CHAPTER 9 SOLAR DESALINATION - MIT

1 CHAPTER 9. SOLAR DESALINATION . John H. Lienhard,1, Mohamed A. Antar,2 Amy Bilton,1 Julian Blanco,3 &. Guillermo Zaragoza4. 1. Center for Clean Water and Clean Energy, Room 3-162, Department of Mechanical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139-4307, USA. 2. Department of Mechanical Engineering, King Fahd University of Petroleum and Minerals, Dhahran, Saudi Arabia 3. Plataforma SOLAR de Almeria, Carretera de Senes s/n, 04200 Tabernas (Almeria), Spain 4.

2 Visiting Professor of Electrical Engineering, King Saud University, Riyadh, Saudi Arabia . Address all correspondence to John H. Lienhard E-mail: In many settings where freshwater resources or water supply infrastructure are inadequate, fossil energy costs may be high whereas SOLAR energy is abundant. Further, in the industri- alized world, government policies increasingly emphasize the replacement of fossil energy by renewable, low-carbon energy, and so water scarce regions are considering SOLAR -driven DESALINATION systems as a supplement to existing freshwater supplies.

3 Even in regions where petroleum resources are copious, SOLAR -driven DESALINATION is attractive as a means of con- serving fossil fuel resources and limiting the carbon footprint of DESALINATION . Finally, in set- tings that are remote and off-the-grid, a SOLAR driven DESALINATION system may be more eco- nomical than alternatives such as trucked-in water or DESALINATION driven by diesel-generated electricity. This article reviews various technologies that couple thermal or electrical SOLAR energy to thermal or membrane based DESALINATION systems.

4 Basic principles of DESALINATION are reviewed. SOLAR stills and humidification-dehumidification DESALINATION systems are dis- cussed. Membrane distillation technology is reviewed. Current designs for SOLAR coproduction of water and electricity are considered. Finally, photovoltaic driven reverse osmosis and elec- trodialysis are reviewed. The article concludes by summarizing the prospects for cost efficient SOLAR DESALINATION . 1. INTRODUCTION. Water scarcity is a growing problem for large regions of the world. Scarcity results when the local fresh water demand is similar in size to the local fresh water supply.

5 Figure 1. shows regions of the world in which water withdrawal approaches the difference between evaporation and precipitation, resulting in 3 The primary drivers of increasing water scarcity are population growth and the higher consumption associated with rising standards of living. A lack of infrastructure for water storage and distribution is also a fac- tor in the developing world. Over time, global climate change is expected to affect existing water resources as well, potentially altering the distribution of wet and arid regions and ISSN: 1049 0787; ISBN: 1 978 56700 311 6/12/$ + $ 277.

6 C 2012 by Begell House, Inc. 278 A NNUAL R EVIEW OF H EAT T RANSFER. NOMENCLATURE. Acol area of SOLAR collector, m2 LEP liquid entry pressure, bar Amem reverse osmosis membrane surface L distance between water surface and area, m2 glass cover, m Apanel PV panel area, m2 M molecular weight, g mol 1. C0 PV panel performance constant, V m p mass flow rate of purified water, kg s 1. C1 PV panel performance constant, Md hourly distillate collected, kg m 2. V K 1 N molar flow rate, mol s 1. Cf c average concentration of water in n PV model diode ideality factor (Sec.)

7 7). the membrane feed channel, mg L 1 n depreciation period in years (Sec. 6). Cp concentration of reverse osmosis Nu Nusselt number permeate water, mg L 1 P pressure, Pa cp specific heat at constant pressure, pf polarization factor J kg 1 K 1 ppm parts per million, mg kg 1. Enet annual net electricity delivered to Pw water partial pressure (at T w ), mm Hg the grid, kWh Pwg water partial pressure (at T g ), mm Hg FF membrane fouling factor Q rate of heat transfer into system, J s 1. Fs radiation shape factor Q least minimum (reversible) rate of heat G Gibbs energy of per mole, J mol 1 transfer to separate, J s 1.

8 Grad SOLAR irradiation, W m 2 q charge of an electron, C. GOR gained output ratio qb heat loss through still material to H enthalpy per mole, J mol 1 surroundings (ground), W m 2. Hsol daily SOLAR incidence on SOLAR qc convection heat transfer from water to collector, J m 2 day glass cover, W m 2. hf g latent heat of vaporization, J kg 1 qga heat transfer from the glass cover to h heat transfer coefficient, W m 2 K 1 ambient air, W m 2. hf g latent heat of evaporation qe evaporation heat loss from water to (difference between the enthalpy of glass cover, W m 2.)

9 Saturated vapor and that of saturated Rs PV panel series resistance, . liquid at specified temperature), Ra Rayleigh number J kg 1 Rsh PV panel shunt resistance, . I PV panel current, A Re Reynolds number I0 reverse saturation current, A S entropy per mole, J mol 1 K 1. I ph PV panel light generated current, A S gen rate of entropy generation in system, k thermal conductivity, W m 1 K 1 J s 1 K 1. KA membrane permeability for water, SW specific work (per unit mass of m bar 1 s 1 purified water), J kg 1. KB membrane permeability for salt, T cell PV cell temperature, K.

10 M s 1 T temperature, K. K f uel annual fuel cost, e T0 system temperature, K. K invest total investment of the plant, e TH high temperature from which heat is K O&M annual operation and maintenance supplied, K. costs, e TCF water permeability temperature k Boltzmann constant, J K 1 correction factor kd real debt interest rate Ub heat transfer coefficient between the kinsurance annual insurance rate basin and surrounding soil, W m 2 K 1. S OLAR D ESALINATION 279. NOMENCLATURE (Continued). V PV panel operating voltage, V w water Vp volume of purified water produced per day, m3 day Acronyms V p volume flow rate of purified water, AGMD air gap membrane distillation m3 s 1 CSP concentrating SOLAR power.