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This paper explains the energy mix of China's overseas electricity investments across Belt and Road Initiative (BRI) recipient countries. We focus on Indonesia and Pakistan. Our research is based on both newly gathered project-level data and in-depth interviews with stakeholders of Chinese-backed power plants in Indonesia and Pakistan. We examine (1) why Chinese actors are involved in renewable power generation in Pakistan and not in Indonesia, and (2) why Chinese-backed coal-fired projects in Pakistan are cleaner than in Indonesia. We argue that variations along the three dimensions – scope, governance regime, and issue linkage – lead to different energy mixes in Chinese-invested power plants across BRI countries. This framework specifies how supply and demand factors interact across multiple levels regarding the formulation and implementation of China's overseas electricity projects. Our findings shed new light on the environmental implications of BRI projects and the dynamics of renewable energy development in emerging markets. [ABSTRACT FROM AUTHOR]

Central tower concentrating solar power systems are moving to the forefront to become the technology of choice for generating renewable electricity, but their widespread implementation is limited by cost. Heliostats contribute almost 50% to the plant's cost and are thus the most significant element in central tower systems. For both large and small-area heliostats, the drive elements demonstrate the largest cost element in these systems. While large-area heliostats (>100 m2) have proven offer the best economy compared to other sizes, they require high-torque drives due to the heavy steel-based support structure. Heliostat costs could be reduced by decreasing the support structure's weight, avoiding large drive units and reducing energy consumption. However, the structure must be able to cope with the aerodynamic loads imposed upon them during operation. Although honeycomb sandwich composites have been widely used where high structural rigidity and low weight are desired, there is an absence of studies that rigorously investigated their suitability as the structure for heliostat mirror. Here, a fluid-structure interaction study investigated, for several loading conditions at various tilt and wind incidence angles, the aero-structural behavior characteristics of honeycomb sandwich composites used as a heliostat support structure. The honeycomb sandwich panel showed markedly different behavior characteristics at various operational conditions. The effect of tilt orientation on the sandwich panel's maximum deflection and stresses became more pronounced as wind velocity increased above 10 m/s, and increasing wind incidence angle reduced their magnitudes at different rates. The supporting components and torque tube had a noticeable wind-shielding effect, causing pronounced changes in the deflection and stresses experienced by the heliostat. The worst operational condition was at a tilt angle of 30° with wind flow of 20 m/s at 0° to the heliostat surface. However, the heliostat maintained its structural integrity according to relevant optical and material failure standards. [ABSTRACT FROM AUTHOR]

In this work, detailed investigations of convection heat loss from conical cavity receiver of solar parabolic dish collector using a numerical method and artificial neural network have been performed. The convective heat loss from the cavity receiver is primarily influenced by geometrical parameters, receiver orientation, and wind characteristics. The heat loss estimation is carried out by considering wind speed (V = 0–10 m/s), wind direction ( ψ = 90 ° and −90 °), receiver tilt ( γ = 0–90 °), diameter to height ratio (d/h = 0.5–1.5), and surface temperature (Ts = 500–800 K). The utmost heat loss occurs at a tilt of 60 ° for d/h < 1 and 75 ° for d/h ≥ 1 in head-on high wind speed, while in back-on high wind speed, it occurs at a tilt of 30 ° for all d/h values. The heat loss is lowest at 90° for V > 4 m/s. The d/h value of 0.5 performs well compared to other values. Further, the correlation for the Nusselt number has been proposed for the conical cavity receiver. [ABSTRACT FROM AUTHOR]

A thermodynamic analysis was performed on a newly developed concentrated solar power (CSP) technology known as the Cross-Linear (CL), which addresses the issue of cosine loss in conventional CSP technology. The analytical model has been developed and validated using experimental data collected at the experimental site situated in Bhopal, India. The analysis was performed under direct normal irradiance of 775 W/m2 with the key objective to determine the optimum inlet condition of the heat transfer fluid (HTF) considering three optimization parameters: HTF outlet temperature, energy, and exergy efficiency of the receiver. Also, the exergy of the solar field is investigated depending on the available solar irradiation throughout the day for three different configurations of the heliostat field. After a comprehensive analysis of the results, the optimal air inlet temperature range was observed to be between 373 and 423 K, and the optimal air mass flow rate was overserved to be 0.0925 kg/s (333 kg/h), which provides energy and exergy efficiency values within 50% to 60% and 28% to 34%, respectively. The maximum electrical exergy efficiency for 30 kW plant capacity is observed to be around 70% at solar noon with a cosine factor of around 0.9 for 4-hour duration. [ABSTRACT FROM AUTHOR]

