Accurate forecasting is the key factor in promoting wind power consumption and improving the stable operation of power systems. A short-term wind power forecasting (WPF) and uncertainty analysis method based on whale optimization algorithm (WOA), least squares support vector machine (LSSVM), and nonparametric kernel density estimation (NPKDE) was proposed in this paper. The advantages of WOA (fast convergence speed and high convergence accuracy) were used to optimize the penalty factor and kernel function width of the LSSVM model, and the calculation speed and forecasting accuracy of the LSSVM model were improved. The training sample set is classified according to the wind speed interval, and the WOA-LSSVM forecasting model is trained by subclass after classification to further improve the accuracy of short-term WPF. The NPKDE method is used to accurately calculate the probability density distribution characteristics of the forecasting error of wind power, and the confidence interval of the WPF is accurately calculated based on the probability density distribution characteristics. The calculation results show that the forecasting accuracy of the WOA-LSSVM model is higher than those of the LSSVM, long short-term memory (LSTM), and particle swarm optimization and least squares support vector machine (PSO-LSSVM) models, and the forecasting accuracy of the WOA-LSSVM model can be further improved after classifying the training sample set. The coverage of the confidence intervals in different time scales is higher than the corresponding confidence level, indicating that the NPKDE method can accurately describe the probability density distribution characteristics of the WPF errors.

A new eutectic chloride molten salt, MgCl 2 -KCl-NaCl (wt% 45.98–38.91–15.11), has been recognized as one of the most promising high-temperature heat transfer fluids (HTF) for both heat transfer and thermal storage for the third-generation concentrated solar power (CSP) systems. For the first time, some essential thermophysical properties of this eutectic chloride molten salt needed for basic heat transfer and energy storage analysis in the application of concentrating solar power systems have been experimentally tested and provided as functions of temperature in the range from 450 °C to 700 °C. The studied properties include heat capacity, melting point, heat of fusion, viscosity, vapor pressure, density, and thermal conductivity. The property equations provide essential database for engineers to use to calculate convective heat transfer in concentrated solar receivers, heat exchangers, and thermal storage for concentrated solar power plants.

In this paper, a ZnO/CdS/CuO:Co solar cell was prepared on a glass/indium oxide (ITO) substrate. First, we use RF-sputtering to deposit the window (ZnO) layer by optimizing the oxygen pressure while keeping the RF power at 200 W. Fourier transform infrared and X-ray reflectometry spectra were carried out, and it is found that 30% of O 2 is the optimal percentage to obtain the best density and the best refractive index for the ZnO layer. The CdS layer was then deposited by the sol–gel method to align the energy bands, and a layer of CuO:Co with a thickness of 750 nm was deposited, also by reactive RF-sputtering technique. Finally, the electrical contacts were made by depositing circular silver electrodes. The obtained photovoltaic activity of device confirms that the aforementioned method is promising for further future optimizations.

Current state-of-the-art development of concentrated solar power (CSP) applications targets cost-effective and highly efficient processes in order to establish commercialization of these technologies. The design of solar receivers/reactors and their respective flow configuration have a direct impact on the operational performance of the solar thermochemical processes. Thermal efficiencies, reaction kinetics, and other key output metrics are the intrinsic result of the chosen configuration. Therefore, reactor design optimization plays a crucial role in the development of solar thermochemical applications. In this study, a computational fluid dynamics (CFD) model of a directly-irradiated cavity receiver has been developed. The CFD-domain is coupled with incoming radiation that is obtained by using Monte Carlo ray tracing (MCRT). Experimental campaigns of the cavity receiver were carried out using a 7-kW high flux solar simulator (HFSS) as a radiative source. Temperature readings were obtained at different locations inside the cavity receiver for both wall and gas temperatures. In order to mimic naturally changing insolation conditions, the HFSS was run at different power levels. Heat flux at the aperture of the solar receiver was experimentally characterized. The acquired heat flux maps validated the intermediate results obtained with the MCRT method. The coupled computational model was validated against the measured temperatures at different locations inside the receiver. Computed temperature contours inside the receiver confirmed the experimentally observed non-uniformity of the axial temperature distribution. The validated analysis presented in this paper was then used as a baseline case for a parametric study. Design optimization efforts were undertaken toward obtaining temperature uniformity and achieving efficient heat transfer within the fluid domain. Enhanced flow circulation was achieved which yielded temperature uniformity of the receiver at steady-state conditions. The outcome of this parametric analysis provided valuable insights into the development of thermal efficient solar cavity receivers. Hence, findings of this study will serve as a starting point for the future solar reactor design. For example, it was found that reversing flow direction has an adverse effect on the temperature uniformity inside the receiver. Similarly, increasing the inlet angle does not positively affect the temperature distribution and hence should be chosen carefully when designing a solar reactor.

