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Solar pond is one of the latest technologies that have been used to produce fresh water in different countries. The studied solar pond consists of a metal floor and glass walls. In this research, a mathematical model is presented with the aim of estimating salt deposition. The results show that proposed model has high accuracy. Results show that sum of square error and relative error of proposed equation are equal to 3.048E−14 and 0.11214, respectively. In addition, the p-value and square error of proposed model have been validated. Results show that p-value of temperature and shear stress has a significant contribution in salt deposition. This research shows that R-Squared of proposed model is equal to 0.9359. This value indicates good validity of the proposed model. [ABSTRACT FROM AUTHOR]

The rising global energy demand necessitates innovative solutions for harnessing renewable energy sources. Solar ponds have received attention as they present a viable means to address this challenge by absorbing and storing solar radiation. This article provides a comprehensive review of solar pond technology, including its principles, applications, heat extraction mechanisms, and approaches to optimize performance, with special attention to the salt-gradient solar pond. Additionally, the article identifies challenges that currently hinder the large-scale adoption of solar pond technology and offers recommendations for future research. By providing a detailed analysis of the current trends and future research directions, this paper seeks to contribute to the ongoing efforts to improve these systems, exploring various approaches to increase their efficiency and make them more economical and environmentally sustainable. [ABSTRACT FROM AUTHOR]

The cheapest and pollution-free method of producing drinkable water is solar distillation utilizing solar stills. However, the solar stills operate at lower-than-optimal efficiency, presenting significant room for improvement. Researchers have identified various techniques, modifications, and improvements to enhance efficiency in solar distillation. Notably, a solar pond is integrated with the solar still to boost performance, with the solar pond dramatically enhancing solar efficiency. In this research, four factors were identified as significantly influencing the performance of the solar stills: the concentration of sodium chloride (NaCl) in the solar pond, mini solar pond zones connected to the solar still, and the angles of internal and external reflecting mirrors. Three levels for each parameter were chosen for our study. The Taguchi method was utilized to identify the optimum level of these four parameters that maximizes performance. The best combination for maximizing efficiency was identified as connecting the solar still to the lower converting zone of the mini solar pond, using water containing 4 kg of NaCl, setting the internal reflecting mirror at 0°, and fitting the external reflecting mirror above the solar pond at 140°. This combination achieved a daily efficiency increase to 57.14%. Theoretical values were compared with experimental outcomes, showing that the solar still operated most efficiently between 12:00 and 14:00 h. The findings suggest not only immediate applications for improving solar still designs but also a pathway for future research into cost-effective desalination processes. [ABSTRACT FROM AUTHOR]

Design of economical and effective solar ponds which are useful thermal energy storage devices, remains a huge challenge. The present work aims at investigating the thermal performance of low cost mini salt gradient solar pond. The portable pond was fabricated as a rectangular configuration having a volume of 0.5m³. Polystyrene and high density polyethylene sheets were employed for insulating the walls. The top of the pond was covered with a slender glass so that the dust accumulation could be prevented without affecting the absorption of solar radiation. Sodium chloride salt was used as the medium and the three salt gradient regions namely lower convective, non-convective, and upper convective regions were established through injection filling technique. The temperature and salt gradient data were observed experimentally for a period of 20 days at Coimbatore, India. The pond could absorb significant amount of available radiation (around 65%) and the maximum temperature of the pond was observed to be 49 °C. Frequent washing of the water surface is necessary to maintain stable salt gradient. Nevertheless, portable pond fabricated with low cost materials exhibited good potential of storing solar energy for solar thermal applications. [ABSTRACT FROM AUTHOR]

This research focuses on the influence of water turbidity on the thermal efficiency of solar ponds, innovative devices designed for the concurrent collection and storage of solar energy utilizing salinity gradients. A three-dimensional simulation approach is employed to analyze solar ponds under varying turbidity conditions, namely clear, slightly turbid, and very turbid water. The findings reveal that increased turbidity levels lead to reduced solar radiation penetration, consequently decreasing the temperature in the pond's bottom storage zone. Notably, the presence of a temperature profile across horizontal planes in solar ponds, as identified in this study, challenges the adequacy of conventional onedimensional models in explaining certain phenomena. This insight casts doubt on the widely accepted concept of distinct upper and lower convective zones within solar ponds, suggesting a need to re-evaluate this hypothesis. Moreover, the ground beneath solar ponds is posited as a potential secondary heat storage zone. The study proposes the strategic placement of heat exchangers in the central circular ground plane, just beneath the bottom of the pond. This positioning is recommended to optimize heat extraction efficiency while circumventing the placement of exchangers in the corrosive Lower Convective Zone (LCZ), thereby reducing maintenance costs. The findings underscore the necessity of considering three-dimensional aspects in solar pond analyses for a more comprehensive understanding of their thermal behavior. [ABSTRACT FROM AUTHOR]

A solar pond is an environment‐friendly system for storing thermal energy. Solar ponds can balance the energy supply and demand when incorporated with PCM. Solar thermal energy can be stored inside the solar pond and used for solar drying, desalination, and power production. The present study reports the heat change in the solar pond with or without PCM and nanoparticles. From the literature, it was found that handling phase change material is difficult, and added nanomaterials are used to settle with time, which reduces the efficacy of the system. The novelty of present study is to examine the performance of nanoparticle‐embedded paraffin the sensible energy storage in the solar pond. The experiment has been performed, and results have been investigated/compared for four cases, namely, (i) solar pond, (ii) solar pond with heat storage (ie, paraffin wax [PW]), (iii) solar pond with aluminum oxide (Al2O3) mixed PW, and (iv) solar pond with copper oxide (CuO) mixed PW. The results show that with the addition of 1% and 2%, Al2O3 and CuO in PW, the thermal conductivity is increased by 2.94%, 5.92%, 2.99%, and 6.01%, respectively, compared to basic paraffin wax. It can be observed from the results that with the inclusion of CuO in paraffin wax solar pond temperature was high during non‐sunshine hours compared to other solar ponds. The results also show that sensible energy without heat storage material is negligible during non‐sunshine hours compared to heat storage and nanoparticle‐embedded heat storage solar ponds. Incorporating CuO in paraffin wax showed significant potential to store heat energy. [ABSTRACT FROM AUTHOR]

The realm of sustainable energy systems has seen the salt gradient solar pond (SGSP) emerge as an eco-friendly solution for thermal energy storage. This research explores the use of an East-West (EW) reflector and coal cinder additive (CC) to enhance the energy efficiency of the inner zones of a salt gradient trapezoidal solar pond (SGTSP). In this work, SGTSP with EW and CC systems were designed, fabricated, and analyzed based on an energy point of view and compared with standard SGTSP systems. It also provides a shading area analysis based on the slant angle of the SGSP system, offering valuable insights into the system's performance for low-grade heat source thermal applications. The study found that the EW reflector significantly increased the average solar intensity by 33.2%. The addition of coal cinder additive raised the average temperature of the lower convection zone by 24.1%. The SGTSP with EW reflector and coal cinder (SGTSP-EWR&CC) reached a maximum average temperature of 83.85°C, with a 42% higher energy efficiency in the lower convection zone compared to the conventional SGTSP (SGTSP-C). Further, the SGTSP's potential for thermal energy storage and providing practical strategies for enhancing its energy efficiency is showcased. [ABSTRACT FROM AUTHOR]

