INTERNATIONAL CONFERENCE ON SOLAR COOKING
KIMBERLY - SOUTH AFRICA
26th - 29th NOVEMBER, 2000
In many countries of the world, the use of solar
thermal systems in the agricultural area to conserve vegetables, fruits,
coffee and other crops has shown to be practical, economical and the
responsible approach environmentally. Solar heating systems to dry food and
other crops can improve the quality of the product, while reducing wasted
produce and traditional fuels - thus improving the quality of life, however
the availability of good information is lacking in many of the countries
where solar food processing systems are most needed.
This work presents the performance of several
individual, medium and large-scale food processing systems, which
incorporate solar drying. Demonstrated achievements through individual
medium and large scale commercial applications will be studied, emphasizing
technology transfer in rural areas. Works studied are catalogued with
summaries, and use of the Internet is featured as a medium to facilitate the
availability of this information.
"Drying is an excellent way to preserve food and
solar food dryers are an appropriate food preservation technology for a
sustainable world." Actually, solar food drying is one of the oldest
agricultural techniques related to food preservation, but every year,
millions of dollars worth of gross national product are lost through
spoilage. Reasons include, ignorance about preservation of produce,
inadequate transportation systems during the harvest season (mostly climate
related), and the low price the rural farmer receives for products during
the harvest season.
Drying of crops can change this trend and is
useful in most areas of the world, especially those without a high humidity
during the harvesting season. If drying of produce were widely implemented,
significant savings to farmers would be achieved. These savings could help
strengthen the economic situation of numerous developing governments as well
as change the nutritional condition in these same countries. Unfortunately
many of the areas that could benefit from solar drying technology lack
adequate information related to how to employ this technology and which
technology to use under specific conditions. Many of the latest
developments in solar drying technology, as well as significant achievements
through applying this body of knowledge are not available in libraries or
the Universities of developing countries. However, modern science has
provided a new resource that helps bridge this information void. The World
Wide Web, commonly know as the INTERNET can provide the solution to rapidly
spreading new information and applications of known information into areas
of greatest need.
1. SOLAR DRYING
Drying preserves foods by removing enough
moisture from food to prevent decay and spoilage. Water content of properly
dried food varies from 5 to 25 percent depending on the food. Successful
drying depends on:
enough heat to draw out moisture, without
cooking the food;
dry air to absorb the released moisture; and
adequate air circulation to carry off the
When drying foods, the key is to remove moisture
as quickly as possible at a temperature that does not seriously affect the
flavor, texture and color of the food. If the temperature is too low in the
beginning, microorganisms may grow before the food is adequately dried. If
the temperature is too high and the humidity too low, the food may harden on
the surface. This makes it more difficult for moisture to escape and the
food does not dry properly. Although drying is a relatively simple method
of food preservation, the procedure is not exact.
Renown solar cooker designer and Sustainable
Living expert Barbara Kerr tells us that, "food drying is a very
simple, ancient skill. It requires a safe place to spread the food where dry
air in large quantities can pass over and beside thin pieces. Sun is often
used to provide the hot dry air. Dry, clean air including dry cold air from
any source will dehydrate food. Draping food over branches or spreading it
on wide shallow baskets on the roof is an old widespread tradition still in
use around the world. Many other arrangements have been used to support a
thin spread of food pieces. Some options that have been used are to thread
the pieces on a cord or a stick and hang it over a fire, wood stove or from
the rafters. Or one can bundle herbs or strawflowers and suspend them from
bushes or a door knob or nails in rooms with good ventilation." Of the
many dryer types available, Barbara recommends the downdraft system. What's
more, her booklet A REVIEW OF SOLAR DRYING, advises that
nutritionally, dried food is ranked by the United States Food and Drug
Agency as better than canning, and just under freezing. She states that the
tastes are related to the food, but there is some uniqueness in their flavor
Markus Häuser and Omar Ankila
, co-authors of the MOROCCO MANUAL OF SOLAR DRYING, inform us that
traditional sun drying methods often yield poor quality, since the produce
is not protected against dust, rain and wind, or even against insects,
birds, rodents and domestic animals while drying. Soiling, contamination
with microorganisms, formation of mycotoxins, and infection with
disease-causing germs are the result. They assert that the drying equipment
used in industrialized countries overcomes all of these problems, but
unfortunately is not very well suited for use in developing countries
because it requires substantial investments and a well-developed
infrastructure. They further maintain that solar drying facilities combine
the advantages of traditional and industrial methods, namely low investment
costs and high product quality.
