karthik solar ponds report

7/30/2019 Karthik Solar Ponds Report

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Introduction

Formally known as a salinity gradient solar pond, solar ponds are an alternative source of

harnessing the suns energy to heat water that can be converted to electricity. This

technology is very basic and easy to use with adequate land space and proper design. For

residential use, ponds need to be at least 12x12 feet and 3 feet deep and for commercial use

ponds must be sized according to their functionality. Solar ponds require lots of sunlight

and salt water. The first solar pond was discovered in the early 1900s in Transylvania and

was naturally occurring. Following this discovery these ponds were replicated and dubbed

solar ponds.

How they work

Solar ponds can be naturally occurring; however, most ponds are man-made. Once the

pond is dug, the pond must be lined with an impermeable lining, preferable one that is

insulating. Then the pond is filled with salty water. Once the sun hits the pond the water

warms and divides into three layers. The top layer, known as the surface zone, is composed

of primarily freshwater due to the fact that salt typically settles at the bottom of water.

The middle layer is known as the insulation zone. The insulation zone has a higher salt

concentration than the surface zone. Crucial to a solar pond is the bottom layer known as

the storage zone. The storage zone is where all the hot water is held and this is what is

converted into electricity. The hot salt water produced is similar in chemical

characteristics to brine.


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Diagram of the different layers of a solar pond

In a typical freshwater pond, when the sun penetrates the water the layers that are heated

up rise to the top of the pond and release the heat into the atmosphere. This is how a pond

maintains a constant temperate. The oxygen in warm water is greater than cold water.

This causes warm water to rise to the top of the water body and this heat is then released.

However, in a solar pond this process does not happen. Instead the water that is warmed is

unable to rise to the top due to the salt concentration. Therefore, the warm water stays at

the bottom of a pond and gets hotter and hotter with the more sunlight it receives. The

bottom layer of a solar pond can reach 178 degrees farenheit.

What allows a solar pond to be used as an energy source is that a pipe is placed at the

bottom of the pond and draws the warm/ hot water out of the pond by a pump and is

circulated through a piping system that utilizes the heat. It is similar to how radiant heat,

or solar hot water heaters use the warm water. Once the water has run through the pipe it

is deposited back into the pond in the storage zone so this water can be heated again. This

system is a close system so is quite efficient in terms of water retention. Typically this is

how a solar pond is used for heating purposes.


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Solar ponds can be used in all climates as Long as there is plenty of sun. Even when a pond

is frozen over, a salient gradient solar pond still produces hot water. Therefore, they can

be used all over the United States and the world.

Using a solar pond

Solar ponds have a number of uses. They are effective for heating facilities such as

industrial complexes, greenhouses, and agricultural building. When used for heat, it is

hard to regulate the temperature; therefore solar ponds are typically used in situations that

the heat temperature does not have to be regulated.

Solar ponds are also used to produce electricity. In this case, the hot water produced isused to spin a turbine which generates electricity.

5Some solar ponds rely on solar

powered pumps to push the water through the piping. This is a renewable and

environmentally friend system for electricity production.

A visual demonstration of how a solar pond is used to generate electricity
http://climatelab.org/Solar_Ponds#ref_5http://climatelab.org/Solar_Ponds#ref_5http://climatelab.org/Solar_Ponds#ref_5


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Solar ponds can also be used for desalinization. Since the saltiest water separates into the

storage and insulation zone, the top layer of water is fresh, potable water. In fact, the

United States government used solar pond technology for this purpose:

The Water Desalination Research and Development (DesalR&D) Program was

authorized by Congress under the Water Desalination Act (Act) of 1996. The Act

authorized program funding beginning October 1997 for a six year period. To start

the program, funding was appropriated at $3.7 million for fiscal year 1998... The Act

is based on the fundamental need in the US and world-wide for additional sources of

potable water.

Solar ponds have the above mentioned uses and are valuable for a producing renewable

and environmentally friendly heat and electricity.

Solar ponds in India:

Table enlist the various solar ponds constructed in India. The first solar pond in India was

constructed at Central Salt and Marine Chemicals Research Institute (CSMCRI) in

Bhavnagar, Gujarat in 1971. Extensive studies on heat extraction pattern, effect of rainfall

on salinity gradient and overall variation of temperature profiles were conducted atIndian Institute of Science, Bangalore in 1984. Another pond of 400 m areas was

constructed at Mysore, Karnataka around 1990 with the purpose of meeting the hot water

requirements of a village. A 6000 m area solar pond was commissioned by Government of

India and executed by Gujarat Energy Development Agency (GEDA), Gujarat Dairy

Development Corporation Limited (GDDC) and Tata Energy Research Institute (TERI)

at Bhuj, Gujarat State. Its cost was Rs.3.167 million and could supply 80000 litres of hot

water at 70oC daily for washing, cleaning of aluminium cans, pasteurising and boiler

activity. The pond was successfully established by the end of 1990 and developed liner leak

due to high LCZ temperature of 99C during May 1991. The pond was then operated from

September, 1993 to February, 1995 and thereafter it was dysfunctional up to March 1996

due to lack of funds. The pond has again been commissioned from July 1996 and


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operational till date. A similar project has been sanctioned to Pondicherry Electricity

Board.

