Reduction Of Exergy Losses Research Articles

Exergy analysis of hybrid nanofluids with optimum concentration in a plate heat exchanger

This paper highlights an investigation on the comparative analyses of exergetic performance with optimum volume concentration of hybrid nanofluids in a plate heat exchanger (PHE). Different types of hybrid nanofluids (Al2O3 + MWCNT/water, TiO2 + MWCNT/water, ZnO + MWCNT/water, and CeO2 + MWCNT/water) as coolant have been tested. Proportion of 0.75% of nanofluid has been found to be the optimum volume concentration. The requisite thermal and physical properties of the hybrid nanofluids were measured at 35 °C. Various exergetic performance parameters have been examined for comparing different hybrid nanofluids. The highest reduction in exergy loss of CeO2 + MWCNT/water hybrid nanofluid has been obtained at a concentration of about 24.75%. Entropy generation decreased with the increase in volume concentration. The results established that CeO2 + MWCNT/water hybrid nanofluid can be a promising coolant for exergetic performances in a PHE.

Reviewing the relationship between thermal reservoir parameters and geothermal energy output

This meta-study draws upon contemporary literature to examine parameters of thermal reservoirs and their relationships to geothermal power station output metrics. The objectives of the meta-study are to identify trends and quantify the influence of each parameter on the system as a whole. This study provides a framework for industry and researchers exploring new potential geothermal fields. Six reservoir parameters – well depth, temperature, enthalpy, mass flow rate, thermal gradient and crust thickness – were plotted against the net electrical output per production well (Enet/well) and exergy efficiency (ηB) of 64 geothermal facilities. The meta-study identified that reservoir temperature has the greatest proportionality to power output, with yields above 10MWe exhibited only for high enthalpy reservoirs exceeding 500K. Well depth has the greatest inverse proportionality to exergy efficiency, with upper limit values declining below 80% for wells deeper than 3000m. Well depth has a similar trend line, though lesser correlation, as reservoir temperature to power output. Crust thickness has an inverse correlation to exergy efficiency, with upper limit values dropping from 100% to 65% as thickness increased from 30 to 45km. There was significant clustering of data points in most trendless plots, suggesting a considerable degree of homogeneity between currently tapped reservoirs and turbine efficiencies. The low number of well-defined data trends implies a high degree of complexity arising from the relationships between reservoir parameters that make quantification problematic. Despite this difficulty, examination of the aforementioned parameters suggests that although hotter reservoirs are usually found at greater depths, the hottest and shallowest reservoirs should be prioritized for use in order to return maximal power outputs and reduce exergy losses that occur along large lengths of piping.

Influences of syngas pretreatment on the performance and energy distribution in an IGCC power plant

Raw syngas pretreatment mainly includes cooling and cleanup and has significant influences on the performance of integrated gasification combined cycle (IGCC) power plant. This investigation sets up IGCC system model based on coal water slurry gasification by using Thermoflex software, aiming to survey how syngas quenching, syngas cooling temperature variation and syngas hot desulfurization will affect the performance as well as energy distribution of an IGCC power plant. The validity of IGCC model was verified by simulating the well-known commercial Tampa Polk IGCC power plant via comparing calculation results with reference data. Then four cases of IGCC power plants adopting different raw syngas pretreatment conditions were simulated based on the verified Tampa Polk IGCC model. Calculation results indicated that, comparing with base case, syngas quenching and an increase of 50°C in syngas cooling temperature both caused larger energy loss by syngas condensate water, leading to 7% and 0.4% decrease in power plant net efficiency. On the contrary, syngas hot desulfurization promoted gas turbine power output and prevented energy loss by syngas condensate water, resulting in a rise of net efficiency by 1.3%. Based on detailed energy distribution analyses, it is concluded that a reasonable syngas pretreatment route should be essentially beneficial to reduce exergy loss caused by irreversible heat transfer processes during syngas cooling and cleanup.

