Techno-economic analysis of solar still with nano-phase change material and heating coil A novel app
* Author to whom correspondence should be addressed.
Journal of Thermal Engineering 2025, Vol. 11, Issue 2, pp. 476-492; doi.org/10.14744/thermal.0000928
Abstract
Keywords: Economic; Heating Coil; Nanoparticles; PCM; Solar Still
Introduction
With the fast rise in population and the growing problem of environmental pollution, there is an urgent need to make natural water safe for people to use. As water treatment requires significant energy, and due to the recent increases in conventional fuel costs, there is a growing necessity to explore alternative energy sources. Solar
energy, which is both clean and sustainable, is becoming a popular choice for various applications [1]. One effective application is the use of single-slope solar distillers for desalinating water, providing an easy and efficient method for producing clean drinking water. On Earth, only 2.7% of water is fresh and accessible through rivers, lakes, and groundwater. The World Health Organization asserts that
*Corresponding author. *E-mail address: anand.kushwah@niet.co.in This paper was recommended for publication in revised form by Editor-in-Chief Ahmet Selim Dalkılıç Published by Yıldız Technical University Press, İstanbul, Turkey Yıldız Technical University. This is an open access article under the CC BY-NC license (http://creativecommons.org/licenses/by-nc/4.0/).
drinking water must be safe for all ages. In India, however, increasing population and industrial activity are expected to make access to clean water more challenging, leading to water shortages in both urban and rural areas. Addressing this issue requires affordable water treatment technologies that comply with Environmental Protection Agency guidelines. Among the available options, solar stills stand out for their low construction costs and zero electricity requirements, though their yield remains limited. Researchers are working to improve the efficiency of solar stills to better meet the demand for safe drinking water [2]. For numerous developed and emerging countries, freshwater scarcity is increasingly viewed as a primary concern, exacerbated by ongoing population growth, industrialization, and agricultural development. It is projected that by 2030, there will be a 40% reduction in freshwater resources. Solar energy serves as a principal renewable energy source for a variety of applications, including electricity generation, water desalination, water and air heating, solar drying, and solar cooking. Distillers provide several notable advantages for remote and island locations where the high cost of transporting filtered water, due to a lack of freshwater resources, is a significant issue. It is more economical to design a distillation system that utilizes readily available materials, is low-maintenance, and supports environmentally friendly infrastructure. Solar stills are an effective technique for harnessing solar energy for water purification. They offer two primary benefits: they are relatively simple and safe to operate, and they are environmentally friendly. By using solar energy, they reduce reliance on fossil fuels and hazardous materials, which in turn lowers global warming emissions. Nevertheless, a significant drawback of solar stills is their lower efficiency compared to other desalination methods, producing only 2–5 litres of purified water per square meter per day in basic models. The reliance on traditional energy sources has posed substantial energy challenges in recent decades, making solar stills a practical solution for providing fresh water to small, isolated communities. A no. of studies has been carried out to improve the productivity as well as thermal efficiency of SS systems [3, 4]. Numerous solar still system geometries, such as stepped solar still [5], [6], half barrel solar still [7], pyramid solar still [8, 9] conventional solar still [10-13], trays solar still [14], single slope solar still [15-19], double slope solar still [20], and tubular solar still [21] have been put to the test in a variety of design and operating scenarios. In addition, the performance of solar still systems has been improved by the introduction of reflectors [22], nanoparticles [10], phase change material [23], wick material [24], fins [25], and spinning components [6]. Andre et al. created a thermal model to optimize and predict performance of solar stills, testing ideas for improving efficiency by examining factors like wall design and shadowing effects. Their findings showed that conventional solar stills performed significantly better with reduced water depth, increased wall height, enhanced insulation, and the addition of reflectors [26]. Dumka et al. improved the performance of conventional
