This review categorizes the thermal energy storage (TES) technologies—sensible heat, latent heat, and thermochemical storage—and evaluates their development, application, and performance within central receiver-based concentrated solar power plants. This study explores the progression of TES systems, delineating the evolution from technologies such as saturated steam and molten salt, first used in the Eurelios power plant in 1980 as a protective storage solution for 30 minutes, to commercial molten salt storage capacities of up to 15 hours. This study also examines emerging research and development technologies aimed at achieving higher efficiencies and operating temperatures. The objective is to identify technological trends, assess the efficacy of different TES systems, and highlight future directions for research and application.

Central receiver-based systems in concentrated solar power (CR-CSP) have evolved significantly from their early beginnings with grid-connected plants in the early 80 s to a growing share of commercial deployments aiming to be competitive in the energy transition era. This paper presents a historical review of CR-CSP solar tower projects worldwide, emphasizing key technological milestones, deployment trends, and innovation phases from early demonstration plants to modern hybrid configurations at plant level. The major contributions of this paper are the graphical timeline of central receiver projects (visually mapping the emergence, decline, resurgence, and current standardization of CR-CSP systems), and the categorization of plants based on system configuration into four main categories considering: system configuration, heat transfer fluid, thermal energy storage method, and deployment model (stand-alone, co-location, and hybrid). To support the analysis, a dual-stream methodology was adopted, combining a literature-based review of historical development with a database-driven analysis of current and under-construction CR-CSP plants. The work contextualizes the evolution of CR-CSP technologies and identifies strategic directions for the future direction of the technology. The findings highlight the importance of technology standardization, modular design, and stakeholder collaboration in reducing costs, improving scalability, and supporting low-carbon energy goals, guiding future CR-CSP development. guiding future CR-CSP development. This paper forms Part 1 of a two-part series. Part 2: Components Categorization and Future Prospects builds on this foundation by analyzing subsystem technologies and innovation pathways to guide future R&D and deployment strategies.

This study presents a comprehensive historical and technological categorization of the key components in central receiver-based concentrating solar power (CR-CSP) systems. It examines the evolution of heliostat fields, receivers, heat transfer fluids (HTFs), thermal energy storage (TES), and power blocks across operational, under-construction, and demonstration projects. Using a dual-stream methodology that integrates peer-reviewed literature with real-world project data, the paper identifies critical design transitions, material choices, and deployment trends that have shaped the current state of CR-CSP technology. The analysis highlights how high-temperature receiver configurations, emerging TES strategies, and alternative HTFs are enabling greater dispatchability and hybrid integration. Two future deployment scenarios are proposed: (1) the co-location of CR-CSP with low-cost renewable sources to leverage TES for grid stability, and (2) the use of CR-CSP for direct industrial heat applications, bypassing conversion losses. These findings provide strategic guidance for researchers, developers, and policymakers aiming to advance the technical and economic feasibility of CR-CSP systems in the global energy transition.

This work proposes a novel concentrating solar power (CSP) plant configuration aiming at a high operation temperature of 1000°C. The thermal energy storage system (TES) would be the focus of this research by modifying it and proposing four configurations to enhance the overall efficiency of high-temperature solar power towers. The objective is to identify the most thermodynamically efficient designs by analyzing the literature on the different components and comparing them to a reference base case of a conventional 100 MWe solar power tower plant (2-tank molten salt TES) operating at 565°C. The proposition consists of a Brayton/Rankine combined cycle with a double cascade TES. In the proposed cascade TES, the primary unit consists of a high-temperature air/ceramic packed-bed thermocline operating at 1000°C, while the secondary unit is a single molten salt tank used as sensible heat. The secondary TES is used as a heat sink during charge, improving efficiency and reducing the size of the air/ceramic-packed bed by extracting the thermocline out of the tank. Excess energy stored in the secondary TES is utilized for preheating during discharge. The methodology incorporates evaluating various combinations of solar block, TES, and power block integration. Combinations are selected from a comprehensive literature review. The study focuses on night-time operations. Further analysis of the cost-benefit of the designs would be required to compare the overall energy production and furthermore the LCOE.

Central receiver-based concentrated solar power (CSP) systems play a crucial role in solar energy technology, particularly for their ability to operate at higher temperatures than conventional linear concentrators, and for better integration of thermal energy storage in a more direct manner. This paper methodically examines the development and classification of central receiver-based CSP technologies, including power towers, solar furnaces, and beam-down configurations. It aims to emphasize the operational advantages and challenges of these technologies through a literature review. Through an in-depth examination of strategic pathways, including hybridization and co-location, this study reveals critical trends in market deployment frameworks, underpinning the future of CSP integration in the transition to renewable energy solutions.

