Solar Energy In Agriculture its uses.pptx

KEY OBJECTIVE OF THE
ASSIGNMENT
• To understand the principles, types, and applications of solar driers and
photovoltaic systems in agriculture.
GROUP3: Ayikoru, Musema, Obulejo, Abedigamba, Lucy,
Andeku, & Zuberi
1

QUESTION 1. Solar driers:
a. Describe the conventional method of drying in agriculture. Highlight its
disadvantages.
b. Explain the two types of solar driers.
c. Detail the working principles of the natural convection solar drier and its typical
characteristics.
d. Provide a description of the cabinet drier, including its components and
operations.
e. Discuss the force convection solar drier, specifically how it uses hot air for
drying grains.
Andeku, & Zuberi
2

a. Conventional methods of drying in agriculture
The conventional method of drying in agriculture is to spread the produce on mats
or trays in the sun. This method is simple and inexpensive, but it has a number of
disadvantages:
It is slow and inefficient, especially in cloudy or humid weather.
The produce is exposed to dust, insects, and other contaminants.
The produce can be over-dried or under-dried, which can affect its quality and
shelf life.
Andeku, & Zuberi
3

Illustration of conventional methods of
drying
Andeku, & Zuberi
4

Disadvantages of conventional drying
methods:
Slow and inefficient
Produce is exposed to contaminants
Produce can be over-dried or under-dried
Andeku, & Zuberi
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b. Types of solar driers
There are two main types of solar driers: natural convection solar driers and forced
convection solar driers.
Natural convection solar driers use the natural movement of air to circulate the heated
air through the dryer chamber. These driers are typically less expensive and easier to build
than forced convection solar driers, but they are also less efficient.
Forced convection solar driers use fans or other mechanical devices to circulate the
heated air through the dryer chamber. These driers are more efficient than natural
convection solar driers, but they are also more expensive and complex to build.
Andeku, & Zuberi
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c. Working principles of a Natural
Convection Solar Drier
A natural convection solar drier is a simple type of solar drier that uses the natural
movement of air to circulate the heated air through the dryer chamber. These driers
are typically made of a wooden or metal box with a transparent top. The produce is
placed on racks inside the box, and the heated air from the sun circulates around the
produce, drying it out.
Typical characteristics of natural convection solar driers:
Simple and inexpensive to build
Less efficient than forced convection solar driers
Suitable for drying a variety of crops, including fruits, vegetables, grains, and
legumes
Can be used in both sunny and cloudy weather
Andeku, & Zuberi
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d. Description of the Cabinet Drier
A cabinet drier is a type of forced convection solar drier that is made of a wooden or
metal box with a transparent top and bottom. The produce is placed on racks inside
the box, and a fan circulates the heated air from the sun around the produce, drying
it out.
Components of a cabinet drier:
Wooden or metal box
Transparent top and bottom
Racks for holding the produce
Fan
Andeku, & Zuberi
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Illustration of cabinet Drier
Andeku, & Zuberi
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Operation of a cabinet drier:
The produce is placed on the racks inside the boxes.
The lid of the box is closed.
The fan is turned on.
Finally the heated air from the sun circulates around the produce, drying it out.
Andeku, & Zuberi
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e. The Forced Convection Solar Drier
A forced convection solar drier is a type of solar drier that uses fans or other
mechanical devices to circulate the heated air through the dryer chamber. These
driers are more efficient than natural convection solar driers, but they are also more
expensive and complex to build.
Forced convection solar driers typically consist of three main components:
A solar collector: This is a flat plate or evacuated tube collector that absorbs solar
energy and heats the air.
A fan: This circulates the hot air over the grains to be dried.
A drying chamber: This is where the grains are placed to be dried.
Andeku, & Zuberi
11

