Pathways for integrated concentrated solar power - Desalination: A critical review

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Pathways for integrated concentrated solar power - Desalination: A critical review Amr Omar a, Amir Nashed a, Qiyuan Li b, Greg Leslie b, Robert A. Taylor c, * a

School of Mechanical and Manufacturing Engineering, University of New South Wales, Sydney, NSW, 2052, Australia School of Chemical Engineering, University of New South Wales, Sydney, NSW, 2052, Australia c School of Photovoltaic and Renewable Energy Engineering, University of New South Wales, Sydney, NSW, 2052, Australia b

A R T I C L E I N F O

A B S T R A C T

Keywords: Concentrated solar power Desalination Freshwater Waste heat Reverse osmosis Multi-effect distillation Condenser Cogeneration Levelized cost of electricity Levilized cost of water Payback period

Concentrated solar power (CSP) plants provide the means to generate dispatchable, renewable electricity in high direct normal incidence (DNI) locations around the world. Due to the strong inverse correlation between DNI resources and freshwater resources, most of the best potential CSP sites also lack sufficient freshwater resources. Thus, an attractive natural symbiotic pathway exists for developing CSP plants integrated with desalination (D) technology, particularly for sites in proximity to large bodies of salty water (e.g., seawater or saline ground­ water). As such, this review critically explores the potential for five CSP-D designs proposed in the literature. Overall, this critical review compares and contrasts the major integration designs on the basis of common merits and limitations. A key finding of this review is that the choice of the most feasible CSP desalination integration is not a straightforward process. It was found that the details surrounding where energy extraction takes place from the CSP cycle can make a significant impact on the feasibility of the plant. In general, waste heat coupling and electrical-driven reverse osmosis integration were found to provide the best technical and economical results. However, no clear-cut ‘winning’ design could be concluded from this review. In fact, the water and energy losses of the condenser were found to significantly shift the results between the two designs. As such, we hope that this review will help guide researchers and engineers towards CSP-D development which has the highest chance of commercial uptake.

1. Introduction Energy and water security represent two of the biggest challenges of the 21st century as the global population and the global economy continue to grow exponentially (albeit at a relatively slower rate than the 20th century) [1]. Even in locations with high solar resources, both water and energy demand are still met — to a large degree — through the use of fossil fuels [2]. In arid regions where significant energy is required to provide fresh water (via pumping, transportation, and treatment), this creates a complex web of social, environmental, geopolitical, and economic issues, which could potentially be mitigated through the use of local solar resources. For this reason, researchers have focussed on developing technologies which cogenerate energy and water from renewable energy sources [3]. Solar-driven energy and water cogeneration have the most potential in locations where solar and seawater resources are abundant, such as the Middle East and North Africa [4–8], tropical islands (>10,000 in Indonesia and the Philippines

alone [9]), and the many other sunny, coastal regions of the world [10]. Solar desalination technologies essentially enable populations to thrive in these regions of the world, regardless of the variabilities in rainfall [11]. One solution for cogenerating water and electricity — the focus of this review — is the integration of a desalination process with a concentrated solar power (CSP) plant [12]. This type of technology is an attractive solution in such regions since it can deliver two critical products for sustainable economic development, potentially at a reasonable cost [13]. Such cogeneration plants also provide environ­ mental benefit (offsetting emissions) and foster local economic activity (creating skilled plant design, construction and operation jobs) as compared to competing conventional technologies [14]. With recent record-breaking (contracted) electricity prices of 6.1 and 7.3 US c=MWh reported for a 700 MW CSP plant in Dubai [15] and a 150 MW plant in South Australia [16], respectively, CSP has become a cost-effective, dispatchable electricity generation option. Rather than just making electricity, an opportunity exists to utilize waste heat from

* Corresponding author. E-mail address: [email protected] (R.A. Taylor). https://doi.org/10.1016/j.rser.2019.109609 Received 7 May 2019; Received in revised form 14 November 2019; Accepted 17 November 2019 1364-0321/© 2019 Elsevier Ltd. All rights reserved.

Please cite this article as: Amr Omar, Renewable and Sustainable Energy Reviews, https://doi.org/10.1016/j.rser.2019.109609

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Nomenclature

MSF OTC PTC PV RO S–CO2 SEC SHC ST TES TVC WCC WHR

Abbreviations ACC Air Cooled Condenser CSP Concentrated Solar Power D Desalination DNI Direct Normal Incidence GOR Gain Output Ratio HTF Heat Transfer Fluid IP Intermediate Pressure LCOE Levelized Cost of Electricity LCOW Levelized Cost of Water LT Low-Temperature MED Multi-Effect Distillation

the CSP system’s Rankine cycle as an alternative to rejecting to the at­ mosphere or a nearby water reservoir. Thus, little of the salable energy theoretically needs to be consumed to run a well-integrated thermal based desalination process, maximizing the value of the CSP asset [17]. Further, CSP-D opens the door to shared capital equipment and some operational synergies (e.g., flexible operation around peak pricing) that could maximize the combined power and freshwater revenue relative to a power-only CSP plant [18,19]. Recent studies have shown that CSP-D plants — if deployed — can make a significant contribution to both the electricity and water needs of arid regions. For example, a study by Trieb et al. indicated that a 200 MW CSP plant operating in Dubai could deliver 1.5 billion kWh= y of electricity and 60 million m3 =y of freshwater, enough power for 250,000 people and enough freshwater for 50,000 people [20]. This is in stark contrast to the ~1.5 million tonnes of oil equivalent energy per year that would be required to produce the same amount of water from a con­ ventional fossil-fueled desalination plant [21]. Further, with respect to The Paris Agreement, a CSP-D plant could reduce emissions by > 300, 000 tonnes of CO2 equivalent annually, if compared with the conven­ tional fossil-fueled desalination plant [22]. While CSP-driven desalination technologies still sit at a relatively low technology readiness level, PV-RO systems have enjoyed a high level of commercial adoption [23–28]. Three factors have helped PV-driven RO systems achieve success: (1) RO is currently the leading desalination technology (e.g. with non-solar-derived electricity),

Multi-Stage Flash Desalination Once-Through Cooling Parabolic Trough Collector Photovoltaic Reverse Osmosis Supercritical CO2 Specific Electrical Consumption Specific Heat Consumption Solar Tower Thermal Energy Storage Thermal Vapor Compressor Wet Cooling Condenser Waste Heat Recovery

producing ~65% of the world’s desalinated water [29–31] due to its high energy efficiency [32–35] (especially for brackish water applica­ tions [36,37]); (2) the relatively low costs of mass production based on the learning curves from (1) [32,38–40]; and (3) PV systems have become the leading technology for new installations of electricity gen­ eration [41], with recent utility-scale PV plant wholesale electricity prices dipping as low as 3 US c=kWh [42]. Following rapid mass pro­ duction cost reductions, large-scale PV plants are now cheaper than even the incremental cost of running most conventional coal-based plants [42]. Despite these trends, PV and RO have only really been integrated at small scales (e.g. < 5000 m3/y) [36]. One challenge is the intermittency of PV systems which would likely require batteries, or some other form of energy storage, to avoid ramping the RO system up and down to rapidly or too frequently [43]. Thus in comparison to PV-RO, CSP-D plants coupled with thermal storage, which are an order of magnitude cheaper than batteries [44], are expected to provide an economical improvement over PV-RO system [45]. Fundamentally, CSP-D plants might also be able to utilize more of the incident solar energy resource than PV-RO since it is thermody­ namically more efficient to turn sunlight into heat rather into electricity. Numerous review papers are available on solar-driven desalination systems in the literature, but, most of these reviews only provide a general overview/description of the different technologies and the recent developments for each technology [18,21,46–52]. Several other informative reviews focus on specific solar desalination technologies,

Fig. 1. CSP plant schematic diagram. 2

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average plant sizes (the largest operational CSP plant in 2019 is the 397 MWe Ivanpah plant [63], while China has several coal plants with more than 6 GWe nameplate [64] e.g., 15 times larger), lower capacity factors (CSP’s maximum reported capacity factor did not exceed 60% [65] due to the diurnal/seasonal resource unless auxiliary gas heaters are used, whereas coal can reach a capacity factor of 95% [66]), and lower heat source temperatures (~600� C maximum solar receiver temperature [67] compared to 1500� C maximum combustion temperatures in fossil fuel plants [68]). These factors mean that complex power augmentation methods, such as regenerative feed heating and multiple steam reheat steps between turbine stages, are necessary to get most out of the heat source [69]. Furthermore, the typical CSP plant has thermal storage systems, rather than fossil fuel reservoir, to extend its operation time and improve its dispatchability. The most common CSP storage system relies on the two-tank design, a hot and cold system. More details on different CSP technologies and operation can be found in the literature [70,71].

