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Parabolic trough systems require accurate, reliable, and robust solar trackers to achieve their maximum thermal efficiency. This paper presents a dual closed-loop control strategy for single-axis solar trackers of parabolic trough systems. This strategy consists of the use of a dual control feedback through the integration of a typical photodiode-based solar sensors, to perform the coarse control, and a proposed shadow-based visual device that performs the fine position adjustment. A comparative analysis between a simple closed-loop control, typically used in parabolic trough systems, and the proposed control algorithm was conducted. Experimental tests were carried out for several days under different weather conditions. The experimental results showed that the mean solar tracking error obtained with the simple control was 0. 97 ° , while the error of the proposed dual control was 0. 21 ° ; i.e., the error decreased by 78%, demonstrating greater stability and robustness of solar tracking. The proposed strategy proved to be a technically and economically feasible option to increase accuracy, reliability, and robustness in single-axis solar tracking systems of parabolic trough systems. • Dual closed-loop control algorithm for one-axis solar trackers. • Visual-based device to estimate the Sun's apparent position. • High thermal efficiency of PTC systems due to low solar tracking error. [ABSTRACT FROM AUTHOR]

Advanced cleaning strategies for parabolic trough collectors at concentrated solar power plants maximize the yield and minimize the costs for cleaning activities. However, they require information about the current soiling level of each collector. In this work, a novel, data-driven method for soiling estimation with machine learning for parabolic trough collectors is developed using gloss values as a surrogate for soiling values. Operational data and meteorological data from the solar field Andasol-3 with changing time horizons are used together with various Machine Learning techniques to estimate the soiling of every collector in the field. The best results were achieved with a Decision Tree model, with a coefficient of determination of R 2 = 0. 77 from the maximum value of 1 and a mean squared error of M S E = 6. 14 for the determination of specific soiling values. A second metric to evaluate the quality of soiling predictions from the models classifies whether soiling is above or below a cleaning threshold was also investigated. Model results are compared to soiling measurements that indicate the need for cleanings. Cleaning recommendations are derived and compared with the current fixed-time cleaning schedule of Andasol-3. All models show an improvement over the cleaning schedule currently in use. The use of a Decision Tree model increases the detected necessary cleanings by 12.2 %, while the number of unnecessary cleanings are reduced by 14.3 %. This has the potential to reduce operational costs and increase the solar field yield. The dataset used in this work is made publicly available https://doi.org/10.5281/zenodo.7061913 , along with the code to reproduce all results, which can be found at https://doi.org/10.5281/zenodo.7554806. • Data-driven soiling model for parabolic troughs with process and meteo data. • Comparison of various machine learning models and dataset sizes. • Evaluation of model for soiling prediction and cleaning schedule optimization. • Investigation of the most important model inputs via permutation feature importance. • Code and dataset available at (https://doi.org/10.5281/zenodo.7554806 , https://doi.org/10.5281/zenodo.7061913). [ABSTRACT FROM AUTHOR]

• A compact solar collector was designed and optimized for integration with buildings. • Optical/thermal performances were analyzed through theory, simulation and experiment. • Annual optical and thermal efficiencies are 57.6 % and 30.6 % @ 250 °C, respectively. • The tilt angle within latitude ± 10.5° has little effect on the optical efficiency. • The efficiencies can improve by manufacturing accuracy, vacuum degree and emissivity. Process industry consumed 15 % to 30 % of the global energy, and 40 % of it is thermal energy demand in the range of 80 °C-250 °C. To produce mid-temperature heat, a new solar collector was designed with heat pipe evacuated tube, including several parallel micro-parabolic troughs, heat pipes, double-layer vacuum tubes contained in a compact frame and an external mechanical solar tracker. In addition, the selective absorbing coating (SAC) was applied on the inner surface of the vacuum tube, and the gap between the heat pipe and the vacuum tube was filled with heat transfer oil. Since the height of the designed collector was only 124.5 mm, it can be easily integrated with buildings. Genetic algorithm (GA) was used to optimize the structural parameters based on maximum obtained solar energy of the collector, and theoretical analysis and numerical simulation are carried out for optical and thermal performance of the collector. The analytical and numerical results showed that the annual average optical efficiency is 57.6 % and the thermal efficiency is 30.6 % at 250 °C when the normalized temperature difference is 0.23. By exergy analysis, the collector has a maximum exergy efficiency of 15.5 % with operating temperature of 204.4 °C, which is the station of the best thermal performance of the collector. Furthermore, theoretical model was verified to be valid by a prototype. Overall, the proposed collector is suitable for mid temperature industrial applications and integrated with rooftop. [ABSTRACT FROM AUTHOR]

• The use of thermal oil in the PTC resulted in better results in the 3E analyzes. • PTC with incidence angle equal to zero, promotes lower rate of exergy destruction. • The rated PTC can mitigate up to 18.58 tons of CO 2 over its lifetime. A solar heating system operating in thermosyphon regime was experimentally evaluated in this study. The system consisted of a stationary parabolic trough solar collector (PTC) with thermal storage. The effect of three collector inclination angles (0°, +5°, and +10°) and two thermal fluids (water and thermal oil, denoted as WPTC 0° and OPTC 0°) were evaluated on the exergetic, enviroeconomic, and exergoeconomic (3E) performance of PTC. The average exergetic efficiencies for the evaluated cases were 10.84, 11.75, 12.97, and 19.73% for WPTC +10° , WPTC +5° , WPTC 0° , and OPTC 0° , respectively. It was observed that about 50% of the input exergy is lost in all cases evaluated, indicating that some improvements could be incorporated to recover part of this loss. WPTC 0° had the lowest average destroyed exergy among the inclinations (35%). For the case using thermal oil, the average exergy destroyed was 28%. OPTC 0° showed the best results in exergetic terms. OPTC 0° also presented the highest values of the exergoeconomic parameter among all the evaluated cases, and WPTC 0° presented the highest values among the evaluated inclinations. The energy and carbon payback times obtained were 0.848 and 0.569 for the WPTC 0° and 0.923 and 0.608 for the OPTC 0° , respectively. [ABSTRACT FROM AUTHOR]

• Concentration ratio formula for a circular concentrator with flat receiver is presented. • Development reveals existence of two concentration ratio regimes. • One regime relies on the caustics while the other relies on the rays from the rim. • The circle can match the concentration of the parabola for large acceptance angles. We present a simple analytical formula for the geometric concentration ratio of a circular trough optical concentrator coupled to a flat (planar) receiver. The receiver is sized to achieve full collection (no spillage) for any combination of acceptance and rim angle. The development reveals the existence of two concentration ratio regimes, one controlled by the edge ray caustics, and the other controlled by the intersection of the edge rays from the rim alone. Notably, we show that in the latter rim ray regime, the circular trough achieves the exact same geometric concentration ratio as a parabolic trough. The provided formula fills a gap towards the development of a complete catalogue of concentration ratio formulas for different concentrator/receiver geometries. [ABSTRACT FROM AUTHOR]

[Display omitted] • PLAL efficiently synthesizes MoS 2 /EG nanofluid with average dia. of 55 nm. • Higher laser wavelengths lead increased formation of MoS 2 Nanosheets. • Longer ablation reduces MoS 2 NPs bandgap, increasing nanosheets formation. • Laser parameters impact on the optimization of optical and thermal stability of nanofluid. • PTC with CSF (twist ratios < 1) improve efficiency; optimized MoS 2 /EG nanofluid improves Nu. by 6 %. Concentrating solar power plants equipped with parabolic trough collectors (PTC), widely installed globally, require heat transfer enhancements in their hydraulic systems. This paper explores replacing conventional heat transfer fluids with 2D-MoS 2 /EG nanofluids, synthesized using the pulsed laser ablation in liquid (PLAL) method. Due to the layer-dependent physical properties of MoS 2 nanosheets, tunability of PLAL in synthesizing uniform MoS 2 monolayer nanosheets in EG with enhanced thermal conductivity and stability for solar PTC is essential and it is not studied thoroughly yet. Thus, this study aims to provide insights into the influence of varying laser parameters on the optical, structural, and thermal properties of MoS 2 -EG nanofluids and their thermal-hydrodynamical performance in solar PTC. Results show that longer ablation time, especially at higher laser energies, reduces the bandgap, thereby effectively increasing nanosheet formation. This is confirmed by phonon modes indicative of monolayer nanosheets that were outcomed from RAMAN spectroscopy. Zetasizer analysis shows that increasing the laser wavelength from 532 nm to 1064 nm reduces nanoparticle average size from 88.6 nm to 55 nm. Conversely, higher laser energy increases particle size. The optimized nanofluid improved thermal conductivity by 12.5 % at 25 °C and 13.5 % at 75 °C, maintaining a 7 % enhancement after 30 days. Analytical evaluations of solar PTC under single and counter swirl flows (SSF and CSF) show that CSF configurations with a lower twist ratio (0.4) outperform SSF, improving performance by 67 %. Furthermore, introducing optimized nanofluid by PLAL enhances performance by an 6 %. These findings underscore the potential of synthesizing MoS₂/EG nanofluids with higher thermal conductivity and stability via PLAL for enhancing CSP thermal systems. [ABSTRACT FROM AUTHOR]

