This presentation describes the solar distillation, solar pond, solar dryer

1. APPLICATION OF SOLAR ENERGY:
SOLAR DISTILLATION, SOLAR POND AND SOLAR DRYER
Dr. Ajay Singh Lodhi
Assistant Professor
College of Agriculture, Balaghat
Jawahar Lal Krishi Vishwa Vidyalaya, Jabalpur (M.P.)

2. SOLAR DISTILLATION
 Fresh water is a necessity for the sustenance of life
and also the key to Man’s prosperity. It is generally
observed that arid, semi arid and coastal areas
which are thinly populated and scattered, one or
two family members are always busy in bringing
fresh water from a long distance. In these areas
solar energy is plentiful and can be used for
converting saline water into distilled water. The
pure can be obtained by distillation in the simplest
solar still, generally known as the “basin type solar
still”.

3.  Solar water still is shown schematically in fig, it consists of a
blackened basin containing saline water at a shallow depth,
over which is a transparent air tight cover that encloses
completely the space above the basin. It has a roof-like shape.
The cover which is usually glass may be of plastic, is sloped
towards a collection trough. Solar radiation passes through
the cover and is absorbed and converted into heat in the black
surface. Improve water in the basin or tray is heated and the
vapour produced is condensed to purified water on the cooler
interior of the roof. The transparent roof material transmits
nearly all radiation falling on it and absorbs very little; hence
it remain cool enough to condense the water vapour. The
condensed water flows down the sloping roof and is collected
in through at the bottom. Saline water can be replaced in the
operation by either continuous operations or by batches.

4. SOLAR POND
 One way to tap solar energy is through the use of solar ponds.
Solar ponds are large-scale energy collectors with integral
heat storage for supplying thermal energy. It can be use for
various applications, such as process heating, water
desalination, refrigeration, drying and power generation.
 The solar pond works on a very simple principle. It is well-
known that water or air is heated they become lighter and
rise upward e.g. a hot air balloon. Similarly, in an ordinary
pond, the sun’s rays heat the water and the heated water
from within the pond rises and reaches the top but loses the
heat into the atmosphere through convection, or evaporates,
taking heat with it. The net result is that the pond water
remains at the atmospheric temperature. The solar pond
restricts this tendency by dissolving salt in the bottom layer
of the pond making it too heavy to rise.

5.  A solar pond can store solar heat much more efficiently
than a body of water of the same size because the
salinity gradient prevents convection currents. Solar
radiation entering the pond penetrates through to the
lower layer, which contains concentrated salt solution.
The temperature in this layer rises since the heat it
absorbs from the sunlight is unable to move upwards to
the surface by convection. Solar heat is thus stored in
the lower layer of the pond.
 A solar pond has three zones.
 The top zone is the surface zone, or UCZ (Upper
Convective Zone), which is at atmospheric temperature
and has little salt content.
 An upper convective zone of clear fresh water that acts
as solar collector/receiver and which is relatively the
most shallow in depth and is generally close to ambient
temperature.

6.  The bottom zone is very hot, 70°– 85° C, and is very
salty. It is this zone that collects and stores solar energy
in the form of heat, and is, therefore, known as the
storage zone or LCZ (Lower Convective Zone).
 A lower convective zone with the densest salt
concentration, serving as the heat storage zone. Almost
as thick as the middle non-convective zone, salt
concentration and temperatures are nearly constant in
this zone.
 Separating these two zones i.e. UCZ and LCZ is the
important gradient zone or NCZ (Non-Convective Zone).
Here the salt content increases as depth increases,
thereby creating a salinity or density gradient.
 A gradient which serves as the non-convective zone
which is much thicker and occupies more than half the
depth of the pond. Salt concentration and temperature
increase with depth.

7.  Though solar ponds can be constructed anywhere, it is
economical to construct them at places where there is low
cost salt and bittern, good supply of sea water or water for
filling and flushing, high solar radiation, and availability of
land at low cost. Coastal areas in Tamil Nadu, Gujarat,
Andhra Pradesh, and Orissa are ideally suited for such solar
ponds.

8. APPLICATIONS
 The heat from solar ponds can be used in a variety of
different ways.
 First, since the heat storing abilities of solar ponds are
so great they are ideal for use in heating and cooling
buildings as they can maintain a fairly stable
temperature.
 These ponds can also be used to generate electricity
either by driving a thermo-electric device or some
organic Rankine engine cycle - simply a turbine powered
by evaporating a fluid (in this case a fluid with a lower
boiling point).
 Finally, solar ponds can be used for desalination
purposes as the low cost of this thermal energy can be
used to remove the salt from water for drinking or
irrigation purposes.

