Exergy Analysis of Solar Still with Sand Heat Energy Storage

This paper studies the experimental and exergy analysis of solar still with the sand heat energy storage system. The cumulative yield from solar still with and without energy storage material is found to be 3.3 and 1.89 kg/m², respectively for 8-h operation. Results show that the exergy efficiency of the system is higher with the least water depth of 0.02 m (m_w = 20 kg). Competitive analysis of second law efficiency shows that the exergy efficiency improves the system by 30% than conventional single slope solar still without any heat storage. The maximum exergy efficiency with energy storage material is found as 13.2% and it is less than the conventional solar still without any material inside the basin.     

Performance of solar still with a concave wick evaporation surface

Surfaces used for evaporation and condensation phenomenon play important roles in the performance of basin type solar still. In the present study, a concave wick surface was used for evaporation, whereas four sides of a pyramid shaped still were used for condensation. Use of jute wick increased the amount of absorbed solar radiation and enhanced the evaporation surface area. A concave shaped wick surface increases the evaporation area due to the capillary effect. Results show that average distillate productivity in day time was 4.1 l/m² and a maximum instantaneous system efficiency of 45% and average daily efficiency of 30% were recorded. The maximum hourly yield was 0.5 l/h. m² after solar noon. An estimated cost of 1 l of distillate was 0.065 $ for the presented solar still.     

Experimental analysis and exergy efficiency of a conventional solar still with Fresnel lens and energy storage material

This study focuses on the experimental investigation and exergy analysis of a modified solar still (MSS) with convex lenses on glass cover to collect the solar radiation at the focus on surface water. A comparative analysis of the performance and yield of the MSS with convex lenses and the conventional single slope SS were carried out for the same climatic condition of Tanta (Egypt). Similarly, the effect of modification in the SS using convex lenses, with or without black stones, on the freshwater yield is experimentally investigated. The results indicated that the lenses focus the solar radiation to the water placed in the basin and increase the water‐glass temperature difference (T _w – T _g). The yield of freshwater from the MSS with the convex lenses is comparatively higher than that of the conventional SS (26.64%). In addition to convex lenses in the inner cover surface, freshwater yield improved by 35.55% by adding blue stones as energy material inside the basin under constant water mass of 30 kg. The maximum exergy efficiency of the SS with lenses and blue stones was 11.7%, while the SS with lenses alone was 4%. The quality of freshwater produced after desalination was well within the World Health Organization standards. The total dissolved solids and pH after desalination were 22 mg/L and 8.08, respectively.     

Further studies on double solar still

This paper is devoted to the development of a transient model of the performance of a double solar still and its validation by experiments. the dependence of the daily output of the distillate on wind velocity, ambient temperature and daily insolation has been studied analytically. It is seen experimentally that the presence of a black dye in the lower basin increases the distillate output by 10 to 15 per cent.     

A hybrid high efficiency single-basin solar still

In this work, an attempt has been made to enhance the distillate output of a single-basin solar still by coupling it with a flat plate solar collector and by coating a thin layer of SnO₂ on one side of the transparent cover plate. The heat transfer fluid was circulated between the still and the collector through a heat exchanger and storage tank by thermosyphonically induced flow. It was observed that good insulation around the storage tank considerably increased the yield at night due to the decrease of ambient temperature. Thermosyphonically induced flow eliminated the need for pumps and control units. A layer of SnO₂ on the transparent cover lowered the thermal radiation loss, one of the major sources of heat energy loss in a solar still. Values for solar radiation, ambient air temperature, salt-water temperature in the basin, temperature of air-vapour mixture within the still, input and output temperatures of the heat exchanger heat transfer fluid, and the distillate yield were collected by a data acquisition system. After making the above modifications, the distillate yield was measured to be 6·745 litres per square metre per day for a September solar radiation of 17820 KJ at Istanbul-Gebze. To compare the distillate yield, a conventional solar still with similar dimensions to those of the improved still was constructed. The overall efficiency of the improved still was found to be 3·26 times the efficiency of the conventional still.     

