Solar Organic Rankine Cycle System Research Articles

Comparison Of The Electricity Generation Potentials Of Solar ORC Designed With Different Fluids Depending On Instantaneous Solar Radiation In Four Districts Of Türkiye

In this study, the solar Organic Rankine Cycle (ORC) system was analyzed to meet some of the electrical energy needed in large and medium-sized buildings and large enterprises such as hotels from solar energy. A simulation study was conducted for different districts in Türkiye that are rich in solar energy potential. These counties and the provinces they are affiliated with; Silifke-İçel, Alanya-Antalya, Bodrum-Muğla, Çeşme-İzmir. The power value transferred to the ORC was determined by considering the instantaneous radiation values and sunshine durations for the districts. The performance of solar ORC was determined by comparing fluids from three different organic fluid types. Organic fluids and types used in design; benzene-aromatic hydrocarbon, cyclohexane-alkane, octamethylcyclotetrasiloxane (D4)-siloxane. Considering the maximum electrical energy values obtained from Solar ORC in the summer months, it was seen that 205 MWh electricity generated was obtained for Silifke with benzene at a heat source temperature of 223 oC in July. Maximum solar parabolic trough collector (PTC) specific electric power value was determined as 59.52 W/m2 in Alanya district with benzene in June. When the four districts are evaluated together, it has been determined that benzene performs better than cyclohexane by 3.8% on average and 23% better than D4. When the annual electrical energy values are examined, the highest production was determined as 1625 MWh with benzene fluid in Alanya district.

A novel solar-driven Organic Rankine Cycle system based on the two-stage solar thermal collection and accumulation

Solar thermal power has attracted much attention because it is instrumental to solar energy storage and power grid peak shaving. Among the various solar thermal power technologies, the Organic Rankine Cycle stands out as a prevalent choice for low and intermediate-temperature (80 – 200 °C) solar thermal power generation applications. However, it is required of the concentrating solar collectors for medium temperature supply and its performance is greatly affected by the off-design operation owing to variable solar irradiance. In this paper, a novel solar-driven Organic Rankine Cycle system that consists of a two-stage solar thermal collection and accumulation design is proposed to solve the above issues. Two-stage non-concentrating solar plants are adopted to harvest global solar irradiance and regulate system operation. Two-stage energy accumulators can not only mitigate the influence of the solar irradiance fluctuation on the Organic Rankine Cycle off-design running but also enhance the temperature drop of thermal energy storage. Through the experimental test and numerical simulation, the results indicate that the influence of solar irradiance on the Organic Rankine Cycle steady operation has been weakened (reducing power output fluctuation range by approximately 70%), and the overall system efficiency has also been improved by 43.85%. Consequently, the solar Organic Rankine Cycle system proposed in this paper exhibits superior thermal performance compared to the conventional systems and is conducive to the advancement of the non-concentrating solar thermal power system.

Performance Assessment of Direct Vapor Generation Solar Organic Rankine Cycle System Coupled with Heat Storage

Phase change materials employed as thermal energy storage can aid in maximizing the use of stored solar energy. The current research examined the impact of three kinds of phase change materials (PCMs) on the dynamic performance of a solar organic Rankine cycle (ORC) system based on a direct vapor production. A number of evacuated flat plate collectors, a condenser, an expander, and an organic fluid pump make up this system. The thermodynamic cycle model of the direct vapor generation (DVG) solar ORC system was combined with the finite difference model of a phase change material heat storage tank created in MATLAB. The effect of PCMs (Organic, Inorganic and Eutectic PCMs) on the collector, ORC, and system efficiency, net power output, PCM temperature, and heat stored was studied weekly, monthly, and annually. Among the selected PCMs, Mg(NO3)2.6H2O had the highest system efficiency at 9.34%; KNO3-NaNO2 had the highest net power output at 33.80 kW; and MgCl2.6H2O stored the maximum energy of 20.18 MJ annually. Under the given operational and boundary conditions, the spring and fall were preferable to the summer and winter months for storing heat from phase change materials.