For centuries people of various nations have
been preserving dates, figs, apricots, grapes, bananas, pineapples, other
fruits, herbs, cassava, yams, potatoes, corn, peas, onions, garlic, carrots,
peppers, milk, coffee, meat, and fish by drying.
But drying is also beneficial for hay, copra
(kernel of the coconut), tea and other income producing non-food crops. It
is worth noting that until around the end of the 18th century
when canning was developed, drying was virtually the only method of food
1.3 Benefits of Solar Dried Food
"Dried foods are tasty, nutritious, lightweight,
easy-to-prepare, and easy-to-store and use. The energy input is less than
what is needed to freeze or can, and the storage space is minimal compared
with that needed for canning jars and freezer containers.
"The nutritional value of food is only minimally
affected by drying. Vitamin A is retained during drying; however, because
vitamin A is light sensitive, food containing it should be stored in dark
places. Yellow and dark green vegetables, such as peppers, carrots, winter
squash, and sweet potatoes, have high vitamin A content. Vitamin C is
destroyed by exposure to heat, although pretreating foods with lemon,
orange, or pineapple juice increases vitamin C content.
"Dried foods are high in fiber and carbohydrates
and low in fat, making them healthy food choices. Dried foods that are not
completely dried are susceptible to mold.
"Microorganisms are effectively killed when the
internal temperature of food reaches 145 degrees Fahrenheit (F)."
an expert in alternative energies and instructor at Appalachian State
University, Boone, NC informs us, " Food scientists have found that by
reducing the moisture content of food to between 10 and 20%, bacteria,
yeast, mold and enzymes are all prevented from spoiling it. The flavor and
most of the nutritional value is preserved and concentrated. Vegetables,
fruits, meat, fish and herbs can all be dried and can be preserved for
several years in many cases. They only have 1/3 to 1/6 the bulk of raw,
canned or frozen foods and only weigh about 1/6 that of the fresh food
product. They don’t require any special storage equipment and are easy to
1.4 Solar Drying Recommendations
The El Paso Solar Energy Association
provides some practical information and links to other resources. They state
that their information is prompted by the need for solar dryers in areas
where fruit is plentiful in summer months, but because there is no simple
and economic method to preserve it, much of it is left to rot, while in the
winter there is hunger.
They agree that solar food drying can be used in
most areas but clarify that how quickly the food dries is affected by many
variables, especially the amount of sunlight and relative humidity. They
provide some basic guidelines to drying food.
Most of the resources researched recommend
pre-treatment of the food, such as blanching, (boiling/steaming).
Wash fresh fruits and ripe vegetables
Effective drying is accomplished with a
combination of heat and air movement.
Remove 80 to 90% of moisture from the food.
Typical drying times range from 1 to 3 days,
again depending on sun, air movement, humidity, quantity, and type of
Once the drying process has started it
should not be interrupted, do not allow to freeze.
Direct sunlight is not recommended.
Temperature ranges of 100 to 160 degrees F.
(37.2 C to 71.2 C) will effectively kill bacteria and inactivate
enzymes, although temperatures around 110 degrees F. (43.2 C) are
recommended for solar dryers.
Too much heat especially early in the
process will prevent complete drying.
Food should be cut into thin slices, less
than 1/2" thick (1.25cm) and spread out on trays to allow free air
Rotate trays 180 degrees daily for uniform
drying. Move dryer food to bottom racks.
Safe tray materials include Stainless steel
rack - wood slats - cheesecloth - Teflon - Teflon coated fiberglass -
nylon - food grade plastics
Allow food to cool completely before storing.
Store food in airtight jars or plastic
containers, and do not expose dried food to air, light or moisture.
Most fruits taste great dried including
apples, apricots bananas, grapes etc.
Vegetables are best reconstituted by
covering with cold water until they are near original size. They can be
added in their dry form to soups/stews. Vegetables can also be ground
into powders and used for instant soups or flavoring.
1.5 Solar Drying Can Improve
Dehydration of vegetables and other food crops
by traditional methods of open-air sun drying is not satisfactory, because
the products deteriorate rapidly. Furthermore, traditional methods do not
protect the products from contamination by dirt, debris, insects, or germs.
