Concentrating Solar Thermal Power Systems Research Articles

HelioCon: A roadmap for advanced heliostat technologies for concentrating solar power

Heliostat-based concentrating solar-thermal power (CSP) systems can offer immense potential to provide low-cost, dispatchable renewable thermal and electrical energy to help achieve 100% decarbonized energy infrastructure in the United States. Heliostats are a major determinant of both capital cost and performance of state-of-the-art commercial molten salt towers and Generation 3 CSP systems. In 2021, the U.S. Department of Energy (DOE) Solar Energy Technologies Office (SETO) launched the Heliostat Consortium (HelioCon), a five-year initiative to advance heliostat technologies. The HelioCon mission is threefold: (1) establish strategic core testing and modeling capabilities and infrastructure at national labs; (2) support heliostat technology development in relevant industries; and (3) serve as a central repository to integrate industry, academia, and other stakeholders for heliostat technology research, development, validation, and deployment. In this Perspective, HelioCon presents a roadmapping study on advancing heliostat technologies, intended as a central reference for the entire CSP community.

Exploring efficiency limits for molten-salt and sodium external cylindrical receivers for third-generation concentrating solar power

Third-generation concentrating solar-thermal power (CSP) systems are proposed which aim to halve the cost of electricity from CSP. This work demonstrates that a transition from state-of-the-art cylindrical molten nitrate salt receivers with a peak concentrated solar flux of 1MW/m2 and a heliostat field optical error of 3mrad to future cylindrical sodium receivers with a peak flux of 1.8MW/m2 and a heliostat field optical error of 1mrad could enable the exergy output of CSP receivers to be increased significantly, by 25% at design point, while keeping the general system design very similar. This comparison is conducted on a large dataset established with a detailed field and receiver energy balance model considering field aiming, peak receiver flux and hydrodynamics. It is based on design point simulations, and is independent from cost considerations. At high temperatures, the optimal configurations achieve their gains only with very accurate heliostats and when the peak flux is increased, while at low temperatures, there is nothing to be gained from very high peak flux limits on external tubular receivers. This underscores the critical importance of high heliostat accuracy for high-temperature CSP systems design. For the third-generation, high-temperature (740 °C) sodium receiver configuration considered, it is found that the upper limit to thermal–optical efficiency of optimised receivers at design-point is around 88 %.

Experimental Study of Eutectic Molten Salts NaCl/KCl/ZnCl2 Heat Transfer Inside a Smooth Tube for High-Temperature Application

AbstractEutectic salts NaCl-KCl-ZnCl2 and NaCl-KCl-MgCl2 are two of the chloride salt systems that are promising for being used as high-temperature heat transfer fluid (HTF) and thermal energy storage (TES) materials in a wide range of temperatures from 230 °C to 750 °C in concentrated solar thermal power systems. To conduct measurement of the heat transfer coefficient of the molten salt at high temperatures, a circulation system and instrumentation of flow and heat transfer was constructed. Experimental measurement of the convective heat transfer coefficients of NaCl-KCl-ZnCl2 (molar fraction: 13.8–41.9–44.3%) inside tubes has been accomplished to find the most suitable heat transfer correlations. Experience of salt processing and operation of the high-temperature heat transfer test system was obtained. Two correlations, Dittus-Boelter equation and Gnielinski’s correlation for Nusselt number against Reynolds number and Prandtl number, are evaluated using the test results, and the latter correlation is recommended due to its better agreement of prediction against tested data.

Estimation of the losses in potential concentrated solar thermal power electricity production due to air pollution in China

The concentrated solar thermal power (CSP) industry is projected to expand rapidly in China in the next 30 years. However, anthropogenic aerosol emissions reduce direct radiation (Rdir) reaching the surface, resulting in the losses of potential CSP electricity production in China. In this study, we applied various models to estimate daily Rdir, and the results showed that the gradient boosting with categorical features support (CatBoost) model was superior to other models, and coefficient of determination (R), root mean square error (RMSE) and mean absolute error (MAE) were 0.96, 1.99 MJ m−2 day−1 and 1.92 MJ m−2 day−1, respectively. We used Rdir data set at 839 stations across China derived by CatBoost model to calculate losses of the potential CSP electricity production from aerosol emissions. The results showed that the potential CSP electricity production decreased by 12.9% (136 kWh) on average at provincial level during 1961–2015. It is plausible that air quality will continue to improve from now due to the success of previous air pollution control measurements and the commitment to the United Nations of “Carbon Neutrality”. It was found that returning to direct radiation levels in 1960s could yield a 15.8% increase in potential CSP electricity production, equal to 28.4–79 TWh with the expected 2050 CSP installation capacities. The corresponding economic benefits could reach 17.1–56.9 billion RMB in 2050. The findings in this study will be beneficial for siting, designing and optimizing CSP systems in China.

