Solar Radiation Solar radiation is the primary natural energy source of the Earth'

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Solar RadiationSolar radiation is the primary
natural energy source of the Earth.

• Solar radiation mainly emanates as
  electromagnetic radiation from the surface of the
  sun (photosphere). It is originated by several
  nuclear fusion processes in the interior of the
  sun.

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The solar irradiance incident on a given plane on
the earths surface is determined by

• sun-earth astronomy
• (Physical (radiative) properties of the
  sun, sun-earth distance)
• solar geometry
• (latitude, declination, solar time,
  azimuth and tilt angle of receiving surface)
  
• extinction processes in the atmosphere
• (absorption and scattering by air molecules,
  water vapor, air mass)
• available radiant flux at the surface (direct,
  diffuse)

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Fundamentals of Solar Radiation

• Sun is a sphere comprised of layers of gases that
  radiates energy to the solar system at an
  equivalent blackbody temperature of 5760 K
• Generally accepted that energy generation is a
  H2 to He thermonuclear reaction
• 1.5 x 1017 kWh falls on the land of earth, but
  only small fraction of this can be used

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Thermal Radiation Fundamentals

• Thermal radiation a kind of electromagnetic
  energy which all bodies emit because of
  temperature
• Solar Radiation - 0.1 to 3 µm
• Thermal Radiation 0.1 to 100 µm

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Beam Radiation, Gb, Ib, Hb

• direct solar radiation that is received on
  surface which has not been scattered by
  atmosphere
• Diffuse Radiation, Gd, Id, Hd
• solar radiation received on a surface after
  scattering by the atmosphere has changed it
  direction
• Total Solar Radiation, G, I, H
• sum of the beam and diffuse components of solar
  radiation.

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• The Core
• The Sun's core has a tremendously high
  temperature and pressure. The temperature is
  roughly 15 million C. At this temperature,
  nuclear fusion occurs.

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• The Radiative Zone (or radiation zone)
• The next layer out from the core is this zone
  which emits radiation. This radiation diffuses
  outwards. The temperature ranges from 15 million
  C to one million C.

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• The Convective Zone
• In this next layer, photons continue to make
  their way outwards via convection (towards lower
  temperature and pressure). The temperature ranges
  from one million C to 6,000 C.

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• The Photosphere
• This is the lower atmosphere of the Sun and
  the part that we see (since it emits light at
  visible wavelengths). This layer is about 300
  miles (500km) thick. The temperature is about
  5,500C.

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• The Chromosphere
• This reddish layer is an area of rising
  temperatures. The temperature ranges from 6,000
  C (at lower altitudes) to 50,000 C (at higher
  altitudes). This layer is a few thousand miles
  (or kilometers) thick.

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• The Corona
• This is the outer layer of the Sun's
  atmosphere. The corona extends for millions of
  miles and the temperatures are tremendous,
  reaching one million C.

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Basic properties of the Sun

• distance from Earth 150,000,000 km
• mass 300,000 x mass of Earth
• volume 1,000,000 x Earth
• gravity on the surface 28 x Earth
• luminosity (total energy output) 4x1026 watts
• surface temperature 6,000 K
• composition 71 H (hydrogen), 27 He (helium)

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Sun Earth Relationships

• The earth is nearly spherical with a diameter
  of about 7,900 miles (12.7 x 103 km). It makes
  one rotation about its axis every 24 hours and
  completes a revolution about the sun in a period
  of approximately 365 1/4 days. The earth
  revolves around the sun in a nearly circular
  path, with the sun located slightly off center of
  the circle. The earth's mean distance to the sun
  is about 9.3 x 107 miles (1.5 x 108 km).

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• The suns rays striking the earth are not
  exactly parallel. The included angle (2?s) is
  about ½ degree, as shown figure.

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Sun Earth Relationships

• Around January 1, the earth is closest to the sun
  while on around July 1 it is most remote, about
  3.3 farther away. Since the intensity of solar
  radiation incident upon the top of the atmosphere
  varies inversely with the square of the earth-sun
  distance, the earth receives about seven per cent
  more radiation in January than in July.

