renewable energy sources for desalination
TRANSCRIPT
Solar Energy 75 (2003) 375–379
www.elsevier.com/locate/solener
Renewable energy sources for desalination
Eftihia Tzen a,*, Richard Morris b,1
a Centre for Renewable Energy Sources, 19th km Marathonos Ave., GR-190 09 Pikermi, Greeceb Richard Morris & Associates, 9 Letham Drive Newlands, Glasgow, UK
Received 6 June 2003; accepted 10 July 2003
Abstract
Renewable energy sources (RES) coupled to desalination offers a promising prospect for covering the fundamental
needs of power and water in remote regions, where connection to the public electrical grid is either not cost effective or
not feasible, and where the water scarcity is severe. Stand-alone systems for electricity supply in isolated locations are
now proven technologies. Correct matching of stand-alone power supply desalination systems has been recognized as
being crucial if the system is to provide a satisfactory supply of power and water at a reasonable cost. The paper covers
plants installed since 1990 on the coupling of the two technologies. The main driver promoting the take up of this
technology is that water is a limiting factor for many countries in the Mediterranean region. This paper presents the two
technologies, RES desalination, and describes the most promising couplings such as PV–reverse osmosis, wind-
mechanical-vapor compression, geothermal-multieffect distillation, etc as well as technologies selection guidelines. Also,
included applications and lessons learned from specific applications as well as data on the economics. RES for desa-
lination is an important challenge and useful work has been done. However in order to provide practical viable plants,
much remains to be done.
� 2003 Elsevier Ltd. All rights reserved.
1. Introduction
The provision of fresh water is becoming an in-
creasingly important issue in many areas in the world. In
arid areas potable water is very scarce and the estab-
lishment of a human habitat in these areas strongly
depends on how such water can be made available.
Desalination of seawater and brackish water is one of
the ways of meeting water demand. Renewable energy
systems have mostly been developed to serve the elec-
tricity needs via a network utilizing locally available
energy resources. Production of fresh water using desa-
lination Technologies driven by RES is thought to be
viable solution to the water scarcity at remote areas
* Corresponding author. Tel.: +30-210-6603300; fax: +30-
210-6603301.
E-mail addresses: [email protected] (E. Tzen), richard.mor-
[email protected] (R. Morris).1 Tel.: +44-141-637-3146; fax: +44-141-585-0515.
0038-092X/$ - see front matter � 2003 Elsevier Ltd. All rights reserv
doi:10.1016/j.solener.2003.07.010
characterized by lack of potable water and lack of an
electricity grid. In recent years the European Union has
intensified R&D efforts in this field. Worldwide, several
RES desalination pilot plants have been installed and
the majority have been successful in operation. Virtually
all of them are custom designed for specific locations
and utilize solar, wind or geothermal energy to produce
fresh water.
The present work presents a combination of the two
technologies, RES and desalination, and describes the
most promising couplings such as photovoltaic (PV)–
reverse osmosis (RO), wind-RO, wind-mechanical vapor
compression, etc. Also included are design guidelines,
applications and lessons learned from specific plants as
well as data on the economics. Operational data and
experience from these plants can be utilized to achieve
higher reliability and cost minimization.
Although RE powered desalination systems cannot
compete with conventional systems in terms of the cost
of water produced, they are applicable in certain areas
and are likely to become more widely feasible solutions
in the near future.
ed.
RO62%
ED5%
MSF10%
MED14%
VC5%
Other4%
Fig. 1. Desalination processes used in conjunction with re-
newable energy.
376 E. Tzen, R. Morris / Solar Energy 75 (2003) 375–379
2. Technologies combination and selection guidelines
The selection of the appropriate RES desalination
technology depends on a number of factors. These in-
clude, plant size, feed water salinity, remoteness, avail-
ability of grid electricity, technical infrastructure and the
type and potential of the local renewable energy resource.
Among the several possible combinations of desali-
nation and renewable energy technologies, some seem to
be more promising in terms of economic and techno-
logical feasibility than others. However their applica-
bility strongly depends on the local availability of
renewable energy resources and the quality of water to
be desalinated. In addition to that, some combinations
are better suited for large size plants, whereas some
others are better suited for small scale application.
Before any process selection can start, a number of
basic parameters should be investigated. The first is the
evaluation of the overall water resources. This should be
done both in terms of quality and quantity (for brackish
water resource). Should brackish water be available then
this may be more attractive as the salinity is normally
much lower (<10,000 ppm), and hence the desalination
of the brackish water should be the more attractive
option. In inland sites, brackish water may be the only
option. On a coastal site seawater is normally available.
