Economic development through solar drying technologies
Wiji Senadeera, School of Advanced Manufacturing and Mechanical
Engineering, University of South Australia, Australia and Dumindra
Senanayake, Maharana Pratap University of Agriculture and Technology,
PROCESSING FOOD INDUSTRY: Processing of vegetables into durable
products during surplus production and seasonal super-abundance can go a
long way in reducing the post harvest losses. Sri-Lanka is a producer
and consumer of vegetables.
The processing food industry and export market of vegetables can be
an instrument of diversification for generating income and employment
for small and marginal farmers.
Processing of various vegetables is picking up in other countries in
the SAARC region. The processed form of vegetables can be exported
easily and in turn help to earn much needed foreign exchange.
Vegetables are an important constituent of diet and provide
significant nutrients depending upon their nature especially vitamins,
mineral and fibres. Some vegetables like carrots, cauli flower are
highly seasonal and are usually available in plenty in some seasons of
In the peak season, the selling price becomes too low leading to
heavy losses to the grower and also there is an unnecessary stock in the
market resulting in the spoilage of large quantities.
Because of its seasonal nature of availability, a need was felt to
preserve the vegetable over a period of time to use it during off
seasons. Preservation of vegetables can prevent the huge wastage and
make them available in the off-season at remunerative prices.
In recent food technology literature, processing and preservation of
numerous vegetable products have been reported. Because of its seasonal
nature of availability, efforts were made since from the past to extend
the shelf life of vegetables by dehydration, in order to use it during
Various drying methods such as hot air, freeze microwave, infrared
and fluidized bed drying have been practiced for dehydration of
vegetables. These technologies need sophisticated equipment and skill
training, the adoption of which appears difficult at field/rural level.
Though mechanical dryers, powered by electricity or fuel, help in
producing quality products in mass scale, they are seldom adopted by
small- scale entrepreneurs and farmers of most developing countries, due
to heavy installation costs involved and large operating cost because of
it being energy intensive process.
To save the energy and thereby reducing the operation cost, use of a
solar collector in conjunction with- mechanical dryer (convective dryer)
could give synergetic effect i.e. producing quality dried product at low
cost. Solar energy is fast becoming an important alternative source of
energy as it can be tapped at selectively low cost.
The use and application of solar energy therefore, cannot be under
emphasized. Development of a solar assisted convective dryer will help
in drying a variety of fruits and vegetables under controlled conditions
at relatively lower cost and is expected to be well adopted at farmers
level, as well as fruits and vegetable drying industries.
Drying and dehydration technology:
Drying and dehydration technology would be one of the best practices
towards increasing the consumption of the population under the current
insufficiency in vegetable consumption. Besides, the precooked and
dehydrated convenience items, which are ready to eat, will serve people,
in highly urbanized cities, in many ways. The lower-mass, compact size
and stability of dried foods make them ideal in any situation.
The principal of using drying as a preservative method is that
enzymes responsible for the breakdown of foods or the growth of
microorganisms are inhibited when the amount of available water is very
low. During the past few decades, considerable efforts have been made to
understand some of the chemical and biochemical changes that occur
during dehydration and to develop methods for preventing undesirable
Longer shelf life, product diversity and volume reduction are the
reason for the popularity of dried fruits and vegetables, and this could
be expanded further with improvements in product quality and process
Solar drying technologies developed in other countries:
Solar drying relies, as does sun drying, on the sun as its source of
energy. Solar drying differs from sun drying in that a structure, often
of very simple construction, is used to enhance the effect of the
Compared with sun drying, solar dryers can generate higher air
temperatures and consequential lower relative humidities, which are both
conductive to, improved drying rates and lower final moisture contents
of the dried crop. As a result the risk of spoilage is reduced, both
during the actual process and in subsequent storage.
Development of solar drying technologies in Sri-Lanka
It has been reported that there has been very little actual
penetration of solar drying technology so far in Sri-Lanka. In the
initial phase of their dissemination, identification of suitable areas
for using solar dryers would be extremely helpful in providing the
required momentum for their market penetration.
One of the possible areas of immediate intervention in this direction
appears to be the solar drying of cash crops such as tobacco, tea,
coffee, small cardamom, chilli powder, coriander, ginger, turmeric
powder, pepper, onion flakes and garlic flakes etc.
For such crops, even with the capital intensive nature of solar
dryers, the unit cost of solar drying is expected to be a small fraction
of the selling price of the final dried product.
An initiative by Sri-Lankan scientists has to be started estimate the
potential of solar crop drying and the useful energy required for drying
of different cash crops, the fraction of the total production of
different cash crops which can be dried by solar dryers, and solar
collector area required for this purpose has to be estimated.
The amounts of different fuels that would be saved by solar drying
and the Co2 emissions mitigation potential of solar drying of crops in
Sri-Lanka is also an important study.