salinity gradient energy potential at the hyper saline...
TRANSCRIPT
lable at ScienceDirect
Renewable Energy 86 (2016) 154e162
Contents lists avai
Renewable Energy
journal homepage: www.elsevier .com/locate/renene
Salinity gradient energy potential at the hyper saline UrmiaLake e ZarrinehRud River system in Iran
Arash Emdadi a, *, Petros Gikas b, Maria Farazaki b, Yunus Emami c
a Energy Institute, Istanbul Technical University, 34469, Maslak, Istanbul, Turkeyb School of Environmental Engineering, Technical University of Crete, 73100, Chania, Greecec Mechanical Engineering Department, Urmia University of Technology, Urmia, P O 57155- 419, Iran
a r t i c l e i n f o
Article history:Received 23 October 2013Received in revised form25 July 2015Accepted 7 August 2015Available online xxx
Keywords:Renewable energyBlue energySalinity gradient energyReverse electrodialysis (RED)Pressure retarded osmosis (PRO)Urmia Lake
* Corresponding author.E-mail addresses: [email protected] (A. Emdadi
(P. Gikas), [email protected] (Y. Emami).
http://dx.doi.org/10.1016/j.renene.2015.08.0150960-1481/© 2015 Elsevier Ltd. All rights reserved.
a b s t r a c t
Salinity gradient has globally high potential for electric energy production, especially where low salinityrivers discharge into hyper-saline lakes. Lake Urmia is world's second hyper-saline lake, with a number oflow salinity rivers discharging into the lake, the most significant of which is ZarrinehRud River. Based onthermodynamic calculations and on field data, the theoretical potential of energy production at theabove system has been calculated between 400 and 1000 MW, while the technical potential is expectedbetween 40 and 50% of that.
Two processes for the production of electricity from salinity gradients were investigated: PRO and RED.The revenue of such attempt is a function of membrane cost, power density, lifetime expectation and saleprice of electric power. Based on the available technology, the project is expected to be viable if mem-branes with power density above 5 W/m2 and 10 years lifetime expectancy or 10 W/m2 and 5 yearslifetime expectancy will be used. The cost of membranes for a 25 MW plant has been estimated between75 and 150 million USD, while the cost of electric energy from a full-scale PRO plant is expected to bebetween 65 and 130 USD/MWh (comparable with the cost of electric energy generated from otherrenewable energy sources).
© 2015 Elsevier Ltd. All rights reserved.
1. Introduction
The increased global demand for energy has resulted in therecent decade to overconsumption of fossil fuels. However, fossilfuel energy is not a sustainable option, as fossil fuel reserves arefinite, while the emission of carbon dioxide during the use of fossilfuels exacerbates the green house effect in the atmosphere. Alter-natively, the use of renewable energy sources, such as anaerobicdigestion, geothermal power, wind power, small-scale hydropower,solar power, biomass power, tidal power and wave power canprovide green energy in a far more sustainable way [1]. One of theleast exploited renewable energy sources is salinity gradient power[2,3], hereto the energy that is released whenever two aqueoussolutions with different salinity concentrations mix together [2],known as “blue energy”. From the thermodynamics point of view,the driving force for energy production during the mixture of
solutions with salinity gradients is the Gibbs free energy gradient,as Gibbs free energy indicates the spontaneous available energywhich is available in a closed system [4]. Gibbs free energy of asystem is a positive function of chemical potential, which (for asolution) is a positive function of the concentration of a dilutedcomponent. Thus, the higher the salt concentration, in an aqueoussolution, the greater the potential for energy release, when theabove solution is mixed with fresh water (or water with low saltconcentration). The potential of salinity gradient power as a com-mercial renewable energy source, has been considered since1950s[5], such potential may be utilized for electric energy production incases which a low salinity river flows in to salty lake. The produc-tion of energy from salinity gradients has low environmentalimpact, as the mixture of the river water with the saline water ofthe lake occurs naturally, at the mouth of the river, and thegenerated energy is released as heating energy to the localenvironment.
As mentioned above, energy extraction through the reverseelectrodialysis process was first reported by Pattle [5], while Mur-phy [6] utilized the latter process for the desalination of brackishwater. Lacey [7] proposed the basic mathematical equations for the
A. Emdadi et al. / Renewable Energy 86 (2016) 154e162 155
reverse electrodialysis process, while Weinstein and Leitz [8] usedLacey's equations to predict the electrical energy yield. Furtherequations for the estimation of the performance of reverse elec-trodialysis unit for salinity gradient power (SGP) extraction wasconducted by Forgacs [9]; while an alternative approach for thecalculation of energy potential for the reverse electrodialysis pro-cess has been proposed by Emren and Bergstrom, who proposedthe use of the activities of solutions instead of concentrations [10].
A few pilot facilities have been established to exploit the salinitygradient energy potential [11]. In November 2009, the Norwegianutility company “Statkraft” launched a 10 kW prototype plant inTofte, south of Oslo, Norway. Statkraft's prototype plant funnelsfreshwater from Tofte River and salty water from a neighboringfjord into two adjoining chambers separated with a thin permeablemembrane. The freshwater forces its way through, driving up thelevel and pressure on the saltwater side, which in turn drives aturbine to produce electricity. On the other hand, REDstack (a spin-off Dutch R&D company) Wetsus (centre of excellence for sus-tainable water technology, The Netherlands) (www.wetsus.nl), isnow scaling up its 5 kWpilot plant, at the salt refinery in, Harlingen,The Netherlands, to a 50 kW demonstration plant, located inBreezanddijk.