Application of novel framework based on ensemble boosted regression trees and Gaussian process regression in modelling thermal performance of small-scale Organic Rankine Cycle (ORC) using hybrid nanofluid

This work examined the thermal performance of a small-scale solar organic Rankine cycle system, in which a flat plate solar collector was employed to supply heat to the organic Rankine cycle system. In the ORC system, WO 3 +MWCNT/water nanofluid was employed for the solar collector, while MWCNT/R141b nano-refrigerant was used in the ORC system. In the first stage, the thermal and exergy efficiency of the ORC system was experimentally examined at different flow rates and concentrations of nanofluid. As a result, the peak thermal efficiency of 73.21% was attained at 3 L per minute (lpm) of nanofluid flow rate and 1.5 vol% of nanofluid concentration. Moreover, a significant increase in energy and exergy efficiency by 8.52% and 6.30%, respectively, was observed for 0.5 vol% of nanofluid concentration and 3 lpm of nanofluid flow rate in the collector. In the second stage, the experimental data was utilized to develop contemporary ensemble machine learning algorithms such as boosted regression trees (BRT) and Gaussian process regression (GPR) aiming to predict the solar collector's energy efficiency and the ORC system's energy-exergy efficiency. The GPR-based models performed exceptionally well as Pearson's coefficient (R), coefficient of determination (R 2 ), mean squared error (MSE), and root mean squared error (RMSE) were 0.9999, 0.9998–0.9999, 0.0015–0.0524, and 0.0124–0.0723, respectively. For BRT-based model the R, R 2 , MSE and RMSE were 0.9604–0.9949, 0.97–0.99, 0.0969–0.8783, and 0.3113–0.9372. Theil's U2 was employed to calculate the uncertainty in the prediction framework, which was determined to be in the range of 0.002–0.00369 for GPR and 0.00228–0.1414 for the BRT-based model. Overall, both machine learning algorithms performed well, although GPR did better than BRT across the board. • Thermal performance of a solar-aided ORC system was modeled with GPR and BRT. • Peak thermal efficiency of ORC system reached 73.21% at 3 lpm of nanofluid flow rate. • Energy and exergy efficiency were increased by 8.52% and 6.30% as using nanofluid. • GPR-based models worked with exceptionally good indicators of R, R 2 , MSE, and RMSE. • Nanofluid flow rates were the most influential factor on ORC system performance.

Hybrid solar desalination system for generation electricity and freshwater with nanofluid application: Energy, exergy, and environmental aspects

In this investigation, a hybrid energy conversion system is proposed and evaluated for energy, exergy, and environmental criteria for generating power and freshwater. The system comprises of a Humidifier Dehumidifier Desalination (HDD) system for producing freshwater, an organic Rankine cycle system for generating electric power, and a solar Parabolic Trough Concentrator for absorbing solar energy as the desalination heat source. Different working fluids including Al2O3, Cu, CuO, TiO2, and MWCNT nanoparticles in oil as the base fluid are examined. The influence of different nanofluids on the performance of the system is investigated as the main goal of this study. Environmental impacts of the suggested system are studied. Results show that the thermal efficiency of the Parabolic Trough Concentrator was with the application of Cu/oil nanofluid as about 62.4%. It is illustrated that the amount of freshwater production can be increased by raising the nanofluid concentration. The freshwater production varies between nearly 15.28 kg/h to 15.46 kg/h with the application of nanofluid. The organic Rankine cycle net work and total efficiency improved with increasing nanofluid concentration. Also, it can be concluded that the application of MWCNT/oil with a concentration of 5% volume fraction has shown the highest exergy efficiency of 4.7%. It was concluded the suggested desalination system with application of the solar organic Rankine cycle system, in addition to producing fresh water and power, significantly reduced amounts of CO2 emissions in the environment. Finally, it should be mentioned that the ideal system was analyzed and the gains from the use of nanofluids are very small.

Solar organic Rankine cycle and its poly-generation applications – A review

The solar Organic Rankine Cycle system seems to be one of the most reliable renewable energy-based technologies to satisfy major energy demands. Solar organic Rankine cycle based poly-generation systems are energy-efficient systems that can generate various useful energy outputs, including electricity, heating, cooling, drying, desalination, and hydrogen. As a result, combining solar organic Rankine systems with poly-generation units is the most efficient way of generating multiple useful outputs while still using a renewable energy source. The present review study focuses on exploiting the solar organic Rankine cycle and its poly-generation applications. Novel experimental and numerical study of different researchers focusing on the Solar Organic Rankine cycle with different solar collectors’ integration along with different organic working fluids are discussed in this paper. The review study mainly focuses on the cogeneration, trigeneration, and poly-generation applications of the solar organic Rankine cycle. In the end, the future scope part of this study will surely help the researcher and engineers for further improvement in the solar organic Rankine system.

