A solar vapor generator constructed by U.S. academics cleans or desalinates water by making near maximum use of solar energy during evaporation. The system is designed to minimize the amount of heat loss during the solar purification process.

The low-cost system, based on carbon-coated paper (CP) affixed to expanded polystyrene (EPS) foam, could address global drinking water shortages, especially in developing areas and regions affected by natural disasters.

A prototype of the solar still. Credit: University at BuffaloThe solar still uses the EPS as a thermal insulator and porous paper coated in carbon black to absorb water. The carbon black absorbs sunlight and transforms the solar energy into heat used during evaporation.

Salt, bacteria, or other unwanted elements are left behind as the liquid moves into a gaseous state during evaporation. As the water vapor cools and returns to a liquid state, it is collected in a separate container without the undesirable constituents.

Only 12% percent of the available energy was lost during the evaporation process, a rate the research team believes is unprecedented. The accomplishment is made possible, in part, because the device converts only surface water, which evaporated at 44 C (111 F).

A thermal efficiency of about 88% was obtained under 1 sun without concentration, corresponding to the evaporation rate of 1.28 kg (m² h)⁻¹. When scaled up to a 100 cm² array in a portable solar water still system and placed in an outdoor environment, the freshwater generation rate is 2.4 times of that of a leading commercial product.

Tests indicate the still is capable of producing 3 to 10 liters of water per day, which is an improvement over most commercial solar stills of similar size that produce 1 to 5 liters per day.

Participating in the research were researchers from the University at Buffalo of the State University of New York, Fudan University in China, and the University of Wisconsin-Madison.