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It is indeed seldom that a specialised subject can be considered independently. Usually it is allied to and embodied in a systematic sequence of principles, and its field is generally an integral part of a reflection of some broader conception. This is especially true of this thesis, which is concerned with the climatic environmental influences on regional architecture. In the process of evolving the passive solar aspects, theoretical considerations yielded some interesting details and solutions. Examples studied showed a great variety of design principles. Thus as the material grew it suggested an entity -a theme itself. Cont/d.

with the development of a low-grade energy engine in the School of Mechanical Engineering at Cranfield, there began a venture towards utilizing the Sun's power to operate the engine via a thermodynamic cycle, in an Egyptian desert area, i. e latitude 3Q0N. The derived mechanical power is to drive an irrigation pump at the site. The solar thermal system is to operate in a Rankine-cycle using an organic working fluid. The engine is in the form of a multi-vane expander. The solar-energy collector comprises of an array of gravity-assisted heat- pipes each enclosed within a cylindrical high-vacuum glass tube. The irrigation water which is to be sucked from below ground level, is also to cool the shell-and-tube condenser. The first section(i. e. PART A) of this thesis is a presentation of some design optimization concepts in the development of the thermodynamically operated solar-energy system. As in any desert area dust will constitute a problem, reducing the harnessing capability of the collector array. Regular cleaning would therefore be essential. However, cleaning a large array (1000) of such fragile tubes in situ is unlikely to be accomplished without cracks and breakages occurring. This perhaps means that the high-vacuum which is essential for each collectors continued adequate thermal performance could be easily lost. The collectors are also considered expensive. For example, one tube with an effective aperture area of about 0.102ml costs about twenty pounds Sterling. These and the fact that the maximum anticipated working temperature in the organic Rankine-cycle would be about 1201 C, led to the study into a means other than evacuation of reducing thermal losses from the receiver of a flat-plate solar-energy collector in the second section (i. e. PART B). A flat-plate collector employing a simple slatted convection suppression device was studied. It was shown that a flat-plate collector employing an effective convection suppression device and an initial cost of about £1o0/m'would be more cost effective than the evacuated-tube collector, when employed to activate the pilot power plant for operatinq temperaures of (80-X120)° C. The cost per peak watt could be reduced by an average value of about 15% depending upon the'operating temperture. Whereas the break-even time against electricity could be reduced by about 4%. However, the overall efficiency of the power plant could fall by an average value of about 23%, depending upon the operating temperature.

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Presented here is an analysis of some of the existing methods used for the determination of the series resistance of solar cells which is one of the key parameters in solar cell fabrication and technology together with the diode ideality factor and the reverse saturation current. These methods are based on the network analysis of the single-exponential lumped constant parameters model which has been accepted as being operationally sufficient to describe the current-voltage characteristics of the solar cell. The methods analyzed in this study are divided into two main groups. Methods using two I-V characteristics and methods using a single I-V output curve. For comparison purposes, all methods are applied first using data extracted from existing I-V curves and then using in-lab measurements of a commercial solar cell. It is demonstrated that the determination of the series resistance of solar cells using two I-V characteristics has several advantages over methods using a single I-V output curve. It becomes evident that methods which use a single I-V output curve are only accurate for cells operating under very high illumination conditions. At normal intensities, however, such methods result in erroneous R(s) values. This is due to the assumption of a constant diode ideality factor along the entire I-V output curve used in the derivation of these methods. It is shown that this assumption is inaccurate at normal intensity levels and can be appropriate only under very high illuminations. Three new methods are proposed in this study. One of the methods presents a new approach in determining the solar cell equation parameters. The new approach relies upon treating the diode ideality factor of the solar cell as a variable that is a function of both the terminal current and the light intensity level. The method uses two I-V output curves at different illumination levels in determining all solar cell parameters: The series resistance, the diode ideality factor and the reverse saturation current. Although somehow tedious, the new approach shows that, for accurate modeling of solar cells and prediction of illuminated characteristics at different light levels based on the single-exponential model, the diode ideality factor should be treated as a variable while the series resistance is held constant. Comparison between all methods is presented and a reasonable judgement and recommendations concerning the best method to be used are given.

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No description available.