Hybridizing concentrating solar power (CSP) with photovoltaics (PV) offers a pathway to combine low-cost daytime generation with dispatchable nighttime supply. This study compares two CSP-PV hybridization concepts for Midelt, Morocco, under a common tender-style design framework: (i) a co-located configuration in which PV and CSP interact at the grid level and (ii) an EH-integrated configuration in which an electric heater (EH) uses PV electricity to heat molten salt in a topping cycle. The main contribution of this study lies in the two-stage optimization workflow, in which leading candidates are selectively re-simulated at higher temporal resolution. This workflow is applied to a common design framework that compares EH-integrated and co-located concepts while considering multiple PV technologies and a broad set of interdependent sizing variables. A surrogate-assisted genetic algorithm evaluates more than 200,000 candidate designs across PV technology, inverter size, TES capacity, EH capacity, and battery energy storage system (BESS) size. The optimization minimizes the levelized cost of energy (LCOE) subject to a 200 MWel export limit, a CAPEX ceiling, and a nighttime-delivery constraint of CFnight >= 39%. Candidate designs are screened at 600 s and selectively re-simulated at 120 s, showing that temporal refinement affects not only KPI values but also candidate feasibility, final ranking, and preferred component sizing. The lowest-LCOE solution is the EH-integrated bifacial configuration, achieving 64.5% overall capacity factor, CFnight=39.1%, less than 0.1% curtailment, a specific CAPEX of $4698/kW, and an LCOE of 7.29 cent/kWh. Pareto-front and parameter-trend analyses further show that stricter nighttime-delivery targets shift the dominant sizing levers and define a neighborhood of near-optimal solutions rather than a single fixed design.

Geothermal-solar hybridization is evaluated for the 80 MWel Kizildere 2 (KZD2) triple-flash geothermal power plant with a binary ORC bottoming cycle in T & uuml;rkiye. This paper develops a high-resolution simulation model val idated against 2023 operational data and assesses three solar augmentation pathways: (i) PV to offset auxiliaries, (ii) concentrating solar thermal (CST) via parabolic trough collectors (PTC), and (iii) PTC with indirect molten-salt thermal energy storage (PTC + TES). Economic performance was evaluated under both a fixed feed-in tariff (FiT) and an open-market framework using normalized hourly prices derived from 2016-2020 market data. PV offsetting auxiliary consumption increases net electricity production by up to 7.4%. For CST cases, domi nant gains arise from using solar heat to preheat the cooler KZD1 supplementary stream such that the combined inlet mass flow and temperature approach design conditions. The selected PV + PTC hybrid configuration increases annual electricity generation by 17.5%, with a levelized cost of additional electricity (LCOAE) of 3.61 c$/kWh, while PV + PTC+TES raises the annual yield by 28.0%, at an LCOAE of 7.27 c$/kWh. The in crease in open-market revenue slightly exceeds FiT outcomes due to alignment with higher-priced hours (17.5% vs. 18.4% for PV + PTC; 28.0% vs. 28.7% for PV + PTC+TES). Mixed-framework results indicate discounted payback within five years for PV + PTC when the FiT remains applicable for five years, followed by an open-market scenario with a $100/MWh ceiling, while higher ceiling prices strengthen the case for TES. Overall, PV + PTC emerges as the most cost-effective near-term option, with TES adding value under price volatility and improved dispatch strategies.