A typical Forced Convection Solar Drier
Andeku, & Zuberi
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How forced convection solar driers use hot
air for drying grains
Forced convection solar driers use hot air to dry grains by passing the heated air
over the grains as;
The solar collector absorbs solar energy and heats the air.
The fan then circulates the hot air over the grains to be dried, ensuring that they
are dried evenly.
The hot air absorbs moisture from the grains and carries it away. The grains are
dried when their moisture content is reduced to a safe level.
Andeku, & Zuberi
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Advantages of forced convection solar
driers:
More efficient than natural convection solar driers
Can dry grains more quickly and evenly
Less susceptible to the effects of weather
Disadvantages of forced convection solar driers:
More expensive and complex to build than natural convection solar driers
Require a source of electricity to power the fan
Andeku, & Zuberi
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NB;
• Overall, solar driers are a promising technology for drying agricultural produce.
They offer a number of advantages over conventional drying methods, including
improved efficiency, reduced product contamination, and better quality control.
Solar driers can be used to dry a variety of crops, including fruits, vegetables,
grains, and legumes. They are also a good option for farmers in developing
countries, as they can be made from local materials and do not require a lot of
energy to operate.
Andeku, & Zuberi
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QUESTION.2)
Solar photovoltaic systems:
a. Define photovoltaics (PV) and photovoltaic cells.
b. Describe the photovoltaic effects and how it converts sun light into electricity.
c. Explain the main components of solar photovoltaic system, including solar
panels, control units and batteries.
d. List and briefly describe five applications of solar photovoltaic systems in
agriculture.
e. Discuss the types of materials used in the PV cells, focusing on crystalline and
thin-film materials. Highlight advantages and limitations of each.
f. Provide an overview of the heat transfer process in solar PV panels and how it
affects their efficiency.
Andeku, & Zuberi
16