Three-dimensional secondary concentrators positioned at the entrance of solar thermal receivers, in tandem with point-focusing primary concentrators have been a subject of study and experimentation since the 1980s owing to their demonstrated ability to enhance the optical and thermal performance of Concentrating Solar Power (CSP) systems operating at high temperatures. They have been also proposed to reduce costs by rendering the overall optical system more tolerant of primary concentrator tracking and surface slope error. In certain CSP and thermal (CST) applications and configurations, the integration of 3D secondary concentrators is vital to meeting temperature and flux density requirements. This paper presents a comprehensive review of the prototypes that have been tested thus far, detailing their characteristics and enumerating the engineering, material science, testing, modeling and optimization challenges. Measures to address thermal management and related fabrication problems are discussed. The underlying theory of non-imaging optics and essential optical design considerations are summarized. Finally, the ongoing developments of reflective materials suitable for high-temperature applications in 3D secondary concentrators are examined, along with an evaluation of the most promising candidates. Priorities for filling research gaps and comprehensive design approaches are identified (based on testing of prototypes reported in the literature).

Concentrated solar thermal (CST) systems, capable of driving high-temperature processes up to 2000 K, hold significant potential for chemical and industrial applications. This paper reviews methods for measuring concentrated solar flux, focusing on their role in calculating key optical performance metrics such as concentration ratio and optical efficiency. It also explores the challenges associated with these measurements. Flux measurement methods are categorized into direct and indirect approaches. Direct methods use heat flux gauges positioned on a stationary or moving target to measure solar flux, while indirect methods rely on a CCD or CMOS camera, a Lambertian target, and a heat flux gauge. The camera captures images of solar radiation, which are calibrated to heat flux values using readings from the heat flux gauge. Heat flux gauges are a critical component of both direct and indirect measurement methods. This study also reviews and compares various types of heat flux gauges, including Gardon radiometers, Schmidt-Boelter gauges, Kendall radiometers, heat flux microsensors, and calorimeters. The comparison considers factors such as maximum flux rating, response time, durability, water-cooling requirements, cost, and measurement uncertainty. Calibration techniques for these gauges are also discussed. It is observed that indirect methods are commonly used for measuring concentrated solar flux due to their higher resolution, which enables them to identify hot spots and measure concentrated solar flux more accurately than direct methods. The key challenges in measuring concentrated solar flux include calibrating sensors under solar conditions, ensuring sensor durability, accounting for environmental factors, and managing cost considerations.

The development of electricity storage solutions is crucial to support the integration of variable renewable electricity sources in electricity systems. This study experimentally characterizes a state-of-the-art full-scale electrical thermal energy storage (ETES) system in outdoor conditions. The system integrates a 600 kWhth hightemperature latent heat storage module and a 13 kW(e) Stirling engine. The heat storage module uses an 88Al-12Si metallic alloy as the phase change material to store electricity converted to thermal energy by a resistive heater in charging mode. The Stirling engine uses hydrogen as the working fluid for re-electrification (discharging). The system uses liquid sodium as the heat transfer fluid between the latent heat storage module and both the charging (electrical heater) and discharging (engine) sub-systems. Over the characterization period, the ETES prototype produced stable electricity at an average rate of 10.5 +/- 1 kW for 13 consecutive hours daily with overall and power block first-law efficiencies of 23 % and 25 %, respectively. The effective storage utilization ratio varied between 0.58 and 0.94 depending on the discharge parameters. The response time was <5 s for output power regulation. The results highlight the potential of this latent heat thermal energy storage system to satisfy long-duration electricity storage applications and therefore contribute to the stabilization of electricity grids.

The challenge of imbalances between renewable energy supply and grid demand underscores the significance of energy storage in microgrids. This research presents an empirical assessment of the operational capabilities of a full-scale Electrical Thermal Energy Storage (ETES) prototype system named Thermal Energy Storage Power On Demand (TES.POD®), in solar-abundant and harsh desert conditions. The system incorporates a high-temperature commercial-scale latent heat thermal energy storage, integrated with a Stirling engine. Over a continuous span of 10 days, from September 26th to October 6th, 2022, the input and output power, as well as the heat transfer fluid temperatures during charging and discharging were monitored to assess the power block and system efficiencies. Results from the experiments reveal that this prototype effectively maintains a near-constant electricity production rate of 10.5 ± 1 kW for a discharge duration of 13 hours. Average cycle efficiency stands at 23%, while power block efficiency reaches 25%. These findings collectively suggest the system's potential for applications involving long duration thermal energy storage.