solar still employing 100 cotton sacks packed with sand at different water depths. Outcomes of this research indicated that CSS has more productivity (31%) using sandbags compared to general CSS [27]. Dumka et al. evaluated the theoretical as well as practical study on CSS using fixed ring magnets. The results demonstrated that CSS has more productivity (49%) using permanent magnets than CSS [28]. Panchal et al. evaluated the thermal performance of CSS using mixture of carbon powder and black paint at various concentrations. As the concentration of carbon powder varied in the range of 20-40%, the productivity also improved in the range of 10.5-17%. Due to this concept, water temperature increases and heat transfer rate also increases [29]. Panchal et al. developed an advanced single slope solar still coupled with ETSC and small calcium stones also used [30]. The experimentation procedure was categorized in two cases: In Case-I solar still assisted with ETSC and Case-II solar still coupled with ETSC using calcium stones. The findings indicated that productivity of SS increases as 114% and 105% in both cases respectively. Also, SS yield improved by 20% by using rock stone bed, which act as an energy storing devices. Murugavel and Srithar fabricated a novel double slope basin type SS using different wick materials as well as aluminium fins. It was observed that large quantity of mass distillate produced using light black cotton cloth [31]. Alawee et al. investigated a double slope solar still with elevated basin [32]. Multiple approaches are used to make a profit from solar intensity that hits the back wall of solar still. Younes et al. evaluated the performance analysis of corrugated absorber as well as half-barrel absorber solar still using wick material on side walls of SS. Purpose of wick material to enhance surface area at where water evaporates and protects side walls of solar still from direct beam radiation. Due of which, rate of evaporation and condensation improved whereas rate of heat losses decreased. It was noted that corrugated SS and half-barrel SS had per day yield 139% and 154% respectively more compare to CSS [7]. Elamy et al. investigated various methods to enhance the performance of a coiled solar still (COSS). One key approach involved the addition of a vertical wick distiller (VWSS) equipped with built-in reflectors positioned downstream from the COSS. The findings highlighted substantial improvements in distillate production resulting from these modifications. The COSS alone demonstrated a 76% increase in daily output compared to a conventional solar still (CSS). When a heating coil and internal reflectors were incorporated, productivity surged by an impressive 92%. This configuration exhibited a remarkable 209% increase in distillate production relative to the CSS, a figure that soared to 269% with the inclusion of a heating coil, VWSS, and an external condenser. The addition of a fan to the MCOSS further enhanced efficiency to 68%. Notably, incorporating nanomaterial-infused paraffin wax (PCM-Ag) with the MCOSS featuring the VWSS resulted in a striking 246% increase in productivity compared to the standard design. Additionally, the research indicated a significant reduction in the cost of freshwater production, with the cost per litre determined to be $0.024 for the CSS and a substantially lower $0.0126 for the MCOSS with a fan [33].
Essa et al. developed a new system in which a rotating disc fitted on back side wall of CSS. The whole experimentation work was carried out in two phases. In Phase-I the rotating disc is used with wick material, while in phase-II, the rotating disc is used with wick material. Results demonstrated that corrugated disc SS with wick material produced 124% more drinkable water [34]. Nakade A et al. developed a system that integrates an evacuated tube solar collector (ETSC) with a thermal energy storage (TES) system, utilizing pure paraffin wax and nano-enhanced phase change materials (NEPCM) for desalination. This innovative setup incorporates two water tanks linked to the ETSC, allowing for a two-phase system that effectively doubles the water output. The PCM section is filled sequentially: initially with pure paraffin wax, followed by the addition of NEPCM, which consists of paraffin wax infused with aluminium oxide (Al2O3). This configuration enables the water tank to be heated to temperatures ranging from 54 to 128 °C. The results demonstrate a significant increase in freshwater yield, with an enhancement of 60.09% achieved through the use of NEPCM compared to pure paraffin wax in the TES. Additionally, energy efficiency saw a notable improvement of 49.91% with NEPCM over the conventional paraffin wax [35]. Younes et