Introduction -- Solar and Wind Energy

In recent years the scientific community has begun to explore the many alternatives of using solar energy in terms of solar energy conversion schemes. These, in general, may be classified according to use. We can talk about solar to low-grade thermo residential heating and cooling applications. We can talk about solar to high-grade heat for such applications as steam powered generation and certain high-temperature conversion processes. We can talk about solar to electrical for either residential or for large power production installations; and we can talk about wind to electrical and this would, of course, come in both large and small packages. We can talk about wind to mechanical in terms of storage schemes or for direct use in mechanical energy. Along with these basic conversion processes comes a whole myriad of problems of processing, storage and utilization of energy in its many forms, and perhaps the biggest problem associated with the utilization of solar and wind energy comes in an indecision which comes from results from having too many alternatives. The scientist today is confronted with the task of performing a preliminary cost and value analysis in an effort to justify any system that he introduces, and to me this seems to describe the current status of many of the solar energy schemes that we are considering. It is hoped that the speakers here today can place some of the solar energy conversion schemes into proper perspective, not only in relation to other energy resources, but in relation to one another

Solar-Cell Design Based On A Distributed Diode Analysis

The front surface of a p-n junction solar cell has resistive losses associated with the diffused layer, the metal-semiconductor contact, and the grid structure. These losses are analyzed by considering the spatially distributed nature of the p-n junction and the grid conductors. This distributed diode analysis is especially useful for solar cells operated under concentrated sunlight conditions. The results show the dependence of the V-I characteristics and the maximum power output per unit cell on the ratio of the diffused layer resistance to the junction dynamic resistance. This ratio can assist the designer in establishing proper grid structure geometries and should typically be less than 0.1 if the power output per unit cell is to be within 3 percent of that for the lossless case. Experimental measurements are reported which confirm the theoretical calculations. An analysis of the grid conductor losses associated with multiple-connected unit cells shows the disastrous effect that the grid header resistance can have on the performance of a solar cell. The results indicate that the use of a tapered header conductor to decrease the metal coverage may actually worsen cell performance. Copyright © 1978 by The Institute of Electrical and Electronics Engineers, Inc

Free Electron Density Measurements By IR Absorption In CdS

A contactless method for determining the spatial variation of the free carrier density in CdS is presented. The method involves the correlation of IR transmission with the free carrier density via the IR absorption coefficient. Preliminary measurements indicate a free electron density sensitivity of less than 5x1014 cm-3 and a spatial resolution which is limited only by the spot size of a CO2 (λ=10.6 μm) laser; this should be of the order of 100 μm. Experimental results indicate that the predominate scattering is due to impurity interaction at room temperature; this is indicative of the high degree of compensation in CdS

Electrodeposition And Analysis Of Tin Selenide Films

Sn1±xSe films have been electrodeposited from aqueous solutions containing SnCl2 and ionically dissolved SeO2 or H2SeO3 and DMF solutions containing SnCl2 and molecularly dissolved selenium powder. The as-deposited films ranged from amorphous to polycrystalline and exhibited indirect or nondirect bandgaps from 0.85 to 0.95 eV. There was little difference between the appearance or material data of the films grown by the two techniques. Direct reaction between Sn++ and H2SeO3 or HSeO3_ in the aqueous solutions yielded a Se/SnxSe suspension/precipitate. Although this does not seem to have any serious effect on the deposition process, it does produce a decrease in the concentration and possibly a change in the composition of the ions in solution, as well as preventing in situ observation of the deposit and making the cleaning of the apparatus more difficult. Annealing slightly increased the Se/Sn ratio of microanalyzed layers near the substrate-deposit interface, and erased all x-ray diffraction structure. The bandgaps of the annealed films were shifted from approximately 0.9 eV to approximately 1.30 eV, consistent with the increased Se/Sn ratio. The films exhibited weak cathodic photocurents during deposition and photoconductance (ΔG/G⋍0.05) after deposition. The conductivity of Sample D (Sn0.91Se) was estimated to be on the order of 10 -4(Ω-cm)-1. Conductance-temperature plots indicated activation energies between 0.44 and 0.51 eV, probably indicative of deep acceptor levels and consistent with the p-type thermal voltage, millisecond photoconductance decay times, and the optical bandgaps. © 1986, The Electrochemical Society, Inc. All rights reserved

A Combined Digital-Analog Tracker for Terrestrial Applications

A combined Digital-Analog Tracker is suggested to allow maximum efficiency in a solar-electrical energy converter, utilizing a twelve-foot parabolic collector. The analog tracker compares solar beam radiation to ambient (diffuse) light to obtain optimum placement of the collector when the sun is visible. The digital portion of the tracker utilizes a wired program which derives information on solar position from a non-volatile random-access semiconductor memory. This arrangement allows accurate mapping of the sun even when the sun is obscured by atmospheric phenomena which would make mapping impossible

