Solar Thermal and Photovoltaic Field Engineer Training Course
Solar Thermal and Photovoltaic Field Engineer Training Course
Solar Thermal and Photovoltaic Field Engineer Training Course
Training course
Prepared by
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: CONTENTS:
Section A: Renewable Energy
Chapter 1: Introduction to Renewable Energy
1.1 What is Renewable Energy?
1.2 Indian Renewable Energy Program
1.3 Jawaharlal Nehru National Solar Mission (JNNSM)
6-13
6
9
11
14-34
14
14
15
16
18
22
23
24
29
30
32
Drawings:
Pyranometer
Pyranometer with shaded ring
Sunshine recorder
35-38
36
37
38
40-69
40
42
43
45
47
48
49
52
59
63
65
68
70-80
70
71
73
75
76
78
81-91
81
82
83
84
85
90
91
92-95
96-101
Drawings:
Solar cell crosssection
Configuration block diagram of PV systems
Solar lantern
102-107
103
104
107
109-116
109
109
111
112
114
116
117-128
117
117
118
2
7.4 Working principle of a flat plate collector & evacuated tube collector- thermosiphon
action
121
7.5 Major components of a solar water heater
123
7.6 Hard water problems
127
7.7 Installation guidelines
127
Chapter 8: Solar Cooker
129-137
129
129
136
138-139
140-144
Drawings:
Solar water heater thermosyphon
Solar water heater collector
Solar water heater installation layout
Solar cooker box type
Solar cooker parabolic type
145-150
146
147
148
149
150
151-192
193-206
208
Solar
The source of all energy given out by the sun lies in its core. In this hydrogen atoms are
fused together to make helium. This results in release of a large amount of energy at the rate
of 3.86x1026 Joules per second. Solar energy has been in use since long for heating and
drying etc. Presently, it is being used for lighting homes and buildings, producing electricity
and heating water etc. More the amount of solar energy received by us on earth, more useful
it will be.
Wind
Earth absorbs the suns heat at different rates. Thus one point gets more heated than the
other. It moves the air giving rise to wind energy. This form of energy has been in use for
thousands of years in one way or the other. In the olden times, people used the wind for
sailing in the sea. Wind machines were earlier used to pump water. We now use energy in
the wind to produce electricity.
Biomass
It is a natural matter that makes up plants and trees. Sunlight is absorbed during a process
known as photosynthesis. Some of the sunlight remains inside the plants and trees. This
form of energy is called as biomass. It can be used to produce heat, electricity and even fuel
to run automobiles.
Small Hydro
It is a clean method of producing electricity from a trapped wall of water. Just like the wind,
the earth naturally produces flowing waters. These can be in the form of rivers, streams and
water falls etc. Water energy or hydro power was used in the past to run flour mills etc. As
water flows, modern turbines change energy into electricity.
Geothermal
The geothermal energy is heat from deep within the earth. Some materials just decay in the
earths crust and give out energy. Such energy can be taken out and used to produce both
heat and electricity.
Tidal
Tidal energy is created by the relative motion of earth, moon and sun. The gravitational
contact is also present amongst them. Mostly, every coastal region has two high and two
low tides in nearly 24-hour period. However, this type of energy use is still quite small
worldwide.
Wave
Water covers around 70% of the earths surface. The sea waves hold enough energy in them.
This gives rise to wave energy which can be trapped. It can then be used for generating
some useful power. However, this type of energy use is also still very low.
Quite clearly, solar energy is at work here and there rather everywhere. We must try
to use it for meeting some of our daily energy needs. If, not now, then when can we
think about its use?
These new sources of energy need some technology support. Table 1.1 gives all possible
technology choices etc.
Table 1.1: Technology Choices
Primary Energy
Source
Representation
Solar radiation
Sun
Biomass
1.2
Important
End-use Energy
Electricity
Electricity
Heat, Electricity
Wind power
Atmospheric
motion
Wave motion
Ocean currents
Earth
Moon
Technology choices
For conversion
Solar Photovoltaic (PV) Cell
PV power plant
Solar collector
Solar thermal power plant
Hydropower
Geothermal
Tides
Electricity
Electricity
Heat, electricity,
fuel
Electricity
Heat, Electricity
Electricity
India has enough sunshine, fast blowing wind in some areas, lot of water sources and plenty
of biomass matter. The Ministry of New and Renewable Energy (MNRE) has been running a
country wide programme since long. Under this programme, a large number of products
and systems have been installed so far (Table 1.2 below). These have benefited the rural
people the most. Several organizations have helped MNRE to achieve such a large scale
gain. These mainly include the following:
State Nodal Agencies for renewable energy (there is one such agency in every state which
implements the RE programme within that state)
Indian Renewable Energy Development Agency (IREDA)/Nationalised Banks etc. (provide
soft loans etc. to different types of end-users etc.)
manufacturers of the renewable energy devices (those who produce the products and
systems)
Non governmental Organisations/Voluntary agencies/Village Energy Committees (those
which carry out rural surveys and maintain the systems in some cases as well)
Academic and Technical Institutes/Research Laboratories (those which help in developing
technology etc.)
The Jawaharlal Nehru National Solar Mission (JNNSM) has just taken off. A total
solar power capacity of 20,000 MW is expected to come up under this mission by
2022. One of the most important tasks is to prepare a large number of well trained
Solar technicians. The Industrial Training Institutes (ITIs) numbering around 6000
can take part in this exercise. These technicians can then install, operate and
maintain the solar energy systems in any part of our country.
Target for
2010-11
Achievement
duringMarch
2011
Total
achievement
during 201011
Cumulative
achievement
up to 31.03.2011
2350.35
307.22
143.50
321.50
7.50
14157.10
3042.63
997.10
1667.53
19.00
53.46
26.59
3156.66
37.66
19974.48
3.50
66.92
301.61
14.47
117.34
1.12
5.80
6.98(1397)
*** We had included some figures pertaining to off-grid solar products like SL, HLS, SLS
and solar thermal collectors etc. in the earlier version. What about their inclusion here as the
training programme/material deals with these products essentially?
Source: www.mnre.gov.in
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Additional goals
promote research and development, mass awareness generation and develop trained
and well skilled human resource to meet the upcoming needs of solar industry as a
whole
expand the scope and coverage of earlier incentives for industries to set up PV
production facilities in India
Table 1.3 shows the phase-wise total and annual targets set by the JNNSM
S.
No
Activity
Achievements
in 2009
Phase-I
Phase-II
Phase-III
2010-13
2013-17
2017-2022
1000
200
7
3000
800
8
16000
1000
5
Total
(under MNRE
programme)
1
2
3
4
6
2.4
3.3
1.3
20000
2000
20
20
11
12
Channel Partners
Renewable Energy Service Providing Companies
Financial Institutions as Aggregators
Financial Integrators
System Integrators
Programme Administrators
Financing
MNRE subsidy
Soft re-finance facility to Banks through IREDA
Ministry has also supported the establishment of a national centre for PV research and
education (NCPRE) at IIT Mumbai and a Solar lighting laboratory at The Energy and
Resources (TERI), Delhi.
Summary remarks:
RE technologies are still more costly than the electricity produced from the fossil fuels (like
coal, oil and gas).RE sector in India is still in the early stages of market development. RE
programme development still needs a helping hand from both the government and public
at large.
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The Sun
2.2
The sun emits radiation in the entire electromagnetic spectrum from gamma rays to radio
waves. Thus the radiant energy is a combination of energy released by layers having
different temperatures.This type of radiation is simply known as the solar radiation. The
solar radiation spectrum is made of the following few components:
about 6.4% of the total energy is contained in Ultra-violet (UV) region (< 0.38 m)
another 48% is contained in the visible region (0.38 m < < 0.78 m)
remaining 45.6% is contained in the Infrared region (>0.78 m)
The amount of solar radiation present is not the same everywhere as you will know below.
It is quite important to understand the following few terms in respect to this radiation.
Beam radiation
It is that part of solar radiation that reaches the earths surface without any change in
direction. That is why it is also known as the direct radiation.
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Diffuse radiation
It is that part of radiation whose direction gets changed before touching the earths surface.
This happens as it gets scattered i.e. here and there.
Total solar radiation
The sum of the beam and diffuse components of solar radiation is called total solar
radiation. Total solar radiation on a horizontal surface is commonly known as global
radiation.
Irradiance
The solar irradiance G is the rate at which the radiant energy is incident on a unit area of a
surface. It is marked in terms of W/m2.
Insolation
The incident solar radiation is also known as insolation. Generally, the insolation for a
specific time period (commonly one hour) is represented by symbol I. While as, symbol H is
used to give insolation for the day. The H and I values are indicated by W-h/m2/day and
W-h/m2/h respectively. In case, both H and I values are measured on an hourly basis; I
numerically becomes equal to G.
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the earth moves around the sun in an egg-shaped orbit. The surface of earth gets a little
more solar energy when the sun is closer to the earth.
the earth is nearer the sun when it is summer in the southern hemisphere and winter in
the northern hemisphere.
the earths axis of rotation has a tilt of 23.5. It also plays a part in knowing the amount
of sunlight that hits the earth at a given location.
sunlight changes from one hour to the other due to earths rotation.
the sun is low in the sky during the early morning and late afternoon. The sun is at its
highest point at noon.
on a clear day, earth gets the maximum possible amount of solar energy around noon.
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and some of it is diffuse. The sum of direct and diffuse radiation is commonly known as
Global solar radiation. Brief features of these types of radiation are given in Table 2.1 below:
Figure 2.2 shows these components of solar radiation.
Figure: 2.2: Components of solar radiation
Key features
Radiation
Direct/Direct
Normal
radiation
Diffuse
radiation
Solar
Remarks
technology
applicable
Comes directly from
the sun
Does not get reflected
off the clouds, dust,
the ground or other
objects
Strikes the plane of a
solar module at a 90
degree angle
Flat plate
collectors
(nonconcentrating
type)
Flat plate
collectors
Figure 2.3 presents the percentage amount of solar radiation lost due to the absorption and
scattering etc. Simply put, just around less than half (47%) of the solar radiation finally
makes its way on the earths surface.
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Symbol
Name
Description
Location
Latitude
Location
Declination
Location
Hour-angle
Solar position
Solar altitude
Angular
location north
or south of
equator
Angular
position of the
sun at solar
noon with
respect to
equatorial plane
Displacement of
the Sun E or W
of due S
Angle of the
sun above
horizon
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Sign
Range
North positive
-900<-1<-+ 900
North positive
-23..450<-d
+23..45023..450
East negative
West positive
Positive
00 at Sunrise,
sunset 00<-
+900
Type
Symbol
Name
Description
Sign
Solar position
Solar zenith
Positive
00<- s<-900
Solar position
Solar
azimuth
East negative
West positive
Wall-orientation
Wall azimuth
Angle of the
sun from the
normal of
earths surface,
90 0-
East or west
position of the
sun from due S
1. East or
west
position
of the
wall
from
due S
00 at due south
can be greater
than 900
00 at due south
00 <- p<-+/1800
Wall-orientation
Surface tilt
Positive
Wall-sun
orientation
Wall-Solar
azimuth
Angle of the
surface relative
to the
horizontal
Angle between
the solar
azimuth and
wall azimuth
Wallsunorientation
Solarincident
Angle between
the surface
normal and the
sun
Positive
East negative
West positive
Positive
Range
00 horizontal
900 vertical
1800 upside
down
00, when wall
and solar
azimuth
coincide
Cos i is the
fraction of
surface
projected in the
insolation
direction
Source: www.uidaho.edu
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low angle. Thus these rays are more spread out. It also results in lower amount of energy at
any spot. That is not all; as winter nights are longer and days remain short. Thus the earth
does not get warmed up properly. Figure 2.5 shows the sun path in three different situations
_._._._._ In winters
_______ On equinox days
.. In summers
hemisphere. It is quite Interesting to note the relative position of sun under different seasons
of the year. Earth is closest to the sun in December, which is the winter time in the northern
hemisphere.
Figure 2.6: Apparent Planetary motion of the sun
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22
23
S=monthly average of the sunshine hours per day at the location (h)
Smax=monthly average of the maximum possible sunshine hours per day at the location i.e.
the day length on a horizontal surface (h)
a, b= constants obtained by fitting data
The definition of what a clear day means was not quite clear then. Page suggested that Hc
be replaced by Ho. It is the monthly average of the daily extra-terrestrial radiation which
would fall on a horizontal surface at a given location
Hg/Ho=a +b (S/Smax)
Values of a and b have been obtained for many cities in India as given in Table 2.2 below.
Ho is the mean of the value (Ho) for each day of the month.
Table 2.2: Constants and b in the equation for the Indian Cities
Location
Ahmedabad
Bangalore
Bhavnagar
Kolkata
Goa
Jodhpur
Kodaikanal
Madras
Mangalore
Minicoy
Nagpur
New Delhi
Pune
Shillong
Srinagar
Thiruvananthapuram
Vishakapatnam
0.28
0.18
0.28
0.28
0.30
0.33
0.32
0.30
0.27
0.26
0.27
0.25
0.31
0.22
0.35
0.37
0.28
0.48
0.64
0.47
0.42
0.48
0.46
0.55
0.44
0.43
0.39
0.50
0.57
0.43
0.57
0.40
0.39
0.47
3.0
3.9
2.8
1.3
2.1
2.0
2.9
3.5
4.2
1.4
1.6
3.0
1.9
3.0
4.7
2.5
1.2
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Pyranometer
It measures the global solar radiation. This instrument is more in use while dealing with the
setting up of flat plate system such as solar modules etc. A Pyranometer is an instrument
which measures either global or diffuse radiation over a hemispherical field of view (refer to
drawing of section A for schematic diagram). Following few are its most important design
cum working features:
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26
Pyrheliometer
It measures the intensity of direct solar radiation. This instrument is more in use when
planning the installation of concentrated solar power systems. Key design cum working
features of this instrument (Figure 2.10) are as under:
Sunshine Recorder:
It is a simple device to record hours of sunlight in a day. It is generally made of a glass
sphere that focuses the sun rays on a graduated paper strip. A track is burnt along the strip.
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This corresponds to the time when the sun is shining. Sunshine Recorder records the actual
duration of sunshine (Figure 2.11).
Suryamapi
Suryamapi is a simple hand-held device to measure the solar radiation. It uses a silicon solar
cell to sense the incoming radiation (Figure 2.12). This cell simply acts as a photo or light
sensor. The unit of measurement in this case is mA/cm2.
Figure 2.13 gives a quick glimpse of the impressions marked by a sunshine recorder.
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29
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Advantages
it runs on a freely flowing fuel (1.8 x 1011 MW) which is there as long as sun lasts
it is available nearly everywhere and to everybody at no cost
it can be used to produce heat or electricity without a by-product (i.e. a residue)
there is no burning of any combustible material (like coal for example in a thermal
power plant)
there is no risk of any radioactive exposure (unlike the one in a nuclear power plant)
it can produce electricity or heat without any noise level
it is quite safe to use
Limitations
it is a dilute form of energy
it has a high initial capital cost
it varies throughout the day (daily, seasonal and local variation)
it still needs an expensive storage like a deep cycle battery for night time use
Latitude
It is the angle made by the radial line joining the location to the centre of the earth, with the
projection of the line on the equatorial plane. By convention, latitude is measured
positivefor the northern hemisphere. It varies as -900 <- <-90 0.