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The earth's revolution about the sun

• At the winter solstice (sun directly overhead
  Tropic of Capricorn (23.5 S)) (around December
  22) the North Pole is inclined 23.5 degrees away
  from the sun. All points on the earth's surface
  north of 66.5 degrees north latitude are in total
  darkness while all regions within 23.5 degrees of
  the South Pole receive continuous sunlight.
  (24-hr darkness above Arctic Circle, 24-hr
  daylight below Antarctic Circle )

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the sun's rays at time of winter solstice
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The earth's revolution about the sun

• At the time of the summer solstice (sun directly
  overhead Tropic of Cancer (23.5 N)) (around
  June 22), the situation is reversed. At the
  times of the two equinoxes (around March 22 and
  September 22), both poles are equidistant from
  the sun and all points on the earth's surface
  have 12 hours of daylight and 12 hours of
  darkness.( 24 hours of daylight above Arctic
  Circle and 24 hours of darkness below Antarctic
  Circle )

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the sun's rays at time of summer solstice
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• Declination, ds the angle between the earths
  equatorial plane and the plane of its revolution
  around the sun. The Earth's axis of rotation is
  tilted 66.5 degrees with respect to its orbital
  plane around the sun and its axis of rotation is
  inclined 23.5 degrees from the perpendicular,
  with respect to this plane.

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-23,45º ds 23,45º
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DERIVED SOLAR ANGLES
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• Slope ß
• the angle between the plane of the surface and
  the horizontal, also called the tilt angle 0º
  ß 180º

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• Zenith Angle, ?z
• the angle between the beam radiation and the
  vertical also the angle of incidence on a
  horizontal surface.

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• Surface Azimuth Angle, ?
• the deviation of the projection on a
  horizontal plane of the normal to the surface
  from due south, east is negative and west is
  positive
• -180º ? 180º

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DERIVED SOLAR ANGLES

• Table of surface azimuth angle

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• Solar Azimuth Angle, ?s
• the angle between south and the projection of
  the beam radiation on a horizontal plane, east is
  negative and west is positive.

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• Solar Altitude Angle
• angle between the horizontal and the line to
  the sun (or the suns rays), the complement of
  the zenith angle.

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SOLAR RADIATION MEASUREMENT

• Experimental determination of the energy
  transferred to a surface by solar radiation
  requires instruments that will measure the
  heating effect of direct solar radiation and
  diffuse solar radiation. There are two general
  classes of solar radiation measuring devices.

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• The instrument used to measure direct normal
• or beam radiation is referred to as a
• pyrheliometer.

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• The other instrument, called a pyranometer, is
  able to
• measure total radiation within its hemispherical
  field
• of view. A pyranometer can also be used to
  measure
• diffuse radiation alone by shading the sensing
• element from the suns direct rays.

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• Dünyaya günesten gelen enerji, Dünyada bir
  yilda kullanilan enerjinin 20 bin katidir.
• Günes, 5 milyar yil sonra tükenecektir.

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• Günes isiniminin tamami yeryüzeyine ulasmaz, 30
  kadari dünya atmosferi tarafindan geriye
  yansitilir.

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• Günes isiniminin 50si atmosferi geçerek dünya
  yüzeyine ulasir. Bu enerji ile Dünyanin
  sicakligi yükselir ve yeryüzünde yasam mümkün
  olur. Rüzgar hareketlerine ve okyanus
  dalgalanmalarina da bu isinma neden olur.

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• Günesten gelen isiniminin 20si atmosfer ve
  bulutlarda tutulur.

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• Yeryüzeyine gelen günes isiniminin 1den azi
  bitkiler tarafindan fotosentez olayinda
  kullanilir.

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• Dünyaya gelen bütün günes isinimi, sonunda isiya
  dönüsür ve uzaya geri verilir