Khan2018

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Renewable and Sustainable Energy Reviews
journal homepage: www.elsevier.com/locate/rser
A hybrid renewable energy system as a potential energy source for water
desalination using reverse osmosis: A review
Meer A.M. Khana,⁎
, S. Rehmanb
, Fahad A. Al-Sulaimana
a
Center of Research Excellence in Renewable Energy (CoRERE), Research Institute, King Fahd University of Petroleum & Minerals, Dhahran 31261, Saudi Arabia
b
Center of Engineering Research, Research Institute, King Fahd University of Petroleum & Minerals, Dhahran 31261, Saudi Arabia
A R T I C L E I N F O
Keywords:
Renewable energy
Hybrid renewable energy systems
RO Desalination
Solar PV desalination
Wind desalination
A B S T R A C T
The water needs of the inhabitants of Saudi Arabia are met by desalination powered by electricity generated
from fossil fuel. Excessive burning of fossil fuels results in faster depletion and causes an adverse impact on the
local environment. Reverse osmosis (RO) desalination based on a hybrid renewable energy system (HRES) has
emerged as a cleaner alternative. The primary objective of this review is to assess the current status of utilizing
renewable energy for small and large-scale water desalination plants. An overview of the expansion of domestic
and global desalination plant capacities is presented with the evaluation of Saudi Arabia’s renewable energy
potential. Numerous studies on coupling various combinations of renewable energy sources to power desali-
nation processes are reviewed. A comprehensive analysis of the trends and technical developments of PV-RO,
Wind-RO, and hybrid PV-Wind-RO for a wide range of capacities over the past three decades is provided.
Designing and modeling HRES-RO desalination systems using different combinations of renewable energy
sources are thoroughly analyzed and the technical aspects of their performance are presented. The application of
a range of optimization and sizing software tools available for conducting pre-feasibility analysis and the
comparison of the available software tools for HRES-RO desalination are also presented. The study also de-
monstrated that the replacement of fossil fuel with renewable energy for desalination will significantly decrease
greenhouse gas emissions. The review also highlights the effect of solar and wind profiles on the economics of
desalination powered by renewables. The economic analysis indicates a significant decrease in the cost of water
production by hybrid PV-wind-RO systems, implying good prospects for the technology in the near future.
Finally, the study provides a flowchart depicting the steps involved in installing a hybrid PV-wind-RO system
in KSA.
1. Introduction
Water and energy are the essential commodities in the present
world for sustaining life. A major portion of the globe is covered by
water bodies primarily in the form of oceans, seas, and bays, in addition
to ground water and other salt water bodies. Only 3% of the total assets
of water is available in the form of freshwater, while the remaining 97%
is salt water [1]. Most of the freshwater is either available underground
which is hard to reach or in the form of frozen glaciers, permafrost, and
ice. Approximately 70% of the total consumption of water is used for
agriculture, while industries account 20%, and the remaining 10% is
used to meet the overall household needs. Water scarcity is the major
problem facing by the world at present with increasing demands of
good quality of water in many regions due to the massive increase in
the population and the growth of the economies [2]. Water from seas
and other saline water bodies are not suitable for direct human con-
sumption, agricultural and industrial purposes. According to the World
Health Organization (WHO) standards, the maximum allowable limit of
total dissolved solids (TDS) in water is around 500 ppm. However, these
water bodies have TDS in the range of 10,000–45,000 ppm [3]. Thus,
shortage of freshwater in many areas can be alleviated by the desali-
nation of saline water.
Desalination is the process of the removal of salts from the feed-
water, typically containing a high concentration of salts (brine), to
produce freshwater (containing a low concentration of salts) [4]. De-
salination is one of the earliest forms of water treatment used by
mankind, which has become a sustainable alternative solution for water
scarcity problem in the residential and industrial sectors. Water desa-
lination became lifesaving technology, especially in the Middle East and
African countries where the rainfall is inadequate. Among the countries
https://doi.org/10.1016/j.rser.2018.08.049
Received 22 January 2018; Received in revised form 7 June 2018; Accepted 24 August 2018
⁎
Corresponding author.
E-mail address: meerkhan@kfupm.edu.sa (M.A.M. Khan).
Renewable and Sustainable Energy Reviews 97 (2018) 456–477
1364-0321/ © 2018 Elsevier Ltd. All rights reserved.
T

in the Middle East, Saudi Arabia is a vast country with its inhabitants
distributed far and wide. Thus, the country has resorted to seawater
desalination and transportation of sweet water by various means to the
interior regions to meet its freshwater demands.
A detailed analysis of the global, regional, and domestic or re-
sidential utilization of sweet water and the available renewable energy
sources in Saudi Arabia are provided in this section. In Section 2, the
state-of-the-art technological advancements for water desalination
based on renewable energy, such as wind, solar, and hybrid renewables
are discussed. The goal of this review is to survey the leading desali-
nation technologies based on renewables and demonstrate the suit-
ability of renewable-energy-based water desalination for both small and
large-scale sweet water production. Renewable energy sources such as
wind and solar are abundant in almost every part of the Kingdom of
Saudi Arabia. Hence, renewable energy can be economically utilized for
the distributed small-scale production of sweet water in remote areas.
This approach will reduce the dependency on fossil fuel for water de-
salination and minimize the cost and risk of water distribution to re-
motely located populations of Saudi Arabia. As sweet water can be
produced close to remotely located populations, the utilization of re-
newable energy for water desalination will minimize the sweet water
transportation costs.
1.1. Global desalination capacities
Water desalination technologies were developed several decades
ago due to the fact that 42 cities of the 71 largest cities that do not have
access to adequate freshwater resources are located along a coast [5].
International Desalination Association (IDA) indicates that currently,
about 18,500 desalination plants operating in 150 countries with a
maximum contracted capacity of around 99.8 million cubic meters of
water per day as of 2017 [6]. The largest producers of desalinated water
according to the IDA are Saudi Arabia, UAE, Spain, Kuwait, and Algeria
[7]. Despite the fact that desalination technology is an energy-intensive
process, it is best suited for remote areas where there is no other al-
ternative. One example of oil abundant Middle East countries where
energy is available at a low cost but the cost of transportation of sweet
water is high [8]. Recent estimates indicate that about 53% of the
world's desalination potential is installed in the Middle East and North
Africa (MENA) regions followed by North America and Asia [9] as
shown in Fig. 1.
In the United States, 325 desalination facilities are operational.
According to the Texas Water Development Board [10], Florida is the
leading region utilizing desalination technology in states with 150 op-
erational desalination plants and their capacities to increase by another
25% by 2025, equivalent to 33 million cubic meters per day [11]. Texas
has 46 desalination facilities with an aggregate capacity of 465,605 m3
/
day [10]. About 1,000 desalination plants are operational in India with
Nomenclature
m3 Cubic meter
ppm Parts per million
TDS Total dissolved solids
RES Renewable energy system
SW/BW Seawater / Brackish water
ERD Energy Recovery Drive
V Volts
W Watts
kW Kilowatt
MW Megawatt
GW Gigawatt
PW Petawatt
kWp Kilowatt peak
kWh/m3
Kilowatt-hour per cubic meter
GWh Gigawatt hour
TWh Terawatt hour
Ah Ampere-hour
m2
Square meter
h/day Hours per day
l/day Liters per day
L/min Liters per minute
m3
/day Cubic meter per day
m3
/h Cubic meter per hour
m/s Meter per second
LCOE Levelized cost of Energy
$/m3
US dollar per cubic meter
$/kWh US dollar per kilowatt hour
ipvc PV module current
Vpv PV module voltage
Iph Photo-generated current in a PV cell
Ns No. of solar cell is series
Np No. of solar cells in parallel
η Ideality factor of diode
IRS Reverse saturation current
vT Thermal voltage
Pmax Maximum power output of a PV module
λ Tip speed ratio
ω Wind turbine speed
v Wind speed
Cp Maximum power coefficient
β Blade pitch angle
A Swept area of the blade
IPV Total current of a PV system
IWC Total current of a wind system
IL Load current
Q Charge transfer in a battery
Cbat Battery capacity
ηc Battery coulomb efficiency
Δ Self-discharge coefficient
Edeg energy generated by the diesel engine
Pdeg Rated power of diesel generator
ηDeg Diesel generator efficiency
ηoverall Total efficiency of the generator
QF Feed water flow
QB Brine water flow
QP Portable water
Ωf Motor pump angular speed
θvr Valve reject opening
Ce Feed water salinity
Qp Permeate flow
CoW Cost of Water
Fig. 1. Distribution of worldwide desalination capacity adapted from [9].
M.A.M. Khan et al. Renewable and Sustainable Energy Reviews 97 (2018) 456–477
457