The global potential for salinity gradient is enormous. By ac-counting for the discharge of all rivers into the ocean, the totalpower, due to SGP, may be calculated between 1.4 and 2.6 TW[12e15], which is between 40 and 80% [11] of the global demandsfor electricity. It is thus obvious the significance of the salinitypower and the potential role that it may play in the future in theglobal energy balance.
The present manuscript, examines the potential for electricalenergy production from salinity gradients, at the mouth of Zarri-nehRud River, in Lake Urmia e a high salinity lake in NorthwesternIran. Despite the fact that the renewable energy potential of Iranhas been assessed by a large number of studies, there are notpublished works on energy production potential from SGP. Thepresent work attends to provide a spherical view of the abovementioned issue, by the calculation of the theoretical and technicalSGP potentials, the proposal of the best available technology andthe estimation of the cost of such plant for the production ofelectrical energy, at the mouth of ZarrinehRud River in Lake Urmia.
2. Geographical and regional concepts
2.1. Lake Urmia
Urmia Lake is the 20th largest lake by area and the 2nd hypersaline lake on earth [16]. It is located at Northwestern Iran, at theborders of East and West Azerbaijan provinces, at latitude between37 and 38 and longitude between 45 and 46 [17] (Fig.1). The surfacearea of the lake has been severely reduced the last decade; in 2009,it was about 3100 m2, with length at northesouth direction be-tween 140 and 144 km and width between 16 and 63 km [18,19].
Themaximum depth of the lake is 16m, and contains more than50 islands [20]. Lake Urmia is divided into north and south part,separated by a causewaywith awater corridor; howeverwater flowbetween the two parts is minimal [21]. The average annual pre-cipitation on the lake is about 341 mm, while the average tem-perature is about 11.2 �C, with average maximum and minimum2.5 �C (January) and 23.9 �C (July), respectively. A number ofendemic species live in the lake, with Artemia urmiana being themost significant, with numerous applications in aquaculture [21].Lake Urmia has been proclaimed as an “international wetland”according to Ramsar convention, and as a “conserved region ofbiosphere” under the umbrella of UNESCO. In general, morphology,chemistry and sediments of Urmia Lake resemble those of the Great
Salt Lake in Utah, U.S.A [20]. Significant variations of the level ofwater surface have been historically monitored. Water level hadreached a maximum at 1995, then it was decreased sharply andstabilized to a lower level [22]. Fig. 2 depicts the level of the surfaceof the water in Lake Urmia between 1931 and 2006.
Lake Urmia is supplied with water by about 30 large and smallrivers, which discharge about 4.6 million cubic meters of water onannual basis [23]. All rivers carry fresh water into the lake, exceptAji Chay and some seasonal creeks which convey saline water, asthey flow through salt domes near the city of Khoy [24,25]. Thepoints of discharge and the percentage annual contribution ofwater of the most significant rivers to Lake Urmia are shown inFig. 3. Based on Fig. 3, ZarrinehRud River is by far the major watersource for Lake Urmia.
A number of studies have been conducted to determine theconcentration of anions and cations in the lake. Naþ,Kþ,Ca2þ andMg2þ are the main cations, while Cl�;HCO�
3 ; SO2�4 are the main
anions, however, significant variations in ions concentration hasbeen reported. Lake Urmia has been characterized as oceanic typebecause of the predominant existence of sodium, chloride andsulfate ions [26]. Table 1 summarizes the findings of various studieson ions concentrations for Lake Urmia. For some of those, like Ca2þ,significant variations have been reported between the north andsouth parts of the lake. NaCl is the major salt constituent of LakeUrmia and thus, more extended data on NaCl concentration areavailable. “Urmia Regional Water Resources Organization” hascarried out a monitoring program for the determination of saltsconcentration in Lake Urmia. The average values of the relative datafor the salts ions concentrations for year 2008 are firstly presented,in Table, while the procedures and methods for the determinationof concentrations of the various ions are provided in Table 2.
2.2. ZarrinehRud River
ZarrinehRud River is the biggest river that debouches into UrmiaLake (Fig. 3), with average annual flow of approximately 1583million cubic meters of water. ZarrinehRud River is about 302 kmlong; it emanates from Chehelcheshme Mountains, and crosses anumber of cities in Iran, such as ShahinDezh, Keshavarz andMiandoabbefore, before reaching the south part of Lake Urmia. Asstated above (see Fig. 3), ZarrinehRud River contributes about 42%of the total river water discharged into Lake Urmia [24]. The averagedischarge of Zarrineh Rud River into Urmia Lake for the period 1988to 2008, at the Sarighamish station has been monitored by “UrmiaLake RegionalWater Organization”, and is firstly presented in Fig. 4.According to Fig. 4, the flowrate of ZarrinehRud River variessignificantly from year to year. For the studied period, themaximum annual average flowrate (approximately 120 m3/s) hasbeen monitored on 1992, while the minimum annual averageflowrate was below 10 m3/s. The observed significant variationsmay be attributed to climate conditions variability as well as toanthropogenic activities.
The concentrations of various dissolved components in Zarri-nehRud River for the period 2005e2009, measured by the “UrmiaEnvironment Organization” and “Urmia Regional Water Organiza-tion”, which are firstly presented in the present manuscript, areshown in Fig. 5. Based on the available data for 2005e2009, theconcentrations of various ions in the water of ZarrinehRud Riverwere relatively stable, with the exemption of the last year (2009),where a significant increase is observed (Fig. 5).