Solar declination
Since the earths axis of rotation is inclined at an angle of 23.450 to the axis of its orbit around
the sun, this tilt causes the seasonal variations in available solar radiation at any location.
The angle between the earth-sun line (through their centres) and the plane through the
equator is called the solar declination. It varies between -23.450 on 21 December to + 23.450
on June 21. Further, declinations towards the north of the equator are positive, whereas
those to the south are negative.
It is the angle made in the horizontal plane between the line due south and the projection of
the normal to the surface on a horizontal plane. As per the convention, due south is taken as
zero, east of south is positive and west of south is negative. Hence it varies as -1800 1800
Slope
It is the angle between the plane of the surface concerned and the horizontal plane. It varies
as 0 1800. >900 means that the surface has a downward facing component.
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Take for example, January 14 is year day 14 and February 16 is year day 47. As is well
known, there are 365/366 days in a year. The earths axis is tilted at around 23.45 degrees
with respect to the earths orbit around the sun.
Equation of time
There is a small change in the solar time with respect to the local standard time. It takes
place due to the movement of earth around the sun. This time difference is commonly
known as the equation of time. It is useful to know while trying to find out the suns
position for any solar energy related calculations. The approximate formula for equation of
time in minutes is as under:
Eqt*=-14.2 sin ((n+7)/111)
(it is for year day n between 1 and 106)
Eqt=4.0 sin ((n-106)/59)
(it is for year day n between 107 and 166
Eqt=-6.5 sin ((n-166)/80)
(it is for year day n between 167 and 246
Eqt=16.4 sin ((n-247)/113)
(it is for year day n between 247 and 365)
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34
Drawing
35
36
37
F
B
38
39
Well, photo simply means light. It has come from a Greek word phos. Voltaic means
producing an electric current. This word has come from the name of Alessandro Volta. He
worked on electricity during the seventeenth century. Thus Photovoltaic (PV) in a combined
way means producing electricity under light (sunlight in this case). A solar cell is a device
which does this simple trick. The photons or energy packets as these are known energise cell
material i.e. a semiconductor made generally of silicon. Figure 3.1 illustrates this simple
looking but highly complex process of solar energy conversion into some useful electricity
via this device only.
A solar cell works like a simple flashlight battery. It also has a negative and positive
terminal.
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Eg (eV)
Crystalline silicon
1.1
Amorphous silicon
1.4 -1.8
Cadmium Telluride
1.55
Copper indium
diselenide
Gallium Arsenide
1.05
1.43
Simply assume if, energy band gap is zero, then what happens? Well, all photons can
contribute to the photo current. It will then gain a maximal value. However, the photovoltage will be zero in that case. A bigger gap stops some photons from producing electronhole pairs. It simply means a reduced photo-current too, while the photo-voltage goes up.
Thus between the limits for the conversion efficiency (=0 for Eg=0 and =0 as Eg tends to
infinity), there must be lie a value of Eg, for which is maximal).Lower bandgaps generally
yield higher currents. This is because they absorb a large part of the spectrum. Typical
materials to fall in this category are silicon (1.1 e V and Germanium.
In a way, energy band gap is just like a boundary wall. Ideally it should neither be cake
walk nor a tedious one. It too would then welcome all friendly interfaces.
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42
It is thus clear that a cell must be made of a light absorbing material. In this case, it is the
sunlight, which is made of energy packets like the photons. The energy (E) of a photon is
related to the wavelength by the simple equation:
E=hc/
Here h= Plancks constant=6.62x1027 erg-s
and c=velocity of light=3x108 m/s
Putting these values in the above equation, we get E=1.24/
Here E is in electron-volts (eV) and is in microns
Silic
on
Ingo
t
Waf
er
PV
Cell
Mod
ule
Syst
em
Material processing
The journey of a solar cell begins with silica (sand). Silica is nothing but Silicon dioxide. It is
treated in a blast furnace thus giving metallurgical grade silicon. This form of silicon is not
very pure. So, it is cleaned further to make it very pure. Silicon got in this way is better
known as electronic grade. It is also called feedstock from which a wafer is then made.
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Wafer development
The above feedstock is melted in a crucible. It is either pulled/grown as a cylinder (single
crystal) or as a polycrystal. A small quantity of boron is mixed during the melting process. It
thus produces the p-type silicon material. The end product is called ingots or bricks and is
shaped/cut in the way required. These are then sawn into thin slices better known as
wafers by the blade saws. Single crystal is also known as mono-crystalline, while polycrystal
is also known as the multi-crystalline.
Sand is an ordinary material. But, to make solar cell is no ordinary job. It needs modern
pieces of machines to make it. Thinner the solar cell becomes, more difficult it becomes to
work on it.
Diffusion
The wafer at this stage is p-type. An n-type material (phosphorus) is now diffused into the
wafer. The simple idea is to create a P-N junction.
Anti-reflection Coating
Silicon nitride and titanium oxide are generally used on the surface. This helps to bring
down the surface reflection of the sunlight further
Metallization
It is required to make a contact between the front and back surface. The simple idea is to
collect the electricity that a cell is now able to make. Silver is the most commonly used
material to develop such contacts. Silver in the form of a paste is screen printed onto the
front and back surfaces. The last step is to heat these pastes so as to form good quality ohmic
contacts.
44
45
Figures 3.4-3.6 present a view of both the crystalline silicon and thin film technologies
Figure 3.6: Left hand and right hand view of a thin film Cadmium Telluride
46
47
Voc is the voltage between the positive and negative terminals when no current is
drawn (i.e. unlimited load resistance)
Isc is the current when the positive and negative terminals are connected to each other
(i.e. zero load resistance). The short circuit current increases with the intensity of
sunlight. More the intensity more is the number of photons produced. In turn, it means
more number of electrons too.
The above I-V curve may be understood in terms of the following few steps:
voltage is shown on the X-axis
current is shown on the Y-axis
specific operating point is found by the electrical load (device or appliance)
connected to a PV system.
I-V points are plotted between the short circuit current point (Isc). At this point, the
device produces maximum current and zero voltage.
the other point is the Open circuit voltage (Voc), where the device produces
maximum voltage and zero current.
48
the point at which a PV device delivers its maximum power output and operates at
its highest efficiency is known as its maximum power point.
the voltage and current values at the maximum power point are referred to as
maximum power voltage (Vmp) and the maximum power current (Imp).
The module short circuit current goes up with bright sunshine. On the other hand, the
module open circuit voltage decreases slightly instead of going up too. Thus a bright
sunshine has its negative side too.
49
50
Tables 3.2 & 3.3 sum up the efficiency values as well costof these technologies as under:
Technology
Thin film
Cell efficiency at
STC*
Amorphous
Silicon
Cadmium
Telluride
CIGS
5-7%
8-11%
711%
Module
efficiency
Area needed
per kWp
(for modules)
15 m2
11 m2
10 m2
Single
Crystalline
Poly
Crystalline
16-19%
14-15%
13-15%
12-14%
~7 m2
~8m2
Efficiency
feature
Cost
Consideration
Whether
manufactured
in India (Y/N)
Indicative
cost per peak
Watt for
Module
Indicative
System
Cost
Key cost
determinants
Monocrystalline
silicon
Most efficient
cells/module
Most expensive
Rs. 110
Silicon grade
used
Polycrystall
ine silicon
Less efficient
cells/module
s (in
comparison
to monocrystalline
silicon)
Far less
efficient than
both monocrystalline
and poly
crystalline
silicon
More efficient
than
amorphous
silicon
Less expensive
than monocrystalline
silicon
Rs. 100
Less expensive
than crystalline
silicon (i.e.
mono + poly)
Amorphous
Silicon
Cadmium
Telluride
Least expensive
of all
Technology
type
Physical and
Technical
Specifications
Rs 90/Wp
Source of
Purchase
Manufacturin
g cost of
under
$1/Wp
51
Volume of
purchase to
be procured
Figure 3.7 gives an illustrated view of a crystalline silicon based solar module.
52
53
Charge controller
A battery needs to be handled with great care. It can get damaged if, we try to put more
charge into it. Taking out more charge from it is equally harmful for a battery. These two
stages are better known as overcharging and deep discharging. A battery is not able to
control charge on its own. This work is done by a simple automatic device known as a
charge controller in the following way:
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it senses the battery charge and switches off the charging current. Thus no damage to
the battery can take place.
it disconnects the appliances when battery charge goes below a set limit.
prevents reverse current
a fast blow glass fuse is also provided to save electronic circuit from damage under
short circuit or any other load conditions
Small is beautiful in this case too. Very small PV systems may not need a charge
controller at all. Small currents are not likely to damage good-quality batteries.
However, it is not the same case while dealing with slightly large systems.
Inverter
A solar system produces DC power. However, our home appliances generally run on AC
power. So, one needs a device to change DC power into more usable AC power. A simple
example is that of a compact fluorescent lamp or a CFL. The device which does this trick of
conversion from DC to AC is known as Inverter. These are of many different types and
capacities too.
Support structure
A solar module is a very sensitive piece of equipment. It can not be simply placed either on
ground or roof. It also needs to collect the sunshine at an angle. There is one more need here
i.e. of keeping a module safe from any strong winds. The support structure generally takes
care of all these needs.
Junction boxes
It is a meeting point for many wires. These may be from a row of modules or from modules
to a battery bank. A junction box is made of an un-breakable material i.e. polycarbonate. It
makes use of copper connectors for a high current flow. This way, wires remain safe from
any moisture etc.
55
Several combinations of systems can be made using these key components. Figure 3.10 gives
a schematic view of four different types of Solar PV systems. A direct coupled system does
not make use of a battery. One of the best examples of this system use is a solar water
pumping system. The quantity of water that does not get used during the day is stored in a
storage tank. Stand-alone systems continue to meet the lighting demand for example in the
rural areas. Some of the most common examples are the solar lantern, home lighting system
and street lighting system etc. The grid connected systems are now being installed to feed
the solar power directly to the grid. These type of systems generally do not use the battery
storage. Hybrid power systems are mainly designed to keep down the cost of a solar PV
system. PV-diesel and PV-wind hybrid power systems are the most common examples of a
hybrid power system.
56
battery. The charging current of these cells does not add up in a series connection. The
manufacturers of the module generally rate a module in terms of Watt Peak. It is the most
common unit of measure and represents the following:
identifies the power output of a cell, module or array at mid day under a clear-sky sun.
this power output is defined at a sunlight intensity of 100 mW/cm2.
actual power output of a PV system changes with the brightness of sun
Just think of a clear sunny day. The power given out by the module will move up from
zero in the morning to its maximum near midday (noon). Then it will decrease as night
comes. The same is more or less true with many other forms of human activity too.
57
Cell connections
Parallel: Current increases;
V constant
Series: V increases;
Current constant
Figure 3.13: Current and Voltage gains via series and parallel connection of cells
58
Tilt angle
A solar module should be put up in the proper path of sun. Thus module is tilted at an
angle. It is roughly equal to the latitude of the place where a module is put up. Any error in
the tilt angle will lead to loss of some amount of power.
Dust
The modules need to be kept as clean as possible. The dust settles on the module surface
mostly in the dry season. So, proper care should be taken to clean the glass surface of a
module regularly. Remember, dust may cause energy losses as high as 5-10%
Shading
Solar module faces the sun all day long. There should be no shade present on it. So, keep on
looking for any extended tree branches, plants and TV anteenas etc. Thus, place the panels
where they won't be in the shade. Figure 3.14 shows the net effect of shading on the power
output expected from a solar module.
A solar module is made of a string of individual solar cells. These are connected in series
with one another. The current output from the whole module is limited to that passing
through the weakest link cell. Take for example one cell from 36 cells in a module. In case,
it is fully shaded, the power output from the module will come down to zero. However, if,
one cell is 50% shaded, then the power output from the module will reduce by 50% only.
59
A shaded cell becomes like a high resistance. It can even result in overheating of the
cell. This is so as the unshaded cells try to force current through this high resistance
cell. Is this not like a totally opposite case of a human being trying to lie down in
shade to feel a cooling effect without any force at all?
Light Intensity
The brighter the sunlight the more power the panels will produce. So, if, there is 1000
watts/m2 of sunlight, you will see almost the full rated output of the panel. But, if there is
500 watts/square meter only, you will see half the rated power of the panel. Figure 3.15
shows a clear effect on the module current as a result of changing values of solar insolation.
It goes up in direct proportion with the increasing solar insolation. The same is not the case
with the module voltage.
60
Insolation Dependence
Temperature
Modules are tested at a standard temperature of 250C . The higher the temperature, the
lower is the power output of a module. Simply put, a module loses power at higher
temperatures. The cell temperature can reach around 70 degrees C under the bright
sunlight. The power in case of crystalline silicon cells decreases by about 0.4 to 0.5% per
degree C of temperature increase above 25 degree C. Amorphous silicon modules have a
lower temperature coefficient of about 0.2 to 0.25% per degree C of temperature increase.
Some may quickly think about solar modules producing more power at higher
temperatures. However, it is just not true, moreso in case of crystalline silicon modules.
These type of modules lose as much as 16% of the available power at air temperature of
around 350C. Thin film modules on the other hand lose just half the power at high
temperatures.
Figure 3.16 presents the effect of increasing temperature (s) on the module voltage. The
voltage reduces as the temperature goes up. The same is not the case with module current.
Thus it can be said that power output of a module comes down with reducing values of
solar insolation and increasing temperatures.
61
Temperature Effect
Temperature coefficients
dI
SC
0 . 1 Am
deg C
dT
dV OC
2 . 2 mV deg C
dT
dP MAX
0 . 5 % deg C
dT
Cabling losses
Some loss of power can take place through cables. The solution lies in choosing a large
diameter wire size to bring down the loss
Improper connections
Poorly made electrical connections produce resistance. It can thus result in less power going
to the batteries. Make them tight and keep them clean too.
62
Normal
Range
Typical
Value
Remarks
0-20%
5-10%
5-10%
0-20%
5-10%
5-8%
0%
5%
5%
16% (at 60
degrees C)
5%
7%
1-5%
2%
10-20%
15%
The back surface of solar modules often gets very hot in places like Gujarat and Rajasthan.
This means presence of heat. Efforts are now being made to transfer this wasted heat to a
liquid. Experimental systems of this type are better known as PV/T (thermal) systems.
63
Table 3.5 shows various steps in the battery charging process as under:
Type of
Charge
Charging need
Remarks
Main
Charge
Top-up
Charge
Equalisation
Charge
Maintenance
Charge
Charge Controller:
It is a simple device to keep a watch on the battery state of charge. It decides as to when a
battery needs a charging current. It also makes sure that a battery does not get overcharged.
