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Six different arrangements of ribbed tube are employed to improve the performance of parabolic trough receiver (PTR) in this paper. Detailed analyses of flow structure, thermal performance, flow resistance and overall thermo-hydraulic performance are conducted. The results indicate that the symmetrical anticlockwise arrangement of double inclined ribs (SADIR) and symmetrical clockwise arrangement of single inclined ribs (SCSIR) achieve the flow pattern with a pair of counter-rotating vortexes and obtain the best performance with reductions in peak temperature and heat loss reaching up to approximately 177 °C and 80.1%. Nusselt number of the SADIR and SCSIR are about 1.58–3.21 and 1.41–2.98 times that of the PTR with plain tube, respectively. The enhanced PTRs with ribbed tubes achieve great improvements in overall thermo-hydraulic performance at low Reynolds number (Re

As concentrating solar power technologies progressively move to maturity, large-scale concentrating solar power plants have elicited increasing attention. The thermodynamic simulation and economic analyses of a 50 MW parabolic trough concentrating solar power plant in northwest China were conducted in the present work. The effects of meteorological conditions, including direct normal irradiance and ambient temperature, on the off-design performances were investigated by simulation calculations. Furthermore, economic and sensitive analyses were conducted based on the annual simulation. Results show that the back-pressure of air-cooled condenser fluctuated with both ambient temperature and power generation. The power generation of summer and autumn days would decrease by 0.53–1.38 MW for the rise of condenser back-pressure. The clouds mainly affected the molten salt level of hot tank in thermal energy storage. In the economic analysis, with the decrease of the feed-in tariff from 16.6 ₵/kWh to 8.6 ₵/kWh, the maximum total net income dropped from 6.65 M$ to 2.43 M$. The optimal design condenser back-pressure rose from 5.0 kPa to 5.5 kPa. Moreover, the optimal design back-pressure of air-cooled condenser was not sensitive to the cloud effect in certain range, but the total net income had a sharp drop from 7.37 M$ to 4.95 M$.

Utilization of direct steam generation (DSG) is a culmination point in the solar power plants with parabolic trough collectors. For these systems that working temperatures commonly exceeds 400 °C, while thermal oils cannot be employed due to inflammability dangers and thermal stability issues, water is used as the working fluid. Great heat transfer coefficient of boiling, especially nucleate boiling regime, is much beneficial for increasing heat transfer rate but reaching the critical heat flux region is a trouble. In This region, thermal fluctuations occur and it leads to fracture in the collector. Nanofluids as a new generation of coolants are evaluated in solar parabolic trough collectors and the critical heat flux ascertain with Look up Table method. In the present study effects of adding nanoparticles to the pure water is numerically investigated. Silver, aluminum, gold, nickel and titanium dioxide are considered in this study. The results show that the distance at which the critical heat flux occurs, (known as critical length) is improved significantly by adding various concentrations of mentioned nanoparticles, and especially for Au-H2O and Al-H2O nanofluids in a volume concentration of 2%, the calculated values are respectively 2.7 and 2.3 times the critical length for the pure water.

In this paper, two types of nanoparticles are used in a solar direct absorption parabolic trough collector (DAPTC). Nanosilica and multi-wall carbon nanotube (MWCNT) with two different volume fractions are used in ethylene glycol (EG) in the experimental section. A glass-glass absorber tube is utilized as the receiver, and the working nanofluid goes through the tube. The computational fluid dynamics (CFD) method is used for simulating the process, and it is validated by experimental data. The volume fractions of the nanoparticles in the base-fluid are 0.1–0.5% and 0.1–0.6% for nanosilica and MWCNT, respectively. The nanofluid including 0.6% MWCNT/EG has the highest outlet temperature which is equal to 346.1 K. The experimental results used to validate the CFD procedure. In the last step, a multi-layer perceptron neural network is trained using the data obtained from the CFD model. It has been shown that the outputs of the network have good agreement with the CFD results. Both the CFD and the ANN methods were compared, and the advantages and disadvantages of each technique in modelling the problem have been discussed.

The objective of this work is the investigation of a nanofluid-based compound parabolic collector under laminar flow conditions. The examined nanofluid is Syltherm 800/CuO with 5% volumetric nanoparticle concentration and the examined temperature range is from 25 °C up to 300 °C. The analysis is performed in SolidWorks Flow Simulation Studio using a developed computational fluid dynamics model. Moreover, it is essential to state that this work is conducted under laminar flow conditions because the laminar flow regime is common for the compound parabolic collectors. It is found that the mean value of the thermal efficiency is 1.24% while the maximum 2.76% for inlet temperature equal to 300 °C. Moreover, it is found that the mean and the maximum heat transfer coefficient enhancements were 16.16% and 17.41% respectively, while the maximum pumping work increase was found to be 16.09%. However, the calculated pumping work demand was too low in all cases and this fact indicates that the increase of the pressure drop with the nanofluid is not a limitation in the present problem. In the end, the exergy efficiency enhancement is found to be up to 2.60%, while the overall efficiency enhancement up to 2.76% with the use of nanofluid.

Nowadays, a large part of the scientific community efforts, dedicated to Concentrated Solar Power (CSP) technologies, are focused on improving the efficiency and reducing the costs. This work presents a flexible, highly customizable, dynamic model that simulates the transient thermal behavior of a solar field in order to use it for optimization, performance evaluation and control tasks purposes. The model is based on the detailed physical principles described in a previously paper which has been extended with an exergetic approach, recommendation made by the author of the previous paper in order to improve the model. The model has been developed using the ThermoCycle library and implemented in the equation-based object-oriented modeling language Modelica. An experimental campaign has been carried out in a real facility in order to calibrate and validate the model. Energetic and exergetic analysis are also presented in this work.

A new distributed energy system integrating a solar thermochemical process with a double-axis tracking parabolic trough collector is proposed to address the challenges on large seasonal variations of solar-to-fuel efficiency and insufficient utilization of solar energy in exiting distributed energy systems. Low-energy level discontinuous solar energy is upgraded into the chemical energy of syngas via the solar thermochemical process, which is easy to be stored. The double-axis tracking parabolic trough collector is deployed to the solar thermochemical process to eliminate the cosine loss completely to increase the annual thermodynamic efficiency. With the consideration of the variation of solar energy, the coupling between user’s loads and energy outputs in the proposed system is investigated, and the favorable on-design and off-design thermochemical performances are numerically validated. Results indicate that the solar fuel production and the solar power production in the proposed system increase approximately 27% annually as compared with the reference system.

The use of insert flow is a promising technique for increasing the performance of parabolic trough solar collectors. The objective of this work is to investigate the use of multiple cylindrical longitudinal inserts in the parabolic trough solar collector LS-2 module. Totally 15 cases are investigated with a computational dynamic model developed in SolidWorks Flow Simulation. More specifically, the reference empty tube, one case with a single insert, eight cases with two inserts flow, three cases with three insert flow and two cases with four insert flow. It is found that the use of more inserts leads to higher thermal, exergy and overall efficiency performance of the collector. Moreover, it is found that the exact location of the inserts plays a significant role in the results. The pumping work is found to be generally low in all the cases, the fact that proves that the increase in the pressure drop is not so important in the total system performance. The global maximum efficiency is found for the case with the four inserts and in this case, the thermal efficiency is enhanced 0.656%, the thermal losses are reduced about 5.63% and the heat transfer coefficient is increased 26.88%. The results of this work can be used for the proper design of multiple inserts design in solar systems.

