Passive Solar Distillation Research Articles

Mathematical Study of a Double-Slope Passive Solar Distiller with Water Heater Condenser

In this article, the inevitable condensation losses from the back-side glass cover of a passive single-basin double-slope distiller (PSDD) were recovered in heating water inside a glass solar water heater (SWH) to produce hot water as an auxiliary product of the distiller. The transient thermal performance of the PSDD-SWH was mathematically modeled and compared to a conventional PSDD in actual weather circumstances. Compared to a conventional PSDD, the results revealed that the thermal efficiency of the PSDD-SWH increased by 18% to 83% during the day. In addition, increasing the water mass inside the water heater from 3kg to 18kg increased the thermal efficiency of the PSDD-SWH by about 50% despite decreasing the total distillate by less than 1%. Moreover, the thermal performance of the PSDD-SWH, in terms of distillate production, hot water temperature, and thermal efficiency boomed in hot climates with high solar irradiation and high ambient temperatures. Furthermore, insulating the glass covers of the PSDD-SWH during off-sun hours significantly enhanced the thermal performance of the PSDD-SWH.

Ultra-high freshwater production in multistage solar membrane distillation via waste heat injection to condenser

Passive solar membrane distillation (MD) is an emerging technology to alleviate water scarcity. Recently, its performance has been enhanced by multistage design, though the gains are marginal due to constrained temperature and vapor pressure gradients across the device. This makes condenser cooling enhancement a questionable choice. We argue that condenser heating could suppress the marginal effect of multistage solar MD by unlocking the moisture transport limit in all distillation stages. Here, we propose a stage temperature boosting (STB) concept that directs low-temperature heat to the condensers in the last stages, enhancing moisture transport across all stages. Through STB in the last two stages with a heat flux of 250 W m−2, a stage-averaged distillation flux of 1.13 L m−2 h−1 S−1 was demonstrated using an 8-stage MD device under one-sun illumination. This represents an 88% enhancement over the state-of-the-art 10-stage solar MD devices. More notably, our analysis indicates that 16-stage STB-MD devices driven by solar energy and waste heat can effectively compete with existing photovoltaic reverse osmosis (PV-RO) systems, potentially elevating freshwater production with low-temperature heat sources.

Synergizing theory and experiment: Enhancing solar distillation performance with external reflector in a passive 4-stage model

Passive multi-stage solar distillers are pivotal in sustainable water purification, effectively utilizing solar energy. This study addresses the underexplored impact of reflective characteristics by integrating an aluminum reflector with radiation-trapping properties into a passive 4-stage solar distiller leveraging both experimental and theoretical methodologies. The influence of reflector height and angle on solar input, water production rate, and the Gain Output Ratio (GOR) was examined. Findings revealed a water production rate of 5.98 kg∙m−2hr−1and a GOR enhancement to 156 % at an optimal reflector setup of 40 mm height and 120° angle. Theoretical analysis assessed heat distribution and thermal efficiency across various air gaps and solar radiation levels. Evaporation emerged as the dominant heat mechanism, achieving 91 % thermal efficiency in the first stage with a 6.5 mm air gap and 1.50 kW∙m−2 of reflected solar radiation. Conversely, a 16 mm gap significantly lowered efficiency to 72 % in the last stage due to increased lateral heat loss. Transient analysis of the newly defined dissipation percent showed that narrower air gaps boosted heat retention in the distiller for evaporation and greater heat dissipation through the last stage, optimizing heat recycling for thermal applications. Increasing the solar input leads to sustained dissipation capacity.

Experimental and analytical examinations of a single-glazed solar still desalination with a spray-feeding water system with an artificial neural network

