Optimization of Solar Energy to foster the Evaporative Crystallization Process at Lake Katwe, Uganda

Abstract: Lake Katwe located in Kasese district, is an explosion crater in western rift valley and is the largest of the eight explosion crater lakes in the Katwe-Kikorongo volcanic field, containing a renewable source of natural mineral salts. Salt is produced for 6 months of the year during the dry seasons. There are over 10,000 mud-lined pans of varying sizes between an estimated 200-300 m2 and 1m depth. Currently, rudimentally methods based on solar evaporation and crystallization to produce raw salt crystals are used for salt extraction at the lake. These rudimentary methods used to exploit the resource make this endeavor unsustainable.  As a result, relatively small quantities of the product are realized and often times of poor quality; therefore, this research sought to devise sustainable practical guidelines, procedures or techniques that could address the aforementioned problems. A methodology was adopted to characterize the site weather conditions, a model to mimic the actual solar evaporation process, and an economic analysis to ascertain the economic viability of the process. A Davis Pro2 weather station was used to monitor the weather conditions. The evaporation rate was also monitored by use of a standard class A evaporation pan. In the evaporimeter, the brine layer was very small and therefore the lumped heat capacity analysis was employed for the model calculations. The Net Present Value (NPV) and the Benefit Cost Ratio (BCR) methods were used to ascertain the economic availability of the process. Generally, there are four clear cut seasons annually; two wet seasons from May to June and October to January and two dry seasons from February to April and July to September respectively. With the relative humidity ranging from 36 % to 95 %, very intermittent wind regimes with speeds of up to 12 m/s whose direction varies considerably, an annual precipitation of 900 mm, evaporation rates of up to 2160 mm annually, and ambient temperatures varying from 24°C to 38°C coupled with an insolation of up to 965 W/m2. The model predicted evaporation rates increasing with increasing brine temperatures. An economic analysis that examined the process for a period of three years yielded a BCR that is greater than one and an NPV of about 17 million Uganda shillings thus ascertaining the huge potential of this venture if more efficient expertise and technologies are sought.