Dr. Patel Badari Narayana, MGIT unit II Introduction to Solar Radiation

Renewable Energy Sources For ECERenewable Energy Sources For ECE
B.Tech. IV Year II Sem. L/T/P/C
Course Code:
Name of The Faculty:
Dr. P. Badari Narayana
M.Tech (Energy Systems), P.hD.,
Associate Professor,
Dept. of Mechanical Engg.
Renewable Energy Sources Unit II
Topic:
SOLAR RADIATION

Syllabus * Unit II
• Solar Energy System
• Solar Radiation
• Availability
• Measurement & Estimation
• Solar Thermal Energy Conversion Devices and Storage
• Applications of Solar PV Conversion
• Applications of Solar Thermal Energy Conversion Devices
• Applications of Solar Energy Systems

Ways to Change Our Global Climate
Change energy from
the Sun
Change reflection from
the atmosphere and
planet
Change composition
of the atmosphere

• Radiation from the Sun
– Changes in energy radiated from the Sun
– Changes in Earth’s distance from the Sun
– Changes in Earth’s inclination relative to the Sun
• Atmospheric composition
– Changes in concentration of gases in atmosphere that absorb energy
(“greenhouse gases”)
• Through natural processes (volcanic emissions, emissions from
flora and fauna, soil, etc)
• Through the action of humans (consumption choices)
• Reflectivity of the planet
– Changing the reflectivity of the surface (snow, ice, forests, soot, etc)
– Changing the reflectivity of the atmosphere (clouds, aerosols)
How can these climate factors change?

Solar Radiation
• Sun is a star with a surface
temperature of ~5780K
• The Sun emits radiation
over a wide spectrum of
wavelengths out into space
• As radiation spreads out
into space, it is spread out
over an increasingly large
area 4pr2
• A small amount of that
energy is intercepted by
the Earth in it’s orbit
around the Sun. r is the radius at which the planet orbits the Sun

Major Uses of Solar Energy
oDaylight
oDrying Agricultural Products
oSpace Heating
oHeating Water
oGenerating Electrical Power
oConcentrating Solar Power
oPhotovoltaics

The Solar Resource
• Before we can talk about solar power, we need to talk about
the sun
• Need to know how much sunlight is available
• Can predict where the sun is at any time
• Insolation : incident solar radiation
• Want to determine the average daily insolation at the solar
system installation site
• Must choose effective locations and panel tilts of solar panels
10

The Sun and Blackbody Radiation
• The Sun
– 1.4 million km in diameter
– 3.8 x 1020 MW of radiated electromagnetic energy
• Black bodies
– Both a perfect emitter and a perfect absorber
– Perfect emitter – radiates more energy per unit of surface area than a
real object of the same temperature
– Perfect absorber – absorbs all radiation, none is reflected
• Temperature in Kelvin is temperature in Celsius + 273.16
11

Plank’s Law
• Plank’s law – wavelengths emitted by a blackbody depend
on temperature
8
5
3.74 10
14400
exp 1
E
T





  
  
  
• λ = wavelength (μm)
• Eλ = emissive power per unit area of black body (W/m2-μm)
• T = absolute temperature (K)
12

Electromagnetic Spectrum
Source: en.wikipedia.org/wiki/Electromagnetic_radiation
Visible light has a wavelength of between 0.4 and 0.7 μm, with
ultraviolet values immediately shorter, and infrared immediately
longer
13

288 K Blackbody Spectrum
The earth as a black body; note 0.7 m is red. Most all is infrared range, which is why
the earth doesn’t glow!
Figure 7.1
Area under curve is the total radiant power emitted
15

Radiation from
surface of Sun =
63 X 106 W/m2
Radiation at the top of
the Earth’s atmosphere
~1360 W/m2
(solar “constant”)
Earth is ~150 x 106
km from the Sun
Radiation from an
object falls off by the
inverse square of the
distance
Area of a sphere =
4pr2
Radius of sphere = r

Stefan-Boltzmann Law
• Total radiant power emitted is given by the
Stefan –Boltzmann law of radiation
4
E A Ts
• E = total blackbody emission rate (W)
• σ = Stefan-Boltzmann constant = 5.67x10-8 W/m2-K4
• T = absolute temperature (K)
• A = surface area of blackbody (m2)
17