al. evaluate the effect of 04 rotating discs on SS’s side and back wall. Finned shape discs give better SS results than corrugated and flat-type discs. The yield enhancement over CSS for finned type, flat type, and corrugated type disc SS was 106%, 68%, and 86%, respectively [36]. Abdullah et al. modified the CSS by implementing the internal trays on rear side wall. It was observed that 95% more drinkable water was produced in trays SS using internal and external reflectors compared to CSS. Also, the yield of SS can be achieved 108% more than CSS by increasing the trays [37]. Abdullah A.S et al. examined how various modifications impacted the performance of a half-cylindrical solar still (HCYSS). By comparing each modification’s distillate yield to a baseline, the research found that the HCYSS outperformed CSS by 55%. Key enhancements included a convex surface absorber, which boosted yield to 6300 ml/m²- 94% higher than the CSS’s 3250 ml/m². The corrugated convex design further increased yield by 123%. The most significant improvement came from combining a reflector and PCM-Ag composite, achieving a remarkable 184% increase in productivity and an efficiency of 61.5%. These results suggest that the HCYSS’s optimized design could significantly enhance solar desalination efficiency [38]. A comprehensive review of previous research highlights that while several strategies have been developed to enhance the solar intensity on the back wall of solar stills, including rotating discs, vertical wicks, and trays, there has been no investigation into the specific processes of heating and condensation on the back wall itself. This experiment introduces a novel approach by delivering cold feed water through a copper coil attached to the back wall to enhance condensation and increase the temperature of the feed water. By lowering the back wall’s temperature with the copper coil heater, the experiment effectively minimizes heat loss to the surrounding air. The study also examines
the impact of combining a Phase Change Material (PCM) bed with ZnO nanoparticles, as well as the use of an external condenser with an electric fan.
Materials And Methods
This section covers the details of the fabrication and installation processes as well as the experimental procedures implemented. Material Used For the experiment, a 2 mm thick stainless-steel sheet (thermal conductivity of 58 W/m2K, density 7.80 g/cm³), 20 mm thick plywood, and 20mm thick polystyrene (thermocol) were procured from the local market in Gwalior, M.P., India. The system was enclosed using 4mm thick toughened glass, and a condenser was constructed on the back wall of the solar still using a 5mm diameter copper tube.
Methodology
In the current research, two different types of solar still (SS) systems were developed at the Solar Energy Lab of Madhav Institute of Science & Technology, Gwalior, India. The first type is a conventional solar still (CSS), while the second is an advanced solar still (ASS), as depicted in Figures 1 and 2. The CSS is constructed using a 2mm thick stainless-steel sheet, with a detailed description provided in Table 1. The system is enclosed with a 4mm thick toughened glass that acts as a condensing surface. To collect the condensate water, an inclined trough is attached to the lower edge of the solar still. The ASS is designed similarly to the CSS but includes several modifications, classified into three categories. Category I: A copper tube heater (5m length and 5mm diameter) is integrated. This copper coil also functions as a condenser since cold water entering it condenses some of the steam. An inclined trough beneath the copper coil on the back wall of the solar still collects the condensate. Category II: To enhance the SS yield, a 6-watt, 100mm diameter DC fan is mounted on the rear wall of the SS to extract steam to an external condenser, thereby improving the condensation process. Category III: A 20mm PCM-ZnO nanoparticle layer is added underneath the absorber plate. Additionally, the interior and exterior of the SS system are painted black to increase solar absorptivity. The primary objective of this study is to install a copper tube heater on the back wall of the CSS to preheat the feed water before it enters the SS. This installation also reduces the back wall temperature, minimizing heat loss to the surrounding air. The use of the copper heating coil increases the evaporation and condensation rates, raising the temperature of the glass covers. To lower the glass temperature and enhance production, two strategies were employed: Fan extraction: Steam is extracted from the distiller using a fan and condensed inside the feeding tank, thereby increasing the temperature of the feed water and helping to decrease the glass cover temperature.
