Techno-economic analysis of solar distillation systems

The techno-economic analysis of a solar distillation system incorporating the effect of subsidy, rainfall water, salvage value and maintenance costs of the system is presented. The analysis is carried out by two methods, namely the marginal efficiency of capital and the average cost per year. The rate of inflation in maintenance costs is also incorporated. It is observed that the cost per kWh for producing distilled water as calculated by the average cost per year method is lower than that calculated using the marginal efficiency method. Irrespective of earlier research, it is established that the rate of increase in maintenance costs reduces the optimum lifetime of the system, and, for a practical system, the rate of increase in the maintenance costs must exceed the inflation rate and cannot be taken as constant.     

Performance of indirect solar cabinet dryer

In this paper, the development and testing of a new type of efficient solar dryer, particularly meant for drying vegetables and fruit, is described. The dryer has two compartments: one for collecting solar radiation and producing thermal energy and the other for spreading the product to be dried. This arrangement was made to absorb maximum solar radiation by the absorber plate. In this dryer, the product was loaded beneath the absorber plate, which prevented the problem of discoloration due to irradiation by direct sunlight. Two axial flow fans, provided in the air inlet, can accelerate the drying rate. The dryer had six perforated trays for loading the material. The absorber plate of the dryer attained a temperature of 97.2 °C when it was studied under no load conditions. The maximum air temperature in the dryer, under this condition was 78.1 °C. The dryer was loaded with 4 kg of bitter gourd having an initial moisture content of 95%, and the final desired moisture content of 5% was achieved within 6 h without losing the product colour, while it was 11 h for open sun drying. The collector glazing was inclined at a particular angle, suitable to the location, for absorption of maximum solar radiation. A detailed performance analysis was done by three methods, namely ‘annualized cost method’, ‘present worth of annual savings’ and ‘present worth of cumulative savings’. The drying cost for 1 kg of bitter gourd was calculated as Rs. 17.52, and it was Rs. 41.35, in the case of an electric dryer. The life span of the solar dryer was assumed to be 20 years. The cumulative present worth of annual savings over the life of the solar dryer was calculated for bitter gourd drying, and it turned out be Rs. 31659.26, which was much higher than the capital cost of the dryer (Rs. 6500). The payback period was calculated as 3.26 years, which was also very small considering the life of the system (20 years). So, the dryer would dry products free of cost during almost its entire life span. The quality of the product dried in the solar dryer was competitive with the branded products available in the market.     

Economic analysis of a G.I. sheet multiwick solar distillation plant

On account of the energy crisis, several types of solar energy devices have been developed and marketed in various parts of the world with varying degrees of thermal performance. The economic aspect of these solar energy devices becomes more significant when they replace those devices which use conventional fuels. In this paper, an economic analysis of one of the solar energy devices, namely a G.I. sheet multiwick solar distillation plant, has been presented taking into account the various factors, viz. the lifetime of the system, salvage values of the system, interest rate and maintenance cost.     

Techno-economic feasibility analysis of solar thermal systems

This communication introduces the basic concepts for techno-economic feasibility assessment of various solar thermal systems in a dynamic and market oriented economic environment. An analytical expression for calculating the payback period is derived by assuming a non-linear increase in maintenance cost and incorporating subsidy and salvage values. Further, a method is evolved to ascertain the lifetime of the system for an optimal return on investment mode, incorporating capital inflation during the lifetime and a non-linear increase in maintenance cost. The results for the payback period have been used, along with the lifetime, to optimize the cost of the system.     

