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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 desalination of water is a process wherein the brackish water is purified by removing the salts. With increasing demand for fresh water, there is a vast scope for development of sea water desalination process. A number of methods exist for the desalination process, but solar desalination method promises to save energy in today’s energy crunch scenario. A novel solar desalination setup is proposed here. It uses an elliptic hyperboloid concentrator and a helical receiver along with a multi-tray desalination unit to purify water in the most effective manner. The helical receiver proposed in the present work aims at the Dean Flow effect in order to enhance heat transfer in laminar flow. The effectiveness of this property with respect to various physical parameters has been observed and an optimum design has been suggested based on this. The elliptic hyperboloid concentrator is a special design for concentrating solar radiation because of it offers to operate at high efficiency without the requirement of tracking. A detailed ray-tracing code was developed to simulate the radiation incident on the concentrator and an accurate estimation of the optical efficiency was made based on this. The two systems were integrated in order to arrive at a maximum output level for the solar desalination system as a whole.

Abstract Harnessing solar energy to provide for the thermal needs of buildings is one of the most promising solutions to the global energy issue. Exploiting the additional surface area provided by the building’s facade can significantly increase the solar energy output. Developing a range of integrated and adaptable products that do not significantly affect the building’s aesthetics is vital to enabling the building integrated solar thermal market to expand and prosper. This work reviews and evaluates solar thermal facades in terms of the standard collector type, which they are based on, and their component make-up. Daily efficiency models are presented, based on a combination of the Hottel Whillier Bliss model and finite element simulation. Novel and market available solar thermal systems are also reviewed and evaluated using standard evaluation methods, based on experimentally determined parameters ISO 9806. Solar thermal collectors integrated directly into the facade benefit from the additional wall insulation at the back; displaying higher efficiencies then an identical collector offset from the facade. Unglazed solar thermal facades with high capacitance absorbers (e.g. concrete) experience a shift in peak maximum energy yield and display a lower sensitivity to ambient conditions than the traditional metallic based unglazed collectors. Glazed solar thermal facades, used for high temperature applications (domestic hot water), result in overheating of the building’s interior which can be reduced significantly through the inclusion of high quality wall insulation. For low temperature applications (preheating systems), the cheaper unglazed systems offer the most economic solution. The inclusion of brighter colour for the glazing and darker colour for the absorber shows the lowest efficiency reductions (

This article outlines several enhancements made to autonomous renewable energy systems (ARES)-I, the Cardiff School of Engineering's hybrid photovoltaic and wind energy simulation program. The resulting program, ARES-II, unlike the majority of other hybrid simulation programs, predicts the battery state of voltage (SoV) rather than its state of charge (SoC). Loss of load (LoL) occurs when the battery voltage drops below the low voltage cut off limit. Given load and weather profiles, ARES-II is able to predict the occurrence of loss of load thus giving a direct measure of the system autonomy. The enhanced model also predicts the effect of different battery temperatures on the LoL. Experimental work has shown a significant change in storage battery resistance and capacity with temperature. Incorporating battery temperature effects into the battery algorithm is a novel advancement in hybrid system voltage simulation. Further refinements have also been made to the voltage controller algorithms. Accurate modelling of the non-linear action of the low voltage controller is of paramount importance when predicting loss of load probability for hybrid systems. Combining all the above features and incorporating them into ARES-II produces a simple, accurate and reliable method for hybrid system design and LoL prediction as a function of the combined variability in the weather and load.

The aim of this work is to evaluate the potential direct and diffuse solar radiation aggregated at a point location in an urban area. With the three-dimensional (3D) SOlar RAdiation Model (SORAM) presented here, the paper makes three key contributions. Firstly, the model augments the Perez et al. (1990) model by accounting for the aggregated contribution of diffuse radiation using ray-tracing methods. Secondly, the model demonstrates the use of a randomly generated city building distribution and terrain map to simulate the 3D urban solar radiation exposure at any time or over a selected time period. Thirdly, we validate our results using empirical sunlight data measured from a real urban area (Sheffield Solar Farm), and also validate our results against the Perez et al. (1990) model under conditions of no shading.

This paper presents the development of a method to control the light output from a prototype hybrid lighting system. This system transports daylight from a heliostat with a concentrating fresnel lens to a luminaire in a windowless room, via a large core liquid fiber optic. The main artificial lighting system is located outside of the building without the possibility for dimming due to the lamp type chosen. Consequently a control strategy is needed in order to minimize the switching cycles of the lamps (severe reduction in lamp life) while at the same time maintain the lighting levels in the interior.

Abstract Building-integrated photovoltaic (BIPV) panels are emerging as a useful technology for helping to achieve net-zero energy buildings. At this time, the main drawback with BIPV systems is the cost per kilowatt per hour of electricity generated. Besides cheaper production of photovoltaic panels, increases in their efficiency can be obtained by reducing panel temperatures. This is often achieved by adding a cavity beneath the panels to allow ventilation of the rear of the panel. However, the details of airflow in the cavity and the effect on cooling have not been rigorously researched. Life-time enhancement against degradation is also an effective technique to reduce the cost of electricity generated. Moisture ingress and thermal stresses are among the primary reasons for degradation of BIPVs; these processes are directly affected by air and moisture flow around the panels. The surface temperature thermography and airflow observations performed in this work helps to understand the transport mechanisms above and below the panels. For this purpose, a novel setup was developed consisting of a building model with a mock BIPV panel plus a solar simulator placed inside an atmospheric wind tunnel. Particle image velocimetry (PIV) and infra-red thermography were performed to simultaneously monitor the surface temperature and airflow above and below the panel. The study clearly shows how the accelerated airflow within the cavity increases the heat exchange between the PV and airflow and consequently reduces the PV temperature. It is also shown that the stepped open arrangement of panels is more effective in reducing the temperature comparing to a flat arrangement. This arrangement also has a better resistant against the air and moisture ingress.

Abstract A computer modeling analysis has been undertaken of the energy savings resulting from the installation of two transwalls in a horticultural glasshouse. The transwalls in this case consist of clear plastic bags filled with a water-dye solution and contained within a steel mesh cage. The annual energy savings are in the range 20 to 15%, depending on evapotranspiration, for both sites considered, one in the West of Scotland, one in Southeast England. The higher heat load of the West of Scotland site makes it more cost effective resulting in a payback period in the range 2 1 2 to 5 1 2 years. The corresponding figures for Southeast England are 4 to 8 years. The optimum thickness of the transwall is 15 cm, and the optimum dye concentration is 20 ppm of Lissamine Red 3GX.