PCM-ZnO nanoparticle layer: A 20mm PCM-ZnO nanoparticle layer is placed underneath the absorber plate. In present study, we focused on the physical principles underlying the operation of the system, particularly the thermal dynamics involved in the phase change materials
Component Solar still Plywood Thermocol Steel sheet Glass cover Iron stand Basin area Lower height Height of back wall Inclination angle Latitude of site location DC fan Types Copper tube Length of copper tube heater Diameter of copper tube Thickness of PCM-ZnO layer
Description 20mm (Thickness) 20mm (Thickness) 2mm (Thickness) 4mm (Thickness) 02 ((Thickness 5mm) 1m × 1m 0.2m 0.7m 26o 26.2183° N, 78.1828° E
06. W DC solar powered
Table 2. Description of instruments and uncertainty Used measuring devices
(PT-100 and PT-1000 sensor) Infrared Temperature gun (HTC, MTX-2)
5.67. W/m2
and the role of ZnO nanoparticles in enhancing the thermal conductivity.
Thermal dynamics The PCM bed functions by absorbing excess thermal energy during the day and releasing it when needed, thus improving the system’s efficiency. The phase transition of the PCM is critical, as it allows for efficient energy storage and management, which is crucial for maintaining optimal operation during periods of low solar irradiance.
Role of ZnO nanoparticles ZnO nanoparticles contribute to increased thermal conductivity and enhanced heat transfer rates. Their presence in the working fluid helps facilitate faster evaporation rates, improving the overall efficiency of the desalination process. A physical discussion of how the size, shape, and concentration of ZnO nanoparticles impact heat transfer can provide valuable insights.
A solarimeter (Megger PVM 210) is mounted to record direct beam radiation and diffused solar radiation at regular intervals. K-type thermocouples are used to record the temperature at different locations of the SS (CSS and ASS).
Uncertainty Estimation Table 2 provides details on the instruments used for evaluating ambient air properties, including their accuracy, range, standard uncertainty, and the uncertainty in the measured variables. If X1, X2...…Xn are the independent variables affecting the observed parameter Y, uncertainty in observed variable U(Y), is computing using Eq. 1[39]: (1) Where, U(Y) is the total uncertainty, u2(x1), u2(x2), …., u (xn) are uncertainties of independent variables. 2
External condenser dynamics The design and operation of the external condenser, coupled with the electric fan, play a significant role in maximizing condensation efficiency. The fan increases air circulation, promoting more effective heat exchange, which can lead to higher water collection rates.
Thermal Efficiency of the System The thermal efficiency of a solar still system can be computed by following relations.[40]:
Experimental observations We will include a more detailed analysis of experimental observations related to thermal performance, evaporation rates, and overall system efficiency, including how these parameters interact within the physical framework of the system.
Latent heat of vaporisation according to water temperature can be determined as [41]:
Instrumentation for Recording Observations • A data logger (Data Taker DT85 series 3, Australia) is installed to record relative humidity (Rh) and ambient air temperature. The experimental work is conducted from 10:00 to 18:00 hours. • An anemometer (Dynalab DLAW 8701) is used to measure the airflow rate (m/s) over the glass covers of both the CSS and ASS.
Economic Analysis The objective of system modification is to lower production costs while also increasing water productivity. Various factors, including setup size and design, insulation
and fabrication materials used in SS, site location, labour costs, and feed water quality, raise the cost of producing SS water. [15]. Capital recovery factor (CRF) can be evaluated as follows: (5) While F = current capital cost, therefore the fixed annual cost (FAC) and Annual salvage value (ASV) can be calculated as: (6) Further, current capital cost (F) can be rewritten as: F=Cost of system+Cost of Nanopartcles+Cost of all needed deviesc+Labour cost ASV=(SFF)S
The value of S =0.2F, SFF= Sinking fund factor and can be determined using Eq. 8 (8) Total yearly expense (TAC) can be computed using the following relations: (9) Therefore, AMC = Costs of yearly upkeep, which includes the cost of paint, labour cost, sealing material cost, and all breakdowns cost. That measured to be 15% of FAC. It may be written as[15]: (10) The price of distilled water per litre (CPL) can be computed as: (11) The time consumed by the experimental setup to return the invested cost is known as the payback period. The payback period (np) For the advanced system is calculated as: (12)
Nano fluid Preparation Nanoparticles are hydrophobic by nature. To make them hydrophilic, certain methodologies have been implemented.
