Economic Analysis of a 

Brackish Water PhotovoltaicOperated (BWRO-PV) 

Desalination System 

Preprint 

Ali Al-Karaghouli and Lawrence L. Kazmerski 

National Renewable Energy Laboratory 

To be presented at World Renewable Energy Congress XI 

Abu Dhabi, United Arab Emirates 

September 25-30, 2010 

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Conference Paper 

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October 2010 

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Economic Analysis of a Brackish Water Photovoltaic-Operated 

(BWRO-PV) Desalination System 

Ali Al-Karaghouli* and Lawrence L. Kazmerski
 

National Renewable Energy Laboratory
 

Golden, Colorado 80401 (USA)
 

* Corresponding author: ali.al-qaraghuli@nrel.gov 

Abstract 

The photovoltaic (PV)-powered reverse-osmosis (RO) desalination system is considered one of the most 

promising technologies in producing fresh water from both brackish and sea water, especially for small 

systems located in remote areas. We analyze the economic viability of a small PV-operated RO system 

with a capacity of 5 m

3

/day used to desalinate brackish water of 4000 ppm total dissolve solids, which is 

proposed to be installed in a remote area of the Babylon governorate in the middle of Iraq; this area 

possesses excellent insolation throughout the year. Our analysis predicts very good economic and 

environmental benefits of using this system. The lowest cost of fresh water achieved from using this 

system is US $3.98/ m3

, which is very reasonable compared with the water cost reported by small-sized 

desalination plants installed in rural areas in other parts of the world. Our analysis shows that using this 

small system will prevent the release annually of 8,170 kg of CO2, 20.2 kg of CO, 2.23 kg of CH, 1.52 kg 

of particulate matter, 16.41 kg of SO2, and 180 kg of NOx. 

Keywords: water desalination, PV system, economic analysis, greenhouse gases reduction, remote area. 

1. Introduction 

Combining renewable energy systems with reverse-osmosis (RO) water desalination offers a viable 

solution to the scarcity of water in remote areas, especially in regions characterized by plentiful solar 

radiation such as the middle of Iraq. The main desirable features for these combined systems are low cost 

(when the site is far enough from the grid), low maintenance requirements, simple operation, very high 

reliability, and suitability for both sea and brackish water. 

Brackish water photovoltaic-operated desalination systems (BWPV-RO) use a standard RO system, but 

are powered by batteries charged by PV arrays. Batteries used in PV-RO systems keep a constant flow for 

24 hours a day, thus maximizing the production and they make use of the invested capital. They also 

maintain the quality of the produced water and help in managing membrane fouling. Without batteries (to 

reduce system capital cost), the power available from a PV array varies with the intensity of sunshine; to 

make the best use of this available power, a connected RO system must also operate at variable power. 

Again, this is contrary to the normal operation of mainstream RO systems. The efficiency of the RO 

system must be maintained over a broad range of operating power; this is particularly challenging in the 

balance of the plant. Numerous desalination plants using a PV-RO system with and without batteries have 

been implemented in different parts of the world [1]. 

In this work, the BWPV-RO system were analyzed economically by using HOMER software program 

developed by the U.S National Renewable Energy Laboratory [2] and information from Pure Aqua for 

water treatment and reverse osmosis company [3]. 

2. RO System Selection 

In an RO system, water analysis is required before selecting a system. Based on the water analysis, one 

can determine the pre-filtration required before the RO unit. In addition, the water analysis will determine 

the type, number, and configuration of membranes, as well as the pumps and motors. The pre-treated feed 

water is forced by a high-pressure pump to flow across the membrane. The desalted water (permeate 

1 
 

 

 

 

 

 

 

 

 

 

 

 

 

water) passes through the membrane, whereas the majority of the dissolved solids is rejected from the 

membrane as high-pressure brine. Brackish-water RO systems usually operate at a higher (water) 

recovery ratio than seawater systems. Thus, the proportion of the energy in the concentrate is lower and 

the importance of brine-stream energy recovery is reduced. Post-treatment is necessary before the water 

end-use. Figure 1 shows a schematic diagram of a BWRO unit. 

Figure 1. Schematic diagram of a BWRO unit. 

3. HOMER Input Data 

The solar radiation data for the Babylon governorate in the middle of Iraq (32o 29” N latitude and 45o 28” 

E longitude) were obtained from the NASA surface meteorology and solar energy Web site [4]. The 

annual average solar radiation for this region is 5.52 kWh/m2

/day. Figure 2 shows the site solar resource 

profile over a 1-year period. The proposed PV system used to power the RO units, which will be analyzed 

by HOMER, consists of PV modules, batteries, charge controller, inverter, auxiliary diesel generator, and 

the rest of the balance-of-systems (i.e., modules structure, wiring, fuses, and other system safety devices). 

The prices for the PV system devices were taken from the Solarbuzz Company report [5] for solar energy 

electricity. 

Figure 2. Monthly average solar radiation and clearance index. 

