Combining Heliostat Solar Energy and Reverse Osmosis: Thermoeconomic Analysis for Power Generation and Freshwater Production

Subject Areas : Hybrid renewable energy systems

Seyyed Masoud Seyyedi ¹ , Seyyed Mostafa Ghadami ²

1 -
2 -

Received: 2025-06-16 Accepted : 2025-06-24 Published : 2025-09-18

Keywords: Solar energy, Heliostat Reverse Osmosis, Power Generation, Freshwater Production, Thermoeconomic,

Abstract :

The simultaneous production of electricity and fresh water is one of the needs of human society and the topics of interest for designers of energy systems. In the present work, a heliostat solar farm is combined with a reverse osmosis desalination unit to produce electricity and fresh water. Firstly, thermodynamic analysis is performed to calculate thermodynamic properties of each state including mass, temperature, pressure and enthalpy. Then thermoeconomic analysis is performed to calculate the cost of electricity and fresh water. The effects of design variables (pressure ratio of air compressor, the efficiencies of gas turbine and air compressor and number of heliostats), environmental parameters (air temperature and solar direct normal irradiance) and economic parameters (interest rate and economic life of components) on the profit from the sale of system products (electricity and fresh water) are investigated. The results reveals that the maximum values of profit are 582.5, 841.7 and 1093 $/h for number of heliostats  1800, 2200 and 2600, respectively at . Also, the amount of fresh water produced  increases from 166.6   to 194  (16.4% increasing) as  goes up from 750  to 910 . The value of profit ascends from 841.7 $/h to 1310 $/h (55.6% increasing) when interest rate decsends from 12% to 10% for n = 25, too

References:

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Full-Text:



Renewable Energy and Smart Systems Journal     Vol. 2, No. 1, 2025: 1-11
	Renewable Energy and Smart Systems
	journal homepage: https://sanad.iau.ir/journal/res

 

Combining Heliostat Solar Energy and Reverse Osmosis: Thermoeconomic Analysis for Power Generation and Freshwater Production

 

 

Seyyed Masoud Seyyedi1,4,¹, Seyyed Mostafa Ghadami2,4² Mozhdeh Karamifard3,4

 

1Department of Mechanical Engineering, AK.C., Islamic Azad University, Aliabad Katoul, Iran

2Department of Electrical Engineering, AK.C., Islamic Azad University, Aliabad Katoul, Iran

3Department of Physics, AK.C., Islamic Azad University, Aliabad Katoul, Iran

4Energy Research Center, AK.C., Islamic Azad University, Aliabad Katoul, Iran

 

 

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[1] * Corresponding author.

E-mail address: [e-mail] (S.M. Seyyedi).

[2] * Corresponding author.

E-mail address: [e-mail] (S.M. Ghadami)