The paper evaluates the EW-1000 Atmospheric Water Generation-Vapor Compression Refrigeration system (AWG-VCRS) as a sustainable alternative to seawater desalination in the GCC. Conducted in Masdar City, Abu Dhabi, from July 2023 to January 2024, the study measured temperature, humidity, energy consumption, and water production. Key findings include a peak water production of 1500 LPD in September and an average Specific Energy Consumption (SEC) of 0.26 kWh/L. Productivity decreased by 71% in cooler, dryer months. With a coefficient of performance (COP) of 3.6, the system aligns with conventional air conditioners, highlighting its potential for enhancing water security in arid regions.

Improper alignment is one of the key parameters that affect the performance of a concentrated solar parabolic dish (SPD). The receiver must have a flux distribution that is as uniform as feasible for an SPD to operate at its optimum performance. The aim of this research is to align a SPD from ZED Solar [1], which is recently installed at Khalifa University's Masdar Institute Solar Platform in Abu Dhabi, United Arab Emirates. This dish's future application involves integration with a photo-electrochemical hydrogen production reactor, which demands a multi-aimpoint alignment approach for optimal performance. To facilitate this alignment, the sunspots of all facets are initially aligned within a 200 mm diameter circle around the focal point using the on-sun alignment method. During the alignment, the dish was placed in sun-tracking mode, with all facets covered except the one being aligned. The reflection of the facet on the target was observed using a camera. The facet was adjusted until the aimpoint was oriented in the optimal position. The average time to align one facet, including cleaning, loosening the front nuts, and replacing the covers, was found to be around 15 minutes. The complexity of the bolt mounts, rust on the bolts, and the use of a manlift contributed to the prolonged alignment process. Despite these challenges, the on-sun alignment method proved to be an accurate way of aligning the facets of a concentrated SPD.

ReThink Seramic - Flora is an innovative ceramic material made from 100 % recycled materials. Due to its affordability, suitable thermal performance, and low pressure drop in packed bed thermal energy storage (TES), it is considered as a promising storage material option for high-temperature TES applications including concentrated solar power (CSP) plants. In the present study, a validated CFD model is used to analyze the thermal performance of the sustainable ceramic at high temperature (1000 degrees C) for a commercial-scale packed bed. The paper focuses on modeling the charging/discharging processes and cyclic behavior based on threshold tem-perature, where dispersion thermal conductivity was considered. The effective thermal conductivity is affected when the dispersion thermal conductivity and the radiation heat transfer are taken into account in the model. The addition of dispersion conductivity leads to a variation in effective thermal conductivity in the range of 28.9-39.9 (W/m.K) for temperature range of 0-1000 degrees C, while the addition of radiation heat transfer leads to a small variation in effective thermal conductivity based on two correlations from literature. The results show excellent thermal performance, with thermal exergy efficiency of 88 % for a full charge/discharge cycle. The net exergy efficiency for seven repeated cycles increased from 73.4 to 88.7 %, where thermal and pressure drop exergy losses are considered. The performance of ReThink Seramic - Flora is compared to the one of a commercial alumina-based TES material product. Thermal exergy efficiency for alumina is higher; however, the alumina -based product showed high pressure drop losses, leading to lower net exergy efficiency.

The scarcity of fresh surface water resources combined with the over-exploitation of groundwater reserves across the Gulf Cooperation Countries (GCC) has increased the dependence on seawater desalination to satisfy drinking water requirements. However, the predominance of high relative humidity and temperatures within this region, offers an unrivalled potential for atmospheric water generation (AWG). Most AWG techniques are currently limited to emergency response or remote locations where conventional water production/distribution strategies are ineffective or prohibitive. This study presents an analysis of various scalable AWG techniques including direct cooling of air using Vapour Compression Refrigeration Systems (VCRS) and Air Conditioner Condensate Recovery (ACCR). Three commercial VCRS-type AWG units were evaluated at the same time during a 4-month field test in summer 2022 in Masdar City, Abu Dhabi, UAE and their performances were correlated to the relative humidity and temperature of the inlet air in both indoor and outdoor conditions. In addition, up to 30.8 L.day(-1).TR-1 of AC condensates were collected from a 7.87 m(3).s(-1) Fresh Air Handling Unit that was installed on the roof of a University building. This study demonstrates the potential of AWG as a promising solution to increase water security across arid countries by offering a complementary option to desalination without brine generation.