The theoretical transient analysis of a recompression cycle is considered while directly heating the working fluid, CO2, in a solar trough field. The analysis explores the temporal behavior of the system’s performance for three distinct, minute-based, solar irradiation profiles: (i) daylong perfectly clear skies, (ii) instantaneous on-off cloud shading and (iii) partially cloudy day. The key objective is to study the effect of the solar intermittency on the heat exchangers, solar collector and on the overall cycle’s behavior – the thermal capacitance of the two first components is considered. The calculations reveal that, even though auxiliary heating systems was not considered, the heat capacitance of the working fluid and parabolic collector assembly is capable of instantaneously smoothing out the cycle’s performance for on-off clouding conditions, such as the net power and thermodynamics efficiencies – note that the cycle’s performance disregards the parabolic trough efficiency. Differently, the overall system’s efficiency, which is regarded as the product of the efficiencies of the cycle and parabolic trough, is much more sensitive to irradiation changes. The study also specifically considers the effect of the clouding intensity and time, with the former being measured as fraction of clear sky irradiation on the system’s performance. The analysis shows that it is possible to quantify the time scale available such that an auxiliary heating system delivers heat to the working fluid during a clouding scenario allowing the plant to work steadily.

Parabolic trough collectors are among the most mature solar concentrating technologies which are applied in numerous applications. The enhancement of their performance is a crucial issue in order to be established as a feasible technology. The use of internal fins is one of the most interesting techniques for enhancing the heat transfer phenomena in the flow as well as for increasing the collector’s performance. However, their utilization leads to higher pressure losses. The objective of this paper is to investigate the optimum number and location of the internal fins in the absorber of a parabolic trough collector. The examined fins have 10 mm length and 2 mm thickness, while their shape is rectangular. Various numbers of fins are investigated in various locations inside the absorber and in every case, the collector’s performance is investigated by taking into account the increase of the Nusselt number and of the friction factor. According to the final results, the internal fins have to be placed in the lower part of the absorber where the higher amount of the solar heat flux is concentrated. A multi-objective procedure proved that the absorber with three fins in the lower part is the optimum case with 0.51% thermal efficiency enhancement.

This study aims to find the optimal way to integrate a parabolic trough solar field into a gas fired combined cycle. The combined cycle studied here is composed of a gas turbine and a triple pressure bottoming Rankine cycle. A general layout is proposed and allows the integration of the solar source at all levels of temperature. A thermodynamic model is proposed to evaluate the performance of the system and then coupled to a constrained nonlinear optimization algorithm that uses a hybrid optimization technique combining Particle Swarm Optimization (PSO) and Gravitational Search Algorithm (GSA). This gives the optimal configuration of the heat exchanger networks used to harvest the solar source and the exhaust gases of the gas turbine. The effect of the system’s main parameters on the solar integration performance was investigated such as the amount of the solar heat rate injected to the bottoming cycle, the mass flow rate of the solar source, the inlet temperature of the solar source and the outlet temperatures of the high pressure super-heater n°1 and the re-heater n°1. The approach used here is general and gives finally the real potential of the integration of a parabolic trough solar field into a combined cycle.

Conventional parabolic trough solar receivers are widely used to harvest heat energy at temperatures ranging from 400 °C to 550 °C. However, high temperatures cause excessive heat loss in solar receivers. Two types of novel solar receivers with an inner metal radiation shield (RS), one with solar selective absorbing coating on the outer surface and one without, were proposed and constructed to improve the thermal performance of solar receivers. Experiments were conducted in an enthalpy difference lab, and mathematical models with spectral radiant distributions were established to predict the thermal performance of the solar receivers. A comparison between the simulated and experimental results showed satisfactory consistencies. Predictions were obtained using the models with the root mean square deviation of less than 6%. The novel solar receiver without solar selective absorbing coating on the outer surface of the RS showed superior performance at absorber temperatures exceeding 550 °C. At the absorber temperature of 600 °C, the percentage of heat loss reduction of the receiver with solar selective absorbing coating and of that without reached 23.4% and 24.2%, respectively.

Overall energy efficiency remains a large and unexploited resource in combined cooling, heating, and power systems driven by solar energy. This study aims to explore the configuration effects on such systems using parabolic trough collector and organic Rankine cycle (ORC) technologies. The configurations are concisely clarified into sequential and parallel connections, in which a single-effect absorption chiller and a heat exchanger are considered for cooling and heating, respectively. A comprehensive assessment framework is proposed by establishing the thermodynamic performance, system size, and economic models. Under reasonable thermodynamic boundary conditions, the optimal operational parameters are obtained via a Pareto frontier solution for such a system, with an ORC of 200 kW. Promising technical solutions and enhancement potential are justified and quantified by means of system simulations and comparison on the annual time scale.

The concentrated photovoltaic thermal (CPVT) system is one of the heat and power generation systems that have received special attention in recent decades. In this paper, a novel CPVT system with Al2O3 nanofluid flow into porous channel coupled with a domestic heat pump (CPVT-HP) is evaluated from energy, exergy and economics viewpoints. In addition, mass flow rate of the nanofluid through the CPVT is thermo-economically optimized. The study is divided into three parts of Computational fluid dynamics (CFD) analysis of the CPVT, optical analysis of parabolic trough concentrator (PTC) and thermo-economic analysis of the proposed CPVT-HP system. The continuity, Brinkman momentum and energy equations are employed as governing equations for CFD analysis considering the average solar flux using optical calculations. Then, energy-exergy-economic optimization is performed on the proposed domestic CPVT-HP system in Mashhad city of Iran during November to February. The validation results show that the numerical simulation obtained for the proposed model has an acceptable agreement with the experimental data. Results show that with increasing the nanofluid mass flow rate, the PV cell temperature and nanofluid outlet temperature decease which lead to increases in PV cell efficiency and CPVT energy efficiency while the exergy efficiency of the CPVT system decreases. It is also found that the maximum performance of the porous channel collector is obtained for the pore diameter and the porosity of 0.9 mm and 95%, respectively. Finally, based on energy-exergy-economic analysis and Pareto method, the optimal nanofluid mass flow rate of the integrated CPVT-HP system is achieved equal to 0.01382 kg/s.

