Assessment of Water Bodies of United Arab Emirates Coastal Sabkhas as Potential Sites for Natural...

Assessment of Water Bodies of United Arab EmiratesCoastal Sabkhas as Potential Sites for Natural Salinity

Gradient Solar PondsF. M. Howari1; F. N. Sadooni2; and P. C. Goodell3

Abstract: Increasing population and growing demands from both agriculture and industry in the United Arab Emirates �UAE� necessitatethe need to provide inexpensive fresh water. The only feasible source of such water is desalination. The coastal area of the United ArabEmirates especially in Abu Dhabi is formed of a series of hypersaline �47%°� lagoons surrounded by salt-encrusted flat sabkhas. Suchwater bodies may be used as salinity gradient solar ponds �SGSPs� to generate clean electricity that can be used in desalination plants. Thegeologic and climatic conditions of this region are compared with El Paso, Texas, USA where there is a well-established SGSP technol-ogy. It is concluded that the water and air temperature, solar radiation, and geologic setting support the possibility of using this technologyin the UAE and especially in Abu Dhabi. Cost analyses also suggest that the generation of electricity and its use in desalination plants areeconomically feasible.

DOI: 10.1061/�ASCE�0733-9402�2008�134:4�111�

CE Database subject headings: Solar energy; United Arab Emirates; Water supply; Desalination.

Introduction

Along with the deterioration in the quality of existing water sup-plies, the growing world population eventually means that two-thirds of the population will lack sufficient fresh water by the year2025 �Chaibi and Jilar 2004; Virk et al. 2001�. This will makedesalination of water and the associate required energy sources animportant issue �Nelsen 1980; Lu et al. 2001�. There is an urgentneed to investigate potential renewable energy resources for waterdesalination �Al Hawaj and Darwish 1994; Xu et al. 1994�. Theuse of solar energy has been recommended by many authors �Car-dona et al. 2002; Cler and Newell 1990�. The main problems withthe use of solar energy in large scale desalination plants are therelatively low productivity rate, the low thermal efficiency, andthe considerable land area required. Their positive aspects, how-ever, are that they provide clean energy at a low operation cost�Andrews and Akbarzadeh 2002; Nielsen 1990�. This makes themsuitable for small-scale production, especially in remote arid areasand islands such as those in the United Arab Emirates. The lowenvironmental impact as well as the easy operation and mainte-nance are also incitements for this technology �Goodell et al.2004; Dai and Zhang 2000�.

The United Arab Emirates �UAE�, the site of this study is oneof the most arid places on the planet, with rainfall that can be aslow as 2 mm a year. The demand on water is, however, increasingby almost 10% a year. This is fueled by a rising population andhigher demand from expanding agriculture and industry. Thismakes desalination an attractive solution for the UAE due to �1�the lack of fresh surface and groundwater resources; �2� the avail-ability of saline water; and �3� the abundance of traditional energyresources such as oil and gas. However, in order to sustain a freshwater resource, a consideration of a renewable energy resourcefor desalination of water should be considered to secure cleanwater for the coming generations, and reduce the adverse envi-ronmental impacts, especially related to carbon emissions. Thus,desalinating water by mean of solar energy, especially salinitygradient solar ponds �SGSPs� may represent an attractive solution�Kunze 2001; Andrews and Akbarzadeh 2002; Hull et al. 2002;Al Hawaj and Darwish 1994�.

SGSPs, also known as advanced solar ponds �ASPs�, collectand store solar energy in the form of heat, which can be extractedfor several purposes �Nielsen 1985; Hull et al. 1989; Rubin andBemporad 1989�. A SGSP is chemically saturated with halite�NaCl� at about 2–3 m of the pond bottom, sometimes up to 4 m.Salinity and temperature increase toward the bottom of the pondtakes place �Tabor and Weinberger 1980; Hull et al. 1989;Andrews and Akbarzadeh 2005�. Methods for setting up solarponds ranging in size from tens of m2 to tens of ha have beenestablished �Zangrando 1980�. Heat has been successfullyextracted from these solar ponds and used for industrial pro-cess heating �Andrews and Akbarzadeh 2002; Lu et al. 2000�,space heating �Rabl and Nielsen 1975�, power generation, anddesalination process �Lu et al. 2000�. There are two basic types ofsolar ponds: the shallow and the salt-gradient ponds. Both areequivalent to horizontal flat-plate collectors, since they are non-concentrating, accept both direct and diffuse solar energy, and arelimited to low temperature applications.

