Solar Thermal Power Generation System Research Articles

Recent advances of spectrally selective absorbers: Materials, nanostructures, and photothermal power generation

With the increasing development of photothermal techniques in various fields, particularly concentrated solar power (CSP) systems and solar thermoelectric generators (STEGs), the demand for high-performance spectrally selective absorbers (SSAs) has grown significantly. These SSAs are essential in achieving high solar absorption and minimal infrared thermal loss, thereby significantly enhancing solar utilization efficiency. This need becomes particularly critical in CSP systems, where high temperatures are pivotal for improved efficiency. However, the necessity for high temperatures imposes stringent requirements on the fabrication of SSAs, given the inherent trade-off between optical performance and thermal stability. SSAs typically require nanoscale thin films, but they are prone to oxidation and diffusion at high temperatures. Recent developments in photothermal materials, including ceramic composites, MXenes, high-entropy materials, and graphene, offer promising solutions to enhance SSAs’ performance. This review article provides a comprehensive evaluation of the latest advancements in these emerging photothermal materials. We summarize the strategies for integrating these advanced materials with already established nanostructures, which is a highly promising approach for the development of advanced SSAs. Additionally, the review explores the application of SSAs in CSP systems and STEGs to boost power generation efficiency. We conclude by summarizing the challenges and opportunities in the field of high-temperature SSAs, offering valuable insights into the development of high-performance SSAs and their role in solar-thermal power generation systems.

Analysis of the Operating Characteristics of a Photothermal Storage Coupled Power Station Based on the Life-Cycle-Extending Renovation of Retired Thermal Power Units

Analysis of the Operating Characteristics of a Photothermal Storage Coupled Power Station Based on the Life-Cycle-Extending Renovation of Retired Thermal Power Units

Studies on the thermal cycle performance of solar thermal power generation under different heat sources

Solar thermal power generation is an important way to solve the future power demand, and some countries have entered the commercial application stage. According to the heat source temperatures provided by different solar thermal collector systems, different thermodynamic cycle modes of power generation systems were proposed so that the appropriate thermal cycle modes and working mediums at different heat source temperatures were obtained. The results show that, under a low-temperature heat source, in an organic Rankine cycle with R600 as the working medium, the cycle efficiency is 13.40% when the temperature of the turbine inlet is 100°C and the pressure is 1.5 MPa; the cycle thermal efficiency is 12.00% when the temperature of turbine inlet is 90°C. Under the conditions of medium temperature heat source, in the Rankine cycle with regenerative heat and R141b as a working medium, the efficiency is about 26.59% when the temperature of the turbine inlet is 220°C and the pressure is 3.0 MPa. Under the conditions of a high-temperature heat source, in the reheat extraction steam Rankine cycle, the theoretical cycle efficiency can reach 34.32% when the temperature of the turbine inlet is 380°C, the pressure is 8 MPa, and the condensation temperature is 41.5°C. The studies can provide a fundamental basis for the design of solar thermal power generation systems with different heat source conditions.

The thermal shock resistance of in-situ synthesized mullite absorption and storage integrated ceramics for solar thermal power generation

Solar high-temperature thermal power generation systems require thermal storage materials with excellent thermal shock resistance due to the large temperature difference during operation (in the range of 20–800 °C). In this study, mullite-based absorption and storage integrated ceramics were prepared using low-cost bauxite and kaolin as raw materials and Fe2O3 as additive. The effect of Fe2O3 on the thermal shock resistance of mullite-based ceramics was investigated. The results showed that the absorption and bending strength of sample BK4 (bauxite: 50 wt%, kaolin: 50 wt%, Fe2O3: additional 11 wt%) increased by 2.98% (89.8%) and 8.00% (147.10 MPa), with a storage thermal density of 1185.75 kJ kg−1 after 30 thermal shock cycles. The mechanism for the excellent thermal shock resistance of the ceramics is revealed from the aspect of the changes in phase and microstructure of the samples induced by the changes in the mass transfer rate during the thermal shock process. It was calculated that a unit volume of BK4 (with a raw material cost of about 154.22 USD) could generate 974.95 kW h of electricity (saving 119.92 kg of coal) when used in a solar thermal storage system.