a capacity of 291,820 m3
/day [12]. China is also among the leading
countries with 57 desalination plants of varying capacity. The largest is
the Tianjin seawater desalination plant developed by IDE with a ca-
pacity of 200,000 m3
/day [13]. Plants commissioned worldwide re-
cently, based on the capacities and energy consumption as given by the
Global Water Intelligence (GWI) Desaldata are summarized in Table 1.
A review highlighting the technological development and cost
trends of most popular commercial desalination processes, including
multi-effect distillation (MED), multistage flash distillation (MSF),
vapor compression (VC), reverse osmosis (RO), and electrodialysis (ED)
[15,16]. Almost all of the energy consumed by conventional desalina-
tion plant is derived from the combustion of fossil fuels, which con-
tribute to global warming and acid rain with the emission of green-
house gases (GHGs) as well as other harmful releases [17]. In addition,
the fossil fuel reserves are depleting, new and alternative clean and
renewable energy sources must be harnessed for energy security and
future sustainable development. According to Demirbas [18], the pet-
roleum reserves will be exhausted in less than 50 years if the con-
sumption continues at the present rate.
1.2. Domestic desalination capacity trend
Majority of the countries in the Middle East are located in the semi-
arid and arid regions with high evaporation rates. These regions rely on
conventional power generation resources for the desalination of sea-
water to meet the freshwater requirements [19]. In Saudi Arabia, the
Saline Water Conversion Corporation (SWCC) plays a major role in
providing desalinated water, with 28 plants in operation along the Red
Sea and the Arabian Gulf coasts. The actual desalinated water supplied
and the designed capacity during the year 2010 was 833.1 and 905.7
million cubic meters, respectively. By 2015, over a period of six years,
the actual water supplied increased to 1443.6 million cubic meters
(around 60% increase in the designed capacity) as shown in Fig. 2.
The average daily production of sweet water in 2015 was around 4
million cubic meters per day which increased to 5 million cubic meters
per day by the end of 2017 [21]. By 2025, SWCC has planned to boost
the water production to 8.5 million cubic meters per day. The SWCC
produces desalinated water using the dual-cycle MSF system driven by
electrical power. Thus, the dual-purpose desalination plants not only
generate the power required for the desalination process but also export
the excess energy to the Saudi Electric Company (SEC). Hence, the
SWCC is also involved in power generation with a production capacity
of 30.03 million MWh in 2015 [20]. An Independent Water & Power
Project (IWPP) at Shuaibah, is operating on a dual-cycle plant with
power generation and desalinated water capacities of 900 MW and
880,000 m3
/day, respectively [22]. Similarly, Jubail IWPP with in-
tegrated water and power facility has a power generation capacity of
2745 MW and desalination capacity of 800,000 m3
/day, respectively
which uses MED and thermal vapor compression (TVC) techniques
[23]. Jeddah Phase IV uses RO membranes to produce 400,000 m3
/day
of sweet water sufficient to meet the water requirements of five million
people [24].
1.3. Domestic renewables scenario
The fundamental constraint of a desalination framework is that it
requires a huge amount of energy. The utilization of renewable sources
such as solar, wind, hydro, biomass, and geothermal to operate desa-
lination plants as a promising sustainable solution to supply freshwater
in regions where energy is scarce has been explored [25]. The countries
of the Middle East have emerged as key players in the use of sustainable
power sources, including solar, wind, hydro, and other sources with an
installed capacity of renewables of 18.9 GW, with the Saudi Arabia
share of 92 MW [26].
The major strengths of KSA in the area of renewable energy are the
presence of high solar radiation levels with average yearly values of
over 2200 kWh/m2
and longer duration of sunshine hours [27–35]. The
Kingdom has made strategies to deploy 9.5 GW of renewable energy
capacity according to Saudi Vision 2030 [36]. Recent years have wit-
nessed a significant growth in projects that harness solar energy. Some
of the commissioned and planned projects in Saudi Arabia are given in
Table 2. A 10.5 MW capacity photovoltaic (PV) power plant (solar car
park) was commissioned by Saudi Aramco in 2012. Two other plants of
relatively of smaller capacity with installed capacities of 5.4 MW and
3.5 MW were set up in Jeddah and Riyadh, respectively, in 2013 [37].
Princess Noura Bint Abdul Rahman University in Riyadh has installed a
solar thermal plant with a 25 MW rated capacity capable of producing
900,000 liters of hot water daily for students and various laboratories in
the university [38]. The Layla PV project involves the construction of
50 MW solar photovoltaic power plant and involves the installation of
solar panels, generators, transformers and transmission lines [37]. A
100 MW solar PV power plant is expected to be commissioned in Mecca
by 2018 [37]. Sakaka 300 MW PV power plant project awarded to
ACWA Power is expected to be commissioned by 2019 [39]. (Table 2).
In this paper, many technologies used for the desalination of water
using renewable sources of energy are reviewed. As solar energy is
abundantly available and is clean, it can be used to generate the power
required for the desalination plants. Wind energy is another promising,
clean, and a renewable source of energy available in Saudi Arabia
[40–48], which can be used to generate power for operating
Table 1
Most recently commissioned desalination plants [6,14].
NAME Capacity (m3
/d) Location Energy consumption Commissioned
year
Carlsbad desalination plant 204,390 San Diego, USA < 3.3 kWh/m3
2015
Al Ghubrah independent water project 191,000 Oman 3.2–4 kWh/m3
2015
Al Fujairah IWPP expansion 136,000 UAE – 2015
Sadara Marafiq 148,800 Saudi Arabia 4.35 kWh/m3
2016
Barka IWPP expansion 56,780 Oman 4.2 kWh/m3
2016
Ras Abu Fontas A3 163,656 Qatar 4.5 kWh/m3
2017
Aqaba 13,680 Jordon 3.2 kWh/m3
2017
Fig. 2. The amount of desalinated water produced by the SWCC from 2010 to
2015 [20].
458

desalination plants, especially in the coastal areas. Due to the inter-
mittent nature of the wind and solar resources, in most cases, a single
renewable energy source is not sufficient to meet the power require-
ments for maintaining uninterrupted operation of desalination plants.
Hence, hybrid renewable power systems have been designed [49–53]
and integration of desalination power plants will be a promising option.
Major advances in the exploitation of solar and wind energy resources
have paved the way for using renewable energy resources to provide
the necessary energy for operating small-scale and large-scale desali-
nation plants [54].
2. Desalination and renewable energy
2.1. Desalination technologies
A range of seawater desalination technologies has been developed
to meet the demand of freshwater in arid regions of the world in the
past two to three decades. Although a variety of sophisticated desali-
nation methods are available for freshwater production, extensive re-
search and development (R&D) activities are being undertaken to im-
prove the existing technology and reduce the cost of desalination [55].
Commercially acceptable, economically viable and reliable desalination
processes are based on two main methods as shown in Fig. 3.
a. Thermal or distillation methods include MSF, MED, and VC pro-
cesses.
b. Membrane methods include RO and ED processes.
Currently, RO is the most effective water desalination technology
that does not require thermal energy. Power consumption for the RO
process ranges from 2 to 5 kWh/m3
depending upon the type of water
selected for desalination, i.e., brackish water or seawater [57]. A typical
RO system includes a pre-treatment and post-treatment process, high-
pressurized pumps, an assembly of the membranes. In general, the
energy consumption of an RO plant can be reduced from 8 kWh/m3
to 4
kWh/m3
by the installation of an energy recovery device (ERD) [58].
Thus, most of the current RO plants are equipped with an energy re-
covery system, where the energy of the pressurized brine (untreated
water remaining after the RO process) is transferred to the feed-water
by means of pressure exchangers. Thus, the cost of RO based desali-
nation has been reduced both due to the improvement in the membrane
technologies and the introduction of energy recovery drives [59]. On
the other hand, some emerging technologies such as membrane dis-
tillation (MD) and forward osmosis (FO) have demonstrated and have
the potential for treating highly saline water with a minimum energy
consumption [60].
The global desalination capacity have grown significantly, in 2012
RO technology accounted for 55% followed by MSF and MED providing
35% and 11%, respectively [61]. According to the IDA, by 2014 RO
technology progressed significantly and accounted for 65% of the de-
salination capacity followed by MSF with 21%, and other methods
accounting for the remainder as shown in Fig. 4 [62]. The RO tech-
nologies for seawater desalination plants was first commercialized in
1980 in the MENA region with the installation of a plant in Jeddah,
Saudi Arabia [63]. The high salinity and the extreme temperatures in
the Gulf region are important parameters in determining the choice of
the desalination technology. Membrane desalination technique (espe-
cially RO) has been extensively used to increase the desalination ca-
pacities in areas other than the Gulf [64]. The use of RO membrane
technology has grown rapidly in the past 40 years in two different
applications; (i) seawater reverse osmosis (SWRO) and (ii) brackish
water reverse osmosis (BWRO). The RO modules can be arranged either
in series or in parallel or even as a combination of both [65]. In some
cases, the desalination process involves a combination of both thermal
and membrane technologies to produce potable water [66]. The
adoption of a simple configuration incorporating the MSF and single
stage RO processes has been described by Osman [67]. A hybrid de-
salination plant based on MSF and RO technologies was commissioned
in 2014 by the SWCC in Ras Al-Khair, with a capacity of 728 million
liters of water per day [68].
Desalination based on RE sources is a now emerging as a technology
for producing potable water without leaving a carbon footprint. Fig. 4
shows a breakdown according to the renewable energy source used for
desalination in 2014 [64]. Many small-scale RE based desalination
plants have been installed and successfully operated with minimal
maintenance. However, their output is negligible when compared to the
global capacities [17,25,56,66], [69–71]. Solar PV dominates its share
in renewable energy by contributing 43% of in water desalination fol-
lowed by solar thermal 27% and Wind 20% respectively [72], as de-
picted in Fig. 4. Possible options for water desalination based on re-
newable energy sources are shown in Fig. 5.
Thermal and electrical energy are the two forms of energy that can
be extracted from RE sources. Thermal energy can be used to power
desalination processes such as those based on MSF, MED, MD, solar
still, and humidification-dehumidification (HD) techniques, while
electrical energy can be used to power desalination processes such as
those based on RO and ED techniques.
2.2. Solar powered desalination
Solar energy is the most abundant forms of energy available on the
planet, reaching earth’s surface at a rate of 120 Petawatt (PW). Thus,
the energy received from the sun in a single day is sufficient in the
world’s energy demand for at least 20 years [73]. Solar-driven desali-
nation is one of the most promising technologies due to its environ-
ment-friendly nature [74,75]. Solar-driven desalination technologies
can be broadly classified into indirect and direct collecting methods.
Solar stills and HD desalination are the simplest methods that fall
under the direct collecting methods. Indirect solar collecting methods
are used in commercial desalination processes, such as MSF, MED, and
Table 2
Solar Projects in Saudi Arabia [37]& [38].
Name Size Location Year
Saudi ARAMCO solar car park 10.5 MW Dhahran 2012
Princess Noura Bint Abdul Rahman university 25 MW Riyadh 2012
King Abdulaziz international airport development
project
5.4 MW Jeddah 2013
KAPSARC project 3.5 MW Riyadh 2013
KAPSARC II Project 1.8 MW Riyadh 2014
Layla PV power plant 50 MW Riyadh 2015
Al-Khafji PV plant 15 MW Khafji 2017
Solar energy project 100 MW Mecca 2018a
Sakaka PV power plant 300 MW Jouf 2019a
a
Are expected to be operational.
Desalination
Multi Stage Flash
Distillation
Multi Effect
Distillation
Vapor
Compression
Thermal Process Membrane Process
Reverse Osmosis
Electrodialysis
Fig. 3. Desalination Techniques.
459

