Showing papers in "International Journal of Solar Energy in 1995"
TL;DR: In this paper, the inverted water trickle was used for flat plate collectors for solar distillation, which is based on the flow of a thin layer (trickle) of water on the back of the absorber plate.
Abstract: The concept of inverted water trickle, which has been recently developed for use in flat plate collectors. is utilized for solar distillation. The concept is based on the flow of a thin layer (trickle) of water on the back of the absorber plate. This layer is maintained attached to the plate by means of a wire screen welded to it, together with the effect of surface tension force. As the water moves downward along the plate, and if the flow of water is very small, then it is heated up and evaporated. The vapor is transferred to an adjacent compartment where it is condensed and collected. The main features of this concept are: 1. Elimination of condensation on the glazing thereby increasing solar radiation reaching the absorber plate. 2. Increasing the temperature difference between the evaporator and the condenser, which leads to an increase in the productivity of the basin-type stills. It is believed that such an increase affects positively the new concept. In the present work the still was designed, bui...
17 citations
TL;DR: In this paper, it is argued that wind energy has a higher value than that of centralised plant, since it is fed into the low voltage distribution network and it follows that the price of wind energy is converging with its value.
Abstract: SYNOPSIS The economics of wind energy have improved rapidly in the past few years, with improvements in machine performance and increases in size both contributing to reduce costs. These trends are examined and future costs assessed. As bank loan periods for wind projects are shorter than for thermal plant, the effect on the price of wind energy is discussed. It is argued that wind energy has a higher value than that of centralised plant, since it is fed into the low voltage distribution network and it follows that the price of wind energy is converging with its value. The paper also includes a brief review of the capacity credit of wind plant and an assessment of the cost penalties which are incurred due to the need to hold extra plant on part load. These penalties are shown to be small.
17 citations
TL;DR: In this article, the authors presented the plausible costs of photovoltaic power plants of concentration, based as much as possible on the recent experience of solar thermal plants, and showed that high concentration systems based on Si or tandem cells seem to be the most promising.
Abstract: Plausible costs of photovoltaic power plants of concentration are presented. Costs are based as much as possible on the recent experience of solar thermal plants. Efficiencies, on the existing world experience of PV power plants. The result is that the costs of concentrating photovoltaic plants should be of 0.08 ECUs/ kWh, about 1/3 of that of flat module plants, and of the same order of magnitude, even lower, than those attributed to solar thermal plants of present technology. For the future, high concentration systems based on Si or tandem cells seem to be the most promising, also in the range of costs of the advanced solar thermal plants.
16 citations
TL;DR: In this article, a simple solar still coupled to an external condenser, to enhance the yield, is modeled and analytically investigated, based on actual meteorological data, and it is shown that the yield improvement depends upon both brine level and the surface area provided for heat removal.
Abstract: A simple solar still coupled to an external condenser, to enhance the yield, is modeled and analytically investigated. The analysis is general in nature and not limited to a particular condenser features. The present analysis, based on actual meteorological data, shows that the yield improvement depends upon both brine level and the surface area provided for heat removal. For an ideal still with negligible thermal inertia (water depth approaches zero) an auxiliary condensing surface at a temperature below the glass temperature decreases the daily yield. The still yield is improved for brine levels up to 10 cm above this level additional heat removal from the still does not significantly improve the daily productivity. The productivity for the limiting condition when the auxiliary condensing surface is maintained at the ambient temperature is also presented and discussed.
13 citations
TL;DR: Theoretical and experimental investigations have been carried out on a flat-plat collector using covers employing Transparent Insulation Material (TIM), and it has been found that for a minimum front heat loss coefficient an air gap of 20 mm between the plate and the TIM and 15 Ã m between the TIM between the outer cover should be used as discussed by the authors.
