Desalination by OC-OTEC: Economy and Sustainability Subhashish Banerjee Md Nor Musa Abu Bakar Jaafar Ocean Thermal Energy Centre (OTEC), University Technology of Malaysia, Kuala Lumpur, Malaysia Abstract The scope of ocean thermal energy conversion system (OTEC) in resolving the future water crisis has been examined alongside the commonly used desalination methods in vogue using fossil fuels. Economic eval- uation and sustainability assessment have been carried out for different sizes of open cycle OTEC (OC-OTEC) plants and compared with RE systems such as solar and wind energy. The scope of utilizing the OTEC-operational upwelled deep ocean water (DOW), as the raw material for mineral water production with the possibility of earning huge royalty, was also assessed. The breakeven point on power generation cost of the OC-OTEC plant size, below which power cost escalates sharply, could also be determined. Based on the studies of different types of OC-OTEC plants, the trend line equations giving cost of power, as well as the reduced power cost on the basis of the royalty as may be earned from the by-product water production, could also be ascertained. It was concluded that the combined role on the availability of by-product potable water and upwelled cold water as mineral water resource from OTEC proved to be a better route to meet future water scarcity than the conventional methods using fossil fuels, OTEC being economically viable and also sustainable. Sustainability of OC-OTEC from CO 2 emission and fossil fuel depletion saving were also compared with wind and solar energy. The latter though economically nonviable in desalination issue showed comparable sustainability. R&D areas for increased water production with performance improve- ment of OTEC could also be identified. INTRODUCTION There is a global crisis in the demand of usable water with simultaneous requirement of energy for its produc- tion. With increased population rise, urbanization, and global warming inviting draughts, floods, and sea-level elevation, water shortage is likely to be more acute by the turn of the 21 st century. [1] Since all types of water purification needs energy, which is obtained mostly from the fossil fuels, such water purification is likely to fur- ther aggravate global warming from enhanced GHG emission. To cite an example of 2008, desalinated water production required to meet the needs of 6.8 billion of the world population was 52 million m 3 /day. This needed 1.42 million metric tons of fuel (oil)/day, which led to the simultaneous emissions of 156 metric tons of CO 2 /day. [2] Such production of desalinated water finds use as pota- ble water, domestic, industrial purposes, etc. Since the quantity of such production of water cannot be compro- mised, it is the fossil fuel use which is required to be changed into renewable energy (RE) systems for achiev- ing sustainable development to minimize GHG emission and depletion of fossil fuel resources. It thus urges tapping the scope of use different types of RE systems, including ocean thermal energy conversion system (OTEC), for usable water production with simultaneous examination of their economic viability and sustainability gains, as regards the CO 2 emission and fossil fuel depletion It is a fact that 97% of the earth’ s water resource lies in its oceanic bodies, though ocean constitutes only 71% of the planet. [3] Thus oceanic water and brackish water are considered to be the main resources for water desalination, for lowering the TDS (total dissolved solids) to tolerable limits, purifying from the bacteria, for availing potable water, etc. Of course, water treatment from resources such as rivers or lakes, and from aquifer zones (pumping up the water), are also in vogue. Keeping in view the above perspective, the following studies have been undertaken:  Review of the commonly used desalination methodol- ogies, examining the respective technologies with their energy requirement and economy.  Outlining the working principle of the open cycle (OC)-OTEC that yields usable water from its opera- tional process.  Examining the water production economy and sustain- ability (saving of CO 2 emission and fossil fuel depletion) from OC-OTEC of different designs and categories. Encyclopedia of Energy Engineering and Technology, Second Edition DOI: 10.1081/E-EEE2-120053006 Copyright © 2016 by Taylor & Francis. All rights reserved. 1