摘要：The purpose of this paper is first to briefly describe the usual routes of biomass thermochemical conversion and then to discuss the possibility of using concentrated solar energy to provide the necessary heat for the processes. Gasification, fast and slow pyrolysis are more particulary described. They can be carried out for the preparation of a vast range of possible products that can be used as energy carriers and/or as a source of chemical commodities. The gasification processes are intended for the preparation of gas mixtures (CO, H_2, etc.) for chemical synthesis, heat or electricity generation. The fast pyrolysis formerly carried out for gas production (CO, H_2, light hydrocarbons, etc.) is now mainly studied with the objective to produce liquids (bio-oils).
摘要：Waste tyre and plastic such as polyethylene terephthalate can be utilized as a useful material for conversion of solar energy into chemical energy by solar thermochemical gasification into synthesis gas (CO+H_2) using concentrated solar energy. In the present paper, the gasification of waste tyre (C: 86 wt./100, H: 8.4 wt./100) and of PET (C_10H_8O_4)_n, were studied using ZnO as a donor of oxygen in the infra-red furnace at 1373 K. For the gasification of tyre, most of the chemically bound hydrogen was converted into H_2(62 /100) and CH_4 (29 /100) gases, while 71 mole/100 of the inherent carbon was gasified to CO (36 /100), HC_4 (29 /100), C_2H_4 (2 /100), And CO_2 (4 /100) in 200 s of the decomposition reaction.
摘要：In this work we have analysed and modelled one-minute probability distribution function of solar direct and diffuse irradiance conditioned on the optical air mass. For this purpose, we have used one-minute data acquired in a radiometric station located in southeastern Spain (37.13°N, 3.63°W, 687 m a.m.s.l.). The study has been made over the dimensionless indices k_b and k_d. We have found marked bimodality in the k_b distribution function and asymmetry associated with the unimodal function of one-minute k_d values.
摘要：Several mathematical models to represent the behavior o the inside temperature of screenhouses were developed. Thesemodels take into account different screenhouse configurations as well as the fact that the roof can be built of a single or double layer of cover. The influence of four types of commercial screens (Lumite 32 and 50, and Tildenet 32 and 50) on inside screenhouse temperatures was analyzed. The concept of cooling through water spray was mathematically represented. Experimental data on real screenhouses was obtained at the Benin station of the International Institute of Tropical Agriculture (IITA-Benin), Republic of Benin, Africa.
摘要：In this report, a comprehensive survey on the current state of catalyst applications in the field of solar energy transformation and storage is presented. Corresponding catalyzed solar chemical processes include the pyrolysis of carbonaceous compounds for the production of hydrogen, the production of filamentous carbon as well as the synthesis of unsatureated hydrocarbon compounds by rapid direct heating of methane and quenching of the reaction products.
摘要：An industrial model solar water heating system is designed and installed, to heat and supply 110 000 liters of hot water at 85 deg. C per day for an egg powder making plant. It consists of a solar collector field (2560 m~2), four thermally insulated not water storage tanks (57.5 m~3 capacity each) and the heat distribution system with electrically operated pumps and pneumatic valves for circulation of water. It is equipped with a PC based data acquisition system to monitor the process parameters, a fault detection system to monitor the Status of various subsystems and controls for automatic operation of the system. Performance studies Conducted on the various subsystems and on the system as a whole revealed that it is delivering the designed Thermal output, and the net savings in furnace oil consumption is 78 /100 on an annual basis.
摘要：Two different principles of thermoelectric cogeneration solar collectors have been realized and investigated. Concerning the first principle, the thermoelectric collector (TEC) delivers electricity indirectly by first producing heat and subsequently generating electricity by means of a thermoelectric generator. Concerning the second principle, the photovoltaic-hybrid collector (PVHC) uses photovoltaic cells, which are Cooled by a liquid heat-transfer medium. The characteristics of both collector types are described.
摘要：This paper presents a model for prediction of the cooking power of a solar cooker based on three controlled parameters (solar intercept area, overall heat loss coefficient, and absorber plate thermal conductivity) and three uncontrolled variables (insolation, temperature difference, and load distribution). The model basis is a fundamental energy balance equation. Coefficients for each term in the model were determined by regression analysis of experimental data. The model was validated for commercially available solar cookers of both the box and concentrating types. The valid range of model application includes most of the feasible design space for family-sized solar cookers. The model can be used to estimate the cooking capacity of existing box type and concentrating type solar cookers. It can also be used to find the combinations of intercept area and heat loss coefficient required to cook a given quantity of food in a given climate.
