~ Pergamon

Renewable Energy, Vol. 14, Nos. 1-4, pp. 345-349, 1998 © 1998 Published by Elsevier Science Ltd. All rights reserved

Printed in Great Britain P l h S0960-1481 (98) 00088-3 0960-1481/98 $19.00+0.oo

POTENTIAL FOR ECONOMIC SOLAR DESALINATION IN THE MIDDLE EAST

ROSHDY A. ABDELRASSOUL

Electrical Engineering Department, King Saud University, PO Box 800, Riyadh 11421, Saudi Arabia

E-mail : Roshdy@ksu.edu.sa

ABSTRACT

Fresh water forms only about 1% of the total water available on earth. Technologies for the desalination of seawater have considerably matured in the last decade . However, the energy required for the desalination is usually expensive in arid areas where fresh water is required. Renewable energy provides a clean, free, and low-maintenance source of energy for desalination, limited only by their initial cost, and the variability of the available energy. In this paper the potential use of solar energy for the desalination of seawater in the Middle East is evaluated. Multi-Stage Flash (MSF) desalination requires large amounts of energy, while Reverse Osmosis (RO) desalination is more energy efficient. Solar distillation is a very simple and direct method that may be used, requiring only large fiat areas of land, having no running energy costs and being very suitable for remote areas. Photovoltaics is another promising renewable energy source for seawater desalination in the Middle East. It is best suited for the RO and Electrodialysis (ED) methods. The desalination plant doesn't need to run continuously, and therefore no storage batteries are required. Diesel and / or natural gas may be used as a backup energy. © 1998 Published by Elsevier Science Ltd. All rights reserved.

KEYWORDS

Solar desalination, photovoltaics, reverse osmosis.

INTRODUCTION

Water Resources in the Middle East

Fresh water forms only about 1% of the total water available on earth. Fig. l shows the per Capita share of water in Middle East countries in the years 1995 and 2020 (Abou Rayan, 1997) It is clear that several of these countries already have an acute potable water shortage, and that the problem will increase by the year 2020.

345

346 R.A. ABDELRASSOUL

6000

~ 3000

2000

/ ' ° "

.~o ..~ . ~ , . j ~ .--.i~ ~

Fig. 1 Per Capita share of water in Middle East countries in the years 1995 and 2020.

Water Desalination in the Middle East

The worldwide capacity of desalination plants has tremendously grown during the last 10 years, mostly in the Middle East oil-rich countries. An IDA desalting plants inventory showed a worldwide capacity of more than 1.8x106 m3/day in 1993 (Morris, 1997). Except for three Gulf countries, most of the Middle East countries do not have large seawater desalination projects, as shown in Fig. 2, which displays the renewable water resources and desalination Capacity in 1994 in Middle East countries.

140000 T

=ooo~ ~

80000 oooo/ 40000

20000

o .~-,.~ ~ , a , ~ , g ~ ' - _~ . = ~ . ~ ® ~ ~ ~ c ~ ® O E ~ ~ . - ' E

1800

1600

1400

1200

1000

800

600

40O

2OO

0

Fig. 2 Renewable water resources and desalination capacity in 1994 in Middle East countries.

Potential for economic solar desalination in the Middle East 347

SOLAR DESALINATION

Seawater desalination methods may be divided into those involving a phase transition (distillation methods), such as Multi-Stage Flash (MSF), Solar Distillation, Multi-Effect Boiling (MEB), and Vapor Compression (VC), and those which don't involve a phase transition (membrane methods), such as Reverse Osmosis (RO), and Electrodialysis (ED). All seawater desalination processes require significant amounts of energy to produce potable water.

Solar energy is the major undepletable source of renewable energy. It is quite ironic that the abundance of solar energy is the cause for the water problems in arid areas. About 4.5 x l09 m3/yr, of water is currently obtained worldwide from fuel-fired desalination plants, but it is unfortunate that for producing potable water we are polluting the atmosphere ( Farinelli, et al., 1993). In the Gulf area 95% of its water supply is obtained by desalination of seawater, where the desalination plants are fueled with oil. A recent study

• - 9 3 shows that the demand for potable water in Eg,::(pt is estimated to be 12.9 x 10 m/Yr. By the year 2025, almost 3.5 times the present demand of 3.7 x 10" m3/Yr., and the water required in order to respond to the economic development plans - if it will increase in the same manner - will be 150 x 109 m3/yr. (Megahed, et al., 1991).

Solar enegy technology may be divided into photovoltaics (PV) and solar thermal conversion. Each may be used in a flat-plate configuration (one sun) or concentrator. Solar desalination processes may be divided into direct methods, in which the solar collectro and the desalination unit are one integral unit, and indirect methods, where solar energy is first converted to usable heat or electric power, which is then used as the energy source for the desalination plant.

