Tower Plant Research Articles

Thermomechanical behavior of mechanical attachments in solar power tower receivers under preheating conditions: A numerical study

Thermal deflection of receiver tubes in solar power tower plants is typically reduced by means of mechanical attachments, each one consisting of a clip and a guide through which a rod connected to a reradiating wall can freely slide. As a side effect, these mechanical attachments act as heat sinks, promoting a local temperature reduction in the tube during the receiver preheating, thus increasing the risk of crystallization of the molten salt during the subsequent filling of the receiver. Additionally, the mechanical attachments and the tube are subjected to thermal stresses during the preheating of the system, remarking the importance of considering both thermal and mechanical effects during the design of these elements. This study uses three-dimensional thermomechanical simulations to characterize the behavior of both the mechanical attachment and the tube during the preheating of a solar power tower receiver. The results revealed that the areas of maximum stress occur in the tube, clip, and guide sequentially as the preheating process progresses. The maximum stresses are located in the connections of the clip with both the tube and the guide. An extensive parametric sweep on the dimensions of the mechanical attachment revealed a trade-off between the minimum temperature and the maximum stress of the tube. Based on this analysis, an optimal solution for the dimensions of the clip and guide in terms of their height is proposed. The systematic study here presented can serve as a basis for the design of improved mechanical attachments able to ensure an adequate minimum temperature of the tube during the preheating while keeping the stress of the system within acceptable limits.

Performance analysis of a solar based novel trigeneration system using cascaded vapor absorption-compression refrigeration system

Solar power tower technique has a strong potential among several solar systems for large-scale power generation. It is crucial to make new, efficient trigeneration unit for solar power tower plant. This work makes a novel supercritical Brayton cycle based combined cycle in which helium is considered as the working fluid for power generation. The cascaded vapor absorption-compression refrigeration system is integrated with traditional Brayton cycle for recovering waste heat to produce additional heating and low temperature cooling effects for food storage. The energy, exergy efficiency and power output of the proposed plant were found as 28.82%, 39.53% and 14,865 kW respectively. The COPcooling and COPheating values were observed as 0.5391 and 1.539 respectively at 850 W/m2 of direct normal irradiation, 80 °C of generator temperature (Tc) and -20°C of evaporator temperature (Te). Solar sub system is responsible for high exergy destruction around 78.18% (22,763 kW) of total destruction of the overall plant. Moreover, parametric study reveals that performance of trigeneration system is highly affected by the heliostat and receiver efficiency, Tc, Te and inlet temperature of helium turbine. Also, a comparison with related earlier research has demonstrated that the performance of the current system is superior to that of systems based on the Rankine cycle and supercritical CO2 cycles.

Structural Performance-Based Design Optimisation of a Secondary Mirror for a Concentrated Solar Power (CSP) Plant

Concentrated Solar Power (CSP) plants use mirrors to reflect and concentrate sunlight onto a receiver, to heat a fluid and store thermal energy, at high temperature and energy density, to produce dispatchable heat and/or electricity. The secondary mirror is a critical component in the optical system of certain Solar Power Tower plants (SPT), as it redirects the concentrated sunlight from the primary mirror onto the receiver, which can be arranged at ground level. In this study, we propose a design optimisation for the secondary mirror of a CSP plant. The design optimisation method consists of two steps. The first step involves the use of the finite element simulation software Abaqus 2022 to analyse the structural performance of the secondary mirror under thermal loads and wind. The second step consists of the use of simulation results to identify the combination of design parameters and best performances, with respect to both design constraints and structural safety. This is carried out by developing an algorithm that selects those configurations which satisfy the constraints by using safety coefficients. The proposed optimisation method is applied to the design of a potential configuration of a secondary mirror for the beam-down of the CSP Magaldi STEM® technology, although the methodology can be extended to other components of CSP plants, such as primary mirrors and receivers, to further enhance the structural performance of these systems.