To maximize the utilization of solar energy, this study focuses on the investigation of a realistic performance of a photovoltaic/concentrated solar power hybrid using a developed wavelength-selective filter. The hybrid system is proposed for the modification and improvement of the performance of the currently operating solar electric generating station VI parabolic trough plant in California, USA. In the hybrid, photovoltaic system converts only the useful wavelengths after the splitting of the solar irradiance by the wavelength-selective filter, and the concentrated solar power uses the remaining wavelengths. Most relevant studies presented the hybrid performance using hypothetical filters instead of realization. Even studies utilizing realized filters have only used annual mean values to assess hybrid performance. Due to the intrinsic properties in real filters, the hybrid performance can be varied accordingly throughout the day and year. As a result, by presenting annual performance based on the measured optical properties of a real filter, this study intends to address this research gap. According to the findings, the proposed hybrid performed 9% better than the solar electric generating station VI concentrated solar power. The hybrid system was also 4% more efficient than the virtual photovoltaic-alone system. The proposed hybrid’s Levelized Cost of Electricity is 9% lower than the solar electric generating station VI concentrated solar power. Even if the proposed filter accounts for 18.4% annual optical loss from the incident solar power, the proposed hybrid is still very promising for retrofitting and enhancing aged concentrated solar power plants.

Decomposing methanol to hydrogen and carbon monoxide in solar parabolic trough receiver-reactors is a promising way for solar energy utilization, which converts solar energy to chemical energy. Due to the non-uniform boundary heat flux of receivers and the varying concentration of methanol, the porosity distribution of catalyst should be carefully designed to improve the thermochemical reaction performance. In this contribution, we theoretically analyze the relations of such factors as temperature, mass fraction of gas mixture, porosity distribution, and reaction rate, establish a optimization model by adapting the largest conversion rate of methanol as an optimization objective together with such constraints as the continuity equation, the momentum equation, the energy conservation equation, the species equations, and the fixed total mass of catalyst, apply the variational principle to derive the governing equations for optimization of catalyst porosity distribution, and finally take a solar parabolic trough receiver–reactor with methanol decomposition reaction as an example to show the applications. When the surface heat flux as well as the total mass of porous catalyst are given, solving the newly deduced governing equations directly gives the optimal porosity distribution of catalyst under different working conditions. Meanwhile, the optimized non-uniform porosity distribution of catalyst will effectively improve the conversion rate of the methanol, e.g. from 52.3% to 72.3% when E = 40, which provide a guidance for catalyst design to improve the thermochemical reactions performance.

The aim of the study was to find the performance of parabolic trough solar collector used for the dehydration process of seasonal fruits with the effect of air flow rates. The experiment was carried out with the three levels of air mass flow rates i.e. F1, F2 and F3 and two levels of a diameter of the absorber i.e. D1 and D2 with the concentration ratio of 60. Statistical analysis showed that Efficiency, moisture lost per hour and drying time of the apples dried by parabolic trough solar collector was significantly (P

The reliability of heat collection element (HCE) in parabolic trough collector (PTC) system is of importance to the solar thermal energy harvesting. The present work proposes the 2D-finite volume method (FVM) and 3D-finite element volume (FEM) coupled model to conduct the thermal load and bending analysis of the HCE of direct-steam-generation (DSG) PTC solar power plant. The emphasis is focused on the evaporation and superheating stages of a DSG loop in re-circulation mode due to the presence of the phase-change process and the relatively lower heat transfer performance, respectively. It is found that the thermal deflection is far less than 1 cm for a 4-m HCE in the evaporation stage. However, in the superheating stage with DNI = 1000 W m −2 ( DNI being the direct normal irradiance), the circumferential temperature difference and the deflection of a 4-m HCE can reach up to 48 °C and 2.16 cm, respectively. It should be pointed out, based on the present work, that the non-uniform heating and local overheating issues exist in the evaporation and superheating stages, respectively, the latter of which seems more serious and potentially causes damage.

The use of supercritical carbon dioxide becomes more and more intense because of the higher thermal efficiency of thermodynamics cycles operating (Brayton and Rankine) with this working fluids. The objective of this work is to investigate the utilization of this working fluid in parabolic trough collector for various operating conditions. The pressure level, the inlet temperature and the mass flow rate are the examined parameters for the parametric analysis of the collector which is performed in energetic/thermal and exergetic terms. A thermal model is developed in EES (Engineering Equation Solver) and it is validated with literature data. According to the final results, low-pressure levels (80 bar) have to be used in low-temperature levels while higher pressure levels (200 bar) are proper for higher temperature levels. The global maximum exergetic efficiency is achieved for inlet temperature equal to 750 K and it is 45.3%. In the last part of this study, the efficiency map of the collector is introduced for evaluating the collector performance. This depiction combines the thermal and the exergetic efficiency with the inlet temperature as a parameter and it is a useful tool for determining the optimum operating region of the collector.

Solar thermal power generation is currently an attractive solar electricity technology. Currently, we face an important issue of lower annual solar-to-power efficiency (approximately 10.0%) using parabolic trough technology because the direct normal irradiance instantly varies, and the solar thermal power cycle always derivates from the designed operation. Here, we investigate a middle-temperature solar-driven Kalina cycle that uses a parabolic trough collector with a variable concentration ratio. From lower to higher direct normal irradiance, both the aperture area of collector and the flow process of the Kalina cycle can be changed. As a result, a much border direct normal irradiance of 100–1000 W/m2 achieves a solar-to-power efficiency of 4–20%, resulting in an annual solar-to-power efficiency of approximately 14%. Furthermore, the interactions are analyzed among direct normal irradiance, the aperture area of the collector, and the flow process of the thermal cycle. An operation method for off-design conditions is proposed to greatly improve the annual solar-to-power efficiency, offering a pathway to efficiently utilize a border range of direct normal irradiance.

The influences of sunshape and incident angle on the optical performance of the parabolic trough solar collector (PTC) are investigated comprehensively based on Monte Carlo Ray Tracing (MCRT) method and theoretical analysis. This study adopts the acceptance-rejection sampling method, instead of the direct sampling method, for random variable sampling to reduce computing complexity. Both the energy proportion bounded by any angle span in the optical cone and the end loss caused by any incident angle are derived theoretically. It is revealed that the sunshape has great effects on the optical performance of a PTC, which should be taken into consideration in practice. The geometrical configuration of the PTC, especially the absorber tube diameter, should be determined to meet the energy requirement based on local sunshape (circumsolar ratio) conditions. It is also found that the end loss, caused by the incident angle, weakens the optical efficiency. Larger aperture width and smaller absorber diameter will cause greater end loss for constant incident angle. When the absorber length is long enough, the effect of incident angle will be negligible. In a range of small focal lengths, the optical efficiency increases with the increase of focal length, and then decreases constantly with further increasing focal length. Findings in this paper can be used as reference or guidance for designing and optimizing PTC’s structure in practice.

In this article, three dimensional turbulent flow for Syltherm heat transfer fluid in absorber tube of solar system with turbulators is simulated. The thermo-hydraulic characteristics of solar parabolic trough collector with porous rings are investigated numerically. The numerical simulation is implemented by using Computational Fluid Dynamics (CFD). The impact of distance between rings and the inner diameter of the rings on the thermal performance of the collector are evaluated. The heat transfer fluid is Syltherm 800 and the analysis is carried out based on Re-Normalization-Group (RNG) k–e turbulent model. The results show that the heat transfer characteristics of solar parabolic trough collector enhances by inserting the porous rings in tubular solar absorber. Also, by decreasing the distance between porous rings, the heat transfer characteristic increases but by increasing the inner diameter of the porous rings, the Nusselt number reduces.

