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.     

High performance of a simple design, two effects, solar distillation unit

Under a passive mode of operation, a transient analysis of a new, simple design, two effects, solar distillation unit is presented. The unit consists mainly of a single sloped basin solar still of a shutter fashion type reflector, purging its vapor to a second effect still connected at the shaded side of the first effect still. Based on energy balance for the different components of the two effects distillation unit, hourly variations in the unit energies, temperatures, productivity and efficiency were obtained. The effects of some design, operational and environmental parameters on the distillation unit productivity are presented. On the basis of the numerical computations, it was observed that the unit first to second effects volume ratio, solar intensity, base and side wall insulation and initial temperature of the basin water significantly influence the unit's productivity. The daily productivity increases to a high as 10.7 kg/m².day for the proposed unit under the climatic conditions of Dhahran, Saudi Arabia. The proposed distillation unit is simple, passive and adds no design, operation or maintenance complexities over the conventional single effect basin solar still.     

The thermal performance of an ethanol solar still with fin plate to increase productivity

This article presented an indoor experiment on developing a mathematical model for predicting the productivity of an ethanol solar still of basin type. The test still contained a horizontal evaporating surface and a condensing surface inclined 14° to a horizontal. Various concentrations of ethanol–water solution were employed for this experiment. The distillation temperature range included boiling point. The collected data were used to estimate the mass-transfer coefficient and mass transfer conductance of the solar still. Accordingly, a mathematical model was developed based on the Spalding theory of convection and the Fick's law of diffusion. In order to increase the performance at the outdoor conditions, a basin solar still was integrated with a set of fin-plate fitting in the still basin for distillation of a 10%v/v alcohol solution. It was found that the productivity of the modified solar still was increased by 15.5%, compared to that of a conventional still. Moreover, the predicted still efficiency by the model could increase to 46% when a number of fins that raised an effective absorptance were increased. Condition of high concentration output and high productivity was investigated. Monthly mean productivity and efficiency of the still were found to increase with daily mean insolation.     

On the characteristics of multistage evacuated solar distillation

This paper proposes a new multistage evacuated solar distillation system that was designed to increase the productivity and improve the efficiency of the simple solar still. The solar still works by virtue of the higher evaporation rate under vacuum conditions. A mathematical model for the system was developed and used to optimize the system design. Fluent software was used to simulate the simultaneous heat–mass processes of the still. NASTRAN software was used for the structural analysis. The system components were fabricated and the overall system was assembled. The preliminary results showed a significant improvement of the overall productivity. Indeed, the total productivity of the solar still is affected very much by changing the internal pressure. The productivity decreased as the pressure increased due to the lower evaporation rates at the higher pressure values. The influence of the characteristic height variation on the still's estimated productivity was found to be very strong. As the height increases the productivity decreases significantly.     

Solar desalination using humidification dehumidification processes. Part I. A numerical investigation

A numerical investigation of a humidification dehumidification desalination (HDD) process using solar energy is presented. The HDD system consists mainly of a concentrating solar water heating collector, flat plate solar air heating collector, humidifying tower and dehumidifying exchanger. Two separate circulating loops constitute the HDD system, the first for heating the feed water and the second for heating air. A mathematical model is developed, simulating the HDD system, to study the influence of the different system configurations, weather and operating conditions on the system productivity. The model validity is examined by comparing the theoretical and experimental results of the same authors. It is found that the results of the developed mathematical model are in good agreement with the experimental results and other published works. The results show also that the productivity of the unit is strongly influenced by the air flow rate, cooling water flow rate and total solar energy incident through the day. Wind speed and ambient temperature variations show a very small effect on the system productivity. In addition, the obtained results indicate that the solar water collector area strongly affects the system productivity, more so than the solar air collector area.     

DESIGN STUDY OF A MULTIWICK-CUM-CONVENTIONAL SOLAR STILL-CUM-SOLAR HOT WATER SYSTEM

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.     

