Development of a low cost, floating type, multi-effect solar still module

The solar still module to be presented here has been designed to operate as a floating unit on the surface of shallow (0.5 - 3 m deep) ponds. It is made of corrosion resistant plastic materials and consists mainly of a cupola shaped polycarbonate (PC) glazing fixed upon a floating frame; distillate troughs to collect fresh water that condense on the glazing, and a heat exchanger supplied with a low pressure air pump to utilize, to a greater or lesser extent, the condensation heat of the distillate. The floating frame and the heat exchanger are made of low cost polypropylene (PP) tubes. To achieve high operational temperatures and, thereby, high thermal efficiency, the solar radiation is absorbed on the water surface by a black wick, which is heat insulated from the deeper layers. The new module does not contain such usual solar still components as still body and back insulation, and therefore, significant cost reduction can be achieved. Since the productivity of the new module is much higher than that of the conventional type stills, the cost of fresh water can be further decreased. Using commercially available plastic materials, solar still modules of about 10 m(2) still area can be fabricated. To diminish side losses of the bulk water, serial arrangement of such modules covering several hundred-m2 pond area are considered. In the present paper the results of the indoor testing and optimization of a 2 m long, 0.5 m wide and 0.5 m deep laboratory scale module and the estimated economic features of the plant module are discussed.