Variability of measured Global Horizontal Irradiation throughout Qatar

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This paper presents a study of up to six years of ground measurements of Global Horizontal Irradiation (GHI), the total solar radiation arriving on a horizontal surface, collected by 12 automatic weather stations throughout Qatar. The year-to-year and monthly variations of daily GHI are calculated for each station; the average found is 5.80kWh/m<sup>2</sup>/day, a total of 2116kWh/m<sup>2</sup>/year. Spatially, the monthly averages through the country vary with a relative standard deviation of up to 4% with respect to the country averages; in general, higher GHI is found in the south and north regions of Qatar, except at the northern tip of the country, and lower values are found mainly in the central latitudes, close to the industrial areas. Frequency distributions of daily GHI present two peaks, which are found to correspond to two distinct periods of the year: one from March to September, with most frequent GHI values around 7kWh/m<sup>2</sup>/day, and one from October to February, centred around 4.5kWh/m<sup>2</sup>/day. A similar study can be advisable for other areas with comparable climate or topographies, since these two solar seasons might also be present and, if found, should be considered in the design and implementation of photovoltaic-based systems. Finally, the monthly clearness index (ratio of ground-level GHI to top-of-the-atmosphere GHI) is presented for each location and for Qatar as a whole from ground measurements and compared to longer-term satellite-based values. The annual average of clearness index for Qatar from ground measurements is 0.64, indicative of clear-sky conditions most of the year. GHI is the fuel of photovoltaic systems, so its study is fundamental for such applications, and also provides a reference for the derivation of solar radiation data from models or satellite observations.

Original languageEnglish
Pages (from-to)169-178
Number of pages10
JournalSolar Energy
Publication statusPublished - 1 Sep 2015


  • Clearness index
  • Frequency distribution
  • Seasonal solar variation
  • Solar resource assessment

ASJC Scopus subject areas

  • Renewable Energy, Sustainability and the Environment
  • Materials Science(all)

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