The complexity of the cascading solar-thermal-mechanical-electrical energy conversion in concentrated solar power (CSP) plants urges to develop an accurate and fast analytical methodology for on-site use. Herein, we propose a novel fully-coupled multi-level analytical methodology, where multi-dimensional model (0-1-2-3 Model) is developed to address the optical-hydraulic-thermal-elastic synergistic issue in CSP plants: (i) At system-level, the 0 Sub-Model reveals the heat-work transformation in power block in the view of thermodynamics; (ii) At loop-level, the 1 Sub-Model uncovers the collection, concentration and transformation of solar energy into the working fluid in the loop on account of 1D thermo-hydraulics; (iii) The 2 Sub-Model, employing 2D finite volume method (FVM), figures out the detailed circumferential temperature profile of receiver tubes in terms of composite heat transfer; (iv) At component-level, the 3 Sub-Model, using 3D finite element method (FEM), brings insight into the nonuniform-temperature-induced deformation of receiver tubes focusing on the thermo-elastics. The 0-1-2-3 Model enables both system-level performance prediction and component-level targeting insight in a remarkably high-efficient way with guaranteed accuracy. In comparison, the computational time of a full 3D model is 15 times longer than that of the proposed 0-1-2-3 Model for a typical 4-m heat collection element (HCE) and it goes up to 23 times longer for a 24-m loop section. To make the proposed model easily understood, a CSP plant with parabolic trough collector (PTC) and direct steam generation (DSG) technologies is applied. It was found that under the rated conditions, the energy and exergy efficiencies of the plant are 18.89% and 20.26%, respectively.

Parabolic Trough Collectors (PTC) provides thermal solar energy at medium temperature, and in order to increase the thermal level, the solar system can be coupled to upgrading devices, such as Absorption Heat Transformers (AHT). In this paper, a feasibility analysis of the PTC system operating as thermal source of an AHT is described. The PTC and AHT units were tested and, based on the experimental data of each system, a heat transfer analysis was carried out in order to propose a single system. Two case studies were analysed: In the first, the evaporator temperature was close to the generator temperature (84.6 and 85.2 °C respectively) and a simultaneous flow from the heat source was used; in the second case, the evaporator temperature was lower than the generator temperature (79.6 and 86.7 °C respectively) and a serial flow from the heat source was proposed. Results show that, for the absorber temperature of 101 °C, the calculated generator and evaporator heat loads were 1.50 and 1.34 kW respectively in Case 1, and 0.86 kW for both components in Case 2. For Case 1, the PTC system required 6.0 m 2 in order to provide two mass flows of 6.00 × 10 −02 and 5.35 × 10 −02 kg/s for generator and evaporator at 89 °C. For Case 2, one mass flow of 6.60 × 10 −02 kg/s at 89 °C for generator and evaporator must be satisfied by a 3.7 m 2 PTC system.

In this paper, an integrated numerical model was established to solve the complex energy transfer in a parabolic trough collector (PTC) by combining Monte Carlo ray tracing and finite volume method. Based on the model, the thermal performance of the PTC using supercritical CO 2 (s-CO 2 ) as the heat transfer fluid (HTF) was studied and analyzed. The results indicate that the solar fluxes on the receiver walls are non-uniform, which results in the non-uniform temperatures on the walls and in the s-CO 2 . Moreover, the optical efficiency of 84.19% is achieved at normal incidence. The circumferential temperature difference (Δ T c ) of the absorber is found to be within 18–60 K under typical conditions, and it decreases with increasing inlet velocity ( v in ) and decreasing inlet temperature ( T in ). Studies on the flow and heat transfer characteristic indicate that the secondary flow occurs on the cross-section due to the buoyancy. The velocity of the secondary flow in the pseudo-critical region can be one magnitude order larger than that in the high temperature region, which leads to strong heat transfer enhancement in the former. Studies on the energy conversion performance indicate that the PTC can achieve the collector efficiencies of 18.78–84.17% and 81.93–84.17% at the typical conditions for Brayton and Rankine cycles, respectively, where the efficiency increases with decreasing T in and increasing v in . Additionally, corresponding efficiency equations have also been obtained. The information from this study will provide a reference for the design and operation of the PTCs using s-CO 2 as HTF.

Solar energy is a promising energy source for covering a great variety of applications from low up to high temperature levels. In this study, the most mature concentrating technology, a commercial parabolic trough collector (Eurotrough ET-150), is investigated energetically and exergetically for a great temperature range from 300 K to 1300 K. Pressurized water, Therminol VP-1, nitrate molten salt, sodium liquid, air, carbon dioxide and helium are the examined working fluids; each one to be studied in the proper temperature range. In the first part of this study, the optimum mass flow rate is determined to every working fluid separately. After this point, the exergetic and the energetic performance of the collector operating with all these working fluids is examined. The final results prove that the liquid sodium leads to the global exergetic maximum efficiency (47.48%) for inlet temperature equal to 800 K, while the maximum exergetic performance of helium, carbon dioxide and air to be 42.21%, 42.06% and 40.12% respectively. Moreover, pressurized water is the best working medium for temperature levels up to 550 K, while carbon dioxide and helium are the only solutions for temperatures greater than 1100 K. The thermal analysis is performed with the EES tool.

Small-scale double-axis parabolic trough collector (PTC) is suitable for solar thermochemical reactions and solar-aided coal-fired power plants. In the present work, the double-axis PTC is numerically investigated and an optimized tracking strategy is proposed. That is to maintain PTC at the half-day optimal azimuth angles in the morning and afternoon, shifting at solar noon, in order to maximize the annual received solar radiation amount. The half-day optimal azimuth angle is found correlated to the latitude and varies diversely through a year. A normalized rating method is proposed to generally evaluate the performance of the proposed tracking strategy under theoretical and practical conditions. The results indicate that the recommended regions and periods to apply the proposed tracking strategy are low and middle latitudes ( φ = −60° to 60°) and autumn and winter seasons ( N day = 266–80), respectively, where the performance is rated above 0.6 regarding the traditional single-axis and double-axis tracking strategies. Experiments have been carried out on a 300 kWt double-axis PTC rig in Langfang, Hebei, China, in early November. Compared to the north-south single-axis tracking strategy, the proposed optimized tracking strategy (14° NW) shows roughly 68.8% higher in heat gain and 15–17 percentage points boost in collector efficiency.

