SOLAR WATER DESALINATION

Seawater desalination is an important process to meet the fresh water demand. It plays a crucial role in the socio-economic development for many communities and industrial sectors. Currently there are more than 14,000 desalination plants in operation worldwide producing several billion gallons of water per day. Fifty seven percent are in the Middle East and and Gulf region where large scale conventional heat and power plants are installed. However since they are operated using fossil fuels, they are becoming  expensive to operate and the pollution and greenhouse gas emission they produce are increasingly recognized as harmful to environment. The integration of renewable energy resources in desalination and water purification is becoming more viable as cost of conventional systems increase, commitments to reducing greenhouse gas emissions are implemented and target for exploiting renewable energy are set. Thus, solar energy could provide a sustainable alternative to drive the desalination plants, especially in countries which lie on the solar belt such as Africa, the Middle East, India, Pakistan and China. There are two types of solar water desalination, the direct and indirect.

Direct Method

The direct method uses solar collectors to distillate directly. The solar collector traps sun's energy to obtain fresh water through the process of evaporation and condensation. One such type  of desalination is the solar still which distills water by using the heat of the sun to evaporate water which may be cooled and collected, thereby purifying it.

Solar Still (source: Wikipedia)

Indirect Method

This method comprises of two sub systems: a solar collection system and a desalination system. The solar collection system may either be used to collect heat energy of the sun using solar collectors and supply it via heat exchanger to a thermal desalination plant, or to convert solar radiations to electricity using photovoltaic cells and then to power an electric driven desalination process like reverse osmosis system.

Reverse Osmosis Plant (source Wikipedia)