Design, modelling and optimisation of a small-scale Solar Organic Rankine Cycle system for rural power generation

This research study develops the design and model of a Solar Organic Rankine Cycle (SORC) coupled to a bio-digester for small-scale generation in rural areas, in Betulia, Colombia. Moreover, the model is optimised employing a Genetic Algorithm with the software Matlab and the thermodynamic library CoolProp. The objective variables were the mass flow rate of the working fluid, the pressure and temperature of the expander inlet, the solar collectors’ type and the temperature of the water circuit for the bio-digester. The results indicate an overall efficiency between 8.42 and 9.45% with a Levelized Cost of Energy (LCE) between 3.85 and 5.63 £/W. Additionally, the power output is directly related to the mass flow rate of the working fluid. Likewise, increasing the scale of the SORC decreases the LCE. Finally, the results suggest that a superheated fluid reduces the efficiency and the LCE and can deliver more heat to the bio-digester. It is advisable the utilisation of a scroll expander and a counter-flow plate exchanger with a Direct Vapour Generation configuration. The model is a flexible tool capable of integrating more equations and components, with the evaluation of different fitness functions.

A holistic thermoeconomic assessment of small-scale, distributed solar organic Rankine cycle (ΟRC) systems: Comprehensive comparison of configurations, component and working fluid selection

In this paper, results from comprehensive thermoeconomic assessments of small-scale solar organic Rankine cycle (ORC) systems are presented based on weather data in London, UK, which is taken as representative of a temperate climate with modest temperature changes, mild winters and moderate summers. The assessments consider a range of: (i) solar collector types (flat-plate, evacuated-tube, and evacuated flat-plate collectors); (ii) power cycle configurations (basic/recuperative, partial/full evaporating, and subcritical/transcritical cycles); (iii) expander types (scroll, screw, and piston) and designs; and (iv) a set of suitable working fluids. All possible solar-ORC system designs are optimised by considering simultaneously key parameters in the solar field and in the power cycle in order to obtain the highest electricity generation, from which the best-performing systems are identified. Selected designs are then subjected to detailed, annual simulations considering the systems’ operation, explicitly considering off-design performance under actual varying weather conditions. The results indicate that, among all investigated designs, solar-ORC systems based on the subcritical recuperative ORC (SRORC), evacuated flat-plate collectors (EFPCs), a piston expander, and isobutane as the working fluid outperforms all the other system designs on thermodynamic performance, whilst having the highest annual electricity generation of 1,100 kW·h/year (73 kW·h/year/m2) and an overall thermal efficiency of 5.5%. This system also leads to the best economic performance with a levelised cost of energy (LCOE) of ~1 $/kW·h. Apart from the specific weather data used for these detailed system simulations, this study also proceeds to consider a wider range of climates associated with other global regions by varying the solar resource available to the system. Interestingly, it is found that the optimal solar-ORC system design remains unchanged for different conditions, however, the LCOE can drop below 0.35 $/kW·h and payback times can be shorter than 16 years in high solar-resource regions, even in the absence of incentives that would otherwise lead to even better economic performance. This work complements previous efforts in the literature by considering the full design and operational features of solar-ORC systems, thereby providing valuable guidance for selecting appropriate cycle configurations, components, working fluids and other characteristics and, for the first time, presents a comprehensive comparison of such systems in small-scale applications.

A geospatial analysis approach for the operational assessment of solar ORC systems. Case study: Performance evaluation of a two-stage solar ORC engine in Greece

Renewable energy potential depends on many variables that vary both in space and time. Therefore, geospatial analysis approaches may effectively support proper planning and technoeconomic analysis. In this study, a simulation model of a two-stage Organic Rankine Cycle (ORC) engine combined with evacuated tube solar collectors was developed and applied throughout Greece. The simulation model uses daily meteorological data for a thirty-four years reference period. These data are downscaled in hourly time step and used to predict the system's performance in spatially distributed form based on experimental data. The obtained results are statistically analysed and a set of ranking maps presenting various aspects of the integrated system performance is created. The results indicate that there is a profound spatial variability. The interannual average power production ranges spatially between 17.4 and 27.7 kWh/d, the total efficiency between 0.022 and 0.028 and the corresponding energy cost between 0.41 and 0.7 €/kWh. Finally, the effect of climate variability on energy production performance and the presence of trends are investigated. The proposed approach was proven to be an effective tool for the assessment of the feasibility and potential of a solar heat-to-power engine for Greece and to be expanded in other regions as well.