[Display omitted] • Conducting optimization in the MED desalination plants. • Transforming the process into a solar-powered one. • Making determination of cost-effectiveness by utilizing sensitivity analysis. • Parametric optimization of the multiple effect distillation process utilizing fossil fuels. • Identifying the most suitable solar collector and HTF from economic standpoint. The utilization of multi-effect distillation (MED) in thermal desalination processes is more widespread owing to lower energy consumption. The focus of this paper is to optimize the performance of MED through process optimization. It aims to identify the optimal operating conditions that result in maximum water and power production. Additionally, it investigates the potential of using solar renewable energy as a substitute for the current fossil energy source. Subsequently, a switch to solar energy was made with a focus on an economically viable approach. The research explored the best-suited collector and fluid for heat transfer among the 8 types of molten salt for use in the collector. Subsequently, an economic and sensitivity analysis was conducted using this procedure. The outcomes indicated that by enhancing the stated procedure, it was found that 27.93 Megawatt (MW) of heat would be required when 6938 ton/h of natural gas are burned. Additionally, the 4-effect MED process produced 6.123 MW of electricity and 116.5 cubic meters per hour (m3/h) of freshwater. The gain output ratio (GOR) of the process saw an uptick from 2.75 to 3.328, whereas MED efficiency showed progress from 13.76 to 49.218 %. The parabolic trough collector (PTC) collector outperforms the linear Fresnel collector (LFC) and solar dish (SD) collector in terms of efficiency among other results. To store heat for the rest of the day and night and supply thermal energy for the entire process, 155,542 square meters (m2) of this collector are necessary. Additionally, in regards to the thermal fluid of the PTC collector, coastal chemical registered heat transfer salt (HITEC salt), a commercial mixture of solar salt, has exhibited superior performance over other molten salts (for a total expenditure of 50 million dollars over two decades). In addition, the economic analysis has indicated a return rate of 32.46 % for the investment and a capital recovery period of 3.08 years for the process. The implementation of the mentioned process in renewable mode results in the avoidance of 18.5 tons per hour (ton/h) of carbon dioxide (CO2) emissions. [ABSTRACT FROM AUTHOR]

To ensure efficient and reliable operation of a concentrating solar-thermal power (CSP) plant, its solar collector field needs to accurately focus sunlight. The optical efficiency and structural integrity of the solar collectors is significantly influenced by wind conditions in the field. In this study, we present insights into dynamic wind loading on parabolic trough CSP collectors. We derive novel conclusions by analyzing a first-of-a-kind measurement campaign of wind and structural loads, performed at an operational CSP plant. Previous research primarily relied on wind tunnel tests and simulations, leaving uncertainty about wind loading effects in operational settings. We demonstrate that the parabolic trough field significantly alters the turbulent wind field within the collector field, especially under winds perpendicular to the trough rows. Our measurements within the trough field show reduced wind speeds, changes in wind direction and turbulence properties, and vortex shedding from the trough assemblies. These modifications to the wind field directly impact both static and dynamic support structure loads. Our measurements reveal higher wind loads on trough assemblies compared to those observed previously in wind tunnel tests. The insights from this study offer a novel perspective on our understanding of wind-driven loads on CSP collectors. By informing the development of next-generation design tools and models, this research paves the way for enhanced structural integrity and improved optical performance in future parabolic trough systems. • Wind loads on concentrating solar collectors impact their performance and reliability. • We measure wind loading on parabolic trough collectors in an operational plant. • We show novel insights about how a turbulent flow interacts with the collector field. • Static and dynamic wind loads on collectors are higher than observed previously in wind tunnels. • We characterize vortex shedding off exterior collectors. [ABSTRACT FROM AUTHOR]

Hybrid concentrated solar power/photovoltaic systems (CSP/PV) combine the advantages of the two separate systems while reducing their drawbacks. The design of such a hybrid system is challenging due to the various trade-offs between the thermal and electrical performance, and the overall system complexity. A reliable simulation model that includes all relevant optical, thermal, and photovoltaic aspects, can therefore be extremely useful to analyse the combined system performance and fine-tune the various design parameters. While multi-physics modelling of photovoltaic systems is well established, this is not the case for hybrid CSP/PV. In this paper, a novel multi-physics framework is presented for a hybrid system consisting of a parabolic trough with integrated PV cells covered by a dichroic coating, focusing incident sunlight towards a thermal receiver. Instead of monofacial PV cells, bifacial cells are considered for harvesting also the diffuse and ground reflected light at the back of the trough. The presented framework relies on an existing simulation tool for PV modules, that is combined with a ray-tracer that includes the spectral beam splitting functionality of the coating, and a novel 1.5D thermal model for the receiver tube. Long term outdoor monitoring results are used to predict the averaged, time-resolved annular thermal and electric energy yield of the system. This energy production is compared for three different multilayer coating designs with an increasing amount of (TiO 2 , SiO 2) layers. These results show that the amount of reflected sunlight towards the thermal receiver can be enhanced at the expense of the transmitted sunlight towards the PV cells, when a higher number of layers are used. The reduction of the incident power on the PV cells is however almost fully compensated by the enhanced spectral match of the transmitted light with the spectral response of the considered bifacial cells, in addition to the enhanced cell efficiency due to the lower thermalization losses. This results in superior system efficiency, for the application scenario where the generated thermal energy is also converted in electrical energy, and geographical locations with sufficient direct sunlight; a conclusion that is drawn from comparing the total electrical energy yield in Spain and Belgium, as a function of the thermal to electrical conversion fraction. [Display omitted] • Demonstration of a novel multi-physics simulation framework for hybrid CSP/PV systems. • Integration of long-term monitoring results allows predictive energy yield modelling. • Usage of bifacial PV cells enhances CSP/PV system efficiency for diffuse sunlight. • Number of layers in spectral beam splitter has crucial impact on system performance. • Geographical location determines potential application scenarios of hybrid CSP/PV. [ABSTRACT FROM AUTHOR]

• A comparative study of three cases for tabular solar still was carried out. • Enhanced tabular solar still with air injection, nanocoating and nanofluid was studied. • An energy, exergy, and economic analyses for the system were conducted. • The advanced tabular solar still distillate production cost per liter was 0.032$. • The advanced tabular solar still productivity has a 79.88 % increase over classic still. Nowadays, due to freshwater scarcity intensifying, researchers are actively seeking to improve solar desalination, a technology with immense potential, but there are still limitations in production capacity. This study investigated the integration of various additives in tubular solar still (TSS) at three configurations. In Case I, a V-corrugated basin and an air parabolic trough collector (PTC) equipped with evacuated tubes were integrated. Then, with the same attachments, CuO nanocoating was applied to the basin surface in Case II, aiming to enhance heat absorption. Finally, in Case III, CuO nanofluid was used in the presence of all previous enhancers. The system was studied during summer days with weather parameters having average ranges (minimum – peak) of 32.5–37.5 °C (ambient temperature), 318.5–1000 W/m2 (solar radiation), and 1.1–2.3 m/s (wind speed). The results were very acceptable and competitive. All modified configurations of the advanced TSS (ATSS) significantly increased distillate production compared to the classic TSS (CTSS), with a range of 49.84–79.88 %. Case III stood out as the most successful configuration, achieving outstanding gains in both energy and exergy efficiencies. Compared to the CTSS, Case III boasted an impressive 83.69 % improvement in energy efficiency and a staggering 242.45 % increase in exergy efficiency. This refers to a system that not only produces more desalinated water but also does so with significantly less wasted energy, making it a more environmentally sustainable solution. Case III also offered a good economic advantage with a 13.51 % cost reduction compared to CTSS. [ABSTRACT FROM AUTHOR]

• Parabolic trough collector with MXene based Syltherm 800 industrial oil was studied numerically. • MXene-based nanofluids exhibit enhanced thermophysical properties, largely due to MXene's favorable localized surface plasmonic resonance (LSPR) effect. • A higher Nusselt number indicates improved heat transfer and improved exploitation of solar energy. • The MXene/Syltherm 800 nanofluid has the lowest required solar radiation. • According to environmental and economic analyses, the emission rate for MXene/Syltherm 800 is approximately 0.031 $/day, while for the base fluid, the cost is 0.033 $/day. This study examines LS-2 parabolic trough collectors (PTCs) using MXene/Syltherm 800 nanofluids for enhanced solar power generation, focusing on energy, exergy, environmental, and economic (4E) aspects. Despite MXenes' remarkable thermophysical properties, their application in nanofluids is underexplored. This research aims to fill this gap by analyzing the performance of MXene nanofluids across varied inlet temperatures (277 °C to 377 °C) and Reynolds numbers (104 to 22,000), areas often neglected in prior studies. Employing a rigorously verified one-dimensional heat transfer model, the study compares MXene/Syltherm 800 nanofluid (0.1 wt%) with other nanofluids like Al 2 O 3 , TiO 2 , and SiO 2 in Syltherm 800, highlighting the exceptional thermophysical properties of MXene-based nanofluids. This superiority is attributed mainly to the localized surface plasmonic resonance (LSPR) effect, which significantly enhances solar heat interaction. For an inlet temperature of 377 °C and Reynolds number of 104, MXene/Syltherm 800 nanofluid achieves a notable thermal efficiency increase of 6.572 %. MXene/Syltherm 800 consistently outperforms in various conditions, showcasing significant environmental benefits in energy and exergy analyses: MXene/Syltherm 800 nanofluid leads to reduced CO 2 emissions and associated costs compared to the Syltherm 800. Specifically, at 377 °C and a Reynolds number of 104, MXene/Syltherm 800 nanofluid records a CO 2 emission of 2.343 kg/day, lower than Syltherm 800′s 2.453 kg/day, alongside a corresponding reduction in emission costs. Future studies should investigate MXene's stability, synthesis, embodied energy, and potential in carbon capture. [ABSTRACT FROM AUTHOR]

