Optimization of number of collectors for integrated PV/T hybrid active solar still

The aim of this paper is to optimize the number of collectors for PV/T hybrid active solar still. The number of PV/T collectors connected in series has been integrated with the basin of solar still. The optimization of number of collectors for different heat capacity of water has been carried out on the basis of energy and exergy. Expressions of inner glass, outer glass and water temperature have been derived for the hybrid active solar system. For the numerical computations data of a summer day (May 22, 2008) for Delhi climatic condition have been used. It has been observed that with increase of the mass of water in the basin increases the optimum number of collector. However the daily and exergy efficiency decreases linearly and nonlinearly with increase of water mass. It has been observed that the maximum yield occurs at N = 4 for 50 kg of water mass on the basis of exergy efficiency. The thermal model has also been experimentally validated.     

Exergetic utilization of solar energy for feed water preheating in a conventional thermal power plant

This communication is based on exergy concept for the utilization of solar thermal energy in a Rankine cycle‐based fuel‐fired thermal power plant (FFTPP). It has been shown that solar thermal energy as an aided source for feed water preheating helps to reduce the exergy loss in feed water heater (FWH) of Rankine cycle and develops more work than that could have been produced in a solar thermal power plant (STPP). It has been found that this enhancement in work increases for low‐pressure FWHs. For further illustration, a case study has been carried out of a typical 50 kW STPP and a 220 MW FFTPP. The effect of utilizing the same input solar thermal energy of typical STPP, if used as an aided source in a 220 MW FFTPP for feed water preheating is investigated. The work output of STPP is 59.312 kW, while the extra work output of FFTPP by using solar thermal energy of STPP is 90.27 kW. It has been found that the efficiency of work conversion of aided solar thermal energy in FFTPP is higher than the efficiency of work conversion in STPP. Copyright © 2009 John Wiley & Sons, Ltd.     

The fabrication of efficiency-improved W-series interconnect type of module by balancing the performance of single cells

Large dye-sensitized solar cells (DSCs) are usually fabricated as module types instead of single cell types, because the overall efficiency of an area-expanded single DSC is decreased by its large surface resistances and low fill factor (FF). The general DSC module designs are the parallel grid, series interconnect, and series monolithic types. The W-series interconnect type of module has some advantages, such as its easy fabrication and simple structure. Moreover, it also avoids the reduction in the FF. However, it has an efficiency imbalance between the single cells, because of the discrepancy in their luminous intensity. Therefore, the fabrication of the W-series interconnect type of module will be cost-effective only if the problem of its efficiency imbalance is solved. In this study, the thickness of the Pt layer, which has a very high reflection rate, and that of the electrolyte layer are minimized and the transmitted light is reflected by a metallic thin film in order to increase the number of photons absorbed by the dye molecules in the module. As a result, the performance of the efficiency-balanced W-module is improved by approximately 1% as compared to that of the conventional module.     

Improved Jsc in CIGS thin film solar cells using a transparent conducting ZnO:B window layer

A comparative study of the cell performance of CIGS thin-film solar cells fabricated using ZnO:Al and ZnO:B window layers has been carried out. ZnO:B films were deposited by RF magnetron sputtering using an undoped ZnO target in a B₂H₆–Ar gas mixture. The short-circuit current (J_sc) was found to improve upon the replacement of the ZnO:Al layer with ZnO:B layers. This improvement in J_sc is attributed to an increase in quantum efficiency due to the higher optical transmission of the ZnO:B layer in the near-infrared region. The best cell fabricated with a MgF₂/ZnO:B/i-ZnO/CdS/CIGS/Mo structure yielded an active area efficiency of 18.0% with V_oc=0.645 V, J_sc=36.8 mA/cm², FF=0.76, and an active area of 0.2 cm² under AM 1.5 illumination.     

