Some Knowledge

It is not hard to build a solar food dehydrator.  This device is basically a box with glazing that holds screen racks for the placement of sliced vegetables or fruits.  If you can’t think of your own design, there are several books on the market that have plans.  A quick search on the Internet shows that there are even plans available online for these dehydrators.

The principle of the solar food dryer is fairly simple.  Heat and light are radiated by the sun.  On a sunny day an enclosed glazed box will build up a considerable amount of heat.  One way to design a cheap solar food dryer is to find an old windowpane.  If possible, for safety, this windowpane should have some kind of frame.  A large window is not necessary if you are only planning on drying a small amount of food.  For larger quantities, such as if you are planning on starting a sundried tomato business, look for larger windows.  While it is expensive, plexiglass may make a better glazing material than glass, as it will not break if something falls on your drier and the glazing will not be damaged by hail.

Once you have your glazing it is time to take some measurements and get some dimensions.  You will want to set your glass at an angle to the ground which will depend on the latitude of your location.  Polar regions will require a higher angle than tropical regions.  A good plan is to go outside on a typical day at noon and measure the angle of a shadow.  Measure the length of the shadow and the height of the object casting the shadow.  You could divide these measurements to get the tangent of the angle of the sun, or you could just use this ratio directly in the design of your box.  To use the terms from highschool geometry, the run of your angle should be the rise of the angle on your box.  This will get you a surface at 90 degrees to the sun, which is what you want.

You will need some plywood or particle board to build your box.  You will need some slots cut into the board, or some runners nailed to the board for the screen trays.  Screen is pretty cheap, and tray frames can be made out of wood.  The important thing to remember when designing your solar dryer is to allow holes for air circulation.  You will want to direct hot air to move over your food so it dries effectively.  You will want to paint the inside of the box black to absorb all the heat from the sun.  You might want to put in baffles to direct the flow of air in your dryer.  You will need to screen over the ventilation holes to keep bugs out of your food.  You will want to paint or varnish the outside of your dryer to protect it from the weather.  Your box should also have legs to hold it off the ground for good air circulation.  Air intake holes should be on the bottom of the drier to keep out rain.

A solar food dryer is a good way to use solar energy to preserve your food.  A dryer can often be made out of recycled materials and can be used for years if it is built well.  Home-dried fruits, vegetables, and herbs can keep for a long time and will provide nutritious food without the added chemicals of commercially-processed items.