• Assessing the performance of a solar power systems based on 1 kW of capacity can lead to unfavorable decisions. • In terms of effective utilization of land area, photovoltaic solar power systems with horizontal single-axis tracking are the best option for low latitudes. • Nine solar power systems (4 photovoltaic and 5 concentrated solar power) were analyzed computationally considering high-sunshine regions, and were categorized into 3 tiers based on their energy generation intensity (EGI). • Three land-use oriented performance metrics were defined: monthly energy generation intensity (MGI), daily energy generation intensity (DGI), and hourly energy generation intensity (HGI); and were used to interpret the performance of different solar power systems in the summer and in the winter. • Adding solar tracking to photovoltaic power systems at low latitudes near the Tropic of Cancer has a limited improvement that may not justify the expenses and added complications. • There is consistency between the solar simulation tools: Energy3D and PVWatts Calculator, in terms of analyzing PV systems with fixed orientations or two-axis solar tracking. • There is consistency between the solar simulation tools: Energy3D and PVGIS, in terms of optimizing the angular orientation of fixed PV panels, and identifying months of peak performance. • Computer models are very useful in predicting the performance of solar power systems, thereby facilitating improved design and parametric optimization. • Adding absorbers to a linear Fresnel reflector system without adding a proportional number of reflectors (keeping the same ratio of reflectors to absorbers) is not recommended, and can actually cause a performance penalty. Solar radiation can be utilized for electricity generation through two main categories of solar power technologies: (1) photovoltaic (PV), and (2) concentrated solar power (CSP). In this study, three-dimensional computer models of electricity generation from 9 different solar power systems (4 PV and 5 CSP) using the simulation program Energy3D were used to establish a generic ranking of these systems in terms of the expected electric energy output during one year per unit land area. This performance metric is referred to as energy generation intensity (EGI), with 'energy' here referring to electric energy in particular. The analysis is aimed for low-latitude zones near the Tropic of Cancer. Solar power systems composed of long rows of connected PV modules, with single-horizontal-axis solar tracking (variable tilt), or with fixed optimized orientation were found to have the best EGI. On the other hand; heliostats with solar towers, PV units with single-vertical-axis solar tracking, and PV units with two-axis solar tracking were found to have the lowest EGI. Other four CSP systems: parabolic dishes, parabolic troughs, linear Fresnel reflectors (LFR), and compact linear Fresnel reflectors with two absorbers formed an intermediate group. Considering all of the 9 solar systems, the estimated EGI ranged from 113.1 kWh/year.m2 to 227.2 kWh/year.m2. The monthly contributions to EGI were contrasted; and daily and hourly energy generation intensities were examined on December 21 and June 21. Minor validation was performed using the simulation tool PVWatts Calculator for benchmarking, and using the web application PVGIS for PV systems calculation. [ABSTRACT FROM AUTHOR]

• Use the camera to shoot at different angles to obtain a complete flux profile. • Inversion method of traversal combined operation based on simplified algorithm. • Identify the types and values of the optical errors in the flux profile. • Flux image-based diagnosis of the Gaussian slope, gravity deformation and align error. In practice, there are multiple optical errors existing in parabolic trough concentrator, which respectively have a unique effect on the flux distribution on the wall of the absorber, causing it to deviate from the ideal operating condition. Diagnosis for multiple errors is difficult. The effect of combined optical errors on the flux distribution can be modelled using convolution operations. In this study, the flux patterns under multiple types of optical errors are traversed and combined, and the actual flux distribution profiles of the parabolic trough concentrator measured by a camera-based method are compared to identify the Gaussian slope error, gravity deformation error and alignment error of the concentrator. This indicates that it is feasible to invert the flux profile on the absorber wall and diagnose the types and values of the corresponding optical errors of the concentrator. [ABSTRACT FROM AUTHOR]

• A novel flat reflector was incorporated into a PTC to improve overall performance. • An optimal diameter of the AT was also studied to meet the 580 °C outlet temperature and maximum temperature below 600 °C. • AT's optimal diameter was 70 mm for this design reaching a 75% optical efficiency and 60.8% thermal efficiency at DNI = 1000 W/m2. • The optical efficiency could be increased by 4–12% and improved the uniformity by 2%–22% through adding a novel FR. Using a larger-aperture parabolic trough concentrator can reduce cost and improve cycle efficiency. At present, the maximum output temperature of the typical parabolic trough concentrator systems is lower than the set 580 °C. Here a novel flat reflector was incorporated into the absorber tube to improve the intercept factor and optical efficiency and hence the overall performance. At the same time, the optimal diameter of the collector tube was also researched to meet the outlet temperature exceeding the set 580 °C and the absorber tube's maximum temperature below 600 °C. A large-aperture parabolic trough concentrator (8 m aperture wide with 80° half rim-angle) is used as a case to demonstrate the effect of a flat reflector and advantages of the optimal absorber tube. Results obtained through simulations show that, in the large-aperture parabolic trough concentrator system with the flat reflector, the optimal diameter of the absorber tube was 70 mm for this design reaching 75% optical efficiency and 60.8% thermal efficiency at DNI = 1000 W/m2 and 53% daily average thermal efficiency for DNI = 400–1000 W/m2. Through adding a flat reflector, the optical efficiency and the uniformity were increased by 4–12% and 2–22% respectively, but the benefit gradually decreases with increasing the absorber tube diameter. To meet the requirement of outlet temperature more than 580 °C and absorber tube's maximum temperature below 600 °C and reduce the thermal strain, a scheme of adjusting flow rate was incorporated. [ABSTRACT FROM AUTHOR]

• Parabolic trough control with irradiation class dependent parameter. • All sky imager for the generation of spatial irradiation maps. • Robustness analyses for real applications. Parabolic trough (PT) power plants focus the sun's irradiation onto an absorber tube using collector mirrors to increase the temperature of the heat transfer medium (HTF). In the power plant, the HTF is used to generate electricity. To heat up the HTF, PT solar fields are set up in large areas and pipes are used to distribute the HTF in the solar field. The control system adjusts the temperature by changing the mass flow into the solar field and the focusing of the individual collectors. Transient conditions such as cloud passage are the main challenge for the system. State of the art control schemes use information from a few irradiation measuring points in the solar field. These measurement points are precise for the individual location but cannot accurately represent the irradiation situation in the whole solar field. In this paper, a control system that uses spatially resolved irradiation information from all sky imager systems is investigated. First, the control system was developed and tested in various simulation runs under ideal conditions. The focus of this work is to investigate the robustness of the control concept under non-ideal conditions. For this purpose, the simulation conditions are adapted to real situations and the behavior of the control system is analyzed. A robust behavior of the control system is shown in the simulations under different non-ideal scenarios. Overall, an improvement in electrical yield of 1.4% can be achieved compared to a reference without access to spatially resolved irradiance data. [ABSTRACT FROM AUTHOR]

Parabolic trough collectors are widely used to generate thermal and/or electrical energy from direct solar irradiation. These collectors use parabolic mirrors to precisely focus sunlight onto so-called absorber tubes. The optimal design and geometric alignment of all necessary components is essential in order to achieve a high degree of efficiency and a high energy yield. However, this optical fine-tuning process can be quite challenging and is in many cases avoided by using absorber tubes with larger diameters, which in turn cause greater thermal losses and a higher material effort. This paper describes a simple, yet reliable and quantifiable way to measure the optical performance of a parabolic trough collector using a commercial multi-junction solar cell (CPV). The presented measurement system allows for convenient adjustment of the parabolic mirror and the effective optimization of the overall collector design. The theoretical background is discussed and the test setup is described in detail. Measurement results are presented, ranging from the determination of the actual optical concentration ratio, the optimal centering and height adjustment of the absorber tube to the measurement of the contribution of the individual mirror segments, revealing that the investigated industrial parabolic trough collector can be improved in terms of optical accuracy. Finally, an optical surveillance of the mirror using a line laser was performed to validate the results. • New way to measure the optical performance of a parabolic trough collector. • Multi-junction solar cell (CPV) are used as a light sensor. • Theoretical background and various measurement setups and results are presented. • Optical concentration ratio of 128 x was measured with a parabolic trough collector. [ABSTRACT FROM AUTHOR]

• Solar industrial process heat (SIPH) plant dynamic model and simulation. • Flexible heat integration for SIPH increases solar share by 13.0%. • Flexible heat integration for SIPH reduces LCOH by 10.4%. • Proposed optimized SIPH plant reduces air pollutants by 17.4%. This study focuses on the modeling and simulation of a novel design and operation of a solar industrial process heat (SIPH) plant that uses a parabolic trough collector system for generating process heat. The SIPH plant incorporates flexible heat integration (FHI) by having two options for heat sinks as well as a flexible collection temperature for the heat transfer fluid. Leveraging the degrees of freedom created by FHI allows an optimized operating scheme to be created which maximizes the solar heat delivered to the industrial processes. Yearly results for a 27 MW-t plant located in Salt Lake City, UT are simulated for a base case and a case utilizing optimized FHI. For the main process temperature case presented, FHI increases the total solar share by 13.0% and reduces the levelized cost of heat of the SIPH plant by 10.4% relative to the base case. Three case study days are presented which highlight how FHI maximizes solar share, specifically during mornings, afternoons, and days with intermittent solar conditions. An environmental analysis is also performed showing that the SIPH plant can reduce harmful emissions by 15.4% for the base case and 17.4% for the FHI case compared to a plant that only utilizes a natural gas furnace for process heat. Overall, the work thoroughly explores an effective operating scheme for a SIPH plant, helping to make it more economical and environmentally beneficial. [ABSTRACT FROM AUTHOR]

[Display omitted] • A solar parabolic trough reactor shape optimization model is developed. • Catalytic tube shape described by Bézier parameterization curve. • Optimize the catalytic tube shape to enhance the methanol conversion efficiency. • Filling with metal foam reinforced PCM to improve reactor transient performance. • Less catalyst and higher overall performance are achieved in optimized reactor. Solar parabolic trough thermochemical reactor (SPTR) exhibits poor comprehensive performance due to the intermittent solar influence. In this work, a Bézier parametric curve-based shape optimization model is presented for designing the methanol steam reforming reaction-based SPTR filled with metal foam enhanced phase change material. Combined with the SPTR multi-field model, the catalytic tube shape in SPTR is well optimized by Globally Convergent Method of Moving Asymptotes, and finally an optimized rose-shaped catalytic tube with maximum methanol conversion efficiency is obtained. The SPTR performances of unoptimized original, customized and optimized tubes under constant and fluctuating solar flux are also analyzed and discussed in detail. The results show that the optimized tube and the small inlet cone-frustum tube have a better overall performance than the original tube, with about 67% reduction in catalyst usage. Especially for the optimized tube with optimal steady performance, methanol conversion efficiency, solar thermochemical efficiency and hydrogen yield are relatively improved by 4.3%, 8.2% and 2.4%, respectively, as compared to the original tube. The transient performance of the optimized tube also shows a relative increase of 8.6% and 8.2% in average conversion and hydrogen yield, and the reaction is more stable and safe in flux fluctuations. [ABSTRACT FROM AUTHOR]