Table 1 Specific energy requirements for the different desalination technologies [83]. Desalination Technology

Specific Energy Requirements

Multi-Stage Flash

20–27 kWh=m3

Multi-Effect Distillation

14–21 kWh=m3

Seawater Reverse Osmosis

4–6 kWh=m3

Brackish Water Reverse Osmosis

1.5–2.5 kWh=m3

such as humidification-dehumidification (HDH) [53,54], solar stills [55], and HDH and solar stills together [56], but these also just provide overviews of the recent developments on these topics. There are also a few studies focusing on technology selection and comparisons among the solar-driven desalination technologies [11,19,50,54,57–62]. Therefore, it was concluded that most, if not all, existing reviews are limited by the fact that they rarely dig deeper into investigating the different integration designs and/or the ideal operating conditions. This review paper, therefore, zooms in on the technical aspects of physically integrating CSP with desalination technologies. Thus, the present review aims to address the following essential, but unaddressed, questions for future development in this field:

2.2. Desalination processes Desalination processes are mainly divided into phase change pro­ cesses, i.e. ones that mimic the natural water cycle, and membranebased processes, which rely on an active force to separate salt ions from water across a porous material. In the former, water is evaporated, leaving behind non-volatile substances. The vapor is condensed later, in a separate container or stage to obtain pure water. In contrast, Reverse Osmosis and Electro-Dialysis (ED), typically need electricity to operate [72,73]. Thermal desalination processes can utilize the heat from solar ther­ mal systems, such as flat plate and evacuated tube collectors. Conversely, most membrane-based desalination processes can utilize solar-derived electricity (i.e. PV modules) to power high-pressure pumps. More details on coupling desalination with modular solar en­ ergy can be found in the literature [4,45,51,74–76]. A comprehensive review of each desalination technology [77–80] and its economic per­ formance [40] can be found in the literature. Reverse osmosis is a process that is economically viable with a salt rejection between 94%–99% across a range of feedwater types from brackish water (salinity is in the range of 500 mg=L to 10,000 ppm) to seawater (~30,000 ppm) [81]. Comparatively, MSF and MED are used for high saline feedwater types (>20,000 ppm) accounting for 92% and 99% of the total seawater desalination, respectively [82]. The total specific energy requirements for MSF, MED and RO are shown in Table 1. According to the International Desalination Association (IDA) report [29], owing to its simplicity, relatively low energy cost and high reli­ ability, RO accounts for 84% of the total 16,000 operational desalination plants [84,85]. RO produces 70% (~65 million m3 =d) of the total global desalinated water (92.65 million m3 =d) [86]. Whereas, the two major

➢ Which energy flows in the CSP plant allow for optimum system integration? ➢ What are the merits and limitations of each CSP-D configurations? ➢ Can a thermal-driven thermal desalination method (e.g., MED) compete with RO? If yes, under what circumstances? ➢ What research gaps remain for achieving commercially viable CSP-D designs? 2. Overview 2.1. CSP technology Fig. 1 shows a typical CSP plant. Solar irradiation is concentrated using mirrors onto a linear receiver, i.e. Parabolic Trough Collectors (PTC), or a central receiver, i.e. Solar Tower (ST). In either case, the absorbed concentrated irradiation is then used to heat a heat transfer fluid (HTF) to drive a power block, usually a Rankine cycle. By design, this power block is relatively standard, so that much of the same wellproven technology from fossil fuel power plants can be utilized. Aside from the source of heat (solar vs. hydrocarbons), there are few significant differences between a CSP plant and a conventional fossil fuel-powered plant. One such difference is that the method used to condense the exhaust steam may change; for example, dry cooling is used instead of evaporative cooling in a water-scarce, yet high direct incidence, resource climate. Additionally, CSP has generally lower

Fig. 2. (a) Global desalination production in 2007 (b) Average annual spending growth from 2013 to 2020 [87,88]. 3

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Fig. 3. CSP - desalination integration approaches.

thermal technologies, MSF and MED adopted by 343 and 895 opera­ tional plants, respectively, produce 18% and 7% of the total global desalinated water, respectively. In fact, these three aforementioned desalination technologies account for 94% of the total desalinated water produced across the globe [86]. Fig. 2 presents the global desalination production capacity and the average annual spending growth in the different regions. Reverse osmosis is by far, the most widespread as the largest worldwide installed capacity [89]. However, technology advancement carried out in MED processes has brought it to be competitive with the RO technology. Intriguingly, since CSP generates both heat and elec­ tricity, either or both can be used to drive desalination processes.

the desalination system using the CSP’s waste heat, RO systems driven by grid electricity represent a well-developed technology that could readily be integrated with CSP plants. Conversely, very few studies investigated coupling the desalination process at integration points upstream in the CSP plant (e.g., in the receiver loop or the thermal storage tanks). Each study has applied a different analysis technique to assess their designs. The analysis method of the different literature studies are summarized in Table 2. 3.1. Waste heat design (integration point 1) The power block of a large scale CSP plant will dump about 30% of its energy as waste heat to the environment through the steam con­ densers [89–91]. In utilizing this energy flow, a thermal desalination plant can partially (or even fully) replace the condenser. Fig. 5 illustrates this option, wherein a thermal desalination process directly takes in the turbine exhaust, condenses the steam, and then sends it back to the power cycle in nearly the same concept as a condenser. While this option can make a robust economic argument (trading out one piece of capital equipment for another), the exhaust steam temperature and flowrate must nominally match well with the needs of the thermal desalination system. Crucially, the thermal desalination system will also need to be of similar robustness/reliability to the condenser system it replaces [69]. As shown in Fig. 4, it is clear that most studies in the literature seek to take advantage of the “free” waste heat of the power plant (i.e. inte­ gration point 1). One of the earliest studies to consider this approach was conducted by Trieb et al., in 2002 [20]; it should be noted though that even this study was pre-dated by several studies on using the waste heat from conventional fossil-fuel power plants to drive a desalination pro­ cess. In general, Trieb et al. proposed the idea of using a MED process to condense the turbine’s exhaust steam and replace the condenser, but no analysis was conducted. Ortega-Delgado et al. compared different seawater desalination integration designs with a parabolic trough CSP plant with a direct steam generation [108]. Their first configuration (MED 1) have placed the MED process in parallel with the condenser, where the condenser is kept for reliability purposes. The exhaust pressure is increased to 0.312 bars and 70� C saturation temperature to drive the MED plant. Since the condensation pressure must rise to drive the MED system, in addition to the excess electricity required by the MED to circulate the water, the net thermal efficiency and exergetic efficiency of the CSP plant decreased. Moreover, the system’s LCOW was found to be more than double that of a conventional fossil fuel-driven MED’s plant, 1.239 € =m3 compared to

3. Coupling CSP with desalination Summing up on the literature (discussed in detail below), there are five main integration points for integrating a desalination process with a CSP plant, as shown in Fig. 3. Conceptually, each of these points taps into the flow of energy from one component to the next. There is a great opportunity to better utilize the incident solar energy in a CSP plant since 80% of the solar energy harvested by the solar field is “labelled” as losses [90–92]. There is a considerable amount of literature available which zooms in on analyzing specific integrated CSP desalination designs. Fig. 4 shows the percentage of studies that investigated the different coupling designs mentioned above. Although most of the studies attempt to drive

Fig. 4. Percentage of studies studying specific integration method. 4

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plant to operate when the MED system is not operational. According to the authors, this configuration allows better management of the energy fluctuations during CSP plant operation than replacing the condenser with the MED process. To further extend the possibility to use the waste heat to drive the MED system, Frantz and Seifert focused on optimizing the CSP-MED operation [105]. Firstly, the authors optimized the MED gain output ratio (GOR), which is defined as the ratio of the distillate mass to the input steam mass to the heating steam temperature, cooling water mass flow rate and heat transfer area. Secondly, they assessed the effect of the steam temperature and MED’s heat transfer area on the annual water and electricity production. Thus, their analysis had a different approach from most CSP desalination studies in the literature, where the desali­ nation plant typically had fixed operating conditions and design. The results showed that water production could be increased by over 50% for a 30% increase in the MED heat transfer area. Conversely, the annual water production is doubled if the heating steam temperature, i.e. the turbine exhaust steam, increases from 65 � C to 90 � C. However, this increase in temperature resulted in an 11% lower electricity generation. While it was not part of the study, an economic assessment of the feasibility of operating at a higher steam temperature would have been beneficial. For instance, is it worth sacrificing 11% of electricity generated to produce twice the water?

Table 2 Analysis methods of choice in the literature. Author

Energy Analysis

Alarcon-Padilla and Garcia-Rodriguez (2007) [93] Moser et al. (2011) [94] Palenzuela et al. (2011) [95] Palenzuela et al. (2011) [96] Olwig et al. (2012) [97] Palenzuela et al. (2013) [98] Antipova et al. (2013) [99] Hassabou et al. (2013) [100] Iaquaniello et al. (2014) [101] Casimiro et al. (2014) [102] Palenzuela et al. (2015) [69] Casimiro et al. (2015) [103] Palenzuela et al. (2015) [104] Frantz and Seifert (2015) [105] Fylaktos et al. (2015) [106] Moser et al. (2015) [107] Ortega-Delgado et al. (2016) [108] Papanicolas et al. (2016) [109] Valenzuela et al. (2017) [110] Laissaoui et al. (2017) [111] Mata-Torres et al. (2017) [112] Laissaoui et al. (2017) [113] Wellmann et al. (2018) [114]

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3.2. Intermediate pressure steam design (integration point 2)

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A thermal driven desalination plant can also be coupled with the CSP’s power block by taking some intermediate pressure steam from the turbine (e.g., integration point 2, as shown in Fig. 6). Various designs have been proposed for driving a thermal desalination process with in­ termediate pressure steam. Perhaps the most straightforward configu­ ration — least efficient — is to diverge steam directly from the turbine and feed to the desalination unit. To avoid a high reduction in the overall plant’s efficiency, i.e. to prevent diverting too much useful steam from the turbine, the intermediate pressure steam can be partially mixed with the exhaust steam through a thermal vapor compressor (TVC) [118]. Alternatively, a heat pump can be used to lift the temperature of the waste steam before mixing it with the inter-stage steam from the turbine [93,119–121]. Additionally, employing a heat pump would also require diverting some of the electricity generated by the plant, e.g., Integration point 3. Ortega-Delgado et al. investigated the performance of driving a MED process by diverging some steam from the intermediate stage of the turbine [108]. The extracted steam (62.63 � Cat saturated condition) has the potential to generate electricity, indubitably, which is instead diverted to drive the MED process. Nevertheless, this configuration showed higher efficiency than the first integration method (waste heat recovery approach). The reason for this is that the freshwater capacity is smaller than the first configuration. However, this configuration has a more substantial effect on the CSP’s efficiency due to diverting a flow with a higher exergetically useful steam towards the desalination unit. In different studies by Palenzuela et al. they investigated different design configurations that can be used to couple a MED process with the intermediate pressure steam [69,95,96,116,117]. One of Palenzuela’s et al. designs for this coupling was to drive the MED process by mixing the turbine’s steam with the exhaust steam through a thermal vapor compressor (CSP-TVC-MED) [98]. The fully expanded steam (37� C at saturation conditions), which is considered as the entrained vapor, was mixed with a small amount of steam extracted from the turbine (satu­ rated vapor at 17 Bars, 204� C), the motive steam. The results showed that for the same plant capacity (50 MWe), the CSP-TVC-MED required nearly double the amount of heating steam as the waste heat recovery system (Integration point 1), where back pressure is applied to the tur­ bine outlet (Integration point 1). Another configuration investigated by Palenzuela’s team made use of the permeate vapor from the MED as the entrained vapor to the TVC