RO [75]. Solar stills and HD desalination methods utilize solar energy
directly to produce distilled water. The solar still replicates the natural
hydrological cycle of evaporation and condensation, the simplest form
being the evaporation of water in a container and the condensation of
the water vapor on the top cover to produce potable water. A detailed
literature review on solar stills is provided in [76,77]. In the HD de-
salination method, hot air is passed over salty water to humidify the air,
followed by the condensation of the water vapor in the humid air to
obtain sweet water. A review highlighting various HD methods can be
found in [78,79]. Ali et al. [75] have published an overview and an
economic analysis of an HD plant based on solar energy in Jeddah,
Saudi Arabia. A solar chimney is also capable of converting solar
thermal energy into kinetic energy which shall be converted into
electrical energy. The kinetic motion of the heated air moving upwards
through the chimney can operate the turbo-generator located at the
bottom of the chimney to produce power [80]. Zuo et al. [81] have
reported a study evaluating an integrated solar chimney power plant
and a desalination system using mathematical modeling.
Indirect desalination processes involve the conversion of solar en-
ergy into electrical or thermal energy to run a range of membrane and
thermal processes of desalination. These can be divided into two broad
methods; (i) capturing and utilizing the thermal energy from the sun,
and (ii) the use of PV devices to generate electricity [49]. An argument
can be made that solar thermal systems are the better-suited methods
for powering desalination processes over solar PV systems, considering
that the thermal energy can be utilized directly with little or no
transformation into electrical energy [82]. On the other hand, solar
energy can be utilized to power SWRO plants through a PV array that
harnesses solar radiation and produces electricity. Also, solar collectors
can be used either in the concentrating mode or the non-concentrating
mode to harness heat to power distillation methods [83].
2.3. Photovoltaic powered RO desalination
Photovoltaic systems convert the direct incident solar radiation into
electrical energy based on the principle of the photoelectric effect dis-
covered by Becquerel in 1839. As this method can use diffused com-
ponents of the incoming solar radiation, PV technology is suitable for
areas with both high and low direct solar irradiance. PV powered de-
salination systems are commercially available as standalone systems
[84]. The main difficulty for such systems is the high initial cost and the
intermittent nature of solar energy. With the significant advances in the
field of photovoltaics, these systems are preferred to conventional
generators due to several reasons. They are environment friendly, i.e.,
no sound and air pollution, require minimum maintenance, and can
generate power throughout their lifespan [66]. PV-powered desalina-
tion systems include PV arrays, inverters, battery banks, and thermal or
membrane processes for desalination [66]. In PV-RO desalination sys-
tems, direct current (DC) electricity is generated by the PV arrays can
be used to run the high pressure pumps to feed water to exude the
permeate from the RO membranes [85]. As described by Mahmoud and
Ibrik [86], either RO or ED water desalination technology can be con-
nected to a PV generator, that provides a feasible option for desalina-
tion in remote areas [86]. A schematic representation of a PV-RO
Fig. 4. A breakdown of water desalination capacity based on the technology and the type of renewable energy used.
Fig. 5. Options for desalination technologies based on renewable energy resources.
460

system is shown in Fig. 6. The system comprises of a PV generator, a
pre-treatment setup, a membrane assembly, and a post-treatment setup.
The power generated from the PV system is supplied to the RO plant to
drive the pumps required for the desalination process. Pre-treatment
involves filtration to remove sand, silt, or organic residues that are
present in the intake. Post-treatment ensures the chemical balance of
the desalinated water, thus maintaining the required pH of the water.
Research and commercialization of PV-RO desalination technolo-
gies have been underway for more than three decades. Gaining a
thorough understanding of this technological trend is extremely im-
portant. In 1979, a small solar PV project was established by Petersen
et al. [87] to power an RO unit with a freshwater production capacity of
1.5 m3
/day. The system was made of 14 PV panels, producing 2.5 kWp
power and occupying an area of 30 m2
[87]. With the concept of in-
tegrating PV and RO systems, the world’s first solar power-driven sea-
water reverse osmosis system was installed in Jeddah, Saudi Arabia in
early 1980′s by Boesch [88]. This plant generated a peak output power
of 8 kWp from 210 mobile Tyco PV modules. The modules were con-
nected to charge a battery bank of 40 batteries to drive a two-stage
membrane RO system that produced 4.5 L/min of fresh water with a
recovery rate of 22% [88]. In 1998 Gocht and Sommerfeld [89] in
Jordon, conducted a study on a pilot plant comprising of a direct PV
coupled reverse osmosis system with a freshwater capacity of 40 m3
/
day. The estimated daily energy consumption of the plant was 125
kWh/d. The simulation study was performed on a plant configuration
consisting of a 32 kWp PV generator and a battery storage of 120 kWp.
The authors performed a socio-economic evaluation using the UNIDO
approach for the cost-benefit analysis (CBA). The following three cases
were evaluated for the CBA:
Case 1. 24 h of RO system operation per day powered by a PV array
Case 2. 08 h of RO system operation per day powered by a PV array
Case 3. 10 h of RO system operation per day powered by a diesel
generator
Case 2 demonstrated better economic performance than Case 1.
Gocht and Sommerfeld [89] preferred and recommended Case 2, con-
sidering the socio-economic and environmental parameters, even
though Case 3 performed economically better than the other two cases.
Tzen et al. [90] conducted a study on an autonomous PV-RO de-
salination system to cater to the potable water needs of a rural com-
munity. The study location was Chbeiika Center, about 50 km south of
Tan-Tan city near the Atlantic coast of Morocco. The RO system with a
load of 9 kW was operated by PV generators producing 20.5 kW of
power. The performance of the PV array and battery sizing was
evaluated along with an economic analysis and is reported in [90].
Hasnain and Alajlan [91] conducted a research and development pro-
ject at the King Abdullah City for Science and Technology (KACST) in
the Energy Research Institute (ERI) to power an RO water desalination
plant based on a solar PV system in Riyadh, Saudi Arabia. A total of
11.78 kWp of power was required from the PV panels to operate the
pumps and the RO units. As the amount of rejected brine from these
units was significantly high, a solar still plant with a capacity of 5.8 m3
per day was designed and integrated to the existing PV-RO plant to
utilize the brine water instead of discharging it to the environment
[91]. The proposed design can serve as a 100% solar-powered desali-
nation plant dedicated to a given location with an estimated cost of
water of US$ 0.5/m3
.
Suleimani and Nair [92] have conducted an experimental analysis
in Oman on a system comprising of 23.2 m2
PV generators with a peak
capacity of 3.25 kWp, a 200 Ah boost charge battery, a charge con-
troller, and an inverter interlinked to the RO process capable of gen-
erating an output flow of up to 7.5 m3
/day. The authors estimated the
cost of production to be $ 6.52/m3
over the 20-year lifetime of the plant
[92]. The Energy and Water Research Center of the Canary Islands
Technological Institute (CIEA-ITC) and Aachen University of Applied
Sciences installed an RO plant that has an average water production
rate ranging from 0.8 to 3.0 m3
/d at the test fields in Pozo Izquierdo,
Gran Canarian Island. The plant included a stand-alone 4.8 kWp PV
system and an additional battery storage of 60 kWh (Herold and Nes-
kakis [93]). Thomson and Infield [94] have also performed an analysis
of a PV powered seawater RO desalination system without battery
storage. A modest PV array was selected to generate 2.4 kWp, yet
promising to deliver a constant output of 3 m3
/day over a complete
year at a test location in Eritrea. Considering the battery failure pro-
blems faced in areas with hot weather conditions, the use of batteries
was avoided by using sophisticated inverters, motor pumps, and em-
ploying a control algorithm for maximum power point tracking (MPPT)
of the PV array for better energy and cost efficiency of the overall
system [94]. In Australia, Cheah [95] reported commercialization of a
PV-RO unit by the Solar Energy Systems (SES) under the umbrella of the
Murdoch University. The plant was designed, installed, and commis-
sioned to produce 378 L/day of freshwater from feedwater containing
TDS of up to 5000 ppm. As many as 20 systems were installed in a
desert location of Australia, with a water recovery of only 15–20% and
energy consumption of 1.3 kWh/m3
. Water production varies day to
day due to the fluctuations of the available solar power in the area [95].
Abdallah et al. [96] have described a test rig built by coupling two
PV arrays rated at 35 W to power motors and pumps to generate the
torque necessary to drive an RO desalination system in Jordan.
Fig. 6. A schematic representation of a PV-RO system.
461