This paper details the development process of ceramics made out of 100% electric arc furnace (EAF) steel slag, to be used as a shaped homogenous thermal energy storage (TES) media in packed-bed thermocline systems for high-temperatures industrial waste heat recovery, concentrated solar power (CSP), and Carnot batteries applications, among others. The main objective of this study was to investigate the influence of different process parameters on the properties of the resulting ceramics. The samples have been characterized in terms of bulk density, apparent solid density, and water absorption to identify the best values for different process parameter. The best properties were obtained for samples prepared with heat-treated slag powders, pressed at 300 MPa and fired at 1300? for 8 h under a static air atmosphere. The optimal bulk density was 3.1 g/cm(3), and the water absorption was 1.2%wt. The measured specific heat capacity was 1026, 1181 and 1216 J/(kg.K) at 200, 400 and 600 ?, respectively, while the thermal conductivity values were 1.53, 1.50 and 1.37 W/(m.K) at the same temperatures. This work confirms the feasibility of manufacturing TES ceramics out of EAF steel slags, using equipment and techniques well-known in the refractory industry.

Scarcity in fresh surface water resources combined with over-exploitation of groundwater reserves across the Middle East has increased the reliance on seawater desalination to meet the demand for potable water. The prevalence of high humidity and temperatures within this region, however, offers unprecedented potential for atmospheric water generation to complement classical desalination technologies. This review presents emerging technologies developed for atmospheric water generation focused on the Middle East and critically assesses their performance in terms of water production yield and quality. A review of the life cycle assessments performed to date, to introduce techno-economic analysis and current limitations, will also be presented to compare mature technologies, such as desalination and wastewater reuse technologies. The development of strategies to enable diversified and decentralized water production is key to many arid countries to limit the need for large-scale and permanent costly infrastructures, reduce environmental pressure associated with over-utilisation of limited resources and brine discharge, and permit a transition where water needs are decentralized and managed at the local level. This review offers perspectives on these aspects and is aimed at presenting the first pertinent roadmap for atmospheric water generation technologies within the Middle East.

Thermal energy storage (TES) is used in renewable energy systems such as concentrated solar power (CSP) or electric thermal energy storage (ETES) plants to provide heat for dispatchable power production. This paper presents the experimental results of a new 100% recycled ceramic material, ReThink Seramic - Flora, for used in sensible heat packed-bed thermal energy storage. Results are compared to conventional alpha-alumina (alumina) materials. The study focuses on a full charge-discharge cycle and multiple repeated partial charge-discharge cycles. Air was used as the heat transfer fluid (HTF) with an inlet temperature of 150 degrees C. Three flow rates were considered in the study, 0.0034 m(3)/s, 0.0048 m(3)/s, and 0.0061 m(3)/s (5-9 SCFM). The thermal performance of ReThink Seramic - Flora was analyzed and compared to alumina in terms of energy stored/recovered, temperature distribution, thermal exergy efficiency, pressure drop, and net exergy efficiency (combined thermal and pressure drop losses). The results showed that alumina beads have higher performance in terms of thermal exergy efficiency than ReThink Seramic - Flora. The exergy efficiency increased from 46.8% to 55.4% for alumina and from 44.6% to 51.6% during full charge/discharge process at three flow rates. Pressure drop results indicate exergy losses over the flow rates from 3.6% to 7.9% for alumina and 2.5% to 5.1% for ReThink Seramic - Flora. This results in net exergy efficiencies at the three flow rates of 43.2%, 47.1%, and 47.5% for alumina compared to 42.1%, 45.4%, and 46.5% for ReThink Seramic - Flora.

Concentrating solar power (CSP) with thermal energy storage (TES) presents the major advantage over solar photovoltaics of dispohability. High thermodynamic efficiencies achieved by collecting and storing heat at higher temperatures, and recent maturing of the technology, are making molten-salt central receiver plants the preferred option for CSP. To explore potential further improvements in CSP efficiency and cost the world's first direct absorption molten salt volumetric receiver/storage system was built at pilot scale, commissioned and monitored. In this demonstration a 100 kWth beam-down tower directs solar radiation through a final concentrator into the open aperture of a 1.94 m high and 1.25 m internal diameter tank receiver situated near the ground. The receiver tank is filled with 3,800 kg of 60-40 wt% NaNO3-KNO3 and serves as a stratified or mixed single tank thermal store that can satisfy evening peak loads or provide baseload power through the night. Compared to the parasitic loads of a conventional tower-receiver plant, the energy needed for salt transport from receiver to TES and morning preheat is negligible for this new system. The hot-spot problem of tubular receivers is eliminated and. the combined receiver/storage tank reduces component costs. In-situ initial melting was accomplished using solar energy as the primary input. Thermal stratification was maintained by daily cycling of a divider plate and occasional mixing plate actions and hot spots were never observed during several months' operation between 250 and 500 C. Three cycles of complete salt freezing and in-situ on-sun re-melting were tested with no operational difficulty and no discernible damage.