Research on non-equilibrium condensation of supercritical carbon dioxide in sCO2 power systems

Based on the consideration of sustainable development and energy efficient transformation, people propose using renewable energy to upgrade traditional power generation systems. The supercritical carbon dioxide (sCO2) Brayton cycle has a great utilization potentiality in thermodynamic systems, such as solar thermal power generation systems. When the CO2 fluid flows into the compressors of sCO2 power systems, there is a risk of non-equilibrium condensation due to local expansion and acceleration, which seriously threatens the stability of the whole system. The convergent-divergent nozzle is usually used to study non-equilibrium condensation. In this paper, the wet steam model is used to simulate the non-equilibrium condensation of the CO2 fluid near its critical region in a convergent-divergent nozzle. The phase change model and the thermophysical equation of state are verified by experimental data. The non-equilibrium condensation process is analyzed, and the droplet nucleation process and droplet growth process are described. Non-equilibrium condensation releases the latent heat and forms a condensation shock wave. The influences of the shock wave effect on temperature, pressure, and other parameters are discussed. The initial condensation position and critical subcooled temperature under different inlet conditions are analyzed.

Improved corrosion resistance of AISI 321 steel to molten Al-Si alloy by aluminizing and laser shock peening

The service life of AISI 321 steel for solar thermal power generation system is strongly dependent on its corrosion resistance. In the present work, therefore, the influence of aluminizing and subsequent laser shock peening (LSP) treatment on corrosion resistance of AISI 321 steel against molten Al-Si alloy was investigated. These two treatments are found to lower the corrosion rate of AISI 321 steel. Concretely, microstructural characterizations showed that the aluminized layers were oxidized during heating process of corrosion test after aluminizing. Such oxide layer could remarkably decrease the diffusion rate of Al and Si elements. On the other hand, high density dislocation was introduced on the surface layer of AISI 321 steel after aluminizing and subsequent LSP treatment, enabling the rapid growth of thicker and denser oxide film at the early stage of corrosion. And the residual stress introduced by LSP treatment could inhibit the formation of cracks and favor the formation of stronger bonds between the corrosion products. As a result, clear improvement was observed in the corrosion resistance of the AISI 321 steel treated by aluminizing and LSP.

Performance analysis of solid heat accumulator used in tower solar thermal power generation system

In recent years, solar energy, wind energy and other new energy sources have been highly praised, especially solar energy, which is considered as one of the cleanest renewable new energy sources, and solar thermal power stations have been built in many countries. Tower solar photothermal power generation is a heat absorber that reflects sunlight to the top of the tower through heliostat field. Molten salt absorbs heat through the heat absorber, heats water supply and promotes thermal power generation. However, solar energy is intermittent and unstable, so the tower solar thermal power station is equipped with heat storage molten salt tank. Solid heat storage technology has the advantages of cheap heat storage medium, no harm to the environment, strong reliability and operability of the system, and can provide cost-effective heat storage solutions for industrial process heat energy and power generation. In this paper, the molten salt tank is replaced by a solid heat accumulator. After the molten salt absorbs heat during the day, part of it heats the heat accumulator through the unit tube in the heat accumulator to store the heat in the heat accumulator, and the other part heats the water to promote the steam power cycle. At night, the heat accumulator heats the molten salt to release heat, which continues to promote the steam power cycle. In this paper, CFD software will be used to numerically simulate the change of temperature characteristics inside the solid regenerator with the time of heat storage and release, and draw the temperature nephogram and change curve.

A Review of Flow and Heat Transfer Characteristics of Supercritical Carbon Dioxide under Cooling Conditions in Energy and Power Systems

Supercritical carbon dioxide (SCO2) is widely used in many fields of energy and power engineering, such as nuclear reactors, solar thermal power generation systems, and refrigeration systems. In practical applications, SCO2 undergoes a cooling process significantly when it is cooled near the pseudo–critical point. Because of the drastic variations in thermo–physical properties, the heat transfer characteristics fluctuate, affecting the heat exchange and overall cycle performance. This paper summarizes extensive experiments and numerical simulations on the cooling process of SCO2 in various application scenarios. The effects of various working conditions, such as mass flow, working pressure, pipe diameter, flow direction, and channel shapes, are reviewed. The applicability and computational results using different numerical methods under different working conditions are also summarized. Furthermore, empirical correlations obtained in experiments at different conditions are included. The present review can provide a helpful guideline for the design of effective cooling systems or condensers so that the accuracy of the design and efficiency of the system can be improved.

