Geothermal source potential for water desalination – Current status and future perspective

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Geothermal source potential for water desalination – Current statusand future perspectiveQ2

Veera Gnaneswar GudeQ1

Department of Civil and Environmental Engineering, Mississippi State University, Mississippi State, MS 39762, USA

a r t i c l e i n f o

Article history:Received 17 August 2015Received in revised form13 December 2015Accepted 17 December 2015

Keywords:DesalinationGeothermal energyCogenerationCapacity factorSustainability

a b s t r a c t

Direct use and power generation based on geothermal sources is growing at a steadfast pace around theworld. Although available abundantly in many parts of the world, geothermal energy sources have beenunder-utilized in desalination applications. Geothermal sources have the potential to serve as excellentheat sources for thermal desalination processes. Since thermal desalination processes require largequantities of heat sources, geothermal based energy source represents a feasible, sustainable, and anenvironmentally friendly option. The advantage with geothermal source is that it can act as a heat sourceand a storage medium for process energy utilization. If these water sources have high dissolved solids,then they can serve as feed water for the desalination process. Since external energy consumption isminimized except for the mechanical energy requirements, geothermal enabled desalination processescould have less environmental impacts when compared to other nonrenewable energy driven desali-nation processes. Cogeneration schemes for simultaneous water and power production are also possiblewith geothermal sources as well as poly generation with multiple process benefits involving cooling andheating applications. This paper provides the present state-of-the-art of geothermal desalination withdiscussion on the benefits of geothermal desalination over other renewable and nonrenewable energydriven desalination configurations. Present status of the worldwide geothermal desalination and thepotential for future developments in this technological area were discussed in detail with case studies forAustralia, Caribbean Islands, Central America, India, Israel, the Kingdom of Saudi Arabia, UAE, USA, andSub-Saharan Africa.

& 2015 Published by Elsevier Ltd.

Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22. Desalination processes, operation principles, and renewable energy application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2.1. Energy requirements for desalination processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32.2. Renewable energy powered desalination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

3. Geothermal energy utilization around the world . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44. Why geothermal desalination? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

4.1. Capacity factor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44.2. Comparable costs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64.3. Efficient resource utilization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64.4. Energy savings in geothermal applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64.5. Integrated uses for geothermal energy sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

5. Global geothermal desalination – current status . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75.1. Geothermal water composition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75.2. Geothermal water for membrane desalination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75.3. Recent studies on geothermal desalination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85.4. Selection of desalination process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

5.4.1. Plant size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

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Please cite this article as: Gude VG. Geothermal source potential for water desalination – Current status and future perspective.Renewable and Sustainable Energy Reviews (2015), http://dx.doi.org/10.1016/j.rser.2015.12.186i

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5.4.2. Geothermal energy quality and quantity and other renewable energy sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125.4.3. Desalination technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125.4.4. Feed water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135.4.5. Product water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135.4.6. Brine disposal. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135.4.7. Techno-economic requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

6. Challenges and considerations for geothermal desalination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136.1. Land use. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146.2. Geological hazards. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146.3. Waste heat releases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146.4. Atmospheric emissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146.5. Water footprint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146.6. Noise and social impacts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

7. Future potential for geothermal desalination around the world . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147.1. Geothermal desalination potential in the USA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167.2. Geothermal desalination potential in the Kingdom of Saudi Arabia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187.3. Geothermal desalination potential in United Arab Emirates – UAE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187.4. Geothermal desalination potential in Israel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187.5. Geothermal desalination potential in Australia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197.6. Geothermal desalination potential in the Caribbean Islands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197.7. Geothermal desalination potential in the Central America . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

7.7.1. Costa Rica. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217.7.2. El Salvador . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217.7.3. Guatemala . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227.7.4. Honduras . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227.7.5. Nicaragua . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227.7.6. Panama. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

7.8. Geothermal desalination potential in India . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237.9. Geothermal desalination potential in the Sub-Saharan Africa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

7.9.1. Ethiopia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 247.9.2. Kenya . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

8. Techno-economics of geothermal desalination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259. Concluding remarks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

1. Introduction

Providing clean water for human consumption has become amajor challenge at local, regional, national and global levels [1].This is mainly due to increasing demand prompted by populationgrowth and urbanization [2]. Over the last century, global popu-lation has tripled while water demand per capita has doubled,resulting in a six-fold increase in water withdrawals. This suggeststhat not only has the number of water users increased globally, butindividual consumption rate has also increased due to high livingstandards. For example, Energy Information Administration (EIA)reports a population increase of 70 million in USA alone by 2030.The direct domestic water demand and indirect industrial, agri-cultural, and environmental water demand needed to sustain thisgrowth is expected to place serious strains on currently availablewater resources. At the same time, this growth in population isexpected to increase the electricity demand by approximately 50%[3], which will place additional demands on available watersources in USA. For example, thermoelectric power plantsaccounted for 48% of the total water withdrawal in the US in theyear 2000. The consumptive use of water for electricity productioncould more than double from 3.3 billion gallons per day in 1995 to7.3 billion gallons per day in 2030 [4]. Although this consumptiveuse is not high compared to the total US consumption of 100 bil-lion gallons/day, large volumes of water are to be dedicated tothermoelectric power plant operation.

Although 71% of the earth’s surface is covered with water, theoceans hold over 95% of this water, all of which is salt water notsuitable for drinking purpose, while the remainder (about 2.5%) isfresh water in rivers, lakes, and underground, and polar ice caps,

which is expected to supply most needs for human and relatedconsumption. On the other hand, freshwater demand is expectedto rise sharply at global level. About 3 million people, i.e., 40% ofthe current world population do not have access to clean and safedrinking water [5]. In addition, 90% of infectious diseases arecaused by consumption of unsafe water. Moreover, the WorldResources Institute predicts that by 2025, at least 3.5 billion peoplewill experience water shortages [6]. Global agencies (includingWHO, UNDP, UNICEF, etc.) expect that 24 of the least developedcountries, many of them along coastal areas without access tofreshwater and electricity, need to more than double their effortsto reach the Millennium Development Goals (MDGs) for basichealth, sanitation, and welfare. Seawater can serve as an excellentwater source in many of these countries which also indicates theneed for development of sustainable technologies for waterproduction.

The relation between water and energy source production andutilization is inseparable (Fig. 1). Provision of clean water inevi-tably requires energy, which is currently being provided essen-tially by nonrenewable fossil fuels. It has been estimated thatproduction of 1 m3 of potable water by desalination requires anequivalent of about 0.03 tons of oil [7]. Extraction and refining offossil fuels and production of energy not only places additionaldemands on water, but also results in pollution of water sourcesand air (greenhouse gas emissions). Thus, the projected globaldemand for clean water supply for the future will significantlyaccelerate not only depletion of fossil fuel reserves but also con-comitant environmental damage and emission of greenhousegases [8]. This situation provides the basis for renewable energy

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utilization for water production to solve the energy–water–environment trilemma.

The purpose of this paper is to provide a general overview ofthe renewable powered desalination technologies and provide aspecific case for geothermal source based desalination and itspotential for energy- and pollution-free desalination. This resourcehas been under-utilized for various reasons. The benefits of geo-thermal desalination over other renewable energy driven desali-nation and the present status of worldwide geothermal desalina-tion are discussed. In addition, the potential for future develop-ments in this technological area are discussed in detail supportedby case studies for Australia, Caribbean Islands, Central America,India, Israel, the Kingdom of Saudi Arabia, UAE, USA, and Sub-Saharan Africa.

2. Desalination processes, operation principles, and renewableenergy application

Desalination is a process that separates dissolved solids (mostlysalts) from a saline water source to produce fresh water driven byan evaporative process (thermal desalination) or a mechanicalfiltration (membrane separation) process [2,9]. Thermal desalina-tion is based on the principle of evaporation of freshwater in theform pure water vapors from the saline water and condensation ofthe same on a cold surface to produce nearly pure water free ofdissolved solids. Membrane processes employ a physical barrier(membrane) which allows the water molecules to permeatethrough, to produce permeate with considerably low concentra-tion of dissolved solids. Thermal processes require large quantitiesof heat energy to evaporate pure water, and membrane processesrequire high quality electrical energy to apply the mechanicalpressure on the membrane to cause separation.

Thermal desalination technologies include solar distillation(SD) such as solar stills and active and passive solar desalinationsystems; multi-effect evaporation/distillation (MED); multi-stageflash distillation (MSF); thermal vapor compression (TVC) andmechanical vapor compression (MVC). Membrane processesinclude electrodialysis (ED) and reverse osmosis (RO). Other pro-cesses that involve a combination of the two principles in a singleunit or in sequential steps to produce pure or potable waterinclude membrane distillation (MD) and reverse osmosis com-bined with MSF or MED processes [2]. The principles of operationfor the desalination technologies were discussed elsewhere[2,9,10].

2.1. Energy requirements for desalination processes

Energy requirements for desalination vary from process toprocess. Thermal desalination processes require both thermal andelectrical energy for evaporation, process hydraulic flow andtransport of the feed and product water. Membrane desalination

processes require electrical energy to supply the mechanicalenergy for membrane separation and pumping in and distributionout of the plant. Fig. 2 shows the specific energy consumption forthermal and membrane desalination processes in terms of kJ ofenergy required for producing one unit of freshwater in kilograms[9–12]. It can be noticed that the MSF process has the highestspecific energy consumption while the seawater reverse osmosis(SWRO) process has the lowest specific energy consumption fol-lowed by multi-effect distillation technology. For this reason anddue to its inherent simplicity, the SWRO process is the preferreddesalination method for both brackish and seawater desalinationaround the world. However, when large quantities of cheap orlow-cost thermal energy sources are expected as in the case ofpower plants, thermal desalination is favorable to developcogeneration plants where thermal energy demands for desali-nation can be supplied without additional energy consumptionexcept for the mechanical energy requirements [13–18]. Thermaldesalination is also preferred in locations with high TDS (totaldissolved solids) saline waters with seasonal issues which makepretreatment process a challenge for reverse osmosis process [19].Multi-effect desalination technology is beneficial with low to highthermal energy utilization and a higher thermodynamic efficiencywithin the system.

Table 1 shows the equivalent electrical energy requirements fordesalination processes expressed in kWh/m3 of freshwater pro-duction [9]. From this table, it can be inferred that membraneprocesses require higher electrical energy for freshwater produc-tion for both with and without energy recovery options. It shouldalso be noted that electrical energy is a prime (highest form)quality energy that could probably be used for other high valuebeneficial uses such as air-conditioning and other processes thatproduce high value products. At the same time, for thermal pro-cesses, the availability of steam is important whether it is pro-duced solely for desalination purpose or in conjunction withpower production.

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Fig. 1. Energy–water–environment nexus through desalination for the world.

Fig. 2. Specific energy consumption for thermal and membrane desalination pro-cesses and greenhouse gas emissions for unit freshwater production.

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2.2. Renewable energy powered desalination

The potential renewable energy-desalination technology com-binations are shown in Fig. 3. The renewable energy sources (RES)should be integrated with the relevant desalination technologythat has the best capability to utilize available energy in the mostefficient manner [20,21]. Some renewable energy source depen-dent desalination technologies must be placed together on samesite (co-location) and some do not have this requirement [2].Accordingly, the following thermal desalination-renewable energycombinations require colocation (located on same site): wind–shaft–MVC; solar thermal–TVC; solar thermal–MSF; solar ther-mal–MED; solar thermal–SD; geothermal–TVC; geothermal–MSFor MED. The other electricity-driven combinations that do notrequire co-location are: (a) wind–MVC; (b) wind–RO; (c) solar PV–RO; (d) solar PV–MVC; (e) geothermal–MVC; and (f) geothermal–RO. Geothermal energy sources are unique in their applicationsdue to their physical and chemical characteristics. These can beemployed both in membrane and thermal desalination processesdependent on the location, geothermal water physical and che-mical characteristics. The details are discussed in later sections.

