471-2004-1-solar ponds, Ömer bÜyÜkkidik, a. ceylan serhadoÐlu, 2004-1

7/30/2019 471-2004-1-SOLAR PONDS, MER BYKKIDIK, A. CEYLAN SERHADOLU, 2004-1

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A TECHNICAL SEMINARON

SOLARPONDS

SUBMITTED BY

KARTHIK V

1RV12MPD14


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OUTLINE

1. INTRODUCTION

2. WHAT A SOLAR POND IS 2.1 WORKING PRINCIPLE

3. TYPES OF SOLAR PONDS 3.1 NONCONVECTING 3.2 CONVECTING

4. APPLICATIONS


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5. EXAMPLES OF SOLAR PONDS 5.1 BHUJ SOLAR POND 5.2 El PASO SOLAR POND

5.3 PYRAMID HILL SOLAR POND

6. COST

7. ADVANTAGES and DISADVANTAGES

8. CONCLUSION

REFERENCES


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1. INTRODUCTION

The sun is the largest source of renewable energyand this energy is abundantly available in allparts of the earth. It is in fact one of the best

alternatives to the non-renewable sources ofenergy [1].

Solar energy has been used since prehistorictimes, but in a most primitive manner. Before

1970, some research and development wascarried out in a few countries to exploit solarenergy more efficiently, but most of this workremained mainly academic [2].


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After the dramatic rise in oil prices in the 1970s,several countries began to formulate extensiveresearch and development programmes to exploit

solar energy [2]. One way to tap solar energy is through the use of

solar ponds. Solar ponds are large-scale energycollectors with integral heat storage for supplyingthermal energy. It can be use for various

applications, such as process heating, waterdesalination, refrigeration, drying and powergeneration [1]


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2. WHAT A SOLAR POND IS

A solar pond is a body of water that collects andstores solar energy. Solar energy will warm abody of water (that is exposed to the sun), butthe water loses its heat unless some method is

used to trap it. Water warmed by the sun expandsand rises as it becomes less dense. Once itreaches the surface, the water loses its heat tothe airthrough convection, or evaporates, takingheat with it. The colder water, which is heavier,

moves down to replace the warm water, creatinga natural convective circulation that mixes thewater and dissipates the heat. The design of solarponds reduces either convection or evaporation inorder to store the heat collected by the pond.They can operate in almost any climate [3].


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A solar pond can store solar heat much moreefficiently than a body of water of the same sizebecause the salinity gradient prevents convection

currents. Solar radiation entering the pondpenetrates through to the lower layer, whichcontains concentrated salt solution. Thetemperature in this layer rises since the heat it

absorbs from the sunlight is unable to moveupwards to the surface by convection. Solar heatis thus stored in the lower layer of the pond [4].


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2.1 WORKING PRINCIPLE

The solar pond works on a very simple principle.It is well-known that water or air is heated theybecome lighter and rise upward. Similarly, in an

ordinary pond, the suns rays heat the water andthe heated water from within the pond rises andreaches the top but loses the heat into theatmosphere. The net result is that the pond waterremains at the atmospheric temperature. The

solar pond restricts this tendency by dissolvingsalt in the bottom layer of the pond making it tooheavy to rise [1]. You can see a shematic view ofa solar pond in Figure 1.


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Fig. 1 Shematic View Of A Solar Pond [5].


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A solar pond is an artificially constructed waterpond in which significant temperature rises arecaused in the lower regions by preventing the

occurrence of convection currents. The morespecific terms salt-gradient solar pond or non-convecting solar pond are also used. The solarpond, which is actually a large area solar collector

is a simple technology that uses water- a pondbetween one to four metres deep as a working

material for three main functions [6].


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Collection of radiant energy and its conversioninto heat (upto 95 C)

Storage of heat

Transport of thermal energy out of the system[6].


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The solar pond possesses a thermal storagecapacity spanning the seasons. The surface areaof the pond affects the amount of solar energy itcan collect. The bottom of the pond is generallylined with a durable plastic liner made frommaterial such as black polythene and hypalonreinforced with nylon mesh. This dark surface atthe bottom of the pond increases the absorptionof solar radiation. Salts like magnesium chloride,sodium chloride or sodium nitrate are dissolved inthe water, the concentration being densest at the

bottom (20% to 30%) and gradually decreasingto almost zero at the top. Typically, a saltgradient solar pond consists of three zones [6].


