AbstractsEconomics

Economically viable solar stills

by I. (Ian) Goldie




Institution: Stellenbosch University
Department: Chemistry
Degree: PhD
Year: 2003
Keywords: Chemistry
Record ID: 1416723
Full text PDF: http://hdl.handle.net/10019.1/53401


Abstract

ENGLISH ABSTRACT: The use of solar distillation as a means of desalination to provide potable water to communities in remote and arid regions has often been discarded on economic grounds mainly because of the inherent low efficiency of relatively expensive solar distillation units (solar stills). Closer analysis of this constraint showed that by following a mainly Physical Chemistry approach (rather than the traditional engineering one), the technology could be made more economically attractive through (1) lowering the construction cost of the solar still and / or (2) increasing its operational life and / or (3) increasing its efficiency. The study into different solar still designs showed that, despite its limitations, the basin solar still is preferred due to its simplicity, ease of operation and low maintenance. Given the solar distillation process as formulated in this study, substitute durable components could be identified and optimised for this design. A basin solar still that costs about 80% less than a reference unit without an apparent drop in performance was consequently developed and successfully tested up to full plant scale. An in-house experimental facility that simulates solar still behaviour under controlled environmental conditions was developed to simulate conditions of lower radiation intensity and productivity, which enabled research into performance enhancement and microbiological water quality. It was found that (a) absorption of the radiation by the water plays an important part in productivity and that a productivity decrease of up to 33% can be expected as the black interior lining becomes contaminated, (b) the simulated winter productivity of the basin still was about 25% of the summer value due to the lesser amount of solar radiation hours, the lower angles of radiation incidence 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 particular reflector configuration is fixed behind the basin, and (d) the microbiological pasteurisation temperature is less than the distillation onset temperature. This study played an important role in making solar still technology affordable for use by poor, rural communities, as was demonstrated by the successful use of the research product (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 this research, which addressed relevant construction and performance factors influencing the economic viability of the specific solar still. The following outcomes of this study can be regarded as new contributions to the field of solar distillation technology, namely (a) a test matrix that can be used to screen solar still construction materials at component level, (b) an evaluation model that can be used to determine the economic viability of solar stills at a given location, (c) a laboratory testing facility to study solar still…