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: etzen@cres.gr (E. Tzen), richard.mor-

ris14@ntlworld.com (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

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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

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