractive option for a near term, coal-fired power generation system. What is more, its major components are already adopted in conventional power plants and only the hydrogen combustors and the high temperature turbine require technology development.

Abstract In recent years coal-fired power plants have increased their role in the global energy scenario and in this framework environmental issues require a sustainable use of coal and great efforts for greenhouse gas reduction. With this aim, this paper reports on a comparative performance assessment of two power generation technologies: the Ultra Super Critical (USC) steam plant and the Integrated Gasification Combined Cycle (IGCC) plant. Performances were assessed referring to typical commercial size plants (400–500 MW) integrated with CO 2 capture systems. The study is based on simulation models specifically developed through Aspen-Plus® and Gate-Cycle® software platforms. The USC plant is integrated with a SNOX section that removes simultaneously nitrogen and sulfur oxides without producing process wastes and with lower power requirements compared to traditional FGD systems. The USC plant is also integrated with a low temperature CO 2 capture/compression section based on a MEA chemical absorption process. The IGCC plant is based on a Texaco entrained bed gasifier, fed by a coal–water slurry and high purity oxygen, integrated with a triple-pressure reheat combined cycle. The IGCC is integrated with a syngas cooling and treatment section composed of radiant and convective coolers, a water gas shift section and a low temperature CO 2 capture system based on a physical absorption process. The performance assessment of USC and IGCC power plants was carried out by varying the main operating parameters of both power sections and gas treatment sections. For both plants an in-depth analysis of performance penalties due to the CO 2 capture systems was carried out, evaluating the influence of CO 2 removal technology and efficiency.

Abstract This paper is focused on the ongoing studies at the Ottana Solar Facility, a new experimental power plant located in Sardinia (Italy). The facility consists of a 630 kW CSP plant and a 400 kW CPV plant. The CSP section includes a solar field based on linear Fresnel collectors using thermal oil as heat transfer fluid and a two-tank direct thermal storage system with a storage capacity of about 15 MWht. The electricity generation is carried out in the Turboden 6HR Special ORC unit. This paper presents a description of the CSP plant characteristics and an analysis of its expected performance. In particular, the results of the simulation activities aimed at assessing the influence of different operational strategies on the CSP plant behavior and, particularly, on the ORC performance are explained and discussed. The simulation models of the main sections of the CSP plant were developed in accordance with literature data and specific information given by the manufacturers. The results provide a useful basis for the future development of the management schemes during the experimental campaigns on the CSP plant.

AbstractThis paper presents the experimental set-up built at the DIMCM of Cagliari University to study a thermal energy storage (TES) system based on alumina beads freely poured into a carbon steel tank using air as heat transfer fluid. The system is instrumented with several thermocouples to detect axial and radial temperature distribution as well as reservoir wall temperature. Experimental temperature distribution along the storage system was compared with the numerical ones obtained by a two-phase one dimensional Schumann model. Numerical results show good agreement with the experimental results if thermal properties are considered as temperature dependent and the experimental temperature profile at the top of the bed is used for simulations.