Using solar stills to desalinate salt water effectively provides clean water in remote areas at affordable prices. It is well-established that a crucial factor in enhancing the efficiency of solar desalination systems is increasing brackish water's surface evaporation rate by minimizing surface tension and boosting thermal energy. However, recent studies and proposed ideas indicate a limited and insufficient focus on this aspect. As a response, this research introduces a novel approach to raising the temperature of saline water. This is achieved through a system that involves simultaneous saline water spraying and circulation, affecting all factors and effectively reducing the surface evaporation rate. This approach impacts factors influencing surface evaporation rates and offers advantages such as low thermal inertia, reduced surface tension, and enhanced thermal energy within the desalination system. Therefore, the main goal of this study will be to improve the performance of the solar desalination system through circulating preheated salt water spray and using artificial neural networks and machine learning algorithms to obtain the function of predicting the amount of fresh water produced. The results of this study show that the evaporative heat transfer coefficient of the introduced system is significantly larger than that of the conventional solar still unit, with an average difference of about 43.98%. Also, the results of daily water output in both systems show a significant increase and superiority of 28.75% in freshwater production for the modified system. Also, the efficiency of the improved system is 65.18% higher than that of the passive solar distillation system, and the cost per liter was 0.059 ($/L/m2). The results of this study highlight the effectiveness of the saltwater spraying technique in enhancing the performance of solar desalination systems, making it a valuable prospect for future industrial applications in desalination systems and into energy systems for smart cities as a sagacious strategy towards clean and sustainable process.

Optimal size of spherical rock salt balls as low-cost thermal storage materials for performance augmentation of hemispherical solar distillers: Experimental investigation and thermo-economic analysis

Passive solar distiller is one of the vital solutions to alleviate freshwater shortage problems. However, the production from solar distillers is limited due to their low efficiency. In this work, an experimental investigation is carried out to ameliorate the freshwater product of a hemispheric solar distillatory. Spherical rock salt balls are embedded in the basin saline water to improve the absorption rates for efficacious heat transfer of salty water and also act as a low-cost sensible energy storage material to promote the basin saltwater temperature in the inadequacy of solar irradiation periods. To determine the optimum size of the spherical salt balls that maximizes the best freshwater production of hemispherical distillers, four diversified sizes of salt balls (0.50, 1.0, 1.50, and 2.0 cm) are investigated and compared with the reference hemispheric solar distillatory (RHSD) under the same hot conditions of ElOued, Algeria. The findings indicated that the freshwater product of hemispheric solar distillers for using the spherical rock salt balls reached 6.77, 6.25, 5.92, and 5.67 kg/day.m2 for spherical rock salt balls sizes of 2.0, 1.50, 1.0, and 0.50 cm, respectively, compared to 4.65 kg/day.m2 yielded by the RHSD. The enhancement in the freshwater production for the usage of spherical rock salt balls reached 45.6%, 34.4%, 27.3%, and 21.9%, respectively. Moreover, under these conditions, the amelioration in the daily energy efficiency for utilizing the spherical rock balls is estimated to be 43.91%, 33.22%, 26.10, and 21.13%, respectively, compared to the RHSD. Additionally, the hemispheric distillers using the spherical salt balls show respectively a 28.83%, 23.47%, 19.73%, and 16.84% reduction in the freshwater production cost in comparison with that of RHSD. Conclusively, it is inferred that spherical salt balls with a size of 2.0 cm achieved the maximum thermo-economic performance of the hemispheric solar distillatory.

Techno-Economic and Enviroeconomic Analysis Review of Distinct Passive and Active Solar Distillation Still

Water scarcity is an issue that stems from the overconsumption and misuse of fresh water supplies, which leads to shortages and decreased quality of life. It most affects developing countries that do not have the infrastructure in place to mitigate these factors. Solar still become most suitable method for water purification in these types of places due to its cheapness and easily made from locally available materials. Current paper concentrate on a detailed techno-economic and enviroeconomic analysis of distinct configurations of active and passive solar distillation stills. Distilled water production, cost per litres, environmental cost comparison has been done between different types of passive and active solar still. Active solar still has a higher system cost compared to passive solar due to the addition of thermal energy by different components and mechanisms. Based on the results, minimum cost per litre is obtained for passive conventional solar still with the spherical ball as heat storage material and in case of active solar still, with PV module, reflectors, air-cooling technique are 0.0136 $/l and 0.0092 $/l, respectively. On the basis of energy, the highest environmental cost was found for AMSSFS air-cooled with evacuated mode (1456.38 $), while the lowest was found for active solar stills with N - Flat Plate Collectors (44 $).

