Monthly Archives: December 2013

The Solar Dryer, Part 4: Construction

  There were few hand tools available at the farm, and almost none (except quite a few hammers) in working condition. The Taneeb family maintains a strangely large collection of—for example—old wire-cutters fused by corrosion into immovable wire-cutter-shaped hunks of iron. There were no power tools, and anyway no grid power at the farm. Fayez was able to borrow a diesel generator and a gigantic hammer-drill; and we purchased, among other things, a screwdriver, hand saw, sets of drill- and screwdriver bits for the power-drill. For one day, one student brought both a battery powered screwdriver and a circular saw.

Assembling the base and legs.

Assembling the base and legs.

 Use of the generator with the huge hammer-drill to drive #4 screws into up-cycled lumber was not the most efficient or ecological solution, but it made it possible to make progress quickly on the construction and complete the solar dryer in the time we had. After spending much of the two weeks on discussion, other activities with the larger Global Campus group, recovering and preparing the materials, tracking down and purchasing new materials when needed; the final design choices, cuts, and assembly took place in a dense, intense, and surprisingly well choreographed final few days. By this time, everyone had a clear idea of what we were doing, and the group worked smoothly to create the final product we had imagined together and prepared for.

This was when we realized that something was really taking shape.

This was when we realized that something was really taking shape.

 In addition to purchasing new fasteners (although many were recovered from the found lumber) we also bought new polyethylene sheeting, plastified metal mesh for the drying trays, and of course the solar panel. The three fans were recovered from old computers out of necessity; new 12V computer fans were simply not available in Tulkarm. I would have preferred to buy these new, and intend to replace them next time I visit the farm. Three kitchen strainers were purchased for use as inlet filters over the fans.

placing the main working surface

placing the main working surface

 The final product differs from the designs in Lorenz-Ladener in several ways: The roof is more peaked, simply because this is the way the students built it and I didn’t notice until after the roof beams were cut and assembled. Readers of this report should be aware that in Northern Europe, with less intense sunlight and lower ambient temperatures, this could be a problem; in Palestine, the inside of the dryer immediately reached temperatures of around 40C on a mild autumn day, despite the high roof and the light color of the dryer interior.

the team in consultation

the team in consultation

 

Our initial idea was to paint the floor of the dryer a slightly darker color—the recovered plywood we used had been painted white—or to lay brown paper on part or all of the floor. But as mentioned, the dryer quickly reached ideal temperatures as it was; we have left it for now. There is a thermometer in the dryer, and the Taneeb family will experiment with it to determine if we need to darken the Solar Dryer interior.

fabricating the trays

fabricating the trays

 Lorenz-Ladener make no mention of it, but in Tamera we learned that it was an absolute necessity to protect the Solar Dryer from ants. As in Tamera, we incorporated water-traps into the legs of the Solar Dryer.

Both the roof beams, and a tray, are visible here.

Both the roof beams, and a tray, are visible here.

 

 

 

 

The Solar Dryer, Part 3: Design & Materials

 The first steps in Tulkarm were 1) to discuss with Fayez and his family their plans for the Solar Dryer, 2) to begin to discuss the basic plans and design parameters with the students, and 3) to inquire about available tools and materials.

Fayez did have interest, and specific intentions, for the Solar Dryer. The practice of sun-drying fruits and vegetables exists in the local culture of course, though the habit is largely disappearing. It was gratifying to hear how often the local response to the solar dryer was to remark that everyone’s grandparents had sun-dried excess farm production, and that we–the internationals of the Global Campus–were merely bringing a reminder of wisdom already present in the community. This assuaged our fears of being (or of being seen as) well-intentioned, neo-colonialist aid workers.

The “Solar Dryer Group” consisted of myself; one international participant with some experience in Tamera; and several students in in Agricultural Engineering from the local university. The group had a fairly sold core—Wafa, Inas, Baha’, Adul Rachman, and Bashir; eveyone was encouraged to support group needs, occasionally working in the kitchen for example, and to visit other procjets. As a result, not everyone was present every day, and other participants came to us occasionally. I leave these details to general discussions of the Global Campus in Palestine, available elsewhere.

The first step with the group, after having discussed Fayez’s plans, was to look at the pictures in the aforementioned book, and discuss the airflow and temperature requirements. I still have the first drawings I made, which were based on standard sizes of lumber in Europe, and the expectation of access to hand- and power tools.

Initial drawings for our solar dryer.

Initial drawings for our solar dryer.

