Solar Receiver Research Articles

Thermal stress in externally irradiated tubes of solar central receivers with a gas–particle fluidized dense suspension

One of the objectives of the new generation of concentrating solar power plants is to increase the actual temperature limit (565 °C) up to or near 1000 °C. An alternative heat transfer fluid that could help to reach this objective is the use of a fluidized dense gas–particle suspension ascending through a vertical tube. Since the predominant cause of rupture in solar receivers is the creep-fatigue damage process, which is mostly influenced by the maximum temperatures and stress experienced along the tube, the main objective of this work is to numerically study the thermomechanical behavior of a non-uniform externally irradiated tube where particles are fluidized and moves upwards. The heat transfer problem in the two media present (i.e. dense suspension of particles and tube wall) was solved separately: a Computational Particles Fluid Dynamic model solves the heat transfer in the particles, whereas a three dimensional Finite Volume model simulates the heat conduction through the tube wall to obtain the temperature profile, which serves as input to calculate the thermal stress of the tube with an analytical method. Higher thermal stresses were obtained for an absorbed power of 250 kW/m2 (σVM,max=219MPa) compared to that for an absorbed power of 500 kW/m2 (σVM,max=72MPa) due to the lower temperature difference between the front and rear sides of the tube caused by the more pronounced increase of the radiative losses in the front side of the tube compared to that at the rear side. The thermomechanical behavior of a particle receiver was compared to that of a molten salt receiver. For an incident solar flux of 500 kW/m2, the particle receiver reduced the maximum thermal stress by 73% compared to the molten salt receiver. However, the tube’s maximum temperature exceeded the working limit for stainless steel tubes. In order for the receiver to survive heat fluxes characteristic of solar power plants, research into technological solutions that allow to improve the effectiveness of the heat transfer rate from the tube to the particle flow is necessary.

Energy Advantages and Thermodynamic Performance of Scheffler Receivers as Thermal Sources for Solar Thermal Power Generation

This article examines the prospects of Scheffler solar receivers integrated into renewable energy power plants for civil applications. This kind of solar receiver can offer satisfactory energetic performance with acceptable energy conversion efficiency when compared to other technologies to harness solar energy since the high-quality focal receiver can reduce heat losses also supposing great levels of evaporation temperature. In this research, energetic optimization and a broad assessment of Scheffler-type solar receivers are thoroughly conducted for variable sun radiation and considering a broad range of working conditions. To achieve this goal, thermodynamic optimization of the chief factors was attained via a numerical model which calculated the energy efficiency of the Scheffler solar receiver at part-load working conditions by computing all energy losses negatively affecting the heat exchange phase in the cavity receiver. The results obtained in this study show that the solar collector efficiencies of Scheffler receivers appear more promising than that of usual parabolic trough collectors; moreover, Scheffler receivers persisted with less sensitivity to reductions in solar radiation intensity. For these reasons, solar power systems based on Scheffler-type systems can be used from tens to hundreds of kW to ensure the energetic supply of small urban settlements with acceptable efficiency, optimistic investments, simple construction and reduced overall sizes.

Performance assessment of solar tower collector based integrated system for the cogeneration of power and cooling

Integrating solar energy systems is an essential measure in advancing worldwide sustainability objectives and offers a sustainable, environmentally friendly approach to reducing greenhouse gas emissions and pollutants. To this direction, the proposed system integrating solar tower collector, supercritical CO2, organic Rankine cycle, and single effect absorption refrigeration cycles shows potential as an efficient and sustainable solution for meeting energy and cooling demands. A detailed thermodynamic evaluation has been performed to gain valuable understanding of the energy and exergy performance, enabling the assessment of thermal and exergy efficiencies, exergy destructions, and heat losses. Results show that this study found the thermal efficiency of the proposed system to be 47.35 % for R245fa, 48.59 % for R123, and 52.32 % for toluene. In addition, the exergy efficiency was obtained at 40.99 % for R245fa, 42.41 % for R123, and 46.67 % when toluene is used as a working fluid. With all investigated working fluids of organic Rankine cycle, toluene achieved the highest thermal and exergy efficiency of the proposed power-cooling cogeneration system, while R245fa achieved the lowest energetic and exergetic performance. Among the various ORC working fluids investigated under operating conditions, toluene demonstrated the highest turbine power output (3202 kW), whereas R245fa exhibited the lowest turbine power output (2804 kW). The refrigeration output for all ORC working fluids studied was found to be 988.8 kW. Additionally, the primary contributor of exergy destruction rate in the proposed system was determined to be the solar tower receiver, contributing 73.24 %, 67.80 %, and 66.19 % to the total for the toluene, R123, and R245fa working fluids, respectively.