摘要：The cylindrical latent heat storage tanks considered here are part of a domestic heating system. In this study, the performances of such energy storage tanks are optimized theoretically. Two different models describing the diurnal transient behaviour of the phase change unit were used. The first is suited to tanks where the phase change material (PCM) is packed in cylinders and the heat transfer fluid (HTF) flows parallel to it (mode 1). The second is suited to tanks where pipes containing the fluid are embedded in the PCM (mode 2). The problem (treated as two-dimensional) is tackled with an enthalpy-based method coupled to the convective heat transfer from the HTF. A series of numerical tests are then undertaken to assess the effects of various PCMs, cylinder radii, pipe radii, total PCM volume in the tank, mass flow rates of fluid, and inlet temperatures of the HTF on the storing time. In addition, optimal geometric design of the store depending on these parameters and PCMs is presented.
摘要：Several hybrid and solar-only configurations for molten-salt power towers were evaluated with a simple economic model, appropriate for screening analysis. The solar-specific aspects of these plants were highlighted. In general, hybrid power towers were shown to be economically superior to solar-only plants with the same field size. Furthermore, the power-booster hybrid approach was generally preferred over the fuel-saver hybrid approach. Using today's power tower technology, economic viability for the solar power-boost occurs at fuel costs in the neighborhood of $8.90 to $15/MW h ($2.60 to $4.40/MBtu. low heating value) depending on whether coal-based or gas-turbine-based technology is being offset. These fuel prices exist today in certain areas of the world (e.g. India). The cost of CO_2 avoidance was also calculated for solar cases in which the fossil fuel cost was too low for solar to be economically viable. The avoidance costs are competitive with other proposed methods of removing CO_2 from fossil-fired power plants and appear to be within the range of interest ( < $29/mt) to environmental protection organizations such as the Global Environmental Facility.
摘要：A composite desiccant dehumidifier made of mixed inert and desiccant materials is investigated. A heat and mass transfer model that incorporates the composite nature of the structure is discussed. The model includes both gas-side and solid-side resistances for heat and mass transport. The solid-side resistance for the mass transport includes gas-phase diffusion and surface diffusion. The effectiveness for moisture removal and heat transfer during adsorption and desorption processes in such a dehumidifier during single blow operation is investigated. Results are presented for composite structures made of silica gel and inert materials of different compositions and thermophysical properties.
摘要：Liquid desiccants are widely used in many solar applications. In order to analyze the performance of the system using desiccant technology, the thermophysical properties of desiccants are essential. In particular, the vapor pressure of the liquid desiccant is one of the important properties in air dehumidi-fication. In this paper, an attempt is made to predict this property based on a classical thermodynamics approach and it is found that the predicted values for lithium chloride agree very well with the experimental results. The desired sorption properties can also be obtained by mixing the desiccants, which is another method of developing a new cost-effective liquid desiccant. In this paper, simple mixing rules are used to predict the vapor pressure, density, and viscosity of the desiccant mixture, namely calcium chloride and lithium chloride. It is found that the interaction parameter need not be included in calculating the density and vapor pressure of the above mixture but must be included in predicting the viscosity.
摘要：A simple substitution method is proposed for the dynamic estimation of Angstroem's coefficients which play a significant role in the relationship between the global radiation and the sunshine duration. After explaining the physical meaning of the coefficients, their mathematical estimation procedures are presented on the basis of successive global radiation and sunshine duration record substitutions into the model. This new procedure yields a series of parameter estimations, the arithmetic averages of which are closely related to the classical regression method estimates. The series of model parameters estimation provide an ability to assess these parameters statistically. Consequently, such a dynamic parameter estimation procedure evaluates and enables one to make interpretations with their normal and extreme values. The methodology is applied to 28 radiation measurement stations all over Turkey. Angstroem equation parameters' regional variations are obtained for the whole country. Additional necessary relative frequency distribution functions of these parameters appeared in the form of beta distribution.
摘要：Expressions for the Linke, T_(Lvis), and Unsworth-Monteith, T_(Uvis), turbidity parameters in the visible region of the solar spectrum are derived. They are based on new determinations of the visible transmittances for the various atmospheric constituents obtained by spectrally integrating the wavelength-dependent atmospheric transmittances. Application of the T_(Lvis) and T_(Uvis) expressions for Athens is made for the first time; this is done from measurements of direct solar irradiance in the period 1992-1995. A linear interdependence between T_(Lvis) and T_(Uvis) is derived, as in the case of their broadband counterparts. The seasonal, monthly and daily variations of these turbidity parameters are also investigated.
