The clear day horizontal beam irradiation is also defined as that incident on a horizontal surface on a clear day, viz., KT > 0.7. The clear day horizontal beam index Kbc is defined in terms of the extraterrestrial solar irradiation Ho as
Kb, c = Hb/Ho for Kt > 0.7 (4.12)
where Hb is the horizontal beam irradiation on a clear day. Once again, if there is a particular month with either a very small number or zero days that meet the KT > 0.7 threshold, then it may be lowered by small deficits.
The solar horizontal beam irradiation database consisting of the years 1991 to 2006 was utilized to perform an in-depth analysis similar to that performed for the horizontal diffuse irradiation and the results are presented in Fig. 4.5.
Fig. 4.5 Analysis of the solar horizontal beam irradiation for Beer Sheva (1991-2006)
It is observed from Fig. 4.5, that the magnitudes of the monthly average clear day horizontal beam irradiation values based upon the Iqbal filter are closest to the corresponding average of the maximum daily horizontal beam irradiation measured each year. Also, it is observed that the magnitudes of the monthly average daily horizontal beam irradiation values approach that of the corresponding Iqbal filter values during the summer months. This, once again, testifies to the prevalence of clear sky conditions during the summer months in Beer Sheva, cf., Ianetz et al. (2000).