3. Geothermal energy utilization around the world

Geothermal source can be utilized for various direct usesincluding bathing and swimming, cooling and snow melting,agricultural drying, aquaculture pond heating, greenhouse heat-ing, space heating, industrial process heat and use, geothermalheat pumps, and power generation. Worldwide geothermal utili-zation trend for various applications between 1995 and 2015 isshown in Fig.4 (data taken from [22]). It can be noted that geo-thermal heat pump application is increasing consistently over theyears. Other significant uses include bathing and swimming andspace heating. The countries with the largest installed capacity arethe USA, China, Sweden, Norway and Germany, accounting forabout 63% of the installed capacity and the five countries with thelargest annual energy use were: China, USA, Sweden, Turkey andJapan, accounting for 55% of the world use. Based on geothermalutilization per land area, the top countries can be listed as Neth-erlands, Switzerland, Iceland, Norway and Sweden (TJ/area). Basedon the population, the top countries include Iceland, Norway,Sweden, Denmark and Switzerland (TJ/population). The largestincreases in geothermal energy use (TJ/yr) over the past five yearsare in the United Kingdom, Netherlands, Korea (Republic), Norwayand Iceland; and the largest increases in installed capacity (MWt)are in the United Kingdom, Korea (Republic), Ireland, Spain andNetherlands, due mostly to the increased use of geothermal heatpumps [23]. Acknowledging the wide applications of geothermalsources, this review article will focus on the feasibility of geo-thermal energy based desalination for fresh water production. Thefollowing sections discuss the rationale, critical features, feasibility

studies, and global potential for geothermal desalination in thenear future.

4. Why geothermal desalination?

There are several benefits associated with the use geothermalsources for various domestic and industrial applications. Geo-thermal energy is a proven and well-established commercialtechnology for electricity production, district heating and coolingand industrial process applications. Geothermal energy can beused for desalination due to following advantages [9,24–27]:

i) Geothermal energy sources have a high capacity factor whichprovides a stable and reliable heat supply ensuring stability ofthermal desalination as well as reverse osmosis. Capacityfactors is defined as the resource availability both in terms ofquantity and quality (over a period of time of application)

ii) Geothermal production technology (extraction of hot waterfrom underground aquifers) is mature. It is unaffected by theseasonal changes and weather fluctuations.

iii) Typical geothermal source temperatures are in the range of70–90 °C in most parts of the world, which are ideal for low-temperature MED desalination. High grade sources above100 °C can be used for power generation and other processheat application

iv) Geothermal desalination is cost-effective, and simultaneouspower and water production is possible.

v) Geothermal desalination is environmentally friendly becauseit is the only renewable energy used in the process with noemissions of air pollutants and greenhouse gasses related tofossil fuels.

vi) Geothermal desalination saves imported fossil fuels which canbe used for other purposes improving local energy securityand environmental sustainability.

vii) Geothermal sources have relatively lower surface area or landrequirements per unit (MW) of all renewable energy sources(for example: 20 MWth¼10 m�10 m well size) and energydemand can be matched from smallest to the largest energy-consuming utilities.

4.1. Capacity factor

Unlike the other renewable sources, geothermal sources can berelied upon for their availability both in quantity and quality.Geothermal energy can be considered inexhaustible if it can beoperated in a closed loop configuration. Geothermal sources varyin temperatures providing flexibility for various process applica-tions. These applications may include integrated configurations toprovide additional benefits while supporting desalination process.Additional benefits could be air-conditioning, district heating,process heating and cooling applications. Another important factorof the geothermal sources is the capacity factor which is related tothe availability of an energy source in both quantity and quality. Itrefers to the ratio of actual energy generated by a system to theavailable energy source. Capacity factor is an important variable tobe considered for scalability and operation of a technology. Whencompared with other renewable energy sources such as solar,wind, and biomass sources, the capacity factor for geothermalsource is very high. The capacity factors for various renewableenergy sources are shown in Fig. 5 [28,29].

The capacity factor for a resource can be influenced by resourceavailability, processing equipment or transmission variability, andother external factors such as power market fluctuations [27,28].In solar energy applications, the amount of energy that can beextracted is limited by the harvesting capacity of the process

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Table 1Equivalent electrical energy consumption for desalination processes.

Process Steam energy (kWh/m3)

Electrical energy(kWh/m3)

Equivalent electricalenergy (kWh/m3)

MSF 7.5–11 2.5–3.5 10–14.5MED 4–7 2 6–9VC – 7–15 7–15SWRO – 4–6 (with ER) 4–6 (with ER)

7–13 (without ER) 7–13 (without ER)BWRO – 0.5–2.5 0.5–2.5ED – 0.7–2.5 0.7–2.5






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Fig. 4. Geothermal energy source utilization around the world.

Fig. 3. Renewable energy applications for desalination including geothermal energy.






equipment and materials in use. Similarly, the wind energy cap-ture potential will be diminished by its intensity and fluctuationsand the mechanical efficiency of the turbine unit and electricalenergy converter. Biomass availability is seasonal and dependenton the climate and other resource availability such as water andland. Geothermal sources are not an exception but suffer to a lessextent from these constraints. For geothermal sources, the capa-city factor may be influenced by the constrained resources, aclogged well, change in subsurface conditions and loss in wateravailability.

4.2. Comparable costs

Geothermal sources compare well with other renewable andnon-renewable electricity production technologies [28]. As shownin Fig. 6, the electricity production costs (for OECD countries in2011 electricity prices) for geothermal source driven power plantsare within comparable range for wind, biomass and hydroelectricpower plants [30]. This range is also comparable with the costs forconventional energy sources such as natural gas, coal and oilsources. This indicates that water production driven by eitherthermal energy or electricity derived from geothermal sourcescould be economical.

4.3. Efficient resource utilization

Various renewable energy resources are available that suit theenergy needs of different desalination processes. Currently, theresources which are well explored and exploited for desalination

applications include solar energy (harvested by solar collectors orphotovoltaic modules), wind energy, geothermal energy, and waveenergy [2]. Sustainable use of these resources depends on theconversion technology employed and the end-user process con-figuration. Sustainability, in this context, can be interpreted as howthe available energy resource is being utilized. Conserving, recy-cling and increasing the efficiency of the conversion technologiesare some approaches which result in a sustainable use of anenergy resource. For instance, daily solar energy available on thesurface of the earth is roughly 15000 times greater than the dailyenergy consumption of the world population [31], which meansthat only much less than 0.001% of the daily solar energy capturedin energy devices could solve the energy problems of the world.However, the maximum energy conversion rate of the currentphotovoltaic modules in the market has not exceeded 15% to date.In this context, geothermal sources present as an efficient andexcellent energy source which can be utilized in both energy andheat generation with minimum energy losses.

4.4. Energy savings in geothermal applications

Energy savings otherwise not possible with other renewablesources are shown in Fig. 7 [32,33]. Geothermal sources can beused for various process heat applications, cooling and desalina-tion applications. Potential energy-cost savings using geothermalsources for process heat are shown in Fig. 7a. The cases are pre-sented for oil prices $90/bbl and $40/bbl and compared with costsavings by geothermal sources at 100 °C, 115 °C, and 130 °C. Thiscomparison shows potential savings of 50%, 66% and 75% forgeothermal sources at 100 °C, 115 °C, and 130 °C respectively. Also,possible electricity savings in different cooling applications arecompared for electricity driven decentralized (packaged or splits)and water cooled electric chillers with geothermal drivenabsorption and adsorption chiller configurations at 100 °C, 115 °C,and 130 °C (Fig. 6b). This comparison indicated potential electricitysavings of 45%, 50% and 62% for geothermal sources at 100 °C,115 °C, and 130 °C respectively. Similarly for desalination applica-tions, multi-effect desalination (MED) with geothermal sources at100 °C, 115 °C, and 130 °C as heat sources will result in savings of46%, 85%, 88% and 89% for hybrid MED with SWRO and for geo-thermal sources at 100 °C, 115 °C, and 130 °C respectively (Fig. 7c).MED unit is compared due to possibility of low-enthalpy geo-thermal sources in most parts of the world and for its lowerthermal energy requirements in comparison with MSF process.

4.5. Integrated uses for geothermal energy sources

Desalination plants can be designed to integrate other bene-ficial uses for geothermal sources as shown in Fig. 8. For example,higher quality geothermal energy can be used to produce power,followed by desalination using both thermal and membrane pro-cesses, then for applications in food processing, refrigerationplants and district heating or cooling systems, heating of buildingspaces, greenhouses and soil heating, industrial process heat andagricultural drying and fish farming. When the source temperatureis too low, a heat pump scheme could be utilized to extract theenthalpy which can be converted to high quality heat. If the sourcetemperature is very high, then it can be used to produce electricityin a co-generation scheme to accommodate desalination for waterproduction. This would reduce the overall costs, environmentalimpacts and the land footprint. As shown in Fig. 8, agricultural andaqua-cultural uses require the lowest temperatures, with valuesfrom 25 to 90 °C. Space heating requires temperatures in the rangeof 50–100 °C, with 40 °C useful in some marginal cases andground-source heat pumps extending the range down to 5 °C.

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Fig. 5. Capacity factor (in percent) ranges reported for various renewable energysources.

Fig. 6. Comparison of the electricity prices derived from renewable and non-renewable energy sources in 2011 electricity prices for OECD countries.






Cooling and industrial processing normally require temperaturesover 100 °C [34].

5. Global geothermal desalination – current status

Fig. 9 shows the hottest geothermal source locations aroundthe world [110]. It can be noted that these locations match withthe water scarce and desert regions around the world in mostcases. This map also resembles the solar map for the worldwideresources where water sources are limited. This clearly indicatesthat water-scarce regions can definitely benefit from locallyavailable geothermal sources. Hottest geothermal spots are foundin northwestern and southwestern parts of the USA, Mexico,Central America and Caribbean Islands, and Middle Easterncountries and North African regions. Depending on the sourcetemperature, various desalination technologies can be integratedwith the geothermal sources. Geothermal sources with

temperatures between 40 and 70 °C can be used for low tem-perature desalination applications which include simple evapora-tion basins (such as solar stills), membrane distillation or lowtemperature multi-effect distillation units (LTMED) and humidifi-cation–dehumidification processes. Higher grade heat sources(470 °C) can be used for either multi-effect evaporation (MED) ormulti-stage flash (MSF) desalination processes. Much highersource temperatures between 120 and 200 °C are suitable forcogeneration schemes (Fig. 10). The choice of desalination tech-nology also depends on the desired capacity and other factorswhich are discussed in later sections.

5.1. Geothermal water composition

The geothermal water composition is characterized by themacroelements of the reservoir rock and the subsurface environ-ment to which it is exposed most of the time. The most frequentlyobserved elements with high concentrations are Naþ , Kþ , Ca2þ ,Mg2þ , HCO3

� , CO32� , SO4

2� , and CO2. Other micropollutants areheavy metals such as mercury, copper, lead, silver, iron, zinc,arsenic, manganese, chromium, beryllium, selenium, vanadium,cadmium, nickel, strontium, uranium, cobalt, gallium, and anti-mony. Some other elements of Boron, and Silica could be presentin geothermal waters as well [35]. Boron and Silica are seriousproblems if present in high concentrations.

Dissolved gas and solid forms of the components have differentequilibria, which can be affected by different factors (changes intemperature or pressure) and shifted towards scaling. Geothermalfluids usually contain high dissolved salts and other ion con-centrations, generally reported as Total Dissolved Solids (TDS).Sodium chloride is the most predominant salt component presentdissolved form adding salinity to the geothermal waters. A widerange of TDS concentrations were reported for various geothermalwells across the United States as shown in Fig. 11 [26]. TDS for hightemperature geothermal waters (4150 °C) was reported between2500 mg/L and 81,000 mg/L while for medium temperature geo-thermal waters (90–150 °C), a TDS range of 1100 mg/L 8200 mg/L.Most of the TDS concentrations were reported between 500 mg/Land 5000 mg/L. very high concentrations between 260,000 mg/Land 280,000 mg/L have been reported for a geothermal plant(Hudson Ranch I and II) in California. Fig. 11 was adapted from arecent review article by Finster et al. [35] on geothermal fluids[35].

5.2. Geothermal water for membrane desalination

Feed water temperature influences the production rates inmembrane desalination. Low temperature feed water has higherviscosity and higher resistance to pass through the membranewhile high feed water temperature produces high flux (higherproduction) due to lower viscosity. Membrane processes requirehigher mechanical energy to pump the cold feed water in winterseasons to meet the daily production rates or higher quantities offeed water needs to be processed. Geothermal waters with highsalinity (TDS) can serve as feed water from which freshwater canbe produced. An increase in permeate flux of 60% was reportedwhen the feed water temperature was increased from 20 °C to40 °C [10].

The relation between the permeate flux rate and the feed watertemperature is shown in Fig. 12 [36]. It should be noted that thetemperature tolerance of the RO membranes is in the range 20–35 °C. Fig.12 inset shows the fraction of the permeate flow thatwould be affected by the feed water temperature. The permeateflux rate increases by 34% when the feed temperature is increasedfrom 25 °C (1000 m3/d) to 35 °C (1344 m3/d) theoretically [10]. Inother words, roughly a 6.1% increase in permeate flow rate for

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Fig. 7. Potential oil, electricity, and energy savings for geothermal source drivenprocess heat, cooling and desalination applications. Thermal energy requirementsfor an MED process can be reduced significantly corresponding to the sourcetemperature.






every 2 degree temperature difference can be achieved by utilizingprocess waste heat sources. When process waste heat is notavailable, utilizing solar collectors or geothermal waters is a fea-sible option.