Abstract: Theoretical and experimental investigations have been carried out on a flat-plat collector using covers employing Transparent Insulation Material (TIM). It has been found that for a minimum front heat loss coefficient an air gap of 20 mm between the plate and the TIM and 15 mm between the TIM and the outer cover should be used. The collector performance indicates that there is no advantage in using a TIM for domestic hot water heating, but that it could usefully be employed for medium temperature applications, i. e. aboye 80°C. A value of U/rη0=3.53 W/m2K has been achieved for the flat-plate collector with 100 mm TIM encapsulated between two Teflon films and an outer Tedlar cover.
13 citations
TL;DR: In this article, the principle of OTEC and the history and results of research and development for an OTEC plant using the open and closed Rankine cycle are described, and the busbar cost of the OTEC is compared with that of conventional power plants.
Abstract: Ocean Thermal Energy Conversion (OTEC) is a system of converting thermal energy into electricity by using the temperature difference between warm water at the surface of the ocean and cold water at its depths. In this paper, first, the principle of OTEC and the history and results of research and development for an OTEC plant using the open and closed Rankine cycle are described. The busbar cost of OTEC is compared with that of conventional power plants, and the Kalina cycle is also shown.
11 citations
TL;DR: In this article, the optimal size of photovoltaic (PV) array and motor/pump subsystems for maximum utilisation of PV water pumping systems is investigated.
Abstract: Proper sizing of photovoltaic (PV) array and motor/pump subsystem are essential for maximum utilisation of PV water pumping systems. A proper matching of electromechanical loads to a PV array is a great problem in many PV systems. This is mainly related to the non-linear, solar irradiance and cell temperature-dependent voltage and current characteristics of the PV array generator. In a proper matching system, the electrical energy supplied to the load is close to the maximum available array energy. The load matching factor is one of the basic comparison method used in the optimisation of PV water pumping systems. Optimisation of PV pumping system can be made from a simple non-linear mathematical model and from experimental data. From this optimisation technique, array configuration can be determined using the required rated power of the motor/pump subsystem and the I-V characteristic of a single cell. Conversely, the optimal size of motor/pump subsystem can be determined from a known array configuration. ...
9 citations
TL;DR: In this article, a floating sponge solar still designed for sea water desalination is presented, where an optimum thickness of 150mm was obtained for the tested material which had a density of 16 kg/m.
Abstract: A floating sponge solar still designed for sea water desalination is presented. Experimental evaluation of the still performance with possible practical applications are also given. These experiments were carried out on a laboratory model which was built and tested under outdoor climatical conditions. A single-sloped cover was used with four different sponge thicknesses to investigate the still performance. An optimum thickness was thus obtained for the maximum productivity. This optimum thickness was found to be 150mm for the tested material which had a density of 16 kg/m. The maximum productivity of the still was found to be 3.1 litres/day, obtained with the optimum thickness of sponge material and the single-sloped cover. A double-sloped cover was also used with the optimum sponge thickness obtained from the previous tests to examine its effect. The results obtained show that the double sloped cover increased the productivity of the still by some 58%, to 4.9 litres/day, with the same still efficiency. ...
9 citations
TL;DR: In this article, the performance of a glazed solar collector/regenerator for an open-cycle absorption solar cooling system using aqueous lithium chloride solution as the working fluid was tested at Kaohsiung, Taiwan under a humid climate.
Abstract: The performance of a glazed solar collector/regenerator (C/R) for an open-cycle absorption solar cooling system using aqueous lithium chloride solution as the working fluid was tested at Kaohsiung, Taiwan under a humid climate. The results indicate that the peak system efficiency is 15.2% and the day-average efficiency is 14.1%. The effects of parameters on the C/R performance are studied, and the non dimensional correlations for heat and mass transfer were given.
8 citations
TL;DR: In this paper, the authors focused on the potential use of solar ponds as a primary heating system in a greenhouse and developed models to simulate both the solar pond and the greenhouse thermal behavior based on conventional energy balance equations.