Wien’s Displacement Rule
• The wavelength at which the emissive power per unit area
reaches its maximum point
max
2898
T
 
18
 
( )
absolute temperature
wavelength
T K
m 


 
5800 , 0.5
288 , 10.1 considered as a blackbody
Sun:
Earth:
max
max
T K m
T K m
 
 
 
 

Extraterrestrial Solar Spectrum
19
FIGURE 4.2 The extraterrestrial solar spectrum compared with a 5800 K blackbody.
Masters, Gilbert M. Renewable and Efficient Electric Power Systems, 2nd Edition. Wiley-Blackwell

Solar Intensity: Atmospheric Effects
Sun photosphere
“AM” means “air mass”
Intensity
Extraterrestrial
sunlight (AM0)
Sunlight at sea level at 40°
N Latitude at noon (AM1.5)
20

Air Mass Ratio
• AM1.5 – assumed earth’s surface average
• Air mass ratio = 1 (“AM1”) – sun directly overhead
• AM0 – no atmosphere
2
1
1
air mass ratio =
s n
:
i
m
h
h 

As sunlight transits the atmosphere, energy is absorbed
21
FIGURE 4.3
The air mass ratio m is a measure of the amount
of atmosphere the sun's rays must pass through
to reach the earth's surface.
Masters, Gilbert M. Renewable and Efficient Electric Power
Systems, 2nd Edition. Wiley-Blackwell

Solar Spectrum on Earth’s Surface
m is higher when the sun is
closer to the horizon
Notice blue light attenuation
with higher m,
 sun appears reddish at
sunrise and sunset
22Blue is 450 nm, Red is 700 nm
C.A. Gueymard, The sun’s total and
spectral irradiance for solar energy
applications and solar radiation models.
Solar Energy, vol. 76, 423-453 (2004)
https://en.wikipedia.org/wiki/Simple_Model_of_the_Atmospheri
c_Radiative_Transfer_of_Sunshine_(SMARTS)#cite_ref-1

INDIA is well above the equator(0* latitude)..
The latitudinal extent of INDIA is-
8*4′28″ N to 37*17′53″ N.. TROPIC OF CANCER(23.5*N latitude)cuts INDIA into exactly 2
equal halves..(see in the image above).This imaginary line passes through 8 INDIAN states..

India is well above the Equator, India lies to the north of equator.

The Earth’s Orbit
FIGURE 4.5 The tilt of the earth's spin axis with respect to the ecliptic
plane is what causes our seasons. “Winter” and “Summer” are
designations for the solstices in the Northern Hemisphere.
25

Solar Declination
• δ varies between +/- 23.45˚
• Assuming a sinusoidal relationship, a 365 day year,
and n =81 is the spring equinox,
 
360
23.45sin 81
365
n
 
    26
FIGURE 4.6
Masters, Gilbert M. Renewable and Efficient Electric Power Systems, 2nd Edition

The Sun’s Position in the Sky
• Predict where the sun will be in the sky at any time
• Pick the best tilt angles for photovoltaic (PV) panels
Solar declination
27
FIGURE 4.6
Masters, Gilbert M. Renewable and Efficient Electric Power Systems, 2nd Edition

Solar Noon and Collector Tilt
• Solar noon – sun is directly
over the local line of longitude
• At solar noon, sun’s rays are
 to the collector’s face
28
Tilt of 0 is straight up,
Tilt of 90 is perpendicular
FIGURE 4.8
A south-facing collector tipped up to an angle equal to its latitude is
perpendicular to the sun's rays at solar noon during the equinoxes
Masters, Gilbert M. Renewable and Efficient Electric Power Systems, 2d Ed. Wiley-Blackwell

Altitude Angle βN at Solar Noon
• Altitude angle at solar noon βN – angle between the sun and the
local horizon
• Zenith – perpendicular axis at a site
90N L   
FIGURE 4.9 The altitude angle of the sun at solar noon

Solar Position at Any Time of Day
30

ss

FIGURE 4.10
Masters, Gilbert M. Renewable and Efficient Electric Power
Systems, 2nd Edition. Wiley-Blackwell
The sun's position is described by
• Altitude angle
• Azimuth angle ϕS
By convention, ϕS is considered ‘+’ before solar noon
ss

