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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 Molten salts have high solidification temperatures, so they easily solidify in the receiver tube when the incident energy fluxes are very low due to clouds drifting and floating across the sky. Additional energy and time are then wasted to thaw the frozen solid with the salt freeze/thaw cycles eventually damaging the receiver. Therefore, operators need to adopt appropriate operating strategies to ensure that the salt remains molten during extended cloudy periods. The present study presents a thermo-hydraulic dynamic model of a molten salt receiver to investigate the heat transfer processes. The model is based on the Badaling 1 MWth receiver experiment with three experimental groups of tests modeled to validate the thermal hydraulic model in both the direct-filling mode and the S-type flow mode. The model results agree well with the experimental measurements with maximum relative errors of 0.4% for the outlet temperature and 0.9% for the surface temperatures. Then, a sensitivity analysis is conducted to better illustrate the flow distribution and surface temperatures, including the effects of the flow resistance, inlet temperature, cloudy duration, and valve abnormalities. Finally, the results indicate that the S-type flow mode should be used to prevent solidification for cloudy conditions.

Abstract Our purpose in the future will be the forecast of the global radiation for region of Hungary and certain stations. As a first step in this study we try to determine the average daily values of the relative global radiation from values of cloud coverage using satellite pictures and from other meteorological parameter (visibility). First the relative global radiation was considered as a parabolic function of the cloud coverage. A close relationship was obtained between the amount of cloud measured in tenth and the daily average value of the relative global radiation. To correct this formula the visibility was used for calculation of the relative global radiation above the cloud amount. The value of the multiple correlation coefficient was 0.96 for Budapest, and 0.91 for region of Hungary. This fact indicates a sufficiently correct formula for calculation of the global radiation.

Abstract Currently, the excess light above a light saturation point cannot be harnessed for plant growth in conventional greenhouse covers. In this study, we developed a solid compound parabolic concentrator (CPC) cover for use in greenhouses to convert excess light into heat. Optical simulation software was used to track the sunlight at different incident angles over time. We also conducted experiments to determine the transmittance and heating power of the solid CPC coating under real weather conditions. The maximum instantaneous thermal efficiency and thermal energy of a single solid CPC cover plate were 32.2% and 353 W/m2, respectively. The simulation results were in good agreement with the experimental output power and the trend of the actual transmittance of the covering material. The transmittance of the covering material was low when the midday sun was intense, and the transmittance was relatively high in the morning and afternoon. The variation of red and blue light in the greenhouse with the spectrum was analyzed at the same time. Studies have shown that this new greenhouse covering material can better adjust the brightness, make the illumination in the greenhouse more uniform, and thus improve the thermal environment in the greenhouse. The heat pipes converted excess light into heat, thereby achieving comprehensive utilization of solar light and heat.

Abstract Site adaptation refers to procedures for correcting systematic errors in an extended period of gridded modeled data using a short period of ground-based measurements used as unbiased reference. Traditionally, site adaptation leverages a single gridded product and issues point predictions. Currently, remote-sensed and reanalysis data are available from different sources providing multiple versions of estimates of a same atmospheric variable, for any location on Earth. These datasets allow what is called an ensemble prediction. In this regard, this contribution proposes a probabilistic site-adaption framework, and describes how one can use parametric and nonparametric techniques within the framework. On top of the stand-alone probabilistic site-adaption methods, heuristics are optionally used to combine quantiles, to further improve the accuracy of site adaptation. To exemplify the framework, global horizontal irradiance data from 26 sites worldwide with different climate characteristics and weather regimes are used to side-adapt the corresponding predictions from up to 5 satellite-derived databases and 2 reanalyses spanning various periods, collectively. It is found that the proposed site-adaptation methods using multiple gridded products are able to attain, on average, a 5 W/m 2 reduction in continuous ranked probability score than that leveraging just a single product.

Abstract The random installation of various solar energy equipment on building roofs has caused visual damage to the cityscape. Keeping the rooftop equipment out of sight of the pedestrians is a new solution to eliminate visual pollution. Based on the complex urban street canyons, this paper describes a physical and mathematical model relating to the limiting height of equipment installations at any position on the roof. It is found that the limiting height of equipment varies with the building roof height, the street width, and other factors. In addition, for a case with four main urban roads, the variation patterns for the limiting height of rooftop equipment changed with the street width and the distance from the installation to the parapet have been established, which is of great relevance for determination of the limiting equipment height in actual installations. The research can not only help to remove visual pollution from rooftop equipment in street canyons, and provide a guide for the selection and installation of solar equipment, but can also provide significant information for urban space planning and building design.

Abstract Accurate prediction of building energy performance requires precise information of the local climate. Typical weather year files like test reference year (TRY) and typical meteorological year (TMY) are commonly used in building simulation. They are also essential for numerical analysis of the sustainable and renewable energy systems. The weather year file of one city is often employed by the nearby cities for such purposes. In this paper, the developments of customized weather year formulation are reviewed. The key issues are discussed making reference to two neighboring cities, Hong Kong and Macau, using their weather data records over a century, and the typical weather year files developed. The findings support the preference of TMY over TRY. It is also suggested that the TMY selection process should include the most recent meteorological observations, and should be periodically reviewed to well reflect the long-term climate change.

Abstract Due to the worldwide energy crisis and environmental issues, the so-called green ship is recently urgent to be developed for energy-saving and emission-reduction. When a photovoltaic (PV) system is installed on a ship, solar generation can provide auxiliary energy as backup of engine. However, different from the land-based PV system with fixed position, the marine PV system always suffers from complex and frequently-changed environmental conditions, e.g. the partial and dynamic shading, so a maximum power point tracking (MPPT) approach with higher accuracy and faster response is required. In this paper, a novel configuration of large-scale PV array on green ocean-going ship is studied, and its MPPT problem is described as a large-scale optimization model. Then, a meta-heuristic optimization is employed to solve this model offline, and the model predictive control is employed to achieve the online MPPT control in real-time. Result of simulation experiments shows that the proposed configuration and MPPT approach can achieve effective performance, and also can improve the output power under complex environmental conditions significantly.

Abstract The global radiation is recorded at several stations on the Earth. The information about its spectral composition is poor. In this paper the spectral composition means the ratio of spectral global radiation measured by coloured glass filter domes to the total global radiation. From the measurements made by Klein and Goldberg it follows that the monthly ratios vary significantly from place to place, while the variations from month to month at one place are significant only at the station which lies near to the North Pole. The Budapest data proved the dominant effect of cloudiness on the spectral composition of global radiation. This effect is in good statistical relationship with the relative global radiation. The regression constant tabulated in this paper do not contain the error of zero point elevation which is due to the overheating of glass filters by the absorbed solar radiation.