A solar crop dryer for rural areas

Abstract

In most rural areas, food waste is a problem experienced by farmers during the post-harvest period. The main reason for the losses is the degradation of foods during the postharvest period due to high moisture content and poor initial moisture control in these foods. Farm drying methods often compound this problem by contaminating the produce with foreign matter. The losses have a huge impact on farmers, agricultural industry, consumers and on the global economy in general. With famine and frequent droughts due to inadequate rainfall, preserving the available food reserves plays an important role. With the high solar potential levels of South Africa and the rest of the continent, this research assumes the problem of how post-harvest food and moisture content can be addressed if suitable solar dryers are availed to the region. Open sun drying is the main traditional method used for drying crops and fruits in Africa. Its disadvantages include contamination (exposure to dust), infestation (exposure to animals and insects) and exposure to rain due to no enclosures in the system. In effect, moisture control is difficult. This project, therefore, describes a design, construct, test and cost approach to tackling the problem at a rural farm level. The basic assumption is rural farmers desire to reduce postharvest losses hence need to adopt affordable low cost, low technology methods in controllably drying their produce. It was decided that enclosed solar crop drying was feasible due to the high solar radiation levels during harvest times. Therefore, two different dryers designs with 1.5m2 and 2m2 glazing area were designed, constructed, tested and direct costs estimated. Key design variables were identified whilst different fruit and vegetable products were tested against a control open-air drying system with solar radiation, temperatures and moisture losses monitored. In addition, a modification of the dryer to give a simple automatic indication of readiness of particular foods is given. This characteristic distinguishes it from other designs attempted elsewhere. Both designs reduced drying times to less than one day at the beginning of Cape Town's winter season while open-air drying was problematic, lasting up to one week. The direct cost of each dryer was under ZAR2000. After tests, it was therefore concluded that the designs are feasible and are now ready for redevelopment for commercial purposes.