Technical strategy for reapplying coatings on solar tower receiver tubes using concentrated flux

Reapplying the coating is crucial to restore optimal receiver performance. However, the heat treatment must be conducted onsite since the receiver cannot be removed from the tower. This study explored effective strategies for maximizing the coating’s performance after reapplication. The impact of different aimpoint strategies on the receiver’s surface temperature was analyzed using the heliostat field and the three-dimensional receiver model. Experimental tests were conducted using a solar lamp to study temperature variation curves of coatings on different tube panels under various aiming strategies, and absorptance was then measured. The optimal recoating strategy was determined through a comprehensive analysis of the system’s power generation and its Levelized Cost of Energy across its entire lifecycle. The “image size priority” strategy led to significant temperature variations among tube panels and within each panel. In contrast, the “segmented target flux” strategy effectively minimizes temperature differences, ensuring that over 91.25 % of the receiver tube panel reached temperatures above 550 °C. Comparatively, under the “image size priority” and “segmented target flux” strategies, the coating’s absorptance at the molten salt inlet panel is lower by 1.84 % and 0.10 %, respectively, compared to the standard sample. The effectiveness of the “segmented target flux” strategy becomes more pronounced with shorter recoating intervals. The research contributes to enhancing the maintenance performance of the coating and the operational efficiency of the receiver.

Remote Measurement of Heliostat Reflectivity with the Backward Gazing Procedure

Concentrated solar power is a promising technique enabling renewable energy production with large scale solar power plants in the near future. Estimating quantitatively the reflectivity of a solar concentrator is a major issue, since it has a significant impact on the flux distribution formed at the solar receiver. Moreover, it is desirable that the mirrors can be measured during operation in order to evaluate environmental factors such as day/night thermal cycles or soiling and ageing effects at the reflective surfaces. For that purpose, a backward gazing method that was originally developed to measure mirror shape and misalignment error was developed. The method operates in quasi real-time without disturbing the heat production process. It was successfully tested at the Themis solar tower power plant in Targasonne, France. Its basic principle consists in acquiring four simultaneous images of a Sun-tracking heliostat, captured from different observation points located near the thermal receiver. The images are then processed with a minimization algorithm allowing the determination of the reflectance and slopes errors of the mirrors. In this communication, it is shown that the algorithm allows one to get quantitative reflectivity maps at the surface of the heliostat. The measurement is fully remote and is used to evaluate surface reflectivity that depends on optical coatings quality and soiling effects. Preliminary results obtained with a Themis heliostat are presented. They show that reflectivity measurements can be carried out within repeatability about ± 5% Peak-to-Valley (PTV) and 1% RMS. Ways to improving these numbers are discussed in the paper.

Managing Heat Transfer Intensity in a Fluidized Particle-in-Tube Solar Receiver

Particle flow structure and associated heat transfer coefficient are examined as a function of temperature in a single-tube fluidized bed solar receiver operating in upward particle flow mode. It is found that temperature has a strong effect on both fluidization regimes and wall-to-bed heat transfer coefficient that varies in the range 800-1200 W/(m2.K). Turbulent fluidization regime results in the most intense heat transfer between the irradiated wall and the fluidized particle.

Solar Field and Receiver Model Validation of the Next-CSP MW-Scale Prototype

This study presents a comparison of both modelling and experimental results obtained on the solar field and the receiver of the MW-scale particle driven CSP unit implemented at the Themis solar tower (France) in the framework of the Next-CSP H2020 European project. At partial load, ~900 kW, the simulated data concerning the incident power at the receiver aperture are consistent with the measured values with less than 5% difference from the experimental results. The difference is higher for the particle temperature and the thermal efficiency as a function of particle mass flow rate. It ranges between 12 and 98°C for measured particle temperature of 430 and 300°C respectively. For the thermal efficiency, the difference varies strongly with the experiments from approximately 12% to 50% (relative). The main cause of discrepancy between the experimental and the calculated results is attributed to the heterogeneity of the solar flux distribution on the receiver tubes.

