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[en] Solar thermal is a promising renewable energy supplying technology that is being introduced slowly in industrial activities. Integration of solar thermal energy in a complex process, in combination with other energy provision devices, must be evaluated carefully, in order to obtain its maximum capacity and performance. This study tackles the integration of the thermosolar technology in a dairy process, sited in a climatic zone where diffuse irradiation is the meaningful one, based on two well developed thermodynamic tools: pinch and exergy analysis. Both tools have been utilized in the context of a low and middle temperature for the production of hot water for the steps of the dairy process. A combined implementation of both methodologies, helped by economical estimation, provides a powerful tool that allows finding the best integration of thermosolar and, by this, taking substantial design decisions. - Highlights: ► Integration of solar thermal energy in an industrial process was assessed. ► Pinch and exergy analysis were used to determine the optimal energy supply configuration. ► Solar thermal energy reduces the fossil energy demand with a moderate investment.
[en] The exergy analysis (availability or second law analysis) is applied to the photovoltaic thermal solar collector. Photovoltaic thermal collector is a special type of solar collector where electricity and heat are produced simultaneously. The electricity produced from the photovoltaic thermal collector is all converted into useful work. The available quantity of the heat collected can readily be determined by taking into account both the quantity (heat quantity) and quality ( a function of temperature) of the thermal energy. Therefore, using the concept of exergy allows heat produced from the thermal collector and the electricity generated from the photovoltaic cells to be compared or to be evaluated on the basis of a common measure such as the effectiveness on solar energy collection or the total amount of available energy. In this paper, the effectiveness of solar energy collection is called combined photovoltaic thermal exergy efficiency. An experimental setup of a double pas photovoltaic thermal solar collector has been deigned, fabricated and tested. (author)
[en] Highlights: ► A new spectral decomposing approach has been introduced for concentrating PVs. ► Both heating and electrical energy have been gained by CPVCS. ► The full spectrum of solar energy has been utilized by the novel CPVCS. ► The energy and exergy efficiencies were found as 7.3% and 1.16% respectively. ► The energy production cost has been stated as 6.37 $/W. - Abstract: In the present study, a novel Concentrating Photovoltaic Combined System (CPVCS) based on the spectral decomposing approach is introduced, modeled, tested experimentally and evaluated thermodynamically and economically. In this study, energy and exergy analyses of the system have been evaluated, economical analysis has been performed and the experimental results have been compared to data obtained by the control system. As a result, energy efficiencies of concentrator, vacuum tube and overall CPVCS have been determined to be 15.35%; 49.86%; and 7.3% respectively. Similarly the second law (exergy) efficiencies of concentrator, vacuum tube and overall CPVCS are 12.06%; 2.0%; and 1.16% respectively. The cost of energy production has been stated as 6.37 $/W and it is predicted that this value could be decreased by improving the system performance
[en] Highlights: • A solar-driven Kalina cycle is investigated by advanced exergoeconomic analysis. • The highest exergy efficiencies are related to the separator and turbine with the values. • Rotary machinery have more than 83% avoidable share of exergy destruction rate. - Abstract: A Kalina cycle driven by solar energy resource is evaluated by conventional exergy and exergoeconomic analysis methods. Because conventional exergy analyses isn’t able to give information about costs of the irreversibilities and investment, advanced exergy is investigated. Based on the conventional exergy analyses, the most exergy destruction occurs in a heater with a value of 94.44 kW. Also the highest exergy efficiencies are related to the separator and turbine with the values of 99.67% and 89.81%, respectively. Advanced exergy analyses demonstrates absorber (1.3 $/h) and one of the pumps (0.009 $/h) have the highest and lowest exergy destruction cost rate, respectively. Also the results show turbine (85.88%) and separator (1.105%) have the highest and lowest exergoeconomic factor, respectively. Finally, in order to determine optimum point of the inlet temperatures and pressure ratio of the pumps and turbine (rotary machines), a parametric study is applied at different stages.
[en] This paper studies the experimental and exergy analysis of solar still with the sand heat energy storage system. The cumulative yield from solar still with and without energy storage material is found to be 3.3 and 1.89 kg/m2, respectively for 8-h operation. Results show that the exergy efficiency of the system is higher with the least water depth of 0.02 m (mw = 20 kg). Competitive analysis of second law efficiency shows that the exergy efficiency improves the system by 30% than conventional single slope solar still without any heat storage. The maximum exergy efficiency with energy storage material is found as 13.2% and it is less than the conventional solar still without any material inside the basin.
[en] In this work, the thermodynamic performance of a single slope solar still with cotton cloth energy storage medium was compared with a simple solar still without energy storage. Two solar stills with similar dimensions (one with cotton cloth energy storage and another without energy storage) were fabricated and investigated its performance under the hot humid climatic conditions of Chennai in India during the summer months of 2017. The performance was evaluated in terms of energy and exergy analysis based on first and second law of thermodynamics, respectively, for 2 mm, 4 mm, 6 mm and 8 mm cotton cloth thickness. The results showed that the maximum energy and exergy efficiency of a solar still was observed to be 23.8% and 2.6%, respectively, for 6 mm cotton cloth thickness. The results confirmed that the cotton cloth regenerative medium has enhanced the still productivity by about 24.1% when compared to the solar still without heat storage.
