Solar heating and disinfection of water : an application for rural areas in Southern Africa
Nieuwoudt, Mechiel Nicolaas
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Life is not easy for the low-income rural population of Southern Africa. This includes those living in the informal settlements around cities. It is in part due to shortcomings in basic services such as water, sanitation and electricity. More than half of the households are without running water. One of the day-to-day problems is gathering and carting sufficient water for domestic use from communal water sources. The water is often of dubious quality, and waterborne pathogens cause a range of bacterial, viral and parasitic diseases. Children and people with compromised immunities are especially at risk. Traditional energy sources for heating this domestic water, such as firewood and charcoal, are also scarce and expensive. This, inevitably, leads to a compromise in hygienic practices, and have a negative outcome on the health of the people. A device is thus envisaged that can assist the people in transporting, disinfecting and heating their water. The use of solar energy for heating the water will reduce the dependency on traditional and conventional energy sources. Southern Africa is blessed with abundant solar insolation. As a result, solar water heating was selected to be used for this device, but it must then have the ability to store the hot water until at least in the evening. The technology and regulatory background of solar water heating were studied. An ICS type solar water heater, with insulation and glazing, was selected for implementation. The mobility of the device was modelled on the familiar wheelbarrow; therefore the device was christened as the Solar Heat Barrow, or SHB. The physical and performance requirements of the SHB were determined and specified. A study of the history and practice of water disinfection led to the realisation that solar pasteurisation, though possible in the SHB, will not reliably meet the day-to-day requirements. An additional requirement for chemical disinfection was formulated. A concept was generated for a disinfectant dispenser that could be added to the SHB where necessary. This device was named the Dispenser. It could, however, not use chlorine as disinfectant due to the chemical's sensitivity to heat degradation. A South African produced disinfectant, Steripure, was then selected for this purpose. Prototype Solar Heat Barrows, in two batches of ten and fifteen, were manufactured using representative processes. The first batch was tested for performance and conformance to requirements. It showed that the goals set were mostly fulfilled. In mid-winter, water could be heated to an average of 60°C by mid-afternoon. Water at 40°C was still available at 20:00, and this performance could easily be improved with simple human intervention. Some problems were experienced in both manufacturing and testing. It can, however, be solved with relatively straightforward development of the device. A single prototype of the Dispenser was also manufactured. It served the purpose of proving the functional principles, and a large scale manufacturing approach would be needed for further development. The manufacturing process thereof especially has to be addressed. The use of Steripure in the Dispenser, from the perspectives of both disinfection and longevity at temperature, will also have to be proven. The commercial viability and user acceptance of the Solar Heat Barrow were evaluated. A costing exercise showed that the direct production cost of units would come to approximately R 380. With the additional costs of operations, distribution and marketing, the units would have to sell for at least R 600 to be commercially viable. This would depend on a market for 60 000 units over a five year period, which was shown to be realistic. Assuming the same market, the Dispenser will have to be sold for at least R 100 to be commercially viable. Users in the rural community of Mabedlane, KwaZulu Natal, evaluated the second batch of fifteen SHB units over a two-month period. Although they were more than satisfied with the performance of the SHB, none could afford to pay more than R 100 for the product. Other surveys in the informal settlements around Pretoria indicated that a selling price of R 300 could still attract reasonable sales. It was, however, shown that a policy environment does exist, in South Africa in particular, to count on institutional support for some of the shortfall in affordability.
- Engineering