The salinity of the water at the mouth of ZarrinehRud River inUrmia Lake has been measured by a number of studies. Karbassiet al. have measured the salinity in various locations of Urmia Lake,to lie between 228 and 340 g/L [23]. The geographical locations ofsome of the measurements, the geographical position of the
Fig. 1. Topographic image of Urmia Lake and major rivers [19].
Fig. 2. Water surface level fluctuations of Lake Urmia over the past 80 years [22].
A. Emdadi et al. / Renewable Energy 86 (2016) 154e162156
Fig. 3. Map of Urmia Lake with location of mouths of most significant input rivers andthe percentage of annual contribution of water. ZarrinehRud River I by far the biggestriver discharging in Urmia Lake.
Table 2Procedures and methods utilized by the “Urmia Regional Water Resources Or-ganization” for the determination of the concentrations of various ions in LakeUrmia.
Component Method
Naþ Flame photometryCl� Volometery (Titration) with AgNO3
Mg2þ EDTA titrationCa2þ EDTA titrationSO2�
4 TurbidimetryCO2�
3 Volometery (Titration) with H2SO4
Kþ Flame photometryHCO�
3 Volometery (Titration) with H2SO4
A. Emdadi et al. / Renewable Energy 86 (2016) 154e162 157
monitoring stations at the mouth of ZarrinehRud River and theconcentrations of various ions are shown in Table 3.
3. Salinity gradient energy
3.1. Theoretical approach
As mentioned in the introduction, salinity gradient is a greatdriving force for energy production, which is attributed to thechemical potentials, and consequently to the difference of Gibbsfree energy. The available energy which is produced when mixing1 m3 of diluted solution with 1 m3 of concentrated solution, can becalculated as the difference of the Gibbs free energies of resultingbrackish solution minus the summation of the Gibbs free energiesof the original system (Equation (1)) [31].
DGmix ¼ Gb � ðGc þ GdÞ (1)
The Gibbs free energy for an ideal solution is equal to thesummation of the chemical potentials of the individual substances
Table 1Concentration of dissolved ions in Lake Urmia, as have been reported in the literature.
Year Naþ (g/L) Kþ (g/L) Mg2þ (g/L) Ca2þ (g/L)
1967 110.041975 89.601987 90.391987 e e 2.49e2.67 0.20e0.641994 83.90 0.71 3.46 0.391995 65.242000 119.64 1.50 0.37 1.642001 114.752003 113.972005 e e e e
2006 e e e e
2008 125.32 2.34 15.61 2.282008 133.622008 125 2.63 11.3 0.552009 112.65 0.19 1.12 0.622010 e e 3.65e4.59 0.56e0.16
a Data from the present research.
(Equation (2)):
G ¼Xi
mini (2)
Furthermore, the chemical potential of component i, (mi) for anideal solution, may be calculated as [2]:
mi ¼ m+i þ ViDP þ RT ln xi þ jzijFD4 (3)
The difference in Gibbs free energy due to the mixing of thediluted and concentrated solutions (DGmix) may be calculated formEquations (1)e(3), as follows (Equation (4)):
DGmix ¼Xi
�Gi;b �
�Gi;c þ Gi;d
��
¼Xi
���ni;c þ ni;d
�RTlnxi;b
�� �ni;cRTlnxi;c
þ ni;dRTlnxi;d��
(4)
By substituting the molar ratio (n) by (CV), Equation (4) can berewritten as follow (Equation (5)), where the energy release isgiven as a function of measurable parameters:
DGmix ¼Xi
�Ci;cVcRT ln
�xi;c
�þ Ci;dVdRT ln�xi;d
�
� Ci;bVbRT ln�xi;b
��(5)
The amount of energy which is theoretically available due to themixing of two aqueous solutions, with i diluted compounds, isgiven by Equation (5). Obviously, the greater the salinity gradient,the higher the energy released. Thus, the energy that is theoreti-cally available due to river discharge into a saline lake may be
Cl� (g/L) SO2�4 (g/L) HCO�
3 (g/L) Reference
169.96 [27]138.40 [27]139.61 [27]93.82e125.31 0.59e0.88 0.24e0.45 [28]75.73 6.83 1.00 [24]100.76 [27]208 19.31 0.47 [17]177.25 [27]176.03 [27]190.95e92.98 e e [29]178e182 e e [29]223.09 24.02 3.4 a
206.38 [27]216 22.4 1.38 [23]191.45 17.47 0.60 [30]176.20e201.30 10.49e29.84 0.14e0.50 [29]
Fig. 4. Average discharge (m3/s) of ZarrinehRud River into Urmia Lake for the period 1988 to 2008.Source: Urmia Regional Water Resources Organization
Fig. 5. Concentration of different ions of ZarrinehRud River in recent years.Sources: Urmia Environment Organization and Urmia Regional Water Organization
Table 3Locations of monitoring stations and concentrations of various ions at the mouth of ZarrinehRud River in Urmia Lake determined in 2009 [23].