Study of Heat Flux Density of Dish Solar Cavity Heat Absorber

The solar cavity heat absorber is the core component of a solar thermal power generation system; its structure and installation position directly affect the efficiency of the heat absorber. To study the influence of these factors on the performance of the heat absorber, in this paper, a numerical simulation of dish solar collector optics is constructed based on the Monte Carlo method, and the distribution characteristics of heat flux density under different heat absorber structures and installation positions are analyzed. The results show that the heat flux density on the inner wall surface of the absorber has a linear relationship with the solar radiation intensity; under the same cavity depth, the energy received by the cylindrical, dome, and inverted cone absorbers is easier to deposit on the top. The heat flux density on the top surface of the inner cavity presents an annular distribution law. As the position of the heat absorber moves away from the dish solar collector surface, the top energy is gradually transferred to the circumferential surface. When the heat absorber is in position B, the total power ratio of different heat absorber structures entering the cavity can reach 99%. At this time, the circular type of heat absorber is more conducive to the full heat absorption of the working medium.

Study on dynamic model and dynamic characteristics of Delingha 50 MW trough solar field

China General Nuclear Power Group (CGNPC) Delingha 50 MW parabolic trough solar thermal power plant is the first commercial trough solar plant in China, and its solar field consists of 190 parallel heat collecting loops. For large-scale trough solar plant, balancing the flow rate of heat absorbing medium in each loop and stabilizing the outlet temperature are the key technologies and difficult problems. Regarding the Delingha 50 MW solar field as the research object, this paper mainly focusing on the dynamic characteristics of flow and heat transfer in the solar field. The hydrodynamic calculation model and the heat transfer dynamic model are established on the real-time dynamic simulation platform STAR-90. With the actual operation data, the built solar field model is validated by comparing the simulation results. On this basis, the disturbance simulations of direct normal irradiance (DNI), heat transfer oil’s mass flow and heat transfer oil’s inlet temperature are carried out. The dynamic response curves of disturbance and the thermal inertia time constant of the loops are obtained. The conclusions lay a theoretical foundation for the formulation of outlet medium’s temperature control strategy in the solar field of large-scale trough solar thermal power generation system.

Experimental study on heat transfer performance of high temperature heat pipe with large length-diameter ratio for heat utilization of concentrated solar energy

• A conceptual model of dish concentrated solar receiver based on finned high temperature heat pipe (HTHP) is designed. • A batch of HTHPs with large length to diameter ratio and excellent performance were prepared. • The frozen start-up, steady heat transfer and consecutive operation performance of the HTHP with large length to diameter ratio are studied theoretically and experimentally. • A finned HTHP with excellent performance is prepared, and its enhanced heat transfer capacity was verified by experiment. Solar receiver, as the core device of the dish concentrated solar thermal power generation system, is becoming a research focus and has attracted much attention. High temperature heat pipe, which works by following the principle of vapor–liquid circulation, has the ability to flatten the temperature of the hot spot, and maintain excellent heat transfer performance with the illumination of concentrated facula with inhomogeneous ultra-high energy flux density; Through the structural design, the compressed air flows outside of the high temperature heat pipe, and thus, compared with flowing in the pipe, the heat transfer coefficient is increased and the flow resistance is reduced. In view of the above advantages, we designed a dish concentrated solar receiver with finned high temperature heat pipe as the core heat transfer device, prepared a high temperature heat pipe with a large length-diameter ratio, and conducted a quantitative performance study comprehensively and systematically. The present study verified the safety and stability of the high temperature heat pipe with the illumination of concentrated facula with inhomogeneous ultra-high energy flux density, theoretically analyzed the process of frozen start-up and heat transfer limits of high temperature heat pipe, explored the reasonable frozen start-up mode, carried out the parameter optimization and consecutive long-time operation stability test, and quantitatively verified the enhanced heat transfer capacity of finned high temperature heat pipe through the experiment. The results show that the HTHP prepared by the same process can operate safely and stably with the illumination of concentrated facula at the average energy flux density of 2.3 × 10 6 W/m 2 , and maintain a high temperature above 700 ℃ as well as excellent temperature uniformity, which fully verifies the feasibility and superiority of HTHP as the core heat transfer device of the dish concentrated solar receiver. In addition, these results can provide quantitative experimental data and theoretical reference for the design and development of the dish concentrated solar receiver.

