Monday, June 11, 2012

Build a SOLAR FOOD Dehydrator

Build a SOLAR
Preserve your Dehydrator
harvest with
free energy
from the sun.
By Eben Fodor
is carried away with the hot air. But do
solar food dryers work well? Are they
practical? Yes, but first let me put this
topic in the context of creating a healthy
and sustainable food supply.
Food preservation is the key to extending
the summer’s precious bounty of locally
grown produce throughout the year.
If you’re like me, you would prefer a
method that’s easier and requires less energy
than canning.
Freezing is commonly viewed as the
most convenient preservation method, but
freezers require a constant source of electricity.
Your food will be vulnerable to
power outages and mechanical failures,
and freezer burn will limit the storage life
of most foods to about six months.
Drying is an excellent method of food
preservation that maintains a high level of
flavor and nutrients, while providing a
convenient, compact, easy-to-store supply
of your favorite produce. Electric food
dryers work fine, but I don’t care for the
constant noise, heat and odors they add to
my house. Electric dryers also take away
valuable counter space for weeks on end
and can attract ants and other pests. The
electricity to run them costs about a dollar
a load. The convenience of electricity does
not compare to the satisfaction of drying
food with free solar energy.
Disenchanted with electric drying, I
began experimenting with solar drying.
With a background in engineering and solar
energy, I soon designed and built my
first solar dehydrator. I was delighted to
watch the sun quickly dehydrate my organic
fruits and veggies. It worked even
better than I had hoped, drying large
batches of food in one to two days. I dried
my entire surplus of garden and orchard
produce, leaving nothing to waste. The following
year, I grew a larger garden so I
could dry even more food.
If you’re wondering whether solar drying
could be right for your location, consider
that I live in Eugene, Ore., at a latitude
equivalent to Bangor, Maine. We receive
lots of rain, but fortunately, we also receive
enough sunshine during the summer and
fall harvest seasons to successfully dry all our
crops with solar energy. If you can get two
days of sunshine in a row with some regularity,
solar food drying will work for you.
But for those times when the sun is hiding,
a backup heating system still can help.
I added 200-watt light bulbs as heating
elements so I could finish drying my produce
any time the weather turned cloudy.
The author and his
SunWorks solar food
dryer. Left: Warm
temperatures inside
the food dryer create
a convection current
that circulates air
through the dryer.
Dried foods store well in airtight containers
and will keep for up to one year.
Hot, moist air exits through
screened top vents
Fixed side vent
Food screens
Absorber plate
Cool, fresh air enters through
screened opening at bottom August/September 2006 67
A solar food dehydrator can be made in
many designs, ranging from the simple to
the complex, and from small to large. For
the home gardener, a good solar food dehydrator
has these qualities:
• It dries food quickly—on par with a
good electric food dryer.
• It has venting controls that allow for
easy adjustment of drying temperature
and airflow.
• It’s easy to load, unload and clean.
• It’s easy to set up and put away, with
little or no assembly.
• It’s relatively compact and lightweight
for portability.
• It’s weather-resistant and keeps your
food dry in the event of rain.
• It has sturdy and durable construction
for a long life of outdoor operation.
• It’s pest-proof, and all vent openings
are screened.
• The food trays are made from durable,
nonstick and food-safe materials.
Now that you know the basics about
solar food dryers, where do you go for designs?
Surprisingly, you won’t find much
useful information on the Internet. If you
search, you will find plans for solar dryers
made from cardboard and duct tape. Skip
these and stick with the handful of high
quality dehydrators that meet my criteria.
My book The Solar Food Dryer provides information
on some of the better designs
and includes complete plans for building
the SunWorks dehydrator I designed
(shown on Page 67).
The easiest solar food dryer to build is
a “hot box,” a design in which the food is
enclosed and protected in a box with a
68 MOTHER EARTH NEWS August/September 2006
This simple solar hot box dries food by
capturing solar radiation, which raises the
interior temperature of the box.
Glass or old window
Drying tray
Vent holes in bottom and
sides should be screened
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clear covering on top (shown
on opposite page). Screened
holes should be in the bottom
and sides, so warm,
moist air can exit the dryer.
To increase airflow and efficiency,
you’ll have to modify
the simple hot-box design.
Many high-performance designs
are based on the strategy
of separating the two functions
of a solar food dryer:
gathering heat and drying the
food. The New Mexico dehydrator
shown below illustrates
this approach.
My design, the SunWorks,
integrates the solar collector
and food drying cabinet into a
compact configuration, which
uses both direct heating (like
the solar hot-box dryer) and
indirect heating from the absorber
plate. The airflow is optimized for
even drying, and ventilation is achieved by
natural convection (see diagram, Page 67).
You don’t need to be a solar whiz to operate
a solar dehydrator—just place it in a
sunny spot oriented to the south and load
it with food. If you will be around during
the day, you can speed drying by occasionally
repositioning the dryer to track the sun
as it moves across the sky. Many foods will
dry in one day of sunshine. Wet foods such
as tomatoes or pears will require a second
day. They should be dry enough after the
first day to stay in the dehydrator overnight.
Food Drying Favorites
Fruits: apples, apricots, bananas, blueberries,
grapes (seedless), peaches, pears,
plums and strawberries.
Vegetables: broccoli, carrots, cauliflower,
corn, green beans, onions, peas (sweet, in
pod), peppers, potatoes, summer tomatoes,
zucchini and other squash.
Mushrooms and herbs are excellent, too!
The New Mexico solar food dryer design combines direct and indirect solar heating.
Direct sunlight heats the racks of food in the upper part of the dryer, while the
corrugated metal absorber plate at the bottom of the dryer promotes indirect heating by
creating a convection current of hot air that travels upward through the racks of food.
Are You Ready?
What Would You Do?
Try to imagine what it would be
like to live for a week without
food or water.
How would you answer your
children when they say
“I’m hungry”
Nobody truly likes to think
about it, but it can happen.
A major disruption in food
and water provisions.
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times of emergency.
Food and Water are at the top of
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Always start with food that is at its peak
freshness and ripeness—simply wash, slice
to your desired thickness and place in your
solar dryer. I get great results without any
blanching or pre-treatments. The dried
food consistently looks and tastes great.
The flavor is better than anything I find in
supermarkets, and it’s free of sulfites (a sulfur-
based preservative) and other additives
found in commercial dried foods.
Most people think about drying food in
August, when they can’t keep up with the
supply from their gardens. But there is
abundant solar energy in the spring for drying.
In May or June, you can start capturing
early season crops such as peas, blueberries
and strawberries. Then you’ll be ready for
your summer and fall bumper crops of
beans, plums, peaches, apples and squash.
As you think about how much fun you
will have with a solar food dryer, consider
that by preserving and storing produce, you
can expand your garden and grow more of
the things you’d like to enjoy year-round,
such as tomatoes. A solar food dehydrator is
a great way to maintain a nutritious and
tasty supply of high quality, locally grown
foods all year long. A good dehydrator will
produce outstanding results, along with the
satisfaction of saving energy and money by
harnessing the power of the sun.d
Eben Fodor is the author of The Solar
Food Dryer, a MOTHER EARTH NEWS “Book for
Wiser Living” from New Society Publishers.
To order, see Page 127. He is an avid organic
gardener with a background in solar
energy and engineering. For more information,

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