High collecting temperature in parabolic trough collectors (PTCs) induces considerable radiative heat loss of solar receivers, which causes significant negative effects on heat-collecting efficiency. ...Structural optimized solar receivers with inner radiation shield achieved superior thermal performance for reducing heat loss. Based on widely commercial EuroTrough and PTR70 solar receivers, the optimized solar receivers are numerically applied to a small thermal-collection field with 72 m loop using molten salt as heat transfer fluid to validate their enhanced overall performance. Mathematical models relying on spectrum parameter calculation and working fluid volume unit method are established to simulate the energetic and exergetic performances of the solar receivers. The influence of solar irradiance on parabolic trough collector system is studied, and all-day system efficiencies in different areas in China are investigated to validate the performance of the proposed solar receivers in real condition. Results show that the PTCs with novel solar receivers exhibit outstanding energetic and exergetic performances compared with conventional receivers. The heat loss reduction percentage of the novel receivers reaches approximately 24.0% when the absorber temperature is 600 °C. The heat-collecting efficiency and exergetic efficiency are effectively raised by 7.1% and 4.7%, respectively, at an inlet temperature of 580 °C.
•Energetic and exergetic performance of PTC with novel solar receivers is studied.•Mathematical models with spectral radiant distribution are built and validated.•All-day PTC system efficiency in different areas in China is calculated.•The radiation heat loss of the novel receiver is reduced by around 24.0%.•Thermal and exergetic efficiencies of novel receiver are raised by 7.1 and 4.7%.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
A novel solar evacuated receiver as the key part of parabolic trough collector (PTC) was designed and constructed by authors. The novel evacuated receiver (NER) with an inner radiation shield can ...significantly decrease heat loss at higher operating temperatures when compared with the traditional evacuated receiver (TER). A thermodynamic model relying on the spectrum parameter model of radiation heat transfer was developed to predict the performances of evacuated receivers. Also, experiments using the novel evacuated receiver and traditional evacuated receiver were conducted in the laboratory under different parametric conditions to validate results obtained for the simulation. A comparison between simulation results and experimental data demonstrated that the model was able to yield satisfactory consistencies and predictions to a reasonable accuracy (with the root mean square deviations less than 6%). Results indicated that the novel evacuated receiver has a role in decreasing the total heat loss of receiver compared with the traditional receiver when the working temperature is higher than 296 °C, the heat loss reduction percentage of the novel evacuated receiver reaches 19.1% when the operating temperature is 480 °C, and the value of this percentage would be greater at higher working temperatures.
•A high-temperature solar evacuated receiver with a radiation shield was proposed.•Mathematical models with spectral radiant distribution were established.•Experiments were conducted in an enthalpy difference lab to validate the models.•The effects of environmental variables on the receiver were investigated.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Prospects for parabolic trough collector are growing as the market increasingly values concentrated solar-thermal utilization. Parabolic trough solar receivers, the key components of parabolic trough ...collector system, seriously suffer degradation of photothermal conversion performance at high operating temperature due to considerable emissive heat loss, which exerts significantly negative influence on the overall performance and development of parabolic trough collector and subsequent thermal utilization systems. This study examines the spectral emissive heat loss and circumferential heat transfer characteristics around the parabolic trough solar receiver. In this framework, a new concept is proposed, i.e. the negative thermal-flux region in which negative net heat gain occurs, accordingly enlightening and giving birth to new optimization strategies for reducing emissive heat loss of the parabolic trough receiver. A novel parabolic trough receiver with an inner radiation shield in the negative thermal-flux region is designed, manufactured and comprehensively tested. The results show a validity of the existence of the negative thermal-flux region and great potential of new optimization methods to achieve breakthrough enhancement of heat-collecting performance in parabolic trough collector system. Compared with the prototype solar receiver, the heat loss of proposed solar receiver is effectively reduced by 28.1% at absorber temperature of 600 °C, the heat-collecting and exergetic efficiencies are significantly enhanced by 12.9 and 17.6% at the solar irradiance of 600 W/m2 and inlet temperature of 550 °C.
•Negative thermal-flux region occurring in solar receiver is discovered.•New optimization strategies different from the conventional ones are concluded.•Comprehensive experiments about the proposed solar receivers are carried out.•Heat loss, thermal and exergetic efficiency models with high precision are established.•The proposed optimization method has great potential for the system performance enhancement.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
It is still a great challenge for the concentrated solar thermal (CST) technology to promote the utmost out of solar energy further because the CST's receiver generally discards the longer wavelength ...spectra to prevent radiative heat loss due to high temperatures. Spectrum splitting is a well-known technology generally used in multi-energy cogeneration devices, such as Photovoltaic/thermal (PV/T) systems, aiming to improve photoelectrical efficiency. In this study, the solar spectrum splitting technology is employed in the CST system to take full advantage of solar radiation through enhanced absorptions and conversions of piecewise solar radiation. The exergy efficiency of a beam-splitting photothermal (BSPT) system is used to evaluate its effectiveness. Here, the mechanisms of beam splitting under different splitting wavelengths (λsp) and concentration ratios (Cr) are investigated. Furthermore, the influence of the split number is evaluated, and the performance of the dual-segment BSPT system is compared with traditional photothermal systems with real and assumed coatings. It shows that beam splitting can play an excellent role in improving exergy performance. The exergy efficiency improvement ratio of the BSPT stabilizes at around 9% when λsp is 1300 nm, and the proposed dual-segment BSPT system can maintain an excellent performance even under off-design working conditions.