Synthesis of ZnO nanoparticles ZnO nanoparticles were synthesized using a sol-gel method. This involved dissolving zinc acetate in a solvent, typically ethanol, followed by the addition of a stabilizing agent, such as polyvinyl alcohol (PVA), to prevent agglomeration during the formation process. The solution was stirred and heated to promote the formation of ZnO. Preparation of ZnO nano fluid The ZnO nanoparticles were then dispersed in a base fluid, such as distilled water or ethylene glycol. A surfactant was added to enhance stability and prevent sedimentation. The mixture was subjected to ultra-sonication for a specific period to achieve a uniform dispersion of the nanoparticles within the fluid. Stability testing To ensure the stability of the ZnO Nano fluid, zeta potential measurements were conducted. A zeta potential greater than ±30 mV indicates good stability, which minimizes the risk of agglomeration over time. Homogeneity check Visual inspection and sedimentation tests were performed periodically to check for any signs of agglomeration or settling of the nanoparticles. Figure 3 illustrates the steps involved in the preparation of Nano fluids. It has been observed that most researchers use surfactants and dispersants to make nanoparticles soluble in water. The presence of surfactants and dispersants raises the boiling point of water, causing it to evaporate more slowly. The detailed specification of ZnO nanoparticles is given Table 3. Concentration of nanoparticles is determined using Eqs.13-14 [15].The selection of ZnO nanoparticles in the current work, due to their exceptional photocatalytic properties, high thermal conductivity, and stability under UV and visible light. ZnO nanoparticles enhance the evaporation rate by efficiently absorbing solar energy and converting it into heat. Additionally, they help improve the overall efficiency of water purification by breaking down contaminants through photo catalysis, making the desalination process faster and more effective. (13) Constitutive equation The constitutive equation for Nano fluids is an extension of the classic fluid mechanics equations, incorporating the effects of the dispersed nanoparticles. One commonly used model to describe the effective thermal conductivity knf of a Nano fluid is given by the following equation: (14)
Where: knf = effective thermal conductivity of the Nano fluid. kb = thermal conductivity of the base fluid. kp = thermal conductivity of the nanoparticles. ϕ = volume fraction of the nanoparticles. This equation accounts for the interactions between the base fluid and the nanoparticles, providing a means to predict the thermal conductivity of the resulting Nano fluid based on the properties of the individual components. Additionally, other properties such as viscosity and specific heat may also need to be modified based on the concentration and type of nanoparticles used, leading to further constitutive relations for those properties.
Results And Discussion
A copper heating coil is employed to elevate the feed water temperature, enhancing vaporization and condensation rates without enlarging the projected area of the
solar still. The effects of incorporating a DC fan, EC, and PCM will also be discussed in subsequent sections. Various parameters were recorded during the experimentation, including solar radiation, yield of potable water, airflow velocity, and temperatures at different locations (glass cover, basin, PCM, and water). Origin Pro 2024b was used to draw graphs. Performance Analysis of ASS Using Heating Coil (ASS) The performance evaluation of ASS has been compared with that of CSS. Figures 4 and 5 indicate the hourly variation in solar intensity, glass cover temperature, air temperature, and basin water temperature (BWT). Average water temperature difference b/w ASS and CSS was noted as 0-12°C. It is because of copper heating coil that water is automatically fed into the ASS, and it is also observed that feed water temperature is higher in the range of 0-10°C as compared to conventional SS. It is necessary to know that the feed water of CSS is approximately at room temperature. Maximum water temperature and glass cover temperature were recorded as 75°C & 55°C and 63°C &
Figure 4. Variation in solar radiation, ambient temperature, and temperature of feed water for CSS and ASS (with heating coil).
