Salinity Gradient Solar Pond Research Articles

Performance of solar pond integrated with photovoltaic/thermal collectors

This article aims to propose and study a new system design for renewable energy called photovoltaic/ solar pond. This new system involves cooling the arrays of the photovoltaic/thermal collectors, which are installed beside the salinity gradient solar pond with a heat exchanger that is installed behind each solar cell. Thermal energy gained by the photovoltaic/thermal collectors was stored in the heat storage zone using a heat exchanger system. An experimental assessment was performed to examine the thermal performance of the mini PV/solar pond. The experiments were carried out for five months, starting from September 2019 and ending in January 2020, in Kirkuk, Iraq. During this period, temperature, salinity, and power generation were recorded in real-time. The experimental results confirmed that the maximum total efficiency value of the system was 37.67% which was recorded in September. Besides, the highest value of the daily thermal efficiency was 30% for September, while the ultimate value of the daily electrical efficiency was 9.357% as recorded in December. The current result agrees well with other experimental studies in the same field.

Experimental study on thermal behavior of new mixed medium phase change material for improving productivity on salt gradient solar pond

Five identical cylindrical salinity-gradient solar ponds (SGSPs) with internal heat exchanger were constructed and operated. In order to optimize the performance of the SGSPs, mixtures of NaCl and Na2SO4 were used. Radiation flux, temperature of the zones, ambient temperature, inlet, and outlet temperature of the internal heat exchangers were measured. It was shown a controlled amount of Na2SO4 improves the thermal and salinity stability of the pond in the normal operation and heat extraction and lowers the pond temperature drop ratio to the water outlet temperature drop during the heat extraction, which means an improvement in the energy storage capacity. The pond with higher percentage of Na2SO4 requires less time to stabilize. Higher percentage Na2SO4 reduces the density gradient between the upper and lower convective zones of the pond and leads to rapid destruction of the upper layer. Maximum ability of heat extraction corresponds to the pond with 0.75% Na2SO4. In addition, to prevent the algae growth at higher percentage Na2SO4, spraying of HCl on the pond surface was used.

Determination of optimum insulation thicknesses for salinity gradient solar pond’s bottom wall under different climate conditions

The salinity gradient solar pond is one of the most efficient tools that can be used to collect, convert and store the solar energy. The performance of solar pond specially depends on heat losses from it. The performance of the solar pond could be improved by using the thermal insulation on the bottom and sides of the solar pond. Determination of insulation thickness is very important; it is commonly estimated based on the climate conditions, insulation materials and economic parameters. Therefore, in this study, the optimum insulation thickness, cost and energy savings were calculated for a salinity gradient solar pond under different climate conditions. An economic analysis was applied to obtain the optimum value of the insulation thickness when the polyurethane was used as the insulation material. For this purpose, the temperature of the lower layer of the solar pond was calculated using the one-dimensional unsteady heat transfer model inside the pond. The model and the literature experimental lower layer temperatures showed a good agreement, with the average deviation of 5%. They also had the same trend in all months of the year. The results revealed that the optimum insulation thickness strongly depended on the solar irradiance and the ambient temperature. This study also found that by introducing the optimum insulation thickness of 62–122 mm, according to the climate conditions, in the solar pond’s bottom wall, the energy saving could be enhanced by 36.7–55.2% as compared with the solar pond without insulation.

Finite element modelling of the thermal performance of salinity gradient solar ponds

Solar ponds are a promising technology to capture and store solar energy. Accurate, reliable and versatile models are thus needed to assess the thermal performance of salinity gradient solar ponds. A CFD simulation set-up has been developed in this work to obtain a fully versatile model applicable to any practical scenario. Also, a comparison between the results obtained with an existing one-dimensional MATLAB model and the two- and three-dimensional CFD models developed in this work has been carried out to quantify the gain in accuracy and the increase in computational resources needed. The two and three-dimensional models achieve considerably higher accuracy than the 1-D model. They are subsequently found to accurately evaluate the heat loss to the surroundings, the irradiance absorbed by the solar pond and the thermal performance of the pond throughout the year. Two geographic locations: Bafgh (Iran) and Kuwait City, have been evaluated.