Thus it is important to connect a solar module via a charge controller to a battery. A charge
controller is also known as a charge regulator. It is rated on the amount of current that
comes from the PV array. Take for example a controller rated at 20 amps. In simple words, it
means that we can connect up to 20 amps of solar panel output current to this single
controller. Following few types of controllers are being used in a solar system at present:
PWM
The most advanced charge controllers make use of a charging principle known as Pulsewidth-Modulation or simply PWM. Two of its key features are:
it allows a battery to be charged very efficiently
battery life is increased in the process
64
MPPT
This is one more type of controller, which also includes the maxiumum power point
tracking or simply MPPT. Two of its key features are:
maximizes the amount of current (going into a battery from the solar array)
output voltage from a panel is reduced.
Disconnect
Battery
Compensation
Feature (BTC)
Inverter
A Solar power system produces DC current. It is usually stored in a lead-acid battery.
Inverter is a device which changes this stored power into standard AC electricity. Nearly all
lighting, appliances, motors, etc., are designed to use AC power. In an inverter, direct
current (DC) is switched back and forth to produce alternating current (AC). Then it is
transformed, filtered, stepped, etc. The clear goal is to make the inverter output (waveform)
acceptable to all types of loads. Two basic output designs of the inverter are as under:
Sine wave-can run almost anything
Modified sine wave-changes DC to AC very efficiently; cheaper than sine wavinverters.
Most inverters produce 120VAC. However, these can be provided with a step-up
transformer to produce 120/240VAC.
65
ampere of current flow for one hour. Then its ampere-hour capacity is taken as 1 Ah. Now,
if, it can give 100A current for 1 hour, then its ampere-hour capacity will be 100 Ah.
Those producing batteries generally rate their batteries as per a standard method. The
battery is discharged at a constant rate of current over a fixed period of time. This time
period is taken either as 10 or 20 hours. Thus a 100 Ah battery is rated to offer 5A for 20
hours at room temperature. It is interesting to note the following few points:
Rate in Amperes = capacity in Amp- hours / Time in Hours (i.e. C/T)
battery capacity will decrease as temperature comes down but life is increased
battery capacity will increase as temperature goes up but life is decreased
battery charging voltage also changes with temperature
Parallel
The batteries of equal voltage and capacities are joined together. The idea is to increase the
ampere-hour capacity of the battery bank. In this case, the positive terminals of all batteries
are connected together. Similarly, all the negative terminals are connected together. The
final voltage remains unchanged. However, the capacity of the battery bank is now the sum
of capacities of individual batteries. Figures 3.18-3.21 show the series and parallel
arrangement of different capacities of batteries.
66
67
At present, batteries of the following few types mostly are being used in the solar systems
(Table 3.6)
Table 3.6 :
S.No.
Type of battery
Voltage of battery
1.
2.
6 V / 12V
2V/12V
Recommended
Depth
of
discharge
15-25 %
Up to 80 %
1.2 V
3.6V/3.7V
100 %
Up to 90 %
3.
4.
Sulphation
Sulphation normally occurs in lead acid batteries. It results from longer time operation at
part state of charge. This effect reduces battery life.
68
Hybrid systems
It is possible to mix a solar system with another source of power like wind turbine or a
diesel generator etc. This type of system can be a stand-alone system or even connected to
the local grid. The most important advantages of putting up a hybrid system are as under:
uses not just one but two naturally occurring renewable energy sources like sun and
wind at one place
helps to keep the cost of a solar PV system down by increasing the capacity of the
other source. Remember it costs far less to put up a wind energy system
69
Nearly 77 billion liters of kerosene oil are burnt in kerosene lamps every year. It amounts
to
4.1.1
theBrief
use of
Cost
1.3comparison
million barrels of oil per day. In India alone, nearly 67.6 million rural
households use kerosene oil for lighting as per the National Sample Survey Organisation
(NSSO) figures for 2008. Is this not enough to make the whole world think much more
Table 4.1 below gives the estimated cost of lighting from various sources. The cost of
seriously about the use of solar lanterns?
kerosene oil has been changing quite often. Solar lighting comes at a zero fuel cost.
Table 4.1 gives a comparative cost figures for various lighting sources
Lighting
system
Candle
Kerosene
lamp
Solar lantern
Solar home
system
AC
electricity
Typical
cost
(US$/klm per hr)
Remarks
2.00
The running cost of kerosene oil lamp and solar lanterns may be
the same. However, a solar lantern has got many advantages
over the oil lamp
0.10-100
0.10-4.00
0.04
0.01
70
Basic operation
Sunlight falls on the module during the day to make electricity. This electrical energy passes
through the electronic circuitry to the battery. In turn, the battery gets charged and stores
energy. This energy is then available for lighting the fluorescent lamp/light emitting diode
in the lantern at night. A single charge can operate a CFL for 3-4 hours and LED for a longer
duration of 5-6 hours.
Major applications
This lamp can be used both indoors and outdoors. However, it has been designed keeping
in view the following few applications:
room lighting (in the non-electrified remote areas)
emergency lighting
as a table lamp
camping
patrolling streets and farms
hawker/vendor stalls
adult education centers/health Centres
71
based lanterns have been developed. These use lesser amount of power and work for more
number of hours as well. The Ministry of New and Renewable Energy (MNRE) is
encouraging the use of both the CFL and LED type lanterns. Solar manufacturers are trying
to bring down the cost of lanterns.
CFL Lantern
Solar module is a separate part of a solar lantern. The other two main components i.e.
battery and CFL are housed inside the body (plastic or fibreglass) of a lantern. **Figure 4.1
show the front view of a CFL based lantern. The solar module is connected to the battery via
Handel
Top outer
Top Inner
MS Rod
CFL
Earth Strip
Red LED for low battery indication
Chimney
LED night lamp
Green LED for Battery Charging indication
CFL holder
Rocker Switch
Battery status indicator
Main Housing
Push Button
Base plate
LED lantern
The physical form of this model is nearly similar to a CFL model. The major difference is
that it has a number of small LEDs in place of a single CFL. **Figure 4.2 presents a front
view of the lantern. It has an additional feature of brightness control. The simple idea is to
save power while making the desired use of a lantern.
72
CFL Model
LED Model
Remarks
Solar Module
(crystalline Silicon
(X-Si)/Thin film)
Battery
(sealed maintenance free)
Compact
Fluorescent
Lamp
Charge Controller (on a
PCB assembly)
Fuse
Solar Module
(X-Si/Thin film)
SMF , Li-ion
73
Module
Battery
Lamp
No.
capacity
Capacity
Wattage
(Wp)
(Ah)
Fuse
rating
Charging
Charging
Average
Cable/
Time per
day
Working
Hours
(hours)
Per day
length
Operating
temperature
(0C)
1.
3Wp
(6V)
4 Ah,
6V
3W
1A
2-core
(5m)
7-8
2-3
0-50
2.
5Wp
(6V)
4Ah,
6V
5W
1A
2-core
(5 m)
6-8
3-4
0-50
3.
10 Wp
(12 V)
7 Ah,
12V
7W
1A
2-core
(5m)
6-8
4-5
0-50
4.
10 Wp
12 V
7 Ah,
12 V
9W
1A
2-core
(5m)
6-8
2-3
0-50
Charging
Time
Average
Operating
temperature
Module
Battery
LED
Fuse
Charging
No.
Capacity
Capacity
Wattage
rating
Cable/
(Wp)
length
Per day
(hours)
Working
hours
(0C)
Per day
1.
2.5-5
4.5 Ah,
6V
0.75 W
1A
2-core
(4m)
6-9
0-50
2.
2.5-5
1.50W
1A
0-50
2.5-5
2.25W
1A
2-core
(4m)
2-core
(4m)
6-9
3.
4.5 Ah,
6V
4.5 Ah, 6
V
6-9
0-50
4.
3.0
4.5 Ah, 6
V
2.25 W
1A
2-core
(4m)
6-9
0-50
5.
2.5-5
4.5 Ah,
6V
4.50W
1A
2-core
(4m)
6-9
0-50
74
Solar Module
It collects the sunlight and changes it into useful electricity. This electricity is then stored in
the battery for running the lamp source (CFL/LED) at night.
Battery
The battery gets charged/discharged via an efficient electronic circuit. It thus keeps the
battery safe both against the overcharging and deep discharging too.
CFL/LED
CFL is an energy efficient lamp. Like for example, a 7W-CFL gives light equivalent to that of
a 40-Watt ordinary incandescent bulb. On the other hand, LED is a special type of diode. It
emits light when connected to a DC power supply.
Electronics/PCB card
In a CFL lantern, the electronics used with the lantern is made of charge controller/inverter
circuit. While as, the driver circuit takes the place of an inverter circuit in a LED lantern.
Protective indications
These are incorporated in the Printed Circuit Board (PCB) in case of both the CFL/LED
based lanterns.
75
keep the ON/OFF switch in the OFF position while charging the battery in the
lantern
The battery starts getting charged and green LED glows
The battery gets fully charged and green LED stops glowing
Take care to disconnect the module from the lantern during the night time
The SLCS is designed to charge both the CFL and LED type lanterns.
However, two different types of junction boxes are set up. Key advantages of a solar
charging station are:
cost of charging the lantern is lower for a poor user
it runs with lesser number of problems too
Technical specifications of a SLCS
LEDs use just a small amount of power in comparison to the CFls. It thus helps to keep the
cost down too. Table 4.5 below gives an idea about the capacities of all major components.
Table 4.5: Component ratings of lanterns
Module
Lamp
Battery
Junction
Charging
Capacity
Wattage
Type
Box
Cord
CFL
Lantern
1x80 Wp
10x7 W
12
V
storage
battery
10 ports
10 (around 2
mtr.length)
LED
lantern
1x30 Wp
LEDs
6V storage
battery
10 ports
Remarks
77
be adapted to a 12V-12V JB only. In both these cases, the solar panel voltage is assumed to
be 12 V. There are a few vital reasons to have this type of matching combination (s). Failing
which, it will result in a lower efficiency of charge conversion/availability too
Lanterns
Solar module charges the lantern battery via a junction box. Once fully charged, lantern is
removed from the junction box. It is then free to be used a mobile source of lighting. The
full description of lanterns has been given in the last section.
Figure 4.3 shows a view of the solar lantern based centralized charging station
78
see if, any of the modules is stopping the sunlight from reaching the other module
grout the modules to the roof (concrete/tiles/slates etc.) with bricks, cement and sand
use a four pole mounting structure to position the panel on pitched roofs (wood/thin
metal sheet/rough tiles etc.)
keep the modules bolted with such a structure at a height of 6 feet above the ground
make the modules secure by fixing with anti-theft screws
always use a metallic frame of MS flat/angle iron to fabricate the mounting structure
for modules
it must allow to tilt a module to horizontal between 0-45 degrees
Installation and operation of the Junction box:
choose a clean space for the mounting of five junction boxes (for charging of 5x10
lanterns)
it should be just above the top of the rack on which the solar lanterns are kept
fix the junction box on the wall using a proper screw arrangement
connect the lanterns to the respective junction boxes by wires tied together by a spiral
wire
use a proper polyvinyl conduit (PVC) to connect wires/cables between the solar panel
and junction boxes
connect the red wire (positive of the solar module) with the positive terminal in the
junction box
connect the black wire (negative of the module) to the negative terminal of the junction
box
Indications: Connection (s) between a module and the junction box is alright, if, the green
LED of the junction box glows.
Physical inspection of the solar lantern:
check the lantern for any type of damage from outside
check if, the fuse is in its place
if, not, unscrew the cap of the fuse holder
put the fuse inside the fuse holder
close the fuse cap by giving it a reverse twist
Checking the lantern operation:
remove the gummed tape, if, put on the ON/OFF switch (two position facility)
press down the switch to the on position & watch the CFL glow
CFL may not glow but the red LED glows
it means the battery is low, charge it quickly
check the fuse in case both the CFL and red LED fail to glow
contact the system installer/supplier in that case
Connecting the lanterns with junction boxes.
79
80
81
Solar Module
It is mainly made of crystalline silicon cells. At the most two modules of 37 Wp are needed
to run models III&IV
Battery
It is a flooded electrolyte positive tubular plate battery. Simply put, it needs very low but
regular maintenance
Inverter
It is a transistor based on push pull operation. A push-pull is a type of electronic circuit
which can drive either a positive or a negative current into the load. The inverter has an
input voltage of 120 V and operates at more than 80% efficiency
Charge controller
82
It is just possible that solar module may be producing more electricity. A battery may not be
needing all of this electrical charge. A charge controller just does that and much more as
mentioned below:
Boost charging
Float charging
Low voltage disconnect function
Load reconnect voltage
Temperature compensation
Maximum solar charging current
Maximum load current
Dimension
Weight
Self consumption
Maximum wire size
Ambient temperature range
Case protection
Efficiency
Inverter
Type: transistor based push pull type
Input voltage 12 VDC
Efficiency
> 80%
83
lamp instead of a CFL. Following few are some of the most important advantages of a LED
system over the conventional CFL based lighting unit:
LED lamps give high amount of brightness at a low power consumption
LED based systems thus need very small solar panels as compared to the higher
capacity panels in case of a CFL system
Likewise, small capacity battery (ies) too come into the charging frame
LED lamps have a life of more than 50,000 hours as compared to around 10,000
hours for a CFL. In turn, this reduces the cost of lamp replacement too
LED based systems are available at a lower cost than the CFL based systems thus
indicating its higher market potential too.
Item
Battery (Ah)
Mod-
Mod-
Mod-
Mod-
SHS
SHS
SHS
II
III
IV
II
III
18
37
2X37/
2X37/
30
40
50
1X74
1X74
20
40
75
75
40
60
75
5A
5A
5A
/10A
5A/10A
5A
1OA
10A
1(9/11)
2(9/11)
2(9/11)
4(9/11)
3(7)
4(7)
6(7)
12 V LMLA/SMF
(dry charged)
3
Charge
Controller (12 V)
Fan
(<20 W)
Battery box
84
S.No.
Item
Mod-
Mod-
Mod-
Mod-
SHS
SHS
SHS
II
III
IV
II
III
DC Fan 14 W
85
Figure 5.2: schematic diagram of Model nos. I-IV for Solar Home System
Figure 5.3: schematic diagram of Model nos. 1-3 for Solar Home System
86
Battery Charging
Lead-acid storage batteries are the most common type of batteries used in the solar systems.
These are made of a number of matching cells. Also, these cells have two different lead
plates. These plates are dipped in electrolyte. Electrolyte is a solution of sulfuric acid and
water. As the battery cell gets electrical energy (charges), the other delivers (gives out)
electrical energy (discharges). So, there is a change in the chemical composition of the
battery plates. The strength of electrolyte also changes. The voltage depends on the
following two parameters mainly:
type of electrode materials used
type of electrolyte used
In general, the voltage per cell in a lead-acid battery is 2.1 Volts per cell. The electrical
energy is produced by the chemical action between the electrode materials and the
electrolyte. The chemical actions start and electrical current flows from the battery. This
takes place as soon as there is a circuit connection between the positive and negative
terminals. The electrical current flows as electrons via the outside circuit.
