Course No.

PHY- 3101(A), Renewable Energy, Physics Discipline, KU

Chapter – 1
Introduction

Md. Shohel Parvez

Assistant Professor
Physics Discipline, Khulna University, Khulna
Conventional and non-conventional energy source
Conventional energy sources are these, which are non-renewable and
have finite supplies . In general oil, gas, wood, petrolium etc. are
conventional energy sources.
Non-conventional energy sources are those which are renewable.
These sources are permanent sources. These type of sources are:
Solar Thermal
Solar energy
Solar Photovoltaic

Wind energy, Bio-mass, Bio-gas, Tidal-energy, Nuclear-energy etc.

are non-conventional energy sources.
Differences between solar thermal and solar photovoltaic
Different Energy Estimated
Total energy reserve „R‟ can be given by the equation

𝑛:1
′
1 + 𝑟/100) −1
𝑅 = 𝑃 ,* -
𝑟/100
Where, 𝑃′ = Present production rate
r = Energy growth rate
n = number of years
Coal Reserve
Coal resources in the world are estimated to be 5 × 106 Mt of which
Mt=megatonnes
nearly 90% is in the USA, the USSR and China.
Oil Reserve
The total initial reserve of oil in the world are estimated to be
 2000 × 109 barrels. This can be improved with new finds. The
amount of oil extracted up to 1970 is around 230 × 109 barrels i.e.
about 11% of the reserve has been used so far.
Natural Gas Reserve
Actual figures of the reserve of natural gas are not readily available,
but a roughly estimate is possible by assuming 170𝑚3 of gas is
produced along with each barrel of oil produced. Which will work out to
340 × 1012 𝑚3 of natural gas. It is also estimated that it could last far
approximately same time as crude oil.
Estimated reserve of solar energy
* 1 + 𝑟/100) 𝑛:1 − 1
𝑅 = 𝑃′ 𝑟 … … … (1)
100
Now solar energy falling on the earth is

1016 𝑤𝑎𝑡𝑡
𝑃′ ⋍
𝑦𝑒𝑎𝑟
If 5% is used i.e. r = 5% and n = 1, then from Eqn. (1) we get

5 2
1:100
𝑅 = 1016 5
100

= 2.05 × 1016 watts/year

If we used 5% of the total solar energy falling on the earth surface, then
it will be 50 times of our required energy.
The estimated world energy demand in the year 2000 was 5 × 1012 𝐾𝑤ℎ
per year.
Characteristics of the Sun
The sun is a sphere of intensely hot gaseous matter. Heat is generated
continuously by thermonuclear fusion reactions, which convert hydrogen
atoms to helium atoms. This energy is radiated from the sun in all
directions and a very small fractions of it reaches the earth.
Earth receives this radiant energy from sun which is vast and hot
mass of hydrogen helium gases in the proportion of 4:1. In the sun,
energy is generated in its central core which may be considered as a
nuclear reactor. The energy is released in accordance with the following
reaction.
41 𝐻1 −→ 2𝐻𝑒 4 + 26.7𝑀𝑒𝑉
The energy in the above reaction results from the fact that four protons
have a total uncombined mass of 4.0304 and mass of helium nucleus is
4.0027 . Thus 0.0277 mass units of matter are converted into energy
according to the relation ,

𝐸 = 𝑚𝑐2

The principle characteristics of sun

1. Mass, 𝑀 = (1.991 ± 0.002) × 1030 𝐾𝑔

2. Radius, 𝑅 = (6.960 ± 0.001) × 108 𝑚

3. Luminosity, 𝐿 = 3.9 × 1026 𝑤𝑎𝑡𝑡𝑠

4. Mean distance from Earth = 1.49 × 1011 𝑚

 5. The composition of sun is 70% 𝐻, 28% 𝐻𝑒, 2% others .

6. Average density , 𝜌 = 1.410 ± 0.002 𝑔𝑚/𝑐𝑚3

7. Temperature (average on the surface), 𝑇 = 5760 ± 50 𝑘

The 99% wavelength fall on the range 0.2 − 4.0 𝜇𝑚 on the surface 7%
ultra violate radiation (𝛿𝜔) < 0.38 𝜇𝑚, 47.3% visible light
(𝑀𝜔) (0.3 − 0.78 𝜇𝑚 ) 45.7% Infrared radiation (𝐿𝜔) > 0.78 𝜇𝑚.