Copper is essential to the energy transition due to its exceptional electrical and thermal conductivity, making it critical for power generation, transmission, storage, and renewable energy systems. In 2023, Chile accounted for roughly 25% of global copper production, a leading position driven by mining and smelting activities that are highly energy-intensive, consuming nearly 37% of national electricity and 20% of heat demand, primarily for comminution, electro-refining, smelting, and converting processes that also require substantial fuel and oxygen inputs. Such high energy use, combined with the need for both fuel and oxygen in pyrometallurgical operations, highlights the need for alternative pathways capable of supplying these inputs while reducing fossil fuel dependence. In this regard, this study assesses the techno-economic feasibility of a Hybrid Sulfur (HyS) cycle for the co-production of hydrogen (H-2) and oxygen (O-2). The techno-economic analysis focuses on a copper smelting facility in northern Chile with an annual output of 100 kt. Results indicate that the HyS cycle can achieve lower overall energy consumption than Proton Exchange Membrane (PEM) electrolysis when two conditions are present: (i) the electricity demand of PEM exceeds 50 kWh(ele)/kg(H2), and (ii) the HyS process operates under favorable conditions, characterized by high H2SO4 decomposition temperatures (similar to 1400 K), highly concentrated H2SO4 feeds ( > 75 wt%) at the decomposition inlet, and highly effective heat recovery. Based on conservative electrical and fuel prices and a limited heat recovery the estimated Levelized Cost of Hydrogen (LCOH) is 5.74 +/- 1.04 (sic)/kg(H2). PEM and alkaline electrolysis are mature and widely deployed technologies for green hydrogen production; however, their economic feasibility remains highly dependent on electricity prices, which poses challenges in regions without stable access to low-cost electricity. In contrast, the HyS cycle relies predominantly on thermal energy, particularly in the sulfuric acid decomposition section, and is therefore less sensitive to electricity price volatility. This characteristic makes the HyS cycle a promising option for the co-production of hydrogen and oxygen in Chile's pyrometallurgical copper industry, contributing to decarbonization. Nevertheless, challenges related to scale-up and material durability remain.

This paper presents HelioSliders, an innovative, pattern-free methodology for heliostat field design that is appli cable to both single-focus and multi-focus Solar Tower systems. By projecting the heliostat mirror outlines onto a horizontal plane-using perspective projection from a designated aim point for blocking and parallel projec tion along the sun vector for shading-the algorithm generates two-dimensional blocking and shading contours. These representations are used in a 2D rigid-body simulation in which each heliostat is dynamically repositioned within defined inner and outer boundaries. The algorithm ensures that the overlapping of the blocking and shad ing contours of neighboring heliostats is minimal. An artificial gravitational force draws the heliostats toward the receiver, thereby minimizing spillage and atmospheric attenuation. The HelioSliders method is demonstrated through optical benchmarks using ray tracing, where its perfor mance is compared with three reference designs that cover both conventional single-focus Solar Tower systems and advanced multi-focus Beam-Down configurations. Compared to the reference designs, HelioSliders achieved a relative increase in annual optical efficiency of 1.4%, 0.9% and 0.8% and a relative reduction in field area of 21.0%, 13.2% and 0.3%, for the Gemasolar, PS10 and Bi-Focal Beam-Down scenarios, respectively. Sensitivity analyses show that optimizing parameters-HelioSliders algorithm-related, but also system-related, such as the heliostat aspect ratio-can further improve annual optical efficiency and reduce the field's physical footprint. The results highlight that HelioSliders offers a versatile, computationally efficient, and adaptable framework for designing highly efficient heliostat fields.

Mirror soiling reduces reflectance and decreases plant yield in concentrating solar power systems. Conventional pointwise reflectometers for cleanliness assessment are accurate yet slow and sparse. In this study, we refine LiDAR-based method that converts raw laser scanner intensity into a calibrated, viewpoint-independent backscat ter signal and maps cleanliness across heliostat fields. A calibration pipeline corrects detector response, distance, and incidence angle to produce standardized backscatter, followed by a monotonic empirical mapping to flectometer cleanliness. Field tests at an operational tower plant show a strong inverse correlation between LiDAR and reflectometer measurements (Spearman's rank correlation of-0.94 for calibration). Across four dependent perimeter validations, the LiDAR mean cleanliness matched portable handheld reflectometer (pFlex) within 0.10-0.72% per mirror (absolute mean difference 0.34% for validation), while paired-sample MAE and RMSD were 2.31-2.91% and 2.88-3.72%, respectively. Compared to pointwise reflectometers, the method enables fast, illumination-independent, centimetre-resolution mapping, supporting improved yield estimates, optimized receiver operation, and water-and cost-efficient cleaning strategies.

In concentrated solar thermal technologies, plant operators usually monitor the soiling of their solar field with handheld reflectometers. These measurements can be used for yield calculations and to adapt cleaning strategies: if the reflectometer reading falls below an empirically established threshold, the solar field should be cleaned. There are several commercial reflectometers available for this purpose, but all of them measure at different combinations of wavelength, acceptance angle or incidence angle. It is the purpose of this study to bring the readings from all main commercial reflectometers to the same representative value, enabling their comparison with one another and the translation of these readings into a meaningful reflectance parameter. Thus, different handheld reflectometers are correlated with a laboratory reflectometer, capable of measuring in the whole solar spectral region, covering a wide range of incidence and acceptance angles. The most significant parameter is the near-specular solar-weighted reflectance, measured at the typical incidence and acceptance angles for a given plant, as it is the most precise parameter to describe the reflected energy from the solar field. The correlations for all included reflectometers, show highly linear correlations over a wide range of soiling levels with low deviations. Consequently, the correlations presented herein enable the plant operators at the studied site to compute the near-specular solar-weighted reflectance from their reflectometer readings. and, with that, increase the significance of the measurements without collecting any additional data. The work also establishes a detailed procedure to derive this type of correlations at any site of interest.