Investigating the potential to add solar tower and parabolic trough technology to aid coal-fired power generation could be a valuable intermediate step along the route to decarbonisation while making use of an existing assets, that would have a high efficiency and percentage contribution to utilise solar energy to reduce coal consumption. Based on the plant model of a typical 600 MWe coal-fired plant with the addition of tower and trough solar heat sources developed in Ebsilon Professional platform, the model predictive controller is developed in this study, incorporating the information of predictive weather data and real power load, to minimise accumulative coal consumption in a specific time horizon. Simulations on a typical day and a 10-day consecutive period are performed to observe the benefits and operation processes with a model predictive controller. Compared with a standard controller that doesn’t make use of future solar and load predictions, the typical day simulation shows, that the coal consumption reduction using a predictive control approach is increased by 21.3-tonne (13.6%), and 320.0-tonne (20.3%) in the 10 consecutive day simulation. The absolute difference of reduction tends to be most significant in high radiation conditions (day 2), which gave a 61.7-tonne (34.3%) saving. The improvement appears to be achieved by dispatching the thermal energy storage ability to store more energy and discharging thermal energy optimally. The benefits from this approach is insensitive to forecast error and shows sensitivity to system configurations, which tends to be greater with sufficient solar energy input but inadequate thermal storage capacity. While the general area of solar aided coal-fired plants have been investigated in various configurations by others, this paper is novel in that it examines the benefit of using future weather forecast data within a model predictive controller to significantly improve the potential solar contribution such a plant can use. As such it quantifies the potential improvements such an approach may achieve. In summary, the application in the solar tower and parabolic trough aided coal-fired power generation system improved the understanding of the benefits and the limitations in using the model predictive control in the operation process.

Quantification of the thermal stress-induced deformation issue of the heat collection element (HCE), which is hardly avoidable during the practical operation of parabolic-trough (PT) concentrated solar power (CSP) plants is of primary importance, especially with direct steam generation (DSG) technology. However, currently-available analysis methods are either inefficient or inaccurate. In the present work, a trans-dimensional multi-physics coupled analysis method is proposed. The method consists of a one-dimensional loop-level thermo-hydrodynamic model, which efficiently predicts the global performance of loop, and three-dimensional optical-hydrodynamical-thermal-mechanical coupled model, which accurately quantifies the local deformation of HCE. The information exchange between the two models is accomplished through a self-developed coupling code. After model validation by experimental data, the proposed method is applied in different cases for the preheating, boiling (annular/stratified flow pattern), and superheating sections of a DSG-PTC loop. The worst scenario is found to exist in the superheating section, giving the maximum circumferential temperature difference of 29 K and the maximum z-deviation of −1.67 cm. When it is stratified flow (x = 0.56) in the boiling section, the corresponding values are 21 K and 0.69 cm. It should be noted that, considering the practical installation errors and the interaction between HCE and concentrator, the deformation not only changes the distribution of heat flux but also potentially causes optical loss. Meanwhile, the results verify the capability of the proposed analysis method in performing thermal stress deformation analysis on entire loop, which can be further extended to various forms of line-focused CSP technologies.

Combing solar energy systems and polygeneration units is an optimal way of producing useful outputs by utilizing a renewable energy source. Most of the polygeneration systems studied in the literature utilize only one solar collector whereas the studies on multiple solar source polygeneration systems are limited. On the other hand, multiple source polygeneration systems are of great interest in zero energy buildings. Hence, this study proposes a novel polygeneration system powered by two solar sources. Photovoltaic thermal and parabolic trough collectors are used in a series configuration with water as working fluid for this purpose. The proposed system is equipped with an ejector - compression refrigeration cycle (VCRC) with two different temperature levels (above zero and sub-zero) and an organic Rankine cycle (ORC) to provide cooling, heating, and power. The water out coming from the photovoltaic thermal (PVT) unit is used to cool the VCRC condenser, and hence it is preheated before entering the parabolic trough collector (PTC) resulting in reduced sizing and the cost of the PTC unit. In this study, the impact of parameters such as water flow rate in PVT-PTC circuit, the effect of working fluid in the ORC cycle, and solar irradiation are investigated using the first and second laws of thermodynamic and economic analysis. The results show that in the same conditions, R123, R600, R245fa, R600a refrigerants have higher energy efficiency, respectively, so that the highest energy efficiency of 70.78% and exergy efficiency of 10.70% were calculated for R123 refrigerant. Furthermore, it is shown that the highest energy and exergy efficiency cannot be achieved together. Also, the results showed a payback period of 6.4 years for the proposed system.

Advanced parabolic trough systems are the promising technologies for the production of usable heat and electrical power. Here we study the effects of hot water temperature adjustment concept and optical concentrator on the thermal and electrical efficiencies of a new PTC/HTTEG configuration, which comprises parabolic trough concentrator and hybrid tubular thermoelectric generator. The hybrid tubular thermoelectric generator (HTTEG) was integrated within the collector tube, where the hot water is passed between the inner side of the absorber tube and the top surface of the HTTEG. Meanwhile, to create a large temperature difference across the HTTEG sides, a cold water is passed along the inner side of the HTTEG. A low consumption pump was energized using HTTEG power in order to keep the hot water temperature at 95 °C for a long time (temperature adjustment concept). Numerical simulations show that the improvement in performance of the hybrid system highly depends on the adjustment concept and optical concentrator. As the solar concentration ratio increases, the overall efficiency of the hybrid system increases significantly to 76.21% and the amount of hot water reaches to a maximum value of about 846.77 Liter/Day for a concentration of 30 suns. Also, the power generated by the HTTEG and hot water temperature stay stable at 71.37 W and 95 °C, respectively, due to the hot water temperature adjustment effect. To validate the results of numerical model, a new validation method was proposed and discussed. The comparison of results obtained with results of the exact solution indicates a good agreement.

The main goal of this investigation is the detailed analysis of a solar-driven trigeneration system under dynamic operation. Parabolic trough solar collectors are coupled with a sensible storage tank and feed a trigeneration unit which includes an organic Rankine cycle for electricity production and an absorption heat pump for heating and cooling production. The absorption heat pump is driven by the waste heat from the organic Rankine cycle condenser which operates at 120 °C. The total configuration is investigated on a dynamic basis by using the TRNSYS software. The analysis is conducted for locations in Greece and in Cyprus, while the majority of the results are presented for Athens. Firstly, the unit is optimized and it is found that for a solar field area of 100 m2, the optimum tank energetically has 1 m3 storage volume and the optimum heat source mass flow rate is 0.125 kg s−1. The results show that the system is able to operate efficiently for 8 months, from March up to October with a mean yearly energy efficiency of 36.43%. The results indicate that Athens is the best location for a solar-driven system in Greece, while Larnaca in Cyprus is the overall best location due to its higher solar potential. More specifically, the simple payback period in Athens is found at 12 years while in Larnaca at 7.8 years.