A study by Akwasi Ayensu from the Dept. of Physics at the University
of Cape Coast, Cape Coast, Ghana demonstrates that food items dried in a
solar dryer were superior to those which were sun dried when evaluated in
terms of taste, color, and mould counts. He asserts, and many others agree
that solar drying systems must be developed to utilize this energy resource
to improve food preservation.
This translates into quality products that can
be stored for extended periods, easily transported at less cost while still
providing excellent nutritive value.
2 The Dryer Systems
For the purpose of classifying the cases
studied, categories have been established according to the intended use of
each type of system. Conclusions reached are summarized, and links
(directions for email or Internet) are given to facilitate additional
research by individuals.
2.3 Individual Family Units
Individual family units can be described as
those systems designed to dehydrate small quantities of fruits, vegetables
or herbs for the purpose of extending the availability of these products at
the family level.
2.1.1 Details about family units
from the Centre Neuchâtelois de cuisine solaire / ULOG Suisse Romande whose
web address is http://www.ulog.ch
communicates that ULOG's activity with drying is going on a low level
relative to their other activities. They sell plans and kits and finished
'Euro-family-dryers' which is the small wooden model designed by Uli
Oehler maybe 15 years ago (see picture).
is also know for the famous A-frame collapsible dryer. The author's
organization, Sobre la Roca teaches the use and fabrication of this
portable dryer in Bolivia, South America
According to Neville Jackson, from
Tingha, NSW, Australia; for around $50 you can make a drying cabinet
and enjoy the fruits (and veggies) of your labor all year. He explains that
dried foods lose most of their contained moisture, retain most, if not all,
of their vitamins and minerals, and take up little space. At his web site
http://www.organicdownunder.com/solar_dryer.htm, Neville also provides
various procedures for drying.
suggests that solar dryers and water-heaters as an alternative
technology are more easily accepted and can serve as stepping stones towards
similarly built solar cookers. "They do not have the cultural barriers to
overcome, that solar cookers experience," he adds. Follow this link to
learn about his experiences teaching family sized solar dryer systems in
Nepal, Mongolia and Peru. -
Dr. Youssef Arfaoui
, with the Forum for Energy and Development, INFORSE, Denmark writes, "Solar
Dryers make the difference between waste and value of surplus mango fruits
in Uganda. They create new possible exports to Europe." He informs us that
the number of the units in operation are still not satisfactory, as the
technology is new and people (especially small farmers) must get used to
it, even if the system is very simple. He says that, "Often, they do not
believe that this one can be effective, because it looks so simple".
Further clarifying that in total 11 units are in
operation in Uganda, with about 4 -units operating in Paidha - Nebbi
district for 3 years, about 4 - units operating in Masindi - Masindi
district for 1.5 years, and about 3 - units operating in Hoima - Hoima
district, during 2 years.
The costs depend of the size of the unit. It is
very cheap as the materials are locally available. For the one in the
picture, the price is about 20 US$. Increasing the size, increases the
prices also (max 50 US$) otherwise, the units will be expensive for the
farmers. The prices can be reduced according to the number of units produced.
In a direct email communication with the author,
Dr. Arfaoui states, "My personal opinion, is that during the presentation at
the seminar, you shall emphasize on the user training and the attitude
changing, when starting to use the dryer." He adds "for further
clarification, please do not hesitate to contact me at
In two articles published in Home Power
magazine, Dennis Scanlin provides a broad range of information as
well as detailed construction techniques for an indirect chimney type dryer
system. Some of the topics covered include; factors affecting food drying,
recommended drying temperatures, relationships between air flow and dryer
temperature, possible temperature related problems, how to get the correct
temperature and air flow, collector design, dryer construction and related
The second article, expands on data gathered
over 2 years as well as document experiments with design changes, including
external reflector use and vent variations. Both articles are tremendously
instructive. It should be noted that the systems detailed in Scanlin's
papers are adequate for small-scale commercialization as well as individual
family use. Scanlin has also demonstrated considerable proficiency
designing and building small solar timber drying systems.
All of these systems provide the benefits
required of solar dryers, plus their size permits small-scale food
conservation. They have the added advantage of being portable.