Deposition of CdTe by spray pyrolysis

We report the spray pyrolysis of thin films of CdTe which show promise as a base material for solar cell applications. The films predominately show a zinc blende structure and appear to be intrinsic. Microprobe analysis indicates an excess of cadmium but this is not detectable by X-ray diffraction or from electrical conduction measurements. Measurements indicate a nominal direct bandgap of 1.47 eV and an absorption coefficient of the order of 104 cm−1. The room temperature electrical resistivity is of the order of 107 Ω cm

A Solar-Hydrogen Energy Conversion Scheme for Agricultural Use

A solar energy activated system is presented which can produce hydrogen and hydrogen-derived fuels (methanol) for use on farms. The device, named solar-kine , also can produce fertilizer (anhydrous ammonia) as a byproduct of the hydrogen. A cost analysis shows that solar-kine may be mass-producible and sold to farmers for between $7,200 and$14,700. This is equivalent to giving the fanner energy at a price of $1.79 to$3.66 per million BTU\u27s (in 1974 dollars). Presently (Spring, 1974) regular gasoline used in tractors at 43¢ per gallon, represents a cost to the farmer of $3.77 per million BTU\u27s. As oil-based fuels increase in price in the next few years, solar-kine may represent a reasonable alternative to keep food prices down. The solar-kine system uses concentrated solar energy which can be converted into a high-density electric current by means of a thermionic heat engine. The rejected heat and electric current from the thermionic converter is supplied to an electrolysis cell which, in turn, produces hydrogen and oxygen gas. Chemical process equipment will use the hydrogen and oxygen to produce a methanol (CH3OH) fuel supply for internal combustion engines used on farm machines. The hydrogen can also be used to manufacture ammonia, ammonium nitrate (NH4NO3), and ammonium sulfate [(NH4)2SO4)] fertilizers. The following materials can be produced which are useful to the farmer: a) hydrogen gas, b) oxygen gas, c) liquid tractor fuel, d) fertilizer, e) ammonia, f) electricity, and e) heat energy We feel that any unconventional energy system, such as solar-kine, must interface and serve the conventional use of fuel energy if it is to have lasting merits. This is why we feel that it is desirable to have the complete conversion of solar energy into a liquid fuel that is safe to handle and store, and which also can be used in any conventional fossil-fuel burning system with minimum modifications. Solar energy is compatible with our environment; it is free, and its supply cannot be exhausted. It is also available at any geographic location without requiring transportation to the user\u27s site (See Fig. 2). Its major advantage over fossil fuel comes from the fact that it does not add any net heat content to the earth [5,6]. A small on-site energy system is best for the farmer because, a) It can be mass produced at 106 or more, units per year,b) Power levels needed by farms are low, 100-500 KW, c)Farm energy is used over a large geographical area, d)The main source of energy (the sun) is everywhere available,e) Heat rejected from the heat engine (thermionic) is used in other portions of the system to increase overall efficiency, and may be used in part to heat buildings,f) The farmer would be energy-independent from the price and supply undulations of the industrial complex,g) Legal considerations which regulate the large energy distribution systems would not apply, or affect, the proposed system as used by the farmer,h) Last, and possibly most important, the farmer would have a dependable fuel supply at the lowest possible cost. In the future, the proposed system will supply energy at a cost much lower than petroleum-derived energy

Photoluminescence In Spray-pyrolyzed CdTe

We report very intense photoluminescence in spray-pyrolyzed CdTe at 77 K. We also notice striking similarities in the luminescence spectra, decay, and temperature dependence between CdTe and other thin-film semiconductors, which we interpret in terms of recombination at defect sites in intergranular regions

Photoluminescence And Raman Studies Of CdS Films Grown By Metal-organic Chemical Vapor Deposition On Si{111} Substrates

CdS epitaxial films grown using metal-organic chemical vapor deposition on Si{111} substrates at growth temperatures ranging from 270 to 325 °C have been characterized using photoluminescence and Raman spectroscopy. Out of all the samples the best optical behavior is obtained from that grown at the lowest temperature. Samples grown at the lowest temperature exhibited increased intensity of the bound excitonic peaks and reduced emission at the defect-related luminescence region. The Raman spectra were compatible with the film surface being normal to the c axis, indicating a preferred growth orientation. © 1992

Growth Of Tungsten Selenide Films Through Pyrolytic Conversion And Anodic Electrooxidation Of Ammonium Selenotungstate ((NH4)2WSe4)

WxSey thin films have been prepared by the spray pyrolysis and anodic electrodeposition of solutions of ammonium selenotungstate, (NH4)2WSe4, with y/x usually between two and three for the sprayed films and y x\u3e\u3e1 for the electrodeposited films. The sprayed films indicated regions of crystalline WSe2 and have optical absorbance spectra consistent with a mixture of WSe2, WSe3, and selenium. The electrodeposited films are totally amorphous, highly photoconductive, and have optical absorbance spectra typical of amorphous or vitreous selenium. The sprayed films transform into WO3 at temperatures greater than 350°C in the presence of oxygen wile the electrode-posited films tend to evaporate and/or decompose upon annealing. © 1985