It becomes obvious that to set up SGSP water should be

1Center for International Energy and Environmental Policy and theBureau of Economic Geology, Jackson School of Geosciences; Univ. ofTexas at Austin, University Station, Box X, Austin TX 78713–8924 �cor-responding author�. E-mail: [email protected]

2Environmental Studies Center, Qatar Univ., P.O. Box 2713, Doha,Qatar.

3Geological Science Dept., Univ. of Texas at El Paso, El-Paso,TX 79968.

Note. Discussion open until May 1, 2009. Separate discussions mustbe submitted for individual papers. The manuscript for this paper wassubmitted for review and possible publication on January 17, 2007; ap-proved on April 21, 2008. This paper is part of the Journal of EnergyEngineering, Vol. 134, No. 4, December 1, 2008. ©ASCE, ISSN 0733-9402/2008/4-111–120/$25.00.

JOURNAL OF ENERGY ENGINEERING © ASCE / DECEMBER 2008 / 111

charged with NaCl to the point that the bottom water wouldbecome chemically saturated with it �Zangrando 1980; Goodellet al. 2004�. Thus, the pond could literally be built on salt as inthe case of coastal or inland sabkhas of the UAE, where abun-dance of halite and evaporite minerals occur �Sadooni et al.2005�. In the present study, a comparison will be made betweenthe geographical and geological settings of a proposed solar pondin Abu Dhabi, UAE with other locations where SGSP is alreadyconstructed, and in use. The SGSPs in El Paso, Texas have beenchosen because of similarity of their geological and climatologi-cal settings with Abu Dhabi, and due to the availability ofpublished data �Lu et al. 2001�. The study also attempts to assessthe cost of producing electricity and desalinating water for theproposed SGSP in Abu Dhabi. The cost estimates considered theprices of land, salt, generators, capacity, land clearing, and other

factors that will be presented later, as the variables of interest�Table 1�. The cost estimates and analyses are based on the meth-ods suggested by �Ried et al. 1985; Chaibi and Jilar 2004; Luet al. 2000; Goodell et al. 2004�.

Location

The study site is situated along the coastal area of Abu Dhabi inthe United Arab Emirates, which is characterized by the presence

Table 1. Descriptive Statistics of the Predicted Water Temperature �Tw�of the Proposed SGSP of Abu Dhabi

Parameter TwP AD 7-04 TwP Elp 7-04 TwP AD 9-99

Mean 76.26483 87.12483 90.74483333

Median 76.645 87.505 91.125

Mode 75.694 86.554 90.174

Standard deviation 2.677367 2.677367 2.677367346

Sample variance 7.168296 7.168296 7.168295904

Skewness 0.078271 0.078271 0.078271251

Range 9.217 9.217 9.217

Minimum 72.183 83.043 86.663

Maximum 81.4 92.26 95.88

Fig. 1. Satellite image showing different saline water bodies in the investigated areas

Saline water

Salt crust composedMainly of halite andgypsum

Tidal channel

Fig. 2. High resolution IKNOS image demonstrating the geomor-phology of the studied area

112 / JOURNAL OF ENERGY ENGINEERING © ASCE / DECEMBER 2008

of flat, salt-encrusted surfaces. This area lies between 20°50� and26°N and 51° and 56°E and is up to 16 km wide. Its averageslope is 1:3,000 and situated above the level of present-day hightide in the so-called supratidal zone �Fig. 1�. Straddling the Tropicof Cancer, the climate of the study area is hot and the temperatureoften exceeds 47°C before midday in July. The officially pub-lished temperatures are actually the precise air temperature. Thestudy site formed of a complex coastal area formed of sabkhasand lagoonal saline water bodies; it has been chosen on bases offield and remote sensing investigations �Fig. 2�. Extensive urban-ization and nearby development is being carried out in this area.This could make the construction of a desalination plant as acomponent of the ongoing development activities, and that is oneof the reasons that motivated this study.

Theoretical Background of SGSPs

A typical salinity-gradient solar pond consists of three distinctzones: the upper convective zone �UCZ�, which is uniform with adensity close to the seawater; the middle or nonconvective zone�NCZ�, which has a relatively linear density gradient, and thelower convective zone �LCZ�, which is uniform with a densityclose to the saturated brine �Fig. 3�. The solar radiation encoun-tering the surface of a solar pond is transferred to the lower zoneand heats it up �Hull et al. 1989; Tabor and Weinberger 1980�.The middle layer acts as a thermal insulator, preventing the lossof energy, collected at the LCZ, except by conduction, which is aslow process. The energy stored at the LCZ, may be utilized by aheat exchanger �Fig. 3�. The presented scheme in Fig. 3 demon-strates properly engineered heat removal equipment ready towork for several industrial mineral production facilities includingdesalination. In other words, the salinity-gradient solar pond is

constructed in a manner that the convective circulation in thepond is prohibited by making the bottom water much denser thanthe surface water. In doing so, the solar radiation absorbed in thedeep water can be stored �Andrews and Akbarzadeh 2005�. In thissetup, the gradient zone could, hence, be said to work as an in-sulator for the storage layer. Heat is extracted by passing the brinefrom the storage zone through an external heat exchanger. Good-ell et al. �2004� indicated that in SGSP, a vertical density andtemperature gradient is created, and requires maintenance andmonitoring to ensure that the gradient is effective.

