Renewable energy driven desalination systems modelling

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  • discussed as an innovative approach to desalinate water economically and in an environmentally friendly manner. The stochasticnature of renewable energy sources (RES) which results in the use of expensive energy storage systems usually limits the penetrationof RES to the power generation system of a region. Desalination systems can utilise in a more economically ecient way the avail-

    able RES potential. The energy produced is consumed for potable water production which can be stored economically for a largeperiod of time before consumption. An integrated model for the use of renewable energies (wind, solar) in the desalination of sea-water has been developed in the context of REDDES project. In this work, a model is developed where desalination technologies are

    coupled with RES power systems to produce potable water at the lower possible cost. The presented model is incorporated in theREDDES software. 2005 Elsevier Ltd. All rights reserved.

    Keywords: Renewable energy systems; Water desalination systems; Energy eciency; Water security

    1. Introduction

    The limited market penetration of renewable sourcesof energy (RES) can be attributed to a large number ofconstraints, including problems related to nancing, reg-ulation, technical issues, lack of information, educationand training. The stochastic nature of RES which resultsin the use of expensive energy storage systems usuallylimits the penetration of RES to the power generationsystem of a region. The produced energy varies in timeas wind speed or solar radiance varies and the powerhas to be consumed directly or else it will be lost. RESpenetration in the desalination industry does not facethe same barriers as in the case of RES for electricity

    power production. In the case of RESedesalinationcoupling the energy is consumed directly for water pro-duction, the water can be stored cheaply in large quan-tities and for long periods [1].

    Several desalination processes have been developedbut not all of them are reliable and in commercial use.The most important processes are split into two maincategories [1]:

    Thermal (or distillation) processes: Multi-StageFlash Distillation (MSF), the Multi-Eect Distilla-tion (MED), the Thermal Vapour Compression(TVC) and the Mechanical Vapour Compression(MVC) processes.Renewable energy driven de

    C. Koroneos*, A. D

    Laboratory of Heat Transfer and Environmental

    P.O. Box 483, 541 2

    Received 10 January 20

    Available online

    Abstract

    Renewable energy sources for powering desalination processewhere the use of conventional energy is costly or unavailable. Re

    Journal of Cleaner Productio* Corresponding author. Tel.: C30 231 0995968; fax: C30 231

    0996012.

    E-mail address: koroneos@aix.meng.auth.gr (C. Koroneos).

    0959-6526/$ - see front matter 2005 Elsevier Ltd. All rights reserveddoi:10.1016/j.jclepro.2005.07.017salination systems modelling

    ompros, G. Roumbas

    Engineering, Aristotle University of Thessaloniki,

    4 Thessaloniki, Greece

    05; accepted 6 July 2005

    19 September 2005

    s is a very promising option especially in remote and arid regionsnewable energy driven desalination systems have been extensively

    n 15 (2007) 449e464

    www.elsevier.com/locate/jclepro Membrane processes: Reverse Osmosis (RO) andElectrodialysis (ED) processes. ED is conned to de-salination of brackish water while RO can be usedfor both, brackish and seawater desalination.

    .

  • desalination processes.f. Geothermal-heateThermal Vapour conversion(TVC)

    g. Geothermal-heateMulti-Stage Flash Distillation(MSF)

    RES

    Solar

    Wind PV system

    Shaft Electricity

    ROMVC ED

    Fig. 1. Coupling of RES withGenerally, solar thermal distillation application aresolar assisted rather than stand-alone. These unitsare suitable when low enthalpy energy is also avail-able. These systems are not considered suitable for

    GeothermalSolar-Thermal

    Heat

    MEDMSFTVCThe selection of a process usually is based on severalparameters, such as site conditions, local circumstances,energy availability, etc. The best desalination systemfor a particular application will be the system that reli-ably produces water of the expected quality and quantityat reasonable cost.

