			Home About us Contact

Solar Energy (solar + energy)

Distribution by Scientific Domains

Engineering	32%
Chemistry	32%
Life Sciences	16%
Polymers and Materials Science	12%
Earth and Environmental Science	6%

Terms modified by Solar Energy

solar energy conversion

Selected Abstracts

Integration of Solar Energy into Absorption Refrigerators and Industrial Processes

CHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 9 2010
E. A. Tora
Abstract Absorption refrigeration is gaining increasing attention in industrial facilities to use process heat for partially or completely driving a cooling cycle. This paper introduces a systematic approach to the design of absorption refrigeration systems for industrial processes. Three sources of energy are considered to drive absorption refrigerators: excess process heat, solar energy, and fossil fuels. To handle the dynamic nature of solar energy, hot water tanks are used for energy storage and dispatch. Thermal pinch analysis is performed to determine the amount of available excess heat and the required refrigeration duty. Next, a multiperiod optimization formulation is developed for the entire system. The procedure determines the optimal mix of energy forms (solar versus fossil) and the dynamic operation of the system. Three case studies are solved to demonstrate the effectiveness and applicability of the devised procedure. [source]

Thinnest Two-Dimensional Nanomaterial,Graphene for Solar Energy

CHEMSUSCHEM CHEMISTRY AND SUSTAINABILITY, ENERGY & MATERIALS, Issue 7 2010
Yun Hang Hu Prof.
Abstract Graphene is a rapidly rising star in materials science. This two-dimensional material exhibits unique properties, such as low resistance, excellent optical transmittance, and high mechanical and chemical stabilities. These exceptional advantages possess great promise for its potential applications in photovoltaic devices. In this Review, we present the status of graphene research for solar energy with emphasis on solar cells. Firstly, the preparation and properties of graphene are described. Secondly, applications of graphene as transparent conductive electrodes and counter electrodes are presented. Thirdly, graphene-based electron- (or hole) accepting materials for solar energy conversion are evaluated. Fourthly, the promoting effect of graphene on photovoltaic devices and the photocatalytic property of graphene,semiconductor composites are discussed. Finally, the challenges to increase the power conversion efficiency of graphene-based solar cells are explored. [source]

Heterointegration of Pt/Si/Ag Nanowire Photodiodes and Their Photocatalytic Properties

ADVANCED FUNCTIONAL MATERIALS, Issue 18 2010
Yongquan Qu
Abstract Photocatalyst mediated photoelectrochemical processes can make use of the photogenerated electrons and holes onsite for photocatalytic redox reactions, and enable the harness and conversion of solar energy into chemical energy, in analogy to natural photosynthesis. However, the photocatalysts available to date are limited by either poor efficiency in the visible light range or insufficient photoelectrochemical stability. Here, it is shown that a Pt/Si/Ag nanowire heterostructure can be rationally synthesized to integrate a nanoscale metal-semiconductor Schottky diode encased in a protective insulating shell with two exposed metal catalysts. The synthesis of Pt/Si/Ag nanowire diodes involves a scalable process including the formation of silicon nanowire array through wet chemical etching, electrodeposition of platinum and photoreduction of silver. The Pt/Si/Ag diodes exhibit highly efficient photocatalytic activity for a wide range of applications including environmental remediation and solar fuel production in the visible range. In this article, photodegradation of indigo carmine and 4-nitrophenol are used to evaluate the photoactivity of Pt/Si/Ag diodes. The Pt/Si/Ag diodes also show high activity for photoconversion of formic acid into carbon dioxide and hydrogen. [source]

Heterointegration of Pt/Si/Ag Nanowire Photodiodes and Their Photocatalytic Properties

Bio-inspired Photoelectric Conversion Based on Smart-Gating Nanochannels

ADVANCED FUNCTIONAL MATERIALS, Issue 16 2010
Liping Wen
Abstract Inspired by the light-driven, cross-membrane proton pump of biological systems, a photoelectric conversion system based on a smart-gating, proton-driven nanochannel is constructed. In this system, solar energy is the only source of cross-membrane proton motive force that induces a diffusion potential and photocurrent flowing through the external circuit. Although the obtained photoelectric conversion performance is lower than that of conventional solid photovoltaic devices, it is believed that higher efficiencies can be generated by enhancing the protonation capacity of the photo-acid molecules, optimizing the membrane, and synthesizing high-performance photosensitive molecules. This type of facile and environmentally friendly photoelectric conversion has potential applications for future energy demands such as the production of power for in vivo medical devices. [source]