The Government of India has evinced keen interest in solar pond research by providingfinancial aid to the ponds constructed at Bhuj and Pondicherry. However, serious efforts

are required to make this technology economically viable.

Solar ponds

Location Year Area SaltusedBhavnagar,Gujarat 1971 1200 Bittern

Pondicherry 1980 100 Sodiumchloride

Bhavnagar,Gujarat 1980 1600 Bittern

IIT,Kharagpur 1983 16 Sodiumchloride

IISc,Bangalore 1984 240 Sodiumchloride

Bhuj,Gujarat 1990 6000 Bittern

Masur,Karnataka 1990 400 Sodiumchloride

ScopeofSolarPonds:

The solar ponds are widely considered as the low temperature energy storage devices

havinguseinwiderangeofprocessapplications.Thefollowingsectiondealswithscopeof

the applicationsofsolarpondheatadoptedinvariousprocesses.

Greenhouseheating

SokolovandArbel demonstrated theuseoffreshwatersolarpondforgreenhouse heating

purpose.Thepondcomprisedanexcavation intheearthwithlinerandathintopcover.

Thewaterwasusedasaheattransferringfluidduringperiodsofsolarradiation.Energy


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was deliveredtothegreenhousebypumpinghotwaterfromtheupper layerofthepond

througha heatexchanger.Thewaterreturnedafterheatextractiontothebottomofsolar

pond. In another study, Arbel and Sokolov studied different collector materials havingdifferentmaterial properties andconcludedthattheuseofappropriatematerialimproves

the solar pond performance. Riva studied a 20 m2

solar pond for two years before

constructingabiggerpond of140-160m2

area.Theenergyefficiencywasfoundtobe10

to 20percentduringpreliminary testing.The energywas intended for airheating in a

dryerof40-50m2

area.

Processheatindairyplants

ThehotwaterrequirementsforsterilisationandpasteurisationinadairyplantatBhujof

KutchdistrictofGujaratStateisbeingmetfromasolarpondof6000m2

areas.Thehot

watertemperaturewasintherangeof84to95

o

Cduringthepond operationperiod.

Desalination:

Desalinationinvolvestheprocessofobtainingfreshwaterfordrinkingandirrigation from

eitherbrackishorsalinewateraftersuitabletreatment. Thesolarenergyhas beenutilized

fordistillationofbrackishorsalinewaterforaverylongtime.Asolarpondmulti effect

distillation (SPMED) system as shown inFig comprises a set of evaporative condensers


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and heat exchanger extracting heat from the solar pond. The fresh water is produced

through repetitive cycles of evaporation and condensation, using low temperature heat

fromthesolar ponds.

Schematicdiagramofsolarponddesalination

1. Multistageflashpan,2. Freshwater3.Brackishwater 4.HotBrine 5.Heatexchanger

6.Coldbrine 7.Solarpond 8.Diffuser

Tabor(1975)showedthatapondof1/3km2areacouldoperateamulti-effectdistillation

unit,withanannualmeanoutputof4000m3

/dayatarateofUS$0.67/m3

.Hefurther

remarked that a solar pond desalination plant produces about 5 times the quantity

produced from simple tray typesolarstill.A20000m2

solarpond inItalywasused for

desalinationofseawaterto produce120toffreshwater/day.

Powerproduction

Some of themajor solarpondpowerplants are listed inTable 2.3. In theseplants, the

solution from the lower convective zone is pumped to a heat exchanger that acts as

evaporator for an organic Rankine cycle. Trieb et al made a comparative analysis of

different solar electricity generation options and found that solar pond produces

electricityatacostof0.254 GermanMarks (DM)/kWhasagainst1.198GermanMarks

(DM)/kWhforphotovoltaiccells.

Prominentsolarpondsusedforelectricitypowergeneration

Name/site Power,kW Pondarea,m2 Operationperiod

EinBoqek,Israel 150 6250 1979-1986


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BeithHaArava,Israel5000 250000 1984-1989

AliceSprings,15 1600 1985-1989

ElPaso,UnitedStates70(Electricity)

3350 1986-tilldate

Hotwaterapplicationsinagriculture:

Manyoftheagriculturaloperationsinvolvehotwaterapplicationfordifferentpurposes.

Some of them includepaddy soaking inparboiling, sugarcane sett treatment, vegetable

blanching, washing of cans in dairy industry and domestic hot water consumption.

Traditionally, parboiling process involves soaking of rough rice in water at ambient

temperatureinmasonrytanksfor3daysandsteamingofdrainedpaddy.Themethodwas

later improvedtosoakthepaddyinhotwaterataround70o

Cforfewhoursdepending

upon the type of parboiling method. This method could eliminate unwanted odours

associatedwithtraditional methodandreducethesoakingtimefromafewdaystoafew

hours.

Heat therapy of sugarcanesetsbeforeplanting is desirable to raise the crop free

from seedpiecediseasesandcertaininsectpests.Conventionallythesetsaretreatedinhot

waterata temperatureof50o

Cfor2hoursandat54o

Cfor4hoursinhumidhotair.