Clinker, constituting approximately 72% of cement's composition, is produced through an energy-intensive process that significantly contributes to CO2 emissions. This study explores the integration of a solar calciner into the Chilean cement industry, particularly in the Antofagasta region, which is characterized by high solar energy irradiation, with an annual DNI of 3,250 kWh/m2. This region also accounts for approximately 30% of the country's cement sector energy consumption. In this context, this study evaluates two Concentrated Solar Thermal (CST) scenarios: the Top of Tower (TT) system and the Beam-down (BD) system, assessing their technical and economic feasibility for reducing CO2 emissions in the calcination process. The findings suggest that both CST systems could substantially reduce CO2 emissions in the calciner. However, economic feasibility remains a challenge, primarily due to the low cost of coal, which is the main fuel in the Chilean cement industry. Additionally, the efficiency of the solar calciner is found to be crucial for achieving maximum emission reductions, for the scalability of the technology, and for its future adoption in Chile's cement industry. Although the Levelized Cost of Heat (LCOH) for the proposed plants is currently higher than the coal-fired calciners in which is produced about 90% of current clinker production in Chile, potential reductions in heliostat costs, coupled with an increase in carbon taxes beyond the current value of 5 USD/tCO2, could significantly improve the economic viability of CST plants in Chile's cement industry.

Clinker, a crucial component in cement production constitutes about 72% of cement's composition, is formed by heating limestone and other materials in a calciner and in a rotary kiln. This process is highly energy- intensive and, therefore, a major source of CO2 emissions in cement production. In this context, this paper analyzes the potential integration of a solar calciner into the Chilean cement industry. Specifically, it examines and compares two Concentrated Solar Thermal (CST) scenarios: (I) the Top of Tower (TT) system and (II) the Beam-down (BD) system. These scenarios are evaluated for their economic and technical feasibility in reducing CO2 emissions in the calcination process. The analysis focuses on the region of Antofagasta, Chile, which has an annual DNI of 3,250 kWh/m2. Notably, Antofagasta consumes 30% of the energy used in the cement sector in Chile. Key parameters influencing CO2 emission reduction are examined, with an emphasis on the potential for greater reductions through increasing solar field size and thermal energy storage capacity. However, economic feasibility still faces significant challenges, primarily due to the low cost of coal in Chile. Moreover, the efficiency of the solar calciner is identified to be crucial for maximizing CO2 emission reductions in the calcination process, highlighting its importance for scaling up this technology and its widespread adoption in the Chilean cement industry. Despite the LCOH for the proposed plants being higher than the conventional coal-fired calciners, potential reductions in heliostat costs and higher carbon taxes from the current levels of 5 USD/tCO2 could enhance the economic viability of CST plants in Chile. Furthermore, potential CO2 emission reduction projections in the Chilean cement industry until 2050 are evaluated based on the implementation of CST systems in the calcination process and the alternatives proposed by the Instituto del Cemento y Hormig & oacute;n, such as reducing the clinker/cement ratio, co-processing, and reducing the cement content in concrete. The study forecasts potential reductions in specific CO2 emissions, which may down to 630 kgCO2/tclinker in an optimistic scenario, and to approximately 661 kgCO2/tclinker in a pessimistic scenario. This represents a reduction of 25% and 21%, respectively, from current specific emission levels of 839 kgCO2/tclinker in Chile. Further reductions are expected by incorporating carbon capture technologies, which focus on the main source of CO2 emissions: the calcination chemical reaction, which produces about 556 kg-