1. Introduction

Simultaneous production of electricity and fresh water is a basic need in most remote areas. Solar energy can be applied to power generation directly using photovoltaic (PV) solar cells or indirectly using a solar thermal system [1]. Due to the shortage of fresh water in the world, fresh water is produced using seawater. There are various methods for producing fresh water as shown in Fig. 1 [2]. Many researchers have tried to provide cogeneration systems for producing electricity and fresh water. In 2010, a combined solar organic Rankine cycle with reverse osmosis desalination process was proposed by Nafey and Sharaf [3]. They performed energy and exergy analysis and cost evaluations for their proposed cycle. In 2016, exergoeconomic analysis of a solar farm coupled with a two-stage direct reverse osmosis (RO) system has been conducted by Mokhtari et al. [4]. In 2016, Yari et al. [5] proposed a novel cogeneration system for producing power and fresh water using solar energy. In 2016, Noorpoor et al. [6] examined exergy analysis and optimization of a multi-generation system for electricity, heating, cooling and fresh water, where solar energy and sugarcane biomass were used. In 2017, a cogeneration system based on a series two-stage organic Rankine cycle integrated with a reverse osmosis desalination (RO) unit was proposed Nemati et al. [7]. The system produced the consumed electricity and fresh water of a ship. In 2017, integration of an eco-design strategy for small RO desalination system driven by photovoltaic energy was performed by Monnot et al. [8]. In 2018, the thermodynamic performance of a solar-based multi-generation system designed to produce hydrogen, cooling, heating, and freshwater was evaluated by Yilmaz [9]. In 2019, Farsi and Dincer [10] extended a multigeneraton system driven by a geothermal source for generating power, hydrogen, cooling and freshwater. In 2020, the waste energy of a steam power plant was employed for the production of fresh water by Ghorbani et al. [11]. Solar collectors and auxiliary boilers were applied for providing the required heat for the steam power plant. In 2020, exergoeconomic and exergoenvironmental analyses of a desalination plant were conducted by Lourenço and Carvalho [12]. Their system consists of an internal combustion engine, a Rankine-based heat recovery unit, and a seawater RO system. In 2020, Ghorbani et al. [13] proposed a hybrid renewable energy system for production of power and fresh water using parabolic trough solar collectors. The system produced electricity (459.9 MW) and freshwater (3628 kgmol/h). In 2020, Mohammadi et al. [14] designed a gas turbine combined cycle to produce electricity, cooling and freshwater. In 2020, a renewable-based energy system was proposed by Lourenço and Carvalho [15]. Their system produced electricity and fresh water. In 2020, Mohammadi et al. [16], evaluated several hybrid trigeneration configurations based on a gas turbine combined cycle for generating electricity, cooling and freshwater. In 2021, comprehensive techno-economic analysis of a compressed air energy storage hybridized with solar and desalination units was performed by Alirahmi et al. [17]. In 2022, thermoeconomic analysis for a combined solar energy system with RO desalination unit was performed by Assareh et al. [18]. In 2022, Yuksel et al. [19] proposed a solar-fed multigeneration plant that provided power, freshwater, cooling, methane, ammonia, hydrogen and urea. It consisted of a PTC field, a steam Rankine cycle, an ORC, a RO unit, an absorption chiller, a hydrogen compression system, a PEM electrolyzer, as well as ammonia, methane, and urea generation systems. The energy and exergy efficiencies was determined at 66.12%, and 61.56%, respectively and the cost of producing hydrogen was 1.94 $/kg. In 2024, an integrated energy system was proposed by Abouzied et al. [20]. It included three subsystems: a biogas-fired GTC, a modified S-CO₂ recompression cycle for supplementary electricity generation, and a MED unit for distilled water production.

 

 

 

Fig.1: Different methods of water desalination [2]

 

2. Reverse osmosis unit (RO)

RO is a physical process that uses the osmosis phenomenon, that is, the osmotic pressure difference between the salt water and the pure water to remove the salts from water [21]. In 1996, Malek et al. [22] provided a realistic economic model that relates the various operational and capital cost elements to the design variable values. In 2011, a good review article was written by Pangarkar and Sane [23]. In 2012, a RO desalination process with multiple-feed and multiple-product was investigated by Lu et al. [24]. In 2014, a multi-objective optimization of RO networks for seawater desalination was proposed by Du et al. [25]. In 2017, for the desalination system, Blanco-Marigorta et al. [26] reviewed the exergy efficiencies of several RO systems, which varied between 2% to 92%.

3. System descriptions

Heliostat is generally referred to a set of mirrors that are located around a rotating axis and reflect sunlight to a central receiver. Fig. 2 shows a schematic view of the proposed combined system that consists of an air compressor, a solar heliostat field (to generate hot air), a gas turbine (to generate power) and a RO distillation unit (to produce fresh water). In first, the air enters the air compressor and is compressed, and then it is heated after passing through the solar heliostat field. Hot air enters the gas turbine to generate power, while the outlet is still at a high temperature. A part of the produced electricity is sold to the grid and another part is consumed by the desalination unit to produce fresh water.

 

Fig. 2: Schematic view of the proposed combined system

 

4. Mathematical Modeling

 

The mass and energy balance equations for each component must be written. Also, an economic model must be developed.