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An upper convective zone of clear fresh waterthat acts as solar collector/receiver and which isrelatively the most shallow in depth and isgenerally close to ambient temperature,

A gradient which serves as the non-convectivezone which is much thicker and occupies more

than half the depth of the pond. Saltconcentration and temperature increase withdepth,

A lower convective zone with the densest saltconcentration, serving as the heat storage zone.

Almost as thick as the middle non-convectivezone, salt concentration and temperatures arenearly constant in this zone [6].


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When solar radiation strikes the pond, most of it isabsorbed by the surface at the bottom of the pond.The temperature of the dense salt layer thereforeincreases. If the pond contained no salt, the bottomlayer would be less dense than the top layer as theheated water expands. The less dense layer wouldthen rise up and the layers would mix. But the saltdensity difference keeps the layers of the solarpond separate. The denser salt water at the bottomprevents the heat being transferred to the top layer

of fresh water by natural convection, due to whichthe temperature of the lower layer may rise to asmuch as 95C [6].


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3. TYPES OF SOLAR PONDS

There are two main categories of solar ponds:

nonconvecting ponds, which reduce heat loss by

preventing convection from occurring within the

pond; and convecting ponds, which reduce heat loss

by hindering evaporation with a cover over the

surface of the pond [2].


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3.1 CONVECTING SOLAR PONDS

A well-researched example of a convecting pondis the shallow solar pond. This pond consists ofpure water enclosed in a large bag that allows

convection but hinders evaporation. The bag hasa blackened bottom, has foam insulation below,and two types of glazing (sheets of plastic orglass) on top. The sun heats the water in the bagduring the day. At night the hot water is pumped

into a large heat storage tank to minimize heatloss. Excessive heat loss when pumping the hotwater to the storage tank has limited thedevelopment of shallow solar ponds [3].


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Another type of convecting pond is the deep, saltlesspond. This convecting pond differs from shallowsolar ponds only in that the water need not be

pumped in and out of storage. Double-glazing coversdeep saltless ponds. At night, or when solar energyis not available, placing insulation on top of theglazing reduces heat loss [3].


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3.2 NONCONVECTING SOLAR PONDS

There are two main types of nonconvectingponds: salt gradient ponds and membrane ponds.A salt gradient pond has three distinct layers ofbrine (a mixture of salt and water) of varying

concentrations. Because the density of the brineincreases with salt concentration, the mostconcentrated layer forms at the bottom. The leastconcentrated layer is at the surface. The saltscommonly used are sodium chloride and

magnesium chloride. A dark-colored materialusually butyl rubber lines the pond. The darklining enhances absorption of the sun's radiationand prevents the salt from contaminating thesurrounding soil and groundwater [3].


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As sunlight enters the pond, the water and thelining absorb the solar radiation. As a result, thewater near the bottom of the pond becomeswarm up to 93.3C. Although all of the layers

store some heat, the bottom layer stores themost. Even when it becomes warm, the bottomlayer remains denser than the upper layers, thusinhibiting convection. Pumping the brine throughan external heat exchanger or an evaporator

removes the heat from this bottom layer. Anothermethod of heat removal is to extract heat with aheat transfer fluid as it is pumped through a heatexchanger placed on the bottom of the pond [3].


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Another type of nonconvecting pond, themembrane pond, inhibits convection by physicallyseparating the layers with thin transparent

membranes. As with salt gradient ponds, heat isremoved from the bottom layer [2]. In figure 2you can see an example of salt gradient solarpond.


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Fig. 2 Salt Gradient Solar Pond [7].


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4. APPLICATIONS

Salt production (for enhanced evaporation orpurification of salt, that is production of vacuumquality salt)

Aquaculture, using saline or fresh water (to grow,for example, fish or brine shrimp)

Dairy industry (for example, to preheat feedwater to boilers)

Fruit and vegetable canning industry

Fruit and vegetable drying (for example, vine fruitdrying) Grain industry (for grain drying) Water supply (for desalination) [4].