•Piecewise concentrated photothermal utilization based on solar beam splitting was proposed.•A mathematical model based on spectral parameters was established.•Novel beam-splitting photothermal system (BSPT) system harvested superior performance.•Exergy efficiency of BSPT system was significantly enhanced by around 9%.•The BSPT system possessed excellent adaptability to the variable working conditions.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•A silica aerogel-based photovoltaic/thermal (PV/T) collector is proposed.•The aerogel-based PV/T collector significantly suppress radiation heat loss.•The thermal performance of the aerogel-based ...PV/T collector is enhanced by 46%.•The performance of aerogel-based PV/T is equivalent to that of spectrally selective PV/T with a thermal emissivity of 0.1.•The exergy efficiency of the aerogel-based PV/T collector is increased by16.2%.
Photovoltaic/thermal (PV/T) collector can convert incident sunlight into electrical and heat energy simultaneously. However, compared with the solar thermal collector, the radiative heat loss of the PV/T absorber is larger since the spectrally selective PV/T absorber is difficult to design and fabricate after introducing PV cells, which leads to lower thermal efficiency. Thus, an approach that can reduce the radiative heat loss of the PV/T collector without the requirement for spectrally selective PV/T absorber is emergently needed. Here, a novel aerogel-based PV/T collector is proposed to suppress radiative heat loss and improve efficiency by introducing the silica aerogel that is highly transparent to sunlight and opaque to infrared light, as well as ultra-low effective thermal conductive into the PV/T collector. A numerical model is established to evaluate the performance of the aerogel-based PV/T collector, and the results present that the heat loss of the PV/T collector at the operating temperature of 70°C can be dramatically reduced by approximately 75% after using the silica aerogel and the thermal efficiency can also be increased by 46%. Moreover, a parametric study is conducted to investigate the influence of solar radiation, ambient temperature, and emissivity of the PV/T absorber on the performance of the aerogel-based PV/T collector. This study is devoted to exploring a new method to suppress the radiative heat loss of the PV/T collector and enhance its solar harvesting performance correspondingly, which gives a reference for the design of high-performance PV/T utilization.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Solar selective absorbing coatings that absorb solar irradiation and emit infrared radiation have a significant impact on the thermal efficiency of the receivers. The spectrum parameters heat ...transfer model and the non-ideal coating curve model are established. The cutoff wavelength of coatings is comprehensively optimized, and the effect of the optical properties of the coating on overall performance is analyzed. Results show that the optimal cutoff wavelength rises with the solar irradiation flux but decreases with increased absorber temperature. Sensitivity analysis results of the coating optical properties indicates that the thermal efficiency significantly decreases with increasing slope width. The change range of the thermal efficiency at the temperature of 200 °C is ±0.1%, resulting from a ±1 μm variation in slope width, whereas the range at 600 °C is ±6.5%. Spectral absorptivity analysis shows that the coating absorptivity has nearly same positive influence on thermal efficiency under different temperatures and irradiation fluxes, whereas emissivity analysis reveals an evidently different negative effect on the receiver performance. Finally, the annual optimal cutoff wavelength decreases with increasing temperature but increases with solar irradiation. The optimal cutoff wavelength decreases from 2.23 μm at 200 °C to 0.78 μm at 600 °C in Phoenix.
•The spectrum parameters heat transfer model and non-ideal coating model are established.•The optimization of the cutoff wavelength of coatings is carried.•Effects of key optical parameters on the selective coating performance are investigated.•The annual optimal cutoff wavelength in different places is explored.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
As a high solar concentration technology, the solar tower power (STP) system is an appealing approach to generate high-grade thermal energy and achieve high thermal-to-electric efficiency. In this ...study, the authors notice the solar flux distribution characteristic of the central receiver and combine the advantages of lower average operation temperature of the direct steam generation (DSG) loop and higher efficiency of the molten salt (MS) loop. A hybrid solar tower system that involves steam and MS as the heat transfer fluids is proposed for improving the thermal efficiency of STP systems. The receiver of the hybrid system is divided into two sections, which are respectively designed for the MS and DSG loop, namely MS-DSG system. By comparing the DSG-MS system to the traditional system, the DSG-MS system demonstrates significant heat loss reduction of 31.8 GWh in Lhasa and 34.5 GWh in Tonopah, and the corresponding electricity outputs are improved by 6.22% and 5.82% with a MS receiver panel number of 8. The steam outlet quality of the DSG loop is insensitive to the overall performance of the systems. It is indicated that the steam quality can be adjusted for ensuring two-phase heat transfer stability and safe operation of the receiver. Moreover, the hybrid system also gives a flexible adjustment of thermal energy storage capacity by optimizing receiver panel number for different heat transfer fluid loop.