[en] Highlights: • Single slope solar still coupled with N-identical PVT FPCs has been proposed. • EPBT of the proposed still is found to be 89.90% lower than that of N-PVT-CPC-SS. • An improvement of 27.5% in water production cost over N-PVT-CPC-SS is achieved. • LCCE of N-PVT-FPC-SS is 56.25% higher than that of N-PVT-CPC-SS. - Abstract: This paper communicates the improvement in performance of single slope solar still (SS) by including N identical partially covered photovoltaic thermal (PVT) collectors. Three models have been considered namely, SS included with N identical partially covered PVT flat plate collectors (N-PVT-FPC-SS); SS included with N identical partially covered PVT compound parabolic concentrator collectors (N-PVT-CPC-SS) and conventional SS (CSS). In this work, yearly production of potable water, energy, exergy, energy metrics, cost of distillate output and cogeneration efficiency have been computed for the proposed N-PVT-FPC-SS at 0.14 m water depth under optimized condition for New Delhi, India. Results obtained have been compared with results reported by researchers previously and it has been concluded that exergy based energy payback time is lower by 89.90% and 44.45%; energy production factor is higher by 46.67% and 31.11%; life cycle conversion efficiency is higher by 56.25% and 37.50% and production cost of potable water is lower by 27.05% and 3.20% for the proposed N-PVT-FPC-SS than N-PVT-CPC-SS and CSS respectively. The proposed system can produce potable water on commercial scale and at the same time, it can meet DC electrical power need.
[en] Ground source heat pumps (GSHPs), often referred to as geothermal heat pumps (GHPs), offer an attractive option for heating and cooling residential and commercial buildings owing to their higher energy efficiency compared with conventional systems. GSHPs have been used for four years in the Turkish market, although they have been in use for more years in developed countries. The purpose of this study is to present an energy and exergy analysis of a GSHP system with a 50 m vertical 1.25 in. nominal diameter U-bend ground heat exchanger. This system was applied to a 65 m2 room in the Solar Energy Institute, Ege University, Izmir, for the first time at the university level in Turkey. The Institute, built in 1986, has a livable floor area of 3000 m2 and uses passive solar techniques. The heating and cooling loads of the room studied were 3.8 and 4.2 kW at design conditions, respectively. The system was commissioned in May 2000, and performance tests have been conducted since then. The exergy transports between the components and the consumptions in each of the components of the GSHP system were determined for the average measured parameters obtained from the experimental results in February 2001. The exergy diagram (the Grassmann diagram) was also presented for the GSHP system studied to give quantitative information regarding the proportion of the exergy input that is dissipated in the various system components
[en] Energy systems are meaningful devices which are based on basic laws of physics to take energy at one end and transform it into another form with optimum efficiency. Scientists, engineers always strive to make systems more efficient and lighter. This motive acts as driving force to bring about new technologies, materials and alternative approaches. Nanofluids are that kind of materials which have revolutionized energy absorbing, transporting and storage systems. Various parameters which are cardinal in thermal performance enhancement are drastically modified when material changes into nanoform. These parameters are thermal conductivity, heat transfer coefficient, optical extinction coefficient, electrical conductivity, viscosity, density, metallic property. When materials changes its phase from bulk to nano, surface to volume ratio changes tremendously. In our experimental analysis we have chosen nanofluids (MgO+CNTs)/H2O Hybrid for evaluating performance of and flat plate solar collector for exergy efficiency, entropy generation and thermal efficiency. Exergy efficiency indicates how system is efficient to convert available energy into useful work. We have gone through preparation of nanofluid along with characterization. Experimental analysis established that at 1% volume concentration and the flow rate 21/min exergetic efficiency (second law efficiency) for (MgO+CNTs)/H2O nanofluid is enhanced by ∼28 % compare to water, ∼13% compare to MgO. Entropy generation rate, which is penalty increases insignificantly at lower concentration for MgO hybrid compare to MgO. But enhancement in exergy efficiency dominates over increment in entropy generation rate. We can conclude that nanofluid based energy transporting systems are more efficient in terms of performance and energy saving. (author)
[en] This paper presents the development of a bottom-up stock model to perform a holistic energy study of the Mexican non-domestic sector. The current energy and exergy flows are shown based on a categorisation by climatic regions with the aim of understanding the impact of local characteristics on regional efficiencies. Due to the limited data currently available, the study is supported by the development of a detailed archetype-based stock model using EnergyPlus as a first law analysis tool combined with an existing exergy analysis method. Twenty-one reference models were created to estimate the electric and gas use in the sector. The results indicate that sectoral energy and exergy annual input are 95.37 PJ and 94.28 PJ, respectively. Regional exergy efficiencies were found to be 17.8%, 16.6% and 23.2% for the hot-dry, hot-humid and temperate climates, respectively. The study concludes that significant potential for improvements still exists, especially in the cases of space conditioning, lighting, refrigeration, and cooking where most exergy destructions occur. Additionally, this work highlights that the method described may be further used to study the impact of large-scale refurbishments and promote national regulations and standards for sustainable buildings that takes into consideration energy and exergy indicators. - Highlights: • A bottom-up physics model was developed to analyse the Mexican commercial stock. • A detailed energy analysis by climate, buildings and end-uses is presented. • The Mexican non-domestic sector as a whole has an exergy efficiency of 19.7%. • The lowest regional exergy efficiency is found at the hot-humid region with 16.6%. • By end use, the highest exergy destructions are caused by HVAC and lighting