Solar distillation under climatic conditions of Egypt

Solar distillation in a single basin was studied theoretically under the climatic conditions of Alexandria, Egypt. The unsteady energy equations for the glass cover, water and basin were simultaneously solved. The effects of saline water depth, insulation thickness and wind speed on the still productivity were evaluated. A year-round study showed that the productivity of the still strongly depends on the solar radiation and ambient temperature. The daily still productivity varies from 1.1 to 5.2 kg/m² of basin area with an annual average of 3.16 kg/m². The solar still efficiency variesfrom 0.34 to 0.49 with an annual average of 0.42. The daily total still production increased with decreasing the water depth and increasing the insulation thickness. Increasing the wind speed resulted in a relatively small reduction in still productivity. The maximum production rate occurred after the peak in solar radiation and the time lag increases with the increase in water depth.     

Experimental evaluation of a single-basin solar still using different absorbing materials

Single-basin solar stills can be used for water desalination. Probably, they are considered the best solution for water production in remote, arid to semi-arid, small communities, where fresh water is unavailable. However, the amount of distilled water produced per unit area is somewhat low which makes the single-basin solar still unacceptable in some instances. The purpose of this paper is to study the effect of using different absorbing materials in a solar still, and thus enhance the productivity of water. Experimental results show that the productivity of distilled water was enhanced for some materials. For example, using an absorbing black rubber mat increased the daily water productivity by 38%. Using black ink increased it by 45%. Black dye was the best absorbing material used in terms of water productivity. It resulted in an enhancement of about 60%. The still used in the study was a single-basin solar still with double slopes and an effective insolation area of 3 m².     

Present status and future of crystalline silicon solar cells in Japan

Crystalline silicon solar cells show promise for further improvement of cell efficiency and cost reduction by developing process technologies for large-area, thin and high-efficiency cells and manufacturing technologies for cells and modules with high yield and high productivity.In this paper, Japanese activities on crystalline Si wafers and solar cells are presented. Based on our research results from crystalline Si materials and solar cells, key issues for further development of crystalline Si materials and solar cells will be discussed together with recent progress in the field. According to the Japanese PV2030 road map, by the year 2030 we will have to realize efficiencies of 22% for module and 25% for cell technologies into industrial mass production, to reduce the wafer thickness to 50–100 μm, and to reduce electricity cost from 50 Japanese Yen/kWh to 7 Yen/kWh in order to increase the market size by another 100–1000 times.     

The use of a thermal energy recycle unit in conjunction with a basin-type solar still for enhanced productivity

A recently developed thermal energy recycling unit operating under forced air circulation was attached to a conventional, basin-type solar still to enhance overall still productivity. In this unit, a relatively large fraction of the latent heat of condensation of the distillate is utilized to preheat and evaporate the feedstock. The system performance was tested in the laboratory using a solar simulator. The solar still was double glazed and no condensation was observed on the inner glazing when operating in the thermal energy recycling mode. The overall system productivity was about three times that of a conventional (single-effect) basin-type solar still. The advantages of the proposed system design are the following: (i) the solar still productivity can be enhanced significantly and at a reasonable cost; (ii) non-wetting glazings (e.g. certain plastic glazings) can be utilized, since in this mode of operation the glazing does not function as a condensation surface; (iii) as a result, the thermal losses from the outer surface of the glazing to the ambient can be reduced significantly by the use of double glazings; (iv) the system is very adaptable to the utilization of an external waste energy source (e.g. wet steam or hot saturated air) for nocturnal distillation, viz. operation in the absence of solar radiation.     

Theoretical and experimental studies of an ethanol basin solar still

A transient-state mathematical model for an ethanol basin solar still based on Spalding's work was developed. Driving force B was defined based on the mass balance between the evaporating (S) and condensing (G) surfaces. Mass transfer conductance (g) was obtained from an indoor experiment. Then productivity could be calculated. In order to validate the model an ethanol basin solar still was tested under outdoor conditions. The model had RMSEs of 4% and 23% of the measured mean temperature and productivity. The mean productivity was 0.33 kg/h when the mean solar radiation input was 1.95 MJ/m²/h. The simulated distillate concentrations were 74, 59 and 24%v/v for ethanol solution concentrations of 50, 30 and 10%v/v. The monthly means of the simulated daily productivity and total daily solar radiation were linearly correlated.

An indoor experimental equipment of the same type as that used for the outdoor experiments was constructed. Ethanol solutions with concentrations of 10–100%v/v were distilled. The ethanol solution temperature varied between 40 and 70 °C. The experimental data from the still was then used to find the g used for the above mathematical model. The still height had a slight effect on the productivity. Increasing the ethanol solution concentration by not more than around 80% v/v could improve the still productivity.     

