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TBG: How does Solar Food Drying work?
Solar drying is a low cost method of drying food.  It is important to understand moisture in food and the properties of the air around us.

All food contains moisture which comes in three forms: liquid, solid & gas.  This moisture is what microorganisms need to live and thrive, so in order to stop microorganism growth you may reduce this moisture to a safe level to preserve and extend the shelf-life of your harvest.

The design of the Solar Dryer harnesses the power of the sun’s rays to raise temperatures within the unit to between 110 - 130 degrees Farenheit. This heat lowers relative humidity while increasing absolute humidity, so that the air inside the unit attempts to reach the absolute humidity of the climate outside the unit by taking moisture from the food.

Coupled with proper air circulation, this is what makes the solar dryer work.

                           

TGB: What kind of Solar Dryer Designs have you developed?

There are three basic designs of solar dryers that you may follow when building your own solar dryer: direct absorption, indirect heating, and mixed mode. In this project a direct absorption solar dryer was designed because it was found to be the most sustainable for Hawaii’s needs.

In these designs the food is placed inside a cabinet or “hot box” which allows the rays of the sun to heat up food and air around it. A compartment with a transparent roof and insulated walls is used, but if designed properly all the walls can be transparent. These may also use reflectors at the bottom of the compartment to increase light (metal or foil).

Ventilation holes are required to promote proper air circulation. Indirect heating dryers dry the food with heated air collected by a “solar panel”. The food is placed in an insulated heating chamber with proper air circulation.

These models are effective but cost a lot of money. Mixed Mode dryers are a combination of the other two designs. Food is heated directly by the sun but additional heat is collected with the “solar panel”. These can cost about $1300EC to build, effective but expensive.

Businesses attempting to expand and produce higher quality products should look into building one of these models (for the purposes of this project and the situation in Hawaii the direct absorption model is the best fit). When constructing your dryer be sure to follow the design carefully, because the angles achieved are vital for efficient processing.

INFO FROM:  http://thegreenbackpack.tumblr.com/