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< prev - next > Energy Solar energy KnO 100296_Solar drying (Printable PDF)
Solar drying
Practical Action
The great advantage of open-air drying is that it there is minimal capital outlay. It is labour-
intensive, although where labour is cheap this is not a drawback. An important advantage of
solar drying is that the product is protected from rain, insects, animals and dust. This improves
the hygiene and quality of the product as well as avoiding the covering, or transferring the crop to
a sheltered area during rain. Solar drying, especially when using fans, gives some control of the
drying process at elevated temperatures, and can be faster, which reduce the likelihood of mould
growth and spoilage of the product. However care is needed when drying food at too high a
temperature since too rapid drying can result in the outside of the food becoming dry on the
outside and still wet on the inside. This is called “case-hardening”. This can give a false
impression that the whole food is dry. On subsequent storage the trapped moisture will migrate
to the outside of the food, raising the humidity and resulting in mould growth and spoilage.
Solar driers compared to fuel-fired dryers
The choice between using solar radiation or fuel-fired dryers using, for instance, wood, charcoal,
diesel, gas or electricity depends upon the equipment capital cost, cost of raw material to be
dried, operating costs of running the dryer and the likely price obtained for the final dried
product. Fuel heating allows much better control of the drying operation than solar heating and
does not depend on the sun to be shining. However, it is possible to combine solar drying with a
fuel-source to reduce fuel costs. Such systems include pre-heating of air by solar energy.
Choice of solar dryer
The choice between alternative types of solar drier will depend on local requirements including
scale of operation as well as the budget available. If intended for smallholder farmers drying
crops for their own needs then capital cost may well be the main constraint and so low-cost
plastic-covered tent or box driers may be the most suitable choice. However, commercial farmers
with an assured market for their product may consider banks of fan-assisted, glass-covered solar
dryers more appropriate for their needs.
Innotech Ingenieursgesellschaft mbH
Weilemer Weg 27
D-71155 Altdorf
Tel: + 49 (0)7031 / 74 47 41
Fax: + 49 (0)7031 / 74 47 42
Hohenheim Dryer
All India Coordinated Research Project on Renewable Sources of Energy for Agriculture &Agro
Based Industries
Cascade Electro Thermic Pvt Ltd
3, Cascade Layout, Luna Nagar
Coimbatore - 641 025
Tel: 91 422 2402406 / 2402506
91 422 2401576 / 2400254