Enzymatic deconstruction of xylan for biofuel production

GCB BIOENERGY, Issue 1 2009
DYLAN DODD
Abstract The combustion of fossil-derived fuels has a significant impact on atmospheric carbon dioxide (CO2) levels and correspondingly is an important contributor to anthropogenic global climate change. Plants have evolved photosynthetic mechanisms in which solar energy is used to fix CO2 into carbohydrates. Thus, combustion of biofuels, derived from plant biomass, can be considered a potentially carbon neutral process. One of the major limitations for efficient conversion of plant biomass to biofuels is the recalcitrant nature of the plant cell wall, which is composed mostly of lignocellulosic materials (lignin, cellulose, and hemicellulose). The heteropolymer xylan represents the most abundant hemicellulosic polysaccharide and is composed primarily of xylose, arabinose, and glucuronic acid. Microbes have evolved a plethora of enzymatic strategies for hydrolyzing xylan into its constituent sugars for subsequent fermentation to biofuels. Therefore, microorganisms are considered an important source of biocatalysts in the emerging biofuel industry. To produce an optimized enzymatic cocktail for xylan deconstruction, it will be valuable to gain insight at the molecular level of the chemical linkages and the mechanisms by which these enzymes recognize their substrates and catalyze their reactions. Recent advances in genomics, proteomics, and structural biology have revolutionized our understanding of the microbial xylanolytic enzymes. This review focuses on current understanding of the molecular basis for substrate specificity and catalysis by enzymes involved in xylan deconstruction. [source]

UV and global solar radiation in ,ód,, Central Poland

INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 1 2010
Agnieszka Podstawczy
Abstract With the overall aim of quantifying urban atmospheric effects on different parts of the solar spectrum, a multi year analysis of data collected at ,ód, was undertaken. UV (290,400 nm) and global solar radiation measured by means of a Kipp and Zonen CUV3 radiometer and a Kipp and Zonen CM11 pyranometer in the center of ,ód, between 1997 and 2001 are analysed. The mean annual sum of global and UV solar radiation equaled 3710.8 MJ m,2 and 154.1 MJ m,2, respectively. The minimum monthly total of solar energy occurred in December (48.7 M Jm,2,global; 2.1 MJ m,2,UV); however, the maximum monthly total occurred atypically in May (620.9 MJ m,2,global; 25.3 MJ m,2,UV). UV clearness index (Kuv) is approximately half of the clearness index of the global solar radiation, indicating greater attenuation of that part of the spectrum (Kuv 0.14 in December to 0.26 in May). A linear regression model was fitted to the daily values of UV and global (g) solar irradiation (Duv = a + Dgb). The slope coefficient b and the coefficient of determination equal 0.039 and 0.98, respectively. Cloudiness exerts an important control on the solar radiation flux at the ground level and for the relation between UV and global solar radiation. The convective clouds caused an increase of global and UV solar irradiance by about 10,20% compared to clear days, the enhancement resulting from reflections. On clear days, UV comprises 3.3,4% of global solar irradiance (10-min values) on average, while during cloudy weather it increases to 8%. The results presented have implications for understanding the radiative transfer of UV and global solar radiation in the atmosphere over an urban area and the influence of clouds on transmission of solar radiation flux. Copyright © 2009 Royal Meteorological Society [source]

Improved Stirling engine performance through displacer surface treatment

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 3 2010
Halit Karabulut
Abstract This study intended to improve the performance of the beta-type Stirling engine, being developed by the authors for solar energy and low-grade heat sources, by means of displacer surface treatments. Three different displacers were manufactured and tested where one of them was without any surface treatment, other was zirconium coated with 0.15,mm thickness, and the other was helically knurled with 0.30,mm track depth. Because of good thermo-physical properties, helium was used as the working fluid. The heat was supplied by an LPG burner. Tests were conducted at 360±10°C hot end temperature. The highest engine power was obtained with knurled displacer as 250,W at 545,rpm speed and corresponding to this power 4.38,Nm torque was obtained. This was followed by coated and smooth displacers. Power increments provided by the knurled displacer are 40 and 60% compared with the zirconium-coated and untreated displacers. Increments of knurled displacer's torque compared with that of coated and untreated displacers are 13 and 30%, respectively. Copyright © 2009 John Wiley & Sons, Ltd. [source]

A closed-loop proposal for hydrogen generation using steel waste and a prototype solar concentrator