 

 These drawings were about ideas and communication, and not a blueprint for building. The main reason for this was the desire to use material available locally, ideally to “upcycle” material from the waste stream, and designs. This meant that the design would depend on what was around.

These bits of framed plywood were available for a number of construction projects on the farm.

These bits of framed plywood were available for a number of construction projects on the farm.

 For example Fayez had already brought some “scrap” wood—plywood and pallets—to use during the Global Campus. Two of these, end to end, came very close to fitting the initial drawings of the dryer. We needed quite a bit more lumber, which we found a few hundred meters from the farm, at a kind of scrap yard. This yard was probably also the origin of the wood already at the farm.

 

Just outside the scrapyard fence. The wood we picked out is piled for collection.

Just outside the scrapyard fence. The wood we picked out is piled for collection.

By weight, nearly the entire Solar Dryer was built with recovered materials. (We’ll mention the exceptions as they come up.) This was a conscious choice. The construction process would have taken only a few days, had we bought new materials.

In any case, nearly all the final design decisions were made by the student team, with only the occasional veto from me. Adapting to available materials was therefore quite natural.

 

The Solar Dryer, part 2

The Solar Dryer-Background

The Solar Dryer that we built on the farm of Fayez Taneeb in Tulkarm, Palestine, is based on existing solar dryers in Tamera, Portugal; and on the designs proposed in the book Sechoirs Solaires by Claudia Lorenz-Ladener. More information and background about the first solar dryer in Tamera is available here: http://www.tamera.org/index.php?id=889 .

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 Designs from this book (in French but translated from a German original) were the basis for the solar dryers in Tamera, Portugal; and in Tulkarm, Palestine.


The basic “tunnel” solar dryer is essentially a table-top greenhouse, with active ventilation provided by electric fans and a dedicated photovoltaic panel. It provides optimal airflow and temperature for drying food; in an environment protected from animals, UV radiation, weather, and contamination. The basic design goal is to maintain, when in sunlight, a constant airflow of about 50 m3 per hour per m2 of surface; and a temperature of between 30C and 50C, the ideal being about 40C. Once constructed, the Solar Dryer is entirely autonomous and “off grid,” and supports both local food autonomy and economic resilience.

One of the Tunnel-Type Dryers, from Lorenz-Ladener's book.

One of the Tunnel-Type Dryers, from Lorenz-Ladener’s book.

Many of these dryers have been built around the world. from the smallest versions of about 2 m2, as proposed by the book mentioned above, up to dryers of 40 m2. The current tunnel-type solar dryer in Tamera is about 18m2.

The design principles are very simple, and many variations are both possible and often desirable. My colleagues in Tamera assured me that for hot, sunny climates, such as Portugal or Israel-Palestine, some changes are appropriate. For example, the designs in the book, developed in central Europe, include leaving the first meter of the dryer empty and painted matte black, to warm incoming air. I was assured that even in the Alentejo, this was not needed to achieve the needed temperatures.

The Solar Dryer in Tulkarm was a result of a combination of these published designs, experience from Tamera, the locally available tools and materials, and the creative impulses of our group. The details will be available in upcoming posts.

The Solar Dryer, part 1

Note: There will be, in the next week or so, a series of fairly technical posts about the Solar Dryer built in Palestine during the Tamera Global Campus.

The completed Solar Dryer, in position. The PV panel is not visible, but the separation wall is in the background.

The completed Solar Dryer, in position. You can’t see the PV panel, but the separation wall is visible in the background.

Introduction:

As a member of the team of the Tamera Global Campus in Israel-Palestine, my main role was to coordinate the design and construction of a “Solar Dryer,” a solar-powered food dehydrator, on the farm of Fayez Taneeb in Tulkarm, Palestine.

This project had a number of goals, one of which was to provide the Taneeb family farm with a food dryer, to allow them to preserve seasonal surpluses of fruits and vegetables. The other main intentions of the project were pedagogical; our wish was that the young Palestinians working with us leave with a full understanding of how and why to build a Solar Dryer.

The construction of the Solar Dryer was successful completed within the time-frame in Tulkarm, Palestine. It was built almost exclusively of recovered materials (most fasteners, the polyethylene sheeting, the photovoltaic panel, were purchased new). The students reported at the end that they had a complete understanding of the Solar Dryer, having fully participated in every stage of its design and construction. The students also engaged deeply with the more complex human and ecological questions raised by the Global Campus. For example, the political significance of local food and energy autonomy, was readily appreciated and discussed.

In the time we had, we were not able to see the Solar Dryer put into use. The important question of how this technology will be integrated into the lives of the people that use it, will have to be a subject for follow-ups, and further visits.