 

4.1. Thermodynamic analysis

 

Ø       Air compressor (AC):

 The outlet temperature of air compressor can be calculated by [27]:

Article info	Abstract
Keywords: Solar energy Heliostat Reverse Osmosis Power Generation Freshwater Production Thermoeconomic	The simultaneous production of electricity and fresh water is one of the needs of human society and the topics of interest for designers of energy systems. In the present work, a heliostat solar farm is combined with a reverse osmosis desalination unit to produce electricity and fresh water. Firstly, thermodynamic analysis is performed to calculate thermodynamic properties of each state including mass, temperature, pressure and enthalpy. Then thermoeconomic analysis is performed to calculate the cost of electricity and fresh water. The effects of design variables (pressure ratio of air compressor, the efficiencies of gas turbine and air compressor and number of heliostats), environmental parameters (air temperature and solar direct normal irradiance) and economic parameters (interest rate and economic life of components) on the profit from the sale of system products (electricity and fresh water) are investigated. The results reveals that the maximum values of profit are 582.5, 841.7 and 1093 $/h for number of heliostats  1800, 2200 and 2600, respectively at . Also, the amount of fresh water produced  increases from 166.6  to 194  (16.4% increasing) as  goes up from 750  to 910 . The value of profit ascends from 841.7 $/h to 1310 $/h (55.6% increasing) when interest rate decsends from 12% to 10% for n = 25, too.
Article history: Received: 16 06 2025 Accepted: 24 06 2025

The air compressor work is calculated as follows:

(1)

Ø       Solar Heliostat field (SHF):

The total amount of solar energy in heliostats is given by Eqs. (3) and (4) [2].

(2)

Heat losses can be quantified by Eq. (5).

	(3)
	(4)

Finally, the heat transfer rate between air and receiver can be calculated by:

	(5)
	(6)

Ø       Gas turbine (GT):

The outlet temperature of gas turbine can be calculated by [27]:

(7)

The gas turbine work is calculated as follows:

(8)

The net work of solar power cycle is calculated as follows:

(9)

 

The power consumption for the desalination unit pump  is obtained by Eq. (11):

(10)

­­

The main equations required for modeling the RO unit are represented in Appendix A. Here, the electrical fraction is define by:

­

(11)

[

(12)

 

4.2. Thermoeconomic analysis

 

Now, the thermoeconimc model is presented. The cost rate of each component  is given by [1]:

(13)

where the capital recovery factor (CRF) is a function of the lifetime of components  and interest rate  and can be calculated by:

(14)

Also, the operation time of the system and the coefficient operation are considered 12 hours per day (from 6 to 18) and 0.85, respectively. Therefore, .

The present worth is defined as:

(15)

where

(16)

and

(17)

where  is the salvage percentage. Appendix A presents the total capital investment (TCI) cost for each component.

The average cost of electricity  is obtained by:

(18)

The average cost of fresh water  is obtained by:

(19)

Revenue  means money that can be earned from the sale of electricity and fresh water and can be calculated as follows:

(20)

where  and  [1]:

Finally, Profit can be obtained by:   

(21)

where

(22)

 

5. Results and discussion

Here, firstly a comparisson between the present results with other works is presented and then the effects of the main parameters on the performance of the system are investigated.

5.1. Model validation

Table 1 presents the predefined values for modeling the proposed system. Also, Table 2 presents the obtained results based on the values of Table 1. To model the proposed cogeneration system for electricity and fresh water production, an Engineering Equation Solver (EES) code was extended. The comparison between the obtained results for the RO desalination unit with the data reported by Nafey et al. [3] and Kianfard et al. [28] is outlined in Table 3. The comparison shows a good agreement between the results.

 

 

 

 

Table 1: Modeling input parameters [1, 3, 18]

	(23)
and
	(24)

 

Tables 2: Results based on the values of Table 1

Parameter	Definition	Amount
Power system
	Ambient temperature	20
	Ambient pressure	101.3
	Direct normal irradiance	850
	Number of heliostats	2200
	The area of heliostats	60
	The receiver local temperature	1000
	The gas turbine inlet temperature	750
	Heliostat efficiency	0.71
	Surface emissivity of the receiver	0.88
	Wind speed	5
	Compressor pressure ratio	6
	Gas turbine efficiency	0.85
	Air compressor efficiency	0.82
RO unit
	Feed water temperature	25
	Salt rejection percentage	0.9944
	Seawater salinity	45000 ppm
	Number of elements	7
	Price of the pressure vessel	7000 $
	Fouling factor	0.85
	Recovery ratio	0.30
	Number of pressure vessels	42
	Each membrane price	1200 $
	Element area	35.4
	Density of fluid	1020
	Pump efficiency	0.80
Element type	FTSW30HR-380	-
Economic parameters
	Working hour per year	3723 hr
	Interest rate	0.12
	Lifetime of components	25 year
	Maintenance factor	1.06
	Salvage percentage	15 %
	Electrical fraction	0.05
	Selling price of electricity	0.12
	Selling price of fresh water	3

