Solar & Wind Technology最新文献

The validity of various models for predicting the solar radiation on inclined surfaces was investigated by employing 2-year measured hourly irradiation data on horizontal and vertical surfaces for Nicosia, Cyprus. Models using isotropic and anisotropic distribution of sky radiance are evaluated. The results indicate that the annual root mean square error for all the tested algorithms varies from 3.6 to 7%.

The performance of a flat-plate collector, set up in a driving loop, has been studied when some parameters such as the solar irradiance, the saturation temperature or the absorber characteristics vary. A steady-state model of the collector has been studied. The equations are developed for a fluid in which first sensible heat transfer occurs, then boiling. The experimental and theoretical results are compared and it is concluded that the total heat loss conductance cannot be assumed as constant. The collector efficiencies have been calculated for different conditions.

A modular system for the supply of remote electrical consumers was developed, which makes possible a variable integration of wind energy and photovoltaic plants in connection with a diesel engine and battery storage. The wind energy converters, equipped with asynchronous generators, and a fast pitch control, work in parallel with a synchronous generator. The generator is driven by a diesel engine by means of an overrunning clutch, and is started by a small d.c. motor. If the diesel is off, or the starting process by the d.c. motor is finished, the synchronous generator works as a rotating phase-shifter and takes over voltage control and supply of reactive power. The speed versus power control of the wind energy converters makes possible an optimized parallel operation with the diesel-generator unit, and also directly takes over frequency control when operated singly without the diesel engine. The location of the wind turbine does not depend on the site of the diesel engine, because control cables are not necessary. To avoid too frequent starting of the diesel, a storage battery is installed. This paper describes the electrical and control design as well as the experience with the following, already built plant:

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  -coupling of two wind turbines for the supply of water irrigation pumps,

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  -combination of two WECs with a battery and a diesel-set,

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  -combination of two WECs with a photovoltaic generator and a battery.

Electricity supply to rural and remote areas in developing countries is a major problem because of the large costs, population distribution, and inaccessibility of remote communities to grid extension. In Fiji, less than 40% of the rural population has access to grid electricity, most of these in the two major islands. The potential for the generation of electricity through burning biomass fuels such as sawmill and crop wastes is substantial, particularly for areas close to sawmills and forest logging sites. After establishing the availability and costs of various biomass fuels in Fiji, a system for the utilization of such wastes is described. The 25 kW rural area power supply (RAPS) system consists of a simple, low-cost furnace/boiler to generate steam which powers a simple, reciprocating steam engine to drive an alternator to supply the load. With the existence of an adequate thermal load (such as for crop drying or for hot water), an electricity/heat cogeneration system can be installed with the engine exhaust steam supplying the heat load. The advantages of such a supply system are discussed along with problems and system economics in comparison to an existing wood-fired cogeneration system.

Cu₂S/Si heterojunctions have been fabricated by chemically depositing Cu₂S thin films on n-type CSi substrates. Films grown on glass slides side by side had a thickness of 0.5 microns, resistivity of 2 × 10⁻¹ ohm cm and optical band gap of 1.9 eV. Ohmic back contact was made by electroless technique. The front grid was a spring-loaded metal mesh. Junction characteristics were measured on as-grown and air-annealed samples in dark and under illumination of 80 mW/cm². Annealing at 200°C showed substantial improvement on the junction characteristics. Typical values obtained on annealing are J_sc 110 μA/cm², V_oc 120 mV and F.F. = 0.36. Suggestions for further improvement are also mentioned.

A model for predicting diurnal changes in wind speed has been developed for the Fathailya area, located 30 km northeast of Baghdad. This model was based upon hourly values of wind speed for the period of 1984–1987. The hourly average of monthly diurnal variations of wind speeds and air temperatures showed that they have the same patterns and that these patterns change seasonally in the same manner. The model uses a truncated sin wave function to predict daytime wind speed changes and an exponential function to predict night-time wind speeds. Inputs for the model are latitude, date and daily wind travel. The closeness of the calculated wind speeds to the measured value was checked by comparing the average differences and the standard deviation of the average maximum of 1.6 m/s for February to a minimum of 0.8 m/s for October.

Hourly and daily global and diffuse solar radiation data measured on a horizontal surface during the period 1983–1987 for Amman, Jordan are studied and analyzed. The observed ratios between monthly mean hourly to daily global and diffuse radiation are determined. The applicability of various radiation models for the estimation of hourly global and diffuse radiation from daily values of global and diffuse radiation, respectively, for Amman is tested against measured data. The normal distribution curve suggested by Jain [Solar Wind Technol.5, 7 (1988)] is found suitable for predicting hourly global radiation for Amman and it has shown excellent agreement with the observed values amobgst all other models used. The classical equation of Liu and Jordan [Solar Energy4, 1 (1960)] produced satisfactory results of hourly diffuse radiation which are much closer to the observed values as compared to that obtained using other suggested models. Comparison between results obtained using various radiation models is made by calculating the root mean squared error, RMSE, for each model used.

Analysis of a solar operated two-stage LiBrH₂O cycle is presented. The cycle has the advantages that it can operate at a higher ambient temperature and at a lower generator temperature than those required by the single stage cycle. The performance of the cycle is predicted and compared to the performance of the single stage cycle at various design conditions. Four design parameters are identified to control the performance of the cycle. These parameters are the heat sink temperature, the evaporator temperature, the generator temperature, and the intermediate pressure. Numerical correlations are developed to specify the minimum allowable sink temperature, the minimum and maximum allowable generator temperature and the coefficient of performance of both the single-stage and the two-stage cycles. By defining a system thermal ratio for the combined absorption machine and a flat plate collector, the performances of the integrated systems are evaluated and compared when using both cycles. Conditions at which the performance of the solar operated two-stage cycle is superior to that of the solar operated single stage cycle are defined.

From data about the relative sunshine hours and the atmosphere's transmissivity, we reconstitute the temporal and geographical evolution of the solar radiation for Algeria. This study shows that the annual average solar radiation is more marked by the astronomical factors whereas the monthly radiation is rather dependent on meteorological phenomena. Descriptive maps are drawn and the analyses of the results are discussed.