Floating vertical solar still for desalination of marsh water

The performance of a floating conical solar still used for producing drinking water in brackish marsh areas has been investigated. The new proposed still consists of a vertical conical-shaped blackened cotton wick installed inside a floating transparent glass cover of similar shape. The base section of the floating cover was properly designed to allow the bottom of the wick to soak directly in the brackish water. Multiple linear regression equations, relating global solar radiation, ambient air temperature, and wind speed with the productivity of the still, have been developed. The regression analysis showed that the daily global solar radiation can be adopted alone to predict still productivity with acceptable accuracy. Results also showed that there is good competition between the proposed conical still and the conventional basin-type solar still concerning productivity and operation requirements. Recommendations have been made to use this type of still for ensuring fresh drinking water in marsh areas where the natural supply of fresh water is inadequate.     

Effect of metal oxide nanofluids on the performance of passive solar still single slope for two different absorbent plates

This study aims to improve the performances of a solar still single slope using metal oxide nanofluid (Al₂O₃–water, Cu₂O–water, and TiO₂–water). The numerical study was carried out for the climatic conditions of Agadir, Morocco, with different concentrations of nanofluids inside a basin equipped with an absorber plate with two different absorptivities. The numerical study is based on thermal balance equations applied on different solar system components and solved using the Runge Kutta method. The numerical model is validated by comparing our results with the literature available data. A comparison study of the effect of these nanofluids on solar still productivity is done. The results show that the productivity of the solar still using nanoparticles Cu₂O, TiO₂, and Al₂O₃ are 7.38, 7.1, and 7.064 kg m⁻² day⁻¹, respectively. It is obtained that the maximum efficiency of the solar still is found to be 55.27% by using cuprous oxide nanoparticles. Furthermore, an enhancement in solar still productivity of 6.36%, 19.54%, and 33.25% is obtained by dispersing 1%, 3%, and 5% volume fraction of Cu₂O nanoparticles in pure water, respectively compared to the conventional solar. Moreover, the impact of the absorptivity of the absorber plate on the solar still effectiveness is investigated. Two types of coatings are considered to change the absorber plate absorptivity. The results indicate that the efficiencies of the solar system are 58.81% and 51.77% using an absorber plate with 0.95 and 0.85 of absorptivity, respectively.     

Comparative analysis of active and passive solar heating systems with transparent insulation

The objective of this research is to achieve a high solar fraction in social housing, for which investment costs are strictly limited. Six houses have been built in the east of France: two with active (solar collectors) and four with passive (Trombe walls) solar heating systems. Two types of transparent covers are compared: a capillary structure and a simpler polycarbonate plate. The project was monitored during 1 year. Experimental measurements as well as simulation results are presented in this article. The use of simulation allowed a comparison of the various systems on a common basis, i.e., minimizing the effect of different occupants behaviour. Compared to the less expensive cover, transparent insulation increased the productivity of the air collectors 25% and doubled the gain of the Trombe wall. Thanks to passive or active controls, the thermal comfort was not reduced by the solar systems in summer nor in mid-season.     

Enhancing of solar still productivity using vacuum technology

In this study the effect of applying vacuum inside the solar still on its productivity is presented. The effect of vacuum inside the still is to avoid any heat transfer due to the convection in the still. So the heat loss from the water in an insulated still is due to the evaporation and radiation only. Hence, the air mass transfer is not included in the analysis. In presence of vacuum the effect of the non-condensable gas which reduces the rate of condensation is also avoided. The results show that applying vacuum inside the solar still increases the water productivity about 100%, i.e. enhancing the efficiency about 100%. This can be considered as the maximum increase in the productivity of the still up to now.     