CFD analysis on the influence of helical carving in a vortex flow solar reactor

Solar thermal cracking of natural gas is a promising technology, which has attracted researchers in recent years for its potential to lead to the development of CO₂ free hydrogen production process. However, experimental access to the reaction chamber of solar cracking reactors is a challenge due to the high temperature process as the instruments capable of measuring fluid flow cannot survive the medium inside the reactor. However, computational fluid dynamics (CFD) can provide an insight into the flow, where experimental access is limited or not possible. This paper presents a CFD analysis for directly irradiated solar thermochemical reactor to characterize the influence of flow behavior on the heat transfer and solar cracking process. The heat transfer by radiation from carbon particles is considered by providing global absorption and scattering coefficients in the computational domain obtained from Mie code. The flow field is based on RNG k–? model derived using renormalization group theory. This technique accounts for the effect of swirl on turbulence thereby enhancing accuracy for the swirl flows. Validation of the numerical results is carried out by making a comparison with the experimental results. Highlighting the effects of carving on the solar reactor walls, this study presents numerical analyses of solar reactor geometry for two cases; namely, when there is no vortex forming carving in the cavity, and when there is vortex forming helical carving. The results show that carving has significant influence on the flow behavior, however, it has very little effect on the outlet temperature. The numerical results also show that the radiative heat transfer mechanism is the dominant means of heat transfer compared to the effects of conduction and convection.     

Economic analysis of solar systems

This paper presents a review of various economic strategies to evaluate solar energy systems. A techno-economic criterion for solar collectors has also been presented. The analysis has been illustrated with specific examples of solar drying and solar hot water systems.     

Cost analysis of different solar still configurations

The enhancement of the productivity of the solar desalination system, in a certain location, could be attained by a proper modification in the system design. Therefore, different design configurations could be found in literatures. However, the increase in the system productivity with high system cost may increase also the average annual cost of the distillate. Cost analysis of different design configurations of solar desalination units is essential to evaluate the benefit of modification from the economical point of view. The main objective of this work is to estimate the water production cost for different types of solar stills. In this paper 17 design configurations are considered. Systems with higher and lower values of productivity are considered in this investigation. A simplified model for cost analysis is applied in this study. The results show that, the best average and maximum daily productivity are obtained from solar stills of single-slope and pyramid-shaped. The higher average annual productivity for a solar still is about 1533 l/m² using pyramid-shaped while the lower average annual productivity is about of 250 l/m² using modified solar stills with sun tracking. The lowest cost of distilled water obtained from the pyramid-shaped solar still is estimated as 0.0135 $/l while highest cost from the modified solar stills with sun tracking is estimated as 0.23 $/l.     

Exergy analysis of solar energy applications

Solar energy is a clean, abundant and easily available renewable energy. Usage of solar energy in different kinds of systems provides scope for several studies on exergy analysis. In the present work, a comprehensive literature review has been carried out on exergy analysis of various solar energy systems. The systems considered under study are solar photovoltaic, solar heating devices, solar water desalination system, solar air conditioning and refrigerators, solar drying process and solar power generation. The summary of exergy analysis and exergetic efficiencies is presented along with the exergy destruction sources.     

Thermal analysis of honeycomb solar pond

A solar pond consisting of honeycomb panels placed on a thin layer (～ 1 cm) of silicone oil floating on the body of a hot water reservoir is considered and analysed for the heat transfer processes in the system. An explicit expression for the transient rate of heat extraction at constant temperature is derived to obtain the annual variation of retrieved heat flux. The year-round thermal performance of the system has been investigated. For a solar pond with a 10 cm high honeycomb structure, annual average efficiencies of 65, 48, 33 and 24% are predicted for retrieved heat flux at temperatures of 40, 60, 80 and 90°C, respectively. A comparison between honeycomb solar pond and salt-gradient solar pond is also presented.     

Optimum tilt of solar collector for maximum natural flow

A theoretical treatment to determine the natural flow rate through a flat plate collector having heat losses is made. The governing equations have been expressed in terms of Grashof and Prandtl numbers and a dimensionless heat loss parameter. The method predicts the optimum tilt of the flat plate collector for the maximum draught for a given latitude and insolation. The experimental verification of the theoretical results shows a fair agreement.

