WHY SOLAR DRYING

 To reduce water in a crop thereby inhibiting enzymatic activity that may promote senescence and decay. This will extend its shelf life for further processing or value addition.

 To reduce food wastage, reduce weight, ease storage and transportation.

To maintain dietary diversification on and off agricultural season. 

To increase income generation where farmers sell the dried fruits and vegetables off season.

ADVANTAGES OF DRYING

• It permits early harvesting and reduces the field losses of the products.
• Reduces the risk of field losses caused by wild and domestic animals.
• It permits better planning of the harvesting season.
• It reduces spoilage in storage drastically.
• It permits the farmer to sell products at better prices during early period of harvesting season.
• Quality of the product gets enhanced significantly and hence farmer gets more money for the product.
• It maintains most nutrients which would otherwise be used up in the plant by chemical reactions.
• The bargaining position of the farmer to maintain relatively constant price of his products and reduces post- harvest loss.
• It lowers transportation costs since most of the water are taken out from the product during the drying process making the produce less bulky.
• Drying is more advantageous on highly perishable crops such as tomatoes. These perish after a few days once they are ripe.

THE SOLAR CABINET DRIER

The main principle of this low-cost solar cabinet dryer is based on greenhouse effect where the solar heat is trapped inside the drying chamber and thus increases the temperature level. It is a mixed-mode solar cabinet dryer. Here both direct and the indirect solar energy collected in the chamber heats up the food products.

The Solar cabinet drier uses direct or natural convection. The agricultural product is placed in shallow layers in a blackened enclosure with a transparent cover. The solar radiations are directly absorbed by the product itself. The food product is heated up and the moisture from the product evaporates and goes out by the natural convection or circulation.

SOLAR CABINET DRIER STRUCTURE

• The solar cabinet dryer consists of a wooden box of certain width and length (length is generally kept as three times its width), insulated at its base and preferably at the sides and covered with greenhouse plastic.
• The inside surfaces of the box are coated with black paint and the product to be dried is kept in the trays made of shed cloth bottom.
• These trays loaded with product are kept through a door provided on the rear side of the drier.
• The shed cloth has holes through which fresh outside air is sucked automatically.
• Holes are also provided on the upper sides of the dryer that are covered with gauze wire through which moist warm air escapes.
• This dryer has given encouraging results and reduced the drying time by one third compared to open sun drying.

See the attachment for drawings of the cabinet structural plan.

MATERIALS NEEDED IN THE CONSTRUCTION OF THE SOLAR DRIER

FABRICATION OF THE CABINET SOLAR

• Cut brandering for frame, door and tray.
• Fix these using 3” nails.
• Paint using wood primer.
• After it dries paint using JD Wood paint
• Fix the greenhouse plastic to the doors, frame top, sides and back.
• Fix gauze wire to the frame.
• Fix shade cloth to the trays.
• Fix the hinges, hasp and clap to the doors.

A diagram showing the Solar Cabinet structural plan

Illustration of the drying process

Drying or dehydration of material means removal of moisture from the interior of the material to the surface and then to remove this moisture from the surface of the drying material.

The drying of product is a complex heat and mass transfer process which depends on external parameters such as temperature, humidity and velocity of the air stream; drying material properties like surface characteristics (rough or smooth surface), chemical composition (sugar, starches, etc) physical structure (porosity. density. etc.); size and shape of the product.

The rate of moisture movement from the product inside to the air outside differs from one product to another and very much depends on whether the material is hygroscopic or non-hygroscopic. Non-hygroscopic material can be dried to zero moisture level while the hygroscopic materials like most of the food products will always have a residual moisture content.

This moisture in hygroscopic material may be a bound moisture (remains) in the material due to closed capillaries or due to surface forces) or unbound moisture which remains in the material due to surface tension of water.

When the hygroscopic material is exposed to air, it will either absorb moisture or desorb moisture depending on the relative humidity of air.

The equilibrium moisture content (EMC) will soon be reached when the vapour pressure of water in the material becomes equal to the partial pressure of water in the surrounding air.

 The equilibrium moisture content is, therefore, important in the drying since this is the minimum moisture to which the material can be dried under a given set of drying conditions.

 When this equilibrium is reached then the drying rate becomes zero.

Advantages of the Solar Cabinet Drier

• These dryers do not use fan or blower to be operated by electrical energy.
• They are low in cost and easy to operate.
• Ease of fabrication.
• Materials are readily available in the country.
• Portable
• Products are protected against flies, rain and dust; product can be left in the dryer overnight during rain, since dryers are waterproof.
• Prevent fuel dependence and reduces the environmental impact.

Disadvantages of the Solar Cabinet Drier

• Slow drying.
• No control of temperature and humidity.
• Adequate solar radiation is required.
• Small quantity can be dried.
• Some products change colour and flavour due to direct exposure to sun.

 MANAGEMENT OF SOLAR DRIER

Orientation

 - put in prevailing wind direction

- in a place with maximum sun exposure

- level and clean ground

 Regular cleaning (cleaning after every removal of dried product)

 Monitor and repair (Loose nails)

Clean and Store under a shed or inside a building when not in use.

Keep way from buildings and trees.

WHAT CAN BE DRIED IN THE SOLAR DRIER

FRUITS:

Indigenous and exotic such as umnyii, umviyo, bananas, apples etc.

 VEGETABLES:

 Indigenous and exotic such as ulude, okra/idelele, rape, carrots, cabbage, garlic, ginger.

CONCLUSION

 Drying fruits and vegetables using the cabinet solar drier can be effective nutritionally and economically particularly for farmers.