Solar Drying

Overview

Preservation of agricultural produce is one of the central problems faced by developing countries. And as time goes on, these problems will be aggravated by the growing dietary needs of these countries increasing populations.

In many developing countries large quantities of fruits and vegetables spoil due to inadequate infrastructure, insufficient processing capacities, and growing marketing difficulties caused by intensifying competition and protectionism in the worldwide agricultural markets. Up to 70 per cent of agricultural products spoil during the traditional process of open-air drying, especially in tropical and subtropical regions. Drying these products can help solve these problems, while also making an important contribution to improving the population's income and supply situation.

However, traditional sun drying methods often yield poor quality, since the produce is not protected against dust, rain and wind, or even against insects, birds, rodents and domestic animals while drying. Soiling, contamination with microorganisms, formation of mycotoxins, and infection with disease-causing germs are the result. The drying equipment used in industrialized countries overcomes all of these problems, but unfortunately is not very well-suited for use in most developing countries because it requires substantial investments and a well-developed infrastructure.

In comparison to the traditional way of drying outside in an open field, solar dryers prevent contamination of produce by dust, insects, etc., thereby ensuring quality. They allow small-scale farmers to transform their harvest into storable and tradable goods, which they can sell off-season at higher prices. The constant temperature and ventilation allows a consistent drying process, which results in better product quality and higher prices. However, the investments costs of solar dryers vary highly depending on the size of the solar dryer, locally available materials and environmental conditions, such as slope and exposition of the side or rainy seasons.

Solar Drying - Hohenheim II-type Solar Tunnel Dryer

Solar drying facilities combine traditional and industrial methods, meaning low investment costs and high product quality. The ―Hohenheim‖-type solar tunnel dryer combines simple construction, use of renewable energy and easy handling. The model is equipped with a photovoltaic (PV) driving fan with a power requirement of 20-40 W. The thermal energy gained from solar radiation is up to 60 kWh/day (equivalent to 15 kg of firewood). A cooperative development between the Institute for Agricultural Engineering in the Tropics and Subtropics of Hohenheim University and INNOTECH Engineering Ltd., solar tunnel dryers are in commercial operation in more than 60 countries all over the world.

Further Information

• M. Häuser, O. Ankila (1997) - Solar Drying in Morocco - Experience with Solar Drying in Marocco from the GTZ Special Energy Programme (SEP); Overview on technologies, drying techniques, and economics.
• Matthew G. Green, Dishna Schwarz (2001): Solar Drier Plans: PGCP Coconut Drier and Kenya Black Box Drier; GTZ-GATE.
• Matthew G. Green, Dishna Schwarz (2001): Solar Drying Technology for Food Preservation; GTZ-GATE.
• Matthew G. Green, Dishna Schwarz (2001): Solar Drying Equipment: Notes on Three Driers; GTZ-GATE.