Comparison of Aiming Point Strategy Algorithms and Their Assessment for Volumetric Solar Receivers

The present work summarizes the work done within the scope of CATION, CHLOE, and HECTOR projects related to the aiming point strategies optimization algorithms applied to volumetric solar receivers. Several optimization methods have been applied in the literature for optimizing the aiming strategy of solar power tower plants. However, the use of these algorithms for the requirements of volumetric solar receivers and solar fuel applications has not been accomplished. Herein, the problem is formulated as a constrained optimization problem whose objective function is a combination of the total power on the receiver surface and the flux homogeneity. A comparison of the results is presented in this work. It will be seen that TABU search and SA algorithms are the most efficient in terms of computation time and, in addition, the first one shows very good results in power and spillage. The rest of the mentioned algorithms are much slower and, in general, the results are slightly worse.

Efficient Computation of Radiative Heat Recovery from Porous Ceramic Monoliths for Efficient Solar Thermochemical Fuel Production

Solar thermochemical hydrogen (STCH) produced by heat-driven water-splitting is a promising route for producing green hydrogen and other zero-emission synfuels. However, the efficiency of STCH must be dramatically increased for it to make an impact on decarbonization efforts. We have previously presented a novel Reactor Train System (RTS) for significantly increasing the efficiency of STCH by employing heat recovery from the redox material and efficient gas exchange processes. In this paper we present a higher-fidelity model for the RTS that accommodates the slow heat diffusion through the STCH redox material. For this purpose, a novel method is introduced for transient modelling of radiative heat in participating media. This method, called GREENER: Generalized Radiation Exchange Factors and Net Radiation, combines the accuracy of Monte Carlo Ray Tracing with the low computational cost of the P1 or Rosseland diffusion approximations. Along with STCH, GREENER has application for modelling volumetric solar receivers, high temperature heat recovery systems like heat exchangers and regenerators, and packed bed reactors. Using the GREENER method, the RTS counterflow radiative heat exchanger is shown to achieve heat recovery effectiveness greater than 70%. The performance of non-uniform porous redox morphologies is evaluated, and high-performing configurations are identified.

Theoretical and experimental study on the effect of the heat shield on the trough solar cavity receiver in alpine areas

The large heat loss of the cavity receiver limits its application in parabolic trough collectors, matching the environmental factors in alpine areas, in this paper, adding a glass cover plate as a heat shield at the aperture of the trough inverted trapezoidal cavity receiver is investigated. To quantify the optimization of the system performance by adding, an analytical study is carried out for the cavity receiver using theoretical calculations of heat transfer and indoor experimental tests, while “thermal uniformity” is introduced as an indicator of the temperature distribution inside the cavity, and further verifies experimentally by the outdoor real-area environment. The findings indicate that adding a heat shield is significantly effective in reducing heat loss in windy areas. At the flow rate of 250 L/h and inlet temperature of 323 K, the maximum experimental heat loss value is significantly reduced by 70.01 % in the range of 1–5 m/s wind speeds compared to the one without a heat shield. When the wind direction is from −60° to 60°, the heat loss inside the cavity is small after adding, forming a stable stratified flow, and the thermal uniformity decreases by only 0.02, indicating that the stability of the temperature field inside the cavity is high. Furthermore, outdoor validation experiments demonstrate a slower change in heat loss rate with adding the heat shield compared to without, the growth rate of the former is close to 1/3 that of the latter, with a maximum suppressed heat loss rate of 23.49 %. This study provides the theoretical basis and data guidance for optimizing cavity receiver performance in alpine areas.

Heat transfer enhancement in pressurized solar cavity receivers with densely packed metallic wire mesh

Pressurized solar receivers are promising candidates as heat sources for integration with high-efficiency closed-loop air and supercritical carbon-dioxide based Brayton cycles. This paper focuses on the heat transfer enhancement of such a solar receiver using inline stacked wire mesh fibers in the heat transfer fluid flow path. The study involves modelling, characterization, and performance evaluation of a cavity-receiver with densely packed wire meshes. A new experimentally validated hybrid numerical approach is presented for modelling the inline stacked wire mesh layers. Initially, a direct numerical simulation at the pore scale on a representative elementary volume (REV) of the wire mesh geometry is performed for determining the hydrodynamic and thermal characteristics of the medium. Subsequently, these hydrodynamic and thermal properties are used to define a volume-averaged macroscopic porous medium. Experiments are performed using a rectangular channel stacked with stainless steel wire meshes, heated using a plate heater, and pressurized air supplied using a reciprocating compressor. Both numerical and experimental studies are performed for a Reynolds number range of 28 to 213 resulting in a Nusselt number range of 7.2 to 213. The porous medium model predictions for pressure gradient are within 17 %, while predictions for outlet air temperature are within 5 % of the experimentally obtained values. The study predicts a maximum heat transfer enhancement of five times in a channel stacked with wire meshes compared to the case of a clear channel, but incurring a peak pressure drop of only about 1.1 kPa.

