1. Introduction
Water is one of the most abundant resources on earth. However,
most of it, about 97%, is saline water in the oceans and the
remaining 3% is freshwater. The freshwater scarcity is becoming an
increasingly significant problem in many areas around the world
[1]. Desalination has been demonstrated to be a promising and
viable technology to provide drinking water [2]. But the main issue
impeding the wider use of desalination technologies is the high
economic cost involved, especially due to intensive energy consumption
[3]. In addition, current use of conventional fossil fuels as
main power source is increasingly raising concerns over climate
change and promoting global awareness for carbon dioxide emission
reduction and cleaner energy supplies [4]. In fact, because of
the shortage of freshwater, the opportunity for the use of renewable
energy to power small seawater and brackish water desalination
has become possible in many small cities and villages on the
coastal areas and in many of the remote small villages and cities in
the mainland [5]. Regions like GCC (Gulf Cooperation Council)
countries [6] have many hours of sun shine which also makes solar
energy an attractive source of renewable energy in those areas [7].
Actually, renewable energy powered RO (reverse osmosis)
desalination and the optimum operation management have been
widely studied in previous literature [8e13]. Among the renewable
energy powered RO desalination applications, stand-alone PVRO
plant has been demonstrated to be feasible both in terms of techniques
and costs in lab-scale and pilot-scale systems [14e17]. At
present, it is considered as a proper solution for small-scale desalination
applications in rural areas with high solar insulation [18].
The effectiveness of the stand-alone plant depends on the location,
geographical conditions, topography of the site, and the capacity of
the plant. Bilton et al. presented a generalised methodology to
evaluate the feasibility of small-scale PVRO systems in challenging
environment [19]. Their findings indicate that the freshwater cost
of PVRO is economically feasible for most remote areas with high
availability of solar energy [20]. Fraidenraich et al. proposed a
simple and general theoretical procedure for estimating the SEC
(specific energy consumption) to evaluate feasibility of a PVRO
plant and validate the methodology with experiments [21]. During
the last decade, with the significant development in optimal designs
[22,23] and control strategies [24,25] for PVRO plants, the cost
of freshwater has considerably reduced. However, the sunshine is
not available at night. In order to prolong the operational hours, and