Figure 5. Variation in basin water and glass cover temperature with the time of day for both systems. 47°C in ASS and CSS, respectively, at 13:00h. Similarly, higher feed water temperature of ASS was noted as 72°C at13:00h. Glass cover temperature for ASS revealed higher values than that for conventional SS by around 0 - 7°C due to higher evaporation and condensation rates for ASS compare to CSS as a result of more water temperature for
ASS. From Figure 4, it was observed that the solar intensity fluctuated in the range of 0- 1070W/m2K. The maximum solar radiation was noted as 1070W/m2K at 12:00h and started decreasing. The hourly variations in yield between advanced SS and conventional SS were compared and are shown in
Figure 6. Hourly variation in productivity and accumulate productivity for ASS and CSS. Figure 6. The graph illustrates that advanced SS consistently outperforms conventional SS in daily productivity. This superiority can be attributed to higher rates of BWT, evaporation, and condensation in advanced SS compared to conventional SS. At 13:00h, the maximum fresh water yield reached 860 ml/m2 and 485 ml/m2 for advanced SS and conventional SS, respectively. Over the course of the period, advanced SS achieved a cumulative yield of 5500 ml/m2, which is nearly 77% higher than the 3090 ml/m2 achieved by conventional SS, as depicted in Figure 7. The present study results are much better compare to previous work conducted by Elamy et al. [33]. The COSS alone demonstrated a 76% increase in daily output compared to a conventional solar still (CSS). When a heating coil and internal reflectors were incorporated, productivity surged by an impressive 92%. Performance Evaluation of ASS with Heating Coil and External Condenser (ASS-EC) The temperature of the glass covers in advanced solar still (ASS) has been reduced using an axial DC fan and an external condenser to improve the condensation process. By employing an external condenser with heating coils, the glass cover temperature and basin water temperature of ASS can be increased by 0-2°C and 0-7°C, respectively, compared to conventional solar stills (CSS). The suction fan in ASS-EC lowers the internal pressure, thereby reducing the temperature of salt water. Additionally, the suction fan directs most of the water vapour inside ASS towards the external condenser (EC). This process results in the condensation of low-temperature water vapour on the inner surface of the glass cover. Figures 7 and 8 illustrate the
hourly variations in solar intensity, glass cover temperature, air temperature, and basin water temperature (BWT), respectively. Additionally, it was noted that the solar intensity fluctuated in the range of 0-1090W/m2K. The maximum solar radiation was noted as 1070W/m2K at 12:00h and started decreasing. Higher water temperature and glass cove temperature were achieved as 71°C & 51°C and 62°C & 47°C in ASS-EC and CSS, respectively, at 13:00h. It was also observed that maximum basin water temperature (69°C) attained in ASS at13:00h and after that begins to go down. The variation of hourly yield for ASS-EC and CSS has been compared and displayed in Figure 9. The yield of fresh water reached 7000 ml/m2 and 3200 ml/m2 per day in ASS-EC and CSS, respectively, at 13:00h. Hence, ASS-EC has a 119% more distillate production compared to CSS. As a result, the productivity of ASS has increased by about 42% employing the EC. This is mostly because having fan increases productivity and the suction fan, which circulates air inside the solar still above the salty water, accelerates evaporation by creating some turbulence. Furthermore, the suction fan draws most of the vaporised water from the saline water into EC. The current works finds are in the same with literature work. When a heating coil and internal reflectors were incorporated, productivity surged by an impressive 92%. This configuration exhibited a remarkable 209% increase in distillate production relative to the CSS, a figure that soared to 269% with the inclusion of a heating coil, VWSS, and an external condenser [33].