A method to calibrate the hot wire anemometer at the desired temperature is evolved for the range of velocities encountered in practice for the flat plate solar collector.     

Derivation of the solar geometric relationships using vector analysis

The standard mathematical approach used in deriving equations to describe the apparent motion and position of the Sun is spherical trigonometry. Additionally, the derivation of the equations for the intensity of the direct beam radiation, incident on the surface of a solar collector or architectural surface, also generally relies on the same approach. An alternative approach utilizing vector analysis is used to derive all of these equations. The technique greatly simplifies the derivation of equations for quantities such as the declination, altitude and azimuth of the Sun, and the intensity of the direct beam radiation on a tilted panel with an arbitrary orientation. Additionally, it allows a simple derivation of the equations needed to accurately describe the Equation of Time and the right ascension.     

Thermal analysis of constant flow partitioned solar pond

This paper presents the thermal analysis of the process of heat extraction by circulating water layer through the convective zone of a partitioned solar pond. The observed variation of atmospheric air temperature and solar intensity is assumed periodic. Explicit expressions for the transient rate and temperature at which heat can be extracted by circulation of water at constant flow rate, are derived. Numerical computations corresponding to solar heat flux and atmospheric air temperature measurement at New Delhi during the year 1974 have been made, and the optimization of the flow rate as well as the depth of the convective-non-convective zones in the pond have been investigated. The optimum heat retrieval efficiency of 27.5%, 34% and 40% corresponding to heat retrieval temperatures of 97°C, 60.5°C and 45.5°C, respectively, are predicted for water flow rates of 2 × 10^?4, 5 × 10^?4 and 10^?3 kg/s.m², respectively. The load levelling in retrieved heat flux improves as flow rates are lowered, and the non-convective zone is oversized. With the non-convective zone depth near optimum, an increase in the depth of the heat extraction zone considerably influences the retrieved heat flux; it shifts its maximum to winter months and deteriorates the load levelling. The variability in flow rate required for the maintenance of constant temperature of the heat extraction zone is also investigated. It is found that the required variability is less for higher temperatures of the extraction zone and larger depths of non-convective zone.     

Technical feasibility assessment of a solar chimney for food drying

Solar dryers use free and renewable energy sources, reduce drying losses (as compared to sun drying) and show lower operational costs than the artificial drying, thus presenting an interesting alternative to conventional dryers. This work proposes to study the feasibility of a solar chimney to dry agricultural products. To assess the technical feasibility of this drying device, a prototype solar chimney, in which the air velocity, temperature and humidity parameters were monitored as a function of the solar incident radiation, was built. Drying tests of food, based on theoretical and experimental studies, assure the technical feasibility of solar chimneys used as solar dryers for agricultural products. The constructed chimney generates a hot airflow with a yearly average rise in temperature (compared to the ambient air temperature) of 13 ± 1 °C. In the prototype, the yearly average mass flow was found to be 1.40 ± 0.08 kg/s, which allowed a drying capacity of approximately 440 kg.     

Design and development of a simple solar dehydrator for crop drying

In this paper, a simple solar collector cum crop drying system is described. The categorical objectives of this paper are (1) to identify a suitable medium capacity solar drying system and (2) to study analytically and experimentally the performance characteristics of this newly fabricated solar drying system. The drying ratio, rehydration ratio, culinary and organoleptic characteristics, of Methi and Bhendi crops were studied and presented in this paper.     

