Operation Of Solar Pond Research Articles

Multivariate analysis of the operational parameters and environmental factors of an industrial solar pond

The stability of an industrial Salinity Gradient Solar Pond (SGSP) has been studied by applying classical Principal Component Analysis (PCA) on three datasets with a different number of variables and time evolution. Temperature, density and heat extraction have been measured in the upper convective (UCZ), non-convective (NCZ) and low convective (LCZ) zones in a 500 m2 solar pond, located near Granada, South of Spain. Local environmental weather conditions have been also considered in the data analysis. Two operational seasons of the solar pond were considered in order to establish: (1) PCA exploratory models for 2014–2015 operational period and (2) to validate the obtained results during the 2015–2016 operational period. PCA results showed that three factors explained the variance in the monitored stability gradients. The first factor was related to the major effect of the seasonal temperature variation on the entire stability gradient. The second factor, related to the diurnal temperature variation, solar irradiance and wind variables, showed a strong impact on the solar pond temperature and salinity gradients and could affect strongly the UCZ and its border with the NCZ. The third factor affected the stability of salinity and temperature gradients at the LCZ and its border with the NCZ. The latter was related to the increase in temperature and salinity at the bottom of the solar pond, which suggests special attention during the initial formation and settlement of the salinity gradient and the subsequent heat extraction activities. This paper shows PCA modelling as a powerful tool for solar pond operation process surveillance and control.

Solar pond as a low grade energy source for water desalination and power generation: a short review

Water and energy are thoroughly linked: water is required to generate, transfer, and use the lot characteristics of energy; and energy is demanded to extract, treat, and distribute water. Shortage in clean water deems as the main challenge facing the world as a result of the escalating in the energy consumption required for desalinating the sea/brackish water which increases costs and provokes on the marine life and environment due to the high concentrate solute produced from desalination plants. Solar pond is a reservoir of water with different salt concentration implements to gather and store the incident solar energy which it can be employed later on in different thermal energy applications, such as industrialized heating process, electricity power generation, farming crop drying and cooling of houses. In this paper a short but concentrated review of the literatures that dealt with the implemented of the solar pond to illustrate succinctly the historical background for the solar ponds as well as the most word-wide established solar ponds. In addition to the theoretical background of heat and mass transfer which governed the solar pond operation is presented and discussed.

An experimental and numerical study of evaporation reduction in a salt-gradient solar pond using floating discs

Salt-gradient solar ponds are water bodies that act as solar collectors with integrated storage that are a promising renewable energy source for low-temperature applications. Evaporation is an important challenge for efficient operation of solar ponds, especially in arid locations without water sources to replenish the evaporative losses. In this work, transparent partial covers were used to investigate how evaporation suppression affects both the water and energy balance of a laboratory-scale solar pond. In our experiments, the evaporation reduction efficiency was related to the cube root of the relative covered area. This evaporation reduction efficiency is smaller than that of natural water bodies because of the influence of the warm lower convective zone. Also, as the covered fraction of the surface area increased, the thickness of the non-convective zone decreased and the heat losses through this zone increased. As a result, the temperature in the lower convective zone did not increase as the covered fraction increased. Nonetheless, the heat content within the solar pond slightly increased, demonstrating that the reduction of evaporation improves the heat storage capacity of the pond. Moreover, an economic analysis showed that although the evaporation reduction efficiency in solar ponds is smaller than that of natural water bodies or reservoirs, the benefits related to the additional energy collected in the solar pond when reducing evaporation overcome the smaller water saving benefits. Therefore, suppressing evaporation in solar ponds not only is valuable in locations with no water to replenish the evaporative losses but also improves its economic benefits.

Passive small scale electric power generation using thermoelectric cells in solar pond

Solar ponds have been widely utilised in providing low grade heat needed for industrial processes and for heating applications <100 °C. In this paper, a small scale passive electric power generation unit was devised for generating electricity from the heat available in the solar pond. The power generation unit proposed operates without the use of a pump and involves no moving parts. The design of the power generation unit was finalised after performing a comprehensive theoretical study on the possible geometrical arrangements. The power generation unit was fabricated and tested experimentally. The power generation unit consists of 120 commercially available thermoelectric cells accommodated in the outer and inner layers of this dual layer power generation unit. The power generation unit had produced a maximum power of 40.8 W under the condition of Th = 99 °C. Under the normal operation of solar pond, the lower convective zone will have a temperature that lies within in the range of 40 °C –80 °C. Thus, maximum output in the range of 19.5 W–27.4 W is more realistic for the system proposed with the heat to electric conversion efficiency ranges between 0.37%–0.68%.