INTRO; PHOTOVOLTAIC SYSTEM
• A photovoltaic system, also photovoltaic power system, solar PV system, PV
system or casually solar array is a power system designed to supply usuable solar
power by means of photovoltaics.
• Photovoltaics(PV) is a method of converting solar energy into direct current
electricity using semiconducting materials that exhibit the photovoltaic effects.
• Photovoltaic system employs solar panels composed of a number of solar cells to
supply usuable solar power.
• Power generation from solar PV has long been seen as a clean sustainable energy
technology which draws upon the planet’s most plentiful widely distributed
renewable energy source-the SUN
Andeku, & Zuberi
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a. Photovoltaic (PV) and photovoltaic cells
• The word „photovoltaic“ consists of two words: photo, a Greek word for light,
and voltaic, which defines the measurement value by which the activity of the
electric field is expressed, i.e. the difference of potentials.
• Photovoltaic (PV) is the conversion of light into electricity directly using
semiconductors or is the direct conversion of light energy into electrical energy
using semiconductor materials. (Green, 2010)
• Photovoltaic systems use cells to convert sunlight into electricity. Converting
solar energy into electricity in a photovoltaic installation is the most known way of
using solar energy
• Can be used to generate electricity in both urban and rural areas, and they can be
used to power a variety of devices, from homes and businesses.
Andeku, & Zuberi
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Photovoltaic systems cont’
• Photovoltaic cells, also known as solar cells, are the basic building blocks of PV
systems or,
• Photovoltaic cell: Is a semiconductor device that converts light energy into
electrical energy. (Green, 2010)
• Example, Photovoltaic cells are made from semiconductor materials, such as
silicon, which absorb sunlight and convert it into electricity. Photovoltaic cells are
used in a variety of applications, including solar panels, solar chargers, and solar
power plants.
• Photovoltaic cells are becoming increasingly popular as a source of renewable
energy because they are clean, quiet, and reliable. Photovoltaic cells can be used to
generate electricity in both urban and rural areas, and they can be used to power a
variety of devices, from homes and businesses to electric vehicles.
Andeku, & Zuberi
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b. The photovoltaic effect and how it converts
sunlight into electricity
• The “photovoltaic effect” is the basic physical process through which a solar cell
converts sunlight into electricity.
• Photovoltaic (PV) cells are made up of at least 2 semi-conductor layers. One layer
containing a positive charge, the other a negative charge.
• Sunlight consists of little particles of solar energy called photons. As a PV cell is
exposed to this sunlight, many of the photons are reflected, pass right through, or
absorbed by the solar cell.
• When enough photons are absorbed by the negative layers of the semi-conductor
material. Due to the manufacturing process of the positive layer, these freed
electrons naturally migrate to the positive layers creating a voltage differential,
similar to a household battery.
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Photovoltaic effect cont’
• When the 2 layers are connected to an external load, the electrons flow
through the circuit creating electricity.
• Each individual solar energy cell produces only 1-2 watts.
• To increase power output, cells are combined in a weather tight
package called a solar module.
• These modules (from one to several thousands) are then wired up in
serial and / or parallel with one another, into what’s called a solar array
to create the desired voltage and amperage output required by the
given project.
Andeku, & Zuberi
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c. Main components of a solar photovoltaic
system
The main components of a solar photovoltaic system are:
• Solar panels: Solar panels are made up of a number of PV cells connected
together. They are used to convert sunlight into electricity.
• Control units: Control units regulate the voltage and current produced by the
solar panels. They also protect the system from damage caused by overvoltage or
overcurrent.
• Batteries: Batteries store the electricity generated by the solar panels so that it can
be used at night or when there is no sunlight.
• Others includes; cabling, solar trackers, solar inverter, charge controller etc.
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Illustrations of Photovoltaic (PV) system
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d. Five applications of solar photovoltaic
systems in agriculture
• Powering irrigation systems: Solar PV systems can be used to power irrigation
systems, which can help farmers to improve their crop yields.
• Powering water pumps: Solar PV systems can be used to power water
pumps, which can help farmers to access water for irrigation and other purposes.
• Operating crop monitoring systems: Solar PV systems can be used to power
crop monitoring systems, which can help farmers to track the growth and health of
their crops.
• Drying agricultural produce: Solar PV systems can be used to power solar
driers, which can help farmers to reduce crop losses and extend the shelf life of
their produce.
• Providing electricity to rural areas: Solar PV systems can be used to provide
electricity to rural areas that do not have access to the grid.
Andeku, & Zuberi
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e. Types of materials used in PV cells
The PV cells are classified into two main technologies ie;
The thin-film technology
The silicon film technology and this is further divided into two ie;
Monocrystalline.
Polycrystalline.
Other materials include, cadmium telluride, gallium arsenide thin film, epitaxial
silicon.
Andeku, & Zuberi
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Types of materials used in PV cells
cont’……
The thin-film technology
• In this, Silicon is deposited
continuous on a base material such as
glass, metal or polymers.
• The efficiencies ranges from 5% to
13%
• They consists of layers about 10 µm
• thick compared with 200-300 µm
layers for crystalline silicon cells.
The silicon film technology
Currently makes up 86% of PV markets
and are very stable with modules
efficiencies 10-16%
• Monocrystalline PV cell-the
conversion efficiency ranges from
13% to 17%,are widely commercially
been used
• Polycrystalline PV cell-the
production of these cells is
economically more efficient compared
to Monocrystalline. Efficiency ranges
from 10% to 14%
Andeku, & Zuberi
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Illustration of materials used in PV cells
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Advantages and limitations of crystalline
and thin-film PV cells
Type of PV cell Advantages Limitations
Crystalline High efficiency/ very stable
with module efficiency of
10-16%
Expensive
Thin-film Less expensive as has low
cost of substrates and
fabrication process
Lower efficiency/ not very
stable
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Other types of materials used in PV cells
• Cadmium telluride; is the only thin film material so far to rival crystalline silicon
in cost/watt. However cadmium is highly toxic and tellurium supplies are limited.
• Gallium arsenide thin film; the semiconductor material gallium arsenide( GaAs)
is also used for single thin film solar cells.
• Epitaxial silicon; Solar cells made with this technique can have efficiencies
approaching those of water-cut cells, but at appreciably lower costs.
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f. The following are the heat transfer processes
and their effects on solar PV panels.
• Solar absorption
Solar PV panels are designed to absorb sunlight and convert it into electricity. When
sunlight hits the PV cells, they absorb photons and this energy is converted into
electrical energy through the photovoltaic effect.
• Heat generation
Not all of the absorbed sunlight is converted into electricity. Some of the energy is
converted into heat due to resistive losses in the PV cells and other components of
the solar panel. This heat generation is an inherent byproduct of the conversion
process.
• Temperature rise
As the solar panel absorbs sunlight and generates heat, its temperature begins to rise.
This rise in temperature can lead to a reduction in the panels energy conversion
efficiency. Solar panels are more efficient at lower temperatures, and excessive heat
can have detrimental effects on their performance.
Andeku, & Zuberi
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f. cont’………
• Heat dislocation
To maintain optimal efficiency, solar panels need to dissipate the heat generated.
This is typically achieved through conduction, convection, and radiation. Solar
panels are often designed with heat sinks or thermal management systems to
facilitate this heat dissipation.
• Temperature coefficient
The temperature coefficient is a measure of how solar panels efficiency decreases as
its temperature rises. Solar panels are rated at standard test conditions(STC),
typically 250C, and their efficiency can decrease as the temperature exceeds this
value. The temperature coefficient varies from one panel to another and is an
important factor to consider when evaluating the performance of solar panels in
different environmental conditions.
Andeku, & Zuberi
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f. cont’………
• Impact on energy output
High temperatures can reduce the energy output of solar panels. If a
solar panel becomes too hot, its electrical efficiency can decrease,
causing a drop in the amount of electricity it generates. This is one
reason why solar panels are often mounted with an air gap beneath
them, to allow for airflow and cooling
• Cooling solution
Various cooling solutions can be implemented to mitigate the negative
effects of heat on solar panels. These solutions include active cooling
systems like fans or water cooling, as well as designing panels with
materials that have high thermal conductivity.
Andeku, & Zuberi
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f. cont’………
• In summary, heat transfer in solar PV panels can have a significant impact on
their energy conversion efficiency. Excessive heat can reduce a panels output,
making it essential to consider temperature management and cooling strategies to
maximize the energy production and longevity of solar panels.
• To improve the efficiency of solar PV panels, it is important to keep them cool.
This can be done by mounting them in a well-ventilated area or by using cooling
systems.
Andeku, & Zuberi
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Heat transfer process in solar PV panels
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Qtn3. Challenges and future trends associated with the
adoption of solar driers and photovoltaic systems in
Agriculture.
• A solar drier: is a device that uses solar energy to dry agricultural produce. Solar driers
can be used to dry a variety of crops, including fruits, vegetables, grains, and legumes.
• Solar driers work by absorbing solar energy and using it to heat air. The heated air is then
circulated through the dryer chamber, where it dries the produce. Solar driers can be
either passive or active.
• Passive solar driers rely on natural convection to circulate the heated air. Active solar
driers use fans or other mechanical devices to circulate the heated air.
Andeku, & Zuberi
35