Performance analysis of double basin solar still with evacuated tubes

Solar still is a very simple device, which is used for solar distillation process. In this research work, double basin solar still is made from locally available materials. Double basin solar still is made in such a way that, outer basin is exposed to sun and lower side of inner basin is directly connected with evacuated tubes to increase distillate output and reducing heat losses of a solar still. The overall size of the lower basin is about 1006 × 325 × 380 mm, the outer basin is about 1006 × 536 × 100 mm Black granite gravel is used to increase distillate output by reducing quantity of brackish or saline water in the both basins. Several experiments have conducted to determine the performance of a solar still in climate conditions of Mehsana (latitude of 23°59′ and longitude of 72°38′), Gujarat, like a double basin solar still alone, double basin solar still with different size black granite gravel, double basin solar still with evacuated tubes and double basin solar still with evacuated tubes and different size black granite gravel. Experimental results show that, connecting evacuated tubes with the lower side of the inner basin increases daily distillate output of 56% and is increased by 60, 63 and 67% with average 10, 20 and 30 mm size black granite gravel. Economic analysis of present double basin solar still is 195 days.     

Thermal performance of “still on roof” system

This paper presents an analysis of periodic heat flux through a roof, on which a solar still has been placed. It is seen that on a typical hot day in Delhi, for high reflectivity of the bottom of the basin (on account of deposits or otherwise) the daily heat flux in the room gets reduced by 40% and the production of distilled water is 0.6 kg/m² day; the produced swings in the heat flux also get reduced in magnitude. For a typical cold day in Delhi, if a black dye is mixed with basin water the daily heat flux in the room increases by a factor of two and the yield of the distillate becomes 5.0 kg/m² day.     

An experimental study of hybrid photovoltaic thermal (PV/T)-active solar still

In this paper a new self-sustainable hybrid photovoltaic thermal (PV/T)-integrated-active solar still has been designed and tested for composite climate at I.I.T. New Delhi (28°32′N, 77°12′E). The PV system is used to generate electricity to run the pump (60 W and 18 V) as well as thermal energy to heat the water in the collector. The proposed design of hybrid-active solar still can be used at any remote location because of its self-sustainability. The experiments were performed on the set-up for different water depths and for different running duration of the pump. It has been observed that the hybrid-active solar still gives a higher yield (more than 3.5 times) than the passive solar still. It has also been observed that the daily distillate yield and thermal efficiency of the hybrid-active solar still remain almost the same for all water depths in the basin by reducing the daily running period of the pump from 9 to 5 h. This running period of the pump reduced saves 43% of the power used to run the pump with 9 h running, without affecting the performance of the solar still. This work also deals with exergy analysis of the system. Copyright © 2008 John Wiley & Sons, Ltd.     

Comparative thermal performance evaluation of an active solar distillation system

In this paper, thermal models of all types of solar collector‐integrated active solar stills are developed based on basic energy balance equations in terms of inner and outer glass temperatures. In this paper, hourly yield, hourly exergy efficiency, and hourly overall thermal efficiency of active solar stills are evaluated for 0.05 m water depth. All numerical computations had been performed for a typical day in the month of 07 December 2005 for the climatic conditions of New Delhi (28°35′N, 77°12′E, 216 m above MSL). The thermal model of flat‐plate collector integrated with active solar still was validated using the experimental test set‐up results. Total daily yield from active solar still integrated with evacuated tube collector with heat pipe is 4.24 kg m^?2 day^?1, maximum among all other types of active solar stills. Copyright © 2007 John Wiley & Sons, Ltd.     

Exergy‐based performance analysis of packed‐bed solar air heaters

This paper presents an experimental investigation of the thermal performance of a solar air heater having its flow channel packed with Raschig rings. The packing improves the heat transfer from the plate to the air flow underneath. The dimensions of the heater are 0.9 m wide and 1.9 m long. The aluminium‐based absorber plate was coated with ordinary black paint. The characteristic diameter of the Raschig rings, made of black polyvinyl chloride (PVC) tube, is 50 mm and the depth of the packed‐bed in flow channel is 60 mm. Energy and exergy analyses were applied for evaluating the efficiency of the packed‐bed solar air heater. The rate of heat recovered from the packed‐bed solar air heater varied between 9.3 and 151.5 W m^?2, while the rate of thermal exergy recovered from the packed‐bed solar air heater varied between 0.04 and 8.77 W m^?2 during the charging period. The net energy efficiency varied from 2.05 to 33.78%, whereas the net exergy efficiency ranged from 0.01 to 2.16%. It was found that the average daily net energy and exergy efficiencies were 17.51 and 0.91%, respectively. The energy and exergy efficiencies of the packed‐bed solar air heater increased as the outlet temperature of heat transfer fluid increased. Copyright © 2004 John Wiley & Sons, Ltd.     