2.3 Medium Scale Commercial
Good Export Income with a Good Solar Dryer
. Medium scale systems meet the need of individual's and of groups,
cooperatives, or associations to supply a greater quantity of product under
constant conditions, thus empowering them to reach more markets.
2.3.1 Details about Medium Scale
The Uganda dryer
, believed to be derived from the Peace Corps model developed around
1986, is our bridge between family scale and village scale. Excerpts from
an article of the Sustainable Energy Newsletter provided by Judit Szoleczky
demonstrate that the Uganda dryer meets the criteria for both individual and
medium scale commercial use.
Fruits and vegetables are abundant in Uganda.
With the right processing, they can provide farmers with a good income. They
can be dried using a solar dryer, then transported and sold in the big
cities, exported, or saved to be used during the dry season's food shortages.
The dried fruits processed in the dryers have
been tested and exported to the UK. It is now known that they have a big
market in the UK and all over Europe. After the introduction of the dried
mangoes to the UK, the farmer groups could not meet the increased demand of
a UK-based importer and still guarantee the same high quality. Presently, a
small-scale export trade has been established. The dried fruit is now
produced and exported from Kampala by several farmer groups like the
Gukwatamanzi Farmers Association, which has 60 members, the Christian Rural
Services of Nebbi West Nile, which has 40 members; and the Uganda National
The second-quality selection of the dried fruit,
which can not be exported, can be stored for later private consumption.
School children are also able to have dried fruit as part of their lunches
during the school hours. A large number of fruits and vegetables can be
dried, including peas, corn, cabbage, broccoli, peppers, herbs, melon,
plums, beets, onions, squash, tomatoes, asparagus, celery, bananas, and, of
For more information on this dryer contact
MS Uganda, 54 B, Kira Road, PO Box 6331, Kampala, Uganda. Ph:+256 41530764,
fax +256 41530765 e-mail:
In the paper, USE OF A SCALED DOWN SOLAR
TIMBER DRYER AS A PILOT FOR COPRA DRYING, Professor Oliver Headley
, renown author and investigator specializing in the field of solar energy,
describes how a 6 m2 artisanal solar timber dryer was developed as a
scaled down version of a 30 m2 solar timber dryer so that artisans and small
scale operators could dry their timber and improve the quality of the
furniture they manufactured. He explains that, "other configurations of
crop dryers have been tested in the Caribbean, but this model is designed to
be sufficiently versatile to dry several different materials hence it may be
used throughout the year and there is no need for a capital item to be idle
while the owner is paying interest on the loan used to acquire it." This
work informs us that the use of a solar dryer to dry copra was done in an
effort to save on the cost of diesel fuel which is used by the large scale
copra dryers on the coconut estates in South Trinidad. Copra is the dried
kernel of the coconut (Cocos nucifera) and coconut oil is normally extracted
from it and used in the manufacture of soap, margarine and glycerol. The
paper concludes that, "A dryer of this type should have wide applicability
throughout the Third World."
The article, SOLAR DRIED FRUIT BOON TO
KENYA'S RURAL FARMERS, by Sam Gonza acquaints us with the
advantages of solar drying of mangoes as practiced by women's groups in
Kitui District of Eastern Kenya. Beatrice Kingori of GTZ-ITFSP
comments that there is a big scope for the business of providing solar
dried fruit in local markets in Africa. "What is lacking is awareness.
Our people need sensitization of the nutritional benefits of solar dried
food items," she explains. The dryer has a glass top surface of about 1.5
square meters and is rotated to follow the sun in the course of the day.
There are three tiers of racks inside the dryer and they are inter-changed
within the solar kiln device to ensure uniform drying. According to Ms
Kingori, each solar dryer unit can handle 10 to 15 kilograms of fresh fruit
per day, which reduces to 0.75 to 1.5 kilograms of dried fruit per day. This
yields a ratio of about 15 to 1. "Ideally, the drying process should take
place in a single day. If you leave it overnight there is likelihood of
deterioration of quality," she specifies.
http://ines.gn.apc.org/africa/afrpre30.htm#APS2796F will provide you
with further details as well as information on a nutritious beverage.
