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Abstract Molten nitrate salts are widely used as heat transfer and energy storage medium in Concentrated Solar Power (CSP) systems. Solar Salt (60 wt% NaNO3-40 wt% KNO3) is the commercial binary molten nitrate salt, which is the preferred energy storage material with high density, high specific heat, low melting point, high thermal stability, and low vapor pressure. This paper explored the effects of impurity Cl− on the thermophysical properties of Solar Salt, including liquidus temperature, density, viscosity, and thermal stability. The results showed that Cl− can significantly reduce the liquidus temperature, and when Cl− was less than 0.5 wt%, the liquidus temperature of molten salt system decreased within 1 °C. On the other hand, Cl− had little effect on the density, viscosity and thermal stability of the mixed molten salt system at 400 °C, but at high temperature Cl− will promote the volatilization of components. By analyzing the thermostatic stability at 565 °C, it was found that the total mass loss changes less than 0.3% when Cl− was less than 0.01 wt%. After comprehensive analysis, the conclusion is that the upper limit of Cl− is preferably less than 0.1 wt% for keeping good thermal performances of Solar Salt.

Abstract Recently in exploiting green energy, solar power generation is a must-be trend and approach, especially for the countries with nature resource shortage. However, how to build solar power plants with the best power generation efficiency in limited spaces is always a crucial issue. In this paper, the approach of finding the optimum models of generating solar power is proposed to build solar power plants for different environments in Taiwan. First, we collect all the data from existing solar power farms, including (1) design methods of power generation, (2) actual power generation, and (3) surrounding environments. Then, after a series of preprocessing steps and system analysis on them, the optimal models of generating solar power could be mined out. Finally, in the experiments, we evaluate the system from five aspects regarding to input and output parameters. As a result, we observe that using the majority voting strategy improves the system accuracy and helps engineers build solar power plants with the maximum power generation.

Abstract Exergy analysis is very helpful for reducing irreversibility and rising the efficiency of solar collectors. The major objective of the present study is to organize a review on exergy analysis of different parabolic solar collectors. The effects of various flows and geometrical parameters of parabolic thermal collectors on the exergy efficiency were presented and discussed. In addition, comparative study was carried out to select the best solar thermal system for maximum exergy efficiency with minimal thermal losses. This study indicated that the hybrid nanofluids enhanced the exergy efficiency significantly as compared to without hybrid nanofluids. Passive techniques comprising twisted tape inserts, fins and insertion of swirl devices in the stream for changing the stream patterns causes to interrupt the thermal boundary layer and accordingly high exergy efficiency. This review would also throw light on the scope for further research and recommendation for improvement in the existing solar thermal collectors. Finally, this work will be beneficial for the scholars working on exergy analyses of solar parabolic collectors.

Abstract The ground-level spectral distribution of direct solar irradiance at Reunion Island was measured for six bands covering the spectrum of solar radiation. The measurements, distributed over one year, were made under clear sky conditions with a pyrheliometer (Eppley, NIP) and six large pass-band flat filters. Good stability of spectral irradiances as a function of Solar height allows us to propose approximate relationships which significantly characterize the irradiance into each spectral band. Measurements at Reunion vary significantly from data obtained with the same apparatus in a northern hemisphere continental area (Lyon). The determination of aerosol attenuation coefficients, for different spectral bands, allows the establishment of a mean curve, for these coefficients as a function of wavelength, characteristic of marine aerosols.

Abstract In this paper, the experimental performance of a 45 m2 solar field of non-tracking external compound parabolic (XCPC) collectors installed at the University of California, Merced is described. The solar field was operated during July-August 2020 in both clean and dirty conditions and at varying operating temperatures (70, 135, 170 °C) while operating an air heater, thermal evaporator, and double effect absorption chiller. Performance data was used to develop an instantaneous solar field performance model which was then incorporated into an annual performance model using TMY3 data to estimate yearly production from the solar field. The model predicts an annual generation of ∼1100 kWh/m2-year at 80 °C, ∼1000 kWh/m2-year at 100 °C, ∼900 kWh/m2-year at 120 °C, ∼800 kWh/m2-year at 140 °C, and ∼700 kWh/m2-year at 160 °C in California. The XCPC technology is currently expected to have an installed cost of $300/m2 and an annual operations and maintenance cost of $6.5/m2-year. Over a 25 year lifetime it provides a levelized cost of heat at 2–4 cents per kWhth delivered. This is below the cost of commercial natural gas in California and at temperatures ≤ 120 °C below the cost of industrial natural gas, which highlights the potential of the XCPC technology for decarbonizing thermal applications such as water and space heating, drying, sterilization, desalination, evaporation, low pressure steam, double effect absorption chilling, process heating, and more. The lifetime cost of emissions reductions is ∼$169 per metric ton of avoided CO2 when replacing natural gas, ∼$137/MT CO2 when replacing propane, and ∼$83/MT CO2 when replacing electric heating.