Thermodynamic design and parametric performance assessment of a novel cogeneration solar organic Rankine cycle system with stable output

In areas rich in solar energy, meeting the energy requirement using renewable energy sources can address environmental issues by reducing the use of fossil fuels. In this study, thermodynamic design, simulation, daily and monthly evaluation of a novel cogeneration solar organic Rankine cycle (ORC) system with the capability of electricity and domestic hot water (DHW) production with stable output are performed under transient environmental conditions. The main components of the integrated system are a solar field based on parabolic dish concentrators (PDCs), a direct thermal energy storage (TES) system using two separate tanks, and an ORC power field which was modeled using TRNSYS software. In this system, intending to generate 200 KW of electricity, Benzene fluid in a recuperative ORC indicated a better performance than Cyclohexane, Toluene, and n-Hexane fluids with an energy efficiency of 21.89% and the lowest required inlet temperature for the turbine as 266.1 °C. The highest working hours of the system were obtained in the middle months of the year with an average DHW production of 12.8 h/day (more than 200 m3/day) and 9.1 h of electricity generation. While during the coldest month of the year (December), the system could provide 4.1 h of DHW with 74.5 m3/day of storage. Also, with the annual average of energy efficiency for the solar field as 78.9%, thermal and electric efficiency of the integrated system was calculated as 69.4% and 15.08%, respectively. From the economic analysis of the proposed system, the net annual benefit of the system and return of capital’s period were calculated as 150,815.3 US$ and 7.3 years, respectively.

Techno-Economic Optimization of Medium Temperature Solar-Driven Subcritical Organic Rankine Cycle

The present work focuses on the techno-economic assessment and multi-objective genetic algorithm optimization of small-scale (40 kWth input), solar Organic Rankine Cycle (ORC) systems driven by medium-to-high temperature (up to 210 °C) parabolic dish (PDC) and trough (PTC) collectors. The ORCs are designed to maximize their nominal thermal efficiency for several natural hydrocarbon working fluids. The optimization variables are the solar field area and storage tank capacity, with the goal of minimizing the levelized cost of produced electricity (LCoE) and maximizing the annual solar conversion efficiency. The lowest LCOE (0.34 €/kWh) was obtained in Athens for a high solar field area and low storage tank capacity. Meanwhile, the maximum annual solar conversion efficiencies (10.5–11%) were obtained in northern cities (e.g., Brussels) at lower solar field locations. While PTCs and PDCs result in similar efficiencies, the use of PTCs is more cost-effective. Among the working fluids, Cyclopentane and Cyclohexane exhibited the best performance, owing to their high critical temperatures. Notably, the systems could be more profitable at higher system sizes, as indicated by the 6% LCoE decrease of the solar ORC in Athens when the nominal heat input was increased to 80 kWth.

Effect of phase change materials on the performance of direct vapor generation solar organic Rankine cycle system

Phase change materials used for the storage of thermal energy can play a critical role in the efficient use and conservation of solar energy. The effect of the different types of phase change materials on the thermodynamic performance of a direct vapor generation solar organic Rankine cycle system is evaluated in this study. The system consists of an array of evacuated flat plate collectors, phase change material based thermal storage, expander, condenser, and organic fluid pump. The thermodynamic cycle model of the ORC system is integrated with phase change material heat storage tank that is modeled using the finite difference method in MATLAB. The thermodynamic performance of the system is analyzed by using 12 different phase change materials. Effect of phase change materials on the thermodynamic performance of organic Rankine cycle including the net power output, rise and fall in the working fluid temperature, and on the amount of energy stored and released are evaluated and compared for charging and discharging mode. The results indicate that MgCl2·6H2O has shown the highest overall system’s efficiency. However, KNO2–NaNO3 and Acetamide have resulted in maximum ORC and collector efficiency, respectively. Moreover, Acetamide, KNO2–NaNO3 and Mg(NO3)2·6H2O have shown maximum rise and fall in organic fluid temperature, maximum net power and maximum amount of energy stored and released during charging and discharging mode. Salt hydrates have shown overall better performance among the selected PCMs in terms of overall system efficiencies and the amount of energy stored and released.