The influence of different flow regimes on heat transfer performance and exergy loss of Al2O3/DI-water and CuO/DI-water nanofluids

The convective heat transfer performance and energy efficiency of Al2O3/DI-water and CuO/DI-water nanofluids flowing through a straight vertical tube was experimentally studied for laminar, transitional and turbulent flow regimes. A circulating rig was built to conduct the experiments at constant heat flux and various particle concentrations of 0.20, 0.30 and 0.50wt% for both of the nanofluids. Specifically, the influence of transitional flow on the heat transfer coefficient, friction factor and exergy loss of the nanofluids were analysed. An improvement in the convective heat transfer coefficient for both Al2O3 and CuO nanofluids was found when compared to DI-water at all flow conditions. The maximum enhancement of 25% in heat transfer coefficient was observed for the 0.50wt% CuO nanofluid. At laminar flow conditions, the pumping power was similar for all the working fluids, however, it was more pronounced under the transitional and turbulent flow regimes with an average of 3.9% increment in pumping power for CuO nanofluids. Besides, the highest energy efficiency was found to be 84% with 12.8% and 3.45% average reduction in exergy loss for 0.50wt% of CuO/DI-water nanofluid in laminar and turbulent flow conditions, respectively. New correlations are also proposed based on the experimental results, which can predict the Nusselt number for both nanofluids in laminar and turbulent flow regimes with high accuracy. It was concluded that the copper oxide nanofluid might be a good candidate for heat transfer applications because of their superior heat transfer performance in comparison to other classes of nanofluids as well as DI-water. Therefore, these types of nanofluids can be used to improve the heat transfer in many industrial sectors with more effective way.

Exergy analysis of a solar-powered vacuum membrane distillation unit using two models

A detailed exergy analysis of a solar powered VMD unit was performed using two models: the ideal mixture model and the model using the thermodynamics properties of seawater. The exergy flow rates of process steam, given by the two models differed of about 18%, on average. Despite these differences, the two models agree that during the step of condensation, the most important fraction of exergy was destroyed. Moreover, in this work, two forms of exergy efficiency are calculated. The overall exergy efficiency of the unit with reference to the exergy collected by the solar collector was 3.25% and 2.30% according to Cerci and Sharqawy models, respectively. But, it was 0.182% and 0.128%, when referenced to the exergy of solar radiation, according to Cerci and Sharqawy models, respectively. Besides, the utilitarian exergy efficiency was 9.96%. Since the heat exchanger, the hollow-fiber module and the condenser have a very high exergy performance, then it can be concluded that the enhancement or reduction of exergy losses will be mainly by recovering heat lost in brine discharges and in the rejection of the cooling water. In addition, the influence of the rejection rate on exergy efficiencies was studied.

Exergy-based operation optimization of a distributed energy system through the energy-supply chain

Developing sustainable energy systems is crucial in today's world because of the depletion of fossil energy resources and global warming problems. Application of exergy principles in the context of energy supply systems may achieve efficient energy-supply chains and rational use of energy in buildings. This paper presents an exergy-based operation optimization of a distributed energy system by considering the whole energy-supply chain from energy resources to user demands. The problem is challenging in view of the complicated interactions of energy devices and the modeling of exergy losses. To capture these complicated interactions, energy networks are established with exergy losses modeled at the energy conversion step, which accounts for the largest part of the total exergy loss in the whole energy-supply chain. A multi-objective mixed integer programming problem is formulated. The problem is efficiently solved by the novel integration of surrogate Lagrangian relaxation and branch-and-cut. The Pareto frontier, including the best possible trade-offs between the economic and exergetic objectives, is obtained by minimizing a weighted sum of the total energy cost and total exergy loss occurring at the energy conversion step. Results demonstrate that the use of high-quality energy resources is reduced by the reduction of exergy losses, leading to sustainability of energy supply systems.

Effect of chevron angle on heat transfer performance in plate heat exchanger using ZnO/water nanofluid

The present experimental investigation focuses on the effect of symmetric (β∼30°/30° and 60°/60°) and mixed (β∼30°/60°) chevron angles in PHE on comparative energetic and exergetic performance for nanofluid-water. The particle volume concentration of selected ZnO/water nanofluid being used as coolant lies in range 0.5–2.0%. The experimental findings elucidates the detailed observations of the effect of different chevron angles in PHE on heat transfer rate ratio, heat transfer coefficient ratio, overall heat transfer coefficient ratio, pumping power ratio, performance index ratio, exergy loss, non-dimensional exergy loss, qualitative response of system by exergetic efficiency, total entropy generation and contribution of irreversible heat transfer arises due to frictional losses by Bejan number. Experimental observation confirm that optimum enhancement in heat transfer rate ratio, heat transfer coefficient ratio and optimum reduction in exergy loss are obtained at β∼60°/60° for 1.0% particle volume concentration of ZnO/water nanofluid. Total entropy generation also minimized for this configuration, which is 41.78% and 26.94% for β∼60°/60° as compared to β∼30°/30° and β∼30°/60° in PHE respectively. Bejan number is the highest for β∼60°/60° in PHE indicates reduction in irreversible heat transfer due to frictional losses, thus improving the qualitative response of the system.