Heat recovery capacity and water desalination performance of passive solar vacuum tube distiller

The direct thermal distillation utilized the solar vacuum tube was a seawater desalination technology with quite a development potentiality. Therefore, an efficient passive solar vacuum tube distiller (P-SVTD) with a heat recovery function was developed in this paper, which realized the integration operation of raw water vaporization and high-temperature steam self-pressurization. It also had the character of simultaneously carrying out boiling vaporization and interfacial vaporization. The mechanisms of photo-thermal conversion and heat-mass transfer in the whole operation process of P-SVTD were analyzed. The theoretical calculation models of water yield (msh) and heat recovery rate (HRR) were presented. The water desalination performance, temperature level of recovered heat, and HRR of P-SVTD were measured to obtain the comprehensive photo-thermal conversion efficiency (HE) of P-SVTD. The results showed that the optimal depth ratio of the vapor–liquid interface to the vaporized-pressurized cavity was 0.9718. The water yield of P-SVTD was positively correlated with the total solar irradiance on the inclined plane by the trend of an exponential function. The average temperature level of recovered heat, HRR, and HE of P-SVTD were 74.30 °C, 28.68 %, and 87.43 %, respectively. And the rejection capacity (REJ), the decreased degree of conductivity, and the pH of P-SVTD were close to 100.00 %, 100.00 %, and 7.00, respectively, which showed excellent desalination capacity. The research provided solid technical and theoretical support for promoting the large-scale application of passive solar distillation technology.

Marangoni Effect Drives Salt Crystallization Away from the Distillation Zone for Large-Scale Continuous Solar Passive Desalination.

Solar desalination shows great potential in dealing with global water scarcity. A multistage passive solar distiller with thermal localization is especially attractive for its high-water yield. However, achieving long-term stability in large-scale devices remains a challenge because of the easy accumulation of crystallized salt inside the distiller. Here, we reported that the Marangoni effect can drive crystallized salt away along a long distance in a capillary wick, which endow the multistage passive solar distiller with the ability of salt-rejecting. In a 36 h continuous testing, the salinity of the distillation zone is limited below 12 wt % and crystallized salt only accumulates outside the device. The water yield is about 1.7 kg m-2 h-1 in a three-stage device, with a solar-to-vapor conversion efficiency of 114% under one sun. This novel design proves a new principle for high efficiency and long-term stable solar desalination.

Textured and Rigid Capillary Materials for Passive Energy‐Conversion Devices

AbstractPassive energy‐conversion devices based on water uptake and evaporation offer a robust and cost‐effective alternative in a wide variety of applications. This work introduces a new research avenue in the design of passive devices by replacing traditional porous materials with rigid capillary layers engraved with optimized V‐shaped grooves. The concept is tested using aluminum sheets, which are machined by femtosecond laser and covered by silica or functionalized by oxygen plasma to achieve stable long‐term capillary properties. The durability of the proposed material is experimentally evaluated when functioning with aqueous salt concentrations: both the coated and functionalized specimens exhibit stable wettability after being immersed in saltwater for all the duration of the experiments (≈250 h in this work). The proposed new class of materials is envisaged for use in passive solar or thermal energy‐conversion devices. As a case study, a time‐discretized capillary model is coupled with a validated lumped‐parameters heat and mass transfer model, aiming to estimate the maximum size and productivity of a passive solar distiller employing porous materials of known thermal and capillary properties. This study paves the way to the use of a new class of rigid, highly thermally conductive materials that can significantly improve the performance of passive devices by simplifying the assembly of multistage setups, thus helping to extend their use to real‐scale applications.

Experimental Study of the Effect for Water Depth on the Mass Transfer of Passive Solar Still Chemical Solutions