Evaporation suppression and solar energy collection in a salt-gradient solar pond

Evaporation represents a significant challenge to the successful operation of solar ponds. In this work, the suppression of evaporative losses from a salt-gradient solar pond was investigated in the laboratory. Two floating element designs (floating discs and floating hemispheres) and a continuous cover were tested; all three covers/elements were non-opaque, which is unique from previous studies of evaporation suppression in ponds or pools where increasing temperature and heat content are not desired. It was found that floating discs were the most effective element; full (88%) coverage of the solar pond with the floating discs decreases the evaporation rate from 4.8 to 2.5mm/day (47% decrease), increases the highest achieved temperature from 34°C to 43°C (26% increase), and increases heat content from 179 to 220MJ (22% increase). As a result of reduced evaporative losses at the surface, the amount of heat lost to the atmosphere is also reduced, which results in lower conductive losses from the NCZ and the LCZ and hence, increased temperatures in the NCZ and LCZ. The magnitude of evaporation reduction observed in this work is important as it may enable solar pond operation in locations with limited water supply for replenishment. The increase in heat content allows more heat to be withdrawn from the pond for use in external applications, which significantly improves the thermal efficiencies of solar ponds.

Effect of Water Distribution Ways on the Operation of Solar Pond

An experimental study on the evolution of the salinity profiles in the salinity gradient solar ponds was executed using a small model pond. The body of the simulated pond is a cylindrical plastic tank, with 50 cm height and 45 cm diameter. The salinity gradient was established in the laboratory tank by using the salinity redistribution technique. The measurements were taken during a period of 20 days of experimentation. This period of time allowed the existence of salt diffusion from the storage zone to the surface. Results obtained from this study show that when the ratio of brine/water is 1/1, the salinity gradient layer can sustain a longer time and the lower convective zone is thicker, which is benefit to store solar energy.

Experimental study of natural brine solar ponds in Tibet

Abstract A salinity gradient solar pond (SGSP) is a simple and effective way of capturing and storing solar energy. The Qinghai-Tibet Plateau has very good solar energy resources and very rich salt lake brine resources. It lacks energy for its mineral processes and is therefore an ideal location for the development and operation of solar ponds. In China, solar ponds have been widely applied for aquaculture, in the production of Glauber’s salt and in the production of lithium carbonate from salt lake. As part of an experimental study, a SGSP using the natural brine of Zabuye salt lake in the Tibet plateau has been constructed. The pond has an area of 2500 m 2 and is 1.9 m deep. The solar pond started operation in spring when the ambient temperature was very low and has operated steadily for 105 days, with the LCZ temperature varying between 20 and 40 °C. During the experimental study, the lower convective zone (LCZ) of the pond reached a maximum temperature of 39.1 °C. The results show that solar ponds can be operated successfully at the Qinghai-Tibet plateau and can be applied to the production of minerals.

Desalination coupled with salinity-gradient solar ponds

Thermal desalination by salinity-gradient solar ponds (SGSP) is one of the most promising solar desalination technologies. Solar ponds combine solar energy collection with long-term storage and can provide reliable thermal energy at temperature ranges from 50 to 90°C. Solar-pond-powered desalination has been studied since 1987 at the El Paso Solar Pond Project, El Paso, Texas. From 1987 to 1992, the search mainly focused on the technical feasibility of thermal desalination coupled with solar ponds. Since 1999, the research has focused on long-term reliability, improvement of thermodynamic efficiency, and economics. During this period, a small multi-effect, multi-stage flash distillation (MEMS) unit, a membrane distillation unit, and a brine concentration and recovery system (BCRS) were tested over a broad range of operating conditions. The most important variables for the MEMS operation were flash range, concentration level of reject brine, and circulation rate of the first effect. The brine concentration and recovery system is part of the goal of developing a systems approach combining salinity-gradient solar pond technology with multiple process desalination and brine concentration. This system approach, called zero discharge desalination, proposes concentrating brine reject streams down to near NaCl saturated solutions and using the solution to make additional solar ponds. In addition to presenting the test results on the MEMS and BCRS units, this paper also presents a summary of solar pond operation experiences obtained from the 16-year operation at the El-Paso solar pond.