The importance of statistical analysis in the field of energy for environmental engineering is shown in this research paper, in which the adequacy of the data sets of clarity index with the model of “best” probability (based on the criteria used) was studied. In Campo Grande which is the capital of the Brazilian state of Mato Grosso do Sul, located in the Center-West region of the country, there is a predominance of the atmospheric conditions of low cloudiness, with a high frequency of days with a clear sky and in consequence a low-frequency of days with cloudy sky. The aerosols resulting from the burning of sugarcane influence the sky conditions in Campo Grande thus reducing the frequency of the clear sky.

This study uses the Reynolds-averaged Navier–Stokes (RANS) equations to validate a canopy model by computing a fully developed wind flow within and above a horizontally homogeneous dense forest as in the work of Dalpé and Masson. The model is paired with a modified k– ε turbulence closure. A set of boundary conditions (BCs) that rely on the law of the wall for a sustainable atmospheric boundary layer (ABL) is used. All simulations are conducted in the open source software OpenFOAM v.2.4.0 (OpenCFD Ltd (ESI Group)). Two practical aspects are considered in the validation process. First, an accurate leaf area index (LAI) integration to exactly fit the wind shear is evaluated. Since the physical foliage parameters may not be accessible for all type of forests, a generic leaf area density α distribution is tested. The results of this test show that a generic distribution is sufficient for preliminary analyses to improve accuracy of wind flow predictions over forested terrain. Second, the approach of Dalpé and Masson is limited to cyclic BCs which are not practical for real sites. For cases without cyclic BCs, imposing a proper slope on the inlet velocity profile is of high importance. This condition can be achieved through adjustment of the roughness length at the inlet.

This paper presents characterization of a new high flux solar simulator consisting of a 10 kW Xenon arc via indirect heat flux mapping technique for solar thermochemical applications. The method incorporates the use of a heat flux gauge (HFG), single Lambertian target, complementary metal oxide semiconductor (CMOS) camera, and three-axis optical alignment assembly. The grayscale values are correlated to heat flux values for faster optimization and characterization of the radiation source. Unlike previous work in heat flux characterization that rely on two Lambertian targets, this study implements the use of a single target to eliminate possible errors due to interchanging the targets. The current supplied to the simulator was varied within the range of 120–200 A to change the total power and to mimic the fluctuation in sun's irradiance. Several characteristic parameters of the simulator were studied, including the temporal instability and radial nonuniformity (RNU). In addition, a sensitivity analysis was performed on the number of images captured, which showed a threshold value of at least 30 images for essentially accurate results. The results showed that the flux distribution obtained on a 10 × 10 cm 2 target had a peak flux of 6990 kWm −2 , total power of 3.49 kW, and half width of 6.25 mm. The study concludes with the illustration and use of a new technique, the merging method, that allows characterization of heat flux distributions on larger areas, which is a promising addition to the present heat flux characterization techniques.