The identification and evaluation of the renewable
energy resources in the area, completes the basic steps to
be performed towards the design of a RES driven de-
salination system. Renewable energy driven desalination
technologies mainly fall into two categories. The first
category includes distillation desalination technologies
driven by heat produced by RES, while the second in-
cludes membrane and distillation desalination technol-
ogies driven by electricity or mechanical energy
produced by RES. The most promising and applicable
RES desalination combinations are shown in Table 1.
(Desalination Guide Using Renewable Energies, 1998).
Such systems should be characterized by robustness,
simplicity of operation, low maintenance, compact size,
Table 1
RES desalination combinations
RES technology Feed water salinity
Solar energy
Solar thermal Seawater
Seawater
Photovoltaics Seawater
Brackish
Brackish
Wind energy Seawater
Brackish
Seawater
Geothermal Seawater
easy transportation to site, simple pre-treatment and
intake system to ensure proper operation and endurance
of a plant at the often difficult conditions of the remote
areas. Concerning their combination, the existing expe-
rience has shown no significant technical problems.
The most popular combination of technologies is the
use of PVwith reverse osmosis (see Figs. 1 and 2) (Morris,
2000). PV is particularly good for small applications in
sunny areas. For large units, wind energy may be more
attractive as it does not require anything like as much
ground. This is often the case on islands where there is a
good wind regime and often very limited flat ground.
With distillation processes, large sizes are more attractive
due to the relatively high heat loses from small units.
Energy cost is one of the most important elements in
determining water costs where the water is produced
from desalination plants. Some energy-consumption
data for traditional desalination plants using different
desalination techniques are given below. These data
refer to conventional operated plants in operation at
their nominal power consumption and production.
Desalination technology
Multi-effect distillation (MED)
Multi-stage flashing (MSF)
Reverse osmosis (RO)
Electrodialysis (ED)
Reverse osmosis (RO)
Mechanical vapor compression (MVC)
Multi-effect distillation (MED)
Solar PV43%
Solar Thermal27%
Wind20%
Hybrid10%
Fig. 2. Energy sources for desalination.
E. Tzen, R. Morris / Solar Energy 75 (2003) 375–379 377
• For RO systems: 5.9 kWh/m3 without energy recov-
ery (large production plants), 3–4 kWh/m3 with en-
ergy recovery (using a turbine)
• For ED systems: 1.22 kWh/m3 (for feed water salin-
ity of 3000 ppm and product salinity of 500 ppm).
This consumption is increased by the operation time:
increment of 50% after 2.5 operation years
• For VC systems: 8.5–16 kWh/m3, depending on size
plants.
As can be seen from the above figures, RO, requires
significantly less electrical or mechanical energy to treat
seawater than any of the other processes. Hence it is the
natural choice in most instances.
Among the technologies selection another parameter
is the type of connection of the two technologies. A re-
newable desalination plant can be designed to operate
coupled to the grid or off-grid (stand-alone––autono-
mous system). Where the system is grid connected, the
desalination plant can operate continuously as a con-
Table 2
RES Desalination applications
Plant location Water type Desalination unit,
capacity
RE
Abu Dhabi, UAE SW 80 m3/d MED 18
Lampedusa, Italy SW 3+2 m3/h RO 10
University of Almeria,
Spain
BW 2.5 m3/h RO 23
Maagan Michel, Israel BW 0.4 m3/h RO 3.5
W
ITC, Gran Canaria SW 50 m3/d MVC 23
Almeria, Spain,
CIEMAT, DLR
SW 3 m3/h MED 6.5
Syros island, Greece SW 900 m3/d RO 50
Kimolos island,
Greece (Karytsas
et al., 2002)
SW 80 m3/d MED G
CRES, Greece SW 130 lt/h RO 4
SW: seawater.
BW: brackish water.
ventional plant and the renewable energy source merely
acts as a fuel substitute. Where no electricity grid is avail-
able, autonomous systems have to be developed which
allow for the intermittent nature of the renewable energy
source. Due to the dispersed population that character-
izes the South Mediterranean and Gulf areas, relatively
small systems are used to cover the potable water needs in
remote villages. The main desirable features for such
systems are the low cost, low maintenance requirements,
simple operation, as well as the high reliability.