Experiment and dynamic simulation of micro gas turbine combined with concentrated solar power system

The solar micro gas turbine (SMGT) system is a promising solution to address the instability and intermittency of renewable energy sources. Its dynamic characteristics under unstable input conditions and uncertain output load demands are crucial for peak shaving. This paper constructs an SMGT system based on experiments with micro gas turbine (MGT) and concentrated solar power (CSP), analyzing the impact of integrating CSP system on the MGT. Then the performance of the SMGT under varying ambient conditions and load demands is studied. Results show that in grid-connected mode, the turbine speed of MGT and SMGT is determined by ambient temperature and set power, with electrical efficiency decreasing as temperature and DNI increase. The solar receiver in the SMGT should maximize temperature increase while maintaining pressure loss below 55 kPa. Additionally, a higher heat capacity can reduce sensitivity to ambient changes but also extends stabilization time. Under real solar radiation, the SMGT system can keep constant power within 0.6% fluctuation, with a solar share of 36.5%. When combined with photovoltaic, the hybrid system’s maximum power fluctuation does not exceed 2.6%, with a solar share of 48.8%. This study provides guidance for optimizing SMGT systems and their application in peak shaving scenarios.

Numerical study of temperature distribution in a solar receiver with a focus on water heating in an internal helical tube

Solar energy is one of the clean energies that many researchers have focused on. This study used the Monte Carlo Ray Tracing (MCRT) method in MATLAB coding to calculate the water temperature inside a solar receiver containing a spiral coil through which water passes. To guess the amount of solar radiation that would hit the receiver and figure out the temperature of the water coming out, the Monte Carlo method was used. The three cases were: a change in the receiver's exposure time to solar radiation (t = 2, 4, 6, 8, 10 h); a change in the gas flow rate (Qg = 5, 10, 15, and 20 L/min); and a change in the water flow rate (from 2 to 20 with an increase of 2 L/min in each case. The study found that the gas volume flow rate (Qg) slightly affected the thermal distribution at Qg = 5 L/min, Tg = 358 C, and at Qg = 20 L/min, Tg = 352 C, while the water volume flow rate (Qw) and time directly affected the water temperature. The study showed that the thermal distribution was stable at 8 and 10 h. At 8 h, the water reached a maximum temperature of 153 °C at Qg = 5 and Qw = 2. When Qg = 5 L/min and Qw = 2 L/min, the receiver wall temperature reached 322 °C, the receiver backplate temperature (Tbp) reached 498 °C, and the gas temperature (Tg) reached 354 °C. At QG and Qw = 20, the water temperature dropped to 46 °C. This showed that the volume flow rate significantly affected the temperature.

A Feedback Control Strategy to Regulate the Temperature in a Nonlinear Solar Receiver

Abstract The substantial energy provided by the sun is a promising substitute for traditional heat sources in various industrial applications. However, the transient nature of solar energy still poses a significant challenge to its widespread utilization. This work presents a methodology for regulating the temperature within a solar receiver by dynamically adjusting incoming sunlight through the aperture using a controlled iris mechanism. The performance of this technique is experimentally compared with the gas flowrate control method, which is typically used in industry. The proposed control system, grounded in the physical model of the solar receiver, underwent experimental testing under varying conditions, including different gas flowrates, simulator power levels, and aperture sizes. The collected data were then analyzed to estimate a simplified model of the solar receiver. A model predictive controller (MPC) is implemented using the model estimations, and its performance was assessed by tracking two set points (335 and 325 °C) over a period of 2 h. The experimental testing of both control systems indicates the superiority of iris mechanism over gas flowrate controller in terms of robustness, settling time, and smoothness. A hybrid control system utilizing both aperture size and gas flowrate is also developed and tested during the operation of the solar receiver via computer simulations.