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 5 2009
Abdul-Majeed Azad
Abstract An economically viable and environmental-friendly method of generating PEM grade hydrogen has been proposed and is by the reaction of certain metals with steam, appropriately called ,metal,steam reforming',MSR. The drawbacks of conventional processes (hydrogen and carbothermic reduction schemes) are overcome by resorting to solution-based reduction schemes and are made economically feasible using iron oxides from steel industry's mill-scale waste. A novel aqueous-based room temperature technique using sodium borohydride (NaBH4) as the reducing agent has been developed that produces highly active nanoscale iron particles (,40,nm). By using hydrazine as an inexpensive and, compared with NaBH4, more stable reductant, body centered cubic iron particles with ,5,nm edges were obtained via solvothermal process under mild conditions from acid digested mill-scale waste. The nanoscale zerovalent iron (nZVI) powder showed improved kinetics and greater propensity for hydrogen generation than the coarser microscale iron. The rate constants for the MSR were obtained for all the reduction schemes employed in this work and are given by khydrogen=0.0158,min,1kcarbon=0.0248,min,1ksodiumborohydride=0.0521,min,1 and khydrazine=0.1454,min,1, assuming first order kinetics. Another innovative effort converted the magnetite waste directly into nZVI under solvothermal conditions, thus obviating the sluggish and time-consuming acid dissolution step. This particular aspect has significant ramification in terms of time and cost of making the iron precursor. To initiate and sustain the somewhat endothermic MSR process, a solar concentrator consisting of a convex polyacrylic bowl with reflective aluminum coating was fabricated and evaluated. This unique combination of mill-scale waste as iron source, hydrazine as reductant, mild process conditions and solar energy as the MSR actuator obviates several drawbacks plaguing the grand scheme of producing and delivering pure and humidified H2 to a PEMFC stack. Copyright © 2008 John Wiley & Sons, Ltd. [source]

The effects of momentum diffusers and flow guides on the efficiency of stratified hot water seasonal heat stores

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 10 2008
V. Panthalookaran
Abstract Hot water seasonal heat stores (HWSHS) carry the solar thermal energy from energy-rich seasons of the year over to energy-poor seasons so as to ensure the availability of solar energy throughout the year. Momentum diffusers and flow guides are designed to charge and discharge the harvested solar thermal energy within HWSHS in a stratified manner to enhance the efficiency of the solar systems. To evaluate the efficiency of an HWSHS, a characterization scheme developed for general stratified thermal energy stores (TES) (Sol Energy 2007; 81:1043,1054) is used. It addresses the First Law and Second Law concerns over a TES simultaneously. This study is confined to systems that use the same nozzles at fixed positions in both charging and discharging cycles. Different parameters related to axial, conical and radial diffusers as well as a variety of flow-guide designs are studied. The results suggest that a nozzle that brings about better diffuser action by minimizing entropy generation may not necessarily improve the energy response and guarantee better overall efficiency of the HWSHS. Of all, the different nozzle designs experimented with the conical diffusers with smaller angles of diffusion produced the best overall efficiency. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Analytical and numerical investigation of the solar chimney power plant systems

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 11 2006
Ming Tingzhen
Abstract There is a surge in the use of the solar chimney power plant in the recent years which accomplishes the task of converting solar energy into kinetic energy. As the existing models are insufficient to accurately describe the mechanism, a more comprehensive model is advanced in this paper to evaluate the performance of a solar chimney power plant system, in which the effects of various parameters on the relative static pressure, driving force, power output and efficiency have been further investigated. Using the solar chimney prototype in Manzanares, Spain, as a practical example, the numerical studies are performed to explore the geometric modifications on the system performance, which show reasonable agreement with the analytical model. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Numerical and analytical calculations of the temperature and flow field in the upwind power plant

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 6 2004
Henry Pastohr
Abstract The upwind power plant is an interesting system to generate electrical power from free solar energy. The authors have carried out an analysis to improve the description of the operation mode and efficiency. The pressure drop at the turbine and the mass flow rate have a decisive influence on the efficiency. This can be determined only by coupling of all parts of an upwind power plant. In this study the parts ground, collector, chimney and turbine are modelled together numerically. The basis for all sections is the numerical CFD programme FLUENT. This programme solves the basic equations of the thermal fluid dynamics. Model development and parameter studies particularly arise with this tool. Additional to the calculations using FLUENT a simple model is developed for comparison purposes and parameter studies. The numerical results with FLUENT compare well with the results given by the simple model, therefore, we can use the simple model for parameter studies. The basis for the geometry is the prototype Manzanares. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Comparison of energy and exergy efficiencies of an underground solar thermal storage system