The latter case poses the problem of renewable en-
ergy variability because most energy systems lack an
inherent energy storage mechanism. Desalination sys-
tems have traditionally been designed to operate with a
constant power input (Tzen et al., 2002). Unpredictable
and non-steady power input, force the desalination plant
to operate in non-optimal conditions and may cause
operational problems. Each desalination system has
specific problems when it is connected to a variable
power system. For instance, the reverse osmosis (RO)
system has to cope with the sensitivity of the membranes
regarding fouling, scaling, as well as unpredictable
phenomena due to start–stop cycles and partial load
operation during periods of oscillating power supply. On
the other hand the vapor compression system has con-
siderable thermal inertia and requires considerable en-
ergy to get to the nominal working point. Thus, for
autonomous systems a small energy storage system,
usually batteries, should be added to offer stable power
to the desalination unit. Clearly this only applies to
small electrically driven systems. Thermal storage can be
added for thermal systems in the form of hot oil or hot
water but is expensive. Any candidate option resulting
from the previous parameters should be further screened
through constraints such a site characteristics (accessi-
bility, land formation, etc.) and financial requirements.
S installed power Commissioning
year
Unit water cost
62 m2, collectors 1984 8 USD/m3
0 kWp PV 1990 �6.5 €/m3
.5 kWp PV 1990 –
kWp PV, 0.6 kW 1997 –
/T+3 kW diesel
0 kW W/T 1988
MWht collectors 1988 �3.5 €/m3
0 kW W/T 1998 –
eothermal, 61 �C 2000 –
kWp PV,1 kW W/T 2002 –
378 E. Tzen, R. Morris / Solar Energy 75 (2003) 375–379
3. RES desalination applications and lessons learned
Over the last two decades in particular, numerous
desalination systems utilizing renewable energy have
been constructed. Almost all of these systems have been
built as research or demonstration projects and were
consequently of a small capacity. It is not known how
many of these plants still exist but it is likely that only
some remain in operation. The lessons learnt have
hopefully been passed on and are reflected in the plants
currently being built and tested. Table 2 provides a
number of RES Desalination installed plants.
E. Tzen, R. Morris / Solar Energy 75 (2003) 375–379 379
Concerning the coupling of the two technologies no
major technical problems have been referred.
From the existing experience important parameters
for the sufficient operation and performance of such
systems are the proper design and sizing of the RES
desalination system as well as the fully automation of
the system due to the need of reducing the staff re-
quirements and increasing system reliability. For the
autonomous hybrid system much work should be done
on the system control for optimum exploitation of the
renewable energy sources. Finally, cost is an important
parameter that affects the market force and should be
considered mainly by the manufacturers of both tech-
nologies, RES desalination.
As stated earlier, most of the RES desalination plants
constructed to date have been either as research or
demonstration projects. The results of this work will no
doubt bear fruit in the future as desalination processes
become more robust and more energy efficient. In par-
allel to this, developments in renewable energy are
providing more reliable devices at cheaper prices. These
trends are liable to continue for the foreseeable future.
4. Conclusions
The worlds water needs are increasing dramatically.
New wind, solar and other renewable technologies that
can be used for desalination are rapidly emerging with
the promise of economic and environmental viability on
a large scale. There is a need to accelerate the develop-
ment of novel water production systems from renew-
ables. Particularly there is a need for a much stronger
effort in R&D and D currently inadequate in Europe,
which should include a closer collaboration between the
RE and Desalination Industries, together with research
institutes as well as co-operation namely with Europe’s
neighbors in the Mediterranean area and Middle East
and Africa. Additionally, acceleration of information
dissemination, education and training on RES desali-
nation is a necessity. Keeping in mind the climate pro-
tection targets and strong environmental concerns,
future water desalination around the world should be
increasingly powered by solar, wind and other clean
natural resources. Such environmentally friendly sys-
tems should be potentially available at economic costs.
References
Desalination Guide Using Renewable Energies, 1998. THER-
MIE Programme, CRES, Greece, ISBN 960-90557-5-3.
Karytsas, K. et al., 2002. The Kimolos Geothermal Desalina-
tion Project. In: Proceedings of the International Workshop
on Possibilities of Geothermal Energy Development in the
Aegean Islands Region, Milos Island, Greece, pp. 206–219.
Morris, R., 2000. UNESCO Workshop June 2000, Santorini,
Greece.
Tzen, E., Sigalas, M., et al., 2002. Design and development of a
hybrid autonomous system for seawater desalination. In:
Proceedings of PV in Europe––From PV Technology to
Energy Solutions Conference, Rome, Italy, pp. 1154–1156.