利用太阳能进行地板供暖的探讨

介绍了地板供暖的特点,直接及间接利用太阳能进行地板供暖的几种形式、工作原理、施工操作要点和技术经济情况。     

Space and time evolution of the plasma in a PDP cell: Comparisons between simulations and experiments

We have used a macroscopic discharge cell to study the space and time evolution of the plasma in geometry similar to real matrix and coplanar PDP cells with a scaling factor of around 100 (dimensions 100 times larger, pressure 100 times smaller, i.e., 1‐cm gap length, 5‐torr pressure). Discharges in pure neon and in a xenon‐neon mixture with 10% xenon have been investigated. The measurements have been compared with results from a two‐dimensional fluid model of the discharge.     

Multilayered large‐area WO3 films on sheet and mesh‐type stainless steel substrates for photoelectrochemical hydrogen generation

The objective of this study is to demonstrate the significant improvement in the photoelectrochemical (PEC) hydrogen generation by a photoanode owing to the increased surface area of the substrate. In this work, multilayered tungsten oxide (WO₃) films have been successfully synthesized onto the large‐area sheet (9 × 9cm²) and mesh (1 × 20cm²) ‐type stainless steel (SS) substrates using screen printing and brush painting methods, respectively. All the WO₃ films are porous and nanocrystalline (30–80 nm) in nature with a monoclinic crystal structure as revealed from X‐ray diffraction and scanning electron microscopy studies. The PEC water splitting study is performed under simulated 1 SUN illumination (AM1.5 G) in a typical two‐electrode cell configuration with WO₃ photoanode and Pt wire immersed in 0.5 M H₂SO₄ electrolyte. The photocurrent as well as hydrogen generation rate for WO₃ photoanodes coated on the plane SS sheet substrate is relatively low and showed minimal change with increasing film thickness. On the other hand, the photocurrent as well as the hydrogen generation is enhanced by a 3–4 fold degree for the WO₃ photoanodes coated on SS mesh. We attribute such efficient water splitting to the increment in the filling factor of the WO₃ material due to the large effective surface area of the SS mesh as compared to the SS sheet substrate. Copyright © 2011 John Wiley & Sons, Ltd.     

Improved efficiency of Al0.36Ga0.64As solar cells with a ppnn structure

Improvement of efficiency of Al_0.36Ga_0.64As solar cells is advanced in two aspects of minority-carrier lifetime: reduction of majority-carrier concentration in the emitter and base layers, and reduction of deep levels in the back-surface-field (BSF) layer. A pp⁻n⁻n structure is proposed to optimize the use of the effect of reduced majority-carrier concentration, and its effectiveness verified in a preparatory experiment on Al_0.3Ga_0.7As solar cells. A very poor photoluminescence (PL) decay time (below 0.3 ns) of a BSF layer heavily doped with Si becomes 14-fold longer when Se is applied to the dopant instead of Si, resulting in an improvement of the external quantum efficiency near the absorption edge. These two aspects of this study lead to the realization of 16.6% efficiency under 1-sun, AM 1.5 global conditions with an Al_0.36Ga_0.64As solar cell.     

Thin-film encapsulation of polymer-based bulk-heterojunction photovoltaic cells by atomic layer deposition

This study demonstrated thin-film encapsulation of bulk-heterojunction polymer photovoltaic cells, utilizing a process based on atomic layer deposition (ALD) that both prevented degradation caused by ambient gases and served as an annealing step that increased the initial efficiency of the cells. With the ALD temperature set at 140 °C and the total deposition time set at 1 h, the photovoltaic cells, based on blended poly-3-hexylthiophene (P3HT) and [6,6]-phenyl C₆₁ butyric acid methylester (PCBM), were optimally annealed during encapsulation, achieving a power conversion efficiency (PCE) of 3.66%. Encapsulating the cells with a 26 nm Al₂O₃/HfO₂ nanolaminated film overcoated with an epoxy resin protection layer enabled the cells to obtain an in-air degradation rate that was similar to cells that were stored in nominally O₂/H₂O-free atmosphere. The nanolaminated structure of the encapsulation film resolved the issue of hydrolysis-induced aging observed with Al₂O₃ films, owing to the hydrophobicity of the HfO₂ layers. Additionally, extended exposure of the ALD precursors during the ALD process significantly improved the coverage of the ALD films over the P3HT/PCBM active layer at the perimeter of the cells.