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 4 2004
H. Hüseyin Öztürk
Abstract In this experimental study, solar energy was stored daily using the volcanic material with the sensible heat technique. The external heat collection unit consisted of 27 m2 of south-facing solar air collectors mounted at a 55° tilt angle. The dimensions of the packed-bed heat storage unit were 6 × 2 × 0.6 m deep. The packed-bed heat storage unit was built under the soil. The heat storage unit was filled with 6480 kg of volcanic material. Energy and exergy analyses were applied in order to evaluate the system efficiency. During the charging periods, the average daily rates of thermal energy and exergy stored in the heat storage unit were 1242 and 36.33 W, respectively. Since the rate of exergy depends on the temperature of the heat transfer fluid and surrounding, the rate of exergy increased as the difference between the inlet and outlet temperatures of the heat transfer fluid increased during the charging periods. It was found that the average daily net energy and exergy efficiencies in the charging periods were 39.7 and 2.03%, respectively. The average daily net energy efficiency of the heat storage system remained nearly constant during the charging periods. The maximum energy and exergy efficiencies of the heat storage system were 52.9 and 4.9%, respectively. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Operational results of an intermittent absorption cooling unit

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 9 2002
Ali R. El-GhalbanArticle first published online: 15 JUL 200
Abstract The concept of solar cooling is appealing because the cooling load is in phase with the intensity of solar energy. Many system arrangements or cycles are employed to achieve solar cooling, such as Absorption, desiccant or Rankine-vapour compression systems. The technical feasibility of driving an absorption-cooling unit by a low-temperature heat source (such as solar energy using a simple flat-plate collector) for air-conditioning applications is investigated in this work. This study aims to design and construct a prototype for an intermittent absorption refrigeration system and to examine its implementation. The operating characteristics of the considered unit are extensively investigated. In order to accomplish this strategy, the prototype was integrated in a test rig designed for this purpose and equipped with the necessary measuring instruments to determine the required operating criteria of the unit. The energy added or extracted to or from the different unit components is calculated and the system performance is analysed. The C.O.P of the unit is found to be 19% which is 2% lower than the designed value, which could be regarded as an encouraging result for more studies in this field. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Fundamentals of exergy analysis, entropy generation minimization, and the generation of flow architecture

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 7 2002
Adrian Bejan
Abstract This paper outlines the fundamentals of the methods of exergy analysis and entropy generation minimization (or thermodynamic optimization,the minimization of exergy destruction). The paper begins with a review of the concept of irreversibility, entropy generation, or exergy destruction. Examples illustrate the accounting for exergy flows and accumulation in closed systems, open systems, heat transfer processes, and power and refrigeration plants. The proportionality between exergy destruction and entropy generation sends the designer in search of improved thermodynamic performance subject to finite-size constraints and specified environmental conditions. Examples are drawn from energy storage systems for sensible heat and latent heat, solar energy, and the generation of maximum power in a power plant model with finite heat transfer surface inventory. It is shown that the physical structure (geometric configuration, topology) of the system springs out of the process of global thermodynamic optimization subject to global constraints. This principle generates structure not only in engineering but also in physics and biology (constructal theory). Copyright © 2002 John Wiley & Sons, Ltd. [source]

CFD modelling and experimental investigation of an ejector refrigeration system using methanol as the working fluid

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 2 2001
S. B. Riffat
Abstract This paper presents results of computational fluid dynamic (CFD) analysis and experimental investigation of an ejector refrigeration system using methanol as the working fluid. The CFD modelling was used to investigate the effect of the relative position of the primary nozzle exit within the mixing chamber on the performance of the ejector. The results of the CFD were used to obtain the optimum geometry of the ejector, which was then used to design, construct and test a small-scale experimental ejector refrigeration system. Methanol was used as the working fluid, as it has the advantage of being an ,environmentally friendly' refrigerant that does not contribute to global warming and ozone layer depletion. In addition, use of methanol allows the ejector refrigeration system to produce cooling at temperatures below the freezing point of the water, which of course would not be possible with a water ejector refrigeration system. CFD results showed that positioning the nozzle exit at least 0.21 length of the mixing chamber throat's diameter upstream of the entrance of the mixing chamber gave better performance than pushing it into the mixing chamber. Experimental values of coefficient of performance (COP) between 0.2 and 0.4 were obtained at operating conditions achievable using low-grade heat such as solar energy and waste heat. Copyright © 2001 John Wiley & Sons, Ltd. [source]

