The Solar Powered Fruit and Vegetable Drier.
There is a lot of demand for more food preservation in rural areas as people are encouraged to generate income from agri-business activities. As the potential for this activity is so high in most countries, the Solar Dryer is an increasingly popular technology.

There is no rule of thumb for size with solar dryers - they can be made any size. The amount of heat collected by a reasonable collecter can exceed 1000 watts per square metre at noon.

It is important for the air flow to be controllable. In the beginning the air turnover is relatively high and the temperature low. As the food items dry out, the flow is slowed so that the collector heats up the air to a higher temperature. This continues to dry out the food more and more.

Almost all food that is going to be kept for several months has to be blanched and/or sulphured. While many people object to the use of sulphur in preserved food, it is effective and cheap.

Great care and a dose of wisdom must be used with stored food. Thre is a lot of printed material on drying food, including the book "Dry It, You'll Like It!" which describes very small scale drying.

The Solar Dryer pictured on the right was designed to be transported around Swaziland's rural areas to demonstrate the idea. It is made with a fibreglass IBR covering on the collector which is very impact resistant. There are a large number of shelves (15) because it was inteded to be able to dry spinach leaves which are large but very light-weight. If one was drying much weightier fruit like peach halves or mangoes, far fewer shelves would be used.

At the top of the drying cabinet (last picture) can be seen the controlling vents. There are two, the left one is fully open and hte right one is closed. Air enters through the space under the bottom tray. A lock is fitted so that food can be left inside overnight. The vents should be closed at night to prevent cold moist air entering the cabinet.

All manner of food can be dried including raw beef (for making Kilishi), fruit, leafy vegetables, seeds, coconut (copra) and chopped vegetables.

For the sulphurization of the final products another simple cabinet of box is required.

For the blanching of food, large pots are used. Remember to include the fuel and time costs of the pre-drying and post-drying operations in your costing exercise. They can be significant.

There is a large and expanding market for dried, chopped vegetables for the soup making industry. If you are considering promoting a drying project, look into the possiblity that you could become a contracted supplier to a soup packaging company.
Folding, portable solar dryer:

Erected unit, air entry holes visible:

Rear view, door closed:

Rear View, door open showing trays
(which are refrigerator shelves):
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