•The hybrid solar tower system using steam and MS as the HTF is proposed.•Convection and radiation heat losses reduction of 24.8% and 42.4% are reported.•Electricity output of the plant in Lhasa is improved by 6.22%.•The hybrid system gives a flexible adjustment of the thermal storage.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•The cascade supercritical carbon dioxide Brayton-steam Rankine cycle is proposed.•Long-time, cost-effective storage for solar carbon dioxide cycle system is possible.•The heat gain of novel system ...is improved by 7.1 MWh.•The electricity production of the cascade system is improved by 9.5% at design point.•Stable power generation is guaranteed in a wide range of solar radiation.
A novel solar power tower system that integrates with the cascade supercritical carbon dioxide Brayton-steam Rankine cycle is proposed to tackle the challenges of a simple supercritical carbon dioxide system in solar power systems. It provides a large storage capacity and can react to the fluctuation of solar radiation by adjusting the mass flow rate of molten salts in the receiver and heat exchanger. The fundamental is illustrated and comprehensive mathematical models are built. Energy and exergy analysis in the heat collection and power conversion processes is conducted. A comparison between the novel system and simple supercritical carbon dioxide system is made at a design plant output of 10 MW. Results indicated that: (1) the cascade system has a lower receiver inlet temperature, wider temperature difference across the receiver, higher specific work of the thermal energy storage system and lower mass flow rate of the working fluids. The solar-thermal conversion efficiency of the receiver is improved significantly. The heat gain of the tower receiver of the novel system is 53.4 MWh, which is about 7.1 MWh more than that of the simple system. The electricity production of the cascade system is improved by 9.5% at design point; (2) The novel system can generate constant electricity in a wide range of solar radiation and offer flexible control strategy for heat collection and storage. It is a promising option for central solar tower technology with a high efficiency, large storage capacity and short payback period.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPUK, ZRSKP
•A novel parabolic solar receiver with a transparent radiation shield was proposed.•Mathematical models with spectral radiant distribution were built and validated.•The effects of the radiation ...shield parameters on the receiver were studied.•The radiation heat loss of the novel receiver is reduced by around 14.9%.•Thermal efficiency of the proposed receiver is raised by 4.4%.
Solar evacuated receiver as a key part of parabolic trough collector (PTC) suffers considerable heat loss at high operating temperature, which exerts significantly negative effects on the overall performance of PTC system. Based on the fact of maldistributed solar irradiation around the inner absorber tube, a novel solar evacuated receiver with an inner transparent radiation shield (TRS) is proposed and designed. The heat loss of the proposed solar evacuated receiver is numerically studied by the established heat transfer model based on the spectral parameters. The heat-collecting efficiency of a commercial UrssaTrough solar collector installed with PTR 70 receivers using therminol VP-1 as heat transfer fluid is investigated to validate the performance of the proposed solar receiver. Moreover, the influences of the property parameters of films on the two sides of the TRS on the solar receiver are also studied. Comparisons between simulated and experimental results show the differences of their heat-collecting efficiencies are lower than 1%, which demonstrates that the model can yield satisfactory consistency with the experimental results. The simulation results show that the novel receiver exhibits dramatically superior thermal performance to that of the traditional receiver. The heat loss reduction percentages of the novel receiver can reach approximately 15.7% and 14.9% when the absorber temperatures are 400 °C and 600 °C, and the thermal efficiency can be enhanced by 0.93% and 4.42% at inlet temperatures of 400 °C and 580 °C, respectively.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
•A hybrid system integrating direct steam generation and molten salt is proposed.•The thermodynamic and economic evaluation model are established and validated.•The electricity production of the ...hybrid system in Tonopah is increased by 14.0%.•Levelized cost of electricity is decreased to 0.116 €/kWh by hybrid system in Tonopah.
A novel hybrid parabolic trough power system that integrates direct steam generation and molten salt systems is proposed in this study to stably and efficiently operate solar power plants. The feedwater from the power block is preheated and evaporated in a low temperature direct steam generation solar field. A high-temperature solar field using molten salt as heat transfer fluid is employed to superheat and reheat the steam to 540 °C. The heat transfer model based on energy conversion and balance is applied to numerically investigate the overall performance of various power plants. This paper presents a comparative study of the effects of different locations, steam turbines, and system configurations on the outputs of the power plants. The hybrid systems exhibit favorable system stability and reliability and an excellent overall performance. The molten salt loop percentages of hybrid systems with and without reheat section are only 45.1% and 37.4%, which lead to low energy loss in the operation period and low molten salt freezing protection energy. The annual thermal energy productions of the hybrid systems with and without the reheat section in Tonopah are 685.1 and 691.7 GWh, and the percentages of energy required for freezing protection of those systems are 3.2% and 2.7%, respectively. The hybrid systems with reheat section exhibit optimal electricity production and economic performances compared with those of other configurations. The electricity production increments of novel systems in Tonopah and Lhasa are 14.0% and 14.8%, respectively, compared with those of molten salt systems.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPUK, ZRSKP