Performance Investigation of Solar Organic Rankine Cycle System With Zeotropic Working Fluid Mixtures for Use in Micro-Cogeneration

Abstract Overall, there are numerous sustainable sources of renewable, low-temperature heat, principally solar energy, geothermal energy, and energy produced from industrial wastes. Extended utilization of these low-temperature alternatives has a certain capacity of decreasing fossil fuel use with its associated very hazardous greenhouse gas emissions. Researchers have commonly recognized the organic Rankine cycle (ORC) as a feasible and suitable system to produce electrical power from renewable sources based on its advantageous use of volatile organic fluids as working fluids (WFs). Researchers have similarly shown an affinity to the exploitation of zeotropic mixtures as ORC WFs due to their capability to enhance the thermodynamic performance of ORC systems, an achievement supported by improved fits of the temperature profiles of the WF and the heat source/sink. This paper determines both the technical feasibility and the benefits of using zeotropic mixtures as WFs by means of a simulation study of an ORC system. This study analyzes the thermodynamic performance of ORC systems using zeotropic WF mixtures to produce electricity driven by low-temperature solar heat sources for use in buildings. A thermodynamic model is created with an ORC system with and without a regenerator. Five zeotropic mixtures with diverse compositions between 0 and 1 in 0.2 increments of R245fa/propane, R245fa/hexane, R245fa/heptane, pentane/hexane, and isopentane/hexane are assessed and compared with identify the best blends of mixtures that are able to produce superior efficiency in their system cycles. Results disclosed that R245fa/propane (0.4/0.6) with regenerator produces the highest net power output of 7.9 kW and cycle efficiency of 9.4% at the operating condition with a hot source temperature of 85 °C. The study also investigates the effects of the volume flow ratio, and evaporation and condensation temperature glide on the ORC’s thermodynamic performance. Following a thorough analysis of each mixture, R245fa/propane is chosen for a parametric study to examine the effects of operating factors on the system’s efficiency and sustainability index. It was found that the highest cycle efficiency and highest second law cycle efficiency of around 10.5% and 84.0%, respectively, were attained with a mass composition of 0.6/0.4 at the hot source temperature of 95 °C and cold source temperature of 20 °C with a net power output of 9.6 kW. Moreover, results revealed that for zeotropic mixtures, there is an optimal composition range within which binary mixtures are tending to work more efficiently than the component pure fluids. In addition, a significant increase in cycle efficiency can be achieved with a regenerative ORC, with cycle efficiency in the range 3.1–9.8% versus 8.6–17.4% for ORC both without and with regeneration, respectively. In conclusion, utilizing zeotropic mixtures may well expand the restriction faced in choosing WFs for solar-powered ORC-based micro-combined heat and power (CHP) systems.

Effect of working fluids on the performance of phase change material storage based direct vapor generation solar organic Rankine cycle system

Working fluids can play a critical role in the working of an organic Rankine cycle system. A direct vapor generation solar organic Rankine cycle embedded with phase change material storage is analyzed in this study. The system comprised of an array of evacuated flat plate collectors, phase change material based thermal storage, expander, condenser, and organic working fluid pump. The storage tank model is modeled using a finite difference method in MATLAB programming environment while the 1D model of ORC system is used to evaluate the system performance. After a careful screen, 12 dry and isentropic working fluids were selected and their impact on the performance of the heat storage tank and the overall system is evaluated. The results show that the system efficiencies increase and decrease with the increment and decrement in the critical temperature of the working fluid. Moreover, the rise and fall of working fluid temperature, phase change material temperature, and the quantity of energy stored and released generally increase with an increase in the critical temperature of the working fluid. At the evaporation temperature of 10 °C higher and lower than the melting point temperature of the phase change material, Benzene has achieved the highest system efficiencies of 10.7% & 10.4% during charging and discharging mode, respectively. However, the maximum the rise and fall of working fluid temperature, phase change material temperature, and the quantity of energy stored and released during charging and discharging mode is attained by Heptane which is found to be 5.35 °C & 7.34 °C, 0.48 °C & 0.44 °C and 13.81 MJ & 23.04 MJ, respectively. Heptane has shown overall best performance among the selected working fluids and found to be feasible for phase change material storage based direct vapor generation solar ORC system.