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Process heat

Studies have indicated that there is excellentscope for process heat applications (i.e. waterheated to 80 to 90 C.), when a large quantity ofhot water is required, such as textile processingand dairy industries. Hot air for industrial usessuch as drying agricultural produce, timber, fishand chemicals and space heating are other

possible applications [6].


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Desalination

Drinking water is a chronic problem for manyvillages in India. In remote coastal villages where

seawater is available, solar ponds can provide acost-effective solution to the potable drinkingwater problem. Desalination costs in these placeswork out to be 7.5paise per litre, which comparesfavourably with the current costs incurred in thereverse osmosis or electrodialysis/desalination

process [6].


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Refrigeration

Refrigeration applications have a tremendousscope in a tropical country like India. Perishable

products like agricultural produce and life savingdrugs like vaccines can be preserved for longstretches of time in cold storage using solar pondtechnology in conjunction with ammonia based

absorption refrigeration system [6].


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5. EXAMPLES OF SOLAR PONDS

5.1 BHUJ SOLAR POND

5.2 El PASO SOLAR POND



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5.1 BHUJ SOLAR POND

The 6000-square-metre solar pond in Bhuj, thefirst large-scale pond in industrial environment tocater to actual user demand, supplied totally

about 15 million litres of hot water to the dairy atan average temperature of 75C betweenSeptember 1993 and April 1995 [8]. In figure 3you can see the Bhuj solar pond.


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Fig. 3 The Bhuj Solar Pond [1].


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It was the first experiment in India, whichsuccessfully demonstrated the use of a solar pondto supply heat to an actual industrial user. But,

sadly, the Bhuj solar pond, constructed by theTata Energy Research Institute (TERI), today liesin disuse for want of financial support andgovernment policy to help this eco-friendly

technology grow [9].


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The Bhuj solar pond was conceived as a researchand development project of TERI, which tookover nine years to establish, to demonstrate thefeasibility of using a salt gradient pond for

industrial heating [9].

The solar pond is 100 m long and 60 m wide andhas a depth of 3.5 m. The pond was then filledwith water and 4000 tonnes of common salt was

dissolved in it to make dense brine [1].


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5.2 EL PASO SOLAR POND

The El Paso Solar Pond project is a research,development, and demonstration project initiatedby the University of Texas at El Paso in 1983. It

has operated since May 1986 and has successfullyshown that process heat, electricity, and freshwater can be produced in the southwesternUnited States using solar pond technology [10].You can see the picture of El Paso Solar Pond in

figure 4.


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Fig. 4 El Paso Solar Pond [10].


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The El Paso Solar Pond project began when the

University of Texas at El Paso discovered anexisting pond which has a 3350 square meter

area and 3 meter depth located at Bruce Foods, acanning plant in northeast El Paso, Texas [10]. Infigure 5 you can see another view of El Paso SolarPond.


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Fig. 5 Closer View of El Paso Solar Pond [10].


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Over 90 graduate and undergraduate studentshave been involved in the project, performingtasks ranging from construction to applied

research. In addition, numerous students havedone projects related to the pond, gainingvaluable experience in equipment design andconstruction, lab techniques, problem solving,instrumentation, and documentation [10].


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The solar pond provides a unique opportunity todo research in such areas as double diffusiveconvection, wind/wave interaction, flow instratified fluids, and computer modeling. Inaddition, the state of the art equipment on siteprovides an excellent opportunity for energyefficiency studies, cost analysis, system studies,heat exchanger [10].


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A consortium of RMIT University, Geo-EngAustralia Pty Ltd and Pyramid Salt Pty Ltd hascompleted a project using a 3000 square metre

solar pond located at the Pyramid Hill salt worksin northern Victoria to capture and store solarenergy using pond water which can reach up to

80C [11].In Figure 6 you can see the picture of

this solar pond.


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Fig. 6 The Pyramid Hill Solar Pond [12].


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Pyramid Salt will use the pond's heat not only inits commercial salt production but also foraquaculture, specifically producing brine shrimpsfor stock feed. It is planned in a subsequent stage

of the project to generate electricity using theheat stored in the solar pond, thus making thislocal industry more energy self-sufficient.