Through the Paris Agreement, Parties to the UNFCCC have reached a landmark to fight climate change. Aligned with this, the European Union has set itself an ambitious long-term goal of reducing greenhouse gas emissions by 80–95% (in comparison to 1990 levels) by 2050. Combating climate change within the above framework calls for a wide-scale deployment of renewable energy technologies (RETs). Although the contribution of renewable energy sources (RES) in the electricity mix has significantly increased, the focus has been on intermittent RETs, whereas the required system flexibility is (mainly) provided by conventional power plants. The transition toward a more sustainable energy supply, and in the case of the European energy system, the decarbonization of the electricity sector through the deployment of renewable energy technologies, is an issue of high interest among policymakers and researchers. With high shares of renewable energy, electricity system flexibility gains importance. The in-feed of variable RES-electricity (RES-e) can be balanced by energy storage and dispatchable electricity generation technologies, significantly increasing the market value of RETs combinations. Such currently available RETs include (among others) Concentrated Solar Power (CSP) with thermal energy storage (TES), solar photovoltaic (PV) with storage (electrochemical storage or electrical thermal energy storage (ETES)), hydropower, hybrid power systems, and biomass. All these technologies can provide dispatchable power, as they have some kind of energy storage, e.g. dam, battery or thermal storage. However, dispatchable RES-e face significant challenges in high RES penetration scenarios, which originate from the fact that the increased electricity system services offered (e.g. intraday, balancing, ancillary services, etc.) are not fully taken into account in their revenue streams. In this framework, market and regulatory adaptations could drive the market uptake of dispatchable RETs. More specifically, collaborative efforts could play an important role in achieving the European energy transition at lower cost than purely national approaches, as renewable sources could be exploited at locations that require low support costs by offering high potential (good renewable resources), thus leading to lower overall system costs. In particular, the establishment of the ‘enabling framework’ as defined by the recast RES Directive 2018/2001 (Art. 3(5)), and especially the cooperation mechanisms (joint projects, statistical transfers, joint support schemes) that support regional development of RETs projects, could be a key element for collaborative CSP projects (Boie and Del Rio 2021). This Special Issue aims to contribute to the better understanding of the importance of dispatchability and flexibility, and to highlight the policy and regulatory conditions needed in order for dispatchable RETs to be further deployed, supporting a fully decarbonized energy supply.

This paper presents an innovative approach of utilizing electric arc furnace (EAF) slags in value-added applications, particularly as storage media for high-temperature thermal energy storage (TES) systems, applied to next- generation of central receiver concentrated solar power (CSP) plants. EAF slag is a solid industrial waste produced in large quantities in metallurgy worldwide and commonly sent to dump sites. Due to steel slag's chemical composition of metal and non-metal oxides, advanced ceramic bodies can be prepared using thermally treated EAF slag powder. The crystallographic stability of oxidized EAF slag powder was confirmed by XRD analysis that revealed the absence of any crystal phase transformation at elevated temperatures up to 1200 °C. Advanced ceramic entirely recycled from locally UAE produced EAF slag was prepared following the method of cold compaction of ceramic powder. For sensible heat TES materials, a high density is desired to maximize the storage capacity. Therefore, the final product bulk density was examined by studying the influence of parameters such as (i) the applied compaction pressure, (ii) the firing temperature, (iii) the binder weight percentage, and (iv) the firing time. Findings showed that a compaction pressure of 186 MPa resulted in relatively dense green ceramic bodies. The firing of these bodies at 1200 °C with a dwell time of 3 hours resulted in ceramic products with a bulk density in the range of 2500 kg/m3 that could be potentially used as TES media.

The beam-down solar concentrator at the Masdar Institute Solar Platform (Abu Dhabi, United Arab Emirates) is optimally coupled with a final optical element (FOE) to maximize the net power recovered by an upward-facing solar receiver. The FOE is designed as a converging reflective passage of hexagonal cross-section to further concentrate the solar flux onto the solar receiver. We develop efficient ways to optimize the orientation of the tower central reflectors simultaneously with the geometry and size of the FOE. Net power recovered by the receiver and optimized dimensions of the FOE designs are presented as a function of FOE internal surface reflectivity and the height of its inlet with respect to the ground. Setups where the receiver aperture is 3 m above the ground that are optimized simultaneously with an 85%-reflective FOE absorb 20% additional power incoming from the central reflector than equal setups optimized without an FOE. Such optimal FOE designs remain feasible, with inlet-to-outlet lengths below 2 m. The results may be applied to the design of other beam-down projects with planar central reflectors.