Economically viable solar stills

[摘要] ENGLISH ABSTRACT:The use of solar distillation as a means of desalination to provide potable water tocommunities in remote and arid regions has often been discarded on economicgrounds mainly because of the inherent low efficiency of relatively expensive solardistillation units (solar stills). Closer analysis of this constraint showed that byfollowing a mainly Physical Chemistry approach (rather than the traditionalengineering one), the technology could be made more economically attractive through(1) lowering the construction cost of the solar still and / or (2) increasing itsoperational life and / or (3) increasing its efficiency.The study into different solar still designs showed that, despite its limitations, thebasin solar still is preferred due to its simplicity, ease of operation and lowmaintenance. Given the solar distillation process as formulated in this study, substitutedurable components could be identified and optimised for this design. A basin solarstill that costs about 80% less than a reference unit without an apparent drop inperformance was consequently developed and successfully tested up to full plantscale.An in-house experimental facility that simulates solar still behaviour under controlledenvironmental conditions was developed to simulate conditions of lower radiationintensity and productivity, which enabled research into performance enhancement andmicrobiological water quality. It was found that (a) absorption of the radiation by thewater plays an important part in productivity and that a productivity decrease of up to33% can be expected as the black interior lining becomes contaminated, (b) thesimulated winter productivity of the basin still was about 25% of the summer valuedue to the lesser amount of solar radiation hours, the lower angles of radiationincidence onto the cover and the decrease in water area receiving direct radiation, (c)an annual productivity increase of about 10% can be obtained when a particularreflector configuration is fixed behind the basin, and (d) the microbiologicalpasteurisation temperature is less than the distillation onset temperature. This study played an important role in making solar still technology affordable for useby poor, rural communities, as was demonstrated by the successful use of the researchproduct (basin solar still) in a pilot drinking water plant at a typical target community.This was made possible through the use of evaluation models developed as part of thisresearch, which addressed relevant construction and performance factors influencingthe economic viability of the specific solar still.The following outcomes of this study can be regarded as new contributions to thefield of solar distillation technology, namely (a) a test matrix that can be used toscreen solar still construction materials at component level, (b) an evaluation modelthat can be used to determine the economic viability of solar stills at a given location,(c) a laboratory testing facility to study solar still behaviour under controlledconditions and (d) a solar still design that has been optimised and tested for local fieldapplication.

[发布机构] Stellenbosch University