Diagnosis of an alternative ammonia process technology to reduce exergy losses

Ammonia production through more efficient technologies can be achieved using exergy analysis. Ammonia production is one of the most important but also one of most energy consuming processes in the chemical industry. Based on a panel of solutions previously developed, this study helps to identify potential areas of improvement using an exergy analysis that covers all aspects of conventional ammonia synthesis and separation. The total internal and external exergy losses are calculated as 3,152 and 6,364kJ/kg, respectively. The process is then divided into five main functional blocks based on their exergy losses. The reforming block contains the largest exergy loss (3,098kJ/kg) and thus the largest potential for improvement including preheating cold feed through an economizer, developing technology towards isobaric mixing, and pressure drop reduction in the secondary reformer as the main contributors to the irreversibility (1,302kJ/kg) in this block. The second largest exergy loss resides in the ammonia synthesis block (3,075kJ/kg) where solutions such as reduced temperature rise across the compressor, proper compressor isolation, reducing undesired components such as argon in the reactor feed, and using lower temperatures for reactor outlet streams, are proposed to decrease the exergy losses. Throttling process in the syngas separator is the key contributing mechanism for the irreversibility (1,635kJ/kg exergy losses) in the gas upgrading block. The exergy losses in the residual ammonia removal block (833kJ/kg exergy losses) are mainly due to the stripper and the absorber column where a modified column design might be helpful. The highest exergy loss in the preheating block belongs to the compressors (518kJ/kg exergy losses) where a lower inlet temperature and better system isolation could help to reduce losses.

증기의 감온·감압과정에서의 엑서지 손실 및 저감방안 분석

The present paper presented and applied an exergy analysis method to evaluate the magnitudes and the locations of exergy losses in the conventional desuperheating and depressurizing process of high pressure and temperature steam delivery system. In addition, for the reduction of exergy losses occurred in conventional process, the present study proposed new alternative processes in which the pressure reducing valve and the desuperheater of conventional process are substituted with steam turbine and heat exchanger, and their effects on exergy loss reduction and exergy efficiency improvement are theoretically investigated and compared. From the present analysis results, the total exergy loss caused in conventional desuperheating and depressurizing process accounted for 66.5% of exergy input and 85% of the total exergy loss was due to the mixing between steam and cold water(e.g desuperheating). However, it was shown from the present analysis results that the present alternative processes can additionally reduce exergy loss by maximum 92.7% of the total exergy loss in conventional process, and can also produce additional and useful energy, the electricity of 220.6 kWh and the heat of 54.3 MJ/hr.

Natural convection in rhombic enclosures with isothermally heated side or bottom wall: Entropy generation analysis

The energy efficient convection systems can be designed by reducing exergy losses. In this context, the analysis on the entropy generation during natural convection in the fluid-filled (Prandtl number, Pr=0.015−1000) rhombic enclosures with various inclination angles (φ) has been carried out for the efficient thermal processing in various applications such as the chemical reactor modeling, underground coal gasification, and nuclear reactors. The enclosure is subjected to the differential heating (case 1) and Rayleigh–Benard convection (case 2). The conduction based static solution occurs only for φ=90∘ and it is observed that the conduction based static solution disappears with a slight perturbation of φ at Rayleigh number, Ra≥2×103 irrespective of Pr in case 2. The active zones of the heat transfer irreversibility (Sθ) and fluid friction irreversibility (Sψ) are found to occur near the isothermal walls for all φs irrespective of Pr in both the cases at Ra=105. In addition, the active zones of Sψ are also found to occur near the adiabatic walls of the cavity for all φs irrespective of Pr in both the cases at Ra=105. Also, the region between the fluid layers of primary circulation cells acts as the strong active zone of Sψ for all φs in case 2 at lower Pr (Pr=0.015) and Ra=105. The total entropy generation (Stotal) and maximum heat transfer rates (Nu¯) are found to be significantly low for φ=30∘ in both the cases at Ra=105 irrespective of Pr. Analysis of heating patterns and geometrical orientations relates the exergy to irreversibilities which establishes that the rhombic cavity (φ=30∘) with the differential heating pattern may be the optimal design based on the energy efficient perspective.