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0.57 € =m3 [115]. The authors attributed the high LCOW to the low ca­ pacity factor of the CSP-MED plant, which was found to be less than 25%. Another detailed techno-economic analysis was performed by Palenzuela et al. who had several studies in the literature [69,95,96,98, 104,116,117]. The authors also looked at driving a MED process with the turbine’s exhaust steam at 70� C, i.e. not fully expanded steam. Their earliest published study in 2011 shown the integration of a MED process in a large scale CSP plant with a capacity of 50 MWe to produce 48,498 m3 =d of freshwater [96]. In the same year, a similar study was published but with a smaller freshwater capacity of 14,400 m3 =d [95]. Finally, one of their latest studies in 2015, they have carried out a comprehensive comparative techno-economic analysis for two specific locations: Almeria and Abu Dhabi with different condensation technologies [69, 104,116]. Casimero et al. conducted a comprehensive feasibility study for using a MED process in parallel with the condenser in a CSP parabolic trough plant [102]. The study focused on assessing the impact of the cooling method for the turbine exhaust steam and whether using MED in parallel with the condenser will show better performance. The MED system was placed in parallel with a once-through cooling method to enable the CSP 5

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Fig. 5. Thermal desalination waste heat recovery (Integration point 1).

Fig. 6. Inter-Stage steam driven desalination (Integration point 2).

Fig. 7. (a) TVC-MED configuration (b) MED-TVC configuration. 6

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before mixing it with the turbine’s motive steam (MED-TVC). Note that the motive steam is from the turbine’s intermediate stage. TVC is typi­ cally used in large-scale applications to increase the MED GOR, in which the permeate vapor at the last effect is recycled. The configurations of the two different TVC with MED are shown in Fig. 7. Another interesting study was conducted by Alarcon-Padilla and Garcia-Rodriguez [93] to use a heat pump coupled with MED. A heat pump has some benefits over a TVC, namely that it can operate at part-load; conversely, TVC technology can only operate at full load conditions since its geometry is specifically designed to operate under certain conditions [122]. Thus, heat pumps can, perhaps, better handle the variability of the energy supply from solar resources. The MED heat pump system concept operates by lifting the temperature of the waste heat to ensure the delivery of constant temperature feed to the first effect of the MED. In addition, the heat pump can be integrated in such a way that it fully recovers the heat from the produced permeate vapor of the MED. This allows the possibility to eliminate the MED’s condenser. The results of Alarcon-Padilla and Garcia-Rodriguez study [93] showed that coupling a heat pump with MED can reduce the energy consumption by half when compared with the standard MED system. In addition, it was found that the thermal energy and power specific con­ sumption is reduced by 55% and 12%, respectively, when compared with the stand-alone MED system [123]. However, while this configu­ ration requires half of the thermal energy, it requires double the exergy to operate the heat pump. As a result, the heat pump – MED design will always be limited to be coupled through the high exergetic stream.

desalination technology, so it appears in many studies as the benchmark design to compare against different CSP-D configurations. Thus, most of the studies in the literature compared their proposed coupling technique with CSP-RO. Ironically, this ‘benchmark’ seems to show significant differences between studies. Since the RO process adds another load to the CSP plant, the net thermal is expected to decrease due to the increase in the heat input to the system. Note that the variation in efficiency drop among the different literature studies is due to the author’s assumptions of the RO specific electricity consumption and the water production capacity. To investigate the feasibility of coupling RO with CSP, Hassabou et al. conducted a simple analysis for as CSP-RO plant in the Gulf region based on a fixed RO specific energy consumption and assumed CSP electricity cost of 18.5 € c=kWh in the GCC countries [100]. The study claimed that CSP-RO is competitive with conventional fossil fuel-fired cogeneration power and thermal desalination plants in the Gulf region with an estimated unit cost of water of 2.3 € =m3 . However, the authors acknowledged that RO might not be the best option for GCC countries due to the high temperature, salinity and turbidity of the Red Sea. This limitation is also reported in other studies in the literature [125]. Ortega-Delgado et al. compared CSP-RO with conventional gridconnected RO plant [108]. Their first operation method is that the RO system uses all the electricity generated from the CSP plant (CSP’s generator is not connected to the grid). Whereas, the second operation method is that the RO system gets electricity from the grid to operate for 24 h. It was found that the first operation method has a higher LCOW when compared with the grid-driven RO system. This high LCOW was attributed to the low capacity factor of the CSP plant where the RO plant was only operating at an assumed value of 6 h a day. In other words, for the same capital cost of the RO plant, the conventional grid-connected RO plant had four times more water production. For this reason, one may argue that the analysis could provide more insight if compared to a CSP-RO plant with thermal storage and backup gas heater that allow 24 h of operation.

3.3. Grid (or pre-grid) design (integration point 3) Electricity generated from the CSP plant can be used to power a pressure-driven desalination process such as RO (Fig. 8). In that case, the desalination process is merely another electric load supplied by the CSP plant. Nevertheless, the main advantage of this option is that the elec­ tricity generated on-site is typically much cheaper, i.e. lower than the wholesale price (and much lower than the retail price) since it does not require transmission [93,96]. In addition, since both the electricity price and solar resource are transient quantities, there may be some compel­ ling economic/operational reasons to choose this option. For instance, the electricity price can go low, or even below 0 $=kWh, so transmitting electricity to the grid may not be desirable at certain (sunny) times [124]. Reverse Osmosis technology is considered the most mature

3.4. Thermal storage integration design (integration point 4) Another option is to tap into the thermal storage loop to drive a thermal desalination plant without directly sacrificing electricity gen­ eration, as shown in Fig. 9. The heat from thermal storage can also be used to boost up the waste heat energy to provide the necessary energy to drive a thermal desalination process. However, using stored solar

Fig. 8. Electrically driven desalination (Integration point 3). 7

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Fig. 9. Thermal storage driven desalination (Integration point 4).

energy effectively reduces the CSP’s operational time for a given amount of storage capacity, which in turn, will reduce the annual electricity generated. Nevertheless, an advantage of this approach is that tapping an upstream energy flow allows the desalination system to utilize energy prior to all the thermal losses that occur in the power cycle. A key example of this design was reported in Palenzuela et al. [98], who proposed two configurations using the heat from the thermal storage. In the first configuration, a reheater is used to boost the tem­ perature of the exhaust steam, using the heat from the molten salt, before driving the MED process. Whereas in the second configuration, the same exhaust steam is heated up using the energy from the thermal storage before being mixed with the intermediate pressure steam in a thermal vapor compressor. In other words, this configuration is a com­ bination of Integration point 2 and Integration point 4. It was found that the latter configuration requires double the steam of the former configuration. As a result, the first configuration’s solar field is 44% smaller than the second configuration, which significantly cuts the capital cost. However, it is worth mentioning that the authors failed to give any information about how the desalination process affects the operation of the thermal storage system (e.g., freezing of the salt, optimal sizing, lost opportunity costs of a lower state of charge, etc.).

possible by integrating the heat extraction directly from the solar col­ lectors, as shown in Fig. 10. This is relatively straight-forward relative to the integration with the power block since it just requires a heat exchanger to extract energy from the working fluid in the receiver loop. However, to avoid any loss of plant capacity, the solar field size would need to be increased slightly to adjust the necessary heat to the thermal desalination system. Hassabou et al. [100] applied a transient numerical analysis to assess the effect of variable weather conditions on a CSP-MSF plant. Their design uses a PTC system loop to heat the feed seawater directly, where there is no electricity generated to the grid. The analysis focused on optimizing the CSP-MSF system regarding the solar field area and the thermal storage capacity to maximize the solar fraction. The results show that increasing the collector size has a more significant effect on improving the solar fraction of the plant than increasing the storage tank size. However, the study ignored the effect of excess heat, which is delivered at higher solar fractions. Such excess heat would result in increasing the temperature of the thermal storage beyond its degrada­ tion point. Besides, without a way to dump the excess heat once the storage is full, it will become impossible to keep the MSF top brine temperatures within acceptable values resulting in scaling issues due to the high-top brine temperature [126].

3.5. Solar field integration design (integration point 5) The thermal desalination plant can also be placed as far upstream as

Fig. 10. Heat transfer fluid driven desalination (Integration point 5). 8

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3.6. CSP-MED-RO (A hybrid configuration) (integration points 1 and 3)

desalination systems. Some studies have investigated the energy and cost performance of one particular design, and other focused on a more comparative analysis between different Integration points, and some on certain component effect (e.g., condensation method) on the CSP-D performance. The results of the abovementioned studies are summa­ rized in Table 3. One key opportunity (and challenge) of thermal desalination plants is that they can be coupled at different locations in the CSP plant (uti­ lizing Integration Points 1–5, excluding Integration Point 3). Although most of the studies in the literature have found that using a lowtemperature MED to replace part or all of the CSP’s condenser yield the best performance, there may yet be some opportunity for using upstream heat or mixing energy from several of the Integration points to obtain optimum transient operation. Nevertheless, all the studies re­ ported to date in the literature have concluded that the best two inte­ gration options are: the waste heat recovery approach and the RO approach. So far, there was no clear answer on which desalination technology is better to use with CSP, and which Integration point is best suited to running the desalination process. Thus, the remainder of this review will be dedicated to presenting compiled performance metrics, critical analysis, and discussion surrounding the approaches mentioned to ascertain the best way(s) for coupling CSP with a desalination process. While these options may have some distinct advantages, this review paper will mainly focus on the bulk of the literature, downstream coupling methods.