The sun rotates about its axis ,but not as a rigid body . [The period of
rotation varies from about 25 earth days at its equator to about 27 days
at 40˚ latitude .]
Fig-1 : Spectral distribution of solar radiation
Energy production inside the sun:

The basic energy producing process in the sun is the fusion of

hydrogen nuclei into helium nuclei. This can take place in several
different reaction sequences. The most common of which the proton-
proton cycle. The total evolved energy is 26.7 MeV per 4
2He nucleus
formed –

41𝐻1 ⟹ 4
2𝐻𝑒 + 26.7 𝑀𝑒𝑉, Since 26.7 𝑀𝑒𝑉 𝑖𝑠 4 × 10;12 𝐽

The reaction take place in the presence of C and 𝑁2 . Since the mass
of the helium nucleus is less than four protons, therefore there is a
missing mass after the reaction which has been converted into energy.
The sun consists of 70% hydrogen, 28% helium and 2% of other
element.
 Eventually the hydrogen in the sun‟s core will be exhausted and then
the sun will swell to become a red giant star and later subside into a
white dwarf .
The energy is radiated as e.m. waves in all directions from the sun
and very small fraction of it reaches the earth.

Zenith

Zenith is a point on the celestial sphere directly over the observer‟s

head . The Zenith would change with respect to the location. zenith
zenith
Astronomical
Zenity horizon

Nadir
Air mass
It is the path length of radiation through the atmosphere considering
the vertical path at sea level as unity.
The air mass m is the ratio of the path of the sun‟s rays through the
atmosphere to the length of path when the sun is at the zenith .
𝑃𝑎𝑡𝑕 𝑙𝑒𝑛𝑔𝑡𝑕 𝑡𝑟𝑎𝑣𝑒𝑟𝑠𝑒𝑑 𝑏𝑦 𝑠𝑢𝑛 𝑟𝑎𝑦
Air mass, m =
𝑣𝑒𝑟𝑡𝑖𝑐𝑎𝑙 𝑑𝑒𝑝𝑡𝑕 𝑜𝑓 𝑡𝑕𝑒 𝑎𝑡𝑚𝑜𝑠𝑝𝑕𝑒𝑟𝑒

Except for very low solar altitude angles, the air mass is equal to the
cosecant at the altitude angle .Thus at sea level 𝑚 = 1.
It is also defined by the equation
𝑚 = 𝑆𝑒𝑐𝜃𝑧 ; 𝜃𝑧 < 70°, when 𝑚 > 3
𝑚 = 0 ; just above the earth atmosphere .
 𝑚 = 1; when sun is at zenith.
𝑚 = 2; when zenith angle is 60˚.
Solar Constant

Fig: Schematic of sun-earth relationship

The solar constant (𝐼𝑠𝑐 ) is defined as the total energy received from the
sun, per unit time , on a surface of unit area kept perpendicular to the
radiation in space just outside the earth‟s atmosphere when the earth is at
its mean distance from the sun.

The unit of solar constant is 𝜔 ⁄ 𝑚2. At the mean earth-sun distance of

𝑟 = 1.5 × 1011 𝑚. The solar constant is
𝐼𝑠𝑐 ≈ 1353 𝑤𝑚;2
≈ 1.940 𝑐𝑎𝑙/𝑐𝑚2 𝑚𝑖𝑛

The unit “Langley” is some time used , 1 𝐿𝑎𝑛𝑔𝑙𝑒𝑦 = 1 𝑐𝑎𝑙/𝑐𝑚2 of solar

radiation received in one day.
Solar Intensity
Solar energy falling perpendicularly per cm over the surface of the
earth.
The variation of solar intensity I on any day is given by,

360 𝑛 − 2
𝐼 = 𝐼𝑠𝑐 1 + 0.33 cos
365
The cosine term corrects for Earth
s slightly elliptical orbit. It makes
the Sun ~3.3% stronger near
360𝑛
perihelion (early January) and ~3.3 ≈ 𝐼𝑠𝑐 1 + 0.033 cos
% weaker near aphelion (early 365
July). The total swing is ~6.6%.