Thermodynamic and thermoeconomic analysis of three cascade power plants coupled with RO desalination unit, driven by a salinity-gradient solar pond

Solar-based organic Rankine cycles (ORCs) for power supply of reverse osmosis (RO) desalination units are the most energy-efficient technologies for brackish water and seawater desalination within the small-to-medium electricity ranges (<500kW). To collect and absorb solar energy, various collectors are devised, where among all, solar pond (SP) has been considered as a low-cost solar collector for a long working period. Meantime, conventional ORC/RO systems have a low condensing pressure and density, and consequently a turbine with large volume should be designed. The best solution is design of a desalination system powered by a cascade ORC or KC (Kalina cycle), using thermal heat of a SP for long-term applications. With this regard, three new cascade systems based on ORC and KC are proposed and thermodynamic and thermoeconomic analysis of the proposed systems are carried out. It is found that the ORC/ORC/RO system has the highest net power, power efficiency, and exergy efficiency as well as lowest SUCP (sum unit cost of product) and total exergy destruction. However, the total exergy rate of loss of the ORC/ORC/RO system was around 20% higher than that of the ORC/KC/RO system and approximately 10.81% lower than that of the KC/KC/RO system. Among all components, three components of condenser, cascade heat exchanger, and vapor generator had the highest exergy destruction in the ORC/KC/RO, ORC/ORC/RO, and KC/KC/RO systems, respectively. In addition, among all systems, the ORC/ORC/RO system had the lowest product cost rate and loss cost rate of 2185.83 $/h and 309.65 $/h, respectively. The results of case study simulation for the Bushehr Port indicated that the time between May and August can be the most appropriate time in a year in order to extract more thermal heat from the solar pond for the proposed power/desalination systems. Furthermore, the most economical month for the proposed power/desalination was June due to the low value of SUCP (72.42 $/kWh) since more fresh water was produced in this month.

Performance comparison of two new cogeneration systems for freshwater and power production based on organic Rankine and Kalina cycles driven by salinity-gradient solar pond

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 m2 was used to produce 145.8 m3h fresh water, it is found that the same fresh water amount can be attained with a solar pond with 35500 m2, hence obviously increasing pond area from this value will increase fresh water capacity of the proposed plant.

Investigation of temperature development in salinity gradient solar pond using a transient model of heat transfer

Solar pond utilizes a salinity gradient to trap thermal energy in the storage zone. The stored heat can be employed for several potential applications. A transient analysis is carried out to investigate the effect of various parameters such as variation of the thickness of zones, ground conditions, and surface losses on the temperature development of solar pond. The numerical model is validated with experimental results from two different locations obtained from the literature. The thickness of each zone is determined based on the maximum temperature of LCZ and fast warm-up time under the meteorological conditions of Bhavnagar. The thickness of UCZ, NCZ, and LCZ are selected as 0.3 m, 1.3 m, and 1.5 m, respectively, for the subsequent study of the solar pond. It is found that a phase difference of nearly 42 days occurs between maximum values of solar radiation and temperature of LCZ for a given set of conditions. The dependence of LCZ temperature on the thickness of NCZ and ground conditions is also presented. A detailed assessment of surface losses shows the evaporation loss to be higher than convection and radiation losses. The impact of evaporation loss is highest in the temperature of UCZ and LCZ; however, the change in the LCZ temperature due to surface losses is minimal. Also, the shading area should be considered for the investigation of smaller area of pond. Solar pond with larger area requires less duration to acquire high temperature.

Improved Thermal Efficiency of Salinity Gradient Solar Pond by Suppressing Surface Evaporation Using an Air Layer

Salinity gradient solar ponds (SGSPs) provide a tremendous way to collect and store solar radiation as thermal energy, and can help meet the critical need for sustainable ways of producing fresh water. However, surface evaporation results in the loss of both water and heat. This study therefore theoretically investigates the effect on temperatures within an SGSP when its surface is covered with a layer of air encased in a nylon bag. An earlier SGSP model was slightly modified to add the air layer and to estimate the temperature distributions of the upper layer or the upper convective zone (UCZ) and the bottom layer or lower convective zone (LCZ). The results for a year-long period showed that adding the air cover increased the LCZ temperature to a maximum of 94°C in July, with a total average increase of about 9% over the uncovered pond. In the UCZ, temperatures showed an average increase of approximately 45%, reaching a maximum of 34°C. The temperature of the air layer was meanwhile found to be close to the ambient temperature and behaved identically. These findings invite future experimental and theoretical investigations into the use of air layers to prevent surface evaporation, thereby enhancing the efficiency of SGSPs as a source of clean energy.