Abstract: To maintain prescribed temperature levels inside a greenhouse for plant growth, diesel fuel was used in the past, however due to increased fuel prices, greenhouse heating expenses have reached such levels that conservation and alternative methods are becoming attractive. Such alternatives include solar passive heating, and solar ponds. Although there are several methods of heating a greenhouse, the present paper focused on the potential use of solar ponds as a primary heating system. The possibility of supplying all heating requirements of a greenhouse through a solar pond has been theoretically investigated. Models to simulate both the solar pond and the greenhouse thermal behavior were developed based on conventional energy balance equations. Numerical techniques were used to estimate daily greenhouse heating and cooling requirements and the performance of the solar pond as a heating system.
8 citations
TL;DR: In this paper, the TRNSYS program was used to simulate the performance of a thermosyphon type domestic solar water heating system which is used in the West Bank.
Abstract: TRNSYS program was used to simulate the performance of a thermosyphon type domestic solar water heating system which is used in the West Bank. The system installation and operation parameters were optimized including collector tilt angle, the hot water storage tank volume and location relative to the collector, and the hot water consumption pattern and daily rate.
TL;DR: In this article, a model of a solar space power station is developed and the usual material properties are introduced and their influence on the system performance is analyzed, including geometric factors and the concentration ratio.
Abstract: A model of a solar space power station is developed. The usual material properties are introduced and their influence on the system performance is analyzed. The geometric factors and the concentration ratio are accurately defined and taken into account in case of five types of mirrors usual in solar power applications. Both design and operational optimizations are envisaged. Universal graphs are drawn for the optimum ratio between the collector and radiator area and for the maximum power. A brief comparison between three usual types of mirrors (conical, parabolic cylinder and paraboloidal) is performed.
TL;DR: In this paper, the applicability of several theoretical and empirical models which compute diffuse radiation on a horizontal surface were compared and tested for their applicability to one location in die eastern Mediterranean basin in general, on the basis of statistical error tests.
Abstract: Solar radiation measurements at one location in Cyprus are used to test the applicability of several theoretical and empirical models which compute diffuse radiation on a horizontal surface. Two types of correlation tests were used [1]: the first correlates the ratio of diffuse-to-global solar radiation with the “clearness index” KT; and the second correlates the ratio of diffuse-to-global solar radiation with the fractional sunshine. Therefore, the selected models for discussion are compared and tested for their applicability to one location in die eastern Mediterranean basin in general, on the basis of statistical error tests. A comparative study of the models shows that Page's model [3], based on the first type of correlations and Hay's one [13] based on the second type of correlations, are equally accurate for the greater Cypriote environment. Finally, two statistical equations are proposed for estimating diffuse radiation for solar energy applications in the greater environment of Cyprus.
TL;DR: In this article, an algorithm for calculating the collection efficiency for any time period has been developed, which shows that the maximum daily collection efficiencies ηc,d all over the year are obtained for the N-S orientation at sites having latitude angles ≤ 15°.
Abstract: Parabolic trough solar collector PTC is often oriented with its axis horizontally in the North-South or East-West direction. However, it may be set in a position where its axis makes an angle Ψ with the south direction. The main objective of the present work is to study the effect of this angle on the collection efficiency. An algorithm for calculating the collection efficiency for any time period has been developed. The results obtained by using this algorithm by using this algorithm show that the maximum daily collection efficiencies ηc,d all over the year are obtained for the N-S orientation at sites having latitude angles Φ ≤ 15°. For latitude angles Φ > 15°, ηc,d are much higher in summer days than in winter ones for N-S orientation. In the case of orienting die collector with an angle 70° lt; Ψ ≤ 90°, ηc,d are higher in winter days than in summer ones This orientation is preferable to obtain almost constant output of PTC through the whole year. The results show also that a trough oriented with an an...
TL;DR: In this article, the authors discuss a methodology for shaping a range of collaborating future societies through a conscious democratic process, instead of having more or less arbitrary events and interest groups determine the path of change.