Optical Efficiency Analysis of Primary Mirror in LFR-CSP

The linear Fresnel solar thermal power generation system is one of the most representative forms of solar thermal power generation system at present. The primary mirror, as the main mirror, plays a key role in the photothermic conversion process of the collector tube. In this paper, the solar position and the optical efficiency of the primary mirror in LFR-CSP are modeled and analyzed. The light reflection process of primary mirror by solar position through four dimensions of solar declination angle, solar time angle, altitude angle and azimuth angle is studied, and the distribution law of solar position parameters in different seasons and different times throughout the year is analyzed. It is found that the variation range of chord efficiency of a single mirror element in the whole day is 75 %-93 %. The position of a mirror element in winter solstice has the greatest impact on the end loss of more than 1 %, but the summer solstice has no effect.

Multi-model adaptive predictive control of superheated steam temperature of DSG solar parabolic-trough collector based on heat-steam ratio and its reference trajectory

The direct steam generation (DSG) solar thermal power generation system has obvious inertia and nonlinearity in the response of superheated steam temperature. Due to the intermittent and random fluctuations of solar irradiation, the DSG system frequently undergoes large changes in operating conditions, which results in a very complicated problem of controlling the superheated steam temperature at the collector outlet. This paper proposed a multi-model adaptive control scheme based on the heat-steam ratio and its reference trajectory for the control problem of the outlet steam temperature of the DSG solar parabolic-trough collector. Firstly, through analyzing the dynamic characteristics of the superheated steam temperature, the main factors and the main nonlinear characteristics that lead to the nonlinearity of the steam temperature response are revealed. Secondly, taking the ratio of solar irradiation to the outlet steam flow (heat-steam ratio) as the characteristic parameter based on the nonlinear characteristics of the system, the DSG collector system is divided into several linearized subspaces, and then the corresponding steam temperature predictive sub-model set and steam temperature adaptive predictive control scheme are established. Finally, a smooth switching strategy based on the reference trajectory of the nonlinear characteristic parameter (heat-steam ratio) is established in response to the frequent or large switching of the controller caused by the large changes in the operating conditions, which effectively improved the stability of the temperature control process of the superheated steam at the DSG collector outlet. In this paper, the effectiveness of the above-mentioned control scheme has been preliminarily verified through simulation experiments.

Coordination control for Integrated Solar Combined Cycle thermoelectric coupling

Improving the utilization of solar energy and promoting the development of integrated energy systems, solar thermal power generation systems are researched and widely used. In the integrated solar combined cycle thermoelectric system, traditional power generation equipment as an auxiliary energy source mitigates fluctuations because of solar energy’s intermittent nature and uncertainty. However, because of the difference in response speed of different power generation equipment, it leads to imbalance of supply and demand power, which affects the smooth operation of the system. This paper proposes a novel coordination control method for integrated solar combined cycle thermoelectric coupling system. To solve the different energy response speed mismatches problem, an inertial power compensation scheme is proposed based on the established solar energy cogeneration system model, and the dynamic performance and robustness of the system are improved. In this paper, the intelligent optimization algorithm is used to optimize the parameters to improve the control precision of the controller. Finally, the paper carries out multi-scenario simulation with the 50MW solar thermal power generation and the 50MW gas turbine to verify the effectiveness and stability of the proposed coordination control method.

Power Generation System of Solar Heat using Stirling Engine

Renewable energy, a domestically produced energy source, is attracting increasing attention as an important sustainable energy source in terms of improving energy self-sufficiency and reducing greenhouse gas emissions. In this regard, renewable energy utilization technologies are expected to realize sustainable development. In this research, we aim to construct a system that can collect sunlight and solar heat with a parabolic dish and generate electricity with a Stirling engine (SE). First, we evaluated the operational performance of the α-model SE, which employs a spirit lamp and an electric heater as heat sources. Finally, we executed a performance test of the constructed parabolic dish/SE combined solar thermal power generation system. As a result, when the total solar radiation amount is about 900 W/m2, a temperature difference of about 180°C is obtained between the SE heat cap and the surface of the low temperature side cylinder in about 3 minutes, and it is confirmed that the LED load lights up at an output voltage of 2V.