Discharging
The battery begins to discharge as soon as any load i.e.an appliance is switched on. The
discharge actually begins when sulphuric acid in the electrolyte acts on lead peroxide in the
positive plates. Similarly the lead acts on the negative plates to form a new compound i.e.
lead sulphate. The moment the sulfate in the electrolyte is used up, the battery stops
producing electricity. That means it simply discharges.
CFL
A CFL tube is flled with a noble gas like argon, neon, helium. It also contains a small
amount of mercury. On heating it the mercury becomes a vapour. The inside of the tube is
coated with a phosphorescent material (mostly phosphorus). There is electronic ballast in
the base of a bulb. It boosts the line voltage up high enough to ionize the gas inside the bulb.
With this the mercury also vapourises inside the tube. The ionized gas and the ionized
mercury vapour give out ultraviolet light (UV). The UV light strikes the phosphorus. In
turn, it produces white light good enough to light a room. Table 5.3 gives a comparative
luminous efficacy of different categories of lighting sources.
87
TableTable
5.3: comparative
luminous
efficiency
16 : Luminous efficacy
of a source
and efficiency for various light sources
category
Type
Overall luminous
efficacy
Overall luminous
efficiency
Incandescent
13.8-15.2
2.0-2.2%
16.7-17.6-19.86
2.4-2.6-2.9%
5-12.6-17.5
0.7-1.8-2.8%
Fluorescent
9-32 W Fluorescent
46-75
8-11.45%
Light Emitting
Diode
58.5-82.9
55.1-81.9
69.0-93.1
8.6-12.1%
8.1-12.1%
10.1-13.6%
Gas Discharge
65-115
100-200
85-150
9.5-17%
15-29%
12-22%
Charge Controller
It is an important part of nearly all power systems that charge batteries. The purpose is to
keep the batteries properly charged and safe. The basic functions of a controller are very
simple:
stop overcharging of the battery
block the reverse current
protect from electrical overload
show the battery status
indicate the flow of power
Stopping overcharge
A battery may reach its full charge at some time of the day. It means that it can no longer
store more energy coming in from a solar module. The battery voltage will get too high, if,
more charge is put in a fully charged battery. Water breaks into hydrogen and oxygen and
bubles out fast. It looks as if, it is boiling. This way lot of water is lost. It may thus lead to a
small explosion in the battery. That is not all as it may degrade quickly. Overheating of the
battery can also take place. Such a condition may also lead to shutting down of inverter.
Simply put, stopping overcharging is a matter of decreasing the flow of energy to the
battery after it reaches a certain voltage. The voltage may come down due to lower
88
sunshine. Then again the controller may allow the battery to obtain the full charge. This is
what is commonly known as voltage regulating. Simply put, the controller looks at the
voltage and in turn regulates the battery charging. Some controllers regulate the flow of
energy to the battery by switching the current fully on or fully off. It is called on/off control.
Some more type of controllers bring down the current slowly. It is typically known as the
pulse width modulation (PWM).
A controller with a PWM feature holds the voltage more constant. If, it has a two-stage
regulation, it will first hold the voltage to a safe maximum for the battery to reach
fullcharge. Then, it will drop the voltage lower to sustain a trickle charge. A two-stage
process maintains a full charge but brings down the water loss.
A solar module works by moving current through the battery in one direction. At night, the
module may pass a small amount of current in the opposite direction. Thus battery gets
discharged a bit. In most controllers, charge current passes through a semiconductor
(transistor). It works like a valve to control the current. Thus it stops the reverse current
without any extra effort. In some controllers, an electromagnet coil opens and closes a
mechanical switch. It is more commonly known as a relay. The relay switches off at night to
stop the reverse current.
Set points
The voltage at which the controller changes the charge rate are known as the set points. The
value of these points depends upon the following few parameters:
expected type of battery use
type of battery
choice of the system designer
Interestingly, some controllers have adjustable set points. While others may simply have
fixed points only.
89
90
first connect the controller and then the battery to avoid any voltage on the wires
connect the wire leading to the solar array with correct polarity
first connect the controller and then the modules
take care to see that positive and negative wires are placed close to each other
connect the wires leading to loads with correct polarity
first connect the wires to the load and only then to the controller
Electrical connection
keep the battery on a full charge for 2-3 days
connect the battery to the system only after getting fully charged
do not switch on the loads for 2-3 days (when battery is on a full charge)
connect the array cable to charge controller with proper polarity
keep the switch in OFF position and connect the load cables and battery cables to the
charge controller
check if charging is proper-measure the charging current in series with array cable
using current meter
switch on the load i.e. lamps for their normal operation
Electrical disconnection
disconnect the load cables by keeping the switch in off position
disconnect the array cables
5. 7 Summary Remarks
Solar PV technology has made good progress since its early days. The processes to make
wafers, cells and modules are definitely using lesser amount of energy now. The equipment
i.e. the machines are also able to produce more number of these products on a per day basis.
The number of PV products and systems is growing by the day. Urban areas are also finding
its useful for a number of applications. However, the initial cost of the PV products is still on
a higher side. These systems still need to be maintained like any other conventional
products. That is where the role of trained solar technicians becomes important. They can
assemble, install and importantly, maintain these systems. In this way, they will get a good
work opportunity to connect with a sunrise technology.
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92
A. Both the solar cell and dry cell battery carry charge across the positive and negative
terminals
Q. Is strength of the Sun also related to the time of the day in any manner?
A. Yes, the intensity of the sun varies all day through, reaching its peak value at noon time
Q. Is it always true that a large area cell will produce more power than a small area cell?
A. Yes, it is generally so. However, the lone exception is the concentrator solar cell of a very
small area but with a very high efficiency
Q. How many number of individual cells are joined together to make a thin film solar
module?
A. Thin film module is a monolithic unit unlike a number of individual cells forming a
crystalline silicon module
Q. Is it possible to produce the same amount of power from a) crystalline silicon module,
b) amorphous silicon module of same frame area?
A. No, that is not the case as the amount of power produced depends on the primary
constituent of a solar module i.e. the cell (s)
Q. What is the best way to protect solar cells from rain and snow?
A. Solar cells in the case of a widely used crystalline silicon module are formed into a
weather resistant assembly before it makes its way into the field.
Q. Does a solar module make up for a full PV system?
A. No, a solar module is not the full range of system by itself. It is supported by the balance
of system components like a battery, charge controller, support structure and wiring etc.
Q. Does a solar battery store all the charge being produced by a solar cell?
A. No, it does not accept all the charge for a number of reasons
Q. If not, then which is the device at work to stop more charge from going into a battery?
A. The device which controls the amount of charge going in and out of the battery is
commonly known as the Charge Controller or a charge regulator .
Q. Can solar power be used to run AC appliances directly without anything in between the
battery and the load?
93
94
Q. Does combined charging of lanterns add more charge in one battery than the other?
A. No, it does not happen. Each and every battery gets charged as per its individual charge
retaining capacity
Q Is it okay to take out all the charge from a battery on one day and then fill it up with the
full charge the very next day?
A. No, it is not at all a healthy practice. A battery should be discharged according to its
permitted depth of discharge or simply DOD. This value is generally up to 80% for a solar
battery
Q. Sun shines for most parts of the year. Then is it really necessary to maintain a Solar PV
system?
A. Yes, a solar system needs some simple maintenance too. Like for example, it is important
to wipe the module surface clean of the dust etc. from time to time. Only then maximum
amount of sunlight will pass through it.
Q. Does a solar system make any definite noise? If, not, then how do we know if, it is really
working?
A. No, it neither makes any noise nor produces any smoke . In the modern day system, an
electronic display is available which gives the value of voltage and current produced by a
solar module all through the day
Q. Is it possible to switch off a solar PV system even when the sun is shining fairly bright
during the day?
A Yes, a solar system is provided with operational and safety controls. So, it is quite possible
to switch off a solar system for example during the repairing stages etc.
95
=(100x55)/(1000x1)
=5.5%
2. Calculate the peak Watt of a solar module when:
Pin (Solar Insolation)=1000 W/m2
Efficiency of the Module ()=7.5%
am (area of the Module)=1m2
Steps:
Formulae used is
Wp=(Efficiency/100) x Pinx area of the module
=(7.5/100) x1000x1
=75
3. A 0.5 m2 module produces 35 Wp. How much power will the same module produce in
case the area is doubled? Consider solar insolation of 100 W/m2
Steps:
a) Calculate the efficiency first
=(100xWp)/(Pinxam)
=(100x35)/(1000x0.5)
=7%
b) Now calculate the Peak Watt by using the formulae
Wp=(/100)x(Pinxam)
= (7/100)x(1000x1)
=70
96
5. Calculate the total Watt requirement of an office room in an ITI. It is using the following
few loads:
Compact Fluorescent Lamp(CFL)- 2 nos. of 11 W + 1 no. of 20 W
Fans- 3 nos. of 20 W
Television-1 no. of 40 W
Steps:
Prepare the following type of Table:
Load type
Number
CFL
CFL
Fan
TV
2
1
3
1
11
20
20
40
2*11=22
1*20=20
3*20=60
1*40=40
=22+20+60+40
=142 W
7. Calculate the total Watt-hour requirement of the above load as per the following:
Hours of daily use (CFLs)= 4
Hours of daily use (Fan)=8
Hours of daily use (TV)=3
Load type
Number
Hours of use/
Load
day
(Wh/day)
=22x4
=88
=20x4
=80
=60x8
=480
=40x3
=120
CFL
11
2*11=22
CFL
20
1*20=20
Fan
20
3*20=60
TV
40
1*40=40
=
88+80+480+120
=768 Wh
8. Calculate the Array load (as per the above) Wh/day when:
Battery efficiency=80%
Charge Conroller efficiency=90%
Steps:
Array load= Total daily load (Wh/day)/(Battery efficiency*Charge Controller efficiency)
= (768)/(0.8x0.9)
=1066 Wh/day
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10. A total solar capacity of 250 Wp is needed. Calculate the number of modules when:
a) 40 Wp modules are available
b) 50 Wp modules are available
b) 125 Wp modules are available
Steps:
Choose the total capacity as:
6 modules of 40 Wp
5 modules of 50 Wp
2 modules of 125 Wp
11) The daily load is 1066 Wh/day. Calculate the battery capacity needed
Steps:
The formulae used is :
Battery capacity= (Daily load x reserve backup)/(Nominal Voltage x Depth of discharge)
Here:
a) reserve backup is the number of days i.e. no-sunshine days, for which the extra charge in
the battery is needed
b) Depth of discharge is the maximum possible charge that can be withdrawn from a battery
without causing any damage to it
Assume reserve backup = 2 days
Depth of discharge (DOD)=60%=0.6
Using these values in the above equation gives
Battery capacity= (1066 x2)/(12 x 0.6)
= 296 Ah
= 300 Ah
98
13) A solar battery is rated at a capacity of 100 Ah. Calculate the number of hours for which
this capacity can be used
Steps:
Battery capacity= ampers x no of hours
So it depends on the current drawn and the duration for which it is drawn.
Thus a 100 Ah battery can be used in many different combinations such as
a) 5 hours (20 A x 5h)
b)10 hours (i.e. 10 Ax 10 h
c) 15 hours (i.e. 6.7 A x 15 h)
14) Calculate the total water head, if, water is to be pumped from a height of say 13 m using
a solar water pumping system. It then has to be pumped to a storage tank placed at a height
of 13 m. The dynamic head of the system (i.e. frictional losses of lifting water to the storage
tank are included) is around 6m.
Steps:
Total water head= Static head + dynamic head + height of the storage tank
= 13 +6 +13
=32 m
15) Calculate the daily water demand in a village with a population of around 700 (around
140 households). Assume the per person water demand is around 35 ltrs per day
Steps:
Use the following formulae:
Daily water demand = Population x daily water demand
= 700 x 35
=24500 ltrs/day
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16) Using the above values, calculate the daily water demand in m3/day
Steps:
Daily water demand =24500 ltrs/day
Daily water demand in m3/day= 24500/1000
= 24.5 m3/day
17) Calculate the energy required if, volume of the water that has to be pumped for a certain
year say 2011 is 24.5 m2/day. The total head is 32 m
Steps:
Energy required= mass of water x gravity x total water head (in Joules or kilojoules)
= 24.5 x 9.8 x 32 x0.28 (1 KJ=0.28 Wh)
= 2151 Wh/day
18) Calculate the array load as per the values mentioned in Q. 16 above
Steps:
Array load= Energy required/System Efficiency
= 2151/0.85
= 2530.5 Wh
19) Calculate the array size for the water pumping application as per Q. 18 above
Steps:
Array size= Array load/(Solar Insolation x mismatch factor)
= 2530.5/(5.5 x 0.85)
= 2530.5/4.67
= 542 Wp
20) Calculate the lumens per watt for in case of a a) 100 ordinary light bulb and b) 11 W
CFL
Steps:
Lumens per watt is a simple measure of as to how much light is going to be produced for
each watt of energy consumed
Using standard efficacy ratings, it is possible to know lumens per watt as under:
a) a 100 W bulb usually gives 1800 lumens
Thus lumens per watt is simply=lumens/lamp wattage
=1800/100
=18 lumens per watt
100
101
Drawing
102
103
PV array
Charge controller
Battery
DC load
Inverter
AC load
104
AC load
PV array
Inverter/Power
Conditioner
Distribution panel
Electric Utility
105
PV array
Rectifier
Charge controller
DC Load
Battery
Inverter
AC Load
106
107
108
Calorific value
Efficiency
Fuel saved
(kcal/kg)
(%)
(kg/annum)
Firewood
4708
17.3
2127
Kerosene
9122
50.0
380
Liquified Petroleum
Gas
(LPG)
10882
60.0
265
Charcoal
6940
28.0
891
Diesel
10004
75.0
231
Electricity
90.0
~1500 kWh
Just think of what you would gain by using a solar water heater. Well you would
support technologies so good for our environment and gain some thing in
monetary terms too.
109
Applications like these are met at various temperatures These are also known as heat
grades. Table 6.2 gives such temperature values along with a list of applications as under:
Table 6.2: Heat grades and applications
S.No. Heat
grade
Temperature
range
Possible Applications
1.
Low
grade
<100C
Water heating
Air heating
Drying
Refrigeration
Space heating
Desalination
2.
Medium
grade
100-300C
Cooking
Steam generation for industrial applications
Drying
Refrigeration
Power generation
Water desalination
Water pumping
3.
High
Grade
>300C
Power generation
Today, a large number of solar thermal products/systems are available in the marketplace.
Out of these, solar water heaters and solar cookers are the most widely used systems so far.
Given below is a brief introduction of these applications.
Is it not like getting worry free by handing over our every heat energy need to the care of
mighty Sun? Only thing is that we need to give it a chance to do that for at least one of our
most important needs.