This work researches producing electricity and hydrogen production performance of a solar pond integrated with parabolic trough solar collectors. The system consists of parabolic trough solar collectors and a solar pond with a surface area of 100 m2 and 200 m2, an organic Rankine cycle operating with n-butane for electricity production, a proton exchange membrane for generating hydrogen, and a mushroom production unit. The system was operated for five mass flow rates m ˙ 1 = 0.350 k g / s , m ˙ 2 = 0.355 k g / s , m ˙ 3 = 0.360 k g / s , m ˙ 4 = 0.365 k g / s , m ˙ 5 = 0.370 k g / s. To improve the overall system performance, n-butane is selected as the operating fluid in the organic Rankine cycle and the waste heat of the organic Rankine cycle was used to heat the mushroom production unit. In addition, the preheating water produced by the solar pond was transferred to the parabolic trough solar collectors via a pump. The temperature of this preheated water was quickly raised by the parabolic trough solar collectors and pumped to the organic Rankine cycle. Thus, the organic Rankine cycle's electricity generation performance was also tried to be increased. With efficient electricity produced, the hydrogen production performance of the proton exchange membrane was improved. Thus, the amount of hot water, electricity, and hydrogen produced in the integrated system, the organic Rankine cycle, the parabolic trough solar collectors, and the energy and exergy efficiencies of the entire system were determined daily for five different masses. As a result, for five different masses, it was found in which mass the system performed the best. The whole system was analyzed with the engineering equation solver program. It was found that the system performs best at noon for all mass flow rates. It was also found that the performance of the system, the amount of electricity, and the hydrogen it produced increased as the amount of mass decreased. It was seen that hydrogen can be produced as 534.32 g and 519.06 g for m ˙ 1 and m ˙ 5 in a day, respectively. The energetic and exergetic efficiencies of the system were also found to be a maximum of 13.77% and 5.79% for m ˙ 1. • Hydrogen production of a different solar integrated system. • Thermodynamic performances of the parts of the system and overall system. • The comparison of the hydrogen production for five different mass flow rates. • The effect of thermal energy on hydrogen production in a day. [ABSTRACT FROM AUTHOR]

In this research, the efficiency of a solar distillation system as a passive technique in the process of water distillation from wastewater was investigated. The solar distillation process is proposed as a desalination process with zero discharge (ZD), in order to prevent salt water from entering to the sea and using salt water. In this study, three solar ponds with three different floors were used. Laboratory data show that the density of wastewater varies between 1.09 and 1.27 g/cm3 when using simple flooring. The amount of density changes when using floor covering made of nanozinc oxide is between 1.05 and 1.21 g/cm3. Laboratory data show that changes in density when using flooring made of nanoaluminum oxide are between 1 and 1.17 g/cm3. The laboratory results show that heat capacity of the wastewater decreases with increase in the depth of the effluent. Results show that flooring made of nanoaluminum oxide increases the rate of evaporation by about 17% and flooring made of zinc oxide by about 11%. [ABSTRACT FROM AUTHOR]

In this work, the effect of with and without phase change materials for long‐term heat storage of a salt gradient solar pond was investigated both experimentally and numerically. Some phase change materials, whose thermal values are close to the operating temperature of the solar pond were selected and examined from fatty acids (camphene, decanoic acid, and palmitic acids) and paraffin derivatives (paraffin wax, C20‐C33, and C16‐C28). A series of experimental studies were then performed with phase change temperature, latent heat and thermal stability, a differential scanning calorimetry, and a thermogravimetric analyzer for sheath, decanoic acid, and palmitic acid. The temperature and enthalpy curve of each phase change material was calculated by months and compared to the solar pond and the longest‐term heat storage was determined. Study shows that the maximum efficiency of the solar pond can be achieved with 24.58% Camphene in November and 22.57% Paraffin C20‐C33 in December. Thus, the camphene shows the best longest‐term heat storage performance thanks to its high melting temperature and density and latent fusion heat. It is one of the best suitable options to improve the heat storage performance of solar ponds. [ABSTRACT FROM AUTHOR]

We present models for convection in a mixture of viscous fluids when the layer is heated from below and simultaneously the pointwise volume concentration of one of the fluids is heavier below. This configuration produces a problem of competitive double diffusion since heating from below promotes instability, but the greater density of fluid below is stabilizing. The fluids are of linear viscous type which may contain Kelvin–Voigt terms, but density gradients due to the mixture appear strongly in the governing equations. The density gradients give rise to Korteweg stresses, but may also be described by theory due to Kazhikhov and Smagulov. The systems of equations which appear are thus highly nonlinear. The instability surface threshold is calculated and this is found to have a complex nonlinear shape, very different from the linear ones found in classical thermohaline convection in a Navier–Stokes fluid. It is shown that the Kazhikhov–Smagulov terms, Korteweg terms and Kelvin–Voigt term play a key role in acting as stabilizing agents but the associated effect is very nonlinear. Quantitative values of the instability surface are displayed showing the effect Korteweg terms, Kazhikhov–Smagulov terms, and the Kelvin Voigt term have. The nonlinear stability problem is addressed by means of a generalized energy theory deriving different results depending on which underlying theory is employed. [ABSTRACT FROM AUTHOR]

• Thermal-hydraulic performance of solar ponds having ST equipped with modified TTs. • Good agreement between numerical and experimental results (less than ± 11% deviations). • Overall performance index from 1.08 and 3.76 for the optimal m and T in. • Noticeable effects on flow features of working fluid by employing variable twist pitches. • Highest heat extraction with ST enhanced by TTs with LH arrangement of twist pitches. The thermal energy collected and stored by solar ponds is usually extracted by using some heat exchangers, where curved tubes form their core. The present study aims to appraise the performance of a serpentine tube under varied mass flow rates and inlet temperatures of the working fluid. Three different types of twisted tapes nominated as uniform twist pitches (U), low to high twist pitches (LH), and high to low twist pitches (HL) are employed to enhance the heat extraction rate. This article is the first report addressing the application of non-uniform twisted tapes as turbulators in a serpentine tube. In this regard, a solar pond simulator containing salt water is designed and fabricated. Numerical simulations are also carried out to display the transport phenomena inside the models. The numerical results are compared with the experimental data, and a close agreement is found. From the thermal point of view, the sequence of twisted tapes is LH > HL > U, while it follows the order of U > LH > HL according to the frictional loss. The findings demonstrate that depending on operating conditions, the heat extracted by the modified cases is 4 to 70% more than the base model. It is also found that employing non-uniform twisted tapes results in lower flow resistance compared to the uniform case. The pressure drop augmentations produced by U, LH, and HL TTs are 26.5%, 17.5%, and 10.4%. Further, the overall performance index is higher than unity for all the enhanced cases. The best case is the twisted tape having low to high twist pitches (LH) which has an average performance index from 2.03 to 2.71. [ABSTRACT FROM AUTHOR]

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A study has created a solar pond model. The pond's performance in terms of heat storage and electric power generation using TEG is analyzed using this model. The impact of various parameters, such as covering the pond's surface with plastic and using reflectors to focus on the intensity of solar radiation, will be investigated. A pyramidal pond with a base size of 0.64 square meters was used to validate the model. And it has a 6.25 square meter surface area. There's also a 1.35-meter depth. The walls are inclined at a 60-degree angle. TEG was also used to determine the pond's electrical capacity. The addition of a plastic cover and reflectors enhanced the efficiency of the pond's operation from 12.1% to 27.5%, according to the findings. At a lower layer temperature of 60 degrees Celsius, the electrical capacity reached 104 watts with a TEG operating efficiency of 8.9%. [ABSTRACT FROM AUTHOR]

There has been a practice of converting saltwater into potable water using solar stills for more than a century. Their production is only 2,000–5,000 mL/m² ·d, considering all the modifications. The process of production is expensive and inconvenient. The double basin solar stills are the only recommended solution to this problem. In this work, the performance of a double basin solar still with exterior reflectors, lower basin with flat plate collector (FPC) and mini solar pond has been examined and it was executed in Francis Xavier Engineering College, Tirunelveli, Tamil Nadu, India (latitude 11.9089° N, longitude 79.7589° E) with 09.00 to 19:00 h on a daily basis for a period of 20 d. Further, it has been examined whether the modifications have an impact on the effectiveness of double basin. Even in double basins, the 100 cm² × 100 cm² upper basins have a 5-step tray inside the lower basins for stability. There is a total of 25 compartments in each tray, having five portions each section. Materials, such as granite, for storing the heat is present in each unit. The yield of distilled water has been increased to 5,650 mL/m² ·d, when the external reflectors were installed. The yield has further increased to 6,249 mL/m2 ·d when the double basin solar still is connected to the FPC and small solar ponds. The overall yield due to the modifications has been increased by 127.5%. [ABSTRACT FROM AUTHOR]