At the local level this will be a significant boost inan area with high unemployment and a depressed

economy[12].


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6. COST OF SOLAR PONDS

As technology develops, the energy needs ofcommunities increases. This energy need isprovided from different energy sources known astraditional energy sources, such as coal, fuel oils,

geothermal energy, hydraulic energy, and nuclearenergy. These energy sources have somedisadvantages. The first three of these energysources have limited life times. Hydraulic energyis an insufficient energy source, and nuclearenergy has some unsolved environmental andsafety problems. Therefore, the researchers havecondensed their studies on new alternativeenergy sources known as renewable energysources [13].


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These are biomass, biogas, wind energy, waveenergy, hydrogen energy, and solar energy.

Solar energy among these energy sources is themost abundant and considerable research is beingcarried out in this area. In figure 7 you can see atable which is comparing initial costs of differentwater heating systems. And in figure 8 the annualmaintenance and fuel expenses and, the sum of

these expenses for different water heatingsystems (1991 prices) [14].


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Fig. 7 The Initial Costs of Several Water HeatingSystems(1991 prices).


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Fig. 8 Annual Maintenance And Fuel Expenses And TheSum Of These Expenses For DifferentWater Heating Systems (1991 Prices).


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Salinity gradient solar ponds, although notdramatically cheaper than other disposalmethods, may still be a viable option especially incircumstances where the unit cost of power is

very high or where access to a power grid islimited. Moreover, the actual cost of utilizingSGSPs may be lower than reported when otherfactors are taken into account, such as savingsincurred by bypassing the waste disposalpermitting process, the environmental savingsassociated with using a renewable fuel, or taxbreaks that may be developed for facilities thatuse renewable fuels [11].


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7. ADVANTAGES ANDDISADVANTAGES

Low investment costs per installed collectionarea.

Thermal storage is incorporated into the collector

and is of very low cost. Diffuse radiation (cloudy days) is fully used.

Very large surfaces can be built thus large scaleenergy generation is possible.

Expensive cleaning of large collector surfaces in

dusty areas is avoided[15].


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Solar ponds can only be economically constructedif there is an abundance of inexpensive salt, flatland, and easy access to water. Environmental

factors are also important. An example ispreventing soil contamination from the brine in asolar pond. For these reasons, and because of thecurrent availability of cheap fossil fuels, solarpond development has been limited [3].


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8. CONCLUSION

Solar ponds can be effectively used asreplacements in industries that use fossil fuel togenerate thermal energy. Solar ponds can be usedfor process heating, refrigeration, waterdesalination, production of magnesium chloride,bromine recovery from bittern, enhancement ofsalt yield in salt farms. It will be the future energysource.


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REFERENCES

1.http://edugreen.teri.res.in/explore/renew/pond.htm

2.http://edugreen.teri.res.in/explore/renew/solar.html

3.http://www.eere.energy.gov/consumerinfo/factsheets/aa8.html

4.http://www.rmit.edu.au/browse/Our%20Organisation%2FFaculties%2FEngineering%2FSchools%20and%20Departments%2FAerospace,%20M

echanical%20and%20Manufacturing%20Engineering%2FResearch%20and%20Development%2FSolar%20Pond/


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5.[http://www.poemsinc.org/FAQsalinity.html#2

6.http://mhatwar.tripod.com/thesis/solar/solar_ponds.html

7.http://gore.ocean.washington.edu/fluids/fluids98/Students/Neil/

8.http://www.teriin.org/case/bhuj.htm

9.http://www.financialexpress.com/fe/daily/200

00814/fco13049.html 10.http://www.solarpond.utep.edu


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11.http://www.greenhouse.gov.au/renewable/recp/solar/three.html

12.http://wrri.nmsu.edu

13.http://www.ece.utep.edu/research/Energy/Pond/pond.html

14.http://journals.tubitak.gov.tr/physics/issues/fiz-98-22-6/fiz-22-6-6-97061.pdf

15.http://www.teriin.org/case/solar.htm

471-2004-1-solar ponds, Ömer bÜyÜkkidik, a. ceylan serhadoÐlu, 2004-1

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