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

• 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

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 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/ft2 hr or 4.921 MJ/m2 hr or 1.960 cal/cm2 min.

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 O 2 , water vapor, and other components including Co 2

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 Co 2, 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.

ATMOSPHERIC EFFECTS

Global Radiation Budget

Incoming: Percentage of total

3 Absorbed by atmosphere and clouds : 21

4 Reflected by earth’s land-sea surface : 4

Outgoing:

1 Heat transported upward by convection and turbulence : 10

2 Heat transported upward through evaporation : 22

3 Net loss of energy in the form of long wave radiation : 16

( 4µ to 120µ with the peak at 10µ )

RADIATION BUDGET

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 () 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 (z), altitude () and azimuth angle (Az) at a particular position of the sun.

• The altitude angle of the sun () 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 (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 ( + z = /2)

Solar zenith, altitude and azimuth angles (northern hemisphere), z = zenith

angle, =solar altitude, Az=solar azimuth

SUN SPECTRUM

OR SOLAR SPECTRUM

• 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

RADIATION

Radiation emission and absorption is controlled by various laws of Physics:

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

• 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 :

AC

AB atmosphere

the of

depth vertical

travelled length

path

actual

= cosec  = Sec  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

RADIATION MEASUREMENTS

Sunlight that reaches the earth’s surface has two components:

Direct or beam radiation

The sum of Direct and Diffused that actually

Reaches the surface of module

COMPONENTS OF SOLAR RADIATION

S.NO PARAMETER INSTRUMENTS USED

with shading ring

MONITORING OF WEATHER DATA AT

SEC

Indian solar Radiation Data Base -

HISTORY

Derived Radiation data

The network of 145 stations covers all major climatic zones

In the country

Total 482 tables

Contains

Global, diffuse and direct solar radiation on horizontal

and tilted surfaces

Other meteorological parameters

Also includes :

•Extraterrestrial solar radiation

•Number of clear sky days

•Clearness index

•Precipitable water

•Surface pressure

Revised & Updated Handbook of Solar Radiation

Project undertaken by Solar Energy Centre with IMD

accurate data

• New meteorological stations added in Indian network

• More in-depth analysis

• Analysis being carried out on recent data collected during

1986-2000

• Data being presented in a format suitable to carry out

computer based design optimization studies

The draft revised handbook expected in December 2006

Solar Resource Assessment

Information of solar radiation

as available on the ground

surface

• Quantity

• Spatial distribution

• Temporal characteristics

India lies in the solar belt

of the world A potential

region for utilizing solar

energy

NREL- SEC India Solar Resource Maps

(2010)

END PART-I

THANK YOU !!