Solar Power Plants Part1

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.


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

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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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7 m=0 extraterrestrial

m=1 at sea level


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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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.


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Any place on the earth is identified by longitude andlatitude


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


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23.45 degree


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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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zenith angle the angle formed by the solar rays andthe vertical (zenith) direction; this angle and - arecomplementary;

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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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The solar declination the angle formed between thesolar ray and the equators plane measured on thesolar midday plane


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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


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:



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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



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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


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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.


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Angle of incidence i: The angle between the solar raysand the normal to the surface is called the.

i=+


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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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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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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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.


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TRNSYS data



What is the concentration??

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Reflector

area

Receiver

area


Why the concentration??

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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


Concentrating solar power technology

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Solar Power Plants Part1

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