Altitude Angle and Azimuth Angle
• Hour angle H – earth rotation
(degs) until sun is overhead
• Earth rotates at 15˚/hr….
• At 11 AM solar time, H = +15˚
(the earth needs to rotate 1 more
hour)
• At 2 PM solar time, H = -30˚
 
15
hour angle hours before solar noon
hour
H
 
  
 
31

Sun Path Diagrams for Shading Analysis
• Shading PV panel (or portion) greatly reduces energy output
• Able to model the sun’s position at all times  Site the PV array
Using Sun Path Diagram
• Sketch azimuth & altitude angles of trees, buildings, other
obstructions
32
• Sections Covered on the
Sun Path Diagram indicate
times when the site will be
shaded

Sun Path Diagrams for Shading Analysis
33
40 N

Sun Path Diagram for Shading Analysis
• Trees to the southeast, small building to the southwest
• Can estimate the amount of energy lost to shading
34
FIGURE 4.14 A sun path diagram with superimposed obstructions makes it easy to
estimate periods of shading at a site

Clear Sky Direct-Beam Radiation
• Direct beam radiation IBC – passes in a straight line
through the atmosphere to the receiver
• Diffuse radiation IDC – scattered by molecules in the
atmosphere
• Reflected radiation IRC – bounced off a
surface near the reflector
35

Extraterrestrial Solar Insolation I0
• Starting point for clear sky radiation
calculations
• I0 passes perpendicularly through an
imaginary surface outside of the earth’s
atmosphere
• Ignoring sunspots, I0 can be written as
• SC = solar constant = 1.377 kW/m2
• n = day number
2
0
360
SC 1 0.034cos (W/m )
365
n
I
  
     
  
In 1 year, < .5 I0
reaches earth’s surface
as a direct beam
36
I0 varies only due to
eccentricity in the
earth's orbit

Attenuation of Incoming Radiation
km
BI Ae

• IB = portion of the radiation
that reaches earth’s surface
• A = apparent extraterrestrial
flux
• k = optical depth
• m = air mass ratio
The A and k values are location dependent, varying with
values such as dust and water vapor content
37

Calculating Air Mass Ratio M
• At any point in time, the air mass ratio (m) depends upon the sun’s
altitude angle, 
• Example: For Urbana L = 40.1 N, on Spring Equinox  = 0, say H = +15
(one hour before local noon)
38
sin cos cos cos sin sinL H L   
 
2
708sin 1417 708sinm    
         sin cos 40.1 cos 0 cos 15 sin 40.1 sin 0
sin 0.7388 47.6
1.35m

 
      
   


Solar Insolation on a Collecting Surface
• Direct-beam radiation is just a function of the
angle between the sun and the collecting surface
(i.e., the incident angle q:
• Diffuse radiation is assumed to be coming from
essentially all directions to the angle doesn’t
matter; it is typically between 6% and 14% of the
direct value.
• Reflected radiation comes from a nearby surface,
and depends on the surface reflectance, r,
ranging down from 0.8 for clean snow to 0.1 for a
shingle roof.
cosBC BI I q
39

Tracking Systems
• Most residential solar PV systems have a fixed mount, but
sometimes tracking systems are co₹t effective
• Tracking systems are either
– single axis (usually with a rotating polar mount [parallel to
earth’s axis of rotation), or
– two axis (horizontal [altitude, up-down] and vertical [azimuth,
east-west]
– Tracking systems add cost & maintenance needs
40

Tracking System Performance
41
FIGURE 4.30 Comparing clear-sky insolation striking various trackers and fixed and fixed-tilt
collector on May 21, latitude 33.7° (Atlanta). Numbers in parentheses are kWh/m2/d

Monthly and Annual Insolation
• For a fixed system the total annual output is somewhat
insensitive to the tilt angle, but there is a substantial variation
in when the most energy is generated
42
• Peak insolation is usually considered 1
kW/m2
• Which is known as "One Sun.“
• Insolation units: kWh/m2 per day,
which is equivalent
to hours per day of peak insolation

Ken Youssefi Introduction to Engineering – E10 44
A major drawback of most renewable energy
sources is the high cost. To spur a huge rise in
use, prices must come down and efficiencies
must go up (better technology)
Typical efficiencies for commercial applications:
15% - 20%
Panasonic company has the most efficient, 25.6%

Ken Youssefi Introduction to Engineering, E10 45
Reported timeline of solar cell energy conversion efficiencies
(National Renewable Energy Lab.)