PARAMETER SENSITIVITY ANALYSIS OF A DIRECTLY
IRRADIATED SOLAR DRYER WITH INTEGRATED COLLECTOR
by Ajit K. Mahapatra and L. Imre
, describe their efforts to examine the effect of different time dependent
and time independent input parameters on the various output parameters of a
tunnel-type directly irradiated solar agricultural dryer with integrated
collector. A prototype consisting of a small radial flow fan and a solar
tunnel dryer with an integrated collector part was tested in Hungary, drying
chamomile. The drying of 43 kg of chamomile from an initial moisture
content of 75 per cent (w.b) to a final moisture content of 7 per cent (w.b)
took 57 hours.
J. Salom, O. Ortega, and J.J. Felipe
provide an important mathematical model
for designing chimney type indirect solar dryers. This interesting work
supports the hypothesis that the introduction of solar dryers in developing
countries can improve the traditional methods of food preservation. They
state that simulation models of drying systems are needed in the development
of solar dryers. And that the knowledge of drying parameters is important to
obtain valuable information about the state of the product, the air
(temperature and humidity) and the efficiency of the dryer.
from the organization Solarebruecke has provided details on several
dryer types including a solar-dryer called "Icaro". In a email
communication he states, "among the dryers I very much favor is the
Icaro-type. The space is well used, the goods prepared for drying are not
exposed to sunlight and I'm quite sure that using a higher chimney one can
do without the fan." He adds that, "at our home we have also used our 8sqm
Scheffler-dish for drying." But he believes it makes sense only to put it
to that use if you have a big dish anyway, as some way of using it more
effectively by giving it additional tasks.
Medium scale commercial systems have the
advantage of allowing the producer to increase the commercial yield of crops
by utilizing what is normally lost in spoilage. The products are also
eligible for exportation to areas where they may receive a higher price for
their goods. Capital outlay for these systems is not as tremendous as in
large-scale commercial systems, and studies demonstrate that in many cases
the investment can be recuperated in less than 1.5 years.
2.3 Large Scale Commercial
Large-scale commercial applications require
greater capitalization, and are designed to dry very large quantities of
product with better control of temperature and hygienic conditions. These
systems are appropriate for associations or village cooperatives as well as
large commercial farming operations.
2.3.1 Details about Large Scale
Michael Götz with the ULOG organization advises
that for larger, commercial dryers, Jean-Claude Pulver (in
Paraguay: email@example.com) and
Alec Gagneux (
Alecgagneux@hotmail.com) have considerable practical experience.
taught a course on the Ulog A-frame dryer in Kalamarca Bolivia in October of
1999, in which the author participated. At that time he demonstrated
photographs of several commercial dryers including tunnel dryers constructed
by him in Paraguay. Through a recent email communication, Jean-Claude
informs of building a shed type dryer with rock heat storage in the
Dominican Republic to dry 200 MT of organic grown cocoa. This hybrid system
has the ability of adding another heat source to insure good drying year
representing GTZ, communicated that "we promote a solar dryer called "
Höhenheimer tunnel dryer" developed by a German company. This dryer
is rather big and suitable for groups of farmers or farmer collectives. If
you are interested in that dryer you can read the details at:
Ms Schwarz also informs us of a solar
dryer-mailing list which is set up for sharing experiences in solar drying
technologies adding that, "It would be very nice if you all could give some
inputs to the list." Her email direction is
Although Oliver Headley and William Hinds title
their excellent work - MEDIUM SCALE SOLAR CROP DRYERS FOR AGRICULTURAL
PRODUCTS, it is included here among the large-scale systems because it
describes the design and operation of two solar agricultural dryers.
One has a capacity of ten tonnes of hay, while the other a capacity of seven
tonnes of onions. These systems are compared with two other "medium scale"
solar dryers which are used for fruit and timber. The work states that,
"Solar dryers of this size need to have mechanically driven fans for air
circulation which are powered by mains electricity. In all four cases; they
are economically viable so long as they do not have to compete with cheap
natural gas." They maintain that, "In isolated communities, solar energy is
quite often the only heat source which can be used to dry low cost
agricultural products economically."
