A theoretical study is presented on combined heat transfer by conduction, convection and radiation in a rectangular cavity with an aspect ratio of 1 to 0.2. Constant flux solar radiation at a given incidence angle is transmitted through one of the vertical boundaries and they are absorbed by the enclosure walls. The temperature distribution within the cavity is computed in an iterative manner by the net radiation method, using solution results from the heat transfer by conduction and natural convection. It is found that the radiation and conduction have a significant effect on the flow field and heat transfer. The induced radiation has a stabilizing effect on the flow field with a tendency to make the secondary cells disappear. This effect increases with increasing solar radiation intensity and incidence angle and with decreasing aspect ratio. As a result, the net energy absorbed and transferred through the end wall is also increased. A correlation for combined heat transfer is also derived which can be used in passive solar wall collector design.
Solar radiation measured by the Jordanian Meteorological Department (using actinographs) at six Jordanian sites during some, or most, of the period from 1971 to 1987 has been analysed to determine the monthly, and thus the yearly, optimum tilt angles for both single row and multi-rows of photovoltaic arrays operating in such sites. Also a comparison between the solar energy captured by a stationary mounting structure and that captured by a variable-angle mounting structure is carried out. Relative to structures of constant tilt angle the results obtained show an improvement of 5.6% by using PV-mounting structure of adjustable tilt angle.
The main objective of the present paper is to investigate the economic viability of the solar domestic hot water systems for industrial processes in Khartoum, Sudan. The industries covered in this study are soft drinks and vegetable oil. The economic viability investigation is based on life-cycle savings calculations. The economic analysis and the performance of the solar domestic hot water systems were predicted using the f-chart design method. Monthly average meteorological data are used to calculate both the annual solar fraction and the life-cycle savings. The results showed that the solar energy systems have a great potential in industrial process, and significant life-cycle savings can be achieved with solar heating systems.
Small modular power plants, 1–1200 kW in capacity, using locally available energy sources are described. The main advantages of these units are: high reliability, high availability and low maintenance. Examples of units using geothermal, solar, fossil fuel, wood and hybrid systems in remote places are given.
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.
Direct current motors are employed in photovoltaic water pumping systems; therefore, the understanding of the system operation and the matching of the system components (arrays and dc motor type) are important factors of the system design. The present study deals with the performance analysis of dc motors (series and shunt motors) powered by a solar cell array (without bypass and with bypass diode) under different shadowing conditions. The result shows that the shunt motor gives good matching to the solar cell array under shadow conditions and it has better shadow tolerance.
Hourly global and diffuse insolation data for Guadeloupe have been compared with different models. Liu-Jordan's model for the global component and Collares-Pereira's model for the diffuse component give the best fit to our data. This result to emphasize the universal aspect of these modelizations.
To gain more information on stand alone power supply (SAPS) systems in Victoria the Victorian Solar Energy Council and the State Electricity Commission of Victoria recently carried out a two-part study on these systems. In the first part of the study, 12 homes with SAPS systems, in widespread areas of the state, were fitted with monitoring equipment to gather solar, wind and system energy data. The second part of the study was an attitude survey of SAPS system homeowners, carried out under contract by AGB-Spectrum, a market research organization. The results of both study segments are being used in the production of instructional brochures for the public and to provide feedback to the homeowners and the solar industry.
In order to meet the growing energy demand, natural energy sources like water, sun and wind should be used as much as possible because of their advantages of being clean, inexpensive and renewable. This paper presents an entirely new system of wind turbine, which allows a radical increase of wind potential in the north-eastern wind called the “bora”. The “bora” occurs in Senj for 4.117 hours annually at an average speed of 8.35 m/s. It always comes from the ENE quadrant, which is essential for this system. If electric power is to be generated on a large scale the free air stream in which conventional wind turbines operate should be replaced by a programmed, concentrated stream in nozzle, similarly to what has already been done with hydropower by means of dams. As to the wind power plant Senj, nozzles would be erected in a semiconductive dam to direct the accelerated air mass to the turbine rotor and then by means of a deflector behind the rotor to ensure a reduction in velocity in order to obtain the maximum performance. A greater number of wind turbines in the nozzle, arranged as sections one next to the other, form an array (row) or a wind dam. If several arrays are then placed one after another it is possible to obtain a large wind power plant. Because of the variations in the behaviour of the “bora” and its multiplication in the nozzle, it is necessary to provide double control, both on the stator and the rotor, so as to ensure favourable operating characteristics.
This paper establishes a standardization procedure in which results are presented in ready-to-use charts for the economic evaluation of biogas plants. It is hoped this work will alleviate controversial reports on cost-effectiveness of biogas systems. Also, it is found that these systems are the most economic among renewable energy systems using a standardized procedure for their comparison augmented by the generated spider diagrams wherein most probable costing production values for each system are directly compared.
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: •-coupling of two wind turbines for the supply of water irrigation pumps,•-combination of two WECs with a battery and a diesel-set,•-combination of two WECs with a photovoltaic generator and a battery.
In 1984 Kelp Industries converted a seaweed drying kiln from oil to wood firing. Annual oil cost savings of over $100,000 are now being achieved. Based on detailed resource assessment, and a 15 year contract of sale, wood supply to the company is assured. Retention of money in the island economy has had a community benefit, viability of logging operations has been improved, and Kelp Industries are now more internationally competitive.