Dependency of Air Heating and Cooling for Karbala Buildings on a Salinity Gradient Solar Pond Area

Dependency of Air Heating and Cooling for Karbala Buildings on a Salinity Gradient Solar Pond Area

Dependency of Air Heating and Cooling for Karbala Buildings on a Salinity Gradient Solar Pond Area

Dependency of Air Heating and Cooling for Karbala Buildings on a Salinity Gradient Solar Pond Area

Feasibility investigation of a humidification-dehumidification (HDH) desalination system with thermoelectric generator operated by a salinity-gradient solar pond

Water distillation via solar energy is investigated potentially as an appreciable topic across the globe in recent decades. While many high-efficient solar collectors are developed for this objective, it is discovered that solar pond with big size can be more cost-effective than many types of high-efficient collectors. In pursuance of this objective, plausibility of extracting thermal heat from a salinity-gradient solar pond (SGSP) set-up for water distillation via a humidification-dehumidification (HDH) system is scrutinized under privilege of thermodynamics laws. Furthermore, due to the fact that solar pond's pumps consume more power for their task, two thermoelectric generators (TGEs) are posited to use waste heat of the discarded brine and distilled water to generate electricity for power demands. Single-criterion optimization is executed for the suggested set-up and the results are presented for the Urmia lake in Iran. Considering maximization of distilled water scenario, the findings outlined that 4.5 m3/h distilled water and 3.16 kW net electricity can be generated with cogeneration Gain-Output-Ratio (CGOR) of 1.56 and exergy-based CGOR (ECGOR) of 4.87%. Also, the designed desalination unit generated more fresh water between 22 May and 22 July for Urmia province, while more electricity is generated between 21 April and 21 May. Among all constituents of the introduced SGSP/HDH system, dehumidifier attributed as the major site of loss by exergy destruction of 15.23 kW. At last, an exhaustive parametric evaluation is established to scrutinize impact of some preeminent design parameters on the targets. It is exhibited that the CGOR can be maximized with desalination flow ratio, while the ECGOR can be maximized with lower-convective zone temperature.

Investigating potential benefits of a salinity gradient solar pond for ejector refrigeration cycle coupled with a thermoelectric generator

Extraction of thermal heat from a salinity-gradient solar pond (SGSP) as a way of accumulating solar energy, stockpiling and taking merit of it for medium and low temperature demands is presented as an interesting topic in recent decades. This reliable supply of heat can be used for low-temperature refrigeration systems to yield cooling load for residential applications. For this purpose, theoretical investigation of ejector refrigeration cycle (ERC) driven by a SGSP is carried out to produce cooling output. Also, thermoelectric generator (TEG) is used as a potential device replacing condenser of the ERC for the sake of bolstering performance of the fundamental system by producing power, using heat from SGSP. To express viscosity effect of refrigerant through different components of ejector, available numerical correlations are used and it is demonstrated that this deliberation highly increases the accuracy of ejector mathematical modeling. An extensive thermodynamic evaluation on the basis of the mass-, energy-, and exergy-based balance relations for disparate constituents of the introduced system is executed and the outcomes are corroborated with those of experiential approaches. Moreover, performance of the integrated system is optimized by maximizing energy efficiency as well as exergy efficiency for an optimal solar pond. At the optimum mode, the outcomes of modeling portrayed that the introduced system can culminate in furnishing cooling capacity of 9.216 kW and net electricity of 1.026 kW, respectively, at lower convective zone (LCZ) temperature of 359.7K, LCZ's thickness of 1.003m, non-convective zone of 1.339m, upper convective zone of 0.102m, and solar pond area of 189,476m2. Under this optimum condition, the energy and exergy efficiencies are evaluated around 28.26% and 29.95%, respectively, using R245fa as working fluid in the ERC. In the optimal scenario, the ERC should be designed with primary pressure of 0.49 MPa, secondary pressure of 0.098 MPa, mass entrainment ratio of 0.3046, nozzle efficiency of 96.77%, mixer efficiency of 95.52%, and diffuser efficiency of 76.7%.

Industrial Heating application of a Salinity gradient solar pond for salt production

This research is investigating the possibility of using heat stored in solar ponds for salt drying. At present, Pyramid Salts, a salt producing company located in the north of Victoria, Australia, use electric heaters to heat ambient air from around 20 °C to around 70 °C in their salt crystallizers for salt drying. This research paper aims to develop a solar PV driven heat pump coupled with a solar pond to supply necessary hot air. According to the collected data solar pond performance in Pyramid Hill indicates that heat will be available at the bottom of the pond between 35 °C to 50 °C (winter to summer). Coupling the salinity gradient solar pond with the heat pump is the novelty of this research paper. The heat pump’s evaporation boosts from ambient temperature to available solar pond heat (40 °C) and above 24/7 all year around. As a result, the amount of electrical energy saving in this project has been estimated to be about 1 GWh per year. In this work, the preliminary data on the developments of salinity, temperature, and turbidity profiles will be considered and discussed.