4. HOMER Optimization Analysis 

In HOMER, the best possible or optimal system configuration is the one that satisfies the user-specified 

constrains at the lowest total net present cost (NPC) [2]. In this analysis, to supply 5 m3

/day of fresh water 

using an RO/PV system, we considered two cases: 

2 

Saline

Feedwater

Pre-Treatment

High

Pressure

Pump

Membrane

Assembly

Concentrate

Discharge

Fresh

Water

Fresh

Water

Post-Treatment
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

A. BWRO-1500 unit/PV system running 24 hours per day 

B. BWRO-6000 unit/PV system running 6 hours per day. 

For case A, the RO unit daily load and peak wattage was found to be 20 kWh/day and 1.62 kW, 

respectively [3]. At a diesel fuel price of US$0.4/liter and 0% interest rate (I.R.), the results of the 

HOMER analysis show that the optimum PV system comprises 4.1 kW of PV modules, a 1.6-kW 

inverter, 40 batteries (6 V and 25 Ah each), and a 1.8-kW auxiliary diesel generator. The total system 

NPC is US$53,988, and the cost of electricity produced is US$0.296/kWh. When using the PV system 

only, the system comprises 5 kW of PV modules, a 1.6-kW inverter, and 50 batteries (6 V and 325 Ah 

each). The total NPC is US$56,800, and the cost of electricity produced is US$0.314/kWh. When using a 

diesel generator only, a 1.8-kW unit is required, and the system NPC is US$90,150 and electricity 

production cost is US$0.494/kWh. Table 1 shows the HOMER optimization results for this case. 

Table 1. HOMER optimization results for case A at 0% interest rate and US $0.4/L of diesel 

For case B, the RO unit daily load and peak wattage was found to be 7.2 kWh/day and 2.3 kW peak, 

respectively [3]. At a diesel fuel price of US$0.4/liter and at 0% interest rate, the results of the HOMER 

analysis show that the optimum PV system comprises 1.6 kW of PV modules, a 2.0-kW inverter, 6 

batteries (6 V and 325 Ah each), and a 1.0-kW diesel generator. The total system NPC is US$16,984 and 

the cost of produced electricity is US$0.259/kWh. When using a PV system only, the system comprises 3 

kW of PV modules, a 2.0-kW inverter, and 6 batteries (6 V and 325 Ah each). The total NPC is 

US$23,250 and the cost of electricity produced is US$0.356/kWh. When using a diesel generator only, a 

1.8-kW unit is required, and the system NPC is US$24,499 and the electricity production cost is 

US$0.374/kWh. Table 2 shows the HOMER optimization results for this case. 

Table 2. HOMER simulation result for case B at 0% interest rate and US $0.4/L diesel fuel 

3 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

To study the effect interest rate and the change in fuel price, we considered an I.R. of 6% and a fuel price 

of US$1.0/liter. Table 3 shows the change in electricity production cost for the three systems due to the 

change in I.R. and fuel price. 

Table 3. Cost of electricity for the three systems and both types of units 

Electricity Production Cost (US$/kWh) 

PV System and Auxiliary Generator PV System Only Generator Only 

RO-1500 unit 

24 h/day load 

RO-6000 unit 

6 h/day load 

RO-1500 unit 

24 h/day load 

RO-6000 unit 

6 h/day load 

RO-1500 unit 

24 h/day load 

RO-6000 unit 

24 h/day load 

I.R. $0.4/L $1.0/L $0.4/L $1.0/L $0.4/L $1.0/L $0.4/L $1.0/L $0.4/L $1.0/L $0.4/L $1.0/L 

0% 0.296 0.309 0.259 0.273 0.314 0.314 0.356 0.356 0.494 0.749 0.374 0.596 

6% 0.445 0.503 0.426 0.489 0.532 0.532 0.663 0.663 0.512 0.767 0.412 0.636 

5. Water Production Cost 

Several parameters have a large impact on the price of the permeate water produced by an RO unit. These 

parameters include the following: 

1. Initial cost of the unit 

2. Installation cost of the unit 

3. Cost of electricity or fuel needed to operate the unit 

4. Operation cost of the unit 

5. Membranes and filters replacement cost 

6. Maintenance and repair cost. 

The cost of produced water is found by calculating the lifetime system cost (i.e., initial, operation, 

replacement, and maintenance costs) divided by the amount of water in m3 produced during the lifetime of 

the RO unit. The initial and other costs (20-year lifetime) for the RO units are taken from the Pure Aqua 

Company’s information on water treatment and reverse osmosis (Table 4), and HOMER calculated the 

cost of electricity or fuel needed to run these units. Table 5 shows the estimated price of the fresh water 

produced. 