It is clear that the solarpondshave agreat scope in agricultural applicationswith low

temperature requirements. It is equally important to understand the practical aspects

involved withtheoperationandmaintenanceofsolarpondssothattherealsituationsolar

pondscanbe properlymanaged.


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ManagementofSolarPonds:

Solarpondsneedspecialtechniquesofoperationandregularmaintenance.Followingare

afewpracticalaspectsofoperatingasolarpond.

Operational

The operational aspects essentially involve the methods of filling a solar pond in the

beginningandmanagingitforcontinuoususe.

Fillingthepond

Thefillingofpondassumessignificanceasitinvolvestheestablishmentofdensity gradient

alongthesolarponddepth.Zangrando developed atechniquethatwaswidely adaptedin

other ponds. This technique involves the filling of solar pond initially with high saline

solution to a depth equal to depth of lower convective zone + half the depth of no

convective zone.Later thedilution ismade starting from the interfaceof the two zones.

Thismethodof fillingthepondiswidelypractised.

Maintenanceofbrinetransparency

Algal growth mainly affects brine transparency. Chlorination provides the solution to

control algal growth.Scientists reported similar measure for ammonium sulphate solar

pond.

Topzoneflushing

Due to salt diffusion from lower layers to the top layers, the flushing of top zone is

necessary to maintain the salt gradient stability in the solar pond. Top zone flushinginvolves the processofremovalof topsaline layerand injecting freshwater to thepond

surface.Shermanand Imberger suggestedfrom theirsimulationstudythat nowashing

was required if the salinity in the top zone was less than 3 per cent and therewas no


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tangiblebenefittomaintain the topzoneat less than2percentsalinity. Otherworkson

topzoneflushinginvolvedtopzone flushingatregularintervals.

Heatextraction

Anexternaltubularheatexchangerforheatextractionfromthesolar pond was also used.

However the0.1kWpumpused topump thesaltsolution from lowerconvectivezone to

theheatexchangerdevelopedshaftsealfailureafterafewhoursofoperation.Solarpond

experiments were conductedwith threeheat exchangersviz.,a titaniumheat exchanger

(external),acopperheatexchanger(immersed),andaplasticheatexchanger(immersed).

Outof these the copperheat exchangerwas found tobemost reliable.Hull etal (1985)

demonstrated polypropyleneheatexchangerthoughitseffectiveness is lessthanthatofa

copperheat exchanger.Shellandtubeheatexchanger with aheat transferareaof36.1m2

foraheatdutyof341000kcal-hr-1

was used forhotwater supply to thedairyplant in

Bhuj.Theheatexchangercouldoperateforalmosttwoyearswithoutanymajorproblem.

Further,thesteelpipesusedforpipingoftheheatexchangercorrodedseverelyinayear

and werereplacedbypolypropylenepipes.Useofsubmergedheatexchangerswasruled

outforlarge ponds.

Problemsfrequentlyencountered:

Solarpondsbeingrelativelyanewdevelopmentstillencountera fewpractical problems

during its operation.The following sectiondealswith some of the frequently occurring

problems experiencedinthesolarpondoperation.

Linerleak

Linerleakisoneofthemostcommonproblemsreportedinthecontextofsolarpondsin

India. Srinivasan (1992) reported salt leak due to liner failure in a solar pond


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constructed at Masur, Karnataka. The leak forced to abandon the solar pond. The

damage to the liners occurred in the regions where the temperature exceeded 75oC.

Though the liner leak in thispond is attributed torecycledplasticsused in liner, people

felt that the leakcould have stilloccurreddue to the lowoven lifeofLDPEmaterial.A

similarsaltleakwasreportedat Bhuj,GujaratonaccountoflinerfailurewhentheLCZ

temperature increased to99o

C.Solar ponds constructedatPondicherryandHublialso

facedtheproblemoflinerleakforcingthem to beabandoned.

Corrosionofmaterial

Scientists reported the possibility of rapid corrosion of copper metal by ammonium

sulphate.Intheabsenceofchlorine,ammoniahasarelatively lowcorrosiononsteeland

aluminium.Some of themreportedoffrequentshutdownofthetitaniumheatexchanger

becauseofseal failure in thebrinepump.Studies were done on thecorrosionofcopper

tubes immersed in storagezone.About1% ofdecreaseofmassofcopper inayearwas

estimated.

Conclusion

Overall, solar ponds are an effective source of renewable and environmentally sustainable heat

and energy. However, widespread adaptation of this technology has not been successful do to

the limited uses of solar ponds. The main constraint for solar ponds is the amount of land they

require. This issue makes developing solar ponds in many part of the world not cost

effective. On the upside, solar ponds can complement commercial electricity production nicely

as showcased in Israel. As the use of oil and coal for electrical and heat production faces more

scrutiny, solar ponds will be a nice addition to a diverse portfolio of renewable and

environmentally friendly energy sources.


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REFRENCES1.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%2FEngineer

ing%2FSchools%20and%20Departments%2FAerospace,%20Mechanical%20and

%20Manufacturing%20Engineering%2FResearch%20and%20Development%2FS

olar%20Pond/

karthik solar ponds report

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