07 Alternative energy sources (solar energy)

cyclic heat engines operating at maximum power conditions. This upper limit is a function of both the functional temperature dependence and of heat transfer and relevant system parameters.

00/02727 Optimum slope angle and orientation of solar collectors for different periods of possible utilization Bari, S. Energy Conversion & Monugemenr, 2000, 41, (8). 855-860. A method to determine the optimum slope angle and orientation of solar collectors for different periods of operation (1-365 days) at any position in the Malaysian territory is described. The method utilizes both the direct and diffuse components of solar radiation. The ASHRAE standard atmosphere is used to calculate the direct component, whereas the isotropic diffuse model is used to calculate the diffuse component. For intermittent applications of solar energy such as crop drying, the optimum slope angle as well as the orientation can be found conveniently and accurately by this method.

00102728 Performance analysis of a solar process heat system Eskin, N. Energy Conversion & Manogemenr, 2000, 41, (It), 1141-l 154. This paper describes the results of a simulation study, validated by experimental results of a solar process heat system and represents the unsteady performance analysis of the system. The study focuses on the effect that the collector flow rates, temperature distribution and stratifica- tion have on the overall thermal and exergetic performance of the particular systems. The simulation is performed for the process heat system established in Izmir, Turkey. The analysis considers the unsteady-state thermal and exergetic analysis of the collector and the storage tank individually. The variation of the storage tank temperature is evaluated along the height of the storage tank at every hour during a day. The values obtained from the measurements at the Izmir Organize Sanayi Bolgesi- Industrial Process Heat System are compared with the predicted simulation results. The effects of the mass flow rates and temperature distribution of the load and collector on the performance of the system are discussed. The simulation results indicate that the exergetic efficiency is highly dependent on the ratio of mass flow rates and the use of an auxiliary heater in the system.

00102729 Prediction and performance assessment of mean hourly global radiation Gueymard, C. S&r Energy, 2000, 68, (3), 285-303. Using a large dataset of 135 stations encompassing very diverse geographic locations (82.5”N to 67.6”s) and climate, two new models are presented to predict the monthly-average hourly global irradiation distribution from its daily counterpart. It is found that a quadratic in the sine of solar elevation fits the data very well at all locations. Other parameters include the mean monthly clearness index, K,, the average day length and the daily average solar elevation. Based on this dataset, a detailed performance assessment is conducted for these new models, as well as for six model of the literature. Their respective performance is discussed, particularly with respect to the latitudinal effect. The proposed models appear to correctly predict irradiations even for a very low sun typical of near-polar night conditions. The accurate predictions of the newly proposed ‘daily integration model’ translate into the lowest yearly-average and site-average Root Mean Square Difference, a statistic obtained by comparison with 21 722 measured hourly irradiations. However, it is stressed that the performance of this kind of model is seriously limited by artefacts due to shading (e.g. from mountains) and, more importantly, by strong morning/afternoon radiative asymmetries due to local or climatological influences, which cannot be predicted from just daily irradiation data.

00102730 Qualification test procedure for solar absorber surface durability Carlsson, B. Solar Energy Marrrials & Solar Cells, 2000, 61, (3) 255-275. A general test procedure for the qualification of solar absorber surface durability has been developed based on the results of a comprehensive case study performed within the framework of the IEA Solar Heating and Cooling Programme Task X. It was assumed, in the development of the qualification procedure, that the intended use of the absorber surface to be qualified, was in single-glazed flat plate solar collectors for domestic hot water production. The absorber surface should be considered qualified if it met the requirement of a design service life of 25 years with maximum loss in the optical performance of the absorber surface corresponding to a 5% relative reduction in the performance of a solar domestic hot water system. The testing procedure, consisting of three kinds of constant load- accelerated life-time tests, was limited to simulation of the following three kinds of absorber surface degradation processes: (a) high-temperature degradation, e.g. oxidation, (b) degradation by the action of moisture or condensed water on the absorber surface, e.g. hydration or hydrolysis and (c) degradation caused by high humidity air containing a small concen- tration of sulphur dioxide as an airborne pollutant, e.g. atmospheric corrosion. To quantify expected environmental stress on the absorber surface related to the environmental factors of interest, microclimate data, representing typical service conditions for absorbers in single-glazed flat plate collectors for domestic hot water production were used.

00102731 Round robin on accelerated life testing of solar absorber surface durability Brunold, S. Solar Energy Moreriuls & Solar Cells. 2000, 61, (3). 239-253.