The most common use for solar thermal technology is for domestic water heating.
Hundreds of thousands of domestic hot water systems are in use worldwide.
Solar cooking
A solar cooker is a device which cooks food on solar energy. The most popular solar cooker
in India is a box type cooker. There is another type of solar cooker which uses a reflector. It
is designed to concentrate (i.e. focus) the incoming solar radiation over a small area. This
type of cooker is able to yield higher temperatures.
110
Solar drying
There are a number of agricultural and forest products around us. These contain some
moisture i.e. water, which needs to be dried up. Using sun for drying of wood for example
has been quite an old application. It is now possible to dry these things efficiently using
solar dryers. These dryers are of two main types mainly i.e. passive means radiative (used
to dry fruits, cash crops and fish etc.) and forced convection (i.e.using fan) dryers.
Solar desalination
Solar energy can be used to change the salty or sea water into clean water. Pure water thus
obtained can very well find use in batteries, hospitals, laboratories and schools etc. In this
process, water is first evaporated. It is then condensed as pure water.
Solar pasteurization
Water may not be always safe to drink. So, it is heated to a temperature of around 65C for
nearly 6 minutes. This way, germs and insects are removed.
Space heating, cooling and passive construction
Solar energy can be used for heating of buildings too. These buildings are generally located
in the high altitude areas and face cold months. Heating can be done either by liquid or air
collectors. It is also possible to use solar energy for space cooling applications. The passive
construction helps to get maximum possible sunlight inside a building. The simple idea is to
keep a building cool in summer and warm in winter. It is thus possible to save up to 90% of
the energy otherwise needed to cool or heat a building.
111
Key uses
Domestic
Institutional (educational
institutions etc.)
Industrial
Solar collector is the basic element of a solar thermal system. It makes the above uses
possible. The heart of a thermal system is commonly known as solar collector. It is made of
headers (i.e. a pipe that runs across the edge of a solar collector), risers (i.e. the pipes that
distribute the heat transfer liquid across an absorber) and absorber fins (made out of
copper). The solar radiation is absorbed by the fins. It is then changed into a usable form of
thermal energy by heating the water within it. This heated water is stored inside the solar
tank.
Greenhouse effect
To some there are two meanings of the Greenhouse effect. There is a naturally occurring
greenhouse effect, which keeps the earths climate warm and worth living too. The other
one is the manmade greenhouse effect. It is basically an increase in the earths natural
greenhouse effect due to addition of greenhouses gases like carbon dioxide. These type of
gases mainly come from the burning of fossil fuels like coal, petroleum and natural gas.
112
A black surface absorbs heat on facing sun. The same is true of a car parked out in the sun.
Inside of the car gets quite hot, if, windows are left closed. The solar radiation passes
through the glass window of the car, but can not come out of it. The simple reason is that it
gets trapped inside. This heat trapping process is yet another common example of
Greenhouse effect.
Absorption of radiation
A black body happens to be the most efficient absorber of radiation. That is why a black
painted surface is used for this specific purpose in a solar thermal device. Solar radiations
of different wavelengths get converted into heat. In general, a working fluid say water is in
a close contact with the blackened surface. This way it can take this heat. Such a temperature
increase can be put to use for heating water, distillation, cooking and for drying too. The
temperature that is obtained in this manner will mainly depend on the following few things:
mass of the working fluid
heat absorbing capacity
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It is quite possible to obtain a high efficiency of conversion for the solar thermal devices.
Solar PV devices in contrast generally have modest conversion efficiencies.
Principle of reflection
Just think of the ordinary light rays. These change their direction when they reflect off a
surface. So reflection takes place when light changes direction as a result of bouncing off a
surface like the commonly used mirror. The rays move from one transparent medium to the
other. The simple law of reflection states that on reflection from a smooth surface, the angle
of the reflected ray is equal to the angle of incident ray. Thus this principle can be utilized
for concentrating solar radiation at a point or on an area in solar thermal collector systems.
Conduction
It is one of the three routes in which heat is either transferred or simply lost.It basically takes
place due to the temperature difference between two surfaces of the same material. Heat
transfer is directly through the material
Convection
It is the second form of heat transfer. Within this, liquid, or gas such as air is heated. It then
moves away from the source of heat and replaced by a cooler material. Take for example the
natural convection. Here the heated fluid becomes lighter on account of expansion. It then
moves away from the source and replaced by heavier cooler fluid. Now let us take the case of
forced convection. In this case, the fluid is driven by some external force. It could well be a
fan, pump or simply wind. It is then heated by coming in contact with the source of heat.
Following which, it carries the heat away under the influence of an external force.
Radiation
It is regarded as the third route of heat transfer or loss. Radiation takes place via transfer of
energy through an empty space. Remember the amount of heat transferred is proportional to
the difference between the fourth power of absolute temperature of the radiating surface and
the radiation receiving surface.
114
sheet or fibre-glass cladding. Special attention must be paid to insulation if the hot water
piping is inside the brick walls. The loss of heat to wall from pipe in the wall is many times
more than the loss of heat from exposed pipe to air. Cold water piping and hot water piping
must be kept separate
Table 6.4 below compares different types of heat insulation materials.
Table 6.4: Basic properties of insulating materials
Insulting
Density
Material
Thermal
Moisture
Conductivity
absorption
Expanded Polystyrene 15
15
0.040
medium
Expanded Polystyrene 30
30
0.037
medium
Extruded Polystyrene
32
0.27
medium
36
0.018
low
Phenolic foam
32
0.027
low
Cellular foam
125
0.41
low
Mineral wool
24
0.045
very high
Just think of when the air outside is cold; you may want to care for your skin by
wearing a set of warm clothes. The simple idea is to keep the cold out and the body
warmth intact. A thermal insulation in a solar water heater does almost similar by not
allowing the warmth of hot water to go away.
Heat pipe
Heat pipe is commonly made of copper material. It is hollow with the space inside
evacuated. There is a small amount of purified water and some special additive inside the
pipe. The simple idea is to change the state of such a liquid i.e. from a liquid state to a
vapour. The heat pipes used in the solar collectors have a boiling point of only 300C . So,
when the heat pipe is heated above this temperature, the water vaporises. This vapour
moves up quickly to the top of a heat pipe transferring heat. As this heat is lost at the top,
the vapour condenses i.e. becomes a liquid. It then comes back to the bottom of the heat
pipe thus beginning the process once again.
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Technology
FPC/ETC
Solar Concentrator
FPC/ETC
116
Common Applications
Water heating
Air heating (drying, space heating)
Cooking
Desalination etc.
However, out of these many applications, the present course curriculum will deal with solar
water heating and solar cooking technology uses only.
117
absorber plate
fluid conducting pipes (consisting of bottom and top headers and riser tubes)
glass cover
insulation
casing or a collector box
A solar water heater of 100 liter per day capacity can easily meet the hot water needs of 4-5
persons. It can pay for itself in 3-4 years when no electricity is used for water heating. That is
not all, as it can even stop the emission of 1.5 tonnes of carbon dioxide per year. Still better is
to know that it enjoys a long life of 15-20 years.
The collector box is in the form of an open top, shallow box. It has insulting fibre glass at the
bottom and sides. Within the box lies the absorber plate. Above it like a window is the glass
plate cover.
Why use solar water heaters
100 LPD SWH can replace an electric geyser for residential use and thus save 1500
units of electricity annually
SWHs of 100 litres capacity each can contribute to a peak load shaving of 1 MW
SWH of 100 litres capacity can prevent emission of 1.5 tonnes of CO2 per year
118
119
Left to its own, a solar water heater works quite silently rather going un-noticed. That
is the beauty of this system, which does not seek your presence. It sits pretty on just a
small
space of
2 sq.m.,
while
leaving untouched
rest of the rooftop space for some
7.3
Simple
idea
of an
Evacuated
tube collector
other uses of course.
120
Advantages offered:
it is simpler in design and cheaper too
it is being produced much more widely
its operation and maintenance needs are simple
Disadvantages:
heat loss takes place within the frame by convection
it has a low efficiency
it needs more panel area to collect the heat
does not work efficiently in cold climates
Now there is one more solar collector technology at work. It is commonly known as the
Evacuated Tube Collector (ETC) or simply vacuum tube technology. This new design
overcomes the above mentioned disadvantages of a flat plate collector.
121
within the tank sinks into the tube. It gets heated and moves up again. In this way,
convection current takes place. It heats all the water in the system very fast.
Glass tube is formed by fusing two co-axial glass tubes at both the ends. Air between
the two glass tubes is evacuated to create vacuum which works as an insulation.
Outer surface of inner tube in the evacuated tube collector forms the collector area
Absorber coating shall be applied on the outer walls of inner tube selectively to
absorb the solar radiation to collect energy and to convert light energy into heat
energy.
formation of scale is faster in FPC based system than in ETC based system
122
Table 7.2 below gives a quick comparison between a flat plate collector and an evacuated
tube collector.
Table 7.2: Comparison between a flat plate collector and evacuated tube collector
Flat Plate Collector (FPC)
Pumps
Key task of the pump is to push/circulate water through the absorbers in a collector. This
type of function is not needed in the simplest design i.e. flat plate collector.
123
Controls
Some kind of control features are needed in such systems as use pumps or backup heaters.
Thermostat with the help of switches controls the pump operation etc. Minimum and
maximum water level cut-off functions are also used in some designs.
Heat Exchangers
The type of water that is to be heated may not always be clean. It could be dirty or contain
some chemicals or may even lead to scale deposition. It being so, the collector water is
contained in a close loop. This water on getting heated heats up the used water via heat
exchanger. Such an exchanger could be made of ordinary steel, stainless steel or even
copper.
Stands
The collectors are placed outside to face the sun all day long. These are mounted on the
stands generally made of angle iron.
Backup heaters
Sunshine may not be available always. To take care of such days, an electric heater is used.
It could well be kept inside the main hot water storage tank.
Sacrificial anode
It is a simple device which prevents the stainless steel tank from galvanic corrosion by being
more reactive to hard water.
Other components
There are a few more components within a solar water heater such as:
pressure and temperature gauges
air vents
cold water tank
gate valves for adjusting flows
water flow meter
solenoid valve in cold water line
124
Thermosiphon
In the thermosiphon system, the water circulates from the collector to storage tank by
natural convection and gravity. The water gets heated in the collector so long as the
absorber keeps collecting heat. It then moves to the storage tank which is placed slightly
above. Figure 7.4 shows a basic design of a thermosiphon type solar water heating system.
The cold water at the bottom of the storage tank runs into the collector to replace the hot
water discharged into the tank. Brighter the sunshine, quicker will be the circulation.
Advantages:
simple to operate
easy to maintain
125
somewhat cheaper
Disadvantages:
To sum it up, a solar water heater offers the following few important advantages:
saves up to 1500 units of electricity per year
easy to use
near zero maintenance
safe to use
long life
pollution free
These benefits are now increasing the use of solar water heaters in the below mentioned
areas:
homes, hostels, hotels, guesthouses & hospitals
industrial process heating in food processing, textiles, dyeing, metal plating,
pharmaceutical etc
milk diaries & chilling plants
126
Following few are the most important steps to handle the hot water problem:
Water softener for entire building water treatment
Special designed heat exchanger system
Inline water softeners like magnetic devices
Use of vacuum tube collectors (Caution generally for low pressure only)
127
for larger tank sizes, the height requirement may go up to 10 feet or higher
for systems of size larger than 3000 liters per day, customer may choose forced
circulation system.
these systems may also be used for smaller than 3000 litres/day capacity also where
thermo-siphon system can not be used due to limitation of height of the cold water
tank.
128
129
and cooking) is the steam solar cooker. This type of cooker is better known as Shafler (after
its inventor) dish.
It is possible to make the inner box from galvanized iron, mild steel or aluminium sheet.
Black paint is used both on the sides and bottom of the box. The space between the outer
box and the inside box is packed with insulating materials like glass wool or thermoCole
etc. A mirror is in place to increase the solar radiation input on the absorber surface. The
cooking containers have tight covers. These are commonly made of aluminium or stainless
steel material. Such containers are painted dull black on the outer surface. The simple idea is
to make them absorb the solar radiation directly. Following few are the most important
parts of a solar cooker:
outer body
inner cooking box/tray
insulation
double glass lid
mirror
cooking pots
side window
materials
G.I. sheet, Aluminium sheet, M.S. Channels, Glass, Mirror ,Asbestos fibre Sheet,
Glass wool, Caster wheel, Black board paint, Hinge, lock, Screws and other
miscellaneous items.
Hand saw, Hand shear, Portable drilling machine, Hammer, Screwdriver, Pliers,
Measuring tape Painting brush etc
The surface of the cooking box exposed to solar radiation and the outer surfaces of
cooking pots should always be kept coated with black paint/selective coating
material.
131
There should be no leakage of hot air through the joints or any other portion of the
cooker
The lid with double glass system should be perfectly sealed so that water vapour, do
not enter into the space between the glass surfaces and get condensed reducing the
transmission of sunlight through the lid
Gasket and mirror should be replaced as and when needed
In all box type solar cooker offers a huge market potential estimated at around 97
million units. As against this, less than a million units have been deployed so far
in India
Disadvantages
1. it is a slow way of cooking food
2. it can not be used during the cloudy days
132
can be tested. This is mainly required to ensure a high degree of field performance
reliability. It is also for the reason to discourage the manufacture cum use of poor quality
devices. The Bureau of Indian Standards (BIS) is an accredited body for publishing the test
standards. The Solar Energy Centre (SEC) of the Ministry of New and Renewable Energy
(MNRE) is an apex testing cum certification facility for the solar thermal devices too. BIS
has so far published the following few standards in respect of the box type solar cookers.
IS 13429 (Part 2):2000, Solar cooker- Box type - Specification, Part 2 -Components.
IS 13429 (Part 3):2000, Solar cooker- Box type - Specification, Part 3 -Test methods
Two tests associated with IS 13429 are known as the stagnation test and full load
test. Accordingly, there are two performance parameters available for testing of this
specific cooker. These are commonly known as Figures of merit FI and F2 and whose
respective values should not lie below 0.12 and 0.40. Evaluation of FI and F2
involves the measurement of following few parameters:
Solar irradiance
temperature of cooking tray
water temperature
ambient air temperature
133
134
large families and small institutions can readily benefit from its simple usage
potential to save around 10 LPG cylinders per year based on an effective use
proven technology in extreme climates actively promoted by MNRE
Following few are the most important components of a solar steam cooking system:
parabolic concentrators
central sun tracking system
steam header pipe
solar energy receivers
135
136
Key properties of this type of glass also known as toughened glass are as under:
low iron content (58 parts per million)
anti-reflection coating treatment-i.e. decreases the reflection of sunlight
high transmittance (>96%) i.e. allows maximum possible sunlight to pass through it
The main applications of the tempered glass are both for the solar photovoltaic and solar
thermal device applications. Simply put, it is used as the front surface cover of a solar
module besides that of a solar collector.