This paper presents an extension of the "Maximum Front Method" for assessing the spatially varying Bidirectional Reflectance Distribution Function on curved surfaces, specifically the receiver of a Solar Tower. The receiver, which links the solar field and the thermal cycle of a ST, operates under high solar concentrations and temperatures. This method is vital for efficient plant operations, enabling regular assessment of the receiver coating quality, early detection of degradation, and facilitating other measurement techniques. The paper discusses the challenges faced with the far field SVBRDF measurement when dealing with complex surfaces, including the trajectory of the light spot, and dealing with distance dependant reference intensity values. These challenges were addressed through a geometric approach and simulations were carried out using blender® to validate the method, showing its effectiveness on cylindrical and structured surfaces. However, accurately determining each component's spatial position was a persistent challenge for the practical demonstration. The paper suggests future research could consider line overlaps to maintain the evaluated area and develop methods to determine pipe positions directly from captured images. In conclusion, this method provides a foundation for solar tower receiver applications to monitor receiver state and improve robustness and efficiency in solar tower operation.

The publication provides an insight into current developments in solar thermal process heat generation. In the first chapter, the experiences with the commissioning of a parabolic trough field at a chemical factory in Turnhout, Belgium are shared. Chapter 2 describes the layout of a parabolic trough field with pressurised water storage at a brewery in Seville, Spain. Finally, there is an overview of developments in solar thermal process heat: The share of concentrating collectors rised in 2023 and more developers signed heat supply contracts, mainly for large-scale solar industrial heat plants.

The 3D-shape round-robin initiative aims to compare the main geometric parameters of 3D shape measurements for parabolic-trough mirror panels, assessed using equipment developed and employed by each participating institution: ENEA, F-ISE, DLR, NREL, and SNL. Except ENEA equipment, all the other are based on deflectometry, also call fringe-reflection method. The round-robin is based on circulating 6 trough mirror panels (3 inner and 3 outer) of RP3 dimensions, with a focal length of 1710 mm, between participating laboratories; a simple and rugged supporting fixture together with precise instruction on how to use it have been provided to make the comparison more reliable. ENEA wrote a custom evaluation software for comparing the results. We observe a reasonable agreement among the mean values of the deviations of height and slopes from the ideal parabola: standard deviation better than 0.1 mm, 0.5 mrad and 0.3 mrad for z, slopeX and slopeY, respectively. The agreement is improved when a software realignment procedure for setting the height values on the support points to the expected ideal values is applied. The absolute difference between pairs of evaluators is sometimes greater than the declared experimental uncertainty; investigation into these deviations is still ongoing.

Modelling and Simulation of Concentrated Solar Power (CSP) plants is a crucial requirement for future growth and improvement of the technology. In this paper, the development of a functional and reliable model of a Parabolic Trough Collector (PTC) power plant is presented and validated with existing five-year operational data of a 50 MWel plant equipped with seven hours full load thermal storage, located in Spain. A mean absolute error of 2.53% between the simulation and plant data was found when considering net energy generated over the five-year period. Subsequently, an optimized maintenance plan is proposed, and the plant behavior is forecasted. The new maintenance strategy is developed to optimize the mirrors current cleaning schedule, thereby mitigating significant detrimental soiling effects on the optical efficiency while reducing water and fuel consumption. Results show an increase in solar gain by 0.46% and reductions in water usage and fuel consumption by 22.1% and 22.3%, respectively.

An optimized mass flow distribution of heat transfer fluid (HTF) and its understanding are essential for an effective solar field operation in a concentrated solar thermal (CST) system. Typically, the flow of HTF through a solar field of linear concentrating collectors is divided into different loops and the flow rate in different loops may differ. While the mass flow distribution aims for a constant and high outlet temperature from the solar field, valuable insights into the efficiency of individual loops can be deduced from the mass flow distribution itself. Nevertheless, a spatially high-resolution measurement of mass flow in the solar field is typically not yet implemented. This paper demonstrates that the mass flow of a loop can be determined by briefly focusing and defocusing individual collectors and thus without additional measurement equipment as needed for common measurements. For this purpose, a measurement campaign with over 100 individual experiments was conducted at the Evora Molten Salt Platform (EMSP) test facility. Based on the resulting thermal step response and its measurement considering various temperature sensors, the mass flow of the test loop was determined using the Time-of-Flight (ToF) method, yielding a mean deviation of less than 5% compared to the mass flow measured by mass flow meters and a high precision with a mean standard deviation of 0.3% for multiple measurements under identical conditions. Therefore, this method offers a high potential for enhanced early fault detection of loops or individual collectors with reduced efficiency as well as improved predictive maintenance.