Self-heat recuperative heat circulation processing with thermoelectric device

Self-heat recuperation (SHR) technology has been proven to reduce exergy loss in different process systems, which lead to large energy savings due to its non-combustion process. The purpose of this research is to develop a novel self-heat recuperative heat circulation system using thermoelectric (TE) device as a heat circulator for gaseous and non-gaseous systems. The small ΔT usage of TE heat circulator enables the use of the high efficiency region of TE devices. A mathematical simulation of the performance of a TE heat circulator considering the effects of surface area, heat transfer coefficient and pellet height is presented in this study. Using a TE heat circulator with a surface area of 1m2 to boil 1kg of HFE-7100® an energy reduction of 82% was calculated compared to the conventional fired heater case.

Minimisation of exergy losses in mono high pressure nitric acid process

Nitric acid production plant is self-sufficient in energy. It is a net exporter of energy. But its exergy efficiency is very low. Turbocompressor, which utilises work produced by recovered heat, is used to maintain pressure in the process. Large amount of heat is taken out from cooler condenser by using cooling tower water. In this paper, energy and exergy analysis of mono high pressure nitric acid process is carried out. Both turbocompressor and cooler condenser are accounting to 33.28% of total exergy destruction. An attempt has been made to reduce exergy losses in both equipments by using a practical approach. Heat available in cooler condenser is recovered by using the organic Rankine cycle (ORC) within available practical limits of the plant. Exergy analysis of ORC shows that 42% of the losses in cooler condenser are reduced.

Entropy generation analysis for laminar thermal augmentation with conical strip inserts in horizontal circular tubes

Our previous investigations demonstrated that conical strip inserts have good thermo-hydraulic performances based on evaluation criteria of the First Law of Thermodynamics. The present work is dedicated to further analyze the performances of these inserts from a viewpoint of entropy generation. Effects of alignment method and geometrical parameters on entropy generations of laminar heat transfer in the tubular flow are investigated. Local entropy generations are presented for discussion. Results show that entropy generation rates caused by non-staggered strips are about 81.1% that of staggered alignment, while the heat transfer rates and PECs of the former are about 33.8% and 13.5% larger than the latter counterparts, respectively. Moreover, the entropy generation rate (and thus irreversible loss) caused by heat transfer process overwhelms the counterpart by viscous flow. The total entropy generation number of enhanced tube, ranging between 0.0657 and 0.0975, is most sensitive to geometry angle with a maximum averaged relative variation of 32.2%. Its variation trend with Re is concave with a pit at Re = ∼600. In brief, non-staggered inserts with a larger geometry angle and smaller strip-wall gap and pitch, facilitate a better thermo-hydraulic performance at Re = ∼600 from the viewpoint of exergy loss reduction.

Exergy Analysis of Energy Consumption for Central Air Conditioning System

The energy consumption of several central air conditioning systems in summer was researched by the method of exergy analysis. Combined with actual example,the exergy loss of all the equipments and the exergy efficiency of three systems were calculated. The results show that the exergy efficiency of three systems is very low. Relatively speaking, the exergy efficiency of primary return air conditioning system with supplying air in dew point is highest. The equipment of highest exergy loss is air-conditioned room, while the exergy loss of surface air cooler is smallest. Based on this, several improvement measures were proposed to reduce exergy loss and improve exergy efficiency.

