Renewable energy sources for desalination

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    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

    depends on how such water can be made available. and utilize solar, wind or geothermal energy to produce

    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

    *Corresponding author. Tel.: +30-210-6603300; fax: +30-

    210-6603301.

    Solar Energy 75 (2003)E-mail addresses: etzen@cres.gr (E. Tzen), richard.mor-

    ris14@ntlworld.com (R. Morris).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

    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 specic plants as

    well as data on the economics. Operational data andplants 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 PVreverse osmosis, wind-

    mechanical-vapor compression, geothermal-multieect distillation, etc as well as technologies selection guidelines. Also,

    included applications and lessons learned from specic 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

    characterized by lack of potable water and lack of an

    electricity grid. In recent years the European Union has

    intensied R&D eorts in this eld. 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 specic locationsRenewable energy so

    Eftihia Tzen a,*,a Centre for Renewable Energy Sources, 19th

    b Richard Morris & Associates, 9

    Received 6 June 200

    Abstract

    Renewable energy sources (RES) coupled to desalinat

    needs of power and water in remote regions, where conne

    not feasible, and where the water scarcity is severe. Stand1 Tel.: +44-141-637-3146; fax: +44-141-585-0515.

    0038-092X/$ - see front matter 2003 Elsevier Ltd. All rights reservdoi:10.1016/j.solener.2003.07.010ces for desalination

    hard Morris b,1

    arathonos Ave., GR-190 09 Pikermi, Greece

    m Drive Newlands, Glasgow, UK

    cepted 10 July 2003

    ers a promising prospect for covering the fundamental

    to the public electrical grid is either not cost eective or

    ne systems for electricity supply in isolated locations are

    375379

    www.elsevier.com/locate/solenerin the near future.

    ed.

  • 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

    easy transportation to site, simple pre-treatment and

    intake system to ensure proper operation and endurance

    of a plant at the often dicult conditions of the remote

    areas. Concerning their combination, the existing expe-

    rience has shown no signicant 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 at 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 dierent

    desalination techniques are given below. These data

    refer to conventional operated plants in operation at

    their nominal power consumption and production.

    MSF10%

    MED14%

    VC5%

    Other4%

    376 E. Tzen, R. Morris / Solar Energy 75 (2003) 375379others are better suited for small scale application.

    Before any process selection can start, a number of

    basic parameters should be investigated. The rst 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 (

  • For RO systems: 5.9 kWh/m3 without energy recov-ery (large production plants), 34 kWh/m3 with en-

    ergy recovery (using a turbine)

    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

    specic problems when it is connected to a variable

    Solar PV43%

    Solar Thermal27%

    Wind20%

    Hybrid10%

    Fig. 2. Energy sources for desalination.

    RE

    E. Tzen, R. Morris / Solar Energy 75 (2003) 375379 377 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: 8.516 kWh/m3, depending on sizeplants.

    As can be seen from the above gures, RO, requires

    signicantly 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 o-grid (stand-aloneautono-

    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

    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.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 startstop 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 oer 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 nancial 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) 3753793. 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 reected in the plants

    currently being built and tested. Table 2 provides a

    number of RES Desalination installed plants.

  • 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

    the promise of economic and environmental viability on

    a large scale. There is a need to accelerate the develop-

    on Possibilities of Geothermal Energy Development in the

    Aegean Islands Region, Milos Island, Greece, pp. 206219.

    E. Tzen, R. Morris / Solar Energy 75 (2003) 375379 379Concerning the coupling of the two technologies no

    major technical problems have been referred.

    From the existing experience important parameters

    for the sucient 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 sta 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 aects the market force and should beMorris, 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 EuropeFrom PV Technology to

    Energy Solutions Conference, Rome, Italy, pp. 11541156.ment of novel water production systems from renew-

    ables. Particularly there is a need for a much stronger

    eort 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 Europes

    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 Workshopdoubt bear fruit in the future as desalination processes

    become more robust and more energy ecient. 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

    Renewable energy sources for desalinationIntroductionTechnologies combination and selection guidelinesRES desalination applications and lessons learnedConclusionsReferences

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