Factors Affecting Efficiency
• Sunlight consists of a spectrum of
wavelengths – semiconductor materials
cannot respond to the full spectrum
• As much as 30% of light is reflected from
the surface of the cell (only absorbed
light can produce electricity)
• Impurities can cause the charge to
“recombine” and therefore not generate
electricity

Other Factors Affecting Efficiency
• Angle of incidence of the sun
• Dirt, snow, or other impurities on cell surface
• Shading (even a small amount of shading
reduces output dramatically)
• Cloud cover

Atoms
Protons - carrying positive charge
Neutrons - charge neutral
Electrons - carrying negative charge
An atom is composed of 3 particles:
• Nucleus consists of Protons and
neutrons and electrons orbit
around the nucleus
• The number of protons and
electrons are the same, therefore
an atom, as a whole, is electrical
charge neutral.
• Different materials have different
number of particles in their atoms.

Atoms
Each atom has a specific number of electrons,
protons and neutrons. But no matter how many
particles an atom has, the number of electrons
usually needs to be the same as the number of
protons. If the numbers are the same, the atom is
called balanced, and it is very stable.
So, if an atom had six protons, it should also have six
electrons. The element with six protons and six
electrons is called carbon. Carbon is found in
abundance in the sun, stars, comets, atmospheres of
most planets, and the food we eat. Coal is made of
carbon; so are diamonds

Atoms
• In some materials, atoms have loosely attached
electrons. An atom that loses electrons has more
protons than electrons and is positively charged. An
atom that gains electrons has more negative
particles and is negatively charge. A "charged" atom
is called an "ion."
• Electrons can be made to move from one atom to
another. When those electrons move between
the atoms, a current of electricity is created. The
electrons move from one atom to another in a
"flow." One electron is attached and another
electron is lost.

Conductors & Insulators
Insulators
Insulators are materials that hold their electrons very tightly
(high bonding force). Electrons do not move through them
very well.
Rubber, plastic, cloth and glass are good insulators and have
very high resistance.

Conductors & Insulators
Conductors
Other materials have some loosely held electrons,
which move through them very easily. These are called
conductors.
Most metals – like copper, aluminum or steel – are
good conductors.

Electric Current
Ping Hsu Introduction to Engineering – E10 53
• Electric current is the flow of positive
charge. 1 Amp = 1 Coulomb per second.
• Electric current is an effect of the flow of
free electrons which carries negative
charge. (6.28 x 1018 electrons = -1
Coulomb).
• Positive charge flow (current) and negative
charge flow (electron flow) are the same in
magnitude but in the opposite direction.
• By convention, current flow is used in
analyzing circuits. Electron flow is used
ONLY for describing the physical behavior
of electric conduction of materials.
Water flow
(electron flow)
Bubble
Flow
(current
flow)

Clicker Question
Q1. What type of electric charge does an
atom carry?
(a) Positive charge
(b) Negative charge
(c) Neutral
(d) Radiation charge
(e) Magnetic charge

Clicker Question
Q2. What type of electric charge does the
nucleus of an atom carry?
(a) Positive charge
(b) Negative charge
(c) Neutral
(d) Radiation
(e) Magnetic

Silicon atom has 14 electrons and 14 protons.
The outer 4 electrons, together with the 4 from their adjacent atoms, form “octets”
which is a stable structure. Electrons don’t “wandering off” (i.e., free) from this
structure.
56
14+ 14- 14+ 14-
14+ 14- 14+ 14--
14+ 14- 14+ 14-
14+ 14-
14+ 14-
14+ 14-
e-e-
e-e-
e-
e-
e-
e-
e-
N
e-
e-
e-
e-
e-
e-
e-
e-
e-
e-
e-
e-
e-
e-
14+
Ping Hsu

Octet structure
(Only outer orbit electrons are shown)
57Ping Hsu

58
When sunlight strikes a piece of Silicon, however, the solar
energy knocks and frees electrons from their atom structure
(the octets structure)
14+ 14- 14+ 14-
14+ 14- 14+ 13-
14+ 14- 14+ 14-
14+ 14-
14+ 14-
14+ 14-
1-
Heat or light
Freed electron
e-e-
e-e-
e-
e-
e-
e-
e-
N
e-
e-
e-
e-
e-
e-
e-
e-
e-
e-
e-
e-
e-
e-
14+
Ping Hsu