Monitoringstation number
Longitude Latitude Naþ (g/L) Ca2þ (mg/L) Mg2þ (g/L) Kþ (g/L) Cl� (g/L) SO2�4 (g/L) HCO�
3 (g/L) Salinity (mol/L)
1 45� 250 33.5100 37� 160 6.6300 125 559 11.17 2.62 216.21 21.67 1.38 5.712 45� 220 22.8600 37�190 46.300 121 560 11.32 2.71 212.65 21.84 1.378 5.673 45� 280 33.2900 37� 200 0.8900 129 559 11.28 2.69 219.91 21.42 1.349 5.844 45� 350 21.8900 37� 250 27.7200 130 548 11.23 2.59 224.28 22.56 1.355 5.91
A. Emdadi et al. / Renewable Energy 86 (2016) 154e162158
expressed as a function of the salinities of themergingwater bodiesand of river flow. In practice, the amount of energy that can beexploited is lower than the theoretical amount, due to masstransfer limitations, changes in operating pressure, non idealbehavior of solutions and environmental impacts [2,32,33].
3.2. Technological approach
As explained above, the driving force for energy release due tosalinity gradient is the difference in Gibbs free energy (between thesolutions), which is directly related to the difference in chemicalpotential, which can be linked to the differences in osmotic pres-sures. In practice, the exploitation of energy which is produced dueto river discharge into a saline water body (e.g.: sea or saline lake)
may be done using a number of technologies, the most common ofwhich are:
(i) pressure retarded osmosis (PRO) [34,35],(ii) reverse electrodialysis (RED) [5,36e38].(iii) vapor pressure gradient [39],(iv) the so called ‘hydrocratic generators’ [40],(v) mechanochemical processes [41],(vi) membrane-less hydro-voltaic cells [42],(vii) mixing entropy batteries [43],(viii) capacitive technologies [44,45] and(ix) nano reverse electrodialysis [46,47].
From the above technologies, PRO and RED are in the stage of
A. Emdadi et al. / Renewable Energy 86 (2016) 154e162 159
commercialization for salinity gradient projects [48] and are goingto be further studied below.
The driving force of PRO is the difference in osmosis pressurebetween the two solutions [35,49e51]. The process operates inreverse direction to that of reverse osmosis, which is used for thedesalination of sea or brackish water. It has been calculated that thepressure head between 0.5 mol/L seawater (concentrated solution)and fresh water (diluted solution) is about 24 atm [52], which isequal to water pressure of 240 m [53]. The depressurization of thediluted high salinity water can drive a hydro-turbine to produceelectrical current [1]. A number of studies [2,32,48,54] show thatthe electrical energy production by the PRO process is affected by anumber of factors, such as, temperature, membrane thickness andcomposition, current density and membrane power density. Forgiven temperature the osmotic pressure is a linear function of NaClconcentration [2]. On the other hand, temperature may have arelatively small effect in osmotic pressure; but it has a considerableeffect on water flux, and thus in electric energy production [31].Loeb and Normanwere the first to support the financial viability ofthe PRO process [34]. According to PRO process, low and highsalinity water streams (after filtration to remove solid particles) aredirected to the opposite sites of a semi-permeablemembrane. Thus,water molecules from the diluted solution cross the membrane tothe concentrated solution, with subsequent increase of the highconcentration stream flow. The resulting increased volumetric flowof pressurized fluid is then conveyed to a turbine for the productionof electricity.
Reverse electrodialysis (RED) may be used alternatively for theproduction of electricity from salinity gradients RED takes advan-tage on the selective migration of ions through a selective mem-brane, due to concentration gradient. The ions are moving towardsthe anode (cations) and the cathode (anions), producing DC elec-trical current [2,5,55].
In general, the PRO process is more favorable for power gener-ation using concentrated saline brines (such as the water of thehypersaline Urmia lake), while RED process is more applicable forpower generation using seawater and river water [2]. Moreover,PRO in general can achieve higher energy efficiencies and higherpower densities, compared to RED [ns1], while it has been tried forlonger period due to the readily commercial availability of PROmembranes [56].
4. Potential for energy production at the Urmia Lake e
ZarrinehRud River system
4.1. Theoretical and technical potential
The theoretical potential for energy production from salinitygradient (U), due to the discharge of a low salinity river to a highsalinity lake (or to the sea), is a function of river discharge flowrate(Q), temperature (T) and river and saline lake (or sea) salinity (CDand CC, respectively) [11]. Obviously, all the above factors are var-iable with time and season, thus average values may be used toestimate the theoretical potential for energy production (U), whichmay vary significantly with season [11]. Forgacs [48] has proposedan equation (Equation (6)), for the estimation of the theoreticalpotential for energy production (U), based on the average values ofthe parameters mentioned above.
U ¼ Q � 2RT�CD ln
2CDCD þ CC
þ CC ln2CC
CD þ CC
(6)
It is thus obvious that an estimation of ZarrinehRud Riverflowrate and salinity, at the mouth of the river, and salinity of LakeUrmia are required, to estimate the theoretical potential for energy
production. However, the technical potential for energy productionis significantly lower. The energy efficiency for a PRO systems hasbeen reported between 40 and 50%, compared to the thermody-namic energy potential [32,57e59].
As NaCl is by far the prevail salt Lake Urmia, all calculations arebased on NaCl concentrations. Based on available data related to thesalinity of the lake and at the mouth of the river in the lake (Table 1and Fig. 5), as well as river discharge flowrate (Fig. 4), and onEquation (6), the theoretical and technical potential of energyproduction, due to salinity gradient at the mouth of ZarrinehRudRiver at Lake Urmia (at temperature 298 K), are shown in Table 4(technical potential has been assumed between 40 and 50% oftheoretical potential [32,57e59]). Significant variations of theo-retical potential for energy production due to salinity gradient atthe mouth of ZarrinehRud River at Lake Urmia are observed, whichshould be primarily attributed to the variations of river flowrate. Onthe other hand, the increase of the salinity of Lake Urmia, which isobserved after 2000, has a positive effect to the energy productionpotential [61].
