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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 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 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 The J–V equation of an illuminated solar cell is implicit and recently it is shown that this equation can be expressed explicitly using rational function considering pade approximants. Here an explicit model for J–V characteristic is proposed using equivalent rational function form having two shape parameters. This model allows a simple closed form estimation of maximum power point voltage. The proposed explicit model is validated using wide variety of solar cells.

Abstract Cadmium selenide (CdSe) nanoparticles were synthesized in aqueous medium using mercaptopropionic acid (MPA) as the stabilizer at the temperature 100 °C. Air stable sodium selenite (Na2SeO3) was used as the selenium source. The synthesized particles were used to co-sensitize the TiO2 nanotubes with N3 dye. Ex-situ linker assisted method was used to sensitize the nanotubes by CdSe nanoparticles. Electrochemical anodization technique was employed to prepare TiO2 nanotubes in the presence of hydrogen fluoride (HF) as electrolyte. A solar cell was fabricated using co-sensitized TiO2 nanotubes by N3 dye/CdSe nanoparticles as the anode and platinum coated fluorine doped tin oxide (FTO) electrode as the cathode. Polysulphide ( S 2 - / S x 2 - ) mixture was used as the electrolyte. UV–Visible, SEM, AFM and TEM analysis were used to characterize the synthesized particles and TiO2 nanotubes.

Abstract The cooperative effect of hybrid Au-Ag nanoparticles and organic-inorganic cathode interfacial layers to advance the power conversion efficiency (PCE) of regio regular (rr) P3HT:PCBM based polymer solar cells (PSCs) are systematically demonstrated. In this work initially, two types of plasmonic nanoparticles (NPs), namely, citrate stabilized gold (AuNPs) and silver (AgNPs) were separately synthesized and then physically blend together with three different volume ratio [AuNPs + AgNPs (25:75), AuNPs + AgNPs (50:50) and AuNPs + AgNPs (75:25)]. These three blended NP solutions were then mixed together in the PEDOT:PSS (20 v/v %) hole extraction layer (HEL) to form three new NPs doped HEL and their effect on the rr-P3HT:PCBM based PSCs were systematically analyzed. For dual organic-inorganic cathode interfacial layers, two organic hole blocking materials, BPhen and BCP were used for enhanced charge collection in combination with LiF:Al as conventional cathode electrode. The collective effect of hybrid NPs with the dual cathode interfacial layers was examined with two varying active polymer blends, rr-P3HT:PC61BM and rr-P3HT:PC71BM. It has been found that the PCE increases considerably for both the active blend systems, with PEDOT:PSS + [AuNPs:AgNPs (25:75)] + BCP:LiF:Al as the modified cathode electrode. This is due to suitable electronic energy level matching of BCP:LiF:Al and active blend with the excellent surface plasmon property of the AuNPs:AgNPs (25:75) in the UV–Visible region compared to AuNPs:AgNPs (50:50) and AuNPs:AgNPs (75:25). Devices having configuration PEDOT:PSS + [AuNPs:AgNPs (25:75)] as HEL, rr-P3HT:PC71BM as active blend and BCP:LiF:Al provided PCE, ɳmax = 5.71% with Jsc = 16.44 mA/cm2, Voc = 0.58 V, FF = 60% and device with rr-P3HT:PC61BM as active blend layer was showing as PCE, ɳmax = 5.31% with Jsc = 14.77 mA/cm2, Voc = 0.58 V and FF = 62% with the same PEDOT:PSS + [AuNPs:AgNPs (25:75)] layer and BCP:LiF:Al. These results conclusively described a very simple technique in which the cooperative effect of plasmonic hybrid metals nanoparticles and dual cathode interfacial layers outstandingly enrich the PCE and in general the complete nature of rr-P3HT:PCBM based PSCs.

Abstract A general procedure for determining the optimum geometry of a reflector-augmented solar collector which produces a desired pattern of flux-augmentation is described. The example used for illustration is a stationary collector whose winter performance is to be improved. Consideration both a flat-plate collector with a bottom reflector and one with a top reflector led to distinct differences in their optimum configuration and performance being identified. Since either systems can be used to augment winter flux, a criterion for selecting the appropriate system is given. This criterion is based on the displacement in collector tilt from latitude inclination.

Abstract In a linear Fresnel reflector field, parallel rows of reflectors in a collector direct the incident sun rays towards a common linear receiver. Some portion of reflector aperture remains unused due to end effect, inter-row shading and blocking. In addition to these factors, cosine effect, cleanliness factor, reflectivity of reflectors, intercept factor, transmissivity of receiver cover, reflectivity of secondary reflector, absorptivity of absorber tube and thermal losses are other factors that contribute to energy losses and thus affect net energy collection by the heat transfer fluid in the absorber, electricity generation and cost of electricity. Conventionally, the collectors are oriented either along North–South or East–West directions in most cases. However the energy collection, electricity generation and cost of electricity need to be found out for all possible collector-orientations lying between North–South and East–West. This can be used in designing collectors for places where the available land strip does not align with any of these two directions. In this work, explicit analytical expressions for energy losses due to cosine effect, end effect, shading and blocking are derived for any desired time interval as functions of length ( L ) and width ( w ) of aperture of reflector-row, spacing between adjacent reflector-rows ( p ), number of reflector-rows in a collector ( n ), height of receiver ( H ), collector-orientation angle ( Ω ) and location. The expressions for the net energy collected by the working fluid, electricity generated by a collector and the cost of electricity are presented. The effects of L , w , p , n , H , Ω and location on energy losses, net energy collection by fluid, electricity generation and cost of electricity are studied. The minimum cost of electricity is found out for different collector-orientations at various locations and relative comparisons have been made. The corresponding collector parameters, annual energy collection by fluid and the annual electricity generation are also found out.