Photovoltaic materials, past, present, future

This paper traces briefly the history of this photovoltaic materials and it tries to look at possible future scenarios. A large part of the paper is concerned with silicon although from solid-state physics we know that silicon is not the ideal material for photovoltaic conversion. From the first solar cell developed at Bell Laboratories in 1954 photovoltaics was dominated by silicon. The reasons for this dominating position are investigated. Crystalline silicon today has a market share of 86% which is almost equally distributed between single crystal and cast silicon. Amorphous silicon has another 13%. The main endeavor is to reduce cost. Present trends in the crystalline field are reviewed. The conventional technology still has significant potential for cost reduction but this comes only with increasing volume. A problem to be solved is the supply of solar-grade silicon material. Other future possibilities include thin film crystalline silicon on different substrates. Because of the low absorption coefficient of silicon light trapping is required. True thin film materials need only 1–2 μm of material. Amorphous silicon, copper indium diselenide (CIS) and CdTe are hopeful approaches for very cost-effective solar cells. Some other, more speculative materials and concepts are described at the end of this paper     

Hydrogen dissociation and diffusion on transition metal (= Ti,Zr, V,Fe, Ru,Co, Rh,Ni, Pd,Cu, Ag)-doped Mg(0001) surfaces

The kinetics of hydrogen absorption by magnesium bulk is affected by two main activated processes: the dissociation of the H₂ molecule and the diffusion of atomic H into the bulk. In order to have fast absorption kinetics both activated processed need to have a low barrier. Here we report a systematic ab initio density functional theory investigation of H₂ dissociation and subsequent atomic H diffusion on TM (= Ti, V, Zr, Fe, Ru, Co, Rh, Ni, Pd, Cu, Ag)-doped Mg(0001) surfaces. The calculations show that doping the surface with TMs on the left of the periodic table eliminates the barrier for the dissociation of the molecule, but the H atoms bind very strongly to the TM, therefore hindering diffusion. Conversely, TMs on the right of the periodic table do not bind H, however, they do not reduce the barrier to dissociate H₂ significantly. Our results show that Fe, Ni and Rh, and to some extent Co and Pd, are all exceptions, combining low activation barriers for both processes, with Ni being the best possible choice.     

Solar optical properties of thin films of Cu, Ag, Au, Cr, Fe, Co, Ni and Al

The optical properties of metal coated glass substrates have been investigated. Thin films of various thicknessesof the noble metals: Cu, Ag, Au, the transition metals: Cr, Fe, Co, Ni and the free electron-like metal Al were thermally evaporated onto glass substrates. The front and backside reflectance and the transmittance between 0.35 and 15 μm were measured. The obtained data were used to calculate the integrated values of solar reflection and transmission as a function of metal film thickness. The application of metal films on domestic windows as sun-screens and heat-mirrors are discussed. It is concluded that Cu is the best coating in a window system if good heat insulating properties are desired. This is due to its ability to remain continuous at very thin film thicknesses. An infra-red reflectance of 86 per cent combined with a solar transmittance of 55 per cent was obtained for a 70film. For solar heat-protection Au-films are found to be superior owing to their transmittance peak in the middle of the visible wavelength region. The transition metals are less selective than the noble metals, but due to their flat response-curves in the visible range they cause a smaller change in colour of the transmitted and reflected light.     

Flexible, long-lived, large-area, organic solar cells

We report herein large area (>10 cm²), interconnected organic solar cell modules both on glass substrates as well as on flexible ultra-high barrier foils, reaching 1.5% and 0.5% overall power conversion efficiency under AM1.5 conditions. Series connection is described, as these modules consist of up to three cells. Using our flexible barrier material, a shelf lifetime of polythiophene-based solar cells of 6000 h could be realized. Furthermore, we compare the photovoltaic performance of efficient conjugated polymer:fullerene solar cell modules with established technologies. Under typical indoor-office lighting, our modules are competitive with these systems.     