Solar stills for community use—digest of technology

The many factors that influence the productivity of solar stills are discussed in three categories: atmospheric variables, design features and operational techniques. Data on the large solar stills which have been operated are tabulated, and productivity curves are given for several basin-type stills. The economics of solar distillation is also considered, and an equation is presented to calculate the cost of producing fresh water. A primary area for further work is identified, that of proving the durability of improved materials by the successful long-term operation of large solar stills. Solar distillation appears well suited for the supply of potable water to small communities where the natural supply of fresh water is inadequate or of poor quality, and where sunshine is abundant. The capital cost of large permanent-type solar stills can be as low as $1 per ft² of basin area, which is equivalent to $10 to $15 per daily gallon output, depending on the yearly amount of solar radiation and rainfall collection. The corresponding distilled water cost is between $3 and $4 per 1000 gal. These water costs are generally lower than those associated with other types of desalination equipment in plant sizes of up to, perhaps, 50,000 gpd.     

Performance analysis in stepped solar still for effluent desalination

In this work, a stepped solar still and an effluent settling tank are fabricated and tested for desalinating the textile effluent. The effluent is purified in an effluent settling tank. In this tank, large and fine solid particles are settled and clarified. The settled effluents are used as raw water in the stepped solar still. For better performance, the stepped solar still consists of 50 trays with two different depths. First 25 trays with 10 mm height and the next 25 trays with 5 mm height are used. Fin, sponge, pebble and combination of the above are used for enhancing the productivity of the stepped solar still. A maximum increase in productivity of 98% occurs in stepped solar still when fin, sponge and pebbles are used in this basin. Theoretical analysis agrees well with experimental results.     

Solar dryer for leather and a comparative study on the characteristics of open-, solar- and electrical-dried leathers

Solar energy is a cost effective, eco-friendly and pollution-free concept. It can prove to be a major energy saver for tannery application such as hot water production and leather drying. For achieving leather of good quality, controlled processing techniques are to be adopted. In order to achieve faster drying rates for higher productivity and economy in drying, a forced type of solar dryer set-up with an electrical back-up was developed. This paper illustrates the data on three different drying processes namely the open, solar and electrical drying. The data includes physical properties, surface texture, thickness variation and area reduction of leather. By controlling the drying temperature and relative humidity in solar drying, it is possible to achieve physical characteristics closer to open drying for higher productivity and cost-effective results.     

Catalytic thermochemical reactor/receiver for solar reforming of natural gas: Design and performance

The advantages of thermochemical conversion of concentrated solar energy using catalytic processes are discussed. The design of a solar volumetric thermochemical reactor/receiver (TCRR) with catalytic absorber, method for synthesis of catalytically activated ceramics, and preparation of catalytic absorber have been described. The prototype TCRR was tested in the high flux solar furnace at the DAC, Cologne by using the dioxide reforming of methane. The tests were performed to check the main concept of the TCRR design and catalytic absorber, to study the influence of solar flux distribution, the reagent flows and their ratio on the productivity or conversion, determine the reagent's conversion depending on the focal point disposition with respect to the absorber, and to study the efficiency of the thermochemical conversion. The chemical and total efficiencies of the CO₂–methane conversion were calculated using the experimentally measured concentrations of the reaction products. The highest overall efficiency achieved in these experiments was 30% with the Ni–Cr catalytic absorber.     

Development of high efficiency large area silicon thin film modules using VHF-PECVD

This paper reviews recent work on the development of thin film silicon solar modules and cost-effective production technology. Noting the potential of VHF-PECVD for high rate and high quality deposition, we initiated development of a-Si solar modules. In the first stage, we succeeded in up-scaling a-Si high quality uniform deposition at a high rate of over 1.0 nm/s to a substrate area of 1.1 × 1.4 m² to achieve high productivity. Next, the large area a-Si solar modules with stable aperture efficiency of 8% were developed, and the commercial production of a-Si solar modules commenced in October 2002. In the second stage, aiming at stable efficiency of 12%, which could make the PV power generating cost below residential electricity prices in combination with cost-effective production technology, we have been developing a-Si/μc-Si tandem solar modules. Recently, tandem modules of 40 × 50 cm² in size with a μc-Si i-layer prepared at a deposition rate of 2.1 nm/s yielded initial conversion efficiencies of 11.1%. As for small sized μc-Si single cells, technologies with a high deposition rate of 2.5 nm/s and efficiency of 8.8% have already been developed. In addition, by improving the up-scaling and light-trapping techniques, we will achieve our current goal of 12% stable efficiency for a-Si/μc-Si tandem modules at a deposition rate of over 2.0 nm/s, leading to cost-effective mass production.