Development of a low-cost, high-efficiency solar distillation unit for small-scale use in rural communities

Abstract

Providing access to safe drinking water becomes increasingly difficult on a worldwide level. Various regions of the Mexican Highlands have issues of groundwater contamination in terms of inorganic (e.g. arsenic or fluoride) or bacteriological parameters, which are exceeding the es- tablished limits in the Norma Oficial Mexicana (Official Mexican Standard) (NOM) for drinking water. One of the affected areas is the Altiplano region in the federal state of San Luis Potosí. Most of the rural communities in the region do not have access to (adequate) technology for groundwater purification and thus their inhabitants are exposed to the elevated levels of con- tamination which are potentially the cause for diseases, such as the fluorosis. Due to the facts of marginalization and poverty it is vital to investigate towards decentralized and economical technologies which can be applied on a small-scale level. A low-cost and “low-tech” approach is necessary in order to provide the people with a technology which they can construct, oper- ate and maintain themselves. A promising approach is the technology of solar distillation for drinking water supply on domestic level, making use of the high regional potential of solar en- ergy. It is proven that this technology is capable of removing nearly any type of contaminants (inorganic and bacterial) from the raw water. The simplest and most durable form of imple- mentation is the passive shallow-basin, single-slope solar still. The mayor drawback consists in its low daily output of drinking water (about two to five liters per square meter of insolated area). In the scope of the thesis, so-called passive energy augmentation measures are applied to the aforementioned design, in order to raise the distillate output to an adequate level for the drinking water supply of a small family of four members with a demand of approximately eight liters per day (considering the amount of pure ingestion). A prototype unit of the passive solar still is built and its parameters of distillate output, energy efficiency and construction costs are determined, considering two different configurations. An additional analysis of the distillate quality is made. The first configuration of the prototype is mainly characterized by a low water level in the evaporation basin and raw water pre-heating, whereas the second configuration adds reflective side- and rear wall coating inside the distillation chamber. Furthermore, a prototype of an active solar still is designed, incorporating an additional energy source (solar air collector) for higher process temperatures and therefore augmentation of the daily distillate yield. The emphasis in construction was put on the use of local, economical and recycled materials as far as possible, in order to lower the costs, attain a high reproducibility and to facilitate the possi- bility of autonomous self-construction in rural areas...