El Paso Solar Pond

The El Paso Solar Pond, a research, development, and demonstration project operated by the University of Texas at El Paso, is a salinity-gradient solar pond with a surface area of 3,000 m2 and a depth of 3.2 m. The pond utilizes an aqueous solution of predominantly sodium chloride (NaCl). The surface convective zone, main gradient zone, and bottom convective zone are approximately 0.6 m, 1.4 m, and 1.2 m, respectively. The project, located on the property of Bruce Foods, Inc., was initiated in 1983 in cooperation with the U.S. Bureau of Reclamation. Since then, the El Paso Solar Pond has successfully developed a series of technologies for solar pond operation and maintenance, as well as demonstrated several different applications. In 1985, the El Paso Solar Pond became the first in the world to deliver industrial process heat to a commercial manufacturer; in 1986 became the first solar pond electric power generating facility in the United States; and in 1987 became the nation’s first experimental solar pond powered water desalting facility. Currently, the major research at El Paso Solar Pond is focused on desalination and brine management technologies. The long-term goal of this research is to develop a systems approach for desalination/brine management via a multiple process desalination coupled with solar ponds. This systems approach will reuse the brine concentrate rejected from desalting plants thereby negating the need for disposal (zero discharge), and provide additional pollution-free renewable energy for the desalting process.

A desalination plant using solar heat as a heat supply, not affecting the environment with chemicals

The project concerns the design, optimization, construction, assembling, start-up and extensive monitoring of a full-titanium desalinator. The operational tests took place at the site of the solar pond of the University of Ancona (Italy). Data collected during manufacturing tests and, in particular, during the start-up and the operation of the plant under various conditions, are being utilized for improving expertise on heat recovery with highly corrosive fluids, on co-generation plants aimed at producing electricity and fresh water, and on desalination fed by solar energy. One major output of the project is the assessment of data which permits an evaluation of the additional cost of the full-titanium desalinator with respect to a traditional technology, with the added benefits of (a) better heat transmission through tube bundles, which means better performance; (b) a reduced need for chemicals and maintenance activities; and (c) improved plant reliability and duration. The research program has three main aims: (1) the improvement of the economics of solar desalination, namely desalination of water through operation of solar ponds; (2) the demonstration of thermal performance, maintenance and chemical requirements, reliability and overall costs of a full-titanium desalination plant through operation of a plant of meaningful size in order to disseminate the technology of full-titanium desalination plants in the electric-energy production industry for use in co-generation units; and (3) the improvement of knowledge regarding industrial-size use of heat recovery from highly corrosive fluids.

Performance of 1700 m2 solar pond operation in arid zone

A 1700 m2 solar pond was constructed in the desert of Kuwait where severe weather conditions prevail in all seasons. The paper describes in detail a diffuser design for the gradient establishment, gradient stability, and thermal performance of the pond. The main problem encountered in operating the pond was mixing between the upper zone and the gradient zone, even when the wind speed was as low as 5 m/s. No mixing between the gradient and the lower connective zone was observed. The wind effect was severe in causing mixing even when the upper convective zone increased to 0.90 m.

Turbulent Mixing in Stratified Fluids

ion layer in the oceanic benthic boundary layer against the stratification of the lutocline, and the growth of the planetary boundary layer (PBL) due to the turbulent mixing at the tropopause. Such mixing processes are of importance in studying and controlling various biological activities and the dispersion of pollutants in the environment. Pertinent engineering situations include mixing at the thermocline due to the dis­ charge of buoyant jets from power plants [e.g. ocean thermal-energy con­ version (OTEC)]; water-qua lity control in stratified, multi port reservoirs; control of mixing during the operation of solar ponds; and mixing of methane gas in mine shafts. Mixing mechanisms in stratified fluids depend on the nature of the external forcing and the background

Performance of solar ponds with wind suppressors

Abstract The effect of wind suppressors on the performance of a 4 m 2 solar pond, operating under the environment of the Arabian Gulf area characterized by windy, hot and humid conditions, is investigated experimentally. In addition to using screen nets on the pond's perimeter, two arrangements of wind suppressors of PVC floating pipes are considered. Climatological data relevant to the operation of solar ponds in this area namely wind speeds and evaporation rates are presented. Results of both salinity and temperature over a one year period are presented to evaluate the effect of wind suppressors and thermal insulation on the performance of the pond. The gradient zone was disturbed by invoking localized convective zones of different thicknesses to examine the effect of wind suppressors on the healing of those zones. Results show that wind suppressors of the floating piping type, can considerably slow down the movement of the upper convective-gradient zone interface and prohibit any formation of localized convective zones. Thermal insulation is a prerequisite for operating small solar ponds even in hot climates.

Effect of scattering and absorption on solar pond efficiency

This article outlines the minimum set of concepts of hydrological optics required for an understanding of solar energy penetration into bodies of water. The practical application of these concepts to solar ponds, especially by means of the Monte Carlo modeling procedure, is discussed, and an account is given of the optical measurements that need to be made in order to arrive at an understanding of radiation transfer within any given solar pond. The results are presented of a series of Monte Carlo calculations of the behavior of solar radiation within idealized but realistic solar ponds with optical properties covering a wide range of values. The effect on energy collection efficiency of varying the concentration of colored substances, the scattering coefficient, and the albedo of the bottom are explored in detail. The optical criteria that must be satisfied for successful solar pond operation are briefly discussed.