Study on Dynamic Model and Dynamic Characteristics of Solar Field of 50 Mw Trough Solar Thermal Power Generation Plant

Solar thermal power generation solves the problem of fluctuation and intermittency through energy storage system, and can bear the basic power load and peak load regulation. It is an important technical way for China's energy structure transformation. As a complex thermal system with multivariable disturbance, large inertia and large delay, the operation control of the solar field is a difficult issue. In this paper, the solar field of the first 50 MW trough solar thermal demonstration power plant in China is taken as the research object. Based on the topological structure and working principle of the solar field and the basic laws of optics and thermodynamics, the hydrodynamic calculation model and the heat transfer dynamic model are developed. The correctness of the model is verified by comparing the simulation results with the actual operation data. On this basis, the disturbance simulations are carried out. In addition, the dynamic response curves of step disturbance and the inertia time constant of the heat collecting loops are obtained. The conclusions of this paper have important guiding significance for the operation control strategy formulation and system optimization design of trough solar thermal power generation system.

Experimental investigation of solar organic Rankine cycle with parabolic trough concentrator using nitrate salt as heat transfer and storage fluid

Nitrate salt with low melting point as heat transfer and storage fluid simplifies the heat transfer, storage, and exchange processes, and organic Rankine cycle as heat and power conversion system can realize the distributed energy supply. This study experimentally investigated the solar organic Rankine cycle with parabolic trough concentrator using nitrate salt as heat transfer and storage fluid, and the main problems and phenomena during the operation process have been described and analyzed in detail. Experimental results showed that the temperature difference of collector tube changes with direct normal irradiation and lags behind the changes of direct normal irradiation. Molten salt heat storage system can effectively restrain the temperature fluctuation at the collector tube outlet. The abrupt temperature drop at the evaporator inlet was caused by the heat imbalance between R123 and nitrate salt and inappropriate design of the evaporator. The effects of expander inlet pressure and expansion ratio on the ORC electrical power output were obtained at different superheating degrees of the expander inlet. The researches on each component are instructive to the technology of the parabolic trough concentrated solar power generation system with molten salt as heat transfer and storage fluid and provide some guides for the subsequent research. Furthermore, the energy and exergy analyses on overall system were developed, and results indicated the system average efficiency can reach 1.5%. Novelty statement Experimental study on parabolic trough concentrated solar ORC system with nitrate salt as heat transfer and storage medium were firstly analyzed. Single screw expander was firstly applied in a real solar thermal power generation system and showed a stable performance. Dynamic changes on the temperatures of PTC, molten salt tanks, and ORC were shown, and energy and exergy analyses on overall system were carried on.

Design and performance analysis of compressed CO2 energy storage of a solar power tower generation system based on the S-CO2 Brayton cycle

Two kinds of S-CO2 Brayton cycle tower solar thermal power generation systems using compressed CO2 energy storage are designed in this paper. The energy storage system uses excess solar energy to compress CO2 near the critical point to a high-pressure state for energy storage during the day, and the high-pressure CO2 is heated by a gas-fired boiler or the heat of stored high-temperature molten salt at night, so that it enters the turbine for work and drives the generator to generate electricity. The traditional molten salt heat storage scheme and the proposed compressed CO2 energy storage system model are established with Ebsilon software, and then the equipment selection, structure layout, and parameter design processes are carried out for the energy storage and heating systems. The thermoeconomic and technoeconomic indexes of the three energy storage schemes are calculated under the operating conditions of a typical day. The results show that the efficiency of the combined cycle is higher than that of other organic working fluids when T-CO2 is used as the bottom cycle working fluid. The integrated scheme of compressed CO2 energy storage and auxiliary combustion has the highest average daily efficiency (26.62% on summer solstice and 23.04% on winter solstice) and the lowest initial equipment investment. However, due to the additional cost of natural gas, the scheme has the highest levelized cost of energy (LCOE) at $0.1168/kWh. The LCOE of the integrated scheme of compressed CO2 energy storage and molten salt heat storage was the lowest at $0.1046/kWh.

