Build a Solar Heater to Dry Fruit Cheaply

QUESTION: We would like to dry (preserve) fruits and vegetables that we buy on sale and some from our own garden. Is there any way to use solar heat to dry them instead of heating up our kitchen by using the oven?

ANSWER: Preserving fruits and vegetables by drying is a prefect match with solar energy. Drying is the most natural and most nutritious method to preserve foods. Dried food takes up very little space and lasts a very long time. Using heat from the sun is free and it does not create any pollution or contamination of the environment or your food.

You should be able to build an inexpensive solar food dryer yourself, using old scrap materials you may already have around your house. The savings in buying larger quantities of fruits and vegetables on sale should easily pay back its cost in one summer alone. A typical-sized dryer will preserve a 20- to 30-pound load of produce in about two days.

The key to an effective solar food dryer is designing it to maintain a moderate temperature, about 110 degrees, in the dryer. There must also be adequate air circulation in it and around the food to carry away the moisture-laden air.

One effective design of a solar food dryer is basically a large open-top plywood box. For the top, use an old storm window with a solar collector plate immediately under it. This flat black collector plate absorbs the sun’s heat, yet blocks its direct rays from striking the food. Direct sun causes food to lose its color and much of its nutritional content.

Build the plywood box with screen-covered vent holes in the top and the bottom ends. The hot, moist air naturally exhausts out of the top vent, thus drawing cool, dry air in the bottom vent. It is important to properly size the vent holes, or there may be too much or too little air flow to keep the dryer at the proper drying temperature.

Attach legs to the box to tilt it up from horizontal at an angle equal to your area’s latitude angle. This faces it most directly toward the fall and spring sun. Attach the shelf supports on the interior sides so they are level when the box is tilted up.

Make the screen-covered shelves slightly smaller than the length of the shelf supports. Then stagger every other shelf flush against the back of the box. This forces the warm air to wind back and forth across all the shelves to get to the top outlet.

Once you become familiar with your solar food dryer, you will learn to adjust the interior temperature by tilting the dryer higher or lower and adjusting optional small movable vent covers.

You can write to me for Utility Bills Update No. 198 showing do-it-yourself instructions and diagrams and a material list for making a solar food dryer. Please include $1.25 and a self-addressed business-size envelope. Send your requests to James Dulley, c/o Los Angeles Times, 6906 Royalgreen Drive, Cincinnati, Ohio 45244.