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Abstract Thermal performance of three naturally ventilated public buildings in which the wind tower is an important architectural freature is studied. One of the three builidings as well as it's wind tower is instrumented for temperature, relative humidity and airflow velocity measurements, and the other two are instrumented for temperature measurement. The results have led to a discussion concerning the degree of wind tower effectiveness in achieving thermal comfort.

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 Solar water evaporation has been a topic of interest in recent years due to its applications in desalination, power generation, and heating. As water is not a good absorber of light, seeding it with light-absorbing particles can enhance evaporation efficiency. Activated carbon (AC) is one such material with desirable absorption properties for this application. However, particle sizes in granular and powder activated carbon can vary significantly. In this work, AC particles of different sizes are analyzed and their effect on evaporation rate is studied. It is found that particle sizes less than or comparable to solar wavelength spectrum produce higher evaporation efficiencies under independent scattering conditions ( f v 0.6 % ). It is also found that the solar absorption coefficient reaches between 0.98 and 0.9 for a volume fraction as low as 0.01%. The evaporation efficiency is 57.3% and 38.2% higher than for pure water evaporation for size of 80 nm and 8 μm, respectively, for a volume fraction of 0.01%. A parametric analysis is performed to identify the respective effect on evaporation rate.

Abstract In this paper we propose a time-dependent, three-dimensional model for the efficiency of a nanofluid-based direct-absorption parabolic trough solar collector under a turbulent flow regime. The model consists of a system of equations: a partial differential equation for conservation of energy, and a time-dependent radiative transport equation describing the propagation of solar radiation through the nanofluid. Writing the model in dimensionless form reveals four controlling dimensionless numbers: one describing the relative importance of conduction and advection and three describing the heat loss to the surroundings. Realistic parameter values are applied to reduce the model further and these indicate that two of the dimensionless groups have a much smaller impact on the performance of the solar collector. We use the resulting solution for the temperature to calculate an analytic expression for the collector’s efficiency. This expression permits optimisation of design parameters such as particle loading, incoming radiative intensity, receiver dimensions, the inlet temperature, and solar concentration ratio.

Abstract The factors determining the efficiency of a single-effect, horizontal solar still are presented in terms of component efficiencies. From a knowledge of the equations governing the internal and external heat transfer it is possible to postulate an ideal solar still whose efficiency is the ultimate attainable. This indicates that an efficiency of about 60 per cent is the upper limit. Experimental work with a high efficiency solar still has shown that in practical installations it is highly unlikely that efficiencies much greater than 50 per cent would be attained.

Abstract The vacuum solar receiver is the key component of a parabolic trough solar plant, which plays a prominent role in the gross system efficiency. Recently, China’s first high temperature vacuum receiver, Sanle-3 HCE, has been developed and produced by Southeast University and Sanle Electronic Group. Before being utilized in China’s first parabolic trough solar plant, accurately estimating the thermal properties of this new receiver is important. This paper first establishes and optimizes a 1-D theoretical model at Matlab program to compute the receiver’s major heat loss through glass envelope, and then systematically analyzes the major influence factors of heat loss. With the laboratorial steady state test stand, the heat losses of both good vacuum and non-vacuum Sanle-3 receivers were surveyed. Comparison shows the original 1-D model agrees with the ends covered test while remarkably deviating from end exposed test. For the purpose of identifying the influence of receiver’s end to total heat loss, an additional 3-D model is built by CFD software to further investigate the different heat transfer processes of receiver’s end components. The 3-D end model is verified by heating power and IR temperature distribution images in the test. Combining the optimized 1-D model with the new 3-D end model, the comparison with test data shows a good accordance. At the same time the heat loss curve and emittance curve of this new receiver are given and compared with those of several other existing receivers as references.

Abstract A new method of tracking the maximum power point (MPP) of a photovoltaic (PV) module exploiting the effects of the inherent characteristic resistances of the photovoltaic cells is proposed in this paper. An analysis of the mathematical model of the IV characteristic of the PV module revealed a possibility of estimating the MPP from its characteristic parameters such as the open circuit voltage (Voc), short circuit current (Isc), series resistance (Rse) and the shunt resistance (Rsh). The first stage of estimation process, for obtaining the voltage at the MPP, was facilitated by the effects of the series and shunt resistance on the IV characteristic of the PV module and the second stage of estimation process was facilitated by the combined process of the first stage of estimation and the condition for extracting the maximum power from the mathematical model of the pv characteristic of the PV module. The estimated voltage at the MPP in the second stage of estimation was found very close to the true MPP. The effectiveness of tracking the MPP with the proposed method has closely matched with the true MPP. This was validated by the results obtained through simulations and experiments. An analysis of the effects of degradation on the performance of the proposed technique showed that the performance was excellent during the first few years and with the update of characteristic resistances in the proposed algorithm the performance was found to be almost invariant. The successful experimental results obtained with a 100 Wp PV module indicate that the technique can be favourably implemented for standalone PV power systems.

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 Recently bifacial n-type passivated emitter and rear totally diffused (PERT) monocrystalline silicon solar cells have become one hot spot in photovoltaic (PV) industries, due to good bifaciality, high and stabilised conversion efficiency. Unlike passivated emitter and rear contacts (PERC) structure, n-PERT solar cells require the use of a thin and uniform back surface field (BSF) layer, usually achieved by phosphorus doping. In this study, we optimised the phosphorus diffusion process in terms of surface concentration, junction depth and carrier lifetime. The effects of different phosphorus BSF were investigated by fabricating n-type front and back contact (nFAB) PERT solar cells using industrial feasible approaches and M2 size Czochralski (Cz) monocrystalline Si wafers (6 in., 244.32 cm2). Good phosphorus profiles were developed, which gives low parasitic absorption, low contact resistance and low J0 value when passivated with silicon nitride (SiNx) layer. The optimised champion cell shows a high Voc of 666.5 mV, Jsc of 40.2 mA/cm2, fill factor of 79.9%, efficiency of 21.43% from front side-illumination, together with a good bifaciality factor of 93.0%.