Energy and exergy analysis of fuels

Purpose – The purpose of this study is to carry out energy and exergy analysis of fuels. Production of power and heat in industrialized countries is almost entirely based on combustion of fuels. Usually, combustion takes place in boilers or furnace; well-designed boilers have high thermal efficiencies of > 90 per cent. Even very high efficiencies, close to 100 per cent can be achieved depending on the applied fuel and boiler type. These high thermal efficiencies do suggest that combustion processes are highly optimized and do not need further improvements with regard to their thermodynamic performance. Second law (entropy or exergy) evaluations, however, shows that thermodynamic losses of boiler and furnaces are much larger than the thermal efficiencies do suggest. During combustion, air is predominantly used. When using air, the adiabatic combustion temperature depends only on the properties of fuel and air. The determining parameters for optimal fuel utilization are the fuel type, their composition and moisture content, the air temperature and air factor at combustion inlet. Design/methodology/approach – Following assumptions are made for the analysis: calculation on the basis of 100 kg of dry and ash free fuel entering the control volume; fuel entering the control volume at T0, P0 and reacting completely with air entering separately at T0, P0 to form CO2, SO2, N2 and H2O, which exit separately at T0, P0 (T0 = 298 K; P0 = 1 atm); all heat transfer occurs at temperature T0; and the chemical exergy of the ash has been ignored The availability change and the irreversibility for chemical reactions of hydrocarbon fuels were studied because fuel and dry air composed of O2 and N2 react to form products of combustion in the restricted dead state, and fuel and dry air composed of O2 and N2 react to form products of combustion which end up in the environmental (unrestricted) dead state. The difference between the above two statement, is the chemical availability of the product gases as they proceed from the restricted to the unrestricted dead state. These evaluations were made in terms of enthalpy and entropy values of the reacting species. T0 extend these concepts to the most general situation, it is considered a steady-state control volume where the fuels enters at the restricted dead state, the air (oxidant) is drawn from the environment, and the products are returned to the unrestricted dead state. Findings – It is evident from the analysis that an air factor of 1.10-1.20 is sufficient for liquid fuels, whereas solid fuels will require air factors of 1.15–1.3. When the temperatures of the products of combustion (Tp) are cooled down to that of T0, the maximum reversible work occurs. From the analysis, it is clear that the rather low combustion temperature and the need for cooling down the flue gases to extract the required heat are the main causes of the large exergy losses. The maximum second law efficiency also occurs when Tp is set equal to T0. The maximum second law efficiency per kilo mole of fuel is found to be 73 per cent, i.e. 73 per cent of the energy released by the cooling process could theoretically be converted into useful work. It is evident that reducing exergy losses of combustion is only useful if the heat transferred from the flue gas is used at high temperatures. Otherwise, a reduction of exergy loss of combustion will only increase the exergy loss of heat transfer to the power cycle or heat-absorbing process. The exergy loss of combustion can be reduced considerable by preheating combustion air. Higher preheat temperatures can be obtained by using the flue gas flow only for preheating air. The remainder of the flue gas flow can be used for heat transfer to a power cycle or heat-absorbing process. Even with very high air preheat temperatures, exergy losses of combustion are still > 20 per cent. The application of electrochemical conversion of fuel, as is realized in fuel cells, allows for much lower exergy loses for the reaction between fuel and air than thermal conversion. For industrial applications, electrochemical conversion is not yet available, but will be an interesting option for the future. Originality/value – The outcome of the study would certainly be an eye-opener for all the stakeholders in thermal power plants for considering the second law efficiency and to mitigate the irreversibilities.

A novel nuclear combined power and cooling system integrating high temperature gas-cooled reactor with ammonia–water cycle

A nuclear ammonia–water power and refrigeration cogeneration system (NAPR) has been proposed and analyzed in this paper. It consists of a closed high temperature gas-cooled reactor (HTGR) topping Brayton cycle and a modified ammonia water power/refrigeration combined bottoming cycle (APR). The HTGR is an inherently safe reactor, and thus could be stable, flexible and suitable for various energy supply situation, and its exhaust heat is fully recovered by the mixture of ammonia and water in the bottoming cycle. To reduce exergy losses and enhance outputs, the ammonia concentrations of the bottoming cycle working fluid are optimized in both power and refrigeration processes. With the HTGR of 200MW thermal capacity and 900°C/70bar reactor-core-outlet helium, the system achieves 88.8MW net electrical output and 9.27MW refrigeration capacity, and also attains an energy efficiency of 69.9% and exergy efficiency of 72.5%, which are higher by 5.3%-points and 2.6%-points as compared with the nuclear combined cycle (NCC, like a conventional gas/steam power-only combined cycle while the topping cycle is a closed HTGR Brayton cycle) with the same nuclear energy input. Compared with conventional separate power and refrigeration generation systems, the fossil fuel saving (based on CH4) and CO2 emission reduction of base-case NAPR could reach ∼9.66×104t/y and ∼26.6×104t/y, respectively. The system integration accomplishes the safe and high-efficiency utilization of nuclear energy by power and refrigeration cogeneration.