Despite being a mature technology, CSP plants with thermal energy storage (TES) are unable to achieve the levelized cost of electricity (LCOE) values of commerical PV plants. The high costs of the tower, heliostat field, and thermal energy storage (TES), among other factors, hinders the achievement of such values. In this study, we present a multi-tower plant with two solar concentration technologies: each tower features a cavity thermal receiver (coupled to a molten salt TES and a power block) and a concentrated photovoltaic (CPV) receiver. The shared investment costs of the solar field and the tower may allow to obtain more competitive economic indicators. This study goals to analyze the techno-economic feasibility of the hybrid solution by evaluating the LCOE and the Cost of Valued Energy (COVE) of different system configurations (e.g. 4, 8 and 12 h of TES). Optimal system configurations reach a LCOE and a COVE of 56.8 €/MWh and 61.9 €/MWh, respectively. Highly favorable results compared to the values obtained for a conventional tower CSP plant with molten salts TES: 106.05 €/MWh, and 90.27 €/MWh. In conclusion, the present study proves the tecno-economic viability of a multi-tower plant hybridizing two solar concentrating technologies: thermal and concentrated photovoltaics.

Canting errors, resulting from misalignments of heliostat facets, pose a significant challenge to solar power plants' efficiency. Traditional methods of alignment are time-consuming and costly. This paper presents an innovative approach utilizing Terrestrial Laser Scanning (TLS) technology for precise and fast heliostat alignment. The method involves point cloud processing, paraboloid fitting, and heliostat facet’s screw adjustments. A case study at Thémis solar tower demonstrates the effectiveness, resulting in a significant improvement in optical quality and power output.

The accumulation of dust particles on solar collectors can gradually degrade optical performance in solar systems — a phenomenon known as soiling. Additionally, the formation of dew on collectors during early mornings introduces new mechanisms that can impact the soiling process. This study investigates the influence of dew on soiling for uncoated solar mirrors using an artificial soiling station. Several experiments were performed changing testing parameters (e.g. sample tilt, dust amount, dew quantity) and monitoring the outcomes with a range of devices including reflectometers, microscopy, scales, and a luminance camera. The outcomes indicated that condensation becomes relevant for condensation loads above 60gm−2 and its impact is significantly affected by the tilt angle of the samples. When samples are flat or with low tilt, condensation cycles cause particle dispersion, reducing cleanliness by up to 2%. On the contrary, for high tilt angles, a honeycomb-like soiling patterns with highly reflective regions appear, enhancing cleanliness restoration by 2.3%. These findings suggest tilting dewy collectors as a passive self-cleaning strategy.

In recent years, great efforts have been made to reach a consensus on heliostat testing best practices. A specific SolarPACES task was launched to provide a Heliostat Testing Guidelines document for single heliostat evaluation with a focus on prototype validation and qualification. Such guidelines are not well-suited for heliostat evaluation in operating commercial heliostat fields. The commercial implementation of the Central Receiver technology is burdened by the lack of a demonstrated cost-effective methodology to test solar fields, particularly during the commissioning and operation phases of the plant. To address heliostat characterization challenges, the SolarPACES funded Project “Analyze Heliostat Field” aims to set the basis towards a SolarPACES guideline for Heliostat Field Performance testing under a common framework. This is by means of a review of the existing methodologies, R&D and industrial stakeholders information sharing and preparation of a future quantitative comparison and validation plan. As part of the development of this project, several meetings and a workshop involving the SolarPACES community was organized to share knowledge and experience in the measurement and characterization of heliostat fields using a range of technologies and procedures. Research centers and companies from 5 different and distant countries have actively participated in these meetings, sharing their experiences, needs and interests. This paper summarizes the outcome of this international collaborative effort and the prospects for future close collaborations sustained over time.

Beam-down solar towers are presented as an alternative to conventional solar towers that allow modular design, easily adaptable to industrial environments. Secondary reflectors are a key component in this type of configuration, due to the high concentration of radiation received from the solar field. The results of a technical and economic study of new secondary reflectors, based on a polished stainless-steel substrate with silver PVD coating and a system of protective layers, are presented and compared with aluminum reflectors, currently used in such configurations. For this, twelve different designs, grouped in three cases are simulated using ray tracing and finite elements. The results show that the steel reflectors reach lower temperatures compared to aluminum reflectors, allowing for greater durability. Additionally, the optical efficiency of the plant was determined, and it was estimated that steel reflectors can reduce the LCOH of the plant by approximately 3.5%.