Another potentially feasible configuration uses both MED and RO processes (e.g., the combined use of Integration points 1 and 3), as shown in Fig. 11. Iaquaniello et al. performed a techno-assessment on the hybrid system, in the case where the MED had ten effects driven by the condenser’s waste heat from the power block along with a single pass RO driven by all the electricity generated from the turbine [101]. The RO and MED were hybridized such that they share the same seawater intake and brine outfall to reduce the cost. This configuration also gives the additional benefit of increasing the feed water tempera­ ture for the RO, which increases the permeate flux [127]. The authors compared the specific greenhouse gasses emissions of the hybrid CSP-RO-MED plant with a gas turbine operating continuously in parallel where the flue gasses of the latter is used as a backup heater for the CSP plant, with that of a conventional RO plant driven by combined cycle generation producing the same amount of water. The results showed that hybrid RO-MED had only 10% lower emissions per kg of desalinated water than the conventional RO system. Such a small improvement in emissions is reasonable due to the low capacity factor of the CSP plant (34%). The other main reason is the higher efficiency achieved by the combined cycle plant (32%) compared to the low efficiencies of inde­ pendent gas and steam turbines (24% and 19.5%, respectively) for the solar-assisted plant. Although care must be taken to not over-constrain the model, a fair comparison would keep the efficiencies constant to focus the results of the CSP alone. The study also showed that LCOW of 0.73 € =m3 could be obtained for a solar-assisted hybrid MED-RO configuration with an overall capacity of approximately 62,000 m3 =d. According to the authors, this LCOW is comparable to a conventional RO plant with similar capacity (0.6–0.65 € =m3 ). Smaller plants (e.g. 20,500 m3 =d) yielded a higher LCOW (0.97 € =m3 ), due to the effect of scale on costs and the turbine’s efficiency. While the effect of preheating the salt water before going to the RO plant was not considered in their analysis, the authors indicated that hy­ bridizing the RO and MED plants would reduce the seawater intake and brine outfall by 17% and 30%, respectively.

4. Discussion 4.1. Waste heat recovery: critical review For the waste heat recovery configuration (Integration point 1), studies reported different efficiency values. The main differences within each study’s design conditions were the condensation temperature. For instance, Palenzuela et al. used a condensation temperature between 35� C and 60� C depending on the location of the CSP plant and the type of condenser used [69]. Whereas, Ortega-Delgado et al. [108] used 30� C and Mata-Torres et al. used 35� C [112] as the condensation tempera­ ture. As might be expected, when the condensation temperature is raised, the CSP’s efficiency decreases. Thus, for MED integration, a higher exhaust steam temperature results in a lower net thermal effi­ ciency from not fully expanding the steam. Fig. 12 summarizes the net

3.7. Literature review summary The conducted review demonstrates that there are many studies in the literature that have investigated the potential to hybridize CSP with

Fig. 11. CSP-MED-RO configuration (Integration points 1 þ 3). 9

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Table 3 Summary of the CSP-D studies available in the literature. Ref

Configuration

PB Configuration

Thermal Storage

Integration Point

Plant Capacity

Net Efficiency

LCOE

LCOW

[69]

PTC þ LT-MED

Multi-Stage Regenerative Feedwater Heating

6.5 h

1

50 MWe 35,607–m3 =d42,927 m3 =d

30.02%– 30.41%

16.6 c€=kWh 18.7 c€=kWh

0.83–€ =m3 0.96 €= m3

25.49%– 28.41%

17.7 c€=kWh 21.8 c€=kWh

0.83–€ =m3 1.05 €= m3

[95]

PTC þ LT-MED þ TVC

1þ2

PTC þ LT-MED TVC

2

24.46%– 26.33%

18.8 c€=kWh 22.7 c€=kWh

0.83–€ =m3 1.05 €= m3

PTC þ RO

3

26.86%– 30.85%

17.4 c€=kWh 20.8 c€=kWh

0.79–€ =m3 1.01 €= m3

PTC þ LT-MED

Reheat Rankine Cycle

PTC þ TVC-MED PTC þ TVC-MED PTC þ RO [96]

[97]

PTC þ RO

24 h operation

2

50 MWe 14,400 m3 =d

4 3 Reheat Rankine Cycle

NA

3

PTC þ LT-MED

1

PTC þ LT-MED þ TVC PTC þ MED

2þ3 Multi-Stage Regenerative Feedwater Heating

0 h, 6 h and 12 h

PTC þ RO

50 MWe 48,498 m3 =d

1

42 MWe 24,000 m3 =d

3

31.50%

25.2 c€=kWh

1.93 €=m3

28.00% 26.61% 32.73%

NA NA 25.1 c€=kWh

NA NA 1.87 €=m3

24.4%

21.8 c€=kWh

0.64 €=m3

26.6%

20.7 c€=kWh

0.70 €=m3

21.6%

23.7 c€=kWh

0.70 €=m3

34.1%*

NA

0.94–$=m3 1.22 $= m3

38.5%*

NA

0.91–$=m3 1.08 $= m3

[99]

PTC þ RO

Simple Rankine Cycle

24 h operation

3

7.58 MWe 7344 m3 =d

25.0%

NA

0.88 €=m3 – 1.01 €= m3

[101]

PTC þ MED þ RO

Steam Cycle þ Gas Turbine for backup

4h

1þ3

2.252 MWe 20,596 m3 =d

19.5%

NA

0.97 €=m3

[102]

PTC þ MED

Multi-Stage Regenerative Feedwater Heating

6h

1

111 MWe 16,400 m3 =d

36.2%

NA

NA

[103]

PTC þ LT-MED TVC

Multi-Stage Regenerative Feedwater Heating

13 h

1

99 MWe 36,112 m3 =d

34.2%

NA

NA

[105]

ST þ MED

Simple Rankine Cycle

13 h

1

3 MWe 3000 m3 =d

NA

NA

NA

[106]

ST þ MED

NA

NA

1

4 MWe 5035 m3 =ds

NA

25.0 c€=kWh 25.9 c€=kWh

€=m3

NA

25.5 c€=kWh 26.1 c€=kWh

€=m3

NA

NA

0.79–€ =m3 1.80 €= m3

ST þ RO [107]

[108]

PTC þ MED

3 Multi-Stage Regenerative Feedwater Heating

14 h operation

1

50 MWe 30,000 m3 =d

0.457–€=m3 0.463 0.517–€=m3 0.526

PTC þ RO

3

NA

NA

0.75–€ =m3 1.02 €= m3

PTC þ MED þ RO

1þ3

NA

NA

0.75–€ =m3 1.19 €= m3

13.1 c€=kWh

1.24 €=m3

PTC þ MED

Multi-Stage Regenerative Feedwater Heating

NA

1

5 MWe 1067 m3 =d

31.1%

PTC þ MED

2

5 MWe 908.8 m3 =d

32.1%

1.27 €=m3

PTC þ RO

3

5 MWe 1067 m3 =d

NA

1.06 €=m3

4 MWe m3 2 d 100 MWe 60,000 m3 =d

NA

NA

NA

NA

13.1 c$=kWh 15.2 c$=kWh

0.68–$=m3 0.91 $= m3

[109]

ST þ MED

Simple Rankine Cycle

NA

1

[110]

ST þ PV þ MED

Multi-Stage Regenerative Heating

11 h–17 h

1

[112]

PTC þ MED

Multi-Stage Regenerative Feedwater Heating

BES 24 h operation

1

50 MWe 36,746–m3 =d37,183 m3 =d

10.81%– 18.89%

14.1 c$=kWh 19.9 c$=kWh

0.75–$=m3 2.16 $= m3

[113]

ST þ MED

Simple Rankine Cycle

NA

1

50 MWe 22,568 m3 =d

38%

NA

NA

[114]

ST þ LTD

Multi-Stage Regenerative Feedwater Heating

18 h

1

12.4–13.9 MWe NA

NA

19.7 c$=kWh 22.1 c$=kWh

1.30–$=m3 2.78 $= m3

thermal efficiency drop when driving a MED plant with the turbine’s waste heat energy in the reviewed studies. Note that some of these thermal efficiency drops were estimated by the authors of this review from the data presented in the papers. A simple parametric study was applied by changing the condensation

temperature before coupling the MED and calculating the net efficiency decrease. It can be observed that the trendline (our analysis) shown in Fig. 13 falls very near the points reported in the literature, excluding Casimiro et al. [102,103] results. Casimiro et al. investigated different operating conditions while having the MED and the condenser in 10

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Fig. 12. CSP-MED waste heat recovery design net thermal efficiency decrease.