This paper studies a method to enhance the performance of solar thermal parabolic trough power plants. The method can be applied to new designs and existing plants at a low cost and with minor modifications. It is called the turboefficiency concept because it is based on increasing the solar–electric efficiency of the plants by means of standard, low pressure turbines. These turbines would only be used at periods of high solar radiation, during which the solar resource exceeds the nominal power of the plant. By letting the solar field generate a minimal excess steam, and using it to power the small turbines coupled to pumps, the heat transfer fluid can be driven across the solar field saving the consumption of electricity of the normal electric pumps. This electricity would be sent to the grid, thus increasing the net production of the plant. The turboefficiency concept is based on standard, low cost components, and is conceived so as to be installed on an existing plant with minor modifications, during any of the programmed stops. A well known 50 MW plant design has been modelled and the turboefficiency concept has been modelled onto it. Then the increase in net electricity production has been estimated on two locations with slightly different solar irradiation profiles. This has been carried out for several sizes of the solar field. Results show that a minimum increase of several hundred of MWh can be expected in the case of a small solar field, in the order of 0.8% of the total annual production. Large solar fields, as those used with plants with thermal energy storage systems, can increase their annual production up to 2.1%. A preliminary economic assessment of installing the turboefficiency concept on an existing plant shows an improvement on the LCOE of a conventional plant can range from just over 0.1% to well over 1.3% for larger fields. • Novel method for powering the HTF pumps has been proposed. • The yearly electricity production is increased between 0.8% and 2.1%. • The effect of the solar size has been studied. • The simulation models are validated. [ABSTRACT FROM AUTHOR]

• New non-invasive method for mass flow determination for CSP via temperature sensors. • Time of Flight method successfully applied for mass flow determination in CSP plants. • Successful validation of ToF in CSP plants with PTC at loop level and subfield level. • Time of Flight method measures 94% of mass flow with deviations less than 5% • Mass flow determination method for efficiency improvement in commercial CSP plants. To maximize the thermal efficiency of Concentrating Solar Power (CSP) plants with a Parabolic Trough Collector (PTC) field, mass flow of the individual loops must be controlled carefully with the aim of achieving optimal loop outlet temperatures. An individual mass flow control has only been introduced in recent power plants, while a mass flow measurement with high temporal and spatial resolution has not yet been implemented. In this paper, the "Time-of-Flight" (ToF) method for the determination of the mass flow distribution through the individual loops of the solar field in a CSP plant is presented, based on measuring thermal step responses only with temperature sensors existing in typical power plant configurations. The ToF method is presented and validated with exemplary operational measurement data from the power plant Andasol III and determines the mass flow distribution through the solar field, measuring 94 % of the data within ±5 % of full scale. Knowledge and a good understanding of the mass flow distribution within the solar field enables the application of measures to increase the efficiency of power plant operation through improved loop balancing and improved early fault detection. For plants that already have high temporal and spatial resolution temperature measurements this ToF method enables the determination of the mass flow distribution without the installation of additional measuring equipment, and can thus be a powerful tool for the improvement of operation and predictive maintenance. [ABSTRACT FROM AUTHOR]

• Overall concept of centrifugal solar particle receiver-driven solid sulphur-based thermochemical cycle. • Commercial and composition-modified bauxite-based particles evaluated in non-solar-irradiated rigs. • Cu,Mn-modified bauxite particles showed high, stable SO 3 conversion for more than 1000 h. • Composition modification improved particles ' absorptance. • Thermomechanical properties of modified particles proved inferior to those of commercial ones. The present work is part of an approach targeted on demonstrating a concentrated solar energy-driven thermochemical cycle employing solid elemental sulphur as a chemical energy vector and a seasonal solar energy storage medium. In exploring the concept of coupling this cycle to a centrifugal particle solar receiver, bauxite-based particles, commercial and composition-modified, were tested and validated with respect to their suitability for simultaneous operation as solar energy harvesting media and sulphur trioxide splitting catalysts. Long-term catalytic activity tests exceeding 1000 h of operation at 850 °C, demonstrated that properly composition-modified bauxite particles were capable of achieving stable SO 3 conversion exceeding 70% (about 80% of equilibrium value under conditions studied) and exhibiting no or negligible loss of catalytic performance after this extended operation. In addition, such composition modification enhanced the particles' solar irradiation absorptance, which resulted in substantially higher than that of their commercial, non-modified bauxite counterparts. Commercial bauxite particles on the other hand, demonstrated much better mechanical strength, flowability, and attrition- and thermal shock resistance together with measurable, yet lower catalytic activity, which deteriorated with prolonged on-stream exposure. The combined results obtained advocate for the eventual selection of an "allothermal" cascaded sulphur trioxide splitting/sulphuric acid decomposition reactor, containing a non-moving catalytic bed that is heated indirectly by a moving bed of high-temperature (≥900 °C) non-modified commercial bauxite particles irradiated in the centrifugal solar particle receiver. [ABSTRACT FROM AUTHOR]

• The new olive mill sludge treatment arrangement solves the problem of water retention and the presence of oil covering the sludge. • The drying air temperature could be maintained above 100 °C for 10 h. • A drying air temperature of 128 °C was observed for a 3 m/s airflow speed. • Solar thermal energy supplied annually, leads to avoiding about 15899.69 kg (eq) of CO2 emission. The olive mill sludge treatment system developed in this study is an indirect solar dryer driven by a solar parabolic trough collector (PTC). A heat exchanger is implemented to heat air with hot oil coming from the solar collector. The developed hot air dryer can treat up to 50 kg of olive mill sludge distributed over six trays at once. The designed system and its components are described, along with their experimental and simulated performance evaluations. With a mean direct normal irradiation (DNI) higher than 800 W/m2 and a 3 m/s airflow speed, a maximum drying air temperature of 128 °C was measured. The drying air temperature could be maintained above 100 °C for 10 h. This high temperature is advantageous for the drying problems associated with the presence of oil in the sludge to be dried. The high temperature can also reduce the drying time required to achieve the target moisture content needed for sludge valorization as biomass by 30%. The designed dryer configuration with an adjustable air blower leads to homogeneous sludge treatment. As a result, the position of the sludge inside the drying chamber has no significant effect on the drying rate. The overall analysis shows that maximum thermal efficiency of 58% can be achieved with the 23,909 kWh of thermal energy generated by the system throughout the simulated year of operation. This solar thermal energy supply leads to the mitigation of 15899.69 kg (eq) of CO 2 emissions. [ABSTRACT FROM AUTHOR]

• The absorber tube of parabolic trough collector is modified with the creation of slits within the arc-plug insertion. • Two different variants of slits of 2 mm and 1 mm thicknesses are considered. • Effects of viscous dissipation upon the enhancement of thermal efficiency (η) of modified parabolic trough collector is studied. • The effect of Brickman number upon the Nusselt number (Nu) and convective heat transfer coefficient (h) is also studied. This paper investigates the effect of slits within the arc-plug insert of the solar parabolic trough receiver (PTR). In order to predict the performance of the parabolic trough collector (PTC) with arc-plug slits within the absorber tube; two different variants of slits of 2 mm and 1 mm thicknesses are considered. Then, each of the variants of slits with different thicknesses are varied in terms of numbers of their occurrence in the arc-plug. The 2 mm thickness slits are varied in 5, 7, and 9 numbers with uniform space of separation between them in the arc-plug. While 1 mm thickness slits are varied from 11 to 13 in numbers and also maintaining uniform space of separation between them like in 2 mm thickness slits. The objective is to determine the effects of viscous dissipation within the slits of the arc-plug of PTR; and also, the optimized version of the slit with its numbers. It is found that 2 mm slits with 9 in numbers showed the highest value of thermal efficiency as compared to all other cases. The thermal efficiency (η) of the PTC with arc-plug slits are seen to be about 1.642 times of conventional PTC; whereas, 1.309 times of arc-plug without slits. Therefore, it is always beneficial to use slits within inserts of PTCs for its performance enhancement; but, the selection of slit's thickness and its numbers plays a vital role in its application. [ABSTRACT FROM AUTHOR]

• Experimental performance of 45 m2 non-tracking solar thermal array described. • Performance evaluated at 80 °C, 135 °C, and 170 °C in dirty and clean conditions. • Annual thermal generation estimated 1000 kWh/m2 at 100 °C and 700 kWh/m2 at 160 °C. • $300/m2 installed, $6.5/m2 annual O&M, levelized cost of heat 2–4 cents per kWh. • Applications in desalination, evaporation, steam generation, process heating. In this paper, the experimental performance of a 45 m2 solar field of non-tracking external compound parabolic (XCPC) collectors installed at the University of California, Merced is described. The solar field was operated during July-August 2020 in both clean and dirty conditions and at varying operating temperatures (70, 135, 170 °C) while operating an air heater, thermal evaporator, and double effect absorption chiller. Performance data was used to develop an instantaneous solar field performance model which was then incorporated into an annual performance model using TMY3 data to estimate yearly production from the solar field. The model predicts an annual generation of ∼1100 kWh/m2-year at 80 °C, ∼1000 kWh/m2-year at 100 °C, ∼900 kWh/m2-year at 120 °C, ∼800 kWh/m2-year at 140 °C, and ∼700 kWh/m2-year at 160 °C in California. The XCPC technology is currently expected to have an installed cost of $300/m2 and an annual operations and maintenance cost of $6.5/m2-year. Over a 25 year lifetime it provides a levelized cost of heat at 2–4 cents per kWh th delivered. This is below the cost of commercial natural gas in California and at temperatures ≤ 120 °C below the cost of industrial natural gas, which highlights the potential of the XCPC technology for decarbonizing thermal applications such as water and space heating, drying, sterilization, desalination, evaporation, low pressure steam, double effect absorption chilling, process heating, and more. The lifetime cost of emissions reductions is ∼$169 per metric ton of avoided CO 2 when replacing natural gas, ∼$137/MT CO 2 when replacing propane, and ∼$83/MT CO 2 when replacing electric heating. [ABSTRACT FROM AUTHOR]