The utility of a solar pond depends on the amount of its ther-mal energy storage, and on the construction costs plus mainte-nance expenses �Xu et al. 1994; Glueckstern 1995; Hafez andEl-Manharawy 2002�. The thermal performance of a solar pondis a function of solar irradiation, heat losses from the sides tothe surroundings and from the LCZ towards the upper layers,ultimate storage capacity, and the effectiveness of the heat ex-changer system. Solar ponds require wide land area, water andsalt �Lu et al. 2000; Andrews and Akbarzadeh 2005; Incroperaand DeWitt, 2002; Cler and Newell 1990�. This explains theneed to locate them in wastelands or in deserts, close to remotecommunities.

Methodology

Climatological Comparison and Regression Analyses

Comparison has been attempted between the climatic andgeochemical setting of Abu Dhabi sabkhas and other regionswhere SGSPs are already constructed, and in use. El Paso, Texashas been chosen because of the similarity of arid climates ofboth regions mostly throughout the year, and because of the

Fig. 3. Diagram showing the different solar pond zones and heat generation mechanism


availability of data from El Paso SGSP �Xu et al. 1995; Lu et al.2001�. For both locations, climatological data were obtained andgraphically compared. Multiple regression analyses were usedto model the relation between ambient temperature �Ta�, watertemperature �Tw�, water density ��, and water depth �D� forEl Paso SGSP. Tw, �, and density were obtained from Lu et al.�2000�; Ta values were obtained for the same day in which theother variables were collected from published climatologicalrecord �e.g., http://www.wunderground.com�. The statisticalanalyses and modeling activities was carried out using JMP soft-ware package. The actual Tw values for El Paso SGSP were plot-ted against the predicted Tw for El Paso and Abu Dhabiconsidering the actual Ta in that day �on Sept. 1, 1999�. Othersimilar comparisons were done for July and August.

To check the validity of the encountered hydrochemical andmineralogical conditions of Abu Dhabi as a favorable SGSP, sedi-ments and water samples were collected from the natural smalllagoons of Abu Dhabi and were analyzed for their mineralogicaland hydrochemical characteristics. The collected water samplesfrom Abu Dhabi were analyzed for major cations, anions, andsalinity, while the collected sediment samples were analyzed for

mineralogy using XRD. The hydrochemical data were graphedusing Plotchem software package and interpreted together withthe mineralogical analyses.

Cost Analyses

Previous economic modeling studies provided computer codesand information relevant to cost analyses of SGSP for the produc-tion of medium grade industrial heat �Reid et al. 1985�, electricity�Lu et al. 2000�, and pure water �Lu et al. 2001�. In the analysesreported in this study, these codes were used to estimate costsusing a variety of variables. The following variables were consid-ered in the economic analyses: �1� thermal efficiency is 0.14, andpower generation efficiency is 0.01, as determined by experienceon small sized SGSPs. This value is used throughout, althoughlarger ponds may be more efficient and another value can beconsidered; �2� a constant cost per kW capacity of the ORCgenerator of $2,020 /kW cost has been used. Larger enginesshould have lower unit costs, but this has not been accounted forhere; and �3� for water desalinization, recovery ratios and productproperties are parameters determined in large pilot plant experi-

Fig. 4. Comparison of ambient temperature between El Paso, Texas and Abu Dhabi, UAE


ments. Capital, pretreatment, and operation costs are included assuggested by Goodell et al. �2004�. Input data rely on previousstudies done by several authors �Reid et al. 1985, Lu et al. 2000,Lu et al. 2001, Goodell, et al. 2004�.