The authors of this paper conclude that, "Solar
crop dryers are a cost effective solution to some of the problems of food
preservation in sunny climates. In places where fossil fuel is cheap and
readily available, such as natural gas in Trinidad & Tobago, the decision to
use solar dryers may be based on purely environmental considerations, since
the economics of the dryer do not allow it to compete with cheap natural
gas. The solar dryer with the least initial capital cost is one which uses
an existing farm building or adds a solar air heater to an existing
conventional crop dryer." Their results suggest that relating to large
scale commercial systems, "while multi-crop dryers may seem to be an ideal
solution, the fact is that most operators prefer to have a dryer which is
dedicated to one or two crops or to a specific kind of crop, fruit for
example, since the compromises inherent in a multi-purpose dryer often
result in reduced efficiency for its primary product."
An in-depth study from 1997 titled FIELD
PERFORMANCE OF A SOLAR TUNNEL DRIER, states that the solar tunnel
drier of the Hohenheim University has achieved a fair degree of success
in many countries and details the performance and economics of this type of
solar drier in Thailand. From this investigation it was determined that
solar tunnel dryers were developed to eliminate some of the problems related
to conventional solar dryers. The authors ascertained that compared to
other solar dryers, the capacity of the tunnel dryer is much higher. Adding
that significant reduction in drying time, high quality of the dried
material and complete protection from rain, dust and insects are the main
advantages of the solar tunnel dryer.
What's more, around 150 dryers in 28 different
tropical and subtropical countries are now in operation. Prototypes have
been produced locally at prices between 1,000 and 1,500 US$ in Sri Lanka,
Turkey and Morocco including the PV-drive forced ventilation. In Turkey,
mass production of the solar tunnel dryer has already been initiated. In
1995, around 100 tons of dried figs and apricots were produced using 10
solar tunnel dryers. It is estimated that up to the end of 1996 at least 50
solar tunnel dryers will be installed there. In Sri Lanka, local production
started in April 1996.
According to the authors, the experience
obtained on solar tunnel dryer operation in Thailand and the performance
based on the field shows that;
The tunnel dryer performs better than
normal sun drying and the quality of the product is also better in terms
of cleanliness, texture and color.
Better control of the drying process
is possible when compared to other dryers.
Dried bananas from solar tunnel dryer
command a much higher price than the conventionally dried bananas and
therefore could be a useful device for the value addition of
agricultural products in developing countries.
, and Juergen Blumenberg give us a stimulating example of a variation
of the solar tunnel dryer in their excellent document titled Solar Drying
of Apples in Nepal. Besides describing how they installed an
adapted solar drying system at the community of Marpha, Mustang, Nepal, to
dry the annual overproduction of 10 tonnes of apples and other agricultural
goods of the village; they deal with alternative ways of project management
to avoid the well known failures of the conventional and expensive technical
aid programs conducted by big organizations.
This report's conclusions are so
non-conventional that they are reproduce here in its entirety:
The experiences made during the realization of
this small scale project of technical aid to developing countries showed
that it may be more effective to manage such programs with a small financial
input including a certain contribution by the partners than to work with
enormous budgets like practiced by most of the big aid organizations.
Furthermore there are a few suppositions for starting such programs:
· the project should be initiated by the aid
· the village should be participated financially
· the project should involve a local experienced
· the technique should be as simple and adapted
· the system should use only local materials
During the realization-phase it is very
important to take the social structure of the area into consideration and to
utilize it in favour of the project. Another aspect that should not be
neglected is to give the villagers the possibility to participate
practically and to follow and influence the project in all the different
phases. And if the know-how transfer to the users can be turned out smoothly
the project has the best chances to be successful even after the last
foreigner left the site.
Throughout Latin America, the drying of the
harvested green coffee beans contributes significantly to the destruction of
the remaining rainforests. Conventional coffee dryers consume
large amounts of wood and electricity to dry the beans after the washing
process. In Central America, an estimated 16,000 acres of forest are
destroyed to supply the firewood used to dry the coffee production each
harvest. The Solar / Biomass Drying System developed and
marketed by SUN UTILITY NETWORK INC. helps to reduce deforestation by
using the sun’s energy to dry the harvest.