Effect of Phase Change Material Storage on the Dynamic Performance of a Direct Vapor Generation Solar Organic Rankine Cycle System

Solar energy is a potential source for a thermal power generation system. A direct vapor generation solar organic Rankine cycle system using phase change material storage was analyzed in the present study. The overall system consisted of an arrangement of evacuated flat plate collectors, a phase-change-material-based thermal storage tank, a turbine, a water-cooled condenser, and an organic fluid pump. The MATLAB programming environment was used to develop the thermodynamic model of the whole system. The thermal storage tank was modeled using the finite difference method and the results were validated against experimental work carried out in the past. The hourly weather data of Karachi, Pakistan, was used to carry out the dynamic simulation of the system on a weekly, monthly, and annual basis. The impact of phase change material storage on the enhancement of the overall system performance during the charging and discharging modes was also evaluated. The annual organic Rankine cycle efficiency, system efficiency, and net power output were observed to be 12.16%, 9.38%, and 26.8 kW, respectively. The spring and autumn seasons showed better performance of the phase change material storage system compared to the summer and winter seasons. The rise in working fluid temperature, the fall in phase change material temperature, and the amount of heat stored by the thermal storage were found to be at a maximum in September, while their values became a minimum in February.

Thermodynamic, Economic and Sustainability Analysis of Solar Organic Rankine Cycle System with Zeotropic Working Fluid Mixtures for Micro-Cogeneration in Buildings

Globally there are several viable sources of renewable, low-temperature heat (below 130 °C), particularly solar energy, geothermal energy, and energy generated from industrial wastes. Increased exploitation of these low-temperature options has the definite potential of reducing fossil fuel consumption with its attendant very harmful greenhouse gas emissions. Researchers have universally identified the organic Rankine cycle (ORC) as a practicable and suitable system to generate electrical power from renewable sources based on its beneficial usage of volatile organic fluids as working fluids (WFs). In recent times, researchers have also shown a preference towards deployment of zeotropic mixtures as ORC WFs because of their capacity to improve thermodynamic performance of ORC systems, a feat enabled through the greater matching of the temperature profiles of the WF and the heat source/sink. This paper demonstrates the thermodynamic, economic and sustainability feasibility, and the notable advantages of using zeotropic mixtures as WFs through a simulation study of an ORC system. The study examines first the thermodynamic performance of ORC systems using zeotropic mixtures to generate electricity powered by a low-temperature solar heat source for building applications. A thermodynamic model is developed with a solar-driven ORC system both with and excluding a regenerator. Twelve zeotropic mixtures with varying compositions are evaluated and compared to identify the best combinations of mixtures that can yield high performance and high efficiency in their system cycles. The study also examines the effects of the volume flow ratio, and evaporation and condensation temperature glides on the ORC’s thermodynamic performance. Following a detailed analysis of each mixture, R245fa/propane and butane/propane are selected for parametric study to investigate the influence of operating parameters on the system’s efficiency and sustainability index. For zeotropic mixtures, results disclosed that there is an optimal composition range within which binary mixtures are inclined to perform more efficiently than the component pure fluids. In addition, a substantial enhancement in cycle efficiency can be obtained by a regenerative ORC, with cycle efficiency ranging between 3.1–9.8% and 8.6–17.4% for ORC both without and with regeneration, respectively. Results also revealed that exploiting zeotropic mixtures could enlarge the limitation experienced in selecting WFs for low-temperature solar ORCs. Moreover, a detailed economic with a sensitivity analysis of the solar ORC system was performed to evaluate the cost of the electricity and other economic criteria. The outcome of this investigation should be useful in the thermo-economic feasibility assessments of solar-driven ORC systems using working fluid mixtures to find the optimum operating range for maximum performance and minimum cost.

Performance Analysis of Solar Organic Rankine Cycle with Stable Output Using Cyclopentane/Cyclohexane Mixtures▴

AbstractKeeping output stable is necessary for solar organic rankine cycle (SORC) considering variable solar irradiation conditions. In this study, zeotropic mixtures are introduced into SORC with stable output. Evaporation pressure and turbine inlet temperature are optimized with the overall system efficiency as optimization objective. Comparisons are drawn between the basic SORC and regenerative SORC. The influences of zeotropic mixture composition on the overall system efficiency, ORC efficiency, heat source outlet temperature, mass flow rate of heat source and working fluids and temperature rise of internal heat exchanger (IHE) are analyzed. The results show that zeotropic mixtures can slightly increase the overall system efficiency of the basic SORC system compared with the optimal pure working fluid system, but for the regenerative SORC system, the optimal overall system efficiency is higher when pure cyclohexane is used. When cyclopentane mole fraction is 0.4, the overall system efficiency of the basic SORC system reaches maximal value of 16.08%, which is 0.12% higher than for the optimal pure working fluids system, relatively. Under the optimum conditions, the optimal overall system efficiency of the regenerative SORC system is 52.11% higher than that of the basic SORC system.