Double Diffusive Effects on Solar Pond Gradient Zones

The salt gradient solar pond NCZ is a diffusive interface that operates at relatively large R/sub RHO/ magnitudes. When growth of an interface occurs, the growth rate is of a magnitude similar in order to that of the slower diffusing component. Erosion rates are not very well quantified at present, however, trends observed indicate that erosion is most significant in the transition zone. In addition, erosion rates increase as an interface progresses to lower R/sub RHO/ values in the transition zone. The results of the Univeristy of Illinois experiments and observation of actual solar ponds indicate that the transition zone is a strong enough barrier preventing practical operation of solar ponds at lower R/sub RHO/ values. Systems using components other than NaCl should be examined to determine their suitability as solar pond components. If the transition zone can be correlated to the diffusivity ratio, then two areas of research may be useful. First, optimizing of a pond's performance based on diffusivity ratio for various density stabilizing components would be necessary. Second, research into potential methods for stabilizing the boundary layer regions may help extend solar pond operational limits to R/sub RHO/ values less than those of the transition zone.

Rayleigh-Jeffreys stability of thermohaline stratified fluids subject to arbitrary temperature and salinity gradients

The stability of a horizontal layer of fluid of infinite extent and having a vertical density stratification due to arbitrary temperature and salinity gradients is studied for various sets of homogeneous boundary conditions. A sufficient condition for stability, i.e., for the maintenance of the original stratification is obtained in the form of a relation between the thermal Rayleigh number, Ra T and the solute Rayleigh number, Ra s . For no initial flow, the relation ▪ is obtained as a sufficient condition for all sets of boundary conditions, where P T and P s are the thermal and solute Prandtl numbers, respectively, and df T and df s are mean values of the gradients of the initial temperature and solute distributions. This condition is a natural modification of that previously obtained for the case of constant thermal and salinity gradients [1, 10, 16], namely ▪ The condition is applicable to situations in which the physical boundary conditions are not well-defined, e.g., in practical engineering development and operation of solar ponds.

Development of a simple instrument for determination of salt concentration profile in the operation of solar ponds

The development and construction details of an instrument to measure densities of the brine at different depths in a solar pond are presented and discussed. Using a vertically moving sampling tube, brine is drawn from the pond and then is fed to the bottom of a conical container in which a sealed conical glass vessel is fully submerged. The bouyancy force exerted by the water on the sealed glass vessel is measured by a system of cantilever beam and strain gauges. The output of the strain gauge bridge is proportional to the density of the fluid passing through the conical container. It is shown that this instrument can be effectively used to determine the salt concentration profile in salt gradient solar ponds.

A parametric study on solar ponds

A linear relation between the efficiency of solar ponds and factor θ d H which is the temperature difference between the pond bottom and the ambient divided by the average insolation is presented. This relation, which has been developed based on a steady state analysis provides valuable information on the relative importance of the parameters involved in the operation of solar ponds. It is found that the existence and the thickness of the top convective zone has a profound negative effect on the yield of solar ponds. The optimum thickness of the density gradient layer under various conditions is also presented. The effect of ground losses is discussed, and it is shown that for the case of wet soil, especially if the level of the underground water is high, the pond should be thermally insulated. It is also shown that the steady state analysis can predict with good accuracy the yearly average response of solar ponds under transient conditions.

Introduction of a passive method for salt replenishment in the operation of solar ponds

A passive method for the replenishment of salt in solar ponds is suggested, based on the natural circulation of water caused by density differences. Water, from a selected depth in the solar pond, is passed through a salt bed in an adjacent tank, where its salinity is increased before it is returned to the bottom region of the solar pond. The difference between the densities, at the points of intake and outlet, provide the driving force for the natural circulation. Careful system design ensures that this circulation will transport enough salt to the bottom region of the pond to compensate for its upward diffusion in salt gradient solar ponds. This method negates the need for the pumping installation normally required for salt replenishment; and it provides a simple, self-regulating, and reliable method for density control in the bottom region of solar ponds.

Under ground thermal storage in the operation of solar ponds

The thermal interaction between a large solar pond and the surrounding ground is considered. For a given sinusoidal variation of the temperature at the bottom of the pond, the time-dependent temperature profiles in the ground are calculated and the corresponding heat fluxes to or from the ground as functions of time are obtained. The temperature variations in the ground for several years are plotted and the heat transfer between the solar pond and the ground thermal storage is discussed. The efficiency of the heat recovery is studied and its significance is pointed out.