Where n is the day of the year.

Beam radiation
The portion of the incident solar radiation which comes directly from
the apparent solar disc, without reflections from other objects is called
 direct or beam radiation. These radiations are received from the sun
without change of direction.
Diffuse radiation
The diffuse radiation is that solar radiation received from the sun
after its direction has been changed by reflection and scattering by the
atmosphere.
Total Solar Radiation
Total solar radiation or global solar radiation is all solar radiation
incident on a surface including scattered, reflected and direct .Total does
not include radiation that has been absorbed by matter and then re-
emitted, because most of the radiation is at longer wavelength (>3μm). It
re-emission is mostly in the infrared region (> 3 μm).
is also known as terrestrial solar radiation.
 It is also defined as the total solar radiation energy received on a
horizontal surface of unit area (1 sq. cm.) on the ground in unit time (i.e.,
1 day).
Unit: 𝑤/(𝑚2 𝑑𝑎𝑦) = 𝑒𝑛𝑒𝑟𝑔𝑦 / (𝑚2 𝑑𝑎𝑦) = (𝑐𝑎𝑙./ 𝑐𝑚2 𝑑𝑎𝑦).

Extra-terrestrial Solar Radiation

The extra-terrestrial solar radiation is the radiation which comes from
the sun directly and is not diffused by any obstacle.
Difference between Beam & Diffused radiation

Beam Radiation Diffuse Radiation

Definition Definition

In this case ,the solar radiation In this case ,the solar radiation
received from the sun without received from the sun after its
change of its direction direction has been changed.

Equator
It is an imaginary great circle normal to the earth‟s axis . The equator
divides the earth into two hemisphere called Northern and southern
hemispheres.
Meridian
An imaginary great
circle passing through the
reference point and the two
poles, intersecting the
equator at the right angles, is
called the prime (or
Greenwich) meridian or line
of longitude.
It is an imaginary great ϕ
ω
circle dividing the earth
equally to two parts.
The basic Earth and Sun angles are-
a) Latitude (𝜙)
b) Hour angle (ω)
c) Sun declination (δ)
The position of a point Q on the earth surface with respect to (on) the
sun‟s rays is known at any instant if the latitude(φ), hour angle (ω) for
the point, and the sun declination (δ) are known. These fundamental
angles are shown by the previous fig. Point 𝑄 represents a location on
the northern hemisphere.
Latitude (𝜙)
The latitude of a point on the surface of the earth is its angular distance
north or south of the equator measured from the centre of the earth.
 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 the latitude will measured as “ + 𝑣𝑒 ” for northern
hemisphere.

Hour angle (ω)

It is the angle representing the position of the sun with respect to
clock hour and with reference to sun‟s position at 12 noon.
The hour angle is the angle through which the earth must turn bring
the meridian of a point directly in the line with the sun‟s rays.
One hour is equivalent to ,(2π/24)=0.262 rad or (360/24)=15˚.
Consequently 1min= 15′ , 1𝑠 = 15′′
It is measured from noon, based on Local Solar Time (LST) or Local
Apparent Time (LAT) being ( + 𝑣𝑒) in the morning and ( − 𝑣𝑒) in the
positive toward the east negative toward the west
afternoon.

Sun’s Declination (δ)

The declination, δ is the angular distance of the sun‟s ray north (or
south) of the equator. It is the angle between a line extending from the
centre of the sun to the centre of the earth and the projection of this line
upon the earth‟s equatorial plane.
This is the direct consequence of the tilt and it would vary between
23.5˚ on June 22 to -23.5˚ on December. At the time of summer solstice,
(sun standing still. For maximum or minimum declination the sun
appears to stand still ) the sun‟s rays would 23.5˚ north of the earth‟s
equator (δ=23.5˚)
At the equinoxes (equal night, the nights are equal when the
declination of the sun is zero ). The sun declination would be zero. At the
time of winter solstice, the sun‟s ray would be 23.5˚ south of the earth‟s
equator (δ=23.5˚).
Solar Radiation Geometry
The solar radiation geometry is given below :