Thermal analysis of porous volumetric receivers of concentrated solar dish and tower systems

Abstract In this article, thermal analysis of Solar volumetric receiver used in concentrated solar thermal power systems is studied. A cylindrical volumetric receiver used in the parabolic dish collector and solar power tower is analyzed using a finite element method based tool COMSOL multiphysics software. A non uniform Gaussian distribution based heat influx is applied at the receiver to mimic the actual conditions. The steady state operation of the receiver is studied for various porosity and thermal conductivity of the solid phase. Different parameters of Gaussian distributions corresponding to different flux profile conditions are studied. The Gaussian profile heat flux amounting to 1 MW/m2 results in the Gaussian like temperature distribution of the fluid phase near the receiver exit region. Higher thermal conductivity of 200 W/(m K) coupled with the high porosity of 0.7 leads to the better operational efficiency of the receiver. Lower porosity results in higher peak temperature in the fluid phase and higher thermal conductivity laterally spreads the temperature across the receiver. The intermittent solar flux condition is realized through transient response study of flux conditions. The temperature gain rate in transient case is found to be approximately 24 K/s while the temperature drop is around 29 K/s.

High temperature thermal storage materials with high energy density and conductivity

A metastable miscibility gap in the C-Al binary phase diagram has been exploited to produce macroscopically solid phase-change enhanced thermal energy storage materials. With 50% by volume of Al or Al-12.7%Si dispersed in a graphite matrix, the materials have thermal conductivity of ∼150 W/m K, energy densities of 0.9 and 1.1 MJ/L for ΔT = 100 °C and energy storage/delivery temperatures centred around 660 °C and 577 °C respectively. These characteristics are matched to both direct-steam and fluid-mediated concentrated solar thermal power systems using conventional Rankine cycle steam turbine-generator technology. Powder metallurgy processing combined with a low-temperature binder ensures a non-percolating inverse microstructure in which the phase change Al or Al-Si particles are securely encapsulated, thereby overcoming the usual containment problems associated with metallic phase change materials. The graphite and binder system used have been shown to be stable upon short-term thermal cycling or holding at the maximum expected operating temperature.

Zirconia nanoparticles embedded spinel selective absorber coating for high performance in open atmospheric condition

Spectrally selective absorber coatings which have high thermal stable at temperatures ≥ 500°C in open air atmosphere are more beneficial for all types of concentrated solar thermal power (CSP) applications. In order to achieve this, high crystalline zirconia nanoparticles are synthesized via Lyothermal process were embedded into a spinel matrix to form a novel composite solar selective absorber layer (Mn-Cu-Co-Ox-ZrO2). To enhance the absorption substantially, an ink-bottle type mesoporous MgF2 nanoparticles are synthesized via novel route have been deposited further. As a result, a novel tandem absorber system (Mn-Cu-Co-Ox-ZrO2/MgF2) has been developed with α/ε = 0.97/0.17 @500°C. The composite layer comprises of tetragonal phase Zirconia particles which were uniformly distributed in the spinel matrix responsible for high optical performance and high thermal stability. These properties are thoroughly investigated by micro X-ray diffraction (µXRD), X-ray photoelectron spectrometer (XPS) and Elemental mapping by Energy filtered transmission electron microscope (EF-TEM) technique. This novel composite absorber layer developed by a facile route exhibits superior stability up to 700°C ideally in the air makes a promising advancement for the cost-effective power generation by CSP systems.