Solar ponds are characterized by high storage capacity and the ability to provide a stable and continuous power source. Careful selection of the extraction rate helps to maintain supply temperature in a range suitable for the operation of an absorption unit. This study proposed a system in which a solar pond is coupled with an absorption chiller to investigate the resulting advantages. The chiller is cooled by using water of the upper convective zone, which ensures that the limit of deterioration of its performance is not reached and eliminates the need for an expensive cooling system. The key parameters in terms of ambient temperature, solar radiation, pond specifications, and cooling and refrigeration temperatures are investigated to optimize the proposed system design. The prediction of the model showed good agreement with the experimental results. By choosing the appropriate place to implement the system, such as the Dead Sea area, which enjoys favorable climatic conditions, it was found that a pond with an area of 3000 m2 can produce a heat rate at a temperature of 80 °C that can drive a chiller with 126.3 kW cooling capacity, with overall COP of 0.183. Based on this study, it appears that this type of system is feasible and suitable for cooling production, especially in hot regions. [ABSTRACT FROM AUTHOR]

• A three-zone extraction system in solar ponds for desalination is proposed. • Temperature drop across exchanger surfaces is considered. • Simplified model is validated with theoretical results of literature. • Possible extraction mechanisms are compared quantitatively and qualitatively. • Influence of user defined parameters on distillate output is investigated. A solar pond from which thermal energy is extracted from its non-convective zone (NCZ), lower convective zone (LCZ) and the ground below is modelled in transient state. The novelty of the study lies in the fact that heat extraction in each of the three zones is considered to be realistic, taking into account temperature drop across the exchanger surfaces. The pertinent weather parameters are described by curve fitting as series of sinusoidal time functions. Using these expressions, implicit finite difference method is used to solve the five coupled partial differential equations involved in the analysis, and the scaled down model is validated with simpler models available in the literature. To quantify the practical utility of pond, the final outgoing water stream heated from the pond is fed to a large scale solar still to assess the usefulness in a desalination application. Annual distillate production of the still coupled to such a pond is calculated and its variation with various manually adjustable parameters is studied. A total of 9 such parameters have been investigated. It is observed that there are five pond parameters related to pond's operation that possess optimum values that maximize annual distillate production. These are: NCZ and LCZ thicknesses, NCZ and LCZ exchanger pipes' radii, and ground extraction mass flow rate. An increase in any of the remaining parameters: upper convective zone (UCZ) thickness, ground exchanger pipes' radius and NCZ , LCZ extraction mass flow rates generate a decrease in distillate produced. It is also revealed that extraction should be carried from how many zones depends on the application coupled to the pond, and in this case, where the application is a solar still, LCZ with ground extraction turns out to be the best choice. Further, the assumption of ideal NCZ and ground extraction used in the literature is seen to overestimate system output by nearly 46%. Therefore, this model is a generalized one and various other single or dual zone extraction models available so far become subsets of it. This generalized model presented here can serve to design such a triple zone extraction based solar pond system in a realistic and practical manner and help evaluate suitable values of user-controlled variables that yield maximum output of the application to which the pond supplies energy. [ABSTRACT FROM AUTHOR]

In the direct contact membrane distillation (DCMD) system, the temperature polarization due to boundary layer formation limits the system performance. This study presents the experimental results and heat transfer analysis of a DCMD module coupled with a salinity gradient solar pond (SGSP) under three different flow channel configurations. In the first case, the feed and permeate channels were both empty, while in the next two cases, the feed and permeate channels were filled with a porous spacer material. Two different spacer geometries are examined: 1.5 mm thick with a filament angle of 65°, and 2 mm thick with a filament angle of 90°. The study considers only the heat transfer due to conduction by replacing the hydrophobic membrane normally used in a DCMD module with a thin polypropylene sheet so that no mass transfer can occur between the feed and permeate channels. The Reynolds number for all three configurations was found to be between 1000 and 2000, indicating the flow regime was laminar. The flow rate through both the feed and permeate sides was the same, and experiments were conducted for flow rates of 5 L/min and 3 L/min. It has been found that the highest overall heat transfer coefficient was obtained with the spacer of 2 mm thickness and filament angle of 90°. [ABSTRACT FROM AUTHOR]

• Features, factors, and facets of solar pond design and construction. • El Paso Solar Pond experience as the basis for design specifications. • Design and planning ensure solar pond reliable and sustainable operation. • Purpose of solar ponds provides focus for design and configuration. Over the last four decades, salinity gradient solar pond (SGSP) science and technologies have advanced in practical projects. In this work, we show that understanding a salinity gradient solar pond's purpose provides the focus for preparing a preliminary design and physical configuration. This paper aims to share lessons learned in designing and constructing the El Paso Solar Pond. Features, factors, and facets of solar pond design and construction are presented straightforwardly to inform and guide planning for future work. Emphasis is on sodium chloride-based ponds, the base salt used for the El Paso Solar Pond. However, lessons learned are pertinent to additional salt source configurations. Reference to solar ponds operating in Australia and Israel provides design and construction insights. Careful design and planning prior to construction ensure the solar pond operates reliably and sustainably. [ABSTRACT FROM AUTHOR]

• Heat extraction using supercritical carbon dioxide from solar pond is proposed. • Optimized operating conditions are identified for heat pump applications. • Operating pressure primarily influences the heat extraction rate, followed by mass flux. • Heat extraction is increased by up to 85% compared to conventional systems. • Centrifugal force superiority over gravitational force in spiral coil tubes is identified. Heat pumps integrated with renewable energy sources represent an efficient approach to residential heating and cooling, with minimal environmental impact and reduced carbon emissions. While these systems have been extensively researched, there is a necessity to broaden their scope by investigating novel approaches to energy capture and storage that are adopted to the specific characteristics of the region. This study analyzes the effects of different operating parameters on heat extraction from a solar pond integrated with a heat pump using carbon dioxide under transcritical conditions. Subsequently, an optimization examination is conducted to assess and determine the conditions required to achieve the maximum heat extraction rate and the minimum pumping power. The outcomes of this investigation demonstrate that the carbon dioxide mass flux and operating pressure exert a greater influence on the responses compared to the inlet temperature of carbon dioxide and the lower convective zone temperature of the solar pond. Additionally, within the investigated range of mass flux, the highest level of heat extraction occurs at operating pressures near the critical point of carbon dioxide, approximately 7.5 MPa. To meet the demand for maximum heat extraction from the solar pond, the optimal conditions result in an overall performance improvement of 2.61 times compared to the reference state. Furthermore, optimizing the system to maximize heat extraction from the solar pond while using the minimum pumping power results in a total performance enhancement of 4.13 times. [ABSTRACT FROM AUTHOR]