摘要：The main results of a feasibility study of a combined cycle electricity generation plant, driven by highly concentrated solar energy and high-temperature central receiver technology, are presented. New developments in solar tower optics, high-performance air receivers and solar-to-gas turbine interface, were incorporated into a new solar power plant concept. The new design features 100% solar operation at design point, and hybrid (solar and fuel) operation for maximum dispatchability. Software tools were developed to simulate the new system configuration, evaluate its performance and cost, and optimize its design. System evaluation and optimization were carried out for two power levels. The results show that the new system design has cost and performance advantages over other solar thermal concepts, and can be competitive against conventional fuel power plants in certain markets even without government subsidies.
摘要：When exterior global/direct and diffuse illuminance, as well as zenith luminance, is regularly measured and recorded, a selection and specification of the most light efficient skylight conditions is needed. A routine representation of all 1- or 5-minute data on the P-G-D diagram can show extreme diffuse, i.e. skylight ratios normalized to the simultaneous extraterrestrial horizontal illuminance level, which indicate the bright cloudy sky conditions. A new method of cluster analysis was developed to select sky conditions associated with sunlight under specific turbidity or cloudiness conditions at actual solar altitudes, while a rough classification of the sky luminance pattern is possible using the ratio of zenith luminance to diffuse illuminance. Some characteristic data recorded in Bratislava, Slovakia during 1995 and during the three year period 1994-1996, demonstrate the parametrization and selection method used, and document detailed dynamic changes occurring during the brightest days.
摘要：In large-scale photovoltaic generators, the arrangement of modules with different electrical characteristics could involve a considerable mismatch between the single components resulting in a power loss. This means the actual power is less than the sum of the maximum output powers of the individual PV modules, operating at same irradiance-temperature conditions. To reduce the mismatch losses and to calculate it under operating conditions, a statistical approach based on Monte Carlo simulation techniques, has been developed and validated. The simulation model shows that it is possible to meet the required mismatch level, with a random arrangement, starting from a modules population characterized in terms of short circuit current, I_(sc) and open circuit voltage V_(oc), by a probability density function with a imposed variance. The method has been successfully applied for a 100 kWp standard unit photovoltaic generator, the computational results have shown good agreement with the experimental data.
摘要：The wind speed data represented in the form of frequency curves show the shape of a potential model. The Weibull and Lognormal models are used for this purpose, with hourly mean wind speed data. This study deals with the estimation of the annual Weibull and Lognormal parameters from 20 locations in Navarre. The suitability of both distributions is judged from the R~2 coefficient with a linear regression for the Weibull distribution and a nonlinear regression for the Lognormal distribution. Both approaches give a good fit, giving better results for the Weibull distribution. A comparison between the estimation and the production for a wind farm is offered.
摘要：We derive the theoretical upper limit for concentration of direct solar radiation at low latitudes with nontracking concentrators from the projected solid angle sampled by the apparent motion of the sun, for the case where the energy efficiency is referred to the energy incident on the entrance aperture. Based on the fact that the solar radiation is not uniformly distributed within this projected solid angle and that the apparent solar motion is known, we derive the optimal acceptance as a function of direction and time, which means rejecting the lower density radiation and switching off the device when losses would be higher than gains. Just as a device may gain concentration by rejecting radiation from certain directions, it can also gain by not operating at all, thus avoiding losses at certain times. Trough-type systems, which have translational symmetry, cannot be ideal nontracking concentrators, but for low losses they perform only slightly worse than general three-dimensional concentrators.
摘要：A series of full-scale measurements in the real environment were made to assess the magnitude and variability of wind-induced convective heat transfer from a raised heated surface mounted directly on to the pitched roof of a domestic size building. The heated plate had dimensions similar to those of a typical flat-plate solar collector (1.81 x 0.89 m~2), giving a Reynolds number range of approximately 1 x 10~5 to 5 x 10~5. The measured forced convective heat transfer coefficient h_w was correlated against the wind speed V and the wind direction prevailing at the site of the building during the periods of measure-ment. For a range of wind directions it was found that both power and linear relationships between h_w and V adequately represented the experimental results. Some sheltering effects were observed when the heated plate was leeward to the prevailing wind direction. Values of h_w measured in this study were in good agreement with data derived from previous wind tunnel and field work.