4.2. Economical aspects
As in any full scale project, financial aspects are of determinedimportance, and have to be studied. The membranes are the mosthighly priced components of a PRO installation, thus the revenuefrom sales of electrical current is directly related to the efficiency,cost and lifetime of membranes, as well as the sale price of electricenergy. Achilli and Childress [54] have proposed an equation torelate the above parameters (Equation (7)), assuming that the totalconstruction cost of the PRO plant is proportional to the membranearea used.
RevenueMembrane area$Year
¼ Power density$Energy price (7)
Current power densities in practice (for PRO systems) are up toabout 3 W/m2, for mixing seawater with river water, while aboutdouble to quadruple power densities are achieved for mixing RObrine (about double salt concentration as compared with seawater)with river water [32,48,56]. The use of new generation membranescan push the power density for mixing seawater with river water to5W/m2, while for RO brinee river water system, power densities of10 W/m2 may be achievable [56,48,60,61]. As the salinity of UrmiaLake water is about five times that of the RO brine, a power densitybeyond 10 W/m2 is expected to be achievable, using new genera-tionmembranes. On the other hand, the current cost of membranesis between 20 and 40 USD/m2 [62], with the cost of the mostadvanced ones lies to upper level and beyond the aforementionedcosts.
A correlation between the total revenue per membrane surfacearea, through the lifetime of the membranes, versus the sale priceof electric energy per kWh is shown in Fig. 6. Calculations havebeen performed for a number of combinations of membrane life-times (5 or 10 years) and power densities (2.5, 5, 10 W/m2). Thus,for example, considering energy price of 0.10 USD/kWh, powerdensity of 5 W/m2, and membrane lifetime of 10 years, total reve-nue per square meter (for the 10 years period) of 43.8 USD/m2 iscalculated. For a project to be viable, the above revenue should atleast be higher than the cost of replacing membranes. From Fig. 6, itis obvious that for a viable project, at current electric energy saleprice of 0.1 USD/kWh, a system with membrane's power density5 W/m2 and lifetime at last 5 years or power density 2.5 W/m2 andlifetime of 10 years, maybe marginally viable (if low cost mem-branes can be used). However, it seems that projects will be viable ifthey utilize membranes with power densities above 5 W/m2 and
Table 4Theoretical and estimated technical potential of energy production due to salinity gradient at the mouth of ZarrinehRud River at Lake Urmia.
Year River discharge (m3/s) Salinity of lake (mol/L) Salinity of river (mol/L) � 10�3 Theoretical potential (MW) Technical potential (MW) (estimated)
1994 33.5 1.69 0.48 194.0 77.6e97.01995 34.8 2.84 0.58 335.7 134.3e167.82000 23.0 5.20 0.40 446.3 178.5e223.12001 70.0 5.00 0.48 1199.6 479.8e599.82003 24.0 4.96 0.44 408.5 163.4e204.22008 33.5 5.82 0.83 621.7 248.7e310.8
Fig. 6. Correlation between the total revenue per membrane surface area, through the lifetime of the membranes, versus the sale price of electric energy, for a number ofcombinations of power densities and membrane lifetimes. (A) power density 2.5 W/m2, lifetime 5 years, (B) power density 2.5 W/m2, lifetime 10 years or power density 5 W/m2,lifetime 5 years, (C) power density 5 W/m2, lifetime 10 years or power density 10W/m2, lifetime 5 years, (D) power density 10W/m2, lifetime 10 years. The shadowed band indicatesthe current cost of membranes per m2. For a project to be viable, the revenue per membrane area used should be inside or above the shadowed area.
A. Emdadi et al. / Renewable Energy 86 (2016) 154e162160
lifetime above 10 years, or power densities above 10 W/m2 andlifetime above 5 years used (if advanced, new generation mem-branes have to be used). Alternatively, the project may be viable ifenergy price will be subsidized (as is currently the norm in EU andin USA for energy produced from renewable sources), if themembrane cost will be reduced, or if the power densities ofmembranes will be increased.
As full scale plants have not been constructed, yet, accurateestimation of the capital cost of a full scale PRO plant for Urmia lakecannot be performed. The larger PRO plant has a capacity of 10 kW.It has been installed by St in Tofte, in SE Norway [48]. Based onTable 4, a PRO facility with capacity 25 MW can be installed at themouth of ZarrinehRud River in Urmia Lake. Assuming the use ofmembranes with power density between 5 and 10 W/m2, and amembrane area between 2.5 and 5 (the above is in agreement withthe estimation by Refs. [48], who calculated that a 25 MW PROplant, at the mouth of the river to the sea, will require about 5million m2 of membrane). Thus assuming membrane cost of 30USD/m2, the cost of membranes for such plant will be between 75and 150 million USD. Based findings reported by Enomoto et al.(2010) [63], the cost of membranes (including support system anddiscount), in a complete PRO system accounts for about 70% of totalconstruction cost, while the cost for civil engineering works isabout 11% and the cost for electric works accounts about 15%. Thus,the cost of a complete PRO plant, with capacity 25 MW can beestimated to be between 107 and 214 million USD (correspondingto 4.8e9.6 million USD/MW). Nijmeijer and Metz [48], have esti-mated that the cost of electric energy, from a full-scale PRO system
should be between 65 and 130 USD/MWh. Both estimations are inthe same range as other renewable technologies, such as windpower, wave and tidal power, and biomass based power, though inthe high side.