• Integration of a 10,000 m2 area solar pond in a salt work is investigated. • A mathematical model is used for LCZ temperature prediction. • A simple method is presented for salinity gradient development. • Economic and environmental benefits are evaluated through a parametric study. • Construction and operating costs of the solar pond are estimated. The process of salt manufacture in a salt work in Sabzevar in Northeast Iran is presented. A multi-faceted application to integrate a salinity gradient solar pond as part of the salt work process is presented addressing the reduction of parasitic energy losses such as the energy used for salt rock crushing and saving the amount of fossil fuel (natural gas) needed for brine heating. The solar pond with an area of 100 × 100 m2 and depth of 3 m is proposed to be constructed on the site of salt work. A partitioning wall with some opening heights equal to the desired position of the interface of lower convective (LCZ) and non-convective zones (NCZ) in its lower section, divides part of the area of this pond, say 5 percent or 500 m2. The separated area is designated to act as a salt charger and salt storage. The rock salt deposited in the salt charger dissolves into the LCZ of the pond and produces hot saturated brine solution. Results indicate that 100 tons of pure salt may be obtained from the extraction of 320 m3 of hot saturated brine consisting of 73 wt% water and 27 wt% salt. This is the nominated daily salt production of the factory. The proposed system will help to streamline the process of salt manufacture and reduce the environmental footprint. Using locally available meteorological data of Sabzevar, it is shown that such a pond may produce hot brine at an average temperature of 65 °C in summer and 37 °C in wintertime with a loading of 20% of the input irradiation. The gradient zone of the pond may be setup by placing a layer of low salinity water over saturated brine, allowing for salt diffusion to take place. Formation of large amplitude surface waves increases the salt diffusion and a salinity profile will develop in few months. A parametric study was performed to assess the enviro and economic effects of the proposed 10,000 m2 solar pond. The amount of fresh water to be injected to the solar pond is calculated to compensate for evaporation of pond surface as well as production of concentrated brine containing 100 tons of salt per day. Computer simulation shows that about 59,000 MJ/day thermal energy may be extracted from the pond in June. This is equal to a saving of about 1,576 kg/day of methane. Considering the price of methane this would be a financial saving of 283 $/day. The rate of reduction in CO 2 emission is estimated to be 4,335 kg/day in June. Considering a carbon price of 30 $/ton, the above reduction in CO 2 will be equivalent to savings of 130 $/day related to the environment. These calculations are extended to all months of the year and results presented. For demonstration, feasibility of using an existing old cylindrical fuel storage tank (2,000 m3, 3.3 m deep) as a container for a 600 m2 outdoor solar pond nearby the factory buildings, is proposed for pilot study. The shading effect is examined by scaling down a 3D model of the reservoir and its adjacent buildings for different months of the year, using Helidon device available at RMIT University of Australia. According to the simulation performed, it seems that the presence of buildings around the fuel tank does not have a significant shading effect on the surface of the demonstration solar pond. [ABSTRACT FROM AUTHOR]

• Present study focuses on the design methodology and different thermodynamic aspects of a SGSP. • Thermodynamic analysis of SGSP for energy, exergy, heat transfer, and shading effect has been discussed. • Discussion upon factors affecting the thermal performance of solar ponds is helpful to design them. • PCMs and extended fins are found as the two economic solutions to enhance the thermal performance of solar ponds. Solar energy is a clean source of renewable energy and people around the world are getting a lot of benefits day by day through the utilization of solar energy technology. Among various solar energy systems, a solar pond is a good energy device which is liable to be the most economic large-scale solar collector. It also has the benefit of being its own thermal energy storage (TES). The present review article focuses on the design methodology and different thermodynamic aspects of a salinity gradient solar pond (SGSP) along with its socio-economic benefits. Thermodynamic analysis of SGSP for energy, exergy, heat transfer, and shading effect has been discussed in much supportive way to the students, research scholars and solar professionals. Technical and general recommendations for future works show the research gap and a great possibility of further research on SGSPs. Overall, through this review study, the one can design a solar pond and carry out a complete thermal analysis of a SGSP with a simple approach. [ABSTRACT FROM AUTHOR]

A solar pond is a simple system that collects and stores heat for thermal and electrical applications. Heat storage and heat extraction are the key factors in the solar pond. Salt is added to the pond with fresh water to form a salinity gradient solar pond (SGSP). The solar pond comprises of three zones, namely, the upper convective zone (UCZ), the non-convective zone (NCZ) and the lower convective zone (LCZ). The LCZ is also called the storage zone. Generally, the LCZ stores the heat energy of the incoming solar radiation, and this heat may be used for various applications. In this paper, a review is done on the study of solar ponds with various designs and modifications, heating methods, use of floating devices, use of baffle plates, use of heat exchangers, use of flat plate collectors, use of different types of insulation, etc. [ABSTRACT FROM AUTHOR]

A new system to generate electric power by integrating a thermal regenerative electrochemical cycle (TREC) with a solar pond and underground heat exchanger is proposed. Thus far, there are relatively limited available studies in the literature about integrating TREC with renewable thermal systems. To the best of the authors' knowledge, this work is a first attempt to investigate the integration of TREC with solar ponds. The solar pond serves two purposes: It is the hot driving source for operating the TREC power system and an energy storage medium to maintain, sustain, and stabilize its performance. The underground heat exchanger serves similar purposes as well but as the cold thermal sink. The novelty of the proposed system is in being a stable and sustainable electric power generator because of having low-cost hot and cold reservoirs that serve as the source and sink of thermal energy and storage domains. A theoretical model has been initially proposed and validated by verifying its predictions with published experimental results. The model is utilized to describe, investigate, and understand the performance of the integrated system. The most critical parameters that affect the performance of the integrated system have been detected and tracked. [ABSTRACT FROM AUTHOR]

• Thermodynamic model of a novel solar pond-assisted OTEC system is developed. • Extraction temperature's role on the system power generation potential is analyzed. • Comparative studies of OTEC system using KC, RC, and TEG is carried out. • Ideal thermal efficiency of the system is 3.97% with extraction temperature at 86 ℃. • The system using KC outperforms RC and TEG in annual power generation. The low thermal efficiency of ocean thermal energy conversion (OTEC), resulting from narrow temperature difference in ocean thermal energy, can be improved by introducing a solar pond to preheating warm seawater entering the OTEC system. Therefore, a solar pond-assisted OTEC system is proposed and its thermodynamic model is developed in this paper. By this model, the role of extraction temperature and pumping depth of cold seawater on power generation potential of the system are analyzed. Furthermore, a comparative analysis is conducted among solar pond-assisted OTEC systems using Rankine cycle, Kalina cycle, and thermoelectric module from thermodynamic, economic, and environmental aspects. The results indicate that the overall thermal efficiency is only 3.97 % for solar pond-assisted OTEC system using Carnot cycle at an extraction temperature of 86 °C. The solar pond-assisted OTEC system using the Kalina and Rankine cycles produce almost the identical annual power generation, which significantly outperforms the system employing thermoelectric module. The exergy efficiency of the thermoelectric module improves with higher extraction temperatures, while Rankine and Kalina cycles demonstrate optimal extraction temperatures of 80 °C and 75 °C. Moreover, the systems using Rankine cycle, Kalina cycle, and thermoelectric module exhibit minimum levelized CO 2 emission of electricity at 0.961 kg/kWh, 0.98 kg/kWh, and 10.7 kg/kWh, respectively. [ABSTRACT FROM AUTHOR]

Salinity gradient solar ponds are a promising technology for harnessing/storing solar thermal energy. The energy storage capacity of solar ponds can be enhanced by incorporating phase change materials (PCMs). However, the low thermal conductivity of PCMs can negatively affect energy charging/discharging rates. In this study, an external energy storage system filled with CuO nanoparticle-enhanced PCM was employed to improve the performance and stability of a solar pond. The results were compared with water and pure PCM (paraffin) as control materials. Energy and exergy analysis was used to assess the effects of nanoparticles and their concentration on the overall solar pond performance. According to the results, the upper convective zone temperature remained consistent across all experiments and varied within the same range throughout the day. A slight temperature variation at specific times indicated the stability of the developed solar pond system. The system's exergy (energy) efficiency was increased from 10.72% (51.83%) for water to 14.71% (70.1%), 22.77% (82.13%), and 25.93% (87.58%) for PCM, PCM with 1 wt% nanoparticles, and PCM with 2 wt% nanoparticles, respectively. Incorporating nanoparticle-enhanced PCMs in external heat exchangers can effectively improve the stability and performance of solar pond systems. [Display omitted] • Nanoparticle-doped phase change material (PCM) improved the solar pond stability. • An external heat exchanger filled with PCM enhanced the solar pond performance. • The upper convective zone temperature remained consistent across all experiments. • The maximum energy efficiency (87.58 %) was found for 2 wt% nanoparticle-doped PCM. • 2 wt% nanoparticle-doped PCM provided the highest energy efficiency (25.93 %). [ABSTRACT FROM AUTHOR]

