Solar Power Plants Part1

Solar Power Plants
Part 1
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Sun power and how much we receive (Extraterrestrial
radiation)

Atmospheric effect on
Terrestrial radiation)

solar

Solar time

Solar Geometry and Angles
Solar Radiation data

Solar Power Concentration

radiation

received

(

Extraterrestrial Radiation
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Radiation intensity
Hsun=σT^4

Extraterrestrial Radiation
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Radiation intensity
Hsun=σT^4

Radiation intensity
HEarth=(Rsun2/D2)*Hsun

D≈1.496E11 m
Average
Hearth=1366
w/m2
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The solar constant ICS

The average energy radiated by the Sun per time
unit on a unitary surface situated outside the Earth’s
atmosphere and perpendicular to the Sun’s rays. It
measures 1367 W/m2.

Extraterrestrial Radiation
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Not all the solar radiation from the sun received by the
earth surface only a fraction of it can be used

Extraterrestrial Radiation
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Air mass: the path length which light takes through the
atmosphere normalized to the shortest possible path
length (that is, when the sun is directly overhead

Extraterrestrial Radiation
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m=0 extraterrestrial

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m=1 at sea level

Extraterrestrial Radiation
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Definitions
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The extraterrestrial radiation I0(t)
The daily solar radiation intensity due to the change of the
distance between the sun and the earth during the year

Such that n(t) is the number of day in the year starting from
1 at 1 January and ending with 365 at 31 December

Extraterrestrial Radiation
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Terrestrial Radiation
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Definitions
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Beam radiation (direct solar radiation): the solar radiation received
from the sun without having been scattered by the atmosphere
Diffuse radiation: the solar radiation received form the sun after its
direction has been changed by scattering by the atmosphere.

Total (Global) solar radiation: the sum
of the beam and diffuse radiation on a
surface.

Terrestrial Radiation
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Definitions
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Reflected radiation: the part that is reflected on the sand or water
and then received on a surface.
Irradiance I or G [w/m2]: the rate at which radiant energy is
incident on a surface per unit area of surface.

Terrestrial Radiation
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Any place on the earth is identified by longitude and
latitude Φ

Solar Time
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Local Solar Time (LST) and Local Time (LT)
Twelve noon local solar time (LST) is defined as when the sun is highest in
the sky. Local time (LT) usually varies from LST because of the
eccentricity of the Earth's orbit, and because of human adjustments such
as time zones and daylight saving.

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Local Standard Time Meridian (LSTM)

The Local Standard Time Meridian (LSTM) is a reference meridian used
for a particular time zone and is similar to the Prime Meridian, which is
used for Greenwich Mean Time. The LSTM is illustrated below.

Solar Time
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Local Standard Time Meridian (LSTM)

Solar Time
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LST=LT+TC/60

Equation
of time

TC (time correction)=4´(longitude-LSTM)+EoT
LSTM=15˚ .ΔTGMT

Solar Time
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Solar Time
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Example 1

Calculate the solar time in Zagazig corresponding to
standard time 10:30 AM, at 29 January. longitude of
Zagazig is 31.5° E, time zone GMT+2
LST=LT+TC/60
TC (time correction)=4´(longitude-LSTM)+EoT
LSTM=15˚ .ΔTGMT=30˚

B =(360/365)*(29-81)=-51.82
EoT= -13.1721 min
TC (time correction)=4´(31.5 - 30)+ -13.1721 =-7.1721 min
LST= 10.5-7.1721 /60 = 10.380465
Solar time = 10 22´ 49´´ AM

10 22´ 49´´

Solar Geometry and Angles
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23.45 degree

Solar Geometry and Angles
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http://astro.unl.edu/naap/motion3/animations/sunmotions.html

Solar Geometry and Angles
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Solar height or altitude or elevation α- the angle
formed by the direction of the solar rays and their
projection on a horizontal plane.

ζ

Solar Geometry and Angles
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zenith angle ζ the angle formed by the solar rays and
the vertical (zenith) direction; this angle and α- are
complementary;

ζ

Solar Geometry and Angles
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Solar azimuth Ψ, which indicates the variance of the
solar rays’ projection on the horizon’s plane as regards
the south; by convention, eastward orientations are
negative while westward orientations are positive;

ζ

Solar Geometry and Angles
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The solar declination δ the angle formed between the
solar ray and the equator’s plane measured on the
solar midday plane

Solar Geometry and Angles
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Gives the declination in radians

Solar Geometry and Angles
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Hour angle HA, which indicates the angular distance
between the Sun and its midday projection along its
apparent trajectory on the celestial vault.

HA= (LST-12)*15°

Solar Geometry and Angles
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The Position Of The Sun In The Sky
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Relations between solar angels

To calculate sunrise and sunset put elevation as zero and
rearrange:

Solar Geometry and Angles
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The Position Of The Sun In The Sky
Example 2: calculate the altitude and solar azimuth angels for
Zagazig (latitude of 30.57°N and longitude 31.5˚E) at 9.5 AM on 13
February
13 Feb d =31+13=44

δ=ASIN(SIN(23.45)*SIN(360*(44-81)/365))=-13.69 °

Solar Geometry and Angles
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The Position Of The Sun In The Sky
HA= (LST-12)*15°
LST=LT+TC/60= 9.5+ [4´(31.5 - 30)+ -13.1721 ]/60=9.38
HA =(9.38-12)*15=-39
α=ASIN(SIN(-13.69)*SIN(30.57)+COS(-13.69)*COS(30.57)*COS(-39))=31.98˚

ψ =-46.129

Solar Geometry and Angles
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Inclination β, the inclination of the surface compared
to the horizontal,
Surface’s azimuth γ , the angle that the projection on
the normal to the surface’s horizontal plane has to
rotate to superimpose itself on the southern direction.

Solar Geometry and Angles
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Angle of incidence i: The angle between the solar rays
and the normal to the surface is called the.

i=α+β

Solar Radiation data
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Pyrheliometer

Measures direct solar radiation. The
receiving surfaces are perpendicular to
the line joining Sun and receiver.
Diaphragms ensure that only direct beam
radiation and a narrow annulus of sky
around the sun is detected.
It is usually provided with solar tracker to
validate perpendicular sun rays and
measure of direct solar radiation only

Solar Radiation data
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Pyranometers

Measures the global solar radiation
received on a horizontal surface.
They are also used to measure solar
radiation on surfaces inclined to the
horizontal.
Other global solar irradiance measuring
devices that are available on the market
and are cheaper than pyranometers
possess a solar cell as a receiver

Solar Radiation data
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Albedometer

The combination of one upward and one
downward oriented pyranometer is
called an albedometer. It measures both
the global and reflected radiation.

Solar Radiation data
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Typical Meteorological Year data (TMY).
1-Measuring solar radiation hourly for various years
2-The data for the month that has the average
radiation most closely equal to the monthly
average over the whole measurement period is
then chosen as the TMY data for that month.
3-This process is then repeated for each month in
the year. The months are added together to give a
full year of hourly samples.

Solar Radiation data
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Solar Radiation data
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TRNSYS data

Solar Power Concentration
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What is the concentration??
Reflector
area

Receiver
area

Solar Power Concentration
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Why the concentration??

Solar Power Concentration
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the concentration calculations
Line focus (2D)

Parabolic troughs; CLFR

Cmax,2 D  1 / sin  S
Point focus (3D)

Central receiver systems,
parabolic concentrators (dishes)

Cmax,3D  1 / sin  S
2

Solar Power Concentration
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Concentrating solar power technology