• An LCOE analysis was created to assess the feasibility of spectral filtering systems. • Hybrid Si and GaAs systems were compared to a conventional parabolic trough system. • The hybrid systems can be economically viable depending on the solar multiple. The field of concentrating photovoltaic-thermal (CPV-T) systems based on nanofluid spectral filtering has advanced significantly in the past decade. However, there is still a need to perform economic feasibility analyses for these systems. In this work, an assessment of the cost of implementation of CPV-T power plants using the spectral-splitting technique was performed. Three types of solar power plant were analyzed, including a purely thermal parabolic trough, a hybrid Si-based, and a hybrid GaAs-based power plant. The levelized cost of energy (LCOE) algorithm included inputs obtained from random variables to obtain LCOE values and energy generation for each type of power plant as a probability distribution. The results show that a purely thermal parabolic trough system has a minimum LCOE of 13.29 ¢/kWh at a solar multiple of 1.75, while the hybrid Si and hybrid GaAs power plants had a minimum LCOE of 17.83 ¢/kWh at a solar multiple of 2.5, and 14.50 ¢/kWh at a solar multiple of 3. The results in this work demonstrate that spectral-splitting CPV-T power plants can achieve energy costs comparable to conventional parabolic power plants depending on the solar multiple, solar cell material, and technical and financial variables. [ABSTRACT FROM AUTHOR]

[Display omitted] • Eight absorbers with different simple geometries are used to address the attributes of the concentration ratio distribution over their surfaces. • A parabolic shaped absorber is found to provide a uniform distribution of the concentrated solar flux. • Operation with free absorber is found to result in a more uniform distribution as compared with operations with fixed absorber. • Two optimal shapes of the absorber have been obtained. Parabolic trough collector stands out as the most proven and widely adopted technology for concentrating solar power. A simple mathematical model based on dividing the trough's aperture and the surface of the absorber into small segments is developed herein. The model is used to investigate the influence of the design and operational parameters on the distribution of the concentrated solar flux over. In this study, eight absorbers with different geometries are considered and the effect of the rim angle, absorber's geometry, and operational mode on the distribution of the concentrated solar flux over their surfaces have been addressed. For all absorbers, it has been found that increasing the rim angle results in reducing the intensity of the concentrated solar flux with increase in its coverage area. The distribution of the concentrated solar flux over the surface of the parabolic shaped absorber (ABS.6) is found to be uniform over the portion of the surface located between its two rims. It has also been demonstrated that the operation under free absorber mode can help in redistributing the concentrated solar flux over the absorber surface resulting in a more uniform distribution compared to that over the surface of the fixed absorber. From the combined geometries of the investigated absorbers two optimal shapes are obtained and are found to perform much better than the circular absorber ABS.1. [ABSTRACT FROM AUTHOR]

• Methodology to identify the best integration scenario of solar process heat is presented. • The methodology includes data gathering, performance simulation, and pinch analysis. • It was applied to a case study: a parabolic trough collector into a grape juice company. • Solar heat integration at process level increased the solar fraction. A Chilean company dedicated to grape juice production used a 696 m2 parabolic trough collector to pre-heat the feed water of a liquefied petroleum gas boiler in a temperature range of 20–90 °C. During 2017 the solar field generated 241 MWh th of heat, a low value for a concentration collector of such dimensions located in a place with high irradiation. This study presents a methodology to identify enhanced scenarios of solar heat integration into a grape juice industry and among them select the best scenario from an energetic perspective. This methodology started with data gathering of the thermal processes of the industry and the solar field (monitoring campaign and logbook of the industry) to generate the annual thermal demand. In a second step, the maximum theoretical generation potential of the solar field (1,107 MWh th) was obtained with simulations in TRNSYS 18. Then, a Pinch Analysis to the process streams was performed to confirm that a higher solar heat integration potential (520 MWh th) existed. The next step consisted of identifying different scenarios to increase the solar heat integration and analyzing them with simulations in TRNSYS 18 to identify the best-case scenario. The main increase on the solar fraction was achieved for the scenario when the collector working temperature was increased up to 140 °C and when heat was integrated at process level. Furthermore, it was concluded that one of the reasons for low solar fraction was the low thermal demand during months with high solar irradiation. [ABSTRACT FROM AUTHOR]

• Novel concept for high-performance practical linear solar concentrators. • Realizing how the Fresnel strategy can be applied to aplanatic optics. • Multiple embodiments for the linear Fresnel aplanatic concentrator. • Analytic derivation of key concentrator characteristics. • Evaluation of the basic tradeoff between concentration and intercept factor. We propose the linear aplanatic Fresnel reflector (LAFR) as a novel optical design that is suitable for solar thermal power plants. It comprises a segmented primary reflector and a totally stationary secondary mirror and receiver. We show that it is capable of attaining the high intercept factors of conventional parabolic troughs at high concentration, while offering the practical and lower-cost benefits of linear Fresnel reflectors. The fact that dual-mirror Fresnel concentrators can be aplanatic had been overlooked, mainly due to the perception that Fresnel concentrators offer only one degree of design freedom (specifically, the shape of the secondary mirror). The problem is that the two leading orders of geometric aberration must be eliminated to achieve aplanatism, and hence two degrees of design freedom are necessary. After identifying the solar tracking strategy of the segmented primary reflector as the additional degree of design freedom, we derive analytic relations for its placement and curvature. The secondary mirror shape follows directly from the basic aplanatic formalism. We demonstrate that practical high-performance LAFR designs can achieve intercept factors as high as 0.84 at concentration values of ~26. [ABSTRACT FROM AUTHOR]

• S-CO 2 properties are strongly temperature-dependent in the operating conditions of PTC. • S-CO 2 properties vary considerably while passing through the receiver tube. • The net heat flux from one half of the heat collecting element is always negative. • The thermal efficiency of PTC varies slightly during a typical summer day. • Change of available solar incidence dramatically alters the outlet temperature of PTC. Recently, supercritical carbon dioxide, S-CO 2 , has been suggested for utilization as the working fluid in solar thermal power plants. Replacing current working fluids with S-CO 2 , however, is not a straightforward task. This work numerically investigates the heat transfer and flow filed in a parabolic trough solar collector which carries S-CO 2. A full-scale three-dimensional model of the parabolic trough is developed and analyzed using the Star CCM + software. The variation of carbon dioxide's thermophysical properties inside the receiver tube is considered. The computational model is validated against a set of experimental data published by Sandia National Laboratories with no more than a 2.81% error margin. The numerical experiment is carried out at five different times during a typical summer day in Albuquerque, NM. Numerical results confirm that in all cases, heat loss from the upper half of the receiver tube is more than the absorbed solar incidence on that side. At noon, when the absorbed heat flux on the lower surface of the receiver tube reaches its maximum at 29810 W/m2, the net heat loss flux from the upper half of the receiver tube reaches 2622 W/m2. Consequently, the heat transfer from the upper half of the receiver tube unfavorably impacts the thermal efficiency of the parabolic trough. Additionally, while from 8 AM to 12 PM thermal efficiency drops less than 2.4%, the S-CO 2 temperature increment grows over 182%. A reverse trend occurs from noon to 4 PM, mainly due to the change in the available solar incidence. [ABSTRACT FROM AUTHOR]

• Defocusing the four collectors of a loop may be needed to avoid overheating. • Defocusing collectors with fixed temperature set-points may not be the optimal way. • Exhaustive set-point tracking may not be needed in all the collectors. • FeedForward controllers can be enough to help the fourth collector defocus control. • Optimal temperature set-points can be obtained through an optimization process. One of the main control objectives in parabolic trough solar thermal plants is to maintain the outlet temperature around an operating point. For this, a synthetic oil flow is used as the main control variable. However, another crucial system of the plant is the defocusing safety system of the collectors to prevent the oil temperature from exceeding an upper limit to prevent its degradation. This will occur, in general, when the oil flow reaches the maximum possible and is not able to regulate anymore the temperature. This mechanism is generally applied based on heuristic rules and partial or total defocus, which leads to a large number of actuator actions and temperature oscillations. In commercial plants, this defocus mechanism is applied firstly to the last collector, and as necessary, other collectors are defocused. In addition, it must be taken into account that loops' parameters will be, in general, different. In this work, a FeedForward-based strategy is proposed to control the outlet temperature of collectors 1, 2 and 3 of a solar plant using the defocus angle as the manipulated variable. It is also proposed to dynamically obtain the set-point temperatures for the first 3 collectors through an optimization based on the concentrated parameter model. The results of the simulations are presented in different situations where the good performance of the strategy is observed. It is shown how the dynamic modification of the set-points can avoid possible energy losses on occasions where a fixed set-point of temperature is not the optimal option. [ABSTRACT FROM AUTHOR]