Proposal of a new design of central solar receiver for pressurised gases and supercritical fluids

This work presents a novel design of microchannel central receiver for pressurised gases and supercritical fluids in solar tower plants. It consists of a radial arrangement of vertical absorber panels that converge on the central axis of the tower. The absorber panels comprise compact structures, whose compactness is increased in one flow pass compared to the previous one, as the fluid is heated. This concept reduces radiation heat losses due to its light-trapping geometry and increases heat transfer to the thermal fluid without over penalising its pressure drop.For the receiver assessment, it has been developed a thermal resistance model characterising the fluid heating along the panel height and the temperature gradient between parallel channel rows of the compact structure across the panel thickness. Once the thermal and optical boundary conditions are defined, an optimisation analysis of the main geometrical parameters of the receiver has been accomplished. The receiver performance is evaluated by means of a global exergy efficiency referred to the solar subsystem, which computes the receiver heat losses, the fluid pressure drop and the optical efficiency of the heliostat field in which the receiver is integrated. For each parametric optimisation, the configuration that maximises this efficiency is identified.

Enhancing the Thermal Performance of a Central Tower Tubular Solar Receiver With Direct Steam Generation by Using Internal Fins and Thicknesses Variation

Abstract This study provides a comprehensive analysis of the thermal behavior of tubular solar receivers used for direct steam generation, focusing on the effects of different wall thicknesses and longitudinal rectangular fins on the internal surface. The study evaluated six tubes, including two tubes with distinct wall thicknesses (5 mm and 3 mm) without fins and four tubes with fins but varying configurations. These tubes represent external tubular receivers used in solar central tower plants and operate at 4.5 MPa with a nonuniform solar flux averaging 0.8 MW/m2. Adding longitudinal fins to the tubes significantly reduced the maximum temperature on the irradiated surface and improved heat transfer to the fluid. The study concluded that the 45F5 receiver, which has three fins on the internal section, outperforms the other receivers, presenting a higher vapor generation. Furthermore, the 45F5 geometry enhances heat transfer, allowing the lowest maximum Biot number. These results are crucial for designing tubular solar receivers with direct steam generation systems and improving their efficiency in generating energy from renewable sources.

Waste heat recovery potential in the thermochemical copper–chlorine cycle for hydrogen production: Development of an efficient and cost-effective heat exchanger network

With the finite nature of fossil fuel resources and related environmental issues, it is necessary to replace fossil-fuel-based hydrogen production methods with more sustainable ones. For the clean production of hydrogen, the copper-chlorine (Cu–Cl) thermochemical cycle is a favorable choice. However, internal waste heat recovery of the cycle is essential to improve the efficacy of the system. In this paper, the waste heat recovery potential of the four-step Cu–Cl cycle is investigated, to support the design of a new cost-effective and high-performance heat exchanger network. Pinch analysis is executed to find the optimum rates of cold and hot utilities for this cycle. Three heat exchanger network cases are investigated which include case 1, without heat recovery; case 2, with 16 heat exchangers; and case 3, with 11 heat exchangers. The effect of varying design parameters on the energy system's efficiency and cost-related parameters are also explored here. Based on the pinch analysis results, the minimum heating and cooling and the maximum recoverable heat, on a normalized basis, are 333.3 kJ/mol H2, 76.9 kJ/mol H2, and 134.4 kJ/mol H2, respectively. Moreover, for cases 1, 2, and 3 the thermal efficiencies are calculated as 33.3%, 41.1%, and 40.5%, respectively. Additionally, it is observed that, when the thermal energy of the cycle is supplied from a solar power tower plant, the levelized cost of hydrogen for case 1 is 9.6 $/kg H2, for case 2 is 7.9 $/kg H2, and for case 3 is 7.8 $/kg H2.

Triple-Objective Optimization of SCO2 Brayton Cycles for Next-Generation Solar Power Tower

In this paper, the SCO2 Brayton regenerative and recompression cycles are studied and optimized for a next-generation solar power tower under a maximum cycle temperature of over 700 °C. First, a steady-state thermodynamic model is developed and validated, and the impacts of different operating parameters on three critical performance indexes, including the cycle thermal efficiency, specific work, and heat storage temperature difference, are analyzed. The results reveal that these performance indexes are influenced by the operating pressures, the SCO2 split ratio, and the effectiveness of the regenerators in complex ways. Subsequently, considering the three performance indexes as the optimization objectives, a triple-objective optimization is carried out to determine the optimal operating variables with the aim of obtaining Pareto solutions for both cycles. The optimization indicates that the regenerative cycle can achieve the maximum heat storage temperature difference and the maximum specific work of 396.4 °C and 180.6 kW·kg−1, respectively, while the recompression cycle can reach the maximum thermal efficiency of 55.95%. Moreover, the optimized maximum and minimum pressure values of both cycles are found to be around 30 MPa and 8.2 MPa, respectively. Additionally, the distributions of the optimized values of the regenerator effectiveness and the SCO2 split ratio show different influences on the performance of the cycles. Therefore, different cycles with different optimized variables should be considered to achieve specific cycle performance. When considering thermal efficiency as the most important performance index, the recompression cycle should be adopted. Meanwhile, its SCO2 split ratio and the regenerator effectiveness should be close to 0.7 and 0.95, respectively. When considering heat storage temperature difference or specific work as the most important performance index, the regenerative cycle should be adopted. Meanwhile, its regenerator effectiveness should be close to 0.75. The results from this study will be helpful for the optimization of superior SCO2 cycles for next-generation solar tower plants.