Modeling of a solar power plant in Iran

Parabolic Trough Concentrating Solar-thermal Power (CSP) technology represents one of the most promising options among available CSP systems for generating renewable electricity at utility scale. Within geographical boundaries of the Islamic Republic of Iran, there are a large number of potential sites with solar insolation levels around 1800kwh/mˆ2.yr. The power plant complex in Yazd (a city in middle of Iran) is selected as a study site. Two computational codes are used for modeling of different configurations of solar power plants. These are the Pilksolar's performance model and Fichtner's cycle process calculation software. In this article two plant configurations are considered. They are the standalone solar electricity generating system (SEGS). And, integrating a solar field into a combined cycle plant, the Integrating Solar combined cycle System (ISCCS). Performance calculations for these configurations are carried out and a comparison between the methods is made. It shows that integrating solar plants into the Iranian grid may be considered as an action to counter production losses from the gas turbines due to high summer ambient temperatures.

Minimum system entropy production as the FOM of high temperature heat transfer fluids for CSP systems

Abstract High temperature heat transfer fluids are used in concentrated solar thermal power (CSP) plants to receive heat from a solar concentrator and then transfer it to a working fluid (such as water, air, or super critical CO 2 ) in a thermal power system. For various high temperature heat transfer fluids, such as, synthetic oils, various molten salts, and liquid metals, a general criterion is proposed in this work to evaluate the merit of fluids regarding their transport properties. For the goal of transferring a desired amount of heat, a fluid that causes less entropy production is believed to have better figure of merit (FOM). This is due to the fact that entropy production is associated with the destruction of exergy or useful energy. The entropy production in a heat transfer system in a solar thermal power plant includes the part due to the processes of heat addition and removal and the other part due to pressure losses in the flow in heat exchangers and pipes. Theoretical analysis and relevant equations for total entropy production are derived. As an example, the FOM for several heat transfer fluids used in CSP industry are compared for the goal of heat transport in the range of 50 MW th to 600 MW th . The modeling provides a fundamental approach for the comparison of various heat transport systems which may have different designs and using different heat transfer fluids/media (gas, liquid, or solid particles) in CSP systems.

Potential of Concentrating Solar Power in Canada

In this paper, results of an analysis to assess the potential of concentrating solar thermal power applications in Canada are presented. First, a direct normal solar resource (DNI) resource map for Canada is introduced. This map indicates the locations where the DNI is the highest in Canada and is derived from the most recent Perez's SUNY satellite-based solar resource model Version number 3. Second, the methodology and results of a GIS analysis to identify the locations of the most suitable lands for concentrating solar thermal power (CSP) applications in Canada are discussed. The total areas of the CSP-suitable lands are presented in a tabulated and a map formats for each of the Canadian provinces where there is a maximum DNI solar resource. Third and finally, results of a technical economical analysis for two CSP system designs are discussed. The two CSP systems considered include parabolic trough with synthetic oil heat transfer fluid with and without storage, molten salt power tower with and without storage.

A novel power block for CSP systems

Concentrating Solar Thermal Power (CSP) and in particular parabolic trough, is a proven large-scale solar power technology. However, CSP cost is not yet competitive with conventional alternatives unless subsidized. Current CSP plants typically include a condensing steam cycle power block which was preferably designed for a continuous operation and higher operating conditions and therefore, limits the overall plant cost effectiveness and deployment. The drawbacks of this power block are as follows: (i) no power generation during low insolation periods (ii) expensive, large condenser (typically water cooled) due to the poor extracted steam properties (high specific volume, sub-atmospheric pressure) and (iii) high installation and operation costs. In the current study, a different power block scheme is proposed to eliminate these obstacles. This power block includes a top Rankine cycle with a back pressure steam turbine and a bottoming Kalina cycle comprising another back pressure turbine and using ammonia–water mixture as a working fluid. The bottoming (moderate temperature) cycle allows power production during low insolation periods. Because of the superior ammonia–water vapor properties, the condensing system requirements are much less demanding and the operation costs are lowered. Accordingly, air cooled condensers can be used with lower economical penalty. Another advantage is that back pressure steam turbines have a less complex design than condensing steam turbines which make their costs lower. All of these improvements could make the combined cycle unit more cost effective. This unit can be applicable in both parabolic trough and central receiver (solar tower) plants. The potential advantage of the new power block is illustrated by a detailed techno-economical analysis of two 50 MW parabolic trough power plants, comparing between the standard and the novel power block. The results indicate that the proposed plant suggests a 4–11% electricity cost saving.