Qtn3. Challenges and future trends associated with the
adoption of solar driers and photovoltaic systems in
Agriculture.
• Photovoltaic (PV) systems: are devices that convert sunlight into electricity. PV systems
can be used to power a variety of agricultural equipment, including irrigation systems,
water pumps, and crop monitoring systems.
• PV systems can also be used to power solar driers. This can make solar drying more
convenient and efficient, as it eliminates the need for a separate source of heat.
• Solar driers and PV systems can be used together to improve agricultural productivity
and sustainability. For example, a farmer could use a PV system to power a solar drier,
which could be used to dry fruits and vegetables after harvest. This would help to reduce
crop losses and extend the shelf life of the produce.
Andeku, & Zuberi
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QTN3. CHALLENGES.
Solar driers and photovoltaic (PV) systems are two promising technologies that can be
used to improve agricultural productivity and sustainability. However, there are a number of
challenges associated with their adoption, including:
High initial cost: Solar driers and PV systems can be expensive to purchase and install.
This can be a barrier to adoption for smallholder farmers, who often have limited access
to capital.
Lack of awareness and technical expertise: Many farmers are not aware of the benefits
of solar driers and PV systems, or they lack the technical expertise to operate and
maintain them. This can lead to underutilization and poor performance.
Andeku, & Zuberi
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QTN3. CHALLENGES CONT’.
• Limited availability of spare parts and maintenance services: In some areas, it can be
difficult to find spare parts and maintenance services for solar driers and PV systems. This
can make it difficult to keep the systems running in good condition.
• Climate factors: The performance of solar driers and PV systems can be affected by
climate factors such as cloud cover, rainfall, and humidity. This can make it difficult to
rely on these technologies consistently.
• Integration with existing farming practices: Solar driers and PV systems need to be
integrated with existing farming practices in order to be effective. This can be a challenge,
especially for smallholder farmers who may have limited resources and expertise.
Andeku, & Zuberi
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QTN3. SOLUTIONS
Despite these challenges, there are a number of things that can be done to
promote the adoption of solar driers and PV systems in agriculture. These
include:
Government subsidies and financial incentives: Governments can provide
subsidies and other financial incentives to help farmers purchase and install solar
driers and PV systems.
Awareness raising and training programs: Farmers need to be educated about
the benefits of solar driers and PV systems, and they need to be trained on how to
operate and maintain these systems.
Andeku, & Zuberi
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QTN3. SOLUTIONS CONT’
Local production and distribution of solar driers and PV systems: Local
production and distribution of solar driers and PV systems can help to reduce costs
and make these technologies more accessible to farmers.
Development of new and improved solar drying and PV
technologies: Continued research and development is needed to develop new and
improved solar drying and PV technologies that are more affordable, efficient, and
reliable.
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References
• Expert consultation on planning the development of sun drying techniques in
Africa
http://www.fao.org/inpho/vlibrary/x0018e/X0018E00.htm
• Grain storage techniques
http://www.fao.org/docrep/t1838e/T1838E00.htm
• Jayakrishnan, K. K., & Kumar, S. (2010). Forced convection solar drying of
agricultural products: A review. Renewable and Sustainable Energy Reviews,
14(7), 1547-1561.
• Green, M. A. (2010). Solar cells: Operating principles, technology, and system
design. Prentice Hall.
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