8.3.1 Painting of solar cooker and metal pot i.e. heat absorption,
reflection
The colour of a material has a very great effect on the thermal properties of a material. It
comes into play when the material is exposed to the solar radiation i.e. heat. The metal pots
in a box type solar cooker for example are normally painted black. Remember the paint used
should not be toxic (i.e.. a toxic paint may give off fumes even at the room temperature.
Just think of why you like the light coloured dresses in summer than the dark ones.
Everything on which the sunlight falls absorbs heat from it. However, black surfaces
absorb heat better than the light coloured and white surfaces. The same principle is
at work in case of a solar cooker too.
That means it would give off even more fumes at cooking temperatures. It is also important
that paints on pots are kept thin. The simple reason is that thick paints may lead to some
insulation.
137
138
Q. How long will the water heated by solar energy remain hot in the tank?
A. Hot water is generally stored in an insulated water tank. Thus water can remain hot
without any major change in temperature for around 24 hours.
139
140
Q 4. Calculate the savings in electricity consumption per day using the above data. Assume
the ambient temperature to be 25C
Steps:
Savings in electrical consumption per day=Capacity (LPD) x (temperature of hot waterambient
Temperature/(860 x efficiency of electrical heater)
=100 x (60-25)/(860 x 0.8)
=5.08 kWh/day
=5 kWh/day
Q 5. Calculate the heat available for a solar water system of 200 LPD capacity taking a
collector area of 4 sq. m. Consider the hot water temperature requirement as 600C and
ambient temperature as 250C
Steps:
Heat available= Capacity (LPD) x (temperature of hot water-ambient Temperature/(860 x
efficiency of electrical heater)
=200 x (60-25)/(860 x 0.8)
=10.08 kWh/day
=10 kWh/day
Thus it is quite clear that as capacity of a solar water heater doubles, so does the heat
available
Q.6 Calculate the cost of electricity saved at Rs. 5 per unit taking into account the electricity
saving under Q.No. 4 above
Steps:
Take number of solar days in a year as 300 for a good sunny location like Delhi
Per unit cost of conventional power= Rs. 5 (for a location like Gurgaon)
Cost of electricity saved = Heat available x no.of days x cost per unit
= 10 x 300 x 5
= Rs. 15000/Q.7 Calculate the pay back period for a solar water heating system of 200 LPD capacity
A. Assume the cost of a 200 LPD system as Rs. 39000/- &
Per unit cost of electricity=Rs. 5
Pay back period= Cost of the system/Cost of electricity saved
= 39000/15000
= ~ 2.6 years
So a user can get back the cost of a 200 LPD solar water heater in less than 3 years.
Q.8 Calculate the maximum temperature of the water that can be obtained in case of a 500
LPD solar water heater. This is nearly equivalent to 10 m2 of the collector area. Assume that
it has to give hot water at 600C by supplementing/replacing the existing electric geysers
141
Steps
Average solar insolation available = 5.5 kWh/m2
Temperature of hot water= 600C
Ambient temperature= 250C
Cost of electricity= Rs. 5
Efficiency of electrical heater=80%
Efficiency of solar hot water system=50%
Hot water requirement for a small hostel=500 LPD
Life of the system=15 years
Heat available = 5.5 x 10 x 860 x 0.5 kcal/day
=23650 kcal/day
Maximum temperature that can be
obtained= (23650/500) + 250C
= 72.30C
Q.9 Calculate the maximum quantity of water that can be obtained at 600C using the
assumptive data presented in Q. 8 above
Steps
Maximum quantity of water that can be obtained at 600 C= Heat available /Temperature of
hot water-ambient temperature)
= 23650/(60-25)
=675. 71 LPD
Q.10 Calculate the focal length of a parabolic dish solar cooker
Step
Use the following formulae
F= R2/4D
Here F is the focal length
D is the depth of dish
R is the radius of its rim
a) Depth of the reflector measured along the axis of paraboloid from its vertex to the plane
of rim=1.8478 times the focal length
b) Radius of the rim is equal to 2.7187 times the focal length
142
Q.11 Calculate the amount of energy that must be added to heat water from 500 F F (i. e.
100C) to 1200F ( i.e. 49 0C)
Steps
Use the following formulae to calculate the energy needed
Q=C* m* (Tout-Tin)
Here
Q amount of heat added in joules
C= specific heat of water i.e. 4.18 J/gm x0C
m= mass of water
Tout= outlet water temperature (490C)
Tin=inlet water temperature
Use the density of water=1g/cm3
( 1gallon=3785 cm3=3785g
Thus Q=(4.18)*3785 x (49-10)
=632852 joules
Remember there are 1.055 x108 joules per therm=0.006 therms
Remember there are 3.600 x 106 joules per kWh
Thus 6, 30,000 J=0.18 kWh
Tables: Symbols and sign convention for sun and related angles
Quantity
Altitude
Surface tilt
Symbol
Azimuth (of
surface)
Declination
Incidence (on
surface)
Zenith angle
Latitude
Hour angle
Reflection (from
R
surface)
Solar radiation
Global irradiance or
solar flux density
Beam irradiance
Diffuse irradiance
Global irradiation
Beam irradiation
Diffuse irradiation
Atmospheric radiation
Irradiation
,i
z
W m-2
Gb
Gd
H
Hb
Hd
W m-2
W m-2
J m-2
J m-2
J m-2
W m-2
143
To get
BTU (British Thermal Unit)
BTU/Hr
BTU/(Hr)(sq.ft.)
BTU/(sq.ft.)
BTU/(Hr.) (sq.ft.)
BTU/Hr.)/(sq.ft.)
BTU/(Hr)/(sq.ft.)/Deg.F
Kilojoules
Kilocalories (kcal)
BTU
Horsepower-hours
Watt-hours
Watt-hours
Watt-hours
kWh
144
Drawing
145
146
147
148
149
150
151
Introduction
A solar Photovoltaic system works without making any noise or pollution.. This is because
it has no moving parts at all. The power producing part i.e. the module is the most
important part of this system. So, it makes sense to study this component in all possible
ways. The practical units for this solar photovoltaic course curriculum mainly deal with the
following:
physical and Technical inspection of a solar module
physical and Technical inspection of a battery
technical inspection of CFL, Charge Controller, Inverter, LED driver etc.
Key Conclusions:
Knowing the Physical & Technical Specifications
152
Design
A solar module is produced in a factory. It is generally made of single crystal and
polycrystalline solar cells. These cells are encapsulated using stabilized polymer i.e.
Ethylene Vinyl Acetate (EVA). The back cover of the module is made of Tedlar-polystertedlar. The glass through which the sunlight passes is made of toughened glass. The frame
is made of anodized aluminum to mount the modules easily.
Specifications
A module manufacturer normally gives information both on the physical and technical
specifications. These are generally called the module ratings. It is very important to know
these specifications before doing some simple experiments on a solar module.
Table 1: Physical observations
Parameter
Unit
Number of Cells
Dimensions (lengthxwidthxthickness)
Weight
10W
37W
50W
Nos.
mm
kg
Symbol
Unit of
measurement
Voc
Isc
Pmax
V
A
Watt
Pmin
Watt
Rated Current
Rated Voltage
IMpp
VMPP
A
V
10W
37W
50W
* Under Standard Test Conditions (Irradiance 1000 W/m2, Cell temperature 25 degrees C, Air Mass 1.5)
Environmental rating
A module is placed outdoors. So, it gets exposed to all types of weather like for example
Sun, rain, snow, dust storm etc. The module should be able to put up with these things. The
module manufacturer gives the following type of ratings:
153
Unit
45C 2
-40C to + 85C
85%
Key Conclusions:
Connecting the modules in series and parallel arrangement
A solar module has two terminals. These are marked just like the positive and negative ends
in an ordinary battery. The red colour wire is generally for the positive side and a black wire
is for the negative side. Small systems like a home lighting system generally run on a 12 V
battery. However, some other appliances may be working on 24 V. Simply put, two
modules of 12 V are then to be joined in series. In a series connection, voltages add up
keeping the current same as that for a single module. The opposite happens in a parallel
connection of modules. Here the currents add up keeping the voltage same as that for a
single module. It is interesting to note here that a standard battery is 12 V. That is why, if
you use a solar module, 12 V would be the most common voltage. However, that does not
mean that there can not be a different voltage. One can easily combine several modules to
get a higher output voltage like 24V, 48 V etc., if, needed.
Try the following few steps
Items needed:
Solar Modules (37 Wp-2 nos.)
Multimeter
Connecting wires
Connecting pins
Step-by-step method
For series combination of modules:
1. Connect the positive terminal of one module to the negative of the second module or
vice versa .
2. Now measure the current and voltage values at the remaining two terminals of solar
module using a multimeter as shown below
3. Note down these values
154
Figure 1 :
4. Connect the positive of one module to the positive end of the second
5. Connect the negative of one module to the negative end of the second module
6. Repeat the measurement of current and voltage at the two ends with a multimeter
7. Note down these values
8. Mark up the difference in values of I and V under a) series and b) parallel modes
Data Table:
Module
S. NO
Module
Individual
Individual
Series Connected
Parallel connected
Capacity
Voltage
(V)
Voltage
Current
Voltage
(Wp)
Current
(A)
1
2
3
4
155
Current
Key Conclusions:
Measuring the Open Circuit Voltage and Short Circuit Current of a Module
A solar module is expected to run a load. Be it a lantern or a home lighting system. So, when
the load is being run, voltage of the module will decrease. Now if, no load is being run, the
voltage will not decrease. Instead, it will be the maximum voltage that a module can
produce under a clear sun. This value of voltage (minus any load) is known as the Open
circuit voltage or simply Voc. In the same way, Short circuit current (Isc) is the maximum
current than a module can produce without any load present. Voc is measured when the
resistance is set at infinity (open circuit current=zero). Isc is measured when the resistance is
set at zero (Voltage=zero).
Items needed:
Solar Module
Multimeter
Connecting pins
Step by Step method
1. Take the module out in the Sun
2. Do not connect the module to any load
3. Set the multimeter in the current mode
4. Touch the probes of the voltmeter directly to the modules positive and negative
terminals
5. Record the voltage on the multimeter (that is set in voltage mode, thus behaving
like a voltmeter)
6. Change the position of probes in the multimeter from voltage mode to current mode
7. Now touch the probes of ammeter (multimeter in current mode) directly to the
modules positive and negative terminals
8. Record the current
Note: Dont measure the voltage while multimeter is set in current mode .
156
Key Conclusions:
Knowing the values of minimum and maximum values for a resistor
The Current-Voltage (I-V) plot of a solar module gives knowledge of various important
parameters. In general, variable resistance method is used for the purpose. As the resistance
is increased from zero to infinity, current and voltage are measured. The minimum and
maximum resistances required from the variable resistor are:
Step-by-step method
1. Make a note of the Voc and Isc measured in the last activity
2. Calculate the Rmin value by using the formulae- Rmin= Voc/4Isc
3. Calculate the Rmax value by using the formulae-Rmx=4 Voc/Isc
Key Conclusions:
Plotting the Current-Voltage characteristics of a Solar Module
The current-voltage (I-V) of a PV module is based under the Standard Test Conditions
(STC). The STC condition on a clear day is taken as 1000 watts of solar energy per square
metre (1000 W/m2 or 1 kW/m2). It is also known as one sun or peak sun. Current
expressed in amperes is plotted on the Y-axis and Voltage in volts is shown on the X-axis.
The power available from a module at any point on the curve is just a simple product of
current and voltage at that point. It is expressed in terms of Watts (W= VxA). There is a
point on the knee of the I-V curve, where the maximum power output is present.
Items needed:
Solar Module
Voltmeter (multimeter in voltage mode)
Ammeter (multimeter in current mode)
Variable resistor
Connecting wires
Pyranometer/Suryamapi
Surface temperature thermometer
Measurement conditions
1. I-V curves should generally be measured under clear sky and within two hours of
solar noon to obtain irradiance values near the standard test condition irradiance of
1000 W/m2
2. Cell temperature should be allowed to stablise before being measured
157
3. During the measurement, the I-V curve, data points should be taken as quickly as
practical to minimize the effect of a change in the irradiance level or a change in the
cell temperature during the test period
Step-by-step method
1. wire the circuit as shown in the figure
2. tilt the module towards the sun to maximize irradiance
3. record the Voc and Isc values
4. on the data sheet, record the irradiance reading and cell temperature
5. adjust Rvar to zero ohms or short-circuit (voltage becomes zero)
6. record the short circuit current IsC
7. increase the amount of resistance, Rvar, until the voltage reading is approximately
th the estimated Voc. (for example, if, the estimated Voc is 24 volts, adjust Rvar until
the voltmeter reads 6 V)
8. record the current and voltage readings
9. increase Rav until the voltage is increased by approximately 2 V
10. record the current and voltage readings
11. repeat steps 8&9 until the maximum Rvar is reached or the current becomes zero
12. Disconnect Rvar from the test circuit (current becomes zero)
13. Plot the current and voltage values thus recorded
158
Current
(amperes)
Isc=
Voc=
Power
(Watts)
Pmax
(Watts)
Vmp
(Volts)
Imp
(amperes)
Key Conclusions:
Plotting Current-Voltage characteristics at different values of solar Irrdiance
The I-V characteristic of a solar module depends on the solar irradiance (sunlight) incident
upon the module. It also depends on the operating temperature of the cells. That is why
these parameters should also be measured. Sunlight changes throughout the day. It has the
maximum value at noon time. Each PV module has a characteristic I-V output for a specific
cell temperature and irradiance level.
159
Items needed:
Solar Module
Voltmeter
Ammetre
Variable resistor
Connecting wires
Pyranometer/Suryamapi
Surface temperature thermometer
Step-by-step procedure
1. wire the circuit as shown in the figure
2. tilt the module towards the sun to maximize irradiance
3. record the irradiance reading and cell temperature, for the tilt of module
4. adjust Rvar to zero ohms or short-circuit (voltage becomes zero)
5. record the short circuit current IsC
6. increase the amount of resistance, Rvar, until the voltage reading is approximately
th the estimated Voc. For example, if, the estimated Voc is 24 volts, adjust Rvar until
the voltmeter reads 6 V
7. keep the pyranometer sensor on the module surface in the path of sun
8. note down the value of solar radiation (in W/m2) or Mw/cm2
9. record the current and voltage readings
10. increase Rav until the voltage is increased by approximately 2 V
11. record the current and voltage readings against different values of solar radiation
12. repeat steps 8&9 until the maximum Rvar is reached or the current becomes zero
13. disconnect Rvar from the test circuit (current becomes zero)
14. plot the current and voltage values thus recorded on a graph paper
160
Voltage (V)
Current
(amperes)
Power
(Watts)
(W/m2)
Pmax
(Watts)
Vmp
(Volts)
Imp
(amperes)
Key Conclusions:
Measuring the effect of Cell temperature on the Current-Voltage characteristics
As cell temperature increases, current increases slightly. However, voltage decreases
more . The net result is reduction in power. Cell temperature is measured by placing a
surface temperature probe or sensor at the back surface of the module.
