Materials for photothermal solar energy conversion

Commencally or potentially available selective and non-selective absorber surfaces for solar heat collectors are reviewed and the state-of-the-art of solar collector corrosion processes is outlined. The review of available published literature has indicated that a lack of quantitative information exists, relative to corrosion of collector surfaces. Available information (mostly qualitative) on durability aspects and corrosion of solar receiver surfaces is described to indicate potential corrosion problem areas and corrosion prevention possibilities. An outline of appropriate durability tests is presented.     

Selective surfaces for high temperature solar photothermal conversion

High performance, low cost, selective surfaces which are chemically and thermally stable are a key limiting problem in the development of the thermal applications of solar energy. This review deals with selective coatings that withstand high temperatures. After indicating the comparative advantages of selective over black-body absorbers, the different ways of generating selectivity are briefly investigated. The physicochemical requirements that must be met, in addition to the specific optical properties that are needed, are established, and criteria for the choice of materials are given. Finally several examples of selective surfaces are described and some trends for further research in the field are discussed.     

Materials aspects of wave energy converters

There is current interest in renewable energy sources and the United Kingdom is favourably located with respect to wave energy. This review describes briefly the device concepts being pursued in the Department of Energy Programme and considers the materials aspects of full-scale Wave Energy Converter (WEC) development. Emphasis is placed on generic problems rather than areas specific to individual devices. Present estimates put the cost of WEC development relatively high. Thus, effort in the future will be directed at reducing these costs, particularly those of the main structure and mooring system, and the optimum use of materials will be essential. In certain areas gaps in existing materials technology have been identified and experimental programmes initiated.     

Thermomechanical cycles in martensite energy converters

We have studied the quantitative relationships governing the formation of thermomechanical cycles in heat engines with operational elements fabricated out of materials exhibiting the shape memory effect. With this purpose in mind, we have conducted experiments for two of the most common regimes under which materials function, namely: with a rigidly fixed amplitude of strain deformation, and for a scheme involving interconnected elements. We have plotted numerous phase diagrams in stress-strain-temperature coordinates and we have optimized such cycles in terms of their energy parameters. It has been established that the capacity of a metal to transform heat into mechanical work depends substantially on the form of the phase diagram, and this is at its maximum for sign- variable symmetric limit cycles. We undertook a theoretical calculation (and achieved positive results) of phase diagrams involving the application of structural-analytic theory insofar as this pertains to the functional properties of materials exhibiting the shape memory effect.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 59, No. 2, pp. 269–277, August, 1990.     

Jet electrohydrodynamic signal energy from converters

Translated from Inzhenerno-fizicheski Zhurnal, Vol. 60, No. 4, pp. 680–692, April, 1990.     

Characterization of solar selective molybdenum black films

It has been found possible to prepare excellent solar selective molybdenum black films by a modified catholic electrodeposition technique. These films have been characterized using XPS, AES depth profiling, SEM, chemical analysis, X-ray diffraction and VIS-IR reflectance spectroscopy. The study shows that the film is composite of MoO₃ matrix containing fine nickel and copper particles. It is also observed that the copper concentration increases from the surface of the film towards the substrate. Reported solar selectivity can be explained using the Maxwell Gannett theory along with the stacked layer treatment developed by Anderson.     

Preparation and properties of RF sputtered indium-tin oxide thin films for applications as heat mirrors in photothermal solar energy conversion

In the present research, in order to deposit indium-tin oxide (ITO) thin films the method of RF reactive sputtering was used. Sputtering of two types indium-tin targets in the presence of oxygen as reactive gas was made. The technological parameters were optimized to obtain films with good quality on different substrates. The films' microstructure was studied by TEM and SAED. To identify the optical properties of the films the methods of infrared spectrometry and laser ellipsometry were used. UV-VIS spectrophotometry showed the high visible transmittance of the RF sputtered ITO films. Heating of the substrates during the films sputtering and their post deposition thermal treatment also were studied. The ultimate goal of the present research activities was to develop new technological processes leading to low-cost, highly effective optical coatings for application in photo thermal solar energy conversion and utilization.     

Biological solar energy

Through the process of photosynthesis, the energy of sunlight has been harnessed, not only to create the biomass on our planet today, but also the fossil fuels. The overall efficiency of biomass formation, however, is low and despite being a valuable source of energy, it cannot replace fossil fuels on a global scale and provide the huge amount of power needed to sustain the technological aspirations of the world population now and in the future. However, at the heart of the photosynthetic process is the highly efficient chemical reaction of water splitting, leading to the production of hydrogen equivalents and molecular oxygen. This reaction takes place in an enzyme known as photosystem II, and the recent determination of its structure has given strong hints of how nature uses solar energy to generate hydrogen and oxygen from water. This new information provides a blue print for scientists to seriously consider constructing catalysts that mimic the natural system and thus stimulate new technologies to address the energy/CO2 problem that humankind must solve. After all, there is no shortage of water for this non-polluting reaction and the energy content of sunlight falling on our planet well exceeds our needs.     