Exergy analysis for fuel reduction strategies in crude distillation unit

Inefficient furnaces and heat exchangers contribute to the depletion of fossil fuel problem due to higher fuel demand and higher carbon emission. The method of exergy analysis is applied to the furnace and crude preheat train (CPT) in a crude distillation unit (CDU) to determine performance benchmark of the system. This paper presents exergy analysis and strategies to reduce exergy loss through process modification. The highest exergy loss was found to be located at the inlet furnace. The proposed options for fuel reduction strategies are reduction of heat loss from furnace stack and overall cleaning schedule of CPT. The feasibility and economic analysis for both options are investigated. From the results, overall cleaning schedule of CPT contributes to the highest energy saving of 5.6%. However, reduction of heat loss from furnace stack is the highest cost saving by about 6.4%.

Self-heat Recuperative Heat Circulator with Thermoelectric Device

Self-heat recuperation (SHR) technology has been proven to reduce exergy loss in different process systems, which lead to large energy savings due to its non-combustion process. The purpose of this research is to develop a novel self-heat recuperative heat circulation system using thermoelectric (TE) device as a heat circulator for non-gaseous systems. Most research involving TE coolers is related to maximizing the temperature difference (ΔT) of a device, whereas in self-heat recuperative heat circulator, a large ΔT is not required, but only a minimum temperature difference between the surfaces of the TE device and process fluid (ΔTmin) for self-heat exchange is required in order to use it as a heat circulator. The lower ΔT can improve COP of TE devices significantly.

Dish Stirling Advanced Latent Storage Feasibility

Dish-Stirling systems have been demonstrated to provide high-efficiency solar-only electrical generation, holding the world record at 31.25%. This high efficiency results in a system with a high possibility of meeting the DOE SunShot goal of $0.06/kWh. Current dish-Stirling systems do not incorporate thermal storage. For the next generation of non-intermittent and cost-competitive solar power plants, we propose a thermal energy storage system that combines latent (phase-change) energy transport and latent energy storage in order to match the isothermal input requirements of Stirling engines while also maximizing the exergetic efficiency of the entire system.This paper reports on the technical advantages and challenges of dish Stirling with storage, to make a preliminary estimate as to the technical feasibility of such a system. The proposed system with storage incorporates high temperature latent transport and latent storage, providing an exergetic match to the isothermal input of the Stirling cycle. The transport from the receiver to the storage, and from storage to the engine, is accomplished with advanced sodium heat pipes. The storage is in a solid-liquid phase change material (PCM), likely a metallic eutectic to reduce exergy losses in thermal conduction.We model a dish Stirling system at a block level, using a combination of real data from several dish systems with and without heat pipe transport, and determine annual energy production and revenue streams based on Barstow California weather data and Southern California Edison Time of Day pricing. We optimize the system on solar multiple, capacity of storage, and several operational strategies.We find that a storage system using metallic eutectic phase change storage results in a feasible physical embodiment, with mass, volume, and complexity suitable for 25kWe dish Stirling systems. The results indicate a system with 6hours of storage and a solar multiple of 1.25 provides the optimum impact to LCOE and profit for the range of cases studied.A storage system applied to dish Stirling will leverage the current high performance systems, increasing the value to the utilities and transmission entities. A feasible embodiment has been proposed, which with sufficient development will re-establish dish Stirling as a leading energy option.

On the improvement of annual performance of solar thermal power plants through exergy management

SUMMARY Advancing in the learning curve of solar thermal power plants (STPP) requires detailed analysis for reducing exergy losses in the energy conversion chain. This requirement should be applied to any configuration proposed for the solar field and the power block. The aim of this work is to perform this type of analysis for two ways of structuring the power plant. The first plant structure consists of a subdivision of the solar collector field into specialized sectors with specific goals conveying different requirements in temperature. The second plant structure is based on a dual thermal energy storage system with a defined hierarchy in the storage temperature. The subdivision of the solar field into different sectors reduces the exergy losses in the heating process of the working fluid. Moreover, the average temperature of the heat transfer fluid in the solar field decreases when it is compared to the conventional solar field, reducing this way the exergy losses in the collectors. The dual thermal energy storage system is devised for keeping the exergy input to the power block at its nominal level for long periods of time, including post-sunset hours. One of the storage systems gathers a fluid heated up to temperatures above the nominal value and the second one is the classical one. The combination of both allows the manager of the plant to keep the nominal operation of the plant for longer periods than in the case of classical system. Numerical simulations performed with validated models are the basis of the exergy analyses. The configurations are compared to a reference STPP in order to evaluate their worth. Furthermore, the behaviour of the configurations is analysed to study the irreversibility of the included devices. Special attention is paid to the storage systems, as they are a key issue in both plant structures. Copyright © 2013 John Wiley & Sons, Ltd.