Sustainable desalination using solar energy

Global potable water demand is expected to grow, particularly in areas where freshwater supplies are limited. Production and supply of potable water requires significant amounts of energy, which is currently being derived from nonrenewable fossil fuels. Since energy production from fossil fuels also requires water, current practice of potable water supply powered by fossil fuel derived energy is not a sustainable approach. In this paper, a sustainable phase-change desalination process is presented that is driven solely by solar energy without any reliance on grid power. This process exploits natural gravity and barometric pressure head to maintain near vacuum conditions in an evaporation chamber. Because of the vacuum conditions, evaporation occurs at near ambient temperature, with minimal thermal energy input for phase change. This configuration enables the process to be driven by low-grade heat sources such as solar energy or waste heat streams. Results of theoretical analysis and prototype scale experimental studies conducted to evaluate and demonstrate the feasibility of operating the process using solar energy are presented. Predictions made by the theoretical model correlated well with measured performance data with r(2) > 0.94. Test results showed that, using direct solar energy alone, the system could produce up to 7.5 L/day of freshwater per m(2) of evaporator area. With the addition of a photovoltaic panel area of 6 m(2), the system could produce up to 12 L/day of freshwater per m(2) of evaporator area, at efficiencies ranging from 65% to 90%. Average specific energy need of this process is 2930 kJ/kg of freshwater, all of which can be derived from solar energy, making it a sustainable and clean process. (C) 2010 Elsevier Ltd. All rights reserved.