Hrayshat [97] has proposed a standalone RO desalination unit for
brackish water, powered by a PV array, and prediction of water pro-
duction depending on the solar irradiance at 10 selected sites is simu-
lated. The desalination unit is composed of a three-phase motor driven
by an electrical power system, a PV generator consisting of 22 mono-
crystalline silicon modules each of 50 W peak power, battery storage, a
charge controller, and an inverter (Hrayshat [97]). The author de-
monstrated that the PV brackish water reverse osmosis (PV-BWRO)
system is a technically viable solution for isolated communities without
access to freshwater of usable quality [97]. Mohamed et al. [98] have
compared the performance of a PV-SWRO system equipped with an
ERD with and without battery storage. The designed system consists of
18 PV modules each of 47 Wp power for driving the DC motor con-
nected to a 315 Ah battery bank via a charge controller. The proposed
system was found to be promising with 0.35 m3
/d of freshwater pro-
duction in the winter consuming 4.6 kWh/m3
of energy at a cost of €
7.8/m3
[98]. Aybar et al. [99], have conducted a pilot study of a PV-
powered RO desalination system comprising of a PV array with peak
power of 30 W, a 24 V battery for stabilized input to the RO unit,
booster pumps, and a 5 stage RO unit. The system was found to be
technically as well as economically viable with about 50–100 l/day of
freshwater production [99].
Khayet et al. [100] have optimized a PV-powered desalination plant
for brackish water desalination constructed by coupling an RO system
with a solar thermal system. The low- and high-pressure pumps were
run using a set of batteries powered by three PV panels of 120 Wp each.
The optimized RO plant guaranteed a continuous production of 0.2 m3
/
day with an energy consumption of only 1.2–1.3 kWh/m3
[100]. Pe-
terson and Gray [101] tested a solar-powered RO desalination unit for a
period of 16 months in Brisbane, Australia. The bore pumps were
driven by solar arrays rated at 1.44 kW and equipped with a tracking
system. The pilot plant was designed to deliver 3.36 million liters of
permeate during the trial period of 16 months from November 2008 to
February 2010 [101]. Bilton and Dubowsky [102] have proposed a
computer-designed modular approach for PV-RO at different locations
using a wide range of components, including 5 different motors, 7
pumps, 6 PV panels each with a power rating of 225 W and a mounting/
tracking configuration, and 8 RO membranes. The RO and PV units
were coupled through power electronic devices to form a PV-RO system
that produces 350 L of freshwater on a sunny Boston summer day. The
systems were sized to produce 1 m3
, 5 m3
, and 20 m3
of freshwater at a
cost of $4.71/m3
, $3.45/m3
, and $3.01/m3
, respectively [102].
Shawky et al. [103] have designed and tested a small mobile pro-
totype of a PV-RO driven desalination plant without batteries and with
a production capacity of 4–5 m3
/d. They attempted to maximize the
output of the 6 PV panels by including an automatic tracking adjust-
ment system with an inclination from 0° to 60°. Shawky et al. [103]
made use of a programmable logic controller (PLC) to perform the
following two important functions; (i) command a motor to rotate the
PV panels to the proper inclination based on the time of the day, and (ii)
run a PV-panel cleaning system to keep the panels free of dust. The
proposed solar SWRO water desalination facility with a projected
treatment capacity of 60,000 cubic meters per day in Al-Khafji, Saudi
Arabia, was expected to be operational in future [104]. A medium
voltage solar powered power plant with an estimated installed capacity
of 15 MW is integrated with this desalination plant and the national
grid to reduce the operational costs and the emission of harmful gases.
The RO units are divided into 6 trains, which will facilitate the optimal
usage of variable solar power levels [104].
2.4. Wind-powered RO desalination
The most widely used renewable energy source next to solar energy
is wind energy for powering desalination plants with a small capacity
[69]. Electrical power generated by wind farms/turbines are used for
powering desalination plants. Wind turbine technology is commercially
mature technology and is emerging as a promising solution for seawater
desalination, especially in the coastal regions where higher wind re-
sources are available [105]. The desalination processes using RO driven
by wind energy can be operated in both islanding and grid-connected
modes of operation. Even though a wind energy system (WES) cannot
guarantee continuous operation of an RO plant, energy can be stored in
the form of desalinated water to meet the demand when the plant is not
operating [106]. Small desalination plants integrated with independent
wind energy systems have an enormous potential for the transformation
of brackish water/seawater into potable water at a reduced cost [107]
and [69]. Although a standalone wind-RO plant, without battery sto-
rage, was proposed as a cost-effective desalination system, the fluctu-
ating nature of wind can decrease production and even halt the process
in the absence of wind [105]. Using a battery and generator backup
solves this problem and a wind-diesel-RO plant can produce freshwater
and electricity even in the absence of wind [108]. Veza et al. [109]
proposed a wind-ED experimental plant. Details of the existing wind-RO
desalination plants commissioned at geographically distinct locations
are given in Table 3.
A typical wind-RO system consists of a wind generator, a charge
controller, a battery bank, an inverter, and an RO plant. The operation
of a wind-RO plant begins with power generation from wind turbines
(WTs) that charge the battery banks and powers the desalination plant
by running high pressure pumps to feed water into the RO membranes.
The battery bank maintains the stability of the power system and stores
energy for use when the wind is not available. The charge controller
prevents the batteries from overcharging. A diesel generator can also be
connected as a backup to directly power the RO unit [113]. Fig. 7 shows
the basic configuration of a wind-RO desalination system.
The historical development of the RO process based on wind energy
in terms of capacity buildup, technological advancement from a single
source of renewable energy to renewable-energy-based hybrid power
systems, advances in the development of RO membranes, and other
factors for the period from 1979 to 2017 are summarized in Table 4.
Table 3
Details of commissioned wind-RO desalination plants [110–112].
Plant and location Commissioning year Water type Capacity of RO desalination unit Nominal power supply from
W/T
SECa
Canary Island, Spain 1984 SW/BW 200 m3
/d 42 kW 5 kWh/m3
Canary Island, Spain 2002 SW 5000 m3
/d 2.64 kW 2.9 kWh/m3
CERST, UK 2004 SW 500 l/d 2.5 kW
ENERCON, Mediterranean 2005 SW/BW 7.5–15 m3
/h 2.5 kW (SW) 2–2.8 kWh/m3
(BW)
0.8–1.3 kWh/m3
ENERCON, Germany 2006 SW/BW (SW) 175–1400 m3
/d (BW)
350–2500 m3
/d
200 kW 2–2.5 kWh/m3
AEROGEDESA, Spain 2015 SW 18 m3
/d 15 kW 8.4 kWh/m3
a
SEC is Specific Energy Consumption; SW is Seawater; BW is Brackish Water.
462

2.5. Hybrid PV-wind powered RO desalination
The key advantage of a hybrid PV-wind system is that the desali-
nation unit can be operated in the absence of one of the energy sources.
Manolakos et al. [126] have developed software to perform simulations
of a hybrid PV-wind-RO system. They studied various combinations of
renewable energy sources, such as solar and wind, with and without
battery storage, and with a diesel backup engine. Rehman and El-Amin
[127] and Rehman and Sahin [128] have described the optimization of
the design of a hybrid power system for power generation applications
in a remotely located area. In this section, a detailed review of desali-
nation based on an HRES is presented to exploit the potential of hybrid
PV-wind-powered desalination systems. A typical RO desalination
configuration based on HRES can be schematically represented as
shown in Fig. 8.
The basic operation of a hybrid PV-wind with battery or diesel
generator backup for an RO system begins with the power generation
from the hybrid system to run the RO unit and charge the battery bank.
A charge controller continuously monitors the charging and discharging
of the batteries, so as to run the pumps associated with the RO unit
continuously without any fluctuations. A backup generator can also be
placed in the system, which can be operated under peak load conditions
at a low level or non-availability of solar or wind energy or both to
compensate the intermittent nature of these natural energy sources.
Selected hybrid PV-wind-RO desalination plants with battery or
diesel backup options are listed in Table 5. Table 5 indicates that the
battery backup option is sufficient for small water desalination quan-
tities in the range of 1–5 m3
of water per day. However, for larger
systems with a capacity of a few tens to few hundred cubic meters per
day, one must have either grid-connected power backup or a diesel
generator as the backup option.
As indicated in Table 5, an RO plant with a capacity of 3.12 m3
/d
consumes 16.5 kWh of energy from the hybrid power system for each
cubic meter of water produced [130,131]. For a relatively large RO
plant with a capacity of 300 cubic meters per day, the specific energy
requirement of 4.3 kWh/m3
is provided by a hybrid power system
consisting of 50 kWp of PV and 275 kW of wind capacities along with
grid backup [132]. A review of the technical growth in HRES-RO de-
salination from 2001 to 2014 is summarized in Table 6.
2.6. Coupling of RO desalination with a renewable energy system
Many studies on both experimental and theoretical analysis of
coupling the RO desalination technique with a renewable energy
system have been conducted. Table 7 provides a summary of the survey
described in the previous sections. The information in Table 7 indicates
that extensive experimental and theoretical studies on coupling PV and
Wind energy to power RO systems have been conducted. Even though
satisfactory theoretical research on hybrid systems has been conducted,
there is still a large gap to bridge between theoretical studies and de-
signing experimental units for hybrid PV-wind-RO systems.
3. Modeling of HRES for water desalination
Hybrid systems are designed by combining two or more renewable
or non-renewable energy sources. A hybrid system can be developed by
integrating PV with a diesel generator or a wind turbine with a diesel
generator operating either with or without battery storage. If both
sources of energy are renewables, such as a PV-wind system, then the
system can be identified as a hybrid renewable energy system. A typical
HRES system also includes a range of power electronic devices such as
converters, inverters etc., for their integration to the load for running
high-pressure pumps that feed water to the RO unit. In the following
section, methodologies adapted for modeling of the individual com-
ponents are described.
3.1. Individual modeling of RO and HRES
The design of an HRES depends on the individual performance of
the components. Thus, the individual components, i.e., PV modules,
wind turbines, the diesel generator, and the RO unit, should be modeled
first, followed by integrating them to realize the complete unit.
3.1.1. Modeling of the PV system
A PV cell is modeled by an equivalent circuit formed by a current
source in parallel with a diode. This is also called a single diode model
of a PV cell, which is shown in Fig. 9. Bellia et al. [147] and Rahim et al.
[148] have described the modeling of a PV cell array in MATLAB/Si-
mulink.
The net output PV current is given by Eq. (1), [149] described
below:
= −
⎡
⎣
⎢ −
⎤
⎦
⎥
⎜ ⎟
⎛
⎝
+ ⎞
⎠
i N I N I e 1
pvc p ph p RS
V
N
i R
N
nv
/
pv
s
pvC s
p
T
(1)
where, ipvc is the PV module current, Vpv is the voltage, Iph is the photo
generated current, Ns is the number of cells in series, Np is the number
of cells in parallel, n is the ideality factor of the diode, IRS is the reverse
Fig. 7. Schematic representation of a typical wind-RO desalination system.
463

