Best-Ever Solar Food Dehydrator Plans: 12 Simple Steps To Completion
Why This Is the Best Food Dehydrator
I’ve built many dehydrators over the years and enlisted teams of students to study all of the variables. We’ve made adjustments to improve the performance, simplify the construction, reduce the cost, and increase the durability and portability of food dehydrators. Following are several of the most effective strategies our tests have established over the years to produce the best food dehydrator you can build.
Vents and airflow. Temperature, airflow, humidity and food density will all affect a dehydrator’s performance. Ideally, you’ll want high temperatures and heavy airflow, but because changes in one factor also affect all the others, the best food dryers must achieve a balance among these variables.
You can control the temperature and humidity inside this food dryer by regulating the airflow with its adjustable vents. The vents are essential for effective operation: As cool air enters at the bottom and heats up in the collection box, the warmed air must rise into the drying chamber where it will absorb moisture from the food before exiting through the upper vents. When you close the vents, the air movement stops — and so does the fast, efficient drying of food.
Fully opened vents cause the airflow to increase and the temperature to decrease. Temperature is more significant than airflow in affecting the rate at which food dries, so we partially close the vents to increase the temperature. In general, more airflow (fully opened vents) is important during the early stages of food drying, while higher temperatures (partially closed vents) are more effective in the later stages of drying.
Reflectors. No official scientific standard determines the ideal drying temperature for food. The most common preferred range falls between 110 and 140 degrees. Higher temperatures also destroy harmful bacteria, enzymes, fungi, insect eggs and larvae. But temperatures that are too high can cause vitamin C loss — and food begins to cook at 180 degrees.
To bring the temperature into the ideal range, we tried adding external reflectors to cast more solar energy into the collector box. For the best performance, though, we discovered that the dryer with reflectors had to be relocated several times throughout the day, and its angle had to be adjusted as the sun moved across the sky. Based on our experiences, external reflectors usually aren’t worth the trouble.
Installing a reflector inside the collector box is an easy way to boost the temperature without the hassle of an exterior reflector. Gluing aluminum foil to the bottom interior of the collection box (underneath the absorber screen) will increase the temperature inside by more than 20 degrees. Our dryer with an interior reflector can surpass 200 degrees on sunny, 75-degree days with the vents closed. By opening the vents 1 to 2 inches, we can bring the range down to a more reasonable 120 to 155 degrees.
Glazing. The top of the collector box must be covered with glazing so the sun’s energy can penetrate and be soaked up by the absorber screen inside. The best material is a fiberglass-reinforced polyester (FRP) known as Sun-Lite HP. This glazing is thick, durable and translucent, and is used in many solar technologies. You can purchase it in a variety of widths and lengths from the Solar Components Corporation, and easily cut it to fit the top of your dehydrator.
We found that adding a second layer of glazing increases temperatures inside the dryer by approximately 10 degrees. But the price of the glazing material — about $2.50 per square foot — doesn’t improve performance enough to justify the added expense.
Absorber. This is a technical name for some simple materials installed beneath the glazing to absorb the sun’s heat and transmit it to the surrounding air. Our trials show that the best absorber is made of either charcoal-colored aluminum window screen or the type of metal lath used in plaster work. Screen is cheaper and easier to work with, but some of our tests showed that lath produces significantly higher temperatures, which justifies the added expense. At least 20 additional tests demonstrated that including six layers of steel lath, painted black and set on the diagonal, is ideal.
Build It Yourself
You can construct this solar dehydrator using locally available materials — exterior-grade plywood, FRP glazing, metal screening or lath, and miscellaneous parts. New materials will cost about $300, or you could recycle supplies already on hand. Most home workshops will already stock the necessary equipment. Expect construction time to take 20 to 40 hours, depending on your woodworking expertise.
My students and I have developed a solar food dryer that works extremely well and isn’t costly to build. I encourage you to build the dehydrator to our specifications and put it to work to stock your home larder with nutritious, sun-dried food.
• One 4-by-8-foot sheet of 3/4-inch plywood, exterior grade
• One 4-by-8-foot sheet of 1/4-inch plywood, exterior grade
• Five 1-by-6s, 8 feet long, pressure-treated
• Two 2-by-4s, 8 feet long, pressure-treated
• 2 wheels, 8-inch-diameter
• 36-inch-long, 1/2-inch-diameter steel axle
• 2 heavy-duty hinges
• Six 27-by-96-inch sheets of metal lath
• 3 square feet aluminum screen
• One 2-by-6-foot sheet of FRP (fiber-reinforced plastic)
• 30 square feet food-grade screening
• Heavy-duty aluminum foil, 25-foot roll
• 3/4-by-1/8-inch aluminum battens, 16 feet total length
• 1 1/4-inch No.8 exterior-grade Phillips flat-head screws (100 or more)
• 1 5/8-inch No. 8 exterior-grade Phillips flat-head screws (about 30)
• 1-inch No. 8 round-head screws (about 20)
• Eight 3/8-by-3-inch bolts, nuts and washers
• Four 3/8-by-4-inch bolts, nuts and washers
• 4 hook-and-eye fasteners
• 1/4-inch staples
• Exterior-grade latex paint and primer, any light color
• High-temperature spray paint, black
• Waterproof glue
• Silicone caulk
• Weather stripping
• Circular saw with rip guide
• Router with 3/4-inch straight bit and cutting guide
• Electric drill with No. 8 pilot-hole and countersinking bits
• 2 sawhorses
• Long straightedge
• Marking pencil
• Framing square
• Tape measure
• Staple gun
• Caulk gun
• Tin snips
• Utility knife
• Heavy work gloves