PV BASIC PART 1 ITECH 2012-Dr. O.S. SASTRYDIRECTOR, PV TESTINGSOLAR ENERGY CENTRE

SPV BASICS- PART 1

Dr. O.S. SASTRY
DIRECTOR, PV TESTING
SOLAR ENERGY CENTRE
PH. 0124-2579213; Fax: 0124-2579207e.mail: sastry284
@yahoo.in


Energy Determines the Quality of Life


Resource Estimation is Very Important
We study about the Solar radiation Resource


LECTURE FORMAT
•

Understanding SUN

•

SUN Spectrum

•

AIR MASS ( AM x)

•

How to Measure Radiation ?

•

Solar Radiation Mapping

•

How to Obtain Ground Data ?

•

How to Obtain Satellite Data ?


UNDERSTANDING SUN


The SUN
Source of
all
Energy
Produces
Energy
from H2
4H1 →He4 + 2β + + 2ν + 25 MeV
E = mc2


The Solar Constant

• The geometry of the sun - earth relationship is schematically
shown in the figure.
• The eccentricity of the earth’s orbit is such that the distance
between the sun and earth (1.495 × 1011m) varies by 1.7 per
cent.
• The sun sub-stends an angle of 32' at the earth because of its
large size and distance.
• The radiation emitted by the sun reaches un-attenuated up to
the outside of the atmosphere and thus is a fixed intensity.
• The solar constant (Ion) is the energy received from the sun,
per unit time, on a unit area of surface perpendicular to the
direction of radiation, at a mean earth-sun distance, outside
the earth atmosphere.
• The latest value of solar constant is 1366.8 ± 4.2 watts/m2 or
433 Btu/f2 hr or 4.921 MJ/m2 hr or 1.960 cal/cm2 min.


ATMOSPHERIC EFFECTS
On incoming radiation:
1. Solar radiation having wavelength less than 0.29µ(UV) is absorbed in ozone layer.
Thus the atmosphere cuts off most of the ultraviolet part of solar radiation.
2. The solar radiation, that traverse the atmosphere downward, is further subjected to
depletion by scattering and reflection by air molecules, aerosols and clouds.
3. The infrared portion of the solar radiation, which traverses the atmosphere
downward, also suffers depletion by selective absorption at various wavelengths by
O2, water vapor, and other components including Co2
On outgoing radiation:
1. The long wave radiation (4µ - 120 µ), that is emitted upward by the earth, also suffers
selective absorption by water vapor and Co2, which leads to heating of the
atmospheric layers.

2. The atmosphere is transparent for 8µ - 12µ and most of the terrestrial radiation
escapes into space through this window.


Global Radiation Budget


RADIATION BUDGET
Incoming:
1. Backscattered to space by Air
2. Reflected by clouds
3. Absorbed by atmosphere and clouds
4. Reflected by earth’s land-sea surface
5. Absorbed by earth
Outgoing:
1. Heat transported upward by convection and turbulence
2. Heat transported upward through evaporation
3. Net loss of energy in the form of long wave radiation
( 4µ to 120µ with the peak at 10µ )

Percentage of total
: 6
: 21
: 21
: 4
: 48

: 10
: 22
: 16

Basic Earth – Sun Angles
• For calculating solar radiation and designing solar devices, the
knowledge of sun’s path in the sky, on various days in a year at a
particular place is a pre-requisite.
• Solar altitude angle (α) and solar azimuth angle (Az) are the two
coordinates locating the sun in the sky.
• The apparent solar path on a particular day is shown in the figure
thereby showing sun’s zenith angle (θ z), altitude (α) and azimuth
angle (Az) at a particular position of the sun.
• The altitude angle of the sun (α) is defined as the angle in a vertical
plane between the sun’s rays and the horizontal projection of the
sun rays.
• The azimuth angle (Az) is the angle in the horizontal plane
measured from the south (northern hemisphere) to the horizontal
projection of the sun rays. Displacements east of south are negative
and west of south are positive.
• The zenith angle (θ z) is the angle between sun’s rays and the line
perpendicular to the horizontal plane i.e. the angle of incidence of
beam radiation on a horizontal surface (α + θ z = π/2)


Solar zenith, altitude and azimuth angles (northern hemisphere), θ z = zenith
angle, α=solar altitude, Az=solar azimuth


SUN SPECTRUM
OR

SOLAR SPECTRUM


RADIATION
• Process of energy transportation between two points without the help of
any medium.
• Such energy is also termed as radiation.
• Radiation energy is in the form of electromagnetic waves either of single
wavelength (monochromatic) or may occupy a band of wavelength
(spectrum).
• Various spectra of electromagnetic waves are known by different name
depending upon their uses and wavelength
1. Radio Waves

2. Micro Waves

3. Infrared Rays

4. Visible Light

5. Ultraviolet Rays 6. X-Rays
7. Gamma Rays


LAW’S OF RADIATION
Radiation emission and absorption
controlled by various laws of Physics:
•Kirchoff’s Law
•Stefan’s law
•Wien’s displacement law

•Plank’s law
•Bears law.

is


How Solar Energy is Generated? And Its Components
• Originates
with
the
thermonuclear
fusion
reactions occurring in the
sun.
• The sun is, in effect, a
continuous fusion reactor.
•
The fusion reaction in
which hydrogen (i.e. four
protons) combines to form
helium (i.e. one helium
nucleus) accompanied by a
0.7 percent loss of mass and
converted to energy is the
source of energy in the SUN.
Solar Energy Consists of entire electromagnetic spectrum (visible light,
infrared, ultraviolet, x-rays, and radio waves).


ACTUAL SOLAR SPECTRUM

SOLAR RADIATION
• The spectrum nearly resembles to that of a black body
at approximately 6000K.
• The spectrum ranges from a fraction of a nm to
hundreds of meter
•

The region between 250 nm to 3000 nm carries 98%
of the total emitted energy.

• The visible spectrum region from 400 nm to 770 nm
carries 50% of its energy with maxima around 550 nm.



UNDERSTANDING AIR MASS (AM X)


The distance travelled by the sunbeam in the earth’s atmosphere is responsible for the
amount of scattering, absorption and reflection of solar radiation. The shortest distance
travelled by the sunbeam in the atmosphere is when the sun is at the Zenith and is longest
when the sun is rising or setting. Airmass ‘m’ is defined as :

actual path length travelled
AB
m=
=

vertical depth of the atmosphere AC
= cosec α = Sec φ Z
m = 0 when outside the earth atmosphere
m = 1 when sun is at the Zenith
m = 2 when Zenith angle is 60°



Most African, Latin American countries and India are in the solar
belt of the world, A potential for utilizing solar energy