Table 4
Technological trends and advances in wind-RO desalination from 1979 to 2017.
S. No. Year / Ref System description and performance
1. 1979/ [87] • A wind-powered RO system was established to power an RO unit producing 9 m3
/day of freshwater with specific energy consumption of 11 kWh/m3
.
• In this project, a wind turbine rated power at 6 kW having the rotor diameter and a hub height of 10 m was selected for generating power.
2 1994/ [114] • A standalone reverse osmosis system was proposed based on a wind energy converter (WEC) for delivering freshwater from drilled wells in Jordan.
• The horizontal-axis pitch controlled machine, Aeroman WEC was employed to generate a constant voltage and frequency of 380 VAC and 50 Hz,
respectively.
• Two different scenarios depending on the hub height of the WEC for two different wind speeds (4.4–4.7 m/s), to drive 14 kW and 20 kW wind turbines
respectively were assessed.
a) The 14 kW WEC was designed to pump 1 m3
potable water from the well and desalinate at the rate of 8000 m3
/year, which comes at a cost of US$ 1.7/
m3
to $1.4/m3
.
b) The 20 kW WEC was designed to pump 1 m3
potable water from the well and desalinate at the rate of 12,000 m3
/year, which comes at a cost of US$ 1.2/
m3
to $0.98/m3
.
• A comparison was also performed for the two cases with a diesel generator, and the disel generated RO systems were found to be much expensive than
the above two cases.
3 1997/ [115] • Two serious problems hindering the operation of wind-powered RO desalination plants were identified.
1. Determining the optimum size of the plant subject to the type of membrane and turbine used.
2. Determining the site characteristics.
4 2001/ [116] • The study focused on the comparison of RO plants based on wind power versus conventional energy.
• Some important parameters such as the levelized cost, climatic conditions, nominal power of the WTs, plant capacity, and the cost of the RO modules
and WTs were analyzed.
• Three wind turbines were selected for comparison with a nominal power rating of 600 kW, 600 kW, and 750 kW for an RO system with a range of
capacities from 200 to 3000 m3
/day with a specific energy consumption ranging from 3.5 to 6.5 kWh/ m3
.
5 2002/ [117] • A computer model of a system was presented for a remote location with abundant wind resources. The model comprised of a wind turbine generator
rated at 2.2 kW to power a variable-flow RO desalination unit.
• Storage batteries were not included, making the system completely dependent on instantaneous wind resources.
• The average specific energy consumption of the model was about 3.4 kWh/m3
for a flow rate of 8.5 m3
/d.
6 2002/ [118] • A prototype for BWRO desalination powered from wind energy was designed and tested on the north coast of Oahu, Hawaii.
• The plant consisted of four sub-systems: a multi-vaned wind turbine, a module for RO, a pressure/flow stabilizer, and a feedback control system.
• The control mechanism allowed the system to function adequately under a low ambient wind speed of 5 m/s or even less, thus producing a flow rate of
up to 13 L/min.
• The measured energy efficiency of the system was 35%.
7 2005/ [119] • The Thermo-economic study for wind-powered RO plant for seawater in the Canary Islands was conducted.
• The system comprised of 3 wind turbines each with a 3-blade rotor, a rotor diameter of 43 m, and nominal power of 600 kW feeding an RO plant with a
nominal capacity of 3,000 m3
/d and a recovery ratio of 35%.
8 2006/ [120] • This research explored the potential for integrating wind power with reverse osmosis system to increase the water supply.
• Desalination and wind technologies, including the growth trends, cost, emerging technologies, and thereby specifying hotspots Via GIS for areas such as
Egypt, Haiti, Libya, Saudi Arabia, South Africa, Yemen etc. are summarized in this study.
9 2006/[121] • In November 2006, an SWRO desalination plant with a total extended capacity of 250,000 m³ /day to increase the existing capacity of 140,000 m³ /
day to satisfy 17% of Perth’s needs was established. The project cost was around AUS $387 million.
• The energy consumption of the giant SWRO plant was 24 MW, of which about 4–6 kWh/ m³ demand is taken care by 80 MW Emu Downs Wind Farm
comprising of 48 wind turbines.
10 2011/ [122] • In this study, the most suitable design for SWRO desalination driven by off-grid wind energy systems under a simulated environment was determined.
• The WTs considered in this comparative analysis were rated at 100 kW, 225 kW, and 300 kW.
• Two SWRO plant designs possibilities were considered and compared;
1. A fixed capacity SWRO plant with one train of 1000 m3
/d when wind resources are available.
2. Varying capacity SWRO with 3 RO trains. One train with a capacity of 200 m3
/d and the other two with a capacity of 400 m3
/d operating independently,
depending upon the availability of wind energy.
11 2011/ [123] • In the region of Tenes, Algeria, a detailed analysis of seawater reverse osmosis desalination using wind energy resources was conducted.
• A feasibility study for obtaining energy from a wind energy farm with 5 wind turbines of type Bonus 2 MW installed in the coastal region with a capacity
of 5000 m3
/d was conducted.
12 2013/ [124] • In this study, the potential of supercapacitors for the safe operation of a wind-powered RO system under fluctuating wind conditions was investigated.
• A super-capacitor coupled to a wind-membrane system tends to charge if the wind speed is greater than 7 m/s. Otherwise, the capacitor discharges
eventually to a threshold value determined by the control electronics.
• A wind turbine simulator was designed by gearing the 1 kW wind turbine generator to an induction motor provided with a vector frequency inverter.
The control operation was performed using the LabVIEW interface.
• SEC of the system was around 2.7 kWh/m3
• The super-capacitors were found to be very effective in absorbing the fluctuations of wind from about 15 s to 20 min and were very reliable for the
integration with wind-powered RO.
13 2016/ [125] • Technical and economic study of a small-scale SWRO system powered by a wind energy system for Gökçeada islands, Turkey, was presented.
• The analysis was performed using wind turbines with different rated speeds ranging from 6 kW to 30 kW for an off-grid RO system. The cost of water
produced by this system was between the US $2.962 and the US $6.457/m3
. On the other hand, the cost was predicted to be US$ 0.866/m3
to 2.846/m3
for the grid-connected system, with the levelized cost of electricity ranging from the US $ 0.077–0.155/kWh.
• The use of a 30-kW wind turbine coupled to an RO system eliminates the release of 80,028 tonnes of CO2 annually by producing water at a 30% recovery
ratio and a specific energy consumption of 4.38 kWh/m3
.
14 2016/ [112] • The intermittent nature of wind energy can cause severe problems including the negative effects on the membrane process, decreased lifespan of the
components, and the increased complexity of the plant configuration, operation, and control.
• Following strategies were proposed to overcome these problems:
1. Utilization of an energy storage system such as batteries, super-capacitors, flywheels etc., for maintaining constant operation of the RO units.
2. The use of a hybrid energy system of different configurations such as a combination of wind with solar PV along with diesel generators.
3. Adjusting operating conditions of the RO process to match the RO capacity.
15 2017/ [111] • The wind turbines on new generation are designed to operate even at low wind speeds was investigated for well-suited GCC sites based on a
geographical information system (GIS) for Wind-RO.
• Evaluation of technical performance and costs analysis, was conducted for several wind-driven RO sites in Abu Dhabi.
464

saturation current, and nvT is the thermal voltage. According to Eq. (1),
the output current is directly dependent on the irradiance and tem-
perature. Many techniques are available for locating the MPPT of the
system. Kolsi et al. [150] have highlighted the methods proposed for
locating the MPPT, such as perturbation and observation (P&O) control,
hill climb method, incremental conductance method, neural networks,
and many more techniques. Thus, the maximum power expression is
given by Eq. (2);
=
P I V
*
max max max (2)
PV systems require power electronic devices for their integration to
the grid. The primary requirement of the PV system to be integrated
into the grid is boosting its output voltage. Kolsi et al. [150] specified
boost, buck, and buck-boost converters for this purpose. These con-
verters have two modes of operation ie; discontinuous conduction mode
(DCM) or continuous conduction mode (CCM). In a grid-connected
photovoltaic system, the operation and design of these inverters are key
for achieving high-efficiency power output for different configurations.
Hassaine et al. [151], have presented three different inverter topologies
for the PV system as shown in Fig. 10, defined as the central inverter,
string inverter, and multi-string inverter [151]. Kjaer et al. [152] have
also presented similar inverter topologies for a single and multiple PV
module applications.
3.1.2. Modeling of a wind system
Wind turbines have been installed in many countries for power
generation, and they have also been integrated with water desalination
units. Based on their design considerations, they have been classified
into the following three main categories: (i) The fixed speed wind
turbine, with a generator, directly connected to a grid, (ii) The variable
speed wind turbines with a full power converter in a stator circuit, and
(iii) The slip ring induction motor and converter in a rotor circuit as
described by Petru and Thiringer [153]. Soetedjo et al. [154] describe a
building block of a wind energy system (Fig. 11). A wind generator
consists of a wind turbine coupled to a permanent magnet synchronous
generator (PMSG). A three-phase diode rectifier is used to convert the
three-phase AC voltage to DC. The buck converter is a DC-DC converter
used for voltage input, and the output ratio is controlled by a PWM
signal from the MMPT controller. The entire system feeds a load which
runs the high-pressure pumps in the RO desalination system.
The mechanical power generated by a wind turbine is given by Eq.
(3). In this equation, the tip speed ratio λ
( ) is the ratio of the turbine
speed ω
( ) to the wind speed v
( ). Maximum power coefficient C
( )
p is
achieved when the tip speed ratio reaches the optimal value (λopt). A
nonlinear relationship exists between Cp and both the tip speed ratio
and the blade pitch angle β
( ). The detailed dynamics of the wind gen-
erator system can be found in [154].
= =
P C λ β ρAv whereλ
ωR
v
1
2
( , )
p
3
(3)
Abdullah et al. [155] conducted a detailed review on MPPT tech-
niques such as the tip speed ratio (TSR) control, optimal torque (OT),
power signal feedback (PSF), perturbation and observation (P&O)
control, and many other methods. Rahman and Rahim [156] proposed
an intelligent adaptive neuro-fuzzy inference system (ANFIS) for
tracking the maximum power point. The proposed MPPT technique
does not require any mechanical sensors for the measurement of the
wind speed and it estimates the maximum power [156].
3.1.3. Modeling of the battery
A battery is used as an energy storage device, primarily for storing
electrical energy for optimal utilization of the intermittent renewable
energy resources, assuring a continuous energy supply. In some appli-
cations, electricity can be stored by converting it to another form such
as kinetic, potential, or chemical energy. Rahman et al. [157] have
published a review on advanced energy storage systems, focusing on
the need for storing electrical energy produced from renewable energy
sources to meet the demand under the extreme climatic conditions of
Saudi Arabia. Their study recommended that some of the features as-
sociated with batteries, such as their low cost, long life battery cycle,
high efficiency, mature technology, ability to withstand high ambient
temperatures, large power and energy capacities, and the en-
vironmentally benign nature should be exploited to store the power
generated from renewables. Nair and Garimella [158] have focused on
some of these technologies, including batteries, fuel cells, flywheels,
and super-capacitors. Bajpai and Dash [159] have shown that the
Fig. 8. A schematic representation of a hybrid PV-wind RO desalination system.
Table 5
Selected hybrid PV-wind-RO desalination plants with a backup/storage system.
Capacity
(m3
/d)
SEC
(kWh/m3
)
PV share
(kWp)
Wind
share
(kW)
Battery
capacity
(kWh)
Ref.
3 – 3.5 0.6 36 [129]
3.12 16.5 3.96 0.9 44.4 [130,131]
2.2 3.3–5.2 0.846 1 7.56 [131,132]
1 3.74 0.6 0.89 21 [133]
300 4.3 50 275 Grid back up [134]
30 – 4.6 5 Diesel engine
back up
[75]
465