Flow simulation and assessment of a salinity gradient solar pond development

Abstract The main purpose of salinity gradient solar ponds (SGSPs) is to store the maximum possible solar thermal energy. A well-established salinity and temperature gradients are the main points to achieved optimum storage efficiency. In this work, a high-fidelity model is developed using computational fluid dynamics (CFD) to simulate the SGSP behavior under hot climate regions. The model is able to simulate the double convective effect by solving Navier-Stokes and energy equations, simultaneously. Brines with different salinities (i.e. 10%,15, and 25%) are used to investigate their role on the developed salinity/temperature gradients. Simulation results show the successful establishment of the three zones (i.e. upper convective, non-convective, and lower convective) with relatively stable salinity and temperature gradients. However, injecting the lower convective zone (or storage zone) with 10% saline brine results in preserving the highest storage temperature of around 79.2°C after flow time of six hours.

Prediction of solar pond performance parameters using artificial neural network

In this paper, artificial neural networks (ANNs) model was used to predict the performance parameters of a laboratory model salinity gradient solar pond (SGSP), which is used for supplying hot water. Experiments were conducted on three different solar ponds provided with and without twisted tapes in the flow passage of the in-pond heat exchanger during the month of May 2015 at Chennai weather conditions in India. The performance parameters of solar pond such as outlet water temperature, efficiency of solar pond and effectiveness of in-pond heat exchanger were determined experimentally for two different flow rates of Reynolds numbers 1,746 and 8,729. The experimental data obtained from the observations were utilised for training, validating and testing the proposed artificial neural network model. The parameters like incident solar radiation, inlet water temperature, lower convective zone (LCZ) temperature and flow rate are responsible for the outlet water temperature of the solar pond. Based on the experimental readings as inputs a computational program was developed in Python. This program was trained using artificial neural network with back propagation algorithm to predict the outlet water temperature of the in-pond heat exchanger. The results predicted using the model developed is in good agreement with the experimental results.

On increasing the thermal mass of a salinity gradient solar pond with external heat addition: A transient study

In salinity gradient solar ponds (SGSPs) solar thermal energy is mainly stored in the lower-convective zone (LCZ) the volume of which defines the thermal mass of storage. The present study explores the provision of increasing the heat storage in a SGSP by increasing the thermal mass of it. It also addresses the method of enhancing the thermal performance of a SGSP by increasing the thermal mass, while adding heat from external sources. Earlier studies have proved that adding external heat to the SGSP for storage enhances the thermal performance of it significantly. This study aims to prove that increasing the thermal mass of storage further increases the energy efficiency of a SGSP when external heat is added to it. A hybrid system of a SGSP coupled with evacuated tube solar collectors (ETSCs) is used in this study. Several parameters like storage temperature in LCZ, heat addition flux and heat addition efficiency of ETSC, instantaneous efficiency of SGSP, heat extraction from SGSP are studied in this paper for different cases of with and without heat addition and with normal and enhanced thermal mass. It is found that increasing thermal mass can significantly enhance the thermal performance and efficiency of a SGSP.

Improvement of salt gradient solar ponds’ performance using nanoparticles inside the storage layer

The solar pond is one of the usual tools used for solar energy harvesting in the world, although its low efficiency is still a big challenge. In this study, to enhance the thermal efficiency of the laboratory-scale salinity gradient solar pond, three different nanoparticles, i.e., SiO2, Fe3O4, and ZnO, were dispersed into a salt-water solution as the based liquid. Nanoparticles’ mass concentrations used in the based liquid were 0.012%, 0.036%, and 0.06%. The simulated sunlight thermal energy was supplied by a 500 W halogen lamp. The prepared nanofluids were used as lower layer of the pond. Approximately 3 days after filling the pond, the stable salinity gradient was formed and after almost 2 days of exposure to the simulated sunlight, the temperature of the pond layers reached thermal equilibrium. The results showed that lower layer temperature increased continuously with nanoparticles’ concentration, for all nanofluids. Based on the measured temperature, the pond thermal performance was calculated, showing that all mentioned nanoparticles could enhance the thermal efficiency of the SGSP. The maximum lower layer temperature (~ 47 °C) and thermal efficiency enhancement ratio (35.13%) were obtained for the 0.06% ZnO nanofluid. This nanofluid showed the minimum light scattering (particle size parameter = 0.248) and transmittance (near zero) over the UV–Vis wavelength, leading to the increased thermal efficiency of the pond, as compared to the SiO2 and Fe3O4 nanofluids. In addition, using nanoparticles, the time required to reach equilibrium conditions in the pond was decreased, with the maximum of about 9 h.

