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03274 The prospects for solar thermal jet engines
07 99103267 Modeling the altitude effect on solar UV radiation Dvorkin, A. Y. and Steinberger, E. H. Solar Energy, 1999, 65, (3), 181187. A simple numerical model that describes the altitude effect of solar UV flux under cloud-free conditions was developed and tested. The model computes the direct and diffuse UV irradiances for the wavelength range 290-385 nm, at any sub-polar location and time (restricted to arid areas). The input parameters include extraterrestrial solar irradiance, ozone content and vertical distribution, aerosol amounts and size distribution, SOz and NO* contents, surface albedo and solar zenith angle. Model results were compared with measurements made in the tropical Chilean Andes for altitudes up to 5500 m above sea level. The model and data show good agreement. For the measured direct component a linear increase with altitude was assumed, whereas model results, computed up to 15 km altitude, exhibit a non-linear behaviour. However, in the lowest few kilometres a linear regression was adequate for both model and measurements. As for the diffuse component, the variation with altitude strongly depends on wavelength and solar zenith angle. At short wavelengths and large solar zenith angles, a pronounced maximum occurs at a level which depends on these parameters. The maximum cannot be observed when integrating over the UV-A range. This behaviour can be understood by taking into account the sources of the diffuse flux at any given level in the atmosphere. Numerical model and parametric analyses of an 99103266 inflatable solar heater Medved, S. et al. Solar Energy, 1999, 65, (4) 263-270. A new solar heater model, called SOLARBALL’, which is shaped as an inflatable hemisphere is introduced. This solar heater is above all distinguished by its small weight and volume. The final form is blown up by the user. The objective of this work was to develop a mathematical and a numerical model to analyse solar radiation and heat transfer in such a heater. The numerical model was verified by a series of experiments. After successful verification, the numerical model was used for the parametric analyses to establish the time required to heat water for different meteorological data, size of reflector and optical properties of the transparent cover, reflector and absorber surface. It was found out that typical optical efficiency and overall heat transfer coefficient of the hemispherical solar heater are between 0.45 to 0.5 and 0.6 to 1.6 W/m2 K respectively. By standardized conditions, the required heating time for heating 0.33 1 of water varies between 15 and 25 min according to the construction parameters. On a simple analytical model for solar chimneys 99103269 Padki, M. M. and Sherif, S. A. Int. /. Energy Res., 23, (4), 345-349. For the analysis of a solar chimney a set of differential equations was developed. The equations are integrated by making a few simplifying assumptions and expressions for the power generated and the efficiency are obtained in closed form algebraic formulas. The analytical model is shown to consistently underpredict the performance by 4-6% vis-d-vis the differential model. Operational experience of a residential 99i93270 photovoltaic hybrid system Peterson, Jr., J. W. et al. Solar Energy, 1999, 65, (4), 227-235. The operational experience acquired with a photovoltaic (PV) hybrid system installed as a line extension alternative at a residence located in northern New York State is presented. The system includes an 850W PV array, 25 kWh worth of battery storage and a 4 kW propane generator. The paper features a detailed analysis of the energy flows through the system and quantifies all losses caused by battery storage round-trip, rectifier and inverter conversions and non-optimum operation of the generator and of the PV array. Also analysed is the evolution of end-use electricity consumption since the installation of the PV hybrid system. Optimization of n-doping in n-type a-Si:H/p-type 99103271 textured c-Si heterojunction for photovoltaic applications Tucci, M. Solar Energy Materials & Solar Cells, 1999, 57, (3), 249-257. A heterostructure based on p-doped textured wafers of crystalline silicon is investigated on which a buffer of lightly n-doped amorphous layer and an n+-doped layer were deposited. In particular, the effect of n-doping of amorphous silicon on the photovoltaic characteristics of the heterojunctions is studied. Performance analysis of a grid-connected 99103272 photovoltaic system Sidrach-de-Cardona, M. and Lopez, LI. M. Energy, 1999, 24, (2), 93-102. Grid-connected photovoltaic systems are required to introduce photovoltaic solar energy into urban areas, To analyse these systems, a 2.0 kW, power system has been installed at the University of Malaga, Spain. The array power output was estimated by using measured I-V curves for the installed modules with minimization of mismatch losses. The supplied grid energy and main performances are described. The effects on system yield of threshold-inverter and coupling losses of the inverter to the grid have been studied. During 1997, the system supplied 2678 kWh to the grid, i.e. the mean daily output, was 7.4 kWh. The annual performance ratio was 64.5% and the optimal value 67.9%.
