Solar & Wind Technology最新文献

Swaziland has many energy resources including biomass, coal, hydro and solar. These resources, in particular biomass, supply a major proportion of energy consumption, but all petroleum products and most coal and electricity are imported from or via South Africa. Swaziland could increase self-reliance, at a financial cost, by substituting local coal for imports, and by generating more electric power from biomass, coal or hydro sources. Ethanol for 20% petrol blending should soon be produced from molasses. Deforestation is evident in the country and suggests that fuelwood demand exceeds the sustainable supply from accessible land: this is an issue in both national and individual self-reliance. Supply and demand could be matched by using wood more efficiently; increasing the supply; and substituting other energy sources. Stoves and afforestation programmes can succeed only if they meet the perceived needs of individual consumers, and require proper market research and marketing. Fuel substitution shows limited promise, but hydro- and photovoltaic systems might assist rural development.

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.

Two empirical models for estimating monthly mean daily total solar global radiation on a horizontal surface have been tested for its applicability to Iberian Peninsula. The models are simple empirical formulae developed by Sivkov, and Goldberg and Klein, respectively. Only a few modifications have been suggested. The agreement between the measured and the estimated values is remarkable and the models are both recommended for use in any location in Spain.

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.

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.

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.

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.