Solar ponds are systems that store solar energy in salt water as heat energy. In order to store heat energy for a long time in solar pond, the heat insulation should be done well. In this study, the effect of phase change materials was investigated to improve the insulation of the pond and to store the heat energy for a longer time. The melting temperature is a key parameter in the selection of phase change materials. The temperature distribution of the solar pond was examined and phase change materials with melting temperatures in the range of the pond average temperature ±10 °C were selected. Three different phase change materials were used in the walls of the solar pond for insulation. The temperature and enthalpy changes of the system were calculated numerically for a year. The heat storage ratio of the solar pond was determined by using the obtained enthalpy and solar radiation data. Consequently, the heat storage ratio of the pond with glass-wool is maximum 20.95% in July and minimum 7.92% in January. The heat storage ratio of the solar pond which paraffin C18, capric acid and paraffin 44 are used as phase change materials is maximum 32.22%, 34.85%, and 47.81% in December, respectively. It is observed that the appropriate selection of phase change materials is provided a longer storage time for solar ponds. [ABSTRACT FROM AUTHOR]

In the present work, a novel "nanofluid-based wick-type integrated solar still" has been designed, fabricated, and tested under on-sun conditions to assess its diurnal and nocturnal performance characteristics. Herein, floating wicks were placed inside the basin of single slope-single basin solar still. Furthermore, the basin water was supplied with external thermal energy collected by a nanofluid-based volumetrically absorbing solar collector (NBVASC) during the sunshine hours (9 am to 6 pm) and from the solar pond during the non-sunshine hours. In essence, the benefits of volumetric as well as surface heating have been synergized to significantly enhance the distillate production rate. Volumetric or bulk heating allows for enhanced sensible heat storage in the NBVASC, and the presence of wicks in the still's basin lends localized surface heating of basin water – thus considerably improving the evaporation rates. Rigorous on-sun testing of "nanofluid-based wick-type integrated solar still" showed significant improvements relative to the conventional solar still; distillate productivity and efficiency enhancements on the order of 111.1% and 89.9%, respectively, were recorded (with exergy efficiency of 3.40%). [ABSTRACT FROM AUTHOR]

In this paper, a salinity gradient solar pond (SGSP) is used to harness the solar energy for hydrogen production through two cycles. The first cycle includes an absorption power cycle (APC), a proton exchange membrane (PEM) electrolyzer, and a thermoelectric generator (TEG) unit; in the second one, an organic Rankine cycle (ORC) with the zeotropic mixture is used instead of APC. The cycles are analyzed through the thermoeconomic vantage point to discover the effect of key decision variables on the cycles' performance. Finally, NSGA-II is used to optimize both cycles. The results indicate that employing ORC with zeotropic mixture leads to a better performance in comparison to utilizing APC. For the base mode, unit cost product (UCP), exergy, and energy efficiency when APC is employed are 59.9 $/GJ, 23.73%, and 3.84%, respectively. These amounts are 47.27 $/GJ, 29.48%, and 5.86% if ORC with the zeotropic mixture is utilized. The APC and ORC generators have the highest exergy destruction rate which is equal to 6.18 and 10.91 kW. In both cycles, the highest investment cost is related to the turbine and is 0.8275 $/h and 0.976 $/h for the first and second cycles, respectively. In the optimum state the energy efficiency, exergy efficiency, UCP, and H 2 production rate of the system enhances 42.44%, 27.54%,15.95%, and 38.24% when ORC with the zeotropic mixture is used. The maximum H 2 production is 0.47 kg/h, and is obtained when the mass fraction of R142b, LCZ temperature, pumps pressure ratio, generator bubble point temperature are 0.603, 364.35 K, 2.12, 337.67 K, respectively. • The stored heat of a salinity gradient solar pond is used for H 2 production. • Thermoelectric generators and zeotropic mixture are employed. • NSGA-II is used to find the optimum point of the system. • In optimum state η e n , η e x , UCP, and m ˙ H 2 are 6.31%, 34.63%, 44.7 $/GJ, and 0.47 kg/h. [ABSTRACT FROM AUTHOR]

In this study heat extraction ratio of a solar pond was investigated numerically by using the Discrete Ordinates Method (DOM) with the direct solver PARDISO by using nested dissection multithreaded preordering algorithm, and the findings without exchanger were compared with experimental data to validate simulation accuracy of numerical approaches in the Mediterranean climatic condition. The solar pond was modeled with the same dimension as a previous experimental system and a heat exchanger was placed in the heat storage zone and simulation to take out the hot water at a certain flow was performed with the commercial software COMSOL. The solar position was defined for Adana and ambient data was obtained by processing the ASHRAE Weather Data Viewer 5.0. As a result, the maximum and minimum heat extraction ratio (HER) is calculated as 13.39 % in July and 2.96 % in September for a flow rate of 0.007 kg/s; 24.27 % in June, and 3.23 % in September for a flow rate of 0.014 kg/s, respectively. [ABSTRACT FROM AUTHOR]

We present a model for convection in a Kelvin–Voigt fluid of order one when the layer is heated from below and simultaneously salted from below, a problem of competitive double diffusion since heating from below promotes instability, but salting from below is stabilizing. The instability surface threshold is calculated and this has a complex shape. The Kelvin–Voigt parameters play an important role in acting as stabilizing agents when the convection is of oscillatory type. Quantitative values of the instability surface are displayed. The nonlinear stability problem is briefly addressed. [ABSTRACT FROM AUTHOR]

Globally, energy is a dynamic element that makes people's major energy demands. There are a variety of energies; the one that is stupendous potential is solar. Solar energy is an efficient problem solving one to eliminate pollution from the environment and water scarcity. This review article provides the accomplishments in the progress of the solar pond, solar desalination and integration of both the systems in the recent years. The solar pool is one of the thermal energy storing systems which perform as a huge solar radiation collector to capture and store sun's rays. The accumulated heat in the solar pool is weighed as the low category thermal energy. Hence, to enhance the performance upgrades are mandatory. Initially, use of unique salts and various additives is studied. And then, ingenious empirical works and several layers for minimizing the thermal losses from the upper and lower layers are exhibited. Heat removal techniques from the heat storage zone and mathematical model analysis are discussed. In addition, solar desalination unit is one of the possibilities for the effective production of sweet water from any form of polluted water (marine, brackish and contaminated water). Solar still is a trouble-free device utilized by condensation and evaporation processes to improve the limpidity of the water with the utilization of solar energy. This work made an attempt to classify various still designs with the greater volume of production. And also it analyzes the new innovations and thermal energy transfer process to reach at positive judgment. Desalination system performance is low for conventional approach, as desalination plant efficiency is relative to inlet water temperature, to upgrade it the solar pond coupled to desalination unit. With the exploitation of brine concentration and recovery system and multi-stage flash, fins and flat plate collector helps to elevate the beneficial solar pond and desalination output. This comprehensive review will guide the imminent researchers who desire to accelerate the performance of the pond and desalination units further. [ABSTRACT FROM AUTHOR]