5.3. Recent studies on geothermal desalination

The application of geothermal water in desalination is a rela-tively unexplored technical concept [37]. Limited number of stu-dies evaluating the potential of geothermal water as a heat sourcefor desalination are available. High-temperature geothermalenergy sources are suitable for electricity production while low-temperature sources can be used for desalination. Hot brines maybe fed directly to power or large distillation plants. Here, a briefreview on the geothermal energy driven thermal, membrane andhybrid (membrane desalination, humidification and dehumidifi-cation) desalination technologies is presented.

The first study of geothermal desalination was proposed andanalyzed by Awerbuch et al. in 1976 to produce power and waterfrom geothermal brines in a novel process [38]. In this process, aseparator, steam turbine and a MSF unit were included. Theseparator was used to make sure that the steam flashed from thehot brine extracted from the geothermal production well wascirculated in the steam turbine while the non-evaporated hotbrine was used as the feed water to the MSF unit to producefresh water.

An earlier study at East Mesa test site evaluated the feasibility ofgeothermal energy driven vertical tube evaporator (VTE), MSF and ahigh temperature electrodialysis (HTED) desalination processes [39].Smooth and enhanced heat transfer surfaces (tubes) were used inthe distillation units while previously tested Teflon-backed mem-branes, dacron and polypropylene-backed membranes in thin cell

configurations were investigated in HTED process. Data was col-lected to analyze the heat transfer coefficients, tube fouling andscaling effects, feed, brine and product compositions, cell-pairresistance, current efficiency, membrane fouling and scale effects.To control the effects of calcium carbonate, silica, and barium sulfatescaling, a pretreatment consisting of poly-phosphonate addition indistillation units and acidification was done for electrodialysis. MSFand VTE units were tested at high and low temperatures at 270°Fand 190°F while HTED operation included two-stage and three-stageoperations at 140°F and 160°F respectively.

The advantage with geothermal sources is that energy output isgenerally invariant with less intermittence problems making themideal for thermal desalination processes. Another possible advan-tage with geothermal waters is that the feed water itself can bereplaced by the geothermal waters; in other words, the geother-mal water can serve both as feed and heat transfer medium fordesalination. Karystsas has described a case study of a lowenthalpy geothermal energy driven seawater desalination plant onthe Milos Island in Greece [40]. The proposed design consists ofcoupling MED units to a geothermal groundwater source withtemperatures ranging from 75 °C to 90 °C. The study showed thatthe exploitation of the low enthalpy geothermal energy wouldhelp save the equivalent of 5000 TOE/year for a proposed plantcapacity of 600–800 m3/day of fresh water. Even in the case oflimited geothermal energy, thermal desalination processes such asMED, thermal vapor compression (TVC), single-stage flash dis-tillation (SF) and MSF can benefit greatly when coupled to geo-thermal sources by economizing considerable amounts of energyneeded for pre-heating.

Bouchekima [41] analyzed the performance of solar still inwhich the feed water is brackish geothermal water in SouthAlgeria. Most geothermal sources in South Algeria have low

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Fig. 8. Integrated configurations for geothermal energy sources – polygeneration for multiple benefits.






enthalpy with maximum temperatures of 60–70 °C. A solar dis-tillation (capillary film solar distiller) system was developed andits performance was studied. Theoretical analyses of the heat andmass transfer mechanisms inside this solar distiller were com-pared with experimental results from the distillation unit. Withheat recovery in the capillary film distiller was able to produce upto 20 L/m2/d while a conventional solar still could produce 5–6 L offresh water per square meter per day of collector surface.

Bourouni [42] demonstrated an aero-evapo-condensation pro-cess which was found to be promising for cooling as well as fordesalting geothermal water. Heat and mass transfer in the processwas evaluated through modeling and experimental studies withgeothermal temperatures in the range of 60 and 90 °C. Twoexperimental pilot studies were used. The latter, installed,respectively, in France and the south of Tunisia, was supplied byfuel and geothermal energy. In another study, a geothermal springwith a water temperature of about 70 °C was used to evaluate theheat transfer of air–water-vapor mixtures in the aero-evapo-condensation process [43]. The influence of different thermal

and hydrodynamic parameters on the unit performances was alsoinvestigated. The experimental results correlated well with thetheoretical predictions. The geothermal desalination costs for thisprocess were compared with other desalination options. The costsfor this process were $1.15/m3 when powered by geothermal

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Fig. 9. Hottest geothermal energy sQ3 ources around the world which are suitable fordesalination, cogeneration and poly-generation schemes [110].

Fig. 10. Geothermal energy applications in desalination and cogeneration (waterand power production).

Fig. 11. Major constituents of geothermal waters in the USA [35].

Fig. 12. Relationship between the permeate flow and the feedwater temperature ina SWRO process [10].






energy sources; however, when heat is supplied by a fuel source,the cost was $4.80/m3. While the costs for other options wereestimated as follows. MSF with back-pressure steam-turbine –

$1.57/m3; MSF with gas turbine and waste-heat boiler – $1.44/m3;MSF/TVC with gas turbine and waste-heat boiler – $1.31/m3; andreverse osmosis single-stage with energy recovery – $1.39/m3.Mohamed and El Minshawy, conducted theoretical and experi-mental studies on desalting water using humidification–dehumi-dification processes similar to Bourouni et al., in Egypt [44].

A new brackish water greenhouse desalination process pow-ered by geothermal energy source was proposed by Mahmoudi etal. [45]. This process is suitable for cold and dry weather commonin arid regions, as in Algeria. This process was also similar to thehumidification and dehumidification of air. In this process, aground heat exchanger was used to increase the temperature ofthe geothermal waters acceptable for the proposed desalinationprocess which included evaporative and condensing surfaceswhile heating the greenhouse. They reported that geothermalenergy is the most promising application for inland brackish waterdesalination.

An integrated configuration including a multi-effect boilingunit and a MSF unit was evaluated in a feasibility study utilizinggeothermal sources in Baja California, Mexico [46]. The geothermalsource was available as a heat source at 80 °C. In this process, anoptimum desalinated water (freshwater) to geothermal source(heat source water) was found to be 1:14. In another study, coastalgeothermal desalination plant including MSF-MED configurationwas studied. The prototype was developed and tested at a geo-thermal source temperature of 80 °C. This study reported a muchsmaller ratio of 1:5.9 for the freshwater to geothermal source.About 20 m3/d of freshwater was produced from a geothermalheat flow of 118 m3/d [47].

SephtonWater Technology developed a pilot project for simu-lating process conditions for a demonstration project for show-casing its viability under commercial conditions [48,49]. Theyperformed several tests that simulate process conditions in severaleffects across the range of a 15 Effect VTE (vertical tube eva-porator) Plant. The VTE distillation process applied to an MEDplant design with low cost non-commercial geothermal steam asan energy source may prove to be cost competitive compared toother desalination technologies. A 15-effect plant could produceup to 14 pounds of distilled water for each pound of geothermal

steam used. VTE technology could also have the advantage ofdischarging much lower volumes of concentrated brine than othermethods. A recovery rate in excess of 80% from a seawater sourceis typical in this process. They used heat (non-commercial lowpressure steam; temperature: 100 °C) from a geothermal powerplant to reduce salinity of Salton Sea using MED in which a verticaltube evaporator distillation process was applied for geothermaldesalination [48,49]. The freshwater production of the pilot unit(MED/VTE 2 effects) and the demonstration unit (MED/VTW 15effects) were 18.9 and 79.5 m3/day, respectively, and the respec-tive consumptions were 454 and 3402 kg/h [48,49]. Table 2 pro-vides a summary of the process conditions for various geothermalinstallations around the world. This table shows the geothermalwater temperatures and the flow rates required in differentdesalination processes including MED, MSF, vertical tube eva-porator, humidification–dehumidification, and membrane dis-tillation. The geothermal water flow requirements and the costsdepend on the desalination process configurations.

Kamal [50] had shown that enhancement of feed water tem-perature for seawater reverse-osmosis plants located in southernCalifornia induced a substantial reduction in the cost of potablewater. The membrane productivity increase is about 2–3% per 1 °Cincrease of the feeding temperature. Most of the membranescommercialized for RO desalination processes can tolerate tem-peratures up to 40 °C. However, few membrane suppliers offernew membranes for high-temperature applications. For example,BackpulseableTM membranes (polypropylene tubular membranes)can tolerate temperatures up to 60 °C. It is important to note thatan increase of the feeding water of the RO desalination plant ofGabes to 40 °C (temperature tolerance of most commercializedmembranes) will increase its productivity of about 20–30%.

A fluidized bed crystallizer and an air-gap membrane distilla-tion (AGMD) unit were investigated for the suitability of geo-thermal energy sources by Bouguecha and Dhabi [51]. The mem-brane surface area in the AGMD was 6470.04 cm2 per cell in athree-cell AGMD unit. The membranes were supported by poly-propylene grids in 12 mm thick Plexiglas frames. Cooling plateswere included to provide condensation of the water vapor. Saltwater concentrations were tested between 3 and 35 g/L con-centrations and the permeate flux decreased with increase in thesalt concentration. This was attributed to vapor reduction due tosalt interference effect, increased temperature polarization and

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Table 2A summary of geothermal desalination installations around the world.

Location Process description Process conditions References

Baja California, Mexico Combination of Multi-Effect Distillation (MED) andMulti-Stage Flash (MSF), called “Multi-Flash with Hea-ters” (MFWH).

An initial temperature of 150 °C, 4 m3 of sea water were required toproduce 1 m3 of desalinated water. At an initial temperature of 80 °C,14 m3 of geothermal water was required.

[46]

Kimolos, Greece A two stage MED with distillation under vacuum invertical tubes

Geothermal water flow rate of 60 m3 /h at a wellhead temperature of61–62 °C from a borehole of 188 m deep. Total production of freshwater is 80 m3/day

[40]

Produced water cost is estimated of the order of 1.6€/m3 (includingonly annual operation costs)

Tunisia Humidification and dehumidification process (HD) At 75–90 °C geothermal temperatures, 75% energy savings werereported for a geothermal powered desalination process.

[43]

Produced water cost is estimated as $1.2/m3

Tunisia MD coupled with multiple effect distiller That study found that the best operating parameters are 85 °C for afeed brine temperature at the evaporator inlet and a circulation flowof about 170 kg/h. Under these conditions, a GOR value of 3.7 and awater production of 16 kg/h may be reached. The integration of onemembrane module distiller as a second step at the MED outlet permitsan increase of distilled water production by about 7.5% and improve-ment of the energetic efficiency by practically 10%.

[51]

Salton sea/Imperialvalley (USA)

MED/VTE 2 effects T¼100 (steam) at 454 kg/h; Freshwater production rate of 18.9 m3/d [48,49]MED/VTE 15 effects T¼100 (steam) at 3402 kg/h; Freshwater production rate of

79.5 m3/d






concentration polarization. Further, the effect of process para-meters such as temperature and feed flow rate were evaluated. Anincrease of the permeate flow with feed velocity seems to reachmaximum value asymptotically to 7.5 kg m–2 h–1.

In a recent study, geothermal potential of the Greek island ofNisyros located in the southeastern part of the Aegean Sea fordesalination of seawater and power production, in separate andcoupling schemes was evaluated [52]. A multi-effect distillationwas preferred in this study due to its lower specific energyrequirements and lower scaling potentials due to low temperatureoperation. Exergy analysis of the desalination plant was alsoconducted to understand thermodynamic performance of thedesalination plant. Further, a life cycle analysis was performed onthe MED desalination-power production coupling scheme. Theenvironmental impacts were reported to be negligible whencompared with a fossil fuel powered cogeneration plant. More-over, in this process, waste heat from the power plant was utilizedin the desalination process eliminating associated environmentalemissions.

Boron concertation seems to be an issue with geothermalwaters limiting their applications and other beneficial uses. Sinceboron at elevated levels can cause reproductive and develop-mental toxicity in animals as well as affecting crops, additionalboron removal processes must be added to desalination plants.Significant amount of work was performed by researchers inPoland and Turkey on various geothermal waters, even containing

radioactive compounds such radium, radon and tellurium. InPoland, due to increasing water stress levels, geothermal watersare increasingly evaluated for their beneficial uses [53]. Severalhybrid technologies integrating membranes (microfiltration,ultrafiltration, and reverse osmosis) and ion exchange resins andelectrodeinonization processes were evaluated to decrease theBoron concentrations to the acceptable levels (usually below1.0 mg/L).