5. Conclusions
Salinity gradient has globally a high potential for the productionof renewable energy, and thus it is worth to examine the process incases where low salinity rivers discharge into hyper-saline lakes.The production of energy from salinity gradients has low envi-ronmental impact, as the mixture of the river water with the salinewater of the lake occurs naturally, at the mouth of the river. LakeUrmia is world's second hyper-saline with a number of low salinityrivers discharging into the Lake, the most significant of which isZarrinehRud River. Based on thermodynamic calculations and onliterature and field data, the theoretical potential of energy pro-duction has been calculated between 400 and 1000 MW, while thetechnical potential is about 20e30% of the above values. A signifi-cant average yearly fluctuation for the above potential has beenobserved, which may be primarily attributed to ZarrinehRud Riverflowrate fluctuations and secondary to fluctuations of the salinity ofLake Urmia.
Two processes for the production of electricity from salinitygradients were investigated: the pressure retarded osmosis (PRO)process and the reverse electrodialysis (RED) process, with PROprocess being the most advantageous. The revenue of such attemptis a function of membrane cost, power density and lifetime
A. Emdadi et al. / Renewable Energy 86 (2016) 154e162 161
expectation, as well as sale price of electric power. Based on theavailable technology, the project is expected to be viable if mem-branes with power density above 5 W/m2 and 10 years lifetimeexpectancy or 10 W/m2 and 5 years lifetime expectancy will beused (if advanced, new generation membranes have to be used).The cost of membranes/full plant for a 25 MW plant has beenestimated between 75 and 150/107e214 million USD, respectively,while the cost of electric energy from a full-scale PRO plant is ex-pected to be between 65 and 130 USD/MWh (comparable with costof electric energy generated from other renewable energy sources).
Nomenclature
DGmix Gibbs energy change (J/mol)G Gibbs energy (J/mol)Gb Gibbs energy of brackish (J/mol)Gc Gibbs energy of concentrated solution (J/mol)Gd Gibbs energy of diluted solution (J/mol)mi Chemical potential of component i in the solution (J/mol)ni Molar concentration of component i in the solution (mol)m0i Molar free energy under standard conditions (J/mol)Vd Volume of diluted solution (m3)Vb Volume of brackish solution (m3)VC Volume of concentrated solution (m3)Vi Molar or specific volume of component i (m3/mol)DP Pressure change compared to atmospheric conditions
(Pa)T Absolute temperature (K)R Universal gas constant (8.314 J/(mol∙K))xi Mole fraction of component iCC Concentration of salt in the concentrated solution (mol/
m3)CD Concentration of salt in the diluted solution (mol/m3)D4 Electrical potential difference (V)U Theoretical potential (J/s)zi Valence of anion (eq/mol)F Faraday constant (96,485 C/eq)Q Discharge (m3/s)
References
[1] E. Brauns, Towards a worldwide sustainable and simultaneous large-scaleproduction of renewable energy and potable water through salinitygradient power by combining reversed electrodialysis and solar power?Desalination 219 (2008) 312e323.
[2] J. Post, J. Veerman, H.V.M. Hamelers, G.J.W. Euverink, S.J. Metz, K. Nijmeijer,C.J. Buisman, Salinity-gradient power: evaluation of pressure-retarded os-moses and reverse electrodialysis, J. Membr. Sci. 288 (2007) 218e230.
[3] J. Post, C.H. Goeting, J. Valk, S. Goinga, J. Veerman, P.J.F.M. Hack, Towardsimplementation of reverse electrodialysis for power generation from salinitygradients, Desal Water Treat. 16 (2010) 182e193.
[4] W.J. Gibbs, On the Equilibrium of Heterogeneous Substances, Transactions ofthe Connecticut Academy III, 1876, pp. 343e524, 108e284 and (1878).
[5] R.E. Pattle, Production of electric power by mixing fresh and salt water in thehydroelectric pile, Nature 174 (1954) 660.
[6] G.W. Murphy, The Minimum Energy Requirements for Sea Water ConversionProcess, Office of Saline Research and Development Report 9, U.S. GovernmentPrinting Office, Washington, DC, 1956.
[7] R.E. Lacey, Development of osmionic process and factors influencing thechoice of membranes, in: Symposium on Saline Water Conversion, NationalAcademy of Sciences/National Research Council Publication 568, Washington,DC, 1958, pp. 224e232.
[8] I. Weinstein, F. Leitz, Electric power from differences in salinity: the dialyticbattery, Science 191 (1976) 557.
[9] C. Forgacs, Generation of Electricity by Reverse Electrodialysis (RED), in BGUN-rda, Ben-Gurion University of the Negev, Israel, 1975.
[10] A. Emren, S. Bergstrom, Salinity power station at the Swedish west-coast epossibilities and energy-price for a 200 MW plant, in: Miami lnt. Conf. OnAlternative Energy Sources, Miami, U.S, 1977, pp. 887e889.
[11] J. Kuleso, K. Kroeze, J. Post, B. Fekete, The potential of blue energy for reducingthe emission of CO2 and non- CO2greenhouse gases, J. Integr. Environ. Sci. 7(2010) 89e96.