We present a model for convection in a Navier–Stokes–Voigt fluid when the layer is heated from below and simultaneously salted from below, the thermosolutal convection problem. Instability thresholds are calculated for thermal convection with a dissolved salt field in a complex viscoelastic fluid of Navier–Stokes–Voigt type. The Kelvin–Voigt parameter is seen to play a very important role in acting as a stabilizing agent when the convection is of oscillatory type. The quantitative size of this effect is displayed. Nonlinear stability is also discussed, and it is briefly indicated how the global nonlinear stability limit may be increased, although there still remains a region of potential sub-critical instability, especially when the Kelvin–Voigt parameter increases. [ABSTRACT FROM AUTHOR]

• An innovative design has been proposed for maximizing the heat extraction. • Annular grooving is a cost-effective method that eliminates the need for using ancillary heat improvement methods. • A complete multi-objective performance (Nu, f, j-factor, and TPF) analysis. • Geometrical (d g and P g), hydraulic (Dean), and Pr (Therminol-55, Ethylen-glycol, and water) were considered as variables. • The proposed model is justifiable since TPF > 1for all cases. In the present numerical study the ring-shape depressions were created on the wall of spiral pipe that can be employed as a heat exchanger in the solar ponds. Unlike available literature that focused on the optimization of solar ponds through its nature recognition, present study tried to propose an efficient passive method for maximizing heat extraction. This is a simple and cost-efficient technique for enhancing the overall performance of salinity-gradient solar ponds through augmentation of turbulence inside the modified piping system and yielding higher heat extraction accordingly. Indeed, the introduced practical technique not only prevents the increment of size and volume of the piping system but also makes it needless to use additional supplementary equipment like turbulator or even air injectors. Moreover, this is a good way to prevent fouling inside piping system which bears huge costs. 3D numerical simulation was done based on Finite Volume Method (FVM) and turbulent flow simulated by RNG k-epsilon model. Due to the steady-state nature of this problem pressure–velocity coupling algorithm was adopted. The effect of several decisive parameters including Dean, Pr (fluid type and inlet temperature), groove distance, and groove depth on Nu, f, j-factor, and TPF was studied. Interestingly, it was turned out that the values of thermal performance factor (TPF) for all cases were above 1 which shows the justifiability of made modifications. For all flow rates water has the highest Nu and the lowest friction factor compared to Theminol-55 and Ethylene-glycol. Groove pitch of 20 mm makes the highest values of Nu so that 168, 195, and 216 were the maximum obtained Nu for cases with groove depth of 0.7 mm, 1 mm, and 1.3 mm, respectively (working fluid was water and Dean = 1615). Said statement is true for f where its maximum values were 0.1, 0.14, and 0.2, respectively, for cases with groove depth of 0.7 mm, 1 mm, and 1.3 mm (working fluid was water and Dean = 269). The highest Nu of Therminol-55, Ethylene-glycol, and water were 100, 114, and 216, respectively for groove pitch of 20 mm. [ABSTRACT FROM AUTHOR]

• Dual zone extraction in transient state with variable thermofluidic parameters. • Time and space dependent effectiveness of exchangers within the solar pond. • Optimized size of exchanger pipe is proposed. • Conventional and real assumptions yield up to 69% deviation in annual efficiency. • Conventional and real assumptions also yield 9% deviation in entropy generation. The transient performance of a salt gradient solar pond, which experiences heat extraction from both gradient and storage regions has been studied for annual performance via accounting for the overall heat transfer coefficient across heat exchangers. The proposed method after reduced complexities is satisfactorily validated with theory and experiment-based results of pertinent literature. The novelty of the work lies in the fact that, the temperature drop across both non-convective and lower-convective zone exchanger surfaces has been accounted by using a local time and space dependent heat transfer coefficient. Here, it takes into the consideration free convection from the pond to the exchanger surface, and forced convection from the exchanger surface to flowing working fluid. Further, temperature variation of thermo-fluidic parameters of water involving, viscosity, density and thermal conductivity is considered. Detailed numerical investigation reveals that by neglecting this coefficient which is assumed in conventional studies, it can lead to significant errors in the prediction of transient temperature profiles in the pond and the exchangers. Calculations reveal an error of about +69% in the annual extraction efficiency and about −9% in entropy production if the conventional assumption is used as opposed to realistic technique presented herein. Interestingly, the present study reveals that there is an optimum radius of exchanger pipe in each of non-convective and lower convective zones that maximises the annual extraction efficiency. This work presents a useful analysis to assess multi zone extraction from solar ponds under transient state in a more practical and accurate manner. [ABSTRACT FROM AUTHOR]

Solar energy is a promising renewable resource for meeting energy demands, with solar pond systems offering efficient thermal energy storage. Integrating Phase Change Materials (PCMs) and nanoparticles into solar ponds has shown potential to enhance energy storage capacity and thermal performance. This study focuses on optimizing the energy storage capacity of a solar pond system by employing Response Surface Methodology (RSM) to analyze the combined effects of PCM and nanoparticles integration. As input parameters for the optimization process, variables such as pond depth, salinity gradient, insulating materials, and solar radiation were taken into account. To maximize energy collecting and storage efficiency, the goal was to determine the ideal combination of these characteristics. To optimize the temperature distribution, Taguchi's L13 orthogonal array method and ANOVA were used. The results of the study indicate that the solar pond configurations with AgTiO 2 /Paraffin wax and CNT/Paraffin wax exhibited significantly higher energy storage capacities compared to the plain paraffin wax solar pond. Specifically, the AgTiO 2 /Paraffin wax solar pond showed an energy storage capacity increase of 7.48⁒, while the CNT/Paraffin wax solar pond exhibited an increase of 3.82⁒, in comparison to the plain paraffin wax solar pond. These findings highlight the substantial improvements in energy storage achieved by incorporating nanoparticles (AgTiO 2 and CNT) into the paraffin wax as phase change materials within the solar pond system. The optimization study's findings showed that solar pond system performance has significantly improved. [ABSTRACT FROM AUTHOR]

A solar pond (SP) is a remarkable growth of renewable energy technology that has stored solar energy for storage purposes and is used in many solar thermal applications. It is also utilized for many purposes, such as heating, cooling, space heating, air conditioning, and many more. The present paper shows the use of an SP to improve the yield of solar still (SS) by providing hot water through the heat energy stored in it. It also reveals the use of shallow and mini SPs with SS to improve yield. Various future research works on SS using SPs have also been included in this paper. From the current review paper, it was concluded that the SP increases the yield of the SS. [ABSTRACT FROM AUTHOR]

Present study provides a numerical simulation with experimental validation of the modified spiral piping system employed in solar ponds. The most important part of the solar ponds that plays a key role in its performance is its piping system, which has not been considered appropriately so far. To enrich this field, grooving the wall of the spiral piping system (which is considered to be placed at the lower convective zone (LCZ)) was adopted as an improvement mechanism. It is worth mentioning that in this innovative modification technique grooves were made in an annular form on the wall of spiral pipe with various spacing. Although made changes increases the extraction of heat from pond, it intensifies irreversibility to some extent. Therefore, various decisive parameters including distance between the grooves, depth of grooves, flow rate, fluid type, and inlet temperature (Pr) were considered to explore their contribution to entropy generation. Moreover, to find out which of Nu∗ (or Q) or S' gen outweighs the other one, the effect of said parameters analyzed based on the multi-criteria design concepts like η W − S and N H. Three different working fluid including water, ethylene-glycol, and therminol-55 were used at different inlet temperatures (283K, 303 K, and 323 K) to cover a Pr range of 3.35–744. The obtained results show that with increment of flow rate and the depth of grooves also decreasing the pitch of grooves increases entropy generation. The maximum increment of N H is about 26% when the depth of grooves is the highest and the pitch of grooves is the lowest. Results proved that, therminol-55 and ethylene-glycol are recommended when the inlet temperature goes up. The overall performance of solar pond is in a most desirable condition when η W − S = 0.125. Image 1 • Implementing a novel technique to modify the spiral piping system utilized in solar ponds. • Hydrothermal irreversibility analysis of the system to pinpoint adverse conditions in heat extraction. • The effect of fluid type, Re, Pr, and geometrical parameters were considered. • Evaluations were performed based on multi-criteria design concepts like η W − S and N H. [ABSTRACT FROM AUTHOR]