Design-Optimization of Solar-Collector Tilt Angle for Annual-Maximum and Seasonal-Balanced Energy Received

Abstract A detailed research study was performed on the annual energy received by a fixed-tilt solar collector. A new clear-sky model of solar radiation was developed by combining existing clear-sky models. Then, this model, was used to perform optimizations with two different objectives. The first objective is to achieve the maximum-annual solar energy received by a solar panel, while the second is to balance its energy received so that it is more uniform over the course of a year. Each of these objectives have differing optimum tilt values, depending on the location and usage of a solar receiver system. The novelty of this investigation is the use of the aforementioned solar model with a unique algorithm for multiple optimizations for these two different objectives, which results in two different optimum tilt angles that are in turn different from the widely accepted rule-of-thumb that recommends an angle that is equal to the latitude. The solar radiation results obtained with the model used herein were experimentally confirmed through comparison with measured weather data for a number of locations with different sky clearness indexes as well as comparison with those of other studies found in the literature. A major contribution of this study are the plots and tables showing optimum tilt angles as estimated by the model as well as with empirical data. By selecting the appropriate tilt angle, a designer can now decide to either maximize annual electrical energy production or else to balance delivery of electricity over the year.

Titania-Based Coral-Structured Solar Absorber Coating with Improved Scalability and Durability at High Temperature.

Solar energy harvesting and storage are essential in the future mix of renewable energy technologies. Hierarchical coral-structured coatings have been shown to yield high solar absorptance in concentrating solar thermal (CST) systems. However, interfacial delamination and scalability challenges owing to material complexity pose significant hurdles for the widespread industrial adoption of these hierarchical CST coatings. Here, a coral-structured coating is proposed whose black pigments are strongly bonded by titania, which is a material that mitigates interfacial delamination. Importantly, this coating follows a facile deposition procedure suitable for large-scale solar receivers. The drone-deposited coating inhibits cation diffusion and maintains a stable solar absorptance of even after long-term (3000 h) high-temperature ( ) aging. The scalability of developed coating represents a substantial advancement in the implementation of light-trapping enhancement and maintenance approaches across a wide range of CSTapplications.

Carbon nanotube heat absorber for efficient direct-heating of liquid tin in a solar receiver

A new approach that use vertically-aligned carbon nanotubes (VACNT) as heat absorbers is proposed for efficient direct solar heating of liquid tin in a solar receiver integrated with beam-down optics. Plate-type CNT heat absorbers were prepared by adjusting the concentration of CNTs in the processing solvent m-cresol. The prepared CNT absorber exhibited an increase in bulk density and the formation of a densely packed nanotubes skeleton with a higher CNT concentration in m-cresol. Thermal conductivity, a key design factor for solar absorbers, showed a stronger correlation with skeletal density than with bulk density. Heat absorption characteristics of the solar liquid tin receiver (50 mm-i.d., 60 mm-high) with the CNT absorbers integrated with a Fresnel lens (0.98 m i.d.) were determined. The tin temperature in the receiver with the CNT absorber reached a maximum of 728 °C. Bare tin exhibited system efficiency of 27.7 % and receiver efficiency of 38.3 %, but tin heating through the CNT plates exhibited system efficiency of up to 48.4 % and receiver efficiency of 64.3 %, showing a system heat absorption rate 1.75 times higher. The thermal absorption efficiency was proportional to the skeletal density of the plates, and the thermal absorption of the system was dominated by the efficient transfer of absorbed heat in the energy absorption region. The energy flow and heat loss in the receiver system were analyzed. Although the bare tin receiver exhibited a high heat loss of 27.1 % owing to the low emissivity or high reflectivity of the tin surface, the heat loss in the CNT absorber plates with high absorptivity was only 0.9 %. The flat plate-shaped transmission window in the receiver caused significant reflective heat loss and convective heat loss owing to head-on wind. Based on the energy flow analysis, improvement approaches for enhancing the thermal efficiency of the proposed receiver system are suggested.