modeling of a battery in HRES depends on various battery parameters
including the following; (i) state of charge (SOC), (ii) rate of charging/
discharging, (iii) battery storage capacity, and (iv) temperature. A flow
representation of an autonomous HRES with a battery is shown in
Fig. 12 [160].
The net operational current in a battery at any time is given by Eq.
(4). If >
I 0 the battery is charging and if <
I 0 the battery is in the
discharge state. The charge transferred during one-time step (Q), is
given by Eq. (5)
= + −
I I I I
PV WG L (4)
∫
=
+
Q I dt
t
t
n
n 1
(5)
Sinha and Chandel [161] have expressed the battery SOC during the
charging process using Eq. (6).
+ = − +
SOC t SOC t σ t I t Δt
η t
C
( 1) ( ). [1 ( )] [ ( ). .
( )
]
bat
c
bat (6)
where, Cbat is the capacity of the battery, ηc is the coulombic efficiency
of the battery, and Δ is the self-discharge coefficient.
3.1.4. Modeling of a generator
In an HRES, if the renewable energy sources or the batteries cannot
meet the requirements of the load, then diesel generators are used for
power backup. The selection of the diesel generator depends on the
nature and type of load. These diesel generators are modeled in such a
way that they operate between 80% and 100% of their kW rating [162].
The rated capacity of the installed generator should be decided based
on the following guidelines [163]:
1. The rated capacity of the diesel generator must be equal to the
maximum load of the system.
2. If the generator is used for charging the batteries, then the current
produced by the generator should be one-fifth of the battery capa-
city.
The energy generated (E )
deg can be defined by Eq. (7), where Pdeg is
the rated power and ηDeg is the efficiency of the diesel generator. The
overall efficiency ηoverall is given by Eq. (8).
=
E t P t xη
( ) ( )
deg deg Deg (7)
=
η η xη
overall brake thermal generator (8)
3.1.5. Modeling of the RO system
Reverse osmosis is a membrane-based technique in which the nat-
ural flow direction is reversed with the application of external pressure
on the high concentration side of the membrane. The feed-water pres-
sure should be very high in order to overcome the osmotic pressure and
Table 6
Technological trends of hybrid PV-wind-RO desalination from 2001 to 2014.
S. No. Year/ Ref System description and performance
1 2001/ [129] • A stand-alone hybrid PV-wind system was designed for operating an RO desalination plant of capacity 3 m3
/d running for four hours.
• For the hybrid system, Siemens PV modules were chosen. The solar panels were arranged in 32 modules in parallel and 2 modules in series along with a
wind generator rated at 600 W. A two-day storage battery and a diesel generator for back up were also provided.
• Control techniques were employed to manage the production and maintain the quality of water from the RO units as well as managing the data
acquisition system.
2 2004/ [135] • Techno-economic analysis of an SWRO desalination unit powered by a stand-alone hybrid PV-wind system was performed for a village in Chania,
Greece. The system was equipped with a brine energy recovery system.
• Three Filmtec spirally wound membranes that produce water at a flow rate of 0.5 m3
/h with a recovery ratio of 23% were used.
• For the analysis, more than 200 PV panels rated at a peak power of 150 W from Siemens were connected in series and parallel along with a battery bank
and four wind turbines of different ratings (1 kW, 2 kW, 4 kW, and 10 kW).
• Authors concluded that 40% PV and two 4 kW wind turbines were best suited for operating the membrane system in a cost-effective manner.
• A comparison was also performed, and the authors found that the cost of water for PV alone to be 6.64 €/m3
, while it was 5.21 €/m3
for the PV-wind
hybrid system.
3 2005/ [134] • SWRO desalination with a capacity of 300 m3
/d was powered by an integrated PV-wind system with grid backup in Libya.
• The nominal load for the experimental operation of the RO desalination plant was 60 kW, which was met with 50 kWp of PV and 275 kW of wind turbine
capacity.
4 2008/ [136] • This study focused on the control strategies and state analysis of an autonomous desalination system driven by a PV and wind generator connected to
induction machines via a DC link.
• A control strategy based on power, voltage and current control with MPPT was considered.
5 2010/ [137] • The economic evaluation of a stand-alone hybrid PV-wind desalination plant was performed using a numerical computer algorithm.
• The proposed scheme consisted of an RO desalination system powered by a solar PV and wind generation system and a pumped storage unit.
• During surplus power generation from RES, few pumps are operated to store water in a reservoir. When there is insufficient power generation by the PV-
Wind system, the stored water is used to run a hydro turbine that in turn powers the desalination units.
6 2011/ [138] • Financial and economic feasibility of the proposed configuration was evaluated by innovative and efficient cost-effective methods for producing
potable water by combining two technologies.
• The study considered a concept of desalination which employs solar collectors to operate an RO desalination plant based on the organic Rankine Cycle
(ORC) and a PV generator to serve as a hybrid system.
• A PV module with a power capacity of 95 kW and a turbine with a power capacity of 250 kW coupled to a battery with a rated capacity of 144 kWh were
considered.
7 2012/ [139] • The design and optimization of an HRES comprising a PV-wind system along with battery storage were performed to feed a BWRO desalination plant
of 100 m3
/d for a project site situated in south India.
8 2013/ [140] • A hybrid solar/wind powered reverse osmosis system was modeled and a simulation was performed to optimize the minimum cost per cubic meter of
potable water for Dhahran, Saudi Arabia.
• A constant RO load of 1 kW was maintained for running the system for 12 or 24 h/day.
• For 12 h/day operation, the levelized cost of energy was US$ 0.624/kWh for a system comprising of 40 PV modules (50 W each), 2 wind turbines (1 kW
each), and 6 batteries (253 Ah each).
• For 24 h/day operation, the levelized cost of energy was US$ 0.672/kWh for a system comprising of 66 PV modules (50 W each), 6 wind turbines (1 kW
each), and 16 batteries (253 Ah each).
9 2014/ [141] • In this study, a small-scale unit comprising a hybrid PV-wind-generator system was designed to generate electricity as well as drinking water for 1000
inhabitants. Disaster-prone locations such as Nairobi in Kenya and Nyala in Sudan were selected as test locations.
• The designed model consisted of the following components: 22 solar PV modules of 5 kW rated power, a wind turbine with a 1 kW rated power output, a
diesel generator of 1.5 kW rated power along with 6 batteries (12V, 200 Ah), and an RO− 200 unit from pure Aqua Inc.
• A control algorithm was used to maintain the power system reliability and availability.
466

Table 7
Coupling of RO desalination with a renewable energy system.
Type of Analysis Reference Stand-alone System Backup or Grid Connected System
System without
Battery
System with Battery Hybrid System
PV-
RO
Wind-
RO
PV-
Battery-
RO
Wind-
Battery-
RO
PV-
Diesel-
RO
PV-Wind-
Diesel-RO
PV-Wind-
Battery-RO
PV-
Grid-
RO
Wind-
Grid-RO
PV-
Wind-
Grid -RO
PV-Wind-
Diesel-RO
PV-Wind-
Diesel-
Grid-RO
[87] ✓ ✓
[88] ✓
[91]
[92,93] ✓
[94] ✓
Experimental [96,97],and [101] ✓
[103] ✓
[142,143] ✓
[118] ✓
[121] ✓
[129] ✓ ✓
[134] ✓
[89] ✓
[90] ✓
[102] ✓
[114,120,122] and
[125]
✓
Theoretical [119] ✓
[144] ✓ ✓ ✓ ✓ ✓
[75,112] ✓
[135,140] ✓
[141] ✓ ✓
[145] ✓
[146] ✓
Fig. 9. Single diode PV cell model.
(a) Central Inverter (b) String Inverter (c) Multi-string Inverter
Fig. 10. Proposed inverters for connecting a PV system to the load.
Fig. 11. The conﬁguration of a wind energy system [154].
467

the membrane resistance [164]. An RO desalination plant consists of
the following three stages as described by Jiang et al. [165]: (i) Unit for
the pretreatment of feed water, (ii) The membrane assembly, and (iii)
Unit for the post-treatment of water. For operating the system, many
high-pressure pumps are required, and a schematic diagram of the
system is shown in Fig. 13.
Bilton et al. [166] have provided a volumetric relationship for an
RO plant using Eq. (9),
= +
Q Q Q
F B P (9)
where, QF is the feedwater flow in liters per second, and QB and QP are
the brine and permeate flows, respectively. The plant recovery ratio (R)
is given by Eq. (10), [166].
=
R
Q
Q
P
F (10)
Chaaben et al. [167], have proposed a static model of a desalination
unit indicating input and output variables as shown in Fig. 14. The
manipulated variables or the input variables of the RO plant are the
angular speed Ωf of the motors of the pumps and the valve reject
opening θvr. The feedwater salinity Ce is considered a disruptive input.
3.2. Modeling and performance of a hybrid PV and wind RO system
Smaoui and Krichen [168] have studied the dynamic modeling of a
photovoltaic system powering a desalination unit (Fig. 15). The system
consists of a PV generator operating at the maximum power, employing
a boost converter equipped with an MPPT tracker. The power generated
is passed through an inverter and a filtering assembly before feeding it
to the continuous load. The balance between consumption and pro-
duction is maintained by installing a battery bank that uses a current
reversible chopper. Some control loops were also modeled so as to
maximize the PV generator power, provide DC voltage regulation, and
facilitate inverter control.
Yousef and Anis [169] have studied the performance of a water
desalination plant powered by a standard PV array with and without
battery backup (Figs. 16 and 17). The system with a battery is designed
to operate for 24 h a day. The area designated ‘BD’ in Fig. 16 clearly
shows the continuous operation of the RO unit with the battery storage
indicated by ‘BC’. As energy is available only during sunshine hours, the
energy should be stored during daytime to use in the night to meet the
power requirement PL. In Figs. 16 and 17, T1 and T2 indicate 8 h per day
operation, Tsr indicates the time of sunrise, and Tss the time of sunset.
The results depicted in Fig. 17 indicate that the process comes to a halt
in the absence of sunlight when battery backup is not available. Yousef
and Anis [169] also studied the performance of a hybrid system con-
sisting of a PV array and a diesel generator along with a battery charger
for RO desalination (Fig. 18). The performance diagram clearly shows
that the diesel generator takes over the operation of the RO unit in the
absence of sunlight. The area designated ‘D’ in Fig. 18 shows the con-
tinuous operation of the desalination process for 24 h using the diesel
and PV hybrid power system.
Alghoul et al.[170] examined the varying climatic performance of
600-Watt RO load for desalination system powered by 2 kW PV system
in Malaysia. The effect of battery during the day time and night time
operations are studied for two typical years. For the day time operation
mode, the battery autonomy was around 11 h per day and for the night
time operation mode it was around 11.5 h as shown in Fig. 19. It was
found that the battery bank, in day time operation mode, was reduced
to 50% (11 h) due to battery room temperature conditions.
General [171] has illustrated the possible configurations of a wind-
driven RO desalination system in the SIMULINK environment (Fig. 20).
In configuration Fig. 20 (a) the wind turbine is mechanically coupled to
the gearbox, while in configuration (b) direct electrical coupling is
used. In configuration (c) electrical coupling is used along with a bat-
tery. These configurations were proposed for running pumps associated
with the RO system.
Generaal [171] showed that the torque generated by the wind tur-
bine meets the torque requirements of the pump in the mechanically
coupled system. If the torque produced by the wind turbine is low, the
angular velocity of the wind turbine will decrease, thereby increasing
the torque, and vice versa. In practice, there will be a difference in the
torque generated by the turbine and the torque required by the pump.
This difference in the torque causes the acceleration of the wind tur-
bine. Thus, angular wind turbine velocity can be calculated with respect
to the difference in torque. The torque generated in the pump is a
function of the feed pressure of the membrane, which in turn is a
function of the salt concentration in water. If the above requirements
are met for the torque, then the system can deliver water as a function
of the angular velocity of the pump.
Generaal [171] also studied an electrically coupled wind-driven RO
system As electrical coupling operates in a different manner, both
pumps and the wind turbine operate independently. This model ac-
counts for various losses such as the rectifier losses, motor pump losses,
inverter losses, and battery charging and discharging losses. Hence, the
produced sweet water will be a function of these losses.
4. Sizing methodology and economics of an HRES-RO system
In the installation of a hybrid renewable system, it is essential to
know the proper sizes of the individual components of the system.
Component sizing and optimization is important because they are in-
fluenced by factors such as the system economics, reliability, and the
Fig. 12. A schematic representation of an HRES connected to a battery and a
load.
Fig. 13. Schematic representation of the RO
desalination process.
Fig. 14. Unit static model of an RO desalination unit.
468