Solar energy can be stored and used via employment of SGSP (salinity-gradient solar pond) for low- and medium-temperature applications. Capturing thermal heat of a SGSP for cogeneration of electricity and freshwater for residential applications can lead to outstanding outcomes. To address this need, theoretical analysis of two cogeneration systems driven by a SGSP under the same conditions is carried out to produce freshwater and electricity by integrating an organic Rankine cycle (ORC) and a Kalina cycle (KC) with a reverse osmosis (RO) desalination unit. Also, a thermoelectric generator (TEG) with a heat exchanger is used as a potential device to improve performance of the systems in order to generate more power, using heat from upper convective zone. The energy and exergy balance equations are employed to different components of the systems for the Urmia lake in Iran, and the findings are credited by the available numerical and experimental data. The results of simulation demonstrated that the SGSP-ORC/RO system can provide freshwater and net electricity of 4 m3/h and 29.6 kW, respectively, when R600a is used in the ORC, while the SGSP-KC/RO system can produce freshwater and net output electricity of 3.3 m3/h and 15.5 kW, respectively. Under this condition, the cogeneration-based Gain-Output-Ratio (CGOR) and exergy efficiency for the SGSP-ORC/RO system are calculated 8.3 and 47.2%, respectively, whereas the CGOR and exergy efficiency for the SGSP-KC/RO system are calculated 6.9 and 26.0%, respectively. At last, a comprehensive parametric study is carried out to provide a technical enlightenment for designers of the systems. In comparison with the previous model, where a flat plate collector (FPC) with surface area of 21110 m 2 was used to produce 145.8 m 3 h fresh water, it is found that the same fresh water amount can be attained with a solar pond with 35500 m 2 , hence obviously increasing pond area from this value will increase fresh water capacity of the proposed plant. • A SGSP for cogeneration of electricity and freshwater based on ORC and KC is used. • Performance of the proposed system is enhanced using TEG. • Feasibility of the proposed hybrid systems is investigated from first and second laws of thermodynamics viewpoint. • A comparative study between these two proposed hybrid systems is presented. [ABSTRACT FROM AUTHOR]

In this paper, the concept of heat extraction from the gradient zone (GZ) in solar ponds has been analyzed in a more realistic manner to overcome the drawbacks of previously conducted studies. For this purpose, a net heat transfer coefficient has been invoked to investigate the heat transfer occurring from the GZ to the exchanger installed in this zone, in addition to the storage zone (SZ). Analytical solutions for temperature profiles in the GZ and the corresponding exchanger have been obtained which are further used to investigate various aspects of the thermal performance of the pond. The consideration of realistic heat transfer across the GZ exchanger reveals that the ideal thickness of GZ yielding maximum power output is always under-predicted by the idealized assumption of the literature. Unlike intuitive perception, the conventional assumption of an infinite heat transfer coefficient does not affect the pond stability because, for all practical purposes, the critical salt diffusion rate predicted by it is always larger than the actual critical value required for ensuring stable pond operation. However, as expected, the rate of exergy destruction caused by the pond's operation is found to be underestimated by the idealized assumption. This study provides a useful analytical tool to make more realistic predictions on various performance parameters of solar ponds utilizing the heat stored in their GZ. [ABSTRACT FROM AUTHOR]

This paper deals with the modelling of solar ponds for different sizes to calculate saturation time and temperature by using discrete ordinates method. The modeled solar pond is a subsoil type and aimed to minimize the heat losses by isolating side wall and ground with foam with the thickness of 10 cm in all cases. In the model, upper convective zone is 10 cm deep and non-convective zone consists of five layer and each layer is 10 cm deep and storage zone depth ranges from 40-400 cm. Therefore, the solar pond totally consists of seven layers. The saturation temperature was found to be about 322 K for 12 different solar pond. For a depth of 40 cm, the equilibrium temperature was reached in 1000 hours, 1300 hours for 60 cm, 1400 hours for 80 cm, 1500 hours for 100 cm, 1600 hours for 120 cm, 1750 hours for 1140 cm, 1800 hours for 180 cm, 2700 hours for 200 cm, 1800 hours for 250 cm, 3400 hours for 300 cm, and 6000 hours have passed for 400 cm. As the depth increases, time to reach to the equilibrium temperature increases but increment amount of water and time to reach equilibrium temperature shows a proportional increase. At the same time we calculated that, when we increase the width of the pond by keeping the depth constant, the saturation temperature and the time did not changed for the seven different cases. [ABSTRACT FROM AUTHOR]

• Improved model to assess ground heat recovery in solar ponds is developed. • Considerable deviations with respect to the conventional assumption are observed. • Ground heat extraction considerably affects the pond stability. • Present model reveals larger optimal NCZ thickness against prevailing assumptions. • Entropy generation is underestimated by the assumption of present literature. This work revisits the idea of ground heat extraction in solar ponds by addressing various limitations associated with the conventional assumption of perfect heat transfer. For this, an overall heat transfer coefficient, U has been introduced to analyse the heat extraction taking place from the ground beneath the pond. The pond's thermal performance is analysed for different values of U using closed form solutions and significant departure is seen with respect to the conventional assumption of an infinite U. Temperature distributions across various zones are obtained which exhibit deviation from the ideal distributions. It is also observed that the optimum size of non-convective zone yielding maximum efficiency depends on the effectiveness of ground heat extraction. Further, calculations are made for the minimum salt diffusion rate required to sustain stable pond operation. It is observed that the idealized exchanger performance assumption underestimates this critical value and a design based on it may initiate instability. Finally, calculations are made for the net entropy production rate which is also seen to be under-predicted with the existing theory. The present work can therefore prove useful for making an accurate assessment of the performance and stability of solar ponds involving ground heat extraction. [ABSTRACT FROM AUTHOR]

In this paper, we have numerically studied the phenomenon of unidimensional convectionconduction equation in a channel, cylinder and sphere immersed in a solar pond. Then we have studied bidimensional case in a heat exchanger, which undergoes an external heat flow provided by solar pond. We carried out the discretization of the mathematical model by finite differences method (explicit scheme). Calculation codes in Fortran language have been created for the temperature distribution in all these geometries. We presented the numerical results in terms of temperature profile functions, one- and two-dimensional, in laminar flow regime, for various parameters. We also present a study by COMSOL of the same phenomenon on these geometries. This study can be presented by two methods, the first using the physical model and the second using the mathematical part of COMSOL. [ABSTRACT FROM AUTHOR]

To cope with the large energy consumption in the most commercial desalination processes, along with the growing concern about climatic change resulting in CO2 emission, much effort has been made since almost four decades to use renewable energies to run desalination units. Among the numerous desalination processes driven by renewable energies, the seawater greenhouse received much attention for decentralized production of fresh water. The paper deals with an innovative hybrid approach of seawater desalination that has been explored. It combines a seawater greenhouse (SWGH) with a solar pond to produce more fresh water. Furthermore, it enables a better management of brine, which represents a major issue for all desalination processes. Indeed, the rejected brine of the SWGH will be recycled, by using it in a solar pond as a heat storage plant and a heat source to warm the air to more or less than 70°C at the inlet of the second evaporator of the SWGH. The process scheme and the mathematical and software models of both the classical SWGH and of its hybridization with a solar pond are presented. The calculations show that the fresh water production rate of the new SWGH concept is more than five times higher than of the classical SWGH one. Simulations on different Moroccan sites were realized as a case study, to estimate the added value of the new SWGH model and, at the same time, to compare its profitability in these implantation locations. [ABSTRACT FROM AUTHOR]