Components,formulations, solutions,evaluation, and application of comprehensive combustion models

Development and application of comprehensive, multidimensional, computational combustion models are increasing at a significant pace across the world. While once confined to specialized research computer codes, these combustion models are becoming more readily accessible as features in commercially available computational fluid dynamics (CFD) computer codes. Simulations made with such computer codes offer great potential for use in analyzing, designing, retrofitting, and optimizing the performance of fossil-fuel combustion and conversion systems.The purpose of this paper is to provide an overview of comprehensive combustion modeling technology as applied to fossil-fuel combustion processes. This overview is divided into three main parts. First, a brief review of the state-of-the-art of the various components or submodels that are required in a comprehensive combustion model is presented. These submodels embody mathematical and numerical representations of the fundamental principles that characterize the physico-chemical phenomena of interest. The submodel review is limited to those required for characterizing non-premixed, gaseous and pulverized coal gasification and combustion processes. A summary of the submodels that are available in representative computer codes is also presented.Second, the kinds of data required to evaluate and validate the predictions of comprehensive combustion codes are considered. To be viewed with confidence, code simulations must have been rigorously evaluated and validated by comparison with appropriate experimental data, preferably from a variety of combustor geometries at various geometric scales. Three sets of validation data are discussed in detail. Two sets are from the highly instrumented, pilot-scale combustor called the controlled profile reactor (CPR) (one natural gas-fired and one coal-fired), and the other set is for a full-scale, corner-fired 85 MW_e utility boiler.Third, representative applications of comprehensive combustion models are summarized, and three sets of model simulations are compared with experimental data. The model simulations for the three test cases were made using two commonly used, CFD-based computer codes with comprehensive combustion model features, PCGC-3 and FLUENT 4.4. In addition to the standard version of FLUENT, predictions were also made with a version of FLUENT incorporating advanced submodels for coal reactions and NO pollutant formation.     

阳光·希望·成长——2009太达杯国际太阳能建筑设计竞赛作品评析

立足于灾后重建的建筑设计,必须注重低造价、低技术策略的运用,充分利用自然资源,适应可持续发展的要求.太阳能等绿色技术的融入,丰富了建筑设计的内涵,增加了可实施性.介绍了2009国际太阳能建筑设计竞赛获奖作品从基地调研、环境应对、建筑组合到技术融入的系列构思过程,从而在灾后重建过程中通过建筑传递给人们阳光与希望.     

Energy requirements for water production,treatment, end use,reclamation, and disposal

Energy is consumed at every stage of the cycle of water supply, treatment, use and disposal. The intensity of energy consumption (kW h/m³) depends upon the specific technologies applied at each stage of the water cycle. For some technologies, the intensity may be relatively low, whereas the intensity of other technologies is substantially greater. This report surveys the available literature on energy intensity for water use in the municipal and agricultural sectors and separates the process into several stages. Water supply, water treatment, residential end use, wastewater treatment, and agriculture end use are considered. Representative values of the energy consumed per unit water are given for a broad range of processes. Water extraction and pumping from ground and surface sources is considered. The energy intensity of treatment required for different types of water source is found to vary widely between the extremes of relatively fresh surface waters, which use energy mainly in pumping, and seawater, which requires desalination. Energy usage for different methods of irrigation including pressurized as well as surface irrigation is studied. The energy intensity of residential end use is very high relative to other parts of the water supply cycle. Processes such as heating water, washing clothes and dishes, and cooking are briefly studied within the water end-use stage. Hot water usage is responsible for making end use the most energy intensive stage of the water cycle. Hot water use in different buildings is briefly reviewed. Wastewater treated with various processes is considered, and the energy intensity is found to be highest when advanced wastewater treatment methods are applied. Energy consumption in the agricultural sector, which is principally related to irrigation pumping, is generally of lower energy intensity than for the municipal treatment or end use.