The solar cavity receiver performance is considerably influenced by wind specifications in the parabolic dish system. This paper performs experiments to study the effects of wind direction and speed on the heat losses from a bicylindrical cavity receiver at different inclinations. A range of wind speeds from 0.3 to 5.7 m/s and the three head-on, back-on, and side-on wind directions for the side-facing and downward-facing cavity situations are examined. The cavity surface temperature distribution shows a jump due to the particular shape of the cavity and the sharp corner between two cylinders. The results show that the head-on wind yields a higher combined convection heat loss in contrast to the back-on and side-on wind directions for all wind speeds and cavity inclinations except 90° (vertically downward-facing) where the effects of wind directions are the same. For the lower side-on wind speeds, increasing cavity inclination results in decreasing combined convective loss, while on the contrary the change in the combined convective loss is very small regardless of the cavity inclination at higher wind speeds above 4 m/s. Moreover, for the back-on wind, comparing to the other wind directions, the combined convective loss is lower. For all wind directions and speeds, the horizontal cavity receiver gives lower forced convective loss compared with the natural convective loss. For the downward-facing cavity, an empirical correlation has been developed for the combined Nusselt number with respect to the Reynolds number, Grashof number, cavity inclination, wind direction, and the absolute temperature ratio. The proposed correlation supports the experimental results by a deviation within ±20%. Moreover, the uncertainty analysis revealed that the relative expanded uncertainty of combined Nusselt number varies between 2.1% and 16.3%, depending upon the cavity inclination, wind speed and direction. [ABSTRACT FROM AUTHOR]

GNSS signals are affected when solar activity causes sudden variations in the density of the ionosphere. Few studies concentrate on positioning performance of IGS stations using different GNSS receivers under different geomagnetic storm conditions. This paper for the first time presents IF and UC PPP positioning performance of stations with different receivers during the quiet, moderate, intense, and super storms period. Firstly, a comprehensive investigation of geomagnetic storms effects on the occurrence of GPS cycle-slip and PPP positioning performance have been presented. Secondly, the influences of geomagnetic storms on the occurrence of cycle-slip and IF PPP positioning performance for stations using receivers provided by 'JAVAD', 'LEICA', and 'TRIMBLE' manufacturers have been comprehensively studied. Finally, this study investigates the geomagnetic storms effects on IF PPP positioning performance of stations using receiver types 'JAVAD TRE_G3TH DELTA', 'JAVAD TRE_3 DELTA', 'LEICA GR25', and 'TRIMBLE NETR9' by analysing observed data collected at mid-latitude region. [ABSTRACT FROM AUTHOR]

Improving the overall performance of parabolic trough collectors (PTCs) represents the best method to reduce the cost of energy produced. The goal is to increase their potential to generate more useful heat, particularly at high ranges of temperatures. Therefore, various techniques have been thoroughly examined in the literature. Indeed, the non-uniform heat flux on the PTC receivers induces overheating of the absorber tube and significant thermal stress, which requires the use of expensive materials. It also reduces the overall thermal performance of the system. To overcome these issues, practical solutions must be introduced. In this paper, integrated spherical pins are used and different configurations have been proposed and investigated. To do so, a numerical model that combines optical and thermal aspects has been developed. For this, the Monte Carlo ray tracing technique (MCRT) is coupled with the finite volume method (FVM). Also, experimental tests on the MicroSol-R platform have been used to validate the numerical models. A number of energetic and exergetic performance indices are used to analyze the potential improvements due to the use of spherical pins. The analysis showed that the use of pins increases the heat transfer coefficient by up to 27.2% and reduces the heat loss by up to 9.32% compared with conventional smooth tubes. Moreover, it is found that the performance evaluation criterion (PEC) can be enhanced by up to 24.92%. Consequently, when using a solar receiver with five pins (which was selected as the best configuration among the examined configurations), the overall efficiency and the exergetic efficiency are increased by up to 4.1% and 2.2%, respectively. Indeed, the use of pins inside the solar receiver is a practical solution to improve the efficiency of the PTC system and has the potential to reduce the thermal stress on the receiver thanks to the high heat transfer coefficient. It also helps prevent overheating and reduce thermal losses by keeping the maximum temperature within a suitable operational range. [ABSTRACT FROM AUTHOR]