    The feasible RESedesalination technology combina-tions are very clearly demonstrated in Fig. 1. The dier-ent power forms derived from RES are coupled withthe equivalent desalination technology. The RESedesalination coupling schemes under examination couldbe divided in two categories:

    1. RESedesalination coupling schemes that require theRES unit and the desalination unit to be located inthe same area. Such couplings are:a. Wind-shafteMechanical Vapour Compression(MVC) coupling

    b. Solar thermal-heateThermal Vapour conversion(TVC)

    c. Solar thermal-heateMulti-Stage Flash Distilla-tion (MSF)

    d. Solar thermal-heateMulti-Eect Distillation(MED)

    e. Solar thermal-heateDistillation

    h. Geothermal-heateMulti-Eect Distillation (MED)2. RESedesalination coupling schemes that do notrequire the RES unit and the desalination unit tobe located in the same area. Such couplings are:a. Wind-electricityeMechanical Vapour Compres-sion (MVC) coupling

    b. Wind-electricityeReverse Osmosis (RO)c. Solar PV-electricityeReverse Osmosis (RO)d. Solar PV-electricityeMechanical Vapour Com-

    pression (MVC) couplinge. Geothermal-electricityeMechanical VapourCom-pression (MVC) coupling

    f. Geothermal-electricityeReverse Osmosis (RO)

    A short assessment of each technically feasible appli-cation can be made:

    Thermal-distillation processes. Thermal distillationplants such as MED, MSF or TVC can utilise solarthermal energy or geothermal energy. Thermal pro-cesses require a high-energy input (due to the energyrequired for change of phase) and also auxiliary elec-tricity for pumping needs. Solar thermal systems areheavily dependent on solar radiation and weatherconditions and they need large heat accumulators.

    450 C. Koroneos et al. / Journal of Cleaner Production 15 (2007) 449e464

  • small scale and remote areas. Geothermal systemsare ideal for thermal-distillation processes but arelimited to areas where geothermal elds exist.

    Solar PVeRO. The electricity form PV systems canbe used to drive high-pressure pumps in RO desali-nation plants. The main advantage of PVedesalina-tion systems is their ability to develop small sizedesalination plants. The energy production unit con-sists of a number of photovoltaic modules, whichconvert solar radiation into direct electric current(DC). DC/AC inverters have to be used becauseRO uses alternating current (AC) for the pumps.Energy storage (batteries) is required for PV outputpower smoothing or for sustaining system operationwhen insucient solar energy is available.

    WindeRO/MVC. Wind energy can be coupled withRO and MVC processes for the desalination of wa-ter. RO and MVC require electrical or mechanicalenergy as primary energy input, which can be pro-vided from a single wind turbine or a wind farm.The selection between the technologies depends onthe feed water quality and the required product waterquality. MVC, as all distillation processes producewater with very low salinity (below 20 ppm totaldissolved solids). Membrane processes (RO) pro-duce water with higher salinity (500 ppm TDS).Because of the variability of the wind speed, it isdicult to predict the energy output. Appropriatepower control and conditioning systems are re-quired in order to match the ratio of the power in-put to the desalination load.

    Because of the spatial distribution of the RES, RESedesalination coupling schemes that do not require theRES unit and the desalination unit to be located in thesame physical area are of special interest. In the presentpaper, wind energy and solar PV coupled with RO andMVC are examined. The models were developed in theframework of the Renewable Energy Driven DESalina-tion (REDDES) project which was funded by the EU [2].

    2. Renewable energy sources

    2.1. Modelling of solar photovoltaic energy (PV)

    Many types of semiconductor materials can convertlight into electrical power by means of the photovoltaic(PV) eect, but only a few of them have been used assolar cells to date. The commercial market for PV cellstoday is dominated by crystalline silicon (Si). Howeverother materials, notably amorphous silicon (a-Si), cad-mium telluride (CdTe), copper indium diselenide(CuInSe2, CIS), and gallium arsenide (GaAS), are alsoavailable and substantial investments are being made

    C. Koroneos et al. / Journal of Cleain their development [3].When light is absorbed by a solar cell, electrons are re-leased and move according to the internal electric poten-tial so that when a load is connected across the contactsan electric current ows. The voltage across a solar cell isprimarily dependent on the design and the materials ofthe cell, whilst the electrical current depends primarilyon the incident solar irradiance and the cell area. Theoutput from a typical solar cell, which is exposed to thesun, increases from zero at sunrise to a maximum at mid-day and then falls again to zero at dusk. The ratio of elec-trical power produced by a solar cell to the incident solarirradiance is known as the PV cell eciency.

    Groups of cells are mounted together on a glass plateand wired in series to form a PVmodule typically around0.5 m2 in size. Groups of modules can be connected to-gether electrically to form a PV array. PV arrays canbe mounted on a xed structure or on a sun-trackingstructure to maximize the incident solar radiation.

    The power production capacity of a PV array isexpressed in Watt-peak (Wp) units. A PV cell of 1 Wpproduces 1 W of electrical energy when exposed to solarirradiance of 1000 Wm2 at a cell temperature

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