The technologies adopted for seawater desalination in the Middle Ease should be independent of the expected depletion of fossil fuels, on the one hand, and also should not be adding to the pollution of the environment, on the other hand. Solar energy is the most important renewable source of energy, particularly in the Middle East which enjoys an abundant incidence of solar radiation of 3,000 - 3,500 hours of sunshine per Year, and receives more than 5.0 kW/m 2 of solar energy per day (Sayigh, et al., 1984). Solar Energy is also more economical and safer to use for water desalination than nuclear energy. The use of solar energy for water desalination has been investigated and used for some time. The devices used heat saline water by the sun's rays so that the production of water vapor increases and is then condensed on a cool surface. An example of this type of process id the green house solar still. Nowadays simple, reliable and low cost methods to collect and store the necessary heat for a continuos day-and-night production of water by means of low temperature seawater evaporation and condensation cycles similar to a normal multi-stage flash distillation (MSD) and multiple effect distillation (MED)are having wide application in the Gulf area. In these operations seawater is being heated by the solar system and evaporates via a vacuum process. The boiling point of water drops down to only 35 °C under vacuum. In these processes it is also possible to recuperate the high amount of evaporation heat by condensating the vapor with the help of the colder seawater which enters and runs through the plant, thus getting preheated before, picking up the solar heat for its evaporation. Recently, a solar desalination experimental plant was built in Abu Dhabi, U.A.E., which has a maximum capacity of 120 m3/day of distillate (EI-Nashar, et al, 1987). This plant is now the world's largest solar desalination pilot plant currently in operation.

Salt can be removed from water by a number of different physical and chemical processes, however, the multi-stage flash distillation and the reverse osmosis are the most common ones. These two processes make up about 86% of the total. The remaining 14% is made up of the other methods, e.g. multiple effect, electrodialysis, vapor condensation .... etc.

348 R.A. ABDELRASSOUL

Other methods of solar seawater desalination would call for large area of phtovoltaic ceils which convert sun energy into electricity, which is then used for highly pressurizing and pumping seawater through membranes using the well known principle of reverse osmosis. Battery storage would also be necessary to overcome the strongly intermittent nature of solar radiation {BenChikh, 1995). Energy storage in batteries is only practical for small-scale plants, due to the cost of batteries, however, since water can be stored relatively easily, the intermittent production of potable water is not a problem. A number of PV-RO plants for small-scale production have been constructed, and all of which proved to be reliable (Morris, 1997), PV plants are virtually maintenance free. Only surface cleaning is required.

ECONOMICS OF DESALINATION

Desalination facilities exist in more than 120 countries. The capital and operating costs for the desalination have tended to decrease over the years. In 1990, the total production costs, including capital recovery, for brackish water systems having capacities of 4,000 to 40,000 m3/d was $0.25 to $0.60 ~,r m3, and that for potable water by seawater desalting for plants having capacities of 4,000 to 20,000 m / d was $1.00 to $4.00 per m 3, in the USA (Buros, 1990). Morris (1997) compared the energy and total costs of water desalination using different techniques, Fig. 3. The cost of electricity generated form photovoltaic cells is still high, and therefore it should only be used in conjunction with processes which have high energy efficiencies. This means RO for seawater and (Electrodialysis Reversal) EDR for brackish water.

Energy Costs

r=====l q

r J

~IED/R

$1m 3

Total Costs

i

!

I-===1

I l

f - - - - - - i

$/m 3

Fig. 3 Energy costs and total costs of water desalination using different techniques.

CONCLUSIONS

The cost of potable water produced from desalination plants using solar energy as the main source of energy can be much less than the cost of the same water produced from desalination plants using conventional energy sources. The use of renewable energy sources in desalination plants will save fossil fuels for other applications, minimize pollution of the environment, and provides a free, continuous, clean source of energy, beside being simple and easy to operate and maintain. As the cost of potable water increases, the cost of utilizing solar energy and of solar cells decreases, and it becomes competitive, particularly for remote areas.

Potential for economic solar desalination in the Middle East 349

REFERENCES

Abdelrassoul, R. A. and E .M. A. Rassoul (1996). Prospects of solar desalination inEgypt. First International Water Technology Conference, IWTC'96, Alexandria, Egypt, 26 - 29 February.

Abou Rayan, M. (1997). Prospects of solar desalination. Second International Water Technology Conference, IWTC'97, Alexandria, Egypt, 28 - 31 March, 339 - 354.

BenChikh, O. and M. Abou-Rayan (1995). Technologie de Dessalement de l'eau. UNESCO, Paris.

Buros, O. K. (1990). The Desalting ABC, prepared for the International Desalination Association.

E1-Nashar, A. M. and A. M. E1 Baghdadi (1987). Seawater distillation by solar energy. Desalination, 61, 49 - 66.

Farinelli, U., B. Ischinger, and H. Tabor (1993). Solar enegry - A peaceful energy. World Solar Summit, UNESCO, Paris, 5 - 9 July.

Megahed, M. M. and S. S. Mekhemer (199l). Dealination in the Egyptian Context. IAEA First Regional Meeting: Nuclear Desalination as a Source of low cost potable water, Cairo, Egypt.

Morris, R. (1997). Desalination options using renewable energy sources. Second International Water Technology Conference, IWTC'97, Alexandria, Egypt, 28 - 31 March, 49 - 71.

Sayigh, A. M. and D. Jarrer (1984). Solar Mapping of the Arab World.