Results and Discussion

Climatology and Geochemical Comparisons

Ambient temperature values were constructed for both of thestudied areas, namely, Abu Dhabi, UAE, and El Paso, Texas. The

ambient temperatures, although comparable, were higher in AbuDhabi �Fig 4�. Overall, the temperature in Abu Dhabi is higherthan the air temperature in El Paso. This is in line with the globaldistribution of solar radiations shown in Fig. 5; Abu Dhabi re-ceives more solar radiation than El Paso. However, solar radiationin the Abu Dhabi area was high around 10 months of the year�Fig 6�a��. This may indicate that Abu Dhabi is far more exposedto solar radiation throughout the year. The higher solar radiationvalues in the UAE were recorded in April, May, June, July, andAugust, and it was in the following order: June�May�April�July�August�September. The reported solar radiation valuesare associated with high inland and seawater temperature. Thosevalues have raised the sea temperature about 43°C �Fig. 6�b��.Those temperature values are expected to be higher in the nearbylagoons and water bodies of the coastal sabkhas because of thesemiclosed nature of those basins, and because of the dark colorof algal mats. These algal materials act as a dark linear and in-crease heat absorbent, and also because of the possible salinitygradient in some locations. However, the temperature of the wateris expected to be higher at higher depth �e.g., 1–2 m� due to thepossible salinity gradient.

Fig. 5. Average annual solar radiation on a horizontal surface atground level in W m−2, maxima are found in and in the vicinity of thestudy area �NASA’s Earth Radiation Budget Experiment�

Fig. 6. Monthly solar radiation values of the study area andassociated nearby seawater temperature

Fig. 7. Trilinear diagram showing chemical composition of watersamples


This salinity gradient is likely to happen because of the hydro-chemical nature of the water. The hyrdochemical results of ana-lyzed water indicate that it is charged with Na and Cl. It is achloride dominated type �Fig. 7�. The x-ray profile given in Fig. 8shows that the most abundant mineral in the analyzed samples ishalite with a subordinate amount of gypsum. Surface and nearsurface water temperatures of the shallow lagoons of Abu Dhabiwere measured in several locations during June 2004, and thetemperature ranged from 40–45°C in the afternoon. It is ex-pected that deeper depths would have much higher temperaturevalues. The presented comparison here can be considered as cur-sors that the climatic and geochemical setting of Abu Dhabi issuitable for the construction of Natural SGSPs.

Multiple Regression Analyses

Data on water and air temperature, as well as on specific gravityversus depth were obtained from El Paso SGSP �Fig. 9�, and therelation was modeled using multiple regression analyses usingJMP software package. The temperature of water was predicted interms of air temperature, as well as depth and specific gravity ofwater of El Paso SGSP. Similar predictions were done for AbuDhabi on the assumption that the favorable geochemical condi-tions for SGSP construction are available as demonstrated earlier.The obtained relation is given next

Tw = 190.77 + 0.16*depth + 3.62*Ta − 250.9*density

The simulated graphs for Tw based on Ta for El Paso are givenin Fig. 10; in this figure, Ta were considered for Sept. 1, 1999.Average ambient temperature values of Sept. 1, 1999, July andAugust 2004, were used to predict Tw for Abu Dhabi and the

results are given in Table 1. As it can be observed, the values ofthe Tw for El Paso and Abu Dhabi are comparable.

The differences between Ta and Tw for the same period wereplotted on Andrews and Akbarzadeh �2005� graphical solutionfor the thermal efficiency of a solar pond �Fig. 11�. The ther-mal efficiency is high in July and August 2004 for Abu Dhabi�32–34%�. Andrews and Akbarzadeh �2005� indicated heat ex-traction from the gradient layer substantially improves the ther-mal efficiency of the solar pond. The enhancement is mostpronounced when all heat extraction takes place from the gradientlayer and none from the LCZ, the q̇=0case. For example, a solarpond with the parameters assumed and delivering heat at a rate ofabout 45 W /m2 and a temperature of 50°C above ambient willoperate at an efficiency of just over 22% if heat is extracted justfrom the LCZ �the C�0 curve�. The same pond will be able to

Fig. 8. X-ray diffraction pattern showing the mineralogy of thecollected sediment samples from the study area

Fig. 9. Relation between depth and water density of El Paso SGSP�original data obtained from Lu et al. �2001��

Fig. 10. Relation between the actual water temperature �Tw� and thepredicted water temperature �Tw predicted�

Fig. 11. Efficiency versus temperature difference �Tp�d�−Ta� forvarying heat capacity rate per unit area of pond and heat extractionrate per unit area of pond from the LCZ �q̇� in W /m2, the upperbounding curve corresponds to heat extraction from the gradient layeronly �q̇=0�, and the lower bounding curve to heat extraction from theLCZ only �C�0� �adapted from Andrews and Akbarzadeh �2005��


Table 2. Cost Production and Economic Analysis for Water Desalination Using SGSP as Energy Source Considering Salt Is Not Free of Charge