[Display omitted] • The LVC + RSR + SCR configuration enhances carbon capture with a 31 % exergy efficiency. • Solar integration enhances efficiency through synergistic solar-thermal practices. • Solar thermal power plants efficiently cut carbon emissions. • The LVC + RSR + SCR configuration boosts exergoeconomic efficiency by 3.4 %. • Development of post combustion carbon capture technology by doing sustainability. The extensive use of carbon capture methods is severely hampered by their high energy consumption, which frequently outweighs the advantages to the environment. The benefits of carbon capture systems in reducing climate change cannot be understated, notwithstanding this downside. In the worldwide effort to address climate change, the capacity to capture and store carbon emissions from power production facilities and industrial processes plays a key role in reducing overall greenhouse gas emissions. To enhance sustainability and minimize emissions, the study assesses the impact of system configuration modifications, including LVC + RSR, RSS, and various combinations. A solar-powered scenario is introduced, involving a trough or compound solar collector, such as LVC + RSR + SCR, LVC + RSR + SCSS, TSF, and LVC + RSR + SCSS + RSS. The findings indicate that, although the TSF design eliminates the substantial energy penalty, it outperforms the conventional configuration in energy efficiency but falls short in exergy and exergoeconomic efficiency. In contrast, the LVC + RSR + SCR configuration demonstrates superior performance across the three dimensions of energy efficiency, exergy, and exergoeconomic factors, with gains of 31 % in exergy and 3.4 % in exergoeconomic efficiency, while reducing the energy penalty to 11 %. [ABSTRACT FROM AUTHOR]

• PTC technology is slightly more efficient than LFC technology up to T HTF = 140 °C. The opposite is true above 150 °C. • The efficiency of the installation (E cf /energy demanded) depends on both the installed collector surface and the installation layout (series–parallel). • The C T E U depends mainly on the economy of scale factor and the %U (necessary to match the demand profile with the generation profile). • For medium sizes (10 GWh), the C T E U for LFC technology is lower than for PTC. For large sizes (60 GWh) there is hardly any difference. • The difference in performance of the installation between the most favourable and unfavourable location is approximately 35.7 %. Real energy consumption data were taken from the 17 most important companies of the dairy industry distributed across different Spanish geographical locations, studying the technical and economic feasibility of integrating solar concentration technologies suitable for the required thermal level of medium temperature in that industrial sector. The results show that the percentage of use of available thermal energy (%U) and the size of the solar plant, in addition to many other variables such as location, are decisive parameters for determining the cost of generating thermal energy and comparing it with the cost of conventional energies (natural gas, diesel and fuel oil). A 20-year time horizon is considered and three different scenarios are taken into account as regards the price evolution. Likewise, it is observed that, as the temperature of the heat transfer fluid rises, the generation of thermal energy decreases. The prices of solar thermal energy would improve the conditions offered by any conventional fuel (natural gas, diesel and fuel oil), unlike what happened just 2 years ago with natural gas. The lowest thermal power generation costs would be 3.41c€/kWht for LFC technology, and 3.69c€/kWht for PTC technology, both in Granada; being much lower than current prices (21 November 2022) for conventional fuels: 10.53c€/kWht for diesel (5.48c€/kWht, in 2021); 6.08c€/kWht for fuel oil (3.70c€/kWht, in 2021); and 7.29c€/kWht (Band I3) and 7.71c€/kWht (Band I4) for natural gas (2.35c€/kWht for Band I3 and 1.99c€/kWht for Band I4 in 2021). [ABSTRACT FROM AUTHOR]

[Display omitted] • Novel MXene/C-dot hybrid nanofluid was synthesized for application in DAPTC. • Nanofluid concentration was optimized for DAPTC and corrosion study was conducted. • Hybrid nanofluid exhibited least corrosion rate of 0.6 mm/year in corrosion analysis. • Hybrid nanofluid based system showed high photothermal efficiency of 47.5% Nanofluids having exceptional thermo-optical characteristics can enhance the performance of direct absorption solar collectors (DASC). Conventional nanofluids have either high optical properties or thermal properties. In this study, carbon quantum dot (C-dot) nanomaterial with high stability and optical absorption along the UV range, and MXene nanoparticles with high thermal conductivity and absorption along visible and near-infrared (NIR) spectral range was selected for synthesizing a hybrid nanomaterial with synergistic thermo-optical properties. Hybrid MXene/C-dot nanofluid exhibits higher stability, thermal conductivity, and complementary absorption properties of individual nanomaterials. A two-step method was used for the synthesis of nanofluids using water as the base fluid. Thermal conductivity, UV–Vis-NIR spectroscopy, and stability analysis were conducted on nanofluids, and the concentration was optimized for corrosion study and application in direct absorption parabolic trough collector (DAPTC). Optimised concentrations of C-dot, MXene, and hybrid nanofluids were 0.15 wt%, 0.1 wt% and 0.15 wt%, respectively. The corrosion study states that copper electrodes dipped in the hybrid nanofluid exhibited the least corrosion rate of 0.6 mm/year with an anticorrosion efficiency of 64.5 % over DI water. Thermal efficiency and entropy generation in the system with different HTFs were measured and compared with that of the base fluid. The study shows that C-dot and MXene/C-dot nanofluids were producing the highest efficiencies of 50.5 % and 47.5 % at a flow rate of 1.2 lpm. This study shows that hybrid MXene/C-dot nanofluid exhibited exceptional thermal stability, reduced corrosion effects, and considerable enhancement in photothermal conversion efficiency of the DASC. [ABSTRACT FROM AUTHOR]

• Optimal solar thermal systems (STS) identified for tropical solar adsorption cooling (SADCS). • PSO Algorithm & TRNSYS unveiling most efficient STS for Malaysia's SADCS. • Collector area impact boosting solar energy conversion & profit, reducing CO2 Emissions. • ETC dominance preferred heat supplier for adsorption chiller in tropical climates. • PVT's dual power & heat generation is key to highest energy savings & techno-economic potential. The technology and performance of solar adsorption cooling systems have reached maturity, enabling them to meet the growing demand for air conditioning. High upfront and operating costs have, however, hindered the commercial spread of solar adsorption cooling systems. Comparing the solar adsorption cooling system with commercial air conditioners, the solar thermal system offers superior efficiency. In order to enhance the techno-economic potential of solar adsorption cooling in Malaysia, this study developed a combination of analytical and conceptual frameworks in the form of a multilayer computational network to identify the most efficient solar thermal system. TRNSYS, MATLAB, and REFPROP software were used to model and simulate the solar adsorption cooling system. A Particle Swarm Optimization algorithm (PSO) implemented in MATLAB and linked to TRNSYS was then used to determine the optimal components and variables for each solar thermal system. To determine the most efficient solar thermal system, a techno-economic assessment was conducted to evaluate the solar adsorption cooling system incorporating optimized solar thermal systems. The findings reveal that among the various types of collectors investigated, the evacuated tube collectors demonstrated the highest efficiency in providing the necessary heat energy for the adsorption cooling system. In contrast, the linear Fresnel reflector collector and parabolic trough collectors display exceptional performance, mainly under clear sky conditions. Meanwhile, the photovoltaic-thermal collectors exhibit the greatest energy-saving and techno-economic potential. This advantage arises from their ability to simultaneously generate power and heat, taking advantage of the cost disparity between electricity and natural gas in Malaysia. [ABSTRACT FROM AUTHOR]

This research advances the field of Concentrating Solar Power (CSP) by offering a comprehensive assessment of freeze-recovery strategies for molten salt parabolic trough collectors, essential for the next generation of CSP plants. Employing a cutting-edge transient 3D Conjugate Heat Transfer (CHT) model, the research elucidates the significant yet previously underestimated role of natural convection in the phase transition of solidified salts. The study demonstrates that the strategic inclusion of impedance heating not only accelerates the defrosting process but also minimizes thermal stresses within the absorber tubes, ensuring mechanical integrity. Moreover, the dual-method approach, which combines solar and impedance heating, reveals a potential to improve the Levelized Cost of Electricity (LCOE) by 4% annually following a complete freeze event. The research conclusively suggests that this synergistic strategy could yield substantial operational cost savings while maintaining the structural robustness of CSP systems. The presented findings provide a detailed blueprint for enhancing plant resilience and economic viability, opening new avenues for operational excellence in CSP technology. • 3D model for salt melting in HCEs, aligned with experimental data, enhances accuracy. • Salt melt times reduced significantly through combined solar and impedance heating. • Freeze recovery within HCE stress limits confirms mechanical safety. • Potential over 4% annual LCOE reduction after full freeze events with new methods. • Melting slowed in non-illuminated HCE areas due to axial heat flow reliance. [ABSTRACT FROM AUTHOR]

• Implementation of a phosphate sludge dryer using a PTC loop as an energy source. • At average and minimum flowrates, air temperatures of 105 °C and 123 °C enable the target moisture. • All temperatures follow similar trends as DNI, which affects moisture sludge value. • Air temperature stays constant, enabling the target humidity throughout the sunny day. • On a cloudy day, the target moisture was achieved in only 25% of the drying time. This study presents an experimental analysis of a phosphate sludge drying prototype that uses a Parabolic Trough Collector (PTC) solar technology as an energy source. The interconnection of the system's three components, namely the PTC loop, oil-air heat exchanger (HX), and rotary dryer, is described. Experiments were carried out for each sub-system separately considering three air and Heat Transfer Fluid (HTF) flowrates, a drying temperature up to 135 °C, and a phosphate sludge flowrate of 5 kg/h. Results show that to dry sludge at the target humidity (≤7%), air at 105 °C is sufficient when operating at the average flowrate, this temperature increases to 123 °C at lower flowrate. The overall system was tested under the Moroccan semi-arid conditions for three typical days. All temperature profiles follow similar trends as Direct Normal Irradiation (DNI) variation; this latter influence the final sludge moisture value. During the sunny day, 32 kg of sludge was dried at the target moisture content throughout the day, with a relatively stable temperature (130 ± 4 °C). This amount decreased to 7 kg on the cloudy day while the target moisture content was achieved only 25% of the drying time. A back-up energy source or a thermal storage system is recommended to improve the drying performance during cloudy periods. [ABSTRACT FROM AUTHOR]