 

Table 3: Comparisson between the present results with Refs. [3] and [28]

Parameter	Value
	1578
	29979
	31557
	613.3
	184
	429.3
	3034
	8.576
	0.0858
	2.515
	841.7

 

5.2. Effects of active parameters

 

Fig. 3 shows the values of profit versus pressure ratio of compressor at different values of number of heliostats. It discovers that the values of profit reach a maximum value at . The maximum values of profit are 582.5, 841.7 and 1093 $/h for number of heliostats   1800, 2200 and 2600, respectively at . Therefore, the profit increases from 582.5 $/h to 1093 $/h (87.6%) when the number of heliostats increases from 1800 to 2600 at optimum conditions.

 

Fig. 3: Variations of profit versus  at different values of

Fig. 4 demonstrates the amount of electricity sold to the grid  and the amount of fresh water produced  versus pressure ratio of compressor at . It is interesting to note that the maximum values for  and  occur at  while the maximum value of profit occures at at . These values are 30438 kW and 185.9  at .

 

Fig. 4: Variations of  and  versus  

Fig. 5 shows the cost of electricity  and the cost of fresh water   versus pressure ratio of compressor. Here, the minimum values for  and  occur at . The minmum values are 0.0856  and 2.51  at . These values are less than the selling price of electricity and selling price of fresh water in Table 1. Figures 3, 4 and 5 emphasizes that the objective function must be clearly defined during optimization.

 

Fig. 5: Variations of  and versus  

 

Fig. 6 presents the varations of  and  versus direct normal irradiance . As it can be seen, these values increase with increasing . For example, the values of  increase from 25976 kW to 32381 kW (24.6% increasing) and  increases from 166.6  to 194  (16.4% increasing) as  goes up from 750  to 910 .

 

Fig. 6: Variations of  and  versus  

Fig. 7 shows the varations of  and  versus direct normal irradiance . As it can be seen, these values decrease with increasing . For example, the value of  decreases from 0.0966  to 0.0806  (16.5% decreasing) and  decreases from 2.576  to 2.485  (3.5% decreasing) as  goes up from 750  to 910 . 

 

Fig. 7: Variations of  and versus  

 

Fig. 8 presents a comparison between the values of profit for different values of direct normal irradiance at three different values of gas turbine efficiency  and air compressor efficiency . The figure discovers that the values of profit increase with increasing the values of  and . For example, the value of profit increases from 841.7 $/h to 1028 $/h (22.1% increasing) when  ascends from 0.85 to 0.88 at . Also, the value of profit increases from 841.7 $/h to 931 $/h (10.6% increasing) when  ascends from 0.82 to 0.85 at .

Also, Table 4 represents the exact values ​​associated with Fig. 8.

 

 

Fig. 8: Variations of profit for various values of  at different values of  and

 

 

Table 4: The values of Profit ($/h) at different values of  ,  and

Variable (Unit)	Nafey and Sharaf [3]	Kianfard et al. [28]	Present work
	7.680	8.01	7.766
	1131	1180	1132
	485.9	485.9	485.9
	340.1	340.12	340.13
	64180	64150	64178
	250	253	252
	0.9944	0.9944	0.9944
	6850	6845	6843.9

 

Tables 5 and 6 show the values of  and  for different values of direct normal irradiance at three different values of gas turbine efficiency . These tables discover that the values of  and  increas with increasing the values of . For example, the values of   increase from 29979 kW to 33348 kW (11.2% increasing) when  ascends from 0.85 to 0.88 at . Also, the values of  increase from 184  to 197.9  (7.5% increasing) when  ascends from 0.85 to 0.88 at .

Table 5: The values of  at different values of  and

1

 

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