greenhouse gas (GHG) emissions (Khair and Ansari [172]). The selec-
tion of the most suited technology also depends on the availability of
resources at a given site or location where the system is to be installed.
Proper sizing is required to determine the wind generator capacity, a
number of PV panels, batteries, and their respective capacities, and the
type and capacity of the inverter. Although oversizing of the compo-
nents or resources may be required to account for the ﬂuctuating nature
of renewable sources of energy, it may make the system relatively
costly. Thus, it is important to consider environmental parameters such
as solar irradiance and wind speed for the proper and economical
Fig. 16. Model and performance of an RO de-
salination system powered by a PV array with
battery backup (adapted from [169]).
Fig. 15. Complete electrical model of a PV-RO system with power electronic components (adapted from [168]).
Fig. 17. Model and performance of an RO desalination
system powered by a PV array without battery backup
(adapted from [169]).
Fig. 18. Model and performance of an RO desalination
system powered by a hybrid PV-diesel generator system
with battery backup (adapted from [169]).
Fig. 19. Solar PV and Battery proﬁle (a) Daytime operation mode (b) Nighttime Operation mode.
469

design of an HRES-RO system. A range of software tools and approaches
have been developed and reported in the literature for sizing and op-
timizing these systems [173]. Apart from the software tools, iterative
algorithms such as the genetic algorithm (GA), particle swarm optimi-
zation (PSO), and cuckoo search algorithm (CSA) can be used as re-
ported in the literature [174,175]. Intelligent technologies such as
neural networks and fuzzy logic [176] have also been used for opti-
mizing HRES and wind farm designs, as described in [177,178]. Some
of these tools have been implemented for optimal sizing of renewable
energy sources powering RO desalination units as reported in the lit-
erature [179–182]. Peng et al. [183] stated that among various evo-
lutionary algorithms, hybrid optimization techniques provide the best
solution by reducing the system cost and reliability and at the same
time increasing the fresh water production.
4.1. Software tools
A range of software programs is available for evaluating the per-
formance and sizing of hybrid renewable energy systems. Erdinc and
Uzunoglu [173] and Sinha and Chandel [184] have published a com-
prehensive review of available software packages. Many software
packages have been reported in the literature for sizing of HRES, such
as HOMER, Hybrid 2, RETScreen, HybSim, and Hybrids [184]. Some of
these tools are summarized in Table 8 in terms of their capabilities,
advantages, and disadvantages. Depending upon the type of application
and the input and output variables, a schematic representation of an
HRES-RO system defining the inputs and outputs for HOMER is shown
in Fig. 21.
Dehmas et al. [123] have conducted a study of a wind-powered RO
desalination plant with a capacity of 5000 m3
/day in Algeria assuming
a lifespan of 25 years. The analysis was performed using RETScreen at a
total estimated cost of US$ 22 million. Table 9 summarizes the tech-
nologies and software used to conduct the system sizing and economic
analysis for RO desalination powered by renewable energy in Algeria
(5000 m3
/d), India (100 m3
/d), Saudi Arabia (5 m3
/d, 6850 m3
/d, and
190,000 m3
/d), Iran (10 m3
/d), and the UAE (14,000 m3
/d). HOMER
and RETScreen are some of the software packages employed for de-
signing and optimizing the hybrid power systems.
4.2. Economic analysis and the effect of solar and wind profile on
desalination
Economic analysis is the backbone of any system that is expected to
implement in real-world. Numerous studies on the comparison of the
technical and economic performance of desalination processes based on
renewable energy resources have been conducted [187]. A comparison
of the different capacities for various locations having average daily
solar radiation ranging from 4.6 kWh/m2
/day to 6.6 kWh/m2
/day and
the effect of a solar profile on the cost of water is presented in Table 10.
The data presented in Table 10 indicates that the prospects for solar
based desalination technology have improved, and the cost of water
production has decreased over the time. The cost of water production
for PV-RO ranges from 34.21 $/m3
to 0.825 $/m3
. For example, the
specific energy consumption of a PV-RO system in Morocco and Gran
Canaria during 1998 (Table 10) was high due to the inefficient tech-
nology available at the time, ultimately making the cost of water pro-
duction quite high. The cost of water production by PV-RO systems
during the year 2008 in UAE and Greece (Table 10), was still high due
to the fact that both systems were fully PV power dependent without
any backup and moreover the feedwater salinity is quite high. As the
technology progressed, in 2015 a study conducted by Alsheghri et al.
[188] at Abu Dhabi, reported low cost of water desalination indicating
0.825 $/m3
for a PV-RO system. RO plants with a capacity of 10 m3
were designed for three different locations namely Boston, Los Angeles,
and Saudi Arabia with respective average daily solar radiation is 4.4,
5.6 and 6.6 kWh/m2
/day (Table 10), and the cost of water was found to
be 7.01, 5.64 and 4.96 $/m3
respectively. It is evident that as the solar
(a) Mechanical Coupling
(b) Electrical Coupling
(c) Electrical Coupling with battery
Wind energy
system
Wind energy
system
Wind energy
system
Fig. 20. Different types of mechanical and electrical coupling for a wind-RO
system.
Table 8
Comparison of available software tools for HRES.
Software Analysis type Advantages Disadvantages
HOMER • Technical
• Emission
• Economic
• Sensitivity
• Friendly and easy to use
• Easy to understand and provides a self-learning environment.
• Provides a graphical representation of the design and results
• Hourly simulation for a complete year.
• Integration with MATLAB
• Effect of temperature on solar PV is included.
• Black Box code
• Models used are based on first-degree linear equations
• Time series data in the form of daily average data cannot be used.
• Only the trial version is free. The professional version has to be
purchased.
RETScreen • Financial
• Technical
• Environmental
• Easy to use as it is MS Excel-based spreadsheet software.
• Strong meteorological database and product database available from
NASA only
• Downloadable free of charge
• Few data input options
• Limited options for search, visualization, and graphical features.
• No provision for importing time series data files
• Temperature effect on solar PV is not included.
Hybrid 2 • Technical
• Economic
• User-friendly
• Uses a GUI for designing projects
• Multiple electrical load option
• Many resource data files
• Downloadable free of charge
• Lacks Flexibility
• Limited access to parameters
470

radiation increases the cost of water production reduces substantially.
The levelized cost of water is also a function of feed water salinity apart
from the daily solar irradiance. For the case reported in Table 10 for
Iran and Iraq, both the sites have similar daily solar radiation profiles,
but the cost of water estimated for Iran is 1.96 $/m3
and that for Iraq
0.93 $/m3
corresponding to the feedwater salinity of 39600 ppm (sea-
water) and 3000 ppm (Brackish water) respectively.
The cost of water produced by wind-RO desalination technologies
ranges from 15.75 $/m3
to 0.66 $/m3
as in Table 11. However, a re-
latively low cost of water (0.66 $/m3
) was estimated for Adrar site
located in Algeria [199]. Triki et al. [199] conducted analysis for three
different sites having average wind speeds ranging from 6.3 m/s, 5.8 m/
s, and 5.1 m/s and the cost of water for the respective location were
estimated to be 0.66 $/m3
, 0.7 $/m3
. 075 $/m3
respectively. For the
case of turkey with an average wind speed of 5.3 m/s and feed water
salinity of 37000 ppm, the cost of water was estimated to be 2.846
$/m3
. The capacity of desalination will also have an effect on the de-
salination economics, this can be related by the example of Greece in
2006, although Greece has abundant wind resources but the plant ca-
pacity is considered to be 96 which is relatively very small, as a result,
the cost of water is quite high. Hence Table 11 clearly shows that the
cost of water produced by Wind RO technology is subjected to many
factors such as wind speed, feed water TDS and the capacity of the
desalination plant.
The water production cost by using PV-Wind RO ranges from 1.4
$/m3
to 6.12 $/m3 Table 12 In a comparison of PV-wind-RO plants in
Table 9
Software tools used for evaluating the performance of RO desalination based on renewable energy.
S. No. Site Type of system Capacity Software tool CoWa
Ref
1 Algeria Wind-RO 5000 m3
/day RETScreen – [123]
2 India PV-wind-RO 100 m3
/day HOMER 0.63 $/m3
[139]
3 Saudi Arabia PV-Wind-RO 5 m3
/day HOMER 3.69–3.81 $/m3
[140]
4 Saudi Arabia PV-RO 6850 m3
/day HOMER 0.85 $/m3
[185]
190,000 m3
/day 0.89 $/m3
5 Iran PV-Wind-RO 10 m3
/day HOMER/ MATLAB 3.74 $/m3
[186]
6 UAE Wind-RO 14,000 m3
/day − 1.57–2.11 $/m3
[111]
a
CoW is Cost of water.
Fig. 21. Schematic representation of the application of HOMER for HRES-RO.
Table 10
Economic analysis and the effect of solar profile on PVRO desalination cost.
S. No. Location/year Average daily radiation (kWh/m2
/day) TDS (ppm) Capacity (m3
/day) SEC*(kWh/ m3
) Backup CoW ($/m3
) Ref
1 Morocco/1998 4.6 40,000 3.7 18.5 Battery 34.21 [90]
2 Gran Canaria/1998 5.67 35,000 0.8 18.75 Battery 17 [189]
3 Oman/2000 5.5 1010 6.5 1.29 Battery 8.51 [92]
4 Egypt/2001 6 2000 1 4.17 Battery 3.73 [190]
5 Brazil 5.2 35,000 7.2 0.84 − 7.8 [191]
6 Eritrea/2002 5.8 40,000 3 − − 2.65 [94]
7 Nevada/2004 5.2 3500 1.5 1.3 Battery 3.64 [95]
8 Greece/2008 4.6 – 0.82 4.6 No Backup 9 [98]
9 UAE/2008 6 45,000 20 7.33 No Backup 7.34 [192]
10 New Mexico/ 2010 5.2 – 1 – – 13 [193]
11 Boston/2011 4.4 32,664 10 2.92 – 7.01 [166]
12 Los Angeles/ 2011 5.6 33,505 10 3 – 5.64 [166]
13 Saudi Arabia/2011 6.6 38,340 10 3.3 – 4.96 [166]
14 Egypt/ 2012 6.2 33000 150 7.3 Grid & Battery 2.562 [194]
15 Egypt/ 2012 6.2 34,000 300 4.6 Grid & Battery 1.82 [194]
16 Abu Dhabi/2015 5.61 – 200 6.99 Grid Backup 0.825 [188]
17 Algeria/ 2017 5.94 37000 50,000 2.5–6.6 No backup 1.32–1.8 [195]
18 Iraq/2017 5.5 3000 2000 – – 0.93 [196]
19 Iran/ 2017 5.4 39600 228 0.83 Battery 1.96 [197]
20 Iran/2018 5.4 – 10 4 Diesel 1.59 [198]
471