Thermal performance of 500 m2 salinity gradient solar pond in Granada, Spain under strong weather conditions

In this study, an experimental investigation of temperature performance and efficiency of an industrial solar pond during strong winter conditions is presented. Several temperature sensors connected to a data logger were used to measure the temperature gradient in a 500 m2 solar pond. During the winter 2015 there was a snowfall in the solar pond of Granada (Spain), reaching a minimum air ambient temperature of −2.4 °C. The temperature of the storage zone in Granada solar pond remained constant (around 40 °C) indicating the system responds positively to weather variations and confirming the fundamental role of the salinity gradient as a thermal insulation layer. The stored energy during January 2015 was 13.3 GJ, the weekly efficiency reached 10% and finally, the solar pond was able to provide 247.1 MJ to the flotation unit during the week of the snowfall.

Increasing the storage capacity of a solar pond by using solar thermal collectors: Heat extraction and heat supply processes using in-pond heat exchangers

In this study, an experimental investigation of the performance of a salinity gradient solar pond (SGSP) integrating solar collectors is presented. The SGSP is located in Barcelona (Spain) and has a cylindrical tank 3 m in height and 8 m in diameter with a total area of 50 m2. For this purpose, four solar thermal collectors (10 m2) are integrated, as an external source of heat, with the solar pond pilot plant in order to increase the storage capacity and its overall efficiency. The aim of this study is to evaluate heat extraction and heat supply processes from and to the SGSP under different seasonal conditions. Two in-pond heat exchangers are used, a conventional one situated on the bottom of the pond and a second one covering the lateral wall area of the pond. Heat extraction and supply experiments are performed using both heat exchangers individually or both at the same time. The experiments are conducted under two different seasonal temperature conditions: winter (February and March) and summer (July). The variations of the temperature inside the pond during the heat extraction/supply tests are monitored and analyzed. The results have indicated that the use of solar collectors as an extra source of heat for the solar pond led to a 50% increase in the daily efficiency during the cold season tests, while heat extraction only appeared as the best option during the warm season tests. Higher daily efficiency and heat supply results can only be obtained if large amounts of heat are extracted, otherwise, the daily efficiency of the solar pond could decrease. Finally, the solar collectors can be considered a good alternative for avoiding a significant decrease in solar pond temperatures (especially during the cold season), which would not only result in a significant energy storage efficiency improvement but also increase the capacity of the solar pond to supply heat to an external application.

Cyclic heliothermal behaviour of the shallow, hypersaline Lake Hayward, Western Australia

Lake Hayward is one of only about 30 hypersaline lakes worldwide that is meromictic and heliothermal and as such behaves as a natural salt gradient solar pond. Lake Hayward acts as a local groundwater sink, resulting in seasonally variable hypersaline lake water with total dissolved solids (TDS) in the upper layer (mixolimnion) ranging between 56 kg m−3 and 207 kg m−3 and the deeper layer (monimolimnion) from 153 kg m−3 to 211 kg m−3. This is up to six times the salinity of seawater and thus has the highest salinity of all eleven lakes in the Yalgorup National Park lake system. A program of continuously recorded water temperature profiles has shown that salinity stratification initiated by direct rainfall onto the lake’s surface and local runoff into the lake results in the onset of heliothermal conditions within hours of rainfall onset.The lake alternates between being fully mixed and becoming thermally and chemically stratified several times during the annual cycle, with the longest extended periods of heliothermal behaviour lasting 23 and 22 weeks in the winters of 1992 and 1993 respectively. The objective was to quantify the heat budgets of the cyclical heliothermal behaviour of Lake Hayward.During the period of temperature profile logging, the maximum recorded temperature of the monimolimnion was 42.6 °C at which time the temperature of the mixolimnion was 29.4 °C.The heat budget of two closed heliothermal cycles initiated by two rainfall events of 50 mm and 52 mm in 1993 were analysed. The cycles prevailed for 11 and 20 days respectively and the heat budget showed net heat accumulations of 34.2 MJ m−3 and 15.4 MJ m−3, respectively. The corresponding efficiencies of lake heat gain to incident solar energy were 0.17 and 0.18 respectively. Typically, artificial salinity gradient solar ponds (SGSP) have a solar radiation capture efficiencies ranging from 0.10 up to 0.30. Results from Lake Hayward have implications for comparative biogeochemistry and its characteristics should aid in identification of other hitherto unknown heliothermal lakes.