Figure 7. Variation in solar radiation, ambient temperature, and feed water temperature for CSS and ASS+EC.
Figure 8. Variation in basin water and glass cover temperature for both systems. Performance Analysis of ASS with Heating Coil and ZnO + PCM (ASS-PCM) To improve productivity, a combination of phase change material (PCM) and ZnO nanoparticles was utilized as a thermal storage bed beneath the absorber plate of an active solar still (ASS). This setup was designed to enhance energy efficiency by leveraging the unique properties of the materials. The experiment incorporated a heating coil and PCM
to lower the glass cover temperature, storing energy during periods of high solar intensity and releasing it when needed. The role of temperature in PCM is crucial for the charging and discharging processes, with energy stored as either sensible or latent heat, depending on the PCM’s temperature relative to its melting point. Energy is stored during the charging phase and released during the discharging phase.
Figure 9. Hourly variation in productivity and accumulated productivity for ASS+EC and CSS. Figure 10 displays the temperature changes of PCM and water for both the ASS-PCM and a conventional solar still (CSS). PCM with ZnO nanoparticles demonstrated superior thermal conductivity and lower melting and solidification temperatures compared to PCM without nanoparticles. The temperature data show a gradual increase from early morning until about 13:00 hours for both the water and PCM temperatures in ASS-PCM and CSS, followed by a
decline. Heat transfer occurred from the absorber to the PCM before 13:00 hours and from the PCM back to the absorber afterward, as the PCM temperature dropped to match the ambient temperature. Figure 10 also highlights that the temperature difference between the water in ASSPCM and CSS was more pronounced during the discharging period than during the charging period, due to the heat transfer from the PCM to the ASS-PCM absorber.
Figure 10. Variation in temperature for ASS, CSS, and ASS-PCM-ZnO.
Figure 11. Representation of productivity and accumulated productivity. Figure 11 presents the hourly and cumulative productivities for ASS-PCM and CSS. The trends indicate that ASSPCM consistently performed more efficiently than CSS in terms of yield throughout the experiment. This efficiency is attributed to higher basin water temperature (BWT), evaporation, and condensation rates in ASS-PCM compared to CSS. The cumulative yield of ASS-PCM (6600 ml/m²) was nearly 113% higher than that of CSS (3090 ml/m²), as
shown in Figure 11. Consequently, the productivity of ASSPCM increased by about 36% due to the use of PCM. Thermal Efficiency and Increased Yield of ASS Thermal efficiency and freshwater yield are critical metrics in assessing the thermal performance of a solar still (SS) system. The improvement in productivity for an active solar still (ASS) compared to a conventional solar still (CSS) is illustrated in Figure 8 as a percentage increase. The thermal
Figure 12. Relationship between daily productivity increase and efficiency.
Steel sheet Glass cover Iron stand and ducts Production Wood Thermocol Oil paint Float DC fan Copper tube for heating coil Phase change material ZnO Nanoparticles PV panel Silicone gel Labor cost
efficiency for each configuration is presented in Figure 12. The maximum thermal efficiency and corresponding yield improvements are quantified as follows: 46% and 77% for ASS with a heating coil, 53% and 119% for ASS with an external condenser (ASS-EC), and 51% and 113% for ASS with PCM-ZnO nanoparticles. Cost Analysis Fixed prices of both ASS and CSS with different modifications are listed in Table 4. Furthermore, assumptions (no. of working days in a year, interest rate, and system lifetime) and estimates for variables used in economic analysis are discussed in Table 5. Desalinated freshwater’s acquired prices were correspondingly 0.030, 0.023, and 0.021 $/l for the CSS, ASS-PCM, and ASS-EC. Environmental Analysis Environmental analysis is crucial in assessing the impact of advanced solar still (ASS) systems on the environment.