Cavity receiver integrated with parabolic dish collector is an essential component of the solar thermal energy conversion process for high-temperature applications, such as power generations, process heat demand, and industrial applications. This paper is focused on a comprehensive review and representation of research on solar cavity receiver. The majority of research concentrated on the highest thermal efficiency with the least amount of heat loss and their interactions with solar cavity receiver geometries. The review consists of various combinations of the receiver's geometries along with different heat transfer fluids, and it also give suggestions to improve the performance of the system based on optimized geometrical and operational parameters. The existing literature primarily focused on the experimental and numerical procedures used with different technologies to improve the efficiency of the solar power system. The decrements in heat losses experienced during the conversion of solar energy into thermal energy is used to determine the efficiency of parabolic dish collector systems. The evaluation of convection and radiation losses is essential to improve the thermal performance of the solar power system. Heat loss models and correlations have been discussed to understand the heat loss mechanism for cavity receiver. The present study analyzes a wide range of parameters that affect cavity receiver performance, including aspect ratio, concentration ratio, optimum receiver length, receiver aperture, tilt angle, and inclination angle. The benefits of air curtains, receiver coatings, and other heat transfer enhancement techniques are also briefly reviewed and expected to be useful in modeling and design of cavity receiver with parabolic dish collector system to improve overall performance. One of the most significant aspects of this article is that it covers a wide range of cavity literature encountered in other engineering systems, power generation, and a wide range of other industrial and domestic applications. The cylindrical cavity receiver has shown an average thermal efficiency of 63.9 % using nano-fluid and 56.44 % for pure thermal oil. The hemispherical cavity receiver has shown the daily mean thermal efficiency of 82.66 % using novel soybean oil-based MXene nanofluid. Under the constant parameters, and solar irradiation intensity 300 to 1100 W / m 2 , the receiver thermal efficiency varies from 80% to 90%. In case of conical cavity receiver, the maximum thermal efficiency achieved with thermal oil is 78.7%. [ABSTRACT FROM AUTHOR]

This article presents an optical investigation of a corrugation cavity receiver for a 100 m2 parabolic dish collector (PDC). The performance of PDC depends on the selection of the receiver and its mounting distance from the collector base (H) to receive a high amount of reflected radiation. This work performs optical modeling for PDC with a designed corrugation cavity receiver using commercial software, ASAP® 2013. The motivation for this study is derived from the fact that the entrapped internal reflection within the receiver optimizes the system's optical efficiency. The receiver geometry is such that it attributes to increasing internal reflection and average heat flux intensification. The present optical model is validated with the available literature. The influential geometrical and optical parameters of the receiver have been optimized by simulation by varying the aperture diameter (da,r) from 0.504 to 0.604 m, surface absorptivity (α) from 75 to 95%, receiver coil's outer and inner pitch (Po and Pi) from 0.00667 to 0.00909 m, and angle of taper (θi) from 50° to 56° for H = 5.35–5.65 m. The performance of the optimized receiver is compared with the conical cavity receiver and is found to be excellent among all values of H. This optical modeling can be expected to be helpful for engineers and researchers in designing the optimized optical receiver for solar parabolic dish collector systems. [ABSTRACT FROM AUTHOR]

This paper is related to the solar radiation concentrating at two focus points, at which three stages of receivers are located. It refers to the improvement of the thermal collection efficiency of the parabolic dish concentrator (PDC) system by using a twin-staged concentrator and three-staged receiver system. It discloses system design that concentrates the incident solar energy in varying proportions subsequently at low-, medium-, and high-temperature solar cavity receiver stages. It is seen that the modified design demonstrated increased thermal collection efficiency as compared to the conventional single-stage system. It improved the system efficiency by about 12.4% for lesser flow Reynolds number (Re). For the entire studied flow range, the average percentage increase in system thermal efficiency is about 8.6%. The twin-stage system demonstrated insignificant improvement in the flow transition zone. In the case of a developed system, the percentage contributions of losses by conduction, convection, and radiation are varying from 1.5–2.7%, 59–62%, and 36–37%, respectively. [ABSTRACT FROM AUTHOR]