Modeling solar still production using local weather data and artificial neural networks

A study has been performed to predict solar still distillate production from single examples of two different commercial solar stills that were operated for a year and a half. The purpose of this study was to determine the effectiveness of modeling solar still distillate production using artificial neural networks (ANNs) and local weather data. The study used the principal weather variables affecting solar still performance, which are the daily total insolation, daily average wind velocity, daily average cloud cover, daily average wind direction and daily average ambient temperature. The objectives of the study were to assess the sensitivity of the ANN predictions to different combinations of input parameters as well as to determine the minimum amount of inputs necessary to accurately model solar still performance. It was found that 31-78% of ANN model predictions were within 10% of the actual yield depending on the input variables that were selected. By using the coefficient of determination, it was found that 93-97% of the variance was accounted for by the ANN model. About one half to two thirds of the available long term input data were needed to have at least 60% of the model predictions fall within 10% of the actual yield. Satisfactory results for two different solar stills suggest that, with sufficient input data, the ANN method could be extended to predict the performance of other solar still designs in different climate regimes.     

Photocatalytic conversion of CO2 into methanol using graphitic carbon nitride under solar,UV laser and broadband radiations

Photocatalytic conversion of carbon dioxide into methanol using highly efficient g‐C₃N₄, in conjunction with three different radiations (solar radiation, broad‐band ultraviolet (UV)–visible lamp, and laser beam) is presented. The optical, structural, and morphological properties of the synthesized g‐C₃N₄ were studied using advanced analytical techniques like Fourier transform infrared spectroscopy, UV–visible spectrometer, X‐ray diffraction, high‐resolution transmission electron microscopy, high‐angle annular dark field, and X‐ray photoelectron spectroscopy. The relative merits of the three sources of radiation in the presence of g‐C₃N₄ were studied in terms of key figures of merit of the photocatalytic process, namely, methanol production yield and quantum yield. As expected, after 40 min of irradiation, 355‐nm laser (40 mJ/pulse, 10 Hz) with g‐C₃N₄ rendered the best methanol production yield (510 μmol g ^{? 1} h ^{? 1}), followed by solar radiation (130 μmol g ^{? 1} h ^{? 1}), and UV broadband lamp. This indicates that the photon flux and the spectral properties of incident light are the key factors for the enhancement of methanol production yield. Although the methanol production yield with 355‐nm laser radiation is quite impressive because of the inherent high photon flux and the monochromatic nature of laser, the methanol yield of 130 μmol g ^{? 1} h ^{? 1} with natural sunlight is quite an important result, as it can be used for the development of large‐scale solar fuel generation facilities by harnessing the naturally abundant solar radiation. Copyright © 2017 John Wiley & Sons, Ltd.     

Performance enhancement of dye‐sensitized solar cells via cosensitization of ruthenizer Z907 and organic sensitizer SQ2

Cosensitization is a highly effective technique to enhance the photovoltaic performance of a dye‐sensitized solar cell. The main objective of this work is to improve the performance of dye‐sensitized solar cell using cosensitization approach and investigation of the effect of the organic cosensitizer concentration on the power conversion efficiency of the fabricated solar cell devices. In this work, Z907, a ruthenium dye, has been cosensitized with SQ2, an organic sensitizer, and an overall efficiency of 7.83% has been achieved. The fabricated solar cells were evaluated using UV‐Vis spectroscopy, current‐voltage (I‐V) characteristics, and electrochemical impedance spectroscopy analysis. Our results clearly indicate that the concentration of organic cosensitizer strongly affects the photovoltaic performance of fabricated solar cells. Upon optimization, the cell fabricated with 0.3 mM Z907 + 0.2 mM SQ2 dye solution demonstrated J_sc (mA/cm²) = 21.38, V_oc (mV) = 698.37, FF (%) = 52.46, and power conversion efficiency of η (%)  = 7.83 under standard AM1.5G 1 sun illumination (100 mW/cm²). It was observed that the efficiency of cosensitized solar cells is significantly superior than that of individual sensitized solar cells (Z907 [η  = 5.08%] and SQ2 [η  = 1.39%]). This enhancement in efficiency could be attributed to the lower electron‐hole recombination rate, decrease in competitive absorption of I^?/I^?₃, and less dye aggregation because of the synergistic effect in cosensitized solar cells.     