Desalination of spent geothermal waters for beneficial uses waspursued in Poland. Three different geothermal waters were treatedusing the double stage membrane process. The sites were Podhalebasin (GT-1), Polish Lolands (GT-2) and Western CarpathianMountains (GT-3). These geothermal waters had a wide range ofconcentrations of minerals including high iron, strontium, boronand silica [54,55]. A process schematic of the membrane process isshown in Fig. 13. The geothermal water characteristics are shownin Table 3 [54,55].

A hybrid membrane desalination technology consisting ofultrafiltration and reverse osmosis (UF–RO) membranes wasevaluated for boron removal [56]. The purpose of this study was toreduce the concentrations of salinity and micro pollutants such asarsenic, iron and fluoride to make them suitable for drinking wateror surface discharge. This system consisted of a pretreatmentfacility which has a mechanical filter, iron removal stage and anultrafiltration module. Spiral wound DOW FILMTEC BW30HR-440ipolyamide thin-film composite RO membranes were used.

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Fig. 13. Schematic of a double stage RO process for recovering spent geothermal waters for drinking purposes in Poland.

Table 3Geothermal desalination feed and product water compositions studied in Poland and Turkey.

Composition GT-1 feed GT-2 feed GT-3 feed GT-1 product GT-2product

GT-3product

Balcova, Turkeyfeed

Izmir-Turkey (1)feed

Izmir-Turkey (2)feed

Naþ (mg/L) 466.8 2297 9492 40.88 151.8 575.1 353.5 280–310 324–363Kþ (mg/L) 45.2 27.2 83.1 0.83 1.76 8.19 26.55 26–31 27-45Ca2þ (mg/L) 196 146.8 71.24 o10 0.24 7.11 28.17 14–22 20-22Mg2þ (mg/L) 42.7 26.2 36.6 o0.1 0.1 1.905 2.14 1.4–3.9 2.3–5.8Cl� (mg/L) 536 3574 12815 7.6 11.2 1294 208.96 189–190 160–169SO4

2� (mg/L) 938.2 193.7 3 6.4 o3.0 o3.0 176.56 162–164 153–174HCO3

� (mg/L) 561–586 617–666F- (mg/L) 2.6 0.696 1.050 0.137 0.078 0.104 7.72 – –

As (mg/L) 0.026 0.0005 0.094 0.001 o0.005 0.006NO3

� (mg/L)pH 8.9–9.0 7.2–7.4EC (μS/cm) 3550 10,960 35,500 417 1887 4500 1746–1836 1679–1772TDS (mg/L) 2561.8 6556 2447 181.5 291.6 2588 861–916 840-887Salinity (‰) 0.88–0.93 0.7Turbidity (NTU) 0.43–1.54 11.5–25.5B (mg/L) 8.98 2.53 96.73 0.24 0.159 32.98 8.5-9.5 10.3–11.4 8.8-11.4Uranium 238U, mBq/L

3.770.3 2.570.3 10.671.0 r0.50 r0.50 r0.50

Uranium 234U, mBq/L

5.970.3 2.270.3 9.470.9 r0.50 r0.50 r0.50

Radium 226Ra, mBq/L

514760 272710 615714 18.072 r2.0 r2.0

Radium 228Ra, mBq/L

157755 242738 607745 r47.075 r10.0 r10.0

Radon 222Rn, Bq/L 5.470.4 5.070.6 0.770.3Tritium, TU/L 0.070.4 0.770.4 0.170.4 0.070.3 0.070.4 0.370.4Gross α, mBq/L 6207150 300760 9107180 r50 r50 r50Gross β, mBq/L 11507340 3707110 12507380 r100 r100 r100






Considering the presence of high Boron concentrations, a two-stage RO system with water reaction adjustment before the RO-2stage was designed. Geothermal water was split into two streamsin the membrane process, a permeate stream (treated water) and aretentate stream that contained separated salts and dissolvedmineral contents.

Different Boron concentrations (2.5 mg B/L, 8.98 and96.73 mg B/L) of spent geothermal waters were tested [56]. Theremoval efficiencies were reported as 56%, 48%, and 12% respec-tively for 2.5, 8.98 and 96.73 mg B/L concentrations. High pHconditions (around 10 and 11) resulted in up to 97% removal. Otherremoval efficiencies were 96–97% with respect to conductivity,and 94% with respect to SiO2, 92% for fluoride and not less than84% for arsenic. Scaling studies on the membranes after eightmonths of operation through morphological evaluation of sedi-ments in the electron scanning microscope image and through theanalysis of the chemical composition of the sediments crystallizedon the membrane revealed silicates (SiO2) and aluminosilicates(Al2SiO5) as well as barite (BaSO4) and copper sulfate (CuSO4)crystalline structures and Calcium phosphate as well as celestite(SrSO4) and strontianite (SrCO3) sediments. A high rejection rate ofradionuclides was also obtained, ranging from 70.7% to 99.6%[57,58].

A bench scale ion-exchange-microfiltration integrated processwas evaluated for boron removal from geothermal waters con-taining high concentrations (8.9 mg/L) [59]. A small flow of 100–200 mL/h of geothermal water was processed through the unit todetermine the effect of process parameter and their optimization.A Boron exchange resin Diaion CRB02 was used in this process. Inthis study, 4.2 g/L of resin with 45–125 mm particle size range wasfound to be optimum for a flow rate of 0.5 mL/min to achieveboron removals that make them suitable for beneficial uses. Forlow Boron concentration, low particle sizes seemed to be opti-mum. In another study [60], a hybrid process coupling ionexchange with ultrafiltration was developed with ion exchangeresin Dowex XUS-43594.00 with an average particle diameter of20 μm. The ultrafiltration membrane module was (ZW-1, GE) usedto filter the resin suspensions. A reverse osmosis process coupledwith ion-exchange and ultrafiltration unit was tested for boronremoval in Turkey using brackish geothermal water [61]. Boronselective chelating ion exchange resin Dowex (XUS 43594.00) witha particle size of 20 μm was used for removal of boron. A sub-merged hollow fiber type ultrafiltration membrane module (ZW-1) was used for filtration. Effect of such process variables as resinconcentration in the suspension, flow rates of fresh and saturatedion exchange resins, and flow rate of permeate on the efficiency ofthe hybrid process for boron removal from RO permeate of geo-thermal water was studied. The geothermal water at around 60 °Cwas transferred to the feed tanks and kept for one to two daysuntil the geothermal water cooled down to the room temperature(around 25 °C). Then, it was filtered through the sand filter andcartridge filters. The antiscalant to prevent precipitation of silicatewas dosed to the filtered geothermal water. The pre-treated geo-thermal water was fed to RO membranes via a high pressurepump. The characteristics of geothermal water used for RO testsare shown in Table 3. Type ultrafiltration module (GE-Zenon ZW-1UF module with an effective membrane surface area of 0.047 m2

and nominal pore diameter of 0.04 μm) at the same flow rate offeed solution (RO permeate of geothermal water). The ROpermeate samples containing 4.75–5.15 mg B/L were collectedfrom the mini pilot-scale BWRO plant.

Electrodeionization was also used to remove boron and silicafrom the permeate of a RO (BW-30-2540, Dow FilmTech) process[62]. The concentration of boron remaining in the permeate was5.9 mg/L which was reduced to 0.4 mg/L and silica was decreasedfrom 0.3 mg Si/L to 0.1 mg Si/L with a layered bed configuration of

EDI system when a 40 V of voltage was applied to the EDI system[63]. Further, this group also investigated the potential of a novelchelating resin poly(N-(4-vinylbenzyl)-N-methyl-D-glucamine) (P(VbNMDG)) [64]. The sorption performance of this resin wascompared with boron selective commercial resin Diaion CRB02containing N-methyl-D-glucamine (NMDG) groups for boronremoval from geothermal water. The P(VbNMDG) resin gave ahigher sorption capacity and faster kinetics than that of DiaionCRB02 for boron removal from geothermal water. Experimentaldata obtained from boron selective ion exchange resins Diaion CRB02 and Dowex (XUS 43594.00) in fixed-bed column studies wereanalyzed using Yoon–Nelson and Thomas models. It was shownthat both models were successful in predicting the process effi-ciencies due to a good fit with experimental data.

5.4. Selection of desalination process

The following factors need consideration when selecting adesalination process suitable for geothermal applications [10,65]:(a) plant size; (b) availability of geothermal energy sources andother renewable energy sources; (c) desalination processes;(d) feed water characteristics; (e) product water quality require-ments; (f) brine disposal options; and (g) energy intensity of thedesalination process

5.4.1. Plant sizeThe plant size depends on the water demand, feed water

concentrations, sources, and water storage capacity. If feed waterquality is high, then a bypass flow can be introduced in the plantdesign which may decrease the size of the desalination plant. Asurvey of available feed water sources should be conducted toevaluate the desalination potential for a specific community. It isdesirable to identify suitable quality and quantity of feed watersources suitable for desalination. Based on the historical trends onwater utilization for a specific community, the water demand percapita can be estimated which can be further translated into dailyplant capacity. Regional statistics can be used in cases the waterdemand data is not available.

5.4.2. Geothermal energy quality and quantity and other renewableenergy sources

A survey of available geothermal water sources is important indetermining the desalination plant type, capacity, and the eco-nomics. The chemical and physical characteristics of geothermalwaters are critical in the design of a heat extraction and utilizationscheme [35]. High temperature geothermal waters are suitable forcogeneration schemes whereas low temperature geothermalwaters are suitable for low temperature desalination processesdescribed in case studies earlier. Other renewable energy sourcessuch as solar, wind and wave and biomass sources should also beidentified in a case where integrated and mixed energy sources aredesirable for process flexibility. For the solar and wind energysources, estimates of possible thermal and electrical generationcapacities and storage capacities should be available.

5.4.3. Desalination technologySelection of appropriate desalination process (whether a

membrane or a thermal process) depends on the geothermalenergy source characteristics such as the temperature and the flowcapacities [2]. The selection process is also influenced by the feedwater quality (e.g., salinity), technical readiness of the community,plant size, infrastructure and maintenance skills for the desalina-tion plant and the type and potential of other renewable energysources and the availability of grid electricity and the remotenessof the community as well as the local climate conditions. Lowtemperature geothermal sources are suitable for small scale

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desalination processes such as low temperature MED, membranedistillation, humidification–dehumidification and high tempera-ture RO processes. High temperature geothermal waters also allowfor cogeneration schemes integrating desalination with powerproduction.

5.4.4. Feed waterThe feed water characteristics should be evaluated to deter-

mine a suitable desalination process. If low concentration TDS feedwater is available, then membrane processes can be favored. Thisalso depends on the geothermal energy source temperature.Nanofiltration and reverse osmosis processes can be employed forlow temperature geothermal energy and low TDS ground watercombinations. Electrodialysis process may also fit this purposebetter for low TDS feed water. For high TDS concentrations, MSF orMED processes are preferred when high quality geothermal watersare available. SWRO process can be considered for low geothermalwater temperatures.

5.4.5. Product waterDesired product quality should be determined based on the

end use. Industrial processes may require high quality distillateswhich can be produced by thermal desalination plants. Potablewater from low TDS waters can be produced from membraneprocesses. Blending options can be considered where possible aslong as the requirements for the product water can be met withsome reliable process configuration. Other agricultural and fishfarm and animal feed operations may not require high qualitypotable waters. Desalination processes may prove to be cost-prohibitive for the agricultural applications.

5.4.6. Brine disposalBrine disposal and management issues cannot be ignored for

any desalination plant. Inland desalination plants would have toconsider different disposal and management options from thecoastal desalination plants. It was shown that inland desalinationhas less environmental impacts when compared with seawaterdesalination. Disposal into oceans is a commonly practicedmethod for coastal desalination plants while evaporation ponds orsewer disposal is a better option for inland desalination plants.Zero liquid discharge configurations can be used to enhance thewater recovery thereby minimizing the waste brine disposal issuesalbeit at a higher cost.

5.4.7. Techno-economic requirementsEnergy source and the desalination energy requirements play a

critical role in determining the desalination process. Consideringthe aforementioned information on the match of desalinationprocess energy requirements and the type and quality of thegeothermal sources, a process that has lowest energy footprintwith reliable and robust performance should be chosen a fresh-water supply option. Techno-economic analyzes should also con-sider the feed water characteristics such as concentration andtemperature to be connected with the process performance interms of performance ratio, heat losses, and other economic con-siderations and process related issues.