The present study characterizes the typical high capacity lead-acid batteries used in photovoltaic power plants for various discharge rates. A comparison between non agitated and electrolyte circulating batteries has been made. Very linear performance for the electrolyte circulating batteries, even at high discharge rates, has been one of the most interesting results of this study, thus allowing us to predict cell behaviour over the whole range. Results have been compared with those obtained from low capacity elements, concluding in a slightly higher but much more constant efficiency. Charge efficiency values were found to be constant in the photovoltaic operating range, not depending on circulation conditions.
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.
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.
A long term research programme investigating the production, processing and utilization of triglyceride oils/fats as diesel fuel substitutes has recently been completed. Vegetable oils and animal fats when converted into esters have been conclusively shown to be technically suitable for use as fuels for compression ignition engines. They can be blended with diesel fuel at any level or used neat. Conversion into esters is a simple chemical process which can be carried out on a small or large scale. Current values of crude oil at around US$20/barrel make it an uneconomic proposition to produce and process vegetable oils for fuel purposes. In the longer term if and when oil prices rise again, the use of vegetable oil fuels may become an economically viable option. In the meantime research programmes continue in countries aiming to utilize surplus rural land and in those wishing to become independent of unreliable oil product imports.
In this paper a very simple model for predicting the daily global solar radiation at any Italian location using as input of a few extensively measured meterological parameters is proposed. In fact the daily radiation G (MJ m−2) is here correlated only with the sunshine duration s (h) and the noon altitude of the sun on the 15th of the month hn (degrees) by the following equation: G= Ks0.5(sin hn)1.15 where only one value of the factor K is used. The validity of this formula is verified fixing K = 7.8 and using the data from 34 Italian stations displaced at various latitudes, altitudes or geographical situations (inland or coastal site). The test results show that the deviations of computed values of G from measured ones are generally very low; the maximum error of estimates do not exceed 10% for all tested stations with exception of three locations (Napoli, Macerata and Pian Rosá) having very particular microclimates. Therefore these deviations become less than 10% assigning to factor K the values of 7.0, 9.7 and 11.7 for Napoli, Macerata and Pian Rosá, respectively. Consequently the very simple model proposed is suitable and useful to predict the daily global solar radiation at all Italian locations which lack actinometric instruments, independently of the latitude and the altitude of the place, with good reliability.
Renewable energy resources can provide a viable alternative to the existing energy supply system, particularly in the developing countries. This paper first gives an outline of the conventional energy resources and then discusses in detail the significance of utilization of renewable energy sources in the development of remote areas of Pakistan, which consists of about 75% of its total population. Considering and outlining the indigenous renewable energy potential, and the course of the country's development, some newly established projects and the extent of their application are elucidated. The prospects of renewable energy sources for the remaining 25% urban population of Pakistan are also discussed.
In a previous paper Coppolino has proposed a very simple model for predicting the monthly mean daily global solar radiation G(MJm−2 day−1) at any Italian location using as input only the sunshine duration s (hours) and the noon altitude of the sun on the 15th of the month hn (degrees). The correlation suggested is G = 7.8s0.5(sin hn)1.15. Herein the validity of this model is verified by extending its application to dat from 24 stations displaced at various latitudes, altitudes above sea level and geographical situations in the European, African, Asian and North American areas. Furthermore the validity of this model to fit the data of the tested stations is compared with that of the well-known linear Ångström equation. The test results show that: (a) The correlation proposed by Coppolino fits well enough the measured data of the monthly mean daily global radiation for all tested stations, independent of their latitude, altitude above sea level, meteorological conditions and geographical situation (inland or coastal site). In fact the related standard per cent error of estimate Φ(%) is less than 10% for all tested locationswith the exception of Goose Bay, Canada, for which it is a little higher than 10%. (b) Although the values of the regression constants of the Ångström equation vary from location to location and for some locations from north to month, the values of Φ(%) referring to the two compared correlations are nearly equal to each other for each station considered. Consequently it must be deduced that the very simple model suggested by Coppolino is suitable and useful to predict the monthly mean daily global solar radiation with good reliability, even in the locations of the European, African, Asian and North American areas lacking actinometric instruments but provided with sunshine duration data.
Incoming solar radiation, insolation, is an important factor in many processes occuring at the earth surface. These include natural processes such as energy and moisture flux, photosynthesis, evapotranspiration, as well as quantities of interest in solar energy applications, such as energy available for focusing and non-focusing solar collectors and photovoltaic cells. In Brazil, solar radiation has been measured from 1978 through a network of pyranometers distributed all over the country. In the area limited by 15° and 34°S latitude and 40° and 67°W longitude, insolation estimates have been made using the geostationary satellite (GOES) from May 1982 to June 1984. It was thus possible to compare the simultaneous daily values of global solar radiation corresponding to the Southern part of Brazil during 1982 and 1983. The purpose of this paper is to analyse the accuracy of the estimates, presenting the results of the comparison. They show that standard error of the satellite-derived daily insolation values when compared against pyranometers is in the range of 15–30% of the mean values. Therefore, operational estimation of surface insolation in this region using GOES data appears normally feasible.