Co-optimisation of the heliostat field and receiver for concentrated solar power plants

In a concentrated solar power (CSP) tower plant, it is essential to understand the performance of the subsystem formed by the heliostat field and the receiver, operated with an optimal aiming strategy that guarantees the safety and lifetime of the receiver while maximising performance. State-of-the-art studies optimise the heliostat field, aiming strategy and the receiver independently. However, the field and the receiver are interdependent and co-optimisation of the field-receiver subsystem is necessary to obtain the optimal configuration. Fast and accurate annual performance assessments of the subsystem are needed to calculate the annual energy output and the Levelised Cost of Energy (LCOE) of the full CSP system. In this study, a co-optimisation method is proposed based on coupled instantaneous optical, thermal and mechanical models integrated into a system-level model for annual simulation of full system and economics. The resulting system-model is then used for design optimisation based on a genetic algorithm. Several techniques are implemented to make this complex and computationally expensive problem tractable. The proposed method is used to optimise the design of two systems composed of a surround field and a liquid sodium-cooled cylindrical external receiver for first the annual performance and then the LCOE. The good behaviour of the method is confirmed by a sensitivity study. The LCOE-based optimisation leads to a less efficient system than the efficiency-based optimisation but a higher capacity factor. The methods presented are applicable to other CSP plant configurations, including state-of-art molten salt power tower plants.

Parametric Study and Optimization of No-Blocking Heliostat Field Layout

Generating electric power using solar thermal systems is effective, particularly for countries with high solar potential. In order to decide on a relevant location to implement the solar tower plant and develop the mathematical model of a no-blocking heliostat field, a meteorological assessment was discussed in this paper. In addition, a parametric study was examined to evaluate the effect of the designed parameters (heliostat size, heliostat height from the ground, tower height, receiver aperture, and the minimum radius) on the solar field’s performance. The preliminary solar field was then compared to the final design using the optimal design parameters. The obtained results showed that “Tamanrasset City” satisfied the necessary conditions for implementing a solar tower plant. According to preliminary solar field generation, no heliostat blocked its neighbor with a blocking efficiency of 100%. An analysis of its performance revealed that the optimized solar field would be capable of producing 15, 6571 MW, operating at an optical efficiency of 76.95%, and the enhancement rate of both efficiency and power output was 8.1%.

An operation strategy and off-design performance for supercritical brayton cycle using CO2-propane mixture in a direct-heated solar power tower plant

Adding propane to CO2 can improve the thermal efficiency of the supercritical Brayton cycle under high condensation temperatures. Integrating the thermal energy system in a direct-heated solar power tower plant can maximize the thermal utilization of solar energy. In this paper, the thermodynamic model of the plant is constructed, and an operation strategy is proposed to realize round-the-clock operation by flexible scheduling of solar, molten salt, and fossil fuel energy supply. Notably, the potential of adding propane to CO2 in the plant was analyzed by comparing the off-design performance and the operation behavior under typical days. The results show that the thermal efficiency of the plant using CO2-propane is not only 1.63% higher than the original, but also the adequate utilization time of solar energy will be prolonged by 0.3 h. In addition, the hot molten salt filling rate of the CO2-propane system is more sensitive to changes with direct normal irradiance. However, the performance of the system will deviate from the optimal design value when the heating mode is switched. The achievements from this paper have testified the CO2-propane cycle is better than the initial cycle in the direct-heated solar power tower plant under off-design conditions. The system scheme and operation strategy can be regarded as valuable references for CO2-based mixtures application.