This paper presents FluxTracer, an advanced open source computer tool to assist in the analysis, design, and optimization of solar concentrators and receivers. FluxTracer is a postprocessor for Monte Carlo ray tracers used to simulate the optical behavior of solar concentrating systems. By postprocessing the rays generated by the ray tracer, FluxTracer can partition into volumetric pixels (voxels) a region of interest in three-dimensional (3D) space defined by the user and compute for each voxel the radiant power density of the concentrated solar radiation. Depending upon the set of rays provided by the ray tracer, it may be able to integrate the radiant power density in every voxel over time. The radiant energy density analysis described is just one of the analyses that FluxTracer can carry out on the set of rays generated by the ray tracer. This paper presents the main analyses that FluxTracer can provide. It also presents examples of how the information provided by FluxTracer can be used to assist in the analysis, design, and optimization of solar concentrators and receivers. FluxTracer is the first of a series of components of an open-source computational framework for the analysis, design, and optimization of solar concentrators and receiver, being developed by The Cyprus Institute (CyI) and the Australian National University (ANU).

The eutectic mixture of MgCl 2 –KCl molten salt is a high temperature heat transfer and thermal storage fluid able to be used at temperatures up to 800 °C in concentrating solar thermal power systems. The molten salt thermophysical properties are reported including vapor pressure, heat capacity, density, viscosity, thermal conductivity, and the corrosion behavior of nickel-based alloys in the molten salt corrosion at high temperatures. Correlations of the measured properties as functions of molten salt temperatures are presented for industrial applications. The test results of tensile strength of two nickel-based alloys exposed in the molten salt at a temperature of 800 °C from 1-week length to 16-week length are reported. It was found that the corrosion and strength loss is rather low when the salt is first processed to remove water and oxygen.

The potential applicability of a developed recycled textile material, based on acrylic spinning waste, as thermal insulation is conducted. The prepared acrylic spinning waste (AS) is thermo-physically characterized in terms of density, air permeability, and thermal conductivity. The results show that the density and air permeability are 10.583 kg/m 3 and 1100 L/m 2 /s, respectively. In addition, the thermal conductivity is found to be 38.27 mW/(m K). The developed thermal insulator is then tested in a thermally controlled reduced scale cavity. Two walls of the cavity are outfitted with AS at two different locations and compared to the walls without AS. The comparison is made based on the wall surface temperature and heat flux. A reduction in surface temperature is observed in the walls outfitted with AS, compared to wall without AS. Indeed, compared to a control wall, the peak heat fluxes are reduced by 27.23% and 18.67%, respectively, related to the walls with AS at location 1 and location 2. The obtained results show that the AS is a competitive thermal insulation material and can increase the thermal performance of the building walls.

This paper evaluates the effectiveness of phase change materials (PCMs) for the improvement of summer thermal comfort in lightweight buildings. Experiments have been carried out using PCM in the form of DuPont Energain wallboards in combination with a roof. Two factors influencing the effectiveness of PCM (thickness and location of PCM layer) have been investigated. An experimental study was carried out using two identical test cavities submitted to Casablanca weather. Thermal performance such as the roof surface temperatures and heat flux densities, through the envelope, have been studied. The results indicated that, compared with reference room (without PCM), the thermal storage allows solar radiation to be stored and released up to 6–7 h after solar irradiation; this has effects on both the reduction of daily temperature swings (up to 2 °C) and heat flux (more than 88%). It has been proved that the PCM with a thickness of 10.52 mm on the outer face of the roof has good thermal insulation effect and energy efficiency potential.

Ion-implantation is an advanced technology to inject dopants for shallow junction formation. Due to the ion-induced sputtering effect at low implant energy where dopants tend to accumulate at the silicon surface, the excess ion doses can be easily removed via a surface chemical wet etching process. By taking advantage of the dose limitation characteristic, we proposed a novel method to form shallow emitters with various dopant densities. Two integration flows have been investigated: (1) wet etch after implantation before junction anneal and (2) wet etch after implantation and junction anneal. The two integration flows observed a difference in the density of doping impurities during the thermal process, which is related to the substrate recombination rates. Selective emitter (SE) structures with the two types of integration flows were characterized. Comparing the blanket emitter and SE structures with two types of etching methods, the device with wet etch before annealing process achieved the best effective carrier lifetime of 53.05 μ s, which leads to a higher short circuit current density. Hence, this SE cell demonstrated a better blue response and shows an improvement in the conversion efficiency.