An experimental study on a passive solar distiller in the Tikrit city on (latitude line"34 36onorth, longitude line "45 43o east), and purpose of that study to raise the efficiency andproductivity of the solar distiller. And then design the monoclinic solar distiller and add reflectorplate and a solar concentrate. The Practical tests were conducted at a rate of every half-hourfrom the beginning of February to the beginning of the month of June. The study began bycomparing the solar distiller that contain the concentrates and without contain it. Then study theinfluence of adding coal and chemical solutions, like blue Thymol solution and bluebromophenol solution to see the additions effect on the productivity and efficiency of distiller,and also The study was conducted to see the effect of the water depth on the productivity ofdistiller with take four water depths within the basin are (2,1.5,1,0.5) cm of water. The tests wereconducted in weather conditions close. and the results of the study, That distilled added hisconcentrates improved its productivity by 46% and efficiency increases 43% with non-use ofconcentrates, and coal increased efficiency by 36% and productivity improved up to 38%, theaddition of blue Thymol solution increases the efficiency by 19% and productivity by 16%, aswell as bromophenol solution increase productivity by 23% and improve efficiency by 25%,when comparing the additions found that the best one is coal. Through the study of the depth ofthe water show that increases productivity and efficiency by reducing the depth of the water inthe basin distiller.

Energy Analysis of Passive Solar Distillation Unit

The energy analysis of a passive solar distillation unit was the focus of this study. A 40-liter solar distillation plant was constructed and adjusted for the intended output of 5 liters of distilled water. The developed unit's performance was monitored from 8 a.m. to 5 p.m. Even so, the solar produced 4.5 liters of fresh water per m2 each day. According to the solar still's updraft assessment, the maximum daily energy efficiency was found to be 38.27 percent.

Economic Evaluation of Passive Solar Distillation System

A economic analysis of passive solar distillation unit is presented in the paper. Initial cost and maintenance costs, life of the system and estimates the cost of unit mass of distilled water were used to evaluate net present worth (NPW), benefit-cost ratio, payback period (PP) and internal rate of return (IRR) of solar distillation unit. Net Present Worth (NPW), Benefit-cost ratio, Payback Period (PP) and Internal Rate of Return (IRR) was calculated and found to be Rs. 26945.72, 1.5632, 1.538 year and 50 per cent respectively. This study found solar energy is one of the most attractive resources of energy to generate distilled water.

Influence of Various Basin Types on Performance of Passive Solar Still: A Review

Passive solar still is the simplest design for distilling seawater by harnessing solar energy. Although it is undeniable that solar still is a promising device to provide an additional freshwater source for global increasing water demand, low thermal efficiency along with daily distillate yield are its major disadvantages. A conventional solar still can produced 2 to 5 L/m2day. Various studies have been carried out to improve passive solar stills in terms of daily productivity, thermal efficiency, and economic effectiveness. Most of the researches that relate to the daily output improvement of passive solar still concentrates on enhancing evaporation or/and condensation processes. While the condensation process is influenced by wind velocity and characteristics of the condensed surface, the evaporation process is mainly affected by the temperature of basin water. Different parameters affect the brackish water temperature such as solar radiation, design parameters (for example water depth, insulators, basin liner absorptivity, reflectors, sun tracking system, etc). The inclined angle of the top cover is suggested to equal the latitude of the experimental place. Moreover, the decrease of water depth was obtained as a good operational parameter, however, the shallow water depth is required additional feed water for ensuring no dry spot existence. Reflectors and sun-tracking systems help solar still absorb as much solar intensity as possible. The internal reflector can enhance daily yield and efficiency of stepped solar still up to 75% and 56% respectively, whereas, passive solar still with the support of a sun-tracking system improved daily yield up to 22%. Despite large efforts to investigate the impact of the different parameters on passive solar distillation, the effect of the basin liner (including appropriate shapes and type of material), needs to be analyzed for improvement in practical utilization. The present work has reviewed the investigation of the solar still performance with various types of basin liner. The review of solar stills has been conducted critically with rectangular basin, fins basin, corrugated basin, wick type, steps shape, and cylindrical shape basin with variety of top cover shapes. The findings from this work conclude that the basin liner with a cylindrical shape had better performance in comparison with other metal types and provides higher freshwater output. Stepped type, inclined, fin absorber, and corrugated shapes had the efficient performance. Further exploration revealed that copper is the best-used material for the productivity of passive solar still.