6. Challenges and considerations for geothermal desalination

An ideal geothermal source should be available at reasonabledepths, easily accessible and at a quality suitable for intendedapplication and close to the point of application [66]. The mainrequirements for identifying a good geothermal resource can besummarized as follows [25]:

� A high temperature for good power plant efficiency (for acogeneration scheme);

� A large quantity of stored heat for resource longevity;� A low rate of liquid production per unit of energy reinjection

well sites available at a lower elevation than production fordisposal under gravity;

� Produced fluids with a near-neutral pH for low corrosion ratesin wells and plants;

� Adequate permeability to ensure adequate outputs fromindividual wells;

� A low tendency for scaling in pipelines and wells;� Low elevation and easy terrain for access roads;� A low risk of volcanic activity and hydrothermal eruptions;� Proximity to electrical load or transmission lines.

The basic steps involved in geothermal source utilization fordesalination applications are as follows: identification of geo-thermal reservoir beneath the surface, estimation of geothermalreservoir volume and its type (temperature, flow, and pressure,chemical characteristics of the fluid, saturated steam or hot water)and estimation of future availability of geothermal reservoir. Someother important factors need to be considered for successfulimplementation of geothermal desalination plants. The majorissues are related to land use, geological hazards, waste heat,atmospheric releases, water footprint, noise and socio-economicissue which are discussed next [67]. Table 4 lists the differenttypes of environmental, socio-economic impacts associated withgeothermal power plants and possible desalination schemes andtheir probability of occurrence, severity and the duration ofimpacts [68]. Some events and their impacts have low probabilityof occurrence with short and long-term impacts. A number ofenvironmental regulations may apply for the environmentalimpacts caused by geothermal power and water facilities. Theseregulations and the requirements may vary from region to region.A summary of environmental regulations applicable for geother-mal operations is shown in Table 5 [68]. Regulations are coveredunder “Clean Water Act, “Clean Air Act” and “Solid Waste Man-agement”, noise control, “Occupational Safety and Health Act”, andEndangered Species Act enforced by the United States Environ-mental Protection Agency (USEPA). These regulations correspondto the environmental impacts presented in Table 4.

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Table 4Environmental impacts of geothermal source based power production anddesalination.

Impact Probability ofoccurring

Severity ofconsequence

Duration ofimpact

Air quality emissions Low Medium Short-termSurface water discharge Medium Low to medium Short-term to

long-termUndergroundcontamination

Low Medium Long-term

Land subsidence Low Low to medium Long-termHigh noise levels High Medium to high Short-termWell blowouts Low Low to medium Short-termConflicts with culturaland archeologicalfeatures

Low to medium Medium to high Short-term tolong-term

Social economicproblems

Low Low Short-term

Chemical or thermalcontamination

Medium Medium to high Short-term tolong-term

Solid waste disposal Medium Medium to high Short-term






6.1. Land use

Geothermal energy systems require significant land areas forenergy extraction as well as the geothermal water treatment andmanagement. About 1.2–2.7 tm2 of land area is required per eachMW energy production. Higher land footprint are reported forthose facilities managing the geothermal brines. High capacityflash-steam plants require low land footprints. Plants with rein-jection of geothermal waters also require low land footprints.

6.2. Geological hazards

Geothermal power plants involve excessive extraction and cir-culation of geothermal waters and excavation of land deep intosoils is a must. This might cause seismic instability at some loca-tions although not a large impact. Continued extraction of geo-thermal waters may also cause land subsidization. In someextreme conditions, although uncommon, hydrothermal explo-sions may take place or a sudden release of pressure (steam)caused by earth quakes.

6.3. Waste heat releases

Geothermal wells for either direct use or power productionrelease significant amounts of high temperature waters. This ismainly due to the large quantities of geothermal flows and inef-ficient electricity conversion. In case of power plants with coolingtowers, the waste heat releases are even higher than other con-ventional power plants. In most cases, the waste heat is released inthe form of vapors into the atmosphere, into any artificial ponds orother receiving water bodies.

6.4. Atmospheric emissions

Geothermal wells release significant amounts of non-condensable gases such as H2S, CO2, and CH4, mainly associatedwith flash-steam and dry steam power plants. Other minor pol-lutants are Hg, Ammonia, Radon, and Boron. A wide range of 4–740 g/kWh of CO2 are released from a variety of power plants [58].Some studies report as low as 0–40 g/kWh with a common aver-age range of 80–100 g/kWh. Concerning sulfur dioxide emissions,between 0.159 and 1 g/kWh have been reported [69,70]. Green-house gas, CH4, is also another common pollutant which isreleased in very small concentrations. Other gases of interest arenitrogen oxides. Other pollutants such as arsenic, boron, ammoniaand mercury are of major concern in some locations.

6.5. Water footprint

Water is required from the initial stage of drilling a geothermalwell to its operation. The water requirements for drilling havebeen reported between 5 and 30 m3 which depends on the geol-ogy, technology and the depth [71]. Power generation with air orhybrid cooling plants consume water between 0 and 1.5 m3/MWhwhile water cooling towers consume up to 17 m3/MWh [72]. Inaddition, the brines released from these wells are substantial oftenreinjected into the wells but spills often occur which introduce thepollutants belonging to heavy metals and other toxic substances.Geothermal brines in addition have the disadvantage of high saltconcentration that creates in general operational problems, hardscale formation and concentrated brine disposal, if not near thesea [73]. The scale formation could be mainly due to the hydrogensulfide and ammonia in geothermal heat sources [48,49].

6.6. Noise and social impacts

Well excavation, drilling and operations all involve noise issues,some esthetic issues can be anticipated in some locations. Thenoise levels from each well and the combined impacts depend onthe number of wells and drilling technology in use. Social impactswould be creation of job opportunities for local communities. Thismay be a limited benefit since skilled labor will be required forgeothermal operations. Geothermal energy and water productioncan benefit remote communities which lack access to otherrenewable energy resources and connection to the grid. In somecases were geothermal wells are operated for tourism and othertransient community uses, the local economies can be improved.

7. Future potential for geothermal desalination around theworld

Geothermal energy sources are used either directly or indir-ectly for various uses around the world. Direct uses include variousprocess heat applications, district heating and many other bene-ficial uses while indirect use may include power generation andheating and cooling applications. The worldwide installed capacityfor geothermal systems designed for direct use was 50, 383 MWtand the heat consumption was 438,071 TJ (121,696 GWh) in 2010[22,34,74]. Geothermal energy is used directly (for heating, leisureand balneological purposes, in agriculture and aquaculture wherethermophilic species are bred, etc.) in 78 countries of the world[74]. In terms of annual heat consumption, the top five countries

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Table 5Environmental regulations to be considered for geothermal source based power production and desalination in the USA.

Laws & regulations Air Surfacewater

Geothermalfluids

Solidwaste

Liquidwaste

Noise Subsidence/seismicity

Culturalresources

Biologicalresources

Federal Water Pollution Control Act(NPDES)

� �

Safe Drinking Water Act (UndergroundInjection Control Regulations)

� �

Clean Air Act �Resource Conservation and RecoveryAct (RCRA)

� �

Toxic Substance Control Act � �National Environmental Policy Act(NEPA)

� � � � � � � � �

Noise Control Act �Geothermal Resource OperationalOrder #4

� � � � � � � � �

Occupational Safety & Health Act(OSHA)

� � � � �

Endangered Species Act �






that use geothermal energy are China, the USA, Sweden, Turkeyand Japan, which together account for 55 % of total annual globalgeothermal heat consumption [34]. Electricity from geothermalsteam is generated in 24 countries, including the USA, Philippines,Indonesia, Mexico and Italy. In Europe, low-temperature energyresources prevail, i.e. water reservoirs with temperatures below150 °C. These are mainly present in sedimentary – limestone,dolomite, sandstone – and igneous (crystalline, volcanic) rocks[34,74]. Geothermal energy is usually used directly, but alsoindirectly – to generate electricity in binary cycle power plants(Austria, Germany). Between 2010 and 2014, direct utilization ofgeothermal power (electricity production) increased by 45% (at atotal capacity of 70,329 MWt) which represents an annual growthof 7.7% [22]. In 2014, the total thermal energy utilization aroundthe world increased by nearly 39% (at a total capacity of587,786 TJ/yr or 163,287 GWh/yr) at an annual growth rate of 6.8%.About 55% of geothermal energy is used for ground-source heatpumps, nearly 20% used for bathing and swimming, 15% for spaceheating, 4.5% greenhouses and others for industrial process heat-ing, fish farming, agricultural uses and agricultural drying andraceway heating. The use of geothermal energy corresponds tolarge saving in fossil fuels and associated environmental pollution.For example, current world savings of fuel oil are 350 millionbarrels in the form of geothermal electricity which also eliminatesthe environmental pollution of CO2, SOX and NOX by 148.3, 1.02,0.031 million tons of oil equivalent respectively. Direct geothermalheat utilization also saves 175 million barrels of fuel oil andassociated environmental pollution of CO2, SOX and NOX by 74.1,0.51, 0.015 million tons of oil equivalent respectively.

The role of geothermal energy in global electricity production isexpected to increase sharply as shown in Fig. 14. It is estimated byIEA that the geothermal electricity production could reach up to1400 TWh per year contributing up to 3.5% of the global electricityproduction in the year 2050 [75]. This contribution will avoidalmost 800 million tons (Mt) of CO2 emissions per year. Mean-while, geothermal heat utilization around the world might reach5.8 EJ (1600 TWh thermal energy) annually contributing to totalheat demand by up to 4% in the year 2050. Fig. 14a and b showsthe projected worldwide geothermal growth trends between 2010and 2050 in terms of electricity production (TWh/yr) as well asdirect use (EJ/yr) respectively. Fig. 14c and d shows the number ofwells drilled and the investments in billion between 2010 and2014 respectively.

Between 2015 and 2030, rapid expansion of geothermal elec-tricity and heat production will take place, dominated by accel-erated deployment of conventional high-temperature hydro-thermal resources, driven by relatively attractive economics butlimited to areas where such resources are available. Deployment oflow- and medium-temperature hydrothermal resources in deepaquifers will also grow quickly, reflecting wider availability andincreasing interest in their use for both heat and power. By 2050,more than half of the projected growth comes from exploitation ofubiquitously available hot rock resources, mainly via enhancedgeothermal systems. Substantially higher research, developmentand demonstration resources are needed in the next decades toensure enhanced geothermal systems becomes commerciallyviable by 2030.

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Fig. 14. Predicted geothermal power generation growth trends around the world up to year 2050: (a) electricity production – TWh/yr; (b) direct heat utilization – EJ/yr;(c) Number of wells drilled between 2010 and 2014 (total – 2218 wells; key: 2 -112: 2 countries, 112 wells); (d) investments in billions between years 2010 and 2014 (2–$2.160 B: 2 countries, $2.160 billion).






Geothermal energy sources can be used in regions where waterscarcity is highly pronounced. There are several regions in theworld facing severe water stress due to either physical waterscarcity or economic water scarcity. Physical water scarcity meansthat the water sources in these regions are being depleted due toexcess demands and uses. Economic water scarcity may refer tothe inability to produce potable quality water for human con-sumption. Economic water scarcity may be compounded if thewater sources contain high dissolved solids. Economic waterscarcity can be eliminated by using “free” or “low cost” energysources such as geothermal heat sources. Fig. 15 shows the waterstressed regions in the world. Some regions with acute watersource shortages and economic water scarcity are highlightedwhich will be discussed in this section. It is interesting to note thatthese water stressed regions correspond with high temperaturegeothermal sources (see Fig. 9). The geothermal source potentialand the desalination application feasibility for countries namely,Australia, Caribbean Islands, Central America, India, Israel, King-dom of Saudi Arabia, UAE, USA, and Sub-Saharan Africa are pre-sented in the following sections.

7.1. Geothermal desalination potential in the USA

Coastal counties constitute only 17 percent of the total landarea of the United States (not including Alaska), but account for 53percent of the total population [76]. This ratio of coastal countypopulation to the population of the United States as a whole hasremained relatively stable since 1970. Coastal county population isnot growing significantly faster than noncoastal population, butrather it is the continued population growth in the limited landarea of coastal counties that is of growing importance and thefocus of increasing attention. For example, Florida cannot meet itsfuture demand for water by relying solely on the development oftraditional ground and surface water sources [77]. The state’swater demand is expected to grow by 425% to about 8.7 billiongallons per day by the year 2025. To meet the growing demand,Florida must diversify water sources to include environmentallysound use of saltwater, brackish surface and ground waters, thecollection of wet-weather river flows, and reuse of reclaimedwater and storm water. The same situation prevails in Texas andCalifornia. As of 2005, approximately 2000 desalination facilitieslarger than 0.3 million gallons per day (MGD) were operating inthe United States, with a total capacity of 1600 MGD, which

represents more than 2.4% of total U.S. municipal and industrialfreshwater use [78,79]. Currently, one US facility uses thermal(evaporation/distillation) processes, following an initial reverseosmosis (RO) stage. All other processes use only membranes fordesalination. The membrane processes used are brackish water RO(BWRO), nanofiltration (NF), seawater RO (SWRO), and electro-dialysis reversal (EDR). Microfiltration (MF) is sometimes used aspretreatment. Most of the MF/NF and MF/RO plants are waste-water treatment facilities. NF processes are used both for mem-brane softening and for removing specific organics and pathogens.