DRYING EFFECTS OF TWO AIR-DRYING SHELTERS IN A PILOT TEST ON SULTANA GRAPES

JOURNAL OF FOOD PROCESS ENGINEERING, Issue 1 2010
LINGLING LI
ABSTRACT The drying effects of sultana grapes in two different air-drying shelters were tested and analyzed. Ten different thin-layer drying mathematical models were compared according to their coefficients of determination and,2test. The Wang and Singh model was found to be the most suitable for describing the air-drying curves of sultana grapes. As compared with the local traditional shelter, the reformed shelter with a greenhouse can reduce about 12,18% of air-drying time, increase about 23% in green-grade rate of raisins and increase 33% in the effective moisture diffusivity of sultana grapes. PRACTICAL APPLICATIONS Grapes are one of the most popular and palatable fruits in the world. The preservation of grapes by drying is a major industry in many parts of the world where grapes are grown. Drying grapes, either by open sun drying, shade drying or mechanical drying, produces raisins. Air-drying of solar energy has been demonstrated to be cost-effective and could be an effective alternative to traditional and mechanical drying systems, especially in locations with good sunshine during the harvest season. The traditional air-drying shelter of grapes has been used for thousands of years in Asia and other places around the world. However, less investigation was done about the drying characteristics and the optimization of the shelter. The work of this manuscript provides interesting information that is useful for design of the drying shelter of raisins and for the improvement of raisin quality, especially using air-drying of solar energy. [source]

A simple device for the evaluation of the UV radiation index

METEOROLOGICAL APPLICATIONS, Issue 2 2003
Giuseppe Rocco Casale
The solar ultraviolet radiation (UV) flux density at the earth's surface depends on the incoming solar energy and the transmission properties of the atmosphere. UV radiation is strongly absorbed by ozone in the spectral range 200,310 nm, while the attenuation is increasingly weaker at longer wavelengths. Following the discovery of the Antarctic ozone hole in 1985, the risk of a possible UV increase at ground level, due to the observed stratospheric ozone depletion, has heightened the interest within the scientific community given the potentially harmful effects on terrestrial and aquatic ecosystems. Spectroradiometers, broad-band meters and dosimeters may be used for measurements of solar UV. In addition, radiation transfer models can be used to quantify UV irradiances at various times and locations, provided that the extraterrestrial solar radiation and the state of the atmosphere are known. Information about UV radiation at the earth's surface is given by the ultraviolet index ,UVI', which is defined as the effective integrated irradiance (280,400 nm) weighted by the erythemal action spectrum. The UV Index is widely used by many international weather services as an indicator of UV levels at the earth's surface providing public awareness of the effects of prolonged exposure to the sun's rays. The aim of this paper is to present a device capable of estimating the UV Index. This device is a compact disc, used as a sundial, and is based on modelled UV irradiances derived from the STAR radiative transfer model (System for Transfer of Atmospheric Radiation). The device was tested in an urban setting under clear sky conditions. Copyright © 2003 Royal Meteorological Society [source]

Light-driven Hydrogen Production by a Hybrid Complex of a [NiFe]-Hydrogenase and the Cyanobacterial Photosystem I

PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 3 2006
Masaki Ihara
ABSTRACT In order to generate renewable and clean fuels, increasing efforts are focused on the exploitation of photosynthetic microorganisms for the production of molecular hydrogen from water and light. In this study we engineered a ,hard-wired' protein complex consisting of a hydrogenase and photosystem I (hydrogenase-PSI complex) as a direct light-to-hydrogen conversion system. The key component was an artificial fusion protein composed of the membrane-bound [NiFe] hydrogenase from the ,-proteobacterium Ralstonia eutropha H16 and the peripheral PSI subunit PsaE of the cyanobacterium Thermosy-nechococcus elongatus. The resulting hydrogenase-PsaE fusion protein associated with PsaE-free PSI spontaneously, thereby forming a hydrogenase-PSI complex as confirmed by sucrosegradient ultracentrifuge and immunoblot analysis. The hydrogenase-PSI complex displayed light-driven hydrogen production at a rate of 0.58 ,mol H2· mg chlorophyll,1· h,1. The complex maintained its accessibility to the native electron acceptor ferredoxin. This study provides the first example of a light-driven enzymatic reaction by an artificial complex between a redox enzyme and photosystem I and represents an important step on the way to design a photosynthetic organism that efficiently converts solar energy and water into hydrogen. [source]

Engineering photosynthetic light capture: impacts on improved solar energy to biomass conversion