𝜃𝑧

𝛾𝑠
 The three additional angles are shown in figure and are defined as
follows
Altitude angle α (solar altitude)
The angle between the projection of the sun‟s rays on the horizontal
plane and the direction of sun‟s rays (passing through the point).
Zenith angle (𝜽𝒛 )
It is complementary angle of sun‟s altitude angle .It is a vertical angle
between the sun‟s rays and a line perpendicular to the horizontal plane
through the point ,i.e. the angle between the beam from the sun and the
vertical.
Θz = (π/2)-α
 At sunset and sunrise α=0, θz = π/2 .
Solar Azimuth angle (𝜸𝒔 )
It is the angle on a horizontal planes between the line due to south
and the projection of the sun‟s rays on the horizontal plane.
Explanation of Day Length
Zenith angle (θz) can be expressed interms of 𝜙, 𝛿, 𝜔𝑠
cos 𝜃𝑧 = cosϕ cos 𝜔𝑠 cos𝛿 + sinϕ sin𝛿
At sun set or sun rise 𝜃𝑧 = 90˚ , so the hour angle 𝜔𝑠 is

𝑠𝑖𝑛ϕ 𝑠𝑖𝑛𝛿
𝑐𝑜𝑠𝜔𝑠 = − 𝑐𝑜𝑠ϕ 𝑐𝑜𝑠𝛿 = −tan ϕ tan 𝛿
 𝜔𝑠 = 𝑐𝑜𝑠 ;1 (−tan ϕ tan 𝛿)
Since 15˚ angle = 1 ℎ𝑜𝑢𝑟 , the day length (in hour)
2𝜔𝑠 2 ;1 (−tan ϕ tan 𝛿)
𝑇𝑑 = 1𝑠 = 15 𝑐𝑜𝑠

The value for an inclined surface for facing south. We get ,

𝜔𝐵𝑡 = 𝑐𝑜𝑠 ;1 ,− tan ϕ − 𝛽 tan𝛿-
The corresponding day length (in hour) is then given by ,

𝑇𝑑 = 2 15 𝑐𝑜𝑠 ;1 − tan ϕ − 𝛽 tan 𝛿

Therefore, the length of the day is as function of latitude and solar

declination.
Surface Azimuthal Angle (𝜸)
It is the angle of deviation of the normal to the surface from the local
meridian , the zero point being south , east positive and west negative.
Incident Angle (θ)
It is the angle being measured between the beam of rays and normal
to the plane.
Slope (β)
It is the angle between the horizontal and the tilled plane.
 The spectrum of electromagnetic radiation is usually divided into
wavelength bands as shown below.
−6
(1 𝑚𝑖𝑐𝑟𝑜𝑛 = 1𝜇 = 10 𝑚).
Approximate range Name
𝜆 < 10;8 𝜇 Cosmic rays

10;8 < 𝜆 < 10;5 𝜇 Gamma rays

10;5 < 𝜆 < 10;2 𝜇 X-rays

2 × 10;2 < 𝜆 < .38𝜇 Ultra-violet rays

.38 < 𝜆 < 0.78𝜇 Visible light rays

0.78 < 𝜆 < 102 𝜇 Infrared rays

102 < 𝜆 < 1010 𝜇 Radio waves

 of the whole spectrum of electromagnetic waves we can sense only
those that have wavelengths between approximately 0.1 to 100 microns.
Electromagnetic waves falling within these limits cause our body to heat
up. Hence these waves are called 'thermal radiation‟. Visible light rays
occupy a very narrow band of the thermal radiation spectrum .

Wavelength range 0-.38 0.38- 0.78 0.78 – 4.0

Approximation energy 95 640 618
Approximate percentage 7% 47.3% 45.7%
of total energy