[12] J. Isaacs, R. Seymour, The ocean as a power resource, Int. J. Environ. Stud. 4(1973) 201e205.
[13] R.S. Norman, Water salination: a source of energy, Science 186 (1974)350e352.
[14] G.L. Wick, W.R. Schmitt, Prospects for renewable energy from the sea, Mar.Technol. Soc. J. 11 (1977) 16e21.
[15] S. Loeb, One hundred and thirty benign and renewable megawatts from theGreat Salt Lake? The possibility of hydroelectric power by pressure retardedosmosis, Desalinisation 141 (2001) 85e91.
[16] T. AhmadzadehKokya, A.H. Pejman, E. MahinAbdollahzadeh,B. AhmadzadehKokya, M. Nazariha, Evaluation of salt effects on some ther-modynamic properties of Urmia Lake water, Int. J. Environ. Res. 5 (2011)343e348.
[17] J. Touloie, Hydrogeochemistry of Urmia Lake, in: The First Oceanology Con-ference of Iran, Tehran, 1998, pp. 20e23.
[18] H. L€offler, BeitragezurKenntnis der IranischenBinnegewasser. II. Regional-Limnologische Studie Mitbesondere Berücksichtigungder Crustaceeenfauna,Int. Rev. Ges. Hydrobiol. Hydrogr. 46 (1961) 309e406.
[19] M. Djamali, J.L. de Beaulieu, M. Shah-hosseini, V. Andrieu-Ponel, P. Ponel,A. Abdolhossein Amini, H. Akhani, S.A.G. Leroy, L. Stevens, H. Lahijani,S. Brewer, A late Pleistocene long pollen record from Lake Urmia, NW Iran,Quatern Res. 69 (2008) 413e420.
[20] M.R. Fazeli, H. ToWghi, N. Samadi, H. Jamalifar, Effects of salinity on -caroteneproduction by Dunaliellatertiolecta DCCBC26 isolated from the Urmia saltlake,north of Iran, Biores Technol. 97 (2005) 2453e2456.
[21] T.J. Abazopoulos, N. Agh, G. Van Stappen, S.M. Razavi Rouhani, P. Sorgeloos,Artemia sites in Iran, J. Mar. Biol. Ass. 86 (2006) 299e307.
[22] R. Manaffar, S. Zare, N. Agh, A. Siyabgodsi, S. Soltanian, F. Mees, P. Sorgeloos,P. Bossier, G. Van Stappen, Sediment cores from Lake Urmia (Iran) suggest theinhabitation by parthenogeneticArtemia around 5,000 years ago, Hydro-biologia 671 (2011) 65e74.
[23] A. Karbassi, G. NabiBidhendi, A. Pejman, M. Esmaieli Bidhendi, Environmentalimpacts of desalination on the ecology of Lake Urmia, J. Gt. Lakes. Res. 36(2010) 419e424.
[24] S. Alipour, Hydrogeochemistry of seasonal variation of Urmia Salt Lake, Iran,Saline Syst. 2 (2006) 1e19.
[25] M. Zeinoddini, M.A. Tofighi, F. Vafaee, Evaluation of dike-type causeway im-pacts on the flow and salinity regimes in Urmia Lake, Iran, J. Gt. Lakes. Res. 35(2009) 13e22.
[26] H.P. Eugster, L.A. Hardie, Saline lakes, in Lakes, Chemistry, Geology, Physics,Spriger, New Yourk, 1978.
[27] M. Shahrabi, Lakes and Oceans of Iran, Internal Report, Geological Survey ofIran, Tehran, 1993, pp. 10e15.
[28] G. Azari Takami, The Use of Artemia from Ormia Lake (Iran) as Food forSturgeon, in: Artemia research and its Application, Ecology, Culturing, Use inAquaculture Wetteren, vol. 3, Universa Press, 1987, pp. 467e468.
[29] L. Esmaeili Dahesht, H. Negarestan, A. Eimanifar, F. Mohhebi, R. Ahmadi, Thefluctuations of physicochemical factors and phytoplankton populations ofUrmia Lake, Iran, Iran. J. Fish. Scie 9 (2010) 368e381.
[30] N. Heidari, M. Roudgar, N. Ebrahimpour, Thermodynamic quantities andUrmia Sea water evaporation, Saline sys 6 (2010) 1e6.
[31] P. Długolecki, A. Gambier, K. Nijmeijer, M. Wessling, The practical potential ofreverse electrodialysis as process for sustainable energy generation, Env. Sci.Technol. 43 (2009) 6888e6894.
[32] T. Thomsen, T. Holt, The potential for power production from salinity gradi-ents by pressure retarded osmosis, J. Membr. Sci. 335 (2009) 103e110.
[33] J. Veerman, R.M. de Jong, M. Saakes, S.J. Metz, G.J. Harmsen, Reverse elec-trodialysis: comparison of six commercial membrane pairs on the thermo-dynamic efficiency and power density, J. Membr. Sci. 343 (2009) 7e15.
[34] S. Loeb, R.S. Norman, Osmotic power plants, Science 189 (1975) 654e655.[35] S. Loeb, Production of energy from concentrated brines by pressure retarded
osmosis, Preliminary technical and economic correlations, J. Membr. Sci. 1(1976) 49e63.
[36] R.E. Pattle, Electricity from fresh and salt water-without fuel, Chem. Proc. Eng.35 (1955) 351e354.