PLANT BIOTECHNOLOGY JOURNAL, Issue 6 2007
Jan H. Mussgnug
Summary The main function of the photosynthetic process is to capture solar energy and to store it in the form of chemical ,fuels'. Increasingly, the photosynthetic machinery is being used for the production of biofuels such as bio-ethanol, biodiesel and bio-H2. Fuel production efficiency is directly dependent on the solar photon capture and conversion efficiency of the system. Green algae (e.g. Chlamydomonas reinhardtii) have evolved genetic strategies to assemble large light-harvesting antenna complexes (LHC) to maximize light capture under low-light conditions, with the downside that under high solar irradiance, most of the absorbed photons are wasted as fluorescence and heat to protect against photodamage. This limits the production process efficiency of mass culture. We applied RNAi technology to down-regulate the entire LHC gene family simultaneously to reduce energy losses by fluorescence and heat. The mutant Stm3LR3 had significantly reduced levels of LHCI and LHCII mRNAs and proteins while chlorophyll and pigment synthesis was functional. The grana were markedly less tightly stacked, consistent with the role of LHCII. Stm3LR3 also exhibited reduced levels of fluorescence, a higher photosynthetic quantum yield and a reduced sensitivity to photoinhibition, resulting in an increased efficiency of cell cultivation under elevated light conditions. Collectively, these properties offer three advantages in terms of algal bioreactor efficiency under natural high-light levels: (i) reduced fluorescence and LHC-dependent heat losses and thus increased photosynthetic efficiencies under high-light conditions; (ii) improved light penetration properties; and (iii) potentially reduced risk of oxidative photodamage of PSII. [source]

Light use efficiency of dry matter gain in five macro-lichens: relative impact of microclimate conditions and species-specific traits

PLANT CELL & ENVIRONMENT, Issue 1 2000
K. Palmqvist
ABSTRACT Relations between irradiance (I) and lichen growth were investigated for five macro-lichens growing at two sites in Sweden. The lichens represented different mycobiont,photobiont associations, two morphologies (foliose, fruticose) and two life forms (epiphytic, terricolous). The lichens were transplanted at two geographically distant sites in Sweden (1000 km apart) from Sept 1995 to Sept 1996 in their typical microhabitats, where microclimate and growth were followed. Between April/May and Sept 96, the terricolous species had a dry matter gain of 0·2 to 0·4 g (g DW),1 and the epiphytes 0·01 to 0·02 g (g DW),1. When related to area, growth amounted to 30 to 70 g m,2 for the terricolous species and to 1 to 4 g m,2 for the epiphytes. There was a strong correlation between growth and intercepted irradiance when the lichens were wet (Iwet), with 0·2 to 1·1 g lichen dry matter being produced per MJ solar energy. Across the 10 sets of transplants, light use efficiencies of dry matter yield (e) ranged between 0·5 and 2%, using an energy equivalent of 17·5 kJ g,1 of lichen dry matter. The higher productivity of the terricolous species was due to longer periods with thallus water contents sufficient for metabolic activity and because of the higher mean photon flux densities of their microhabitat. A four-fold difference in photosynthetic capacity among the species was also important. It is concluded that lichen dry matter gain was primarily related to net carbon gain during metabolically active periods, which was determined by light duration, photon flux density and photosynthetic capacity. [source]

Conjugated polymers with tethered electron-accepting moieties as ambipolar materials for photovoltaics

POLYMER INTERNATIONAL, Issue 8 2007
Antonio Cravino
Abstract Conjugated polymers are of increasing interest as semiconductors for soft (opto)electronic devices, including photovoltaic elements. A promising conversion of solar energy into electrical energy is possible with blends of soluble electron donor-type conjugated polymers and fullerenes as electron-acceptor, transporting component. This approach, called bulk-heterojunction, suggested the preparation of intrinsic ambipolar materials to control simultaneously the electronic and morphological properties. On these bases, the covalent grafting of acceptor moieties onto conjugated backbones seemed attractive for the preparation of intrinsically ambipolar polymeric materials (,double-cable' polymers) as an alternative to donor,acceptor composites. The design, characterisation and application of this novel class of polymers are reviewed taking into account the current understanding of organic photovoltaics. Copyright © 2007 Society of Chemical Industry [source]

Solar membrane natural gas steam-reforming process: evaluation of reactor performance

ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 1 2010
M. De Falco
Abstract In this work, the performance of an innovative plant for efficient hydrogen production using solar energy for the process heat duty requirements has been evaluated via a detailed 2D model. The steam-reforming reactor consists of a bundle of coaxial double tubes assembled in a shell. The annular section of each tube is the reaction zone in which Ni-based catalyst pellets are packed, whereas the inner tube is a dense Pd-based selective membrane that is able to remove hydrogen from the reaction zone. By coupling reaction and hydrogen separation, equilibrium constrains inside the reactor are circumvented and high methane conversions at relatively low temperatures are achieved. The heat needed for the steam-reforming reaction at this low operating temperature can be supplied by using a molten salt stream, heated up to 550 °C by a parabolic mirror solar plant, as heating fluid. The effects on membrane reactor performance of some operating conditions, as gas mixture residence time, reaction pressure and steam-to-carbon ratio, are assessed together with the enhancement of methane conversion with respect to the traditional process, evaluated in the range 40.5,130.9% at the same operating conditions. Moreover, owing to the use of a solar source for chemical process heat duty requirements, the greenhouse gases (GHG) reduction is estimated to be in the range 33,67%. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source]