161
Items needed:
Solar Module
Voltmeter (multimeter in voltage mode)
Ammetre (multimeter in current mode)
Variable resistor
Connecting wires
Pyranometer/Suryamapi
Surface temperature thermometer
Step-by-step method
1. Wire the circuit as shown in the figure
2. Tilt the module towards the sun to maximize irradiance
3. On the data sheet, record the irradiance reading and cell temperature, for the tilt of
module
4. Adjust Rvar to zero ohms or short-circuit (voltage becomes zero)
5. Record the short circuit current IsC
6. Increase the amount of resistance, Rvar, until the voltage reading is approximately
th the estimated Voc. For example, if, the estimated Voc is 24 volts, adjust Rvar until
the voltmeter reads 6 V
7. Keep the temperature probe at the back surface of the module
8. Note down the temperature
9. Record the current and voltage readings
10. Increase Rav until the voltage is increased by approximately 2 V
11. Record the current and voltage readings against different values of temperature
12. Repeat steps 8&9 until the maximum Rvar is reached or the current becomes zero
13. Disconnect Rvar from the test circuit (current becomes zero)
14. Plot the current and voltage values thus recorded on a graph paper
15. Note the power output values corresponding to Voc and Isc
162
Voltage (V)
Current
(amperes)
Power
(Watts)
(degrees C)
Pmax
(Watts)
Vmp
(Volts)
Imp
(amperes)
Key Conclusions:
Basic Introduction and Testing of Electronic components
Most of the solar photovoltaic systems use charge controllers. These circuits are fabricated
on the Printed Circuit Boards or simply the PCB. The PCB itself has several components
(like resistors, capacitors, transistors, diodes and integrated circuits etc.) joined together. The
ratings or the values of these components change from one solar device application to the
other. However, their working principle remains more or less the same. This section deals
with the simple testing methods of these components as under
163
Resistors
Resistance is just like a hole in a bucket of water. More water will come out of the bucket if
a hole is big. Less water will come out if, the hole is small. The simple reason is that a small
hole will resist the flow of water more than a large one. Thus, a material with a high
electrical resistance may be thought of as a small hole in a bucket. Metals generally have a
low resistivity allowing the electricity to pass through them. Different metals have different
resistivity. Take for example copper. It has a low resistivity in direct comparison to iron
with a high resistivity. That is why copper wire is used in the wiring cables. The simple unit
for measurement of resistivity is Ohm. The resistance of a given material depends upon its
length (l) and the area of cross-section (a). Increase in the length of wire increases the
resistance. While as, increase in thickness of wire decreases the resistance of the wire.
Band 1
value
Band 2
value
Band 3
value
Multiplier value
for Band 3
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
1
1
2
3
4
5
6
1
10
100
1000
10000
100000
10,00,000
100, 00,000
100,000,000
1000,000,000
164
Band 4
Value Tolerance
20%
10%
5%
Activity: Calculate the R-value of various resistors on the basis of above Table
Testing of a Resistor
It is basically related to its being open. If a resistor becomes open, then its resistance
increases very much. That also means it will pass no current. A simple multimeter can check
a resistor. If, it is open, then it shows a resistance much higher than its rated value. Do not
touch the lead of a multimeter while checking the resistance value
Activity: Measure the R value of various resistors using a multimeter
Capacitor
A capacitor is basically used to store electricity in the form of an electrical charge. The basic
formula related to the capacitors is C=QV (Q is the amount of charge, V is the voltage).
Capacitance is measured in Farads. The most common types of capacitors are:
air
mica
paper
ceramic
electrolytic
Digit A
0
1
2
3
4
5
6
7
8
9
Digit B
0
1
2
3
4
5
6
7
8
9
Multiplier D
Tolerance (T)
Tolerance (T)
>10 pf
<10 pf
x1
x10
X100
X1000
X10000
X100000
X1000000
20%
1%
2%
3%
4%
5%
2.0
0.1%
0.25
3%
4%
0.5%
x0.01
X0.1
X 0.1
0.01
+80%, -20%
10%
5%
10%
1.0
Testing of a capacitor
A simple ohm meter can test a capacitor easily. Choose megaohm range while testing a
capacitor.
Put across the lead of ohm meter across the two leads of the capacitor. A good capacitor
would show less resistance in the beginning and will go up by and by. If, ohmmeter reading
shows a zero value, then it means it is short circuited. In case, the ohm meter needle shows
165
the high resistance value very suddenly, it means capacitor is in an open circuit condition.
This type of testing is done only for electrolytic capacitors. Rests of the capacitors are
checked by a capacitor meter.
Diodes
These are normally made of semi conducting materials like Germanium and Silicon. n-type
and p-type diodes are the most common ones. A diode is generally used to make the
current flow in one direction only. It is often used between a battery and solar module. It
allows a battery to get charged by a module during the day. However, it stops the current
from flowing from battery to the module at night. The other important use of diode is to
change AC into DC.
Figure 2 :
Diode symbolBrief idea about wire sizing
Electric current is carried through the wires. It is very important to choose a right size of the
wire. Such a size is normally given in terms of mm2. This measurement is in fact the crosssectional area of the wire. The larger that area the higher the current it can carry. Now think
if, a wire size used is small for the amount of current passing through it, it can result in:
a) overheating
b) fire
c) risk to the human life
166
Table below gives a sample idea about the PVC insulated multistranded copper conductor
as under:
S.No.
Nominal
Area
Number
and
Current Carrying
(sq.mm.)
Size
Wire
1.
1.00
14/0.3 mm
11.0
2.
1.50
22/0.3mm
13.0
3.
2.00
28/0.3 mm
15.0
4.
2.50
36/0.3mm
18.0
5.
4.00
56/0.3mm
24.0
Remarks
Capacity
of
(amps)
It is quite clear that more the nominal area,
higher is the current carrying capacity of the wire
Remember household circuits are often wired with two different types of wires i.e. 12 gauge
and 14-gauge. The 12 gauge wire has a diameter of 1/12 inch and the 14-gauge wire has a
diameter of 1/14 inch. Thus a 12-gauge wire is wider than a 14-gauge wire. It simply means
that a 1 2 gauge wire will allow a larger current to pass through it. It is just like water
running out of a wide pipe. The 12-gauge wire is used in such circuits, as are protected by
20-amp fuses and circuit breakers. While as the 14-gauge wire finds use in such circuits, as
are protected by 15 amp fuse and circuit breakers. The simple reason is that a 12-gauge wire
offers lesser resistance to flow of an electric current than a 14-gauge wire.
Note, in an electrical system, the wire should not be sized with voltagr drops exceeding 3%.
For a 12V system, the maximum voltage drop should be less than 12 (V)x 3%=0.36 V. There
are standard tables available for the purpose of choosing a right wire size.
Testing of Diodes
A diode has a cathode (negative) and an anode (positive). The positive probe of the ohm
meter is put on the cathode and negative probe of the ohm meter on the anode. The needle
of the meter shows a deflection thus indicating resistance. Reverse these connections now.
No such deflection is noticed.
Checking of Zener diode
A zener diode shows just the opposite reading in comparison to the other diode types. This
simply means that when the positive probe of the ohm meter is put on the cathode and
negative probe on the anode, there is no deflection as such. The reverse is also true. It
simply happens because cathode is positive in a zener diode and anode is negative.
Transistor
167
It is an electronic device which controls the flow of an electric current. It has got at least
three electrodes. Transistor is made of p and n type materials. It has got a P-n-p junction.
The first part i.e. the base acts as an emitter thus producing charge. The second part is
known as collector. It collects the charge emitted. In between these two junctions is base. It
can either be a p-type or a n-type. The base controls the amount of charge in the collector. A
transistor is mainly equivalent to two diodes. The one on the left side is known as emitter
base diode and the one on the right side is base collector diode. It is possible to combine P-N
and N-P junctions in two ways. A transistor is basically of two different types namely:
a) N-P-N
b) P-NP
Figure 3 :
Transistor testing
NPN
take an ohm metrer. Place the negative probe of the metre on the base and
positive probe on the collector.
the needle of metre will show some deflection thus indicating resistance
remove the positive probe from the collector and place it on the emitter
it will show the deflection thus indicating some resistance
now place the positive probe on the base and negative probe on the collector
there will be no deflection of the needle
now keep the positive probe on collector, negative probe on emitter followed up
by poisitive probe on the emitter and negative probe on the collector
in both these cases, no deflection of the needle will take place
PNP
keep the negative probe of an ohm metre on the base
keep the positive probe of an ohm metre on the collector
notice if, there is any delection- there is none
now keep the positive probe on the base and negative probe on the collector
and notice if, there is any electric current in the process
168
Transformer
A simple single phase transformer is made of two electrical conductors. These are
commonly known as the primary coil and secondary coil. The primary is fed with a varying
alternating electric current. It then creates a varying magnetic field around the coil. In
practical transformers, the primary and secondary conductors are coils of wire usually
copper. The high current-low voltage windings have fewer turns of wires. The high voltagelow current windings have more turns of wires. Step up- the secondary has more turns than
the primary. Step down-the secondary has fewer than the primary. Core is of great
importance in a transformer. Ferrite core is the best suited. Transformer is essentially used
to increase voltage in an inverter circuit
Figure 4 :
Relay
It is simply a switch which is under the control of another circuit. Historically, electric relays
were made with electromagnets. These continue to be in use today as well. However, in
some cases, solid state relays are now being used. The key difference is that electromagnetic
relays have moving parts. There are no such moving parts in the solid state relay. A relay
can control an electric output, which is higher than the electrical input that it receives.
Relays can turn on and off in response to things like, a current overload, irregular current
etc.
169
Testing of a EM relay
Apply 12 V input to the relay and see if, gets ON or not
At times, a relay may get ON, but may fail to develop a contact due to a loose held
spring
Figure 5
Check the relay and change if, defective
At times, low voltage from the battery may fail to switch on a relay and light does
not glow
The contact of relay may get dirty or a capacitor connected in parallel with it may get
damaged-then a chattering sound may be heard
Change the relay quickly
Figure 6
MOSFET
A MOSFET is a semiconductor device.It is a device used to amplify or switch electronic
signals. It can be thought of as a transistor that is controlled by voltage rather than current
170
Figure 7:
Opto-Coupler
There are situations where signals and data need to be transferred from one sub system to
another within a piece of electronic equipment. It can even be from one piece of equipment
to the other without making a direct ohmic electrical connection. An auto coupler can do
this task very well. It typically comes in a small 6-pin or 8-pin IC package. These are mainly
a combination of two distinct devices i.e.an optical transmitter, typically a gallium arsenide
based LED. The second part is an optical receiver such as a phototransistor. These two are
separated by a transparent barrier. It stops any flow of current but does allow the passage of
light
Figure 8:
Drum coil/Inductor coil
It is a coil for producing a high voltage from a low voltage source. It stores energy in the
form of a magnetic field. The simplest form of an inductor is made of a wire loop or coil. The
inductance depends directly on the number of turns in the coil, radius of the coil. It also
depends on the type of material around which the coil is wound
171
Micro Controller IC
It is a small computer on a single integrated circuit. It can be thought of as a miniaturized
electronic circuit that combines a number of electronic components. These mainly include
the resistors, capacitors, transistors and diodes into one small piece
Driver circuit
It is an electrical circuit or other electronic component used to control another circuit or
other component, such as a high power transistor.
Inverter Circuit
It is an electrical device which converts direct current (DC) into alternating current (AC)
Printed Circuit Board
Semiconductor components are normally mounted on the PCBs. This is because the
electrical paths on a PCB are perfect for the needs of most of the semiconductors. It thus
offers conductive pathways, tracks or traces etched from copper sheets laminated onto a
non-conductive substrate
Figure 9:
172
Figure 10:
Activity II- Demonstration of different models of the following few lighting systems:
a) Solar Lantern (individual charging)
b) Solar Lantern (Centralised charging)
c) Solar Home System
Physical appearance
Solar lantern is available in two different models. These use CFL and LEDs as the lighting
source. Both these models will be made available for the training purpose. Similarly, solar
home system comes in several models. Crystalline silicon modules together with thin film
amorphous silicon module are to be demonstrated alongwith:
batteries of different types (sealed maintenance free-lead acid battery, NiMH
Lithium ion battery batteryl)
lamps of different types (Compact fluorescent lamp, Light Emitting Diodes)
junction boxes of CFL and LED lanterns
all electronic and electrical components
The solar modules of different capacities have already been dealt with in the beginning. So,
it is intended to demonstrate the physical form of the following:
sealed maintenance free batteries (4.5 Ah, 7 Ah)
low maintenance free batteries (40 Ah)
components on the PCB assemblies of solar lantern
electronic components on the PCB assembly of charge controller for solar home
system
173
Table below shows the upper and lower charging voltage limits for a standard 12 V
battery:
Parameter
Value
Rated Voltage
Over charge protection
Over discharge Cutoff
Over discharge resume
Over Voltage cutoff
Over Voltage resume
Voltage drop (input to battery)
Voltage drop (battery to load)
No load current draw
12 V
14.4 0.3 VDC
110.3 VDC
120.3 VDC
16.5 VDC
15.0 VDC
0.5 VDC
0.2 VDC
Below 5 mA
174
Wire cutter
Wire strippers
Soldering iron and wire
Circuit Testing
The above mentioned component circuits are commonly tested. Key objective of
testing circuits is as under:
ensures correct battery consumption
ensures longer life of battery and CFL tubes
ensures that the battery does not get overcharged/deep discharged
Following three type of circuits are to be tested as a part of the practical training:
Lantern circuit- related to testing of frequency, current and voltage settings,
under/over charge settings
Inverter circuit (lamp)-related to testing of frequency, current and voltage setting
Charge controller Circuit-under/over charge setting
Protection testing (short circuit, reverse current flow )
Remember to keep a multimeter at hand, power supply, tools and soldering iron for
testing of the above mentioned circuits
Testing and Repair of an Inverter
Defect
Solution
Take out the lamp from the charge controller and connect it
directly to a battery
Check the battery voltage, it should be 12 V
Check the ON/OFF Switch to see if, it is damaged
Check the fuse and replace a defective one by a 1.5 A fuse
Check all the connections of tube light
Check the battery polarity
175
B. Load circuit
1.
2.
3.
4.
The positive supply of the battery goes to common C contact via switch and fuse
If, battery is okay, then relays C and N/C contact are connected
In this way, the battery supply is available at the load terminal
Simply means that the lamp will glow, if, it is connected
C. Control circuit
1. Control circuit gets the supply directly from diode D2
2. Reference voltage is set via R2, D3 and P1
3. R3, R4, R6, R7, R8 are voltage dividers, which means that battery voltage can be
measured
4. On 16 pin nos. 6&7, both rising and falling voltages can cause yellowing (i.e burning)
of pin no.1
5. LED burns at a voltage of 11.8 V
6. When the battery voltage reaches near 11.0 V, according to voltage on R3 and R4,
then it switches on transistor Q2.