Capacity Factors over the Lifetime of Solar Thermal and Photovoltaic Plants

The levelized cost of energy (LCOE) encompasses capital costs, operations and maintenance (O&M), and performance over the lifetime of a power plant. This parameter, important to compare renewable energy projects, is computed assuming an annual relative performance deterioration over the lifetime of the plant. The performance deterioration is revised to reflect operating data of the latest solar photovoltaic (PV) and concentrated solar power (CSP) plants. From data for the largest of these plants built in the United States over the last decade, we note a marked initial growth phase in the performance of PV plants likely originating from a refinement of design and improvement in the O&M, followed by a limited decline, and a stable performance in the CSP plants of the simplest and more reliable parabolic trough (PT) design without thermal energy storage (TES). It is therefore suggested to consider an annual performance deterioration 0–0.25% for novel photovoltaic plants, and 0% for novel CSP plants PT without TES. The performance deterioration of the novel CSP plants of the solar tower design or plants with TES cannot be assessed based on the lack of data. The suggested changes slightly reduce the LCOE of solar plants, by thus making them more competitive with wind plants.

Techno-economic assessment and optimization of the performance of solar power tower plant in Egypt's climate conditions

Egypt is a sunbelt nation with plenty of solar resources and significant wasteland areas, particularly in its southern and western regions. Concentrating solar power technologies are tried-and-true renewable energy systems that use solar radiation to produce electricity in nearby nations. These technologies have the potential to reduce costs in the future. Comprehensive techno-economic research has not been conducted to assess the potential for the solar power tower technique in Egypt; instead, solar photovoltaic and parabolic trough systems are given the majority of the attention. The major goal of this article is to persuade the Egyptian government to pursue solar power tower technology and meet the accompanying difficulties. Using system advisor model software, six distinct locations were used to simulate a 100 MW plant for solar power tower technology. Based on a thorough technical solar power tower site evaluation research, these zones were examined. To achieve the lowest levelized cost of electricity (LCOE), thermal energy storage and solar field size optimization are carried out. The Benban location, with outputs of 521,228.8 MWh and 0.1130 $/kWh, respectively, has the greatest produced energy and the lowest levelized cost of electricity, according to the findings. The ideal design for the solar power tower plant was shown by the results to be a solar multiple of 2.8 with a thermal energy storage of 8 h. The solar power tower plant's lowest levelized cost of electricity might then be reduced, in accordance with the optimum configurations, to 0.1057 $/kWh.

Optimization and performance analysis of a near-zero emission SOFC hybrid system based on a supercritical CO2 cycle using solar energy

Renewable energy represented by solar energy has the characteristics of intermittency and fluctuation. To ensure that the grid can operate safely and stably after the large-scale grid connection of renewable energy power, a new hybrid system consisting of a solid oxide fuel cell (SOFC), a solar power tower plant, and a supercritical CO2 (S-CO2) Brayton cycle is proposed in this study from the perspective of energy, exergy, and economy. By utilizing the cold source loss of the S-CO2 cycle to provide part of the energy required for the alkaline electrolyzer, it can efficiently produce and store hydrogen, achieving zero greenhouse gas emissions while increasing efficiency. Meanwhile, the high-temperature exhaust gas from SOFC is recovered by the S-CO2 cycle. The system considers two operation modes, switching two types of S-CO2 cycle configurations to efficiently utilize solar energy according to the variation of solar radiation energy. The thermal efficiency of the proposed system is improved by 16.61% and 6.88% compared with the other two typical S-CO2 cycle power generation systems, and the net power output reaches 8.0 MW. A parameter study shows that increasing the split ratio is beneficial to improve the thermodynamic performance of the system. However, at a split ratio less than 0.76, it is beneficial to the total cost rate of the system. The results of multi-objective optimization show that the exergy efficiency of the combined system and the total system cost rate reach 56.86%, 513.10$/h and 56.45%, 481.59$/h for the system with an additional simple S-CO2 cycle and the system with an additional recompression S-CO2 cycle, respectively, and the optimum point is selected by the TOPSIS and LINMAP methods.