Performance assessment of convective heat transfer in tubes with a temperature difference in the high‐temperature solar power generation system

Heat transfer enhancement technology provides many advantages in heat exchanger applications. Thermal energy storage is a technology that stocks thermal energy by heating or cooling a storage medium so that the stored energy can be used later for heating and cooling applications and power generation. The experimental investigation was carried out for heat convection in tubes with significant temperature differences (400 and 600°C), which were used convective heat transfer in a tube with air-water steam and heat conduction oil in the high temperature solar thermal power generation system. From the experiment, the results recorded with an average maximum temperature for air, water, and steam up to 422.4, 413.9, and 405.7℃, respectively, with the outer wall temperature of 600℃. Similarly, for an external wall temperature of 400°C, the average maximum temperature was obtained up to 351.2, 310.9, and 308.1℃, respectively. Therefore, from the experimental results, when the diameter of the flow pipe is higher than that of pipe diameter, then the effect of flow velocity on heat flow temperature was uncertain. At last, from the results, we conducted that the empirical correlation of convective heat transfer in a tube with temperature difference exceeding 100℃ obtained. The results showed that the increase of temperature thermal energy storage system could effectively enhance heat transfer and the calculation results can be used to optimize the performance of the high-temperature thermal energy storage system. Novelty impact statement Assessment of convective heat transfer in tubes with a temperature difference in the high-temperature is performed. The increase of temperature in thermal energy storage system could effectively enhance heat transfer. Carried out the study for different temperature thermocouples tube bundles with Nu, Re, and Pr. Conducted the empirical correlation of convective heat transfer in a tube with temperature difference.

Combined use of volumetric expanders and Scheffler receivers to improve the efficiency of a novel direct steam solar power plant

This research proposes an innovative solar thermal plant able to generate mechanical power through an optimized system of heliostats with Scheffler-type solar receivers coupled with screw-type steam expanders. Scheffler receivers appear to perform better than parabolic trough collectors due to the high compactness of the focal receiver, which minimizes convective and radiative heat losses even at high vaporization temperatures. At the same time, steam screw expanders are volumetric machines that can be used to produce mechanical power with satisfactory efficiency also by admitting two-phase mixtures and with further advantages compared to steam turbines: low working fluid velocities, low operating pressures, and avoidance of overheating. This study establishes a mathematical model to assess the energetic advantages of the planned solar thermal power system by evaluating the solar-to-electricity efficiency for different off-design working conditions. For this purpose, a numerical model on the Scheffler receiver is initially investigated, thus assessing all the energy losses which affect the heat transfer phase. A thermodynamic model is then developed to evaluate the energy losses and performance of the screw expander under real working conditions. Finally, parametric optimization of the solar energy conversion is performed in a wide range of operating conditions by establishing thermodynamic formulations related to the whole solar electricity generation system. Water condensation pressure and vaporization temperature are so optimized with respect to global energy conversion efficiency which, under the best operating conditions achieved in this research, rises from 10.9% to 14.4% with increasing solar irradiation intensity. Hence, the combined use of screw expanders and Scheffler receivers for solar thermal power system application can be a promising technology with advantages over parabolic dish concentrators. Novelty statement This research proposes an innovative direct steam solar power plant based on an SRC, with water utilized as both heat transfer and working fluid, equipped with Scheffler solar receivers as a thermal source and screw expanders as work-producing devices. Technical studies and energy assessments of this kind of SEGS at part-load operation do not exist in scientific literature; after reviewing the literature, it was determined that volumetric expanders have been rarely combined with Scheffler receivers for solar thermal power system application. In effect, combined use of screw expanders and Scheffler-type solar concentrator in a direct steam solar power system represents a completely new plant configuration; however, as a promising DSG solar system, at present numerical model of this new sort of SEGS is lacked in literature and the optimum operating conditions have yet to be defined. For this reason, the chief objective of this paper is to define a first parametric optimization of all thermodynamic variables involved to maximize global efficiency of the proposed solar thermal power generation system for ordinary working conditions.