parallel. Their MED plant only operates at nominal conditions for a determined percentage of the exhaust vapor from the turbine. Whereas, the remaining vapor is condensed via the condenser. In other words, the MED and the condenser are operating in parallel at 70� C saturation conditions. However, this does not explain why the turbine’s efficiency is not significantly affected when increasing the saturation conditions from 30� C to 70� C. Casimiro et al. also did not report their methods to model their configurations. It is also expected that the turbine inlet temperature affects the ef­ ficiency drop when coupling a desalination system with CSP. The overall thermal efficiency increases as the turbine inlet temperature increases in conventional power plants [128]. In the case of CSP plants, solar tower (ST) technology is more efficient than parabolic trough collectors (PTC) for this very reason, since it can reach higher temperatures [129]. Since raising the turbine outlet temperature/pressure by a set amount (e.g. from 35� C to 70 � C and 0.056 bars–0.031 bars) will take a larger chunk out of the available work in the PTC plant’s steam, it is expected that studies which have used ST plant versus PTC plants, will observe less efficiency drop from utilizing ST plant’s waste heat, due to the Carnot efficiency. For instance, assuming the turbine inlet temperatures for a PTC and ST plants are 400 � C and 565 � C, the Carnot relative efficiency decrease from raising the exhaust temperature from 35� C to 70� C is shown in Fig. 14. To date, however, no study has performed a sensitivity analysis on changing the turbine inlet temperature to see its relative impact on CSP-D performance.

cooling condenser (WCC), and once-through cooling (OTC) method. Air cooling condensers are often used with CSP plants since they are likely to be installed in dry arid regions. However, this technology is very inef­ ficient since it uses air as the heat transfer medium, which has a very low heat transfer coefficient. For conventional steam cycles, the wet cooling condenser is most common [130]. In this technology, cooling water evaporates in cooling towers to remove heat from the cycle and condense the exhaust steam. At the opposite end of the spectrum, once-through cooling can be used when power plants are installed next to a large water body. For this technology to work for CSP desalination system, the combination of high electricity demand, high water avail­ ability, high direct normal solar resources, and a large non-potable water resource all need to be relatively co-located. One of the key findings of this literature study is the effect of the condensation temperature on the performance of the CSP-D. Palenzuela et al. are one of the few authors that investigated how can different condenser types affect the results of the CSP-D performance [116]. Their results indicated that the net thermal efficiency, which includes all the pumping power required by the CSP block and the MED process, is heavily dependent on the condensation temperature. Fig. 15 presents the net efficiency before and after integrating the MED process to the CSP plant. Note that Palenzuela et al. did not present the net efficiency values of the stand-alone CSP system; hence, the efficiency values were estimated using back-of-the-envelope calculations. The red brackets indicate the condensation temperature used in the stand-alone CSP plant, whereas the black brackets indicate the relative percentage decrease when replacing the condenser with the MED process. It is shown that the evaporative water cooling has the highest net efficiency since it has the lowest condensation temperature and low electricity consumption, resulting in operating the turbine at maximum

4.1.1. Condenser technology effect on the CSP-D performance Some studies in the literature investigated the effect of the condenser on the performance of CSP-D. It was found that the type of condenser technology has a more significant impact on determining the feasibility of a particular CSP-D configuration. Three different technologies are used to condense the exhaust steam from the turbine: Dry cooling or aircooling condenser (ACC) method, evaporative water-cooling or wet

Fig. 13. CSP-MED WHR efficiency relative decrease vs. condensation temper­ ature parametric study (Integration point 1).

Fig. 14. Carnot efficiency relative decrease of PTC and ST. 11

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Fig. 15. Net thermal efficiency before and after integrating the MED process (a) Abu Dhabi (b) Almeria (Red brackets indicate the condensation temperature of the condenser) (Black brackets indicate the relative percentage decrease in the net thermal efficiency). (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)

efficiency. However, it also shows that the relative percentage decrease in net efficiency due to the integration of the MED process is the highest. This is due to the large increase from a 37� C /45� C to a 70� C exhaust saturation conditions. Additionally, in the case of Abu Dhabi, CSP-MED showed an efficiency improvement than CSP once-through cooling since OTC has a high-power consumption. This indicated that in certain conditions, replacing the condenser with a MED process can improve the performance of the plant.

whether a thermal-driven technology (e.g., MED) or an electric pumpdriven technology (e.g., RO) should be used. Since RO is wellestablished and relatively low cost, it appears to offer the lowest LCOW, but thermal desalination has a lot of potential for development and provides benefits for integration with concentrated solar power plants [94,107]. The main drawback of RO that it requires electrical power to operate, which limits its commerciality to be integrated with CSP plants. Additionally, RO is a membrane technology; desalinating high saline seawater is unfavorable. Whereas, countries with high solar resources are at the Mediterranean basin, which arguably has one of the highest saline water (greater than 40,000 ppm), high temperature, high turbidity and high marine life [131]. Nevertheless, in the waste heat recovery design (Integration point 1), using the MED plant as the CSP’s condenser incurs a liability/risk, since the electricity and water generation processes become coupled. In other words, the CSP cannot operate unless the MED operates, and vice versa. This also adds the question of how reliable can the MED process be? A way to fix this dependency complication is by placing the MED system in parallel with the condenser. While this is not as cost effective, it enables more flexibility to operate the CSP and the desalination plants somewhat independently. Furthermore, in considering the simple coupling of RO to the CSP plant, there was surprising little agreement on the performance of the RO plant. In fact, some studies showed that CSP-RO has a better per­ formance and payback period than CSP-MED WHR design, and other studies showed the opposite. However, Palenzuela et al. have found that the geographical location has a large effect on which is better CSP-MED WHR or CSP-RO. At high saline locations, such as the Persian Gulf re­ gion, RO specific electricity consumption is considerably high that makes CSP-RO, regardless of the condenser technology, performance worse than CSP-MED WHR. However, at low saline reservoirs, CSP-RO is more economical and better than CSP-MED WHR design.

4.2. Intermediate pressure steam design: critical review It was reviewed earlier that there are various coupling techniques can be used to attach a desalination plant within the intermediate pressure steam from the turbine. Fig. 16 compares the reported net thermal efficiency relative decrease in using the different designs when compared with the stand-alone CSP plants. Palenzuela and her team carried out a thorough investigation of the different configuration designs that utilize the intermediate pressure steam from the turbine [98]. Their reported efficiency values with different condensation methods as well as the estimated relative net efficiency drop are presented in Fig. 17. It was reported that the MED-TVC shows a better performance than the TVC-MED system, regardless of which condenser type is used. Additionally, MED-TVC was found to be more economical than TVC-MED. Yet, the authors did not explain why MED-TVC showed better results than TVC-MED [69]. In addition, Palenzuela has concluded that in the case of using ACC or OTC, CSP-MED-TVC is more efficient than CSP-RO. 4.3. Thermal desalination versus reverse osmosis While there are many possible configurations for coupling CSP with desalination, perhaps, one of the more central questions surrounds

Fig. 16. CSP-D Integration point 2 design net thermal efficiency decrease. 12

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Fig. 19. LCOE and LCOW of coupling MED with intermediate pressure steam (Integration point 2).

replacing the condenser. The condenser accounts for 3% of the total investment cost of the CSP plant [114]. If it is possible to replace this 3% cost with the desalination investment cost, this can provide a significant boost to the economic feasibility of coupling CSP with thermal desali­ nation process. However, it has to be noted that there were some studies like Palenzuela et al. [69,95,96,98,104,116,117] where they did not consider the condenser costs in the Integration point 2 configurations. Coupling a MED process by the intermediate pressure steam from the turbine, on average, showed the worse performance. A breakdown of the LCOE and LCOW of this configuration for specific studies is presented in Fig. 19. A study by Palenzuela et al. [95] and Ortega-Delgado et al. [108] integrated the MED process directly to the intermediate pressure steam without TVC. As a result, the LCOE and LCOW were significantly higher than integrating a TVC with the MED process. This is due to the direct extraction of high exergetic steam from the turbine to operate the MED process. Whereas the use of TVC provides an alternative solution of extracting less exergetic steam from the turbine and mix it with less exergetic exhaust steam. It was shown that using TVC can lower the cost of electricity and the cost of water. In fact, TVC seems to allow the cost of water to be competitive with the waste heat integration design. However, utilizing a CSP-MED with TVC still shows a considerable high LCOE. This is because the waste heat integration uses free energy to drive the MED, whereas TVC requires the bypass of useful steam from the turbine. Nevertheless, Mata-Torres et al. claim that a reduction in the parabolic trough prices can make the intermediate pressure integration approach a competitive design [112]. However, this price reduction, indubitably, would benefit all the different coupling designs and not only the Integration point 2 design. Overall, although extensive research has been carried out on using intermediate pressure steam, no single study has proven that using the coupling design mentioned above (Integration point 2) can improve upon the economic feasibility of CSP-RO.

Fig. 17. Net thermal efficiency before and after integrating the MED process through Integration point 2 (a) Abu Dhabi (b) Almeria (Black brackets indicate the relative percentage decrease in the net thermal efficiency).

