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Energy storage systems are increasingly gaining importance with regard to their role in achieving load levelling, especially for matching intermittent sources of renewable energy with customer demand, as well as for storing excess nuclear or thermal power during the daily cycle. Compressed air energy storage (CAES), with its high reliability, economic feasibility, and low environmental impact, is a promising method for large-scale energy storage. Although there are only two large-scale CAES plants in existence, recently, a number of CAES projects have been initiated around the world, and some innovative concepts of CAES have been proposed. Existing CAES plants have some disadvantages such as energy loss due to dissipation of heat of compression, use of fossil fuels, and dependence on geological formations. This paper reviews the main drawbacks of the existing CAES systems and presents some innovative concepts of CAES, such as adiabatic CAES, isothermal CAES, micro-CAES combined with air-cycle heating and cooling, and constant-pressure CAES combined with pumped hydro storage that can address such problems and widen the scope of CAES applications, by energy and exergy analyses. These analyses greatly help us to understand the characteristics of each CAES system and compare different CAES systems.

Lifetime prediction and improvement of solid oxide fuel cell (SOFC) devices require a reliable electrochemical model that supports the implementation of degradation phenomena. This study comprises two parts. This Part I describes the calibration of an electrochemical model based on physical principles for simulation at the stack scale. Part II presents the further implementation of degradation models. A distinction is made between the two most common cathode materials, lanthanum strontium manganite and lanthanum strontium cobalt ferrite. The experimental data used for the parameter estimations was gathered by two segmented setups. The calibrations enabled to reproduce adequately the measurements over a wide range of operating conditions. The optimal values of the physical parameters were inside the ranges reported in literature. Unambiguous discrimination could not be achieved between variations (i) in the choice of electrode rate-determining steps, (ii) data on the properties of the materials found in literature and (iii) empirical relations for the steam-methane reforming reaction. However, these model variations do not affect significantly the predicted magnitudes and distributions of the field variables assumed to govern the degradation processes at the SRU scale, compared with the uncertainties on the degradation phenomena to be implemented in Part II. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3596433] All rights reserved.

Hybrid solar thermal power plants (with parabolic trough type of solar collectors) featuring gas burners and Rankine steam cycles have been successfully demonstrated by California's Solar Electric Generating System (SEGS). This system has been proven to be one of the most efficient and economical schemes to convert solar energy into electricity. Recent technological progress opens interesting prospects for advanced cycle concepts: a) the ISCCS (Integrated Solar Combined Cycle System) that integrates the parabolic trough into a fossil fired combined cycle, which allows a larger exergy potential of the fuel to be converted. b) the HSTS (Hybrid Solar Tower System) which uses high concentration optics (via a power tower generator) and high temperature air receivers to drive the combined cycle power plant. In the latter case, solar energy is used at a higher exergy level as a heat source of the topping cycle. This paper presents the results of a thermoeconomic investigation of an ISCCS envisaged in Tunisia. The study is realized in two phases. In the first phase, a mixed approach, based on pinch technology principles coupled with a mathematical optimization algorithm, is used to minimize the heat transfer exergy losses in the steam generators, respecting the off design operating conditions of the steam turbine (cone law). In the second phase, an economic analysis based on the Levelized Electricity Cost (LEC) approach was carried out for the configurations, which provided the best concepts during the first phase. A comparison of ISCCS with pure fossil fueled plants (CC+GT) is reported for the same electrical power load. A sensitivity analysis based on the relative size of the solar field is presented.This paper was presented at the ECOS'00 Conference in Enschede, July 5-7, 2000

A model-based Design of Experiments method was employed for the optimisation of measurements on a Solid Oxide Fuel Cell (SOFC). Based on a simplified SOFC model, a variation of the D-optimality was used as optimisation criterion for the calculation of optimal experimental designs (determinant of the covariance matrix with weighting factors). Solutions for different numbers of design points were calculated and the behaviour of optimisation criteria as functions of the number of design points as well as of the number of repetitions of measurements was analysed. A new type of graph was introduced which depicts the behaviour of optimisation criteria for constant number of measurements. This approach showed that, for constant numbers of measurements, the precision is higher and therefore the reliability in the cell’s model identification is improved when repeated measurements of a small set of optimal design points are effectuated, instead of many different measurements. Finally, a sensitivity analysis was performed showing the influence of the parameter values on the values of the optimisation criterion and the optimal measurements. The used methodology and its theoretical conclusions may be used as a basis for development of diagnostics tools or filtering existing data for optimal parameter estimations.

The aim of the paper is to present an energy system optimization method, based on the Fuel Impact Formula, able to overcome typical limitations of previous formulations. In particular, the methodology allows time dependent production levels to be considered and on-off operation and presence-absence of any component to be modelled by means of binary decision variables and inequality constraints. These often happen if the synthesis and operation of Combined Heat and Power (CHP) systems are considered at the same time. Moreover, the effect of replacing actual not linear thermodynamic inputs-output relations of each component with linear, or even proportional ones, is highlighted in the paper. Finally, an example of application is shown, dealing with a multi-component DH and CHP system in the tertiary sector.

An atmospheric combustor model with optical access for non-premixed swirl-stabilized flames was developed in order to investigate the combustion behavior of gas turbine fired with low caloric syngases and to create a data-base for the validation of numerical combustion models. In the present work, newly developed fully 3-D PIV measurements of the combustor aerodynamics at cold conditions are presented together with detailed wall temperature measurements in hot conditions. These data are respectively used to validate the combustor numerical model from an aerodynamic point of view and as boundary conditions when combustion simulations with different approaches are carried out. Thermocouple traverses data and global emissions analyzers results are then used as reference data for combustion models validation. Propane, as reference fuel, and a synthetic mixture of CH4, CO, CO2, and H2 are considered. The reactive flow was solved with two modeling approaches, namely the ED-FR and the flamelet combustion models. With the EDFR approach the propane-air combustion simulation was performed with a simple two-step reaction mechanism, while the syngas-air combustion case was simulated with a four-step one. Because flamelet model can treat multi-step chemical mechanisms with limited computational effort, a GRI 3.0 comprehensive mechanism and a reduced mechanism developed by Smooke have been used in this study to reproduce the syngas combustion process. As a whole, ED-FR model provide good agreement with the experimental thermal field while flamelet models correctly predicts the temperature trend, but with some local overestimation. As far as emissions are concerned, the Smooke flamelet approach proved to be the most reliable.

This work is part of a study aiming to achieve high efficiency and low emissions in a marine propulsion system. In order to significantly enhance the efficiency of a propulsion plant, it is possible to recover the exhaust gas heat normally rejected to the atmosphere and the heat of the cooling water usually rejected to the sea. The study examines the possibility of energy recovery applying ORC (Organic Rankine Cycle) technology; this technology is very effective for recovering waste heat from low temperature sources, both from the thermodynamic and the economic standpoint. When a "combined cycle" ORC-diesel engines set up is considered for this size of engines, an increase in power output of about 10% can be expect. In addition, a significant amount of heat is released at low temperature and could be used by other ship services, or by other thermal users, in case of land based applications. In the present study several possible thermodynamic cycles are simulated using the Aspen® code, considering also different working fluids. The results are evaluated in both thermodynamics and economics terms.