Solar energy is among the cleanest and most adaptable in comparison with other renewable energy sources. Considering the request for long-term using of solar collectors, developing and enhancing the performance of these systems has become one of the main subjects. Parabolic trough solar collector (PTSC) is one of the best usual solar collectors. improving the thermal performance of PTSC concentrates several attention and different approaches are evaluated to maximize the collector thermal efficiency with a reasonable penalty in the pressure drop and energy losses. For this reason, the use of different nanofluids as working fluids, as well as the use of various absorbers (receivers) are the major challenges and techniques which are examined. Therefore, in this study, a novel parabolic trough solar collector (PTSC) using U type tube is designed and manufactured. To increase the operational temperature, evacuated tube is used and performance of the mentioned system is experimentally examined using both distilled water and CuO nanofluid as working fluids. It should be noted that, CuO is selected as nanoparticle and water as base fluid. CuO/nanofluid. Absorption spectrum results of CuO/nanofluid at different resting times by using Ultraviolet–Visible (UV–Vis) spectroscopy examined. Experimental results for the changes in three important parameters including, performance index (PI), thermal efficiency as well as pressure drop are obtained for different mass flow rates including, 1, 3 and 5 L/min and also three particle volumetric concentrations including 0.01%, 0.05% and 0.08%. The results showed that, thermal efficiency, pressure drop and PI is mostly affected and increased by mass flow rate and nanofluid volume fraction. In addition, based on the experimental results, maximum thermal efficiency and performance index are obtained respectively 71% and 1.74, corresponding in the case of nanofluid with 0.08% volume fraction and mass flow rate of 5 L/min.

The CO2 transcritical Rankine cycle (CO2-TRC) has a great potential for the application in concentrating solar power (CSP) system due to the advantages of using low- and medium- temperature sources and compact structures. However, the cloud passages always lead to the suddenly varied heat input to the system, while understanding the system’s response to the cloud disturbance may enable the operational stability which is viable for driving the advanced CO2-TRC system. In this study, a dynamic thermodynamics model is developed to simulate the response behaviors of the simple and regenerative CO2-TRC based trough CSP systems under various cloud disturbances. The results show that by examining the system’s performances, the cloud thickness mainly affects the variation range, while the cloud cover duration mainly affects recovery time. At the same cloud thickness, the recovery time for the regenerative system could be about three times longer than that for the simple system. Subject to the cloud with same cover duration, the simple system tends to reach the stable state in the shorter time. As the collector is shaded by a moving cloud, the system’s recovery time is almost same but the system efficiency has the smaller decrease as compared to the stationary cloud coverage with the same duration. These results allow determining the optimal design and operating scheme of the CO2-TRC based CSP systems to increase the output power and operating stability.

The Organic Rankine Cycle (ORC) technology is recognized to supply electricity from low temperature waste heat and solar energy sources. When the ORC system is heated by solar energy it uses two-fluids and two-loops, producing a relatively low thermal efficiency. To increase the ORC applicability, a solar energy assisted ORC system of single loop is proposed. The aim is to reduce the ORC heat transfer losses, minimize the equipment initial and maintenance cost and enhance the thermal efficiency. This is achieved by using bladder tanks which may improve drastically the ORC technical and economic performance. This method allows the heating to vary in the collector keeping the turbine inlet condition as a constant, impacting on the heat transfer losses and simplifying the configuration. The paper shows that an ORC of a single fluid can keep a constant turbine inlet despite the mass flow rate variations due to the suns radiation incidence, therefore, reducing the risk of likely faults in the turbine caused by high frequency vibration. An ORC enhanced 10.54% thermal efficiency is obtained with 0.5 kg/s of R1233zd(E) and a pressure ratio = 5, powered by parabolic trough collectors to generate 10 kW during eight hours per day. The ORC competitiveness is dictated by a total generation cost of 54.3 $/MWh and the advantages of a single working-fluid single loop simplicity for overall configuration.

The prediction of thermal distributions around the heat collector element (HCE) is a key issue for the safety and efficiency in parabolic-trough solar collectors. Obtaining 3D temperature fields involving the non-uniform heat flux distribution (NUHFD) around the receiver becomes an essential matter for modelling and simulation tools. Several 3D numerical studies have been implemented using computational fluid dynamics (CFD) commercial software, but with high computational effort. As an alternative, 3D HCE models coupled to 1D heat transfer fluid (HTF) problem results in a much lower computational cost and accuracy enough. In the present work, a realistic 3D HCE − 1D HTF model under an unsteady formulation of the partial differential equations is implemented to properly calculate the receiver thermal distribution. The model is solved using the finite volume method, involving the NUFHD through a Monte Carlo ray-tracing method implemented in SolTrace. Its main novelty is to involve a correction factor (CF) in the standard heat transfer coefficient (HTC) correlations for uniform boundary conditions (BC), due to their inability to correctly predict the absorber thermal profiles. The suggested CF is based on the azimuthal local Nusselt reported in past studies for circumferentially-varying BCs, and on the absorber experimental data from the Direct Solar Steam (DISS) test facility. The model is validated in the AZTRAK platform and the superheated steam region of the DISS facility under steady-state conditions. The heat transfer variables mean deviations are lower than 2.4 % and 7.0 % for AZTRAK and DISS facilities, respectively. The involvement of a CF in the DISS facility improves the accuracy of absorber cross-section thermal gradients predictions, reducing the mean deviations from 22.2 % (without considers it) to 6.9 % . Otherwise, the verifications against previously models in AZTRAK platform certify the necessity to correct the standard HTC, but the absence of absorber thermal profiles experimental data inhibits its validation.

The aim of this work is to analyse the integration of solar industrial process heat with novel latent heat storage systems by means of a representative case study that has a demand profile with different temperature levels. To that end, an innovative thermal storage system is proposed to support the contribution of the solar field to the industrial heat demand. The storage system considered is based on the latent heat of the solid–solid transition of pentaglycerine and it seems particularly interesting for industrial applications with space limitations and low temperature differences. Additionally, it may suppose further advantages in terms of corrosion, degradation and low cost of raw material. Thermal tests have confirmed the suitability of pentaglycerine as storage material for such applications. In this case study, a solar field with parabolic-trough collectors coupled to a pasteurization process has been considered. To analyse the expected behaviour of the proposed system, a simulation model has been developed in TRNSYS. This model defines, for the first time in the literature, a complete set of operation modes and control strategies specific to concentrating solar collectors for industrial process heat applications with latent storage, able to deal with the required variable temperature levels. Annual simulations have been performed using locations and meteorological data of Graz (Austria) and Plataforma Solar de Almeria (Spain). The simulation results show that the percentage of annual heat demand covered with solar energy could be increased from 20% to 27% in Graz or from 40% to 52% in the PSA by using 3 h of latent heat storage.

By making the nanofluids separately flowing into two concentric segmentations in a direct-absorption parabolic-trough solar collector (DAPTSC), we recently showed that the dual-nanofluid DAPTSC with a semi-cylindrical reflective coating could reduce the heat loss to the environment by employing the nanofluid of lower concentration in the outer section while the nanofluid of a higher concentration in the inner section. In this work, we propose to replace the semi-cylindrical reflective coating with a semi-cylindrical absorbing coating for exploiting both volumetric and surface absorption of the solar radiation. It is shown that the DAPTSC with a hybrid of volumetric and surface absorption can achieve a significantly higher thermal efficiency than the previous design of a DAPTSC with a reflective coating, especially when the absorption coefficients of the nanofluids are low. This opens a new opportunity of further reducing the nanoparticle concentration in a DAPTSC.