Storage of solar energy

A framework is presented for identifying appropriate systems for storage of electrical, mechanical, chemical, and thermal energy in solar energy supply systems. Classification categories include the nature of the supply system’s setting; the type of energy supplied ; the type of solar energy collection system used (including ‘ indirect ’ solar energy, such as wind and hydropower) ; the type of energy stored ; and some other characteristics of the storage system. A global insolation summary is used to exhibit the diversity of requirements for solar energy storage in different settings. Comments are then made on the need and opportunities for 24 hr storage of electrical energy in batteries; backup systems that use stored chemical fuel derived from solar energy; storage of intermediate temperature heat as heat of hydration of compounds such as sulfuric acid; annual storage of low temperature heat in fresh water ponds or aquifers; and annual storage of ice produced in places with cold winters. Arguments are presented for using a systems approach to the selection of solar energy storage methods appropriate for use in specific types of settings.     

Preparation and properties of substrate PVA-GO composite membrane for solar photothermal conversion

Solar thermal desalination (STD) is a promising and sustainable techno- logy for extracting clean water resources. Whereas recent studies to improve STD performance primarily focus on interfacial solar evaporation, a non-traditional bottom heating method was designed in this study. Herein, we prepared the polyvinyl alcohol/graphene oxide (PVA-GO) composite membrane and adhered to the bottom of a beaker using crystallized PVA. The GO was loaded on a non-woven fabric and different concentrations of PVA were compared for their effect on the evaporation efficiency. The results showed that the addition of PVA increased the evaporation rate. The surface characteristic of GO membrane without PVA was a fibrous filamentous structure as observed by SEM, whereby the fibers were clearly visible. When the PVA concentration reached 6%, the non-woven fiber was completely wrapped by PVA. Under the action of a fixed light intensity, the photothermal conversion rates of GO, 2% PVA-GO, 4% PVA-GO and 6% PVA-GO membrane device could reach 39.93%, 42.61%, 45.10% and 47.00%, respectively, and the evaporation rates were 0.83, 0.88, 0.94 and 0.98 kg·m⁻²·h⁻¹, respectively. In addition, the PVA-GO composite membrane showed an excellent stability, which has significance for industrial application.     

Plasmonic Cu27S24 nanocages for novel solar photothermal nanoink and nanofilm

Copper sulfide(CuxS)as a plasmonic solar photothermal semiconductor material that expands the light collection range by altering localized surface plasmon reson...     

OM太阳能住宅综述

介绍了OM太阳能住宅在冬季夏季不同工况时的运行原理,在冬季白天,通过屋面的空气夹层吸收储存热量,并由气流带至住宅内的各种蓄热体进行储存,日落到次日清晨时蓄热体慢慢放热,从而保持了房间的温度.夏季时,屋面空气夹层可以形成一个隔热层,一方面,可以利用OM处理箱生产热水;另一方面,也可以把余热通过OM处理箱直接排出房间,因此此隔热层的存在可以使房间内维持相对较低的温度.接下来概述了其特点及比较优势,展望了其发展前景.并对此类住宅的发展研究提出了一些自己的看法与建议.     

Submicrometer gratings for solar energy applications

Diffractive optical structures for increasing the efficiency of crystalline silicon solar cells are discussed. As a consequence of the indirect band gap, light absorption becomes very ineffective near the band edge. This can be remedied by use of optimized diffraction gratings that lead to light trapping. We present blazed gratings that increase the optically effective cell thickness by approximately a factor of 5. In addition we present a wideband antireflection structure for glass that consists of a diffraction grating with a dielectric overcoat, which leads to an average reflection of less than 0.6% in the wavelength range between 300 and 2100 nm.     

Absorption phenomena in organic thin films for solar cell applications investigated by photothermal deflection spectroscopy

A high sensitive approach is presented to detect in particular the low level absorption features in pure and blended organic semiconductor films, revealing a.o. defect induced sub gap absorption and new interactions between the materials. Because sub bandgap absorption features are typically characterized by very low absorption coefficients, it is not possible to resolve them using common transmission and reflection measurements. Therefore the very sensitive and ground state spectroscopic technique of Photothermal Deflection Spectroscopy (PDS) has been developed, and introduced to characterize thin films of MDMO-PPV and PCBM, as well as films of MDMO-PPV containing an increasing amount of PCBM ranging from 5 to 90% weight fraction. The measured spectra of MDMO-PPV are interpreted in terms of defect induced absorption phenomena. The spectral position of the observed transitions in PCBM have been determined and verified. The PDS-study on MDMO-PPV/PCBM blended films revealed for the first time interaction between the two materials in the ground state. To get more insight in the interaction mechanism between the constituting materials a systematic Transmission Electron Microscopy (TEM) study has been carried out to reveal the morphology of the films. The obtained TEM-results on nanomorphology of the blended films show clear correlations with the PDS-results.     

Electrochemical photovoltaic cells for solar energy conversion

Photoelectrochemical cells have attracted much more attention recently due to their feasibility as low-cost solar energy conversion devices and hence a number and variety of papers have appeared. Although some review papers have been published, no comprehensive review of electrochemical photovoltaic cells has been made. The present review is devoted to a survey of most of the dimensions of ECPV cells.Starting with photoelectrochemical processes, relevant theoretical background is presented including redox potentials, interface of the semiconductor-liquid junction and Butler-Volmer relation, etc. Much emphasis is given to the requirements of semiconductor electrodes, electrolytes, counter electrods and various cell configurations in ECPV cells. Results on photocorrosion, stability, etc. of the electrodes and the effect of temperature on the performance of the ECPV cell are discussed. Up-to-date data on various ECPV cells are presented and the current situation is discussed. In the light of this, various new materials are attractive. Finally, results on ECPV storage cells and their potential applications are discussed.