Dynamic creep and stress performances of the packed-bed thermal energy storage tank with molten salt EPCM particles

In the concentrating solar power (CSP), the high-temperature creep and stress concentration greatly affect the safety performance of the packed-bed thermal energy storage (TES) tank with encapsulated phase change materials (EPCMs). Therefore clearly analyzing the dynamic creep and stress distribution is an effective way to optimize the mechanical performance of EPCM-TES tank. In the study, a commercial scale EPCM-TES tank applied in 50MWe tower plant is designed. Then an integration model coupling FVM and FEM applied in EPCM-TES structure is established, where the real mechanical loads and cyclic temperature distribution are considered in stress analysis model. Based on the coupled model, the dynamic creep and stress performances of the EPCM-TES tank in charging and discharging are studied. The results are concluded as follows. (1) In charging, when the tank wall is gradually heated, the creep damage is produced on wallboards installed above 4.4 m height. Because of the tank wall continue to be heated by the high-temperature EPCMs fillers after charging, the creep phenomenon further occurs on the rest of wallboards installed below 4.4 m height. In discharging, when the tank wall is cooled by cold salt, the creep damage of the whole wallboard can be avoided. (2) The creep damage time of tank wallboards varies greatly along the height direction. In 25ys design life, the maximum creep time happens on top wallboard which is 105,000 h and occupies almost 47.9 % of the total operation time. (3) Most wallboards installed above 2.2 m height are always in elastic state with lower stress level in charging and discharging, whereas the plastic damage induced by stress concentration always occurs at the fillet weld location of bottom wallboard in charging. The study provides insights on the optimization design of the molten salt EPCM-TES tank in CSP for lower stress level and creep damage time.

Dynamic Thermal Transport Characteristics of a Real-Time Simulation Model for a 50 MW Solar Power Tower Plant

A dynamic simulation model of a heliostat field and molten salt receiver system are developed on the STAR-90 simulation platform. In addition, a real-time simulation model coupling the above two models is built to study the photothermal conversion process of Delingha’s 50 MW solar power tower plant. The nonuniform and time-varying characteristics of the energy flux density on the receiver surface and the dynamic characteristics under different operating conditions are studied. The operational process of the receiver of a typical day is simulated. It was found that there was a strong positive correlation between the energy flux and DNI, and the maximum energy flux density on the surface of the heat absorbing tube panel moved from the first tube panel to the fourth in sequence from 12:00 to 18:00. At the same time, the energy flux density of the last four panels decreased gradually along the arrangement order of the panels. DNI, molten salt mass flow rate and inlet temperature step disturbance simulations are carried out, and the response curves of the molten salt outlet temperature and tube wall temperature are obtained. The conclusion of this paper has important guiding significance for the establishment of an operational strategy for photothermal coupling in a molten salt solar power tower plant.

A feedforward-feedback control strategy based on artificial neural network for solar receivers

In a solar power tower plant, the stability of the receiver’s outlet temperature is required for high-efficiency and safe operation. However, the dramatic variation of solar energy caused by clouds is a severe challenge for keeping the temperature steady at the outlet. To solve this problem, a feedforward-feedback control strategy based on an artificial neural network is proposed herein to cope with the fluctuation of solar energy by regulating the receiver’s mass flow rate. The feedforward controller based on artificial neural network can quickly respond to the change of solar energy, while the feedback controller can make the receiver achieve an expected ultimate temperature. The performance of the proposed control strategy is comprehensively evaluated and compared with PID controller under different conditions. The results show that the proposed control strategy can significantly reduce the fluctuation of receiver’s outlet temperature. For the step variation of direct normal irradiance ranging from −15 % to 15 %, the proposed control strategy can confine the temperature deviation within ± 1 °C. For the real dramatical and continuous direct normal irradiance variation, the temperature deviation is limited to 5 °C under the proposed control strategy, while it exceeds 30 °C under the PID controller only. The results provide an alternative efficient strategy for the receiver’s mass flow control to keep a steady outlet temperature under the fluctuation of the solar resource.

Influence of eccentricity on the thermomechanical performance of a bayonet tube of a central solar receiver