9. SOLAR DRYING
Processes during sun drying
 Exposing agricultural products to wind and sun is the preservation
method practiced over centuries throughout the world. Cereals,
legumes and green forages are dried in the field immediately after
harvesting. Fruits, vegetables, spices and marine products as well as
threshed grains are spread out in thin layers on the ground or trays,
respectively. Other methods include hanging the crop underneath a
shelter, on trees or on racks in the field.
 During sun drying heat is transferred by convection from the
surrounding air and by absorption of direct and diffuse radiation on
the surface of the crop. The converted heat is partly conducted to the
interior increasing the temperature of the crop and partly used for
effecting migration of water and vapour from the interior to the
surface. The remaining amount of energy is used for evaporation of the
water at the surface via convection and radiation. The evaporated
water has to be removed from the surrounding of the crop by natural
convection supported by wind forces.
 Under ambient conditions, these processes continue until the vapour
pressure of the moisture held in the product equals that held in the
atmosphere. Thus, the rate of moisture desorption from the product to
the environment and absorption from the environment are in
equilibrium, and the crop moisture content at this condition is known
as the equilibrium moisture content. Under ambient conditions, the
drying process is slow, and in environments of high relative humidity,
the equilibrium moisture content is insufficiently low for safe storage.

10. Processes during solar drying
 The objective of a dryer is to supply the product with
more heat than is available under ambient conditions,
thereby increasing sufficiently the vapour pressure of the
moisture held within the crop and decreasing
significantly the relative humidity of the drying air and
thereby increasing its moisture carrying capacity and
ensuring sufficiently low equilibrium moisture content.
 There are two types of solar driers.
1. Natural convection solar drier
2. 2. Forced convection solar dryer

11.  Natural convection solar drier:
Natural air-drying is an in bin drying system with the
following typical characteristics:
 Drying process is slow, generally requiring 4 to 8 weeks.
 Initial moisture content is normally limited to 22 to 24%.
 Drying results from forcing unheated air through grain at
airflow rates of 1 to 2 cfm/bu (cubic feet of air per minute per
bushel).
 Drying and storage occur in the same bin, minimizing grain
handling.
 Bin is equipped with a full-perforated floor, one or more high
capacity fans, a grain distributor and stairs
 Cleaning equipment is used to remove broken kernels and
fines.

12. CABINET DRIER
 It can be of fixed type and
also of portable type.
Generally, it has an area of
about 3 x 5 m2 glass sheet
fixed at the top at an angle of
about 0 to 30o. Holes are
provided at the bottom and
at the topsides for airflow by
natural convection. Wire
meshed black tray is
provided to the material to
be dried.

13. Forced convection solar dryer (Hot air system):
 In these, the collectors are provided with duct.
Generally, a duct of 2.5 cm depth is provided. It is made
out of two plates welded together lengthwise. Cold air is
blown through a blower into the collectors, which gets
heated during the passage through it. The hot air thus
available is then used for drying the products kept on
the shelves of driers. This hot air takes away the
moisture of the products and is let out through a
properly located outlet.
1. Absorber with ducting
2. Blower with motor and
3. Drying bin

14. Description (Forced convection solar dryer)
 This drier has three main components viz., flat plate collector,
blower and drying bin.
 The area of the collector is 8m2. It is divided into 4 bays each
having 2m x 1 m absorber area.
 The absorber is made of corrugated G.I. sheet and is painted
with dull black colour.
 Another plain G.I. sheet placed 5 cm below the absorber plate
creates air space for heating. This sheet is insulated at the
bottom with glass wool and is supported at the bottom with
another plain G.I. sheet.
 The absorber is covered at the top with two layers of 3 mm
thick plain glass.
 The unit is supported on all sides with wooden scantling and
is placed at the horizontal facing south.
 Baffle plates are provided in the air space. The air space is
open at the bottom to suck atmospheric air and at the top it is
connected to a duct leading to suction side of the blower. The
blower is of 80 m3 / min, capacity run by 3HP electric motor.
 The delivery side of the blower is connected to the plenum
chamber of a circular grain holding bin.

15. Advantages of solar drying can be summarized as
follows:
 The higher temperature, movement of the air and lower
humidity, increases the rate of drying.
 Food is enclosed in the dryer and therefore protected
from dust, insects, birds and animals.
 The higher temperature deters insects and the faster
drying rate reduces the risk of spoilage by micro
organisms.
 The higher drying rate also gives a higher throughput
of food and hence a smaller drying area (roughly 1/3).
 The dryers are water proof and the food does not
therefore need to be moved when it rains.
 Dryers can be constructed from locally available
materials and are relatively low cost.
 More complete drying allows longer storage

16. Thank You