Post on 15-Nov-2015
description
Part 1
Solar Power Plants
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2 Sun power and how much we receive (Extraterrestrialradiation)
Atmospheric effect on solar radiation received (Terrestrial radiation)
Solar time
Solar Geometry and Angles
Solar Radiation data
Solar Power Concentration
Extraterrestrial Radiation
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Radiation intensity
Hsun=T^4
4D1.496E11 m
Radiation intensity
Hsun=T^4
Radiation intensity
HEarth=(Rsun2/D2)*Hsun
Average
Hearth=1366
w/m2
The solar constant ICSThe average energy radiated by the Sun per timeunit on a unitary surface situated outside the Earthsatmosphere and perpendicular to the Suns rays. Itmeasures 1367 W/m2.
Extraterrestrial Radiation
Not all the solar radiation from the sun received by theearth surface only a fraction of it can be used
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Extraterrestrial Radiation
Air mass: the path length which light takes through theatmosphere normalized to the shortest possible pathlength (that is, when the sun is directly overhead
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Extraterrestrial Radiation
7 m=0 extraterrestrial
m=1 at sea level
Extraterrestrial Radiation
Definitions
The extraterrestrial radiation I0(t)
The daily solar radiation intensity due to the change of thedistance between the sun and the earth during the year
Such that n(t) is the number of day in the year starting from1 at 1 January and ending with 365 at 31 December
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Extraterrestrial Radiation
9Extraterrestrial Radiation
Definitions
Beam radiation (direct solar radiation): the solar radiation receivedfrom the sun without having been scattered by the atmosphere
Diffuse radiation: the solar radiation received form the sun after itsdirection has been changed by scattering by the atmosphere.
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Total (Global) solar radiation: the sumof the beam and diffuse radiation on asurface.
Terrestrial Radiation
Definitions
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Reflected radiation: the part that is reflected on the sand or waterand then received on a surface.
Irradiance I or G [w/m2]: the rate at which radiant energy isincident on a surface per unit area of surface.
Terrestrial Radiation
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Any place on the earth is identified by longitude andlatitude
Terrestrial Radiation
Solar Time
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.
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.
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Solar Time
Local Standard Time Meridian (LSTM)
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LST=LT+TC/60
TC (time correction)=4(longitude-LSTM)+EoT
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Equation
of time
LSTM=15 .TGMT
Solar Time
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Solar Time
Example 1
Calculate the solar time in Zagazig corresponding tostandard time 10:30 AM, at 29 January. longitude ofZagazig is 31.5 E, time zone GMT+2
LST=LT+TC/60
TC (time correction)=4(longitude-LSTM)+EoT
LSTM=15 .TGMT=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 10 22 49
Solar time = 10 22 49 AM
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Solar Time
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 height or altitude or elevation - the angleformed by the direction of the solar rays and theirprojection on a horizontal plane.
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Solar Geometry and Angles
zenith angle the angle formed by the solar rays andthe vertical (zenith) direction; this angle and - arecomplementary;
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Solar Geometry and Angles
Solar azimuth , which indicates the variance of thesolar rays projection on the horizons plane as regardsthe south; by convention, eastward orientations arenegative while westward orientations are positive;
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Solar Geometry and Angles
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The solar declination the angle formed between thesolar ray and the equators plane measured on thesolar midday plane
Solar Geometry and Angles
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Solar Geometry and Angles
Gives the declination in radians
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Hour angle HA, which indicates the angular distancebetween the Sun and its midday projection along itsapparent trajectory on the celestial vault.
HA= (LST-12)*15
Solar Geometry and Angles
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
The Position Of The Sun In The Sky
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Example 2: calculate the altitude and solar azimuth angels for
Zagazig (latitude of 30.57N and longitude 31.5E) at 9.5 AM on 13
February
13 Feb d =31+13=44
=ASIN(SIN(23.45)*SIN(360*(44-81)/365))=-13.69
Solar Geometry and Angles
The Position Of The Sun In The Sky
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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
=ASIN(SIN(-13.69)*SIN(30.57)+COS(-13.69)*COS(30.57)*COS(-39))=31.98
=-46.129
Solar Geometry and Angles
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Inclination , the inclination of the surface comparedto the horizontal,
Surfaces azimuth , the angle that the projection onthe normal to the surfaces horizontal plane has torotate to superimpose itself on the southern direction.
Solar Geometry and Angles
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Angle of incidence i: The angle between the solar raysand the normal to the surface is called the.
i=+
Solar Geometry and Angles
Pyrheliometer
Measures direct solar radiation. Thereceiving surfaces are perpendicular tothe line joining Sun and receiver.Diaphragms ensure that only direct beamradiation and a narrow annulus of skyaround the sun is detected.
It is usually provided with solar tracker tovalidate perpendicular sun rays andmeasure of direct solar radiation only
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Solar Radiation data
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 measuringdevices that are available on the marketand are cheaper than pyranometerspossess a solar cell as a receiver
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Solar Radiation data
Albedometer
The combination of one upward and one downward oriented pyranometer is called an albedometer. It measures both the global and reflected radiation.
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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 averageradiation most closely equal to the monthlyaverage over the whole measurement period isthen chosen as the TMY data for that month.
3-This process is then repeated for each month inthe year. The months are added together to give afull year of hourly samples.
Solar Radiation data
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Solar Radiation data
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TRNSYS data
Solar Radiation data
Solar Power Concentration
What is the concentration??
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Reflector
area
Receiver
area
Solar Power Concentration
Why the concentration??
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Solar Power Concentration
the concentration calculations
Line focus (2D)Parabolic troughs; CLFR
Point focus (3D)Central receiver systems,
parabolic concentrators (dishes)
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SDC sin/12max,
SDC 2
3max, sin/1
Solar Power Concentration
Concentrating solar power technology
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