Abstract: This text is not about predicting the future, but rather aims at discussing a methodology for shaping a range of collaborating future societies through a conscious democratic process, instead of having more or less arbitrary events and interest groups determine the path of change. The underlying belief is, that mere exists infinitely many possible futures, and that we can decide which one we want to be headed towards, as the outcome of a democratic process that lets our individual value system and preferences come into full play.
TL;DR: In this paper, the authors proposed a thermal energy storage system that uses a water lake as a thermal storage over the four seasons, which can be used for mostly regional cooling in a solar energy-based rural community.
Abstract: For promoting efficient use of energy, a new concept is required that society can choose to make a positive approach toward a solar energy based rural community which maximizes harmony with nature. This basic concept lead to a new proposal of a system to use a water storage over the four seasons: a system which uses a water lake as a thermal energy storage. Thermocline measurements were made at the Uchikawa Dam Lake located in Kanazawa, Ishikawa, Japan to evaluate several kind of energy contents as a new energy supply potential. The data indicated that the system could be developed with full potential as a seasonal energy storage to be used for mostly regional cooling. This concept seems interesting to invite internationally an energy efficient society to be employed in LDCs as well as in developed countries.
TL;DR: In this paper, the performance of diffusion stills used in solar distillation was studied theoretically under the climatic conditions of Alexandria, Egypt, and the effects of the air gap spacing, inlet water flow rate, insulation thickness and wind speed on the daily production were evaluated.
Abstract: The performance of diffusion stills used in solar distillation was studied theoretically under the climatic conditions of Alexandria, Egypt. The governing equations for unsteady heat and mass transfer inside vertical and inclined stills were solved numerically for the glass cover, absorber plate and the water layer. The study covered all angles of tilt between horizontal and vertical positions for the twelve months of the year. The effects of the air gap spacing, inlet water flow rate, insulation thickness and wind speed on the daily production were evaluated. The daily still productivity strongly depends on the solar radiation and ambient temperature and varies between 0.5 and 5 Kg/m2. An optimum angle of tilt is given for each month of the year. The daily yield increased with increasing the insulation thickness and decreasing the gap spacing or inlet water flow rate. The effect of wind speed was almost negligible up to 5 m/s.
TL;DR: In this article, a screening level simulation model for wind/diesel systems is described for use to give a quick overview of the possible appropriateness of a wind and diesel system and indicate whether more detailed analysis would be of use.
Abstract: This paper describes a screening level simulation model for wind/diesel systems. It is intended for use to give a quick overview of the possible appropriateness of a wind/diesel system and indicate whether more detailed analysis would be of use. The model was developed for use on personal computers and to trade complexity for ease of operation. The wind/diesel system modeled may include: 1) Wind regime, 2) One or more wind turbines, 3) System electrical load 4) One or more diesel generators, 5) Dump load, 6) Short term storage, and 7) System controller. The model does not consider storage explicitly, but does distinguish between the no storage and minimal storage (power smoothing) systems. This work is based on the more detailed simulation models previously developed at the University of Massachusetts, but uses probabilistic methods rather than time series data inputs. As such it requires only mean and standard deviation of wind speed and load for each month or season. The model functions by assuming that...
TL;DR: Since 1975, when the first energy R&D programme was drawn up by the Council of Ministers, 5 successive multiannual programmes on renewable energies have been implemented by the European Commission in Brussels as mentioned in this paper.
Abstract: Since 1975, when the first energy R&D programme was drawn up by the Council of Ministers, 5 successive multiannual programmes on renewable energies have been implemented by the European Commission in Brussels. The total budget spent on project support by the Commission during this period was 350 Mio ECU. The main emphasis has been on photovoltaics, biomass, wind energy and solar applications in buildings. The paper will summarize the main achievements of this European effort.
TL;DR: In this paper, an attempt has been made to develop an analytical expression for an instantaneous thermal loss efficiency factor for a summer greenhouse, based on energy balance equations for each component of the greenhouse in a steady state condition.