United States is rich in geothermal sources spread around mostparts of the country [80]. High temperature geothermal sourcesare more concentrated in the Midwest, southwest and northwestparts of the country as shown in Fig. 16a. Geothermal energy isused for electric power generation and direct utilization in theUnited States. The present installed capacity (gross) for electricpower generation is 3477 MWe (installed) with 2542 MWe net(running) delivering power to the gird producing approximately16,517 GWh/yr for a 74% net capacity factor. Geothermal electricpower plants are located in California, Nevada, Utah and Hawaiiwith recent installation in Alaska, Idaho, New Mexico and Oregon,with 312 MWe being added the last five years. The two largestconcentrations of plants are at The Geysers in northern Californiaand the Imperial Valley in southern California [81].

Interestingly, the south Q4west region is also lacking surface watersources [82]. Arizona, California, Nevada and Texas are experien-cing severe drought and water supply issues. Geothermal watersources also vary in their quality shown in temperatures. Tem-peratures higher than 200 °C are suitable for power generationplants while temperatures between 100 °C and 200 °C are moresuitable for desalination and other industrial process heat andpoly-generation applications (Fig. 16a). The match between thewater issues and the availability of geothermal sources indicates agreat potential and a critical role geothermal energy sources in theportfolio development of energy and water sources for USA.

The locations of geothermal power plants are shown in Fig. 16b.The single projects are shown as geysers whereas the multiplenumber of projects at nearby and close proximity locations areshown in green circles with numbers. Clusters of projects can benoticed in western Nevada, the Salton Sea, the Geysers resourcearea and Southern Oregon/Northern California. These projects allfall in highly desirable areas that geothermal developers areactively pursuing to develop geothermal power projects. With

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Fig. 15. Water stress regions in the world.






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Fig. 16. Geothermal source potential and the source temperatures in the USA (a); geothermal power plant locations in the USA (b). The green circles indicate multiple(number of) projects that are at the same location or in very close proximity to one another while the geyser icon indicates a single project at that location [70]. (Forinterpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)






recent severe drought issues California State is now forced to lookinto other freshwater supply options. Desalination powered bygeothermal sources presents an excellent opportunity for thisregion and the same applies to Arizona. Some parts of Nevada andNew Mexico are also very low in ground water and surface watersources. Geothermal desalination and cogeneration schemes arevery attractive for this region as well.

7.2. Geothermal desalination potential in the Kingdom of SaudiArabia

Some regions of Middle East are found to be rich in geothermalenergy. For example, the kingdom of Saudi Arabia has a few largegeothermal hotspots. Saudi Arabia is the largest country in the gulfcooperation council with a population of 28 million people and agross domestic product (GDP) of nearly SAR 2163 billion (US$577.6 billion) in 2011 [83]. Fossil fuels such as oil and gas sourcesare utilized in electricity production to meet the 240 TWh demandnationwide which is estimated to reach up to 736 TWh by 2020.About 80% of the electricity is utilized for cooling purposes andsignificant electricity consumption is reported for water produc-tion which is about 17 million kWh. The country's CO2 emissionfrom fuel combustion has increased from 252,000 Gg in 2000 to446,000 Gg at present with contribution by oil is 175,000 Gg andby gas is 77,000 Gg [84]. The current per capita emission of CO2

has increased to 0.016 Gg from 0.012 Gg in 2000.Petroleum consumption at national level increases by 10%

annually, electric-peak demand increases by 6% annually, and theinstalled electricity generating capacity at end of 2009 was 40 GW.However, energy demand, driven by economic and social devel-opment, is rapidly increasing and an additional 35 GW capacity isneeded to meet this demand by the end of 2023 at a capitalinvestment of SR 55 billion [85]. Saudi Arabia with the highestconcentration of industrial activities in the GCC region and con-sequently the highest level of CO2 emission from industrial pro-cesses, is likely to witness increased environmental pollution asthe Kingdom continues to emerge from a developing to a devel-oped country status. Fig. 17 shows the trends in CO2 emission costsduring the years between 1980 and 2010 [83]. Between 2010 and2030, the costs are expected rise sharply due to population growthand rapid development. Among the many factors, power, waterand transportation sectors are expected to experience growthsignificantly. Fig. 17 also shows the energy consumption for thesesectors during years 1980 and 2010. This rate of consumption is

unsustainable even if abundant fossil fuel reserves are available.Considering the rapid consumption of local oil reserves (due todomestic consumption) and increased CO2 emissions associatedwith their use, Saudi Arabia is now investigating into imple-menting renewable footprint for water and power sectors. In theseefforts, they identify geothermal water sources suitable for powergeneration. Preliminary assessment shows that high temperature(13–220 °C) geothermal resources are available along the east andwest coast lines of the country. It is estimated that 23�109 kWh ofgeothermal resource is available in wet geothermal systems. Esti-mated geothermal reserves were reported as stored heat energy of1.713�1017 J (rock and fluid) and a geothermal reserve potential of26.99 MWt. Geo-thermometers are applied to estimate, subsurfacetemperature, heat flow (flux) and discharge enthalpy. Theseparameters are found to be 136 °C, 183 mW/m2 and 219 kJ/kg,respectively [85].

Geothermal sources in Saudi Arabia can be mainly classified aslow enthalpy (sedimentary aquifers) resources mainly availableeastern part of the country, medium enthalpy resources (hotsprings) available in western and southwestern parts of thecountry, and high enthalpy resources such as basaltic lavas andHarrats [86]. As seen in Fig. 17, two major areas of geothermalsources are found in Saudi Arabia. Volcanic areas along the Red Seacan serve as potential for medium to high enthalpy resources forpower generation while the sedimentary basins along the ArabianGulf may have large low-enthalpy resources suitable for desali-nation, cooling and low temperature steam generation.

7.3. Geothermal desalination potential in United Arab Emirates –UAE

Similar to Saudi Arabia, the major electricity consumption inUAE is due to cooling and water production after the transporta-tion sector. UAE is also considering options to reduce its non-renewable energy footprint especially for water desalination. Mostof the desalination capacity (about 80%) in the country is based onMSF process which is energy-intensive. High TDS seawater and itspretreatment are the major causes for installing thermal desali-nation systems. Cogeneration schemes are utilized to increase theresource utilization efficiencies. Geothermal energy has not beenutilized much in UAE except for uses in agricultural, fisheries andfarming applications. Since UAE is not located on high thermalgradient geological locations, geothermal sources can be used forcooling applications in absorption chillers and low temperaturedesalination (multi-effect distillation, MED). It is estimated thatabout 0.8% of industrial energy needs could be met by geothermalsource by year 2030 [87]. Low temperature desalination processeshave lower specific energy requirements and a higher thermo-dynamic efficiency. Other advantages include lower corrosionrates, low-cost materials of construction with a longer plant life,lower scaling, lower heat losses, and shorter start-up periods. Themotive energy for driving the low temperature processes may alsobe provided by low grade heat sources (renewable energy) orprocess waste heat to achieve better economies [88].

7.4. Geothermal desalination potential in Israel

Israel suffers from lack of water sources due to 60% of its landbeing occupied by the Negev desert [89] combined with urbangrowth and excess pumping. The annual water availability perperson in Israel is 250 m3 which is four time lower than thestandard water stress indicator (1000 m3 per person per year)below which the countries are said to experience severe waterstress [90,91]. Four major initiatives are taken to increase thewater availability in Israel which are (i) integrated management ofLake Kinneret and groundwater aquifers, (ii) rain harvesting via

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Fig. 17. Energy requirements for power, water and transport sectors in the King-dom of Saudi Arabia (inset) up to 2010, future projections of associated CO2

emission costs up to 2030 and geothermal source major locations in Saudi Arabiaand locations of some desalination plants (e.g., Haqi, Duba,Yanbu, Jeddah, Aziza,Shu-Aiba, Albirk and Shuqaiq on the west coast, Kafji, Jobail, and Khobar on the eastcoast) (data taken from Ref. [83]).






large reservoirs, (iii) wastewater reuse for irrigation and (iv)desalination of seawater and brackish ground water.

Israel has a very high ratio of geothermal energy utilization toits land area [92]. The country ranks second on a world ranking listof TJ of geothermal energy used per area. Current geothermalsource utilization is rated at 2200 TJ/yr. In 2010, the geothermalcapacity of the country includes 27.6 MWt and 512.0 TJ/yr forgreenhouse heating; 31.4 MWt and 989.0 TJ/yr for fish farming;and 23.4 MWt and 692 TJ/yr for bathing and swimming, giving atotal for the country of 82.4 MWt and 2193 TJ/yr [34]. Geothermalsource was mainly applied in agriculture, greenhouses and formedical and recreational purposes.

Desalination has been the plan for the nation to meet the waterneeds which has been evaluated several times over the past fewdecades. Assuming geothermal resource availability, Ophir eval-uated two brine sources at 110 °C and 130 °C for multi-effect dis-tillation. Freshwater costs for this system were estimated as 0.5$/ton [93]. Potential for geothermal sources in Israel was assumedto be very low. However, geological survey by the ministry ofnational infrastructures of Israel recently reported the geothermalmap of the country (see Fig. 18). With reliable borehole tempera-ture data from many locations, they were able to estimate thegeothermal source temperatures at different depths [94]. In earlierstudies, it was determined that Ashdod, Caesarea and north east ofthe Carmel range have adequate geothermal sources [92]. Heatflux was found to be relatively high at the south end of GolanHeights and in southern Israel. Presence of magmatic sources, andhigh thermal conductivity shallow basements were believed to bethe causes for geothermal sources. In many parts of Israel, geo-thermal source temperatures are higher than 150 °C at depthsgreater than 6 km and close to 200 °C at depths of 8 km. thesesources are suitable for power production through enhancedgeothermal systems. The availability of these sources also presentstremendous opportunities for desalination either by MED or MSFtechnologies in cogeneration schemes [95]. This might address thelong battle of Israel against desertification and low water resourceavailability [96].

7.5. Geothermal desalination potential in Australia

Geothermal source temperature profile for Australia is shownin Fig. 19. Existing desalination plant locations are also identifiedon this map [97]. It can be noted that high grade geothermalsources as high as in the range of 160–235 °C may be available insome parts of the country. These sources are suitable for powergeneration and cogeneration or poly-generation schemes and

many other applications [98]. It is interesting to note that highquality geothermal source availability does not match with thelocation of desalination plants. This means that geothermal sour-ces are available in remote areas suitable for desalination appli-cations. Australia has many inland, small communities that facesevere drought and water scarcity issues. Implementation ofgeothermal desalination to maximize freshwater recovery is aresource-efficient option for these locations.

Australia has a district heating facility in Portland, Victoriawhich was also decommissioned in 2006 due to environmentalconcerns of geothermal fluid discharges [34]. A summary of theindividual uses of geothermal direct-use in terms of installedcapacity and annual energy use is: 2.3 MWt or 43.5 TJ/yr for fishfarming; 11.29 MWt or 138 TJ/yr for bathing and swimming; andan estimated 2.50 MWt or 12.86 TJ/yr for geothermal heat pumps,for a total utilization of 16.09 MWt or 194.36 TJ/y [99].

In many countries which are rich in geothermal sources, itsapplications are limited by the resource availability. For example,geothermal sources are too far to transport to the point of appli-cation in many cases such as in urban communities due to highcosts. In some cases the drilling costs are too high to reach thedepths. A broader example would be the availability of geothermalsource in Europe. About 70% of geothermal source available inEurope is concentrated in six countries, with 33% power produc-tion in Sweeden. At global level, most of the geothermal producedpower (about 54 TWh) is reported from 24 countries only [75].Low power production efficiencies is another limitation for geo-thermal power plants growth [100]. Other issues to be consideredfurther are development risks, economic and financial risks, publicperceptions and support, development of innovative desalinationtechnologies and public perceptions and support [101,102].

