How to build a simple solar food dryer
Solar drying is often the cheapest, most environmentally friendly means of preserving food. This simple solar food dryer is designed especially for drying leafy vegetables. You can build one in less than an hour.
Video Script:
Gardeners often take advantage of seasonal surpluses by canning, freezing, and drying extra food. Where malnutrition is prevalent families rarely own freezers and often lack the resources for safe canning. In these communities solar drying is often the simplest, cheapest, most environmentally friendly means of preserving extra food from the garden. Solar drying leaf vegetables is especially easy and takes less time and less heat than drying fruit or meat.
We have successfully used variations on this simple solar leaf dryer in a dozen different countries. They can be built in an hour with simple hand tools by someone with no carpentry experience.
Here’s how to build one.
Begin by cutting out the wood. Today we are making two identical 24 X 30 inch frames from pine lumber 1 ½ inches on each side. So we have cut 4 – 30” pieces; 4-21” pieces, and 4-12” braces with 45 degree angles cut on both ends. You can make a larger dryer, but any smaller than this tends to not get warm enough for efficient leaf drying. Dryers over 3 feet or a meter on each side are difficult for one person to handle.
Nail or screw the frames together.
Then cover one of the frames with a resistant screen or mesh. Heavy duty pet screen intended to keep dogs from breaking through screen doors is ideal, but greenhouse shade cloth, or quarter inch metal mesh can also be used. With the metal mesh you’ll need to put some plastic screen between the drying leaves and the metal. Fiberglass screen isn’t recommended because the tiny glass fibers can end up in the dried leaves. Staple the screen onto the frame pulling it tight. Then trim off the excess screen. This is the dryer bottom.
Then nail the 4 corner braces over the screen. These braces will reinforce the dryer and also serve to raise it up a bit to allow better air flow.
Spread greenhouse grade polyethylene sheet over the other frame (the dryer top). This is a 6 mil thick clear plastic that is treated to block ultraviolet rays from the sun. Don’t use regular plastic polyethylene sheet. This is very important because UV radiation destroys vitamin A in the leaves are also quickly degrades regular polyethylene.
Staple the plastic sheet securely to the frame. Wrap it over the sides of the frame and staple those as well. If you don’t have a staple gun small nails will work. Try using either short roofing nails or finishing nails bent over to resist the plastic pulling loose.
Next staple or nail a strip of screen onto all 4 sides of the dryer top. This should be 4 or 5 inches wide and will help keep flies and dust out of the dryer.
Surprisingly, greenhouse plastic is often available in the tropics because greenhouses are increasingly used to produce specialty flowers and fruit for export. A greenhouse roll is enough for dozens of solar leaf dryers. Where greenhouse plastic is not available the dryer top can be covered with old sheet metal roofing painted flat black.
Now you are ready to try out your dryer. Putting a piece of plastic under the dryer will prevent moisture from the ground being absorbed by your leaves.
Raising one side a bit will allow the sun’s rays to hit the dryer at a more direct angle and heat up more quickly. This also allows any unexpected rain to drain off the dryer.
In cool or cloudy weather setting some shiny metal behind the dryer will reflect additional solar energy on to the dryer. Rooftop tests in Mexico demonstrated improved performance with the reflectors.
Where ants are a big problem we set the dryer up on short plastic legs that sit in cans full of water. Only the most enthusiastic ants can make it through this obstacle course to eat your drying leaves.
There are a lot of variations on these simple dryers. One of the most innovative was developed by the Nicaraguan women’s organization FUPROSOMUNIC. It uses tiny solar collectors and repurposed old computer fans to increase the airflow in the dryers whenever the sun is shining.
It is not hard to build a solar leaf dryer by yourself, but it is more fun as a group project. A group that builds the dryers together usually offers more mutual support for using them to make leaf powder.
View this video on YouTube (and subscribe to our channel at Leaf for Life @ YouTube)