Energetisch und bauphysikalisch optimierte Sanierung eines Baudenkmals in Görlitz

BAUPHYSIK, Issue 3 2007
Christian Conrad Dipl.-Ing.
Mit den angewendeten Sanierungsmassnahmen an einem barocken Gebäude in Görlitz (Innendämmung Straßenfassade, WDVS Hoffassade, Solaranlage, Lüftungsanlage mit WRG, Grauwassernutzung und Fußbodenabwasserheizung) wurden unter Einhaltung der Auflagen des Denkmalschutzes die Energieeffizienzklasse A+ erreicht, die Belange des Umweltschutzes berücksichtigt und die Dauerhaftigkeit und Zuverlässigkeit der Konstruktionen gewährleistet. Die erreichten Ergebnisse werden u.a. mit instationären Simulationsrechnungen (Wärme-, Luft- und Feuchtetransport in kapillarporösen Baustoffen) für die einzelnen Bauteile und instationären Simulationsrechnungen anlagentechnischer Komponenten verifiziert. Dabei wird bauphysikalisch der Einfluss der hohen Bauwerksmasse ganzjährig quantifiziert. Die Auswirkungen der eingesetzten Anlagentechnik auf historische Bauteile, wie z. B. die Holzbalkendecken, werden untersucht. Auf der Grundlage der Erfahrungen zur Vermeidung der Kondensat- und Reifbildungen bei hochdämmenden geneigten Verglasungen wurde gemeinsam mit einem ortsansässigen Glaswerk eine neue Wärmeschutzverglasung mit einer außenliegenden Beschichtung entwickelt/kombiniert und eingesetzt. Optimized energy saving rehabilitation of a baroque building monument. With the rehabilitation of the baroque building Handwerk 15 in Görlitz the authors achieved the energy efficiency class A+ under observance of all conditions from preservation of historic buildings and monuments, taking into account the environmental issues as well as durability and safety of the constructions in the house. The rehabilitation includes the internal thermal insulation of the historically valuable façade on the street side, the thermal insulation of the façade on the backyard side, the use of solar energy for hot water and for the support of heating especially in summer for heating the ground floor, a ventilation system with heat exchanger, the use of gray water generated from domestic processes such as laundry and bathing, and an underfloor heating for the ground floor with waste water as medium. The measurement results will be verified with numerical simulations (temperature, air, moisture transport in porous materials) of the separate building constructions and the technical components. The physical influence of the high building mass is quantified. The effects of the HVAC system on the historical building construction like for instance the timber beam floor will be investigated. Based on experiences about avoiding condensate and hoarfrost on inclined insulated glass together with a glass producing firm a new insulate glass with a special coating was developed. [source]

Integration of Solar Energy into Absorption Refrigerators and Industrial Processes

Irrungen und Wirrungen um Biokraftstoffe.

CHEMIE IN UNSERER ZEIT (CHIUZ), Issue 5 2010
Biokraftstoffe sind nicht per se nachhaltig
Die jährliche Photosyntheseleistung auf der Erde übersteigt die anthropogene CO2 -Produktion. Dies legt eine energetische Nutzung der Biomasse nahe und hat die Entwicklung von Biokraftstoffen erheblich gefördert. In vielen Fällen verstößt die Nutzung von Biokraftstoffen jedoch gegen Prinzipien der Nachhaltigkeit. Für die Deckung des Weltenergiebedarfes durch Biomasse würde die gesamte verfügbare landwirtschaftliche Nutzfläche benötigt. Diese Einsicht hat eine kritische Teller-oder-Tank-Diskussion ausgelöst. Energetisch und ökologisch effizienter als die Nutzung von Biokraftstoffen wäre der Anbau schnellwachsender Hölzer und deren direkte Verstromung im Kraftwerk. Die mit großem Abstand effizienteste Nutzung der Sonnenenergie erlauben Photovoltaik und Solarthermie. Wegen ihrer hohen Energiedichte werden flüssige Biokraftstoffe der zweiten Generation aber dort, wo die Elektromobilität an Grenzen stößt, auch in Zukunft Anwendung finden. The annual photosynthesis on the Earth exceeds the anthropogenic CO2 production. This suggests an energetic use of biomass and has greatly promoted the development of biofuels. In many cases, however, the use of biofuels is breaking the rules of sustainability. To meet the world's energy demand from biomass would require the total available agricultural land. This insight has a critical plate or tank discussion triggered. Energetically and environmentally more efficient than the use of biofuels would be the cultivation of fast-growing timber and its direct use in coal power plants for electricity production. By far the most efficient use of solar energy is provided by photovoltaic and solar heat use. Because of their high energy density liquid second-generation biofuels will be applied also in future in such cases where electrical mobility has its limits. [source]