Plant capacity �MGD� 1 2 5 10 20 25

�m3 /day� 3,785 7,570 18,925 37,850 75,700 94,625

TDS of feed water �mg/L� 3,000 3,000 3,000 3,000 3,000 3,000

Membrane filtration

Recovery ratio 0.70 0.70 0.70 0.70 0.70 0.70

Production rate �m3 /day� 2,650 5,299 13,248 26,495 52,990 66,238

TDS of product �mg/L� 60 60 60 60 60 60

TDS of reject �mg/L� 9,860 9,860 9,860 9,860 9,860 9,860

Electricity consumption �kWh/day� 13,248 26,495 66,238 132,475 264,950 331,188

RO water cost �$ /m3� 1.64 1.40 1.14 0.97 0.83 0.79

Thermal distillation

Recovery ratio 0.90 0.90 0.90 0.90 0.90 0.90


TDS of product �mg/L� 10 10 10 10 10 10

Economy ratio 4.0 4.0 4.0 4.0 4.0 4.0

Thermal energy �kWh/day� 165,073 330,147 825,367 1,650,733 3,301,466 4,126,833

Electricity �kWh/day� 4,952 9,904 24,761 49,522 99,044 123,805

Thermal desal equipment cost $202,500 $405,000 $1,012,500 $2,025,000 $4,050,000 $5,062,500

ORC Engine

Total electricity consumption �kWh/day� 18,199.7 36,399.4 90,998.5 181,997.0 363,994.0 454,992.5

Capacity �kW� 758.3 1,516.6 3,791.6 7,583.2 15,166.4 18,958.0

Cost of ORC engine $1,531,808 $3,063,616 $7,659,040 $15,318,080 $30,636,161 $38,295,201

Solar radiation

�kWh /m2 /day� 5.7 5.7 5.7 5.7 5.7 5.7

�MBtu/acre/day� 77.8 77.8 77.8 77.8 77.8 77.8

Solar pond

Thermal efficiency 0.14 0.14 0.14 0.14 0.14 0.14

Power generation efficiency 0.01 0.01 0.01 0.01 0.01 0.01

Pond size �Ha� 21 41 103 207 414 517

Solar pond costs

Land cost �$/Ha� 0 0 0 0 0 0

Land clearing cost �$/Ha� 0 0 0 0 0 0

Dike height �m� 4.5 4.5 4.5 4.5 4.5 4.5

Unit price of liner �$ /m2� 8 8 8 8 8 8

Unit area capital cost �$/Ha� 21,600 21,600 21,600 21,600 21,600 21,600

Subtotal capital cost of solar pond $446,815 $893,630 $2,234,075 $4,468,150 $8,936,300 $11,170,375

Solar pond instrumentation $65,857 $91,715 $169,287 $298,573 $557,147 $686,434

Salt �tons� 165,487 330,974 827,435 1,654,870 3,309,741 4,137,176

Unit salt cost �$/ton� 10 10 10 10 10 10

Salt cost $1,654,870 $3,309,741 $8,274,352 $16,548,703 $33,097,406 $41,371,758

Total capital cost $2,370,043 $7,763,701 $19,349,253 $38,658,507 $77,277,013 $96,586,267

Interest rate for capital expenses 6% 6% 6% 6% 6% 6%

Depreciation �year� 25 25 25 25 25 25

Annualized cost $185,401 $607,329 $1,513,629 $3,024,128 $6,045,127 $7,555,627

O & M

Maintenance �$/year� $18,540 $54,659.60 $121,090.29 $211,688.97 $362,707.63 $377,781.33

Electricity @ $0.05 /kWh �$/year� $90,378 $180,755 $451,888 $903,776 $1,807,553 $2,259,441

Total annual cost $294,318 $842,744 $2,086,607 $4,139,593 $8,215,388 $10,192,849

Product water

TDS �mg/L� 500 500 500 500 500 500

Bypass rate �m3 /day� 667 1,333 3,333 6,666 13,332 16,665


Overall water cost �$ /m3� $1.19 $1.12 $0.96 $0.85 $0.77 $0.74


Table 3. Cost Production and Economic Analysis for Water Desalination Using SGSP as Energy Source Considering Salt Free of Charge