Three eutectic salts from a system of halide salts NaCl–KCl–ZnCl 2 were chosen for detailed study of thermal and transport properties with the objective of developing a next generation high-temperature heat-transfer fluid (HTF) for concentrated solar thermal power (CSP) technology. The acceptable range of the working temperatures for the HTF is from below 250 °C to at least 800 °C. The tested properties are presented here for the three candidate eutectic salts, including melting point, heat of fusion, heat capacity, vapor pressure, viscosity, density, and thermal conductivity. Data-fitted equations are provided for all the measured properties for convenience in engineering application. It is concluded that the three eutectic salts can satisfy the needs for a high-temperature HTF and thus are recommended as a new generation high-temperature HTF.

Site-specific assessment of wind turbine design requires verification that the individual wind turbine components can survive the site-specific wind climate. The wind turbine design standard, IEC 61400-1 (third edition), describes how this should be done using a simplified, equivalent wind climate established from the on-site distribution functions of the horizontal mean wind speeds, the 90% quantile of turbulence along with average values of vertical wind shear and air density and the maximum flow inclination. This paper investigates the accuracy of fatigue loads estimated using this equivalent wind climate required by the current design standard by comparing damage equivalent fatigue loads estimated based on wind climate parameters for each 10 min time-series with fatigue loads estimated based on the equivalent wind climate parameters. Wind measurements from Boulder, CO, in the United States and Høvsøre in Denmark have been used to estimate the natural variation in the wind conditions between 10 min time periods. The structural wind turbine loads have been simulated using the aero-elastic model FAST. The results show that using a 90% quantile for the turbulence leads to an accurate assessment of the blade root flapwise bending moment and a conservative assessment of the tower bottom for-aft bending moment and low speed shaft torque. Currently, IEC 61400-1 (third edition) neglects the variation in wind shear by using the average value. This may lead to a nonconservative assessment of blade root flapwise fatigue loads, which are sensitive to wind shear. The results in this paper indicate that using a 75% quantile for the wind shear at each wind speed bin leads to an appropriate, but conservative, assessment of the fatigue loads. However, care should be taken when using this approach for components where low or negative wind shears can lead to large fatigue loads. This is the case for some drivetrain components where a lower quantile may be required.

A solar-driven aerosolized particle reactor under vacuum was tested for carbothermal reduction of zinc oxide using concentrated solar power. The reactor concept is based on the downward flow of zinc oxide and carbon particles, which are indirectly heated by an opaque intermediate solar absorption tube. The particles are rapidly heated to reaction temperature and reduced within residence times of less than 1 s. In the continuous feeding experiments, maximum sustained temperatures close to 2000 K and heating rates as fast as 1400 K min −1 could be achieved for pressures between 1 and 1000 mbar. Reactant conversions of up to 44% were obtained at 1000 mbar. It was found that a reduction in system pressure leads to a decreased particle residence time (as low as 0.09 s), and therefore low conversion (as low as 1%), thus partially diminishing the positive thermodynamic effects of vacuum operation. Experimental results validate the robust and versatile reactor concept, and simultaneously highlight the necessity of balancing the system design in order to optimize the conflicting influence of vacuum operation and reacting particle residence time.

A new structure for CuIn 1− x Ga x Se 2 (CIGS) solar cell is investigated. The structure consists of an absorber layer with constant bandgap placed next to the cadmium sulfide (CdS) buffer layer and a graded bandgap absorber layer positioned near the molybdenum (Mo) back contact. This leads to a reduced recombination rate at the back contact and enhances collection of generated carriers by additional induced drift field. The structure provides higher efficiency than previous structures. Optimum value of bandgap, thickness, and doping level of the layers are determined to reach maximum efficiency. Moreover, a trap density model is interpolated and applied in the simulations.