• New in-house 3D model for raytracing analyses of Linear Fresnel Collectors. • Study of the optical and energy efficiency of a real Fresnel plant. • Plant geometry optimization considering gap between mirrors and receiver height. • Maximization of the radiant energy arriving at the receiver aperture area. • Optimum value of the receiver height is not unique all over the year. Despite their few installations, Linear Fresnel Collectors (LFC) represent a very promising technology for efficient solar energy exploitation at medium to high temperatures thanks to their lowest land area per electric energy ratio. Their first appearance was in the '60, thanks to Professor Giovanni Francia realizations at the University of Genova, Italy. This research aims to determine the performance of a LFC and perform parametric studies through 3D ray-tracing simulations. The in-house developed code accounts for all geometrical parameters of the mirrors and receiver assembly, including mirror dimensions, curvature and distance, primary mirror optical errors, receiver aperture area and elevation, secondary mirror compound parabolic shape. The present study includes a detailed investigation on shading, blocking and end effect issues while introducing 6 different different optical and energy efficiency definitions. A parametric analysis is applied to the distance between mirrors and the receiver height. After the code validation against Tonatiuh, the calculations are performed to analyse in details the performance of a real LFC plant in Morocco. The peak optical efficiency of the test case plant has been estimated up to 87% but it is demonstrated the selection of the efficiency definition is crucial for performing successful geometry optimizations. [ABSTRACT FROM AUTHOR]

• Hybrid PTC-TES-biomass ORC-based polygeneration system design for a commercial centre. • The system produces the annual electricity consumed in the commercial centre. • Thermoeconomic analysis provides the cost of the internal flows and final products. • Investment costs reduction leads to system economic feasibility in the medium term. • The system displaces 96.1% of the CO 2 emissions relative to a conventional system. Hybrid renewable polygeneration systems are regarded as key solutions for the sustainable energy supply of buildings. While solar heating and cooling comprises a wide range of technologies, there has been limited research on the combined production of power and cooling only, with little or no heat demand. This study designs and analyzes a hybrid solar–biomass ORC-based polygeneration system from energy, economic, and environmental viewpoints. The polygeneration system is designed to cover the electricity and cooling demands of a commercial center located in Zaragoza, Spain. A parabolic trough collector field coupled with thermal energy storage, and an auxiliary biomass boiler supply heat to an Organic Rankine Cycle (ORC), which generates electricity to cover electrical demands and to produce cooling in mechanical chillers. The biomass boiler supports the solar thermal production to ensure a stable and reliable heat supply to the ORC. The system is connected to the electric grid, so that electricity purchases and sales are possible. The equipment sizing is performed with the goal of achieving a high renewable fraction in the total electricity consumed by the commercial center. The analysis of the proposed plant includes the hourly operation throughout the year, complemented by an economic assessment, considering investment and operation costs, and an estimate of the environmental benefits of the plant. Also, a thermoeconomic analysis is developed to determine the cost formation process of the internal flows and final products of the plant. The unit cost of each flow is broken down into investment and operation cost components. Sensitivity analyses of the investment cost, interest rate, biomass price, and electricity selling price discount are made. The results show that, in economic terms, the system is not presently viable, since the cost of the electricity produced (279.07 €/MWh) is much higher than the electricity purchase price (126.70 €/MWh). In environmental terms, the system is capable of displacing 96.1% of the CO 2 emissions and 85.6% of non-renewable primary energy consumption relative to a conventional system consuming grid electricity only. [ABSTRACT FROM AUTHOR]

The present review defines the state of the art of parabolic trough collectors and identifies the concepts in the framework of innovation's requirements. These are the increase of operating temperatures and of the power plant's overall efficiency, as well as the cost reductions of the solar field by eliminating components and the reduction of parasitic power consumption (Pitz-Paal et al., 2007). The study investigates 34 collector concepts and classifies them according to their main structural features like mechanisms or materials. The categories include conventional collectors in Category A, collectors with alternative structure and sheet reflectors in Category B, with non-metallic materials like sandwich composite structures and concrete in Category C, with enclosed aperture in Category D and with fixed focus in Category E. For the technical-economic comparison, two conventional collectors vs. 14 innovations are analysed, following a design engineering method. The definition of a metric table defines the technical comparison criteria for those collectors suitable for thermo-oils or molten salts as heat transfer fluid. Results show that collectors operating with molten salts, instead of thermo-oil, have a significant techno-economic potential for utility scale application, for instance, the Molten Salt Trough, the UltimateTrough and the SkyFuelDSP (dispatchable solar power) as forerunners of their respective categories. Results show also that the inflatable Heliovis collector operating with thermo-oil has a relevant economic potential. [ABSTRACT FROM AUTHOR]

• A comprehensive thermal hydraulic model of the solar field has been established. • An improved operation strategy of the plant has been developed. • The mechanism of optimization has been detailed explained. • The best operation strategy with nonuniform and degraded collectors has been chosen. In a commercial parabolic trough solar power plant (PTSPP), the solar field (SF) is large-scaled and consists of hundreds of parabolic trough collector (PTC) loops. The PTSPP performance is determined by an appropriate operation strategy of the SF, which is implemented by adjusting the outlet temperature, the flowrate, and the flow distribution through the valves and pump to make the PTSPP output cost-effective. Majority of the published literature study the behavior of the SF with an assumption that all the PTC loops have uniform perfect performance. Due to the lack of appropriate model and algorithm, although operating with nonuniform and degraded PTCs is inevitable for a realistic SF, there is scarcely any literature studies how to develop an optimal operation strategy under this situation. The present paper aims at solving this problem by establishing a PTSPP model and developing an improved operation strategy (IOS). The PTSPP model consists of an improved thermal hydraulic model of the SF and a simplified but effective model of the power block, and the IOS combines the features of both global and distributed operation strategy. Based on the model and the IOS, the mechanism of optimization is illustrated in a uniform case, and then according to the comparison and analysis, the most appropriate strategy for the nonuniform case is determined among three representative strategies. Compared with the traditional operation strategy, the chosen strategy can improve the net electric generation by 3.4% with the low computational cost and good engineering feasibility. [ABSTRACT FROM AUTHOR]

This paper presents a review of windows filled of water-based liquids which absorbs solar radiation and will be referred to herein as water-based windows (WBWs). These liquids have spectrally-selective and high thermal capacity properties for optical and thermal performance improvement. A WBW relates to windows that features transparent, semi-transparent, colorless or colored visual performance. Its profile consists of liquid layers inside clear or solar control multilayer glazing or tubular structures. A detailed analysis of WBW design differences and performance is carried out and studies were classified according to common characteristics regarding two main categories: WBW without and with fluid exchange. Optical and thermal methodologies are evaluated, highlighting the limitations and accomplishments for future researches. A water-filled WBW can transmit more light compared to the same glazing when empty. It can also perform substantially better than many commercially available glazing products, in terms of either promoting solar heat gain or reducing cooling demand. There was a predominance of cases with better heating performance for WBWs without fluid exchange. On the other hand, most cases of WBWs with fluid exchange where better for cooling performance if the circulating fluid was not preheated. Also, water heated in WBWs can be applied in the building facilities. [ABSTRACT FROM AUTHOR]

• Solar tubular receiver equipped with Raschig Rings tested in solar furnace. • Discrete Element Method (DEM) used to model the porous media. • CFD model validated against hydraulic and thermal experimental data. • Performance Evaluation Criteria (PEC) calculated to assess the thermal enhancement. In the context of central solar tower systems, tubular receivers are among the most appealing absorber solutions: the absorbed solar radiation is transferred from the tube external surface to the heat transfer fluid (HTF) flowing within the absorber. In the case of air as HTF, very high temperatures of the coolant can be obtained in principle, thus increasing the efficiency of the downstream thermodynamic cycle. To explore the possible applicability of a porous medium made of Raschig Rings (RRs), already successfully adopted in the heat removal from the resonant cavity of a technological device, the gyrotron, where the heat flux can go up to 20–25 MW/m2 and removed by subcooled water, a mock-up of a planar receiver equipped with RRs has been tested in a solar furnace, using air as coolant. The test results are presented here and analyzed 1 1 Based on experiments carried out at the Plataforma Solar de Almeria.. Furthermore, a numerical model of the mock-up, where the RRs are modeled in detail by the Discrete Element Method, is presented and its capability to reproduce the measured data demonstrated. The model shows, for the tested configuration, an enhancement of the heat transfer of a factor of ~5 with respect to a plain channel with the same envelope, and a Performance Evaluation Criteria of 2–2.5 when the device is compared to the same receiver configuration, but without RRs. [ABSTRACT FROM AUTHOR]

• Integration of Small Parabolic Trough collectors (SPTC) in Hybrid thermal energy production system for bitumen heating maintaining process. • Optimization of the proposed hybrid SPTC-fossil fuel-thermal storage system through thermal energy flow management. • Defining an innovative strategy of optimization with different double-objective function. • Combining trial and error method, multi-nodes method and genetic algorithm to resolve and optimize the equations system obtained from the proposed system modelling. • Optimized results are provided for different thermal storage capacities. Solar energy integration in heat consuming processes is a promising replacement for fossil energy. We are interested in a small Solar Parabolic Trough Collectors field combined with a sensible heat storage reservoir. Unfortunately, such a system has a higher cost than fossil energy and is challenging to optimize. Therefore, this work's main objective is to provide an optimized design and management to minimize energy cost (EC) and maximize renewable energy utilization fraction (REF). This study is done by optimizing the sizing and the thermal energy flow management of a hybrid solar-fossil fuel energy system. The optimization problem is formulated based on mass and energy conservation equations, heat transfer phenomena modeling, correlations, and economic data. We resolved it by combining trial and error method, multi-node calculation procedure, and genetic algorithm. To evaluate our method, we studied a hybrid solar-fossil fuel energy system used for the bitumen heat maintaining process in Rabat region-Morocco. The evaluation considered different thermal storage capacities. Using our optimization, we reached REF ≥ 40% and EC < 0.05US$/kWh for small thermal capacities and REF ≥ 85% and EC less than 0.2US$/kWh for large thermal capacities. This is equivalent to saving, respectively, more than 0.75 and 1.5 tons of CO2 emissions/year/kW for small and large thermal storage capacities. Other important recommendations are also provided in this work. [ABSTRACT FROM AUTHOR]