For simplicity, we only show the charge of free electrons
(-1) and the corresponding positive charges (14-13= +1) at the
nucleus.
59
Heat or light
Freed electron
The freed electrons randomly move within the material. This
random motion of charge cannot be utilized for power
generation. In order to utilize the energy from the sun, this
flow of charges must be directed in one direction.
Ping Hsu

N-type (Negative Type) Semiconductor
Introduction to Engineering – E10
A small amount of impurity (doping) such as Phosphorus, arsenic , or antimony
is mixed into a Silicon base and this forms an N-type material. Antimony has 5
outer orbit electrons. Therefore, when bonded with Silicon, there is one electron
extra to form the stable octet configuration. This extra electron is loosely
bonded.
These loosely bonded electron helps with conducting current. The conductivity
is not nearly as good as a true conductor. That’s why it is called a
“semiconductor”.

P-type (Positive Type) Semiconductor
A small amount of impurity such as boron, aluminum or gallium is
mixed into a Silicon base. Boron has 3 outer orbit electrons.
Therefore, when bonded with Silicon, it is one electron short to
form the stable octet configuration. This type materials can, on
the other hand, easily accept one electron.
For simplicity, this characteristic of ‘easily accepting electron’ is
represented by a “hole” with a positive charge and a
corresponding negative charge at the nucleus.

63
• Although there are free electrons and holes in N-type and P-type
materials, they are charge neutral.
• N-type materials conduct electric current (supports movement of
charge) by the free electrons ----- just like metal but with fewer
free electrons than that in metal.
Water flow
(electron flow)
Bubble
Flow
(current
flow)
• P-type materials conduct electric current
(supports movement of charge) by electric
“holes”. When electrons jump from hole to
hole in one direction, the holes appear moving
in the opposition direction. Similar to the
situation when you turn a filled water bottle
upside down; as the water moves downward
(electrons), the bubbles (holes) moves up.
Ping Hsu

64
Interesting things happen when you put an N-type material in
contact with a P-type material.
P-type (neutral) N-type (neutral)
Before making the contact:
Ping Hsu

65
P-type
(Negatively charged!)
N-type
(Positively charged!)
In the boundary layer, the free electrons in the N-type materials
combine with the holes in the P-type. Consequently, the P-type
side of the boundary layer is negatively charged and N-type side
is positively charged.
Negative charge in P-type material prevents the free electrons in the
rest of the N-type material to continue to migrate into the P-type.
(Negative charge repels negative charged free electrons.)
The boundary lay is called PN-junction or depletion region.
boundary
layer
Ping Hsu

Diffusion establishes “built-in” electric field.
n-type and p-type materials brought together.

When sunlight strikes atoms in the P-N Junction and knocks
out more electrons (and creates corresponding holes), the
free electrons are expelled by the negative charge on the
P-type side and hence move towards the N-type side.
P-type
(Negatively charged)
N-type
(Positively charged)
sunlight

If a load is connected across the cell, electric current is formed
and the energy is transmitted to the load.
P-type N-type
sunlight
pn junction
Pn junction
Pn junction

Summary
Introduction to Engineering – E10

Q3. The purpose of the PN junction in a solar
cell is
(a) to generate free electrons
(b) to generate holes
(c) to isolate P and N materials
(d) to accelerate the electrons flow
(e) to direct the direction of electron flow
Clicker Question

Q4. P-type material conducts current by
(a) Metallic element
(b) Free electron
(c) Electric ‘holes’
(d) Conductor
(e) Insulator
Clicker Question

Photovoltaic Cell
Solar panels capture sunlight and convert it to electricity using photovoltaic
(PV) cells like the one illustrated above.

Major Components in a typical PV installation
• PV Panels – solar cells
• Charge Controller
1. Match the panel voltage
and battery voltage
2. Extract maximum power
from the panel
3. Prevent over-charge
• Battery - hold energy
• Inverter - convert DC to
60Hz AC for compatibility
with the power line voltage.

Dr. Patel Badari Narayana, MGIT unit II Introduction to Solar Radiation

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