According to the information they provided, this
solar coffee-drying process has several product-quality and economic
the low-temperature process, conducted right
after harvest, relies on consistent heat, gently circulated across the
coffee beans, optimally preserving the quality and taste of the beans;
the solar drying process gives small growers
the capacity to dry their coffee beans themselves, which adds value to
the product since dry beans are stable and much more valuable than beans
that must be sold wet (as coffee "parchment") to intermediaries for
This sophisticated solar coffee dryer
incorporates well-established renewable-energy technologies such as solar
thermal collectors, photovoltaics, heat exchangers, and biomass burners. The
dryer consists of a coffee bean drying chamber, a solar thermal collector
array to generate heat, a solar-electric photovoltaic array and battery bank
to power fans and pumps, as well as a small biomass burner/water thermal
storage backup system fueled by coffee parchment for nighttime and rainy or
cloudy periods. The system has been used in three consecutive harvests, in
1994-1997, in Costa Rica and Honduras, receiving an enthusiastic endorsement
from the growers and their cooperatives.
has developed solar crop-drying systems
to improve product quality, reduce use of conventional fuels and reduce
product wastage. Enermodal offers the following services to crop drying
design of solar crop-drying systems
monitoring of crop-drying performance
technical and economic evaluation of solar
Their projects include the following:
technical and economic feasibility study of
the world-wide potential for solar crop-drying systems (for the
International Energy Agency)
design assistance on solar crop-drying
systems in southeast Asia for rubber, tea and fruit
design of a passive solar drying-shed for
The drying system for drying tealeaves in
Thailand was designed and constructed by Enermodal. More information is
available through this link:
Innotech Engineering Co. Ltd.
manifests extensive experience in solar dryer technology. They have systems
in over 35 countries, principally variations of the tunnel dryer.
With or with out bio - backup, these dryers are being successfully used to
dry bananas in countries such as Thailand. More information, including
details of their other activities is available at
Every study analyzed in this section implied the
economical desirability of utilizing solar and solar biomass drying systems
on a large commercial scale. Benefits are almost immediate compared to
other cost intensive methods. The ability to control climate and hygiene
add significant value to the product being treated. The apple-drying
example in Nepal demonstrated that an overproduction of 10 tonnes of product
was recuperated and placed in marketable condition because of this
technology. The case of drying bananas in Thailand established that dried
bananas from a solar tunnel dryer command a much higher price than the
conventionally dried bananas and therefore could be a useful device for the
value addition of agricultural products in developing countries. Coffee
treated with this temperature and humidity controlled technology
considerably increased its value over conventionally cured products.
3. In Real Life
Lack of information through traditional mediums
in developing countries impedes the dissemination of valuable and even
essential agricultural techniques. Because of this condition, successes are
isolated and potential benefits delayed. Malnutrition and poverty persist
in areas where during harvest time there is an abundance of food but
scarcity between harvests. Unless actions are taken, no changes
4. What This Means
It is necessary to move forward and implement
solar food processing programs from family units to large-scale commercial
systems. Advances in technology have already been demonstrated.
Methodology is proven. Private enterprises, in combination with Non
Governmental Organizations need to acquire and put into practice the
technology that exists now.
As we look ahead to what we can do, let us keep
in mind some key points from this investigation:
Solar food drying is a very simple skill
easily assimilated into most cultures.
The use of solar dryer systems to conserve
vegetables, fruits, coffee, and other crops is practical, economical and
Solar dryer systems improve the quality of
the product, while reducing wasted produce and traditional fuels.
Solar dried products reduce storage and
transportation costs as well as associated problems from climatic
Solar dryers are a cost-effective solution
to food preservation in sunny climates.
Implementing the use of solar drying systems
will result in significant savings to farmers and open new markets.
Solar dryer systems improve the quality of
Solar dryer system technology now in
existence can be adapted to meet almost every agricultural need.
There is an absence of good information
about solar dryer technology in the countries where solar food
processing is most needed.
Utilization of available resources such as
the Internet can fill the information void in developing countries.
5. What we can do.
Those interested in utilizing solar dryer
technology can acquire more in-depth information by following the links
that have been included with many of the sources cited.
NGOs should form partnerships with Private
Enterprises to disseminate and implement this technology in the areas
where it is most needed.
Individuals or organizations currently
engaged in promoting or developing solar dryer technology should
identify themselves and electronically share information.
A database of this technology should be
established and publicized.
Governments should give priority to programs
that utilize solar dryer technology, as well as develop incentives to
encourage implementation and dissemination of it.
David E. Whitfield V., Director
P.O. Box 4723 La Paz, Bolivia
Tel. +591 - 2 - 421001
Emails - firstname.lastname@example.org /