Plant capacity �MGD� 1 2 5 10 20

�m3 /day� 3,785 7,570 18,925 37,850 75,700

TDS of feed water �mg/L� 3,000 3,000 3,000 3,000 3,000

Membrane filtration

Recovery ratio 0.70 0.70 0.70 0.70 0.70

Production rate �m3 /day� 2,650 5,299 13,248 26,495 52,990

TDS of product �mg/L� 60 60 60 60 60

TDS of reject �mg/L� 9,860 9,860 9,860 9,860 9,860

Electricity consumption �kWh/day� 13,248 26,495 66,238 132,475 264,950

RO water cost �$ /m3� 1.64 1.40 1.14 0.97 0.83

Thermal distillation

Recovery ratio 0.90 0.90 0.90 0.90 0.90


TDS of product �mg/L� 10 10 10 10 10

Economy ratio 4.0 4.0 4.0 4.0 4.0

Thermal energy �kWh/day� 165,073 330,147 825,367 1,650,733 3,301,466

Electricity �kWh/day� 4,952 9,904 24,761 49,522 99,044

Thermal desal equipment cost $202,500 $405,000 $1,012,500 $2,025,000 $4,050,000

ORC engine

Total electricity consumption �kWh/day� 18,199.7 36,399.4 90,998.5 181,997.0 363,994.0

Capacity �kW� 758.3 1,516.6 3,791.6 7,583.2 15,166.4

Cost of ORC engine $1,531,808 $3,063,616 $7,659,040 $15,318,080 $30,636,161

Solar radiation

�kWh /m2 /day� 5.7 5.7 5.7 5.7 5.7

�MBtu/acre/day� 77.8 77.8 77.8 77.8 77.8

Solar pond

Thermal efficiency 0.14 0.14 0.14 0.14 0.14

Power generation efficiency 0.01 0.01 0.01 0.01 0.01

Pond size �Ha� 21 41 103 207 414

Solar pond costs

Land cost �$/Ha� 0 0 0 0 0

Land clearing cost �$/Ha� 0 0 0 0 0

Dike height �m� 4.5 4.5 4.5 4.5 4.5

Unit price of liner �$ /m2� 8 8 8 8 8

Unit area capital cost �$/Ha� 21,600 21,600 21,600 21,600 21,600

Subtotal capital cost of solar pond $446,815 $893,630 $2,234.075 $4,468,150 $8,936,300

Solar pond instrumentation $65,857 $91,715 $169,287 $298,573 $557,147

Salt �tons� 165,487 330,974 827,435 1,654,870 3,309,741

Unit salt cost �$/ton� 10 10 10 10 10

Salt cost $0 $0 $0 $0 $0

Total capital cost $715,172 $4,453,961 $11,074,902 $22,109,804 $44,179,607

Interest rate of capital expenses 6% 6% 6% 6% 6%

Depreciation �year� 25 25 25 25 25

Annualized cost $55,946 $348,419 $866,353 $1,729,577 $3,456,026

O & M

Maintenance �$/year� $5,595 $31,357.69 $69,308.26 $121,070.42 $207,361.54

Electricity @ $0.05 /kWh �$/year� $90,378 $180,755 $451,888 $903,776 $1,807,553

Total annual cost $151,918 $560,532 $1,387,550 $2,754,424 $5,470,940

Product water

TDS �mg/L� 500 500 500 500 500

Bypass rate �m3 /day� 667 1,333 3,333 6,666 13,332


Overall water cost �$ /m3� $1.10 $1.03 $0.87 $0.77 $0.68


deliver heat at the same temperature but with an efficiency ofabout 28% if the heat removed from the LCZ is reduced to35 W /m2, and instead additional heat is removed from the gradi-ent layer at the rate of 21 W /m2 �corresponding to heat capacityrate of C=0.42 W /m2 /K� additional details and examples aregiven in Andrews and Akbarzadeh 2005.

Cost Analyses

Tables 2–4 were derived based on the method suggested by Riedet al. �1985�, Lu et al. �2000�, and Goodell et al. �2004� and theygive a summary of the economic feasibility for electricity, anddesalinated water. Sabkhas sites that have the unique financialopportunities presented by the presence of salt �NaCl�, and land.However, the cost analyses based on the different scenarios of thevariable listed in the first left side column of Tables 1–3 yieldedthe results in their respective final rows. Those rows show the costof the production of one m3 of fresh water on the assumption thatsalt has a low price. Based on this scenario, the price of producingfresh water ranges from 0.7$ /m3 to 1.19$ /m3. However, by con-sidering that the salt is free of charge, the cost of desalinatingwater was decreased and ranged from 0.68 to 1.10$ /m3. Table 3shows a low case scenario for producing electricity, and the leastobtained was 0.03$/khwh. Other iterations between the high andlow cost can be made; some have already been made and arepresented and discussed in Goodell et al. �2004�.

Possible SGSPs Technology Applicationsin the UAE

1. Medium grade industrial heat is the cheapest, easiest, mostdirect product of a SGSP. In El Paso, Texas, the SGSP heatexchanger is used to preheat boiler feed water for the BruceFoods canning operation, and this production has been con-tinuous for 15 years. Many other demonstrations have beencarried out �Goodell et al. 2004�. Processed heat has manyuses in industrial mineral production facilities.