4.4. Economic critical comparative analysis When comparing the economic aspect of coupling MED through waste heat recovery (Integration point 1) versus intermediate pressure steam (Integration point 2), utilizing the waste heat provides better metrics in terms of both the levelized cost of electricity and water. From the literature, the average LCOE and LCOW of the three leading coupling methods (waste heat recovery, intermediate pressure steam coupling and reverse osmosis) are presented in Fig. 18. It is clearly shown that coupling through waste heat has better economic performance. The main reason for that is utilizing the ‘free’ waste heat energy from the turbine. Additionally, the reduction in the capital cost savings of

4.4.1. Payback period analysis All studies in the literature that conducted an economic analysis on CSP-D used the LCOE and LCOW as their cost indicators. However, to find a ‘real answer’ of economic feasibility, it is better to determine the integrated plant’s payback time. Using Palenzuela et al. LCOE and LCOW results [104], we estimated the payback period by assuming a fixed selling price of 1 € =m3 and 20.5 € c=kWh for water and electricity, respectively. Fig. 20 presents the estimated payback period of the different Palenzuela et al. configurations. It was found that the RO-WCC payback period was close to that of MED WHR, which was considered by Palenzuela et al. as the best coupling method. CSP-MED WHR and CSP-RO WCC are the only two configurations that have a payback period

Fig. 18. Average LCOE and LCOW of the different Integration point designs . 13

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plant’s economic value, especially in locations with high photovol­ taic penetration where the electricity prices are highly peaky and/or in seasonal droughts. 6. Conclusion The present critical review aimed to address specific questions, which would lead to a deeper understanding of best practice towards the integration of a desalination system with a CSP plant. A central question among these is where to extract energy from the CSP plant. To address this, much of this review was dedicated to elucidating the relative merits and limitations of each design (based upon the literature and the au­ thor’s critical analysis) in terms of efficiency and techno-economic trade-offs. It should be noted that some questions, such as the absolute commercial viability of a CSP-D system, remain unanswered. Overall, this review suggests that with further development, well-designed thermal desalination systems can compete with electrically-driven RO plants. This review has highlighted five different places to integrate a desalination system with a CSP plant. The two most upstream locations — the heat transfer loop and the thermal storage tanks — have the advantage of using heat before thermal losses are incurred in the power block. However, these two options have not been considered in detail in the literature, likely due to the fact that they may add capital cost via a larger solar field area or storage tank volume. Two of the downstream locations allow thermal energy to be extracted from the power block. Intermediate pressure steam can be taken from the lower stages of the turbine or waste heat can be pulled from the outlet of the turbine. In addition, these streams can also be mixed, where a thermal vapor compressor device can be used to increase the thermal efficiency of the turbine by mixing waste energy with thermal energy from steam from intermediate stages of the turbine. To ensure the turbine outlet tem­ perature is suitable for driving the desalination system (usually ~70� C), the leading concept is not to increase the saturation conditions of the steam exiting the turbine, thereby limiting its expansion state. In either case, the turbine performance suffers to some degree in order to provide the necessary heat to the desalination system. The final coupling method, which represents perhaps the most straightforward approach, involves using some of the electricity generated by the CSP plant to drive the pump used in Reverse Osmosis plant. In reviewing the literature available for these options, the main conclusions were:

Fig. 20. Calculated payback period of Palenzuela et al. configurations [104].

shorter than 16 years. Conversely, CSP-TVC-MED OTC has the longest payback period of 17.9 years. In addition, since WCC has a high water consumption, it is LCOW was relatively high, but the least LCOE due to its high efficiency. Conversely, the high energy use of OTC and the high condensation temperature of ACC have made their LCOE high, but low LCOW. Nevertheless, that was not enough to balance the scale and show that the configuration with WCC has a short payback period. Nonetheless, it should be noted that the authors have overlooked the condenser’s cost in their economic analysis, which is expected to alter the payback period results. Furthermore, according to Palenzuela et al. results [104], replacing the condenser with MED provides the shortest payback period. However, eliminating the condenser is unlikely to gain much commercial traction because of the dependency creates between CSP and desalination operation. 5. Research outlook Based on the critical review conducted in this study, there is an abundant room for further progress in determining the feasibility of CSPD. To develop a full picture on this topic, the following research points are more worth of further investigation:

➢ It was found that the condenser technology and condenser temper­ ature can significantly affect CSP-D performance. If the turbine operates at a very low back pressure, the relative net thermal effi­ ciency decrease will be significant when replacing the condenser with the MED process. A 15% relative net thermal efficiency drop is measured when increasing the turbine exhaust operation properties from 30� C to 70� C at saturation conditions, as compared with a 5% net thermal efficiency decrease at 60� C saturation conditions. ➢ No clear-cut answer as to which is technically better between the WHR approach and the CSP-RO approach was found. Nevertheless, the performance of both designs is profoundly affected by the geographical location and the condensation temperature. Under certain conditions of low salinity and low condensation temperature, CSP-RO has the edge on CSP-MED. However, in high saline locations, CSP-MED shows a better performance. ➢ In terms of the economic aspect, there was no clear answer on which technology is more economically attractive. Most studies have used the levelized cost of electricity and the levelized cost of water as their cost metric. However, based on this review, the authors would

➢ Analysis on the effect of the condenser used in a CSP-D plant, by taking into account: condenser technology, condenser cost and climate conditions. ➢ Exploration of the concept of extracting heat directly from the HTF loop, perhaps, a more economical operation than downstream integration. ➢ In contrast to the use of the conventional steam cycle CSP plant, which is highly sensitive to its temperature and pressure conditions as found in this review, incorporating desalination into advanced power block cycles might offer some advantages. For example, su­ percritical CO2 (S–CO2) power cycles operate at higher input tem­ peratures and lower pressure ratios but do not have limitations in terms of saturation conditions in the turbine [132]. While the S–CO2 power cycle is more complex since it requires more reheat/recup­ eration [133], this fact also leads to more opportunities to extract heat from its heat exchangers (e.g. during the precool of the CO2 fluid before the compression stage). ➢ Evaluation of optimally timing energy delivery to storage, water production and power generation. This could help boost a CSP-D

14

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suggest that a better cost indicator for CSP-D is to calculate the payback period than individual product cost indicators. ➢ We estimated and compared the payback period for selected studies and found that CSP designs with once-through cooling condenser provide the longest payback period for the integrated system, while systems with water-cooled condenser showed the shortest payback period. Additionally, CSP-RO with a WCC had a very similar payback period with CSP-MED WHR design (15.7 years vs. 15 years, respectively).

[16] [17] [18] [19] [20]

Overall, while integrating CSP-D offers substantial complementary benefits to achieving sustainable energy and water generation, there is no doubt that the development and deployment of CSP-D will take several more years. It certainly a topic worthy of continued research and development because integrating a desalination process with a CSP plant will have a considerable positive socio-economic and environ­ mental impacts, particularly at larger scales which could provide a low production cost. At present, it was found that both RO and MED based CSP-D are indeed economically viable in that their payback period is less than their plant life, but further development (or government in­ centives) are needed to achieve a commercially relevant payback period to play a more significant role in the future.

[21] [22] [23] [24] [25]

Declaration of interests

[26]

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

[27] [28]

Acknowledgements

[29]

This work was supported by the financial support from the Australian Research Council (ARC LP160100622), Australia.

[30] [31]

References

[32]

[1] Al-Alili A, Hwang Y, Radermacher R. Review of solar thermal air conditioning technologies. Int J Refrig 2014;39:4–22. [2] Omar A, Saghafifar M, Mohammadi K, Alashkar A, Gadalla M. A review of unconventional bottoming cycles for waste heat recovery: Part II - Applications. Energy Convers Manag 2019;180:559–83. [3] Conor R, Winpenny J. The water-energy nexus, in: water and Energy. The United Nations World Water Development Report. Paris: UNESCO - United Nations Educational; 2014. [4] Abu-Arabi M, Rizzuti L, Ettouney H, Cipollina A. Status and prospects for solar desalination in the MENA region. Netherlands: Springer; 2007. [5] Chaibi M. An overview of solar desalination for domestic and agriculture water needs in remote arid areas. Desalination 2000;127:119–33. [6] Gorjian S, Ghobadian B. Solar desalination: a sustainable solution to water crisis in Iran. Renew Sustain Energy Rev 2015;48:571–84. [7] Quteishat K, Abu-Arabi. Promotion of solar desalination in the MENA region. Muscat, Oman: Middle East Desalination Research Center; 2012. [8] Trieb F, Muller-Steinhagen H. Concentrating solar power for seawater desalination in the Middle East and North Africa. Desalination 2008;220:165–83. [9] Central Intelligence Agency (CIA). The world factbook. CIA; 2018 [Online]. [10] Nashed A, Sproul A, Leslie G. Water resources and the potential of brackish groundwater extraction in Egypt: a Review. J Water Supply Res Technol - Aqua 2014;63. [11] Reif J, Alhalabi W. Solar-thermal powered desalination: its significant challenges and potential. Renew Sustain Energy Rev 2015;48:152–65. [12] Allal H, Cottret N, Trieb F, Moser M, Soler R, Tusseau M, Scharfe J, Tomasek M, Kern J, David I, Savoldi E. MED-CSD-Combined solar power and desalination plants: techno-economic potential in Mediterranean Partner Countries. Paris; 2010. [13] Gunzbourg J, Larger D. Cogeneration applied to very high efficiency thermal seawater desalination plants. Desalination 1999;125:203–8. [14] Raluy R, serra L, Uche J. Life cycle assessment of desalination technologies integrated with renewable energies. Desalination 2005;183:81–93. [15] Graves L, Everington J. Sheikh Mohammed bin Rashid announces winning contract for world’s largest CSP solar project. The National; 2017 [Online]. Available: https://www.thenational.ae/business/energy/sheikh-mohammed-bin

[33] [34] [35] [36] [37] [38] [39] [40] [41] [42] [43]

[44] [45] [46] [47]

