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Why Dry? This Summer Try Solar Drying
by Eben Fodor
Ironic that our most popular forms of food preservation--freezing and canning--are the most energy intensive while other methods such as drying and lacto-fermentation are nearly forgotten arts. This excerpt from the new book The Solar Food Dryer (New Society Publishers, 2006) reminds us that solar energy can be as delicious as it is practical.
Each day the sun rises, warms the Earth back up, and powers the entire biosphere. There is plenty of extra sunshine available to dry your food. On a clear day, up to 1,000 Watts of solar energy are available for our use per square meter of area of the Earth's surface.This means that a solar food dryer with a horizontal window (or glazing) area of one square meter will have up to 1,000 Watts (3,413 Btu/hr) of solar power available to dry food. However, this is at noon on a clear summer day. Typical operating conditions for a solar dryer will vary depending on weather, geographic location, season, and of course, time of day.
Solar food drying is a great way to learn more about the sun and solar energy. By using a solar dryer you will gain an appreciation for the remarkable potential of this plentiful energy source. You will learn how to efficiently harness solar energy and put it to work preserving your food. And you will discover that it's easier than you might think.
More and more people are discovering the joys and benefits of growing their own food and buying fresh, local produce. Garden foods are seasonal, resulting in the boom-and-bust cycle. First, you can't wait to savor your first vine-ripe tomato. In no time you've got more tomatoes than you can give away. Then frost hits and the party's over.
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Some gardeners turn to canning and freezing to preserve their nutritious bounty. Drying is a third option that has some distinct advantages. Drying is simple and easy: If you can slice a tomato, you can dry food. Dried foods retain more nutrients than canned foods and don't require the energy of a freezer. Dried food is concentrated, reducing bulk and weight to ½ to 1/15 th that of hydrated food. Drying requires fewer containers and less storage space. A power failure (or mechanical failure) can result in the loss of all your frozen foods, but your dried foods will be A-ok.
Dried foods are convenient and easy to handle. Use as much as you want, and put the rest back for later. Take them with you on hikes, camping, or vacations — they're light and hold up well under a wide range of conditions. Dried foods can last about as long as frozen foods, which are subject to freezer burn.
Drying can actually improve the flavor of many foods. Bananas are fantastic fruits, but dried bananas are heavenly. A Roma tomato is almost too bland to eat fresh, but dried it's a treat your tastebuds will savor. Watery Asian pears are sometimes a little disappointing. Dried, they are among the finest treats on the planet.
Indoor electric food dryers have become very popular in recent years. These dryers generally work well. But they do have some drawbacks. They require electricity around the clock — 100 to 600 Watts is typical. An electric dryer costs about one to two dollars per load for the electricity to operate it. These electricity costs eat into the savings of doing it yourself. Electric dryers also take up vital counter space and release all the moisture, heat and odors indoors. The heat and moisture from electric dryers comes at the most unwelcome time of year — the summer harvest, when it's still hot outside. Sometimes the odors are pleasant, but when they continue for days and weeks, they become a nuisance and can attract pests, like ants and fruit flies, into your home. And there is the constant humming of the electric fan. If you have a sunny area on your patio, deck, or back yard, a solar food dryer can produce outstanding results without any of these hassles.
Solar food dryers have zero operating costs. Dry all you want — it's free! Solar food dryers are easy to use and fairly easy to build — if you know just a few simple solar design concepts. Once you learn how to put the sun's energy to work, you can experiment with many possible designs. Or simply follow the detailed instructions provided here to build a high-performance solar dryer of your own.
Using the sun to dry food may be the oldest form of food preservation, dating back thousands of years. For many prehistoric people, dried fruits, berries, grains, fish, and meat were essential to surviving the cold winters. Hanging or laying food out in the open air and sunshine was the simplest method available for drying and preserving the food collected over the summer. Historic photos show the common Native American practice of using drying racks.Native Americans dried meat, fish, berries, and roots in the sun.
But simple outdoor sun drying leaves a lot of room for improvement. Your precious food will take a while to dry and will be subject to possible rotting and assault from rain, wind, dust, rodents, bugs, and, well, you get the idea. These problems are readily solved with a welldesigned solar dryer that uses a few modern materials such as glass, plywood, screens, and adjustable vents.
While "solar dryer" could refer to a tray set out on your deck, in this book, the term is used to refer to a durable, enclosed, weatherproof design that takes advantage of basic solar energy design principles to efficiently and securely dry food. "Sun drying" refers to simply placing food out in the open sunshine to dry. The solar food dryer stays outside and efficiently harnesses the sun's power to dry food much faster than ordinary sun drying.The sun has a surprising amount of energy and a solar food dryer is a great way to get acquainted with the impressive nature of solar power.