Experimental Validation of the Thermal Processes Modeling in a Solar Still

Passive solar distillation is cheap and energy-efficient technology but its main disadvantage is low productivity. Thus, there are many attempts to improve solar stills’ productivity, and one of them is changing the mass of the water. This paper presents the results of validation of the thermal processes modeling in a solar still (SS). In order to validate the model, the experimental studies were conducted in a laboratory to ensure uniform climatic conditions. The studies were carried out for 10 kg, 15 kg, and 20 kg of water under three different solar irradiance conditions. The results show that 10 kg and 20 kg of water ensure the highest and the lowest daily productivity, respectively, independently of solar irradiance. When the water mass is 10 kg, the solar still’s productivity is 800 mL/m2/day, 3732 mL/m2/day, and 9392 mL/m2/day for low, medium, and high solar irradiance, respectively. Additionally, it is found that reducing the water mass from 20 kg to 10 kg can improve solar still’s productivity by a maximum value of 21.6%, which is obtained for low solar irradiance. The proposed mathematical model allows predicting the performance of the SS. The results of the theoretical calculations are in good agreement with the results of the experiments. The minimum and maximum deviation between the actual and theoretical productivity of the SS is 1.1% and 8.3%, respectively.

Improvement in the performance and cost of passive solar stills using a finned-wall/built-in condenser: An experimental study

In the current study, a passive single-slope solar distillation unit has been proposed. An incorporated condenser has been integrated into the system to promote the condensation rate and hence improve the unit productivity. External fins have been used as a means to enhance the condenser performance further. The system performance has been examined experimentally for seven consecutive summer days in Mashhad city located at 36° 18′56.12″ N latitude and 59° 34′4.66″ E longitude. The unit yield and efficiency have been compared to the corresponding data for a conventional solar still tested in Tehran city. The results reveal that using fins increases the distillate in the condenser by 35%. But, there is only a 5% increase in the total unit productivity due to a reduction in distillate on the glass cover by 8%. Compared to the typical solar still tested in Tehran, up to 92.3 and 86% increase in daily productivity can be achieved using the current still with and without fins, respectively. The thermal efficiency of the currently proposed structure is about double than is it for the traditional solar still. The economic feasibility of the current solar still has been compared to some passive and active designs found in the literature, where it has been found not only efficient but less costly as well. The system without fins is the least expensive with CPL=0.007$/l/m2, while the one with fins is slightly more expensive with CPL=0.0117$/l/m2 but still economically outstanding.

Current Status of Theoretical and Practical Research of Seawater Single-Effect Passive Solar Distillation in Mexico

Solar distillation is a practical alternative for freshwater production in arid zones where seawater is abundant. The attractiveness of this approach resides in the simplicity of the solar still, equipment used to produce saline-free water for drinking, intensive agriculture, domestic use and other purposes. A solar still is an apparatus exposed to solar radiation that consists essentially of a basin with a solar collector where saline water is deposited and covered with a transparent inclined glass plate. The system operates as a greenhouse where the heated seawater evaporates and condensates on the inner surface of the cover. The distillate yield is collected in an external container. A research group in Mexico has been working for years doing research on the process of freshwater production with solar stills. Various research aspects have been addressed, among which are mathematical modeling of the physical phenomenon, practical research by building solar stills with different geometries and sizes, and the proposal of a process for mass-production manufacturing of solar stills with technology innovations. This paper is an overview of some of the most relevant results obtained by these research efforts.

Viability assessment of solar distillation for desalination in coastal locations of Indian sub-continent – Thermodynamic, condensate quality and enviro-economic aspects

In the current investigation, viable solar desalting sites in coastal India are identified by detailed thermodynamic and enviro-economic analyses. Mathematical model developed for thermodynamic performance assessment is validated using experiments conducted in inclined solar distillation unit under the climatic condition of Chennai (13.08°N, 80.27°E). Distillation unit produced high quality condensate even from highly saline (40,600 to 60,656 mg/L salinity) feed water. Availability analysis indicated the magnitude of improvement potential, availability destruction, losses and ways for further improvement. Maximum condensate yield, energy and availability efficiency of distillation unit is around 7.09 L/d, 53.45% and 5.39%, respectively for Nellore (one of the east coast locations). Condensate production cost of 18.16 to 32.78 USD/kL and desired availability output of 1.80 to 3.38 kWh/USD invested are observed for the distillation unit at 5.0% interest rate. Maximum yearly average life cycle conversion efficiency, net carbon-dioxide, sulphur-dioxide and nitrous oxide emission alleviated by the unit is around 39.19%, 25.83 tons, 185.73 kg and 75.86 kg, respectively. Viability assessment indicated positive signs for deployment of solar distillation units in 14 locations of coastal India. The proposed solar distillation unit requires lower evaporation area compared to other passive solar distillation units installed in India for the same production capacity.