Dendrimers: A Mimic Natural Light-Harvesting System

CHEMISTRY - AN ASIAN JOURNAL, Issue 5 2010
Yi Zeng Dr.
Abstract In natural photosynthetic systems, a large array of chlorophyll molecules surrounds a single reaction center and channels the absorbed solar energy to the reaction center, ultimately resulting in ATP production. Dendrimers are well-defined tree-like macromolecules having numerous chain ends all emanating from a single core, which makes them an attractive candidate for light-harvesting applications. More importantly, their synthesis is controllable and the accurate positioning of chromophores can be achieved. Photoinduced electron transfer and energy transfer are main processes involved in photosynthesis. Studies on these processes in dendritic systems are important for the future application of dendrimers in optoelectronic devices. In this Focus Review we will discuss recent advances of light-harvesting dendrimers and emphasize the energy transfer and electron transfer characteristics in these systems. [source]

Thinnest Two-Dimensional Nanomaterial,Graphene for Solar Energy

The Role of Chemistry in the Energy Challenge

CHEMSUSCHEM CHEMISTRY AND SUSTAINABILITY, ENERGY & MATERIALS, Issue 2 2010
Robert Schlögl Prof.
Chemistry with its key targets of providing materials and processes for conversion of matter is at the center stage of the energy challenge. Most energy conversion systems work on (bio)chemical energy carriers and require for their use suitable process and material solutions. The enormous scale of their application demands optimization beyond the incremental improvement of empirical discoveries. Knowledge-based systematic approaches are mandatory to arrive at scalable and sustainable solutions. Chemistry for energy, "ENERCHEM" contributes in many ways already today to the use of fossil energy carriers. Optimization of these processes exemplified by catalysis for fuels and chemicals production or by solid-state lightning can contribute in the near future substantially to the dual challenge of energy use and climate protection being in fact two sides of the same challenge. The paper focuses on the even greater role that ENERCHEM will have to play in the era of renewable energy systems where the storage of solar energy in chemical carries and batteries is a key requirement. A multidisciplinary and diversified approach is suggested to arrive at a stable and sustainable system of energy conversion processes. The timescales for transformation of the present energy scenario will be decades and the resources will be of global economic dimensions. ENERCHEM will have to provide the reliable basis for such technologies based on deep functional understanding. [source]

Water Splitting on Semiconductor Catalysts under Visible-Light Irradiation

CHEMSUSCHEM CHEMISTRY AND SUSTAINABILITY, ENERGY & MATERIALS, Issue 6 2009
Rufino
Abstract Splitting image: Sustainable hydrogen production is a key target for the development of alternative, future energy systems that will provide a clean and affordable energy supply. This Minireview focuses on the development of semiconductor catalysts that enable hydrogen production via water splitting upon visible-light irradiation. Sustainable hydrogen production is a key target for the development of alternative, future energy systems that will provide a clean and affordable energy supply. The Sun is a source of silent and precious energy that is distributed fairly all over the Earth daily. However, its tremendous potential as a clean, safe, and economical energy source cannot be exploited unless the energy is accumulated or converted into more useful forms. The conversion of solar energy into hydrogen via the water-splitting process, assisted by photo-semiconductor catalysts, is one of the most promising technologies for the future because large quantities of hydrogen can potentially be generated in a clean and sustainable manner. This Minireview provides an overview of the principles, approaches, and research progress on solar hydrogen production via the water-splitting reaction on photo-semiconductor catalysts. It presents a survey of the advances made over the last decades in the development of catalysts for photochemical water splitting under visible-light irradiation. The Minireview also analyzes the energy requirements and main factors that determine the activity of photocatalysts in the conversion of water into hydrogen and oxygen using sunlight. Remarkable progress has been made since the pioneering work by Fujishima and Honda in 1972, but he development of photocatalysts with improved efficiencies for hydrogen production from water using solar energy still faces major challenges. Research strategies and approaches adopted in the search for active and efficient photocatalysts, for example through new materials and synthesis methods, are presented and analyzed. [source]