• Simultaneous application of solar/hydro/biomass/geothermal renewable resources. • Achievement of water/biofuel by a renewable hybrid system with a focus of solar energy. • Reaching higher water/biofuel's yield and lower production cost. This study aimed to design and construct a quadruple solar/hydro/biomass/geothermal hybrid system, using a techno-economic analysis for water/biofuel production as energy carriers. First, in the case of the ground source heat pump-assisted microalgal culture pond, three influencing factors including light intensity, salinity, and air injection were investigated for maximum biomass production. Then, in the parabolic trough collector, the flow rate of operating fluid, the used hybrid nanoparticles, and their ratios were considered for obtaining the highest thermal efficiency. After, providing a better solar still distiller for the highest water production efficiency, the pressure, fluid's flow rate, and the depth of solar still were investigated. Finally, the water/heart supply of producing biodiesel from the pond's biomass in the trans-esterified conversion reactor was provided from the distiller/collector. The results indicated that using a 300-lx light intensity, a 3-g/L salinity, and a 0.4-L/min air injection in the pond, a 3-L/min nanofluid, including CuO/GO (4:1) and mass fraction of 0.4 in the operating fluid in the collector, a 2.5-cm water depth under a 0.4-bar pressure in the distiller, and a 1.8-wt%/wt catalyst concentration under a reaction temperature of 55 °C at 50 min in the reactor would yield the best water/biofuel production efficiency of 55%/80%. [ABSTRACT FROM AUTHOR]

• Temperature control in a solar receiver using a novel variable aperture mechanism. • PID and model predictive control for variable aperture temperature regulation. • Variable aperture can recover up to 54% of intercepted spilled solar radiation. • Solar receiver's temperature experimentally maintained within ±1.5 °C of set point. • Experimental testing of PID flow rate and aperture coupled control strategy. A novel and compact variable aperture mechanism coupled to flow channels for recovery of spilled solar power was implemented on a cavity-type solar receiver to regulate its temperature and compensate for the sun's transient variations. PID and model predictive control methods were initially numerically tested and tuned, and then experimentally tested using a 10 kW e high flux solar simulator for set point tracking and disturbance rejection under simulated sun's direct normal irradiance. The variable aperture demonstrated a promising performance in regulating the solar receiver's average temperature by maintaining it within ±1.5 °C of its set point under experimental transient variations. The aperture mechanism's high performance was achieved while capturing approximately 54% of intercepted spilled solar power, which can be used to preheat the feedstock for better process efficiencies or made available to a secondary end-use process. Additionally, the aperture mechanism was shown to reduce the receiver's temperature drop in the absence of solar radiation by closing the variable aperture blades which reduced re-radiation losses from the receiver's cavity. Finally, two other control strategies were experimentally investigated, namely PID feedstock flow rate controller and PID multiple-input single-output controller that can manipulate both the variable aperture size and feedstock flow rate. In all cases and despite severe solar power fluctuations, the variable aperture mechanism demonstrated a promising performance in regulating the temperature in a solar receiver and compensating for the sun's transient variations. [ABSTRACT FROM AUTHOR]

• A first of its kind 1 MW concentrating solar power plant in a desert environment. • Experimental demo of the solar salt tech in parabolic trough collectors up to 550 °C. • Testing operation procedures and methods in a stand-alone plant with molten salts. • Analysis of heat losses, overall solar field performances and management issues. • Interplay between a gas-fired back-up heater and the concentrating solar field. The use of molten salt as Heat Transfer Fluid (HTF) in linear concentrators to reach temperatures >500 °C has received increasing interest in the CSP sector. So far, some experiences have been carried out on small test loops, while results obtained on larger (pre-commercial) plants have not been thoroughly published in the open literature, yet. This paper reports results obtained and lessons learned during the experimental operation of a CSP plant using Molten Salts (MS) as HTF in linear Parabolic Trough (PT) collectors. This demonstration has been carried out in the framework of the EU project MATS and refers to a stand-alone and fully-integrated 1 MWe CSP plant built in a typical desert environment in Egypt. With about 10,000 m2 mirrors' surface, the MS-PT solar field of MATS plant is the first of its kind and size. The solar field was in operation for more than 2500 h with solar salt circulation under different conditions, including start-up, draining, night circulation and solar tracking tests. The technical issues dealing with the management of a MS-PT solar field (and, in general, in linear concentrators) are discussed. Results demonstrated the reliability of the MS-PT technology for future exploitation on commercial scale plants. [ABSTRACT FROM AUTHOR]

• PV retrofit can increase yearly energy production by ~30% for plants with solar multiple above 1.5. • increasing fraction of solar flux reflected by dichroic mirror increases the yield from PV retrofit. • The increased electrical production declines as the plant solar multiple is decreased. Solar power for electricity production comes from either photovoltaics or concentrating solar power plants. The former has seen rapid growth and expansion due to the rapid fall in global prices, while the latter has seen moderate growth due to ability to cheaply store thermal energy for later use. Hybridization, or combining photovoltaics with concentrating solar power represents a potential way for lowering cost while enabling long term storage. Over 5 GW of capacity exist worldwide using parabolic trough style technology for concentrating solar power which presents a unique option for optimization in the form of a photovoltaic retrofit. While it is possible to analyze the performance with detailed physics models, it is necessary to create a model that can handle simulating the plant level performance to fully understand the potential performance. Here, the first utility scale plant level model of a hybrid photovoltaic-concentrating solar power plant is developed. The model is applied to existing concentrating solar power plants around the world utilizing RP-3 mirrors without thermal energy storage to understand the impact on electricity production. Model results indicate that the photovoltaic retrofit can increase yearly electricity production by up to 30% for plants with solar multiples exceeding 1.5, and that increasing the fraction of solar energy reflected further increases the yield. The increased electrical production declines as the plant solar multiple is decreased. The minimum LCOE observed was $0.07/kWh for plants with larger solar multiple and fraction of solar energy reflected to the PV is 50% of the total aperture. [ABSTRACT FROM AUTHOR]

Solar energy is an auspicious renewal energy source because of its abundant availability and its flexibility to be converted into heat or into electricity. Concentrated solar power technologies are promising units for producing electricity in large scale applications and parabolic trough solar collector is the most matured technology for these plants. The objective of this paper is to summarize and to discuss the current status of parabolic trough collector commercial power plants around the world and the technological developments in various constituents of such concentrated solar power plants. More specifically, this review includes various developments in the concentrators and receiver tubes in order to enhance both the thermal and the optical efficiencies. Moreover, the different existing and newly developed heat transfer fluids are discussed in this work and the emphasis is given in the discussion of the different operating temperature levels, the storage system and the applications that use different fluids. Furthermore, different tracking options of the parabolic trough solar collector are examined, different storage technologies, as well as various power cycles and their modifications to enhance the overall efficiency of the parabolic trough collector-based power plants are discussed in detail. The final conclusions of this work indicate the recent developments and the future designs of the parabolic trough solar collector power plants. [ABSTRACT FROM AUTHOR]

In solar thermal plants, as in any industrial process, it is important to maintain good control of the system and, more importantly, to have a good security system to avoid exceeding the safety limits of the components and avoid their degradation. In the case of solar thermal plants, one of the main components is the Heat Transfer Fluid (HTF), which must be kept below a maximum temperature. Although the temperature of the fluid, in general, will be controlled by modifying the flow-rate, when the plant is saturated HTF temperature is kept under limits by defocusing of the collectors. In this paper, an analysis of the control of the defocus control applied to the different collectors is presented. A Model Predictive Control technique will be applied to control the temperature by defocusing two and four collectors in different situations. It is shown how controlling the temperature by defocusing only two collectors is not sufficient in all situations and that controlling by defocusing the four collectors solves this problem in addition to maintaining the defocus actions in areas with high control authority. • Defocusing only two collectors has some advantages but it may not be sufficient. • Two defocus control stages are not enough in cases of significant power limitations. • More levels of defocus control must be added to avoid temperature excess. • Using a four collector strategy can deal with all situations. • Defocusing four collectors provides a more comfortable control area. [ABSTRACT FROM AUTHOR]

• Selective black cobalt coatings (BC) are viable for solar thermal collectors. • Electrodeposition is a robust and scalable BC fabrication method. • BC films on Pt are stable to 750 °C; on stainless steel – nickel to 300 °C. • The BC selective film is hydrophobic and stable under weathering. • The BC coating has been demonstrated in solar thermal collectors. We report on the electrodeposition of nickel/black cobalt selective coatings, and evaluate the performance stability as a function of the substrate material, the temperature of heat treatments, and under accelerated weathering conditions. The black cobalt absorber material is shown to be stable up to 750 °C, and the performance stability for a stainless steel substrate with a nickel/black cobalt selective coating after 200 h at 300 °C is demonstrated, with a solar absorptance of 95% and thermal emittance of 7% (at 100 °C). The galvanostatic electrodeposition process has been scaled up to collector size, and is demonstrated both for a flat plate and a tubular substrate. A copper flat plate of 193 cm × 12 cm connected to a riser tube was coated, and a single-fin solar thermal collector was evaluated under realistic outdoor conditions. The collector produced essentially the same amount of heat as an identical reference collector with a commercial TiNOX selective coating. In addition, the coating was applied to a copper tube for a 3 m parabolic trough collector. The selective coating is hydrophobic and withstands an accelerated weathering test, illustrating the viability of black cobalt electrodeposition for the fabrication of solar collectors for low and high temperature applications. [ABSTRACT FROM AUTHOR]