MAXIMUM GLOBAL SOLAR RADIATION AT ZAGREB a case study

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MAXIMUM GLOBAL SOLAR RADIATION AT ZAGREB a
case - study
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Some Basic Concepts

• Solar constant - the rate of of total solar
  energy at all wavelengths incident on a unit area
  exposed normally to rays of the sun at the mean
  sun earth distance, (1AU 1.496 10km).
• r the sun earth distance.
• Eccentricity correction factor for the earth's
  orbit
• a day number of the year ( 1 January
  1,,31 December 365 )

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Astronomical Concepts

• Celestial sphere great circles are coordinate
  axes in astronomical coordinate system
• Equatorial coordinate system a projection of
  geographical coordinate system to celestial
  sphere
• - declination - 0to 90 for nothern
  hemisphere and from 0 to 90 for southern
  hemisphere
• - hour angle - 0-24 h counting from the
  noon, it changes 15 per hour

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Solar Declination

• The formula (Cooper,1969.) giving the approximate
  value of solar declination (degrees) is
• Sunrise angle formula is
• geographic latitude

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EXTRATERRESTRIAL SOLAR IRRADIATION

• - the amount of solar energy during a given
  period of time that would be received at the
  surface if there were no atmosphere present
  MJmday.
• irradiation during a day from sunrise to sunset

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Solar Radiation - Background Information

• direct or beam radiation - the radiation
  arriving on the ground directly in line from
  solar disc
• diffuse radiation - the scattered radiation
• global (total or hemispherical ) radiation - the
  sum total of direct and diffuse radiation

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• Measurment of global radiation - by a
  pyramometer sensing elements are flat surfaces
  exposed normally to solar rays and are based on
  thermoelectric, thermomechanical or photovoltaic
  principles
• Data are recorded on hourly basis the daily
  global radiation on a horizontal surface, H, is
  obtained from an integration over a day of the
  corresponding hourly global radiation, I
  

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Data

• Data of hourly global radiation for March and
  April through 11 years (1990. 2000.) are
  measured at Horvatovac 4549'N, 1559'E, h
  181m and Puntijarka 4555'N, 1598'E, h
  998m.
• Daily global radiation is calculated and then
  the frequency distribution is derived.
• Clearness index parameter KT. - defined as a
  ratio of the global radiation on the horizontal
  surface to the daily extraterrestrial radiation
  on a horizontal surface
• Values of KT can never reach 1.0 because of
  absorption, backscattering and reflection of
  incoming solar radiation.

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• The - test to determine which
  distribution best fits data

• Why the we expect normal distribution?

- Radioactive decay
we cann't predict the behavior of every part of
the observed system
- Random collisions of the gas particles in
the atmosfere
- Micro level - random process - Macro level
the time evolution of system
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Results

• Normal distribution Puntijarka, April
• 
  Horvatovac, March
• Gamma distribution Puntijarka, March
• - - - Horvatovac,
  April

frequency
classes
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• The results may be presented with curves where
  the clearness index is plotted against the
  frequency of occurence expressed in terms of
  fractional time

Puntijarka, March
Horvatovac, March
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• fractional time f during which daily global
  radiation is ecqual to or less than a certain
  value
• the top 2 of days have a clearness indeks above
  0.55, or 98 of days have a c.i. bellow 0.55

Puntijarka, April
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• correlation coefficient, r
• March rM 0.79
• April rA 0.76
• The regression lines

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• Those days with maximum global solar radiation is
  determined separately for Horvatovac and
  Puntijarka for each month
• - great correspondence because the days with
  maximum global radiation (18.3.1991., 24.4.1997)
  are the same at each station.

Maximum values of KT
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• Average long term values of KT for Horvatovac and
  Puntijarka