The high efficiency of concentrated solar power (CSP) in energy conversion makes it a very attractive device for using solar energy as a substitute of nonrenewable energy sources. The open volumetric receiver plays an important role in the performance of a CSP. The optimized design of solar receiver implies the thorough knowledge of the heat transfer between the air and the foam and of the temperature distribution in the receiver. Heat transfer in the cylindrical SiC porous volumetric receiver of a solar tower, undergoing the impact of concentrated solar radiation, is investigated numerically in this paper. Governing equations are written with the volume averaging technique. A two-equation model for the energy equation, under the local thermal nonequilibrium assumption, is used. Numerical simulations are carried out through the commercial code COMSOL Multiphysics. The solid and fluid temperatures, the fluid velocity and the pressure drop, for various boundary and morphological conditions, are predicted and discussed. The receiver efficiency is finally maximized carrying out an extended parametric analysis of process parameters. [ABSTRACT FROM AUTHOR]

A quantitative analysis of total radiation heat loss from a cavity receiver is numerically studied. Gaussian eliminations method is used to solve the set of radiosity equations to estimate total radiation heat losses from entire cavity surface. The radiation heat loss increases with increase in cavity wall temperature, aspect ratio, and emissivity. For the aspect ratios (L/d) in the range of 2–3, the view factor of all cavity surfaces is lower and most suitable for design. The mean radiation heat loss model always overestimates the radiation heat loss and the overall effect of temperature, aspect ratio, and emissivity may estimate mean radiation heat loss even 14% higher as compared to total loss from entire cavity. The mean radiation model is not appropriate to design a large size, high temperature cavity with low emissivity cavity material. [ABSTRACT FROM AUTHOR]

In this paper, optimisation of the supercritical COBrayton cycles integrated with a solar receiver, which provides heat input to the cycle, was performed. Four S-COBrayton cycle configurations were analysed and optimum operating conditions were obtained by using a multi-objective thermodynamic optimisation. Four different sets, each including two objective parameters, were considered individually. The individual multi-objective optimisation was performed by using Non-dominated Sorting Genetic Algorithm. The effect of reheating, solar receiver pressure drop and cycle parameters on the overall exergy and cycle thermal efficiency was analysed. The results showed that, for all configurations, the overall exergy efficiency of the solarised systems achieved at maximum value between 700°C and 750°C and the optimum value is adversely affected by the solar receiver pressure drop. In addition, the optimum cycle high pressure was in the range of 24.2–25.9 MPa, depending on the configurations and reheat condition. [ABSTRACT FROM AUTHOR]

In concentrating solar power plants, there is a strong incentive to increase the collection temperature and the overall exergy efficiency of the system. Some molten glass mixtures are attractive working fluids for high temperature solar thermal heat collection because optimized glass mixtures can be more stable, less-toxic, and less-corrosive than, for example, molten salts at high temperatures (≥1000°C). A specific phosphorous pentoxide glass mixture is considered in this study to explore its performance in a molten glass falling film central receiver design for collection of heat at conditions resulting in a mini-film with a thickness less than 3mm. In our falling molten glass thin film, the phosphate glass flow is treated as a laminar, Newtonian and gravity-driven flow over a slightly inclined flat plate using an explicit finite difference scheme to evaluate its heat transfer performance for a direct absorption receiver concept. One of the main challenges of modeling transport in the molten glass is the strong dependence of its viscosity on temperature. To incorporate this effect in our numerical analysis, a temperature-dependent viscosity model is used in the momentum equation to model the fluid behavior as it flows down the surface and is progressively heated. An exponential function is used to model the viscosity as it changes with temperature to properly fit the measured the viscosity data provided by Halotechnics. Also, a variable film thickness model analysis is implemented to treat the variation in film thickness that results from the viscosity variation with temperature. In order to avoid stability issues, the finite difference scheme is organized in terms of nondimensional parameters that include all important properties that govern the system. The results of our model indicate that thinning of the film as it flows over the heated surface enhances the heat transfer performance on the lower portion of the receiver system. The heat transfer coefficient increases instead of remaining constant (as normally expected for fully developed laminar flows) on the lower portion of the heated surface. The results further indicate that using a thin mini-film of molten glass for solar thermal heat collection provides high heat transfer performance and enhances the exergy collection. [ABSTRACT FROM PUBLISHER]