Characteristic Equation Development for Single-Slope Solar Distiller Unit Augmented With N Identical Parabolic Concentrator Integrated Evacuated Tubular Collectors

Abstract In this communication, characteristic equation for single-slope solar still augmented with N alike parabolic concentrator integrated evacuated tubular collectors has been developed which is also valid for N alike evacuated tubular collectors integrated single-slope solar distiller unit as well as passive single-slope solar distiller unit. The developed equation is similar in the form to Hottel-Whillier-Bliss equation which was developed for flat plate collector. The analytical equation development for the proposed system involves the writing of equations for its different components on the ground of equating net energy input to net energy output. The results obtained for the proposed system have been compared with the results of N alike evacuated tubular collectors integrated single-slope solar distiller unit and passive single-slope solar distiller unit. It has been concluded that the mean value of instantaneous efficiency for N alike parabolic concentrator integrated evacuated tubular collectors is higher by 42.86% and 50.82%; daily generation of freshwater is higher by 49.73% and 74.34%; and daily exergy is higher by 78.71% and 93.35% than the corresponding values for N alike evacuated tubular collector integrated single-slope solar distiller unit and passive single-slope solar distiller unit for the same basin area in that order.

Performance and cost analysis of a modified built-in-passive condenser and semitransparent photovoltaic module integrated passive solar distillation system

Abstract In present paper, the performance of single slope solar still integrated with SPV module and passive condenser has been studied for the hot climatic conditions of New Delhi, India. The analysis has been carried out by developing a thermal model of the system. The effect of packing factor (βc = 0, 0.25, 0.45, 0.65 and 0.85) of the solar cell of different PV technologies (c-Si, p-Si, a-Si, CIGS, CdTe etc.) has been investigated. The overall energy efficiency of the system is analytically found to be maximum- 57.5%, 55.2%, 53.4%, 53.1%, and 41.4% for βc = 0.85, 0.65,0.45,0.25 and 0 respectively for c-Si SPV module. Moreover, the productivity of the system is calculated and found to be 1.78 kg, 2.83 kg, 3.66 kg, 4.12 kg and 4.92 kg per day for βc = 0.85, 0.65, 0.45, 0.25 and 0 respectively for c-Si SPV module. It is self-sustained system and economical in rural sector; and the electrical, thermal and overall energy efficiency of the system can be controlled or limited by changing the packing factors of the SPV module according to our requirement. It not only fulfills the electricity requirement (maximum value of thermal and electrical energy gain is 3.98 kW h and 0.38 kW h (βc = 0.85) respectively for c-Si SPV module) but also enhance the system productivity as compared to the conventional solar distillation systems. Cost analysis have also been performed to get the cost per liter of potable water produced by the system.

Experimental assessment on passive solar distillation system on Mount Tochal at the height of 3964 m: Study at high altitude

About 130,000,000 and 4,500,000 million people live at an altitude between 2000‐2500 and 3500–5200 above sea level respectively. Although, there are lots of water resources at high altitude which most of them are raw/impure/saline water. Also, there is not enough research on the performance of small-scale solar desalination systems at highlands. The main purpose of this paper is to present the impact of altitude on the performance of a single slope single basin solar still. Two identical passive solar still at the top of Mount Tochal and city of Tehran with 3964 and 1171 m of height are tested respectively. A series of experiments during four days from 24.07.2018 to 27.07.2018 are performed. All experiments are conducted by considering the effect of all important environmental conditions and performed by two separate teams at the mountain and Tehran simultaneously. All experiments were started and ended at the same time. Findings show that maximum hourly yield at the summit of Tochal and Tehran reaches to 720 and 500 ml/m2/h respectively. Total productivity at the mountain is higher by about 56.1% rather than that in Tehran. The cost of produced water at Tochal and Tehran evaluated about 0.0112 and 0.0087 $/liter/m2 respectively.