Alternative
energy sources (solar energy)
99103273 A phosphorus doped (n-ty e) carbon/boron doped (p-type) silicon photovoltaic solar cell Prom a natural source Krishna, K. M. et al. Carbon, 1999, 37, (3), 531-533. The prospects for solar thermal jet engines 99103274 Glazkov, V. V. and Sinkevich, 0. A. High Temp., 1998, 36, (5), 820-822. The use of solar energy was examined for use in jet engine-type propulsion units for spacecraft. The solar energy would be utilized as heat collected by solar concentrators such as parabolic mirrors. A solar concentrator with a mass of 200 kg will have a total mass of -500 kg, including a graphite heat storage facility that would allow the engine to operate in the Earth’s shadow. There are many possible options for the ‘fuel’ for the solar jet engine, but it would emphasize using liquid wastes as this would control the build-up of wastes inside the space vehicle. Uses of the propulsion unit include, thrusting and station-keeping of a lOO-ton space station, an interorbit ‘tug’ to transfer satellites to higher orbit and to provide thrust for interplanetary flights. 99m3275 Reduction reactor using solar energy Tamaura, H. and Konishi, S. Jpn. Kokai Tokkyo Koho JP 10 279,955 [98 279,955] (Cl. ClOJl/OO), 20 Ott 1998, Appl. 97/83,524, 2 Apr 1997, 5 pp. (In Jaoanese) For the purpose of coal gasification, a reduction reactor using solar energy includes a solar/chemical reactor for the reduction of coal by irradiating sunlight on mixed particles of coal and magnetite. A hydrogen-generating reactor generates hydrogen through reaction of steam with wustite formed from the reduction reaction of coal. The magnetite is simultaneously recycled to the solar/chemical reactor. Simulation model of a CPC collector with 99103276 temperature-dependent heat loss coefficient Fraidenraich, N. et al. Solar Energy, 1999, 65, (2), 99-110. Described is a mathematical model for the optical and thermal performance of non-evacuated CPC solar collectors with a cylindrical absorber, when the heat loss coefficient is temperature-dependent. Detailed energy balance at the absorber, reflector and cover of the CPC cavity yields heat losses as a function of absorber temperature and solar radiation level. Using a polynomial approximation of those heat losses, the thermal efficiency of the CPC collector was calculated. Numerical results show that the performance of the solar collector (n vs. ATf(O)/1& is given by a set of curves, one for each radiation level. Based on the solution obtained to express the collector performance, the authors plot efficiency against the relation of heat transfer coefficients at absorber input and under stagnation conditions. The set of characteristic curves merge, then, into a single curve that is not dependent on the solar radiation level. More conveniently, linearized single plots are obtained by expressing efficiency against the square of the difference between the inlet fluid temperature and the ambient temperature divided by the solar radiation level. The new way of plotting solar thermal collector efficiency, such that measurements for a broad range of solar radiation levels can be unified into a single curve, enables us to represent the performance of a large class of solar collectors, e.g. flat plate, CPC and parabolic troughs, whose heat loss functions are well represented by second degree polynomials. Solar fiber-optic mini-dishes: a new approach to 99103277 the efficient collection of sunlight Feuermann, D. and Gordon, J. M. Solar Energy, 1999, 65, (3), 159-170. A new concept for efficient solar energy concentration and power delivery is proposed - one that offers substantial advantages in efficiency, compactness, reduced mechanical loads and ease of fabrication and installation relative to conventional solar designs. The design exploits the availability of low-attenuation optical fibres, as well as the practical advantages of mass producing highly accurate very small parabolic dishes. The system’s building block is a miniature (e.g. 0.2 m diameter) solar dish which concentrates sunlight into a single optical fibre. The fibre transports power to a remote receiver. A second-stage concentrator can boost flux levels to those approaching the thermodynamic limit and can be performed either in each individual dish or collectively in one or more larger devices at the entrance to the remote receiver. Collector modules, close-packed with mini-dishes, are mounted on individual trackers close to the ground. Systems are modular and can be employed in central power generation ranging from a few kilowatts to tens of megawatts. Designs for maximum efficiency attaining collection efficiencies as high as 80% and maximumconcentration designs realizing flux levels of 30,000 suns, are achievable. Stanwell solar power a shining success 99103276 Anon QGM/, 1999, 100, (1167), 38. In this article an intended development of the Stanwell power station near Rockhampton, Queensland, is discussed. The station will be the home to an innovative $6 million solar power project that will reduce greenhouse gas emissions. The project has been awarded a $2 million Renewable Energy Showcase grant. The project engineers are said to have ‘developed a unique way to use the sun to assist in the generation of power’. The sun’s rays will be used to heat water which is converted to steam and used in the electricity generation process. A large array of reflectors or mirrors will be used to collect the energy from the sun and redirect and focus it. These mirrors will automatically track the sun across the sky. The first stage is planned to be producing solar energy during the second half of 1999 and the full plant is expected to be in place by the end of 2000.
