ESTIMATED MONTHLY AVERAGE GLOBAL RADIATION FOR TURKEY AND ITS COMPARISON WITH OBSERVATIONS

Global solar radiation data obtained from actinographs of the Turkish State Meterological Service were compared with data obtained from pyrh eliometers that were established recently to determine if the actinogr aph data were usable in practice. It has been found that the observed actinograph data have a rather high error rate with 14.7% annual and 4 2.1% monthly averages. It has, however, not been possible to smooth th ese errors as they are absolutely random. Thus, a well known quadratic model was used to produce available radiation data. A quadratic relat ionship between solar insolation and duration of solar radiation data has been investigated in order to estimate monthly average global irra diance for Ankara, Antalya, Samsun, Konya, Urfa and Izmir. The data fr om August 1993 to July 1995 have been used in the quadratic model. But , observations of izmir differ from other stations covered for about f our years. Solar insolation data used in the quadratic model were obta ined from the pyrheliometer with model CR10. Duration of bright sunshi ne data were obtained from a Slap, Frans or Muller sunshine recorder w ith 60 degrees global lens. A general quadratic formula was found that represents the whole of Turkey. The estimated monthly average global solar radiation data, then, were produced from this quadratic formula. Comparison of the estimated and measured values showed that the quadr atic model was able to estimate global radiation with about a 4% annua l relative error and the estimated data seemed to be more reliable tha n the data measured by actinograph. (C) 1997, Elsevier Science Ltd.