A solar air receiver with porous ceramic structures for process heat at above 1000 °C – Heat transfer analysis

Abstract Concentrated solar energy can be used as the source of heat at above 1000 °C for driving key energy-intensive industrial processes, such as cement manufacturing and metallurgical extraction, contributing to their decarbonization. The cornerstone technology is the solar receiver mounted on top of the solar tower, which absorbs the incident high-flux radiation and heats a heat transfer fluid. The proposed high-temperature solar receiver concept consists of a cavity containing a reticulated porous ceramic (RPC) structure for volumetric absorption of concentrated solar radiation entering through an open (windowless) aperture, which also serves for the access of ambient air used as the heat transfer fluid flowing across the RPC structure. A heat transfer analysis of the solar receiver is performed by means of two coupled models: a Monte Carlo (MC) ray-tracing model to solve the 3D radiative exchange and a computational fluid dynamics (CFD) model to solve the 2D convective and conductive heat transfer. Temperature distributions computed by the iteratively coupled models were compared with experimental data obtained by testing a lab-scale 5 kW receiver prototype with a silicon carbide RPC structure exposed to 3230 suns flux irradiation. The receiver model is applied to optimize its dimensions for maximum efficiency and to scale up for a 5 MW solar tower.

Development of Ti3SiC2 MAX phase tubular structures for solar receiver applications

Solar receiver tubes are key components of concentrating solar-thermal power (CSP) systems that harvest solar energy. For better efficiency, the Gen3 CSP receivers, which collect heat into a heat transfer fluid, require a temperature exceeding 700 °C during operation and need to perform under extreme conditions of high temperature and high thermal stress. Operators are seeking CSP designs using new high-temperature structural materials with high thermal conductivity and high creep resistance to achieve a design life of 30 years and thus help recover the plant capital cost sooner. MAX phase materials, which consist of an early transition metal element, an A-group element, and carbon or nitrogen, are expected to exhibit high creep resistance as well as high fracture toughness. In this paper, we describe fabricating both (1) dense Ti3SiC2 MAX phase disks and (2) short-length tubes using field-assisted sintering technology (FAST). First, the disk samples that we fabricated are fully dense and contain ≈90 % Ti3SiC2 MAX phase materials and ≈10 % TiC phase materials. We determined a flexure strength of 519 ± 32 MPa by conducting a four-point bending test at room temperature with rectangular bar samples of ≈100 % density. The thermal conductivity of the Ti3SiC2 MAX phase samples, measured by light-flashing analysis, decreases linearly from a value of 41 W·m−1·K−1 at room temperature to a value of 36 W·m−1·K−1 at 650 °C. A solar reflectance measurement of the Ti3SiC2 MAX phase revealed that, temperature increases from 400 to 1400 °C, thermal emittance increases from 0.39 to 0.49, while selectivity decreases from 1.8 to 1.4, respectively. Whereas the surface oxidized MAX phase samples after 100 h exposure to air at 1000 °C exhibit that of SiC.Next, we discuss fabrication of the crack-free Ti3SiC2 MAX phase tubular structures accomplished by using FAST processing in graphite bedding. A Ti3SiC2 MAX phase content of > 95 % with traceable ≈3% remaining TiC phase and ≈15 % porosity were demonstrated after high-temperature annealing. An average fracture strength of ≈250 MPa was determined with Ti3SiC2 MAX phase tubes of ≈85 % density by diametral compression testing at room temperature. Our work demonstrated that using FAST processing to produce Ti3SiC2 MAX phase tubular structures for CSP receiver applications is a viable approach.

Energetic and Exergetic Analyses of a Double-Pass Tubular Absorber for Application in Solar Towers

Abstract The present research integrates the concept of double-pass (DP) flows with high-temperature solar receivers to introduce an innovative design aimed at minimizing heat losses and optimizing performance. The new DP system was developed using a tubular absorber derived from billboard solar tower technology and operated with air as the heat transfer medium. Computational fluid dynamic models are developed based on an experimental campaign conducted at a solar furnace facility. The computational analyses indicated that employing the DP design instead of single-pass (SP) absorbers results in an average enhancement of energy and exergy efficiency by 35% and 225%, respectively, across all test conditions. However, this enhancement is accompanied by an average increase in pressure drop of ∼60%. The detailed exergy analysis also revealed the contribution of each term in the exergetic performance, identifying the exergy destruction between the sun and the absorber as the primary source, accounting for an average of ∼65% of the total inlet exergy for both SP and DP absorbers. Consequently, the DP presents itself as a promising alternative design for future solar tower configurations, offering improved Nu numbers up to ∼50% in air-based solar systems.