As degradation by ageing of solar absorber surfaces was identified to be an important quality factor, the Working Group MSTC (‘Materials in Solar Thermal Collectors’) of the IEA-SHCP (Internarional Energy AgencpSolur Heating and Cooling Programme) worked out a general test procedure for accelerated lifetime testing (ALT) of these materials, based on methods established by the former Task X of the IEA SHCP. The qualification test procedure was adopted by IS0 and is presently dealt within ISOjTC 180 ‘Solar Energy’. The standard proposal in detail describes a procedure how to test the long-term stability of an absorber surface for the use in flat plate collectors for domestic hot water systems. The collectors service lifetime is assumed to be 25 years, at least. Degradation caused by thermal loads, high humidity and condensation and sulphur dioxide are regarded. In order to examine the feasibility and reproducibility of the test method the Working Group MSTC initiated a round robin test in accelerated life testing of solar absorber surfaces. The test was performed according to the IS0 standard proposal dated January 1997. In total. live different industrially manu- factured absorber coatings were available to the three participating laboratories. Tests concerning the thermal stability as well as the resistance to high humidity and condensation were performed by all three labora- tories. The test for determiningabsorber surface corrosion resistance to air of high humidity containing sulphur dioxide was carried out by one lab only. The outcome of the round robin test shows very good agreement of the results of the different coatings tested for all of the laboratories. The feasibility and reproducibility of the method was ful!y confirmed.

00/02732 Solar energy in western civilisation Perlin, J. So/or Progress, 1999, 20, (4), 14. Over the last 2500 years people in the west have successfully harnessed the sun’s energy in many different and practical ways for their benefit. This paper will discuss the different strategies western people have used to make use of the sun in the last 2500 years. It will describe the conditions that allowed the different solar applications to succeed as well as present the reasons for their demise or stagnation.

00/02733 Statistical investigation of the optimal averaging time for solar irradiance on horizontal and vertical surfaces in the UK Craggs, C. Solar Energy, 2000, 68, (2) 179-187. As output from photovoltaic (PV) panels is closely related to sunlight levels, monitoring solar irradiance levels is crucial for system design and predictive purposes. With advances in PV technology, urban sites at northerly locations, where both horizontal and vertical solar irradiance make significant contributions, are becoming increasingly important. The aim of this paper is to compare solar irradiance for horizontal and vertical orientations and to assess the relative effectiveness of differing averages, from 10 min to 1 h, for use in short-term prediction of solar irradiance levels for a UK site. Vertical and horizontal solar irradiance observations were collected from a monitoring station on the roof of a five-stores building at an urban site in Newcastle-upon-Tyne, UK (latitude 55”N). Data for IO-min periods were collected for 13- or 15-day periods in two summers (1994, 1995) and two winters (1993, 1994). Although mean levels for horizontal and vertical irradiance were different, as expected, general patterns were very similar indicating the possibility of predicting vertical irradiance from horizontal at the same location. IO-min, 20-min. 30-min and l-h averaging times were compared utilising autocorrelation coefficients and ARIMA models to assess the information lost when using longer averaging intervals. For consideration of short-term changes, IO-min averages were most informative whilst hourly averages were substantially poorer.

00102734 Steady-state and dynamic performance analysis of PV supplied DC motors fed from intermediate power converter Mummadi, V. C. Solrrr Energy Murerials & Solrrr Cells, 2000, 61, (4), 365 381. The steady-state and transient performance of PM and series motors coupled to a centrifugal pump supplied from a Photovoltaic source through an intermediate buck-boost converter is analysed. The effect of duty ratio selection based on maximum power operation of PV source and maximum daily gross mechanical power is investigated on the solar cell array operating point, motor armature voltage, armature current and motor efficiency variation. Studies are carried out by formulating the mathemat- ical models for photovoltaic source, DC motors, power converter and load. Starting with torque variation, torque magnification factors expressions are derived and their variations plotted for the above two cases. Simulation software is developed for the transient and steady-state analysis of PV supplied DC motors for different duty ratios of power converter and solar insolations. Steady-state and transient performance characteristics are presented. The performance of PM DC motor is compared with the series motor operating under identical conditions.

00102735 Sulphidation of electrodeposited cuprous oxide thin films for photovoltaic applications Wijesundara, R. P. Solar Energy Malerials & Solar Cells, 2000, 61, (3). 277- 286. Electrodeposited cuprous oxide thin films on iridium-doped tin oxide (ITO) substrates were sulphided by exposing them to a spray of aqueous solution of sodium sulphide or to a mixture of hydrogen sulphide and nitrogen gases. Both methods produced light darker and darker films having different photovoltaic characteristics in a solar cell structure. The photovoltages produced by the light darker films under AM 1.5 illumination was negative

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