Simple multiple wick solar still: Analysis and performance

This paper presents the design, analysis and performance of a multiple wick solar still, in which blackened wet jute cloth forms the liquid surface which can be oriented to intercept maximum solar radiation and attain high temperatures on account of low thermal capacity. The wet surface consists of a series of jute cloth pieces of increasing length separated by thin black polythene sheets, resting on foam insulation supported by a net of nylon ribbon; these pieces are arranged along an incline and their upper edges are dipped in a saline water tank. Suction by the cailliary action of the cloth fibre provides a thin sheet of liquid on the cloth; the arrangement ensures that all the surface, irradiated by the sun is wet at all times. The results of an analysis based on Dunkle's relation[16] are in excellent agreement with the observed performance of the still. On a typical cold sunny day in Delhi (viz. 6 February 1980) the distillate output was 2.5 l/m² day, corresponding to an overall efficiency of 34 per cent (as compared to a maximum of 30 per cent for basin type still). The still costs less than half of the cost of a basin type still of same area and provides a higher yield of distillate.     

Enhancement of distillate output of double basin solar still with vacuum tubes

The latent heat of condensation is lost to the atmosphere; hence it is not utilized to increase distillate output of single basin solar stills. This difficulty was overcome by attaching an additional basin to the main basin. The performance of the double basin solar still was also increased by attaching vacuum tubes to the lower basin; hence the lower basin possessed a higher temperature throughout the day. The latent heat of condensation of the bottom basin was also utilized to increase distillate. But the distillate output of the top basin was even lower compared with that of the bottom basin. This paper proposed a novel approach to increase the distillate output of the double basin solar still attached with vacuum tubes by introducing different sensible energy storage materials like pebbles, black granite gravel and calcium stones to increase the basin area. Experiments were conducted in climate conditions of Mehsana (23.6000° N, 72.4000° E) Gujarat from April to September 2013 with a constant water depth of 2 cm in the top basin with and without the use of basin materials. The results showed that the distillate output of basin material with calcium stones is greater (74%) compared with that of black granite gravel and pebbles. The integration of vacuum tubes with solar still greatly increases the distillate output of the solar still by providing hot water at the lower basin.     

Potential solar earth-water distillate yields in Africa

A model for predicting solar earth-water distillate yield for soil moisture contents up to saturation is presented. The model developed by join-point analysis for a 20 cm tall solar still with reflective interior siding is: Water Yield = C1(SR) + C2(T_MIN) + C3(T_MAX) − 30.65 + C4(T_MAX − 30.65) + C5(MC − 8.0 + C6(MC − 8.0 + I Where SR, T_MAX, T_MIN, and MC represent the total daily solar radiation, maximum and minimum daily temperatures, and soil moisture content, respectively. C1, C2, C3, C4, C5, and C6 are the regression coefficients in the predictive model, and I is the intercept. The model indicates that maximum yield can be obtained at 8% soil moisture. The equation is used to predict potential earth-water distillate yields for 8 locations in Africa. Four levels of soil moisture content (5, 10, 15, and 20% by dry weight), and 50% and 100% of clear-day solar radiation and appropriate temperature values are used. For the four tested soil moisture contents the predicted daily earth-water yields vary from a minimum of 0.56 1 m⁻²-day⁻¹ at 5% soil moisture and 50% solar radiation to a maximum of 2.12 1 m⁻²-day⁻¹ at 10% soil moisture and 100% solar radiation. Distillate yields increase as soil moisture content increases from 5 to 10%. Above 10% soil moisture, the earth-water yield decreases as the moisture content increases. Distillate yield varies with soil moisture in the following manner: Y_10% > Y_15% > Y_20% > Y_5%, where Y is the predicted yield.     