15

-rashid-announces-winning-contract-for-world-s-largest-csp-solar-project-1. 628906. [Accessed 12 September 2018]. Kraemer S. SolarReserve breaks CSP price record with 6 cent contract. SolarPaces; 2017 [Online]. Available: http://www.solarpaces.org/solarreserve-breaks-cspprice-record-6-cent-contract/. [Accessed 12 September 2018]. Fernandez-Garcia A, Zarza E, Valenzuela L, Perez M. Parabolic trough solar collectors and their applications. Renew Sustain Energy Rev 2010;14:1695–721. Blanco J, Malato S, Fernandez-Ibanez P, Alarcon D, Gernjak W, Maldonado M. Review of feasible solar energy applications to water processes. Renew Sustain Energy Rev 2009;13:1437–45. Al-Karaghouli A, Kazmerski L. Energy consumption and water production cost of conventional and renewable-energy-powered desalination processes. Renew Sustain Energy Rev 2013;24:343–56. Trieb F, Nitsch J, Kronshage S, Schillings C, Brischke L, Knies G, Czisch G. Combined solar power and desalination plants for the Mediterranean region sustainable energy supply using large-scale solar thermal power plants. Desalination 2002;153:39–46. Kalogirou S. Seawater desalination using renewable energy sources. Prog Energy Combust Sci 2005;31:242–81. Department for environment food and rural affairs (DEFRA). Greenhouse gas conversion factor repository. 2015 [Online]. Available: http://www.ukconver sionfactorscarbonsmart.co.uk/. Lamei A, Van Der Zaag P, Von Munch E. Impact of solar energy cost on water production cost of seawater desalination plants in Egypt. Energy Policy 2008;36: 1748–56. Bilton A, Wiesman R, Arif A, Zubair S, Dubowski S. On the feasibility of community-scale photovoltaic-powered reverse osmosis desalination systems for remote locations. Renew Energy 2011;36:3246–56. Childs W, Dabiri A, Al-Hinai H, Abdullah H. VARI-RO solar-powered desalting technology. Desalination 1999;125:155–66. Shalaby S. Reverse osmosis fesalination powered by photovoltaic and solar Rankine cycle power systems: a review. Renew Sustain Energy Rev 2017;73: 789–97. Ali A, Tufa R, Macedonio F, Curcio E, Drioli E. Membrane technology in renewable energy driven desalination. Renew Sustain Energy Rev 2018;81:1–21. Salcedo R, Antipova E, Boer D, Jimenez L, Guillen-Gosalbez G. Multi-objective optimization of solar Rankine cycles coupled with reverse osmosis desalination considering economic and life cycle environmental concerns. Desalination 2012; 286:358–71. International Desalination Association (IDA). Water desalination report. IDA; 2013. Greenlee L, Lawler D, Freeman B, Marrot B, Moulin P. Reverse osmosis desalination: water sources, technology, and today’s challenges. Water Resour 2009;43(9):2317–48. Cipollina A, Micale G, Rizzuti L. Seawater desalination, green energy and technology. Berlin Heildelberg: Springer; 2009. Wade N. Distillation plant development and cost update. Desalination 2001;136: 3–12. Garcia-Rodriguez L. Renewable energy applications in desalination: state of the art. Sol Energy 2003;75:381–93. Beccali M, Sorce M, Galletto J. The potential of renewable energies in sicily for water desalination applications. Springer; 2007. Elimelech M, Phillip W. The future of seawater desalination: energy, technology, and the environment. Science 2011;333(6043):712–7. Gnaneswar V, Nirmalakhandan N, Deng S. Renewable and sustainable approaches for desalination. Renew Sustain Energy Rev 2010;14(9):2641–54. IEA. Water desalination using renewable energy. 2012. Milow B, Zarza E. Advanced MED solar desalination plants. Configurations, costs, future - seven years of experience at the Plataforma Solar de Almeria (Spain). Desalination 1997;108(1–3):51–8. Borsani R, Rebagliati S. Fundamentals and costing of MSF desalination plants and comparison with other technologies. Desalination 2005;182(1–3):29–37. Reddy K, Ghaffour N. Overview of the cost of desalinated water and costing methodologies. Desalination 2007;205:340–53. Renewable energy policy network for the 21st century (REN21), “renewables 2018 global status report. 2018. International Renewable Energy Agency (IRENA). Renewable power generation costs in 2017. IRENA; 2018. Mito M, Ma X, Albuflasa H, Davies P. Reverse osmosis (RO) membrane desalination driven by wind and solar photovoltaic (PV) energy: state of the art and challenges for large-scale implementation. Renew Sustain Energy Rev 2019; 112:669–85. International Renewable Energy Agency (IRENA). Electricity storage and renewables: costs and markets to 2030. Abu Dhabi: IRENA; 2017. Fiorenza G, Sharma V, Braccio G. Techno-economic evaluation of a solar powered water desalination plant. Energy Convers Manag 2003;44:2217–40. Ali M, Fath H, Armstrong P. A comprehensive techno-economical review of indirect solar desalination. Renew Sustain Energy Rev 2011;15(8):4187–99. Chandrashekara M, Avadhesh Y. Water desalination system using solar heat: a review. Renew Sustain Energy Rev 2017;67:1308–30.

Renewable and Sustainable Energy Reviews xxx (xxxx) xxx

A. Omar et al. [48] Zhang Y, Sivakumar M, Yang S, Enever K, Ramezanianpour M. Application of solar energy in water treatment processes: a review. Desaliantion 2018;428: 116–45. [49] Sharon H, Reddy K. A review of solar energy driven desalination technologies. Renew Sustain Energy Rev 2015;41:1080–118. [50] Eltawil M, Zhengming Z, Yuan L. A review of renewable energy technologies integrated with desalination systems. Renew Sustain Energy Rev 2009;13: 2245–62. [51] Esfahani I, Rashidi J, Ifaei P, Yoo C. Efficient thermal desalination technologies with renewable energy systems: a state-of-the-art review. Korean J Chem Eng 2016;33:351–87. [52] Trieb F, Muller-Steinhagen H, Kern J, Scharfe J, Kabariti M, AlTaher A. Technologies for large scale seawater desalination using concentrated solar radiation. Desalination 2009;235:33–43. [53] Parekh S, Farid M, Selman J, Al-Hallaj S. Solar desalination with a humidification-dehumidification technique - a comprehensive technical review. Desalination 2004;160(2):167–86. [54] Al-Hallaj S, PS, Farid M, Selman J. Solar desalination with humidificationdehumidification cycle: review of economics. Desalination 2006;195(1–3): 169–86. [55] Aybar H. Mathematical modeling of an inclined solar water distillation system. Desalination 2006;190(1–3):63–70. [56] Thakkar H, Sankhala A, Ramana P, Panchal H. A detailed review on solar desalination techniques. Int J Ambient Energy 2018:1–22. [57] Pouyfaucon A, Garcia-Rodriguez L. Solar thermal-powered desalination: a viable solution for a potential market. Desalination 2018;435:60–9. [58] Li C, Goswami Y, Stefanakos E. Solar assisted sea water desalination: a review. Renew Sustain Energy Rev 2013;19:136–63. [59] Pugsley A, Zacharopoulos A, Mondol J, Smyth M. Global applicability of solar desalination. Renew Energy 2016;88:200–19. [60] Modi A, Buhler F, Andreasen J, Haglind F. A review of solar energy based heat and power generation systems. Renew Sustain Energy Rev 2017;67:1047–64. [61] Shatat M, Worall M, Riffat S. Opportunities for solar water desalination worldwide: Review. Sustain Cit Soc 2013;9:67–80. [62] Subramani A, Badruzzaman M, Oppenheimer J, Jacangelo J. Energy minimization strategies and renewable energy utilization for desalination: a review. Water Res 2011;45:1907–20. [63] National Renewable Energy Lab (NREL). Ivanpah solar electric generating system. 2015. [64] Taipower. 2008 Sustainability reports - power generation and transmission. 2008. [65] National Renewable Energy Laboratory (NREL). Concentrating solar power. 2017 [Online]. Available: https://atb.nrel.gov/electricity/2017/index.html?t¼sc. [Accessed December 2018]. [66] OpenEI. Transparent cost database. 2018. https://openei. org/apps/TCDB/#blank. [67] Pitz-Paal R. Concentrating solar power systems. In: EPJ Web of conferences; 2016. [68] Media B. Green car congress: new Siemens gas turbine exceeds original rated output: 60%þ efficiency. 2015 [Online]. Available, http://www.greencarcong ress.com/2009/10/siemens-20091004.html. [Accessed December 2018]. [69] Palenzuela P, Alarcon-Padilla D, Zaragoza G. Large-scale solar desalination by combination with CSP: techno-economic analysis of different options for the Mediterranean Sea and the Arabian Gulf. Desalination 2015;366:130–8. [70] Morrison G, Rosengarten G. Solar thermal energy design. 2012. Sydney, NSW. [71] Duffie J, Beckman W. Solar engineering of thermal processes. John Wiley & Sons Inc.; 2006. [72] Pinnekamp J, Friedrich H. Membrane technology for waste water treatment. FiWVerlag; 2006. [73] Miller J. Review of water resources and desalination technologies. 2003. [74] Banat F, Qiblawey H. Membrane desalination driven by solar energy. Springer; 2007. [75] Zejli D, Elmidaoui A. Moroccan potentialities of renewable energy sources for water desalination. Soringer; 2007. [76] Li Q, Beier L, Tan J, Brown C, Lian B, Zhong W, Wang Y, Ji C, Dai P, Li T, Clech P, Tyagi H, Liu X, Leslie G, Taylor R. An integrated, solar-driven membrane distillation system for water putification and energy generation. Appl Energy 2019;237:534–48. [77] Nashed A. High recovery rate solar driven reverse osmosis and membrane distillation plants for brackish groundwater desalination in Egypt. Sydney: University of New South Wales; 2014. [78] Howe E. Fundamentals of water desalination. New York: Marcel Dekker Inc.; 1974. [79] Porteous A. Desalination technology developments and practice. Applied Science Publishers; 1984. [80] Porteous A. Saline water distillation processes. 1975. [81] Li Q, Lian B, Wang Y, Taylor R, Dong M, Lloyd T, Liu X, Tan J, Ashraf M, Waghela D, Leslie G. Development of a mobile groundwater dealination system for communities in rural India. Water Res 2018;144:642–55. [82] Qasim M, Badrelzaman M, Darwish N, Darwish N, Hilal N. Reverse osmosis desalination: a state of the art review. Desalination 2019;459:59–104. [83] Abdelkareem M, Assad M, Sayed E, Soudan B. Recent progress in the use of renewable energy sources to power water desalination plants. Desalination 2018; 435:97–113. [84] Shenvi S, Isloor A, Ismail A. A review on RO membrane technology: developments and challenges. Desalination 2015;368:10–26.