In this paper, thermal performance of solar pond for different condition was numerically investigated by using discrete ordinates method to facilitate a greater understanding of the effects of relative various condition on thermal performance improvement of solar pond. For this, a 3-D prototypes of solar ponds with square cross-sections were simulated for the oversoil and subsoil, insulated and uninsulated, open on and off conditions. The direction of sunlight (zenith angle and the solar elevation) was automatically computed from the latitude, longitude, time zone, date, and time. The estimated solar position is accurate for a date between year 2000 and 2199, due to an approximation used in the Julian Day calendar calculation. Seasonal temperature variation of solar pond was calculated for the full period of one year starting from March and calculated data were compared with experiment to validate simulation accuracy of heat transfer model. Result indicates that temperatures in the summer time were calculated at around 55 °C, while temperatures in the winter were in the range of 20 to 30 °C and temperature changes between 30 °C and 40 °C in spring and autumn. [ABSTRACT FROM AUTHOR]

Summary: In this study, the energetic and exergetic efficiencies of a salt gradient cylindrical solar pond (SGCSP) that integrated and nonintegrated evacuated tube solar collectors (ETSCs) are investigated to improve daily heat preservation performance of the heat storage zone (HSZ). The integrated system is consisted of an SGCSP and four ETSCs. The SGCSP has a surface area of 2 m2, a depth of 1.65 m, salty water layers at different densities, and HSZ in which the cylindrical serpentine type heat exchanger (CSHE) is located. Thus, the daily effects of the heat storage performance of both the ETSCs and the SGCSP in the winter season was determined experimentally. The analysis of the data regarding the efficiencies of the system is investigated separately by means of experimental studies where the SGCSP is integrated and nonintegrated with the ETSCs. The number of ETSCs integrated with SGCSP is increased to 1, 2, 3, and 4, respectively, and each of the five different experimental systems is performed separately. The temperature distributions of the integrated system are measured by a data acquisition system on 11 different points per hour. The efficiencies are calculated using the data obtained from these studies. Consequently, the energetic and exergetic efficiencies of the SGCSP are obtained without collectors as 10.4% and 4.3% and with one collector as 12.83% and 6.15%, with two collectors 14.88% and 8.25%, with three collectors 16% and 9.35%, and finally with four collectors 16.94% and 10.3%, respectively. Furthermore, the theoretical efficiencies are found to be consistent with the experimental results obtained by increasing the collector numbers. [ABSTRACT FROM AUTHOR]

A new three-zone heat extraction system and its analytical model for maximizing the thermal power output of salt gradient solar ponds against a given volume is proposed. The present study considers internal heat exchangers installed within the non-convective zone (NCZ), lower-convective zone (LCZ), and the ground below the pond. The work is validated against a simplified version of the model (eliminating ground and bottom-zone heat extractions) available in the existing literature. Contrary to the conventional practice of optimizing only the middle-zone pond thickness, here, the newly proposed expression is used to find ideal values of both the middle- and bottom-zone thicknesses of the pond along with its cross-sectional area. The present work acknowledges that although the three-zone heat extraction system is the best, yet if a choice for two-zone heat extraction is to be made between the NCZ-LCZ and ground-LCZ, then the former is a better alternative. The power output is observed to increase asymptotically with mass flow rates of the three heat exchangers. However, their values must lie much below their theoretical asymptotic limits and their selection is regulated by constructional and operational constraints. These involve a minimum pond depth to offset surface evaporation, ground seepage water loss, and constraints preventing turbulent flow in heat exchangers to reduce friction loss and pumping power. This work recommends using three heat exchangers instead of either one or two and provides cardinal guidelines to extract heat in an ideal manner for a fixed solar pond volume. [ABSTRACT FROM AUTHOR]

• Solar pond supplies thermal energy to MED plant. • PRO and chloralkali processes are employed to use the rejected brine. • The impacts of weather conditions, salinity, and solar pond geometry are studied. • The energy and exergy efficiencies reach 16.4% and 1.4%, at 600 W/m2. • The integrated system produces 4345 and 124 kg of chlorine and hydrogen, annually. The proposed system uses the thermal energy storage characteristic of the solar pond to power a multi-effect desalination (MED) process with a total fresh water production of approximately 14,000 m3 annually. Pressure retarded osmosis (PRO) alongside photo-assisted chloralkali reactor are employed to utilize the brine rejected from the desalination process. The inclusion of PRO is proposed to take advantage of the salinity difference that occurs as a result of the preparation of the solar pond and desalination process. The quest for zero salt discharge in the proposed energy system configuration is undertaken through the introduction of a photo-assisted chloralkali reactor, which is conducted utilizing the power generated from PRO, and solar pond storage arrangement. This solar pond and desalination coupling system will achieve independence from conventional energy sources, which will lead to a significant contribution to the reduction of greenhouse gas emissions caused by fossil-fuel driven desalination. At solar irradiation of 600 W/m2, the overall energy and exergy efficiencies can reach 16.4% and 1.4%, respectively. The annual average overall energy efficiency of 11.4% is achieved utilizing the integrated system, whereas the average overall exergy efficiency is about 0.9%. Parametric studies are performed to examine the impacts of ambient conditions, irradiance, solar pond geometry, brine salinity, and the total number of MED effects on the performance of the overall integrated system. In addition to the sensitivity analysis, the potential to improve overall energy and exergy efficiencies and fresh water production of the proposed system is demonstrated. [ABSTRACT FROM AUTHOR]

In this work, a unified renewable energy system has designed to assess the electricity and hydrogen production. This system consists of the evacuated tube solar collectors (ETSCs) which have the total surface area of 300 m2, a salt gradient solar pond (SGSP) which has the surface area of 217 m2, an Organic Rankine Cycle (ORC) and an electrolysis system. The stored heat in the heat storage zone (HSZ) transferred to the input water of the ETSCs by means of an exchanger and thereby ETSCs increase the temperature of preheated water to higher level as much as possible that primarily affects the performance of the ORC. The balance equations of the designed system were written and analyzed by utilizing the Engineering Equations Solver (EES) software. Hence, the energy and exergy efficiencies of the overall system were calculated as to be 5.92% and 18.21%, respectively. It was also found that hydrogen generation of the system can reach up to ratio 3204 g/day. • Daily energy and exergy variations of the solar radiation for the SGSP and ETSCs. • Hydrogen production in electrolysis system by using the thermal energy. • The effect on power generation of thermal performance of a solar pond. • Hydrogen production performance of the integrated system. • Effect of boosted thermal energy on power generation. [ABSTRACT FROM AUTHOR]

Highlights • A generalized model for solar pond analysis is proposed. • Effects of different wall profiles and cross sections are studied. • New model is validated with theoretical and experimental results of literature. • Optimized profile always converges to a vertical wall for any cross section. • A cost effective alternative to other performance enhancing techniques is proposed. Abstract This study carries a generalized model-based constrained analysis to optimise the wall profile of a solar pond. For this analysis, different profiles are studied which include linear, concave parabolic and convex parabolic walls with circular and square cross sections. The present optimisation is particularly aimed at maximizing the efficiency of the pond with reference to a given volume of water and top area. At first, the available literature model is modified to incorporate the variation of the local cross sectional area of the pond. A scaled down and unconstrained version of the present model has been then validated against theoretical and experimental results available in the literature. The constrained optimisation analysis reveals that, each of the profiles converges to the vertical shape towards maximizing the power output. For a fixed volume pond of any geometry, the pond efficiency is driven by a mutual trade-off between the available solar energy, its absorption and energy lost by conduction. It is envisaged that a vertical wall offers more output from the pond than an equal volume pond of any other geometry. The present work provides a direct procedure to assess the performance of solar pond involving any geometry and offers a cost effective alternative to other performance enhancing techniques. [ABSTRACT FROM AUTHOR]