Fuel and Energy Abstmcts
September
1999
343
Alternative
energy sources (solar energy)
99103273 A phosphorus doped (n-ty e) carbon/boron doped (p-type) silicon photovoltaic solar cell Prom a natural source Krishna, K. M. et al. Carbon, 1999, 37, (3), 531-533. The prospects for solar thermal jet engines 99103274 Glazkov, V. V. and Sinkevich, 0. A. High Temp., 1998, 36, (5), 820-822. The use of solar energy was examined for use in jet engine-type propulsion units for spacecraft. The solar energy would be utilized as heat collected by solar concentrators such as parabolic mirrors. A solar concentrator with a mass of 200 kg will have a total mass of -500 kg, including a graphite heat storage facility that would allow the engine to operate in the Earth’s shadow. There are many possible options for the ‘fuel’ for the solar jet engine, but it would emphasize using liquid wastes as this would control the build-up of wastes inside the space vehicle. Uses of the propulsion unit include, thrusting and station-keeping of a lOO-ton space station, an interorbit ‘tug’ to transfer satellites to higher orbit and to provide thrust for interplanetary flights. 99m3275 Reduction reactor using solar energy Tamaura, H. and Konishi, S. Jpn. Kokai Tokkyo Koho JP 10 279,955 [98 279,955] (Cl. ClOJl/OO), 20 Ott 1998, Appl. 97/83,524, 2 Apr 1997, 5 pp. (In Jaoanese) For the purpose of coal gasification, a reduction reactor using solar energy includes a solar/chemical reactor for the reduction of coal by irradiating sunlight on mixed particles of coal and magnetite. A hydrogen-generating reactor generates hydrogen through reaction of steam with wustite formed from the reduction reaction of coal. The magnetite is simultaneously recycled to the solar/chemical reactor. Simulation model of a CPC collector with 99103276 temperature-dependent heat loss coefficient Fraidenraich, N. et al. Solar Energy, 1999, 65, (2), 99-110. Described is a mathematical model for the optical and thermal performance of non-evacuated CPC solar collectors with a cylindrical absorber, when the heat loss coefficient is temperature-dependent. Detailed energy balance at the absorber, reflector and cover of the CPC cavity yields heat losses as a function of absorber temperature and solar radiation level. Using a polynomial approximation of those heat losses, the thermal efficiency of the CPC collector was calculated. Numerical results show that the performance of the solar collector (n vs. ATf(O)/1& is given by a set of curves, one for each radiation level. Based on the solution obtained to express the collector performance, the authors plot efficiency against the relation of heat transfer coefficients at absorber input and under stagnation conditions. The set of characteristic curves merge, then, into a single curve that is not dependent on the solar radiation level. More conveniently, linearized single plots are obtained by expressing efficiency against the square of the difference between the inlet fluid temperature and the ambient temperature divided by the solar radiation level. The new way of plotting solar thermal collector efficiency, such that measurements for a broad range of solar radiation levels can be unified into a single curve, enables us to represent the performance of a large class of solar collectors, e.g. flat plate, CPC and parabolic troughs, whose heat loss functions are well represented by second degree polynomials. Solar fiber-optic mini-dishes: a new approach to 99103277 the efficient collection of sunlight Feuermann, D. and Gordon, J. M. Solar Energy, 1999, 65, (3), 159-170. A new concept for efficient solar energy concentration and power delivery is proposed - one that offers substantial advantages in efficiency, compactness, reduced mechanical loads and ease of fabrication and installation relative to conventional solar designs. The design exploits the availability of low-attenuation optical fibres, as well as the practical advantages of mass producing highly accurate very small parabolic dishes. The system’s building block is a miniature (e.g. 0.2 m diameter) solar dish which concentrates sunlight into a single optical fibre. The fibre transports power to a remote receiver. A second-stage concentrator can boost flux levels to those approaching the thermodynamic limit and can be performed either in each individual dish or collectively in one or more larger devices at the entrance to the remote receiver. Collector modules, close-packed with mini-dishes, are mounted on individual trackers close to the ground. Systems are modular and can be employed in central power generation ranging from a few kilowatts to tens of megawatts. Designs for maximum efficiency attaining collection efficiencies as high as 80% and maximumconcentration designs realizing flux levels of 30,000 suns, are achievable. Stanwell solar power a shining success 99103276 Anon QGM/, 1999, 100, (1167), 38. In this article an intended development of the Stanwell power station near Rockhampton, Queensland, is discussed. The station will be the home to an innovative $6 million solar power project that will reduce greenhouse gas emissions. The project has been awarded a $2 million Renewable Energy Showcase grant. The project engineers are said to have ‘developed a unique way to use the sun to assist in the generation of power’. The sun’s rays will be used to heat water which is converted to steam and used in the electricity generation process. A large array of reflectors or mirrors will be used to collect the energy from the sun and redirect and focus it. These mirrors will automatically track the sun across the sky. The first stage is planned to be producing solar energy during the second half of 1999 and the full plant is expected to be in place by the end of 2000.
Fuel and Energy Abstmcts
September
1999
343