Newsletter-Jan-June-2015

Solar Powered Dryer
By Andrew Shepherd
Over 50% of agricultural crops in some areas of Nigeria are wasted because they deteriorate in
quality after harvesting and are thrown away. If more of the harvested crops could be preserved
it would provide food for later in the year when prices are higher and people go hungry.
A traditional method of preserving food is by sun drying, which has the advantage of almost no
cost, but the disadvantage that the food must be dried for several days, and is subject to insects
and wind carried contaminants, so the final product is of low quality. Dried food retains almost
all of its nutritional value, and normally keeps their natural taste.
A purpose-built solar dryer keeps food clean during the drying process, with very low operating
cost. There are many variants, from a plastic box for a single family, to industrial scale dryers
with an externally powered fan.
One variant is a solar tunnel dryer. These have a transparent cover that allows the sun to heat
the contents, as in a greenhouse, and a flow of air through the tunnel to carry away moisture.
Some have a solar powered fan to draw air through the tunnel, and some rely on natural convection
in a chimney at one end. They can achieve temperatures high enough to eliminate most micro-organisms,
and a practical dryer costing a few thousand Euros can completely dry 100kg of
produce, e.g. Cassava, in one to three days. This type of dryer has been successfully used in Kenya,
Uganda, Thailand and Sri Lanka.
Solar Dryer
An example of a solar dryer