Flux density measurement applied to central receiver systems delivers the spatial distribution of the concentrated solar radiation on the receiver aperture, measures receiver input power, and monitors and might control heliostat aimpoints. Commercial solar tower plants have much larger aperture surfaces than the receiver prototypes tested in earlier research and development (R&D) projects. Existing methods to measure the solar flux density in the receiver aperture face new challenges regarding the receiver size. Also, the requirements regarding costs, accuracy, spatial resolution, and measuring speed are different. This paper summarizes existent concepts, presents recent research results for techniques that can be applied to large-scale receivers and assesses them against a catalog of requirements. Direct and indirect moving bar techniques offer high measurement accuracy, but also have the disadvantage of large moving parts on a solar tower. In the case of external receivers, measuring directly on receiver surfaces avoids moving parts and allows continuous measurement but may be not as precise. This promising technique requires proper scientific evaluation due to specific reflectance properties of current receiver materials. Measurement-supported simulation techniques can also be applied to cavity receivers without installing moving parts. They have reasonable uncertainties under ideal conditions and require comparatively low effort.

The optimization of the selection of heliostat aim points in a solar power tower plant with the objective of an increased overall efficiency represents a NP-hard optimization problem of high dimension. This paper presents a universal procedure for the purpose of aim point optimization based on the ant colony optimization metaheuristic that uses the principles of swarm intelligence. The applicability of the developed aim point optimization procedure to central receiver systems is demonstrated on a test case, for which the electrical power of a concentrated photovoltaic (CPV) receiver is maximized for a selected operating point. The example of a CPV receiver was chosen due to its nonlinear and nonmonotonous dependency of efficiency and flux density. It is shown that the optimization result is very close to the theoretical maximum.

A new concept for long-term solar thermal storage is based on the absorption properties of aqueous calcium chloride. Water, diluted and concentrated calcium chloride solutions are stored in a single tank. An immersed heat exchanger and stratification manifold are used to preserve long-term sorption storage, and to achieve thermal stratification. The feasibility of sensible heating the tank via large-scale natural convection without mixing salt solutions is demonstrated via measurements of velocity, CaCl2 mass fraction, and temperature in a 1500 l prototype tank. Experiments are conducted over a practical range of the relevant dimensionless parameters. For Rayleigh numbers from 3.4 × 108 to 5.6 × 1010 and buoyancy ratios from 0.8 to 46.2, measured Sherwood numbers are 11 ± 2 to 62 ± 9, and the tank is thermally stratified. Convective mixing between salt layers is inhibited by the presence of a steep density gradient at the interface between regions of differing mass fraction. The predicted storage time scales based on mixing via natural convection for the reported Sherwood numbers are 160–902 days.

The thermodynamical efficiency of a solar power tower power plant with an open volumetric air receiver depends among others on the operational strategy of the receiver. This strategy includes, on the one hand, controlling the distribution of irradiated power on the receiver surface via aim point optimization, and on the other hand, controlling the air mass flow rate and its distribution by choosing suitable dimensions of fixed orifices and controlling air flaps. The maximum mass flow rate of the receiver as an indication of the thermal power is commonly used as a quality function when assessing new component designs, comparing different operational strategies, or evaluating the role of aim point optimization for the open volumetric air receiver technology. In this paper, a method is presented to maximize the mass flow rate of the receiver using given technical capabilities of the receiver technology like orifices and air flaps for a desired air outlet temperature of the receiver. The method is based on dynamic programming, a general technique for solving decision making problems where a complex problem can be split up into a sequence of simpler ones. The potential of the method is demonstrated for a prototype solar thermal power tower with open volumetric air receiver technology.