Seawater desalination is one of the most promising fields in terms of solar energy application, mainly due to water scarcity, seawater availability and high levels of solar radiation occurring together in many parts of the world. There is an increasing need for renewable energy-powered desalination systems, as this seems to be the sole environmental friendly alternative to the conventional fossil fuel powered systems. Renewable energy sources coupled with desalination offer a promising prospect for covering the fundamental needs of power and water especially in remote regions, where water scarcity is severe and the connection to public electricity grid is either not cost effective, or not feasible.
Green Water II system is a stand-alone PV or wind-powered desalination system, especially viable for areas that are not easily accessible or have no access to electricity. Green Water II system works outside of the electricity grid; the energy produced from PV or wind installation is stored in batteries. The system consists of energy generation and power consumption optimisation module, a pre-treatment module, reducing the level of salinity and the oils together with a module for desalinating as well as fat removal.
Energy generation module consists of PV cells or wind turbines, batteries, charge controller and inverter. An inverter is included in the system to convert the direct current (DC) generated by the PV or wind modules to the alternating current form (AC). The PV or wind installation is integrated with a reverse osmosis desalination system indirectly via energy storage system. PV and wind installations charge batteries and then supply the pump DC motor through the batteries.
The desalination system used in Green Water II is the reverse osmosis (RO) technology, which uses the principles of osmosis to remove salt and other impurities. It is achieved by transferring water through series of semi-permeable membranes. Standard osmosis involves a solvent, such as water, naturally moving from the area of low solute concentration, through a membrane, to the area of high solute concentration. The movement of pure solvent reduces the free energy of the system by equalizing solute concentrations on each side of the membrane, generating osmotic pressure. Applying an external pressure to reverse the natural flow of solvent is called reverse osmosis. To create clean water by using this process, seawater or brackish water is pressurized against one surface of the membrane, causing salt-depleted water to move across the membrane, releasing clean water from the low-pressure side.
RO can remove many types of molecules and ions, making it suitable for potable and industrial uses. This technology is particularly suitable for integration with renewable electricity producing technologies (such as PV and wind turbines), and Green Water II combines the most advanced RO developments with innovative PV and wind technologies.