7.6. Geothermal desalination potential in the Caribbean Islands

The 11 Caribbean islands (St. Kitts and Nevis, St. Lucia, St.Vincent and the Grenadines, Montserrat, Grenada, Dominica,Netherlands Antilles, Guadeloupe, and Martinique) compriseactive volcanoes, fumaroles, and hot springs. These features createexcellent geothermal water sources (Fig. 20) [103,104]. This geo-thermal phenomena is caused by the westward subduction of theNorth Atlantic crustal plate beneath the Caribbean plate. Subsur-face temperatures recorded in the region range from ambient tomore than 290 which was confirmed by measurement in a welldrilled in 2013 on Montserrat. These geothermal sources are idealfor power generation and desalination in a cogeneration scheme.These island nations also lack fresh water sources (see Fig. 15). A

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Fig. 18. Geothermal source gradients at different depths (4, 6, 8, and 10 km depths) in Israel and heat flux (mW/m2) [94].






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100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132Fig. 20. Possible geothermal sources and the volcanic locations in the Caribbean region [103].

Fig. 19. Geothermal source availability and gradients in Australia and locations of existing major desalination plants.






combination of the renewable geothermal source and utilization ofwaste heat from the power generation cycles for desalination canbe considered a sustainable approach.

The total geothermal capacity in the Caribbean Islands isreported as 0.10 MW thermal, or 2.78 TJ/yr which is equivalent to0.77 GWh/yr with a load factor of 0.85. The individual islands havethe following potentials as reported in a previous report [105].

� St. Kitts and Nevis – 50 MWe� St. Lucia – 680 MWe� St. Vincent and the Grenadines – 890 MWe� Montserrat – 940 MWe� Grenada – 1110 MWe� Dominica – 1390 MWe� Netherlands Antilles – 3000 MWe� Guadeloupe – 3500 MWe� Martinique – 3500 MWe

Over the recent years, there has been increasing interest ingeothermal exploration and negotiations for the rights to utilizegeothermal sources in this region. Three successful slim holeswere drilled on Nevis. The government of Dominica and IcelandicDrilling, Inc. initiated the drilling of three exploratory slim holes inthe Wotton Waven district in 2010 while in St. Lucia, the govern-ment signed a Memorandum of Agreement with UNEC Corpora-tion for exploration and development in the Sulfur Springsregions. The Dominica drilling has confirmed the existence of acommercially viable resource with temperature up to 240 °C and a10 MWe power plant for domestic use is planned. In 2013, twowells were successfully drilled and tested on Montserrat. Finally,negotiations for the rights to explore and develop geothermalresources began in 2013 in St. Vincent and in Grenada. Direct usesfor bathing on Nevis Island, St. Lucia, and at several small spas inDominica and in Grenada, with a total installed capacity of0.103 MWt and annual energy use of 2.775 TJ/yr were reported[104].

The only geothermal power plant operating in the Caribbean atthis time is a 15 MW plant in Guadeloupe [106]. In Dominica, aproduction well with a capacity to produce 11.4 MW is planned. Agreater exploitation of Dominica’s geothermal resource (poten-tially up to a total of 100 MWþadditional capacity) is also antici-pated. Both Saint Lucia and Nevis have drilled slim-hole wells, buthave not drilled exploratory wells. Saint Lucia is carrying out 3Gstudies and slim-hole drilling with the support of the World Bankand the Government of New Zealand. In contrast, Nevis drilled asuccessful slim-hole well and signed a concession agreement witha developer in September 2014.

Saint Vincent and the Grenadines and Grenada are in the earlystages of exploring and have not drilled slim-hole wells [107,108].However, Saint Vincent expects to complete a geothermal plant by2018. Saint Vincent partnered with Emera and Reykjavik Geo-thermal to carry out surface exploration, which was completed inJuly 2015. The results of the surface exploration studies suggestthe existence of 300 MW of potential, and project developers willadvance directly to exploratory drilling without drilling slim-holewells. Grenada began surface exploration in December 2014 withthe support of the Government of New Zealand. Geothermalenergy has the potential to generate a cumulative 20,170 GWh inthe Eastern Caribbean (including energy exported to Guadeloupeand Martinique) by 2034. About 10,490 GWh of this potentialsource is expected be consumed by Dominica, Grenada, Saint Kittsand Nevis, Saint Lucia, and Saint Vincent and the Grenadines, withthe remaining amount exported. It shows promise for thesedevelopments that the water desalination projects can be pursuedalongside the power sector development.

7.7. Geothermal desalination potential in the Central America

Central American countries, Guatemala, Honduras, El Salvador,Nicaragua, Costa Rica, and Panama, fall in the “Ring of Fire” (hot-test geothermal spots, see Fig. 9) in the Pacific Ocean. Owing tothis fact, these countries have abundant geothermal sources sui-table for various beneficial uses [109]. An installed capacity of493 MW from seven geothermal wells was reported in 2008which is equivalent to approximately a 5% of the total installedcapacity. Most geothermal capacity is concentrated in El Salvador(204 MW) and Costa Rica (163 MW), followed by Nicaragua(87 MW) and Guatemala (49.5 MW). For the region as a whole,geothermal generation accounted for 7.9% (3131 GWh) of totalelectricity production in 2008; El Salvador has one of the highestpercentages of power generation from geothermal in the world ataround 24 percent.

The geothermal potential for power generation in CentralAmerica is estimated to be between 3000 and 13,000 MW andapproximately 50 sites have been identified for eventual devel-opment, including in Costa Rica (10), El Salvador (4–13), Guate-mala (8–13), Honduras (6–7), Nicaragua (10), and Panama (5). Theupper capacity estimate indicates that geothermal could supplynearly all of the region’s electricity demand. There seems to be ahigh uncertainty in these estimations due to the variations inmeasurement methods. However, the current installed capacity ofless than 500 MW suggests that the regional potential is sig-nificantly underexplored and underdeveloped. Major geothermalpower plant locations and process details are shown in Fig. 21.

7.7.1. Costa RicaThe Central American volcanic belt passes through Costa Rica,

evidenced by numerous volcanoes and geothermal areas. CostaRica has an installed capacity of 165 MW electricity generationwith an annual output of 1131 GWh. Direct use was reportedmostly for swimming pools in the tourism industry. The estimatedinstalled capacity for direct-use is 1.0 MWt and the annual energyuse is 21.0 TJ/yr [111]. The government-owned power companyconducted a nationwide assessment of geothermal source poten-tial in 1980s. With the Government support and good manage-ment, this company has developed considerable expertize ingeothermal development. It also established a dedicated geother-mal department with its own drilling capabilities and facilities.Exploration work on the slopes of the Rincon de la Vieja volcano atthe Las Pailas and Borinquen geothermal fields has resulted in thediscovery of high-temperature fields. Considering availability ofgeothermal sources, further developments in this technologicalarea might play an important role in addressing the energy andwater issues in this country.

7.7.2. El SalvadorSimilar to Costa Rica, El Salvador lies on the Central American

volcanic belt and there is thus a plentiful geothermal resource[109]. La Geo (the geothermal power company in El Salvador) is amixed capital enterprise partnership between the Governmentand a strategic investor (the Italian power company ENEL), hasdeveloped geothermal sources in this country. El Salvador has aninstalled capacity of 204 MW electricity generation with an annualoutput of 1422 GWh. The main emphasis has been on using theresource for power generation produced by two power plants atAhuachapán (95 MWe), and at Berlín (109.4 MWe) which wereconstructed La Geo. This company also expanded its operationsinto neighboring countries, notably Nicaragua. The electricitymarket in El Salvador is fully competitive, and geothermal projectsmust compete with other sources of electricity; there are nospecific incentives for geothermal electricity in this country.

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7.7.3. GuatemalaTwo geothermal power generation fields were developed at

Zunil and Amatitlan Zunil locations in 1990s [109]. Guatemala hasan installed capacity of 52 MW electricity generation with anannual output of 289 GWh. Direct use of geothermal heat isreported concrete construction block curing (Bloteca plant) andfruit dehydration (Agro-Industrias La Laguna). A total installedcapacity of 2.3 MWt with an annual output of 56.5 TJ is reported in2013. The direct-use of geothermal energy in the country in thepast has been used for medical purposes, agriculture, anddomestic use [112]. The exploration concession and power devel-opment are open to the private sector, which is expected to bearall exploration risks.

7.7.4. HondurasSix geothermal sites were identified as a result of geothermal

feasibility studies in the 1970s and 1980s. Direct use capacity of1.93 MWt with an annual output of 12.5 GWh is reported. Anumber of swimming pools are reported using geothermal energy.The potential was considered modest, with the Platanares fieldbeing the most promising. Geothermal development in Hondurasinvolves the Government providing concessions to private com-panies for the development of the resource. Three fields wereconcessioned: the Pavana and Azacualpa fields to Geopower S.A.and the Platanares field to Geoplatanares. In the case of the Pla-tanares project, exploration had been conducted since the 1980swith public resources and international help, but is now beingdeveloped by the private sector. In 2010 the Government finalizeda competitively-bid tendering process and awarded the Platanaresproject which would make it more attractive to the investors.

7.7.5. NicaraguaNicaragua’s net geothermal electricity output has been on a

rising trend since 1999 and in 2008 it was recorded as 289.8 GWh,just under 10% of total net generation [109]. Current estimationssuggest that Nicaragua would have the largest geothermalpotential in Central America and there is considerable interest onthe part of the Government to develop the resources. With theelectricity sector reforms in the 1990s, the Government hasawarded seven concessions for resource exploration to the privatecompanies. Some of the concessions are under active developmentbut it is unclear if the country’s private sector driven approach willbe successful. Nicaragua is the only country in the region that hasestablished a specific Geothermal Law which provides a number ofassurances for geothermal developers, namely the rights andobligations of concessionaires and fiscal benefits.

7.7.6. PanamaGeothermal exploration in Panama has taken place since the

mid-1970s, with mixed results. Currently, the most promisingfields are Cerro Colorado (24 MW estimated) and Valle de Antón(18 MW estimated). The drillings in the latter were scheduled totake place in the late 1990s, but the development of the projectwas suspended due to environmental concerns from local resi-dents (Valle de Antón is a popular tourist area). Geothermalpotential was estimated at 42 MW at Baru-Colorado Area (24 MW)and Valle de Anton area (18 MW). There are no geothermal plantsin operation as of now. A 5 MW Baru-Colorado geothermal powerplant is currently planned by Centram Geothermal Inc. [113].

Geothermal development faces several challenges in thesecountries which can be listed as risks associated with investment,legal and regulatory framework, competing interests and weakpolicies, mitigation and response to environmental impacts and

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Fig. 21. Geothermal power plant locations and the process details in the Central American Countries (Sander, 2015).






integrated power sector planning including the conventional fossilfuel derived electricity and the geothermal electricity. Existingconditions for geothermal development in these countries aresummarized in Table 6. The geothermal electricity costs for thisregion are estimated to be between 7.2 and 8.9¢/kWh with cor-responding capital costs between US$4000–5000/kW. The mostoptimistic capital costs for a capital cost of US$2500/kW, levelizedcosts would be around 5–6 US cents/kWh.

7.8. Geothermal desalination potential in India

Major hot spring groups in India, their tectonic settings andsurface water temperatures are shown in Fig. 22 [114]. Most hotsprings occur in the foothills or river valleys and the waters arepredominantly meteoric in origin. Geothermal springs have beenused mainly for balneological purposes and religious tourism.However, India is yet to produce electric power from geothermalenergy, except for a nominal, 5 kW, binary plant at Manikaran thatwas operational for a very short time only. Fig. 22 also shows the

heat flow (mW/m2 shown in bold italics) at different locations aswell as thermal gradients (°C/km) at the corresponding locations.

To date the only direct-use of geothermal energy in the countryis for bathing, swimming and balneology and in a few cases as asource of energy for cooking. Since 80% of electricity generation inIndia is spent for space cooling, a large amount of CO2 can be savedusing geothermal heat pumps. This use is currently being inves-tigated. The increase in the annual geothermal use for balneology,bathing and swimming has gone from 2545 TJ in 2010 to 4152 TJ in2014, with an installed capacity is 981 MWt. It is estimated that5.0 MWt and 150 TJ/yr is used for cooking, which is included in theother category. Thus, the total for the country is 986 MWt and4302 TJ/yr. [115].

India is facing pressing demands for electricity supplies. Theestimated geothermal potential is serval orders of magnitudehigher than the demands in India. For example the granites inAndhra Pradesh state have a minimum reserve of111,200�1012 kWh while the State’s electricity deficit is of theorder of 25�109 kWh. Similarly in the State of Madhya Pradesh

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Table 6Assessment of General Conditions for Geothermal Development in the Central America.