Effects of external reflector and glass cover cooling on thermo-enviro-economic performance of a stepped solar still

In the current research work, performance enhancement of stepped solar still (SSS) having an external reflector (ER) and glass cover cooling (GCC) arrangements is presented. The individual and combined effects of ER and GCC on the performance of SSS have been evaluated and compared with simple SSS. The GCC reduces the glazing temperature significantly and results in increased distillate. The ER reflected the solar radiation inside the basin that increases the water temperature, consequently increasing distillate. The SSS having ER and GCC (SSS-ER-GCC) gave a maximum distillate of 4.340 kg/m² which was observed, respectively, 12.43%, 3.21%, and 1.36% higher than that of simple SSS, SSS with ER (SSS-ER) and SSS with GCC (SSS-GCC). The average energy efficiency of SSS-ER-GCC was evaluated as 40.78%, which was found to be 14.36%, 7.84%, and 10.64%, respectively, higher than that of simple SSS, SSS-ER, and SSS-GCC. The carbon credits earned and CO₂ mitigation were found the maximum for SSS-ER-GCC having values $65.96 and 4.40 tons, respectively. The economic payback period was found the minimum (490 days) for SSS-ER-GCC.     

Development of a tube-type solar still equipped with heat accumulation for irrigation

A tube-type solar still is found to be suitable for use in desert irrigation. The effectiveness of a heat accumulator with regard to distillate productivity is experimentally and numerically verified. The heat accumulator consists of tube bundles immersed in wax in order to utilize the latent heat of wax. The dynamic response to stepwise variation of irradiative intensity verified the contribution of wax to an increase of productivity only when the phase change of wax occurred. The effective distillate productivity was found to be 294.3 g/m² during the cyclic stepwise change of irradiative intensity, from 200 to 600 W/m² and back. Velocity vectors driven by natural convection and temperature contours estimated by numerical simulation verified the effectiveness of the heat accumulator especially after peak solar intensity. The latent heat of wax effectively contributed to a 15% increase in total distillate productivity per day. The still can feasibly meet irrigation water supply demands above an irrigative threshold of 17 MJ/m² d.     

Solar distillation of olive mill wastewater

A solar still was employed for the dewatering of olive mill wastewater over a series of consecutive days. The collected distillate and the remaining pulp were analyzed to test the method for treating agro-food industry wastewater. The efficiency of solar distillation of olive mill wastewaters was examined. Due to reduced energy consumption and relatively high temperatures achieved in the still, solar distillation could be applied in any process where separation of liquid and solid phase is required. A quantity of olive mill wastewater was left inside the solar still for 9 days, under outdoor conditions. Critical quality parameters (e.g. chemical oxygen demand, pH, total and volatile solids, total Kjeldahl nitrogen) were determined by daily sampling of both the distillate and the basin liquid. In addition, solar radiation and liquid, glass and ambient temperatures were recorded. It was shown that the distillate produced was free from solids, 80% lower in terms of COD and 90% in terms of TKN, while the basin residual was in solid form with only 15% water concentration and without any odor emissions.     

Sand erosion of solar glass: Specific energy uptake,total transmittance,and module efficiency

Surface roughness, R_Z, normal transmittance, Τ_N, total transmittance, Τ_T, and photovoltaic (PV) module efficiency, η_S, were measured for commercial solar glass plates and PV test modules identically sandblasted with different loads of quartz sand (200–400 μm), impact inclination angles, and sand particle speed. Measured data are presented versus the specific energy uptake during sand blasting, E (J/m²). Cracks, adhering particles, and scratch‐like textures probably caused by plastic flow phenomena could be observed after sand blasting. Their characteristic size was much smaller than that of sand particles. After blasting and subsequent cleaning, the glass surface was still covered with adhering glass particles. These particles, cracks, and scratch‐like textures could not be removed by cleaning. For sand blasting with α = 30° inclination angle and E = 30 000 J/m², normal transmittance, total transmittance, and relative module efficiency decreased by 29%, 2% and ∽2%, respectively. This finding indicates that diffusive transmission of light substantially contributes to PV module efficiency and that the module efficiency decrease caused by sand erosion can be better estimated from total than by normal transmittance measurements.