Table 4. RO capital and operating cost 

Item RO-1500 Unit (US$) RO-6000 Unit (US$) 

1. Initial and installation cost 

2. Operation labor cost 

3. Membrane cost 

10,000 

62,940 

5,000 (1 every 2 years) 

15,000 

62,940 

20,000 (4 every 2 years) 

Table 5. Cost of fresh water for the three systems and both types of load 

Water Production Cost (US$/m3) 

PV System and Auxiliary Generator PV System Only Generator Only 

RO-1500 unit 

24 h/day load 

RO-6000 unit 

6 h/day load 

RO-1500 unit 

24 h/day load 

RO-6000 unit 

6 h/day load 

RO-1500 unit 

24 h/day load 

RO-6000 unit 

24 h/day load 

I.R. $0.4/L $1.0/L $0.4/L $1.0/L $0.4/L $1.0/L $0.4/L $1.0/L $0.4/L $1.0/L $0.4/L $1.0/L 

0% 3.98 4.04 4.43 4.49 4.06 4.06 4.82 4.82 4.80 5.80 4.89 5.78 

6% 5.14 5.38 5.67 5.91 5.49 5.49 6.61 6.61 5.40 6.42 5.61 6.48 

4 
 

 

 

 

 

 

 

 

 

 

The cheapest price is found to be US$3.98 per m3 of fresh water at 500ppm produced by the RO500 unit operated by a PV system and auxiliary generator at diesel price of US$0.4/L and 0% 

I.R. If it is difficult to provide diesel and adequate maintenance to the generator in a remote area, 

then the second choice is to use PV system only to run the RO unit. The price of the fresh water 

produced from this system is US$4.06 which is still a reasonable price compared to water price 

we could get by using a diesel generator alone in remote areas. The cost of the produced fresh 

water is shown in table5. 

6. Environmental Benefits of Using PV-Operated RO System 

Our HOMER software analysis calculated the reduced amounts of greenhouse gases (GHG) and 

found that a significant annual reduction is achieved using this small system, as presented in 

Table 6. 

Table 6. GHG emission reduction 

Pollutant CO2 CO Hydrocarbon Particulate Matter SO2 NOX 

Emission (kg/yr) 8,170 20.2 2.23 1.52 16.41 180 

7. Conclusion 

We used HOMER software to find the optimum power system to run two types of small RO 

units to desalinate brackish water (from 4000 to 500 ppm total dissolved solids). One of these 

units runs for 24 hours per day (RO-1500), and the other runs for 6 hours per day (RO-6000) to 

produce the same amount of fresh water (5 m3/day). The results show that the optimum system 

uses a PV system with an auxiliary diesel generator for both types of RO units. The PV system 

NPC, the cost of electricity produced to run the RO-1500 unit and the cost of the fresh water 

produced from this unit is found to be US$53,998, US$0.296/kWh, and US$3.98/m3 

respectively. For the RO-6000 unit, we found the PV system NPC, cost of electricity, and cost of 

fresh water produced to be US$16,998, US$0.259/kWh, and US$4.43/m3

, respectively. The cost 

of the produced water is very reasonable compared to the cost of water produced by desalination 

plants installed in remote areas in other parts of the world. The environmental benefits of using 

the PV system are also significant, as shown in Table 11. The results of this study show the 

economic feasibility and advantage of using this type of system in remote areas. 

8. References 

[1] C. Fritzmann, J. Löwenberg, T. Wintgens, and T. Melin (2007) State-of-the-art of reverse osmosis desalination, 

Desalination 216, pp. 1–76.
 

[2 HOMER: The Micro-Power Optimization Model. Software produced by NREL. Available
 

at www.nrel/gov/HOMER; 2004. 

[3] Pure Aqua for water treatment and reverse osmosis company, www.pureaqua.com. 

[4] NASA Surface Meteorology and Solar Energy, 2004. Available from http://eosweb.larc.nasa.gov/sse/. 

[5] Solarbuzz LLC, August 2008. Solar Energy Electricity Prices Report. Available from www.solarbuzz.com. 

5 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Economic Analysis of a Brackish Water Photovoltaic-Operated 

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14. ABSTRACT (Maximum 200 Words) 

The photovoltaic (PV)-powered reverse-osmosis (RO) desalination system is considered one of the most 

promising technologies in producing fresh water from both brackish and sea water, especially for small 

systems located in remote areas. We analyze the economic viability of a small PV-operated RO system 

with a capacity of 5 m3/day used to desalinate brackish water of 4000 ppm total dissolve solids, which is 

proposed to be installed in a remote area of the Babylon governorate in the middle of Iraq; this area 

possesses excellent insolation throughout the year. Our analysis predicts very good economic and 

environmental benefits of using this system. The lowest cost of fresh water achieved from using this 

system is US $3.98/ m3, which is very reasonable compared with the water cost reported by small-sized 

desalination plants installed in rural areas in other parts of the world. Our analysis shows that using this 

small system will prevent the release annually of 8,170 kg of CO2, 20.2 kg of CO, 2.23 kg of CH, 1.52 kg 

of particulate matter, 16.41 kg of SO2, and 180 kg of NOx. 

15. SUBJECT TERMS 

water desalination; PV system; economic analysis; greenhouse gases reduction; remote area 

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