Effect of use of MWCNT/oil nanofluid on the performance of solar organic Rankine cycle

In the current study, a solar-driven organic Rankine cycle (ORC) system was thermodynamically, economically and environmentally investigated. A focal point concentrator with two different cavity-shape receivers was investigated as the ORC heat source. More specifically, the cylindrical and the hemispherical cavity receivers were examined and compared as the most usual and promising choices. MWCNT/oil nanofluid and R113 were used as the solar heat transfer fluid and ORC working fluid respectively. The main aim of this research is an investigation of different cavities in the solar dish and the investigation of the impact of the use of nanofluids in the solar system by different points of view. The results of this work showed that the hemispherical cavity receiver with nanofluid is the most efficient choice with 21.4% system efficiency, while the use of pure thermal oil in the hemispherical cavity leads to 18.9%. On the other hand, the use of the cylindrical cavity leads to 17.8% and 15.8% system efficiency with nanofluid and pure thermal oil respectively. The levelized cost of electricity (LCOE) was 0.077 €/kWh and 0.076 €/kWh for the cylindrical and hemispherical cavity receiver respectively. Moreover, it was concluded that the solar ORC system with the hemispherical cavity receiver as the ORC heat source had resulted in more positive environmental influence related to the cylindrical one.

Integration of solar latent heat storage towards optimal small-scale combined heat and power generation by Organic Rankine Cycle

Abstract Thermal energy and distributed electricity demand are continuously increased in areas poorly served by a centralized power grid. In many cases, the deployment of the electricity grid is not economically feasible. Small-scale Organic Rankine Cycle (ORC) appears as a promising technology that can be operated by solar energy, providing combined heat and power (CHP) generation. Additionally, thermal energy storage can ensure stable and continuous operation in case of scarce thermal energy availability. This paper evaluates the potential application of latent heat storage to enhance solar ORC performance at operating temperatures between 80 °C and 140 °C, aiming at improving the efficiency and capacity of ORC for low-cost non-concentrating solar-thermal collectors. Three thermal energy storage scenarios are considered. Scenario 1 and 2 consist of reference cases based on a solar ORC system integrated with a conventional hot water tank and a pressurised water tank. Scenario 3 implements a storage unit based on a phase change material. The simulation was carried out through models developed in TRNSYS for solar energy balance and ASPEN for ORC system performance. The results show that solar latent heat storage tank can provide 54% of useful collector gains with a higher and narrower temperature range in the evaporator, increasing the annual thermal energy capacity by 19%, reducing annual heat losses by 66% and decreasing the investment cost by 50% in comparison with a pressurised water tank. It also allows increasing the efficiency of ORC cycle by approximately 18% (from 8.9% to 10.5%) with a higher net generated power than a conventional water tank integration, scaled up from 498 W to 1628 W. These results highlight the potential benefits that latent heat integration provides to improve the low-cost solar ORC performance for powering electricity and thermal energy supply.

Thermoeconomic analysis on a molten salt parabolic trough‐based concentrated solar organic Rankine cycle system

Solar thermal electricity generating technology is an alternative solution to energy crises and environmental problems, which has caused wide concern in recent decades. In this paper, a molten salt parabolic trough-based concentrated organic Rankine cycle system is proposed and investigated. A quadribasic nitrate salt with low melting temperature is employed as a heat transfer and storage medium. A stable heat transfer and economic model is established with Matlab. The radial and axial temperature distributions in the collector tube are obtained, and the impact of condensation and evaporation temperatures on the heat transfer area is analyzed. Results show that the temperature along the axial direction linearly increases, and the temperature at the collector tube exit decreases with the increase of molten salt mass flow rate. The maximum temperature difference along the radial direction of the collector tube happens in the annular gap. Heat transfer and thermodymanic analysis indicates that condensation temperature has a more evident effect on heat transfer area than that of evaporation temperature. An increase in condensation temperature leads to a decrease in the evaporator area, the condenser area increases, and the total area decreases. Economic analysis indicates the collector cost plays a predominant role in total capital costs, and decreasing molten salt mass flow rate can considerably reduce collector cost. Levelized energy cost sensitivity analysis indicated that operation time per year has a more evident effect than that of the four factors. Heat transfer and economic analysis on the system helps in the selection of operation parameters.