This work numerically evaluates the thermal and mechanical behaviors of eccentric bayonet tubes to be used in external central receivers of solar power tower plants. A bayonet tube is composed of two tubes, one inside the other, creating circular and annular sections, through which the molten salt of the receiver sequentially flows. Eccentricity in the annular section is achieved by displacing the axis of the interior tube with regard to the exterior one. For comparative purposes, two examples of conventional tubes (single tubes with circular cross-sections with diameters of 25mm and 50mm) are also investigated in this work to compare their performances with those of bayonet tubes. The results obtained with the eccentric configurations show an enhancement of the heat transfer to the molten salt and a reduction of the tube wall overheating compared with the concentric bayonet tubes and the largest simple tube. For conditions representative of the normal operation of a solar power tower, eccentric bayonet tubes could reduce the pressure drop by 30.8% and increase the convective heat transfer achieved in a concentric configuration of the bayonet tube by 26.1%. Nevertheless, this pressure drop was considerably higher than those obtained in the smallest and largest simple tubes, which were 1.28 bar and 0.13 bar, respectively. To investigate whether the enhancement of the convection heat transfer experienced by bayonet tubes compensates for their higher pressure drop or not, a Performance Evaluation Criterion (PEC) was proposed and used to compare the global performance of bayonet tubes with that of conventional tubes. The bayonet tubes with eccentricity 0.45 obtained the largest PEC, which was up to 13% higher than reference conventional tubes. Enhancement of the tube wall refrigeration produced when increasing the eccentricity is reflected in the maximum tube temperature and thermal stresses, which are found to diminish by approximately 8.8% with the highest eccentricity. In addition, the largest eccentric bayonet tube layout obtains the smallest peak temperatures compared to conventional tubes. The lower inertial moment of the smallest conventional tube indicates that its thermal stress is 2.1% lower than the stress obtained in the most eccentric layout analyzed in this work. Nevertheless, the time to rupture associated with creep damage of the eccentric bayonet tube is 1.04 times higher than that obtained in the smallest simple tube, demonstrating that bayonet tubes could be a potential alternative to the current tubes of external tubular receivers.

THERMAL EVALUATION OF A SOLAR POWER TOWER EXTERNAL RECEIVER WITH LIQUID METAL AS HEAT TRANSFER FLUID IN NORTHERN CHILE

Molten salts have been the main heat transfer fluids used in solar power tower plants in recent times, but their limited operating temperatures limit the efficiency of current solar plants and their competitiveness. One option to improve the efficiency is to use liquid metals instead of molten salts, which in addition to withstanding temperatures even above 1000°C, have excellent thermophysical properties. This paper shows the comparative thermodynamics evaluation of a solar power tower external receiver using different liquid metals and molten salts as heat transfer fluid (HTF), located in northern Chile, a location with a high solar potential and where an important plant of this type recently started operation and others are projected. Tonatiuh and Engineering Equation Solver software were used to develop the work and implement the model. The results show that the operation with liquid metals produces lower energy efficiency than molten salts due to the higher operating temperatures, which significantly increase thermal losses, mainly radiative ones. However, the better thermophysical properties of some liquid metals, especially sodium, make the efficiency reduction not so relevant (only 2 percentage points in this analysis). It would be expected that this reduction in efficiency could be compensated by the increase in the thermal efficiency of the thermomechanical cycle in the case of electricity production due to the fact of operating at higher temperatures, but this work shows that the exergy efficiency of the process with liquid sodium is only 2 percentage points higher than with solar salt. Therefore, the reduction of losses, especially radiative losses, which can be as much as 400% greater than that ocurring with solar salt, becomes a necessity if we want to take advantage of the potential represented by being able to operate solar systems at temperatures higher than the current ones, with liquid metals or any other material.

Effect of Climate Change and Water Scarcity on the Viability of Solar Tower Plants

Effect of Climate Change and Water Scarcity on the Viability of Solar Tower Plants

Thermodynamic assessment of the dry-cooling supercritical Brayton cycle in a direct-heated solar power tower plant enabled by CO2-propane mixture

This paper proposes an improved recompression combined cycle configuration to explore the potential of using CO2-propane in a direct-heating solar power tower (SPT) plant. The effects of critical parameters on overall performance were detailly analyzed. The exergy distribution of CO2 and CO2-propane cycles was compared respectively after being optimized by a genetic algorithm. The results show that the exergy loss of regenerators was reduced, and the entire exergy efficiency of the SPT plant was improved by configuring two high-temperature regenerators. The cycle performance of propane, serving as the second additive, becomes more significant when the cooling temperature is increased. The overall thermal efficiency of the CO2-propane-configured SPT plant is 2.08% higher than using CO2 alone at a condensation temperature of 50 °C. Meanwhile, the exergy efficiency of the SPT plant with CO2-propane cycle decreases less (1.67%) than CO2 (2.02%) when the condensation temperature rises from 42 °C to 50 °C. However, the temperature difference of the receiver would decrease when using CO2-propane. This study provides a valuable reference for the application of CO2-propane mixture in the dry-cooling Brayton cycle of the direct-heated SPT plant.