Greece and Libya (feed water salinity up to 40,000 ppm), the cost of
water produced by a grid-connected system in Libya was 4.03 $/m3
,
which is more economical compared to the battery backup system in
Greece with a cost of water production of 6.12 $/m3
. Cherif et al. [201]
carry out a study showing how the solar and wind profiles affect the
hybrid PV wind RO desalination product output. The study was con-
ducted in Tunisia, with an average daily solar radiation and wind speed
as 5.04 kWh/m2
/day and 8 m/s respectively. As the summer months,
July and August have high energy production from PV system, the
product output is also high for these months. The conclusion can be
drawn that the product water is a function of energy generation from
hybrid PV-wind which in turn is a function of solar and wind avail-
ability profiles.
Gökçek and Gökçek [125] has stated that the high penetration of
renewable energy sources for desalination results in minimizing the
carbon footprint. Karaghouli and Kazmerski [202] from the National
Renewable Energy Laboratory (NREL) have concluded in their analysis
of a small PV-RO system with a capacity of producing 5 m3
/day, driven
by a 5 kW PV system along with a battery assembly, that it is capable of
preventing the release of 8170 kg of CO2 and other hazardous gases
annually in a remote area of Iraq. Similarly, Fthenakis et al. [185] have
claimed that their proposed PV-RO system with an estimated capacity
of 190,000 m3
/day powered by a 148 MW PV system provided with a
backup diesel generator can eliminate 832 million tons of CO2 annually.
5. Concluding remarks
Desalination technology based on renewable energy has established
a new trend as it has become a feasible option for freshwater produc-
tion. The global and domestic trends in the desalination capacity and
technological developments are highlighted in this review. Exploitation
of the renewable energy potential of Saudi Arabia for both large- and
small-scale desalination applications was also reviewed. Water con-
sumption has increased drastically owing to the increased population,
which requires increasing the freshwater production significantly. The
use of renewable energy resources is encouraged to meet the growing
power demand and supplement the existing energy sources for the
production sweet water. The distributive nature of the renewable en-
ergy sources is ideally suited to supply power in areas which are not
connected to the grid. The use of renewable energy will also reduce the
emission of greenhouse gases into the local environment.
• An overview of RE-based desalination, particularly PV-RO, wind-
RO, and PV-wind-RO technologies, considering the fact that the use
of RO membranes is the preferred method of desalination, is pro-
vided in this review. Many configurations and combinations of PV
and wind to provide the power required by the RO process are
presented here. The functioning of an RE based desalination system
is sensitive to many parameters, including the site, energy tech-
nology (PV, wind, or even both), grid or battery power backup,
desalination technology, and the specific energy consumption of the
RO plant. In some cases, the coupling of RE-based desalination
technology and the existing desalination system can be beneficial to
serve the purpose, while in some cases it may not be true. A sum-
mary of the available technologies with the capacity and cost of
water production is given below:
i. The PV energy based desalination systems in use are available in
different sizes ranging from 0.8 m3
/d to 60,000 m3
/d with an ap-
proximate cost of US$ 34.21/m3
to 0.825/m3
.
ii. Wind energy based desalination plants are available in sizes ranging
from 1 m3
/d to 250,000 m3
/d with an approximate cost of US$
15.75/m3
to 0.66/m3
.
iii. Desalination systems based on wind-PV hybrid energy have been
implemented in many countries with the size ranging from 3 m3
/d
to 83,000 m3
/d. The cost of water from systems varies from US$
6.12/m3
to 1.4 $/m3
.
• A review of published studies shows that the cost of sweet water
production depends on factors such as the capacity or the size of the
desalination plant, solar or wind profile of the location, TDS of the
feed water, type of renewable resource used for power generation,
and off-grid or grid-connected operation. Apart from these factors,
the size of the PV, wind, or the hybrid power system is a key factor
governing the cost of the complete unit and thereby the cost of
water production. The option of integrating an existing desalination
system with hybrid renewable energy power generation is more
economical than using either PV or wind alone. Furthermore, opti-
mizing the design of the hybrid renewable energy system to be in-
tegrated with an RO plant is a critical step in lowering the cost of
water production.
• Modeling studies of the use of PV systems, wind energy systems,
battery storage, diesel generators, an RO system as the desalination
Table 11
Economic analysis and the effect of wind profile on Wind RO desalination cost.
S. No. Location/year Wind Speed (m/s) TDS (ppm) Capacity (m3
/day) SEC* (kWh/ m3
) Backup CoW ($/m3
) Ref
1 Jordan/1994 6.6 1500 22 − Diesel 1.7 [114]
2 Canary Island/2005 6.3 − 3000 18 − 0.89 [119]
3 Greece/2006 8.2 − 96 10 − 15.75 [200]
4 Egypt/2012 5.3 34,000 300 4.6 Grid & Battery 1.4 [194]
4 Algeria/ 2013 6.3 2933 3720 1.75 − 0.66 [199]
5 Algeria/ 2013 5.8 2933 3315 1.75 − 0.7 [199]
6 Algeria/ 2013 5.1 2933 2843 1.75 − 0.75 [199]
7 Turkey/2016 5.3 37000 24 4.38 Grid backup 2.846 [125]
8 Abu Dhabi/2017 6 42,000 7000 4 – 4.57 [111]
Table 12
Economic analysis and the effect of solar and wind profile on PV-Wind-RO desalination cost.
S. No. Location/year Daily solar radiation (DSR) and Wind Speed TDS (ppm) Capacity (m3
/day) SEC* (kWh/ m3
) Backup CoW ($/m3
) Ref
1 Greece 2004 DSR: 4.4 kWh/m2
/day Wind: 4.3 m/s 40,000 6–12 6.3 Battery 6.12 [135]
2 Libya/2005 DSR: 5 kWh/m2/day Wind: 4.4 m/s 42,000 300 8.67 Grid backup 4.03 [134]
3 Greece/2010 DSR: 4.4 kWh/m2/day Wind: 4.3 m/s − − Hydro turbine 2.97 [137]
4 Egypt/ 2012 DSR: 5 kWh/m2/day Wind: 5.3 m/s 34,000 300 4.6 Grid & Battery 1.4 [194]
5 Saudi Arabia/2013 DSR: 5.6 kWh/m2/day Wind: 5.08 m/s − 5 5 Battery 3.81 [140]
472

unit, and designing of hybrid power energy systems as well as the
integration of the renewable energy options with RO plants were
also reviewed.
• Accurate sizing of the HRES-RO system can facilitate the determi-
nation of the initial investment and the selection of one or more
most suited renewable energy sources for a particular site. A range
of sizing and optimization tools and algorithms for designing eco-
nomically viable HRES-RO systems were also identified in this re-
view. These tools not only facilitate economic analysis but are also
useful for estimating the reduction in GHG emissions.
• The environment-friendly RE based desalination plants are expected
to be economical and able to mitigate the exponentially growing
power demands in Saudi Arabia. Renewable energy resources such
as wind and solar, which can be exploited efficiently and effectively,
are abundant in Saudi Arabia.
Steps involved in installation of hybrid PV-wind-RO system in KSA
The steps involved in the installation of a hybrid PV-wind-RO de-
salination system in Saudi Arabia are depicted as a flowchart in Fig. 22.
To summarize, the process begins with the identification of the need for
desalination and estimating the capacity of the desalination plant that
will satisfy the requirements of the consumers of the remote location in
KSA. A suitable site will be selected for which the plant will be de-
signed, and the power consumption for driving RO desalination plant
will be estimated. The relevant site parameters, such as the solar ra-
diation, wind speed, temperature etc., will be studied for the selected
site for a period of five to ten years. Depending on this study, suitable
RE sources will be chosen for the design or sizing of a PV-wind in-
tegrated RO system. If the integration is not feasible the site selection
process will be repeated until the most favorable site for harnessing
renewable energy sources is selected. After designing the system, a
detailed technical and economic analysis, to estimate the Cost of Water
(CoW) per cubic meter, will be undertaken. If the CoW for the hybrid
PV-wind-RO system (CoW (2)) is less than the CoW of the conventional
desalination plant (CoW (1)), then the Hybrid PV-wind-RO system can
be installed. Otherwise, it is necessary to redesign and resize the system
until the optimum CoW is obtained.
Finally, this study recommends that a detailed techno-economic
evaluation be conducted for chosen remotely located communities for
RO plants of different sizes and different renewable energy resources
depending on the daily requirement of fresh water. The exploration of
the use of renewable energy resources for water desalination, particu-
larly the PV-wind hybrid power system with and without battery
backup, has many benefits.
Acknowledgment
The authors acknowledge the resources and support provided by the
Center of Research Excellence in Renewable Energy and the Center for
Engineering Research at King Fahd University of Petroleum & Minerals
for this work. This research did not receive any specific grant from
funding agencies in the public, commercial, or not-for-profit sectors.
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