Global Horizontal Radiation
also called Global Horizontal Irradiance; totalsolar radiation; the sum ofDirect Normal Irradiance (DNI),Diffuse Horizontal Irradiance (DHI), andground-reflected radiation;however, because ground reflected radiation is usually insignificant compared to directand diffuse, for all practical purposes global radiation is said to be the sum of directand diffuse radiation only:
      GHI = DHI + DNI * cos (Z)
  where
      Z is the solarzenith angle.
Click Shining On (Figure 3) to see solar components
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