solar geometry .ppt

Solar Radiation Geometry

Ch.Bhanu prakash,

Assistant Prof.

Department of ME VIT

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Solar Geometry

• Solar Geometry describes the relationship between the sun and earth or more importantly

• The relationship of solar radiation. • The product of the sun with any location on the

earth.

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Important geometrical parameters, which describe Earth-Sun relations

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Nature of the solar resourceEarth’s orbit ain’t circular

Nature of the solar resourceEarth’s orbit: Variation in radiation

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1,300

1,350

1,400

1,450

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Irra

dia

nc

e (

W/m

2 )

Nature of the solar resourceEarth is tilted 23. 450

solstice

• Either of the two times in the year, the summer solstice and the winter solstice, when the sun reaches its highest or lowest point in the sky at noon, marked by the longest and shortest days.

• Either of the two times a year when the sun is at its greatest distance from the celestial equator: about June 21, when the sun reaches its northernmost point on the celestial sphere, or about December 22, when it reaches its southernmost point.

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Nature of the solar resource

Earth is tilted 23.45• On the winter solstice (December 21)

– The north pole has its maximum angle of inclination away from the sun

– Everywhere above 66.55 N (90-23.45) is in darkness for 24 hours, Everywhere above 66.55 S is in sunlight for 24 hours

– the sun passes directly overhead over the tropic of Capricorn (23.45 S)

• On the equinox (March 22 & September 22)– Both poles are equidistant– the day is exactly 12 hours long – the sun passes directly overhead over the equator– The sun tracks a straight line across the sky

• On the summer solstice (June 22)– The reverse of the winter solstice

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Nature of the solar resourceSolar geometry

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Beamradiation

Nature of the solar resourceSolar geometry: Hour angle

Rotation

Beamradiation

Meridian

• A meridian (or line of longitude) is the half of an imaginary great circle on the Earth's surface, terminated by the North Pole and the South Pole, connecting points .

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Meridian

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Hour angle

• It is the angle through which the earths must turn to bring the meridian of a point directly in line with the sun rays.

• It is the angle measured in the earths equatorial plane.

LST

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LST

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Nature of the solar resourceSolar geometry: Sun angles

z

s

s

N

South E

W

Zenith


z = Zenith angle – the angle between the vertical (zenith) and the line of the sun

s = Solar attitude angle – the angle between the horizontal and the line to the sun

s = Solar azimuth angle – the angle of the projection of beam radiation on the horizontal plane (with zero due south, east negative and west positive)

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Incident angle

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Incident angle

• It is the angle being measured b/w the beam of rays and normal to the plane

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Z = Zenith Angle = Latitude = Declination = Hour angles = Solar azimuth

angles = Solar attitude

angle


cos cos cos cos sin sinz

sin cos cos sin sincos

cosss

Note: & should be the same sign

s = Sunset angle = Declination = Latitude

Note:Day length is in hours

Nature of the solar resourceSolar geometry: Sun angles: Sunset angle

and day length

cos tan tans

12Day length cos tan tan

15

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Nature of the solar resourceSolar geometry: Collector angles

z

s

s

N

SouthE

W

Zenith


= Slope – the angle between the plane of the collector and the horizontal

= Surface azimuth angle – the deviation of the projection on a horizontal plane of the normal to the collector from the local meridian (with zero due south, east negative and west positive)

= Angle of incidence – the angle between the beam radiation on the collector and the normal

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cos cos sin sin sin

cos cos sin cos

sin cos

s s

s s

s

cos sin sin cos cos sin cos

cos cos cos cos sin sin cos

cos sin sin sin

= Angle of incidence

s = Solar attitude angle

= Surface azimuth angle

s = Solar azimuth angle

= Collector slope

= Declination = Latitude = Hour angle

Sun angles

Earth angles

ss = Sunset angle = Declination = Latitude = Collector

slope


cos tan tanss

Northern Hemisphere

cos tan tanss

Southern Hemisphere

System designIrradiance: Variables

• Latitude at the point of observation

• Orientation of the surface in relation to the sun

• Day of the year

• Hour of the day

• Atmospheric conditions

System designIrradiance on a horizontal surface

, cosb b n zG G

,b nG

bG

Gb = Beam Irradiance normal to the earth’s surface (W/m2)Gb,n = Beam Irradiance (W/m2)z = Zenith angle

,b TG,b nG

, , cosb t b nG G Gb,t = Beam Irradiance normal to a tilted surface (W/m2)Gb,n = Beam Irradiance (W/m2) = Angle of incidence

System designTilt: Beam radiation

, ,,

,

cos cos

cos cosb t b n

b tb b n z z

G GR

G G

,b nG,b tG

bG

,b nG

System designTilt: Beam radiation

Solar AnglesDescribe the sun position relative to a vertical surface

Solar Altitude: β (beta)

Vertical angle to sun position

Solar Azimuth: Φ (phi)

Horizontal bearing angle from south

Surface Azimuth: Ψ (psi)

Surface horizontal bearing angle from south

Surface Solar Azimuth: γ (gamma)

Angle between solar and surface azimuths

γ = Φ - Ψ

Sign Conventions

Angles east of south are negative

Angles west of south are positive

+ -

S

-90º90º

0º

-45º45º

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solar geometry .ppt

Documents

solar radiation geometry

bhanu prakash