Abstract: In this technical note, an attempt has been made to develop an analytical expression for an instantaneous thermal loss efficiency factor for a summer greenhouse. The analysis is based on energy balance equations for each component of the greenhouse in a steady state condition. Effect of design and climatic parameters have also been taken into account. An ideal condition has been achieved analytically, for a best summer greenhouse. The nature of characteristic curve obtained by the present model has been compared with the experimental results obtained by others.
TL;DR: In this article, an experimentally validated model was used to simulate integral passive solar water heaters for five diverse European locations and a design nomogram was produced via correlations of diurnal solar savings fractions.
Abstract: Using an experimentally validated model, annual hour-by-hour simulations of integral passive solar water heaters were undertaken for five diverse European locations. Via correlations of diurnal solar savings fractions, a design nomogram is produced.
TL;DR: In this article, a simple method is presented for the prediction of the modules' energy production which is based on solar radiation data, the module's peak power and a quality factor QM.
Abstract: The real energy production of photovoltaic (PV) systems differs significantly from predictions which are based on standard test conditions (STC) for PV-modules. By taking into account the physical differences between real boundary conditions and STC, energy prediction becomes possible with high precision. The most important effects such as non-vertical incidence of real solar radiation, the real means of solar radiation and the means of real module temperatures will be investigated and their influence on energy production given. Based on these findings, a simple method will be presented for the prediction of the modules ‘ energy production which is based on solar radiation data, the modules’ peak power and a quality factor QM. In a next step the quality factor for PV systems will be presented and compared with real data from European PV plants and the German 1000-roofs project. It will be shown that the quality factor is ideally suited to determine the systems-engineering quality of a PV plant independent...
TL;DR: In this article, the authors investigated the solar collector-reflector system from the point of view of enhancing the performance for water heating and developed an analytical model for evaluating the enhanced energy yield and the water temperature.
Abstract: This communication presents an investigation of solar collector-reflector systems from the point of view of enhancing the performance for water heating. An analytical model is developed for evaluating the enhanced energy yield and the water temperature. The model takes into account the exchange factor between the collector and the reflector and shading effect of the reflector on the collector. Numerical results are presented for the summer and winter season of a typical year in Delhi climate. Il is found that the addition of reflector on collector increases the solar yield on the collector and the overall thermal performance of the collector. The enhancement in the solar yield on the collector is about 44% in winter and 15% in summer conditions, which is consistent with more hot water demand in winter.
TL;DR: In this paper, an analytical expression for the collector efficiency factor (F') has been derived which is based on energy balance equations of a compact N built in storage cum flat plate water heater.
Abstract: In this technical note, an analytical expression for the collector efficiency factor (F') has been derived which is based on energy balance equations of a compact N built in storage cum flat plate water heater. Effects of various water heater parameters namely the fin efficiency factor (F), tank spacing (W), an absorber thickness (8), spacing between an absorber and the glass cover (Lg), the operating temperature range etc. on the collector efficiency factor (F') have been studied. The collector efficiency factor (F') depends significantly on the number of tanks in the water heater.
TL;DR: In this article, a simple first harmonic approximation method has been used to predict the temperature variations as a function of depth and time for different soils (ordinary light soil, heavy soil, organic soil and sand) and soil conditions (dry, damp and wet).
Abstract: The annual temperature variations in earth with depth from the surface offers, by its natural characteristics, a phase lag and reduced variation in the maximum and minimum temperatures. The temperature profiles vary for different soils and soil conditions. Soil temperatures are found to be an explicit function of soil thermal properties, particularly the thermal diffusivity. The earth temperatures stabilize at certain depth, where the annual swings in temperature are negligible and this stabilizing depth varies for different soils. A simple first harmonic approximation method has been used to predict the temperature variations as a function of depth and time for different soils (ordinary light soil, heavy soil, organic soil and sand) and soil conditions (dry, damp and wet). The results are a helpful indicator for deciding external design temperatures for the design of earth sheltered or ground coupled spaces.