[37] R.E. Pattle, Improvements to electric batteries, in Patent GB731729, 1955.[38] M. Tedesco, A. Cipollina, A. Tamburini, G. Micale, J. Helsen, M. Papapetrou,
Reapower e use of desalination brine for power production through reverseelectrodialysis, in: Proceedings of International Conference “Water Is Neces-sary for Life, WIN4LIFE”, September 2013, pp. 19e21. Tinos, Greece.
[39] M. Olsson, G.L. Wick, J.D. Isaacs, Salinity gradient power-utilizing vapor-pressure differences, Science 206 (1979) 452e454.
[40] W. Finley, E. Pscheidt, Hydrocratic Generator, in: US Patent 6.313.545 B1,2001.
[41] M.V. Sussman, A. Katchalsky, Mechanochemical turbine: a new power cycle,Science 167 (1970) 45e47.
[42] G. Lagger, H. Jensen, J. Josserand, H.H. Girault, Hydro-voltaic cells. Part 1.Concentration cells, J. Electroanal. Chem. 545 (2003) 1e6.
[43] F.L. Mantia, M. Pasta, H.D. Deshazer, B.E. Logan, Y. Cui, Batteries for efficientenergy extraction from a water salinity difference, Nano Lett. 11 (2011)1810e1813.
[44] D. Brogioli, Extracting renewable energy from a salinity difference using acapacitor, Phys. Rev. Lett. 103 (2009) 058501, http://dx.doi.org/10.1103/PhyRevLett.103.058501.
[45] B.B. Sales, M. Saakes, J.W. Post, C.J.N. Buisman, P.M. Biesheuvel,
A. Emdadi et al. / Renewable Energy 86 (2016) 154e162162
H.V.M. Hamelers, Direct power production from a water salinity difference ina membrane-modified supercapacitor flow cell, Environ. Sci. Technol. 44(2010) 5661e5665.
[46] D.K. Kim, C. Duan, Y.F. Chen, A. Majumdar, Power generation from concen-tration gradient by reverse electrodialysis in ion-delective nanochannels,Microfluid Nanofluid 9 (2010) 1215e1224.
[47] W. Guo, L. Cao, J. Xia, F.Q. Nie, W. Ma, J. Xue, Y. Song, D. Zhu, Y. Wang, L. Jiang,Energy harvesting with single-ion-selective nanopores: a concentration-gradient-driven nanofluidic power source, Adv. Funct. Mater. 20 (2010)1339e1344.
[48] K. Nijmeijir, S. Metz, Chapter 5, Salinity gradient energy, Sustain. Sci. Eng. 2(2010) 95e139.
[49] S. Loeb, Large-scale power production by pressure retarded osmosis, usingriver water and sea water passing through spiral modules, Desalination 143(2002) 115e122.
[50] S. Loeb, Energy production at the Dead Sea by pressure retarded osmosis:challenge or chimera, Desalination 120 (1998) 247e262.
[51] S.E. Skilhagen, J.E. Dugstad, R.J. Aaberg, Osmotic power-power productionbased on the osmotic pressure difference between waters with varying saltgradients, Desalination 220 (2008) 476e482.
[52] L. BromIey, S. Singh, P. Ray, S. Srivhar, S. Read, Am. Inst. Chem. Eng. J. 20(1971) 326.
[53] L. Gerald, Wick Power from salinity gradients, Energy 3 (1978) 95e100.[54] A. Achilli, A.E. Childress, Pressure retarded osmosis: from the vision of Sidney
Loeb to the first experimental installation e review, Desalination 261 (2010)205e211.
[55] J.R. Wilson, Demineralization by Electrodialysis, Butterworths Scientific Pub-lications London, The University Press, Glasgow, 1960.
[56] G.Z. Ramon, B.J. Feinberg, E.M.V. Hoek, Membrane-based production ofsalinity-gradient power, Energy Env. Sci. 4 (2011) 4423e4434.
[57] N.Y. Yip, M. Elimelech, Comparison of energy efficiency and power density inpressure retarded osmosis and reverse electrodialysis, Environ. Sci. Technol.48 (2014) 11002e11012.
[58] N.Y. Yip, M. Elimelech, Thermodynamic, Energy Efficiency, Analysis of powergeneration from natural salinity gradients by pressure retarded osmosis, En-viron. Sci. Technol. 46 (2012) 5230e5239.
[59] F. Helfer, C. Lemckert, Y.G. Anissimov, Osmotic power with pressure retardedosmosis: theory, performance and trends e a review, J. Membr. Sci. 453(2014) 337e358.
[60] J. Post, H.V.M. Hamelers, C.J.N. Buisman, Energy recovery from controlledmixing salt and fresh water with a reverse electrodialysis system, Env. Sci.Technol. 42 (2008) 5785e5790.
[61] Q. She, D. Hou, J. Liu, K.H. Tan, C.Y. Tan, Effect of feed spacer induced mem-brane deformation on the performance of pressure retarded osmosis (PRO):implications for PRO process operation, J. Membr. Sci. 445 (2013) 170e182.
[62] A. Zhu, P.D. Christofides, Y. Cohen, On RO membrane and energy costs andassociated incentives for future enhancements of membrane permeability,J. Membr. Sci. 344 (2009) 1e5.
[63] H. Enomoto, M. Fujitsuka, T. Hasegawa, M. Kuwada, A. Tanioka, M. Minagawa,A feasibility study of pressure-retarded osmosis power generation systembased on measuring permeation volume using reverse osmosis membrane,Electr. Eng. Jpn. 173 (2010) 8e20.