2. Electricity generation has been accomplished at several sites.An organic Rankin cycle generator from Ormat Turbines�http://www.ormat.com.home.htm� �Ormat Technologies2008� is the engine of choice, and recent prices have beenused in the economic analysis. This engine is widely used forelectricity generation from geothermal brines, and the bot-tom, hot, salty water layer in the SGSP is a simple analog ofgeothermal brine. SGSP electricity is available on demand;due to the high thermal storage capacity of the pond, theenergy is available at night and during cloudy weather, andits delivery has a high degree of reliability.

3. SGSP desalinization examples have an extended history. Luet al. �2001� recently described successful experiments usinga multieffect, multistage �MEMS� evaporator combined witha brine concentration and recovery system �BCRS�.

4. Aquaculture of brine shrimp and fish aided by SGSPs has

Table 4. Low Cost Production and Economic Analysis for Electricity

Electricity production

Capacity �kW� 100 500 1,000 2,000 4,000 5,000

Solar radiation

�kWh /m2 /day� 5.7 5.7 5.7 5.7 5.7 5.7

�MBtu/acre/day� 77.8 77.8 77.8 77.8 77.8 77.8

Solar pond

Thermal efficiency 0.01 0.01 0.01 0.01 0.01 0.01

Pond size �Ha� 4 21 42 84 168 211

Solar pond costs

Land cost �$/Ha� 0 0 0 0 0 0

Land clearing cost �$/Ha� 0 0 0 0 0 0

Dike height �m� 4.5 4.5 4.5 4.5 4.5 4.5

Unit price of liner �$ /m2� 8 8 8 8 8 8

Unit area capital cost �$/Ha� 21,600 21,600 21,600 21,600 21,600 21,600

Subtotal capital cost of solar pond 90,947 454,737 909,474 1,818,947 3.637,895 4,547,368

Solar pond instrumentation $45,263 $66,316 $92,632 $145,263 $250,526 $303,158

Salt �tons� 33,684 168,421 336,842 673,684 1,347,368 1,684,211

Unit salt cost �$/ton� 0 0 0 0 0 0

Salt cost $0 $0 $0 $0 $0 $0

Equipment costs

ORC engine $202,000 $1,010,000 $2,020,000 $4,040,000 $8,080,000 $10,100,000

Total capital cost $338,211 $1,531,053 $3,022,105 $6,004,211 $11,968,421 $14,950,526

Interest rate for capital expenses 6% 6% 6% 6% 6% 6%

Depreciation �year� 25 25 25 25 25 25

Annualized cost $26,457 $119,769 $236,409 $469,690 $936,250 $1,169,531

O & M

Maintenance �$/year� $2,646 $10,779.23 $18,912.75 $32,878.28 $56,175.02 $58,476.53

Total annual cost $29,103 $130,548 $255,322 $502,568 $992,425 $1,228,007

Electricity production �kWh/year� 876,000 4,380,000 8,760,000 17,520,000 35,040,000 43,800,000

Electricity cost �$/kWh� $0.03 $0.03 $0.03 $0.03 $0.03 $0.03


been investigated, and has proved to be successful in theproduction of this important protein source.

Conclusions

The United Arab Emirates is among the most arid places on earthwith only a few mm of rain annually. Exploding population andhigh demands from both industry and agriculture impose severepressure on the limited water resources. The coastal area of thecountry is formed of a series of shallow lagoons and estuariessurrounded by large, flat salt-encrusted sabkhas and have theunique financial opportunities presented by the presence of salt�NaCl�. The presence of such shallow saline water bodies underextremely arid climatic conditions make them suitable for thegeneration of clean energy using solar ponds. Such energy can beused for desalination plants. Comparison of the geologic and cli-matic conditions of this region with El Paso, Texas, USA wherethere is a well-established SGPS technology, supports this notion.The ambient temperatures for the two locations are comparablebut it is higher in Abu Dhabi. Moreover, solar radiation in AbuDhabi is found to be high during around 10 months of the year.These high values are associated also with high inland and sea-water temperature values. Dark, algal materials lining these la-goons also contributed to the high sea water temperature, which isround 43°C. Multiple regression analysis of the water and airtemperature as well as the specific gravity versus water depth forboth El Paso and Abu Dhabi was conducted. Resultant data sug-gest that Abu Dhabi has higher potentiality for SGPS. Cost analy-ses of a wide range of options indicate that the production ofelectricity and the use of such energy for desalination are eco-nomically feasible.