Thermal performance, economic and environmental life cycle analysis of thermosiphon solar water heaters

In this paper, the environmental benefits or renewable energy systems are initially presented followed by a study of the thermal performance, economics and environmental protection offered by thermosiphon solar water heating systems. The system investigated is of the domestic size, suitable to satisfy most of the hot water needs of a family of four persons. The results presented in this paper show that considerable percentage of the hot water needs of the family are covered with solar energy. This is expressed as the solar contribution and its annual value is 79%. Additionally, the system investigated give positive and very promising financial characteristics with payback time of 2.7 years and life cycle savings of 2240 € with electricity backup and payback time of 4.5 years and life cycle savings of 1056 € with diesel backup. From the results it can also be shown that by using solar energy considerable amounts of greenhouse polluting gasses are avoided. The saving, compared to a conventional system, is about 70% for electricity or diesel backup. With respect to life cycle assessment of the systems, the energy spent for the manufacture and installation of the solar systems is recouped in about 13 months, whereas the payback time with respect to emissions produced from the embodied energy required for the manufacture and installation of the systems varies from a few months to 3.2 years according to the fuel and the particular pollutant considered. It can therefore be concluded that thermosiphon solar water hearting systems offer significant protection to the environment and should be employed whenever possible in order to achieve a sustainable future.     

Performance analysis of a solar photovoltaic operated domestic refrigerator

This paper describes the fabrication, experimentation and simulation stages of converting a 165 l domestic electric refrigerator to a solar powered one. A conventional domestic refrigerator was chosen for this purpose and was redesigned by adding battery bank, inverter and transformer, and powered by solar photovoltaic (SPV) panels. Various performance tests were carried out to study the performance of the system. The coefficient of performance (COP) was observed to decrease with time from morning to afternoon and a maximum COP of 2.102 was observed at 7 AM. Simulations regarding economic feasibility of the system for the climatic conditions of Jaipur city (India) were also carried out using RETScreen 4. It was observed that the system can only be economically viable with carbon trading option taken into account, and an initial subsidy or a reduction in the component costs – mainly SPV panels and battery bank.     

Modeling of the optimum tilt of a solar chimney for maximum air flow

The aim of this work is to develop a mathematical model to determine the tilt that maximizes natural air flow inside a solar chimney using daily solar irradiance data on a horizontal plane at a site. The model starts by calculating the hourly solar irradiation components (direct, diffuse, ground-reflected) absorbed by the solar chimney of varying tilt and height for a given time (day of the year, hour) and place (latitude). In doing so it computes the transmittance and absorbance of the glazing for the various solar irradiation components and for various tilts. The model predicts the temperature and velocity of the air inside the chimney as well as the temperatures of the glazing and the black painted absorber. Comparisons of the model predictions with CFD calculations delineate the usefulness of the model. In addition, there is a good agreement between theoretical predictions and experiments performed with a 1 m long solar chimney at different tilt positions.     

Exergy analysis of integrated photovoltaic thermal solar water heater under constant flow rate and constant collection temperature modes

In this communication, an analytical expression for the water temperature of an integrated photovoltaic thermal solar (IPVTS) water heater under constant flow rate hot water withdrawal has been obtained. Analysis is based on basic energy balance for hybrid flat plate collector and storage tank, respectively, in the terms of design and climatic parameters. Further, an analysis has also been extended for hot water withdrawal at constant collection temperature. Numerical computations have been carried out for the design and climatic parameters of the system used by Huang et al. [Huang BJ, Lin TH, Hung WC, Sun FS. Performance evaluation of solar photovoltaic/thermal systems. Sol Energy 2001; 70(5): 443–8]. It is observed that the daily overall thermal efficiency of IPVTS system increases with increase constant flow rate and decrease with increase of constant collection temperature. The exergy analysis of IPVTS system has also been carried out. It is further to be noted that the overall exergy and thermal efficiency of an integrated photovoltaic thermal solar system (IPVTS) is maximum at the hot water withdrawal flow rate of 0.006 kg/s. The hourly net electrical power available from the system has also been evaluated.     

Transient analysis of double basin solar still

The effect of water flowing over the upper glass cover of a double basin solar still on its transient performance has been presented. A comparative study of the daily distillate production of a double basin solar still with and without water flowing over the upper glass cover has been made, and some interesting conclusions have been drawn. Numerical calculations have been made for a typical hot day (viz 2 May 1980) in Delhi.