7. The coil of the relay gets a supply, then the relay current goes through contact C or
N/O
8. The battery supply does not reach the load now and red LED strarts glowing
Solution
176
Defect
Solution
177
j.
Remove the red and black connectors from the battery terminals along with the
plastic insultors
178
Testing of a battery
The electrolyte in a wet lead-acid battery is a mixture of sulfuric acid and water. A battery
can be tested in a number of ways. The simple idea is to know if, it stores the charge
properly. This calls for a measurement of battery voltage. Remember, there is a definite
relationship between the specific gravity of a battery and its state of charge. The most
reliable method is the measurement of specific gravity and battery voltage. Following few
tools are needed for this purpose:
Hydrometer
Digital Voltmeter
Remember, it is not possible to test a sealed battery in this way.
Testing procedure
About the hydrometer
It is a low cost float-type hand held device used to measure the concentration of sulfuric
acid (specific gravity) of battery electrolyte (battery acid). A hydrometer is a glass barrel or
plastic container with a rubber nozzle or hose on one end. It has a soft rubber bulb on the
other end. Within the container is a float and calibrated graduations used for the specific
gravity measurement.
Step-by-step procedure:
remember if, a battery has been charged or discharged within the last four hours
if so, remove the surface charge of the deep cycle battery to be tested.
Use a load that is around 33% of the ampere-hour capacity of the battery for about 5
minutes
wait for around ten minutes before taking any measurements
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Specific Gravity
1.265
1.225
1.190
1.155
1.120
Voltage
12 V
6V
12.7
12.4
12.2
12.0
11.9
6.3
6.2
6.1
6.0
6.0
Battery capacity
The most common battery rating is the ampere-hour rating or simply Ah. It is a unit of
measurement for the battery capacity. This is obtained by multiplying a current flow in
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amperes by the time in hours of discharge. Take for example a battery which gives 5
amperes for 20 hours. It can deliver 5 amperes times 20 hours or 100 ampere-hours. Table 1
shows the Watt-hours in case of a solar system as under:
Load (Watt)
Use= hours/day
Watt-hours
4
8
16
32
12
12
12
12
48
96
192
384
Battery size
It can be worked out as under:
a) divide the Watt-hours per day by the DC System Voltage
b) the value obtained is that of Average Ah/day
c)divide the Ah per day thus obtained by the Discharge limit
d) the value obtained is that of battery capacity in Ah
Watt-hours
DC System
Average Ah
Autonomy
Discharge
Battery
Battery
Per day
Voltage
Per day
Days
Limit
Ah
Available
Ah
32
48
64
96
128
192
256
384
12
12
12
12
12
12
12
12
2.67
4.00
5.33
8.00
10.67
16.00
21.33
32.00
1
1
1
1
1
1
1
1
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
5.33
8.00
10.67
16.00
21.33
32.00
42.67
64.00
7
14
14
18
26
40
48
64
Battery maintenance
It is important to keep a battery in good health. The same can be done by a) its regular
cleaning, b) checking of specific gravity of electrolyte at regular intervals and c) regular
charging
181
5. check if, the battery terminals are corroded. It simply means if, any white powder is
present on them?
6. clean them with a solution of baking powder and water
7. put back the cleaned terminals and tighten the bolts
8. use petroleum jelly or grease on the connected terminals
9. keep a wet cloth on the tight bolts for some time to get loose
take out the caps of each of the cells though one at a time
check the electrolyte level
remember to keep the acid level within two cms of the battery top
add ionized distilled water till it is around 2 cms below the top of the battery
do not ever add the rainwater/tapwater/acid to the battery
Other components
Checking the module junction box
1. the junction box is at the back of a solar module
2. check it to ensure that the wiring is tight
3. see if, it is free of any insects and rats etc.
182
Risk involved
Due to what
Solar Module
Battery
Charge Controller
Lamp
Remember: defect in any one part may stop the system from working normally
183
Troubleshooting-Solar lantern
A solar lantern is a very useful source of lighting. It works on a simple principle of
electricity production, storage and its use. However, some thing or the other may go wrong
with it at times. So, it is important to take a note of the problem solving steps as under. This
whole procedure is generally known as the troubleshooting.
Problem
Possible cause
Solution
Lantern not
working
Fuse failure
Not getting
sufficient
Backup
Charging indicator
not glowing
184
Dos
always keep the solar module in the sun at a suitable angle
if, the angle is not known, then keep the module in the sun on a horizontal surface
charge the lantern for a full day before its first use
in case the red LED glows, charge the battery of the lantern till green LED switches
off
try to use the lantern daily for 2-3 hours
charge the battery on a regular basis, even if, the lantern may not be in use
charge the battery, even if, lantern is out of order for some time
store the lantern in a clean dry state
Donts
do not keep the module in shade at any time
do not try to open the solar panel in any case
do not allow dust to settle on the glass surface of a panel
do not allow any bird droppings to settle permanently
do not scratch the glass surface to remove bird droppings with any sharp object
do not ever use any chemicals/detergents for cleaning (it may damage the plastic
parts)
do not expose the lantern to direct Sunlight
do not clean the lantern/solar module with acid, detergent or any other chemical
do not allow the lantern to get wet (solar module may get wet)
do not pull out the panel from the lantern by pulling hard the wire
do not try to remove the fixed diffuser for changing the lamp
do not keep the lantern in a fully discharged condition for more than a month
(otherwise, the battery may get damaged permanently)
do not connect the lantern to the AC mains supply
185
186
always charge the LED lanterns through LED junction box only
always charge the CFL lanterns through CFL junction box only
Solar Modules
always clean the solar module with a moist cotton cloth
check and ensure proper connection of wires from the module to the junction box.
this is ensured by observing that the green LED of the junction box is glowing when
there is sunlight
Donts
Do not connect the lantern to AC mains supply
Troubleshooting-Solar Home System
Solar systems are mostly installed in the remote areas of our country. These systems must
work without any problems. However, some minor problems may come up at times. A solar
technician should be able to fix up most of these problems on his own. Table below shows
the possible reasons and their solutions in a typical SHS:
Symptom
Part
involved
Check cause
Check/remedy
Lamp
does not
glow
Luminiare
Fuse failure
Luminiare
Loose terminals
Luminiare
Lamp failure
Luminiare
Charge
controller
Loose
187
a.
b.
a.
b.
Tighten the
Symptom
Part
involved
Check cause
connection at
the battery
c.
Check/remedy
connection of
the terminals
and lugs
Battery not
charged
connections
and replace the
lug if, found
loose
c1. If, no indication,
tighten the loose
connections at the
module end
c2. If, no rated current
found at module end,
replace the module
c3. If, point nos 1&2
are okay, then replace
the PCB
d. Battery wrong
polarity
Module
modules should be covered or shaded from the sun by an unclear sheeting, before
any electrical connections are made to the modules
modules should be mounted firmly onto the structure as per the foundation details
and the installation plan mentioned in the drawing
construction of the structure must not be attempted in high winds
CFLs
protect all the lamps from rain, snow, condensation of droplets or water
do not stare at the lamp directly
ensure safe throwing away of the lamps after use
188
Charge Controller
Charge controller is necessary to monitor and to allow sequence of operation so that solar
energy is utilized efficiently
Battery
batteries must be placed in a well ventilated area
lift the batteries only by the handles
keep these upright at one place
try to use a protective gear while filling the electrolye in the batteries
do not overfill the batteries above the maximum level indicator
do not smoke in the battery room
check for any traces of acid on the battery housing, racks and connectors
check for any traces of corrosion on racks and compartments
importantly, care well for the battery
LED Driver
Use of high brightness LEDs is a new trend in the area of lighting. These LEDs offer the
following few advantages:
longer life
higher efficiency
lower maintenance cost
As such, a LED driver is needed to maintain constant current in the LEDs. Generally, it is a
DC-DC Step up/down converter.
189
Donts
1. do not short the battery terminals
2. do not reverse the polarity of the battery cables
190
3. do not top up the battery with electrolyte. It is to be used only for the initial
preparation
4. do not short the charge controller terminals
5. do not use excess load other than what is supplied with the system
191
Item
No
Digital Multimeter
De-Soldering Pump
Nose Plier
10
Solder Wire
11
12
Tweezer
13
Flat File
14
Camal Cutter
15
Adjustable wrench
16
PVC Tape
17
Compass
18
19
Hydrometer
192
193
III.
IV.
V.
VI.
Sub-activity: Grading of the Solar flat plate collector systems on the basis of following
information
S.No.
Item
Class-I
Class-II
Class-III
1.
Collector Box
Anodised Aluminum
Alumnium
Mild steel
2.
Absorber
Panel
Fin
Risers and
Headers
Copper
Copper
Copper
Copper
Copper
Copper
Mild Steel,
Galvanised
Steel or Copper
Steel or Copper
3.
Coating
Black paint
4.
Gasketing
Silicone rubber
EPDM
Neoprene or Rubber
5.
Cover glass
Tempered/low iron
Toughened
Window glass
194
S.No.
Item
Class-I
Class-II
Class-III
float glass
Window/float glass
6.
Insulation
Polyurethene (PUF)
7.
Sealants
Silicone
Silicone
8.
Piping
All Copper
Galvanised Iron
B class
Galvanised Iron
A class
9.
Screw, bolts
and nuts
Zinc coated/Nickel
plated/mild steel
II.
III.
IV.
V.
VI.
195
use minimum of hot water piping length (to reduce heat and friction losses)
hot water storage tank is to be placed at a minimum height of 50 cm above the outlet
of collector
c) Quality of water
check the water quality-it should be soft/treated
Remember water soluble salts in hard water are responsible for corrosion, formation of
scales or deposits in the collectors, pipes and storage tank
d) water supply tank location
direct connection of water supply to the solar water heating system is ruled out in
most of the cases
cold water supply tank should be at least a foot above the top of a solar hot water
tank to make easy gravity flow to the system
Remember: in a pumped system, the cold water supply can be anywhere, above or below
the collectors-however, it should be near to the installation
e) Shading
Check, if, the site is free of shade all the year round
Remember: Shading takes place due to parts of the house itself such as chimeys, domes and
overhangs and also the surrounding buildings and trees located around the collectors
f) Minimum distance between rows of collectors
Check if, shadow does not come on the collector
It is important to keep a minimum distance between the rows of collectors for an easy
erection and maintenance too. Sufficient care is also needed to ensure that one row does not
cast any shadow on another at any time during the day. The minimum distance is given by
D=L Sin /Tan (66.5-latitude)
Where =collector tilt, L= collector length
Installation related:
use only the suitable size of piping-otherwise the output temperature will drop
take care that hot water piping is fully insulated from the solar tank up to the usage
points
ensure that the hot water piping is not more than 10 mtrs or 30 feet. If, it is more than
this, the output temperature will come down because of excess heat loss
196
Guidelines-Civil Foundation
foundation may be plain cement concrete (PCC) or reinforced cement concrete
(RCC) depending on the installation site
The PCC foundation of the structure legs shall be done with M20 grade (M indicates
mixing) of mix ratio of cement/sand /jelly in the ratio 1:1.5:3)
Component
Diameter D (mm)
Height H (mm)
Collector legs
150
75
150
150
Activity: General maintenance schedule for SWH components (Dos and Donts)
To get the maximum possible benefit from the system, follow these easy steps:
Dos
1. ensure that the tank is always full and never runs dry
2. ensure that the stored hot water is used once a day either during morning or evening
3. ensure that the full quantity of stored hot water is used within a period of 1 hour
4. ensure that the cold water piping gate is open always
5. ensure that the vent pipe is kept open always
6. ensure that only recommended pipes and pipe sizes are put to use
7. ensure that the collector glass is cleaned at least once every week or depending on
the local dust conditions
8. ensure that no shadow falls on the collectors during any time of the day throughout
the year
Donts
1. do not cover the collectors when the system is in use
197
2. do not put up any objects which can cast shadow on the collectors
3. do not draw the hot water when the temperature booster is on
4. do not draw the stored hot water more than once per day
5. do not run the collectors dry
198
Time to time maintenance is very essential to keep solar water heating system working.
Table mentions the steps that one needs to follow:
Maintenance requirements of Solar Water Heating System:
Component
Maintenance needed/
Expected result
Improvement in
Issues
Observations
System performance
Glass is broken
System fails to
work/system
performance is low
No damage to glass
results
Absorber
coating
Performance is poor
Absorber panel
risers
Smooth flow,
Efficiency of the system
increases
Absorber panel
Corrosions and
leakages
Absorber-riser
sealing
Collector Box
Circulating
water pumps
Pressure
gauges
Good monitoring
Air locks
Collectors
glazing
Air vents
Storage tanks
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Not
enough hot
water
Part
involved
Likely
Collector
(s)
Piping
Solar
tank
Check
Check/Solution
1. Shading
2. Dirty
glazing/glass
2. Gate valves
partially closed
3. Flow blockage
Cause
Piping
1. Gate valve
completely closed
2. No cold water
supply to the system
Flow blockage
200
Indication
Cold water
at usage
point
Water
leakage
Part
involved
Likely
Check
Check/Solution
Piping
Loss of hotness/hot
water drawn is more
than once a day
Draw/use complete
amount of hot water in a
span of 1 hour in a day
Make up
tank
No Polypropylene
glycol/antifreeze
solution in the
makeup tank
Weather
Bad weather
Switch on the
temperature booster
Cause
Piping
End fitting/pipe
fittings are loose
Collector
Tank
III.
IV.
V.
201
and shape of the dish is such that a point focus is formed on being exposed to the sun.
Under this activity, it is planned to carry out the following few sub-activities:
understand the specifications of each major component
understand the role of each major component
demonstrate a fully working model of a parabolic type dish cooker
understand the point focus nature of the dish
S.No.
Element/Parameter
Specifications
1.
Dish diameter
2.
Aperture shape
Circular/square/rectangular
3.
Aperture area
4.
Aperture shape
Circular/Square/Rectangle
5.
Reflector material
6.
Supporting frame of
the dish
7.
8.
Tracking mechanism
202
III.
IV.
V.
VI.
VII.
VIII.
IX.
Dos
always use a large pot for cooking
only use such pots as fit well in the support provided
use only the black painted pots
turn the reflector in such a way that you will be standing in its shade while putting
on or checking the pots
put the lid tightly on the cooking pots
use cloth or oven gloves for touching the pots
use sunglasses for precautionary measures while working
203
Donts
do not stand right in front of the cooker
do not allow small children to go close to it
do not leave a reflector without any cover (after dismanting the cooker)
do not ever look into the reflector
do not put small pots on the cooker
do not try to cook such food as need constant stirring
Maintenance schedule
wash the reflector with a wet cloth or a sponge soaked in water
rinse the reflector with water after that
use a dry piece of cloth to remove any stains after washing
do not use metallic things as these may cause scratches on the surface of the reflector
sheets
only use dark cooking vessels
204
205
206
207
208