An innovative hybrid solar-municipal solid waste power system has been proposed for advancing the waste-to-energy and solar thermal energy technologies. The integration is realized by exploiting the useful heat harvested from sunlight in the parabolic trough collectors to reheat the working steam of the incineration plant and promote the steam temperature. Consequently, the steam cycle performance can be remarkably improved with the efficient utilization of solar energy. The hybrid design was thermodynamically and economically assessed based on a 500 t/d incineration plant, and the performance enhancement mechanism was revealed. Furthermore, a sensitivity analysis was conducted to examine the performance of the hybrid system under various solar conditions. The results indicated that the ideal steam cycle efficiency is boosted by 0.93 percentage points when adopting the proposed solution. The solar energy contributes to producing 1.17 MW net power with a solar-to-electricity efficiency of 21.59% at the design point. The integrated system performs excellently for most of the year, and the annual solar-to-electricity of 16.19% is achieved. Regarding a lifespan of 30 years, the levelized electricity cost of the solar-aided reheating system is as low as 0.1202 $/(kW∙h). Hence, the novel design is thermodynamically and economically suitable.

A dynamic optical model was established for the Yanqing solar field at the parabolic trough solar thermal power plant and a simulation was conducted on four separate days of clear weather (March 3rd, June 2nd, September 25th, December 17th). The solar collector assembly (SCA) was comprised of a North-South and East-West layout. The model consisted of the following modules: DNI, SCA operational, and SCA optical. The tracking angle characteristics were analyzed and the results showed that the East-West layout of the tracking system was the most viable. The average energy flux was simulated for a given time period and different SCA layouts, yielding an average flux of 6 kW/m 2 , which was then used as the design and operational standards of the Yanqing parabolic trough plant. The mass flow of North-South layout was relatively stable. The influences of the defocus angles on both the average energy flux and the circumferential flux distribution were also studied. The results provided a theoretical basis for the following components: solar field design, mass flow control of the heat transfer fluid, design and operation of the tracking system, operational safety of SCAs, and power production prediction in the Yanqing 1 MW parabolic trough plant.

This paper evaluated the influences of three kinds of geometrical deformations including global deformation, local rotation deformation and local linear deformation, on the optical performance of parabolic trough solar collector (PTC). An optical analysis of PTC system with different geometrical deformations was performed with the Monte Carlo Ray-Trace method to predict the optical efficiency and the radiation flux distribution on the receiver. The results show that the elliptic profile of the concentrator mirror results in a local hot spot on the receiver, which may shorten the receiver service life, among those cases with different global deformations. The optical performance of parabolic trough concentrator is almost not affected by rotation angle in the range of −0.3 to 0.3°. And the optical efficiency could be maintained above 90% of that under non-deformation condition when the linear deformation length is less than 6.0% of half aperture width. The local deformation at the bottom of the concentrator induces a more apparent deficit of the performance compared with the case of top local deformation. Additionally, the optical efficiency is inversely proportional to the length of part which is removed from the concentrator.

The use of gas working fluids in concentrating solar collectors is an easy way to operate in high temperature levels. This study is an energetic and exergetic comparison of various gas working fluids in a commercial parabolic trough collector (PTC). Air, nitrogen, carbon dioxide, helium, neon and argon are the examined working fluids. The objective of this study is to determine the optimum operating conditions for every working fluid and to make a parametric comparison among the examined gasses. Mass flow rate and fluid inlet temperature are the examined parameters in order to predict which combination of these leads to maximum exergetic efficiency. The final results proved that helium is the best working fluid for inlet temperature up to 700 K, while carbon dioxide is the most appropriate solution for higher temperature levels. The global maximum of the exergetic efficiency is achieved with helium operating to 640 K inlet temperature and 0.035 kg/s mass flow rate. Moreover, it is essential to state that the optimum mass flow rate depends on the operating temperature level for every examined working fluid. For this study, a detailed numerical model is developed in Engineering Equator Solver (EES), including all the proper energetic and exergetic equations.

Achieving the goals of the U.S. Department of Energy (DOE) Sunshot initiative requires (1) higher operating temperatures for concentrating solar power (CSP) plants to increase theoretical efficiency, and (2) effective thermal energy storage (TES) strategies to ensure dispatchability. Current inorganic salt-based TES systems in large-scale CSP plants generally employ molten nitrate salts for energy storage, but nitrate salts are limited in application to lower temperatures—generally, below 600 °C. These materials are sufficient for parabolic trough power plants, but they are inadequate for use at higher temperatures. At the higher operating temperatures achievable in solar power tower-type CSP plants, chloride salts are promising candidates for application as TES materials, owing to their thermal stability and generally lower cost compared to nitrate salts. In light of this, a recent study was conducted, which included a preliminary survey of chloride salts and binary eutectic systems that show promise as high temperature TES media. This study provided some basic information about the salts, including phase equilibria data and estimates of latent heat of fusion for some of the eutectics. Cost estimates were obtained through a review of bulk pricing for the pure salts among various vendors. This review paper updates that prior study, adding data for additional salt eutectic systems obtained from the literature. Where possible, data are obtained from the thermodynamic database software, FactSage. Radiative properties are presented, as well, since at higher temperatures, thermal radiation becomes a significant mode of heat transfer. Material compatibility for inorganic salts is another important consideration (e.g., with regard to piping and/or containment), so a summary of corrosion studies with various materials is also presented. Lastly, cost data for these systems are presented, allowing for meaningful comparison among these systems and other materials for TES applications. Because chloride salts may be employed as either sensible heat storage in the molten phase or as sensible and latent heat thermal energy storage (LHTES) as phase change materials (PCMs), cost of the candidate salt systems are presented on a cost per unit mass basis (sensible heat storage application) and a cost per unit latent heat of fusion basis (latent heat storage application). A total of 133 chloride salt systems were investigated.

The aim of this paper is to study the thermodynamic performance of a proposed integrated solar/North Benghazi combined power plant under Libyan climatic conditions. The parabolic trough collector field with direct steam generation was considered as solar system. Two modes of operations with the same solar field area are considered: fuel saving mode in which the generated solar steam was used to preheat the combustion air in the gas turbine unit and power boosting mode in which the generated solar steam was added into the steam turbine for boosting the electrical power generated from steam turbine unit. Moreover, the economic impact of solar energy is assessed in the form of benefit/cost ratio to justify the substitution potential of such clean energy. This study shows that, for fuel saving mode: the annual saving of natural gas consumption and CO 2 emission are approximately 3001.56 and 7972.25 tons, respectively, in comparison with the conventional North Benghazi combined cycle power plant. For power boosting mode: the annual solar share of electrical energy is approximately 93.33 GW h. The economic analysis of solar supported plant has indicated that the benefit/cost ratios are 1.74 and 1.30 for fuel saving and power boosting mode, therefore, then fuel saving mode is more economical than power boosting mode for the same solar field area, moreover, it reduces the greenhouse CO 2 emission in order to avoid a collapse of the word climate.