Ranking Upfront riskmitigation

Legal and regulatoryframework

Resource inventory Environment al and socialimpacts

Integrated power sectorplanning

Costa Rica 2 H M M L HEl Salvador 1 H S M M HGuatemala 4 M M M M MHonduras 5 L L L M LNicaragua 3 M H S M SPanama 5 L L L L L

H¼high (favorable); S¼substantial; M¼medium; and L¼ low (unfavorable).

Fig. 22. Geothermal sourceQ5 availability in India [114,115] (Chandra Shekharam and Chandrasekhar, 2010).






the granites have a minimum reserve of 24,464�1012 kWh whilethe State’s consumption is about 33�109 kWh [116]. Even a Statelike Tamil Nadu in south India, that has no reported wet geo-thermal sites, has potential for enhanced geothermal systems(EGS). The combined power generation capacity of the wet andEGS is estimated at 18,348�1014 kWh. This will wipe out thepower deficit (620�109 kWh) of India by 2030 and make Indiaenergy independent.

Direct use of geothermal sources for these regions was esti-mated. In 2014, the Himalayas had a 335 MWt capacity with anannual utilization of 1055 TJ. West coast and SONATA haveinstalled capacities of 22 MWt and 18 MWt. Bakreshwar has aninstalled capacity of 148 MWt. Considering the source tempera-tures, the feasibility of heat pump applications can be pursued inthe states of Jammu and Kashmir, Himachal Pradesh and parts ofUttarakhand which experience severe winter conditions for longperiods. Space cooling requirements in most parts of India havegrown several fold in the recent years with the growth in econ-omy. Enhanced Geothermal Systems have not been explored inIndia. The primary requirement for such a resource is the occur-rence of high temperatures (typically upwards of 150 °C) at eco-nomically viable depths (typically the top 1–4 km of the Earth’scrust). Areas of anomalous high heat flow, high heat-producinggranites and other silicic igneous intrusive bodies having a depthextent of a few kilometers, could be possible targets for futureexploration efforts in the country [114].

Geothermal sources seem to match with the regions with highwater stress locations in the country. For example, the highlypopulated cities in the east coast and west coast are in the geo-thermal regions. These areas have high TDS ground waters whichneed to be treated by desalination processes. Coastal regions couldmake use of geothermal sources for thermal desalinationprocesses.

7.9. Geothermal desalination potential in the Sub-Saharan Africa

Few countries in Sub-Saharan African region contain geother-mal sources suitable for power generation [117]. Varying levels ofgeothermal exploration and research have been undertaken inDjibouti, Eritrea, Uganda, Tanzania, Zambia, Malawi and

Madagascar, but the potential for electricity generation is highestin Ethiopia, Kenya, Uganda and Tanzania, which are all part of theGreat Rift Valley. Government representatives from Ethiopia,Uganda, Tanzania and Eritrea are interested in the use of small-scale geothermal plants for rural electrification mini-grid systems,although this has not yet been attempted. Based on its extensiveexpertize in geothermal power, Kenya's principal power genera-tion company, KenGen, has assisted neighboring countries,including Rwanda, Eritrea and Zambia in the assessment anddevelopment of their geothermal resources. Geothermal powerhas also been successfully exploited in some northern Africancountries, using geothermal fluid for irrigation of oases as well asheating and irrigation of greenhouses. The estimated sourcepotentials for geothermal energy in 2008 are as follows [118,119]:

Kenya – 3000 MWeEthiopia – 41000 MWeDjibouti – 230–860 MWeUganda – 450 MWeTanzania – 150 MWe

Power generation potentials from conventional and renewableenergy (coal, gas, geothermal, hydro, and wind) sources for variouscountries are shown in Fig. 23 [120]. It can be noted that onlyKenya and Ethiopia have the potential for geothermal powerproduction. The two countries together have an installed totalgeothermal power capacity of 217 MW. Countries like Eritrea,Sudan, Uganda, Djibouti, and Tanzania carried out or are in theprocess of conducting detailed geothermal investigations. Othercountries in the region such as Comoros, Burundi, Malawi, DRC,Rwanda, Mozambique and Zambia have not gone beyond thereconnaissance geothermal resource exploration and resourcepotential inventory [121]. Geothermal development in Ethiopiaand Kenya will be discussed here.

7.9.1. EthiopiaGeothermal energy utilization is reported in various hotels for

bathing and swimming facilities, mainly in Addis Abba area. Theseare estimated at 2.2 MWt and 41.6 TJ/yr [34]. The Government ofEthiopia and the Ethiopian Electric Power Corporation entered

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100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132Fig. 23. Geothermal energy growth potential in Sub Saharan Africa.






into a project agreement with Reykjavik Geothermal (Iceland) toestablish the Corbetti Geothermal Power Plant which will be thefirst independent power producer project in Ethiopia’s history.Power America (USAID – United States Agency for InternationalDevelopment) program has been working in these countries toincrease the renewable energy generation capacity. According tothis master plan, the 7 MW geothermal at Aluto Langano pilotplant will be expanded to 5000 MW in 2037. Corbetti and sur-rounding fields will develop up to 1000 MW capacity.

7.9.2. KenyaKenya progressed well in exploring geothermal energy for

power generation. It has an installed capacity of 127 MW,equivalent to about 11% of the country’s installed electricity gen-eration capacity [25]. Kenya’s power investment plan envisages amajor increase in geothermal power in current projections indi-cating that the resource’s contribution to the country’s installedcapacity would increase to about 30%. With 14 prospect sites –

Suswa, Longonot, Olkaria, Eburru, Menengai, Arus-Bogoria, LakeBaringo, Korosi, Paka, Lake Magadi, Badlands, Silali, Emur-uangogolak, Namarunu and Barrier – Kenya has an estimated5000–10,000 MW of generation capacity available at these loca-tions1. Immediate plans are for the development of some5000 MW of power from geothermal by 2030.

Direct-use of geothermal energy has not grown significantlysince 2010 and greenhouse heating remains the leader with 50 haheated for growing roses that are air-freighted daily to Europe andother world-wide locations [117,122]. The installed capacity forthese greenhouses is estimated at 16 MWt and annual energy useof 126.62 TJ/yr. Heat is only required normally from around2:00 AM to 7:00 AM, but the heat also provides a dry environmentthat limits fungus growth. In addition pyrethrum drying is stillbeing carried out at a plant constructed in the 1920s near Ebburuestimated at 1.0 MWt and 10 TJ/yr. At the Olkaria II power plant,the waste water is being piped to a swimming pool, locallyreferred to as “the blue lagoon”, estimated at 5 MWt and 40 TJ/yr.Changing rooms have also been built on site. The Lake Bororia SpaResort has a pool at 0.4 MW and 6 TJ/yr. The total for the countryis: 22.4 MWt and 182.62 TJ/yr [122].

There are several barriers that need to be overcome for geo-thermal development in Sub Saharan African Countries. The up-front drilling costs are beyond the local economic affordabilitywhich needs support from other foreign developed countries. Thepotential and utilization capacities are underestimated or poorlyunderstood. The governmental priorities are too diverse which arespread among health, education, and housing for the people.Limited human and technical capacity indicates the critical role ofprivate investment in these areas. However, private sectorinvestment also has to overcome several hurdles. These can beidentified as lack of appropriate regulations, tariffs, policies, andlaws. Concession agreements protecting the private investmentare weak. This can be avoided by improving the in-country insti-tutional policy and simplifying the project finance while improv-ing negotiation experience and skills [123].

8. Techno-economics of geothermal desalination

Desalination costs depend on various factors which include thedesalination process configuration, energy source, financial pack-age and the local capital, and operation and maintenance costs.Table 7 shows the desalination cost for thermal and membranedesalination processes at different capacities. Desalination costsdecrease with increasing capacity in general. The costs will besignificantly affected by the energy source and the source watercharacteristics. For example, brackish water desalination can be

cost-effective while seawater desalination is both energy- andcost-intensive as shown in Table 7. A recent evaluation of geo-thermal powered desalination costs suggests that geothermal ROis more cost-effective than geothermal MED, despite the lowefficiency of the geothermal electricity power plant that providesthe electricity to the RO [95]. It was found that geothermal RO hasa levelized water cost of ($2.06/m3) that is 17% lower than geo-thermal MED ($2.48/m3).

Renewable energy driven desalination processes are in generalmore expensive than the conventional energy driven desalinationprocesses. This is due to the low cost of fossil-fuel derived energysources. Among the renewable energy sources, the capital costs forgeothermal electricity is very competitive, although it is a recov-ered over a longer period of time (see Fig. 23a). The capital costsare comparable to coal based electricity production. As discussedin this article, geothermal sources are more suitable for locationswhere other renewable energy sources have more challenges andin remote locations. These communities are usually small in sizerequiring low desalination plant capacities. For small commu-nities, the energy demands would be low. A comparison of dieselgenerated electricity with geothermal electricity are shown inFig. 23b. It shows that the electricity costs decrease with theproduction capacity but the geothermal electricity costs can becomparable at lower end of capital costs and better financialpackages. This shows the potential for cost-competitive desalina-tion powered by Q6geothermal sources (Fig. 24).

9. Concluding remarks

Renewable energy sources, though freely available, still have avery high value and need to be utilized efficiently or utilized in a“sustainable manner”. Among the renewable energy sources,geothermal sources allow for efficient resource utilization due totheir high capacity factor, especially in desalination applications.Since geothermal sources vary in quality and quantity, suitable andenergy-efficient desalination or cogeneration schemes should be

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Table 7Desalination costs for various desalination processes for various capacities.

Capacity of desalinationplant (m3/day)

Desalination cost (US$/m3)

Desalination processMulti-effect distillation,MED

Less than 100 2.5–10

12,000–55,000 0.95–1.95Greater than 91,000 0.52–1.01

Multi-stage flash, MSF 23,000–528,000 0.52–1.75Vapor compression 1000–1200 2.01–2.66

Type of feed waterReverse Osmosis –

Brackish waterLess than 20 5.63–12.9

20–1200 0.78–1.3340,000–46,000 0.26–0.54

Reverse Osmosis –

SeawaterLess than 100 1.5–18.75

250–1000 1.25–3.9315,000–60,000 0.48–1.62100,000–320,000 0.45–0.66

Brackish water [ ] Conventional 0.21–1.06 (€/m3)Photovoltaic 4.50–10.32 (€/m3)Geothermal 2.00 (€/m3)






integrated for efficient resource utilization. High temperature(high-enthalpy) geothermal sources can be used in cogenerationschemes for simultaneous power and water production usingmulti-stage flash distillation, multi-effect distillation technologies.Low temperature desalination processes can be coupled with lowtemperature (low-enthalpy) geothermal sources. Low temperaturedesalination processes have lower specific energy requirementsand a higher thermodynamic efficiency. Apart from the above,other advantages include lower corrosion rates, low-cost materialsof construction with a longer plant life, lower scaling, lower heatlosses, and shorter start-up periods.

Geothermal source utilization around the world is expected toincrease significantly in the future, mainly in direct heat utilizationand electricity production and industrial application uses. Inconjunction with this development, geothermal source utilizationin desalination applications should be assigned priority in waterstressed areas to combat the negative environmental impacts bythe non-renewable energy powered desalination. However, a sui-table regulatory framework and specific incentives and subsidiesshould be provided to encourage the development of geothermaldriven desalination industry. Not all geothermal sites are suitablefor desalination application which needs to be carefully evaluatedcase by case. Uncertainties related to resource characteristics andits availability (reservoir volume and other flow, pressure andtemperature characteristics) should be determined in advance tomatch the life span of the desalination plants. Due to inefficienciesin the power generation scheme, cogeneration schemes may notsuitable in all locations. For this scenario, a suitable combination ofa desalination process and a geothermal source should be identi-fied with a preliminary assessment and evaluation procedure. Theeconomics and environmental impacts of the desalination plantsshould be assessed with site-specific information to eliminatefuture failures.

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http://www.irena.org/remap

http://www.ga.gov.au/scientific-topics/energy/resources/geothermal-energy-resources

http://www.ga.gov.au/scientific-topics/energy/resources/geothermal-energy-resources

http://www.geothermal.org/Annual_Meeting/PDFs/Central%20America.pdf

http://www.geothermal.org/Annual_Meeting/PDFs/Central%20America.pdf

http://https://www.pangea.stanford.edu/ERE/db/WGC/papers/WGC/2015/01011.pdf

http://https://www.pangea.stanford.edu/ERE/db/WGC/papers/WGC/2015/01011.pdf

http://www.e-parl.net/eparliament/pdf/081024%20East%20Africa%20Geothermal%20Toolkit.pdf

http://www.e-parl.net/eparliament/pdf/081024%20East%20Africa%20Geothermal%20Toolkit.pdf