Abstract Utilization of solar thermal power for high temperature fuel production has the potential to significantly reduce the fossil fuel dependence of our current economy. Over the past two decades, remarkable progress has been made in the development of solar driven thermochemical reactors for the production of hydrogen and syngas as they are promising energy carriers for transportation, domestic and industrial applications. However, there are solar peculiarities in comparison to conventional thermochemical processes – high thermal flux density and frequent thermal transients because of the fluctuating insolation-, and conventional industrial thermochemical reactors are generally not suitable for solar driven reactors. Therefore, solar-specific modifications of reactor design are necessary to realize efficient solar driven thermochemical processes. In solar thermochemical reactors, the methods for solar-heating particulate solid feedstock to high temperatures can be broadly classified as solar “directly” and “indirectly” absorbing reactors. On solar thermochemical processes involving reacting solid particles at high temperatures, such as “solar two-step water splitting with metal oxides” and “solar gasification”, various types of solar directly and indirectly absorbing particle reactors have been developed. In this review, recent development of solar particle reactors for the above solar thermochemical processes is described.

Abstract The current manuscript applies a previously developed and validated evaporative cooling theoretical model to a wide range of scenarios aiming to infer the actual effectiveness of evaporative cooling on building roofs as a way to reduce the excessive thermal load. The presented analysis is divided in three main sections, one of parametric nature, which considers standard or idealized variation for wind speed, solar irradiation, ambient temperature and relative humidity, one using real weather data and the third one that based on TMY data from several locations around the world, which are employed to evaluate the applicability of evaporative cooling for different climates. The parametric analyses indicate that air relative humidity and temperature variations present, arguably, the strongest influence on the performance of the evaporative cooling compared to other roof heat gain reduction methods. The global analysis indicates that arid climates such as BSk and BWh, from the Koppen classification, are more likely to display encouraging results with respect to the evaporative cooling whereas in humid equatorial climates the benefits are modest.

Abstract The forecasting of the downwelling surface solar irradiances is required by the operators of solar powered plants to predict the power output of the plant. The purpose of this study is to use aerosol optical depth and columnar water vapor forecasts by the chemistry transport model CHIMERE, coupled with the Weather Research and Forecast (WRF) model, as inputs in the REST2 model to predict the day-ahead clear-sky global horizontal, direct normal and diffuse horizontal irradiances at hourly steps. A dataset of quality-assured and cloud-screened surface solar irradiance measurements collected from 44 sites scattered throughout Saudi Arabia was used to validate the predicted surface solar irradiances. The validation for the day-ahead forecasting of the clear-sky global horizontal irradiance for the data of all 44 stations combined exhibits a bias (relative to the mean reference value) of 0%, a relative root mean square error of 4% and a correlation coefficient of 0.993. Respectively, the clear-sky direct normal irradiance exhibits values of 0%, 15% and 0.769, while the clear-sky diffuse horizontal irradiance values are 0%, 35% and 0.542. The errors in the inputs are also investigated. The results are satisfactory and pave the way to the inclusion of the attenuation due to clouds with the final aim of predicting the surface solar irradiance under all-sky conditions.

Abstract A major problem in the operation of photovoltaic (PV) panels is the need for frequent maintenance and cleaning. In the present work, the effect of a self-cleaning, photocatalytic, antireflective glass coating on the efficiency of PV panels is investigated. The optical and photocatalytic properties of the coating were determined via UV–vis spectroscopy and degradation of organic pollutant Methylene Blue, respectively. Increased light transmittance in the visible light region and enhanced self-cleaning of the coated in comparison to the uncoated glass was demonstrated. The adhesion and the stability of the coating were tested in conditions of thermal fluctuations, UV weathering and sandblasting. The outdoor performance of coated and uncoated PV panels and arrays were monitored for several months at different climate conditions (Greece and China) in order the extra energy produced due to coating to be measured. An average 5–6% gain was found for both cases for the entire period of time. It was established that specific conditions such as intensity and angle of the incident light, occurrence of rain and sand storms influence significantly the power difference (ΔPm) between coated and uncoated PV panels. The increase of ΔPm under diffused light (cloudy day) and irradiation with high incident angle (morning, evening) reached ∼20% and 30% respectively, that were related to the anti-reflecting property of the glass coating. The coated surface showed better dust removal ability due to its superhydrophilicity (θ = 6°). The superior efficiency of coated panels as well as the low-cost spraying procedure without any post-deposition treatment render the nanocomposite SurfaShield G coating very important especially for northern regions with limited sunlight periods.