Gurel, Ali Etem/0000-0003-1430-8041 WOS: 000381530600091 A new, mixed-mode, fluidized bed drying system was developed using a solar energy system. The system was comprised of a solar air collector, a parabolic trough collector, and a heat pump system. The performance of the fluidized bed drying system was assessed by conducting energy and exergy analyses. This fluidized bed dryer was used to investigate the drying kinetics of mint leaves. The temperatures of the air used for drying by the solar energy system and the heat pump system were 45 and 50 degrees C, respectively. The energy and exergy efficiencies of the system were found to be 50 and 26%, respectively. The heating coefficient of performance (HCOP) was suggested as a new performance parameter of a solar energy system. The heat pump system had a coefficient of performance (COP) value of five. In other words, the heating coefficient of performance of this solar energy system was 10. (C) 2016 Elsevier Ltd. All rights reserved.

Nanofluid with unique mechanical, optical, and thermal properties, offers unique advantages over conventional fluids. In this paper, the applications of nanofluids on the parabolic trough collector (PTC) systems are investigated. A multi-field coupling simulation based on Finite Element Method (FEM) is implemented to investigate the performances of the PTC system using Al2O3/synthetic oil nanofluid as heat transfer fluid (HTF) with non-uniform heat flux distributions. The effect of Al2O3 particle concentrations and the influences of the key operating parameters on the PTC systems are also investigated. The numerical results are compared with experimental data and good agreement is obtained, proving that the proposed numerical model is feasible. It is found that the temperature gradients and the maximum temperature in the absorber are greatly reduced by using Al2O3/synthetic oil nanofluid. The temperature gradients and the deformation of the absorber decrease with the particle concentrations. The bending of the absorber decreases from 2.11 mm to 0.54 mm when the volume fraction increases from 0 to 0.05. Compared with the PTCs using synthetic oil, the collector efficiencies of the PTC systems using Al2O3/synthetic oil nanofluid are higher, moreover, the changes of temperature in the absorber with the direct normal irradiance (DNI), the inlet temperature, and the inlet velocity are remarkable reduced. This work provides a fundamental reference to the application of nanofluid in the PTC system.

Coal-fired power plants are the dominant form for power generation in many countries, even though they are the main contributor to the current environmental crises. The solar aided coal-fired power plant is an attractive new way to reduce the coal consumption by using solar energy. From the perspective of operational mechanism and coupling property, an all-condition mechanism model of the solar aided coal-fired power plant is proposed in this paper. The operation of an N600-24.2/566/566 supercritical coal-fired power plant hybridized with parabolic trough solar collectors is simulated using Matlab/Simulink in the fuel saving mode. And a new evaluation index of solar energy is proposed to reasonably assess solar energy contribution to the solar aided coal-fired power plant. When the solar steam is used to replace the extraction steam in the feedwater heating system, the change of the main steam, the reheat steam, and the extraction steam are discussed as the coupling property is taken into account. Furthermore, thermal economic analysis is carried out to optimize the solar steam replacement and the entrance of inlet feedwater to the solar field. Moreover, the efficiency and output power of the high pressure cylinder, the intermediate pressure cylinder, and the low pressure cylinder are discussed when the extraction steam is replaced by the solar steam in the feedwater heating system. Finally, the output power shock of the solar aided coal-fired power plant caused by the fluctuation of Direct Normal Irradiance is assessed. It is found that the strong fluctuation of Direct Normal Irradiance affects the power quality of the solar aided coal-fired power plant significantly.

Design and optimization of a solar power plant are very complex and require many calculations, data and time. From this point of view, artificial neural network (ANN) models are desired options to determine techno-economic performances of this kind of plants. Therefore, the objective of this study is to investigate the feed-forward back-propagation learning algorithm with three different variants; Levenberge Marguardt (LM), Scaled Conjugate Gradient (SCG), and Pola-Ribiere Conjugate Gradient (CGP), used in the ANN to find the best approach for prediction and techno-economic optimization of parabolic trough solar thermal power plant (PTSTPP) integrated with fuel backup system and thermal energy storage. The obtained statistical parameters showed that LM algorithm with 38 neurons in a single hidden layer looks as the best ANN model to predict the annual power generation ( PG net ) and levelized cost of electricity (LCOE) of the presented PTSTPP. Moreover, the obtained weights from this topology were used in the LCOE analysis for determining the optimum system design. It is therefore available to get a minimum LCOE of 8.88 Cent/kWh from the new optimized plant when the plant characteristics are; 34 °C and 850 W/m2 for both design ambient temperature and solar radiation, 23 m for row spacing, 1.7 for solar multiple, and 2.5 h number of hours for the storage system.

Direct absorption solar collectors (DASCs) form a new class of collectors that directly harvest sun beams via a working fluid. They offer several advantages over their conventional surface absorption counterparts such as reduced surface heat loss and increased solar irradiance absorption. The optical and thermo-physical properties of the working fluid may be improved and system efficiency may be enhanced in direct absorption solar collectors (DASCs) by introducing nanoparticles into the base fluid. The present study investigates, both analytically and experimentally, the effects of CuO/Water nanofluid on the efficiency of a direct absorption parabolic trough collector (DAPTC). The theoretical analysis of DAPTC is based on the power-law with the objective of simulating a turbulent flow into the receiver pipe. Comparison of the results obtained from the model and the experimental measurements reveals a good agreement between the two sets of data, indicating that they can be exploited to validate the numerical solution. Moreover, modeling results indicate that the average radial temperature and energy generation terms due to the solar irradiance absorbed and scattered by the nanoparticles decrease with increasing distance from the receiver pipe wall. It is also found that the solar irradiance is absorbed and converted into a significant amount of sensible heat along the length of the receiver pipe. Finally, the results of both the numerical and the experimental investigations of the DAPTC collector show that the thermal efficiency of the system improves as a result of increased nanoparticle volume fraction and nanofluid flow rate.

Although most of recent commercial Solar Thermal Power Plants (STPP) installed worldwide are parabolic trough plants, it seems that Linear Fresnel Collectors (LFC) are becoming an attractive option to generate electricity from solar radiation. Contrary to parabolic trough collectors, the design of LFC receivers has many degrees of freedom, and two basic designs can be found in the literature: single-tube and multi-tube design. This article studies the single-tube design, for which a thermal model has been developed. This model has been thought to be accurate enough to characterize the heat transfer in a non-elementary geometry and flexible enough to support changes of the characteristic parameters in the receiver design. The thermal model proposed is based on a two-dimensional, steady-state energy balance, in the receiver cross section and along its length. One of the features of the model is the characterization of the convective and radiative heat transfer in the receiver cavity, as it is not an elementary geometry. Another feature is the possibility of studying the receiver performance with different working fluids, both single-phase or two-phase. At last, the receiver performance has been characterized by means of the energy and exergy efficiency. Both variables are important for a complete receiver thermal analysis, as will be shown in the paper. The model has been first applied to the comparative study of the thermal performance of LFC receivers based on the value of some parameters: selective coating emissivity in the tube and inlet fluid thermal properties, for the case of using water/steam. As a second result, the model has also been used to predict the performance of different working fluids: synthetic oil, water/steam, molten salt and air, also comparing the results of the Fresnel technology with those obtained in reference parabolic trough loops.