A well-designed solar dryer dries food quickly — typically in one to two days — by capturing the sun's energy to produce heat and move air across the food.Warmer air is lighter and rises (like a hot air balloon) in a process called natural convection. Natural convection can be used like a "solar fan" to speed drying.
Designs for solar food dryers and solar cookers proliferated in the 1970s as interest in alternative energy and solar-heated homes peaked. Far too many of these designs used cardboard, tin foil and plastic wrap. The solar dryer designs described in this book are sturdy, dependable, highly effective, easy to use, weather resistant and will provide many years of enjoyment and savings.
Is Solar Food Drying Right for Me?
At this point, you may be asking "Is solar food drying really a good idea, and is it right for me?" With a little guidance, you will never regret going solar. If you are not technically inclined and don't want to learn the details about solar energy, you will still be successful, because using solar energy is intuitive. You just have to do what's obvious. In fact it's hard to screw it up.
Occasionally I find disparaging comments about solar food drying, such as "solar dryers are not suitable for humid climates," or "solar dryers won't work in areas without lots of sunshine." A good solar dryer will work well in most of the world and anywhere in the Lower 48 states where you can get two days of sunshine in a row with some regularity. In fact, just about anywhere you can grow a successful outdoor vegetable garden, you can use a solar dryer. Outdoor temperature and humidity levels have only minor impact on solar food drying. You can successfully dry foods in the muggiest climates and at outdoor temperatures down to about 45°? F.Clouds, however,will diminish drying quite a bit. An overcast day will leave your solar dryer sputtering. For this reason, a backup electric heat option is a good idea to protect against unpredictable weather changes.
Why Haven't I Heard More About Solar Food Dryers?
If solar food dryers are so great, why aren't lots of people using them? Solar food drying started to take off in the late 1970s when energy prices spiked and interest in solar technology peaked. There was quite a bit of experimentation, and many solar food dryer designs emerged. But with little research funding and no promotion, they never achieved much popular status. The 1980s and 1990s were periods of economic expansion and interest in energy conservation and renewable energies was all but forgotten. But energy prices are heading skyward again, resulting in a broad reawakening the importance of sustainable alternative energies. Along with the growing awareness of our over-reliance on fossil fuels, we are seeing an increased interest in healthy eating, high-quality organic produce, local food production, and sustainable living. Solar food drying is an obvious part of the solutions to these challenges.
Another factor that may have held solar food drying back in the past was a perceived lack of convenience and performance. Designs for solar dryers have ranged from shoe boxes covered with plastic wrap (a good science experiment) to big bulky contraptions that have to be assembled every time they're used. There is a happy medium.
There is plenty of power in the sun to dry food quickly, so good performance simply requires proper design. Solar dryers can be highly effective and on par with the best electric dryers. Because solar dryers need to collect sunshine for power, they must have a certain bulkiness associated with the glazing area.The larger the capacity of the dryer, the more sunshine is needed to power it.
This book features an original dryer design — the SunWorks SFD — which was originally constructed from scrap and recycled materials. This provided me with the added pleasure of minimizing consumption of natural resources. The design is built with new materials to standardize the construction process. Once you have materials on hand, you can build this dryer in a weekend. Several other designs are illustrated to give you an idea of the range of design possibilities.
The SunWorks dryer described in this book was designed to be compact, lightweight, and portable, but still have enough capacity for the serious home gardener. Since there are many ways to harness the sun, a number of other good solar dryer designs are also described in this book. Everyone with a vegetable garden or a passion for locally grown produce should consider getting a solar food dryer. If you haven't been hearing about them yet, you soon will!
The Bigger Picture
I often get blank looks when I mention solar food drying to people. But then I ask them to think about how important food is, how dependent we are on importing foods from far away, how the quality of those foods is often not the best, and how our long-distance food supply depends on fossil fuels for shipping and storage. The alternative is to expand the local food supply. But when the local growing season is over, what can we do to extend our local self-reliance in a sustainable manner? It all starts to become clear: Solar food drying is the renewable energy solution to the local food supply challenge. Sure, as long as fossil fuels remain cheap, lots of people will continue to buy winter grapes and plums from Chile, peppers from Mexico, tomatoes from artificially heated hothouses, and apples and pears from refrigerated storage warehouses. But this energy-intensive food supply system seems vulnerable and beyond our control. And the nutritional quality and safety of the food is often questionable. Solar food drying is simply the healthy, sustainable alternative. And it's ready to work for you today!
Additional information (including dryer plans):
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