TL;DR: In this paper, an economic evaluation of solar thermal power generation for Indian conditions is presented, which incorporates case study of parabolic trough collector technology for power generation in 30 MW scale taking into account various options such as Solar Alone and Solar Hybrid.
Abstract: This paper presents economic evaluation of solar thermal power generation for Indian conditions. The study incorporates case study of parabolic trough collector technology for power generation in 30 MW scale taking into account various options such as Solar Alone and Solar Hybrid. Sensitivity analysis by varying plant load factor, discount rate and the capital cost etc. has also been carried out for both - the Solar Alone and Solar Hybrid case. It is found that Solar Hybrid system is a better option than Solar Alone and the cost of power generation is competitive with conventional means. It is also concluded that unit cost of generation is critically dependent on the capital cost of the plant, discount rate and the number of units generated.
TL;DR: In this article, the performance and economic evaluation of a solar heating and cooling system was studied using the transient simulation program (TRNSYS) using the domestic water heating load, space heating load and cooling load of a typical Egyptian house were considered.
Abstract: In this investigation, the performance and economic evaluation of a solar heating and cooling system was studied using the transient simulation program (TRNSYS). The domestic water heating load, space heating load, and the cooling load of a typical Egyptian house were considered. The study involves five different localities which were chosen to represent the climatic changes all over Egypt. These localities are: Aswan (Upper Egypt), Kharga (Western Desert), Asyout (Middle Egypt), Cairo (Cairo), and Marsa Matrouh (Mediterranean).
TL;DR: In this article, the spectral and broad-band solar ultraviolet radiation for die period 1979-1993 were calculated considering the total ozone values, derived from both the satellite Nimbus-7, and the ground-based Dobson spectrophotometer.
Abstract: Daily broad-band and spectral measurements of solar ultraviolet radiation reaching the ground at Athens, Greece (38°N, 24°E) during 1989-1993 in conjunction with daily total ozone measurements deduced from satellite and ground-based instrumentation were used to investigate their association. Furthermore, employing a new parametric model, the spectral and broad-band solar ultraviolet radiation for die period 1979-1993 were calculated considering the total ozone values, derived from both the satellite Nimbus-7, and the ground-based Dobson spectrophotometer.
TL;DR: In this article, the productivity of solar stills has been investigated and the effects of design changes on the productivity have been shown, based on energy balances of different components of the system.
Abstract: There has been considerable effort as to the manner in which the productivity of solar stills is affected by many of the designs and operating variables. To assist in designing the stills of improved performance, design parameters involved in the operation of the system have been considered in this paper. Curves showing the magnitude of the effects of design changes on the productivity are presented. Numerical computations, which are based on energy balances of different components of this system, confirm the productivity improvement in between 23.6% to 51.2% depending on the water-flow-rate from the vertical water column on the multiwicks. This design incorporates a multiwick solar still and a conventional basin type solar still. Hot water at considerably higher than the ambient temperature may be obtained at different flow rate from this design as well.
TL;DR: In this article, the effect of changing the radial spacing on the rated MW and the total number of heliostats in the field is also computed and depicted, and a set of charts for the spillage factor are developed for solar central receiver system design.
Abstract: Some of the reflected beam radiation from a heliostat field bypasses the receiver surface. The spillage factor which is a measure of how much of reflected beam radiation actually intercepted by the receiver surface, is calculated and plotted for easy access. The variation of ihe spillage factor with tower height, external cylindrical receiver size, dimensionless radial distance from the tower is computed and plotted. The value of the rated MW energy absorbed by an external cylindrical receiver, is investigated, and its relations to the tower height, the site location and the field radius are given. The effect of changing the radial spacing on the rated MW and the total number of heliostats in the field is also computed and depicted. The developed set of charts for the spillage factor are believed to be very useful for solar central receiver system design.