[85] Antony A, Branch A, Leslie G, Le-Clech P. Impact of membrane ageing on reverse osmosis performance - implications on validation protocol. J Membr Sci 2016; 520:37–44. [86] Jones E, Qadir M, van Vliet M, Smakhtin V, Kang S. The state of desalination and brine production: a global outlook. Sci Total Environ 2019;657:1343–56. [87] UNESCO Centre for Membrane Science and Technology. Emerging trends in desalination: a review. Canberra, Australia: Australian Government - National Water Commission; 2008. [88] Global Water Intelligence. Global water market 2017 - volume 1. Oxford, United Kingdom: Media Analytics; 2017. [89] Pankratz T. IDA desalination yearbook 2012-2013. Oxford, UK: Media Analytics Ltd; 2011. [90] Bishoyia D, Sudhakara K. Modeling and performance simulation of 100 MW PTC based solar thermal power plant in Udaipur India. Case Stud Thermal Eng 2017; 10:216–26. [91] Gandrud C, Allaire J, Russell K, Yetman C. D3 JavaScript network graphs from R. Rstudio; 2017. [92] Hinkley J, Hayward J, Curtin B, Wonhas A, Boyd R, Grima C, Tadros A, Hall R, Naicker K. An analysis of the costs and opportunities for conentrating solar power in Australia. Renew Energy 2013;57:653–61. [93] Alarcon-Padilla D, Garcia-Rodriguez L. Application of absorption heat pumps to multi-effect distillation: a case study of solar desalination. Desalination 2007;212: 294–302. [94] Moser M, Trieb F, Kern J, Allal H, Cottret N, Scharfe J, Tomasek M, Savoldi E. The MED-CSD project: potential for concentrating solar power desalination development in Mediterranean countries. J Solar Energy 2011;133(3). [95] Palenzuela P, Zaragoza G, Alarcon D, Blanco J. Simulation and evaluation of the coupling of desalination units to parabolic-trough solar power plants in the Mediterranean region. Desalination 2011;281:379–87. [96] Palenzuela P, Zaragoza G, Alarcon-Padilla D, Guillen E, Ibarra M, Blanco J. Assessment of different configurations for combined parabolic-trough (PT) solar power and desalination plants in arid regions. Energy 2011;36:4950–8. [97] Olwig R, Hirsch T, Sattler C, Glade H, Schmeken L, Will S, Ghermandi A, Messalem R. Techno-economic analysis of combined concentrating solar power and desalination plant configurations in Israel and Jordan. Desalin Water Treat 2012;41:9–25. [98] Palenzuela P, Zaragoza G, Alarcon-Padilla D, Blanco J. Evaluation of cooling technologies of concentrated solar power plants and their combination with desalination in the Mediterranean area. Appl Therm Eng 2013;50:1514–21. [99] Antipova E, Boer D, Cabeza L, Guillen-Gosalbez G, Jimenez L. Multi-objective design of reverse osmosis plants integrated with solar Rankine cycles and thermal energy storage. Appl Energy 2013;102:1137–47. [100] Hassabou A, Spinnler M, Polifke W. Technoeconomic canalysis of medium and large-scale desalination plants driven by concentrated solar systems in the MENA region. In: The mediterranean green energy forum; 2013. [101] Iaquaniello G, Salladini A, Mari A, Mabrouk A, Fath H. Concentrating solar power (CSP) system integrated with MED-RO hybrid desalination. Desalination 2014; 336:121–8. [102] Casimiro S, Cardoso J, Alarcon-Padilla D, Turchi C, Ioakimidis C, Mendes J. Modeling multi effect distillation powered CSP in TRNSYS. In: “SolarPACES; 2014. [103] Casimiro S, Cardoso J, Ioakimidis C, Mendes J, Mineo C, Cipollina A. MED parallel system powered by concnetrating solar power (CSP). Model and case study: trapani, Sicily. Desalin Water Treat 2015;55(12):3253–66. [104] Palenzuela P, Alarcon-Padilla D, Zaragoza G, Blanco J. Comparison between CSP þMED and CSPþRO in Mediterranean area and MENA region: techno-economic analysis. Energy Procedia 2015;69:1938–47. [105] Frantz C, Seifert B. Thermal analysis of a multi effect distillation plant powered by a solar tower plant. In: International Conference on concentrating solar Power and chemical energy systems SolarPACES 2014; 2015. [106] Fylaktos N, Mitra I, Tzamtzis C, Papanicolas C. Economic analysis of an electricity and desalinated water cogeneration plant in Cyprus. Desalin Water Treat 2015; 55:2453–70. [107] Moser M, Trieb F, Fichter T, Kern J, Hess D. A flexible techno-economic model for the assessment of desalination plants driven by renewable energies. Desalin Water Treat 2015;55:3091–105. [108] Ortega-Delgado B, Garcia-Rodriguez L, Alarcon-Padilla D. Thermoeconomic comparison of integrating seawater desalination processes in a concentrating solar power plant of 5 MWe. Desalination 2016;392:102–17. [109] Papanicolas C, Bonanos A, Georgiou M, Guillen E, Jarraud N, Marakkos C, Montenon A, Stiliaris E, Tsioli E, Tzamtzis G, Votyakov E. CSP cogeneration of electricity and desalinated water at the pentakomo field facility. In: AIP conference proccedings; 2016. [110] Valenzuela C, Mata-Torres C, Cardemil J, Escobar R. CSP þ PV hybrid solar plants for power and water cogeneration in Northern Chile. Sol Energy 2017;157: 713–26. [111] Laissaoui M, Nehari D, Ouinas D. Analysis of the feasibility of combined concentrating solar power with Multi Effect Desalination for Algerian Coast. Int J Renew Energy Resour 2017;7(3):1145–54. [112] Mata-Torres C, Escobar R, Cardemil J, Simsek Y, Matute J. Solar polygeneration for electricity production and desalination: case studies in Venezuela and Northern Chile. Renew Energy 2017;101:387–98. [113] Laissaoui M, Touil A, Nehari D. Thermodynamic analysis of the combined CSP and desalination in Algeria. In: “In energy proceedia; 2017. La Rochelle, France. [114] Wellmann J, Meyer-Kahlen B, Morosuk T. Exergoeconomic evaluation of a CSP plant in combination with a desalination unit. Renew Energy 2018;128:586–602.

16

A. Omar et al.

Renewable and Sustainable Energy Reviews xxx (xxxx) xxx [125] Al-Ahmad M, Abdul-Aleem F. Scale formation and fouling problems effect on the performance of MSF and RO desalination plants in Saudi Arabia. Desalination 1993;93:287–310. [126] Shams El Din A, El-Dahshan M, Mohammed R. Scale formation in flash chambers of high-temperature MSF distillers. Desaliantion 2005;177:241–58. [127] El-Sayed E, Ebrahim S, Al-Saffar A, Abdel-Jaward M. Pilot study of MSF/RO hybrid systems. Desalination 1998;120:121–8. [128] Omar A, Saghafifar M, Gadalla M. Thermo-economic analysis of air saturator integration in conventional combined power cycles. Appl Therm Eng 2016;107: 1104–22. [129] Sargent and Lundy Consulting Group. Assessment of parabolic trough and power tower solar technology cost and performance forecasts. National Renewable Energy Laboratory NREL; 2003. [130] H. Ballegooyen, “Condenser applications,” Gryphon International Engineering Services, Inc., St. Catharines, Ontario, Canada. [131] Simon D, Meijer P. Salinity stratification of the Mediterranean Sea during the Messinian crisis: a first model analysis. Earth Planet Sci Lett 2017;479:366–76. [132] Lee H, Kim H, Jang C. Compatibility of candidate structural materials in hightemperature S-CO2 environment. In: Supercritical CO2 power symposium; 2014. Pittsburgh. [133] Ahn Y, Bae S, Kim M, Cho S, Baik S, Lee J, Cha J. Review of supercritical CO2 power cycle technology and current status of research and development. Nuclear Eng Technol 2015;47:647–61.

[115] Muhanna N. “Water cost in southern Spain,” revolve water. April 2017 [Online]. Available, http://www.revolve-water.com/spain-water-prices/. [Accessed July 2018]. [116] Palenzuela P, Zaragoza G, Alarcon-Padilla D. Characterisation of the coupling of multi-effect distillation plants to concentrating solar power plants. Energy 2015; 82:986–95. [117] Palenzuela P, Alarcon-Padilla D, Zaragoza G. Concentrating solar power desalination plants. New York: Springer; 2015. [118] Al-Juwayhel F, El-Dessouky H, Ettouney H. Analysis of single-effect evaporator desalination systems combined with vapor compression heat pumps. Desalination 1997;114:253–75. [119] Elshamarka S. Absorption heat pump for a potable water supply in a solar house. Appl Energy 1991;40:31–40. [120] Mandani F, Ettouney H, El-Dessouky H. LiBr-H2O absorption heat pump for single-effect evaporation desalination process. Desalination 2000;128:161–76. [121] Siqueiros J, Holland F. Water desalination using heat pumps. Energy 2000;25(8): 717–29. [122] Hassan A, Darwish M. Performance of thermal vapor compression. Desalination 2014;335:41–6. [123] Zarza E, Ajona J, Leon J, Gregorzewski A, Genthner K. Solar thermal desalination project at the Plataforma Solar de Almeria. Sol Energy Mater 1991;24:608–22. [124] Smith A. “Solar power drives electricity prices below zero during the middle of the day,” Financial Review. 11 July 2018 [Online]. Available: https://www.afr. com/business/energy/solar-energy/solar-power-drives-electricity-prices-belowzero-during-the-middle-of-the-day-20180720-h12xbd. [Accessed January 2019].

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