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What problem does it solve?

Low quality water plays a key role in bad health and living conditions. It is estimated that approximately 1.6 million human lives could be saved every year if access to drinkable water, services of water depuration and hygiene could be improved upon. We can enumerate in the world at least 50 conflicts between countries for causes tied to the property, the distribution and the use of water, and it is likely that an ulterior decrease in water resources will make these conflicts more acute and will provoke new ones (Legambiente Veneto 2007). The not homogeneous distribution of water has been one of the major causes of social inequalities: the population of the richest countries (approximately 11% of humanity), besides owning 84% of the wealth, consumes 88% of the resources, including water.

Many technologies for water desalination have been developed, particularly in tropical zones, in order to solve these problems. Desalination is a fast-growing global technology, with a production of 26 million m3 per day and with an investment estimated to be equal to 70 billions of dollars in next the 20 years (data from ESCWA 2001 - United Nations Report).

Figure 1. Ability to the systems of desalination in various zones (Häberle 2001)

Desalinated water production, however, is more pronounced in industrialized countries, and excludes the territories that would mostly require technologies to facilitate the access to a primary resource like water.

The solar still imitates, within its isolated system, the natural cycle of water, forcing its yield and efficiency. The mechanism of water potabilization is based on the evaporation of the starting solution, generating condensation of the vapor itself and obtaining distilled and drinkable water. Salts and miscellaneous polluting agents present in the starting solution sink to the bottom and are eliminated afterwards.

The direct exploitation of the solar energy has always attracted researchers in several fields, including desalination. The first investigator who created a large-scale system of solar desalination was Carlos Wilson, in 1872, in Las Salinas (Chile). Wilson realized a system of solar stills, 4450 m2 large, with daily production of 17.8 m3, a yield of 4 l/m2/day and a 40 years life span. In the ‘40s many patents were filed pertaining small and practical portable solar stills that were adapted for life-rafts or ships and used extensively by the US Navy [Telkes, 1945]. Currently, this type of systems is used almost only for research.

Solar still solve important issues linked to water potabilization. They have been devised in order to desalinate sea water, producing drinkable water for human use. These solar stills can also be used in isolated areas and require low costs of installation and maintenance.

The solar still SOLWA, thanks to its features and with very simple modifications, presents a wider range of applications. Indeed, it can be used to purify not only water rich in salts but also waters with various miscellaneous polluting agents suspended within. It helps drying refuse sludge deriving from systems of biological depuration. It helps stabilize animal waste from farms, preventing the pollution of lands and reducing the volume to eliminate.

An important feature of the SOLWA solar still is that it does not require operating costs, being powered only by solar energy, as opposed to other conventional technologies in the field (inverse osmosis, MSF , MED, electrodialysis, etc). Furthermore, SOLWA does not require maintenance and operates immediately once set up, with no need for specific technical or manual knowledge.

SOLWA has 56% efficiency, compared to 50% of other solar stills. The estimated water production in tropical countries is more than 10 l/m2/day. The SOLWA does not produce pollution of any type, neither chemical nor thermal.