References

Al Hawaj, O., and Darwish, M. A. �1994�. “Performance characteristicsof a multi effect solar pond desalting system in an arid environment.”Desalination, 96, 3–10.

Andrews, J., and Akbarzadeh, A. �2002�. “Solar pond project: Stage 1—Solar ponds for industrial process heating.” End of Project Rep. forproject funded under Renewable Energy Commercialization Program,Australian Greenhouse Office, RMIT, Melbourne, Australia.

Andrews, J., and Akbarzadeh, A. �2005�. “Enhancing the thermal effi-ciency of solar ponds by extracting heat from the gradient layer.” Sol.Energy, 78, 704–716

Cardona, E., Culotta, S., and Piacentino, A. �2002�. “Energy saving withMSF-RO series desalination plants.” Desalination, 153, 167–171.

Chaibi, M. T., and Jilar, T. �2004�. “System design, operation and perfor-mance of roof-integrated desalination in greenhouses.” Sol. Energy,76, 545–561.

Cler, G. L., and Newell, T. A. �1990�. PONDFEAS—A feasibilitystudy and design tool for salt gradient solar ponds. user’s manual,U.S. Army Construction Engineering Research Laboratory-Champaign and Univ. of Illinois, Urbana-Champaign, Ill., versionFY90.

Dai, Y. J., and Zhang, H. F. �2000�. “Experimental investigation of a solardesalination unit with humidification and dehumidification.” Desali-nation, 130, 169–175.

Glueckstern, P. �1995�. “Potential uses of solar energy for seawater de-salination.” Desalination, 101, 11–29.

Goodell, P. C., Lu, R., Howari, F., and Ghrefat, H. �2004�. “Energy sav-ings for favorable industrial mineral facilities worldwide.” IndustrialMinerals (London), 37, 67–78.

Hafez, A., and El-Manharawy, S. �2002�. “Economics of seawater of ROdesalination in the Red Sea region, Egypt. Part 1: A case study.”Desalination, 153, 335–347.

Hull, J., Nielsen, C. E., and Golding, P. �1989�. Salinity gradient solarponds, CRC, Boca Raton, Fla.

Incropera, F. P., and DeWitt, D. P. �2002�. Fundamentals of heat and masstransfer, 5th Ed., Wiley, New York.

Kunze, H. �2001�. “A new approach to solar desalination for small- andmedium-size use in remote areas.” Desalination, 139, 35–41.

Lu, H., Walton, J. C., and Swift, A. H. �2000�. “Zero discharge desalina-tion.” Int. Desalination and Water Reuse Quarterly, 10�3�, 35–43.

Lu, H., Walton, J. C., and Swift, A. H. �2001�. “Desalination coupledwith salinity-gradient solar ponds.” Desalination, 136, 13–23.

Nielsen, C. E. �1980�. “Nonconvective salt-gradient solar ponds.” Solarenergy technology handbook, W. C. Dickinson and P. N. Cheremisi-noff, eds., Chap. 11, Marcel Dekker, New York.

Ormat Technologies. �2008�. �http://www.ormat.com/home.htm�.Rabl, A., and Nielsen, C. E. �1975�. “Solar ponds for space heating.” Sol.

Energy, 17, 1–12.Reid, R. L., Swift, A. H. P., Boegli, W. J., Kane, V. R.and Castaneda, B.

A. �1989�. “Design, construction, and initial operation of a 3,355 m2

solar pond in El Paso.” ASME J. Sol. Energy Eng., 111, 330–337.Rubin, H., and Bemporad, G. A. �1989�. “The advanced solar pond

�ASP�: Basic theoretical aspect.” Sol. Energy, 43, 35–46.Sadooni, F., Howari, F., Hamza, W., and Abd El-Gawad, E. �2005�.

“Modern arid coastal sabkhas of the UAE: Spatial and temporal evo-lution, sedimentology and geochemistry.” Proc., Sixth Annual U.A.E.Univ. Research Conf., Research Affairs, Vol. 6, SC1-14.

Tabor, H., and Weinberger, Z. �1980�. “Nonconvecting solar ponds.”Solar energy handbook, J. F. Kreider and F. Freith, eds., McGraw-Hill, New York, 10

Virk, G. S., Ford, M. G., Denness, B., Ridett, A., and Hunter, A. �2001�.“Ambient energy for low-cost water desalination.” Desalination, 131,149–156.

Xu, H., Sandoval, J. A., Lu, H., Golding, P., and Swift, A. �1994�. “Op-erating experience with the El Paso solar pond.” Proc., Joint SolarEngineering Conf., ASME, 503–511.

Zangrando, F. �1980�. “A simple method to establish salt gradient solarponds” Sol. Energy, 25, 467–470.


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