Table-(b)
Table shows solar radiation in various portions of the spectrum. The area
under the entire curve is the solar radiation, we see that the visible part of
the solar(radiation) energy spectrum carries about half of its total energy.
ESTIMATION OF MONTHLY AVERAGE SOLAR RADIATIONS
Monthly average horizontal solar radiation 𝐻𝑎𝑣 was given by Angstrom
(1924) , Which is –
𝑛
𝐻𝑎𝑣 = 𝐻0′ (𝑎′ )+ 𝑏′
𝑁
Where 𝑎′ and 𝑏′ are arbitrary constant (𝐹𝑟𝑒𝑖𝑡𝑧 1951, suggested that
𝑎′ = 0.35 and 𝑏 ′ = 0.61)
𝐻0′ = Monthly average horizontal solar radiation for a clear day.
𝑛 = Average daily hours of bright sun shine for same period .
𝑁 = Maximum daily hours of bright sunshine for the same period .
𝐻0′ can be obtained from standard chart. The day length can be obtained
from standard chart or from equation.
 2
𝑁 = 𝑇𝑑 = 𝑐𝑜𝑠 ; (−𝑡𝑎𝑛ϕ𝑡𝑎𝑛𝛿)
15

The better form of equation (1) is suggested by Page (1964)

𝑛
𝐻𝑎𝑣 = 𝐻0 𝑎+𝑏
𝑁
Where ,
𝐻0 = The average monthly in ionization at the top of the atmosphere and
a, b are modified constant depending upon the location .
𝐻0 can be obtained by charts or also can be obtained by the calculations-

24
𝐻0 = 𝐼𝑠𝑐 ,*1 + 0.33cos(360𝑛 /365)+*(cos𝜑 cos𝛿 sin𝜔
𝜋

+ (2𝜋𝜔/360) sin𝜑) sin𝛿+-.

Classification of solar energy utilization
Direct Method:
i. Solar thermal technology.
ii. Solar photovoltaic technology
iii. Solar hydrogen gas production technology.

Indirect Method
The indirect method is in the term of wind , biomass , bio-gas , water
power, ocean temperature difference.
 Solar thermal technology is the way of transforming solar heat
into useful energy using collectors.
 Solar photovoltaic energy technology is the most useful way of
harnessing solar energy by directly converting it into electricity by
means of solar photovoltaic cells.
  Solar hydrogen gas production technology is still at an embryonic
stage.
Classifications of solar energy measuring equipment's

Instruments

Pyrheliometer Pyranometer Pyrgeometer Pyradiometer

(measure direct (measure direct and (measure terrestrial (measure solar
radiation) diffuse radiation) radiation) and terrestrial
radiation)

1. Angstrom
pyrheliometer
2. Abbot silver disk
pyrheliometer Eppley Yellot
3. Eppley pyrheliometer pyranometer pyranometer
Pyranometer
The instruments that measure global solar radiation on a horizontal
surface are called pyranometers. These have a view angle of 2π
steradians. The most common pyranometer are based on detection of
difference between the temperature of black surfaces and white surface
(which reflect most solar radiation) by thermopiles. Properly protected
from wind and compensated for changes in ambient temperature, the
thermopiles give millivolt signals that can be readily detected, recorded
and integrated over time .
There are three types of pyranometer. Working principle of them are
given below:
Eppley Pyranometer
It is based on the above principle and has become the most common
instrument in use. It has concentric silver rings 0.25 mm thick,
appropriate coated black and white, with either 10 or 50 thermocouple
junctions to detect temp difference between the coated rings .
 Later models use wedges arranged in a circular pattern with alternate
black and white coatings . The disks on wedges are enclosed in a
hemispherical glass cover. The output can be recorded on a strip chart or
a digital print out of integrated values over a pre-selected duration
(quarter , half or an hourly) can be obtained . The most likely used males
of this type are Eppley(USA), Kipp and Zoaen(Netherlands) and
EKO(Japan). The response time is of the order of several seconds. This is
a fairly precise instrument and is employed by most of the metrological
observations.
(2) The second type of pyranometer use silicon solar cells as sensors .
These are less expensive compared to the three types . The response time
is fast , less than a millisecond. However, it has a limited spectral
sensitivity and is not recommended where precise measurements are
required.
(3) The third type uses bi-metallic strips as sensors. The receiving
surface consists of a bimetallic strip printed back mounted between two
similar strips of bimetallic shielded from solar radiation. The bimetallic
strips are connected to a leaver mechanism with a pan arm and the
movement of the pan which are proportional to the temperature
difference between the exposed and shielded bimetallic one recorded on
a rotating drum fixed with a chart.