Ass-Pcm
System lifetime Interest rate per annum Workings days per annum Setup fixed price Average production of
desalinated water Price of desalinated water Annual maintenance cost Annual salvage value
Table 6. Embodied energy of used materials [10] Materials used
Plywood (for structure) Thermocol (for insulation) Copper tube Stainless steel Al frame Paint Fitting materials(valve and nozzle) DC fan made of plastic Oil paint PV panels ZnO nanoparticles Electricity wire Al T and L-shaped joint Glass Total embodied energy
Table 8. Outcomes of environmental parameters Environmental factors
Solar still systems are exemplary sustainable solutions that have no adverse effects on the atmosphere. The first step in this analysis is to calculate the embodied energy for both advanced and conventional solar stills. Table 6 details the embodied energy for various materials used in the fabrication of both systems. The assumptions and calculations used in the environmental analysis are outlined in Table 7. Key metrics calculated include Embodied Energy Payback Time (EBPT), CO2 mitigation, carbon credit earned, CO2 emitted, and net CO2 mitigation over the system’s lifetime (Table 8).
Conclusion
The experimentation was conducted to compare the thermal performance, efficiency, and productivity of potable water between conventional solar stills and advanced solar stills (including variations with a heating coil, external condenser, and ZnO-PCM) under identical meteorological conditions. A copper heating coil was installed in the back
wall of the solar still to enhance the feed water temperature, improve the condensation process, and lower the back wall temperature of the solar still. The results yielded the following conclusions:
1. The cumulative yield of advanced solar stills (5500 ml/
m². day) was nearly 77% higher than that of CSS (3090 ml/m². day).
2. The yield of freshwater at 13:00h was 7000 ml/m². day
for advanced solar stills - external condenser and 3200 ml/m². day for conventional solar stills. Thus, advanced solar stills using - an external condenser produced 119% more distillate than conventional ones, resulting in a productivity increase of about 42% for advanced solar stills external condenser.
3. The cumulative yield of advanced solar stills-PCM (6600
ml/m². day) was approximately 113% higher than conventional solar stills (3090 ml/m². day), as shown in Figure 11. Consequently, the productivity of advanced solar stillsPCM increased by about 36% with the use of PCM.
4. The maximum thermal efficiency and improved yield
were 46% & 77% for advanced solar stills with a heating coil, 53% & 119% for advanced solar stills with - an external condenser, and 51% & 113% for advanced solar stills with ZnO-PCM, respectively.
5. CO2 emissions depend on the embodied energy of
the materials fabricating the solar still system. Since advanced solar stills includes auxiliary devices compared to conventional solar stills, CO2 emissions are 52.83% higher in advanced solar stills.
The high thermal conductivity of ZnO nanoparticles offers great potential for enhancing heat transfer in the desalination system. Future developments could explore the use of advanced nanomaterials like ZnO in combination with other nanoparticles to achieve even greater thermal efficiency, which would result in faster water evaporation and higher desalination rates. As solar desalination technology evolves, integrating PCMs and ZnO nanoparticles could make off-grid, self-sustaining desalination systems more practical for remote, water-scarce regions. These systems could be powered solely by renewable energy, making them ideal for regions with limited infrastructure, such as islands, deserts, or rural communities.
Nomenclature
area of the system (m2) Advanced solar still Conventional solar still External condenser Heating coil latent heat of vaporization, average solar intensity interest per annum (assumed 12%), appliances losses transmission losses hourly distillate Mass of water (ml) Mass of nanoparticles (gm) no. of life in years Phase change material DC fan power Solar still salvage value of the system after n years Temperature of water (°C)
Ethics
There are no ethical issues with the publication of this manuscript.
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KUSHWAH, A.; KUMAR, A.; GAUR, M.K. Techno-economic analysis of solar still with nano-phase change material and heating coil A novel app. Journal of Thermal Engineering 2025, Vol. 11, pp. 476-492. https://doi.org/10.14744/thermal.0000928