Performance characteristics of a concentrated solar volumetric absorber are examined numerically. The thermal system considered consists of parabolic trough, glass tube, absorbing plate, and slurry containing 7% lauric acid as a phase change material and water as a carrier fluid. To assess the effect of the absorbing plate on performance characteristics, two locations of the absorbing plate on the glass tube surface are incorporated in the analysis. A selective surface is considered at the absorber plate surface for improved absorption of solar radiation and reduced thermal emission due to temperature increase at the surface. Temperature ratio, gain parameter, and pump power loss parameters are introduced to quantify the performance characteristics of the volumetric receiver. The study is extended to include the effect of Reynolds number on the receiver performance characteristics. A heating model incorporating radiation, convection, and conduction is adopted to simulate the thermal process. It is found that the gain parameter of the concentrated solar volumetric receiver improves by 15% when the absorber plate is located at the left face of the glass tube opposing the trough surface. The effect of Reynolds number on gain parameter is found to be inconsiderable. [ABSTRACT FROM AUTHOR]

This article presents the use of a wire mesh in optimising the performance of two volumetric solar receivers that use oil as a heat transfer fluid. Computational fluid dynamics models have been used to optimise the receivers. Varied parameters (including the use of a wire mesh) of the receiver models were changed in the optimisation process. Based on the models, prototype receivers were developed and tested. After that, the models were validated against experiments and the results compare well. The results indicate that the use of a wire mesh placed inside a receiver improves its performance. An optimal wire mesh porosity was found as ≈0.95 mainly because the efficiency is increased without inducing an adverse pressure drop inside the receiver. [ABSTRACT FROM PUBLISHER]

The thermal performance of a cylindrical solar cavity with a convective boundary is modeled using Monte Carlo ray tracing to evaluate the impact of the geometry and the spectral characteristics of the surface on the absorption efficiency and the spatial distribution of temperature. Increasing cavity size for a fixed aperture size increases absorption efficiency and reduces wall temperature. Inconel, which serves effectively as a selective surface, provides the highest absorption efficiencies at over 90%. A surface coating of aluminum oxide produces a more uniform and lower average temperature distribution. [ABSTRACT FROM AUTHOR]

Results are reported of a numerical analysis of conduction heat loss from a parabolic trough solar receiver with controlled pressure within the annular gap between the tubular absorber and the glass vacuum jacket. A direct simulation Monte Carlo (DSMC)model of rarefied gas within the annular gap is coupled to radiation heat transfer for directional- and spectral-dependent concentrated incident solar radiation. This modeling approach is valid for high Knudsen numbers, and consistently predicts slightly higher heat loss than a continuum model using slip boundary conditions in the range of pressures of interest around 1 Pa. 3-D simulations of axial flow through the annular gap predict higher gas conductance by the DSMC method than by slip flow models, with values converging as pressure increases. [ABSTRACT FROM AUTHOR]

Thermal large eddy simulations are carried out in order to study the convective flow in a solar receiver. We investigate the impact of thermal gradients on a turbulent channel flow with imposed wall temperatures for two turbulent Reynolds numbers based on the friction velocity (180 and 395). In this configuration, the flow is subsonic, while temperature variations can be strong and induce significant variations of the fluid properties. The low Mach number equations are considered. The influence of the variations of the conductivity and the viscosity is first investigated. We show that the influence of these properties can be considered constant only for weak temperature gradients. The thermal subgrid-scale modeling is studied and we conclude that for a temperature ratio of 2, we can use a constant subgrid-scale Prandtl number. Finally, we focus on the increase of the temperature ratio that emphasizes the flow dissymmetry and modifies the fluctuations profiles. The physical mechanism responsible for these modifications is explained. [ABSTRACT FROM PUBLISHER]